Universal Hydrogel Adhesives with Robust Chain Entanglement for Bridging Soft Electronic Materials

Universal Hydrogel Adhesives with Robust Chain Entanglement for Bridging Soft Electronic Materials | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Universal Hydrogel Adhesives with Robust Chain Entanglement for Bridging Soft Electronic Materials Jungmok Seo, Yejin Jo, Yurim Lee, Jeong Hyun Heo, Yeonzu Son, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4169072/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 12 Jul, 2024 Read the published version in npj Flexible Electronics → Version 1 posted 11 You are reading this latest preprint version Abstract Ensuring stable integration of diverse soft electronic components for reliable operation under dynamic conditions is crucial. However, integrating soft electronics, comprising various materials like polymers, metals, and hydrogels, poses challenges due to their different mechanical and chemical properties. This study introduces a dried-hydrogel adhesive made of poly(vinyl alcohol) and tannic acid multilayers (d-HAPT), which integrates soft electronic materials through moisture-derived chain entanglement. d-HAPT is a thin (~ 1µm) and highly transparent (over 85% transmittance in the visible light region) adhesive, showing robust bonding (up to 3.6 MPa) within a short time (< 1 min). d-HAPT demonstrates practical application in wearable devices, including a hydrogel touch panel and strain sensors. Additionally, the potential of d-HAPT for use in implantable electronics is demonstrated through in vivo neuromodulation and electrocardiographic recording experiments while confirming its biocompatibility both in vitro and in vivo . It is expected that d-HAPT will provide a reliable platform for integrating soft electronic applications. Physical sciences/Engineering/Electrical and electronic engineering Physical sciences/Materials science/Materials for devices Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Soft electronics have received significant attention due to their potential to revolutionize human-machine interaction by bridging the mechanical disparity between traditional rigid electronics and soft tissues 1 – 3 . These soft electronic devices are composed of soft and rigid building blocks. The soft building blocks usually comprise stretchable and flexible polymers 4 , 5 , and hydrogels 6 , 7 , serving as deformable substrates, interconnectors, and electrodes. These soft building blocks facilitate the conformal contact between the device and the human body, allowing reliable sensing of various biological signals or stimulation of body tissue. In particular, many studies have introduced hydrogel-based electronic devices by exploiting the distinctive properties of hydrogels, including their high water content, low Young’s modulus, and biocompatibility 7 , 8 . However, the realization of soft electronics with only soft components is considered infeasible due to limitations in handling the tasks of data processing or transmission. Therefore, the use of rigid electronic components (e.g., IC chips and printed circuit boards (PCBs)) is essential 9 . These soft and rigid components should be seamlessly integrated and robustly combined for the reliable operation of the devices under dynamic movement conditions. However, achieving stable integration is challenging due to their inherent differences in chemical and mechanical properties. For instance, the strong adhesion of hydrogels (wet materials) to other building blocks (dry materials) is difficult owing to their high water content, which prevents intimate contact and adhesion between them. Therefore, universal adhesion strategies that achieve flexible but robust integration not only at dry/dry interfaces but also at wet/dry interfaces are required. Stable integration of the building blocks using conventional adhesives has been inappropriate due to unstable bonding interface and biocompatibility. For example, cyanoacrylate-based superglues are frequently adopted for their immediate bonding capability. However, the bonded interface lacks flexibility, and resistance to mechanical stress, and temperature 10 . Besides, typical superglues could not be cured on silicone-based elastomers such as polydimethylsiloxane (PDMS) and Eco-flex, which are extensively used in soft electronic devices. Furthermore, the cytotoxicity of cyanoacetate and formaldehyde has been a concern as toxic components could be released during the degradation of polycyanoacrylate 11 . Epoxies are also widely adopted as adhesives for soft electronics. Nonetheless, they have limited adhesion to certain plastics and require a long curing time. In addition, the difficulty of controlling the shape of the soldered form restricts their applications for minimized soft electronic devices 12 . Silver pastes provide electrical connectivity and adhesiveness. However, cytotoxicity and poor bonding strength hinder bioelectronic applications 12 , 13 . Most importantly, these conventional adhesives enable the bonding between dry and rigid materials, but stable bonding of soft or wet materials remains a challenge due to their differences in mechanical modulus and water content. To improve the bonding properties of the conventional adhesives, surface activation, and a modified cyanoacrylate-based adhesive were introduced as the adhesion strategies that establish conformal bonding interfaces to soft materials, including hydrogels. However, each strategy showed limited selectivity, and biocompatibility was not investigated. Therefore, there is a need to develop universal and reliable adhesion strategies that offer biocompatibility, flexibility, electrical adaptability, and the capability to facilitate robust bonding and integration of various soft/rigid and wet/dry electronic materials. Hydrogel adhesives are emerging as potential breakthroughs for biocompatible and universal adhesive materials. Nature-derived hydrogel adhesives (e.g., chitosan-based 14 , 15 , gelatin-based 16 , 17 , and mussel-inspired 18 , 19 ) exhibit non-selective adhesion due to their abundant functional groups. The functional groups within the adhesive facilitate the physical and chemical interactions with adherents. However, these adhesives usually result in thick bonding interfaces and have relatively low bonding strength, which hinders their application in electronics. Recently, dry hydrogel adhesives that improve the bonding strength of typical hydrogel adhesives have been introduced, utilizing their maximized water-swellable property 20 – 22 . Dry hydrogels rapidly absorb the surrounding moisture and undergo rapid hydration and swelling. This enhances the molecular chain mobility that facilitates the formation of tough bonding interfaces through diverse mechanical interactions and entanglement. This property of dry hydrogels holds immense potential as adhesive materials. Consequently, there have been reports on the development of dry hydrogel adhesives that seamlessly attach soft electronic devices and tissues 23 , 24 . However, their effectiveness in integrating the building blocks that comprise soft electronic devices remains unexplored. Here, we introduce a universal and biocompatible dried-hydrogel adhesive made of poly(vinyl alcohol) (PVA) and tannic acid (TA) multilayers (d-HAPT) that enable robust bonding and integration of diverse soft/rigid and wet/dry building blocks. d-HAPT exhibits softness, biocompatibility, and excellent adhesion properties by taking advantage of dry hydrogel adhesives. Especially, the abundant functional groups in TA and moisture-derived chain entanglement facilitate the robust integration of dry/dry materials (DD bonding) and wet/dry materials (WD bonding) regardless of their mechanical and surface properties. d-HAPT is successfully applied to substrates of various sizes, from small electrodes to large Si wafers by dip, spray, or brush coating. Moreover, d-HAPT has a thin thickness of less than 1µm and exhibits high transparency with a transmittance of over 85% in the visible light region while enabling strong integration within 1 min. The DD bonding strength of metals and polymers was 4 MPa and 600 kPa, respectively. Moreover, the tough hydrogel was firmly attached to the d-HAPT-coated Eco-flex substrate even at 630% elongation. To demonstrate the practical adaptability of d-HAPT in wearable soft electronics, we fabricated hydrogel-based wearable devices including a touch panel and strain sensors. Each device maintained stable adhesion and operation in bending and stretching situations. Furthermore, non-toxicity was demonstrated by in vitro and in vivo biocompatibility tests. Given the biocompatibility of d-HAPT, implantable soft electronic devices based on it have been developed to perform in vivo neuromodulation and electrocardiographic recording. Considering the biocompatibility, adhesiveness, and versatility, d-HAPT could be a promising candidate adhesive to replace conventional adhesives used for sophisticated soft electronics. Results Integration of soft electronic devices facilitated by d-HAPT Figure 1 a shows a schematic of possible applications of d-HAPT in soft electronic devices composed of various components comprising a soft substrate, electrodes, rigid electronics, and a flexible interconnector. The integration of these materials is seamlessly facilitated by d-HAPT via two distinct adhesion mechanisms: 1) dry/dry materials bonding (DD bonding) and 2) wet/dry materials bonding (WD bonding). DD bonding enables adhesion among dry materials including elastomers, plastics, rigid electronics, metals, etc. As illustrated in Fig. 1 a(i), d-HAPT coated on the substrates swells by absorbing a little interfacial water, which leads to chain entanglement of d-HAPT. The subsequent mild thermal treatment facilitates robust bonding between the substrates by evaporating moisture in d-HAPT instantly. WD bonding utilizes the water-rich property of hydrogels leading to the attachment of them to the dry substrates (Fig. 1 a(ii)). When the hydrogel is attached to the d-HAPT-coated substrate, d-HAPT absorbs the water at the interface of the hydrogel matrix. The absorbed water leads to the diffusion of polymer chains of adhesive into the hydrogel matrix, thereby entangling the hydrogel network. These two bonding mechanisms accomplish robust adhesion of diverse materials with a broad spectrum of mechanical moduli, attributed to the swellable and soft nature of hydrogel constituents of d-HAPT. Figure 1 b and c show representative examples showing the efficacy of DD bonding and WD bonding. To demonstrate the robustness of DD bonding, polymethyl siloxane (PDMS) ( E ≈ 1 MPa) discs were attached to Eco-flex substrates ( E ≈ 120 kPa) (Fig. 1 b and Supplementary Movie 1) 25 . The strong adhesion is maintained even when the sample is subjected to repeated areal strain of up to 350%. Furthermore, to confirm the strong adhesion of hydrogel bonding, we designed a light-emitting diode (LED) circuit system employing a conductive hydrogel (Fig. 1 c and Supplementary Movie 2). The conductive hydrogel was adhered to a pair of stainless steel (SS) components coated with d-HAPT ( E ≈ 200 GPa). The emitted light from the LED remained stable even when the hydrogel underwent a 200% extension of its initial length. These outcomes comprise substantial evidence that d-HAPT enables robust adhesion between various materials, enduring mechanical stresses including cyclic elongation and relaxation. Fabrication and characterization of d-HAPT Figure 2 a shows the schematic illustration of the d-HAPT fabrication process through layer-by-layer (LbL) deposition onto substrates. TA layer was adopted as the first layer, because of its capacity to interact with various materials attributed to the plentiful galloyl groups in TA molecules. It is known that the hydroxyl groups in the TA molecule induce hydrogen bonds and metal coordinate bonds, whereas benzene rings bring about hydrophobic interaction and π – π interaction 26 . These diverse physical and chemical interactions facilitate the stable TA-driven surface coating on a variety of materials, regardless of the substrate being organic/inorganic, and hydrophilic/hydrophobic. Sequentially, the PVA and TA layers are alternately stacked. PVA is a polymeric component that increases adhesion by forming multidentate bonds with TA through hydrogen bonds 18 . Furthermore, the strong hydrogen bond at the interface of the PVA and TA layer allows the uniform deposition of PVA/TA multilayers 18 , 27 . ATR-FTIR spectroscopy analysis was conducted to affirm the successive layer stacking via the LbL assembly process and the presence of the strong hydrogen bonding interlinking each layer (Fig. 2 b). Each step is denoted as T n P m , where n and m indicate the number of TA layers and PVA layers, respectively. After the coating of the primary TA layer, the broad and dull peak showed at 3100–3500 cm − 1 , indicating a hydroxyl group (–OH) stretching band 28 . Upon the introduction of the subsequent PVA layer, the methylene group (–CH 2 –) stretching peaks at 2908 and 2941 cm − 1 , characteristic of PVA, appear alongside the OH-stretching band 29 . This result demonstrates the successful deposition of the PVA layer after the initial TA layer. Moreover, as successive layers are stacked, the OH-stretching peak gradually shifts to higher wavenumbers, from 3295 cm − 1 for pure PVA to 3349 cm − 1 for the T 3 P 2 . The obvious blue shift of the peak suggests the enhancement of strong hydrogen bonding between PVA and TA during LbL assembly 30 , 31 . The stepwise thickness growth seen in Supplementary Fig. 1, provides additional confirmation of the continuous and stable multilayer coating achieved through the LbL assembly technique. According to the thickness data, the PVA layer is dominant in terms of thickness, and the overall thickness of the adhesive remains within the submicron scale (958.9 ± 25 nm). The SEM image visualized a sub-1 µm thick d-HAPT conformally coated on the glass substrate, similar to the thickness measurement data above (Fig. 2 c and Supplementary Fig. 2). The areal surface roughness (S a ) data analyzed by the laser confocal microscope image (0.014 µm) and AFM image (0.0171 µm) further clearly demonstrated the uniformity of the dip-coated d-HAPT (Fig. 2 d, e). Additionally, the spray-coated, and brush-coated d-HAPT are investigated (Fig. 2 f and Supplementary Fig. 3). The thickness and roughness of spray-coated d-HAPT was 3.2 µm and 0.022 µm, and that of brush-coated d-HAPT was 4.5 µm and 0.163 µm. These results indicate that the d-HAPT-coated surfaces are uniform irrespective of the coating methods. The versatility of coating methods is a notable advantage in applicability across a wide spectrum ranging from wide wafer scale to meticulous electrodes (Supplementary Fig. 4). Additionally, d-HAPT can be fabricated into a free-standing film, enhancing its practical application (Supplementary Fig. 5). For d-HAPT to establish a robust bonding at the interface of two materials, it must remain securely affixed to the substrate, even under the influence of external forces. Therefore, to demonstrate the mechanical stability of d-HAPT, a crosscut test was conducted (Fig. 2 g). A series of optical images demonstrate the results of the crosscut test onto two other substrates: glass (hydrophilic) and TPU (hydrophobic). For both substrates, d-HAPT is kept securely after 10 cycles of tape peeling. Moreover, the transparency of d-HAPT was assessed using ultraviolet-visible (UV–Vis) spectroscopy (Fig. 2 h). The d-HAPT-coated glass substrates exhibit a transmittance of approximately 85% across the entire visible light spectrum (400–750 nm). This exceptional transparency is attributed to the ability of the d-HAPT to coat the substrate conformally and uniformly as confirmed above. In contrast, when solutions of TA and PVA were mixed and coated on glass (referred to as 'Mixed'), the transmittance dropped dramatically to below 40%. Visual observations of the samples with optical images corroborate these results. In the case of a mixed sample, it appears blurry behind the glass. Opacity is caused by the formation of yellowish precipitates in the case the PVA and TA solutions are mixed due to the strong hydrogen bond between PVA chains and TA molecules. Whereas the transparency of d-HAPT-coated glass closely resembles that of bare glass, enabling clear visibility of text and colors behind the glass. This is due to the controlled formation of hydrogen bonds at the interface of the PVA layer and TA layer. Consequently, the LbL approach yields a uniformly surfaced d-HAPT with minimal diffuse reflection and high transparency. This suggests that the d-HAPT could provide reliable alignment of the chips and electrodes demonstrating its potential application in optical soft electronic devices. DD bonding mechanism and durability of the adhesion Figure 3 a illustrates the DD bonding process and its underlying mechanism. For DD bonding, interfacial water should be formed between d-HAPT-coated dry surfaces. The dry hydrogel constituents of d-HAPT allow it to swell by absorbing the interfacial water, thereby increasing chain mobility 20 , 32 . The enhanced chain mobility leads to the entanglement of chains across the dry substrates. Subsequently, a mild heat is applied to evaporate the residual water of d-HAPT. This causes the entangled chains to aggregate and be fixed, which leads to robust bonding between the dry substrates. To investigate the effect of heating temperature on the adhesion, SS substrates were bonded under various temperature conditions (70 to 160°C) with a fixed bonding time of 1 min (Supplementary Fig. 6). The results showed strong integration of substrates at all temperature conditions, with increasing bonding strength with the increasing bonding temperature (from 3 MPa at 70°C to 5.5 MPa at 160°C). This is attributed to the different interfacial water evaporation rates affecting the aggregation and fixation of chains. Moreover, the effect of heating time was investigated by bonding PDMS substrates at temperature conditions of 70 and 100°C for 1 and 5 min (Supplementary Table 1). These results indicate that substrates can be effectively bonded under various temperature and time conditions. Suitable bonding conditions can be selected according to the specific characteristics of the substrate. To ensure a simple and fast process, the standard bonding condition was determined to be 130°C for 1 min in this article, which can be easily achievable with a hair iron (Supplementary Fig. 7 and Supplementary Movie 3). Figure 3 b presents an optical image of d-HAPT bonded PDMS substrates. The d-HAPT showed high transparency in the visible light region (Supplementary Fig. 8). Additionally, it exhibits exceptional flexibility, attributed to the softness of hydrogel-based components within d-HAPT. The cross-sectional SEM image reveals seamless bonding between the PDMS substrates and the d-HAPT (Fig. 3 c). Furthermore, the boundary of the d-HAPT was not visible, affirming that the two d-HAPT layers effectively entangled during the bonding process. To assess bonding strength, lap shear tests were conducted on various materials widely adopted for soft electronic devices, including metals and polymers (Fig. 3 d). Initially, two identical metal substrates were bonded using a hair iron in standard condition. The bonding strength for these metals exceeded 2.5 MPa, with stainless steel demonstrating the highest bonding strength over 4 MPa (4.1 ± 1.2 MPa for SS, 2.6 ± 0.5 MPa for aluminum (Al), 2.5 ± 0.9 MPa for Copper (Cu)) (Fig. 3 e). These values are 50 times higher than the bonding strength observed in other hydrogel-based adhesives capable of attaching metals with an intensity of up to 80 kPa 14 , 18 . Figure 3 f shows the strong adhesion of SS substrates sufficient to support a 20 kg water tank. This excellent adhesion in metals is attributed to the metal coordinate bonds, and hydrogen bonds between TA and PVA 18 , 27 . Subsequently, the bonding strength of polymer substrates was investigated (Fig. 3 g). Considering the glass transition temperature of polymers, the bonding condition was adjusted to 1 min in a drying oven at 100°C. The bonding strength exceeded 500 kPa for all polymer materials (637.6 ± 105 kPa for polyimide (PI), 556.7 ± 98 kPa for acryl, 537.911 ± 60 kPa for polypropylene (PP)). In the case of PDMS, they were stretched without debonding until fracture occurred due to the inherent stretchability of PDMS. The fractured section of the samples corresponds to a non-adhered region, signifying that d-HATP sufficiently withstands the stress that induces PDMS breakage (Fig. 3 h). These overall results demonstrate that d-HAPT could form strong bonds between the same materials. For practical applications, adhesive compatibility between different materials is crucial. Bonding heterogeneous substrates presents more challenges compared to bonding the same materials, primarily due to the disparities in mechanical and chemical properties among materials. Nevertheless, d-HAPT with abundant functional groups enables robust bonding regardless of substrate properties. To evaluate this, lap shear tests were conducted across various substrate combinations. Samples were prepared by sandwiching a material with a lower modulus (substrate 2) between two substrates with higher moduli (substrate 1) to minimize the effect of deformation of elastomer substrates during measurements (Fig. 3 i). The samples exhibited effective integration to a large extent that elastomer substrate 2 (Eco-flex, PDMS) fractured during testing (Fig. 3 j, k). Consequently, d-HAPT facilitates robust adhesion among diverse materials and substrate combinations through a substrate bonding process, all accomplished within a short time. In conclusion, d-HAPT holds promise for integrating solid materials used in soft electronic devices regardless of material properties. To demonstrate the remarkable performance of d-HAPT as an adhesive, a comparative analysis was conducted against the existing adhesives used in soft electronics (Fig. 3 l and Supplementary Table 2) 33 – 36 . d-HAPT is a thin adhesive that enables rapid and robust bonding (shear strength ≈ 200 kPa, T-peel strength ≈ 4 N/cm for soft materials) (Supplementary Fig. 9). A few polymer-based adhesives with comparable bonding strength and thickness were reported, but they required prolonged heat treatment for chain entanglement (2 days), or adhesive network stabilization (> 10 min) compared to d-HAPT. In the case of hydrogel-based adhesives, the polar groups within their network facilitate instant bonding between soft materials. However, d-HAPT exhibits stronger adhesion than the hydrogel-based adhesives, even at a thousandth of thickness. WD bonding mechanism and durability of the adhesion Hydrogel has been a promising candidate for advanced soft electronics by leveraging soft and tissue-like properties. Nonetheless, integrating hydrogels with diverse materials poses a significant challenge due to their innate water-rich composition and exceptionally low modulus 37 , 38 . As the hydrogel is susceptible to heat applied during thermal bonding, a modified bonding process has been adopted for bonding between hydrogel and dry substrates (WD bonding). Figure 4 a illustrates the WD bonding process and its underlying mechanism. To attach the hydrogels, they are simply placed onto the adhesive-coated substrates. Then, the d-HAPT absorbs the water at the interface with the hydrogel matrix, leading to the diffusion of its hydrogel polymer chains into the d-HAPT. These diffused hydrogel chains become entangled with the d-HAPT, ultimately resulting in the integration of hydrogel and substrates. Figure 4 b demonstrates the mechanical robustness of WD bonding. When the polyacrylamide (PAAm)-Alginate tough hydrogel is affixed to the d-HAPT-treated Eco-flex substrate, it exhibits remarkable stretchability. The bonded substrates endured strains over 600% of their original length without delamination. This stable adhesion between the hydrogel and Eco-flex remained intact even when the sample was fractured. In contrast, when the tough hydrogel was attached to an untreated Eco-flex substrate, the hydrogel was delaminated from the substrate not being stretched along with the elastomer (Fig. 4 c). This outcome implies incomplete adhesion between the hydrogel and the elastomer substrate and demonstrates the crucial role of d-HAPT in establishing a robust hydrogel-elastomer interface. To evaluate the bonding strength of WD bonding, lap shear tests were conducted by sandwiching hydrogels between substrates with various combinations (Fig. 4 d). Three types of hydrogels were selected: a tough hydrogel (PVA-TA) 39 , a single-network hydrogel (PVA) 37 , and a double network tough hydrogel (PAAm-Alginate) 37 , 40 . These hydrogels adhere robustly on the d-HAPT coated substrates compared to the bare substrates (Fig. 4 e). The differences in bonding strength between hydrogels were attributed to the inherent mechanical properties and degree of polymer chain diffusion. In the case of PVA-TA tough hydrogel, the PVA polymer chain easily diffuses into the d-HAPT leading to the strong adhesion strength. However, single-network PVA hydrogel shows comparatively low bonding strength due to its inherent low mechanical modulus and weak cohesion. For PAAm-Alginate hydrogel, long-chain and dissipative polymer networks are densely entangled, which hinders the active diffusion of the hydrogel chains into the d-HAPT. Nevertheless, the intact interface of PVA hydrogel and PAAm-Alginate hydrogel with the substrates during the tests evidenced their stable integration (Supplementary Fig. 10, 11). Remarkably, each hydrogel exhibited a similar bonding strength across all substrates (Fig. 4 f and Supplementary Fig. 12). This uniformity could be attributed to the universal adhesion of d-HAPT on the substrate, which is derived from the abundant functional groups within TA molecules. These adhesion test results demonstrate that d-HAPT could offer a stable and universal WD bonding interface despite its relatively low bonding strength, showing intriguing potential for a dry hydrogel adhesion strategy. Existing adhesion strategies for hydrogels have employed hydrogel pre-gel solutions to induce adhesion to substrates 37 , 38 . Although these approaches offer the advantage of a stronger interfacial toughness, they face practical limitations, requiring additional curing processes. Additionally, specific chemical modifications must be performed depending on the hydrogel. However, d-HAPT facilitates stable adhesion to soft substrates regardless of its mechanical and chemical properties owing to moisture-derived robust chain entanglement. This presents a significant advantage for practical application providing convenience in the process and versatile applicability. To demonstrate the durability and applicability of the d-HAPT as an adhesive for hydrogel-based electronics, we fabricated a simple stretchable circuit system (Fig. 4 g and Supplementary Movie 4) using conductive hydrogel. The hydrogel was 3D printed on d-HAPT-treated Eco-flex to serve as the interconnector. Then, LED chips coated with d-HAPT by brushing were adhered to the hydrogel interconnectors. The fabricated device exhibited stretchability, without any delamination of LED chips. Upon applying a voltage to both ends, the light of the LED was turned on and maintained even when the device was stretched to 150% of its initial length. The diminished light intensity was recovered as soon as the device was relaxed to its original length suggesting the stable adhesion of the soft and rigid components via d-HAPT. Supplementary Table 3 demonstrates the comparison of various adhesion methods that attach various building blocks of soft electronics 23 , 24 , 33 – 38 , 41 , 42 . While some studies exhibit the exceptional adhesive strength, none of them show multifunctional adhesive properties including soft/soft, rigid/rigid, soft/rigid, soft/hydrogel, and rigid/hydrogel and their electrical applications. Wearable electronics applications Figure 5 a illustrates the wearable touch panel comprising three layers: an upper ionic hydrogel layer for touch sensing, a flexible flat cable (FFC) for signal transmission, and a lower PDMS layer serving as an insulator 6 . The conformal assembly of the layers was secured using d-HAPT, which substantially contributed to sustained sensing performance and reliable signal transmission. For example, maintaining stable interconnection between the ionic hydrogel and the FFC is challenging during dynamic body movement due to their relatively minor contact area and mechanical mismatch. However, d-HAPT exhibited strong adhesion at the interface of the FFC cable and touch panel enduring applied strains (Supplementary Fig. 13 and Supplementary Movie 5). The transparent ionic hydrogel layer was colored purple for visualization. As the FFC cable adhered to the hydrogel was pulled, the hydrogel was also stretched showing stable interfaces. Upon further pulling, a fracture was initiated on the hydrogel without debonding of the FFC cable, as seen in the inset. This durable adhesion enables the stable operation of wearable touch panels even in dynamic conditions. The operational principle of this wearable touch panel is based on a surface capacitive system, as elucidated in Fig. 5 b. A uniform electrostatic field is established across the touch panel by applying an identical alternating current voltage to its four corners. When a finger contacts the touch panel, the touch point becomes grounded, allowing current to flow from the corner electrodes toward the touch point. To investigate the current at the four corners depending on the touch position, we evaluated the current variations as contacting with Point 1 to Point 4 on the panel surface sequentially. Visible difference in current was observed upon the contact of a finger (Fig. 5 c). Notably, it was confirmed that the current was proportional to touch point proximity to the corner electrodes. Based on this outcome, the formula was deduced to investigate the correlation between the current measured at the corners and the specific touch point (Supplementary Fig. 14). A controller board was employed to convert the current data to the position on the touch panel. This wearable touch panel was attached to the forearm seamlessly and interfaced with a computer system through the controller board (Supplementary Fig. 15, 16). To test the reflection of the touch on the monitor, we wrote the word ‘BLISS’ on the touch panel (Fig. 5 d and Supplementary Movie 6). As a result, high-resolution letters were successfully acquired, despite minor distortions along the edges. Additionally, a video game, avoiding obstacles by jumping while running, was performed using this touch panel. As shown in Fig. 5 e, tactile interaction with the touch panel induced the character jumps (Supplementary Movie 7). These results suggest that the hydrogel touch panel integrated through d-HAPT successfully operated on the forearm. The hydrogel strain sensors are promising bioelectronic applications exhibiting the capability of monitoring various human movements. However, their practical utility has been hampered by unstable connections between integrating components, such as a substrate, a cable, and a sensing layer. The difficulty causes problems in maintaining its shapes and securing consistent data acquisition during vigorous physical motion. In response to these issues, we have introduced a ring-shaped wearable strain sensor designed to mitigate the risk of detachment from the body (Fig. 5 f). The foundational design comprises a stretchable Eco-flex substrate fashioned into a circular configuration. On this substrate, a carbon nanotube (CNT) hydrogel 43 responsible for sensing, and a conductive thread for transmitting data were affixed by utilizing d-HAPT. The fabricated strain sensors exhibited excellent softness due to the intrinsic stretchability of conductive hydrogel and Eco-flex. As a result, this ring-shaped wearable strain sensor offers stretchability, enabling repeated use while ensuring the user’s comfort. To comprehensively assess the versatility and robustness of this strain sensor, sensors were applied to distinct joints, such as a finger, a wrist, and an elbow (Fig. 5 g-i). Notably, even during the bending of these joints, the measurement of the electrical resistance was seamless without any disruption to the hydrogel-substrate interface. Although the resistance modulation was inherently influenced by the range of motion within the joints, a resistance alteration rate across all cases exceeded 20%. Also, the gauge factor (GF) of this sensor was 1.22, surpassing that of the existing strain sensors. Leveraging the exceptional sensitivity of the sensor, precise angle-dependent sensing capabilities were demonstrated on the finger (Fig. 5 j). Additionally, extensive stretching cycles of the strain sensor were systematically conducted to evaluate the durability of the sensor. Throughout 300 stretching cycles, the strain sensor consistently exhibited stable and reliable sensing characteristics, attesting to its robustness and durability (Fig. 5 k). Consequently, d-HAPT enabled the stable operation of wearable soft electronics by providing robust adhesion between each building block. These devices were capable of sensing signals accurately even in bending and stretching situations that occur during the use of soft electronics. Biocompatibility of d-HAPT Soft electronics have gained prominence as a solution to mechanical challenges in implantable devices such as neural probes 44 , artificial vascular sensors 45 , and electronic sutures 46 . For implantable devices, the materials should be non-toxic. To evaluate the biocompatibility of d-HAPT for implantable devices, a series of in vitro cell viability and morphological analyses were conducted. As shown in Fig. 6 a, the d-HAPT-coated on the flexible PI film was incubated with NIH3T3 fibroblasts in cell culture media using a transwell system. The cell biocompatibility test using transwell insert investigates the effect of physiological environment change on the cells by allowing cells to be in indirect contact with the tested materials. The results of the live/dead assay and the CCK-8 assay showed no significant differences in cell viability after incubation for 1, 3, and 5 days (Fig. 6 b and Supplementary Fig. 17, 18). Moreover, analyzation of cell morphological changes can serve as another biomarker to evaluate the material’s biocompatibility (Fig. 6 c and Supplementary Fig. 19). When foreign materials are implanted, activated inflammation can cause fibroblasts to undergo morphological changes, transitioning from a healthy spindle shape to a pathological circular shape as a result of cytoskeletal remodeling. The morphology of the fibroblast was evaluated using cell aspect ratio after TRITC phalloidin staining. The results showed no significant differences in bare PI and d-HAPT-coated PI. Also, d-HAPT-bonded PDMS devices were implanted into the subcutaneous region of mice to investigate in vivo biocompatibility (Fig. 6 d). To mimic actual application conditions and prevent the potential of enzymatic degradation of PVA and TA, the devices were encapsulated. After 7 days of implantation, the devices were retrieved and remained intact without any detachments, suggesting the durability of d-HAPT in the physiological environment (Fig. 6 e). Histological staining with Hematoxylin & eosin (H&E), toluidine blue (TB), and Masson's trichrome (MT) staining indicated that the implanted device did not trigger significant inflammatory responses or necrosis of surrounding tissues (Fig. 6 f). Furthermore, there was no observed increase in mast cells, as highlighted by organ arrows, or noticeable increase in collagen deposition. To evaluate any systemic response triggered by the implantation, serum levels of Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) were measured before and after 3, 7, and 10 days of implantation (Fig. 6 g). There were no significant alterations in AST and ALT serum levels between the Sham and implanted groups across all time points, indicating that implantation did not induce hepatotoxic effects. Implantable bioelectronics applications Given that the adhesive showed biocompatibility in vitro and in vivo experiments, we fabricated the implantable bioelectronic devices to evaluate the feasibility of d-HAPT as an adhesive for implantable applications (Fig. 6 h). To fabricate the device, a PVA-liquid metal composite was printed on d-HAPT coated PDMS substrate as stretchable hydrogel electrodes. Then a FFC was integrated through the DD bonding process, similar to the structure of soft electronics illustrated in Fig. 1 a. The device was firmly integrated despite the application of external forces, such as bending or stretching deformation (Fig. 6 i). Using this device, we first performed in vivo neuromodulation on the rat sciatic nerve (Fig. 6 j). As the stimulation was applied, leg of the rat responded showing different moving angle upon increase in the applied current (Fig. 6 k). The electrocardiogram signal was also recorded using the identical device (Fig. 6 l). P wave, QRS complex, and T wave, which play a vital role in diagnosing various cardiac disorders, were distinctly confirmed through the analyzed signal (Fig. 6 m). In both sciatic nerve stimulation and electrocardiogram recording, the d-HAPT stably integrated the soft electronics during the intense movement of the leg and heart owing to the excellent adhesiveness. These overall results suggest the potential of d-HAPT for diverse implantable electronics. Discussion The chemical and mechanical mismatches between materials used in soft electronics have hindered the instant and stable bonding of these materials using conventional adhesives. In this study, we have introduced a simple yet effective dry hydrogel adhesive with biocompatibility and softness that could bring a paradigm shift in adhesion strategy for soft electronics. As a promising strategy for instant adhesion to diverse soft electronic materials, d-HAPT robustly interfaces them regardless of the types and shapes of the materials either dry or wet ones. The sub-micron d-HAPT exhibits excellent uniformity, transparency, and mechanical stability. Its water-swellable property enables strong bonding of diverse materials through the adhesive’s polymer chain entanglement, upon absorbing moisture. Using d-HAPT, the hydrogel touch panel and strain sensors were fabricated, which demonstrated the applicability of wearable soft electronics. d-HAPT also showed excellent biocompatibility in both in vitro and in vivo experiments. Furthermore, the neuromodulation on the sciatic nerve, and recording of the electrocardiogram signal were successfully performed with implantable soft electronic devices integrated with d-HAPT. Overall, the excellent mechanical stability, softness, and biocompatibility of d-HAPT present a promising approach for utilizing hydrogel adhesives in a wide range of applications, from wearable to implantable biomedical engineering. Methods Materials The chemicals were purchased and used without further purification. Poly(vinyl alcohol) (PVA, M w 89,000–98,000), tannic acid (TA), acrylamide (AAm), acrylic acid (AA), N, N’-methylenebis(acrylamide) (MBAA), ammonium persulfate (APS), tetramethyl-ethylenediamine (TEMED), ammonium persulfate (APS), sodium alginate were purchased at Sigma Aldrich. A carbon nanotube (CNT) was purchased at Nanolab, Korea. Lithium chloride (LiCl) was purchased at Duksan, Korea. Gallium and Indium were purchased at AliExpress, China. Preparation of d-HAPT PVA (2.5% w/v) was dissolved in deionized (DI) water at 140°C by stirring at 300 rpm for 2 hours. TA solution was prepared by dissolving TA (2.5% w/v) in DI water using a vortex mixer. Substrates were coated layer by layer using the PVA and TA solution with a dip coater with a speed of 130 mm/min. The first and the last layer were designed to be the TA layer. Before depositing each layer, the samples were dried at 45°C for 10 min. To fabricating d-HAPT into a free-standing film, T 4 P 3 layers were dip-coated with 7.5% w/v of TA and PVA solution at a speed of 130 mm/min. Preparation of Hydrogels The hydrogels were fabricated as described in the previous research. To synthesize PVA hydrogel, PVA (4,000 mg) was dissolved in DI water (20 mL) at 140°C while stirring for 20 min. The PVA solution was poured into the mold. The PVA solution was freeze-thawed at temperatures between − 20 and 25°C to yield the PVA hydrogel. To synthesize PVA-TA hydrogel 39 , TA (4,000 mg) was dissolved in the PVA solution at 140°C. After 2 hours of stirring, the viscous PVA-TA solution was fabricated. The PVA/TA solution was spread on the mold to make its thickness 2 mm. Then, the PVA-TA solution was frozen and subsequently thawed to yield the PVA-TA hydrogel. The carbon nanotube (CNT) conductive hydrogel was fabricated following our previous research 43 . To synthesize PAAm-LiCl hydrogel, a precursor solution was obtained by dissolving AAm monomer (146.35 mg/ml), MBAA (0.07% of AAm), APS (0.1% of AAm), 0.4 µL/mL of TEMED, and LiCl in DI water. The solution was poured into the mold with a thickness of 3mm. Then, the PAAm-LiCl hydrogel was cured for 4 hours at room temperature 47 . To fabricate PAAm-Alginate hydrogel, alginate (29 mg/ml) was dissolved in DI water by stirring for an hour at room temperature. An AAm precursor solution (AAm monomer (666 mg/ml), MBAA (0.06% of AAm), APS (0.75% of AAm), and TEMED (2 µl/ml)) was added to the alginate solution. The PAAm-Alginate solution was poured into the mold with a thickness of 3mm. After 4 hours of the curing process, the PAAm-Alginate hydrogel was fabricated 48 . d-HAPT Characterization The chemical structures were analyzed through ATR-FTIR (Vertex 70, Bruker, USA) with a range of 2800 to 3800 cm - 1 . The thickness was analyzed using a surface profiler (DektakXT stylus Profiler, Bruker), and the surface morphology was acquired through AFM (NX-10, Park Systems), FE-SEM (IT-500HR, JEOL), and laser confocal microscope (VK-X3050, Keyenece). The mechanical stability was tested using a cross-cut test (ISO 2409). Cross-cut adhesion test (ISO 2409) was performed to test the durability of the coating. 100 blocks of size 10×10 mm 2 were formed on the d-HAPT coated glass and TPU surface by scratching the surface using a crosscutter. Then, the adhesive tape was attached to the surface and removed from it. This process was repeated 10 times, and the integrity of the coating was assessed. The transmittance was measured using a UV–Vis spectrophotometer (V-650, JASCO) with a wavelength range of 300 to 900 nm. Bonding process For DD bonding, the interfacial water is formed on d-HAPT-coated surfaces by dipping, brushing, or spraying. Then, the substrates were overlapped for a minute to induce moist absorption, thereby the polymer chain entanglement. The overlapped samples were heated for 1 min to evaporate residual interfacial water, leading to chain fixation. The heating temperature varied with the substrates from 100 to 130°C. For WD bonding, the hydrogel was placed on the coated surface of the substrate for 1 min. Lap shear tests The bonding strength was measured through lap shear tests using a tensile testing machine (Multitest-dV, Mecmesin). The samples were prepared with a bonding area of 15×20 mm 2 . The tests were performed with a constant peeling speed of 5 mm/min. The bonding strength was detected with a 2500 N load cell. T-peel tests Peel strength was measured using the combination of two stretchable substrates of PDMS and Eco-flex. Two substrates with a size of 10×40 mm 2 were bonded with an adhered area of 10×10 mm 2 using d-HAPT. Then, the peel strength of the samples was tested using a tension tester (Multitest-dV, Mecmesin), with a strain rate of 50 mm/min. Stretchable hydrogel circuit The d-HAPT was formed on the Eco-flex and the electrodes of the LED chips (Adafruit LED, Adafruit). CNT·TA·PVA·PAA hydrogel was printed on the substrate using a 3D printer (EZROBO-5GX 3D printer, Iwashita) with a dispenser (AD3300C dispenser, Iwashita). Then, the coated LED chips were placed on the printed circuit. DC power supply (DP832, Rigol) was used to turn on LED chips. Wearable touch panel The wearable touch panel was fabricated by placing the PAAm/LiCl hydrogel with a thickness of 3mm on the d-HAPT-coated PDMS. Four vertexes of the ionic hydrogel were attached to the d-HAPT-coated FFCs (flat flexible cables) for connecting the touch panel to the devices that analyzed current changes caused by contact. To measure the degree of changes in current from touch, an AC voltage of 100 kHz from − 1 to 1V was applied to the vertexes using a function generator (AFG1022, Tektronix). Then the current was measured through the multimeter (34461A, Keysight) at each point. To confirm the operation of the wearable touch panel, FFCs attached to the touch panel were connected to a controller board (EXII-7720SC, 3M Touch Systems). Software MT7(3M, MicroTouch) was used as a calibration tool for the touch panel. Strain sensor d-HAPT-coated Eco-flex was used as a substrate, which is windable to body parts such as a finger, a wrist, and an elbow. CNT·TA·PVA·PAA hydrogel was placed on the substrate to measure the changes in resistance by bending the joint. For the measurement, the hydrogel was connected to the multimeter using the coated conductive thread (conductive stainless thread, DFRobot). In vitro biocompatibility test The 5×5 mm 2 bare and d-HAPT-coated PI film was prepared. Afterward, a two-chamber transwell system (8 µm pore size; Corning Inc.) was introduced for cell viability and analysis of morphological change. The prepared PI films were placed on the insert and incubated with cells thorough the experimental time. The NIH-3T3 fibroblast cells (0.5×10 5 cells/mL) were cultured in 6 well cell culture plates with 1.5 mL of Dulbecco′s Modified Eagle′s Medium - high glucose (DMEM) supplemented with 10% bovine calf serum and 1% penicillin-streptomycin. Cell viability was evaluated using a Live/Dead kit (L3224, Invitrogen, USA) according to the manufacturer's instructions. The intensity of fluorescence cell images was measured using an inverted fluorescence microscope (IX81, Olympus, Japan) with a 10× magnification. Similarly, morphological change was measured following the aspect ratio calculation method which is the major cell axis divided by the minor one. For visualization, the cytoskeleton of NIH 3T3 cells was stained using an Alexa 594-conjugated phalloidin (Thermo Scientific, Pittsburgh, PA, USA). The cell morphology was evaluated using a confocal microscope (LSM 980, Carl Zeiss, Oberkochen, Germany) and calculated by the ImageJ/FIJI software program. In vivo biocompatibility test d-HAPT-bonded PDMS (10×10×1 mm 3 ) was subcutaneously implanted into 6-week-old male CD-1 (ICR) mice for 3, 7, and 10 days. The animal experimental protocols were approved by the Institutional Animal Care and Use Committee of Yonsei University College of Medicine (IACUC No. 2023-0097), and all experiments adhered to the guidelines set by an Association for the Assessment and Accreditation of Laboratory Animal Care (AAALAC)-accredited facility. Within this facility, animals were housed under 12-hour alternating light/dark cycles and had unrestricted access to food and water. Before the mice were anesthetized using ketamine (100 mg/kg) and Rompum (10 mg/kg). Mice were procured from Orient Bio Incorporation, Seongnam, Korea. To assess any hepatotoxicity resulting from d-HAPT, blood samples were drawn through retro-orbital bleeding both before and after 3, 7, and 10 days of implantation (n = 4 for both the Sham and implanted groups). Blood was collected in heparinized capillary tubes (Micro-Hematocrit Capillary Tube Plain, Kimble Chase, Vineland, NJ, USA) and left to clot in a serum separation tube (BD Microtainer, BD, Franklin Lakes, NJ, USA) at room temperature for 2 hours. Subsequently, the samples underwent centrifugation at 300 g for 15 min, followed by 10 min at 600 g twice, after which the supernatant serum was extracted and stored at -80°C. Levels of AST and ALT in the serum were determined using a Dri-Chem 4000i biochemical analyzer (Fujifilm, Tokyo, Japan). For histological evaluations, mice were euthanized 3- and 7 days post-implantation, after which the implants and surrounding skin tissues were extracted and preserved in 10% formalin (Sigma-Aldrich, St. Louis, USA). The preserved tissues were then processed (ASP300S, Leica Biosystems, Nussloch, Germany), and embedded in paraffin blocks (Histo Core Arcadia, Leica Biosystems. Samples were then sectioned to a thickness of 4 µm and mounted onto slides (RM2255, Leica Biosystems) in preparation for histological staining with Hematoxylin and Eosin (H&E), Toluidine blue (TB), and Masson's Trichrome (MT). Implantable bioelectronic device applications All surgical procedures for mice were performed in accordance with protocols approved by the Institutional Animal Care and Use Committee (IACUC) at Korea Advanced Institute of Science and Technology (KAIST). 12-week-old female Sprague-Dawley rats (Koatech, South Korea) were anesthetized with isoflurane (5% induction, 2% maintenance). A heating pad was used to maintain the body temperature of the rat. To fabricate the implantable device, the composite of 3g of liquid metal (75% gallium and 25% indium) and 2 ml of PVA solution (5 wt%) is prepared as electrodes. 1 mm × 7 mm size of two electrodes were spray-printed on a 6 mm × 10 mm d-HAPT-coated PDMS substrate using a mask placed 2 mm apart. Subsequently, the d-HAPT-coated FFC was connected to the electrodes through DD bonding. Sciatic nerve stimulation Incision along the left thigh was made to expose the sciatic nerve. The electrodes are gently placed beneath the sciatic nerve in order to contact the epineurium. The biphasic current was administered at a frequency of 10 Hz, with a pulse duration of 25ms and current ranging from 0.03 to 0.09 mA, using an isolated pulse stimulator (2100, A-M systems). The leg movement was quantified using a protractor positioned beneath the leg. Electrocardiogram recording An acute tracheotomy was conducted, and the rat was intubated using a ventilator (VentElite Small Animal Ventilator, Harvard Apparatus) at a rate of 80 breaths per minute. Following a thoracic cavity incision, the ribs were carefully dissected to expose the heart. Subsequently, working and reference electrodes were positioned on the left ventricle. The electrocardiogram signals were recorded with an electrophysiology system (Lab Rat, Tucker-Davis Technologies). The recorded signals underwent bandpass filtering within the range of 0.3 Hz to 50 Hz. Informed consent The research participants in the images in Fig. 5 agree to the publication of these photographs. It was confirmed that a study using wearable devices simply touching the skin doesn’t need institutional review board approval. Statistical analysis The data of all experiments were statistically analyzed with a minimum sample size of 3 using Graphpad Prism 8 software (Graphpad Software Inc., USA). In the statistical analysis between groups, the unpaired t-test was used. ns was considered not significant. Statistical analyses for the in vivo study were performed using SPSS software (Version 26.0, IBM, Armonk, NY, USA). The Wilcoxon signed-rank test was employed to compare pre- and post-implantation data. A p -value of less than 0.05 was considered indicative of statistical significance. Declarations Data availability Data included in this manuscript is available and will be shared upon request. Acknowledgements This work was financially supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Project numbers: NRF-2022R1A2C4001652). Author information These authors contributed equally: Yejin Jo and Yurim Lee Authors and Affiliations School of Electronic and Electronic Engineering, Yonsei University, Seoul 03722, Republic of Korea Yejin Jo, Yurim Lee, Tae Young Kim, Kijun Park, Soye Kim & Jungmok Seo Department of Physiology Yonsei University College of Medicine Seoul 03722, Republic of Korea Jung Hyun Heo & Yoonhee Jin Program of Brain and Cognitive Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea Yeonzu Son Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea Seongjun Park Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea Seongjun Park KAIST Institute for NanoCentury (KINC), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea Seongjun Park Contributions Yejin J. and Y.L. contributed equally to this work. Yejin J. and Y.L. designed the experiment, analyzed the data, and wrote the manuscript. Yejin J. synthesized and characterized d-HAPT. Yejin J., Y.L., and S.K. performed mechanical tests. Yejin J., Y.L. conducted the experiment about the wearable electronics. Yejin J., J.H.H., and T.Y.K. performed the biocompatibility assay. Y.S. conducted the experiment regarding the implantable electronics. Yoonhee J., S.P., and J.S. were responsible for administrating this project. J.S. and K.P. revised and edited the manuscript. J.S. proposed the original concept and managed all aspects of this work. All authors discussed the results and commented on the manuscript. Corresponding authors Correspondence to Jungmok Seo Ethics declarations Competing interests The authors declare no competing interests. References Rao, Z. et al. Soft electronics for the skin: from health monitors to human–machine interfaces. Advanced Materials Technologies 5, 2000233 (2020). Byun, S.-H. et al. 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Additional Declarations (Not answered) Supplementary Files SInpjFE.docx Supplementary Information SupplementaryMovie1.mp4 Supplementary Movie 1 SupplementaryMovie2.mp4 Supplementary Movie 2 SupplementaryMovie3.mp4 Supplementary Movie 3 Supplementarymovie4.mp4 Supplementary Movie 4 Supplementarymovie5.mp4 Supplementary Movie 5 Supplementarymovie6.mp4 Supplementary Movie 6 Supplementarymovie7.mp4 Supplementary Movie 7 Cite Share Download PDF Status: Published Journal Publication published 12 Jul, 2024 Read the published version in npj Flexible Electronics → Version 1 posted Editorial decision: revise 22 Apr, 2024 Review # 2 received at journal 20 Apr, 2024 Review # 1 received at journal 20 Apr, 2024 Review # 3 received at journal 15 Apr, 2024 Reviewer # 3 agreed at journal 09 Apr, 2024 Reviewer # 2 agreed at journal 09 Apr, 2024 Reviewer # 1 agreed at journal 09 Apr, 2024 Reviewers invited by journal 08 Apr, 2024 Submission checks completed at journal 27 Mar, 2024 Editor assigned by journal 26 Mar, 2024 First submitted to journal 26 Mar, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4169072","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":289065928,"identity":"9d4990cf-3e8a-4d97-b314-005ed53344e4","order_by":0,"name":"Jungmok Seo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABC0lEQVRIiWNgGAWjYBACxgYwlQBmPwCzmREiBLUwGxClBQrACtgk0EWwAuYZuYdf3ahIY5Bvbz5WzVNxx56fnYHxww+GtHycDpuRl2adcyaHweDMsbTbPGeeJc5sZmCW7GHIsWzAqSXHzDi3rYLBQCLH7DZv2+EEg8MMDNIMDBUGuG2BapGf/8asGKjF3v4wA/NvAlqMH+e25TAw3OAxYwZqYdzAzMAGtCUHt5aeN2bMOWfSeAzOpCVLzjlzOHHGYcY2yx6DNJxaDNtzjD/nVCTLybcfPvjhTcVhe/7+w4dv/KhIxq2lARIdPCAOEw/E5gYGBpwaGBjkgVHzAe7KH7gVjoJRMApGwQgGAE9oUPFE2oMwAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-8898-044X","institution":"Yonsei University","correspondingAuthor":true,"prefix":"","firstName":"Jungmok","middleName":"","lastName":"Seo","suffix":""},{"id":289065929,"identity":"d58dc0e4-5b1e-40ae-a038-c48df733e4e8","order_by":1,"name":"Yejin Jo","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Yejin","middleName":"","lastName":"Jo","suffix":""},{"id":289065930,"identity":"16ccacd5-7827-48e4-83db-7ffc0c0ea52e","order_by":2,"name":"Yurim Lee","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Yurim","middleName":"","lastName":"Lee","suffix":""},{"id":289065931,"identity":"5cda64fa-4633-41aa-bd52-5ccc744faead","order_by":3,"name":"Jeong Hyun Heo","email":"","orcid":"","institution":"Yonsei University College of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Jeong","middleName":"Hyun","lastName":"Heo","suffix":""},{"id":289065932,"identity":"cae6edad-6712-4864-95be-e253a2e1e92f","order_by":4,"name":"Yeonzu Son","email":"","orcid":"","institution":"Korea Advanced Institute of Science and Technology (KAIST)","correspondingAuthor":false,"prefix":"","firstName":"Yeonzu","middleName":"","lastName":"Son","suffix":""},{"id":289065933,"identity":"1e72ad3e-b466-4536-a43e-122795845623","order_by":5,"name":"Tae Young Kim","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Tae","middleName":"Young","lastName":"Kim","suffix":""},{"id":289065934,"identity":"9b1d1b04-15f5-4fa3-a242-8c1d63116a34","order_by":6,"name":"Kijun Park","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Kijun","middleName":"","lastName":"Park","suffix":""},{"id":289065935,"identity":"753cfe98-d61a-4c34-a128-edfd1a6dbf7e","order_by":7,"name":"Soye Kim","email":"","orcid":"","institution":"Yonsei University College of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Soye","middleName":"","lastName":"Kim","suffix":""},{"id":289065936,"identity":"7fae2542-10de-49a8-add6-9dd46463a455","order_by":8,"name":"Yoonhee Jin","email":"","orcid":"","institution":"Yonsei University College of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Yoonhee","middleName":"","lastName":"Jin","suffix":""},{"id":289065937,"identity":"b896ab4b-c904-4ebd-a8c3-283a5ddc9729","order_by":9,"name":"Seongjun Park","email":"","orcid":"https://orcid.org/0000-0002-1981-9628","institution":"Korea Advanced Institute of Science and Technology (KAIST)","correspondingAuthor":false,"prefix":"","firstName":"Seongjun","middleName":"","lastName":"Park","suffix":""}],"badges":[],"createdAt":"2024-03-26 10:26:48","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4169072/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4169072/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41528-024-00327-x","type":"published","date":"2024-07-12T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54599990,"identity":"6931e20c-2603-45d5-af7b-6db8c5c683d0","added_by":"auto","created_at":"2024-04-12 20:49:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":893004,"visible":true,"origin":"","legend":"\u003cp\u003eUniversal d-HAPT bridging diverse materials in soft electronics (a) Schematic of a soft electronic device consists of a soft substrate, electrode, rigid electronics, and flexible interconnector which were integrated using d-HAPT via i) DD bonding and ii) WD bonding. (b) Stretching of round-shaped PDMS discs attached to Eco-flex substrate via DD bonding over 350% strain without detachment. (c) Robust bonding of ionic conductive hydrogel and stainless steel (SS) to a light-emitting diode (LED) via WD bonding, which were stretched over 200%.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/c5bb99e0bbcb103f70af8f64.png"},{"id":54600153,"identity":"39560842-2063-40c7-a5ab-22364a512ea3","added_by":"auto","created_at":"2024-04-12 20:57:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":821393,"visible":true,"origin":"","legend":"\u003cp\u003eFabrication process of d-HAPT and its characterization (a) Schematic illustration of d-HAPT fabrication process and its mechanism. (b) ATR-FTIR spectra with a wavenumber range from 3800 to 2800 cm-1 for each coated layer of d-HAPT. (c) Side view of d-HAPT coated on the glass. (d) Laser confocal microscope images of d-HAPT coated on the glass. (e) 2D and 3D AFM images of d-HAPT coated on the glass. (f) The SEM images and laser confocal microscope images of spray-coated, and brush-coated d-HAPT. (g) Schematic of the cross-cut test and optical images of d-HAPT coated on glass and TPU after the cross-cut test. (h) Transmittance of bare glass, PVA/TA mixed solution coated glass, and d-HAPT coated glass with a wavelength range from 300 to 900nm and their optical images on the printed hue circle.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/9bc4b6ace278888782429d21.png"},{"id":54599993,"identity":"bbb29a56-5327-4afa-be9a-73611841e4a2","added_by":"auto","created_at":"2024-04-12 20:50:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":609602,"visible":true,"origin":"","legend":"\u003cp\u003eDD bonding mechanism and durability of the adhesion (a) Schematic illustration of two dry substrates adhered through DD bonding. (b) Optical image of PDMS substrates integrated using d-HAPT. (c) Side view SEM image of the adhered PDMS substrates. (d) Illustration of lap shear test of sample fabricated by bonding two identical substrates. (e) Bonding strength of d-HAPT on metal substrates including SS, aluminum, and copper substrates (\u003cem\u003en\u003c/em\u003e=4). (f) Optical image of SS substrate enduring shear stress of 20 kg. (g) Bonding strength of d-HAPT on polymer substrates including polyimide, acryl, polypropylene, and PDMS substrates (\u003cem\u003en\u003c/em\u003e=4). (h) Optical images of overlapped PDMS via d-HAPT and fracture formation after applied shear stress. (i) Schematic Illustration of lap shear test of sample fabricated by bonding two different substrates. (j) Bonding strength of samples attached with various combination of metal and polymer substrates (\u003cem\u003en\u003c/em\u003e=4). (k) Top and side view of TPU/Eco-flex sample fractured due to shear stress. (l) Comparison of d-HAPT with other adhesives used to attach stretchable materials based on three conditions (thickness, bonding strength, and bonding time).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/65152ba1b209dab00d188c4e.png"},{"id":54600154,"identity":"69325461-8996-461e-85c0-c71e7df8887c","added_by":"auto","created_at":"2024-04-12 20:58:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":619244,"visible":true,"origin":"","legend":"\u003cp\u003eWD bonding mechanism and durability of the adhesion (a) Schematic illustration of WD bonding between hydrogel and a dry substrate. (b) Hydrogel (PAAm-Alginate) attached to d-HAPT coated eco-flex enduring extensive tensile stress without debonding. (c) The hydrogel attached to eco-flex without d-HAPT delaminated while strain motion. (d) Illustration of lap shear test of hydrogel sandwiched between two identical substrates. (e) Bonding strength of WD bonding on PVA-TA, PVA, and PAAm-Alginate hydrogel attached to the PDMS, PI, and SS (\u003cem\u003en\u003c/em\u003e=3). (f) Lap shear test result of PAAm-Alginate hydrogel attached to the various dry substrates (PDMS, Pi, and SS) demonstrating uniform bonding strength regardless of the materials. (g) Structure of stretchable hydrogel circuit integrated via d-HAPT, and demonstration of its adhesion stability upon stretching motion.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/9b5884a962002df8b976f3a4.png"},{"id":54599996,"identity":"24f22f7a-53eb-4769-8074-81697b116212","added_by":"auto","created_at":"2024-04-12 20:50:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":558801,"visible":true,"origin":"","legend":"\u003cp\u003eWearable electronics applications (a) Schematic of a wearable touch panel integrated using d-HAPT. (b) Working principle of the wearable touch panel with four points sensing. (c) Current measurement data for each point upon contact. (d-e) Operation of (d) drawing letters and (e) video games via the wearable touch panel. (f) Schematic of a ring-shaped strain sensor fabricated using d-HAPT, which could sense different ranges of human motions in joints. (g-h) Measurement of resistance changes upon joint movement for (g) a finger, (h) a wrist, and (i) an elbow. (j) Resistance changes depending on the bending angle. (k) The ring-shaped strain sensor's stability upon repetitive bending deformation shows negligible resistance changes without debonding over multiple stretches.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/2b479b092cc5d73faed75c94.png"},{"id":54600156,"identity":"cdfffcca-9205-456b-bd29-8c05fda07f36","added_by":"auto","created_at":"2024-04-12 20:58:01","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1142353,"visible":true,"origin":"","legend":"\u003cp\u003eBiocompatibility of d-HAPT and implantable bioelectronic device applications (a) Schematic of \u003cem\u003ein vitro \u003c/em\u003ecell biocompatibility test for d-HAPT-coated PI film. (b) Fluorescence microscopic images of live/dead staining on NIH3T3 cells of bare and coated polyimide (PI) film, and statistical analysis (\u003cem\u003en\u003c/em\u003e=3) (scale bars, 100 µm). (c) Fluorescence microscopic image of TRITC phalloidin staining on NIH3T3 cell of bare and coated PI film and statical analysis of the cell morphology. (d) Schematic of \u003cem\u003ein vivo\u003c/em\u003e biocompatibility test by implanting d-HAPT-bonded PDMS disc into the subcutaneous space of mice. (e) Optical images of implanted mouse and removed the device after 7-days of implantation. (f) Representative histological images of 7-days post-subcutaneous implantation, stained with Hematoxylin and Eosin (H\u0026amp;E), Toluidine blue (TB), and Masson's Trichrome (MT) (scale bars = 50 µm). Orange arrows in TB-stained sections indicate mast cells. (g) Serum Aspartate aminotransferase (AST), and Alanine aminotransferase (ALT) levels were measured before implantation and at 3-, 7-, and 10-days post-implantation (\u003cem\u003en\u003c/em\u003e = 4). Statistical analysis was performed using the Wilcoxon signed-rank test. (*\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05, **\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.01, ***\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.001, and ****\u003cem\u003eP\u003c/em\u003e \u0026lt; 0.0001). ns, not significant. (h) Schematic of implantable bioelectronic device application. (i) Optical images of bending and stretching of the implantable device. (j) Optical image of a device implanted to stimulate the sciatic nerve. (k) Leg moving angle and optical image with various stimulation currents. (\u003cem\u003en\u003c/em\u003e = 3). (l) Optical image of a device implanted to monitor the \u003cem\u003ein\u003c/em\u003e \u003cem\u003evivo \u003c/em\u003eelectrocardiogram. (m) Electrocardiogram monitoring using an implanted device.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/fa7649a9f460bf1d3a9aa628.png"},{"id":60209780,"identity":"f64701ec-8b51-49b6-8c48-5a25c4432ac5","added_by":"auto","created_at":"2024-07-13 07:09:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6462166,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/e5db2d8f-7e23-48bc-8f99-f8664310fa68.pdf"},{"id":54599995,"identity":"8d064d56-4493-49d1-963b-c4bee1164bf8","added_by":"auto","created_at":"2024-04-12 20:50:00","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":19361563,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SInpjFE.docx","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/c460ab0a1a5f75d794df9367.docx"},{"id":54599998,"identity":"960d697d-28ca-4eb2-9c48-b2b31af5d960","added_by":"auto","created_at":"2024-04-12 20:50:00","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":44991605,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 1\u003c/p\u003e","description":"","filename":"SupplementaryMovie1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/12ee657525001e6e4150c72b.mp4"},{"id":54599999,"identity":"56ea170e-28ab-4771-bb7a-5479ba625686","added_by":"auto","created_at":"2024-04-12 20:50:00","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":42244442,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 2\u003c/p\u003e","description":"","filename":"SupplementaryMovie2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/a85902c14591d7b00b655442.mp4"},{"id":54599997,"identity":"5b6426b9-ddfd-4a51-90e6-d785fe7249b7","added_by":"auto","created_at":"2024-04-12 20:50:00","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":30948916,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 3\u003c/p\u003e","description":"","filename":"SupplementaryMovie3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/9675f5b8ea3ef74c226e69fb.mp4"},{"id":54600001,"identity":"b23eedd8-db18-4ef6-b675-152984dcf098","added_by":"auto","created_at":"2024-04-12 20:50:01","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":88952511,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 4\u003c/p\u003e","description":"","filename":"Supplementarymovie4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/dbf2bd8011658b2cffae90df.mp4"},{"id":54600000,"identity":"24057adb-5deb-44a4-97a7-339a020796b4","added_by":"auto","created_at":"2024-04-12 20:50:01","extension":"mp4","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":30505550,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 5\u003c/p\u003e","description":"","filename":"Supplementarymovie5.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/f24bb574b5ac724339453daa.mp4"},{"id":54600003,"identity":"1322f107-8379-49f4-9147-02947a7bb9db","added_by":"auto","created_at":"2024-04-12 20:50:01","extension":"mp4","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":47707836,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 6\u003c/p\u003e","description":"","filename":"Supplementarymovie6.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/83af9be8cc8b9c378cb2687d.mp4"},{"id":54600002,"identity":"5ddfbacf-e1e3-46ca-9810-6115e250f9c5","added_by":"auto","created_at":"2024-04-12 20:50:01","extension":"mp4","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":42109186,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Movie 7\u003c/p\u003e","description":"","filename":"Supplementarymovie7.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4169072/v1/eae0c1c13b7bf001ec33ea0f.mp4"}],"financialInterests":"(Not answered)","formattedTitle":"Universal Hydrogel Adhesives with Robust Chain Entanglement for Bridging Soft Electronic Materials","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSoft electronics have received significant attention due to their potential to revolutionize human-machine interaction by bridging the mechanical disparity between traditional rigid electronics and soft tissues\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. These soft electronic devices are composed of soft and rigid building blocks. The soft building blocks usually comprise stretchable and flexible polymers\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, and hydrogels\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, serving as deformable substrates, interconnectors, and electrodes. These soft building blocks facilitate the conformal contact between the device and the human body, allowing reliable sensing of various biological signals or stimulation of body tissue. In particular, many studies have introduced hydrogel-based electronic devices by exploiting the distinctive properties of hydrogels, including their high water content, low Young\u0026rsquo;s modulus, and biocompatibility\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. However, the realization of soft electronics with only soft components is considered infeasible due to limitations in handling the tasks of data processing or transmission. Therefore, the use of rigid electronic components (e.g., IC chips and printed circuit boards (PCBs)) is essential\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. These soft and rigid components should be seamlessly integrated and robustly combined for the reliable operation of the devices under dynamic movement conditions. However, achieving stable integration is challenging due to their inherent differences in chemical and mechanical properties. For instance, the strong adhesion of hydrogels (wet materials) to other building blocks (dry materials) is difficult owing to their high water content, which prevents intimate contact and adhesion between them. Therefore, universal adhesion strategies that achieve flexible but robust integration not only at dry/dry interfaces but also at wet/dry interfaces are required.\u003c/p\u003e \u003cp\u003eStable integration of the building blocks using conventional adhesives has been inappropriate due to unstable bonding interface and biocompatibility. For example, cyanoacrylate-based superglues are frequently adopted for their immediate bonding capability. However, the bonded interface lacks flexibility, and resistance to mechanical stress, and temperature\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Besides, typical superglues could not be cured on silicone-based elastomers such as polydimethylsiloxane (PDMS) and Eco-flex, which are extensively used in soft electronic devices. Furthermore, the cytotoxicity of cyanoacetate and formaldehyde has been a concern as toxic components could be released during the degradation of polycyanoacrylate\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Epoxies are also widely adopted as adhesives for soft electronics. Nonetheless, they have limited adhesion to certain plastics and require a long curing time. In addition, the difficulty of controlling the shape of the soldered form restricts their applications for minimized soft electronic devices\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Silver pastes provide electrical connectivity and adhesiveness. However, cytotoxicity and poor bonding strength hinder bioelectronic applications\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Most importantly, these conventional adhesives enable the bonding between dry and rigid materials, but stable bonding of soft or wet materials remains a challenge due to their differences in mechanical modulus and water content. To improve the bonding properties of the conventional adhesives, surface activation, and a modified cyanoacrylate-based adhesive were introduced as the adhesion strategies that establish conformal bonding interfaces to soft materials, including hydrogels. However, each strategy showed limited selectivity, and biocompatibility was not investigated. Therefore, there is a need to develop universal and reliable adhesion strategies that offer biocompatibility, flexibility, electrical adaptability, and the capability to facilitate robust bonding and integration of various soft/rigid and wet/dry electronic materials.\u003c/p\u003e \u003cp\u003eHydrogel adhesives are emerging as potential breakthroughs for biocompatible and universal adhesive materials. Nature-derived hydrogel adhesives (e.g., chitosan-based\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, gelatin-based\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, and mussel-inspired\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e) exhibit non-selective adhesion due to their abundant functional groups. The functional groups within the adhesive facilitate the physical and chemical interactions with adherents. However, these adhesives usually result in thick bonding interfaces and have relatively low bonding strength, which hinders their application in electronics. Recently, dry hydrogel adhesives that improve the bonding strength of typical hydrogel adhesives have been introduced, utilizing their maximized water-swellable property\u003csup\u003e\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. Dry hydrogels rapidly absorb the surrounding moisture and undergo rapid hydration and swelling. This enhances the molecular chain mobility that facilitates the formation of tough bonding interfaces through diverse mechanical interactions and entanglement. This property of dry hydrogels holds immense potential as adhesive materials. Consequently, there have been reports on the development of dry hydrogel adhesives that seamlessly attach soft electronic devices and tissues\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. However, their effectiveness in integrating the building blocks that comprise soft electronic devices remains unexplored.\u003c/p\u003e \u003cp\u003eHere, we introduce a universal and biocompatible dried-hydrogel adhesive made of poly(vinyl alcohol) (PVA) and tannic acid (TA) multilayers (d-HAPT) that enable robust bonding and integration of diverse soft/rigid and wet/dry building blocks. d-HAPT exhibits softness, biocompatibility, and excellent adhesion properties by taking advantage of dry hydrogel adhesives. Especially, the abundant functional groups in TA and moisture-derived chain entanglement facilitate the robust integration of dry/dry materials (DD bonding) and wet/dry materials (WD bonding) regardless of their mechanical and surface properties. d-HAPT is successfully applied to substrates of various sizes, from small electrodes to large Si wafers by dip, spray, or brush coating. Moreover, d-HAPT has a thin thickness of less than 1\u0026micro;m and exhibits high transparency with a transmittance of over 85% in the visible light region while enabling strong integration within 1 min. The DD bonding strength of metals and polymers was 4 MPa and 600 kPa, respectively. Moreover, the tough hydrogel was firmly attached to the d-HAPT-coated Eco-flex substrate even at 630% elongation. To demonstrate the practical adaptability of d-HAPT in wearable soft electronics, we fabricated hydrogel-based wearable devices including a touch panel and strain sensors. Each device maintained stable adhesion and operation in bending and stretching situations. Furthermore, non-toxicity was demonstrated by \u003cem\u003ein vitro\u003c/em\u003e and \u003cem\u003ein vivo\u003c/em\u003e biocompatibility tests. Given the biocompatibility of d-HAPT, implantable soft electronic devices based on it have been developed to perform \u003cem\u003ein vivo\u003c/em\u003e neuromodulation and electrocardiographic recording. Considering the biocompatibility, adhesiveness, and versatility, d-HAPT could be a promising candidate adhesive to replace conventional adhesives used for sophisticated soft electronics.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eIntegration of soft electronic devices facilitated by d-HAPT\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea shows a schematic of possible applications of d-HAPT in soft electronic devices composed of various components comprising a soft substrate, electrodes, rigid electronics, and a flexible interconnector. The integration of these materials is seamlessly facilitated by d-HAPT via two distinct adhesion mechanisms: 1) dry/dry materials bonding (DD bonding) and 2) wet/dry materials bonding (WD bonding). DD bonding enables adhesion among dry materials including elastomers, plastics, rigid electronics, metals, etc. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea(i), d-HAPT coated on the substrates swells by absorbing a little interfacial water, which leads to chain entanglement of d-HAPT. The subsequent mild thermal treatment facilitates robust bonding between the substrates by evaporating moisture in d-HAPT instantly. WD bonding utilizes the water-rich property of hydrogels leading to the attachment of them to the dry substrates (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea(ii)). When the hydrogel is attached to the d-HAPT-coated substrate, d-HAPT absorbs the water at the interface of the hydrogel matrix. The absorbed water leads to the diffusion of polymer chains of adhesive into the hydrogel matrix, thereby entangling the hydrogel network. These two bonding mechanisms accomplish robust adhesion of diverse materials with a broad spectrum of mechanical moduli, attributed to the swellable and soft nature of hydrogel constituents of d-HAPT. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and c show representative examples showing the efficacy of DD bonding and WD bonding. To demonstrate the robustness of DD bonding, polymethyl siloxane (PDMS) (\u003cem\u003eE\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;1 MPa) discs were attached to Eco-flex substrates (\u003cem\u003eE\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;120 kPa) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and Supplementary Movie 1)\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. The strong adhesion is maintained even when the sample is subjected to repeated areal strain of up to 350%. Furthermore, to confirm the strong adhesion of hydrogel bonding, we designed a light-emitting diode (LED) circuit system employing a conductive hydrogel (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec and Supplementary Movie 2). The conductive hydrogel was adhered to a pair of stainless steel (SS) components coated with d-HAPT (\u003cem\u003eE\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;200 GPa). The emitted light from the LED remained stable even when the hydrogel underwent a 200% extension of its initial length. These outcomes comprise substantial evidence that d-HAPT enables robust adhesion between various materials, enduring mechanical stresses including cyclic elongation and relaxation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eFabrication and characterization of d-HAPT\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the schematic illustration of the d-HAPT fabrication process through layer-by-layer (LbL) deposition onto substrates. TA layer was adopted as the first layer, because of its capacity to interact with various materials attributed to the plentiful galloyl groups in TA molecules. It is known that the hydroxyl groups in the TA molecule induce hydrogen bonds and metal coordinate bonds, whereas benzene rings bring about hydrophobic interaction and \u003cem\u003eπ\u003c/em\u003e\u0026ndash;\u003cem\u003eπ\u003c/em\u003e interaction\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. These diverse physical and chemical interactions facilitate the stable TA-driven surface coating on a variety of materials, regardless of the substrate being organic/inorganic, and hydrophilic/hydrophobic. Sequentially, the PVA and TA layers are alternately stacked. PVA is a polymeric component that increases adhesion by forming multidentate bonds with TA through hydrogen bonds\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Furthermore, the strong hydrogen bond at the interface of the PVA and TA layer allows the uniform deposition of PVA/TA multilayers\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. ATR-FTIR spectroscopy analysis was conducted to affirm the successive layer stacking via the LbL assembly process and the presence of the strong hydrogen bonding interlinking each layer (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Each step is denoted as T\u003csub\u003en\u003c/sub\u003eP\u003csub\u003em\u003c/sub\u003e, where n and m indicate the number of TA layers and PVA layers, respectively. After the coating of the primary TA layer, the broad and dull peak showed at 3100\u0026ndash;3500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating a hydroxyl group (\u0026ndash;OH) stretching band\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Upon the introduction of the subsequent PVA layer, the methylene group (\u0026ndash;CH\u003csub\u003e2\u003c/sub\u003e\u0026ndash;) stretching peaks at 2908 and 2941 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, characteristic of PVA, appear alongside the OH-stretching band\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. This result demonstrates the successful deposition of the PVA layer after the initial TA layer. Moreover, as successive layers are stacked, the OH-stretching peak gradually shifts to higher wavenumbers, from 3295 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for pure PVA to 3349 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the T\u003csub\u003e3\u003c/sub\u003eP\u003csub\u003e2\u003c/sub\u003e. The obvious blue shift of the peak suggests the enhancement of strong hydrogen bonding between PVA and TA during LbL assembly\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. The stepwise thickness growth seen in Supplementary Fig.\u0026nbsp;1, provides additional confirmation of the continuous and stable multilayer coating achieved through the LbL assembly technique. According to the thickness data, the PVA layer is dominant in terms of thickness, and the overall thickness of the adhesive remains within the submicron scale (958.9\u0026thinsp;\u0026plusmn;\u0026thinsp;25 nm). The SEM image visualized a sub-1 \u0026micro;m thick d-HAPT conformally coated on the glass substrate, similar to the thickness measurement data above (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;2). The areal surface roughness (S\u003csub\u003ea\u003c/sub\u003e) data analyzed by the laser confocal microscope image (0.014 \u0026micro;m) and AFM image (0.0171 \u0026micro;m) further clearly demonstrated the uniformity of the dip-coated d-HAPT (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, e). Additionally, the spray-coated, and brush-coated d-HAPT are investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef and Supplementary Fig.\u0026nbsp;3). The thickness and roughness of spray-coated d-HAPT was 3.2 \u0026micro;m and 0.022 \u0026micro;m, and that of brush-coated d-HAPT was 4.5 \u0026micro;m and 0.163 \u0026micro;m. These results indicate that the d-HAPT-coated surfaces are uniform irrespective of the coating methods. The versatility of coating methods is a notable advantage in applicability across a wide spectrum ranging from wide wafer scale to meticulous electrodes (Supplementary Fig.\u0026nbsp;4). Additionally, d-HAPT can be fabricated into a free-standing film, enhancing its practical application (Supplementary Fig.\u0026nbsp;5). For d-HAPT to establish a robust bonding at the interface of two materials, it must remain securely affixed to the substrate, even under the influence of external forces. Therefore, to demonstrate the mechanical stability of d-HAPT, a crosscut test was conducted (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg). A series of optical images demonstrate the results of the crosscut test onto two other substrates: glass (hydrophilic) and TPU (hydrophobic). For both substrates, d-HAPT is kept securely after 10 cycles of tape peeling. Moreover, the transparency of d-HAPT was assessed using ultraviolet-visible (UV\u0026ndash;Vis) spectroscopy (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). The d-HAPT-coated glass substrates exhibit a transmittance of approximately 85% across the entire visible light spectrum (400\u0026ndash;750 nm). This exceptional transparency is attributed to the ability of the d-HAPT to coat the substrate conformally and uniformly as confirmed above. In contrast, when solutions of TA and PVA were mixed and coated on glass (referred to as 'Mixed'), the transmittance dropped dramatically to below 40%. Visual observations of the samples with optical images corroborate these results. In the case of a mixed sample, it appears blurry behind the glass. Opacity is caused by the formation of yellowish precipitates in the case the PVA and TA solutions are mixed due to the strong hydrogen bond between PVA chains and TA molecules. Whereas the transparency of d-HAPT-coated glass closely resembles that of bare glass, enabling clear visibility of text and colors behind the glass. This is due to the controlled formation of hydrogen bonds at the interface of the PVA layer and TA layer. Consequently, the LbL approach yields a uniformly surfaced d-HAPT with minimal diffuse reflection and high transparency. This suggests that the d-HAPT could provide reliable alignment of the chips and electrodes demonstrating its potential application in optical soft electronic devices.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eDD bonding mechanism and durability of the adhesion\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea illustrates the DD bonding process and its underlying mechanism. For DD bonding, interfacial water should be formed between d-HAPT-coated dry surfaces. The dry hydrogel constituents of d-HAPT allow it to swell by absorbing the interfacial water, thereby increasing chain mobility\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. The enhanced chain mobility leads to the entanglement of chains across the dry substrates. Subsequently, a mild heat is applied to evaporate the residual water of d-HAPT. This causes the entangled chains to aggregate and be fixed, which leads to robust bonding between the dry substrates.\u003c/p\u003e \u003cp\u003eTo investigate the effect of heating temperature on the adhesion, SS substrates were bonded under various temperature conditions (70 to 160\u0026deg;C) with a fixed bonding time of 1 min (Supplementary Fig.\u0026nbsp;6). The results showed strong integration of substrates at all temperature conditions, with increasing bonding strength with the increasing bonding temperature (from 3 MPa at 70\u0026deg;C to 5.5 MPa at 160\u0026deg;C). This is attributed to the different interfacial water evaporation rates affecting the aggregation and fixation of chains. Moreover, the effect of heating time was investigated by bonding PDMS substrates at temperature conditions of 70 and 100\u0026deg;C for 1 and 5 min (Supplementary Table\u0026nbsp;1). These results indicate that substrates can be effectively bonded under various temperature and time conditions. Suitable bonding conditions can be selected according to the specific characteristics of the substrate. To ensure a simple and fast process, the standard bonding condition was determined to be 130\u0026deg;C for 1 min in this article, which can be easily achievable with a hair iron (Supplementary Fig.\u0026nbsp;7 and Supplementary Movie 3).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb presents an optical image of d-HAPT bonded PDMS substrates. The d-HAPT showed high transparency in the visible light region (Supplementary Fig.\u0026nbsp;8). Additionally, it exhibits exceptional flexibility, attributed to the softness of hydrogel-based components within d-HAPT. The cross-sectional SEM image reveals seamless bonding between the PDMS substrates and the d-HAPT (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Furthermore, the boundary of the d-HAPT was not visible, affirming that the two d-HAPT layers effectively entangled during the bonding process. To assess bonding strength, lap shear tests were conducted on various materials widely adopted for soft electronic devices, including metals and polymers (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Initially, two identical metal substrates were bonded using a hair iron in standard condition. The bonding strength for these metals exceeded 2.5 MPa, with stainless steel demonstrating the highest bonding strength over 4 MPa (4.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 MPa for SS, 2.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 MPa for aluminum (Al), 2.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 MPa for Copper (Cu)) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). These values are 50 times higher than the bonding strength observed in other hydrogel-based adhesives capable of attaching metals with an intensity of up to 80 kPa\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef shows the strong adhesion of SS substrates sufficient to support a 20 kg water tank. This excellent adhesion in metals is attributed to the metal coordinate bonds, and hydrogen bonds between TA and PVA\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Subsequently, the bonding strength of polymer substrates was investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). Considering the glass transition temperature of polymers, the bonding condition was adjusted to 1 min in a drying oven at 100\u0026deg;C. The bonding strength exceeded 500 kPa for all polymer materials (637.6\u0026thinsp;\u0026plusmn;\u0026thinsp;105 kPa for polyimide (PI), 556.7\u0026thinsp;\u0026plusmn;\u0026thinsp;98 kPa for acryl, 537.911\u0026thinsp;\u0026plusmn;\u0026thinsp;60 kPa for polypropylene (PP)). In the case of PDMS, they were stretched without debonding until fracture occurred due to the inherent stretchability of PDMS. The fractured section of the samples corresponds to a non-adhered region, signifying that d-HATP sufficiently withstands the stress that induces PDMS breakage (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). These overall results demonstrate that d-HAPT could form strong bonds between the same materials. For practical applications, adhesive compatibility between different materials is crucial. Bonding heterogeneous substrates presents more challenges compared to bonding the same materials, primarily due to the disparities in mechanical and chemical properties among materials. Nevertheless, d-HAPT with abundant functional groups enables robust bonding regardless of substrate properties. To evaluate this, lap shear tests were conducted across various substrate combinations. Samples were prepared by sandwiching a material with a lower modulus (substrate 2) between two substrates with higher moduli (substrate 1) to minimize the effect of deformation of elastomer substrates during measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). The samples exhibited effective integration to a large extent that elastomer substrate 2 (Eco-flex, PDMS) fractured during testing (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej, k). Consequently, d-HAPT facilitates robust adhesion among diverse materials and substrate combinations through a substrate bonding process, all accomplished within a short time. In conclusion, d-HAPT holds promise for integrating solid materials used in soft electronic devices regardless of material properties.\u003c/p\u003e \u003cp\u003eTo demonstrate the remarkable performance of d-HAPT as an adhesive, a comparative analysis was conducted against the existing adhesives used in soft electronics (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003el and Supplementary Table\u0026nbsp;2)\u003csup\u003e\u003cspan additionalcitationids=\"CR34 CR35\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. d-HAPT is a thin adhesive that enables rapid and robust bonding (shear strength\u0026thinsp;\u0026asymp;\u0026thinsp;200 kPa, T-peel strength\u0026thinsp;\u0026asymp;\u0026thinsp;4 N/cm for soft materials) (Supplementary Fig.\u0026nbsp;9). A few polymer-based adhesives with comparable bonding strength and thickness were reported, but they required prolonged heat treatment for chain entanglement (2 days), or adhesive network stabilization (\u0026gt;\u0026thinsp;10 min) compared to d-HAPT. In the case of hydrogel-based adhesives, the polar groups within their network facilitate instant bonding between soft materials. However, d-HAPT exhibits stronger adhesion than the hydrogel-based adhesives, even at a thousandth of thickness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eWD bonding mechanism and durability of the adhesion\u003c/h2\u003e \u003cp\u003eHydrogel has been a promising candidate for advanced soft electronics by leveraging soft and tissue-like properties. Nonetheless, integrating hydrogels with diverse materials poses a significant challenge due to their innate water-rich composition and exceptionally low modulus\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. As the hydrogel is susceptible to heat applied during thermal bonding, a modified bonding process has been adopted for bonding between hydrogel and dry substrates (WD bonding). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea illustrates the WD bonding process and its underlying mechanism. To attach the hydrogels, they are simply placed onto the adhesive-coated substrates. Then, the d-HAPT absorbs the water at the interface with the hydrogel matrix, leading to the diffusion of its hydrogel polymer chains into the d-HAPT. These diffused hydrogel chains become entangled with the d-HAPT, ultimately resulting in the integration of hydrogel and substrates.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb demonstrates the mechanical robustness of WD bonding. When the polyacrylamide (PAAm)-Alginate tough hydrogel is affixed to the d-HAPT-treated Eco-flex substrate, it exhibits remarkable stretchability. The bonded substrates endured strains over 600% of their original length without delamination. This stable adhesion between the hydrogel and Eco-flex remained intact even when the sample was fractured. In contrast, when the tough hydrogel was attached to an untreated Eco-flex substrate, the hydrogel was delaminated from the substrate not being stretched along with the elastomer (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). This outcome implies incomplete adhesion between the hydrogel and the elastomer substrate and demonstrates the crucial role of d-HAPT in establishing a robust hydrogel-elastomer interface. To evaluate the bonding strength of WD bonding, lap shear tests were conducted by sandwiching hydrogels between substrates with various combinations (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). Three types of hydrogels were selected: a tough hydrogel (PVA-TA)\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e, a single-network hydrogel (PVA)\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e, and a double network tough hydrogel (PAAm-Alginate)\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. These hydrogels adhere robustly on the d-HAPT coated substrates compared to the bare substrates (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). The differences in bonding strength between hydrogels were attributed to the inherent mechanical properties and degree of polymer chain diffusion. In the case of PVA-TA tough hydrogel, the PVA polymer chain easily diffuses into the d-HAPT leading to the strong adhesion strength. However, single-network PVA hydrogel shows comparatively low bonding strength due to its inherent low mechanical modulus and weak cohesion. For PAAm-Alginate hydrogel, long-chain and dissipative polymer networks are densely entangled, which hinders the active diffusion of the hydrogel chains into the d-HAPT. Nevertheless, the intact interface of PVA hydrogel and PAAm-Alginate hydrogel with the substrates during the tests evidenced their stable integration (Supplementary Fig.\u0026nbsp;10, 11). Remarkably, each hydrogel exhibited a similar bonding strength across all substrates (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef and Supplementary Fig.\u0026nbsp;12). This uniformity could be attributed to the universal adhesion of d-HAPT on the substrate, which is derived from the abundant functional groups within TA molecules. These adhesion test results demonstrate that d-HAPT could offer a stable and universal WD bonding interface despite its relatively low bonding strength, showing intriguing potential for a dry hydrogel adhesion strategy. Existing adhesion strategies for hydrogels have employed hydrogel pre-gel solutions to induce adhesion to substrates\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. Although these approaches offer the advantage of a stronger interfacial toughness, they face practical limitations, requiring additional curing processes. Additionally, specific chemical modifications must be performed depending on the hydrogel. However, d-HAPT facilitates stable adhesion to soft substrates regardless of its mechanical and chemical properties owing to moisture-derived robust chain entanglement. This presents a significant advantage for practical application providing convenience in the process and versatile applicability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo demonstrate the durability and applicability of the d-HAPT as an adhesive for hydrogel-based electronics, we fabricated a simple stretchable circuit system (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg and Supplementary Movie 4) using conductive hydrogel. The hydrogel was 3D printed on d-HAPT-treated Eco-flex to serve as the interconnector. Then, LED chips coated with d-HAPT by brushing were adhered to the hydrogel interconnectors. The fabricated device exhibited stretchability, without any delamination of LED chips. Upon applying a voltage to both ends, the light of the LED was turned on and maintained even when the device was stretched to 150% of its initial length. The diminished light intensity was recovered as soon as the device was relaxed to its original length suggesting the stable adhesion of the soft and rigid components via d-HAPT.\u003c/p\u003e \u003cp\u003eSupplementary Table\u0026nbsp;3 demonstrates the comparison of various adhesion methods that attach various building blocks of soft electronics\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan additionalcitationids=\"CR34 CR35 CR36 CR37\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. While some studies exhibit the exceptional adhesive strength, none of them show multifunctional adhesive properties including soft/soft, rigid/rigid, soft/rigid, soft/hydrogel, and rigid/hydrogel and their electrical applications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eWearable electronics applications\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea illustrates the wearable touch panel comprising three layers: an upper ionic hydrogel layer for touch sensing, a flexible flat cable (FFC) for signal transmission, and a lower PDMS layer serving as an insulator\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. The conformal assembly of the layers was secured using d-HAPT, which substantially contributed to sustained sensing performance and reliable signal transmission. For example, maintaining stable interconnection between the ionic hydrogel and the FFC is challenging during dynamic body movement due to their relatively minor contact area and mechanical mismatch. However, d-HAPT exhibited strong adhesion at the interface of the FFC cable and touch panel enduring applied strains (Supplementary Fig.\u0026nbsp;13 and Supplementary Movie 5). The transparent ionic hydrogel layer was colored purple for visualization. As the FFC cable adhered to the hydrogel was pulled, the hydrogel was also stretched showing stable interfaces. Upon further pulling, a fracture was initiated on the hydrogel without debonding of the FFC cable, as seen in the inset. This durable adhesion enables the stable operation of wearable touch panels even in dynamic conditions. The operational principle of this wearable touch panel is based on a surface capacitive system, as elucidated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. A uniform electrostatic field is established across the touch panel by applying an identical alternating current voltage to its four corners. When a finger contacts the touch panel, the touch point becomes grounded, allowing current to flow from the corner electrodes toward the touch point. To investigate the current at the four corners depending on the touch position, we evaluated the current variations as contacting with Point 1 to Point 4 on the panel surface sequentially. Visible difference in current was observed upon the contact of a finger (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). Notably, it was confirmed that the current was proportional to touch point proximity to the corner electrodes. Based on this outcome, the formula was deduced to investigate the correlation between the current measured at the corners and the specific touch point (Supplementary Fig.\u0026nbsp;14). A controller board was employed to convert the current data to the position on the touch panel. This wearable touch panel was attached to the forearm seamlessly and interfaced with a computer system through the controller board (Supplementary Fig.\u0026nbsp;15, 16). To test the reflection of the touch on the monitor, we wrote the word \u0026lsquo;BLISS\u0026rsquo; on the touch panel (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed and Supplementary Movie 6). As a result, high-resolution letters were successfully acquired, despite minor distortions along the edges. Additionally, a video game, avoiding obstacles by jumping while running, was performed using this touch panel. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee, tactile interaction with the touch panel induced the character jumps (Supplementary Movie 7). These results suggest that the hydrogel touch panel integrated through d-HAPT successfully operated on the forearm.\u003c/p\u003e \u003cp\u003eThe hydrogel strain sensors are promising bioelectronic applications exhibiting the capability of monitoring various human movements. However, their practical utility has been hampered by unstable connections between integrating components, such as a substrate, a cable, and a sensing layer. The difficulty causes problems in maintaining its shapes and securing consistent data acquisition during vigorous physical motion. In response to these issues, we have introduced a ring-shaped wearable strain sensor designed to mitigate the risk of detachment from the body (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef). The foundational design comprises a stretchable Eco-flex substrate fashioned into a circular configuration. On this substrate, a carbon nanotube (CNT) hydrogel\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e responsible for sensing, and a conductive thread for transmitting data were affixed by utilizing d-HAPT. The fabricated strain sensors exhibited excellent softness due to the intrinsic stretchability of conductive hydrogel and Eco-flex. As a result, this ring-shaped wearable strain sensor offers stretchability, enabling repeated use while ensuring the user\u0026rsquo;s comfort. To comprehensively assess the versatility and robustness of this strain sensor, sensors were applied to distinct joints, such as a finger, a wrist, and an elbow (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg-i). Notably, even during the bending of these joints, the measurement of the electrical resistance was seamless without any disruption to the hydrogel-substrate interface. Although the resistance modulation was inherently influenced by the range of motion within the joints, a resistance alteration rate across all cases exceeded 20%. Also, the gauge factor (GF) of this sensor was 1.22, surpassing that of the existing strain sensors. Leveraging the exceptional sensitivity of the sensor, precise angle-dependent sensing capabilities were demonstrated on the finger (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ej). Additionally, extensive stretching cycles of the strain sensor were systematically conducted to evaluate the durability of the sensor. Throughout 300 stretching cycles, the strain sensor consistently exhibited stable and reliable sensing characteristics, attesting to its robustness and durability (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ek). Consequently, d-HAPT enabled the stable operation of wearable soft electronics by providing robust adhesion between each building block. These devices were capable of sensing signals accurately even in bending and stretching situations that occur during the use of soft electronics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eBiocompatibility of d-HAPT\u003c/h2\u003e \u003cp\u003eSoft electronics have gained prominence as a solution to mechanical challenges in implantable devices such as neural probes\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e, artificial vascular sensors\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e, and electronic sutures\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. For implantable devices, the materials should be non-toxic. To evaluate the biocompatibility of d-HAPT for implantable devices, a series of \u003cem\u003ein vitro\u003c/em\u003e cell viability and morphological analyses were conducted. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, the d-HAPT-coated on the flexible PI film was incubated with NIH3T3 fibroblasts in cell culture media using a transwell system. The cell biocompatibility test using transwell insert investigates the effect of physiological environment change on the cells by allowing cells to be in indirect contact with the tested materials. The results of the live/dead assay and the CCK-8 assay showed no significant differences in cell viability after incubation for 1, 3, and 5 days (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;17, 18). Moreover, analyzation of cell morphological changes can serve as another biomarker to evaluate the material\u0026rsquo;s biocompatibility (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec and Supplementary Fig.\u0026nbsp;19). When foreign materials are implanted, activated inflammation can cause fibroblasts to undergo morphological changes, transitioning from a healthy spindle shape to a pathological circular shape as a result of cytoskeletal remodeling. The morphology of the fibroblast was evaluated using cell aspect ratio after TRITC phalloidin staining. The results showed no significant differences in bare PI and d-HAPT-coated PI. Also, d-HAPT-bonded PDMS devices were implanted into the subcutaneous region of mice to investigate \u003cem\u003ein vivo\u003c/em\u003e biocompatibility (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed). To mimic actual application conditions and prevent the potential of enzymatic degradation of PVA and TA, the devices were encapsulated. After 7 days of implantation, the devices were retrieved and remained intact without any detachments, suggesting the durability of d-HAPT in the physiological environment (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee). Histological staining with Hematoxylin \u0026amp; eosin (H\u0026amp;E), toluidine blue (TB), and Masson's trichrome (MT) staining indicated that the implanted device did not trigger significant inflammatory responses or necrosis of surrounding tissues (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef). Furthermore, there was no observed increase in mast cells, as highlighted by organ arrows, or noticeable increase in collagen deposition. To evaluate any systemic response triggered by the implantation, serum levels of Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) were measured before and after 3, 7, and 10 days of implantation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg). There were no significant alterations in AST and ALT serum levels between the Sham and implanted groups across all time points, indicating that implantation did not induce hepatotoxic effects.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eImplantable bioelectronics applications\u003c/h2\u003e \u003cp\u003eGiven that the adhesive showed biocompatibility \u003cem\u003ein vitro\u003c/em\u003e and \u003cem\u003ein vivo\u003c/em\u003e experiments, we fabricated the implantable bioelectronic devices to evaluate the feasibility of d-HAPT as an adhesive for implantable applications (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eh). To fabricate the device, a PVA-liquid metal composite was printed on d-HAPT coated PDMS substrate as stretchable hydrogel electrodes. Then a FFC was integrated through the DD bonding process, similar to the structure of soft electronics illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The device was firmly integrated despite the application of external forces, such as bending or stretching deformation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ei). Using this device, we first performed \u003cem\u003ein vivo\u003c/em\u003e neuromodulation on the rat sciatic nerve (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ej). As the stimulation was applied, leg of the rat responded showing different moving angle upon increase in the applied current (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ek). The electrocardiogram signal was also recorded using the identical device (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003el). P wave, QRS complex, and T wave, which play a vital role in diagnosing various cardiac disorders, were distinctly confirmed through the analyzed signal (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003em). In both sciatic nerve stimulation and electrocardiogram recording, the d-HAPT stably integrated the soft electronics during the intense movement of the leg and heart owing to the excellent adhesiveness. These overall results suggest the potential of d-HAPT for diverse implantable electronics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe chemical and mechanical mismatches between materials used in soft electronics have hindered the instant and stable bonding of these materials using conventional adhesives. In this study, we have introduced a simple yet effective dry hydrogel adhesive with biocompatibility and softness that could bring a paradigm shift in adhesion strategy for soft electronics. As a promising strategy for instant adhesion to diverse soft electronic materials, d-HAPT robustly interfaces them regardless of the types and shapes of the materials either dry or wet ones. The sub-micron d-HAPT exhibits excellent uniformity, transparency, and mechanical stability. Its water-swellable property enables strong bonding of diverse materials through the adhesive\u0026rsquo;s polymer chain entanglement, upon absorbing moisture. Using d-HAPT, the hydrogel touch panel and strain sensors were fabricated, which demonstrated the applicability of wearable soft electronics. d-HAPT also showed excellent biocompatibility in both \u003cem\u003ein vitro\u003c/em\u003e and \u003cem\u003ein vivo\u003c/em\u003e experiments. Furthermore, the neuromodulation on the sciatic nerve, and recording of the electrocardiogram signal were successfully performed with implantable soft electronic devices integrated with d-HAPT. Overall, the excellent mechanical stability, softness, and biocompatibility of d-HAPT present a promising approach for utilizing hydrogel adhesives in a wide range of applications, from wearable to implantable biomedical engineering.\u003c/p\u003e "},{"header":"Methods","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eThe chemicals were purchased and used without further purification. Poly(vinyl alcohol) (PVA, M\u003csub\u003ew\u003c/sub\u003e 89,000\u0026ndash;98,000), tannic acid (TA), acrylamide (AAm), acrylic acid (AA), N, N\u0026rsquo;-methylenebis(acrylamide) (MBAA), ammonium persulfate (APS), tetramethyl-ethylenediamine (TEMED), ammonium persulfate (APS), sodium alginate were purchased at Sigma Aldrich. A carbon nanotube (CNT) was purchased at Nanolab, Korea. Lithium chloride (LiCl) was purchased at Duksan, Korea. Gallium and Indium were purchased at AliExpress, China.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of d-HAPT\u003c/h2\u003e \u003cp\u003ePVA (2.5% w/v) was dissolved in deionized (DI) water at 140\u0026deg;C by stirring at 300 rpm for 2 hours. TA solution was prepared by dissolving TA (2.5% w/v) in DI water using a vortex mixer. Substrates were coated layer by layer using the PVA and TA solution with a dip coater with a speed of 130 mm/min. The first and the last layer were designed to be the TA layer. Before depositing each layer, the samples were dried at 45\u0026deg;C for 10 min. To fabricating d-HAPT into a free-standing film, T\u003csub\u003e4\u003c/sub\u003eP\u003csub\u003e3\u003c/sub\u003e layers were dip-coated with 7.5% w/v of TA and PVA solution at a speed of 130 mm/min.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Hydrogels\u003c/h2\u003e \u003cp\u003eThe hydrogels were fabricated as described in the previous research. To synthesize PVA hydrogel, PVA (4,000 mg) was dissolved in DI water (20 mL) at 140\u0026deg;C while stirring for 20 min. The PVA solution was poured into the mold. The PVA solution was freeze-thawed at temperatures between \u0026minus;\u0026thinsp;20 and 25\u0026deg;C to yield the PVA hydrogel. To synthesize PVA-TA hydrogel\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e, TA (4,000 mg) was dissolved in the PVA solution at 140\u0026deg;C. After 2 hours of stirring, the viscous PVA-TA solution was fabricated. The PVA/TA solution was spread on the mold to make its thickness 2 mm. Then, the PVA-TA solution was frozen and subsequently thawed to yield the PVA-TA hydrogel. The carbon nanotube (CNT) conductive hydrogel was fabricated following our previous research\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. To synthesize PAAm-LiCl hydrogel, a precursor solution was obtained by dissolving AAm monomer (146.35 mg/ml), MBAA (0.07% of AAm), APS (0.1% of AAm), 0.4 \u0026micro;L/mL of TEMED, and LiCl in DI water. The solution was poured into the mold with a thickness of 3mm. Then, the PAAm-LiCl hydrogel was cured for 4 hours at room temperature\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. To fabricate PAAm-Alginate hydrogel, alginate (29 mg/ml) was dissolved in DI water by stirring for an hour at room temperature. An AAm precursor solution (AAm monomer (666 mg/ml), MBAA (0.06% of AAm), APS (0.75% of AAm), and TEMED (2 \u0026micro;l/ml)) was added to the alginate solution. The PAAm-Alginate solution was poured into the mold with a thickness of 3mm. After 4 hours of the curing process, the PAAm-Alginate hydrogel was fabricated\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003ed-HAPT Characterization\u003c/h2\u003e \u003cp\u003eThe chemical structures were analyzed through ATR-FTIR (Vertex 70, Bruker, USA) with a range of 2800 to 3800 cm\u003csup\u003e-\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The thickness was analyzed using a surface profiler (DektakXT stylus Profiler, Bruker), and the surface morphology was acquired through AFM (NX-10, Park Systems), FE-SEM (IT-500HR, JEOL), and laser confocal microscope (VK-X3050, Keyenece). The mechanical stability was tested using a cross-cut test (ISO 2409). Cross-cut adhesion test (ISO 2409) was performed to test the durability of the coating. 100 blocks of size 10\u0026times;10 mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e were formed on the d-HAPT coated glass and TPU surface by scratching the surface using a crosscutter. Then, the adhesive tape was attached to the surface and removed from it. This process was repeated 10 times, and the integrity of the coating was assessed. The transmittance was measured using a UV\u0026ndash;Vis spectrophotometer (V-650, JASCO) with a wavelength range of 300 to 900 nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eBonding process\u003c/h2\u003e \u003cp\u003eFor DD bonding, the interfacial water is formed on d-HAPT-coated surfaces by dipping, brushing, or spraying. Then, the substrates were overlapped for a minute to induce moist absorption, thereby the polymer chain entanglement. The overlapped samples were heated for 1 min to evaporate residual interfacial water, leading to chain fixation. The heating temperature varied with the substrates from 100 to 130\u0026deg;C. For WD bonding, the hydrogel was placed on the coated surface of the substrate for 1 min.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eLap shear tests\u003c/h2\u003e \u003cp\u003eThe bonding strength was measured through lap shear tests using a tensile testing machine (Multitest-dV, Mecmesin). The samples were prepared with a bonding area of 15\u0026times;20 mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The tests were performed with a constant peeling speed of 5 mm/min. The bonding strength was detected with a 2500 N load cell.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eT-peel tests\u003c/h2\u003e \u003cp\u003ePeel strength was measured using the combination of two stretchable substrates of PDMS and Eco-flex. Two substrates with a size of 10\u0026times;40 mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e were bonded with an adhered area of 10\u0026times;10 mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e using d-HAPT. Then, the peel strength of the samples was tested using a tension tester (Multitest-dV, Mecmesin), with a strain rate of 50 mm/min.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eStretchable hydrogel circuit\u003c/h2\u003e \u003cp\u003eThe d-HAPT was formed on the Eco-flex and the electrodes of the LED chips (Adafruit LED, Adafruit). CNT\u0026middot;TA\u0026middot;PVA\u0026middot;PAA hydrogel was printed on the substrate using a 3D printer (EZROBO-5GX 3D printer, Iwashita) with a dispenser (AD3300C dispenser, Iwashita). Then, the coated LED chips were placed on the printed circuit. DC power supply (DP832, Rigol) was used to turn on LED chips.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eWearable touch panel\u003c/h2\u003e \u003cp\u003eThe wearable touch panel was fabricated by placing the PAAm/LiCl hydrogel with a thickness of 3mm on the d-HAPT-coated PDMS. Four vertexes of the ionic hydrogel were attached to the d-HAPT-coated FFCs (flat flexible cables) for connecting the touch panel to the devices that analyzed current changes caused by contact. To measure the degree of changes in current from touch, an AC voltage of 100 kHz from \u0026minus;\u0026thinsp;1 to 1V was applied to the vertexes using a function generator (AFG1022, Tektronix). Then the current was measured through the multimeter (34461A, Keysight) at each point. To confirm the operation of the wearable touch panel, FFCs attached to the touch panel were connected to a controller board (EXII-7720SC, 3M Touch Systems). Software MT7(3M, MicroTouch) was used as a calibration tool for the touch panel.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eStrain sensor\u003c/h2\u003e \u003cp\u003ed-HAPT-coated Eco-flex was used as a substrate, which is windable to body parts such as a finger, a wrist, and an elbow. CNT\u0026middot;TA\u0026middot;PVA\u0026middot;PAA hydrogel was placed on the substrate to measure the changes in resistance by bending the joint. For the measurement, the hydrogel was connected to the multimeter using the coated conductive thread (conductive stainless thread, DFRobot).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eIn vitro biocompatibility test\u003c/h2\u003e \u003cp\u003eThe 5\u0026times;5 mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e bare and d-HAPT-coated PI film was prepared. Afterward, a two-chamber transwell system (8 \u0026micro;m pore size; Corning Inc.) was introduced for cell viability and analysis of morphological change. The prepared PI films were placed on the insert and incubated with cells thorough the experimental time. The NIH-3T3 fibroblast cells (0.5\u0026times;10\u003csup\u003e5\u003c/sup\u003e cells/mL) were cultured in 6 well cell culture plates with 1.5 mL of Dulbecco\u0026prime;s Modified Eagle\u0026prime;s Medium - high glucose (DMEM) supplemented with 10% bovine calf serum and 1% penicillin-streptomycin. Cell viability was evaluated using a Live/Dead kit (L3224, Invitrogen, USA) according to the manufacturer's instructions. The intensity of fluorescence cell images was measured using an inverted fluorescence microscope (IX81, Olympus, Japan) with a 10\u0026times; magnification. Similarly, morphological change was measured following the aspect ratio calculation method which is the major cell axis divided by the minor one. For visualization, the cytoskeleton of NIH 3T3 cells was stained using an Alexa 594-conjugated phalloidin (Thermo Scientific, Pittsburgh, PA, USA). The cell morphology was evaluated using a confocal microscope (LSM 980, Carl Zeiss, Oberkochen, Germany) and calculated by the ImageJ/FIJI software program.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eIn vivo biocompatibility test\u003c/h2\u003e \u003cp\u003ed-HAPT-bonded PDMS (10\u0026times;10\u0026times;1 mm\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e) was subcutaneously implanted into 6-week-old male CD-1 (ICR) mice for 3, 7, and 10 days. The animal experimental protocols were approved by the Institutional Animal Care and Use Committee of Yonsei University College of Medicine (IACUC No. 2023-0097), and all experiments adhered to the guidelines set by an Association for the Assessment and Accreditation of Laboratory Animal Care (AAALAC)-accredited facility. Within this facility, animals were housed under 12-hour alternating light/dark cycles and had unrestricted access to food and water. Before the mice were anesthetized using ketamine (100 mg/kg) and Rompum (10 mg/kg). Mice were procured from Orient Bio Incorporation, Seongnam, Korea. To assess any hepatotoxicity resulting from d-HAPT, blood samples were drawn through retro-orbital bleeding both before and after 3, 7, and 10 days of implantation (n\u0026thinsp;=\u0026thinsp;4 for both the Sham and implanted groups). Blood was collected in heparinized capillary tubes (Micro-Hematocrit Capillary Tube Plain, Kimble Chase, Vineland, NJ, USA) and left to clot in a serum separation tube (BD Microtainer, BD, Franklin Lakes, NJ, USA) at room temperature for 2 hours. Subsequently, the samples underwent centrifugation at 300 g for 15 min, followed by 10 min at 600 g twice, after which the supernatant serum was extracted and stored at -80\u0026deg;C. Levels of AST and ALT in the serum were determined using a Dri-Chem 4000i biochemical analyzer (Fujifilm, Tokyo, Japan). For histological evaluations, mice were euthanized 3- and 7 days post-implantation, after which the implants and surrounding skin tissues were extracted and preserved in 10% formalin (Sigma-Aldrich, St. Louis, USA). The preserved tissues were then processed (ASP300S, Leica Biosystems, Nussloch, Germany), and embedded in paraffin blocks (Histo Core Arcadia, Leica Biosystems. Samples were then sectioned to a thickness of 4 \u0026micro;m and mounted onto slides (RM2255, Leica Biosystems) in preparation for histological staining with Hematoxylin and Eosin (H\u0026amp;E), Toluidine blue (TB), and Masson's Trichrome (MT).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eImplantable bioelectronic device applications\u003c/h2\u003e \u003cp\u003e All surgical procedures for mice were performed in accordance with protocols approved by the Institutional Animal Care and Use Committee (IACUC) at Korea Advanced Institute of Science and Technology (KAIST). 12-week-old female Sprague-Dawley rats (Koatech, South Korea) were anesthetized with isoflurane (5% induction, 2% maintenance). A heating pad was used to maintain the body temperature of the rat. To fabricate the implantable device, the composite of 3g of liquid metal (75% gallium and 25% indium) and 2 ml of PVA solution (5 wt%) is prepared as electrodes. 1 mm \u0026times; 7 mm size of two electrodes were spray-printed on a 6 mm \u0026times; 10 mm d-HAPT-coated PDMS substrate using a mask placed 2 mm apart. Subsequently, the d-HAPT-coated FFC was connected to the electrodes through DD bonding.\u003c/p\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003eSciatic nerve stimulation\u003c/h2\u003e \u003cp\u003eIncision along the left thigh was made to expose the sciatic nerve. The electrodes are gently placed beneath the sciatic nerve in order to contact the epineurium. The biphasic current was administered at a frequency of 10 Hz, with a pulse duration of 25ms and current ranging from 0.03 to 0.09 mA, using an isolated pulse stimulator (2100, A-M systems). The leg movement was quantified using a protractor positioned beneath the leg.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e \u003ch2\u003eElectrocardiogram recording\u003c/h2\u003e \u003cp\u003eAn acute tracheotomy was conducted, and the rat was intubated using a ventilator (VentElite Small Animal Ventilator, Harvard Apparatus) at a rate of 80 breaths per minute. Following a thoracic cavity incision, the ribs were carefully dissected to expose the heart. Subsequently, working and reference electrodes were positioned on the left ventricle. The electrocardiogram signals were recorded with an electrophysiology system (Lab Rat, Tucker-Davis Technologies). The recorded signals underwent bandpass filtering within the range of 0.3 Hz to 50 Hz.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eInformed consent\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research participants in the images in Fig. 5 agree to the publication of these photographs.\u0026nbsp;It was confirmed that a study using wearable devices simply touching the skin doesn\u0026rsquo;t need institutional review board approval.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eStatistical analysis\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data of all experiments were statistically analyzed with a minimum sample size of 3 using Graphpad Prism 8 software (Graphpad Software Inc., USA). In the statistical analysis between groups, the unpaired t-test was used. ns was considered not significant. Statistical analyses for the \u003cem\u003ein vivo\u003c/em\u003e study were performed using SPSS software (Version 26.0, IBM, Armonk, NY, USA). The Wilcoxon signed-rank test was employed to compare pre- and post-implantation data. A \u003cem\u003ep\u003c/em\u003e-value of less than 0.05 was considered indicative of statistical significance.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData included in this manuscript is available and will be shared upon request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Project numbers: NRF-2022R1A2C4001652).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThese authors contributed equally: Yejin Jo and Yurim Lee\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAuthors and Affiliations\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSchool of Electronic and Electronic Engineering, Yonsei University, Seoul 03722, Republic of Korea\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYejin Jo, Yurim Lee, Tae Young Kim, Kijun Park, Soye Kim \u0026amp; Jungmok Seo\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDepartment of Physiology Yonsei University College of Medicine Seoul 03722, Republic of Korea\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJung Hyun Heo \u0026amp; Yoonhee Jin\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eProgram of Brain and Cognitive Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYeonzu Son\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDepartment of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSeongjun Park\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDepartment of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSeongjun Park\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eKAIST Institute for NanoCentury (KINC), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSeongjun Park\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eContributions\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYejin J. and Y.L. contributed equally to this work. Yejin J. and Y.L. designed the experiment, analyzed the data, and wrote the manuscript. Yejin J. synthesized and characterized d-HAPT. Yejin J., Y.L., and S.K. performed mechanical tests. Yejin J., Y.L. conducted the experiment about the wearable electronics. Yejin J., J.H.H., and T.Y.K. performed the biocompatibility assay. Y.S. conducted the experiment regarding the implantable electronics. Yoonhee J., S.P., and J.S. were responsible for administrating this project. J.S. and K.P. revised and edited the manuscript. J.S. proposed the original concept and managed all aspects of this work. All authors discussed the results and commented on the manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eCorresponding authors\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to Jungmok Seo\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eCompeting interests\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eRao, Z. \u003cem\u003eet al.\u003c/em\u003e Soft electronics for the skin: from health monitors to human\u0026ndash;machine interfaces. Advanced Materials Technologies 5, 2000233 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eByun, S.-H. \u003cem\u003eet al.\u003c/em\u003e Mechanically transformative electronics, sensors, and implantable devices. 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Nature electronics 4, 185\u0026ndash;192 (2021).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-flexible-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjflexelectron","sideBox":"Learn more about [npj Flexible Electronics](http://www.nature.com/npjflexelectron/)","snPcode":"41528","submissionUrl":"https://submission.springernature.com/new-submission/41528/3","title":"npj Flexible Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4169072/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4169072/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEnsuring stable integration of diverse soft electronic components for reliable operation under dynamic conditions is crucial. However, integrating soft electronics, comprising various materials like polymers, metals, and hydrogels, poses challenges due to their different mechanical and chemical properties. This study introduces a dried-hydrogel adhesive made of poly(vinyl alcohol) and tannic acid multilayers (d-HAPT), which integrates soft electronic materials through moisture-derived chain entanglement. d-HAPT is a thin (~\u0026thinsp;1\u0026micro;m) and highly transparent (over 85% transmittance in the visible light region) adhesive, showing robust bonding (up to 3.6 MPa) within a short time (\u0026lt;\u0026thinsp;1 min). d-HAPT demonstrates practical application in wearable devices, including a hydrogel touch panel and strain sensors. Additionally, the potential of d-HAPT for use in implantable electronics is demonstrated through in vivo neuromodulation and electrocardiographic recording experiments while confirming its biocompatibility both \u003cem\u003ein vitro\u003c/em\u003e and \u003cem\u003ein vivo\u003c/em\u003e. It is expected that d-HAPT will provide a reliable platform for integrating soft electronic applications.\u003c/p\u003e","manuscriptTitle":"Universal Hydrogel Adhesives with Robust Chain Entanglement for Bridging Soft Electronic Materials","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-12 20:49:54","doi":"10.21203/rs.3.rs-4169072/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"revise","date":"2024-04-22T05:44:46+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-04-20T14:59:56+00:00","index":2,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-04-20T14:11:18+00:00","index":1,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-04-15T21:34:52+00:00","index":3,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-04-09T14:39:54+00:00","index":3,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-04-09T05:07:37+00:00","index":2,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-04-09T04:04:07+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewersInvited","content":"","date":"2024-04-09T02:40:37+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-03-27T13:45:53+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-26T10:24:54+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj Flexible Electronics","date":"2024-03-26T10:24:53+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-flexible-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjflexelectron","sideBox":"Learn more about [npj Flexible Electronics](http://www.nature.com/npjflexelectron/)","snPcode":"41528","submissionUrl":"https://submission.springernature.com/new-submission/41528/3","title":"npj Flexible Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"cb697e19-1982-41ea-9e76-793d4fd08f65","owner":[],"postedDate":"April 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":30436245,"name":"Physical sciences/Engineering/Electrical and electronic engineering"},{"id":30436246,"name":"Physical sciences/Materials science/Materials for devices"}],"tags":[],"updatedAt":"2024-07-13T07:09:17+00:00","versionOfRecord":{"articleIdentity":"rs-4169072","link":"https://doi.org/10.1038/s41528-024-00327-x","journal":{"identity":"npj-flexible-electronics","isVorOnly":false,"title":"npj Flexible Electronics"},"publishedOn":"2024-07-12 04:00:00","publishedOnDateReadable":"July 12th, 2024"},"versionCreatedAt":"2024-04-12 20:49:54","video":"","vorDoi":"10.1038/s41528-024-00327-x","vorDoiUrl":"https://doi.org/10.1038/s41528-024-00327-x","workflowStages":[]},"version":"v1","identity":"rs-4169072","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4169072","identity":"rs-4169072","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}