Advancements in Sustainable Conductors: Exploring the Potential of Polybutadiene-Based Urethane and Eutectic Gallium Indium Composites for Autonomous Self-Healing, Stretchable, and Deformation-Resistant Electrical Applications

Advancements in Sustainable Conductors: Exploring the Potential of Polybutadiene-Based Urethane and Eutectic Gallium Indium Composites for Autonomous Self-Healing, Stretchable, and Deformation-Resistant Electrical Applications | 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 Research Article Advancements in Sustainable Conductors: Exploring the Potential of Polybutadiene-Based Urethane and Eutectic Gallium Indium Composites for Autonomous Self-Healing, Stretchable, and Deformation-Resistant Electrical Applications Tran Duc Khanh, Jinho Joo, Jong-Woong Kim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4142846/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In the burgeoningfield of wearable electronics, flexible and durable conductors that can maintain consistent electrical properties under various conditions are critically needed. This research investigates the potential of a composite material combining eutectic gallium-indium (EGaIn) with a polybutadiene-based urethane (PBU) to meet these demands. EGaIn is selected for its superior conductivity, which is attributed to its low melting point, allowing for consistent performance. However, the challenge lies in its integration with encapsulating polymers due to poor adhesion qualities and the complexity of treatment methods required for successful amalgamation. Moreover, the high cost of EGaIn poses additional hurdles for its practical application. Addressing these issues, our study introduces a novel EGaIn-PBU composite, which not only ensures robust electrical conductivity but also exhibits remarkable self-healing properties and recyclability, thus promising sustainability. The composite leverages the advantageous properties of both components: EGaIn offers reliable conductivity, and PBU provides flexibility and the ability to self-recover after damage, which are imperative for wearable applications. Additionally, the composite maintains exceptional electrical resistance stability, withstanding mechanical strains up to 135% without compromising performance. The material's self-healing capability is attributed to the autonomous mending properties of EGaIn and the reversible Diels-Alder reactions in the PBU matrix. The result is an efficient restoration of the composite’s original properties upon incurring damage. Furthermore, the composite's adaptability is showcased through its printability, allowing for precise patterning conducive to custom-designed wearable devices. Conclusively, the developed EGaIn-PBU composite represents a transformative advancement in flexible electronics, combining high performance with environmental friendliness. Eutectic gallium indium Self-healing composite Stretchable electrodes Heaters Patternable composite Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction The exploration of wearable and flexible electronic devices continues to advance significantly as the global demand for sophisticated healthcare monitoring systems, intelligent mobile technologies, and related applications intensifies [ 1 – 3 ]. These developments necessitate materials and components that not only retain their functionality over prolonged periods but are also engineered to be stretchable—possessing sufficient rigidity to endure typical environmental challenges without degradation [ 4 ]. Among the myriad configurations of pliable electronics, thin-film technologies have emerged as particularly prevalent, owing to their minimal thickness and a Young's Modulus that mirrors that of human skin, facilitating compatibility and comfort [ 5 , 6 ]. The availability of numerous polymers capable of yielding skin-friendly thin films has largely addressed concerns related to user interface; the current challenge, however, lies in identifying a dependable conductive medium that can efficiently facilitate electrical conduction across various structural formations. Historically, flexible conductive materials such as the percolated networks of silver nanowires (AgNWs) and electrodes based on two-dimensional materials have been extensively documented. These materials exhibit commendable performance under minimal strain conditions. However, they are prone to irreversible damage and subsequent performance deterioration when subjected to extensive strains, exceeding tens of percent [ 7 , 8 ]. In this context, the emergence of so-called liquid metals, which remain liquid at room temperature, represents a transformative development. These substances are not only impervious to damage from structural alterations but also exhibit the high electrical conductivity characteristic of traditional metals, positioning them as promising candidates for flexible electrode applications [ 9 ]. Eutectic gallium-indium (EGaIn), a specific category of liquid metal, has garnered particular interest. Beyond the aforementioned benefits, EGaIn distinguishes itself by its biocompatibility. Unlike mercury, a substance known for its potential to adversely affect the respiratory and nervous systems, EGaIn is deemed safe for direct physical interaction [ 10 , 11 ]. This safety profile, combined with its physical and electrical properties, has facilitated the widespread integration of EGaIn into various research domains, including inkjet printing technologies, microfluidics, and microelectronic integrations, among others [ 12 – 14 ]. This broad applicability underscores the potential of EGaIn as a pivotal material in the ongoing evolution of wearable and flexible electronics, promising to address current limitations while opening new avenues for innovation. The inherent fluidity of EGaIn at room temperature, while offering unique advantages in terms of electrical conductivity and flexibility, also poses significant challenges in terms of device stability and durability. This fluidity leads to a precarious adherence of EGaIn to substrates, particularly when subjected to physical forces or alterations in orientation, which can result in the separation of EGaIn from the substrate. The theoretical foundation for this behavior lies in the principles of fluid dynamics and surface tension. The adhesive forces between the liquid metal and the substrate must overcome the cohesive forces within the liquid metal itself to maintain a stable interface. When external stresses disrupt this balance, detachment occurs, compromising the electrical pathways critical for device functionality. To address these challenges, recent research has explored the amalgamation of EGaIn with various polymers, aiming to leverage the viscoelastic properties of polymers to enhance adhesion and stability without significantly detracting from the electrical performance of EGaIn [ 9 , 12 , 13 , 15 ]. The approach to amalgamate EGaIn with polymers is underpinned by advanced concepts in polymer science which take into account the influence of polymer morphology on material properties. Through careful modification of molecular weight, cross-linking density, and copolymer composition, polymers can be synthesized to span a spectrum of mechanical properties, ranging from high elasticity to increased rigidity. This meticulous engineering enables the creation of composites which not only robustly bond EGaIn to substrates but also maintain the pliability required to meet the dynamic demands of wearable electronics. Despite the promising aspects of this approach, it ushers in intricate interactions between the composite's mechanical resilience and its ability to heal autonomously. From a theoretical standpoint, the field of composite materials illuminates the inherent tension in achieving equilibrium between these two attributes. Augmenting the composite with polymer enhances mechanical stability and can mitigate leakage of EGaIn; however, it might concurrently restrict the natural, fluidic behavior of EGaIn that is essential for self-repair. This restriction stems from fundamental discrepancies between the metallic properties of EGaIn—characterized by quick and reversible restoration via fluid movement and droplet coalescence—and those of polymeric substances, which are typically defined by permanent deformation or rupture under duress. The self-healing characteristic of EGaIn is essentially a reflection of its capacity to reduce surface energy through the merger of discrete droplets, propelled by the metal’s substantial surface tension. In stark contrast, polymers, particularly when cross-linked, are not predisposed to such reversible actions, owing to their solidified state and the enduring nature of their cross-linked junctions. Consequently, while the polymer matrix acts as an anchor for EGaIn, it also has the potential to limit the motion of EGaIn particles, thereby hindering their propensity to coalesce and self-mend in the event of damage. Several composites have been introduced to advance the field of liquid metal-based soft electronics, each with its own set of capabilities and limitations. For instance, cross-linked block copolymers showcased remarkable elasticity and inherent self-healing abilities, yet they lacked the ability for intricate patterning and required significant pressure to initiate conductivity [ 16 , 17 ]. In contrast, certain polydimethylsiloxane (PDMS)-EGaIn composites offered precision in conductive patterning but were characterized by a lower threshold for strain (up to 100%) and lacked self-healing properties [ 18 , 19 ]. Alternative matrices, such as fibrous structures, presented high tensile strain capacities, yet similarly fell short in self-repairing functionality [ 20 – 22 ]. In the particular case of PDMS-EGaIn composite electrodes, the theoretical considerations emphasize the compromises involved. PDMS is prized for its high flexibility and compatibility with biological tissues, enhancing the composite's pliability and stretchability. Nevertheless, should damage befall the composite, PDMS’s elasticity does not inherently support the reintegration of EGaIn, thus disrupting the liquid metal's innate self-healing process. This delineates a critical area for further research and development to optimize the synergistic properties of polymer-liquid metal composites for electronic applications. Herein, the composite's core is a polybutadiene-based urethane (PBU), chosen for its thermo-reversible Diels-Alder reaction attributes. The Diels-Alder reaction is a selective and efficient cycloaddition that yields a cyclohexene system, and crucially for this application, it can reverse at higher temperatures, allowing the material to "self-heal" by reverting Diels-Alder adducts to the original diene and dienophile at around 120°C. The controlled reversibility of covalent bonds formed during the Diels-Alder reaction empowers the PBU matrix to repair itself after damage. To minimize side reactions at elevated temperatures and preserve the composite's integrity, furan-maleimide is incorporated due to its strong affinity for forming reversible links. The liquid metal-polymer blend was optimized using percolation theory principles, carefully calibrating the ratio and mixing speed to ensure the conductive filler forms a network without spilling out, considering EGaIn's tendency to separate due to high surface tension. Mechanical durability is showcased by minimal resistance variation under extensive deformation, attested by extensive cycling tests. The composite's thermal properties enable self-healing without material degradation. Post-healing, the composite regains its original strain rate, indicating excellent potential for dynamic use. This composite material has been adeptly engineered to function as an efficacious heating element, and it has demonstrated a propensity for autonomous self-healing concurrent with the thermal emission process. For precise patterning critical for electronic functionality, a stencil mask technique was applied, allowing for the creation of intricate, sharp-edged designs at the micro-scale. The composite has demonstrated high accuracy and sensitivity as a motion detector, responding to minute movements, which proves its promise for integration into sophisticated electronic systems and self-healable and stretchable wearable devices. 2. Experimental Section 2.1 Materials and Reagents Hydrogenated hydroxyl-terminated polybutadiene (Krasol HLBH-P 2000, Mn = 2100 g/mol) was procured from Cray Valley. Isophorone diisocyanate (IPDI) and dibutyl dilaurate (DBTDL), the reactive components and catalyst, respectively, were sourced from Sigma-Aldrich. Methyl ethyl ketone (MEK), utilized as the solvent in the synthesis process, was acquired from Daejung Chemicals. A customized diol, synthesized from glycerol 1,2-carbonate and furfuryl amine obtained from TCI Chemicals, served as the chain extender. Bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (BMI) from TCI Chemicals was employed as the self-healing agent in the formulation of the PBU. EGaIn alloy, the conductive filler, was also purchased from Sigma-Aldrich. Sodium hydroxide (NaOH) 1M was purchased from Daejung Chemicals to agitate small particles of EGaIn into bulk EGaIn. 2.2 Synthesis of Diol The diol, pivotal in enabling the polyaddition reaction between the polyol and IPDI, was synthesized by reacting 13.1 g of glycerol 1,2-carbonate with 10.79 g of furfuryl amine. The reactants were combined and subjected to magnetic stirring at 60°C for three hours within an oil bath. 2.3 Preparation of PBU Substrate To synthesize the PBU matrix, 4 g of HLBH-P 2000, 0.43 g of the prepared diol, 0.89 g of IPDI, and 4.5 g of MEK were mixed with 4 drops of DBTDL as the catalyst. This mixture was then stirred magnetically at 60°C for 2 h. Subsequently, a quantified amount of BMI was introduced to the reaction mixture to complete the PBU synthesis. The stirring continued for an additional 30 min under the same conditions. The resultant PBU mixture was then subjected to spin coating at 1500 rpm for one min to form a thin film, which was subsequently dried at 60°C overnight, creating the substrate for the conductive composite. 2.4 Fabrication of PBU-EGaIn Composite For the fabrication of the PBU-EGaIn composite, bulk EGaIn was first subjected to probe sonication in ethanol using a VCX750 ultrasonic processor (Vibra-Cell) for 30 min. The sonication regimen involved multiple cycles, alternating between 3 s of sonication and 3 s of rest, spanning a total of 3 h. Following sonication, the resultant smaller EGaIn droplets were integrated into the PBU mixture at various ratios. The composite mixture then underwent planetary mixing using a paste mixer (Thinky Supermixer, Japan) for 2.5 min before being applied to the bare PBU substrates via spin coating and allowed to cure at ambient temperature. A detailed schematic of the synthesis process can be found in Figure S1 . For patterning, the PBU-EGaIn composite was applied to the PBU substrate using stencil masks. The patterning process entailed placing a mask, designed using AutoCAD software and bearing predefined shapes, onto the substrate. The composite was then distributed uniformly using a rubber putty knife, carefully maintaining an optimal angle to avert leakage. This step was performed expeditiously to ensure proper curing of PBU at room temperature. Following this, the stencil mask was swiftly and cleanly removed, leaving behind the desired pattern. To enhance adhesion between the PBU substrate and the composite, an Ar/O 2 plasma treatment was administered to the PBU surface prior to patterning. 3. Results and discussion In pursuit of establishing the optimal EGaIn proportion to enhance the electrical conductivity within the composite framework, a meticulous series of syntheses was executed, incorporating varying concentrations of EGaIn. Quantitative electrical resistance measurements were carried out for composites with EGaIn loadings ranging from a minimal 5% up to a substantial 50%. It was observed that the resistance exhibited a significant diminution upon incorporating 50% of the alloy, declining precipitously from an initial magnitude of approximately 10 5 Ω to a markedly lower 83 Ω. This substantial reduction signals the approach toward the percolation threshold, a critical juncture characterized by the formation of a continuous conductive cluster that markedly enhances electron mobility within the composite (as illustrated in Fig. 1 a). Further morphological elucidation was conducted using an optical microscope (OM) ( Figure S2 ). It was discerned that at EGaIn incorporations beneath 33%, the metal particulates—exhibiting an assortment of shapes—were homogeneously distributed throughout the PBU substrate. Despite this distribution, the particulates remained distinct and electrically discrete. At a concentration of 50% EGaIn, the emergence of nascent EGaIn collectives was noted, yet these assemblies did not coalesce into a pervasive conductive network. Elevating the EGaIn content to 55% precipitated a substantial decline in electrical resistance, as per the analyses. This observation was corroborated by surface examinations that verified the conductivity enhancement was a direct consequence of the interconnected network formed amongst EGaIn droplets. These droplets, predominantly within a 10 µm diameter range, exhibited non-spherical geometries, a manifestation of the diminished surface energy resulting from the enveloping urethane matrix [ 23 , 24 ]. Upon examining samples with 67% metal loading, a denser metallic network was apparent, yet this did not correspond to a discernible resistance decrement. Consequently, in light of the comprehensive electrical and morphological insights, the composite formulation endowed with 55% EGaIn was elected as the superior candidate for the development of the PBU-EGaIn composite, optimizing electrical conductivity whilst upholding the structural cohesion of the composite. In the realm of composite materials science, the size of particles within a matrix is a paramount consideration, particularly when dealing with a substance such as liquid metal which exhibits a high surface energy. This intrinsic characteristic of EGaIn is pivotal as it significantly influences the propensity of the metal filler to breach the confines of its host polymer matrix. In an endeavor to rigorously scrutinize this phenomenon, the mixing speeds were modulated across a spectrum of 800 to 2000 rpm, all the while maintaining a constant EGaIn mass fraction at 55% (Fig. 1 b). The cyclic strain test was meticulously deployed to ascertain the impact of EGaIn droplet dimensions on the composite's performance, denoted as PBU-EGaIn. Scientifically, it was ascertained that there exists an inverse correlation between the planetary mixing velocity and the composite's mechanical stability; however, the variation in electrical resistance over an extended period of 10,000 seconds did not demonstrate notable fluctuation, plateauing at a resistance value of approximately 2.65 Ω. Disparities in the samples' resistivity were less pronounced, yet the mechanical response of the composites under tensile stress was divergent (as shown in Fig. 1 b). OM images illuminated the scenario: at varying mixing speeds, the EGaIn droplets amalgamated to form conductive pathways, with lower velocities being requisite for agglomerating larger particles (refer to Figure S3 ). Such outcomes imply the utilization of both planetary mixing and sonication techniques as effective means to fragment larger liquid metal droplets into diminutive entities, subsequently achieving homogenization and eventual dispersion within the viscous polymeric matrix. In addition to morphological assessments, X-ray diffraction (XRD) analysis provided insights into the composite's internal structure. The semi-crystalline architecture of the pristine PBU was manifested through broad XRD peaks at 20°. Contrastingly, the composite material showcased an additional peak at 37°, indicative of the amorphous nature of the thoroughly integrated EGaIn within the PBU matrix (as depicted in Fig. 1 c). Further granularity on the particle size distribution within the composite was obtained through the examination of the 2000 rpm mixed samples. The analysis, portrayed in Fig. 1 d, revealed that a majority of the particles fell within a diameter range of 6 to 8.5 µm. This level of detail was achieved by employing two-dimensional (2D) analysis on OM photographs, utilizing thresholding techniques to delineate the brighter urethane matrix from the darker EGaIn filler. It is critical to note that the diminutive size of the EGaIn particles is integral to the retention of the liquid metal within the polymer matrix [ 25 ]. Smaller particle dimensions inherently present a higher resistance to the flow, impeding the escape of EGaIn from the composite, thereby enhancing the material's overall stability and integrity. In order to inspect the wetting behavior among samples with different speeds, contact angle analysis was carried out, initially, the pure alloy had angles higher than 130°, due to especially high surface tension coming from the metallic bonds [ 26 ]. However, once EGaIn was dispersed in the polymer matrix, the droplets were beaded up, making it easier for PBU to fully encapsulate, indicating that the wetting ability of the composite is better than the alloy. And the angles decreased slightly as the shear mixing speed was accelerated, from more than 130° to approximately 80° (Fig. 2 ). As EGaIn particles are covered inside the polymer, the wettability of the composites was better than the pristine liquid metal. Furthermore, droplets with smaller sphere radius would result in a higher pressure difference between the liquid metal and the polymer, due to the Young-Palace equation: $$\varDelta P=\gamma \frac{2}{R}$$ 1 where R is the sphere radius of liquid metal particles. Without the impact of an electric field, there is no pressure variation across the alloy surface. According to the above equation, as the radius is the denominator, it is inversely proportional to \(\varDelta P\) , on the other hand, this value favors the capillary force, as depicted in Eq. ( 2 ). A stronger capillary force would generate sufficient power to breach the metal oxide layer, thus connecting the percolating interconnection among EGaIn particles and bringing higher conductivity to the composite [ 27 ]. $${F}_{capillary}=2\pi \gamma \alpha \text{s}\text{i}\text{n}\phi \text{sin}\left(\phi +\theta \right)+\pi {\alpha }^{2}{\text{s}\text{i}\text{n}}^{2}\phi \varDelta P$$ 2 Upon the determination of the optimum EGaIn content and the precise mixing velocity, the capabilities of the composite were subject to rigorous evaluation. A singular test specimen, meticulously dimensioned to 30 mm by 10 mm, was subjected to a cyclic strain analysis, testing the material up to 135% strain—a figure proximal to the ultimate tensile strain limit of 145%. This specimen was securely mounted on a custom-engineered fatigue testing device, with terminal connections established with the probes of an LCR meter to facilitate the acquisition of resistance data. Documentation of each strain increment was methodically performed as denoted in Figure S4 , with the duration of each experimental iteration extending to 1500 s. In the quiescent state, the specimen presented an initial resistance value of 2.5 Ω. At the imposition of 50% strain, the resistance experienced a nominal increase to 2.6 Ω, a value that persisted steadfastly through the conclusion of the inaugural test sequence, therefore the relative resistance change ( ΔR/R 0 ) at 50% strain is extremely small (around 2%). Escalating the strain to 75% and subsequently to 100% correlated with a proportional augmentation in resistivity, registering values of 2.72 Ω and 2.75 Ω, respectively. Crucially, at an exigent strain level of 135%, the resistance variation remained confined to an increment of approximately 0.6 Ω, which, within the domain of electrical conductivity, is considered to be a tolerable fluctuation as elucidated in Fig. 3 a. The resistance's progressive uptrend witnessed over the course of the cyclic testing could potentially be ascribed to the composite's limited temporal allowance for the recuperative reformation of its percolated conductive network. Despite this, the maximal differential in resistance observed between the composite in a restive state and at full extension did not surpass the marginal value of 0.5 Ω, a testament to the composite's exceptional mechanical stability. Further investigations explored the impact of disparate stretching velocities on resistance variability. Given the requisite for stability in wearable sensor applications, irrespective of motion dynamics, the lateral velocity of the fatigue testing apparatus was varied to simulate real-world conditions and ascertain resistance metrics across different frequencies. The experimental outcomes revealed that resistance disparities between the unstressed and maximally strained states were insubstantial and exhibited independence from the imposed movement frequencies as depicted in Fig. 3 b. Moreover, the endurance and uniformity of the composite were corroborated through a rigorous 50,000-cycle stretching regimen conducted at strains approaching the material's limit (presented in Fig. 3 c). Even after an extended series of tests, the resistance steadfastly hovered around 3.1 Ω. Additionally, the interrelation between applied direct current (DC) voltage and measured current was scrutinized under diverse conditions to authenticate the insubstantial resistance deviations upon deformation (illustrated in Fig. 3 d). These comprehensive scientific inquiries affirm the superior conductive performance of the PBU-EGaIn composite, significantly bolstering its applicability in the domain of soft electronics, where the juxtaposition of electrical integrity and mechanical suppleness is of paramount importance. The thermal characteristics of the PBU-EGaIn composite, specifically in its role as a stretchable electrode, were subjected to thorough scientific examination. The phenomenon of Joule heating, a principle where heat generation is the result of electrical current traversing through a conductive material, was exploited in these investigations. The application of direct current for heating, as well as for the concurrent measurement of the ensuing electrical current, was accomplished using a sophisticated source meter. A temperature of 120°C was identified as the optimal thermal benchmark for the composite, a point at which the Diels-Alder reaction is known to proceed with requisite efficiency to initiate the self-healing process within the PBU matrix, as substantiated by prior research [ 28 ]. The composite's temperature distribution during Joule heating was meticulously recorded using a high-precision digital multimeter and an advanced infrared-ray camera. Upon the administration of a 4.5 V direct current, the heating rates across the composite were observed to be prompt, with samples at unaltered, 50%, and 100% strain levels reaching the desired temperature threshold within 2 min. In contrast, the sample subjected to nearly its maximum strain capacity exhibited a marginally extended heating duration, approaching three minutes to attain the 120°C threshold (Fig. 4 a). A subsequent experimental series employed a stepwise increase in voltage intensities, beginning from 0.5 V and escalating to 3.5 V. Each voltage increment was applied only after it was ascertained that the preceding voltage could no longer induce a significant thermal rise. These trials demonstrated that the extent of mechanical deformation was proportional to the time required to achieve the heating target. Notably, a specimen without any strain required approximately 1100 s to reach the designated temperature (Fig. 4 b), with this timeframe progressively lengthening, reaching 1210 s for the specimen subjected to the most extensive strain (Fig. 4 c-f). These rigorous experimental evaluations confirm the PBU-EGaIn composite's proficiency in Joule heating, showcasing its capability to respond thermally in a prompt and controlled manner, a property essential for applications necessitating quick thermal modulation in tandem with flexible material properties. The ability to precisely manage thermal response is imperative for the activation of self-healing mechanisms within smart materials, offering a robust solution for the maintenance and longevity of soft electronic systems. Infrared (IR) thermographic imaging was utilized to scrutinize the distribution of heat across the composite thin film as a function of its mechanical strain, detailed in Fig. 5 . Each column represents a specific strain level, with the upper, middle, and lower rows capturing distinct thermal states. The top row images illustrate the junctures at which the hottest zones approximate the target temperature, while the middle row images document the attainment of 120°C at the sample's core—a temperature conducive to the Diels-Alder reaction, which is central to the self-healing process of the composite. The bottom row images reflect the thermal signature after 1 min of heating, under an applied voltage of 3.5 V for all conditions. Initially, in the unstressed state of the composite (sample's length = 18 mm), an even heat distribution was observed across the surface, with a minimal temperature gradient due to the high density of the metallic filler uniformly embedded within the polymer matrix. This homogeneity ensures efficient electron mobility and, consequently, uniform Joule heating. Upon elongation of the sample to 100% and 135% of its original length (extending from 18 mm to 36 mm and 42 mm, respectively), a marked deviation in thermal distribution was observed. The areas adjacent to the voltage application sites manifested intensified IR emission, evidenced by a darker appearance in the central region, indicative of cooler temperatures due to its increased distance from the DC source. This effect was most pronounced at a strain of 135% (total length = 42 mm), where the thermal disparity reached up to 10°C. In comparison, the unstrained and 100% strained samples (total length = 36 mm) exhibited thermal differentials of merely 1°C and 5°C, respectively. Such temperature variations can be explicated by the elongated conductive pathways, characterized by a diminished surface contact area and more extensive liquid bridges within the stretched composite. These altered geometric configurations lead to increased resistance to electron flow, particularly impacting the central region due to its relative remoteness from thermoelectric influence [ 29 ]. Consequently, over a time span of 60 s, the strained specimens exhibited significant temperature deltas, most notably the sample at 135% strain, which only managed to attain a peak temperature of 91.7°C. In the domain of wearable technology, high endurance and intrinsic self-healing capabilities are imperative to address and rectify damages such as incisions. To quantitatively evaluate the self-healing efficacy of the PBU-EGaIn composite, a sequential IR thermal analysis was conducted. This analysis comprised three distinct investigative conditions, each represented in separate columns of Fig. 6 : the initial intact state, the subsequent state following incision, and the final state after the self-healing process. Upon making an incision in the composite film with a razor blade, a marked decrease in temperature was discernible in the IR images, particularly pronounced when the composite was subjected to mechanical strain. This phenomenon was characterized by an increased thermal footprint at the site of the damage, indicating a significant deviation from the composite's nominal temperature, which was adeptly identified by the IR camera's coldest point detection feature (blue crosshairs, as depicted in the middle column of Fig. 6 ). To initiate the self-healing process, the damaged composite samples were restored to an unstressed state, and a DC voltage was applied. This electrical input triggered the outflow of liquid metal droplets from the matrix due to the material's inherent high surface tension. Realigning the severed interfaces facilitated the re-establishment of electrical conductivity through the liquid metal pathways. Subsequent heating mediated the melting of the polymeric substrate adjacent to the cut, thereby re-liquefying the polymer and enabling it to bridge the incision, effectively reconstituting the composite's integrity. Post-healing, the composites exhibited remarkable resilience, maintaining functional integrity under strains of 100% and 135%, as demonstrated in the second and third rows of Fig. 6 , respectively. The self-healing process was underpinned by the Diels-Alder reaction, which within the PBU matrix, utilizes furan groups from the diol component and maleic anhydride from the BMI to form reversible cross-links. The thermal and chemical conditions favorable for this self-healing reaction, specifically the retro-Diels-Alder reaction, have been thoroughly characterized in the referenced literature [ 30 – 33 ], providing a robust scientific foundation for the composite's reparative abilities. This signifies that our electrodes are capable of autonomous self-healing. High-resolution digital imaging was conducted concurrently with thermal analysis to meticulously document the surface topography of the samples, thereby enabling an in-depth morphological evaluation subsequent to the recovery process, as depicted in Figure S5 . With regard to the composites' elasticity, the self-healed specimens exhibited an unimpaired retention of their original strain characteristics. This conservation of mechanical robustness intimates that the self-healing mechanism entails the strategic cleavage of three pi bonds within the polymeric lattice—specifically, two pi bonds from the diene component and one pi bond from the dienophile—during the [4 + 2] cycloaddition reaction. The process culminates in the formation of two novel sigma bonds while concurrently regenerating an additional pi bond. Such intricate molecular reconfiguration is critical for reinstating the composite's inherent tensile properties, reflecting the efficacious restoration of the polymer network after damage. The intricacies of this self-healing response have been expounded in the scientific literature as indicated in reference [ 34 ]. In addition to the topological assessment, the conductive and thermal properties of the self-healed composite were rigorously evaluated. The composite underwent two distinct types of damage: a single intersecting incision and multiple intersecting incisions. From an electrical standpoint, in its pristine state, both the minimal and maximal resistance values exhibited a gradual increase throughout the testing period; nonetheless, the range between these values remained stable (as shown in Fig. 7 a). Conversely, after undergoing the self-healing process, the PBU-EGaIn composite maintained a consistent resistivity, irrespective of being in a relaxed state or fully elongated. With a single incision, the resistance discrepancy was less than 0.5 Ω, while for multiple incisions, it was 1.5 Ω. Even in the scenario of multiple incisions, post-recovery, the absolute maximum resistance observed was only 4 Ω, indicating the material's continued excellent conductivity (as illustrated in Figs. 7 b and c ). Concerning the thermal conductivity, both one-time damaged and multiply damaged healed specimens were able to reach the critical temperature required to initiate the Diels-Alder reaction. However, this process was protracted, taking approximately five minutes. Voltage step tests were performed for both types of damaged conditions: the single incision required 1250 s to reach the desired thermal state, while the multiple incisions required about 1400 s (depicted in Figs. 7 d and e ). Furthermore, the efficiency of the healing process was quantitatively analyzed across varying degrees of sample elongation. It was observed that the healing efficacy diminished proportionally with increased sample length. This can be attributed to the dispersion of the same quantity of liquid metal over an augmented surface area, which inherently reduces the density of the conductive network, thereby impacting the composite's capacity for heat generation and, consequently, its ability to facilitate self-repair (as indicated in Fig. 7 f). This inverse relationship between stretching magnitude and healing proficiency highlights the challenges in maintaining healing efficiency in composites subjected to extensive mechanical deformation. The PBU-EGaIn composite demonstrated the capability to be precisely patterned into specific micro-sized configurations, which is a pivotal technological advancement. Employing a stencil mask technique, uniform dots with diameters of 50 µm were successfully fabricated, which holds significant promise for applications in print circuit board (PCB) manufacturing, as evidenced by the creation of a 4×4 dot array with equidistant spacing (refer to Fig. 8 a). Subsequent figures, 8b and 8c , illustrate the formation of a cross and a right angle, each with a meticulous thickness of 100 µm. The edges of these patterns were remarkably defined, with the fabricated surfaces exhibiting a high degree of smoothness. Moreover, the stencil technique proved adept at producing complex designs, as demonstrated by the defect-free, intricate pressure sensor pattern, which included exceptionally thin lines with no overlap (shown in Fig. 8 d). The clarity of the patterning was further pronounced under mechanical strain; fine individual lines retained their distinct separation, as shown in Fig. 8 e. The composite's autonomous self-healing capability was rigorously evaluated across a spectrum of intricate geometrical configurations, showcasing consistent recovery irrespective of the complexity or number of inflicted damage sites. This validation was methodically conducted through controlled experiments wherein two composite specimens, featuring predetermined patterns responsible for conveying electric signals to a light emitting diode (LED), underwent deliberate damage at specified locations (refer to Figure S6 , first row). Subsequent analysis revealed that following damage, as evidenced by the LEDs ceasing to illuminate ( Figure S6 , second row), the self-repair mechanism efficiently reinstated the conductive pathways in both instances, thereby facilitating the reactivation of the LEDs ( Figure S6 , third row). Further elucidation of the healing dynamics was pursued using a field emission scanning electron microscope (FESEM), which provided visual insights into the closure of a gap initially measuring approximately 60 µm in width ( Figure S7a ). The observed closure of the gap progressed discernibly, culminating in complete sealing, with the resultant mend being readily discernible ( Figure S7 b-d ). Additionally, atomic force microscopy (AFM) analysis quantified the reduction in dimensions of the incision post-healing, revealing a decrease in both width and depth of the composite from approximately 5 µm to nearly 2 µm, and from around 3 µm to approximately 0.5 µm, respectively ( Figure S7e ). The refined morphological features and high-resolution patterning observed in the composite can be attributed to the altered surface tension of the PBU-EGaIn compound. This alteration arises from the encapsulation of the liquid metal component within the polymeric matrix, resulting in a transition from an oxide-encased state to one where the polymer matrix predominantly encapsulates the alloy, thereby influencing its surface energy properties [ 35 ]. The proficient patterning capabilities demonstrated by the PBU-EGaIn composite represent a significant advancement in the realm of stretchable circuits, offering a versatile and practical material solution for sophisticated electronic applications. The PBU-EGaIn composite, a synthesis of PBU and employing EGaIn, exhibits superlative properties that make it an exemplary candidate for applications in wearable electronics due to its remarkable elasticity and stability. Its performance as a wearable motion sensor was systematically evaluated, capitalizing on its potential to monitor and analyze human movement with high fidelity. The composite was strategically affixed to joints such as fingers, wrists, and knees, regions that commonly experience a range of motion. The quantification of motion was facilitated through the measurement of relative capacitance changes ( C / C 0 ) employing two extrinsic conductive leads to ensure consistent and secure connectivity to the LCR meter. The application of the patterned composite for sensing tasks was particularly advantageous in instances necessitating compact sensors. During the digit articulation test, the capacitance variation between flexed and extended digit positions was minor ( C / C 0 ≈ 8%) indicating the composite's nuanced sensitivity to subtle movements, as shown in Fig. 9 a. In contrast, actions that involve broader ranges of motion, such as wrist rotation, elicited more pronounced capacitance signals, demonstrating the sensor's ability to detect varying degrees of articulation. The ultrathin nature of the patterned sensor, highlighted in the inset of Fig. 9 b, is not merely an aesthetic advantage but also functionally crucial. It ensures that the sensor is non-intrusive and harmonizes with the wearer's natural movements, a pivotal characteristic for wearable technology to be truly integrated into everyday use without impeding the user. For larger joints like the knee, which undergo more extensive motion, an expanded sensor footprint was necessary to cover the area adequately and capture the full dynamic range of movement. The signals acquired from such extensive motion were proportionately larger, reflecting the sensor's ability to scale its sensitivity with the amplitude of the subject's activity (Fig. 9 c). Furthermore, the prompt and precise capacitive response to the wrist's movement, as illustrated in Fig. 9 d, showcases the sensor's exceptional responsiveness—a critical aspect in real-time motion detection and feedback. This responsiveness is a testament to the composite's ability to rapidly modulate its electrical properties in synchronization with physical deformations, a quintessential attribute for the development of advanced and intuitive wearable electronics. Despite the PBU-EGaIn composite’s remarkable flexibility and straightforward self-healing capabilities, it was acknowledged that in certain scenarios the composite may not be suitable for direct reuse following damage. Consequently, a meticulous recycling protocol was devised to segregate and reclaim the liquid metal, leveraging its near-complete recyclability [ 36 ]. The reclamation process encompassed two principal stages. The initial phase involved the thermal dissolution of PBU: the fully cured composite was subjected to heat treatment at 140°C in the presence of MEK. This procedure facilitated the depolymerization of PBU, aligning with the retrograde Diels-Alder reaction, whereby the crosslinked network decomposed into distinct imide and furan entities [ 34 ]. Notably, this step did not compromise the integrity of the conductive alloy, which boasts a melting point substantially exceeding 2000°C, thus remaining unaffected [ 37 ]. Subsequent to the dissolution of the polymeric matrix, the isolated EGaIn particulates underwent a series of MEK washes, followed by sonication to extricate any lingering polymer residues. Once liberated into the environment, the liquid metal droplets reinstated their inherent high surface tension, a characteristic that is particularly pronounced under extreme pH conditions [ 38 , 39 ]. For the oxide layer removal and reinstatement of the metal's original interfacial tension, a 1 M sodium hydroxide (NaOH) solution was employed, effectively stripping the oxide layer. This facilitated the coalescence of the dispersed metal particles into a singular, cohesive drop, a transformation depicted in Figure S8 . This systematic recovery process underscores the sustainability aspect of the PBU-EGaIn composite, offering an environmentally considerate option for the lifecycle management of materials used in stretchable electronics. Our investigation entailed a comprehensive comparative analysis aimed at benchmarking the performance characteristics of the PBU-EGaIn composite developed in this study against existing research paradigms. The examination encompassed a spectrum of composite configurations, each designed to imbue the material with specific attributes such as stretchability, minimal resistance variation under mechanical strain, self-healing capabilities, and recyclability, as delineated in Table 1 [ 40 – 48 ]. Notably, the composite we developed stands out for its unique amalgamation of these properties, a feat unparalleled by preceding materials. Across a range of performance metrics, our composite consistently demonstrated either superior or commensurate performance when juxtaposed with previous research findings. Furthermore, the material exhibits an exceptional ability for autonomous self-healing, particularly when deployed as a heating element, a distinctive characteristic not observed in earlier studies. We are confident that the innovation presented in this research represents a significant breakthrough in addressing a critical challenge inherent in conventional stretchable soft electronics. Table 1 Comparative analysis of PBU-EGaIn composite with previous noteworthy studies incorporating liquid metal or similar materials for stretchable electrode applications. Composite components Maximum strain (%) Resistance change at 50% strain ( ΔR/R 0 ) (%) Self-healing ability Recyclability References PBU and EGaIn 135 2 Yes Yes This work Polyphenol and EGaIn 70 1.18 No No [ 40 ] Lignin and EGaIn 0 Unavailable No Yes [ 41 ] PDMS and MXene/AgNWs/Galinstan 140 0.5 Yes No [ 42 ] TPU and indium 50 0.6 No No [ 43 ] Ecoflex and galinstan 180 0.5 No No [ 44 ] Polyimide and graphene 240 0.1 No No [ 45 ] SMCF and galinstan 373 0.3 No No [ 46 ] PDMS and EGaIn 100 5 No No [ 47 ] EcoFlex and EGaIn 100 10 No No [ 48 ] 4. Conclusion This study has culminated in the development of an innovative PBU-EGaIn composite characterized by remarkable stretchability, minimal resistance variation under mechanical strain, superior stability, autonomous self-healing, and recyclability. The material demonstrates the ability to maintain electrical conduction with minimal resistance values, not exceeding 4 Ω, under various degrees of mechanical strain up to 135%. The composite's thermal response is noteworthy; it efficiently attains temperatures of up to 120°C in a short time frame. Reaching this critical thermal threshold triggers the Diels-Alder reaction, which underpins the composite's autonomous self-healing process, allowing for the restoration of the PBU layer's integrity after damage. The repaired areas regain functional normalcy, a testament to the exceptional self-healing efficacy of the material. In addition to its restorative properties, the PBU-EGaIn composite has been engineered to support precise patterning through a simple stencil mask technique, attributed to its reduced surface tension. This capability enhances its suitability for intricate designs required in advanced electronic applications. When leveraged as a motion detector, the composite performs admirably, demonstrating high sensitivity and responsiveness, effectively detecting subtle movements. Furthermore, the composite boasts high-resolution patterning capabilities, capable of sensing even the slightest movement with pronounced responsivity—a critical feature for wearable technology. The practical implications of this are profound, opening avenues for the integration of the PBU-EGaIn composite into the burgeoning field of soft, wearable electronics. In instances where the material does not manifest self-healing properties, a strategic two-step recycling protocol has been established. This process efficiently recovers the valuable EGaIn, underscoring the sustainability of the composite by ensuring that the constituent materials can be reused, thereby contributing to the principles of circular economy within material science. Abbreviations EGaIn eutectic gallium-indium PBU polybutadiene-based urethane AgNWs silver nanowires PDMS polydimethylsiloxane IPDI isophorone diisocyanate DBTDL dibutyl dilaurate MEK methyl ethyl ketone BMI bis(3-ethyl-5-methyl-4-maleimidophenyl)methane OM optical microscope XRD X-ray diffraction 2D two-dimensional DC direct current IR infrared PCB printed circuit board LED light emitting diode FESEM field emission microscope AFM atomic force microscope NaOH sodium hydroxide. Declarations Funding This work was supported by National Research Foundation of Korea (NRF) grants (Number 2020M3H4A3081895, RS-2023-00247545 and 2022R1A2C1010353) funded by the Korean government (MSIP). Competing interests The authors declare no competing interests. Authors’ Contribution Jong-Woong Kim and Jinho Joo supervised the whole research process. Jong-Woong Kim and Jinho Joo contributed to the study's conception and design. 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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-4142846","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":287336041,"identity":"0f3630f1-ccb4-41c2-aade-9c3376cdf01e","order_by":0,"name":"Tran Duc Khanh","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Tran","middleName":"Duc","lastName":"Khanh","suffix":""},{"id":287336043,"identity":"d3d78ec4-85a5-424f-bf1f-406014db9147","order_by":1,"name":"Jinho Joo","email":"","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":false,"prefix":"","firstName":"Jinho","middleName":"","lastName":"Joo","suffix":""},{"id":287336044,"identity":"a070af91-2f6c-42ba-a4c1-40aa13fd91c2","order_by":2,"name":"Jong-Woong Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAo0lEQVRIiWNgGAWjYHCCBIkPDAkGIJYE0VokZ5CqhUGahyQtBjcSHt62+ZNmbHCA+eBtHiK1JFvntuWYGRxgS7YmSovZjYQ06dyGChuDAzxm0sRrsfgD0sL/jQQtDGwgh/GwEafF/syDZMvetjRjycNsxpZziNEi2Z6TeOPHn2TDvuPND2+8IUYLg0BOAoTBTJRyEOA/foBotaNgFIyCUTBCAQDMVDHcMpNCWgAAAABJRU5ErkJggg==","orcid":"","institution":"Sungkyunkwan University","correspondingAuthor":true,"prefix":"","firstName":"Jong-Woong","middleName":"","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2024-03-21 10:42:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4142846/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4142846/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54354069,"identity":"a9eace1b-31dc-4c58-b7bc-3fec711f35be","added_by":"auto","created_at":"2024-04-09 09:19:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":86787,"visible":true,"origin":"","legend":"\u003cp\u003eIllustrative depictions of the PBU-EGaIn composite's characteristics: (a) Graph showcasing the percolation threshold as a function of varied EGaIn volumetric ratios; (b) A plot delineating the correlation between resistance stability and the velocity of planetary mixing (EGaIn wt.% = 55%; Strain level = 135%); (c) XRD patterns contrasting the molecular structure of unadulterated PBU with the EGaIn-infused PBU composite; (d) A distribution analysis of EGaIn particulate diameters within the composite, correlated with a mixing speed of 2000 rpm (EGaIn wt.% = 55%).\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/00999558c9aab3858d972c20.png"},{"id":54353565,"identity":"27d43ff8-8870-4ab0-938d-8c94373a8df0","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":369199,"visible":true,"origin":"","legend":"\u003cp\u003eWetting characteristics of EGaIn and PBU-EGaIn composites on a pristine PBU film: (a) Comparative graph of the average contact angles for pure EGaIn and PBU-EGaIn mixtures; Visual documentation of contact angles for (b) unaltered EGaIn; (c) PBU-EGaIn mixed at 800 rpm; (d) PBU-EGaIn mixed at 1000 rpm; (e) PBU-EGaIn mixed at 1500 rpm; (f) PBU-EGaIn mixed at 2000 rpm, elucidating the effects of shear mixing speed on the wettability of the composites.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/0791e5d01585eab60739f134.png"},{"id":54353567,"identity":"760c9bee-8613-4c3c-9c69-39f8380e5b3e","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":89305,"visible":true,"origin":"","legend":"\u003cp\u003eEvaluation of the conductive efficacy of the PBU-EGaIn composite: (a) Graphical representation of the composite's conductivity under cyclic strain testing at incremental stretching intensities; (b) Conductivity persistence of the composite under cyclic strain at 135% elongation, across a spectrum of applied frequencies; (c) Longitudinal stability assessment over 50,000 cycles at a constant strain of 135%; (d) Characterization of current-voltage relationships in response to varying degrees of mechanical strain.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/267d004ebd97397ebcfb60a6.png"},{"id":54353572,"identity":"f52e8703-621d-45b3-bfa2-88e74c6306b5","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":92472,"visible":true,"origin":"","legend":"\u003cp\u003eThermal response of the PBU-EGaIn composite under Joule heating: Constituent composition at 55% and mixed at 2000 rpm. (a) Graph illustrating the heating kinetics of the composite subjected to a constant 4.5 V DC across varying degrees of strain. Sequential heating curves of the composite at progressive strain levels with incrementally increasing applied voltages: (b) Unstrained; (c) 50% strain; (d) 75% strain; (e) 100% strain; (f) Near-fracture strain of 135%.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/e1a955ddf7dc189ff2158544.png"},{"id":54353569,"identity":"5c862bb0-7543-43dc-8cea-537bbe7dbe3d","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":898011,"visible":true,"origin":"","legend":"\u003cp\u003eThermographic analysis of Joule heating under mechanical strain: (a) Infrared images captured at the instance when the highest temperature regions of the samples attained approximately 120 °C; (b) Infrared images documenting the moment when the central area of the samples reached a temperature proximate to 120 °C; (c) Infrared images recorded subsequent to a 60-s duration of heating, with an applied voltage of 3.5 V across the samples.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/316b205020216a5842ff4279.png"},{"id":54353568,"identity":"612399b5-556a-41b2-97b6-176eeac8d794","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":689588,"visible":true,"origin":"","legend":"\u003cp\u003eThermographic visualization of the PBU-EGaIn composite’s response to mechanical stress and subsequent self-healing: (a) In the unaltered state; (b) Under 100% strain; (c) At the near-fracture strain of 135%. Columns one, two, and three depict the composite sequentially in its pristine state, following the infliction of damage, and after undergoing the self-healing process, respectively.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/ce2395313019731435b814ba.png"},{"id":54353573,"identity":"91674175-5ac3-4f40-92c8-475761c4376b","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":96770,"visible":true,"origin":"","legend":"\u003cp\u003eEvaluation of the self-repairing capabilities of the PBU-EGaIn composite: (a) Electromechanical performance under cyclic strain in its pristine state; (b) Electromechanical behavior post-recovery from a single incision; (c) Electromechanical response following restoration after multiple intersecting incisions. Assessment of the thermal recuperation post-self-healing from (d) A single incision; (e) Multiple intersecting incisions. (f) Comparative analysis of self-healing efficiency across varying extents of sample elongation.\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/a145753e50d59e14167a66bd.png"},{"id":54353571,"identity":"cb5939c3-4460-4bd5-b69f-c790784e3941","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":931867,"visible":true,"origin":"","legend":"\u003cp\u003eDemonstrating the precision patterning of PBU-EGaIn composite onto a pristine PBU substrate: (a) A uniformly spaced dot matrix suitable for PCB applications; (b) A precisely formed cross symbol; (c) An accurately angled right symbol; (d) An intricate pattern adeptly printed onto the substrate (indicated by a 10 mm scale bar); (e) The detailed pattern displayed under tensile strain.\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/8f720b401e68896d3d00faba.png"},{"id":54353570,"identity":"76df0007-2598-4f1a-bc31-f3c8005e3df6","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":176662,"visible":true,"origin":"","legend":"\u003cp\u003eEvaluation of the PBU-EGaIn composite's capacitance variability in response to physical movement: (a) When adhered to a finger; (b) Conforming to the contours of a wrist; (c) Positioned on a knee; (d) Capacitance fluctuation correlated with the wrist's flexion at variable velocities (Inset: Photographic depiction of the sensor deployed in situ).\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/e3db28e05dc1e5a6ea729766.png"},{"id":55803460,"identity":"bcca1154-1a4e-4d0e-bd33-931bc6982d51","added_by":"auto","created_at":"2024-05-03 13:46:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5859244,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/5a820313-1dc6-4125-9f68-93b54174b900.pdf"},{"id":54353574,"identity":"521363c1-e1d4-4397-974a-4c8f33a0d634","added_by":"auto","created_at":"2024-04-09 09:11:14","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":13794332,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryinformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/7a39673109b7e97c871d76f1.docx"},{"id":54353564,"identity":"8ac21946-cb94-48da-86ed-e235eba0f12c","added_by":"auto","created_at":"2024-04-09 09:11:13","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":656034,"visible":true,"origin":"","legend":"\u003cp\u003eThis research delineates the development of a patterned, autonomously self-healing stretchable conductor that exhibits superior thermal and electrical conductivity, retaining its intricate design integrity even when subjected to high-strain conditions.\u003c/p\u003e","description":"","filename":"GA.png","url":"https://assets-eu.researchsquare.com/files/rs-4142846/v1/8e15d888e11b483ddb8e3d28.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Advancements in Sustainable Conductors: Exploring the Potential of Polybutadiene-Based Urethane and Eutectic Gallium Indium Composites for Autonomous Self-Healing, Stretchable, and Deformation-Resistant Electrical Applications","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe exploration of wearable and flexible electronic devices continues to advance significantly as the global demand for sophisticated healthcare monitoring systems, intelligent mobile technologies, and related applications intensifies [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. These developments necessitate materials and components that not only retain their functionality over prolonged periods but are also engineered to be stretchable\u0026mdash;possessing sufficient rigidity to endure typical environmental challenges without degradation [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Among the myriad configurations of pliable electronics, thin-film technologies have emerged as particularly prevalent, owing to their minimal thickness and a Young's Modulus that mirrors that of human skin, facilitating compatibility and comfort [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The availability of numerous polymers capable of yielding skin-friendly thin films has largely addressed concerns related to user interface; the current challenge, however, lies in identifying a dependable conductive medium that can efficiently facilitate electrical conduction across various structural formations.\u003c/p\u003e \u003cp\u003eHistorically, flexible conductive materials such as the percolated networks of silver nanowires (AgNWs) and electrodes based on two-dimensional materials have been extensively documented. These materials exhibit commendable performance under minimal strain conditions. However, they are prone to irreversible damage and subsequent performance deterioration when subjected to extensive strains, exceeding tens of percent [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In this context, the emergence of so-called liquid metals, which remain liquid at room temperature, represents a transformative development. These substances are not only impervious to damage from structural alterations but also exhibit the high electrical conductivity characteristic of traditional metals, positioning them as promising candidates for flexible electrode applications [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Eutectic gallium-indium (EGaIn), a specific category of liquid metal, has garnered particular interest. Beyond the aforementioned benefits, EGaIn distinguishes itself by its biocompatibility. Unlike mercury, a substance known for its potential to adversely affect the respiratory and nervous systems, EGaIn is deemed safe for direct physical interaction [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. This safety profile, combined with its physical and electrical properties, has facilitated the widespread integration of EGaIn into various research domains, including inkjet printing technologies, microfluidics, and microelectronic integrations, among others [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. This broad applicability underscores the potential of EGaIn as a pivotal material in the ongoing evolution of wearable and flexible electronics, promising to address current limitations while opening new avenues for innovation.\u003c/p\u003e \u003cp\u003eThe inherent fluidity of EGaIn at room temperature, while offering unique advantages in terms of electrical conductivity and flexibility, also poses significant challenges in terms of device stability and durability. This fluidity leads to a precarious adherence of EGaIn to substrates, particularly when subjected to physical forces or alterations in orientation, which can result in the separation of EGaIn from the substrate. The theoretical foundation for this behavior lies in the principles of fluid dynamics and surface tension. The adhesive forces between the liquid metal and the substrate must overcome the cohesive forces within the liquid metal itself to maintain a stable interface. When external stresses disrupt this balance, detachment occurs, compromising the electrical pathways critical for device functionality. To address these challenges, recent research has explored the amalgamation of EGaIn with various polymers, aiming to leverage the viscoelastic properties of polymers to enhance adhesion and stability without significantly detracting from the electrical performance of EGaIn [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe approach to amalgamate EGaIn with polymers is underpinned by advanced concepts in polymer science which take into account the influence of polymer morphology on material properties. Through careful modification of molecular weight, cross-linking density, and copolymer composition, polymers can be synthesized to span a spectrum of mechanical properties, ranging from high elasticity to increased rigidity. This meticulous engineering enables the creation of composites which not only robustly bond EGaIn to substrates but also maintain the pliability required to meet the dynamic demands of wearable electronics. Despite the promising aspects of this approach, it ushers in intricate interactions between the composite's mechanical resilience and its ability to heal autonomously. From a theoretical standpoint, the field of composite materials illuminates the inherent tension in achieving equilibrium between these two attributes. Augmenting the composite with polymer enhances mechanical stability and can mitigate leakage of EGaIn; however, it might concurrently restrict the natural, fluidic behavior of EGaIn that is essential for self-repair. This restriction stems from fundamental discrepancies between the metallic properties of EGaIn\u0026mdash;characterized by quick and reversible restoration via fluid movement and droplet coalescence\u0026mdash;and those of polymeric substances, which are typically defined by permanent deformation or rupture under duress.\u003c/p\u003e \u003cp\u003eThe self-healing characteristic of EGaIn is essentially a reflection of its capacity to reduce surface energy through the merger of discrete droplets, propelled by the metal\u0026rsquo;s substantial surface tension. In stark contrast, polymers, particularly when cross-linked, are not predisposed to such reversible actions, owing to their solidified state and the enduring nature of their cross-linked junctions. Consequently, while the polymer matrix acts as an anchor for EGaIn, it also has the potential to limit the motion of EGaIn particles, thereby hindering their propensity to coalesce and self-mend in the event of damage. Several composites have been introduced to advance the field of liquid metal-based soft electronics, each with its own set of capabilities and limitations. For instance, cross-linked block copolymers showcased remarkable elasticity and inherent self-healing abilities, yet they lacked the ability for intricate patterning and required significant pressure to initiate conductivity [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In contrast, certain polydimethylsiloxane (PDMS)-EGaIn composites offered precision in conductive patterning but were characterized by a lower threshold for strain (up to 100%) and lacked self-healing properties [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Alternative matrices, such as fibrous structures, presented high tensile strain capacities, yet similarly fell short in self-repairing functionality [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In the particular case of PDMS-EGaIn composite electrodes, the theoretical considerations emphasize the compromises involved. PDMS is prized for its high flexibility and compatibility with biological tissues, enhancing the composite's pliability and stretchability. Nevertheless, should damage befall the composite, PDMS\u0026rsquo;s elasticity does not inherently support the reintegration of EGaIn, thus disrupting the liquid metal's innate self-healing process. This delineates a critical area for further research and development to optimize the synergistic properties of polymer-liquid metal composites for electronic applications.\u003c/p\u003e \u003cp\u003eHerein, the composite's core is a polybutadiene-based urethane (PBU), chosen for its thermo-reversible Diels-Alder reaction attributes. The Diels-Alder reaction is a selective and efficient cycloaddition that yields a cyclohexene system, and crucially for this application, it can reverse at higher temperatures, allowing the material to \"self-heal\" by reverting Diels-Alder adducts to the original diene and dienophile at around 120\u0026deg;C. The controlled reversibility of covalent bonds formed during the Diels-Alder reaction empowers the PBU matrix to repair itself after damage. To minimize side reactions at elevated temperatures and preserve the composite's integrity, furan-maleimide is incorporated due to its strong affinity for forming reversible links. The liquid metal-polymer blend was optimized using percolation theory principles, carefully calibrating the ratio and mixing speed to ensure the conductive filler forms a network without spilling out, considering EGaIn's tendency to separate due to high surface tension. Mechanical durability is showcased by minimal resistance variation under extensive deformation, attested by extensive cycling tests. The composite's thermal properties enable self-healing without material degradation. Post-healing, the composite regains its original strain rate, indicating excellent potential for dynamic use. This composite material has been adeptly engineered to function as an efficacious heating element, and it has demonstrated a propensity for autonomous self-healing concurrent with the thermal emission process. For precise patterning critical for electronic functionality, a stencil mask technique was applied, allowing for the creation of intricate, sharp-edged designs at the micro-scale. The composite has demonstrated high accuracy and sensitivity as a motion detector, responding to minute movements, which proves its promise for integration into sophisticated electronic systems and self-healable and stretchable wearable devices.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and Reagents\u003c/h2\u003e \u003cp\u003eHydrogenated hydroxyl-terminated polybutadiene (Krasol HLBH-P 2000, Mn\u0026thinsp;=\u0026thinsp;2100 g/mol) was procured from Cray Valley. Isophorone diisocyanate (IPDI) and dibutyl dilaurate (DBTDL), the reactive components and catalyst, respectively, were sourced from Sigma-Aldrich. Methyl ethyl ketone (MEK), utilized as the solvent in the synthesis process, was acquired from Daejung Chemicals. A customized diol, synthesized from glycerol 1,2-carbonate and furfuryl amine obtained from TCI Chemicals, served as the chain extender. Bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (BMI) from TCI Chemicals was employed as the self-healing agent in the formulation of the PBU. EGaIn alloy, the conductive filler, was also purchased from Sigma-Aldrich. Sodium hydroxide (NaOH) 1M was purchased from Daejung Chemicals to agitate small particles of EGaIn into bulk EGaIn.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of Diol\u003c/h2\u003e \u003cp\u003eThe diol, pivotal in enabling the polyaddition reaction between the polyol and IPDI, was synthesized by reacting 13.1 g of glycerol 1,2-carbonate with 10.79 g of furfuryl amine. The reactants were combined and subjected to magnetic stirring at 60\u0026deg;C for three hours within an oil bath.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Preparation of PBU Substrate\u003c/h2\u003e \u003cp\u003eTo synthesize the PBU matrix, 4 g of HLBH-P 2000, 0.43 g of the prepared diol, 0.89 g of IPDI, and 4.5 g of MEK were mixed with 4 drops of DBTDL as the catalyst. This mixture was then stirred magnetically at 60\u0026deg;C for 2 h. Subsequently, a quantified amount of BMI was introduced to the reaction mixture to complete the PBU synthesis. The stirring continued for an additional 30 min under the same conditions. The resultant PBU mixture was then subjected to spin coating at 1500 rpm for one min to form a thin film, which was subsequently dried at 60\u0026deg;C overnight, creating the substrate for the conductive composite.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Fabrication of PBU-EGaIn Composite\u003c/h2\u003e \u003cp\u003eFor the fabrication of the PBU-EGaIn composite, bulk EGaIn was first subjected to probe sonication in ethanol using a VCX750 ultrasonic processor (Vibra-Cell) for 30 min. The sonication regimen involved multiple cycles, alternating between 3 s of sonication and 3 s of rest, spanning a total of 3 h. Following sonication, the resultant smaller EGaIn droplets were integrated into the PBU mixture at various ratios. The composite mixture then underwent planetary mixing using a paste mixer (Thinky Supermixer, Japan) for 2.5 min before being applied to the bare PBU substrates via spin coating and allowed to cure at ambient temperature. A detailed schematic of the synthesis process can be found in \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e. For patterning, the PBU-EGaIn composite was applied to the PBU substrate using stencil masks. The patterning process entailed placing a mask, designed using AutoCAD software and bearing predefined shapes, onto the substrate. The composite was then distributed uniformly using a rubber putty knife, carefully maintaining an optimal angle to avert leakage. This step was performed expeditiously to ensure proper curing of PBU at room temperature. Following this, the stencil mask was swiftly and cleanly removed, leaving behind the desired pattern. To enhance adhesion between the PBU substrate and the composite, an Ar/O\u003csub\u003e2\u003c/sub\u003e plasma treatment was administered to the PBU surface prior to patterning.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003eIn pursuit of establishing the optimal EGaIn proportion to enhance the electrical conductivity within the composite framework, a meticulous series of syntheses was executed, incorporating varying concentrations of EGaIn. Quantitative electrical resistance measurements were carried out for composites with EGaIn loadings ranging from a minimal 5% up to a substantial 50%. It was observed that the resistance exhibited a significant diminution upon incorporating 50% of the alloy, declining precipitously from an initial magnitude of approximately 10\u003csup\u003e5\u003c/sup\u003e Ω to a markedly lower 83 Ω. This substantial reduction signals the approach toward the percolation threshold, a critical juncture characterized by the formation of a continuous conductive cluster that markedly enhances electron mobility within the composite (as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Further morphological elucidation was conducted using an optical microscope (OM) (\u003cb\u003eFigure S2\u003c/b\u003e). It was discerned that at EGaIn incorporations beneath 33%, the metal particulates\u0026mdash;exhibiting an assortment of shapes\u0026mdash;were homogeneously distributed throughout the PBU substrate. Despite this distribution, the particulates remained distinct and electrically discrete. At a concentration of 50% EGaIn, the emergence of nascent EGaIn collectives was noted, yet these assemblies did not coalesce into a pervasive conductive network. Elevating the EGaIn content to 55% precipitated a substantial decline in electrical resistance, as per the analyses. This observation was corroborated by surface examinations that verified the conductivity enhancement was a direct consequence of the interconnected network formed amongst EGaIn droplets. These droplets, predominantly within a 10 \u0026micro;m diameter range, exhibited non-spherical geometries, a manifestation of the diminished surface energy resulting from the enveloping urethane matrix [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Upon examining samples with 67% metal loading, a denser metallic network was apparent, yet this did not correspond to a discernible resistance decrement. Consequently, in light of the comprehensive electrical and morphological insights, the composite formulation endowed with 55% EGaIn was elected as the superior candidate for the development of the PBU-EGaIn composite, optimizing electrical conductivity whilst upholding the structural cohesion of the composite.\u003c/p\u003e \u003cp\u003eIn the realm of composite materials science, the size of particles within a matrix is a paramount consideration, particularly when dealing with a substance such as liquid metal which exhibits a high surface energy. This intrinsic characteristic of EGaIn is pivotal as it significantly influences the propensity of the metal filler to breach the confines of its host polymer matrix. In an endeavor to rigorously scrutinize this phenomenon, the mixing speeds were modulated across a spectrum of 800 to 2000 rpm, all the while maintaining a constant EGaIn mass fraction at 55% (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The cyclic strain test was meticulously deployed to ascertain the impact of EGaIn droplet dimensions on the composite's performance, denoted as PBU-EGaIn. Scientifically, it was ascertained that there exists an inverse correlation between the planetary mixing velocity and the composite's mechanical stability; however, the variation in electrical resistance over an extended period of 10,000 seconds did not demonstrate notable fluctuation, plateauing at a resistance value of approximately 2.65 Ω. Disparities in the samples' resistivity were less pronounced, yet the mechanical response of the composites under tensile stress was divergent (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). OM images illuminated the scenario: at varying mixing speeds, the EGaIn droplets amalgamated to form conductive pathways, with lower velocities being requisite for agglomerating larger particles (refer to \u003cb\u003eFigure S3\u003c/b\u003e). Such outcomes imply the utilization of both planetary mixing and sonication techniques as effective means to fragment larger liquid metal droplets into diminutive entities, subsequently achieving homogenization and eventual dispersion within the viscous polymeric matrix. In addition to morphological assessments, X-ray diffraction (XRD) analysis provided insights into the composite's internal structure. The semi-crystalline architecture of the pristine PBU was manifested through broad XRD peaks at 20\u0026deg;. Contrastingly, the composite material showcased an additional peak at 37\u0026deg;, indicative of the amorphous nature of the thoroughly integrated EGaIn within the PBU matrix (as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Further granularity on the particle size distribution within the composite was obtained through the examination of the 2000 rpm mixed samples. The analysis, portrayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, revealed that a majority of the particles fell within a diameter range of 6 to 8.5 \u0026micro;m. This level of detail was achieved by employing two-dimensional (2D) analysis on OM photographs, utilizing thresholding techniques to delineate the brighter urethane matrix from the darker EGaIn filler. It is critical to note that the diminutive size of the EGaIn particles is integral to the retention of the liquid metal within the polymer matrix [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Smaller particle dimensions inherently present a higher resistance to the flow, impeding the escape of EGaIn from the composite, thereby enhancing the material's overall stability and integrity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to inspect the wetting behavior among samples with different speeds, contact angle analysis was carried out, initially, the pure alloy had angles higher than 130\u0026deg;, due to especially high surface tension coming from the metallic bonds [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. However, once EGaIn was dispersed in the polymer matrix, the droplets were beaded up, making it easier for PBU to fully encapsulate, indicating that the wetting ability of the composite is better than the alloy. And the angles decreased slightly as the shear mixing speed was accelerated, from more than 130\u0026deg; to approximately 80\u0026deg; (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). As EGaIn particles are covered inside the polymer, the wettability of the composites was better than the pristine liquid metal. Furthermore, droplets with smaller sphere radius would result in a higher pressure difference between the liquid metal and the polymer, due to the Young-Palace equation:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\varDelta P=\\gamma \\frac{2}{R}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eR\u003c/em\u003e is the sphere radius of liquid metal particles. Without the impact of an electric field, there is no pressure variation across the alloy surface. According to the above equation, as the radius is the denominator, it is inversely proportional to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\varDelta P\\)\u003c/span\u003e\u003c/span\u003e, on the other hand, this value favors the capillary force, as depicted in Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). A stronger capillary force would generate sufficient power to breach the metal oxide layer, thus connecting the percolating interconnection among EGaIn particles and bringing higher conductivity to the composite [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${F}_{capillary}=2\\pi \\gamma \\alpha \\text{s}\\text{i}\\text{n}\\phi \\text{sin}\\left(\\phi +\\theta \\right)+\\pi {\\alpha }^{2}{\\text{s}\\text{i}\\text{n}}^{2}\\phi \\varDelta P$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUpon the determination of the optimum EGaIn content and the precise mixing velocity, the capabilities of the composite were subject to rigorous evaluation. A singular test specimen, meticulously dimensioned to 30 mm by 10 mm, was subjected to a cyclic strain analysis, testing the material up to 135% strain\u0026mdash;a figure proximal to the ultimate tensile strain limit of 145%. This specimen was securely mounted on a custom-engineered fatigue testing device, with terminal connections established with the probes of an LCR meter to facilitate the acquisition of resistance data. Documentation of each strain increment was methodically performed as denoted in \u003cb\u003eFigure S4\u003c/b\u003e, with the duration of each experimental iteration extending to 1500 s. In the quiescent state, the specimen presented an initial resistance value of 2.5 Ω. At the imposition of 50% strain, the resistance experienced a nominal increase to 2.6 Ω, a value that persisted steadfastly through the conclusion of the inaugural test sequence, therefore the relative resistance change (\u003cem\u003eΔR/R\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e) at 50% strain is extremely small (around 2%). Escalating the strain to 75% and subsequently to 100% correlated with a proportional augmentation in resistivity, registering values of 2.72 Ω and 2.75 Ω, respectively. Crucially, at an exigent strain level of 135%, the resistance variation remained confined to an increment of approximately 0.6 Ω, which, within the domain of electrical conductivity, is considered to be a tolerable fluctuation as elucidated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. The resistance's progressive uptrend witnessed over the course of the cyclic testing could potentially be ascribed to the composite's limited temporal allowance for the recuperative reformation of its percolated conductive network. Despite this, the maximal differential in resistance observed between the composite in a restive state and at full extension did not surpass the marginal value of 0.5 Ω, a testament to the composite's exceptional mechanical stability.\u003c/p\u003e \u003cp\u003eFurther investigations explored the impact of disparate stretching velocities on resistance variability. Given the requisite for stability in wearable sensor applications, irrespective of motion dynamics, the lateral velocity of the fatigue testing apparatus was varied to simulate real-world conditions and ascertain resistance metrics across different frequencies. The experimental outcomes revealed that resistance disparities between the unstressed and maximally strained states were insubstantial and exhibited independence from the imposed movement frequencies as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. Moreover, the endurance and uniformity of the composite were corroborated through a rigorous 50,000-cycle stretching regimen conducted at strains approaching the material's limit (presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Even after an extended series of tests, the resistance steadfastly hovered around 3.1 Ω. Additionally, the interrelation between applied direct current (DC) voltage and measured current was scrutinized under diverse conditions to authenticate the insubstantial resistance deviations upon deformation (illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). These comprehensive scientific inquiries affirm the superior conductive performance of the PBU-EGaIn composite, significantly bolstering its applicability in the domain of soft electronics, where the juxtaposition of electrical integrity and mechanical suppleness is of paramount importance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe thermal characteristics of the PBU-EGaIn composite, specifically in its role as a stretchable electrode, were subjected to thorough scientific examination. The phenomenon of Joule heating, a principle where heat generation is the result of electrical current traversing through a conductive material, was exploited in these investigations. The application of direct current for heating, as well as for the concurrent measurement of the ensuing electrical current, was accomplished using a sophisticated source meter. A temperature of 120\u0026deg;C was identified as the optimal thermal benchmark for the composite, a point at which the Diels-Alder reaction is known to proceed with requisite efficiency to initiate the self-healing process within the PBU matrix, as substantiated by prior research [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The composite's temperature distribution during Joule heating was meticulously recorded using a high-precision digital multimeter and an advanced infrared-ray camera. Upon the administration of a 4.5 V direct current, the heating rates across the composite were observed to be prompt, with samples at unaltered, 50%, and 100% strain levels reaching the desired temperature threshold within 2 min. In contrast, the sample subjected to nearly its maximum strain capacity exhibited a marginally extended heating duration, approaching three minutes to attain the 120\u0026deg;C threshold (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). A subsequent experimental series employed a stepwise increase in voltage intensities, beginning from 0.5 V and escalating to 3.5 V. Each voltage increment was applied only after it was ascertained that the preceding voltage could no longer induce a significant thermal rise. These trials demonstrated that the extent of mechanical deformation was proportional to the time required to achieve the heating target. Notably, a specimen without any strain required approximately 1100 s to reach the designated temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), with this timeframe progressively lengthening, reaching 1210 s for the specimen subjected to the most extensive strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec-f). These rigorous experimental evaluations confirm the PBU-EGaIn composite's proficiency in Joule heating, showcasing its capability to respond thermally in a prompt and controlled manner, a property essential for applications necessitating quick thermal modulation in tandem with flexible material properties. The ability to precisely manage thermal response is imperative for the activation of self-healing mechanisms within smart materials, offering a robust solution for the maintenance and longevity of soft electronic systems.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eInfrared (IR) thermographic imaging was utilized to scrutinize the distribution of heat across the composite thin film as a function of its mechanical strain, detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Each column represents a specific strain level, with the upper, middle, and lower rows capturing distinct thermal states. The top row images illustrate the junctures at which the hottest zones approximate the target temperature, while the middle row images document the attainment of 120\u0026deg;C at the sample's core\u0026mdash;a temperature conducive to the Diels-Alder reaction, which is central to the self-healing process of the composite. The bottom row images reflect the thermal signature after 1 min of heating, under an applied voltage of 3.5 V for all conditions. Initially, in the unstressed state of the composite (sample's length\u0026thinsp;=\u0026thinsp;18 mm), an even heat distribution was observed across the surface, with a minimal temperature gradient due to the high density of the metallic filler uniformly embedded within the polymer matrix. This homogeneity ensures efficient electron mobility and, consequently, uniform Joule heating. Upon elongation of the sample to 100% and 135% of its original length (extending from 18 mm to 36 mm and 42 mm, respectively), a marked deviation in thermal distribution was observed. The areas adjacent to the voltage application sites manifested intensified IR emission, evidenced by a darker appearance in the central region, indicative of cooler temperatures due to its increased distance from the DC source. This effect was most pronounced at a strain of 135% (total length\u0026thinsp;=\u0026thinsp;42 mm), where the thermal disparity reached up to 10\u0026deg;C. In comparison, the unstrained and 100% strained samples (total length\u0026thinsp;=\u0026thinsp;36 mm) exhibited thermal differentials of merely 1\u0026deg;C and 5\u0026deg;C, respectively. Such temperature variations can be explicated by the elongated conductive pathways, characterized by a diminished surface contact area and more extensive liquid bridges within the stretched composite. These altered geometric configurations lead to increased resistance to electron flow, particularly impacting the central region due to its relative remoteness from thermoelectric influence [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Consequently, over a time span of 60 s, the strained specimens exhibited significant temperature deltas, most notably the sample at 135% strain, which only managed to attain a peak temperature of 91.7\u0026deg;C.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the domain of wearable technology, high endurance and intrinsic self-healing capabilities are imperative to address and rectify damages such as incisions. To quantitatively evaluate the self-healing efficacy of the PBU-EGaIn composite, a sequential IR thermal analysis was conducted. This analysis comprised three distinct investigative conditions, each represented in separate columns of Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e: the initial intact state, the subsequent state following incision, and the final state after the self-healing process. Upon making an incision in the composite film with a razor blade, a marked decrease in temperature was discernible in the IR images, particularly pronounced when the composite was subjected to mechanical strain. This phenomenon was characterized by an increased thermal footprint at the site of the damage, indicating a significant deviation from the composite's nominal temperature, which was adeptly identified by the IR camera's coldest point detection feature (blue crosshairs, as depicted in the middle column of Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). To initiate the self-healing process, the damaged composite samples were restored to an unstressed state, and a DC voltage was applied. This electrical input triggered the outflow of liquid metal droplets from the matrix due to the material's inherent high surface tension. Realigning the severed interfaces facilitated the re-establishment of electrical conductivity through the liquid metal pathways. Subsequent heating mediated the melting of the polymeric substrate adjacent to the cut, thereby re-liquefying the polymer and enabling it to bridge the incision, effectively reconstituting the composite's integrity. Post-healing, the composites exhibited remarkable resilience, maintaining functional integrity under strains of 100% and 135%, as demonstrated in the second and third rows of Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, respectively. The self-healing process was underpinned by the Diels-Alder reaction, which within the PBU matrix, utilizes furan groups from the diol component and maleic anhydride from the BMI to form reversible cross-links. The thermal and chemical conditions favorable for this self-healing reaction, specifically the retro-Diels-Alder reaction, have been thoroughly characterized in the referenced literature [\u003cspan additionalcitationids=\"CR31 CR32\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], providing a robust scientific foundation for the composite's reparative abilities. This signifies that our electrodes are capable of autonomous self-healing.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eHigh-resolution digital imaging was conducted concurrently with thermal analysis to meticulously document the surface topography of the samples, thereby enabling an in-depth morphological evaluation subsequent to the recovery process, as depicted in \u003cb\u003eFigure S5\u003c/b\u003e. With regard to the composites' elasticity, the self-healed specimens exhibited an unimpaired retention of their original strain characteristics. This conservation of mechanical robustness intimates that the self-healing mechanism entails the strategic cleavage of three pi bonds within the polymeric lattice\u0026mdash;specifically, two pi bonds from the diene component and one pi bond from the dienophile\u0026mdash;during the [4\u0026thinsp;+\u0026thinsp;2] cycloaddition reaction. The process culminates in the formation of two novel sigma bonds while concurrently regenerating an additional pi bond. Such intricate molecular reconfiguration is critical for reinstating the composite's inherent tensile properties, reflecting the efficacious restoration of the polymer network after damage. The intricacies of this self-healing response have been expounded in the scientific literature as indicated in reference [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn addition to the topological assessment, the conductive and thermal properties of the self-healed composite were rigorously evaluated. The composite underwent two distinct types of damage: a single intersecting incision and multiple intersecting incisions. From an electrical standpoint, in its pristine state, both the minimal and maximal resistance values exhibited a gradual increase throughout the testing period; nonetheless, the range between these values remained stable (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Conversely, after undergoing the self-healing process, the PBU-EGaIn composite maintained a consistent resistivity, irrespective of being in a relaxed state or fully elongated. With a single incision, the resistance discrepancy was less than 0.5 Ω, while for multiple incisions, it was 1.5 Ω. Even in the scenario of multiple incisions, post-recovery, the absolute maximum resistance observed was only 4 Ω, indicating the material's continued excellent conductivity (as illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb and \u003cb\u003ec\u003c/b\u003e). Concerning the thermal conductivity, both one-time damaged and multiply damaged healed specimens were able to reach the critical temperature required to initiate the Diels-Alder reaction. However, this process was protracted, taking approximately five minutes. Voltage step tests were performed for both types of damaged conditions: the single incision required 1250 s to reach the desired thermal state, while the multiple incisions required about 1400 s (depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed and \u003cb\u003ee\u003c/b\u003e). Furthermore, the efficiency of the healing process was quantitatively analyzed across varying degrees of sample elongation. It was observed that the healing efficacy diminished proportionally with increased sample length. This can be attributed to the dispersion of the same quantity of liquid metal over an augmented surface area, which inherently reduces the density of the conductive network, thereby impacting the composite's capacity for heat generation and, consequently, its ability to facilitate self-repair (as indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ef). This inverse relationship between stretching magnitude and healing proficiency highlights the challenges in maintaining healing efficiency in composites subjected to extensive mechanical deformation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe PBU-EGaIn composite demonstrated the capability to be precisely patterned into specific micro-sized configurations, which is a pivotal technological advancement. Employing a stencil mask technique, uniform dots with diameters of 50 \u0026micro;m were successfully fabricated, which holds significant promise for applications in print circuit board (PCB) manufacturing, as evidenced by the creation of a 4\u0026times;4 dot array with equidistant spacing (refer to Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). Subsequent figures, \u003cb\u003e8b\u003c/b\u003e and \u003cb\u003e8c\u003c/b\u003e, illustrate the formation of a cross and a right angle, each with a meticulous thickness of 100 \u0026micro;m. The edges of these patterns were remarkably defined, with the fabricated surfaces exhibiting a high degree of smoothness. Moreover, the stencil technique proved adept at producing complex designs, as demonstrated by the defect-free, intricate pressure sensor pattern, which included exceptionally thin lines with no overlap (shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ed). The clarity of the patterning was further pronounced under mechanical strain; fine individual lines retained their distinct separation, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ee.\u003c/p\u003e \u003cp\u003eThe composite's autonomous self-healing capability was rigorously evaluated across a spectrum of intricate geometrical configurations, showcasing consistent recovery irrespective of the complexity or number of inflicted damage sites. This validation was methodically conducted through controlled experiments wherein two composite specimens, featuring predetermined patterns responsible for conveying electric signals to a light emitting diode (LED), underwent deliberate damage at specified locations (refer to \u003cb\u003eFigure S6\u003c/b\u003e, first row). Subsequent analysis revealed that following damage, as evidenced by the LEDs ceasing to illuminate (\u003cb\u003eFigure S6\u003c/b\u003e, second row), the self-repair mechanism efficiently reinstated the conductive pathways in both instances, thereby facilitating the reactivation of the LEDs (\u003cb\u003eFigure S6\u003c/b\u003e, third row). Further elucidation of the healing dynamics was pursued using a field emission scanning electron microscope (FESEM), which provided visual insights into the closure of a gap initially measuring approximately 60 \u0026micro;m in width (\u003cb\u003eFigure S7a\u003c/b\u003e). The observed closure of the gap progressed discernibly, culminating in complete sealing, with the resultant mend being readily discernible (\u003cb\u003eFigure S7 b-d\u003c/b\u003e). Additionally, atomic force microscopy (AFM) analysis quantified the reduction in dimensions of the incision post-healing, revealing a decrease in both width and depth of the composite from approximately 5 \u0026micro;m to nearly 2 \u0026micro;m, and from around 3 \u0026micro;m to approximately 0.5 \u0026micro;m, respectively (\u003cb\u003eFigure S7e\u003c/b\u003e). The refined morphological features and high-resolution patterning observed in the composite can be attributed to the altered surface tension of the PBU-EGaIn compound. This alteration arises from the encapsulation of the liquid metal component within the polymeric matrix, resulting in a transition from an oxide-encased state to one where the polymer matrix predominantly encapsulates the alloy, thereby influencing its surface energy properties [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The proficient patterning capabilities demonstrated by the PBU-EGaIn composite represent a significant advancement in the realm of stretchable circuits, offering a versatile and practical material solution for sophisticated electronic applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe PBU-EGaIn composite, a synthesis of PBU and employing EGaIn, exhibits superlative properties that make it an exemplary candidate for applications in wearable electronics due to its remarkable elasticity and stability. Its performance as a wearable motion sensor was systematically evaluated, capitalizing on its potential to monitor and analyze human movement with high fidelity. The composite was strategically affixed to joints such as fingers, wrists, and knees, regions that commonly experience a range of motion. The quantification of motion was facilitated through the measurement of relative capacitance changes (\u003cem\u003eC\u003c/em\u003e/\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e) employing two extrinsic conductive leads to ensure consistent and secure connectivity to the LCR meter. The application of the patterned composite for sensing tasks was particularly advantageous in instances necessitating compact sensors. During the digit articulation test, the capacitance variation between flexed and extended digit positions was minor (\u003cem\u003eC\u003c/em\u003e/\u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;8%) indicating the composite's nuanced sensitivity to subtle movements, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea. In contrast, actions that involve broader ranges of motion, such as wrist rotation, elicited more pronounced capacitance signals, demonstrating the sensor's ability to detect varying degrees of articulation. The ultrathin nature of the patterned sensor, highlighted in the inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb, is not merely an aesthetic advantage but also functionally crucial. It ensures that the sensor is non-intrusive and harmonizes with the wearer's natural movements, a pivotal characteristic for wearable technology to be truly integrated into everyday use without impeding the user. For larger joints like the knee, which undergo more extensive motion, an expanded sensor footprint was necessary to cover the area adequately and capture the full dynamic range of movement. The signals acquired from such extensive motion were proportionately larger, reflecting the sensor's ability to scale its sensitivity with the amplitude of the subject's activity (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ec). Furthermore, the prompt and precise capacitive response to the wrist's movement, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ed, showcases the sensor's exceptional responsiveness\u0026mdash;a critical aspect in real-time motion detection and feedback. This responsiveness is a testament to the composite's ability to rapidly modulate its electrical properties in synchronization with physical deformations, a quintessential attribute for the development of advanced and intuitive wearable electronics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDespite the PBU-EGaIn composite\u0026rsquo;s remarkable flexibility and straightforward self-healing capabilities, it was acknowledged that in certain scenarios the composite may not be suitable for direct reuse following damage. Consequently, a meticulous recycling protocol was devised to segregate and reclaim the liquid metal, leveraging its near-complete recyclability [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The reclamation process encompassed two principal stages. The initial phase involved the thermal dissolution of PBU: the fully cured composite was subjected to heat treatment at 140\u0026deg;C in the presence of MEK. This procedure facilitated the depolymerization of PBU, aligning with the retrograde Diels-Alder reaction, whereby the crosslinked network decomposed into distinct imide and furan entities [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Notably, this step did not compromise the integrity of the conductive alloy, which boasts a melting point substantially exceeding 2000\u0026deg;C, thus remaining unaffected [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Subsequent to the dissolution of the polymeric matrix, the isolated EGaIn particulates underwent a series of MEK washes, followed by sonication to extricate any lingering polymer residues. Once liberated into the environment, the liquid metal droplets reinstated their inherent high surface tension, a characteristic that is particularly pronounced under extreme pH conditions [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. For the oxide layer removal and reinstatement of the metal's original interfacial tension, a 1 M sodium hydroxide (NaOH) solution was employed, effectively stripping the oxide layer. This facilitated the coalescence of the dispersed metal particles into a singular, cohesive drop, a transformation depicted in \u003cb\u003eFigure S8\u003c/b\u003e. This systematic recovery process underscores the sustainability aspect of the PBU-EGaIn composite, offering an environmentally considerate option for the lifecycle management of materials used in stretchable electronics.\u003c/p\u003e \u003cp\u003eOur investigation entailed a comprehensive comparative analysis aimed at benchmarking the performance characteristics of the PBU-EGaIn composite developed in this study against existing research paradigms. The examination encompassed a spectrum of composite configurations, each designed to imbue the material with specific attributes such as stretchability, minimal resistance variation under mechanical strain, self-healing capabilities, and recyclability, as delineated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e [\u003cspan additionalcitationids=\"CR41 CR42 CR43 CR44 CR45 CR46 CR47\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Notably, the composite we developed stands out for its unique amalgamation of these properties, a feat unparalleled by preceding materials. Across a range of performance metrics, our composite consistently demonstrated either superior or commensurate performance when juxtaposed with previous research findings. Furthermore, the material exhibits an exceptional ability for autonomous self-healing, particularly when deployed as a heating element, a distinctive characteristic not observed in earlier studies. We are confident that the innovation presented in this research represents a significant breakthrough in addressing a critical challenge inherent in conventional stretchable soft electronics.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparative analysis of PBU-EGaIn composite with previous noteworthy studies incorporating liquid metal or similar materials for stretchable electrode applications.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposite components\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaximum strain (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eResistance change at 50% strain (\u003cem\u003eΔR/R\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e) (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSelf-healing ability\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRecyclability\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePBU and EGaIn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e135\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eThis work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolyphenol and EGaIn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLignin and EGaIn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUnavailable\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePDMS and MXene/AgNWs/Galinstan\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e140\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eYes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTPU and indium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEcoflex and galinstan\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolyimide and graphene\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSMCF and galinstan\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e373\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePDMS and EGaIn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEcoFlex and EGaIn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study has culminated in the development of an innovative PBU-EGaIn composite characterized by remarkable stretchability, minimal resistance variation under mechanical strain, superior stability, autonomous self-healing, and recyclability. The material demonstrates the ability to maintain electrical conduction with minimal resistance values, not exceeding 4 Ω, under various degrees of mechanical strain up to 135%. The composite's thermal response is noteworthy; it efficiently attains temperatures of up to 120\u0026deg;C in a short time frame. Reaching this critical thermal threshold triggers the Diels-Alder reaction, which underpins the composite's autonomous self-healing process, allowing for the restoration of the PBU layer's integrity after damage. The repaired areas regain functional normalcy, a testament to the exceptional self-healing efficacy of the material. In addition to its restorative properties, the PBU-EGaIn composite has been engineered to support precise patterning through a simple stencil mask technique, attributed to its reduced surface tension. This capability enhances its suitability for intricate designs required in advanced electronic applications. When leveraged as a motion detector, the composite performs admirably, demonstrating high sensitivity and responsiveness, effectively detecting subtle movements. Furthermore, the composite boasts high-resolution patterning capabilities, capable of sensing even the slightest movement with pronounced responsivity\u0026mdash;a critical feature for wearable technology. The practical implications of this are profound, opening avenues for the integration of the PBU-EGaIn composite into the burgeoning field of soft, wearable electronics. In instances where the material does not manifest self-healing properties, a strategic two-step recycling protocol has been established. This process efficiently recovers the valuable EGaIn, underscoring the sustainability of the composite by ensuring that the constituent materials can be reused, thereby contributing to the principles of circular economy within material science.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEGaIn\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eeutectic gallium-indium\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePBU\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003epolybutadiene-based urethane\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eAgNWs\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003esilver nanowires\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePDMS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003epolydimethylsiloxane\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eIPDI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eisophorone diisocyanate\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDBTDL\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003edibutyl dilaurate\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMEK\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003emethyl ethyl ketone\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBMI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ebis(3-ethyl-5-methyl-4-maleimidophenyl)methane\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eOM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eoptical microscope\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eXRD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eX-ray diffraction\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e2D\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003etwo-dimensional\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003edirect current\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eIR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003einfrared\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePCB\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eprinted circuit board\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eLED\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003elight emitting diode\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eFESEM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003efield emission microscope\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eAFM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eatomic force microscope\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNaOH\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003esodium hydroxide.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by National Research Foundation of Korea (NRF) grants (Number 2020M3H4A3081895, RS-2023-00247545 and 2022R1A2C1010353) funded by the Korean government (MSIP).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJong-Woong Kim and Jinho Joo supervised the whole research process. Jong-Woong Kim and Jinho Joo contributed to the study\u0026apos;s conception and design. Material preparation, data collection, and analysis were performed by Tran Duc Khanh. The manuscript was written by Tran Duc Khanh and Jong-Woong Kim. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eThe online version contains supplementary material available at\u0026hellip;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTruong KV, Hayles A, Bright R, Luu TQ, Dickey MD, Kalantar-Zadeh K, Vasilev K (2023) Gallium liquid metal: Nanotoolbox for antimicrobial applications. 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Nat Electron 6:154\u0026ndash;163. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41928-022-00914-8\u003c/span\u003e\u003cspan address=\"10.1038/s41928-022-00914-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Eutectic gallium indium, Self-healing composite, Stretchable electrodes, Heaters, Patternable composite","lastPublishedDoi":"10.21203/rs.3.rs-4142846/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4142846/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn the burgeoningfield of wearable electronics, flexible and durable conductors that can maintain consistent electrical properties under various conditions are critically needed. This research investigates the potential of a composite material combining eutectic gallium-indium (EGaIn) with a polybutadiene-based urethane (PBU) to meet these demands. EGaIn is selected for its superior conductivity, which is attributed to its low melting point, allowing for consistent performance. However, the challenge lies in its integration with encapsulating polymers due to poor adhesion qualities and the complexity of treatment methods required for successful amalgamation. Moreover, the high cost of EGaIn poses additional hurdles for its practical application. Addressing these issues, our study introduces a novel EGaIn-PBU composite, which not only ensures robust electrical conductivity but also exhibits remarkable self-healing properties and recyclability, thus promising sustainability. The composite leverages the advantageous properties of both components: EGaIn offers reliable conductivity, and PBU provides flexibility and the ability to self-recover after damage, which are imperative for wearable applications. Additionally, the composite maintains exceptional electrical resistance stability, withstanding mechanical strains up to 135% without compromising performance. The material's self-healing capability is attributed to the autonomous mending properties of EGaIn and the reversible Diels-Alder reactions in the PBU matrix. The result is an efficient restoration of the composite’s original properties upon incurring damage. Furthermore, the composite's adaptability is showcased through its printability, allowing for precise patterning conducive to custom-designed wearable devices. Conclusively, the developed EGaIn-PBU composite represents a transformative advancement in flexible electronics, combining high performance with environmental friendliness.\u003c/p\u003e","manuscriptTitle":"Advancements in Sustainable Conductors: Exploring the Potential of Polybutadiene-Based Urethane and Eutectic Gallium Indium Composites for Autonomous Self-Healing, Stretchable, and Deformation-Resistant Electrical Applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-09 09:11:09","doi":"10.21203/rs.3.rs-4142846/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a4044ddc-f277-4270-b8bf-0493ecf3fd9e","owner":[],"postedDate":"April 9th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-05-03T13:38:17+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-09 09:11:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4142846","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4142846","identity":"rs-4142846","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}