Programmable and rapid responsive self-sensing soft actuator based on asymmetric poly (N-isopropylacrylamide)/alginate hydrogel with reversible network

Programmable and rapid responsive self-sensing soft actuator based on asymmetric poly (N-isopropylacrylamide)/alginate hydrogel with reversible network | 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 Programmable and rapid responsive self-sensing soft actuator based on asymmetric poly (N-isopropylacrylamide)/alginate hydrogel with reversible network Xingchen Cui, Xinyu Liu, Shuai Wang, Fuqiang Fan, Shunsheng Ye, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9571010/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 Hydrogel-based soft actuators hold significant promise in the domain of bionic soft robots and flexible drives. Nonetheless, current hydrogel actuators are limited by their lack of shape reprogrammability. Herein, a novel reprogrammable hydrogel actuator based on reversible coordination bond is prepared via simple chemical crosslinking. The patterned structures of actuator are created within the hydrogel actuators by incorporating a ferric (Fe 3+ ) ion crosslinked sodium alginate (SA) network within a composite gel made up of poly(N-isopropylacrylamide) (PNIPAM) and polyaniline (PANI). The remarkable photothermal conversion efficiency of PANI fillers enables the actuator to precise demonstrates rapid remote NIR-induced deformation. Utilizing a mask technique, these actuators exhibit diverse NIR-driven deformation such as bending, folding, and twisting. Significantly, the addition of dynamic coordination bonds facilitates the erasing and reprogramming of specific deformations on the actuator through the application of reducing agents. Moreover, the interpenetrating conductive PANI chains endow the actuator with low hysteresis electric self-sensing capacity to monitor its deformation. This study emphasizes the potential of hydrogel soft actuators for programmability, offering insights into the applications of bionic soft robots and intelligent mechanical systems. Programmable Hydrogel Soft actuator Self-sensing Rapid responsive Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Adaptive self-morphing systems are ubiquitous in nature. A wide range of biological systems, including animals, plants and cells, can realize morphological transformation under external environmental stimuli. [ 1 – 5 ] For example, the Venus flytrap can sense insects and close its traps through stimuli-responsive deformation to capture prey. [ 6 – 8 ] Such natural phenomena have greatly promoted the research and development of deformation-responsive actuating materials. [ 9 – 17 ] In general, the core working mechanism of actuating materials relies on the construction of anisotropic structures with differential swelling and shrinking behaviors. Various specific actuation behaviors can be regarded as the synergistic combination of independent deformation in different local regions of materials. [ 18 – 21 ] Accordingly, the fabrication of flexible soft actuators with precisely programmable deformability usually requires the construction of high-precision patterned architectures (e.g., crosslinked and aggregated structures) inside actuating materials to regulate the local deformation of each region. [ 22 – 29 ] Nevertheless, most currently reported synthetic soft actuators are restricted to a single actuation mode. Meanwhile, they generally lack shape reprogramming capability due to the inability to dynamically reconstruct the internal patterned structures of materials. [ 5 , 30 ] Once a customized structural pattern is fabricated for an actuating material, the local structure of each region becomes permanently fixed and unchangeable. Consequently, the resultant actuators only achieve a single and fixed deformation mode without reconfigurability. Therefore, to mimic natural soft actuation systems with flexible morphing characteristics, it is of great significance to develop reprogrammable soft actuators with reconfigurable and switchable multi-mode actuation. Such actuators can adapt to diverse task requirements and complex and changeable practical environments. Despite great efforts, it is still challenging to prepare a rapid-responsive and reprogrammable hydrogel actuator with functional features. In this work, a semi-interpenetrating conductive hydrogel (SL-s-IPN) composed of PNIPAM and PANI was selected as the substrate. [ 31 ] On this basis, a programmable asymmetric hydrogel actuator based on coordination bond was rationally designed. By virtue of the dynamic coordination between Fe 3+ and sodium alginate (SA), a patterned and programmable dual-network SA-Fe 3+ /SL-s-IPN hydrogel actuator was fabricated with the assistance of a mold. The sponge-like SL-s-IPN hydrogel network with integrated actuation and sensing functions serves as the actuating component, while the Fe 3+ -crosslinked SA network acts as a dynamically programmable component. Benefiting from the patterned design of the SA-Fe 3+ network, the as-prepared hydrogel actuator can achieve large-angle and diverse programmable deformation under thermal and near-infrared (NIR) stimulation. Notably, the Fe 3+ and SA network are dynamically crosslinked via coordination bonds. After soaking in a reducing agent, Fe 3+ in the crosslinked network can be reduced to Fe 2+ , which erases the pre-designed patterned structure and eliminates the original deformation performance of the hydrogel actuator. Through the secondary introduction of Fe 3+ ions, a new patterned network can be reconstructed inside the hydrogel, endowing the actuator with brand-new stimuli-responsive deformation behaviors. (Fig. 1 ) Furthermore, taking advantage of the unique self-sensing capability of the SL-s-IPN matrix, the reprogrammed hydrogel actuator maintains excellent electrical self-sensing performance. Real-time feedback on large-scale shape morphing can be realized by monitoring dynamic electrical signal variations. This programmable hydrogel actuator constructed based on dynamic coordination bonds provides a new strategy for the development of reversible flexible devices. 2. Experimental 2.1 Materials. N-isopropylacrylamide (NIPAM) and 2-Hydroxy-4'-(2-hydroxyetho-xy)-2-methylpro-piophenone (initiator2959) were purchased from TCI (Shanghai) Development Co., Ltd. N, N'-methylenebisacrylamide (BIS), aniline (ANI), and hydrochloric acid (HCl) were purchased from Energy Chemical (Shanghai). Ammonium peroxodisulfate (APS) was purchased from Alfa Aesar (Tianjin) Chemical Co., Ltd. Ferric chloride hexahydrate (FeCl 3 ·6H 2 O), sodium alginate (SA) and sodium citrate (SC) were purchased from China National Pharmaceutical Group Corp. All above reagents were used without further treatment. 2.2 Synthesis of sponge like PNIPAM hydrogel (SL-PNIPAM) . The SL-PNIPAM hydrogel was prepared by reported methods. [ 31 ] Briefly, 226 mg NIPAM, 2 mg BIS and 2 mg initiator2959 was mixed in 1ml of DI water to form a monomer solution. Then, the aqueous solution was bubbled with N 2 for 15 min to remove the air in solution. Eventually, the prepared solution was cast into silicone rubber molds with different thickness (30 mm*30 mm*0.5 mm, 30 mm*30 mm*1 mm, 30 mm*30 mm*1.5 mm, respectively) and exposed to UV light (365 nm,2 W/cm 2 ) for 30 min at 40°C to form SL-PNIPAM hydrogel. The sample was placed in DI water for 3 days to remove excess components. 2.3 Synthesis of sponge like semi-interpenetrating network of PNIPAM/PANI hydrogel (SL-s-IPN). To get the sponge like semi-interpenetrating network of PNIPAM/PANI hydrogel, PANI chains were polymerized into the PNIPAM network utilizing in-situ oxidative polymerization. [ 31 ] Firstly, the samples were heated to 80 ℃ for 6 h to remove the water from gel matrix. And then, the samples were immersed into 10 mL aqueous solution with 0.2 M aniline and 1 M HCl to absorb aniline monomer for 2 h. Precooled 10 mL aqueous solution with 0.2 M APS and 1 M HCl was added to the aniline solution in an ice bath to react for 12 h to fabricate the SL-s-IPN hydrogel. 2.4 Preparation of programmed SA-Fe 3+ /SL-s-IPN asymmetric hydrogel. The SA-Fe 3+ / SL-s-IPN asymmetric hydrogel was prepared via crosslinking SA network on one side of SL-s-IPN hydrogel. Firstly, the obtained SL-s-IPN hydrogel was immersed in SA solution of 1 wt% for 12h to fully absorb dissociative SA chains. And then, the SL-s-IPN hydrogel film containing SA chains was tiled on the surface of slide, and the 3D printing mold with different pattern was tightly attached above the sample. Next, the FeCl 3 solutions was dripped into the groove of the mold to form the programmed SA-Fe 3+ / SL-s-IPN asymmetric hydrogel. The concentration parameters and cross-linking time parameters for the fabrication of hydrogel are summarized in Table S1 and Table S2 . Eventually, the samples were placed in DI water for 3 days to remove the excess SA chains and Fe 3+ ions. 2.5 Manufacture of NIR light driven programmable SA-Fe 3+ /SL-s-IPN hydrogel actuator. To get the soft actuator, the SA-Fe 3+ / SL-s-IPN asymmetric hydrogel was cut into a desirable shape and crosslinked at the specified position. And then, a tunable near-infrared light (wavelength = 808 nm) with different intensity was irradiated on the surface of whole sample to generate deformation of the actuator. The whole deformation process of actuator was recorded by optical camera in real time. Herein, four types of soft actuators were fabricated. For the strip-shape actuator and planar actuator, the spot of NIR light was irradiated on the sample constantly. For the scroll actuator, the spot of NIR light was irradiated on the sample from left to right (or right to left). For the walker actuator, the pulsed NIR light was irradiated on the left (or right) of sample according to fixed frequency. 2.6 Erasing and reprogramming of SA-Fe 3+ /SL-s-IPN hydrogel actuator. Herein, sodium citrate (SC) was selected as reductant to converse the Fe 3+ to Fe 2+ , decrosslinking the SA network of asymmetric hydrogel and erasing the deformability of hydrogel actuator. Specifically, the programmed SA-Fe 3+ /SL-s-IPN hydrogel actuator was immersed in SC solution of 50 mg/mL for 12 h to remove the SA network. And then, the sample was soaked in DI water for 12 h to remove the excess ions. Eventually, the programmed asymmetric hydrogel reverted back to original SL-s-IPN hydrogel and lose its light-induced deformability. Notably, the erased sample can be endowed with new programming patterns by immersed in SA solution and crosslinked by Fe 3+ . The programming-erasing loop is reversible and can be repeated multiple times. 2.7 Characterization. The Fourier transform infrared (FT-IR) spectra were recorded by an IR spectrophotometer (Bruker VERTEX70) in the scanning range of 4000 − 400 cm − 1 , the samples were obtained by a KBr disk technique. Scanning electron microscopy (SEM) micrographs were taken by Hitachi SU8010 at an acceleration voltage of 5 kV. The hydrogel samples were first frozen in liquid nitrogen and then placed in a freeze dryer for 24 h to remove all the moisture. The front, back, and cross sections of hydrogel samples were coated with gold by a sputter coater before being observed by SEM. 3. Results and discussion The fabrication process of the asymmetric hydrogel is illustrated in Fig. 1 . With the assistance of a mold, a crosslinked sodium alginate (SA) network is formed on the upper layer of the SL-s-IPN hydrogel, thereby constructing an asymmetric structure in the designated region. To clarify the distribution of the two hydrogel networks in the SA-Fe 3+ /SL-s-IPN hydrogel, the surface, reverse side and cross-sectional micromorphology of the samples were systematically characterized via scanning electron microscopy (SEM). As shown in Fig. 2 a-c, the SEM results reveal that the as-prepared SA-Fe 3+ /SL-s-IPN hydrogel possesses a typical asymmetric structure, and distinct micromorphologies are observed on the two sides of the sample. Specifically, the cross-linked side incorporated with Fe 3+ exhibits a relatively smooth surface (Fig. 2 a), a compact and uniform SA-Fe 3+ layer is covered on the top of the original porous SL-s-IPN hydrogel, leading to a low surface roughness. On the contrary, the uncross-linked side without Fe 3+ incorporation retains the intrinsic sponge-like porous structure of the pristine SL-s-IPN hydrogel, which displays a rough surface with abundant micron-sized pores (Fig. 2 b). The cross-sectional SEM images further verify that the SA- Fe 3+ /SL-s-IPN hydrogel consists of two structurally distinct layers. As shown in Fig. 2 c, two well-adhered hydrogel morphologies can be clearly distinguished in the cross-section. The cross-linked layer presents a dense structure with a smaller thickness, while the uncross-linked layer without Fe 3+ shows a loose structure with a larger thickness and abundant open pores, maintaining the original morphological characteristics of SL-s-IPN. Energy dispersive spectroscopy (EDS) was adopted to analyze the elemental distribution of the hydrogel. In the SA- Fe 3+ /SL-s-IPN hydrogel, the Fe element content is relatively high on the cross-linked side, demonstrating that this region is mainly composed of crosslinked SA-Fe 3+ hydrogel. In comparison, the uncross-linked side exhibits a low Fe content, suggesting that this part is dominated by the original SL-s-IPN hydrogel. The cross-sectional elemental distribution confirms a gradient distribution of Fe elements within the hydrogel, which further evidences the successful construction of the asymmetric structure. To further identify the chemical compositions of the hydrogel samples, Fourier transform infrared spectroscopy (FT-IR) characterization was conducted on the SA- Fe 3+ /SL-s-IPN hydrogel, and the corresponding results are displayed in Fig. 2 d. The characteristic peaks at 1652 cm -1 and 1545 cm -1 are assigned to the stretching vibrations of -C = O and -NH in PNIPAM, respectively. The absorption peaks at 1577 cm -1 and 1498 cm -1 correspond to the quinoid and benzenoid rings of PANI, while the peak at 1742 cm -1 is attributed to the stretching vibration of -CO- in SA. These results confirm that the SA- Fe 3+ /SL-s-IPN hydrogel integrates the SA- Fe 3+ network, PNIPAM network and PANI molecular chains, and the three components are successfully combined into a unified system. Given the intrinsic thermoresponsive property of PNIPAM, the resultant SA- Fe 3+ /SL-s-IPN hydrogel also exhibits temperature-responsive behavior. Benefiting from its unique bilayer structure, the cross-linked side and uncross-linked side of the SA- Fe 3+ /SL-s-IPN hydrogel deliver discrepant thermoresponsive capacities. To quantitatively investigate the difference in swelling performance between the two sides, a single hydrogel sample was cut into two equal parts, and the swelling behaviors of the cross-linked region and uncross-linked region were separately measured in water at different temperatures. As shown in Fig. 2 e, when the ambient temperature increases from 5°C to 50°C, the equilibrium swelling ratio of the Fe 3+ -free side decreases from 20.8 to 5.8. Under the same temperature variation, the equilibrium swelling ratio of the Fe 3+ -crosslinked side declines from 17.7 to 11.6. The swelling ratio difference (ΔSR) between the two sides at various temperatures is calculated to be 15.0 and 6.1, respectively (Figure S1 ). This indicates that the introduction of Fe 3+ regulates the swelling performance of different regions in the hydrogel, and the Fe 3+ crosslinking treatment weakens the temperature-dependent swelling variation capacity. This phenomenon can be explained by the increased proportion of non-responsive SA- Fe 3+ network and the decreased proportion of thermoresponsive PNIPAM network on the crosslinked side. Moreover, the non-responsive SA-Fe 3+ network may form an interpenetrating polymer structure with the PNIPAM network, which restricts the conformational transition space of PNIPAM chains. Consequently, the variation range of the swelling ratio is reduced on the crosslinked side under variable temperature conditions. PANI contained in the SL-s-IPN hydrogel possesses excellent photothermal conversion performance. After introducing the Fe 3+ -crosslinked SA network, the obtained SA- Fe 3+ /SL-s-IPN hydrogel also achieves favorable photothermal conversion capability. As illustrated in Fig. 2 f, the surface temperature of the hydrogel rises significantly under near-infrared (NIR) irradiation, and the maximum surface temperature gradually increases from 25.2°C to 70.2°C with the elevation of light intensity. After five consecutive NIR irradiation cycles (Figure S2 ), the hydrogel maintains stable photothermal conversion performance, revealing outstanding photothermal stability. Under continuous NIR irradiation, the surface temperature rises rapidly and reaches a plateau within approximately 30 s (Figure S3 a). Once the NIR light is turned off, the surface temperature gradually drops and fully recovers to the initial state within 60 s (Figure S3 b). These results demonstrate that the fabricated SA-Fe 3+ /SL-s-IPN hydrogel possesses superior and reversible photothermal conversion performance. Benefiting from the differential swelling behavior inside the SA-Fe 3+ /SL-s-IPN hydrogel, a one-dimensional SA-Fe 3+ /SL-s-IPN actuator with stimuli-responsive deformation capability was successfully fabricated. The actuation mechanism is illustrated in Fig. 3 a. At first, both sides of the SA-Fe 3+ /SL-s-IPN hydrogel remain swollen, and the actuator exhibits no obvious shape deformation. Upon NIR irradiation, temperature elevation induces shrinkage on both sides of the hydrogel. The uncross-linked side of hydrogel undergoes a more significant shrinkage, whereas the Fe 3+ -crosslinked side presents a slight volume contraction. Such discrepant shrinkage generates asymmetric stress distribution within the material, thereby enabling the one-dimensional SA-Fe 3+ /SL-s-IPN actuator to achieve specific bending deformation. Optical photos show that the bending angle of the hydrogel actuator gradually increases with the increase of light intensity. (Fig. 3 a, Movie S1) Notably, the effects of experimental parameters, including sample thickness, ion concentration and crosslinking duration, on the bending performance of the one-dimensional actuator were systematically investigated. The results indicate that the optimal sample thickness for maximizing the bending angle is 0.5 mm (Figure S4 ), and the optimized ion concentration and crosslinking time are 0.005 mol/L and 20 min, respectively (Figure S5 ). The correlation between light intensity and actuator bending angle was recorded and summarized in Fig. 3 b. As the NIR light intensity increases from 0 W/cm 2 to 2.79 W/cm 2 , the bending angle gradually increases from the initial − 30° to over 270°, with a total angular variation exceeding 300°. A positive correlation is observed between the bending angle and incident light intensity. Furthermore, the response kinetics of the one-dimensional SA-Fe 3+ /SL-s-IPN actuator were characterized (Movie S2). As shown in Fig. 3 c, under NIR irradiation of 2.79 W/cm 2 , the actuator rapidly bends to the maximum angle and reaches a steady equilibrium state within 20 s, with an average angular response rate of 15 °/s. After removing the NIR irradiation, the actuator can recover to its original state within an ultrafast period of approximately 6 s (Fig. 3 d). The rapid recovery performance is attributed to the unique sponge-like porous structure of the hydrogel, which facilitates high-frequency and continuous deformation behavior. [ 31 ] In addition, the cyclic stability of the actuator during repeated bending was evaluated. As presented in Fig. 3 e, the actuator maintains favorable bending performance after 70 consecutive cycles, demonstrating great potential for long-term and repeated stable operation. Benefiting from the unique programmability, flexible actuators based on the SA-Fe 3+ /SL-s-IPN hydrogel can achieve various reversible deformation behaviors including bending and twisting by patterning different regions on the hydrogel matrix. As shown in Fig. 4 a, the one-dimensional actuator realizes multiple deformation modes under near-infrared (NIR) stimulation through regional patterning. For example, when only the middle area of the hydrogel is programmed, the one-dimensional actuator folds from both ends to the center. After patterning both ends synchronously, the two sides bend simultaneously to form a closed loop structure. When the two ends are patterned along opposite directions, the actuator can spontaneously deform into an S-shape under planar NIR irradiation. By introducing diagonal patterns with different orientations, the actuator achieves left-handed or right-handed torsional deformation in sequence, exhibiting reversible morphing with high degrees of freedom. This flexible twist deformation facilitates the application of hydrogel actuators in more complex environments. (Movie S3) Compared with the simple folding behavior of the existing homogeneous hydrogel actuators, the SA-Fe 3+ /SL-s-IPN hydrogel actuator can be driven by a single optical stimulus, accompanied by larger deformation amplitude and more sophisticated deformation modes. In addition to customizable 1D-to-2D deformation, diverse two-dimensional hydrogel films can be obtained via simple cutting treatment, which further enables 2D-to-3D shape transformation. As displayed in Fig. 4 b, flexible grippers with two, three, four and five arms were fabricated by cutting the SA-Fe 3+ /SL-s-IPN hydrogel. Combined with the template method, different regions of these grippers were endowed with controllable bending capacity. Driven by NIR light, all grippers with distinct structures can complete rapid grasping movements. As presented in Fig. 4 c, a hand-shaped hydrogel actuator was fabricated. Herein, only the programmed finger segments possess bending capability, while non-programmed fingers remain undeformable. With the assistance of the template method, Fe 3+ patterning was performed on independent fingers of the hand-shaped hydrogel to realize regional functional regulation. For instance, localized programming on the thumb enables the actuator to bend the thumb under NIR irradiation to produce a specific gesture. Similarly, by integrating multiple programming strategies, the actuator can generate a series of distinct gestures in sequence upon NIR stimulation, thus achieving the output of gesture information. Thanks to the unique programmable actuation performance of the SA-Fe 3+ /SL-s-IPN actuator, an actuator with unidirectional curling and unidirectional walking capacities was rationally designed and fabricated. As shown in Fig. 5 a, when a spot near-infrared (NIR) laser irradiates the sample surface from left to right, the actuator curls synchronously along the same direction. Interestingly, such curling behavior is governed by the irradiation direction. Once the light direction is reversed from left-to-right to right-to-left, the curling direction of the actuator changes accordingly. (Movie S4) Therefore, the spatiotemporal deformation behavior of the flexible actuator can be precisely regulated by controlling key parameters, including the spatial position, irradiation direction and light intensity of NIR stimulation. The unique curling actuation originates from the rapid response and recovery kinetics of the SA-Fe 3+ /SL-s-IPN hydrogel. Under localized NIR irradiation, the exposed hydrogel region undergoes rapid response and localized deformation. As the NIR light spot moves from left to right, the localized bending behavior propagates synchronously, thereby achieving unidirectional curling actuation. In addition to light-triggered unidirectional curling, an actuator with unidirectional walking performance was further developed by applying pulsed localized light stimulation. As illustrated in Fig. 5 b, a controllable NIR light source was placed above the left side of the actuator to provide localized stimulation. Upon NIR irradiation, the left segment of the actuator bends obviously; after the light is switched off, the deformed region gradually recovers to its original flat state. During the recovery process, the asymmetric deformation generates a rightward thrust, which drives the actuator to move rightward and completes a single walking cycle. (Movie S5) By repeating the on-off light irradiation in a cyclic manner, the actuator can continuously migrate toward the right side and realize NIR-driven unidirectional walking. Similarly, the locomotion direction of the walker can be readily adjusted by changing the irradiation direction. Notably, benefiting from its intrinsic asymmetric structure, this walker requires no additional auxiliary ratchet plates during locomotion and can walk steadily on arbitrary flat substrates, exhibiting superior locomotion flexibility and environmental adaptability. In summary, combined with excellent deformation programmability and favorable electrical self-sensing properties, the flexible actuators based on SA-Fe 3+ /SL-s-IPN hydrogel hold promising application potential in diverse fields such as biomimetic materials and artificial soft robotics. Homogeneous hydrogel actuators exhibit unique phototactic locomotion behaviors. However, in certain practical application scenarios, phototaxis may impair the operational stability of actuators. Unstable light irradiation directions can lead to irregular deformation orientations and further reduce working efficiency. Therefore, it is imperative to develop anti-phototactic flexible actuators that can maintain stable performance under light irradiation from diverse directions. Different from phototactic actuators whose deformation relies on localized optical stimulation, the distinctive deformation of the SA-Fe 3+ /SL-s-IPN actuator originates from its intrinsic asymmetric internal structure. Consequently, the SA-Fe 3+ /SL-s-IPN actuator possesses unique anti-phototactic locomotion characteristics. The photo-induced deformation performances of the unprogrammed homogeneous SL-s-IPN actuator and the programmed SA-Fe 3+ /SL-s-IPN actuator were systematically compared. As shown in Fig. 6 a, the pristine one-dimensional SL-s-IPN actuator presents obvious phototactic behavior under incident light from different directions, and its motion direction changes synchronously with the variation of light orientation. In contrast, the programmed SA-Fe 3+ /SL-s-IPN actuator achieves stable and predefined unilateral curling regardless of incident light directions (Fig. 6 b), demonstrating excellent deformation controllability. Such stable curling behavior is determined by the inherent asymmetric structure rather than external localized light stimulation. Thus, the actuator can sustain consistent deformation under multi-directional light irradiation. In conclusion, the as-prepared SA-Fe 3+ /SL-s-IPN actuator is more suitable for practical application scenarios that require steady and reliable deformation performance. In the SA-Fe 3+ /SL-s-IPN hydrogel, the coordination interaction between Fe 3+ and carboxyl groups within the SA-Fe 3+ network exhibits dynamic reversibility. After reduction treatment with a reducing agent, Fe 3+ in the SA-Fe 3+ network is reduced to Fe 2+ , which triggers the decrosslinking of the SA-Fe 3+ hydrogel network. Consequently, the asymmetric SA-Fe 3+ /SL-s-IPN hydrogel reverts to the original homogeneous SL-s-IPN hydrogel and loses its deformation capability (Fig. 7 a). Therefore, the photo-induced deformation performance of the hydrogel actuator can be effectively erased via soaking in a reducing agent solution. As shown in Fig. 7 b, the photo-responsive deformation behavior of the one-dimensional SA-Fe 3+ /SL-s-IPN actuator completely disappears after reducing agent treatment. Under near-infrared irradiation, the actuator only undergoes simple shrinkage, rather than the folding, bending or twisting deformation observed before erasure. The reduction of Fe 3+ to Fe 2+ destroys the crosslinked SA-Fe 3+ network and eliminates the intrinsic asymmetric structure of the hydrogel. Without this structural difference, the actuator fails to produce unique programmed deformation under external stimuli. To further investigate the effect of the reducing agent on the microscopic morphology, SEM characterization was performed on the erased hydrogel samples (Figure S6 ). After soaking in the reducing agent, both sides of the sample present identical sponge-like porous structures, and the originally dense SA-Fe 3+ layer is completely removed. These results confirm that the Fe 3+ -crosslinked SA network is eliminated after erasure, and the hydrogel transforms from an asymmetric structure into an isotropic and homogeneous SL-s-IPN network. Notably, the erased hydrogel can regain brand-new photo-induced deformation performance by re-soaking in SA solution and reconstructing Fe 3+ crosslinking. As illustrated in Fig. 7 c, a hand-shaped soft actuator was firstly programmed to bend the index and middle fingers to achieve Shape I gesture under NIR irradiation. Subsequently, reducing agent treatment was adopted to erase the original bending functions and eliminate the initial photo-responsive deformation behavior. Finally, by repeating SA immersion and Fe 3+ crosslinking with redesigned templates, the same palm-shaped actuator was reprogrammed to bend the thumb and little finger, realizing a Shape II gesture transformation. Accordingly, diverse reversible deformation modes can be readily realized on a single hydrogel material through the repeated dynamic cycle of “programming-erasing”. Owing to the unique electrical self-sensing and actuating properties of SL-s-IPN hydrogel under NIR irradiation, [ 31 ] the SA-Fe 3+ /SL-s-IPN hydrogel actuator derived from the SL-s-IPN matrix exhibits comparable self-sensing capability. With the assistance of real-time monitoring equipment (Fig. 8 a), the electrical signal variation of the one-dimensional SA-Fe 3+ /SL-s-IPN hydrogel actuator during actuation was systematically investigated. Benefiting from its inherent asymmetric structure, the developed actuator achieves photoinduced deformation under large-area NIR irradiation with improved deformation controllability. As shown in Fig. 8 b, within a single light on/off cycle, both the bending angle and current signal increase synchronously upon planar NIR light excitation. The flexible actuator reaches a steady state of bending deformation and electrical response within approximately 15 s. After the NIR light is turned off, the bending angle and electrical signal gradually decrease and fully recover to the initial levels in around 15 s, demonstrating favorable deformation self-sensing performance. As presented in Fig. 8 c, under continuously pulsed NIR irradiation, the bending deformation and electrical signals of the actuator rapidly respond and recover. No obvious attenuation of bending amplitude or electrical output is observed over 10 consecutive bending–recovery cycles, indicating excellent stability of the self-sensing behavior. This capability of large-angle photoinduced motion effectively compensates for the limitations of locally stimulated flexible hydrogel actuators, the proposed SA-Fe 3+ /SL-s-IPN hydrogel actuator is believed to show significant potential for the fabrication of soft robot facing complicated and changeable application scenarios. 4. Conclusions In summary, a patterned and programmable SA-Fe 3+ /SL-s-IPN hydrogel actuator has been successfully fabricated. Relying on the reversible crosslinking between Fe 3+ and sodium alginate (SA) networks, the dynamically crosslinked SA-Fe 3+ network with programmable, erasable and rewritable characteristics was constructed within a semi-interpenetrating hydrogel matrix composed of PNIPAM and PANI. Benefiting from the uniquely patterned structure, the SA-Fe 3+ /SL-s-IPN actuator can perform diverse reversible deformations under the NIR light stimulation. In virtue of the dynamic reversibility of the SA-Fe 3+ network, the deformation behavior of the actuator exhibits favorable erasability and rewritability, enabling a single hydrogel actuator to achieve multiple distinct shape transformations. Attributed to the excellent self-sensing performance of the SL-s-IPN hydrogel, the deformation degree of the SA-Fe 3+ /SL-s-IPN hydrogel actuator can be effectively monitored by recording real-time changes in electrical signals. This novel self-sensing hydrogel actuator with integrated programmable, erasable and rewritable functions provides a promising foundation for the development of next-generation flexible robots with custom-tunable deformation capabilities. Declarations CRediT authorship contribution statement Xingchen Cui : Writing-original draft, Conceptualization, Software, Formal analysis, Data curation. Xinyu Liu : Visualization, Resources. Shuai Wang : Visualization, Resources. Fuqiang Fan : Methodology, Formal analysis, Resources. Shunsheng Ye : Visualization. Yu Fu : Writing-review & editing, Resources, Project administration, Conceptualization, Supervision. Bing Zhang : Validation, Data curation, Visualization. Tieqiang Wang : Writing-review & editing, Supervision, Conceptualization, Resources, Funding acquisition, Formal analysis. Xiaoqian Xu : Writing-review & editing, Resources, Supervision, Funding acquisition. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contribution Xingchen Cui: Writing-original draft, Conceptualization, Software, Formal analysis, Data curation. Xinyu Liu: Visualization, Resources. Shuai Wang: Visualization, Resources. Fuqiang Fan: Methodology, Formal analysis, Resources. Shunsheng Ye: Visualization. Yu Fu: Writing-review & editing, Resources, Project administration, Conceptualization, Supervision. Bing Zhang: Validation, Data curation, Visualization. Tieqiang Wang: Writing-review & editing, Supervision, Conceptualization, Resources, Funding acquisition, Formal analysis. Xiaoqian Xu: Writing-review & editing, Resources, Supervision, Funding acquisition. Acknowledgement This work was supported by the National Natural Science Foundation of China (22075039, 22175030, 22101042), Fundamental Research Funds for the Central Universities (N2205007), Liaoning Provincial Science Foundation (2023-MSBA-055), The Foundation of the Liaoning Revitalizing Talents Program (XLYC2403175). We also specially thank the Analytical and Testing Center at Northeastern University for experimental and instrumental support. Data availability Data will be made available on request. References Adak NC, Lee W (2024) A comprehensive review of 4D-printed thermo-responsive hydrogel-based smart actuators for solar steam generation: Advanced design, modeling, manufacturing, and finite element analysis. Prog Mater Sci 148:101377 Ding A, Tang F, Alsberg E (2025) 4D printing: A comprehensive review of technologies, materials, stimuli, design, and emerging applications. Chem Rev 125(7):3663–3771 Sun L, Li Z, Zhang Y, Lu Y, Zhang S (2025) Stimuli-responsive shape-morphing soft actuators: metrics, materials, mechanism, design and applications. Prog Mater Sci 155:101531 Yang J, Dong Z, Liu H, Tian Y (2025) Bioinspired self-sensing hydrogel actuators: From mechanisms to applications. 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Sci Adv 11(8):eads3058 Chen Y, Valenzuela C, Liu Y, Yang X, Yang Y, Zhang X, Ma S, Bi R, Wang L, Feng W (2025) Biomimetic artificial neuromuscular fiber bundles with built-in adaptive feedback. Matter 8(2):101904 Song Z, Wu T, Zhang L, Song H (2025) Multi-responsive and self-sensing flexible actuator based on MXene and cellulose nanofibers Janus film. J Colloid Interface Sci 688:183–192 Bayati A, Rahmatabadi D, Khajepour M, Baniassadi M, Abrinia K, Bodaghi M, Baghani M (2025) 4D printing of composite thermoplastic elastomers for super-stretchable soft artificial muscles. J Appl Polym Sci 142(29):e57177 Bai C, Kang J, Wang Y (2025) Kirigami-inspired light-responsive conical spiral actuators with large contraction ratio using liquid crystal elastomer fiber. ACS Appl Mater Interfaces 17(9):14488–14498 Yue T, Lu C, Tang K, Qi Q, Lu Z, Lee L, Bloomfield-Gadlha H, Rossiter J (2025) Embodying soft robots with octopus-inspired hierarchical suction intelligence. Sci Robot 10(102):eadr4264 Yang D, Feng M, Sun J, Wei Y, Zou J, Zhu X, Gu G (2025) Soft multifunctional bistable fabric mechanism for electronics-free autonomous robots. Sci Adv 11(5):eads8734 Youn JH, Jang SY, Hwang I, Pei QB, Yun S, Kyung KU (2025) Skin-attached haptic patch for versatile and augmented tactile interaction. Sci Adv 11(12):eadt4839 Zhang B, Cui X, He W, Shao L, Wang T, Meng F, Fu Y (2023) Asymmetric metal-organic framework-based mixed matrix membrane for reversible self-assembling 3D architecture. ACS Appl Polym Mater 5(9):7090–7097 Chen L, Zhang Y, Zhang K, Li F, Duan G, Sun Y, Wei X, Yang X, Wang F, Zhang C, Li S, Cao X, Ma C, Jiang S (2024) Multi-stimuli responsive, shape deformation, and synergetic biomimetic actuator. Chem Eng J 480:148205 Sun W, Song Z, Wang J, Yi Z, He M (2024) Preparation of patterned hydrogels for anti-counterfeiting and directional actuation by shear-induced orientation of cellulose nanocrystals. Carbohydr Polym 332:121946 Shang M, Ma S, Ma J, Guo L, Liu C, Xu X (2024) Somatosensory actuators based on light-responsive anisotropic hydrogel for storage encryption of information systems. Chem Eng J 496:153895 Ma X, Zhou Y, Bian S, Li Z, Jiang Y, Zhang S, Li S, Li Y (2026) Wireless and programmable electrochemical soft actuators of ionogels for tracking and liquild control. Sens Actuators B 458:139722 Zhang Y, Yao X, Yu J, Qin H, Cong H (2026) Gradient crosslinking of anisotropic hydrogels for programmable shape morphing and actuation. Chin Chem Lett 37(6):112041 Geng W, Wu J, Zhang Y, Zhen Y, Guo X (2026) Freestanding covalent organic polymer membranes with flexible skeletons for solvent-responsive actuation. Chem Eng J 534:174508 He E, Xiao J, Xu Z, Sheng W, Chen S, Gai S, Lu W, Wang J (2026) A novel method of welding deformation control based on programmable multi-point flexible supports. J Manuf Process 168:135–147 Sharma A, Naskar S, Mukhopadhyay T (2026) Programmable shape morphing and space deployment through graded derivatives of origami architectures. Space: Science & Technology. 6: 0363 Zhang Q, Zhang G, Xiao L, Li C, Zhang Q, Ge F (2026) Dynamic cross-linking and spatially programmable actuation toward actively moving and reprogrammable liquid crystal elastomer actuators. ACS Appl Polym Mater 8(7):5318–5328 Zhu Y, Zhu F (2026) 4D-printed reversible morphing structures: experimental study and a simplified phase transition model. Compos Struct 383:120150 Cui X, Zhang B, Shao P, Li L, Ye S, Fan F, Fu Y, Meng F, Wang T (2025) Sponge-like PNIPAM/Fe3O4/PPy composite hydrogel actuator with rapid response, self-sensing and multiple manipulating manners for complex application scenarios. Chem Eng J 522:168066 Bai HY, Zhu QL, Cheng HL, Wen XL, Wang ZJ, Zheng Q, Wu ZL (2025) Muscle-like hydrogels with fast isochoric responses and their applications as soft robots: a minireview. Mater Horiz 12(3):719–733 Cui X, Liu Z, Zhang B, Tang X, Fan F, Fu Y, Zhang J, Wang T, Meng F (2023) Sponge-like, semi-interpenetrating self-sensory hydrogel for smart photothermal-responsive soft actuator with biomimetic self-diagnostic intelligence. Chem Eng J 467:143515 Additional Declarations No competing interests reported. Supplementary Files SupportingInformation.docx MovieS1.mp4 MovieS3.mp4 MovieS4.mp4 MovieS5.mp4 MovieS2.mp4 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9571010","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":638625407,"identity":"94ed6cb6-032d-4e4f-aa3e-5ef127b21e69","order_by":0,"name":"Xingchen Cui","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAArUlEQVRIiWNgGAWjYFACxgYGhgoIU4IELWdI0wLS1UaKFv4ZyW0SP+fZRRscYD54m4fBLo+gFokbic2GvduSczccYEu25mFILiaoxUAisfEx47YDQC08ZtI8DAcSG4jQ0nCYcQ5IC/83orUAbWkA28JGnBaJMw+bDXuOJefOPMxmbDnHIJmwFv729GcSP2rscvuONz+88abCjrAWBGAGu5N49aNgFIyCUTAK8AAAqus6gBA/+IgAAAAASUVORK5CYII=","orcid":"","institution":"China Medical University","correspondingAuthor":true,"prefix":"","firstName":"Xingchen","middleName":"","lastName":"Cui","suffix":""},{"id":638625408,"identity":"044b0f5a-b851-4bb0-9535-04562b18bb74","order_by":1,"name":"Xinyu Liu","email":"","orcid":"","institution":"Shengjing Hospital of China Medical University","correspondingAuthor":false,"prefix":"","firstName":"Xinyu","middleName":"","lastName":"Liu","suffix":""},{"id":638625409,"identity":"8fd98306-92ae-44e1-85f0-144a97206d4c","order_by":2,"name":"Shuai Wang","email":"","orcid":"","institution":"The People’s Hospital of Liaoning Province","correspondingAuthor":false,"prefix":"","firstName":"Shuai","middleName":"","lastName":"Wang","suffix":""},{"id":638625410,"identity":"92d8569e-c3b4-4748-a80d-df96e84aa54b","order_by":3,"name":"Fuqiang Fan","email":"","orcid":"","institution":"Northeastern University","correspondingAuthor":false,"prefix":"","firstName":"Fuqiang","middleName":"","lastName":"Fan","suffix":""},{"id":638625411,"identity":"8ac42629-bf3a-49e4-b2c4-273ca7b95134","order_by":4,"name":"Shunsheng Ye","email":"","orcid":"","institution":"Northeastern University","correspondingAuthor":false,"prefix":"","firstName":"Shunsheng","middleName":"","lastName":"Ye","suffix":""},{"id":638625412,"identity":"16ae2a23-77cb-4e20-8a8f-d7124568c72d","order_by":5,"name":"Yu Fu","email":"","orcid":"","institution":"Northeastern University","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Fu","suffix":""},{"id":638625413,"identity":"051c470b-214f-4123-9c78-c651a4acb2b3","order_by":6,"name":"Bing Zhang","email":"","orcid":"","institution":"Shenyang University of Chemical Technology","correspondingAuthor":false,"prefix":"","firstName":"Bing","middleName":"","lastName":"Zhang","suffix":""},{"id":638625414,"identity":"02c4dd4b-4cb6-4023-93c1-e5d4597daee2","order_by":7,"name":"Tieqiang Wang","email":"","orcid":"","institution":"Northeastern University","correspondingAuthor":false,"prefix":"","firstName":"Tieqiang","middleName":"","lastName":"Wang","suffix":""},{"id":638625415,"identity":"e1c8babf-ecd0-4fab-a3ca-a76bd905d901","order_by":8,"name":"Xiaoqian Xu","email":"","orcid":"","institution":"China Medical University","correspondingAuthor":false,"prefix":"","firstName":"Xiaoqian","middleName":"","lastName":"Xu","suffix":""}],"badges":[],"createdAt":"2026-04-30 02:38:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9571010/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9571010/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109280961,"identity":"e104cbb6-4633-415b-b4c6-b5bba4d883d7","added_by":"auto","created_at":"2026-05-14 17:39:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":397295,"visible":true,"origin":"","legend":"\u003cp\u003eProgramming and erasing process of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN asymmetric hydrogel.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/84fe5c084acfc114312a0a97.png"},{"id":109280954,"identity":"86406b78-b0b5-4f64-9adc-67fb1bc8848c","added_by":"auto","created_at":"2026-05-14 17:39:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1000627,"visible":true,"origin":"","legend":"\u003cp\u003e(a-c) SEM image (above) and EDS mapping image (below) of cross-linked side, uncross-linked side, and\u0026nbsp; cross-section of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel membrane, scale bar=10 μm; (d) FT-IR spectra of PNIPAM, PANI, SA-Fe\u003csup\u003e3+\u003c/sup\u003e and SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN; (e) Swelling ratio of cross-linked side and uncross-linked side of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel; (f) Maximum surface temperature of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel under NIR illumination with different intensities.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/fa1b111b837953b2c9214bdf.png"},{"id":109280988,"identity":"f75aee7b-4758-4943-acf4-8716877d72fb","added_by":"auto","created_at":"2026-05-14 17:39:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":459882,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic and digital images of the bending deformation of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN strip actuator under NIR irradiation with different intensities, scale bar=10 mm; (b) Irradiation intensity dependent bending angle of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN strip actuator; (c) Response kinetics of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN strip actuator under NIR irradiation of 2.79 W/cm\u003csup\u003e2\u003c/sup\u003e; (d) Recovery kinetics of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN strip actuator under NIR irradiation of 2.79 W/cm\u003csup\u003e2\u003c/sup\u003e; (e) Oscillatory bending-recovering behavior of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN strip actuator under NIR irradiation of 2.79 W/cm\u003csup\u003e2\u003c/sup\u003e for 70 cycles.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/e0e9d199bb43690970a1d3b8.png"},{"id":109281005,"identity":"35a29f78-3485-4e99-ba5c-49158c0feaeb","added_by":"auto","created_at":"2026-05-14 17:39:42","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":503244,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Light-induced deformation of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN rectangle membrane with different programmed patterns (b) Light-induced grab process of programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN gripper with different arms; (c) Light-induced gesture change of programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hand-like actuator, light intensity= 2.79 W/cm\u003csup\u003e2\u003c/sup\u003e, scale bar=10 mm.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/bad348ae1a63a72713d715c8.png"},{"id":109280959,"identity":"6cd90b42-ec98-49f9-9417-128c1964a331","added_by":"auto","created_at":"2026-05-14 17:39:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":424090,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Curling deformation of programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN rectangle membrane induced by moving NIR laser; (b) Crawling behavior of programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN rectangle membrane induced by pulsed NIR light, light intensity=2.79 W/cm\u003csup\u003e2\u003c/sup\u003e, scale bar=15 mm.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/99399daeaf6aea670281f5ba.png"},{"id":109280982,"identity":"59d72960-bc7c-4b8a-9842-e4bbc1cff3bb","added_by":"auto","created_at":"2026-05-14 17:39:29","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":623488,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Unsteady deformation of unprogrammed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN pillar under the NIR irradiation from different directions; (b) Steady deformation of programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN pillar under the NIR irradiation from different directions, light intensity=2.79 W/cm\u003csup\u003e2\u003c/sup\u003e, scale bar=10 mm\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/ac208a3b513206f099af3b3a.png"},{"id":109280958,"identity":"f1f0a44b-8456-4ae2-8f7f-fe336f5bb76b","added_by":"auto","created_at":"2026-05-14 17:39:15","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":500291,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Scheme of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator before and after erasing; (b) Light-induced deformation of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN rectangle membrane after erasing; (c) Continuously erasing-reprogramming process of the same SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN gripper and its deformation under NIR irradiation, light intensity=2.79 W/cm\u003csup\u003e2\u003c/sup\u003e, scale bar=10 mm.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/f708c91da0f6ab41a5ab74e6.png"},{"id":109281006,"identity":"68e2ac5b-6835-4628-8fb8-2f8a3773bed4","added_by":"auto","created_at":"2026-05-14 17:39:43","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":365866,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic illustration of electric circuit connected for self-sensing SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator; (b) The real-time electrical signal and bending angle of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator before and after the NIR irradiation; (c) Electrical monitoring signal and bending angle of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator under the NIR light for 10 cycles, light intensity=2.79 W/cm\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/1f9f73317008f923e930c4f8.png"},{"id":109306552,"identity":"35d93c18-4a9c-41a4-b215-b099c77225f2","added_by":"auto","created_at":"2026-05-15 10:11:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4523158,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/829385cc-a34e-46ef-a782-ef8da56de248.pdf"},{"id":109280955,"identity":"61cc5de0-2483-44fb-b400-210e0b14070a","added_by":"auto","created_at":"2026-05-14 17:39:10","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":699659,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/0d2356f25d1b3b5f2f0784a1.docx"},{"id":109281009,"identity":"c34804d2-8a41-4ef2-8582-b9bdad9926ad","added_by":"auto","created_at":"2026-05-14 17:39:47","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3167894,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/f1488994c506c4ea49c449be.mp4"},{"id":109280957,"identity":"c72f29fe-60cf-41ed-a9db-f6d6f3573562","added_by":"auto","created_at":"2026-05-14 17:39:15","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3149842,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/e3dafad4699d5cf32ff09f84.mp4"},{"id":109280960,"identity":"dab7e570-27cd-4d33-9ecf-e603fbeda7ce","added_by":"auto","created_at":"2026-05-14 17:39:25","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":3368811,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/55d2db29f02c0d767ba99225.mp4"},{"id":109280964,"identity":"90c60c1f-c4fb-4a23-8fa2-9221f79e12e5","added_by":"auto","created_at":"2026-05-14 17:39:28","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":4508221,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS5.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/289377930e96ba5b5ea5d9fe.mp4"},{"id":109280956,"identity":"ba07a301-eb2c-4b67-8d88-b0aa76caec3b","added_by":"auto","created_at":"2026-05-14 17:39:12","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":5407021,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9571010/v1/7f346cff117ebfae53f512f9.mp4"}],"financialInterests":"No competing interests reported.","formattedTitle":"Programmable and rapid responsive self-sensing soft actuator based on asymmetric poly (N-isopropylacrylamide)/alginate hydrogel with reversible network","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAdaptive self-morphing systems are ubiquitous in nature. A wide range of biological systems, including animals, plants and cells, can realize morphological transformation under external environmental stimuli. [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] For example, the Venus flytrap can sense insects and close its traps through stimuli-responsive deformation to capture prey. [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] Such natural phenomena have greatly promoted the research and development of deformation-responsive actuating materials. [\u003cspan additionalcitationids=\"CR10 CR11 CR12 CR13 CR14 CR15 CR16\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] In general, the core working mechanism of actuating materials relies on the construction of anisotropic structures with differential swelling and shrinking behaviors. Various specific actuation behaviors can be regarded as the synergistic combination of independent deformation in different local regions of materials. [\u003cspan additionalcitationids=\"CR19 CR20\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] Accordingly, the fabrication of flexible soft actuators with precisely programmable deformability usually requires the construction of high-precision patterned architectures (e.g., crosslinked and aggregated structures) inside actuating materials to regulate the local deformation of each region. [\u003cspan additionalcitationids=\"CR23 CR24 CR25 CR26 CR27 CR28\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] Nevertheless, most currently reported synthetic soft actuators are restricted to a single actuation mode. Meanwhile, they generally lack shape reprogramming capability due to the inability to dynamically reconstruct the internal patterned structures of materials. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] Once a customized structural pattern is fabricated for an actuating material, the local structure of each region becomes permanently fixed and unchangeable. Consequently, the resultant actuators only achieve a single and fixed deformation mode without reconfigurability. Therefore, to mimic natural soft actuation systems with flexible morphing characteristics, it is of great significance to develop reprogrammable soft actuators with reconfigurable and switchable multi-mode actuation. Such actuators can adapt to diverse task requirements and complex and changeable practical environments. Despite great efforts, it is still challenging to prepare a rapid-responsive and reprogrammable hydrogel actuator with functional features.\u003c/p\u003e \u003cp\u003eIn this work, a semi-interpenetrating conductive hydrogel (SL-s-IPN) composed of PNIPAM and PANI was selected as the substrate. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] On this basis, a programmable asymmetric hydrogel actuator based on coordination bond was rationally designed. By virtue of the dynamic coordination between Fe\u003csup\u003e3+\u003c/sup\u003e and sodium alginate (SA), a patterned and programmable dual-network SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator was fabricated with the assistance of a mold. The sponge-like SL-s-IPN hydrogel network with integrated actuation and sensing functions serves as the actuating component, while the Fe\u003csup\u003e3+\u003c/sup\u003e-crosslinked SA network acts as a dynamically programmable component. Benefiting from the patterned design of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e network, the as-prepared hydrogel actuator can achieve large-angle and diverse programmable deformation under thermal and near-infrared (NIR) stimulation. Notably, the Fe\u003csup\u003e3+\u003c/sup\u003e and SA network are dynamically crosslinked via coordination bonds. After soaking in a reducing agent, Fe\u003csup\u003e3+\u003c/sup\u003e in the crosslinked network can be reduced to Fe\u003csup\u003e2+\u003c/sup\u003e, which erases the pre-designed patterned structure and eliminates the original deformation performance of the hydrogel actuator. Through the secondary introduction of Fe\u003csup\u003e3+\u003c/sup\u003e ions, a new patterned network can be reconstructed inside the hydrogel, endowing the actuator with brand-new stimuli-responsive deformation behaviors. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) Furthermore, taking advantage of the unique self-sensing capability of the SL-s-IPN matrix, the reprogrammed hydrogel actuator maintains excellent electrical self-sensing performance. Real-time feedback on large-scale shape morphing can be realized by monitoring dynamic electrical signal variations. This programmable hydrogel actuator constructed based on dynamic coordination bonds provides a new strategy for the development of reversible flexible devices.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials.\u003c/h2\u003e \u003cp\u003eN-isopropylacrylamide (NIPAM) and 2-Hydroxy-4'-(2-hydroxyetho-xy)-2-methylpro-piophenone (initiator2959) were purchased from TCI (Shanghai) Development Co., Ltd. N, N'-methylenebisacrylamide (BIS), aniline (ANI), and hydrochloric acid (HCl) were purchased from Energy Chemical (Shanghai). Ammonium peroxodisulfate (APS) was purchased from Alfa Aesar (Tianjin) Chemical Co., Ltd. Ferric chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), sodium alginate (SA) and sodium citrate (SC) were purchased from China National Pharmaceutical Group Corp. All above reagents were used without further treatment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e2.2 Synthesis of sponge like PNIPAM hydrogel (SL-PNIPAM)\u003c/b\u003e.\u003c/h2\u003e \u003cp\u003eThe SL-PNIPAM hydrogel was prepared by reported methods. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] Briefly, 226 mg NIPAM, 2 mg BIS and 2 mg initiator2959 was mixed in 1ml of DI water to form a monomer solution. Then, the aqueous solution was bubbled with N\u003csub\u003e2\u003c/sub\u003e for 15 min to remove the air in solution. Eventually, the prepared solution was cast into silicone rubber molds with different thickness (30 mm*30 mm*0.5 mm, 30 mm*30 mm*1 mm, 30 mm*30 mm*1.5 mm, respectively) and exposed to UV light (365 nm,2 W/cm\u003csup\u003e2\u003c/sup\u003e) for 30 min at 40\u0026deg;C to form SL-PNIPAM hydrogel. The sample was placed in DI water for 3 days to remove excess components.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Synthesis of sponge like semi-interpenetrating network of PNIPAM/PANI hydrogel (SL-s-IPN).\u003c/h2\u003e \u003cp\u003eTo get the sponge like semi-interpenetrating network of PNIPAM/PANI hydrogel, PANI chains were polymerized into the PNIPAM network utilizing in-situ oxidative polymerization. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] Firstly, the samples were heated to 80 ℃ for 6 h to remove the water from gel matrix. And then, the samples were immersed into 10 mL aqueous solution with 0.2 M aniline and 1 M HCl to absorb aniline monomer for 2 h. Precooled 10 mL aqueous solution with 0.2 M APS and 1 M HCl was added to the aniline solution in an ice bath to react for 12 h to fabricate the SL-s-IPN hydrogel.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Preparation of programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN asymmetric hydrogel.\u003c/h2\u003e \u003cp\u003eThe SA-Fe\u003csup\u003e3+\u003c/sup\u003e/ SL-s-IPN asymmetric hydrogel was prepared via crosslinking SA network on one side of SL-s-IPN hydrogel. Firstly, the obtained SL-s-IPN hydrogel was immersed in SA solution of 1 wt% for 12h to fully absorb dissociative SA chains. And then, the SL-s-IPN hydrogel film containing SA chains was tiled on the surface of slide, and the 3D printing mold with different pattern was tightly attached above the sample. Next, the FeCl\u003csub\u003e3\u003c/sub\u003e solutions was dripped into the groove of the mold to form the programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/ SL-s-IPN asymmetric hydrogel. The concentration parameters and cross-linking time parameters for the fabrication of hydrogel are summarized in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e. Eventually, the samples were placed in DI water for 3 days to remove the excess SA chains and Fe\u003csup\u003e3+\u003c/sup\u003e ions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Manufacture of NIR light driven programmable SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator.\u003c/h2\u003e \u003cp\u003eTo get the soft actuator, the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/ SL-s-IPN asymmetric hydrogel was cut into a desirable shape and crosslinked at the specified position. And then, a tunable near-infrared light (wavelength\u0026thinsp;=\u0026thinsp;808 nm) with different intensity was irradiated on the surface of whole sample to generate deformation of the actuator. The whole deformation process of actuator was recorded by optical camera in real time. Herein, four types of soft actuators were fabricated. For the strip-shape actuator and planar actuator, the spot of NIR light was irradiated on the sample constantly. For the scroll actuator, the spot of NIR light was irradiated on the sample from left to right (or right to left). For the walker actuator, the pulsed NIR light was irradiated on the left (or right) of sample according to fixed frequency.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Erasing and reprogramming of SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator.\u003c/h2\u003e \u003cp\u003eHerein, sodium citrate (SC) was selected as reductant to converse the Fe\u003csup\u003e3+\u003c/sup\u003e to Fe\u003csup\u003e2+\u003c/sup\u003e, decrosslinking the SA network of asymmetric hydrogel and erasing the deformability of hydrogel actuator. Specifically, the programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator was immersed in SC solution of 50 mg/mL for 12 h to remove the SA network. And then, the sample was soaked in DI water for 12 h to remove the excess ions. Eventually, the programmed asymmetric hydrogel reverted back to original SL-s-IPN hydrogel and lose its light-induced deformability. Notably, the erased sample can be endowed with new programming patterns by immersed in SA solution and crosslinked by Fe\u003csup\u003e3+\u003c/sup\u003e. The programming-erasing loop is reversible and can be repeated multiple times.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Characterization.\u003c/h2\u003e \u003cp\u003eThe Fourier transform infrared (FT-IR) spectra were recorded by an IR spectrophotometer (Bruker VERTEX70) in the scanning range of 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the samples were obtained by a KBr disk technique. Scanning electron microscopy (SEM) micrographs were taken by Hitachi SU8010 at an acceleration voltage of 5 kV. The hydrogel samples were first frozen in liquid nitrogen and then placed in a freeze dryer for 24 h to remove all the moisture. The front, back, and cross sections of hydrogel samples were coated with gold by a sputter coater before being observed by SEM.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003eThe fabrication process of the asymmetric hydrogel is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. With the assistance of a mold, a crosslinked sodium alginate (SA) network is formed on the upper layer of the SL-s-IPN hydrogel, thereby constructing an asymmetric structure in the designated region. To clarify the distribution of the two hydrogel networks in the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel, the surface, reverse side and cross-sectional micromorphology of the samples were systematically characterized via scanning electron microscopy (SEM). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-c, the SEM results reveal that the as-prepared SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel possesses a typical asymmetric structure, and distinct micromorphologies are observed on the two sides of the sample. Specifically, the cross-linked side incorporated with Fe\u003csup\u003e3+\u003c/sup\u003e exhibits a relatively smooth surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), a compact and uniform SA-Fe\u003csup\u003e3+\u003c/sup\u003e layer is covered on the top of the original porous SL-s-IPN hydrogel, leading to a low surface roughness. On the contrary, the uncross-linked side without Fe\u003csup\u003e3+\u003c/sup\u003e incorporation retains the intrinsic sponge-like porous structure of the pristine SL-s-IPN hydrogel, which displays a rough surface with abundant micron-sized pores (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). The cross-sectional SEM images further verify that the SA- Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel consists of two structurally distinct layers. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, two well-adhered hydrogel morphologies can be clearly distinguished in the cross-section. The cross-linked layer presents a dense structure with a smaller thickness, while the uncross-linked layer without Fe\u003csup\u003e3+\u003c/sup\u003e shows a loose structure with a larger thickness and abundant open pores, maintaining the original morphological characteristics of SL-s-IPN. Energy dispersive spectroscopy (EDS) was adopted to analyze the elemental distribution of the hydrogel. In the SA- Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel, the Fe element content is relatively high on the cross-linked side, demonstrating that this region is mainly composed of crosslinked SA-Fe\u003csup\u003e3+\u003c/sup\u003e hydrogel. In comparison, the uncross-linked side exhibits a low Fe content, suggesting that this part is dominated by the original SL-s-IPN hydrogel. The cross-sectional elemental distribution confirms a gradient distribution of Fe elements within the hydrogel, which further evidences the successful construction of the asymmetric structure.\u003c/p\u003e \u003cp\u003eTo further identify the chemical compositions of the hydrogel samples, Fourier transform infrared spectroscopy (FT-IR) characterization was conducted on the SA- Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel, and the corresponding results are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed. The characteristic peaks at 1652 cm\u003csup\u003e-1\u003c/sup\u003e and 1545 cm\u003csup\u003e-1\u003c/sup\u003e are assigned to the stretching vibrations of -C\u0026thinsp;=\u0026thinsp;O and -NH in PNIPAM, respectively. The absorption peaks at 1577 cm\u003csup\u003e-1\u003c/sup\u003e and 1498 cm\u003csup\u003e-1\u003c/sup\u003e correspond to the quinoid and benzenoid rings of PANI, while the peak at 1742 cm\u003csup\u003e-1\u003c/sup\u003e is attributed to the stretching vibration of -CO- in SA. These results confirm that the SA- Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel integrates the SA- Fe\u003csup\u003e3+\u003c/sup\u003e network, PNIPAM network and PANI molecular chains, and the three components are successfully combined into a unified system.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGiven the intrinsic thermoresponsive property of PNIPAM, the resultant SA- Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel also exhibits temperature-responsive behavior. Benefiting from its unique bilayer structure, the cross-linked side and uncross-linked side of the SA- Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel deliver discrepant thermoresponsive capacities. To quantitatively investigate the difference in swelling performance between the two sides, a single hydrogel sample was cut into two equal parts, and the swelling behaviors of the cross-linked region and uncross-linked region were separately measured in water at different temperatures. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee, when the ambient temperature increases from 5\u0026deg;C to 50\u0026deg;C, the equilibrium swelling ratio of the Fe\u003csup\u003e3+\u003c/sup\u003e-free side decreases from 20.8 to 5.8. Under the same temperature variation, the equilibrium swelling ratio of the Fe\u003csup\u003e3+\u003c/sup\u003e-crosslinked side declines from 17.7 to 11.6. The swelling ratio difference (ΔSR) between the two sides at various temperatures is calculated to be 15.0 and 6.1, respectively (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). This indicates that the introduction of Fe\u003csup\u003e3+\u003c/sup\u003e regulates the swelling performance of different regions in the hydrogel, and the Fe\u003csup\u003e3+\u003c/sup\u003e crosslinking treatment weakens the temperature-dependent swelling variation capacity. This phenomenon can be explained by the increased proportion of non-responsive SA- Fe\u003csup\u003e3+\u003c/sup\u003e network and the decreased proportion of thermoresponsive PNIPAM network on the crosslinked side. Moreover, the non-responsive SA-Fe\u003csup\u003e3+\u003c/sup\u003e network may form an interpenetrating polymer structure with the PNIPAM network, which restricts the conformational transition space of PNIPAM chains. Consequently, the variation range of the swelling ratio is reduced on the crosslinked side under variable temperature conditions.\u003c/p\u003e \u003cp\u003ePANI contained in the SL-s-IPN hydrogel possesses excellent photothermal conversion performance. After introducing the Fe\u003csup\u003e3+\u003c/sup\u003e-crosslinked SA network, the obtained SA- Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel also achieves favorable photothermal conversion capability. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef, the surface temperature of the hydrogel rises significantly under near-infrared (NIR) irradiation, and the maximum surface temperature gradually increases from 25.2\u0026deg;C to 70.2\u0026deg;C with the elevation of light intensity. After five consecutive NIR irradiation cycles (Figure \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e), the hydrogel maintains stable photothermal conversion performance, revealing outstanding photothermal stability. Under continuous NIR irradiation, the surface temperature rises rapidly and reaches a plateau within approximately 30 s (Figure \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003ea). Once the NIR light is turned off, the surface temperature gradually drops and fully recovers to the initial state within 60 s (Figure \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003eb). These results demonstrate that the fabricated SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel possesses superior and reversible photothermal conversion performance.\u003c/p\u003e \u003cp\u003eBenefiting from the differential swelling behavior inside the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel, a one-dimensional SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator with stimuli-responsive deformation capability was successfully fabricated. The actuation mechanism is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. At first, both sides of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel remain swollen, and the actuator exhibits no obvious shape deformation. Upon NIR irradiation, temperature elevation induces shrinkage on both sides of the hydrogel. The uncross-linked side of hydrogel undergoes a more significant shrinkage, whereas the Fe\u003csup\u003e3+\u003c/sup\u003e-crosslinked side presents a slight volume contraction. Such discrepant shrinkage generates asymmetric stress distribution within the material, thereby enabling the one-dimensional SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator to achieve specific bending deformation. Optical photos show that the bending angle of the hydrogel actuator gradually increases with the increase of light intensity. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, Movie S1)\u003c/p\u003e \u003cp\u003eNotably, the effects of experimental parameters, including sample thickness, ion concentration and crosslinking duration, on the bending performance of the one-dimensional actuator were systematically investigated. The results indicate that the optimal sample thickness for maximizing the bending angle is 0.5 mm (Figure \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e), and the optimized ion concentration and crosslinking time are 0.005 mol/L and 20 min, respectively (Figure \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe correlation between light intensity and actuator bending angle was recorded and summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. As the NIR light intensity increases from 0 W/cm\u003csup\u003e2\u003c/sup\u003e to 2.79 W/cm\u003csup\u003e2\u003c/sup\u003e, the bending angle gradually increases from the initial\u0026thinsp;\u0026minus;\u0026thinsp;30\u0026deg; to over 270\u0026deg;, with a total angular variation exceeding 300\u0026deg;. A positive correlation is observed between the bending angle and incident light intensity. Furthermore, the response kinetics of the one-dimensional SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator were characterized (Movie S2). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, under NIR irradiation of 2.79 W/cm\u003csup\u003e2\u003c/sup\u003e, the actuator rapidly bends to the maximum angle and reaches a steady equilibrium state within 20 s, with an average angular response rate of 15 \u0026deg;/s. After removing the NIR irradiation, the actuator can recover to its original state within an ultrafast period of approximately 6 s (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The rapid recovery performance is attributed to the unique sponge-like porous structure of the hydrogel, which facilitates high-frequency and continuous deformation behavior. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] In addition, the cyclic stability of the actuator during repeated bending was evaluated. As presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, the actuator maintains favorable bending performance after 70 consecutive cycles, demonstrating great potential for long-term and repeated stable operation.\u003c/p\u003e \u003cp\u003eBenefiting from the unique programmability, flexible actuators based on the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel can achieve various reversible deformation behaviors including bending and twisting by patterning different regions on the hydrogel matrix. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, the one-dimensional actuator realizes multiple deformation modes under near-infrared (NIR) stimulation through regional patterning. For example, when only the middle area of the hydrogel is programmed, the one-dimensional actuator folds from both ends to the center. After patterning both ends synchronously, the two sides bend simultaneously to form a closed loop structure. When the two ends are patterned along opposite directions, the actuator can spontaneously deform into an S-shape under planar NIR irradiation. By introducing diagonal patterns with different orientations, the actuator achieves left-handed or right-handed torsional deformation in sequence, exhibiting reversible morphing with high degrees of freedom. This flexible twist deformation facilitates the application of hydrogel actuators in more complex environments. (Movie S3) Compared with the simple folding behavior of the existing homogeneous hydrogel actuators, the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator can be driven by a single optical stimulus, accompanied by larger deformation amplitude and more sophisticated deformation modes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition to customizable 1D-to-2D deformation, diverse two-dimensional hydrogel films can be obtained via simple cutting treatment, which further enables 2D-to-3D shape transformation. As displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, flexible grippers with two, three, four and five arms were fabricated by cutting the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel. Combined with the template method, different regions of these grippers were endowed with controllable bending capacity. Driven by NIR light, all grippers with distinct structures can complete rapid grasping movements. As presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, a hand-shaped hydrogel actuator was fabricated. Herein, only the programmed finger segments possess bending capability, while non-programmed fingers remain undeformable. With the assistance of the template method, Fe\u003csup\u003e3+\u003c/sup\u003e patterning was performed on independent fingers of the hand-shaped hydrogel to realize regional functional regulation. For instance, localized programming on the thumb enables the actuator to bend the thumb under NIR irradiation to produce a specific gesture. Similarly, by integrating multiple programming strategies, the actuator can generate a series of distinct gestures in sequence upon NIR stimulation, thus achieving the output of gesture information.\u003c/p\u003e \u003cp\u003eThanks to the unique programmable actuation performance of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator, an actuator with unidirectional curling and unidirectional walking capacities was rationally designed and fabricated. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, when a spot near-infrared (NIR) laser irradiates the sample surface from left to right, the actuator curls synchronously along the same direction. Interestingly, such curling behavior is governed by the irradiation direction. Once the light direction is reversed from left-to-right to right-to-left, the curling direction of the actuator changes accordingly. (Movie S4) Therefore, the spatiotemporal deformation behavior of the flexible actuator can be precisely regulated by controlling key parameters, including the spatial position, irradiation direction and light intensity of NIR stimulation. The unique curling actuation originates from the rapid response and recovery kinetics of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel. Under localized NIR irradiation, the exposed hydrogel region undergoes rapid response and localized deformation. As the NIR light spot moves from left to right, the localized bending behavior propagates synchronously, thereby achieving unidirectional curling actuation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn addition to light-triggered unidirectional curling, an actuator with unidirectional walking performance was further developed by applying pulsed localized light stimulation. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, a controllable NIR light source was placed above the left side of the actuator to provide localized stimulation. Upon NIR irradiation, the left segment of the actuator bends obviously; after the light is switched off, the deformed region gradually recovers to its original flat state. During the recovery process, the asymmetric deformation generates a rightward thrust, which drives the actuator to move rightward and completes a single walking cycle. (Movie S5) By repeating the on-off light irradiation in a cyclic manner, the actuator can continuously migrate toward the right side and realize NIR-driven unidirectional walking. Similarly, the locomotion direction of the walker can be readily adjusted by changing the irradiation direction. Notably, benefiting from its intrinsic asymmetric structure, this walker requires no additional auxiliary ratchet plates during locomotion and can walk steadily on arbitrary flat substrates, exhibiting superior locomotion flexibility and environmental adaptability. In summary, combined with excellent deformation programmability and favorable electrical self-sensing properties, the flexible actuators based on SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel hold promising application potential in diverse fields such as biomimetic materials and artificial soft robotics.\u003c/p\u003e \u003cp\u003eHomogeneous hydrogel actuators exhibit unique phototactic locomotion behaviors. However, in certain practical application scenarios, phototaxis may impair the operational stability of actuators. Unstable light irradiation directions can lead to irregular deformation orientations and further reduce working efficiency. Therefore, it is imperative to develop anti-phototactic flexible actuators that can maintain stable performance under light irradiation from diverse directions. Different from phototactic actuators whose deformation relies on localized optical stimulation, the distinctive deformation of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator originates from its intrinsic asymmetric internal structure. Consequently, the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator possesses unique anti-phototactic locomotion characteristics.\u003c/p\u003e \u003cp\u003eThe photo-induced deformation performances of the unprogrammed homogeneous SL-s-IPN actuator and the programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator were systematically compared. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, the pristine one-dimensional SL-s-IPN actuator presents obvious phototactic behavior under incident light from different directions, and its motion direction changes synchronously with the variation of light orientation. In contrast, the programmed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator achieves stable and predefined unilateral curling regardless of incident light directions (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb), demonstrating excellent deformation controllability. Such stable curling behavior is determined by the inherent asymmetric structure rather than external localized light stimulation. Thus, the actuator can sustain consistent deformation under multi-directional light irradiation. In conclusion, the as-prepared SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator is more suitable for practical application scenarios that require steady and reliable deformation performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel, the coordination interaction between Fe\u003csup\u003e3+\u003c/sup\u003e and carboxyl groups within the SA-Fe\u003csup\u003e3+\u003c/sup\u003e network exhibits dynamic reversibility. After reduction treatment with a reducing agent, Fe\u003csup\u003e3+\u003c/sup\u003e in the SA-Fe\u003csup\u003e3+\u003c/sup\u003e network is reduced to Fe\u003csup\u003e2+\u003c/sup\u003e, which triggers the decrosslinking of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e hydrogel network. Consequently, the asymmetric SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel reverts to the original homogeneous SL-s-IPN hydrogel and loses its deformation capability (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). Therefore, the photo-induced deformation performance of the hydrogel actuator can be effectively erased via soaking in a reducing agent solution. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb, the photo-responsive deformation behavior of the one-dimensional SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator completely disappears after reducing agent treatment. Under near-infrared irradiation, the actuator only undergoes simple shrinkage, rather than the folding, bending or twisting deformation observed before erasure. The reduction of Fe\u003csup\u003e3+\u003c/sup\u003e to Fe\u003csup\u003e2+\u003c/sup\u003e destroys the crosslinked SA-Fe\u003csup\u003e3+\u003c/sup\u003e network and eliminates the intrinsic asymmetric structure of the hydrogel. Without this structural difference, the actuator fails to produce unique programmed deformation under external stimuli.\u003c/p\u003e \u003cp\u003eTo further investigate the effect of the reducing agent on the microscopic morphology, SEM characterization was performed on the erased hydrogel samples (Figure \u003cspan refid=\"MOESM6\" class=\"InternalRef\"\u003eS6\u003c/span\u003e). After soaking in the reducing agent, both sides of the sample present identical sponge-like porous structures, and the originally dense SA-Fe\u003csup\u003e3+\u003c/sup\u003e layer is completely removed. These results confirm that the Fe\u003csup\u003e3+\u003c/sup\u003e-crosslinked SA network is eliminated after erasure, and the hydrogel transforms from an asymmetric structure into an isotropic and homogeneous SL-s-IPN network. Notably, the erased hydrogel can regain brand-new photo-induced deformation performance by re-soaking in SA solution and reconstructing Fe\u003csup\u003e3+\u003c/sup\u003e crosslinking. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec, a hand-shaped soft actuator was firstly programmed to bend the index and middle fingers to achieve \u003cem\u003eShape I\u003c/em\u003e gesture under NIR irradiation. Subsequently, reducing agent treatment was adopted to erase the original bending functions and eliminate the initial photo-responsive deformation behavior. Finally, by repeating SA immersion and Fe\u003csup\u003e3+\u003c/sup\u003e crosslinking with redesigned templates, the same palm-shaped actuator was reprogrammed to bend the thumb and little finger, realizing a \u003cem\u003eShape II\u003c/em\u003e gesture transformation. Accordingly, diverse reversible deformation modes can be readily realized on a single hydrogel material through the repeated dynamic cycle of \u0026ldquo;programming-erasing\u0026rdquo;.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOwing to the unique electrical self-sensing and actuating properties of SL-s-IPN hydrogel under NIR irradiation, [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator derived from the SL-s-IPN matrix exhibits comparable self-sensing capability. With the assistance of real-time monitoring equipment (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea), the electrical signal variation of the one-dimensional SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator during actuation was systematically investigated. Benefiting from its inherent asymmetric structure, the developed actuator achieves photoinduced deformation under large-area NIR irradiation with improved deformation controllability. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb, within a single light on/off cycle, both the bending angle and current signal increase synchronously upon planar NIR light excitation. The flexible actuator reaches a steady state of bending deformation and electrical response within approximately 15 s. After the NIR light is turned off, the bending angle and electrical signal gradually decrease and fully recover to the initial levels in around 15 s, demonstrating favorable deformation self-sensing performance.\u003c/p\u003e \u003cp\u003eAs presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec, under continuously pulsed NIR irradiation, the bending deformation and electrical signals of the actuator rapidly respond and recover. No obvious attenuation of bending amplitude or electrical output is observed over 10 consecutive bending\u0026ndash;recovery cycles, indicating excellent stability of the self-sensing behavior. This capability of large-angle photoinduced motion effectively compensates for the limitations of locally stimulated flexible hydrogel actuators, the proposed SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator is believed to show significant potential for the fabrication of soft robot facing complicated and changeable application scenarios.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn summary, a patterned and programmable SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator has been successfully fabricated. Relying on the reversible crosslinking between Fe\u003csup\u003e3+\u003c/sup\u003e and sodium alginate (SA) networks, the dynamically crosslinked SA-Fe\u003csup\u003e3+\u003c/sup\u003e network with programmable, erasable and rewritable characteristics was constructed within a semi-interpenetrating hydrogel matrix composed of PNIPAM and PANI. Benefiting from the uniquely patterned structure, the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN actuator can perform diverse reversible deformations under the NIR light stimulation. In virtue of the dynamic reversibility of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e network, the deformation behavior of the actuator exhibits favorable erasability and rewritability, enabling a single hydrogel actuator to achieve multiple distinct shape transformations. Attributed to the excellent self-sensing performance of the SL-s-IPN hydrogel, the deformation degree of the SA-Fe\u003csup\u003e3+\u003c/sup\u003e/SL-s-IPN hydrogel actuator can be effectively monitored by recording real-time changes in electrical signals. This novel self-sensing hydrogel actuator with integrated programmable, erasable and rewritable functions provides a promising foundation for the development of next-generation flexible robots with custom-tunable deformation capabilities.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e \u003cb\u003eCRediT authorship contribution statement\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eXingchen Cui\u003c/b\u003e: Writing-original draft, Conceptualization, Software, Formal analysis, Data curation. \u003cb\u003eXinyu Liu\u003c/b\u003e: Visualization, Resources. \u003cb\u003eShuai Wang\u003c/b\u003e: Visualization, Resources. \u003cb\u003eFuqiang Fan\u003c/b\u003e: Methodology, Formal analysis, Resources. \u003cb\u003eShunsheng Ye\u003c/b\u003e: Visualization. \u003cb\u003eYu Fu\u003c/b\u003e: Writing-review \u0026amp; editing, Resources, Project administration, Conceptualization, Supervision. \u003cb\u003eBing Zhang\u003c/b\u003e: Validation, Data curation, Visualization. \u003cb\u003eTieqiang Wang\u003c/b\u003e: Writing-review \u0026amp; editing, Supervision, Conceptualization, Resources, Funding acquisition, Formal analysis. \u003cb\u003eXiaoqian Xu\u003c/b\u003e: Writing-review \u0026amp; editing, Resources, Supervision, Funding acquisition.\u003c/p\u003e\u003cp\u003e \u003ch2\u003eDeclaration of Competing Interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eXingchen Cui: Writing-original draft, Conceptualization, Software, Formal analysis, Data curation. Xinyu Liu: Visualization, Resources. Shuai Wang: Visualization, Resources. Fuqiang Fan: Methodology, Formal analysis, Resources. Shunsheng Ye: Visualization. Yu Fu: Writing-review \u0026amp; editing, Resources, Project administration, Conceptualization, Supervision. Bing Zhang: Validation, Data curation, Visualization. Tieqiang Wang: Writing-review \u0026amp; editing, Supervision, Conceptualization, Resources, Funding acquisition, Formal analysis. Xiaoqian Xu: Writing-review \u0026amp; editing, Resources, Supervision, Funding acquisition.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (22075039, 22175030, 22101042), Fundamental Research Funds for the Central Universities (N2205007), Liaoning Provincial Science Foundation (2023-MSBA-055), The Foundation of the Liaoning Revitalizing Talents Program (XLYC2403175). We also specially thank the Analytical and Testing Center at Northeastern University for experimental and instrumental support.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e\u003cp\u003eData will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAdak NC, Lee W (2024) A comprehensive review of 4D-printed thermo-responsive hydrogel-based smart actuators for solar steam generation: Advanced design, modeling, manufacturing, and finite element analysis. Prog Mater Sci 148:101377\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDing A, Tang F, Alsberg E (2025) 4D printing: A comprehensive review of technologies, materials, stimuli, design, and emerging applications. 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Chem Eng J 467:143515\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":"Programmable, Hydrogel, Soft actuator, Self-sensing, Rapid responsive","lastPublishedDoi":"10.21203/rs.3.rs-9571010/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9571010/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHydrogel-based soft actuators hold significant promise in the domain of bionic soft robots and flexible drives. Nonetheless, current hydrogel actuators are limited by their lack of shape reprogrammability. Herein, a novel reprogrammable hydrogel actuator based on reversible coordination bond is prepared via simple chemical crosslinking. The patterned structures of actuator are created within the hydrogel actuators by incorporating a ferric (Fe\u003csup\u003e3+\u003c/sup\u003e) ion crosslinked sodium alginate (SA) network within a composite gel made up of poly(N-isopropylacrylamide) (PNIPAM) and polyaniline (PANI). The remarkable photothermal conversion efficiency of PANI fillers enables the actuator to precise demonstrates rapid remote NIR-induced deformation. Utilizing a mask technique, these actuators exhibit diverse NIR-driven deformation such as bending, folding, and twisting. Significantly, the addition of dynamic coordination bonds facilitates the erasing and reprogramming of specific deformations on the actuator through the application of reducing agents. Moreover, the interpenetrating conductive PANI chains endow the actuator with low hysteresis electric self-sensing capacity to monitor its deformation. This study emphasizes the potential of hydrogel soft actuators for programmability, offering insights into the applications of bionic soft robots and intelligent mechanical systems.\u003c/p\u003e","manuscriptTitle":"Programmable and rapid responsive self-sensing soft actuator based on asymmetric poly (N-isopropylacrylamide)/alginate hydrogel with reversible network","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-14 17:38:13","doi":"10.21203/rs.3.rs-9571010/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":"8bec1025-52ee-4d47-b532-2653d3af5730","owner":[],"postedDate":"May 14th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Rejected","date":"2026-05-15T09:54:24+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-15T01:45:30+00:00","index":27,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-12T01:43:03+00:00","index":26,"fulltext":""},{"type":"reviewerAgreed","content":"328378171050868267357246676144981350064","date":"2026-05-11T01:01:45+00:00","index":25,"fulltext":""},{"type":"reviewerAgreed","content":"165025920583183443453717550849047069181","date":"2026-05-07T23:39:34+00:00","index":23,"fulltext":""},{"type":"reviewersInvited","content":"13","date":"2026-05-05T19:31:26+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-05-04T15:13:28+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-05-01T12:26:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Advanced Composites and Hybrid Materials","date":"2026-04-30T02:30:36+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-15T10:10:06+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-14 17:38:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9571010","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9571010","identity":"rs-9571010","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}