Bioinspired hydrophobic pseudo-hydrogel for programmable shape-morphing

Bioinspired hydrophobic pseudo-hydrogel for programmable shape-morphing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Bioinspired hydrophobic pseudo-hydrogel for programmable shape-morphing Heng Deng, Xu Xianchen, Zhigang Wang, Zefan Chai, Yuhang Hu, Tony Huang, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4784733/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Jan, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Inspired by counterintuitive water-swelling ability of the hydrophobic moss of the genus Sphagnum (Peat moss), we introduce a novel material—hydrophobic pseudo-hydrogel (HPH), composed of a pure hydrophobic silicone elastomer with a tailored porous structure. In contrast to conventional hydrogels, HPH achieves water-swelling through capillary forces and surface tension, presenting an unexpected water-swelling capability in hydrophobic matrices. We establish a theoretical framework elucidating the interplay of poro-elasto-capillary and surface tension forces, providing insights into the swelling behavior. By systematically programming the pore structure, we demonstrate tunable, anisotropic, and programmable swelling. This leads to dedicated self-shaping transformations. Incorporating magnetic particles, we engineer HPH-based soft robots capable of swimming, rolling, and walking. This study demonstrates a unique approach to achieve water-responsive behavior in hydrophobic materials, expanding the possibilities for programmable shape-morphing in soft materials and soft robotic applications. Physical sciences/Materials science/Soft materials/Wetting Physical sciences/Materials science/Soft materials/Self-assembly Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Water-swelling is a widespread phenomenon characterized by the absorption of water molecules from the surrounding environment into the matrix of swellable materials, leading to volume expansion. This phenomenon is observed in nature, as seen in plant cells and soils exhibiting hygroscopic swelling when exposed to aqueous environments 1 , 2 . Additionally, it is a common occurrence in everyday technologies, such as kitchen sponges or disposable diapers 3 , 4 . The exploration of water-swelling phenomena has broad implications in fundamental science, and the development of innovative materials. In this context, hydrogels have become exemplary artificial materials 5 . These are cross-linked polymer networks capable of absorbing up to approximately ten times their dry weight in water while maintaining structural integrity 6 , 7 , 8 , 9 . Hydrogels find applications in various fields, including drug delivery 10 , 11 , energy harvesting 12 , soft tissue scaffolds 13 , sensors 14 , soft actuators 15 , and soft robotics 16 . The remarkable swelling behaviors of hydrogels result from the hydrophilic nature of their polymeric matrix. The hydrophilicity arises from the presence of hydrophilic chemical residues 17 , such as hydroxylic (-OH) 18 , carboxylic (-COOH) 19 , and amidic groups, serving as binding sites that attract and retain water molecules, causing an increase in polymer volume 20 . It is important to note that the majority of reported instances of water-swelling involve materials with inherent hydrophilicity. This raises a paradoxical question: Can water swelling be achieved using purely hydrophobic materials? Given that hydrophobic materials typically repel water and resist swelling, this question appears counterintuitive. However, nature, with its diverse and ingenious designs, offers a compelling example in the form of Sphagnum , a plant that defies conventional expectations. In its desiccated state, Sphagnum exhibits hydrophobic characteristics due to its lignin-rich surface 21 . However, when immersed in water, this hydrophobic material undergoes rehydration, remarkably retaining water at a rate ten times its own weight 22 . With such excellent retention capabilities, Sphagnum is commonly utilized in horticulture to control water content in soil 23 , 24 . The intriguing phenomenon of the rehydration of hydrophobic Sphagnum is attributed to its inherent microporous structure, resembling a sponge with myriad tiny pores and spaces. The microporous structure can harness surface tension-induced capillary forces to draw in water 25 , 26 . The surface tension force, initiated by a small amount of water, cascades to attract more water, overcoming the inherent repelling forces of dried hydrophobic tissues (Fig. 1 a and Fig. S1 ). Inspired by the microporous structure of Sphagnum , we have engineered water swellable materials using pure hydrophobic silicone elastomer endowed with a porous structure. This innovative material, named hydrophobic pseudo-hydrogel (HPH), achieves unconventional water-swelling phenomena in a purely hydrophobic matrix through physically designed microstructures. We use the term "pseudo" here to indicate a resemblance to hydrogels in terms of water-swelling ability (Fig. 1 b), despite the fact that HPH is not a hydrogel as the underlying material is hydrophobic (Fig. 1 c). In contrast to conventional hydrogels, where swelling involves molecular chain-level physicochemical interactions between water and the hydrophilic polymer backbone or lateral chains, the HPH utilizes capillary forces and surface tension to accumulate water in microscopic pore structures (Fig. 1 d). Our investigation observes this fascinating phenomenon and also provides a theoretical explanation. We propose a theoretical framework elucidating the interplay of poro-elasto-capillary and surface tension forces, establishing a foundation for understanding and controlling swelling behavior in hydrophobic matrices. We establish a correlation between swelling in this HPH and intricate pore structure, emphasizing pore size. Moreover, by systematically programming the pore structure within the elastomer, we demonstrate the realization of anisotropic and programmable swelling in this HPH. This programming capability extends to the achievement of dedicated and programmable self-shaping transformations 27 , 28 . Additionally, we combine magnetic particles with self-shaping HPH to prepare magnetically driven soft robots 29 , 30 capable of basic behaviors such as swimming, rolling and walking (Fig. 1 e). This counterintuitive material paves the way for fabricating adaptive, responsive soft materials, which can be used in soft actuation, implantation, flexible electronics, and other emerging materials applications. Results and Discussions To empirically validate our hypothesis, we developed a hydrophobic pseudo-hydrogel (HPH) using Ecoflex 00–30, a commercially available silicone rubber known for its hydrophobic properties. To induce a porous structure within the HPH, we employed a sacrificial template method using NaCl microparticles as the template, with details provided in Fig. S2 and the "Methods" section. The cross-sectional morphology of the pristine silicone elastomer, as shown in Fig. 2 a, was non-porous, and it exhibited a surface contact angle of 100° ( Fig. S3a ), confirming its hydrophobic nature. Following the pore-forming treatment, the HPH displayed a porous structure, as illustrated in Fig. 2 b, where the HPH was fabricated using template particles approximately 60 µm in size. It is crucial to note that the pore-forming treatment is a purely physical process, leaving the physicochemical properties of the elastomer unchanged. The surface contact angle of the HPH was 105° ( Fig. S3b ), indicating that the physical porosity does not compromise the hydrophobic properties of the material itself. And the increase of the contact angle was attributed to the formation of porous microstructures on the elastomer surface 31 . Unlike the pristine elastomer, which did not swell when immersed in water for an extended period (six days) (Fig. 2 c), the HPH, despite retaining its hydrophobic nature, unexpectedly undergoes swelling when immersed in water. As shown in Fig. 2 d, after 132 hours of immersion, the volume of the HPH expands over twofold compared to its original size. The water-swelling ability of HPH prompts us to reminiscent of conventional hydrogels. In the case of conventional hydrogels, their water-swelling capability is rooted from their intrinsic hydrophilicity. These hydrogels typically consist of highly hydrophilic networks of polymer chains. Consequently, water serves as a thermodynamically compatible solvent for such hydrophilic networks, facilitating easy wetting of the dried hydrogel by permeating the hydrophilic polymeric network. Upon wetting, the hydrophilic polymer chains undergo solvation by water, creating an osmotic pressure gradient between the hydrogel and the surrounding aqueous environment. This gradient drives more water molecules from the surroundings into the hydrogel polymeric network, resulting in a macroscopic swelling phenomenon 32 , 33 . In contrast, HPH is a purely hydrophobic material, implying a distinct swelling mechanism compared to conventional hydrogels. Inspired by the capillary-induced swelling observed in hydrophobic Sphagnum , we speculate that capillary forces also play a pivotal role in the swelling of HPH. The swelling process of HPH can be delineated into wetting and expansion stages, similar to the swelling process of hydrogels, as schematically illustrated in Fig. 2 e-g. Given the hydrophobic nature of HPH, water cannot readily penetrate its polymeric network for wetting. However, upon immersion of HPH in water, hydrostatic pressure compelled water into the micropore structure of HPH. During this process, the air in the micropore structure was replaced by water, evidenced by the experimental observation of bubbles emerging from the HPH surface when immersed in water ( Fig. S4 ). Upon the entry of water into the pore structures under hydrostatic pressure, two menisci form between water/air and water/elastomer due to the unique geometry of the pore structures (Fig. 2 e) 34 , 35 . Owing to cohesive forces among water molecules, the meniscus of water/elastomer generates a capillary force induced by liquid-elastomer surface tension along the periphery ((θ H−W1 + θ H−W2 )·π·R H−W /180°) of the meniscus. Its vertical component of capillary force propels the water moving into pores, and the F inner can be expressed as $$\:{F}_{inner}=\frac{2{\theta\:}_{H-W1}\pi\:{R}_{H-W}}{{180}^{^\circ\:}{F}_{H-W}\text{cos}\theta\:}\:\left(1\right)$$ θ denotes the angle between the force exerted by the hydrophobic pore wall on water and the vertical direction. Simultaneously, a capillary force induced by liquid-air surface tension is generated in the opposite direction, expelling water from the pore structures 36 , and the F outer can be expressed as $$\:{F}_{outer}=\frac{{\theta\:}_{A-W}\pi\:{R}_{A-W}}{{180}^{^\circ\:}{F}_{A-W}\text{cos}{\theta\:}_{1}}\:\left(2\right)$$ θ 1 denotes the angle between the force exerted by air on water and the vertical direction. Given the hydrophobic and low surface energy nature of the HPH surface, which strongly repels water, the liquid-elastomer surface tension 37 , 38 generates a significantly stronger capillary force than the liquid-air surface tension 39 ( \(\:{F}_{inner}>{F}_{outer})\) . Consequently, a net force acting on the water droplet propels liquid movement into the pores. This capillary force continues to progress, drawing water into the pore structures of HPH and concurrently expelling the originally entrapped air ( Fig. S5 ). It is important to note that, despite water entering the HPH during the wetting process, it merely replaces the volume of air within the HPH, without expanding the overall volume of the material. To elucidate this dynamic behavior of the wetting process, we plotted the volume change of HPH against time (t), as depicted in Fig. 2 h. During the initial 30 minutes of being immersed, no significant changes in volume were observed. Concurrently, we monitored the mass change of the HPH, revealing a continuous increase. This weight increment indicates that the denser water is replacing the air inside the HPH. After approximately 30 minutes of immersion, the volume of the HPH begins to steadily increase, marking the commencement of the expansion stage. Due to capillary forces, continuous imbibition is sustained, leading to the high stretchability of the elastomer and resulting in macroscopic volume expansion (Fig. 2 g). On one hand, the elastomer's expansion increases the radius of the pores, leading to a decrease in capillary force. On the other hand, the elastomer's expansion generates an increasing elastic force that impedes water imbibition. Ultimately, a balance is achieved between the capillary force and the elastic force, resulting in the equilibrium expansion of HPH. As depicted in the volume curve (Fig. 2 i), the swelling of HPH reaches an equilibrium state after 144 hours of immersion. The swelling behavior of HPH is also evident in the microscopic pore structure changes. In Fig. S6 , a thin film of HPH (~ 78 µm) immersed in water is observed under a microscope, clearly revealing the pore structure. Approximately 10 minutes later, the pore sizes on the HPH surface progressively increase with the prolonged immersion time, eventually reaching equilibrium ( Fig. S7 ). The swelled HPH was also investigated by Environmental Scanning Electron Microscope (ESEM). As shown in the cross-sectional ESEM images of swelled HPH ( Fig. S8 ), the pore structure of HPH after swelling is demonstrated, showing that its pore size ranges from 80 to 200 µm. This result matches the swelling rate of macroscopic HPH, confirming the unity between microscopic and macroscopic observations. It should be noted here that, at the critical transition point between the wetting and expansion stages, a small portion of air remains sealed by the water inside the HPH (Fig. 2 f), playing an important role in the subsequent expansion process. If all the air within the HPH were evacuated, leaving only the water/elastomer interface, the capillary force induced by surface tension around the pore periphery would be nullified, resulting in the absence of a driving force to draw water in. However, we consistently observe an increase in both volume and weight of the HPH. This sustained imbibition should be attributed to the trapped air, which generates asymmetric capillary forces (Fig. 2 g). By analyzing the volume and weight curves, we calculated that the density of the HPH at the transition point was 0.927 g/cm³, an intermediate value between the fully dried and fully wetted states. This suggests that at the transition point, about 11.69% of the pore volume is occupied by air ( Fig. S9 ), supporting the hypothesis of entrapped air. To futher demonstrate the importance of residual air in the pore for HPH swelling, we performed vertical water absorption and swelling experiments on long strips of HPH. The HPH strip was positioned perpendicular to the surface of red ink, with their lower ends immersed in the ink ( Fig. S10 ). Unlike immersing HPH in water, where air is easily trapped in the hydrophobic matrix, this setup allows water to be transported upward from the bottom of the HPH, wetting the pores layer by layer. This process expels most of the internal air from the HPH, leaving only a small portion to provide the driving force for the subsequent expansion process. As a result, the swelling ratio of HPH strips in the vertical swelling experiment is significantly lower than the one fully immersed in water. The observed swelling ratio in this setup is only 130%, demonstrating the crucial role of residual air in achieving full swelling. As discussed earlier, the water-swelling process of HPH is linked to capillary forces induced by liquid-elastomer surface tension along the periphery of the pore meniscus, which is also associated with the radius of the pores. Thus, by adjusting the pore size within HPH, the water-swelling ability of HPH becomes tunable. To explore the relationship between pore structure and elastomer swelling, the tunable pore sizes in the HPH were achieved by manipulating the size of the soluble template NaCl particles. The internal pore structures of HPH with different pore sizes are illustrated in Fig. S11 . Observations reveal that smaller pore sizes correspond to a faster water absorption rate of HPH and a larger swelling size (Fig. 3 a, and Fig. 3 b). Additionally, there exists a threshold pore size determining whether swelling will occur in HPH. Obvious swelling is observed only when the pore size is less than 152 µm. Conversely, when the pore size exceeds 152 µm, the pore structure in HPH is wetted but does not exhibit obvious expansion. This could be attributed to the fact that, when the pore size exceeds 152 µm, the capillary forces generated by surface tension are insufficient to overcome the elastic force of the elastomer and induce expansion. To further elucidate the intriguing pore size-related water-swelling phenomena of HPH, detailed principal calculations have been conducted to unveil the underlying mechanism, as shown in Fig. 3 c, According to Gor et al. 40 , in porous media with regularly spaced pores, the engineering strain of a single thick-walled cylindrical unit cell can approximate the overall volumetric strain. To account for pore interaction, analysis is conducted on seven adjacent thick-walled cylindrical unit cells. In a single thick-walled cylindrical unit cell, pore walls endure internal pressure \(\:{p}_{i}\) , while the effect of neighboring pores on the central cell is akin to an external boundary pressure \(\:{p}_{o}\) . The water-swelling of HPH will provide the unbalanced force contributed by the surface tension near the liquid-solid interface, which will provide a driven pressure \(\:{p}_{c}\) to break the balance between the internal pressure and external pressure. As Fig. 3 d shows, before HPH wetting, \(\:{p}_{i}={p}_{o}\) , and the HPH will not swell. When we place the HPH in the water, this balance will be broken, and \(\:{P}_{i}+{P}_{c}\gg\:{P}_{o}\) . When pressurized liquid is injected into porous media with dual porosity, it undergoes two typical stages sequentially. Firstly, the macroscopic pores are rapidly filled, compressing the liquid inside the pores and exerting pressure on the pore walls, thereby stiffening the structure. Secondly, the pressurized liquid in the macroscopic pores gradually permeates into the microscopic pores within the framework under the driving force of pressure gradients, leading to complex changes in the overall macroscopic elastic behavior of the structure. Compared to the second stage, the first stage is typically completed in a very short time. Therefore, the focus here is mainly on the evolution of the macroscopic equivalent properties of porous media during the liquid infiltration process in the second stage. The HPH will swell very fast, thus, the pore pressure in porous media during the swelling will be \(\:\:{P}_{f}=（{P}_{i}+{P}_{c}）-{P}_{o}\) . In porous media containing fluids, there exist complex coupling effects between the solid framework and the pore fluid. The fluid pressure acting on the pore walls has a significant influence on their macroscopic mechanical behavior. A thorough understanding of the equivalent mechanical properties of fluid-containing porous media is crucial for promoting their practical engineering applications. Previous research has addressed this issue to some extent 41 . However, a systematic understanding is still lacking. Therefore, here, we analyze this problem based on a micromechanical model. Firstly, a theoretical model predicting the effective modulus of dry porous media will be established, followed by an analysis of the influence of pore pressure. The pore load modulus in porous media can be expressed as $$\:{M}_{pd}=\frac{E\{\left[1+\left(1+\nu\:\right)k\right]-[1-(1+\nu\:)(1-2\nu\:)k\left]\xi\:\right\}}{\left(1+\nu\:\right)\{\left(1-2\nu\:\right)\left[1-\alpha\:\left(1+\left(1+v\right)k\right)\right]-[\alpha\:\left(1-\left(1+\nu\:\right)\left(1-2\nu\:\right)k\right)\xi\:-1\left]\right\}\xi\:}\:\left(3\right)$$ In Fig. 3 e, it can be observed that for nanoporous specimens with the same porosity, as the pore size decreases, the influence of surface effects becomes increasingly apparent. Conversely, for specimens with the same pore size, the higher the porosity, the more pronounced the surface effects. Additionally, soft surfaces lead to a decrease in the poroelastic modulus with decreasing pore radius. This means that the higher porous HPH will more fully and more easily swell with water. Thus, the equivalent volume modulus of porous media can be defined by the formula, $$\:{K}_{pd}=\frac{E(1-\xi\:)}{2[\left(1-\nu\:\right)+(1+\nu\:\left)\xi\:\right](1-\alpha\:\xi\:)}\:\left(4\right)$$ And the equivalent Young’s modulus of porous media can be defined by the formula, $$\:{E}_{pd}=\frac{E{\left(1-\xi\:\right)}^{3}}{\left(1-\alpha\:\xi\:\right)}\text{exp}\left\{\frac{3\alpha\:\xi\:\left[2+\left(1+\alpha\:\right)\xi\:\right]}{2\left[2-\left(2-\alpha\:\right)\xi\:\right]}\right\}\:\left(5\right)$$ As shown in Fig. 3 f, the equivalent Young’s modulus will decrease very fast due to the change of porosity. So the HPH strain under the pore pressure of swelling water can be expressed as \(\:\epsilon\:={P}_{f}/{M}_{pd}\) . Since HPH exhibits similar water-swelling ability to conventional hydrogels, it functions similarly and has similar potential applications. Conventional hydrogels have been extensively studied as self-morphing materials due to their water-triggered shape transformation phenomena. The development of self-morphing materials is inspired by the widespread shape-transformation phenomena observed in plants 42 , generating growing interest in various fields such as energy harvesting, metamaterials, soft robotics, sensors, and multifunctional bioscaffolds. In the following section, we explore the potential applications of HPH as programmable water-responsive self-morphing materials. Typically, the shape transformation of hydrogels arises from inhomogeneous swelling behaviors within the material. Traditional shape-morphing hydrogels achieve this by incorporating diverse components with different swelling behaviors in response to specific stimuli. However, introducing diverse components may encounter intrinsic limitations, such as unstable interfaces and time-consuming fabrication. Therefore, it is of great significance to develop monocomponent hydrogel that enable precisely programmable deformations 43 . Our HPH materials can take the advantages of the microstructure programmed swelling ability to realize monocomponent self-morphing materials ( Fig. S12 ). By controlling the pore structural domain in HPH, programmable and localized swelling can be achieved, which then driving the controllable shape-morphing of HPH. The fabrication method is detailed in Fig. S13 . The porous domain in HPH (the domain with swelling properties) serve as the active component, while the non-porous domain, unresponsive to water stimulus, serve as passive component. The perfect bonding between the active and passive components is attributed to the fact that they are both Ecofelx 00–30 ( Fig. S14 ). Consequently, non-uniform volume changes generate internal stresses at their interfaces, inducing out-of-plane shape transformation. Initially, we investigate the self-buckling deformation of HPH by laterally arranging porous (active) and nonporous (passive) components. As illustrated in Fig. 4 a, a series of concentric patterns is programmed in HPH, where in-plane heterogeneous swelling leads to modulated internal stresses, resulting in 3D deformations. Upon immersion in water, the planar concentric circle HPH evolves into Enneper's surfaces with controllable wrinkles. In Fig. 4 a, we demonstrate patterned surfaces with three to six wrinkles. For more intricate in-plane patterning, a periodically patterned HPH is prepared, featuring an array of non-swellable discs embedded in the swellable HPH framework. In this configuration, each compartmentalized swellable and porous domain is surrounded by four non-porous and non-swellable discs, leading to an alternating concave-convex 3D shape (Fig. 4 b). In addition to self-buckling shape transformation, HPH can also achieve self-bending and twisting (Fig. 4 c) by arranging the porous structural gradient across the thickness of materials. Figure 4 c provides several examples of swelling-induced 3D HPH achieved through unidirectional or bidirectional folding. More examples of swelling-induced shape transformation in HPH, which borrow techniques and ideas from conventional self-morphing hydrogels such as kirigami and responsive mechanical buckling, are demonstrated in Fig. S15 . Furthermore, a reconfigurable and assembled responsive lattice can be achieved. Additionally, as shown in Fig. 4 d, we prepared a series of self-folding HPH strips and then assembled these strips into lattice by using 3D-printed dock connectors. These HPH strips can be assembled into various types of responsive lattice with different connection configurations as shown in Fig. 4 d and Fig. S16 . These responsive lattices serve as a common platform for designing soft mechanical metamaterials capable of negative swelling ratios. Upon swelling, the lattice shown in Fig. 4 d achieves a negative swelling with area change of 29% and 25%. In contrast to previous literature, our responsive lattice composed by HPH strips is dismountable with reassembling ability, enabling the recycling of self-folding HPH units into reconfigurable metamaterials. Finally, like conventional hydrogels, HPH can be combined with functional components to achieve emergent actuation properties and performance 30 . Here, by incorporating magnetic NdFeB microparticles into the monocomponent self-morphing HPH, we report hybrid materials that are actuated by a magnetic field after swelling-induced shape transformation. For conventional hydrogels, before incorporating NdFeB, the NdFeB should undergo surface passivation, such as coating with a thin layer of silica, to prevent its corrosion in the matrix of hydrogel 44 .In contrast, our HPH is composed of the hydrophobic silicone elastomer, which is an ideal matrix for NdFeB and has been reported in many literatures. As shown in Fig. 5 a and Fig. S17a , by harnessing the self-buckling deformation of HPH, we obtained a floating robot featuring a buckled buoy and a magnetic propelling tail. The buckled buoy provides enough buoyancy force to keep the robot floating on the water surface. Under magnetic actuation by an N52 magnet (magnetic field strength of 0.5 T), the magnetic propelling tail flaps the water, propelling the floating robot forward (Fig. 5 b and Movie S1 ). The swelling-induced deformation not only changes the shape of the magnetic robots but also alters the magnetization profiles inside the materials. Illustrated in Fig. 5 c and Fig. S17b , we initially design a flat magnetic HPH film with a simple planar magnetization profile. With this simple planar magnetization profile, it is challenging to realize magnetic actuation movement for the HPH film. After swelling-induced shape transformation, the HPH film rolls into a wheel-like structure. Moreover, such self-rolling shape transformation also deforms the original simple planar magnetization profiles in the HPH film, resulting in 3D axially divergent magnetization. With this more complex 3D magnetization and the wheel-like shape, the HPH film can achieve wheel rolling movement under magnetic actuation (Fig. 5 d and Movie S2 ). Figure 5 e and Fig. S17c exhibits another example by adopting self-morphing to tune the magnetization profile to realize delicate magnetic actuated movement. Our design involves a planar cross-shaped HPH film endowed with two magnetic "legs". In the planar structure, these two "legs" cannot be used for walking. Upon swelling-induced shape transformation, these two magnetic "legs" can stand up to support the HPH body. Under magnetic actuation, the standing HPH robot can alternate its magnetic "legs" to walk forward (Fig. 5 f and Movie S3 ). Conclusion In summary, our study introduces an interesting hydrophobic pseudo-hydrogel (HPH) inspired by the water-swelling phenomenon of hydrophobic Sphagnum . The HPH, despite its hydrophobic nature, exhibits unconventional water-swelling through capillary forces and surface tension in its designed microstructures. The entrapped air during the wetting process plays a crucial role in sustaining continuous imbibition, leading to macroscopic volume expansion. Tunable water-swelling is achieved by manipulating pore size, highlighting its potential for diverse applications. The programmable self-morphing ability of HPH enables controlled shape transformations, offering versatility for soft robotics and reconfigurable metamaterials. Incorporating magnetic particles enhances actuation capabilities, exemplified by the creation of floating robots with distinctive movements. This hydrophobic material provides a novel avenue for designing adaptive, responsive soft materials with implications in various fields. The theoretical framework established in this study contributes to the understanding and control of water-swelling behavior in hydrophobic matrices, paving the way for future advancements in material science and engineering. Methods Materials Part A and Part B of Ecoflex™ 00–30 (Smooth-On, lnc.). Sodium chloride (NaCl) was purchased from Sinopharm Chemistry Reagent Co. Ltd. (Shanghai, China). Magnetic nanoparticles (MQFP, NdFeB) were purchased from Magnequence. N52 magnet (Jiahao Magnetic Products, Dongguan, 0.5 T). Characterization SEM (Japan, Hitachi, SU8010) was used to observe the microstructure of the porous structure of the elastomer. Metallographic optical microscope (XK-200, Shenzhen Sinico Optical Instrument Co.) was used to observe the changes in the porous structure of the elastomer films with the time of water absorption and swelling. The contact angle was measured by Contact Angle Measurement Instrument (JC2000D1, Powereach). Desiccator (DHG-9076A, Shanghai Jinghong) was used to provide the required ambient temperature for the crosslinking of elastomers. Thermostatic Magnetic Stirrer (MS-H380-Pro, Beijing Dalong) was used to heat and disperse polymers to prepare homogeneous solutions. Mechanical high-speed disperser (SWFS-400, Shanghai Sower) was used to disperse magnetic particles encapsulated in polymers. Laboratory mill (RS200, Retsch) was used for crushing raw materials to obtain materials with different particle sizes. Preparation of porous elastomer : The process began with the introduction of raw NaCl materials into the mill's container. Activation of the mill initiates the fragmentation of these materials, resulting in particles of varying sizes. These differing-sized particles are subsequently sorted through the use of sieves with varying mesh dimensions. The separated particles are then meticulously placed into sealed bags, with each bag containing particles of a specific size. These bags are then stored in a dryer to ensure their preservation for future use. In the subsequent stage, Part A and Part B are combined in a 1:1 mass ratio. Following this, NaCl particles of distinct sizes are incorporated based on the predetermined polymer-to-template proportion. Upon thorough mixing (no visible sodium chloride particles exposed), the resultant blend of polymer precursor and template-infused NaCl forms. This blend is introduced into a polymethyl methacrylate (PMMA) mold that has been precisely cut using a CO 2 laser. Utilizing a spatula, the blend is leveled within the mold before the entire assembly is placed into an oven at 60 ℃ for 30 min for the purpose of inducing cross-linking. Upon the completion of the cross-linking process, the elastomer embedded with the template is delicately extracted from the mold. Subsequent to extraction, the elastomer undergoes immersion in deionized water. The elastomer is then removed from the water and allowed to dry once it reaches a stable size following the swelling process. This procedure ultimately culminates in the production of a porous elastomer, ready for utilization. Preparation of structurally complex 2D precursors To start, we initiate the process by precisely shaping PMMA sheets using a CO 2 laser, creating predetermined structures. Subsequently, employing a stepwise template method, we generate 2D precursors. These precursors serve as the foundation for the subsequent stages. The intricate structure of the desired pattern was brought out by strategically infusing an AB mixture, combined with NaCl, into specific areas. This mixture acts as a deformation-driven layer, enabling the creation of distinctive structural features. Meanwhile, the remaining areas are filled with pure AB adhesive, functioning as a binding layer. This intricate interplay results in the emergence of a diverse array of complex 3D structures, including captivating buckling and folding formations. Preparation of magnetically driven soft robots : Similar to the process described above for the fabrication of porous elastomers, a meticulous template method was used for the fabrication of magnetically driven robots. This method consists of a series of systematic steps, starting with the design of the mold. Subsequently, the optimal filling material is selected for each part of the mold. The filling process is gradual: First, the main part is filled with pure AB-type adhesive, while the remaining parts are shielded by the mold. After the AB-binder in the initial part has solidified, a second mold part is withdrawn. This step introduces a mixture of AB-adhesive injected with sodium chloride. After solidification, a third mold section was removed and filled with a mixture of magnetic particles and AB adhesive (1:1 mass ratio). This composite is then cured to finalize the first layer of the structure. Subsequent layers are produced in the same way. after the AB adhesive has fully cured, the elastomer with the specific structure can be removed and immersed in water. This immersion dissolves the NaCl template and eventually forms a porous magnetic elastomer. Declarations 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. Supplementary Materials Electronic supplementary information (ESI) is available. Acknowledgments The work was supported by National Natural Science Foundation of China (No. 52303163), Guangdong Basic and Applied Basic Research Foundation (No. 2022A1515110026) Data availability Data will be made available on request. References Lopez-Garrido J, Ojkic N, Khanna K, Wagner FR, Villa E, Endres RG et al (2018) Chromosome Translocation Inflates Bacillus Forespores and Impacts Cellular Morphology. Cell 172(4):758 Taha MR, Alsharef JM, Al-Mansob RA, Khan TA (2018) Effects of nano-carbon reinforcement on the swelling and shrinkage behaviour of soil. Sains Malaysiana 47(1):195–205 Ha J, Kim J, Jung Y, Yun G, Kim D-N, Kim H-Y (2018) Poro-elasto-capillary wicking of cellulose sponges. Sci Adv 4(3):eaao7051 Capezza AJ, Newson WR, Muneer F, Johansson E, Cui Y, Hedenqvist MS et al (2023) Greenhouse gas emissions of biobased diapers containing chemically modified protein superabsorbents. 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Nano-Micro Lett 15(1):79 Mendez K, Whyte W, Freedman BR, Fan Y, Varela CE, Singh M et al (2023) Mechanoresponsive Drug Release from a Flexible, Tissue-Adherent, Hybrid Hydrogel Actuator. Adv Mater : 2303301 Park CS, Kang Y-W, Na H, Sun J-Y (2024) Hydrogels for bioinspired soft robots. Prog Polym Sci : 101791 Xue Z, Wang S, Lin L, Chen L, Liu M, Feng L et al (2011) A novel superhydrophilic and underwater superoleophobic hydrogel-coated mesh for oil/water separation. Adv Mater 23(37):4270–4273 Wang H, Li J, Ding N, Zeng X, Tang X, Sun Y et al (2020) Eco-friendly polymer nanocomposite hydrogel enhanced by cellulose nanocrystal and graphitic-like carbon nitride nanosheet. Chem Eng J 386:124021 Li D, Zhan W, Zuo W, Li L, Zhang J, Cai G et al (2022) Elastic, tough and switchable swelling hydrogels with high entanglements and low crosslinks for water remediation. Chem Eng J 450:138417 Lan J, Shi L, Xiao W, Zhang X, Wang S (2023) A Rapid Self-pumping Organohydrogel Dressing with Hydrophilic Fractal Microchannels to Promote Burn Wound Healing. Adv Mater : 2301765 Koivuranta E, Hietala M, ?mm?l? A, Oksman K, Illikainen M (2017) Improved durability of lignocellulose-polypropylene composites manufactured using twin-screw extrusion. Compos A Appl Sci Manuf 101:265–272 Shabeta M (2017) Biotechnological importance of sphagnum mosses. EuroBiotech J 1(2):198–199 Shaw AJ, Carter BE, Aguero B, da Costa DP, Crowl AA (2019) Range change evolution of peat mosses (Sphagnum) within and between climate zones. Glob Change Biol 25(1):108–120 Ma XY, Xu H, Cao ZY, Shu L, Zhu RL (2022) Will climate change cause the global peatland to expand or contract? Evidence from the habitat shift pattern of Sphagnum mosses. Glob Change Biol 28(21):6419–6432 Hauber F, Konrad W, Roth-Nebelsick A (2020) Aerial roots of orchids: the velamen radicum as a porous material for efficient imbibition of water. Appl Phys A 126(11) Niño GR, González D, Fonseca A, Ruiz CM (2015) Tropical’s Sphagnum peat moss, an efficient alternative to clean up oil spills. Enpromer 2:1–6 Wang ZJ, Hong W, Wu ZL, Zheng Q (2017) Site-Specific Pre‐Swelling‐Directed Morphing Structures of Patterned Hydrogels. Angew Chem Int Ed 56(50):15974–15978 Zhang Y, Liu K, Liu T, Ni C, Chen D, Guo J et al (2021) Differential diffusion driven far-from-equilibrium shape-shifting of hydrogels. Nat Commun 12(1):6155 Lee Y, Koehler F, Dillon T, Loke G, Kim Y, Marion J et al (2023) Magnetically Actuated Fiber-Based Soft Robots. Adv Mater 35(38):2301916 Li C, Lau GC, Yuan H, Aggarwal A, Dominguez VL, Liu S et al (2020) Fast and programmable locomotion of hydrogel-metal hybrids under light and magnetic fields. Sci Rob 5(49):eabb9822 Wang G, Li A, Zhao W, Xu Z, Ma Y, Zhang F et al (2021) A review on fabrication methods and research progress of superhydrophobic silicone rubber materials. Adv Mater Interfaces 8(1):2001460 Na H, Kang YW, Park CS, Jung S, Kim HY, Sun JY (2022) Hydrogel-based strong and fast actuators by electroosmotic turgor pressure. Sci (New York NY) 376(6590):301–307 Graeber G, Díaz-Marín CD, Gaugler LC, Zhong Y, El Fil B, Liu X et al (2024) Extreme water uptake of hygroscopic hydrogels through maximized swelling‐induced salt loading. Adv Mater 36(12):2211783 Hauber F, Konrad W, Roth-Nebelsick A (2020) Aerial roots of orchids: the velamen radicum as a porous material for efficient imbibition of water. Appl Phys A 126:1–17 Wang Y, Chen S, Liu Y (2016) Spontaneous uptake of droplets into non-wetting capillaries. Comput Fluids 134:190–195 Gruener S, Sadjadi Z, Hermes HE, Kityk AV, Knorr K, Egelhaaf SU et al (2012) , . Anomalous front broadening during spontaneous imbibition in a matrix with elongated pores. Proceedings of the National Academy of Sciences 109(26): 10245–10250. Fazle Rabbi K, Ho JY, Yan X, Ma J, Hoque MJ, Sett S et al (2022) Polydimethylsiloxane-silane synergy enables dropwise condensation of low surface tension liquids. Adv Funct Mater 32(19):2112837 3D Bioinspired (2020) Microstructures for Switchable Repellency in both Air and Liquid. Adv Sci Zhang L, Guo Z, Sarma J, Zhao W, Dai X Gradient Quasi-Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids. Advanced Functional Materials Kolesnikov AL, Budkov YA, Gor GY (2020) Density functional theory model for adsorption-induced deformation of mesoporous materials with nonconvex pore geometry. J Phys Chem C 124(37):20046–20054 Liu M, JianGan, YixiangHanaor, Dorian AH (2019) Multiscale modeling of the effective elastic properties of fluid-filled porous materials. Int J Solids Struct 162 La Porta CA, Lionetti MC, Bonfanti S, Milan S, Ferrario C, Rayneau-Kirkhope D et al (2019) , . Metamaterial architecture from a self-shaping carnivorous plant. Proceedings of the National Academy of Sciences 116(38): 18777–18782. Hu H, Huang C, Galluzzi M, Ye Q, Xiao R, Yu X et al (2021) Editing the Shape Morphing of Monocomponent Natural Polysaccharide Hydrogel Films. Res (Washington DC), : 9786128 Kim Y, Parada GA, Liu S, Zhao X (2019) Ferromagnetic soft continuum robots. Sci Rob 4(33):eaax7329 Additional Declarations There is NO Competing Interest. Supplementary Files SIHydrophobicpseudohydrogel.docx HPHMovieS1.mp4 Supplementary vidieo of swimming robots HPHMovieS2.mp4 Supplementary vidieo of rolling robots HPHMovieS3.mp4 Supplementary vidieo of walking robots Cite Share Download PDF Status: Published Journal Publication published 21 Jan, 2025 Read the published version in Nature Communications → 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4784733","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":334658950,"identity":"2e1f3693-0933-49e6-b487-e66b69c971cd","order_by":0,"name":"Heng Deng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYDCCAwwMzCCaH8JlJkGLZAPJWgwOEKuF73jv4dcFFXfsNh8/Y/yCocI6sYH97AG8WiTPnEuznnHmWfK2MzlmFgxn0hMbePIS8GoxuJFjZszbdjjZ7AaPmQFj2+HEBgkeA/xa7r8Bavl3ONl4BkjLP2K03OAxfszbcNjOQILH+AFjAxFaJIFeYOY5djhB4kxaGUPCsXTjNp4c/Fr4gAH1mafmsD1/++HNHz7UWMv2s5/BrwUI2CSARGIDiJEA4hJSDwTMH4CEPYwxCkbBKBgFowADAADaL0g/LyqeYwAAAABJRU5ErkJggg==","orcid":"","institution":"China University of Geosciences","correspondingAuthor":true,"prefix":"","firstName":"Heng","middleName":"","lastName":"Deng","suffix":""},{"id":334658951,"identity":"259b7187-1fcd-4265-8d70-8afb4331ab89","order_by":1,"name":"Xu Xianchen","email":"","orcid":"https://orcid.org/0000-0002-9784-0019","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Xu","middleName":"","lastName":"Xianchen","suffix":""},{"id":334658952,"identity":"484394af-d422-44c7-bb35-a4e6053fff36","order_by":2,"name":"Zhigang Wang","email":"","orcid":"","institution":"China University of Geosciences","correspondingAuthor":false,"prefix":"","firstName":"Zhigang","middleName":"","lastName":"Wang","suffix":""},{"id":334658953,"identity":"0080c994-4a7c-4fd6-bf48-44fc978aaf9f","order_by":3,"name":"Zefan Chai","email":"","orcid":"","institution":"Univrsity of Missouri, Columbia","correspondingAuthor":false,"prefix":"","firstName":"Zefan","middleName":"","lastName":"Chai","suffix":""},{"id":334658954,"identity":"67f6c09b-8757-427b-8b91-6ea0865884ea","order_by":4,"name":"Yuhang Hu","email":"","orcid":"","institution":"China University of Geosciences","correspondingAuthor":false,"prefix":"","firstName":"Yuhang","middleName":"","lastName":"Hu","suffix":""},{"id":334658955,"identity":"4a20fa95-d6f7-481d-9a83-f3fae8effbf9","order_by":5,"name":"Tony Huang","email":"","orcid":"https://orcid.org/0000-0003-1205-3313","institution":"Duke University","correspondingAuthor":false,"prefix":"","firstName":"Tony","middleName":"","lastName":"Huang","suffix":""},{"id":334658956,"identity":"cc8077cd-9870-4890-878e-06ce157a294c","order_by":6,"name":"Cheng Zhang","email":"","orcid":"https://orcid.org/0000-0003-1559-7412","institution":"Nanjing Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Cheng","middleName":"","lastName":"Zhang","suffix":""},{"id":334658957,"identity":"f3be2afe-cc01-4607-8fff-54df0bf5cb20","order_by":7,"name":"Wesley Collyer","email":"","orcid":"","institution":"Duke University","correspondingAuthor":false,"prefix":"","firstName":"Wesley","middleName":"","lastName":"Collyer","suffix":""},{"id":334658958,"identity":"92b771a1-c026-4090-a4dc-e7b7df55d439","order_by":8,"name":"Chunjie Yan","email":"","orcid":"","institution":"China University of Geosciences","correspondingAuthor":false,"prefix":"","firstName":"Chunjie","middleName":"","lastName":"Yan","suffix":""}],"badges":[],"createdAt":"2024-07-23 00:40:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4784733/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4784733/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-56291-1","type":"published","date":"2025-01-21T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":61646915,"identity":"55b5ebce-bfc7-4c7d-8a4d-7a32fb7ef6de","added_by":"auto","created_at":"2024-08-02 11:22:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1544792,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e Depicts models of dried \u003cem\u003eSphagnum\u003c/em\u003echaracterized by a porous surface facilitating efficient water absorption and storage. \u003cstrong\u003eb)\u003c/strong\u003e Illustrates the schematic of a hydrophilic hydrogel, showcasing its water absorption and swelling properties. \u003cstrong\u003ec)\u003c/strong\u003e Presents a schematic representation of a hydrophobic elastomer immersed in water, maintaining its original state. \u003cstrong\u003ed)\u003c/strong\u003e Demonstrates the water absorption and swelling behavior of a porous hydrophobic elastomer after immersion in water. \u003cstrong\u003ee)\u003c/strong\u003eDisplays schematics of two composite systems: one combining porous elastomer with pure elastomers for programmable self-shaping transformations, and the other combining porous elastomers with magnetic elastomers for the preparation of magnetically driven robots.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/d5e2055648ffbc0edc6fade6.png"},{"id":61646533,"identity":"3a46ef75-8e2a-4e82-85c4-6c71bf0cad06","added_by":"auto","created_at":"2024-08-02 11:14:37","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1556765,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e Schematic of pure elastomer and SEM (Scanning Electron Microscope) image of a smooth cross-section. \u003cstrong\u003eb)\u003c/strong\u003e Schematic of a porous elastomer and SEM image of a smooth cross-section. \u003cstrong\u003ec)\u003c/strong\u003e The Optical picture of a pure elastomer sample in its original state after water immersion. \u003cstrong\u003ed)\u003c/strong\u003e The Optical picture of the water-absorbing and swelling behavior of a porous elastomer sample after immersion in water. \u003cstrong\u003ee)\u003c/strong\u003e The force analysis schematic during the wetting stage with large amount of air stored in the pore structure of HPH. \u003cstrong\u003ef)\u003c/strong\u003e The force analysis schematic during the wetting stage with rarefied air entrapped in the pore structure of HPH. \u003cstrong\u003eg)\u003c/strong\u003e The force analysis schematic during the expansion stage with rarefied air entrapped in HPH. \u003cstrong\u003eh)\u003c/strong\u003e The curves of mass and volume change versus time of porous elastomer after immersed in water. \u003cstrong\u003ei)\u003c/strong\u003e The swelling ratio versus time curves of porous elastomers formed by pore-making with templating agents of particle size 60 μm.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/6a5215df76f2231d4a6dae84.png"},{"id":61646914,"identity":"388f6c50-a967-4330-92b0-53e2e5c92008","added_by":"auto","created_at":"2024-08-02 11:22:37","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":854845,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea) \u003c/strong\u003eThe swelling ratio versu time of HPH with different pore sizes. \u003cstrong\u003eb)\u003c/strong\u003e The optical image of HPH with different pore sizes before and after immersed in water. \u003cstrong\u003ec)\u003c/strong\u003e Diagram of 2D ordered porous media with triangular arrangement of holes. \u003cstrong\u003ed)\u003c/strong\u003e Porous media are filled with various phases of fluid. \u003cstrong\u003ee) \u003c/strong\u003eTheoretical prediction results of between pore load modulus versus porosity. \u003cstrong\u003ef)\u003c/strong\u003e Theoretical prediction results of pore equivalent Young’s modulus versus porosity.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/5511d32e39fad48fc4838655.png"},{"id":61646535,"identity":"ca81cdc5-da83-4e75-9fef-2a8c05fcb018","added_by":"auto","created_at":"2024-08-02 11:14:37","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2378145,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e The planar schematic, optical and post-deformation fluorescence photographs of Enneper's surfaces with controllable wrinkles. \u003cstrong\u003eb)\u003c/strong\u003e The planar schematic, optical and post-deformation fluorescence photographs of the buckling structure. \u003cstrong\u003ec)\u003c/strong\u003eThe planar schematic, optical and post-deformation fluorescence photographs of the folding structure.\u003cstrong\u003e d)\u003c/strong\u003e The schematic of initial unit of the assembled lattice and the planar schematic, optical and post-deformation fluorescence photographs of lattice structures.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/10c2cc986b77b0f259c5b594.png"},{"id":61646537,"identity":"1cf73e05-9467-40ba-a2f8-68a36e969551","added_by":"auto","created_at":"2024-08-02 11:14:37","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":394621,"visible":true,"origin":"","legend":"\u003cp\u003eA schematic of the swimming robot \u003cstrong\u003e(a)\u003c/strong\u003e and time lapse optical photographs of swimming robot (2s time interval) \u003cstrong\u003e(b)\u003c/strong\u003e in motion driven by a magnetic field. A schematic of the rolling robot \u003cstrong\u003e(c)\u003c/strong\u003e and time lapse optical photographs of rolling robot (4s time interval) \u003cstrong\u003e(d)\u003c/strong\u003e in motion driven by a magnetic field. A schematic of the walking robot \u003cstrong\u003e(e)\u003c/strong\u003eand time lapse optical photographs of walking robot (nonconstant interval between images) \u003cstrong\u003e(f) \u003c/strong\u003ein motion driven by a magnetic field.\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/5b8f4f99df987636a7a4fa35.jpeg"},{"id":74339012,"identity":"b1cf953a-f0fe-4dc7-85a3-f8d52d21e41a","added_by":"auto","created_at":"2025-01-21 08:11:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7269242,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/6e83875d-e6b7-4ee8-93d5-be9201567a63.pdf"},{"id":61646540,"identity":"34fc8505-2071-4a46-a896-6411da7d0860","added_by":"auto","created_at":"2024-08-02 11:14:37","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":9826623,"visible":true,"origin":"","legend":"","description":"","filename":"SIHydrophobicpseudohydrogel.docx","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/fdc2855b9296c02d27c6b9f2.docx"},{"id":61646538,"identity":"03bc1537-d0d9-41dc-a0d6-7f2d28410403","added_by":"auto","created_at":"2024-08-02 11:14:37","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":14530184,"visible":true,"origin":"","legend":"Supplementary vidieo of swimming robots","description":"","filename":"HPHMovieS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/b30d0dd7497cfc250c5dc7e7.mp4"},{"id":61646916,"identity":"9cbf9e3f-55aa-49bb-b2b8-69393b126f81","added_by":"auto","created_at":"2024-08-02 11:22:37","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":9813421,"visible":true,"origin":"","legend":"Supplementary vidieo of rolling robots","description":"","filename":"HPHMovieS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/fd81a745d0270ca15c6561a8.mp4"},{"id":61646917,"identity":"f8bbdc5d-d771-4770-93cc-890b0ee5559d","added_by":"auto","created_at":"2024-08-02 11:22:37","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":8058181,"visible":true,"origin":"","legend":"Supplementary vidieo of walking robots","description":"","filename":"HPHMovieS3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-4784733/v1/c77ab6572e8949230fd4e65c.mp4"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Bioinspired hydrophobic pseudo-hydrogel for programmable shape-morphing","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWater-swelling is a widespread phenomenon characterized by the absorption of water molecules from the surrounding environment into the matrix of swellable materials, leading to volume expansion. This phenomenon is observed in nature, as seen in plant cells and soils exhibiting hygroscopic swelling when exposed to aqueous environments\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Additionally, it is a common occurrence in everyday technologies, such as kitchen sponges or disposable diapers\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. The exploration of water-swelling phenomena has broad implications in fundamental science, and the development of innovative materials. In this context, hydrogels have become exemplary artificial materials\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. These are cross-linked polymer networks capable of absorbing up to approximately ten times their dry weight in water while maintaining structural integrity\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Hydrogels find applications in various fields, including drug delivery\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, energy harvesting\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, soft tissue scaffolds\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, sensors\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, soft actuators\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, and soft robotics\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. The remarkable swelling behaviors of hydrogels result from the hydrophilic nature of their polymeric matrix. The hydrophilicity arises from the presence of hydrophilic chemical residues\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, such as hydroxylic (-OH)\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, carboxylic (-COOH)\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, and amidic groups, serving as binding sites that attract and retain water molecules, causing an increase in polymer volume\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. It is important to note that the majority of reported instances of water-swelling involve materials with inherent hydrophilicity. This raises a paradoxical question: Can water swelling be achieved using purely hydrophobic materials? Given that hydrophobic materials typically repel water and resist swelling, this question appears counterintuitive.\u003c/p\u003e \u003cp\u003eHowever, nature, with its diverse and ingenious designs, offers a compelling example in the form of \u003cem\u003eSphagnum\u003c/em\u003e, a plant that defies conventional expectations. In its desiccated state, \u003cem\u003eSphagnum\u003c/em\u003e exhibits hydrophobic characteristics due to its lignin-rich surface\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. However, when immersed in water, this hydrophobic material undergoes rehydration, remarkably retaining water at a rate ten times its own weight\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. With such excellent retention capabilities, \u003cem\u003eSphagnum\u003c/em\u003e is commonly utilized in horticulture to control water content in soil\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. The intriguing phenomenon of the rehydration of hydrophobic \u003cem\u003eSphagnum\u003c/em\u003e is attributed to its inherent microporous structure, resembling a sponge with myriad tiny pores and spaces. The microporous structure can harness surface tension-induced capillary forces to draw in water\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. The surface tension force, initiated by a small amount of water, cascades to attract more water, overcoming the inherent repelling forces of dried hydrophobic tissues (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and \u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eInspired by the microporous structure of \u003cem\u003eSphagnum\u003c/em\u003e, we have engineered water swellable materials using pure hydrophobic silicone elastomer endowed with a porous structure. This innovative material, named hydrophobic pseudo-hydrogel (HPH), achieves unconventional water-swelling phenomena in a purely hydrophobic matrix through physically designed microstructures. We use the term \"pseudo\" here to indicate a resemblance to hydrogels in terms of water-swelling ability (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), despite the fact that HPH is not a hydrogel as the underlying material is hydrophobic (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). In contrast to conventional hydrogels, where swelling involves molecular chain-level physicochemical interactions between water and the hydrophilic polymer backbone or lateral chains, the HPH utilizes capillary forces and surface tension to accumulate water in microscopic pore structures (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). Our investigation observes this fascinating phenomenon and also provides a theoretical explanation. We propose a theoretical framework elucidating the interplay of poro-elasto-capillary and surface tension forces, establishing a foundation for understanding and controlling swelling behavior in hydrophobic matrices. We establish a correlation between swelling in this HPH and intricate pore structure, emphasizing pore size. Moreover, by systematically programming the pore structure within the elastomer, we demonstrate the realization of anisotropic and programmable swelling in this HPH. This programming capability extends to the achievement of dedicated and programmable self-shaping transformations\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Additionally, we combine magnetic particles with self-shaping HPH to prepare magnetically driven soft robots\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e capable of basic behaviors such as swimming, rolling and walking (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee). This counterintuitive material paves the way for fabricating adaptive, responsive soft materials, which can be used in soft actuation, implantation, flexible electronics, and other emerging materials applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussions","content":"\u003cp\u003eTo empirically validate our hypothesis, we developed a hydrophobic pseudo-hydrogel (HPH) using Ecoflex 00\u0026ndash;30, a commercially available silicone rubber known for its hydrophobic properties. To induce a porous structure within the HPH, we employed a sacrificial template method using NaCl microparticles as the template, with details provided in \u003cb\u003eFig. S2\u003c/b\u003e and the \"Methods\" section. The cross-sectional morphology of the pristine silicone elastomer, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, was non-porous, and it exhibited a surface contact angle of 100\u0026deg; (\u003cb\u003eFig. S3a\u003c/b\u003e), confirming its hydrophobic nature. Following the pore-forming treatment, the HPH displayed a porous structure, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, where the HPH was fabricated using template particles approximately 60 \u0026micro;m in size. It is crucial to note that the pore-forming treatment is a purely physical process, leaving the physicochemical properties of the elastomer unchanged. The surface contact angle of the HPH was 105\u0026deg; (\u003cb\u003eFig. S3b\u003c/b\u003e), indicating that the physical porosity does not compromise the hydrophobic properties of the material itself. And the increase of the contact angle was attributed to the formation of porous microstructures on the elastomer surface\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Unlike the pristine elastomer, which did not swell when immersed in water for an extended period (six days) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), the HPH, despite retaining its hydrophobic nature, unexpectedly undergoes swelling when immersed in water. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, after 132 hours of immersion, the volume of the HPH expands over twofold compared to its original size.\u003c/p\u003e \u003cp\u003eThe water-swelling ability of HPH prompts us to reminiscent of conventional hydrogels. In the case of conventional hydrogels, their water-swelling capability is rooted from their intrinsic hydrophilicity. These hydrogels typically consist of highly hydrophilic networks of polymer chains. Consequently, water serves as a thermodynamically compatible solvent for such hydrophilic networks, facilitating easy wetting of the dried hydrogel by permeating the hydrophilic polymeric network. Upon wetting, the hydrophilic polymer chains undergo solvation by water, creating an osmotic pressure gradient between the hydrogel and the surrounding aqueous environment. This gradient drives more water molecules from the surroundings into the hydrogel polymeric network, resulting in a macroscopic swelling phenomenon\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. In contrast, HPH is a purely hydrophobic material, implying a distinct swelling mechanism compared to conventional hydrogels.\u003c/p\u003e \u003cp\u003eInspired by the capillary-induced swelling observed in hydrophobic \u003cem\u003eSphagnum\u003c/em\u003e, we speculate that capillary forces also play a pivotal role in the swelling of HPH. The swelling process of HPH can be delineated into wetting and expansion stages, similar to the swelling process of hydrogels, as schematically illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee-g. Given the hydrophobic nature of HPH, water cannot readily penetrate its polymeric network for wetting. However, upon immersion of HPH in water, hydrostatic pressure compelled water into the micropore structure of HPH. During this process, the air in the micropore structure was replaced by water, evidenced by the experimental observation of bubbles emerging from the HPH surface when immersed in water (\u003cb\u003eFig. S4\u003c/b\u003e). Upon the entry of water into the pore structures under hydrostatic pressure, two menisci form between water/air and water/elastomer due to the unique geometry of the pore structures (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee)\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. Owing to cohesive forces among water molecules, the meniscus of water/elastomer generates a capillary force induced by liquid-elastomer surface tension along the periphery ((θ\u003csub\u003eH\u0026minus;W1\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;θ\u003csub\u003eH\u0026minus;W2\u003c/sub\u003e)\u0026middot;π\u0026middot;R\u003csub\u003eH\u0026minus;W\u003c/sub\u003e/180\u0026deg;) of the meniscus. Its vertical component of capillary force propels the water moving into pores, and the F\u003csub\u003einner\u003c/sub\u003e can be expressed as\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:{F}_{inner}=\\frac{2{\\theta\\:}_{H-W1}\\pi\\:{R}_{H-W}}{{180}^{^\\circ\\:}{F}_{H-W}\\text{cos}\\theta\\:}\\:\\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eθ denotes the angle between the force exerted by the hydrophobic pore wall on water and the vertical direction. Simultaneously, a capillary force induced by liquid-air surface tension is generated in the opposite direction, expelling water from the pore structures\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, and the F\u003csub\u003eouter\u003c/sub\u003e can be expressed as\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{F}_{outer}=\\frac{{\\theta\\:}_{A-W}\\pi\\:{R}_{A-W}}{{180}^{^\\circ\\:}{F}_{A-W}\\text{cos}{\\theta\\:}_{1}}\\:\\left(2\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eθ\u003csub\u003e1\u003c/sub\u003e denotes the angle between the force exerted by air on water and the vertical direction. Given the hydrophobic and low surface energy nature of the HPH surface, which strongly repels water, the liquid-elastomer surface tension\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e generates a significantly stronger capillary force than the liquid-air surface tension\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{F}_{inner}\u0026gt;{F}_{outer})\\)\u003c/span\u003e\u003c/span\u003e. Consequently, a net force acting on the water droplet propels liquid movement into the pores. This capillary force continues to progress, drawing water into the pore structures of HPH and concurrently expelling the originally entrapped air (\u003cb\u003eFig. S5\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eIt is important to note that, despite water entering the HPH during the wetting process, it merely replaces the volume of air within the HPH, without expanding the overall volume of the material. To elucidate this dynamic behavior of the wetting process, we plotted the volume change of HPH against time (t), as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh. During the initial 30 minutes of being immersed, no significant changes in volume were observed. Concurrently, we monitored the mass change of the HPH, revealing a continuous increase. This weight increment indicates that the denser water is replacing the air inside the HPH. After approximately 30 minutes of immersion, the volume of the HPH begins to steadily increase, marking the commencement of the expansion stage. Due to capillary forces, continuous imbibition is sustained, leading to the high stretchability of the elastomer and resulting in macroscopic volume expansion (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg). On one hand, the elastomer's expansion increases the radius of the pores, leading to a decrease in capillary force. On the other hand, the elastomer's expansion generates an increasing elastic force that impedes water imbibition. Ultimately, a balance is achieved between the capillary force and the elastic force, resulting in the equilibrium expansion of HPH. As depicted in the volume curve (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei), the swelling of HPH reaches an equilibrium state after 144 hours of immersion. The swelling behavior of HPH is also evident in the microscopic pore structure changes. In \u003cb\u003eFig. S6\u003c/b\u003e, a thin film of HPH (~\u0026thinsp;78 \u0026micro;m) immersed in water is observed under a microscope, clearly revealing the pore structure. Approximately 10 minutes later, the pore sizes on the HPH surface progressively increase with the prolonged immersion time, eventually reaching equilibrium (\u003cb\u003eFig. S7\u003c/b\u003e). The swelled HPH was also investigated by Environmental Scanning Electron Microscope (ESEM). As shown in the cross-sectional ESEM images of swelled HPH (\u003cb\u003eFig. S8\u003c/b\u003e), the pore structure of HPH after swelling is demonstrated, showing that its pore size ranges from 80 to 200 \u0026micro;m. This result matches the swelling rate of macroscopic HPH, confirming the unity between microscopic and macroscopic observations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt should be noted here that, at the critical transition point between the wetting and expansion stages, a small portion of air remains sealed by the water inside the HPH (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef), playing an important role in the subsequent expansion process. If all the air within the HPH were evacuated, leaving only the water/elastomer interface, the capillary force induced by surface tension around the pore periphery would be nullified, resulting in the absence of a driving force to draw water in. However, we consistently observe an increase in both volume and weight of the HPH. This sustained imbibition should be attributed to the trapped air, which generates asymmetric capillary forces (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg). By analyzing the volume and weight curves, we calculated that the density of the HPH at the transition point was 0.927 g/cm\u0026sup3;, an intermediate value between the fully dried and fully wetted states. This suggests that at the transition point, about 11.69% of the pore volume is occupied by air (\u003cb\u003eFig. S9\u003c/b\u003e), supporting the hypothesis of entrapped air. To futher demonstrate the importance of residual air in the pore for HPH swelling, we performed vertical water absorption and swelling experiments on long strips of HPH. The HPH strip was positioned perpendicular to the surface of red ink, with their lower ends immersed in the ink (\u003cb\u003eFig. S10\u003c/b\u003e). Unlike immersing HPH in water, where air is easily trapped in the hydrophobic matrix, this setup allows water to be transported upward from the bottom of the HPH, wetting the pores layer by layer. This process expels most of the internal air from the HPH, leaving only a small portion to provide the driving force for the subsequent expansion process. As a result, the swelling ratio of HPH strips in the vertical swelling experiment is significantly lower than the one fully immersed in water. The observed swelling ratio in this setup is only 130%, demonstrating the crucial role of residual air in achieving full swelling.\u003c/p\u003e \u003cp\u003eAs discussed earlier, the water-swelling process of HPH is linked to capillary forces induced by liquid-elastomer surface tension along the periphery of the pore meniscus, which is also associated with the radius of the pores. Thus, by adjusting the pore size within HPH, the water-swelling ability of HPH becomes tunable. To explore the relationship between pore structure and elastomer swelling, the tunable pore sizes in the HPH were achieved by manipulating the size of the soluble template NaCl particles. The internal pore structures of HPH with different pore sizes are illustrated in \u003cb\u003eFig. S11\u003c/b\u003e. Observations reveal that smaller pore sizes correspond to a faster water absorption rate of HPH and a larger swelling size (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Additionally, there exists a threshold pore size determining whether swelling will occur in HPH. Obvious swelling is observed only when the pore size is less than 152 \u0026micro;m. Conversely, when the pore size exceeds 152 \u0026micro;m, the pore structure in HPH is wetted but does not exhibit obvious expansion. This could be attributed to the fact that, when the pore size exceeds 152 \u0026micro;m, the capillary forces generated by surface tension are insufficient to overcome the elastic force of the elastomer and induce expansion.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further elucidate the intriguing pore size-related water-swelling phenomena of HPH, detailed principal calculations have been conducted to unveil the underlying mechanism, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, According to Gor et al.\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e, in porous media with regularly spaced pores, the engineering strain of a single thick-walled cylindrical unit cell can approximate the overall volumetric strain. To account for pore interaction, analysis is conducted on seven adjacent thick-walled cylindrical unit cells. In a single thick-walled cylindrical unit cell, pore walls endure internal pressure \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{p}_{i}\\)\u003c/span\u003e\u003c/span\u003e, while the effect of neighboring pores on the central cell is akin to an external boundary pressure \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{p}_{o}\\)\u003c/span\u003e\u003c/span\u003e. The water-swelling of HPH will provide the unbalanced force contributed by the surface tension near the liquid-solid interface, which will provide a driven pressure \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{p}_{c}\\)\u003c/span\u003e\u003c/span\u003e to break the balance between the internal pressure and external pressure. As Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed shows, before HPH wetting, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{p}_{i}={p}_{o}\\)\u003c/span\u003e\u003c/span\u003e, and the HPH will not swell. When we place the HPH in the water, this balance will be broken, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{i}+{P}_{c}\\gg\\:{P}_{o}\\)\u003c/span\u003e\u003c/span\u003e. When pressurized liquid is injected into porous media with dual porosity, it undergoes two typical stages sequentially. Firstly, the macroscopic pores are rapidly filled, compressing the liquid inside the pores and exerting pressure on the pore walls, thereby stiffening the structure. Secondly, the pressurized liquid in the macroscopic pores gradually permeates into the microscopic pores within the framework under the driving force of pressure gradients, leading to complex changes in the overall macroscopic elastic behavior of the structure. Compared to the second stage, the first stage is typically completed in a very short time. Therefore, the focus here is mainly on the evolution of the macroscopic equivalent properties of porous media during the liquid infiltration process in the second stage. The HPH will swell very fast, thus, the pore pressure in porous media during the swelling will be\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:{P}_{f}=（{P}_{i}+{P}_{c}）-{P}_{o}\\)\u003c/span\u003e\u003c/span\u003e. In porous media containing fluids, there exist complex coupling effects between the solid framework and the pore fluid. The fluid pressure acting on the pore walls has a significant influence on their macroscopic mechanical behavior. A thorough understanding of the equivalent mechanical properties of fluid-containing porous media is crucial for promoting their practical engineering applications. Previous research has addressed this issue to some extent\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. However, a systematic understanding is still lacking. Therefore, here, we analyze this problem based on a micromechanical model. Firstly, a theoretical model predicting the effective modulus of dry porous media will be established, followed by an analysis of the influence of pore pressure. The pore load modulus in porous media can be expressed as\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:{M}_{pd}=\\frac{E\\{\\left[1+\\left(1+\\nu\\:\\right)k\\right]-[1-(1+\\nu\\:)(1-2\\nu\\:)k\\left]\\xi\\:\\right\\}}{\\left(1+\\nu\\:\\right)\\{\\left(1-2\\nu\\:\\right)\\left[1-\\alpha\\:\\left(1+\\left(1+v\\right)k\\right)\\right]-[\\alpha\\:\\left(1-\\left(1+\\nu\\:\\right)\\left(1-2\\nu\\:\\right)k\\right)\\xi\\:-1\\left]\\right\\}\\xi\\:}\\:\\left(3\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, it can be observed that for nanoporous specimens with the same porosity, as the pore size decreases, the influence of surface effects becomes increasingly apparent. Conversely, for specimens with the same pore size, the higher the porosity, the more pronounced the surface effects. Additionally, soft surfaces lead to a decrease in the poroelastic modulus with decreasing pore radius. This means that the higher porous HPH will more fully and more easily swell with water. Thus, the equivalent volume modulus of porous media can be defined by the formula,\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:{K}_{pd}=\\frac{E(1-\\xi\\:)}{2[\\left(1-\\nu\\:\\right)+(1+\\nu\\:\\left)\\xi\\:\\right](1-\\alpha\\:\\xi\\:)}\\:\\left(4\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAnd the equivalent Young\u0026rsquo;s modulus of porous media can be defined by the formula,\u003cdiv id=\"Eque\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Eque\" name=\"EquationSource\"\u003e\n$$\\:{E}_{pd}=\\frac{E{\\left(1-\\xi\\:\\right)}^{3}}{\\left(1-\\alpha\\:\\xi\\:\\right)}\\text{exp}\\left\\{\\frac{3\\alpha\\:\\xi\\:\\left[2+\\left(1+\\alpha\\:\\right)\\xi\\:\\right]}{2\\left[2-\\left(2-\\alpha\\:\\right)\\xi\\:\\right]}\\right\\}\\:\\left(5\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, the equivalent Young\u0026rsquo;s modulus will decrease very fast due to the change of porosity. So the HPH strain under the pore pressure of swelling water can be expressed as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\epsilon\\:={P}_{f}/{M}_{pd}\\)\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eSince HPH exhibits similar water-swelling ability to conventional hydrogels, it functions similarly and has similar potential applications. Conventional hydrogels have been extensively studied as self-morphing materials due to their water-triggered shape transformation phenomena. The development of self-morphing materials is inspired by the widespread shape-transformation phenomena observed in plants\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e, generating growing interest in various fields such as energy harvesting, metamaterials, soft robotics, sensors, and multifunctional bioscaffolds. In the following section, we explore the potential applications of HPH as programmable water-responsive self-morphing materials. Typically, the shape transformation of hydrogels arises from inhomogeneous swelling behaviors within the material. Traditional shape-morphing hydrogels achieve this by incorporating diverse components with different swelling behaviors in response to specific stimuli. However, introducing diverse components may encounter intrinsic limitations, such as unstable interfaces and time-consuming fabrication. Therefore, it is of great significance to develop monocomponent hydrogel that enable precisely programmable deformations\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. Our HPH materials can take the advantages of the microstructure programmed swelling ability to realize monocomponent self-morphing materials (\u003cb\u003eFig. S12\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBy controlling the pore structural domain in HPH, programmable and localized swelling can be achieved, which then driving the controllable shape-morphing of HPH. The fabrication method is detailed in \u003cb\u003eFig. S13\u003c/b\u003e. The porous domain in HPH (the domain with swelling properties) serve as the active component, while the non-porous domain, unresponsive to water stimulus, serve as passive component. The perfect bonding between the active and passive components is attributed to the fact that they are both Ecofelx 00\u0026ndash;30 (\u003cb\u003eFig. S14\u003c/b\u003e). Consequently, non-uniform volume changes generate internal stresses at their interfaces, inducing out-of-plane shape transformation. Initially, we investigate the self-buckling deformation of HPH by laterally arranging porous (active) and nonporous (passive) components. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, a series of concentric patterns is programmed in HPH, where in-plane heterogeneous swelling leads to modulated internal stresses, resulting in 3D deformations. Upon immersion in water, the planar concentric circle HPH evolves into Enneper's surfaces with controllable wrinkles. In Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, we demonstrate patterned surfaces with three to six wrinkles. For more intricate in-plane patterning, a periodically patterned HPH is prepared, featuring an array of non-swellable discs embedded in the swellable HPH framework. In this configuration, each compartmentalized swellable and porous domain is surrounded by four non-porous and non-swellable discs, leading to an alternating concave-convex 3D shape (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eIn addition to self-buckling shape transformation, HPH can also achieve self-bending and twisting (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec) by arranging the porous structural gradient across the thickness of materials. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec provides several examples of swelling-induced 3D HPH achieved through unidirectional or bidirectional folding. More examples of swelling-induced shape transformation in HPH, which borrow techniques and ideas from conventional self-morphing hydrogels such as kirigami and responsive mechanical buckling, are demonstrated in \u003cb\u003eFig. S15\u003c/b\u003e. Furthermore, a reconfigurable and assembled responsive lattice can be achieved. Additionally, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed, we prepared a series of self-folding HPH strips and then assembled these strips into lattice by using 3D-printed dock connectors. These HPH strips can be assembled into various types of responsive lattice with different connection configurations as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed and \u003cb\u003eFig. S16\u003c/b\u003e. These responsive lattices serve as a common platform for designing soft mechanical metamaterials capable of negative swelling ratios. Upon swelling, the lattice shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed achieves a negative swelling with area change of 29% and 25%. In contrast to previous literature, our responsive lattice composed by HPH strips is dismountable with reassembling ability, enabling the recycling of self-folding HPH units into reconfigurable metamaterials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFinally, like conventional hydrogels, HPH can be combined with functional components to achieve emergent actuation properties and performance\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Here, by incorporating magnetic NdFeB microparticles into the monocomponent self-morphing HPH, we report hybrid materials that are actuated by a magnetic field after swelling-induced shape transformation. For conventional hydrogels, before incorporating NdFeB, the NdFeB should undergo surface passivation, such as coating with a thin layer of silica, to prevent its corrosion in the matrix of hydrogel\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e.In contrast, our HPH is composed of the hydrophobic silicone elastomer, which is an ideal matrix for NdFeB and has been reported in many literatures. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cb\u003eFig. S17a\u003c/b\u003e, by harnessing the self-buckling deformation of HPH, we obtained a floating robot featuring a buckled buoy and a magnetic propelling tail. The buckled buoy provides enough buoyancy force to keep the robot floating on the water surface. Under magnetic actuation by an N52 magnet (magnetic field strength of 0.5 T), the magnetic propelling tail flaps the water, propelling the floating robot forward (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb and \u003cb\u003eMovie S1\u003c/b\u003e). The swelling-induced deformation not only changes the shape of the magnetic robots but also alters the magnetization profiles inside the materials. Illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and \u003cb\u003eFig. S17b\u003c/b\u003e, we initially design a flat magnetic HPH film with a simple planar magnetization profile. With this simple planar magnetization profile, it is challenging to realize magnetic actuation movement for the HPH film. After swelling-induced shape transformation, the HPH film rolls into a wheel-like structure. Moreover, such self-rolling shape transformation also deforms the original simple planar magnetization profiles in the HPH film, resulting in 3D axially divergent magnetization. With this more complex 3D magnetization and the wheel-like shape, the HPH film can achieve wheel rolling movement under magnetic actuation (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed and \u003cb\u003eMovie S2\u003c/b\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee and \u003cb\u003eFig. S17c\u003c/b\u003e exhibits another example by adopting self-morphing to tune the magnetization profile to realize delicate magnetic actuated movement. Our design involves a planar cross-shaped HPH film endowed with two magnetic \"legs\". In the planar structure, these two \"legs\" cannot be used for walking. Upon swelling-induced shape transformation, these two magnetic \"legs\" can stand up to support the HPH body. Under magnetic actuation, the standing HPH robot can alternate its magnetic \"legs\" to walk forward (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef and \u003cb\u003eMovie S3\u003c/b\u003e).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, our study introduces an interesting hydrophobic pseudo-hydrogel (HPH) inspired by the water-swelling phenomenon of hydrophobic \u003cem\u003eSphagnum\u003c/em\u003e. The HPH, despite its hydrophobic nature, exhibits unconventional water-swelling through capillary forces and surface tension in its designed microstructures. The entrapped air during the wetting process plays a crucial role in sustaining continuous imbibition, leading to macroscopic volume expansion. Tunable water-swelling is achieved by manipulating pore size, highlighting its potential for diverse applications. The programmable self-morphing ability of HPH enables controlled shape transformations, offering versatility for soft robotics and reconfigurable metamaterials. Incorporating magnetic particles enhances actuation capabilities, exemplified by the creation of floating robots with distinctive movements. This hydrophobic material provides a novel avenue for designing adaptive, responsive soft materials with implications in various fields. The theoretical framework established in this study contributes to the understanding and control of water-swelling behavior in hydrophobic matrices, paving the way for future advancements in material science and engineering.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cstrong\u003eMaterials\u003c/strong\u003e \u003cp\u003ePart A and Part B of Ecoflex\u0026trade; 00\u0026ndash;30 (Smooth-On, lnc.). Sodium chloride (NaCl) was purchased from Sinopharm Chemistry Reagent Co. Ltd. (Shanghai, China). Magnetic nanoparticles (MQFP, NdFeB) were purchased from Magnequence. N52 magnet (Jiahao Magnetic Products, Dongguan, 0.5 T).\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCharacterization\u003c/strong\u003e \u003cp\u003eSEM (Japan, Hitachi, SU8010) was used to observe the microstructure of the porous structure of the elastomer. Metallographic optical microscope (XK-200, Shenzhen Sinico Optical Instrument Co.) was used to observe the changes in the porous structure of the elastomer films with the time of water absorption and swelling. The contact angle was measured by Contact Angle Measurement Instrument (JC2000D1, Powereach). Desiccator (DHG-9076A, Shanghai Jinghong) was used to provide the required ambient temperature for the crosslinking of elastomers. Thermostatic Magnetic Stirrer (MS-H380-Pro, Beijing Dalong) was used to heat and disperse polymers to prepare homogeneous solutions. Mechanical high-speed disperser (SWFS-400, Shanghai Sower) was used to disperse magnetic particles encapsulated in polymers. Laboratory mill (RS200, Retsch) was used for crushing raw materials to obtain materials with different particle sizes.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of porous elastomer\u003c/b\u003e: The process began with the introduction of raw NaCl materials into the mill's container. Activation of the mill initiates the fragmentation of these materials, resulting in particles of varying sizes. These differing-sized particles are subsequently sorted through the use of sieves with varying mesh dimensions. The separated particles are then meticulously placed into sealed bags, with each bag containing particles of a specific size. These bags are then stored in a dryer to ensure their preservation for future use. In the subsequent stage, Part A and Part B are combined in a 1:1 mass ratio. Following this, NaCl particles of distinct sizes are incorporated based on the predetermined polymer-to-template proportion. Upon thorough mixing (no visible sodium chloride particles exposed), the resultant blend of polymer precursor and template-infused NaCl forms. This blend is introduced into a polymethyl methacrylate (PMMA) mold that has been precisely cut using a CO\u003csub\u003e2\u003c/sub\u003e laser. Utilizing a spatula, the blend is leveled within the mold before the entire assembly is placed into an oven at 60 ℃ for 30 min for the purpose of inducing cross-linking. Upon the completion of the cross-linking process, the elastomer embedded with the template is delicately extracted from the mold. Subsequent to extraction, the elastomer undergoes immersion in deionized water. The elastomer is then removed from the water and allowed to dry once it reaches a stable size following the swelling process. This procedure ultimately culminates in the production of a porous elastomer, ready for utilization.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003ePreparation of structurally complex 2D precursors\u003c/strong\u003e \u003cp\u003eTo start, we initiate the process by precisely shaping PMMA sheets using a CO\u003csub\u003e2\u003c/sub\u003e laser, creating predetermined structures. Subsequently, employing a stepwise template method, we generate 2D precursors. These precursors serve as the foundation for the subsequent stages. The intricate structure of the desired pattern was brought out by strategically infusing an AB mixture, combined with NaCl, into specific areas. This mixture acts as a deformation-driven layer, enabling the creation of distinctive structural features. Meanwhile, the remaining areas are filled with pure AB adhesive, functioning as a binding layer. This intricate interplay results in the emergence of a diverse array of complex 3D structures, including captivating buckling and folding formations.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of magnetically driven soft robots\u003c/b\u003e: Similar to the process described above for the fabrication of porous elastomers, a meticulous template method was used for the fabrication of magnetically driven robots. This method consists of a series of systematic steps, starting with the design of the mold. Subsequently, the optimal filling material is selected for each part of the mold. The filling process is gradual: First, the main part is filled with pure AB-type adhesive, while the remaining parts are shielded by the mold. After the AB-binder in the initial part has solidified, a second mold part is withdrawn. This step introduces a mixture of AB-adhesive injected with sodium chloride. After solidification, a third mold section was removed and filled with a mixture of magnetic particles and AB adhesive (1:1 mass ratio). This composite is then cured to finalize the first layer of the structure. Subsequent layers are produced in the same way. after the AB adhesive has fully cured, the elastomer with the specific structure can be removed and immersed in water. This immersion dissolves the NaCl template and eventually forms a porous magnetic elastomer.\u003c/p\u003e"},{"header":"Declarations","content":"\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\u003cp\u003e \u003ch2\u003eSupplementary Materials\u003c/h2\u003e \u003cp\u003eElectronic supplementary information (ESI) is available.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe work was supported by National Natural Science Foundation of China (No. 52303163), Guangdong Basic and Applied Basic Research Foundation (No. 2022A1515110026)\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\u003eLopez-Garrido J, Ojkic N, Khanna K, Wagner FR, Villa E, Endres RG et al (2018) Chromosome Translocation Inflates Bacillus Forespores and Impacts Cellular Morphology. 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Sci Rob 4(33):eaax7329\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4784733/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4784733/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eInspired by counterintuitive water-swelling ability of the hydrophobic moss of the genus \u003cem\u003eSphagnum\u003c/em\u003e (Peat moss), we introduce a novel material\u0026mdash;hydrophobic pseudo-hydrogel (HPH), composed of a pure hydrophobic silicone elastomer with a tailored porous structure. In contrast to conventional hydrogels, HPH achieves water-swelling through capillary forces and surface tension, presenting an unexpected water-swelling capability in hydrophobic matrices. We establish a theoretical framework elucidating the interplay of poro-elasto-capillary and surface tension forces, providing insights into the swelling behavior. By systematically programming the pore structure, we demonstrate tunable, anisotropic, and programmable swelling. This leads to dedicated self-shaping transformations. Incorporating magnetic particles, we engineer HPH-based soft robots capable of swimming, rolling, and walking. This study demonstrates a unique approach to achieve water-responsive behavior in hydrophobic materials, expanding the possibilities for programmable shape-morphing in soft materials and soft robotic applications.\u003c/p\u003e","manuscriptTitle":"Bioinspired hydrophobic pseudo-hydrogel for programmable shape-morphing","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-02 11:14:32","doi":"10.21203/rs.3.rs-4784733/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"2225b1be-3958-4428-9d59-076e6508ed00","owner":[],"postedDate":"August 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":35438855,"name":"Physical sciences/Materials science/Soft materials/Wetting"},{"id":35438856,"name":"Physical sciences/Materials science/Soft materials/Self-assembly"}],"tags":[],"updatedAt":"2025-01-21T08:11:25+00:00","versionOfRecord":{"articleIdentity":"rs-4784733","link":"https://doi.org/10.1038/s41467-025-56291-1","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-01-21 05:00:00","publishedOnDateReadable":"January 21st, 2025"},"versionCreatedAt":"2024-08-02 11:14:32","video":"","vorDoi":"10.1038/s41467-025-56291-1","vorDoiUrl":"https://doi.org/10.1038/s41467-025-56291-1","workflowStages":[]},"version":"v1","identity":"rs-4784733","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4784733","identity":"rs-4784733","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}