Bioinspired hydrophobic pseudo-hydrogel for programmable shape-morphing

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.