Concentric ice-templating of ultracompressible tough hydrogels with bioinspired circumferentially aligned architecture

Materials with circumferentially aligned fibers, such as intervertebral discs and arteries, are abundant in nature but challenging to replicate artificially, despite their mechanical advantages. Although ice-templating can create bioinspired materials, the achievable structures remain limited to simple forms, such as honeycomb, lamellar, and radial structures. Here, we developed a unique ice-templating technique that constructs circumferential fibrous structures in hydrogels through slow freezing. Enhanced with rotary compression annealing, these hydrogels exhibit record-breaking features that cannot concurrently be achieved in conventional ice-templated and top-performing tough hydrogels, including high tensile properties, isotropic fatigue threshold of 2320 joules per square meter, ultracompressibility (8% strain after 500 cycles), and extraordinary burst pressure of 1.6 bar while maintaining 85 weight % water content. These properties enable opportunities in robotics, including hydrogel pneumatic grippers and an untethered bioinspired robotic fish that exhibits high-force actuation and long-term robustness. Our approach enriches the diversity of bioinspired structures in artificial materials, establishing exceptional mechanical properties through cross-length scale structural design.