Conformational entropy-driven hydrogel actuators with high toughness

The development of high-performance hydrogel actuators for flexible robotics and biomedicine is fundamentally limited by an inherent trade-off between mechanical strength and rapid actuation, which remains a major challenge for system design. Herein, we propose a strategy to balance mechanical properties and rapid actuation in hydrogel actuators by leveraging polymer chain conformational changes. The hydrogel actuators were prepared in a one-pot and freeze-thaw process by cross-linking N, N-diethylacrylamide, poly(vinyl alcohol) (PVA), and sodium alginate (SA) using bis(acryloyl)-(L)-cystinate (BISS). The resulting hydrogel exhibits exceptional mechanical properties, including a tensile strength of 176.5 kPa, an elongation at break of 832.8 %, and a rapid actuation speed of 21°·s⁻¹ . The enhanced mechanical properties originate from hydrogen bonding and physical entanglement induced by PVA and SA, whereas the fast actuation stems from disulfide bond rearrangement, which increases polymer chain entropy. UV irradiation cleaves the disulfide bonds, reducing the storage modulus plateau at low angular frequencies by decreasing network entanglement and thereby enabling entropy-driven photomechanical programming. This work will advance the development and practical application of tough fast-actuating hydrogel actuators in intelligent soft robotics.