Cold-induced shape memory hydrogels for strong and programmable artificial muscles

Thermo-responsive shape memory hydrogels generally achieve fixation at low temperatures, and recovery high temperatures. However, these hydro-gels usually suffer from poor mechanical properties. Herein, we present a unique poly(acrylic acid)/calcium acetate hydrogel with cold-induced performances as ultrastrong artificial muscles. Since the groups could form aggregate temperatures thus induce association of network, can be fixed into temporary upon heating recover to its original in cold environment. Moreover, programmable process is realized by adjusting fixing time. In addition, enables application demonstration bio-inspired muscles an ultrahigh work density 45.2 kJ m−3, higher than that biological (∼8 m−3).