Triple physically cross-linked hydrogel artificial muscles with high-stroke and high-work capacity

Owing to the high-water content and excellent biocompatibility, polymeric hydrogels are good candidates to mimic natural muscles in biomedical and bioengineering fields, but the low stroke and low work capacity limited them to be used as artificial muscles. Herein, inspired by the ordered structure of skeletal muscles, high performance anisotropic hydrogels comprising of triple physically cross-linked networks are developed by the electrostatic interactions between positively charged tunicate cellulose nanocrystals (TCNC) and –COO− of polymers, hydrophobic association of stearyl methacrylate (SMA) moiety in sodium dodecyl sulfate (SDS) micelles, and –COO−/Fe3+ ionic coordination. The elastic potential energy can be stored in polymeric networks by locking the pre-stretched hydrogel via ionic coordination, which can be released by dissociating the ionic coordination under acidic condition. Based on their excellent mechanical property reinforced by TCNCs, the developed hydrogel artificial muscles exhibit high actuation stroke (75 %) and high-work capacity (210 J kg−1), which are higher than those of skeletal muscles. These hydrogel muscles demonstrated potential for wide applications in being designed as biceps to lift skeleton’s arm and as micromotors to drive boat model under acidic condition because of their high-stroke, high-work capacity and comparable output efficiency with natural muscles.