With the rapid development of artificial intelligence, more and more smart flexible materials have been applied to soft robots, and given these robots “senses” and “acts”. The most common option is stimulus-responsive hydrogel, especially thermo-responsive hydrogel featuring high water-content and excellent biocompatibility. However, low response rate and strong dependence on water environment enable them to be greatly limited in practical use for soft sensors and actuators. So we adopted poly(methacrylic acid-co-3-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate) (PMAA-co-DMAPS) to construct a novel UCST&LCST Janus hydrogel for osmosis-driven programmable soft actuator. Particularly, PMAA-co-DMAPS copolymers with different monomer ratios display huge transition between upper critical solution temperature (UCST) and lower critical solution temperature (LCST). Once integrated into one, reverse thermo-responsive capability will contribute to increase response rate of the Janus hydrogel. And single material source also favor enhancement on inherent compatibility to realize internal water circulation. Within 45 minutes, the Janus hydrogel underwent a large bending angle of 960° from 385° to -575° as the ambient aqueous phase was heated up from 10 to 50 oC. The results of microscopic morphology and ion penetration testing showed that, heat can induce obvious transition of porosity and density, and then make water molecules exchanged through the bonding interface between the UCST and LCST side. It is anticipating to leave the Janus hydrogel from aqueous environment and broaden their applications.

Osmosis-driven programmable soft actuator based on UCST&LCST janus hydrogel of P(MAA-co-DMAPS)

ACS Spring 2022

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