Moisture-Responsive Actuators Based on Hyaluronic Acid with Biocompatibility and Fast Response as Smart Breather Valves

Moisture-responsive actuators with biocompatibility, fast response, and tough interfacial bonding are developed as smart breather valves for humidity management. The proposed actuators are featured with a bilayer structure consisting of a moisture-sensitive methacrylated hyaluronic acid (HAMA) layer and a moisture-inert porous poly(vinylidene fluoride) (PVDF) layer. The HAMA/PVDF bilayer films are fabricated by casting HAMA precursor solutions on the ethanol-treated porous PVDF films first and then converting the precursor solutions into crosslinked HAMA hydrogels via UV-initiated crosslinking. The fabricated HAMA/PVDF bilayer films exhibit rapid, reversible, and repeatable moisture-responsive bending performances upon the change of environmental relative humidity. The molecular weight and mass concentration of HAMA in a precursor solution affect the moisture-responsive actuating speed of the HAMA/PVDF bilayer films, and the fastest response time needed for completing 70% of the moisture-responsive deformation of a HAMA/PVDF bilayer film can be as short as 0.5 s. Due to the fast moisture-responsive bending property and biocompatibility, the HAMA/PVDF bilayer films are successfully developed into smart breather valves by designing and patterning them into fence-like structures and then equipped on the outdoor masks for efficient management of humidity inside the masks. The proposed moisture-responsive actuators show great potential in various applications, especially those related to environmental humidity management.