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.

A simple microfluidic strategy is proposed for the controllable preparation of calcium alginate/chitosan (CaA/CS) microcapsules with ultrathin shells for peroxidase immobilization. In this study, the composite microcapsules are composed of CaA and CS, which are beneficial to improve the stability of CaA microcapsules, and are generated using a two-stage capillary microfluidic device. The inner layer of the composite capsule shells is ionically cross-linked CaA, and the outer layer is covalently cross-linked CS. Moreover, the Fe3O4 magnetic nanoparticles are added to facilitate the recovery and reuse of the composite microcapsules. The morphology, permeability, encapsulation efficiency, enzyme activity, and reusability of CaA/CS microcapsules are investigated. The overall thickness of the double-layered shell is about 346 nm. Meanwhile, the microcapsules have good molecular selective permeability, excellent encapsulation performance, stable enzyme activity, and good stability for reusability. The composite microcapsules retained above 80% of residual activity after six recycle uses. The developed novel strategy for fabricating peroxidase-immobilized CaA/CS microcapsules with ultrathin shells is of great potential value for enzyme immobilization applications.