Solvent volatilization annealing-prepared Janus film with asymmetric bioadhesion and inherent biological functions to expedite oral ulcer healing

Fabrication of layered bioadhesives with asymmetric bioadhesion, on-demand detachment and inherent biological functions remains a great challenge. This work reports a novel and generalizable solvent volatilization-induced annealing (SVA) strategy to prepare a Janus film with an integrated dual layer structure, asymmetric adhesion, on-demand detachment and inherent biological functions. Depositing polyvinyl pyrrolidone/caffeic acid/lipoic acid (PVP/CA/LA) ethanol solutions onto an ethylcellulose (EC) layer and applying SVA strategy can integrate two layers in molecular-level to obtain the dual-layered Janus film. Porous PVP/p(CA-LA) surface pressed onto wet tissues can absorb interfacial water to form tight tissue contact, and their functional groups can form abundant bonds to induce robust bioadhesion. In contrast, dense EC surface limits water absorption and exhibits minimal adhesion of proteins, cells and tissues. Furthermore, the adhered Janus film can be detached by using a glutathione/sodium bicarbonate solution. Additionally, CA and LA provide the film with desired antibacterial, antioxidant, and anti-inflammatory properties. Finally, by providing the antibacterial and anti-inflammatory microenvironment, the Janus film promotes angiogenesis and significantly expedites the healing of the oral ulcers in rats. This work not only introduces a novel approach for preparing multi-layered and asymmetric materials, but also paving the way for developing adhesive materials with inherent biological functions.