Fast self-assembly of microporous silk fibroin membranes on liquid surface.

The air-liquid interface has been used to create micro- and nanostructured polymeric membranes. Here, we employed a novel silk fibroin (SF) solution to create ultrathin membranes effectively on the surface of subphase (30 wt% ammonium sulphate). The SF droplets spread instantaneously at the air-liquid interface driven by the surface tension difference between subphase and SF solutions. Conformational changes for SF molecules from disordered structure to ordered structure occur simultaneously. During the process, SF molecules self-assemble by rearranging hydrophobic and hydrophilic domains to minimize the free energy of the system. Dehydration and denaturation of proteins by high concentration of salt in the subphase promote the polymer solidification. Phase separation results in the porous structure of the SF membrane. Mixing aqueous gelatin with SF solution causes the reduction of pore size, porosity and mechanical properties of the membranes. More aqueous gelatin hinders the polymer solidification within short time. The as-prepared membranes have excellent transparency and cytocompatibility, which have potential for the applications of biotechnology, biomedicine and organ-on-chip.