Fabrication of porous silk fibroin/cellulose nanofibril sponges with hierarchical structure using a lithium bromide solvent system

Abstract

Porous silk fibroin (SF) sponges have been widely used in biomaterials due to their excellent biocompatibility and tunable degradability. However, it remains a challenge to construct porous SF materials with 3D nanofibrous structure mimicking extracellular matrix. In this study, a novel strategy was developed to fabricate SF/cellulose sponges with micro-nano hierarchical structure through using a lithium bromide aqueous solution system. It was found that the cellulose can be partially dissolved by lithium bromide solution to form abundant cellulose nanofibrils (CNFs). Therefore, the porous SF/CNF sponge was directly prepared after dissolving SF/cellulose blend in lithium bromide solution. The structure and performance of sponges can be regulated by adjusting SF/cellulose ratio. Raising the cellulose ratio enhanced the compression strength and water swelling ratio of sponges, but restrained the 3D spatial distribution of CNFs in the pore space. As SF content increased to 50%, CNFs homogeneously dispersed and formed the porous sponges with micro-nano hierarchical structure. FTIR and XRD results showed cellulose II and silk II structure in composites, and suggested the presence of intermolecular interaction between SF and cellulose. The enzymatic degradation results showed that the degradation rate of sponges could be regulated by the SF component, which significantly promoted degradability. The results provide promising scaffold candidate with tunable nanostructure and degradability.