Silk fibroin-poly(lactic acid) biocomposites: Effect of protein-synthetic polymer interactions and miscibility on material properties and biological responses

A protein-polymer blend system based on silkworm silk fibroin (SF) and polylactic acid (PLA) was systematically investigated to understand the interaction and miscibility of proteins and synthetic biocompatible polymers in the macro- and micro-meter scales, which can dramatically control the cell responses and enzyme biodegradation on the biomaterial interface. Silk fibroin, a semicrystalline protein with beta-sheet crystals, provides controllable crystal content and biodegradability; while noncrystallizable PDLLA provides hydrophobicity and thermal stability in the system. Differential scanning calorimetry (DSC) combined with scanning electron microscope (SEM) showed that the morphology of the blend films was uniform on a macroscopic scale, yet with tunable micro-phase patterns at different mixing ratios. Fourier transform infrared analysis (FTIR) revealed that structures of the blend system, such as beta-sheet crystal content, gradually changed with the mixing ratios. All blended samples have better stability than pure SF and PLA samples as evidenced by thermogravimetric analysis. Protease XIV enzymatic study showed that the biodegradability of the blend samples varied with their blending ratios and microscale morphologies. Significantly, the topology of the micro-phase patterns on the blends can promote cell attachment and manipulate the cell growth and proliferation. This study provided a useful platform for understanding the fabrication strategies of protein-synthetic polymer composites that have direct biomedical and green chemistry applications.