Tuning the properties of silk fibroin biomaterial via chemical cross-linking

Abstract

Protein-based biomaterials with innovative and controlled performance are being sought due to their unique characteristics for use in biomedical fields such as neural implants, drug delivery systems, cell-based therapies and soft tissue engineering. Here, we present a versatile approach for the synthesis of photo-crosslinkable fibroin silk biomaterial with highly tunable mechanical, chemical and biodegradation properties. Unlike the crystalline rich silk fibroin reported previously, the covalently cross-linked fibroin protein photoresist (FPP) via controlled light-induced radical grafting, allows generating a new amorphous biomaterial with tunable properties. It appears that the use of photo-reactive acrylate groups to cross-link FPP induces plasticity that can be tuned by changing the photoinitiator concentration of the film. Tensile strength measurements revealed that elasticity was higher for FPP UV-cross-linked materials with higher concentration of photoinitiator. FTIR and relative humidity measurements showed that hydrophilicity was higher for UV-cross-linked FPP. These materials display stiffness between 0.01-1.5 GPa and tensile strains up to 60%, covering a significant portion of the properties of native soft biomaterials. Besides, in vitro proteolytic degradation of the photocrosslinked FPP films demonstrate a tunable degradation rate over a period ranging from hours to weeks. Those biomaterials have been successfully micropatterned by photolithography techniques across several orders of magnitude (μm to cm) and a systematic study of direct patterning of the fibroin protein to form high fidelity and high-resolution structures has been reported. It was also shown that the fabricated protein features are well suited to cell adhesion. The development of protein-based material with controlled and tunable elasticity that can be easily photo-patterned into centimeter, micrometer and nanometer components will allow a wide range of applications in biomedical fields requesting a natural functional tissue.