Physically Crosslinked and Chemically Photocrosslinked Silk Hydrogel Manipulated via Molecular Weight Control

Abstract

In this study, alkaline hydrolysis was utilized using heat-alkaline treatment (HAT) method to manipulate the silk hydrogel properties. By regulating the hydrolysis time (10-180 min), a broad molecular weight range of silk fibroin (SF) could be obtained (77.2-258.6 kDa). The change of molecular weight of SF also greatly affected the physical properties (i.e., swelling ratio, shear modulus, transparency) of SF hydrogel. As a result of structural analysis, the molecular weight of SF played a crucial role in the construction of microstructure of SF hydrogel. These findings indicate that physically crosslinked SF hydrogels of variable physical properties can be fabricated based on molecular weight control. However, this manipulation could not improve the mechanical property (i.e., brittleness) of typical SF hydrogel in addition to a long gelation time. Chemical crosslinking of SF can overcome these problems by making strong covalent bond in a network within predictable gelation time. Therefore, new strategy was developed for making chemically photo-crosslinked SF hydrogel without using of fresh SF aqueous solution. By lowering the molecular weight of SF, the stability of SF aqueous solution could be enhanced and consequently, this allowed direct chemical modification of SF. Subsequently, photo-crosslinkable silk fibroin methacrylate (SFMA) was synthesized using the hydrolyzed SF and chemically photo-crosslinked SF hydrogel (SFMA hydrogel) could be fabricated with a rapid gel formation. The structural characteristics, physical properties, and performance of chemically crosslinked SF hydrogel were intensively examined on the effect of immobilized MA amount on SF and molecular weight of SF. It is expected that SFMA hydrogel has a high potential use in biomedical applications due to its excellent gel properties and performance (e.g., transparency, resiliency, and injectability).