Chemically cross-linked silk fibroin hydrogel with enhanced elastic properties, biodegradability, and biocompatibility

Introduction In this study, the synthesis of SF hydrogel via a chemical cross-linking reaction using γ-ray irradiation was investigated and the resultant hydrogel was characterized. Two different hydrogels were investigated:... [ view full abstract ]

Introduction
In this study, the synthesis of SF hydrogel via a chemical cross-linking reaction using γ-ray irradiation was investigated and the resultant hydrogel was characterized. Two different hydrogels were investigated: SF P-gel induced by β-sheet structure and chemically cross-linked hydrogel prepared by γ-ray irradiation. The secondary structures and strengths of the gels were compared. Furthermore, the swelling behavior, biodegradation, and cell viability of human mesenchymal stem cells (hMSCs) on the SF hydrogel were evaluated.

Methods
Freshly regenerated SF solutions of various concentrations (2.3%–7.9%) were poured into a petri dish and irradiated with γ-rays from a Co-60 source. The radiation dose varied from 15–60 kGy and the dose rate was 15 kGy/h, at room temperature. The irradiated samples were cut into small pieces to compare with SF P-gel with regard to various properties.

Result and discussion
The radiation technique seems to be an excellent pathway for the preparation of hydrogels because polymer solutions undergo chemical cross-linking on irradiation to yield a hydrogel. By contrast, most chemical cross-linking reactions of SF can induce a modification of proteins, resulting in structural destabilization and inflammation by exposure to toxic organic solvents and cross-linking agents. In this study, the SF C-gel was prepared by γ-ray irradiation, which induced intermolecular cross-linking reactions. In order to investigate the effect of irradiation on the gelation of the SF solution, the solutions were γ-ray irradiated at various doses of 15, 30, 45, 60, 75, and 90 kGy. Regardless of the SF concentration and irradiation doses, SF hydrogel was formed immediately after irradiation, as shown in Figure 1A. However, as shown in Figure B, cracks occurred in the hydrogel at doses higher than 60 kGy. A suitable absorption dose for an SF solution was 60 kGy. Therefore, the experiment was performed using the dose of 60 kGy.