Objective: To evaluate an injectable Thai silk fibroin/collagen in situ-forming hydrogel induced by surfactant as a carrier to encapsulate cell and growth factor for bone regeneration.

Materials and Methods: Silk fibroin/collagen hydrogels induced by a surfactant mixture of oleic acid and poloxamer-188, both with and without rat mesenchymal stem cells (MSCs) and/or human platelet-rich plasma (PRP), were injected into 6-mm bone defects in an ulnar diaphysis of 2-month old Wistar rats. In situ gel formation was observed intraoperatively. Longitudinal assessment of bone regeneration was done by plain radiograph, micro-CT scan, and histology analysis.

Results: At 12 weeks, more new bone formation was found in the study groups with hydrogel injection compared with the control group, but the difference was not statistically significant. Limited foreign body reaction was observed. The hydrogel degraded into fragments, which were still histologically observed at 12 weeks. Differences in morphometric parameters and histological results could not be demonstrated among the hydrogel groups with or without cell and/or growth factor.

Conclusion: The injectable surfactant-induced Thai silk fibroin/collagen in situ-forming hydrogel has potential for promoting bone formation with good biocompatibility, although evidence of the efficacy in encapsulation of MSCs and growth factor for delivery was not yet clear.

Keywords: Silk, Fibroin, Hydrogel, Collagen, Cell encapsulation, Growth factor carrier, Bone regeneration