Abstract: PURPOSE: To develop an injectable thermosensitive hydrogel composite scaffold loaded with a high-activity integrin α5β1-binding peptide and to evaluate its ability to promote osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) as well as to enhance mandibular bone defect repair. METHODS: A high-activity integrin α5β1-binding peptide was synthesized using the Fmoc solid-phase peptide synthesis method and incorporated into an Arg-Gly-Asp（RGD） modified alginate-based thermosensitive hydrogel to fabricate an injectable peptide-hydrogel composite scaffold. The microstructure and mechanical properties of the scaffold were characterized by scanning electron microscopy and mechanical testing. In vitro, hBMSCs were cultured on the scaffolds; cell proliferation was assessed using the CCK-8 assay, and osteogenic differentiation was evaluated by alkaline phosphatase (ALP) staining. In vivo, a mandibular bone defect model was established in New Zealand white rabbits, and the composite scaffold was implanted into the defect sites. New bone formation was assessed by micro-computed tomography (Micro-CT), HE staining, Masson's trichrome staining, and immunohistochemical analysis of collagen type I alpha 1 chain (COL1α1) and osteocalcin (OCN), followed by statistical analysis. RESULTS: The peptide-hydrogel composite scaffold exhibited good injectability at room temperature and rapidly gelled at body temperature, forming a uniform porous microstructure. In vitro, compared with the control group, the high-activity integrin α5β1-binding peptide significantly promoted hBMSCs adhesion and proliferation and enhanced osteogenic differentiation. In vivo, the peptide-loaded hydrogel group showed significantly increased trabecular thickness (Tb.Th), trabecular number (Tb.N), and bone volume fraction (BV/TV%), along with a markedly reduced trabecular separation (Tb.Sp). Micro-CT and histological analyses demonstrated substantially enhanced new bone formation within the defect region. Immunohistochemical staining further revealed higher expression levels of COL1α1 and OCN than those in the control groups, indicating enhanced osteogenic activity. CONCLUSIONS: The high-activity integrin α5β1-binding peptide significantly improves bone regeneration efficiency by promoting hBMSC adhesion, proliferation, and osteogenic differentiation. The injectable thermosensitive hydrogel composite scaffold loaded with this peptide showed favorable biocompatibility and robust osteogenic repair capacity in a rabbit mandibular defect model, suggesting its potential value as a bone tissue engineering strategy for mandibular defect repair.

Key words: Mandibular defect, Bone tissue engineering, Integrin-binding peptide, Bone regeneration