Bioresorbable Bone Graft Composed of an RGD-Enriched Recombinant Human Collagen Polypeptide Induced Neovascularization and Regeneration of Mature Bone Tissue

Bone graft materials provide a scaffold for migrating cells for bone regeneration. One of the major challenges is to support adequate neovascularization in the graft materials and bone tissue. Vascular endothelial cells have been shown to recognize the integrin-binding Arg-Gly-Asp (RGD) sequence in natural extracellular matrix (ECM) molecules. Here, we report a bone graft material composed of an RGD-enriched recombinant polypeptide based on human type I collagen alpha 1 chain (RCPhC1) and propose a category of bone graft materials called the recombinant bone matrix. RCPhC1 demonstrated significantly increased human umbilical vein endothelial cell attachment in vitro and was further processed through freeze casting and heat crosslinking processes to generate porous granular bone graft, in which RGD sequences remained canonical. When grafted in the rat model, RCPhC1 bone graft demonstrated a uniquely increased presence of CD34+ endothelial cells within the graft material. Bone tissue was found directly in contact with the pore structure of RCPhC1 bone graft, resulting in the regeneration of large bone tissue. By contrast, the combined demineralized and decellularized bone allograft containing bone collagen in the ECM did not show vascular formation within the graft material. When applied to canine tooth extraction socket, RCPhC1 bone graft rapidly induced highly vascularized regenerating tissues, which became a mature bone with the bone marrow tissue. These results indicate that RCPhC1 bone graft is a promising material and generated highly active bone tissues, which rapidly matured.