The limited supply and poor mechanical properties of autograft bone have prompted a search for alternatives. Considering that synthetic injectable biomaterials typically lack the osteogenic properties of autograft, there is a compelling need for an injectable biomaterial that possesses mechanical properties comparable to host bone and also actively remodels.  To address this clinical need, we are developing injectable low-porosity biocomposites comprising mineralized allograft bone particles in a biodegradable polyurethane matrix. Recombinant human bone morphogenetic protein-2 (rhBMP-2) was added to some formulations to enhance the osteogenic properties of low porosity injectable composites, and the effects of rhBMP-2 dose on new bone formation at 6 and 12 weeks were investigated in a rabbit model. Biocomposites exhibited compressive strengths comparable to trabecular bone. Histological sections and mCT images of the biocomposites without rhBMP-2 after 6 and 12 weeks of implantation revealed extensive allograft resorption, cellular infiltration, and new bone formation.  Appositional new bone growth was observed, as well as bridging of residual allograft bone particles (A) by new bone (NB), suggesting that the biocomposites remodeled by creeping substitution of the allograft with minimal resorption gaps.  Incorporation of rhBMP-2 enhanced new bone formation relative to the biocomposite without rhBMP-2, as evidenced by the presence of less residual allograft bone particles and more new bone. Thus by providing the favorable properties of injectability, weight-bearing mechanical strength, and active remodeling, the biocomposites may be a promising approach for developing functional biomaterials that maintain sufficient mechanical strength while remodeling to form new bone.

Low porosity injectable biocomposites incorporating rhBMP-2 enhance bone remodeling in a rabbit femoral plug model

242nd National Meeting (2011)

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