(696b) Injectable Allograft Bone-Polyurethane Composite Foam Scaffolds: Tuning Mechanical Properties by Controlling Scaffold Porosity

Injectable biomaterials offer several advantages relative to implants due to their ability to cure in situ, thus enabling filling of irregularly-shaped contours using minimally invasive procedures. In this study, we have developed injectable, biodegradable polyurethane (PUR) scaffolds with allograft mineralized bone particles (MBP) or surface-demineralized MBP (SDBP) as fillers for the treatment of orthopaedic craniofacial bone defects. The three-component system comprising allograft bone, polyester triol hardener, and isocyanate prepolymer is mixed by hand and injected as a paste, which subsequently foams and cures in situ. By varying the composition of the polyol hardener component, composites with tunable porosities, mechanical properties, and cure times have been prepared. The compressive strengths, which are highly dependent on the scaffolds' porosity, were in the range of 4.39 ? 47.4 MPa. The mechanical properties were similar to those of tough plastics, with yield strains exceeding 5% for all but the highest porosity materials tested. Thus it is possible to prepare tough composites that are resistant to the brittle fracture observed clinically for calcium phosphate cements. These biomaterials also support cellular viability and proliferation. The PUR scaffolds can be combined with growth factors such as BMP-2 to enhance healing of bone defects.

MBP/PUR and SDBP/PUR scaffolds were injected into New Zealand White rabbit bilateral femoral plug defects. Histological and X-ray studies suggest that after six weeks the scaffolds undergo substantial remodeling and integration with host tissue, while supporting the ingrowth of cells and new tissue. Future studies will investigate their applicability for regenerating craniofacial bone in a critical-sized rabbit calvarial defect model.