(192g) Effect of Matrix Particle Size and Loading On the Overall Performance of Injectable Allograft/Polyurethane Composite Bone Void Fillers

Treatment of craniofacial and orthopedic bone defects is a challenging problem due to the requirements for both biological and mechanical properties. While autograft bone is an attractive choice for treating bone defects, it is limited in supply and can be difficult to fabricate into shapes conforming to irregularly shaped defects. Injectable, settable biomaterials eliminate this problem with the ability to cure and conform to wound geometry in situ. We have developed injectable allograft/polymer composite bone void fillers (BVF) for the treatment of metaphyseal bone defects, and evaluated their potential to promote bone healing in a rabbit femoral condyle plug model. The BVF comprised allograft bone particles (small: <100 µm or large: 100-500 µm), demineralized bone matrix (DBM), and a reactive two-component lysine-derived polyurethane (PUR). For the synthesis of the PUR phase, two polyester triol formulations were tested with varying percentages of glycerol, E-caprolactone, and DL-lactide. The PUR biocomposites supported cellular infiltration and remodeling in femoral condyle defects in rabbits at 8 and 16 weeks. µCT images show that the BVF integrated with host bone. Histological sections were stained with H&E and Goldner’s trichrome to qualitatively assess the in vivo inflammatory response and the quality of new bone in the scaffolds. Analysis of the histological sections suggests that small allograft particles and DBM hindered new bone formation, possibly due to the smaller pore size distributions characteristic of these materials compared to the scaffolds with larger allograft particles. Histological sections also revealed minimal evidence of an adverse inflammatory response induced by unreacted components from the biocomposite or degradation products from the cured polymer. From all the compositions evaluated in this study, the biocomposite with 47 mass% of large allograft particles, no DBM, and porosity in the range of 45-50% offers the best alternative for the treatment of metaphyseal bone defects. These results underscore the potential of the injectable biocomposites technology for effectively balancing the need for mechanical strength and active remodeling of bone grafts.