The ultimate goal of this research proposal is to develop novel in situ polymerizable, biodegradable hydrogels for treating dental defects with guided bone regeneration. Based on a novel highly unsaturated linear copolyester developed in our laboratory, poly(propylene fumarate-co- ethylene glycol) (P(PF-co-EG)), these hydrogels will have a covalently bound osteopontin (OPN) peptide for enhancing bone growth while diminishing fibrous infiltration. The peptide will be appropriately spaced from the hydrogel network to provide for sufficient interaction between the peptide and osteoblast receptors. The unsaturated linear P(PF-co-EG)-co-OPN peptide copolyester will be crosslinked in situ via an addition polymerization with N-vinyl pyrrolidinone. Additional components of an injectable formulation will include gelatin porogen, a radical polymerization initiator, and an accelerator. A three-step approach will be followed to engineer optimal in situ polymerizable hydrogels using novel video microscopy and image analysis techniques developed in our laboratory. The first step will involve the production of thin films of hydrogels exhibiting minimal or no adhesion of either fibroblasts or osteoblasts. After choosing the polymer compositions that eliminate non-specific cell adhesion, bioactive thin films will then be produced and evaluated. Finally, the hydrogel/peptide formulations that minimize adhesion and migration of fibroblasts while promoting adhesion and migration of osteoblasts will be tested using a three-dimensional cell/polymer model developed in our laboratory to determine the optimal porosity and pore size of hydrogel scaffolds for maximum bone formation in vitro. The efficacy of the optimized peptide composite formulation to form new bone in an orthotopic site to restore osseous continuity will be tested using an acute segmental critical-size long-bone defect model in rats. New bone formation and graft consolidation to host bone will be assessed radiographically as a function of time. Light and fluorescence microscopy will allow quantitative and qualitative analyses of the extent, character and dynamics of new bone formation. The mechanical properties of the grafted bones will be measured to verify restoration of the integrity of the reconstituted region under functional loads. The proposed project will provide clinically valuable information regarding new injectable dental biomaterials for guided bone regeneration. It will lead to a major advance in treating dental defects using biocompatible and biodegradable polymers which are becoming particularly important because of the renewed concern for the safety of non-degradable implants and the potential for disease transmission with allografts.
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