The design, synthesis, characterization, and mechanical testing of a novel degradable polymeric biomaterial for use as a bone substitute

This work focuses on the development of a candidate material for temporary synthetic bone. The material is a particulate filled composite based on an unsaturated linear polyester. The components are mixed with a monomer that cross links the double bonds of the unsaturated polyester. Degradation occurs via hydrolytic degradation of backbone polymer's ester linkages. This strategy of prepolymer synthesis via condensation polymerization in the laboratory followed by cross linking the unsaturated prepolymer via radical polymerization at surgery offers design flexibility. The radical polymerization allows curing during surgery to facilitate reconstruction of various shaped bone defects. The laboratory synthesis of the prepolymer allows alterations of its composition and physical properties to effect desired properties in the resulting composite material. The effects of several composite material formulation recipes on the in vitro mechanical properties and in vivo histologic characteristics of the resulting material are presented. The prepolymer molecular weight, presence of a leachable salt, and amount of cross linking monomer had strong effects on the resulting strength and modulus of the composite. These strengths were of a magnitude appropriate for consideration of the material as a temporary trabecular bone substitute. The in vivo studies in a rat proximal tibia model demonstrated progressive growth of new bone against the receding surface of the degrading material, and insinuation of new bone trabeculae into the interior of the degrading specimen. There was an absence of a foreign body inflammatory response to the presence of this material over a five week time span. The material is an attractive candidate for temporary replacement of trabecular bone. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)