BONE REGENERATION ON SURFACE-MODIFIED POLYMERIC IMPLANTS

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Two major areas of biomaterials which present the biomedical industry and orthopedic community with a formidable challenge pertain to their use in joint replacement and tissue engineering. Inability of most materials used in orthopedic implants to form an interfacial bond with bone is often associated with loosening and failure. This, and the growing interest in tissue engineering and the great promise this technology holds for use in critical biomedical applications directed our attention to explore the use of proprietary surface activation and microcellular foam technologies to develop unique substrates to achieve tissue regeneration about key polymeric implants. Thus, the primary objective of Phase I of this program is to determine the feasibility of achieving bone regeneration about surface-phosphonylated polypropylene (PP), polyethylene (PE), and polylactide/glycolide (PLG) substrates with and without microporous skin, when placed at 6 to 8 weeks as transcortical implants in goat femur. Thus, Phase I entails (1) the preparation of an absorbable PLG; (2) conversion of PLG, PE and PP to implantable rods; (3) formation of microporous skin on one set of rods; (4) surface phosphonylation and characterization of the rods with and without microporous skin; (5) implanting surface modified PLG rods as in 5, which have been treated with a cell attachment factor; and (7) conducting a histological examination and push-out tests of the retrieved femur segments to determine bone regeneration and/or ingrowth, and bone/implant interfacial bond strength. Results of Phase I study will be used in the design of Phase II plans which include conducting (1) detailed animal study on optimally surface-modified ultrahigh molecular weight polyethylene (UHMW-PE) bone implants; (2) development of a selected orthopedic device and completing safety study on an implant prototype; and (3) pursuing in vitro and in vivo studies on the sue of unique phosphonylated microporous PLG copolymers as scaffold for bone regeneration. PROPOSED COMMERCIAL APPLICATION: Successful application of the surface phosphonylation technology in conjunction with an easily formed microporous and/or surface-microtextured implant is expected to have an immediate, positive impact on the development of cementless, polymeric bone prostheses with hybridized bone/implant interface. This is expected to (1) find immediate application in high and low load- bearing components of artificial joints and hard tissue resurfacing, and (2) provide a new incentive to pursue development of fiber-reinforced polymeric composites as substitutes for metals in several orthopedic implants.