DEVELOPMENT OF SELF-ANCHORING BONE IMPLANTS .1. PROCESSING AND MATERIAL CHARACTERIZATION

We recently designed and produced a family of new swelling-type materi als that are potentially capable of self-fixation in bone. These mater ials are designed to absorb body fluids and swell by small amounts, wh ich will allow the implants made from these materials to achieve self- fixation by an expansion-fit mechanism. The developed material system is essentially a crosslinked random copolymer based on poly(methyl met hacrylate-acrylic acid). For potential structural (load-bearing) bioim plant applications, we reinforced this copolymer with AS-4 carbon and Kevlar 49 fibers. The details of processing these materials and the st eps involved in optimizing their microstructures are presented in this article. A set of mechanical tests were performed on these materials in both dry and swollen conditions to measure their moduli and yield s trengths. In the dry state, the copolymers were found to exhibit Young 's moduli in the range of 3 to 4 GPa and yield strengths in the range of 70 to 85 MPa. The reinforced composites exhibited moduli in the ran ge of 15 to 65 GPa and yield strengths in the range of 125 to 500 MPa. Upon controlling the volumetric swelling in these materials to be les s than about 10%, the loss in mechanical properties was found to be le ss than about 30%. These hygromechanical properties are well suited fo r self-anchoring bone implant applications. (C) 1997 John Wiley & Sons , Inc.