**4.1 Carbon fiber polymeric composites**

Carbon fiber ultra-high-molecular weight polyethylene (UHMWPE) composites were introduced in the early 1980s as tibial bearings.(Fruh 1998) However, the clinical performance was poor with many revisions. Load can be transferred only by compressive forces between the fibers and matrix, resulting in an inefficient reinforcement. Carbon fiberreinforced epoxy composites (CFRP) were introduced in Europe in the late 1980s as acetabular components with alumina femoral heads. Simulator studies reported a wear rate of 1 to 3 µm per million cycles. Canine hips with CFRP cups were implanted in six dogs for up to 5.5 years with no adverse consequences. A clinical study began in 1989, and 101 patients received cups of CFRP. In cases of revision, there were few particles in the tissue and the biologic response was benign. The wear of retrieved components was 6.1 to 6.3 µm/year. These wear rates are comparable to those seen with HXPE materials. Epoxy resins are thermoset materials and cannot be shaped other than by machining once they have "set" via chemical reaction. Many thermoplastic composites can be shaped by combinations of heat and pressure and "set" thereafter. Polyether ether ketone (PEEK) is a thermoplastic high performance polymer that is attractive as a composite matrix owing to its strength, toughness, stability, and biocompatibility.(Wang 1999)
