Method of making an endoprosthesis of compact thermoplastic composite

Abstract

An endoprosthesis of compact thermoplastics including composite materials is disclosed. The endoprosthesis includes a plurality of prefabricated fibers such as carbon or aramid. Thermoplastics such as polyacrylates, polyaryl ether ketones, polycarbonates, polyether sulphones, polyethylenes or polyproplyenes are used as a binding agent. The prefabricated fibers have an internal core with predominately longitudinally oriented fibers and an enclosing covering with mutually intersecting fibers. The prefabricated fibers are cut to a length which is preferably five times their minimum diameter. The fibers are oriented substantially parallel to the major axis of the endoprosthesis. During molding and even in shallow cross- sections relative to the major axis of the endoprosthesis, each prefabricated fiber is at least partially overlapped by an adjoining prefabricated fiber. It is preferred that the prefabricated fibers at their ends take various forms including tapering, bevelled, and may have scooped, spherical or dished areas. A compression mold is used. The compression mold defines a female cavity which contains the elongate male profile of the endoprosthesis. Preheated prefabricated fibers are placed into the compression mold of the endoprosthesis. The fibers are all generally parallel to the major axis of the mold. Relative to cross-sections taken across the major axis of the mold, the number and array of the fibers varies as the particular cross-section varies. Specifically, at large cross-sections many fibers are found; at small cross-sections, the fibers are reduced in number.