Vacuum Compression Moulding Presses - Articles & Resources

Method for Compression Molding a Cross-linked Preform
This invention relates to improved bearings for use in orthopaedic implant prosthesis and particularly to methods for making ultra high molecular weight polyethylene or UHMWPE bearings by molding a cross- linked preform by the application of sufficient heat and pressure. Such UHMWPE resin is commonly used for bearings in hip, knee, shoulder and elbow prostheses. Typically, the stock or the molded bearings are irradiated and subsequently heat treated or heat annealed. The irradiation generates molecular cross-links and free radicals. The free radicals are subsequently eliminated by the heat treating processes.

This invention is directed to a method for molding a bearing from a preform which has previously been cross-linked by obtaining such a preform and placing it in a press mold defining the desired bearing shape or near net shape and applying heat and pressure in the mold to form the bearing. The preform may be produced from irradiated polymer resin to form cross-links and free radicals followed by a molding process. Also, in some embodiments, the irradiated UHMWPE preforms may already be heat treated to quench the free radicals.

The present invention is designed to reduce the amount of wear debris generated from UHMWPE bearings. Such wear debris has been associated with bone and soft tissue deterioration leading to implant loosening, which may necessitate even revision surgery. The present invention is also to improve the wear resistance of UHMWPE bearings. Additional features of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.

Source: http://www.wipo.int/