UHMWPE Orthopedic Implants
Because of its toughness, friction properties and inertness, ultrahigh molecular weight polyethylene is a good candidate material for orthopedic implants. (RDC 1/5/2011)
“The use of synthetic polymers, e.g., ultra high molecular weight polyethylene, with metallic alloys has revolutionized the field of prosthetic implants, e.g., their use in total joint replacements for the hip or knee. Wear of the synthetic polymer against the metal of the articulation, however, can result in severe adverse effects which predominantly manifest after several years. Various studies have concluded that such wear can lead to the liberation of ultrafine particles of polyethylene into the periprosthetic tissues. It has been suggested that the abrasion stretches the chain folded crystallites to form anisotropic fibrillar structures at the articulating surface. The stretched-out fibrils can then rupture, leading to production of submicron sized particles. In response to the progressive ingress of these polyethylene particles between the prosthesis and bone, macrophage-induced resorption of the periprosthetic bone is initiated. The macrophage, often being unable to digest these polyethylene particles, synthesize and release large numbers of cytokines and growth factors which can ultimately result in bone resorption by osteoclasts and monocytes. This osteolysis can contribute to mechanical loosening of the prosthesis components, thereby sometimes requiring revision surgery with its concomitant problems.” [Merrill et al, US Patent 7,858,671 (1`2/28/2010)]
Applications
Implants
Medicine
Orthopedic Implants
Orthopedics
Ultrahigh Molecular Weight Polyethylene (UHMWPE)
Recent US Patents
1/4/2011
7,863,348
Ultra high molecular weight polyethylene articles and methods of forming ultra high molecular weight polyethylene articles
Abt and Schneider-Storrer of Zimmer, Switzerland, formed implantable articles from a crosslinked ultrahigh molecular weight polyethylene ("UHMWPE") blend stabilized with Vitamin E. The crosslinked UHMWPE blend may be prepared by combining the UHMWPE material and vitamin E prior to irradiating the UHMWPE blend with electron beam radiation at a sufficient radiation dose rate to induce crosslinking. The crosslinked UHMWPE blend may be incorporated into a variety of implants, and in particular, into endoprosthetic joint replacements. (RDC 7/18/2011)
12/28/2010
7,858,671
Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices
Merrill et al of General Hospital and Massachusetts Institue of Technology, Massachusetts,formeda medical prosthesis for use within the body which is formed of radiation treated ultra high molecular weight polyethylene having substantially no detectable free radicals. Preferred prostheses exhibit reduced production of particles from the prosthesis during wear of the prosthesis, and are substantially oxidation resistant. (RDC 7/7/2011)
9/28/2010
7,803,310
Crosslinked Polyethylene Article
Ultrahigh molecular weight polyethylene (UHMWPE) is a useful implant bearing material for articulating joints. However, wear debris can result in lysis of the surrounding tissue requiring corrective surgery. Cheal has developed a more stable and wear resistant material by crosslinking and reducing oxidation during fabrication. The preform is, first, crosslinked by gamma or electron beam radiation. After crosslinking, the material is kept in a low oxygen environment until use. He shapes the crosslinked preform by machining in a low oxygen environment, heat-treats the shaped implant in a low-oxygen environment, and carefully inspects the final product for conformance to specifications. The product is kept in an oxygen free environment until implantation. The key is to keep the material, after irradiation, in as oxygen free atmosphere as possible until use.