Biomet Manufacturing Corporation

Jordan H Freedman

David W Schroeder

H Gene Hawkins

Brian David Salyer

James E Gunter

David Wayne Schroeder

Heat treating UHMWPE by applying pressure with radial constraint at suitable times during a heating protocol reduces or eliminates cavitation, which is otherwise observed to occur when the UHMWPE is heated to a temperature above 300&#xb0; C. Heat treated UHMWPE can undergo subsequent processing involving crosslinking, deformation, doping with antioxidant, and homogenizing or annealing. Heating during these steps can be carried out even above the onset melt temperature of the UHMWPE without loss of physical properties.

Method for making ultra high molecular weight polyethylene

Methods provide a non-eluting antioxidant doped UHMWPE in the form of an implant bearing component. The process includes the steps of: (a) providing a preform; (b) irradiating the preform with &#x3b3;-irradiation to crosslink the UHMWPE; (c) doping the crosslinked preform by exposing it to an antioxidant composition at a temperature below the melting point of the UHMWPE; (d) removing the doped material from contact with the antioxidant composition; and then (e) annealing by heating the doped material at a temperature above 30&#xb0; C. and below the melting point of the UHMWPE; followed by (f) making an implant bearing component from the doped material, wherein at least 1 mm but no more than about 15 mm of material are removed to make the component.

Antioxidant doping of crosslinked polymers to form non-eluting bearing components

Solid-state deformation processing of crosslinked high molecular weight polymers such as UHMWPE, for example by extrusion below the melt transition, produces materials with a combination of high tensile strength and high oxidative stability. The materials are especially suitable for use as bearing components in artificial hip and other implants. Treated bulk materials are anisotropic, with enhanced strength oriented along the axial direction. The material is oxidatively stable even after four weeks of accelerated aging in a pressure vessel containing five atmospheres of oxygen (ASTM F2003). Because of its oxidative stability, the deformation processed material is a suitable candidate for air-permeable packaging and gas sterilization, which has thus far been reserved for remelted crosslinked UHMWPE.

Solid state deformation processing of crosslinked high molecular weight polymeric materials

Solid-state deformation processing of crosslinked high molecular weight polymers such as UHMWPE, for example by extrusion below the melt transition, produces materials with a desirable combination of physical and chemical properties. Crosslinked bulk materials are heated to a compression deformable temperature, and pressure is applied to change a transverse dimension of the material. After cooling and stress relieving, a treated bulk material is obtained that has enhanced tensile strength in the axial direction orthogonal to the dimension change. In preferred embodiments, medical implant bearing materials are machined from the treated bulk material with the in vivo load bearing axis substantially parallel or coincident with the axial direction of the treated bulk material.

A radiation crosslinked (50 kGy), pressure-treated UHMWPE material has been developed by applying compressive force on a crosslinked polymer in a direction orthogonal to an axial direction. The deformed material is then cooled while held in a deformed state. The resulting material is anisotropic, with enhanced strength oriented along the axial direction. The directionally engineered material is oxidatively stable even after four weeks of accelerated aging in a pressure vessel containing five atmospheres of oxygen (ASTM F2003). Because of its oxidative stability, the deformation processed material is a suitable candidate for air-permeable packaging and gas sterilization, which has thus far been reserved for remelted highly crosslinked UHMWPEs.

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Fort Wayne, IN, United States of America

Jordan H Freedman