Packaging and Sterilization of UHMWPE

Summary of Sterilization Processes for UHMWPE Implants. Note that Gamma Air Sterilization Is Listed as a Historical Reference, for Comparison Purposes Only 

Sterilization process Packaging type Gamma radiation dose Contemporary method  

Gamma inert Barrier packaging, reduced oxygen atmosphere 25-40 kGy Yes 

The purpose of this chapter is to review historical and contemporary packaging and sterilization methods for UHMWPE. Obviously, all of the sterilization methods currently employed by the orthopedic community fulfill their intended purpose, namely the eradication of bacterial agents, which may result in sepsis and premature revision. The diverse sterilization methods in current use reflect the lack of scientific consensus as to which of the currently favored sterilization methods provides the most advantageous long-term UHMWPE product for the ultimate user, namely the patient. 

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During the 1990s, the packaging and sterilization of UHMWPE was a controversial topic. As recently as 1995, UHMWPE was typically sterilized with a nominal dose of 25 to 40kGy of gamma radiation in the presence of air. By 1998, all of the major orthopedic manufacturers in the United States were either sterilizing UHMWPE using... 

In the Longevity process, the UHMWPE bars are warmed, placed in a carrier on a conveyor, and are exposed to electron beam radiation, with a total dose of 100 kGy. The UHMWPE does not heat above the melt transition during the crosslinking. After irradiation, the UHMWPE is heated above the melt temperature (>135°C) for stabilization of free radicals. Components are then machined from the Longevity material, enclosed in gas-permeable packaging, and sterilized by gas plasma. 

This Handbook is organi2ed into three main sections. The first section, consisting of three chapters, reviews the basic scientific and engineering foundations for UHMWPE. For example, in Chapter 2, we explain how UHMWPE must be formed into bulk components from the resin powder using extrusion or compression molding techniques. In Chapter 3, we review the techniques associated with sterilization and packaging of UHMWPE implants. 

An example of historical air-permeable packaging used with gamma sterilization, consisting of a box, two nested, polymeric packages, and an inner foam insert (Osteonics, Allendale, NJ). The UHMWPE component is not shown. 

The UHMWPE material used for Polycentric components was RCH 1000. Gunston sterilized the UHMWPE tibial components he personally manufactured using an autoclave. However, orthopedic companies like Howmedica, which fabricated most of the Polycentric components implanted during the 1970s, sterilized their UHMWPE components with gamma radiation and used air-permeable packaging. 

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