UHMWPE sterilization

Costa L., M.P. Luda, L. TrossarelU, et al. 1998a. Oxidation in orthopaedic UHMWPE sterilized by gamma-radiation and ethylene oxide. Biomaterials 19 659-668. 

Costa L, Luda MP, Trossarelli L, Brach del Prever EM, Crova M, GalUnaro P. Oxidation in Orthopaedic UHMWPE Sterilized by gamma-radiation and ethylene oxide. Biomaterials. 1998 19 659-68. 

Chamley personally held strong views on the subject of UHMWPE sterilization. In personal correspondence with Thackrays, dated October 17, 1971, Chamley discusses seven reasons why gamma sterilization is preferable to ethylene oxide. The context of this letter is apparently in response to the suggestion by an official from the Scottish... 

While data related to contact stress is useful, it is not the sole governing entity with respect to failure of UHMWPE components. Factors that influence the oxidation of the UHMWPE (e.g., steriUzation, type, packaging), in combination with load distribution, affect its performance. Improvements in TAR UHMWPE component clinical perfoimance likely occurred not only from the development of congruent designs that minimized contact stress but also improvements in UHMWPE sterilization and packaging (e.g., the STAR device, which was gamma sterilized in air and is currently sterilized in a nitrogen-vacuum). 

If the mechanism proposed by Mallegol [55] was true, then vitamin E would not react when polymer is aged in inert atmosphere, typically during the UHMWPE sterilization by y radiation. It is in contradiction with results obtained by Costa et al. [57] according to which vitamin E is consumed when polymer is irradiated under nitrogen, at a (paradoxically) higher rate than when polymer is irradiated under air (Figure 3.3). 

Radiation Sterilization. In addition, the method of radiation sterilization to improve the wear resistance of UHMWPE components has been modified (24). This has typically involved packaging the PE cups either in an inert gas (25), in a partial vacuum or with an oxygen scavenger (12). 

R.M. Streicher, Sterilization and long-term aging of medical-grade uhmwpe, Radiat. Phys. Chem., 46 893-896, 1995. Proceedings of the 9th International Meeting on Radiation Processing, 1994, Pt. 1. 

Additional source of information for UHMWPE acetabular cups arises from the quantitative analysis of polarized Raman spectra. Figure 17.6 shows photographs and the outcome of such analysis for two acetabular cups, which were retrieved after substantially different in vivo lifetimes. The retrieved acetabular cups were both belonging to male patients and sterilized by y-rays, but produced by different processes. One acetabular component (manufactured in 2002 by Biomet Inc.) was prepared by isostatic compression molding and sterilized before implantation by a dose of 33 kGy of y-rays. It was retrieved due to infection after 2 years 5 months. This cup will be referred to as the short-term retrieval. The other retrieval (manufactured in 1995 by Zimmer Inc.) was prepared by Ram-extruded molding and sterilized in air by a dose of 25-37 kGy of y-rays. For this latter cup, the follow-up pe-... 

H.H. Trieu, R. Avent, Effect of sterilization on shelf-aged UHMWPE tibial inserts, in Transactions of the 21st Annual Meeting of the Society for Biomaterials,... 

Comparing Figs. 28 and 29, accelerated aging affects the fatigue resistance of all UHMWPE samples. Again, gas-plasma and ethylene oxide sterilization as well as the nonsterilized product show little differences after aging,... 

Fig. 28 FCP rates as function of stress intensity factor range for unaged UHMWPE (GUR 4150HP) following different sterilization methods...

UHMWPE comes from a family of polymers with a deceptively simple chemical composition, consisting of only hydrogen and carbon. However, the simplicity inherent in its chemical composition belies a more complex hierarchy of organizational structures at the molecular and supermolecular length scales. At a molecular level, the carbon backbone of polyethylene can twist, rotate, and fold into ordered crystalline regions. At a supermolecular level, the UHMWPE consists of powder (also known as resin or flake) that must be consolidated at elevated temperatures and pressures to form a bulk material. Further layers of complexity are introduced by chemical changes that arise in UHMWPE due to radiation sterilization and processing. 

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. 

Understanding basic chemical structure and morphology is an important starting point for appreciating the unique and outstanding properties of UHMWPE. The chapters that follow and describe the processing, as well as the sterilization, of UHMWPE will continue to build on the conceptual foimdation established in this introduction. 

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

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. 

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. 

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