ABSTRACT
This chapter presents a summary of research on orthopedic Ultra high molecular-weight polyethylene (UHMWPE). It highlights how free-radical research has played, and continues to play, a key role in each stage of its improvements for orthopedic applications. The theory behind Electron Spin Resonance (ESR) is based on the magnetic moment of unpaired electrons in an atomic or molecular structure. An ESR spectrum, therefore, may represent a combination of any number and type of radical species depending on factors such as the irradiation environment, radiation type and dose, and temperature. Vitamin E donates hydrogen to the free radicals of UHMWPE in order to stabilize them. In this process, vitamin E becomes a free radical itself, although a more stable type, relative to radicals of UHMWPE. The flow chart shows stages of improvement the UHMWPE has gone through since its first application in 1960. During each period of improvement, the focus of the experimental work was “how to control” the free radicals.
