Nano- and Microindentation Testing of UHMWPE

Previous chapters in this book have focused on the engineering aspects of tribological testing of UHMWPE for hip and knee implants and the methods used to characterize wear particles have been reviewed. An area that lacks in our overall analysis of the process of wear in UHMWPE is the study of fundamental aspects of wear behavior by way of the structure, properties, and performance of UHMWPE on the scale of both the deformation events that lead to wear, and the particles that are formed from the wear of UHMWPE. Wear processes of UHMWPE include abrasive (both two and three body), adhesive, and fatigue wear, and each of these results in the development of particles of UHMWPE that are on the scale of microns or smaller. It is only logical, therefore, to be concerned with the mechanical behavior of UHMWPE on the scale of particles generated in vivo during normal wear generation. That is, since the process of wear particle generation takes place on the scale of microns and smaller, the structure, properties, and performance of UHMWPE on the scale of microns or smaller are all critical to understand how UHMWPE wears. Therefore, the goal of this chapter is to describe the work that has been done to explore the structure, properties, and performance of UHMWPE on the scale of microns or smaller. The chapter will focus on work that has involved in the use of mechanical test methods like nanoindentation, microindentation, or, in general, depth-sensing indentation (DSI) testing along with techniques that require the atomic force microscope (AFM), and/or other high magnification imaging methods (e.g., scanning electron microscopy (SEM)). Thus, this work will describe indentation testing/SEM/AFM characterization of UHMWPE and will review various testing approaches and the effects of geometry, processing, degradation, and deformation. Briefly, the geometric relationship between the tip and sample plays a role in the analysis of indentation data.