The effect of IPN surface modification on the mechanical properties of UHMWPE.

This paper investigates the effect of IPN surface treatment on the mechanical properties of ultra high molecular weight polyethylene (UHMWPE). Traditional UHMWPE was modified by introducing poly-L-lysine (PLL) into their surface and forming a semi-interpenetrating network (IPN). Tensile, creep and fatigue tests were performed on these IPN and the control specimens. The tensile and creep results show that the IPN modification did plasticize the UHMWPE in that it decreased modulus and strength, increased ductility, and degraded creep resistance. However, these property changes are not so large as to be unacceptable. In the fatigue tests, there were no failures of control nor IPN samples up to 10 million cycles.

Clinical wear of 63 ultrahigh molecular weight polyethylene acetabular components: effect of starting resin and forming method.

This study compares the clinical wear rates and implant characteristics of 63 surgically retrieved acetabular components. All components were made by the same manufacturer, implanted by the same surgeon, in articulation against the same type of femoral component, and revised for the same reason; 19 were made from directly compression molded, calcium stearate free, ultrahigh molecular weight polyethylene (UHMWPE) and 44 were made from machined, ram extruded, calcium stearate containing UHMWPE. There were significant differences in wear, duration, and wear rate between the molded (type I) and machined (type II and III) components. Most importantly, the wear rates of type I (molded) components were significantly (p < 0.0001) lower than the wear rates of type II, type III, and type II and III components as a group (all machined). The machined components had wear rates 2.3 times greater than the molded components. The wear rates between the two different groups of machined components (type II and III) were not significantly different. The scanning electron microscope observations did not reveal any major differences in wear mechanisms between the three types of components, although the machined components did show more evidence of brittleness. The molded components were better consolidated (or had less fusion defects) than the ram extruded components.

Comparison of the in vivo wear rates of 43 surgically retrieved direct compression molded and ram extruded ultra high molecular weight polyethylene acetabular components.

The objective of this study was to investigate retrieved ultra high molecular weight polyethylene (UHMWPE) liners from Total HIp Arthroplasty (THA) revisions. The amount of in vivo wear on compression molded v. ram extruded and machined acetabular liners was the focus of comparison between 43 surgically retrieved samples. The principal experimental methods were scanning electron microscope (SEM) observations and a fluid displacement method to quantify volumetric wear. SEM observations revealed similar wear mechanisms between the compression molded and ram extruded and machined UHMWPE retrieved liners. More third body wear corresponded with more volumetric in vivo wear. This study found that the ram extruded and machined UHMWPE liners had a significantly larger average wear rate than the compression molded UHMWPE liners. In order to determine whether the observed difference in wear rates can be attributed to the different types of UHMWPE processing, a more controlled experiment would have to be performed.