An easy technique to digest and isolate UHMWPE wear particles from a hip joint simulator.

The size and morphology of polyethylene wear particles isolated from in vitro tests were analysed in this study. There are some major controversies emerging in the literature that will only be resolved by careful particles analysis. Since it is difficult to identify the factors that affect size and morphology of the wear particles, the goal of this study was to compare four different polymer wear debris isolation techniques (base method and acid treatment) under identical conditions in a hip joint simulator to obtain polyethylene wear particles. We investigated achieving particulate isolation by using a different approach to the one reported in the literature that involved an easier and streamline method of particle debris isolation. The new method, compared to the previous one, used a strong base, normal centrifugation, and filtration to digest the serum constituents thus isolating the polyethylene particle debris from lubricant. In all four methods the isolation involved some or all of the following steps: density gradient separation, centrifugation or ultracentrifugation, and washing. However, a requirement for all these techniques was that the lubricant had to be devoid of organic compounds in order to effectively image and count the particle debris. The results from these studies clearly show that this new method of particle isolation is easier and more streamlined than the three methods analysed and reported in literature because it did not involve ultracentrifugation and is quicker.

Sodium-azide versus ProClin 300: influence on the morphology of UHMWPE particles generated in laboratory tests.

Ultra-high molecular-weight polyethylene (UHMWPE) has been used in total joint replacement for the last three decades and is currently the best polymer available for this use. Nevertheless, the wear of UHMWPE remains a serious clinical problem. Polyethylene wear debris has been identified as a cause of osteolysis and a major factor reducing the life of the total hip arthroplasty. Debris generated at the articular surfaces enters the periprostethic tissue where it is phagocyted by macrophages. Studies have shown that particles in the 0.1-10microm size range are particularly important in causing adverse cellular reactions resulting in osteolysis. The morphology, size, mass, and number of wear particles produced in a hip joint simulator are influenced by the tribological conditions used during the experiment. This paper shows that the morphology of the UHMWPE particles generated in vitro is influenced by the type of lubricant used. This study compared, quantitatively and qualitatively, particles generated in vitro using bovine calf serum as lubricant with two different preservatives: sodium azide and ProClin 300. No significant difference was observed with regards to wear between the two types of lubricant used. Quantitative analysis of the wear particles showed that particles generated in serum with sodium azide were not [corrected] morphologically different from those produced in serum with ProClin 300 [corrected]

The performance of gamma- and EtO-sterilised UHMWPE acetabular cups tested under severe simulator conditions. Part 2: wear particle characteristics with isolation protocols.

Ultra-high molecular-weight polyethylene (UHMWPE) has been used in total joint replacement for the last three decades. Despite the recent advancements in prosthesis design, the wear of UHMWPE remains a serious clinical problem; the release of wear debris may induce osteolysis and implant loosening. Controlling the quality of the polyethylene is essential to improve its wear resistance and any potential adverse effect caused by processing, manufacturing or sterilisation should be avoided. To evaluate the influence of the sterilisation method (gamma-irradiation and ethylene oxide (EtO)-treatment) and third-body particles, gamma- and EtO-sterilised UHMWPE acetabular cups were tested against CoCrMo femoral heads in a hip joint simulator run for 2.5million cycles in bovine calf serum in the presence of third-body polymethylmethacrylate (PMMA) particles. A method not requiring ultra-centrifugation has been proposed for the isolation of polyethylene wear debris from the serum lubricant. SEM analysis allowed debris shape and morphology to be determined, and the wear mechanism operating in this study to be hypothesised. The morphological features of the wear debris were in agreement with clinical findings, enabling the hip simulator function to be validated. Micro-Raman spectroscopy coupled to PLS analysis showed that the mechanical friction during in vitro tests induced significant crystallinity changes in all the cups. The most significant changes were observed for the EtO-sterilised cups, which showed the highest weight loss.

Reversible trapping of acid and base vapours into an amphoteric crystalline material.

Exposure of the solid zwitterion [CoIII(eta 5-C5H4CO2H)(eta 5-C5H4CO2)] to hydrated vapours of volatile acids (HCl, CF3CO2H, HBF4) or bases (NH3, NMe3, NH2Me) quantitatively produces the corresponding salts; the heterogeneous reactions are fully reversible, as the acid or base molecules can be removed by thermal treatment, regenerating the starting material.