Wear behavior of UHMWPE against DC-pulsed plasma nitrided and duplex treated AISI 316L used in hip joint replacements

E. PEREZ; L. PAZOS; E. DE LAS HERAS; B. PARODI; P. CORENGIA; I. BRACERAS

Garmisch-Partenkirchen

Congreso; PSE 2008. The Eleventh International Conference on Plasma Surface Engineering; 2008

European Joint Committee on Plasma and Ion Surface Engineering

Total Hip Replacement (THR) are exposed to a complex combination of physical, mechanical and chemical requirements. Wear debris may induced negative biological effects (osteolyisis, inflammation) and is considered as one of the most important limiting factor for a long implant life. The severity of these reactions depends on the number, size and shape of the wear particles. Hard coatings are being evaluated, among others, to improve tribological properties of artificial joints. The effect of surface modification on wear processes was analyzed by test performed with an Amsler Machine TypeA-135 reproducing a realistic loading cycle for a normal working condition, including a micro-separation gap. According to the literature, ultra high molecular weight polyethylene (UHMWPE) mass loss curves can show three periods: a running-in-period, a steady-state period and a severe wear period. Furthermore, they could be correlated with different worn surface features. Surface hardness and surface roughness of the counterface and polymer degradation can severely influence the wear behavior of the UHMWPE. The aim of this investigation is to study the influence of DC pulsed plasma nitriding and a duplex treatment on the wear behavior of the tribosystemUHMWPE-AISI316L used in hip joints replacements. The obtained results show that surface modification of the counterface improves the wear behavior of UHMWPE, specially the duplex treatment. A higher counterface hardness value improved the wear behavior of the tribosystem UHMWPE-AISI316L. For Nitriding and Duplex conditions, folding and polymeric adhesion were not observed on the worn surfaces of UHMWPE. This means that no severe wear period occurred. The FTIR spectra showed no differences between the tested and the untested samples. Therefore, polymer oxidation did not influence the wear behavior of the UHMWPE.