Effect of counterface on the tribology of UHMWPE in the presence of proteins

Artificial joints in orthopedics occupy a principal position owing to the i ncrease in number of cases suffering from arthritis and associated diseases in addition to impairment caused by accidents. In this work, one of the mo st commonly used joint material, i.e. ultrahigh molecular weight polyethyle ne (UHMWPE), was tested against the duplex stainless steels instead of the conventional 316 L stainless steel. The UHMWPE was found to exhibit the low est friction coefficient and wear rates when lubricated with water followed by globulin and glucose. The friction coefficient in the presence of egg a lbumen was higher along with high wear rates recorded. Post-test evaluation of surface roughness and wear scar/track analysis was performed to identif y the wear mechanisms. Worn surfaces were analyzed using a differential sca nning calorimeter for changes in crystallinity with sliding. The specimens tested under lubricated conditions with glucose, egg albumen and globulin i ndicated the presence of reaction products on the worn surface. Adhesive an d corrosive wear mechanisms were the predominant modes of wear identified o n the polymer samples. The wear tracks indicated that the proteins did reac t with the counterface material forming a thin deposit on them. Low tempera ture nitriding of the duplex stainless steel counterfaces were performed an d the UHMWPE specimens were tested under similar conditions against the nit rided surfaces. Low temperature nitriding of the counterface did result in improved tribological behavior of UHMWPE and the corrosive effects were min imal. (C) 2001 Elsevier Science B.V. All rights reserved.