The effect of roughness on the tribological behavior of the prosthetic pair UHMWPE/TiN-coated stainless steel.

The effect of roughness on the tribological behavior of the prosthetic pair ultra high molecular weight polyethylene (UHMWPE)/TiN coated stainless steel was investigated. Standard and polished TiN coated stainless steel pins were tested against either standard or smooth UHMWPE disks. Hanks' Balanced Salt Solution (HBSS) and bovine serum albumin (BSA) solution in HBSS were used as lubricants. Friction and wear were determined using a pin-on-disk apparatus and the wear mechanisms were investigated through optical microscopy, scanning electron microscopy, and atomic force microscopy. The results showed that the decrease in the roughness led to a reduction of the friction coefficient and of the wear rate of UHMWPE. However, the most important effect was achieved through the decrease in the roughness of the hard TiN counterface while keeping the standard UHMWPE surface. If BSA was added to HBSS, a strong decrease of both the friction coefficient and the polymeric wear was observed independently of the roughness of both the TiN and the polyethylene surfaces. Abrasive and fatigue wear mechanisms are proposed to interpret the experimental results.

Adsorption of albumin on prosthetic materials: implication for tribological behavior.

The orthopedic prosthesis used to substitute damaged natural joints are lubricated by a pseudosynovial fluid that contains biological macromolecules with potential boundary lubrication properties. Proteins are some of those macromolecules whose role in the lubrication process is not yet completely understood. In a previous work, we investigated the influence of the presence of albumin, the major synovial protein, upon the tribological behavior of three of the most used pairs of artificial joint materials: ultra high molecular weight polyethylene (UHMWPE) against counterfaces of alumina, CoCrMo alloy, and 316L stainless steel. Albumin was found to cause a significant decrease in the friction coefficient when the counterfaces were metallic because transfer of UHMWPE was avoided, but this effect was much weaker in the case of alumina. The objective of the present work was to look for an explanation for these differences in tribological behavior in terms of albumin adsorption. With this goal, studies on adsorption of bovine serum albumin (BSA) on the counterface materials, from a biological model fluid (Hanks' balanced salt solution), were carried out using radiolabeled albumin ((125)I-BSA), X-ray photoelectron spectroscopy, and atomic force microscopy. The conclusion from all techniques is that the driving force for albumin adsorption is higher on the metals than on alumina. These results confirm that the greater the amount of protein adsorbed on the counterface, the more efficient is the protection against the transfer of polymeric film to the counterface.