EVALUATION OF THE FRICTIONAL-PROPERTIES OF AN ELASTOMER WITH ENHANCEDLIPID-ADSORBING ABILITY

Wear particle production in load-bearing orthopaedic implants is one o f the major factors currently limiting the service life of the implant . Most of the research carried out to date in attempting to solve this problem has used the approach of finding more wear-resistant biocompa tible material pairs. In contrast, other researchers have attempted to reduce wear by encouraging elastohydrodynamic him formation through t he use of elastomeric bearing surfaces. Unfortunately, these elastomer ic bearing surfaces have poor tribological properties when a fluid him is not present. Boundary lubrication of an elastomeric orthopaedic be aring may alleviate some of these difficulties. The purpose of this re search was to fabricate and characterize an elastomeric material that had a surface capable of specifically adsorbing a naturally occurring boundary lubricant. Dipalmitoyl phosphatidylcholine (DPPC) has been pr eviously shown to be able to act as a boundary lubricant at stresses t hat occur in human load-bearing joints such as the hip and knee; there fore, DPPC was chosen for use in this study. It was expected that in a n aqueous liposome suspension the static coefficient of friction mu(s) of such a material would be lower, and increase less quickly over tim e, than a similar material without an ability to adsorb specifically D PPC when articulated against a polished chrome steel ball bearing. The lipid-adsorbing elastomer did not possess the desired tribological pr operties. This result was attributed to the polymer adsorbing the DPPC in the liposome phase and not in the bilayer phase, and interaction a mong the polymeric surface, DPPC and water. This approach to lubricati ng orthopaedic bearings was shown to have some merit, but a great deal of work needs to be done before such an approach can be used on a cli nically available material.