Analysis of frictional behavior and changes in morphology resulting from cartilage articulation with porous polyurethane foams.

Porous polyurethane foams (PUR) have been extensively evaluated as meniscal replacement materials and show great promise enabling infiltration of cells and fibrocartilage formation in vivo. Similar to most materials, PUR demonstrates progressive degeneration of opposing cartilage; however, the damage mechanism is impossible to determine because no information exists on the frictional properties of PUR-cartilage interfaces. The goals of this study were to characterize the frictional behavior of a cartilage-PUR interface across a range of articulating conditions and assess the resulting morphological changes to the cartilage surface following articulation. Articular cartilage was oscillated against PUR or stainless steel using phosphate-buffered saline (PBS) and synovial fluid as lubricants. Following friction testing, cartilage and PUR samples were analyzed with environmental scanning electron microscopy and histological staining to determine changes in tissue morphology. Stribeck-surface analysis demonstrated distinct lubrication modes; however, boundary mode lubrication was dominant in cartilage-PUR interfaces and the low-friction pressure-borne lubrication mechanism present in native joints was absent. Microscopy noted obvious wear, with disruption of the collagen architecture and concomitant proteoglycan loss in cartilage articulated against PUR. These data collectively point to the importance of frictional properties as design parameters for implants and materials for soft tissue replacement. Published by Wiley Periodicals, Inc. J Orthop Res 28:1292-1299, 2010.