Tribological evaluation of biomedical polycarbonate urethanes against articular cartilage

Abstract

This research investigated the in-vitro wear and friction performance of polycarbonate urethane (PCU) 80A as they interact with articular cartilage, using a customised multidirectional pin-on-plate tester. Condyles were articulated against PCU 80A discs (Bionate(center dot) I and Bionate(center dot) II) (configuration 1) and the results arising from these tests were compared to those recorded during the sliding of PCU pins against cartilage plates (configuration 2). Configuration 1 produced steadily increasing coefficient of friction (COF) (up to 0.64 +/- 0.05) and had the same trend as the cartilage on stainless steel articulation (positive control). When synovial fluid rather than bovine calf serum was used as lubricant, average COF significantly decreased from 0.50 +/- 0.02-0.38 +/- 0.06 for condyle on Bionate(center dot) I (80AI) and from 0.41 +/- 0.02-0.24 +/- 0.04 for condyle on Bionate(center dot) II (80AII) test configurations (p < 0.05). After 15 h testing, the cartilage on cartilage articulation (negative control) tests showed no cartilage degeneration. However, different levels of cartilage volume loss were found on the condyles from the positive control (12.5 +/- 4.2 mm(3)) and the PCUs (20.1 +/- 3.6 mm(3) for 80 AI and 19.0 +/- 2.3 mm(3) for 80AII) (p > 0.05). A good correlation (R-2 = 0.84) was found between the levels of average COF and the volume of cartilage lost during testing; increasing wear was found at higher levels of COF. Configuration 2 showed low and constant COF values (0.04 +/- 0.01), which were closer to the negative control (0.03 +/- 0.01) and significantly lower than configuration 1 (p < 0.05). The investigation showed that PCU is a good candidate for use in hemiarthroplasty components, where only one of the two articulating surfaces is replaced, as long as the synthetic material is implanted in a region where migrating cartilage contact is achieved. Bionate(center dot) II showed better tribological performance, which suggests it is more favourable for use in hemiarthroplasty design.