(568q) Lubricant Effects On Injured Cartilage

The friction coefficient between wet cartilage surfaces was measured using a pin-on-disc tribometer under an alumina-on-pin vs. cartilage-on-disc (AC) testing configuration. Several substances were dissolved in the phosphate buffered saline (PBS) solution to act as lubricants: 10,000 molecular weight (MW) polyethylene glycol (PEG), 100,000 MW PEG and chondroitin sulfate (CS), all at 100 mg/ml concentration. Scanning electron microscopy photographs of the cartilage specimens revealed limited wear due to the experiment. Our results for healthy articular cartilage samples show that both 100mg/ml CS and 100,000 MW PEG in PBS reduce the friction coefficient of articular cartilage by ~40%. Relating the measured friction coefficient with the Hersey number, our results are consistent with a Stribeck curve, indicating that the friction coefficient of cartilage under AC testing-configuration depends on a combination of hydrodynamic and boundary lubrication mechanisms. To mimic onset of osteoarthritis, we managed to mechanically damage the surface of the cartilage samples used in our experiments. Our results show that the physically injured cartilages yield higher friction coefficients than those observed for healthy cartilage, which is consistent with the nature of osteoarthritis. We relate the measured friction coefficient to the extent of mechanical damage, as quantified via SEM images of the cartilage samples.