The effect of hyaluronic acid and phospholipid based lubricants on friction within a human cartilage damage model

The lubricating abilities of different formulations of high molecular weight hyaluronic acid (HA), dipalmitoyl phosphatidylcholine (DPCC) and mixtures of both HA and DPCC were assessed in an in vitro model. Levels of start-up friction were determined using an osteoarthritis (OA) damaged human cartilage model set within a specially designed friction rig. To examine the long term benefits of HA, the extent of penetration of HA into cartilage tissue was investigated using fluorescently labelled HA and confocal microscopy. It was found that in this model, all formulations of HA and the majority of DPCC lubricants reduced friction (HA 5 and 10 mg ml−1, DPPC 200 mg ml−1 reductions of 51.9%, 46.7% and 46.5% respectively), compared to a Ringers solution control. Lubrication was found not to be concentration dependant for HA formulations, but concentration was key for DPCC lubrication (100 mg ml−1 reduced friction by only 15.9%). By combining HA and DPCC (HA/DPPC; 5 mg ml−1/100 mg ml−1 and 10 mg ml−1/200 mg ml−1), a further improvement was noted (69.5% and 61.9%, respectively) as the mean levels of friction were reduced by up to a further 17% than the most effective individual formulation (HA 5 mg ml−1). Penetration of HA into bovine cartilage by up to 300 μm from the surface was observed over a 48 h period. It was observed that HA specifically targeted the chondrocytes as it was primarily found within the lacunae surrounding the cells.