Constituents and pH changes in protein rich hyaluronan solution affect thebiotribological properties of artificial articular joints

The relationship between the coefficient of friction and pH value or protei n constituents of lubricating fluid, together with viscosity, were studied within a bearing surface model for artificial joint, ultra-high molecular w eight polyethylene (UHMWPE) against stainless steel (SUS), using a mechanic al spectrometer. Four lubricants were tested in this study: sodium hyaluron ate (HA), HA with albumin, HA with gamma -globulin, and HA with L alpha -di palmitoyl phosphatidylcholine (L alpha -DPPC). The coefficient of friction between UHMWPE and SUS in HA with albumin or HA with gamma -globulin varied from 0.035 to 0.070 depending on angular velocity and pH. The coefficient of friction in HA or HA with L alpha -DPPC varied from 0.023 to 0.045 depen ding on angular velocity and pH. The variation in pH for HA with albumin ha d a large effect on the coefficient of friction at low range of angular vel ocity with viscosity independence. The variation in pH for HA with gamma -g lobulin had a large effect on the coefficient of friction with viscosity de pendence at high angular velocity. The addition of L alpha -DPPC showed a s mall effect on the coefficient of friction at low angular velocity. This st udy confirms that the presence of albumin in the lubricant promotes pH depe ndence and viscosity independence of the tribological properties at low spe ed while the presence of globulin promotes pH and viscosity independence at low speed and promotes pH and viscosity dependence at high speed in the lu brication of UHMWPE against SUS. This study supports the clinical hypothesi s that the effect of constituents and pH changes in periprosthetic fluid fo r the lubrication is a clue toward resolving many complications after total joint replacement. (C) 2001 Elsevier Science Ltd. All rights reserved.