Effects of synovial fluid constituents on friction between UHMWPE and CoCrMo

Abstract

In this study, the reciprocating pin-on-plate sliding test was conducted between ultra-high molecular weight polyethylene (UHMWPE) and CoCrMo alloy with test lubricants containing representative synovial fluid constituents, such as proteins, hyaluronic acid, and phospholipids, to understand their effects on the in vivo friction and wear characteristics of implanted joint prostheses. To explore some details of the friction and wear process, the wear track remaining on the UHMWPE plate specimens was morphologically analyzed by laser microscopy and chemically analyzed by Fourier transform infrared (FTIR) spectroscopy. The influence of each constituent on the rheological properties of the test lubricant was also evaluated using a rotational rheometer. We observed that proteins had a definitive impact on the friction and wear process; proteins adsorbed on the UHMWPE surface and increased friction and wear by changing the predominant friction and wear mechanism from abrasive to adhesive. Phospholipids also increased friction while hyaluronic acid decreased friction by increasing the viscosity of the lubricants and enhancing the fluid dynamic effect. However, when phospholipids and hyaluronic acid were mixed with proteins, they enhanced the entrainment of the protein molecules into the contact area and increased the wear of UHMWPE.