Role of hydrophobicity on the adsorption of synovial fluid proteins and biolubrication of polycarbonate urethanes: Materials for permanent meniscus implants

Both absorption and release of synovial fluid components lubricate the porous natural meniscus, whereas only adsorption can lubricate non-porous meniscus prostheses. The aim of this study was to establish the adsorption characteristics of the synovial fluid proteoglycan 4 (PRG4) and albumin on modified and unmodified polycarbonate urethane (PCU) and determine the effects on the coefficient of friction. PCU was modified with surface-tethered C18 chains (mPCU). Self-assembled monolayers (SAM) on gold were also used to generate higher and lower hydrophobicities. Protein adsorption and coefficients of friction were measured by quartz crystal microbalance and colloidal probe atomic force microscope. PRG4 formed a thick viscoelastic layer and significantly decreased the coefficient of friction on PCU and mPCU, with an exceptionally low coefficient of friction measured on mPCU (0.02 +/- 0.02) due to its soft surface. Albumin formed a thin rigid layer with a much higher coefficient of friction on mPCU (1.14 +/- 0.19). Albumin blocked PRG4 adsorption when simultaneously added to PCUs, and coefficients of friction of 0.48 +/- 0.24 (PCU) and 0.49 +/- 0.17 (mPCU) were measured. Albumin adsorption on hydrophobic substrates (water contact angle >= 70 degrees +/- 4 degrees) dramatically increased the coefficient of friction (3.41 +/- 1.21 on hydrophobic SAM), indicating that increased hydrophobicity through hydrocarbon surface modification of PCU carries tribological risks. (C) 2015 Elsevier Ltd. All rights reserved.