Smart PEEK Modified by Self-Initiated Surface Graft Polymerization for Orthopedic Bearings

Poly(ether-ether-ketone) (PEEK)s are a group of polymeric biomaterials with excellent mechanical properties, chemical stability, and nonmagnetism. In the present study, we propose a novel self-initiated surface graft polymerization technique, using which we demonstrate the fabrication of a highly hydrophilic and biocompatible nanometer-scale layer on the surfaces of PEEK and carbon fiber-reinforced PEEK (CFR-PEEK) by the photoinduced graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) without using any photoinitiators. The thus formed hydrophilic and smooth 100-nm-thick PMPC-grafted layer caused a significant reduction in the sliding friction of the bearing interface because the thin water film and hydrated PMPC layer acted as extremely efficient lubricants (so-called fluid-film lubrication or hydration lubrication). Fluid-film lubrication suppressed the direct contact of the counterbearing surface with the PEEK substrate and thus reduced the frictional force. A PMPC-grafted layer is therefore expected to significantly increase bearing durability. Furthermore, the PMPC-grafted layer shows unique phenomena, e.g., it prevents damage of the metal counter surface regardless of the carbon fiber content of CFR-PEEK. Smart PEEK using the self-initiated surface graft polymerization of MPC should lead to development of novel orthopedic bearings.