Wear reduction of orthopaedic bearing surfaces using polyelectrolyte multilayer nanocoatings

This work explores the use of conformal polyelectrolyte multilayer (PEM) coatings for wear reduction of orthopedic bearing surfaces. These films, with easily tunable architectures, provide excellent adhesion to a wide variety of metallic, plastic, and ceramic substrates. For this study, PEM films, only a few hundred nanometers thick, were assembled by sequential adsorption of poly(acrylic acid) and poly(allylamine hydrochloride). It was observed that the pH of the polylectrolyte solutions used for film assembly needs careful consideration to avoid any adverse effects on film structure when exposed to physiological conditions of pH and ionic strength. The wear reducing capacity of these coatings in the presence of bovine calf serum-lubricant solution was established for metal/metal systems at the meso/microscale over 30 cycles of reciprocating motion, as well as for the commonly used metal/ultra-high molecular weight polyethylene (UHMWPE) system over 500,000 cycles of bi-directional motion in a macroscale pin-on-disk test. In the latter case, the use of the films reduced UHMWPE wear by up to 33% when compared with the uncoated control. This is the first clinically relevant laboratory demonstration of the wear-reducing ability of these films. Further optimization will be needed before this novel class of materials can be used by the orthopedic community.