Nanocrystalline Zirconia Orthopedic Coating for Reduced Poyethylene Wear

DESCRIPTION (provided by applicant): In this program a new zirconia coating will be developed for orthopedic applications. Ion beam assisted deposition will be used to grow a phase stabilized nanocrystalline zirconium oxide wear layer with a continuously-graded metallic/ceramic adhesion layer. In an articulating joint system pairing polyethylene wear surfaces with a hard, smooth metallic surface can minimize polyethylene wear. Zirconia has several properties that make it an excellent couple for wear resistance applications. Zirconia is extremely hard and, due to a unique phase change property, it exhibits "transformation toughening." Small cracks are pinched off before propagating. Phase stability will be achieved by incorporating yttria in the coating. Due to grain size in the nano-scale, Spire's zirconia will exhibit extraordinary hardness and a super-plasticity that will further increase toughness. Excellent adhesion of the wear layer to the substrate will be achieved with a continuously graded transition layer. This layer will present a pure metallic zirconium surface to the ion-cleaned CoCr substrate and will be gradually oxidized until the outer surface is mostly zirconium. The nano-crystalline zirconia wear layer will adhere to the transition layer through its native ionic bond. In this program we will develop a new form of zirconium oxide suitable for orthopedic applications that, due to its hardness and smoothness, will minimize polyethylene wear debris. Minimizing orthopedic wear debris is critical because wear debris leads to aseptic loosening of the implant. This loosening is one of the leading causes of implant failure leading to revision surgery.