Title: CoCr/TiN Superlattice Hard Coatings for Spinal Implants: The objective of this program is to develop a hard, wear resistant TiN/CoCr coating for Ti or CoCr spinal implants with the benefits of a superlattice structure. Superlattices are thin films comprised of many alternating layers of materials with differing mechanical properties. A super-hardening phenomenon occurs when the layer spacing is in a specific range. For most materials, this occurs at lattice spacings from 5-15 nm. The mechanical properties of these nano-scaled structures are very different than those of monolithically grown coatings of the same constituents. In addition to improved hardness, superlattices exhibit an unusual wear mechanism which controls defect propagation and reduces the size of wear pits and debris. These unique properties are not intrinsic to the materials; rather they are a result of how the materials are arranged and the nano-scale of the structure. This new wear surface technology is well suited to protect orthopedic implants from excess wear. We will develop the constituent base material processes and the technology required to control multiple layer thicknesses at the nano-scale. TiN/CoCr superlattices of varying lattice spacing will be grown and the characteristic lattice spacing determined. We will develop an understanding of the wear properties of a TiN/CoCr superlattice as a function of lattice spacing, and we will be able to demonstrate how the wear properties are inherent to the nano-scaled laminar structure rather than simply the grain structure of the layered materials. Then, we will wear test coupons with peak and non-peak lattice spacings and compare them against coatings of monolithically grown TiN, CoCr, and a composite of TiN-CoCr. We expect to demonstrate significant reduction in wear of polyethylene in bench top tribological tests. Work in this program will lead to coating real implants for simulation tests in a Phase II grant. Ultimately, this work will allow us to offer a commercially viable coating to the orthopedic community. We expect that applying nano-scale layered coating systems known as superlattices to spinal implants will significantly extend their useful life. Our hope is that by improving implant life expectancy we can help make disk replacement implants a competitive alternative to fusion techniques, and expand the population of patients that can benefit from these devices. ? ?
