HIPNANOLAM · Biocompatible and wear protective carbon based nanolaminate films for hip replacement joint applications

Stress shielding is one phenomenon that commonly affects joint prostheses causing loosening of the prosthesis. This problem is common and it affects nearly all metal prosthesis components currently used. Wear of orthopaedic implant materials is an issue of high importance some alloys degrade at an average rate of 0.02–0.06 mm/year. Corrosion, fatigue, friction, and wear are the main surface characteristics that are considered when designing prostheses. The potential release of cobalt, chromium, nickel, aluminium, and vanadium ions, which exhibit allergic, carcinogenic, and/or toxic interactions with human tissues is also a significant issue to eliminate when selecting materials for surface treatments. Finally, a well controlled pinhole-free finish is necessary to uniformly provide these properties over the entire device surface. Diamond like carbon is an ideal surface coating for prosthetic joints, because it is atomically smooth, low friction, wear resistant, inert, and immune to scratching by third body wear particles. Furthermore, it prevents the release of metal ions into the surrounding tissues. Hydrogen-free diamondlike carbon is greatly preferred over for joint prosthesis applications, in which a low friction surface under humid conditions is required. Novel nanostructured carbon-based functionally-graded multilayer-nanolaminate systems using hard ceramic layers (e.g. WC, TiC), with either hard a-C:H, hydrogen-free amorphous C (a-C) or tetrahedral amorphous C (ta-C) individual layers, ranging from a few nanometres to approximately 100 nm in thickness, combine the bioactive and biocompatible properties of DLC coatings and also have the flexibility to impart lubricity in various environments, yet maintain hardness, and dramatically increase toughness.