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

Final Report Summary - HIPNANOLAM (Biocompatible and wear protective carbon based nanolaminate films for hip replacement joint applications)

Objectives:

Stress shielding is one phenomenon that commonly affects biomedical joint prostheses, resulting in loosening of these implants. 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 since 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 (DLC) 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 DLC is greatly preferred for joint prosthesis applications, in which a low friction surface under humid conditions is required. Novel nano-structured 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.

Work performed and main results:

Development of biocompatible and protective carbon based nanostructured films / coatings for hip replacement joint applications. Work included the deposition and characterisation of structure, mechanical, tribological, biocompatibility and cell-attachment properties of a series of carbon based nanostructure coatings with the possibility to tailor their properties by adjusting the amorphous carbon (a-C:H) content. Low sliding friction coefficients (approximately 0.2) and relative low wear rates were observed in high contact pressure tests. Cell viability and consequent attachment potential appears to be increasing with coating nanocrystallinity.

Expected final results and their potential impact and use:

The development of new multifunctional biocompatible nanocomposite coatings to increase significantly the implant lifetime of joint prostheses. Introduction of the next generation of implants coated with highly wear resistant and strongly adherent biocompatible coatings, with no release of harmful elements, to enhance the life cycle of prosthetic joints (currently, between approximately 5 and 20 years), since implants are inserted in people at progressively younger ages and the demographic profile being such that in the coming years there will be a peak in the number of middle aged people requiring implants. Within the biomedical industry it is generally recognised that coatings are now required to prolong prosthetic lifetime and reduce the release of carcinogenic elements into the body. Coating implants with protective functional films could reduce or alleviate the problems described above and extend the lifetime of the implants and improve the quality of life of patients.