Joint replacement is one of the most commonly performed orthopaedic operations. A total joint replacement has an average life span of about 15 years. The reason for implant failure may be due to one or more of several factors, but often is caused by wear particles from the bearing surface of the implant. Wear particles from implants have been linked to inflammation which lead to bone loss and, eventually, implant loosening, Sargeant et al, “Hip Implants: Paper V. Physiological Effects”, Materials & Design, 27 (2006) 287-307. The chemistry and particle size of such particles have been found to be of high importance to the inflammation response, Sargeant et al (2006) and Sargeant et al, “Hip Implants—Paper VI—Ion Concentrations”, Materials & Design 28 (2007) 155-171.
Cobalt chromium (CoCr) based metals are commonly used as biomaterial for implants and have been shown to be relatively good, biocompatible materials for joint applications. Their mechanical properties are adequate for use as load-bearing joint implants. However, experiments have shown that CoCr particles released from implants due to wear and corrosion can restrain bone growth, Aspenberg et al, “Benign response to particles of diamond and SiC: bone chamber studies of new joint replacement coating materials in rabbits”, Biomaterials, 17 (1996) 807-812. Titanium alloys and stainless steels have also been used frequently in joint implants, Sargeant et al (2006). The main risks with metal alloy implants are release of metal ions due to corrosion and wear, and these metal ions can be carcinogenic. The wear particles may also lead to bone resorption, Sargeant et al (2007).
Use of a liner of ultra high molecular weight polyethylene (UHMWPE) against a metal or ceramic head, having a relatively low measured coefficient of friction, has been proposed, but the UHMWPE liner often gets worn and produces a relatively large amount of wear particles that can cause aseptic loosening, Xiong et al, “Friction and wear properties of UHMWPE/Al2O3 ceramic under different lubricating conditions”, Wear, 250 (2001) 242-245.
Alumina (Al2O3) and zirconia (ZrO2) ceramics have been used in joint replacements to provide high wear resistance and chemical inertness. However, ceramic materials have a poor tensile strength and alumina components in joint replacements have been shown to release wear particles due to low toughness. The particles released from alumina and zirconia are also inert and will not be resorbed by the body. However, there are other ceramic materials that have shown promising results. For example, silicon nitride (Si3N4) has a higher fracture toughness and is more resistant to microcrack propagation than alumina, Bal et al, “Fabrication and Testing of Silicon Nitride Bearings in Total Hip Arthroplasty: Winner of the 2007 ‘HAP’ PAUL Award”, The Journal of Arthroplasty, 24 (2009) 110-116.
One solution to the problems related to bulk metal joint implants or ceramic joint implants is to coat a metal joint with a more wear resistant, low corrosion ceramic coating, for example, a titanium nitride coating. However, the problems of inert wear particles causing long term problems such as inflammation and aseptic loosening have not been resolved.
Accordingly, a need exists for wear and corrosion resistant biomedical implants, especially for use as artificial joints, to overcome the problems of wear particle formation and assorted high inflammation.
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