THE ROLE OF REFRACTORY ELEMENT BASED COATINGS ON THE TRIBOLOGICAL ANDBIOLOGICAL BEHAVIOR OF ORTHOPEDIC IMPLANTS

In the area of orthopaedic implants, particularly hip joint replacemen ts, only three groups of metals and alloys are considered suitable as load - bearing implant materials, namely Ti - Ti alloys, Co - Cr alloy s and 316L stainless steel. As a result of problems, largely associate d with failure of the anchoring poly methyl methacrylate (PMMA) bone c ement, the survival of present-day load - bearing prostheses cannot be guaranteed beyond 10 to 12 years. This limited lifespan has essential ly limited joint replacements to the elderly. However, the increased n umber of younger patients requiring replacements has accentuated the n eed for joint prostheses with improved performance and longevity. The introduction of joint prostheses however with significantly enhanced d urability in rum accentuates problems associated with implant loosenin g, wear, corrosion and, in particular, biological incompatibility. At present, very few monolithic materials are capable of satisfying all s ervice requirements, The solution may lie in the use of coating techno logy, creating new materials/surfaces with unique combinations of prop erties that cannot be achieved from the use of monolithic materials al one. The first part of this paper reviews the types of coatings that h ave been used, or are currently being considered as implant materials, to include porous metallic coatings, ''bio-active'' (hydroxyapatite, bioglasses) and ''bio-inert'' (alumina) ceramic coatings. Their advant ages and limitations will be discussed. The second part will focus on recent developments in the use of refractory element based coatings, w ith specific reference to work conducted on sputtered niobium and tant alum. Possible avenues for research to include advanced coating (multi layered / multicomponent) systems, surface treatments and duplex engin eering will be reviewed.