PREPARATION OF BIOACTIVE TI AND ITS ALLOYS VIA SIMPLE CHEMICAL SURFACE-TREATMENT

A simple chemical method was established for inducing bioactivity of T i and its alloys. When pure Ti, Ti-6Al-4V, Ti-6Al-2Nb-Ta, and Ti-15Mo- 5Zr-3Al substrates were treated with 10M NaOH aqueous solution and sub sequently heat-treated at 600 degrees C, a thin sodium titanate layer was formed on their surfaces. Thus, treated substrates formed a dense and uniform bonelike apatite layer on their surfaces in simulated body fluid (SBF) with ion concentrations nearly equal to those of human bl ood plasma. This indicates that the alkali- and heat-treated metals bo nd to living bone through the bonelike apatite layer formed on their s urfaces in the body. The apatite formation on the surfaces of Ti and i ts alloys was assumed to be induced by a hydrated titania which was fo rmed by an ion exchange of the alkali ion in the alkali titanate layer and the hydronium ion in SBF. The resultant surface structure changed gradually from the outermost apatite layer to the inner Ti and its al loys through a hydrated titania and titanium oxide layers. This provid es not only the strong bonding of the apatite layer to the substrates but also a uniform gradient of stress transfer from bone to the implan ts. The present chemical surface modification is therefore expected to allow the use the bioactive Ti and its alloys as artificial bones eve n under load-bearing conditons. (C) 1996 John Wiley & Sons, Inc.