RESEARCH ARTICLE


Bioactive Titanate Layers Formed on Titanium and Its Alloys by Simple Chemical and Heat Treatments



Tadashi Kokubo*, Seiji Yamaguchi
Department of Biomedical Sciences, College of Life and Health Sciences, Chubu University 1200 Matsumoto-chow, Kasugai, Aichi 487-8501 Japan


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Creative Commons License
© Kokubo and Yamaguchi; Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to the author at the Department of Biomedical Sciences, College of Life and Health Sciences, Chubu University, 1200 Matsumoto-chow, Kasugai, Aichi 487-8501 Japan; Tel: 81-75-951-164; Fax: 81-75-957-164; E-mail: kokubo@isc.chubu.ac.jp


Abstract

To reveal general principles for obtaining bone-bonding bioactive metallic titanium, Ti metal was heat-treated after exposure to a solution with different pH. The material formed an apatite layer at its surface in simulated body fluid when heat-treated after exposure to a strong acid or alkali solution, because it formed a positively charged titanium oxide and negatively charged sodium titanate film on its surface, respectively. Such treated these Ti metals tightly bonded to living bone. Porous Ti metal heat-treated after exposure to an acidic solution exhibited not only osteoconductive, but also osteoinductive behavior. Porous Ti metal exposed to an alkaline solution also exhibits osteoconductivity as well as osteoinductivity, if it was subsequently subjected to acid and heat treatments. These acid and heat treatments were not effective for most Ti-based alloys. However, even those alloys exhibited apatite formation when they were subjected to acid and heat treatment after a NaOH treatment, since the alloying elements were removed from the surface by the latter. The NaOH and heat treatments were also not effective for Ti-Zr-Nb-Ta alloys. These alloys displayed apatite formation when subjected to CaCl2 treatment after NaOH treatment, forming Ca-deficient calcium titanate at their surfaces after subsequent heat and hot water treatments. The bioactive Ti metal subjected to NaOH and heat treatments has been clinically used as an artificial hip joint material in Japan since 2007. A porous Ti metal subjected to NaOH, HCl and heat treatments has successfully undergone clinical trials as a spinal fusion device.

Keywords: : Artificial hip joint, bioactive Ti, bone-bonding ability, osteoconduction, osteoinduction, spinal fusion device, titanium metal, Ti-based alloy.