Effect of spatial design and thermal oxidation on apatite formation on Ti–15Zr–4Ta–4Nb alloy Atsushi Sugino a,b, * , Chikara Ohtsuki a , Kanji Tsuru c , Satoshi Hayakawa c , Takayoshi Nakano d , Yoshimitsu Okazaki e , Akiyoshi Osaka c a Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya-shi, Aichi 464-8603, Japan b Nakashima Medical Division, Nakashima Propeller Co. Ltd., 688-1, Joto-Kitagata, Okayama-shi, Okayama 700-8691, Japan c Division of Chemical and Biological Chemistry, Graduate School of Natural Science and Technology, Okayama University, 3-1-1, Tsushima-naka, Okayama-shi, Okayama 700-8630, Japan d Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita-shi, Osaka 565-0871, Japan e Institute for Human Science and Biomedical Engineering, National Institute of Advanced Science and Technology, 1-2, Namiki, Tsukuba-shi, Ibaraki 305-8564, Japan Received 11 February 2008; received in revised form 15 May 2008; accepted 17 July 2008 Available online 30 July 2008 Abstract Apatite formation on the surface of titanium and its alloys is effective for inducing osteoconductivity when implanted in bony defects. The aim of this study was to investigate the effects of thermal oxidation on apatite formation in macro-grooves on Ti–15Zr–4Ta–4Nb. Thermal oxidation at 500 and 600 °C in air led to modification of the Ti–15Zr–4Ta–4Nb surface to rutile phase titanium oxide. Ti–15Zr– 4Ta–4Nb thermally oxidized at 500 °C in air showed no changes in metallographic structure, but not at 600 °C. After soaking in a sim- ulated body fluid for 7 days, the formation of apatite could be observed on the internal surfaces of macro-grooves 500 lm deep and wide on Ti–15Zr–4Ta–4Nb thermally oxidized at 500 and 600 °C in air. These results indicate the potential for osteoconductivity of Ti–15Zr– 4Ta–4Nb without changing its metallographic structure, by fabricating only the macro-grooves, i.e., spatial design, and by performing thermal oxidation at 500 °C. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Titanium alloy; Apatite; Bioactivity; Thermal oxidation; Macro-grooves 1. Introduction Osteoconductivity, which means bone growth on a mate- rials surface, is one of the most desirable characteristics in the development of novel titanium-based implants. Various sur- face treatments have been proposed to provide osteoconduc- tivity to titanium and its alloys, with the potential for apatite formation related to osteoconductivity. Currently, the most popular surface treatment for commercial artificial joints and dental implants is plasma-spray coating with hydroxy- apatite. Plasma-sprayed hydroxyapatite on titanium has been reported to show beneficial effects such as osteoconduc- tivity and direct-bone bonding ability [1]. However, the pro- cess has disadvantages attributed to the high temperatures used during the process, such as the possibility of fracture at the interface between the titanium and the hydroxyapatite due to the residual stress at the interface, and changes in the composition, porosity, crystallinity, and structure of the plasma-sprayed hydroxyapatite [2]. Several chemical treat- ments with NaOH [3,4] or H 2 O 2 solutions [5,6] have also been reported to provide spontaneous apatite-forming abil- ity to titanium metals in the body environment. These treat- ments produce Ti–OH groups in a titania hydrogel layer on 1742-7061/$ - see front matter Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actbio.2008.07.014 * Corresponding author. Address: Nakashima Medical Division, Naka- shima Propeller Co. Ltd., 688-1, Joto-Kitagata, Okayama-shi, Okayama 700-8691, Japan. Tel.: +81 86 279 6278; fax: +81 86 279 9510. E-mail address: a.sugino@nakashima.co.jp (A. Sugino). Available online at www.sciencedirect.com Acta Biomaterialia 5 (2009) 298–304 www.elsevier.com/locate/actabiomat