               !" # Dilek TEKER a , Can Poyraz SAĞ b , Mehmet DİNÇER c , Sedat ALKOY d and Koray ÖZTÜRK e Gebze Institute of Technology, Materials Science and Engineering Department, Cayirova Campus Gebze, Kocaeli, 41400, Turkey a dteker@gyte.edu.tr, b cpsag@gyte.edu.tr, c mdincer@gyte.edu.tr, d sedal@gyte.edu.tr, e k.ozturk@gyte.edu.tr $: Hydrothermal modification, Simulated Body Fluid, Biomimetic, Coatings  Hydrothermal surface modifications of the titanium specimens were performed (i) at 200 ºC under 1.5 MPa pressure, and (ii) at 230 ºC under 2.5 MPa pressure. To see the effect of an ion implantation, two different aqueous hydrothermal environments were selected: (i) de-ionized water and (ii) calcium containing de-ionized water. Hydrothermally treated titanium surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and found to become rich with Ca when Ca- containing hydrothermal environment was used. The surface-modified titanium specimens were then kept immersed in 1.5X simulated body fluid (SBF) for 1, 2, 3 and 4 weeks. The bio- mimetically formed coatings were characterized using scanning electron microscopy (SEM) and X- ray diffractometer (XRD). Crack formations and, consequently, severe peelings were observed after drying for all the coatings on the substrates that were treated hydrothermally using only de-ionized water. The Ca implanted titanium surfaces, on the contrary, were able to develop crack-free and quite cohesive coatings. Up to two weeks of immersion and after drying, no-cracks were observed in the coatings when the substrates were treated at higher temperature and under higher pressure (230 ºC and 2.5 MPa for the present investigation).  Hydrothermal treatment is one of the methods to modify the outer-most layer of the metal substrates for bio-mimetic coating [1,2]. Titanium metal surfaces have been treated in various aqueous environments which contain ions such as calcium, sodium, potassium and phosphate to contribute to the formation of apatite coating [3-7]. The starting substrate surfaces can, therefore, be charged with the desired ions from the solution. The surface of the passive oxide layer on the metal is changed into a very thin and gel-like or amorphous layer [8,9]. This type of layers are reported be effective in facilitating the nucleation of the “bone like” apatite mineral in SBF through the tentative ion-exchange mechanism [10]. The apatite formation is initiated by the exchange reaction between the ions on the substrate (e.g. Ca 2+ ) and the H 3 O + ions in the adjacent SBF. Through this reaction, the surface becomes rich in OH - groups. Then, the positively charged Ca 2+ ions in the SBF migrate back to the surface to form an amorphous calcium and titanium containing layer (probably calcium titanate). This layer, then, reacts with the negatively charged phosphate ions in the SBF and turns into an amorphous calcium phosphate. Since amorphous calcium phosphate is metastable in the SBF, it transforms into an apatite and forms bio-mimetically grown “bone-like” layer on the substrate [11-13]. Advances in Science and Technology Vol. 63 (2010) pp 402-407 © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AST.63.402 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 78.179.210.151-26/09/10,19:57:29)