Characteristics of multi-layer coating formed on commercially pure titanium for biomedical applications Dilek Teker a , Faiz Muhaffel a , Meryem Menekse b , Nevin Gul Karaguler b , Murat Baydogan a,c , Huseyin Cimenoglu a, ⁎ a Department of Metallurgical and Materials Engineering, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey b Department of Molecular Biology and Genetics, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey c Prof. Dr. Adnan Tekin Material Sciences and Production Technologies Applied Research Center, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey abstract article info Article history: Received 22 February 2014 Received in revised form 11 October 2014 Accepted 17 December 2014 Available online 18 December 2014 Keywords: Commercially pure titanium Micro-arc oxidation Titanium oxide layer Hydroxyapatite Biocompatibility Antibacterial surface An innovative multi-layer coating comprising a bioactive compound layer (consisting of hydroxyapatite and calcium titanate) with an underlying titanium oxide layer (in the form of anatase and rutile) has been developed on Grade 4 quality commercially pure titanium via a single step micro-arc oxidation process. Deposition of a multi-layer coating on titanium enhanced the bioactivity, while providing antibacterial characteristics as compared its untreated state. Furthermore, introduction of silver (4.6 wt.%) into the multi-layer coating during micro-arc oxidation process imposed superior antibacterial efficiency without sacrificing the bioactivity. © 2014 Elsevier B.V. All rights reserved. 1. Introduction As an implant material, commercially pure titanium (Cp-Ti) and Ti6Al4V alloy are attractive materials because of their low elastic mod- ulus (closer to that of bone), lightweight (low density), non-magnetic properties, low thermal conductivity, high corrosion resistance and good biocompatibility [1–3]. Their enhanced corrosion resistance and biocompatibility arise from instantaneous formation of a compact nano- meter thick titanium oxide (TiO 2 ) layer on the surface when exposed to any oxygen containing environment [4]. However, this native oxide layer cannot resist against destructive mechanical effects and prevent release of alloying elements into the body fluid. In fact, excess concen- trations of the alloying elements lead to detrimental biological re- sponses [5,6]. For instance, toxic effect of vanadium along with its contribution to cardiac and renal dysfunction associated with hyperten- sion, Parkinson's disease and depressive psychosis has been established [7–11]. Moreover, aluminum has a high potentiality to cause neurolog- ical dysfunctions, anemia, epileptic disease and osteomalacia [9,10]. In this respect, Cp-Ti appears as the most convenient implant material for dental applications, where high mechanical strength is not a priority. Despite the release of alloying elements, Ti6Al4V alloy is generally pre- ferred for manufacturing load bearing orthopedic implants due to the high strength requirements [12]. Mechanical and chemical processes (i.e. sand blasting and etching, respectively) are usually employed to increase the surface area of the implants, because rough surfaces with high surface area induce me- chanical interlocking between the bone and the implant [13]. As a mat- ter of fact, rough surfaces slightly stimulate osseointegration which would take place in several months after implantation. It has been re- ported that bioactive surfaces play a significant role in early stages of implantations due to better osteoconductive properties promoting fast attachment and proliferation of osteoblast cells [14]. One of the key issues in long term success of implantation is the de- velopment of infections leading to inflammation around the implants. It is well known that, infections increase the risk of implant failure not only at early stages of implantation but also after complete osseointegration. A clinical study demonstrated that about 7.7% of den- tal implantations faced with failures in five years related to infections caused by various bacteria [15]. Although, rough surfaces provide better binding between dental implant surface and bone, high roughness in- creases in the risk of peri-implantitis, which may even result in tissue destruction and bone loss [16–19]. In this respect, surfaces of implants should provide efficient solutions against poor osteoconductivity and insufficient cell attachment as well as infections related to bacterial bio-film formation. There is a possibility for reducing the bacteria Materials Science and Engineering C 48 (2015) 579–585 ⁎ Corresponding author at: Istanbul Technical University Ayazaga Campus, Faculty of Chemical and Metallurgical Engineering, Department of Metallurgical and Materials Engineering, Maslak, 34469 Sariyer, Istanbul, Turkey. E-mail address: cimenogluh@itu.edu.tr (H. Cimenoglu). http://dx.doi.org/10.1016/j.msec.2014.12.058 0928-4931/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec