Innovative surface modification of orthopaedic implants with positive effects on wettability and in vitro anti-corrosion performance M. Mozafari 1 , E. Salahinejad* 2 , S. Sharifi-Asl 3 , D. D. Macdonald 3 , D. Vashaee 4 and L. Tayebi 5,6 In this work, sol–gel derived bioactive glass/zirconium titanate coatings were uniformly deposited on stainless steel orthopaedic implants, by using carboxymethyl cellulose as a particulate dispersant in the sol. The surface features, wetting, and in vitro electrochemical corrosion behaviour of the coated samples were evaluated. It was found that, by applying the coating on the substrate, the water contact angle was decreased, which is indicative of an improvement in the implant hydrophilicity. Also, the coating improved the corrosion resistance of the metallic implant, as realised by an increase in the corrosion potential and a decrease in the corrosion current density. Indeed, this coating acted as a physical protective barrier which retards the electrolyte access to the metal surface and thereby electrochemical processes. Keywords: Ceramic coating, Corrosion resistance, Hydrophilicity, Implant Introduction It has been frequently reported that conventional orthopaedic and dental implants do not appropriately bond or integrate to natural tissues. In this regard, bioactive coatings become of interest, in order to improve the bonding quality of implants. When highly bioactive surfaces are needed, bioactive glass materials can be used as coatings on implants. However, their disadvantage lies in their low mechanical strength and often low adhesion to the substrate. 1,2 The development of composite coat- ings containing bioactive glass materials can be a viable approach to obviating this drawback. For instance, Kamalian et al. 3 synthesised and characterised compo- sites of crystalline magnesium silicate and bioactive glass. They concluded that the addition of magnesium silicate could improve the mechanical strength of the bioactive glass matrix without deteriorating its bioactivity. On the other hand, zirconia based and titania based ceramics have been recently used for biomedical applica- tions, due to their superior characteristics, such as suitable fracture toughness, strength, and biocompatibility. Impor- tantly, zirconium titanate (ZrTiO 4 ) coatings have recently attracted attention for biomedical purposes. 4,5 In this regard, Devi et al. 6 prepared ZrTiO 4 coatings by a non- hydrolytic sol–gel method on a metallic substrate, and reported excellent characteristics, such as facilitation of the formation of apatite on the metal. In this work, ZrTiO 4 was employed as the second component of the above-described bioactive composite coatings. Multilayer bioactive glass/ZrTiO 4 thin films were deposited on stainless steel samples using a sol–gel, spin-coating method. Then, the wettability and elec- trochemical corrosion behaviour of the samples were investigated. Materials and methods Bioactive glass powders with the composition of 60SiO 2 – 36CaO–4P 2 O 5 (in mol.-%), and ZrTiO 4 sol (containing 2 wt-% carboxymethyl cellulose) were prepared accord- ing to the method described elsewhere. 7 To prepare bioactive glass/zirconium titanate coatings, a sol contain- ing 50 wt-% of bioactive glass and 50 wt-% of ZrTiO 4 was spin-coated on austenitic Type 316L stainless steel substrates at 3000 rev min 21 for 60 s. The coated samples were dried at 80uC for 1 h in an oven. Sintering was conducted under a nitrogen atmosphere by raising the temperature at a heating rate of 5uC min 21 to 700uC, holding at that value for 1 h, followed by cooling at the same furnace after turning off. Because of the low carbon 1 Bioengineering Research Group, Nanotechnology and Advanced Materials Department, Materials and Energy Research Center (MERC), PO Box 14155-4777, Tehran, Iran 2 Faculty of Materials Science and Engineering, K.N. Toosi University of Technology, Tehran, Iran 3 Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, CA 94720, USA 4 School of Electrical and Computer Engineering, Helmerich Advanced Technology Research Center, Oklahoma State University, Tulsa, OK, USA 5 School of Materials Science and Engineering, Helmerich Advanced Technology Research Center, Oklahoma State University, Tulsa, OK, USA 6 School of Chemical Engineering, Oklahoma State University, Stillwater, OK, USA *Corresponding author, email erfan.salahinejad@gmail.com; salahinejad@ kntu.ac.ir ß 2014 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 28 February 2014; accepted 2 June 2014 DOI 10.1179/1743294414Y.0000000309 Surface Engineering 2014 VOL 30 NO 9 688