Electrochemical deposition of bioactive coatings on Ti and Ti–6Al–4V surfaces Mihai V. Popa, Jose Maria Calderon Moreno, Monica Popa, Ecaterina Vasilescu ⁎, Paula Drob, Cora Vasilescu, Silviu I. Drob Romanian Academy, Institute of Physical Chemistry “Ilie Murgulescu”, Spl. Independentei 202, 060021 Bucharest, Romania abstract article info Article history: Received 23 February 2011 Accepted in revised form 7 April 2011 Available online 22 April 2011 Keywords: Cathodic electrodeposition Coating structure Brushite Hydroxyapatite Corrosion behavior Morphology Passivating coatings of brushite (CaHPO 4 ·2H 2 O) were obtained on Ti and Ti–6Al–4V ELI alloy substrates by cathodic polarization. After soaking in Ringer's solution for 48 h brushite was transformed to hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) as confirmed by XRD, FT-IR and Raman spectroscopy. Electrochemical cyclic polarization curves of the coated biomaterials obtained in Ringer's solution at pH values of 7.1 and 8.91 as well as in Hank's Balanced Salt Solution (HBSS) at pH value of 7.4 show a nobler behavior than of the uncoated biomaterials. The coated biomaterials had lower corrosion rates than the uncoated biomaterials suggesting a protective character of the hydroxyapatite coating. Electrochemical impedance spectra (EIS) revealed capacitive behavior, owing to the protective, very resistant layer, the thickness of which increased with soaking time. The coated biomaterials presented higher electropositive open circuit potentials compared to the uncoated biomaterials as result of the protective effect of the coating. The morphology of the coatings changed with soaking time as the coatings became denser, smoother and better adhering. Hence such coatings may provide favorable structure for cell adhesion and proliferation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Titanium and its alloys are used as implant materials due to their very good biocompatibility, corrosion resistance and mechanical properties [1–4]. Titanium and titanium alloys directly bond to bone but the bonding and the bone ingrowth are slow processes compared with requested healing periods for implant. Therefore, an unfavorable fixation with the bone affects the implant life. In- teractions between biomaterial and biological fluid occur at their interface and depend on surface chemistry, energy, roughness and topography [5–7]. Different methods were used to modify surfaces, to improve their bonding to bone: ion implantation [8], chemical etching [7], chemical oxidation [5,9], etc. Another method is the coating of the implant surface with the thin film of calcium phosphate com- pounds or hydroxyapatite [10]. It is known that calcium compounds are osteoconductive and thus improve the fixation between bone tissues and implant [11]. These coatings can be applied by plasma spraying [12–14], magnetron sputtering [15], chemical reactions [16– 22], high velocity oxy fuel spraying (HVOF) and high velocity suspension flame spraying (HBSFS) [23], soaking in supersaturated Ca/P solutions [24,25], biomimetic processes [24] and electrodeposi- tion [26–30]. However, many of these methods have limitation including the difficulty to coat surfaces with cavities or complex shape, to mimic all aspects of biological tissues, to chemically bond with optimum adhesion, to resist under abrasion, wear, scratch, etc. Electrodeposition is a relative new method and is attractive because it is applied from aqueous solutions, at room temperature, at low cost and can relatively quickly coat irregular objects; also, a high degree of control of deposit can be obtained and the corrosion of metallic surface is minimized during the deposition process. In this paper, hydroxyapatite coatings on Ti and Ti–6Al–4V ELI alloy surface were obtained by two steps. Initially, a brushite film (CaHPO 4 ·2H 2 O) was obtained by cathodic electrodeposition. Subse- quently, a hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ) coating was formed by soaking for 48 h in Ringer's solution of pH = 7.1. The behavior of this coating in Ringer's and Hank's solutions was studied by electrochem- ical methods and scanning electron microscopy (SEM). 2. Experimental 2.1. Materials The samples as cylindrical electrodes were obtained from Ti and Ti–6Al–4V ELI ingots. The bare electrodes were mirror-polished (with 400 to 2000 grit emery paper and alumina suspension), fixed in a Stern–Makrides mount system, washed with bi-distilled water, ultrasonically degreased in acetone and dried in air. Surface & Coatings Technology 205 (2011) 4776–4783 ⁎ Corresponding author at: Institute of Physical Chemistry “Ilie Murgulescu”, Spl. Independentei 202, 060021 Bucharest, Romania. Tel./fax: + 40 21 3121147. E-mail address: ec_vasilescu@yahoo.com (E. Vasilescu). 0257-8972/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2011.04.040 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat