Dipcoating of poly (ε-caprolactone)/hydroxyapatite composite coating on Ti6Al4V for enhanced corrosion protection Mohd Faiz Mohd Yusoff a,b , Mohammed Rafiq Abdul Kadir a , Nida Iqbal a , Mas Ayu Hassan c , Rafaqat Hussain d, ⁎ a Medical Implant Technology Group, Faculty of Biosciences and Bioengineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia b Kulliyyah of Dentistry, International Islamic University Malaysia, Kuantan Campus, 25200, Kuantan, Malaysia c Faculty of Mechanical Engineering, Universiti Malaysia Pahang, Pekan Campus, 26600, Pekan, Pahang, Malaysia d Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia abstract article info Article history: Received 20 November 2013 Accepted in revised form 21 February 2014 Available online 1 March 2014 Keywords: Hydroxyapatite Poly (ε-caprolactone) Dipcoating Ti6Al4V Corrosion protection Surface modification of metallic implants is often required to facilitate positive interaction between the im- plant and the surrounding hard tissue. In the present study, a polymer-ceramic composite coating of poly (ε-caprolactone)/hydroxyapatite (PCL/HA) was successfully deposited on a Ti6Al4V substrate by dip coat- ing technique in chloroform suspension at room temperature. The influence of PCL concentration and dip coating parameters was studied and the process parameters were optimized to obtain a homogeneous, crack free, densely packed and adhesive coating. The surface of coating was rough and contained surface level pores, which are necessary for ingrowth of osseous tissue. The corrosion behaviour of the coated sub- strates was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), the results of which showed that the composite coating of PCL/HA substantially enhanced the corro- sion resistance of Ti6Al4V alloy. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Titanium (Ti) and its alloys are widely used for dental and orthopedic prostheses owing to their favourable mechanical properties, low cyto- toxicity, good corrosion resistance and biocompatibility [1–3]. One of the main requirements for implant longevity is high corrosion resistance. The formation of an oxide layer on Ti surface occurs rapidly upon contact with air. This oxide layer is considered instrumental in decreasing the dissolution rate of metal implant in the biological environment [4,5]. Moreover, the presence of an oxide layer also enhances the bioactivity of Ti in body fluid as it provides site for the deposition of calcium and phosphate compounds via an ionic exchange process with apatite from the bone tissue [6]. However, the oxide layer does not promote the for- mation of a hydroxyapatite layer, which is integral for the rapid fixation of an implant. Several studies have reported excessive levels of Ti ions in the vicinity of the implanted Ti based implants. The released Ti ions can combine with biomolecules and result in adverse biological reac- tion [7,8]. The coating of bioactive ceramic on metal implants is an effec- tive approach to solve corrosion-related problems and improve the biocompatibility of metallic implants. Hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (- OH) 2 ) is a synthetic material, which promotes osteointegration and thus accelerates tissue fixation at the implant surface during the early stages of implantation [9,10]. Dip coating is a promising technique which consists of three stages; dipping, withdrawing, and drying (Fig. 1). This technique of- fers numerous advantages such as inexpensive setup, process sim- plicity, uniformity of deposition, low processing temperature, and the ability to coat complex shapes and patterns [11,12]. Additionally, the coating amount and thickness can be controlled by adjusting the concentration of suspension, the number of dips and varying the withdrawal speed. Heat treatment of coated substrate is often required to densify the coating layer, to increase coating-implant bonding, and eliminate porosity [13,14]. However, too high a sintering temperature can lead in degradation of the metallic sub- strate (oxidation and impaired mechanical properties) and also phase transformation of HA into non-crystalline phase which increases the dissolution rate in body fluid [15,16]. Furthermore, thermal stresses originating from the difference in thermal coefficient be- tween the ceramic coating and metallic implant results in the forma- tion of micro-cracks and delamination of the coating from the substrate [17]. PCL is a semi-crystalline aliphatic polymer with good biocom- patibility, sustained biodegradability, and remarkable mechanical properties [18–20]. In this study, we report the deposition of highly compact polymer-ceramic composite coating of PCL/HA onto Ti6Al4V substrate, which does not require post-depositional heat treatment for densification. The effect of PCL concentration on cor- rosion behaviour was also studied by potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). Surface & Coatings Technology 245 (2014) 102–107 ⁎ Corresponding author. Tel.: +60 7 5535587; fax: +60 75536222. E-mail address: rafaqat@kimia.fs.utm.my (R. Hussain). http://dx.doi.org/10.1016/j.surfcoat.2014.02.048 0257-8972/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat