Colloids and Surfaces B: Biointerfaces 107 (2013) 130–136 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces B: Biointerfaces jou rnal h om epa g e: www.elsevier.com/locate/colsurfb Corrosion protection performance of porous strontium hydroxyapatite coating on polypyrrole coated 316L stainless steel D. Gopi a,b,∗ , S. Ramya a , D. Rajeswari b,c , L. Kavitha b,c a Department of Chemistry, Periyar University, Salem 636 011, Tamilnadu, India b Centre for Nanoscience and Nanotechnology, Periyar University, Salem 636 011, Tamilnadu, India c Department of Physics, Periyar University, Salem 636 011, Tamilnadu, India a r t i c l e i n f o Article history: Received 4 December 2012 Received in revised form 22 January 2013 Accepted 23 January 2013 Available online 7 February 2013 Keywords: 316L stainless steel Strontium hydroxyapatite Biopolymer Bilayer coatings Electrochemical deposition a b s t r a c t Polypyrrole/strontium hydroxyapatite bilayer coatings were achieved on 316L stainless steel (316L SS) by the electropolymerisation of pyrrole from sodium salicylate solution followed by the electrodepo- sition of porous strontium hydroxyapatite. The formation and the morphology of the bilayer coatings were characterised by Fourier transform infrared spectroscopy (FT-IR) and high resolution scanning elec- tron microscopy (HRSEM), respectively. The corrosion resistance of the coated 316L SS specimens was investigated in Ringer’s solution by electrochemical techniques and the results were substantiated with inductively coupled plasma atomic emission spectrometry (ICP-AES). The passive film underneath the polypyrrole layer is effective in protecting 316L SS against corrosion in Ringer’s solution. Moreover, we believe that the top porous strontium hydroxyapatite layer can provide potential bioactivity to the 316L SS. © 2013 Elsevier B.V. All rights reserved. 1. Introduction 316L SS is widely used as an implant material in orthopaedic applications due to its excellent mechanical properties, availability at low cost and ease of fabrication. The corrosion resistance of 316L SS is actually due to the presence of a thin oxide film on its surface, known as passive film. This protective oxide layer may still allow a significant release of ions in vivo conditions [1,2]. Hence, the surface treatment for the specimens is imperative to improve its corrosion resistance in physiological fluid [3–8]. Also, since the 316L SS are not bioactive, in order to ensure the biocompatibility, osteointegra- tion and corrosion resistance of these kind of materials, the surface of the metallic implants are usually treated with osteointegrating or osteoconductive biomaterials such as calcium phosphate ceramics. Among these biomaterials, hydroxyapatite [HA, Ca 10 (PO 4 ) 6 (OH) 2 ] seems to be the most investigated biomaterial during the last decade [6,9–15] which stimulates natural bone growth at the inter- face of the prosthetic device. It has excellent biocompatibility and similar composition and structure to human tissues [16,17]. In addi- tion, HA coating protects the substrate against corrosion in the biological environment, and acts as a barrier against the release ∗ Corresponding author at: Department of Chemistry, Periyar University, Salem 636 011, Tamilnadu, India. Tel.: +91 427 2345766; fax: +91 427 2345124. E-mail addresses: dhanaraj gopi@yahoo.com (D. Gopi), kavithalouis@yahoo.com (L. Kavitha). of metal ions from the substrate into the environment (from pros- thesis to tissues) [12,18]. However, synthetic HA cannot be used in load bearing applica- tions because of its brittleness, poor mechanical properties and lack of strength. In order to overcome this obstacle, hydroxyapatite has been substituted with various additional elements, such as stron- tium, magnesium, zinc and titanium to improve its mechanical strength [19,20]. Skeletal metabolism of strontium (Sr) is believed to play an important role in human body. There is growing evi- dence that Sr influences bone remodelling with a reduction of bone resorption, an increase in the formation of new bone and a decrease in the risk of bone fracture [21–24]. Clinical studies have demon- strated that Sr enhances osteoblast proliferation while inhibiting the differentiation of osteoclasts for anti-osteoporosis purposes [25–28], explaining the considerable interest in Sr as an additive to HA. Because of Ca and Sr share the properties of group 2A elements, the Sr can readily substitute Ca in HA. The resultant composite not only improved the biocompatibility and bioactivity of HA but also increased its compressive strength and biodegradation rate [27]. Several techniques have been reported for the development of bioactive coatings onto the implant surfaces, such as, dip coating, biomimetic, pulsed laser deposition, plasma spraying, electrochemical deposition, micro-arc method, electrophoretic etc. [29–34], Compared to other preparation methods, we preferred electrochemical deposition technique as it has recently attracted considerable attention due to a relatively low process temperature, the ability to deposit on porous or complex shapes of substrate, the convenience to control the coating properties and the availability 0927-7765/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfb.2013.01.065