Hierarchical polymer nanocomposite coating material for 316L SS implants: Surface and electrochemical aspects of PPy/f-CNTs coatings A. Madhan Kumar a , P. Sudhagar b , Akira Fujishima b , Zuhair M. Gasem a, * a Center of Research Excellence in Corrosion, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia b Photocatalysis International Research Center, Research Institute for Science & Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan article info Article history: Received 3 March 2014 Received in revised form 23 August 2014 Accepted 26 August 2014 Available online 9 September 2014 Keywords: Polypyrrole MWCNTS Corrosion abstract Biocompatible nanocomposite coatings can be synthesized to offer improved surface properties for biomaterials and biomedical implants. Nanocomposite coatings containing polypyrrole (PPy) matrix reinforced with functionalized multi-wall carbon nanotubes (f-CNTs) were deposited on 316L SS sub- strates using electrochemical route. FT-IR, XRD, SEM, and TEM were employed to characterize the nanocomposite microstructure. High resolution imaging showed relatively uniform dispersion of the CNTs in the nanocomposite with a typical tubular structure. Micro-indentation tests revealed improvement in the hardness of the PPy/CNTs coatings. Measurement of the contact angle indicated enhanced surface wettability of the nanocomposite coatings. The corrosion behavior of 316L SS samples coated with PPy/CNTs was studied in SBF medium. The corrosion potential and the breakdown potential of coated 316L SS substrates shifted to more noble values as compared to uncoated 316L SS samples. The results suggest that incorporating CNTs as reinforcements in PPy coatings can provide enhanced prop- erties in terms of surface hardness, biocompatibility, and corrosion resistance. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanotubes (CNTs) are considered to be ideal nano- reinforcing candidate for high-strength polymer composites intended for biological applications due to their small size, high surface area, extraordinary mechanical strength, high thermal conductivity [1]. CNTs also appear to provide additional advantage in terms of inducing mineralization of hydroxy apatite (HAP) in biocompatibility studies [2]. In addition, functionalization of CNTs with carboxylic acid groups has been found to improve their sol- ubility and biocompatibility and initiate mineralization on poly- mers as a biomimetic material [2], which supports the growth of HAP. Recently, it has been reported that covalent functionalization of CNTs enhanced the biocompatibility of CNTs with reduced cytotoxic effects [3]. Thus, functionalized CNTs are promising re- inforcements for polymer based coatings for a variety of biomedical applications. In general, novel polymer nanocomposites require uniform dispersion of CNTs in the polymer matrix which entail a strong CNT/polymer interaction. Enhancement in the properties of composites is usually dependent on the interfacial interactions between the reinforcements and the polymer matrix. Thus, extensive attention has been focused on the improvement of the interaction between CNT and polymer matrix. It is well-known that delocalized p electrons from CNTs can bond with the p electrons of conducting polymers (CPs) to form pep non-covalent bonds in nanocomposites with coreeshell structure [4]. Among various CPs, polypyrrole (PPy) has been much exten- sively considered owing to its unique properties, such as high conductivity, good environmental stability, and easy preparation [5]. In addition, PPy offers superior flexibility in terms of con- structing a desired material properties and surface chemistry using different dopants, which have made it a promising candidate for preparing CNT/CP nanocomposite. Researchers have shown that PPy properties can be modified by introducing a small percentage of CNTs and that they disperse well in PPy matrix with greatly enhanced mechanical properties [6]. Electropolymerization of CPs has been proven to be a viable technique for the synthesis and deposition of CPs allowing the fabrication of polymer coatings with high levels of conductivity and chemical stability [7]. The electrochemical synthesis of CNTs/PPy nanocomposite coatings can be applied directly on implants for biomedical applications. This investigation offers an attempt to prepare nanostructured polymer composite coatings reinforced with functionalized MWCNTs for orthopedic implants. The * Corresponding author. Tel.: þ966 538801789; fax: þ966 538604818. E-mail addresses: madhankumar@kfupm.edu.sa, madhanchem@gmail.com (A. Madhan Kumar). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2014.08.073 0032-3861/© 2014 Elsevier Ltd. All rights reserved. Polymer 55 (2014) 5417e5424