Synthesis of calcium hydrogen phosphate and hydroxyapatite coating on SS316 substrate through pulsed electrodeposition Rajib Chakraborty a, ⁎, Srijan Sengupta b , Partha Saha a , Karabi Das b , Siddhartha Das b a Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India b Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India abstract article info Article history: Received 18 May 2016 Received in revised form 21 June 2016 Accepted 19 July 2016 Available online 20 July 2016 The orthopaedic implants for human body are generally made of different biomaterials like stainless steels or Ti based alloys. However, it has been found that from surface properties point of view, none of these materials is attractive for fast tissue or cell growth on the surface of implant. This is one of the most important criteria to as- sure quick bonding between implant and body tissues vis-à-vis minimum recovery time for the patient. Keeping in view of the above facts, this work involves the pulsed electro-deposition coating of biocompatible hydroxyap- atite and its group compounds from a diluted bath of calcium and phosphate salt at various current densities over the biomaterial sheet of SS316. SEM study confirms different morphologies of the coatings at different current densities. Characterization techniques like X-ray diffraction, SEM with EDX and FTIR have been used to confirm the phase and percentage quantity of hydroxyapatite compound in the depositions. This coating can serve as a medium for faster tissue growth over the metallic implants. © 2016 Elsevier B.V. All rights reserved. Keywords: Pulsed electrodeposition Bio-compatible coating Calcium hydrogen phosphate Hydroxyapatite 1. Introduction Over past few decades, researchers have been successfully able to develop different bio-compatible materials and technologies related to joint replacement in human body. These materials are inert to human body fluid which runs between tissues over the bone to circulate oxygen and nutrients [1]. Human joints actuate by the contraction and expan- sion of the thousands of muscle or tissues surrounded over them. The actuation signal comes from our brain through neurons network to those tissues over the joint and based on their chronological expansion or contraction specific joint structure moves in three dimensional planes as desired. Now if any of these tissues is not suitably bonded with a particular portion of the joint, the chronological sequence of three dimensional movements will be interrupted at that particular se- quence of operation which may lead to a malfunction of the movement of the joint. It is very essential that every single tissue surrounding the joint adheres strongly to the surface of the implant in micrometre level [2–4]. Till now, most of the developed bio-materials capable of replacing human body joints, used to be evaluated mostly based on the mechan- ical properties like strength, wear resistance, ductility etc. But, it is equally important to ensure a good surface adherence and faster tissue growth [5,6]. In order to have a better adhesion of tissues over the joints, it is rec- ommended to have sufficient porosity and increased surface micro- roughness over the implants which can only be achieved through a po- rous coating over the implant surface [7]. As of now, most of the im- plants are made of metal surfaces in order to achieve the desired wear resistant or toughness in the joints throughout the specific life period of the joints, which is about 10 to 20 years. Any polycrystalline metal surface/coating consists of multi-oriented grain structure with different surface energy. These differences in surface energy create anisotropic bonding of tissues over the implant surface which may lead to partial detachment. Furthermore, in metallic alloys, segregation takes place at the grain boundaries which also create a variation in surface energy vis-à-vis bonding energy [8]. In order to overcome this surface energy variation problem, a bioac- tive material coating is envisaged over the implant metal surface. Re- searchers have found that the best bioactive coating is hydroxyapatite, which is one of the major elements in our natural bone [9,10]. Over the last decade several techniques have been tried to develop coating of bioactive hydroxyapatite over the implant material [11,12]. A few successful coating techniques are sol-gel technique, pulsed laser deposi- tion, laser cladding etc. [13]. Among these methods, only plasma spray method is clinically accepted till now. However, plasma spray method suffers from some drawbacks such as extremely high application tem- perature which effect homogeneity of the coatings and structure of me- tallic implants, because of unpredictable phase changes of calcium- phosphorous ceramic during coating, particle release and delamination [14]. Materials Science and Engineering C 69 (2016) 875–883 ⁎ Corresponding author. E-mail address: rajibju4@gmail.com (R. Chakraborty). http://dx.doi.org/10.1016/j.msec.2016.07.044 0928-4931/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec