Abstract—In this study, the powders of Ni and Ti with 50.5 at.% Ni for 12 h were blended and cold pressed at the different pressures (50, 75 and100 MPa).The porous product obtained after Ni-Ti compacts were synthesized by SHS (self-propagating high- temperature synthesis) in the different preheating temperatures (200, 250 and 300oC) and heating rates (30, 60 and 90oC/min). The effects of the pressure, preheating temperature and heating rate were investigated on biocompatibility in vivo. The porosity in the synthesized products was in the range of 50.7–59.7 vol. %. The pressure, preheating temperature and heating rate were found to have an important effect on the biocompatibility in-vivo of the synthesized products. Max. fibrotic tissue within the porous implant was found in vivo periods (6 months), in which compacting pressure 100MPa. Keywords—NiTi, biomaterial, SHS, biocompatibility. I. INTRODUCTION ITI shape memory alloys (SMAs) are materials widely used in numerous biomedical applications (orthodontics, cardiovascular, orthopedics, urology, etc.) due to their good biocompatibility, unique shape memory properties, mechanical properties, superior damping capability, excellent corrosion resistance and wear resistance [1-8]. Since their mechanical properties are closer to those of cortical bones than stainless steels and titanium alloys [9], porous NiTi alloys show promising potential in the application of bone implantation. The porous structure also allows the ingrowths of new bone tissue along with the transport of body fluids, thus ensuring a harmonious bond between the implant and the body [4]. Measurements in literature suggests that NiTi alloy is safe and biocompatible due to its surface oxide film which is composed mainly of titanium oxide and acts as a barrier to prevent nickel from corrosion and ion leaching [10]. However, some negative side effects have been pointed out [9]. For example, the osteogenesis process and osteonectin synthesis activity in NiTi alloys are unfavorable compared to stainless steels and titanium alloys, Cell death rate is severe on NiTi alloys and proliferation of human gingival fibroblasts on NiTi samples with rough surface is slow compared to stainless steels and Ti alloys with the same surface roughness. The short-term biocompatibility of porous NiTi was determined to be comparable to that of dense NiTi. Moreover, in vivo standard allergy potential evaluation showed that porous NiTi Gul Tosun and Nuri Orhan are wtih Firat University, Technology Faculty Metalurgy and Material Engineering Department, 23119 Elazig, Turkey Hatice Eröksüz, Ali Said Durmuş, and Emine Ünsaldi are with Firat University, Faculty of Veterinary,23119 Elazig, Turkey edicine Latif Özler is with Firat University, Technology Faculty, Mechanical Engineering Department, 23119 Elazig, Turkey has no potential to produce irritation, systemic toxicity reactions, or sensitization in animal models [11]. Porous NiTi SMAs have been fabricated with powder metallurgy (PM) processes such as self-propagating high- temperature synthesis (SHS), metal injection molding (MIP), hot isostatic pressing (HIP) and spark plasma sintering (SPS) [4, 5, 12, 13]. These processes can avoid the problems associated with casting, like segregation or extensive grain growth and have the added advantages of precise control of composition and easy realization of complex part shapes [13]. The occurrence or amount of fibrosis inside the porous NiTi implant in bone tissue has not been assessed before. Rhalmi et al. [14] reported some fibroplasia and bone marrow within the pores of the porous NiTi implant. The aim of this study was to find out the possible cytotoxic effects of NiTi implant material in vivo. NiTi implants with 50.5 at. % Ni was fabricated by SHS at the different preheating temperatures, heating rates and pressures. The effects of the pressure and duration in vivo were investigated for the biocompatibility of implant material. II. MATERIAL AND METHOD A. Experimental Procedure for Production Titanium and nickel powders were used to produce porous NiTi alloy implants. The raw materials were 325 mesh Titanium (99,5 % in wt.) and Nickel (99,8% in wt.) powders. Characteristic features of powders used are given in Table I. TABLE I CHARACTERISTICS OF TI AND NI POWDERS [http://www.alfa-chemcat.com, 2007] Feature of Material Nickel Titanium Purity (%) 99.8 99.5 Spesific gravitiy (g/mol) 58,71 47,9 Powder dimension (mesh) -325 -325 Melting heat ( o C) 1453 1680 Spesific weight (g/cm 3 ) 8,9 4,507 Boiling heat ( o C) 2832 3260 The mixed powders of Ni and Ti with 50.5 at.% Ni were blended for 12 hours and then cold pressed in a cylindrical die with 10 mm diameter under different compaction pressures using a hydraulic press. The cold compacted porous samples were heated under different heating rates with the protection of high purity argon gas (99.9%) of about 0.1 MPa in a furnace. The samples were ignited under different preheating temperatures using electrical discharge pulse (14 kV and 30 mA). Once ignited, combustion waves could self-propagate along the axis to the other end of the compact in a very short time, and then porous NiTi implants were obtained by Biocompatibility of NiTi Alloy Implants in vivo Gul Tosun, Emine Ünsaldi Latif Özler, Nuri Orhan, Ali Said Durmuş, and Hatice Eröksüz N World Academy of Science, Engineering and Technology International Journal of Biomedical and Biological Engineering Vol:7, No:6, 2013 271 International Scholarly and Scientific Research & Innovation 7(6) 2013 scholar.waset.org/1307-6892/299 International Science Index, Biomedical and Biological Engineering Vol:7, No:6, 2013 waset.org/Publication/299