لیلا فتح یونس نژند

Despite having the superior mechanical properties, NiTi alloy could not meet all clinical requirements for implants. The bio-inert surface of this alloy is one of the reasons for failing its implantation. Releasing the high amount of harmful nickel ions from NiTi alloy is another serious concern causing allergic problems such as inflammation and cells death. Therefore, the surface modification of this alloy is necessary for improving its performance in the biomedical applications. In this work, the surface modification of NiTi was carried out by pretreatment and applying the bioactive calcium phosphate coating. For pretreatment of NiTi alloy, we used two different processes of alkaline treatment in 5 M NaOH solution at 60 °C for 24 hour and heat treatment at 500 ˚C for 30 minute. Moreover, a bioactive coating of calcium phosphate was applied by pulsed current electrochemical deposition at a constant current density of 15 mA/cm2 and duty cycle of 0.1 on the pretreated surface of NiTi. The results showed that heat treatment further decreased the nickel release from NiTi into Ringer's solution as compared to the alkaline treatment. Moreover, wettability of the NiTi sample pretreated with these two processes was different that affected the microstructure of the top calcium phosphate coating. In fact, the higher surface tension resulted from increasing the wettability caused the formation of porosities with larger size in the microstructure of the coating applied by electrochemical deposition method.