Enhanced corrosion protection of NiTi orthopedic implants by highly crystalline hydroxyapatite deposited by spin coating: The importance of pre-treatment

NiTi shape memory alloy has found broad applications in orthopedics and dentistry due to its superelasticity, shape memory effect, high corrosion performance, and biocompatibility. New horizons for biomedical applications of NiTi can be opened by improving its corrosion resistance and surface characteristics. The corrosion resistance and biological characteristics of NiTi can be improved by appropriate pre-treatments, such as mechanical polishing, acid chemical etching followed by immersion in an alkali solution and heat treatment, followed by the deposition of a nano-HAp layer by sol-gel spin coating. To deposit a highly crystalline nano-HAp coating, the synthesized HAp coatings were calcined in the temperature range 400-600 degrees C and the further investigations were carried out on an optimum coating of HAp calcined at 600 degrees C. Results indicated that the type of pre-treatment influenced the final properties of coated NiTi. While heat-treated NiTi resulted in superior corrosion behavior and in-vitro bioactivity, NiTi treated by acid etching followed by immersion in an alkali solution provided the highest hydrophilicity. The contact angle of water on the HAp-coated, heat treated NiTi was 21% lower than that on mechanically polished NiTi. The HAp coating enhanced the final characteristics of pre-treated NiTi irrespective of the type of pre-treatment. A decrease of 75% in Ni2+ ion release and a 212% increase in polarization resistance for HAp-coated, heat treated NiTi showed its superior corrosion resistance in Ringer's solution at 37 degrees C under static conditions, compared to mechanically polished NiTi.

Automated summary

NiTi shape memory alloy has broad applications in orthopedics and dentistry due to its superelasticity, shape memory effect, high corrosion performance, and biocompatibility. New horizons for biomedical applications of NiTi can be opened by improving its corrosion resistance and surface characteristics through appropriate pre-treatments. The type of pre-treatment influences the final properties of coated NiTi, with different treatments showing different advantages such as superior corrosion behavior, in-vitro bioactivity, or hydrophilicity. The deposition of a highly crystalline nano-HAp coating enhances the final characteristics of pre-treated NiTi, leading to superior corrosion resistance compared to mechanically polished NiTi.