Surface modified NiTi smart biomaterials: Surface engineering and biological compatibility

NiTi metallic biomaterials have a broad spectrum of clinical applications from heart stents to orthopedic implants. Recently, the use of NiTi smart biomaterials has received growing attention due to their striking features, including a low elastic modulus, shape memory behavior and acceptable biocompatibility. However, leaching of Ni ions from the surface of NiTi, the need for decreased elastic modulus and the desire for improved biological properties, including better material-cell interactions, biomineralization, and antibacterial activity, have provided the driving force for a wide variety of surface-modification techniques to address these problems before using NiTi in vivo. Depending on the target application, both dry and wet coating techniques have been employed to deposit biocompatible and bioactive layers over NiTi smart biomaterials. The influence of such coatings on the biological characteristics of the NiTi is illustrated. R&D activities have proved fruitful but much work needs to be done before clinical use of coated-NiTi.