Equiatomic NiTi, also called Nitinol, that contain nearly equal amount of nickel and titanium has a huge potential for use as a biomaterial in comparison to other traditional materials due to its shape memory and super elastic characteristics. Tadeusz Hryniewicz at Division of BioEngineering and Surface Electrochemistry, Koszalin University of Technology, Koszalin, Poland evaluated an overview of recent R&D related to NiTi based shape memory alloys. Discussing about the likely-looking applications and uses of NiTi based shape memory alloys as biomaterials; the issues of Nitinol Biocompatibility and optimistic approach to overcome these issues are also presented.
The findings by researcher Tadeusz Hryniewicz & a co-author suggest that shape memory alloys remember their shape because of the moelastic martensitic phase metamorphosis and that such alloys have an edge over in terms of large recoverable strain which allows them to exert continuous pressure during use.
A review of modification methods applied to Nitinol titanium based inter metallic compound utilized as biomaterial for medical applications, is performed. A range of techniques used for Nitinol improvement, commencing from its manufacture, chemical processing, heat treatment, mechanical treatment, including plasma ion implantation, coating to handle corrosion resistance, reducing nickel leaching, water boiling, electro polishing, improving vascular compatibility, Osseo assimilation, and/or disinfection.
Author Tadeusz Hryniewicz press for Nitinol alloying by adding a 3rd element to replace Ti or Ni which is thought to have a remarkable effect on corrosion resistance, phase transformation, biocompatibility of newly produced ternary Nitinol alloy. Though, the ternary nitinol alloys –except for NiTiCr in wires & NiTiCu in actuators employed as a pulling-pushing instrument in minimally invasive spine operation – has failed to found a large-scale industrial application yet. But one of the highly potent surface completing operations used for metallic biomaterials, with a special attention aimed to Nitinol, becomes visible as magneto electropolishing (MEP).
The author brings into notice another unique feature of metal samples after MEP is their de-hydrogenation observed both in titanium and Nickel. In reality, the weariness resistance of Nitinol after MEP referred to, dependent on the displacement and refinement of inclusions, increases from 3 to 7 times.
In effects of processing on the properties and biomedical applications of Nitinol as Arch Wire, Guided Wire, in Stent, in orthopaedics and in endoscope is presented. Biomedical applications of nitinol are linked with transformation temperatures of nitinol nearly to body temperature. Due to nitinol property of low elastic modulus close to natural bone compound and compressive strength higher than natural bone substance makes it a perfect material for biomedical implant applications. In medical field, nitinol has various other applications; for example, can be used as a guided wire, which can be utilized in joining broken bones, as an orthodontic wire or brace and as a heart valve tool to be used as a stent in cardiovascular treatments, artificial kidney, artificial organs, and as actuator in ureteral stenosis after kidney transplantation. Endoscopes are utilized in the common areas of the medical industry. A significant improvement was made in the controllability & flexibility of endoscopes with the use of Applications of Nitinol as Guided Wire shape memory alloy in Endoscopes.
As a saliva solution, pitting corrosion of nitinol works better than SS304 stainless steel. Corrosion resistance of NiTi is markedly lower in fluoridated saliva than in nonfluoridated saliva
One of the most recent developments in applying shape memory materials for biomedical applications is for orthodontic treatment. The author comments: As opposed to cobalt-chrome wires and stainless steel, Nitinol wires, due to their ultra elastic attributes, will enable the dentist to exert gentle and uninterrupted force to teeth, minimizing the likeliness of patient’s discomfort, and tissue hyalinization. Hence, the author deduces the use of NiTi alloy to be widespread, particularly during the first course of orthodontic treatment, when teeth are severely misaligned. Attaching NiTi arch wires to brackets, teeth can move in a controlled manner. In these conditions, Nitinol is in plateau area (on average 1–8% exertion) and discharge constant strain.
Briefly speaking, the author says that NiTi offers a large number of biomedical applications and there is also a good reference book on the biomedical applications of shape memory alloys by famously expert professors in the field of shape memory alloys – Prof. Hideki Hosoda from Tokyo Institute of Technology, Japan, and Miyazaki from the University of Tsukuba.