It is projected that by 2015 there will be 133 million Americans over 45, the age at which the increased incidence of heart diseases is documented. Many will require stents (small metal-mesh sleeves implanted in unclogged arteries by angioplasty). This multi-billion dollar industry, with over 2 million patients worldwide, 15% of whom use Nitinol (a NiTi Alloy) stents, has experienced a decline in sales recently, due in part to Thrombosis in about two out of 1000 per year in stable patients with relatively simple artery blockage. Thrombosis is a sudden blood clot that forms inside drug-eluting stents. As a result, the Food and Drug Adminstration, the American Heart Association, and others are calling for a new generation of stents, new designs and different alloys that are more flexible and more adaptable to the arteries. The future of Nitinol as a biomaterial therefore depends on a better understanding of mechanisms by which Nitinol surface can be rendered stable and inert, yet retain flexibility and machinability. Additionally, Ni enrichment and its leaching from the Nitinol surface must be controlled due to its carcinogenicity and deleterious effects in the liver and kidney. Ni also causes necrosis. Therefore, I propose to conduct standard American Society of Testing and Materials (ASTM) potentiodynamic and potentiostatic corrosion tests on the ternary alloys of Nitinol (Ni51Ti49)1-xTax system in the range of 0-20 atomic % Ta to evaluate the corrosion resistance in biological media. Ta, added as a ternary element in the NiTi-alloys, has been proven to impart X-ray visibility, stability, corrosion resistance and other beneficial effects. Inductively Coupled Plasma Analysis will be used to monitor Ni release in biological media. Biocompatibility will be assessed by observing the growth of cells on the material's surface and exploring blood compatibility [platelet spreading, protein adsorption, cell proliferation, inflammatory mediators, etc.] The Nitinol surfaces will be characterized using XRD, DSC, EPMA, Raman Spectroscopy, SEM, etc. I am of the opinion that this applied research effort could improve upon the in-vivo safety and performance profile of NiTi as used in coronary and peripheral arteries, as well as in bodily passageways where the alloy is subjected to corrosivity extremes, ultimately resulting in the even more widespread efficacious medical use of advanced Nitinol alloys
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| Pulletikurthi, C; Munroe, N; Gill, P et al. (2011) Cytotoxicity of Ni from Surface-Treated Porous Nitinol (PNT) on Osteoblast Cells. J Mater Eng Perform 20:824-829 |
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| Haider, Waseem; Munroe, Norman; Pulletikurthi, Chandan et al. (2009) A Comparative Biocompatibility Analysis of Ternary Nitinol Alloys. J Mater Eng Perform 18:760-764 |
