Fabrication of graded TiN coatings on nitinol occluders and effects on in vivo nickel release.

A nano-structured TiN/Ti coating with a total thickness of 0.9 mum was deposited on nitinol cardiac occluders using the filtered multi-arc vacuum ion plating technique at less than 300 degrees C. The coating was composed of laminated TiN/Ti layers with thickness of about 100 nm. The cardiac occluders made of a nitinol mesh with and without a graded nano-structured titanium nitride (TiN) coating were implanted into the hearts of rams. The nickel concentration of the whole blood of the animals were measured one week, one month, three months, and six months after implantation and compared to that before operation. The nickel concentration in the neo-endocardium covered occluders was also measured using graphite furnace atomic absorption spectrophotometry. After one week, the nickel content in the blood increased by a factor of three compared to the level before operation and decreased afterwards returning to the normal level after six months when endothelialization was complete. Statistical analyses showed that the TiN coating could mitigate nickel release into blood (P<0.01). For example, the nickel concentration released from the control increased from about 2.65+/-1.20 microg/kg, the normal concentration, to 7.30+/-1.00 microg/kg but just from 2.56+/-1.16 microg/kg to 4.68+/-1.29 microg/kg from the TiN coated occluder after 7 days. The nickel concentration in the neo-endocardium covered and TiN coated occluders reached 17.0+/-8.05 microg/kg in two months after implantation. In comparison, it was 31.0+/-5.72 microg/kg for the occluder without the TiN coating. While normal concentration of nickel in endocardium is also 2.6+/-1.09 microg/kg. Our results demonstrate that the graded TiN coating can significantly reduce nickel release into the endocardium (P<0.01) under in vivo conditions.