Publication Date

Spring 2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

General Engineering

Advisor

Guna S. Selvaduray

Keywords

Nickel Leaching, Nitinol, Nitriding, Oxidation, Surface Modification

Subject Areas

Materials Science; Biomedical engineering

Abstract

Nitinol is widely used as a biomaterial for implantable medical devices but can be susceptible to nickel leaching. Our research was aimed at determining nickel leaching from surface treated Nitinol samples, treated as follows: mechanical polishing (untreated), oxidation, and nitriding+oxidation (5 different nitriding temperatures). Five specimens from each category were immersed in 40 mL PBS solution and incubated at 37°C over 91 days. Nickel concentration readings were taken at regular intervals. After 91 days, the average nickel concentration in the PBS solution was (a) 0.223 mg/L, SD 0.017, untreated, (b) 7.68 mg/L, SD 6.405, 1000°C nitriding+oxidation, and (c) 3.914 mg/L, SD 1.78, oxidation-only. The concentration readings had large standard deviations implying differences in surface characteristics after treatment. The increased nickel leaching from treated samples was thought to be due to atomic diffusion and exposure of the nickel-rich sublayers to PBS after oxide layer delamination. These sublayers formed after formation of thick (>1 µm) TiO2 layers during oxidation.

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