Influence of nickel ion release on leukocyte activation: a study with coated and non-coated NiTi shape memory alloys

Abstract Owing to their mechanical and thermal memory properties, nickel–titanium shape memory alloys (NiTi-SMA) are very interesting for biomedical applications. In most cases, medical implants are initially exposed to a blood-containing environment. The potential release of Ni ions needs to be considered because it counteracts a good biocompatibility and may well influence the release of mediators from adherent and surrounding leukocytes. Two different leukocyte fractions (PMN, PBMC) were isolated from peripheral blood and were added to calcium phosphate-coated or non-coated NiTi. The supernatants were analyzed for cytokine content. Ni-ion release of coated, non-coated and etched NiTi samples was analyzed by graphite furnace atomic absorption spectrometry. Additionally, cytokine release studies were performed with exogenously added Ni ions. In the presence of NiTi a significant, but low increase in the release of IL-1ra, IL-6 and IL-8 was observed. In contrast, coated NiTi led to an elevated release of all analyzed cytokines. Ni-ion release ranged from 60 μg/l (non-coated NiTi) to 8 mg/l (coated or etched NiTi). Incubations of leukocytes and exogenously added Ni chloride (≤2.4 mg/l) did not lead to a significant modulation in cytokine generation. An increased cytokine release was only observed at 24 mg/l Ni chloride.