Materials scientists at the Friedrich Schiller University of Jena, Germany, have examined implants made of nickel-titanium alloy in a long-term study and have determined that the release of nickel from wires made of nickel-titanium alloys is very low. They found that the metal was also safe over longer periods of time.

An occluder made of a nickel-titanium alloy. These medical im plants are used for the correction of a defective cardiac septum. (Credit: Jan-Peter Kasper/ FSU)

While any metal object containing nickel may be hazardous to someone with a nickel allergy, nickel-titanium alloys are increasingly being used as material for cardiovascular implants in minimal invasive surgery. Once implanted, these alloys can release small amounts of nickel due to corrosion phenomena, leading to concern that over a long period of time, this could lead to a nickel contamination in the patient’s body causing more health problems.

The scientists conducted the first long-term study on this, examining nickel release in detail. The objects that they examined included fine wires from a superelastic nickel-titanium alloy that are applied in the form of occluders, for example. The implant can be mechanically drawn into the shape of a thin thread, which then can be placed in a cardiac catheter and ideally, remain in the patient’s body for years or decades.

The researchers exposed samples of the wires, which underwent different mechanical and thermal pre-treatment, to highly purified water. They then examined the release of nickel according to pre-defined time intervals. They successfully developed a reliable test routine to measure the process of the nickel release over an eight-month period.

They found that in the first days and weeks, depending on the pre-treatment of the material, considerable amounts of nickel may get released due to the mechanical strain of the implant during the surgery. However, in the long run, nickel release decreases to amounts of a few nanograms per day and is, therefore, far below the amount of nickel that most people absorb through their daily food intake.