Passivation of magnetic material used in cell culture environment

Magnetic materials have been widely used for various electromagnetic actuators. However, there still exists a corrosion problem for most magnetic materials when used in a biological cell environment. The metal ions released can cause cytotoxicity. In this paper, we characterize the corrosion of a soft-magnetic FeCo alloy, which has been adopted in our magnetic tweezers, in several cell culture media. Obvious accelerated corrosion was observed in cardiomyocyte and neuronal cell media, but not in Dulbecco's Modified Eagle Medium. To eliminate the corrosion we examined electrochemical deposition of polypyrrole as well as pyrolytical deposition of parylene C for passivation. It was found that the quality of polypyrrole deposition was insufficient in the area near the edges of the tweezers tips where they had been laser-cut. However, the parylene C coating exhibited excellent isolation properties. In addition, parylene C-coated magnetic parts can also withstand repeated high magnetic field application. The cell viability of in vitro cultures exposed to the passivated material was inspected by live/dead cell staining. Both cardiomyocyte and primary neuronal cells could be cultured on parylene C coated magnetic parts for up to three weeks.