Fe–Pd based ferromagnetic shape memory actuators for medical applications: Biocompatibility, effect of surface roughness and protein coatings

Abstract

Ferromagnetic shape memory (FMSM) alloys constitute an exciting new class of smart materials that can yield magnetically switchable strains of several percent at constant temperatures and frequencies from quasi-static up to some kilohertz. In addition to their FMSM properties, these alloys can still be operated as conventional shape memory materials and also exhibit related superelasticity, which are both important features for use in medical devices. In this study, extensive in vitro assessments demonstrate for the first time that vapor-deposited single crystalline Fe70Pd30 thin films and roughness graded polycrystalline splats of the same stoichiometry exhibit excellent biocompatibility and even bioactivity in contact with different cell types—a prerequisite for medical applications. The present study shows that fibroblast and epithelial cell lines, as well as primary osteoblast cells, proliferate well on Fe–Pd. The number of focal contacts, important for strong tissue bonding, can be improved with different binding agents from the extracellular matrix. However, even without coating, there is clear evidence that cells on Fe–Pd substrates behave similarly to control experiments. Additionally, cytotoxic effects of polycrystalline surfaces with various roughness profiles can be excluded, giving another tunable parameter for applying Fe–Pd magnetically switchable membranes in, e.g., stents and valves.