Ferromagnetic Cilia

In this chapter we derive and compare the different types of magnetic actuations—namely actuation by gradient force and actuation by torque—with strong focus on scaling behaviours in view of miniaturization. We also compare ferromagnetic and (super‐)paramagnetic materials and discuss their differences with respect to actuation amplitude and their respective advantages. We then present the development of a ferromagnetic polymer made from iron nanoparticles and polydimethylsiloxane and describe a process that can structure this material into high aspect ratio lying artificial cilia with a length of 300 μm. These ferromagnetic artificial cilia were actuated with a homogeneous rotating magnetic field (μ0H<50 mT) generated with a compact external electromagnet. An asymmetric movement involving torsion could be created when the cilia were provided with a remanent magnetization perpendicular to the plane of rotation of the magnetic field vector. The artificial cilia could be actuated in fluid up to a frequency of ∼50 Hz and in a micro‐fluidic chamber we were able to demonstrate rotational as well as translational fluid movements with fluid velocities up to ∼500 μm s−1.