Curvature driven transport of mouse macrophages in a pulsating magnetic garnet film ratchet

Magnetic fields varying on the colloidal length scale are used for the directed transport of magnetically labeled biological cells. The transport is achieved by using the ratchet effect which relies on an asymmetric, symmetry broken periodic potential where nonequilibrium fluctuations or oscillations generate a net cell current. Ferrofluid ingested mouse macrophages were placed on a magnetic garnet film with alternating stripe domain patterns, and a pulsating magnetic potential is provided by superposing an oscillating magnetic field normal to the film. The symmetry of the resulting periodic stripe potential is broken locally by the curvature of the stripes. We show, both experimentally and theoretically, the curvature of such stripes required for inducing directed transport of the macrophages in the ratchet. This may be useful for microfluidic devices such as a digital colloidal shift register for magnetically labeled biological cells.