Translational and rotational motion control of microgels enabling shoaling and schooling.

A technique for adequate flow control is important in the fields of science and engineering. In this study, we hypothesized that the unrestricted flow control inside a chamber containing 'schools of magnetic particles' might be possible through control of an external magnetic field, biomimicking the flow generated by schools of fish. Microgels based on superparamagnetic iron oxide nanoparticles (SPIONs) and poly(acrylic acid) hydrogels were employed. With an increase in the SPION content, the microgels responded more efficiently to the translational movement of the magnetic field. Rotational movement was more efficiently achieved with anisotropic distribution of SPIONs inside microgels, which was induced by applying a magnetic field immediately prior to crosslinking. The systems of the anisotropic microgels successfully provided microflow for effective mixing in a capillary. This biomimetic flow control may be useful for the control of fluid systems of any micro- or nano-size and any shape, regardless of the tortuosity.