Superparamagnetic swimming microrobots with adjusted magnetic anisotropy

We present the fabrication of soft-magnetic helical micro robots employing two-photon polymerization of a superparamagnetic polymer composite. The proposed fabrication method allows for adjusting the magnetic easy axis independent from the helical shape by aligning the embedded superparamagnetic nanoparticles prior to composite crosslinking. In contrast to conventional, shape-anisotropic helical micro swimmers, the proposed devices possess a magnetic easy axis perpendicular to their helical axis and thus benefit from a significant performance increase including a wobbling-free swimming behavior at low speeds as well as an increase in forward velocity of more than 250%. The presented results highlight the importance of the magnetic easy axis for actuation purposes and imply increased performance for the entire class of superparamagnetic polymer actuators.