Liquid Crystal Polymers as Intrinsically Magnetic and Programmable Soft Materials for Microrobotics.

Magnetic microrobots are emerging as powerful tools for biomedical applications. However, widespread reliance on composite materials to achieve programmed magnetic responsiveness, biomimetic elasticity, and biocompatibility of the microdevices results in complex fabrication protocols involving delicate material and processing optimization. An intrinsically magnetic, programmable, soft, biocompatible, and easily-processable alternative material for development of magnetic microrobots may be liquid crystal polymers (LCPs). To establish LCPs as magnetic systems, this work studies for the first time in detail the manipulation of pristine LCP microobjects with magnetic torques acting on their intrinsic anisotropic diamagnetism. Rotation of planar LCP microdisks in a rotating magnetic field is characterized to identify the step-out frequency, the key characteristic of magnetic microrobots defining the regime in which their motion is synchronized with the field. Frequencies up to 0.6 Hz, comparable to rotational frequencies of biological microswimmers, are achieved using readily available fields below 0.3 T. Furthermore, the magnetic properties of LCP microobjects are programmed via photoalignment to adjust microobject orientation relative to the applied field and step-out frequencies. These findings establish a promising foundation for a new class of advanced microrobots that in the future may combine the magnetic responsiveness of LCPs with their shape-morphing capabilities.