Janus cubes—polymer microparticles coated with metal on one side—self-assemble into various structures under the influence of a magnetic field, and manipulating the magnetic field turns the structures into microbots for use in drug delivery, in cell measurement, or as miniature actuators. At a virtual session at the 2021 International Chemical Congress of Pacific Basin Societies, Orlin Velev, a chemical engineer at North Carolina State University, outlined his group’s work. The researchers use photolithography to create polymer cubes about 10 µm across, then coat one side with a 10-nm layer of chromium topped by a 100-nm layer of cobalt. Placing the cubes between two electromagnets causes them to align and form a chain that stays connected after the field is turned off. Oriented one way (trans), the north-south poles of adjoining magnets align into a stiff connection. In the other orientation (cis), they can flip back and forth, so the chains fold and unfold when a magnetic field is applied. The group has made the chain fold around a cell and applied a magnetic gradient to move the captured cell. Another group at Swiss Federal Institute of Technology (ETH), Zurich, has shown it can control the microbots inside a rabbit eye as a possible microsurgical tool. Velev is studying if by squeezing a cell to measure its stiffness, he can determine whether it is healthy or infected with a virus. A related application involves contracting and expanding the chains to act as microactuators and tiny muscles.