Flexible Magnetic Micropartners for Micromanipulation at Interfaces.

Microrobots working at liquid surfaces have immense potential for micromanipulation in tight and enclosed spaces, whereas constructing agile and functional microrobots with simple structures at liquid surfaces is a great challenge. Herein, a pair of magnetic circular microdisks working as partners at ethylene glycol (EG) surfaces are proposed in order to accomplish flexible locomotion and in situ micromanipulation tasks. The microdisks can be controlled to connect and separate by modulating the orientation of the applied magnetic field. After the two disks connect as an entity, they are transformed into micropartners under an oscillating magnetic field in 3D space. By changing the vertical component of the oscillating field, the micropartners can obtain controllable propulsion through paddling and wriggling modes, and the locomotion speed can reach approximately two body lengths per second. They can also climb a meniscus, and even crawl on a solid surface in a liquid. Finally, this pair of micropartners is demonstrated as a flexible microgripper to implement manipulations at the liquid surfaces, including cargo capture, delivery along prescribed paths, and release.