Dual-laser-actuated operation of small size objects at a liquid interface

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.

Programmable light-driven swimming actuators via wavelength signal switching

Light-driven swimming actuators with different motion modes could lead to many previously unachievable applications. However, controllable navigation often requires focusing light precisely on certain positions of the actuator, which is unfavorable for accurate dynamical operation or in microscale applications. Here, we present a type of programmable swimming actuators that can execute wavelength-dependent multidirectional motions via the Marangoni effect. Several multi–degree of freedom swimming motions have been realized: Forward-and-backward and zigzag actuators can execute one-dimensional (1D) and 2D linear motion, respectively; bidirectional gear rotation as angular motion can be regulated to obtain tunable speeds; and the turning actuator as a “freighter” is able to turn left, right, and go straight for precise maze navigation. A mechanical measurement system is established to quantitatively measure the driving force of the motion directly. The accessible wavelength-selective strategy presented here can inspire further explorations of simple and practical light-driven materials and systems.