Pick up and release of micro-objects: A motion-free method to change the conformity of a capillary contact

We propose a new 3D-printed capillary gripper equipped with a textured surface for motion-free release. The gripper classically picks up micro-objects thanks to the capillary forces induced by a liquid bridge. Micro-objects are released by decreasing the volume of this bridge through evaporation. The latter can be either natural or speeded up by a heating source (an IR laser or the Joule effect). The volume reduction changes the conformity of the contact between the gripper and the object. We analyze the gripper performance and the capillary force generated, and then we rationalize the release mechanism by defining the concept of contact conformity in the context of capillary forces. © 2020 The Royal Society of Chemistry.