A mechanical hand-like functional surface capable of efficiently grasping and non-destructively releasing droplets

Efficient capture and residue free release of microdroplets have important applications in many fields, such as droplet manipulation, targeted drug therapy, microfluidics and so on. In this paper, a novel multi-level functional surface consisting of magnetic-particle-filled microplate arrays is designed and fabricated. Square cavities and convex strips are regularly distributed on the two lateral surfaces of each microplate, respectively. Under the action of magnetic field, the functional surface can firmly grasp droplets. When the magnetic field rotates, the droplets can be spontaneously released. Compared with the existing functional surfaces, the adhesive force of the present multi-level functional surface can reach 252 μN with a large contact angle of 151°, similar to the rose petal. As a “mechanical hand” for transferring droplets, the transfer distance is not controlled and the droplets can be easily released without residue due to the optimal design of microstructures. The mechanism to realize this function is also given in detail.