3D-Printed Bioinspired Cassie-Baxter Wettability for Controllable Microdroplet Manipulation.

It is a great challenge to fabricate a surface with Cassie-Baxter wettability that can be continuously adjusted from hydrophilicity to superhydrophobicity by changing of geometric parameters. In this paper, we propose and demonstrate a bioinspired surface fabricated by using a projection micro-stereolithography (PμSL) based 3D printing technique to address the challenge. Independent of materials, the bioinspired textured surface has a maximum contact angle (CA) of 171°, which is even higher than that of the omniphobic springtail skin we try to imitate. Most significantly, we are able to control the CA of the bioinspired surface in the range of 55-171° and the adhesion force from 71 to 99 μN continuously by only changing the geometric parameters of the bioinspired microstructures. The underlying mechanisms of the CA control of our bioinspired surface are also revealed by using a multi-phase lattice Boltzmann model. Furthermore, we demonstrate potential applications in droplet-based microreactors, nonloss water transportation, and coalescence of water droplets by employing our 3D-printed bioinspired structures with their remarkable precise Cassie-Baxter wettability control and petal effects. The present results potentially pave a new way for designing next generation functional surfaces for microdroplet manipulation, droplet-based biodetection, antifouling surfaces, and cell culture.