Three-Dimensional Maskless Fabrication of Bionic Unidirectional Liquid Spreading Surfaces Using a Phase Spatially Shaped Femtosecond Laser.

Ubiquitous biological processes exhibit the ability to achieve spontaneous directionally guided droplet transport. Maskless three-dimensional (3D) fabrication of various miniature bionic structures, a method applicable to various materials, is subject to processing method limitations. This remains a large obstacle to realizing self-driven, continuous, and controllable unidirectional liquid spreading. Thus, we present a flexible maskless 3D method for fabricating bionic unidirectional liquid spreading surfaces by using a phase spatially shaped femtosecond laser. The laser can be transformed from having Gaussian distributions to having 3D bionic structure field distributions. Furthermore, we fabricated Syntrichia caninervis bionic structures with a spiculate end for unidirectional water spreading; 1 μL droplets had a 16 mm flow length on Si surfaces when the S. caninervis single structure was 34 (length), 8 (width), and 12 μm (height). Furthermore, various bionic structures-Nepenthes, cactus, and moth structures-were fabricated on Si, SiO2, and Ti. We also demonstrated the measurability of two-dimensional (S-shaped) curved flows on Si wafers as well as 3D curved flows on a Ti pipe turning 120° within 2320 ms. Our method can realize high-efficiency maskless 3D processing of various materials and structures (especially asymmetric structures); it is both flexible and fast, effectively expanding the processing capacity of micro-/nanostructures on patterned surfaces. This is of great significance to various domains such as microfluids, fog collection, and chemical reaction control.