Bionic Structured Milli-fluidics: A Review

Bionic structured milli-fluidics, as an emerging interdisciplinary subject of fluidics and biomimetics, is fast developing due to its diverse applications in various fields such as biomedical detection, material synthesis, water collection, etc. Researchers have mimicked natural surfaces with unique milli-structures like <i>Araucaria</i> leaves and cactus to achieve droplet manipulation for milli-fluidics. Furthermore, wetting gradient surfaces and external stimuli, including light, thermal, electricity, magnetism, and acoustics, have been utilized to create energy gradients and enhance bionic structured milli-fluidic performance. We comprehensively review the passive methods (bioinspired structures) and active strategies (external fields) for milli-fluidics. Moreover, the relationships between Laplace pressure, wettability gradients, and milli-fluidics are discussed first. Then, the advantages and disadvantages of different external stimuli are examined, and future directions for the field are suggested as well. Finally, a brief overview of key issues, current obstacles, and emerging trends of bionic structured milli-fluidics is presented, aiming to provide guidance for future research endeavors.