3D Capillary Transistors for Photothermal‐Responsive Unidirectional Liquid Transport

Abstract Unidirectional liquid transport, a special self‐propelled wetting phenomenon observed in natural structures like the Nepenthes pitcher plant peristome, Araucaria leaves, and Crassula muscosa shoots, has inspired scientists to develop various novel microfluidic devices for liquid collection, physical/chemical reactions, and irrigation. Recently, the concept of capillary transistors is proposed to enable a programmable transport area and a significant increase in unidirectional capillary height, which is expected to greatly expand the applications of conventional microfluidic chips. In this work, using black resin as the three‐dimensional (3D) printing material, we construct microfluidic chips with capillary transistors for photothermal‐responsive unidirectional liquid transport. The transistors consist of asymmetric overhanging structures with connected overhangs, allowing for fast, long‐distance, and large‐area unidirectional liquid transport, with a unidirectional capillary height exceeding 90.0 mm—more than double the values reported in most previous studies. Furthermore, smart control of capillary height is achieved by applying external photothermal stimuli to the capillary transistors, demonstrating their potential applications in photothermal‐responsive unidirectional liquid transport and mixing in 3D space. It is envisioned that additional functions such as liquid patterning, desalination, and biochemical microreactions would be developed by engineering capillary transistors and their responsiveness.