Direction-preferred liquid transportation on biomimetic hierarchical gradient microgrooves

Conventional understanding holds that droplets on microgrooves flow symmetrically toward both ends, which limits their utility in applications requiring direction-preferred droplet transport, such as vapor chambers. Inspired by the fog-collecting strategies of cactus spines, we propose a bioinspired hierarchical gradient microgroove (BHGM) that achieves the liquid transport in a preferred direction. By combining primary microgrooves with surface nanostructures, BHGM provides a strong initial driving force for liquid transport. Secondary microgrooves are introduced to increase the liquid–solid contact area, further enhancing capillary pressure. Additionally, gradient interfaces at structural discontinuities create unbalanced surface tension, driving direction-preferred liquid transport. This, in combination with the shape variation of the secondary grooves, regulates the meniscus and enables rapid and heterogeneous liquid movement. The BHGM demonstrates forward capillary wicking over a distance of up to 90 mm in just 12.5 s while reducing reverse wicking time by 53.7%. At the two gradient interfaces from bottom to top, speed reduction rates are only 7.7% and 2.3%, respectively. In addition, the BHGM maintains liquid transport capability even at bending angles of 90° and 120°. This hierarchical design enhances heterogeneous capillary transport efficiency while preserving scalability and adaptability, offering promising potential for practical applications, including improved thermal management in vapor chambers and more efficient fluid control in microfluidics.