3D printing of asymmetric re-entrant microstructure for unidirectional liquid spreading

Abstract

Numerous organisms in nature have developed extraordinary unidirectional liquid spreading capabilities, including the peristome of Nepenthes Pitcher Plant, the back of a desert beetle, spider silk, and the conical spine of a cactus. Unidirectional liquid spreading without the use of external energy has sparked worldwide interest due to its potential applications in fields such as microfluidics, biomedicine, and mechanical engineering. However, the structures in their work were extremely intricate, and the 3D printing machines they used were not inexpensive. Moreover, the unidirectional liquid spreading, in most cases, transports in a linear path of limited capillary rise height. To overcome these challenges, asymmetric re-entrant microstructures were designed and fabricated using Digital Light Processing (DLP) 3D Printer. The unidirectional liquid spreading on the bioinspired asymmetric re-entrant microstructure is propelled by the capillary driving force between two parallel surfaces from the roof of the microstructures to the surface of the substrate. The capillary break, which is the spacing in between horizontal microstructures, is small enough to promote the unidirectional liquid spreading in the forward direction and also to inhibit liquid spreading in the backward direction, hence promoting unidirectional liquid spreading. The performance of liquid transport on the bioinspired asymmetric re-entrant microstructures was significantly impacted by the feature sizes and spacing between adjacent microstructures, according to the project's findings. Within the scope of this project, applications of microfluidic chips and oil-water separation were realized. These findings can help future research work to investigate other potential applications on bioinspired asymmetric re-entrant microstructures for unidirectional liquid spreading.