Biomimetic Water-Repelling Surfaces with Robustly Flexible Structures

Abstract

Biomimetic liquid-repelling surfaces have been the subject of considerable scientific research and technological application. To design such surfaces, a flexibility-based oscillation strategy has been shown to resolve the problem of liquid-surface positioning encountered by the previous, rigiditybased asymmetry strategy; however, its usage is limited by weak mechanical robustness and confined repellency enhancement. Here we design a flexible surface comprising mesoscale heads and microscale spring sets, in analogy to the mushroom-like geometry discovered on springtail cuticles, and then realize this through three-dimensional projection micro stereolithography. Such a surface exhibits strong mechanical robustness against ubiquitous normal and shear compression and even endures tribological friction. Simultaneously, the surface elevates water repellency for impacting droplets by enhancing impalement resistance and reducing contact time, partially reaching an improvement of ~ 80% via structural tilting movements. This is the first demonstration of flexible interfacial structures to robustly endure tribological friction as well as to promote water repellency, approaching real-world applications of water-repelling. Also, a flexibility gradient is created on the surface to directionally manipulate droplets, paving the way for droplet transport.

Robust and durable liquid-repellent surfaces

“…29f), as well as tribological friction. 50 Moreover, these micro structures with re-entrant geometries can also be used to improve the thermodynamic durability of liquid-repellent surfaces, which will be discussed in Section 4.2.2.1.…”

“…First of all, the matrix and surface chemistry should be considered, for example, abrasion-tolerant substrates could partially improve the mechanical durability of liquid-repellent surfaces, 46,47 while carbonfluorine-based surface agents usually generate better chemical durability than carbon-hydrogen-based groups. 48 Next, various special surface textures, such as re-entrant microstructures, 49,50 densely and closely packed nanostructures, 51 self-similar rough structures, 52 hierarchical micro/nano structures, 53 etc., have been designed to enhance the robustness and durability of liquidrepellent surfaces from different aspects. For those substrates covered with liquid-repellent coatings, increasing the bonding strength among them is a universal and effective strategy.…”

Multifunctional Biomimetic Microstructured Surfaces for Healthcare Applications

“…Dini et al utilized 3D projection micro-stereolithography to prepare a biomimetic surface composed of "springs" of mushroom-shaped basic units. [82] The flexible "springs" structure can robustly withstand tribological friction, improve kinetic repulsion during droplet intrusion, and reduce contact time. By designing a nonuniform set of springs to construct an elastic gradient surface, the droplets can be manipulated in a directional manner for droplet transport.…”

Transformable Nanotheranostics Capable of Sensoring Nucleic Acid Drugs’ Spatiotemporal Behaviors

“…This result might be due to the flexible structure of GP and stronger interactions with water molecules. [20] In contrast, the dimer was less flexible, and the rigid ring structure affected the interaction with water molecules, leading to self-assembly to form stable aggregates (Figure 2c). Moreover, the solvent accessible surface area (SASA) was used to evaluate the degree of self-assembly.…”