Various natural materials have hierarchical microscale and nanoscale structures that allow for directional water transport. Here we report an ultrafast water transport process in the surface of a Sarracenia trichome, whose transport velocity is about three orders of magnitude faster than those measured in cactus spine and spider silk. The high velocity of water transport is attributed to the unique hierarchical microchannel organization of the trichome. Two types of ribs with different height regularly distribute around the trichome cone, where two neighbouring high ribs form a large channel that contains 1-5 low ribs that define smaller base channels. This results in two successive but distinct modes of water transport. Initially, a rapid thin film of water is formed inside the base channels (Mode I), which is followed by ultrafast water sliding on top of that thin film (Mode II). This two-step ultrafast water transport mechanism is modelled and experimentally tested in bio-inspired microchannels, which demonstrates the potential of this hierarchal design for microfluidic applications.

normally tend to condense on the protruding solid surface, but the already condensed bulked water film will slow down further condensation. [6][7][8] In nature, many biological samples have developed unique parts to solve the bulked water film-restrained fog condensation, [9][10][11] such as spider silk with spindle-knots [12][13][14] and cactus with cone spines. [15][16][17] Their conical structures can directionally transport condensed water from the tip to the bottom, releasing the tip surface area for further fog condensation. [18][19][20][21][22] Conical structures are usually combined with fog harps to construct fog collectors for highly efficient fog harvesting. [23][24][25][26][27][28] However, the velocity of directional water transport on these conical structures remains of ≈0.5 mm s −1 , which limits further enhancement of fog harvesting by fog collectors.Fortunately, a more efficient fog harvesting and transport mode was discovered on Sarracenia trichomes that has a unique hierarchical microchannel structure around the needle-shaped trichomes (Figure 1a). [29] A thin water film is automatically formed on the hierarchical microchannel structure to generate superslippery capillaries, which remarkably enhances the water transport capability and further reinforces the fog harvesting efficiency of trichomes. The hierarchical microchannel shows greater properties than the uniform microchannel, which can also aid on the development of new microfluidic systems. [30][31][32][33] However, the underlying dynamic mechanism of hierarchical microchannel-induced ultrafast transport on fog harvesting is still ambiguous, and the multiscale structural coupling effect on fog harvesting performance is also a great challenge.Herein, we propose an effective strategy to fabricate a bionic Sarracenia trichome (BST) using a one-step thermoplastic stretching approach on a glass fiber bundle under the constraint of an inner gear pattern. The BST possesses an ondemand hierarchical microchannel structure, whose major channels are confined by an inner gear pattern, as well as junior microchannels are automatically assembled by the glass fiber monofilaments. Its excellent gravity-ignoring fog harvesting property was herein demonstrated, which was governed by a superslippery sliding mode, similar to the real Sarracenia trichome. The capillary condensation and fog harvesting theoretical model of BST was built to further discuss the dynamic Fog harvesting through bionic strategies to solve water shortage has drawn considerable attention. Recently, an ultrafast fog harvesting and transport mode was identified in Sarracenia trichome, which is mainly attributed to its superslippery capillary force induced by its unique hierarchical microchannel. However, the underlying effect of hierarchical microchannel-induced ultrafast transport on fog harvesting and the multiscale structural coupling effect on highly efficient fog harvesting are still great challenges. Herein, a bionic Sarracenia trichome (BST) with an on-demand regular hierarchical ...

Unidirectional liquid transport without any need of external energy has drawn worldwide attention for its potential applications in various fields such as microfluidics, biomedicine and mechanical engineering. In nature, numerous creatures have evolved such extraordinary unidirectional liquid transport ability, such as spider silk, Sarracenia’s trichomes, and Nepenthes alata’s peristome, etc. This review summarizes the current progresses of natural unidirectional liquid transport on 1-Dimensional (1D) linear structure and 2-Dimensional (2D) surface structure. The driving force of unidirectional liquid transport which is determined by unique structure exist distinct differences in physics. The fundamental understanding of 1D and 2D unidirectional liquid transport especially about hierarchical structural characteristics and their transport mechanism were concentrated, and various bioinspired fabrication methods are also introduced. The applications of bioinspired directional liquid transport are demonstrated especially in fields of microfluidics, biomedical devices and anti-icing surfaces. With newly developed smart materials, various liquid transport regulation strategies are also summarized for the control of transport speed, direction guiding, etc. Finally, we provide new insights and future perspectives of the directional transport materials.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202103423.

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