Abstract
Numerous natural systems contain surfaces or threads that enable directional water transport1,2,3,4,5,6,7. This behaviour is usually ascribed to hierarchical structural features at the microscale and nanoscale, with gradients in surface energy8,9 and gradients in Laplace pressure10 thought to be the main driving forces. Here we study the prey-trapping pitcher organs of the carnivorous plant Nepenthes alata. We find that continuous, directional water transport occurs on the surface of the ‘peristome’—the rim of the pitcher—because of its multiscale structure, which optimizes and enhances capillary rise11,12 in the transport direction, and prevents backflow by pinning in place any water front that is moving in the reverse direction. This results not only in unidirectional flow despite the absence of any surface-energy gradient, but also in a transport speed that is much higher than previously thought. We anticipate that the basic ‘design’ principles underlying this behaviour could be used to develop artificial fluid-transport systems with practical applications.
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References
Parker, A. R. & Lawrence, C. R. Water capture by a desert beetle. Nature 414, 33–34 (2001)
Zheng, Y. M. et al. Directional water collection on wetted spider silk. Nature 463, 640–643 (2010)
Ju, J. et al. A multi-structural and multi-functional integrated fog collection system in cactus. Nature Commun . 3, 1247 (2012)
Ishii, D. et al. Water transport mechanism through open capillaries analyzed by direct surface modifications on biological surfaces. Sci. Rep. 3, 3024 (2013)
Bai, H. et al. Direction controlled driving of tiny water drops on bioinspired artificial spider silks. Adv. Mater. 22, 5521–5525 (2010)
Ju, J., Zheng, Y. M. & Jiang, L. Bioinspired one-dimensional materials for directional liquid transport. Acc. Chem. Res. 47, 2342–2352 (2014)
Li, K. et al. Structured cone arrays for continuous and effective collection of micron-sized oil droplets from water. Nature Commun . 4, 2276 (2013)
Chaudhury, M. K. & Whitesides, G. M. How to make water run uphill. Science 256, 1539–1541 (1992)
Daniel, S., Chaudhury, M. K. & Chen, J. C. Past drop movements resulting from the phase change on a gradient surface. Science 291, 633–636 (2001)
Lorenceau, E. & Quéré, D. Drops on a conical wire. J. Fluid Mech. 510, 29–45 (2004)
Taylor, B. Concerning the ascent of water between two glass plates. Phil. Trans. R. Soc. Lond. 27, 538 (1712)
Hauksbee, F. An experiment touching the ascent of water between two glass plates in a hyperbolick figure. Phil. Trans. R. Soc. Lond . 27, 539 (1712)
Juniper, B. E. & Burras, J. K. How pitcher plants trap insects. New Sci. 13, 75–77 (1962)
Ellison, A. M. Nutrient limitation and stoichiometry of carnivorous plants. Plant Biol. 8, 740–747 (2006)
Bohn, H. F. & Federle, W. Insect aquaplaning: Nepenthes pitcher plants capture prey with the peristome, a fully wettable water-lubricated anisotropic surface. Proc. Natl Acad. Sci. USA 101, 14138–14143 (2004)
Bauer, U. & Federle, W. The insect-trapping rim of Nepenthes pitchers: surface structure and function. Plant Signal. Behav . 4, 1019–1023 (2009)
Bauer, U., Bohn, H. F. & Federle, W. Harmless nectar source or deadly trap: Nepenthes pitchers are activated by rain, condensation and nectar. Proc. R. Soc. B 275, 259–265 (2008)
Wong, T. S. et al. Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity. Nature 477, 443–447 (2011)
Lafuma, A. & Quéré, D. Slippery pre-suffused surfaces. EPL 96, 56001 (2011)
Oliver, J. F., Huh, C. & Mason, S. G. Resist to spreading of liquids by sharp edges. J. Colloid Interface Sci. 59, 568–581 (1977)
Sun, M. H. et al. Artificial lotus leaf by nanocasting. Langmuir 21, 8978–8981 (2005)
Zhou, J. W., Ellis, A. V. & Voelcker, N. H. Recent developments in PDMS surface modification for microfluidic devices. Electrophoresis 31, 2–16 (2010)
Vogler, E. A. Structure and reactivity of water at biomaterial surfaces. Adv. Colloid Interface Sci. 74, 69–117 (1998)
Tian, Y. & Jiang, L. Wetting: intrinsically robust hydrophobicity. Nature Mater . 12, 291–292 (2013)
Chu, K.-H., Xiao, R. & Wang, E. N. Uni-directional liquid spreading on asymmetric nanostructured surfaces. Nature Mater . 9, 413–417 (2010)
Concus, P. & Finn, R. On the behavior of a capillary surface in a wedge. Proc. Natl Acad. Sci. USA 63, 292 (1969)
Finn, R. Capillary surface interfaces. Not. Am. Math. Soc . 46, 770–781 (1999)
Lopez de Ramos, A. & Cerro, R. L. Liquid filament rise in corners of square capillaries: a novel method for the measurement of small contact angles. Chem. Eng. Sci. 49, 2395–2398 (1994)
Higuera, F. J., Medina, A. & Linan, A. Capillary rise of a liquid between two vertical plates making a small angle. Phys. Fluids 20, 102102 (2008)
Ponomarenko, A., Quéré, D. & Clanet, C. A universal law for capillary rise in corners. J. Fluid Mech. 666, 146–154 (2011)
Acknowledgements
We thank the National Natural Science Foundation of China (grant nos 51290292, 51175020, 51475029 and 21431009) and the Innovation Foundation of the Beijing University of Aeronautics and Astronautics (BUAA; now Beihang University) for PhD Graduates for providing financial support. We also thank G. Wang and Y. Lai from the National Natural Science Foundation of China, and S. Wang from Tianjin University, for support and discussions.
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Contributions
H.C., P.Z. and L.Z. performed the experiments: H.C. and P.Z. worked on the water transport and the characterization of Nepenthes alata; H.C., P.Z. and L.Z. investigated the capillary rise in the wedge; P.Z. fabricated the artificial Nepenthes surface. H.C., P.Z., L.Z., D.Z. and L.J. collected and analysed the data and proposed the mechanism of water transport on the peristome surface. Y.J. carried out the theoretical analysis of capillary rise in the gradient wedge. H.C., P.Z., Z.H., H.L., D.Z. and L.J. wrote the text. H.C., D.Z. and L.J. conceived the project and designed the experiments.
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Extended data figures and tables
Extended Data Figure 1 The peristome surface and the microcavity.
a, SEM image of a cross-section of the peristome, showing that two-order, regular radial ridges align perfectly to form regular two-order parallel hierarchical microgrooves. b, SEM image showing a side view of the vertical section of a microcavity. The image reveals the microcavity’s geometry in the plane perpendicular to the peristome surface, and shows that the microcavity has a sharp edge with an angle, ϕ, of approximately 2° to 8°.
Extended Data Figure 2 Cross-sections along the wedge corner of a single microcavity.
a–h, Sequential cross-sectional images of the microcavity (moving deeper and deeper into the microcavity) show that it has a gradient wedge corner, with an opening angle that varies from roughly 90.5° to 28.2°.
Extended Data Figure 3 How a single microcavity fills with water.
a, High-speed digital images of water filling a single duck-billed microcavity show that the water rapidly rises along the wedge corner and squeezes air out of the microcavity, rising into the cavity to fill it completely. b, The water-filling process; blue lines correspond to the water boundary change with time.
Extended Data Figure 4 Wettability and chemical composition of the peristome.
a, A water droplet (about 4 μl; white circle) is dropped from a microsyringe and spreads quickly without a significant contact angle, indicating that the peristome is superhydrophilic. The water spreading also shows substantial directionality from the peristome’s inner side to the outer side. b, EDS measuring points along the second-order microgrooves, and associated carbon/oxygen (C/O) values. These six values are almost the same as each other, indicating no notable chemical gradient along the microgrooves.
Extended Data Figure 5 SEM images of PDMS replicas of the peristome.
Like the natural peristome surface, the surfaces of the replicas also possess two-order microgrooves (left); moreover, duck-billed microcavities (right) are distributed along the second-order microgrooves.
Extended Data Figure 6 Directional water transport on natural peristome surfaces and PDMS replicas.
a, b, The natural peristome. a, Water transport occurred when the water droplet made contact with the inner side. b, Water could not be transported when it made contact with the outer side. Thus, the natural peristome has a capacity for directional water transport. c, d, A hydrophobic replica. Water could not be transported from either the inner (c) or the outer (d) side. e, f, A superhydrophilic replica. e, Water was transported from the inner side to the outer side. f, Water could not be transported from the outer side to the inner side.
Extended Data Figure 7 Experimental studies of water rise at various wedge corners.
a, Capillary rise in a fixed wedge, in which the bottom opening angle, α1, equals the top opening angle, α2. The water rise decreases as the opening angle increases. b, Capillary rise in a gradient wedge, with α2 = 5°, and α1 > α2; here, water rise is higher than that in the fixed wedge. c, Capillary rise in a wedge with the opposite gradient to that in panel b; α2 = 90°, α1 < α2. Here, the water rise was the lowest of that seen in these four experiments. The red triangles in a–c show the height of the water rise. d, Capillary rise in a top-closed wedge, with α2 = 0°. The water can rise along the vertical wedge corner to fill the horizontally top-closed wedge independently of α1. Diagrams showing the water rise are at the right of a–d. The heights were limited to 100 mm because of the restricted sizes of the available material. e, The experimental water-rise results show that the water rise generally decreases with increasing α1. Water rise in the gradient wedge (red line) is higher than that in the fixed wedge (black line); the top-closed wedge (yellow line) shows additional horizontal water transport. Water rise was the lowest in the opposite gradient wedge (green line). Error bars indicate standard deviations from at least five independent measurements.
Extended Data Figure 8 Volume of rise water and water-retention time for the four types of wedge corner.
a, Volume of rise water in the four types of wedge—fixed wedge, gradient wedge, opposite gradient wedge, and top-closed wedge. The volume of rise water for the top-closed wedge is the largest, and is about 40% greater than that for the fixed wedge. b, Water-retention time in the four types of wedge. Water-retention time for the top-closed wedge is the longest, and is about twice that for the fixed wedge. Error bars indicate standard deviations from at least five independent measurements.
Extended Data Figure 9 Capillary rise in the gradient wedge, showing relevant variables.
a, Liquid rise in the gradient wedge corner. b, Section view of the liquid rise in panel a. α1, bottom opening angle of a wedge; α2, top opening angle; g, gravitational constant; β1 and β2, angle between the plate and the horizontal plane (β1 = β2); h, height of the intersecting plates; wup, up width of selected small liquid element; wdown, down width; dz, thickness of the small liquid element.
Supplementary information
Directional water transport along a single large channel
A small amount of water (approximately 0.1 μL) was deposited on the inner surface of the peristome. Water was transported along the channel in the direction from the inner side to the outer side of the peristome. The starting boundary line of the deposited water was fixed indicating a water pinning phenomenon in the direction from the outer side to the inner side. (MP4 13267 kb)
Water transport along two neighbouring large channels
Approximately 0.2 μL water was deposited on the peristome surface and water was transported along two neighbouring large channels. Water transport was confined within the separate large channels. (MP4 5010 kb)
Water transport along a single second-order microgroove
Approximately 0.01 μL water was deposited on the peristome surface and the water top boundary was monitored by the high-speed camera. Water initially spread along the wedge corner of the micro-cavity and then extruded air out to fully fill the micro-cavity. Water filling of the next micro-cavity started before the fully filling of the prior micro-cavity and the continuous filling of a single micro-cavity accomplished the water transport from the inner side to the outer side of the peristome. (MP4 2722 kb)
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Chen, H., Zhang, P., Zhang, L. et al. Continuous directional water transport on the peristome surface of Nepenthes alata. Nature 532, 85–89 (2016). https://doi.org/10.1038/nature17189
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DOI: https://doi.org/10.1038/nature17189
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