Directional, passive liquid transport: the Texas horned lizard as a model for a biomimetic ‘liquid diode’

Abstract

Moisture-harvesting lizards such as the Texas horned lizard (Iguanidae: Phrynosoma cornutum) live in arid regions. Special skin adaptations enable them to access water sources such as moist sand and dew: their skin is capable of collecting and transporting water directionally by means of a capillary system between the scales. This fluid transport is passive, i.e. requires no external energy, and directs water preferentially towards the lizard's snout. We show that this phenomenon is based on geometric principles, namely on a periodic pattern of interconnected half-open capillary channels that narrow and widen. Following a biomimetic approach, we used these principles to develop a technical prototype design. Building upon the Young-Laplace equation, we derived a theoretical model for the local behaviour of the liquid in such capillaries. We present a global model for the penetration velocity validated by experimental data. Artificial surfaces designed in accordance with this model prevent liquid flow in one direction while sustaining it in the other. Such passive directional liquid transport could lead to process improvements and reduction of resources in many technical applications.

Passive water collection with the integument: mechanisms and their biomimetic potential

“…Further structures, i.e. grooves or channels, are required to transport water (3) over larger distances or precisely in one direction (Berthier and Silberzan, 2010;Comanns et al, 2015). It is important to note the difference between wetting effects and capillarity.…”

“…Capillary liquid transport can take place in small cavities, such as tubes, ridges or channels, where the capillary forces dominate other major contributing forces such as viscosity, friction or gravitational force (Berthier and Silberzan, 2010). Corresponding surface structures can be found in the granular skin of some toads and elephants (Lillywhite and Licht, 1974;Lillywhite and Stein, 1987), surface channels of moisture-harvesting lizards (Gans et al, 1982;Withers, 1993;Veselý and Modrý, 2002;Sherbrooke et al, 2007;Comanns et al, 2015), flat bugs and wharf roaches (Hoese, 1981;Horiguchi et al, 2007;Ishii et al, 2013), and cavities between feather structures of sandgrouse (Rijke, 1972;Joubert and MacLean, 1973;Rijke and Jesser, 2011). In the case of moisture-harvesting lizards, transportation in channels avoids wetting much of the body surface and hence losing volume by evaporation from a larger area (Comanns et al, 2011;Yenmisȩ t al., 2015).…”

Bioinspired Unidirectional Liquid Spreading Channel–Principle, Design, and Manufacture

“…[11][12][13][14][15][16][17] In recent years, the discovery of numerous natural systems that enable directional liquid transport due to their unique surface structure at the micro-and nanoscale (such as cactus, the pitcher plant, and lizard and spider silk) offers a biomimetic way in the development of an efficient directional spreading surfaces. [18][19][20][21][22] Among these living organisms, Nepenthes alata has gained an increasing attention because of the unique structure on its peristome (Figure 1). The arch-shaped microcavities arranged continuously in the microgrooves lead to a 2D unidirectional liquid spreading with fast speed and long distance properties.…”

“…Although several strategies, including chemical modification, hetero‐wettability fabrication, and temperature differences, have been proposed to induce directional liquid motion, the liquid motion is usually limited to the gradient on the surface and easily influenced by the extra energy including vibrations and heat . In recent years, the discovery of numerous natural systems that enable directional liquid transport due to their unique surface structure at the micro‐ and nanoscale (such as cactus, the pitcher plant, and lizard and spider silk) offers a biomimetic way in the development of an efficient directional spreading surfaces . Among these living organisms, Nepenthes alata has gained an increasing attention because of the unique structure on its peristome ( Figure ).…”

Cutaneous water collection by a moisture-harvesting lizard, the thorny devil (Moloch horridus)

“…The physical ability to harvest moisture is associated with a network of capillary channels, in between the overlapping scales, that enables passive and sometimes directional transport of the collected water to the mouth for drinking (Withers, 1993;Sherbrooke et al, 2007;Comanns et al, 2011Comanns et al, , 2015. Transportation to the mouth for ingestion is necessary, because the integument is substantially waterproof to minimize evaporative water loss (Bentley and Blumer, 1962;Withers, 1993) and this precludes water absorption across the skin.…”