title: 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.
authors.affiliation: Institute of Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany philipp.comanns@rwth-aachen.de.
authors.forename: Philipp
authors.initials: P
authors.lastname: Comanns
authors.affiliation: Institute of Biomedical Mechatronics, Johannes Kepler University, Altenberger Strasse 69, 4040 Linz, Austria.
authors.forename: Gerda
authors.initials: G
authors.lastname: Buchberger
authors.affiliation: Research Center of Non Destructive Testing GmbH (RECENDT), Area of Optical Coherence Tomography, Altenberger Strasse 69, 4040 Linz, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Buchsbaum
authors.affiliation: Institute of Experimental Physics, Department of Soft Matter Physics, Johannes Kepler University, Altenberger Strasse 69, 4040 Linz, Austria.
authors.forename: Richard
authors.initials: R
authors.lastname: Baumgartner
authors.affiliation: Institute of Experimental Physics, Department of Soft Matter Physics, Johannes Kepler University, Altenberger Strasse 69, 4040 Linz, Austria.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kogler
authors.affiliation: Institute of Experimental Physics, Department of Soft Matter Physics, Johannes Kepler University, Altenberger Strasse 69, 4040 Linz, Austria.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Bauer
authors.affiliation: Institute of Biomedical Mechatronics, Johannes Kepler University, Altenberger Strasse 69, 4040 Linz, Austria.
authors.forename: Werner
authors.initials: W
authors.lastname: Baumgartner
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D032701:Biomimetics; D008116:Lizards / Q000378:metabolism*; D008954:Models, Biological; D012867:Skin / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water
keywords: capillaries; directed; microfluidics; passive; wetting