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Accueil du site → Doctorat → Allemagne → 2016 → Water acquisition and water transport on the integument of moisture harvesting lizards : biophysical fundamentals and technical applicability

RWTH Aachen University (2016)

Water acquisition and water transport on the integument of moisture harvesting lizards : biophysical fundamentals and technical applicability

Comanns, Philipp

Titre : Water acquisition and water transport on the integument of moisture harvesting lizards : biophysical fundamentals and technical applicability

Wasserakquise und Wassertransport mit dem Integument feuchtigkeitserntender Echsen : biophysikalische Grundlagen und technische Anwendbarkeit

Auteur : Comanns, Philipp

Université de soutenance : RWTH Aachen University

Grade : Doktors der Naturwissenschafte 2016

Résumé
Moisture-harvesting lizards, such as the Australian thorny devil (Agamidae : Moloch horridus) and two horned lizards (Iguanidae : Phrynosoma cornutum, P. platyrhinos) studied during this thesis, have remarkable adaptations for inhabiting arid regions. Special skin structures enable the lizard to collect water by capillarity and passively transport it to the mouth for ingestion. The ecological role of this mechanism clearly is the acquisition of water from various possible sources. Possible sources were evaluated regarding their potential for water uptake of M. horridus and P. platyrhinos. The water volume required to fill the skin capillary system was determined for both species. Thorny devils standing in water could fill the capillary system and drank its water, whereas desert horned lizards only drank when sprayed with water. Drinking occurred at about 0.67 µL per jaw movement. Water collection from moist sand could only fill the capillary channels to 58 % of their capacity, and none drank water. However, placing moist sand on skin replicas of thorny devils and considering sand shoveling behavior suggest that water collection from moist sand could be considered as the most ecologically-likely source for M. horridus on a regular basis. For P. platyrhinos the total amount of water collection from moist sand was four times less than that of thorny devils. Taking behavioral aspects, such as rain-harvesting posture and nocturnal burrowing, into account, rain appears to be a major water source for P. platyrhinos.Capillary water transport was characterized for live thorny devils using high-speed video analyses. Comparison with preserved specimens showed that live lizards are required for detailed studies of skin water transport. For thorny devils, there was no directionality in cutaneous water transport (unlike Phrynosoma) as water droplets applied to the skin were transported radially. The total capillary volume is reduced to 50 % filling by the time capillary transportation ceases. The channels were found to be hierarchically structured as a large channel between the scales that is sub-divided by protrusions into smaller sub-capillaries. The large cavities were considered to quickly absorb water and the sub-capillaries were identified to extend the transport distance by about 39 %. This potentially reduces the water volume required for imbibition. P. cornutum exhibits a directional water transport, where water is transported preferentially towards the lizard’s snout. It could be shown 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, these principles were used to develop designs for technical demonstrators of functionality. Building upon the Young-Laplace equation, a theoretical model for the local behavior of the liquid in such capillaries is derived. Artificial surfaces designed in accordance with this model and derived design rules prevent liquid flow in one direction while sustaining it in the other. This fluid transport is passive, requiring no external energy. The surface structures were successfully validated for material-liquid combinations such as Plexiglas® with water and hot working tool steel with oils and lubricants. Laser ablation for manufacturing demonstrators was found to require further adaptation of structure designs in order to avoid potential sub-capillaries. However, several fabrications methods can be considered for the great number of potential applications that require such directional, passive liquid transport. In particular, the surface structures could lead to process improvements and reduction of resources in fields of lubrication.

Mots clés  : water uptake (frei) ; directional water transport (frei) ; capillary (frei) ; biomimetics (frei) ; functional principles (frei)

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Page publiée le 4 novembre 2017