Texas horned lizard (Iguanidae: Phrynosoma cornutum)
The lizard’s peculiar scales can collect water from nearly anywhere. Its skin gathers rainwater or moisture from sand and transports it toward the creature’s mouth via a capillary system between its scales.
The German-Austrian team behind the research has already developed plastic designs emulating the Texas horned lizard’s skin in an effort to more closely study its nature and discover possible applications.
The process of harvesting moisture in the lizard’s skin is passive, requiring no effort from the lizard, according to Philipp Comanns, a PhD student from Aachen University in Germany. "And this is independent of where you apply the water to the skin,” he explained in an article by Jonathan Webb, science reporter at the BBC. “You can apply the water to the back, to their front, to the tail . . . and it's always transported fastest towards the mouth."
This effective channeling is possible thanks to the geometric principles inherent in the lizard’s scales. Comanns explains that a pattern of interconnected half-open capillary channels widen from the tail and narrow out toward the mouth to direct moisture.
Microscopic images of the structure of the channels, each less than 0.25 mm wide.
“The more concave the meniscus is, the stronger the capillary force transporting the liquid forward,” Comanns said in the BBC article. "We have the narrowing of the single capillary channels on the one hand, and we have the capillary network and its interconnections on the other hand. These are the two underlying principles that we found to establish this directional transport."
Challenges and Research Applications
Comanns’ team has created two designs consisting of channels laser-etched into glass-like plastics with raised “scales” in between, based on the understanding of the Texas horned lizard’s skin.
The video below depicts an up-close 1 cm section of a design transporting water.
"The capillaries have an undercut and this is really hard to manufacture, so we have to abstract the structure to be able to manufacture it," said Comanns.
The “delightful” example of biomimetics is exciting, but needs to be scaled properly to find any practical use, said Wade Sherbrooke, research associate at the American Museum of Natural History, who was not involved in the research.
"If you got this new design and you put it in sheets on a building, you couldn't run water from the first floor to the fifth floor or anything like that. They're thinking of the micro world," Sherbrooke said in the BBC article.
Researchers currently hope to find applications in distilleries and heat exchangers or see if the discovery could help deliver lubricants within machines.
The findings were published in the Journal of the Royal Society Interface.