What a Dog’s Tongue Can Teach Us About Staying Cool

As electronic components become smaller and more densely packed, keeping them within safe operating temperatures becomes more difficult. Existing cooling strategies come with practical trade-offs involving heat transfer, energy use, noise, and integration. Air-based systems may become noisy when higher flow rates are needed, while liquid-based systems often rely on powered pumps.

Thin-film evaporative cooling offers another option. It removes heat as liquid changes into vapor and can operate below the boiling point without an external energy supply. Its performance, however, depends on maintaining a thin, stable layer of liquid. If the film becomes too thick, heat transfer slows; if it becomes too thin, the surface can dry out.

Sit, Stay, Evaporate

In a recent study published in ACS Nano, researchers turned to an experienced thermal manager: the canine tongue. Because dogs have few sweat glands, panting and the evaporation of saliva from the tongue play central roles in regulating body temperature. A steady supply of saliva keeps the tongue moist as evaporation occurs.

Using micro-computed tomography and electron microscopy, the team examined Beagle tongues at several length scales. Their analysis revealed nanosized, hairlike structures on the larger filiform papillae, a feature that had not been characterized previously. This arrangement combines structures at two different scales, creating pathways that may assist both saliva movement and evaporation.

The researchers used the tongue architecture as a model for an engineered silicon material they call a bioinspired cross-scale continuous surface, or BioCCS. The material pairs microscale grooves with arrays of nanowires. Capillary forces move water through the grooves, and the nanowires help distribute it into a more uniform layer.

Putting the Canine Design to the Test

The nanostructures also influenced water at the molecular level. Raman spectroscopy showed that BioCCS had a smaller proportion of strongly hydrogen-bonded interfacial water than flat, microstructured, or nanostructured comparison surfaces. The authors interpret this shift as evidence that water molecules face less resistance when leaving the liquid interface.

In droplet tests, BioCCS produced an evaporation rate 11.2 times that of a flat surface and 54% higher than the natural tongue. For a separate heated test, the researchers placed the lower portion of BioCCS in a water reservoir, allowing capillary action to supply the exposed cooling area. At 80 °C, BioCCS reached a mass flux of 31.36 kg h⁻¹ m⁻² and dissipated 150% more heat than the unmodified surface.

The model focuses primarily on the effects of physical structure, leaving questions about the role of surface chemistry for future investigation. For now, the study provides a solid framework for designing passively supplied evaporative surfaces for electronics and other technologies that rely on phase-change cooling.

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