Underwater surfaces can become dirty because dirt, algae and bacteria accumulate on them scientists call “pollution”.” But furry mammals like beavers and otters, which spend most of their lives wet, manage to avoid slimy fur. These antifouling properties are due in part to one of fur’s unique properties – the fact that each hair can flex and bend as the animal moves.
I am a mechanical engineer which studies fluid dynamics or the behavior of fluids. My team lately published a study showing that fur moving back and forth in a stream of dirty water accumulated less than half the amount of dirt compared to fur held rigidly at both ends.
While many animals have fur that appears to be self-cleaning, semi-aquatic mammals have the most dirt-resistant or “antifouling” fur.
In our recent study, we compared the fur fibers of beavers, otters, springboks, coyotes and other species using a stream of water containing titanium dioxide, a common cosmetic additive. Titanium dioxide easily attaches to surfaces such as skin. Our team pumped dirty water through individual fibers in a closed loop for 24 hours, then cleaned the fibers to measure the amount of titanium dioxide accumulated in them.
My colleagues and I then used mathematical techniques to combine all of the fur’s properties into a single number that predicted its antifouling behavior. We considered each strand of fur’s ability to bend, fluid flow through it, and other unique characteristics of each species.
We found that the ability to bend was crucial to keeping the animal’s coat clean.
Why is it important?
Pollution can damage the affected surface. When fur becomes dirty, the pattern of individual strands on the animal’s skin is disrupted, and the animal may have difficulty staying warm or dry.
Industrial deterrent methods often used to protect the bottoms of ships and the insides of pipes use harmful chemicals and consume energy and materials, unlike naturally created solutions.
Discovering how fur naturally stays clean could lead to more environmentally friendly solutions to preventing pollution in water supplies, the marine environment and even medicine. Solutions may include surfaces with parts that can bend and move, or those that have small hairs on the surface.
Fur research is also revealing more about how these mammals evolve to survive in different environments.
What is still unknown
Animal fur and the process of regrowth both are complextherefore, we still do not fully understand how all the intricate properties of fur, from texture and length to cross-sectional shape and environmental conditions, affect cleanliness.
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Hair strands in fur do not always move individually. In animals, the hairs are tightly packed and probably groom each other by rubbing as the host moves. We cannot yet say whether rubbing and moving affects the cleanliness of the host animal.
What’s next
My colleagues and I have just delved into the secret of cleanliness in furry mammals, and there is much more we can test. Future work could expose fur to biological contaminants such as bacteria and algae, or look at the role fur plays in cleanliness.
The only mammal known to actually become polluted is the sloth – algae grows on their fur.
