Your dog smells and tracks mud through the house, sure, but isn’t it a wonder that Mr. Barks isn’t a walking bundle of detritus? And what about those itty-bitty fruit flies—shouldn’t a few particles of dust be all it takes to ruin their aerodynamics?
These are the questions asked by physicist-biologists David Hu of Georgia Tech and his graduate student Guillermo Amador of the Max Planck Institute. The two recently published a review in the Journal of Experimental Biology and a follow-up article in Discover. Their research isn’t just fascinating in its own right (wait until you hear the bit about chinchillas and SUVs), it has some ingenious implications for the design of dirt-sensitive tech like lenses and solar panels.
Hair seems like a hygienist’s nightmare. It comes down to surface area—the more surface an object has, the more space there is for dust and other particles to accumulate. (My readers may remember that the “hairy” feet of geckos, and their relatively massive surface area, is what enables the lizards to stick to even smooth surfaces.)
In this regard, it seems we’re lucky we’re the hairless ape. But even the hairiest ape hasn’t got anything on Apis (i.e. honeybees) in sheer pound-for-pound hairiness. Per the researchers’ Discover article:
“We people have about 100,000 hairs on our head. The number of hairs on other animals is comparatively staggering. A butterfly has 100 billion hairs, more than 10 times that of a beaver. The bee has 3 million hairs, the same number as a squirrel.”
When the researchers extrapolated from hair to surface area, the results become downright flabbergasting:
“We found that on average, hair increases an animal’s apparent surface area by a factor of a hundred. Thus, a cat has a surface area of a ping pong table. (This explains why its [sic] so hard to get pets clean.) A chinchilla has the surface area of an SUV. And a sea otter has the surface area of a hockey rink.”
What this means is that hygiene is potentially a massive energy sink for animals—animals that would “rather,” in an evolutionary sense, be using that energy to find food or find mates. There’s been a strong selective force shaping animals to stay clean in the most efficient ways possible. “Effective cleaning,” the researchers observe, is as much about “designing a surface that is ready to facilitate [cleaning]” as it is designing a good cleaning tool.
The crux: “An animal gets clean for free if it has the right kind of surface. If we have this mindset, perhaps we can design new devices that get clean for free too.”
They single out solar panels and bee eyes. Both need to let light in. Solar panels don’t produce as much power as they can each year due to the accumulation of dust. When viewed through a scanning electron microscope, a bee’s eye looks like a pincushion; to Hu and Amador it looks like inspiration:
“Imagine solar panels designed like insect eyes. Thin filaments could be placed periodically to suspend dust above the panel, but still allow light to penetrate. Cleaning the panel would amount simply to swiping it with another brush. Just like the insects, the panel could get clean without the use of water or chemicals. Similarly, video cameras, the eyes of robots could be rimmed with eyelashes to reduce deposition. Building synthetic hairy systems is the subject of our National Science Foundation grant, Engineering Insect Eyes.”
Borrowing ideas from nature is a proud tradition in engineering. And why not? Natural selection has been shaping organisms for at least 3.5 billion years. When its aims and our own align, as they did with burrs of the burdock plant and Swiss engineer George de Mestral’s shared desire to attach one object to another, inventions are born.
The other natural applications of hair extend well beyond dust—“nanoscale pincushions” on the wings of cicadas are so small and sharp they actually pop bacteria “like water balloons.” Sea otter fur is extremely dense, repels water, and provides excellent insulation. The whiskers of cats and rodents are exquisite sensory devices. Long, short, flaxen or waxen, hair is undeniably a prime target for biomimicry.
In closing, Hu and Amador challenge the reigning paradigm of the iFuture and instead offer a much more hirsute vision of a techno-utopia:
“We typically envision future robots covered in smooth shiny surfaces, like a chrome-buffed automobile. But in nature, smooth surfaces are hardly the norm. Future tabletops may have nano-size posts that stretch and kill bacteria on contact. Robotic rovers may be covered with hairs that sense their environments, suspend particles and enable easy cleaning. Indeed, the future may be looking rather hairy.”