The next time you get caught in the rain, thank your eyelashes for keeping your vision clear.
Experiments with human eyelashes and eyelash-mimicking fibers show some properties that help remove water from the eyes, researchers from the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences report Dec. 20 in Advances in science.
The outer part of an eyelash, or cuticle, acts as a “micro-ratchet,” researchers report. Water can flow easily from the root to the top, but not the other way around, thanks to the scales that overlap like shingles on a roof. When the scientists dipped loose eyelashes in water and pulled them back out, it took more force to move the eyelash when the water was working against the ratchet than when it was going with it. And by dripping water onto loose eyelashes, the researchers showed that the hairs are hydrophobic, meaning that water rises on them and tends to roll off.
The cilia approximate a shape called a brachistochrone, a curve that minimizes the time it takes to get from point A to B under the force of gravity. Using arrays of nylon fibers with similar dimensions and elasticity as eyelashes, the researchers compared fibers in the shape of a brachistochrone with fibers that were straight or curved in another shape. The drops slipped faster than the brachystochrone.
Known for dust protection, lashes aren’t known for their water-absorbing superpowers (SN: 24.2.15). Besides helping in a rainstorm, the effect can come into play when you’re bathing, sweating, or crying. However, beauty treatments can inhibit this ability. Mascara can cause eyelashes to attract water instead of repelling it, the scientists point out, and twisting the eyelashes changes their shape.
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