Amazing stuff! Next time you lose an eyelash ...
"... Now, a new study has revealed that human eyelashes are good for more than just catching dust and looking pretty. As researchers report in Science Advances, they also actively fling water droplets away from the eyes, helping to keep vision clear when we swim, sweat, and cry (or shower). In the future, the team writes, the findings could inspire the design of better waterproof materials.
The scientists conducted numerous experiments, including dripping water on people’s eyelashes—using a soft plastic nozzle, they note, “to avoid stabbing the volunteers.” To analyze the lashes’ shape and structure, they also dipped individual hairs into pools of water before slowly pulling them out. These tests demonstrated that eyelashes are made up of densely-packed, hydrophobic fibers, which cause water to bead up and roll off when it makes contact. In addition, each lash is covered with overlapping scale-like cells. This “micro-ratchet” structure, the study authors write, allows water to flow easily from root to tip but blocks it from moving in the opposite direction.
The researchers also discovered that the curved, flexible structure of a human eyelash mimics a shape known as a brachistochrone curve, which physicists define as the quickest path an object can take between two points under the influence of gravity. A ball rolls faster, for example, down a ramp that starts out steep and gradually flattens than down a ramp with a uniform slope. Thanks to this curved shape, droplets that land on an eyelash are propelled rapidly away from the eye—a bit like a child getting launched off the end of a water slide. ..."
From the abstract:
"Numerous organisms exploit asymmetrical capillary forces generated by unique fiber or asymmetrical tapered structures to rapidly eliminate undesired liquid for survival in moist or rainy habitats.
Human eyelashes, the primary protector of eyes, use a yet-to-be-fully-understood mechanism to efficiently transfer incoming liquid for vision safeguarding. Here, we elucidate that human eyelashes featuring a hydrophobic curved flexible fiber array with surface micro-ratchet and macro-curvature approximating the Brachistochrone is adept at directionally and rapidly expelling incoming liquid to maintain clear vision. These structural attributes are sequentially used for liquid drainage, starting from anisotropic retention via micro-ratchet, followed by the elastic expulsion among deflected hydrophobic flexible fiber arrays and culminating in the fastest sliding off along a Brachistochrone path, which together reduce the contact time by about 20% of that on rigid linear slopes. Investigating the intricate relationship between multistructure and draining efficiency of human eyelashes may inspire the design of advanced liquid-repelling edges on outdoor devices to maintain dryness."
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