Structural analysis reveals how human eyelashes promote water excretion

Throughout human evolution, body and facial hair has decreased significantly, but eyelashes remain a distinctive feature. The physiological or functional purpose of eyelashes (traditionally thought to be to catch dust or filter air) has long been debated.

However, a team of Chinese researchers recently discovered the characteristics of human eyelashes. Their studies revealed that eyelashes are composed of hydrophobic curved and flexible fiber arrays, characterized by surface microratchets and macrocurvature approximating the Blachystochrone curve. This structure allows the eyelashes to expel incoming fluid quickly and directionally, thus maintaining clear vision.

The hydrodynamic benefits of eyelashes, especially their ability to drain unwanted fluid from the eye to maintain visual clarity, have received little attention. For example, while washing your face or during intense physical activity, your eyes are exposed to a large amount of water and sweat without impairing your clear vision.

The study, published in the December 20 issue of Science Advances, was carried out by Professor Jiang Lei and his group at the Institute of Physical and Chemical Technology, Chinese Academy of Sciences.

The research team aimed to investigate the interaction between water and the flexible fiber arrangement of eyelashes. They began by characterizing the structure, wettability, and water evacuation process of human eyelashes. We then investigated how the flexibility, wettability, and curvature of the fiber arrangement affected drainage.

Based on their results, the researchers uncovered a control mechanism governing the transmission direction and contact time resulting from the multiscale asymmetric structure and nonuniform elastic deformation of the fiber array. They also developed a quantitative computational model to calculate the elastic forces acting on the fiber array.

This research also led to the design of high-speed liquid transfer edges that mimic eyelashes, including aesthetic and protective false eyelashes, waterproof imaging devices, and vented structures.