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Human bodies have integrated systems to take care of themselves. The cells that line our lungs, noses, brains, and reproductive systems have eyelashes, tiny, hair-like structures designed to sweep fluids, cells, and microbes to stay healthy. But the mechanisms behind their movement are not well understood.
A team of researchers from the McKelvey School of Engineering and the School of Medicine at Washington University in St. Louis wanted to determine how the length affected the mechanical effectiveness of the flapping of the eyelashes. They found that most mechanical parameters, including strength, torque, and power, increased in proportion to the length of the eyelashes, but there was an "ideal point" in terms of effectiveness. The results provide insight into the eyelashes in humans and how defects result in diseases, such as primary ciliary dyskinesia, badociated with chronic respiratory infections, right-left axis changes, and heart defects. The results will be published in the April 9 issue of Biophysical Journal.
The study was led by Mathieu Bottier, Postdoctoral Fellow in Philip Bayly's Laboratory, Lilyan & E. Lisle Hughes Professor of Mechanical Engineering and Director of the Department of Mechanical and Materials Science; and the laboratory of Susan K. Dutcher, Professor of Genetics, Cell Biology and Physiology at the Faculty of Medicine. Researchers used high-speed video microscopy to badyze a model for eyelashes to determine their mechanical parameters. After badyzing nearly 400 videos, the team found that the most effective threshing of eyelashes was 10 to 12 microns in natural length, about one-fifth the width of a human hair.
"We did not expect short eyelashes to be periodic," said Bottier. "Eyelashes move all, but we find no tendency to beat – nothing has been synchronized – and that was our first discovery."
The team used Chlamydomonas reinhardtii, a unicellular green algae that normally swims with two propulsive tails and is frequently used as a model for mammalian eyelashes. Bottier and Kyle Thomas, an undergraduate student specializing in biomedical engineering, used a mutant with a single eyelash running on site, allowing longer video recording. They removed the eyelash and then recorded the regrowth by video. It took about 90 minutes for the cilium to return to its normal length. Although its waveform differs slightly from that of standard eyelash, its main features are similar.
"We wanted to see the lash beat, as we did with the video," said Bottier. "Then we asked how we could describe it, and the best way was to look at the average time, we recorded five or six cycles of beats that recur periodically, and from those five or six we can reconstruct a average, which will eliminate any outliers. "
The cilium is beaten by a series of elbows that start at the base and extend to the tip. The team found that periodic beats began when the eyelashes exceeded the length of two to four microns, which meant that a critical length was needed for the eyelashes to beat. In previous research, scientists had not studied lashes less than five or six microns, Bottier explained. Another new observation is that the beat frequency in the periodically flapping eyelashes is fairly constant over the normal range of eyelash length, although it decreases slightly as the length increases from 4 microns to 12 microns, said Bayly. .
This work may help to understand the human mutations that make eyelashes short and how short eyelashes will affect the patient's outcome, Dutcher said.
Thomas said that the research provided a better understanding of eyelash functioning and the causes of the oscillations.
"There are many different models presented on the causes of this flexion pattern, so this study has determined which models are the most accurate and which ones may have inaccuracies, so we can understand when a malfunction of the eyelashes occurs. which causes it to spark discussion about how we are going to deal, "said Thomas.
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