http://techxplore.i2p/news/2019-05-soft-robots.html
Imagine water moving through a straw—the thinner the straw, the more difficult it is for water to pass through. Using this principle, the researchers, led by Katia Bertoldi, the William and Ami Kuan Danoff Professor of Applied Mechanics at SEAS, carefully selected tubes of different sizes to control how quickly air moves through the device.