Engineers working on technological innovations from solar cells to stretchy electronics have drawn inspiration from the Japanese art of kirigami. The lesser-known cousin of origami, which involves cutting and folding paper, helps to create three-dimensional shapes from flat, paper-like materials or to add form-fitting flexibility.
Now scientists using kirigami have developed a new type of no-slip shoe sole that mimics the texture of snakeskin, reports Nicola Davis for the Guardian. The authors of the new research, published this week in the journal Nature Biomedical Engineering, say their innovation could help cut down on injuries from falls, particularly among older people.
“Falls are the leading cause of death for older adults and the second leading cause of occupational-related deaths,” Giovanni Traverso, an engineer at the Massachusetts Institute of Technology and co-author of the new research, says in a statement from Harvard University. “If we could control and increase the friction between us and the ground, we could reduce the risk of these types of falls, which not only cost lives but billions of dollars in medical bills every year.”
The paper also cites prior research showing that broken hips are among the injuries that can result from slip-and-fall incidents and that nearly half of older patients with hip fractures are unable to return to living independently.
“Through this work we set out to address the challenge of preventing falls, particularly on icy, slippery surfaces, and developed a kirigami-based system that facilitates an increase of friction with a surface,” says Traverso in a statement from MIT.
The grippy new sole is made of a thin sheet of steel that is riddled with precise cuts that allow it to bristle like the scales of a snake when bent, according to a statement from Harvard University about the new research. The kirigami-style cuts in the steel sheet allow it to transform from a smooth surface into a spiked sole ready to dig in for traction, and back again.
“What we are trying to do is augment, or add on, to [existing systems like studs or rubber soles] to have a better grip on slippery surfaces, whether it be ice or whether it be oily surfaces in certain occupations,” Traverso tells the Guardian. He also says the kirigami soles were inspired by “friction-enhancing” adaptations in nature, such as snakeskin, which allows serpents to slither through their environment, and the semi-retractable claws of cheetahs, which can be extended to provide extra traction during high-speed pursuit of prey.
To develop the pattern of cuts used in their prototype soles, the researchers conducted a series of experiments testing the friction generated by different patterns, materials, shapes and arrangements on various surfaces, according to the statement from MIT. They eventually found that cuts of interlocking concave curves worked best and tested them on the shoes of human volunteers walking across a one-inch thick sheet of ice. The special soles created roughly 20 to 35 percent more friction than standard shoes and boots on their own, reports Andrew Liszewski of Gizmodo. The new traction system outperformed traditional crampons on ice in the researchers’ tests and were both lighter and easier to take on and off, according to the Harvard statement.
“By adding [dimpling to the sole] and combining with kirigami needles, we expect to observe further friction enhancement, [above] 35 percent,” Sahab Babaee, an engineer at MIT and first author of the research, tells the Guardian.
“Walking is a dynamic process so we wanted to develop a system that was also dynamic and could respond to movement,” Traverso adds.
Though the researchers initially set out to prevent ice-related slips, they think their grippy soles could also have broader commercial applications in wet or oil-slicked work places, according to the statement from MIT.
“We see this either as an add-on or it could be incorporated into the sole directly,” Traverso tells the Guardian. “We hope that [people] can rush out and buy these soon, and that is what we are working towards.”