麻豆影院

A research team led by CU 麻豆影院 has designed a new kind of synthetic 鈥渟kin鈥� as slippery as the scales of a snake.

The research, published recently in the American Chemical Society journal , addresses an underappreciated problem in engineering: Friction.听

Yifu Ding, senior author of the new paper, explained that every day, machines from robots to cars lose tremendous amounts of energy simply because their parts rub together. To try to reduce that loss, he and his colleagues took cues from nature鈥攕pecifically, its most slithery members.听

鈥淎 snake鈥檚 body is soft enough that it can twist itself into all kinds of shapes,鈥� said Ding, a professor in the Paul M. Rady Department of Mechanical Engineering. 鈥淚t can also move really fast if it needs to, in part because its skin has such low friction.鈥�

In their latest study, the researchers developed a tool called solid-liquid interfacial polymerization (SLIP) that allows them to lay a thin layer of skin onto existing surfaces like rubber or stretchy materials called elastomers. That layer looks a lot like the scales of a snake and can turn an otherwise sticky surface into a slip hazard. 听

The technology could be a boon for machines that battle friction but can鈥檛 tolerate getting wet.

鈥淭here are a lot of new engineering applications, like soft robots or wearable sensors, where you can鈥檛 use these traditional liquid lubricants,鈥� said Ding who is also part of the Materials Science and听Engineering Program at CU 麻豆影院. 鈥淩ather, you have to modify the surface itself.鈥�

That鈥檚 now possible, thanks to the oft-hated snake.听

What鈥檚 in a scale?

Snakes, from striped garter snakes to bright-green vine snakes, owe a lot of their success to their scales. If you put one of these small structures under a microscope, you鈥檒l notice that they鈥檙e made up of many layers of tissue stacked on top of each other.

鈥淭he top layer is like keratin, what our fingernails are made of,鈥� Ding said. 鈥淚t鈥檚 very brittle and stiff. Then the scale gradually transitions to a much softer material below.鈥�

That combination of hard on top of soft gives snakes their edge, helping them to keep their friction low while still remaining flexible. It鈥檚 also the feature that Ding and his colleagues wanted to replicate in the lab.

The group began with a base made out of polydimethylsiloxane (PDMS), an elastic material common in many medical technologies. The researchers then used the SLIP technique to place a thin, scale-like layer of synthetic material onto that foundation.听

The method, Ding explained, works by mixing small molecules into a film of liquid, then using light to get them to fall out of suspension鈥攁 bit like peas sinking to the bottom of a bowl of soup. Once there, those building blocks infiltrate the PDMS and form a hybrid skin layer.

This results in the laboratory equivalent of snakeskin boots.

鈥淣othing sticks to it,鈥� Ding said. 鈥淵ou can touch it, and your finger will slip.鈥�

Slipping and sliding

To prove just how snake-like their invention is, he and his colleagues鈥攊ncluding Mengyuan Wang, who recently earned her PhD from CU 麻豆影院鈥攔an a series of seemingly simple tests. The group attached weights to both the hybrid and normal PDMS, then put them on various slanting surfaces.

The team鈥檚 snakeskin-treated PDMS skidded down even slight inclines, Wang said, while the plain material didn鈥檛 budge.

鈥淧DMS is really sticky,鈥� Wang said. 鈥淓ven when you completely flip it upside down, it will still stick to surfaces.鈥�

The team鈥檚 snakeskin has similar levels of friction to many ceramic materials and shiny metals, the group found. Ding added that the SLIP method is nimble enough that it can lay down this skin in any pattern, including in shapes that spell out words.听

The group still has a lot of work ahead of it before it can start applying its slippery surface to real robot joints. But the research is yet another reason to thank a friendly snake.听

鈥淲hen we鈥檙e designing new materials, we don鈥檛 always know what kind of structure to make,鈥� Ding said. 鈥淏ut if there鈥檚 an example in nature, it鈥檚 already proven that it can work, so we can just mimic that.鈥�