Harvard Researchers' Biomaterial is Among Smoothest Surfaces Ever

Harvard scientists have developed a biomaterial with less friction than Teflon, one of the smoothest materials ever developed.

The new material, called SLIPS—Slippery Liquid-Infused Porous Surfaces—likely will have applications ranging from fuel transportation to bacterial prevention to medical equipment.

Tak-Sing Wong, a postdoctoral fellow at the School of Engineering and Applied Sciences who led the project, drew inspiration for the new material from a carnivorous plant that lures prey into its cupped leaves that are too slippery to escape from.

Wong’s new material, described in a study published in Nature last week, derives its frictionless features from the structural orientation of the carnivorous pitcher plant’s leaf surface.

“Our surface pretty much consists of two components: One is a rough and porous surface, and the second component is the liquid, which is infiltrated within this porous solid,” Wong said. “So this liquid is actually a little bit above the porous solid.”

The surface layer of liquid embedded in new material is so smooth that it repels many other substances, including oil.

This repelling property will make SLIPS a prime candidate for coating the insides of oil pipelines, which will greatly reduce pipe resistance and make energy transport more efficient, according to Wong.

There are numerous other possible applications for SLIPS, including preventing the formation of ice in refrigerator coils and repelling blood on medical tubing.

Wong compared the repellent process of SLIPS to hydroplaning.

“After raining, the road has a very thin layer of water on top of it. And under the tire now you see a very thin layer of water, which starts to loosen the gripping, or loses the friction, such that the car will start hydroplaning on the surface,” he said.

In addition, SLIPS are extremely durable due to their self-healing nature.

Wong said that when an object impacts a liquid, an indent is made on the liquid surface. But once the object is removed, the fluid nature of the water allows it to refill the space that was occupied, in effect “self-healing.” Because SLIPS are coated in liquid, they react similarly.

“The versatility of SLIPS, their robustness and unique ability to self-heal makes it possible to design these surfaces for use almost anywhere, even under extreme temperature and pressure conditions,” said materials science professor Joanna Aizenberg, who oversaw the project. “It potentially opens up applications in harsh environments, such as polar or deep sea exploration, where no satisfactory solutions exist at present.”