Columbia Researchers Create Material that can Drive Soft Robots

Ozgur Sahi, associate professor of biological sciences and physics at Columbia University, conducted a research recently with colleagues in his laboratory to demonstrate the possibility of fabricating materials to make soft actuators that are flexible, strong, and most importantly resistant to water damage. These soft actuators are devices capable of transforming energy into physical motion.

There's a growing trend of making anything we interact with and touch from materials that are dynamic and responsive to the environment. We found a way to develop a material that is water-resistant yet, at the same time, equipped to harness water to deliver the force and motion needed to actuate mechanical systems.

Ozgur Sahin, Associate Professor of Biological Sciences and Physics, Columbia University

On May 21st 2019, this research was published online in Advanced Materials Technologies.

The conventional robotic systems are mostly hard as they comprise of metallic structures that can function only with a computer. Soft robots are developed using materials that do not use a firm skeleton or electricity in order to provide mechanical strength. They are simpler to build and less costly than hard robots, more capable of intricate motions and safer to use around humans.

The Columbia researchers developed the new material by blending spores and adhesives. These spores refer to units developed by bacteria that are mostly used as food supplements. They are known to provide an alternative to materials like synthetic polymers that are mostly used in hard actuators and also much better than the gels commonly used in soft actuators. When compared to the new material, gels respond very slowly and fail to produce force or high power and also do not function well when in direct contact with water.

Even though the distinct spores are water-resistant, they are very small and hence will have to be bound together by a photochemical process. In this process, high-intensity light immediately binds them together into a composite material. A cost-effective, commercially available UV light used in salons to cure nail polish was employed by the researchers.

After it becomes dry, the material is arranged in a layered stack to form a microscopic structure that expands or contracts with moisture or humidity, creating the force and motion of mechanical work.

"It's like making sheets or surfaces from sand," says postdoctoral research scientist Onur Cakmak, lead author of the study and a member of the research team. "The material is very granular."

Directed by the pattern design, the porous composite can fold, bend, and unfold in reaction to water or humidity. This bestows the soft actuators adaptability and agility to their environments, quite similar to organisms in nature. The capacity to be patterned, says Cakmak, "is essential if you want to make useful systems out of these materials."

Sahin visualizes a number of probable applications for the new material, from real-world items to artistic creations. Actuators designed using the water-resistant, humidity-responsive composite could be used to open a building's windows when the humidity increases greatly. The material could also be incorporated into fabric in athletic clothing to help sweat evaporate at a faster rate. "We're providing material for designers to work with and get their ideas realized quickly," Sahin says.

Applications designed to function for years still need additional testing, he adds, but those designed for shorter time frames might already be equipped for use.

As we work on this, we also learn many other possible uses, some related to design and others to materials that could be part of the products around us. Those could be places where the impact of this could be sooner.

Ozgur Sahin, Associate Professor of Biological Sciences and Physics, Columbia University

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