Water-activated material may find applications in robotics

Columbia University team develops composite containing bacterial matter that responds to humidity 

Most soft robotics systems rely on synthetic polymers which respond to external stimuli to produce their movement. However, such polymers tend to be slow to respond, cannot generate high power or force, and fail on contact with water. The Columbia team, based in the laboratory of Ozgur Sahin, an associate professor of biological sciences of physics, has an outer material which is not only completely resistant to water but actually responds to its presence by delivering force and motion.

An electron microscopy image of the spore-adhesive composite

In a paper in Advanced Materials Technologies, the Columbia team describes their material as a composite made from spores – it is produced by bacteria that are often used as food supplements – and ultraviolet-curable adhesives.

The composite is formed in sheets which are stacked together to form a structure that expands or contracts in response to humidity or moisture as the spores swell or shrink. Depending on the design of the pattern of the assembly of composite sheets, the assembly can bend, fold, or unfold.

The ability to be patterned, said postdoctoral research scientist Onur Cakmak, lead author of the study and a member of the research team, “is essential if you want to make useful systems out of these materials.”

Among the applications envisaged for these devices are automatic window opening systems for buildings which are triggered if the humidity passes a threshold value.

It will also be added to fabrics and clothing to help sweat evaporates faster, Sahin suggested.

“We’re providing material for designers to work with their ideas realised quickly,” he said.

Applications which are designed to work for a relatively short period might already be ready for use, while those designed to function for years will need further testing, he added.