The journal Science publishes the research in its March 9 issue.
Researchers used a photomask and ultraviolet (UV) light to "print" a pattern onto a sheet of polymers, a technique called photolithography. In the absence of UV exposure, the polymer will swell and expand uniformly when exposed to water, however when polymer molecules within the sheet were exposed to UV light they became crosslinked--more rigidly linked together at a number of points--which prevented them from expanding when water was added. Patterning the amount of crosslinking across an entire sheet allowed researchers to control how much each area swelled. A second exposure to a carefully selected pattern of UV light allowed them to create specific 3-D shapes.
The work, supported by National Science Foundation (NSF) Faculty Early Career Development and Materials Research Science and Engineering Centers awards, is a collaborative effort between polymer engineering and physics, with both theoretical and experimental aspects.
"This paper reports an interesting fusion of experimental technique and theory to develop an innovative method for making self-actuating materials that will assume a desired three-dimensional shape," said Daryl Hess, a program director in the division of materials research at NSF.
For more information on this discovery, read the news release from the University of Massachusetts Amherst.