Image courtesy of Anna Balazs
Local regions of gel shrink when exposed to light through a photomask apeture. As the photomask shifts to the right, the region that is now in the dark swells, and the newly illuminated region shrinks. Multiple passes of mask induce continual swelling/shrinking of contiguous regions resulting in directed movement of the sample.
Computational modeling has demonstrated that polymer gels functionalized with a light absorbing dye can be made to undergo both multiple dynamic shape changes and sustained, directed motion solely under illumination by light. This remarkable functionality in a “synthetic” material essentially mimics the ability of certain biological species to dramatically alter their shape and form in response to environmental cues as a means to defend against predators.
This fabrication approach permits polymeric materials to be molded and re-shaped, thereby making them adaptable and reusable for multiple applications. Also, the ability to remotely manipulate the sample’s motion is critical for driving multiple samples to recognize and dock into each other to form dynamically reconfigurable complex material architectures.
Certain biological species, e.g., the mimic octopus and cuttlefish, change their form and texture when confronted with predators or exposed to danger. If this biological feature could be emulated in a synthetic material such that it can repeatedly adopt different shapes in response to changing surroundings or programmable external stimuli, then the same material could be used for multiple applications, alleviating the need to make new components. Using computational simulations, researchers at the University of Pittsburgh have demonstrated for the first time that polymer gels can be controllably cast into light-induced shapes, with each shape having a different structure and hence, potentially a different use. The polymers contained an attached light-absorbing dye whose molecular structure and shape can be altered by light and thus, permitted control over the gel’s swelling or shrinking. Simulations showed that the gels could be seamlessly and reversibly configured into a variety of complex, three-dimensional shapes by varying the pattern of illuminating light by use of photo masks. Available experimental data are in good agreement with these simulation results, thereby validating the computational approach. Furthermore, the simulations also demonstrated that by repeatedly moving the light back and forth over the sample, the gels underwent sustained, directed motion, another biomimetic behavior. These results demonstrate that a material can undergo both multiple dynamic shape changes and directed motion solely in response to light, suggesting the possibility of light-induced processes for predictably assembling and disassembling multiple components on demand. It represents an important step towards the realization of adaptive, reconfigurable complex architectures in engineered materials.
University of Pittsburgh
DOE, Office of Science, Basic Energy Sciences program
Olga Kuksenok and Anna C. Balazs, “Modeling the Photoinduced Reconfiguration and Directed Motion of Polymer Gels”, Advanced Functional Materials, 2013, 23, 4601–4610. [DOI: 10.1002/adfm.201203876]