Material scientists from ETH Zurich (the Swiss Federal Institute of Technology Zurich), who say that they were inspired by plant components like pine cones that respond to external stimuli, have developed a new means of producing composite materials from a variety of materials that adopt a pre-programmed shape autonomously.
Plant components that bend, roll or twist in response to external stimuli such as temperature or moisture are fairly common and most often to disperse seeds. Pine cones, for instance, close their scales when wet and open them again once they have dried out. André Studart, a professor of complex materials at ETH Zurich's Department of Materials, and his group have now applied their knowledge of these movements to produce a composite material with comparable properties.
In pine cones, two firmly connected layers lying on top of each other inside a scale expand in different ways under the influence of water because of the rigid fibers within the layers. Thus inspired, the scientists produced a similar moving material in the lab by adding ultrafine aluminium oxide platelets as the rigid component to gelatin—a swellable material—and pouring it into square molds. The surface of the platelets were pre-coated with iron oxide nanoparticles to make them magnetic. This enabled the researchers to align the platelets in the desired direction. Then, on top of the first layer, they poured a second with the same composition, differing the direction of the rigid elements.
The scientists cut this double-layered material into strips. Depending on the direction in which these strips were cut compared to the direction of the rigid elements in the gelatin pieces, the strips bent or twisted differently under the influence of moisture.
