Tag Archives: Jonathan S. Sander

Bend it, twist it, roll it—composites inspired by nature

Researchers at ETH (Swiss Federal Institute of Technology) Zurich have developed a new composite material with bioinspired microstructures, from the Apr. 16, 2013 news item on Nanowerk,

Plant components that bend, roll or twist in response to external stimuli such as temperature or moisture are fairly commonplace in nature and often play a role in the dispersal of 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 the knowledge of how these movements come about to produce synthetically a composite material with comparable properties …

The Apr. 16, 2013 ETH Zurich news article by Maja Schaffner, which originated the news item, goes on to describe how the pine cone comes by its abilities,

Studart and co-workers knew from the literature how pine cone scales work: two firmly connected layers lying on top of each other inside a scale are responsible for the movement. Although the two layers consist of the same swellable material, they expand in different ways under the influence of water because of the rigid fibres enclosed in the layers. In each of the layers, these are specifically aligned, thus determining the direction of expansion. Therefore, when wet only one of the two layers expands in the longitudinal direction of the scale and bends on the other side.

The scientists then devised an artificial means of achieving the pine cone’s ability to swell in two orientations (from the article),

Inspired by nature, the scientists began to produce a similar moving material in the lab by adding ultrafine aluminium oxide platelets as the rigid component to gelatine – the swellable base material – and pouring it into square moulds. The surface of the aluminium oxide platelets is pre-coated with iron oxide nanoparticles to make them magnetic. This enabled the researchers to align the platelets in the desired direction using a very weak rotating magnetic field. On the cooled and hardened first layer, they poured a second one with the same composition, differing only in 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 gelatine pieces, the strips bent or twisted differently under the influence of moisture: some coiled lengthwise like a pig’s tail, others turned loosely or very tightly on their own axis to form a helix reminiscent of spiral pastries. “Meanwhile, we can programme the way in which a strip should take shape fairly accurately,” explains Studart.

The researchers also produced longer strips that behave differently in different sections – curl in the first section, for instance, then bend in one direction and the other in the final section. Or they created strips that expanded differently length and breadthwise in different sections in water. And they also made strips from another polymer that responded to both temperature and moisture – with rotations in different directions.

However, Studart was most interested in rotational movements (from the article),

“Bending movements,” he says, “are relatively straightforward.” Metallic bilayer compounds that bend upon temperature changes are widely used in thermostats, for instance. The new method, however, is largely material-independent, which means that any material that responds to external stimuli – and, according to Studart, there are quite a few – can potentially be rendered self-shaping. “Even the solid component is freely selectable and can be made magnetically responsive through the iron-oxide coating,” he says.

Here’s a link to and a citation for the article,

Self-shaping composites with programmable bioinspired microstructures by Randall M. Erb, Jonathan S. Sander, Roman Grisch, & André R. Studart. Nature Communications 4, Article number: 1712 doi:10.1038/ncomms2666 Published 16 April 2013

This article is behind a paywall.

According to Schaffner’s article, Studart believes this work could have applications in the field of medical devices and for self-shaping ceramic devices.