Researching ways to make smart materials capable of autonomous, and often sensory, behaviour The Ke Functional Materials Group at Dartmouth College in Hanover, New Hampshire, has 3D printed a polymer capable of lifting up to 15 times its own weight.

The material enables further research into how motion can be controlled on a molecular level, within objects and devices that perform functions outside of human reach. As, for example, in controlled drug release devices within the body, or biobots that could lead to developments in tissue engineering.

Gif shows the 3D printed rotaxane polymer expanding to “lift” weight upon addition to water. Clip from Supporting Information of Ring Shuttling Controls Macroscopic Motion in a Three-Dimensional Printed Polyrotaxane Monolith by Qianming Lin, Dr. Xisen Hou and Dr. Chenfeng Ke

Dumbbell molecules?

The polymer 3D printed by Dr. Ke et al. includes nanoscopic, dumbbell shaped, rotaxane molecules with a ring across the bar. As the ring moves across this axel, these molecules are able to turn chemical energy into motion.

The dumbbell/ring structure of a rotaxane molecule. Image by Chenfeng Ke, CC BY-ND

The dumbbell/ring structure of a rotaxane molecule. Image by Chenfeng Ke, CC BY-ND

Aligning too many of the molecules within a polymer cancels out the reaction due to their random orientation. With this in mind, the Ke Lab used polyrotaxanes in place of pure rotaxane molecules. In this case, the dumbbell shape of the molecule contains multiple rings along the axel. Adding water to a polyrotaxane molecule fuses the rings together, meaning that all the billions of molecules within a polymer can work together.

Arrangement of polyrotaxane molecule pre (left) and post (right) addition of water. Image by Chenfeng Ke, CC BY-ND

Arrangement of polyrotaxane molecule pre (left) and post (right) addition of water. Image by Chenfeng Ke, CC BY-ND

3D printed lattice structure

The polyrotaxane material is then 3D printed in a lattice structure. The interlinking shape ensures the co-dependent movement of the structure, and also becomes crucial when returning the material to its original state. After 3D printing, the polymer is cured with light.

As water is used to make the lattice rise, a solvent is added to flatten it – a process the researchers found to be repeatable over a number of times.

In tests, this process enabled the lattice to lift the wright of a small coin.

Stages of the 3d printed polyrotaxane lattice and respective molecular structures. Figure via Qianming Lin, Xisen Hou, and Chenfeng Ke.

Stages of the 3d printed polyrotaxane lattice and respective molecular structures. Figure via Qianming Lin, Xisen Hou, and Chenfeng Ke.

The full paper of these findings can be accessed online here. It is published in Angewandte Chemie journal (International Edition) and co-authored by Qianming Lin, Xisen Hou, and Chenfeng Ke.

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Featured image shows ‘Angie’. Photo by Greg Westfall, imagesbywestfall on Flickr 

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