Mar 23, 2017 | By Benedict

The lab of Chenfeng Ke, Assistant Professor of Chemistry at Dartmouth College, has used 3D printing to create create a smart material capable of lifting 15 times its own weight. The material works by turning mechanically interlocked molecules called rotaxanes into nanoscale machines.

The 3D printed smart material lifts an aluminum plate

Rotaxanes, dumbbell-shaped molecules that can convert energy into movement, are sometimes referred to as “nanomachines” thanks to their ability to perform tasks in response to stimuli. Making them work like real machines, however, has proved tricky. Since groups of these rotaxanes can consist of billions of randomly oriented individuals, the “motion” actually occurs in every direction at once, generally resulting in no useful function whatsoever.

To make the most out of rotaxanes, scientists need to devise a way of controlling their orientation and synchronizing their motion. That’s no mean feat, but Dartmouth College chemistry expert Chenfeng Ke seems to have found a way of doing so—with the help of 3D printing.

The assistant professor’s lab has been using a family of molecules called polyrotaxanes, which have multiple rings on a molecular axle, and which can be strengthened and controlled with greater ease.

The research group found that, by adding water to a group of polyrotaxanes, they could cause the rings of the tiny molecules to stick together instead of moving side to side. This makes the molecules stiffer, and allows the researchers to make a complex system of billions of these stronger molecules, all correctly oriented for work.

With the rings of the polyrotaxanes locked into position side by side, the lab was able to 3D print a polymer mixture containing the molecules into lattice-like structures. “After 3D printing out the polymer, we used a photo-curing process—similar to the UV lamp that hardens nail polish at a salon—to cure it,” Ke said. “We were left with a material that had good 3D structural integrity and mechanical stability.”

Chenfeng Ke's lab found that polyrotaxanes (below) were more useful than rotaxanes

The researchers found that a 3D printed lattice cube structure was best for maximizing the material’s ability to deform, something that increased its ability to carry out useful work. By using a solvent to change the polyrotaxanes’ ring structure from randomly shuttling to stationary and then back again, the researchers could easily control the movement of the material.

“Just like moving beads to strengthen or weaken a string, this shape-changing is critical because it allows the amplification of molecular motion into macroscopic motion,” Ke said.

The results obtained from testing the mechanical function of these 3D printed materials were more than impressive. According to the researchers, a 3D printed lattice cube made of this smart material could lift a small coin measuring 1.6 millimeters and weighing 15 times that of the cube.

Importantly, this is just the beginning for the 3D printed manipulation of rotaxanes. “We hope this advance will enable scientists to further develop smart materials and devices,” Ke commented. “For example, by adding contraction and twisting to the rising motion, molecular machines could be used as soft robots performing complicated tasks similar to what a human hand can do.”



Posted in 3D Printing Materials



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