3-D printing with custom molecules creates low-cost mechanical sensor

Imagine printing out molecules that can respond to their surroundings.

A research project at the University of Washington merges custom chemistry and 3-D printing. Scientists created a bone-shaped plastic tab that turns purple under stretching, offering an easy way to record the force on an object.

“At the UW, this is a marriage that’s been waiting to happen – 3-D printing from the engineering side, and functional materials from the chemistry side,” said Andrew J. Boydston, a UW assistant professor of chemistry. He is corresponding author on a recent paper in the American Chemical Society’s journal of Applied Materials and Interfaces.

Gregory Peterson and Michael Larsen, UW doctoral students in chemistry, created a polymer, or plastic made up of many repeated units strung together, and fed the soft plastic into the UW chemistry lab’s commercial 3-D printer.

One print head contained polycaprolactone, similar to what a 3-D printer company sells as Flexible Filament. The other print head contained a plastic that is 99.5 percent identical but the UW team made occasional insertions of a molecule, spiropyran, that changes color when it is stretched.

“We wanted to demonstrate that the functional chemistry could be incorporated readily into already printable materials,” Boydston said. “We found that designer chemistry can be incorporated into 3-D printing very rapidly.”

The printed tab is a piece of white plastic with barely visible stripes that turn purple under force. It acts as an inexpensive, mechanical sensor with no electronic parts. The whole device took about 15 minutes to print from materials that cost less than a dollar.

The sensor might be used to record force or strain on a building or other structure. Boydston would like to develop a sensor that also records the speed of the force, or impact, which could allow for a football helmet that changes color when hit with sufficient force.

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