A new mechanical sensor with a wide range of potential uses has been developed, through the merging of 3D printing and designer molecules. This manufacturing process utilizes molecules that can react to their environments, including the ability to change color when force is exerted on an object.

University of Washington (UW) researchers developed a tab, imprinted with dark yellow markings. When this tab is stretched, the markings turn purple. This technology could potentially be used to easily record force on objects, acting as a next-generation detector.

A polymer was created from tiny units of materials, and the flexible material was fed into a 3D printer. This device uses a pair of heads to manufacture custom items. One of these heads contained polycaprolactone, also known as Flexible Filament, commonly used in 3D printers. The other contained 99.5 percent polycaprolactone, along with 0.5 percent spiropyran, a chemical that changes colors when it undergoes stretching.

The device can be produced quickly and inexpensively. The tabs produced during the experiment took less than 15 minutes to create, at a cost of under a dollar each.

"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," Andrew J. Boydston, assistant professor of chemistry at UW, said.

In the near future, a similar device might be used to record strains within a building, providing early warning of material stresses. The sensor can be created with the color-changing material printed in any shape desired, including letters, bars, or distributed evenly around the device.

Further development of the sensor could lead to a material that would record not just the strain on a system, but the force over time. Such an advance could lead to the manufacture of football helmets that would change color upon receiving an impact of a certain force, potentially reducing harm from concussions.

"Maybe the material isn't currently under stress, but it had been several times prior to your observing it. And so these types of materials could record that load history," Boydston said.

Spiropyran is an organic compound, known to chemists since the early 20th Century. However, it was not until 1952 that researchers discovered the chemical could change colors under certain conditions. Today, many scientists are hoping the substance may be utilized in a wide variety of applications, including construction and healthcare.

Development of the new device for recording stress was detailed in the journal Applied Materials and Interfaces.

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