New Color-Changing Paint Reveals Impact Force Without Sensors

Researchers at Tufts University have developed a new impact-revealing paint that changes color based on the force of a hit. This innovation offers potential applications for health and safety monitoring, specifically in the areas of sports concussion prevention and orthopedic analysis.

The paint could be used on football helmets to monitor impacts that reach concussion levels. In a clinical setting, the coating could be placed on shoe insoles to allow healthcare providers to analyze the gait of orthopedic patients.

The development comes from the Tufts University Silklab, led by professor of engineering Fiorenzo Omenetto. Omenetto and research assistant professors Giulia Guidetti and Marco Lo Presti created the substance to quantitatively measure the force and location of an impact without relying on sensors or electronic circuitry. The research was published in the journal Advanced Science.

The Science of Color-Changing Polymers

The coating consists of tiny spherical particles, each approximately the size of a human blood cell. These particles feature a core made of a color-changing polymer called polydiacetylene, which is encased in a harder polymer shell composed of silk fibroin proteins derived from common silk moths.

When the surface is subjected to mechanical stress—such as being stretched, twisted, or squeezed—the chemical backbone of the inner polymer twists at a microscopic level. This physical change alters how electrons move along the length of the polymer, which in turn changes how the electrons absorb photons.

This process triggers a visual transition in the paint, moving from a deep blue to a bright red. Because the intensity of the red color increases in proportion to the force of the impact, the paint functions as a built-in force meter.

According to Guidetti, You can tune the hardness of the shell so that you can extend the response of the paint to different levels of forces. The silk protein shell is designed to prevent false triggers, ensuring the color only changes when the surface is hit with a meaningful amount of force.

Measuring Force and Impact

The paint provides a permanent record of both the location and the level of force applied to a surface. If a location is hit multiple times, the paint provides an additive response. These color changes can be converted directly into newtons, the standard unit for measuring force.

In its current iteration, the paint can detect forces ranging from 100 to 770 newtons. This range covers impacts spanning from a light hammer tap to a strong punch from a UFC fighter.

The material is designed for versatility and can be applied through spraying, brushing, or drop casting, where the paint is poured and then evaporated dry. It can form films on various materials, including metal, wood, plastic, and paper.

Omenetto stated, You can paint it on anything from helmets to footwear and clothing, or on ropes and cables to measure stress.

Because the coating does not require electronics, It’s lightweight, inexpensive, and easy to scale. It remains reliable when applied to flexible or curved surfaces, allowing for the capture of detailed and complex impact patterns.

Interdisciplinary Applications

Beyond medical and industrial uses, the researchers collaborated with Grammy Award-winning drummer Terri Lyne Carrington to test the paint on drum skins. This experiment, resulting from a partnership between the Tufts Silklab and the Global Jazz Institute at Berklee College of Music, visualized the location, angles, and forces of drumstick strikes during a performance.

Carrington noted that the technology could be used as a training tool for musicians. She explained, It could help with training drummers to hit the center of the drum head, which is important for sound quality, adding that it would make it easier to see when a drummer’s aim is off or if they are hitting too close to the rim.

The potential applications for the paint extend to other fields as well. It could be used to record the handling history of shipped packages or to analyze surface aerodynamics for planes and cars by measuring subtle changes in pressure. It could also be utilized to measure powerful impacts resulting from industrial or military blast exposure.

Omenetto described the collaboration with musicians as a way to reframe scientific points of view, allowing researchers to address a broader global impact beyond standard laboratory work.