Paint that Changes Colour to Record Impacts ^{CEFR B2}

Researchers at the Tufts Silklab, led by Fiorenzo Omenetto with Marco Lo Presti and Giulia Guidetti, report in Advanced Science a paint that visually records impact location and force without electronics. The coating is made from tiny spherical particles roughly the size of a human blood cell. Each particle houses a core of the colour-changing polymer polydiacetylene inside a protective silk fibroin shell derived from silk moths.

Under mechanical stress the inner polymer shifts from deep blue to bright red. Microscopically, the stress twists the polymer backbone and alters how electrons absorb light, producing the colour change. The silk shell reduces false triggers and can be tuned to respond at different force thresholds. Once the colour has changed it remains, producing a permanent impact map; repeated hits intensify the effect and the degree of change can be converted into newtons. The current formulation detects forces from 100 to 770 newtons, a range the authors compare to a light hammer tap up to a strong punch.

The paint can be brushed, sprayed or drop cast to create films on paper, plastic, wood, metal and on curved or flexible objects. Because it needs no electronic parts it is lightweight, inexpensive and easy to scale up. Possible applications range from football helmets for concussion monitoring, recording handling history of shipped packages and insoles for gait analysis, to surface studies in aerodynamics and assessment of military or industrial blast exposure. The team also collaborated with drummer Terri Lyne Carrington, applying the coating to drumheads; her improvisations from the 2019 album Waiting Game produced abstract visual maps that may help train drummers to improve aim and technique.