Paint that Changes Colour to Record Impacts ^{CEFR B1}

The work comes from the Tufts University Silklab, led by Fiorenzo Omenetto with research assistant professors Marco Lo Presti and Giulia Guidetti. Their research appears in the journal Advanced Science. They developed a coating that records where and how hard impacts occur without any electronic sensors, giving a simple visual measure of force and location.

The coating contains tiny spherical particles about the size of a human blood cell. Each particle has a core of the colour-changing polymer polydiacetylene inside a harder shell made from silk fibroin proteins derived from silk moths. Under mechanical stress the core polymer shifts from deep blue to bright red; at the microscopic level the stress twists the polymer backbone and changes how electrons absorb light, so the colour alters. The silk shell helps prevent false triggers and can be tuned to respond to different force levels.

The colour change remains and creates a permanent map of impacts. Repeated hits at the same spot add to the effect, and the level of colour change can be converted into newtons. The current formulation detects forces from 100 to 770 newtons. The paint can be applied by brushing, spraying or drop casting to paper, plastic, wood, metal and to curved or flexible objects, and it is lightweight, inexpensive and easy to scale. Potential uses include helmets, package tracking, insoles for gait analysis, aerodynamics studies and blast assessment. The team also worked with drummer Terri Lyne Carrington, applying the paint to drumheads to make visual maps of hit patterns.