Artificial nacre is a specialty of the lab and modelled on the biological example of the mussel shell. It consists of countless glass platelets arranged in parallel, which are compacted, sintered and solidified using an polymeric resin. This makes it extremely hard and break-​resistant.

The second layer consists of a polymer to which the researchers have added an indicator molecule synthesized specifically for this application at the University of Fribourg, Switzerland. The molecule is activated as soon as the polymer experiences stretching forces, and this changes its fluorescence. The more the material stretches and the more of these molecules are activated, the more intense the fluorescence becomes.

“We used fluorescent molecules because you can measure the increase in fluorescence very well and you don’t have to rely on subjective perception,” says Tommaso Magrini, lead author of the study, which was recently published in the journal ACS Applied Materials and Interfaces. The system could also have been set up to produce a colour change that would be directly perceptible from the outside. “The perception of colors is subjective and difficult to draw conclusions about changes in the material."

With the help of fluorescence, the researchers can identify overstressed areas within the composite material before fractures form. This allows early detection of vulnerable areas in a structure before catastrophic failure occurs.

Possible applications include load-​bearing structures found in aircraft or vehicles. The next step for researchers is to assess if the material can be produced on an industrial scale. So far, it exists only at laboratory scale as a proof of concept.