Bruises on human skin occur when tissues and muscles in a specific area are injured or damaged by force applied with a blunt object. However, when, for example, a building object is hit, engineers have to examine every inch of the material’s surface to understand the extent of the damage. This process can be simplified by improving the mechanosensitivity of the material, which the scientists did by reporting their results in the journal Macromolecules.

There is such a molecule, spiropyran, which reacts to an external force, changing color upon physical stimulation due to a change in the chemical structure. When introduced into concrete or silicone, it reacts to various mechanical influences by changing color. We are talking about strength, deformation, and various damage. Nevertheless, the mechanosensitivity of spiropyran is too low for practical use. When applied, for example, to silicone, the color changes only after very strong deformation.

A team led by Dr. Jae Kim of the Advanced Composite Materials Research Center of the Korea Institute of Science and Technology (KIST) Advanced Composite Materials Research Center (KIST) has dramatically improved the mechanical sensitivity of spiropyran so that it can be used in wearable sensors and as artificial skin.

Previously, its molecular structure was changed in accordance with the material with which it is synthesized. The KIST researchers took a different route.

They first synthesized the composite material and then added a certain type of solvent to improve sensitivity through its aging process. Scientists monitored changes in color and fluorescence of the composite by monitoring solvent absorption times. It was found that increasing the processing time of the material improves its sensitivity. The spiropyran polymer produced by this new process showed an 850% improvement in sensitivity over previously developed materials.

In the course of this research, a process has been developed that can significantly improve the mechanical sensitivity of smart polymeric materials based on spiopyran. We plan to devote ourselves to a new study in which we apply this technology to futuristic wearable sensors and artificial leather.

Dr. Jaeu Kim from KIST