The artificial skin attached to a person’s knee develops a purple “bruise” when hit forcefully against a metal cabinet.
Photograph adapted from ACS Applied Materials & Interfaces 2021, DOI: 10.1021/acsami.1c0491, courtesy of the American Chemical Society.
Researchers developed an artificial skin that senses force through ionic signals and changes color to provide a visual cue that damage has occurred, which they think will provide new opportunities for detecting damage in prosthetic devices.
Electronic skins, or e-skins, sense stimuli through electron transmission; however, the electrical conductors are not always biocompatible, which can limit their use in prostheses. In contrast, ionic skins, or I-skins, use ions as charge carriers, similar to human skin. These ionically conductive hydrogels have superior transparency, stretchability, and biocompatibility compared with e-skins.
The researchers made an ionic organohydrogel that contained a molecule, called spiropyran, that changes color from pale yellow to bluish-purple under mechanical stress. In testing, the gel showed changes in color and electrical conductivity when stretched or compressed, and the purple color remained for two to five hours before fading back to yellow.
The team taped the I-skin to body parts of volunteers, such as the finger, hand, and knee. Bending or stretching caused a change in the electrical signal but not bruising, just like human skin. However, forceful and repeated pressing, hitting, and pinching produced a color change.
The study, “Colorimetric Ionic Organohydrogels Mimicking Human Skin for Mechanical Stimuli Sensing and Injury Visualization,” was published in ACS Applied Materials & Interfaces.
Editor’s note: This story was adapted from materials provided by the American Chemical Society.
