It looks like magic, but it's just physics: Scientists turn mice transparent

Researchers at the University of Texas at Dallas have made an unusual discovery: a method to turn an animal's skin transparent.

The mice's skin was turned transparent by placing a mixture of water and tartrazine, a common food coloring, on the skull and abdomen. Once the dye was spread on the skin, it became transparent within minutes.

Although it seems very strange, this is possible because the skin is a "spreading medium". Such materials allow light waves to scatter in different directions when reflected back to them. Instead of light passing through, it is refracted.

According to Zihao Ou, the discovery "makes sense" to those with a background in physics, while to others, "it looks like a magic trick."

"We combined the yellow dye, which is a molecule that absorbs most of the light, especially blue and ultraviolet light, with the skin, which is a propagating medium. Separately, these two block the penetration of light. But when we put them together, we managed to make the mice's skin transparent."

The 'magic' happens when light-absorbing molecules dissolve in water and change the solution, causing it to reflect light to match parts of the skin, such as fat.

"It takes a few minutes to happen. It's similar to how a cream or a face mask works: The time depends on how quickly the molecules spread into the skin," said Ou.

The scientists said the mice don't stay that way and revert back to their previous state with a simple wash.

They could see the blood vessels on the surface of the brain through the translucent skin. In the abdomen, the internal organs and muscle contractions that enable the movement of food into the digestive system could be seen.

Although the experiment worked in mice, the researchers have yet to test it in humans, whose skin is 10 times thicker. "It's not yet clear what dose or method it would take to penetrate its full thickness," Ou said.

One of the first applications of this technique will be to improve existing biomedical research methods. "Optical devices such as microscopes cannot be used to study living humans or animals because light does not penetrate tissue. But now that the skin can be made transparent, it will allow us to see the dynamics in more detail. It will fundamentally change existing optical research in biology."

Researchers are testing other molecules, including specially designed materials, that may work better than tartrazine.