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New technique makes skin invisible - yes really

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2 months ago4 min read

TL;DR

Using Yellow Dye #5, a common coloring that's used in products from foods like Twinkies to lipsticks and house paints, Stanford University researchers have been able to see through the skin of mice. In time, human medical uses may follow.

Pixabay License from jillWellington

Overview

H.G. Wells' 1897 novel, The Invisible Man, imagined the scenario where a serum could change the light scattering effects of a man's body to match the surrounding air, and thereby render the man invisible. A couple of decades later, Kramers-Kronig relations described a mathematical principle that applies to light refraction and absorption in different materials. That principle, combined with Lorentz Oscillation, informed the current research.

Reasoning that light absorbing materials could offset the light scattering that's caused by the lipids, water, and protein in our skin, the researchers went in search of such a material. What they found was Yellow Dye #5, or tartrazine.

According to Guosong Hong, PhD, assistant professor of material science, the result is stunning.

If the same technique could be applied to humans, it could offer a variety of benefits in biology, diagnostics, and even cosmetics.

Medscape describes the surprising effect when the researchers removed the fur from mice and applied a mix of water and tartrazine to the skin:

Rubbed on live mice (after areas of fur were removed using a drugstore depilatory cream), tartrazine rendered skin on their bellies, hind legs, and heads transparent within 5 minutes. With the naked eye, the researchers watched a mouse's intestines, bladder, and liver at work. Using a microscope, they observed muscle fibers and saw blood vessels in a living mouse's brain — all without making incisions. Transparency faded quickly when the dye was washed off.

According to Hong, this technique may eventually be used in doctors' offices and hospitals for diagnostic purposes and also to improve the effectiveness of procedures like drawing blood or removing tattoos.

In a separate commentary, Dr. John Gorecki and Dr. Christopher Rowlands suggest that this technique can also be used as,

an (advantageous) alternative to other optical clearing agents currently used in lab studies, such as glycerol, fructose, or acetic acid

And it can even improve existing imaging technologies like MRI and electron microscopy. According to Rowlands, the technique will be especially useful for neurobiologists.

Although tartrazine is already widely available, human medical uses for this transparency capability are still years away. In the meantime, however, the NSF has made an activity available on their web site so that people can see the effect first-hand. This activity involves painting a tartrazine solution on a chicken breast in order to make it transparent. The activity should be done while wearing, "a mask, eye protection, lab coat, and lab-quality nitrile gloves for protection".

In addition to driving this capability towards human medical uses, the researchers are also continuing their search for other materials that might have similar properties.