A new study from Northwestern University in Illinois has synthesized a new form of melanin that could help shield the human skin and fabrics from toxins and radiation.

Selectively porous materials have been a persisting field of interest for chemists and materials scientists. The new study observes the sought-after behavior in fungi that had the properties for ages.

Cryptococcus neoformans using a light India ink staining preparation
(Photo: CDC via Wikimedia Commons)
This photomicrograph depicts Cryptococcus neoformans using a light India ink staining preparation. Life-threatening infections caused by the encapsulated fungal pathogen Cryptococcus neoformans have been increasing steadily over the past 10 years because of the onset of AIDS and the expanded use of immunosuppressive drugs.

Inspired by Fungal Ghosts

The Northwestern University team, led by Nathan Gianneschi, then worked on synthesizing melanin that mimics the behavior of said fungi known for thriving in extreme and hostile environments such as spaceships, inside dishwashers, and even the irradiated compound of Chernobyl. Exceeding their expectations, the new materials also exhibited high porosity - allowing them to capture and hold molecules.

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Melanin is found in a variety of living organisms. On humans, it is mostly on our skin and the back of our eyes. In human skin, as with other animals and plants, melanin is also visually observable for the pigments. Furthermore, melanin helps protect species from environmental factors such as heat and toxins. One example, the turtle-headed sea snake, gets its stripes darker around polluted environments. Also, moths in industrial locations have been observed to turn black as melanin in their wings and exoskeleton absorb the harmful chemicals in soot and smoke.

"Melanin's function isn't fully known all the time and in all cases," said Gianneschi, who also served as a corresponding author on the study. He adds that the substance definitely acts as a "radical scavenger" in human skins, helping protect against UV damage. Their new study has created an incredibly porous material; he adds that fungi might make their synthetic melanin more durable and porous, allowing materials to pass through.

Their study, titled "Allomelanin: A Biopolymer of Intrinsic Microporosity," appears in the Journal of American Chemical Society's latest edition.

Synthetic Melanin as a Shielding Material

The new synthetic material opens an avenue for a number of potential applications. Conventional non-porous materials only allow the adsorption of materials on the surface. On the other hand, porous materials such as allomelanin - the class of nitrogen-free type of melanin found in the fungi - can absorb and hold potentially toxic materials while allowing beneficial materials like air and water to pass through.

Researchers discovered that melanin appeared to be hollow-filled with gaps under the right conditions, as seen by subjecting the material under an electron microscope. They did the same observational tests on the synthetic material - checking its porosity and selectivity for adsorbed materials. In a demonstration of synthetic melanin, researchers illustrated that the material could serve as a protective coating that blocks nerve gas simulants. Researchers then isolated the naturally occurring melanin from the fungal cells, etching biomaterials away and leaving a melanin-containing shell - "fungal ghosts" for their hollow, ghost-like quality.

Another benefit to the new material is that it is simple, easily produced, and highly scalable. It allows the material to be a feasible alternative for protective equipment such as facemasks, shields, and spacecraft manufacturing.

 

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