Cambridge Researchers Develop Beetle-based Edible Ultra-White Coating
It is literally the whitest thing you’ll ever set eyes on. It’s the Cyphochilus beetle, a beetle whose shell is whiter than even the whitest paper, the whitest snow, even the whitest paint.
The Cyphochilus beetle, which is native to South-East Asia, is whiter than paper, thanks to ultra-thin scales which cover its body. Animals produce colours for several purposes, from camouflage to communication, to mating and thermoregulation. Bright colours are usually produced using pigments, which absorb certain wavelengths of light and reflect others, which our eyes then perceive as colour.
To appear as white, however, a tissue needs to reflect all wavelengths of light with the same efficiency. The ultra-white Cyphochilus and L. Stigma beetles produce this colouration by exploiting the geometry of a dense complex network of chitin – a molecule similar in structure to cellulose, which is found throughout nature, including in the shells of molluscs, the exoskeletons of insects and the cell walls of fungi. The chitin filaments are just a few billionths of a metre thick, and on their own are not particularly good at reflecting light.
And now, inspired by this awesome creature, Cambridge researchers have developed a super-thin, non-toxic, lightweight
, edible ultra-white coating that could be used to make brighter paints and coatings, for use in the cosmetic, food or pharmaceutical industries.“White is a very special type of structural colour,” said paper co-author Olimpia Onelli, from Cambridge’s Department of Chemistry. “Other types of structural colour – for example butterfly wings or opals – have a specific pattern in their structure which results in vibrant colour, but to produce white, the structure needs to be as random as possible.”
Starting from tiny strands of cellulose (nanofibrils), the Cambridge researchers, in collaborations with colleagues at Aalto University in Finland, were able to mimic the structure of chitin. By varying the diameter of the nanofibrils, which look a lot like spaghetti, the researchers effectively tuned the opacity of their material, and hence its whiteness. They eventually hit a sweet spot, finding just the right combination of nanofibrils. Each membrane is no thicker than a few millionths of a meter.
The resulting coating is 20 times whiter than paper, and since it’s made from cellulose, it is non-toxic. The Cambridge researchers say that the ultra-thin membranes could be incorporated in the next-generation of bright, sustainable, and biocompatible white materials.
