Anti-reflective coating inspired by fly eyes

Date:
September 16, 2020
Source:
Universite' de Gene`ve
Summary:
The eyes of the fruit fly are covered by a thin and transparent
coating with anti-reflective, anti-adhesive properties. Researchers
discovered that the coating only consists of two ingredients:
retinin and corneal wax. They succeeded in artificially reproducing
the phenomenon on different kinds of surface. This process, which
is very inexpensive and is based on biodegradable materials, could
have numerous applications for contact lenses, medical implants
and textiles.



FULL STORY ==========================================================================
The eyes of many insects, including the fruit fly, are covered by
a thin and transparent coating made up of tiny protuberances with anti-reflective, anti- adhesive properties. An article published in
the journal Nature reveals the secrets of how this nano-coating is
made. The authors, from the University of Geneva (UNIGE) and University
of Lausanne (UNIL) -- together with ETH Zurich (ETHZ) -- show that the
coating only consists of two ingredients: a protein called retinin
and corneal wax. These two components automatically generate the
regular network of protuberances by playing the roles of activator and inhibitor, respectively, in a morphogenesis process modelled in the
1950s by Alan Turing. The multi-disciplinary team even succeeded in artificially reproducing the phenomenon by mixing retinin and wax on
different kinds of surface. This process, which is very inexpensive and
is based on biodegradable materials, was used to obtain nano-coatings
with a morphology similar to that of insects, with anti-adhesive and anti-reflective functionalities that could have numerous applications
in areas as diverse as contact lenses, medical implants and textiles.


==========================================================================
"The nano-coating that covers the surface of the eyes of some insects
was discovered in the late 1960s in moths," begins Vladimir Katanaev, a professor in the Department of Cell Physiology and Metabolism in UNIGE's Faculty of Medicine and the study's lead investigator. "It's made up of a
dense network of small protrusions about 200 nanometres in diameter and
several dozens of nanometres in height. It has the effect of reducing
light reflection." The cornea of an insect without a coating typically reflects about 4% of the incident light, whereas the proportion drops to
zero in insects that do have the covering. Although an improvement of
4% may seem small, it is enough of an advantage -- especially in dark conditions -- to have been selected during evolution. Thanks to its anti-adhesive properties, the coating also provides physical protection
against the tiniest dust particles in the air.

Professor Katanaev moved into this research field ten years ago. In 2011,
he and his team were the first to discover the nano-coating on the eyes
of fruit flies (Drosophila melanogaster). This insect is much more suited
to scientific research than moths, in particular because its genome has
been completely sequenced.

Alan Turing: guiding light Based on their preliminary results, in 2015 Professor Katanaev and his colleagues suggested that the nano-coating
resulted from a morphogenesis mechanism that the British mathematician
Alan Turing had modelled in the 1950s.

This model holds that two molecules are organised automatically to
produce patterns in regular patches or strips. The first serves as
an activator, starting a process where a special pattern emerges and self-amplifies. But it also stimulates the second molecule at the same
time, which acts as an inhibitor and is diffused more quickly. This
model has made it possible to explain natural phenomena on a macroscopic
scale -- such as the spots on a leopard or the stripes on a zebra --
and on a microscopic scale but never yet on the nanoscopic scale.

The Geneva-based researcher has now gathered more evidence to support
this hypothesis. Thanks to biochemical analyses and the use of genetic engineering, Professor Katanaev and his colleagues have succeeded
in identifying the two components involved in the reaction-diffusion
model developed by Turing. This hinges on a protein called retinin and
wax produced by several specialised enzymes, two of which have been
identified. Retinin plays the role of activator: with its initially unstructured shape, it adopts a globular structure upon contact with
the wax and begins to generate the pattern. The wax, on the other hand,
plays the role of inhibitor. The powerplay between the two leads to the emergence of the nano-coating.

Artificial nano-coating "We subsequently managed to produce retinin at
very low cost using bacteria genetically modified for this purpose,"
continues Professor Katanaev. "After purifying it, we mixed it with
different commercial waxes on glass and plastic surfaces. We were then
able to reproduce the nano-coating very easily. It's similar in appearance
to the coating found in insects and has anti-reflective and anti-adhesive properties. We think that we can deposit this type of nano- coating on
almost any kind of surface, including wood, paper, metal and plastic."
Initial tests have shown that the coating is resistant to 20 hours of
washing in water (it is easily damaged by detergent or scratching,
although technological improvements could make it more robust). The anti-reflective properties have already aroused a certain degree of
interest among manufacturers of contact lenses, while the anti-adhesive properties could appeal to the producers of medical implants. Indeed,
this type of coating could make it possible to control where human
cells hook on. Industry already has the techniques needed to obtain
this outcome. But they use harsh methods, such as lasers or acids. The
Geneva team's solution has the advantage of being inexpensive, benign
and totally biodegradable.


========================================================================== Story Source: Materials provided by Universite'_de_Gene`ve. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mikhail Kryuchkov, Oleksii Bilousov, Jannis Lehmann, Manfred
Fiebig &
Vladimir L. Katanaev. Reverse and forward engineering of Drosophila
corneal nanocoatings. Nature, 2020 DOI: 10.1038/s41586-020-2707-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113530.htm

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