Anti-Reflective Nano-Coating Inspired by Fly Eyes

Innovation: Academia

University of Geneva

2020

Image: Carlos Luis Pinto / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

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Modify Light/Color

Color in living systems comes from pigments and the interaction of light with surfaces. Color serves many purposes for living systems, such as attracting prey or mates, providing warnings, or protecting through camouflage. To create the effects needed for each purpose, living systems must control the expression or visibility of pigments and the interactions (such as reflectance and refraction) of light. To do so, they have strategies that modify color or light to increase or decrease the color’s position, intensity, opacity, and more. Male hummingbirds, for example, have brightly colored feather patches on their throats; the coloring comes from pigments, structures that refract light, or a combination of the two. When a male hummingbird hovers near a potential mate, it modifies the angle of these feathers to create a bright, colorful display. However, when it needs to mute the colors to reduce conspicuousness, such as to avoid a predator, it modifies the angle again.

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Protect From Dirt/solids

When dirt and other small solids adhere to living systems, they can slow them down, create blockages, reduce their ability to carry out vital functions, or cause surface wear and tear. Due to electrostatic forces, it’s easy for dirt and other solids to adhere to surfaces, so living systems must overcome those forces. An earthworm, for example, uses a small electric current to keep soil particles from adhering to its body as it moves through the soil. This enables it to move more efficiently by reducing drag.

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Protect From Excess Liquids

While water is essential to life, too much water or other liquids can overwhelm living systems. Excess liquids can, for example, decrease a living system’s access to oxygen, promote excessive bacterial or fungal growth, or strip away soil and nutrients. To prevent the accumulation of excess liquids, living systems must control the movement of liquids across their boundaries or surfaces. They do so using waterproofing materials or structures, slowing flow, and/or facilitating flow to move the liquid away. Plant leaves, for example, commonly have waxy surfaces comprised of water-repelling chemicals to keep water from engorging the leaves or facilitating bacterial and fungal growth.

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Nano-coating from the University of Geneva creates nanoscale surface bumps that help to reduce reflection and adhesion.

Benefits

Biodegradable
Inexpensive

Applications

Contact lenses
Textiles
Medical devices
Renewable energy

UN Sustainable Development Goals Addressed

Goal 12: Responsible Production & Consumption

Bioutilization

Bacteria

The Challenge

Light reflection is a common problem that occurs in many applications. For example, any light that is reflected off solar panels reduces the total amount of energy that can be used, which decreases efficiency. Additionally, when particles such as dust adhere to a surface they block potential light from entering, further reducing apparatus efficiency.

Innovation Details

The coating consists of commercial waxes mixed with the retinin , which is produced by genetically-modified bacteria. Similar to the surface of a fly’s eye, the coating creates tiny bumps that reduce reflection and dirt/dust adhesion. The coating can be used on almost any kind of surface, including wood, paper, metal and plastic. It is also resistant to washing in water for up to 20 hours. However, it can be easily damaged by detergent or scratching, and further improvements are needed to increase resiliency.

Successive enlargements of a fly’s eye. The eye is made up of many facets, which are themselves covered by a thin layer of protuberances a few tens of nanometres high. 1 micrometer (μm) = 1000 nanometers (nm). Photo: Vladimir Katanaev/UNIGE.

Biological Model

The outer surface of many insect eyes, the corneal lens, is covered with a regular pattern of small conical protuberances. These protuberances reduce light reflection by creating a refractive index gradient between the air-lens interface. Additionally, the protuberances create a barrier against dust particles.

See Related Strategy

an elephant hawk-moth photographed head on with its bring pink lower body and yellow top, long legs and big yellow eyes

Biological Strategy

Eyes Are Anti-Reflective

Moths

Eyes of nocturnal moths are anti-reflective due to nanoscale protrusions.

References

Journal article

Reverse and forward engineering of Drosophila corneal nanocoatings

Nature

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