‘India’s navrang bird can help us strengthen solar energy’

Vinod Kumar Saranathan teaches biological sciences at Krea University. Speaking to Times Evoke, Saranathan outlines his discovery of single cell gyroids in bird feathers — and why this could transform technology:

I’ve trained as a physicist but I was always deeply interested in birds. When applying to graduate school at Yale, I wanted to continue my interest in birds alongside researching physics. So, I became a biomedical engineer, working on bird colour. For my PhD, I studied how birds make the colour blue. This contains cyanine, prevalent in plant tissue. Animals also sport blue but they have created an entirely new way of making this — theirs is a structural colour where the physical infraction of light gets scattered by different interfaces. The portion of the visible light that falls on these structures is reinforced and reflected while everything else is not.

A world of wonder, torn asunder

These colour-producing and scattering nanostructures are microscopic, about 500 times smaller than the width of a human hair. These can be arranged periodically or randomly with a hidden order that makes blue look the same, whichever direction you see it from. Consider a laptop, TV or phone. You’d want the same information from these whether you tilt your head this way or that. 

A STUDY IN PHYSICS: Single cell gyroid structures (R) give the pitta bird its intense blue colouration.

However, in fact, there is only a narrow angle where you can actually see the screen with high fidelity. With birds like blue jays though, no matter where you tilt your head, you get back the same information, the same colour through a perfect quasi-random reflector which makes light bounce back. I’ve also researched butterflies with a vivid green on their wings. If you gently touch one, you’ll find a glitter-like substance on your fingers. These glittering entities are single scale cells. As I discovered, each has a unique structure called a gyroid, a crystal like a building block. A single unit is the gyroid where three channels come together, fuse and gyrate away.

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Imagine a cube now — a division makes the cubic material into two equal surfaces. That is a gyroid surface which is an efficient way to increase surface area. But in the case of birds, these surfaces are filled in on one side with keratin, the other side being air — with this arrangement, you get a single gyroid crystal which is actually really hard to synthesize. Somehow, birds evolved to make this structure in their feathers, light interacting with these to create a vivid blue — my research found that over time, the female preference for pure blue in mates led to this unique ordered structure.

‘Colours show how plants and animals communicate constantly with each other’

A single gyroid has superior optical powers. It interacts very well with light and electrons — if we design photovoltaic cells with such single gyroid crystal symmetry, these can extremely efficiently transform solar energy into electrical energy. In fibre optics too, a cladding on fibre opticals using this structure ensures light won’t escape and losses are minimised. Making these structures is extremely hard but the birds offer us a template. My eventual goal is biomimetics where we understand exactly how birds grow these structures — if we can copy this, that will be transformative for human technology.

THE RIGHT LIGHT: Birds have crystalline structures in their feathers which make certain light or colour reflect back to our eyes, their feathers never fading.

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