Feather-inspired films recreate vibrant colors
Many birds are known for their display of brilliant plumage, such as peacocks. Inspired by these feathers, a team of scientists has used nanotechnology to create films in a range of colors.
“[The technology] provide[s] an approach for mimicking the vibrant colors found in avian feathers with a wide range of potential applications in the design of optical devices, functional coatings, and biocompatible products,” the scientists report.
These colorful films are not pigmented. Instead, the colors are determined by the physical structures of the films, called structural colors.
Structural colors are produced when light interacts with a multi-layered material, bending and reflecting the light (in a process known as interference). This results in certain colors being emphasized, while others are subdued. (For more details on interference and structural colors, check out Causes of Colors.)
“What has kept me fascinated for 15 years is the idea that one can generate colors across the rainbow through slight (nanometer scale) changes in structure,” says Matthew Shawkey, a researcher at University of Akron, Ohio, who co-authored the study.
Some birds contain tiny packets of melanin, called melanosomes, in their feathers, that give them colorful sheen, or iridescence. These melanosomes are arranged into certain structures that produce colors by bouncing or absorbing light. (On its own, melanin is dark brown or black pigment, which is also responsible for our skin, hair, and eye colors.)
Scientists created a synthetic version of melanin nanoparticles to mimic structural colors in feathers. Solutions of nanoparticle packets were allowed to evaporate into tightly packed films. The resulting films reflect uniform colors across the surface, from red to green. Being structural, the colors are determined by the thickness of the nanoparticle layers and how tightly these molecules are packed.
“We want to understand how nature uses materials like this, then to develop function that goes beyond what is possible in nature,” says Nathan Gianneschi, a professor at University of California, San Diego, who also co-authored the study.
The films coated with nanoparticles have multiple benefits. Structural colors are resistant to chemical and photo bleaching, so that, unlike pigment-based colors like paints and dyes, they will not fade away overtime. Similar to melanin, the synthetic nanoparticles have the potential to protect the material from UV damage, since they can absorb UV light. They are also biocompatible, biodegradable, and able to be mass produced.
The feather-mimic film has broad applicability, from calorimetric sensors, full color displays, to photonic pigments, according to the scientists who developed the film.
“This idea of biomimicry can help solve practical problems but also enables us to test the mechanistic and developmental hypotheses [of structural colors] we’ve proposed,” Shawkey says.
Nanoparticles synthesized in the study are uniformly spherical. Natural melanosomes in feathers, however, greatly vary in size and shape. The research team plans to expand experiments with synthetic nanoparticles in varying shapes to test how size and shape influence color on the film. The ultimate goal is to create “a biocompatible structural color palette,” the scientists say.
The study is published in American Chemical Society’s ACS Nano and is open access.
In the report, the scientists mention that birds have the largest diversity of structural colors found in nature. It may not be as spectacular as peacock feathers, but my budgie also has iridescent feathers on his lower back. Can you think of other birds with structural colors? 🙂