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From pangolin scales that can stand up to hard hits to colorful but sturdy peacock feathers, nature can do a lot with a few simple molecules.

In a new review paper, a team of international researchers have laid out how engineers are taking inspiration from the biological world鈥攁nd designing new kinds of materials that are potentially tougher, more versatile and more sustainable than what humans can make on their own.

鈥淓ven today, nature makes things way simpler and way smarter than what we can do synthetically in the lab,鈥� said Dhriti Nepal, first author and a research materials engineer at the Air Force Research Laboratory in Ohio.

Nepal along with Vladimir Tsukruk from Georgia Institute of Technology and Hendrik Heinz of CU Boulder听served as co-corresponding authors for the new analysis. The team in the journal Nature Materials.

The researchers, who come from three countries, delve into the promise and challenges behind 鈥渂ioinspired nanocomposites.鈥� These materials mix together different kinds of proteins and other molecules at incredibly small scales to achieve properties that may not be听possible with traditional metals or plastics. Researchers often design them using advanced computer simulations or models. Examples include thin films that resist wear and tear by incorporating proteins from silkworm cocoons; new kinds of laminates made from polymers and clay materials; carbon fibers produced using bioinspired principles; and panes of glass that don鈥檛 easily crack because they include nacre鈥攖he iridescent lining inside many mollusk shells. 听

Such nature-inspired materials could, one day, lead to new and better solar panels, soft robots and even coatings for hypersonic jets, said Heinz, professor in the Department of Chemical and Biological Engineering and Materials Science and Engineering Program听at CU Boulder. But first, researchers will need to learn how to build them from the bottom up, ensuring that every molecule is in the right place.

鈥淥ne of the main challenges in this field is how do we structure these materials down to the atomic level,鈥� Heinz said. 鈥淲e need to know how nature does it so we can try it in the lab and use guidance from computational models.鈥�

Building blocks

In the new study, Nepal, Tsukruk, Heinz and their colleagues take a close look at keratin, one of nature鈥檚 most adaptable building blocks.

These simple proteins, which often form into twisting helical shapes like DNA, can join together in different ways to make a huge variety of structures鈥攆rom human fingernails and hair to porcupine quills, rhinoceros horns and the overlapping scales of pangolins.

鈥淜eratin is everywhere, and we鈥檝e hardly even begun to appreciate its utility,鈥� Nepal said.

That鈥檚 one of nature鈥檚 secrets, she added: Biological materials can exhibit a wide array of complex architectures at many levels鈥攚hat engineers call 鈥渉ierarchical鈥� engineering. 听Some of those structures are large enough to see with the naked eye, while others are so small researchers need powerful microscopes to study them.

The keratin in pangolin scales, for example, takes on a wavy pattern that makes the scales hard to crack. Peafowl feathers, meanwhile, are made up of melanin rods embedded in a matrix of keratin, which allows these adornments to be both colorful and stiff at the same time鈥攑erfect for peacocks that want to spread their tail feathers.

鈥淥ne of the biggest things we can learn from nature is how these materials exhibit multiple functions that work together in perfect synergy,鈥� Nepal said.

From atoms up

Making advanced synthetic materials with multiple functions in the lab, however, can get tricky.

鈥淢ost of current human-made materials are simple, single-component materials with simplistic uniform morphology and composition,鈥� Tsukruk said. 鈥淎nd what we learnt from nature is that much more complex and sustainable organization is required to make new bio-inspired materials for advanced applications in the near future.鈥�

One of the biggest challenges, Heinz said, comes down to models. His research group uses these tools to simulate new kinds of materials at the scale of a few hundred to millions of atoms.听But taking those kinds of tiny designs and scaling them up to the size of something you can actually see becomes an increasingly difficult task.

鈥淔rom the scale of atoms to the millimeter or even centimeter scale, there are so many levels of organization in natural materials,鈥� Heinz said.

Heinz noted that NASA has recently invested in exploring hierarchically-engineered materials for aerospace applications鈥攕uch as stronger and more lightweight panels of nanostructured carbon for use in spacecraft to carry life supplies to Mars. Heinz, for example, is part of a $15 million effort funded by NASA to study these kinds of 鈥渦ltrastrong composites.鈥�

Engineers, he added, are also discovering new ways to make nanocomposites in large quantities in a manufacturing setting. Today, researchers often use tools like 3D printers to make these materials, laying them down drop by drop.

Heinz, Tsukruk, Nepal, and their colleagues are optimistic. Nature, they report, has had millions of years to learn how to construct materials like pangolin scales or oyster nacre as efficiently as possible. Engineers may be able to take clues from pangolins and oysters to build materials without creating a lot of harmful waste in the process.

鈥淚f we learn from nature, we can find alternatives to many current energy-intensive manufacturing processes or hazardous chemicals,鈥� Heinz said.

Krishan Kanhaiya, a recent PhD graduate in chemical and biological engineering at CU Boulder, also served as a co-author on the new study. Other co-authors include researchers from Georgia Institute of Technology; Carnegie Mellon University; Duke University; MIT; University College London; Johns Hopkins University; Deakin University; Tufts University; University of Michigan; University of Cambridge; University of Oxford; University of California San Diego; and Rice University.