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Researchers Explore Nature-Inspired Materials
A new study has looked out taking inspiration from the biological world to create tougher, more sustainable materials, with potential to create new solar panels or coatings for hypersonic jets.
“Even today, nature makes things way simpler and way smarter than what we can do synthetically in the lab,” said Dhriti Nepal, first author and a research materials engineer at the Air Force Research Laboratory in Ohio.
Alongside Nepal and other colleagues, the research team includes Vladimir Tsukruk from the Georgia Institute of Technology and Hendrik Heinz from the University of Colorado Boulder. Their findings were recently published in the journal Nature Materials.
Bioinspired Nanocomposites
For their research, the international team looked at the benefits and challenges of “bioinspired nanocomposite” materials, which mix together different kinds of proteins and other molecules at incredibly small scales to achieve properties that may not be possible with traditional metals or plastics.
CU Boulder reports that researchers often design these materials 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’t easily crack because they include nacre, or the iridescent lining inside many mollusk shells.
Learning from pangolins and peacocks: Researchers explore next-gen bio-inspired structural materials @NatureMaterials https://t.co/vkHrQSMKip
— Phys.org (@physorg_com) November 28, 2022
“One of the main challenges in this field is how do we structure these materials down to the atomic level,” Heinz said. “We need to know how nature does it so we can try it in the lab and use guidance from computational models.”
Specifically, the researchers looked at keratin, a simple protein that often form into twisting helical shapes like DNA. Keratin, one of nature’s “most adaptable building blocks,” can create materials such as human fingernails and hair, porcupine quills, rhinoceros horns or pangolin scales.
Nepal explains that biological materials can exhibit a wide array of complex architectures at many levels—what engineers call “hierarchical” engineering. 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.
“One of the biggest things we can learn from nature is how these materials exhibit multiple functions that work together in perfect synergy,” Nepal said.
“Most of current human-made materials are simple, single-component materials with simplistic uniform morphology and composition,” Tsukruk said. “And 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.”
Heinz shared that one of the biggest challenges came down to models, with his research group using these tools to simulate new kinds of materials at the scale of a few hundred to millions of atoms. However, making the tiny design and scaling them up proved to be a difficult task.
“From the scale of atoms to the millimeter or even centimeter scale, there are so many levels of organization in natural materials,” Heinz said.
While the team remains “optimistic,” they note that nature has had millions of years to learn how to construct these materials efficiently as possible. Therefore, engineers may be able to take clues from animals such as pangolins and oysters to build materials without creating a lot of harmful waste throughout the process.
“If we learn from nature, we can find alternatives to many current energy-intensive manufacturing processes or hazardous chemicals,” Heinz said.
Recent Bio-Inspired Coatings
At the beginning of the year, researchers at the University of Toronto announced they are looking at the adhesion of mussels on surfaces to potentially create new antifouling coatings for infrastructure and medical adhesives. The study, led by Professor Eli Sone, was published in Scientific Reports.
The research team has reportedly been studying zebra and quagga mussels for years at the university’s material science and engineering research lab. These species are native to lakes and rivers in southern Russia and Ukraine, and likely made their way to the Great Lakes in North America in the 80s on ships from Europe.
Since these mussel species can be invasive and cause problems, like displacing native mussel species and fouling boats, water intake pipes and other infrastructure, the team decided to look at new techniques for measuring adhesion of zebra and quagga mussels to various surfaces to develop effective antifouling surfaces.
The team utilized a pair of fine-tipped, self-closing tweezers, a digital camera and a force gauge to measure how much force was required to break the protein-based glue secreted by the mussels. The mussels were collected from the wild and placed on glass, PVC and PDMS substrates to reattach.
Quagga mussels reportedly showed a significantly lower attachment rate on PDMS compared to glass and PVC, while the zebra mussels showed a consistent attachment rate across all three substrates.
Research found that overall the mussels adhered more strongly to glass than they did to plastics. According to the University of Toronto, researchers expected this since glass is inorganic and hydrophilic, similar to the rocks that the mussels use as substrates in nature, while PDMS repels water and is often coated on boat hulls to prevent biofouling.
In February, researchers in China reportedly developed a new superhydrophobic coating that provides several beneficial properties, including the ability to self-clean and prevent corrosion. Inspired by Calliteara pudibunda, a highly elastic type of bristle worm, the polyphenylene sulfide (PSS) composite coating is created by combining expandable graphite and elastic fluororubber.
Wanting to create a superhydrophobic coating that would adhere to rough structures and provide chemical durability, the research team synthesized hydrophobic nanoparticles using the sol-gel method with modified perfluorodecyltrichlorosilane (PFTS). These particles could reportedly expand to create micro- and nanostructures for superhydrophobicity during the treatment, with a water contact angle of 154±1.2 degrees and sliding angle of 3±0.5 degrees.
Additionally, this combination created repairable microstructures that allow the coating to self-heal. The fluororubber resin acts as an elastic micro-support, to increase the coating’s resistance to bear and repair mechanical damage.
The coating is noted to be suited for outdoor application, as it demonstrated “outstanding” self-cleaning and anti-fouling properties to prevent surface contamination. Researchers say they expect to “open a new avenue to realize the large-scale applications of superhydrophobic coatings in harsh environments” with the development of their coating.
And, in May, researchers from Sandia National Laboratories announced that they have developed an environmentally friendly coating inspired by seashells to protect materials in hostile environments, such as satellites in outer space. The new coating is also inexpensive and lightweight in that it is created from sugar burnt to carbon black and interspersed between layers of silica, which is reportedly the most common material found on Earth.
Because the material is so light, it can be sent into space as a protective layer on satellites since comparatively little material is needed to achieve the same resilience as heavier but less effective shielding. The laboratory reports that thicker shield coatings are durable enough to strengthen the walls of pressurized vessels when added ounces are not an issue.
In addition to its light-weight properties, the new coating is also more cost effective. A beryllium wafer, which is currently used in the Z machine and in protective shielding applications, is reportedly 3,800 times more expensive than the new film.
Sandia reports that both coatings can survive temperatures about 1,000 C (1,832 F), but the new coating is also environmentally friendly. Where beryllium can create toxic conditions in environments that must be cleaned after use, only ethanol is added in the new film’s coating process.
To make the coating strong, Sandia scientists used alternating organic and inorganic layers, which is also a major factor in seashell longevity. Hongyou Fan, Sandia manager and paper author, said the organic sugar layers burnt to carbon black act like a caulk and stop cracks from spreading through the inorganic silica.
It also reportedly provides layers of cushioning to increase its mechanical strength, which was previously reported 20 years ago in another attempt by Sandia to mimic the seashell model. Initial testing varied between a few to 13 layers.
