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Biomimetics — Where the Action Is

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Since our last report on biomimetics (the imitation of nature’s designs), several exciting new projects have come to light. Let’s survey some of the research going on around the world that is inspired by biology.

Cactus cooler. How can you clean a fish farm? Use cactus, says the American Chemical Society. An old trick known by rural Mexicans uses prickly pear cactus to clean dirty water, but how does it work? ACS scientists found that mucilage, the gummy substance in some cactus tissues, attracts impurities like arsenic and bacteria (see the video clip in the article). Made up of some 60 sugars, mucilage seems like a useful cleanser for aquariums and fish farms. The scientists want to synthesize the compound to make a “recirculating aquaculture system that uses cactus extract as a cleansing agent.”

Fish cornea. Meet the “elephantnose fish.” Its unique ability to find predators and prey in murky water is inspiring technology that could touch the apple of your eye some day: high-tech contact lenses. The elephantnose fish has a specialized retina that captures and amplifies light. News from the National Institutes of Health tells how researchers at the University of Wisconsin-Madison are learning and imitating this fish’s secrets:

The team took their inspiration from the elephant nose fish’s retina, which has a series of deep cup-like structures with reflective sidewalls. That design helps gather light and intensify the particular wavelengths needed for the fish to see. Borrowing from nature, the researchers created a device that contains thousands of very small light collectors. These light collectors are finger-like glass protrusions, the inside of which are deep cups coated with reflective aluminum. The incoming light hits the fingers and then is focused by the reflective sidewalls. Jiang and his team tested this device’s ability to enhance images captured by a mechanical eye model designed in a lab. [Emphasis added.]

The article describes how their bio-inspired contact lens (5-10 years away) will contain solar cells, sensors and electronics to enhance and focus light. The team is also finding inspiration in the compound eyes of insects, envisioning numerous applications in the line of sight. See the open-access paper in the Proceedings of the National Academy of Sciences (PNAS), where the authors say, “Our work opens up a previously unidentified direction toward achieving high photosensitivity in imaging systems” — inspired by fish and insects.

Dragonfly cornea. Speaking of insects, “Someday, cicadas and dragonflies might save your sight,” another news item from the American Chemical Society says, but not because of their compound eyes. These insects protect their delicate wings with “a forest of tiny pointed pillars that impale and kill bacterial cells unlucky enough to land on them.” Could this secret render artificial corneas and lens implants antibacterial without coatings? By imitating these pillars with Plexiglas or Lucite, researchers at UC Irvine found they work to kill both gram-negative and gram-positive bacteria, depending on the size of the nanostructures they fabricate. “The group has filed for patents on the bactericidal surface and artificial cornea application and hopes to begin animal trials this year.” Biomimetics can make money!

Mussel glue. How mussels and barnacles cling so well underwater has long puzzled scientists, but they sure would like to copy that ability. “The need for bio-inspired wet adhesives has significantly increased in the past few decades (e.g., for dental and medical transplants, coronary artery coatings, cell encapsulants, etc.),” begins another paper in PNAS. Somehow, mussels do it with protein. To copy the animal’s wizardry, therefore, scientists need to identify and understand the molecular interactions of the “mussel foot proteins” involved. Scientists from UC Santa Barbara and Lehigh (Behe’s turf) are making progress. They found out that mussels learned how to manage “a delicate balance between van der Waals, hydrophobic, and electrostatic forces.” You have to know physics as well as biology to succeed here.

Shape shifter. You’ve heard of 3D printing. How about 4D printing? In “Biomimetic 4D Printing,” Nature tells about efforts to imitate “nastic plant motions, where a variety of organs such as tendrils, bracts, leaves and flowers respond to environmental stimuli (such as humidity, light or touch) by varying internal turgor, which leads to dynamic conformations governed by the tissue composition and microstructural anisotropy of cell walls.” We don’t usually think of plant motions, but if seen in time lapse, their motions are real and targeted. If we could 3D-print things that shift their shapes in response to environmental triggers, think of the possibilities: “smart textiles, autonomous robotics, biomedical devices, drug delivery and tissue engineering.” Here’s what the wizards at Harvard’s Wyss Institute for Biologically Inspired Engineering have come up with so far:

Inspired by these botanical systems, we printed composite hydrogel architectures that are encoded with localized, anisotropic swelling behaviour controlled by the alignment of cellulose fibrils along prescribed four-dimensional printing pathways. When combined with a minimal theoretical framework that allows us to solve the inverse problem of designing the alignment patterns for prescribed target shapes, we can programmably fabricate plant-inspired architectures that change shape on immersion in water, yielding complex three-dimensional morphologies.

Bone buildings. Bones and eggshells have the advantage of strength in spite of light weight, Michelle Oyen writes in The Conversation (see her in a video clip in the article). Why don’t we build things like that? Steel and concrete are heavy, and to a world worried about climate change, they are dirty. Why not use clean, lightweight building materials inspired by nature? Caution: basic research needed:

In order to make biomimetic materials, we need to have a deep understanding of how natural materials work. We know that natural materials are also “composites“: they are made of multiple different base materials, each with different properties. Composite materials are often lighter than single component materials, such as metals, while still having desirable properties such as stiffness, strength and toughness.

It’s the biological component, like protein, that’s the secret. Eggshells are 95 percent mineral and just 5 percent hydrated protein but that makes all the difference. Oyen says we can learn nature’s tricks one of two ways: by mimicking the composition of the material itself, or by copying the process by which the material is made. Her lab is working on “neo-bone” at the centimeter scale, but there’s no reason it could not be scaled up to industrial size, she says; it just takes a “major rethink” in how we build things. “The science is still in its infancy, but that doesn’t mean we can’t dream big about the future.”

Frog therapy. Advances in biomimetics come from observation followed by inspiration. Who would have thought that the foam that tiny frogs use to surround and protect their eggs could someday deliver healing drugs to burn patients? At Strathclyde University, the BBC reports, engineers “are taking inspiration from the tiny Tungara frog from Trinidad” to do just that. The frogs use at least six proteins to retain the shape and strength of their egg nest. The scientists have made a synthetic version of frog foam that “could trap and deliver medication while providing a protective barrier between the wound dressing and the damaged skin.” So far, they’re only halfway there. “While foams like these are a long way from hitting the clinic, they could eventually help patients with infected wounds and burns, by providing support and protection for healing tissue and delivering drugs at the same time,” they hope.

Are you getting inspired by biological design? Consider that biomimetics is proving to be a shot in the arm for both basic research and for applied science. Scientists have to understand what they observe, being curious about why a biological solution works (e.g., how does a mussel grip a rock underwater?). Then, with a little imagination, they can envision ways the natural process can be applied. From there, inventors and engineers can get busy trying to imitate the solution. Everyone can profit from the results.