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Natural inspiration 12

The Sceptic's Tarot is not only about tarot, but also creativity. Here are four inventions inspired by nature.

Octopus-inspired wearable sensor

Wearable electronicsWearable electronics is an emerging trend in health sensor technology as they can monitor a variety of human activities, including heart rate and step count.

For a wearable sensor to be effective, they must be flexible and adhere fully to both wet and dry skin, but still remain comfortable to wear. This means that the material the sensing compounds rest upon is crucial.

Woven yarn is popular, but doesn’t always remain in full contact with the skin, particularly if that skin is hairy. Other typically used yarns and threads are vulnerable to wet environments, losing their grip underwater. In dry environments they can be so sticky that it is painful to remove them.

Researchers have now developed a low-cost, graphene-based sensor with a yarn-like substrate that uses octopus-like suckers to adhere to skin.

They coated an elastic polyurethane and polyester fabric with graphene oxide soaked in L-ascorbic acid to aid conductivity while still retaining strength and stretch. They then added a coating of a graphene and poly(dimethylsiloxane) (PDMS) film to form a conductive path from fabric to skin. Finally, they etched tiny, octopus-like patterns on the film.

The resulting sensor can detect a wide range of pressures and motions in both wet and dry environments. The device can also monitor an array of human activities, including electrocardiogram (ECG) signals and pulse and speech patterns, demonstrating its potential use in medical applications.

[Image credit: American Chemical Society.]

Sources

American Chemical Society. (2019, May 22). Octopus-inspired wearable sensor. ScienceDaily. Retrieved November 5, 2019 from www.sciencedaily.com/releases/2019/05/190522120542.htm

Chun, S., Son, W., Kim, D.W., et al. (2019). Water-resistant and skin-adhesive wearable electronics using graphene fabric sensor with octopus-inspired microsuckers. ACS Applied Materials & Interfaces, 11(18). Accessed 6 November 2019 from https://pubs.acs.org/doi/10.1021/acsami.9b04206. The full article may be purchased from ACS Publications at this link.

Double-sided tape to glue tissue

Double-sided tape for sutures
The sticky substances that spiders use to catch their prey in wet conditions have inspired a double-sided tape that can rapidly seal tissues together.

The new tape could replace surgical sutures, which don’t work well in all tissues and can cause complications in some patients. Sutures can stress the tissue and cause infections, pain, and scars.

Tests on tissue from rats and pig show that the new tape can bind tissues such as the lungs and intestines within five seconds. The tape also works well to seal damage to the gastrointestinal tract, preventing leakage that sometimes follows surgery. This leakage can cause sepsis and other potentially fatal complications.

The double-sided tape can also be used to attach implantable medical devices to tissues, including the heart. It works much faster than tissue glues, which usually take several minutes to bind tightly and can drip onto other parts of the body.

It is difficult to form a tight seal between tissues because water on the surface of the tissues interferes with adhesion. Existing tissue glues diffuse adhesive molecules through the water between two tissue surfaces to bind them together, but this process can take several minutes or longer.

Spider glue contains charged polysaccharides that can absorb water from the surface of an insect almost instantaneously, clearing a small dry patch that the glue can adhere to.

Mimicking the glue, the researchers designed a material that first absorbs water from wet tissues and then rapidly binds two tissues together.

Polyacrylic acid, an effective absorbent material used in diapers, absorbs the water. As soon as it is applied, the tape sucks up water, allowing the polyacrylic acid to rapidly form weak hydrogen bonds with both tissues.

These hydrogen bonds and other weak interactions temporarily hold the tape and tissues in place while NHS esters, embedded in the polyacrylic acid, from stronger, covalent bonds with proteins in the tissue. The process takes about 5 seconds.

Either gelatin or chitosan (a hard polysaccharide found in insect shells) allows the adhesive to hold its shape for long periods, making the tape tough enough to last inside the body. Depending on the application the tape is used for, the researchers can control how fast it breaks down in the body.

[Image credit: Nature/authors]

Sources

Trafton, A. (2019, October 31). New adhesive binds wet surfaces in seconds—could replace surgical sutures. SciTechDaily. Retrieved 5 November 2019 from https://scitechdaily.com/new-adhesive-binds-wet-surfaces-in-seconds-could-replace-surgical-sutures/

Yuk, H., Varela, C.E., Nabzdyk, C.S. et al. (2019, October 30). Dry double-sided tape for adhesion of wet tissues and devices. Nature. DOI: doi:10.1038/s41586-019-1710-5. Accessed 5 November 2019 from https://doi.org/10.1038/s41586-019-1710-5. The full article may be purchased from Nature at this link.

Stick like a clingfish

Clingfish suction cupThe Northern clingfish has one of the best suction cups in the world. A small disk on its belly can attach to wet, slimy, and even rough surfaces, and hold up to 230 times its body weight.

Although many marine animals can stick strongly to underwater surfaces—including sea stars, mussels, and anemones—few can release as fast as the clingfish.

The clingfish’s suction cup is the inspiration for an artificial suction cup that presents a strong but reversible sticking force on rough or textured surfaces. These surfaces often cause a manufactured suction cup to fail.

The rim of the disc on the clingfish’s belly is covered with layers of micro-sized, hairlike structures in many different sizes. The layered effect creates more friction along the rim and helps the fish stick to rough surfaces. The entire disk is flexible and elastic, allowing it to adapt and hold on coarse, uneven surfaces.

Potential applications are tagging whales and other marine animals, attaching sensors to fouled aquatic surfaces, or operating underwater vehicles to clean ship hulls. Other fields include sower caddies or industrial processing.

[Image credit: Lead author Petra Ditsche]

Sources

Ditsche, P. & Summers, A. (2019, September 9). Learning from the Northern clingfish (Gobiesox maeandricus): Bionspired suction cups attach to rough surfaces. Philosophical Transactions of the Royal Society B. DOI: 10.1098/rstb.2019.0204. Retrieved 5 November 2019 from https://doi.org/10.1098/rstb.2019.0204. The paper may be purchased from The Royal Society at this link.

Ma, M. (2019, October 6). A better suction cup design—that works on rough surfaces—inspired by Northern clingfish. SciTechDaily. Retrieved 5 November 2019 from https://scitechdaily.com/a-better-suction-cup-design-that-works-on-rough-surfaces-inspired-by-northern-clingfish/

Chameleon smart skin

Chameleon smart skinThe ability of some creatures to alter their colours to camouflage themselves, attract a mate, or intimidate predators, inspired an artificial “smart skin” that changes its colour in response to heat and sunlight.

The chameleon skin of the tetra fish relies not on dyes or pigments as most colours do, but instead on arrays of tiny structures known as photonic crystals. Light reflects from these microscopic surfaces and interferes with other beams of reflected light, producing a colour. The hue changes when the distance between photonic crystals varies, for example when a chameleon tenses or relaxes its skin.

To mimic chameleon skin, researchers embedded photonic crystals in flexible materials, such as hydrogels, and changed their colours by contracting or expanding the material like an accordion. However, these large fluctuations in size can strain the materials and cause them to buckle.

By studying chameleon skin, the researchers noticed that only a small fraction of skin cells actually contain photonic crystal arrays, while the rest are colourless. They concluded that the colourless cells might help accommodate the strain when the photonic crystals contract and expand.

Inspired by this observation, the researchers patterned arrays of photonic crystals in hydrogel and then embedded these arrays in a second, non-colour-changing hydrogel that acts as a supporting layer. Upon heating, the resulting material changed colour but remained the same size.

The smart skin also altered its hue in response to natural sunlight, similar to how a tetra fish does.

The researchers are hoping that the new material could find applications in camouflage, signalling, and anti-counterfeiting.

[Image credit: Adapted from ACS Nano 2019, DOI: 10.1021/acsnano.9b04231]

Sources

American Chemical Society. (2019, September 11). A chameleon-inspired smart skin changes color in the sun. EurekAlert! Retrieved 5 November 2019 from https://www.eurekalert.org/pub_releases/2019-09/acs-acs090619.php

Dong, Y., Bazrafshan, A., Pikutta, A. et al. (2019). Chameleon-inspired strain-accommodating smart skin. ACS Nano, 13(9). pp. 9918-9926. DIO: 10.1021/acsnano.9b04231. Accessed 5 November 2019 at https://pubs.acs.org/doi/abs/10.1021/acsnano.9b04231. The paper may be purchased from ACS Publications at this link.

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