Strong beetles and stronger sandwiches

Tougher than a Volkswagen

Most of us have seen a cockroach. We gasp and jump when we see them scurry across our paths. But good luck trying to kill them—whether stomping on them or hitting them with something heavy—because they can withstand up to 900 times their body weight in crushing force.

Sounds impressive, but they are wholly outdone by Phloeodes diabolicus, aptly known as the diabolical ironclad beetle. This 2.5 cm long creature can withstand 39,000 times its own body weight, comparable to the force of being run over by a car on a dirt road.

So what’s the secret to their superstrength? A collection of jigsaw-like joints and exoskeleton-adjacent support structures, an exoskeleton composed of three layered cuticles, and helically arranged proteins that together give the bugs multilayered protection, according to new work by David Kisailus at the University of California, Irvine, and colleagues (Nature 2020, DOI: 10.1038/s41586-020-2813-8). The arrangement is tough, is flexible, and can withstand significant force, and the researchers think these buggy features could be scaled up for joints, fasteners, and other mechanical engineering products.

But these little bugs aren’t relying on their exoskeleton alone. What makes P. diabolicus unique are their evolved elytra—forewings that have hardened and locked together over time as they’ve lost their ability to fly. These elytra help the beetles withstand more compression than the simple exoskeletons of three other beetles the scientists tested.

To pinpoint the strongest parts of the beetle, the scientists used microcomputed tomography, an imaging technique that is like a combination of an X-ray and a CT scan. They found that most of the strength comes from the interfaces between the elytra and the exoskeleton and a joint that permanently fuses the two elytra together. The other beetles have only simple interlaced supports, making them weaker than the champion P. diabolicus. Because of their structure, diabolical ironclad beetles are also able to squeeze into crevices, much like their distant cousin: the cockroach.

Power lunch

BLT, turkey, egg salad: everyone has a favorite sandwich. The tasty meal might give you energy, but you would likely never think of it as a device to convert mechanical energy into electricity.

A small physical change can convert mechanical energy to electricity with the help of a triboelectric nanogenerator (TENG). The TENG is based on the triboelectric effect, which is responsible for what happens when you rub a balloon on your hair. The friction causes the buildup of electrical charges, and those opposite charges attract, causing your hair to cling to the balloon.

A team led by researchers at the Georgia Institute of Technology, Lanzhou University, and the Chinese Academy of Sciences set out to create a new TENG that was biobased and biodegradable. So they made it from a sandwich—wheat bread and leafy greens, to be specific. When compressed and released, the sandwich produces enough energy to power a light-emitting diode and an alarm (Nano Energy 2020, DOI: 10.1016/j.nanoen.2020.105411).

The scientists tested four types of greens between the bread: celery cabbage, lettuce, Chinese cabbage, and leaf mustard. Under a scanning electron microscope, the veggies appeared to have very similar cell arrangements and shapes, but the sizes varied. Celery cabbage, the leaf with the largest cell size, outperformed its cousins in both voltage and current.

So why was celery cabbage the winner in this experiment? The larger cell size implies a higher water and electrolyte content—better for transporting electrons.

The experiment introduces a different kind of environmentally friendly energy source: one that is 100% edible. Just make sure you take the sensors off first.

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