The double helix of DNA is among the most iconic symbols in science. By imitating the construction of this advanced genetic molecule we now have discovered a manner to make synthetic muscle fibers much more highly effective than these present in nature, with potential functions in lots of sorts of miniature equipment resembling prosthetic fingers and dextrous robotic units.

The ability of the helix

DNA shouldn’t be the one helix in nature. Flip by means of any biology textbook and also you’ll see helices in every single place from the alpha-helix shapes of particular person proteins to the “coiled coil” helices of fibrous protein assemblies like keratin in hair.

Some micro organism, resembling spirochetes, undertake helical shapes. Even the cell partitions of crops can comprise helically organized cellulose fibers.

Muscle tissue too consists of helically wrapped proteins that kind skinny filaments. And there are numerous different examples, which poses the query of whether or not the helix endows a specific evolutionary benefit.

Many of those naturally occurring helical buildings are concerned in making issues transfer, just like the opening of seed pods and the twisting of trunks, tongues and tentacles. These methods share a standard construction: helically oriented fibers embedded in a squishy matrix which permits advanced mechanical actions like bending, twisting, lengthening and shortening, or coiling.

This versatility in attaining advanced shapeshifting could trace on the purpose for the prevalence of helices in nature.

Fibers in a twist

Ten years in the past my work on synthetic muscle tissue introduced me to suppose lots about helices. My colleagues and I found a easy strategy to make highly effective rotating synthetic muscle fibers by merely twisting artificial yarns.

These yarn fibers might rotate by untwisting once we expanded the quantity of the yarn by heating it, making it take up small molecules, or by charging it like a battery. Shrinking the fiber brought on the fibers to re-twist.

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We demonstrated that these fibers might spin a rotor at speeds of as much as 11,500 revolutions per minute. Whereas the fibers have been small, we confirmed they might produce about as a lot torque per kilogram as giant electrical motors.

The important thing was to ensure the helically organized filaments within the yarn have been fairly stiff. To accommodate an general quantity enhance within the yarn, the person filaments should both stretch in size or untwist. When the filaments are too stiff to stretch, the result’s untwisting of the yarn.

Studying from DNA

Extra lately, I spotted DNA molecules behave like our untwisting yarns. Biologists learning single DNA molecules confirmed that double-stranded DNA unwinds when handled with small molecules that insert themselves contained in the double helix construction.

The spine of DNA is a stiff chain of molecules known as sugar phosphates, so when the small inserted molecules push the 2 strands of DNA aside the double helix unwinds. Experiments additionally confirmed that, if the ends of the DNA are tethered to cease them rotating, the untwisting results in “supercoiling”: the DNA molecule kinds a loop that wraps round itself.

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In actual fact, particular proteins induce coordinated supercoiling in our cells to pack DNA molecules into the tiny nucleus.

We additionally see supercoiling in on a regular basis life, for instance when a backyard hose turns into tangled. Twisting any lengthy fibre can produce supercoiling, which is called “snarling” in textiles processing or “hockling” when cables grow to be snagged.

Supercoiling for stronger ‘synthetic muscle tissue’

Our newest outcomes present DNA-like supercoiling may be induced by swelling pre-twisted textile fibers. We made composite fibers with two polyester stitching threads, every coated in a hydrogel that swells up when it will get moist after which the pair twisted collectively.

Swelling the hydrogel by immersing it in water brought on the composite fiber to untwist. But when the fiber ends have been clamped to cease untwisting, the fiber started to supercoil as a substitute.

An untwisted fibre (left) and the supercoiled version (right). Image via Geoff Spinks, author provided