Robots will soon get powerful artificial muscles made from DNA like supercoiling fibres. With DNA being the only helix in nature, scientists have been able to mimic the structure of this complex genetic molecule. This will enable them to develop artificial muscle fibres which will be more powerful than those found in nature.
Potentially these powerful artificial muscles can be used in many miniature types of machinery such as prosthetic hands and agile robotic devices.
Importance of Helix
Helix is not found only in DNA, it is present everywhere.
- Alpha-helix shapes of individual proteins.
- Coiled-coil helix of fibrous protein assemblies like keratin in hair.
- Some bacteria such as spirochetes adopt helical shapes.
- Cell walls of plants can contain helically arranged cellulose fibres.
Similarly, muscle tissues are also composed of helix proteins that form thin filaments. These helical structures help in making things move like the opening of seed pods, twisting trunks, tongues and tentacles.
They are composed of helically oriented fibres embedded in a squishy matrix. This allows complex mechanical actions like bending, twisting, lengthening and shortening, or coiling. This just goes to show their versatility in achieving such complex shape-shifting tasks.
Geoff Spinks and his fellow researchers discovered a simple way to develop powerful rotating artificial muscle fibres by simply twisting synthetic yarns. You can control the rotation by twisting the yarn by heating it to absorb small molecules or charging it like a battery. Shrinking the fibre causes the fibres to retwist.
The researchers were able to demonstrate the fibres to spin a rotor at speeds up to 11500 revolutions per minute. While the fibres were small they were able to produce torque per kilogram as large electric motors.
They further discovered the key to the success was the yarn remains stiff. While the individual filaments either stretch in length or twist in order to accommodate an overall volume to increase in the yarn. If the filaments are too stiff to stretch it results in untwisting of the yarn.
According to biologists, DNA molecules behave like untwisting yarns, when double-stranded DNA unwinds when treated with small molecules that insert themselves inside the double helix structure.
When small inserted molecules are pushed into the two strands of DNA, which is a stiff chain of molecules called sugar phosphates the double helix unwinds. When the ends of the DNA are tethered to stop them from rotating, it leads to supercoiling i.e. the DNA molecule forms a loop that wraps around itself. The special proteins induce coordinated supercoiling in our cells to pack DNA molecules into a tiny nucleus.
You can witness supercoiling in everyday life when your garden hose gets entangled. Twisting a long fibre can produce supercoiling, known as snarling in textiles processing or “hockling” when cables become snagged.
Supercoiling Gives Strong Artificial Muscles
In an experiment, the biologist used pre-twisted textile fibres i.e. two polyester sewing threads. Each was coated with a hydrogel that swells up when it gets wet and then the pair twisted together.
The composite fibre untwisted by swelling the hydrogel when immersed in water. When the fibre ends were clamped to stop untwisting, it began to supercoil instead, shrinking it to 90% of its original length. Mathematically it was equivalent to putting out 1 joule of energy per gram of dry fibre.
In the case of mammals like us, the muscle fibre shrinks up to 20% of the original length to produce a work output of 0.03 joules per gram. To achieve the same lifting results with supercoiling fibre that is 30 times smaller in diameter compared with our own muscles.
Importance of Artificial Muscles
Artificial muscle materials can be used in an application with space limitations. For example, prosthetic hands, though they don’t match the dexterity of human hands. They require more actuators to replicate the full range of motion, grip types and strength of a healthy human.
Electric motors tend to be useless when used in prosthetics as they tend to lose power when they are reduced in size. This is not the case with Artificial muscles as they maintain high efficiency and power output even if they are scaled-down in size.
Artificial muscles can be used to open and close miniature tweezers, these can be part of the next generation of non-invasive surgery or robotic surgical systems.
There have been advances in the field of artificial muscles over the years, yet there is a large area where the performance of natural muscle such as large contractions, high speed, efficiency, long operating life, silent operation and safety for use in contact with humans needs to be taken care of.
Certainly, supercoiling muscles takes us one step closer to using the technology with humans involved in it. In the future, we can see an increase in the speed of response compared to the fibres that presently operate in our body slowly.