While human muscle can tear and heal over time, the same cannot be said about electrically-responsive polymers that are used to create artificial muscles for haptic systems and robots used for experimentation. When these muscles are torn, it’s back to the drawing board for a replacement. A new polymer has been created that offers a very stretchy as well as self-healing alternative for future tests.
This new artificial muscle material was created by a team led by Zhenan Bao, a material scientist at Standford University. The new and improved polymer has some pretty fascinating properties that are proving to be quite beneficial to scientists.
When punctured, it actually fuses itself back together. Such a feat is not normally very functional in ambient conditions. A 2.5 centimeter sheet of this new material can be stretched out to reach lengths as far as 2.5 meters. The muscle is able to expand in a single dimension at a time, while contracting in the other two in order to make up the difference. It can expand by 2.6 percent under an electric field of 17.2 millivolts per meter.
Bao is very well known for work developing more sensitive and life-like electronic skin that is commonly used for robots or prosthetics. Thanks to the new designs, better materials will soon arrive and so will the understanding of how to create more efficient multifunctional materials. Bao says the goal is not to make the strongest artificial muscle, but to learn how to engineer new polymer possibilities with different combinations of properties.
The new self-healing polymers contain a combination of both strong and weak bonds. The strong ones give it improved mechanical strength while the weaker ones form easier. The new material was built with a network of long polymer chains. Molecules holding iron as well as molecules that bond with iron were added to the commonly used elastomer PDMS. As iron bonds break, new ones form and make up for the damage – an occurrence that happens instantly. You can read in detail of the new material in the Nature Chemistry journal.
As of yet, other self-healing polymers will only heal under very strict conditions. Often they are weak to water vapor found in air, becoming damaged when exposed. Others have to be heated or compressed to cause healing reactions to occur at all. The new Stanford material is able to sit in open air for days without a hitch and heals on its own in a room temperature setting. Upon healing, both the electric and mechanical properties are just as strong as they were before the break or tear. The stretchiness of the material was an unexpected side effect, as healing was the sole focus of the testing. This additional component expands this research far beyond expectation, with a wide range of possibilities not only medically but electronically as well.
Researchers say this new muscle can be strained up to 10,000 percent. During testing there wasn’t a machine large enough to test the full limits of the material’s ability to stretch. Students had to pull both ends across the room themselves. Studies are currently underway testing other applications for this new technology. Bao says they hope to build electronic circuits that can heal themselves, and is currently working on fitting polymers with electronic properties to create a full transistor. These would include semiconductors, conductors and dielectric materials that may be used in electronic skin for prosthetics and robots.