New hybrid polymer could lead to artificial muscles

Northwestern University researchers have developed a new hybrid polymer with removable supramolecular compartments that can contract and expand like artificial muscles

The hybrid polymer combines two types of polymers: those formed with strong covalent bonds and those formed with weak non-covalent bonds, known as supramolecular polymers. This gives the hybrid polymer both rigid and soft nano-sized compartments.

Materials scientist Samuel Stupp, the senior author of the study, said: “We have created a surprising new polymer with nano-sized compartments that can be removed and chemically regenerated multiple times.

“The supramolecular soft compartments could be animated to generate polymers with the functions we see in living things. Some forms of these polymers now under development in my laboratory behave like artificial muscles.”

The Northwestern University researchers said that the properties of these nano-sized compartments might one day be used in artificial life-like materials, for delivery of drugs, biomolecules or other chemicals, in materials with self-repair capability and for replaceable energy sources. 

Supp said: “Some of the nanoscale compartments contain rigid conventional polymers, but others contain the supramolecular polymers, which can respond rapidly to stimuli, be delivered to the environment and then be easily regenerated again in the same locations.”

Polymers get their power and features from their structure at the nanoscale. The covalent rigid skeleton of Stupp’s first hybrid polymer has a cross-section shaped like a star – a hard core with arms spiralling out.

In between the arms is the softer material. This is the area that can be animated, refreshed and recharged, features that could be useful in a range of valuable applications.

“The fascinating chemistry of the hybrid polymers is that growing the two types of polymers simultaneously generates a structure that is completely different from the two grown alone,” Stupp said. “I can envision this new material being a super-smart patch for drug delivery, where you load the patch with different medications and then reload it in the exact same compartments when the medicine is gone.”

Stupp and his research team also discovered that the covalent polymerisation that forms the rigid compartment is “catalysed” by the supramolecular polymerisation, thus yielding much higher molecular weight polymers.

Andy Lovinger, a materials science program director at the National Science Foundation, which funded this research, said: “This is a remarkable achievement in making polymers in a totally new way – simultaneously controlling both their chemistry and how their molecules come together.

“We’re just at the very start of this process, but further down the road it could potentially lead to materials with unique properties – such as disassembling and reassembling themselves – which could have a broad range of applications.”

The paper is titled “Simultaneous covalent and noncovalent hybrid polymerizations” and was published in Science.