Polymer may lead to artificial muscles

Scientists have developed a new hybrid polymer that may be used in artificial muscles, for delivery of drugs, biomolecules or other chemicals and in self-repairing materials.

The polymer has both rigid and soft nano-sized compartments with extremely different properties that are organised in specific ways, and can be removed and chemically regenerated multiple times.

It combines two types of known polymers — those formed with strong covalent bonds and those formed with weak non-covalent bonds, well known as “supramolecular polymers”. The integrated polymer offers two distinct “compartments” with which chemists and materials scientists can work to provide useful features, according to researchers from North-western University in the United States.

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

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

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

The strongly bonded covalent compartment provides the skeleton, and the weakly bonded supramolecular compartment can wear away or be used up, depending on its function, and then be regenerated by adding small molecules.

After the simultaneous polymerisations of covalent and non-covalent bonds, the two compartments end up bonded to each other, yielding a very long, perfectly shaped cylindrical filament.

“Some of the nanoscale compartments contain rigid conventional polymers, but others contain the so-called supramolecular polymers, which can respond rapidly to stimuli, be delivered to the environment and then be easily regenerated again in the same locations,” said Samuel I Stupp from Northwestern University.