A new nanoscale hybrid polymer has been found to be capable of chemical regeneration.

By combining rigid and soft compartments from polymers, a team of engineers and materials scientists from Northwestern University developed a polymer that can contract and expand, imitating muscle fibers.

The supramolecular polymer combines polymers with strong covalent bonds and weak non-covalent bonds. By working with the two compartments and manipulating specific orientation, the researchers were able to create a new reactive material.

"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, materials scientist and lead author of the published study.

“The supramolecular soft compartments could be animated to generate polymers with the functions we see in living things," Stupp added.

The covalent rigid skeleton of Stupp's first hybrid polymer combines a hard core with arms spiraling out. The softer core material lies in between the arms. This is the area that can come to life in animation, refreshed and recharged.

Hybrid Polymer Compartments

Covalent polymerization forms the rigid compartment and is catalyzed by supramolecular polymerization. These higher molecular weight polymers have a strongly bonded covalent compartment, the skeleton, while the weak bonding in the supramolecular compartment can be used up partially or completely for a designated function.

In addition, the polymer can regenerate through the addition of small molecules.

After simultaneous polymerizations of covalent and non-covalent bonds, the two compartments then bond to create a long and perfectly shaped cylindrical filament. Using computer simulations, theoretician George Schatz demonstrated how the two types of compartments nicely integrated with breakable hydrogen bonds.

"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,” he concluded.

Polymer Possibilities

Future applications in disassembly and reassembly of materials is possible. Other applications of interest include the creation of artificial muscles or other life-like materials, delivering biomolecules or other chemicals, self-repairing materials and replaceable energy sources.

"This is a remarkable achievement in making polymers in a totally new way; simultaneously controlling both their chemistry and how their molecules come together," said Andy Lovinger a materials science program director at the National Science Foundation.