Northwestern University researchers have developed a new hybrid polymer with removable supramolecular compartments, shown in this molecular model. Credit: Mark E. Seniw, Northwestern University
Imagine a polymer with removable parts that can deliver something to the environment and then be chemically regenerated to function again. Or a polymer that can lift weights, contracting and expanding the way muscles do. These functions require polymers with both rigid and soft nano-sized compartments with extremely different properties that are organized in specific ways. A completely new hybrid polymer of this type has been developed by Northwestern University researchers that might one day be used in artificial muscles or other life-like materials; for delivery of drugs, iomolecules or other chemicals; in materials with self-repair capability; and for replaceable energy sources.
“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. The supramolecular soft compartments could be animated to generate polymers with the functions we see in living things,” he said.
The hybrid polymer combines the 2 types of known polymers: those formed with strong covalent bonds and those formed with weak non-covalent bonds, well known as “supramolecular polymers.” The covalent rigid skeleton of Stupp’s first hybrid polymer has a cross-section shaped like a ninja star – a hard core with arms spiraling out. In between the arms is the softer “life force” material. This is the area that can be animated, refreshed and recharged.
“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,” said Stupp. This team found the covalent polymerization that forms the rigid compartment is “catalyzed” by the supramolecular polymerization, 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 polymerizations of covalent and non-covalent bonds, the two compartments end up bonded to each other, yielding a very long, perfectly shaped cylindrical filament.
Schatz’s computer simulations showed the 2 types of compartments are nicely integrated with hydrogen bonds, which are bonds that can be broken. “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,” Lovinger said. http://www.northwestern.edu/newscenter/stories/2016/01/new-polymer.html
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