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UD research team creates copolymer rings

Darrin J. Pochan
Taking a cue from the human body, researchers from the University of Delaware have discovered an innovative method by which to create supramolecular rings from tri-block copolymer assembly. Rings have long been theoretically predicted, but the realization of the shape had proved elusive until now.

"People have predicted for many years that you can make these rings but until now no one had done it," Darrin J. Pochan, an assistant professor of materials science and engineering who is affiliated with both UD’s College of Engineering and the Delaware Biotechnology Institute, said.

Pochan led the research project in cooperation with Karen Wooley, professor of chemistry at Washington University in St. Louis.

The method, which is based on the introduction of a positively charged molecule that interacts with the negatively charged polymer molecule, is featured in the Oct. 1 issue of Science magazine.

Polymer molecules with both water-loving (hydrophilic) and water-hating (hydrophobic) sections placed in solution are known to self-assemble into a variety of common shapes, such as spheres and cylinders, Pochan said. Researchers had theorized that the polymer molecules also could form into rings after taking the shape of cylinders then closing on themselves, something that had been seen in a minority or temporary state on rare occasions.

Pochan said the researchers turned to another field for the key idea in finding a solution to the problem. "In biology, nature has a lot of interesting strategies for putting big things into small packages," he said. "DNA, for instance, is a negatively charged biopolymer that is meters long if held end to end. But the body takes DNA and wraps it up into really tight circular bundles by making it interact with positively charged proteins called histones for storage in the human chromosome."

Image created by Jeffrey Turner, Washington University
"We are mimicking the body," Pochan said. "Our synthetic polymers are negatively charged in the hydrophilic segment and they only form rings when a positively charged organic salt is present in solution."

The ability to create these rings has the potential to open up a new field of study, using the human body as a model for the design of other synthetic polymers for advanced function and ornate structure. "The body does some fascinating things, and there might be other functions we can mimic in the future," Pochan said. "This seems to be our first hit."

Pochan said the method is of great interest because "it combines a classic synthetic self-assembly system with a biophysical phenomenon."

Pochan credited the finding to increased funding of interdisciplinary projects, saying that scientists from the biology community and from the nanomaterials community have been communicating more directly than in the past. "There are valuable tools on both sides that could lead to a lot of exciting breakthroughs and discoveries in the near future," he said.

The National Science Foundation funded the research through its Nanoscale Interdisciplinary Research Team (NIRT) program.

Pochan’s research team at UD included Honggang Cui and Kelly Hales. The Wooley laboratory at Washington University included Zhiyun Chen and Kai Qi.

Article by Neil Thomas