Going with the flow: Scientists find new way to manipulate DNA

Updated 10:00 AM November 20, 2006

Going with the flow: Scientists find new way to manipulate DNA

By Laura Bailey
News Service

Polymers are large molecules comprising chains of repeating structures, used in everything from the coatings on walls of ships and pipes to reduce flow drag to gene therapy.

But long polymer chains are subject to breakage, called scission. The results of a new U-M study, however, refute much of what scientists previously believed about why polymers break when subjected to strong flows, such as waves crashing against a ship's bow.

This is important for a few reasons, says Michael Solomon, associate professor in the Department of Chemical Engineering, Macromolecular Science and Engineering Program. Broken polymers don't function as intended, and if scientists don't know what causes them to break, they can't keep them from breaking, nor can they design them to break in specific places.

The U-M research helps answer some of those questions, and therefore has implications for the shipping and oil industries, as well as the field of gene therapy, where it could give scientists another tool to control the length of the strands of DNA. In genome sequencing, the first step is to take the genome and break it into small pieces to reassemble it into the DNA strand that is best for further biochemistry, Solomon says.

For the past 40 years, scientists have not understood exactly which forces caused scission, says Solomon, who is the co-author on a paper published last week in the Proceedings of the National Academy of Sciences. The paper, "Universal Scaling for Polymer Chain Scission in Turbulence," defines which flow forces and at what levels those forces cause polymers to break in turbulence.

"This paper understands how they are breaking in a new way that resolves some issues that have been present for 40 years," Solomon said.

The experiments that yielded the prevailing scission theories, Solomon says, did not take into account turbulence in the flow that occurred during the experiments, or how that turbulence attributed to polymers breaking. Those experiments measured only laminar, or smooth flow, which is turbulence-free.

Yet, during its experiments, the team discovered that flow turbulence did indeed exist, and that it was impacting the polymer quite a bit. Through experiments that accounted for turbulent flow, Solomon and co-authors Steven Ceccio, along with then-doctoral student Siva Vanapalli, were able to develop and test formulas for different polymers and pinpoint exactly how they would react to different flows.

Ceccio holds appointments in the departments of Mechanical Engineering and Naval Architecture and Marine Engineering; Vanapalli is now a postdoctoral fellow at Twente University in the Netherlands. The equation developed by their research team can be applied to design flows that break polymers into certain lengths, or to design polymers to withstand certain flows.

"When the polymers are working their best, the friction can be reduced by 70 percent," Ceccio says.

The research is supported by the U.S. Department of Defense. It's part of a larger project to examine many kinds of friction drag, and the U-M team has been conducting experiments at the William B. Morgan Large Cavitation Channel, a Navy-owned facility in Tennessee.

Going with the flow: Scientists find new way to manipulate DNA

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