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Managing Editor  | October 2017

Magnetic tweezers show polymer growth is not continuous process

Researchers at Cornell University (Ithaca, N.Y.) became the first to use magnetic tweezers as a measuring technique for living polymerization and were the first to visualize the formation of a polymer chain at a single polymer level, according to a report from the school.



The researchers showed that "hairballs" form and untangle in polymer growth.
(Cornell University)


The research team discovered that the continuous process that many imagined was the formation of polymers was actually broken up by the creation and unraveling of conformational entanglements, called “hairballs” by the scientists.


The hairballs “produce a step-wise extension pattern of polymer growth, as opposed to more continuous extension as was previously thought.”


“Not only does the discovery of these ‘hairballs’ appear to play a key role in determining the polymerization rates of individual polymers,” the article explained, “this work could also help inform study of living bio-polymerization in cells.”


Scientists used a Grubbs catalyst, which is known for allowing manipulation during experiments, to facilitate the growth of the polymer chain and used magnetic tweezers to measure the chain’s growth in real time.


“The measurement is done by anchoring one end of the growing polymer to a coverslip and the other to the catalyst, which is fitted with a tiny magnetic particle,” the article said.


It added, “Constant application of a magnetic force pulls the particle and stretches the polymer. During polymerization, the insertion of new monomers leads to a lengthening of the polymer chain, and by tracking the position of the magnetic particle, the researchers tracked the growth of the polymer with nanometer-scale precision.”


The researchers discovered that polymerization was not a fluid, continuous process but rather each monomer formed hairballs and the extension of the chain occurred only in “wait-and-jump steps.”


The research was recently published in Science. The abstract stated:


“In chain-growth polymerization, a chain grows continually to reach thousands of subunits. However, the real-time dynamics of chain growth remains unknown. Using magnetic tweezers, we visualized real-time polymer growth at the single-polymer level.


“Focusing on ring-opening metathesis polymerization, we found that the extension of a growing polymer under a pulling force does not increase continuously but exhibits wait-and-jump steps. These steps are attributable to the formation and unraveling of conformational entanglements from newly incorporated monomers, whose key features can be recapitulated with molecular dynamics simulations.


“The configurations of these entanglements appear to play a key role in determining the polymerization rates and the dispersion among individual polymers.”

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