Polymer physicists at the University of Massachusetts Amherst are today reporting the unexpected and previously unknown behavior of a charged macromolecule such as DNA embedded in a charged hydrogel, where it displays what they call a “topologically frustrated” inability to move or diffuse in the gel, a phenomenon they describe in the current Nature Communications.

Polymer physicist professor Murugappan “Muthu” Muthukumar, with postdoctoral researcher Di Jia, used light-scattering techniques to study large DNA molecules’ behavior in a geomesh of 96 percent water, where they expected it to move very slowly, but to eventually diffuse as all previously known systems would behave.

Muthukumar explains, “Scientists have known for more than a century that all molecules have Brownian motion, that is they move around and diffuse, including DNA and other very large molecules. How fast they diffuse depends on the molecule, and large ones can be very slow. This is normal and is what we have observed for more than 100 years.”

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 To limit hospital- and clinic-related infections, institutions have been using new materials, such as one commercially available that mimics shark skin, to inhibit microbes’ ability to stick to high-touch areas such as bed rails and door knobs. But given time, bacteria will accumulate, making this method insufficient, say researchers led by polymer scientist James Watkins at the University of Massachusetts Amherst.

Now in a report available early online today in the American Chemical Society journal ACS Applied Materials & Interfaces, Watkins and chemical engineer Jessica Schiffman, with a team of their graduate students, say they have designed an easily applied coating infused with photocatalytic antimicrobial titanium dioxide (TiO2) nanoparticles that decreases microbial attachment and deactivates those bacteria already attached to surfaces.

As they explain, when TiO2 nanoparticles are exposed to ultraviolet (UV) light, chemical reactions with water and hydroxide molecules form reactive hydroxyl radicals and superoxide ions that rupture the outer membranes of bacteria on contact and lead to cell death. Further, TiO2 nanoparticles are low-cost, widely available and can be incorporated into transparent coatings, unlike more commonly known antimicrobials such as silver and copper. “These advantages make TiO2 an attractive candidate for use in high-touch antimicrobial surface coatings,” they point out.

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Materials that can change shape when exposed to light hold great promise for new applications such as smart building materials that harness solar energy and remotely-controlled micro-robots, but even the most advanced materials developed to date lag far behind systems that operate on traditional chemical or electrical power sources, says polymer scientist Ryan Hayward at the University of Massachusetts Amherst.

Now, the Office of Naval Research has awarded Hayward as lead investigator and a team of researchers at UMass Amherst, the University of California, Riverside, Stanford University, the University of California, Santa Barbara, Kent State University, and the California Institute of Technology a five-year, $7.5 million Multidisciplinary University Research Initiative (MURI) grant to support fundamental research needed to design molecules and material architectures that efficiently convert photon energy into mechanical work.

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Experimental physicists at the University of Massachusetts Amherst today report that they have developed a fast, dynamic new process for wrapping liquid droplets in ultrathin polymer sheets, so what once was a painstaking process taking tens of minutes can now be done in a fraction of a second.

Physics professor Narayanan Menon, with current postdoctoral researcher Deepak Kumar, former postdoc Joseph Paulsen and professor of polymer science Thomas Russell, report their findings in the current issue of Science. 

As Menon explains, many research groups around the world are working on the problem of wrapping liquid droplets to stabilize emulsions, which can be useful in drug delivery systems, for example, or for remediating oil spills.

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