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Spiky “hedgehog particles” for safer paints, fewer VOC emissions

Contact: Gabe Cherry, 734-647-7085,

ANN ARBOR – A new process that can sprout microscopic spikes on nearly any type of particle may lead to more environmentally friendly paints and a variety of other innovations.

Made by a team of University of Michigan engineers, the “hedgehog particles” are named for their bushy appearance under the microscope. Their development is detailed in a paper published in the Jan. 29 issue of Nature.

The new process modifies oily, or “hydrophobic” particles, enabling them to disperse easily in water. It can also modify water-soluble, or “hydrophilic” particles, enabling them to dissolve in oil or other oily chemicals.

The unusual behavior of the hedgehog particles came as something of a surprise to the research team, said Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering.

“We thought we’d made a mistake,” Kotov said. “We saw these particles that are supposed to ‘hate’ water dispersing in it and we thought maybe the particles weren’t hydrophobic, or maybe there was a chemical layer that was enabling them to disperse. But we double-checked everything and found that, in fact, these particles defy the conventional chemical wisdom that we all learned in high school.”

The team found that the tiny spikes made the particles repel each other more and attract each other less. The spikes also dramatically reduce the particles’ surface area, helping them to diffuse more easily.

One of the first applications for the particles is likely to be in paints and coatings, where toxic volatile organic compounds (VOCs) like toluene are now used to dissolve pigment. Pigments made from hedgehog particles could potentially be dissolved in non-toxic carriers like water, the researchers say.

This would result in fewer VOC emissions from paints and coatings, which the EPA estimates at over eight million tons per year in the United States alone. VOCs can cause a variety of respiratory and other ailments and also contribute to smog and climate change. Reducing their use has become a priority for the Environmental Protection Agency and other regulatory bodies worldwide.

“VOC solvents are toxic, they’re flammable, they’re expensive to handle and dispose of safely,” Kotov said. “So if you can avoid using them, there’s a significant cost savings in addition to environmental benefits.”

While some low- and no-VOC coatings are already available, Kotov said hedgehog particles could provide a simpler, more versatile and less expensive way to manufacture them.

For the study, the team created hedgehog particles by growing zinc oxide spikes on polystyrene microbeads. The researchers say that a key advantage of the process is its flexibility; it can be performed on virtually any type of particle, and makers can vary the number and size of the spikes by adjusting the amount of time the particles sit in various solutions while the protrusions are growing. They can also make the spikes out of materials other than zinc oxide.

“I think one thing that’s really exciting about this is that we’re able to make such a wide variety of hedgehog particles,” said Joong Hwan Bahng, a chemical engineering doctoral student. “It’s very controllable and very versatile.”

The researchers say the process is also easily scalable, enabling hedgehog particles to be created “by the bucketful,” according to Kotov. Further down the road, Kotov envisions a variety of other applications, including better oil dispersants that could aid in the cleanup of oil spills and better ways to deliver non-water-soluble prescription medications.

“Anytime you need to dissolve an oily particle in water, there’s a potential application for hedgehog particles,” he said. “It’s really just a matter of finding the right commercial partners. We’re only just beginning to explore the uses for these particles, and I think we’re going to see a lot of applications in the future.”

Kotov is also a professor of chemical engineering, biomedical engineering, materials science and engineering and macromolecular science and engineering. The paper is titled “Anomalous Dispersions of Hedgehog Particles” and based upon work partially supported by the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Support has also been provided by the NSF and the US Department of Defense.

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Posted in All News, Faculty News

January 29th, 2015 by Brandon Baier

2014 Engineering Graduate Symposium Winners

Several BME students earned awards at the Engineering Graduate Symposium held on November 14, 2014.

Eli Vlaisavljevich earned the Richard and Eleanor Towner Prize for Outstanding PhD Research. Eli is a PhD student in Professor Zhen Xu’s Image-Guided Ultrasound Therapy Laboratory.

In the poster presentation Sahar Rahmani earned first place in the Medicine and Translational Research (MTR) category.

The Engineering Graduate Symposium is a college-wide event focusing on graduate student research. This program is open to all College of Engineering current undergraduate and graduate students as well as prospective graduate engineering students from other institutions.

Posted in All News, Student/Post-Doc News

December 19th, 2014 by Brandon Baier

HistoSonics and Coulter Partnership Featured in The Wall Street Journal

U-M Biomedical Engineering and U-M Coulter partnership program spinout HistoSonics Inc. is featured by The Wall Street Journal in an article highlighting the growing trend of universities pushing into the realm of startups. The article is available online.

Posted in All News, Faculty News

December 19th, 2014 by Brandon Baier

BME Fall 2014 News

UMBME Fall 2014 MagazineIn our fall issue of the U-M Biomedical Engineering Magazine, we introduce incoming chair Lonnie Shea and explore the very personal roots of his vision for the department’s future. We survey the world of miniaturized, even wearable, sensors to detect anything from cancer to chemical weapons. Our 2014 Alumni Merit Award winner, Scott Merz, reflects on a career in translation, while our globe-trotting students spend their summers learning and improving lives around the world.


Posted in All News, Spotlight

December 5th, 2014 by Brandon Baier

U-M BME Community Mourns the Loss of Derek Tat

Derek Tat, who was a Ph.D. student in Prof. Cindy Chestek’s lab, passed away late last week in a vehicle accident. Derek was a brilliant student and close friend to the Chestek lab as well as the greater Michigan community. The entire U-M BME family is deeply saddened by the news of his tragic death.

Services for Derek will be held on Thursday, October 23, 2014 from 10:00 am – 12:00 pm at the Muehlig Funeral Chapel in Ann Arbor, Michigan. Derek’s family welcomes all to attend his funeral services. The Chapel’s address is:

Muehlig Funeral Chapel
403 S 4th Ave, Ann Arbor, MI 48104

If you would like to donate or share a memory about Derek, please visit this page:

All proceeds donated to the fund will be sent to the Tat family on November 1st.

Posted in All News, Student/Post-Doc News

October 22nd, 2014 by Brandon Baier

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