ANN ARBOR, Mich.---As with many things in nature, including nanoparticles, two are better than one.

Scientists at the University of Michigan have used electricity to create nanoparticles with two sides, similar to how a fish bobber is made of two colored half shells. The technique could fuel a new research direction in the field, because the limits of size and shape are expanded, said Joerg Lahann, assistant professor of chemical engineering at U-M.

The new particles are exciting for several reasons, Lahann said, and could be used in many applications including targeted drug delivery, or to create new self-assembling particles. The big advantage is that the two sides, or phases, may be modified separately.

A good way to understand this is to picture two full water balloons squished into a see-through jar. The membranes are pressed together but the contents of each balloon could differ, because the membrane separates the two balloons. Scientists could load two different drugs into the particles, one on each side, for use in targeted drug delivery.

The Janus particles are anisotropic, which means as you move through it you have different compositions, a bit like a layer cake. The halves could act as tiny balloons if loaded with different drugs, or other substances. "You could potentially fill each balloon with a different drug," Lahann said. He added it's important to understand that the halves of the nanoparticle are not hollow like balloons though. Rather, the particles are made of a solid plastic.

Using the fish bobber analogy, scientists can chemically alter the surfaces of the two halves to create "patches," chemically altered spots on the particle with different instructions.  The ability to engineer or chemically modify the particles to create different surface patches is crucial to self-assembly of nanoparticles, and also in drug delivery, Lahann said. For example, one of the two sides could be modified to 'dock' at certain proscribed points on a cell membrane or a cell tissue. 

The particles are formed by ejecting polymers from two parallel needles, Lahann said. The needles are close enough together that the polymers merge; think of squeezing out a line of toothpaste with two colors, Lahann said. At the end of the needles, a fluid droplet forms which is then blasted with several thousand volts of electricity. This causes the droplet to elongate and break into nanoparticles. The side-by-side positioning is preserved, hence the formation of the two-sided particles.

The findings are published on-line in Nature Materials, in a paper entitled, "Biphasic Janus Particles with Nanoscale Anisotrophy," co-written by Lahann, Kyung-Ho Roh, and Prof. David Martin, director of the macromolecular science and engineering center at the University of Michigan.

For information about Lahann, see: http://www.engin.umich.edu/dept/cheme/people/lahann. html

The University of Michigan College of Engineering is ranked among the top engineering schools in the country. Michigan Engineering boasts one of the largest engineering research budgets of any public university, at $135 million for 2004. Michigan Engineering has 11 departments and two NSF Engineering Research Centers. Within those departments and centers, there is a special emphasis on research in three emerging areas: nanotechnology and integrated microsystems; cellular and molecular biotechnology; and information technology. Michigan Engineering is seeking to raise $110 million for capital building projects and program support in these areas to further research discovery. Michigan Engineering's goal is to advance academic scholarship and market cutting edge research to improve public health and well-being.  For more information, see the Michigan Engineering home page: http://www.engin.umich. edu



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