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Chemical and Biological Engineering

Associate Professor Paul Nealey

Associate Professor Paul Nealey (27K JPG)

Delivering nanoscale control to meet fabrication constraints

A new technique developed by Associate Professor Paul Nealey and an international team of researchers marries two approaches to lower the cost and improve the control of producing materials at the molecular level. The approach could lead to computers, personal data assistants and cell phones that offer the densest data capacity stored in the tiniest packages.

If the number of transistors in computer chips continues to increase as expected, the sizes of components will need to keep shrinking as well. The goal is to reduce the scale from around 130 nanometers to under 50. (A nanometer equals one billionth of a meter.)

But limitations in lithography hinder achieving those dimensions. Another approach, using long chains of molecules that arrange themselves into patterns on a given surface, has its own set of limitations. By merging the principles of both techniques, Nealey and researchers at the Paul Scherrer Institute in Switzerland developed a hybrid approach. Lithography is used to create patterns in the surface chemistry of a polymeric material. Next, a film of block copolymers is deposited and the molecules arrange themselves into the underlying pattern without imperfections.

One of the most promising applications could be the development of magnetic storage media with nearly the maximum possible capacity per unit area. In addition, the technology could lead to the design of new microelectronic devices with unknown potential.

Suspensions — down to the very fiber of their being

The behavior of fiber suspensions is important to many industrial processes, from papermaking to processing reinforced composites. By understanding and modeling the relationships between fiber properties and interactions, researchers can determine how best to modify variables within the suspension in order to create better products.

For example, Associate Professor Dan Klingenberg has developed a particle-level simulation technique for studying the behavior of flexible fiber suspensions. Individual fibers are modeled as linked, rigid bodies connected by ball and socket joints. The fibers are allowed to bend and twist, but potentials are defined within the joints that resist the bending and twisting. The fibers experience hydrodynamic drag forces, as well as short-range repulsion and frictional interactions between neighboring fibers.

It is well known that flexible fibers tend to aggregate, or "flocculate." The aggregates, termed "flocs," are undesirable in fiber processing as they lead to problems in products such as paper. Klingenberg's group found that the addition of a small amount of water-soluble polymer can dramatically reduce interfiber friction and disperse the fibers, resulting in a dramatic reduction in the apparent viscosity of the fiber suspension. This allows the suspension to flow up to very high fiber concentrations. By exploiting this feature in the development of an extrusion process, whereby concentrated fiber suspensions can be extruded and formed into solid bodies, relatively low-value solids can be combined with the fiber suspension to produce value-added products.

Making the most of stem cells

Like many other kinds of cells used in biomedical research, human embryonic stem cells are stored and transported in a cryopreserved state, frozen to -320 degrees Fahrenheit, the temperature of their liquid nitrogen storage bath.

But when scientists thaw the cells for use in the laboratory, less than 1 percent revive and assume their undifferentiated state. This "blank slate" form is characteristic of stem cells and is essential for the basic science required before the promising cells are ready for the clinic.

But now Assistant Professor Sean Palecek, Howard Curler Distinguished Professor Juan de Pablo and research specialist Lin Ji are putting the finishing touches on a new method for preserving and storing the finicky cells. The work promises to greatly amplify the number of cells that survive their enforced hibernation, that remain undifferentiated, and that are more readily available for research. In addition, with more survivors, genetic variability becomes less of an issue.

By freezing the cells attached to a gel matrix instead of suspended in solution, and adding the chemical trehalose — a disaccharide or sugar that some animals and microbes produce to protect cells and survive in dry, low-temperature conditions — the Wisconsin team was able to increase stem cell survival rates by more than an order of magnitude, with as many as 20 percent of a cell culture surviving the freezing-and-thawing process.

The ultimate goal of the research is to achieve the ideal system for preserving and storing valuable cells, blood and other biological materials in which cells are freeze-dried.


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Copyright 2004 The Board of Regents of the University of Wisconsin System
Date last modified: Thursday, 17-Feb-2005 14:09:29 CST
Date created: 17-Feb-2005