Fiona Mukherjee
Fiona Mukherjee

Liquid Crystal Inventions

by Jackie Swift

Under the right conditions, certain kinds of molecules enter a peculiar state of matter called a liquid crystal. The result is a substance that exhibits some properties of a liquid and some properties of a solid crystal.

A liquid crystal not only behaves strangely itself. It also elicits strange behavior from other materials. When sand particles are put in a liquid crystal, for example, they spontaneously line up to form a chain. Liquid crystal provokes regular particles to interact with each other in irregular ways, explains Nicholas L. Abbott, Chemical and Biomolecular Engineering.

Abbott is leveraging all this unusual behavior to reach unthought-of solutions to environmental and medical challenges. Among his various projects, he is using liquid crystal to identify pollutants in lake water and to reveal minute differences in structures as small and complex as red blood cells.

Revealing Unique, Fingerprint-like Patterns

“The nature of the interactions created in a liquid crystal are really weird,” Abbott says. “That leads to all sorts of organizations of particles you don't see in a simple liquid like water. The interactions between particles in a liquid crystal can have a bipolar nature, like the magnets that you can buy from a hobby shop. In a liquid crystal, however, the interactions of the particles arise from the sensitivity of the liquid crystal to the particles’ surface properties, which influence the way [the liquid crystal] orders itself around them.”

Interactions between the particles and liquid crystal vary according to the composition of the particle, resulting in unique patterns for each material. Using liquid crystal, Abbott and his lab are creating a way to single out specific types of microplastics from the other particles present in a messy, complicated environment like a lake.

Microplastics are microscopic particles of plastic measuring five millimeters or less in diameter. “They’re everywhere,” says Abbott. “The challenge is to identify them and remove them from the environment.”

Some microplastics are purposely manufactured and put into consumer products such as toothpaste and makeup as abrasives or to improve flow. More often, they are produced when larger chunks of plastic degrade and break down. Microplastics end up in oceans, lakes, and rivers, ultimately accumulating in animals and humans. The effects of microplastics on human health and natural ecosystems are still being determined, but there’s no question they are a problem.

“The assemblies that these particles form are like fingerprints.”

Focusing on two common varieties of microplastics—polyethylene and polystyrene—Abbott and his colleagues are using liquid crystal to sense the microplastics’ presence. “The assemblies that these particles form are like fingerprints,” Abbott says. “Certain fingerprints are characteristic of polyethylene and others are characteristic of polystyrene.”

Someday a technician might take a water sample from Lake Erie, for instance, put it on a surface coated with a liquid crystal and examine the sample under an optical microscope. The patterns the particles form on the surface of the liquid crystal will indicate whether a particular microplastic is present in the lake. Once the presence of the microplastic is known, authorities can work to mitigate it.

Red Blood Cells and Malaria

A liquid crystal exerts force unlike a simple liquid. “It’s a bit like a bar of rubber,” Abbott says. “When you bend a bar of rubber you store energy in the bent state, and when you remove your hand from the bar, it bounces back. The same is true of liquid crystal. If you create a cavity in it by putting something into the liquid crystal, it will push back with elastic forces that act on the object.”

Working with Kirk W. Deitsch, Microbiology and Immunology at Weill Cornell Medicine, Abbott is harnessing the elasticity of liquid crystal to explore the effects of malaria on the mechanics of red blood cells. The researchers are inserting mammalian red blood cells into liquid crystal, then observing the stress the liquid crystal puts on the cells.

“The elasticity of liquid crystal changes the shape of a cell,” Abbott says. “Instead of the normal biconcave shape, the blood cell gets elongated like a football. And we can use the way the cell changes to measure the mechanical properties of individual cells very quickly.”

Normal red blood cells are squishy so they can pass easily through small capillaries, Abbott explains. When red blood cells are infected with malarial parasites, however, they become more rigid, blocking capillaries and accumulating in the spleen, causing immune problems.

By studying one cell at a time, the researchers are better able to characterize the mechanical properties of normal cells, which vary, perhaps because of cell age. They can also zero in on the effects of the malarial parasite on a specific cell.

“Most of the methods currently used to characterize red blood cells give population averages,” Abbott says. “Our method can provide much more specific information. Right now we’re focusing first on understanding what’s happening to cells. But our hope is that our work will help other scientists discover a way to prevent some aspect of the malarial parasite’s influence on cell mechanical properties.”

78 Patents and Multiple Startups

Abbott has taken out 78 patents on various breakthrough discoveries, many of them having to do with liquid crystal. He has also cofounded various companies to commercialize some of his discoveries. One of his companies, Platypus Technologies, makes sensors using liquid crystal to amplify events that happen on the face of a surface.

“Basically, we’re using liquid crystal as a reporter of molecular phenomena occurring on surfaces,” Abbott says. “We developed designs of surfaces that capture, for example, gas phase molecules. And when they are captured, they change the interaction of the liquid crystal with the surface and generate a distinct optical appearance.”

Platypus Technologies made use of this approach to create a dosimeter that monitors exposure to hydrogen sulfide in oil refineries and agricultural settings. “It’s a small badge that you wear as you walk around in your workplace all day,” Abbott says. “At the end of the day, you insert it into a reader that will alert you if you have been exposed to levels of hydrogen sulfide that can cause health risks.”

Another of Abbott’s companies, Imbed Biosciences, commercialized a wound dressing he invented some years ago. The dressing is a thin polymer film infused with an exact amount of antimicrobial that is then placed in a precise location on the wound.

“We’ve optimized the loading of the active agent, given that it’s localized,” Abbott says. “Compared to applying an antimicrobial using an ointment, we can reduce the microbial burden in wounds using a much lower amount of active agents.

“It’s a simple idea,” he adds. “But I’ve learned if you want to commercialize something, it needs to be simple.”

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