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Going with the tiniest of flows

The modern age offers abundant opportunities to a person with an interest in medicine, an aptitude for science and mathematics – and a willingness to venture well outside one’s comfort zone.

Growing up in China’s Hubei Province, Xuanhong Cheng dreamed of becoming a doctor. In high school, she learned to appreciate the analytical way engineers view the world.

College enabled Cheng to explore several fields. She earned a B.S. in biology from Wuhan University and then an M.S. in electrical engineering and a Ph.D. in biomedical engineering from the University of Washington.

As a research scientist at Harvard Medical School, and now as an assistant professor of materials science and engineering at Lehigh, Cheng has blended the diverse elements of her academic background with more recently acquired capabilities.

She has worked the past five years, with doctors, scientists and engineers, on small medical devices that automate the diagnosis of disease and promise to bring modern medicine to remote regions of the world.

Developing ideas into products that benefit people, says Cheng, involves more than design, fabrication and testing. It can also require fluency in product development and knowledge of other cultures.

Cheng’s main project is a hand-held device that monitors the progress of HIV by measuring the concentration of lymphocytes, a type of white blood cell, that possess a CD4 receptor. In the lab, that typically requires a dozen steps and must be done in a large machine. Cheng’s goal is to do the test in four steps on the portable device and eventually on a chip. That way, patients can have their blood analyzed without having to live near a lab.

“You can’t design a product without knowing where it’s going to be used. In Africa, our system will have to be robust.” – Xuanhong Cheng

The device is based on microfluidics, or the precise manipulation of fluids at the microscale. After cycling a fingerprick of blood through tiny pouches and capillaries, the device separates CD4 cells from other blood components. Then a reagent counts the CD4 cells by reading their electrical signals.

“A microfluidics device like this can eliminate the need for assays that require large amounts of bloods,” says Cheng. “And an assay on such a small scale can be done much more quickly.”

Cheng’s group has made progress – after overcoming obstacles.

“At first, I thought making the device would be easy,” says Cheng. “Then, working in the lab, I realized it would involve manufacturing and processing, as well as materials science, chemistry and biology.

“Product development requires a different set of skills. What kind of plastic is most biocompatible? What about cost? How do you mold a plastic channel tens of microns in height so that fluid does not get trapped in a 90-degree turn and cause a high background signal?

“And how do you functionalize a plastic surface with an antibody? When it comes to putting a protein onto the geometry of our device, there’s very little expertise.”

Cheng’s group is working with a company to commercialize the device. In late 2009, she and four other researchers made a fact-finding trip to Africa, where the incidence of HIV and AIDS, especially among children, is especially high.

“We spent five days in Kenya visiting clinics and hospitals,” says Cheng. “The purpose of the trip was to learn about infectious disease diagnosis and find out what kind of facilities Africa has.

“You can’t successfully design a product without knowing the setting in which it’s going to be used. The setting in Africa is very poor. Sometimes clinics don’t have electric power, which means our system has to be robust and cheap.”

The group had hoped to begin field-testing its device in Africa before the end of 2010, but technical problems forced a postponement until later in 2011.

“Our device is not yet mature enough,” says Cheng. “When it is, we will go back to Africa to set up a clinical trial.”

It may take several more years before the device reaches the market, says Cheng, but the wait is worth it.

“I chose this field because my work could have a faster impact. It’s exciting to know that the ideas my students and I are working on might one day become products that help someone else.”