Engineers Build Microscopic Labs For Cells
By Robert Ross
VIIBRE researchers conduct nanoscale
experiments in this “clean room.”
You’ve just glimpsed the future of immunology.
Franz Baudenbacher, assistant
professor of biomedical engineering,
is also co-director of VIIBRE.
Professor John Wikswo,
VIIBRE director
Cell sensors destined for labs and home use
Many of the devices the engineers are working on will likely be used by physicians to help determine suitable therapeutic drug regimens or by researchers studying how cells respond to new drug compounds that are still under investigation.
They are designing the smaller sensors, however, for at-home use by individuals, just as pregnancy kits and diabetes monitors are now commonly employed.
Although smaller than 100 microns (a micron is 1/25,000 of an inch and a human hair 70 microns), the devices can hold many cells extracted from the body. They’re ideal for studying cells, safely removed from the human body, as they react to drugs and toxic substances and interact with other cells.
These microfluidic containers are the progeny of an instrument called a "multianalyate microphysiometer," developed under the direction of David Cliffel, assistant professor of chemistry. This instrument contains sensors that can simultaneously measure concentrations of key chemicals that cells consume and excrete – oxygen, glucose and lactic acid – and monitor the health of thousands of cells confined in a small volume.
Vanderbilt engineering researchers, led by Franz Baudenbacher, assistant professor of biomedical engineering and physics, miniaturized Cliffel’s sensors even further so they could record rapid changes in the metabolism and signaling of individual cells. They did it by devising a method for molding micro-channels and valves in a silicone polymer similar to the kind used for soft contact lenses.
The sensors being designed by the Vanderbilt engineers will give scientists the capability to capture, manipulate, grow and study single living cells in tiny containers that are barely larger than the cells themselves.
Last December, VIIBRE began collaborating with Pria Diagnostics LLC, a company that specializes in miniature medical diagnostic instruments. The company’s best-known product so far is a handheld male fertility detector.
The company learned of the university’s involvement in developing microfluidic devices when Vanderbilt engineering graduate David Schaffer applied for a position with the California-based firm. Schaffer didn’t go to work for Pria. Instead, as a VIIBRE project engineer, he now oversees a Vanderbilt-Pria partnership that aims to develop inexpensive devices that can rapidly detect the presence of infectious diseases.
Labs-on-chips simulate body’s environment
In Baudenbacher’s lab, faculty and graduate students are designing microfluidic devices to measure how cardiac myocytes (the muscle cells in the heart) release calcium from their internal stores and cause the cells to contract. These cells, marked with a fluorescent dye that signals changes in the amount of calcium they release, would be placed in a miniature detection system that circulates tiny amounts of a saline solution through microscopic channels, pumps, and valves on silicone and glass chips.
By replicating the body’s natural environment, these labs on microchips will allow researchers to track and study cells in a way that would be impossible to do if they were treated with a drug inside the human body, Baudenbacher says.
It’s also safer for the patient.
In the case of a cancer, which may have different mutations, physicians could extract cancer cells from the patient’s body and apply different drug combinations to them in the microfluidic devices, at no danger to the patient. "You’d be able to customize therapy to a particular patient because you’ve understood how his or her cells respond," Baudenbacher says.
If a patient’s immune system has been compromised by HIV/AIDS or an unknown biological agent, physicians could extract a small number of that person’s T-cells and perform experiments on them in the microfluidic devices to determine which drug works best.
"A lot of external agents suppress the immune system," explains Shannon Faley, a biomedical engineering graduate student in Wikswo’s lab. She’s in a group that is studying how T-cells, the body’s generals in the fight against threats, respond – and fail to respond. "Understanding how T-cells decide what to do gives us an idea of how they’re designed, and how to adjust their responses," she says.
The challenge for engineers is to design ever-smaller containers that perform more tests on cells, without costing a fortune.
A biohazard detector in your pocket
Mark Stremler, assistant professor of mechanical engineering, is working on a Department of Defense and NIH-funded project to develop a sensor system that could detect and identify the presence of dozens of dangerous substances in the environment. Soldiers in battle or first responders to a terrorist attack would use it to identify agents such as anthrax and ricin, or, more important, ones that were previously unknown. It could also help identify dangerous industrial chemicals released into the air following an accident or fire.
Stremler is working with Cliffel’s lab to characterize how cultured cells respond to certain toxic substances in the microphysiometer. The researchers’ aim is to identify the type of dangerous agent depending on how the cells respond to the substance.
With Baudenbacher’s group, Stremler’s team is also working to further miniaturize the microphysiometer, which has a testing chamber smaller than a dime. The testing chamber of the device they’re designing, called a "nanophysiometer," would measure only 20 by 50 microns, with electrodes inside. A single cell’s diameter is 10 microns.
"We could trap about two cells in each chamber and put a large number of chambers in the device," Stremler says. The group is also hoping to reduce the time it takes the sensor to read cell responses – from 50 seconds to one second.
An engineering approach to biological problems
What the engineers conducting research for VIIBRE lack in deep knowledge of a single aspect of biology is more than made up by their analytical approach in tackling problems and their ease in crossing the boundaries of different specialties.
"The engineering approach is to break down the problem into well-defined segments linked to each other through a single variable, and then analyze and resolve each segment in a controlled manner," says Prasad Shastri, assistant professor of biomedical engineering and a polymer science specialist who is working on the microfluidic devices. "This analytical approach offers superior outcomes, as endpoints are well defined and we are able to elucidate the problem in a logical manner."
Shastri studies outcomes in single cells and develops strategies that induce large organizations of cells to form complex tissues such as blood vessels, bone and nerves. "By applying findings in a single-cell system, gained through microfluidics, to materials design, researchers can arrive at solutions such as a drug-delivery strategy to a diseased tissue," he says.
"A good scientist can also break down a problem," Faley says, "but the understanding that we engineers have of basic physical laws and of technology gives us a special insight. We have a wide base of knowledge, which makes us flexible."
Although she is still a student, Faley says that when her research team discusses ways to improve the microfluidic device it is developing, her ideas are taken seriously, and several have been used. A proposal she wrote for a class project proved critical in getting the first DOD funding for the T-cell project.
The VIIBRE engineers all bring a practical viewpoint to the tools they are helping to develop. "We’re a very diverse group, working on many problems and leveraging one project off the others," Baudenbacher says. "You want to use the technologies you develop in multiple areas, because it takes so much time to develop them."
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This article first appeared in ENGINEERING VANDERBILT magazine (Vol. 46, No. 2; October 2005).
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