Originally Published MDDI March 2003
Technology similar to that used to make computer chips may increase understanding of the function of smooth muscle cells and their relation to certain diseases. The new method is being developed by a research team at Johns Hopkins Medical Center (Baltimore). The group has created beds of thousands of independently movable silicone "microneedles" that can assess the force exerted by smooth muscle cells. Each needle tip is painted with proteins that attract muscle cells. The force generated by the cells is then calculated by measuring how far a contracting muscle cell moves each needle.
"What we have is a tool to measure and manipulate mechanical interactions between a single cell and its physical and biochemical surroundings," says Christopher Chen, PhD, associate professor of biomedical engineering. "Cellular mechanics is really important to many normal and pathologic processes in people, and there's a lot we don't understand, even with available technology."
The researchers explain that smooth muscle cells control the expansion and contraction of airways and blood vessels. Thus, the microneedle bed's ability to measure how cell environment affects the strength, duration, and timing of cellular contractions could one day help shed light on such medical conditions as asthma and high blood pressure, they add.
The group believes that the device complements existing techniques that measure forces exerted by contracting cells and overcomes some limitations of those calculation methods, which can be complex. They suggest that the one-piece microneedle bed lends itself to much simpler calculations because each needle moves independently of the others and requires exactly the same force to move. "We know how difficult each needle is to move, and we know where it was originally," Tan explains. "By measuring the direction and magnitude of the deflection of each needle, we can calculate the force each cell exerts."
In their experiment, the researchers coated the needle tips with fibronectin—a protein that forms part of the natural scaffolding between cells. Each smooth muscle cell spread out on the bed of microneedles and then contracted, displacing the needles.
Cell shape was also found to affect how it contracts. The researchers say they have resolved a conflict in scientific reports about cellular forces. Some reports indicated that the greater the area grasped by a cell, the greater force the cell exerted; others showed no such correlation. The microneedle bed tests showed that both observations are correct. Because the bed can directly measure the forces generated at a cell's adhesions, it can show that force increases with adhesion size only above a certain level. "For smaller areas, force and size aren't correlated," says Tan. "The same cell can actually exhibit both scenarios."
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