July 1, 2009: Researchers at the U. of Michigan have developed a microfluidic device that helps analyze the mechanical behavior of biofilms, colonies of bacteria behind most human infectious diseases.
The "lab-on-a-chip" measures the biofilms' resistance to pressure. "Think of biofilms as materials that respond to forces, because how they live in the environment depends on that response," explained Mike Solomon, associate prof. and senior author of the paper, in a statement. And mechanical forces within the body apply here too. "We think a lot of host defense boils down to doing some kind of physical work on these materials, from commonplace events like hand-washing and coughing to more mysterious processes like removing them out of the bloodstream during a serious infection," he said. "Until you know when the materials will bend or break, you don't really know what the immune system has to do from a physical perspective to fight this opponent."
The channel-etched chip (see image), made from a flexible polymer, can study samples of 10μm-50μm biofilms containing 50-500 bacterial cells. Findings suggest greater elasticity than measured with previous methods, and a "strain hardening response" -- i.e., as pressure increased, so did the biofilms' resistance.
The experiments were performed on colonies of Staphylococcus epidermidis and Klebsiella pneumoniae, which are known to cause infections in hospitals; the researchers say the microfluidic device could also be used to measure the resistance of other soft-solid materials, in sectors ranging from consumer products to food science to biomaterials and pharmaceuticals.
The work, partly funded by the National Institutes of Health and the National Institute of General Medical Sciences, was originally published online in February by Langmuir and is the cover story in the journal's July 7 print edition.
(Source: U. of Michigan/College of Engineering