Lab-on-a-Chip Measures Mechanics of Bacteria Colonies

Biofilms experience various kinds of pressure in nature and in the body as they squeeze through capillaries and adhere to the surfaces of e.g., medical devices.

Most bacteria in nature form biofilms. Bacteria are single-celled organisms, but they rarely live alone, said John Younger, associate chair for research in the department of emergency medicine at the University of (U-M) Health System (UHMS; Ann Arbor, MI, USA). Prof. Younger is a coauthor of the study that forms the cover story of the July 7, 2009 edition of Langmuir.

To understand biofilms and their life cycle, it is necessary to consider their genetics as well as their mechanical properties. Biofilms are "materials that respond to forces, because how they live in the environment depends on that response," said Mike Solomon, associate professor of chemical engineering and macromolecular science and engineering, who is senior author of the paper.

The U-M microfluidic device provides the right scale. The channel-etched chip, made from a flexible polymer, allows scientists to study minute samples of between 50 and 500 bacterial cells that form biofilms of 10-50µ in size. Such small samples behave in the device as they do in the body. Tools that require larger samples do not always give an accurate picture of how a particular substance behaves on the smallest scales.

The biofilms studied had a greater elasticity than previous methods had measured. The scientists discovered a hardening response, which means that the more pressure applied to the biofilms, the more resistance the materials put forth.

Mechanical forces are set in motion when we defend ourselves against these bacterial colonies. Gene expression patterns can be studied indefinitely, but until it is known when the materials will bend or break and what the immune system has to do from a physical perspective, how to fight this opponent remains a mystery.

Experiments were performed on colonies of Staphylococcus epidermidis and Klebsiella pneumoniae, which are known to cause infections in hospitals. The new microfluidic device could also be used to measure the resistance of various other soft-solid materials in biomaterials, pharmaceutical fields, consumer products, and food science.

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Department of Emergency Medicine at the University of Michigan Health System