Compressive testing of single yeast cells in liquid environment using a nanoindentation system
- PDF / 582,371 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 5 Downloads / 202 Views
ue to their versatility and accuracy, nanoindentation systems are increasingly used for the characterization of micron-sized particles. Single microbial cells (e.g., yeast cells) can be regarded as micron-sized, liquid-filled biological particles. Applying a nanoindentation system for the compressive testing of those cells offers many options, such as testing in liquid environment. However, diverse experimental problems have to be resolved, especially the visualization of the cells in liquid and the alignment of the surfaces between which the cell is compressed. Single yeast cells were tested using a nanoindenter equipped with a flat punch tip. The deformation behavior of the cells during loading as well as the shape recovery behavior during unloading was investigated. A bursting force was determined as the cell wall was failing at higher deformations. Moreover, the influence of the compression speed on the cell mechanical behavior was characterized. I. INTRODUCTION
In many biotechnological applications, microorganisms are cultivated to make or modify a particular product. The yeast Saccharomyces cerevisiae is an important organism in industrial biotechnology that is used for brewing and baking. During the biotechnological process chain, the organisms are exposed to different kinds of mechanical stress. During cultivation in stirred vessels, fluid forces act on the cells. After the cultivation step, it is often necessary to disrupt the cells to release an intracellular product. In this case, mechanical forces are applied using mechanical disruption devices (e.g., stirred media mills or high-pressure homogenizers).1,2 Inactivation of microorganisms that might be essential for hygienic reasons can be achieved by high-pressure treatment.3 For all these processes, the cell mechanical properties are important. Understanding the mechanical properties of the cells is the key to improving process parameters of the aforementioned industrial processes. Compression testing of single cells has turned out to be an appropriate method to get insights into the cell mechanical behavior. In the past, self-made compression devices were used to investigate the mechanical properties of different microbial cell species (S. cerevisiae, E. coli, S. epidermis).4–7 Single cells were squeezed between two optic fiber probes or between a single optic
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0383 J. Mater. Res., Vol. 23, No. 12, Dec 2008
http://journals.cambridge.org
Downloaded: 18 Mar 2015
fiber and a slide until rupture occurred. The required force was measured by a force transducer. Nowadays, nanoindentation is an established technique that was originally developed to characterize the mechanical properties of traditional homogeneous materials such as metals or ceramics. Commercially available nanoindentation systems allow mechanical testing with displacement accuracy in the subnanometer range and force accuracy in the submicron-Newton range.8 Arbitrary loading functions either force o
Data Loading...
