Monitoring the biomechanical response of individual cells under compression: a new compression device.
ABSTRACT Skeletal muscle cells are sensitive to sustained compression, which can lead to the development of pressure sores. Although it is known that this type of tissue breakdown depends on the magnitude and duration of the applied load, the exact relationship between cell deformation and damage remains unclear. To gain more insight into this process, a method has been developed, that incorporates the use of a new loading device and confocal microscopy. The loading device is able to compress individual cells, either statically or dynamically, while measuring the resulting forces. Experiments can be performed under ideal environmental conditions, comparable with those of a CO2 incubator. First compression experiments on C2C12 mouse myoblasts showed the shape changes that cells undergo during static compression by the loading device. Calculations using the three-dimensional confocal images showed no change in volume and an increase in the surface area of the cell as a result of compression. The device presented here provides a useful way to monitor the biomechanical response of skeletal muscle cells during long-term compression experiments. Therefore it will contribute to the knowledge about strain-induced cell damage, as seen in pressure sores and other mechanically induced clinical conditions.
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ABSTRACT: The bacterium Helicobacter pylori is a major human pathogen and the principal cause of acute and chronic gastritis, gastric and duodenal ulcer disease, and gastric adenocarcinoma. Infection with gastric Helicobacter results in an early infiltration of neutrophils, monocytes, and natural killer cells, followed by an influx of T cells and plasma cells. Although the critical components of this gastric infiltrate that lead to disease are unclear, the Helicobacter felis-infected mouse and other mouse models of Helicobacter-associated gastritis have demonstrated the critical nature of adaptive immunity in the development of gastric epithelial pathology. To further investigate the role of adaptive immunity in this disease, adoptive transfer models of disease have also been utilized. These models clearly demonstrate that it is the host CD4+ T lymphocyte response that is crucial for the development of Helicobacter-associated gastric epithelial changes.Immunologic Research 02/2005; 33(2):183-94. · 3.53 Impact Factor
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ABSTRACT: In recent years, damage directly due to tissue deformation has gained interest in deep pressure ulcer aetiology research. It has been shown that deformation causes muscle cell damage, though the pathway is unclear. Mechanically induced skeletal muscle damage has often been associated with an increased intracellular Ca2+ concentration, e.g. in eccentric exercise (Allen et al., J Physiol 567(3):723–735, 2005). Therefore, the hypothesis was that compression leads to membrane disruptions, causing an increased Ca2+-influx, eventually leading to Ca2+ overload and cell death. Monolayers of differentiated C2C12 myocytes, stained with a calcium-sensitive probe (fluo-4), were individually subjected to compression while monitoring the fluo-4 intensity. Approximately 50% of the cells exhibited brief calcium transients in response to compression, while the rest did not react. However, all cells demonstrated a prolonged Ca2+ up-regulation upon necrosis, which induced similar up-regulations in some of the surrounding cells. Population heterogeneity is a possible explanation for the observed differences in response, and it might also become important in tissue damage development. It did not become clear however whether Ca2+-influxes were the initiators of damage.Experimental Mechanics 01/2009; 49(1):25-33. · 1.55 Impact Factor
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ABSTRACT: The intrinsic cell wall mechanical properties of Baker's yeast (Saccharomyces cerevisiae) cells were determined. Force-deformation data from compression of individual cells up to failure were recorded, and these data were fitted by an analytical model to extract the elastic modulus of the cell wall and the initial stretch ratio of the cell. The cell wall was assumed to be homogeneous, isotropic, and incompressible. A linear elastic constitutive equation was assumed based on Hencky strains to accommodate the large stretches of the cell wall. Because of the high compression speed, water loss during compression could be assumed to be negligible. It was then possible to treat the initial stretch ratio and elastic modulus as adjustable parameters within the analytical model. As the experimental data fitted numerical simulations well up to the point of cell rupture, it was also possible to extract cell wall failure criteria. The mean cell wall properties for resuspended dried Baker's yeast were as follows: elastic modulus 185 ± 15 MPa, initial stretch ratio 1.039 ± 0.006, circumferential stress at failure 115 ± 5 MPa, circumferential strain at failure 0.46 ± 0.03, and strain energy per unit volume at failure 30 ± 3 MPa. Data on yeast cells obtained by this method and model should be useful in the design and optimization of cell disruption equipment for yeast cell processing.Biotechnology Progress 03/2011; 27(2):505-12. · 1.85 Impact Factor