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Bacteria experience substantial physical forces in their natural environment including forces caused by osmotic pressure, growth in constrained spaces, and fluid shear. The cell envelope is the primary load-carrying structure of bacteria, but the mechanical properties of the cell envelope are poorly understood; reports of Young’s modulus of the cell envelope of E. coli are widely range from 2 MPa to 18 MPa. We have developed a microfluidic system to apply mechanical loads to hundreds of bacteria at once and demonstrated the utility of the approach for evaluating whole-cell stiffness. Here we extend this technique to determine Young’s modulus of the cell envelope of E. coli and of the pathogens V. cholerae and S. aureus. An optimization-based inverse finite element analysis was used to determine the cell envelope Young’s modulus from observed deformations. The Young’s modulus of the cell envelope was 2.06±0.04 MPa for E. coli, 0.84±0.02 MPa for E. coli treated with a chemical known to reduce cell stiffness, 0.12±0.03 MPa for V. cholerae, and 1.52±0.06 MPa for S. aureus (mean ± SD). The microfluidic approach allows examining hundreds of cells at once and is readily applied to Gram-negative and Gram-positive organisms as well as rod-shaped and cocci cells, allowing further examination of the structural causes of differences in cell envelope Young's modulus among bacteria species and strains.
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Mechanical characterization of Xenopus laevis oocytes using atomic force microscopy
Mechanical properties are essential for the biological activities of cells, and they have been shown to be affected by diseases. Therefore, accurate mechanical characterization is important for studying the cell lifecycle, cell-cell interactions, and disease diagnosis. While the cytoskeleton and actin cortex are typically the primary structural stiffness contributors in most live cells, oocytes possess an additional extracellular layer known as the vitelline membrane (VM), or envelope, which can significantly impact their overall mechanical properties. In this study, we utilized nanoindentation via an atomic force microscope to measure the Young's modulus of Xenopus laevis oocytes at different force setpoints and explored the influence of the VM by conducting measurements on oocytes with the membrane removed. The findings revealed that the removal of VM led to a significant decrease in the apparent Young's modulus of the oocytes, highlighting the pivotal role of the VM as the main structural component responsible for the oocyte's shape and stiffness. Furthermore, the mechanical behavior of VM was investigated through finite element (FE) simulations of the nanoindentation process. FE simulations with the VM Young's modulus in the range 20–60 MPa resulted in force-displacement curves that closely resemble experimental in terms of shape and maximum force for a given indentation depth.
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- PAR ID:
- 10525609
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of the Mechanical Behavior of Biomedical Materials
- Volume:
- 157
- Issue:
- C
- ISSN:
- 1751-6161
- Page Range / eLocation ID:
- 106648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.jmbbm.2024.106648
