Many tools exist to determine the elasticiy or Young's Modulus of cells. However, sometimes when we compare data obtained by the same approach (By indentation using AFM for instance), we see data ranging from 1 kPa to 10s of MPa. I find it shocking that relatively similar samples can range by this order of magnitude depending on the work. How to know what is true and coherent with the community ? Whats the best approach for such mesuresments ?
I am an AFM specialist, and I'm considering many changes in my experiments
It is a good question. There are a few serious reasons why the quantitative results of biological AFM-based mechanical measurements have very low reproducibility and sometimes they just don't make sense.
1. "Young's Modulus of cell" have no more sense than "Young's Modulus of car". Indeed, a living cell is not just a homogeneous "piece of something". It is an extremely complex dynamical system. Thus, the results (indentation curves) are dependent on lots of biological (age, stage of development, type, part of cell, etc.), chemical (pH, ionic strength, medium, etc.) and physical (temperature, pressure, irradiation, etc.) factors.
2. Lots of possible systematic errors: not accurate measurement of the force constant, contamination/breakage of the tip during the experiment (very common, have to be checked before and after), partial detachment or penetration of the cells, death of the cells, etc.
3. Limited statistics. Indeed, the cells cannot be kept in the AFM's liquid cell forever. The number of curves per experiment is usually limited with this time factor and contamination/breakage of the tip (can be detected with the curves).
4. Interpretation problems. E.g. typically the tip has more complex shape than used in the model.
In view of the foregoing, it is better to avoid quantitative measurements when possible, and examine the relative differences, not absolute values. E.g. if one studies the influence of something to the cells, it would be better to put the cells into the AFM, take some control curves, then add something (chemical, radiation, etc.), and then take more curves. Of course, the control experiments should be done too, e.g. the measurements with at the same timings and conditions for the cells from the same line, but without the examined factor.
Denis Korneev Thanks for clarifying. Indeed, reproducibility is difficult even with the same cell type. I will carry on to look for the ideal approach for my experiments. Good day
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