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Intracellular stresses generated by molecular motors can actively modify cytoskeletal network causing changes in intracellular mechanical properties. We measure the intracellular mechanical properties using passive and optical tweezers-based active microrheology approaches and endogenous organelle particles as probes. Using the fluctuation-dissipation theorem, we compared the two approaches measurements and distinguished thermal and non-thermal fluctuations of mechanical properties in living cells.
(a) A sketch of an optical-tweezers-based cytorheometer. Optical tweezers were used to manipulate an intracellular granular structure (lamellar body, left circle) or an extracellular antibody-coated glass particle (right circle), G’(ω) and G”(ω). (b) Cells obtained by using intracellular organelles as probes. (c) Cells probed with anti-integrin conjugated silica particles attached to the plasma membrane. Solid lines represent a power-law fit to G’.
The imaginary part of the mechanical response function (a”) by active microrheology (dots) and the normalized power spectrum ωC(ω)/2kBT measured by passive microrheology (lines). The right figure shows experimental results of the non-thermal energy to the thermal energy as a function of frequencies.
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