Abstract
Living cells are constantly exchanging momentum with their surroundings. So far, there is no consensus regarding how cells respond to such external stimuli, although it reveals much about their internal structures, motility as well as the emergence of disorders. Here, we report that twelve cell lines, ranging from healthy fibroblasts to cancer cells, hold a ubiquitous double power-law viscoelastic relaxation compatible with the fractional Kelvin-Voigt viscoelastic model. Atomic Force Microscopy measurements in time domain were employed to determine the mechanical parameters, namely, the fast and slow relaxation exponents, the crossover timescale between power law regimes, and the cell stiffness. These cell-dependent quantities show strong correlation with their collective migration and invasiveness properties. Beyond that, the crossover timescale sets the fastest timescale for cells to perform their biological functions.
Highlights
Living cells are constantly exchanging momentum with their surroundings
The storage modulusG′(ω) is well described by a single PL with low exponent of the order of β = 0.2 and the loss modulus G′′(ω) described by two PL regimes, with a lower exponent identical to the exponent ofG′(ω) and a fixed exponent α = 1 for all samples. This ad hoc combination of PL responses is known as power-law structural damping model, and it was used as the theoretical basis to describe the dynamic rheology of cells in several works[14,15,22,23,24,25,26]
We show that cells do exhibit double PL relaxation compatible with the fractional Kelvin-Voigt viscoelastic relaxation model, and that it can be accurately measured with simple AFM force curves
Summary
Living cells are constantly exchanging momentum with their surroundings. So far, there is no consensus regarding how cells respond to such external stimuli, it reveals much about their internal structures, motility as well as the emergence of disorders. Atomic Force Microscopy measurements in time domain were employed to determine the mechanical parameters, namely, the fast and slow relaxation exponents, the crossover timescale between power law regimes, and the cell stiffness. These cell-dependent quantities show strong correlation with their collective migration and invasiveness properties. There are a few studies proposing that cells exhibit a double PL shear modulus, ∣G*(ω)∣ = Aωα + Bωβ, with α > β, where the higher and the lower exponents describe, respectively, the fast and slow dynamic response of the cell[17,18,19,20,21] In this case, the storage modulusG′(ω) is well described by a single PL with low exponent of the order of β = 0.2 and the loss modulus G′′(ω) described by two PL regimes, with a lower exponent identical to the exponent ofG′(ω) and a fixed exponent α = 1 for all samples. The double PL relaxation seems to be a universal response of living cells regardless their health state, and a closer analysis of the relaxation exponents may shed new light on the understanding of how diseases develop and how to fight them
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