Local viscoelasticity of living cells measured by rotational magnetic spectroscopy

TL;DR

This study uses rotational magnetic spectroscopy with magnetic wires to measure the viscoelastic properties of living cell cytoplasm, revealing it behaves as a viscoelastic liquid rather than a gel.

Contribution

It demonstrates a novel application of magnetic wires to quantify cell cytoplasm rheology and clarifies its viscoelastic nature, contrasting previous gel-like assumptions.

Findings

Cytoplasm shear viscosity is 10-100 Pa·s.

Elastic modulus of cytoplasm is 5-20 Pa.

Cytoplasm exhibits a rotational instability indicating viscoelastic liquid behavior.

Abstract

When submitted to a magnetic field, micron size wires with superparamagnetic properties behave as embedded rheometers and represent interesting sensors for micro-rheology. Here we use rotational magnetic spectroscopy to measure the shear viscosity of the cytoplasm of living cells. We address the question of whether the cytoplasm is a viscoelastic liquid or a gel. The main result of the study is the observation of a rotational instability between a synchronous and an asynchronous regime of rotation, found for murine fibroblasts and human cancer cells. For wires of susceptibility 3.6, the transition occurs in the range 0.01...1 rad s-1. The determination of the shear viscosity (10...100 Pa s) and elastic modulus (5...20 Pa) confirms the viscoelastic character of the cytoplasm. In contrast to earlier studies, it is concluded that the interior of living cells can be described as a viscoelastic liquid, and not as an elastic gel.