Scaling the Microrheology of Living Cells

Abstract

We report a scaling law that governs both the elastic and frictional properties of a wide variety of living cell types, over a wide range of time scales and under a variety of biological interventions. This scaling identifies these cells as soft glassy materials existing close to a glass transition, and implies that cytoskeletal proteins may regulate cell mechanical properties mainly by modulating the effective noise temperature of the matrix. The practical implications are that the effective noise temperature is an easily quantified measure of the ability of the cytoskeleton to deform, flow, and reorganize.

Active mechanical stabilization of the viscoplastic intracellular space of Dictyostelia cells by microtubule–actin crosstalk

“…Similar to the mechanical behaviour of polymer melts in glassy states the friction coefficients of the cytoplasm (or the mobility of the beads) were strongly force dependent, which is the characteristic property of viscoplastic materials, together with the existence of threshold forces above which the material starts to flow [44]. This cytoplasmic viscoplasticity may provide an explanation for the glass-like behaviour of the viscoelastic impedance observed by micro-rheometric studies of fibroblasts with rotating magnetic beads [26] or by micropipette studies [14] leading to the conclusion that cells behave as glass-like bodies.…”

“…A variety of colloidal probe microrheometry techniques have been developed over the last few years based on the analysis of Brownian motion [10,23,24] or of the viscoelastic responses evoked by local forces applied through optical traps [10,23] and magnetic tweezers. With magnetic tweezers, viscoelastic responses can be evoked by linear [25] or by torsional [26,27] excitations. The viscoelastic response to force pulses yield relaxation moduli G(t) and relaxation times, while oscillatory force scenarios yield complex viscoelastic impedances.…”

Measuring Cell Viscoelastic Properties Using a Microfluidic Extensional Flow Device

“…One choice of model to capture viscoelastic behavior is the simple two-parameter power law for a time-dependent cell stiffness. This phenomenologic law has been shown to describe cell mechanical behavior for several cell types over a wide range of timescales as measured by several techniques, including optical magnetic twisting cytometry (39,40), atomic force microscopy indentation (41), and microfluidic constriction channel traversal (17). The power law can be expressed mathematically as (39)…”

Superparamagnetic Iron Oxide Nanoparticle Probes for Molecular Imaging

“…25,141 Classifications SPIO sizes range greatly from 2 to 3 nm for citrate inhibited growth SPIO, 89 tens of nanometers for polymercoated polycrystalline iron oxide nanoparticles through to micrometers for orally ingestible contrast agents. Larger diameters are available and are useful in such enterprises as cell tracking 134,58 and separation, 73 cell rheology and membrane deformation, 38,151 and as contrast agents for the gastrointestinal tract, 54 but have limited functionality in molecular imaging applications due to their limited accessibility to the neo-and microvasculature. Categories of SPIO, based on their overall diameter (including iron oxide core and hydrated coating), are noted in the literature 152 as oral-SPIO at between 300 nm and 3.5 µm; standard SPIO (SS-PIO) at approximately 60-150 nm; ultrasmall SPIO (US-PIO) of approximately 10-40 nm 156 ; and monocrystalline iron oxide nanoparticles (MION-a subset of USPIO 34 ) of approximately 10-30 nm.…”