Microrheology of Biological Specimens

Abstract

A great number of important biological phenomena that occur in living organisms demand energy transduction processes that critically depend on the viscoelastic properties of their constituent building blocks, such as cytoplasm, microtubules, and motor proteins. Accordingly, several techniques have been developed to characterize biological systems with complex mechanical properties at micron‐ and nano‐length scales; these are now part of an established field of study known as Microrheology. In this article, we provide an overview of the theoretical principles underpinning the most popular experimental techniques used in such fields, including video particle tracking, dynamic light scattering, diffusing wave spectroscopy, optical and magnetic tweezers, and atomic force microscopy. We report examples of both active and passive microrheology techniques and discuss their applications in the study of biological specimens, where the use of small volumes in controlled environments and the intrinsic heterogeneities of the samples can be critical conditions to both perform and interpret the experiments.

What Caging Force Cells Feel in 3D Hydrogels: A Rheological Perspective

“…When a micron-sized spherical particle is suspended into a viscoelastic fluid at thermal equilibrium, it experiences random forces leading to its Brownian motion, which is driven by the thermal fluctuations of the fluid's molecules. It has been shown that the statistical mechanic analysis of the bead trajectory r(t) ∀ t can be directly related to the linear viscoelastic properties of the surrounding environment by solving a generalized Langevin Equation: [42,45] m a(t…”

“…Moreover, it has been shown that there exists a link between microrheology and bulk rheology measurements. [42,45] This is obtained by retrieving the constitutive equation between the material's shear relaxation modulus G(t) and its shear compliance J(t):…”

Microrheology of semiflexible filament solutions based on relaxation simulations

“…In particular, one can explore passive experimental approaches (e.g., particle tracking videomicroscopy or dynamic light scattering; see Ref. [1] for a review) to extract the mean-squared displacement (MSD) ∆r 2 (τ) a of probe particles with radius a and relate it to the compliance J(τ) of the so-lution through a generalized Stokes-Einstein relationship [20,23], that is,…”

“…Despite of its importance to the well-functioning of almost all biological specimens [1], the viscoelastic response of complex solutions of unentangled semiflexible filaments [2], e.g., collagen, actin, rodlike viruses, amyloid fibrils, microtubules, and DNA, is not yet entirely predictable neither from theory or simulations [3]. Contrary to solutions of cross-linked filaments, where a shear protocol can be used to extract the mechanical properties of the networks [4,5,6,7], the study of the viscoelastic response of solutions of diluted unentangled filaments relies mainly on monitoring the stochastic dynamics of segments in the filament, which means that those methods are based mainly on fluctuations due to Brownian dynamics [8].…”

An analytical framework for 3D microrheology measurements using an optical trap

“…Although held by the trap, the bead still undergoes Brownian motion within a finite volume defined by the trap, and its trajectory can be traced and analysed to deduce the viscoelastic properties of the suspending media. This has proved to be a highly effective technique, especially for the analysis of biological samples [1][2][3][4][5].…”