Bio-Microrheology: A Frontier in Microrheology

Abstract

Cells continuously adapt to changing conditions through coordinated molecular and mechanical responses. This adaptation requires the transport of molecules and signaling through intracellular regions with differing material properties, such as variations in viscosity or elasticity. To determine the impact of regional variations on cell structure and physiology, an approach, termed bio-microrheology, or the study of deformation and flow of biological materials at small length scales has emerged. By tracking the thermal and driven motion of probe particles, organelles, or molecules, the local physical environment in distinct subcellular regions can be explored. On the surface or inside cells, tracking the motion of particles can reveal the rheological properties that influence cell features, such as shape and metastatic potential. Cellular microrheology promises to improve our concepts of regional and integrated properties, structures, and transport in live cells. Since bio-microrheology is an evolving methodology, many specific details, such as how to interpret complex combinations of thermally mediated and directed probe transport, remain to be fully explained. This work reviews the current state of the field and discusses the utility and challenges of this emerging approach.

Magnetic wire-based sensors for the microrheology of complex fluids

“…These later values are again in good agreement with those of the cone-and-plate rheology (Table I). In the Introduction, it was mentioned that the conversion of local µ-rheology variables into macroscopic parameters may be difficult or subjected to large uncertainties [11,43] and that alternate approaches need to be considered. Our experiments on wires submitted to rotational magnetic field show that such approaches exist and can be realized.…”

Multiple‐Particle Tracking and Two‐Point Microrheology in Cells

“…Only in the last decade or so have techniques, termed microrheology, been developed that can characterize cells' dynamic shear modulus over a wide frequency range (Weihs, 2006;Waigh, 2005). Initially, many researchers hoped that these new cell rheology measurements would display characteristic times corresponding to known molecular timescales, such as that of the myosin ATP hydrolysis cycle.…”

“…The challenges of interpreting and modeling cell rheology measurements have several causes (Weihs, 2006). Primary among them is the obvious structural complexity within cells.…”

An historical perspective on cell mechanics

“…c Modern immunofluorescence staining of actin with rhodamine-phalloidin, over a century later, also reveals striated structures in rat cardiomyocytes granules could also be used as markers for viscosity measurements [3,4]. This represents some of the earliest uses of particle tracking in cell mechanics and is essentially a predecessor of modern-particle tracking and microrheology measurements [100,101]. Although this early work was carried out in the 1920s and suffers from an obvious lack of appropriate experimental and theoretical considerations, some of the same issues were being discussed as they are today, such as the influence of the size of the granule, the mesh size of the protoplasm, damage to the cell and the influence of temperature [3,4,102].…”

“…Similarly, an early magnetic microscope developed in 1923 [103] was used to oscillate nickel particles (~16 μm in diameter) inserted into living cells. Aside from the similarities to modern particle micro-rheology [19,20,100,101], this approach is similar in concept to magnetic bead-twisting cytometry [104][105][106]. An early example of magnetic manipulation also involved injecting iron particles into bacteria and observing how fast they were attracted to an electromagnet [4].…”