Brillouin microscopy: an emerging tool for mechanobiology

Abstract

The role and importance of mechanical properties of cells and tissues in cellular function, development as well as disease has widely been acknowledged, however standard techniques currently used to assess them exhibit intrinsic limitations. Recently, a new type of optical elastography, namely Brillouin microscopy, has emerged as a nondestructive, label-and contact-free method which can probe the viscoelastic properties of biological samples with diffraction-limited resolution in 3D. This has led to increased attention amongst the biological and medical research communities, but also to debates about the interpretation and relevance of the measured physical quantities. Here, we review this emerging technology by describing the underlying biophysical principles and discussing the interpretation of Brillouin spectra arising from heterogeneous biological matter. We further elaborate on the technique's limitations as well as its potential for new insights in biology in order to guide interested researchers from various fields.

Intestinal intermediate filament polypeptides in C. elegans: Common and isotype-specific contributions to intestinal ultrastructure and function

“…Hypothesizing that the precise positioning of the IF-rich endotube serves an important mechanical function, we performed Brillouin microscopy. This method allows the contact-free determination of viscoelastic properties in living cells and tissues at subcellular resolution [24][25][26] . To this end, IFC-2e::YFP reporter worms were immobilized by 10% levamisole prior to imaging.…”

“…The Brillouin signal, i.e. the Brillouin frequency shift that is a proxy for stiffness 25,26 , revealed two regions: a central area of high stiffness that is surrounded by a region of low stiffness (yellow to red versus blue in Fig. 4a,b).…”

Tissue rheology in embryonic organization

“…We will then summarize and discuss recent findings on the Box 1: Biophysical tools measuring embryonic tissue rheology Cell/tissue force spectroscopy: Cell/tissue force spectroscopy is an Atomic Force Microscopy (AFM) application used for measuring material properties of cells and tissues. In addition, from the linewidth of the Brillouin peaks the viscosity of the tissue can be obtained (preprint: Prevedel et al, 2019). For probing large-scale material properties within embryonic tissues, typically a large bead is attached to the AFM cantilever in order to avoid probing local cell heterogeneities.…”

“…The longitudinal modulus serves as an approximate for rigidity since it is higher for more rigid materials and lower for less rigid materials. In addition, from the linewidth of the Brillouin peaks the viscosity of the tissue can be obtained (preprint: Prevedel et al, 2019). BM has been used to map 3D ECM stiffness of the notochord in zebrafish embryos (Bevilacqua et al, 2019).…”

Lab-on-a-Chip Technologies for the Single Cell Level: Separation, Analysis, and Diagnostics

“…With the combination of microfluidics, photonic and imaging technologies, it is now possible to study the 3D refractive index of a cell in the sub-micron regime, as Liu et al detailed in their review in 2016 [185]. In addition to this, it is possible to use Brillouin microscopy, where the optical phase shift of a cell gives information about the cells local stiffness and water content, given the local refractive indices are known [186], or measured alongside using one of the techniques listed in Table 1. Three major approaches for probing the cell refractive index can be summarized, as shown in Table 9, below:…”