Recent progress and current opinions in Brillouin microscopy for life science applications

Abstract

Many important biological functions and processes are reflected in cell and tissue mechanical properties such as elasticity and viscosity. However, current techniques used for measuring these properties have major limitations, such as that they can often not measure inside intact cells and/or require physical contact-which cells can react to and change. Brillouin light scattering offers the ability to measure mechanical properties in a non-contact and label-free manner inside of objects with high spatial resolution using light, and hence has emerged as an attractive method during the past decade. This new approach, coined "Brillouin microscopy," which integrates highly interdisciplinary concepts from physics, engineering, and mechanobiology, has led to a vibrant new community that has organized itself via a European funded (COST Action) network. Here we share our current assessment and opinion of the field, as emerged from a recent dedicated workshop. In particular, we discuss the prospects towards improved and more bio-compatible instrumentation, novel strategies to infer more accurate and quantitative mechanical measurements, as well as our current view on the biomechanical interpretation of the Brillouin spectra.

Optical quantification of intracellular mass density and cell mechanics in 3D mechanical confinement

“…While optical properties of cells are accessible in 2D and 3D using optical techniques, mechanical testing of cells has mostly been performed using mechanical or particle probes such as atomic force microscopy (AFM) indentation, 40 micropipette aspiration 41 or optical tweezers. 42 However, with the more recent availability of optical techniques such as Brillouin spectroscopy, 43,44 it is now possible to measure mechanical properties of cells in a contact-free fashion. Its ability to map at high resolution 3D (visco)elastic properties 45,46 in terms of longitudinal modulus M and viscosity Z, has made Brillouin spectroscopy an attractive tool in the biomechanical analysis of biological samples, in this case cells encapsulated in 3D hydrogels.…”

Patient-derived glioblastoma cells (GBM) exhibit distinct biomechanical profiles associated with altered activity in the cytoskeleton regulatory pathway

“…The mapping of cellular mechanics has been achieved using multiple modalities including optical and magnetic tweezer based active rheology, passive rheology, atomic force microscopy and Brillouin microscopy [17,30,31]. Measurements of single cells in suspension can be performed using an optical stretcher and the high throughput, RT-DC system [32].…”

Mechanical Mapping of Bioprinted Hydrogel Models by Brillouin Microscopy

“…Thus, Ω is not only the function of the longitudinal modulus and stiffness but also depends on the refractive index and material density. It has been confirmed, however, that the ratio stays approximately constant in a wide range of biomaterials [22]. The Brillouin linewidth, on the other hand, is proportional to the material viscosity η given by where is the acoustic wave vector [16, 17].…”