Brillouin spectroscopy, based on the inelastic scattering of light from thermally driven acoustic waves or phonons, holds great promise in the field of life sciences as it provides functionally relevant micro-mechanical information. Due to the complexity of biological systems such as cells and tissues, which present spatio-temporal heterogeneities, interpretation of Brillouin spectra can be difficult.
This talk is aimed to introduce Brillouin microscopy as an emerging form of optical elastography and to give an insight into the biophysical quantities retrieved from Brillouin spectra of biological samples. Applications in biosciences will also be covered with an emphasis to clinically relevant studies.
Biological tissues have complex structures, dynamics and interactions between their constituents.
When probing mechanical properties, differences are observed across spatial and temporal scales
owing to the tissue viscoelastic response. Quasistatic mechanical testing, ultrasound and AFM-based
techniques provide the traditional approach to measure stiffness based on the Young’s modulus. A
novel technique in the fields of biophotonics and biomechanics is Brillouin spectroscopy, which is a
contactless optical method to detect viscoelastic properties from the propagation of thermally-driven
acoustic waves or phonons at high frequencies, GHz. A longitudinal elastic modulus is detected,
whose significance in mechanobiology and clinical settings is currently emerging.
Biological tissues have complex structures, dynamics and interactions between their constituents.
When probing mechanical properties, differences are observed across spatial and temporal scales
owing to the tissue viscoelastic response. Quasistatic mechanical testing, ultrasound and AFM-based
techniques provide the traditional approach to measure stiffness based on the Young’s modulus. A
novel technique in the fields of biophotonics and biomechanics is Brillouin spectroscopy, which is a
contactless optical method to detect viscoelastic properties from the propagation of thermally-driven
acoustic waves or phonons at high frequencies, GHz. A longitudinal elastic modulus is detected,
whose significance in mechanobiology and clinical settings is currently emerging.
The biomechanics of living tissues are critical to normal tissue function and disturbances in these properties are widely implicated in aging and disease. Protein fibres of the extracellular matrix (collagen and elastin) are the fundamental mechanical structures in connective tissues such as bone, cartilage and vasculature. We applied Brillouin light scattering (BLS) spectroscopy and quasistatic stress-strain testing to the study of the mechanics and structure of collagen and elastin fibres purified from connective tissues. BLS probes mechanical properties on a microscopic scale in biological tissues and thereby providing insights into structure-function relationships under normal and pathological conditions. The sensitivity of BLS measurements to fibre structure and hydration was investigated using samples mounted onto reflective substrates. We obtained a complete characterization of the mechanical tensor and elastic moduli which could be compared with complementary data from quasistatic stress-strain measurements at different hydration levels, hence giving the full description of fibre viscoelasticity.
Diffusion of two model drugs-benzyl nicotinate and ibuprofen-and the plasma macromolecule albumin across atherosclerotic rabbit aorta was studied ex vivo by attenuated total reflection-Fourier transform infrared (ATR-FTIR) imaging. Solutions of these molecules were applied to the endothelial surface of histological sections of the aortic wall that were sandwiched between two impermeable surfaces. An array of spectra, each corresponding to a specific location in the section, was obtained at various times during solute diffusion into the wall and revealed the distribution of the solutes within the tissue. Benzyl nicotinate in Ringer's solution showed higher affinity for atherosclerotic plaque than for apparently healthy tissue. Transmural concentration profiles for albumin demonstrated its permeation across the section and were consistent with a relatively low distribution volume for the macromolecule in the middle of the wall. The ability of albumin to act as a drug carrier for ibuprofen, otherwise undetected within the tissue, was demonstrated by multivariate subtraction image analysis. In conclusion, ATR-FTIR imaging can be used to study transport processes in tissue samples with high spatial and temporal resolution and without the need to label the solutes under study.
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