Brillouin and Raman microspectroscopy (BRamS) is a scattering technique that simultaneously assesses the mechanical and chemical properties of tissues with micrometric resolution. It has gained increasing attention in the biomedical field over the last decade and has been successfully used for both single-cell studies and whole-tissue characterization under physiological and pathological conditions. In addition, it is non-destructive, non-contact, and does not require labeling, offering the potential for future in vivo applications. The close interdependence between morphology, biochemistry, and mechanics is particularly relevant in the case of musculoskeletal tissues, where the complex structure is well-designed to ensure exceptional mechanical performance. The ability of tissues to resist and adapt to the mechanical and chemical stresses to which they are subjected depends to a large extent on maintaining the correct arrangement of all their components, starting from the microscopic level. In several common degenerative diseases, such as osteoarthritis (OA), the tissue architecture is destroyed by inflammatory processes, resulting in a rearrangement of its entire structure, leading to a complete loss of function and, often the need for prosthetic replacement. In this case, the use of minimally invasive techniques to explore the lesions could become a valuable resource for the surgeon in formulating a more precise diagnosis and, therefore, in providing more appropriate treatments. Here we discuss some of the results obtained by our group in characterizing human musculoskeletal tissue and detecting OA lesions in joints using BRamS.
Vibrational spectroscopy is a powerful probe of molecular structure and its advantages for biomedical and biophysical research, with a special emphasis on proteins, lipids and nucleic acids, are widely recognized in the literature. It is well-known that infrared and Raman spectroscopic techniques are complementary for the structural analysis of any molecule. Although they differ in selection rules, both techniques are rapid, non-destructive and generally do not need special protocols for sample preparation. Fourier-transform infrared (FTIR) microspectroscopy, in particular, allows for fast biochemical imaging of many biological tissues, however, the application of FTIR for the assessment of heart and kidney lesions induced by cardiovascular diseases has been poorly explored.
The multiple scattering (MS) process affects the spectroscopic investigation and the optical imaging of opaque samples. In Brillouin spectroscopy, MS affects the extraction of reliable micromechanical parameters inducing the ill definition of the exchanged wavevector of the scattering process, q. Here, we propose a new experimental method called Polarization Gated Brillouin Spectroscopy (PG-BS) able to disentangle the MS and the ballistic contributions. The results obtained on milk, used as benchmark material, demonstrate both the capability and easy applicability of the proposed method. Exploiting PG-BS for different biological materials can open the route to new frontiers in Brillouin imaging of opaque samples.
Mechanical forces are key to the structure, dynamics, and interactions of living systems. In the last two decades, Brillouin Microscopy (BM) has emerged as a non-invasive optical tool for the mechanical characterisation of biomatter at GHz frequencies and on a microscale. Viscous and elastic properties of biosamples in this spatio-temporal regime are effectively an uncharted territory that is important for the potential impact on function and physiology.
Since its inception, BM has been applied to address a myriad of biological and medical questions and has shown key capabilities for cell mechanobiology and tissue histopathology. Our team has developed and applied BM to study tissue mechanics and revealed the ability of BM to map the acoustic anisotropy of extracellular matrix proteins in isolated fibres and tissue biopsies. For these studies, we have introduced the correlative Brillouin–Raman method as a chemical-specific mechanical probe of biosamples.
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