Preparation of Extracellular Matrix Protein Fibers for Brillouin Spectroscopy

Abstract

Brillouin spectroscopy is an emerging technique in the biomedical field. It probes the mechanical properties of a sample through the interaction of visible light with thermally induced acoustic waves or phonons propagating at a speed of a few km/sec. Information on the elasticity and structure of the material is obtained in a nondestructive contactless manner, hence opening the way to in vivo applications and potential diagnosis of pathology. This work describes the application of Brillouin spectroscopy to the study of biomechanics in elastin and trypsin-digested type I collagen fibers of the extracellular matrix. Fibrous proteins of the extracellular matrix are the building blocks of biological tissues and investigating their mechanical and physical behavior is key to establishing structure-function relationships in normal tissues and the changes which occur in disease. The procedures of sample preparation followed by measurement of Brillouin spectra using a reflective substrate are presented together with details of the optical system and methods of spectral data analysis.

Mechanical Properties of cellulose fibers measured by Brillouin spectroscopy

“…consecutively probing at different angles (scattering wavevectors) can also be used to investigate the full elastic (stiffness) tensor of the fiber material, i.e. tension stiffness and shear stiffness in all three spatial directions, as has been demonstrated for other natural fiber materials (Koski et al 2013;Edginton et al 2016). It is however important to note that the measured properties with BLS are by construction different than those probed with most other mechanical testing techniques.…”

“…Measurement of pulp fiber shear moduli is even more complicated than tensile moduli, and to the best of our knowledge has not been done. BLS has routinely been used to measure mechanical properties and even the complete elastic tensor of biological fibers such as for spider silk (Koski et al 2013), proteins (Randall et al 1979;Speziale et al 2003), collagens (Harley et al 1977;Cusack and Miller 1979;Edginton et al 2016), muscle fibers (Berovic et al 1989), or recently bamboo wood splinters (Williams et al 2019). Being a non-contact method able to measure the full elastic tensor (i.e.…”

Brillouin scattering of phonons in complex materials

“…The study was later extended to include measurements of anisotropy of the elastic constants of collagen, revealing both longitudinal and transverse acoustic waves traveling at different angles to the fiber axis. [41] More recently, a detailed BLS investigation of the mechanical properties of elastin and collagen fibers has been realized by means of an innovative interaction geometry, with samples placed on a reflective substrate to reveal both bulk phonons and parallel to surface (PS) longitudinal and transverse modes (see Figure 4) [37,42].…”

Impact of optical tissue clearing on the Brillouin signal from biological tissue samples

“…Brillouin microscopy is a promising non-invasive and non-destructive technology under commercial development at present. The technique enables researchers to characterize the mechanical properties of both, inert samples and, more recently, biological tissues [1][2][3][4][5][6]. Non transparent samples can limit the possibilities of using Brillouin spectroscopy [7] and therefore, the study of biological samples has been limited to cultured cells and naturally transparent tissues.…”