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Brillouin light scattering (BLS) provides information on micromechanics through the scattering of light from acoustic waves or phonons. It is widely accepted that the mechanical properties within the biological environment are crucial to the health and vitality of the system, and alterations in mechanics can thereby indicate disease. To date, biological applications of BLS have ranged from the measurement of live cells and organisms, to tissues and fibrous proteins, demonstrating potential for diagnosis of pathology and characterisation of mechanics. Despite this, the information contained within the Brillouin spectrum, and its full significance to biological matter, is still a matter of debate, due to fundamental problems in understanding the role of water in biomechanics.
This work aimed to explore the development and application of BLS to the biological environment, using gelatin hydrogels as a model system. Tuning the degree of physical and chemical cross-linking within the hydrogels, enabled the macromechanical properties to be controlled, mimicking a variety of biological states. Brillouin measurements of these hydrogels gave a unique insight into the viscoelastic properties across a wide range of physical states, ranging from the highly hydrated to the glassy phase, and the transition between the two. The introduction of Raman spectroscopy as a correlative technique enabled the chemical composition of the sample to be determined, in addition to the mechanical information provided by BLS. As well as this, a calibration curve derived from Raman spectra and refractometry data, enabled the refractive index of the hydrogels to be predicted, a parameter necessary to calculate the longitudinal elastic modulus from Brillouin measurements. The final focus of this work was on the development of a virtually imaged phase array (VIPA) based Brillouin spectrometer, exploring system design and experimental considerations for Brillouin measurements. This enabled comparison with measurements from a tandem Fabry-Pérot based system, as well as some consideration to the analysis methods used for the interpretation of Brillouin data. Throughout this work, gelatin hydrogels have been used as a platform to investigate the development and application of BLS to biological systems. As simple models for a host of biological systems, the viscoelastic properties revealed by Brillouin spectroscopy set the basis for BLS within the biological environment. |
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