Brillouin Scattering in Collagen-Based Hydrogels

Viscoelastic properties of collagen hydrogels with different protein content (from 0 to 100%) was studied by Brillouin spectroscopy as a model system of biological tissue. From the analysis of the Brillouin spectra, the dependencies of the Brillouin peak width (FWHM) and the value of the gigahertz elastic modulus as a function of the protein concentration in the hydrogel were determined. It is shown that the behavior of the elastic modulus, which changes by almost an order of magnitude, is described with good accuracy in the full range of concentrations considered by the Reuss model. Analysis of the behavior of the Brillouin line width revealed a nontrivial behavior of the FWHM value with increasing protein concentration (FWHM increased almost 8 times), with a maximum at a collagen content of ∼70%. The discovered behavior can be caused by both the heterogeneity of the samples on scales of ∼100 nm during hydrogel dehydration and the influence of the relaxation spectrum on the Brillouin peak.