Translation. Region: Russian Federal
Source: Novosibirsk State University –
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The effect of water on the longitudinal gigahertz elastic modulus of collagen-based hydrogel was studied by a student of the Department of Physical Methods of Solid State Research using optical spectroscopy methods Faculty of Physics, Novosibirsk State University Anna Laktionova under the scientific supervision of Valeria Zykova, PhD in Physics and Mathematics, Senior Researcher at the Institute of Automation and Electrometry SB RAS. The data from this study became the basis for her master’s thesis, which she successfully defended this year. In her work, she used optical research methods – Mandelstam-Brillouin scattering (MBS) spectroscopy and Raman spectroscopy.
— Changes in the elastic properties of biological objects may be associated with disruptions in the functioning of living cells, in such cases, information about the elastic modulus plays a key role. Currently, a contactless and non-invasive technique for characterizing the viscoelastic properties of materials is actively developing – Mandelstam-Brillouin scattering spectroscopy (MBS), which has proven itself in application to biomedical problems. MBS spectroscopy allows obtaining information about the speed of sound in a substance and the gigahertz elastic modulus. However, when studying real biotissues, difficulties arise in interpreting experimental data that are associated with the multicomponent composition of the studied objects and small changes in the elastic modulus due to pathologies occurring in the bioobject. This is due to the fact that the main contribution to the elastic modulus value in the case of real tissues is made by the water component, the content of which is quite high for the case of biological samples. For this reason, researchers often use simpler model two-component objects instead of real tissues, which are hydrogels, in particular, collagen-based hydrogels. By varying the water content, various parameters of viscoelastic properties are achieved, thereby hydrogels imitate the properties of a wide variety of real tissues, explained Anna Laktionova.
Samples of collagen -based hydrogels with different water content were made for conducting research. Further, with the help of a number of optical techniques (RMB, cattle, low -frequency cattle and depolarized light scattering), Anna described the elastic and relaxation properties of manufactured hydrogels. Spectra measurement was made during drying of hydrogel samples in the air. This was done in order to observe how, depending on the content of water in the sample, its elastic properties are changed, determined from the parameters of the spectrum of light scattering. With the dehydration of the sample from the most hydrated state (water content of 99.5 %) to a completely dry elasticity module increases by 6 times. At the same time, significant growth is observed with protein concentrations above 60 %. For a detailed study of such behavior, two spectrometers were required to synchronously measure the spectra of RMB and CRC. In this regard, some difficulties arose. The devices were in different rooms, which could affect the accuracy of measurements: while the sample was transferred from one office to another, it could be subjected to undesirable exposure to external factors, which would lead to its additional drying. To characterize the content of water in the samples and their elastic module from the same point in the process of drying, participants in the experiment, which was conducted in the spectroscopy laboratory of the condensed media of the Institute of Automation and Electrometry of the SB RAS, established a fiber -fiber channel between two spectrometers. This technical solution was implemented for the first time in Russia.
The analysis of the dependence of the Brillouin line position on the protein concentration in the hydrogel showed that the value of the gigahertz elastic modulus changes almost 6 times within the full range of concentrations (water content 0 – 100%). This is a very significant change. Earlier in the literature it was demonstrated that in the case of chemical treatments it is only a few percent. This fact fully demonstrates the strong influence of water. The resulting concentration dependence of the elastic modulus was described by a model considering the hydrogel as a rigid protein framework filled with water.
— From the analysis of the shape of the Brillouin spectrum of hydrogels, a non-trivial dependence of the Brillouin line width on the protein content was obtained. It is generally accepted, at least for single-component systems, that the Brillouin line width characterizes the viscosity of the object under study. However, in our case, everything was not so simple. When the hydrogel dried, the Brillouin line width actually increased to protein concentrations of about 70%, where the dependence extremum was observed. With further dehydration, up to completely dry collagen, the Brillouin line width narrowed. According to our assumptions, the reason for such an unexpected result lies in the influence of relaxation processes on the shape of the Brillouin spectrum of the hydrogel. To confirm this hypothesis, it was necessary to conduct a study using another spectroscopic technique – depolarized light scattering spectroscopy, – said Anna Laktionova.
A comprehensive comparison of the behavior of the RMB line width and the shape of the depolarized spectrum made it possible to verify the relaxation nature of the Brillouin line broadening with a change in water content. The results of RMB spectroscopy of hydrogels with different water contents for several temperatures (25, 0, -10 °C) additionally confirmed the influence of relaxation processes on the Brillouin line width, explained Anna Laktionova.
The analysis of the obtained results allowed us to obtain complete information on the nature of the interaction of the biopolymer matrix with the water component and to study in detail the issue of the influence of the water component on the parameters of the Brillouin spectrum of a hydrogel with different degrees of hydration. The participants of the study came to the conclusion: the work done demonstrates the prospects of the complex application of spectroscopic techniques (RMB, Raman, low-frequency Raman and depolarized light scattering) for characterizing the properties of hydrogels and studying the issue of the interaction of water with the protein matrix.
— It is very important to study the effect of water on the elastic properties of collagen-based hydrogel using optical methods, because such an object is simple enough to interpret spectral data, while it is capable of imitating the mechanical properties of more complex biological objects. This work, using such simple objects as an example, demonstrates the capabilities of optical spectroscopy methods, which in the future can be used to study more complex real tissues, — said Anna Laktionova.
Material prepared by: Elena Panfilo, NSU press service
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