Dehydration of biotissues during their compression

Background and Objectives: Dehydration of tissue is one of the possible mechanisms of mechanical tissue optical clearing. In this study we investigated the effects of dehydration of ex vivo cow muscle tissue samples during their compression on diffuse reflectance spectra of the tissue. The purpose of research was to identify the correlation between the diffuse reflectance of the tissue and its dehydration. Materials and Methods: The dehydration of tissue samples of 20$\times$20$\times$20 mm3 in size was carried out by drying the samples for 17 hours and the dehydration of cylindrical tissue samples with diameter 20 mm and thickness of 25 mm was carried by compressing the samples in a specially designed cell with a nozzle on a fiber optic sensor. In the first case the samples were weighed every hour and the diffuse reflectance spectrum was recorded. In the second case the compression value changed every 6 minutes, before which the samples were weighed and the diffuse reflectance spectrum was also recorded. Results: The dynamics of the reduced weight of the samples both in the dying process and in the compression process were determined. At the end of the drying process, the weights of the samples decreased by 70%. This value corresponded to the degree of hydration of the samples before the experiments. When the pressure on the sample was about 110 kPa, the weights of the samples decreased by 45%. The maximum degree of dehydration of the samples during compression was about 50%. The dehydration of the samples during their drying was accompanied by an increase in their diffuse reflectance. On the contrary, the application of compression led to a decrease in the diffuse reflectance according to a two-exponential law, which is may be explained by the difference in the physical structures of the dehydrated samples. Conclusion: The processes of reducing the diffuse reflectance of the sample and its weight during compression correlate well. As a result, the analysis of changes in the diffuse reflectance of the tissue sample as a result of its compression allows us to evaluate changes in the hydration of the sample. The choice of the wavelength of the probe light can give not only a qualitative, but also quantitative agreement between the two processes.