Ionic diffusion and space charge polarization in structural characterization of biological tissues

Abstract.

In this study, a new approach to the analysis of the low-frequency (1-10⁷ Hz) dielectric spectra of biological tissue, has been described. The experimental results are interpreted in terms of ionic diffusion and space charge polarization according to Sawada’s theory. The new presentation of dielectric spectra, i.e. ($\partial \varepsilon ' / \partial \ln f) \cdot f$ has been used. This method results in peaks which are narrower and better resolved than both the measured loss peaks and an alternative loss quantity $\partial \varepsilon '/ \partial \ln f$. The presented method and Sawada’s expression have been applied to the analysis of changes in the spatial molecular structure of a collagen fibril network in pericardium tissue exposed to glutaraldehyde (GA), with respect to the native tissue. The diffusion coefficient of ions was estimated on the basis of a dielectric dispersion measurement for an aqueous NaCl solution with a well-calibrated distance between the electrodes. The fitting procedure of a theoretical function to the experimental data allowed us to determine three diffusive relaxation regions with three structural distance parameters $d_{\rm s}$, describing the spatial arrangement of collagen fibrils in pericardium tissue. It has been found that a significant decrease in the structural distance $d_{\rm s}$ from 87 nm to 45 nm may correspond to a reduction in the interfibrillar distance within GA cross-linked tissue.