Dielectric properties of natural and demineralized collagen bone matrix

In this paper, measurements of dielectric properties of fluid-saturated cortical and trabecular bovine bones are presented. Results are reported for native and demineralized states from 80 MHz to 1 GHz. A non invasive technique using open-ended coaxial lines is proposed, and compared to invasive configurations. Measurements are performed in time domain and data are processed using system identification techniques in continuous and discrete domains. These are very interesting tools for signal processing when working with time domain spectroscopy data. As a validation test for the system identification technique, data are also obtained in the frequency domain. A clear evidence of relaxation processes around 0.2 to 0.4 GHz is shown, which may be due to the movement of polar side chains of the collagen fibers. A strong difference between the dielectric properties of native and demineralized bones was found. The experiments here reported aim to contribute to a more in-depth knowledge of the relaxation processes due to the fully hydrated collagen matrix and its relation to the mineralized phase.