Measuring and assessment of impedance spectrum of collagen thin films in the presence of deionized water

Abstract

Collagen is the major structural protein in the human body, which plays a significant role in retaining the structural and biological integrity of the extracellular matrix. In this study, the electrical impedance of collagen thin films on gold electrodes on an FR4 substrate was measured in dry and humid states. The magnitude and phase of the measured electrical impedances showed a significant difference (P < 0.05) in the dry and wet conditions. By adding deionized water to the dry collagen thin films, the magnitude of the electrical impedance decreased, indicating an increase in conductance. It can be reasonably inferred that chemical and electrical interactions between the water molecules and the functional groups present in the collagen molecules such as the hydroxyl group are responsible for the increase in the conductance. After adding a certain amount of water, the impedance reduction trend is reversed and an increase is observed. This could be due to the saturation of chemical interactions between the collagen and water molecules: by adding more deionized water to the medium, there is a greater number of free water molecules in the medium, reducing the conductance of the medium and the impedance increases by decreasing concentrations of the ions which are produced from interactions between water and collagen molecules. The quantitative study of this finding has been performed with the help of electrical impedance spectroscopy. Finally, an electrical model was fitted to the measured data which describes the impedance behavior of collagen thin films in the vicinity of water molecules.