Hyaluronic acid — gelatin hydrogels as bioelectrets: Charge transport and dielectric polarization effects

In this work, we study the role of water molecules on the polarization processes activated on hyaluronic acid (HA), and gelatin (Gel) hydrogels at rather low hydration levels, by employing mainly broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC) technique. Our results suggest that the polarization capability of the hydrogels depends strongly on the water fraction, already at temperatures as low as -90 °C, and that charge (protons) long-range mobility is inevitably related with polarization processes in the biomaterials. The polarizabilty enhances strongly at temperatures above the onset temperature for structural rearrangements and conformational fluctuations in the hydrogels. At temperatures below this critical temperature, the polarizability is related to water secondary relaxation process (ν-process) and to polarization process within ice-like structures of hydration water. These findings imply that polarization effects in biomaterials are strongly affected by contributions due to hydration water (even for traces of water).