Evaluation of the interface aging process of polypyrrole–polysaccharide electrodes in a simulated physiological fluid

Abstract

Composite polypyrrole–polysaccharide (PPyPSacc) films, such as polypyrrole–heparin (PPyHep), polypyrrole–chondroitin sulfate A (PPyCS-A) and polypyrrole–hyaluronic acid (PPyHA) have been successfully obtained by optimized electrochemical syntheses. The PPyPSacc samples show dopant-mediated tunable physical properties and good stability in air and in biological fluids. The immobilization of PSacc within the polymer matrix renders the surface samples suitable for cell/substrate communication studies. In order to check the viability of PPyPSacc thin films as electrodes for cell electrostimulation, we studied their interface evolution upon aging in a simulated physiological solution (pH=7.4, 37°C) by using electrochemical impedance spectroscopy, cyclic voltammetry and scanning electron microscopy. At open circuit conditions, the overall impedance of the electrodes increases upon aging as a consequence of a fast accumulation of ions at the interface, also related to the increase of porosity and wettability. As the interface impedance increases, the ionic and electronic transport into the polymer is hindered. Nevertheless, no mechanical degradation of the PPyPSacc samples is observed on aging. After 10 days of aging the PPyHep samples keep about 60% of their initial redox capacity. As a consequence the studied materials are capable to supply electrical stimulations to cells in a biological environment well beyond the conventional time-range.