Study of the stability in different aqueous mediums of polarized PEDOT:PSS

The cell adhesion is a central process in tissue morphogenesis and it is affected by soluble and insoluble chemical signals, by mechanical stiffness and by micro and nanotopographical features. Consequently the tissue engineering has focused on the development of new materials that exploit these phenomena. The discovery of the conducting polymers (CP) has represented a huge opportunity in the improvement of interfaces between electronic materials and living cells, because of their biocompatibility and their ability to conduct both ionic and electronic charges. Moreover, their surface properties (e.g., surface charge, wettability, and conformational and dimensional changes) can be changed reversibly by electrochemical oxidation or reduction. In 1994, Wong et al. [1] discovered that aortic endothelial cells grow differently on oxidized versus reduced polypyrrole films, paving the way for non-invasive control of cell behaviour by electrical means. In the last years, some devices based on CPs were employed to control with electronic stimuli the cell adhesion, but their working principle was not yet fully understood. Fraboni’s research group is studying the growth of human dermal fibroblasts cells on poly 3,4-ethylene dioxytiophene doped with polystyrenesulfonate (PEDOT:PSS) depending on its redox state that was changed before the cell seeding. The aim of this contribution is to study the modifications of oxidized/reduced PEDOT:PSS (vs its native state) that occur when the thin films are soaked in different mediums, such as the Dulbecco's modified Eagle's medium (DMEM). The PEDOT:PSS, that was deposited as thin film by spin coating or electropolymerization, was oxidized/reduced applying a potential of +0.8/-0.9 V versus a saturated calomel electrode (SCE). The behavior of these thin films was investigated in DMEM, buffer phosphate and deionized water using absorption spectroscopy (visible and near infrared) and recording the open circuit potential. The obtained results show that both the reduced and oxidized forms of PEDOT:PSS go back to the native state when the material is soaked in DMEM or buffer phosphate. On the other hand the PEDOT:PSS films in all the studied redox states are stable in deionized water. The Figure 1 shows the disappearance kinetics of the PEDOT:PSS neutral form that is obtained by cathodic polarization. Finally the PEDOT:PPS was studied using absorption spectroscopy and atomic force microscopy when the electrode was biased for very long time (> 10 h) in order to highlight the transformations due to the polarization.