A new biochemical approach for controlled release of dexamethasone from functionalized PEDOT coatings for neural applications

Neural interfaces represent an important tool for enabling better fundamental understanding of the central and peripheral nervous systems, as well as for restoring damaged or lost sensorimotor functions. Conductive polymers,... [ view full abstract ]

Neural interfaces represent an important tool for enabling better fundamental understanding of the central and peripheral nervous systems, as well as for restoring damaged or lost sensorimotor functions. Conductive polymers, including poly(3,4-ethylenedioxythiophene (PEDOT), are typically electrodeposited onto microelectrodes to reduce the total impedance as well as improving the charge storage capacity, necessary for the goal of neural stimulation, for instance. In order to prevent the inflammation of the tissue surrounding the device and the subsequent glial scar formation, which eventually leads to the encapsulation of the implant and device failure, an interesting approach consists in the integration of a PEDOT matrix with anti-inflammatory glucocorticoid such as dexamethasone (DEX). We discuss on the possibility of controlling the drug release from the PEDOT coating via 1) electrochemical stimulus or 2) biochemical trigger.

Method 1. DEX was used as counter ion to counterbalance the positively charged PEDOT chain during electrodeposition. This approach enables an electrochemically controlled drug release system. The typical approach consists on the use of the anionic dexamethasone-phosphate to counterbalance the positively charged PEDOT chain. In such a way the drug is released from the PEDOT film by an electrochemical trigger that can be achieved via pulsed electrical stimuli or cyclic voltammetry in order to reach the neutral reduced state of the conductive polymer matrix, and the subsequent drug release. This approach has two main drawbacks: 1) the need of inducing current-voltage stimulus 2) uncontrollable drug release due to spontaneous ion exchange and subsequent drug diffusion into the bulk solution.  Method 2. In order to circumvent these disadvantages, a new DEX functionalized EDOT monomer was prepared and used to prepare electrodeposited PEDOT coatings in which the drug is chemically linked to the polymer backbone, enabling a biochemically triggered drug release system. The new PEDOT-DEX composite films were electrodeposited onto  Glassy carbon electrodes in order to optimize the deposition method as well as to collect a preliminary evaluation of the stored/released drug.