Towards a biodegradable bioelectronic device on a soft, biodegradable substrate

Poly(3,4-ethylenedioxythiophene) (PEDOT) complexed with chondroitin sulfate (CS) (PEDOT:CS) was prepared and drop-cast films were demonstrated to be conductive, with a best sheet resistance of 4.7 kΩ per square . Novel organic electrochemical transistors (OECTs) based on 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)-crosslinked PEDOT:CS films were demonstrated with a maximum transconductance of 50.5 μS. The OECTs saw an increase in output currents and ON/OFF ratios following 3-days submersion in water, thought to be a result of increased ionic conduction within the swollen matrix. EDC-crosslinked hyaluronic acid (HA) hydrogels were prepared. They were demonstrated to be fully degradable, via hydrolysis, over a 4-day period in a pH 7.4 buffer at 37 °C. The elastic moduli of the hydrogels increased with increasing concentration of EDC used in the crosslinking step. The moduli were found to be between 2 and 50 kPa which were within the range of elastic moduli reported in the literature for the CNS. A simple prototype HA gel with a grafted PEDOT:CS layer was also prepared and forms the basis of a fully degradable OECT. Interest in organic bioelectronic devices to interface between biological systems and synthetic electronic systems is growing rapidly, especially for use in the central nervous system (CNS). Most organic electronic materials used in organic bioelectronic devices, such as PEDOT:poly(styrene sulfonate) (PEDOT:PSS), are not biodegradable and have poor long-term biocompatibility. The use of biomolecules, such as CS, as alternative counter-ions for PEDOT offer away of overcoming these limitations. The biocompatible, biodegradable, and mechanically appropriate device presented in this thesis could be developed further for use in the CNS and for the treatment of spinal cord injuries, of which there were 930,000 cases worldwide in 2016.