Polyterthiophene as an electrostimulated controlled drug release material of therapeutic levels of dexamethasone

Abstract

Polyterthiophene has been investigated as a substrate for the controlled release of dexamethasone, a synthetic glucocorticoid anti-inflammatory drug, which is widely used to help reduce inflammation in the central nervous system. Dexamethasone was incorporated into the polymer as an anionic dopant during electrochemical polymerisation from water–acetonitrile solutions. Optimal polymer synthesis conditions were established to yield reproducible dexamethasone release profiles into a simulated physiological receiving solution. A homogeneous morphology of the polyterthiophene substrate with minimal extraneous features was observed to be critical for achieving reproducibility of release. Release profiles were established using a range of electrochemical stimulation protocols over a 24 h time period. The amount of dexamethasone released from the polyterthiophene under all electrostimulation protocols was at therapeutically relevant levels, with a maximum release of ∼80 μg/cm 2 achieved when the polymer film was in a reduced state. The oxidation state of the polyterthiophene was found to be critical for controlled release of the dexamethasone. Polyterthiophene doped with dexamethasone was observed to auto-reduce when placed into the receiving solution. As a consequence, no significant difference was observed between the unstimulated (auto-reduced) polymer and the electrochemically reduced polyterthiophene. By electrochemically holding the polyterthiophene in the oxidised state, the rate of release of dexamethasone was significantly impeded with ∼40 μg/cm 2 released over a 24 h period.