Electrically Triggered Fluorescein and Dexamethasone Release from Conducting Polymer Hydrogels

Spatially and temporally controlled drug delivery is an important field to address the limitations of conventional pharmaceutical administration. While many effective controlled drug delivery systems exist, the repertoire of systems that additionally present a beneficial mechanical environment to cells remains scarce. To address this, a comprehensive release study of fluorescein as a model drug, and the corticosteroid dexamethasone, from poly(N-isopropylacrylamide)/polypyrrole (pNIPAM/PPy) conducting polymer hydrogels is presented within this study. Cyclic voltammetry and scanning electron microscopy (SEM) indicated that having the pNIPAM hydrogel phase present and doping with drugs reduced PPy thickness and shifted/suppressed redox peaks to some degree but not enough to prevent release. Fluorescein release was initiated by constant reduction, with a maximum of 54.5 ± 6.8 µg/cm² from PPy films and 6.3 ± 1.1 µg/cm² from pNIPAM/PPy. The quantity of fluorescein released was shown to be tunable by modulating the charge passed during PPy electropolymerization. Fluorescein-loaded pNIPAM/PPy samples were capable of multiple cycles of depletion and reloading via re-incorporation through re-oxidation in a fluorescein solution. The stability of pNIPAM/PPy regarding drug release was demonstrated, with no difference in release profiles and quantities after soaking samples for 1, 8, and 15 days. Interestingly, constant reduction did not elicit release of dexamethasone, while a biphasic pulsed potential of ±0.8 V at 0.5 Hz was effective. Minimal leaching of dexamethasone without stimulation was shown, alongside a multi-day, multi-triggerable release profile upon short stimulations. pNIPAM/PPy conducting polymer hydrogels are a promising platform for on/off drug delivery, with a nondegrading matrix, minimal passive drug-leaching, and where the drug payload can be reloaded, all while providing a suitable mechanical environment to interface with living cells.