Cytotoxicity considerations and electrically tunable release of dexamethasone from polypyrrole for the treatment of back-of-the-eye conditions.

Abstract

Age-related macular degeneration (AMD) and diabetic macular edema (DME) are common causes of blindness in people aged over 55 years. Current treatment involves frequent intravitreal administration of corticosteroids such as dexamethasone. The aim of this research was to formulate an electrically controlled delivery system for dexamethasone. Polypyrrole (PPy) was polymerized with dexamethasone sodium phosphate (Dex-P) through two approaches. Firstly, conventional films (CFs) of PPy were electropolymerized by applying a constant current density of 2 mA/cm2 for 4 min. Secondly, for the first time, we report drug-loaded ethanol-washed films (EWFs). EWFs were prepared in the same manner as CFs, except ethanol washing steps were introduced in the middle and at the end of PPy electropolymerization. The ethanol washing removed unbound PPy oligomers resulting in the formation of smooth surfaces with two distinct layers when viewed in cross-section. The EWFs showed superior electrochemical activity compared to CFs. Sustained release was observed from both CFs and EWFs with bursts of release triggered by electrical stimulation. The EWFs were initially more responsive to the electrical trigger, offering future opportunities to fine tune release. The cytotoxicity of aqueous extracts collected from both films was evaluated on human adult retinal pigment epithelium (ARPE-19) cells using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay with negligible toxicity observed. The results suggest PPy-Dex-P films are highly suitable for the development of electro-responsive implants for the treatment of AMD and DME.