Physical characterization of polymer electrolytes as novel iontophoretic drug delivery devices

Polymer electrolytes are solidlike materials formed by dispersing a salt at the molecular level in a high molecular weight polymer such as poly(ethyle ne oxide) (PEO). They have been extensively studied for use in electrochemi cal applications such as batteries and display devices. This paper consider s a novel application of polymer electrolytes as the basis of iontophoretic drug delivery systems. Polymer electrolyte films were cast from solutions of PEO and various drug salts using either water or an acetonitrile/ethanol mixture as the solvent. These films were characterized by variable-tempera ture polarizing microscopy (VTPM), differential scanning calorimetry (DSC), and alternating current (AC) impedance analysis. The films were around 100 -mu m thick and mechanically strong; the optical and thermal methods provid ed evidence that the polymer electrolytes had crystalline and amorphous pha ses, although some drugs may exist in films as nanodispersions. The amorpho us phase is important as ions have greater mobility in this phase and there fore allow a current to be passed when the material is incorporated into a device such as one suitable for drug delivery by iontophoresis. The AC impe dance analysis showed that the conductivity of the films varied between 10( -6) and 10(-3) S cm(-1), depending on the salt, casting solvent, and temper ature. Two drugs in particular were shown to be promising candidates in the se systems: lidocaine hydrochloride and lithium chloride.