Ts. Sahota et al., Physical characterization of polymer electrolytes as novel iontophoretic drug delivery devices, DRUG DEV IN, 25(3), 1999, pp. 307-313
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.