Geometry-Dependent Properties of Physically Crosslinked PPy-PVA Hydrogels Enable Tunable Iontophoretic Drug Delivery

Iontophoresis enables noninvasive transdermal drug delivery. The control of drug release, however, has largely relied on current modulation. Here, we explore geometry-driven factors, gel microstructure, and local electric fields, as alternative levers for regulating drug transport.

To investigate iontophoretic drug delivery, we encapsulate bovine serum albumin (BSA) in polypyrrole-polyvinyl alcohol (PPy-PVA) hydrogels. Five distinct hydrogel geometries were fabricated to impose variation in pore architecture and electric field distribution, including Hilbert curve-based designs that use increased corner density to enhance local electric field strength. Using formulation studies, we determined the ideal PPy content, drug loading efficiency, and current density. Maximum field strength of individual hydrogel geometries was simulated via finite element analysis, and microstructures were characterized by scanning electron microscopy. Lastly, we assessed differences in the transport metrics of the hydrogel geometries through an in vitro study using a Franz diffusion cell and an artificial membrane.

The engineered geometries produced clearly differentiated microstructures and electric field strengths. Drug delivery studies demonstrated that iontophoresis substantially enhanced permeability compared with passive diffusion, with each geometry yielding different profiles in cumulative release, flux, and permeability. Notably, the average iontophoretic permeability was 4.32 × 10^-5 cm s^-2, exceeding values reported in previous studies using artificial membranes.

This study showed that the geometry-driven fabrication of drug-loaded hydrogel can achieve different delivery characteristics in both iontophoretic and passive transport using artificial membranes.

Geometry-mediated control complements existing approaches for iontophoretic drug delivery without requiring individual current-density control.