Electrically controlled release of salicylic acid from poly(p-phenylene vinylene)/polyacrylamide hydrogels.

The apparent diffusion coefficients, Dapp, and the release mechanisms of salicylic acid from salicylic acid-loaded polyacrylamide hydrogels, SA-loaded PAAM, and salicylic acid-doped poly(phenylene vinylene)/polyacrylamide hydrogels, SA-doped PPV/PAAM, were investigated. In the absence of an electric field, the diffusion of SA from the SA-doped PPV/PAAM is delayed in the first 3 h due to the ionic interaction between the anionic drug (SA anion) and the PPV. Beyond this period, SA is dissolved in and can diffuse into the buffer solution through the PAAM matrix. The Dapp of the SA-doped PPV/PAAM is higher than that of the SA-loaded PAAM, and the former increases with increasing electric field strength due to combined mechanisms: the expansion of PPV chains inside the hydrogel; the reduction reaction under a negative potential driving the anionic SA through the PAAM matrix; and the expansion of the matrix pore. The Dapp of SA from the SA-loaded PAAM and the SA-doped PPV/PAAM apparently obey the scaling behavior: Dapp/D0 = (drug size/pore size)m with the scaling exponent m equal to 0.50 at 0.1 V for both SA-loaded PAAM and SA-doped PPV/PAAM. Thus, the presence of the conductive polymer and the applied electric field can be combined to control the drug release rate at an optimal desired level.