Controlled Release From an Electrorheological Fluid Dosage Form: Experimental Results for a Prototype System

Abstract

A new controlled-release technology that is based on electrorheological fluids (ERF) is described, and a model system is investigated. Humidified starch (duration of humidification is 30-35 minutes) was used as a filler material (∼20% w/w) in olive oil to make the ER system, and benzocaine (BZN) was used as the model drug. The average particle size of starch in the olive oil was ∼200 nm. 1N HCl was used as the receiver medium and BZN was assayed by UV spectroscopy at 226 nm. A series of studies was done at five temperatures (25°, 30°, 35°, 40°, and 45°C) and two external electric fields (E-fields) that were generated by applying potential drops across the diffusion apparatus of 0 V and 290 V. Control studies of BZN release from olive oil without filler showed little or no increase in release rates resulting from application of E-fields. In addition, while reversing the polarity for BZN in olive oil caused differences in release rates, these differences were too small to explain the results obtained for the ER systems. It was found that release of BZN increased significantly with the application of the electric field (∼53% increase at 25°C). A plot of the log of the release rate vs 1/T was linear for the 0 V data but deviated from linearity for the 290 V data. The increase in release rates due to the Efield became smaller as the temperature was increased. The results are consistent with (but are not sufficient to prove) the hypothesis that the increased release rate is due to a small amount of ordering of the cornstarch filler particles in response to the applied E-field, which results in a reduction in the tortuosity of the system