Application of electrowetting on dielectric (EWOD) in drug release control and release-on-demand

Abstract

In this paper, a novel application of electrowetting on dielectric (EWOD) systems in controlling drug release is introduced. The application of electric field in changing the wettability of a substrate has been investigated before, and the correlation between the surface wettability and drug release characteristics of drug-eluting constructs has been reported in the literature; however, the effects of electric field on controlling the drug release rate using EWOD phenomenon has not been investigated before. In this paper, changing the interfacial tension between the solid drug-eluting substrate and the liquid media using EWOD and the consequent change in the drug release was targeted. To this aim, an indium tin oxide (ITO) glass substrate was coated with Polydimethylsiloxane (PDMS), acting as the dielectric layer, and the dielectric layer was then coated with layers of Rhodamine B, a model drug, loaded polylactic-co-glycolic acid (PLGA), acting as the biocompatible drug-eluting layer. The wettability dependency of the substrate to direct current (DC) voltages was assessed, and applying 300 V made a significant change in the contact angle, demonstrating enhanced hydrophilic properties. The contact angle did not significantly change by a further increase in voltage, reaching a contact angle saturation. Subsequently, in an in-vitro drug release study, the cumulative drug release of drug-loaded substrates under various voltages was examined, and increasing the voltage by 300 V noticeably increased the drug release in the media. In addition, the dielectric thickness had a direct effect on the contact angle. Lowering PDMS (dielectric layer) thickness decreased the contact angle and enhanced drug release. The polarity of the EWOD setup did not affect the contact angle and the drug release. The release-on-demand process can further be optimized to lower the required voltage while enhancing the drug release rate. This study introduces a novel application of the EWOD phenomenon in drug delivery.