Effects of ferrohydrodynamics on drug transport and retention in drug eluting stents

Abstract

This study examines the transport of magnetized drug particles (MPs) in drug-eluting stents (DESs). The governing equations for multi-species transport in a two-domain consisting of a polymer and media are formulated and solved using the finite volume method. The effects of an external magnetic field (MF) on the distribution of different drug species are analyzed. The MF was found to increase MP concentrations in the tissue and, unexpectedly, in the polymer at the same time. This counterintuitive finding was explained by analyzing the rates of transport through the polymer topcoat and the media top-layer. It was revealed that the rates of transport into and out of the media layer initially decrease and then increase with the MF, with an intermediate regime where the dynamics resemble those without MF. The maximum averaged free drug concentration in the tissue and that of the dissolved drug in the polymer were observed to increase exponentially with the MF implying on the fact that drug delivery becomes more sensitive to the MF at its larger strength. Tracking the drug center of mass revealed a nonmonotonic variation with time consisting of two linear regimes on a time log scale. The slopes of the first regime decreases with the MF while that of the second one is unaffected by the MF. The transition time was shown to increase almost linearly with the MF. The results of this study have promising applications in palliating the tendency for low drug retention from which current DES suffers.