(110g) Magnetically Driven Flows to Deliver Clot-Busting Drugs to Dead-End Arteries

Stroke is the third largest killer and the leading cause of long-term disability in the US. Intravenous (IV) administration of the clot dissolving tissue plasminogen activator (tPA) in the emergency room is the most widely used therapy for the most common ischemic stroke.  However, this therapy is often unsuccessful because the tPA is not delivered in sufficient quantity and fast enough to the clot to be effective.  It is shown here that the clot blocks the artery and prevents flow to it, and the tPA or other clot-busting drugs must diffusive from the junction of a larger open artery.  Diffusion occurs too slowly to be effective. 

It has been demonstrated that the addition of one micron iron particles to the IV fluid coupled with a rotating magnetic field with a field gradient can create a convective flow in blocked vessels off of junctions.  Visual observations indicate that the particles form rotating rods along the wall of the occluded vessel creating a convective flow that can carry tPA much faster than diffusion.  The details of this hypothesized mechanism, however, are unknown.  We present a multiphase, multiscale fluid mechanics model to describe this magnetically driven flow.  At the particle scale conservation equations will describe the local concentration of free particles and particles that chain up to form rods.  It is shown that these rods rotate in the presence of the field and generate localized vorticity that drives the macroscopic convective flow in the vessel.  At the vessel scale conservation of mass and momentum equations describe this magnetically-induced vorticity driven flow. The flow affects the transport of the particles and rods of particles, linking the two scales.  The model equations are solved asymptotically and numerically to understand this unique process for creating convective flows in dead-end or blocked vessels.  The model and simulation tool provide means to more rapidly design and optimize this stroke treatment system.