Anisotropic Transport Through Polymer Layer and Porous Arterial Wall with Binding in Drug-Eluting Stents Using the FEM
Congress: ENCIT
ABSTRACT:
The safety and efficacy of Drug-eluting stents is strongly influenced by the anisotropic transport of the antiproliferative/anti-inflammatory drugs in the arterial wall. Dissolution in the polymer coating and specific binding in the artery wall play an important role in the process. We consider the model of dissolution, transport and binding of sirolimus on an axisymmetric domain representing the polymer coating layer and the porous artery wall in the vicinity of a stent strut. We employ the FEM on an unstructured mesh to discretise the governing equations. We employ a non-linear dissolution model for the dynamics in the coating, and a non-linear saturable binding model that includes both specific and non-specific binding in the arterial wall as separate phases, as proposed by McGinty-2016. The arterial wall is considered an anisotropic porous media and the flow is considered to be governed by Darcy flow. The principal directions of the diffusion tensor are considered to be, in general, non aligned with the Cartesian coordinates and are determined by the gradient of signed distance function computed from the inner arterial wall. The permeability in the polymer coating is considered to be very small, but finite. The endothelium lamina, where present, is modelled as a no-flow boundary. The effect of slow and fast release polymers is considered, showing that the time evolution of the process can be efficiently controlled by the polymer diffusion coefficient. However, the spatial distribution of the sirolimus is greatly influenced by the flow and the arterial wall properties, being therefore susceptible to patient health conditions. The effect of the anisotropic diffusion tensor is seen in the sirolimus concentration distribution around the polymer layer, that becomes considerably higher and more uniform around the stent than in the orthotropic model, and in the enhanced mass flux, resulting form the realignment of the principal directions of the tensor with the direction of the interface.