**5.2.3 Lumen-stent-wall interface: Continuity**

A common assumption for DES mass transport studies is that the intimal layers of the artery are denuded and that the stent is in direct contact with the medial layer of the artery wall (Kolachalama et al., 2009; Balakrishnan et al., 2008, 2007, 2005; Mongrain et al., 2007, 2005). This negates the need to model the endothelial, intima and internal elastic lamina layers. Regardless of the inclusion or exclusion of these layers the continuity equation should be the default setting for all interior boundaries. This condition states that in the absence of sources or sinks, the flux in the normal direction is continuous across the boundary, i.e. the concentration is equal on both sides of the boundary.
