Figure 1. Currently used blood brain barrier (BBB) models.

A) Diagrams demonstrating the varying complexities of transwell BBB models showing direct and indirect co-culture methods; BECs may be cultured alone on a porous membrane transwell across which electrical resistance may be measured to assess BBB integrity. Astrocytes may be co-cultured in the basolateral side of the well to enhance BBB properties, whist in more complex models pericytes or microglia may be included and cultured on the membrane. B) The commercially available Flocel inc. DIV-BBB3D system uses a series of hollow fibers to allow for 3D co-culture of BECs and astrocytes whilst also allowing luminal flow to investigate leukocyte transmigration (Reprinted by permission from Macmillan Publishers Ltd; Journal of Cerebral Blood Flow & Metabolism³¹ Copyright 2011). ECS, extraluminal space.