Fig. 2

Side by side schematic view of various in vitro BBB platforms. a The Transwell apparatus which consists of a vertical side by side diffusion system across a semipermeable microporous membrane. The membrane allows for free passage of nutrients and diffusible factors between the luminal and abluminal compartments. Depending on the membrane’s pore size, cell extravasation across the compartments can be enabled. b Dynamic in vitro BBB model (DIV-BBB). This platform relies on the use of hollow fibers to simulate the architecture of a blood vessel. The hollow fiber can be pre-coated with specific coating factor to enable the adhesion of endothelial cells (generally on the luminal surface of the fiber) and astrocytes or other NVU cell types on the abluminal surface in juxtaposition to the endothelium. A pulsatile pump generates the medium flow across the system, mimicking the blood flow traveling inside the blood vessel. The bundle of hollow fibers is suspended inside a sealed chamber. The artificial capillaries are in continuity with a medium source through a flow path consisting of gas-permeable silicone tubing. Ports positioned on either side of the module allow access to the luminal and abluminal compartments. The system allows generating rheological conditions like those observed in vivo. It also allows for the perfusion and circulation of immune cells as required. c Schematic illustrations of a typical microfluidic platform. The system recapitulates the characteristic of a DIV-BBB but to a much smaller scale. Most of these platforms also enable visual assessment of the cell environment through visual microscopy (including fluorescent, and confocal) to assess cell morphology, distribution, cell contact, etc. Some of the limitations inherent to microfluidic systems include the very small sampling size (for qualitative quantitate assessments) and lack of availability to other researchers with very few exceptions