THE SETUP

A cup inside a well

Endothelial cells grow on a porous membrane at the bottom of a plastic insert. The top compartment stands for the blood and the bottom compartment for the brain.

Two compartments separated by one cell layer: the simplest barrier model.

THE PARTS

What each piece does

Membrane A thin porous plastic such as PET or polycarbonate, with pores about 0.4 to 3 micrometers wide

Top (apical) The compartment that stands in for the blood

Bottom (basolateral) The compartment that stands in for the brain

Coating Proteins such as collagen and fibronectin help the cells attach

Samples can be taken from either side, which makes testing simple.

ADDING NEIGHBORS

Mono-culture and co-culture

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Mono-culture

Endothelial cells alone on the membrane

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Co-culture

Astrocytes or pericytes on the well floor send signals through the medium

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Contact

Cells on opposite sides of the membrane reach through the pores and touch

Support cells usually tighten the barrier.

WHY IT'S POPULAR

Simple, standard, scalable

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Off the shelf

Inserts come in standard sizes that fit standard plates

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Many at once

A plate holds many inserts, so many conditions run side by side

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Established tests

TEER and tracer measurements are well understood

A Transwell is the baseline every other model gets compared with.

THE LIMITS

The missing ingredient is flow

Fluid sits still in a Transwell, so the cells never feel the shear force of flowing blood. The membrane is also thicker and stiffer than a real basement membrane, and the cells grow flat on plastic. The barrier is often leakier than it is in the body.

Flow is the missing ingredient, and that is where chips come in.

UNIT 7 STUDY COMPLETE

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Ready for the Fab Challenge?

You've seen how a Transwell works and why a lack of flow leads researchers to chips.