A master carries the channel pattern as raised ridges, usually made in photoresist on a silicon wafer. Liquid PDMS is poured over it, cured, peeled off, and sealed to glass.
One precise master can mold hundreds of chips.
THE MASTER
Photolithography does the fine work
The master is made with the same kind of photolithography used in microchip fabrication: coat a wafer with a photoresist such as SU-8, expose it through a mask, and develop away the rest. The ridge height sets the channel height, which, as you saw in the shear formula, matters a lot.
The microfabrication in this course's other units is the starting point for chips.
THE MATERIAL
PDMS: great, with a catch
Why it's lovedClear for microscopes, flexible, easy to cast, and permeable to oxygen for the cells
The catchIt can absorb small hydrophobic molecules, which can distort drug measurements
AlternativesThermoplastics such as polystyrene, COC, and PMMA, or 3D printing, avoid this and suit mass production
The best material depends on the drug, and on the production volume.
SEALING
Plasma bonding
A brief burst of oxygen plasma activates the PDMS surface so it bonds permanently to glass or to another PDMS layer. A porous membrane can be sandwiched between two layers, and holes punched through the PDMS make ports for tubing.
The same plasma tools used in chip fabs seal a biology chip.
LIFE GOES IN
From plastic to tissue
CoatFill the channels with matrix proteins such as collagen IV and fibronectin
SeedInject endothelial cells, and flip the chip to seed the other side if needed
AttachWait for the cells to stick, then add medium
PerfuseStart a slow flow, and let the barrier mature over several days
The fabrication is hours of work, and the biology is days.
UNIT 12 STUDY COMPLETE
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Ready for the Fab Challenge?
You've followed a chip from a patterned master to a sealed device and seen the trade-offs of PDMS.