Design and fabrication considerations for micropumps and valves

Design considerations

Factor	What to decide
Flow rate and pressure	Target µL/min and pressure head from the application
Actuation principle	Piezoelectric (fast, high force), thermopneumatic (simple, slow), electrostatic (low power, small stroke), electromagnetic (large force, bulky)
Chamber and diaphragm	Stroke volume, compression ratio, diaphragm material and thickness
Valve type	Passive check valves (no power, simple) or active valves (controllable)
Fluid compatibility	Biocompatibility, low protein adsorption, tolerance to bubbles and particles
Dead volume	Keep small to avoid carry-over and trapped air
Power and size	Low power for portable and implantable use

Fabrication considerations

• Silicon bulk micromachining: KOH or DRIE etching for chambers and valve seats.
• Glass: wet etching and anodic bonding to silicon for sealed, transparent devices.
• Polymers (PDMS, PMMA): soft lithography, hot embossing or injection moulding; low cost and biocompatible.
• Actuator integration: bonding a piezoelectric disc, heater or electrodes to the diaphragm.
• Bonding and sealing: anodic, thermal, adhesive or plasma bonding without clogging channels.
• Fluidic interconnects: reliable, low-leak inlet and outlet ports.
• Packaging and sterilisation: needed for biomedical use.

Exam tip

Split the answer into design and fabrication, and give at least one material and one process for each.