Table 1.

Comparison of pneumatically actuated microsystems

Valve type	Advantages	Limitations	Applications
Lifting-gate valve (normally closed, actuate to open)	High pumping efficiency Used in series to form micropumps	Need for valve passivation to avoid them becoming permanently closed Pumping backflow causes unsteady laminar flow	Precise metering of reagents33 Rapid biosensing and point-of-care diagnostics30
Quake valve (normally opened, actuate to close)	Used to interrupt flow without causing unsteady laminar flow Used to create a concentration gradient	Poor resolution for flow metering The height and the width of the valve cannot be designed independently	Immunoassays50 Cell sorting51
System combination of lifting gate and quake valves	Leveraged the pumping capabilities of normally closed valves for high-efficiency fluidic manipulations Uses normally opened valves to block flow at a targeted location to create isolated chambers Allows the formation of a concentration gradient in channels	Fabrication challenges due to non-compatibility of photoresists and developers for normally closed and normally opened valves	Drug screening to cells Cell co-culture Cell migration to a gradient