ENGINEERING
Microfluidic Valves: Controlling Flow on a Chip
To automate anything on a chip you need to start, stop and route fluid — that means valves. Microfluidic valves range from software-controlled pneumatic membranes to clever passive geometries. Here is an overview.
Why valves matter
Valves enable metering, sequencing and multiplexing — turning a passive channel network into a programmable device. They are central to automating lab-on-a-chip workflows.
Active valves
Active valves are externally controlled. The classic is the pneumatic "Quake" valve: in a two-layer PDMS device, pressurising a control channel deflects a thin membrane to pinch the flow channel shut. Hundreds can be integrated on one chip (large-scale integration). Others are actuated by solenoids, heat or magnetic fields.
Passive valves
Passive valves need no external control. Capillary stop valves use geometry or wettability (see capillary action) to halt flow until a pressure threshold is reached; check valves allow flow in one direction only. These are common in point-of-care cartridges.
Trade-offs
Active valves give precise, dynamic control but need external hardware (pressure lines or electronics). Passive valves are simple and pump-free but less flexible. The right mix depends on how much automation the device needs — and on the flow control strategy around it.
Manufacturing
Multilayer PDMS suits research-scale valve integration. For production, valve function must be designed to survive the move to thermoplastics and injection moulding — part of design-for-manufacture.
Frequently asked questions
What is a microfluidic valve?
An on-chip element that starts, stops or routes fluid, enabling metering, sequencing and automation of microfluidic workflows.
What is a Quake valve?
A pneumatic valve made in two-layer PDMS, where pressurising a control channel deflects a thin membrane to pinch a flow channel closed; many can be integrated on one chip.
What is a capillary (passive) valve?
A valve that uses channel geometry or wettability to halt capillary flow until a pressure threshold is reached, needing no external control — common in point-of-care cartridges.
What is the difference between active and passive valves?
Active valves are controlled externally (pneumatics, electronics) for precise, dynamic control; passive valves rely on geometry and surface properties, are simpler and pump-free, but less flexible.
Automation on a chip
Integrating valves into your device?
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