Explain the function of microfluidic valves.

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Accepted Answer

## Function of microfluidic valves

A microvalve **controls the flow** of liquid or gas in a microfluidic circuit. It decides when, where and how much fluid moves.

### Main functions
- **Start / stop:** open or close a channel.
- **Direct flow:** route fluid to one of several branches.
- **Regulate:** change flow rate or pressure.
- **Isolate:** seal a chamber for reaction (e.g. PCR) or incubation.
- **Meter:** release a precise volume.
- **Prevent backflow:** check valves keep flow one-directional, especially in micropumps.

```mermaid
flowchart LR
    A[Pump] --> B{Microvalve}
    B -->|open| C[Reaction chamber]
    B -->|closed| D[Flow blocked]
    C --> E[Detector]
```

### Classification
| Class | Principle | Examples |
|---|---|---|
| Active | Needs external energy and control | Pneumatic PDMS membrane, piezoelectric, thermopneumatic, electrostatic, electromagnetic |
| Passive | Opens and closes by fluid pressure or geometry | Flap check valve, ball check valve, capillary burst valve |

### Example: pneumatic PDMS valve
A control channel crosses a flow channel with a thin PDMS membrane between them. Pressure in the control channel bends the membrane down and pinches the flow channel shut.

### Exam tip
List 4 or 5 functions, then give the active/passive table.

Function of microfluidic valves

Main functions

Classification

Example: pneumatic PDMS valve

Exam tip

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