Microfluidic Tubing
Working in a microfluidic environment usually requires the use of various fittings and microfluidic tubing, to connect your microfluidic device or your Lab-on-a-chip to the various elements of your microfluidic chip or system.
Tubing enables one to link the various elements of your microfluidic circuit.
How choose the right tubing?
Several parameters must be taken into consideration in order to choose the tubing:
- Tubing dimensions
- Materials
Tubing dimensions
When selecting your tubing, you should become familiar with the tubing dimensions’ influence:
- “OD” means outer diameter.
- “ID” means inner diameter: Diameter of the fluidic path where fluid flows. The inner diameter plays a significant role in the resistivity brought by the tubing: the smaller it is, the more resistant the tubing will be.
- “L” means length. Usually the tubing is made as short as possible to have smaller internal volumes the internal volume of the tubing being the inner section times the length of the tubing. It is also a parameter that takes part in the resistivity of the tubing.
Figure 1: Definition of tubing dimensions (OD, ID and L)
Microfluidic tubing: Inches to millimeters conversion
In many catalogs, tubing dimensions can be displayed in inches, millimeters and mixture of the two. The following chart will help conversion between these two systems.
| Inches | Millimeters |
|---|---|
| 1 | 25.4 |
| 1/8″ | 3.17 |
| 1/16” | 1.58 |
| 0.040″ | 1 |
| 1/32” | 0.794 |
| 0.030″ | 0.75 |
| 0.020″ | 0.5 |
| 1/64″ | 0.397 |
| 0.010″ | 0.25 |
| 0.007″ | 0.175 |
| 0.005″ | 0.125 |
Questions
- I have a 1/16’’ OD tubing. What does it mean?
It means the tubing has an outside diameter (OD) equals to 1/16’’inch (=1,58mm).
- I have a 1/32’’ OD tubing. What does it mean?
It means the tubing has an outside diameter (OD) equals to 1/32’’inch (=0,794mm).
- How to cut my tubing properly?
In order to get clean interface and prevent any clogging or collapsing of the fluidic path, all tubing should be cut with specifically designed cutters.
Materials
A wide range of materials are available for the same ID / OD combination. The material should be selected according to the nature of the reagents flowing through the tubing.
Be careful to check the chemical and biological compatibilities of the tubing material before installing the tubing on your application. Some of the most common materials for microfluidic tubing include:
- PEEK (Polyetheretherketone): Biocompatible, chemically inert to most commonly used solvents, low non-specific adsorption. PEEK tubing is flexible, offers a very smooth internal surface and be easily cut to desired lengths. For low and high-pressure applications. Very small internal diameters available.
- PTFE (Polytetrafluoroethylene, equivalent to the brand name Teflon®): Chemically inert to most commonly used solvent, non-toxic, non-porous, excellent stress-resistance. Flexible and transparent. Mostly for low-pressure applications.
- FEP (Fluorinated ethylene-propylene): Same family as PTFE. Chemically inert to most commonly used solvent and biocompatible. Flexible and transparent. Mostly for low-pressure applications.
- ETFE (Ethylene tetrafluoroethylene): Same family as PTFE and FEP but more rigid and better-suited to higher pressure applications.
- Fused silica (high-purity glass): Mainly for capillary tubing, exists with external diameters smaller than 1/32’’ (360 µm OD, 510 µm OD…). NB: this type of tubing must be cut with ceramic cutters to get clean inlet and outlet.
Low-pressure /high-pressure: With the regulated pressure provided by Fluigent pressure controllers, such as our Flow EZ™, or our OEM offers, going up to 100 psi (7 bars), all fittings and microfluidic tubing used with Fluigent devices can be rated as low-pressure.
How to adapt my tubing? Use sleeves or connectors!
- Sleeves are small hollow cylinders, connectors are special fittings.
- For connecting 1/32’’ OD tubing to standard 10-32 coned port (1/16’’ OD).
- Different internal diameters are available.
- Example: The green sleeve provided with Fluigent FRP LQ KIT has the right internal diameter so that it can be slid over 1/32’’ tubing and has a 1/16’’ outer diameter. Thus, it makes a 1/32’’ tubing locally appear as a 1/16’’ tubing and makes it compatible with fittings designed for 1/16’’ tubing.