The Basics of Microfluidic Tubing & Sleeves

Microfluidic accessories, such as tubing, fittings and connectors are critical tools that strengthen experimental setups, making it possible to simplify and accelerate the discoveries of microfluidicists.
On this page, you will find an introduction to some of the basic principles of microfluidic tubing and sleeves.

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Microfluidic Tubing & Sleeves: Introduction

Microfluidicists share common concerns, such as how to connect all the fluidic elements that make up their experimental setup in a simple and reliable way, and without any leakage to degrade the overall performance. Quality microfluidic accessories can thus have a big impact by giving researchers more flexibility and more time to assess their microfluidic concepts and strategies.

These microfluidic accessories fall into three broad categories:

  • tubing and sleeves, which are generally used to transport small volumes of liquids to your chip
  • unions and adapters, which are used to connect fittings of the same or different threading
  • fittings and connectors, which are used to connect, either with rigid or soft tubing, your microfluidic device or your Lab-on-a-chip to external elements such as pumps and reservoirs

This article is part of a series of short introductions to microfluidic accessories. Other tutorials will provide you more information on unions and adapters for microfluidics, and microfluidic fittings and connectors. To learn more about the tubing and accessories offered by Elveflow, click here.

So, let’s start with some basic information about tubing and sleeves.

Tubing enables you to link the multiple parts of your microfluidic setup: your fluid actuation device (a syringe pump, a peristaltic pump, an Elveflow AF1 or OB1 Pressure Controller) and the reservoirs, containers or sample chambers in which your liquids are stored. All of this is complemented by various additional elements such as injection valves or restrictors…

Tubing & Sleeves : Terms & Conventions

There are several parameters with which you should become familiar in order to make the right choice for your particular experimental needs.

 

 

When selecting microfluidic tubing for use with fittings, the following factors should be kept in mind:

  • Inner Diameter : refers to the diameter of the inside of a microfluidic tube, pipe, or sleeve.
    Often abbreviated “ID” in suppliers catalogs.
  • Outer Diameter  : refers to the diameter of the outside of a microfluidic tube, pipe, or sleeve.
    Often abbreviated “OD” in catalogs.
  • Wall Thickness : refers to the measure of how thick the tubing is.
    Often abbreviated “WT” in catalogs.
  • Length : refers to the length of the tubing.
    Often abbreviated “L” in catalogs.

Tubing & Sleeves : Inches to Millimeters Conversion

Please note that if you are more familiar with the metric system, microfluidic tubing dimensions are usually not given in millimeters. Instead, tubing and sleeve measurements make use of the Imperial Unit system, which commonly uses fractions of inches for size values.
Thus, to facilitate the conversion between the two systems, it might be useful for you to refer to this non-exhaustive list of values. If you have the measurement in inches and need to know the millimeters:

Microfluidic tubing :
Inches to Millimeters Quick Conversion Guide

In order of increasing size…

  •  1/64 inch = 0.39mm
  • 1/32 inch = 0.79mm
  • 1/16 inch = 1.58mm
  • 1/8 inch = 3.17mm
  • 5/32 inch = 3.96mm
  • 3/16 inch = 4.76mm
  • 1/4 inch = 6.35mm
  •  5/16 inch = 7.93mm
  • 3/8 inch = 9.52mm
  • 1/2 inch = 12.70mm
  • 5/8 inch = 15.87mm
  • 3/4 inch = 19.05mm
  • 7/8 inch = 22.22mm
  • 1 inch = 25.40mm
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Microfluidic Tubing : what is a sleeve ?

The presentation of the above elements makes it easier to introduce microfluidic sleeves. So, what exactly is a sleeve?
Sleeves are basically diameter size adapters consisting of small pieces of tubing into which a smaller tube is inserted. The aim is to increase the outer diameter of the inserted tubing so as to make it fit properly into a receiving port designed for larger tubing.

When your tubing is too small to be used with your fitting, you need to play around with the ID and OD values to find a sleeve that can successfully connect your capillary tubing into the receiving port.

In the following picture, for instance, a green F-247 FEP sleeve, with a 1/16’’ outer diameter, has an appropriate internal diameter for sliding over 1/32’’ tubing. Thus, 1/32’’ tubing can be inserted into this sleeve so that it becomes compatible with fittings designed for 1/16’’ OD tubing, which is the most commonly used outer diameter in microfluidic instrumentation setups. The mounting is secured by the compression applied by the ferrule on the tubing when the fitting is screwed on. In our microfluidic kits section, we propose a specific kit developed to make life easier for anyone who wants to use 1/32 OD capillary tubing with fittings designed for 1/16’’ OD tubing.

 

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Microfluidic Tubing : Flow Resistance

 

The resistivity of a tube or circular channel is a function of the inner diameter and length. The ID of the tubing has a key impact on the flow resistance. Tubes with a very small ID values  (500 µm ID and below), often presented as capillary tubing, can lead to a surprisingly high flow resistance. Length also plays an important role in the resistivity of the tubing. These notions can be  used to increase the resistivity in order to enhance the flow rate stability.  Indeed, a simple flow resistance can help you reach low flow rates within a low fluidic resistance setup. If you’re working with droplets, you may be dealing with flow rate instability and pressure variations created by droplet generation. Our Microfluidic Flow Resistance Kit is a simple and fast solution to implement, allowing you more time to focus on what really matters, your science!

 

Microfluidic Tubing & Sleeves : materials used

 

Knowing  the material from which certain types of tubing have been manufactured is particularly important for the  quality of the connection you are making.

Let’s be honest: the perfect material doesn’t exist. You will very often have to choose between pressure resistance and chemical resistance. Therefore you should be very careful about to the nature of the reagents that will flow through your tubing.  In our microfluidic kits section, we propose a specific section dedicated to microfluidic tubing. Regardless of whether it is a matter of fluid transport, fluidic resistance, or flow rate performance improvements, our selection of tubing will bring you complete satisfaction. They are available for an extremely broad range of applications, from general purpose liquid dispensing to droplet microfluidics and syringe pump improvement.

 Some of the most commonly used tubing materials in microfluidic instrumentation setups are :

  • Microfluidic PEEK tubing (Polyetheretherketone): This biocompatible and very chemically compatible material is widely described as the highest performing thermoplastic material currently available because of its remarkable chemical resistance. However, due to a swelling effect, take caution when using methylene chloride, THF, and DMSO. Nevertheless, these qualities make PEEK tubing and capillaries a material of choice in numerous low and high pressure applications.
  • Microfluidic PTFE Teflon tubing (Polytetrafluoroethylene, often described as Teflon® tubing): This transparent, chemically inert and non-toxic material features unmatched chemical resistance and a surface that facilitates flow. Due to its high flexibility, PTFE is mostly used in low pressure applications. When used in microfluidic setups, its rigidity can significantly shorten the response and settling time and lead to an improved reactivity of the system.
  • Microfluidic Tygon tubing : The elasticity and high flexibility of Tygon tubing make it fit tightly to glass and metal and also a material of choice for PDMS device connections. It is also very often used with analytical instruments and pressure controllers, peristaltic pumps, vacuum pumps, or flow switch matrices. The high elasticity of Teflon tubing can be employed in a sophisticated manner to smoothen microfluidic flow rate fluctuations often observed when using a syringe pump.
  • Microfluidic FEP  tubing (Fluorinated ethylene-propylene): This nice alternative to PTFE tubing exhibits many similar properties such as biocompatibility and a remarkable inertia to most chemicals. This flexible material with very good optical clarity is mostly used for low pressure microfluidics.
  • Microfluidic ETFE  tubing (Ethylene tetrafluoroethylene): This material is chemically stronger compared to PTFE, and as such, is highly chemically resistant. Being more rigid than its molecular relative, it is often used in medium pressure applications.
  • Microfluidic PP  tubing (Polypropylene) This tubing offers good resistance to many chemical solutions across the full pH range, making it a material of choice for many standard applications.

 

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