How to choose your tubing for microfluidics?
- 03 Nov, 2020
Tubing is an essential element in the design of your microfluidic platform, being the link between the different components of this platform. As it is in contact with the fluids, the choice of tubing is mainly determined by the chemical compatibility with the fluids you use, but also by other parameters (pressure in the system, compatibility with the elements in your setup, etc.).
Given the large number of materials used, it is easy to get lost. We will try to make your life easier with this review, where we will compare the different types of tubing available on the market and their physico-chemical properties.
Tubing and dimensions
Let's first take a look at some of the dimensions. Indeed, you can quickly get lost among the abbreviations, between OD, ID, WT.
Tubing materials and microfluidics
PTFE tubing (PolyTetraFluoroEthylene, often described as Teflon®)
PTFE has the best performance in terms of chemical and thermal resistance and non-stick properties. Compared to similar fluoropolymers, PTFE offers the best price/performance ratio. In fact, it has many advantages, including: unrivaled chemical resistance, a surface that facilitates flow, non-toxicity and chemical inert properties. In addition, due to its high flexibility, PTFE is mainly used in low-pressure applications. Finally, when used in microfluidics, its rigidity can considerably stabilise the flow rate of the microfluidic installation and shows a better reactivity of the system.
FEP tubing (Fluorinated Ethylene-Propylene)
This attractive alternative to PTFE tubes has many similar properties such as biocompatibility and remarkable inertness to most chemicals but with a lower maximum operating temperature of 200°C. FEP is the preferred material in production of small diameter tubing of continuous lengths. Like PTFE, this flexible material is mainly used for low-pressure microfluidic applications. In addition, thanks to its excellent clarity, it is ideal for sight glass/flow monitoring applications. FEP tubing also has better gas and vapor permeability properties and excellent UV transmission ratings. Finally, FEP tubing has a slightly higher coefficient of friction, a lower continuous operating temperature and is more transparent than PTFE.
PEEK tubing (Poly Ether Ether Ketone)
PEEK is a high-performance technical polymer which mechanical and chemical resistance properties make it highly resistant to thermal degradation. PEEK tubing has one of the highest strength-to-weight ratios of all thermoplastics and can be used in numerous low and high pressure applications. It is inert to most solvents and has a smooth internal surface that increases the swept volume. However, due to a swelling effect, use caution when using methylene chloride, THF, and DMSO. PEEK materials are a good alternative to stainless steel tubing for fluid requirements.
PFA tubing (PerFluoroAlkoxy)
PFA tubing is the right choice when high optical clarity, flexibility and high continuous working temperatures are required. This is because PFA has the same unique properties as PTFE, and its operating temperature is also 260 °C. However, unlike PTFE, it is melt-processable.
ETFE tubing (Ethylene TetraFluoroEthylene)
ETFE resin is chemically inert and offers very good resistance to solvents. It has a stiffer structure than PTFE, FEP and PFA, which allows the tube to better resist the collapse of the inner diameter. In addition, this material offers greater durability and is less permeable to gases than other types of tubing. Its operating temperature can reach up to 80°C.
PP tubing (PolyPropylene)
PP material has the particularity of having a good resistance to many chemical solutions, be it an acid or a base. This aspect makes it a highly appreciated material for many standard applications.
In terms of chemical resistance, silicone tubing has all the characteristics of the other materials presented above, but is translucent and very flexible. This material is also very resistant and biocompatible. An important characteristic of silicone tubing is that it is completely autoclavable, which may be necessary for certain biological applications.
Tubing and connectors
As explained in details here (Internal volume, swept volume, dead volume in microfluidics), it is important to choose connectors that reduce the internal volume as much as possible. Darwin Microfluidcs therefore offers a selection of tubing and connectors with low internal volume, which you can find in the Tubing and Fittings & Connectors sections.