The recommendations below are based on my experience with single-use systems, along with suggestions by technical experts from three tubing suppliers: Steve Wilkowski of Dow Corning, John Stover of NewAge Industries, and Christopher Shields of Saint-Gobain.
IMPACT OF FLUID AND PROCESS CONDITIONSThe first factor to consider when selecting tubing is the nature of the fluid you want to transfer. In single-use bioprocessing, fluids range from proteins or other biological solutions to strong pH adjusters and buffers. Biologicals may be sensitive to ultraviolet light or oxygen, and require opaque or low gas permeability tubing. Acids and bases must be used with chemically compatible tubing. In all cases, it is necessary to select tubing grades with low extractables to ensure minimum levels of leachables.
Once biological stability and chemical compatibility requirements are defined, processing conditions should be considered, including process temperature, pressure, time, and sterilization conditions prior to use. Single-use bioprocesses are generally conducted at temperatures below 40 °C, so most tubing options are compatible. If tube welding and/or sealing is required on the system then meltable tubing will be needed, whereas the use of only quick-connects or sterile connectors eliminates this temperature requirement. Similarly, if the tubing is to be autoclaved, it should be resistant to at least 125 °C.
The next process condition to consider is pressure. Although the lowpressure limits of single-use polymerfilm biocontainers generally limit pressure requirements for system tubing, tubing used upstream of sterilizing filters that are integrity tested prior to use is an exception. Depending on the grade of filter and integrity test method, test pressures can range from 40 psi (2760 mbar) to 70 psi (4825 mbar), or even higher with some mycoplasma or virus filters. To accommodate this, high durometer, braided or otherwise reinforced tubing must be incorporated upstream of the filters to ensure suitable pressure rating for integrity testing. Another exception is where peristaltic pumping is used to drive the process fluid. Tubing selection must consider the strength of the tubing to provide consistent flow and low generation of particulates. Tubing grades recommended for peristaltic pumping are typically qualified for much longer service than would be applied in most single-use applications, but failure to consider pumping suitability after sterilization can lead to significant problems.
Sterilization conditions must be considered when selecting tubing. Most single-use applications are gamma irradiated for sterilization and consequently require gamma stable tubing (generally up to 50 kGy dosage), but it is not uncommon to apply autoclave sterilization for some tubing manifolds and filtration systems, especially during process development and early phase clinical batch manufacturing. The desired sterilization method must be considered in tubing selection. Information on gamma sterilization is provided in the BPSA Guide to Irradiation and Sterilization (1).