TYPES OF TUBING FOR SELECTION
The most common types of tubing used in single-use applications are silicone and thermoplastic elastomers. Silicone tubing
has a long history of safe use for a broad range of bioprocess fluids, and provides high temperature and gamma radiation stability.
Other benefits include flexibility, translucency, biocompatibility, and smooth bore for low adsorption and particulates. Peroxide-cured
grades have been successfully used in laboratory and clinical applications, but platinum-cured silicone is preferred for single-use
systems because of lower extractables. Braided grades are available for high pressure applications. Silicone tubing cannot
be thermo-welded and is limited to pre-assembled systems or connections using quick-connects or sterile connectors.
For tube welding and sealing applications, thermoplastic elastomer (TPE) tubing is required. These are proprietary formulations,
commonly referred to under trade names, and have a good record of safe use and are also preferred where reduced adsorption,
absorption or gas permeability is desired, though they do not have the transparency of silicone tubing. Other specialty formulations
of tubing are also available.
Both silicone and thermoplastic elastomeric tubing are manufactured in numerous proprietary formulations, resulting in different
extractables profiles and other properties. A case study was reported several years ago on the effect of tubing material on
the bubble point values of downstream sterilizing-grade filters (7). Poly(dimethlysiloxane) silicone oil leached from some
grades of tubing (both silicone and thermoplastic elastomer) and was adsorbed on downstream filter surfaces. This reduced
the critical surface wetting energy of the filter membranes, thus impacting post-use bubblepoint values, causing false test
failures. Tubing used upstream of sterilizing filters, and infinal filling, should be considered for low silicone oil, along
with other leachables.
It is common for new users of singleuse systems to consider choosing whatever grade of tubing they have experience with in
their laboratory or clinicalbatch processes, but it is also important to consider the selection and sourcing of tubing by
the single-use system integrator. It is also advantageous for integrators to limit their approved tubing sources, including
inventory control, cost-efficiency, and generation of additional qualification studies (e.g., post irradiation extractables).
Good integrators will also establish quality agreements for traceability and sourcing of raw materials (e.g., resins and elastomers),
change notification protocols, and conduct supplier audits. Consequently, once your fluid and process requirements are defined,
it can be beneficial to consider suitable grades among those already selected and qualified by the single-use system integrator.
Jerold Martin is the senior vice-president of global scientific affairs at Pall Life Sciences, Port Washington, NY, US. 516.801.9086, email@example.com
Jerold is also the chairman of the board and technology committee of the Bio-Process Systems Alliance.
1. BPSA, Guide to Irradiation and Sterilization of Single-use Systems (2008).
2. USP 29–NF 24 General Chapter <87>, "Biological Reactivity Tests, in vitro," 2525.
3. USP 29–NF 24 General Chapter <88>, "Biological Reactivity Tests, in vivo," 2526.
4. BPSA, Component Quality Test Matrices Guide (2007).
5. BPSA, Guides to Extractables and Leachables from Single-use Systems (2008).
6. BPSA, Guides to Extractables and Leachables from Single-use Systems (2010).
7. B.K. Meyer and D. Vargas, PDA J. Pharm. Sci. Technol. 60 (4), 248–253 (2006).