Biocompatible wetted materials are important to avoid contamination
Bioprocessing has very specific requirements for wetted materials, in order to avoid contamination of the bioreactor environment. The main potential contaminants are materials outgassed from elastomers, typically adsorbed onto elastomers during polymerization. While outgassing most commonly occurs under vacuum conditions, it can be a concern in any situation where a pressure drop is present (such as gas input lines for bioreactions). A number of studies have demonstrated outgassing from elastomeric components under a variety of conditions.1 Outgassed components are of concern as they are thought to be inhibitory towards microbial growth and have been shown to have toxic effects in whole animal studies. 2
The ASME Bioprocessing standards call out for specific materials used in construction of bioprocessing equipment. 3 While mass flow meters typically lie outside of the sterile boundary, and should not have contact with the final product, it is still good practice to follow the BPE-2016 standards. Many high performing mass flow meters utilize elastomers to take advantage of the material’s superlative sealing properties, which result in lower leak rates and higher precision mass flow measurement. Mass flow meters also require rigid materials (ranging from inexpensive ABS plastics to exotic stainless steels) for their flow bodies and process connections. Outgassing is a concern, as outgassed components would likely pass through sterilizing filters and are a potential source of process contamination. Therefore the BPE-2016 standards are often applied to mass flow meters, regardless of their position relative to the sterile boundary. 316L stainless steel can be used for elements in the flow path, including flow bodies and laminar flow elements. Less frequently considered, but of greater potential concern are the elastomeric components used in high performance mass flow meters.
To avoid the impacts of outgassing, only USP Class VI elastomers with good permeation resistance should be used. Outgassing is only able to occur after materials have first been permeated – so resistance to permeation is the critical factor in preventing subsequent outgassing. Marco rubber and plastics has published a nice comparison of permeation rates of common elastomers indexed with commonly used gasses. 4 Additionally, elastomers used should be FDA certified. USP Class VI FDA certified elastomers have minimal reactivity and are certified safe for hygienic use.5,6 Finally, only certain corrosion resistant elastomers are recommended by the BPE-2016 standards. While several types of elastomer are available, Viton brand FKM (Fluoroelastomer ASTM D1418) meets the BPE 2016 standards, as well as being available in USP Class VI FDA certified form. Viton branded FKM also carries the implicit guarantee of Dupont’s high quality manufacturing standards. Viton’s outstanding sealing characteristics, permeation resistance, high performance and available certifications make it a logical choice for these applications.
It is also good practice to use only Animal-Derived Ingredient (ADI) free products in bioprocessing. This avoids another potential source of contamination, as well as being an ethically sound practice. Choosing a mass flow meter which meets these requirements for compatibility should be an important part of any purchasing decision – and helps avoid potential contaminations of bioprocesses.
1) Appl. Sci. Converg. Technol. 26(5): 95-109 (2017) http://dx.doi.org/10.5757/ASCT.2017.26.5.95
2) D.B. Meyers, J. Autian, W.L. Guess, Toxicity of Plastics Used in Medical Practice II.: Toxicity of citric acid esters used as plasticizers, Journal of Pharmaceutical Sciences, Volume 53, Issue 7, 1964, Pages 774-777, ISSN 0022-3549, https://doi.org/10.1002/jps.2600530716.
3) ASME – STANDARDS – Bioprocessing Equipment – ASME.org, www.asme.org/products/codes-standards/bpe-2016-bioprocessing-equipment.
4) O-ring Permeation Coefficient Chart Of Common Materials – Marco rubber & plastics, https://www.marcorubber.com/o-ring-permeation.htm
5) Usp Class VI – Foster Corporation, https://www.fostercomp.com/stewardship/usp-class-vi
6) Usp Class VI Testing – Danielly Riberio, https://www.tbplastics.com/usp-class-vi-testing
Mic Chadoir, Ph.D.