All laboratory plasticware contains extractables. These are the compounds in polymers and resins that, under certain conditions, might migrate into anything that contacts the plastic. Extractables can end up in cell-culture media, serum, additives or buffers stored in plasticware. As a result, cells in culture come in contact with many sources of extractables, from filters and flasks to pipettes and multi-well plates, and that interaction could impact the cells.
Keeping track of the extractables that cells encounter is complicated. The same polymer can contain different additives depending on the manufacturer, which changes the potential extractables. The impact of extractables on a cell culture depends on the cell line and how the plasticware is used. Exposing a plastic to a solvent or high temperature can change the quantity of extractables that may leach into solution, for example.
Even when manufacturers test laboratory plasticware for extractables in line with best practices, that data will not cover every possible application. The safety and appropriateness of plasticware for individual cell-culture experiments is a joint responsibility of manufacturers and the scientists using the devices.
The concerns for cell culture contamination
Extractables in plasticware generally come from three sources. First, a resin manufacturer adds additives to enhance the performance of the plastic such as to improve its rigidity, clarity, chemical resistance or temperature compatibility, for example. These additives come from more than 40,000 common compounds. Second, the plasticware manufacturer uses another set of additives such as slip agents to add in manufacturing. Third, contamination can add unintended materials, such as heavy metals to devices.
Given the wide range of potential extractables, the high number of cell lines used in research, and the complex workflows in cell culture, tracking all of the potential problems proves nearly impossible. Consequently, there is currently no wide-ranging study of the impact of extractables on cell lines.
Research can reveal known dangers such as tris(2,4-di-tert.-butylphenyl) phosphite. It is an antioxidant used to improve a plastic’s stability in storage by protecting it from thermo-oxidative degradation. This additive can be used in a wide range of polymers, but its derivatives can be toxic to CHO cells.
The broad array of extractables that might be used and exposed to a variety of conditions create a need for testing.
Testing plastic labware for extractables
All laboratory plasticware contains extractables and only testing can determine the extractables specific to that piece of labware. The United States Pharmacopeia (USP) provides testing methods for extractables. The primary standards are USP <661> for plastics and USP <665> for packaging. With these standards a manufacturer can test plastic labware and packaging for extractables. The resulting data consists of a list of the compounds and their relative concentrations.
A laboratory must test how the labware will respond to being used in specific applications. An extractable’s impact on a culture depends on the cell line, the length of exposure and the conditions, such as pH or temperature. The exposure is also cumulative as cells or media, and other materials, encounter multiple different surfaces during culturing.
It is important for scientists to review the general toxicity data provided by the manufacturer and consult the available literature for data on specific applications of plasticware. If that information fails to cover a laboratory’s plasticware and application needs, the team of scientists working on the particular cell culture can perform their own testing.
Plastic labware: Making the right choice
Reliable plasticware for cell culture should ideally meet USP Class VI, which is a plastics designation from General Chapter <88> of the USP and National Formulary. This standard is a general indicator of toxicity of the plasticware including its extractables.
High-quality plasticware is typically made from virgin resins which reduces uncertainty in the composition. It is also important that manufacturers carefully monitor extractables, maintain knowledge of potentially problematic ones, minimize the use of additives where possible, impose change-control in plasticware, and run rigorous testing procedures. Meeting these standards comes with costs and so lower-cost plasticware is likely not going to be subject to the same level of quality or control.
All plastics contain extractables. This applies to labware as well. For the best protection against extractables damaging cells in culture, knowledge gives scientist an edge—knowledge of the approach taken during manufacture, knowledge of how the plasticware has been tested for extractables before arriving at the laboratory and knowledge of how it is being used by peers around the world.
Scientists who stay updated on the potential extractables in labware, and the possible impacts, are better positioned to minimize the odds of cell-culture contamination. To make the best decision a scientist can talk with manufacturers and other scientists before picking plasticware for their cell-culture projects.
About the author: Nate Starbard is Senior Product Manager, Filtration at Thermo Fisher Scientific.