Portable flow meters to leak test bioreactors

Bioreactors must be leak tested to ensure all seals are tight and that there are no holes or gaps in equipment. Portable flow meters are a convenient tool to leak test bioreactors, using methods that are quantitative, non-invasive, and highly precise.

Leak test bioreactors to ensure operator safety and process integrity

Bioreactors present significant biosafety risks, especially when used to produce viral vaccines. A leak in a bioreactor may be present for a long period of time before it is detected, potentially introducing harmful viral loads to human operators. Leaks can also lead to contamination of the production area and can interfere with the cell culture. Leak testing is therefore critical to ensuring human safety and batch compliance.

Both single-use plastic and multi-use stainless steel bioreactors must be leak-tested. For single-use bioreactors, leak testing ensures that no holes were created in the plastic bioreactor bag during either manufacture or handling: these reactors should be leak tested by the manufacturer and also at point-of-use (once all handling and installation is complete, but before production begins). Together, these measures ensure the integrity of the bioreactor, significantly minimizing the health and safety risks as well as the costly, time-consuming losses associated with compromised products.

Stainless steel bioreactors, meanwhile, must be leak-tested to confirm that all seals and connection points are fully closed. The bioreactors have a large number of penetrations and inlets for equipment including gas lines, stirrers, and sensors. They are also fitted with valves, clamps, and seals, which have the potential to wear and leak. To confirm the reactor is free of leaks before the next batch, leak-testing is conducted after cleaning and sterilization cycles.

Leak testing methods

Traditionally, manufacturers of single-use bioreactors perform leak tests using helium integrity testing. These tests are highly sensitive, able to detect leaks down to 10 µm. As bacteria and other contaminants generally cannot penetrate holes smaller than 15 µm, helium integrity tests confirm that the bioreactor will remain sterile. However, after testing, the bioreactor is removed from the test setup, packaged, shipped, and installed by the end-user – all of which introduce the risk of handling damage.

Point-of-use leak tests therefore become critical, and various methods may be used. For single-use reactors, these are done to ensure that the bag is free of holes; for multi-use stainless steel reactors, these tests ensure the integrity of the reactor and various additional components that are prone to damage or leaks.

Pressure decay tests are common at point-of-use, as they are sensitive enough to detect the larger defects introduced by improper handling. These tests can be fully automated and use only compressed air, making them simple to perform in cleanrooms without introducing helium into a sterile environment where it would not otherwise be present.

Bubble tests, using soapy water or Swagelok Snoop, are simple but often imprecise, and also introduce unnecessary materials into the cleanroom.

Finally, mass flow meters and/or controllers can be used to leak test at point-of-use. A mass flow controller can be used to maintain a steady pressure flow into the bioreactor, and a mass flow meter can be used to detect and measure any leaks. Unlike the other methods discussed, the flow rate measured is precisely equivalent to the leak rate of the reactor. While these readings can be highly sensitive to fluctuations in temperature or pressure, this is unlikely to be an issue in a highly controlled cleanroom environment.

Leak testing methods are imperfect solutions

• Helium tests are highly sensitive, and most capable of detecting tiny leaks – but should not be performed at point-of-use in cleanrooms where helium would not otherwise be present. Furthermore, helium leak tests are time consuming and expensive.
• Pressure decay tests are simple and easy to perform at point-of-use – but they are less sensitive and require an operator to note pressure drops during a period of downtime.
• Bubble tests indicate the exact position of a leak – but are the least sensitive method discussed, showing only the location of larger leaks, and not recommended for cleanrooms.
• Flow meter/controller testing is fastest and can be performed at point-of-use in cleanrooms – but loses accuracy when testing large volumes, and is highly subject to environmental fluctuations. Flow meters which introduce extremely low pressure drops are likely to be most accurate and stabilize fastest in these cases.

Portable flow meters & other devices simplify point-of-use testing in cleanrooms

All of the methods discussed above have portable versions, which allow for the simplest point-of-use testing of both single-use and stainless steel bioreactors once they are already installed in cleanrooms.

To bring helium tests to point-of-use, several companies have designed portable leak testers, which are highly sensitive and much faster than traditional helium integrity tests. These devices are designed to be used at likely or suspected leak sites (such as valves) to show the size and location of the leaks.

Pressure decay tests require only measuring the pressure drop over time – making them inherently portable. Similarly, bubble tests rely on simple tools which, while not ideal for cleanrooms, can easily be transported to point-of-use.

Finally, battery-powered, portable mass flow devices are ideal for cleanroom settings. They can be charged and housed outside of a cleanroom, wiped down and brought inside, then used to leak test single-use or stainless steel bioreactors to ensure human safety and product integrity.