MET tests sample protection

Medical Engineering Technologies used hydrogen leak testing to analyse bags used to prevent cross-contamination of cryogenically preserved tissue samples


Medical Engineering Technologies (MET) of Hythe, Kent has tested bags used to prevent cross-contamination of cryogenically preserved tissue samples on behalf of the National Blood Service.



Many different tissue samples such as stem cells, gametes and bone tissues are stored in liquid or vapour phase nitrogen to maintain their viability for many years. One of the methods used to avoid cross-contamination is wrap-over bags used to create a second later of protection around samples stored in cryo-preservation vessels.



To assess the effectiveness of these bags and their construction materials as a barrier to cross-infection, MET teamed up with the National Blood Service to test a selection of bags from various suppliers. The aim was to rate the over-wrap bags for the level of protection they offer for human tissues from cross contamination in vapour phase nitrogen cryo-storage.



MET selected hydrogen leak testing, as they considered it the method best suited to the detection of the smallest of leaks. This uses a non-explosive mixture of five per cent hydrogen in nitrogen as an extremely sensitive trace gas, along with ‘sniffer’ technology to locate and quantify leaks. Hydrogen gas has very low viscosity and can leak through the smallest of holes. It also has very low background abundance, which makes it highly suitable as a trace gas.



MET supplied and operated an H2000 hydrogen leak locator to compare the performance of various methods of protection. The study successfully ranked over-wrap packaging systems in order of seal and film integrity.



Trace gas testing provides non-destructive testing of medical device and pharmaceutical packaging. MET supplies a wide variety of test equipment and associated validation services.