Pharmaceutical & Medical Packaging News staff

Research work on microbial barrier performance of porous medical packaging materials started in 1998 and led to the creation of an ASTM test method in 2007 (ASTM F2638, Standard Test Method for Using Aerosol Filtration for Measuring the Performance of Porous Packaging Materials as a Surrogate Microbial Barrier). Now in January 2013 it has become an officially recognized standard by the US FDA, which published its reference in its online database.

Why was this work initiated, why did it take that long, and why is this important?
In the middle of the 90s work started to harmonize medical packaging standards within ISO and CEN. It became apparent that there was no globally recognized microbial barrier test method for porous packaging materials used in medical packaging applications. The available test methods were either microbiological test methods with a high variability -- difficult to control and requiring days to complete -- or physical test methods with no correlation to the real world.

A number of medical packaging companies created the Barrier Test Consortium Ltd. (BTC) in 1998 and funded research work done by Alan Tallentire and Colin Sinclair to develop a more relevant test method. The basis of the research was to prove that the filtration of microorganisms follows the same mechanisms as particle filtration.

When an air stream of particles enters a filtration medium, there are several filtration mechanisms that interact. Some depend on the particle size or on the air flow face velocity and some, of course, on the filtration medium itself. At a given particle size, capable of penetrating the pores of the filtration medium, it is possible to determine the face velocity at which maximum particle penetration occurs. The particle penetration potential at that point represents the worst case and is a function of the filtration medium, every material having its typical filtration curve.

Tallentire and Sinclair were able, with sophisticated lab equipment, to prove that spores behave in a similar way. Further, they were able to demonstrate that there was an excellent correlation between maximum penetration results obtained using spores and those obtained with particles, when the test was done in a way to find this point of maximum penetration. This correlation was validated using 16 commercially available porous packaging materials.¹

The research work was completed in 2000 and was the basis to develop a particle filtration test machine that would be reliable, reproducible, and rapid, which then was concluded with the creation of the ASTM test method mentioned above. Anybody who is interested in more details, should consider reading the articles referenced here below.²

The equipment proved to be easy to use and was able to produce results within minutes, but worldwide, there was only one machine available, and it was not until 2012 that an inter-laboratory study was conducted and the test method was revised to include a precision and bias statement.

DuPont Medical and Pharmaceutical Protection has included the test method into the DuPont Tyvek® transition protocol. The method has also been put forward to be included in the annex B of the next revision of EN ISO 11607. It will be useful for qualification of materials and process control, as well as performance and stability testing of sterile barrier systems.

References:

Stay relevant as a medical device packaging engineer 

Thierry Wagner, Regulatory Affairs Director, EMEA DuPont Medical & Pharmaceutical Protection