Microbial Barrier

Microbial Barrier is the property of medical packaging substrates to resist the passage of microbes.

For air impermeable substrates such as polymeric films, the property is demonstrated using a Gurley porosity meter. For air permeable substrates, the process is somewhat more complex, as the ability of the substrate to resist the passage of microbes while allowing the passage of air is related to pore size, air flow rate and a property called "torturous path". One test, known as the LRV method, involves passing air laden with bacteria through the sample at a high flow rate, capturing the microbes that pass through and growing them out in a suitable medium. Counting these and comparing this number with the number of challenge microbes shows how much the test specimen reduced the bacteria count. Since the difference between the number of challenge and counted bacteria is large, it is reported as the log reduction value. For example, if the challenge was 1,000,000 and the number penetrating was counted at 10, the log reduction value would be 5. While no industry standard has been generally accepted for LRV, the method is useful to compare different medical grade papers and non-wovens. A second newer method using aerosol filtration theory and laser particle counting rather microbiological techniques has also been found to be useful. This method is faster, less destructive to the test specimens and involves a concept called maximum penetration rate. This property is determined by graphing the penetration rate at various flow rates and reading the maximum penetration rate from the curve. (Note: PTC does not perform either of these tests in house, but rather has partnered with outside laboratories to have this testing done.)

ASTM F1608 Standard Test Method for Microbial Ranking of Porous Packaging Materials (Exposure Chamber Method)