Integrity Testing of Flexible Containers

Defects as small as 10 μm can be detected without compromising product cleanliness using helium integrity testing.
Nov 01, 2011

Vishwas Pethe
In the biopharmaceutical industry, flexible containers such as plastic bags or liners are often used for bulk intermediate storage, cell culture resuspension, viral inactivation, final formulation, final fill, or as bioreactors. In such applications, the bag is hermetically sealed and sterilized. Sterility of the bag must be maintained to avoid contamination of the product. Any breach of the sterile condition is considered a serious risk and often results in disposal of valuable product, sometimes after significant cost and effort has been expended in the course of making it.

At the moment, disparities exist between defect sizes that are readily detectable using current on-line technology, and the speculated value for the critical defect size (e.g., the defect size at which sterility of a package is lost). Lampi established, and Chen and Keller independantly substantiated, that the critical defect dimension for bacterial penetration for flexible bags is 11 μm or less, while Gilchrist determined that the dimension was nearly twice that: 22 μm (1–4). Blakistone later established that critical defect size was 7 μm (5). Discrepancies in the critical defect size could be attributed to differences in the bio-test methodology, concentrations of test microbes, test times, or positive/negative pressure in the test bag. Therefore, one of the objectives of this article is to determine the critical defect dimension at which sterility breach occurs in biopharmaceutical containers. Such information would provide a foundationfor avoiding inherently problematic conditions, as well as for empirically evaluating and tailoring leak detection equipment for their specific needs.

The package's integrity controls microbial ingress into the package and thereby preserves product sterility. The current technologies employed in the biopharmaceutical packaging industry (e.g., vacuum bubble test, dye-penetration test, pressure-decay test, constrained-plate pressure-decay test) are only capable of reliably detecting leak rates in the range of 10-2 or 10-4 cc/s, which is equivalent to detecting defect sizes in the scale of 90–500 μm. Thus, industry needs a method of testing the integrity of a flexible container that detects defects corresponding to the minimum size needed to block water-borne microbes. This article describes a new test methodology, called helium integrity testing (HIT), that can detect such defects.