A newly revised British Standard describes how to perform microbial barrier testing using the methylene blue particulate penetration method. This blog post explains why the standard has been updated and why it should be used by medical device manufacturers.
So called “terminal sterilization” is the process of sterilizing a product in its final container. The product will very often be a medical device. However, designing packaging for terminally-sterilized medical devices isn’t easy. The device and its packaging must be combined to create a product that performs efficiently, safely and effectively in the hands of the user. Meanwhile many factors influence the packing system design and choice of materials. These include the nature of the medical device, its intended sterilization method, how it’s going to be used, transported and stored, and its expiry date. Developing the right packaging is both critical and complicated.
Requirements and test methods
To help with terminal sterilization packaging design, two series of international standards set out requirements and test methods. They are the BS EN ISO 11607 series and the BS EN 868 series. In particular, BS EN ISO 11607-1:2020 specifies the basic attributes required of materials and pre-formed systems, and also considers the wide range of available materials, devices, packaging system designs and sterilization methods.
Among its requirements this standard requires that porous materials provide an adequate microbial barrier to microorganisms. This gives the sterile barrier system integrity and safeguards the product.
The standard also notes that there’s no universally accepted method of demonstrating microbial barrier properties. However, it goes on to say that evaluation is typically conducted by challenging samples with an aerosol of bacterial spores or particulates under defined test conditions. The standard also lists in an annex the standardized test methods that can be used to demonstrate compliance with its requirements. The test methods aren’t included in the international standard, but it does reference where they can be found, including in BS 6256.
The British Standard
It’s at this point that BS 6256:2021 Packaging for terminally-sterilized medical devices – Method for determination of methylene blue particulate penetration becomes important. This updated British Standard describes how to demonstrate the performance of a porous microbial barrier using the penetration of particles of methylene blue. As noted, this method is listed in BS EN ISO 11607-1:2020 as one of the possible methods of demonstrating microbial barrier properties.
The 2021 standard updates the version that was published in 1989. That standard specified requirements for materials, performance, marking and packaging of steam sterilization paper bags, as well as included the all-important test method for determining methylene blue particulate penetration.
For 2021, we’ve stripped out all the content in the 1989 version that has been superseded by content in the BS EN ISO 11607 and the BS EN 868 series. We’ve also added in some content that was previously referenced, but found in two now-withdrawn British Standards. We’ve promoted the test method into the body of BS 6256 and have ensured that everything in the revised standard is up to date with current practice.
The result is a standard that medical device manufacturers will adopt if they want to demonstrate conformity with the requirements of BS EN ISO 11607-1:2020 using the methylene blue method, since it is the only standard where this test method is to be found.