Pore size and air permeability of packaging
The most important function of a sterile barrier system is to keep the sterile state unchanged during transport and storage. Packaging which is absolutely impermeable for particles of the size of microorganisms would enable this most reliably. Since the packaging must also ensure entry of the sterilizing agent (e.g. superheated and saturated steam, ethylene oxide), the packaging possesses porous components that are permeable to gases or consists entirely of such materials. The packaging therefore acts like a filter in that it allows the gaseous sterilizing agent and the air to pass through, but should prevent microorganisms from penetrating the packaging. In order to ensure these different functions and to coordinate the packaging properties and the physical conditions in the sterilizer with the requirements for effective and inexpensive sterilization, limit values for pore size and permeability for air have been laid down in standards. In the case of paper for steam sterilization, the pore diameter may be a maximum of 35 µm. With ten samples investigated, a single value may not be in excess of 50 µm (EN 868-3). The permeability for air in flexible packaging or the filter in the case of containers is also specified.