Exposure chamber techniques
We developed exposure chamber methods in order to determine the filtration efficiency of flexible or rigid medical packaging systems such as paper sheets, flexible pouches or rigid sterilization containers. Using the exposure chamber method, the filtration efficiency is determined through consideration of the airborne microbial load, the air flow through the packaging and the packaging's volume.
The exposure chambers comprise of a volume 0.5 to 1 m³. Using a vacuum pump the atmospheric pressure can be periodically reduced by 0-250 hPa which leads to an air flow through the permeable component of the packaging. Test packages are loaded with dishes filled with nutrient agar before sterilization. After exposure in the exposure chamber, the packages are cultivated to monitor the bacteria count (whole package microbial challenge test). Then the packages are opened and the number of colonies are registered (Patent No. US 8,053,210 B2; EP 1 485 135 B1).
With the mobile exposure chamber the packaging's filtration efficiencies can be measured by using the airborne microbial quality of the environment, where the packagings are used (eg. central sterile supply department, hospitals, and transport vehicles).
The mobile exposure chamber is designed for on-site application to control
the airborne microbial recontamination of wrapped sterilized products during shelf life.Using the stationary exposure chamber, the filtration efficiency is determined by defined microbiological conditions in the laboratory. A microbial aerosol of Micrococcus luteus is generated by a nebulizer. A glass impinger air sampler is used to determine the mean airborne microbial concentration in the chamber. A gas meter measures the volume of air drawn through the impinger.
The exposure chamber technique we developed consists of the following functions:
pressure-sealed chamber volume: 500 - 1000 L
periodic lowering of the inside pressure of the chamber by 0-250 hPa
increase of the airborne microbial concentration up to 5 microbes per cm³ (stationary exposure chamber)
determination of the microbe count in the air in the chamber by continuous sampling
continuous PC documentation of the air pressure in the chamber
control of the pressure gradient (hPa/s)