Right now, there are two sterilization methods available: chemical and steam. The advantage of chemical sterilization is that there is no need for additional infrastructure, i.e., a steam connection in the lab. Smaller-scale process-development laboratories typically do not have steam readily available. The main disadvantage is that the contamination risk is higher than with steam.
The sterile barrier in the process chain is critical, and the only proven technology to keep ports sterile is steam sterilization. In most cases, however, the implications of contamination are minor in small-volume bioreactors since the value of a potential loss of a batch is low and parallel fermentation processes are run simultaneously anyway.
Steam sterilization is the most common and established technology used to sample a culture from a bioreactor. The advantages of steam sterilization begin with its reputation for robust and reliable performance, ideally suited for larger bioreactors. It has been proven to be quick, clean, and consistent.
Steam sterilization in automated sampling platforms is not without its share of vulnerabilities, however. Since the cell culture sample transport tube, part of the liquid-handling component of this automated system, has to be connected to the online sampling port, there is a risk of cross-contamination.
Also, as mentioned previously, a steam supply would clearly be required, a potentially expensive proposition. There are new developments in the lab-equipment industry, however, where offline steam supply units can provide steam without additional infrastructure in the lab (Figure 1).