Mass Flow Controllers Maximize Bioreactor Performance

Protein Design Labs (PDL) has been able to maximize pilot production control by integrating an automated gas mixing system with Sierra Instruments' microprocessor-based mass flow controllers in their B. Braun Biostat fermenter.
"We had two compelling reasons for specifying mass flow controllers," says Associate Scientist Paul Sauer of PDL's Cell Culture Development group. "The first was that we needed to minimize the formation of foam in the bioreactor's headspace." To minimize foam, PDL needed to reduce the net volume of air and oxygen gases that were being bubbled into the culture medium. The rotameter PDL had been using was not adequate for measuring the low flow rates needed to prevent excessive foaming.

"We now have a high degree of confidence in our flow rate," says Sauer. "When we were using rotameters to control our flow rate at the lower edge, we experienced a substantial amount of foaming. According to the flow tube, we had been flowing at about 60 ml per minute. But after we installed the Sierra MFCs, we realized that we had been flowing at much more than that-perhaps up to three times as much. At a 60 ml setting, the MFCs reduced the foam significantly.

PDL now uses a BBB Biostat® MDC A54 automated fermenter to scale up culture strains to bulk production levels. The six-fermenter Biostat system, configured specifically for PDL, includes a digital control unit (DCU) and 12 Sierra Model 860 Smart Mass Flow Controllers. Working with the B. Braun Biostat fermenter, PDL found that Sierra Instruments mass flow controllers permitted them to flow a precise low volume of air and reduce foam formation.

PDL's second compelling reason for acquiring a Braun system with mass flow controllers was that it offered a more refined tool that provided more information.

"The mass flow controllers, by monitoring and metering gas ratios precisely, also provide an elegant and relatively straightforward way of measuring the oxygen uptake rate (OUR) using the static method 1 that was not possible with solenoid valves."