Presented by Jurjen de Jong
Jurjen de Jong is a bioprocess scientist at Patheon Biologics, Netherlands
Patheon performs cell line development (in-house and with partners) using single-use and stainless steel bioreactors. The company has the capability for fed-batch culture up to 2,000 L and perfusion cell cultures up to 500 L. Therefore, it needs a robust method of controlling and monitoring our bioreactors 24 hours per day, seven days per week.
In this presentation, de Jong described how Patheon is using multifermentation control system (MFCS/win) software (Sartorius Stedim Biotech), which is a supervisory control and data acquisition (SCADA) application. MFCS/win is used to control, monitor, and log parameters from a digital control unit (DCU) on a bioreactor. With MFCS/win users can, for example, send a pH set point (or profile) to the DCU and monitor (and alarm) the values. The resulting controlled values can be plotted or exported for review or approval.
MFCS/win operates in 15-second cycles during each of which set parameters are monitored, a calculation is carried out, and a data point is created. The software can run an S88 (ANSI/ISA- 88) recipe, which is a standard protocol for addressing batch-process control and allows a set point to be programmed or calculations such as media flow rates or cell density to be run. With the S88 recipe, users can work in blocks of operations such as a media-control phase to switch a calculation on or off. Users can set variables, including pH and stirrer speed through MFCS/win using a set point. Variables also can be changed as the result of a function or decision. For example, if the oxygen level is below a specified value, the software can automatically increase the stirrer speed if that has been set as the decision point. Patheon runs many perfusion processes. Using optimized media, the company’s processes are capable of ninefold increases in titers (for example) from 1.1 g/L to 11g/L. Such perfusion processes use continuous addition of nutrients and continuous removal of metabolites, while cells and product are retained in a bioreactor using tangentialflow filtration (TFF) or alternating tangential flow (ATF) applications. Many of the company’s perfusion processes are controlled using MFCS/win with a recipe to ensure that every step is performed at the correct time. Patheon uses two different recipes: For one, all the set points alarms are predefined. The second is a default recipe for which the parameters are adjusted by input on the variables, which is useful for running R&D-type of experiments. The use of recipes allows repeatability and can be used for range finding in (for example) design of experiments (DoE).
To implement the MFCS/win control processes into our perfusion process, we initially produced a flow chart of how the processes should run. We mapped the start phase of the process and asked ourselves, “Is the bioreactor inoculated?” We then went through setting pH, alarms, and controls and determined whether we needed to initiate gravimetrical flow controllers. We mapped the next exponential phase to allow controls where (for example) media feeds are adjusted based on cell density. We specified that if a specific cell density is reached, then the next stationary phase is begun during which different controls may be required such as fixed media flow and active bleed control. To implement that process flow into MFCS/win, we need a method of inputting cell density calculations. This comes from the sample data manager in the software, which calculates viable cell density and adjusts media flow rates automatically to maintain specified cell density. If we need to use a perfusion flow rate (which is lower than our pump is validated for), we can use MFCS/win for pulse-based feeding to a bioreactor. In fed-batch processes, bolus additions can be used. For example, if we want to use a low flow of 10 g/h, we use the software to calculate flow and send this to a (gravimetrical) flow controller to provide pulses of 200 g/h in three minutes, which is the equivalent of a low flow rate of 10 g/h.
MFCS/win is a useful tool for performing technology transfer of a perfusion process to different sites. As with recipes, there is translation step, and then the control principle can be transferred to different control units. Because MFCS/win can communicate with surrounding equipment through object linking and embedding for process control (OPC) connectivity, adding multiple different analytical instruments to a bioreactor is an option (e.g, to monitor biomass and use the data collected as inputs for media supply to control cell density).
In summary, MFCS/win software can be used successfully to control perfusion processes. It is useful for such applications because its one-recipe principle can be used for multiple control units, which makes process transfer simple and ensures uniformity of processes at different manufacturing sites.