Last week, we finished our Ask the Expert discussion on using single-use bioreactors for biopharmaceutical manufacturing. Several questions were asked about implementation of single-use bioreactors including questions on scale up, moving from stainless steel to single-use, single-use bioreactor volumes, perfusion processes, vaccine production, and tips for successful implementation. Also covered were more general questions about single-use systems including leachables, bubble size and consistency, and cost comparisons.

Due to many pressures facing biomanufacturing today including cost effective manufacturing, stringent regulatory requirements and effective capacity management coupled with the many different product demands, many companies are looking for more flexible manufacturing options. In particular, single-use bioreactors and platforms offer many advantages including enabling fast-track manufacturing strategies.

The session, was hosted by Patrick Guertin, Senior Manager, Upstream Process Development and Pilot Plant, Xcellerex, now part of GE Healthcare Life Sciences. Mr. Guertin has 25 years of experience and significant expertise in upstream process development, pilot plant operations and cGMP manufacturing for recombinant therapeutics, monoclonal antibodies and vaccines. His skill set also includes process optimization and scale-up and down procedures in microcarrier, fed-batch and perfusion modes. Mr. Guertin, provided insightful answers based on his extensive experience with the Xcellerex line of single-use stirred-tank bioreactors.

Xcellerex XDR single-use, stirred-tank bioreactors are well-characterized systems that deliver a performance comparable with that of conventional bioreactors from process development to manufacturing scale. The technology has been successfully used in a variety of different applications including mammalian suspension cell culture, microbial fermentation and cultivation of adherent cells using microcarriers.

Session question topics included:

• Scaling up in a single-use system
• Transitioning from stainless steel to a single-use system and necessary staff training
• Tips for successful implementation of a single-use system
• Vaccine production in a single-use bioreactor
• Single-use bioreactors and perfusion
• Single-use bioreactor volumes
• Cost comparisons
• Bubble size and consistency with gas spargers
• Leachables

I have selected a few of the submitted questions and answers to include below. For a full list of questions and answers, please see Ask the Expert discussion on using single use bioreactors of biopharmaceutical manufacturing.

Question:

What are your best tips for succeeding with scale-up from process development to pilot scale and then to large-scale manufacturing? We have a CHO process that delivers well in small-scale but the cell specific productivity decreases when we scale up to a 50 L single-use bioreactor. We have used conventional glass bioreactors during the development phase. The viability is fine but the cells produce more lactate in the 50 L bioreactor and we typically need to add more base to keep the pH level. Our target manufacturing scale is 1000 L. Your advice would be greatly appreciated. Thanks!

The Answer:

One of the first steps is to establish a reliable scale-down model in the bench-top reactors. We have used the XDR-10 in the scale-down mode to design and predict what we will see in the large scale systems. The control methods and hardware are critical. Special attention should be given to the dissolved gasses, both pO2 and pCO2, as these parameters will affect the amount of base required as well. You should examine a sparge porosity you are likely use at large scale. This way you can get a relative understanding of the volume to volume gas requirements. This will also provide process information on the amount of foam that may be generated. Further, this will give an early look at the potential impact of interfacial shear resulting from the sparging. The agitation rate (rpm) should also be closely considered. Often times stress on the cells/culture can alter metabolite profile.

Question:

At a recent conference they discussed problems of inconsistent bubble size from gas spargers and how it affects cells negatively. I believe this is happening to our culture. How do you control bubble size to ensure consistency?

The Answer:

A high quality sparge element with consistent pore sizes is a key feature. There are a few aspects to consider. It could be the inconsistent bubble size, but it could also be a specific sub-set or particular bubble size that is having an impact on the cell health. The range or variations of sparge element pore sizes will obviously dictate the resulting bubbles characteristics and/or foam. It also helps to have the sparge bubbles coming through the shear field of the impeller.

Question:

What would you say are the key components to successful implementation of a single use system for manufacturing biologics in CHO cells? Are there important tips you could share?

The Answer:

One of the key components for single-use system manufacturing is the system’s ability to control the critical process parameters such as dissolved oxygen (D.O.), pH, temperature and agitation within your desired target range. Then, what are the appropriate or optimal control strategies that will achieve these critical process parameters. Dissolved oxygen for example: select a gas sparge element with a porosity that will provide an adequate kLa, without generating an excess amount of foam or negative levels of interfacial shear. This can be achieved through an appropriate sparge pore size, along with appropriate agitation rate (rpm). Additionally, the XDR controller, with the capability for gas cascading (i.e. air/oxygen blending), look-up tables and PID tuning can benefit this process greatly.