Representatives from industry supplier companies address innovations, reliability, barriers to adoption, and the role of singIe-use bioreactors in bioprocessing.
By: Randi Hernandez
While the overall trend toward single-use bioreactors is generally positive, users continue to have some concerns, limiting the widespread implementation of these technologies. BioPharm International spoke with industry experts about the challenges of implementing disposable technologies for bioreactors. Participating in the roundtable are Jacob McNeil, senior product manager, single-use bioreactors at Thermo Fisher Scientific; Warren Ang, product manager, bioprocess at Eppendorf; Parrish Galliher, founder and chief technology officer at Xcellerex, Cytiva; and Mikel Sherman, global product manager of single-use bioreactors at Sartorius Stedim Biotech GmbH.
BioPharm: What are some of the latest innovations regarding single-use bioreactors?
McNeil (Thermo Fisher Scientific): We have seen several advancements in single-use sensors and process analytical technologies to use with single-use bioreactors. In addition, there are improved control systems that allow multiple unit operation and sophisticated feed strategies improving cell yield and increasing titer with single-use bioreactors. Ergonomic features have improved. In addition, there are new systems now specifically designed for microbial fermentation.
Ang (Eppendorf): Most notable is the innovation of single-use bioreactors suitable for microbial fermentations, demanding in energy input as well as heat and mass transfer. Everyone is familiar with the glass autoclavable bioreactor and rocker bag system, which both can arguably be seen as the industry standard for many years. Now, one area of recent innovation is the implementation of rigid-wall stirred-tank single-use bioreactors. For example, the Eppendorf BioBLU single-use vessels are just like traditional glass bioreactors but made out of polymer materials.
Galliher (Cytiva): The latest innovations include higher-power microbial bioreactors, as well as improved capabilities for continuous perfusion. Single-use stirred-tank fermentation technology has been available in smaller scale since 2007, but we are currently seeing an increased interest in adopting this technology also for pilot- to large-scale processes. Single-use sensors are also on the rise, including metabolite, cell mass, and near-infrared sensors.
Facilitation of continuous processing
BioPharm: Can single-use systems facilitate continuous processing?
McNeil (Thermo Fisher Scientific): Yes. There are commercially available products that enable single-use bioreactors to be used for perfusion, thus facilitating continuous processing. These products integrate well with single-use bioreactors.
Ang (Eppendorf): Certain single-use systems are capable of continuous or perfusion processes as long as there is some mechanism or method to withdraw cell-free media. Eppendorf’s BioBLU single-use vessels have the ability to run continuous processes for both suspension cells and adherent cells whether customers are using microcarriers or a packed bed with Fibra-Cel disks to affix and stabilize cells. Both setups allow for cell-free media extraction and permit continued cellular activity inside the vessel.
Galliher (Cytiva): Yes. Because single-use bioreactors are much simpler than stainless steel, they are easier to set up for continuous processing. One example is the ReadyToProcess WAVE 25 bioreactor system that can be used with disposable Cellbag chambers designed for perfusion with an internal floating filter. This allows a small-scale continuous perfusion culture to be set up in just minutes, without the hassle of sterilizing or connecting external perfusion devices.
Another example of how single-use systems can facilitate continuous processing is the ease with which a single-use bioreactor that has been operated in a fed-batch manufacturing process can be readily changed to fit the requirements of a continuous processing operation. The main vessel stays the same regardless of the process mode but the process-specific consumable parts, such as tubing and bags, are disposable and can be tailored for each new run or campaign. The same change in a conventional stainless steel operation may require an extensive re-work of facility infrastructure, and may require an additional investment or facility validation.
Sherman (Sartorius): The same benefits of single-use will apply to continuous processing that apply to batch processing: low capital costs, faster start-up, and fast process changeover. However, there are specific challenges related to high cell densities and connectivity to cell retention systems that have to be addressed carefully.
Reducing maintenance costs
BioPharm: Can single-use bioreactors reduce maintenance costs vs. traditional bioreactors?
McNeil (Thermo Fisher Scientific): Yes. Single-use bioreactors do not require the same utility and piping infrastructure demanded by traditional stainless-steel bioreactor technology, which also reduces space requirement within valuable cleanroom space. Thus, there is much less to maintain. And single-use bioreactor hardware is relatively simple, with much of the actual technology in the single-use consumable itself. Since the consumable is disposed of after each run, there is no maintenance required. Because the single-use system is sterilized through gamma irradiation, qualifications and validation efforts that are usually required with tradition stainless-steel systems are reduced, and as a result, there is less of a risk of product contamination.
Ang (Eppendorf): One of the biggest advantages of implementing single-use vessels is the simplification and in some cases elimination of the tedious vessel prep steps that occupy enormous amounts of time and labor. Especially in cell culture applications, vessel cleaning is very important to prevent the possibility of contamination. It’s not uncommon to have a standard operating procedure that calls for disassembly of every nut, bolt, washer and O-ring. This vessel prep stage plus autoclaving and validation can take as long as 16 hours to turn around a single vessel, whereas our prevalidated BioBLU vessels can be turned around in less than 30 minutes.
Galliher (Cytiva): Yes, the maintenance costs can be reduced since the wetted parts (i.e., the contact material) is thrown away after each run. This eliminates the need for cleaning and sterilization before the next run, which saves time and the associated resource-consuming validation procedures. In addition, the risk of corrosion of stainless-steel components is minimized.
When looking at this from a facility perspective, a process that relies on single-use technology requires a less complex infrastructure in terms of piping, for example, compared to a traditional stainless-steel facility. A simpler infrastructure requires less maintenance and offers yet another opportunity to reduce cost.
Sherman (Sartorius): Single-use bioreactors significantly reduce maintenance costs when compared with traditional bioreactors. The systems themselves are mechanically simpler and the bioreactor bag and tubing assemblies require no maintenance. Also, they require far less support hardware--no CIP and SIP is required and WFI demand is significantly reduced
Barriers to adoption
BioPharm: What are some barriers to single-use bioreactor adoption?
McNeil (Thermo Fisher Scientific): Legacy stainless-steel systems that are already in place make some users reluctant to switch to the more economical, flexible, single-use bioreactors. And although it is an increasingly less common need, single-use bioreactors do not scale up beyond 2000 L. However, end-users now are frequently choosing to scale out rather than up (multiple systems rather than larger tanks).
Ang (Eppendorf): Leachables and extractables have recently been a big concern for single-use processes, especially those using polymer film bags. Even with the growing concern, suppliers are slow to explain how they are addressing it. One molecule identified by Amgen employee Matthew Hammond found bDtBPP to be detrimental to the growth of a number of strains of Chinese hamster ovary cell lines.
Galliher (Cytiva): Some barriers to single-use bioreactor adoption include:
• A much stronger dependence upon the vendor’s supply chain and the need to ensure that the vendor has as robust a supply chain as possible.
• The issues of extractables and/or leachables and the potentially negative impact these impurities can have on specific processes
• The need for additional warehousing and associated logistics to support single-use bioreactor usage
• The increased cost of consumables.
Sherman (Sartorius): Currently, there are already good single-use bioreactors for fed-batch and continuous processes up to the 2000 L scale, which today is seen as the production scale of the future given the titers of modern cell lines. However, there are still challenges to adopting single-use bioreactors to high cell density microbial cultures, especially at larger scale, as the power input and gas flow rates required for such demanding processes pose a significant challenge on single-use components and the whole bioreactor.
Issues with reliability
BioPharm: What are some of the current reliability issues with single-use bioreactors and how are they best resolved?
McNeil (Thermo Fisher Scientific): Recent challenges have related to single-use sensor options for use in single-use bioreactors. In particular, single-use pH sensors have been less than completely dependable. However, this is changing and there are reliable options on the market today. Fundamentally, single-use bioreactors are quite reliable. It is still crucial for the end-user to carefully select the product contact surface (film), hardware, and technology, among other things, that best meet their needs.
Ang (Eppendorf): Many link single-use with drawbacks such as the uncertainty of seam integrity or the apprehension of moving from one technology to another (glass or rocker bag) to a rigid wall single-use vessel because it’s new and there’s a lot of money on the line.
Galliher (Cytiva): Leaks are still occurring too frequently with certain bags and this can be a concern, especially for large-scale processes. The design of the bag needs to be robust and the manufacturing, transport, and handling steps must be optimized to minimize the risk for leaks.
Another potential issue is the availability of timely global service and support. A good relation with the vendor’s local team, with support from global expertise if needed, would be a good starting point for resolving issues quickly and conveniently.
Sherman (Sartorius): In the past two years, the biopharmaceutical industry has reported inconsistent cell growth in bioreactor bags. Recent studies have shown that this can be attributed to a degradation product of a commonly used antioxidant.
Establishing full traceability of raw materials, robust process controls, and meaningful specifications from the polymer resin to the finished bag is crucial. Another issue is related to high cell densities in concentrated fed-batch cultures. The challenge is providing the power input and oxygen transfer necessary to support these cultures and avoid foaming events. A robust agitation, aeration, and exhaust strategy is crucial to enabling these high-value processes.
The flexibility of single-use technologies
BioPharm: Does operation of a single-use bioreactor enable further single-use processes throughout the manufacturing process?
McNeil (Thermo Fisher Scientific): Single-use bioreactors generally impart flexibility and mobility within the facility. With this flexibility comes an increased need for mobility for other operations such as mixing and storage, for example. This adaptability can come from further implementation of single-use products and processes (e.g., mobile single-use mixers and storage bins). It’s generally easier to interconnect single-use products when and where desired as opposed to trying to hybridize with existing stationary steel systems.
Galliher (Cytiva): It depends. On the one hand, a single-use bioreactor can be seen as an independent unit operation that can be placed in both a single-use facility and a traditional facility. In fact, we have sold a number of hybrid facilities with a combination of both single-use upstream and stainless steel systems. On the other hand, introducing a single-use bioreactor into a traditional facility can provide benefits such as better flexibility, less downtime, and less time and effort spent on cleaning validation for that unit operation. This experience and insight can be a driver for the user to explore the opportunity to experience similar benefits for other unit operations.
In addition, single-use technology does require a different approach to manufacturing for certain areas. For example, as a manufacturer with a single-use unit operation you will need to define viable strategies of how to handle leachables/extractables, you will need to look into supply assurance to ensure a long-term viable operation, and you may need to review your on-site logistics and material transport to optimize your operation. Strategies for how to handle these aspects are needed regardless of what single-use operation you are introducing. Once those things are done for the first single-use unit operation, further development of similar strategies for additional single-use unit operations can occur.
Sherman (Sartorius): A single-use bioreactor in the process does enable further single-use processes. The advantage of rapid start-up and fast process changeover can be even further enhanced by using single-use media preparation and clarification.