And when using single-use equipment, the end-user must establish a solid long-term relationship with the bioreactor manufacturer on multiple levels: quality, engineering, and supply chain. The relationship with the single-use equipment vendor is much more important on a long-term basis than it would be with a traditional equipment supplier, since the single-use parts purchase and qualification is a recurring event.
Dr. Golightly: Ironically, some of the industry’s challenges are found both with the developer/manufacturer and eventual end-user of single-use bioreactors. Again, lack of standardization resonates across all involved parties, but resolving this impasse still seems unlikely.
Just as it is difficult for a supplier to change a differentiating design option in the effort to standardize to its peers/competitors; most end-users find it difficult to contemplate the reciprocal change required to re-qualify/re-validate to a new standardized option. If we could re-start the single-use market from its nexus today, things might be different. But in reality, we now face over a decade of installed use and therefore considerable inertia against change.
There remains a persistent discomfort generally put in the category of risk mitigation/supply assurance/business continuity planning for single-use system users. Although this extends from the lack of interchangeability, it also relates to issues even further back in the supply chain, namely those few global entities responsible for the plastics and films used to create single-use systems.
Coupled to general supply assurance is the factor of unknowns associated with these critical components. Although classical L&E (leachable & extractable) studies can provide good background information, what transpires during irradiation, storage, exposure to various components in media, and how certain cell types might simply be more sensitive to certain things remains part of the generally less-well-defined aspect of cell culture bioprocessing.
Dr. Greller: The biggest challenge a cell culture user can face is nonconforming cell growth in a single-use bioreactor bag. Besides the typical issues related to scaleup known from stainless steel bioreactors, new aspects may need to be considered in a risk assessment/root cause analysis of such polymerbased alternatives.
The most discussed topic during the recent years has been leaching of trace levels of cell growth inhibiting substances from films used in single-use bioreactors. During the development of our next-generation film platform, we were able to identify such a component in cooperation with resin suppliers, our strategic partner for the extrusion of the film, and end-users providing sensitive cell lines and analytical tools.
While few bag suppliers might have the buying power to control the resin formulation used in their films as well as the extrusion process, most will need to buy films off the shelf and they may be unable to provide proper change control and traceability all the way to the resin. This may lead to concern at the user side.
Dr. Jagschies: Single-use bioreactors are relatively expensive and have to be handled correctly to avoid damage. Construction of the bags requires mechanical welding of the seams and this needs to be of the highest quality in order to ensure that welds do not come apart and result in lost sterility and consequently loss of the entire run.
The bags are at risk of mechanical failure at three key points: during the vendor’s assembly process, when being removed from the packaging by the end-user, and when being unfolded into the reactor support shell. Manufacturers are continuously looking at ways to improve the robustness of the materials and reduce the risk of such mechanical issues occurring.
The ability to work closely with a vendor is vital as both parties are involved in working to ensure that a complete QA process is in place to make using single-use bioreactors a smooth trouble-free operation. Single-use bioreactor vendors work closely with customers to address QA and so support them in minimizing their risk.
Customers are also looking for additional verification of the bioreactors, including details of leachables and extractables etc., as well as support in the modification of existing processes to develop processes designed specifically for single-use bioreactors. In order to be successful, transferring a process from traditional stainless steel to a single-use bioreactor requires modification to the process because of the difference in features, such as mixing and gas requirements. In addition, customers are also looking to dual-sourcing to address security of supply.
Mr. Lamproye: The main challenges for users are scalability and the transfer from disposable systems to traditional steel cultivation technologies. Nowadays, disposable bioreactors are commonly used from early development steps to clinical trials. Generally these do not offer enough capacity to fulfill the material needs of Phase III trials.
Being sure the disposable systems are representative of what the user will experience with a traditional steel reactor is a key success factor. The problem is the same when scaling-down.
Another thing that has to be addressed is leachables. These elements from the bag that can be released into the culture medium can interact with the product, generating safety or quality issues. Previously, due to limited use of single-use systems, regulatory authorities only required limited data. Since the use of disposable solutions is spreading, it is now necessary to regulate the way users deal with them. Identification and characterization of leachables are a minimum, but it can also be necessary to demonstrate that they are treated in the appropriate manner during the downstream processing step to limit any risks.
Mr. Marner: One challenge for users is similar to that for manufacturers: How can users quickly translate traditional models of bioreactor performance to a single-use architecture?
Users also face the challenges of supply uncertainty, and they want to know that they have a stable partner that provides consistent single-use components year after year. Despite the rapid expansion of single-use technology in the past several years, we see that customers continue to gravitate toward suppliers that have solid histories of quality systems developed using stable supply chains.
Mr. Phillips: Beyond learning what capabilities single-use bioreactors can offer them, customers are faced with the challenge of knowing when to apply single-use technology and when not to.
The other great challenge for customers is that the single-use market is still relatively new. They can have trouble finding exactly what they need and being able to rely on the technology. Some manufacturers are not fully testing products, which results in leaks or contamination, either of which can have hugely negative impacts.
Dr. Rapiejko: One of the biggest challenges for users of single-use bioreactors is the associated inconsistency and unknowns around films and plastics. This is highlighted by Steiger and Eibl (Chemie Ingenieur Technik 2013, 85, No. 1-2, 26–28), which showed that 20% of bioprocess containers tested had a negative impact on cell growth or viability for some cell lines. Lot-to-lot variability is also known to exist for some vendor’s process containers, further adding to the complexity.
The industry is working to understand these issues through partnerships with manufacturers, but this remains a challenge. Users embracing single-use bioreactors are also challenged by concessions they must make to their bioreactor manufacturer. They must accept the basic design (e.g., impeller, sparger, etc.), and limits on its customization. This can be difficult for process engineers who have developed and optimized designs over several years or decades.
Manufacturers must work closely with users to engender their trust by demonstrating that good science and engineering practices were used as the foundation for the design and development of their single-use bioreactors.
Mr. Serway: Ease of set up of a perfusion system to a disposable bioreator due to limited port sizes and locations available, as well as maintaining good agitation/mixing of the cell suspension without damage to cell/cell viability.
Mr. Whitford: As the technology is so new, the field of providers is young and robust. This creates a challenge for users to select the particular product and system provider meeting their diverse and dynamic requirements.
Factors users must consider include the manufacturer’s history in this field, ability to maintain and support the installation throughout the product lifecycle, and their demonstrated propensity to innovate and keep up with the field over time.
Another challenge arises from the nature of the industry. In small molecule manufacturing materials, and equipment are often sourced from disparate and independent providers. But in many cell-based manufacturing modes there is a harmony and interdependency between the manufacturing equipment, the culture materials employed, and efficient operation of the system.
Therefore, it is incumbent upon the user to either carefully validate each component of the platform as part of a compiled system, or to purchase from a supplier who can supply validated systems of equipment including SUBs, culture materials such as media, and any required ancillary tools such as mixing and storage supplies.
Dr. Zoro: The relative fragility of thin film reactors (vs. stainless steel) neccesitates complex, painstaking, and time-consuming manual handling procedures when preparing the reactors and connections. Sterile sampling is also key issue, requiring sacraficial connector arrays and/or considerable operator time for drawing samples, particularly for multiparallel small scale systems.