04/13/2021 | Research meets practice

Single-Use-Systems

A question of character

According to a recent study, the market for single-use equipment in biopharmaceutical production will reach $33.0 billion by 2027. The fast market penetration leads to practical questions regarding the selection and characterisation of single-use systems.

Over the past 15 years, single-use systems (SUS) have become an integral part of biopharmaceutical production. Today they come in various sizes and specifications and for many different processes. Single-use technology is of considerable importance especially at laboratory and pilot scale, but also for the production of biopharmaceuticals and biosimilars. In addition, continuous production strategies with single-use-systems are becoming more relevant. The main application focus of SUS is on the manufacturing of protein-based biotherapeutics from mammalian cell cultures. But they also play a role in the cultivation of plant cell cultures, microorganisms and algae as well as for special products in the food and cosmetics sector. The rapid development with a broad range of technological options has lead to new questions: How do users select the appropriate equipment? How can different single-use systems be compared with each other and to “conventional” equipment?

The fokus lies on

  • A standardised catalogue of experimental methods to determine relevant parameters for the characterisation of single-use bioreactors and mixers
  • Evaluation and validation of these methods
  • Models and criteria for characterisation and scale-up of single-use bioreactors and mixers, mainly in relation to mass transfer

In the laboratory, disposable bioreactors are the rule. Now they are becoming increasingly popular on a production scale as well.

Characterisation from a process engineering perspective

A variety of disposable bioreactors and mixing systems with a volume of up to 6,000 litres (for bioreactors) or 5,000 litres (for mixers) are currently available. These systems differ in terms of the type of power input, mixing and gassing strategy. It is therefore not easy to compare or select a system for a planned application. These questions are addressed in the recent publication “Recommendations for process engineering characterisation of single-use bioreactors and mixing systems by using experimental methods (2nd edition)”. The authors are members of the working group “Up-stream processing” of the DECHEMA expert group “Single-use technology in biopharmaceutical manufacturing”, in which experts from industry and academia work together to provide the community with knowledge-based guidelines. These recommendations are intended to make single-use bioreactors and mixers easier to compare among each other and with conventional glass and stainless steel bio-reactors. Standardised test methods are used and provide manufacturers and users with objective criteria for comparison.

The validated standard operating proce-dures described in the publication provide users with a uniform set of methods to characterise single-use bioreactors and mixers from a process engineering point of view. They can also be applied to reusable systems.

The methods are applicable to single-use systems in different scales and designs and for cell culture and microbial applications. Compared to the 1st edition of the publication, a new method for the determination of the volumetric mass transfer coefficient (kLa value) has been introduced and formulated in a generally applicable manner. The experimental evaluation method now corresponds with the underlying theory of mass transfer as it is present-ed in relevant textbooks on the subject. To support the users of single-use equipment in the application of the new experimental method for determining the kLa value, the working group has also developed an evaluation tool based on Microsoft Excel.

"Single-use systems are popular for growing mammalian cell cultures."

Characterisation with biological approaches

Process engineering characterisation as described above is of utmost importance – but it often provides information on only the ideal bioreactor design or scale-up. A useful supplement is the biological microbial characterisation of bioreactors. This approach is concerned with the evaluation and comparison of the biological performance of a system.

With using a model organism in combination with a standardised cultivation strategy, a bioreactor can be evaluated for a desired process from a biological perspective. The DECHEMA working group “Single-Use microbial” within the expert group “Single-use technology in biopharmaceutical manufacturing” developed a standard process model based on Escheri-chia coli. This microorganism is readily available, grows quickly and has great relevance in the biopharmaceutical industry. The use of a classical medium and a defined process under real and standardised conditions with substrate concentrations changing over time also enables the dynamic investigation of the driving force of oxygen. The classical kLa value measurement method according to the process engineering characterisation can lead to problems at high oxygen inputs. The reason is the often slow response time of the pO₂ probe, which can strongly falsify the measurement results and thus limit the measuring range. Since microbial processes in particular place high demands on the bioreactor system with regard to oxygen transfer, this has a special significance. Thus, the E. coli model process makes it possible to overcome such problems by determining the kLa value during cultivation. Moreover, heat removal can also be investigated in parallel. The E. coli model process is a simple batch process which can be conducted within one working day. An Excel tool for standardised data evaluation is also available. With this approach, single use and reusable bioreactors can be compared under real process conditions, thus sup-porting the investigation and evaluation of various growth-related parameters.

-Recommendations for process engineering characterisation of single-use bioreactors and mixing systems by using experimental methods (2nd Edition), DECHEMA, Dezember 2020

-Recommendation for biological evaluation of bioreactor performance for microbial processes (2nd Edition), DECHEMA, September 2019

Autorin: Dr. Karin Tiemann, Themensprecherin "Pharma”, DECHEMA e.V.

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