Abstract
No matter the scale, stirred tank bioreactors are the most commonly used systems in biotechnological production processes. Single-use and reusable systems are supplied by several manufacturers. The type, size, and number of impellers used in these systems have a significant influence on the characteristics and designs of bioreactors. Depending on the desired application, classic shaft-driven systems, bearing-mounted drives, or stirring elements that levitate freely in the vessel may be employed. In systems with drive shafts, process hygiene requirements also affect the type of seal used. For sensitive processes with high hygienic requirements, magnetic-driven stirring systems, which have been the focus of much research in recent years, are recommended. This review provides the reader with an overview of the most common agitation and seal types implemented in stirred bioreactor systems, highlights their advantages and disadvantages, and explains their possible fields of application. Special attention is paid to the development of magnetically driven agitators, which are widely used in reusable systems and are also becoming more and more important in their single-use counterparts.Key Points• Basic design of the most frequently used bioreactor type: the stirred tank bioreactor• Differences in most common seal types in stirred systems and fields of application• Comprehensive overview of commercially available bioreactor seal types• Increased use of magnetically driven agitation systems in single-use bioreactors
Highlights
Stirred systems have a long tradition in biotechnological processes, especially in the biopharmaceutical industry (Birch 2010; Jossen et al 2017; Clapp et al 2018)
In addition to static and dynamic sealing elements, which are often made of silicon carbide, carbon graphite, or composites of both materials, static fluorocarbon, O-ring seals are required to seal the contact surfaces between the vessel, the shaft, and the sealing elements (EKATO Holding GmbH 2012). This allows mechanical seals to be used for shaft diameters ranging from 5 to 500 mm at temperatures from −200 to +450 °C, pressures up to 450 bar, and rotational speeds of up to 100 m/s (Mörl and Gelbe 2018)
The use and selection of seals or motor couplings are of utmost importance for ensuring sterility in biotechnological production processes
Summary
Stirred systems have a long tradition in biotechnological processes, especially in the biopharmaceutical industry (Birch 2010; Jossen et al 2017; Clapp et al 2018). In addition to static and dynamic sealing elements, which are often made of silicon carbide, carbon graphite, or composites of both materials, static fluorocarbon, O-ring seals are required to seal the contact surfaces between the vessel, the shaft, and the sealing elements (EKATO Holding GmbH 2012) This allows mechanical seals to be used for shaft diameters ranging from 5 to 500 mm at temperatures from −200 to +450 °C, pressures up to 450 bar, and rotational speeds of up to 100 m/s (Mörl and Gelbe 2018). In order to stir a hermetically sealed vessel, and reduce the risk of contamination to a minimum (Menkel 1992) and enable high-pressure processes at far more than 400 bar without the risk of leakage (Dickey 2015), the energy to the impeller must be supplied through the closed vessel wall (EKATO Holding GmbH 2012) For this purpose, power is transmitted using magnetic fields.
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