Bioreactors for Cell Culture

Great progress was achieved in the past decades regarding the development of mammalian cell culture technology [2,34,98-102]. Nevertheless, the design and layout of cultivation systems and bioreactors have to meet cell-specific demands due to the special characteristics of these cells. Selection of a suitable type of cell culture bioreactor system and/or an appropriate operation mode (batch, fed-batch, or perfusion) is affected by technical, biological, economical, and regulatory considerations. 

Shear effects on mammalian cells due to hydrodynamic forces or bubble aeration in bioreactor systems are still one of the most important aspects in the design of these systems. A number of reviews have summarized the main 

Immobilization of cells can be used to enable the cultivation of adherent cells or to grow cells in tissue-like cell densities. These techniques are widely applied, as they offer some solutions to problems inherent in mammalian cell culture such as attachment of adherent cells, protection against shear stress, very high cell densities in a tissue-like environment, and preliminary separation of (extracellular) products and cells, among others. 

To date, stirred-tank bioreactors providing low shear environment by especially designed agitation and aeration systems have been developed [34]. Cultivation systems for immobilized cells such as hollow-fiber, fluidized-bed, and fixed-bed bioreactors are intended to protect the cells from stressful conditions. Nowadays, mammahan cells can be cultivated in volumes up to 20 0001 to produce the necessary quantities of a desired protein. The single-use technology for bioreactor has been successfully implemented on the industrial scale. 

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Singh V (1999), Disposable bioreactor for cell culture using wave-induced agitation, Cytotechnology 30 149-158. 

The problems with jojoba as a commercial crop are the usual ones of domestication and cultivation. It is a slow-growing plant, available only in the wild and therefore has very wide genetic variabiUty. Efforts are underway to select the most promising variants and cultivate these as a crop in the southwestern United States deserts (7). A possible alternative for producing jojoba oil is to culture plant embryos in bioreactors (see Cell culture technology). 

Three major intellectual frontiers for chemical engineers in bioprocessing are the design of bioreactors for the culture of plant and animal cells, the development of control systems along with the needed biosensors and analytical instraments, and the development of processes for separating and purifying products. A critical component in each of these three research areas is the need to relate the micro-scale to the mesoscale. 

Kalogerakis, N. and L.A. Behie, "Oxygenation Capabilities of New Basket-Type Bioreactors for Microcarrier Cultures of Anchorage Dependent Cells", Bioprocess Eng., 17, 151-156(1997). 

Kalogerakis, N., and Behie, L. A., Oxygenation Capabilities of New Generation Three Phase - Two Region Bioreactors for Microcarrier Cultures of Animal Cells, Fluidization VIII, (C. Laguerie, and J. F. Large, eds.), p. 441, Engineering Foundation, Tours, France (1995)... 

Singh V. Wave Bioreactor —Scalable cell culture for 100 mL to 500 L. Genet Eng News 1999 ... 

Several different bioreactor configurations have been described for use in cell culture and fermentation applications. These include stirred tanks, airlift, and hoUow-fiber systems. The majority of bioreactor systems in use for cell culture applications are still of the stirred-tank type. These systems have been used for batch, fed-batch, and perfusion operations. It would not be possible to adequately cover the field of stirred-tank scale-up in the space available here. Instead, this section will touch briefly on the important issues in bioreactor scale-up. For detailed methodologies on stirred-tank bioreactor scale-up, the reader is referred to several review papers on the topic [20,27,28]. 

V. Singh. Wave Bioreactor —scalable cell culture for 100 ml to 500 liters. Genetic Engineering News, April 1999. 

The direct incorporation of biological dopants into inherently conducting polymers is providing a number of new opportunities in areas such as biosensors, bioreactors, and novel surfaces for cell culturing (see Chapter 1). For example, oligonucleotides have been incorporated directly as dopants,63 as has salmon sperm DNA64 and even intact red blood cells.65... 

The total equipment purchase cost was estimated to be around 2.8 million. The most expensive piece of equipment is the bioreactor used for cell culture and virus propagation, priced at 506,000. The cost of unlisted equipment (including the equipment used in the inoculum preparation section) was assumed to represent 20% of the total equipment cost. 

The growth cycle for mammalian cells very closely resembles that of microbes. However, bioreactors for the culture of animal cells differ in several important respects from those employed in the culture of microorganisms, as well as from traditional fermentation equipment. These differences have their genesis in the nature of the walls that encapsulate the mammalian cells, especially the responses of these walls to shear stresses during culture. Indeed, some have suggested that because these walls are so thin relative to those of the bacteria and yeasts traditionally used in fermentation, it would be more appropriate to label the structure that differentiates the animal cell from its environment as a membrane rather than a cell wall. 

Sinclair et al. (79) have compared the environmental (primarily carbon) footprint of a monoclonal antibody (mAb) production facility using traditional stainless steel bioreactors with that of a facility utilizing disposable equipment for cell culture, mixing solutions, holding tanks, and liquid transfer. The mAbs are intended for use in therapeutic applications and are produced in a facility containing three 2000-L disposable bioreactors. The authors cradle-to-grave analysis took into account facility... 

One additional area that is on the horizon is the potential to optimize biologically based processes with microscale equipment. An approach developed by BioProces-sors is a Simcell platform, which is an automated miniaturized system for cell culture development. This platform is capable of running and monitoring hundreds of complex bio-reactions. This automated platform has been used to conduct high-throughput cell culture experiments for process development purposes. The system performs bioreactor operations such as cell inoculation and culture monitoring and control. 

Kalogerakis N, Behie LA. Oxygenation capabilities of new generation three phase two region bioreactors for microcarrier cultures of animal cells. In Large JF, Laguerie C, eds. Fluidization VIII. New York Engineering Foundation, 1995, pp 695-704. 

A single impeller may be sufficient in a vessel as long as the liquid level does not exceed 1-1.25 times the vessel diameter as might be the case for cell-culture bioreactors. Higher microbial bioreactors are typically equipped with several impellers (see Figure 1.15) and usually operated at high speed, resulting in tip velocities of 3 m s . ... 

AmanuUah A, Otero JM, Mikola M, Hsu A, Zhang J, Aunins J, Schreyer HB, Hope JA, Russo AP. 2010. Novel micro-bioreactor high throughput technology for cell culture process development Reproducibility and scalabihty assessment of fed-batch CHO cultures. Biotechnol Bioeng 106 57-67. 

Plant Cell Culture. Air-lift bioreactors have been favored for plant cell systems since these cultures were first studied (4). However, they can give rise to problems resulting from flotation of the cells to form a meringue on the top. It is interesting to note that some reports indicate that stirred bioreactors do not damage such cells (4). 

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