Scale-Up of Upstream Operations

Unit operations for biological products obtained from fermentation or cell culture can largely be subdivided into four parts medium preparation, inoculums expansion, bioreactor, and harvest operations. 

In development or small clinical production runs, complete liquid medium may be most convenient. Economic issues may dictate that at large-scale powdered or liquid concentrate medium be used. Shipment and storage of large volumes of complete liquid medium is less practical at scales greater than 1000 L. 

Culture medium is typically prepared by addition of the base powder or liquid concentrate mixtures to appropriate grade water. These base media mixtures usually contain amino acids, vitamins, cell membrane precursors, antioxidants, and growth factors, to mention some major categories of nutrients. Additional components, such as proteins or lipids, may need to be added separately since they are usually not compatible in powder blends. 

Liquid concentrate medium has emerged recently as an alternative to powdered medium (33,34). For liquid concentrate preparation, medium components are grouped according to solubility criteria. Liquid medium concentrates allow for the preparation of medium in-line, by automated dilution of the concentrates with water of the appropriate quality (35). This would be particularly useful in continuous or perfused processes that require constant preparation of medium. Medium cost and component stability make it a secondary option for batch or fed-batch processes. 

One consideration to bear in mind during the design of inoculums expansion is to demonstrate the genetic stability of the cell line beyond the expected number of generations required to operate at large-scale. This is usually accomplished by conducting measurements of product expression and genetic markers in cells from an extended cell bank (ECB). 

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