Chapter 6: Plant and Animal Cell Bioreactors

Function Microbial System Plant Cell System Bulk mixing To achieve homogeneity of chemical environment in the presence of nutrient sink and product source terms To achieve homogeneity of biomass distribution in the presence of sedimentation due to large size of cell aggregates Oxygen transfer To meet oxygen supply requirements of the biomass, often limiting in scale up To meet oxygen requirement of the growing biomass without depleting the concentration of gaseous products below a critical level Shear Usually unimportant. Usually very important due to large size of cells and aggregates.

Mammalian Cells

Stages in Cell Culture Primary cells Secondary cells Tissue taken from its original site and transferred to an artificial medium for growth Requires the recurrent sacrifice of animals Secondary cells After the first passage of primary cells Have a finite number of passages Continuous or transformed cells Cells that can be subcultured indefinitely

Types of Mammalian Cells Anchorage Dependent cells Require surface attachment to grow They include mostly primary cells and cell lines such as : -Chinese Hamster Ovary cells (CHO), Baby Hamster Kidney Cells (BHK) and Human Fibroblast cells (FS-4)

Suspension cells Cells not requiring any surface attachment Examples are: HeLa cells, hybridoma cells and other tumor cells

Some Aspects of Bioreactor Design Design of Bio –Engineering Equipment Vessel Design (Height : Diameter ratio) Agitation Mechanical seal Stirrer Inlet air Aeration Ports Exhaust air Inoculation port Sampling valve/port Harvest Media Addition Air sterilization

Special Considerations for Mammalian Cell Bioreactor Cells are shear sensitive thus shearing should be minimized Oxygenation through bubbling may damage cells Round bottom culture vessel with aspect ratio of 2:1

Special Modifications Aeration and Mixing

Modes of Operation Batch mode of operation A well established production method; generally used for vaccines and biopharmaceuticals. Low yield of product Batch The operation modes all lack in the ability to select or differentiate between viable and non-viable cells Fed-batch mode High density culture Longer operation and higher yield Accumulation of dead cells and debris Fed-batch Feed Continuous mode High density culture Product can be harvested continuously Limited dilution rate Harvest Feed Continuous

Perfusion Culture Cell Separation Methods in Perfusion Mode High density culture Product can be harvested continuously High productivity Dilution rate not limited Separation of viable and dead cells possible Harvest Cell separation device Feed Recycle Cell Separation Methods in Perfusion Mode 1. Filtration 2. Centrifugation 3. Gravitational settling 4. Immobilisation All Perfusion strategies must meet the following conditions: 1. Stable operation 2. Easy to scale up 3. Versatility:The process can be applied to any cells and any culture medium Volume of the production unit is smaller than normally required with batch culture. Lower investment cost on the bioreactor.

Spin filter bioreactors Cell settler for perfusion culture Perfusion Culture Systems Spin filter bioreactors Cell settler for perfusion culture Centrifugal bioreactor Tangential flow or crossflow filtration device for perfusion culture Packed-bed basket perfusion culture Celligen packed-bed basket reactor (Wang et al.,1993)

Make a comparison of an animal cell bioreactor with a plant cell bioreactor.