Why scale-up animal cell cultures?
To produce significant quantities of an animal cell culture product.
Producing small quantities is good for bench-top laboratory purposes but scale up is necessary for biotechnological purposes.
What are some potential problems to consider when scaling up?
- Ability to keep cells in suspension
- Absolute sterility
- Foaming of serum (due to aeration of the culture)
- Oxygen supply needs to be adequate for survival of cell
What are 2 waste products that need to be considered when deciding on a mode of culture?
Lactic acid - a product of glycolysis and build up of this could lead to overcoming the buffering capacity of the medium. Use Fructose of galactose to get less lactic acid buildup.
Ammonia - can inhibit growth of culture and can be overcome by a steady low concentration of glutamine.
What are the 3 types of mode of culture for scale-up?
- Batch culture: the whole culture is harvested at a certain point after inoculation
- Semi-continuous system: a portion of the culture is removed at intervals and fresh medium is introduced to replenish the loss
- Continuous or perfusion culture: the culture medium is continoually harvested with respect to cells or product and fresh medium is continuously added. Overlfow rate = feeding rate
What is a stirred tank reactor?
A bioreactor that has a round bottom, water-jacketed and has a impeler to agitate the cell suspension.
Size varies from a small bench-top 1-5L to commercial up to 10000L.
Typically made of stainless steel.
What is an airlift reactor?
An airlife reactor is culture fluid circulated by the introduction of gas at the base of a draught tube. The riser (where gas is introduced) and flows upwards while the downcomer is parallel to the riser and connected to it at the top and bottom and flows downwards.
There is no need for moving parts and reduces the risk of contamination.
One downside is the air/liquid interface that the top of the vessel, when the bubbles burst at the liquid interface may cause cell death.
What is cell entrapment?
It is a method of immobilizing cells for large-scale culture in the reactors in that animal cells are entrapped within agarose microbeads 100-200um in size.
Cells are mixed with liquid agarose and put through bead forming device.
Ideal for continuous/perfusion systems
What are some advantages to using cell entrapment as a method of immobilizing cells?
- Increases the stability of normally fragile animal cells
- Makes it easier to seperate the secreted products from the cells
- Able to maintain the cell culture at high cell density for a longer period of time
What is cell encapsulation?
Cells are enclosed in a semi-permiable membrane made of calcium alginate spheres coated with bipolymer (to form semi-permiable membrane).
The spheres are exposed to a calcium chelating agent which re-liquifies the intracellular alginate
What are some advantages of cell encapsulartion?
The permeability of the capsule can be altered (which helps the retention and release of product from capsule)
Can inject the living cells inside the capsules into an animal without being attacked by the immune system
What sorts of surfaces are used to culture anchorage-dependant cells?
- Large T flasks or Petri dishes
- Multiplate propagator / 'cell factory' (picture lasgna)
- Plastic bags
- Roller bottles: most commonly used for scale-up of anchorage-dependant cells. Cells are submerged for about 1/4 of the cycle which allows for gas exchange.
What are microcarriers?
The are beads that cells will coat and used for the growth and maintenance of anchorage-dependent cells in a stirred tank.
They tend to have specific density between 1.03 and 1.10 and 100-250um which allows the beads to float and cells to attach
What are the advantages of microcarriers?
- Large surface to volume ratio
- Easy to seperate cells from secretion products
- Easy to scale up
What are some advantages porous microcarriers?
- Large surface area for growth of anchorage-dependant cells
- Protect cells from shear and air-liquid interface in agitated cultures
- Support a higher cell density per unit of microcarrier bead volume than solid microcarriers
What are some disadvantages of porous microcarriers?
- More difficult to assay cell density since cells are not directly visible under microscope
- Difficult to harvest cells from some porous structures