Question

b)) Identify the role of shear involved in the cell damage for mammalian cell cultures. Microcarrier beads 150 um in diameter are used to calculate recombinant CHO cells 1o for production of growth homone. It is proposed to use a 5-cm turbine impeller to mix the culture in a 4-liter stirred tank. Air and carbon dioxide are supplied by flow through the reactor headspace. The microcarrier uspension has a density of approximately 1010 kg/m and a viscosity of 1.3x103 Pa-s. Estimate the maximum llowable stired speed whicah avoidsturbulent shear damage of the ells le Fluid mass in the impeller zone is roughly equal to pDi; Np' is 5 for turbine impeller]

Answer 1

Answer b)

1. Basically, sheer stress is a type of mechanical stress applicable when the cell comes into contact with a biofluid or liquid system such as blood or lymph.
2. This force is responsible for modification of the physical aspects of the cell along with the regulatory functions as it acts as a signal to initiate a particular associated reaction.
3. Under normal conditions, in a body, the sheer force acts on the cells to undergo changes in their morphology which in turn affects the cells resulting in a particular response.
4. When the cells are cultured in-vitro, they are not grown in a liquid media but are adhered onto surface forming colonies. So, a particular response to be expected would not occur.
5. Let's take an example of the endothelial cells lining the blood vessels which in turn results in either contraction or relaxation of the vessels in the form of stretch.
6. So, when mechanical stress is applied during culturing of the cell in-vitro, it induces physiological changes essential for normal functioning of the cell dealing will cell expression and regulation.
7. However, cells may show susceptibility towards the magnitude of a particular sheer applied. This is accompanied with the duration for which that force is applied which varies for different cell types.
8. Some cells are much susceptible and are more prone to sheer damage which is in turn highlighted from the properties of the fluid system with which the interaction occurs. This can link with the loosening of the cells by altering their cell adhesion properties basically acting by altering the functioning of cell adhesion molecules.
9. So, sheer can play multiple roles including separation of cells to induces neutral uptake, for regulation and to induce physiological changes in cells.