Immobilized Cell Bioreactors,Polycrylamide,Calcium Alginate,Cylinder,Cell Mass,Cell Immobilization

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	Immobilized Cell Bioreactors - These bioreactors are based on cells entrapped either in gels, such as, agarose, agar, chitosan, gelatine, gellan, polyacrylamide and calcium alginate, to produce beads, or in a membrane or metal (stainless steel) screen compartment or cylinder. A simplified version of a device based on metal screen is shown in. The membrane screen cylinder containing cells is kept in a chamber through which the medium is circulated from a recycle chamber. The medium flows parallel to the screen cylinder and diffuses across the screen into the cell mass.
Similarly, products from cells diffuse into the medium and out of the screen cylinder.The membrane/screen compartment housing the cells may be cylindrical or flat, and medium movement may be so adjusted as to flow across the screen compartment rather than parallel to it. The technology is being refined for commercialization. Fresh medium is regularly added to and equivalent volume of used medium is withdrawn from the recycling chamber to maintain its nutrient status. Cell immobilization changes the physiology of cells as compared to that of cells in suspension. This technique is useful where the biochemical of interest is excreted by the cells into the medium.
Product excretion may also be brought about by immobilization itself, or by certain treatments like altered pH, use of DMSO (dimethyl sulfoxide) as a permealizing agent, changed ionic strength of medium, an elicitor, etc. Immobilized cell reactors have the following advantages: (i) no risk of cell wash out, (ii) low contamination risk, (iii) protection of cells from liquid shear, (iv) better control on cell aggregate size, (v) separation of growth phase (in a batch/continuous bioreactor) from production stage (in an immobilized cell bioreactor), (vi) cellular wastes regularly removed from the system, and (vii) cultures at high cell densities.