Positively charged microcarriers

The internal charged groups are not essential and tend to bind medium components unnecessarily. The yield of cells can be improved if only the surface layer of the bead is charged for example 

Beads may be supplied in suspension in PBS but more usually they are supplied dry and require swelling in PBS-A (100 ml/g) for 3 h and washing in PBS-A and autoclaving (15 min at 15 p.s.i.) before use. In the dry form they are stable for more than 2 years. One gram of Cytodex-1 (dryweight) will swell to about 18 ml containing 7 X 106 microcarriers with a surface area of 0.6 m2. 

Bio-Rad Laboratories supply Bio-Carriers . Instead of the cross-linked dextran of the Cytodex microcarriers these have a polyacrylamide matrix with the positively charged dimethylaminopropyl groups linked throughout the matrix. On swelling 1 g dry Bio-Car-riers provides 19 ml packed volume containing 7 X 106 beads with a total surface area of 0.5 m2. Each bead can accommodate 350 cells so that the theoretical value of 2 X 109 cells could grow on 1 g Bio-Carriers. 

For those positively charged microcarriers which swell in aqueous solutions a loading of 3 g dry beads per litre of culture is recommended. 

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Microcarriers fall into three groups (a) positively charged (b) negatively charged and (c) non-ionic. 

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