Optimization of physical parameters for cell attachment and growth on macroporous microcarriers

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Abstract
The rates of cell attachment of the anchorage‐dependent mammalian cell line Vero to the gelatin‐based macroporous microcarrier Cultispher‐G were determined under various conditions. An optimal rate of attachment (0.98 × 10−2 min−1) occurred by an intermittent stirring regimen of 3 min stirring at 40 rpm per 33 min. This stirring regimen appeared to maximize cell‐to‐bead attachment and minimized cell aggregation which occurred at a broadly comparable rate. A further increase in the rate of cell‐to‐bead attachment occurred by preincubation of the microcarriers in serum‐supplemented medium prior to cell inoculation in a serum‐free medium. However, serum supplementation (>5%) was required for maximal cell growth. The pH of the medium had little effect on cell attachment over a broad range (pH 7.1–8.0). An initial cell/bead inoculum of 30 ensured an even distribution of cells on the available microcarriers with a low proportion of unoccupied beads. The rate of cell attachment to Cultispher‐G was an order of magnitude lower than the determined value for the charged dextran microcarrier Cytodex‐1, which was measured as 9.05 × 10−2 min−1. The optimal conditions for cell attachment were significantly different for the two bead types. Cell attachment to the electrostatic surface of the Cytodex‐1 microcarriers was highly dependent on pH and serum supplementation. Cell aggregation during attachment to the Cytodex‐1 microcarriers was minimal because of the higher rate of cell–microcarrier attachment. The porous nature of the Cultispher‐G microcarriers allowed a maximum cell/bead loading of >1400, which was at least 3 times higher than equivalent loading of the cells on Cytodex‐1. The Cultispher‐G matrix also allowed the use of higher agitation rates (up to 100 rpm) in spinner flasks without affecting the cell growth rate or maximum cell density. © 1996 John Wiley & Sons, Inc.