Cell culture growth limitations

This is an equivalent situation to that of the raw material for blood substitutes, and the impurity limits developed for this special application can be used directly. The content of extractable fluorine is a sensitive parameter to characterise the quality of PFCLs. The correlation between the concentration of extractable fluorine in a PFCL and its toxicity was reported by Gervits [19]. Using cell cultures, he was able to correlate the inhibition rate of cell growth to the content of extractable fluorine. Table 2 shows that only very low concentration could be tolerated. 

Trudell and our group, with the generous support of Dr. Hugo Jaurequi, conducted certain cell-culturing experiments on human hepatic cells. Since the effort was self-funded, the scope of the experiments was limited. Nevertheless, we felt we confirmed the viability of a specially designed polyurethane formulation as a substrate for cell growth. 

The mammalian cell culture technique can be employed to produce clinically important biochemicals such as human growth hormones, interferon, plasminogen activator, viral vaccines, and monoclonal antibodies. Traditionally, these biochemicals had been produced using living animals or extracted from human cadavers. As examples, monoclonal antibodies can be produced by cultivating hybridoma cells in the peritoneal cavity of mice, and the human growth hormone to cure dwarfism can be extracted from human cadavers. However, the quantity obtained from these methods is quite limited for the wide clinical usages of the products. 

Animal cells may be anchorage-dependent. Cells that depend on a solid substratum for growth are named adherent cells. These cells normally proliferate in monolayers and show contact inhibition, with the maximum cell yield generally limited by the available surface of the culture vessel. The yield of cells in suspension is not dependent on a solid substratum. 

Ljunggren J, Haggstrom L (1995), Specific growth rate as a parameter for tracing growth limiting substances in animal cell cultures, J. Biotechnol. 42 163-175. 

Berdad C, Tom R, Kamem A (1993), Growth, nutrient consumption, and end product accumulation in Sf9 and BTI-EAA insect cell cultures insights into growth limitation and metabolism, Biotechnol. Prog. 9 615-624. 

Culture medium osmolality has a large influence on animal cell culture. Hyperosmotic conditions, achieved by using salts, CO2, or concentrated media, has been shown as a low-cost method to increase specific productivity of cells. Hybridoma cultures, for instance, show improved productivity with an increase in osmolality (Oh et al., 1993). However, this method is not very popular due to the negative effects on cell growth. The drop in cell growth under hyperosmotic conditions occurs, probably, due to cell death by apoptosis. Thus, expression of anti-apoptotic genes, such as Bcl-2, could allow the use of hyperosmotic conditions to simultaneously limit cell death and increase cell productivity (Kim and Lee, 2002). 

Table 8.1 summarizes a set of mathematical expressions for the description of the specific growth rate during culture. Most of these formulations employ Monod-type structures for cell growth limitation by substrates (Monod, 1949), and structures for byproduct inhibition (Aiba and Shoda, 1969 see Equations 16 and 24). 

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