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Cell-Ess is stable in solution. There are issues with free fatty acid and free cholesterol with stability and solubility. In addition, the carrier may cause a problem. All of these issues have to be monitored and accounted for in cultures lasting over 4 days. With longer cultures, media depletion becomes a concern, and feeds are used to supplement the culture. For free fatty acids, free cholesterol, or cholesterol with a carrier in extended cultures, toxicity becomes a concern with the second or third feed and can be variable from run to run based on the break down or initial stability of the product. Cell-Ess deploys a novel method of delivery so these are not issues when optimized with Cell-Ess.