Development of novel containment systems for freeze-drying

Abstract

This thesis investigates the novel use of paper and Tyvek sterilisation pouches as containment systems to perform various applications of freeze-drying. Their effect on the freeze-drying of a pharmaceutical protein, mass and heat transfer, sterile freeze-drying and containment of microorganisms were examined. Ovine derived Immunoglobulin G (IgG) specific for fluorescein was used as a model biopharmaceutical protein and a range of assays developed to quantify its biological activity, aggregation, turbidity, residual moisture and reconstitution time. IgG was formulated using different carbohydrates and analysed using freeze-drying microscopy to allow precise development of optimum freeze-drying cycles. The IgG was freeze-dried using these cycles and the function and structure of the IgG was shown to be unaffected. Freeze-drying cycles were modified to investigate the effect paper and Tyvek pouches had on the IgG which showed no change in activity or structure. However, pouches decreased sublimation rates and increased process time. Resistance to water vapour, and the subsequent effect on mass and heat transfer during the freeze-drying process, imposed by paper and Tyvek sterilisation pouches, Gore Lyoguard, product dry layer and freeze-drying stoppers were investigated. Pouches presented greater resistance to water vapour movement than the dry product layer, Lyoguard and stoppers. Increasing resistance decreases mass transfer, increases pressure inside the pouches thereby increasing the heat transfer coefficient. A process simulation using nutrient rich media was performed where vials were packaged aseptically and transported to a freeze-drier in a normal laboratory environment. The vials showed no growth of contaminating microorganisms after incubation. In addition, pouches containing nutrient rich media were challenged with aerosolised Saccharomyces cerevisiae and also showed no growth of contaminating microorganisms after incubation. Finally, pouches were demonstrated to be able to contain Escherichia coli during freeze-drying thus preventing contamination of the freeze-drier and the environment.