Ahmad, Asma; (2018) Design and Characterisation of a Scale-Down Platform for the Recovery of Periplasmic Fab’ From E.coli. Doctoral thesis (Eng.D), UCL (University College London).

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Abstract

The need to speed up bioprocessing and to enhance process understanding of the heat extraction process, for the recovery of periplasmic Fab’ from E.coli cells, has led to the development of two workable scale-down models that are capable of predicting the performance of the lab scale and pilot scale process. In this work, a design of experiment (DoE) study was initially conducted at the 2L scale to identify the effect of key parameters such as heating duration (6-14 hours), heating temperature (55-65°C) and specific power input (0.05-0.41W L-1) on the heat extraction process. The results showed that extraction temperature and duration had the most impact on the process whereas specific power input had no significant impact in the range studied. Fluid dynamic studies were conducted on the 2L vessel, and on a scale-down 20mL vessel and shaken 24-well deep square-well (DSW) plate, in order to assess mixing performance under various operating conditions. Mixing time studies were performed on all three models using the dual indicator system for mixing time (DISMT). The mixing time curves between the 2L and 20mL vessel were well matched over the same range of specific power input values and the results showed that mixing time stayed relatively constant for both scales above a specific power input value of 0.05W L-1. Particle image velocimetry (PIV) experiments were also conducted on the 20mL vessel in order to visualise flow patterns and analyse fluid velocity. The data indicated that flow patterns were fully formed at 300rpm (9 x 10-4W L-1) and that velocity stabilised after 0.05W L-1. Mixing time studies in the DSW plate showed that turbulent mixing was achieved above 500rpm. Process verification studies were performed between the two scale-down models and the 2L vessel, and the performance was compared using Fab’ titre, total protein concentration, dsDNA concentration, HCP profiles and Fab’ profiles. The results demonstrated that both models were capable of correctly mimicking the performance in the 2L vessel for a variety of different experimental conditions, using feed material from different batches and using different E.coli strains and Fab’ types, provided that the heating profiles were matched and there was sufficient turbulent mixing at all scales. The results also agreed with data from the DoE and fluid dynamic studies, thus establishing the 20mL vessel and 24-well DSW plate as two feasible scale-down models for the periplasmic heat extraction process.

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