Establishing Ultra Scale-down Tools for the Rational Design of Linked Bioprocesses: Flocculation and Centrifugation

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(i) Background. Scale-down models of individual bioprocess unit operations have previously been established at UCL Biochemical Engineering on centrifugation, membrane filtration, crossflow microfiltration and depth filtration [1-3]. The ultra scale-down (USD) tools radically transform the approach to early manufacturing development by enabling high throughput studies using only millilitre quantities of material to yield industrially-relevant data. Initially, the approached was developed for centrifugation, a major step in biomanufacturing for which no suitable scale-down tool is available for early process studies. The addition of a flocculation step prior to centrifugation is employed to create larger particles which enhances the efficacy of the solid-liquid separation in the centrifuge (4). The flocculation process is complex as its effectiveness is dependent on dosage of flocculating material, flocculation time, and rate of flocculant addition (5). Additionally, mixing processes could either enhance flocculation or cause flocs to break-up. The scale-up of processes involving flocculation need to be characterised based on the combined effect of such time-dependent sub-processes (i.e. 'process kinetics') and process shear. Thus, there is a trade-off between creating stable flocs which enhances centrifugation while maintaining a high over-all product yield during primary recovery. Identifying which parameter in the larger scale process would optimize this trade-off between clarification recovery and product yield is difficult to determine using current laboratory techniques involving flocculation. There is currently no established scale-down technique for flocculation-centrifugation processes which predicts larger scale operations. This highlights the need for scale-down tool for flocculation for the rational design of primary recovery operations.(ii) Aim and objectives. The proposed project builds on the know-how developed at UCL on establishing individual scale-down models. The overall aim of this research is to gain a better mechanistic understanding of several processes before centrifugation which may be influenced by both time-dependent sub-processes (i.e. 'process kinetics') and process shear to establish a linked scale-down that predicts the process interaction experienced at large scale. Specific objectives are as follows:- To create a scale-down model of flocculation of cells typically used in biomanufacturing (such as yeast, CHO cells or homogenized E. coli cells) which can be studied under controlled conditions.- To investigate the mechanism of flocculation of these cells as a function of flocculant type and process conditions- To establish a scale-down methodology for flocculation-centrifugation - To apply the scale-down methodology in understanding and addressing challenges encountered at large scale.