Lawrence, JP; (2015) Microfluidic Tangential Flow Filter and Continuous-Flow Reactor for Bioprocess Development. Doctoral thesis , UCL (University College London).

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Abstract

The development of new biocatalytic processes is hindered by the number of factors that must be investigated and optimised in order to create a robust and reproducible process, particularly where a novel enzyme is involved. It is therefore advantageous to perform process development experiments at micro scale, in order to reduce the material requirement for experimentation and increase experimental throughput by parallelisation. The initial focus of the thesis is on the design of a microfluidic tangential flow filter to test downstream processing conditions. The device was designed for reversible clamp sealing, allowing the simple integration of different filtration membranes, and the seal achieved with the device was shown to be robust up to internal pressures of 100 psi. The filtration device was applied to the recovery of L-erythrulose (ERY) from a synthesis reaction performed using transketolase (TK), where it was demonstrated that the enzyme could be fully retained using a commercially-available membrane, while ERY was able to permeate the membrane freely. The filtration device was joined in-line to the output of a T-junction reactor with a staggered herringbone mixer, used to perform the synthesis reaction. The filter was capable of continuously separating the ERY from the lysate mixture exiting the reactor over the course of several hours, producing 3.6 mg h-1 of pure ERY. A novel multi-input reactor (MIR) is also demonstrated for the purpose of intensifying ERY output, designed to overcome the effect of substrate inhibition on the TK enzyme by mimicking a fed-batch reactor. Feeding strategies were designed for the conversion of various concentrations of the less inhibiting substrate hydroxypyruvate (HPA) and tested in the MIR. A 4.5-fold increase in output concentration and a 5-fold increase in throughput were achieved compared with the single input reactor used in previous experiments. However, conversion in the MIR was reduced at higher concentrations, suggesting that the reaction in the MIR was being inhibited by the evolution of carbon dioxide.

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