Microbioreactor system with integrated mixing scheme, temperature control and optical density measurement for fermentation and biocatalysis experiments

Abstract

The objective of this project is to develop an online microbioreactor system with integrated mixing scheme, temperature control and optical density measurement for fermentation experiment. There are few methods of fabrication used in prototyping microbioreactor designed by using InventorTM software such as micromachining, soft lithography casting and 3D printing. The proposed microbioreactor platform has a working volume of 500-1500 uL and was fabricated from poly(methylmethacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) polymers. The reactor is equipped with independent on/off temperature controller and proportional-integral (PI) agitation rate controller. Furthermore, Beer’s Lambert law was applied in on line optical density measurement at 600 nm with the use of fiber optics. Three different microbioreactors i.e. MBRv 1, MBRv 2 and MBRv 3 were fabricated to solve step by step of various technical aspects. Process control and automation were programmed by using LabVIEWTM software (National Instruments) and implemented by using a data acquisition card (DAQ) for signal transmission. Experimental works were performed to evaluate the workability of each of the main reactor features such as (1) assessment of the measurement and control performance (mixing, temperature and optical density), (2) mixing quality and evaporation test and (3) proof-of-concept via starch hydrolysis and yeast fermentation to demonstrate the workability of the microbioreactor. Enzyme to substrate, E/S ratio, reaction temperature and stirring speed were varied to observe the impact of these reactor variables on the starch hydrolysis process. Results attained includes two main aspects i.e. enzyme catalysed reactions has been successfully performed using the microbioreactor and a low standard deviation (averaging at + 0.03 mg∙mL-1) showed that all experiments were repeatable with error less than 5% of the mean value. In S. cerevisae fermentation, the microbioreactor ran stably for the entire length of operation which was nearly 40 hours with very minimal volume loss i.e. about 2.8 μL∙hr-1 at 37oC in every batch. The microbioreactor has the maximum oxygen transfer rate (OTRmax) of 16.6 mmol∙L-1∙h-1 under the agitation rate of 300 rpm. Cell specific growth rate as high as 0.291 hr-1 was obtained in this condition. The experimental data in the microbioreactor operation was also reproducible in shake flask and bioreactor where comparable growth profiles were attained under a similar mixing time. All in all, it is anticipated that the microbioreactor fabricated in this project would be a potential substitute for shake flasks and/or microtiter plate as experimental tool to facilitate a high throughput bioprocessing experimental work.