Muhd Nazrul Hisham Zainal Alam

Application of microbioreactors in fermentation process development: A review

Biotechnology process development involves strain testing and improvement steps aimed at increasing yields and productivity. This necessitates the high-throughput screening of many potential strain candidates, a task currently mainly performed in shake flasks or microtiter plates. However, these methods have some drawbacks, such as the low data density (usually only end-point measurements) and the lack of control over cultivation conditions in standard shake flasks. Microbioreactors can offer the flexibility and controllability of bench-scale reactors and thus deliver results that are more comparable to large-scale fermentations, but with the additional advantages of small size, availability of online cultivation data and the potential for automation. Current microbioreactor technology is analyzed in this review paper, focusing on its industrial applicability, and directions for future research are presented.

Embedded resistance wire as a heating element for temperature control in microbioreactors

This paper presents the technical realization of a low-cost heating element consisting of a resistance wire in a microbioreactor, as well as the implementation and performance assessment of an on/off controller for temperature control of the microbioreactor content based on this heating element. The microbioreactor (working volume of 100 µL) is designed to work bubble-free, and is fabricated out of the polymers poly(methylmethacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS). The temperature is measured with a Pt 100 sensor, and the resistance wires are embedded in the polymer such that they either surround the reactor chamber or are placed underneath it. The latter can achieve an even temperature distribution across the reactor chamber and direct heating of the reactor content. We show that an integrated resistance wire coupled to a simple on/off controller results in accurate temperature control of the reactor (±0.1 °C of the set point value) and provides a good disturbance rejection capability (corrective action for a sudden temperature drop of 2.5 °C at an operating temperature of 50 °C takes less than 30 s). Finally, we also demonstrate the workability of the established temperature control in a batch Saccharomyces cerevisiae cultivation in a microbioreactor.

Fabrication of microfluidic devices: improvement of surface quality of CO2 laser machined poly(methylmethacrylate) polymer

Laser engraving has considerable potential for the rapid and cost effective manufacturing of polymeric microfluidic devices. However, fabricated devices are hindered by relatively large surface roughness in the engraved areas, which can perturb smooth fluidic flow and can damage sensitive biological components. This effect is exacerbated when engraving at depths beyond the laser focal range, limiting the production of large aspect ratio devices such as microbioreactors. This work aims to overcome such manufacturing limitations and to realise more reproducible and defect free microfluidic channels and structures. We present a strategy of multiple engraving passes alongside solvent polymer reflow for shallow depth ( 500 mu m) features. To examine the proposed methodologies, capillary action and bioreactor microfluidic devices were fabricated and evaluated. Results indicate that the multiple engraving technique could reproduce engraved microfluidic channels to depths between 50-470 mu m, both rapidly (6-8 min) and with low average surface roughness (1.5-2.5 mu m). The layer cutting approach was effective at manufacturing microfluidic devices with depths < 500 mu m, rapidly (< 1 min) and with low surface roughness. Ultimately, the proposed methodology is highly beneficial for the rapid development of polymer-based microfluidic devices.

Development of Low-Cost Microcontroller-Based Interface for Data Acquisition and Control of Microbioreactor Operation

This article presents the development of a low-cost microcontroller-based interface for a microbioreactor operation. An Arduino MEGA 2560 board with 54 digital input/outputs, including 15 pulse-width-modulation outputs, has been chosen to perform the acquisition and control of the microbioreactor. The microbioreactor (volume = 800 µL) was made of poly(dimethylsiloxane) and poly(methylmethacrylate) polymers. The reactor was built to be equipped with sensors and actuators for the control of reactor temperature and the mixing speed. The article discusses the circuit of the microcontroller-based platform, describes the signal conditioning steps, and evaluates the capacity of the proposed low-cost microcontroller-based interface in terms of control accuracy and system responses. It is demonstrated that the proposed microcontroller-based platform is able to operate parallel microbioreactor operation with satisfactory performances. Control accuracy at a deviation less than 5% of the set-point values and responses in the range of few seconds have been recorded.

A portable sensor for cell optical density measurement in microfluidic chips

This paper presents the development of a smartphone-controlled wireless device for cell optical density sensing in microfluidic chips. The footprint of the device is very compact relative to a classical laboratory spectrophotometer, making it a portable device. The cell optical density sensing device consists of an embedded microcontroller, optical sensing components, and a wireless transceiver performing cell optical density measurements in disposable microfluidic chips fabricated from poly(methylmethacrylate) polymers. The device is controlled by an Android application allowing for true portability and the possibility of remote or field operation of the device. The use of microfluidic chips as the sample carrier for optical density detection instead of a plastic cuvette allows users the flexibility to explore and/or conduct a variety of micro-scale chemical analysis using the device which would be difficult in a cuvette-based system. The function of the device is validated through a series of off-line and online optical density measurements using Saccharomyces cerevisae yeast cultures. The device is low cost, small enough to fit in most laboratory flow hood cabinets, and can be easily integrated into miniature bioreactor systems. Moreover, wireless communication enables the user to operate the device using smartphones or rapidly transfer the measured data to an online repository for analysis or storage.

Methodology on scaling-down of membrane separation process into microfluidic platform

The use of membrane separation techniques in microfluidic devices has been gaining interest in many research field particularly in analytical chemistry where such a device is utilised to selectively remove impurities and/or unwanted components for a better detection of analyte of interest. Many different strategies have been reported to combine membranes and microfluidics. In this paper, details on how to fabricate such a micro scale filtration device are discussed. Topics covered include size and operation mode, materials and fabrication methods, strategy to integrate membrane on chip, fluidics (and electrical) interconnects, online measurement and process automation. Each design parameters were reviewed and discussed in accordance to the steps (or methodology) needed to fabricate a microfluidic membrane filtration unit. A low cost fabrication solution using polymers as materials for fabrication and the use of Arduino board for process automation have been suggested to realise a fully automated microfluidic membrane filtration unit.

Effect of impeller design on the rate of reaction of hydrolysis in batch reactor

Lactose is a disaccharide found mostly in milk product. Lactose can cause digestive problem that commonly known as lactose intolerant. Manufacturer pre-treated the milk to produce lactose-free milk. This study aims to investigate the effect of impeller design on the rate of reaction of lactose hydrolysis in batch reactor by utilising immobilised enzyme. Lactose hydrolysis reactions were carried out by adding s-galactosidase (enzyme) into the milk. Alginate was utilised to immobilise the enzyme in order to reuse, enhanced stability and rapid separation of enzymes from the reaction mixture. In this reaction glucose was produced; hence increase sweetness of the milk. Replacing conventional enzymatic processes with immobilised (support) enzyme provides many advantages such as increase the enzyme activity, selectivity, stability and easy recovery from the reaction medium for their reuse. The rate of product formation with different variable such as agitation speed (150 rpm, 250 rpm and 300 rpm) and type of impeller (pitch blade turbine, Rushton turbine, marine propeller and pitch paddle) were investigated. It was found that the highest product formation was with marine propeller at speed 150 rpm with production rate 8.2 mg/L.min, followed by Rushton turbine at speed 250 rpm and pitch blade turbine at speed 300 rpm with production rate 6.2 mg/L.min and 5.4 mg/L.min. Pitch blade shown average of production rate around 3.4 - 4.6 mg/L.min.