Microfluidic devices: useful tools for bioprocess intensification

3D printed ceramics as solid supports for enzyme immobilization: an automated DoE approach for applications in continuous flow

In recent years, 3D printing has emerged in the field of chemical engineering as a powerful manufacturing technique to rapidly design and produce tailor-made reaction equipment. In fact, reactors with complex internal geometries can be easily fabricated, optimized and interchanged in order to respond to precise process needs, such as improved mixing and increased surface area. These advantages make them interesting especially for catalytic applications, since customized structured bed reactors can be easily produced. 3D printing applications are not limited to reactor design, it is also possible to realize functional low cost alternatives to analytical equipment that can be used to increase the level of process understanding while keeping the investment costs low. In this work, in-house designed ceramic structured inserts printed via vat photopolymerization (VPP) are presented and characterized. The flow behavior inside these inserts was determined with residence time distribution (RTD) experiments enabled by in-house designed and 3D printed inline photometric flow cells. As a proof of concept, these structured inserts were fitted in an HPLC column to serve as solid inorganic supports for the immobilization of the enzyme Phenolic acid Decarboxylase (bsPAD), which catalyzes the decarboxylation of cinnamic acids. The conversion of coumaric acid to vinylphenol was chosen as a model system to prove the implementation of these engineered inserts in a continuous biocatalytic application with high product yield and process stability. The setup was further automated in order to quickly identify the optimum operating conditions via a Design of Experiments (DoE) approach. The use of a systematic optimization, together with the adaptability of 3D printed equipment to the process requirements, render the presented approach highly promising for a more feasible implementation of biocatalysts in continuous industrial processes. Graphical abstract.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41981-021-00163-4.

Development of a Microfluidic Platform for R-Phycoerythrin Purification Using an Aqueous Micellar Two-Phase System

Temperature-dependent aqueous micellar two-phase systems (AMTPSs) have recently been gaining attention in the isolation of high-added-value biomolecules from their natural sources. Despite their sustainability, aqueous two-phase systems, and particularly AMTPSs, have not been extensively applied in the industry, which might be changed by applying process integration and continuous manufacturing. Here, we report for the first time on an integrated microfluidic platform for fast and low-material-consuming development of continuous protein purification using an AMTPS. A system comprised of a microchannel incubated at high temperature, enabling instantaneous triggering of a two-phase system formation, and a microsettler, allowing complete phase separation at the outlets, is reported here. The separation of phycobiliproteins and particularly the purification of R-phycoerythrin from the contaminant proteins present in the aqueous crude extract obtained from fresh cells of Gracilaria gracilis were thereby achieved. The results from the developed microfluidic system revealed that the fractionation performance was maintained while reducing the processing time more than 20-fold when compared with the conventional lab-scale batch process. Furthermore, the integration of a miniaturized ultrafiltration module resulted in the complete removal of the surfactant from the bottom phase containing R-phycoerythrin, as well as in nearly twofold target protein concentration. The process setup successfully exploits the benefits of process intensification along with the integration of various downstream processes. Further transfer to a meso-scale integrated system would make such a system appropriate for the separation and purification of biomolecules with high commercial interest.

Tuning Surface Morphology of Fluorescent Hydrogels Using a Vortex Fluidic Device

In recent decades, microfluidic techniques have been extensively used to advance hydrogel design and control the architectural features on the micro- and nanoscale. The major challenges with the microfluidic approach are clogging and limited architectural features: notably, the creation of the sphere, core-shell, and fibers. Implementation of batch production is almost impossible with the relatively lengthy time of production, which is another disadvantage. This minireview aims to introduce a new microfluidic platform, a vortex fluidic device (VFD), for one-step fabrication of hydrogels with different architectural features and properties. The application of a VFD in the fabrication of physically crosslinked hydrogels with different surface morphologies, the creation of fluorescent hydrogels with excellent photostability and fluorescence properties, and tuning of the structure-property relationship in hydrogels are discussed. We conceive, on the basis of this minireview, that future studies will provide new opportunities to develop hydrogel nanocomposites with superior properties for different biomedical and engineering applications.

Inertial Micromixing in Curved Serpentine Micromixers with Different Curve Angles

Micromixers are of considerable significance in many microfluidics system applications, from chemical reactions to biological analysis processes. Passive micromixers, which rely solely on their geometry, have the advantages of low cost and a less-complex fabrication process. Dean vortices seen in curved microchannels are one of the useful tools to enhance micromixing. In this study, the effects of curve angle on micromixing were experimentally investigated in three curved serpentine micromixers consisting of ten segments with curve angles of 180 ° , 230 ° and 280 ° , at Dean numbers between 12 and 87. To characterize and compare the performance of the micromixers, fluorescence intensity maps and mixing indices were utilized. Accordingly, the micromixer having segments with 280 ° curve angle had significantly higher mixing index values up to the Dean number 60 and outperformed the other two micromixers. This was due to the severe distortion of flow streamlines by Dean vortices and the occurrence of chaotic advection at lower Dean numbers. Beyond the Dean number of 70, no difference was observed in the performance of the micromixers and the mixing index at their outlets had the asymptotic value of 0.93 ± 0.02. Furthermore, the flow behavior of the micromixers was numerically simulated to provide further insight about the mixing phenomena.

Flocculation on a chip: a novel screening approach to determine floc growth rates and select flocculating agents

Flocculation is a key purification step in cell-based processes for the food and pharmaceutical industry where the removal of cells and cellular debris is aided by adding flocculating agents. However, finding the best suited flocculating agent and optimal conditions to achieve rapid and effective flocculation is a non-trivial task. In conventional analytical systems, turbulent mixing creates a dynamic equilibrium between floc growth and breakage, constraining the determination of floc formation rates. Furthermore, these systems typically rely on end-point measurements only. We have successfully developed for the first time a microfluidic system for the study of flocculation under well controlled conditions. In our microfluidic device (μFLOC), floc sizes and growth rates were monitored in real time using high-speed imaging and computational image analysis. The on-line and in situ detection allowed quantification of floc sizes and their growth kinetics. This eliminated the issues of sample handling, sample dispersion, and end-point measurements. We demonstrated the power of this approach by quantifying the growth rates of floc formation under forty different growth conditions by varying industrially relevant flocculating agents (pDADMAC, PEI, PEG), their concentration and dosage. Growth rates between 12.2 μm s^-1 for a strongly cationic flocculant (pDADMAC) and 0.6 μm s^-1 for a non-ionic flocculant (PEG) were observed, demonstrating the potential to rank flocculating conditions in a quantitative way. We have therefore created a screening tool to efficiently compare flocculating agents and rapidly find the best flocculating condition, which will significantly accelerate early bioprocess development.

Beyond the bulk: disclosing the life of single microbial cells

Microbial single cell analysis has led to discoveries that are beyond what can be resolved with population-based studies. It provides a pristine view of the mechanisms that organize cellular physiology, unbiased by population heterogeneity or uncontrollable environmental impacts. A holistic description of cellular functions at the single cell level requires analytical concepts beyond the miniaturization of existing technologies, defined but uncontrolled by the biological system itself. This review provides an overview of the latest advances in single cell technologies and demonstrates their potential. Opportunities and limitations of single cell microbiology are discussed using selected application-related examples.

One-domain approach for studying multiphase transport phenomena in biofilm growing systems

The one-domain approach (ODA) was used as an alternative to solve fluid-biofilm interfacial behavior in a 2-D model for diffusion-reaction-convection coupled with prediction of irregular growth of biofilms via a cellular automaton strategy. The simulations exhibited errors of <7% compared with the porosity of a previously reported capillary experimental system. Additionally, biofilm surface geometrical aspects were satisfactorily compared with reports of experimental and similar rigorously simulated benchmark systems. The method developed was applied to simulate typical biofilm systems predicting recirculation flow patterns, interface concentration profiles, and clogging of the inlet section of the capillary tube, which are phenomena that affect the efficiency of diverse biotechnological applications, including membrane bioreactors and biofilters. The ODA method applied to the governing equations of momentum and mass transfer combined with a cellular automaton algorithm is a suitable and straightforward approach for modeling solid-state fermentation at different sophistication levels.

Study of flow behaviors of droplet merging and splitting in microchannels using Micro-PIV measurement

Droplet merging and splitting are important droplet manipulations in droplet-based microfluidics. However, the fundamental flow behaviors of droplets were not systematically studied. Hence, we designed two different microstructures to achieve droplet merging and splitting respectively, and quantitatively compared different flow dynamics in different microstructures for droplet merging and splitting via micro-particle image velocimetry (micro-PIV) experiments. Some flow phenomena of droplets different from previous studies were observed during merging and splitting using a high-speed microscope. It was also found the obtained instantaneous velocity vector fields of droplets have significant influence on the droplets merging and splitting. For droplet merging, the probability of droplets coalescence (η) in a microgroove is higher (50% < η < 92%) than that in a T-junction microchannel (15% < η < 50%), and the highest coalescence efficiency (η = 92%) comes at the two-phase flow ratio e of 0.42 in the microgroove. Moreover, compared with a cylinder obstacle, Y-junction bifurcation can split droplets more effectively and the droplet flow during splitting is steadier. The results can provide better understanding of droplet behaviors and are useful for the design and applications of droplet-based microfluidics.

Microfluidics-Enabled Diagnostic Systems: Markets, Challenges, and Examples

Microfluidics has become an important tool for the commercial product development in diagnostics. This article will focus on current technical demands during the development process such as material and integration challenges. Furthermore, we present data on the diagnostics market as well as examples of microfluidics-enabled systems currently under commercial development or already on the market.

Bioinks for biofabrication: current state and future perspectives

Recent progress in 3D printing technologies is leading a revolution in cell culture methods. These systems rely heavily on bioinks, the raw cells and biomaterials used to create these 3D cultures. These formulations, ranging from cell suspensions to hard acellular thermoplastics, must function with 3D systems and offer biocompatible environments that mimic in vivo tissue characteristics. Although much progress has been made for the production of increasingly complex reproducible 3D tissues, a full biofabrication platform with both improved technology and superior bioinks must be developed. Here, important properties for these materials are examined; recent advances in bioinks are summarized; and finally, future considerations for 3D biofabrication are discussed.

Cascading and Parallelising Curvilinear Inertial Focusing Systems for High Volume, Wide Size Distribution, Separation and Concentration of Particles

Inertial focusing is a microfluidic based separation and concentration technology that has expanded rapidly in the last few years. Throughput is high compared to other microfluidic approaches although sample volumes have typically remained in the millilitre range. Here we present a strategy for achieving rapid high volume processing with stacked and cascaded inertial focusing systems, allowing for separation and concentration of particles with a large size range, demonstrated here from 30 μm–300 μm. The system is based on curved channels, in a novel toroidal configuration and a stack of 20 devices has been shown to operate at 1 L/min. Recirculation allows for efficient removal of large particles whereas a cascading strategy enables sequential removal of particles down to a final stage where the target particle size can be concentrated. The demonstration of curved stacked channels operating in a cascaded manner allows for high throughput applications, potentially replacing filtration in applications such as environmental monitoring, industrial cleaning processes, biomedical and bioprocessing and many more.

Multilayered film microreactors fabricated by a one-step thermal bonding technique with high reproducibility and their applications

We report the versatile uses of multilayered polyimide (PI) film microreactors with various functions including pressure tolerance, three-dimensional mixing and multistep membrane emulsification. Such PI film microreactors were fabricated by a simple one-step thermal bonding technique with high reproducibility. Upon bonding at 300 °C for 1 hour, the thin and flexible film microdevices could withstand pressure up to 8.6 MPa and 16.3 MPa with PI adhesive film or fluoropolymer adhesive, respectively, due to differences in wettability. The hydrophilic and hydrophobic microchannel devices were used to generate monodisperse oil-in-water (O/W) and water-in-oil (W/O) droplets, and polymer micro/nanoparticles at a high generation frequency. A monolithic and chemical resistant film microreactor with a three-dimensional serpentine microchannel was used for the selective reduction of ester to aldehyde by efficient mixing and quenching in a flash chemistry manner, within a several 10(1) millisecond time scale. Furthermore, a novel multilayered film microreactor for organic-aqueous biphasic interfacial reactions was devised by embedding a membrane layer to induce chaotic mixing in both the interface and emulsified phase by flowing through multiple numbers of meshed structures along the hydrophobic channel. This simple and economic fabrication technique significantly facilitates mass production of multilayered film devices that could be useful as a platform for various microfluidic applications in chemistry and biology.

Quantification of the oxygen uptake rate in a dissolved oxygen controlled oscillating jet-driven microbioreactor

BACKGROUND

Microbioreactors have emerged as a new tool for early bioprocess development. The technology has advanced rapidly in the last decade and obtaining real-time quantitative data of process variables is nowadays state of the art. In addition, control over process variables has also been achieved. The aim of this study was to build a microbioreactor capable of controlling dissolved oxygen (DO) concentrations and to determine oxygen uptake rate in real time.

RESULTS

An oscillating jet driven, membrane-aerated microbioreactor was developed without comprising any moving parts. Mixing times of ∼7 s, and k_La values of ∼170 h^-1 were achieved. DO control was achieved by varying the duty cycle of a solenoid microvalve, which changed the gas mixture in the reactor incubator chamber. The microbioreactor supported Saccharomyces cerevisiae growth over 30 h and cell densities of 6.7 g_dcw L^-1. Oxygen uptake rates of ∼34 mmol L^-1 h^-1 were achieved.

CONCLUSION

The results highlight the potential of DO-controlled microbioreactors to obtain real-time information on oxygen uptake rate, and by extension on cellular metabolism for a variety of cell types over a broad range of processing conditions. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A. Enzymatic microreactors in biocatalysis: history, features, and future perspectives

Microfluidic reaction devices are a very promising technology for chemical and biochemical processes. In microreactors, the micro dimensions, coupled with a high surface area/volume ratio, permit rapid heat exchange and mass transfer, resulting in higher reaction yields and reaction rates than in conventional reactors. Moreover, the lower energy consumption and easier separation of products permit these systems to have a lower environmental impact compared to macroscale, conventional reactors. Due to these benefits, the use of microreactors is increasing in the biocatalysis field, both by using enzymes in solution and their immobilized counterparts. Following an introduction to the most common applications of microreactors in chemical processes, a broad overview will be given of the latest applications in biocatalytic processes performed in microreactors with free or immobilized enzymes. In particular, attention is given to the nature of the materials used as a support for the enzymes and the strategies employed for their immobilization. Mathematical and engineering aspects concerning fluid dynamics in microreactors were also taken into account as fundamental factors for the optimization of these systems.

Synthesis and Application of Amine Functionalized Iron Oxide Nanoparticles on Menaquinone-7 Fermentation: A Step towards Process Intensification

Industrial production of menaquione-7 by Bacillus subtilis natto is associated with major drawbacks. To address the current challenges in menaquione-7 fermentation, studying the effect of magnetic nanoparticles on the bacterial cells can open up a new domain for intensified menqainone-7 process. This article introduces the new concept of production and application of l-lysine coated iron oxide nanoparticles (l-Lys@IONs) as a novel tool for menaquinone-7 biosynthesis. l-Lys@IONs with the average size of 7 nm were successfully fabricated and were examined in a fermentation process of l-Lys@IONs decorated Bacillus subtilis natto. Based on the results, higher menaquinone-7 specific yield was observed for l-Lys@IONs decorated bacterial cells as compared to untreated bacteria. In addition, more than 92% removal efficacy was achieved by using integrated magnetic separation process. The present study demonstrates that l-Lys@IONs can be successfully applied during a fermentation of menaquinone-7 without any negative consequences on the culture conditions. This study provides a novel biotechnological application for IONs and their future role in bioprocess intensification.

A peculiar segmented flow microfluidics for isoquercitrin biosynthesis based on coupling of reaction and separation

A segmented flow containing a buffer-ionic liquid/solvent in a micro-channel reactor was applied to synthesize isoquercitrin by the hesperidinase-catalyzed selective hydrolysis of rutin, based on a novel system of reaction coupling with separation. Within the developed microchannel reactor with one T-shaped inlet and outlet, the maximum isoquercitrin yield (101.7 ± 2.6%) was achieved in 20 min at 30 °C and 4 μL/min. Compared with a continuous-flow reactor, reaction rate was increased 4-fold due to a glycine-sodium hydroxide:[Bmim][BF4]/glycerol triacetate (1:1, v/v) system that formed a slug flow in microchannel and significantly increased mass transfer rates. The mass transfer coefficient significantly increased and exhibited a linear relationship with the flow rate. Hesperidinase could be efficiently reused at least 5 times, without losing any activity. The bonding mechanism and secondary structure of hesperidinase indicated that hesperidinase had a greater affinity to rutin at a production rate of 4 μL/min in this segmented flow microreactor.

Microscale technology and biocatalytic processes: opportunities and challenges for synthesis

Despite the expanding presence of microscale technology in chemical synthesis and energy production as well as in biomedical devices and analytical and diagnostic tools, its potential in biocatalytic processes for pharmaceutical and fine chemicals, as well as related industries, has not yet been fully exploited. The aim of this review is to shed light on the strategic advantages of this promising technology for the development and realization of biocatalytic processes and subsequent product recovery steps, demonstrated with examples from the literature. Constraints, opportunities, and the future outlook for the implementation of these key green engineering methods and the role of supporting tools such as mathematical models to establish sustainable production processes are discussed.

Microbioreactors and scale-down models: growth of CHO cells using the Pall Micro24 MicroReactor system

Microbioreactors are increasingly used within animal cell biotechnology to grow mammalian cells for cell line screening and to facilitate process development. Many such devices have been reported in the literature, but only a small number are available commercially. Microbioreactors range in complexity from simple plate-based systems to complex automated parallel bioreactors designed to enable the meaningful scale-down of conventional bioprocesses. The Micro24 MicroReactor system (Pall Life Sciences) fits between these extremes providing 24× 7 mL parallel "bioreactors" with individual monitoring and control of temperature, pH, and dissolved oxygen. Inoculation, sampling, and feed additions are carried out manually in a Biological Safety Cabinet. In this chapter we describe the use of the Micro24 system to carry out screening or process development experiments with CHO cells.

Rapid synthesis of propyl caffeate in ionic liquid using a packed bed enzyme microreactor under continuous-flow conditions

Propyl caffeate has the highest antioxidant activity among caffeic acid alkyl esters, but its industrial production via enzymatic transesterification in batch reactors is hindered by a long reaction time (24h). To develop a rapid process for the production of propyl caffeate in high yield, a continuous-flow microreactor composed of a two-piece PDMS in a sandwich-like microchannel structure was designed for the transesterification of methyl caffeate and 1-propanol catalyzed by Novozym 435 in [B mim][CF3SO3]. The maximum yield (99.5%) in the microreactor was achieved in a short period of time (2.5h) with a flow rate of 2 μL/min, which kinetic constant Km was 16 times lower than that of a batch reactor. The results indicated that the use of a continuous-flow packed bed enzyme microreactor is an efficient method of producing propyl caffeate with an overall yield of 84.0%.

Flow synthesis of phenylserine using threonine aldolase immobilized on Eupergit support

Threonine aldolase (TA) from Thermotoga maritima was immobilized on an Eupergit support by both a direct and an indirect method. The incubation time for the direct immobilization method was optimized for the highest amount of enzyme on the support. By introducing the immobilized TA in a packed-bed microreactor, a flow synthesis of phenylserine was developed, and the effects of temperature and residence time were studied in particular. Calculations of the Damköhler number revealed that no mass transfer limitations are given in the micro-interstices of the packed bed. The yield does not exceed 40% and can be rationalized by the natural equilibrium as well as product inhibition which was experimentally proven. The flow synthesis with the immobilized enzyme was compared with the corresponding transformation conducted with the free enzyme. The product yield was further improved by operating under slug flow conditions which is related to the very short residence time distribution. In all cases 20% diastereomeric excess (de) and 99% enantiomeric excess (ee) were observed. A continuous run of the reactant solution was carried out for 10 hours in order to check enzyme stability at higher temperature. Stable operation was achieved at 20 minute residence time. Finally, the productivity of the reactor was calculated, extrapolated to parallel run units, and compared with data collected previously.

Flow chemistry syntheses of natural products

The development and application of continuous flow chemistry methods for synthesis is a rapidly growing area of research. In particular, natural products provide demanding challenges to this developing technology. This review highlights successes in the area with an emphasis on new opportunities and technological advances.