Microchannel enzyme reactors and their applications for processing

A sustainable and Integrated Microbial Biocatalysis of Resveratrol from Polygonum cuspidatum Siebold & Zucc Using Cellulose-Based Immobilised Aspergillus niger with Deep Eutectic Solvent-Assisted Microreactors

An efficient and green method was developed using deep eutectic solvent assistance to enhance the biotransformation method of producing resveratrol from Polygonum cuspidatum Siebold & Zucc, using cellulose-based immobilised Aspergillus niger in the process. Various deep eutectic solvents (DES) were screened to obtain a superior biocatalytic effect. The increase in DES concentration aggravated the degree of cell membrane damage. Natural deep eutectic solvents (NADES) exhibited a more favourable catalytic effect than DES due to their excellent biocompatibility. This enhancement is associated with the hydrogen bonding donor components present in NADES, with catalytic ability ranking as alcohol-based > sugar-based > organic acid. CHCL/EG exhibited the maximum catalytic effect at 1.0 wt%. Under optimal conditions (pH 6.5; temperature, 29.5 °C; ratio of liquid to solid 20:1 (mL/g), and time 47 h), the resveratrol yield reached 32.79 mg/g, which was 13.06-fold to that of the untreated sample (2.51 mg/g). The residual activity of the cellulose-based microreactor was 81.46% after ten trials. The proposed method was successfully employed, demonstrating higher biocatalysis efficiencies and superior environmental protection compared to conventional solvents for resveratrol biocatalysis.

Microbial production and applications of β-glucosidase-A review

β-Glucosidase exists in all areas of living organisms, and microbial β-glucosidase has become the main source of its production because of its unique physicochemical properties and the advantages of high-yield production by fermentation. With the rise of the green circular economy, the production of enzymes through the fermentation of waste as the substrate has become a popular trend. Lignocellulosic biomass is an easily accessible and sustainable feedstock that exists in nature, and the production of biofuels from lignocellulosic biomass requires the involvement of β-glucosidase. This review proposes ways to improve β-glucosidase yield and catalytic efficiency. Optimization of growth conditions and purification strategies of enzymes can increase enzyme yield, and enzyme immobilization, genetic engineering, protein engineering, and whole-cell catalysis provide solutions to enhance the catalytic efficiency and activity of β-glucosidase. Besides, the diversified industrial applications, challenges and prospects of β-glucosidase are also described.

Capillary Filling in Open Rectangular Microchannels with a Spatially Varying Contact Angle

Capillary flow in microchannels is important for many technologies, such as microfluidic devices, heat exchangers, and fabrication of printed electronics. Due to a readily accessible interior, open rectangular microchannels are particularly attractive for these applications. Here, we develop modifications of the Lucas-Washburn model to explore how a spatially varying contact angle influences capillary flow in open rectangular microchannels. Four cases are considered: (i) different uniform contact angles on channel sidewalls and channel bottom, (ii) contact angles varying along the channel cross section, (iii) contact angle varying monotonically along the channel length, and (iv) contact angle varying periodically along the channel length. For case (i), it is found that the maximum filling velocity is more sensitive to changes in the wall contact angle. For case (ii), the contact angles can be averaged to transform the problem into that of case (i). For case (iii), the time evolution of the meniscus position no longer follows the simple square-root law at short times. Finally, for case (iv), the problem is well described by using a uniform contact angle that is a suitable average. These results provide insights into how to design contact-angle variations to control capillary filling and into the influence of naturally occurring contact-angle variations on capillary flow.

Strategies for Automated Enzymatic Glycan Synthesis (AEGS)

Glycans are the most abundant biopolymers on earth and are constituents of glycoproteins, glycolipids, and proteoglycans with multiple biological functions. The availability of different complex glycan structures is of major interest in biotechnology and basic research of biological systems. High complexity, establishment of general and ubiquitous synthesis techniques, as well as sophisticated analytics, are major challenges in the development of glycan synthesis strategies. Enzymatic glycan synthesis with Leloir-glycosyltransferases is an attractive alternative to chemical synthesis as it can achieve quantitative regio- and stereoselective glycosylation in a single step. Various strategies for synthesis of a wide variety of different glycan structures has already be established and will exemplarily be discussed in the scope of this review. However, the application of enzymatic glycan synthesis in an automated system has high demands on the equipment, techniques, and methods. Different automation approaches have already been shown. However, while these techniques have been applied for several glycans, only a few strategies are able to conserve the full potential of enzymatic glycan synthesis during the process - economical and enzyme technological recycling of enzymes is still rare. In this review, we show the major challenges towards Automated Enzymatic Glycan Synthesis (AEGS). First, we discuss examples for immobilization of glycans or glycosyltransferases as an important prerequisite for the embedment and implementation in an enzyme reactor. Next, improvement of bioreactors towards automation will be described. Finally, analysis and monitoring of the synthesis process are discussed. Furthermore, automation processes and cycle design are highlighted. Accordingly, the transition of recent approaches towards a universal automated glycan synthesis platform will be projected. To this end, this review aims to describe essential key features for AEGS, evaluate the current state-of-the-art and give thought- encouraging impulses towards future full automated enzymatic glycan synthesis.

Highly efficient and recyclable monolithic bioreactor for interfacial enzyme catalysis

HYPOTHESIS

Biocatalysts are key to the realization of all bioconversions in nature. However, the difficulty of combining the biocatalyst and other chemicals in one system limits their application in artificial reaction systems. Although some effort, such as Pickering interfacial catalysis and enzyme-immobilized microchannel reactors, have addressed this challenge an effective method to combine chemical substrates and biocatalysts in a highly efficient and re-usable monolith system is still to be developed.

EXPERIMENTS

A repeated batch-type biphasic interfacial biocatalysis microreactor was developed using enzyme-loaded polymersomes in the void surface of porous monoliths. Polymersomes, loaded with Candida antarctica Lipase B (CALB), are fabricated by self-assembly of the copolymer PEO-b-P(St-co-TMI) and used to stabilize oil-in-water (o/w) Pickering emulsions as a template to prepare monoliths. By adding monomer and Tween 85 to the continuous phase, controllable open-cell monoliths are prepared to inlay CALB-loaded polymersomes in the pore walls.

FINDINGS

The microreactor is proven to be highly effective and recyclable when a substrate flows through it, which offers superior benefits of absolute separation to a pure product and no enzyme loss. The relative enzyme activity is constantly maintained above 93% in 15 cycles. The enzyme is constantly present in the microenvironment of the PBS buffer ensuring its immunity to inactivation and facilitating its recycling.

Biotin-Avidin System-Based Delivery Enhances the Therapeutic Performance of MSC-Derived Exosomes

Exosomes (EXs) shed by mesenchymal stem cells (MSCs) are potent therapeutic agents that promote wound healing and regeneration, but when used alone in vivo, their therapeutic potency is diminished by rapid clearance and bioactivity loss. Inspired by the biotin-avidin interaction, we developed a simple yet versatile method for the immobilization of MSC-derived EXs (MSC-EXs) into hydrogels and achieved sustained release for regenerative purposes. First, biotin-modified gelatin methacryloyl (Bio-GelMA) was fabricated by grafting NHS-PEG₁₂-biotin onto the amino groups of GelMA. Biotin-modified MSC-EXs (Bio-EXs) were then synthesized using an in situ self-assembling biotinylation strategy, which provided sufficient binding sites for MSC-EX delivery with little effect on their cargo composition. Thereafter, Bio-EXs were immobilized in Bio-GelMA via streptavidin to generate Bio-GelMA@Bio-EX hydrogels. An in vitro analysis demonstrated that Bio-EXs could be taken up by macrophages and exerted immunomodulatory effects similar to those of MSC-EXs, and Bio-GelMA@Bio-EX hydrogels provided sustained release of MSC-EXs for 7 days. After subcutaneous transplantation, a more constant retention of MSC-EXs in Bio-GelMA@Bio-EX hydrogels was observed for up to 28 days. When placed in an artificial periodontal multitissue defect, the functionalized hydrogels exhibited an optimized therapeutic performance to regrow complex periodontal tissues, including acellular cementum, periodontal ligaments (PDLs), and alveolar bone. In this context, Bio-GelMA@Bio-EX hydrogels exerted a robust immunomodulatory effect that promoted macrophage polarization toward an M2 phenotype. Our findings demonstrate that MSC-EXs delivered with the aid of the biotin-avidin system exhibit robust macrophage-modulating and repair-promoting functions and suggest a universal approach for the development of MSC-EX-functionalized biomaterials for advanced therapies.

Stability of enzyme immobilized on the nanofluidic channel surface

The lifetime of an enzyme is critical to prevent system failure and optimize maintenance schedules in biological and analytical chemistry. The lifetime metrics of an enzyme can be evaluated from enzyme activity in terms of catalytic cycles per enzyme at various storage times. Trypsin, which is a gold-standard enzyme in proteomics, has been known to decrease activity due to self-digestion. To improve the activity of trypsin, enzyme reactors have developed by immobilizing in micro and nanospace. However, an evaluation method for the catalytic cycle has not been established due to major issues such as nonuniform space, unstable liquid transport, and self-digestion during immobilization in conventional work. To solve these issues, we have previously developed an ultra-fast enzyme reactor with a well-defined nanofabrication method, stable liquid transport, and partial enzyme modification. Here, we aimed to investigate catalytic cycles in a nanochannel. To extend enzyme lifetime efficiently, we have evaluated the optimal immobilization process and catalytic cycles of trypsin. As a result, immobilized enzyme densities by the trypsinogen immobilization process were increased at all concentrations compared to the trypsin immobilization process. To evaluate the lifetime of trypsin, the immobilized enzyme densities and activities were almost the same before and after 72 h of enzyme storage, and the calculated catalytic cycles were 1740. These results indicated that self-digestion of the immobilized enzyme was highly suppressed. Consequently, the reaction efficiency has been evaluated depending on the catalytic cycles from the substrate for the first time, while preventing self-digestion by trypsin.

Microreactor Technology: Identifying Focus Fields and Emerging Trends by Using CiteSpace II

Microreactors have gained widespread attention from academia and industrial researchers due to their exceptionally fast mass and heat transfer and flexible control. In this work, CiteSpace software was used to systematically analyze the relevant literature to gain a comprehensively understand on the research status of microreactors in various fields. The results show that the research depth and application scope of microreactors are continuing to expand. The top 10 most popular research fields are photochemistry, pharmaceutical intermediates, multistep flow synthesis, mass transfer, computational fluid dynamics, μ-TAS (micro total analysis system), nanoparticles, biocatalysis, hydrogen production, and solid-supported reagents. The evolution trends of current focus areas are examined, including photochemistry, mass transfer, biocatalysis and hydrogen production and their milestone literature is analyzed in detail. This article demonstrates the development of different fields of microreactors technology and highlights the unending opportunities and challenges offered by this fascinating technology.

Microfluidic Immobilized Enzymatic Reactors for Proteomic Analyses—Recent Developments and Trends (2017–2021)

Given the strong interdisciplinary nature of microfluidic immobilized enzyme reactor (μ-IMER) technology, several branches of science contribute to its successful implementation. A combination of physical, chemical knowledge and engineering skills is often required. The development and application of μ-IMERs in the proteomic community are experiencing increasing importance due to their attractive features of enzyme reusability, shorter digestion times, the ability to handle minute volumes of sample and the prospect of on-line integration into analytical workflows. The aim of this review is to give an account of the current (2017–2021) trends regarding the preparation of microdevices, immobilization strategies, and IMER configurations. The different aspects of microfabrication (designs, fabrication technologies and detectors) and enzyme immobilization (empty and packed channels, and monolithic supports) are surveyed focusing on μ-IMERs developed for proteomic analysis. Based on the advantages and limitations of the published approaches and the different applications, a probable perspective is given.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Direct Measurement of Initial Rate of Enzyme Reaction by Electrokinetic Filtration Using a Hydrogel-plugged Capillary Device

A novel electrokinetic filtration device using a plugged hydrogel was developed to directly measure the initial rate of enzyme reactions. In the proposed method, the enzyme reaction proceeded only for a short time when the substrate was passed through a thin layer of enzyme trapped by the hydrogel without any lag times for mixing and detection. In experimental conditions, alkaline phosphatase (enzyme) was filtrated at a cathodic-side interface of the plugged hydrogel by molecular sieving effect, providing the thin enzyme zone whose thickness was approximately 100 μm. When 4-methylumberiferyl phosphate (substrate) was electrokinetically introduced into the device after trapping the enzyme, 4-methylumberiferone (product) was generated by the enzyme reaction for only 1.26 s as the substrate passed through the trapped enzyme zone. As a result, the initial rate of the enzyme reaction could be directly calculated to 31.0 μM/s by simply dividing the concentration of the product by the tunable reaction time. Compared to the initial rate obtained by mixing the enzyme and substrate solutions, the value of the maximum velocity of the enzyme reaction was 30-fold larger than that in the mixing method due to the preconcentration of the enzyme by trapping. The Michaelis-Menten constant in the proposed method was 2.7-fold larger than that in the mixing method, suggesting the variation of changes in the equilibrium of complex formation under the experimental conditions.

A Review of the Methods of Modeling Multi-Phase Flows within Different Microchannels Shapes and Their Applications

In industrial processes, the microtechnology concept refers to the operation of small devices that integrate the elements of operational and reaction units to save energy and space. The advancement of knowledge in the field of microfluidics has resulted in fabricating devices with different applications in micro and nanoscales. Micro- and nano-devices can provide energy-efficient systems due to their high thermal performance. Fluid flow in microchannels and microstructures has been widely considered by researchers in the last two decades. In this paper, a review study on fluid flow within microstructures is performed. The present study aims to present the results obtained in previous studies on this type of system. First, different types of flows in microchannels are examined. The present article will then review previous articles and present a general summary in each section. Then, the multi-phase flows inside the microchannels are discussed, and the flows inside the micropumps, microturbines, and micromixers are evaluated. According to the literature review, it is found that the use of microstructures enhances energy efficiency. The results of previous investigations revealed that the use of nanofluids as a working fluid in microstructures improves energy efficiency. Previous studies have demonstrated special attention to the design aspects of microchannels and micro-devices compared to other design strategies to improve their performance. Finally, general concluding remarks are presented, and the existing challenges in the use of these devices and suggestions for future investigations are presented.

MONOPHASIC REACTION WITH A PACKED BED MICROREACTOR: CHARACTERIZATION OF MASS TRANSFER AND REACTION

In this paper, the monophasic catalytic reaction in the microreactor is studied. Several factors that may affect the catalytic reaction are discussed, including the pressure drop, the size of catalyst particles, and the channel structure. Finally, some important conclusions can be reached. The change of pressure drop has an effect on the reaction. For example, the C3H6 conversion rate is 62.88% when the pressure drop is 8[Formula: see text]atm, and the C3H6 conversion rate is 61.78% when the pressure drop is 11[Formula: see text]atm. The effect of the change particle radius is not obvious on the reaction. Enhancing the mixing of substances before entering the reaction domain is helpful to the catalytic reaction. There are different substances concentration in catalyst particles at different positions in microreactors. But from the surface to the inside of catalyst particles, the substances concentration has a clear change rule.

Picoliter enzyme reactor on a nanofluidic device exceeding the bulk reaction rate

A picoliter enzyme reactor using a trypsin immobilized nanochannel realized 25 times faster reaction than the bulk reaction.

Hydrogel/enzyme dots as adaptable tool for non-compartmentalized multi-enzymatic reactions in microfluidic devices

Validating the robustness and activity of hydrogel/enzyme dots as adaptable tool for non-compartmentalized multi-enzymatic reactions in microfluidic devices under continuous flow.

A Compartmented Flow Microreactor System for Automated Optimization of Bioprocesses Applying Immobilized Enzymes

In the course of their development, industrial biocatalysis processes have to be optimized in small-scale, e. g., within microfluidic bioreactors. Recently, we introduced a novel microfluidic reactor device, which can handle defined reaction compartments of up to 250 μL in combination with magnetic micro carriers. By transferring the magnetic carriers between subsequent compartments of differing compositions, small scale synthesis, and bioanalytical assays can be conducted. In the current work, this device is modified and extended to broaden its application range to the screening and optimization of bioprocesses applying immobilized enzymes. Besides scaling the maximum compartment volume up to 3 mL, a temperature control module, as well as a focused infrared spot were integrated. By adjusting the pump rate, compartment volumes can be accurately dosed with an error <5% and adjusted to the requested temperature within less than a minute. For demonstration of bioprocess parameter optimization within such compartments, the influence of pH, temperature, substrate concentration, and enzyme carrier loading was automatically screened for the case of transferring UDP-Gal onto N-acetylglucosamine linked to a tert-butyloxycarbonyl protected amino group using immobilized β1,4-galactosyltransferase-1. In addition, multiple recycling of the enzyme carriers and the use of increased compartment volumes also allows the simple production of preparative amounts of reaction products.

Synthesis of alginate-silica hybrid hydrogel for biocatalytic conversion by β-glucosidase in microreactor

The organic-inorganic hybrid materials have been used in different fields to immobilize biomolecules since they offer many advantages. The aim of this study was to optimize and characterize the alginate-silica hybrid hydrogel as a stable and injectable form for microfluidic systems using internal gelation method and increase the stability and activity of immobilized enzyme for biocatalytic conversions as well. Characterization was carried out by scanning electron microscopy, energy dispersive spectroscopy/mapping, Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, and Fourier-transform infrared spectroscopy analyses, and the shrinkages of monoliths were evaluated. Subsequent to optimizing the enzyme concentration (40 μg), hydrolytic conversion of 4-nitrophenyl β-d-glucopyranoside (pNPG) was performed to understand the behavior of the bioconversion in the microfluidic system. The yield was 94% which reached the equilibrium at 24 h indicating that the alginate-silica gel derived microsystem overcome some drawbacks of monolithic systems. Additionally, bioconversion of Ruscus aculeatus saponins was carried out at the same setup in order to obtain aglycon part, which has pharmaceutical significance. Although pure aglycon could not be achieved, an intermediate compound was obtained based on the HPLC analysis. The developed formulation can be utilized for various life science applications.

Recombinant Escherichia coli BL21-pET28a-egfp Cultivated with Nanomaterials in a Modified Microchannel for Biofilm Formation

The application of whole cells as catalytic biofilms in microchannels has attracted increasing scientific interest. However, the excessive biomass formation and structure of biofilms in a reactor limits their use. A microchannel reactor with surface modification was used to colonize recombinant Escherichia coil BL21-pET28a-egfp rapidly and accelerated growth of biofilms in the microchannel. The segmented flow system of 'air/culture medium containing nanomaterials' was firstly used to modulate the biofilms formation of recombinant E. coil; the inhibitory effects of nanomaterials on biofilm formation were investigated. The results indicated that the segmental flow mode has a significant impact on the structure and development of biofilms. Using the channels modified by silane reagent, the culture time of biofilms (30 h) was reduced by 6 h compared to unmodified channels. With the addition of graphene sheets (10 mg/L) in Luria-Bertani (LB) medium, the graphene sheets possessed a minimum inhibition rate of 3.23% against recombinant E. coil. The biofilms cultivated by the LB medium with added graphene sheets were stably formed in 20 h; the formation time was 33.33% shorter than that by LB medium without graphene. The developed method provides an efficient and simple approach for rapid preparation of catalytic biofilms in microchannel reactors.

Synergy of Microtechnology and Biotechnology: Microreactors as an Effective Tool for Biotransformation Processes§: §The paper was presented at European Biotechnology Congress, 25-27 May 2017, Dubrovnik, Croatia

Despite the fact that microreactors have been present for more than 40 years now and that their potential has been extensively exploited in chemical synthesis, analytics and screening, to date very few biocatalytic processes have been explored in microreactors. It is claimed that enzymatic microreactor technology is exactly in the same place where chemical microreactors were 15 years ago. However, general opinion is that the efforts devoted to the research of micro-enzymatic reactors will inaugurate a new breakthrough in bio-based processing. The aim of this review is to explore the synergy between microtechnology, mainly microreactors, and biotechnology, and to assess its potential, opportunities, challenges and future application in biotechnology.

Simplified immobilisation method for histidine-tagged enzymes in poly(methyl methacrylate) microfluidic devices

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1-step immobilisation for histidine-tagged enzymes onto PMMA surfaces developed.

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1-step method achieved similar enzyme binding efficiency to established protocol.

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Model enzyme reaction gave higher specific activity and similar conversion yields.

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1-step method requires less chemicals and time for PMMA surface preparation.

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1-step method provides rapid and efficient way for enzyme immobilisation.

Poly(methyl methacrylate) (PMMA) microfluidic devices have become promising platforms for a wide range of applications. Here we report a simple method for immobilising histidine-tagged enzymes suitable for PMMA microfluidic devices. The 1-step-immobilisation described is based on the affinity of the His-tag/Ni-NTA interaction and does not require prior amination of the PMMA surface, unlike many existing protocols. We compared it with a 3-step immobilisation protocol involving amination of PMMA and linking NTA via a glutaraldehyde cross-linker. These methods were applied to immobilise transketolase (TK) in PMMA microfluidic devices. Binding efficiency studies showed that about 15% of the supplied TK was bound using the 1-step method and about 26% of the enzyme was bound by the 3-step method. However, the TK-catalysed reaction producing l-erythrulose performed in microfluidic devices showed that specific activity of TK in the device utilising the 1-step immobilisation method was approximately 30% higher than that of its counterpart. Reusability of the microfluidic device produced via the 1-step method was tested for three cycles of enzymatic reaction and at least 85% of the initial productivity was maintained. The device could be operated for up to 40 h in a continuous flow and on average 70% of the initial productivity was maintained. The simplified immobilisation method required fewer chemicals and less time for preparation of the immobilised microfluidic device compared to the 3-step method while achieving higher specific enzyme activity. The method represents a promising approach for the development of immobilised enzymatic microfluidic devices and could potentially be applied to combine protein purification with immobilisation.

Use of bioconjugation with cytochrome P450 enzymes

Bioconjugation, defined as chemical modification of biomolecules, is widely employed in biological and biophysical studies. It can expand functional diversity and enable applications ranging from biocatalysis, biosensing and even therapy. This review summarizes how chemical modifications of cytochrome P450 enzymes (P450s or CYPs) have contributed to improving our understanding of these enzymes. Genetic modifications of P450s have also proven very useful but are not covered in this review. Bioconjugation has served to gain structural information and investigate the mechanism of P450s via photoaffinity labeling, mechanism-based inhibition (MBI) and fluorescence studies. P450 surface acetylation and protein cross-linking have contributed to the investigation of protein complexes formation involving P450 and its redox partner or other P450 enzymes. Finally, covalent immobilization on polymer surfaces or electrodes has benefited the areas of biocatalysis and biosensor design. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.

Protein Stability: Enhancement and Measurement

This article defines protein stability, emphasizes its importance and surveys the field of protein stabilization, with summary reference to a selection of 2009-2015 publications. One can enhance stability by, in particular, protein engineering strategies and by chemical modification (including conjugation) in solution. General protocols are set out on how to measure a given protein's (1) kinetic thermal stability, and (2) oxidative stability, and (3) how to undertake chemical modification of a protein in solution.

Thermomyces lanuginosus lipase-catalyzed synthesis of natural flavor esters in a continuous flow microreactor

Enzymatic catalysis is considered to be among the most environmental friendly processes for the synthesis of fine chemicals. In this study, lipase from Thermomyces lanuginosus (Lecitase Ultra™) was used to catalyze the synthesis of flavor esters, i.e., methyl butanoate and methyl benzoate by esterification of the acids with methanol in a microfluidic system. Maximum reaction rates of 195 and 115 mM min⁻¹ corresponding to catalytic efficiencies (k_cat/K_M) of 0.30 and 0.24 min⁻¹ mM⁻¹ as well as yield conversion of 54 and 41 % were observed in methyl butanoate and methyl benzoate synthesis, respectively. Catalytic turnover (k_cat) was higher for methyl butanoate synthesis. Rate of synthesis and yield decreased with increasing flow rates. For both esters, increase in microfluidic flow rate resulted in increased advective transport over molecular diffusion and reaction rate, thus lower conversion. In microfluidic synthesis using T. lanuginosus lipase, the following reaction conditions were 40 °C, flow rate 0.1 mL min⁻¹, and 123 U g⁻¹ enzyme loading found to be the optimum operating limits. The work demonstrated the application of enzyme(s) in a microreactor system for the synthesis of industrially important esters.

Cross-linked enzyme aggregates (CLEA) in enzyme improvement – a review

Structural and functional catalytic characteristics of cross-linked enzyme aggregates (CLEA) are reviewed. Firstly, advantages of enzyme immobilization and existing types of immobilization are described. Then, a wide description of the factors that modify CLEA activity, selectivity and stability is presented. Nowadays CLEA offers an economic, simple and easy tool to reuse biocatalysts, improving their catalytic properties and stability. This immobilization methodology has been widely and satisfactorily tested with a great variety of enzymes and has demonstrated its potential as a future tool to optimize biocatalytic processes.

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.

Markovnikov addition of imidazole derivatives with vinyl esters catalyzed by lipase TL IM from Thermomyces lanuginosus/K2CO3 in a continuous-flow microreactor

In this work, a simple and efficient method for Markovnikov addition of imidazole derivatives to vinyl esters catalyzed by Lipozyme TL IM/K₂CO₃ in a continuous-flow microreactor was described.

Thermosensitive and mucoadhesive pluronic-hydroxypropylmethylcellulose hydrogel containing the mini-CD4 M48U1 is a promising efficient barrier against HIV diffusion through macaque cervicovaginal mucus

To be efficient, vaginal microbicide hydrogels should form a barrier against viral infections and prevent virus spreading through mucus. Multiple particle tracking was used to quantify the mobility of 170-nm fluorescently labeled COOH-modified polystyrene particles (COOH-PS) into thermosensitive hydrogels composed of amphiphilic triblock copolymers with block compositions EOn-POm-EOn (where EO refers to ethylene oxide and PO to propylene oxide) containing mucoadhesive hydroxypropylmethylcellulose (HPMC). COOH-PS were used to mimic the size and the surface charge of HIV-1. Analysis of COOH-PS trajectories showed that particle mobility was decreased by Pluronic hydrogels in comparison with cynomolgus macaque cervicovaginal mucus and hydroxyethylcellulose hydrogel (HEC; 1.5% by weight [wt%]) used as negative controls. Formulation of the peptide mini-CD4 M48U1 used as an anti-HIV-1 molecule into a mixture of Pluronic F127 (20 wt%) and HPMC (1 wt%) did not affect its anti-HIV-1 activity in comparison with HEC hydrogel. The 50% inhibitory concentration (IC50) was 0.53 μg/ml (0.17 μM) for M48U1-HEC and 0.58 μg/ml (0.19 μM) for M48U1-F127-HPMC. The present work suggests that hydrogels composed of F127-HPMC (20/1 wt%, respectively) can be used to create an efficient barrier against particle diffusion in comparison to conventional HEC hydrogels.

Hydration of acrylonitrile to produce acrylamide using biocatalyst in a membrane dispersion microreactor

In this work, a membrane dispersion microreactor was utilized for the hydration of acrylonitrile to produce acrylamide. Through observation using a microscopy, it was found that the acrylonitrile was dispersed into the continuous phase (the aqueous phase contains nitrile hydratase (NHase)) as droplets with a diameter ranged from 25 to 35 μm, hence the mass transfer specific surface area was significantly increased, and the concentration of acrylamide reached 52.5 wt% within 50 min. By contrast, in stirred tanks, the concentration of acrylamide only got 39.5 wt% within 245 min. Moreover, only a few amounts of acrylonitrile were accumulated in this microreactor system. Through optimizing the flow rate, the concentration of acrylamide reached 45.8 wt% within 35 min, the short reaction time greatly weakened the inhibition of acrylonitrile and acrylamide on the enzyme activity, which is suitable for prolonging the life of free cell.

Synthesis of amino acid using a flow-type microreactor containing enzyme–mesoporous silica microsphere composites

A flow-type microreactor containing composites of the enzyme (glutaminase) and mesoporous silica microspheres with a 23.6 nm pore diameter (SBA23.6) exhibited precise, efficient, and continuous synthesis of theanine.