A novel enzymatic microreactor with Aspergillus oryzae β-galactosidase immobilized on silicon dioxide nanosprings

Wall-Immobilized Biocatalyst vs. Packed Bed in Miniaturized Continuous Reactors: Performances and Scale-Up

Sustainable biocatalysis syntheses have gained considerable popularity over the years. However, further optimizations - notably to reduce costs - are required if the methods are to be successfully deployed in a range of areas. As part of this drive, various enzyme immobilization strategies have been studied, alongside process intensification from batch to continuous production. The flow bioreactor portfolio mainly ranges between packed bed reactors and wall-immobilized enzyme miniaturized reactors. Because of their simplicity, packed bed reactors are the most frequently encountered at lab-scale. However, at industrial scale, the growing pressure drop induced by the increase in equipment size hampers their implementation for some applications. Wall-immobilized miniaturized reactors require less pumping power, but a new problem arises due to their reduced enzyme-loading capacity. This review starts with a presentation of the current technology portfolio and a reminder of the metrics to be applied with flow bioreactors. Then, a benchmarking of the most recent relevant works is presented. The scale-up perspectives of the various options are presented in detail, highlighting key features of industrial requirements. One of the main objectives of this review is to clarify the strategies on which future study should center to maximize the performance of wall-immobilized enzyme reactors.

Enhanced control of bioactivity of tissue plasminogen activator (tPA) through domain-directed enzymatic oxidation of terminal galactose

Introduction: In targeted enzyme prodrug constructs, it is critical to control the bioactivity of the drug in its prodrug form. The preparation of such constructs often involves conjugation reactions directed to functional groups on amino acid side chains of the protein, which result in random conjugation and incomplete control of bioactivity of a prodrug, which may result in significant nontarget effect. Thus, more specific method of modification is desired. If the drug is a glycoprotein, enzymatic oxidation may offer an alternative approach for therapeutic glycoproteins. Methods: Tissue plasminogen activator (tPA), a model glycoprotein enzyme, was treated with galactose oxidase (GO) and horseradish peroxidase, followed by thiolation reaction and conjugation with low molecular weight heparin (LMWH). The LMWH-tPA conjugate was isolated by ion-exchange chromatography followed by centrifugal filtration. The conjugate was characterized for its fibrinolytic activity and for its plasminogen activation through an indirect amidolytic assay with a plasmin-specific substrate S-2251 when LMWH-tPA conjugate is complexed with protamine-albumin conjugate, followed by triggered activation in the presence of heparin. Results: LMWH-tPA conjugate prepared via enzymatic oxidation retained ~95% of its fibrinolytic activity with respect to native tPA. Upon complexation with protamine-albumin conjugate, the activity of LMWH-tPA was effectively inhibited (~90%) whereas the LMWH-tPA prepared by random thiolation exhibited ~55% inhibition. Addition of heparin fully generated the activities of both conjugates. Conclusion: The tPA was successfully modified via enzymatic oxidation by GO, resulting in enhanced control of its activity in the prodrug construct. This approach can be applied to other therapeutic glycoproteins.

Enzymatic Bioreactors: An Electrochemical Perspective

Biocatalysts provide a number of advantages such as high selectivity, the ability to operate under mild reaction conditions and availability from renewable resources that are of interest in the development of bioreactors for applications in the pharmaceutical and other sectors. The use of oxidoreductases in biocatalytic reactors is primarily focused on the use of NAD(P)-dependent enzymes, with the recycling of the cofactor occurring via an additional enzymatic system. The use of electrochemically based systems has been limited. This review focuses on the development of electrochemically based biocatalytic reactors. The mechanisms of mediated and direct electron transfer together with methods of immobilising enzymes are briefly reviewed. The use of electrochemically based batch and flow reactors is reviewed in detail with a focus on recent developments in the use of high surface area electrodes, enzyme engineering and enzyme cascades. A future perspective on electrochemically based bioreactors is presented.

Characterization of Methyl-Functionalized Silica Nanosprings for Superhydrophobic and Defrosting Coatings

Thin non-perfluoroalkoxy superhydrophobic coatings are desirable for heat exchangers because of their lower thermal resistance and reduced environmental concerns. Coatings requirements must also include robustness and longevity and facilitate high defrosting rates in refrigeration applications to warrant their adoption and use. Methyl-functionalized silica nanosprings (SN) possess water droplet static contact angles above 160° with contact angle hysteresis values as low as 6.9° for a sub-micrometer-thick coating. The methyl functional groups render the silica surface hydrophobic, whereas the geometrical and topographical characteristics of the nanosprings make it super-hydrophobic. Results show that SN are capable of removing 95% of the frost from the surface at a lower temperature than the base aluminum substrate. The sub-micrometer SN coating also decreases the time to defrost by ≈1.5 times and can withstand more than 20 frosting-defrosting cycles in a high humidity environment akin to real working conditions for heat exchangers.

A Spring in Performance: Silica Nanosprings Boost Enzyme Immobilization in Microfluidic Channels

Enzyme microreactors are important tools of miniaturized analytics and have promising applications in continuous biomanufacturing. A fundamental problem of their design is that plain microchannels without extensive static internals, or packings, offer limited exposed surface area for immobilizing the enzyme. To boost the immobilization in a manner broadly applicable to enzymes, we coated borosilicate microchannels with silica nanosprings and attached the enzyme, sucrose phosphorylase, via a silica-binding module genetically fused to it. We showed with confocal fluorescence microscopy that the enzyme was able to penetrate the ∼70 μm-thick nanospring layer and became distributed uniformly in it. Compared with the plain surface, the activity of immobilized enzyme was enhanced 4.5-fold upon surface coating with nanosprings and further increased up to 10-fold by modifying the surface of the nanosprings with sulfonate groups. Operational stability during continuous-flow biocatalytic synthesis of α-glucose 1-phosphate was improved by a factor of 11 when the microreactor coated with nanosprings was used. More than 85% of the initial conversion rate was retained after 840 reactor cycles performed with a single loading of enzyme. By varying the substrate flow rate, the microreactor performance was conveniently switched between steady states of quantitative product yield (50 mM) and optimum productivity (19 mM min^-1) at a lower product yield of 40%. Surface coating with silica nanosprings thus extends the possibilities for enzyme immobilization in microchannels. It effectively boosts the biocatalytic function of a microstructured reactor limited otherwise by the solid surface available for immobilizing the enzyme.

Renewable Wood Pulp Paper Reactor with Hierarchical Micro/Nanopores for Continuous-Flow Nanocatalysis

Continuous-flow nanocatalysis based on metal nanoparticle catalyst-anchored flow reactors has recently provided an excellent platform for effective chemical manufacturing. However, there has been limited progress in porous structure design and recycling systems for metal nanoparticle-anchored flow reactors to create more efficient and sustainable catalytic processes. In this study, traditional paper is used for a highly efficient, recyclable, and even renewable flow reactor by tailoring the ultrastructures of wood pulp. The "paper reactor" offers hierarchically interconnected micro- and nanoscale pores, which can act as convective-flow and rapid-diffusion channels, respectively, for efficient access of reactants to metal nanoparticle catalysts. In continuous-flow, aqueous, room-temperature catalytic reduction of 4-nitrophenol to 4-aminophenol, a gold nanoparticle (AuNP)-anchored paper reactor with hierarchical micro/nanopores provided higher reaction efficiency than state-of-the-art AuNP-anchored flow reactors. Inspired by traditional paper materials, successful recycling and renewal of AuNP-anchored paper reactors were also demonstrated while high reaction efficiency was maintained.

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.

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.

Asymmetric surface effect on the configuration of bilayer Si/SiGe nanosprings

This study investigates the asymmetric surface effect on nanosprings composed of Si/SiGe bilayer thin films.

A View Through Novel Process Windows

This mini-review discusses some of the recent work on novel process windows by the Micro Flow Chemistry and Process Technology group at the Eindhoven University of Technology, and their associates. Novel process windows consist of unconventional approaches to boost chemical production, often requiring harsh reaction conditions at short to very short time-scales. These approaches are divided into six routes: the use of high temperatures, high pressures, and high concentrations (or solvent-free), new chemical transformations, explosive conditions, and process simplification and integration. Microstructured reactors, due to their inherent safety, short time-scales, and the high degree of process control, are the means that make such extreme chemistry possible.

Synthetic osteogenic extracellular matrix formed by coated silicon dioxide nanosprings

Background

The design of biomimetic materials that parallel the morphology and biology of extracellular matrixes is key to the ability to grow functional tissues in vitro and to enhance the integration of biomaterial implants into existing tissues in vivo. Special attention has been put into mimicking the nanostructures of the extracellular matrix of bone, as there is a need to find biomaterials that can enhance the bonding between orthopedic devices and this tissue.

Methods

We have tested the ability of normal human osteoblasts to propagate and differentiate on silicon dioxide nanosprings, which can be easily grown on practically any surface. In addition, we tested different metals and metal alloys as coats for the nanosprings in tissue culture experiments with bone cells.

Results

Normal human osteoblasts grown on coated nanosprings exhibited an enhanced rate of propagation, differentiation into bone forming cells and mineralization. While osteoblasts did not attach effectively to bare nanowires grown on glass, these cells propagated successfully on nanosprings coated with titanium oxide and gold. We observed a 270 fold increase in the division rate of osteoblasts when grow on titanium/gold coated nanosprings. This effect was shown to be dependent on the nanosprings, as the coating by themselves did not alter the growth rate of osteoblast. We also observed that titanium/zinc/gold coated nanosprings increased the levels of osteoblast production of alkaline phosphatase seven folds. This result indicates that osteoblasts grown on this metal alloy coated nanosprings are differentiating to mature bone making cells. Consistent with this hypothesis, we showed that osteoblasts grown on the same metal alloy coated nanosprings have an enhanced ability to deposit calcium salt.

Conclusion

We have established that metal/metal alloy coated silicon dioxide nanosprings can be used as a biomimetic material paralleling the morphology and biology of osteogenic extracellular matrix. The coated nanosprings enhance normal human osteoblasts cellular behaviors needed for improving osseointegration of orthopedic materials. Thus, metal-coated nanosprings represent a novel biomaterial that could be exploited for improving success rates of orthopedic implant procedures.

Microfluidic devices: useful tools for bioprocess intensification

The dawn of the new millennium saw a trend towards the dedicated use of microfluidic devices for process intensification in biotechnology. As the last decade went by, it became evident that this pattern was not a short-lived fad, since the deliverables related to this field of research have been consistently piling-up. The application of process intensification in biotechnology is therefore seemingly catching up with the trend already observed in the chemical engineering area, where the use of microfluidic devices has already been upgraded to production scale. The goal of the present work is therefore to provide an updated overview of the developments centered on the use of microfluidic devices for process intensification in biotechnology. Within such scope, particular focus will be given to different designs, configurations and modes of operation of microreactors, but reference to similar features regarding microfluidic devices in downstream processing will not be overlooked. Engineering considerations and fluid dynamics issues, namely related to the characterization of flow in microchannels, promotion of micromixing and predictive tools, will also be addressed, as well as reflection on the analytics required to take full advantage of the possibilities provided by microfluidic devices in process intensification. Strategies developed to ease the implementation of experimental set-ups anchored in the use of microfluidic devices will be briefly tackled. Finally, realistic considerations on the current advantages and limitation on the use of microfluidic devices for process intensification, as well as prospective near future developments in the field, will be presented.

Enzyme-immobilized microfluidic process reactors

Microreaction technology, which is an interdisciplinary science and engineering area, has been the focus of different fields of research in the past few years. Several microreactors have been developed. Enzymes are a type of catalyst, which are useful in the production of substance in an environmentally friendly way, and they also have high potential for analytical applications. However, not many enzymatic processes have been commercialized, because of problems in stability of the enzymes, cost, and efficiency of the reactions. Thus, there have been demands for innovation in process engineering, particularly for enzymatic reactions, and microreaction devices represent important tools for the development of enzyme processes. In this review, we summarize the recent advances of microchannel reaction technologies especially for enzyme immobilized microreactors. We discuss the manufacturing process of microreaction devices and the advantages of microreactors compared to conventional reaction devices. Fundamental techniques for enzyme immobilized microreactors and important applications of this multidisciplinary technology are also included in our topics.