Development of an electrically responsive hydrogel for programmable in situ immobilization within a microfluidic device.

A novel microfluidic channel device with programmable in situ formation of a hydrogel 3D network was designed. A biocompatible hybrid material consisting of iron ion-crosslinked alginate was used as the active porous medium. The sol-gel transition of the alginate was controlled by the oxidation state of Fe ions and regulated by an external electrical signal through an integrated gold plate electrode. The SEM images, FT-IR analysis, and rheological test demonstrated that homogeneous yet programmable hydrogel films were formed. The higher the concentration of the crosslinker (Fe(iii)), the smaller the pore and mesh size of the hydrogel. Moreover, the hydrogel thickness and volume were tailored by controlling the deposition time and the strength of electric current density. The as-prepared system was employed as an active medium for immobilization of target molecules, using BSA as a drug-mimicking protein. The reductive potential (activated by switching the current direction) caused dissolution of the hydrogel and consequently the release of BSA and Fe. The diffusion of the entrapped molecules was optimally adjusted by varying the dissolution conditions and the initial formulations. Finally, the altering electrical conditions confirm the programmable nature of the electrically responsive material and highlight its wide-ranging application potential.

Microfluidic droplet-based liquid-liquid extraction: online model validation.

Droplet-based liquid-liquid extraction in a microchannel was studied, both theoretically and experimentally. A full 3D mathematical model, incorporating convection and diffusion in all spatial directions along with the velocity profile, was developed to depict the governing transport characteristics of droplet-based microfluidics. The finite elements method, as the most common macroscale simulation technique, was used to solve the set of differential equations regarding conservation of moment, mass and solute concentration in a two-domain system coupled by interfacial surface of droplet-based flow pattern. The model was numerically verified and validated online by following the concentrations of a solute in two phases within the microchannel. The relative azobenzene concentration profiles in a methanol/n-octane two-phase system at different positions along the channel length were retrieved by means of a thermal lens microscopic (TLM) technique coupled to a microfluidic system, which gave results of high spatial and temporal resolution. Very good agreement between model calculations and online experimental data was achieved without applying any fitting procedure to the model parameters.

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.

Continuous steroid biotransformations in microchannel reactors.

The use of microchannel reactor based technologies within the scope of bioprocesses as process intensification and production platforms is gaining momentum. Such trend can be ascribed a particular set of characteristics of microchannel reactors, namely the enhanced mass and heat transfer, combined with easier handling and smaller volumes required, as compared to traditional reactors. In the present work, a continuous production process of 4-cholesten-3-one by the enzymatic oxidation of cholesterol without the formation of any by-product was assessed. The production was carried out within Y-shaped microchannel reactors in an aqueous-organic two-phase system. Substrate was delivered from the organic phase to aqueous phase containing cholesterol oxidase and the product formed partitions back to the organic phase. The aqueous phase was then forced through a plug-flow reactor, containing immobilized catalase. This step aimed at the reduction of hydrogen peroxide formed as a by-product during cholesterol oxidation, to avoid cholesterol oxidase deactivation due to said by-product. This setup was compared with traditional reactors and modes of operation. The results showed that microchannel reactor geometry outperformed traditional stirred tank and plug-flow reactors reaching similar conversion yields at reduced residence time. Coupling the plug-flow reactor containing catalase enabled aqueous phase reuse with maintenance of 30% catalytic activity of cholesterol oxidase while eliminating hydrogen peroxide. A final production of 36 m of cholestenone was reached after 300 hours of operation.

Assessment of physical leaching processes of some elements in soil upon ingestion by continuous leaching and modeling.

The physical processes controlling the desorption of some elements (B, Cd, Co, Mn, Ni, and Sr) from soils in a continuous leaching system representing the human stomach are investigated here by fitting experimental leaching data to a mathematical particle diffusion model. Soil samples (50 mg) from Cornwall, UK, contained in a flow-through extraction chamber (ca. 6.5 mL) were intimately contacted with artificial gastric solution at various flow rates (0.42-1.42 mL min(-1)) for up to ca. 4 h, followed by analysis of the fractions collected with inductively coupled plasma mass spectrometry (ICP-MS). The leaching profiles of the various elements were fitted to a mathematical model incorporating two mass transfer processes (liquid film diffusion and apparent solid phase diffusion) to determine the effective external mass transfer coefficient (beta) and the apparent intraparticle soil diffusion coefficient (D(a)). A system of partial differential equations was solved numerically with a finite difference discretization of the computational domain allowing the rate limiting physical desorption process(es) for each element to be determined. The (thermodynamic) driving force of the leaching process is defined by the distribution coefficient (K(d0)) between soil and leachant. Although the K(d0) values investigated are very similar (ca. 6-15 L kg(-1)) for the elements studied with the exception of B (ca. 2.7 L kg(-1)), the leaching profiles are very different due to diffusion-limited processes. The elements may be classified as limited by beta (B, Sr, and Cd), by D(a) (Co, and Mn) or by beta and D(a) (Ni). This results in quantifiable parameters for the liability of elements in soil upon ingestion which may be implemented in future risk assessment protocols.

Estimation of the specific surface area for a porous carrier.

In biofilm systems, treatment performance is primarily dependent upon the available biofilm growth surface area in the reactor. Specific surface area is thus a parameter that allows for making comparisons between different carrier technologies used for wastewater treatment. In this study, we estimated the effective surface area for a spherical, porous polyvinyl alcohol (PVA) gel carrier (Kuraray) that has previously demonstrated effectiveness for retention of autotrophic and heterotrophic biomass. This was accomplished by applying the GPS-X modeling tool (Hydromantis) to a comparative analysis of two moving-bed biofilm reactor (MBBR) systems. One system consisted of a lab-scale reactor that was fed synthetic wastewater under autotrophic conditions where only the nitrification process was studied. The other was a pre-denitrification pilot-scale plant that was fed real, primary-settled wastewater. Calibration of an MBBR process model for both systems indicated an effective specific surface area for PVA gel of 2500 m2/m3, versus a specific surface area of 1000 m2/m3 when only the outer surface of the gel beads is considered. In addition, the maximum specific growth rates for autotrophs and heterotrophs were estimated to be 1.2/day and 6.0/day, respectively.

Modeling and finite difference numerical analysis of reaction-diffusion dynamics in a microreactor.

A theoretical description with numerical experiments and analysis of the reaction-diffusion processes of homogeneous and non-homogeneous reactions in a microreactor is presented considering the velocity profile for laminar flows of miscible and immiscible fluids in a microchannel at steady-state conditions. A Mathematical model in dimensionless form, containing convection, diffusion, and reaction terms are developed to analyze and to forecast the reactor performance. To examine the performance of different types of reactors, the outlet concentrations for the plug-flow reactor (PFR), and the continuous stirred-tank reactor (CSTR) are also calculated for the case of an irreversible homogeneous reaction of two components. The comparison of efficiency between ideal conventional macroscale reactors and the microreactor is presented for a wide range of operating conditions, expressed as different Pe numbers (0.01 < Pe < 10). The numerical procedure of complex non-linear systems based on an implicit finite-difference method improved by non-equidistant differences is proposed.

Oxidation of Coniferyl Alcohol Catalyzed by Laccases from Trametes versicolor.

Oxidation of coniferyl alcohol catalyzed by commercial laccase and crude laccase produced during the submerged cultivation of Trametes versicolor MZKI G-99 in a medium containing the waste from paper industry was investigated. pH of 6.6 and temperature of 35 °C was found to be optimal for coniferyl alcohol oxidation catalyzed by commercial laccase. Based on the initial reaction rate measurements, apparent Michaelis-Menten kinetic parameters for commercial laccase were determined in an aqueous media (Vm = 4.387 U mg-1, Km = 0.025 mmol dm-3), as well as in 1:1 (v/v) methanol: phosphate buffer mixture (Vm = 0.979 U mg-1, Km = 0.019 mmol dm-3). Inhibition of substrate was found for crude laccase and the following apparent kinetic parameters Vm = 9.272 U mg-1, Km = 0.045 mmol dm-3 and Ki = 0.002 mmol dm-3 were estimated. Mathematical model of batch process, which includes double-substrate Michaelis-Menten kinetics with oxygen as the second substrate and mass balances, has been developed and validated in experiments with or without additional aeration. 100 % conversions of up to 0.8 mmol dm-3 of coniferyl alcohol in batch experiment due to the high operational stability of enzymes was realized with both laccases.

Lipase-catalyzed synthesis of isoamyl acetate in an ionic liquid/n-heptane two-phase system at the microreactor scale.

A continuously operated psi-shaped microreactor was used for lipase-catalyzed synthesis of isoamyl acetate in the 1-butyl-3-methylpyridinium dicyanamide/n-heptane two-phase system. The chosen solvent system with dissolved Candida antarctica lipase B, which was attached to the ionic liquid/n-heptane interfacial area due to its amphiphilic properties, was shown to be highly efficient and enabled simultaneous esterification and product removal. At preliminarily selected conditions regarding the type of acyl donor, its molar ratio to alcohol and enzyme concentration, 48.4 g m(-3) s(-1) of isoamyl acetate was produced, which was almost three-fold better as compared to the intensely mixed batch process. This was mainly a consequence of efficient reaction-diffusion dynamics in the microchannel system, where the developed flow pattern comprising of intense emulsification provided a large interfacial area for the reaction and simultaneous product extraction.

Steroid extraction in a microchannel system--mathematical modelling and experiments.

The continuous ethyl acetate extraction of progesterone and 11alpha-hydroxyprogesterone, a reactant and the product of the biotransformation step involved in corticosteroid production, was studied in a microchannel at different flow velocities. In addition, non-steady state batch extraction without mixing was performed and modelled in order to verify the theoretically predicted parameters. In order to analyze experimental data and to forecast microreactor performance, a three-dimensional mathematical model with convection and diffusion terms was developed considering the velocity profile for laminar flow of two parallel phases in a microchannel at steady-state conditions. For the numerical solution of a complex equation system, non-equidistant finite differences were used. Very good agreement between model calculations and experimental data was achieved without any fitting procedure. Due to the efficient phase separation and high extraction yields obtained, the micro scale extraction units were found to be a promising tool for the development of an integrated system of 11alpha-hydroxylation of progesterone by Rhizopus nigricans in the form of pellets.