Numerical simulation of a multi-inlet microfluidic device for biosensing purposes in osteoporosis management

Objectives In this paper, the effect of the position of the inlet and outlet microchannels on the flow profile and the geometry of the recognition chamber for sample pre-treatment in an electrochemical biosensor to be used in osteoporosis management were investigated. Methods All numerical computation presented in this work were performed using COMSOL Multiphysics and Fluent. Simulation was performed for a three-dimensional, incompressible Navier-Stokes flow and so explicit biphasic volume of fluid (VOF) equations were used. Results In the designed microfluidic system, a pressure-driven laminar flow with no-slip boundary condition was responsible for fluid actuation through microchannels in a reproducible approach. Based on the simulation results, the number of outlets was increased and the angel through which the inlets and outlets were attached to the microchamber was changed so that the dead volume would be eliminated and the fluid flow trajectory, the velocity field and pressure were evenly distributed across the chamber. The Re number in the inlets was equal to 4.41, suggesting a laminar flow at this site. Conclusion The simulation results along with the fact that the design change was tested using laser ablated tape and a color dye at different steps provided the researchers with the opportunity to study the changes in a fast and accurate but cheap method. The absence of backflow helps with the cross-talk concern in the channels and the lack of bubbles and complete coverage of the chamber helps with a better surface modification and thus better sensing performance

Synergistic Effect of Elicitors in Enhancement of Ganoderic Acid Production: Optimization and Gene Expression Studies

Ganoderma lucidum is one of the most well-known fungi, and has many applications in medicine. Ganoderic acid is among the valuable secondary metabolites of Ganoderma lucidum, and responsible for the inhibition of the tumor cell growth and cancer treatment. Application of ganoderic acid has been limited because of low yields of its production from Ganoderma lucidum. The present study aims to investigate the synergistic effect of elicitors including methyl jasmonate and aspirin on the production of ganoderic acid derived from Ganoderma lucidum mushroom in a shaken flasks using response surface methodology. The results showed that the optimal dose of methyl jasmonate and asprin significantly impacts on the amount of ganoderic acid production as a response (p<0.05). The proposed model predicted the maximum ganoderic acid production as 0.085 mgml-1 in which the optimal concentrations obtained for methyl jasmonate and asprin were 250 mM and 4.4 mM, respectively. Also the influence of ganoderic acid production on the expression of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase and squalene synthase (two important metabolic pathway genes in ganoderic acid) was investigated, and the results showed that these genes’ expression has increased by 10 and 11 folds, respectively. 

Characterization of gold nanoparticle layer deposited on gold electrode by various techniques for improved sensing abilities

The deposition of gold nanoparticles (AuNPs) on the surface of gold electrode is believed to enhance the electrochemical characteristics of the surface. According to the existing literature, this could be performed in various ways. The purpose of the current study was to compare these results and report the most effective technique. In this regard, the layer-by-layer deposition, self-assembled monolayer technique and electro deposition method were investigated. Our results showed that cyclic voltammetry electrodeposition of AuNPs causes an observable increase in the peak current, causing improved electrode kinetics and a reduction in the oxidation potential (thermodynamically feasible reaction). These modified electrodes also showed several advantages with respect to stability and reproducibility

Анализ методов борьбы с парафиновыми отложениями на месторождениях Западной Сибири

В данной работе рассмотрели проблему парафиновых отложений в систематической и всеобъемлющей форме. В результате исследования были подробно рассмотрены причины образования парафиновых отложений, а также методы борьбы и предупреждение парафиновых отложений.In this paper, we have considered the problem of paraffin deposits in a systematic and comprehensive form. As a result of the study, the reasons for the formation of paraffin deposits, as well as methods for controlling and preventing paraffin deposits, were considered in detail

A new method to quantify the CO 2 sensitivity of micro-organisms in shaken bioreactors and scale up to stirred tank fermentors

Small scale shaken bioreactors (e.g. shake flasks) traditionally equipped with different types of sterile closures are very useful tools in biotechnology. The gas transfer coefficient of the sterile closures (kplug) plays an important role in aeration of shaken bioreactors. The value of kplug depends on the average diffusion coefficient of oxygen (DeO2) and different lengths or/and diameters of the neck of flask. Therefore, in this study, a series of pipes with different lengths or/and diameters filled with cotton for a special shake flask, so-called ventilation flask, were employed. The gas transfer through the sterile closure of the ventilation flasks was characterized. Constant values of CO2 and O2 diffusion coefficient were found in all of the ventilation flasks. Considering these values and the neck geometry, a variety of kplug in ventilation flasks were obtained. Since, decreasing kplug causes a reduction of O2 concentration and an accumulation of CO2 in the gas phase of the shaken bioreactors, a realistic understanding and estimation of gas transfer in shaken bioreactors is advantageous to avoid oxygen limitation or carbon dioxide inhibition of a microbial culture. In this study, an unsteady state gas transfer model for shake flasks was developed and experimentally investigated for a wide range of gas transfer coefficients (kplug). The introduced approach is based on the model of Henzler and Schedel [23], which describes the spatially-resolved gas partial pressures inside the sterile closure, affected by the local gas diffusion coefficients and convective Stefan flow. For further easy processing, the resulting total mass transfer coefficient (kplug) is described as a function of the mass flow through the sterile plug (OTRplug) by an empirical equation. This equation is introduced into a simulation model which calculates the gas partial pressures in the head space of the flask. Additionally, the gas transfer rates through the sterile closure and gas-liquid interface inside the flask are provided. Simulations indicate that neglecting the oxygen in the head space volume of the flask at initial conditions (simple steady state assumption) may lead to an underestimation of the oxygen transfer into the liquid phase. The extension of error depends on the conditions. A good agreement between the introduced unsteady state model and experimental results for the sulfite and biological system confirmed the validity and usefulness of the proposed unsteady state approach. Moreover, a novel and easy method for quantification of CO2-sensitivity of microorganisms in ventilation flask was investigated, using the properties of ventilation flasks. The differences between the values of accumulated CO2 and concentration of oxygen in a culture system in ventilation flasks confirmed the validity of method. The effect of aeration on the removal of CO2 from the fermentation broth has been documented. Additionally, based on the data of the oxygen transfer rate (OTR), obtained by a Respiratory Activity Monitoring System (RAMOS) under a variety of specific aeration rates, the purposed new method was developed as an online monitoring method for CO2 sensitivity of microorganisms in shaken bioreactors.A maximum accumulated CO2 concentration of 12% was derived in both above methods, provided that the cultivation system is carried out under optimal conditions (e.g. the same filling volume (15m1), appropriate media and buffer capacity to control the pH, the suitable OTR (0.05 mol/l/h), operating under non oxygen limitation and RQ¡Ö1). The proper operation condition could be predicted using the unsteady state model. Applying these mentioned method, a significant effect of accumulated CO2 on the biomass concentration, growth rate and lysine product in the fermentation of C. glutamicum DM 1730 was found. Furthermore, the experimental results on Arxula adeninivorans LS3 and Hansenula polymorpha (WT ATCC 34438 and RB11-FMD-GFP) indicated that the CO2 had no effect on these microorganisms. Pseudomonas fluorescens DSM 50090 on yeast extract + glucose and Corynebacterium glutamicum ATCC WT13032 on L-lactate were found to be especially sensitive to CO2, which agree with literature. Some of the important advantages of the new methods are simplicity, lower cost and time consumption, easy of handling and producing similar results as large scale fermentation. Besides, a new aeration strategy from the ventilation flasks to an aerated fermentation system (e.g. measuring flask and stirred tank fermentor) was developed, based on the same concentration of gas compounds (O2 and CO2) in the headspace of these vessels. By applying this method, the concentrations of CO2 and O2 in the gas phase obtained from measuring (aerated) flasks and stirred tank bioreactors were comparable to those obtained from ventilation flasks. Finally in this study a new scale up method from shake flasks to stirred tank bioreactors, concerning the aeration strategy, was investigated based on the effect of CO2 ventilation. Even for different sets of aerations, similar trends were found for the values of the biomass concentration, L-lysine formation, maximum OTR and specific growth rate for fermentation of C .glutamicum DM 1730 as a model organism, in the both scales. Thus, the possibility of scaling up from ventilation flasks to stirred tank bioreactors based on CO2 ventilation criterion was demonstrated

A new method to quantify the CO 2 sensitivity of micro-organisms in shaken bioreactors and scale up to stirred tank fermentors

Small scale shaken bioreactors (e.g. shake flasks) traditionally equipped with different types of sterile closures are very useful tools in biotechnology. The gas transfer coefficient of the sterile closures (kplug) plays an important role in aeration of shaken bioreactors. The value of kplug depends on the average diffusion coefficient of oxygen (DeO2) and different lengths or/and diameters of the neck of flask. Therefore, in this study, a series of pipes with different lengths or/and diameters filled with cotton for a special shake flask, so-called ventilation flask, were employed. The gas transfer through the sterile closure of the ventilation flasks was characterized. Constant values of CO2 and O2 diffusion coefficient were found in all of the ventilation flasks. Considering these values and the neck geometry, a variety of kplug in ventilation flasks were obtained. Since, decreasing kplug causes a reduction of O2 concentration and an accumulation of CO2 in the gas phase of the shaken bioreactors, a realistic understanding and estimation of gas transfer in shaken bioreactors is advantageous to avoid oxygen limitation or carbon dioxide inhibition of a microbial culture. In this study, an unsteady state gas transfer model for shake flasks was developed and experimentally investigated for a wide range of gas transfer coefficients (kplug). The introduced approach is based on the model of Henzler and Schedel [23], which describes the spatially-resolved gas partial pressures inside the sterile closure, affected by the local gas diffusion coefficients and convective Stefan flow. For further easy processing, the resulting total mass transfer coefficient (kplug) is described as a function of the mass flow through the sterile plug (OTRplug) by an empirical equation. This equation is introduced into a simulation model which calculates the gas partial pressures in the head space of the flask. Additionally, the gas transfer rates through the sterile closure and gas-liquid interface inside the flask are provided. Simulations indicate that neglecting the oxygen in the head space volume of the flask at initial conditions (simple steady state assumption) may lead to an underestimation of the oxygen transfer into the liquid phase. The extension of error depends on the conditions. A good agreement between the introduced unsteady state model and experimental results for the sulfite and biological system confirmed the validity and usefulness of the proposed unsteady state approach. Moreover, a novel and easy method for quantification of CO2-sensitivity of microorganisms in ventilation flask was investigated, using the properties of ventilation flasks. The differences between the values of accumulated CO2 and concentration of oxygen in a culture system in ventilation flasks confirmed the validity of method. The effect of aeration on the removal of CO2 from the fermentation broth has been documented. Additionally, based on the data of the oxygen transfer rate (OTR), obtained by a Respiratory Activity Monitoring System (RAMOS) under a variety of specific aeration rates, the purposed new method was developed as an online monitoring method for CO2 sensitivity of microorganisms in shaken bioreactors.A maximum accumulated CO2 concentration of 12% was derived in both above methods, provided that the cultivation system is carried out under optimal conditions (e.g. the same filling volume (15m1), appropriate media and buffer capacity to control the pH, the suitable OTR (0.05 mol/l/h), operating under non oxygen limitation and RQ¡Ö1). The proper operation condition could be predicted using the unsteady state model. Applying these mentioned method, a significant effect of accumulated CO2 on the biomass concentration, growth rate and lysine product in the fermentation of C. glutamicum DM 1730 was found. Furthermore, the experimental results on Arxula adeninivorans LS3 and Hansenula polymorpha (WT ATCC 34438 and RB11-FMD-GFP) indicated that the CO2 had no effect on these microorganisms. Pseudomonas fluorescens DSM 50090 on yeast extract + glucose and Corynebacterium glutamicum ATCC WT13032 on L-lactate were found to be especially sensitive to CO2, which agree with literature. Some of the important advantages of the new methods are simplicity, lower cost and time consumption, easy of handling and producing similar results as large scale fermentation. Besides, a new aeration strategy from the ventilation flasks to an aerated fermentation system (e.g. measuring flask and stirred tank fermentor) was developed, based on the same concentration of gas compounds (O2 and CO2) in the headspace of these vessels. By applying this method, the concentrations of CO2 and O2 in the gas phase obtained from measuring (aerated) flasks and stirred tank bioreactors were comparable to those obtained from ventilation flasks. Finally in this study a new scale up method from shake flasks to stirred tank bioreactors, concerning the aeration strategy, was investigated based on the effect of CO2 ventilation. Even for different sets of aerations, similar trends were found for the values of the biomass concentration, L-lysine formation, maximum OTR and specific growth rate for fermentation of C .glutamicum DM 1730 as a model organism, in the both scales. Thus, the possibility of scaling up from ventilation flasks to stirred tank bioreactors based on CO2 ventilation criterion was demonstrated