Investigation of air bubble behaviour after gas embolism events induced in a microfluidic network mimicking microvasculature.

Gas embolism is a medical condition that occurs when gas bubbles are present in veins or arteries, decreasing blood flow and potentially reducing oxygen delivery to vital organs, such as the brain. Although usually reported as rare, gas embolism can lead to severe neurological damage or death. However, presently, only limited understanding exists regarding the microscale processes leading to the formation, persistence, movement, and resolution of gas emboli, as modulated by microvasculature geometrical features and blood properties. Because gas embolism is initially a physico-chemical-only process, with biological responses starting later, the opportunity exists to fully study the genesis and evolution of gas emboli using in vitro microfluidic networks mimicking small regions of microvasculature. The microfluidics networks used in this study, which aim to mimic microvasculature geometry, comprise linear channels with T-, or Y-junction air inlets, with 20, 40, and 60 µm widths (arterial or venous), and a 30 µm width honeycombed network (arterial) with three bifurcation angles (30°, 60°, and 90°). Synthetic blood, equivalent to 46% haematocrit concentrations, and water were used to study the modulation of gas embolism-like events by liquid viscosity. Our study shows that (i) longer bubbles with lower velocity occur in narrower channels, e.g., with 20 µm width; (ii) the resistance of air bubbles to the flow increases with the higher haematocrit concentration; and lastly (iii) the propensity of gas embolism-like events in honeycomb architectures increases for more acute, e.g., 30°, bifurcation angles. A dimensionless analysis using Euler, Weber, and capillary numbers demarcated the conditions conducive to gas embolism. This work suggests that in vitro experimentation using microfluidic devices with microvascular tissue-like structures could assist medical guidelines and management in preventing and mitigating the effects of gas embolism.

Metabolic regulation boosts bioelectricity generation in Zymomonas mobilis microbial fuel cell, surpassing ethanol production.

Zymomonas mobilis (Z. mobilis), a bacterium known for its ethanol production capabilities, can also generate electricity by transitioning from ethanol production to electron generation. The purpose of this study is to investigate the ability of Z. mobilis to produce bioelectricity when utilized as a biocatalyst in a single-chamber microbial fuel cell (MFC). Given the bacterium's strong inclination towards ethanol production, a metabolic engineering strategy was devised to identify key reactions responsible for redirecting electrons from ethanol towards electricity generation. To evaluate the electroactivity of cultured Z. mobilis and its ethanol production in the presence of regulators, the reduction of soluble Fe(III) was utilized. Among the regulators tested, CuCl2 demonstrated superior effectiveness. Consequently, the MFC was employed to analyze the electrochemical properties of Z. mobilis using both a minimal and modified medium. By modifying the bacterial medium, the maximum current and power density of the MFC fed with Z. mobilis increased by more than 5.8- and sixfold, respectively, compared to the minimal medium. These findings highlight the significant impact of metabolic redirection in enhancing the performance of MFCs. Furthermore, they establish Z. mobilis as an active electrogenesis microorganism capable of power generation in MFCs.

Boosting microfluidic microbial fuel cells performance via investigating electron transfer mechanisms, metal-based electrodes, and magnetic field effect.

The presented paper fundamentally investigates the influence of different electron transfer mechanisms, various metal-based electrodes, and a static magnetic field on the overall performance of microfluidic microbial fuel cells (MFCs) for the first time to improve the generated bioelectricity. To do so, as the anode of microfluidic MFCs, zinc, aluminum, tin, copper, and nickel were thoroughly investigated. Two types of bacteria, Escherichia coli and Shewanella oneidensis MR-1, were used as biocatalysts to compare the different electron transfer mechanisms. Interaction between the anode and microorganisms was assessed. Finally, the potential of applying a static magnetic field to maximize the generated power was evaluated. For zinc anode, the maximum open circuit potential, current density, and power density of 1.39 V, 138,181 mA m-2 and 35,294 mW m-2 were obtained, respectively. The produced current density is at least 445% better than the values obtained in previously published studies so far. The microfluidic MFCs were successfully used to power ultraviolet light-emitting diodes (UV-LEDs) for medical and clinical applications to elucidate their application as micro-sized power generators for implantable medical devices.

The identification and performance assessment of dominant bacterial species during linear alkylbenzene sulfonate (LAS)-biodegradation in a bioelectrochemical system.

The anionic surfactant linear alkylbenzene sulfonate (LAS) is a major chemical constituent of detergent formulation. Regarding the recalcitrant nature of sulfonoaromatic compounds, discharging these substances into wastewater collection systems is a real environmental issue. A study on LAS biodegradation based on bioelectrochemical treatment and in the form of developing a single-chamber microbial fuel cell with air cathode is reported in the present work. Pretreatment study showed LAS concentration of 60 ppm resulted in the highest anaerobic LAS removal of 57%; so, this concentration was chosen to run the MFC. After the sustained anodic biofilm was formed, LAS degradation rate during 4 days in MFC was roughly 76% higher than that in the serum bottle, which indicated the role of the bioelectrochemical process in improving anaerobic LAS removal. Additionally, through 16S rRNA gene sequencing, the dominant bacterial species in the biofilm was identified as Pseudomonas zhaodongensis NEAU-ST5-21(T) with about 98.9% phylogenetic similarity and then a pathway was proposed for LAS anaerobic biodegradation. The MFC characteristics were assessed by pH monitoring as well as scanning electron microscopy and current density evolution.

Fabrication of the macro and micro-scale microbial fuel cells to monitor oxalate biodegradation in human urine.

This study presented the fabrication of macro and micro-scale microbial fuel cells (MFCs) to generate bioelectricity from oxalate solution and monitor the biodegradation in a micro-scale MFC for the first time. The maximum generated power density of 44.16 W m-3 in the micro-scale MFC elucidated its application as a micro-sized power generator for implantable medical devices (IMDs). It is also worthwhile noting that for the macro-scale MFC, the significant amounts of open circuit voltage, oxalate removal, and coulombic efficiency were about 935 mV, 99%, and 44.2%, respectively. These values compared to previously published studies indicate successful oxalate biodegradation in the macro-scale MFC. Regarding critical challenges to determine the substrate concentration in microfluidic outlets, sample collection in a suitable time and online data reporting, an analogy was made between macro and micro-scale MFCs to elicit correlations defining the output current density as the inlet and the outlet oxalate concentration. Another use of the system as an IMD is to be a platform to identify urolithiasis and hyperoxaluria diseases. As a versatile device for power generation and oxalate biodegradation monitoring, the use of facile and cheap materials (< $1.5 per device) and utilization of human excreta are exceptional features of the manufactured micro-scale MFC.

A system-oriented strategy to enhance electron production of Synechocystis sp. PCC6803 in bio-photovoltaic devices: experimental and modeling insights.

Bio-photovoltaic devices (BPVs) harness photosynthetic organisms to produce bioelectricity in an eco-friendly way. However, their low energy efficiency is still a challenge. A comprehension of metabolic constraints can result in finding strategies for efficiency enhancement. This study presents a systemic approach based on metabolic modeling to design a regulatory defined medium, reducing the intracellular constraints in bioelectricity generation of Synechocystis sp. PCC6803 through the cellular metabolism alteration. The approach identified key reactions that played a critical role in improving electricity generation in Synechocystis sp. PCC6803 by comparing multiple optimal solutions of minimal and maximal NADH generation using two criteria. Regulatory compounds, which controlled the enzyme activity of the key reactions, were obtained from the BRENDA database. The selected compounds were subsequently added to the culture media, and their effect on bioelectricity generation was experimentally assessed. The power density curves for different culture media showed the BPV fed by Synechocystis sp. PCC6803 suspension in BG-11 supplemented with NH4Cl achieved the maximum power density of 148.27 mW m-2. This produced power density was more than 40.5-fold of what was obtained for the BPV fed with cyanobacterial suspension in BG-11. The effect of the activators on BPV performance was also evaluated by comparing their overpotential, maximum produced power density, and biofilm morphology under different conditions. These findings demonstrated the crucial role of cellular metabolism in improving bioelectricity generation in BPVs.

Introducing an affordable catalyst for biohydrogen production in microbial electrolysis cells.

This study reports the fabrication of a new cathode electrode assembly using polyaniline (PANI) and graphene on a stainless steel mesh (SSM) as an alternative for the conventional expensive cathode of microbial electrolysis cells (MECs). With respect to the previous efforts to propose an efficient and cost-effective alternative for platinum (Pt) catalysts and cathode electrodes, the present study investigates the assessment of different catalysts to elucidate the potential of the modified SSM cathode electrode for larger-scale MECs. In the case of feeding dairy wastewater to the MEC, the maximum hydrogen production rate and COD removal were obtained by SSM/PANI/graphene cathode and had the values 0.805 m3 H2 m-3 anolyte day-1 and 82%, respectively, at the applied potential of 1 V. These values were only 20% and 7% lower than those of the MEC with Pt on the carbon cloth cathode, respectively. The coulombic efficiencies of SSM/Pt and SSM/PANI/graphene were seen to be 64.48% and 56.67%, respectively. It was also concluded that the fabrication cost of the modified cathode was 50% lower than the conventional cathodes with Pt on the carbon cloth. Finally, the evaluation of the modified cathode performance was achieved based on Fourier transform infrared spectroscopy, linear sweep voltammetry, scanning electron microscopy, and atomic force microscopy.

Interpretation of the electrochemical response of a multi-population biofilm in a microfluidic microbial fuel cell using a comprehensive model.

The present study investigates the diversification and dynamic behavior of a multi-population microfluidic microbial fuel cell (MFC) as a biosensor. The cost effective microfluidic MFC coupled to a comprehensive model, presents a novel platform for monitoring chemical and biological phenomena. The importance of competition among different microbial groups, hierarchical biochemical processes, bacterial chemotaxis and different mechanisms of electron transfer were significant considerations in the present model. The validation of the model using experimental data from a microfluidic MFC shows an appropriate match with the hierarchal biodegradation processes of a complex substrate as well as development of bacterial chemotaxis during multi-population biofilm formation under real conditions. Microfluidic MFC performance, including temporal and spatial distribution of different microbial group concentrations in the biofilm and anolyte bulk, the competitive behavior of different species, bacterial transport parameters and bioelectrochemical characteristics are also assessed.

The effect of different light intensities and light/dark regimes on the performance of photosynthetic microalgae microbial fuel cell.

This study develops a photosynthetic microalgae microbial fuel cell (PMMFC) engaged Chlorella vulgaris microalgae to investigate effect of light intensities and illumination regimes on simultaneous production of bioelectricity, biomass and wastewater treatment. The performance of the system under different light intensity (3500, 5000, 7000 and 10,000 lx) and light/dark regimes (24/00, 12/12, 16/8 h) was investigated. The optimum light intensity and light/dark regimes for achieving maximum yield of PMMFC were obtained. The maximum power density of 126 mW m-3, the coulombic efficiency of 78% and COD removal of 5.47% were achieved. The maximum biomass concentration of 4 g l-1 (or biomass yield of 0.44 g l-1 day-1) was obtained in continuous light intensity of 10,000 lx. The comparison of the PMMFC performance with air-cathode and abiotic-cathode MFCs shows that the maximum power density of air-cathode MFC was only 13% higher than PMMFC.

A novel model for predicting bioelectrochemical performance of microsized-MFCs by incorporating bacterial chemotaxis parameters and simulation of biofilm formation.

Bacterial transport parameters play a fundamental role in microbial population dynamics, biofilm formation and bacteria dispersion. In this study, the novel model was extended based on the capability of microsized microbial fuel cells (MFCs) as amperometric biosensors to predict the cells' chemotactic and bioelectrochemical properties. The model prediction results coincide with the experimental data of Shewanella oneidensis and chemotaxis mutant of P. aeruginosa bdlA and pilT strains, indicating the complementary role of numerical predictions for bioscreening applications of microsized MFCs. Considering the general mechanisms for electron transfer, substrate biodegradation, microbial growth and bacterial dispersion are the main features of the presented model. In addition, the genetic algorithm method was implemented by minimizing the objective function to estimate chemotaxis properties of the different strains. Microsized MFC performance was assessed by analyzing the microbial activity in the biofilm and the anolyte.

Characterization of a microfluidic microbial fuel cell as a power generator based on a nickel electrode.

This study reports the fabrication of a microfluidic microbial fuel cell (MFC) using nickel as a novel alternative for conventional electrodes and a non-phatogenic strain of Escherichia coli as the biocatalyst. The feasibility of a microfluidic MFC as an efficient power generator for production of bioelectricity from glucose and urea as organic substrates in human blood and urine for implantable medical devices (IMDs) was investigated. A maximum open circuit potential of 459 mV was achieved for the batch-fed microfluidic MFC. During continuous mode operation, a maximum power density of 104 Wm(-3) was obtained with nutrient broth. For the glucose-fed microfluidic MFC, the maximum power density of 5.2 µW cm(-2) obtained in this study is significantly greater than the power densities reported previously for microsized MFCs and glucose fuel cells. The maximum power density of 14 Wm(-3) obtained using urea indicates the successful performance of a microfluidic MFC using human excreta. It features high power density, self-regeneration, waste management and a low production cost (<$1), which suggest it as a promising alternative to conventional power supplies for IMDs. The performance of the microfluidic MFC as a power supply was characterized based on polarization behavior and cell potential in different substrates, operational modes, and concentrations.

A combined model for large scale batch culture MFC-digester with various wastewaters through different populations.

In this study, a new model of microbial fuel cell (MFC) was obtained for the first time. The modeled MFC was made using a combination of two approaches; the conduction-based method and two-step anaerobic digestion. Performance of the MFC was based on calculations for current evolution and polarization curves with different subsequent variables of the biofilm and anolyte. The model was able to make predictions for performance of the MFC for a simple substrate to more complex ones. The model was successfully validated with a variety of substrates (acetate, glucose and dairy wastewater) and the results were compared with previously published measurements. The model polarization results showed that is able to predict overshoot as a dynamic phenomenon. The ratio of acetoclastic methanogens to electrogens in the biofilm increased from an average value of 0.63×10(-2) to 1.17×10(-2) by increasing external resistance from 50 Ω to 100Ω . The attached to planktonic cells ratio was computed 0.45 for the glucose-fed MFC and for the dairy wastewater-fed MFC at 50 Ω was 8.86 and at 100 Ω was 5.46.

Parameter estimation and characterization of a single-chamber microbial fuel cell for dairy wastewater treatment.

In this study, for the first time, the conduction-based model is extended, and then combined with Genetic Algorithm to estimate the design parameters of a MFC treating dairy wastewater. The optimized parameters are, then, validated. The estimated half-saturation potential of -0.13 V (vs. SHE) is in good agreement while the biofilm conductivity of 8.76×10(-4) mS cm(-1) is three orders of magnitude lower than that previously-reported for pure-culture biofilm. Simulations show that the ohmic and concentration overpotentials contribute almost equally in dropping cell voltage in which the concentration film and biofilm conductivity comprise the main resistances, respectively. Thus, polarization analysis and determining the controlling steps will be possible through that developed extension. This study introduces a reliable method to estimate the design parameters of a particular MFC and to characterize it.

Single chamber microbial fuel cell with spiral anode for dairy wastewater treatment.

This study reports on the fabrication of a novel annular single chamber microbial fuel cell (ASCMFC) with spiral anode. The stainless steel mesh anode with graphite coating was used as anode. Dairy wastewater, containing complex organic matter, was used as substrate. ASCMFC had been operated for 450 h and results indicated a high open circuit voltage (about 810 mV) compared with previously published results. The maximum power density of 20.2 W/m(3) obtained in this study is significantly greater than the power densities reported in previous studies. Besides, a maximum coulombic efficiency of 26.87% with 91% COD removal was achieved. Good bacterial adhesion on the spiral anode is clearly shown in SEM micrographs. High power density and a successful performance in wastewater treatment in ASCMFC suggest it as a promising alternative to conventional MFCs for power generation and wastewater treatment. ASCMFC performance as a power generator was characterized based on polarization behavior and cell potentials.