Membrane Hydration Research Articles

Key Process and Factors Controlling the Direct Translocation of Cell-Penetrating Peptide through Bio-Membrane.

Cell-penetrating peptide (CPP) can directly penetrate the cytosol (cytolysis) and is expected to be a potent vector for a drug delivery system (DDS). Although there is general agreement that CPP cytolysis is related to dynamic membrane deformation, a distinctive process has yet to be established. Here, we report the key process and factors controlling CPP cytolysis. To elucidate the task, we have introduced trypsin digestion of adsorbed CPP onto giant unilamellar vesicle (GUV) to quantify the adsorption and internalization (cytolysis) separately. Also, the time-course analysis was introduced for the geometric calculation of adsorption and internalization amount per lipid molecule consisting of GUV. As a result, we found that adsorption and internalization assumed to occur successively by CPP molecule come into contact with membrane lipid. Adsorption is quick to saturate within 10 min, while cytolysis of each CPP on the membrane follows successively. After adsorption is saturated, cytolysis proceeds further linearly by time with a different rate constant that is dependent on the osmotic pressure. We also found that temperature and lipid composition influence cytolysis by modulating lipid mobility. The electrolyte in the outer media is also affected as a chemical mediator to control CPP cytolysis by following the Hoffmeister effect for membrane hydration. These results confirmed the mechanism of cytolysis as temporal and local phase transfer of membrane lipid from Lα to Mesh1, which has punctured bilayer morphologies.

An Online Self Cold Startup Methodology for PEM Fuel Cells in Vehicular Applications

This paper puts forward an adaptive cold start strategy for a proton exchange membrane fuel cell (PEMFC) based on maximum power mode. The proposed strategy consists of a water evacuation process after PEMFC shutdown and a self-heating process at PEMFC cold startup. To maximize the performance of the suggested strategy, an optimal operating condition for the cold start procedure is sought first. In this respect, an experimental parametric study is performed to explore the impact of fan velocity, micro-short circuit, anode pressure, and purge procedure on the PEMFC cold start performance. After laying down the proper conditions, the proposed cold start procedure is implemented on a test bench for experimental validations. The self-heating process is based on an online adaptive algorithm that maximizes the PEMFC's internal heat depending on its operating parameters’ variation. In fact, this algorithm attempts to keep the current density at high levels, leading to PEMFC's performance improvement achieved by membrane hydration and temperature increase. The experimental results confirm the effectiveness of the proposed strategy, which presents a fast and cost-effective PEMFC's cold start.

Construction of Nucleolin-Targeted Lipid Nanobubbles and Contrast-Enhanced Ultrasound Molecular Imaging in Triple-Negative Breast Cancer.

To construct aptamer AS1411-functionalized targeted lipid nanobubbles that could simultaneously target abnormally highly expressed nucleolin (NCL) on tumor tissue and neovasculature. Additionally, the study of their contrast-enhanced ultrasound molecular imaging capabilities in vitro and in vivo to explore new methods and approaches for the early and accurate diagnosis of triple-negative breast cancer (TNBC). First, the targeted lipid-nucleic acid molecules were constructed by an amide reaction. Then, the targeted lipid nanobubbles (AS1411-NBs) and nontargeted lipid nanobubbles (NBs) were prepared by membrane hydration, mechanical vibration and centrifugal floatation. The physicochemical characteristics and contrast-enhanced ultrasound imaging capabilities of AS1411-NBs and NBs were compared and analyzed in vitro and in vivo. There were no significant differences between the AS1411-NBs and NBs in their concentration, average particle size or ultrasound imaging capabilities in vitro (P > 0.05). However, AS1411-NBs could simultaneously target NCL in tumor tissue and neovasculature to effectively prolong the duration of contrast-enhanced ultrasound imaging compared to NBs in vivo. The area under the time-intensity curve was significantly different between AS1411-NBs and NBs (P < 0.001), and the drug loading capacity of the AS1411-NBs was also significantly higher than that of the NBs (P < 0.05). Aptamer AS1411-functionalized targeted lipid nanobubbles could significantly prolong the duration of contrast-enhanced ultrasound imaging to achieve dual-targeted ultrasound molecular imaging of tumor tissue and neovasculature. AS1411-NBs also have higher drug loading and targeted drug delivery capabilities compared with NBs, which can provide new methods and approaches for the early accurate diagnosis and effective treatment of TNBC.

Hybrid Hydrate-Membrane Post-combustion CO2 Capture: A Conceptual Process Design and Analyses

Efficient capture and storage of carbon dioxide can avoid the global warming crisis. Gas hydrate, as a novel gas in separation technique, has an excellent potential for separation of CO2 from power plants effluent streams. In this study, synergy analysis is performed between hydrate-based and membrane separation techniques to develop a process for postcombustion carbon dioxide capture (hybrid hydrate membrane CO2 capture or HHMCC). The HHMCC process was simulated in four cases to evaluate the effect of hydrate thermodynamic promoters. The proposed processes were studied from techno-economic aspects by performing energy, exergy, and economic analysis. In comparison to the standalone hydrate-based CO2 capture process, combining membrane and hydrate separation techniques reduces the energy consumed per unit weight of captured CO2. Results showed that by applying hydrate promoters, the capital cost decreases, while the energy consumption reduction is not considerable for two of the promoters considered in this study. The energy consumption and cost of the integrated HHMCC process in the presence of tetra-n-butyl ammonium bromide + dodecyl trimethyl ammonium chloride have been estimated to be 1.87 electrical MJ/kg CO2 and 41.75 U.S. $/ton CO2, respectively.

Bubble Formation in the Electrolyte Triggers Voltage Instability in CO2 Electrolyzers.

SummaryThe electrochemical reduction of CO2 is promising for mitigating anthropogenic greenhouse gas emissions; however, voltage instabilities currently inhibit reaching high current densities that are prerequisite for commercialization. Here, for the first time, we elucidate that product gaseous bubble accumulation on the electrode/electrolyte interface is the direct cause of the voltage instability in CO2 electrolyzers. Although bubble formation in water electrolyzers has been extensively studied, we identified that voltage instability caused by bubble formation is unique to CO2 electrolyzers. The appearance of syngas bubbles within the electrolyte at the gas diffusion electrode (GDE)-electrolyte chamber interface (i.e. ∼10% bubble coverage of the GDE surface) was accompanied by voltage oscillations of 60 mV. The presence of syngas in the electrolyte chamber physically inhibited two-phase reaction interfaces, thereby resulting in unstable cell performance. The strategic incorporation of our insights on bubble growth behavior and voltage instability is vital for designing commercially relevant CO2 electrolyzers.

Antitumor mechanism of MAP30 in bladder cancer T24 cells, and its potential toxic effects in mice

To investigate the antitumor mechanism of MAP30 in human bladder cell line (T24) and its potential toxic effects in mice. In this study, the biological behavior of MAP30's influence on bladder cell was investigated to reveal the antitumor mechanism and role of MAP30 in bladder cancer. MAP30 gene sequence optimized by gene synthesis codon was inserted into the prokaryotic expression vector pET-28a to produce a large amount of target protein in Escherichia coli. The protein product was obtained after purification. Membrane hydration method was used to prepare MAP30 liposome in order to enhance its membrane permeability. The effects of MAP30 on the viability, apoptosis and migration of T24 cell were assessed using 3‑(4,5‑dimethyl‑thiazol‑2‑yl)‑2,5‑diphenyl‑2H‑tetrazolium bromide (MTT), flow cytometric and TUNEL assays, respectively. Mice were transfected with bladder cancer cells for 48 h. The expressions of apoptotic and non-apoptotic proteins were determined using Western blotting. Changes in tumor volume and occurrence of metastasis were assessed using luciferase assay. After 7 days, liver and kidney were excised for histological examination. The levels of reactive oxygen species (ROS), malondialdehyde (MDA), and reduced glutathione (GSH), and activities of catalase and glutathione peroxidase (GPx) were determined in serum or homogenate using enzyme-linked immunosorbent assay (ELISA). The yield of MAP30 after purification was significantly increased. The results of MTT assay showed that MAP30 significantly and concentration-dependently inhibited the proliferation and migration of T24 cells (p &lt; 0.05). The prepared liposomes had uniform hydrated particle size of 132.6 nm, with encapsulation efficiency of 78 %. The inhibitory effect of MAP30 liposome on T24 cells was significantly higher than that of MAP30, and MAP30 significantly increased the number of apoptotic cells (p &lt; 0.05). Western blotting showed that MAP30 significantly promoted the expression of caspase 3 (p &lt; 0.05), but did not significantly affect the expressions of bcl-2 and bax (p &gt; 0.05). It also significantly down-regulated the expressions of NF-kB, JNK and MMP2 (p &lt; 0.05). Tumor formation was significantly inhibited, and tumor volume reduced in bladder cancer-bearing mice after treatment with MAP30 (p &lt; 0.05). Histological examination showed that MAP30 induced mild histological changes in the liver and kidney of mice, and significantly increased the level of MDA at day 1 (p &lt; 0.05). It also significantly and time-dependently increased ROS, but reduced GSH levels and activities of catalase and GPx (p &lt; 0.05). However, MAP30 had no significant effect on DNA (p &gt; 0.05). The apoptotic effect of MAP30 in T24 cells is mediated via activation of caspase-3 signaling pathway. The protein produces mild histological changes in the liver and kidney of mice, but has no significant effect on DNA.

Ultrasound-Mediated Co-Delivery of miR-34a and sPD-1 Complexed with Microbubbles for Synergistic Cancer Therapy.

BackgroundmiR-34a was downregulated and PD-L1 was upregulated in cervical cancer; however, the treatment of cervical cancer lacks precision and targeting. This study explored the ultrasound-mediated co-delivery of miR-34a and sPD-1 complexes with microbubbles for synergistic cancer therapy.MethodsCationic lipid microbubbles (CLMBs) were prepared by membrane hydration and mechanical oscillation. U14 subcutaneous xenograft mice were injected with CLMBs-loaded sPD-1 and miR-34a combined with ultrasound targeted destruction, and tumor volume and tumor weight of mice were measured. TUNEL apoptosis test and the mRNA expression of apoptosis-related gene Bcl-2 and Bax were analyzed by qRT-PCR. Antitumor immune-related cytokines IFN-γ were investigated by qRT-PCR, LDH Cytotoxicity Assay Kit were performed to test cytotoxic T lymphocytes (CTL).ResultsCLMBs were successfully prepared and the plasmid bound to its surface. The tumor volume and weight were specifically decreased by ultrasound-mediated co-delivery of miR-34a and sPD-1 complexes with microbubbles, apoptosis was induced and the apoptosis suppressor gene Bcl-2 was downregulated and proapoptotic gene Bax were upregulated. qRT-PCR analysis revealed that antitumor immunity-related IFN-γ was strongly upregulated in mice, which were treated with CLMBs-loaded sPD-1 and miR-34a combined with ultrasound targeted destruction, and the percentage of CTL was increased.ConclusionThese findings from the study demonstrated that CLMBs could deliver miR-34a and sPD-1, combined with ultrasound targeted destruction, could suppress the tumor tissue growing, induce apoptosis and enhance antitumor immunity in U14 subcutaneous xenograft mice.

Degradation-conscious control for enhanced lifetime of automotive polymer electrolyte membrane fuel cells

A linear time varying model predictive control (LTV-MPC) framework is developed for degradation-conscious control of automotive polymer electrolyte membrane (PEM) fuel cell systems. A reduced-order nonlinear model of the entire system is derived first, including the reactant and coolant supply subsystems and the fuel cell stack. This nonlinear model is then successively linearized about the current operating point to obtain a linear model. The linear model is utilized to formulate the control problem using a rate-based MPC formulation. The controller objective is to ensure offset-free tracking of the power demand, while maximizing the overall system efficiency and enhancing its durability. To this end, the fuel consumption and the power loss due to auxiliary equipment are minimized. Moreover, the internal states of the fuel cell stack are constrained to avoid harmful conditions that are known stressors of the fuel cell components. Membrane dry-out, rapid changes in the membrane hydration, and reactant starvation are among the stressors considered in this work. However, the framework can accommodate further lifetime indicators as needed. Simulation-based studies showcase the utility of the proposed control framework in meeting the outlined objectives.

Inductive Low‐Frequency Processes in PEMFC‐Impedance Spectra

AbstractImpedance spectra of polymer electrolyte membrane (PEM) fuel cells often comprise an “inductive loop” at low frequencies from 1 Hz to 1 mHz additionally to the typically polarization resistances with capacitive behavior between 1 MHz to 1 Hz.To investigate this inductive behavior, systematic variations of operating parameters as humidity, current density and gas compositions are performed. The impedance spectra, including their inductive parts, are deconvoluted by an extended version of the distribution of relaxation times (DRT). Two inductive processes are identified in the DRT and subsequently quantified by fitting the spectra to an extended equivalent circuit model exhibiting negative resistances and constant phase elements.Both inductive processes are depending on relative humidity and current density. The inductive behavior seems to be dominated by the oxygen reduction reaction (ORR) at the cathode, whereas changes in membrane hydration can be excluded as the main cause for the inductive low‐frequency processes. Measurements in symmetrical H2/H2 operating mode prove that the inductive behavior cannot be solely related to the ORR.The ratio of the inductive processes to the ohmic and capacitive loss processes ranges from 15% to 30%. Thus, a considerable cell performance improvement related to the existence of these inductive low‐frequency processes has to be taken into account.

패시브 타입 공랭식 연료전지 성능향상을 위한 캐소드 채널 폭 비율에 대한 수치해석적 연구

In general, a passive air cooled proton exchange membrane fuel cell (PEMFC) operates under an excessive amount of air flow and low humidification conditions, indicating effective control of stack temperature and membrane hydration is of paramount importance for achieving high and stable performance. In this study, we numerically investigate the effects of cathode bipolar plate flowfield design on temperature and water distributions inside a passive air cooled PEMFC. The three-dimensional (3D) non-isothermal PEMFC model is applied to various PEMFC geometries where three different flowfield designs with different ratio and dimensions of air supply channel and cooling channels are taken into account. Simulation results show that the flowfield design with narrow air supply channel and/or wide cooling channel exhibits superior water management performance whereas the effect of oyxgen depletion is minimal due to sufficiently a large amount of air supply conditions. This study clearly demonstrates that the membrane dehydration issue in a passive type air cooled PEMFC can be mitigated by proper design of cathode flowfield.

Transient domains of ordered water induced by divalent ions lead to lipid membrane curvature fluctuations

Cell membranes are composed of a hydrated lipid bilayer that is molecularly complex and diverse, and the link between molecular hydration structure and membrane macroscopic properties is not well understood, due to a lack of technology that can probe and relate molecular level hydration information to micro- and macroscopic properties. Here, we demonstrate a direct link between lipid hydration structure and macroscopic dynamic curvature fluctuations. Using high-throughput wide-field second harmonic (SH) microscopy, we observe the formation of transient domains of ordered water at the interface of freestanding lipid membranes. These domains are induced by the binding of divalent ions and their structure is ion specific. Using nonlinear optical theory, we convert the spatiotemporal SH intensity into maps of membrane potential, surface charge density, and binding free energy. Using an electromechanical theory of membrane bending, we show that transient electric field gradients across the membrane induce spatiotemporal membrane curvature fluctuations.

Dynamic Imaging of Membrane Hydration

Lipid membranes are essential for life: They provide a dynamic compartmentalized environment, a localized space for proteins (e.g. ion channels) to perform their functions, and a selective environment to decide what enters the cell. Although recognized as an essential building block, water is usually treated as a background for biology; mainly because it cannot be measured on the molecular interfacial level of realistic free floating membrane systems. However, water is a crucial mediator of chemical change and determines the structure of the membrane. Water and ions determine the electrostatic environment of the membrane, whether interfacial reactions take place and provide a path for the insertion and functioning of ion channels/pores. The study of lipid membranes is generally pursued by following either a top-down approach, introducing labels to living cell membranes or a bottom-up approach with well-controlled but simplified membrane monolayer or supported membrane models. In the first approach molecular level hydration information is lost, while in the second approach the connection with real bilayer membranes is limited. Recent work in in our laboratory offers an alternative path that ultimately envisions bringing together both top-down and bottom-up approaches. By using intermediate nano-, micro- and macroscale free-floating membrane systems in combination with novel nonlinear optical spectroscopy and imaging methods, we advance the understanding of realistic membranes on a more fundamental level. In this presentation I will introduce those methods and provide an overview of recent advances in understanding membrane molecular structure, hydration, and electrostatics. We demonstrate the failure of electrostatic mean field models, the emerging roles of variable length scale, curvature, confinement and transient ordered water domains by experiments on lipid droplets, liposomes, macroscopic free floating membranes and living neurons.

Partial flooding and its effect on the performance of a proton exchange membrane fuel cell

Water management is one of the key issues for efficient and stable operation of proton exchange membrane fuel cells (PEMFCs). Water flooding easily occurs at the elevated operation current density, especially at the downstreaming of the flow channel where the generated water should flow out. Proper water management should meet the needs of adequate membrane hydration and the avoidance of flooding in the catalyst and gas diffusion layers. Flooding will not only lead to performance losses due to the hindered reactant supply, but also the safety issue because of the cell reversal. A partial flooding model is proposed to investigate the effect of the porosity on the performance of a PEMFC. The results show that high temperature is conducive to the suppression of flooding at low relative humidity, and flooding would lead to the deterioration of mass transfer due to the porosity decrease of gas diffusion layer, especially at high current densities. Partial flooding won’t significantly affect the power generation capacity of the fuel cell, but will cause uneven distribution of current density, resulting in an adverse influence on long-term operation. Moreover, the performance would suffer serious degradation with completely flooding. Once the area inside the PEMFC is seriously flooded, the current density in non-flooded area is up to 4.7 times higher than that in the flooded area, and the performance is difficult to recover even if increasing the stoichiometry of reactants. The study illustrates the importance of the water management at the downstreaming of the fuel cell.

Characterization of novel graphene-based microporous layers for Polymer Electrolyte Membrane Fuel Cells operating under low humidity and high temperature

Water management is one of the major issues hindering the employment of Polymer Electrolyte Membrane Fuel Cells on a large scale. Microporous layers are fundamental for water removal from the cathode, oxygen mass transfer and electrolyte hydration. In this paper, we have employed multiple carbon phases in the MPL composition to identify possible strategies for cell performance improvement at critical conditions such as high temperature and low relative humidity. In particular, we have employed a series of graphene-based particles, in addition to conventional carbon black, because of their excellent electrical and thermal conductivities. Moreover, mixed compositions have been tested to assess possible synergic effects between the two phases. We have determined which properties are responsible for performance improvements at 80 °C and relative humidity of 60% and how MPLs morphological and microstructural features could be tuned in order to increase mass transfer while preserving the electrolyte membrane hydration. Promising results have been obtained and specific morphological properties of graphene nanoplatelets have been identified for a possible optimization of the MPL, however the samples produced are still at an early-stage development and further improvements are needed.

Investigation of current density spatial distribution in PEM fuel cells using a comprehensively validated multi-phase non-isothermal model

In this study, a three-dimensional (3D) multi-phase non-isothermal model of proton exchange membrane (PEM) fuel cell is present to investigate the current density spatial distributions under different output voltages, temperatures, current densities and relative humidities (RH). Two sets of experimental data are selected for validation, including those from the Los Alamos National Laboratory in the United States and the University of Waterloo in Canada. Reasonable agreements are achieved between the model prediction and experimental measurements, indicative of the validity of this 3D model. In addition, it is found that under a higher RH of 50%, most electric current is produced near the cathode inlet, which is primarily due to the local availability of abundant oxygen and hence small transport polarization. Low current occurs near the outlet of the cathode air flow, as a result of oxygen consumption by the oxygen reduction reaction (ORR). Under a lower RH of 25%, the high current density region shifts to the middle of the fuel cell, which is primarily attributed to hydration of the dry membrane by water production. In our case study, the operating temperature has little impact on the current density distribution.

Hybrid dynamic modeling-based membrane hydration analysis for the commercial high-power integrated PEMFC systems considering water transport equivalent

In this paper, the influence mechanism of proton exchange membrane hydration dynamics on the output characteristics of the commercial integrated 150 kW proton exchange membrane fuel cell (PEMFC) systems was investigated under actual operating conditions. On this basis, the control-oriented model was improved for the integrated PEMFC systems. On the one hand, the anode pressure following control and cathode backpressure regulation were equivalently modeled based on analysis of interactive control characteristics of the commercial high-power integrated PEMFC systems. On the other hand, equivalent modeling of membrane hydration dynamics inside the PEMFC stack was achieved, so as to reasonably characterize the effect of liquid water saturation on the output characteristics of the commercial integrated PEMFC systems, under the premise of not significantly affecting the model complexity. Moreover, the effectiveness of the improved control-oriented model was also verified through comparing the simulation and experimental results. Further analyses based on the developed system model showed that, online evaluation and self-healing control of the membrane hydration condition can be realized through dynamic analyses of the system voltage and current according to the differential current injection method such that reasonable membrane hydration condition can be ensured. Furthermore, up to 3.74% enhancement in the system efficiency was achieved in the case of minimized membrane micro-flooding, which was of great significance to improve the service life and operation reliability of the commercial integrated PEMFC systems.

Renewable sources: applications in personal care formulations.

A global tendency for products considered environmentally sustainable, and ecologically obtained led the industry related to personal care formulations to fund the research and the development of personal care/cosmetics containing ingredients from natural resources. Furthermore, consumers are aware of environmental and sustainability issueans, thus not harming the environment represents a key consideration when developing a new cosmetic ingredient. In this study we review some examples of active ingredients or raw materials used in cosmetics/personal care/biomedical products that are coming from either through biotechnological systems, or as byproducts of several industries. A skin formulation containing biosynthetic actives, prepared by us and the study regarding its dermocosmetic properties are also described. The need for the standardization processes, the safety assessment tools, the improvement of the exploitation methods of these renewable sources in order the production to be ecologically and economically better are also discussed.

Optimized Anti-Prostate-Specific Membrane Antigen Single-Chain Variable Fragment-Loaded Nanobubbles as a Novel Targeted Ultrasound Contrast Agent for the Diagnosis of Prostate Cancer.

ObjectivesTo prepare optimized prostate‐specific membrane antigen (PSMA) single‐chain variable fragment (scFv)–loaded nanobubbles (NBs) as a novel targeted ultrasound (US) contrast agent for diagnosis and treatment of prostate cancer (PCa).MethodsProstate‐specific membrane antigen scFv‐loaded NBs were prepared by membrane hydration and biotin‐streptavidin conjugation. Flow cytometry was used to observe the binding rate of the targeted NBs to PSMA‐expressing cells. Contrast‐enhanced US was used to monitor targeted and nontargeted NBs administered to nude mice with 22RV1, LNCaP, and PC‐3 xenograft tumors. The specific binding ability of the targeted NBs was further examined by fluorescence imaging of tumor cryosections.ResultsUniformly sized targeted NBs were successfully prepared (mean ± SD, 485.3 ± 28.4 nm). The NBs showed good stability and bound specifically to LNCaP and 22RV1 cells with high PSMA expression in vitro but did not bind to PC‐3 cells without PSMA expression. The targeted NBs presented good US enhancement, and the results of the in vivo xenograft tumor nude mouse model showed that the peak contrast intensity in LNCaP and 22RV1 cells was significantly higher for the targeted NBs than the nontargeted NBs (P < .05), whereas there was no significant difference in PC‐3 cells. Immunofluorescence results obtained from tumor sections confirmed that the targeted NBs were capable of targeting PSMA‐expressing tumor cells.ConclusionsThese novel PSMA scFv‐loaded NBs have proven to be an excellent US contrast agent for imaging PSMA‐expressing PCa and have the potential to not only enable efficient and safe molecular imaging but also to serve as a delivery system for targeted PCa therapies.

Coupled Response of Membrane Hydration with Oscillating Metabolism in Live Cells: An Alternative Way to Modulate Structural Aspects of Biological Membranes?

We propose that active metabolic processes may regulate structural changes in biological membranes via the physical state of cell water. This proposition is based on recent results obtained from our group in yeast cells displaying glycolytic oscillations, where we demonstrated that there is a tight coupling between the oscillatory behavior of glycolytic metabolites (ATP, NADH) and the extent of the dipolar relaxation of intracellular water, which oscillates synchronously. The mechanism we suggest involves the active participation of a polarized intracellular water network whose degree of polarization is dynamically modulated by temporal ATP fluctuations caused by metabolism with intervention of a functional cytoskeleton, as conceived in the long overlooked association-induction hypothesis (AIH) of Gilbert Ling. Our results show that the polarized state of intracellular water can be propagated from the cytosol to regions containing membranes. Since changes in the extent of the polarization of water impinge on its chemical activity, we hypothesize that metabolism dynamically controls the local structure of cellular membranes via lyotropic effects. This hypothesis offers an alternative way to interpret membrane related phenomena (e.g., changes in local curvature pertinent to endo/exocytosis or dynamical changes in membranous organelle structure, among others) by integrating relevant but mostly overlooked physicochemical characteristics of the cellular milieu.

Acoustic emission as a function of polarisation: Diagnosis of polymer electrolyte fuel cell hydration state

Understanding water management is a crucial aspect in the development of improved polymer electrolyte fuel cells (PEFCs). Separating the performance degradation due to dehydration, water flooding and reactant starvation in PEFCs is a major challenge. In this study, acoustic emission (AE) analysis, a non-invasive and non-destructive diagnostic tool, is utilised to probe water formation and removal inside an operating fuel cell. In the acoustic emission as a function of polarisation (AEfP) method, AE activity from the PEFC is measured in terms of cumulative absolute AE energy (CAEE) hits during operation at discrete points on the polarisation curve. AEfP can identify the presence of liquid water in flow channels and correlate its formation and removal with the level of cell polarisation, and consequent internal temperature. Correlation between acoustic activity and water generation, supply and removal is achieved by varying current (polarisation), cathode air feed relative humidity (RH) and cell temperature, respectively. Features such as initial membrane hydration, liquid water formation, ‘flushing’ and the transition from ‘wet-channel’ to ‘dry-channel’ operation are identified using AE analysis, thereby providing a powerful and easy to implement diagnostic for PEFCs.