Thin Polymer Membrane Research Articles

Sa2039 - Direct Observation of Mucosal Surfaces and Cancer Lesions of the GI Tract using Field-Emission Scanning Electron Microscopy (FE-SEM) with a Thin Polymer Membrane, “Nanosuit®

Sa2039 - Direct Observation of Mucosal Surfaces and Cancer Lesions of the GI Tract using Field-Emission Scanning Electron Microscopy (FE-SEM) with a Thin Polymer Membrane, “Nanosuit®

Buckling and Postbuckling Failure Analyses on a Rectangular Membrane for Touch Panel Applications

Thin conductive polymer membranes are the major sensing structure in resistive touch panels. However, device malfunctions such as early touching and false triggering have been reported during product development and reliability assessment. A surface profile examination has indicated that these membranes have considerable initial warpage, which could be a sign of membrane buckling, since the clamped design of the assembly may cause additional in-plane compression, in turn causing structural buckling. As a result, it is important to analyze the buckling and post-buckling behaviors of conductive polymer membranes due to initial imperfections, residual stress, or assembly issues in order to develop engineering solutions to ensure quality assurance. In this paper, both finite-element analyses and experimental characterizations are performed as the first step toward solving the observed problems. For the buckling analysis, we focus on the correlations between the calculated mode shapes and the observed surface warpage. Post-buckling analysis is also performed for exploring the performance of touch panels with initial warpage. In addition, several experimental investigations are conducted to validate the above mentioned mechanical analyses. The simulation results essentially agree with the observations. Both simulation and experimental investigations indicate that in-plane compression and shear can contribute to the observed failures. Engineering methods to increase buckling rigidity can be helpful for enhancing device reliability.

The counterintuitive impact of separator–electrolyte combinations on the cycle life of graphite–silicon composite electrodes

Thin polymeric membranes such as Celgard are commonly used as separators in Li-ion batteries to ensure high volumetric energy density. Independently, for silicon-based electrodes fluoroethylene carbonate (FEC) is often added to the electrolyte to improve the cycling stability of the cell. Here we demonstrate that, counterintuitively, this separator–electrolyte combination negatively affects the performance of graphite–Si electrodes in half-cells. In a statistical evaluation of the cycling behavior of C–Si electrode cells with various separators and either with or without FEC addition, we show that by improving the solid electrolyte interphase on the silicon particles, FEC addition leads to inhomogeneous current distribution in the electrodes, therefore favoring lithium dendrite growth and leading to irreversible failure with Celgard. In contrast, self-recovery is observed with simple glass-fiber separators. Without FEC, neither dendrites nor failure are observed, but cells with Celgard suffer from poorer electrochemical performance, due to clogging by the thick polymeric layer formed using standard electrolytes, than cells with thicker and hydrophilic separators.

Voltage-Rectified Current and Fluid Flow in Conical Nanopores.

Ion current rectification (ICR) refers to the asymmetric potential-dependent rate of the passage of solution ions through a nanopore, giving rise to electrical current-voltage characteristics that mimic those of a solid-state electrical diode. Since the discovery of ICR in quartz nanopipettes two decades ago, synthetic nanopores and nanochannels of various geometries, fabricated in membranes and on wafers, have been extensively investigated to understand fundamental aspects of ion transport in highly confined geometries. It is now generally accepted that ICR requires an asymmetric electrical double layer within the nanopore, producing an accumulation or depletion of charge-carrying ions at opposite voltage polarities. Our research groups have recently explored how the voltage-dependent ion distributions and ICR within nanopores can induce novel nanoscale flow phenomena that have applications in understanding ionics in porous materials used in energy storage devices, chemical sensing, and low-cost electrical pumping of fluids. In this Account, we review our most recent investigations on this topic, based on experiments using conical nanopores (10-300 nm tip opening) fabricated in thin glass, mica, and polymer membranes. Measurable fluid flow in nanopores can be induced either using external pressure forces, electrically via electroosmotic forces, or by a combination of these two forces. We demonstrate that pressure-driven flow can greatly alter the electrical properties of nanopores and, vice versa, that the nonlinear electrical properties of conical nanopores can impart novel and useful flow phenomena. Electroosmotic flow (EOF), which depends on the magnitude of the ion fluxes within the double layer of the nanopore, is strongly coupled to the accumulation/depletion of ions. Thus, the same underlying cause of ICR also leads to EOF rectification, i.e., unequal flows occurring for the same voltage but opposite polarities. EOF rectification can be used to electrically pump fluids with very precise control across membranes containing conical pores via the application of a symmetric sinusoidal voltage. The combination of pressure and asymmetric EOF can also provide a means to generate new nanopore electrical behaviors, including negative differential resistance (NDR), in which the current through a conical pore decreases with increasing driving force (applied voltage), similar to solid-state tunnel diodes. NDR results from a positive feedback mechanism between the ion distributions and EOF, yielding a true bistability in both fluid flow and electrical current at a critical applied voltage. Nanopore-based NDR is extremely sensitive to the surface charge near the nanopore opening, suggesting possible applications in chemical sensing.

One-step extraction of polar drugs from plasma by parallel artificial liquid membrane extraction.

The new microextraction technique named parallel artificial liquid membrane extraction (PALME) was introduced as an alternative approach to liquid-liquid extraction of charged analytes from aqueous samples. The concept is based on extraction of analytes across a supported liquid membrane sustained in the pores of a thin polymeric membrane, a well-known extraction principle also used in hollow fiber liquid-phase microextraction (HF-LPME). However, the new PALME technique offers a more user-friendly setup in which the supported liquid membrane is incorporated in a 96 well plate system. Thus, high-throughput is achievable, in addition to the green chemistry offered by using PALME. The consumption of organic solvent is minimized to 3-5μL per sample. With a sample volume of 250μL and acceptor solution volume of 50μL, a maximal enrichment factor of five is achievable. Based on these parameters, a new method for extraction of polar basic drugs was developed in the present work. The basic drugs hydralazine, ephedrine, metaraminol, salbutamol, and cimetidine were used as model analytes, and were extracted from alkalized human plasma into an aqueous solution via the supported liquid membrane. The extraction was promoted by a carrier dissolved in the membrane, creating a temporary ion-pair complex between the hydrophilic drug and the carrier. As the model analytes were extracted directly into an aqueous solution, there was no need for evaporation of the extract before injection into LC-MS. Hence, the sample preparation is performed in one step. With optimized conditions, the extraction recoveries were in the range 50-89% from human plasma after 45min extraction. The data from the method evaluation were satisfactory and in line with current guidelines, and revealed an extraction method with substantial potential for high throughput bioanalysis of polar basic drugs.

Assessment of endothelial cell growth behavior in thin film nitinol

Growing clinical needs for less invasive endovascular treatments necessitate the development of advanced biomaterials that exhibit low-profile and enhanced biocompatible properties. One of the endovascular devices is a stent graft, which contains a metallic backbone, covered with thin polymeric membranes such as Dacron® and expandable polytetrafluoroethylene (ePTFE). This device has been widely used for treating various vascular diseases and injuries. While the commercial materials including Dacron® and ePTFE have demonstrated a good feasibility, they were found to induce inflammatory vessel wall reactions with neointimal hyperplasia. Consequently, it causes re-narrowing of the lumen space and thrombogenic issues that ultimately lead the treatment failure. In this paper, we introduced a thin film nitinol (TFN) as an alternative graft material and evaluated the growth behavior of endothelial cells (EC) both qualitatively and quantitatively. As a proof-of-concept study, both untreated nonpatterned film (TFN) and surface treated TFN (S-TFN) materials were used. We compared the adhesion, growth, and proliferation of ECs on a solid (non-patterned) TFN with the two most widely-used commercial graft materials (Dacron® and ePTFE). The in vitro experimental results showed better adhesion and growth of ECs on TFN materials than either ePTFE or Dacron®. Specifically, S-TFN showed approximately twice number of ECs attached on the surface than any other materials tested in this study. In addition, in vivo swine study demonstrated that ECs had a relatively high proliferation on the micropatterrned S-TFN with ~50% surface coverage within two weeks. Both in vitro and in vivo study results of cell growth suggested that TFN materials could be a promising graft material for low-profile endovascular devices.

Voltammetric Ion Selectivity of Thin Ionophore-Based Polymeric Membranes: Kinetic Effect of Ion Hydrophilicity.

The high ion selectivity of potentiometric and optical sensors based on ionophore-based polymeric membranes is thermodynamically limited. Here, we report that the voltammetric selectivity of thin ionophore-based polymeric membranes can be kinetically improved by several orders of magnitude in comparison with their thermodynamic selectivity. The kinetic improvement of voltammetric selectivity is evaluated quantitatively by newly introducing a voltammetric selectivity coefficient in addition to a thermodynamic selectivity coefficient. Experimentally, both voltammetric and thermodynamic selectivity coefficients are determined from cyclic voltammograms of excess amounts of analyte and interfering ions with respect to the amount of a Na(+)- or Li(+)-selective ionophore in thin polymeric membranes. We reveal the slower ionophore-facilitated transfer of a smaller alkaline earth metal cation with higher hydrophilicity across the membrane/water interface, thereby kinetically improving voltammetric Na(+) selectivity against calcium, strontium, and barium ions by 3, 2, and 1 order of magnitude, respectively, in separate solutions. Remarkably, voltammetric Na(+) and Li(+) selectivity against calcium and magnesium ions in mixed solutions is improved by 4 and >7 orders of magnitude, respectively, owing to both thermodynamic and kinetic effects in comparison with thermodynamic selectivity in separate solutions. Advantageously, the simultaneous detection of sodium and calcium ions is enabled voltammetrically in contrast to the potentiometric and optical counterparts. Mechanistically, we propose a new hypothetical model that the slower transfer of a more hydrophilic ion is controlled by its partial dehydration during the formation of the adduct with a "water finger" prior to complexation with an ionophore at the membrane/water interface.

Thin-film-composite hollow-fiber membranes for water vapor separation

Polyethersulfone (PES) hollow fiber membranes were prepared using the phase inversion technique. The surface of the PES hollow fiber membranes consisted of thin film composite polymer membranes. These membranes were prepared by interfacial polymerization using four different aqueous phase monomers: 1,3-benzenedithiol (BDT), m-phenylenediamine (MPD), 1,3,5-benzenetrithol (BTT), and piperazine (PIP). The organic phase monomer, trimesoyl chloride (TMC), was used to produce the covalent organic polymers. Different types of aqueous monomers (with a number of reactive groups) and their structures were optimized to achieve maximum gas permeation efficiency and water vapor/N2 selectivity. All prepared membranes were fully characterized using different analytical techniques. Among all of the prepared thin film composite (TFC) membranes the one prepared with the 1,3-benzenedithiol monomer (TFC-HF-1) exhibited superior results as water vapor permeance 2054 GPU, and the water vapor/N2 selectivity 119. The prepared membrane substrates and TFC membranes were characterized by chemical structure, morphology and separation performance. Overall, the membranes exhibited good performance over the entire investigated range of operating conditions.

Zinc selenide-based large aperture photo-controlled deformable mirror.

Realization of large aperture deformable mirrors with a large density of actuators is important in many applications, and photo-controlled deformable mirrors (PCDMs) represent an innovation. Herein we show that PCDMs are scalable realizing a 2-inch aperture device based on a polycrystalline zinc selenide (ZnSe) as the photoconductive substrate and a thin polymeric reflective membrane. ZnSe is electrically characterized and analyzed through a model that we previously introduced. The PCDM is then optically tested, demonstrating its capabilities in adaptive optics.

Voltammetric Mechanism of Multiion Detection with Thin Ionophore-Based Polymeric Membrane.

The capability to detect multianalyte ions in their mixed solution is an important advantage of voltammetry with an ionophore-based polymeric membrane against the potentiometric and optical counterparts. This advanced capability is highly attractive for the analysis of physiological ions at millimolar concentrations in biological and biomedical samples. Herein, we report on the comprehensive response mechanisms based on the voltammetric exchange and transfer of millimolar multiions at a thin polymeric membrane, where an ionophore is exhaustively depleted upon the transfer of the most favorable primary ion, I(zI). With a new voltammetric ion-exchange mechanism, the primary ion is exchanged with the secondary favorable ion, J(zJ), at more extreme potentials to transfer a net charge of |zJ|/nJ - |zI|/nI for each ionophore molecule, which forms 1:nI and 1:nJ complexes with the respective ions. Alternatively, an ion-transfer mechanism utilizes the second ionophore that independently transfers the secondary ion without ion exchange. Experimentally, a membrane is doped with a Na(+)- or Li(+)-selective ionophore to detect not only the primary ion, but also the secondary alkaline earth ion, based on the ion-exchange mechanism, where both ions form 1:1 complexes with the ionophores to transfer a net charge of +1. Interestingly, the resultant peak potentials of the secondary divalent ion vary with its sample activity to yield an apparently super-Nernstian slope as predicted theoretically. By contrast, the voltammetric exchange of calcium ion (nI = 3) with lithium ion (nJ = 1) by a Ca(2+)-selective ionophore is thermodynamically unfavorable, thereby requiring a Li(+)-selective ionophore for the ion-transfer mechanism.

Transition from ballistic to electrodiffusive transport in free-standing nanometer-sized polymer membranes.

The transition from ballistic to electrodiffusive transport of ions through thin polymer membranes has been investigated by recording single transport events via time-correlated single-particle detection. At the highest kinetic energies investigated, ballistic transport of potassium ions is observed with no discernible energy loss to the membrane. At the lowest kinetic energies investigated (several 100 eV) ions are demonstrated to lose the entire kinetic energy to the membrane. Transport there occurs by electrodiffusion. A transition regime is observed. The transition energy is shown to depend on the thickness of the membrane.

Next generation covered stents made from nanocomposite materials: A complete assessment of uniformity, integrity and biomechanical properties

Covered stents are stents wrapped with a thin polymeric membrane, and are typically used to treat vessel aneurysms and seal perforated arteries. Current covered stents suffer from restenosis due to limitations in material and fabrication methods which leaves metallic struts directly exposed to blood. We have developed a biocompatible and haemocompatible nanocomposite polymer, polyhedral oligomeric silsesquioxane poly(carbonate-urea) urethane (POSS-PCU). We devised a novel combination of ultrasonic spray atomisation system and dip-coating process to produce small calibre covered stents with metal struts fully embedded within the membrane, which also yields greater coating uniformity. Stent-polymer bonding was enhanced via silanisation and coating of reactive pre-polymer. Platelet studies supported the non-thrombogenicity of POSS-PCU. Biomechanical performances including diametrical compliance, bending strength, radial strength and recoil were evaluated and optimised. This proof-of-principle manufacturing technique could lead to the development of next-generation small calibre adult and paediatric covered stents. These stents are currently undergoing preclinical trial. From the Clinical EditorThe use of stents to treat vascular diseases is now the standard of care in the clinical setting. Nonetheless, a major problem of the current stents is the risk of restenosis and thrombosis. The authors developed a nanocomposite material using polyhedral oligomeric silsesquioxane and poly(carbonate-urea) urethane (POSS-PCU) and incorporated into metallic stents. Preliminary data have already shown promising results. It is envisaged that this would further lead to better stent technology in the future.

Voltammetric characterization of ion-ionophore complexation using thin polymeric membranes: asymmetric thin-layer responses.

Selective ion-ionophore complexation in a polymeric membrane is crucial to various sensing applications. In this work, we report on a novel voltammetric approach based on a thin polymeric membrane to determine the stoichiometry and overall formation constant of an ion-ionophore complex. With this approach, a ∼1.6 μm thick ionophore-doped membrane contacts an aqueous solution containing an excess amount of a target ion to facilitate voltammetric ion transfer across the membrane/water interface. Advantageously, the resultant thin-layer voltammogram shows no diffusional effect, which simplifies the theoretical modeling and quantitative analysis of the voltammogram. We predict theoretically that the complexation stoichiometry affects not only the peak current and peak potential of the thin-layer voltammogram, but also the symmetry of the peak shape with respect to the peak potential. Experimentally, a symmetric voltammogram ensures the formation of a 1:1 complex for a Na(+)-selective ionophore. By contrast, the asymmetric shape and peak current of voltammograms are used to demonstrate that a Ca(2+)-selective ionophore forms 1:3 and 1:2 complexes with calcium and magnesium ions, respectively. The complexation stoichiometry is needed to yield the formation constants that are consistent with those determined previously by potentiometry. In addition, both 1:2 and 1:1 complexes are voltammetrically observed with another Na(+)-selective ionophore, which was assumed to form only a 1:2 complex in previous potentiometric studies. The formation constants of both complexes are determined from a single voltammogram to reveal that the preceding formation of a 1:2 complex thermodynamically hampers the voltammetric observation of a 1:1 complex.

Catalysts Based on Earth-Abundant Elements for Catalyzing O2 Reduction in Acidic Electrolytes

Catalysis of the oxygen reduction reaction (ORR) is a key challenge for high power density fuel cells and metal-air batteries. Today, the polymer electrolyte membrane fuel cell (PEMFC) is the most advanced fuel cell type for transportation applications, where high power density is required. The advanced technology readiness of the PEMFC leans on the existence of stable and extremely thin polymer membranes and of highly active platinum-based catalysts for oxygen reduction and hydrogen oxidation. The acidic nature of PEM is however disadvantageous to the electrocatalysis of the sluggish ORR. While advances in platinum-based catalysts are still ongoing,1 economic and resource-based constraints are incentives to start designing today the next generation of ORR catalysts. The latter should ideally be free of rare elements and, in particular, free of Platinum-Group Metals (PGMs) since those metals are all mined from the same ore. Important advances in non-PGM catalysts have been witnessed since 2009,2-4 which is promising toward the long-haul goal of more affordable PEMFC stacks and decreased reliance on limited natural resources. The three aspects of i) synthesis, ii) electrochemical characterisation and iii) spectroscopic characterisation of Fe- and Co-N-C catalysts synthesized using Metal-Organic Frameworks (MOFs) will be discussed. The design of novel sacrificial MOFs and approaches for preparing the catalyst precursors that are subsequently pyrolyzed will be presented. The versatility of MOF materials with respect to the ligand chemistry and topological structure is immense, resulting in thousands of different possible materials. Such materials just started being investigated as sacrificial precursors for the synthesis of Fe(Co)-N-C materials.5-6-7 Results obtained from the electrochemical investigation of the key characteristics of those ORR catalysts, namely initial ORR activity, power performance and durability, will be discussed. In particular, the degradation mechanisms related to transient high-voltage and H2O2 generation during steady-state operation are important.8 Both these degradation types correspond to various oxidative attacks of the carbon-based catalysts. The degradation induced by minute amounts of H2O2 can lead to a decreased ORR activity and/or decreased mass-transport properties of the cathode, depending on the nature of the transition metal element. Ex situ chemical treatment of catalysts with various amounts of H2O2 is a useful approach for simulating the steady-state operando degradation in fuel cell. In this respect, cobalt will be shown to be advantageous compared to iron for long term durability of metal-N-C catalysts. Third, a better identification of the nature and structure of the metal-centred active sites with spectroscopic methods (Mössbauer spectroscopy and X-ray absorption spectroscopy) will be presented. Comparison of computed spectra to experimentally measured spectra is important for identifying the active site structure and for supporting the DFT calculation approaches on model sites with some experimental evidence for the existence of metal-Nx-Cy moieties embedded in or at the edge of graphene sheets.

A sacrificial process for fabrication of biodegradable polymer membranes with submicron thickness.

A new sacrificial molding process using a single mask has been developed to fabricate ultrathin 2-dimensional membranes from several biocompatible polymeric materials. The fabrication process is similar to a sacrificial microelectromechanical systems (MEMS) process flow, where a mold is created from a material that can be coated with a biodegradable polymer and subsequently etched away, leaving behind a very thin polymer membrane. In this work, two different sacrificial mold materials, silicon dioxide (SiO2 ) and Liftoff Resist (LOR) were used. Three different biodegradable materials; polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and polyglycidyl methacrylate (PGMA), were chosen as model polymers. We demonstrate that this process is capable of fabricating 200-500 nm thin, through-hole polymer membranes with various geometries, pore-sizes and spatial features approaching 2.5 µm using a mold fabricated via a single contact photolithography exposure. In addition, the membranes can be mounted to support rings made from either SU8 or PCL for easy handling after release. Cell culture compatibility of the fabricated membranes was evaluated with human dermal microvascular endothelial cells (HDMECs) seeded onto the ultrathin porous membranes, where the cells grew and formed confluent layers with well-established cell-cell contacts. Furthermore, human trabecular meshwork cells (HTMCs) cultured on these scaffolds showed similar proliferation as on flat PCL substrates, further validating its compatibility. All together, these results demonstrated the feasibility of our sacrificial fabrication process to produce biocompatible, ultra-thin membranes with defined microstructures (i.e., pores) with the potential to be used as substrates for tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1192-1201, 2016.

Experimental and numerical studies of a microfluidic device with compliant chambers for flow stabilization

This paper reports experimental and numerical studies of a passive microfluidic device that stabilizes a pulsating incoming flow and delivers a steady flow at the outlet. The device employs a series of chambers along the flow direction with a thin polymeric membrane (of thickness 75–250 µm) serving as the compliant boundary. The deformation of the membrane allows accumulation of fluid during an overflow and discharge of fluid during an underflow for flow stabilization. Coupled fluid-structure simulations are performed using Mooney–Rivlin formulations to account for a thin hyperelastic membrane material undergoing large deformations to accurately predict the device performance. The device was fabricated with PDMS as the substrate material and thin PDMS membrane as the compliant boundary. The performance of the device is defined in terms of a parameter called ‘Attenuation Factor (AF)’. The effect of various design parameters including membrane thickness, elastic modulus, chamber size and number of chambers in series as well as operating conditions including the outlet pressure, mean input flow rate, fluctuation amplitude and frequency on the device performance were studied using experiments and simulations. The simulation results successfully confront the experimental data (within 10%) which validates the numerical simulations. The device was used at the exit of a PZT actuated valveless micropump to take pulsating flow at the upstream and deliver steady flow downstream. The amplitude of the pulsating flow delivered by the micropump was significantly reduced (AF = 0.05 for a device with three 4 mm chambers) but at the expense of a reduction in the pressure capability (<20%). The proposed device could potentially be used for reducing flow pulsations in practical microfluidic circuits.

ChemInform Abstract: Pot‐in‐Pot Reactions: A Simple and Green Approach to Efficient Organic Synthesis

AbstractReview: 134 refs.

ナノスーツ法による生きたままの生物のSEM 内生態観察

ナノスーツ法による生きたままの生物のSEM 内生態観察

Fabrication and stabilization of nanoscale emulsions by formation of a thin polymer membrane at the oil–water interface

Extremely stable O/W nanoemulsions are fabricated by effective assembly of an amphiphilic PEO-b-PCL copolymer at the oil–water interface during phase inversion, which favors formation of a thin PEO-b-PCL film at the interface.

Vertically stacked thin triboelectric nanogenerator for wind energy harvesting

Wind has come to be considered as an attractive energy source due to its abundance, ubiquity, and sustainability in nature. When an energy harvester driven by wind is miniaturized with high-power and robustness, it can be useful for self-powered systems of mobile electronic devices. In this work, a vertically stacked triboelectric nanogenerator (VS-TENG) is investigated. When wind is introduced into the air gap of the VS-TENG, a thin and flexible polymer membrane repeatedly comes in contact with and separates from upper and lower electrodes. This thin device structure makes the VS-TENG suitable for vertical stacking without bulky volume. Vertical stacking not only provides multiplied output power via parallel stacking but also enables utilization of bi-directional wind by a cross stack.