Sub-μm Scale Research Articles

A Multiscale Modeling Approach to Identify and Quantify the Transport Limitations in Proton Exchange Membrane Fuel Cells

The reduction of platinum loading is essential for lowering the cost of Proton Exchange Membrane Fuel Cells (PEMFCs). However, low platinum loadings typically lead to performance losses due to reduced electrochemical active surface area as well as additional local transport losses within the catalyst layer. Experimentally, limiting current analysis provides a helpful tool to investigate the oxygen transport limitations. In this method the limiting current (obtained at cell voltages of about 0.2 V) is measured for different oxygen concentrations and total pressures. The oxygen transport resistance is then calculated from the ratio of oxygen concentration and limiting current. The pressure variation allows separating the pressure dependent and pressure independent parts of this resistance, which are related to transport in the channels, molecular diffusion in the Gas Diffusion Layer (GDL), Knudsen diffusion through the Micro Porous Layer (MPL) and cathode catalyst layer (CCL) plus local transport losses within the CCL, respectively. However, the method does not allow to easily break down the contributions of each cell component and processes to the total resistance, which requires the variation of the components[1].Therefore, within the project FURTHER-FC[2] we develop a multiscale modeling approach for interpreting the experimentally observed transport losses and to quantify the contributions of the different cell components based on their microstructure. On the sub-µm scale a Lattice Boltzmann model is developed to describe the transport within the CCL on the agglomerate scale, taking into account the transport through the ionomer film. This model is used to parametrize the effective local transport resistance[3] for calculation of the reaction kinetics in the cell model. For the GDL/MPL Direct Numerical Simulation (DNS) applied to the real microstructures[4] is used to obtain the effective diffusion coefficients, which are then applied in the cell model. The 2D PEMFC model considers the multicomponent transport, i.e., free flow in the gas channels and transport through the porous media according to Darcy’s law, charge transport, water transport in the ionomer, energy transport as well as the electrochemical reactions. Model validation is performed with limiting current analysis on MEAs with different platinum loading under various pressures and relative humidity. By analyzing the local concentrations within the cell, the model is then used to quantify the contributions of each cell component to the overall oxygen transport resistance. The project FURTHER-FC [2] has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under Grant Agreement No 875025. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research. [1] Daniel R. Baker et al, J. Electrochem. Soc. (2009) 156 B991[2] https://further-fc.eu/[3] T. Jahnke and A. Baricci, J. Electrochem. Soc. 169 (2022) 094514[4] M. Ahmed-Maloum et al., Journal of Power Sources 561 (2023) 232735 Figure 1

From molecular to sub-μm scale: The interplay of precursor concentrations, primary particle size, and carbon nanostructure during soot formation in counter-flow diffusion flames

The focus of this work is on counter-flow diffusion flames of C2H4/air near the sooting limit (fV < 500 ppb) to shed light on the transition of precursor molecules to primary soot particles and their nanostructure. The applied experimental techniques cover non-intrusive methods based on laser-induced incandescence (LII) for determination of soot volume fractions, primary particle sizes, and ratios of refractive indices for absorption at different wavelengths. The methods are complemented by intrusive methods such as sampling with microprobes and analysis of gas composition by gas chromatography and mass spectrometry, particle sizing by differential mobility analysis, and determining carbon nanostructures of particles by high-resolution transmission electron microscopy (HRTEM). For numerical simulation, the well-known ABF-model is applied.The experimentally determined structures of the counter-flow flames could be well reproduced within the experimental uncertainties by the ABF-model for varying fuel mass fractions and strain rates. The numerical simulations identify the different processes during particle formation and the main variation can be attributed to variation of surface growth rates when applying strain rates and fuel mass fractions leading to higher soot volume fractions. Particle size distributions detected in the fuel flow near and below the stagnation plane appear bimodal with distinct maxima at particles sizes about 5 nm and 20 nm. The nanostructure of the primary particles exhibits basic structural units (BSUs), that increase up to the size of 7 Å to 10 Å at increasing soot volume fractions from about 100 ppb to 300 ppb. This coincides with the increase of the mole fractions of the detectable soot precursors with increasing soot volume fraction. The ratios of refractive index functions for absorption E(m,λ532)/E(m,λ1064) and E(m,λ266)/E(m,λ1064) decrease approximately linearly with increasing soot volume fractions. This is corroborated by the analyses of HRTEM-images that clearly bring about increasing sized BSUs with increasing soot volume fractions causing a shift of the absorption to larger wavelengths.

On the exceptional temperature stability of ferroelectric Al1-xScxN thin films

Through its dependence on low symmetry crystal phases, ferroelectricity is inherently a property tied to the lower temperature ranges of the phase diagram for a given material. This paper presents conclusive evidence that in the case of ferroelectric Al1−xScxN, low temperature has to be seen as a purely relative term, since its ferroelectric-to-paraelectric transition temperature is confirmed to surpass 1100 °C and thus the transition temperature of virtually any other thin film ferroelectric. We arrived at this conclusion through investigating the structural stability of 0.4–2 μm thick Al0.73Sc0.27N films grown on Mo bottom electrodes via in situ high-temperature x-ray diffraction and permittivity measurements. Our studies reveal that the wurtzite-type structure of Al0.73Sc0.27N is conserved during the entire 1100 °C annealing cycle, apparent through a constant c/a lattice parameter ratio. In situ permittivity measurements performed up to 1000 °C strongly support this conclusion and include what could be the onset of a diverging permittivity only at the very upper end of the measurement interval. Our in situ measurements are well-supported by ex situ (scanning) transmission electron microscopy and polarization and capacity hysteresis measurements. These results confirm the structural stability on the sub-μm scale next to the stability of the inscribed polarization during the complete 1100 °C annealing treatment. Thus, Al1−xScxN, there is the first readily available thin film ferroelectric with a temperature stability that surpasses virtually all thermal budgets occurring in microtechnology, be it during fabrication or the lifetime of a device—even in harshest environments.

Second harmonic generation signal from type I collagen fibers grown in vitro.

We present a study of the optical second-order nonlinearity of type I collagen fibers grown in vitro via second harmonic generation (SHG) experiments and analyze the observed polarization-resolved SHG signal using previously reported SHG analytical expressions obtained for anisotropic tissue. Our results indicate that the effective second-order nonlinearity measured in the grown fibers is one order of magnitude lower than that of native collagen fibers. This is attributed to the formation of loose and dispersive fibrillar networks of thinner collagen fibrils that constitute the reassembled collagen fibers. This is confirmed by scanning electronic microscopy (SEM) imaging and the polarization dependence of the SHG signal. The measured values of the anisotropy parameter ρ of the reassembled collagen fibers are found to be similar to that obtained for native fibers on the relevant sub-µm scale.

Multiscale ceramic components from preceramic polymers by hybridization of vat polymerization-based technologies

A novel approach to fabricate ceramic structures at multiple scales in a single component, based on the hybridization of additive manufacturing technologies, was developed by combining 3D macro-stereolithography (Digital Light Processing, DLP) with two-photon lithography (2PL), to produce cm-sized sample geometries with sub-μm surface features. The preceramic structures in the sub-μm scale were realized by 2PL directly on easily manageable DLP macro-sized samples of the same ceramic composition. In this way, preceramic structures presenting both features typical of DLP printers (with a minimum size of around 50 μm) and features well below their resolution limit were realized. We report here, for the first time, the realization of polymer-derived ceramic SiOC ceramic components structured in 3D across several length scales (with micron and mesoscale 3D features), produced by pyrolysis at 1000 °C of preceramic parts, without shape distortion during the pyrolysis step.

Nanometer-Scale Operando Imaging on Ionic and Electronic Transport through Polycrystalline Ceramic Solid Electrolytes

Solid electrolyte (SE) is a promising candidate for enabling next generation high-density energy storage devices such as Li/chalcogenide or Li/air batteries. However, one of the major challenges in current SE is either low ion-conductivity or long-term stability: on one hand, SE such as organic polymer or glass ceramic has generally lower ion-conductivity than required by normal charging rate; on another hand, SE such as polycrystalline ceramic has instable problem encountering numerous cycling. Besides chemical and structural perspectives, the instability can also be initiated by highly inhomogeneous ionic conduction and electronic insulation through the SEs, where a point defect or weak point can develop to catastrophic device shunting by locally-enhanced ionic or electronic currents. Ionic and electronic conductivity in polycrystalline ceramic SE can be highly inhomogeneous, due to its structural nonuniformity in both micrometer and nanometer scales. Inexpensive processing such as pressing or liquid-casting can form micrometer-sized defects such as pin-holes. The structural and chemical nature of polycrystalline ceramic has the nm-sized inhomogeneity. All these structural and chemical inhomogeneity can cause significant nonuniform ionic and electronic transport during battery cycling, and further initiate device degradation and failure. However, characterization of the charge transport in SE has been limited in macroscopic scales such as electrochemical voltammetry or impedance spectroscopy. We here present on our recent development of nm-scale ionic and electronic transport imaging technique and the characterization results on two polycrystalline ceramic SEs of Li7P3S11(LPS) and Li1.4Ti1.6Al0.4(PO4)3(LTAP). The imaging technique was implemented by developing AFM-based scanning spreading microscopy (SSRM), which is essentially a half-cell with Li or Li-In alloy as one electrode and the SSRM probe as the other. This setup enables an operando measurement of charge transports, and has the following functions in order to meet the various SE characterization needs: (1) extremely wide range (Up to 1013orders of magnitude) of current sensitivity from 10-16 A (sub-fA) to 10-3 A (mA) for the low and high ionic/electronic conductivity, by using a logarithm current amplifier; (2) variable bias voltage polarity and amplitude to separate ion and electronic transport; (3) accurately position the probe at a point and hold stably for many hours by implementing a close-loop scanner control; (4) controllable probe/electrolyte contact area for balancing resolution and electrical signal strength; (5) controllable contact force (sub-nN to μN) for different hardness of the electrolytes from polymer to inorganic materials. The capability to separate the ionic and electronic conductions is based on the asymmetrical SSRM setup of probe/SE/Li-In. The electrical current under a negative sample bias (Vs) is the electronic conduction through the SE or an electronic leaking current, since there is no Li supply from the probe side (probe is highly-doped diamond-coated Si) and thus no Li ionic current flowing through the SE. Under a positive Vs, the electrical current is sum of electronic leaking and Li ionic currents flowing from the Li-In to the probe sides through the SE. The results on LPS shows huge asymmetrical current as large as 105orders of magnitude (several pA and 10-5 pA under positive and negative Vs), demonstrating the working SE with highly ionic conductivity and highly electronic resistivity (~1011 Ωcm). The asymmetry of LTAP is also large (103 orders) but less than LPS, with 10-1 PA ionic current and 10-4 pA electronic current. The ionic conduction on both the SEs is highly inhomogeneous in sub-μm scale with one to two orders of magnitude fluctuations, reflecting the complexity of SE ionic conduction by the local structural and chemical nonuniformities. For example, grain boundaries, grain orientation, local phase separation, and local chemical non-stoichiometry and aggregations can all have effects on the local ionic conduction in nm-μm scales. The local ionic fluctuation also changes with Vs, indicating the local energy levels of ion transport associated with the local structures. These local nm-scale imaging of ionic and electronic transports is expected to have broad impact on understanding and development of the SEs.

Fabrication of a high-density emitter array for electrospray thrusters using field emitter array process

To improve the thrust density of electrospray thrusters using ionic liquids as the propellant, we have fabricated a high-density emitter array utilizing the fabrication technique of a field emitter array (FEA) or gated nano electron sources. The density of the emitter array can reach approximately 4 million cm−2, which is four orders of magnitude higher than that of conventional electrospray thrusters. Performing deep reactive ion etching from the back side of the same structure as FEAs and removing their Ni cones by dilute nitric acid, we have successfully fabricated sub-μm scale capillary emitters with self-aligned extractor electrodes and ionic liquid reservoirs behind them. Current measurements were also conducted with EMI-BF4 and EMI-DCA as the propellant. Although the ion was not extracted with EMI-BF4 owing to its electrochemical reaction with the electrodes, both positive and negative ion currents were detected using EMI-DCA, where the current density exceeded that of conventional electrospray thrusters.

Digital holographic microscopy for sub-µm scale high aspect ratio structures in transparent materials

This paper discusses a digital holographic microscopy approach for comprehensive and non-destructive inspection of spatially confined structures, which are characterized by the high aspect ratio of their lateral dimensions ( ∼ 1:30) and are fabricated out of transparent materials. Two-photon polymerization is chosen as a high-resolution lithographic technology for manufacturing of corresponding structures out of positive photoresin. The proposed holographic inspection method does not require any numerical methods for aberration correction and thus demonstrates rapid phase map evaluation ( ∼ 250 ms per cycle). Applicability and performance of the method has been successfully tested on a set of samples modelled to resemble step-index structures similar to the lab-on-chip basic elements, e.g. waveguides. In terms of lateral resolution a diffraction-limited operation of the proposed imaging system is ensured while vertical accuracy of 1.61 nm has been demonstrated.

Elemental and topographical imaging of microscopic variations in deposition on NSTX-U and DIII-D samples

Tokamak plasma facing components have surface roughness that can cause microscopic spatial variations in erosion and deposition and hence influence material migration, erosion lifetime, dust and tritium accumulation, and plasma contamination. However, high spatial resolution measurements of deposition on a sub-µm scale of surface roughness have been lacking to date. We will present elemental images of graphite samples from NSTX-U and DIII-D DiMES experiments performed with a Scanning Auger Microprobe at sub-micron resolution that show strong microscopic variations in deposition and correlate this with 3D topographical maps of surface irregularities. The NSTX-U samples were boronized and exposed to deuterium plasmas. The DiMES samples had localized Al and W films and were exposed to dedicated helium plasmas. Topographical maps of the samples were performed with a 3D confocal optical microscope and compared to the elemental deposition pattern. The results revealed localized deposition concentrated in areas shadowed from the ion flux, incident in a direction calculated by taking account of the magnetic sheath.

Sub-micrometer distribution of Fe oxides and organic matter in Podzol horizons

The spatial distribution of soil constituents at the micrometer scale is of great importance to understand processes controlling the formation of micro-aggregates and the stabilization of organic carbon. Here, the spatial distribution of organic and mineral constituents in Podzol horizons is studied by concerted measurements of (i) the content of various forms of Fe, Al, Si and C determined by selective extraction in the fine earth fraction of soil (f < 2 mm); (ii) the elemental composition of the clay fraction (f < 2 μm) with lateral resolution using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and with surface selectivity using X-ray photoelectron spectroscopy (XPS); (iii) the specific surface area (SSA) of fine earth and clay fractions by krypton physisorption.The SSA of the fine earth in illuvial horizons is predominantly due to finely divided Fe oxides, including goethite, characterized by an equivalent particle size of about 10 nm. Kaolinite platelets of about 2 μm size account for a large volume proportion in the clay fraction but have a minor contribution to SSA. Fe oxides and organic matter (OM) are intimately associated. Heterogeneity at the μm scale is created by local variations in the relative amounts of kaolinite and Fe-OM associations. These two kinds of physical entities are in random mixture. Moreover, variation of C/Fe atomic ratios reveals sub-μm scale heterogeneity. The latter is due to variation in the relative proportion of organic compounds and Fe oxides, indicating that aggregation of nanoparticles, and not only mere adsorption or pore filling, plays a role in these associations. In this regard, our results highlight that OM associated with Fe protects Fe oxides against physical displacement and that part of this associated OM is oxidizable by NaOCl treatment. These findings demonstrate that the concept of OM stabilization through association with Fe must be revisited when considering the sub-μm scale level because fine Fe oxide particles can be easily dispersed during oxidation of associated carbon. Combination of physical fractionation and microanalysis (e.g. SEM-EDS, vibrational spectroscopy) offer promising perspectives to clarify the relationship between chemical composition and sub-μm scale architecture, and to better understand soil processes.

Thermal transport in binary colloidal glasses: Composition dependence and percolation assessment.

The combination of various types of materials is often used to create superior composites that outperform the pure phase components. For any rational design, the thermal conductivity of the composite as a function of the volume fraction of the filler component needs to be known. When approaching the nanoscale, the homogeneous mixture of various components poses an additional challenge. Here, we investigate binary nanocomposite materials based on polymer latex beads and hollow silica nanoparticles. These form randomly mixed colloidal glasses on a sub-μm scale. We focus on the heat transport properties through such binary assembly structures. The thermal conductivity can be well described by the effective medium theory. However, film formation of the soft polymer component leads to phase segregation and a mismatch between existing mixing models. We confirm our experimental data by finite element modeling. This additionally allowed us to assess the onset of thermal transport percolation in such random particulate structures. Our study contributes to a better understanding of thermal transport through heterostructured particulate assemblies.

Fraction-specific controls on the trace element distribution in iron formations: Implications for trace metal stable isotope proxies

Iron formations (IFs) are important geochemical repositories that provide constraints on atmospheric and ocean chemistry, prior to and during the onset of the Great Oxidation Event. Trace metal abundances and their Mo-Cr-U isotopic ratios have been widely used for investigating ocean redox processes through the Archean and Paleoproterozoic. Mineralogically, IFs consist of three main Fe-bearing fractions: (1) Fe-Ca-Mg-Mn carbonates, (2) magnetite and/or hematite and (3) Fe-silicates. These fractions are typically fine-grained on a sub-μm scale and their co-occurrence in varying amounts means that bulk-rock or microanalytical geochemical and stable isotope data can be influenced by cryptic changes in mineralogy. Fraction specific geochemical analysis has the potential to resolve mineralogical controls and reveal diagenetic versus primary precipitative controls on IF mineralogy. Here we adapt an existing sequential extraction scheme for Fe-phases (Poulton and Canfield, 2005) to the high Fe-content in IF and the specific three-fraction mineralogy. We optimized the scheme for magnetite-dominated Archean IFs using samples from the hematite-poor Asbestos Hills Subgroup IF, Transvaal Supergroup, South Africa. Previously commonly-used hydroxylamine-HCl and dithionite leaches were omitted since ferric oxides are quantitatively insignificant in these IF samples. The acetate leach was tested at variable temperatures, reaction times and under different atmospheres in order to ensure that all micro-crystalline Fe-carbonates were effectively dissolved, resulting in an optimum extraction for 48h at 50°C under anoxic conditions. The dissolution of magnetite by NH4-oxalate was also tested, resulting in an optimum extraction for 24h under an ambient atmosphere. Finally, a HF-HClO4-HNO3 leach was used to dissolve the residual silicate fraction which has to date not been considered in detail in IF. Accuracy of the extraction technique was generally excellent, as verified using 1) elemental recoveries, 2) comparison of major and trace element distributions against mineralogy and 3) comparison to results from microanalytical techniques.This study focuses on the distribution of three frequently used geochemical proxies in IF; U, Mo and Cr. Molybdenum abundances in the Kuruman and Griquatown IF are low and show an apparent correlation with mineralogical variability, as determined by the sequential extraction. This suggests that changes in bulk-rock mineralogy, rather than redox chemistry might significantly affect Mo stable isotopes. For Cr, a minor bulk-rock stratigraphic increase can be related to the oxide and silicate fraction. However, a positive relationship with Zr indicates that this was also controlled by detrital or volcanic ash input. Uranium is predominantly bound to the silicate fraction and shows clear correlations with Zr and Sc implying detrital reworking under anoxic conditions. The discrepant behaviour of these three proxies indicate that mineralogy should be taken into account when interpreting heterogeneous bulk-rock samples and that fraction specific techniques will provide new insights into the evolution of atmosphere and ocean chemistry.

Subcellular reorganization and altered phosphorylation of the astrocytic gap junction protein connexin43 in human and experimental temporal lobe epilepsy.

Dysfunctional astrocytes are increasingly recognized as key players in the development and progression of mesial temporal lobe epilepsy (MTLE). One of the dramatic changes astrocytes undergo in MTLE with hippocampal sclerosis (HS) is loss of gap junction coupling. To further elucidate molecular mechanism(s) underlying this alteration, we assessed expression, cellular localization and phosphorylation status of astrocytic gap junction proteins in human and experimental MTLE-HS. In addition to conventional confocal analysis of immunohistochemical staining we employed expansion microscopy, which allowed visualization of blood-brain-barrier (BBB) associated cellular elements at a sub-µm scale. Western Blot analysis showed that plasma membrane expression of connexin43 (Cx43) and Cx30 were not significantly different in hippocampal specimens with and without sclerosis. However, we observed a pronounced subcellular redistribution of Cx43 toward perivascular endfeet in HS, an effect that was accompanied by increased plaque size. Furthermore, in HS Cx43 was characterized by enhanced C-terminal phosphorylation of sites affecting channel permeability. Prominent albumin immunoreactivity was found in the perivascular space of HS tissue, indicating that BBB damage and consequential albumin extravasation was involved in Cx43 dysregulation. Together, our results suggest that subcellular reorganization and/or abnormal posttranslational processing rather than transcriptional downregulation of astrocytic gap junction proteins account for the loss of coupling reported in human and experimental TLE. The observations of the present study provide new insights into pathological alterations of astrocytes in HS, which may aid in the identification of novel therapeutic targets and development of alternative anti-epileptogenic strategies.

Rapid Antibiotic Susceptibility Testing of Uropathogenic E. coli by Tracking Submicron Scale Motion of Single Bacterial Cells.

To combat antibiotic resistance, a rapid antibiotic susceptibility testing (AST) technology that can identify resistant infections at disease onset is required. Current clinical AST technologies take 1-3 days, which is often too slow for accurate treatment. Here we demonstrate a rapid AST method by tracking sub-μm scale bacterial motion with an optical imaging and tracking technique. We apply the method to clinically relevant bacterial pathogens, Escherichia coli O157: H7 and uropathogenic E. coli (UPEC) loosely tethered to a glass surface. By analyzing dose-dependent sub-μm motion changes in a population of bacterial cells, we obtain the minimum bactericidal concentration within 2 h using human urine samples spiked with UPEC. We validate the AST method using the standard culture-based AST methods. In addition to population studies, the method allows single cell analysis, which can identify subpopulations of resistance strains within a sample.

Registration procedure for spatial correlation of physical energy deposition of particle irradiation and cellular response utilizing cell-fluorescent ion track hybrid detectors

The hybrid technology cell-fluorescent ion track hybrid detector (Cell-Fit-HD) enables the investigation of radiation-related cellular events along single ion tracks on the subcellular scale in clinical ion beams. The Cell-Fit-HD comprises a fluorescent nuclear track detector (FNTD, the physical compartment), a device for individual particle detection and a substrate for viable cell-coating, i.e. the biological compartment. To date both compartments have been imaged sequentially in situ by confocal laser scanning microscopy (CLSM). This is yet in conflict with a functional read-out of the Cell-Fit-HD utilizing a fast live-cell imaging of the biological compartment with low phototoxicity on greater time scales. The read-out of the biological from the physical compartment was uncoupled. A read-out procedure was developed to image the cell layer by conventional widefield microscopy whereas the FNTD was imaged by CLSM. Point mapping registration of the confocal and widefield imaging data was performed. Non-fluorescent crystal defects (spinels) visible in both read-outs were used as control point pairs. The accuracy achieved was on the sub-µm scale. The read-out procedure by widefield microscopy does not impair the unique ability of spatial correlation by the Cell-Fit-HD. The uncoupling will enlarge the application potential of the hybrid technology significantly. The registration allows for an ultimate correlation of microscopic physical beam parameters and cell kinetics on greater time scales. The method reported herein will be instrumental for the introduction of a novel generation of compact detectors facilitating biodosimetric research towards high-throughput analysis.

β-Cyclodextrin-Based Inclusion Complexation Bridged Biodegradable Self-Assembly Macromolecular Micelle for the Delivery of Paclitaxel.

In this study, a novel adamantanamine-paclitaxel (AD-PTX) incorporated oligochitosan- carboxymethyl-β-cyclodextrin (CSO-g-CM-β-CD) self-assembly macromolecular (CSO-g-CM-β-CD@AD-PTX) micelle was successfully prepared in water through sonication. The formed molecules were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (NMR) spectroscopy, two-dimensional NMR, elemental analysis, and liquid chromatography-mass spectrometry, while the correspondent micelles were characterized by dynamic light scattering and transmission electron microscopy. We showed that the macromolecular micelle contained a spherical core-shell structure with a diameter of 197.1 ± 3.3 nm and zeta potential of −19.1 ± 4.3 mV. The CSO-g-CM-β-CD@AD-PTX micelle exhibited a high drug-loading efficacy up to 31.3%, as well as a critical micelle concentration of 3.4 × 10-7 M, which indicated good stability. Additionally, the in vitro release profile of the CSO-g-CM-β-CD@AD-PTX micelle demonstrated a long-term release pattern, 63.1% of AD-PTX was released from the micelle during a 30-day period. Moreover, the CSO-g-CM-β-CD@AD-PTX micelle displayed cytotoxicity at a sub-μM scale similar to PTX in U87 MG cells, and CSO-g-CM-β-CD exhibited a good safety profile by not manifesting significant toxicity at concentrations up to 100 μM. These results indicated that β-CD-based inclusion complexation resulting in biodegradable self-assembled macromolecular micelles can be utilized as nanocarrier, and may provide a promising platform for drug delivery in the future medical applications.

Binding of heavy metal ions in aggregates of microbial cells, EPS and biogenic iron minerals measured in-situ using metal- and glycoconjugates-specific fluorophores

Aggregates consisting of bacterial cells, extracellular polymeric substances (EPS) and Fe(III) minerals formed by Fe(II)-oxidizing bacteria are common at bulk or microscale chemical interfaces where Fe cycling occurs. The high sorption capacity and binding capacity of cells, EPS, and minerals controls the mobility and fate of heavy metals. However, it remains unclear to which of these component(s) the metals will bind in complex aggregates. To clarify this question, the present study focuses on 3D mapping of heavy metals sorbed to cells, glycoconjugates that comprise the majority of EPS constituents, and Fe(III) mineral aggregates formed by the phototrophic Fe(II)-oxidizing bacteria Rhodobacter ferrooxidans SW2 using confocal laser scanning microscopy (CLSM) in combination with metal- and glycoconjugates-specific fluorophores. The present study evaluated the influence of glycoconjugates, microbial cell surfaces, and (biogenic) Fe(III) minerals, and the availability of ferrous and ferric iron on heavy metal sorption. Analyses in this study provide detailed knowledge on the spatial distribution of metal ions in the aggregates at the sub-μm scale, which is essential to understand the underlying mechanisms of microbe–mineral–metal interactions. The heavy metals (Au3+, Cd2+, Cr3+, CrO42−, Cu2+, Hg2+, Ni2+, Pd2+, tributyltin (TBT) and Zn2+) were found mainly sorbed to cell surfaces, present within the glycoconjugates matrix, and bound to the mineral surfaces, but not incorporated into the biogenic Fe(III) minerals. Statistical analysis revealed that all ten heavy metals tested showed relatively similar sorption behavior that was affected by the presence of sorbed ferrous and ferric iron. Results in this study showed that in addition to the mineral surfaces, both bacterial cell surfaces and the glycoconjugates provided most of sorption sites for heavy metals. Simultaneously, ferrous and ferric iron ions competed with the heavy metals for sorption sites on the organic compounds. In summary, the information obtained by the present approach using a microbial model system provides important information to better understand the interactions between heavy metals and biofilms, and microbially formed Fe(III) minerals and heavy metals in complex natural environments.

振動援用切削によるサブミクロンスケールの表面テクスチャ加工

The vibration-assisted cutting was performed to fabricate surface textures composed of numerous periodical concavo-convex patterns at Sub-μm scale anticipating future usage as the micro/nanotexture mold for injection molding. In the experiment, a modeling wax workpice was machined using a sharply pointed triangular diamond indenter tip vibrated by a piezo actuator in the direction of the cutting depth with μm order amplitude. As a result, a textured surface composed of numerous inverted triangular pyramidal impressions surrounded by pileups are successfully fabricated, and their average dimensions are about 60 nm in height and 580 nm and 900 nm in pitches in cutting and feed directions, respectively.

Direct and accurate measurement of size dependent wetting behaviors for sessile water droplets.

The size-dependent wettability of sessile water droplets is an important matter in wetting science. Although extensive studies have explored this problem, it has been difficult to obtain empirical data for microscale sessile droplets at a wide range of diameters because of the flaws resulting from evaporation and insufficient imaging resolution. Herein, we present the size-dependent quantitative change of wettability by directly visualizing the three phase interfaces of droplets using a cryogenic-focused ion beam milling and SEM-imaging technique. With the fundamental understanding of the formation pathway, evaporation, freezing, and contact angle hysteresis for sessile droplets, microdroplets with diameters spanning more than three orders of magnitude on various metal substrates were examined. Wetting nature can gradually change from hydrophobic at the hundreds-of-microns scale to super-hydrophobic at the sub-μm scale, and a nonlinear relationship between the cosine of the contact angle and contact line curvature in microscale water droplets was demonstrated. We also showed that the wettability could be further tuned in a size-dependent manner by introducing regular heterogeneities to the substrate.

A mineralogical study in contrasts: highly mineralized whale rostrum and human enamel.

The outermost enamel of the human tooth and the rostrum of the whale Mesoplodon densirostris are two highly mineralized tissues that contain over 95 wt.% mineral, i.e., bioapatite. However, the same mineral type (carbonated hydroxylapatite) does not yield the same material properties, as revealed by Raman spectroscopy, scanning electron microscopy, electron microprobe analysis, and synchrotron X-ray diffraction analysis. Overall, the outermost enamel of a tooth has more homogeneous physical and chemical features than the rostrum. Chemical comparison of rostrum and enamel shows bioapatite in the rostrum to be enriched in Na, Mg, CO3, and S, whereas the outermost enamel shows only a slightly enriched Cl concentration. Morphologically, mineral rods (at tens of μm scale), crystallites and prisms (at μm and sub-μm scale), and platelets (at tens of nm scale) all demonstrate less organized texture in the rostrum than in enamel. Such contrasts between two mineralized tissues suggest distinct pathways of biomineralization, e.g., the nature of the equilibrium between mineral and body fluid. This study illustrates the remarkable flexibility of the apatite mineral structure to match its chemical and physical properties to specific biological needs within the same animal or between species.