Μm Resolution Research Articles

Simple, Fast, and Scalable Reverse-Offset Printing of Micropatterned Copper Nanowire Electrodes with Sub-10 μm Resolution.

Copper nanowires (CuNWs) possess key characteristics for realizing flexible transparent electronics. High-quality CuNW micropatterns with high resolution and uniform thickness are required to realize integrated transparent electronic devices. However, patterning high-aspect-ratio CuNWs is challenging because of their long length, exceeding the target pattern dimension. This work reports a novel reverse-offset printing technology that enables the sub-10 μm high-resolution micropatterning of CuNW transparent conducting electrodes (TCEs). The CuNW ink for reverse-offset printing was formulated to control viscoelasticity, cohesive force, and adhesion by adjusting the ligands, solvents, surface energy modifiers, and leveling additives. An inexpensive commercial adhesive handroller achieved a simple, fast, and scalable micropatterning of CuNW TCEs. Easy production of high-quality CuNW micropatterns with various curvatures and shapes was possible, regardless of the printing direction. The reverse-offset-printed CuNW micropatterns exhibited a minimum of 7 μm line width and excellent pattern qualities such as fine line spacing, sharp edge definition, and outstanding pattern uniformity. In addition, they exhibited excellent sheet resistance, high optical transparency, outstanding mechanical durability, and long-term stability. Flexible light-emitting diode (LED) circuits, transparent heaters, and organic LEDs (OLEDs) can be fabricated using high-resolution reverse-offset-printed CuNW micropatterns for applications in flexible transparent electronic devices.

Location-Specific Study of Young Rabbit Femoral Cartilage by Quantitative µMRI and Polarized Light Microscopy.

ObjectiveMicroscopic magnetic resonance imaging (µMRI) and polarized light microscopy (PLM) are used to characterize the structural variations at different anatomical locations of femoral cartilage in young rabbits (12-14 weeks old).DesignFour intact knees were imaged by µMRI at 86 µm resolution. Three small cartilage-bone specimens were harvested from each of 2 femoral medial condyles and imaged by quantitative µMRI (T2 anisotropy) at 9.75 µm resolution (N = 6). These specimens, as well as the other 2 intact femoral condyles, were used for histology and imaged by quantitative PLM (retardation and angle) at 0.25 µm to 4 µm resolutions.ResultsQuantitative MRI relaxation data and PLM fibril data revealed collaboratively distinct topographical variations in both cartilage thickness and its collagen organization in the juvenile joint. Cartilage characteristics from the central location have a 3-zone arcade-like fibril structure and a distinct magic angle effect, commonly seen in mature articular cartilage, while cartilage at the anterior location lacks these characteristics. Overall, the lowest retardation values and isotropic T2 values have been found in the distal femur (trochlear ridge), with predominant parallel fibers with respect to the articular surface. Central cartilage is the thickest (~550 µm), approximately twice as thick as the anterior and posterior locations.ConclusionDistinctly different characteristics of tissue properties were found in cartilage at different topographical locations on femoral condyle in rabbits. Knowledge of location-specific structural differences in the collagen network over the joint surface can improve the understanding of local mechanobiology and provide insights to tissue engineering and degradation repairs.

High content drug screening of primary cardiomyocytes based on microfluidics and real-time ultra-large-scale high-resolution imaging.

High content screening (HCS) plays an important role in biological applications and drug development. Existing techniques fail to simultaneously meet multiple needs of throughput, efficiency in sample and chemical consumption, and real-time imaging of a large view at high resolution. Leveraging advances in microfluidics and imaging technology, we setup a new paradigm of large-scale, high-content drug screening solutions for rapid biological processes, like cardiotoxicity. The designed microfluidic chips enable 10 types of drugs each with 5 concentrations to be assayed simultaneously. The imaging system has 30 Hz video rate for a centimeter filed-of-view at 0.8 μm resolution. Using the HCS system, we assayed 12 small molecules through their effects on the Ca2+ ion signal of cardiomyocytes. Experimental results demonstrated the unparalleled capability of the system in revealing the spatiotemporal patterns of Ca2+ imaging of cardiomyocytes, and validated the cardiotoxicity of certain molecules. We envision that this new HCS paradigm and cutting-edge platform offer the most advanced alternative to well-plate based methods.

Highly sensitive and miniature microfiber-based ultrasound sensor for photoacoustic tomography

A microfiber with large evanescent field encapsulated in PDMS is proposed and demonstrated for ultrasound sensing. The compact size and large evanescent field of microfiber provide an excellent platform for the interaction between optical signal and ultrasound wave, exhibiting a high sensitivity of 3.5 mV/kPa, which is approximately 10 times higher than the single-mode fiber sensor. Meanwhile, a phase feedback stabilization module is introduced into the coherent demodulation system for long-term stable measurement. In addition, a photoacoustic tomography experiment with the microfiber ultrasound sensor is implemented to verify the excellent performance on imaging, with the depth of 12 mm, the highest lateral resolution of 65 μm and axial resolution of 250 μm, respectively. The highly sensitive microfiber ultrasound sensor provides a competitive alternative for various applications, such as industrial non-destructive testing, biomedical ultrasound and photoacoustic imaging.

Characterization of Bacterial Amyloids by Nano-infrared Spectroscopy.

Atomic force microscopy has been used for decades to study the topography of proteins during aggregation but with a lack of information on the secondary structure. On the contrary, infrared spectroscopy was able to study structural changes during the aggregation, but this analysis is complicated due to the presence of different species in mixtures and the poor spatial (~μm) resolution of the FTIR microscopy. Recently, Professor Alexandre Dazzi combined those techniques in the so-called AFM-IR. This method allows acquiring IR spectra at the nanometric scale and becomes a new standard method for the characterization of amyloid fibrils and, more generally, for the aggregation of proteins.

Simultaneous velocity profile and temperature profile measurements in microfluidics

Simultaneous non-intrusive temperature and velocity measurements in flows are of high technological interest, e.g. to study the heat transfer in microfluidic environments. However, a measurement system that offers a low velocity uncertainty and micrometre spatial resolution as well as highly accurate temperature measurements in a single device has not been demonstrated so far. In this work, this problem is solved by combining a Laser Doppler Velocity Profile Sensor (LDV-PS) with Laser-Induced Fluorescence (LIF). Seeding particles are employed, that contain the fluorescent dyes uranine and rhodamine B. The multiple dye approach eliminates the influence of the droplet size. Relative velocity uncertainties of down to 0.4% and a temperature uncertainty of down to 0.24∘C with a spatial resolution of 10μm are achieved in a demonstration air flow experiment. The method has the potential to be optimised for different temperature ranges and uncertainty requirements, making it applicable on a wide range of thermal flows like fuel cells or microbioreactors. A better understanding of heat exchange processes can improve the energy efficiency of microfluidic devices.

A core-based XRF scanning workflow for continuous measurement of mineralogical variations in clastic reservoirs

Clastic reservoir core is routinely characterized using conventional, destructive spot sampling techniques. Whilst spot sampling provides useful textural and compositional information, the samples are typically widely spaced (∼ 25 cm), and hence continuous variation in rock composition/texture is not fully captured. It is therefore important to develop higher-resolution rock characterization techniques. In this paper, compositional data from a micro x-ray fluorescence (µXRF) scanner (hereafter Itrax) was used to demonstrate near-continuous (at 200 µm resolution) mineralogical variations in an ancient sandstone core. Traditionally, Itrax was used for compositional profiling of soft sediment cores, with limited use of this technology with rock cores. The acquired XRF data reveal subtle but systematic vertical compositional/textural trends, that may reflect distribution of major sandstone forming mineral grains, clay minerals, diagenetic carbonate cements and identification of new textural subdivisions in sandstones, which would not otherwise be seen with conventional plug analysis, implying the importance of high-resolution core scanning techniques for continuous measurement of mineralogy in clastic reservoirs.•Limited literature could be found whereby the capability of Itrax scanning has been extended to ancient, clastic cores.•Itrax is a non-destructive technique, where elemental composition is obtained directly at the surface of a split core at resolution significantly higher than conventional plug based techniques.•Itrax data acquisition is a quick process (few hours) and mineral distribution trends can be used as guide for further specialized sampling and detailed investigation of clastic reservoirs.

Imaging of transient phenomena with low coherence lasers comprising arrays of independent microbeams: A laser version of Harold Edgerton’s stroboscope

A longstanding barrier to laser imaging with high spatial and temporal resolution is speckle, the granular interference pattern arising from the coherent interaction of laser radiation with the topography of an illuminated surface. Over the past five decades, scores of mechanical and optical approaches to mitigating or eliminating the impact of speckle have been proposed, including dynamic diffusers, degenerate optical cavities, and random lasers. We describe a laser resonator architecture that allows the spatial coherence and the associated speckle contrast ratio (C) of the laser output to be varied continuously while providing the power necessary for optical imaging of dynamic objects and phenomena with sub-10 ns resolution. Stabilization of a Fabry–Pérot optical cavity with an internal array of microlenses generates thousands of mutually incoherent, parallel microlaser beams, which merge in the far field to form a single beam having a near-Gaussian transverse intensity distribution. For this laser illuminator, C scales as 1/N, where N is the number of microlasers in the array. When Ti:Al2O3 serves as the gain medium, composite beams comprising N > 1000 microbeams are generated with a divergence angle of ∼5 mrad and C < 0.03 for single pulse energies of 8 mJ (∼1 MW peak power). To illustrate the capability of this tunable spatial-coherence laser, images of Drosophila melanogaster in flight and turbomolecular pump vanes rotating at 56 000 rpm are presented. Owing to the brightness and pulse energies available with this laser, imaging a target at a distance of 5 m through dense fog with ∼250 μm resolution has been demonstrated.

Intrauterine alcohol exposure delays growth and disturbs trabecular morphology in 3-week-old Sprague − Dawley rat femur

Introduction: The consequence of gestational alcohol exposure ranges from stillbirth to miscarriage and fetal alcohol syndrome (FAS). FAS is one of the deleterious causes of congenital disabilities, mental and growth retardation. Several studies suggest that low birth weight and impaired bone growth, as well as a decrease in mineralization in utero, may reduce peak bone mass and increase the risk of fractures and osteoporosis later in life. Therefore, the aim of this study was to determine the effects of intrauterine alcohol exposure on the internal architecture of the femur. Material and Methods: Time-mated (n = 13) pregnant Sprague − Dawley dams were assigned to either the ethanol (n = 5), saline control (n = 5) or untreated control (n = 3) group. The former two groups were treated with 0.015 ml/g of 25.2% ethanol and 0.9% saline for the first 19 days of gestation, respectively. The untreated group received no treatment. Once born, the pups were weaned at 21 days. These rats were then terminated. From each dam, two pups were collected resulting in ethanol (n = 10), saline controls (n = 10), and untreated controls (n = 6). The femora of the pups were dissected and scanned using a 3D-μCT scanner (Nikon XTH 225 L) at 15 μm resolution. Trabecular and cortical parameters were analyzed using Volume Graphics Studio® software following reconstruction. Results: We found altered trabecular parameters in the alcohol exposed group. The diaphyseal cortical and medullary cavity proportions were also affected, particularly in the midshaft. Discussion and Conclusion: These results indicate that gestational alcohol exposure may lower bone structural quality by disturbing the internal morphology of the osseous tissue.

Characterization of resistive Micromegas detectors for the upgrade of the T2K Near Detector Time Projection Chambers

The second phase of the T2K experiment is expected to start data taking in autumn 2022. An upgrade of the Near Detector (ND280) is under development and includes the construction of two new Time Projection Chambers called High-Angle TPC (HA-TPC). The two endplates of these TPCs will be paved with eight Micromegas type charge readout modules. The Micromegas detector charge amplification structure uses a resistive anode to spread the charges over several pads to improve the space point resolution. This innovative technique is combined with the bulk-Micromegas technology to compose the “Encapsulated Resistive Anode Micromegas” detector. A prototype has been designed, built and exposed to an electron beam at the DESY II test beam facility.The data have been used to characterize the charge spreading and to produce its map. Spatial resolution better than 600 μm and energy resolution better than 9% are obtained for all incident angles. These performances fulfil the requirements for the upgrade of the ND280 TPC.

Comparison of Petrophysical Properties of Porous Rocks Using NMR, Micro-CT, and Fluid Flow Simulations

Micro-computed tomography (micro-CT) is increasingly utilized to image the pore network and to derive petrophysical properties in combination with modelling software. The effect of micro-CT image resolution and size on the accuracy of the derived petrophysical properties is addressed in this study using a relatively homogenous sandstone and a heterogenous, highly porous bioclastic limestone. Standard laboratory procedures including NMR (nuclear magnetic resonance) analysis, micro-CT analysis at different image resolutions and sizes and pore-scale flow simulations were used to determine and compare petrophysical properties. NMR-derived pore-size distribution (PSD) was comparable to the micro-CT-derived PSD at a resolution of 7 µm for both the rock types. Porosity was higher using the water saturation method as compared to the NMR method in both rocks. The resolution did not show a significant effect on the porosity of the homogeneous sandstone, but porosity in the heterogeneous limestone varies depending on the location of the sub-sample. The transport regime in the sandstone was derived by simulations and changed with the resolution of the micro-CT image. The transport regime in the sandstone was advection-dominated at higher image resolution and diffusion-dominated when using a lower image resolution. In contrast, advection was the dominant transport regime for the limestone based on simulations using higher and lower image resolutions. Simulation-derived permeability for a 400 Voxel3 image at 7 µm resolution in the Berea sandstone matched laboratory results, although local heterogeneity within the rock plays an integral role in the permeability estimation within the sub-sampled images. The simulation-derived permeability was highly variable in the Mount Gambier limestone depending on the image size and resolution with the closest value to a laboratory result simulated with an image resolution of 2.5 µm and a size of 300 Voxel3. Overall, the study demonstrates the need to decide on micro-CT parameters depending on the type of petrophysical property of interest and the degree of heterogeneity within the rock types.

Measuring hidden phenotype: quantifying the shape of barley seeds using the Euler characteristic transform

Abstract Shape plays a fundamental role in biology. Traditional phenotypic analysis methods measure some features but fail to measure the information embedded in shape comprehensively. To extract, compare and analyse this information embedded in a robust and concise way, we turn to topological data analysis (TDA), specifically the Euler characteristic transform. TDA measures shape comprehensively using mathematical representations based on algebraic topology features. To study its use, we compute both traditional and topological shape descriptors to quantify the morphology of 3121 barley seeds scanned with X-ray computed tomography (CT) technology at 127 μm resolution. The Euler characteristic transform measures shape by analysing topological features of an object at thresholds across a number of directional axes. A Kruskal–Wallis analysis of the information encoded by the topological signature reveals that the Euler characteristic transform picks up successfully the shape of the crease and bottom of the seeds. Moreover, while traditional shape descriptors can cluster the seeds based on their accession, topological shape descriptors can cluster them further based on their panicle. We then successfully train a support vector machine to classify 28 different accessions of barley based exclusively on the shape of their grains. We observe that combining both traditional and topological descriptors classifies barley seeds better than using just traditional descriptors alone. This improvement suggests that TDA is thus a powerful complement to traditional morphometrics to comprehensively describe a multitude of ‘hidden’ shape nuances which are otherwise not detected.

Facile Molecular Weight Determination of Polymer Brushes Grafted from One-Dimensional Diffraction Grating by SI-ATRP Using Reflective Laser System.

Gelatin was immobilized selectively on the amide groups-modified bottom of a trench array of a photoresist template with 2 μm resolution by the ethyl(dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide reaction. The gelatin-immobilized line array was brominated to generate a macroinitiator for atom transfer radical polymerization. Poly(methacrylic acid) (PMAA) brushes were grafted from the macroinitiator layer as line arrays of one-dimensional diffraction gratings (DGs) for various grafting polymerization times. A laser beam system was employed to analyze the optical feature with a characteristic diffraction effect of the PMAA DGs at a 45° incident angle along the transverse magnetic and transverse electric polarization. The growth of the PMAA brush lines increased both their heights and widths, leading to a change in the reflective diffraction intensity. The PMAA brushes under various grafting polymerization times were cleaved from the substrate by digestion of gelatin with trypsin, and their molecular weights were obtained by gel permeation chromatography. The change degree of the diffraction intensity varied linearly with the molecular weight of the PMAA brushes over a wide range, from 135 to 1475 kDa, with high correlation coefficients. Molecular weight determination of polymer brushes using the reflective diffraction intensity provides a simple method to monitor their growth in real time without polymer brush cleavage.

Experimental investigations on robotic linear stage traverse error using draw wire sensor

Measuring linear displacement and rotation in robotic joints is vital for end effector positioning and producing the desired trajectory. The output pulse produced by driver system may not be completely converted into rotary motion of the stepper motor due to elevated loading conditions. This necessitates the gauging of stage traverse taking into consideration the effects of minor plays, guide screw pitch non uniformity, ill responses to pulses provided by the driver etc.The current paper presents a technique of measuring the errors occurring in displacement of a ball screw driven linear stage using a draw wire sensor (DW sensor) mounted on a stationary platform. The procedure involves proper design of mounting platform, ensuring orthogonal orientation of the sensor body, wire straightness check in both perpendicular planes and fabrication of wire fixtures. The output pulses from the DW sensor are acquired through NI Labview software using NI USB 6225 Data acquisition system. A mechanical dial gauge with 1 µm resolution and a laser displacement sensor is used to cross verify the obtained data. The results are then used to study the positioning accuracy of the developed 4 axis robotic arm.

Molecular motor-driven filament transport across three-dimensional, polymeric micro-junctions

Molecular motor-driven filament systems have been extensively explored for biomedical and nanotechnological applications such as lab-on-chip molecular detection or network-based biocomputation. In these applications, filament transport conventionally occurs in two dimensions (2D), often guided along open, topographically and/or chemically structured channels which are coated by molecular motors. However, at crossing points of different channels the filament direction is less well determined and, though crucial to many applications, reliable guiding across the junction can often not be guaranteed. We here present a three-dimensional (3D) approach that eliminates the possibility for filaments to take wrong turns at junctions by spatially separating the channels crossing each other. Specifically, 3D junctions with tunnels and overpasses were manufactured on glass substrates by two-photon polymerization, a 3D fabrication technology where a tightly focused, femtosecond-pulsed laser is scanned in a layer-to-layer fashion across a photo-polymerizable inorganic–organic hybrid polymer (ORMOCER®) with µm resolution. Solidification of the polymer was confined to the focal volume, enabling the manufacturing of arbitrary 3D microstructures according to computer-aided design data. Successful realization of the 3D junction design was verified by optical and electron microscopy. Most importantly, we demonstrated the reliable transport of filaments, namely microtubules propelled by kinesin-1 motors, across these 3D junctions without junction errors. Our results open up new possibilities for 3D functional elements in biomolecular transport systems, in particular their implementation in biocomputational networks.

Micro-Raman mapping of VO2 (T) microcrystals orientation

Microcrystals orientation distribution in triclinic vanadium dioxide VO2 (T) films was investigated by polarized Raman scattering with a resolution of few μm and confirmed by electron backscatter diffraction. Euler angles used to describe the orientation of the crystal were determined by two different techniques and good agreement between the values was achieved. Finally, it was demonstrated that Raman scattering could be used to identify the direction of the lattice vector c for (002) crystals in consequence of the triclinic nature of VO2 (T).

Characterization of ice particles in jet fuel at low temperature: 3D X-ray tomography vs. 2D high-speed imaging

The formation of ice crystals in aviation fuels at low temperatures is a major problem to the aviation industry. In this work, a fuel-icing bench from the Institut de la Filtration et des Techniques Séparatives (IFTS) was used to develop two characterization methods for the ice particles in jet A-1 fuel: (i) a 3D ex-situ method using X-ray tomography at low temperature, giving full access to the geometric complexities of the ice particles at 5.5 μm resolution and (ii) a 2D in-situ method using high-speed imaging at 4 μm resolution, allowing real-time measurements of ice particles flowing at high velocity. A large set of process parameters was studied: the circulation time (τ), the water concentration (C) and the interfacial tension (γ) at fixed temperature (θ) ∼ -18±2 °C. Overall, both methods gave consistent results, with particle sizes not exceeding 1 mm and mean sizes between 100 to 300 μm. The shapes of the particles were mainly spherical in 3D (∼ 50%) and circular in 2D (≥ 60%). Same trends were observed with both methods in relation to the process parameters. The grinding effect induced by an increased τ seems to be the most influencing phenomenon in the process, leading to the decrease of the particle size. In contrast, the effect of C is not conclusive, given the detection limit of particles in 2D for high concentrations. This study highlights the specificities of both characterization methods and the influence of the process parameters on the properties of the ice particles in jet fuel.

Plant–environment microscopy tracks interactions of Bacillus subtilis with plant roots across the entire rhizosphere

Our understanding of plant-microbe interactions in soil is limited by the difficulty of observing processes at the microscopic scale throughout plants' large volume of influence. Here, we present the development of three-dimensional live microscopy for resolving plant-microbe interactions across the environment of an entire seedling growing in a transparent soil in tailor-made mesocosms, maintaining physical conditions for the culture of both plants and microorganisms. A tailor-made, dual-illumination light sheet system acquired photons scattered from the plant while fluorescence emissions were simultaneously captured from transparent soil particles and labeled microorganisms, allowing the generation of quantitative data on samples ∼3,600 mm3 in size, with as good as 5 µm resolution at a rate of up to one scan every 30 min. The system tracked the movement of Bacillus subtilis populations in the rhizosphere of lettuce plants in real time, revealing previously unseen patterns of activity. Motile bacteria favored small pore spaces over the surface of soil particles, colonizing the root in a pulsatile manner. Migrations appeared to be directed toward the root cap, the point of "first contact," before the subsequent colonization of mature epidermis cells. Our findings show that microscopes dedicated to live environmental studies present an invaluable tool to understand plant-microbe interactions.

An Analysis of the Progression of Conjunctivalisation after Transplantation of Cultivated Corneal Epithelium.

Purpose To analyse the recurrence of superficial neovascularisation after previous corneal surface reconstruction with cultivated corneal epithelial cells. Materials and Methods Forty-eight eyes underwent autologous transplantation of cultivated corneal epithelium to treat partial or total limbal stem cell deficiency caused by chemical or thermal injury. The carrier for the epithelial sheets was a denuded amniotic membrane. Follow-up was conducted for up to 120 months. Recurrent revascularisation (measured in terms of clock hours affected) was evaluated with slit-lamp examination and the support of confocal microscopy. Results During the long-term observation, only 7 eyes had stable epithelia with no neovascularisation from the conjunctiva. Nineteen eyes developed pathologic vessels in 1 quadrant, with additional 4 eyes developing them in 2 quadrants. Twelve patients developed subtotal or total conjunctivalisation of the corneal surface. They were referred for second cultivated epithelium transplantation (3 patients), allogenic keratolimbal transplantation (7 patients), or keratoprosthesis (2 patients). Six patients withdrew consent. The use of confocal scans of up to 100 µm in resolution enabled the detection of pathologic microvasculature originating from the conjunctiva and the exclusion of stromal vascular ingrowth. Conclusions Local ingrowth of the conjunctiva is a common complication after the transplantation of cultivated epithelial cells. Severe and progressive vascularisation inevitably leads to graft failure. However, if local ingrowth stops before reaching the central cornea, the treatment even with this complication can be considered a success.

Two-color Kerr microscopy of two-dimensional materials with sub-picosecond time resolution.

We present a two-color Kerr microscopy system based on two electronically synchronized erbium-fiber laser oscillators with independently tunable emission energies spanning most of the visible spectrum. Combining a spatial resolution below 2 μm and sub-ps time resolution with high sensitivity and cryogenic sample temperatures, it is ideally suited for studying spin and valley dynamics in a wide range of two-dimensional materials. We illustrate its capabilities by studying a monolayer of the common semiconducting transition metal disulfide MoS2.