Μm Diameter Research Articles

High-Resolution Total Internal Reflection-Based Structural Coloration by Electrohydrodynamic Jet Printing of Transparent Polyethylene Glycol Microdomes.

Total internal reflection (TIR)-based structural coloration is a brilliant strategy to overcome the need for periodic nanostructures and complex fabrication processes. Light entering the microdome structure undergoes TIR, and owing to varying reflection paths, it exhibits a color that changes with the microdome size. Although solution-based printing techniques have been proposed to achieve this effect, they fall short of full-color realization owing to resolution limitations. Herein, we achieved 3628 dpi of full-color and high-resolution structural color images by printing transparent microdome structures with 1.2-9.9 μm diameter using electrohydrodynamic (EHD) jet printing. Additionally, high-resolution EHD jet-printed structural color images display complex encoded information, enhancing the anticounterfeiting effectiveness through their fabrication simplicity and precise control over the microdome size. Because of these advantages, this TIR-based structural coloration technique with EHD jet printing is highly suitable for anticounterfeiting applications.

Interpericyte Tunneling Nanotubes Are Nonuniformly Distributed in the Human Macula.

Pericyte-to-pericyte communication via interpericyte tunneling nanotubes (IP-TNTs) is an important mechanism by which spatial and temporal precision in neurovascular coupling is achieved. This study quantifies the distribution and morphologic characteristics of IP-TNTs in the normal human macula. Ultra high-resolution, three-dimensional microscopic imaging of 11 perfusion-labeled normal human donor eyes was performed. Immunofluorescent markers for collagen IV, glial fibrillary acidic protein, nuclei, α-smooth muscle actin and phalloidin were used to distinguish IP-TNTs from perfused/nonperfused capillaries and glia processes. IP-TNT length, diameter and density in each capillary plexus was quantified and compared. IP-TNTs were present in all capillary plexuses. IP-TNTs bridged capillary segments within and between capillary plexuses but did not connect capillaries to arterioles or venules. Mean length of IP-TNTs was 72.6 ± 39.5µm (range 14.0 to 202µm) and mean diameter was 1.0 ± 0.42µm. IP-TNT length was non-normally distributed with a right-skewed distribution and 43% were 'short' (<55µm). Diameters were greater in the "long" (1.13 ± 0.44µm) than "short" (0.82 ± 0.33µm; P < 0.001) IP-TNTs. Density of IP-TNTs was greater in the superficial vascular plexus (3.80 ± 0.69 per 500µm2) compared to the intermediate (1.85 ± 0.80 per 500µm2; P < 0. 0001) and deep capillary plexus (1.58 ± 0.84 per 500µm2; P < 0.0001). No significant difference in IP-TNT density was found between the four macula quadrants (P = 0.98). The distribution of IP-TNTs in the human macula is non-uniform and is associated with the compartmentalized nature of retinal energy consumption and microvascular perfusion. The nonuniform properties of IP-TNTs may predispose distinct vascular beds to injury in conditions such as diabetes.

High‐performance engineered geopolymer composites: A sustainable approach using recycled brick waste

AbstractThis study examines the viability of using construction waste, specifically recycled brick waste powder (RBWP), as an alternative conventional industrial byproduct (fly ash) in the manufacturing of engineered geopolymer composites (EGC). The EGC mixtures are made with 40 μm diameter and 12 mm length polyvinyl alcohol (PVA) fiber. RBWP replaces class‐F fly ash in EGC by 0, 20%, 40%, 60%, 80%, and 100%. This study produces six distinct EGC mixtures in total. The flexural strength, abrasion resistance, sorptivity, and water absorption of the EGC are investigated. Microstructural characterization is carried out using scanning electron microscopy (SEM). Based on the results, when fly ash is replaced by 40% and 100%, respectively, adding RBWP to the EGC mixes significantly improves flexural strength by 39% and midspan deflection by 169%. Nevertheless, abrasion resistance significantly improves when fly ash is completely replaced with RBWP, even though sorptivity and water absorption increase by about 128% and 240%, respectively. The volume change is reduced by 25.4% when RBWP is used. Furthermore, the SEM study shows that the RBWP undergoes active geopolymerization in the EGC mixes.

Low dielectric properties of alkali-free aluminoborosilicate fiber glasses for PCB applications at 10GHz.

Alkali-free aluminoborosilicate glasses without (GDMC-Si) and with La2O3 addition (GDMC-La) were fabricated with an aim to develop low dielectric glass fibers for use in printed circuit boards (PCBs) as a reinforcing material in high-speed 5G/6G telecommunications application. This study presents the structural, thermo-physical, and dielectric properties of the glasses. The decrease in glass transition temperature (Tg) and the increase in coefficient of thermal expansion (CTE) were found by the addition of SiO2 and La2O3 in the present glass system, which are due to the depolymerization of the glass networks confirmed by the FTIR analysis. The dielectric constants (Dk) and the dissipation factors (Df) of the glasses were investigated at a high frequency of 10GHz. The Dk values of the GDMC-Si and GDMC-La glass systems reached a minimum of 4.50 and 4.75, while their Df values reached a minimum of 2.86 × 10-3 and 3.01 × 10-3, respectively. Notably, the Dk and Df values of the present glasses were lower than the commercial E-glass (Dk: 6.9, Df: 7.0 × 10-3 at 10GHz) and L-glass (Dk: 4.8, Df: 3.0 × 10-3 at 10GHz). Glass fibers with a diameter of 10μm were successfully drawn by the continuous melt-spinning process and their mechanical properties were investigated.

Supercooled Water Droplets Impacting at High Speed on Superhydrophobic Surfaces: Open Questions Related to Icephobicity

It is posited that impact ice adhesion strength on superhydrophobic surfaces is related to droplet impalement. Several gaps still exist in the understanding of how different types of textured surfaces resist the impalement of high‐speed impacting droplets (&lt;102 μm diameter at 102–103 m s−1). A previous study reveals that a pressure balance calculation can predict the wetting state of an impacting drop (≈103 μm diameter at ≈101 m s−1). However, the ability of this model to predict the wetting state of small droplets impacting at high speed or of droplets in a supercooled state has not been reported. To better understand supercooled microdroplet impalement, and to verify the hypothesis that droplet impalement is directly related to ice adhesion strength, herein, the impact behavior of microdroplets in a cold airflow onto surfaces of varying topography and wettability in an icing wind tunnel with support of high‐speed video images are investigated. Although the results do not allow for validating the above hypothesis about impalements and ice adhesion, they show that the difference between supercooled droplet spreading and retraction can be a predictor of ice adhesion strength. However, this relation must be validated with a greater body of data from samples with very diverse surface properties.

Plasticity of 3D Hydrogels Predicts Cell Biological Behavior.

Under 3D culture conditions, cells tend to spread, migrate, and proliferate better in more viscoelastic and plastic hydrogels. Here, we present evidence that the improved cell behavior is facilitated by the lower steric hindrance of a more viscoelastic and plastic matrix with weaker intermolecular bonds. To determine intermolecular bond stability, we slowly insert semispherical tipped needles (100-700 μm diameter) into alginate dialdehyde-gelatin hydrogels and measure stiffness, yield strength, plasticity, and the force at which the surface ruptures (puncture force). To tune these material properties without affecting matrix stiffness, we precross-link the hydrogels with CaCl2 droplets prior to mixing in NIH/3T3 fibroblasts and final cross-linking with CaCl2. Precross-linking introduces microscopic weak spots in the hydrogel, increases plasticity, and decreases puncture force and yield strength. Fibroblasts spread and migrate better in precross-linked hydrogels, demonstrating that intermolecular bond stability is a critical determinant of cell behavior under 3D culture conditions.

Achromatic metalenses for full visible spectrum with extended group delay control via dispersion-matched layers

Achieving achromaticity across the visible light spectrum is crucial for metalenses in imaging systems. Single-layer metalenses struggle with weak focusing power or small aperture sizes due to inadequate group delay control. Multilayer metalenses offer some improvement but come with increased design and fabrication complexity. Here, we demonstrate a strategy using meta-atoms with material layers engineered for matching dispersion, allowing large and fine adjustments of group delay. Our design substantially broadens the group delay range, allowing us to experimentally demonstrate several polarization-independent metalenses operating across the entire visible spectrum (400-700 nm). We design, fabricate, and characterize achromatic metalenses with aperture diameters of 16 μm, 66 μm, 200 μm, and 400 μm, and numerical apertures of 0.27, 0.11, 0.04, and 0.02, respectively. Among them, the 400-μm diameter, 0.02-numerical-aperture metalens is used to demonstrate full-color imaging capabilities. Our results exhibit diffraction-limited performance, high efficiency, and accurate full-color image reproduction.

Verification of linear energy transfer optimized carbon-ion radiotherapy.

Linear energy transfer (LET) verification was conducted using a silicon-on-insulator (SOI) microdosimeter during the commissioning of LET-optimized carbon-ion radiotherapy. This advanced treatment technique is expected to improve local control rates, especially in hypoxic tumors. &#xD;Approach: An SOI microdosimeter with a cylindrical sensitive volume of 30 μm diameter and 5 μm thickness was used. Simple cubic plans and patient plans using the carbon-ion beams were created by treatment planning system, and the calculated LETd values were compared with the measured LETd values obtained by the SOI microdosimeter. &#xD;Main results: Reasonable agreement between the measured and calculated LETd was seen in the plateau region of depth LETd profile, whereas the measured LETd were below the calculated LETd in the peak region, specifically where LETd exceeds 75 keV/μm. The discrepancy in the peak region may arise from the uncertainties in the calibration process of the SOI microdosimeter. Excluding the peak region, the average ratio and standard deviation between measured and calculated LETd values were 0.996 and 7%, respectively. &#xD;Significance: This verification results in the initiation of clinical trials for LET-optimized carbon-ion radiotherapy at QST Hospital, National Institutes for Quantum Science and Technology.

Reflectance mapping with microsphere-assisted white light interference nanoscopy

The characterisation of novel materials presents a challenge that requires new and original developments. To face some of these demands for making measurements at the nanoscale, a new microsphere-assisted white light interference nanoscope performing local reflectance mapping is presented. This technique presents the advantages of being non-destructive, full-field and label-free. A 145 μm diameter microsphere, glued to the end of an optical fiber, is inserted inside the white light interference microscope to improve the lateral resolution from 940 nm to 520 nm. The acquisition and the Fourier transform processing of a stack of interference images superimposed on the virtual image produced by the microsphere allows the extraction of the local reflectance over a wavelength range of 460 nm to 900 nm and a field of view of 8 μm in diameter. The enhancement in the lateral resolution of the reflectance is demonstrated through the spectral distinction of neighboring ripples on a laser-textured colored stainless-steel sample that cannot be resolved without the microsphere, on regions with a surface of 279 × 279 nm2 horizontally spaced 279 nm apart. Future improvements could potentially lead to a lateral resolution of reflectance measurement over a 100 nm diameter area in air, paving the way to sub-diffraction reflectance mapping.

Effect of Microbubble Size, Composition, and Multiple Sonication Points on Sterile Inflammatory Response in Focused Ultrasound-Mediated Blood-Brain Barrier Opening.

Blood-brain barrier opening (BBBO) using focused ultrasound (FUS) and microbubbles (MBs) has emerged as a promising technique for delivering therapeutics to the brain. However, the influence of various FUS and MB parameters on BBBO and subsequent sterile inflammatory response (SIR) remains unclear. In this study, we investigated the effects of MB size and composition, as well as the number of FUS sonication points, on BBBO and SIR in an immunocompetent mouse model. Using MRI-guided MB + FUS, we targeted the striatum and assessed extravasation of an MRI contrast agent to assess BBBO and RNaseq to assess SIR. Our results revealed distinct effects of these parameters on BBBO and SIR. Specifically, at a matched microbubble volume dose (MVD), MB size did not affect the extent of BBBO, but smaller (1 μm diameter) MBs exhibited a lower classification of SIR than larger (3 or 5 μm diameter) MBs. Lipid-shelled microbubbles exhibited greater BBBO and a more pronounced SIR compared to albumin-shelled microbubbles, likely owing to the latter's poor in vivo stability. As expected, increasing the number of sonication points resulted in greater BBBO and SIR. Furthermore, correlation analysis revealed strong associations between passive cavitation detection measurements of harmonic and inertial MB echoes, BBBO, and the expression of SIR gene sets. Our findings highlight the critical role of MB and FUS parameters in modulating BBBO and subsequent SIR in the brain. These insights inform the development of targeted drug delivery strategies and the mitigation of adverse inflammatory reactions in neurological disorders.

Phase changes in burning precursor-laden single droplets leading to puffing and micro-explosion

When producing metal-oxide nanoparticles via flame spray pyrolysis, precursor-laden droplets are ignited and undergo thermally induced disintegration, called ‘puffing’ and ‘micro-explosion’. In a manner that is not fully understood, these processes are associated with the formation of dispersed phases inside the droplets. This work aims at visualizing the interior of precursor-laden burning single droplets via diffuse back illumination and microscopic high-speed imaging. Solutions containing iron(III) nitrate nonahydrate (INN) and tin(II) 2-ethylhexanoate (Sn-EH) were dispersed into single droplets of sub-100 μm diameter that were ignited by passing through a heated coil. At low precursor concentration, 50% of the INN-laden droplets indicate a gas bubble of about 5 μm diameter in the center of the droplet. The bubble persists for several hundred microseconds at a similar size. In almost all of these cases, the bubble expands at some point and the droplet ends up in a micro-explosion. In some of these instances, the droplet’s surface shows spatial brightness modulations, i.e., surface undulations, indicating the formation of a viscous shell. With increasing INN concentration, the fraction of droplets showing surface undulations, gas bubbles, and micro-explosions drastically decreases. This may be associated with a more rigid viscous shell and reduced mobility of bubbles. Bright incandescent streaks originating from the disrupting INN-laden droplets, may indicate sub-micrometer droplets or particles from within the droplets or formed in the gas phase. In contrast, Sn-EH-laden droplets show very fast disruptions, typically less than 10 μs from first visible deformation to ejection of secondary droplets. Bubbles and surface undulations were not observed.Graphical abstract

Direct laser writing of curved SERS for light-guided enhancement

Flexible SERS substrates, typically used on irregular surfaces, have unexplored optomechanical effects that could enhance performance. We developed a micromechanically bending structure, i.e. microbender, to study how bending affects SERS substrates’ performance. Optical simulations of nanopillar arrays on micro-curved surfaces showed a 25–134 % improvement in mean-field localization at the pillar tips for arrays with pillar diameters of 0.4–1 μm, pitches of 0.5–0.8 μm, and heights of 0.5–4.5 μm. Raman measurements showed that SERS intensity increases when in a curved state due to enhanced light scattering, guiding, and field localization. A curved array of 6 μm tall pillars (0.5 μm diameter, 1 μm spacing) produced Raman intensities similar to dense single-voxel arrays with shorter 0.8 μm pillars (0.2 μm diameter, 0.2 μm gaps) in the planar state. This finding suggests that low resolution fabrication technologies can produce curved SERS substrates with similar performance to high resolution planar SERS, offering an alternative to the current “smaller is better” trend through post-fabrication manipulation.

Long-range transport of coarse mineral dust: an evaluation of the Met Office Unified Model against aircraft observations

Abstract. Coarse mineral dust particles have been observed much further from the Sahara than expected based on theory. They have impacts different to finer particles on Earth's radiative budget, as well as carbon and hydrological cycles, though they tend to be under-represented in climate models. We use measurements of the full dust size distribution from aircraft campaigns over the Sahara, Canaries, Cabo Verde and Caribbean. We assess the observed and modelled dust size distribution over long-range transport at high vertical resolution using the Met Office Unified Model, which represents dust up to 63.2 µm diameter, greater than most climate models. We show that the model generally replicates the vertical distribution of the total dust mass but transports larger dust particles too low in the atmosphere. Importantly, coarse particles in the model are deposited too quickly, resulting in an underestimation of dust mass that is exacerbated with westwards transport; the 20–63 µm dust mass contribution between 2 and 3.7 km altitude is underestimated by factors of up to 11 in the Sahara, 140 in the Canaries and 240 in Cabo Verde. In the Caribbean, there is negligible modelled contribution of d &gt; 20 µm particles to total mass, compared to 10 % in the observations. This work adds to the growing body of research that demonstrates the need for a process-based evaluation of climate model dust simulations to identify where improvements could be implemented.

An In Vitro Study of 355‐nm Laser Ablation of Atherosclerotic Lesions Model

ABSTRACTA study of 355 nm laser with high pulse energy across various types of atherosclerotic lesion models is presented. The 355 nm laser pulses (10 ns) are delivered via a single fiber (600 μm diameter), and the ablation of calcified tissue, lipid tissue, and thrombus‐like tissue are studied under varied laser fluence (40–70 mJ/mm2) and repetition rate (5–30 Hz). The contact and noncontact ablation processes of chicken tibia samples (calcified tissue) are compared at 60 mJ/mm2 and 30 Hz, and the size of ablation particles is in the range of 0.1–1 μm. At the same repetition rate, the advancement rate of tricalcium phosphate samples reaches 150 μm/s at 70 mJ/mm2. Calcified and lipid models demonstrate predictable increases in ablation with higher laser fluence and repetition rate. The fresh porcine blood clot samples exhibit high‐quality ablation with good channel effect at 50 mJ/mm2 and 30 Hz.

Microdosing of alteplase leads to thrombolysis in an in vitro flow model of cardiac microvascular obstruction

Abstract Background Cardiac microvascular obstruction (MVO) is a frequent injury of the myocardial microcirculation after successful recanalisation of the occluded coronary artery in myocardial infarction. At least in part, MVO is caused by embolised microthrombi of less than 200 µm diameter [1]. MVO leads to hypoperfusion of the myocardium and negatively affects patient outcomes. However, there is no effective treatment for MVO [2, 3]. Thrombolytic drugs are a promising approach, but they are difficult to deliver to the MVO area, and an increased risk of bleeding limits their use. In a previous study using an in vitro fluidic multi-scale model for MVO [4, 5], it was shown that controlled flow infusion (CFI) with a novel drug-delivering catheter could be used to effectively deliver highly concentrated intracoronary microdoses of a thrombolytic drug to the MVO area [6]. We now aim to investigate how such locally administered drug microdoses can induce thrombolysis as a possible therapeutic approach for MVO treatment. Methods A microfluidic chip (Fig.1) was used to study thrombolysis under flow using different microdoses of the thrombolytic drug alteplase. The chip consists of a tapered straight channel, which traps injected porcine microthrombi without causing complete channel occlusion (Fig. 1A). To mimic intracoronary CFI (consisting of temporary balloon occlusion of a coronary vessel for 90 seconds while drug is injected distally through a catheter) in vitro, microthrombi were incubated (without flow) directly in the chip for 90 seconds with various microdoses of alteplase (Fig. 2A, C). The chip was subsequently perfused with porcine plasma for 25 min (matched for physiological shear stress of 30 dyn/cm²). Conventional intravenous (IV) drug infusion (10 mg dose) resulting in a low systemic alteplase concentration, was mimicked by perfusing microthrombi with porcine plasma containing 2 µg/ml alteplase (Fig. 2B, C). Results Thrombolysis after CFI was concentration dependent, with the lowest microdose (0.3 mg) achieving 24% lysis of the thrombus area and the highest microdose (1.5 mg) achieving 60% lysis. In contrast, conventional IV drug infusion (corresponding to 10 mg alteplase IV dose) only achieved 10% lysis and was not significantly higher than the control perfused with pure porcine plasma. Conclusion Our findings suggest that intracoronary CFI is more efficient at achieving porcine microthrombus lysis than the current standard of IV bolus infusion (2 µg/ml alteplase in the circulating blood). Intracoronary CFI microdosing of fibrinolytic drugs using a drug-delivering catheter is a promising therapeutic approach for treating embolising MVO with a reduced systemic drug burden. Importantly, our intracoronary CFI approach achieves locally 6–40 times higher drug concentrations than a conventional IV drug infusion while reducing the total drug dose 60–300 times (Fig. 2C).

Molybdenum temporary epicardial pacing wires: function and biodegradation

Abstract Cardiac pacing with temporary epicardial pacing wires (TEPW) is used to treat rhythm disturbances after cardiac surgery. Wires typically begin to fail around postoperative day four and are extracted. Occasionally, TEPW cannot be mechanically removed, have to stay in the thorax and may rarely cause serious complications like migration and infection. We aim to develop novel, bioresorbable TEPW which will dissolve over time, even if postoperative removal is unsuccessful. We manufactured prototypical braided molybdenum (Mo) leads (16 Mo wires of 40 µM diameter each, length 18 cm for ex vivo, 7.5 cm for in vivo experiments) coated with the biodegradable polymers poly(lactide-co-glycolic acid) (PLGA, inner coating) and polycaprolactone (PCL, outer coating) for shaping and electrical insulation. Mo electrodes showed similar pacing and sensing properties to conventional steel electrodes (Osypka) in Langendorff-perfused rat hearts, even with somewhat lower stimulation thresholds. In artificial body fluid at 37°C, the polymer-coated Mo electrodes dissolved at a rate of 1.6 ± 0.3 µg/cm2·d (n = 5) compared to uncoated electrodes with 30.3 ± 0.8 µg/cm2·d (n = 4, p &amp;lt; 0.001). Assessing apoptosis and necrosis in human cardiomyocytes and cardiac fibroblasts, we detected no toxicity at Mo concentrations up to 0.52 mM. To test the in vivo properties of Mo TEPW, we sutured them epicardially onto the anterior wall of the heart of female Wistar rats, led them out of the thorax through an intercostal space and placed them in a subcutaneous pocket. We tested electrophysiological properties directly after implantation and after different time periods. Mo TEPW showed similar pacing and sensing properties directly upon implantation and after 2 weeks, with only impedance and slew rate of the sensed R-wave decreasing time-dependently. After one month, all but one pair of Mo electrodes were mechanically broken at their exit from the thorax, the site of assumedly highest mechanical stress. Progressive Mo degradation led to multiple fragmentation of the Mo TEPW after 6 months. The conventional steel TEPW we used as control had similar electrical properties directly after implantation, after 2 weeks and one month without signs of broken electrodes. After 6 months, all but one pair of steel electrodes were mechanically broken at their thorax exit site. Comparing urinary Mo concentration of Mo TEPW treated rats to controls, we saw similar values of 1.9 ± 1.9 µM (n = 6) vs. 0.6 ± 0.2 µM (n = 5, n.s.) after one week. In contrast, we saw a significant increase of 12.1 ± 9.7 µM (n = 5) vs. 1.0 ± 0.9 µM (n = 5, p &amp;lt; 0.001) after 6 months, reflecting the degradation progress. We demonstrate that Mo TEPW are a feasible option for epicardial pacing in vivo for up to 2 weeks and observed the progress of Mo degradation up to 6 months. These findings represent an important step in the development of bioresorbable TEPW as a novel and even safer approach to temporary epicardial pacing.Graphical AbstractIn Vivo Degradation Progress

Hot embossed micropatterned slippery Al 5083 alloys in stagnant and laminar saltwater

Slippery AA 5083 alloy surfaces were fabricated by using ground (mean roughness-Ra = 45±2 µm), polished (Ra = 9±3 µm) and hot embossed micro-patterned specimens, and coating them with silicone oils of varying viscosities (1000−100000 cSt). The surface energy of aluminium alloy (AA) 5083 was estimated to be 850±210 mJ·m−2 using Schultz model. The ground/polished specimens were coated with 12±1 µm and 24±0.3 µm thick oil. They showcased slippery character, wherein apparent water static contact angles (SCAs) of 94±1° to 104±1°, slide-off angles (SAs) of 4±0° to 21±2° and contact angle hysteresis (CAH) of <10° were observed. Also, CAH and SAs revealed an increasing trend with an increase in the oil viscosity, irrespective of the coating thickness or the substrate roughness. In addition, the water droplets bounced-off the oil coated (24 µm thick) surfaces up to Weber no. (We) of 3.91. Furthermore, micro-patterned specimens were fabricated by hot embossing at 300 °C, 17+1 MPa, 5 min and comprise of hexagonally arranged pillars and holes with 6.5−7.1 µm diameter and 9.5−13.6 µm pitch. A key finding is that micro-pillars offered the highest tolerance to shear drainage of oil under saltwater (3.5 wt% NaCl) for up to 7 days, in both stagnant and flowing laminar (Reynolds no.‐Re =247) conditions, as compared to micro-holes and unpatterned surfaces. Interestingly, the slippery properties of oil coated unpatterned AA5083 have retained after 7 days of submersion, showing SCAs ≥ 97±3° and SAs ≤ 14°, despite the negative spreading coefficient of oil on AA5083 under water. Such slippery durable micro-pillared and micro-holed AA5083 surfaces could be highly beneficial for mitigating biological corrosion of ship hulls in marine environments.

Float-Cast Microsieves with Elliptical Pores.

Polymeric microsieves bearing elliptical pores were successfully prepared via float-casting: a dispersion comprising nonvolatile acrylate monomers and ellipsoidal polystyrene particles was spread onto a water surface. The resulting self-organized monolayer was laterally compressed, and the monomer was photopolymerized, giving rise to a membrane comprising ellipsoidal particles laterally embedded in a 0.5 μm thin polymer membrane. The particles were dissolved, leaving behind elliptical pores. These pores had an average length of the major axis of 0.87 ± 0.1 μm and of the minor axis of 0.42 ± 0.07 μm and an aspect ratio of approximately 2. The microsieve bearing these submicrometric elliptical pores was transferred to a hierarchical structure made out of microsieves bearing circular pores of 6 μm diameter on top of a microsieve with 70 μm diameter pores. The resulting hierarchically structured microsieve had a porosity of 0.13. At a pressure difference of typically 103 Pa (Reynolds number aprox. 0.002), the volumetric permeance for water was Pe = /A/Δp = 0.5·10-6 m/s/Pa, the product viscosity·permeance is η·/A/Δp = 0.5·10-9 m. This value is lower than the corresponding values of microsieves with circular pores of similar diameter produced by the same technique. The beneficial effects of higher permeance per pore caused by the elliptical shape are countered by lower porosity caused by less efficient packing of the ellipsoidal particles.

A comparative study on the optical performance of retro-reflective coatings before and after the aging process

Retro-reflective (RR) materials are largely included among the strategies to mitigate Urban Heat Island (UHI) phenomenon in the urban spaces thanks to their optical directional properties. As materials potentially used in the building exterior envelope, RR materials are subjected to outdoor aging and soiling processes, which could alter their optical behaviour. In this perspective, the investigation focuses on the characterization of the optical performance of several types of RR plaster coatings after outdoor aging and soiling processes. The RR plaster coatings were previously developed and studied, before undergoing the outdoor exposure. The RR samples were developed covering the support with a reflective white paint and glass beads. Five different microsphere diameter ranges and three different microsphere superficial density ranges have been employed. In this paper, the RR plaster coatings were tested in terms of optical properties after outdoor aging and soiling and results were compared with data of the same plaster coatings pre-aging. Generally, all RR aged samples show a lower solar reflectance in the Vis region with respect to the pre-aging conditions. The RR behaviour is qualitatively maintained after aging and soiling. The RR sample made of glass beads of 200–300 μm diameter range could represent the best solution both in pre- and post-conditions and both in terms of solar reflectance and retro-reflective behaviour, regardless of the density of microspheres used.

Experimental and statistical methods for microrheological characterization of heterogeneity in human respiratory mucus mimics of health and disease progression

Human respiratory mucus (HRM) is extremely soft, compelling passive microrheology for linear viscoelastic characterization. We focus this study on the use of passive microrheology to characterize HRM heterogeneity, a phenomenon in normal HRM that becomes extreme during cystic fibrosis (CF) disease. Specifically, a fraction of the mucin polymers comprising HRM phase-separate into insoluble structures, called flakes, dispersed in mucin-depleted solution. We first reconstitute HRM samples to the MUC5B:MUC5AC mucin ratios consistent with normal and CF clinical samples, which we show recapitulate progressive flake formation and heterogeneity. We then employ passive particle tracking with 200 nm and 1 μm diameter beads in each reconstituted sample. To robustly analyze the tracking data, we introduce statistical denoising methods for low signal-to-noise tracking data within flakes, tested and verified using model-generated synthetic data. These statistical methods provide a fractional Brownian motion classifier of all successfully denoised, tracked beads in flakes and the dilute solution. From the ensemble of classifier data, per bead diameter and mucus sample, we then employ clustering methods to learn and infer multiple levels of heterogeneity: (i) tracked bead data within vs. outside flakes and (ii) within-flake data buried within or distinguishable from the experimental noise floor. Simulated data consistent with experimental data (within and outside flakes) are used to explore form(s) of the generalized Stokes–Einstein relation (GSER) that recover the dynamic moduli of homogeneous and heterogeneous truth sets of purely flakelike, dilute solution, and mixture samples. The appropriate form of GSER is applied to experimental data to show (i) flakes are heterogeneous with gel and sol domains; (ii) dilute solutions are heterogeneous with only sol domains; and (iii) flake and dilute solution properties vary with probe diameter.