Μm Height Research Articles

Investigation of methods for texturing light-emitting diodes based on AlGaAs/GaAs heterostructures

Investigations of methods for texturing the light-emitting surface of IR light-emitting diodes (LEDs) (wavelength 850 nm) based on AlGaAs/GaAs heterostructures with Bragg reflectors have been carried out. Developed were methods of liquid and plasma-chemical etching of solid solution for creating peaks (pyramids) of different form, 0.2-1.5 μm height. Estimation of the effect of texturing methods and also configuration of peaks on the light-emitting diode electroluminescence intensity has been performed. The increase of the electroluminescence intensity by 25% has been achieved. Keywords: light-emitting diode, texturing, etching methods, electroluminescence.

The obtaining of regular metal and dielectric microstructures based on irradiation-modified polymer films

Based on regular porous polymeric membranes, the synthesis of metal and dielectric spearhead structures with given morphological characteristics was carried out. Copper structures with the ~ 1 μm height and dielectric spearhead microstructures made from iodic acid with the 12 μm height and 1 μm diameter were obtained. The possibility is discussed of using such optical elements to solve the problems of increasing the efficiency of IR radiation detection, signal amplification and conversion to visible and near-infrared ranges. Keywords: regular membranes, spearhead structures, copper, iodic acid, radiation transformations.

Получение регулярных металлических и диэлектрических микроструктур на основе модифицированных при облучении полимерных пленок

Based on regular porous polymeric membranes, the synthesis of metallic and dielectric spearhead structures with given morphological characteristics was carried out. Copper structures with 1 μm height and dielectric spearhead microstructures made of iodoic acid with 12 μm height and 1 μm diameter of were obtained. The possibility of using such optical elements to solve the problems of increasing the efficiency of IR radiation detection, signal amplification and conversion to visible and near-infrared ranges.

Design and simulation of InAsBi PIN photodetector for Long wavelength Infrared applications

In the quest of the potential and superior LWIR photodetector we have designed and simulated InAsBi based PIN photodiode using COMSOL multiphysics. The device is designed with a radius of 5 µm and total height of 1 µm and compared with a InAs based photodiode. In compare to InAs PIN photodiode, our proposed device outperform in several aspects. The responsivity of the device for optical power of 1 µW at 77 K operating temperature and 2 V reverse bias is 10 times as compared to that of InAs. The operating wavelength is shifted from 2.55 to 5.7 µm in case of InAsBi as compared to InAs. Nonetheless, the dark-current at 77 K for an applied reverse bias of 2 V is obtained as 34nA, which is almost 13 times larger than that of InAs device (2.5nA). Our simulated device can act as a benchmark for experimentally investigating InAsBi PIN photodiode as a prospective candidate for highly efficient thermal image sensors, and LWIR photodetectors.

Optimization of injection molded polymer lab-on-a-chip for acoustic blood plasma separation using virtual design of experiment

This study presents the development towards the optimization and manufacturing of a novel cost-effective fully polymer-based ultrasound actuated chip as a Point-of-care (POC) diagnostic platform for blood plasma separation and analysis. The chip was designed following multi-physic functional simulation to obtain optimal dimensions with respect to blood separation enhanced capacity. Initial dimensional guidelines showed most favorable performance to be achieved with design dimensions of 150 µm height, 375 µm width and 34 mm length. The chip encompasses a micro-fluidic channel with a relatively long length compared to the height and the width. As such, main manufacturability challenge is represented by the capability to maintain the channel dimensional conformance throughout the entire length. In order to tackle the challenge and optimize the results, developing a feedback loop was initiated for the device process development where the data of the preliminary micro-injection molding (µIM) production was exploited to implement a simulation-based full-factorial virtual design of experiment (DOE) for all the four materials of interest: polymethyl methacrylate (PMMA), cyclic olefin copolymer (COC), polycarbonate (PC) and polystyrene (PS). The four essential µIM parameters namely, mold temperature, melt temperature, injection velocity and packing pressure were used as factors. Overall, simulations were performed based on the virtual DOE inputs for the four aforementioned materials. The input data for the utilized process parameters in the virtual DOE was provided by our first production batch. Ultimately, in the case of PMMA, parts were molded and characterized based on the process settings that had demonstrated the lowest linear shrinkage in our entire virtual DOE responses. For the linear shrinkage of these parts, a respective width and height difference of 1% and 3.3% between the simulations and production results were obtained. Moreover, as a secondary study sink marks were also inspected and minimized through simulations. Initially, sink marks as deep as 80 µm were spotted on the chip. After the use of optimization cycle the value decreased to as low as 10 µm. The results confirm the positive impact of the virtual experiments for future rapid assessment of potential new chip designs.

The Development of Biomimetic Aligned Skeletal Muscles in a Fully 3D Printed Microfluidic Device.

Human skeletal muscles are characterized by a unique aligned microstructure of myotubes which is important for their function as well as for their homeostasis. Thus, the recapitulation of the aligned microstructure of skeletal muscles is crucial for the construction of an advanced biomimetic model aimed at drug development applications. Here, we have developed a 3D printed micropatterned microfluid device (3D-PMMD) through the employment of a fused deposition modeling (FDM)-based 3D printer and clear filaments made of biocompatible polyethylene terephthalate glycol (PETG). We could fabricate micropatterns through the adjustment of the printing deposition heights of PETG filaments, leading to the generation of aligned half-cylinder-shaped micropatterns in a dimension range from 100 µm to 400 µm in width and from 60 µm to 150 µm in height, respectively. Moreover, we could grow and expand C2C12 mouse myoblast cells on 3D-PMMD where cells could differentiate into aligned bundles of myotubes with respect to the dimension of each micropattern. Furthermore, our platform was applicable with the electrical pulses stimulus (EPS) modality where we noticed an improvement in myotubes maturation under the EPS conditions, indicating the potential use of the 3D-PMMD for biological experiments as well as for myogenic drug development applications in the future.

Extracellular matrix dysfunction in Sorsby patient-derived retinal pigment epithelium

Sorsby Fundus Dystrophy (SFD) is a rare form of macular degeneration that is clinically similar to age-related macular degeneration (AMD), and a histologic hallmark of SFD is a thick layer of extracellular deposits beneath the retinal pigment epithelium (RPE). Previous studies of SFD patient-induced pluripotent stem cell (iPSC) derived RPE differ as to whether these cultures recapitulate this key clinical feature by forming increased drusenoid deposits. The primary purpose of this study is to examine whether SFD patient-derived iPSC-RPE form basal deposits similar to what is found in affected family member SFD globes and to determine whether SFD iPSC RPE may be more oxidatively stressed. We performed a careful comparison of iPSC RPE from three control individuals, multiple iPSC clones from two SFD patients’ iPSC RPE, and post-mortem eyes of affected SFD family members. We also examined the effect of CRISPR-Cas9 gene correction of the S204C TIMP3 mutation on RPE phenotype. Finally, targeted metabolomics with liquid chromatography and mass spectrometry analysis and stable isotope-labeled metabolite analysis were performed to determine whether SFD RPE are more oxidatively stressed. We found that SFD iPSC-RPE formed significantly more sub-RPE deposits (∼6–90 μm in height) compared to control RPE at 8 weeks. These deposits were similar in composition to the thick layer of sub-RPE deposits found in SFD family member globes by immunofluorescence staining and TEM imaging. S204C TIMP3 correction by CRISPR-Cas9 gene editing in SFD iPSC RPE cells resulted in significantly reduced basal laminar and sub-RPE calcium deposits. We detected a ∼18-fold increase in TIMP3 accumulation in the extracellular matrix (ECM) of SFD RPE, and targeted metabolomics showed that intracellular 4-hydroxyproline, a major breakdown product of collagen, is significantly elevated in SFD RPE, suggesting increased ECM turnover. Finally, SFD RPE cells have decreased intracellular reduced glutathione and were found to be more vulnerable to oxidative stress. Our findings suggest that elements of SFD pathology can be demonstrated in culture which may lead to insights into disease mechanisms.

Pillar-Based Mechanical Induction of an Aggressive Tumorigenic Lung Cancer Cell Model.

Tissue microarchitecture imposes physical constraints to the migration of individual cells. Especially in cancer metastasis, three-dimensional structural barriers within the extracellular matrix are known to affect the migratory behavior of cells, regulating the pathological state of the cells. Here, we employed a culture platform with micropillar arrays of 2 μm diameter and 16 μm pitch (2.16 micropillar) as a mechanical stimulant. Using this platform, we investigated how a long-term culture of A549 human lung carcinoma cells on the (2.16) micropillar-embossed dishes would influence the pathological state of the cell. A549 cells grown on the (2.16) micropillar array with 10 μm height exhibited a significantly elongated morphology and enhanced migration even after the detachment and reattachment, as evidenced in the conventional wound-healing assay, single-cell tracking analysis, and in vivo tumor colonization assays. Moreover, the pillar-induced morphological deformation in nuclei was accompanied by cell-cycle arrest in the S phase, leading to suppressed proliferation. While these marked traits of morphology-migration-proliferation support more aggressive characteristics of metastatic cancer cells, typical indices of epithelial-mesenchymal transition were not found, but instead, remarkable traces of amoeboidal transition were confirmed. Our study also emphasizes the importance of mechanical stimuli from the microenvironment during pathogenesis and how gained traits can be passed onto subsequent generations, ultimately affecting their pathophysiological behavior. Furthermore, this study highlights the potential use of pillar-based mechanical stimuli as an in vitro cell culture strategy to induce more aggressive tumorigenic cancer cell models.

Early embryonic developmental stages of the pearl oyster Pinctada radiata (Leach, 1814) from Lattakia coast, Syria

Matured brood stock of Pinctada radiata were collected from Afamia region in Lattakia coast. Three sets of spawning and larval rearing experiments were conducted during the period from July - October 2016 and the pearl oysters were successfully spawned at average temperature 31.5 ± 0.26 °C. After about 60 min, oocytes presented no germinal vesicle, rounded and measured 47.5-55 μm with an average of 50 ± 3.95 μm in diameter. Early stages of embryonic development were recorded and the polar body was observed 15 min after fertilization, trefoil stage at 1 h and 30 min, morula at 3 h and 30 min, blastula at 4 h and 50 min, gastrula at 6 h, trochophore larva at 8 h and veliger larva at 20 h. Veliger larva dimensions were 61.88 ± 3.82 μm for average length along the antero-posterior axis and 51.26 ± 5.14 μm for height along the dorso-ventral axis.

Acetone Sensor Based on FAIMS-MEMS.

In this paper, to address the problems of large blood draws, long testing times, and the inability to achieve dynamic detection of invasive testing for diabetes, stemming from the principle that type 1 diabetic patients exhale significantly higher levels of acetone than normal people, a FAIMS-MEMS gas sensor was designed to detect acetone, which utilizes the characteristics of high sensitivity, fast response, and non-invasive operation. It is prepared by MEMS processes, such as photolithography, etching, and sputtering, its specific dimensions are 4000 μm in length, 3000 μm in width and 800 μm in height and the related test system was built to detect acetone gas. The test results show that when acetone below 0.8 ppm is introduced, the voltage value detected by the sensor basically does not change, while when acetone gas exceeds 1.8 ppm, the voltage value detected by the sensor increases significantly. The detection accuracy of the sensor prepared by this method is about 0.02 ppm/mV, and the voltage change can reach 1 V with a response time of 3 s and a recovery time of 4 s when tested under 20 ppm acetone environment; this has good repeatability and stability, and has great prospects in the field of non-invasive detection of type 1 diabetes.

Fabrication of Si protrusions by local melting of a narrow current path on a Si wafer via resistive heating

Si protrusions were fabricated by surface melting and resolidifying of a Si(111) wafer covered with a 100 nm thick molybdenum (Mo) layer, in which a narrow region was generated using a microgrinder. This region results in a narrow current path and thus localized resistive heating, leading to specific melting of the Si in the path. The melted Si flowed away from the path to both sides, which were at temperatures lower than that of the path. Consequently, two Si protrusions ∼400 μm in height capped with Mo silicide precipitates were formed on each side of the burned-out path, as revealed by scanning electron microscopy with energy-dispersive X-ray spectroscopy. The formation mechanism was discussed in terms of the non-uniform temperature, surface tension, interdiffusion, and freezing-point depression of the surface. This study revealed the potential of fabricating an array of self-assembled Si protrusions by resistive heating of narrow paths.

Application of high current pulsed electron beam irradiation to smoothing of cold spray aluminum bronze coating

The aim of the work was investigation of the effect of high current pulsed electron beam irradiation (HCPEBI) with the energy density Es = 18 J/cm2, 20 pulses on the surface roughness, microstructure, phase composition and microhardness of the near-surface layer of aluminum bronze coating deposited on aluminum alloy using cold spray. Using SEM, line and 3D profilometry it was shown that HCPEBI in the used regime enabled smoothing of relief roughness of ∼50 μm in height. The content of free volume in the layer essentially decreased: there was very low number of small pores instead of big voids and delamination along the particles interfaces. Using XRD and TEM, formation of the ordered β1’ martensite of Cu3Al compound after HCPEBI was revealed. The microhardness of the layer decreased from 5.1 down to 2.2 GPa due to disappearance of the deformation-induced defects and phase transformation.

Thermal and flow characteristics of liquid flow in a 3D-printed micro-reactor: A numerical and experimental study

• Stereo lithography was utilised to construct pin–fin photo-thermal micro-reactors. • 3D printing was successfully utilised to print micro-pin fins inside microchannels. • Thermal and fluid characteristics of constructed micro-reaactors were assessed. • Validated CFD model was used to evaluate velocity and pressure profiles. • Size of pin-fins in micro-reactor was optimised with response surface modelling. In this article, we report on a unique design and build technique based on stereolithographic 3D printing technology (SLA) for constructing ultraviolet cured resin-made micro-reactors. The main objective of this study is gaining insight into the thermal performance of micro-reactors for optofluidic applications. Several micro-reactors equipped with pin fins were manufactured. A high-fidelity test-rig was developed and used to collect data from water flowing in the micro-reactors as they are exposed to various heat flux loading. The measured data was also used for validating the numerical (CFD) models. The CFD models provided in-depth spatial data on the pressure and temperature profiles in the microchannel, which could not be easily measured. The results showed that conventional empirical correlations failed to accurately predict the pressure drop of the system in the microfluidics regime (Re < 190), although are reasonably accurate in the conventional fluid regime (Re > 190). For both regimes, however, CFD results were sufficiently accurate in predicting the temperature and pressure differences across the micro-reactor. It was also identified that pin fins arrangements offer a great design benefit in enhancing heat transfer coefficient in micro-reactors, achieving values up to ∼2300 W/m 2 .K compared to a plain micro-reactor at ∼1875 W/m 2 .K (or 300 W/m 2 .K for conventional combustion systems). A multi-objective optimisation on the geometrical specifications of various pin fins showed that the micro-reactor with pin fins of 250 µm in diameter and 100 µm in height, yielded the best thermo-hydraulic performance of highest thermal transfer coefficient (2100 W/m 2 .K) and the lowest pressure- drop (∼0.1 kPa) across a wide range of heat flux loadings. The outcome of this study has created a significant knowledge and understanding of the flow behaviour in polymer-based micro-channels. It also established a methodology for designing and optimising the thermal–hydraulic performance of optofluidic micro-reactors, with potential loading of nano-photocatalyst mediated in pin fins sites. New correlations for predicting the pressure drop and temperature difference across polymer-based micro-reactors are also developed.

Advancing 3D-Printed Microfluidics: Characterization of a Gas-Permeable, High-Resolution PDMS Resin for Stereolithography.

The rapid expansion of microfluidic applications in the last decade has been curtailed by slow, laborious microfabrication techniques. Recently, microfluidics has been explored with additive manufacturing (AM), as it has gained legitimacy for producing end-use products and 3D printers have improved resolution capabilities. While AM satisfies many shortcomings with current microfabrication techniques, there still lacks a suitable replacement for the most used material in microfluidic devices, poly(dimethylsiloxane) (PDMS). Formulation of a gas-permeable, high-resolution PDMS resin was developed using a methacrylate–PDMS copolymer and the novel combination of a photoabsorber, Sudan I, and photosensitizer, 2-Isopropylthioxanthone. Resin characterization and 3D printing were performed using a commercially available DLP–SLA system. A previously developed math model, mechanical testing, optical transmission, and gas-permeability testing were performed to validate the optimized resin formula. The resulting resin has Young’s modulus of 11.5 MPa, a 12% elongation at break, and optical transmission of >75% for wavelengths between 500 and 800 nm after polymerization, and is capable of creating channels as small as 60 µm in height and membranes as thin as 20 µm. The potential of AM is just being realized as a fabrication technique for microfluidics as developments in material science and 3D printing technologies continue to push the resolution capabilities of these systems.

Ocular wavefront aberrations in acute central serous chorioretinopathy

Background: Central serous chorioretinopathy (CSCR) is a condition of choroidal and retinal pathologies that may affect vision, so we assessed vision by the ocular wavefront in the acute form of CSCR. Methods: This cross-sectional study included 21 cases (16-male, 5-female) of acute onset CSCR was referred to the retina clinic of Nikookari Eye Hospital. Visual acuity and ocular examination with and without pupillary dilation record. Central macular thickness and sub-foveal fluid height of all patients measured by spectral-domain optical coherence tomography (SD-OCT). All of them fulfilled binocular visual function analyzer by Tracy Technology after complete pupillary dilation. The items such as spherical equivalent, total root mean square, total lower-order aberration, total higher-order aberration, defocus, astigmatism, secondary astigmatism, coma, spherical aberration, trefoil, Strehl ratio in point spread function, the average height in the modulation transfer function, and root mean square error registered. Generalized Estimation Equations (GEE) were used to compare two groups of affected CSCR and normal contralateral eyes. Results: The mean uncorrected distance visual acuity in the CSCR eyes is (Decimal Notation) 0.82±0.17 and in the contralateral eyes is 0.95±0.09 (P=0.002). Analysis of macular OCT data CSCR group represents: central foveal thickness 485.9±165.12 μm and mean fluid height 284.3±165.42 μm. The mentioned optical parameters of ocular wavefront aberrations do not have significantly different results in the two groups. Conclusion: Our study showed CSCR reduced uncorrected visual acuity but it did not detect significant ocular wavefront changes in acute CSCR

Facile measurement of cortisol using microchannel embedded Cu-rGO-polymer composite chemiresistive sensor

A phenol precursor-based polymeric film (1 mm thickness), in situ impregnated with Cu and reduced graphene oxide (rGO) as the conductive fillers, is synthesised as the chemiresistive sensor for the stress hormone biomarker – cortisol. The Cu-rGO-polymeric film was engraved with microchannels (200 µm wide × 100 µm height with 200 µm interspacing) using laser ablation technique. The microchannels intensified the wettability of the film with liquid analyte and the speed of detection via capillary action-driven (passive) flow during sensing. In addition, the laser-ablated microchannels exposed the in situ dispersed Cu nanoparticles to the film surface. The surface modification of the microchannels with cortisol monoclonal antibodies, used as the recognition element, induced change in the electrical resistance of the material, corresponding to cortisol concentration. The sensor exhibited a linear response (R2 > 0.99) over the concentration range 1 – 50 µg/dL, with the sensitivity of 2.81 Ω/µg-dL−1 for a contact time of 5 min. With emerging materials and microstructural patterning, the scope of the developed chemiresistive sensor in the current study can be widened to measure a wide range of analytes.

Periodic cylindrical structure of micro‐swelling silicone rubber fabricated by ArF excimer laser

AbstractCylindrical structure of micro‐swelling silicone rubber of approximately 1 μm diameter and 1.5 to 2 μm height was fabricated by the 193‐nm ArF excimer laser‐induced photodissociation of Si‐O bonds of silicone rubber. To be periodically, single layer of silica glass microspheres was aligned on aluminum‐coated silicone rubber during laser irradiation. The silicone rubber underneath each microsphere photochemically swelled, after laser‐ablating aluminum to limit a diameter of the swelling. The aluminum also adjusted a focal point to the surface of silicone rubber to form a hole approximately 0.5 µm diameter centered at each the swelled silicone rubber. A purging O2 molecules in the laser beam path by N2 gas and lowering the laser pulse repetition rate were effective for fabricating the regular cylindrical structure. The regular cylindrical structure of micro‐swelling silicone rubber showed superhydrophobicity.

Low-cost photolithography system for cell biology labs

Abstract Soft lithography, a tool widely applied in biology and life sciences with numerous applications, uses the soft molding of photolithography-generated master structures by polymers. The central part of a photolithography set-up is a mask-aligner mostly based on a high-pressure mercury lamp as an ultraviolet (UV) light source. This type of light source requires a high level of maintenance and shows a decreasing intensity over its lifetime, influencing the lithography outcome. In this paper, we present a low-cost, bench-top photolithography tool based on ninety-eight 375 nm light-emitting diodes (LEDs). With approx. 10 W, our presented lithography set-up requires only a fraction of the energy of a conventional lamp, the LEDs have a guaranteed lifetime of 1000 h, which becomes noticeable by at least 2.5 to 15 times more exposure cycles compared to a standard light source and with costs less than 850 C it is very affordable. Such a set-up is not only attractive to small academic and industrial fabrication facilities who want to enable work with the technology of photolithography and cannot afford a conventional set-up, but also microfluidic teaching laboratories and microfluidic research and development laboratories, in general, could benefit from this cost-effective alternative. With our self-built photolithography system, we were able to produce structures from 6 μm to 50 μm in height and 10 μm to 200 μm in width. As an optional feature, we present a scaled-down laminar flow hood to enable a dust-free working environment for the photolithography process.

Digitally Driven Aerosol Jet Printing to Enable Customisable Neuronal Guidance.

Digitally driven manufacturing technologies such as aerosol jet printing (AJP) can make a significant contribution to enabling new capabilities in the field of tissue engineering disease modeling and drug screening. AJP is an emerging non-contact and mask-less printing process which has distinct advantages over other patterning technologies as it offers versatile, high-resolution, direct-write deposition of a variety of materials on planar and non-planar surfaces. This research demonstrates the ability of AJP to print digitally controlled patterns that influence neuronal guidance. These consist of patterned poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) tracks on both glass and poly(potassium 3-sulfopropyl methacrylate) (PKSPMA) coated glass surfaces, promoting selective adhesion of SH-SY5Y neuroblastoma cells. The cell attractive patterns had a maximum height ≥0.2 μm, width and half height ≥15 μm, Ra = 3.5 nm, and RMS = 4.1. The developed biocompatible PEDOT:PSS ink was shown to promote adhesion, growth and differentiation of SH-SY5Y neuronal cells. SH-SY5Y cells cultured directly onto these features exhibited increased nuclei and neuronal alignment on both substrates. In addition, the cell adhesion to the substrate was selective when cultured onto the PKSPMA surfaces resulting in a highly organized neural pattern. This demonstrated the ability to rapidly and flexibly realize intricate and accurate cell patterns by a computer controlled process.

Effect of microstructures on temperature and stress distributions of an irradiated alumina surface.

Three types of alumina surface irradiated by laser are simulated in this study to investigate stray light ablation. Results indicate that temperature fields of triangular and rectangular microstructures exhibit the "head effect," while overall still exhibit Gaussian distributions. For the stress, there is a notable difference between the microstructure surface and the ideal surface. The most stress concentration occurs at the corners on the microstructure surface termed as the "bottom effect." The maximum tensile stress of a triangular microstructure appears below the midline of the slope. The location of the maximum tensile stress on the triangle first shifts down and then up. The inflection point is 0.9 µm in height of the triangle.