Hollow Pyramids Research Articles

Study on Bioresponsive Gelatin-Hyaluronic Acid-Genipin Hydrogel for High Cell-Density 3D Bioprinting.

The Development of bioresponsive extrudable hydrogels for 3D bioprinting is imperative to address the growing demand for scaffold design as well as efficient and reliable methods of tissue engineering and regenerative medicine. This study proposed genipin (5 mg) cross-linked gelatin (1 to 1.5 g)-hyaluronic acid (0.3 g) hydrogel bioink (20 mL) tailored for 3D bioprinting. The focus is on high cell loading and a less artificial extra-cellular matrix (ECM) effect, as well as exploring their potential applications in tissue engineering. The bioresponsiveness of these hydrogel scaffolds was successfully evaluated at 37 °C and room temperature (at pH 2.5, 7.4, and 9). The rheological and mechanical properties (more than three times) increased with the increase in gelatin content in the hydrogel; however, the hydrogel with the least amount of gelatin showed the best extrusion capability. This optimized hydrogel's high extrusion ability and post-printing shape fidelity were evident from 3D and four-axis printing of complex structures such as hollow tubes, stars, pyramids, and zigzag porous tubular (four-axis) scaffolds (printed at 90 kPa pressure, 70 mm/s speed, 22G needle, fourth axis rotation of 4 rpm). 3 million/mL MC3T3-E1 mouse osteoblast cells were used in preparing 3D bioprinted samples. The in vitro cell culture studies have been carried out in a CO2 incubator (at 37 °C, 5% CO2). In the cytocompatibility study, almost three times more cell viability was observed in 3 days compared to day 1 control, proving the non-toxicity and cell-supportiveness of these hydrogels. High cell viability and cell-to-cell interactions observed at the end of day 3 using this moderately stable hydrogel in 3D bioprinting exhibit high potential for precise cell delivery modes in tissue engineering as well as regenerative medicine.

Sculpting Electrochemically Growing or Grown Microarchitectures.

Microarchitectures with complex interior structures are important for many applications. However, engineering complex interior structures within microarchitectures are challenging. This article reports the introduction of electrochemical sculpting processes to carve the microarchitectures during or after their electrochemical growing process to design the interior structure of the microarchitectures. The electrochemical growing and sculpting process tangle together under the constant voltage electrodeposition mode with their strength depending on the ion concentration gradient and the voltage value. The unique thawing process of the frozen electrolyte is used to create the desired sharp ion concentration gradient, and has the potential to control the strength of the sculpting and the growing processes. How to completely decouple the growing and the sculpting process is further studied to gain more accurate control over the interior structures of the microarchitectures. It is revealed that the sculpting process can be exclusively applied onto the electrochemically grown microarchitectures simply by reversing the electric field without triggering any growing processes. Microarchitectures with complex interior structures, including micropyramids with a single cavity exclusively at the outward or every apex to multi-walled hollow pyramids with designable wall numbers and inter-wall distances are prepared as examples.

Morphology-induced spectral modification of self-assembled WS2 pyramids.

Due to their intriguing optical properties, including stable and chiral excitons, two-dimensional transition metal dichalcogenides (2D-TMDs) hold the promise of applications in nanophotonics. Chemical vapor deposition (CVD) techniques offer a platform to fabricate and design nanostructures with diverse geometries. However, the more exotic the grown nanogeometry, the less is known about its optical response. WS2 nanostructures with geometries ranging from monolayers to hollow pyramids have been created. The hollow pyramids exhibit a strongly reduced photoluminescence with respect to horizontally layered tungsten disulphide, facilitating the study of their clear Raman signal in more detail. Excited resonantly, the hollow pyramids exhibit a great number of higher-order phononic resonances. In contrast to monolayers, the spectral features of the optical response of the pyramids are position dependent. Differences in peak intensity, peak ratio and spectral peak positions reveal local variations in the atomic arrangement of the hollow pyramid crater and sides. The position-dependent optical response of hollow WS2 pyramids is characterized and attributed to growth-induced nanogeometry. Thereby the first steps are taken towards producing tunable nanophotonic devices with applications ranging from opto-electronics to non-linear optics.

Substrate damage in ion-implanted (100) germanium after extended ms flash lamp annealing: Origins and suppression

In this work, the surface damage induced in ion-implanted (100) Ge after extended (20 ms) flash lamp annealing (FLA) at 800–850 °C is investigated and discussed using combined results from scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The induced surface damage has a variety of morphologies including shallow semi-spherical craters, large rectangular-base pyramids with protrusions, and inverted hollow square-base pyramids. The dominant defect morphology depends on the implanted species, the implantation conditions, the flash lamp annealing temperature, as well as on the capping layer used for the Ge surface protection. These results are interpreted using and adapting models developed to describe similar phenomena that take place during flash lamp annealing in Si. From a technological point of view, the most important outcome of this study is that nitrogen co-implantation enhances significantly the robustness of the Ge surface layer, as revealed by the suppression of the induced damage in all cases. Nitrogen co-implants appear to extend the flash lamp annealing thermal budget envelope, which could be useful to achieve a higher level of donor activation in Ge.

Vitis labruska skin extract assisted green synthesis of ZnO super structures for multifunctional applications

Abstract The formation of unique morphologies of zinc oxide (ZnO) super structured frameworks were reported via a simple and eco-friendly route employing Vitis labruska fruit Black Grape Skin (BGS) extract as a fuel. XRD, FTIR, UV–vis, PL, SEM and TEM studies are performed to analyse the formation and characterization of ZnO. XRD confirmed the crystalline nature of the material with hexagonal Wurtzite structure having average crystallite size of ~50 nm. FTIR spectrum shows a band at 532 cm−1 due to the vibrational mode of Zn-O bending. The band gap of the ZnO was found to be 3.26 eV. SEM images confirm the formation of different morphologies like Mysore pak (a popular Indian dessert), canine teeth, hollow pyramids and gems were obtained by varying the weight of BGS. These superstructures were obtained due to the interaction of Zn2+ with BGS extract. TEM images clearly shows lattice spacing of 0.29 nm corresponding to the (002) plane of ZnO. Photoluminescence (PL) spectrum shows strong yellow light emission upon excitation at 320 nm due to the Zn-O defects. Synthesized ZnO nanoparticles (Nps) exhibited good photocatalytic activity for the degradation of Methylene blue (MB) dye. The photocatalytic activity was due to the production of OH˙ radicals during photo irradiation on ZnO Nps. ZnO Nps also exhibited superior antibacterial activity against Staphylococcus aureus and Escherichia coli bacteria. Further, ZnO Nps were also used in the development of novel electrochemical sensing platform towards the electrochemical detection of hydrazine as a model system at very low concentrations having a detection limit of 0.3 µM.

Synthesis of monodisperse ZnO hollow six-sided pyramids and their high gas-sensing properties

Monodisperse ZnO hollow six-sided pyramids were successfully synthesized by a low-cost and simple hydrothermal method at 160°C for 20h without the use of any surfactant or template. The sodium citrate (Na3C6H5O7·2H2O) and glycerol (C3H8O3) played a pivotal role in the growth of hollow six-sided pyramid, and the possible growth mechanism was also proposed based on the experimental facts. Moreover, the gas sensor based on this structure displayed excellent gas sensing properties to ethanol at the optimum operating temperature of 240°C. The response was about 187 and the response-recovery time was around 11 and 9s for 200ppm ethanol, respectively, which indicated that this structure had high sensitivity, fast response-recovery time and good selectivity to ethanol.

Electron beam induced SiO 2 etch selectivity and its application to oxide nano-aperture formation

The influence of SiO 2 etch selectivity induced by electron beam irradiation on the nano-fabrication of sub-wavelength size aperture has been investigated. Initially, oxide hollow pyramids were prepared by square-dot patterning and V-groove formation using TMAH etching of Si and thermal oxidation followed by backside Si removal. The opening of nano-size apertures at oxide pyramid apexes was carried out by wet SiO 2 etching with and without electron beam exposure. It was observed that the aperture diameter varies according to the electron beam exposure, the reason of which can be attributed to the enhanced oxide etch rate due to electron beam irradiation. Direct verification using a double aperture and details of electron beam influence will be discussed.

Effective electromagnetic properties of honeycomb composites, and hollow-pyramidal and alternating-wedge absorbers

Closed-form expressions for the effective electromagnetic material properties of honeycomb composites and electromagnetic absorbers constructed in the shapes of alternating wedges and hollow pyramids are presented. These expressions can be used to efficiently calculate the interaction of electromagnetic fields with periodic structures of said geometries. The effective material properties from these expressions are compared to results obtained from a numerical solution of the actual cross-sectional geometry. Finally, we give guidance on how the expressions presented here and elsewhere can be used for other types of periodic geometries.

Batch fabricated scanning near field optical microscope/atomic force microscopy microprobe integrated with piezoresistive cantilever beam with highly reproducible focused ion beam micromachined aperture

In scanning near field optical microscope (SNOM), an optical probe with aperture diameter well below the optical wavelength is moved over the sample. The sample-probe distance control is one of the key problems in SNOM. Our earlier approach allowed for fabrication of the piezo-SNOM/atomic force microscopy (AFM) probe, however, reproductivity of the process and optical quality of the device were not satisfactory. Now we report an innovative processing sequence, which offers highly reproductive batch processing, typical for semiconductor technology and renders it possible to produce cantilevers playing role of an AFM detector as well as a nanoaperture detector. Moreover, illumination of the aperture is easier because of a wide input opening and its big cone angle. The throughput is in the range of 10−5 and higher. Apertures in hollow pyramids have been formed by direct ion beam drilling with a focused beam of 30 keV Ga+ ions. Direct focused ion beam (FIB) drilling is a reproducible process for hole formation at the 30–100 nm diameter range. Formation of smaller apertures is possible if a special FIB drilling/deposition procedure is applied.

The double-pyramid structure of dendritic ice growing from supercooled water

It is known that ice growing freely from supercooled water has a morphological transition at T=−2.7°C, from a flat dendritic structure at higher temperatures to a twelve-sided double-pyramid structure at lower temperatures. The double-pyramid structure, which can be described as two hollow six-sided pyramids joined at their apices, is built from dendrites growing in well-defined growth directions which are noncrystallographic in the planes normal to the basal plane while their projections on the basal plane retain the hexagonal symmetry. Similar structures have been reported in other hexagonal materials. In order to understand the growth mechanism better, we measured the temperature field in the water around the growing crystals by using the temperature dependence of its refractive index. Since this dependence happens to be zero at the freezing point for regular water (H 2O), we use heavy water (D 2O), and achieve considerably greater sensitivity. The free growth experiments performed with heavy ice reveal that their morphological behavior is similar to regular ice, as well as their velocities and the angle between the pyramids as a function of supercooling. The temperature measurements showed that the interaction between the two sides of the pyramid via the temperature field is weak. This leads to the conclusion that the solution for the growth mode of the dendrites should be found in the single dendrite level. Explanations of this phenomenon are discussed in the light of recent advances in dendritic growth theory – in particular the concept of microscopic solvability – combined with the behavior of the surface tension and the kinetic effect as a function of crystallographic orientation. It can be shown that growth in a low symmetry direction leads to an asymmetrically growing crystal and to asymmetry in the observed temperature field.

Marine Oil Seeps

Petroleum hydrocarbons of both biogenic and thermogenic origin are common constituents of the marine water column and sediment of the continental shelves. Approximately 0.25 million metric tons of oil per year, constituting about 8% of the oil input into the sea, is derived from natural seeps, the rest being anthropogenic. Seepage has occurred world-wide for millions of years and must have been many times greater in the past, when enormous oil deposits, such as the Orinoco Oil Belt, were first exposed to erosion. Although the amount varies from site to site with time, seepage is pervasive in polar and temperate seas. Marine-seep oil is intensely weathered and thus can be distinguished chemically from recent biogenic or undegraded crude oil. The degraded oil from seeps appears to have little deleterious effect on many marine organisms, which ingest and discharge the oil mostly unmetabolized. Chemical analyses suggest that a very large oil-rich layer in the Sargasso Sea originated from a large and as yet undetected seep. Oil seeps have long been used as guides for oil exploration onshore but have been underutilized for this purpose offshore because of oil-plume drift from the site of the seep and because natural oil slicks maymore » be masked by spilled oil. At least one marine seep, in the Santa Barbara Channel, California, is producing oil and natural gas into two hollow steel pyramids from which the oil is collected by work boats and the natural gas is transported to shore by pipeline. This facility effectively reduces atmospheric pollution, controls marine oil pollution from the largest seep in the area, provides emission credits, and yields a modest economic benefit, but the seep is not known to have been used directly in oil exploration.« less

Heat of fusion and lamellar structure of polyethylene single crystal mats

Recently published results for solution crystallized PE single crystals have shown, that the experimental heat of fusionΔH* is higher, if the solvent is exchanged to silicon oil (oil suspension samples) as compared with dried mats. This has been interpreted by the collapse of the original hollow pyramids during drying, inducing lateral defects within the lamellae. The present investigation does not confirm this unexpected result.ΔH* of dried mats (Tc 66 to 91 °C) and of the corresponding oil suspension samples agree within the rather small limits of experimental error. The crystallinities as derived fromΔH*, density or WAXS are in excellent agreement.

Morphology of melt‐crystallized linear polyethylene fractions and its dependence on molecular weight and crystallization temperature

AbstractReplicas and thin‐section electron microscopic studies were made of fractions of linear polyethylene covering the molecular weight range 2.78 × 104 to 6.0 × 106 for a variety of crystallizing conditions. Lamellar crystallites were found under all circumstances; and the supermolecular structure, or crystalline morphology, is in agreement with that previously reported from an analysis of the small‐angle light‐scattering patterns of the same samples under similar crystallization conditions. Details of the crystalline microstructure are also described, which range from truncated hollow pyramids which degenerate as the molecular weight or the undercooling are increased. From these results, it is possible to describe the mechanism of formation of polyethylene spherulites.

Morphology of hollow crystals of II–VI compounds

Published data on hollow crystals of II–VI compounds are reviewed. The experimental conditions for obtaining hollow crystals are discussed and presented systematically in tables. Some inferences concerning the effect of impurities, supersaturation, type of substrate and other factors on the growth of hollow crystals are made. Particular attention is paid to the structure, form and defects of hollow crystals and it is established that they can be classified in the following groups: hollow hexagonal columns and prisms, hollow pyramids, hollow crystals with spiral-like hexagonal form and hollow crystals with a more complex structure consisting of whisker-pyramid-prism. The mechanism and kinetics of the growth of hollow crystals as presented by different authors are discussed.

Sodium-doped hollow CdS crystals

A simple technique is described to grow Na-doped CdS crystals, in the form of hollow hexagonal pyramids, starting from heavily Na-doped powders; the method of preparation of the powders is also described.

Habits of ice grown in supercooled water and aqueous solutions

Abstract At small supercoolings the direction of growth of ice in pure water and aqueous solutions is parallel to the basal plane. As the supercooling is increased the growth direction of the dendrites become inclined at an angle to the basal plane, the angle increasing with supercooling. The most general habit of growth now has the form of two symmetrically situated hollow hexagonal pyramids joined at their apices. At still larger supercoolings further growth ensues from the initial dendrites comprising the pyramidal segments and complex three-dimensional structures are produced which are nevertheless single crystals. It is noted that the pyramidal growth habit occurs also in ice crystals formed from the vapour phase at high supersaturations and in Tyndall figures produced in the melting of ice. The non-rational growth of the dendrites is explained in terms of deposition predominantly on basal surfaces on one side of the dendrite tip and on prism faces on the other, the direction of growth being determin...

Electret domains in individual trioxane polycrystals

Abstract Crystalline trioxane growing under suitable conditions from the dry vapour consists of closed circuits of electret domains. Limited numbers of such domains together constitute individual polycrystals in the shape of polyhedral calyxes, cups, hollow pyramids and the like.

The morphology of poly-4-methyl-pentene-1 crystals

Poly-4-methyl-pentene-1 crystals, obtained from 0·06–0·1 per cent xylene solutions by isothermal growth at temperatures from 57° to 92°C as well as under non-isothermal conditions, were investigated by optical and electron microscopy. Crystals grown at temperature in the 57° to 74°C range have square bases and are about 100 Å thick. Some evidence is given which indicates that growth of one lamella upon another can occur by other than a screw dislocation mechanism. Crystals, obtained from a solution cooled slowly from 125°C, show folds across the centre as well as near the corners. These features suggest that the crystals grow as hollow pyramids which collapse upon removal from suspension as found for polyethylene. Those grown at temperatures from 78°C to 92°C showed similar collapse features in addition to a turning-under at the corners.

On the morphology of polymer crystals

Crystals of isotactic poly-4-methylpentene-1 and of polyoxymethylene have been grown from dilute solution. The X-ray long period has been measured as a function of crystallization temperature for poly-4-methylpentene-1 in xylene and for polyoxymethylene in furfuryl alcohol. Polyoxymethylene crystals are flat-based hexagonal hollow pyramids in which the molecules are parallel to the pyramidal axis. On the other hand, poly-4-methylpentene-1 forms square, nearly planar, lamellae in which the molecules are normal to the layers. The slight departure from planarity suggested by morphological detail is related to a slight distortion of the subcell due to chain-folding.

Morphology of Polymer Single Crystals

Evidence is presented indicating that polyethylene crystals grow in the form of hollow pyramids as well as lamellar crystals. Modes of packing the folded molecules consistent with the nonplanar structure are proposed. Observed electron diffraction patterns and dark-field micrographs are related to the pyramidal morphology. Various sources are described for the screw dislocations which result in spiral growths on crystals of polyethylene and polyoxymethylene.