3D-printed low-voltage-driven ciliary hydrogel microactuators

The influence of low-energy helium plasma on bubble formation in micro-engineered tungsten

Roots of stunted broccoli plants (Brassica oleracea) from the Palo Verde Valley, CA, were observed at various stages of decay. A species of Pythium with large spiny oogonia was microscopically observed and consistently isolated from decayed roots. Isolates produced spherical, intercalary sporangia (average 34.5 μm in diameter) and aplerotic oospores (average 37.3 μm in diameter) in oogonia (average 47.4 μm in diameter) bearing numerous conical spines (average 8.5 μm in height and 5.5 μm basal width) with blunt apices. A representative broccoli isolate (P1) had a 99% internal transcribed spacer (ITS) sequence similarity with Pythium jasmonium (nom. inval., GenBank AF216654.1), a species which has not been formally described. Three other accessions in GenBank also carry the specific epithet of P. jasmonium and were originally isolated from diseased plants in the family Brassicaceae. In our study, these isolates were pathogenic on broccoli and morphologically similar to P1. P1 was pathogenic to 10 cultivated and 12 wild plants in the family Brassicaceae but not to 18 species of cultivated plants belonging to nine other plant families. Mycelial growth of our isolates occurred between <10 and 35°C, with an optimum of 25°C (maximum growth rate 25 mm/day). Our broccoli isolates are related to other species in subclade B of clade J. Members of subclade B include P. mastophorum, P. uncinulatum, P. buismaniae, P. polymastum, and P. megalacanthum. However, the broccoli isolates, in addition to all those in GenBank that carry the specific epithet of P. jasmonium, possess unique ITS, β-tubulin, and cox1 sequences that are sufficiently different from other species in subclade B to justify status as a new species. We propose that isolates previously designated as P. jasmonium (nom. inval.) be renamed as P. brassicum sp. nov. based on their apparent plant family-specific pathogenicity.

We report a study of the determination of polymer cross‐linking, namely the degree of conversion and refractive index of the microstructures created by two‐photon polymerization (TPP). The influence of TPP processing parameters such as laser intensity and scanning velocity is investigated. The degree of conversion is analyzed via Raman microspectroscopy and the refractive index is measured with the interferometric technique employing a Michelson interferometer. Moreover, the relationship between these two properties is revealed and details are discussed. The largest refractive index change that we have obtained is of the order of 10−2. Finally, we propose and demonstrate experimentally the realization of the gradient‐index (GRIN) structure, resulting from a laser‐induced local refractive index modification due to monomer cross‐linking, i.e. degree of conversion. This work implies that the TPP technique is a valuable tool for the fabrication of GRIN microoptics for (in)homogeneous molding of light flow at the micrometer scale. image

A 193-nm ArF excimer laser was used to induce the photodissociation of Si–O bonds of silicone rubber in order to fabricate a periodic micro/nano-suction cup silicone structure, approximately 1 μm in diameter and 2 μm in height at regular intervals of 2.5 μm. The laser was focused on Al-coated silicone rubber by each silica glass microsphere 2.5 μm in diameter, which covered the entire surface of the silicone rubber. The silicone rubber underneath each microsphere photochemically swelled after laser-ablating the coated Al to limit the diameter of the swelling. Simultaneously, the coated Al was able to adjust the focal point to the surface of the silicone rubber to form a hole approximately 500 nm in diameter, centered at the swollen silicone. The dependences of the thickness of the coated-Al and the laser pulse number are discussed, based on the observations of a scanning electron microscope (SEM) and an atomic force microscope (AFM). The superhydrophobic property of the fabricated micro/nano-suction cup structure was successfully found.

SUMMARYA new rhodymeniacean species, Chamaebotrys prolifera, is described from a shallow water habitat in Puerto Rico, representing the first occurrence of the genus in the Atlantic Ocean. Plants, to 5 cm across, are decumbent and comprised of compressed vesicles that are originally proliferously branched at the perimeter. Older vesicles become branched from their dorsal surfaces as well. Branches are septate at their origin and become irregularly shaped with age. Anastomoses between adjacent vesicles is common. Individual vesicles measure to 15 mm in broadest dimension. Vesicle walls consist of two layers of medullary cells and two layers of cortical cells. Tetrasporangia, which occur in diffuse nemathecia, are spherical, to 30 µm in diameter and are cut off terminally from an inner cortical cell. Cystocarps are hemispherical measuring to 800 µm in diameter and 350 µm in height. Spermatangia are apparently cut off randomly from outer cortical cells across the thallus surface. Molecular evidence confirms placement of Chamaebotrys within the Rhodymeniaceae.

Silicon is the primary material of integrated circuit (IC) manufacturing in microelectronic industry. It has high thermal conductivity and superior thermomechanical properties compatible to most semiconductors. These characteristics make it an ideal material for fabricating micro/mini heat pipes and their wick structures. In this article, silicon wick structures, composed of cylindrical pillars 320 μm in height and 30–100 μm in diameter, are developed for studies of phase change capability. Fabrication of the silicon wick structures utilizes the standard microelectromechanical systems (MEMS) approach, which allows the precise definition on the wick dimensions, as well as the heated wick area. On these bases, experimental characterizations of temperature variations versus input heat fluxes, associated with simultaneous visualization on the liquid transport and the dryout, are performed to investigate the wick dimensional effects on the maximum phase change capability. On the wick structure with the pillar diameter/pores of 100 μm and a heated wick area of 2 mm × 2 mm, the phase change reached a maximum heat flux of 1130 W/cm2. Despite of the liquid bottom-feed approach, interactions between liquid and vapor phases enables the heated wick structure absorb liquid from its surrounding wick area, including from its top side with a longer liquid transport path. In contrast, a wick structure with fine pillars (10 μm in diameter) inhibited the generation of nucleate boiling. Evaporation on the meniscus interface becomes the major phase change mechanism. A large heated wick area (4 mm × 4 mm) increases the viscous loss in transporting liquid to wet the entire wick, advancing the dryout at 135 W/cm2. Mass transfer analysis, as well as discussion of the experimental results, indicates that a dimensional ratio r/l (pillar diameter/characteristic length of the heated wick area) is a key parameter in determining the maximum phase change capability. A low r/l ratio enhances heat and mass transport capability, as well as heat transfer coefficient.

A new non-resonant-type piezoelectric actuator with unlimited stroke was proposed, in which two transducers operated in hybrid bending modes were used to generate the desired displacements with micrometer scale. Compared with the PZT stack, both positive and negative dc voltages can be applied on the PZT elements to achieve large displacement. The vertical bending movement was used to control the contact state between the foot and the runner, whereas the runner was pushed by the horizontal bending movement. The operating principle of the stepping-wriggle driving was discussed. The motion planning of the bending transducers with eight steps was developed. The duty ratios and the phase difference of the two signals applied on the vertical PZT elements were 1/3 and 180°, respectively, which insured the reliable positioning of the runner. Excitation voltages with different rise times were applied on the PZT elements to discover its effects on the responses of the bending movements by a transient analysis. It was found that the transducer cost about 2 ms to reach the steady state, in spite of the difference of the rise times, but the rise time showed a significant effect on the oscillation amplitude of the bending motion. The motion trajectories of the driving tip were nearly rectangles with horizontal and vertical steady displacements of $\sim 6.10$ and 5.52 $\mu \text{m}$ , respectively. This paper can provide the guidance for the design of non-resonant-type piezoelectric actuator by bending modes.

We demonstrate the back-end integration of optically broadband, high-NA GaN micro-lenses by micro-assembly onto non-native semiconductor substrates. We developed a highly parallel process flow to fabricate and suspend micron scale plano-convex lens platelets from 6" Si growth wafers and show their subsequent transfer-printing integration. A growth process targeted at producing unbowed epitaxial wafers was combined with optimisation of the etching volume in order to produce flat devices for printing. Lens structures were fabricated with 6 − 11 µm diameter, 2 µm height and root-mean-squared surface roughness below 2 nm. The lenses were printed in a vertically coupled geometry on a single crystalline diamond substrate and with µm-precise placement on a horizontally coupled photonic integrated circuit waveguide facet. Optical performance analysis shows that these lenses could be used to couple to diamond nitrogen vacancy centres at micron scale depths and demonstrates their potential for visible to infrared light-coupling applications.

In this paper we presented the synthesis of TEOS with photoresist in order to use it like a hybrid material for 3D printer on the micrometer scale by means of the two-photon polymerization process, in which two photon are absorbed simultaneously by the material using an ultrafast laser causing its polymerization. We analyzed the mix of TEOS and photoresist with UV-VIS and FTIR spectrometers, checking that complies with two important conditions: has an optical transmission at 780 nm and absorbs at 390 nm. Finally we fabricated micro-structures with a new hybrid material; TEOS does not absorb the laser in this system and does not interfere with the formation of a three-dimensional structure. After formation the 3D microstructure, samples were heated to form the SiO. These samples of microstructures were observed under digital microscope and SEM.

In a heat pipe, operating fluid saturates wick structures system and establishes a capillary-driven circulation loop for heat transfer. Thus, the thermophysical properties of the operating fluid inevitably impact the transitions of phase-change mode and the capability of heat transfer, which determine both the design and development of the associated heat pipe systems. This article investigates the effect of liquid properties on phase-change heat transfer. Two different copper wick structures, cubic and cylindrical in cross section, 340 μm in height and 150 μm in diameter or width, are fabricated using an electroplating technique. The phase-change phenomena inside these wick structures are observed at various heat fluxes. The corresponding heat transfer characteristics are measured for three different working liquids: water, ethanol, and Novec 7200. Three distinct modes of the phase-change process are identified: (1) evaporation on liquid–vapor interface, (2) nucleate boiling with interfacial evaporation, and (3) boiling enhanced interface evaporation. Transitions between the three modes depend on heat flux and liquid properties. In addition to the mode transition, liquid properties also dictate the maximum heat flux and the heat transfer coefficient. A quantitative characterization shows that the maximum heat flux scales with Merit number, a dimensionless number connecting liquid density, surface tension, latent heat of vaporization, and viscosity. The heat transfer coefficient, on the other hand, is dictated by the thermal conductivity of the liquid. A complex interaction between the mode transition and liquid properties is reflected in Novec 7200. In spite of having the lowest thermal conductivity among the three liquids, an early transition to the mode of the boiling enhanced interface evaporation leads to a higher heat transfer coefficient at low heat flux.

Improving the light output power of GaN-based light-emitting diodes through the use of SiO2 cones

An investigation of the dynamic behaviour of a silicon microcalorimeter

The mapping of cellular traction forces is crucial to understanding the means by which cells regulate their physiological function. Polymeric micropillar arrays have been used for measuring cellular traction force. However, the field-of-view of existing measurement methods is limited and the biocompatibility of micropillar arrays needs to be further improved. Since the submicron scale deflection of pillars is typically measured with a 60x objective lens, the field-of-view is limited, ensuring that only a few cells can be imaged at a time, thereby reducing the measurement efficiency. To realize high-throughput cellular force mapping of multiple cells in a large field-of-view, a cell force measurement method was studied based on MEMS-based micropillar arrays. The force-displacement relationship of micropillar was achieved from analytic model and numerical simulation. The micropillar arrays were designed, fabricated and activated to yield force measurement resolution on the scale of nano newton and more in-vivo like microenvironment. The resulting PDMS micropillar was 2 μm in diameter and 6 μm in height. For high throughput cell force mapping, double-sided micropillar arrays and the measuring system based on moiré effect were designed and validated. The double-sided micropillar arrays (DMA) integrate two independent micropillar arrays into a single sensor. Cells were seeded on the top side of the DMA, where they spread, contract and distort pillars under the cell body. The micropillars on the opposite side serve as a reference grating which enables the generation of a two-dimensional moiré pattern with the deflected pillars on the top side upon laser illumination through the DMA. When micropillars on the cell culture side are deflected due to cell contraction, the distorted moiré fringes are readily seen. The cells cultured on DMA may be analyzed using both conventional microscopy and moiré-based force mapping. Compared to the moiré-based method using two independent substrates, the use of DMA precludes the need for precise alignment of two independent samples, simplifying the system and improving moiré pattern contrast. From the force map, it is clear that the maximum force was generated in the center of the cell, near the nucleus, with a force value of approximately 40 nN. Compared to the pillars in the center of the cell, the pillars under lamellipodia were not deflected, though some pillars were entirely involved in the cytoskeleton. The resulting force maps were consistent with the force mapping results using conventional microscopy image analyses, enabling the real-time acquisition of cell force maps from a larger field-of-view. Using optical microscopy and confocal microscopy, cell force measurements were conducted and the image analysis method was discussed. Cell force of human hepatic stellate cell line (LX-2) in their activated status was quantified, which will aid disease study and drug screen related to liver fibrosis. Also the 3 days cell culture on the micropillar arrays indicates that the micropillar arrays was biocompatible.

In this investigation, testes of 20 donkeys ranging from birth to maturity were studied. The postnatal morphologic and morphometric characteristics of donkey’s seminiferous epithelium during the postnatal period were studied. The volume percentage of the tubular compartment (Seminiferous tubules) was about 12.76% in neonates, progressively increased with postnatal age, reaching about 78.42% of the testicular parenchyma in mature donkeys. The seminiferous tubules measured about 205 μm in diameter, and their lining epithelium was about 73.7 μm in height in mature animals. The supporting (Sertoli) and germ cells (gonocytes) were the main components of the seminiferous cord or (tubules). The supporting type gradually decreased in number from neonates through suckling to the premature and mature stages, while they started to acquire the morphological characteristics of mature cells in late suckling period. The gonocytes maintained the same morphological characteristics during the neonatal and suckling periods; however, they showed a slight increase in number during the latter stage. In addition, dividing germ cells were frequently observed. The germ cells were mostly demonstrated in a central position within the testicular cords of neonatal donkeys. In suckling animals, some gonocytes started to contact the basement membrane, whereas in late suckling period, most of germ cells in contact with basement membrane. In premature donkeys, the gonocytes arranged in 2-3 layers between the supporting cells. In addition, the lumination of the seminiferous cords occurred in 1.5 year. The germ cells could be distinguished to spermatogonia, and primary, as well as secondary spermatocytes. Spermatids, at different stages of transformation, were also detected within some seminiferous tubules. In adults, the semniferous cords became more coiled and were totally luminated. All kinds of germ cells could be observed within the seminiferous epithelium, representing the complete seminiferous cycle and spermatogenesis is completed by 2 years of age. The present study provides baseline information for further experiment or quantitative studies exploring normal development of the testis and hormonal regulation of Sertoli cells, spermatogonial stem cells and spermatogenesis in donkey and other related species.

This paper presents the synthesis and evaluation of a carbon molecular sieve membrane (CMSM) grown inside a MEMS-fabricated μ-preconcentrator for sampling highly volatile organic compounds. An array of µ-pillars measuring 100 µm in diameter and 250 µm in height were fabricated inside a microfluidic channel to increase the attaching surface for the CMSM. The surface area of the CMSM was measured as high as 899 m2/g. A GC peak amplification factor &gt;2 × 104 was demonstrated with gaseous ethyl acetate. Up to 1.4 L of gaseous ethanol at the 100 ppb level could be concentrated without exceeding the capacity of this microchip device. Sharp desorption chromatographic peaks (&lt;3.5 s) were obtained while using this device directly as a GC injector. Less volatile compounds such as gaseous toluene, m-xylene, and mesitylene appeared to be adsorbed strongly on CMSM, showing a memory effect. Sampling parameters such as sample volatilities, sampling capacities, and compound residual issues were empirically determined and discussed.