Microstructure and Reliability Comparison of Different Pb-Free Alloys Used for Wave Soldering and Rework

This paper describes the results of an intensive microstructural and reliability study of pin-through-hole (PTH) and surface mount technology (SMT) components which were wave solder assembled using three groups of alloys: (1) near-eutectic Sn-Ag-Cu alloys such as SAC405 and SAC305, (2) low-Ag off-eutectic Pb-free alloys with an Ag content of about 1% and lower, and (3) eutectic Sn-Cu alloys with Ni and other additives. Both primary attach and reworked solder connections using solder fountain and hand rework were studied. The PTH connector types and SMT components were wave solder assembled on a test vehicle. Accelerated thermal cycling (ATC) was conducted at 0°C to 100°C for 6000 cycles. The difference in microstructures, intermetallic formation, Cu dissolution, grain coarsening, and crack formation is shown. The influence of the microstructure after assembly and rework on Weibull plot parameters and failure modes is described for 2512 resistors. Interconnect defects such as nonuniform phase distribution and void formation are discussed. The Sn-Cu-Ni- and Sn-Cu-Ag-Bi-based alloys tested in this study are recommended as potential suitable replacements for SAC305/405 in the wave solder process; no failure was detected up to 6000 cycles at 0°C to 100°C. Although SAC405 demonstrated better barrel fill and lower rate of crack propagation during ATC, after PTH rework, both of the alternative Pb-free alloys have a much lower Cu dissolution rate and definitely outperform SAC405 in ATC. SAC405 glue and wave resistors after primary attachment and rework demonstrate higher reliability than alternative alloys. Early failures relate to alternative alloy characteristics and should be considered for some applications.     

Molecular Drivers of Developmental Arrest in the Human Preimplantation Embryo: A Systematic Review and Critical Analysis Leading to Mapping Future Research

Developmental arrest of the preimplantation embryo is a multifactorial condition, characterized by lack of cellular division for at least 24 hours, hindering the in vitro fertilization cycle outcome. This systematic review aims to present the molecular drivers of developmental arrest, focusing on embryonic and parental factors. A systematic search in PubMed/Medline, Embase and Cochrane-Central-Database was performed in January 2021. A total of 76 studies were included. The identified embryonic factors associated with arrest included gene variations, mitochondrial DNA copy number, methylation patterns, chromosomal abnormalities, metabolic profile and morphological features. Parental factors included, gene variation, protein expression levels and infertility etiology. A valuable conclusion emerging through critical analysis indicated that genetic origins of developmental arrest analyzed from the perspective of parental infertility etiology and the embryo itself, share common ground. This is a unique and long-overdue contribution to literature that for the first time presents an all-inclusive methodological report on the molecular drivers leading to preimplantation embryos’ arrested development. The variety and heterogeneity of developmental arrest drivers, along with their inevitable intertwining relationships does not allow for prioritization on the factors playing a more definitive role in arrested development. This systematic review provides the basis for further research in the field.     

Novel method for the preparation of Cs-containing FAU(Y) catalysts for aniline methylation

Cs-containing FAU(Y)-type zeolite catalysts were prepared by conventional and novel ion exchange procedures followed by incipient wetness impregnation with CsOH. The novel ion exchange procedure involved hydrothermal treatment of NaY zeolite in aqueous solution of CsCl at 140–200 °C for 6–24 h. The samples were characterized by low-temperature nitrogen adsorption, X-ray fluorescence analysis, X-ray powder diffraction, scanning electron microscopy, ²³Na, ²⁷Al and ¹³³Cs magic angle spinning nuclear magnetic resonance, CO₂ and NH₃-Temperature programmed desorption. The results show that hydrothermal treatment at 200 °C allows to obtain higher degrees of ion-exchange (up to 83%) with respect to conventional method giving maximum 66%–69%. Catalytic properties of Cs-containing FAU(Y) were studied in aniline methylation. The yield of N-methylaniline is shown to correlate with catalyst’s basicity. The best catalyst performance was achieved over the catalyst with the highest ion-exchange degree impregnated with CsOH. The selectivity to N-methylaniline over this catalyst reached 96.4%.

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New Frontiers in Peripheral Nerve Regeneration: Concerns and Remedies

Topical advances in studying molecular and cellular mechanisms responsible for regeneration in the peripheral nervous system have highlighted the ability of the nervous system to repair itself. Still, serious injuries represent a challenge for the morphological and functional regeneration of peripheral nerves, calling for new treatment strategies that maximize nerve regeneration and recovery. This review presents the canonical view of the basic mechanisms of nerve regeneration and novel data on the role of exosomes and their transferred microRNAs in intracellular communication, regulation of axonal growth, Schwann cell migration and proliferation, and stromal cell functioning. An integrated comprehensive understanding of the current mechanistic underpinnings will open the venue for developing new clinical strategies to ensure full regeneration in the peripheral nervous system.     

Effects of Microvesicles Derived from NK Cells Stimulated with IL-1β on the Phenotype and Functional Activity of Endothelial Cells

Microvesicles (MVs) are plasma extracellular vesicles ranging from 100 (150) to 1000 nm in diameter. These are generally produced by different cells through their vital activity and are a source of various protein and non-protein molecules. It is assumed that MVs can mediate intercellular communication and modulate cell functions. The interaction between natural killer cells (NK cells) and endothelial cells underlies multiple pathological conditions. The ability of MVs derived from NK cells to influence the functional state of endothelial cells in inflammatory conditions has yet to be studied well. In this regard, we aimed to study the effects of MVs derived from NK cells of the NK-92 cell line stimulated with IL-1β on the phenotype, caspase activity, proliferation and migration of endothelial cells of the EA.hy926 cell line. Endothelial cells were cultured with MVs derived from cells of the NK-92 cell line after their stimulation with IL-1β. Using flow cytometry, we evaluated changes in the expression of endothelial cell surface molecules and endothelial cell death. We evaluated the effect of MVs derived from stimulated NK cells on the proliferative and migratory activity of endothelial cells, as well as the activation of caspase-3 and caspase-9 therein. It was established that the incubation of endothelial cells with MVs derived from cells of the NK-92 cell line stimulated with IL-1β and with MVs derived from unstimulated NK cells, leads to the decrease in the proliferative activity of endothelial cells, appearance of the pan leukocyte marker CD45 on them, caspase-3 activation and partial endothelial cell death, and reduced CD105 expression. However, compared with MVs derived from unstimulated NK cells, a more pronounced effect of MVs derived from cells of the NK-92 cell line stimulated with IL-1β was found in relation to the decrease in the endothelial cell migratory activity and the intensity of the CD54 molecule expression on them. The functional activity of MVs is therefore mediated by the conditions they are produced under, as well as their internal contents.     

Testing the Role of Glutamate NMDA Receptors in Peripheral Trigeminal Nociception Implicated in Migraine Pain

The pro-nociceptive role of glutamate in the CNS in migraine pathophysiology is well established. Glutamate, released from trigeminal afferents, activates second order nociceptive neurons in the brainstem. However, the function of peripheral glutamate receptors in the trigeminovascular system suggested as the origin site for migraine pain, is less known. In the current project, we used calcium imaging and patch clamp recordings from trigeminal ganglion (TG) neurons, immunolabelling, CGRP assay and direct electrophysiological recordings from rat meningeal afferents to investigate the role of glutamate in trigeminal nociception. Glutamate, aspartate, and, to a lesser extent, NMDA under free-magnesium conditions, evoked calcium transients in a fraction of isolated TG neurons, indicating functional expression of NMDA receptors. The fraction of NMDA sensitive neurons was increased by the migraine mediator CGRP. NMDA also activated slowly desensitizing currents in 37% of TG neurons. However, neither glutamate nor NMDA changed the level of extracellular CGRP. TG neurons expressed both GluN2A and GluN2B subunits of NMDA receptors. In addition, after removal of magnesium, NMDA activated persistent spiking activity in a fraction of trigeminal nerve fibers in meninges. Thus, glutamate activates NMDA receptors in somas of TG neurons and their meningeal nerve terminals in magnesium-dependent manner. These findings suggest that peripherally released glutamate can promote excitation of meningeal afferents implicated in generation of migraine pain in conditions of inherited or acquired reduced magnesium blockage of NMDA channels and support the usage of magnesium supplements in migraine.     

Composite multilayer films based on polyelectrolytes and in situ-formed carbon nanostructures with enhanced photoluminescence and conductivity properties

We report a facile route for the fabrication of thin composite films based on polyelectrolytes and carbon nanostructures. Composite films were made by layer-by-layer assembly of polyelectrolyte multilayers utilizing embedded dextran sulfate (Dex) solution as a carbon source. Raman measurements indicate the formation of carbon nanostructures from the Dex precursor over the whole film. Formation of these nanostructures results in enhanced photoluminescence and an increase in conductivity by two orders of magnitude to about 0.055 S cm⁻¹. The latter corresponds to the level of wide-gap semiconductors, in contrast to the initial insulating polyelectrolyte film. A distinct peak of photoluminescence of the films is found in the blue region at the wavelength of 450 nm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47718.     

Magnetothermal Multiplexing for Selective Remote Control of Cell Signaling

Magnetic nanoparticles have garnered sustained research interest for their promise in biomedical applications including diagnostic imaging, triggered drug release, cancer hyperthermia, and neural stimulation. Many of these applications make use of heat dissipation by ferrite nanoparticles under alternating magnetic fields, with these fields acting as an externally administered stimulus that is either present or absent, toggling heat dissipation on and off. Here, an extension of this concept, magnetothermal multiplexing is demonstrated, in which exposure to alternating magnetic fields of differing amplitude and frequency can result in selective and independent heating of magnetic nanoparticle ensembles. The differing magnetic coercivity of these particles, empirically characterized by a custom high amplitude alternating current magnetometer, informs the systematic selection of a multiplexed material system. This work culminates in a demonstration of magnetothermal multiplexing for selective remote control of cellular signaling in vitro.     

Carbon support hydrogenation in Pd/C catalysts during reductive thermal treatment

The resistance of the Pd/C samples towards hydrogenation of the carbon support was studied in the temperature-programmed and isothermal regimes. Carbonaceous graphite-like material Sibunit was used as a carbon support. Pristine Sibunit was additionally graphitized via high temperature treatment (1900 °C) in an inert atmosphere. Both initial and graphitized supports were subjected to oxidative treatment in order to increase the amount of surface functional oxygen-containing groups. Palladium (1 wt%) was supported using an aqueous solution of H₂PdCl₄. All the samples were characterized by a low-temperature adsorption of nitrogen, transmission electron microscopy, and Raman spectroscopy. The graphitization procedure was found to decrease significantly the specific surface area of the support, while the oxidative treatment affects this parameter negligibly. Testing the Pd-containing samples in a hydrogen flow revealed the following order in accordance with amount of methane released: Pd/iSib » Pd/iSib-ox > Pd/gSib > Pd/gSib-ox.