Hardening of Additive Manufactured 316L Stainless Steel by Using Bimodal Powder Containing Nanoscale Fraction

The particle size distribution significantly affects the material properties of the additively manufactured parts. In this work, the influence of bimodal powder containing nano- and micro-scale particles on microstructure and materials properties is studied. Moreover, to study the effect of the protective atmosphere, the test samples were additively manufactured from 316L stainless steel powder in argon and nitrogen. The samples fabricated from the bimodal powder demonstrate a finer subgrain structure, regardless of protective atmospheres and an increase in the Vickers microhardness, which is in accordance with the Hall-Petch relation. The porosity analysis revealed the deterioration in the quality of as-built parts due to the poor powder flowability. The surface roughness of fabricated samples was the same regardless of the powder feedstock materials used and protective atmospheres. The results suggest that the improvement of mechanical properties is achieved by adding a nano-dispersed fraction, which dramatically increases the total surface area, thereby contributing to the nitrogen absorption by the material.     

Nitinol Stents in the Femoropopliteal Artery: A Mechanical Perspective on Material,Design, and Performance

Endovascular stenting has matured into a commonly used treatment for peripheral arterial disease (PAD) due to its minimally invasive nature and associated reductions in short-term morbidity and mortality. The mechanical properties of the superelastic Nitinol alloy have played a major role in the explosion of peripheral artery stenting, with modern stents demonstrating reasonable resilience and durability. Yet in the superficial femoral and popliteal arteries, even the newest generation Nitinol stents continue to demonstrate clinical outcomes that leave significant room for improvement. Restenosis and progression of native arterial disease often lead to recurrence of symptoms and reinterventions that increase morbidity and health care expenditures. One of the main factors thought to be associated with stent failure in the femoropopliteal artery (FPA) is the unique and highly dynamic mechanical environment of the lower limb. Clinical and experimental data demonstrate that the FPA undergoes significant deformations with limb flexion. It is hypothesized that the inability of many existing stent designs to conform to these deformations likely plays a role in reconstruction failure, as repetitive movements of the leg and thigh combine with mechanical mismatch between the artery and the stent and result in mechanical damage to both the artery and the stent. In this review we will identify challenges and provide a mechanical perspective of FPA stenting, and then discuss current research directions with promise to provide a better understanding of Nitinol, specific features of stent design, and improved characterization of the biomechanical environment of the FPA to facilitate development of better stents for patients with PAD.     

Factors impacting long-term pulmonary autograft durability after the Ross procedure

Objective

Although the Ross procedure provides excellent long-term survival and a high quality of life, its use has been limited to relatively few centers. In this study, we evaluated long-term Ross procedure results in adults to assess the predictors of pulmonary autograft durability.

Exceptionally strong easterly wind burst stalling El Ni?o of 2014

Intraseasonal wind bursts in the tropical Pacific are believed to affect the evolution and diversity of El Niño events. In particular, the occurrence of two strong westerly wind bursts (WWBs) in early 2014 apparently pushed the ocean–atmosphere system toward a moderate to strong El Niño—potentially an extreme event according to some climate models. However, the event’s progression quickly stalled, and the warming remained very weak throughout the year. Here, we find that the occurrence of an unusually strong basin-wide easterly wind burst (EWB) in June was a key factor that impeded the El Niño development. It was shortly after this EWB that all major Niño indices fell rapidly to near-normal values; a modest growth resumed only later in the year. The easterly burst and the weakness of subsequent WWBs resulted in the persistence of two separate warming centers in the central and eastern equatorial Pacific, suppressing the positive Bjerknes feedback critical for El Niño. Experiments with a climate model with superimposed wind bursts support these conclusions, pointing to inherent limits in El Niño predictability. Furthermore, we show that the spatial structure of the easterly burst matches that of the observed decadal trend in wind stress in the tropical Pacific, suggesting potential links between intraseasonal wind bursts and decadal climate variations.El Niño, the warm phase of the El Niño–Southern Oscillation (ENSO), is characterized by anomalously warm water appearing in the central and eastern equatorial Pacific every 2–7 years, driven by tropical ocean–atmosphere interactions with far-reaching global impacts (recent reviews are in refs. 1–3). These interactions and El Niño development involve several important feedbacks, including the positive Bjerknes feedback [zonal wind relaxation leads to the reduction of the zonal sea surface temperature (SST) gradient and further wind relaxation] (4). Since the year 2000, there has been a shift in the observed properties of El Niño, including its magnitude, frequency, and spatial structure of temperature anomalies (5, 6). For example, El Niño events occurred more frequently than during the previous two decades, but all were weak, and none reached the extreme magnitude of the 1982 and 1997 events. Concurrently, the rise of global mean surface temperature has slowed down with the so-called global warming hiatus (7–9). The stalled development of the 2014 El Niño presents a showcase to explore the relevant connection and mechanisms of these changes.At the beginning of 2014, many in the scientific community anticipated that a moderate to strong El Niño could develop by the end of the year (10–14) (Fig. S1). In March, the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center announced an “El Niño watch” based on predictions made by dynamical and statistical models (12), attracting attention of the general public. Admittedly, these predictions encompassed large uncertainties because of the stochastic nature of the tropical climate system (15–17). In May, the National Aeronautics and Space Administration (NASA) suggested that 2014 could potentially rival the strongest on-record event of 1997/19998 (Fig. 1B), while acknowledging the large existing uncertainty (14); their projection was supported by satellite observations of strong Kelvin waves evident in sea surface height (SSH) (Fig. 2C). The spread of spring forecast plumes from some climate models, for example that of the European Centre for Medium-Range Weather Forecasts (ECMWF), included the possibility of a failed El Niño (Fig. S1) but only as a low-probability outcome involving unusual instances of weather noise. The observed development fell near the limit of these forecast possibilities after June and July, and eventually, the 2014 warm event barely qualified as El Niño (Fig. 1A).Open in a separate windowFig. 1.El Niño development in (A and C) 2014 and (B and D) 1997. (A and B) Evolution of the Niño3, Niño4, and Niño3.4 indices; the first two indices describe SST anomalies (in degrees Celsius) in the eastern and central equatorial Pacific, respectively, whereas the last index covers the region in between. (C and D) Variation in the zonal wind stress indices. These indices are obtained by averaging wind stress anomalies (in 10⁻² newtons per meter²) in the equatorial Pacific zonally and between 5 °S and 5 °N and then selecting negative (blue; easterly anomalies), positive (red; westerly anomalies), or full values (black) (Materials and Methods). The spatial averaging is intended to take into account both the magnitude and the fetch of the wind bursts. During 2014, two early year WWBs were followed by an exceptional EWB in June (highlighted by pink and blue, respectively). This easterly burst apparently led to a rapid decrease of the Niño indices (A). In contrast, the 1997 El Niño exhibited persistent westerly wind activity throughout the year. The graphs start on January 1.Open in a separate windowFig. 2.Spatiotemporal evolution of the 2014 El Niño. (A–D) Hovmöller diagrams for anomalies in (A) SST, (B) zonal wind stress, (C) SSH, and (D) surface zonal currents in the equatorial Pacific. Time goes downward. The SSH and surface velocity plots highlight the eastward propagating downwelling Kelvin waves, especially pronounced early in the year, and a strong upwelling Kelvin wave midyear. (E and F) El Niño development in 2014 (black line) compared with several historical (E) EP and (F) CP events. The diagrams show the position of the Warm Pool Eastern Edge (degrees of longitude) vs. the Niño3 SST (degrees Celsius) for different months of the year. The Warm Pool Eastern Edge is defined as the position of the 29 °C isotherm at the equator. Numbers indicate monthly averages (1, January; 2, February, etc.). The light vertical line marks the Dateline. In 2014, both the warm pool displacement and Niño3 SST anomalies were exceptionally large during May (month 5), were similar to those in 1997 and 1982 (the strongest events of the 20th century), and then, rapidly decreased by August (month 8).Open in a separate windowFig. S1.The El Niño spring forecasts of the Niño3.4 index from the European Centre for Medium-Range Weather Forecasts (ECMWF). Red lines show 50 ensemble members of the forecast plume initiated in March of 2014; the black dotted line indicates the observed Niño3.4 index. The observed development fell outside the forecast plume in June and July and remained beyond the typical forecast spread after that. Adapted from ref. 13.The question then arises as to which dynamic factors controlled the temporal and spatial development in the tropical Pacific in 2014. This warm event began with a rapid growth, such that, in early June, all major Niño indices (Materials and Methods) along the equator were nearly identical to those during the same time of 1997 (Fig. 1 A and B). A substantial warming also developed along the Peruvian coast (Fig. 3A). Then, the event’s progression slowed down or even reversed. By year end, the equatorial warming barely exceeded 1 °C, but the SST anomaly stretched uncharacteristically across the entire equatorial Pacific almost uniformly (Figs. 1A and ​and2A).2A). Accordingly, the major goal of this study is to investigate this unusual development, identify the main factors that impeded this event, and explore its broad implications.Open in a separate windowFig. 3.The June of 2014 EWB in satellite-based data. (A) The spatial structure of anomalies in surface winds (vectors; in meters per second) and SST (colors; in degrees Celsius) on June 12, 2014, when the burst was strongest. (B) Daily vs. weekly mean values of the zonal wind stress index (10⁻² newtons per meter²) for the period 1988–2014. The blue cross marks the peak value of the June of 2014 EWB. The wind stress index is defined as anomalous zonal wind stress averaged in the equatorial Pacific zonally and between 5 °S and 5 °N (Materials and Methods). Black circles are for the year 2014, red circles are for all El Niño years before 2014, and gray circles are for all other years (La Niña or neutral). Note that the June of 2014 EWB appears strongest in the satellite record for not only daily data but also, weekly averaged values, which confirms that the observations are robust.     

Cell Labeling with Magneto-Endosymbionts and the Dissection of the Subcellular Location,Fate, and Host Cell Interactions

Purpose

The purposes of this study are to characterize magneto-endosymbiont (ME) labeling of mammalian cells and to discern the subcellular fate of these living contrast agents. MEs are novel magnetic resonance imaging (MRI) contrast agents that are being used for cell tracking studies. Understanding the fate of MEs in host cells is valuable for designing in vivo cell tracking experiments.

Procedures

The ME’s surface epitopes, contrast-producing paramagnetic magnetosomal iron, and genome were studied using immunocytochemistry (ICC), Fe and MRI contrast measurements, and quantitative polymerase chain reaction (qPCR), respectively. These assays, coupled with other common assays, enabled validation of ME cell labeling and dissection of ME subcellular processing.

Results

The assays mentioned above provide qualitative and quantitative assessments of cell labeling, the subcellular localization and the fate of MEs. ICC results, with an ME-specific antibody, qualitatively shows homogenous labeling with MEs. The ferrozine assay shows that MEs have an average of 7 fg Fe/ME, ～30 % of which contributes to MRI contrast and ME-labeled MDA-MB-231 (MDA-231) cells generally have 2.4 pg Fe/cell, implying ～350 MEs/cell. Adjusting the concentration of Fe in the ME growth media reduces the concentration of non-MRI contrast-producing Fe. Results from the qPCR assay, which quantifies ME genomes in labeled cells, shows that processing of MEs begins within 24 h in MDA-231 cells. ICC results suggest this intracellular digestion of MEs occurs by the lysosomal degradation pathway. MEs coated with listeriolysin O (LLO) are able to escape the primary phagosome, but subsequently co-localize with LC3, an autophagy-associated molecule, and are processed for digestion. In embryos, where autophagy is transiently suppressed, MEs show an increased capacity for survival and even replication. Finally, transmission electron microscopy (TEM) of ME-labeled MDA-231 cells confirms that the magnetosomes (the MRI contrast-producing particles) remain intact and enable in vivo cell tracking.

Conclusions

MEs are used to label mammalian cells for the purpose of cell tracking in vivo, with MRI. Various assays described herein (ICC, ferrozine, and qPCR) allow qualitative and quantitative assessments of labeling efficiency and provide a detailed understanding of subcellular processing of MEs. In some cell types, MEs are digested, but the MRI-producing particles remain. Coating with LLO allows MEs to escape the primary phagosome, enhances retention slightly, and confirms that MEs are ultimately processed by autophagy. Numerous intracellular bacteria and all endosymbiotically derived organelles have evolved molecular mechanisms to avoid intracellular clearance, and identification of the specific processes involved in ME clearance provides a framework on which to develop MEs with enhanced retention in mammalian cells.

     

Comparative Analysis of African Swine Fever Virus Genotypes and Serogroups

African swine fever virus (ASFV) causes highly lethal hemorrhagic disease among pigs, and ASFV’s extreme antigenic diversity hinders vaccine development. We show that p72 ASFV phylogenetic analysis does not accurately define ASFV hemadsorption inhibition assay serogroups. Thus, conventional ASFV genotyping cannot discriminate between viruses of different virulence or predict efficacy of a specific ASFV vaccine.     

Kir6.2 is required for adaptation to stress

Reaction to stress requires feedback adaptation of cellular functions to secure a response without distress, but the molecular order of this process is only partially understood. Here, we report a previously unrecognized regulatory element in the general adaptation syndrome. Kir6.2, the ion-conducting subunit of the metabolically responsive ATP-sensitive potassium (K(ATP)) channel, was mandatory for optimal adaptation capacity under stress. Genetic deletion of Kir6.2 disrupted K(ATP) channel-dependent adjustment of membrane excitability and calcium handling, compromising the enhancement of cardiac performance driven by sympathetic stimulation, a key mediator of the adaptation response. In the absence of Kir6.2, vigorous sympathetic challenge caused arrhythmia and sudden death, preventable by calcium-channel blockade. Thus, this vital function identifies a physiological role for K(ATP) channels in the heart.