The effect of oxygen pickup during selective laser melting on the microstructure and mechanical properties of Ti–6Al–4V lattices

Additive manufacturing techniques such as Selective Laser Melting (SLM) can produce complex shapes with relatively thin sections and fine detail. However, common materials for the process, such as Ti–6Al–4V, have microstructure and properties that are sensitive to the pickup of interstitial impurities, such as oxygen, which the material will be exposed to during the process. This problem would be especially severe for parts with thin sections, where surface effects can be more significant, and where poor properties may coincide with locally-elevated stress. Here we explore the effects of oxygen level in thin sections with the use of lattice materials (materials which can be considered to consist exclusively of near-surface material). Oxygen levels are artificially raised using repeated melting passes to result in more pickup, leading to significantly reduced ductility and hence reduced strength measured in compression. A ductile to brittle transition in strut failure mechanism is found with increasing number of melting passes, with significant modification in chemistry and crystallographic structure, despite the presence of a similar fine plate-like microstructure throughout

On the additive manufacturing, post-tensioning and testing of bi-material tensegrity structures

An investigation on the additive manufacturing and the experimental testing of 3D models of tensegrity prisms and columns is presented. An Electron Beam Melting facility (Arcam EBM S12) is employed to 3D print structures composed of tensegrity prisms endowed with rigid bases and temporary supports, which are made out of the titanium alloy Ti6Al4V. The temporary supports are removed after the additive manufacturing phase, when Spectra cross-strings are added to the 3D printed models, and a suitable state of internal prestress is applied to the structure. The experimental part of the study shows that the examined structures feature stiffening-type elastic response under large or moderately large axial strains induced by compressive loading. Such a geometrically nonlinear behavior confirms previous theoretical results available in the literature, and paves the way to the use of tensegrity prisms and columns as innovative mechanical metamaterials and smart devices

The effects of powder reuse on the mechanical response of electron beam additively manufactured Ti6Al4V parts

High cost of metal powders has increased the demand for recycling of unmelted powder in electron beam powder bed fusion additive manufacturing process. However, powder characteristics are likely to change during manufacturing, recovery and reuse. It is important to track the evolution of powder characteristics at different stages of recycling to produce components with consistent properties. The present work evaluates the changes in Ti6Al4V powder properties during manufacturing by characterising powder particles at different locations in the powder bed; recovery and reuse, through evaluating the effects of the powder recovery system and sieving for 10 build cycles. Heterogeneous powder degradation occurred during manufacturing with the particles closer to the melt zone showing higher oxygen content and thicker α laths with β phase boundaries. Most of them had a hard-sintered and agglomerated powder morphology in contrast to particles at the edges of the powder bed. Recovery and reuse resulted in a refined particle size distribution, but only marginal change in powder morphology. The increased oxygen caused a slight increase in the yield and tensile strengths of the build. The effect of powder reuse on material elongation, hardness and Charpy impact energy was negligible. The high cycle fatigue performance deteriorated with reuse due to the increased lack-of-fusion defects. This might be attributed to the voids formed in the powder bed due to decrease in the number of fine particles coupled with an increase in the number of high-aspect ratio particles

LASIK monocular en pacientes adultos con ambliopía por anisometropía

ResumenObjetivoDeterminar la eficacia y la seguridad del LASIK en el tratamiento de la ambliopía por anisometropía en pacientes adultos.MétodosSerie de casos. Estudiamos a 12 pacientes adultos ambliopes por anisometropía a los cuales se realizó LASIK monocular de nuestro servicio de Córnea y Cirugía Refractiva. Evaluamos el error refractivo pre y postoperatorio, equivalente esférico (ES), la agudeza visual sin corrección (AVSC) y la agudeza visual mejor corregida (AVMC). La agudeza visual medida por la cartilla de Snellen fue convertida a LogMAR con fines de análisis estadístico.ResultadosLa edad promedio fue de 31.92 (± 12.13) años. El ES preoperatorio promedio en el ojo tratado fue de –3.49 D (± 3.24), el ES promedio del ojo no tratado fue de 0.25 D (± 0.30). La AVSC preoperatoria fue de 1.12 (± 0.3) LogMAR y la AVMC preoperatoria fue 0.31 (± 0.1) LogMAR. El seguimiento promedio fue de 19.1 (rango 6-74) meses. El ES promedio postoperatorio disminuyó a –0.28 (± 0.48). Cinco pacientes (42%) ganaron una línea de visión, un (8%) paciente ganó 2 líneas de visión y un (8%) paciente ganó 3 líneas de visión. El resto (42%) permaneció sin cambios comparados a la AVMC preoperatoria. Se encontraron diferencias estadísticamente significativas entre la AVSC preoperatoria (1.12 [±0.3]) y la AVSC postoperatoria (0.27 [±0.1]) (p=0.002, Z-Wilcoxon) y entre la AVMC postoperatoria (0.23 [±0.12]) y la AVMC preoperatoria (0.31 [±0.1]) (p=0.014, Z-Wilcoxon). No hubo complicaciones relacionadas con la cirugía.ConclusionesLa cirugía refractiva monocular en pacientes con ambliopía por anisometropía es una opción terapéutica segura y efectiva que ofrece resultados visuales satisfactorios, preservando o incluso mejorando la AVMC preoperatoria.AbstractPurposeTo investigate the efficacy and safety of LASIK for the correction of anisometropic amblyopia in adult patients.MethodsA retrospective, case series. We found 12 amblyopic adult patients that underwent monocular LASIK for anisometropía in our Cornea and Refractive service. We evaluated the preoperative and postoperative refractive error, spherical equivalent (SE), uncorrected visual acuity (UCVA) and best corrected visual acuity (BCVA). Snellen visual acuity measurements were converted to LogMAR for statistical purposes.ResultsThe mean age was 31.92 (±12.13) years. The average preoperative SE in the treated eyes was -3.49 (±3.24), the average SE of the untreated eye was 0.25(±0.30). Preoperative UCVA was 1.12 (±0.3) and average preoperative BCVA was 0.31 (±0.1). All patients had LASIK with an average follow-up time of 19.1(6-74) months. The average postoperative SE decreased to -0.28 (±0.48). Five patients (42%) gained 1 line of vision, 1 (8%) patient gained 2 lines of vision, 1 (8%) patient gained 3 lines of vision and the rest (42%) remained unchanged compared to preoperative BCVA. Statistically significant differences were observed between the preoperative UCVA [1.12 (±0.3)] with the postoperative UCVA [0.27 (±0.1)](p=0.002, Z-Wilcoxon) and between the postoperative BCVA [0.23 (±0.12)] with the preoperative BCVA [0.31 (±0.1)] (p=0.014, Z-Wilcoxon). There were no complications related to the surgical procedures.ConclusionsMonocular refractive surgery in adult patients with anisometropic amblyopia is a safe and effective therapeutic option that offers a satisfactory visual outcome, preserving or even improving the preoperative BCVA

Biomarcadores moleculares en la predicción de sarcopenia

A lo largo de la vida se presentan diferentes cambios a nivel de composición corporal, siendo más notorios durante el proceso de envejecimiento. La sarcopenia se define como la pérdida progresiva y constante de la masa muscular magra así como la función y la fuerza del músculo esquelético. Se presenta como un proceso del envejecimiento, en el que el cuerpo experimenta un deterioro progresivo de calidad, reducción de tamaño, número de las fibras musculares, colágeno, modificación de unidad motora que se ha relacionado con el aumento de porcentaje de grasa, cambios hormonales, mecanismos inflamatorios, estrés oxidativo, ingesta de proteínas y actividad física. El envejecimiento puede ser considerado como la resistencia de varios estímulos anabólicos al músculo (sistema nervioso central [SNC], hormona del crecimiento, estrógeno, testosterona, proteína dietética, actividad física, acción de insulina) y posiblemente el desarrollo de varios procesos catabólicos naturales del mismo (inflamación subclínica, producción de citoquinas catabólicas: factor de necrosis tumoral- [TNF- -6 [IL-6], interleucina- - -1, IL- s causas de la sarcopenia todavía no se comprenden claramente, existen muchos mecanismos potenciales que han sido investigados en mayor o menor medida, como la edad, las relacionadas a la enfermedad, nutrición y actividad física. Los criterios para identificar a la sarcopenia incluye la cantidad, función muscular y el rendimiento físico, lo cual, si se llegaran a integrar biomarcadores moleculares en la evaluación clínica, el diagnóstico podría efectuarse de una manera temprana, para evitar la complicaciones asociadas a la fragilida

Methods for Rapid Pore Classification in Metal Additive Manufacturing

The additive manufacturing of metals requires optimisation to find the melting conditions that give the desired material properties. A key aspect of the optimisation is minimising the porosity that forms during the melting process. A corresponding analysis of pores of different types (e.g. lack of fusion or keyholes) is therefore desirable. Knowing that pores form under different thermal conditions allows greater insight into the optimisation process. In this work, two pore classification methods were trialled: unsupervised machine learning and defined limits. These methods were applied to 3D pore data from X-ray computed tomography and 2D pore data from micrographs. Data were collected from multiple alloys (Ti-6Al-4V, Inconel 718, Ti-5553 and Haynes 282). Machine learning was found to be the most useful for 3D pore data and defined limits for the 2D pore data; the latter worked by optimising the limits using energy densities

A synaptically connected hypothalamic magnocellular vasopressin-locus coeruleus neuronal circuit and its plasticity in response to emotional and physiological stress

The locus coeruleus (LC)-norepinephrine (NE) system modulates a range of salient brain functions, including memory and response to stress. The LC-NE system is regulated by neurochemically diverse inputs, including a range of neuropeptides such as arginine-vasopressin (AVP). Whilst the origins of many of these LC inputs, their synaptic connectivity with LC neurons, and their contribution to LC-mediated brain functions, have been well characterized, this is not the case for the AVP-LC system. Therefore, our aims were to define the types of synapses formed by AVP+ fibers with LC neurons using immunohistochemistry together with confocal and transmission electron microscopy (TEM), the origins of such inputs, using retrograde tracers, and the plasticity of the LC AVP system in response to stress and spatial learning, using the maternal separation (MS) and Morris water maze (MWM) paradigms, respectively, in rat. Confocal microscopy revealed that AVP+ fibers contacting tyrosine hydroxylase (TH)+ LC neurons were also immunopositive for vesicular glutamate transporter 2, a marker of presynaptic glutamatergic axons. TEM confirmed that AVP+ axons formed Gray type I (asymmetric) synapses with TH+ dendrites thus confirming excitatory synaptic connections between these systems. Retrograde tracing revealed that these LC AVP+ fibers originate from hypothalamic vasopressinergic magnocellular neurosecretory neurons (AVPMNNs). MS induced a significant increase in the density of LC AVP+ fibers. Finally, AVPMNN circuit upregulation by water-deprivation improved MWM performance while increased Fos expression was found in LC and efferent regions such as hippocampus and prefrontal cortex, suggesting that AVPMMN projections to LC could integrate homeostatic responses modifying neuroplasticity

Mexican oregano essential oils given in drinking water on performance, carcass traits, and meat quality of broilers

The objective of this study was to evaluate the effects of 2 Mexican oregano essential oils (MOO), from Poliomintha longiflora Gray (PLG) and Lippia berlandieri Schauer (LBS), in drinking water (DWt) on the performance, slaughter variables, and meat quality of broilers over a 40 D period of growth. A total of 180 non-sexed Ross-308 broilers (1-day-old) were randomly assigned to 3 treatments with 6 replications each (10 birds per replicate): CON = DWt control (without MOO); PLG = DWt + 400 mg/L of PLG; and LBS = DWt + 400 mg/L of LBS. The CON, PLG, and LBS broilers body weights were similar (P > 0.05) at all times. Feed intake (FI) was different by treatment (P 0.05), although WG for CON was slightly higher. In CON broilers, slaughter weight was highest (P < 0.05), but thigh yield was lowest (P < 0.05). The CON and PLG treatments were lower (P < 0.05) in thigh and leg cooking losses. The PLG treatment presented the highest values (P < 0.05) for breast-meat redness, saturation index, shear force, odor, taste, and overall sensory acceptability. The LBS was higher (P < 0.05) for breast-meat shear force, cohesiveness and resilience, but lower (P <0.05) for sensory attributes. Mexican oregano essential oils at 400 mg/L can serve as natural alternative additives in DWt to improve broiler production and meat quality