Microstructure, mechanical properties, and retentive forces of cobalt-chromium removable partial denture frameworks fabricated by selective laser melting followed by heat treatment.

STATEMENT OF PROBLEM: The effect of heat treatment on the microstructure and mechanical properties of cobalt-chromium (Co-Cr) removable partial denture (RPD) frameworks fabricated by selective laser melting (SLM) is not well understood. PURPOSE: The purpose of this in vitro study was to evaluate the suitability of SLM-fabricated Co-Cr alloys followed by heat treatment as a framework for RPDs by determining the microstructure and mechanical properties. MATERIAL AND METHODS: Dumbbell specimens and RPD frameworks were fabricated by using SLM followed by heat treatment. The effects of the heat treatment on the microstructure were studied by using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Tensile and insertion and removal tests were performed to study the mechanical responses of selective laser melting followed by heat treatment specimens, including the ultimate tensile strength (UTS), 0.2% yield strength (0.2% YS), elongation (E), and retentive forces. Specimens fabricated by using the traditional lost-wax process were used as a control (casting) group. RESULTS: X-ray diffraction indicated that the γ-face-centered cubic phase dominated SLM and selective laser melting followed by heat treatment specimens. Results from optical microscopy and SEM showed microstructural changes under different fabrication and postprocessing heat treatments; it was difficult to observe the grain boundary in the SLM group, whereas submicrometer-scale grains had formed in the selective laser melting followed by heat treatment group. The selective laser melting followed by heat treatment group exhibited the highest elongation and retentive forces compared with the casting and SLM groups. CONCLUSIONS: SLM increased the mechanical properties of Co-Cr alloys. Postprocessing heat treatment further enhanced the tensile ductility. It is suggested that SLM followed by heat treatment is an efficient strategy for fabricating RPD frameworks.

An innovative modulating functions method for pseudo-state estimation of fractional order systems.

In this paper, the objective is to estimate the pseudo-state of fractional order systems defined by the Caputo fractional derivative from discrete noisy output measurement. For this purpose, an innovative modulating functions method is proposed, which can provide non-asymptotic estimation within finite-time and is robust against corrupting noises. First, the proposed method is directly applied to the Brunovsky's observable canonical form of the considered system. Then, the initial value of the pseudo-state is exactly expressed by an algebraic integral formula, based on which the pseudo-state is estimated. Second, the properties and construction of the required modulating functions are studied. Furthermore, error analysis is provided in discrete noise cases, which is useful for improving the estimation accuracy. In order to show the advantages of the proposed method, two numerical examples are given, where both rational order and irrational order dynamical systems are considered. After selecting the design parameters using the provided noise error bound, the pseudo-states of considered systems are estimated. The fractional order Luenberger-like observer and the fractional order H∞-like observer are also applied. Better than the applied fractional order observers, the proposed method can guarantee the convergence speed and robustness at the same time.

Directionally-Dependent Mechanical Properties of Ti6Al4V Manufactured by Electron Beam Melting (EBM) and Selective Laser Melting (SLM).

An investigation of mechanical properties of Ti6Al4V produced by additive manufacturing (AM) in the as-printed condition have been conducted and compared with wrought alloys. The AM samples were built by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) in 0°, 45° and 90°-relative to horizontal direction. Similarly, the wrought samples were also cut and tested in the same directions relative to the plate rolling direction. The microstructures of the samples were significantly different on all samples. α' martensite was observed on the SLM, acicular α on EBM and combination of both on the wrought alloy. EBM samples had higher surface roughness (Ra) compared with both SLM and wrought alloy. SLM samples were comparatively harder than wrought alloy and EBM. Tensile strength of the wrought alloy was higher in all directions except for 45°, where SLM samples showed higher strength than both EBM and wrought alloy on that direction. The ductility of the wrought alloy was consistently higher than both SLM and EBM indicated by clear necking feature on the wrought alloy samples. Dimples were observed on all fracture surfaces.

Spherical Composite Powder by Coupling Polymethyl Methacrylate and Boron Nitride via Spray Drying for Cosmetic Application.

In the present study, spherical composite powder was successfully prepared via spray drying process using polymethyl methacrylate (PMMA) and hexagonal boron nitride (h-BN) powders. The pristine and as-prepared composite powders were examined using scanning electron microscopy, a particle size analyzer, oil absorption, and specific surface area analyses. These powders were then mixed with linseed oil to prepare samples for UV-Visible-Near Infrared spectroscopy investigation to determine their light absorption ability. Blank and powder-added blemish balm creams were examined using a sun protection factor tester and a thermal conductivity tester. In addition, transmittances of these creams were also evaluated. The experimental results show that spray-dried spherical composite powder exhibited good oil absorption ability. The blemish balm cream with 10 wt.% spray-dried composite powder not only exhibited superior sunscreen protection ability, but also good thermal conductivity.

A comprehensive review of recent developments in 3D printing technique for ceramic membrane fabrication for water purification.

Additive manufacturing (AM), which is also commonly known as 3D printing, provides flexibility in the manufacturing of complex geometric parts at competitive prices and within a low production time. However, AM has not been used to a large extent in filtration and water treatment processes. AM results in the creation of millions of nanofibers that are sublayered on top of each other and compressed into a thin membrane. AM is a novel technique for fabricating filtration membranes with different shapes, sizes and controlled porosity, which cannot be achieved using conventional process such as electrospinning and knife casting. In this paper, we review the advantages and limitations of AM processes for fabricating ceramic membranes. Moreover, a brief background of AM processes is provided, and their future prospects are examined. Due to their potential benefits for fabrication and flexibility with different materials, AM methods are promising in the field of membrane engineering.

Characteristics of Plantar Pressures and Related Pain Profiles in Elite Sprinters and Recreational Runners.

BACKGROUND: Plantar pressure measurement is effective for assessing plantar loading and can be applied to evaluating foot performance. We sought to explore the characteristics of plantar pressures in elite sprinters and recreational runners during static standing and walking. METHODS: Arch index (AI) values, regional plantar pressure distributions (PPDs), and footprint characteristics were examined in 80 elite sprinters and 90 recreational runners using an optical plantar pressure measurement system. Elite sprinters' pain profiles were examined to evaluate their most common pain areas. RESULTS: In recreational runners, AI values in males were in the normal range and in females were high arch type. The AI values were significantly lower in elite sprinters than in recreational runners. In elite sprinters, particularly males, the static PPD of both feet was higher at the medial metatarsal bone and the lateral heel and lower at the medial and lateral longitudinal arches. Elite male sprinters' PPD of both feet was mainly transferred to the medial metatarsal bone and decreased at the lateral longitudinal arch and the medial heel during the midstance phase of walking. The lateral knee joint and biceps femoris were the most common sites of musculoskeletal pain in elite sprinters. CONCLUSIONS: Elite sprinters' AI values could be classified as high arches, and their PPD tended to parallel the features of runners and high-arched runners. These findings correspond to the profile of patellofemoral pain syndrome (PFPS)-related plantar pressure. The pain profiles seemed to resonate with the symptoms of high-arched runners and PFPS. A possible link between high-arched runners and PFPS warrants further study.

A rare case of pneumocephalus and pneumorrhachis after epidural anesthesia.

Both pneumocephalus and pneumorrhachis are rare but serious complications following epidural anesthesia. We report a rare case of simultaneous pneumocephalus and pneumorrhachis in a patient after undergoing epidural anesthesia. The patient lost consciousness and received emergent external ventricular drainage for pneumocephalus in another medical center. The patient was clear after external ventricular drain placement until 4 days later, when sudden onset of subdural hemorrhage occurred and an emergent craniectomy was performed. The patient passed away 2 days after craniectomy, due to multiorgan failure. Pneumocephalus with or without pneumorrhachis should be kept in mind when there is a sudden change of consciousness or persistent convulsions after epidural anesthesia.