► Oxidation mechanism of pure tungsten is reviewed between 600 and 800°C. ► Low kinetics are related to initial W18O49 formation. ► Linear kinetics are due to cracking in W18O49 scale. ► Cracking ...favors formation of WO2.92. ► Model proposed for cavity development in the scale and WO3 formation on the surface.
The oxidation behavior of International Thermonuclear Experimental Reactor (ITER)-reference tungsten grade has been evaluated in dry air in the temperature range 600–800°C. At 600°C, the scale remained protective while the integrity of W18O49 layer was kept. Rapid increase in mass gain resulted from massive cracking at local areas in the W18O49 layer. Then, a coarse non-protective columnar WO2.92 scale was developed which favoured rapid inward oxygen transport into the alloy. At 700 and 800°C, growth stresses in the scale were released through local cracking. At this stage, WO2.92 became progressively transformed into WO3 when the oxygen partial pressure increased across the scale thickness.
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Absorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone in the implantation site. In this work, ...biodegradable composites formed by a polylactic acid matrix reinforced with 10%wt. magnesium microparticles were processed and their in vitro degradation investigated during 28days. A joint analysis of the amount of H2 released, the changes in pH in buffered (PBS) and non-buffered media (distilled water), the variations in mass, microstructure and the mechanical performance of the specimens was developed. The main aim was to elucidate the relevance of Mg particles shape on tailoring the degradation kinetics of these novel composites. The results show that the shape of the Mg reinforcing particles plays a crucial role in the degradation rate of PLA/Mg composites, with spherical particles promoting a lower degradation rate than irregular particles. This fact is only partially due to the smaller surface area to volume ratio of the spherical particles. Irregular particles promote a faster formation of cracks and, therefore, an increasingly faster degradation of the polymeric matrix. In every case, the amount of H2 released by the composites was well below that released by monolithic Mg. The pH of PBS during degradation remained always within 7.2 and 7.4. PLA/Mg reinforced with spherical particles retains more than 90% of its mechanical properties after 7days of immersion and more than 60% after 28days.
The increasing demand for temporary orthopaedic implants is the driving force to seek new strategies to decrease costs and simultaneously improve patients comfort as well as simplify surgical procedures. Resorbable medical devices must be developed in order to have an appropriate degradation rate in agreement with the healing rate of bone. We are presenting for the first time results of the degradation kinetics of a new material based on polylactic acid reinforced with 10%wt. Mg microparticles. This work analyzes the relevance of Mg particle shape (irregular and spherical) on tailoring the degradation behaviour of these composites. Conclusions withdrawn from this study help to customize bioabsorbable materials in order to meet the requirements for a specific application and patient.
This work deals with the mechanical characterization by depth-sensing indentation (DSI) of PLLA and PLDA composites reinforced with micro-particles of Mg (up to 15wt%), which is a challenging task ...since the indented volume must provide information of the bulk composite, i.e. contain enough reinforcement particles. The composites were fabricated by combining hot extrusion and compression moulding. Physico-chemical characterization by TGA and DSC indicates that Mg anticipates the thermal degradation of the polymers but does not compromise their stability during processing. Especial emphasis is devoted to determine the effect of strain rate and Mg content on mechanical behavior, thus important information about the visco-elastic behavior and time-dependent response of the composites is obtained. Relevant for the intended application is that Mg addition increases the elastic modulus and hardness of the polymeric matrices and induces a higher resistance to flow. The elastic modulus obtained by DSI experiments shows good agreement with that obtained by uniaxial compression tests. The results indicate that DSI experiments are a reliable method to calculate the modulus of polymeric composites reinforced with micro-particles. Taking into consideration the mechanical properties results, PLA/Mg composite could be used as substitute for biodegradable monolithic polymeric implants already in the market for orthopedics (freeform meshes, mini plates, screws, pins, …), craniomaxillofacial, or spine.
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•PLLA and PLDA composites were reinforced with micro-particles of Mg.•Mg does not compromise the polymer stability during thermoplastic processing.•Mg increases elastic modulus, hardness and resistance to flow of polymers.•Depth-sensing indentation was used to calculate their mechanical properties.•Depth sensing analysis correlates well with uniaxial compression data.
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•Time-dependent mechanical properties of PLA have been studied by DSI experiments.•Time dependence has been considered for calculating DSI properties.•Strain-rate influence on ...indentation modulus and hardness has been explored.•DSI modulus results parallel those obtained by stress–strain and DMA tests.•DSI properties dependence on the degree of crystallinity of PLA has been discussed.
Poly-L-lactic acid, PLLA, is a widely studied biomaterial, currently approved for use in a range of medical devices. Its mechanical properties can be tailored giving the material different crystallinity degrees. PLLA presents a complex non-linear behaviour that depends not only on structural parameters such as crystallinity degree but also on external parameters such as strain rate and temperature. Failure of polymeric implants is attributed to their intrinsic time-dependent performance under static loading conditions. This work explores the potential of instrumented indentation tests as a suitable technique to measure the complex non-linear time-dependent mechanical properties of PLLA. The applicability of the Oliver–Pharr method, typically used in ceramic and metallic materials, is discussed through the sensitivity of elastic modulus, hardness and material creep response to different strain rates. Likewise, the strain rate influence depending on the crystallinity degree is considered, providing important information about viscoelastic behaviour of PLLA. Whereas possible, results are compared with those obtained from tensile and Dynamic Mechanical Analysis tests extracted from the literature.
The oxidation resistance in dry air of pure tungsten and tungsten reinforced with a dispersion of 0.6wt.% Y2O3 nanoparticles has been evaluated between 873 and 1073K, temperature range that divertor ...in fusion power plants should endure during long-term times in the case of loss of coolant accident and/or air ingress in the vessel. Both materials were prepared by a powder metallurgy route involving hot isostatic pressing of ball milled tungsten powders and tungsten with dispersed Y2O3 nanoparticles. The results have been compared with those of pure tungsten processed by conventional techniques. Thermogravimetric tests at 873K revealed that the processing route as well as yttria addition considerably affected the oxidation resistance of pure tungsten. Mass gain of W–0.6Y2O3 at 873K was five and two times lower than that of pure tungsten prepared by conventional processing techniques and by powder metallurgy, respectively. This different behavior was related to changes in the structure and composition of the oxide scale. Above 873K, the kinetics were significantly accelerated for all materials due to the development of a non-protective oxide scale from the earliest oxidation stages, although the kinetics of Y2O3-containing material were still the slowest, specially at 973K. It was analyzed how yttria additions modify the oxidation mechanism of tungsten.
Researching optical effects in nanowires may require a high pump intensity which under ambient conditions can degrade nanowires due to thermal oxidation. In this work we investigated the ...photodegradation of a single Si-doped GaAs nanowire by laser heating in air. To understand the changes that occurred on the nanowire we carried out Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and photoluminescence spectroscopy in laser damaged regions as well as in non-affected ones. From Raman Stokes and anti-Stokes measurements we estimated the local temperature that the oxidation process of the nanowire (NW) surface starts at as 661 K, resulting in two new Raman modes at 200 cm
−1
and 259 cm
−1
. Scanning electron microscopy and energy dispersive X-ray spectroscopy measurements showed a significant loss of arsenic in the oxidized regions, but no erosion of the nanowire. Micro-photoluminescence measurements showed the near-band-edge emission of GaAs along the nanowire, as well as a new emission band at 755 nm corresponding to polycrystalline β-Ga
2
O
3
formation. Our results also indicate that neither amorphous As nor crystalline As were deposited on the surface of the nanowire. Combining different experimental techniques, this study showed the formation of polycrystalline β-Ga
2
O
3
by oxidation of the nanowire surface and the limits for performing spectroscopic investigations on individual GaAs NWs under ambient air conditions.
In order to comprehend the photodegradation of GaAs NWs, we investigated their thermal oxidation process in air induced by laser heating in a broad local temperature range.
This work aims to develop polymer/magnesium composites as new biodegradable and bioresorbable materials for osteosynthesis implants. The polymeric matrix will benefit from the higher strength and ...modulus of the Mg particles, whereas Mg will benefit from the surrounded protective polymeric matrix that will control its degradation rate. To provide a proof of concept a set of specimens were processed by combining solvent casting of PLLA (poly-l-lactic acid) loaded with 30wt% of Mg particles and further molding by compression. Mechanical characterization reveals that reinforcing the polymer matrix with Mg particles improves its mechanical properties (hardness up to 340MPa and yield strength up to 100MPa). Interestingly, Young's modulus determined by ultramicroindentation increases up to 8GPa. From the DSC analysis it follows that the unloaded and loaded polymer has similar crystallinity, which indicates that the improvement in mechanical properties is purely the effect of particle reinforcement.
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► We develop novel PLLA/Mg composites as biodegradable and bioresorbable materials. ► With Mg particles improves yield strength and elastic modulus of PLLA. ► Mg slightly decreases the glass transition temperature of PLLA. ► Mg does not induce crystal nucleation during cooling from the melt
Introduction
Biologics have improved the treatment of rheumatic diseases, resulting in better outcomes. However, their high cost limits access for many patients in both North America and Latin ...America. Following patent expiration for biologicals, the availability of biosimilars, which typically are less expensive due to lower development costs, provides additional treatment options for patients with rheumatic diseases. The availability of biosimilars in North American and Latin American countries is evolving, with differing regulations and clinical indications.
Objective
The objective of the study was to present the consensus statement on biosimilars in rheumatology developed by Pan American League of Associations for Rheumatology (PANLAR).
Methods
Using a modified Delphi process approach, the following topics were addressed: regulation, efficacy and safety, extrapolation of indications, interchangeability, automatic substitution, pharmacovigilance, risk management, naming, traceability, registries, economic aspects, and biomimics. Consensus was achieved when there was agreement among 80% or more of the panel members. Three Delphi rounds were conducted to reach consensus. Questionnaires were sent electronically to panel members and comments about each question were solicited.
Results
Eight recommendations were formulated regarding regulation, pharmacovigilance, risk management, naming, traceability, registries, economic aspects, and biomimics.
Conclusion
The recommendations highlighted that, after receiving regulatory approval, pharmacovigilance is a fundamental strategy to ensure safety of all medications. Registries should be employed to monitor use of biosimilars and to identify potential adverse effects. The price of biosimilars should be significantly lower than that of reference products to enhance patient access. Biomimics are not biosimilars and, if they are to be marketed, they must first be evaluated and approved according to established regulatory pathways for novel biopharmaceuticals.
Key Points
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Biologics have improved the treatment of rheumatic diseases.
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Their high cost limits access for many patients in both North America and Latin America.
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Biosimilars typically are less expensive, providing additional treatment options for patients with rheumatic diseases.
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PANLAR presents its consensus on biosimilars in rheumatology
Overweight postmenopausal women may be more susceptible to bone loss with weight reduction than previously studied obese women. The influence of energy restriction and Ca intake on BMD was assessed ...in 66 individuals. Weight reduction resulted in bone loss at several sites in women consuming 1 g Ca/day and was mitigated with higher calcium intake at 1.7 g/day.
Introduction: Bone loss is associated with weight loss in obese postmenopausal women and can be prevented with calcium (Ca) supplementation. However, because bone loss caused by weight loss may be greater in overweight than obese women, it is not clear whether Ca supplementation is also beneficial in overweight women.
Materials and Methods: We assessed the influence of caloric restriction at two levels of Ca intake on BMD and BMC in 66 overweight postmenopausal women (age, 61 ± 6 years; body mass index, 27.0 ± 1.8 kg/m2). Subjects completed either a 6‐month energy‐restricted diet (WL, n = 47) and lost 9.3 ± 3.9 % weight or maintained weight (WM; 1 g Ca/day, n = 19). Participants in the WL group were randomly assigned to either normal (1 g/day; WL NL‐Ca) or high (1.7 g/day; WL Hi‐Ca) Ca intake. Regional BMD and BMC were measured at baseline and after 6 months.
Results: During normal Ca intake, trochanter BMD and BMC and total spine BMD were decreased more in WL than WM women (p < 0.05). The WL NL‐Ca group lost more trochanter BMD (−4.2 ± 4.1%) and BMC (−4.8 ± 7.1%) than the WL Hi‐Ca group (−1.4 ± 5.6% and −1.1 ± 8.1%, respectively; p < 0.05). There were no significant changes in BMD or BMC at the femoral neck in any group. Weight loss correlated with trochanter BMD loss (r = 0.687, p < 0.001) in the WL NL‐Ca group.
Conclusion: Despite an intake of 1 g Ca/day, bone loss occurred at some sites because of weight loss. Calcium intake of 1.7 g/day will minimize bone loss during weight loss in postmenopausal overweight women.
The aim of this work was to evaluate the impact of applying genomic information in pedigree uncertainty situations on genetic evaluations for growth- and cow productivity–related traits in Nelore ...commercial herds. Records for accumulated cow productivity (ACP) and adjusted weight at 450 days of age (W450) were used, as well as genotypes of registered and commercial herd animals, genotyped with the Clarifide Nelore 3.1 panel (~29,000 SNPs). The genetic values for commercial and registered populations were estimated using different approaches that included (ssGBLUP) or did not include genomic information (BLUP), with different pedigree structures. Different scenarios were tested, varying the proportion of young animals with unknown sires (0, 25, 50, 75, and 100%), and unknown maternal grandsires (0, 25, 50, 75, and 100%). The prediction accuracies and abilities were calculated. The estimated breeding value accuracies decreased as the proportion of unknown sires and maternal grandsires increased. The genomic estimated breeding value accuracy using the ssGBLUP was higher in scenarios with a lower proportion of known pedigree when compared to the BLUP methodology. The results obtained with the ssGBLUP showed that it is possible to obtain reliable direct and indirect predictions for young animals from commercial herds without pedigree structure.
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