Reinforcement effectiveness on mechanical performances of composites obtained by powder bed fusion

New material formulations to be used in Additive Manufacturing machines are one of the major interests in this fast growing field. The possibility to tune functional and mechanical properties, by the addition of reinforcements to a polymeric matrix, is hindered by the low provisional capability of the additive manufactured composite. The inherent anisotropy of layer manufacturing combines with mechanisms of filler dispersion and of filler/matrix adhesion in a complex scenario. The paper entails a critical evaluation of mechanical properties measured for several polymeric composites produced by Powder Bed Fusion, in the perspective of provisional models commonly accepted for composite materials. The models are reviewed versus experimental and literature data. The provisional effectiveness is generally good, except for the case of nanometric or surface treated fillers, or of specific anisotropic microstructures obtained by layer manufacturing

Repercussions of powder contamination on the fatigue life of additive manufactured maraging steel

A wide range of materials is suitable for processing by powder bed fusion (PBF) techniques. Among the latest formulations, maraging steel 18Ni-300, which is a martensite-hardenable alloy, is often used when both high fracture toughness and high strength are required, or if dimensional changes need to be minimised. In direct tooling, 18Ni-300 can be successfully employed in numerous applications, for example in the production of dies for injection moulding and for casting of aluminium alloys; moreover, it is particularly valuable for high-performance engineering parts. Even though bibliographic data are available on the effects that parameters, employed in PBF processes, have on the obtained density, roughness, hardness and microstructure of 18Ni-300, there is still a lack of knowledge on the fatigue life of PBF manufactured parts. This paper describes the fatigue behaviour of 18Ni-300 steel manufactured by PBF, as compared by forging. Relevant negative effects of the cross-contamination of the raw material are originally identified in this paper, which emphasizes the inadequacy of current acceptability protocols for PBF powders. In the absence of contamination, endurance achieved by PBF is found equal to that by forging and consistent with tooling requirements as set out by industrial partners, based on injection moulding process modelling

ANALYST RELUCTANCE IN CONVEYING NEGATIVE INFORMATION TO THE MARKET

This paper investigates one of the main sources of financial markets’ public information: financial analysts’ reports. We analyze reports on S&P 500 index through a multidisciplinary approach integrating behavioral finance with linguistic analysis to understand how financial phenomena reflect in or are deviated by language, i.e. whether financial and linguistic trends follow the same patterns, boosting each other, or diverge. In the latter, language could conceal financial events, mitigating analysts’ feelings and misleading investors. Therefore, we attempt to identify behavioral biases (mainly represented by cognitive dissonances) present in analysts’ reports. In doing so, we try to understand whether analysts try to hide perception of negative price-sensitive events or not, eventually anticipating and controlling the market “mood”. The study focuses on how analysts use linguistic strategies in order to minimize their risk of issuing wrong advice. Our preliminary results show reluctance to incorporate negative information in the reports. A slight asymmetry between the use of positive/negative keywords taken into account and the negative/positive trends of the index seems to emerge. In those weeks characterized by the index poor performances, the frequency of keywords with a negative meaning is lower. On the contrary, in the recovering weeks a higher use of keywords with a positive meaning does not clearly appear. A thorough investigation on the market moods, and the analysis of the text of the reports enable us to assess if and to what extent analysts have been willing to mitigate pessimism or emphasize confidence. Furthermore, we contribute to the existing literature also proposing a possible analysts’ value function based on the Prospect Theory [Kahneman and Tversky, 1979] where analysts try to maximize the value deriving from enhancing their reputation, taking into account the risks that may cause a reputational loss. This theoretical framework supports our preliminary findings and supports the idea that analysts are risk-averse when facing reputational gains and risk-seeking in case of potential reputational losses

VEGF188 promotes corneal reinnervation after injury

Vascular endothelial growth factor A (VEGF) induces angiogenesis and vascular hyperpermeability in ocular tissues and is therefore a key therapeutic target for eye conditions in which these processes are dysregulated. In contrast, the therapeutic potential of VEGF's neurotrophic roles in the eye has remained unexploited. In particular, it is not known whether modulating levels of any of the 3 major alternatively spliced VEGF isoforms might provide a therapeutic approach to promote neural health in the eye without inducing vascular pathology. Here, we have used a variety of mouse models to demonstrate differences in overall VEGF levels and VEGF isoform ratios across tissues in the healthy eye. We further show that VEGF isoform expression was differentially regulated in retinal versus corneal disease models. Among the 3 major isoforms - termed VEGF120, VEGF164, and VEGF188 - VEGF188 was upregulated to the greatest extent in injured cornea, where it was both necessary and sufficient for corneal nerve regeneration. Moreover, topical VEGF188 application further promoted corneal nerve regeneration without inducing pathological neovascularization. VEGF isoform modulation should therefore be explored further for its potential in promoting neural health in the eye

Technological Feasibility of Lattice Materials by Laser-Based Powder Bed Fusion of A357.0

Lattice materials represent one of the utmost applications of additive manufacturing. The promising synergy between additive processes and topology optimization finds full development in achieving components that comprise bulky and hollow areas, as well as intermediate zones. Yet, the potential to design innovative shapes can be hindered by technological limits. The article tackles the manufacturability by laser-based powder bed fusion (L-PBF) of aluminum-based lattice materials by varying the beam diameter and thus the relative density. The printing accuracy is evaluated against the distinctive building phenomena in L-PBF of metals. The main finding consists in identification of a feasibility window that can be used for development of lightweight industrial components. A relative density of 20% compared with fully solid material (aluminum alloy A357.0) is found as the lowest boundary for a 3-mm cell dimension for a body-centered cubic structure with struts along the cube edges (BCCXYZ) and built with the vertical edges parallel to the growth direction to account for the worst-case scenario. Lighter structures of this kind, even if theoretically compliant with technical specifications of the machine, result in unstable frameworks

Efficacy of a Copper-Calcium-Hydroxide Solution in Reducing Microbial Plaque on Orthodontic Clear Aligners: A Case Report

The aim of this study was to investigate the ability of a copper-calcium-hydroxide-based compound to remove microbial plaque naturally produced onto orthodontic clear aligners. A commercially available dental paste, named Cupral, based on copper-calcium-hydroxide, was used. A healthy volunteer (female, 32 years old), undergoing orthodontic treatment with thermoplastic clear aligners was enrolled. By conventional/confocal microscopy and colony-forming unit (CFU) assay, 2-week used aligners were examined for microbial plaque, prior and following exposure to Cupral. Confocal microscopy revealed abundant plaque irregularly distributed onto the aligner surface. Following Cupral treatment, a drastic decrease occurred in plaque thickness and matrix presence. As assessed by the CFU assay, total microbial load approached 10 9 CFUs/aligner, with slight differences in aerobiosis and anaerobiosis culture conditions; six macroscopically different types of colonies were detected and identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Following Cupral treatment, microbial load dropped to undetectable levels, irrespectively of the conditions considered. Exposure of clear aligners to Cupral results in the elimination of contaminating microorganisms; the antimicrobial activity is retained up to 1.25% concentration. Overall, our data describe a novel use of Cupral, a copper-calcium-hydroxide-based compound, in daily hygiene practices with promising results

Beads for Cell Immobilization: Comparison of Alternative Additive Manufacturing Techniques

The attachment or entrapment of microbial cells and enzymes are promising solutions for various industrial applications. When the traps are beads, they are dispersed in a fluidized bed in a vessel where a pump guarantees fresh liquid inflow and waste outflow without washing out the cells. Scientific papers report numerous types of cell entrapment, but most of their applications remain at the laboratory level. In the present research, rigid polymer beads were manufactured by two different additive manufacturing (AM) techniques in order to verify the economy, reusability, and stability of the traps, with a view toward a straightforward industrial application. The proposed solutions allowed for overcoming some of the drawbacks of traditional manufacturing solutions, such as the limited mechanical stability of gel traps, and they guaranteed the possibility of producing parts of constant quality with purposely designed exchange surfaces, which are unfeasible when using conventional processes. AM proved to be a viable manufacturing solution for beads with complex shapes of two different size ranges. A deep insight into the production and characteristics of beads manufactured by AM is provided. The paper provides biotechnologists with a manufacturing perspective, and the results can be directly applied to transit from the laboratory to the industrial scale