Effect of alloying elements on the Sr modification of Al-Si cast alloys

Strontium-based modifier alloys are commonly adopted to modify the eutectic silicon in aluminum-silicon casting alloys by changing the silicon shape from an acicular to a spherical form. Usually, the modifier alloy necessary to properly change the silicon shape depends on the silicon content, but the alloying elements’ content may have an influence. The AlSr10 master alloy’s modifying effect was studied on four Al-Si alloys through the characterization of microstructural and mechanical properties (micro-hardness and impact tests). The experimental results obtained on gravity cast samples highlighted the interdependence in the modification of silicon between the Si content and the alloying elements. After modification, a higher microstructural homogeneity characterized by a reduction of up to 22.8% in the size of intermetallics was observed, with a generalized reduction in secondary dendritic arm spacing. The presence of iron-based polygonal-shaped intermetallics negatively affects Sr modification; coarser silicon particles tend to grow close to α-Fe. The presence of casting defects such as bifilm reduces Sr modification’s beneficial effects, and little increase in absorbed impact energy is observed in this work

Diverse effects of natural and synthetic surfactants on the inhibition of staphylococcus aureus biofilm

A major challenge in the biomedical field is the creation of materials and coating strategies that effectively limit the onset of biofilm-associated infections on medical devices. Biosurfactants are well known and appreciated for their antimicrobial/anti-adhesive/anti-biofilm properties, low toxicity, and biocompatibility. In this study, the rhamnolipid produced by Pseudomonas aeruginosa 89 (R89BS) was characterized by HPLC-MS/MS and its ability to modify cell surface hydrophobicity and membrane permeability as well as its antimicrobial, anti-adhesive, and anti-biofilm activity against Staphylococcus aureus were compared to two commonly used surfactants of synthetic origin: Tween® 80 and Triton™ X-100. The R89BS crude extract showed a grade of purity of 91.4% and was composed by 70.6% of mono-rhamnolipids and 20.8% of di-rhamnolipids. The biological activities of R89BS towards S. aureus were higher than those of the two synthetic surfactants. In particular, the anti-adhesive and anti-biofilm properties of R89BS and of its purified mono-and di-congeners were similar. R89BS inhibition of S. aureus adhesion and biofilm formation was ~97% and 85%, respectively, and resulted in an increased inhibition of about 33% after 6 h and of about 39% after 72 h when compared to their chemical counterparts. These results suggest a possible applicability of R89BS as a protective coating agent to limit implant colonization

Predictors of mortality in patients with Eisenmenger syndrome and admission to the lung transplantation waiting list

Background. Patients with Eisenmenger Syndrome (ES) have very severe irreversible pulmonary hypertension but the criteria for admitting such patients to a lung transplantation waiting list (LTWL) is not clear. Indeed it has been demonstrated that the natural survival of patients with ES is better than the survival achieved through lung transplantation: it follows that no guidelines are available for these patients' admission to an LTWL. The aim of our study was to identify possible predictors of mortality in ES patients in order to reserve admission to the LTWL solely for those patients who would otherwise have the lowest probability of survival. Methods. Since 1991, 57 patients with ES from our rehabilitative centre were admitted to the LTWL of the Division of Cardiac Surgery at San Matteo Hospital, University of Pavia. At the time of the retrospective analysis, patients were divided into a group of non-transplanted survivors (27 patients - 47% of the total) and a group who had died prior to transplantation (16 patients - 28% of the total). The 14 transplanted patients (25% of the total) were not considered in the statistical analysis, considering transplantation as an "external event". Unpaired t tests were used to compare the following factors in the survivors and in those who died: sex, "complexity" of the congenital heart disease underlying the ES, previous cardiac surgery, arterial blood gases, pulmonary function and hemodynamic parameters. Moreover, a stepwise discriminant analysis was performed in order to define a possible set of prognostic factors. Results. PaCO2 was higher in those who subsequently died (36.15±7.42 mmHg) compared with those who survived (32.5±5.33 mmHg), although this difference did not reach a statistical significance (p=0.08). Discriminant analysis defined a model in which a) complexity of the congenital heart disease, b) sex (male) and c) cardiac output were predictive of a higher risk of mortality. Conclusions. This new knowledge can be used in the decision of admission to LTWL in ES patients

In Vitro Models of Bacterial Biofilms: Innovative Tools to Improve Understanding and Treatment of Infections

Bacterial infections are a growing concern to the health care systems. Bacteria in the human body are often found embedded in a dense 3D structure, the biofilm, which makes their eradication even more challenging. Indeed, bacteria in biofilm are protected from external hazards and are more prone to develop antibiotic resistance. Moreover, biofilms are highly heterogeneous, with properties dependent on the bacteria species, the anatomic localization, and the nutrient/flow conditions. Therefore, antibiotic screening and testing would strongly benefit from reliable in vitro models of bacterial biofilms. This review article summarizes the main features of biofilms, with particular focus on parameters affecting biofilm composition and mechanical properties. Moreover, a thorough overview of the in vitro biofilm models recently developed is presented, focusing on both traditional and advanced approaches. Static, dynamic, and microcosm models are described, and their main features, advantages, and disadvantages are compared and discussed

Residual stress analysis applied to HPDC aluminium components: a case study

High-Pressure Die Casting (HPDC) is a casting process largely diffused in the aluminium foundries. By HPDC is possible to obtain aluminium castings with thin walls and high specific mechanical properties in short cycle times. Aluminium HPDC castings are commonly intended for the automotive sector: engine, covers, engine blocks and more in general the powertrain. In recent years, one of the most important focus in the automotive sector is decreasing the powertrain weight, acting on stock allowances in certain parts of the casting. This reduction can affect the dimensional features and in turn the residual stress inside the casting. Despite that, it is possible to obtain beneficial compression states into the castings by mean of post-process operations, such as shot-blasting, to reduce or remove residual stresses by mean of heat treatments. Residual stresses can be assessed by an X-Ray residual stress measurement device, a nondestructive technique that allows observing the process parameters effect into the casting. In this work, after a detailed analysis of the residual stress measurement available for aluminium castings, a powertrain component realized in aluminium alloy EN AC 46000 was analysed. These analyses involved both dimensional response and related residual stresses in the as-cast state and the shot-blasted-state on a valve cover, to understand and prevent the residual stress states into the aluminium castings

Recent Advances in Biomedical, Therapeutic and Pharmaceutical Applications of Microbial Surfactants

The spread of antimicrobial-resistant pathogens typically existing in biofilm formation and the recent COVID-19 pandemic, although unrelated phenomena, have demonstrated the urgent need for methods to combat such increasing threats. New avenues of research for natural molecules with desirable properties to alleviate this situation have, therefore, been expanding. Biosurfactants comprise a group of unique and varied amphiphilic molecules of microbial origin capable of inter-acting with lipidic membranes/components of microorganisms and altering their physicochemical properties. These features have encouraged closer investigations of these microbial metabolites as new pharmaceutics with potential applications in clinical, hygiene and therapeutic fields. Mounting evidence has indicated that biosurfactants have antimicrobial, antibiofilm, antiviral, immunomodu-latory and antiproliferative activities that are exploitable in new anticancer treatments and wound healing applications. Some biosurfactants have already been approved for use in clinical, food and environmental fields, while others are currently under investigation and development as antimicrobials or adjuvants to antibiotics for microbial suppression and biofilm eradication strategies. Moreover, due to the COVID-19 pandemic, biosurfactants are now being explored as an alternative to current products or procedures for effective cleaning and handwash formulations, antiviral plastic and fabric surface coating agents for shields and masks. In addition, biosurfactants have shown promise as drug delivery systems and in the medicinal relief of symptoms associated with SARS-CoV-2 acute respiratory distress syndrome

The effect of sophorolipids against microbial biofilms on medical-grade silicone

Recent medical strategies rely on the search for effective antimicrobials as surface coatings to prevent and treat infections in humans and animals. Biosurfactants have recently been shown to have properties as antiadhesive and antibiofilm agents. Sophorolipids in particular are biosurfactant molecules known to act as therapeutic agents. This study aimed to evaluate antimicrobial properties of sophorolipids in medical-grade silicone discs using strains of clinical relevance. Sophorolipids were produced under fed batch conditions, ESI-MS analyses were carried out to confirm the congeners present in each formulation. Three different products were obtained SLA (acidic congeners), SL18 (lactonic congeners) and SLV (mixture of acidic and lactonic congeners) and were tested against Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 10145 and Candida albicans IHEM 2894. All three congener mixtures showed a biofilms disruption effect (> 0.1% w/v) of 70%, 75% and 80% for S. aureus, P. aeruginosa and C. albicans, respectively. On pre-coated silicone discs, biofilm formation of S. aureus was reduced by 75% using SLA 0.8% w/v. After 1.5 h the inhibition of C. albicans attachment was between 45-56% whilst after 24 h incubation the percentage of inhibition for the cell attachment increased to 68-70% when using SLA 0.8% w/v. Finally, in co-incubation experiments SLA 0.05% w/v significantly reduced the ability of S. aureus and C. albicans to form biofilms and to adhere to surfaces by 90-95% at concentrations between 0.025-0.1% w/v. In conclusion sophorolipids significantly reduced the cell attachment of both tested strains which suggests that these molecules could have a potential role as coating agents on medical grade silicone devices for the preventions of Gram positive bacteria and yeast infections