Sonochemical synthesis and stabilization of concentrated antimicrobial silver-chitosan nanoparticle dispersions

This work reports on a green synthetic route to produce concentrated aqueous dispersions of silver nanoparticles (AgNP) employing high-intensity ultrasound (US) and chitosan (CS) as a non-toxic reducing agent for Ag1 salts and AgNP stabilizer. The sonication simultaneously boosted the synthesis and improved the stability of the AgNP, capping them with CS. Hybrid AgNP-CS antimicrobial dispersions, stable for at least 6 months, were synthesized in a simple single step process. The use of US allowed for applying relatively mild processing temperatures (608C) and reaction time between 30 min and 3 h to obtain concentrated disper- sions of AgNP that otherwise could not be obtained even after 72 h under mechanical stirring at the same reaction conditions. Upon sonication spherical AgNP-CS with a size between 60 and 100 nm were generated, in contrast to the average diameter of 200 nm of the particles obtained by stirring. The antibacterial efficiency of the AgNP-CS hybrids was evaluated against the medically relevant pathogens Staphylococcus aureus and Escherichia coli. The US-synthesized AgNP-CS showed more than 3-fold higher antibacterial activity compared to the particles obtained under stirring, due to their higher concentration and smaller size.Postprint (author's final draft

Nanotransformation of vancomycin overcomes the intrinsic resistance of Gram-negative bacteria

The increased emergence of antibiotic-resistant bacteria is a growing public health concern, and although new drugs are constantly being sought, the pace of development is slow compared with the evolution and spread of multidrug- resistant species. In this study, we developed a novel broad-spectrum antimicrobial agent by simply transforming vancomycin into nanoform using sonochemistry. Vancomycin is a glycopeptide antibiotic largely used for the treatment of infections caused by Gram-positive bacteria but inefficient against Gram-negative species. The nanospherization extended its effect toward Gram-negative Escherichia coli and Pseudomonas aeruginosa, making these bacteria up to 10 and 100 times more sensitive to the antibiotic, respectively. The spheres were able to disrupt the outer membranes of these bacteria, overcoming their intrinsic resistance toward glycopeptides. The penetration of nanospheres into a Langmuir monolayer of bacterial membrane phospholipids confirmed the interaction of the nanoantibiotic with the membrane of E. coli cells, affecting their physical integrity, as further visualized by scanning electron microscopy. Such mechanism of antibacterial action is unlikely to induce mutations in the evolutionary conserved bacterial membrane, therefore reducing the possibility of acquiring resistance. Our results indicated that the nanotransformation of vancomycin could overcome the inherent resistance of Gram-negative bacteria toward this antibiotic and disrupt mature biofilms at antibacterial-effective concentrations.Peer ReviewedPostprint (author's final draft

Differences in the Psychological Profiles of Elite and Non-elite Athletes

One of the main goals of sport psychology is to identify those psychological factors that are relevant for sport performance as well as possibilities of their development. The aim of the study was to determine whether the set of specific psychological characteristics [generalized self-efficacy, time perspective, emotional intelligence (EI), general achievement motivation, and personality dimensions] makes the distinction between athletes based on their (non)-participation in the senior national team, that is, their belonging to the subsample of elite or non-elite athletes depending on this criterion. According to the group centroids it can be said that elite athletes are characterized by a positive high score in self-efficacy, emotionality, present fatalistic time perspective, past positive time perspective, and openness to experience. They are also characterized by low past negative time perspective, emotional competence, and future time perspective. Non-elite athletes have the opposite traits. The results have been discussed in the context of their application in the process of talent selection and development in sport as well as the development of life skills in athletes

Renormalization Group and Infinite Algebraic Structure in D-Dimensional Conformal Field Theory

We consider scalar field theory in the D-dimensional space with nontrivial metric and local action functional of most general form. It is possible to construct for this model a generalization of renormalization procedure and RG-equations. In the fixed point the diffeomorphism and Weyl transformations generate an infinite algebraic structure of D-Dimensional conformal field theory models. The Wilson expansion and crossing symmetry enable to obtain sum rules for dimensions of composite operators and Wilson coefficients.Comment: 16 page

Bacteria-responsive multilayer coatings comprising polycationic nanospheres for bacteria biofilm prevention on urinary catheters

This work reports on the development of infection-preventive coatings on silicone urinary catheters that contain in their structure and release on demand antibacterial polycationic nanospheres. Polycationic aminocellulose conjugate was first sonochemically processed into nanospheres to improve its antibacterial potential compared to the bulk conjugate in solution (ACSol). Afterwards the processed aminocellulose nanospheres (ACNSs) were combined with the hyaluronic acid (HA) polyanion to build a layer-by-layer construct on silicone surfaces. Although the coating deposition was more effective when HA was coupled with ACSol than with ACNSs, the ACNSs-based coatings were thicker and displayed smoother surfaces due to the embedment of intact nanospheres. The antibacterial effect of the ACNSs multilayers was by 40 % higher compared to the ACSol coatings. This fact was further translated into more effective prevention of Pseudomonas aeruginosa biofilm formation. The coatings were stable in absence of bacteria, whereas their disassembling occurred gradually during incubation with Pseudomonas aeruginosa, and thus eradicate the biofilm upon release of antibacterial agents. Only 5 bilayers of HA/ACNSs were sufficient to prevent the biofilm formation, in contrast to the 10 bilayers of ACSol required to achieve the same effect. The antibiofilm efficiency of (HA/ACNSs)10 multilayer construct built on a Foley catheter was additionally validated under dynamic conditions using a model of catheterized bladder in which the biofilm was grown during seven days.M.M.F. acknowledges the support of the European Commissionunder the Marie Curie Intra-European Fellowship (IEF) Program (Grant Agreement ‘‘NanoQuench” FP7-331416)

Size and aging effects on antimicrobial efficiency of silver nanoparticles coated on polyamide fabrics activated by atmospheric DBD plasma

Recently, renewed interest has arisen in silver nanopar@cles for biomedical devices because of their high surface energy, enhanced physicochemical and biological proper@es and extremely large surface area, which provides beAer contact with microorganisms. Atmospheric plasma is an alterna@ve and cost- compe@@ve method to wet chemical nanopar@cles deposi@on methods, avoiding the need of toxic solvents, expensive vacuum equipment and allowing con@nuous and uniform processing of material surfaces. However, there are no reports on the size and @me-dependent an@microbial, physical and chemical surface effects of the silver nanopar@cles immobilized on plasma func@onalized polymers. Thus, the purposes of this study were: (i) the silver nanopar@cle size and aging effects aCer 30 days on the an@microbial ac@vity aCer deposi@on onto DBD plasma-treated polyamide 6,6 fabrics, and (ii) the aging effect on the physico-chemical binding mechanism between different sized silver nanopar@cles and the plasma treaded polyamide 6,6. Five different in size commercial silver nanopar@cles have been employed (10, 20, 40 60 and 100 nm).This work was funded by Portuguese Founda@on for Science and Technology FCT/MCTES (PIDDAC) and co-financed by European funds (FEDER) through the PT2020 program, research project M-ERA-NET/0006/2014 and COMPETE program through FCT within the scope of the project POCI-01-0145-FEDER-007136 and UID/CTM/00264.info:eu-repo/semantics/publishedVersio

Size effects on antimicrobial efficiency of DBD plasma coated silver nanoparticles on textiles

This work studies the surface characteristics, the antimicrobial activity and the aging effect, of plasma pre-treated polyamide 6,6 fabrics (PA66) coated with silver nanoparticles (AgNPs), with the aim to identify the optimum size of nanosilver exhibiting antibacterial properties suitable for manufacturing of hospital textiles. The release of bactericidal Ag+ ions from the 10, 20, 40, 60 and 100 nm AgNPs-coated PA66 surface were function of the particles size, number and aging. Plasma pre-treatment promoted both ionic and covalent interactions between AgNPs and the formed oxygen species on the fibers (Figure 1), favoring the deposition of smaller in diameter AgNPs that consequently showed better immediate and durable antimicrobial effect against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria. Surprisingly, after 30 days of aging, a comparable bacterial growth inhibition was achieved for all the fibers treated with AgNPs of <100 nm in size. The Ag+ in the coatings also favored the electrostatic stabilization of the plasma-induced functional groups on the PA66 surface, thereby retarding the aging process (Figure 2). At the same time, the size-related ratio Ag+/Ag0 of the AgNPs between 40 and 60 nm allowed for controlled release of Ag+ rather than bulk silver. Overall, the results suggest that instead of reducing the AgNPs size, which is associated to higher toxicity, similar long-term effects can be achieved with larger NPs (40-60 nm), even in lower concentrations. Since the antimicrobial efficiency of AgNPs larger than 30 nm is mainly ruled by the release of Ag+ over time and not by the size and number of the AgNPs, this parameter is crucial for the development of efficient antimicrobial coatings on plasma-treated surfaces, and contribution to the safety and durability of clothing used in clinical settings

Influence of fiber orientation on the mechanical response of piezoelectric poly(vinylidene fluoride) electrospun fiber mats

Portuguese Foundation for Science and Technology (FCT) - UID/FIS/04650/2013; Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-3-R (AEI/FEDER, UE) (including the FEDER financial support); Basque Government Industry Department under the ELKARTEK Program. S.R., C.R. and A.F. thanks the FCT for the SFRH/BD/111478/2015, SFRH/BPD/90870/2012 and SFRH/BPD/104204/2014 grants, respectively.info:eu-repo/semantics/publishedVersio