New strategies to fight bacterial adhesion

Initial adhesion of bacteria to biomaterials' surface is assumed to be an important stage in their colonization which may to lead to severe infections and loss of medical devices. Thus, the knowledge of how these microorganisms adhere and which factors affect this phenomenon proves to be of great importance in order to avoid their colonization. Hydrophobicity, charge, roughness and chemical composition of surfaces can rule the adhesion process. A better understanding of all these features is crucial for an effective microorganism’s adhesion control. In this context, it is possible to modify the biomaterials’ surfaces through coatings doped with an antimicrobial agent, in order to prevent biofilm formation. So, this mini-review gives a brief account of aspects involved in bacterial attachment to a surface, highlighting the interactions involved and presenting mechanisms that are being used to fight pathogens adhesion. For this intent, hydrophobicity, morphology and topography of doped silver coatings will be exploited as a new approach for the development of antibacterial surfaces

PVD-grown antibacterial Ag-TiN films on piezoelectric PVDF substrates for sensor applications

This work reports on Ti1-xAgx and Ag-TiNx electrodes deposited by dc/pulsed dc magnetron sputtering at room temperature on poly (vinylidene fluoride) (PVDF) with the purpose to develop sensors for prosthesis. In Ti1-xAgx electrodes, silver content was varied from 0 to 100 at.%; and for Ag-TiNx electrodes, the nitrogen content was varied between 34 to 43 at.% and the Ti/Ag ratio changed from 12.2 to 5.2. The antibacterial activity of the samples was assessed by agar diffusion method. Interestingly, samples from the Ag-TiNx series presented antibacterial activity, in contrast to the samples from Ti1-xAgx series. XPS results showed that the as-deposited samples from the Ag-TiNx series exhibited silver clusters smaller than 4 nm. In order to deepen the results obtained, samples were analysed after the Halo test (antibacterial test), and XPS analyses showed the disappearance of these Ag clusters in agreement with the SEM results, which displayed a visible aggregation and a significant decrease in the number of Ag clusters, suggesting that silver nanoparticles aggregated and diffused through the agar killing bacteria or inhibiting their grown in the vicinity. All results show that Ag-TiNx electrodes are more promising candidates to be used in PVDF sensor protection than Ti1-xAgx electrodesS. M. Marques gratefully acknowledges the funding from the Portuguese National funds through the FCT - Fundacao para a Ciencia e a Tecnologia, (project SFRH/BD/71259/2010). Also, the authors thank the support of FEDER through the COMPETE Programme and of the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2014 and the project Matepro-Optimizing Materials and Processes, ref. NORTE-07-0124-FEDER-000037", co-funded by the "Programa Operacional Regional do Norte" (ON.2 - O Novo Norte), under the "Quadro de Referencia Estrategico Nacional" (QREN), through the "Fundo Europeu de Desenvolvimento Regional" (FEDER).The authors thank the FCT Strategic Project of UID/BIO/04469/2013 unit, the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and the project "BioInd - Biotechnology and Bioengineering for improved Industrial and Agro-Food processes", REF. NORTE-07-0124-FEDER-000028 co-funded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER.The authors thank the FCT Strategic Project of UID/BIO/04469/2013 unit, the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and the Project "BioHealth Biotechnology and Bioengineering approaches to improve health quality", Ref. NORTE-07-0124-FEDER-000027, co-funded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER.The authors thank the FCT Strategic Project of UID/BIO/04469/2013 unit, the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and the Project "BioEnv Biotechnology and Bioengineering for a sustainable world", REF. NORTE-07-0124-FEDER-000048, co-funded by the Programa Operacional Regional do Norte (ON.2 0 Novo Norte), QREN, FEDER

Probing the two-scale-factor universality hypothesis by exact rotation symmetry-breaking mechanism

We probe the two-scale factor universality hypothesis by evaluating, firstly explicitly and analytically at the one-loop order, the loop quantum corrections to the amplitude ratios for O($N$) $\lambda\phi^{4}$ scalar field theories with rotation symmetry-breaking in three distinct and independent methods in which the rotation symmetry-breaking mechanism is treated exactly. We show that the rotation symmetry-breaking amplitude ratios turn out to be identical in the three methods and equal to their respective rotation symmetry-breaking ones, although the amplitudes themselves, in general, depend on the method employed and on the rotation symmetry-breaking parameter. At the end, we show that all these results can be generalized, through an inductive process based on a general theorem emerging from the exact calculation, to any loop level and physically interpreted based on symmetry ideas.Comment: 17 pages, 3 figure

The Role of Fermions in Bubble Nucleation

We present a study of the role of fermions in the decay of metastable states of a scalar field via bubble nucleation. We analyze both one and three-dimensional systems by using a gradient expansion for the calculation of the fermionic determinant. The results of the one-dimensional case are compared to the exact results of previous work.Comment: 15 pages, revtex, 9 figure