Optoelectronics and defect levels in hydroxyapatite by first-principles

Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material e.g. in photo-catalysis), depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately we have the electronic band structure and all that relates to it, including the band gap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the GW approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional, brings a drastic improvement to the band structure. Important side-effects include improvements in the description of dielectric and optical properties, not only involving conduction band (excited) states, but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding $\sigma^{*}$ states along the $\cdots\textrm{OH-OH-}\cdots$ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as testing-model. We find that donor and acceptor transitions obtained within semi-local DFT differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp

Presence of extracellular DNA in the Candida albicans biofilm matrix and its contribution to biofilms

DNA has been described as a structural component of the extracellular matrix (ECM) in bacterial biofilms. In Candida albicans, there is a scarce knowledge concerning the contribution of extracellular DNA (eDNA) to biofilm matrix and overall structure. This work examined the presence and quantified the amount of eDNA in C. albicans biofilm ECM and the effect of DNase treatment and the addition of exogenous DNA on C. albicans biofilm development as indicators of a role for eDNA in biofilm development. We were able to detect the accumulation of eDNA in biofilm ECM extracted from C. albicans biofilms formed under conditions of flow, although the quantity of eDNA detected differed according to growth conditions, in particular with regards to the medium used to grow the biofilms. Experiments with C. albicans biofilms formed statically using a microtiter plate model indicated that the addition of exogenous DNA (>160 ng/ml) increases biofilm biomass and, conversely, DNase treatment (>0.03 mg/ml) decreases biofilm biomass at later time points of biofilm development. We present evidence for the role of eDNA in C. albicans biofilm structure and formation, consistent with eDNA being a key element of the ECM in mature C. albicans biofilms and playing a predominant role in biofilm structural integrity and maintenance.National Institute of Dental & Craniofacial ResearchFundação para a Ciência e Tecnologia (FCT) - SFRH/BD/28222/2006National Institute of Allergy and Infectious Disease

Development of Internet communication and social networking in modern conditions: institutional and legal aspects

The development of the Internet, which has been active over the past two decades, is leading to the formation of new forms of human interaction on the World Wide Web. One of such forms is actually social networks, which from the beginning of their activity are used mainly as a way to ensure human communication. However, such a big number of consumers with the usual ways of buying goods and services, lead to the search for new platforms for companies to do business, which in turn provokes the transition of social networks to a fundamentally new level of activity

Salmonella enterica biofilm-mediated dispersal by nitric oxide donors in association with cellulose nanocrystal hydrogels

Protected by extracellular polymers, microbes within biofilms are significantly more resistant to disinfectants. Current research has been instrumental in identifying nitric oxide donors and hydrogels as potential disinfectant additives. Nitric oxide (NO) donors are considered a very promising molecule as biofilm dispersal agents and hydrogels have recently attracted a lot of interest due to their biocompatible properties and ability to form stable thin films. When the NO donor MAHMA NONOate was dissolved in phosphate saline buffer, it was able to reduce the biomass of well-established biofilms up to 15% for at least 24 h of contact time. Encapsulation of MAHMA NONOate and molsidomine within a hydrogel composed of cellulose nanocrystals (CNC) has shown a synergistic effect in dispersing well-established biofilms: after 2 h of exposure, moderate but significant dispersion was measured. After 6 h of exposure, the number of cells transitioning from the biofilm to the planktonic state was up to 0.6 log higher when compared with non-treated biofilms. To further explore the transport processes of NO donors within hydrogels, we measured the nitric oxide flux from gels, at 25°C for a composite of 0.1 µM MAHMA NONOate–CNC. Nitric oxide diffuses up to 500 µm from the hydrogel surface, with flux decreasing according to Fick’s law. 60% of NO was released from the hydrogel composite during the first 23 min. These data suggest that the combined treatments with nitric oxide donor and hydrogels may allow for new sustainable cleaning strategies

Bacterial Cellulose/Alginate Nanocomposite for Antimicrobial Wound Dressing

Development of novel wound dressing has attracted more and more attentions in recent years. Bacterial cellulose is a biopolymer of great potentials, which features a distinctive three-dimensional structure consisting of an ultrafine network of cellulos nanofibers. In the present study, nanocomposite bacterial cellulose films modified in situ by the addition of alginate during the static cultivation of Gluconacetobacter sucrofermentans B-11267 were produced and then enriching the polymer with an antimicrobial agent tetracycline hydrochloride. The structure of bacterial cellulose and nanocomposite was analyzed by AFM and FTIR. The FTIR spectra displayed the specified interaction between the hydroxyl group of cellulose and the carboxyl group of alginate. The produced bacterial cellulose and nanocomposite were analyzed to determine tensile modulus. The antibacterial activity of nanocomposites were investigated by disk diffusion method. The resulting nanocomposite have high antibiotic activity against Staphylococcus aureus and can be used in medicine as a wound dressing. Keywords: bacterial cellulose, Gluconacetobacter sucrofermentans, alginate, nanocomposite, antibacterial activity, wound dressin

Modeling of the 2D-materials hybrid nanostructures based on ferroelectric polymer PVDF/P(VDF-TrFE) and MoS2 Dichalcogenide

Transition metal dichalcogenide MoS2 monolayers is very promising for many applications, especially in the fields of optics as emitters and detectors, in electronics as transistors. It is first of all due that they have a direct band gap Eg, which is dependent on external applied electric fields. To create such an electric field, it is proposed to use the field induced polarization of ferroelectric polymers such as PVDF and P(VDF-TrFE). These polymers in the ferroelectric phase are capable to create significant polarization in very thin layers, about 5 Å. By combining such ferroelectric layers and MoS2 layers, hybrid nanostructures can be created, that are convenient for design of new photodetectors with controlled properties. The prominent properties of this hybrid structure arise and benefit namely from the ferroelectric-polarization-induced ultra-high electric field of the PVDF or P(VDF-TrFE), that impact on MoS2 layers and control the band gap Eg. In this work, we simulate such a hybrid structure based on PVDF and MoS2 layers and study their features and properties. For calculating MoS2, the methods of density functional theory (DFT) are used, implemented in the VASP program. Semi-empirical methods based on the HyperChem software package are used to model and study both individual layers of the hybrid structure and the features of their joint interaction. The results obtained convincingly show a strong influence on the width of the MoS2 bandgap Eg from the side of the PVDF layers, creating polarization P and an electric field E, which affects MoS2 layers. In addition, the dependence of the band gap Eg under the action of electric field E from the distance between the layers PVDF and MoS2 has been established