National Institute Of Materials Physics - Romania

The iron oxide nanoparticles coated with different surface coatings were studied and characterized by multiple physicochemical and biological methods. The present paper aims at estimating the toxicity in vitro and in vivo of dextran coated iron oxide aqueous magnetic fluids. The in vitro studies were conducted by quantifying the viability of HeLa cells after their incubation with the samples (concentrations of 62.5-125-250-500 mu g/mL at different time intervals). The estimation of the toxicity in vivo of administering dextran coated iron oxide aqueous magnetic fluids (DIO-AMF) with hydrodynamic diameter of 25.73 +/- 4 nm to Male Brown Norway rats has been made. Different concentrations (62.5-125-250-500 mu g/mL) of dextran coated iron oxide aqueous magnetic fluids were administered for 7 consecutive days. Hematology and biochemistry of the Male Brown Norway rats assessment was performed at various time intervals (24-72 h and 21-28 days) after intra-peritoneal injection. The results showed that high concentrations of DIO-AMF (250 and 500 mu g/mL) significantly increased white blood cells, red blood cells, hemoglobin and hematocrit compared to the values obtained for the control group (p < 0.05). Moreover, following the administration of DIO-AMF, the levels of alkaline phosphatase and aspartate aminotransferase increased compared to the control group (p < 0.05). After DIO-AMF administration, no significant difference was observed in the levels of alanine aminotransferase, gamma-glutamyl transpeptidase, urea and creatinine compared to the control group (p < 0.05). The results of the present study showed that dextran coated iron oxide aqueous magnetic fluids in concentrations lower than 250 mu g/mL are reliable for medical and pharmaceutical applications.

The objective of this study consisted of the development of new materials with antimicrobial properties at the nanometric scale that could lead to an increase in therapeutic efficacy and reduction of toxic side effects. This work focuses on obtaining and characterizing stable suspensions with narrow size distribution with antimicrobial properties. The stability of the suspensions obtained by an adapted co-precipitation method was evaluated by ultrasonic measurements. The size and size distribution of the particle populations were determined using scanning electron microscopy (SEM), and dynamic light scattering (DLS). Both methods of analysis showed a narrow distribution of particles. DLS gave a monomodal distribution with hydrodynamic diameters around 38 nm for ciprofloxacin embedded in silver doped hydroxyapatite (AgHA-C) and 45.7 nm for tetracycline embedded in silver doped hydroxyapatite (AgHA-T). The average diameters calculated from SEM were 17 nm for AgHA-C and 19 nm for AgHA-T. Both Ciprofloxacin and Tetracycline influenced the hydroxyapatite structure, which led to the appearance of new vibrational bands characteristic of the specific chemical composition in the FTIR spectrum. The antimicrobial properties of the AgHA-C and AgHA-T suspensions were assessed using the most common reference microbial strains Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231. The results of the in vitro antimicrobial assays determined that the AgHA-C and AgHA-T suspensions exhibited exceptional antimicrobial activity. Moreover, the data revealed that the antimicrobial activity increased with the increase of the incubation time.

In this work, Tungsten(W)-doped TiO2 nanoparticles were synthesized using the sol-gel method and were used as electrode materials in supercapacitor applications. The structural and morphological properties of the prepared samples were analyzed by means of XRD, STEM, TEM, and XPS. The analysis of the defect centers was carried out using EPR spectroscopy. The electrochemical analysis of the assembled supercapacitor was done using cyclic voltammetry, galvanostatic cycling with potential limitation technique, potentiostatic electrochemical impedance spectroscopy, and voltage-holding experiments. All the presented samples showed paramagnetic defects in the EPR analysis, while 0.5% W-doped TiO2 showed a maximum signal intensity. The supercapacitor performance from the synthesized electrode material showed highly encouraging results. The equivalent series resistance (R-s) value for all the designs showed values under "1 omega,' which reflects high conductivity. As the maximum EPR intensity comes from TiO2 doped with 0.5% W, the supercapacitor performance of this sample was tested with a newly designed five-electrode system. This design showed superior performance compared to any other used designs with a specific capacitance of 25.5 F g(-1), with an energy density of 14.16 Wh kg (-1 )at 302 kW kg (-1).

Lately, there is a growing interest in organic photovoltaic (OPV) cells due to the organic materials' properties and compatibility with various types of substrates. However, their efficiencies are low relative to the silicon ones; therefore, other ways (i.e., electrode micron/nanostructuring, synthesis of new organic materials, use of additives) to improve their performances are still being sought. In this context, we studied the behavior of the common organic bulk heterojunction (P3HT:PC70BM) deposited by matrix-assisted pulsed laser evaporation (MAPLE) with/without 0.3% of 1,8-diiodooctane (DIO) additive on flat and micro-patterned ITO substrates. The obtained results showed that in the MAPLE process, a small quantity of additive can modify the morphology of the organic films and decrease their roughness. Besides the use of the additive, the micro-patterning of the electrode leads to a greater increase in the absorption of the studied photovoltaic structures. The inferred values of the filling factors for the measured cells in ambient conditions range from 19% for the photovoltaic structures with no additive and without substrate patterning to 27% for the counterpart structures with patterning and a small quantity of additive.

The paper presents a study concerning the role of ferroelectric filler size and clustering in the dielectric properties of 20%BaTiO3-80%PVDF and of 20% (2%Ag-98%BaTiO3)-PVDF hybrid nanocomposites. By finite element calculations, it was shown that using fillers with epsilon > 103 does not provide a permittivity rise in the composites and the effective dielectric constant tends to saturate to specific values determined by the filler size and agglomeration degree. Irrespective of the ferroelectric filler sizes, the addition of metallic ultrafine nanoparticles (Ag) results in permittivity intensification and the effect is even stronger if the metallic nanoparticles are connected to a higher degree with the ferroelectric particles' surfaces. When using coarse ferroelectric fillers, the probability of clustering is higher, thus favoring the permittivity increase by field concentration in small regions close to the interfaces separating dissimilar materials. The modeling results were validated by an experimental dielectric analysis performed in a series of PVDF-based thick films with the same amount of BaTiO3 fillers or with Ag-BaTiO3 hybrid fillers. Similar trends as predicted by simulations were found experimentally but with slightly higher permittivity values which were assigned to the modifications of the polymer phase composition due to the presence of nanofillers and the local sample inhomogeneity (the presence of clustering, in particular for coarse BaTiO3 grains), which create regions with enhanced local fields.

In this study, we report the performance improvement of wound dressings by covering them with magnetite-based nanostructured coatings. The magnetite nanoparticles (Fe3O4 NPs) were functionalized with Nigella sativa (N. sativa) powder/essential oil and dicloxacillin and were synthesized as coatings by matrix assisted pulsed laser evaporation (MAPLE). The expected effects of this combination of materials are: (i) to reduce microbial contamination, and (ii) to promote rapid wound healing. The crystalline nature of core/shell Fe3O4 NPs and coatings was determined by X-ray diffraction (XRD). Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) have been coupled to investigate the stability and thermal degradation of core/shell nanoparticle components. The coatings' morphology was examined by scanning electron microscopy (SEM). The distribution of chemical elements and functional groups in the resulting coatings was evidenced by Fourier transform infrared (FTIR) spectrometry. In order to simulate the interaction between wound dressings and epithelial tissues and to evaluate the drug release in time, the samples were immersed in simulated body fluid (SBF) and investigated after different durations of time. The antimicrobial effect was evaluated in planktonic (free-floating) and attached (biofilms) bacteria models. The biocompatibility and regenerative properties of the nanostructured coatings were evaluated in vitro, at cellular, biochemical, and the molecular level. The obtained results show that magnetite-based nanostructured coatings functionalized with N. sativa and dicloxacillin are biocompatible and show an enhanced antimicrobial effect against Gram positive and Gram negative opportunistic bacteria.

The aim of this paper is to provide a simple and efficient photoassisted approach to synthesize silver nanoparticles, and to elucidate the role of the key factors (synthesis parameters, such as the concentration of TSC, irradiation time, and UV intensity) that play a major role in the photochemical synthesis of silver nanoparticles using TSC, both as a reducing and stabilizing agent. Concomitantly, we aim to provide an easy way to evaluate the particle size based on Mie theory. One of the key advantages of this method is that the synthesis can be "activated" whenever or wherever silver nanoparticles are needed, by premixing the reactants and irradiating the final solution with UV radiation. UV irradiance was determined by using Keitz's theory. This argument has been verified by premixing the reagents and deposited them in an enclosed space (away from sunlight) at 25 degrees C, then checking them for three days. Nothing happened, unless the sample was directly irradiated by UV light. Further, obtained materials were monitored for 390 days and characterized using scanning electron microscopy, UV-VIS, and transmission electron microscopy.

The treatment of wounds occurring accidentally or as a result of chronic diseases most frequently requires the use of appropriate dressings, mainly to ensure tissue regeneration/healing, at the same time as treating or preventing potential bacterial infections or superinfections. Collagen type I-based scaffolds in tandem with adequate antimicrobials can successfully fulfill these requirements. In this work, starting from the corresponding hydrogels, we prepared a series of freeze-dried atelocollagen type I-based matrices loaded with tannic acid (TA) and chlorhexidine digluconate (CHDG) as active agents with a broad spectrum of antimicrobial activity and also as crosslinkers for the collagen network. The primary aim of this study was to design an original and reliable algorithm to in vitro monitor and kinetically analyze the simultaneous release of TA and CHDG from the porous matrices into an aqueous solution of phosphate-buffered saline (PBS, pH 7.4, 37 degrees C) containing micellar carriers of a cationic surfactant (hexadecyltrimethylammonium bromide, HTAB) as a release environment that roughly mimics human extracellular fluids in living tissues. Around this central idea, a comprehensive investigation of the lyophilized matrices (morpho-structural characterization through FT-IR spectroscopy, scanning electron microscopy, swelling behavior, resistance against the collagenolytic action of collagenase type I) was carried out. The kinetic treatment of the release data displayed a preponderance of non-Fickian-Case II diffusion behavior, which led to a general anomalous transport mechanism for both TA and CHDG, irrespective of their concentrations. This is equivalent to saying that the release regime is not governed only by the gradient concentration of the releasing components inside and outside the matrix (like in ideal Fickian diffusion), but also, to a large extent, by the relaxation phenomena of the collagen network (determined, in turn, by its crosslinking degree induced by TA and CHDG) and the dynamic capacity of the HTAB micelles to solubilize the two antimicrobials. By controlling the degree of physical crosslinking of collagen with a proper content of TA and CHDG loaded in the matrix, a tunable, sustainable release profile can be obtained.

Drinking water contamination has become a worldwide problem due to the highly negative effects that pollutants can have on human organisms and the environment. Hydroxyapatite (HAp) has the appropriate properties for the immobilization of various pollutants, being considered amongst the most cost-effective materials for water decontamination. The main objective of this study was to use synthesized hydroxyapatite for the elimination of Sr2+ ions from contaminated solutions. The hydroxyapatite used in the decontamination process was synthesized in the laboratory using an adapted method. The hydroxyapatite powder (HAp) resulting from the synthesis was analyzed both before and after the elimination of Sr2+ ions from contaminated solutions. The efficiency of the HAp nanoparticles in removing Sr2+ ions from contaminated solution was determined by batch adsorption experiments. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to study the HAp samples before and after the removal of Sr2+ ions. The ability of HAp nanoparticles to eliminate strontium ions from contaminated solutions was established. Moreover, the removal of Sr2+ ions from the contaminated aqueous solutions was highlighted by ultrasound measurements. The value of the stability parameter calculated by ultrasonic measurements after the removal of Sr2+ ions from the contaminated solution was similar to that of double distilled water whose stability was used as reference. The outcomes of the batch experiments and the parameters obtained from Langmuir and Freundlich models indicated that the HAp nanoparticles had a strong affinity for the elimination of Sr2+ ions from polluted solutions. These results emphasized that HAp nanoparticles could be excellent candidates in the development of new technologies for water remediation. More than that, the outcomes of the cytotoxic assays proved that HAp nanoparticles did not induce any noticeable harmful effects against HeLa cells and did not affect their proliferation after 1 day and 7 days of incubation.

The p-n junctions are the building blocks of nowadays electronic devices. The n- or p-type conductivity is obtained in classic semiconductors, like Si, by doping with atoms acting as donors or acceptors, respectively. Doping was used in ferroelectrics to influence the transition temperature, magnitude of some physical properties, but not necessarily conduction type. Therefore, comprehensive studies to obtain true ferroelectric p-n junctions by controlled doping are missing. Recently, it has been shown that Pb(Zr0.2Ti0.8)O-3 films doped with & AP;1% atomic Nb (n-type doping) or Fe (p-type doping) have different orientations of polarization in the as-grown state. Knowing that polarization orientation depends on doping type, the next step is to build ferroelectric p-n homojunctions and to study their properties in relation to ferroelectric polarization. p-n and n-p structures were grown for this purpose by successive deposition of Nb-doped and Fe-doped Pb(Zr,Ti)O-3 layers with different thicknesses. We find that these p-n homojunctions are ferroelectric, but the magnitude of the polarization and coercive field, as well as the dominant polarization orientation in the as-grown state, depend on the conduction type of the first grown layer. The I-V characteristics are quasi-linear, although the interfaces with the electrodes behaves as Schottky contacts. The resistance extracted from the I-V characteristics displays an exponential dependence on temperature, with an activation energy in the range of 0.14-0.17 eV. These results are explained assuming that the total current in the junction is the total of electron and hole injections at the electrode interfaces. It is shown that for relatively low doping concentrations, the current density contains a dominant term with a linear voltage dependence and an exponential temperature dependence, as observed experimentally, and a secondary (correction) term that is dependent on the free carrier density and can induce non-linear voltage dependence when this density is significant.