Lantibiotics, bacteria-sourced antimicrobial peptides, are very good candidates for effective and safe food additives. Among them, nisin is already approved by the EU and FDA, and has been used in ...food preservation for the past 40 years. Now, there is a possibility and strong interest to extend its applicability to biomedicine for designing innovative alternatives to antibiotics. The main obstacle is, however, its naturally narrow spectrum of antimicrobial activity, focused on Gram positive bacteria. Here we demonstrate broadening nisin's spectrum to Gram negative bacteria using a nano-engineering approach. After binding nisin molecules to the surface of gold nano-features, uniformly deposited on spherical carbon templates, we created a nanocomposite with a high density of positively charged groups. Before assembly, none of the components of the nanocomposite showed any activity against bacterial growth, which was changed after assembly in the form of the nanocomposite. For the first time we showed that this type of structure enables interactions capable of disintegrating the wall of Gram negative bacteria. As confirmed by the nisin model, the developed approach opens up new horizons for the use of lantibiotics in designing post-antibiotic drugs.
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•Bottom electrode has a strong influence on the growth of the active layer.•LaNiO3 electrode strongly stabilizes the perovskite phase.•Stabilization is mainly related to increased ...interface roughness.•Increased interface roughness does not have adverse effects on the film properties.
Pulsed-laser deposition was used to prepare Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) thin films on (LaNiO3)/SrTiO3 substrates. We found that the bottom electrode has an immense influence on the properties of the overgrown active layer. Specifically, we found that the use of LaNiO3 (LNO) as the electrode material strongly stabilizes the perovskite phase and significantly expands the process window for the preparation of phase-pure PMN-PT as compared to a direct deposition on SrTiO3 (STO) substrates. Based on our experiments, the stabilization is achieved primarily due to the increased interface roughness, which enhances the sticking of Pb-based species, thereby suppressing the formation of undesired Pb-deficient pyrochlore inclusions. The roughness of the interface does not have adverse effects on the quality of the films. In fact, the film prepared on the LNO/STO template from the Pb-rich target exhibited superior electrical properties as compared to the film prepared directly on STO. By understanding the mechanism, we were able to exploit it and prepare an STO/Nb:STO template with a rough surface, which strongly enhanced the stability of the perovskite phase. This approach can be used to design templates for different device configurations.
Nanotextured magnesium oxide (MgO) can exhibit both antibacterial and tissue regeneration activity, which makes it very useful for implant protection. To successfully combine these two properties, ...MgO needs to be processed within an appropriate carrier system that can keep MgO surface available for interactions with cells, slow down the conversion of MgO to the less active hydroxide and control MgO solubility. Here we present new composites with nanotextured MgO microrods embedded in different biodegradable polymer matrixes: poly-lactide-co-glycolide (PLGA), poly-lactide (PLA) and polycaprolactone (PCL). Relative to their hydrophilicity, polarity and degradability, the matrices were able to affect and control the structural and functional properties of the resulting composites in different manners. We found PLGA matrix the most effective in performing this task. The application of the nanotextured 1D morphology and the appropriate balancing of MgO/PLGA interphase interactions with optimal polymer degradation kinetics resulted in superior bactericidal activity of the composites against either planktonic E. coli or sessile S. epidermidis, S. aureus (multidrug resistant-MRSA) and three clinical strains isolated from implant-associated infections (S. aureus, E. coli and P. aeruginosa), while ensuring controllable release of magnesium ions and showing no harmful effects on red blood cells.
Single-phase Mg3B2O6 and Mg2B2O5 ceramics were prepared by the solid state route and then structurally and dielectrically characterised. The highest Qxf value of 230900 GHz was obtained for a Mg3B2O6 ...ceramic with a density of 97% and 1000-micron sized grains. Considerably lower Qxf values (10000-32000 GHz) were found for the Mg2B2O5 ceramic. Mg3B2O6 and Mg2B2O5 showed dielectric constants of 7.2 and 6.2-7.0, respectively. Both ceramics showed negative temperature coefficients of resonant frequency of -18 to -45 ppm/C.
Composite ceramics based on the spinel Mg2TiO4 were prepared by a conventional mixed‐oxide route. To achieve the temperature stabilization of the dielectric constant, each of the composites was added ...with 7 mol% CaTiO3. The effect of the substitution of isovalent Co for Mg on the microstructure and the microwave dielectric properties of the composite ceramics was also investigated. A maximum Q×f value of around 150–160 THz was obtained for the undoped Mg2TiO4, whereas a reduced Q×f value was observed for an increase in the Co concentration in the system (1−x)Mg2TiO4−xCo2TiO4. Upon doping with 7 mol% CaTiO3, the Q×f value passed through a maximum with increasing Co concentration. Adding ZnO–B2O3 to the composite system based on Co‐doped Mg2TiO4 resulted in a reduction of the sintering temperature by 150°–200°C without any significant degradation in the Q×f value.
Growth of Pb(Mg1/3Nb2/3)O3–33PbTiO3 thin films by pulsed-laser deposition directly on non-conductive SrTiO3 substrates for d33-mode energy harvesters (EHs) was studied, as they offer a higher ...figure-of-merit than d31-mode EHs. It was found that a high defect density, present in the film grown at 0.13 mbar, is manifested in the form of splitting of the (00l) peaks in X-ray diffraction, which was avoided by raising the process pressure to 0.27 mbar. Nevertheless, both films grow in a combined 2D and 3D manner, and form out-of-phase boundaries (OPBs) with a PbO rock-salt structure between the as-grown islands. It was found that the overall composition of the sample with optimized structural and functional properties was Pb1.07Mg0.19Nb0.44Ti0.32O3, which is close to stoichiometric. The surplus of Pb is compensated by the formation of OPBs and Mg deficit maintains macroscopic electroneutrality. In-plane and out-of-plane relative permittivities of 1900 and 980, respectively, imply macroscopic out-of-plane polarization.
To reduce the complexity of LTCC systems, and so accelerate the development of LTCC tapes with new functionalities, it is necessary to reduce the number of phases within a particular tape. This can ...best be done by using glass-free single-phase ceramic systems. We performed a basic characterization of several low-temperature-sintered calcium silicates, germanates and tellurates in order to evaluate their potential as glass-free low-permittivity substrate LTCC materials. Special attention was focused on their microwave and 1 MHz dielectric properties, their sintering behavior and their compatibility with Ag. Two Ca-germanates, which were found to be the most interesting for LTCC applications exhibit a permittivity of ∼10 and low dielectric losses; however, the temperature dependence of permittivity and the sintering temperature must be further reduced. For CaGeO
3 the temperature dependence of permittivity was fully suppressed by the addition of 10 mol% of CaTiO
3.
Solid‐state synthesis of compositions from the Bi2O3–TeO2 system show that, under an oxygen atmosphere, Te4+ oxidizes to Te6+ and yields four room‐temperature stable compounds: Bi2Te2O8, Bi2TeO6, ...Bi6Te2O15, and new a compound with the nominal composition 7Bi2O3·2TeO2. Dense ceramics can be prepared from all these compounds by sintering between 650° and 800°C under an oxygen atmosphere. The permittivity of these compounds varies from ∼30 to ∼54, the Q×f value from 1.100 to 41.000 GHz (∼5 GHz), and the temperature coefficient of resonant frequency from −43 to −144 ppm/K. Bi6Te2O15 and 7Bi2O3·2TeO2 do not react with silver, and, therefore, they have the potential to be used for applications in low‐temperature cofired ceramic (LTCC) technology.
The chemical compatibility of silver electrodes and low‐firing ceramics has been considered, in terms of the existence of a tie line between silver (and/or Ag2O) and the binary oxide compound in the ...corresponding ternary phase diagram. The probability of the existence of the tie line is related to the conditions in the subordinated silver‐based isothermal binary systems. Greater probabilities have been calculated for the systems with fewer silver‐based binary compounds. Based on the concepts that have been developed, several silver‐based isothermal binary systems have been investigated to identify the oxides suitable for the development of low‐temperature cofired ceramics. The developed concept has been tested by investigating the phase relations in the Bi2O3–Nb2O5 and Bi2O3–V2O5 ternary systems with silver. X‐ray and microstructural investigations of bismuth niobates and bismuth vanadates reveal that, as a result of the inertness of Bi2O3 and the reactivity of Nb2O5 and V2O5 toward silver, compounds that are rich in niobium or vanadium react with silver to form ternary Nb/V‐Bi‐Ag oxide compounds, whereas for compounds that are rich in bismuth, tie lines to silver and Ag2O do exist.
The local crystal and domain structures of K0.5Bi0.5TiO3 ceramics were investigated by transmission electron microscopy (TEM) and selected‐area electron diffraction (SAED). The individual grains ...showed a lamellar domain structure, and on the basis of spot splitting along the characteristic crystallographic directions, 90°a–a‐ and 90°a–c‐type domains were identified. Furthermore, lamellar features within the 90° domains were observed, which we presumed were 180° domains; however, in the case of P4mm structures they cannot be distinguished by SAED. The 90° domain boundaries were (011) and (101) twin planes, typical for tetragonal perovskites. The domains could be designated as rotation twins, where the symmetry element describing the relationship between two twin domains is a twofold twin axis 011/101 and the symmetry operation is a 180° rotation. In order to determine the dynamics and the temperature of the phase transformation from the tetragonal to the cubic structures, high‐temperature XRD and in situ heating TEM analyses were performed. The results showed a gradual phase transformation in the temperature range from ∼280° to ∼450°C, where some grains lost their polar domains at a lower temperature than others. These findings confirmed the existence of a binary stability field in which the cubic and tetragonal structures coexist.
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