Multi-doped apatite: Strontium, magnesium, gallium and zinc ions synergistically affect osteogenic stimulation in human mesenchymal cells important for bone tissue engineering.

Functional calcium phosphate biomaterials can be designed as carriers of a balanced mixture of biologically relevant ions able to target critical processes in bone regeneration. They hold the potential to use mechanisms very similar to growth factors naturally produced during fracture healing, while circumventing some of their drawbacks. Here we present a novel phase of carbonated-apatite containing Mg2+, Sr2+, Zn2+ and Ga3+ ions (HApMgSrZnGa). While all dopants decrease the crystallinity, Ga3+ limits crystal growth and enables the formation of a nanosized apatite phase with enhanced specific surface area. Coexistence of the ions enhances degradability and controls solubility of low crystalline, distorted, multi-doped apatite structure, controlled by Ga3+ ions accumulated at the surface. Consequently, HApMgSrZnGa supports the viability of human mesenchymal stromal cells (MSCs) and induces their stimulation along the osteogenic lineage. In addition, the co-released ions has a synergistic antimicrobial effect, particularly within the HApMgSrZnGa-Au(arg) composite with Au(arg) as contact-based antimicrobial. The activity is stable up to two months in vitro. Osteogenic nature and antimicrobial activity, combined in a single biomaterial, are suggesting a well-balanced, multi-doped apatite design applicable as future option in bone regeneration and tissue engineering.

Antimicrobial Polymeric Composites with Embedded Nanotextured Magnesium Oxide.

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.

Simultaneous heteroepitaxial growth of SrO (001) and SrO (111) during strontium-assisted deoxidation of the Si (001) surface.

Epitaxial integration of transition-metal oxides with silicon brings a variety of functional properties to the well-established platform of electronic components. In this process, deoxidation and passivation of the silicon surface are one of the most important steps, which in our study were controlled by an ultra-thin layer of SrO and monitored by using transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), synchrotron X-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED) methods. Results revealed that an insufficient amount of SrO leads to uneven deoxidation of the silicon surface i.e. formation of pits and islands, whereas the composition of the as-formed heterostructure gradually changes from strontium silicide at the interface with silicon, to strontium silicate and SrO in the topmost layer. Epitaxial ordering of SrO, occurring simultaneously with silicon deoxidation, was observed. RHEED analysis has identified that SrO is epitaxially aligned with the (001) Si substrate both with SrO (001) and SrO (111) out-of-plane directions. This observation was discussed from the point of view of SrO desorption, SrO-induced deoxidation of the Si (001) surface and other interfacial reactions as well as structural ordering of deposited SrO. Results of the study present an important milestone in understanding subsequent epitaxial integration of functional oxides with silicon using SrO.

Cobalt Ferrite Nanospheres as a Potential Magnetic Adsorbent for Chromium(VI) Ions.

In the present work the cobalt ferrite nanospheres (CFO NS) were prepared via one-step, templatefree solvothermal method and used as a magnetic adsorbent of chromium(VI) ions. The synthesized materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The XRD results confirmed the cubic spinel structure of CFO NS while the SEM revealed sphere-like morphology with diameters of the CFO NS in the range of 100-300 nm. TEM images showed that each NS is composed of smaller CFO nanoparticles with size around 7-8 nm. The magnetic measurements revealed ferromagnetic character of CFO nanospheres with the maximum saturation magnetization and coercivity of 75 emu/g and 677 Oe, respectively. The synthetized CFO NS were tested as an adsorption material for removal of chromium(VI) ions from aqueous solution. The obtained removal efficiency is in the range from 38 to 88%. The results suggest that the adsorption capacity of CFO NS strongly depends on conditions of the solvothermal synthesis.

Fewer Defects in the Surface Slows the Hydrolysis Rate, Decreases the ROS Generation Potential, and Improves the Non-ROS Antimicrobial Activity of MgO.

Magnesium oxide (MgO) is recognised as exhibiting a contact-based antibacterial activity. However, a comprehensive study of the impact of atomic-scale surface features on MgO's antibacterial activity is lacking. In this study, the nature and abundance of the native surface defects on different MgO powders are thoroughly investigated. Their impacts on the hydrolysis kinetics, antibacterial activity against Escherichia coli (ATCC 47076), Staphylococcus epidermidis and Pseudomonas aeruginosa and the reactive oxygen species (ROS) generation potential are determined and explained. It is shown that a reduction in the abundance of low-coordinated oxygen atoms on the surface of the MgO improves its resistance to both hydrolysis and antibacterial activity. The ROS generation potential, determined in-situ using a fluorescence microplate assay and electron paramagnetic resonance spectroscopy, is not an inherent property of the studied MgO, rather it is a side product of hydrolysis (only for the most highly defected MgO particles) and/or a consequence of the MgO/bacteria interaction. The evaluation of the mutual correlations of the hydrolysis, the antibacterial activity and the ROS generation, with their origin in the surface defects' peculiarities, led to the conclusion that the acid/base reaction between the MgO surface and the bacterial wall contributes considerably to the MgO's antibacterial activity.

Plate-Like Bi4Ti3O12 Particles and their Topochemical Conversion to SrTiO3 Under Hydrothermal Conditions.

Plate-like Bi4Ti3O12 particles were synthesized using a one-step, molten-salt method from Bi2O3 and TiO2 nanopowders at 800 °C. The reaction parameters that affect the crystal structure and morphology were identified and systematically investigated. The differences between various Bi4Ti3O12 plate-like particles were examined in terms of the ferroelectric-to-paraelectric phase transition and the photocatalytic activity for the degradation of Rhodamine B under UV-Alight irradiation. The results encouraged us to conduct further testing of the as-prepared Bi4Ti3O12 plate-like particles as templates for the preparation of plate-like SrTiO3 perovskite particles using a topochemical conversion under hydrothermal conditions. The characteristics of the Bi4Ti3O12 plates and the reaction parameters for which the SrTiO3 preserved the shape of the initial Bi4Ti3O12 template particles were determined.

Nano-engineering the Antimicrobial Spectrum of Lantibiotics: Activity of Nisin against Gram Negative Bacteria.

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.

Biocompatible nano-gallium/hydroxyapatite nanocomposite with antimicrobial activity.

Intensive research in the area of medical nanotechnology, especially to cope with the bacterial resistance against conventional antibiotics, has shown strong antimicrobial action of metallic and metal-oxide nanomaterials towards a wide variety of bacteria. However, the important remaining problem is that nanomaterials with highest antibacterial activity generally express also a high level of cytotoxicity for mammalian cells. Here we present gallium nanoparticles as a new solution to this problem. We developed a nanocomposite from bioactive hydroxyapatite nanorods (84 wt %) and antibacterial nanospheres of elemental gallium (16 wt %) with mode diameter of 22 ± 11 nm. In direct comparison, such nanocomposite with gallium nanoparticles exhibited better antibacterial properties against Pseudomonas aeruginosa and lower in-vitro cytotoxicity for human lung fibroblasts IMR-90 and mouse fibroblasts L929 (efficient antibacterial action and low toxicity from 0.1 to 1 g/L) than the nanocomposite of hydroxyapatite and silver nanoparticles (efficient antibacterial action and low toxicity from 0.2 to 0.25 g/L). This is the first report of a biomaterial composite with gallium nanoparticles. The observed strong antibacterial properties and low cytotoxicity make the investigated material promising for the prevention of implantation-induced infections that are frequently caused by P. aeruginosa.

Formation and properties of nanostructured colloidal manganese oxide particles obtained through the thermally controlled transformation of manganese carbonate precursor phase.

Structurally and morphologically different colloidal manganese oxide solids, including manganosite (MnO), bixbyite (Mn2O3) and hausmannite (Mn(2+)[Mn(3+)]2O4), were obtained through the initial biomimetically induced precipitation of a uniform, nanostructured and micron-sized rhodochrosite (MnCO3) precursor phase and their subsequent thermally controlled transformation into oxide structures in air and Ar/H2 atmospheres. The structures and morphology of the obtained precipitates were investigated using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). Their surface properties were investigated by electrophoretic mobilities (EPM) and specific surface area (SSA) measurements. The results showed that the structurally diverse, micron-sized, spherical manganese oxide particles exhibit unusual and fascinating nanostructured surface morphologies. These were developed through the coalescence of an initially formed, nanosized, crystalline, manganese carbonate precursor phase which, during the heating, transformed into coarser, irregular, elongated, micron-sized, manganese oxide solids. It was also shown that structural transformations and morphological tailoring were followed by significant changes in the physico-chemical properties of the obtained solids. Their SSA values were drastically reduced as a result of the progressive coalescence at the particle surfaces occurring at higher temperatures. The isoelectric points (IEPs) of the obtained manganese oxides were diverse. This is the consequence of their range of crystal-chemical properties that governed the complex physico-chemical processes at the interface of the manganese oxide solid and the aqueous solution. The results of this study may lead to a conceptually new method for the synthesis of high-performance, nanostructured, manganese oxide solids with desirable structural, morphological and surface properties.

Is Nano-Silver Safe within Bioactive Hydroxyapatite Composites?

Because of the abounded presence of the silver-containing products in the market and intensively studied silver-containing biomaterials in the literature, we investigated a hypothesis that stabilizing silver within bioactive hydroxyapatite composite is capable to provide safe and effective antibacterial action. For that purpose nanocomposite made of bioactive, mineral hydroxyapatite (HAp) and antibacterial silver (Ag) is studied for interactions with both, bacterial and human cells. The nanocomposite provides controlled release of Ag ions; induces severe damages in bacterial cells and is capable for strong bacteriostatic and bactericidal action. On the other hand, investigations of the material's interactions with human cells confirm that lower concentrations are highly compatible with osteosarcoma and fetal lung fibroblasts, but at higher concentrations (that provide bacteriostatic and bactericidal influences in bacteria) the material is toxic and capable of inducing morphological changes similar to those observed in bacterial cells.

Silicon surface deoxidation using strontium oxide deposited with the pulsed laser deposition technique.

The epitaxial growth of functional oxides on silicon substrates requires atomically defined surfaces, which are most effectively prepared using Sr-induced deoxidation. The manipulation of metallic Sr is nevertheless very delicate and requires alternative buffer materials. In the present study the applicability of the chemically much more stable SrO in the process of native-oxide removal and silicon-surface stabilization was investigated using the pulsed-laser deposition technique (PLD), while the as-derived surfaces were analyzed in situ using reflection high-energy electron diffraction and ex situ using X-ray photoelectron spectroscopy, X-ray reflectivity, and atomic force microscopy. After the deposition of the SrO over Si/SiO2, in a vacuum, different annealing conditions, with the temperature ranging up to 850 °C, were applied. Because the deposition took place in a vacuum, a multilayer composed of SrO, Sr-silicate, modified Si, and Si as a substrate was initially formed. During the subsequent annealing the topmost layer epitaxially orders in the form of islands, while a further increase in the annealing temperature induced rapid desorption and surface deoxidation, leading to a 2 × 1 Sr-reconstructed silicon surface. However, the process is accompanied by distinctive surface roughening, and therefore the experimental conditions must be carefully optimized to minimize the effect. The results of the study revealed, for the first time, an effective pathway for the preparation of a SrO-induced buffer layer on a silicon substrate using PLD, which can be subsequently utilized for the epitaxial growth of functional oxides.

Photocatalytic properties of TiO2 and TiO2/Pt: a sol-precipitation, sonochemical and hydrothermal approach.

In this work we prepared TiO2 nano-powders and TiO2/Pt nano-composites via three synthesis methods (sol-precipitation, sonochemical method, hydrothermal method) starting with the same precursors and media. To evaluate and compare the physical properties of the prepared materials, X-ray diffraction analysis, BET measurements, FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron microscopy (TEM, HRTEM, SAED) were applied. The results showed changes to the TiO2 phase composition and crystallinity, the specific surface area as well as the platinum's particle shape and size, depending on the method of synthesis. To determine the photocatalytic efficiency of the prepared materials, the photocatalytic discoloration of the methylene blue solution was evaluated using UV-Vis spectroscopy. The important properties required for a high photocatalytic activity, related to the surface characteristics and the phase composition, were determined in terms of the synthesis method. It was concluded that the optimum characteristics were obtained when using the hydrothermal approach, where the TiO2 had two phases, i.e., - anatase and rutile, a Pt-phase in the form of nanoparticles and adsorbed Pt-molecular species, as well as the presence of available free surface hydroxyl groups. Such characteristics had a critical influence on the photocatalytic activity of the final material.

Direct observation of cationic ordering in double perovskite Sr2FeReO6 crystals.

Two kinds of Sr2FeReO6 (SFRO) samples, pristine SFRO and Re-excess SFRO, were prepared and we visualized the local atomic structure in terms of cationic ordering in the prepared SFRO samples via high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). HAADF-STEM results demonstrated the high degree of cationic ordering maintains in both the pristine SFRO and Re-excess SFRO samples. On the other hand, defective structures such as antiphase boundary and Re-deficient phase were observed dominantly in the pristine SFRO, and thus the poor magnetic property in the pristine SFRO is attributed to those defective structures related with the frustrated Fe/Re ordering.

Polymorphism of LaTaTiO6.

Two polymorphs of LaTaTiO6, i.e. monoclinic and orthorhombic, were synthesized by solid-state reaction technique. Both were found to be isostructural with analogous niobium compounds which were used as structural models. Structural characterization was performed on X-ray powder data by Rietveld refinement procedure which resulted in final Rwp values of 7.01 and 7.52% for orthorhombic and monoclinic form, respectively. Comparisons between both title compounds are given and their plausibility is proved by bond valence sums and global instability index calculations. For the monoclinic polymorph, dielectric properties measured at 1 MHz are also given.

Structure of LaTi2Al9O19 and reanalysis of the crystal structure of La3Ti5Al15O37.

The non-perovskite compound LaTi(2)Al(9)O(19) was synthesized and structurally characterized by conventional X-ray powder diffraction and shown to be isostructural with SrTi(3)Al(8)O(19), as confirmed by bond-valence sum calculations. The dielectric properties of LaTi(2)Al(9)O(19) at 1 MHz were measured. The crystal structure of La(3)Ti(5)Al(15)O(37), which is referred to as the most complex structure solved ab initio from X-ray powder diffraction (XRPD) to date, is shown to be incorrect.

Silver nanoparticles on titanate nanobelts via the self-assembly of weak polyelectrolytes: synthesis and photocatalytic properties.

A weak-polyelectrolyte multilayer on a surface of titanate nanobelts (Ti-NBs) was utilized as a template for in situ Ag nanoparticle formation in the fabrication of Ag-loaded Ti-NBs nanocomposites. The polyelectrolyte multilayer (PEM) was fabricated using layer-by-layer self-assembly of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on the surface of high-surface-area titanate nanobelts (Ti-NBs) synthesized using a hydrothermal procedure. The concentration of Ag nanoparticles in the PEM was controlled by repeating the ion-loading/reduction cycle. The subsequent annealing of the Ag/Ti-NBs-PEM nanocomposites yielded nanostructured crystalline Ag/Ti-NBs. Transmission electron microscopy (TEM) techniques (HRTEM, SAED) and x-ray powder diffraction (XRD) were employed to evaluate the morphological, structural and growth characteristics of the silver nanocrystallites in the Ag/Ti-NBs nanocomposites. The UV-vis photoactivity of the as-fabricated nanocomposites was monitored by the degradation of the cationic dye methylene blue (MB). An enhanced UV photo-efficiency was observed for the Ag/Ti-NBs nanocomposites compared with pure Ti-NBs. As-fabricated Ag(x)/Ti-NBs nanocomposites also exhibited visible photoactivity assisted by the near-field amplitudes of the localized surface plasmon resonance (LSPR) of the silver nanoparticles in the 1D nanocomposite.

Crystal Structures of CaLa8Ti9O31 and Ca2La4Ti6O20 Determined from Powder Diffraction Data.

The ceramic materials of CaLa8Ti9O31 and Ca2La4Ti6O20 were synthesized using the solid-state reaction method. The crystal structures were determined from powder diffraction data using direct space methods. Like in similar compounds of the general formula AnBnO3n+2, the title compounds are composed of perovskite-like slabs, separated by oxygen-rich layers, where Ca or La occupy the A site.

Weak polyion multilayer-assisted in situ synthesis as a route toward a plasmonic Ag/TiO2 photocatalyst.

Nanocrystalline Ag/TiO(2) composite thin films were synthesized using a two-step synthesis methodology: the in situ precipitation of Ag nanoparticles followed by an in situ sol-gel reaction of titanium iso-propoxide in a weak polyion multilayer (PEM) template formed by the layer-by-layer (LbL) self-assembly of poly(acrylic acid) (PAA) and polyallylamine (PAH). Because the PEM template is assembled from weak polyions, it contains nonionized carboxylic groups that are able to react with the inorganics, resulting in the formation of a homogeneous Ag(x)/TiO(2)-PEM precursor film, where the content of Ag is controlled by repeating the Ag loading cycle. The subsequent annealing of the precursor yields nanostructured Ag(x)/TiO(2) films with thicknesses controlled by the PEM template on the nanometer scale. Transmission electron, field-emission scanning electron, and atomic force microscopy methods were employed to evaluate the morphology and growth characteristics of the metallic and semiconductor nanocrystallites in the Ag(x)/TiO(2) composite thin films. The as-formed Ag(x)/TiO(2) composite thin films exhibited UV-visible photoactivity monitored by the decomposition of methylene blue (MB). In the near-UV range, the expected photocatalytic behavior of TiO(2) is greatly enhanced because it is assisted by the near-field amplitudes of the localized surface plasmon resonance (LSPR) of the Ag nanoparticles in the Ag(x)/TiO(2) films.

Order-disorder of oxygen anions and vacancies in solid solutions of La2TiO5 and La4Ga2O9.

Successful Rietveld refinements of seven compounds with the formulae La2Ti((1-x))Ga(x)O((5-x/2)), where x = 0.00, 0.20, 0.50, 0.70, 0.90, 0.95 and 1.00, were performed in order to describe the solid solubility between orthorhombic (Pnam) La2TiO5 and monoclinic (P2(1)/c) La4Ga2O9. The relationship between the end-member structures, which are already known, is discussed; the space-group change is a consequence of ordering the oxygen vacancies that become more numerous as Ga is substituted for Ti. The structures of the solid solutions are also described. The lengths of cell edges obey Vegard's rule.

Controlled synthesis of pure and doped ZnS nanoparticles in weak polyion assemblies: growth characteristics and fluorescence properties.

A polyelectrolyte multilayer (PEM) fabricated by the layer-by-layer (LbL) self-assembly of weak polyions of polyacrylic acid (PAA) and polyallylamine (PAH) was applied as a matrix for the in situ nucleation and growth of pure and Mn-doped ZnS nanocrystallites. The nucleation and growth is initiated by the adsorption and binding of the metal ions to the ionized carboxylic groups of the weak polyions within the matrix, followed by the subsequent precipitation of semiconductor nanocrystallites with Na(2)S. Transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV-vis spectroscopy were employed to establish the growth characteristics of the spherical ZnS nanocrystallites in the polyion matrix. The conformational arrangement of polyion chains induced by variation in the assembly pH is the key parameter that affects the structural and morphological characteristics of ZnS nanocrystallites. Repeating the reaction cycle resulted in an increase in the volume density of ZnS nanoparticles and further growth of the initially formed particles by the Ostwald ripening mechanism. The surface passivation of the ZnS nanocrystallites within the polyion matrix enables the enhanced radiative emission of ZnS composite films in the UV range, whereas by doping the ZnS, nanocrystallites show emission characteristic of the manganese ions in the visible region.