In vitro antibacterial effect of forsterite nanopowder: synthesis and characterization.

The aims of this study were the preparation, characterization, and in vitro antibacterial activity evaluation of forsterite (FS, Mg2SiO4) nanopowder obtained by two major methods, namely sol-gel (FSsg) and co-precipitation (FSpp). The main aim was to determine the influence of preparation methodologies on physical properties and in vitro antibacterial activity of obtained forsterite nanopowder. To assess the best working temperature for the preparation of FSsg and FSpp, the synthesis and thermal treatment conditions were optimized on the basis of thermal gravimetric (TG) and differential scanning calorimetric (DSC) analysis performed on the dried gel and dried co-precipitated solid, respectively. The FSsg and FSpp powders were characterized by X-ray powder diffraction (XRD), indicating a high purity for both FSsg and FSpp powders. The morphology of FSsg and FSpp nanopowders was explored by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). In vitro antibacterial activity was investigated using a targeted pathogen, namely Staphylococcus aureus (S. aureus) ATCC 6538 P as tested strain by broth dilution technique and inoculations on nutrient agar to highlight the bactericidal inhibitory effect. FSsg nanopowder has no inhibitory capacity, while FSpp produced inhibition, the effect being bactericidal at a concentration of 10 mg/mL. The superior bactericidal activity of FSpp against FSsg is due to variation in the own surface properties, such as specific surface area (SSA) and nano-regime particle size. The FSpp nanoparticles, NPs, obtained by co-precipitation method are reported for the first time as a novel bactericidal nanomaterial against S. aureus.

Ion release from hydroxyapatite and substituted hydroxyapatites in different immersion liquids: in vitro experiments and theoretical modelling study.

Multi-substituted hydroxyapatites (ms-HAPs) are currently gaining more consideration owing to their multifunctional properties and biomimetic structure, owning thus an enhanced biological potential in orthopaedic and dental applications. In this study, nano-hydroxyapatite (HAP) substituted with multiple cations (Sr2+, Mg2+ and Zn2+) for Ca2+ and anion ( Si O 4 4 - ) for P O 4 3 - and OH-, specifically HAPc-5%Sr and HAPc-10%Sr (where HAPc is HAP-1.5%Mg-0.2%Zn-0.2%Si), both lyophilized non-calcined and lyophilized calcined, were evaluated for their in vitro ions release. These nanomaterials were characterized by scanning electron microscopy, field emission-scanning electron microscopy and energy-dispersive X-ray, as well as by atomic force microscope images and by surface specific areas and porosity. Further, the release of cations and of phosphate anions were assessed from nano-HAP and ms-HAPs, both in water and in simulated body fluid, in static and simulated dynamic conditions, using inductively coupled plasma optical emission spectrometry. The release profiles were analysed and the influence of experimental conditions was determined for each of the six nanomaterials and for various periods of time. The pH of the samples soaked in the immersion liquids was also measured. The ion release mechanism was theoretically investigated using the Korsmeyer-Peppas model. The results indicated a mechanism principally based on diffusion and dissolution, with possible contribution of ion exchange. The surface of ms-HAP nanoparticles is more susceptible to dissolution into immersion liquids owing to the lattice strain provoked by simultaneous multi-substitution in HAP structure. According to the findings, it is rational to suggest that both materials HAPc-5%Sr and HAPc-10%Sr are bioactive and can be potential candidates in bone tissue regeneration.

Advanced Mg, Zn, Sr, Si Multi-Substituted Hydroxyapatites for Bone Regeneration.

PURPOSE: Compositional tailoring is gaining more attention in the development of advanced biomimetic nanomaterials. In this study, we aimed to prepare advanced multi-substituted hydroxyapatites (ms-HAPs), which show similarity with the inorganic phase of bones and might have therapeutic potential for bone regeneration. MATERIALS: Novel nano hydroxyapatites substituted simultaneously with divalent cations: Mg2+ (1.5%), Zn2+ (0.2%), Sr2+ (5% and 10%), and Si (0.2%) as orthosilicate (SiO4 4-) were designed and successfully synthesized for the first time. METHODS: The ms-HAPs were obtained via a wet-chemistry precipitation route without the use of surfactants, which is a safe and ecologically friendly method. The composition of synthesized materials was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The materials were characterized by X-ray powder diffraction (XRD), FT-IR and FT-Raman spectroscopy, BET measurements and by imaging techniques using high-resolution TEM (HR-TEM), FE-SEM coupled with EDX, and atomic force microscopy (AFM). The ion release was measured in water and in simulated body fluid (SBF). RESULTS: Characterization methods confirmed the presence of the unique phase of pure stoichiometric HAP structure and high compositional purity of all synthesized nanomaterials. The doping elements influenced the crystallite size, the crystallinity, lattice parameters, morphology, particle size and shape, specific surface area, and porosity. Results showed a decrease in both nanoparticle size and crystallinity degree, coupled with an increase in specific surface area of these advanced ms-HAP materials, in comparison with pure stoichiometric HAP. The release of biologically important ions was confirmed in different liquid media, both in static and simulated dynamic conditions. CONCLUSION: The incorporation of the four substituting elements into the HAP structure is demonstrated. Synthesized nanostructured ms-HAP materials might inherit the in vivo effects of substituting functional elements and properties of hydroxyapatite for bone healing and regeneration. Results revealed a rational tailoring approach for the design of a next generation of bioactive ms-HAPs as promising candidates for bone regeneration.

Effects of doxorubicin mediated by gold nanoparticles and resveratrol in two human cervical tumor cell lines.

Green synthesis of gold nanoparticles capped with resveratrol (GNPs) and their physical and chemical characterization by UV-vis spectra, FTIR, DLS, XRD, TEM and AFM are reported. The GNPs are highly stable, with average diameter of about 20 nm. Then, supramolecular nanoassemblies of GNPs and doxorubicin (Dox), Dox-GNPs complexes, were prepared and morphologically characterized. The stability of these Dox nanocomplexes is high in phosphate buffer saline as estimated by UV-vis spectra, TEM and AFM analysis. Effects of resveratrol (Resv), Resv-Dox mixtures, GNPs and Dox-GNPs complexes on HeLa and CaSki cells, after 24h drug incubation, were assessed using MTT cell viability assay. Results showed strong anticancer activity for Resv-Dox mixtures and Dox-GNPs complexes in the two human cervical carcinoma cell lines. Clearly, both Resv and GNPs can mediate the anticancer activity of Dox at its very low concentration of 0.1 µg/mL, reaching the cytotoxicity of Dox alone, at its concentration up to 20 times higher. Cytotoxic effects of Resv-Dox mixtures and Dox-GNPs complexes have been found for the first time in HeLa and CaSki cells. Furthermore, the apoptosis induction in HeLa and CaSki cells was evidenced for Resv-Dox mixtures and Dox-GNPs complexes by flow cytometry using Annexin V-FITC/propidium iodide cellular staining. For CaSki cells, the apoptosis was also demonstrated, mainly for the treatment with Dox-GNPs complexes, by MTT formazan cellular staining visualized in phase contrast microscopy. Our results provide strong evidence that novel drug delivery vehicles developed on Dox-GNPs nanocomplexes and Resv could have wide applications in cancer diagnosis and treatment.

New procedure to synthesize silver nanoparticles and their interaction with local anesthetics.

Silver nanoparticles (AgNPs) were prepared in aqueous colloid dispersions by the reduction of Ag(+) with glucose in alkaline medium. Tetraethyl orthosilicate and L-asparagine were added as stabilizers of NPs. The AgNPs were characterized, and their interaction with three local anesthetics (procaine, dibucaine, or tetracaine) was investigated. Optical spectra show the characteristic absorption band of AgNPs, due to surface plasmon resonance. Modifications in the position and shape of this band reflect the self-assembly of metal NPs mediated by anesthetic molecules and the progress in time of the aggregation process. Zeta-potential measuring was applied in order to characterize the electrostatic stability of the NPs. The size and shape of the AgNPs, as well as the features of the assemblies formed by their association in the presence of anesthetics, were evidenced by transmission electron microscopy images. Atomic force microscopy images showed the characteristics of the films of AgNPs deposited on glass support. The effect of the anesthetics could be described in terms of electrostatic forces between the negatively charged AgNPs and the anesthetic molecules, existing also in their cationic form at the working pH. But also hydrophobic and hydrogen bonding interactions between the coated nanoparticles and anesthetics molecular species should be considered.

Selective effect of procaine, tetracaine and dibucaine on gold nanoparticles.

An aqueous colloid dispersion of gold nanoparticles (AuNPs) was prepared by reduction of gold(III) chloride and its interaction with three local anesthetics (procaine, dibucaine or tetracaine) was investigated. Optical spectra reveal the modifications in the absorption band of nanoparticles related to their self assembly mediated by anesthetic molecules and depending on the progress in time of the aggregation process. TEM images show the features of the self assemblies formed by the association of gold nanoparticles in presence of anesthetics, and reveal marked differences in the behavior of the AuNPs against the three anesthetics. The main effect of various anesthetics can be described in terms of electrostatic forces between the negatively charged metal nanoparticles and anesthetic molecules, existing in their cationic form at the working pH. Then, the anesthetics functionalized nanoparticles trigger specific interactions to form different self assemblies through a selective combination of hydrophobic and hydrogen bonding interactions between the coated nanoparticles and anesthetics molecular species.

The effect of arginine on gold nanoparticles in colloidal solutions and in thin films.

Gold nanoparticles were prepared in aqueous colloidal solutions and their interaction with L-arginine solutions at different concentrations was investigated by UV-vis spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The shift towards red of the absorption maximum of gold nanoparticles with increasing L-arginine concentration and in time, and the apparition of a new large band at higher wavelength evidence the formation of assemblies of gold nanoparticles, mediated by the amino acid. TEM images present the progress in the building process of supermolecular structures. Further, the AFM images show the self assemblies of gold nanoparticles capped with L-arginine well ordered in large domains on silanized glass. As a model for the process, we suggest that the positively charged guanidinium group of L-arginine is anchored on the negative citrate capped gold nanoparticles, while the other two functionalities of L-arginine are involved in the bonding between gold nanoparticles. The ability of arginine to specifically bind gold nanoparticles could lead to an increased ability of proteins, containing arginine, to specifically bind to nanogold. Then, they bind other target proteins or different ligands underlying numerous biological and medical applications that range from nanoscale biosensors, cell-cell communications to targeted delivery of drugs to cancer cells.

Procaine effect on human erythrocyte membrane explored by atomic force microscopy.

The procaine effect on human erythrocytes was investigated by atomic force microscopy (AFM) at three procaine concentrations, about 5 x 10(-7) M, 5 x 10(-5) M and 5 x 10(-4) M. The changes in surface morphology of erythrocyte membrane bring direct evidence on the procaine effect on the cell membrane at micro- and nanometer scale. AFM images of the control erythrocytes (without procaine) showed a well defined concave (donut) shape of cells. The structure of control erythrocytes membrane is featured by closely packed nanometer size intra-membranous particles. After the incubation of the fresh blood with increasing procaine concentrations, a progressive increase in both concave depth and surface roughness of erythrocyte membrane was observed. The particles (granules) of the membrane surface increased progressively with increasing procaine concentrations. The changes in the surface morphology of erythrocyte membrane can be associated with the enlargement of surface granules, due to the aggregation of membranous particles within the cell surface, and the domain structure formation induced by procaine. A large number of moderate elevations from 25 nm to almost 40 nm in lateral size were found to be rather uniformly distributed on the surface of whole erythrocytes at low and medium procaine concentrations, respectively. At the highest procaine concentration, the granules of about 80 nm to almost 90 nm lateral size were found to form rows rather well separated. These data are in substantial agreement with the published results obtained on membrane models in the presence of procaine.