Alkali-Treated Alumina and Zirconia Powders Decorated with Hydroxyapatite for Prospective Biomedical Applications.

The alumina and zirconia surfaces were pretreated with chemical etching using alkaline mixtures of ammonia, hydrogen peroxide and sodium hydroxide, and followed with application of the powder layer of Ca-deficient hydroxyapatite (CDH). The influence of etching bath conditions time and concentration on surface development, chemical composition and morphology of medicinal ceramic powders were studied. The following analyses were performed: morphology (scanning electron microscopy), phase composition (X-ray diffraction analysis), changes in binding interactions and chemical composition (FT-Infrared and Energy dispersive spectroscopies). Both types of etchants did not expose the original phase composition changes or newly created phases for both types of ceramics. Subsequent decoration of the surface with hydroxyapatite revealed differences in the morphological appearance of the layer on both ceramic surfaces. The treated zirconia surface accepted CDH as a flowing layer on the surface, while the alumina was decorated with individual CDH aggregates. The goal of this study was to focus further on the ceramic fillers for polymer-ceramic composites used as a biomaterial in dental prosthetics.

Organobeidellites for Removal of Anti-Inflammatory Drugs from Aqueous Solutions.

Diclofenac (DC) and ibuprofen (IBU) are widely prescribed non-steroidal anti-inflammatory drugs, the consumption of which has rapidly increased in recent years. The biodegradability of pharmaceuticals is negligible and their removal efficiency by wastewater treatment is very low. Therefore, the beidelitte (BEI) as unique nanomaterial was modified by the following different surfactants: cetylpyridinium (CP), benzalkonium (BA) and tetradecyltrimethylammonium (TD) bromides. Organobeidellites were tested as potential nanosorbents for analgesics. The organobeidellites were characterized using X-ray powder diffraction (XRD), Infrared spectroscopy (IR), Thermogravimetry and differential thermal analysis (TG/DTA) and scanning microscopy (SEM). The equilibrium concentrations of analgesics in solution were determined using UV-VIS spectroscopy. The intercalation of surfactants into BEI structure was confirmed both using XRD analysis due to an increase in basal spacing from 1.53 to 2.01 nm for BEI_BA and IR by decreasing in the intensities of bands related to the adsorbed water. SEM proved successful in the uploading of surfactants by a rougher and eroded organobeidellite surface. TG/DTA evaluated the decrease in dehydration/dehydroxylation temperatures due to higher hydrophobicity. The Sorption experiments demonstrated a sufficient sorption ability for IBU (55-86%) and an excellent ability for DC (over 90%). The maximum adsorption capacity was found for BEI_BA-DC (49.02 mg·g-1). The adsorption according to surfactant type follows the order BEI_BA > BEI_TD > BEI_CP.

Development of Novel Thin Polycaprolactone (PCL)/Clay Nanocomposite Films with Antimicrobial Activity Promoted by the Study of Mechanical, Thermal, and Surface Properties.

Infection with pathogenic microorganisms is of great concern in many areas, especially in healthcare, but also in food packaging and storage, or in water purification systems. Antimicrobial polymer nanocomposites have gained great popularity in these areas. Therefore, this study focused on new approaches to develop thin antimicrobial films based on biodegradable polycaprolactone (PCL) with clay mineral natural vermiculite as a carrier for antimicrobial compounds, where the active organic antimicrobial component is antifungal ciclopirox olamine (CPX). For possible synergistic effects, a sample in combination with the inorganic antimicrobial active ingredient zinc oxide was also prepared. The structures of all the prepared samples were studied by X-ray diffraction, FTIR analysis and, predominantly, by SEM. The very different structure properties of the prepared nanofillers had a fundamental influence on the final structural arrangement of thin PCL nanocomposite films as well as on their mechanical, thermal, and surface properties. As sample PCL/ZnOVER_CPX possessed the best results for antimicrobial activity against examined microbial strains, the synergic effect of CPX and ZnO combination on antimicrobial activity was proved, but on the other hand, its mechanical resistance was the lowest.

Tribo-Mechanical Properties of the Antimicrobial Low-Density Polyethylene (LDPE) Nanocomposite with Hybrid ZnO-Vermiculite-Chlorhexidine Nanofillers.

Materials made from low-density polyethylene (LDPE) in the form of packages or catheters are currently commonly applied medical devices. Antimicrobial LDPE nanocomposite materials with two types of nanofillers, zinc oxide/vermiculite (ZnO/V) and zinc oxide/vermiculite_chlorhexidine (ZnO/V_CH), were prepared by a melt-compounded procedure to enrich their controllable antimicrobial, microstructural, topographical and tribo-mechanical properties. X-ray diffraction (XRD) analysis and Fourier transform infrared spectroscopy (FTIR) revealed that the ZnO/V and ZnO/V_CH nanofillers and LDPE interacted well with each other. The influence of the nanofiller concentrations on the LDPE nanocomposite surface changes was studied through scanning electron microscopy (SEM), and the surface topology and roughness were studied using atomic force microscopy (AFM). The effect of the ZnO/V nanofiller on the increase in indentation hardness (HIT) was evaluated by AFM measurements and the Vickers microhardness (HV), which showed that as the concentration of the ZnO/V nanofiller increased, these values decreased. The ZnO/V and ZnO/V_CH nanofillers, regardless of the concentration in the LDPE matrix, slightly increased the average values of the friction coefficient (COF). The abrasion depths of the wear indicated that the LDPE_ZnO/V nanocomposite plates exhibited better wear resistance than LDPE_ZnO/V_CH. Higher HV and HIT microhardness values were measured for both nanofillers than the natural LDPE nanocomposite plate. Very positive antimicrobial activity against S. aureus and P. aeruginosa after 72 h was found for both nanofiller types.

Study of the Structure and Antimicrobial Activity of Ca-Deficient Ceramics on Chlorhexidine Nanoclay Substrate.

Novel biomedical composites, based on organically modified vermiculite and montmorillonite with deposited Ca-deficient hydroxyapatite (CDH), were prepared. The monoionic sodium forms of vermiculite and montmorillonite were intercalated with chlorhexidine diacetate (CA). The surfaces of organoclays were used for the precipitation of Ca-deficient hydroxyapatite. The composites with Ca-deficient hydroxyapatite showed very good antibacterial effects, similar to the antimicrobial activity of pure organoclay samples. Better antibacterial activity was shown in the organically modified montmorillonite sample with Ca-deficient hydroxyapatite compared with the vermiculite composite, but, in the case of Staphylococcus aureus, both composites showed the same minimum inhibitory concentration (MIC) value. The antimicrobial effect of composites against bacteria and fungi increased with the time of exposure. The structural characterization of all the prepared materials, performed using X-ray diffraction and FT infrared spectroscopy analysis, detected no changes in the original clay or CDH during the intercalation or precipitation process, therefore we expect the strength of the compounds to be in the original power.

Effects of Ultrasound on Zinc Oxide/Vermiculite/Chlorhexidine Nanocomposite Preparation and Their Antibacterial Activity.

Microbial infection and biofilm formation are both problems associated with medical implants and devices. In recent years, hybrid organic-inorganic nanocomposites based on clay minerals have attracted significant attention due to their application potential in the field of antimicrobial materials. Organic drug/metal oxide hybrids exhibit improved antimicrobial activity, and intercalating the above materials into the interlayer of clay endows a long-term and controlled-release behavior. Since antimicrobial activity is strongly related to the structure of the material, ultrasonic treatment appears to be a suitable method for the synthesis of these materials as it can well control particle size distribution and morphology. This study aims to prepare novel, structurally stable, and highly antimicrobial nanocomposites based on zinc oxide/vermiculite/chlorhexidine. The influence of ultrasonic treatment at different time intervals and under different intercalation conditions (ultrasonic action in a breaker or in a Roset's vessel) on the structure, morphology, and particle size of prepared hybrid nanocomposite materials was evaluated by the following methods: scanning electron microscopy, X-ray diffraction, energy dispersive X-ray fluorescence spectroscopy, carbon phase analysis, Fourier transforms infrared spectroscopy, specific surface area measurement, particle size analysis, and Zeta potential analysis. Particle size analyses confirmed that the ultrasonic method contributes to the reduction of particle size, and to their homogenization/arrangement. Further, X-ray diffraction analysis confirmed that ultrasound intercalation in a beaker helps to more efficiently intercalate chlorhexidine dihydrochloride (CH) into the vermiculite interlayer space, while a Roset's vessel contributed to the attachment of the CH molecules to the vermiculite surface. The antibacterial activity of hybrid nanocomposite materials was investigated on Gram negative (Escherichia coli, Pseudomonas aeruginosa) and Gram positive (Staphylococcus aureus, Enterococcus faecalis) bacterial strains by finding the minimum inhibitory concentration. All hybrid nanocomposite materials prepared by ultrasound methods showed high antimicrobial activity after 30 min, with a long-lasting effect and without being affected by the concentration of the antibacterial components zinc oxide (ZnO) and CH. The benefits of the samples prepared by ultrasonic methods are the rapid onset of an antimicrobial effect and its long-term duration.

Polyethylene/Organo-Inorgano Vermiculites and Their Antimicrobial Properties.

Clay mineral vermiculite was treated with silver and copper nitrate solutions and samples were subsequently modified with organic compound (dodecylamine) via solid-solid melt intercalation. Prepared organo-inorgano vermiculites were used as nanofillers to the polyethylene matrix. Mixtures of polyethylene with vermiculite nanofillers, prepared by melt compounding technique, were pressed into thin plates. Structure changes of prepared powder vermiculite nanofillers and polyethylene/vermiculite composites were studied by X-ray diffraction analysis. The X-ray diffraction patterns of vermiculite nanofillers confirm intercalation of dodecylamine into the vermiculite interlayer. Antimicrobial properties of powder vermiculite nanofillers were evaluated by the minimum inhibitory concentration of samples which is needed to completely stop the bacterial growth and polyethylene/vermiculite composites were evaluated by the number of colony forming units survived on surfaces of composite plates. Different bacterial strains were studied: (1) Gram-positive, represented by bacteria Staphylococcus aureus and Enterococcus faecalis, (2) Gram-negative, represented by bacteria Escherichia coli and Pseudomonas aeruginosa, and (3) yeast, Candida albicans. Powder vermiculite nanofillers and surfaces of polyethylene/vermiculite composites showed good antimicrobial effect against tested bacteria and yeast. Powder vermiculite nanofillers show antimicrobial effect already after 30 minutes of tested time. Composite plates exhibited decrease of colony forming units number about 5-7 logarithmic orders depending on bacteria after 24 hours of tested time.

Stability of Calcium Deficient Hydroxyapatite/Clay Mineral Nanocomposite in Solutions with Different pH.

Hydroxyapatite is one of the building blocks of hard tissues of living organisms. Therefore stability of nanoparticles in experimental solutions of different pH similar to one in human body is important issue for precise tailoring of the synthesis of hydroxyapatite particles on clay mineral substrate. In this study, the stability (amount of CaII and PV released into the water) of calcium deficient hydroxyapatite/clay mineral nanocomposites was investigated. The calcium deficient hydroxyapatite/clay mineral nanocomposites with montmorillonite and two vermiculites (Brazil and Bulgaria) were compared with pure calcium deficient hydroxyapatite. The stability was investigated for 24 h where calcium deficient hydroxyapatite/clay mineral nanocomposites and pure calcium deficient hydroxyapatite were placed into the water solutions with different pH values (pH= 5, 7, and 9). The presence of CaII and PV ions at solutions were determined using atomic emission spectrometry. The calcium deficient hydroxyapatite/clay mineral nanocomposites after stability testing were characterized by X-ray powder diffraction and infrared spectroscopy with Fourier transformation.

Synthesis and Antimicrobial Activity of Polyethylene/Chlorhexidine/Vermiculite Nanocomposites.

The set of polyethylene/clay nanocomposites with increasing amount of antimicrobial nanofiller (3, 6 and 10 wt%) was prepared by melt compounding procedure. The antimicrobial drug chlorhexidine diacetate was loaded into natural clay mineral vermiculite and also to its monoionic sodium form and then these organoclay nanofillers were incorporated into polymeric matrix. The structure of prepared organoclays and nanocomposites was studied by X-ray diffraction analysis and Fourier transforms infrared spectroscopy. Further thermal properties of polyethylene/clay nanocomposites were investigated by thermogravimetric analysis and the surface roughness was evaluated by atomic force microscopy. Finally, organoclays and polyethylene/clay nanocomposites were tested for antimicrobial activity against bacterial strains Staphylococcus aureus, Escherichia coli and yeast Candida albicans. Prepared samples showed a very good antimicrobial activity with long lasting effect. In the case of polyethylene/clay nanocomposites we observed some differences in antimicrobial action between two used antimicrobial nanofillers. These results suggested great potential of using the polymer/clay nanocomposites in the wide range of antimicrobial applications.

Toxicity of the Zinc Oxide and Vermiculite/Zinc Oxide Nanomaterials.

Nanomaterials and nanocomposite materials on the base of zinc oxide (ZnO) are being produced and applied in our daily life at a rapid pace mainly as additives to the different polymer materials. The antibacterial behaviors of ZnO nanoparticles are intensively studied but related health and environmental toxicity assessments are lagging behind. The aim of this work was evaluated the toxic effect of self-synthesized samples (ZnO nanoparticles, vermiculite/ZnO nanocomposite) and one commercial sample of the ZnO nanoparticles, to induce oxidative stress via lipid peroxidation. This ability is one of the indicators of material toxicity. The toxicity results were compared with the results of titanium dioxide nanoparticles as a validated toxic standard. The effect of the major nanoparticles properties as particle and crystallite size, shape, specific phase and composition were evaluated using the dynamic laser diffraction, scanning electron microscopy and X-ray diffraction analysis. The attention was also focused on the influence of the vermiculite (as matrix of nanocomposite samples) and temperature of the nanostructured materials preparation. All samples containing vermiculite are not able to induce peroxidation of lipids in comparison to TiO2 nanoparticles. However, samples of ZnO nanoparticles demonstrate the ability to induce oxidative stress via lipid peroxidation, which decreases with the increasing temperature of preparation and for commercial ZnO was higher than for prepared ZnO nanoparticles.

ZnO/graphite composites and its antibacterial activity at different conditions.

The paper reports laboratory preparation, characterization and in vitro evaluation of antibacterial activity of ZnO/graphite nanocomposites. Zinc chloride and sodium carbonate served as precursors for synthesis of zinc oxide, while micromilled and natural graphite were used as the matrix for ZnO nanoparticles anchoring. During the reaction of ZnCl2 with saturated aqueous solution of Na2CO3a new compound is created. During the calcination at the temperature of 500 °C this new precursors decomposes and ZnO nanoparticles are formed. Composites ZnO/graphite with 50 wt.% of ZnO particles were prepared. X-ray powder diffraction and Raman microspectroscopy served as phase-analytical methods. Scanning electron microscopy technique was used for morphology characterization of the prepared samples and EDS mapping for visualization of elemental distribution. A developed modification of the standard microdilution test was used for in vitro evaluation of daylight induced antibacterial activity and antibacterial activity at dark conditions. Common human pathogens served as microorganism for antibacterial assay. Antibacterial activity of ZnO/graphite composites could be based on photocatalytic reaction; however there is a role of Zn(2+) ions on the resulting antibacterial activity which proved the experiments in dark condition. There is synergistic effect between Zn(2+) caused and reactive oxygen species caused antibacterial activity.