Djordje Janackovic

Corrosion Stability and Bioactivity in Simulated Body Fluid of Silver/Hydroxyapatite and Silver/Hydroxyapatite/Lignin Coatings on Titanium Obtained by Electrophoretic Deposition

Hydroxyapatite is the most suitable biocompatible material for bone implant coatings. However, its brittleness is a major obstacle, and that is why, recently, research focused on creating composites with various biopolymers. In this study, hydroxyapatite coatings were modified with lignin in order to attain corrosion stability and surface porosity that enables osteogenesis. Incorporating silver, well known for its antimicrobial properties, seemed the best strategy for avoiding possible infections. The silver/hydroxyapatite (Ag/HAP) and silver/hydroxyapatite/lignin (Ag/HAP/Lig) coatings were cathaphoretically deposited on titanium from ethanol suspensions, sintered at 900 °C in Ar, and characterized by X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy, attenuated total reflection Fourier transform infrared, and X-ray photoelectron spectroscopy. The corrosion stability of electrodeposited coatings was evaluated in vitro in Kokubos simulated body fluid (SBF) at 37 °C using electrochemical impedance spectroscopy. Bioactivity was estimated by immersion in SBF to evaluate the formation of hydroxyapatite on the coating surface. A microcrystalline structure of newly formed plate-shaped carbonate-hydroxyapatite was detected after only 7 days, indicating enhanced bioactive behavior. Both coatings had good corrosion stability during a prolonged immersion time. Among the two, the Ag/HAP/Lig coating had a homogeneous surface, less roughness, and low values of contact angle.

Kinetics, thermodynamics, and structural investigations on the removal of Pb2+, Cd2+, and Zn2+ from multicomponent solutions onto natural and Fe(III)-modified zeolites

The adsorption of Pb2+, Cd2+, and Zn2+ from equimolar multicomponent solutions onto natural and Fe(III)-modified zeolites was studied by batch experiments in order to determine the influence of the competitive effect on the efficiency ions removal at different initial concentrations and different temperatures. Kinetic and equilibrium studies showed that affinity of both zeolites was the highest for Pb2+ and much lower for Zn2+ and Cd2+. The competitive effect was negligible at lower concentrations, while Zn2+ and especially Cd2+ ions adsorption was suppressed as the concentrations were increased. Affinity of natural zeolite toward the ions was lower than that of the modified zeolite, as was shown for adsorption from single-component solutions. External film diffusion was the rate-controlling step at lower concentrations and for ions of higher affinity for the adsorbent, while intraparticle diffusion was dominant at higher concentrations and for ions of lower affinity for the adsorbent. The increasing spontaneity of the adsorption process with increasing temperature and the positive values of enthalpy of adsorption indicated the endothermic nature of the adsorption process. Structural investigations of the adsorbents loaded with Pb2+, Cd2+, and Zn2+ ions by X-ray photoelectron spectroscopy (XPS) confirmed the higher content of the ions in the surface and subsurface regions of the Fe(III)-modified than of the natural zeolite. XPS depth profiles of the loaded Fe(III)-modified zeolite showed that surface mechanisms of adsorption were dominant in the case of lead and cadmium, while zinc loading on the zeolite sample was governed mainly by an ion-exchange process.

Alumina/silica aerogel with zinc chloride alkylation catalyst: Influence of supercritical drying conditions and aerogel structure on alkylation catalytic activity

Abstract Alumina/silica aerogel with zinc chloride alkylation catalyst, was obtained using one step sol–gel synthesis and subsequent drying with the supercritical carbon dioxide. The high density supercritical carbon dioxide drying conditions resulted in zinc chloride removal from the catalyst surface, surface area and pore volume increase and catalytic activity decrease. The low density supercritical carbon dioxide drying conditions, pore size distribution centred around 6 nm pore radius and high degree of mixed Al–O–Si bonds in the alumina/silica aerogel network, were found to increase the catalytic activity of the obtained aerogel catalysts.

In vitro cell response to Co-containing 1393 bioactive glass

Cobalt ions are known to stimulate angiogenesis via inducing hypoxic conditions and hence are interesting agents to be used in conjunction with bioactive glasses (BGs) in bone tissue engineering approaches. In this work we investigated in vitro cell biocompatibility of Co releasing 1393 BG composition (in wt.%: 53SiO2, 6Na2O, 12K2O, 5MgO, 20CaO, and 4P2O5) derived scaffolds with osteoblast-like cells (MG-63) and human dermal microvascular endothelial cells (hDMECs). Cell viability, cell number and cell morphology of osteoblast-like cells in contact with particulate glass and 3D scaffolds were assessed showing good biocompatibility of 1393 reference material and with 1 wt.% CoO addition whereby 5 wt.% of CoO in the glass showed cytotoxicity. Furthermore for 1393 with 1 wt.% of CoO increased mitochondrial activity was measured. Similar observations were made with hDMECs: while 1393 and 1393 with 1 wt.% CoO were biocompatible and the endothelial phenotype was retained, 5 wt.% CoO containing BG showed cytotoxic effects after 1 week of cell culture. In conclusion, 1 wt.% Co containing BG was biocompatible with osteoblast like cells and endothelial cells and showed slightly stimulating effects on osteoblast-like cells whereas the addition of 5 wt.% CoO seems to exceed the vital therapeutic ranges of Co ions being released in physiological fluids.

The effect of grain size on the biocompatibility, cell–materials interface, and mechanical properties of microwave‐sintered bioceramics

The effect of decreasing the grain size on the biocompatibility, cell-material interface, and mechanical properties of microwave-sintered monophase hydroxyapatite bioceramics was investigated in this study. A nanosized stoichiometric hydroxyapatite powder was isostatically pressed at high pressure and sintered in a microwave furnace in order to obtain fine grained dense bioceramics. The samples sintered at 1200°C, with a density near the theoretical one, were composed of micron-sized grains, while the grain size decreased to 130 nm on decreasing the sintering temperature to 900°C. This decrease in the grain size certainly led to increases in the fracture toughness by much as 54%. An in vitro investigation of biocompatibility with L929 and human MRC-5 fibroblast cells showed noncytotoxic effects for both types of bioceramics, while the relative cell proliferation rate, cell attachment and metabolic activity of the fibroblasts were improved with decreasing of grain size. An initial in vivo investigation of biocompatibility by the primary cutaneous irritation test showed that both materials exhibited no irritation properties.

PVB/sepiolite nanocomposites as reinforcement agents for paper

In order to improve the mechanical properties of paper, 1, 3 and 5 wt. % of sepiolite were dispersed in a poly(vinyl butyral) (PVB) matrix and coated onto the surface of schrenz (110 g m-2). Deagglomerated sepiolite nanofibers in the PVB matrix on the paper surface were observed by scanning electron microscopy. The glass transition temperature of schrenz with PVB/sepiolite coatings was not changed with increasing content of sepiolite. Two different methods were used to evaluate the mechanical properties of the paper sample reinforced with PVB/sepiolite nanocomposites: tensile testing and nanoindentation. The values of breaking force and tensile energy absorption of the reinforced paper samples obtained by tensile testing were increased by up 10 %. The values of the reduced elastic modulus and hardness obtained by nanoindentation were increased by up to 78 %. The best improvement of the mechanical properties was shown by the paper sample coated with PVB/3 wt. % sepiolite nanocomposite.

Enhanced absorption of TiO2 nanotubes by N-doping and CdS quantum dots sensitization: insight into the structure

Anodization of titanium film sputtered on fluorine doped tin oxide (FTO) glass was performed to obtain highly ordered ∼2 μm long and ∼60 nm wide TiO2 nanotubes. The titania films were annealed in ammonia atmosphere to enable the doping with N. The annealing did not affect the nanotubular morphology and the porosity remained open which is a very important requirement for further deposition of CdS quantum dots. The analysis done by transmission electron microscopy (TEM) has shown that the N-doped nanotubes have a smaller interplanar distance as compared to the undoped ones, whose interplanar distance corresponded to anatase phase. This difference was attributed to the N doping and the Sn migration from the substrate, as demonstrated by energy dispersive spectroscopy (EDS) combined with electron energy loss spectroscopy (EELS). The near edge X-ray absorption fine structure (NEXAFS) analysis clearly demonstrated that also the doped TiO2 film has anatase phase. Regarding the chemical composition of the studied samples, the X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoelectron spectroscopy (SRPES) analyses have shown that N is incorporated both interstitially and substitutionally in the TiO2 lattice, with a decreased contribution of the interstitial after ionic sputtering. The shift of the valence band maximum (VBM) position for the doped TiO2 vs. the undoped TiO2 proved the narrowing of the band gap. The CdS/TiO2 films show bigger VBM shifting that can be attributed to CdS deposit. Comparing the absorption spectra of the bare undoped and doped TiO2 samples, it was noticed that the doping causes a red shift from 397 to 465 nm. Furthermore, the CdS deposition additionally enhances the absorption in the visible range (575 nm for undoped TiO2/CdS and 560 nm for doped TiO2/CdS films).

Sepiolite functionalized with N-[3-(trimethoxysilyl)propyl]ethylenediamine triacetic acid trisodium salt. Part II: Sorption of Ni2+ ions from water

Abstract: The sorption of Ni 2+ on the sepiolite functionalized by covalent grafting of N -[3-(trimethoxysilyl)propyl]ethylenediamine triacetic acid trisodium salt, MSEAS, was studied in batch experiments as a function of the initial metal concentration, the equilibration time, pH value, and temperature. The modification of sepiolite resulted in an enhanced Ni 2+ retention with a capacity of 0.261 mmol/g at 298 K. The retention of Ni 2+ ions occurred dominantly by specific sorption and exchange of Mg 2+ ions from the sepiolite structure. The sorption process followed pseudo-second-order kinetics. The sorption equilibrium results were best described by the non-linear form of the Langmuir Sorption Equation. The values of the thermodynamic parameters (enthalpy, free energy and entropy) were calculated from temperature dependent sorption isotherms and these values showed that the sorption of Ni 2+ onto modified sepiolite was endothermic.