Wido H. Schreiner

Improving the osteointegration and bone–implant interface by incorporation of bioactive particles in sol–gel coatings of stainless steel implants

In this study, we report a hybrid organic-inorganic TEOS-MTES (tetraethylorthosilicate-methyltriethoxysilane) sol-gel-made coating as a potential solution to improve the in vivo performance of AISI 316L stainless steel, which is used as permanent bone implant material. These coatings act as barriers for ion migration, promoting the bioactivity of the implant surface. The addition of SiO(2) colloidal particles to the TEOS-MTES sol (10 or 30 mol.%) leads to thicker films and also acts as a film reinforcement. Also, the addition of bioactive glass-ceramic particles is considered responsible for enhancing osseointegration. In vitro assays for bioactivity in simulated body fluid showed the presence of crystalline hydroxyapatite (HA) crystals on the surface of the double coating with 10mol.% SiO(2) samples on stainless steel after 30 days of immersion. The HA crystal lattice parameters are slightly different from stoichiometric HA. In vivo implantation experiments were carried out in a rat model to observe the osteointegration of the coated implants. The coatings promote the development of newly formed bone in the periphery of the implant, in both the remodellation zone and the marrow zone. The quality of the newly formed bone was assessed for mechanical and structural integrity by nanoindentation and small-angle X-ray scattering experiments. The different amount of colloidal silica present in the inner layer of the coating slightly affects the material quality of the newly formed bone but the nanoindentation results reveal that the lower amount of silica in the coating leads to mechanical properties similar to cortical bone.

Microstructural and morphological analysis of pure and Ce-doped tin dioxide nanoparticles

Structural and morphological studies in pure and Ce-doped tin dioxide nanoparticles with high stability against particle growth were performed in samples, obtained using the polymeric precursor method and prepared at different annealing temperatures. A Ce-rich surface layer was used to control the particle size and stabilize SnO2 against particle growth. The formation of this segregated layer can contribute to a decreased surface energy, acting in the driving force, or reducing the surface mobility. Only the cassiterite SnO2 phase was observed below 1000 � C and a secondary phase (CeO2) was observed for the Ce-doped SnO2 at temperatures higher than 1000 � C, when de-mixing process occurs. The evolution of crystallite size, microstrain and morphology of the nanoparticles with annealing temperatures was investigated by X-ray diffraction (XRD), associated to Rietveld refinements, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). # 2002 Elsevier Science Ltd. All rights reserved.

Polyaniline/lignin blends: thermal analysis and XPS

Polyaniline (Pani) base and Kraft lignin (Lig) blend films have been prepared using the solvent evaporation method. The highest lignin concentration used was of 36% (m/m). The thermal behaviour of free standing Pani and of Pani/Lig blends was characterized using thermogravimetric analysis (TGA) and DMTA techniques. The TGA results indicate that Pani/Lig blends have greater thermal stability than the pure polymers. The dynamic mechanical analysis (DMA) experiments indicated that the addition of lignin in the blend occur an impairment of rotation of part of the Pani chain. The possibility of interactions between Pani and lignin is discussed through X-ray photoelectron spectroscopy and DMA measuring. These interactions can occur between Pani chain amine nitrogen and carbonyl group present in the lignin and also between imine nitrogen and hydroxyl groups of lignin.

Structure and properties of polypyrrole/bacterial cellulose nanocomposites

An electrically conducting composite based on bacterial cellulose (BC) and polypyrrole (PPy) was prepared through in situ oxidative polymerization of pyrrole (Py) in the presence of BC membrane using ammonium persulfate (APS), as an oxidant. The electrical conductivity, morphology, mechanical properties and thermal stability of the composites obtained using APS (BC/PPy·APS) were evaluated and compared with BC/PPy composites prepared using as oxidant agent Iron III chloride hexahydrate (FeCl3·6H2O). The morphology of the BC/PPy·APS composites is characterized by spherical conducting nanoparticles uniformly distributed on the BC nanofiber surface, while the composites produced with FeCl3·6H2O (BC/PPy·FeCl3) is composed of a continuous conducting polymer layer coating the BC-nanofibers. The electrical conductivity of BC/PPy·FeCl3 was 100-fold higher than that found for BC/PPy·APS composites. In order to understand the site-specific interaction between PPy and BC functional groups, both composites were characterized by Fourier transform infrared (attenuated total reflectance mode) spectroscopy attenuation reflectance (FTIR-ATR) and X-ray photoelectron spectrometry (XPS). The affinity between functional groups of PPy·FeCl3 and BC is higher than that found for BC/PPy·APS composite. In addition, the tensile properties were also influenced by the chemical affinity of both components in the polymer composites.

Ferromagnetism induced by oxygen and cerium vacancies above the percolation limit in CeO2

We studied the structural, chemical and magnetic properties of non-doped ceria (CeO(2)) thin films electrodeposited on silicon substrates. Experimental results confirm that the observed room temperature ferromagnetism is driven by both cerium and oxygen vacancies. We investigated ceria films presenting vacancy concentrations well above the percolation limit. Irradiation experiments with neon ions were employed to generate highly oxygen defective CeO(2-δ) structures. X-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectroscopy were used to estimate the concentration of Ce(3+) sites in the films, which can reach up to 50% of Ce(3+) replacing Ce(4+), compared to a stoichiometric CeO(2) structure. Despite the increment of structural disorder, we observe that the saturation magnetization continuously increases with Ce(3+) concentration. Our experiments demonstrate that the ferromagnetism observed in ceria thin films, highly disordered and oxygen-deficient, preserving the fluorite-type structure only in a nanometer scale, remains intrinsically stable at room temperature.

Structure, Composition, and Morphology of Electrodeposited Co x Fe1 − x Alloys

We have investigated the structure, composition, and morphology of Co x Fe 1-x alloys prepared on copper substrates under potentiostatic electrodeposition conditions currently used to produce composition modulated alloys. Co x Fe 1-x alloys with x = 1 to 0 have been obtained by simple control of the Co 2+ : Fe 2+ ratio in the bath solutions using the characteristic behavior of the codeposition of the metals. The alloy composition was determined by energy dispersive spectroscopy. X-ray analysis of the structure of deposits indicates texture with coexistence of phases. For higher iron concentrations the alloys are mostly body-centered-cubic with (110) preferred orientation. For higher cobalt concentrations the alloys become mostly hexagonal with (0001) preferred orientation. Scanning electron microscopy was used to analyze the deposit morphology. Except for alloy concentrations of about x = 0.7, where a nonuniform character of deposits with partial cobalt segregation has been observed, the Co-Fe alloys have a rather uniform composition and morphology in the cathodic potentials used for electrodeposition

Synthesis of TiO2 Nanocrystals with a High Affinity for Amine Organic Compounds

This article describes a different approach to the colloidal synthesis of TiO(2) nanocrystals using a polymer melt as a solvent. This approach allowed us to obtain a colloidal dispersion with a high degree of stability in a polymeric solvent, resulting in a transparent colloid. Using this method, it was possible to obtain the TiO(2) nanocrystal with Brønsted acid sites and polymer chains chemically anchored on the nanocrystal surface. The acid surface of those nanocrystals has the chemical property to react in the presence of amine organic compounds and to maintain the colloidal stability. In this way, TiO(2) nanocrystals were combined with a molecular probe containing amine functional groups such as polyaniline. Through the combination of the molecular probe and inorganic nanocrystals, we obtained a hybrid material with interesting chemical, optical, and electronic behavior, making it a promising material for photovoltaic, photochromic, and sensor devices.

The influence of cation segregation on the methanol decomposition on nanostructured SnO2

Abstract Here we describe a new route to synthesize ultrafine rare earth doped and undoped tin oxide particles for catalytic applications. The catalytic behavior observed in SnO2 samples suggests the control of the catalytic activity and the selectivity of the products by the segregation of a layer of a rare earth compound with the increase of the heat-treatment temperature. The ultrafine particles were characterized by means of BET, XPS, TEM, XRD and Rietveld refinement. It was demonstrated that the effects of the dopant on the methanol decomposition reaction and on the H2 selectivity were correlated with the segregation of a rare earth layer on the tin oxide samples.

Covalent grafting of phenylphosphonate groups onto layered silica derived from in situ-leached chrysotile fibers

The reaction of natural chrysotile fibers with phenylphosphonic acid leads to a new grafted material. The layered material, with an interplanar basal distance of 15.2 A, was characterized by powder X-ray diffraction, thermal analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. The experimental data are consistent with the grafting of phenylphosphonate groups to the surface of the layered silica sheets, obtained by the in situ acidic leaching of brucite sheets, from chrysotile.

Intercalation of an oxalatooxoniobate complex into layered double hydroxide and layered zinc hydroxide nitrate.

A Zn/Al layered double hydroxide with molar ratio of 3 was prepared by coprecipitation in alkaline pH and used as a matrix to intercalate the ionic complex diaquadioxalatooxoniobate(V) (DDON), derived from NH(4)[NbO(C(2)O(4))(2)(H(2)O)(2)]2H(2)O. In a similar way, the layered zinc hydroxide nitrate, Zn(5)(OH)(8)(NO(3))(2)2H(2)O, was synthesized, preexpanded with azelate ions ((-)OOC(CH(2))(7)COO(-)), and then intercalated with the niobium complex. For both layered matrices, the results from X-ray powder diffractometry, Fourier transform infrared spectroscopy, and thermal analysis (TG/s-DTA) indicate the presence of the oxalate ion. In addition, results from X-ray photoelectron and Raman spectroscopy indicate the presence of the niobium center bonded to oxygen atoms. Finally, diffuse reflectance UV-vis spectroscopy suggests that the niobium centers are coordinated to oxalate ions. This is the first report of the intercalation of niobium into a layered matrix.