Comparative Characterisation of 3-D Hydroxyapatite Scaffolds Developed via Replication of Synthetic Polymer Foams and Natural Marine Sponges

The production of complex inorganic forms, based on naturally occurring scaffolds offers an exciting avenue for the construction of a new generation of ceramic-based bone substitute scaffolds. The following study reports an investigation into the architecture (porosity, pore size distribution, pore interconnectivity and permeability), mechanical properties and cytotoxic response of hydroxyapatite bone substitutes produced using synthetic polymer foam and natural marine sponge performs. Infiltration of polyurethane foam (60 pores/in2) using a high solid content (80wt %), low viscosity (0.126Pas) hydroxyapatite slurry yielded 84-91% porous replica scaffolds with pore sizes ranging from 50µm - 1000µm (average pore size 577µm), 99.99% pore interconnectivity and a permeability value of 46.4 x10-10m2. Infiltration of the natural marine sponge, Spongia agaricina, yielded scaffolds with 56- 61% porosity, with 40% of pores between 0-50µm, 60% of pores between 50-500µm (average pore size 349 µm), 99.9% pore interconnectivity and a permeability value of 16.8 x10-10m2. The average compressive strengths and compressive moduli of the natural polymer foam and marine sponge replicas were 2.46±1.43MPa/0.099±0.014GPa and 8.4±0.83MPa /0.16±0.016GPa respectively. Cytotoxic response proved encouraging for the HA Spongia agaricina scaffolds; after 7 days in culture medium the scaffolds exhibited endothelial cells (HUVEC and HDMEC) and osteoblast (MG63) attachment, proliferation on the scaffold surface and penetration into the pores. It is proposed that the use of Spongia agaricina as a precursor material allows for the reliable and repeatable production of ceramic-based 3-D tissue engineered scaffolds exhibiting the desired architectural and mechanical characteristics for use as a bone 3 scaffold material. Moreover, the Spongia agaricina scaffolds produced exhibit no adverse cytotoxic response.

The influence of high air entry filter on the testing of unsaturated soils using the axis translation technique

Suction is an important stress variable that is required for reliable predictions of the likely performance of unsaturated soils. The axis translation technique is the best established method of measuring or controlling suction; however, the success of this application is heavily dependent on the rating of the high air entry filter (HAF) and how it is incorporated into the testing system. This paper reports some basic experiments in which samples of unsaturated kaolin were brought to saturation in stages using 5 bar and 15 bar HAFs. The results have shown that the water equilibrium in unsaturated soils is greatly affected by the rating of filters. The findings also suggest that the flow through unsaturated soils is not necessarily governed by the one-dimensional consolidation theory that was developed for saturated soils, and this may be attributed to the bimodal pore size distribution of unsaturated soils.

Surface reactivity enhancement of silica-based glass-ceramic scaffolds

A paradigm shift is taking place from using transplanting tissue and synthetic implants to a tissue engineering approach that aims to regenerate damaged tissues by combining cells from the body with highly porous scaffold biomaterials, which act as templates, guiding the growth of new tissue. The central focus of this thesis was to produce porous glass and glass-ceramic scaffolds that exhibits a bioactive and biocompatible behaviour with specific surface reactivity in synthetic physiological fluids and cell-scaffold interactions, enhanced by composition and thermal treatments applied. Understanding the sintering behaviour and the interaction between the densification and crystallization processes of glass powders was essential for assessing the ideal sintering conditions for obtaining a glass scaffolds for tissue engineering applications. Our main goal was to carry out a comprehensive study of the bioactive glass sintering, identifying the powder size and sintering variables effect, for future design of sintered glass scaffolds with competent microstructures. The developed scaffolds prepared by the salt sintering method using a 3CaO.P2O5 - SiO2 - MgO glass system, with additions of Na2O with a salt, NaCl, exhibit high porosity, interconnectivity, pore size distribution and mechanical strength suitable for bone repair applications. The replacement of 6 % MgO by Na2O in the glass network allowed to tailor the dissolution rate and bioactivity of the glass scaffolds. Regarding the biological assessment, the incorporation of sodium to the composition resulted in an inibition cell response for small periods. Nevertheless it was demonstrated that for 21 days the cells response recovered and are similar for both glass compositions. The in vitro behaviour of the glass scaffolds was tested by introducing scaffolds to simulated body fluid for 21 days. Energy-dispersive Xray spectroscopy and SEM analyses proved the existence of CaP crystals for both compositions. Crystallization forming whitlockite was observed to affect the dissolution behaviour in simulated body fluid. By performing different heat treatments, it was possible to control the bioactivity and biocompatability of the glass scaffolds by means of a controlled crystallization. To recover and tune the bioactivity of the glass-ceramic with 82 % crystalline phase, different methods have been applied including functionalization using 3- aminopropyl-triethoxysilane (APTES). The glass ceramic modified surface exhibited an accelerated crystalline hydroxyapatite layer formation upon immersion in SBF after 21 days while the as prepared glass-ceramic had no detected formation of calcium phosphate up to 5 months. A sufficient mechanical support for bone tissue regeneration that biodegrade later at a tailorable rate was achievable with the glass–ceramic scaffold. Considering the biological assessment, scaffolds demonstrated an inductive effect on the proliferation of cells. The cells showed a normal morphology and high growth rate when compared to standard culture plates. This study opens up new possibilities for using 3CaO.P2O5–SiO2–MgO glass to manufacture various structures, while tailoring their bioactivity by controlling the content of the crystalline phase. Additionally, the in vitro behaviour of these structures suggests the high potential of these materials to be used in the field of tissue regeneration.

Effect of vanadia on physico-chemical and catalytic characteristics of dysprosia

Physico-chemical characterization of DY203/V2O5 systems prepared through wet impregnation method has been carried out using various techniques like EDX, XRD, FTIR. thermal studies, BET surface area, pore volume and pore size distribution analysis. The amount of vanadia incorporated has been found to influence the surface properties of dysprosia. The spectroscopic results combining with X-ray analysis reveal that vanadia species exist predominantly as isolated amorphous vanadyl units along with crystalline dysprosium orthovanadate. Basicity studies have been conducted by adsorption of electron acceptors and acidity and acid strength distribution by temperature programmed desorption of ammonia. Cyclohexanol decomposition has been employed as a chemical probe reaction to examine the effect of vanadia on the acid base property of Dy2O3. Incorporation of vanadia titrates thc Lewis acid and base sites of Dy2O3, while an enhancement of Bronsted acid sites has been noticed. Data have been correlated with the catalytic activity of these oxides towards the vapour phase methylation of phenol

Catalysis by Modified Pillared Clays and Porous Clay Heterostructures

In this venture three distinct class of catalysts such as, pillared clays and transition metal loaded pillared clays , porous clay heterostructures and their transition metal loaded analogues and DTP supported on porous clay heterostructures etc. were prepared and characterized by various physico chemical methods. The catalytic activities of prepared catalysts were comparatively evaluated for the industrially important alkylation, acetalization and oxidation reactions.The general conclusions drawn from the present investigation are  Zirconium, iron - aluminium pillared clays were synthesized by ion exchange method and zirconium-silicon porous heterostructures were Summary and conclusions 259 prepared by intergallery template method. Transition metals were loaded in PILCs and PCHs by wet impregnation method.  Textural and acidic properties of the clays were modified by pillaring and post pillaring modifications.  The shift in 2θ value to lower range and increase in d (001) spacing indicate the success of pillaring process.  Surface area, pore volume, average pore size etc. increased dramatically as a result of pillaring process.  Porous clay heterostructures have higher surface area, pore volume, average pore diameter and narrow pore size distribution than that of pillared clays.  The IR spectrum of PILCs and PCHs are in accordance with literature without much variation compared to parent montmorillonite which indicate that basic clay structure is retained even after modification.  The silicon NMR of PCHs materials have intense peaks corresponding to Q4 environment which indicate that mesoporous silica is incorporated between clay layers.  Thermo gravimetric analysis showed that thermal stability is improved after the pillaring process. PCH materials have higher thermal stability than PILCs.  In metal loaded pillared clays, up to 5% metal species were uniformly dispersed (with the exception of Ni) as evident from XRD and TPR analysis. Chapter 9 260  Impregnation of transition metals in PILCs and PCHs enhanced acidity of catalysts as evident from TPD of ammonia and cumene cracking reactions.  For porous clay heterostructures the acidic sites have major contribution from weak and medium acid sites which can be related to the Bronsted sites as evident from TPD of ammonia.  Pillared clays got more Lewis acidity than PCHs as inferred from α- methyl styrene selectivity in cumene cracking reaction.  SEM images show that layer structure is preserved even after modification. Worm hole like morphology is observed in TEM image of PCHs materials  In ZrSiPCHS, Zr exists as Zr 4+ and is incorporated to silica pillars in the intergallary of clay layers as evident from XPS analysis.  In copper loaded zirconium pillared clays, copper exists as isolated species with +2 oxidation state at lower loading. At higher loading, Cu exists as clusters as evident from reduction peak at higher temperatures in TPR.  In vanadium incorporated PILCs and PCHs, vanadium exist as isolated V5+ in tetrahedral coordination which is confirmed from TPR and UVVis DRS analysis.  In cobalt loaded PCHs, cobalt exists as CoO with 2+ oxidation state as confirmed from XPS.  Cerium incorporated iron aluminium pillared clay was found to be the best catalyst for the hydroxylation of phenol in aqueous media due to the additional surface area provided by ceria mesopores and its redox properties. Summary and conclusions 261  Cobalt loaded zirconium porous clay heterostructures were found to be promising catalyst for the tertiary butylation of phenol due to higher surface area and acidic properties.  Copper loaded pillared clays were found to be good catalyst for the direct hydroxylation of benzene to phenol.  Vanadium loaded PCHs catalysts were found to be efficient catalysts for oxidation of benzyl alcohol.  DTP was firmly fixed on the mesoporous channels of PCHs by Direct method and functionalization method.  DTP supported PCHs catalyst were found to be good catalyst for acetalization of cyclohexanone with more than 90% conversion.

Low-temperature sol-gel preparation of ordered nanoparticles of tungsten carbide/oxide

Tungsten carbide/oxide particles have been prepared by the gel precipitation of tungstic acid in the presence of an organic gelling agent [10% ammonium poly(acrylic acid) in water, supplied by Ciba Specialty Chemicals]. The feed solution; a homogeneous mixture of sodium tungstate and ammonium poly(acrylic acid) in water, was dropped from a 1-mm jet into hydrochloric acid saturated hexanol/concentrated hydrochloric acid to give particles of a mixture of tungstic acid and poly(acrylic acid), which, after drying in air at 100 degrees C and heating to 900 degrees C in argon for 2 h, followed by heating in carbon dioxide for a further 2 h and cooling, gives a mixture of WO, WC, and a trace of NaxWO3, with the carbon for the formation of WC being provided by the thermal carbonization of poly(acrylic acid). The pyrolyzed product is friable and easily broken down in a pestle and mortar to a fine powder or by ultrasonics, in water, to form a stable colloid. The temperature of carbide formation by this process is significantly lower (900 degrees C) than that reported for the commercial preparation of tungsten carbide, typically > 1400 degrees C. In addition, the need for prolonged grinding of the constituents is obviated because the reacting moieties are already in intimate contact on a molecular basis. X-ray diffraction, particle sizing, transmission electron microscopy, surface area, and pore size distribution studies have been carried out, and possible uses are suggested. A flow diagram for the process is described.

Síntese de zeólitas e argilas ácidas pilarizadas a partir de matérias primas naturais

Structural changes in waste for zeolites synthesis are subject of many studies carried out in the synthesis of molecular sieves. These materials are named molecular sieves because they have well defined pore sizes and they have the capacity of select molecules by its size. In this work, it was studied the synthesis processes of two types of molecular sieves: pillared acid clays using as starting material one natural montmorillonite clay and the synthesis of zeolites from a silico-aluminous residue. This residue is a byproduct of the extraction of lithium -spodumene. The preparation of pillared acid clays was performed in two steps: 1° acid treatment of clay samples (time and temperature studies) and 2°pilarization of them with Al13 (Keggin ion). The temperature and acid concentration affect the removal of cations in the structure and porosity of the material obtained. The analysis of X-ray diffraction (XRD) and infrared spectroscopy (IR), showed that increasing the severity of the acid treatment compromises the structural material. Also the pore size distribution is approximately uniform. Despite presenting a structural disorganization, the samples were pillared. As evidenced by XRD increasing the basal spacing, specific area and uniform porosity by adsorption of N2. Regarding the microporous molecular sieves were synthesized zeolites A and NaP1 from a silico-aluminous residue, a byproduct of extracting lithium. The temperature and time of agitation during the synthesis were the most important factors for obtaining zeolite A. The aging of the gel and the highest crystallization time promoted the formation of zeolite NaP1 using a Si / Al ratio = 3.2

Distribuição do Tamanho de Poros em Cascas de Ovos Determinada pela Porosimetria de Mercúrio

Neste trabalho foi aplicada a porosimetria de mercúrio na caracterização da porosidade de cascas de ovos de poedeiras com 28 semanas de idade. Aplicando-se a técnica de porosimetria de mercúrio, pudemos descrever as características associadas a porosidade de modo mais amplo, determinando uma distribuição do tamanho de poros nas cascas de ovos estudadas. Nossos resultados mostraram que a maioria dos poros nas cascas de ovos tem tamanhos entre 1 a 10 mim. Neste artigo introduzimos a técnica de porosimetria de mercúrio como uma nova ferramenta aplicada no estudo de cascas de ovos.

Structural modifications in silica sonogels prepared with additions of poly(vinyl alcohol)

Silica wet gels were prepared from acid sonohydrolysis of tetraethoxysilane (TEOS) and additions of poly(vinyl alcohol) (PVA)-water solution. Aerogels were obtained from supercritical CO(2) extraction. The samples were studied by thermal gravimetric (TG) analysis, small-angle X-ray scattering (SAXS), and nitrogen adsorption. The structure of wet gels can be described as a mass fractal with dimension D equal to 2.0 on the whole length scale experimentally probed by SAXS, from similar to 0.3 to similar to 15 nm. Pure and low-PVA-addition wet gels exhibit an upper cutoff accounting for a finite characteristic length xi of the mass fractal structure. Additions , of PVA increase without modifying D, which was attributed to a steric effect of the polymer in the structure. The pore volume fraction of the aerogels diminishes typically about 11% with respect to that of the wet gels, although nitrogen adsorption could be underestimating some porosity. The pore size distribution of the aerogels is shifted toward the mesopore region with the additions of PVA, in a straight relationship with the increase of xi in the wet gels. The thermal stability of the pore size distribution of the aerogels was studied up to 1000 degrees C.

Effects of poly(vinyl alcohol) additions on the structure of silica xerogels

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural features of silicas prepared in n-heptane/water/ethanol/sodium dodecylsulfate microemulsions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Mass fractal characteristics of silica sonogels as determined by small-angle x-ray scattering and nitrogen adsorption

A sample series of silica sonogels was prepared using different water-tetraethoxysilane molar ratio (r(w)) in the gelation step of the process in order to obtain aerogels with different bulk densities after the supercritical drying. The samples were analyzed by means of small-angle x-ray-scattering (SAXS) and nitrogen-adsorption techniques. Wet sonogels exhibit mass fractal structure with fractal dimension D increasing from similar to2.1 to similar to2.4 and mass-fractal correlation length xi diminishing from similar to13 nm to similar to2 nm, as r(w) is changed in the nominal range from 66 to 6. The process of obtaining aerogels from sonogels and heat treatment at 500degreesC, in general, increases the mass-fractal dimension D, diminishes the characteristic length xi of the fractal structure, and shortens the fractal range at the micropore side for the formation of a secondary structured particle, apparently evolved from the original wet structure at a high resolution level. The overall mass-fractal dimension D of aerogels was evaluated as similar to2.4 and similar to2.5, as determined from SAXS and from pore-size distribution by nitrogen adsorption, respectively. The fine structure of the secondary particle developed in the obtaining of aerogels could be described as a surface-mass fractal, with the correlated surface and mass-fractal dimensions decreasing from similar to2.4 to similar to2.0 and from similar to2.7 to similar to2.5, respectively, as the aerogel bulk density increases from 0.25 (r(w)=66) up to 0.91 g/cm(3) (r(w)=6).

Formation of zirconia foams using the thermostimulated sol-gel transition

In this paper we describe the production of zirconia-based foams by a novel thermostimulated sol-gel route, that employs the foaming of colloidal suspensions prior to the sol-gel transition promoted by small increase of temperature (congruent to3 degreesC). This method produces gelled bodies having porosity >70% in the wet stage, and can be used to produce complex-shaped components. The effect of a foaming agent (Freon11 or CCl3F) and surfactant content on the formation and stability of the foams was analyzed. The rheologic measurements demonstrate that by increasing the surfactant concentration, the gelation time decreases increasing foam stability. As the surfactant concentration and quantity of foaming agent increase, the density decreases and the porosity increases. Hg porosimetry results show that the dry foam presents a bimodal pore size distribution. The family of sub-micrometer pores was attributed to the formation of a microemulsion between Freon11 and water. Scanning electron microscopy analysis shows that the foam structure consists of a three-dimensional network of spherical pores, which may be open and interconnected or closed, at larger or smaller porosities, respectively. Finally these results show that the thermostimulated sol-gel transition provides a potential route for ceramic foam manufacture. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Formation of SnO2 supported porous membranes

In this work, the effect of the substrate microstructure on the formation of SnO2 membranes and of the sintering conditions on their porosity have been analysed. Samples have been prepared by colloidal suspensions cast on alumina or kaolin substrates. Supported membranes have been characterized by Hg porosimetry, MEV, XRD and N-2 adsorption-desorption isotherms. The results show that the narrower pore size distribution of alumina substrate allowed to prepare membranes more homogeneous and free of cracks than that supported on kaolin. The crystallite and pore sizes of the membranes could be controlled by adjusting the temperature of sintering, allowing materials with adequate microstructure with application for ultrafiltration process.

Nanostructure and properties of ZnO films produced by the pyrosol process

Indium doped ZnO films were deposited by the pyrosol process on glass substrates at different temperatures from solutions containing In/Zn molar ratios up to 10%. The nanostructure of the films was investigated using grazing-incidence small angle X-ray scattering (GISAXS). The mass density was determined by X-ray reflectivity and the composition by X-ray photoelectron spectroscopy. The GISAXS measurements revealed an anisotropic pattern for films deposited at 573 and 623 K and a isotropic one for those deposited at higher temperatures. The anisotropic patterns indicate the presence of elongated nanopores with their long axes perpendicular to the film surface. In contrast, the isotropic nature of GISAXS patterns of films grown at high temperatures (673 and 723 K) suggests the presence of spherical voids. The pore size distribution function determined from the isotropic patterns indicates a multimodal size distribution. on the other hand, the measured mass density of the doped films with isotropic nanotexture is higher than that of the anisotropic films while the electric resistivity is significantly lower. This is in agreement with the detected strong reduction of the void density and specific surface area at approximately constant pore size.