29,673 research outputs found
Sol-gel derived hydroxyapatite, fluorhydroxyapatite and fluorapatite coatings for titanium implants
No full textCurrently, most titanium implant coatings are made using hydroxyapatite and a
plasma-spraying technique. There are however limitations associated with the
plasma-spraying process including; poor adherence, high porosity and cost. An
alternative - the sol-gel technique offers many potential advantages but is
currently lacking research data for this application.
Hydroxyapatite (HA), fluorhydroxyapatite (FHA) and fluorapatite (FA) have
been synthesised by a sol-gel method. Calcium nitrate and triethyl phosphite
were used as precursors under an ethanol-water based solution. Different
amounts of ammonium fluoride (NH4F) were incorporated for the preparation of
the FHA and FA sol-gels. Optimisation and characterisation of the sol-gels was
carried out using, X-ray Diffraction (XRD), High Temperature X-Ray Diffraction
(HTXRD), Fourier Transform Infrared Analysis (FTIR) and Differential Thermal
Analysis (DTA).
Rheology and hydrophilicity of the sol-gels showed that increasing fluoride ion
substitution caused an increase in viscosity and contact angle.
The dissolution (Ca2+ and PO4
3-rates) rates of the fluoride-substituted powders
from the sol-gels were considerably lower than that of HA and all rates could be
decreased by increasing the sintering temperature. This suggests the
possibility of tailoring the solubility of any coatings made from the sol-gels
through fluoride ion substitution and increased sintering temperature.
A spin coating protocol has been established for coating the sol-gels onto
titanium. Increasing the coating speed decreased the porosity and thickness of
the coatings. Bond strengths to titanium were investigated. Fluoride substitution
and sintering temperature were shown to be important factors. Cellular proliferation studies revealed that increasing the level of fluoride
substitution in the apatite structure significantly increased the biocompatibility
of the material.
The sol-gel technique may be an alternative to plasma spraying for coating
titanium implants. Furthermore it may also be suitable for producing HA, FHA
and FA as bone grafting materials
Effect of calcium source on structure and properties of sol–gel derived bioactive glasses
No full textThe aim was to determine the most effective calcium precursor for synthesis of sol–gel hybrids and for improving homogeneity of sol–gel bioactive glasses. Sol–gel derived bioactive calcium silicate glasses are one of the most promising materials for bone regeneration. Inorganic/organic hybrid materials, which are synthesized by incorporating a polymer into the sol–gel process, have also recently been produced to improve toughness. Calcium nitrate is conventionally used as the calcium source, but it has several disadvantages. Calcium nitrate causes inhomogeneity by forming calcium-rich regions, and it requires high temperature treatment (>400 °C) for calcium to be incorporated into the silicate network. Nitrates are also toxic and need to be burnt off. Calcium nitrate therefore cannot be used in the synthesis of hybrids as the highest temperature used in the process is typically 40–60 °C. Therefore, a different precursor is needed that can incorporate calcium into the silica network and enhance the homogeneity of the glasses at low (room) temperature. In this work, calcium methoxyethoxide (CME) was used to synthesize sol–gel bioactive glasses with a range of final processing temperatures from 60 to 800 °C. Comparison is made between the use of CME and calcium chloride and calcium nitrate. Using advanced probe techniques, the temperature at which Ca is incorporated into the network was identified for 70S30C (70 mol % SiO2, 30 mol % CaO) for each of the calcium precursors. When CaCl2 was used, the Ca did not seem to enter the network at any of the temperatures used. In contrast, Ca from CME entered the silica network at room temperature, as confirmed by X-ray diffraction, 29Si magic angle spinning nuclear magnetic resonance spectroscopy, and dissolution studies. CME should be used in preference to calcium salts for hybrid synthesis and may improve homogeneity of sol–gel glasses
Films based on bacteriorhodopsin in sol-gel matrices
No full textThe bacteriorhodopsin film in gelatin matrixes which are used as sensitive
elements of integrated optic and fibre-optic sensors of various vapor and gases
components will not be able to carry out the chemical control of aqueous
solutions. In the given paper the results of technological development of
obtaining the bacteriorhodopsin (bR) films in a sol-gel matrix are represented.
The films are obtained in a broad thickness range (from 0.5 to 20 microns) with
various bR concentrations and photosensitize additives. The optimal
technological conditions of obtaining of uniform films with given optical
parameters are defined. The surface morphology and cross section of the obtained
films was studied using an AFM and SEM. The films have a reasonable surface
roughness (~ 100 nm) and a uniform distribution of the purple membrane fragments
in the nanostructured sol-gel glass matrix along the films surface and
thickness. The transmission spectrums have the characteristic for bR the
absorption band, the value of which depends on bR concentration and
technological features of the films deposition. The investigated photosensitive
properties of the obtained films and influence on them of chemical components of
aqueous solutions, allow recommending the thin bR films in sol-gel matrixes for
creation of planar waveguides in the role of components of the chemical sensors
of liquid solutions
PRELIMINARY STUDY FOR USING VINYLTRIACETOXYSILANE AS PRECURSOR IN ENZYME IMMOBILIZATION BASED ON SOL-GEL METHOD
No full textDuring the last years, sol-gel technology has become a well-established method
for the preparation of catalytic active monoliths, bulk, particles and thin films. One reason
for the increasing research activities in this field is the opportunity to obtain versatile
hybrid materials by incorporation of different molecules, like dyes, enzymes, whole cells,
chemicals and drugs. The aim of this research was to evaluate the suitability of
vinyltriacetoxysilane (VTAS) as precursor in sol-gel enzyme immobilization and the
physicochemical characterization of the final products (silica xerogels)
Preparation of sub-micron PZT particles with the sol-gel technique
No full textThis paper describes the production of Pb1.0Zr0.9Ti0.1 ceramic powder, by using metal organic precursors as starting materials. In this study polyvinylpyrrolidone, PVP, was used to create a PZT–PVP sol and then also added as a secondary stage to control the particle size of the powder.
Two different sol–gel routes were used to create PZT powder. Both routes gave similar primary particle sizes in the range, 30–70 nm, but different agglomerate formations. Perovskite PZT powder was created with both routes
Novel sol–gel preparation of (PO)–(CaO)–(NaO)–(TiO) bioresorbable glasses (X = 0.05, 0.1, and 0.15)
No full textQuaternary phosphate-based glasses in the PO–CaO–NaO–TiO system with a fixed PO and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol–gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised sol–gel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), P nuclear magnetic resonance (P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol–gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol–gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly six-fold coordination environment. The P NMR and FTIR results revealed that the glass structure consist of mainly Q and Q phosphate units and the Ti cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing NaO content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol–gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed
Nonoxide Sol-Gel Synthesis of Terbium-Doped Silicon Nitride Phosphors
No full textExposure of solutions of Tb(N(SiMe3)2)3 with SiCl(NEt2)3 in tetrahydrofuran to dry ammonia results in polymeric xerogels. Heating these gels in ammonia leads to amorphous Tb:SiNx phosphors that exhibit bright green luminescence under UV irradiation. MAS-NMR and combustion analysis reveal that the phosphors are silicon nitride materials analogous to those typically produced by sol–gel routes. Photoluminescence behavior is similar to that of Tb:SiNx or Tb:SiO2 films produced by ion implantation that show good electroluminescence activity
Preparation and characterization of suitable insulating and transparent conducting thin films for thin film electroluminescent devices by sol-gel process
No full textThin film electroluminescent (TFEL) displays are attractive because they are light, have low power consumption, wide viewing angle and long lifetime, are extremely rugged and can be used in hostile environments. Recently, there has been a renewed interest in thin film electroluminescent devices because of their promising application to head mounted displays for use in automobiles, aircraft, microsurgery and virtual reality applications. Both conventional and inverted thin film electroluminescent device structures consist of insulating film, transparent conducting film and luminescent layer. In a thin film electroluminescent device, the luminescent layer is sandwiched between two insulating layers. Electrodes outside both insulating layers are used to apply an electric field, with one electrode being transparent.
These thin films are found to be sensitive to preparation conditions and can be prepared by a variety of methods, such as, magnetron sputtering, chemical vapour deposition, reactive electron beam evaporation, reactive thermal deposition, spray pyrolysis, laser ablation and more recently by sol-gel process. Nowadays, the sol-gel process is a wellaccepted technology for the preparation of thin films, monoliths, fibers and monosized powders. Compared to conventional thin film forming processes such as CVD, evaporation or sputtering, sol-gel film formation requires considerably less equipment and is potentially less expensive; however the most important advantage of sol-gel processing over conventional coating methods is the ability to control precisely the microstructure of the deposited film, i.e., the pore volume, pore size and surface area.
The sol-gel process is a method where the substrate to be coated is dipped into a liquid solution containing the active material. When the substrate is removed from the solution a thin layer remains. On exposure to the atmosphere a hydrolysis reaction takes place which solidifies the liquid film.
In this work, all the thin films have been prepared by using sol-gel process. Insulating films of titanium dioxide and tantalum oxide were prepared from titanium and tantalum alkoxides respectively and their characteristics have been investigated. The most important requirements for the insulating layers are high dielectric constant and high electric field strength. The dielectric constants of the films were calculated from the maximum capacitance of the Al/film/Si structure. The maximum dielectric constants for Ti02 and Ta20 5 films were approximately 50 and 82 respectively annealed at 700°C in oxygen. These results suggest that the Ti02 and Ta2Os thin film can be used as a high dielectric constant insulating layer in thin film electroluminescent devices.
Highly conductive and transparent aluminum-doped zinc oxide thin films have been prepared from the solution of zinc acetate and aluminum nitrate in ethanol by the sol-gel process. The effect of changing the aluminum-to-zinc ratio from 0 to 5 at. % and annealing temperature from 0 to 700°C in air, oxygen and nitrogen has been investigated. The resistivities of thin films were measured as a function of annealing temperature and also as a function of aluminum dopant concentration in the solution. As-deposited films have high resistivity and high optical transmission. Annealing of the as-deposited films in atmosphere leads to a substantial reduction in resistivity. The films have a minimum value of resistivity of 1.3xl0'4 Q-cm for 0.8 at. % aluminum-doped zinc oxide annealed at 500°C in nitrogen and a maximum transmission of about 88% when deposited on glass substrates. X-ray diffraction measurements employing CuKa radiation were performed to determine the crystallinity of the ZnO:Al films which showed that the films were polycrystalline with a hexagonal structure when annealed at higher temperatures in air, oxygen and nitrogen.
Transparent conductive indium tin oxide (ITO) thin films have been prepared by a solgel
process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. 0-20 % by weight Sn-doped indium oxide (ITO) films were prepared by heat-treatment at above 400°C. The electrical, optical and structural properties of ITO thin films were investigated. The electrical resistivity was measured by using four-point probe method. The ITO thin films containing 10 wt.% Sn showed the minimum resistivity of p = 8.0xl0'4 Q-cm annealed at 500°C in nitrogen. The films have an optical transparency up to 89% at 900 nm. X-ray diffraction measurements employing CuKa radiation were performed to determine the crystallinity of the ITO films which showed that the ITO films were polycrystalline with a cubic bixbyite structure annealed in air, oxygen and nitrogen.
Aluminum doped zinc oxide thin films have been deposited on titanium dioxide and
tantalum oxide films on glass by sol-gel process. The resistivity of ZnO:Al thin films
deposited on titanium dioxide and tantalum oxide films on glass have a minimum value
of 2.5xl0'3 Q-cm and 9.6xl0'4 Q-cm respectively annealed at 500°C in nitrogen. ZnO:Al
thin films deposited on titanium dioxide film on glass have a higher resistivity than that
deposited on glass. This increase in resistivity on titanium dioxide film is due to the
diffusion of titanium into the zinc oxide layer.
Indium tin oxide thin films have been deposited on titanium dioxide and tantalum oxide
films on glass for thin film electroluminescent devices. The resistivity of ITO films
deposited on titanium dioxide and tantalum oxide films has a minimum value of 9.5x1 O'4
Q-cm and 9.0x10'4 Q-cm respectively annealed at 500°C in nitrogen which are as low as
the resistivity of ITO films deposited on glass. This combination of transparent conductive ITO thin films and titanium dioxide or tantalum oxide insulating layer can be
used for thin film electroluminescent devices
Entrapment of glucoamylase by sol-gel technique in PhTES/TEOS hybrid matrixes
No full textMesoporous silica particles were prepared by the sol-gel method from different alkoxysilane precursors and
used as a host matrix for encapsulation of glucoamylase, an enzyme widely used in fermentative industry. The
aim was to investigate the physico-chemical properties of the different silica powders and their effect on the
enzyme kinetics. The encapsulated enzymes followed Michaelis-Menten kinetics. The Michaelis constant (KM)
and the maximum rate of starch hydrolysis reaction (Vmax) were calculated according to the Michaelis-Menten
and Lineweaver-Burke plots. The values of the Michaelis constant (KM) of the encapsulated enzymes were
higher than those of the free enzyme. The temperature and pH infl uence on the activity of free and immobilized
glucoamylase were also compared. The results of this study show that the enzymes immobilized in organic/inorganic
hybrid silica matrixes (obtained by the sol-gel method), allowing the entrapped glucoamylase to retain
its biological activity, are suitable for many different applications, (medicinal, clinical, analytical)
Characterizing the hierarchical structures of bioactive sol-gel silicate glass and hybrid scaffolds for bone regeneration
No full textBone is the second most widely transplanted tissue after blood. Synthetic alternatives are needed that can reduce the need for transplants and regenerate bone by acting as active temporary templates for bone growth. Bioactive glasses are one of the most promising bone replacement/regeneration materials because they bond to existing bone, are degradable and stimulate new bone growth by the action of their dissolution products on cells. Sol-gel-derived bioactive glasses can be foamed to produce interconnected macropores suitable for tissue ingrowth, particularly cell migration and vascularization and cell penetration. The scaffolds fulfil many of the criteria of an ideal synthetic bone graft, but are not suitable for all bone defect sites because they are brittle. One strategy for improving toughness of the scaffolds without losing their other beneficial properties is to synthesize inorganic/organic hybrids. These hybrids have polymers introduced into the sol-gel process so that the organic and inorganic components interact at the molecular level, providing control over mechanical properties and degradation rates. However, a full understanding of how each feature or property of the glass and hybrid scaffolds affects cellular response is needed to optimize the materials and ensure long-term success and clinical products. This review focuses on the techniques that have been developed for characterizing the hierarchical structures of sol-gel glasses and hybrids, from atomicscale amorphous networks, through the covalent bonding between components in hybrids and nanoporosity, to quantifying open macroporous networks of the scaffolds. Methods for non-destructive in situ monitoring of degradation and bioactivity mechanisms of the materials are also included. © 2012 The Royal Society
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