Sol-gel based materials for biomedical applications

Sol-gel chemistry offers a flexible approach to obtaining a diverse range of materials. It allows differing chemistries to be achieved as well as offering the ability to produce a wide range of nano-/micro-structures. The paper commences with a generalized description of the various sol-gel methods available and how these chemistries control the bulk properties of the end products. Following this, a more detailed description of the biomedical areas where sol-gel materials have been explored and found to hold significant potential. One of the interesting fields that has been developed recently relates to hybrid materials that utilize sol-gel chemistry to achieve unusual composite properties. Another intriguing feature of sol-gels is the unusual morphologies that are achievable at the micro- and nano-scale. Subsequently the ability to control pore chemistry at a number of different length scales and geometries has proven to be a fruitful area of exploitation, that provides excellent bioactivity and attracts cellular responses as well as enables the entrapment of biologically active molecules and their controllable release for therapeutic action. The approaches of fine-tuning surface chemistry and the combination with other nanomaterials have also enabled targeting of specific cell and tissue types for drug delivery with imaging capacity

The sol–gel route: A versatile process for up-scaling the fabrication of gas-tight thin electrolyte layers

Sol–gel routes are often investigated and adapted to prepare, by suitable chemical modifications, submicronic powders and derived materials with controlled morphology, which cannot be obtained by conventional solid state chemistry paths. Wet chemistry methods provide attractive alternative routes because mixing of species occurs at the atomic scale. In this paper, ultrafine powders were prepared by a novel synthesis method based on the sol–gel process and were dispersed into suspensions before processing. This paper presents new developments for the preparation of functional materials like yttria-stabilized-zirconia (YSZ, 8% Y2O3) used as electrolyte for solid oxide fuel cells. YSZ thick films were coated onto porous Ni-YSZ substrates using a suspension with an optimized formulation deposited by either a dip-coating or a spin-coating process. The suspension composition is based on YSZ particles encapsulated by a zirconium alkoxide which was added with an alkoxide derived colloidal sol. The in situ growth of these colloids increases significantly the layer density after an appropriated heat treatment. The derived films were continuous, homogeneous and around 20 μm thick. The possible up-scaling of this process has been also considered and the suitable processing parameters were defined in order to obtain, at an industrial scale, homogeneous, crack-free, thick and adherent films after heat treatment at 1400 °C

Sol–Gel Method Applied to Crystalline Materials

Sol–gel chemistry is a versatile synthesis used to produce modern materials at nearroom temperature. Glasses, ceramics, composites, and new hybrid materials that are not easy to obtain using other methods have been, instead, obtained in the last three decades and nowadays are widely used. Changing the chemical composition, many parameters of the sol-gel process can be adapted to control the properties and the microstructure of the obtained materials. Sol-gel technology is a multidisciplinary science which allows the expansion of materials for many applications. In this Special Issue, special attention is paid to the properties of materials obtained by using sol–gel methods and to their potential applications in environmental science and materials science as in catalysis, optics, electronics, energy, biosensors, medicine, and so on

Processing and Weathering of Sol-Gel Clearcoats for Coil-Coated Steel

Clearcoats provide long-term aesthetics and protection for underlying coating systems, increasing product lifetimes. However, organic clearcoats are predominantly produced using fossil-fuel feedstocks. In search of a sustainable alternative, an experimental investigation was conducted on the development of glass-like clearcoats produced using the sol-gel process. The processing of sol-gel clearcoats over a pigmented polyurethane coating was studied by modifying the sol-gel solution pH, aging, curing, precursor chemistry, and deposition techniques. Under optimal formulation and processing conditions, defect-free sol-gel clearcoats were produced that have potential to be scaled up to a coil-coating line using existing technologies. Mechanical testing demonstrated the coatings had excellent adhesion, hardness, and flexibility. Furthermore, accelerated laboratory weathering tests revealed the sol-gel coatings had superior degradation resistance compared to the organic coatings tested, resulting in negligible colour changes and higher gloss retention after 4000 hours of exposure. The durability and environmental benefits of sol-gel clearcoats highlight their potential as a replacement for traditional organic clearcoats in a variety of applications

Surface Science Engineering through Sol-Gel Process

Sol-gel synthesis is used to obtain coatings that can modify the surfaces of metals to avoid corrosion or to enhance the biocompatibility and bioactivity of metals and their alloys that are of biomedical interest. Anticorrosion coatings composed of smart coatings and self-healing coatings will be described. TiO2, hydroxyapatite, bioglass, and hybrid coatings synthetized by sol-gel technology will be briefly introduced with regard to their role in surface-modifying metals for biomedical purposes. Finally, although there are other approaches to surface-modifying metals for either anticorrosion or biomedical purposes, sol-gel methods have several advantages in controlling surface chemistry composition and functionality

Sol-gel yesterday, today and tomorrow

7000 years ago, the Assyrians made a multicomponent oxide glass. In the 19th century, silica glass was produced from the melt. The origin of the sol-gel process, which almost led to silica glass, stems from the same time, but soon after fell into oblivion. The first sol-gel patent in 1939 demonstrates the formation of SiO2 and TiO2 layers, and in 1953 the first layers were introduced into the market. The further industrial development of the sol-gel dip-coating process led to the present products like the blue car rear-view mirror, the antireflex coatings Mirogard® and the sun-shielding coatings IROX®. It was demonstrated in 1968 that it is possible to make glasses, glass ceramics and ceramics in a well-defined way from multicomponent alkoxides without going through the melt. The first example was the borosilicate glass Duran. After the first publication [1] and an incubation period of several years, a world-wide sol-gel development began, which still lasts, and which is probably best characterized by the slogan "better ceramics through chemistry". Besides thin layers - which probably still are the major sol-gel product - powders, fibres and objects like hollow spheres, plates, rods and tubes were developed. Often the development started with silica glass and then continued with multicomponent oxides. New products are the non-reflecting shop-window glazing Amiran® and the contrast-enhancing screens Conturan® for computer displays. The development of organically modified silicates was stimulated by the rich chemistry which is so typical for sol-gel processes. The future of the sol-gel process is characterized by the manifold chemical possibilities, like PLTZ (Pb-La-Ti-Zr oxides) for optoelectronics, PbTiO3 for piezoelectrics, NASICON (Na3Zr2Si2PO12, e.g. as a superionic conductor) or V2O5 because of its electrical conductivity, and Sb2S3 because of its photosensitivity. Enormous efforts are made for oxidic superconductors (fibres, layers). Furthermore, there ist the combination of inorganic and organic materials with a multitude of applications in photochromics, electrochromics, non-linear optics and much more

Sol-gel processes for protection and synthesis of luminescent materials

Sol-gel chemistry has a very broad application area such as thin films and coatings, monoliths, powders, grains and spheres, fibers, composites, porous gels and membranes. From thin film to powder, different kind of materials with excellent control of stoichiometry, density and microstructure can be synthesized using simple equipment without the need for vacuum at relatively low temperatures. Using sol-gel, material properties can be modified by changing only one parameter during the preparation. Rare earth doped alkaline earth binary and ternary sulfides have a very special place in luminescent materials because of their relatively low synthesis temperature and broad emission spectra upon doping with europium and cerium. Particularly to obtain red or orange emission CaS:Eu2+ and SrS:Eu2+ are considered suitable candidates. Ca1−xSrxS:Eu2+ phosphors with a strong absorption in the blue region are currently also used in white-light emitting diodes. In addition to wavelength converters in LEDs, alkaline earth sulfide phosphors are employed in different areas such as display applications, electroluminescent devices and optical information storage. Nevertheless, the lack of stability with respect to water and other atmospheric components hinders their usage as phosphor hosts. A number of encapsulation techniques have been utilized to improve the stability of sulfide phosphors and sol-gel is the one of the most attractive techniques. This work focuses on thin films, protection coatings, powders and luminescent materials prepared using sol-gel chemistry. TiO2 and Al2O3 powders, thin films and protection layers were synthesized via water free sol-gel. In addition to the optical and structural properties of the products, the effect of the coating on the stability of sulfide particles was investigated. Al2O3 synthesized via sol-gel was also compared with Al2O3 synthesized via ALD (atomic layer deposition) as protection layer. Lastly, undoped and persistent luminescent Eu and Nd-doped CaAl2O4 powders were synthesized via water free sol-gel technique. Effect of the calcinations temperature and the doping concentration on the structure and photoluminescence properties was investigated

Applications of sol-gel materials in analytical chemistry

This thesis describes the development of sol-gel materials for use in analytical chemistry. An overview of the sol-gel process, as well as an introduction to chemical sensors, are presented in Chapter 1. A novel approach to the use of crown ethers for the removal of Sr² is discussed in Chapter 2. Disulfonated, dibenzo-18-crown-6 encapsulated within a sol-gel matrix is used for the removal of strontium (11) ions from aqueous systems. Sol-gel materials doped with crown ethers are shown to exhibit higher uptake of the target metal (Sr²) compared to blank, non-ligand containing gels. In Chapter 3, a chemical sensor based on the deflection of a surface modified silicon microcantilever is presented. A thin film of sol-gel was applied to one side of the micro-cantilever surface using a spin coating procedure. The sensor has been shown to give different responses to vapor phase analytes of varying chemical composition, as well as to varying concentrations of a given analyte. Ethanol, a highly polar molecule, exhibits a strong affinity for the polar sol-gel coating resulting in a large response, pentane, a nonpolar hydrocarbon, shows very little response. The sol-gel coating has also been shown to function as a backbone for the immobilization of chemically selective phases on the cantilever surface. Reaction of the sol-gel film with chlorotrimethylsilane and subsequent capping of the remaining reactive surface silanols with hexamethyldisilazane increase the non-polar nature of the film. This results in an increase in the response of the sensor to non-polar analytes. The effects of film thickness and cantilever structure thickness on response were also investigated

Deposition of YBCO thin films on silver substrate via a fluorine-free sol-gel synthesis

To further develop grain-textured YBCO thin films for conductor development, we deposited, via a fluorine-free sol-gel synthesis, YBCO thin films on non-textured silver substrate. The interface structures were studied by both x-ray diffraction (XRD) and transmission electron microscopy (HRTEM). XRD data indicated that the YBCO films on silver substrate exhibited c-axis grain orientations. Experimental details are reported on the sol-gel synthesis chemistry and XRD and HRTEM characterization of the YBCO thin films. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87877/2/654_1.pd

Molecular forms and fluorescence processes of 9-aminoacridine in thin sol-gel films

Molecular aggregation and fluorescence processes of 9-aminoacridine (9AA) in thin silica gel films have been investigated by the steady state and time-resolved fluorescence measurements. The monomer of 9AA was the preferential species in the sol-gel reaction systems of tetraethylorthosilicate until the gelation occurred. The 9AA molecules formed the dimer or higher aggregates just after preparing the dip-coated thin film from the sol-gel system. The extent of the aggregation decreased in the film prepared from the system in which the reaction further proceeded. This result indicates that the aggregation in the prepared film was gradually prevented by the steric hindrance of the SiO2 network with the progress of the sol-gel reaction. The fluorescence properties of 9AA revealed the behavior of the molecules due to the change in the physicochemical environment in the matrix.ArticleJOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY. 212(1):62-67 (2010)journal articl