Degradation of the surface of a metasilicate glass due to atmosphere moisture

Glasses with low silica content are very susceptible to suffer pronounced degradation when exposed to room atmosphere during short times. In this work the results of the degradation of the surface of a metasilicate glass with composition 2Na2O.1CaO.3SiO2 are presented. Optical and scanning electron microscopy observations, X-ray diffraction, infrared and Raman microprobe spectroscopic measurements of the modified surface of this glass show strong evidences that it is formed essentially by a crystalline carbonate layer.

Effects of Silica Based Biomaterials on Bone Marrow Derived Cells - Material Aspects of Bone Regeneration

Silica based biomaterials, such as melt-derived bioactive glasses and sol-gel glasses, have been used for a long time in bone healing applications because of their ability to form hydroxyapatite and to stimulate stem cell proliferation and differentiation. In this study, bone marrow derived cells were cultured with bioactive glass and sol-gel silica, and seeded into porous polymer composite scaffolds that were then implanted femorally and subcutaneously in rats to monitor their migration inside host tissue. Bone marrow derived cells were also injected intraperitoneally. Transplanted cells migrated to various tissues inside the host, including the lung, liver spleen, thymus and bone marrow. The method of transplantation affected the time frame of cell migration, with intraperitoneal injection being the fastest and femoral implantation the slowest, but not the target tissues of migration. Transplanted donor cells had a limited lifetime in the host and were later eliminated from all tested tissues. Bioactive glass, however, affected the implanted cells negatively. When it was present in the scaffold no donor cells were found in any of the tested host tissues. Bioactive glass S53P4 was found to support both osteoblastic and osteoclastic phenotype of bone marrow derived cells, but it was resistant to the resorbing effect of osteoclastic bone marrow derived cells, showing that bioactive glass is rather dissolved through physicochemical reactions than resorbed by cells. Fast-dissolving silica sol gel in microparticulate form was found to increase collagen formation by bone marrow derived cells, while slow dissolving silica microparticles enhanced their proliferation, suggesting that the dissolution rate of silica controls the response of bone marrow derived cells.

Bioactive Glass in Lumbar Spondylodesis. A Pre-Clinical and Clinical Study

Bioactive glasses (BGs) form a group of synthetic, surface-active, composition-dependent, silica-based biomaterials with osteoconductive, osteopromotive, and even angiogenic, as well as antibacterial, properties. A national interdisciplinary research group, within the Combio Technology Program (2003–2007), developed a porous load-bearing composite for surgical applications made of BG 1–98 and polymer fibers. The pre-clinical part of this thesis focused on the in vitro and in vivo testing of the composite materials in a rabbit femur and spinal posterolateral fusion model. The femur model failed to demonstrate the previously seen positive effect of BG 1–98 on osteogenesis, probably due to the changed resorption properties of BG in the form of fibers. The spine study was terminated early due to adverse events. In vitro cultures showed the growth inhibition of human mesenchymal stems next to BG 1–98 fibers and radical pH changes. A prospective, long-term, follow-up study was conducted on BG–S53P4 and autogenous bone used as bone graft substitutes for instrumented posterolateral spondylodesis in the treatment of degenerative spondylolisthesis (n=17) and unstable burst fractures (n=10) during 1996–1998. The operative outcome was evaluated from X-rays and CT scans, and a clinical examination was also performed. On the BG side, a solid fusion was observed in the CT scans of 12 patients, and a partial fusion was found in 5 patients, the result being a total fusion rate in all fusion sites (n=41) 88% for levels L4/5 and L5/S1 in the spondylolisthesis group. In the spine fracture group, solid fusion was observed in five patients, and partial fusion was found in five resulting in a total fusion rate of 71% of all fusion sites (n=21). The pre-clinical results suggest that under certain conditions the physical form of BG can be more critical than its chemical composition when a clinical application is designed. The first long-term clinical results concerning the use of BG S53P4 as bone graft material in instrumented posterolateral spondylodesis seems to be a safe procedure, associated with a very low complication rate. BG S53P4 used as a stand-alone bone substitute cannot be regarded as being as efficient as AB in promoting solid fusion.

Development of porous glass-fiber reinforced composite for bone implants. Evaluation of antimicrobial effect and implant fixation

Cranial bone reconstructions are necessary for correcting large skull bone defects due to trauma, tumors, infections and craniotomies. Traditional synthetic implant materials include solid or mesh titanium, various plastics and ceramics. Recently, biostable glass-fiber reinforced composites (FRC), which are based on bifunctional methacrylate resin, were introduced as novel implant solution. FRCs were originally developed and clinically used in dental applications. As a result of further in vitro and in vivo testing, these composites were also approved for clinical use in cranial surgery. To date, reconstructions of large bone defects were performed in 35 patients. This thesis is dedicated to the development of a novel FRC-based implant for cranial reconstructions. The proposed multi-component implant consists of three main parts: (i) porous FRC structure; (ii) bioactive glass granules embedded between FRC layers and (iii) a silver-polysaccharide nanocomposite coating. The porosity of the FRC structure should allow bone ingrowth. Bioactive glass as an osteopromotive material is expected to stimulate the formation of new bone. The polysaccharide coating is expected to prevent bacterial colonization of the implant. The FRC implants developed in this study are based on the porous network of randomly-oriented E-glass fibers bound together by non-resorbable photopolymerizable methacrylate resin. These structures had a total porosity of 10–70 volume %, of which > 70% were open pores. The pore sizes > 100 μm were in the biologically-relevant range (50-400 μm), which is essential for vascularization and bone ingrowth. Bone ingrowth into these structures was simulated by imbedding of porous FRC specimens in gypsum. Results of push-out tests indicated the increase in the shear strength and fracture toughness of the interface with the increase in the total porosity of FRC specimens. The osteopromotive effect of bioactive glass is based on its dissolution in the physiological environment. Here, calcium and phosphate ions, released from the glass, precipitated on the glass surface and its proximity (the FRC) and formed bone-like apatite. The biomineralization of the FRC structure, due to the bioactive glass reactions, was studied in Simulated Body Fluid (SBF) in static and dynamic conditions. An antimicrobial, non-cytotoxic polysaccharide coating, containing silver nanoparticles, was obtained through strong electrostatic interactions with the surface of FRC. In in vitro conditions the lactose-modified chitosan (chitlac) coating showed no signs of degradation within seven days of exposure to lysozyme or one day to hydrogen peroxide (H2O2). The antimicrobial efficacy of the coating was tested against Staphylococcus aureus and Pseudomonas aeruginosa. The contact-active coating had an excellent short time antimicrobial effect. The coating neither affected the initial adhesion of microorganisms to the implant surface nor the biofilm formation after 24 h and 72 h of incubation. Silver ions released to the aqueous environment led to a reduction of bacterial growth in the culture medium.

Low frequency Raman scattering in amorphous materials: fused quartz, "pyrex" boro-silicate glass and soda-lime silicate glass

Raman scattering in the region 20 to 100 cm -1 for fused quartz, "pyrex" boro-silicate glass, and soft soda-lime silicate glass was investigated. The Raman spectra for the fused quartz and the pyrex glass were obtained at room temperature using the 488 nm exciting line of a Coherent Radiation argon-ion laser at powers up to 550 mW. For the soft soda-lime glass the 514.5 nm exciting line at powers up to 660 mW was used because of a weak fluorescence which masked the Stokes Raman spectrum. In addition it is demonstrated that the low-frequency Raman coupling constant can be described by a model proposed by Martin and Brenig (MB). By fitting the predicted spectra based on the model with a Gaussian, Poisson, and Lorentzian forms of the correlation function, the structural correlation radius (SCR) was determined for each glass. It was found that to achieve the best possible fit· from each of the three correlation functions a value of the SCR between 0.80 and 0.90 nm was required for both quartz and pyrex glass but for the soft soda-lime silicate glass the required value of the SCR. was between 0.50 and 0.60 nm .. Our results support the claim of Malinovsky and Sokolov (1986) that the MB model based on a Poisson correlation function provides a universal fit to the experimental VH (vertical and horizontal polarizations) spectrum for any glass regardless of its chemical composition. The only deficiency of the MB model is its failure to fit the experimental depolarization spectra.

Sol-Gel Mesoporous Silica Aerogels and Bio Hybrids for Functional Applications

The thesis covers a systematic investigation on the synthesis of silica aerogels and microspheres with tailored porosity, at ambient conditions by varying the experimental parameters as well as using organic templates. Organically modified silica-gelatin and silica-chitosan hybrids were developed for the first time using alkylalkoxysilanes such as MTMS and VTMS. Application of novel silica-biopolymer antiwetting coatings on different substrates such as glass, leather and textile is also demonstrated in the thesis.

Geology and Geochronology of Silica Sands of Coastal Plain of Thiruvananthapuram District, Kerala,India,With Special reference to Late Quaternary Environment

Department of Marine Geology & Geophysics, Cochin University of Science & Technology

Spectroscopic and photoluminescence studies on optically transparent magnetic nanocomposites based on sol–gel glass: Fe3O4

Sol–gel glasses with Fe3O4 nanoparticles having particle sizes laying in the range 10–20 nm were encapsulated in the porous network of silica resulting in nanocomposites having both optical and magnetic properties. Spectroscopic and photoluminescence studies indicated that Fe3O4 nanocrystals are embedded in the silica matrix with no strong Si–O–Fe bonding. The composites exhibited a blue luminescence. The optical absorption edge of the composites red shifted with increasing concentration of Fe3O4 in the silica matrix. There is no obvious shift in the position of the luminescence peak with the concentration of Fe3O4 except that the intensity of the peak is decreased. The unique combinations of magnetic and optical properties are appealing for magneto–optical applications.

Spectroscopic and photoluminescence studies on optically transparent magnetic nanocomposites based on sol–gel glass: Fe3O4

Sol–gel glasses with Fe3O4 nanoparticles having particle sizes laying in the range 10–20 nm were encapsulated in the porous network of silica resulting in nanocomposites having both optical and magnetic properties. Spectroscopic and photoluminescence studies indicated that Fe3O4 nanocrystals are embedded in the silica matrix with no strong Si–O–Fe bonding. The composites exhibited a blue luminescence. The optical absorption edge of the composites red shifted with increasing concentration of Fe3O4 in the silica matrix. There is no obvious shift in the position of the luminescence peak with the concentration of Fe3O4 except that the intensity of the peak is decreased. The unique combinations of magnetic and optical properties are appealing for magneto–optical applications.

Synthesis and characterization of glass-ceramic microspheres for thermotherapy

Glass microspheres containing radionuclides are used to treat liver cancer. A promising alternative therapy is being developed based on the magnetic hyperthermia which is related to the heat supplied by a magnetic material under an alternating current magnetic field. The advantage of this option is that most of killed cells are cancer cells which are more susceptible to the temperature raise. In the present work aluminum iron silicate glasses containing minor glass modifiers and nucleating agents were synthesized as irregular shape particles which were further transformed in microspheres by using a petrol liquefied gas-oxygen torch. The optimized processing parameters which lead to microspheres that give a response to the magnetic field were determined. The dissolution rate in water at 90 degrees C was determined to be 3 x 10(-8) g cm(-2) min(-1). The microsphere size distribution was determined by laser scattering. The crystalline phase responsible for the ferromagnetic response was identified as magnetite. Since this phase has a high saturation magnetization and high Curie temperature, it is potentially useful for biomedical applications. The hysteresis magnetic loop was measured for materials produced in different conditions, and some of them showed to be appropriated for thermotherapy. The ratio Fe(3+)/Fe(total) was determined by Mossbauer spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.

Study of sodium tellurite glass using the thermally stimulated depolarization current technique (TSDC)

In order to have a better understanding of the role of the structure and the defects involved in the polarization processes in an 85TeO(2)-15Na(2)O mol% glass, we used the thermally stimulated depolarization currents (TSDC technique). The TSDC of the non-irradiated sample presented a strong negative peak of current at the temperature of 340 K, preceded by a relatively weak positive peak at about 300 K. after different d.c. voltages of 1200, 1500 and 2000 V were applied. No response was obtained with 1000 V. but the peak intensity increased considerably for voltages above 1200 V. After gamma-irradiation of 25 and 50 KGy doses, a depolarization of the negative peak was observed in the sample submitted to 25 KGy, whereas for the sample irradiated with 50 KGy, six TSDC peaks appeared at regular intervals of 5 KGy, in the temperature range of 100 and 300 K. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Synthesis and characterization of phosphate glass microspheres for radiotherapy applications

Class microspheres containing the radioisotope (32)P, a beta(-) particle emitter, and half-life of 14.3 days, can be easily introduced in specific human organs such as liver, pancreas. and uterus to kill cancer cells. In the present work phosphate glass microspheres were produced with different compositions and particle size distribution in the range of 20- 30 mu m. Two different thermal processes were used to spherodize glass particles originally with irregular shapes. Samples were characterized by X-rays diffraction to check the amorphous structure, energy dispersive X-rays fluorescence spectroscopy to determine the final glass composition, and Fourier transformed infrared spectroscopy to determine the structural groups in the glass structure. The dissolution rate of glass samples in water was determined at 90 degrees C, and in simulated body fluid (SBF) at 37 degrees C. Classes with dissolution rates close to 10(-5) g/(cm(2) day) were obtained, which make them suitable for the present application. Scanning electron microscopy was used to evaluate the shape of the microspheres before and after the dissolution tests. The cytotoxicity tests showed that these microspheres can be used for biological applications. (C) 2008 Elsevier B.V. All rights reserved.

Influence of pH on the incorporation and growth of Pb(2)CrO(5) crystallites in silica matrix

Pb(2)CrO(5) nanoparticles were embedded in an amorphous SiO(2) matrix by the sol-gel process. The pH and heat treatment effects were evaluated in terms of structural, microstructural and optical properties from Pb(2)CrO(5)/SiO(2) compounds. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS), and diffuse reflectance techniques were employed. Kubelka-Munk theory was used to calculate diffuse reflectance spectra that were compared to the experimental results. Finally, colorimetric coordinates of the Pb(2)CrO(5)/SiO(2) compounds were shown and discussed. In general, an acid pH initially dissolves Pb(2)CrO(5) nanoparticles and following heat treatment at 600 A degrees C crystallized into PbCrO(4) composition with grain size around 6 nm in SiO(2) matrix. No Pb(2)CrO(5) solubilization was observed for basic pH. These nanoparticles were incorporated in silica matrix showing a variety of color ranging from yellow to orange.

Internal Residual Stress Measurements in a Bioactive Glass-Ceramic Using Vickers Indentation

The residual stress distribution that arises in the glass matrix during cooling of a partially crystallized 17.2Na(2)O-32.1CaO-48.1SiO(2)-2.5P(2)O(5) (mol%) bioactive glass-ceramic was measured using the Vickers indentation method proposed by Zeng and Rowcliffe (ZR). The magnitude of the determined residual stress at the crystal/glass boundary was 1/4-1/3 of the values measured using X-ray diffraction (within the crystals) and calculated using Selsing`s model. A correction for the crack geometry factor, assuming a semi-elliptical shape, is proposed and then good agreement between experimental and theoretical values is found. Thus, if the actual crack geometry is taken into account, the indentation technique of ZR can be successfully used. In addition, a numerical model for the calculation of residual stresses that takes into account the hemispherical shape of the crystalline precipitates at a free surface was developed. The result is that near the sample surface, the radial component of the residual stress is increased by 70% in comparison with the residual stress calculated by Selsing`s model.

Third-order nonlinearity of Er(3+)-doped lead phosphate glass

The third-order optical susceptibility and dispersion of the linear refractive index of Er(3+)-doped lead phosphate glass were measured in the wavelength range between 400 and 1940 nm by using the spectrally resolved femtosecond Maker fringes technique. The nonlinear refractive index obtained from the third-order susceptibility was found to be five times higher than that of silica, indicating that Er(3+)-doped lead phosphate glass is a potential candidate to be used as the base component for the fabrication of photonic devices. For comparison purposes, the Z-scan technique was also employed to obtain the values of the nonlinear refractive index of Er(3+)-doped lead phosphate glass at several wavelengths, and the values obtained using the two techniques agree to within 15%.