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Calcium phosphate (Ca,P) precipitation behavior on the surface of two bioactive glasses and four bioactive glass composites--two with hydroxylapatite (Ca10(PO4)6 (OH)2) and two with rhenanite (CaNaPO4)--were studied in simulated body fluid (SBF) and in Tris-Buffer at 5, 8, 16, 24, 48, 72, and 144 h. The weight loss of the materials was measured and the amount of precipitation was estimated using scanning electron microscopy with electrochemical detection (SEM-EDX) analysis. The test was repeated for one glass and its respective rhenanite composite every 3 h until 60 h and thereafter every 10 h until 150 h in SBF. Atomic absorption spectroscopy, spectrophotometry, SEM-EDX analysis, and pH measurements were performed on these samples. It is shown that in vitro the composite materials have a higher capacity for Ca,P precipitation than the glasses. Weight losses of the materials correlate well with their composition. Both the glass and Ca,P phases influence the precipitation mechanism and rate. Precipitation begins preferably from the glass phase. Ca,P particles clearly influence the time of onset and rate of precipitation. Cross-sectional EDX analysis of the samples revealed an absence of a clear Si-rich layer in glass A0B0 (SiO2 53.9 mol %, Na2O 27.5, CaO 12.4, P2O5 6.2, Al2O3 0.0 and B2O3 0.0) composites. This was attributed to the presence of extra calcium and phosphate ions on the surface of the material. The ion-concentration and pH change curves offered insight into the mechanism of precipitation. A connection was established between SEM-EDX results and the release curves. Formation of an Si,Ca,Na film was observed that seemed to initiate the Ca,P precipitation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Dissolution and scanning electron microscopic studies of Ca,P particle-containing bioactive glasses. 824 37

Previous studies have shown that the crystallization of glasses in the system K2O-Al2O3-SiO2, in the primary field of leucite, is not possible without modification of the composition. Leucite (KAlSi2O6) is used as a reinforcing phase in some compositions for all-ceramic dental restorations. However, because of their higher coefficient of thermal expansion, these materials cannot be veneered with conventional metal-ceramic porcelains. The purposes of this study were to investigate the crystallization behavior of a glass in the system K2O-Al2O3-SiO2 and to evaluate the effect of heat treatment on the crystal size, percent crystallinity, and coefficient of thermal expansion of the material. Ion-exchanged glass powder was prepared by mixing the glass with rubidium nitrate and heat-treating at 450 degrees C for 4, 8, 24, or 48 h. Bars were made from these powders and baked under vacuum at 1038 degrees C for 2 min. The bars made from the powder ion-exchanged for 48 h were further heat-treated for 4 h at either 800 degrees C, 850 degrees C, 900 degrees C, 950 degrees C, or 1038 degrees C. X-ray diffraction analyses showed cubic leucite was the only crystalline phase in the specimens made from the powders ion-exchanged for 4, 8, 24, or 48 h and baked at 1038 degrees C for 2 min. Further heat treatment for 4 h at either 800 degrees C, 850 degrees C, 900 degrees C, 950 degrees C, or 1038 degrees C promoted the growth of cubic leucite. In addition, a second phase identified as tetragonal rubidium-leucite was present in the specimens heat-treated for 4 h at 1038 degrees C. SEM observations showed that all specimens made from the powders ion-exchanged for 48 h exhibited small spherical crystals dispersed in a glassy matrix. The percent crystallinity ranged from 18.9% to 42.9% and the average particle size was between 0.64 to 1.18 microns. The coefficients of thermal expansion ranged between 8.076 and 8.788 x 10(-6)/degree C.
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PMID:Crystallization kinetics of a low-expansion feldspar glass for dental applications. 965 9

Novel bioactive ceramic hollow microspheres with an apparent density in the range 0.8-1.0 g cm(-3) have been developed as microcarriers for 3-D bone tissue formation in rotating-wall vessels (RWV). Hollow ceramic microspheres with a composition of 58-72% SiO2, 28-42% Al2O3 (wt%) and an apparent density 0.8-1.0 g cm(-3) were pretreated in 1.0 N NaOH for 2 h before being coated with synthesized calcium hydroxyapatite (HA) particulate sol. The HA-coated hollow microspheres were sintered for 1 h at 600, 800 and 1000 degrees C. SEM analysis revealed that the grain size and pore size of the calcium phosphate coating increased with the sintering temperature. FTIR analysis showed that crystalline calcium hydroxyapatite was present in the coatings sintered at 600 and 800 degrees C. When sintered at 1000 degrees C, the coating consisted of alpha-tricalcium phosphate. All the coatings adhered well, independent of sintering temperature. The trajectory analysis revealed that the hollow microsphere remained suspended in a rotating-wall vessel (RWV), and experienced a low shear stress (approximately 0.6 dyn cm(-2)). Cell culture studies using rat bone marrow stromal cells and osteosarcoma cells (ROS 17/2.8) showed that the cells attached to and formed 3-D aggregates with the hollow microspheres in a RWV. Extracellular matrix was observed in the aggregates. These data suggest that these hollow bioactive ceramic microspheres can be used as microcarriers for 3-D bone tissue formation in vitro, as well as for the study of the effects of microgravity on bone cell functions.
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PMID:Fabrication, characterization and evaluation of bioceramic hollow microspheres used as microcarriers for 3-D bone tissue formation in rotating bioreactors. 1037 99

The excimer laser irradiation of thin film amorphous silicon (a-Si) precursors on glass is a suitable method for obtaining high-performance polycrystalline silicon (p-Si) active layers for devices and circuits. By changing the experimental conditions, the recrystallization method generates a variety of microstructures that have direct impact on the material performance. An additional reason for microstructural characterization is introduced by the methods for spatially locating the recrystallization nuclei, used in more ergonomic concepts of device fabrication. Metal and SiO2 strip overlayers have been applied here, on a-Si to fix the position of the solidification seeds after laser melting. The control of many aspects of the thin film microstructure can be achieved with a collection of a few inspection techniques like AFM, SEM, EC contrast, TEM, X-ray diffraction (XRD), some of which require preliminary grain decoration treatment, and some do not. The results of different irradiation experiments, are herein illustrated, enlightened by the above characterization techniques, for providing information on surface morphology, grain arrangement, preferred orientation.
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PMID:Morphological and structural effects of excimer laser treatment of amorphous silicon 1070 80

The aim of this work has been to test the biocompatibility of four bioactive, gel derived glass-ceramic materials of CaO-PO2-SiO2 system, modified by addition of boron, aluminum and magnesium compounds. We have examined the growth, collagen synthesis, adhesion and morphology of NRK rat fibroblasts cultured in direct and indirect contact with biomaterials. The growth of cells cultures has been quantified by two methods: [3H]thymidine incorporation and direct counting of cells. The level of collagen synthesis has been used as a parameter describing metabolic activity of cells. Cellular morphology has been assessed following 24 h and 4 days of culturing cells on biomaterials by using SEM and confocal microscopy, respectively. Additionally, in order to obtain information about the attachment of cells to substratum the presence of focal contacts has been examined. The results of all the experiments have demonstrated that none of the materials under study significantly altered cellular functions that were tested. This indicates that additions of MgO, Al2O3 and B2O3 have not induced cytotoxicity of the materials under study. This qualifies them for further in vivo experiments.
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PMID:Evaluation of biocompatibility of apatite-wollastonite ceramics in fibroblast cultures. 1097 73

To prepare spray-dried powders of poly(D,L-lactic acid) (PLA) or poly-epsilon-caprolactone (P epsilonC) from colloidal suspensions containing indomethacin (IND) using benzyl benzoate (BnB), nanocapsules (NC) were prepared by nanoprecipitation. To select the best NC formulations, increasing drug concentrations were tested (1.0, 1.5, or 2.0 mg/mL). The particle size was measured by Nanosizer. Spray-dried powders (SDP) were prepared by addition of Aerosil 200 into suspensions of NC. IND was assayed by HPLC. Free IND was determined using an Ultrafree. NC-SPD were examined under SEM. The particle sizes of all formulations are in the sub-300 nm range and are IND-associated, with drug recovery close to 100%. After 1 month, the formulations with highest drug content (2.0 mg/mL) showed a decline of total quantity of IND. After spray-drying, IND recovery for SDP presented values above 100%, indicating that the drug was concentrated from loss of mass during the process. To verify the relationship of oil phase with this loss of mass, similar NC (IND 1.5 mg/mL) prepared with Miglyol 810 (MI) were spray-dried, and SEM analysis showed nanostructures adsorbed onto SiO2. Similar nano-structures were not visualized for NC samples prepared with BnB. A swelling experiment showed the complete dissolution of both polymer by the BnB, whereas for MI the polymer masses remained unchanged. In conclusion, BnB is a solvent for PLA and P epsilonC and this ester is entrained during spray-drying. Despite the use of BnB in formulations of NC, PLA, or P epsilonC, colloidal suspensions prepared with BnB could be micelles instead of nanocapsules.
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PMID:Influence of benzyl benzoate as oil core on the physicochemical properties of spray-dried powders from polymeric nanocapsules containing indomethacin. 1119 25

Hydrothermal method was used to prepare the hydroxyapatite (HA) coating on CaO-SiO2-B2O3-Na2O glass. The phase composition, morphology and microstructure of HA coated glass composites were analyzed using XRD, EPMA, FT-IR and SEM techniques. It revealed that HA coating possessed a porous gradient construction; HA coating was tightly bonded with the glass substrate by the interface layer. During the formation of HA coating, the hydrated silica produced by the corrosion of glass substrate in the hydrothermal solution provided favorable sites for apatite nucleation. With the dissolving of HA powder and the growth of apatite small crystallites, Ca+, PO(4 (3-)) ions would precipitate on the surface of glass to form the HA coating. Silicon element released from glass reacted with calcium produced by the dissolution of HA to form the tight reaction layer. HA coating is formed by the mechanism of dissolving-ions immigrating-precipitating pattern.
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PMID:Morphology and formation mechanism of hydroxyapatite coating by hydrothermal method on CaO-SiO2-B2O3-Na2O glass. 1120 48

A comparative study of in vitro bioactivity of a sol-gel glass with composition 55% SiO2-41%CaO-4%P2O5 has been carried out by soaking it in a simulated body fluid (SBF) with and without exchange of this solution. When SBF is kept constant (static assay) the solution composition changes, increasing the Ca2+ concentration and pH as a function of soaking time while these parameters remain nearly constant and very close to human conditions in dynamic conditions. Glass surface is studied by FTIR, XRD and SEM in order to compare the behaviour in the two procedures, revealing that in both cases an apatite-like layer is formed on the glass surface, although there are differences in rate and morphology in this formation. In addition, a study of porosity was carried out by Hg intrusion pointing out the pore distribution and changes in porosity with time for both procedures. A similar behaviour in mesopore region was detected, while macropores remain nearly constant in static conditions, decreasing from 0.48 to 0.12 microm in just 3 h of soaking in dynamic assay.
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PMID:Static and dynamic in vitro study of a sol-gel glass bioactivity. 1145 70

The aim of this work was to investigate machinable glass-ceramics used as oral restoration material in K2O-MgO-Al2O3-SiO2-F glass system. By using of DTA, XRD and SEM investigation, the crystalline structure and characteristics were tested. The chemical composition of WCMM machinable glass-ceramics was defined by the following general formula: (K,Na)Mg3-3x Al2x (AlSi3) O10F2(0.5 < or = x < 0.7). The experimental results show that WCMM is an excellent oral restoration materials in the fabrication of crowns, inlayers and veneers.
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PMID:[The preliminary study on WCMM machinable glass-ceramics]. 1147 98

This work describes the production of silicon carbide using microwaves as the energy source, which was supplied by means of variable power, up to 2000 Watts, magnetron operating at 2.45 GHz. The obtained samples were analyzed by means of X-ray diffraction and observed with electron microscopy (SEM). Temperatures achieved were around 2000 degrees C, which is the upper limit for the beta-SiC growth regime, before getting other SiC polytypes. Analysis of different portions of the sample showed that beta-SiC was the only formed compound, although free SiO2 and graphite were also present. Observations made by SEM demonstrated different crystal growth regime, meaning that thermal conditions were not totally uniform. The amount of beta-SiC found and the relative simplicity of the device prove that production of this material from silica and graphite is possible by applying microwaves as an energy source.
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PMID:Microwaves as an energy source for producing beta-SiC. 1183 50


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