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PubMed2006

[Structure changes of lead silicate glasses induced by UV laser irradiation].

The structure changes of lead silicate glasses induced by UV laser irradiation were studied by UV-visible spectra and electron spin resonance (ESR). The Urbach energies of lead silicate glasses exposed to the 266 nm UV laser increased. This implied that the disorder of the lead silicate glasses was increased. The electron spin resonance experiments showed that the oxygen deficiency centers in lead silicate glass did not change to paramagnetic defects after exposure to 266 nm laser beam, and the absorption peak near 235 nm for lead silicate glass film did not change either. But this absorption peak was bleached after exposure to the 248 nm UV laser.

English Abstract↗

PubMed1989

Thrombin stimulated platelet accumulation on protein coated glass capillaries: role of adhesive platelet alpha-granule proteins.

The generation of trace amounts of thrombin at artificial surfaces in contact with blood is likely to be a contributing factor in thrombosis on biomaterials. Using an in vitro capillary perfusion system, platelet accumulation on glass surfaces, uncoated or precoated with purified bovine collagen or human plasma proteins, was determined in the presence or absence of preadsorbed purified human thrombin. Static adsorption for 15 min at 22 degrees C from solutions of thrombin 100 NIH units (33 micrograms)/ml gave surface concentrations in the range 0.019-0.101 micrograms/cm2. Protein coated capillaries, thrombin treated or untreated, were perfused for 2 min at 37 degrees C with suspensions of washed 111In-labeled human platelets in Tyrode's-albumin buffer containing 40% washed red blood cells, under conditions of controlled, non pulsatile laminar flow (50 s-1 or 2,000 s-1). Platelet accumulation was increased in the presence of surface adsorbed thrombin on uncoated and albumin or fibrinogen coated glass but little affected on fibronectin or collagen coated glass. On von Willebrand factor (vWF) coated glass, thrombin enhancement was observed only at high shear forces. In experiments using antibodies against human platelet alpha-granule proteins, thrombin stimulated platelet deposition in uncoated glass capillaries was inhibited at 2,000 s-1 by anti-vWF and to a lesser extent by anti-fibrinogen but not by anti-thrombospondin antibodies.

Adsorption↗

PubMed1989

[Qualitative studies on the surface crystallization of dental glass ceramics (Dicor)].

The crystallization of enstatite at the surface of Dicor glass during 'ceramization' is proved by electron microscopy and x-ray diffraction. Microprobe measurements demonstrate a loss of potassium and an uptake of calcium in the outer region of the glass-ceramic after ceramization due to an ion exchange between glass and ceramization investment. This investment consists of gypsum and leucite. A thermal analysis reveals the decomposition of gypsum in the range of the ceramization temperature. Calcium diffuses into the surface of the glass while simultaneously potassium leaves the glass. The altered composition allows the crystallization of enstatite.

Ceramics↗

PubMedDate not supplied

The effect of excipients on glass transition temperatures for FK906 in the frozen and lyophilized states.

FK906, a tripeptide, has been used as a model compound to study the effect of excipients on the glass transition temperature for peptides and related compounds in the frozen solution and lyophilized states. Three kinds of excipients were chosen for study, low molecular weight sugars, high molecular weight polymers and salts. Our results indicate that the Gordon-Taylor equation can be used to predict the glass transition temperature of FK906 in the presence of sucrose, lactose, trehalose and maltose in the frozen solutions and in lyophilized products. Dextrans having different molecular weights can have different effects on the glass transition temperature of FK906 in the frozen state. Cooling rate can also have an effect on the glass transition temperature for FK906 frozen solutions in the presence of dextran. Finally, salts have a significant effect on the glass transition temperature of FK906 in the frozen state but not in lyophilized FK906.

Antihypertensive Agents↗

PubMed1993

[Roles of serotonin in glass-bead pulmonary microemboli].

We investigated the role of serotonin release from aggregating platelets in glass-bead microemboli on isolated perfused rabbit lungs. The perfusion was performed at 70 ml/min with a roller pump. The temperature of the perfusion circuit was maintained at 37 +/- 1 degrees C by means of a heat exchanger. 100 microns-diameter glass beads (1 g) were infused via the main pulmonary artery. We examined the concentration of serotonin and the number of platelets in the perfusate and the mean pulmonary arterial pressure before and after glass bead embolization. Administration of PRP (platelet-rich plasma) to the perfusate caused the concentration of serotonin to significantly increase after microembolization. Specific serotonin S2 receptor antagonist (DV-7028) inhibited the increase of serotonin concentration in the perfusate, platelet aggregation, and vasoconstriction. We concluded that in the glass-bead embolization model, serotonin was released from aggregating platelets surrounding the glass beads, and constricted pulmonary microvessels via serotonin S2 receptors on the vascular smooth muscles cells.

Animals↗

PubMedDate not supplied

Eye glasses and dentures in the O.R.: the choice is yours!

Historically, patients have been required to remove their dentures and eye glasses on the pre-surgical ward before being taken to the Operating Room (OR) on the day of surgery. This descriptive study examined the choices made by patients pre-operatively regarding dentures and/or glasses, the reasons given for the choice, and the relative satisfaction with the choice post-operatively. Of the 213 patients enrolled in this study, 66% were female with an average age of 57 years. Only patients wearing eye glasses or dentures were included. Sixty-nine percent of the patients wearing glasses and 85% wearing dentures chose to wear them to the OR. When asked post-operatively about their satisfaction with their choice, 95% indicated that they were very satisfied with their choice and that it was the best decision they could possibly have made. No glasses or dentures were broken or lost during the study.

Adolescent↗

PubMed2005

Residual monomers released from glass-fibre-reinforced composite photopolymerised in contact with bone and blood.

PURPOSE: The aim of this study was to determine the quantity of residual monomers of glass fibre-reinforced composite released into water from the composite that had been photopolymerized in contact with bone and blood. MATERIALS AND METHODS: E-glass fibre reinforced composite (FRC) made of E-glass fibre veil and the bis-GMA-TEGDMA-PMMA resin system was used in the study. In the first group, pieces of non-polymerised FRC were photopolymerised (40 s) in air which influenced the oxygen inhibited resin layer (positive control). In the second group, the FRC was polymerized between two glass plates allowing both surfaces to be well polymerized (negative control). In the test groups, the FRC was polymerized in contact with bone or in contact with blood. FRC specimens from all four groups were incubated in three milliliters of deionised water at 37 degrees C for three days. At the end of the incubation period, the residual monomers were extracted from the water with dichloromethane, and the residual monomers of TEGDMA and bis-GMA quantitatively analysed by HPLC. The degree of monomer conversion was measured by FTIR from the surface of the test specimen. Differences between the groups were analysed using one-way ANOVA (p < 0.05). RESULTS: The total quantity of residual monomers released from FRC polymerized in contact with bone was lower (0.55 wt%) than in the positive control group (0.97 wt%) (p = 0.021), and only slightly exceeded that of the negative control group (0.42 wt%) (p = 0.717). The total quantity of monomers released from FRC polymerized in contact with blood was at the level of the negative control group. The main residual monomer released was TEGDMA. The surfaces of the positive and negative controls showed a clear difference between the degree of monomer conversion, 34.0 and 62.8%, respectively, when analysed with FTIR (p < 0.001). CONCLUSION: The surface of the bone or contact with blood did not significantly inhibit the photoinitiated free radical polymerisation of the dimethacrylate monomer system of the FRC.

Acrylic Resins↗

PubMed2003

Marginal adaptation and fracture resistance of adhesively luted glass fibre-composite reinforced molar crowns with different inner crown surfaces.

OBJECTIVES: This study compared the influence of different inner crown surfaces on the fracture resistance and marginal adaptation of adhesively fixed glass fibre-reinforced molar crowns. MATERIALS AND METHODS: Vectris/Targis crowns were constructed with an inner framework of glass fibres (directly on the tooth) or an inner veneering composite layer between the fibre-framework and the tooth-substance. Both groups were sandblasted inside using Al(2)O(3); 50 microm grain size (200 kPa, 20 s) and silane coated. A control group had the inner fibre framework, but was neither sandblasted nor silane coated. The crowns were adhesively cemented on extracted human teeth, and thermally cycled and mechanically loaded (TCML: 6000 x 5 degrees C/55 degrees C; 1.2 x 10(6) x 50 N, 1.66 Hz). The marginal adaptation before and after TCML was evaluated and the fracture resistance was investigated using a Zwick universal testing machine. RESULTS: After TCML the proportion of 'perfect margin' of the control group decreased significantly at the interface crown/cement. For the variations with an inner fibre framework or inner composite layer the marginal adaptation or fracture resistance did not decrease significantly after ageing. The fracture resistance values were control: 1509N+/-486; inner fibre framework: 1896N+/-342; inner composite layer: 1754N+/-340. CONCLUSIONS: In the case of the investigated fibre framework and veneering composite, the inner surface of glass fibre-reinforced molar crowns can be covered with a composite layer or with a glass fibre framework. Both methods achieve comparable high fracture strengths and reliable marginal adaptation.

Aluminum Oxide↗

PubMed1996

Fibrous glass insulation and cancer: response and rebuttal.

In response to our commentary on fibrous glass and cancer [Infante et al., 1994], three letters have been received by the journal. The arguments put forth in these letters do not lead us to alter our scientific view that fibrous glass insulation is carcinogenic. No information is given in the letters that has not previously been stated. Even though these letters raise the same diaphanous arguments, we believe that to preserve occupational and public health we must respond in detail to ensure that the contentions of the fibrous glass industry do not gain further acceptance. Thus, we respond to each letter in turn: The first by Weiss questions and distorts epidemiologic findings, the second by McConnell attempts to recant his past views on the carcinogenicity of fibrous glass and on the value of rodent bioassays in general, and the third by Hesterberg and Chase impugns our analyses demonstrating a positive cancer response in their study. Lastly, we have not debated every issue raised in these three letters because of space limitations, and have centered our responses on what we consider the major incongruities and falsities in each letter. Likewise, we have been selective in citing only relevant literature, or those reports used by the industry or its consultants to support their views.

Animals↗

PubMed1998

Multiple exposure to arsenic, antimony, and other elements in art glass manufacturing.

Art glass manufacturing is one of the most interesting examples of exposure to complex mixtures. Among the raw materials used are silica sand, borax, carbonates, nitrates of Ca, Na, K, and a great number of compounds that are mainly oxides of As, Sb, Al, Zn, Cr, Ni, Sn, Se, Cd, Mn, Cu, Co, Fe, Nd, Er, Eu, and La. In six art glass factories that use As or Sb as fining agents, the exposure to these elements was investigated in 32 workers by means of environmental and biological monitoring. Analysis was conducted by atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). The results confirmed that As, which is the main carcinogen in glass production, reaches high air concentrations and is generally above the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value-time-weighted average (TLV-TWA) of 10 micrograms/m3. When partly substituted by antimonial compounds, As air concentrations dropped dramatically, while the air levels of Sb (which is considered less toxic but is classified as a class 2B carcinogen by IARC) were relatively low and below the ACGIH TLV-TWA of 500 micrograms/m3. Exposure to As and Sb also differed in the three types of jobs investigated: As was high in oven chargers, Sb was higher in batch mixers, and both elements were low in makers-formers. Eleven to 18 elements were detected: arsenic, Al, Ba, Sb, Pb, and Zn were the elements most frequently measured (in tens, and in some cases hundreds, of micrograms/m3), followed by B, Li, Mn, Se, Sn, Sr, Ce, La, and Nd (in micrograms or in some cases tens of micrograms/m3. The results of biological monitoring for As, Sb, and other elements were in agreement with environmental monitoring data. We concluded that multiple detection of elements is a useful tool (or the evaluation of exposure to complex mixtures such as those used in the art glass industry and that such detection also allows a more accurate evaluation of related epidemiological data.

Antimony↗

PubMed1997

Porous bioactive glass and hydroxyapatite ceramic affect bone cell function in vitro along different time lines.

We describe the effects on cell function of treating porous bioactive glass (BG) such that its surface is a composite of carbonated hydroxyapatite and serum protein. The effects on bone cell function of porous hydroxyapatite (HA) ceramic and porous glass treated to become amorphous calcium phosphate only also were studied subsequent to their having adsorbed a serum protein layer. Substrates treated for different durations were seeded with MC3T3-E1 cells and cultured for 3-17 days. Whereas cells seeded on any substrates, BG and HA produced collagen types I and III, bone sialoprotein, and osteopontin, there were significant differences between HA and BG, and among the various surface conditions created on BG. Covering the glass surface with hydroxyapatite and serum protein enhanced expression of high alkaline phosphatase activity, high rates of cell proliferation, and production of mineralized extracellular matrix. The enhancement may be due to the adsorption of a high quantity of fibronectin from the serum onto the reacted bioactive glass surface.

Biocompatible Materials↗

PubMed1997

Behavior of fetal rat chondrocytes cultured on a bioactive glass-ceramic.

We examined the behavior of fetal rat chondrocytes cultured on a bioactive glass-ceramic containing apatite and wollastonite (A.W.G.C.). Biomaterial surface topography and profiles were evaluated by bidimensional profilometry and revealed a rough surface for the glass-ceramic compared to the plastic coverslips used as controls. Chondrocyte attachment was evaluated by measuring the number of attached cells after one day of culture and by morphological observations. Chondrocytes attached in great numbers to the material surface by means of focal contacts containing vinculin and beta1-integrin. Fluorescent labeling of actin and vimentin revealed a poor spreading of chondrocytes on the bioactive glass-ceramic compared to the plastic coverslips, where the cells appeared to adhere intimately to the surface and exhibited polygonal arrays of stress fibers. During the following days of culture, chondrocytes proliferated, colonized the surface of the material, and, finally, on day 10, formed nodular structures composed of round cells separated by a dense extracellular matrix. Furthermore, these clusters of round cells were positive for type II collagen and chondroitin sulfate, both hard markers of the chondrocyte phenotype. In addition, protein synthesis, alkaline phosphatase activity, and proteoglycan production were found to increase gradually during the culture period with a pattern similar to that observed on control cultures. These results demonstrate that the bioactive glass-ceramic tested in this study appears to be a suitable substrate for in vitro chondrocyte attachment, differentiation, and matrix production.

Actins↗

PubMed1998

In vitro adsorption and activity of enzymes on reaction layers of bioactive glass substrates.

The effects of physiological biomolecules, particularly proteins, on the reactivity of bioactive glasses is being heavily researched. However, the effects of bioactive glasses on the activity of proteins have received little attention. Activity of horseradish peroxidase (HRP) adsorbed to the silica gel and hydroxycarbonate apatite layers of 45S5 bioactive glass was investigated. Surface reactions were terminated after development of a silica gel layer by the addition of edta to the reaction solution, which completely inhibited calcium phosphate formation. Complete loss of HRP activity on the silica gel layer was found to occur within 21 h while a minimal amount of activity from HCA-adsorbed HRP persisted indefinitely. These results show that bioactive glasses may serve as "friendly hosts" for adsorbed proteins, such as biologically active growth factors. These active peptides then, in turn, may generate an increased cellular response in the surrounding tissue, thereby enhancing the biogenic response.

Adsorption↗

PubMed1998

Crystallization kinetics of a low-expansion feldspar glass for dental applications.

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.

Aluminum Silicates↗

PubMed1998

Effect of bioactive glass particle size on osseous regeneration of cancellous defects.

The bioactive glass known as Bioglass or Perioglass (USB) (US Biomaterials, Alachua, FL) has proven to be an effective graft material owing to the apatite layer which forms on the surface of the glass, promoting bone formation. USB particles range in size from 90 to 710 microns in diameter, as determined by optical microscopy. A similar bioactive material, BioGran (OV) (Orthovita, Malvern, PA), was developed to limit the particle size of 4555 to the range between 300 and 360 microns, as determined by sieving. The objective of this study was to histologically and biomechanically compare the 4555 bioactive glass, produced by US Biomaterials, in a wide particle range (USB) to the narrower particle range glass produced by Orthovita (OV) The grafted defects will then be compared to normal cancellous bone (NORM) of the distal femur in rabbits. Histologically, more bone was quantified at both 4 and 12 weeks within the defects filled with USB and NORM when compared to the limbs filled with OV (p < 0.05). The OV particles had greater particle axes and larger particle areas on average than the USB particles (p < 0.05). However, the particle axis and area of the two materials decreased with time at a similar rate. Biomechanically, the USB- and OV-grafted defects had comparable peak compressive load, compressive stiffness, and compressive modulus which were equivalent to normal bone.

Animals↗

PubMed1998

Patterned glass surfaces direct cell adhesion and process outgrowth of primary neurons of the central nervous system.

Glass surfaces were patterned with cell-adhesive regions of laminin adhesive peptides YIGSR, RGD, and IKVAV, and cell-repulsive regions of poly(ethylene glycol) (PEG). The patterns were created by sputter-coating titanium and then gold onto glass coverslips through electron microscope grids. Gold surfaces were modified with cysteine-terminated peptides to have approximately 450 fmol/ cm2 of peptide incorporated on the glass coverslips as determined with radiolabeled CGYIGSR. Amine-functionalized glass coverslips were prepared using an amine-functionalized silane and then further modified with PEG-aldehyde by a Schiff base reduction. All surfaces were characterized by X-ray photoelectron spectroscopy and water contact angles. Hippocampal neurons, plated from a serum-free medium, adhered preferentially to peptide-functionalized surfaces over PEG-modified surfaces. Cell adhesion and neurite outgrowth were limited to the peptide region, demonstrating that neurite outgrowth could be directed by a combination of cell-adhesive and cell-repulsive cues.

Animals↗

PubMed1999

Glass-reinforced hydroxyapatite composites: secondary phase proportions and densification effects on biaxial bending strength.

CaO-P(2)O(5) glasses with additions of MgO and CaF(2) were used as a sintering aid of hydroxyapatite, and glass-reinforced hydroxyapatite composites obtained. Glasses promoted significant changes in the microstructure of the composites, namely with the formation of tricalcium phosphate secondary phases, beta and alpha-TCP. Quantitative phase analysis was performed by the Rietveld method using General Structure Analysis Software. Grain size measurements were carried out on SEM photomicrographs, using a planimetric procedure according to ASTM E 112-88. Flexural bending strength was determined from concentric ring-on-ring testing. Flexural bending strength (FBS) of glass-reinforced hydroxyapatite composites was found to be about twice or three times higher than that of unreinforced hydroxyapatite and tended to depend more on porosity and beta and alpha-TCP secondary phases, rather than on grain size. Traces of alpha-tricalcium phosphate significantly enhanced the strength of the composites. Using the rule of mixtures to estimate the zero porosity bending strength, the Duckworth-Knudsen model applied to the composites gave a porosity correction factor, b, with a value of 4.02. Weibull statistics were also used to analyze biaxial strength data and the level of reinforcement obtained by comparing failure probability for the composites and for the unreinforced hydroxyapatite. Lower activation energies for grain growth were observed for the composites compared to unreinforced hydroxyapatite, which should be attributed to the presence of a liquid glassy phase that promotes atomic diffusion during the sintering process.

Biocompatible Materials↗

PubMed1999

XRD, SEM-EDS, and FTIR studies of in vitro growth of an apatite-like layer on sol-gel glasses.

A glass with a composition (in mole %) of: SiO2 (70), CaO (26), and P2O5 (4) was obtained using a sol-gel method. The in vitro bioactivity of the glass was assessed by determining the changes in surface morphology and composition after soaking in simulated body fluid (SBF) for periods of up to 14 days at 37 degrees C. X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and FTIR analyses of the glass surface after different soaking periods in SBF demonstrated the growth of an apatite-like layer on the glass surface. In the first stage, an amorphous calcium phosphate layer was formed; after 7 days this surface consisted of spheres, with diameters ranging between 2 and 15 microm, composed of needle-like apatite crystallites (250 x 100 nm) with a crystallinity similar to that of a biological apatite.

Apatites↗