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PubMed1994

Calcium phosphate formation on sol-gel-derived bioactive glasses in vitro.

When soluble salts are used in the sol-gel processing of bioactive glasses, the resulting materials are not homogeneous. To produce homogeneous gel-glasses, a sol-gel method using all alkoxide precursors was developed. In this work the in vitro bioactivity of the new all-alkoxide gel-glasses is investigated. Three compositions in the system, CaO-P2O5-SiO2, were studied. Solid samples were soaked in Tris buffer and simulated body fluid (SBF), and the rate of formation of hydroxy carbonate apatite (HCA) on the surface of the glasses was measured by Fourier transform infrared spectroscopy. The solutions were analyzed before and after reaction by inductively coupled plasma. All compositions studied formed a hydroxy carbonate apatite (HCA) layer within 8 h in both test solutions. The HCA layer grew rapidly when SBF was used.

Apatites↗
PubMed1994

Numerical analysis of extracellular fluid flow and chemical species transport around and within porous bioactive glass.

Modeling of the physical phenomena present at the biomaterial-tissue interface provides a valuable tool for examining the underlying mechanisms which influence the overall behavior of the implant-host system. Based on histological data from a previous implantation study (E. Schepers, M. De Clercq, P. Ducheyne, and R. Kempeneers, "Bioactive glass particulate materials as a filler for bone lesions," J. Oral Rehab.; 18, 439-452, 1991, Ref. 1) which documented the differentiation of mesenchymal cells to cells expressing the osteoblastic phenotype in porous bioactive glass, a finite element momentum and mass transport model was constructed. In this analysis, the extracellular compositional variations and fluid flow conditions around and within porous bioactive glass granules were determined. Numerical simulations demonstrated that the interstitial fluid flow around these granules (300-360 microns) is viscosity dominated (low Reynolds number flow) and that the fluid inside the granules remains stagnant. This velocity field results in shear stresses proportional to the velocity gradient at the granule-fluid interface outside the particles and no shear stresses inside the particles. A parametric study on the effect of interstitial fluid flow on chemical species (Na+, Ca+2, HPO(4)-2) transport outside the granules revealed three domains. At low velocities (0-0.1 micron/s), the transport of species is diffusion controlled. At intermediate velocities (1.0-10 microns/s), diffusion and convection contribute to the species transport. The concentration of chemical species is nearly uniform at high velocities (100-800 microns/s). For all three cases, the transport of chemical species within the granules is diffusion controlled. The differences in transport mechanisms and interstitial fluid flow conditions lead to variations in concentrations, reaction rates, and shear stresses between the inside and the outside of the glass granules. These differences may influence cellular migration, attachment, differentiation, and the overall response to these bioactive materials.

Animals↗
PubMed1995

Bioactive bone cement: the effect of amounts of glass powder and histologic changes with time.

A study was conducted to examine the influence of the amount of glass powder added to a bioactive bone cement of our formula on its mechanical and biologic properties. Serial changes in the cement with time were also examined. The bioactive bone cement consisted of CaO-SiO2-P2O5-CaF2 glass powder and bisphenol-a-glycidyl methacrylate resin. Glass powder was added to the cement in 30, 50, 70, and 80% weight ratios. The compressive strengths of the resulting cements (171-239 MPa) were more than double that of polymethylmethacrylate cement (68 MPa). Histologic examination of rat tibiae bearing artificial defects packed with each bioactive cement showed direct bone contact 4 weeks after surgery. The cement with a higher percentage of glass powder showed better direct formation of bone around its periphery with a thicker reactive layer. Under scanning electron microscopic observation, the reactive layer showed increased levels of calcium and phosphorus. Examination of histologic changes up to 26 weeks showed progressive bone formation around the cement and no sign of biodegradation.

Animals↗
PubMed2004

Numerical failure analysis of glass-fiber-reinforced composites.

The purpose of this work was to propose a new numerical model for glass-fiber-reinforced composites. The proposed numerical model was constructed with orthotropic shell, isotropic shell, and beam elements representing glass fiber cloth, silica filler, and the remaining matrix resin, respectively. The proposed model was applied to failure analysis under three-point bending conditions. The validity of the numerical model was checked through comparisons with experimental results. Four types of specimens were used: composite resin, and composite resin with neutral, upper, and lower glass-fiber cloth reinforcement insertions. For all types, close agreement between the analytical and experimental results was confirmed. This indicates that the proposed numerical model is effective for evaluating the mechanical behaviors of glass-fiber-reinforced composites.

Composite Resins↗
PubMed2005

Effect of ion exchange of glazed dental glass ceramics on strength parameters.

Ion exchange treatments can significantly increase the strength of dental glass ceramic core materials by induced compressive residual stresses. However, the core materials of dental restorations need to be veneered or at least to be stained and glazed for esthetic and functional reasons. The objective of this study was to determine the effect of different ion exchange treatments on the strength parameters of stained and glazed glass ceramics. Batches of specimens made of a leucite reinforced dental glass with and without staining and glazing layer, untreated, single ion exchanged (KNO3), and dual ion exchanged (1. KNO3/27, 2. 30 mol% NaNO3/70 mol% KNO3) were tested. The strength of the core material was increased from 117 to 213 MPa by single ion exchange. Staining and glazing increased the strength up to 165 MPa. Single ion exchange of the stained and glazed core caused only a slight additional strength increase up to 173 MPa. The dual ion exchanged stained and glazed core exhibit a strength of 195 MPa and decreased the large strength scatter because of a well-designed residual stress profile. We conclude that dual ion exchange treatments could significantly increase the mechanical reliability of stained and glazed glass ceramic restorations.

Dental Porcelain↗
PubMed2005

Bioactive and biocompatible pieces of HA/sol-gel glass mixtures obtained by the gel-casting method.

Hydroxyapatite (HA)/glass mixtures have shown a faster bioactive behaviour than HA itself. On the other hand, the gel-casting method is a simple and reproducible colloidal method to produce ceramic pieces with complex shapes. In this work, pieces of HA/glass mixtures were prepared by the gel-casting method. A study for obtaining concentrated slurries of these mixtures is reported; the bioactivity and biocompatibility of the obtained pieces have been studied also. The influence of pH, dispersant concentration, the content and milling of glass, and the way to prepare the suspensions were investigated. The lowest viscosity and better rheological properties were achieved with the lowest glass content, when the glass was added after the dispersion of the HA powder and when the glass was not milled after calcination. Fluid suspensions with a high solid content (50 vol.%) could be prepared and well-shaped pieces were obtained from these slurries. These pieces showed in vitro bioactive behavior in simulated body fluid; additionally, the proliferation and spreading assays with osteoblastic cells (HOS) showed that the pieces are biocompatible. The results obtained indicate that the gel-casting of HA/glass mixtures produces bioactive and biocompatible pieces with the required shapes. Therefore, these materials could be good candidates for clinical applications and scaffolds for tissue engineering.

Biocompatible Materials↗
PubMed2005

On the feasibility of phosphate glass and hydroxyapatite engineered coating on titanium.

In this report, bioactive calcium phosphate (CaP) coatings were produced on titanium (Ti) by using phosphate-based glass (P-glass) and hydroxyapatite (HA), and their feasibility for hard tissue applications was addressed in vitro. P-glass and HA composite slurries were coated on Ti under mild heat treatment conditions to form a porous thick layer, and then the micropores were filled in with an HA sol-gel precursor to produce a dense layer. The resultant coating product was composed of HA and calcium phosphate glass ceramics, such as tricalcium phosphate (TCP) and calcium pyrophosphate (CPP). The coating layer had a thickness of approximately 30-40 microm and adhered to the Ti substrate tightly. The adhesion strength of the coating layer on Ti was as high as 30-33 MPa. The human osteoblastic cells cultured on the coatings produced by the combined method attached and proliferated favorably. Moreover, the cells on the coatings expressed significantly higher alkaline phosphatase activity than those on pure Ti, suggesting the stimulation of the osteoblastic activity on the coatings. On the basis of these observations, the engineered CaP coating layer is considered to be potentially applicable as a hard tissue-coating system on Ti-based implants.

Durapatite↗
PubMed2007

Effect of the solution flow rate on the in vitro bioactivity of 2.5CaO x 2SiO(2) glass.

A comparative study of in vitro bioactivity of 2.5CaO x 2SiO(2) glass has been carried out by soaking it in a simulated body fluid, with continuously and periodic exchange of this solution (dynamic and differential protocols). Dynamic assays were carried out at different solution flow rates, 3 mL/h, 6 mL/h, 12 mL/h, to study the influence of flow rate on glass reactivity. Glass surface was studied by Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy so as to compare the behavior in the two procedures, revealing that in both cases an apatite layer is formed on the glass surface, although there are differences on deposition rate and morphology, which are also influenced by the solution flow rate.

Adsorption↗
PubMed2006

Manufacturing, mechanical characterization, and in vitro performance of bioactive glass 13-93 fibers.

Fibers were manufactured from the bioactive glass 13-93 by melt spinning. The fibers were further characterized by measuring their tensile and flexural strength, and their in vitro performance was characterized by immersing them in simulated body fluid, which analyzed changes in their mass, their flexural strength, and surface reactions. The strength of glass fibers is highly dependent on fiber diameter, test method, and possible surface flaws, for example, cracks due to abrasion. In this study, the thinnest fibers (diameter between 24 and 33 microm) possessed the highest average tensile strength of 861 MPa. The flexural strength was initially 1353.5 MPa and it remained at that level for 2 weeks. The Weibull modulus for both tensile and flexural strength values was initially about 2.1. The flexural strength started to decrease and was only approximately 20% of the initial strength after 5 weeks. During the weeks 5-40, only a slight decrease was detected. The flexural modulus decreased steadily from 68 to 40 GPa during this period. The weight of the samples initially decreased due to leaching of ions and further started to increase due to precipitation of calcium phosphate on the fiber surfaces. The mass change of the bioactive glass fibers was dependent on the surface area rather than initial weight of the sample. The compositional analysis of the fiber surface after 24 h and 5 weeks immersion did confirm the initial leaching of ions and later the precipitation of a calcium phosphate layer on the bioactive glass 13-93 fiber surface in vitro.

Biocompatible Materials↗
PubMed1988

Adhesion patterns and cytoskeleton of rabbit osteoclasts on bone slices and glass.

The ability of osteoclasts (OC) to migrate and resorb bone is thought to be dependent on cytoskeletal function and adhesion. Therefore, we investigated the cytoskeleton and the adhesion patterns of rabbit OC on glass and on devitalized bone slices, using specific antibodies to cytoskeletal elements and fluorescence and interference reflection microscopy. Microtubules (MT) were similar in OC on both substrata, and appeared in a pattern typical of that described for many cells. Multiple centriolar complexes were observed in most OC, either as one large aggregate in the center of the cell or dispersed singly or in small aggregates close to individual nuclei. Staining of microfilaments (MF) was similar on both substrata and appeared primarily as an F-actin network. MF distribution was different in OC associated with resorption lacunae with intense staining over those regions. In the OC on glass, high F-actin staining was detectable at the periphery in dots and rosette-like structures, which also stained for vinculin. The adhesion patterns indicated that OC on glass do not make large focal contacts, but appear to make a few tiny focal contacts that are not associated with the rosette-like structures. Most of the undersurface of the OC appeared either to be involved in close contacts or to be separated by distances of greater than 100 nm from the substratum. These studies indicate that the MF distribution and the adhesion patterns of rabbit OC are typical of motile cells, that the distribution of the cytoskeleton of rabbit OC on glass and on bone slices is similar, and that MF may be involved in the morphological changes associated with resorption.

Actin Cytoskeleton↗
PubMed1997

Quantitative risk assessment for a glass fiber insulation product.

California Proposition 65 (Prop65) provides a mechanism by which the manufacturer may perform a quantitative risk assessment to be used in determining the need for cancer warning labels. This paper presents a risk assessment under this regulation for professional and do-it-yourself insulation installers. It determines the level of insulation glass fiber exposure (specifically Owens Corning's R-25 PinkPlus with Miraflex) that, assuming a working lifetime exposure, poses no significant cancer risk under Prop65's regulations. "No significant risk" is defined under Prop65 as a lifetime risk of no more than one additional cancer case per 100,000 exposed persons, and nonsignificant exposure is defined as a working lifetime exposure associated with "no significant risk." This determination can be carried out despite the fact that the relevant underlying studies (i.e., chronic inhalation bioassays) of comparable glass wool fibers do not show tumorigenic activity. Nonsignificant exposures are estimated from (1) the most recent RCC chronic inhalation bioassay of nondurable fiberglass in rats; (2) intraperitoneal fiberglass injection studies in rats; (3) a distributional, decision analysis approach applied to four chronic inhalation rat bioassays of conventional fiberglass; (4) an extrapolation from the RCC chronic rat inhalation bioassay of durable refractory ceramic fibers; and (5) an extrapolation from the IOM chronic rat inhalation bioassay of durable E glass microfibers. When the EPA linear nonthreshold model is used, central estimates of nonsignificant exposure range from 0.36 fibers/cc (for the RCC chronic inhalation bioassay of fiberglass) through 21 fibers/cc (for the i.p. fiberglass injection studies). Lower 95% confidence bounds on these estimates vary from 0.17 fibers/cc through 13 fibers/cc. Estimates derived from the distributional approach or from applying the EPA linear nonthreshold model to chronic bioassays of durable fibers such as refractory ceramic fiber or E glass microfibers are intermediate to the other approaches. Estimates based on the Weibull 1.5-hit nonthreshold and 2-hit threshold models exceed by at least a factor of 10 the corresponding EPA linear nonthreshold estimates. The lowest nonsignificant exposures derived in this assessment are at least a factor of two higher than field exposures measured for professionals installing the R-25 fiberglass insulation product and are orders of magnitude higher than the estimated lifetime exposures for do-it-yourselfers.

Animals↗
PubMed1988

Activation of the alternative complement pathway and generation of stimulating factors for granulocytes by glass fibers.

Continuous-filament glass fibers coated with organic agents, candidate asbestos substitutes, were assessed for their ability to elicit from normal human serum complement-derived cleavage products which are able to stimulate the chemotaxis and the respiratory burst of polymorphonuclear leukocytes. Glass fibers generated chemoattracting and respiratory stimulating factors for polymorphonuclears from human serum. The effect was dose related for chemotaxis from the serum fiber concentration of 75 micrograms/ml to 1,250 micrograms/ml. The serum chemoattracting activity, as well the respiratory stimulation, were dramatically impaired when serum had been preliminarily absorbed with antiC5 antiserum. Since the impairment of chemotactic activity occurred also in the presence of EDTA, but not in the presence of EGTA, we assumed an activation of the alternative complement pathway. Glass fibers were studied in comparison to a UICC sample of Canadian chrysotile asbestos, which is able to activate in vitro the alternative complement pathway. Glass fibers exhibited less ability than asbestos fibers to generate complement cleavage products with chemotactic activity for polymorphonuclears; however, they produced an activity about equal to 80% of a chemotactic standard stimulus such as zymosan-activated plasma.

Asbestos↗
PubMed1985

Glass-ceramic metal composite bone fixation: effect of surface parameters.

The purpose of this study was to compare the rates of bone growth with four different surfaces of cobalt-chrome implants. Two of the implant surfaces were coated by a glass-ceramic of our own composition. One coating was porous. No enhancement of bone ingrowth was found in the glass-ceramic implants. The degree of metal ion contamination was also assessed, and significant, potentially harmful contamination by metal ions was found in the glass-ceramic. This study points out the need for better techniques of coating metal with glass-ceramic to avoid potential carcinogenic effects.

Bone Cements↗
PubMed1976

Colony growth of mouse bone marrow cells in agar contained in glass capillaries.

Mouse bone marrow cells were grown in semi-solid agar contained in glass capillary tubes. Several parameters affecting colony formation in the capillaries were studied. 10(4) cells in 100 mul incubation medium within one capillary produced 22 to 30 colonies of granulocytes and macrophages. Compared with the common petri dishes glass capillaries offer several advantages under the conditions used: 1. A twofold higher plating efficiency. 2. Applicability to optical scanning by light scattering and electronic counting, allowing automation and greatly improving sensitivity, statistical accuracy and reproducibility. Kinetics of colony growth can also be monitored. 3. Diminished risk of bacterial and fungal contamination. 4. A more than tenfold lower need for materials on similar statistical errors. Substituting methylcellulose for agar resulted in colonies of fibroblast-like cells adherent to glass surface. Glass non-adherent cells showed a threefold higher plating efficiency in agar.

Agar↗
PubMed1983

Comparison of adhesion to glass and aggregation of human leucocytes.

C5adesArg-induced leucocyte aggregation and neutrophil adhesion to glass were compared using the same cell separation technique and identical chemicals for preparing the media. Human serum albumin decreased adhesion to glass but had no effect on leucocyte aggregation induced by C5adesArg. In contrast, C5adesArg in Gey's solution with or without HSA, in serum or plasma stimulated leucocyte aggregation in a dose-dependent fashion. However, it did not alter neutrophil adhesion to glass. This indicates that leucocyte aggregation and neutrophil adherence to glass do not necessarily represent equivalent responses taking place on different substrata. Thus they may be mechanistically distinct.

Cell Adhesion↗
PubMed1994

Selective capacity of glass-wool filtration for the separation of human spermatozoa with condensed chromatin: a possible therapeutic modality for male-factor cases?

PURPOSE: The aim of this study was to evaluate chromatin condensation of human spermatozoa following swim-up compared to glass-wool separation. Semen aliquots from men attending an andrological outpatient clinic were processed by means of a swim-up procedure and glass-wool filtration. Chromatin condensation was recorded using aniline blue staining and results were reported according to color intensity of stained sperm heads. Morphometric measurements of sperm heads were performed on stained sperm samples. RESULTS: Glass-wool filtration resulted (i) in a significantly higher total motile sperm count (P < 0.0005) compared to swim-up and (ii) in a significantly higher percentage of normal chromatin-condensed spermatozoa compared to the ejaculate (P < 0.01). CONCLUSION: In contrast, comparing swim-up to the ejaculate, the percentage of matured nuclei (unstained spermatozoa) retrieved following swim-up was significantly lower (P < 0.005). Glass-wool filtration separates human spermatozoa according to motility and size of the sperm head. The size of the sperm head closely correlated with the chromatin condensation quality.

Aniline Compounds↗
PubMed1998

Quantifying the cleanliness of glass capillaries.

I used capillary rise methods to investigate the lumenal surface properties of quartz (fused silica, Amersil T-08), borosilicate (Corning 7800), and high-lead glass (Corning 0010) capillaries commonly used to make patch pipets. I calculated the capillary rise and contact angle for water and methanol from weight measurements. The capillary rise was compared with the theoretical maximum value calculated by assuming each fluid perfectly wetted the lumenal surface of the glass (i.e., zero contact angle, which reflects the absence of surface contamination). For borosilicate, high-lead, and quartz capillaries, the rise for water was substantially less than the theoretical maximum rise. Exposure of the borosilicate, lead, and quartz capillaries to several cleaning methods resulted in substantially better--but not perfect--agreement between the theoretical maximum rise and calculated capillary rise. By contrast, the capillary rise for methanol was almost identical in untreated and cleaned capillaries, but less than its theoretical maximum rise. The residual discrepancy between the observed and theoretical rise for water could not be improved on by trying a variety of cleaning procedures, but some cleaning methods were superior to others. The water solubility of the surface contaminants, deduced from the effectiveness of repeated rinsing, was different for each of the three types of capillaries examined: Corning 7800 > quartz > Corning 0010. A surface film was also detected in quatz tubing with an internal filament. I conclude that these borosilicate, quartz, and high-lead glass capillaries have a film on the lumenal surface, which can be removed using appropriate cleaning methods. The surface contaminants may be unique to each type of capillary and may also be hydrophobic. Two simple methods are presented to quantitate the cleanliness of glass capillary tubing commonly used to make pipets for studies of biological membranes. It is not known if the surface film is of importance in electrophysiological studies of biological membranes.

Capillary Action↗
PubMed2004

Statistical evaluation of potash-lime-silica glass weathering.

Two potash-lime-silica model glasses with compositions similar to those of medieval stained glass were exposed at 26 test sites all over Europe and in North America for 3-6 years. The objectives of this large-scale field exposure programme were: (a) a qualitative analysis of the weathering products formed on the surface of the samples in the (environmental) scanning electron microscope in combination with energy dispersive X-ray microanalysis (ESEM/EDX or SEM/EDX, respectively); (b) a statistical evaluation of the weathering phenomena by applying a multiple linear regression (MLR) analysis to find correlations between the degree of weathering, which was measured in terms of surface coverage with reaction products, and environmental parameters such as the concentration (c) of the acidifying gases SO(2), NO(2) and O(3), the temperature (T) and the relative humidity (RH); and (c) the calculation of a time-dependence function of the weathering process of these glasses. Mainly sulfates of calcium and potassium such as gypsum (CaSO(4).2 H(2)O), arcanite (K(2)SO(4)) and syngenite (CaSO(4).K(2)SO(4).H(2)O) could be identified in the SEM and ESEM. Carbonates, nitrates and many particles deposited on the glass surface were found as well. MLR calculations exhibit significant dependencies of the degree of weathering on T, RH, c(NO(x)), c(SO(2)) and c(O(3)). Applying a time-dependence function of the general form y= a. t(b) (t=time) results in a value of approximately 0.42 for the exponent b, which comes close to values expected from various studies in the literature.

Calcium Compounds↗