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At least 919 records · Page 51Linked to original sources
PubMed2003

Bonding strength of the apatite layer formed on glass-ceramic apatite-wollastonite-polyethylene composites.

Bioactive glass-ceramic apatite-wollastonite (A-W) has been incorporated into polyethylene in particulate form to create new bioactive composites for potential maxillofacial applications. The effects of varying the volume fraction of glass-ceramic A-W filler and the glass-ceramic A-W particle size were investigated by measuring the bonding strength of the bonelike apatite layer formed on the surface of glass-ceramic A-W-polyethylene composites. The bonding strength was evaluated via a modified ASTM C-333 standard in which a tensile stress was applied to the substrate and the strength of the bioactive layer was compared with that formed on commercially available hydroxyapatite-polyethylene composite samples, HAPEX. The composites demonstrated greater bonding strength with increased filler content and reduced filler particle size (maximum 6.9 +/- 0.5 MPa) and a marginally greater bonding strength as compared with HAPEX (2.8 +/- 0.5 MPa), when glass-ceramic A-W-polyethylene composite samples with the same filler content were tested. The higher bonding strength of the apatite layer formed on the A-W-polyethylene composite samples suggests that, in addition to maxillofacial applications, these composites might also be utilized in applications involving higher levels of load bearing.

Adhesiveness↗
PubMed2003

A new quantitative method to evaluate the in vitro bioactivity of melt and sol-gel-derived silicate glasses.

Two melt-derived glasses (45S5 and 60S) and four sol-gel glasses (58S, 68S, 77S, and 91S) have been synthesized. The activation energy for the silicon release was determined, and a very close correlation was observed between this value and published results of the bioactive behavior of the glasses. This relationship can be explained in terms of the influence of chemical composition, textural properties, and structural density on the silanol group formation and silicon dissolution. These measurements provide a quantitative method to evaluate the in vitro bioactivity of SiO(2)-based glasses. Preliminary studies suggest an activation energy gap (Ea) of 0.35-0.5 eV as a boundary between bioactive and nonbioactive glasses.

Biocompatible Materials↗
PubMed2003

Long-term craniofacial osteoblast culture on a sodium phosphate and a calcium/sodium phosphate glass.

The aim of this study was to determine the characteristics of human craniofacial osteoblasts cultured on sodium phosphate glass and calcium-sodium phosphate glass in a long-term culture of up to 28 days. The characteristics studied were attachment, proliferation, alkaline phosphatase activity, collagen-1 production, and mineralization. A comparison of the degradation rate, measured by mass loss of the glasses, which are intended for use as a component of a novel degradable composite for craniofacial bone repair, was also performed. It was our hypothesis that the glass would be degradable with a change in degradation rate observed by calcium addition and support osteoblast proliferation and expression of the above characteristics. The inclusion of calcium into the reaction mixture significantly decreased the degradation rate, and it is suggested that the slower degradation is the result of pseudo crosslinking (ionic crosslinks rather than covalent bonding) of the polyphosphate chains by the calcium ions. Therefore, twice as many P-O bonds will need to be hydrolyzed for dissolution of the metal phosphate to occur, therefore greatly reducing the rate of hydrolysis. Osteoblasts were able to attach, spread, and proliferate in a manner comparable with the positive control, as shown by analysis of variance. Formation of a collagen-rich mineralized matrix was also observed. The results presented here suggest that a biocompatible soluble glass has been produced, which has potential to be included in a novel biodegradable craniofacial implant.

Calcium↗
PubMed2004

Biodegradable radiation delivery system utilizing glass microspheres and ethylenediaminetetraacetate chelation therapy.

Dysprosium lithium-borate (DyLB) glass microspheres have been developed as a biodegradable radiation delivery vehicle for the treatment of rheumatoid arthritis and other diseases. Radioactive microspheres of these glasses are intended to be injected into a joint infected with rheumatoid arthritis to safely deliver a localized dose (100 Gy) of beta radiation. Once injected, the microspheres react nonuniformly with body fluids. The nonradioactive, lithium-borate component is dissolved from the glass, whereas the radioactive (165)Dy reacts with phosphate anions in the body fluids, and becomes "chemically" trapped in a solid, dysprosium phosphate reaction product that has the same size as the unreacted microsphere. The glass microspheres lose approximately 80% of their weight after nonuniform reaction (<1 day), but the dysprosium phosphate reaction product is slowly metabolized by the body over several months. Ethylenediaminetetraacetate (EDTA) chelation therapy can be used to dissolve the dysprosium phosphate reaction product in vitro in <2 h. The dysprosium phosphate reaction product which formed in vivo in the joint of a Sprague-Dawley rat was also dissolved by EDTA chelation therapy in <1 week, without causing any detectable joint damage. The combination of DyLB glass microspheres and EDTA chelation therapy provides a unique "tool" for the medical community because it can deliver a large dose (>100 Gy) of localized beta radiation to a treatment site within the body, followed by complete biodegradability.

Animals↗
PubMed2005

Bone formation in calvarial defects of Sprague-Dawley rats by transplantation of calcium phosphate glass.

The purpose of this study was to investigate the bone-regenerative effect of calcium phosphate glass in vivo. We prepared amorphous calcium phosphate glass powder having a mean particle size of 400 microm in the system CaO-CaF2-P2O5-MgO-ZnO. Calvarial critical-sized defects (8 mm) were created in 60 male Sprague-Dawley rats. The animals were divided into an experimental group and control group of 30 animals each. Each defect was filled with a constant weight of 0.5 g calcium phosphate glass powder mixed with saline. As a control, the defect was left empty. The rats were sacrificed 2, 4, or 8 weeks postsurgery, and the results evaluated using radiodensitometric and histological studies; they were also examined histomorphometrically. When the calcium phosphate glass powders with 400-microm particles were grafted, the defects were nearly completely filled with new-formed bone in a clean healing condition after 8 weeks. It was observed that the prepared calcium phosphate glass enhanced new bone formation in the calvarial defect of Sprague-Dawley rats and could be expected to have potential for use as a hard tissue regeneration material.

Animals↗
PubMed2003

Molecular biologic comparison of new bone formation and resorption on microrough and smooth bioactive glass microspheres.

In a recent in vitro study, chemical microroughening of a bioactive glass surface was shown to enhance attachment of MG-63 osteoblastic cells to glass. The current study was designed to delineate the effects of microroughening on the gene expression patterns of bone markers during osteogenesis and new bone remodeling on bioactive glass surface in vivo. With the use of a rat model of paired comparison, a portion of the medullary canal in the proximal tibia was evacuated through cortical windows and filled with microroughened or smooth bioactive glass microspheres. The primary bone-healing response and subsequent remodeling were analyzed at 1, 2, and 8 weeks, respectively, by radiography, pQCT, histomorphometry, BEI-SEM, and molecular biologic analyses. The expression of various genes for bone matrix components (type I collagen, osteocalcin, osteopontin, osteonectin) and proteolytic enzymes (cathepsin K, MMP-9) were determined by Northern analysis of the respective mRNAs. Paired comparison showed significant differences in the mRNAs levels for specific bone matrix components at 2 weeks: osteopontin was significantly higher (p =.01) and osteonectin significantly lower (p =.05) in bones filled with microroughened microspheres than in those filled with smooth microspheres. Bones filled with microrough microspheres also showed significantly increased ratios of cathepsin K and MMP-9 (both markers of osteoclastic resorption) to type I collagen (p =.02 and p =.02, respectively) at 2 weeks and a significantly increased expression of MMP-9 at 8 weeks (p =.05). The pQCT, histomorphometric, and BEI-SEM analyses revealed no significant differences in the pattern of bone-healing response. Based on these results, microroughening of a bioactive glass surface could trigger temporal changes in the expression of specific genes especially by promoting the resorption part of new bone-remodeling processes. Future studies are needed to evaluate if the observed changes of gene expression are directly related to the microrough surface of any biomaterial or are biomaterial specific.

Animals↗
PubMed2005

Effect of glass dissolution products on the detection of proteins by silver staining.

The influence of glass dissolution on the silver staining of proteins was investigated by reacting glass microspheres of varying chemical durability in boiling Laemmli sample buffer (LSB) for up to 5 min. All three of the investigated glass compositions leached Na+ ions to varying degrees during boiling in LSB, thereby causing an increase in the pH of the sample buffer. The LSB supernatant from the dissolution tests was mixed with unreacted LSB containing human serum albumin (HSA) and standard one-dimensional SDS-PAGE was performed. Silver staining was then used to visualize protein bands within the gel. The 30 Na2O.70 SiO2 glass exhibited pronounced degradation as shown by scanning electron microscopy. Further experiments employing solutions of neat LSB and reacted LSB (i.e., LSB containing glass dissolution products) mixed at varying ratios demonstrated the apparent significance of sample pH in affecting the inhibition of silver staining. The cause of this behavior may be due to an interference with the fixation stage of the staining protocol, thereby resulting in the loss of protein in subsequent rinsing stages.

Buffers↗
PubMed1995

Studies of rifamycin production by Amycolatopsis mediterranei cells immobilized on glass wool.

Cells of Amycolatopsis mediterranei CBS 42575 were immobilized on glass wool for the production of rifamycins B and SV. Glass wool (CORNING type) of 8 microns in diameter has a better entrapment capacity for microbial cells of microorganism than the other types of glass wool used. The most suitable amount of glass wool was 0.8 g/50 ml. The best initial cell concentration used as inoculum was 40 mg cells/50 ml. Repeated batch production of rifamycins by immobilized cells on glass wool was carried out for 6 repeated batches. The results showed that reduction of batch time from 96 h to 48 h does not decrease rifamycin production by immobilized cells.

Actinobacteria↗
PubMed2003

Understanding the physical stability of freeze dried dosage forms from the glass transition temperature of the amorphous components.

Modulated differential scanning calorimetry has been applied to understanding the long-term physical stability of freeze-dried units. It is known that these units are liable to contract on exposure to elevated temperature or humidity. The contraction occurs when the storage temperature is above the glass transition temperature of the amorphous components in the system. The effect of moisture content on the glass transition temperature of the amorphous components in the system has been studied. By combining this information with the moisture sorption isotherm it has been demonstrated that it is possible to predict the temperature and humidity conditions that will induce contraction of the unit. The magnitude of the glass transition temperature is composed of the contribution of each of the amorphous components in the system. It is proposed that it should be possible to develop a more robust system by the rational selection of excipients that increase the glass transition temperature or by modification of the processing conditions to promote crystallization of components that would otherwise depress the glass transition temperature.

Dosage Forms↗
PubMed2004

Estimation of the fragility index of indomethacin by DSC using the heating and cooling rate dependency of the glass transition.

In this study we have investigated the features of the glass transition relaxation of indomethacin using Differential Scanning Calorimetry (DSC). The purpose of this work is to provide an estimation of the activation energy at the glass transition temperature, as well as of the fragility index, of amorphous indomethacin from DSC data. To do so, the glass transition temperature region of amorphous indomethacin was characterized in both cooling and heating regimes. The activation energy for structural relaxation (directly related to glass fragility) was estimated from the heating and cooling rate dependence of the location of the DSC profile of the glass transition. The obtained results were similar in the heating and in the cooling modes. The results on the fragility index of indomethacin obtained in the present study, m = 60 in the cooling mode and m = 56 in the heating mode, are compared with other values previously published in the literature.

Calorimetry, Differential Scanning↗
PubMed1980

Adsorption of antibody and globulin onto glass surfaces.

The amount of globulin adsorbed onto surfaces (97 m2) of porous glass (1 g) in phospate-buffered saline (pH 7.2) was estimated to be 83 mg by frontal analysis. In the adsorption chromatography of rabbit antiserum (the immunoglobulin G class) to horse serum albumin on a porous glass column, immunoglobulin G was not eluted with saline but was eluted with 0.2 M glycine (pH 9) with a recovery of 12%. The yield of immunoglobulin M antibody to sheep red blood cells recovered by elution with saline was 12.3%, and the total yield of immunoglobulin M was 15.8%. Thus, antibody and globulin were well adsorbed onto glass surfaces in physiological saline; immunoglobulin G had a stronger affinity to glass surfaces than did immunglobulin M. These facts should be considered when glass containers are used for purified antiserum.

Adsorption↗
PubMed2004

Glass-chip-based sample preparation and on-chip trypic digestion for matrix-assisted laser desorption/ionization mass spectrometric analysis using a sol-gel/2,5-dihydroxybenzoic acid hybrid matrix.

A glass-chip-based sample preparation method for matrix-assisted laser desorption/ionization mass spectrometric (MALDI-MS) analysis of tryptic digests of proteins and intact cells is described. A MALDI matrix, 2,5-dihydroxybenzoic acid (2,5-DHB), was hybridized with sol-gels to generate a sol-gel-derived material. Taking advantage of the characteristics of sol-gels, the sol-gel-derived material readily adhered to the surface of a glass chip through covalent bonding. Only one step of sample preparation, deposition of the sample solution on the glass chip, was required before MALDI-MS analysis. Because 2,5-DHB was homogeneously dispersed on the sol-gel network structure, good spot-to-spot reproducibility was obtained in MALDI analysis using this approach and the analyte signals were uniform throughout the chip. The modified glass chips were robust and effective for at least 1 week. This glass-chip-based matrix preparation method provides a straightforward approach to developing techniques for analyzing the on-chip enzymatic digestion of proteins and intact cells of microorganisms. Cytochrome C and Escherichia coli were used as analytes to demonstrate the feasibility of this approach. The products of the on-chip enzymatic digests were identified through protein database searches.

Amino Acid Sequence↗
PubMed1992

Cloning of human tumor cell lines in porous glass capillary tubes: a further development of the human tumor stem cell assay.

The conventional human tumor stem cell assay for cloning tumor cells for drug sensitivity testing is limited by its inability to test drug combinations. In an attempt to overcome this limitation, we cloned tumor cell lines within porous glass capillary tubes. In contrast to plastic porous tubes, the porous glass membranes were transparent, and colony formation could be judged on an inverted microscope. Human as well as animal cell lines showed sufficient colony growth. Colonies formed within these porous tubes were homogeneously distributed, and their morphology was similar to those formed in the common stem cell assay. Cloning efficiency and colony size depended on the mean pore diameter of the glass membrane, with best colony growth within tubes with a pore diameter ranging from 8.5 nm to 14 nm. A linear relationship between number of cells seeded and number of grown colonies could be demonstrated for the cell lines MDA-231 and Colo 201. Colony growth achieved within porous glass capillary tubes is comparable to that achieved in Petri dishes and in nonporous tubes. We conclude that the porous capillary cloning system meets the basic suppositions for a quantitative cloning assay. Moreover, the porosity of the glass membrane offers the possibility of variable perfusion of medium and drugs. Further investigations will focus on various perfusion modalities and chemosensitivity testing.

Animals↗
PubMed1996

Bone sialoprotein coated on glass and plastic surfaces is recognized by different beta 3 integrins.

Integrins have important roles in mediating cell-matrix interactions, essential for cell migration and signaling. In bone, integrins are suggested to play a role through their ability to mediate cell attachment to bone matrix proteins. In the present study, the subunit composition of integrins binding bone sialoprotein and osteopontin coated on either glass or plastic surfaces was analyzed using cells isolated from bone. Thus, integrin antibodies to alpha v beta 3, alpha IIb beta 3, alpha v, alpha IIb, and beta 3 and the peptides GRGDSP and KQAGDV were used to define the integrins involved in the attachment in vitro of a preparation of multinucleated cells expressing the enzyme tartrate-resistant acid phosphatase. Binding to osteopontin coated on either glass or plastic surfaces was mediated via the alpha v beta 3 integrin. Interestingly, the isolated cells bound to bone sialoprotein coated on plastic via the alpha v beta 3 integrin, but used a different integrin, alpha IIb beta 3, when the protein was coated on glass. It appears that bone sialoprotein when coated on glass and plastic, respectively, changes conformation, thereby altering the contact surface and subsequently the binding specificity. Alternatively, the protein contains two different binding sites, selectively exposed on glass or plastic as a result of different protein binding. The results demonstrate that bone sialoprotein contains domains, or can change conformation, such that it can interact with either the alpha IIb beta 3 or the alpha v beta 3 integrin. Whether the integrins were located on the multinucleated cells proper or on platelets bound to these cells could not be unequivocally concluded. The possible presence of platelets should, however, be considered when interpreting data from the isolated osteoclast system.

Acid Phosphatase↗
PubMed1996

Titanium and bioactive glass-ceramic coated titanium as materials for keratoprosthesis.

The current problem with keratoprosthesis is the ingrowth of corneal or conjunctival epithelium into the anterior chamber. This may lead to infections and extrusion of the prosthesis as well as to the development of retroprosthetic membrane and secondary glaucoma. Glass-ceramic coated and uncoated titanium has been tested as material for the keratoprosthesis to prevent epithelial ingrowth. Twenty-two Supra-Descemet's membrane keratoprostheses were inserted in the eyes of 22 rabbits for 1, 2, 4, 8, or 12 months. The prosthesis had an optic part made of polymethylmetacrylate (PMMA). The support for the optic part and the flange of the prosthesis were made of titanium. Eleven of the prostheses were coated with glass-ceramic. The histological sections of the enucleated eyes were prepared through the central part of the cornea and the prosthesis using a cutting-grinding method. The histological analysis was made on both halves of the implants separately giving two analysis areas in each eye. All 11 titanium prostheses were retained for the time period planned. Two glass-ceramic coated prostheses were lost at 2 and 4 weeks, respectively. This was caused by difficulties at surgery due to a thick coating. These eyes were excluded from the histological analysis. No significant ingrowth of epithelium was seen in 15/18 (83%) and in 16/22 (73%) of the analysed areas of the glass-ceramic coated and titanium prostheses, respectively. Titanium appears to be a suitable material for the keratoprosthesis. The ingrowth of the epithelium may be hindered further by coating the titanium with bioactive glass-ceramic.

Animals↗
PubMed1990

Cardiac stress in glass bangle workers.

The cardiac cost of work and recovery pulse rates were evaluated in 38 glass bangle workers (mean age 27.8 years, SD 3.4) exposed to radiant heat (46.2 degrees C, SD 5.1) and high ambient temperature (38.2 degrees C, SD 3.4) for a mean period of 11.0 years, SD 3.5 in the glass bangle industry. A reference group of 15 controls (mean age 27.0 years, SD 3.5 unexposed to occupational heat stress served as a comparison. The results showed that the pulse rate increased from a mean basal value of 80.0 beats.min-1, SD 2.7 to 113.2 beats.min-1, SD 11.4 in the exposed workers while in the controls the increase was negligible. Thus the cardiac cost of work was found to be 33.2 beats.min-1, SD 11.1 in the exposed group which was significantly higher (P less than 0.001) than 7.8 beats.min-1, SD 4.2 observed in the control group. Among the exposed workers, 'belanias', who were engaged in the strenuous job of manually rotating the iron roller in the Belan furnace so that the molten glass could be wound in a spiral form, showed the maximum increase in the pulse rate (42.0 beats.min-1, SD 7.5) over the work-shift followed by 'muthias' (31.1 beats.min-1, SD 4.0) who were engaged in removing the glass spirals from the Belan furnace. However, wireman ('tarkashs'), who were engaged in the highly skilled job of making very fine threads of molten glass with the help of an iron roller, showed the smallest increase (19.5 beats.min-1, SD 3.4) in pulse rate over the work-shift.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1999

The effect of long-term water storage on the tensile strength of orthodontic brackets bonded with resin-reinforced glass-ionomer cements.

The purpose of this study was to evaluate in vitro the effect of water storage on the tensile bond strength of orthodontic brackets bonded with Vitremer and Fuji II LC resin-reinforced glass-ionomer cements. Seventy-two extracted human premolars were randomly divided into 6 groups and the bonding strengths of the resin-reinforced glass-ionomer cements were compared to control groups bonded with Concise composite resin at 24 hours and 9 months. The brackets were bonded on prepared teeth and a tensile load was applied to dislodge the brackets held in a special device from Lloyd 1000R testing machine. The effects of duration of water exposure, type of bonding material and interaction between long-term water exposure and type of bonding material on the bonding strength were described using the Weibull regression model. The mean tensile bond strength of resin-reinforced glass-ionomers after 24 hours water storage was significantly lower than the mean of the control samples. The results of this study showed no effect of water exposure on the tensile bond strength of brackets bonded with Vitremer glass-ionomer cement. The mean bonding strength of brackets bonded with Fuji II LC without enamel pre-conditioning significantly increased after 9-months water storage as compared to Fuji samples exposed to water for 24 hours. The results of this investigation allow to conclude: 1. Long-term water storage had not decreased the bond strength of resin-reinforced glass-ionomers applied as orthodontic adhesives, 2. Weibull regression model is an adequate and flexible tool to evaluate the bonding properties of dental materials.

Bicuspid↗
PubMed1990

Antimony and glass pH electrodes can be used interchangeably in 24-hour studies of gastric acidity.

Antimony and glass pH electrodes show almost identical experimental errors in continuously measuring buffer solutions at constant temperature over 24 hr. These errors are lower than the nominal quantization error of the instruments and are not properly described by the 24-hr drift determination. The addition of food particles to the solutions can induce severe reading artifacts. The longer response time reported in vitro of antimony electrodes when moving from pH 1 to pH 7 (3.4 sec vs 0.8 sec with glass electrodes) is irrelevant during in vivo pH-metry studies, because we found that the greatest absolute difference between raw fast acquired (4-6 sec) consecutive pH readings of two commonly used devices was 0.7 pH units in circadian profiles obtained from 413 subjects with various clinical conditions. In our in vivo studies, gastric acidity was monitored continuously with two side-by-side minielectrodes, which were variously combined (antimony-glass, A-G; antimony-antimony A1-A2; glass-glass, G1-G2) and applied on groups of 27 subjects matched for clinical condition. The 24-hr pH means and the 24-hr [H+] means calculated from the acidity profiles obtained with the three electrode combinations, lie on the identity line in each group. Using the Bland-Altman technique for assessing measurement agreement, the differences between the 24-hr pH means and the 24-hr [H+] means obtained with the three combined systems are similar (P = .903 and P = 0.824, respectively) and their 95% confidence limits are comprised within the range (+/-) of the reading error of the measuring systems (namely, +/- 0.3 pH units and +/- 12 mmol/liter in terms of [H+]).(ABSTRACT TRUNCATED AT 250 WORDS)

Antimony↗