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Biomedical subjects

A E Clark

Publications and source records attributed to A E Clark.

At least 37 records · Page 2Linked to original sources
PubMed1996

Autonomy and death.

In this Article, Professor Clark explores the contours of the current debate over physician-assisted death. She beings by focusing on the legal issues raised by statutory attempts to either legalize or criminalize physician-assisted death, with particular emphasis on the constitutional questions that are currently before the United States Supreme Court. She then examines physician-assisted death from both medical and societal perspectives. Professor Clark uses a thought experiment in which assisted death is facilitated by persons other than physicians, and in doing so, questions whether physicians are the proper persons in whom to rest power over assisted death. She points out the irony in a process that would set up physicians as protectors of individual autonomy, and ultimately concludes that by deferring to the medical profession in this process, we risk losing the very autonomy that assisted death is designed to effectuate.

Attitude of Health Personnel↗
PubMed1995

Analysis of the structural features of the C-terminus of GLUT1 that are required for transport catalytic activity.

C-terminally truncated and mutated forms of GLUT1 have been constructed to determine the minimum structure at the C-terminus required for glucose transport activity and ligand binding at the outer and inner binding sites. Four truncated mutants have been constructed (CTD24 to CTD27) in which 24 to 27 amino acids are deleted. In addition, point substitutions of R468-->L, F467-->L and G466-->E have been produced. Chinese hamster ovary clones which were transfected with these mutant GLUT1s were shown, by Western blotting and cell-surface carbohydrate labelling, to have expression levels which were comparable with the wild-type clone. Wild-type levels of 2-deoxy-D-glucose transport activity were retained only in the clone transfected with the construct in which 24 amino acids were deleted (CTD24). The CTD25, CTD26 and CTD27 clones showed markedly reduced transport activity. From a kinetic comparison of the CTD24 and CTD26 clones it was found that the reduced transport was mainly associated with a reduced Vmax. value for 2-deoxy-D-glucose uptake but with a slight lowering of the Km. These data establish that the 24 amino acids at the C-terminus of GLUT1 are not required for the transport catalysis. However, the point mutations of F467L and G466E (26 and 27 residues from the C-terminus) did not significantly perturb the kinetics of 2-deoxy-D-glucose transport. The substitution of R468L produced a slight, but significant, lowering of the Km. The ability of the truncated GLUt1s to bind the exofacial ligand, 2-N-4-(1-zai-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yl-oxy) -2-propylamine (ATB-BMPA), and the endofacial ligand, cytochalasin B, were assessed by photolabelling procedures. The ability to bind ATB-BMPA was retained only in the CTD24 truncated mutant and was reduced to levels comparable with those of the non-transfected clone in the other mutant clones. Cytochalasin B labelling was unimpaired in all four mutated GLUT1s. These data establish that a minimum structure at the C-terminus of GLUT1, which is required for the conformational change to expose the exofacial site, includes amino acids at positions Phe-467 and Arg-468; however, these amino acids are not individually essential.

Affinity Labels↗
PubMed1995

The effects of insulin on the level and activity of the GLUT4 present in human adipose cells.

Human adipose cells are much less responsive to insulin stimulation of glucose transport activity than are rat adipocytes. To assess and characterize this difference, we have determined the rates of 3-O-methyl-D-glucose transport in human adipose cells and have compared these with the levels of glucose transporter 4 (GLUT4) assessed by using the bis-mannose photolabel, 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yloxy)-2-propyl-amine, ATB-BMPA. The rates of 3-O-methyl-D-glucose transport and the cell-surface level of GLUT4 are very similar in the human and rat adipocyte in the basal state. The Vmax for 3-O-methyl-D-glucose transport in fully insulin-stimulated human adipose cells is 15-fold lower than in rat adipose cells. Photolabelling of GLUT4 suggests that this low transport activity is associated with a low GLUT4 abundance (39 x 10(4) sites/cell; 19.9 x 10(4) sites at the cell surface). The turnover number for human adipose cell GLUT4 (5.8 x 10(4) min-1) is similar to that observed for GLUT4 in rat adipose cells and the mouse cell line, 3T3L1. Since 50% of the GLUT4 is at the cell surface of both human and rat adipose cells in the fully insulin-stimulated state, an inefficient GLUT4 exocytosis process cannot account for the low transport activity. The intracellular retention process appears to have adapted to release, in the basal state, a greater proportion of the total-cellular pool of GLUT4 to the cell surface of the larger human adipocytes. These cell-surface transporters are presumably necessary to provide the basal metabolic needs of the adipocyte.(ABSTRACT TRUNCATED AT 250 WORDS)

3-O-Methylglucose↗
PubMed1995

Glucose oxidation and monoamine oxidase activity from the fibroblasts of schizophrenic patients and controls.

Fibroblasts have emerged as one of the best systems in which to study several genetically inherited diseases. Their use avoids the contaminating effects of medication and other environmental factors. Moreover, fibroblast cells cultured in vitro can express several biochemical parameters which are characteristic of neuronal cells. We have studied fibroblast MAO-A and glucose oxidation and platelet MAO-B from schizophrenic patients and control subjects. Fibroblasts from schizophrenics showed an increased glucose oxidation in two different experiments conducted (122% and 126% compared to controls). No changes were found in the levels of fibroblast MAO-A or platelet MAO-B activity. Possibly these alterations in glucose oxidation may be associated with a generalized membrane abnormality which has been reported in schizophrenia.

Adolescent↗
PubMed1995

Cultured human keratinocytes as a model for studying the dopamine metabolism in schizophrenia.

The dopamine hypothesis is the major etiological hypothesis of schizophrenia which proposes that enhanced central nervous system dopaminergic activity is the causative factor for this disease. The hypothesis remains unproven despite decades of research. The major difficulty in studying the disease is due to the unavailability of a suitable animal model. Studies with human blood, cerebrospinal fluid or post-mortem brains lead only to inconclusive results, due to the effects of medication and other environmental factors. No extra-neuronal cells, with the exception of adrenal medulla, have been reported to contain a dopamine metabolic pathway. Literature evidence and our own study suggest that human keratinocytes express the enzymes to synthesize and degrade dopamine. We have compared the properties of tyrosine hydroxylase, the rate-limiting enzyme, from mouse striatum and from human skin keratinocytes cultured in vitro. Moreover we could also detect dopamine beta hydroxylase and catechol-o-methyl transferase in keratinocytes. We propose that human keratinocytes cultured in vitro can be used to study the relevance of dopamine metabolism to schizophrenia under controlled conditions avoiding the effects of medication and other environmental factors.

Animals↗
PubMed1995

Quantitative assessment of dentin bridge formation following pulp-capping in miniature swine.

A quantitative assessment of dentin bridges was conducted on sections prepared from teeth capped with four pulp-capping agents (Bioglass, Life, Demineralized Dentin Matrix, and Teflon) in a micro-swine model. The degree of mineralization of the dentin bridges relative to the adjacent primary dentin was measured using a computer-based image analysis of microradiographs prepared from the sections. The rate of formation of the dentin bridge was measured from fluorescent bands formed in the same sections by a Demeclocycline dentin marker. There were no statistically significant differences in the relative mineral densities of the dentin bridges and the rate of dentin bridge formation under the four pulp-capping agents. These findings support the suggestion that components of the extracellular matrix rather than pulp-capping agents may be important in the formation and mineralization of dentin bridges in repairing dental pulps.

Analysis of Variance↗
PubMed1994

Substitution of tyrosine 293 of GLUT1 locks the transporter into an outward facing conformation.

Tyrosines 292 and 293 in the mammalian glucose transporter GLUT1 have been substituted by either isoleucine or phenylalanine. Chinese hamster ovary clones that were transfected with Tyr-292-->Ile, Tyr-292-->Phe, Tyr-293-->Ile, and Tyr-293-->Phe constructs of GLUT1 were shown, by Western blotting and cell surface carbohydrate labeling, to have expression levels that were comparable with the wild type. The Vmax for 2-deoxy-D-glucose transport was markedly reduced only as a result of the Tyr-293-->Ile mutation. The ability of the Tyr-293-->Ile mutated GLUT1 to bind the exofacial ligand 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yloxy)-2- propylamine (ATB-BMPA) and the endofacial ligand cytochalasin B were assessed by photolabeling procedures. The ability to bind the bis-mannose compound was unimpaired, whereas the ability to bind cytochalasin B was totally abolished, and the level of labeling was lower than in the nontransfected clone. Affinities of the wild-type and Tyr-293-->Ile GLUT1 for D-glucose, the exofacial ligands (ATB-BMPA and 4,6-O-ethylidene-D-glucose), and the endofacial ligand (cytochalasin B) were assessed by the ability of these agents to displace the radioactive ATB-BMPA photolabel. These data indicated that the Tyr-293-->Ile substitution produced no change in the affinity for D-glucose, a relatively small enhancement in the affinity for exofacial ligands, but a large approximately 300-fold reduction in affinity for cytochalasin B, suggesting that the mutated GLUT1 is locked in an outward facing conformation. The observation that the Tyr-293-->Ile mutant transporter can bind nontransported C4 and C6 substituted hexose analogues but cannot catalyze transport is interpreted as indicating that Tyr-293 is involved in closing the exofacial site around C4 and C6 of D-glucose in the transport catalysis process.

Affinity Labels↗
PubMed1994

Substitution at Pro385 of GLUT1 perturbs the glucose transport function by reducing conformational flexibility.

The mammalian glucose transporter, GLUT1, is capable of alternating between two conformations which expose either an outward- or inward-facing ligand binding site. The possibility that these conformational changes are related to the presence of prolines and glycines in transmembrane region 10 was investigated by site-directed mutagenesis. Chinese hamster ovary clones which were transfected with Pro385-->Ile and Pro385-->glycine mutations of GLUT1 were shown, by Western blotting and cell surface carbohydrate labelling, to have expression levels which were comparable with the wild type. The transport activity was markedly reduced as a result of the Pro385-->isoleucine but not in the Pro385-->glycine mutation. The loss of transport activity in the Pro385-->isoleucine clone was associated with loss of labeling by the exofacial photoaffinity ligand, 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis(D-mannos-4 -yloxy)-2- propylamine (ATB-BMPA), but there was no loss in labeling by the inside site-directed ligand cytochalasin B. These results suggest that the transporter cannot adopt the outward-directed conformation in the Pro385-->isoleucine clone. By contrast, the glycine substitution for proline at this position resulted in a retention of the ligand binding properties at both inside and outside sites. We suggest a putative mode of operation of the transporter which involves conformational flexibility about the prolines in transmembrane segment 10 such that helices 11 and 12 can alternately either pack against the outside (ATB-BMPA binding) site in helices 7, 8, and 9 or against the inner (cytochalasin B binding) site at the base of transmembrane segment 10.

Amino Acid Sequence↗
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↗
PubMed1993

Use of bismannose photolabel to elucidate insulin-regulated GLUT4 subcellular trafficking kinetics in rat adipose cells. Evidence that exocytosis is a critical site of hormone action.

The subcellular trafficking of tracer-tagged GLUT4 between the plasma membranes and low-density microsomes of rat adipose cells has been studied. Cell-surface GLUT4 have been initially tracer-tagged in the insulin-stimulated state with the [3H]bismanose photolabel 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yloxy)-2- propylamine. The half-time for internalization of tracer-tagged GLUT4 when insulin is removed by collagenase treatment is similar to that observed for the decrease in immunodetectable GLUT4 in the plasma membranes and the decrease in glucose transport activity in the intact cells. In contrast, internalization of tracer-tagged GLUT4 also occurs when cells are maintained in the continuous presence of insulin even though the plasma membrane level of immunodetectable GLUT4 and glucose transport activity in the intact cells are unaltered. These data show, for the first time, that insulin has little, if any, effect on the rate constant for GLUT4 endocytosis, but instead, primarily increases the rate constant for exocytosis. Tracer-tagged GLUT4 that is returned to the low-density microsomes can be restimulated with fresh insulin to recycle to the plasma membranes and to a steady-state distribution level that is the same as that observed in cells that are maintained in the continuous presence of insulin. These data suggest that the cells' entire complement of GLUT4 is involved in the recycling process. Following insulin stimulation of adipose cells initially in the basal state, the increase in immunodetectable GLUT4 in the plasma membranes precedes the increase in accessibility of GLUT4 to exofacial 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis(D-mannos-4 -yloxy)-2- propylamine photolabeling, and this in turn precedes the increase in cellular glucose transport activity. Such time course data suggest that there may be plasma membrane intermediate states in the GLUT4 trafficking pathway. The kinetic properties of GLUT4 translocation and its recycling have been interpreted in terms of a subcellular trafficking model that identifies exocytosis, possibly involving-hypothetical "docking" and "fusion" steps, as the critical site of hormone action.

3-O-Methylglucose↗
PubMed1993

Tissue response to Bioglass endosseous ridge maintenance implants.

Conical devices placed in the alveolar ridge after tooth extraction have been used clinically for several years to maintain the ridge morphology. In this way, the bone atrophy which occurs after extractions is minimized, and denture fit and function are enhanced. A system using such cones made from Bioglass (registered trademark of the University of Florida) and matching burs has been developed and tested clinically. Average four-year data show a retention rate of over 90%, which compares favorably with other systems using other materials (see Hench et al., 1991). Stanley et al. (to be published), in a review of the four-year clinical data, point out that a few of the cones, although firmly positioned within the alveolar ridge, have a radiolucent zone around the implant. In a clinical study, it is not possible to determine whether this radiolucent zone represents areas of fibrous capsule which are not attached to the implant and therefore compromise its long-term stability, or whether the soft tissue is adherent to the implant and thus contributes to its long-term stability. In a recent study, conical implants identical to those in the clinical trial were placed in the alveolar ridges of dogs and evaluated for up to two years. The adhesion of bone and soft tissue was measured and the development and stabilization of the reactive gel layer monitored. The findings in this animal study support the clinical observations and contribute to an explanation of the success of the Bioglass system in patients.

Alveolar Bone Loss↗
PubMed1992

Site-directed mutagenesis of GLUT1 in helix 7 residue 282 results in perturbation of exofacial ligand binding.

The structure-function relationship of the HepG2/erythrocyte-type glucose transporter (GLUT1) has been studied by in vitro site-directed mutagenesis. Chinese hamster ovary clones in which glucose transporters were transfected were shown by Western blotting with a GLUT1 anti-COOH-terminal peptide antibody to have expression levels of Gln282----Leu, Asn288----Ile, and Asn317----Ile mutations that were comparable with the wild type. All three mutant GLUT1 clones had high 2-deoxy-D-glucose transport activity compared with a nontransfected clone, suggesting that these residues are not absolutely required for the transport function. We have examined the possibility that the inner and outer portions of the transport pathway are structurally separate by measuring the interaction of the mutant transporters with the inside site-specific ligand cytochalasin B and the outside site-specific ligand 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis(D-mannos-4 -yloxy)-2- propylamine (ATB-BMPA). All three mutant GLUT1 clones showed high levels of cytochalasin B labeling, and the N288I and N317I mutants showed high levels of ATB-BMPA labeling. In contrast to the transport and cytochalasin B labeling results, the transmembrane helix 7 Gln282----Leu mutant was labeled by ATB-BMPA to a level that was only 5% of the level observed in the wild type. We have confirmed that this mutant was defective in the outer site by comparing the inhibition of wild-type and mutant 2-deoxy-D-glucose transport by the outside site-specific ligand 4,6-O-ethylidene-D-glucose. 4,6-O-Ethylidene-D-glucose inhibited wild-type transport with a Ki of approximately 12 mM, but this was increased to greater than 120 mM in the Gln282----Leu mutant. Thus, of the 3 residues mutated in this study, only glutamine 282 substitution causes a major perturbation in function, and this is a specific and striking reduction in the affinity for the outside site-specific ligands ATB-BMPA and 4,6-O-ethylidene-D-glucose.

Amino Acid Sequence↗
PubMed1992

Development of an intracellular pool of glucose transporters in 3T3-L1 cells.

The membrane-impermeant bis-mannose photolabel 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yloxy)-2- propylamine (ATB-BMPA) has been used to study the development of an intracellular pool of glucose transporters in 3T3-L1 cells. The subcellular distributions of the transporter isoforms GLUT1 and GLUT4 were determined by comparing the labeling obtained in cells in which the impermeant reagent only had access to the cell surface and the labeling obtained in digitonin-permeabilized cells. ATB-BMPA labeling showed that only GLUT1 was present in preconfluent fibroblasts and that most of the transporters were distributed to the cell surface. In preconfluent fibroblasts, the 2-deoxy-D-glucose transport activity was approximately 5 times higher than in confluent fibroblasts. ATB-BMPA labeling showed that the decrease in transport as cells reached confluence was associated with a decrease in the proportion of GLUT1 distributed to the cell surface. The sequestration of these transporters was associated with the development of an insulin-responsive transport activity which increased by approximately 2.5-fold compared with unstimulated confluent cells. ATB-BMPA labeling showed that insulin stimulation resulted in an approximately 2-fold increase in surface GLUT1 so that about one-half of the available transporters became recruited to the cell surface. Measurements of the changes in the distribution of both GLUT1 and GLUT4 throughout the differentiation of confluent fibroblasts into adipocytes showed that both transporters were sequestered in parallel. Basal levels of transport and photolabeling remained low throughout the differentiation period when the total pool of transporters (GLUT1 plus GLUT4) was increased by approximately 5-fold. These results suggest that the sequestration process was present before new transporters were synthesized. Thus, the sequestration mechanism develops in confluent growth-arrested fibroblasts although the capacity to sequester additional transporters may increase as differentiation proceeds.

3T3 Cells↗
PubMed1992

Kinetic resolution of the separate GLUT1 and GLUT4 glucose transport activities in 3T3-L1 cells.

A bis-mannose-photolabel-displacement method has been developed for resolving the separate kinetic properties of the glucose transporters GLUT1 and GLUT4, which are both present in 3T3-L1 cells. We have quantified the cell-surface transporter abundance (Bmax.) for the two isoforms by displacing radiolabelled 2-N-[4-(1-azi-2,2,2-trifluoroethyl)benzoyl]-1,3-bis-(D- mannos-4-yloxy)-2-propylamine (ATB-BMPA) by non-labelled ATB-BMPA. In cells acutely treated with insulin, the GLUT1 Bmax. was 0.19 microM and the GLUT4 Bmax. was 0.17 microM. In cells which were chronically treated with insulin, the GLUT1 Bmax. was increased by approximately 4-fold to 0.7 microM, whereas the GLUT4 was decreased by approximately 50% (Bmax. = 0.1 microM). However, this large increase in total concentrations of cell-surface transporters (the sum of GLUT1 and GLUT4 concentrations) was not reflected in a large increase in 3-O-methyl-D-glucose transport, suggesting that GLUT1 makes a smaller contribution to transport than does GLUT4. In acutely insulin-treated cells at 37 degrees C, the apparent kinetic parameters for 3-O-methyl-D-glucose transport were Vapp.max. = 0.52 mM.s-1 and Kapp.m = 12.3 mM. In chronically insulin-treated cells the Vapp.max. = 1.24 mM.s-1 and Kapp.m = 23.0 mM. We have measured the displacement of ATB-BMPA by different concentrations of 3-O-methyl-D-glucose to resolve the separate affinity constants of GLUT1 and GLUT4 for this transported ligand. In acute- and chronic-insulin-treated cells the GLUT1 Km for 3-O-methyl-D-glucose was approximately 20 mM, and the GLUT4 Km for 3-O-methyl-D-glucose was approximately 7 mM. An analysis of these data and the 3-O-methyl-D-glucose transport rates was carried out to calculate transport capacity (TK values) for the two isoforms at 37 degrees C. In acute- and chronic-insulin-treated cells the TK values were 0.36 x 10(4) mM-1.min-1 for GLUT1 and 1.13 x 10(4) mM-1.min-1 for GLUT4. Thus GLUT1 has an approximately 3-fold lower transport capacity than GLUT4 at low concentrations of transported sugar. The lower GLUT1 transport capacity was shown to be mainly due to the high Km of GLUT1. The calculated turnover numbers were 7.2 x 10(4) min-1 for GLUT1 and 7.9 x 10(4) min-1 for GLUT4.

3-O-Methylglucose↗
PubMed1992

Trafficking of glucose transporters in 3T3-L1 cells. Inhibition of trafficking by phenylarsine oxide implicates a slow dissociation of transporters from trafficking proteins.

We have compared the rates of insulin stimulation of cell-surface availability of glucose-transporter isoforms (GLUT1 and GLUT4) and the stimulation of 2-deoxy-D-glucose transport in 3T3-L1 cells. The levels of cell-surface transporters have been assessed by using the bismannose compound 2-N-[4-(1-azi-2,2,2-trifluoroethyl)benzoyl]-1,3-bis(D-mannos -4-yloxy) propyl-2-amine (ATB-BMPA). At 27 degrees C the half-times for the appearance of GLUT1 and GLUT4 at the cell surface were 5.7 and 5.4 min respectively and were slightly shorter than that for the observed stimulation of transport activity (t 1/2 8.6 min). This lag may be due to a slow dissociation of surface transporters from trafficking proteins responsible for translocation. When fully-insulin-stimulated cells were subjected to a low-pH washing procedure to remove insulin at 37 degrees C, the cell-surface levels of GLUT1 and GLUT4 decreased, with half-times of 9.2 and 6.8 min respectively. These times correlated well with decrease in 2-deoxy-D-glucose transport activity that occurred during this washing procedure (t1/2 6.5 min). When fully-insulin-stimulated cells were treated with phenylarsine oxide (PAO), a similar decrease in transport activity occurred (t1/2 9.8 min). However, surface labelling showed that this corresponded with a decrease in GLUT4 only (t1/2 7.8 min). The cell-surface level of GLUT1 remained high throughout the PAO treatment. Light-microsome membranes were isolated from cells which had been cell-surface-labelled with ATB-BMPA. Internalization of both transporter isoforms to this pool occurred when cells were maintained in the presence of insulin for 60 min. In contrast with the surface-labelling results, we have shown that the transfer to the light-microsome pool of both transporters occurred in cells treated with insulin and PAO. These results suggest that both transporters are recycled by fluid-phase endocytosis and exocytosis. PAO may inhibit this recycling at a stage which involves the re-emergence of internalized transporters at the plasma membrane. The GLUT1 transporters that are recycled to the surface in insulin- and PAO-treated cells appear to have low transport activity. This may be because of a failure to dissociate fully from trafficking proteins at the cell surface. GLUT4 transporters appear to have a greater tendency to remain internalized if the normal mechanisms that commit transporters to the cell surface, such as dissociation from trafficking proteins, are uncoupled.

3T3 Cells↗
PubMed1992

Compositional dependence of calcium phosphate layer formation in fluoride Bioglasses.

Bioglasses form a double layer composed of apatite and a silica-rich layer when placed in a simulated physiological solution as well as in living tissue [A.E. Clark, C.G. Pantano, and L. L. Hench, "Auger spectroscopic analysis of bioglass corrosion films," J. Am. Ceram. Soc., 59(1-2), 37-39 (1976).]. In the present work, the mechanisms of the calcium phosphate layer and the silica-rich layer formation of fluoride Bioglasses in Tris-buffer solution are studied as a function of the SiO2 content. Fourier Transform Infrared Reflection Spectroscopy (FTIRS) is used to investigate the mechanism of formation of calcium phosphate and silica-rich layers on the glass surface. Ion concentration in reacted solution and elemental depth profiles are obtained by Induced Coupled Plasma Atomic Emission Spectrometry (ICP) and Auger Electron Spectroscopy (AES), respectively. Si--O bonds with one nonbridging oxygen and Si--O--Si bonds form at the early stage of reaction. Strong phosphorus ion uptake occurs when an amorphous calcium phosphate layer crystallizes. Glasses with high silica content (conventional glass) form the silica-rich layer first followed by a calcium phosphate layer on top. However, glasses with low silica content (invert glass) form both layers simultaneously. The rate of apatite formation decreases with increasing SiO2 content, especially in the region of conventional glass compositions. Ion release rates decreases as SiO2 content increases, with a significant change occurring at the compositional boundary between invert and conventional glasses.

Biocompatible Materials↗
PubMed1992

Injectable bioglass as a potential substitute for injectable polytetrafluoroethylene.

Injectable polytetrafluoroethylene (Teflon) and collagen have inherent problems that may prevent their long-term success. In search of a different injectable biomaterial we confirmed in rabbits the safety of injected Bioglass particles suspended in sodium hyaluronate. A second study was performed testing the ability of the Bioglass suspension to increase urethral resistance in pigs. Bioglass particles in suspension have the potential to substitute for polytetrafluoroethylene or collagen in the treatment of urinary incontinence or vesicoureteral reflux.

Animals↗