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1.
Respir Med Case Rep ; 26: 118-122, 2019.
Article in English | MEDLINE | ID: mdl-30603600

ABSTRACT

Idiopathic pulmonary fibrosis (IPF) is a chronic interstitial lung disease of unknown cause that occurs sporadically, but it can also occur in families and so named as Familial Pulmonary Fibrosis (FPF). Some forms of FPF overlaps IPF features, namely the radiological and histological pattern of usual interstitial pneumonia (UIP). Genetic and environmental factors commonly play an important role in the pathogenesis of FPF and the most commonly identified mutations involve the telomerase complex. Here, we report a rare case of FPF in a male at the age of 44, in whom genetic testing showed heterozygous variants for the telomerase reverse transcriptase gene (TERT). Our report highlights the importance of compiling a thorough family history in younger patients identified with UIP serving as a resource for identifying the current and future genetic links to disease. Families with UIP hold a great promise in defining UIP pathogenesis, potentially suggesting targets for the development of future therapies.

2.
Braz J Biol ; 74(1): 175-80, 2014 Feb.
Article in English | MEDLINE | ID: mdl-25055099

ABSTRACT

Water hardness is a property depending on the presence of alkaline earth metals, mainly calcium and magnesium. Among the strategies for water quality monitoring, ecotoxicological assays are performed to minimize impacts and classify water bodies. For these laboratory evaluations parameters are previously defined in the guidelines, including water hardness for both cultivation and testing medium. The present work was performed to evaluate the effects of different levels of water hardness on the survival and reproduction of the freshwater snail Biomphalaria glabrata and discuss the influence of natural water hardness on the results of ecotoxicological tests with these environmental samples. Comparing the groups it was possible to observe that those maintained in waters with least hardness had lower reproductive success, while the groups maintained in highest hardness showed better reproduction. These data show that waters with low hardness make the reproduction of the snail B. glabrata unfeasible, and this reveal a problem for ecotoxicity assays using natural water samples.


Subject(s)
Biomphalaria/drug effects , Fresh Water/chemistry , Animals , Biological Assay , Biomphalaria/physiology , Reproduction/drug effects , Reproduction/physiology , Toxicity Tests , Water Quality
3.
Braz. j. biol ; 74(1): l1805-180, 2/2014. tab, graf
Article in English | LILACS, VETINDEX | ID: biblio-1468163

ABSTRACT

Water hardness is a property depending on the presence of alkaline earth metals, mainly calcium and magnesium. Among the strategies for water quality monitoring, ecotoxicological assays are performed to minimize impacts and classify water bodies. For these laboratory evaluations parameters are previously defined in the guidelines, including water hardness for both cultivation and testing medium. The present work was performed to evaluate the effects of different levels of water hardness on the survival and reproduction of the freshwater snail Biomphalaria glabrata and discuss the influence of natural water hardness on the results of ecotoxicological tests with these environmental samples. Comparing the groups it was possible to observe that those maintained in waters with least hardness had lower reproductive success, while the groups maintained in highest hardness showed better reproduction. These data show that waters with low hardness make the reproduction of the snail B. glabrata unfeasible, and this reveal a problem for ecotoxicity assays using natural water samples.


A dureza da água é uma propriedade dependente da presença de metais alcalino terrosos, principalmente cálcio e magnésio. Entre as estratégias para monitorar a qualidade da água ensaios ecotoxicológicos são realizados para minimizar impactos e classificar os corpos hídricos. Para essas avaliações em laboratório, parâmetros são previamente definidos nos protocolos, incluindo a dureza da água para cultivo e para a água de diluição. O presente trabalho foi realizado para avaliar os efeitos de diferentes níveis de dureza da água sobre a sobrevivência e a reprodução do caramujo de água doce Biomphalaria glabrata e discutir a influência da dureza de águas naturais nos resultados dos testes ecotoxicológicos com estas amostras ambientais. Comparando os grupos foi possível observar que aqueles mantidos em águas com menor dureza tiveram pior sucesso reprodutivo, enquanto os mantidos nas águas com maiores durezas tiveram melhor reprodução. Esses dados mostram que águas com baixas durezas tornam a reprodução do caramujo B. glabrata inviável, e esse fato revela-se como um problema para os ensaios ecotoxicológicos utilizando amostras de água naturais.


Subject(s)
Animals , Biomphalaria , Fresh Water/chemistry , Biological Assay , Biomphalaria/physiology , Water Quality , Reproduction , Reproduction/physiology , Toxicity Tests
4.
Acta Biomater ; 9(3): 5643-52, 2013 Mar.
Article in English | MEDLINE | ID: mdl-23117145

ABSTRACT

The present study aimed to develop a pre-endothelialized chitosan (CH) porous hollowed scaffold for application in spinal cord regenerative therapies. CH conduits with different degrees of acetylation (DA; 4% and 15%) were prepared, characterized (microstructure, porosity and water uptake) and functionalized with a recombinant fragment of human fibronectin (rhFNIII(7-10)). Immobilized rhFNIII(7-10) was characterized in terms of amount ((125)I-radiolabelling), exposure of cell-binding domains (immunofluorescence) and ability to mediate endothelial cell (EC) adhesion and cytoskeletal rearrangement. Functionalized conduits revealed a linear increase in immobilized rhFNIII(7-10) with rhFNIII(7-10) concentration, and, for the same concentration, higher amounts of rhFNIII(7-10) on DA 4% compared with DA 15%. Moreover, rhFNIII(7-10) concentrations as low as 5 and 20µg ml(-1) in the coupling reaction were shown to provide DA 4% and 15% scaffolds, respectively, with levels of exposed cell-binding domains exceeding those observed on the control (DA 4% scaffolds incubated in a 20µg ml(-1) human fibronectin solution). These grafting conditions proved to be effective in mediating EC adhesion/cytoskeletal organization on CH with DA 4% and 15%, without affecting the endothelial angiogenic potential. rhFNIII(7-10) grafting to CH could be a strategy of particular interest in tissue engineering applications requiring the use of endothelialized porous matrices with tunable degradation rates.


Subject(s)
Chitosan/pharmacology , Endothelial Cells/physiology , Fibronectins/pharmacology , Immobilized Proteins/pharmacology , Recombinant Proteins/pharmacology , Tissue Scaffolds/chemistry , Adsorption , DNA/metabolism , Endothelial Cells/drug effects , Fibronectins/chemistry , Fibronectins/isolation & purification , Fluorescent Dyes/metabolism , Humans , Immobilized Proteins/chemistry , Immobilized Proteins/isolation & purification , Microscopy, Electron, Scanning , Neovascularization, Physiologic/drug effects , Porosity , Protein Structure, Tertiary , Recombinant Proteins/chemistry , Recombinant Proteins/isolation & purification , Spectroscopy, Fourier Transform Infrared
5.
J Colloid Interface Sci ; 351(2): 398-406, 2010 Nov 15.
Article in English | MEDLINE | ID: mdl-20810127

ABSTRACT

The characteristic topographical features (crystallite dimensions, surface morphology and roughness) of bioceramics may influence the adsorption of proteins relevant to bone regeneration. This work aims at analyzing the influence of two distinct nanophased hydroxyapatite (HA) ceramics, HA725 and HA1000 on fibronectin (FN) and osteonectin (ON) adsorption and MC3T3-E1 osteoblast adhesion and morphology. Both substrates were obtained using the same hydroxyapatite nanocrystals aggregates and applying the sintering temperatures of 725°C and 1000°C, respectively. The two proteins used in this work, FN as an adhesive glycoprotein and ON as a counter-adhesive protein, are known to be involved in the early stages of osteogenesis (cell adhesion, mobility and proliferation). The properties of the nanoHA substrates had an important role in the adsorption behavior of the two studied proteins and clearly affected the MC3T3-E1 morphology, distribution and metabolic activity. HA1000 surfaces presenting slightly larger grain size, higher root-mean-square roughness (Rq), lower surface area and porosity, allowed for higher amounts of both proteins adsorbed. These substrates also revealed increased number of exposed FN cell-binding domains as well as higher affinity for osteonectin. Regarding the osteoblast adhesion results, improved viability and cell number were found for HA1000 surfaces as compared to HA725 ones, independently of the presence or type of adsorbed protein. Therefore the osteoblast adhesion and metabolic activity seemed to be more sensitive to surfaces morphology and roughness than to the type of adsorbed proteins.


Subject(s)
Ceramics/chemistry , Durapatite/chemistry , Fibronectins/chemistry , Nanoparticles/chemistry , Osteoblasts/chemistry , Osteonectin/chemistry , Adsorption , Animals , Cell Adhesion , Cells, Cultured , Crystallization , Mice , Osteoblasts/cytology , Osteoblasts/metabolism , Particle Size , Surface Properties
6.
J Biomed Mater Res A ; 84(2): 281-90, 2008 Feb.
Article in English | MEDLINE | ID: mdl-17607748

ABSTRACT

This study aims at assessing the influence of the competitive preadsorption of human serum albumin (HSA) and human plasma fibronectin (FN) from binary solutions and 10% plasma on MC3T3-E1 osteoblast adhesion and morphology on two types of TiO2 substrates. One was commercially pure titanium with a titanium oxide layer formed in an H2O2 solution and the other TiO2 sputtered on Si (Sousa et al., Langmuir 2004; 20:9745-9754.). The strategy applied in the present investigation was to compare osteoblast adhesion to surfaces preadsorbed with HSA, FN, HSA/FN = 1, HSA/FN = 200, and 10% plasma. The adsorption of proteins was evaluated measuring the amount and the effectiveness of binding with radiolabeled proteins, 125 I-FN and 125 I-HSA. Our results indicated that MC3T3-E1 osteoblast adhesion correlates well with the amounts of FN and HSA adsorbed on TiO2 surfaces. Also, we found that fewer osteoblasts adhered to both substrates preadsorbed with HSA, HSA/FN = 200, and 10% plasma, after 4 and 24 h, than to the surfaces preadsorbed with FN and HSA/FN = 1. For the latter, FN was able to compensate the inhibitory effect of HSA on osteoblast adhesion. Therefore, the presence of lower amounts of coadsorbed albumin may improve presentation of FN in a more integrin-recognized conformation, suggesting that some degree of molecular packing prevents loss of integrin-binding activity. FN reversibility does not seem to be dependent on the HSA/FN adsorption mass ratio in solution, suggesting that FN competitively adsorbs to TiO2 in a favorable conformation and does not suffers subsequent conformational changes allowing exchange with other FN molecules in solution.


Subject(s)
Albumins/chemistry , Fibronectins/chemistry , Osteoblasts/physiology , Titanium/chemistry , 3T3 Cells , Adsorption , Animals , Cell Adhesion , Coloring Agents , Cytoskeleton/ultrastructure , Data Interpretation, Statistical , Iodine Radioisotopes , Mice , Microscopy, Confocal , Neutral Red , Osteoblasts/ultrastructure , Sterilization
7.
Langmuir ; 23(13): 7046-54, 2007 Jun 19.
Article in English | MEDLINE | ID: mdl-17508764

ABSTRACT

In the present work we analyze the dynamics of fibronectin (FN) adsorption on two different stable titanium oxides, with varied surface roughness, and chemically similar to those used in clinical practice. The two types of titanium oxide surfaces used were TiO2 sputtered on Si (TiO2 sp) and TiO2 formed on commercially pure titanium after immersion in H2O2 (TiO2 cp). Surface characterization was previously carried out using different techniques (Sousa, S. R.; Moradas-Ferreira, P.; Melo, L. V.; Saramago, B.; Barbosa, M. A. Langmuir 2004, 20 (22), 9745-9754). Imaging and roughness analysis before and after FN adsorption used atomic force microscopy (AFM) in tapping mode, in air, and in magnetic alternating current mode, in liquid (water). FN adsorption as a function of time was followed by X-ray photoelectron spectroscopy (XPS), by radiolabeling of FN with 125I (125I-FN), and by ellipsometry. Exchangeability studies were performed using FN and HSA. AFM roughness analysis revealed that, before FN adsorption, both TiO2 surfaces exhibited a lower root-mean-square (Rq) and maximum peak with the depth of the maximum valley (Rmax) roughness in air than in water, due to TiO2 hydration. After protein adsorption, the same behavior was observed for the TiO2 sp substrate, while Rq and Rmax roughness values in air and in water were similar in the case of the TiO2 cp substrate, for the higher FN concentration used. Surface roughness was always significantly higher on the TiO2 cp surfaces. AFM led to direct visualization of adsorbed FN on both surfaces tested, indicating that after 10 min of FN incubation the TiO2 sp surface was partially covered by FN. The adsorbed protein seems to form globular aggregates or ellipsoids, and FN aggregates coalesce, forming clusters as the time of adsorption and the concentration increase. Radiolabeling of FN revealed that a rapid adsorption occurs on both surfaces and the amount adsorbed increased with time, reaching a maximum after 60 min of incubation. Time dependence is also observed for the evolution of the atomic (%) of N determined by XPS and by the increase of the thickness by ellipsometry. TiO2 cp adsorbs more FN than the TiO2 sp surfaces, after 60 min of adsorption, as shown by the radiolabeling data. FN molecules are also more strongly attached to the former surface as indicated by the exchangeability studies. The overall results provide novel evidence that FN spontaneously adsorbs as a self-assembly at TiO2 surfaces as a function of time. The aggregate structure is an intermediate feature shared by some protein fibrillar assemblies at interfaces, which is believed to promote cell adhesion and cytoskeleton organization (Pellenc, D.; Berry, H.; Gallet, O. J. Colloid Interface Sci. 2006, 298 (1), 132-144. Maheshwari, G.; Brown, G.; Lauffenburger, D. A.; Wells, A.; Griffith, L. G. J. Cell Sci. 2000, 113 (10), 1677-1686).


Subject(s)
Fibronectins/chemistry , Titanium/chemistry , Adsorption , Humans , Microscopy, Atomic Force , Wettability
8.
J Mater Sci Mater Med ; 16(12): 1173-8, 2005 Dec.
Article in English | MEDLINE | ID: mdl-16362218

ABSTRACT

Human fibronectin (FN) plays a key role in the biointegration of implants as the success depends on adsorption of proteins like FN [1]. Indeed FN can be an intermediary between the biomaterial surface and cells. The adsorption of human fibronectin (FN) on commercially pure titanium with a titanium oxide layer formed in a H2O2 solution (TiO2 cp) and TiO2 sputtered on Si (TiO2 sp) was studied. Adsorption isotherms and the work of adhesion were assessed by wettability studies, X-ray photoelectron spectroscopy (XPS), and by radiolabelling of FN with 125I, (125)I-FN. Exchangeability of bound FN by free FN, was also evaluated by the radiolabelling technique. Contact angle determinations have shown that FN displays higher affinity for the TiO2 cp surface than for the TiO2 sp. As expected from the surface free energy values, the work of adhesion of FN is higher for the TiO2 cp substrate, the more hydrophilic one, and lower for the TiO2 sp substrate, the more hydrophobic one. The adsorption isotherms were evaluated by two different techniques: radiolabelling of FN (125I-FN) and XPS. TiO2 cp adsorbs more FN than the TiO2 sp surfaces as shown by the radiolabelling data. FN molecules are also more strongly attached to the former surface as indicated by the work of adhesion and by the exchangeability studies. Results using 125I-FN also suggests that FN adsorbs as a multilayer for FN concentrations in solution higher than 100 microg/mL.


Subject(s)
Fibronectins/chemistry , Titanium/chemistry , Adsorption , Humans , Solutions
9.
J Biomed Mater Res A ; 75(2): 387-97, 2005 Nov 01.
Article in English | MEDLINE | ID: mdl-16092111

ABSTRACT

Cell adhesion, migration, and proliferation of a few anchorage-dependent cells cultured on chitosan (Ch) matrices are influenced by the degree of N-acetylation (DA) of Ch. In the present work, we examined the influence of the DA on the attachment, spreading, proliferation, and osteogenic differentiation of rat bone marrow stromal cells (rBMSCs). Ch membranes were characterized in terms of surface morphology, roughness, and wettability, and in terms of adsorption of an adhesive protein, fibronectin (Fn). Chs with DAs in the range of 4 to 49% were used. Among the Ch samples, the DA of 4% led to the highest Fn surface concentration, both from single protein solution and from diluted serum. Furthermore, the levels of Fn adsorbed from serum found for this DA were threefold higher than for the tissue culture polystyrene control, indicating that in the presence of competitive proteins Ch is more specific toward Fn adsorption than tissue culture polystyrene. rBMSCs cultured on Ch carrying a DA of 4% were able to spread, proliferate, and differentiate, reaching a higher level of osteogenic differentiation than on the control, despite the lower cell attachment observed for all Ch samples. Because the Ch sample with a DA of 4% showed the highest Fn adsorption from serum, we suggest that cell adhesion, spreading, and osteogenic differentiation of rBMSCs on Ch may be mediated by the adsorbed layer of Fn.


Subject(s)
Bone Marrow Cells/cytology , Cell Adhesion/physiology , Cell Differentiation/physiology , Chitosan/metabolism , Fibronectins/metabolism , Stromal Cells/physiology , Acetylation , Adsorption , Animals , Cell Shape , Coated Materials, Biocompatible/chemistry , Coated Materials, Biocompatible/metabolism , Cytoskeleton/metabolism , Male , Materials Testing , Rats , Rats, Wistar , Stromal Cells/cytology , Surface Properties
10.
Langmuir ; 20(22): 9745-54, 2004 Oct 26.
Article in English | MEDLINE | ID: mdl-15491210

ABSTRACT

In the present work, the adsorption of human serum albumin (HSA) on commercially pure titanium with a titanium oxide layer formed in a H(2)O(2) solution (TiO(2) cp) and on TiO(2) sputtered on Si (TiO(2) sp) was analyzed. Adsorption isotherms, kinetic studies, and work of adhesion determinations were carried out. HSA exchangeability was also evaluated. Surface characterization was performed by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and wettability studies. The two TiO(2) surfaces have very distinct roughnesses, the TiO(2) sp having a mean R(a) value 14 times smaller than the one of TiO(2) cp. XPS analysis revealed consistent peaks representative of TiO(2) on sputtered samples as well as on Ti cp substrate after 48 h of H(2)O(2) immersion. Nitrogen was observed as soon as protein was present, while sulfur, present in disulfide bonds in HSA, was observed for concentrations of protein higher than 0.30 mg/mL. The work of adhesion was determined from contact angle measurements. As expected from the surface free energy values, the work of adhesion of HSA solution is higher for the TiO(2) cp substrate, the more hydrophilic one, and lower for the TiO(2) sp substrate, the more hydrophobic one. The work of adhesion between plasma and the substrates assumed even higher values for the TiO(2) cp surface, indicating a greater interaction between the surface and the complex protein solutions. Adsorption studies by radiolabeling of albumin ((125)I-HSA) suggest that rapid HSA adsorption takes place on both surfaces, reaching a maximum value after approximately 60 min of incubation. For the higher HSA concentrations in solution, a multilayer coverage was observed on both substrates. After the adsorption step from single HSA solutions, the exchangeability of adsorbed HSA molecules by HSA in solution was evaluated. The HSA molecules adsorbed on TiO(2) sp seem to be more easily exchanged by HSA itself than those adsorbed on TiO(2) cp after 24 h. In contrast, after 72 h, nearly all the adsorbed albumin molecules effectively exchange with other albumin molecules.


Subject(s)
Blood , Serum Albumin/chemistry , Titanium/chemistry , Adsorption , Humans , Solutions , Surface Properties
11.
Bone Marrow Transplant ; 34(8): 683-91, 2004 Oct.
Article in English | MEDLINE | ID: mdl-15322567

ABSTRACT

Up to a third of autologous transplantation candidates fail to mobilize hematopoietic progenitors into the peripheral blood with chemotherapy and/or growth factor treatment, thus requiring innovative mobilization strategies. In total, 20 cancer patients unable to provide adequate PBPC products after a previous mobilization attempt were treated with ancestim (20 microg/kg/day s.c.) and filgrastim (10 microg/kg/day s.c.). In 16 patients, the pre-study mobilization was with filgrastim alone. Eight patients underwent single large volume leukapheresis (LVL) and 12 multiple standard volume leukaphereses (SVL) in both mobilizations. Pairwise comparison of peripheral blood CD34(+) cell concentrations on the day of first leukapheresis failed to document synergism - median CD34(+)/microl of 3.2 (<0.1 to 15.4) and 4.5 (1-28.56) for the pre-study and on-study mobilizations (P = 0.79, sign test), and 4.2 (<0.1-15.4) and 5 (1-28.56), respectively, for the 16 patients previously mobilized with filgrastim alone (P = 1, sign test). The number of CD34(+) cells/kg collected per unit of blood volume (BV) processed was similar in both mobilizations - median 0.1 x 10(6)/kg/BV and 0.09 x 10(6)/kg/BV, respectively (P = 1, sign test). In this phase II study, the combination of ancestim and filgrastim did not allow adequate PBPC mobilization and collection in patients with a previous suboptimal PBPC collection.


Subject(s)
Granulocyte Colony-Stimulating Factor/chemistry , Hematopoietic Stem Cell Mobilization/methods , Leukapheresis/methods , Stem Cell Factor/analogs & derivatives , Stem Cell Factor/chemistry , Stem Cells/cytology , Adult , Antigens, CD34/biosynthesis , Female , Filgrastim , Granulocyte Colony-Stimulating Factor/metabolism , Humans , Leukocytes, Mononuclear/cytology , Male , Middle Aged , Recombinant Proteins , Stem Cell Factor/metabolism , Time Factors , Transplantation, Autologous
12.
J Biomed Mater Res ; 55(1): 45-53, 2001 Apr.
Article in English | MEDLINE | ID: mdl-11426397

ABSTRACT

The deposition of calcium phosphate on chemically polished commercially pure titanium immersed in Hank's balanced salt solution (HBSS) with bovine serum albumin (BSA) (concentrations 0 and 4 mg/mL) has been investigated. Electrochemical techniques, 125I labeling of albumin, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used. A tricalcium phosphate layer with a thickness of ca. 1 microm was formed for periods of immersion in HBSS ranging between 1 and 2 weeks. A concentration of 4 mg/mL of BSA prevented its formation, even for periods as long as 1 month. In the absence of BSA, the electrochemical behavior of titanium specimens was significantly affected by the length of immersion time, reflecting the changes that slowly occur on their surface. In the presence of BSA, the surfaces maintained most of their original electrochemical activity. Surface studies have shown that calcium and phosphate become incorporated in the surface at very early stages of immersion. Albumin, which was rapidly adsorbed on titanium, was slowly desorbed when titanium was placed in HBSS. Protein and phosphate may coexist on the same surface, but initially adsorbed albumin molecules prevent the precipitation of a thick layer of tricalcium phosphate.


Subject(s)
Calcium Phosphates/chemistry , Serum Albumin, Bovine/chemistry , Titanium , Animals , Cattle , Electrochemistry/methods , Iodine Radioisotopes , Microscopy, Electron, Scanning , Serum Albumin, Bovine/ultrastructure , Surface Properties , X-Ray Diffraction
13.
Acta Med Port ; 11(8-9): 773-7, 1998.
Article in Portuguese | MEDLINE | ID: mdl-9951071

ABSTRACT

The author explains the nature, reason and practical implications of determining the International Normalized Ratio (INR) for all clinicians and technical personnel, mainly those who work in laboratories. An exhaustive revision is made of the studies performed by the centres involved in thromboplastin calibration exercises to obtain the International Sensitivity Index (ISI) values.


Subject(s)
Laboratories/standards , Calibration , Diagnostic Errors , Humans , International Cooperation , Liver Failure/diagnosis , Reference Values , Selection Bias , Thromboplastin/analysis , World Health Organization
14.
Anal Chem ; 69(19): 3871-8, 1997 Oct 01.
Article in English | MEDLINE | ID: mdl-21639206

ABSTRACT

The relative electron capture detector (ECD) response to alternative fluorocarbons (AFCs) using gas chromatography are found to be at least 1 order of magnitude lower than that for CFC-12. Detection limits for the chlorofluorocarbons CFC-12, HCFC-22, HCFC-123, and HCFC-124 are found to be 2.5, 90, 30, and 90 pg, respectively. Those for the hydrofluorocarbons are significantly poorer; 14 and 45 ng for HFC-125 and HFC-134a, respectively. HFC-152a was not detected using ECD. Since atmospheric concentrations of these compounds are in the low part-per-trillion level, GC-ECD is apparently not sensitive enough to be used for AFC analysis without substantial preconcentration. Two columns are evaluated for the AFC separation. The Poraplot Q WPLOT column showed good separation ability, though column bleed limits detection performance. A Carboxen 1004 packed column exhibits much lower interference. But separations are time consuming and peak broadening adversely affects limits of detection. Mechanisms for the ECD response are proposed based on thermodynamics and temperature-dependent ECD responses. CFC-12, HCFC-123, and HFC-125 apparently undergo ion-forming dissociative electron capture. The electron capture process for HCFC-22 and HFC-134a appear to form molecular ions. Both mechanisms appear to be operative for HCFC-124 electron capture. Dissociative electron capture rate constants for HCFC-123, HCFC-124, and HFC-125 are estimated to be 3.5 × 10(-)(10), 1.0 × 10(-)(10), and 5.6 × 10(-)(13) cm(3) s(-)(1), respectively at 300 °C.

15.
Biomaterials ; 17(4): 397-404, 1996 Feb.
Article in English | MEDLINE | ID: mdl-8938233

ABSTRACT

The electrochemical dissolution behaviour of Ti6Al4V alloy coated with hydroxyapatite (HA) by plasma spraying was studied in Hank's balanced salt solution (HBSS) and compared with that of polished and grit-blasted passivated surfaces. Two different nominal thicknesses of HA (50 and 200 micro m) were used. Taking a polished passivated surface as reference, grit blasting of the substrate increased the electrical charge used in the oxidation of Ti6Al4V alloy at constant potential, as a result of increased surface area. However, only HA coatings with a thickness of 200 micro m were capable of reducing the charge to values lower than those measured for polished surfaces. Electrochemical impedance spectroscopy has also shown that only 200 micro m thick coatings are effective in reducing the oxidation rate of the substrate. Furthermore, in potentiostatic experiments the 50 micro m thick coating detached from the substrate, which did not occur with the 200 micro m thick coating. However, after 6 months immersion in HBSS, detachment occurred in some regions of both coatings. No titanium, aluminium or vanadium were detected in solution by electrothermal atomic absorption spectroscopy. These data indicate that HA is an effective barrier to metal ion release, even for the thinner coatings, due to formation of metal phosphates or to incorporation of metal ions in the HA structure.


Subject(s)
Alloys/chemistry , Biocompatible Materials/chemistry , Durapatite/chemistry , Titanium/chemistry , Electrochemistry , Microscopy, Electron, Scanning , Potentiometry , Spectrophotometry, Atomic , Time Factors
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