Search Results - (Author, Cooperation:S. M. Best)

2015-08-08

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Drug Evaluation, Preclinical ; Ebola Vaccines/*administration & dosage/immunology ; Ebolavirus/genetics/*immunology ; Genetic Vectors ; Glycoproteins/genetics/*immunology ; Hemorrhagic Fever, Ebola/*prevention & control ; Macaca ; Vesiculovirus ; Viral Proteins/genetics/*immunology

2018-01-09

The American Association of Immunologists (AAI)

0022-1767

1550-6606

Medicine

0017-789X

General, Interdisciplinary

POETRY

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract The structural changes that occur during the transformation of a Ca-deficient apatite, prepared by a wet chemical method, to β-TCp were investigated. X-ray diffraction (XRD) analysis of as-prepared samples and samples calcined at temperatures between 500 and 1100 °C showed that the transformation occurs over the temperature range 710–740 °C, under non-equilibrium conditions. The change in crystallite size with increasing calcination/sintering temperature was studied by XRD using the Scherrer formula. Fourier transform infra-red (FTIR) analysis indicated considerable structural change in samples above and below this temperature range. Changes were observed in the hydroxyl, carbonate and phosphate bands as the calcination temperature was increased from 500 to 1100 °C. Even once a single β-TCP phase is obtained at 740 °C there remains a considerable amount of structural change at temperatures between 740 and 1100 °C. This effect was illustrated by an unusual change in the lattice parameters of the β-TCP structure and significant changes in the phosphate bands of FTIR spectra as the calcination temperature was increased. The results obtained in this study show that the combined experimental techniques of XRD and FTIR are excellent complimentary methods for characterizing structural changes that occur during phase transformations.

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract The structural changes that occur during the transformation of a Ca-deficient apatite, prepared by a wet chemical method, to β-TCP were investigated. X-ray diffraction (XRD) analysis of as-prepared samples and samples calcined at temperatures between 500 and 1100 °C showed that the transformation occurs over the temperature range 710–740 °C, under non-equilibrium conditions. The change in crystallite size with increasing calcination/sintering temperature was studied by XRD using the Scherrer formula. Fourier transform infra-red (FTIR) analysis indicated considerable structural change in samples above and below this temperature range. Changes were observed in the hydroxyl, carbonate and phosphate bands as the calcination temperature was increased from 500 to 1100 °C. Even once a single β-TCP phase is obtained at 740 °C there remains a considerable amount of structural change at temperatures between 740 and 1100 °C. This effect was illustrated by an unusual change in the lattice parameters of the β-TCP structure and significant changes in the phosphate bands of the FTIR spectra as the calcination temperature was increased. The results obtained in this study show that the combined experimental techniques of XRD and FTIR are excellent complimentary methods for characterizing structural changes that occur during phase transformations.

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Porous hydroxyapatite (Endobon®) specimens were implanted into the femoral condyle of New Zealand White rabbits for up to 6 months. After sacrifice, specimens were sectioned for histology and mechanical testing, where the extent of reinforcement by bony ingrowth was assessed by compression testing and fixation was assessed by push-out testing. From histological observations, it was established that the majority of bone ingrowth occurred between 10 day and 5 weeks after implantation and proceeded predominantly from the deep end of the trephined defect, with some integration from the circumferential sides. At 3 months, the implants were fully integrated, exhibiting bony ingrowth, vascularization and bone marrow stroma within the internal macropores. After 5 weeks, the mean ultimate compressive strength of retrieved implants (6.9 MPa) was found to be greater than that of the original implant (2.2 MPa), and by 3 months the fully integrated implants attained a compressive strength of approximately 20 MPa. Push-out testing demonstrated that after 5 weeks in vivo, the interfacial shear strength reached 3.2 MPa, increasing to 7.3 MPa at 3 and 6 months.

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Apatites were prepared with three different fluoride concentrations: 0.0 mM (pure hydroxyapatite) 2.5 mM and 5 mM. Reactions were performed in aqueous medium using a reaction between diammonium orthophosphate and calcium nitrate 4-hydrate and ammonium fluoride at temperatures of 3°, 25°, 60° and 90°C. The effects of reaction temperature and fluoride concentration on the crystal morphology, phase purity and crystallinity of the precipitates were observed, using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and ion chromatography. Transmission electron micrographs revealed that the crystallites precipitated at 3°C were spheroidal, but became increasingly acicular with increasing precipitation temperature. X-ray diffraction results indicated that all the materials produced were phase pure and that the crystallinity of apatites prepared at higher precipitation temperatures was higher than those prepared at lower precipitation temperatures. A significant difference in the a-axis dimension of fluoride-substituted apatites was observed, as compared to hydroxyapatite. FTIR spectroscopy revealed a hydroxyl band at 3568 cm-1, along with a broad peak of adsorbed water in the region of 3568 cm-1 to 2670 cm-1 in the hydroxyapatite and fluoride-substituted apatite powders. Hence by careful selection of the precipitation conditions and fluoride contents, the composition and morphology of fluoride-substituted apatite may be controlled and this has interesting implications for the development of these materials for biomedical implantation.

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract This work documents an investigation into the effect of water on the density and microstructure of carbonate hydroxyapatite in carbon dioxide sintering atmospheres. Carbonate apatites with carbonate contents of between 3.2 and 7.8 wt % were precipitated and the precipitates were formed into dry gels. Isothermal and isochronal sintering experiments were performed under dry carbon dioxide and wet carbon dioxide (containing 3 wt % water) atmospheres. The effect of carbonate content was studied by using two gels both with a green density of 37% and with carbonate contents of 5.8 and 7.8 wt %. Both isothermal and isochronal experiments demonstrated that bloating of the apatite occurred and this behavior was associated with the loss of carbonate from the apatite. It was found that only in wet carbon dioxide atmospheres fully dense translucent carbonate apatite could be formed. 93% dense carbonate apatite was formed after 4 h sintering at temperatures as low as 700 °C. © 2000 Kluwer Academic Publishers

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Hydroxyapatite has been investigated for use in the osseous environment for over 20 years and the biocompatibility of the ceramic and its osseoconductive behavior is well established. Therefore, the use of porous hydroxyapatite for the repair of osseous defects seems promising with potential for complete penetration of osseous tissue and restoration of vascularity throughout the repair site. However, there have been few systematic studies of the effects of physical properties such as macropore size and pore connectivity on the rate and quality of bone integration within porous hydroxyapatite implants. This paper quantifies the early biological response to a well-characterized series of implants with uniform microstructure and phase composition, but differing macrostructures and demonstrates the dependence of the rate of osseointegration on the apparent density of porous hydroxyapatite as a function of pore connectivity. Furthermore, compression testing established that bony ingrowth has a strong reinforcing effect on porous hydroxyapatite implants, which is more pronounced in the lower density implants, as a result of a greater relative volume of bone ingrowth. © 1999 Kluwer Academic Publishers

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Calcium phosphate cements have been the subject of many studies in the last decade because of their biocompatibility, their capacity to fill bone cavities and their hardening properties; properties which are desirable in a broad range of surgical applications. The setting and hardening of these materials are controlled by dissolution–precipitation chemical reactions at room or body temperature and involve crystalline phase transformations. © 1999 Kluwer Academic Publishers

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract The initial setting properties of calcium phosphate cements in the CaHPOv4–α-Ca3(PO4)2 (DCP–α-TCP) system have been investigated. Interest was focused on the pH, workability, cohesion time and initial and final setting times. The addition of CaCO3 modified the structure of the cement reaction product such that it became more similar to the apatite phase in bone mineral. The addition of 10% w/w of CaCO3 reduced the viscosity of the cement pastes resulting in an increase in initial and final setting times and improved injectability. © 1999 Kluwer Academic Publishers

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Titanium–zirconium based alloys containing a small amount of niobium were investigated in order to evaluate their possible use as biomedical materials. Zirconium, which belongs to the IVa group, is known to have good corrosion resistance and biocompatibility similar to titanium. As the titanium–zirconium system shows a complete solid solution, a wide variation of alloy design is available and large quantities of solid-solution hardening must be possible. Niobium, having a β-phase stabilizing effect, was chosen as a ternary element in order to control desirably the microstructure. There have been no reports which suggest its harm to a living body. The alloys containing 2% or 3% niobium showed the highest hardness value after aging heat treatment at 773 K. In contrast to this, no alteration of hardness was seen in specimens aged at 1073 K. Through conventional X-ray diffractometry and in situ X-ray analysis using a hot stage, β-phase precipitation in the A matrix was identified. From the above results, it is concluded that alloys containing 2%–3% niobium are hopeful candidates for new kinds of biomedical alloys, when they are heat treated under suitable conditions. © 1998 Kluwer Academic Publishers

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Dahllite is a synthetic carbonated hydroxyapatite with a carbonate ion content similar to bone mineral. The first objective of this study was to investigate the stoichiometric conditions under which dahllite formation occurs in a powder mixture of α-Ca3(PO4)2, Ca(H2PO4)2 and CaCO3. The second objective was to identify how these conditions apply to commercially available cement, Skeletal Repair System (SRSTM), and other α-Ca3(PO4)2-based cements currently under investigation. The stoichiometric coefficients were found to be a function of both the percentage of carbonate ions incorporated into the hydroxyapatite structure, and the amount of CO2 released during the reaction. As a consequence, a stability field has been obtained where different initial proportions of the reactants in the powder mixture should give the same reaction product if sufficient CO2 is released into the solution. However, increasing amounts of CaCO3 in the initial mixture have been shown to affect the solution pH in such a way that only partial reaction of the reactants takes place. SRSTM and other α-Ca3(PO4)2-based cements have been located inside the stability field and a comparison between their reported setting and hardening properties has been performed. © 1998 Kluwer Academic Publishers

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Substituted apatite ceramics are of clinical interest as they offer the potential to improve the bioactive properties of implants. Carbonate hydroxyapatite (CHA) has been synthesized by an aqueous precipitation method and precipitates with two different levels of carbonate, processed as powders. Sintering experiments were performed to establish the influence of carbonate in significantly reducing the temperature required to prepare high-density ceramics when compared with stoichiometric hydroxyapatite (HA). High-temperature X-ray diffraction was used to characterize the phase stability of the apatites on sintering. Increasing carbonate content was shown to reduce the temperature at which decomposition occurred, to phases of CaO and β-TCP. Mechanical testing, performed using biaxial flexure, showed that the CHA specimens had strengths similar to stoichiometric HA. © 1998 Kluwer Academic Publishers

Electronic Resource

1573-4811

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1573-4811

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Hydroxyapatite has been considered for use in the repair of osseous defects for the last 20 years. Recent developments have led to interest in the potential of porous hydroxyapatite as a synthetic bone graft. However, despite considerable activity in this field, regarding assessment of the biological response to such materials, the basic materials characterization is often inadequate. This paper documents the characterization of the chemical composition, mechanical integrity, macro- and microstructure of a porous hydroxyapatite, Endobon ® (E. Merck GmbH), intended for the bone-graft market. Specimens possesed a range of apparent densities from 0.35 to 1.44 g cm-3. Chemical analysis demonstrated that the natural apatite precursor of Endobon® was not converted to pure hydroxyapatite, but retained many of the ionic substituents found in bone mineral, notably carbonate, sodium and magnesium ions. Investigation of the microstructure illustrated that the struts of the material were not fully dense, but had retained some traces of the network of osteocyte lacunae. Macrostructural analysis demonstrated the complex inter-relationship between the structural features of an open pore structure. Both pore size and connectivity were found to be inversely dependent on apparent density. Furthermore, measurement of pore aspect ratio and orientation demonstrated a relationship between apparent density and the degree of macrostructural anisotropy within the specimens, while, it was also noted that pore connectivity was sensitive to anisotropy. Compression testing demonstrated the effect of apparent density and macrostructural anisotropy on the mechanical properties. An increase in apparent density from 0.38 to 1.25 g cm-3 resulted in increases in ultimate compressive stress and compressive modulus of 1 to 11 MPa and 0.2 to 3.1 GPa, respectively. Furthermore, anisotropic high density (〉 0.9 g cm-3) specimens were found to possess lower compressive moduli than isotropic specimens with equivalent apparent densities. These results underline the importance of full structural and mechanical characterization of porous ceramic implant materials. ©1999 Kluwer Academic Publishers

Electronic Resource

1573-4838

Springer Online Journal Archives 1860-2000

Medicine

Technology

Abstract Calcium phosphate bone cements (CPBC) have been of great interest in medicine and dentistry due to their excellent biocompatibility and bone-repair properties. In this article, a review is presented of the scientific literature concerning precipitate formation during setting reactions of CPBCs. Firstly, the available information has been classified according to the intended final product or calcium phosphate formed during setting reactions. Taking the final product into account, a second classification has been made according to the calcium phosphates present in the original powder mixture. This is the most natural classification procedure because it is based on thermodynamic reasons supported by solubility diagrams for the calcium phosphate salts. By understanding the thermodynamics of calcium phosphate salts in an aqueous solution at room or body temperature it is possible to optimize the manufacturing technology involved in the production of CPBCs. Knowledge of the limitations of this thermodynamic approach opens up new possibilities in the search for CPBCs with better in vitro and in vivo properties for clinical applications. © 1999 Kluwer Academic Publishers

Electronic Resource

0021-9304

calcium phosphate bone cements ; compressive strength ; microstructure ; bone apatite ; Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Medicine

Technology

The hardening properties of calcium phosphate cements in the CaHPO4-α-Ca3(PO4)2 (DCP-α-TCP) system have been investigated with interest focused on the compressive strength and microstructure development. Previous studies have shown that the addition of CaCO3 (CC) leads to a modification of the calcium-deficient apatite structure of the reaction product, which results in a material more similar to the apatite in bone mineral. The addition of 10% w/w of CC to the initial DCP-α-TCP powder mixture resulted, with time, in a retardation of the development of compressive strength. However, the optimum compressive strength reached values up to 40% higher than CC-free samples. This retarding effect also has been monitored as a function of the calcium to phosphorus (Ca/P) ratio of the DCP and α-TCP mixture, showing the importance to the final cement properties of the relative quantities of the reactants in the mixture. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 560-567, 1998.

10 Ill.

Electronic Resource