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B G M Jamieson - One of the best experts on this subject based on the ideXlab platform.
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ultrastructure of the spermatozoon of the tuatara sphenodon punctatus and its relevance to the relationships of the sphenodontida
Philosophical Transactions of the Royal Society B, 1992Co-Authors: John M Healy, B G M JamiesonAbstract:Spermatozoa of the New Zealand tuatara , Sphenodon punctatus punctatus (Gray), are described from light and electron microscopic observations and compared with spermatozoa of other living ‘reptiles’ (Chelonia, Crocodilia, Squamata), birds and mammals. Mature Sphenodon spermatozoa consist of an acrosomal complex (length 4 µm), elongate, helical nucleus (54-56 µm), a relatively short midpiece (7-8 µm), elongate principal piece (74-78 µm) and short end piece (2-4 µm). The acrosomal vesicle and underlying subacrosomal Material Form a double, curved, conical sheath around the nucleus anteriorly. Two parallel, loosely helical, endonuclear canals each containing perforatorial Material, extend posteriorly from the apex of the nucleus to at least 2.5 µm below the base of the acrosomal complex. Rings of several spherical mitochondria are stacked around the elongate distal centriole to Form the midpiece. Each mitochondrion has concentric cristae surrounding a dense central body. Proximal and distal centrioles, although differing markedly in length, are similar in having triplets with an open C tubule. Nine peripheral fibres are intimately associated with the triplets of the distal centriole. A well developed annulus defines the posterior extremity of the midpiece. The principal piece consists of a 9 + 2 axoneme (accompanied anteriorly by nine peripheral fibres) surrounded by a highly electron-dense fibrous sheath and the plasma membrane. Absence of a penis in Sphenodon has not resulted in recognizable modifications of the spermatozoon. Sphenodon shares many spermatozoal features here interpreted as plesiomorphies with crocodiles and turtles, particularly the latter group, but exhibits none of the advanced character states (apomorphies) diagnostic of the Squamata. These data not only underscore the primitive status of living tuatara (recently questioned in the literature) but also militate against a close, sister-group relationship between the Sphenodontida and Squamata.
John M Healy - One of the best experts on this subject based on the ideXlab platform.
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ultrastructure of the spermatozoon of the tuatara sphenodon punctatus and its relevance to the relationships of the sphenodontida
Philosophical Transactions of the Royal Society B, 1992Co-Authors: John M Healy, B G M JamiesonAbstract:Spermatozoa of the New Zealand tuatara , Sphenodon punctatus punctatus (Gray), are described from light and electron microscopic observations and compared with spermatozoa of other living ‘reptiles’ (Chelonia, Crocodilia, Squamata), birds and mammals. Mature Sphenodon spermatozoa consist of an acrosomal complex (length 4 µm), elongate, helical nucleus (54-56 µm), a relatively short midpiece (7-8 µm), elongate principal piece (74-78 µm) and short end piece (2-4 µm). The acrosomal vesicle and underlying subacrosomal Material Form a double, curved, conical sheath around the nucleus anteriorly. Two parallel, loosely helical, endonuclear canals each containing perforatorial Material, extend posteriorly from the apex of the nucleus to at least 2.5 µm below the base of the acrosomal complex. Rings of several spherical mitochondria are stacked around the elongate distal centriole to Form the midpiece. Each mitochondrion has concentric cristae surrounding a dense central body. Proximal and distal centrioles, although differing markedly in length, are similar in having triplets with an open C tubule. Nine peripheral fibres are intimately associated with the triplets of the distal centriole. A well developed annulus defines the posterior extremity of the midpiece. The principal piece consists of a 9 + 2 axoneme (accompanied anteriorly by nine peripheral fibres) surrounded by a highly electron-dense fibrous sheath and the plasma membrane. Absence of a penis in Sphenodon has not resulted in recognizable modifications of the spermatozoon. Sphenodon shares many spermatozoal features here interpreted as plesiomorphies with crocodiles and turtles, particularly the latter group, but exhibits none of the advanced character states (apomorphies) diagnostic of the Squamata. These data not only underscore the primitive status of living tuatara (recently questioned in the literature) but also militate against a close, sister-group relationship between the Sphenodontida and Squamata.
Laura E. Depero - One of the best experts on this subject based on the ideXlab platform.
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Microstructural investigation of nimesulide–crospovidone composites by X-ray diffraction and thermal analysis
Composites Science and Technology, 2003Co-Authors: Paolo Bergese, Elza Bontempi, Italo Colombo, D. Gervasoni, Laura E. DeperoAbstract:Abstract Dispersion into crospovidone is a widely employed method for enhancing the solubility of poorly water-soluble drugs, since the 3D polymeric network stabilizes the active substance in molecular clusters and nano-crystalline phases. Nimesulide loaded into crospovidone shows two polymorphic modifications: the native Material (Form I) and the phase reported on ICDD and CSD databases (Form II). Microstructure and polymorphism of the composites have been investigated as they affect the drug dissolution rate and in vivo absorption kinetics (i.e. the bio-availability of the drug from its dosage Form). Differential scanning calorimetry (DSC) showed that the lower melting Form (Form II) is metastable. X-ray diffraction (XRD) evidenced that the embedded crystalline phases are made up of nano-crystallites and that no significant difference on their size exists. Quantitative analysis of the composites turned out to be a challenge with both XRD (preferred orientation effects and Form I crystalline structure unknown) and DSC (high nimesulide-crospovidone reactivity). Nevertheless, the results suggest a direct correlation between crospovidone and Form II weight fractions.
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microstructural investigation of nimesulide crospovidone composites by x ray diffraction and thermal analysis
Composites Science and Technology, 2003Co-Authors: Paolo Bergese, Elza Bontempi, Italo Colombo, D. Gervasoni, Laura E. DeperoAbstract:Abstract Dispersion into crospovidone is a widely employed method for enhancing the solubility of poorly water-soluble drugs, since the 3D polymeric network stabilizes the active substance in molecular clusters and nano-crystalline phases. Nimesulide loaded into crospovidone shows two polymorphic modifications: the native Material (Form I) and the phase reported on ICDD and CSD databases (Form II). Microstructure and polymorphism of the composites have been investigated as they affect the drug dissolution rate and in vivo absorption kinetics (i.e. the bio-availability of the drug from its dosage Form). Differential scanning calorimetry (DSC) showed that the lower melting Form (Form II) is metastable. X-ray diffraction (XRD) evidenced that the embedded crystalline phases are made up of nano-crystallites and that no significant difference on their size exists. Quantitative analysis of the composites turned out to be a challenge with both XRD (preferred orientation effects and Form I crystalline structure unknown) and DSC (high nimesulide-crospovidone reactivity). Nevertheless, the results suggest a direct correlation between crospovidone and Form II weight fractions.
B Rand - One of the best experts on this subject based on the ideXlab platform.
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carbon carbon composite bearing Materials in hip arthroplasty analysis of wear and biological response to wear debris
Journal of Materials Science: Materials in Medicine, 2004Co-Authors: Graeme I Howling, Eileen Ingham, H Sakoda, T Stewart, J Fisher, A Antonarulrajah, S Appleyard, B RandAbstract:Ultra-high molecular weight polyethylene wear particles have been implicated as the major cause of osteolysis, implant loosening and late aseptic failure in total hip arthroplasties in vivo. This study initially screened 22 carbon–carbon composite Materials as alternatives for UHMWPE in joint bearings. New bearing Materials should satisfy certain criteria – they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of cytotoxic and osteolytic activity. Initial screening was based on wear resistance determined in short-term tribological pin-on-plate tests. Three Materials (HMU–PP(s), HMU–RC–P(s), and SMS–RC–P(s)) which had superior wear resistance were selected for long-term testing. All Materials had very low wear factors and SMS–RC–P(s), which had a wear factor of 0.08±0.56×10−7 mm3/Nm, was selected for the subsequent biological testing and particle size analysis. SMS–RC–P(s) showed good biocompatibility in bulk Material Form and also the wear particles had low cytotoxicity for L929 fibroblasts in culture compared to metal wear particles. Wear debris size analysis by transmission electron microscopy showed that the particles were very small, with the vast majority being under 100 nm in size, similar to metal wear particles. The potential osteolytic effect of SMS–RC–P(s) wear particles was investigated by culturing particles with human peripheral blood mononuclear cells and measuring TNFα production. SMS–RC–P(s) did not significantly stimulate TNFα production at a particle volume to cell number ratio of 80 : 1, indicating that the debris had a low osteolytic potential. The results of this study suggest that carbon–carbon composites, particularly those composed of PAN-based fibers may be important bioMaterials in the development of next generation bearing surfaces for use in total joint replacements that have very low wear rates and reduced osteolytic and cytotoxic potential.
Paolo Bergese - One of the best experts on this subject based on the ideXlab platform.
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Microstructural investigation of nimesulide–crospovidone composites by X-ray diffraction and thermal analysis
Composites Science and Technology, 2003Co-Authors: Paolo Bergese, Elza Bontempi, Italo Colombo, D. Gervasoni, Laura E. DeperoAbstract:Abstract Dispersion into crospovidone is a widely employed method for enhancing the solubility of poorly water-soluble drugs, since the 3D polymeric network stabilizes the active substance in molecular clusters and nano-crystalline phases. Nimesulide loaded into crospovidone shows two polymorphic modifications: the native Material (Form I) and the phase reported on ICDD and CSD databases (Form II). Microstructure and polymorphism of the composites have been investigated as they affect the drug dissolution rate and in vivo absorption kinetics (i.e. the bio-availability of the drug from its dosage Form). Differential scanning calorimetry (DSC) showed that the lower melting Form (Form II) is metastable. X-ray diffraction (XRD) evidenced that the embedded crystalline phases are made up of nano-crystallites and that no significant difference on their size exists. Quantitative analysis of the composites turned out to be a challenge with both XRD (preferred orientation effects and Form I crystalline structure unknown) and DSC (high nimesulide-crospovidone reactivity). Nevertheless, the results suggest a direct correlation between crospovidone and Form II weight fractions.
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microstructural investigation of nimesulide crospovidone composites by x ray diffraction and thermal analysis
Composites Science and Technology, 2003Co-Authors: Paolo Bergese, Elza Bontempi, Italo Colombo, D. Gervasoni, Laura E. DeperoAbstract:Abstract Dispersion into crospovidone is a widely employed method for enhancing the solubility of poorly water-soluble drugs, since the 3D polymeric network stabilizes the active substance in molecular clusters and nano-crystalline phases. Nimesulide loaded into crospovidone shows two polymorphic modifications: the native Material (Form I) and the phase reported on ICDD and CSD databases (Form II). Microstructure and polymorphism of the composites have been investigated as they affect the drug dissolution rate and in vivo absorption kinetics (i.e. the bio-availability of the drug from its dosage Form). Differential scanning calorimetry (DSC) showed that the lower melting Form (Form II) is metastable. X-ray diffraction (XRD) evidenced that the embedded crystalline phases are made up of nano-crystallites and that no significant difference on their size exists. Quantitative analysis of the composites turned out to be a challenge with both XRD (preferred orientation effects and Form I crystalline structure unknown) and DSC (high nimesulide-crospovidone reactivity). Nevertheless, the results suggest a direct correlation between crospovidone and Form II weight fractions.