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Fibrillar Structures (fibrillar + structure)
Selected AbstractsSupercritically-Dried Alginate Aerogels Retain the Fibrillar Structure of the HydrogelsMACROMOLECULAR SYMPOSIA, Issue 1 2008M. Robitzer Abstract Summary: SAXS patterns of a Ca-alginate hydrogel and of the derived alcogel and aerogel have been recorded. All patterns correspond to disordered arrays of rod-like fibrils. The calculated size of the fibrils of the aerogel, 8 nm, is in good agreement with the results of scanning electron microscopy and N2 adsorption. The results suggest that ethanol exchange and CO2 supercritical drying do not affect the spatial organisation of the secondary structures of the gel and that characterisations of the aerogel can provide information on the organisation of the parent hydrogel. [source] All or none fibrillogenesis of a prion peptideFEBS JOURNAL, Issue 18 2001Wen-Quan Zou Amyloid proteins and peptides comprise a diverse group of molecules that vary both in size and amino-acid sequence, yet assemble into amyloid fibrils that have a common core structure. Kinetic studies of amyloid fibrillogenesis have revealed that certain amyloid proteins form oligomeric intermediates prior to fibril formation. We have investigated fibril formation with a peptide corresponding to residues 195,213 of the human prion protein. Through a combination of kinetic and equilibrium studies, we have found that the fibrillogenesis of this peptide proceeds as an all-or-none reaction where oligomeric intermediates are not stably populated. This variation in whether oligomeric intermediates are stably populated during fibril formation indicates that amyloid proteins assemble into a common fibrillar structure; however, they do so through different pathways. [source] Reinforcement of Biodegradable Poly(DL -lactic acid) Material by Equal-Channel Angular ExtrusionMACROMOLECULAR SYMPOSIA, Issue 1 2006Hongxiang Cui Abstract The purpose of this study was to reinforce biodegradable poly(DL -lactic acid) (PDLLA) material using a new method, equal-channel angular extrusion (ECAE). Different processing parameters, including the number of extrusion passes and the process temperature, were investigated to analyze their effect on the PDLLA properties. Experimental results indicate that the mechanical strength of PDLLA increased with the number of extrusion passes. The extrusion temperature also affected the mechanical strength of the PDLLA. After two ECAE passes, the bending strength of PDLLA increased from 83.3 to 178.7 MPa. The bending fracture mode for PDLLA changed from brittle failure for initial specimens to ductile fracture after ECAE processing. SEM micrographs showed that the longitudinal split surfaces of PDLLA are of a fibrillar structure. Taken together, the results suggest that ECAE might represent a useful approach for the preparation of reinforced PDLLA. [source] Formation of a fibrillar morphology of crosslinked epoxy in a polystyrene continuous phase by reactive extrusionPOLYMER ENGINEERING & SCIENCE, Issue 4 2004Françoise Fenouillot An immiscible polymer blend where the dispersed phase is fibrillar was prepared by in situ crosslinking of the minor phase. A model polystyrene/epoxy-amine blend was selected on the basis of rheological (achievement of the fibrillar structure) and reactivity (fast crosslinking) criteria. The system was a polystyrene/diglycidyl ether of bisphenol A (DGEBA)-aminoethyl piperazine (AEP) blend. At the temperature of extrusion, 180°C, the DGEBA is immiscible in PS and heterogeneous material is obtained. The elongational flow imposed by drawing the extrudate at the die exit permitted controlled generation of a fibrillar morphology of the dispersed epoxy phase, with a fiber diameter of 1 ,m and an aspect ratio greater than 100. It was shown that when the amine comonomer was injected into the extruder, its reactivity with DGEBA at high temperature was high enough to ensure partial crosslinking of the epoxy. The fibrils were formed even though the gel point of the epoxy phase was exceeded. However, above a certain critical insoluble fraction that we estimated to be between 45% and 70%, a coarsening of the structure appeared, caused by the decreasing deformability of the domains and their coalescence. Finally, for our system, the crosslinking of the dispersed phase up to 90% of insoluble fraction did not totally stabilize the morphology after the second processing step (injection molding). Polym. Eng. Sci. 44:625,637, 2004. © 2004 Society of Plastics Engineers. [source] Lipid-induced conformational transition of the amyloid core fragment A,(28,35) and its A30G and A30I mutantsFEBS JOURNAL, Issue 10 2008Sureshbabu Nagarajan The interaction of the ,-amyloid peptide (A,) with neuronal membranes could play a key role in the pathogenesis of Alzheimer's disease. Recent studies have focused on the interactions of A, oligomers to explain the neuronal toxicity accompanying Alzheimer's disease. In our study, we have investigated the role of lipid interactions with soluble A,(28,35) (wild-type) and its mutants A30G and A30I in their aggregation and conformational preferences. CD and Trp fluorescence spectroscopic studies indicated that, immediately on dissolution, these peptides adopted a random coil structure. Upon addition of negatively charged 1,2-dipalmitoyl- syn -glycero-3-phospho- rac -(glycerol) sodium salt (PG) lipid, the wild-type and A30I mutant underwent reorganization into a predominant ,-sheet structure. However, no conformational changes were observed in the A30G mutant on interaction with PG. In contrast, the presence of zwitterionic 1,2-dipalmitoyl- syn -glycero-3-phosphatidylcholine (PC) lipid had no effect on the conformation of these three peptides. These observations were also confirmed with atomic force microscopy and the thioflavin-T assay. In the presence of PG vesicles, both the wild-type and A30I mutant formed fibrillar structures within 2 days of incubation in NaCl/Pi, but not in their absence. Again, no oligomerization was observed with PC vesicles. The Trp studies also revealed that both ends of the three peptides are not buried deep in the vesicle membrane. Furthermore, fluorescence spectroscopy using the environment-sensitive probe 1,6-diphenyl-1,3,5-hexatriene showed an increase in the membrane fluidity upon exposure of the vesicles to the peptides. The latter effect may result from the lipid head group interactions with the peptides. Fluorescence resonance energy transfer experiments revealed that these peptides undergo a random coil-to-sheet conversion in solution on aging and that this process is accelerated by negatively charged lipid vesicles. These results indicate that aggregation depends on hydrophobicity and propensity to form ,-sheets of the amyloid peptide, and thus offer new insights into the mechanism of amyloid neurodegenerative disease. [source] Biomimetic Polymer Nanostructures by Injection MoldingMACROMOLECULAR MATERIALS & ENGINEERING, Issue 1 2003Nikolaj Gadegaard Abstract The nanometer scale topography of self-assembling structural protein complexes in animals is believed to induce favorable cell responses. An important example of such nanostructured biological complexes is fibrillar collagen that possesses a cross-striation structure with a periodicity of 69 nm and a peak-to-valley distance of 4,6 nm. Bovine collagen type I was assembled into fibrillar structures in vitro and sedimented onto solid supports. Their structural motif was transferred into a nickel replica by physical vapor deposition of a small-grained metal layer followed by galvanic plating. The resulting inverted nickel structure was found to faithfully present most of the micrometer and nanometer scale topography of the biological original. This nickel replica was used as a die for the injection molding of a range of different thermoplastic polymers. Total injection molding cycle times were in the range of 30,45 seconds. One of the polymer materials investigated, polyethylene, displayed poor replication of the biological nanotopographical motif. However, the majority of the polymers showed very high replication fidelity as witnessed by their ability to replicate the cross-striation features of less than 5 nm height difference. The latter group of materials includes poly(propylene), poly(methyl methacrylate), poly(L -lactic acid), polycaprolactone, and a copolymer of cyclic and linear olefins (COC). This work suggests that the current limiting factor for the injection molding of nanometer scale topography in thermoplastic polymers lies with the grain size of the initial metal coating of the mold rather than the polymers themselves. [source] Ultrastructure of the Harmful Unarmored Dinoflagellate Cochlodinium polykrikoides (Dinophyceae) with Reference to the Apical Groove and Flagellar ApparatusTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 4 2010MITSUNORI IWATAKI ABSTRACT. The external and internal ultrastructure of the harmful unarmored dinoflagellate Cochlodinium polykrikoides Margalef has been examined with special reference to the apical groove and three-dimensional structure of the flagellar apparatus. The apical groove is U-shaped and connected to the anterior sulcal extension on the dorsal side of the epicone. The eyespot is located dorsally and composed of two layers of globules situated within the chloroplast. A narrow invagination of the plasma membrane is associated with the eyespot. The nuclear envelope has normal nuclear pores similar to other eukaryotes but different from the Gymnodinium group with diagnostic nuclear chambers. The longitudinal and transverse basal bodies are separated by approximately 0.5,1.0 ,m and interconnected directly by a striated basal body connective and indirectly by microtubular and fibrous structures. Characteristic features of the flagellar apparatus are as follows: (1) a nuclear extension projects to the R1 (longitudinal microtubular root) and is connected to the root by thin fibrous material; (2) fibrillar structures are associated with the longitudinal and transverse flagellar canal; and (3) a striated ventral connective extends toward the posterior end of the cell along the longitudinal flagellar canal. We conclude, based on both morphological and molecular evidence, that Cochlodinium is only distantly related to Gymnodinium. [source] Combined role of type IX collagen and cartilage oligomeric matrix protein in cartilage matrix assembly: Cartilage oligomeric matrix protein counteracts type IX collagen,induced limitation of cartilage collagen fibril growth in mouse chondrocyte culturesARTHRITIS & RHEUMATISM, Issue 12 2009K. Blumbach Objective Defects in the assembly and composition of cartilage extracellular matrix are likely to result in impaired matrix integrity and increased susceptibility to cartilage degeneration. The aim of this study was to determine the functional interaction of the collagen fibril,associated proteins type IX collagen and cartilage oligomeric matrix protein (COMP) during cartilage matrix formation. Methods Primary chondrocytes from mice deficient in type IX collagen and COMP (double-deficient) were cultured in monolayer or alginate beads. Anchorage of matrix proteins, proteoglycan and collagen content, collagen crosslinks, matrix metalloproteinase activity, and mechanical properties of the matrix were measured. Electron microscopy was used to study the formation of fibrillar structures. Results In cartilage lacking both type IX collagen and COMP, matrilin 3 showed decreased matrix anchorage. Less matrilin 3 was deposited in the matrix of double-deficient chondrocytes, while larger amounts were secreted into the medium. Proteoglycans were less well retained in the matrix formed in alginate cultures, while collagen deposition was not significantly affected. Electron microscopy revealed similar cartilage collagen fibril diameters in the cultures of double-deficient and wild-type chondrocytes. In contrast, a larger fibril diameter was observed in the matrix of chondrocytes deficient in only type IX collagen. Conclusion Our results show that type IX collagen and COMP are involved in matrix assembly by mediating the anchorage and regulating the distribution of other matrix macromolecules such as proteoglycans and matrilins and have counteracting effects on collagen fibril growth. Loss of type IX collagen and COMP leads to matrix aberrations that may make cartilage more susceptible to degeneration. [source] Monitoring retinal ganglion cells in vivoACTA OPHTHALMOLOGICA, Issue 2008M PAQUES Progress in imaging techniques will considerably increase our knowledge on retinal cell pathophysiology and death during optic nerve disesases as a whole. Experimentally, current in vivo imaging using the green laser reflectance mode of the SLO allows noninvasive microscopic-scale definition of the nerve fibers. However, loss of the axons is a late and irreversible event, thus imaging the retinal ganglion cells themselves would be preferable in order to detect diseased states at an earlier stage. Retrogradelly-labelled RGCs can be conveniently seen in vivo, but such imaging require invasive procedures, the effect of which on RGC physiology remains uncertain. The recent development of molecular imaging of apoptotic ganglion cells is promising. The cSLO also allows in vivo imaging of other cellular compartments that are relevant for glaucoma, for instance microglial cells. In humans, current techniques allow imaging of the nerve fiber layer with a relatively low resolution. The GDx evaluates the nerve fiber layer thickness through light polarisation, and high resolution OCT through mapping of its thickness around the optic nerve. Yet, it is likely that these systems lack sensitivity for detection of the early loss of the NFL, and even more for early dysfunction of RGCs. Presently, adaptive optics does not appear to be a technique of choice for the NFL, but technological progress may prove this assertion to be wrong. In the future, techniques allowing increased contrast of fibrillar structures such as en face OCT may prove of interest. [source] | |||||||||||||