Fibril surfaces

In order to see the effect of the compatibilizer more clearly, SEM (scanning electron microscopy) micrographs of the peeled back exposed surface of the spun fibers are shown in Fig. 7. In a noncompatibilized blend, the long TLCP fibrils are bundled together (Fig. 7A). The fibril surface looks quite clean and smooth along the... 

The surface of the fibril provides the interface between the internal structural and mechanical properties of a fibril, and the rest of the extracellular matrix. The surface, therefore, is the most complex area of the fibril in terms of molecular heterogeneity and structure. Caution has to be taken in the comparison of structural and biochemical evidence from complementary techniques since the extraction, dehydration, and sample preparation can cause variation in observations of fibril surface properties (Raspanti et at, 1996). 

Types III, V, and XI—may decorate fibril surfaces with their partially processed N-terminal regions. A possible role of these moieties in the regulation of fibril diameter is discussed later. 

Raspanti, M., Alessandrini, A., Gobbi, P., and Ruggeri, A. (1996). Collagen fibril surface TMAFM, FEG-SEM and freeze-etching observations. Microscopy Res. Tech. 35, 87-93. 

For the studied materials D0 amounts typically to 28 to 150 nm. A plot of smax as a function of creep stress a at a given temperature reveals three distinct regimes each with a straight slope (Fig. 12) the slope is related to the energy r necessary to create the craze fibril surface [60,61] ... 

The polycylic fluorphore fluorene has also been assembled on the outside of fibrils constructed from the amyloidogenic TTR105-115 peptide (Channon et al., 2008). The fluroene unit has the ability to drive self-assembly. However, in this case the fluorene unit was attached to the TTR105-115 sequence which was used to drive fibril formation so that the fluorene unit was displayed on the fibril surface. Channon observed the transfer of... 

The amyloidogenic Sup35 protein has been successfully used to immobilize three enzymes bamase, carbonic anhydrase, and glutathione S-transferase (Baxa et al., 2002). Each of these enzymes was linked to the Sup35 sequence which drives assembly creating three different fusion proteins which successfully formed fibrils displaying functional enzymes on the fibril surface. 

Recently, TTR1 fibrils have been decorated with the classic RGD tripeptide motif isolated from fibronectin, which encourages cell adhesion via integrin cell surface receptors (Gras et al., 2008). This bioactive tag was added to the TTR1 sequence which drives fibril assembly and the tag shown to be exposed on the fibril surface and accessible to cells following assembly. The RGD-modified fibrils were bioactive in a cell dissociation assay which measures the ability of fibrils to competitively bind to cells and induce cell detachment from a surface, as illustrated in Figure 19. In... 

Shomer, I., Frenkel, H., and Polinger, C. (1991). The existence of a diffuse electric double layer at cellulose fibril surfaces and its role in the swelling mechanism of parenchyma plant cell walls. Carbohydr. Polym. 16 199-210. 

In the chiton tooth, the organic framework components are synthesized and secreted by the cells into the extracellular space, and there they self assemble. By the time mineralization is about to occur the cells are tens of micrometers away from many of the mineralization sites. They must therefore operate by remote control. The mineralization sites themselves are within a complex chitin framework, the dimensions of which are in the nanometer range. The sea urchin larval spicule represents the exact opposite situation. Mineralization occurs in a vacuole defined by a membrane, and the entire apparatus is within a consortium of fused cells (the syncytium). The membrane of the syncytium tightly surrounds the growing spicule [74], Therefore, it has been proposed that the cells directly control spicule formation. The mineralization vacuole is subdivided by framework proteins. Nothing is known about the structure of the one nucleation site per spicule in the larvae, but in the adult a well-defined location, enclosed within a framework, has been identified as the nucleation site [83]. Dentin formation is intermediate between the two. It is an extracellular process, and the distances between cells or cell processes and mineralization sites are in the range of tens of micrometers or several micrometers respectively. Nucleation occurs within the fibril or at its surface and is associated with a site on the fibril surface some 7 or 8 nm wide [54]. The space available for crystal growth within the fibril is even smaller in one of the dimensions, namely 2 or 3 nm wide. 

The work conducted by Gustafsson et al. [19] evaluated the particle properties and solid-state characteristics of two different brands of microcrystalline cellulose (Avicel PH101 and a brand obtained from the alga Cladophora sp.) and related the compaction behavior to the properties of the tablets. The difference in fibril dimension and, thereby, the fibril surface area of the two celluloses were shown to be the primary factor in determining their properties and behavior. 

FIGURE 5.3 Cellulose microfibril composed of four elementary fibrils, viewed along the chain axes. The unit cell is shown, and the chains on the elementary fibril surfaces are disordered. Chain ends within the elementary fibrils account for more disorder. The surfaces of the crystallites are related to the crystallographic planes shown in gray. 

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