Hollow fiber structure

Of special interest to intercalation studies are complex non-stoichiometric systems, such as the so-called misfit layer chalcogenides that were first synthesized in the 1960s [45]. Typically, the misfit compounds present an asymmetry along the c-axis, evidencing an inclination of the unit cell in this direction, due to lattice mismatch in, say, the -axis therefore these solids prefer to fold and/or adopt a hollow-fiber structure, crystallizing in either platelet form or as hollow whiskers. One of the first studied examples of such a misfit compound has been the kaolinite mineral. 

Fig. 2.18 Schematic representation of the creation of silica structures from the organogel state of 47 (upper), 45 (middle) and 46 (lower) by sol-gel polymerization, (a) gelators, (b) sol-gel polymerization of TEOS and adsorption onto the gelator superstructures and (c) single hollow fiber structure (upper), spherical structure (middle) and lotus-like structure (lower) of the silica materials formed after calcination.

The UF unit placed in the final stage of the poUshing system has an important function as a final filter to remove particles up to 50-nm size. The UF unit also completely eliminates bacteria from the system. The spiral-type UF imit has a compheated structure that allows particle leakage. On the other hand, the hollow-fiber structure is simple and capable of removing particles completely (Yabe, 1993). Consequently, hollow-fiber-type UF units are widely used in the polishing section of the ultrapure water systems. This ultrafiltration unit should possess the following necessary characteristics (Ishikawa, 1993) ... 

Figure 31.10 Schematic diagram of the influence of shrinkage percentage on dual-layer hollow-fiber structure (Li et al., 2004a).

TFF module types include plate-and-frame (or cassettes), hollow fibers, tubes, monoliths, spirals, and vortex flow. Figures 20-52 and 20-53 show several common module types and the flow paths within each. Hollow fiber or tubular modules are made by potting the cast membrane fibers or tubes into end caps and enclosing the assembly in a shell. Similar to fibers or tubes, monoliths have their retentive layer coated on the inside of tubular flow channels or lumens with a high-permeability porous structure on the shell side. 

DTI has already been demonstrated to be effective in analyzing the internal micro structure of different tissues. For instance, orientation of nerve fiber bundles in the white matter of the brain or hollow fiber orientations in material science can be visualized using DTI [11],... 

The main difference between titania nanotube and the ID nanostructures discussed before is the presence of an hollow structure, but which has significant consequences for their use as catalytic materials (i) in the hollow fiber nanoconfinement effects are possible, which can be relevant for enhancing the catalytic performance (ii) due to the curvature, similarly to multi-wall carbon nanotubes, the inner surface in the nanotube is different from that present on the external surface this effect could be also used to develop new catalysts and (iii) different active components can be localized on the external and internal walls to realize spatially separated (on a nanoscale level) multifunctional catalysts. 

A completely different approach was taken by Koresh and Soffer (1980, 1986, 1987). Their preparation procedure involves a polymeric system like polyacrylonitrile (PAN) in a certain configuration (e.g. hollow fiber). The system is then pyrolyzed in an inert atmosphere and a dense membrane is obtained. An oxidation treatment is then necessary to create an open pore structure. Depending on the oxidation treatment typical molecules can be adsorbed and transported through the system. 

Koresh and Soffer (1983) developed a hollow-fiber gas separation membrane. In principle, polymeric hollow fibers can be porous (macroporosity) or dense. On thermal treatment in vacuum (pyrolysis) a second structural feature, the so-called ultramicroporosity (Koresh and Soffer 1983) was observed. This is due to small gaseous molecules channeling their way out of... 

Hollosep High Rejection Type is characterized by Cellulose Tri Acetate (CTA) hollow fiber with dense membrane structure and high salt rejection, and also by the module configuration favorable for uniform flow of feed water through hollow fiber layers (5 ). These features suggest that Hollosep may be operated under the conditions of higher recovery ratio compared to conventional conditions. 

The success of Matsushita s method and the encouraging developments in our laborabory set the stage for a decade of independent research into what we see as the best technology for the development of a liver-assist device. In a sense, Matsushita s work confirmed the structure of the device and our work confirmed the chemistry of the surface. Matsushita continued his work without the benefit of our technology and has successfully demonstrated the use of his device in a dog model. In a 1999 report, an artificial liver was reported to be equal, and probably superior to the most successful hollow-fiber device. 

The most advanced technology is the extracorporeal hollow fiber reactor. It is currently in Phase III trial and achieved a good Phase II record to support it. Other techniques including a polyurethane system devised in Japan and encapsulated hepatocytes from UCLA are or were in large animal trials. Whether a device is extracorporeal or is intended for implantation, clinical significance requires a suitable scaffold to support a sufficiently large colony of hepatic cells. For both extracorporeal and implant use, the physical structure of the scaffold must meet certain requirements of strength, void volume, biocompatibility, and other parameters. 

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