Surface-active ceramics

Bioglasses are surface-active ceramics that can induce a direct chemical bond between an implant and the surrounding tissue. One example is 45S5 bioglass, which consists of 45% Si02, 6% 4.5% CaO, and 24.5% Na20. The various calcium phosphates have exceUent compatibUity with bone and... 

Neo, M., Kotani, S., Yamamuro, T., Ohtsuki, C., Kokubo, T. and Bando, Y. (1992) A comparative study of ultrastructures of the interfaces between four kinds of surface-active ceramic and bone. Journal of Biomedical Materials Research, 26, 1419-1432. 

Relatively inert ceramics elicit minimal tissue response and lead to a thin layer of fibrous tissue immediately adjacent to the surface. Surface-active ceramics are partially soluble, resulting in ion-exchange and the potential to lead to a direct chemical bond with bone. Bulk bioactive ceramics are fiilly resorbable, have much greater solubility fiian surface-active ceramics, and may ultimately be replaced by an equivalent volume of regenerated tissue. The relative level of bioactivity mediates the thickness of Ae interfacial zone between the biomaterial surface and host tissue (Fig. 13.1). There are, however, no standardized measures of reactivity, but the most common are pH changes, ion solubility, tissue reaction, and any number of assays that assess some parameter of cell function. 

Neo, M., Kotani, S., Fujita, Y., et al. (1992). Differences in ceramic bone interface between surface-active ceramics and resorbable ceramics - a study by scanning and transmission electron-microscopy. J. Biomed. Mater. Res. 26 (2), 255-267. 

Initially in ceramic powder processing, particle surfaces are created tliat increase tlie surface energy of tlie system. During shape fomiing, surface/interface energy and interiiarticle forces are controlled witli surface active additives. 

Poly(vinyl alcohol) will function as a non-ionic surface active agent and is used in suspension polymerisation as a protective colloid. In many applications it serves as a binder and thickener is addition to an emulsifying agent. The polymer is also employed in adhesives, binders, paper sizing, paper coatings, textile sizing, ceramics, cosmetics and as a steel quenchant. 

Microelectronic circuits for communications. Controlled permeability films for drug delivery systems. Protein-specific sensors for the monitoring of biochemical processes. Catalysts for the production of fuels and chemicals. Optical coatings for window glass. Electrodes for batteries and fuel cells. Corrosion-resistant coatings for the protection of metals and ceramics. Surface active agents, or surfactants, for use in tertiary oil recovery and the production of polymers, paper, textiles, agricultural chemicals, and cement. 

Membrane reactors can be considered passive or active according to whether the membrane plays the role of a simple physical barrier that retains the free enzyme molecules solubilized in the aqueous phase, or it acts as an immobilization matrix binding physically or chemically the enzyme molecules. Polymer- and ceramic-based micro- and ultrafiltration membranes are used, and particular attention has to be paid to the chemical compatibility between the solvent and the polymeric membranes. Careful, fine control of the transmembrane pressure during operation is also required in order to avoid phase breakthrough, a task that may sometimes prove difficult to perform, particularly when surface active materials are present or formed during biotransformahon. Sihcone-based dense-phase membranes have also been evaluated in whole-cell processes [55, 56], but... 

Formation of micron and submicron size particles has become particularly important in the material-research and processing. The small size, high surface and surface activity of these crystals and nanocrystals determine their various applications as catalysts, ceramics, electronics, pharmaceuticals, cosmetics etc. and this may explain the world-wide increasing research activities to find the suitable crystallization modes and techniques for processing them [1,2]. 

This special class of brazes reacts chemically with the surfaces of ceramic components to produce wettable products with metallic characteristics, such as TiO, TiC x or TiN x as described in Sections 6.3 and 7.2. Thus the wetting is due to an in situ metallization . By definition, the brazes must contain chemically reactive elements such as Ti that are often added to eutectic brazes similar to those developed for joining metal components. Many sessile drop experiments have shown that active metal brazes can wet a wide range of ceramics when a suitable inert environment is used. Particularly high standards of environmental inertness... 

Gross, U., Kinne, R., Schmitz, H.J., and Strunz, V. (1988) The response of bone to surface active glass/glass-ceramics. CRC Crit. Rev. Biocompat., 4 (2), 25—30. 

The mechanism of action of carboxymethylcellulose (CMC) will be discussed here as an example. Here carboxylic acid group — COOH has a surface active effect with respect to the ceramic particle surface by reacting to form hydrogen bonds with the surface groups of the ceramic particle. The free OH groups of the cellulose molecule act like those of polymeric alcohols with respect to the addition of water molecules. 

Examples HA/autogenous bone surface-active glass ceramics/ poly(methyl methacrylate) (PMMA) surface-active glass/ metal fibers polylactic acid (PLA)Zcarbon fibers PLA/HA PLA/calcium/phosphorus-based glass fibers Tissue attachment Depends on materials... 

Uses Corrosion inhibitor in household cleaners, ceramic tile cleaners, bowl cleaners, petrol, refining equip., HCI sol ns. for industrial cleaning and oil-well acidizing detergent, dispersant for scales in refinery systems surface-active film-former Trade Name Synonyms Polyrad 0515 [Hercules http //WWW. here, com]... 

Porous membrane modules were therefore effectively used in bioreactors as an alternative to direct two-liquid contact systems, as long as phase breakthrough was avoided. This required a careful control of the transmembrane pressure, particularly if surface-active material was produced during bioconversions [126,184, 187]. Fouling problems also developed in membrane-assisted multi-phase separation systems. This was observed by Conrad and Lee in the recovery of an aqueous bioconversion product from a broth containing 20% soybean oil by using ceramic membranes fouling was caused mainly by soluble proteins and surfactants [188]. 

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