Controlled Release of Enzymes

The enzymes are stabilized due to hydrogen-bonding and electrostatic interactions with NH and SiOH groups. Furthermore, the gels retain a significant amount of water necessary for the stability of the encapsulated biomolecules. As a result, almost all of the enzyme (Kl, 94% K3, 98% K4, 100% K5, 100%) is stable and is released from the gels when placed 

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Exploration of this method for controlled release of enzymes to produce flavors of importance in cheese ripening has been pioneered by Kirby and Law (1986), and was recently the subject... 

The vesicles were separated by centrifugation at 30,000 x g from the enzyme solution. Precipitated PC vesicles underwent a washing process once and were resuspended with the phosphate buffer solution (PBS) and adjusted to 25 ml. Stimuli which have the potential to induce the controlled release of enzyme from PC vesicles in suspension were examined in terms of the releasing pattern. Original vesicles suspensions were stimulated by mixing with an equal volume of a stimulus solution in glass vials with... 

Liposomes have been used for years as components of drug delivery systems, and as transdermal carriers of active ingredients in the cosmetic industry (307, 308). More recently, liposomes have found use in the food and nutritional supplement industries. Keller (308) lists more than a dozen nutritional products on the market that have been formulated with novel liposome-based delivery systems. In the food area, hposomes have been studied for their ability to encapsulate and provide controlled release of enzymes (309, 310), and liposome-encapsulated enzymes have been used to accelerate the ripening of cheese (311). 

Barati, R., Jonson, S.J., McCool, S., Green, D.W., Willhite, G.P, and Liang, J.T. (2011). Fracturing fluid cleanup by controlled release of enzymes for polyelectrolyte complex nanoparticles. Journal of Applied Polymer Science, 121 1292-1298. 

Robert Langer, Polymer Systems for Controlled Release of Macromolecules, Immobilized Enzyme Medical Bioreactors, and Tissue Engineering J. J. Linderman, P. A. Mahama, K. E. Forsten, and D, A. Lauffenburger, Diffusion and Probability in Receptor Binding and Signaling Rakesh K. Jain, Transport Phenomena in Tumors... 

Initially, the sol gel compositions were optimized using Congo red dye as the dopant because of its optical properties. This facilitates monitoring of the release process by optical spectroscopy. Next, the gels were evaluated for their stabilization and release of subtilisin. These sol gel matrices bring about controlled release of the encapsulated enzyme molecules as a response to a change in the water content of the medium (Figure 2.20).15... 

Langer, R. 1994. Polymer systems for controlled release of macromolecnles, immohilized enzyme medical hioreactors, and tissne engineering. In Advances in Chemical Engineering, vol. 19. San Diego Academic Press 1-50. 

Robert Langer, Polymer Systems for Controlled Release of Macromolecules, Immobilized Enzyme Medical Bioreactors, and Tissue Engineering... 

Lipid vesicles have to be stable in either liquid suspension or in dried form with minimal unintentional release of enzyme under usual storage conditions. In addition, enzymes have to be released in a controlled manner. Innovative designs are needed to control release. 

HOLLOW-FIBER MEMBRANES. A hollow-fiher membrane is a capillary having an inside diameter of - inn and an outside diameter < I mm and whose wall functions as a semipermeahlc membrane. The fibers can he employed singly or grouped into a bundle which may contain tens of thousands of fibers and up to several million libers as in reverse osmosis (Fig. 11. In most eases, hollow fibers are used as cylindrical membranes that permit selective exchange of materials across (heir walls. However, they can also he used as containers to effect the controlled release of a specific material, or as reactors to chemically modify a permeate as il diffuses through a chemically activated hollow-liher wall. e g., loaded with immobilized enzyme. 

Substances other than enzymes can be immobilized. Examples include the fixing of heparin on polytetrafluoroethylene with the aid of PEI (424), the controlled release of pesticides which are bound to PEI (425), and the inhibition of herbicide suspensions by addition of PEI (426). The uptake of anionic dyes by fabric or paper is improved if the paper is first catonized with PEI (427). In addition, PEI is able to absorb odorizing substances such as fatty acids and aldehydes. Because of its high molecular weight, PEI can be used in cosmetics and body care products, as well as in industrial elimination of odors, such as the improvement of ambient air quality in sewage treatment plants (428). 

Compound A is a novel poly(ester amide) copolymer that can be used as a bioabsorbable coating for the controlled release of drugs. A is a copolymer of four monomers, two of which are amino acids or amino acid derivatives The body s enzymes recognize the naturally occurring amino acids in the polymer backbone, allowing for controlled enzymatic breakdown of the polymer and steady release of an encapsulated drug. Identify the four monomers used to synthesize A then use Figure 28.2 to name the two amino acids. 

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