Microencapsulation techniques

Self-life enhancement by preventing degradative reactions (oxidation, dehydration). 

Numerous preparation technologies available for the encapsulation of core material have been reported [81,82,84]. The present discussion focuses on the different microencapsulation techniques that are more relevant to the coating industries, and also provides a comprehensive review of recently developed methods. In general, microencapsulation techniques are divided into two basic groups, namely chemical and physical, with the latter being further subdivided into physico-chemical and physico-mechanical techniques. Some of the important processes used for microencapsulation are summarized in Table 1.1. 

Chemical processes Physical processes Physico-chemical Physico-mechanical 

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The number of microencapsulated commercial oral formulations available and the volume of these formulations sold annuaUy is comparatively smaU. This may reflect the difficulty of developing new dmg formulations and bringing them successfully to market or the fact that existing microencapsulation techniques have had difficulty economically producing mictocapsules that meet the strict performance requirements of the pharmaceutical industry. One appHcation that is a particularly active area of development is mictocapsules or microspheres for oral deUvery of vaccines (45,46). 

Y. (2010). Microencapsulation techniques, factors influencing encapsulation efficiency. Journal of Microencapsulation, Vol. 27, 3, (June 2010), pp. (187-197), ISSN... 

Fig. 10). A phase separation microencapsulation technique was used to formulate nafarelin acetate in 50 50, 69 31, and 45 55 DL-lactide/glycolide copolymers (120). 

Microencapsulation technique, 13 276-277 Microetching techniques, 19 167 Microextraction, solid-phase, 11 518 Microfermenters, 11 14 Microfibers, 11 186, 240 24 613 Microfibrils, 10 283 11 171 Microfilaments, liquid crystal properties in, 15 111-112... 

A very interesting technique that has been used widely in the MTO-catalyzed olefin oxidation reaction is the microencapsulation technique. This technique uses poly(4-vinylpyridine) (PVP), either 2% or 25% cross-linked with divinylbenzene (PVP-2% or PVP-25%, Fig. 4), as well as poly(4-vinylpyridine-/V-oxide) (PVPN-2%, Fig. 4). In addition, 2% cross-linked PS (PS-2%, Fig. 4, X = CH2) and a mixture of PS-2% and PVP-2% (5 1, Fig. 4, X = N) have been used as support polymers. This approach is based on the physical envelopment of the Lewis-acidic MTO by the PS polymer, enhanced by interactions of the 7t-electrons of the phenyl rings with MTO. In the case of the pyridine-containing polymers, Lewis acid-Lewis base interactions between the pyridine moiety and MTO obviously play an important role. In the case of the PVP and PVPN polymers, MTO can be incorporated in the support matrix by mixing the polymer and MTO in ethanol to obtain the desired immobilized catalyst. 

The first heterogeneous osmium catalyst applicable for asymmetric dihydroxylation reactions was described by Kobayashi and coworkers (Table 9, entry 1) [38, 39]. Osmium tetroxide was enveloped in a polymer capsule by microencapsulation techniques [40,41]. The asymmetric dihydroxylation of transmethylstyrene with poly(acrylonitrile-co-butadiene-co-styrene) microencapsulated (ABS-MC) osmium tetroxide as catalyst, NMO as the cooxidant, and (DHQD)2PHAL as the chiral ligand completed in 88% yield with 94% ee [38]. The catalyst and the chiral ligand were reused in five consecutive runs without loss of activity. However, the use of NMO as cooxidant required the slow... 

Poly(carbodiimides) are sometimes used as adhesive primers. Film forming carbodiimide homo- or copolymers have been used in microencapsulation techniques for pressure sensitive copy paper. Oligomeric acylureas are obtained from polyunsaturated carboxylic acids and carbodiimides as monomers for coatings. ... 

Various microencapsulation techniques have been successfully applied for several years in industry, with a large number of patent applications filed to protect market shares and products, particularly in the area... 

Microencapsulation technology has been used from 1930s in packaging flavors and vitamins. Since the first commercial product was introduced for the carbonless copying paper, the technology has advanced to a new level. Various microencapsulation techniques are available nowadays, and the microencapsulated products are widely used in pharmaceutical, biomedical, agricultural, food, consumer products, and cosmetic industries. Representative applications of microparticles in the pharmaceutical and biomedical industries include ... 

With the recent advance of biotechnology and polymer chemistry, the use of microparticle systems will continue to grow for a variety of applications. The objective of this article is to provide a review of the technical aspects of the microencapsulation techniques that have been widely used in the pharmaceutical industry and recent advances of the technology so that the pharmaceutical scientists can take full advantage of the existing assets of this area in developing new microparticle systems. 

Existing microencapsulation techniques have been reviewed extensively,and for this reason, here we will briefly summarize representative microencapsulation techniques. 

The coacervation method is one of the earliest microencapsulation techniques, which has been used for various consumer products. This method is based on separation of a solution of hydrophilic polymer(s) into two phases, which are small droplets of a dense polymer-rich phase and a dilute liquid phase. Coacervation can be divided into simple and complex coacervation depending on the number of polymers that are involved in the formation of microparticles. 

Sah, H. Microencapsulation techniques using ethyl acetate as a dispersed solvent effects of its extraction rate on the characteristics of PLGA microspheres. J. Controlled Release 1997, 47 (3), 233-245. 

Yeo, Y. Chen, A.U. Basaran, O.A. Park, K. Solvent exchange method a novel microencapsulation technique using dual microdispensers. Pharm. Res. 2004, 21 (8), 1419-1427. 

Recently, sodium alginate has been used for the aqueous microencapsulation of drugs, in contrast with the more conventional microencapsulation techniques which use organic-solvent systems. It has also been used in the formation of nanoparticles. ... 

Kim HY, Baianu IC (1991) Novel liposome microencapsulation techniques for food applications. Trends Food Sci Technol 2 55-61... 

Figure 9.12 Microencapsulation technique. [Reproduced with permission from Kobayashi and Akiyama.24]...

Microencapsulation techniques have been developed to enhance the residual activity of the formula ions by placing a thin chemical shell around the synergized pyrethrins. This allows for a sustained release of the insecticide by diffusion through the shell wall for 30 to 60 days. 

Fig. 5 illustrates the granule particle size distribution as a function of gap size between rotor and stator. As can be seen, the average particle size D(50) is approximately equal to the gap size, and the particle size span (ca. 0.5) is very low and independent of gap size. Typically, the concentration of the binder is 25wt%. In all of the known agglomeration and microencapsulation techniques, the concentration of... 

Lee outlines three different physical methods that are commonly utilized for enzyme immobilization. Enzymes can be adsorbed physically onto a surface-active adsorbent, and adsorption is the simplest and easiest method. They can also be entrapped within a cross-linked polymer matrix. Even though the enzyme is not chemically modified during such entrapment, the enzyme can become deactivated during gel formation and enzyme leakage can be problematic. The microencapsulation technique immobilizes the enzyme within semipermeable membrane microcapsules by interfacial polymerization. All of these methods for immobilization facilitate the reuse of high-value enzymes, but they can also introduce external and internal mass-transfer resistances that must be accounted for in design and economic considerations. 

Liu HY, M.Z. Development of a carbon dioxide-based microencapsulation technique for aqueous and ethanol-based latexes. Langmuir 2002 18 6066-6070. 

Coatings and films Most paints and coatings degrade by a photoelectrochemical mechanism. Applications are summarized that include protective coatings for automobiles, encapsulants for microelectronic devices, electrocatalysts, and microencapsulation techniques for controlled release of electroactive components. 

Microencapsulation techniques are now being actively developed along directions that will have an important impact on electrochemically based industries. Possibilities include the masking of particulate surfaces to prevent specific (and undesirable) reactions as well as the controlled release of electroactive components or inhibitors into the environment (24). The following examples illustrate these techniques. 

While many other microencapsulation techniques also use surface and in situ polymerization methods or, generally, interfacial reactions to produce soluble or insoluble and impermeable or permeable capsule walls, in addition to the coating and spray drying methods that were discussed previously, a growing number of processes de-... 

Gutcho M.H. 1976. Microcapsules and Microencapsulation Techniques (Chemical Technology Review series). Noyes Data. 

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