Microcapsules encapsulation

Select the active ingredient (AI) or drug/pesticide product and the microcapsule encapsulating it by evaluating the controlled release of the AI [Muro-Sune et al. (2005)] through the microcapsule. 

Several studies have utilized CLSM techniques to study the distribution and release of biomolecules incorporated in microcapsules and microspheres and to measure the encapsulation efficiency (9,10). Lipophilic fluorophores have been utilized to locate oil-rich regions within mixed-phase microspheres and to examine the distribution of polymeric components with microcapsules. Encapsulated oil could be differentiated from other components, and other fluorescent markers allowed visualization of polymer distribution in the capsule wall (11). The technique has also been used to explore the... 

Kobayashi, M. Iwasaki, H. Manufacture of microcapsule encapsulating color developer by interfacial polymerization suitable for pressure-sensitive copying paper. JP 11290675, 1999. 

Lin, Y.-H. Wei, C.-S. Composition and method for fabricating microcapsules encapsulating phase-change material. US 20080157415, 2008. 

Hu, J. Xia, Z. Situ, Y Chen, H. Mechanical properties of microcapsules encapsulating DCPD with MF. Journal of Chemical industry and Engineering. (2010), 61, 2738-2742. 

As for animal cell entrapment in hydrogel microparticles or microcapsules, encapsulation procedure should proceed under physiological conditions within a short time (20-30 min), in order to provide cell viability, and to be as simple as possible because all manipulations are carried out under strictly sterile conditions. Taking into account all these requirements, it should be noted that the list of polymer materials and methods for animal cell encapsulation is rather limited. So-called alginate-based carriers (microparticles, micro- and nanocapsules) assure the favorable polymer systems for animal cell immobilization. 

Better control over size and properties of microcapsules (encapsulation by interfacial polymerization [26, 27])... 

Encapsulation of PNIPAM inside non-temperature-sensitive (PSS/PAH) capsules templated on PS cores was achieved by the same ship in a bottle synthesis [37], providing temperature-responsive microcapsules. Encapsulated PNIPAM collapsed when the temperature of the system increased above 34 °C, forming discrete particles inside the capsule, without modification of the shell (Fig. 3.6). This prop-... 

Many terms have been used to describe the contents of a microcapsule active agent, actives, core material, fill, internal phase (IP), nucleus, and payload. Many terms have also been used to describe the material from which the capsule is formed carrier, coating, membrane, shell, or wall. In this article the material being encapsulated is called the core material the material from which the capsule is formed is called the shell material. 

Table 1 Hsts representative examples of capsule shell materials used to produce commercial microcapsules along with preferred appHcations. The gelatin—gum arabic complex coacervate treated with glutaraldehyde is specified as nonedible for the intended appHcation, ie, carbonless copy paper, but it has been approved for limited consumption as a shell material for the encapsulation of selected food flavors. Shell material costs vary greatly. The cheapest acceptable shell materials capable of providing desired performance are favored, however, defining the optimal shell material for a given appHcation is not an easy task.

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

Complex Coacervation. This process occurs ia aqueous media and is used primarily to encapsulate water-iminiscible Hquids or water-iasoluble soHds (7). In the complex coacervation of gelatin with gum arabic (Eig. 2), a water-iasoluble core material is dispersed to a desired drop size ia a warm gelatin solution. After gum arabic and water are added to this emulsion, pH of the aqueous phase is typically adjusted to pH 4.0—4.5. This causes a Hquid complex coacervate of gelatin, gum arabic, and water to form. When the coacervate adsorbs on the surface of the core material, a Hquid complex coacervate film surrounds the dispersed core material thereby forming embryo microcapsules. The system is cooled, often below 10°C, ia order to gel the Hquid coacervate sheU. Glutaraldehyde is added and allowed to chemically cross-link the capsule sheU. After treatment with glutaraldehyde, the capsules are either coated onto a substrate or dried to a free-flow powder. 

Interfacial Polymerization. Many types of polymerization reactions can be made to occur at interfaces or produce polymers that concentrate at interfaces thereby producing microcapsules. Accordingly, this approach to encapsulation has steadily developed into a versatile family of encapsulation processes. Figure 4 schematically illustrates five types of encapsulation processes that utilize these types of reactions. 

A key feature of encapsulation processes (Figs. 4a and 5) is that the reagents for the interfacial polymerisation reaction responsible for shell formation are present in two mutually immiscible Hquids. They must diffuse to the interface in order to react. Once reaction is initiated, the capsule shell that forms becomes a barrier to diffusion and ultimately begins to limit the rate of the interfacial polymerisation reaction. This, in turn, influences morphology and uniformity of thickness of the capsule shell. Kinetic analyses of the process have been pubHshed (12). A drawback to the technology for some apphcations is that aggressive or highly reactive molecules must be dissolved in the core material in order to produce microcapsules. Such molecules can react with sensitive core materials. 

Spray Drying. Spray-dry encapsulation processes (Fig. 7) consist of spraying an intimate mixture of core and shell material into a heated chamber where rapid desolvation occurs to thereby produce microcapsules (24,25). The first step in such processes is to form a concentrated solution of the carrier or shell material in the solvent from which spray drying is to be done. Any water- or solvent-soluble film-forming shell material can, in principle, be used. Water-soluble polymers such as gum arable, modified starch, and hydrolyzed gelatin are used most often. Solutions of these shell materials at 50 wt % soHds have sufficiently low viscosities that they stiU can be atomized without difficulty. It is not unusual to blend gum arable and modified starch with maltodextrins, sucrose, or sorbitol. 

Microencapsulation has much hidden potential for the food industry which promises to be tapped in the future (62). An interesting discussion of the problems that have been encountered while attempting to develop microcapsule formulations for commercial use in food products has been presented (65) and a review provides a number of references to food encapsulation studies (66). 

Microcapsules are used in several film coatings other than carbonless paper. Encapsulated Hquid crystal formulations coated on polyester film are used to produce a variety of display products including thermometers. Polyester film coated with capsules loaded with leuco dyes analogous to those used in carbonless copy paper is used as a means of measuring line and force pressures (79). Encapsulated deodorants that release their core contents as a function of moisture developed because of sweating represent another commercial appHcation. Microcapsules are incorporated in several cosmetic creams, powders, and cleansing products (80). 

The US Air Force has studied the encapsulation of liq monoproplnts such as alkyl nitrates in polymer films to form small spheres much like ball powder for use as gun proplnts (Refs 6, 8 9). Suspension coating techniques were used, and microcapsules were made with gelatin,... 

Microcapsules can be used for mammalian cell culture and the controlled release of drugs, vaccines, antibiotics and hormones. To prevent the loss of encapsulated materials, the microcapsules should be coated with another polymer that forms a membrane at the bead surface. The most well-known system is the encapsulation of the alginate beads with poly-L-lysine. 

The interfacial cross-linking polymerization has been demonstrated to be a suitable method for the production of xylan microcapsules with high drug encapsulation efficiency. SD-... 

Because most food matrices are water soluble, many efforts were directed to the formulation of lipophilic pigments (mainly carotenoids) into water-soluble formulations (powders or gels). For hydrophilic pigments like flavonoids, polar dried microcapsules are the most popular ways to stabilize their functionality. Extracts rich in P-carotene were encapsulated using three different encapsulation techniques (spray drying, drum drying, and freeze drying)." ... 

A leuco dye(s) solution in a nonvolatile solvent is encapsulated in microcapsules 5-10 pm in diameter, and after addition of latex and wheat starch, coated (at about 5 g/m2 as dry solid) on a substrate such as paper, synthetic paper, or plastic film, and dried to give the CB sheet. 

Extending these ideas to enzymatic catalysis, Jiang et al. reported the use of protamine-silica hybrid microcapsules in combination with a host gel-like bead structure to encapsulate several enzymes individually in the enzymatic conversion of C02 to methanol [20]. They used a layer-by-layer (LbL) method where alternately charged layers were deposited on an enzyme-containing CaC03 core. The layers, however, were not polyelectrolytes, but protamine and silica (Scheme 5.6). 

Scheme 5.7 Encapsulation of enzyme microcapsules into a gel-like structure (host gel bead) resulting in a capsules-in-bead microreactor. Reproduced from [20] by permission of The Royal Society of Chemistry.

These two seemingly dissimilar applications have a common basis—both are examples of the pressure-sensitive release of a chemical. How are these products designed Tiny spherical capsules (microcapsules or microspheres) with a glass or polymer shell are filled with a liquid core and glued onto paper. For a scratch-and-sniff ad, the core of the microcapsules contains a liquid with the desired scent for carbonless paper, a liquid ink or dye is encapsulated within the... 

Recently, we proposed an alternative process for encapsulating biomacromolecules within PE microcapsules. This approach involves using nanoporous particles as sacrificial templates for both enzyme immobilization and PE multilayer capsule formation (Figure 7.2, route (I)) [66,67]. Unlike previous LbL encapsulation strategies, this approach is not limited to species that undergo crystallization, and is not dependent upon adjustments in electrostatic interactions within PE microcapsules to alter shell permeability characteristics. The salient feature of this method is that it is applicable to a wide range of materials for encapsulation. 

Fig. 7.2 Schematic representation of the procedure for the encapsulation of enzyme in PE microcapsules (I) and preparing nanoporous protein particles (II) using MS spheres as templates.

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