Microcapsules production

Processes based on fluidized bed coating have been developed (49). In this process, the bioactive agent is dissolved in an organic solvent along with the polymer. This solution is then processed through a Wurster air suspension coater apparatus to form the final microcapsule product. A solvent partition technique based on continuous injection of a polymer-drug solution into flowing mineral oil has been reported (50). 

The large number of variables involved in complex coacervation (pH, ionic strength, macromolecule concentration, macromolecule ratio, and macromolecular weight) affect microcapsule production, resulting in a large number of controllable parameters. These can be manipulated to produce microcapsules with specific properties. Complex coacervate microcapsules have been formulated as suspensions or gels, and have been compounded within suppositories and tablets.[ l... 

The development of early encapsulation technology and preparation of microcapsules dates back to 1950s when Green and coworkers produced microencapsulated dyes by complex coacervation of gelatin and gum Arabic, for the manufacture of carbonless copying paper. The technologies developed for carbonless copy paper have led to the development of various microcapsule products in later years. 

An air atomizing nozzle (nozzle diameter = 0.8 mm) was installed over a beaker containing the precipitation bath (pure water). Air pressure was set to 2.5 bar. The air flow at this pressure was 250 L/h. Polymeric solution (15 wt.% PSf, 10 wt.% vanillin, both solved in DMF) was prepared 24 h before microcapsules production and it was kept in a closed, amber bottle in order to avoid its contact with humid atmospheric air that could cause polymer precipitation and to prevent vanillin degradation by U.V. radiation. The polymeric solution microdroplets were projected onto the precipitation bath and immediately, microcapsules were formed. Finally, capsules were collected by filtration and kept into a desiccator. 

Panisello C, Garcia-Valls R. Polysulfone/vanillin microcapsules production based on vapor induced phase inversion precipitation. Ind Eng Chem Res. 2012 51(47) 15509-15516. 

In order to keep alive cells or to avoid denaturation of proteins, DNA or other nonstable BAG, the methods for preparation of nano- or microparticle-based systems should be rather soft providing encapsulation procedure under physiological conditions (pH, temperature, etc.). We cannot describe in detail all methods presently used for bioencapsulation in nano- and microparticles (microcapsules) but would like to discuss some of them which are presently widely employed, or are rather promising to be used in the nearest future. All presently existing techniques for nano- and microcapsule production for biotechnological and biomedical applications are reviewed by Ian Marison et al. [16]. 

Sanchez-Silva L, Sanchez P and Rodriguez IF (2011), Effective method of microcapsules production for smart fabrics, In Marco Aurelio dos Santos Bernardes (eds). Developments in Heat Transfer, Rijeka, Croatia, InTech. 

Microcapsule production Microparticle formation Melt extrusion Melt injection Complex formation Liposomes Micelles... 

Microcapsules are non-dense spherical shaped volumes. They are formed by a shell (polymeric wall in this case) with an empty volume inside that can be used to encapsulate compounds. The structure of the shell (a thin, dense layer, or a thick, porous layer, etc.), together with its nature (chemistry, material), determines the release rate of the encapsulated compound. There are several ways to obtain microcapsules. Some of these methods are based only on physical phenomena, certain are based on polymerization reactions and others combine both physical and chemical procedures. Most authors agree in classifying them all in two different groups chemical processes (like in-situ polymerization or desolvation in liquid media) and mechanical processes (e.g. spray drying or electrostatic deposition) [44]. A novel technology for microcapsule production, based on the employment of microdevices in continuous mode, has been presented [45]. Immersion precipitation is used in this case, in a way similar to that explained for flat membranes. 

The methacrylamide-MA copolymer has also been studied for purification of industrial waste water/ The disodium salt of MA has been copolymerized with the sodium salt of 2-acrylamido-2-methyl-propanesulfonic acid, using peroxide initiators, to give useful dispersant and deflocculants for water-insoluble compounds of Fe, Ca, Al, and for silt and clay particles/" The copolymers also prevent boiler scale formation, corrosion, etc., without being affected by the hardness of the water. Copolymers prepared in aqueous solutions are claimed to be useful in well wall materials, coatings for microcapsule production, and for paper dry-strength agents. 

Albumin Acacia Complex Coacervation and Microcapsule Production... 

Microencapsulation by coacervation is a common method for microcapsules production. It can be achieved by employing different methods, where the most common one is formation of an insoluble complex of two oppositely charged polymers and its subsequent deposition at surface of dispersed particles (e.g. emulsified oil droplets). In this way, microcapsules with coacervate shell are formed. Composition and microstructure of the coacervate shell are key to determine properties and application of microcapsules. 

Fig. 4. Schematic diagrams that illustrate the different types of interfacial polymerization reactions used to form microcapsules. Reactants X, Y polymerization product (X — Y)—n or —(X—See text for descriptions of cases (a)—(e).

Microcapsules are used in a number of pharmaceutical, graphic arts, food, agrochemical, cosmetic, and adhesive products. Other specialty products also exist, thus the concept of microencapsulation has been accepted by a wide range of industries. In order to illustrate how microcapsules are used commercially, it is appropriate to describe a number of commercial microcapsule-based products and the role that microcapsules play in these products. 

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 formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

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-... 

Microcapsules of PCL and its copolymers may be prepared by aircoating (fluidized bed), mechanical, and, most commonly, solution methods. Typically, the solution method has involved emulsification of the polymer and drug in a two-phase solvent-nonsolvent mixture (e.g., CH2Cl2/water) in the presence of a surfactant such as polyvinyl alcohol. Residual solvent is removed from the tnicrocapsules by evaporation or by extraction (70). Alternatively, the solvent combination can be miscible provided one of the solvents is high-boiling (e.g., mineral spirits) phase separation is then achieved by evaporation of the volatile solvent (71). The products of solution methods should more accurately be called microspheres, for they... 

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... 

Encapsulation within an enteric coat (resistant to low pH values) protects the product during stomach transit. Microcapsules/spheres utilized have been made from various polymeric substances, including cellulose, polyvinyl alcohol, polymethylacrylates and polystyrene. Delivery systems based upon the use of liposomes and cyclodextrin-protective coats have also been developed. Included in some such systems also are protease inhibitors, such as aprotinin and ovomucoids. Permeation enhancers employed are usually detergent-based substances, which can enhance absorption through the gastrointestinal lining. 

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