Microcapsule applications

Sakai, S., Ono, T., Ijima, H. and Kawakami, K. (2001) Synthesis and transport characterization of alginate/ aminopropylsilicate/alginate microcapsule application to bioartificial pancreas. Biomaterials, 22, 2827-2834. 

From the experimental results obtained it seems clear that more work has to be done in the field of microcapsules application to optimize the process. In our opinion, more robust arguments are needed at an experiment level in onier to quantify the benefits of smart textile vvdth specific active principles incorporated. 

Microcapsules are incorporated in a number of products produced by the pharmaceutical, graphic arts, food, agrochemical, cosmetic, and adhesive industries. In order to illustrate the wide range of microcapsule applications, it is appropriate to describe briefly a number of commercial microcapsule-based products and the role that microcapsules play in these products. 

Biomedical and Biotechnology. The use of microcapsules for a variety of biomedical and biological applications has been promoted for many years (42,43). Several biomedical microcapsule applications are in clinical use or have approached clinical use. One application is the use of liquid-filled microcapsules or microbubbles as ultrasoimd contrast agents. Such microcapsules can be formed in several different ways (44). Perfluorocarbon-gas-filled microbubbles with ahiunan albumin shell (45) are FDA (U.S. Food and Drug Administration) approved. 

In addition to a block copolymer, a microcapsule was made from suspension interfacial polycondensation between diacid chloride having aromatic-aliphatic azo group and aliphatic triamine [70,71]. The capsule was covered with a crosslinked structure having an azo group that was thermally stable but sensitive to light so as to be applicable to color photoprinting materials. 

At present there is no reason evident why poly(N-acylhydroxy-proline esters) should not be suitable for the formation of microcapsules or microspheres as well. For microencapsulated drug fonmula-tions the longer degradation times of poly(N-acylhydroxyproline esters) as compared to poly (lactic acid) could again be a distinctive advantage for long-term applications. 

The CB sheet is coated on the back with microcapsules 5 to 10 pm in diameter, in which leuco dye solution in a nonvolatile solvent is contained. The CF sheet is coated on the front with an acidic coreactant such as reactive clay, zinc salt of salicylic acid derivatives, zinc-modified phenolic resin, etc. On the application of pressure, the microcapsule is ruptured in the area delineated by the pressure pattern, and the leuco dye solution is thereby transferred to the CB sheet to bring about a color-forming reaction with acidic coreactant resulting in a distinct image on the surface of the CF sheet. By inserting a middle sheet (or sheets) called the CFB sheet, which is coated on the front and back with acidic coreactant and microcapsules, respectively, multiple copies can be obtained. 

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. 

Various techniques have been developed for the preparation of microcapsules with diameters of 1-5000 pm one of these involves the method of interfacial polycondensa-tion.The following example describes the microencapsulation of a dyestuff, which has practical application in the manufacture of carbon-free copy paper. 

Microcapsule properties make them attractive materials for a wide variety of practical applications. In the area of catalysts, microcapsules provide semipermeable membranes that are readily produced and dispersed. These properties, along with others, have inspired systems that include synthetic or man-made encapsulated catalysts, such as organocatalysts, metal particles, enzymes, and organometallic... 

Gao CY, Donath E, Mohwald H, Shen JC. Spontaneous deposition of water-soluble substances into microcapsules phenomenon, mechanism, and application. Angew Chem Int Ed 2002 41 3789-3793. 

Carbonless copy paper is by far the largest single commercial application of microcapsules. This product consumes thousands of tons of capsules annually. Figure 2. a schematic diagram of a three-part business form, illustrates the concept of carbonless copy paper. 

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