Synthetic microcapsules

Recently, many synthetic polymers such as urea/formalin resin, melamine/formalin resin, polyester, and polyurethane have been widely used as the wall material for the microcapsule, though the gelatin microcapsule is still used. Microcapsules using a synthetic polymer wall have several advantages over those using a gelatin wall (1) the preparation process is simple, (2) the size of the microcapsules is well balanced, (3) the microcapsule concentration can be increased twofold or more and (4) the microcapsules have a high resistance to water and many chemicals. Synthetic microcapsules are prepared by interfacial polymerization or in situ polymerization. 

Other systems which are currently studied as potential drug delivery systems are classified into two groups Firstly carriers which, by nature, form some kind of multi-or unilamellar vesicle, e.g. liposomes, erythrocyte ghosts, synthetic microcapsules, and secondly carriers based on naturally occurring macromolecules such as albumin, DNA, antibodies, Dextran (reviewed in Ref. >). 

Carbonless Copy Paper. In carbonless copy paper, also referred to as pressure-sensitive record sheet, an acid-sensitive dye precursor, such as crystal violet lactone or /V-hen2oy11eucomethy1ene blue, is microencapsulated with a high boiling solvent or oil within a cross-linked gelatin (76,83,84) or in synthetic mononuclear microcapsules. Microcapsules that have a starch binder are coated onto the back of the top sheet. This is referred to as a coated-back (CB) sheet. The sheet intended to receive the image is treated on the front (coated-front (CF)) with an acid. When the top sheet is mechanically impacted, the dye capsules mpture and the dye solution is transferred to the receiving sheet where the acid developer activates the dye. 

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. 

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... 

Palladium nanoclusters in microcapsule membranes from synthetic shells to synthetic cells. 

Although pheromone traps are now widely used for monitoring insect populations, the use of synthetic pheromones in control of insect pests by disruption of pheromone-mediated communication has been much slower to develop, at least in part because of the difficulties of formulation. There are three main types of formulation currently available - hollow fibres, plastic laminates and microcapsules. For several years, the UK Overseas... 

Encapsulant materials can be selected from a wide range of natural or synthetic materials depending on the properties desired in the final microcapsule (Table 24.2). The encapsulant materials in food are more restricted to natural food components (e.g. proteins, sugars, starches, gums, lipids, ceUulosic material) and other ingredients... 

Another coating technique is microencapsulation (see also Section 4.1.3, Figure 94). The technique coats liquid droplets or solid particles and forms microcapsules with diameters between 1 and 5000/im. The coating consists of natural or synthetic polymers and may be dense, permeable, or semi-permeable. Therefore, this technology allows capsules containing a reactive substance to be produced which can be liberated in a controlled fashion by destruction of the skin or by permeation. It is also possible to carry out reactions within the capsules by permeation of reaction partners from the outside. 

Polyelectrolyte complexes can be used as implants for medical use, as microcapsules, or for binding of pharmaceutical products, including proteins. In recent years, a new class of organometallic polymers, polyphosphazenes, has become available. Synthetic flexibility of polyphosphazenes makes them a suitable material for controlled-release technologies. Desirable characteristics of a polymeric system used for drug delivery are as follows ... 

For satisfying amino acid requirements of ruminants, experts developed a procedure, as a result of which the degradation of administered synthetic amino acids takes place in the small- and large intestines and not in the rumen. On the basis of microcapsule coating, the method of dimethionine coating was elaborated, and a plant with several tons of capacity has been established. Daily administration of only a few grams of protected methionine raised milk production by 1.2-1.51/day. 

Microcapsules of synthetic polymer and cyclodextrin Three examples in the literature mention an association between synthetic polymer microcapsules and CyDs [12-14] as a means of encapsulating drugs complexed with CyDs. 

The delivery vehicle of fenvalerate-containing insecticides may account for wide variations in toxic action. For example, fenvalerate microcapsules used to control caterpillar pests (Plutella xylostella, Spodoptera liturd) were most effective with tMn-walled capsules and small particles however, significant protection of nontarget organisms, such as fish, occurred with thicker-walled capsules and larger particles. The popularity of commercial synthetic pyrethroids and their widespread replacement of older, more-toxic compounds in various settings... 

Lensen D, Vriezema DM, van Hest JCM (2008) Polymeric microcapsules for synthetic applications. Macromol Biosd 8 991-1005... 

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