Gelatin 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. 

Gelatin Microcapsules Eurand America (formerly National Cash Register Corp.) Dayton, OH X... 

Hussian, M. R. and T. K. Maji, Preparation of genipin cross-linked chitosan-gelatin microcapsules for encapsulation of Zanihoxylum limonella oil (ZLO) using salting-out method. J. Microencapsul., 25(6) (2008) 414-420. 

Figure 1.12 Gelatin microcapsules containing a phase-change material prepared by the coacervation method (Courtesy C. Habar, Micro-capsules-Technologies).

Li DX, Yan YD, Oh DH, Yang KY, Seo YG, Kim JO, Kim YI, Yong CS, Choi HG. Development of valsartan-loaded gelatin microcapsule without crystal change using hydroxypropyl-methylcellulose as a stabihzer. DrugDeliv. 17 (5) 322-329,2010. 

Huang, K. S., K. Lu, C. S. Yeh et al. 2009. Microfluidic controlling monodisperse microdroplet for 5-fluo-rouracil loaded genipin-gelatin microcapsules. / Control Release 137(1) 15-9. 

Zanthoxylum limonella essential oil Sablnene, Limonene, Terpinen 4 ol glutaraldehyde crosslinked gelatin microcapsules mosquito repellent [12]... 

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.

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. 

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. 

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. 

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,... 

H Takenaka, Y Kawashima, SY Lin. Electrophoretic properties of sulfamethoxazole microcapsules and gelatin-acacia coacervates. J Pharm Sci 70 302-305, 1981. 

The term aqueous phase separation is often more simply described as oil-in-water microencapsulation. The two encapsulation processes described above are examples of this oil-in-water encapsulation. In this process the core material is the oil and it should be immisible in the continuous phase, namely water. A commercial example of aqueous phase separation would be the microencapsulation of an oily flavor such as sour cream with a gelatin wall. These microcapsules would then be dispersed in a dry cake mix. The mechanism of release would be during the moist baking cycle of the cake, moist-heat causing the capsule walls to first swell and then rupture. 

In a microencapsulation method, the encapsulate—usually an oil, flavor, enzyme, or medicinal—is emulsified in a dilute aqueous gelatin sol, a polysaccharide is added, and conditions are adjusted to favor coacervation. The encapsulate should not be truly soluble in the solvent or the cosolutes and the cosolutes should be differentially soluble in the liquid solvent. As much as 60-98% of the labile substance may be harvested by microencapsulation to yield microcapsules in the form of a free-flowing powder (Sirine, 1968). 

The first plot received 500 g.a.i./h of displarlure as NCR gelatin-walled microcapsules containing 2% ai. The formulation, applied as an aqueous suspension, also contained 1 of sticker to aid adhesion of the formulation to foliage. The second plot received 500 g./h. as Herculite Corporation sprayable laminate flakes containing 9.1 ai. The flakes consisted of two layers of vinyl, each 0.08 mm thick on both sides of a central porous layer containing the disparlure the surface area of the flakes was between 7 and 35 mm2 per side. The same sticker as that in the microcapsules was used. The third plot received 330 g.a.i./h as "Conrel" controlled release hollow fibers containing nominally 11.5% ai. a suitable sticker was also incorporated in the formulation. (Note that the use of trade or proprietary names here or elsewhere does not constitute an endorsement by the USDA). 

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