Reservoir-type microcapsules

Yeo, Y. Basaran, O.A. Park, K. A new process for making reservoir-type microcapsules using ink-jet technology and interfacial phase separation. J. Controlled Release 2003, 93 (2), 161-173. 

Mathiowitz [35 0] realizes reservoir-type delivery systems recurring to a photochemical control. Microcapsules, built up by interfacial polymerization of polyamide, also contain azobisisobutyronitrile, a substance that emanates nitrogen due to a photochemical action. Accordingly, after exposition to light, microcapsules internal pressure increases (as a result of nitrogen release) until membrane rupture and consequent contents release. 

FIGURE 11.8 Schematic morphologies of the two types of microcapsules, (a) Core-shell microcapsule or reservoir and (b) matrix type microcapsule. (From Lembo, D. and Cavalli, R., Antivir. Chem. Chemother., 21, 53,2010.)... 

Controlled release formulations are a recent innovation in which the pesticide is incorporated into a carrier, generally a polymeric material (Scher, 1999). The rate of release of the pesticide is determined by the properties of the polymer itself as well as environmental factors. There are mainly two types of CR formulations reservoir devices and monolithic devices. As shown in Figure 2.1, in the reservoir device, the toxicant is enclosed in capsules of thin polymeric material to become microcapsules (1-100 pm in diameter), e.g., Penncap-M microcapsules (methyl parathion). In the monolithic device, the toxicant is uniformly... 

The release rates that are achievable from a single microcapsule are generally 0 order, 1/2 order, or 1st order. 0 order occurs when the core is a pure material and releases through the wall of a reservoir microcapsule as a pure material. The 1/2-order release generally occurs with matrix particles. Ist-order release occurs when the core material is actually a solution. As the solute material releases from the capsule the concentration of solute material in the solvent decreases and a Ist-order release is achieved. Please note that these types of release rates occur from a given single microcapsule. A mixture of microcapsules will include a distribution of capsules varying in size and wall thickness. The effect, therefore, is to produce a release rate different from O , 1/2 , or 1 because of the ensemble of microcapsules. It is therefore very desirable to examine carefully on... 

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