Controlled release formulation microencapsulation

Microspheres and microcapsules of lactide/glycolide polymers have received the most attention in recent years. Generally, three microencapsulation methods have been employed to afford controlled release formulations suitable for parenteral injection (1) solvent evaporation, (2) phase separation, and (3) fluidized bed coating. Each of these processes requires lactide/glycolide polymer soluble in an organic solvent. 

Sol-gel microencapsulation in silica particles shares the versatility of the sol-gel molecular encapsulation process, with further unique advantages. Sol-gel controlled release formulations are often more stable, potent and tolerable than currently available formulations. The benefits of microencapsulation can be customized to deliver the maximum set of benefits for each active ingredient. Overall, these new and stable combinations of active pharmaceutical ingredients (APIs) result in improved efficacy and usability. 

Kaeser-Liard, B. Kissel, T. Sucker, H. Manufacture of controlled-release formulations by a new microencapsulation process, the emulsion-induction technique. Acta Pharm. Technol. 1984, 30 (4), 294-301. 

An important application in agrochemicals is that of controlled-release formulations. Several methods are used for controlled release, of which microcapsules (CS) are probably the most widely used. These are small particles with size range 1-1000 pm consisting of a core material and an outer wall. The latter isolates the core material from the environment and protects it from degradation and interaction with other materials. The core active ingredient is designed to be released in a controlled manner as required. Microencapsulation of agrochemicals is usually carried out by interfacial condensation, in situ polymerization or coacervation, all of which are determined by the interfacial properties. 

Y. Blatt, E. Kimmehnan, D. Cohen, A. Rotman, Microencapsulated and controlled- release formulations of isoflavones from em-iched frachons of soy and other plants, US Patent No. 6,890,561 Bl, assigned to Bio Dar Ltd., Yavne, IL, May 10,2005. 

The product of an emulsion polymerization is known as a latex— polymer particles on the order of 0.05-0.15 pm stabilized by the surfactant. These latexes are often important items of commerce in their own right (think of latex paints or white glue). This process can also be modified slightly for microencapsulation purposes, with the polymer forming a shell surrounding an inner fill material (these capsules are then used in controlled release formulations in a number of fields). 

Sugar-coated products have been marketed that contain KCl in a wax matrix (Slow-K and Kaon-Ct) and are purportedly slow- and controlled-release preparations. Available evidence indicates that these slow-release forms of KCl are occasionally capable of causing local tissue damage and therefore prol5ably should be used with caution for K+ supplementation. Solutions of potassium gluconate, like the tablets, also have been associated with intestinal ulceration. Microencapsulated KCl preparations Micro-K, K-Dur) that are neither enteric coated nor contained within a wax matrix appear to be superior to the wax matrix formulation. 

Microcapsules represent an extra degree of freedom in the formulation or development of these food products. Many of the reasons or causes for the use of microcapsules are covered in a previous symposium (1) and a continued updated review on this subject (2). The use of microcapsules is one means of achieving controlled release of the core or inner material. The term controlled release actually covers a wide range of technologies and microencapsulation is one way of achieving controlled release. In fact, microencapsulation is the dominant means for achieving controlled release both in product volume and dollar value. 

Two distinct controlled release technologies are encapsulation of liquid pesticides and the coating of individual pesticide crystals. Encapsulation of liquid pesticides is an established tool for modem formulators. Commercial microencapsulated pesticide products exist and new developments continue to be made. Coating of individual pesticide crystals without their aggregation is more difficult. While new processes do exist to coat pesticide crystals without aggregation these processes have not yet been utilized to create commercial pesticide products. 

The Proceedings of the International Symposium on the Controlled Release of Bioactive Materials published annually since 1973 (Controlled Release Society, Deerplain, 111.), and the Volumes on Pesticide Formulations and Application Systems (eg, Vol. 13, ASTM STP 1183,1993 American Society for Testing and Materials, Philadelphia, Pa.) are useful sources, as are some issues of the following journals Journal of Controlled Release Journal of Microencapsulation Journal of Agricultural and Food Chemistry Chemosphere and Pest Management Science. 

Al-Qadi S, Grenha A, Carrion-Recio D, Seijo B, Remunan-Lopez C. Microencapsulated chitosan nanoparticles for pulmonary protein delivery In vivo evaluation of insulin-loaded formulations. J Control Release. 2012 157(3) 383-90. 

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