Microencapsulation methods

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. 

N Garti, A Aserin. Pharmaceutical emulsions double emulsions and microemulsions. In S Benita, ed. Microencapsulation-Methods and Industrial Applications. New York Marcel Dekker, 1996, pp 411-534. 

Microencapsulation Methods and Industrial Applications, edited by Simon Benita... 

Benita, S., Ed. Microencapsulation, Methods and Industral Applications, Marcel Deker, New York, 1996. 

A problem especially with oxidation catalysts is that the metals in their highest oxidation state tend to be less strongly associated with a support, so that the reaction conditions can lead to leaching of the metal complex from the support. To overcome this problem, microencapsulation, as an immobilization technique for metal complexes, has been introduced by Kobayashi and coworkers. In the microencapsulation method, the metal complex is not attached by covalent bonding but is physically enveloped by a thin film of a polymer, usually polystyrene. With this technique leaching of the metal can be prevented. In 2002, Lattanzi and Leadbeater reported on the use of microencapsulated VO(acac)2 for the epoxidation of allylic alcohols. In the presence of TBHP as oxidant, it was possible to oxidize a variety of substrates with medium to good yields (55-96%) and diastereomeric ratios (60/40 to >98/2) (equation 42). The catalyst is easily prepared and can be reused several times without significant loss in activity. 

Several other investigators have reported microencapsulation methods based upon polyelectrolyte complexes [289, 343]. For example, oppositely-charged polyelectrolytes (Amberlite IR120-P (cationic) and Amberlite IR-400 (anionic)) were recently used along with acacia and albumin to form complex coacervates for controlled release microcapsule formations [343]. Tsai and Levy [344,345] produced submicron microcapsules by interfacial crosslinking of aqueous polyethylene imine) and an organic solution of poly(2,6 dimethyl... 

Modern Pharmaceutics Third Edition, Revised and Expanded, edited by Gilbert S. Banker and Christopher T. Rhodes Microencapsulation Methods and Industrial Applications, edited by Simon Benita... 

Thies, C. (1996) A survey of microencapsulation processes, in Microencapsulation Methods and Industrial Applications (ed. S. Benita), vol. 17, Marcel Dekker, New York, pp. 1-21. 

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). 

Benoit JP.Marchais H.Rolland H,Van de Velde V (1996) In Benita S (ed),Microencapsulation methods and industrial applications. Marcel Dekker, New York, pp 35-72... 

TABLE 3 Factors in Selection of Microencapsulation Method to Prepare Peptide/Protein-Loaded Microspheres... 

Magdassi, S. Vinetsky, Y. Microencapsulation of oil-inwater emulsions by proteins. In Microencapsulation Methods and Industrial Applications Benita, S., Ed. Marcel Dekker, Inc. New York, 1996 21-33. 

Table 1 Selection of microencapsulation methods for drugs with different properties Microencapsulation Technology... 

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