MICROENCAPSULATION — technological process of a covering of small amounts firm, liquid or gases thin cover of film-forming material.
Microcapsules have an appearance of separate particles of spherical shape or agglomerates of particles with a diameter from 5 to 5000 microns. In pharm. to practice microcapsules of 100 in size — 500 microns are most common.
Contents of microcapsules make from 15 to 99% of their weight and can represent individual substance, mix, dispersions or solutions of substances.
The cover of microcapsules can be various thickness (0,1 — 200 microns), single-layer or multilayer, elastic or rigid, with various resistance to influence of water, organic solvents, heating, pressure etc. Mechanical strength, thickness, permeability and other properties of covers are defined by hl. obr. quality of polymeric material and tekhnol, way of production of microcapsules.
As material for covers of microcapsules use gelatin, albumine, casein, arabic gum, shellac, cellulose derivatives (methyl - ethyl - acetyl - atsetoftalat-, nitrate - and carboxymethylcellulose), polyvinyl alcohol, polyepoxides, polyamides, polyethers, polysiloxane, polyvinylchloride, paraffin, etc.
Release of substances comes from microcapsules at a gap or dissolution of covers, and also by diffusion.
Tekhnol, process of receiving microcapsules consists of preparation of the encapsulated substance (crushing, dispersion) and training of filming agent (dissolution), M.'s implementation, after-treatment of microcapsules (hardening of covers, washing, drying), regeneration of by-products.
On the mechanism of film formation tekhnol, ways M. can be divided into three basic groups: M from solutions of polymers due to regulation of size of solubility of polymeric material in solvent (allocation of a new phase in an aqueous medium, the environment of an organic liquid, etc.); M from fusions of polymeric materials; M due to polymerization or polycondensation of low-molecular substances — components of polymeric materials.
In chemical - pharm, the industries the method M. can be used by production of nek-ry medicines. This method allows to transfer medicinal substances from liquid state to firm loose bodies that facilitates their dosing, use, packing, storage and processing in ready dosage forms (see). Besides, by M. it is possible to receive the drugs releasing biologically active agents in certain departments went. - kish. a path, and also drugs with a controlled speed of release of active agents, edges is defined by permeability and thickness of a cover of microcapsules, solubility of the encapsulated drug in surrounding liquid and permeability of a cover for solution of substance.
The method M. can be used for receiving drugs of long action from the medicinal substances having short effect.
During the receiving medicines by method M. it is possible to reduce irritant action of a number of medicinal substances (e.g., acetilsalicylic to - you), to mask off-flavor and a smell (fish oil, castor oil, extract of an aloe, levomycetinum), to lower a volatility (menthol, marked salicylate), to isolate the medicinal substances reacting among themselves, to protect them from influence of environmental factors, to stabilize unstable medicines (serums, vaccines, enzymes) or the reagents used in medicine (e.g., for production of analyses of urine, blood).
Bibliography: In a k a n J. A. a. Anderson J. L. Capsules, in book: Theory a. practice of industrial pharm., ed. by L. Lach-shap and. lake, p. 420, Philadelphia, 1976, bibliogr.
G. Gryadunova. A. B. Davydov, V. D. Solodovnik.