Process for the preparation of microcapsules or liposomes of con

Details Process for the preparation of microcapsules or liposomes of con Process for the preparation of microcapsules or liposomes of con

1994-12-13

1998-08-11

Kishore, Gollamudi S.

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Liposomes

4284022, 264 41, 264 43, 264 432, 424489, A61K 9127

Patent

active

057924724

DESCRIPTION:

BRIEF SUMMARY
This application is a 37 of PCT/FR93/00035 filed Apr. 2, 1993.
The subject of the present invention is a process for the preparation of microcapsules or liposomes of controlled size by application of a shearing having a constant shear rate to a lamellar phase.
Microcapsule is understood to mean a particle of micron size (0.1 to 10 .mu.m), closed by one or a number of double layers (constituting the membrane) composed of at least one type of surface-active agent (molecule composed of a lipophile part and another hydrophile part which settles at interfaces). This or these membrane(s) enclose(s) in the space a volume of solvent, isolated from the remainder of the solution, which is the encapsulated volume. The encapsulation yield is defined as the percentage of encapsulated volume with respect to the total volume of solvent.
In the specific case of surface-active agents of lipid origins, especially phospholipids, these capsules are known as liposomes.
Many methods for the preparation of microcapsules and liposomes have been described in the literature. The methods proposed include especially methods based on the mechanical dispersion of the surface-active agent(s) in a solvent, methods for the preparation of emulsions of a volatile organic solvent in an aqueous solvent and then evaporation of the organic part, and methods by polymerization of a monomer such as acrylic acid (for example, BE-A-808,034, FR-A-2,504,408, U.S. Pat. No. 3,242,051 or U.S. Pat. No. 4,637,905).
In the case of liposomes, the processes described generally contain methods by emulsification (for example, FR-A-2,315,991, FR-A-2,399,242 and FR-A-2,521,565).
These methods lead, in the best cases, to encapsulation levels of the order of 50% and to relatively polydispersed particles.
The present invention proposes a simple method for the preparation of very concentrated monodispersed microcapsules at a very high encapsulation yield (more than 90%), while controlling very precisely the size of the microcapsules.
This result is obtained by subjecting a single-phase, liquid crystal, lamellar phase to a shearing having a constant shear rate which is homogeneous in space.
This result is astonishing because those skilled in the art would have logically thought that the application of a shearing having a constant shear rate to a lamellar phase would have led to an at least partial orientation of this phase rather than to the manufacture of small isotropic particles of given size.
The subject of the invention is therefore a process for the preparation of microcapsules of controlled sizes, in which a homogeneous, liquid crystal, lamellar phase is prepared comprising at least one surface-active agent and at least one solvent and, if appropriate, a substance intended to be encapsulated, characterized in that this lamellar phase is subjected to a shearing having a constant shear rate.
In a first stage, a homogeneous lamellar phase is prepared consisting of at least one type of surface-active agent (ionic or nonionic) in at least one type of solvent (especially water or a saline or alcoholic aqueous solution). A lamellar phase is defined by a regular stacking of membranes separated by a solvent. This is a liquid crystal phase (smectic-A), characterized by a solid nature in the direction perpendicular to the membranes and a liquid nature in the other two directions. The concentrations are chosen according to the phase diagram of the system which localizes the stability region of the lamellar phase. Generally, this lamellar phase exists in all the surface-active agents/water systems at high concentrations of surface-active agents (>30% by weight). In certain cases, this lamellar phase persists at much lower concentrations of surface-active agents (as far as less than 1-10%).
In practice, 0.5 to 50% by weight especially of surface-active agents with respect to the lamellar phase can be used. These surface-active agents can be both ionic (derivatives of optionally alkoxylated fatty acids, sulphonates, quaternary ammonium derivatives, and the like) and nonion

REFERENCES:
patent: 5091111 (1992-02-01), Neumiller
"Pharmazeutische Technologie", Georg Thieme Verlag, Stuttgart, Germany, 1991 by H. Sucker et al. pp. 5 and 6.
Fukuda, J. Am. Chem. Soc. 108, 2321-2327, 1986.

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