Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1998-07-21
2001-06-05
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S402240, C428S403000, C428S407000
Reexamination Certificate
active
06242099
ABSTRACT:
The present invention relates to the field of microcapsules containing a hydrophobic (or liposoluble) substance of interest.
It also relates to a process for the preparation of these microcapsules and to the application of the latter in cosmetics and pharmaceuticals, in particular.
The use of water-in-oil or oil-in-water emulsions, or of alternative forms of the latter, are advantageous solutions when it is desired to bring liposoluble active compounds into contact with the skin. This technique, which is widely used for cosmetic and pharmaceutical care purposes, reaches its limits when, for example, the molecule must not spread into the horny layers or evaporate or be removed in any other way.
The use of microcapsules or nanocapsules (hereinafter defined by the generic term “microcapsules”) containing liposoluble derivatives is an advantageous alternative to emulsions, in particular when it is desired to make the contact of a molecule with the dermis lasting. Well controlled, the capsules can trap active principles, keeping them isolated or releasing them as desired.
This is because while, for certain derivatives, it is essential to keep them concentrated in order to retain the effectiveness thereof, indeed to increase it, their diffusion with time is desirable for other derivatives. The use of encapsulated molecules makes possible one or the other.
In particular, in the field of anti-sun protection, accelerated skin aging and detrimental changes due to UVA and UVB radiation have made people aware of the dangers of solar radiation and increased the need for protective creams. The main active components of these cosmetics are sunscreens which, although very efficient, are not always very well tolerated by all skin types.
In order to limit, if not overcome, this difficulty, it appears desirable to decrease the contact with the skin during the application of these products by trapping the screening agents in capsules.
Provision has for example been made, in Patent Application EP-A-0,509,904, for microcapsules containing a sunscreen obtained by complex coacervation by means of two colloidal aqueous solutions containing polymers of opposite electrical charge.
Complex coacervation is generally applied to the encapsulation of a material of lipophilic nature emulsified in an aqueous solution of polymers which are intended to form the wall of the microcapsules.
This is because it is generally known that, when two colloidal aqueous solutions respectively containing an anionic polymer and a cationic polymer are mixed in the presence of an emulsified liquid or of a suspended solid, a coacervate is formed deposited around the liquid or solid cores, to form a liquid wall isolating them from the medium. In situ curing of this liquid wall by a crosslinking agent appropriate to the nature of the polymers makes it possible to obtain stable suspended microparticles.
These microparticles are generally formed based on gelatin as cationic polymer and on polysaccharide as anionic polymer.
It is generally possible to produce, by coacervation, capsules with variable sizes in the region of 10 to 100 &mgr;m.
These systems are not completely satisfactory, due either to the type of polymers used to produce the membrane, such as collagen, gelatins, guars or gums arabic, alone or as a mixture, or due to the sizes obtained, when polysaccharides are used, for example.
This is because, in order for protection to be efficient and to no longer result in skin intolerance, the capsules must be particularly impermeable. Moreover, for the photochemical efficiency to endure, at the same concentration, the screening agents must be as fully dispersed as possible and not able to be diluted and the capsules must be as small as possible.
Moreover, the size is an essential factor in the efficiency of the screening agent. The smaller the size, the greater the protection.
It is also possible to produce solid matrix systems, of very small size, of less than a micron, from waxes which have been melted beforehand, emulsified and cooled. Nevertheless, these drastic techniques give permeable spheres which are unstable in conventional cosmetic formulations. Their short lifetime limits their interest.
Such a preparation is described, for example, in Patent Application WO-A-95/28912.
It has now been found, unexpectedly, that it is possible to prepare capsules made of chitin or of one of its derivatives, with a size of less than one mm, which meet both the requirements of impermeability and of very small size and which have an organic biocompatibility which ensures their harmlessness.
Chitin is the structural polymer of arthropods, crustaceans and insects and forms part of the membrane of certain fungi. It provides the endoskeleton of cephalopods with strength. It is in the animal world the counterpart of cellulose in the plant kingdom.
Its distinctive feature is its chemical inertia. It shows little reactivity, is insoluble in most known organic solvents and cannot, either, be thermoformed. It is only by converting it to chitosan that it becomes possible to make use of it.
It is necessary, to modulate the chitin, to proceed in two stages. The first consists in converting the chitin to chitosan and then the second in reconverting the chitosan to chitin.
A description is thus given, in Patent Application EP-A-0,013,181, page 2, of a preparation of chitin by N-acetylation of chitosan with acetic anhydride in a pyridine solution or a perchloric acid solution.
Chitin derivatives have also been prepared. Patent Application EP-A-0,013,181 describes the preparation of N-acetyl carboxyalkylchitin by acetylation of deacetylated carboxyalkylchitin with an anhydride of an organic acid. Other chitin derivatives are also mentioned, such as hydroxyalkylchitins. The material obtained can be shaped as spherical particles which can be used as ion-exchange resins.
Patent Application EP-A-0,021,750 describes a process for the preparation of chitin by acylation of deacetylated chitin in the presence of an organic acid anhydride and of a suspending agent, such as a sorbitan monoester.
Patent Application EP-A-0,026,618 describes a material comprising a mixture of two or more etherified chitin derivatives obtained by the same acetylation process indicated for the two abovementioned documents. The spherical materials obtained can in particular be used as ion-exchange resins.
However, these documents do not in any way describe microcapsules made of chitin or of chitin derivatives.
The Inventors have demonstrated, unexpectedly, that it is possible to convert, in a stable way, an alkyl sulphate or aryl sulphate or phosphate salt of chitosan or of chitosan derivatives by acetylation or by crosslinking or any other coupling method. Moreover, this stable conversion can also be applied to other polymers which react under the same conditions as the abovementioned chitosan salts, namely synthetic polyhydroxylated polyamines. Thus, the invention also applies to synthetic polyhydroxylated polyamines which couple in the presence of sulphate-containing or phosphate-containing surfactants to give, after acetylation or crosslinking, stable salts.
The present invention relates to novel microcapsules, characterized in that they are formed of a wall made of chitin or of chitin derivatives or of polyhydroxylated polyamines or a salt of the latter, the said wall enveloping a hydrophobic substance.
The present invention more particularly relates to novel microcapsules, characterized in that they are formed of a wall made of chitin or of chitin derivatives or a salt of the latter, the said wall enveloping a hydrophobic substance.
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Grandmontagne Bernard
Marchio François
Jacobson Price Holman & Stern PLLC
Le H. Thi
Merck S.A.
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