Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Particulate form
Reexamination Certificate
2000-09-27
2004-02-03
Page, Thurman K. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Particulate form
C424S401000, C424S439000, C424S497000
Reexamination Certificate
active
06685966
ABSTRACT:
A subject-matter of the present invention is composite particles comprising a core based on at least one organic polymer in which is dispersed at least one hydrophobic organic material and an inorganic external coating.
More specifically, the present invention is targeted at the development of an encapsulation system appropriate for the packaging of a hydrophobic active material and for its release in a controlled way.
Encapsulation systems for active materials have already been developed. Mention may very particularly be made, as illustration of these, of those employing specific polymer materials as vehicle for active materials(s). They can be in particular latex microparticles in which the said active materials are dispersed.
However, this encapsulation system is not entirely satisfactory, in so far as it does not make it possible to guarantee that the active material which it comprises will be fully protected with respect to the external environment and vice versa. The fact that the active material is uniformly dispersed within the particles implies that this active material is present at the core of the particle but also at its periphery. As regards more particularly the active material present at the periphery, it is clear that it is exposed at least partially to the external environment. Thus, it remains vulnerable to any physicochemical variation in this environment, such as, for example, modification in pH, temperature or luminosity. It is obvious that this can be reflected by chemical transformations in the accessible active material and/or can contribute to its diffusion outside the particle.
Consequently, this type of encapsulation is not entirely satisfactory in terms of protection of the active material or of control of its release.
The object of the present invention is specifically to provide a novel encapsulation system which makes it possible to eliminate the problems mentioned above.
The invention is targeted at providing composite particles comprising an organic core, the active material(s) being dispersed in the core and this core being isolated from the external environment by a coating of inorganic nature.
This coating or alternatively shell advantageously makes it possible to meet the requirements mentioned above. It guarantees that the active material encapsulated in the organic core is protected with respect to the external environment and makes it possible, if appropriate, to control its diffusion by virtue of the specific choice of the components of this inorganic shell.
A first subject-matter of the present invention is thus composite particles comprising at least
one core composed of at least one organic polymer in which is dispersed at least one hydrophobic active material,
one external coating comprising at least one oxide and/or hydroxide of aluminium, of silicon, of zirconium and/or of a transition metal and
one intermediate layer, present at least partially between the core and the external coating and comprising at least one alkaline earth metal hydroxide.
Another subject-matter of the invention is a process of use in the preparation of the abovementioned composite particles.
The claimed composite particles thus advantageously have a shell of inorganic nature. This inorganic shell is composed of at least two superimposed layers, a layer referred to as an intermediate layer and a layer referred to as an external coating layer. The main function of the intermediate layer is to strengthen the adhesion between the core of organic nature and the outermost layer of inorganic nature.
The coating (or, without distinction, the shell of the external layer) based on oxide and/or on hydroxide may only partially cover or may completely cover each core of organic polymer. It is also possible for this coating to be partially embedded in the intermediate layer covering the core of organic polymer, indeed even in the organic core when the latter is only partially covered with the intermediate layer.
The nature of the organic polymers constituting the core of the composite particles is preferably of the type of that of latex particles, that is to say of (co)polymer particles resulting from conventional processes for the emulsion (co)polymerization of copolymerizable organic monomers.
More generally, this polymer derives from at least one water-immiscible ethylenically unsaturated monomer which can be polymerized by the radical route.
Mention may in particular be made, by way of illustration of the monomers which are suitable for the invention, of vinylaromatic monomers, alkyl esters of &agr;,&bgr;-ethylenically unsaturated acids, vinyl esters of carboxylic acids, vinyl or vinylidene halides, conjugated aliphatic dienes and &agr;,&bgr;-ethylenically unsaturated nitriles.
Mention may in particular be made, by way of illustration of monomers of this type, of styrene, butadiene, acrylonitrile, chloroprene, vinyl or vinylidene chloride, isoprene, isobutylene, vinyl acetate, propylene, butylene and vinylpyrrolidone.
According to a specific form of the invention, the polymer can be a crosslinked polymer. This crosslinking is obtained by incorporation of a crosslinking agent, such as divinylbenzene, ethylene glycol dimethacrylate (EGDIM), allyl methacrylate or methylenebisacrylamide, during the synthesis of the said polymer. The choice of the crosslinking agent is made according to the nature of the monomers under consideration.
The polymer constituting the core of the composite particles according to the invention can also comprise up to 8%, preferably up to 4%, of at least one comonomer carrying ionogenic groups which can be polymerized by the radical route. The comonomer can in particular be a monomer selected from &agr;,&bgr;-ethylenically unsaturated carboxylic acids, sulphonated ethylenic monomers, hydroxyalkyl esters of &agr;,&bgr;-ethylenically unsaturated acids, amides of &agr;,&bgr;-ethylenically unsaturated acids and aminoesters of &agr;,&bgr;-ethylenically unsaturated acids.
Mention may very particularly be made, as examples of these ionogenic groups, of those selected from acrylic, methacrylic, itaconic, maleic, crotonic, para-styrenesulphonic, vinylsulphonic, 2-methacryloyl-oxyethylsulphonic, 2-acrylamido-2-methylpropane-sulphonic and vinylbenzenesulphonic acids, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide, methacrylamide and diethylaminoethyl methacrylate.
The polymer preferably does not comprise monomers with carboxyl or sulpho functional groups.
This polymer is more preferably selected from polystyrenes or copolymers of styrene and of acrylic esters, of styrene and of butadiene or of styrene, of butadiene and of acrylamide.
Mention may more particularly be made of the copolymers of styrene with acrylates or butadiene. They can advantageously be selected from butadiene-styrene copolymers, acrylic copolymers and butadiene-styrene-acrylamide copolymers.
These organic polymers more particularly exhibit a glass transition temperature of between −100° C. and 150°C. According to a particularly advantageous and preferred embodiment of the invention, the glass transition temperature is between −100°C. and 100°C. and more preferably between −150°C. and 100° C.
The polymers which can be employed according to the invention have a particle size of between 0.02 and 5 &mgr;m and preferably between 0.19 and 0.3 &mgr;m.
The diameter of the core of organic polymer incorporating the active material can generally vary between approximately 0.03 and 10 &mgr;m. It is more preferably of the order of 0.1 to 1 &mgr;m.
As regards the external coating of the claimed composite particles, it is composed of at least one oxide and/or hydroxide of aluminium, of silicon, of zirconium and/or of a transition metal.
The term “transition metal” is understood to mean more particularly the metals from the fourth period ranging from scandium to zinc, in so far as the latter are compatible in terms of harmlessness with the targeted application. They are more particularly a titanium, manganese, iron, cobalt, nickel or copper oxide and/or hydroxide.
The oxi
Dominique Dupuis
Roland Reeb
Burns Doane Swecker & Mathis L.L.P.
Page Thurman K.
Rhodia Chimie
Tran S.
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