Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Cosmetic – antiperspirant – dentifrice
Reexamination Certificate
2000-01-06
2002-07-02
Page, Thurman K. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Cosmetic, antiperspirant, dentifrice
C424S400000, C424S422000, C424S427000, C514S844000, C514S845000, C514S846000, C514S912000, C514S937000, C514S938000
Reexamination Certificate
active
06413527
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nanoemulsion based on an anionic surfactant chosen from alkyl ether citrates and on at least one oil having a molecular weight of greater than 400, the ratio by weight of the amount of oily phase to the amount of surfactant ranging from 2 to 10. The invention also relates to a process for the preparation of the said nanoemulsion and to its uses, in particular in the cosmetics, dermatological and/or ophthalmological fields. This nanoemulsion is stable on storage and can comprise large amounts of oil while retaining good transparency and while having good cosmetic properties.
2. Background of the Invention
Nanoemulsions are oil-in-water emulsions, the oil globules of which have a very fine particle size, that is to say a number-average size of less than 100 nm. They are generally manufactured by mechanical fragmentation of an oily phase in an aqueous phase in the presence of a surfactant. In the case of nanoemulsions, the very small size of the oily globules is obtained in particular by virtue of at least one pass through a high-pressure homogenizer. The small size of the globules confers on them cosmetically advantageous properties which distinguish them from conventional emulsions: they are transparent and exhibit a novel texture. They can also carry active agents more efficiently.
Transparent microemulsions are known in the state of the art. In contrast to nanoemulsions, microemulsions are not, strictly speaking, emulsions; they are transparent solutions of micelles swollen by oil, which oil is generally a very-short-chain oil (e.g. hexane or decane) and is solubilized by virtue of the joint presence of a significant amount of surfactants and of cosurfactants which form the micelles. The size of the swollen micelles is very small owing to the small amount of oil which they can solubilize. This very small size of the micelles is the cause of their transparency, as with nanoemulsions. However, in contrast to nanoemulsions, microemulsions are spontaneously formed by mixing the constituents, without contributing mechanical energy other than simple magnetic stirring. The major disadvantages of microemulsions are related to their high proportion of surfactants, leading to intolerance and resulting in a sticky feel during application to the skin. Furthermore, their formulation range is generally very narrow and their temperature stability very limited.
In addition, nanoemulsions are known in the state of the art comprising an amphiphilic lipid phase composed of phospholipids, water and oil. These emulsions exhibit the disadvantage of being unstable on storage at conventional storage temperatures, namely between 0 and 45° C. They lead to yellow compositions and produce rancid smells which develop after several days of storage.
Nanoemulsions stabilized by a lamellar liquid crystal coating, obtained by the combination of a hydrophilic surfactant and of a lipophilic surfactant, are also known. However, these combinations are problematic to prepare. Furthermore, the nanoemulsions obtained exhibit a waxy and film-forming feel which is not very pleasant for the user.
Furthermore, EP-A-728,460 discloses nanoemulsions based on fluid non-ionic amphiphilic lipids. However, these nanoemulsions exhibit the disadvantage of having a sticky effect during application to the skin.
The need therefore remains for nanoemulsions which have neither the disadvantages of those of the prior art nor the disadvantages of microemulsions.
SUMMARY OF THE INVENTION
The present inventors have now discovered, unexpectedly, that the use of an anionic surfactant chosen from alkyl ether citrates and of at least one oil having a molecular weight of greater than 400 (=400 grams per mole) makes it possible to obtain novel nanoemulsions exhibiting all the advantages of known nanoemulsions without their disadvantages.
Accordingly, the present invention provides a nanoemulsion, comprising:
an oily phase dispersed in an aqueous phase and having oil globules with a number-average size of less than 100 nm,
at least one anionic surfactant selected from the group consisting of alkyl ether citrates, and
at least one oil having a molecular weight of greater than 400,
where the ratio by weight of the amount of oily phase to the amount of surfactant is 2 to 10.
The present invention also provides a composition suitable for topical application comprising the inventive nanoemulsion.
The present invention also provides an ophthalmic vehicle comprising the inventive nanoemulsion.
The present invention also provides a pharmaceutical composition comprising the inventive nanoemulsion.
The present invention also provides a method of caring for, treating and/or making up the skin, face and/or scalp, comprising applying the inventive nanoemulsion to the skin, face and/or scalp.
The present invention also provides a method of caring for and/or treating the hair, comprising applying the inventive nanoemulsion to the hair.
The present invention also provides a method of caring for and/or moisturizing the skin, mucous membranes and/or scalp, comprising applying the inventive nanoemulsion to the skin, mucous membranes and/or scalp.
The present invention also provides a method of making the inventive nanoemulsion, comprising combining the oily phase, aqueous phase and anionic surfactant.
The present invention also provides a method of making the inventive nanoemulsion, comprising:
mixing the aqueous phase and the oily phase with vigorous stirring at an ambient temperature ranging from 10 to 80° C. and then homogenizing the mixture at a pressure ranging from 6×10
7
Pa to 18×10
7
Pa.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The nanoemulsions according to the invention generally have a transparent to bluish appearance. Their transparency is measured by a transmittance coefficient at 600 nm ranging from 10 to 90% or else by a turbidity ranging from 60 to 600 NTU and preferably from 70 to 300 NTU, where the turbidity is measured with a Hach Model 2100 P portable turbidimeter. This range for the transmittance coefficient includes all specific values and subranges therebetween, such as 20, 30, 50, 75, 80 and 85%. This range for the turbidity includes all specific values and subranges therebetween, such as 75, 100, 150, 200 and 250 NTU.
The oil globules of the nanoemulsions of the invention have a number-average size of less than 100 nm and preferably ranging from 20 to 75 nm and more preferably from 40 to 60 nm. The decrease in the size of the globules makes it possible to promote the penetration of the active principles into the surface layers of the skin (carrier effect). This size range includes all specific values and subranges therebetween, such as 25, 35, 50, 60, 70, 80 and 90 nm.
The anionic surfactant which can be used in the nanoemulsion of the invention is chosen from alkyl ether citrates and mixtures thereof. In a specific embodiment of the invention, the nanoemulsion of the invention can be devoid of any surfactant other than the alkyl ether citrates.
The alkyl ether citrates which can be used as surfactants in the nanoemulsion according to the invention can be selected in particular from the group consisting of the monoesters, diesters or triesters formed by citric acid and at least one oxyethylenated fatty alcohol comprising a saturated or unsaturated, linear or branched alkyl chain having from 8 to 22 carbon atoms and comprising from 3 to 9 oxyethylene groups, and mixtures thereof. In fact, a mixture of one or more of these citrates can be used in the nanoemulsion of the invention.
These citrates can be chosen, for example, from the mono-, di- and triesters of citric acid and of ethoxylated lauryl alcohol comprising from 3 to 9 oxyethylene groups sold by Witco under the name Witconol EC, in particular Witconol EC 2129, which is predo
Legret Sylvie
Simonnet Jean-Thierry
Sonneville Odile
Evans Charesse L.
L'Oreal
Page Thurman K.
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