Concentrated aqueous dispersion of microgels and cosmetic composition containing same

Abstract

The invention relates to an aqueous dispersion of thermoresponsive poly(oligo-(ethylene glycol) methacrylate) microgels comprising a weight percentage of microgels ranging from 5% to 40%. This dispersion is obtained by partial dehydration of an aqueous dispersion of microgels derived directly from the polymerization of the precursor monomers. The partial dehydration may be performed by zeodration. The invention also relates to an aqueous dispersion of microgels optionally comprising a cosmetic active agent which is encapsulated in a significant amount in the microgels, and to a cosmetic composition formulated from this concentrated aqueous dispersion.

Description

Description Title of the invention: CONCENTRATED AQUEOUS DISPERSION OF MICROGELS AND COSMETIC COMPOSITION CONTAINING IT Technical Field

[0001] The present invention relates to the formulation of aqueous dispersion of microgels and their use in the field of cosmetics. Prior art

[0002] The synthesis of thermosensitive microgels of poly(oligo- (ethylene glycol)methacrylate) in aqueous phase has been described in the literature, but the aqueous dispersions of crosslinked polymer particles obtained are not very concentrated.

[0003] There is therefore a need to provide more concentrated microgel dispersions so that they can be formulated into cosmetic compositions containing other ingredients.

[0004] The formulator must have a basic microgel dispersion available to prepare a whole range of cosmetic products comprising variable proportions of water, without having to modify the concentration of the microgel dispersion used as a formulation ingredient. Having a sufficient quantity of water available to formulate all the ingredients and then being able to combine them with the microgels is particularly desirable when the product includes texturizing or suspending agents.

[0005] It is also desirable to vectorize hydrophilic cosmetic active ingredients in significant quantities in poly(oligo-(ethylene glycol)methacrylate) microgels. Statement of the invention

[0006] The invention consists of providing concentrated microgel dispersions. These dispersions can be used in particular for the formulation of cosmetic products.

[0007] The inventors have found that the methods for synthesizing poly(oligo-(ethylene glycol)methacrylate microgel dispersions by polymerization of precursor monomers described in the prior art are not sufficiently concentrated in microgels to be able to be formulated in a cosmetic product.

[0008] They found that prior art syntheses cannot be carried out in a reaction medium comprising limited water. To obtain more concentrated microgel dispersions, it is therefore necessary to eliminate the water contained in the native microgel dispersions, once the precursor monomer polymerization step is complete.

[0009] The inventors then unexpectedly found that the complete dehydration of a native microgel dispersion of the prior art denatures the structure and properties of the crosslinked polymer particles so much so that, once dry, it is no longer possible to redisperse the microgels in water and incorporate them into the aqueous phase of a cosmetic composition.

[0010] Thanks to the invention, the cosmetic product formulator can therefore freely vary the quantity of water desired in the final product, without having to adapt the microgel synthesis process to each new formula containing them.

[0011] The formulator can also advantageously introduce higher quantities of microgels, while maintaining a proportion of water available to formulate other ingredients in the cosmetic composition. This is very advantageous for the formulation of gelling or suspending agents that require a minimum amount of water to deploy correctly and not form grains in the final composition.

[0012] The dehydration step proposed within the framework of the invention makes it possible to partially dehydrate the polymer particles constituting the microgel so that it remains contractile, to be incorporated directly into a cosmetic composition.

[0013] The inventors surprisingly found that poly(ol igo-(ethylene glycol)methacrylate) microgels can be used as a carrier for cosmetic actives that are highly soluble in water, after finding that prior art protocols described for loading polymer particles with a hydrophilic active are not suitable for this category of actives. Brief description of the drawings

[0014] Figure 1 is a curve representing the variation as a function of time of the temperature of the aqueous dispersion of microgels (Tp) and the temperature of the zeolite (Tz) in a zeodrator. Description of the embodiments

[0015] The subject of the invention is an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol / methacrylate) in which the mass percentage of microgels ranges from 5% to 40%, preferably from 20% to 30%.

[0016] From this concentrated aqueous dispersion, it is possible to obtain an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol / methacrylate) comprising a cosmetic active ingredient which is encapsulated in the microgels, the ratio between the mass of microgels and the mass of active ingredient encapsulated in the microgels is between 3 and 8. The cosmetic active ingredient can be hydrophilic or lipophilic.

[0017] The term “thermosensitive poly(oligo-(ethylene glycol)methacrylate) microgels” means crosslinked polymer particles in spherical form which are composed of a mixture of repeating branched ethylene oxide units and methacrylic acid units, all of which give the microgels colloidal properties as well as sensitivity to temperature variations in water. The polymer particles may optionally comprise a hydrophilic cosmetic active ingredient and / or water. Their size may vary from 100 nm to 500 nm when dry, i.e. when the polymer particles contain less than 2% by mass of water. The microgels are advantageously monodisperse. The microgels are preferably essentially made of or consist of poly(oligo-(ethylene glycol)methacrylate).

[0018] The mass percentage of microgels ranging from 5% to 40% is chosen from a range whose minimum and maximum values ​​are chosen from the group consisting of 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40%. For example, the mass percentage of microgels is included in a range from 10% to 35%. It preferably ranges from 20% to 30%. The mass percentage of water in the aqueous dispersion of microgels ranges, for example, from 60% to 95%, and may be equal to the complement to 100% of the mass percentage of microgels.

[0019] According to a particular embodiment, the aqueous dispersion of poly(oligo-(ethylene glycol)methacrylate) microgels of the invention can be obtained by a process comprising a step of aqueous phase polymerization of at least two monomers in the presence of a crosslinking agent, the first monomer being di(ethylene glycol) methyl ether methacrylate, and the second monomer being an oligo(ethylene glycol) methyl ether methacrylate. The polymerization can be carried out with at least three monomers including the two monomers described above and a vinyl monomer comprising a carboxyl group.

[0020] Oligoethylene glycol methacrylate preferably comprises from 3 to 12 ethylene glycol units, preferably from 6 to 10 ethylene glycol units. Its number-average molar mass (Mn) can range from 400 g / mol to 600 g / mol, preferably from 450 g / mol to 500 g / mol.

[0021] The vinyl monomer comprising a carboxyl group is for example methacrylic acid. In this embodiment, the thermosensitive microgels are poly(oligo-(ethylene glycol)methacrylate / (meth)acrylic acid microgels.

[0022] The three monomers used are preferably di(ethylene glycol) methyl ether methacrylate, oligo(ethylene glycol) methyl ether methacrylate (whose number-average molecular mass Mn is between 450 g / mol and 500 g / mol), and methacrylic acid.

[0023] The crosslinking agent may be chosen from the group consisting of oligo(ethylene glycol) diacrylate comprising from 1 to 10 ethylene glycol units (for example oligo(ethylene glycol) diacrylate whose number-average molecular mass Mn is between 200 g / mol and 300 g / mol), N,N'-methylenebisacrylamide or (ethylene glycol) dimethacrylate.

[0024] Examples of microgels suitable for implementing the invention are described in more detail in application WO 2016 / 110615.

[0025] The mass percentage of microgels in the aqueous dispersion of thermosensitive poly(oligo-(ethylene glycol)methacrylate) microgels can be measured by any method known to those skilled in the art. For example, the percentage of microgels is determined by centrifugation of the dispersion, and by measuring the mass of the supernatant and the pellet.

[0026] The aqueous dispersion of thermosensitive poly(oligo-(ethylene glycol)methacrylate) microgels may consist essentially of crosslinked poly(oligo-(ethylene glycol)methacrylate), water and a hydrophilic or lipophilic cosmetic active ingredient. The term "consisting essentially of" allows for the presence of impurities or residual reagents in the aqueous dispersion.

[0027] The active ingredient is advantageously encapsulated in the microgels, in that the active ingredient is located inside the polymer particles of the microgel.

[0028] The invention makes it possible to propose microgels as a vector for hydrophilic or lipophilic cosmetic active ingredients, because the inventors have surprisingly discovered that it is necessary to have sufficiently concentrated microgel dispersions to be able to encapsulate this type of active molecule in the polymer particles in significant quantities.

[0029] For the purposes of the present invention, the term "cosmetic active ingredient" means a compound capable of exerting a cosmetic effect on the skin, such as, for example, an improvement in the radiance of the complexion, or an improvement in the suppleness, softness, elasticity or firmness of the skin. Another cosmetic effect may be a reduction in the depth of wrinkles.

[0030] A cosmetic active ingredient is said to be "hydrophilic" when the active ingredient is water-soluble, and preferably when the active ingredient has a high water solubility. For example, the active ingredient hydrophilic has a solubility in water measured at 25°C greater than or equal to a value chosen from 0.1 g / L, 1 g / L, 2 g / L, 4 g / L, 6 g / L, 8 g / L, 10 g / , 12 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L and 20 g / L. The solubility can be measured by any measurement known to those skilled in the art.

[0031] The hydrophilic active ingredient is, for example, an organic molecule comprising at least one oxygen atom in a carbonyl, hydroxyl or carboxyl group.

[0032] It has been found that this hydrophilic active ingredient is not encapsulated or is encapsulated in very small amounts when using a native aqueous microgel dispersion of the prior art containing less than 2% by mass of microgels. On the other hand, after concentrating the native microgel dispersion to a percentage of at least 4% by mass of microgels, the amount of hydrophilic active ingredient that is encapsulated in the microgels is increased compared to the amount obtained in the prior art. It is for example greater than or equal to 20%, 30%, 40%, or even greater than 50%. For example, in the case of caffeine, at least 50% of the amount of caffeine that has been mixed with the concentrated aqueous microgel dispersion is encapsulated in the polymer particles after mixing an aqueous caffeine solution and the concentrated microgel dispersion.

[0033] The ratio between the mass of microgels and the mass of hydrophilic or lipophilic active ingredient encapsulated in the microgels is between 3 and 8 or between 3 and 6. The dosage of the hydrophilic or lipophilic active ingredient in the microgel polymer particles can be carried out by a method known to those skilled in the art. The ratio between the mass of microgels and the mass of active ingredient encapsulated in the microgels is calculated by taking i) the mass of microgels not dispersed in water and not containing the active ingredient (also called "dry microgel mass", although the microgels may contain water after removal of the water in which the microgels are dispersed) and ii) the mass of hydrophilic active ingredient (without water).

[0034] The concentrated aqueous dispersion comprises water in an amount which is preferably sufficient to be liquid.

[0035] For the purposes of the present invention, the term "cosmetic active ingredient" means a compound capable of exerting a cosmetic effect on the skin, such as, for example, an improvement in the radiance of the complexion, or an improvement in the suppleness, softness, elasticity or firmness of the skin. Another cosmetic effect may be a reduction in the depth of wrinkles.

[0036] The cosmetic active ingredient may be chosen from 2-ethylhexyl salicylate (octyl salicylate, Escalol®), hyaluronic acid, 4-hydroxy-2-methoxy-5-(oxo-phenylmethyl)benzene sulfonic acid (benzophenone-4), citronellol, salicylic acid, caffeine, phenyl benzimidazole sulfonic acid (Ensulizole®), terephthalylidene dicamphor sulfonic acid (Ecamsule®), and the salts of these compounds.

[0037] The cosmetic active ingredient can also be chosen from bis ethyl hexyloxyphenol methoxyphenyl triazine (Bemotrizinol®), ethyl hexyl triazone (Octyltriazone®), diethylamino hydroxybenzoyl hexyl benzoate (Uvinul A®).

[0038] According to a particularly advantageous embodiment of the invention, the cosmetic active ingredient is caffeine, one of its salts or a plant extract containing it.

[0039] The inventors surprisingly found that poly(oligo-(ethylene glycol)methacrylate / (meth)acrylic acid) microgels can be used as a carrier for caffeine, although this molecule is highly soluble in water. The inventors found that the prior art protocols described for loading polymer particles with a hydrophilic active agent are not suitable for caffeine, so there is a need to provide a method for preparing a cosmetic composition comprising poly(oligo-(ethylene glycol)methacrylate / (meth)acrylic acid) microgels and caffeine.

[0040] The invention also relates to a process for preparing an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate) as described above, said process comprising the following steps: a) providing an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate), the mass percentage of microgels of which is for example between 0.5% and 4.0%, b) partial removal of the water contained in the native aqueous dispersion of microgels to obtain the aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate), which is a concentrated aqueous dispersion of microgels.

[0041] The term "aqueous dispersion of thermosensitive microgels of native poly(oligo-(ethylene glycol)methacrylate)" means a dispersion directly resulting from an aqueous phase polymerization step of di(ethylene glycol) methyl ether methacrylate, oligo(ethylene glycol) methyl ether methacrylate, and a vinyl monomer comprising a carboxyl group, in the presence of a crosslinking agent. These reagents are in accordance with the description given above. The mass percentage of microgels in the native aqueous dispersion may be between 0.5% and 3.0%, between 1.0% and 2.5%, or between 1.5% and 2%.

[0042] The water removal step is complete when the percentage of microgels in the dispersion is between 5% and 40%. After water removal, a concentrated liquid aqueous dispersion of microgels is recovered. This dispersion has the advantage of being able to be diluted in water while keeping the microgels in the dispersed state in water.

[0043] Partial removal of water from the native aqueous microgel dispersion is preferably achieved by zeodration. The duration of the zeodration step is sufficient to remove some of the water from the native dispersion.

[0044] For the purposes of the invention, the term "zeodration" means a process using a reactor containing dehydrated zeolite cassettes in the form of beads which adsorb the water vapor generated by the evaporation of the water contained in a material to be dehydrated which is subjected to an increase in temperature, at controlled pressure.

[0045] According to a particular zeodration process, the native aqueous dispersion of microgels is placed in a zeodrator and then heated to a temperature between 10°C and 40°C. The temperature of the zeolite cassette is preferably in the order of 50°C to 60°C, and the pressure of the zeodrator reactor is brought to a value between 0 and 5 bars.

[0046] Zeodration is carried out for example for a duration of between 160 min and 210 min, for 50g of native aqueous microgel dispersion comprising 2% by mass of microgels.

[0047] According to a specific dehydration protocol, the reactor is evacuated to a value of 5 mbar. The reactor temperature is then increased in stages, for example to 15°C for 7 min, to 20°C for 10 min, to 25°C for 30 min and to 35°C for 30 min.

[0048] By means of the zeodration process, the aqueous dispersion of microgels is partially dehydrated so that the crosslinked polymer particles contain water and retain their thermosensitive property.

[0049] Partially removing the water contained in the microgel dispersion resulting from the polymerization of the precursor monomers allows the production of a concentrated microgel dispersion which can then be used in cosmetic formulations.

[0050] The inventors have surprisingly discovered that a process for completely removing the water contained in the native aqueous dispersion of microgels, such as for example the freeze-drying technique, leads to a product that cannot be formulated in an aqueous phase. Complete dehydration of the microgel dispersion irreversibly deforms the polymer particles. In addition, fully dehydrated microgels are sticky and adhere to the crystallizer glass. To maintain the properties of the microgels, it is therefore necessary to remove some of the water contained in the native dispersion.

[0051] The inventors also found that the gradual and partial evaporation of the water contained in the native microgel dispersion, in an oven or by distillation, in particular by rotary evaporation, certainly allows the dispersion to be concentrated, but the reliability of the final result is not optimal. The process requires repeated weighing until the target microgel content is obtained. In addition, these processes do not allow mass concentrations of microgels greater than 12% to be achieved in the concentrated dispersions, which considerably limits cosmetic applications and the formulation spectrum.

[0052] On the contrary, the inventive concentration process by zeodration is very flexible, reproducible and can be used on an industrial scale.

[0053] The method of the invention advantageously makes it possible to dehydrate a native dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol / methacrylate) without using a chemical desiccant.

[0054] In addition to steps a) and b), the process for preparing an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol / methacrylate) according to the invention may comprise a step c) of incorporating a hydrophilic cosmetic active ingredient into the microgels from the concentrated aqueous dispersion of microgels obtained in step b). Step c) comprises, for example, a step of preparing an aqueous solution comprising the cosmetic active ingredient, and a step of mixing the aqueous solution comprising the cosmetic active ingredient with the concentrated aqueous dispersion of microgels. In a particular embodiment, the cosmetic active ingredient is caffeine, one of its salts or a plant extract containing it. The mass concentration of the hydrophilic active ingredient in the aqueous solution comprising the cosmetic active ingredient is advantageously between 1 g / L and 15 g / L, preferably between 2 g / L and 10 g / L and more preferably between 2 g / L and 5 g / L.

[0055] A final subject of the invention relates to a composition comprising the aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol / methacrylate) as described above, or as capable of being obtained by the preparation process which has just been described. Formulated in a cosmetic composition, the thermosensitive microgels of poly(oligo-(ethylene glycol / methacrylate) may have the INCI name Methylmethacrylate glycol Dimethacrylate crosspolymer.

[0056] The cosmetic composition advantageously contains at least one polysaccharide, the polysaccharide fulfilling a function of suspending agent (also called aqueous gelling agent). It is preferred to use a polysaccharide chosen from xanthan gum, locust bean gum (Ceratonia siliqua), karaya gum (Sterculia urens), diutan gum, or a mixture thereof, in order to optimize the stability of the composition and the dispersion of the microgels in the composition.

[0057] A process for preparing a cosmetic composition of the invention comprising an aqueous gelling agent, such as a polysaccharide, may comprise: - a step of preparing a dispersion of the polysaccharide in water, and - a step of mixing the dispersion of the polysaccharide in water with the aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate).

[0058] The cosmetic composition may advantageously comprise from 1% to 10% by mass, for example from 2% to 8% by mass, of microgels containing the hydrophilic active ingredient. The percentage of microgels containing the hydrophilic active ingredient may range from 3% to 6% by mass.

[0059] Other ingredients such as pH adjusters, preservatives, cosmetic actives that are not encapsulated in the microgels, polyols, oils, perfumes or colorants may be added to the cosmetic composition of the invention.

[0060] The cosmetic composition according to the invention may be in the form of an aqueous composition, for example a gelled aqueous composition such as a serum, an oil-in-water emulsion or a water-in-oil emulsion.

[0061] The invention also relates alternatively to a concentrated aqueous dispersion of microgels comprising a lipophilic active ingredient, a method for its manufacture, as well as a cosmetic composition containing it. Lipophilic active ingredient is understood to mean a cosmetic active ingredient which is not hydrophilic within the meaning of the invention. All the characteristics which have been described in the embodiments relating to a hydrophilic active ingredient apply to the alternative consisting of using a lipophilic active ingredient.

[0062] The invention is described in more detail in the following exemplary embodiments. Unless otherwise stated, the temperature is between 20°C and 25°C, and the pressure is atmospheric pressure.

[0063] Example 1: Preparation of a concentrated aqueous dispersion of microalloys

[0064] Preparation of native microgel dispersion (M A non-concentrated native aqueous microgel dispersion (A) is obtained containing 1.75% microgels and 98.25% by mass of water. The dispersion is prepared according to the synthesis method described in application WO 2016 / 110615 from the monomers di(ethylene glycol) methyl ether methacrylate (MEO2MA), oligo(ethylene glycol) methyl ether methacrylate (OEGMA), methacrylic acid (MAA), in the presence of oligo(ethylene glycol) diacrylate which is the crosslinking agent. The aqueous microgel dispersion obtained, called "native", is the dispersion obtained after the polymerization of the three monomers and the crosslinking agent. The "mass percentage of microgels" is the mass of the pellet obtained by centrifugation of the native aqueous microgel dispersion at 14,000 rpm for 30 min.

[0065] Preparation of a concentrated microgel dispersion CB) according to the invention The step of concentrating the native dispersion (A) is then carried out in a zeodrator to obtain a concentrated microgel dispersion (B). The protocol was as follows. Preparation protocol: • Glass crystallizer diameter: 10 cm - quantity of native aqueous microgel dispersion = 50g • Total drying time: 150 min - 210 min • Tank temperature: 50°C - 60°C • Initial conditions: closing the vent => P= 1000 mBars. The pressure gradually drops to 5 mBars. • Final conditions: Rapid opening of the vent to break the vacuum; return to P= 1000 mBars. • Vacuum: 5 mbar • Drying segments: 7min / 15°C, then 10min / 20°C, then 30min / 25°C, then 30min / 35°C • Evacuation speed: 0.100 mbar / min • Zeolite temp. pre-alarm: 80°C • Zeolite temp alarm: 90°C • Acceptable temperature difference: 1°C • Return to atmosphere: 950 mbar Results : The curve representing the variation as a function of time of the temperature of the aqueous dispersion of microgels and the temperature of the zeolite is reproduced in Figure 1. In this figure, the upper curve, Tz, represents the temperature of the zeolite and the lower curve, Tz, represents the temperature of the zeolite. bottom, Tp, represents the temperature of the aqueous dispersion of microgels whose water quantity decreases over time. The concentrated aqueous microgel dispersion (B) obtained by this process contains 26.1% by mass of microgels and 73.9% by mass of water. The concentrated dispersion (B) obtained is concentrated by a factor of 15 compared to the native dispersion (A). It nevertheless surprisingly presents a homogeneous appearance: the microgels are suspended in water without deposition of a film at the bottom of the crystallizer. The sedimentation of the microgel phase at the bottom of the crystallizer is reversible by simple stirring.

[0066] Preparation of a concentrated microgel dispersion (C) according to the invention The previous preparation protocol was reproduced to obtain a concentrated aqueous dispersion of microgels (C) containing 13.5% by mass of microgels and 86.5% by mass of water. This concentrated dispersion also has a homogeneous appearance. The sedimentation of the microgel phase at the bottom of the crystallizer is reversible by stirring. Such a dispersion can thus be used to encapsulate active ingredients such as caffeine.

[0067] Example 2: Cosmetic care compositions prepared from concentrated microalgae dispersion Formulas according to Table 1 were prepared, all comprising 1% by mass of caffeine. These formulas are cosmetic compositions in accordance with the invention (formulas 1 and 2), and a control (formula 3).

[0068] [Table 1] Preparation of formulas 1 and 2 The process for preparing formulas 1 and 2 includes the following steps: 1 - Preparation of an aqueous caffeine solution: phase B1 An aqueous solution containing 2.3% caffeine by mass (phase B1) is prepared by dissolving anhydrous caffeine powder in water at 50°C. The clear solution is then brought back to room temperature. 2- Mixing the aqueous caffeine solution and the concentrated aqueous microgel dispersion Phase B2 (concentrated microgel dispersion (B)) is poured into phase Bl (caffeine solution) at 35°C to obtain a phase B which is mixed at room temperature under deflocculation for 12 hours. 3 - Preparation of phase A The water is heated to 60°C and then the suspending agent (xanthan gum) is added. Homogenize under a deflocculator at 300 rpm. The other ingredients of phase A are added and then homogenized for 30 min at 800 rpm to obtain a phase A in which the gel is well dispersed. Check that there are no grains of suspending agent, then once homogeneous, let it cool. 4 - Mixing phases A and B Phase B is added to phase A gradually while stirring for 10 minutes under a deflocculator (300 rpm). The resulting compositions are aqueous gels comprising microgels and 1% caffeine by mass. Using a concentrated microgel dispersion allows for a stable formula to be achieved through the formation of the suspending gel. Preparation of control formula 3 To achieve a final microgel content of 4% in control formula 3 starting from the native microgel dispersion (A), it is necessary to take a quantity of native dispersion equal to approximately 90% by mass of the final formula, so that very little water remains available to formulate the other ingredients of the formula. Unlike formulas 1 and 2 according to the invention, the caffeine cannot therefore be solubilized in water prior to mixing with the microgels: the caffeine powder is added directly to the native dispersion of microgels (A). For the same reasons, the other ingredients of phase A (including the suspending agent) are formulated in a very small quantity of water before being mixed with the dispersion containing the caffeine and the microgels. Since it is not possible to heat and vigorously stir the microgel dispersion without risking denaturation, it is not possible to reliably control either the solubilization of caffeine or the gelation produced by the suspending agent. Results The results of the observations on formulas 1 to 3 are presented in Table 2 below: [Table 2] Appearance of the formulas Formulas 1 and 2 (invention) have a homogeneous appearance, the microgels are stabilized thanks to the presence of the suspending agent. Formula 3 (control) is not stable. The presence of grains in the formula is visually observed. At the same microgel ratio in the formula, the use of a concentrated microgel dispersion according to the invention thus makes it possible to solubilize the caffeine separately and to control its complete solubilization. It also makes it possible to add a sufficient quantity of water to phase A so that the suspending agent is fully deployed and effective. final composition is stable, no flocculation of the microgels is observed in the bottom of the bottle. Determination of the level of caffeine encapsulated in microgels During the preparation of the formulas, a sample of the microgel dispersion was taken, into which caffeine was added in powder form (control) or in the form of a solution (invention). After centrifugation of the dispersion, caffeine was measured in the supernatant and in the pellet. In the case of formulas 1 and 2 (invention), caffeine was significantly trapped in the microgels (> 50% encapsulation in the microgels). On the other hand, for the control formula 3, no encapsulation of caffeine in the microgels was observed. Example 3: Serum comprising a dispersion of microalgae according to the invention A cosmetic composition according to Table 3 was prepared, comprising 1% by mass of caffeine and 4% by mass of microgels.

[0069] [Table 3] Preparation protocol The Al phase is heated to 80°C then homogenized under a deflocculator at 300 rpm. A2 is added under a deflocculator and then homogenized for 30 min at 1000 rpm to obtain phase A. Phase B1 is homogenized under magnetic stirring at 60°C to ensure complete solubilization of the caffeine. It is allowed to cool and then B2 is added at room temperature. Stir for 20 minutes under a magnetic stirrer. Then a portion of the water is added and then stirred under a deflocculator for 4 hours, to obtain a phase B. At 40°C, phase B is added to phase A under a deflocculator (300 rpm) and then stirring is continued for 12 hours (300 rpm) at room temperature. The composition obtained is a gelled aqueous composition. Example 4: Essence comprising a dispersion of microaels according to the invention A cosmetic composition was prepared according to Table 4.

[0070] [Table 4] The preparation process is the same as in example 3. The composition is more fluid than in the previous example.

Claims

Claims

1. Aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate) comprising a hydrophilic cosmetic active ingredient which is encapsulated in the microgels, the ratio between the mass of microgels and the mass of hydrophilic active ingredient encapsulated in the microgels is between 3 and 8.

2. Aqueous dispersion of thermosensitive microgels according to claim 1, characterized in that the hydrophilic cosmetic active ingredient is caffeine.

3. A process for preparing an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate) according to claim 1 or 2, said process comprising the following steps: a) providing a native aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate), the mass percentage of which in microgels is between 0.5% and 4%, b) partial removal of the water contained in the native aqueous dispersion of microgels, to obtain an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate), which is concentrated and comprises from 5% to 40% by mass of microgels, c) incorporation of a hydrophilic cosmetic active agent into the microgels from the concentrated aqueous dispersion of microgels obtained in step b).

4. Preparation process according to claim 3, characterized in that step c) comprises a step of preparing an aqueous solution comprising the hydrophilic cosmetic active ingredient, and a step of mixing the aqueous solution comprising the hydrophilic cosmetic active ingredient with the concentrated aqueous dispersion of microgels.

5. Preparation process according to claim 3 or 4, characterized in that the hydrophilic cosmetic active ingredient is caffeine.

6. Preparation process according to claim 5, characterized in that the mass concentration of caffeine in the aqueous solution comprising the cosmetic active ingredient is between 1 g / L and 15 g / L, preferably between 2 g / L and 5 g / L.

7. Cosmetic composition comprising an aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate) and at least one hydrophilic cosmetic active ingredient encapsulated in said microgels, the ratio between the mass of microgels and the mass of hydrophilic active ingredient encapsulated in the microgels being between 3 and 8.

8. Cosmetic composition according to claim 7, characterized in that the thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate) have the INCI name Methylmethacrylate glycol Dimethacrylate crosspolymer.

9. Cosmetic composition according to claim 7 or 8, characterized in that it contains at least one polysaccharide fulfilling a suspending agent function.

10. A process for preparing a cosmetic composition according to claim 9, said process comprising: - a step of preparing a dispersion of the polysaccharide in water - a step of mixing the dispersion of the polysaccharide in water with the aqueous dispersion of thermosensitive microgels of poly(oligo-(ethylene glycol)methacrylate).

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