Nanocapsule synthesis process, cosmetic composition and cosmetic process

Abstract

Nanocapsule synthesis method, cosmetic composition and cosmetic process. The invention relates to a method for synthesizing core-shell nanoparticles comprising an inorganic matrix core including a photolyzable organic compound. The shell is advantageously bio-based, and the hybrid core can be removed by UV irradiation to obtain hollow nanoparticles. Figure for abstract: Fig. 1

Description

Title of the invention: Method for synthesizing nanocapsules, cosmetic composition and cosmetic process technical field

[0001] The present invention relates to the field of organic shell nanocapsules, which are obtained from core-shell nanoparticles. Previous technique

[0002] The production of hollow polymeric nano-objects has been extensively studied in recent years. One strategy for obtaining hollow objects with controlled dimensions consists of using a solid or liquid sacrificial model, coating it with a polymer shell, and then removing the sacrificial core.

[0003] In prior art processes, solid and inorganic monodisperse sacrificial templates, such as silica templates, are destroyed by various methods, the most common being calcination at very high temperatures, the use of a solvent such as THF, or acid hydrolysis with hydrochloric acid or hydrofluoric acid. These methods are aggressive and likely to damage or even destroy the structure of the polymer shell, thus limiting the choice of materials that can constitute it for those skilled in the art.

[0004] The polymer shell can, for example, be deposited by a layer-by-layer method by alternating a cationic polyelectrolyte and an anionic polyelectrolyte, such as poly(styrene sulfonate) and poly(allylamine hydrochloride), or poly(methacrylic acid) and poly(vinylpyrrolidone). Alternatively, the polymer shell can be deposited by covalent grafting onto the surface of the previously functionalized silica cores. Nanocapsules synthesized by this process are, for example, based on poly(caprolactone-β-ethylene glycol), poly(ethylene glycol dimethacrylate-co-methacrylic acid), or N-isopropylacrylamide copolymers, which are resistant to the hydrofluoric acid used to dissolve the silica core.

[0005] However, it would be desirable to propose nanocapsules with controlled dimensions, in particular mono-dispersible, whose shell is made of materials sensitive to chemical treatments and high temperatures, such as natural polymers.

[0006] For medical and cosmetic applications, it would also be desirable to avoid the use of certain solvents and reagents that may have a toxic effect.

[0007] The need therefore remains to synthesize nanocapsules from natural or naturally derived compounds and by minimizing or even eliminating the use of certain solvents, so as to make nanocapsules biocompatible.

[0008] The present invention proposes a solution to this problem by performing a core removal step using a low-temperature physical treatment, so as to preserve the integrity of the bio-based shell and selectively dissolve the core. This physical treatment includes a UV irradiation step. The UV treatment allows for the total or partial dissolution of the core without affecting the shell. Description of the invention

[0009] The invention relates to a method for synthesizing nanocapsules comprising i) a first step of preparing a hybrid silica core by a sol-gel process, incorporating a photolyzable compound during the formation of the gel, ii) a second step of coating the hybrid silica core with a bark to obtain core-bark nanoparticles, and iii) a third step of UV irradiation of the core-bark nanoparticles.

[0010] The process of the invention consists of producing hybrid silica cores by incorporating a UV-sensitive molecule during the synthesis of silica nanoparticles. This molecule ensures the integrity of the inorganic network, notably through covalent bonds, in order to promote the solubilization of the core under UV irradiation. Once the hybrid cores are synthesized, a bio-based organic shell is deposited on the core. The final step consists of irradiating the resulting core-shell nanoparticles with UV rays. The process of the invention advantageously allows the production of monodisperse bio-based nanoparticles of controlled size. Brief description of the drawings

[0011] [Fig-1] The [Fig. 1] is a scan of hybrid silica nanoparticles obtained by scanning electron microscopy. Description of the implementation methods

[0012] A first object of the invention is a process for synthesizing nanocapsules comprising i) a first step of preparing a hybrid silica core by a sol-gel process, incorporating a photolyzable compound during the formation of the gel, ii) a second step of coating the hybrid silica core with a bark to obtain core-bark nanoparticles, and iii) a third step of UV irradiation of the core-bark nanoparticles.

[0013] The generic term “nanocapsules” is used in this description to designate i) essentially spherical hollow nano-objects comprising a solid organic shell – these will then be referred to as hollow nanocapsules, ii) essentially spherical nano-objects comprising a porous solid core and a spherical organic shell, and iii) spherical nano-objects comprising a solid organic shell, a core whose volume is partially empty and which includes a silica nano-object The dense silica nano-object is preferably essentially spherical and its diameter is smaller than that of the core. The nanocapsules are preferably organic nanocapsules, or even more preferably organic polymer nanocapsules, in that their wall (also referred to here as the shell) comprises at least one layer of organic polymer that is adjacent to the core. The core of the nanocapsules can be empty (i.e., filled with air), or consist of a porous silica solid matrix that may include an organic compound or be partially occupied by a silica-based nano-object. Their wall is preferably made of organic material; in this case, their wall is free of metal or silica.

[0014] By “essentially spherical” is meant an object for which the ratio between its largest dimension and its smallest dimension, measured on a 2D image by a method known to a person skilled in the art, is between 0.9 and 1. The nanocapsules of the invention are essentially spherical when the average of the ratios of a sample of at least 100 nanocapsules measured as above is between 0.9 and 1.

[0015] The size of the nanocapsules (the term “size” referring to their largest dimension for non-spherical particles or their diameter for essentially spherical particles) ranges from 10 nm to 1 micron. Their size can range from 250 nm to 550 nm. They are advantageously essentially monodisperse, it being understood that the term “monodisperse” covers a set of nanocapsules whose polydispersity index ranges from 0.01 to 0.20, preferably from 0.05 to 0.1. The thickness of the nanocapsule is advantageously less than 10 nm. This thickness is essentially equal to the thickness of the shell of the core-shell nanoparticles defined below.

[0016] In the present description, a “core-shell nanoparticle” is an object comprising a dense silica-based core covered at least partially, preferably entirely, by an organic shell. Core-shell nanoparticles are essentially spherical and have a size ranging from 10 nm to 1 micron. The shell preferably has a thickness of up to 50 nm, depending on the number of layers.

[0017] The process of the invention includes a first step of preparing a silica core by a sol-gel process, from an organo-alkoxysilane, a tetra-alkoxysilane and a photolyzable organic compound.

[0018] The photolyzable organic compound is preferably a non-polymer compound, that is to say a compound other than a molecule comprising at least two repeating motifs.

[0019] The organo-alkoxysiloxane bears at least one, preferably only one, organic group other than an alkoxy group. The organic group advantageously comprises a reactive group capable of forming one or more chemical bonds with the photolyzable organic compound. The organo- alkoxysilane comprises hydrolyzable alkoxy functions, which are precursors of the silica network, and organic functions which remain attached to the silica skeleton

[0020] By “chemical bond” is meant a covalent bond, a hydrogen bond or a Van der Waals bond.

[0021] A “photolyzable compound” within the meaning of the invention is an organic compound comprising at least one covalent bond that is broken when the compound is exposed to UV radiation. The photolyzable covalent bond is, for example, selected from -N=N-, -COOC-, -CO-OH. In addition to the UV-sensitive covalent bond, the photolyzable compound preferably comprises at least one reactive group capable of forming one or more chemical bonds with the organoalkoxysilane compound by reacting said reactive group with the organic group of the organoalkoxysilane compound. The photolyzable compound is distinct from a biological active ingredient and from a molecule exhibiting surfactant properties. Photoisomerizable azobenzene compounds are not photolyzable compounds within the meaning of the invention, insofar as the azo covalent bond, when exposed to UV radiation, simply changes configuration without being broken.

[0022] “UV radiation” is radiation with a wavelength between 100 nm and 450 nm, preferably between 200 nm and 450 nm, and even more preferably between 300 nm and 400 nm. The UV light source can be a light source known to those skilled in the art, such as a deuterium lamp, a xenon lamp, or a light-emitting diode lamp. The source will be chosen according to the desired irradiation wavelength.

[0023] A photolyzable compound capable of forming covalent bonds with the organo-alkoxysilane compound can be selected. Thus, the photolyzable compound may comprise at least one carboxylic acid function, preferably two carboxylic acid functions, capable of forming at least one amide bond with an amine function of an amino-alkoxysilane. Alternatively, the photolyzable compound may comprise at least one carboxylic acid function, preferably two carboxylic acid functions, capable of forming at least one ester bond with a hydroxyl group of the organo-alkoxysilane.

[0024] Examples of photolyzable compounds are non-aromatic compounds comprising an azo function, for example 2,2'-azobis(2-methylpropionitrile), l,l'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and azobis(2-phenylthio)-2-propane.

[0025] In a particular embodiment, the photolyzable compound may be 4,4'-azobis(4-cyanovaleric acid).

[0026] Organo-alkoxysilane is, for example, an aminoalkyl-silane comprising preferably a primary amine group, preferably located at the end of the alkyl chain, such as 3-aminopropyl triethoxysilane or 3-aminopropyl trimethoxysilane.

[0027] For example, the photolyzable compound is an azobis compound such as 4,4'-azobis(4-cyanovaleric acid) and the organosilane is an amino-silane such as 3-aminopropyl triethoxysilane.

[0028] According to one embodiment, the first step comprises premixing the photolyzable compound and the organosilane, followed by the addition of tetraalkoxysilane in the presence of water. Preferably, the first step comprises premixing the photolyzable compound and the organosilane in such a way as to promote the formation of bonds, preferably covalent bonds, between the two compounds. The sol-gel reaction can then be initiated by adding tetraalkoxysilane in the presence of water, leading to hybrid silica nanoparticles containing the photolyzable compound. The pH of the gelation medium is preferably adjusted with a basic solution such as ammonium hydroxide to achieve a value greater than or equal to 8.

[0029] A person skilled in the art will be able to choose a tetra-alkoxysilane commonly used in sol-gel processes. Tetraethoxyorthosilicate (TEOS) is one example. Tetramethylorthosilicate (TMOS), tetrapropylorthosilicate (TPOS), and tetrabutylorthosilicate (TBOS) can also be used. It is preferable not to use a surfactant during the gelation reaction.

[0030] The ratio between the number of moles of the photolyzable compound and the number of moles of the silica precursors (organo-alkoxysilane and tetra-alkoxysilane) preferably goes from 1 / 11 to 1 / 9.

[0031] The ratio between the number of moles of the photolyzable compound and the number of moles of the organo-alkoxysilane is preferably fixed in a range of 1 / 5 to 1 / 3.

[0032] The sol-gel reaction is carried out in the presence of water, preferably in the presence of a co-solvent such as ethanol. The molar ratio between ethanol and water can advantageously range from 0.09 to 0.20.

[0033] The core-shell nanoparticles are preferably obtained exclusively from the photolyzable compound, organosilane, and alkoxysilane. In particular, they are free of a metal.

[0034] According to a particular embodiment, the hybrid silica core is a silica matrix comprising chemical bonds between the organosilane and the alkoxysilane, and chemical bonds between the photolyzable compound and the organosilane. In the hybrid silica core, at least some of the chemical bonds between the organosilane and the alkoxysilane, and at least some of the chemical bonds between the photolyzable compound and the organosilane, are preferably covalent. The hybrid silica core is A three-dimensional inorganic silica network preferably comprising covalent organic bridges. The organic bridges are preferably homogeneously distributed within the silica network. Alternatively, they can be located in a ring within the hybrid silica core. The photolyzable compound that has reacted with the organosilane is advantageously distributed within a silica network after the sol-gel reaction is complete. The photolyzable compound that has reacted with the organosilane can be homogeneously distributed throughout the entire volume of the hybrid silica core. In one variant, the photolyzable compound that has reacted with the organosilane can be localized within a ring within the hybrid silica core. Finally, in another variant, the photolyzable compound that has reacted with the organosilane can be dispersed throughout the hybrid silica core along a concentration gradient.

[0035] The synthesis process of the invention advantageously allows the deposition of an organic bark whose structure is sensitive to chemical and / or thermal treatments.

[0036] Thus, the organic shell advantageously comprises at least one organic polymer, preferably natural or of natural origin. The nanocapsules obtained in this variant of the synthesis process can be described as "organic polymer nanocapsules," particularly when the hydride silica core has been completely disrupted by UV radiation and the core of the nanocapsule is empty. It will therefore be possible to obtain nanocapsules essentially composed of at least one natural polymer.

[0037] The natural or naturally derived polymer within the meaning of the invention is a raw material that may have undergone physical treatment, such as grinding, drying, or washing, or a chemical transformation consisting of grafting at least one functional group onto its backbone. For example, some or all of the hydroxyl groups of natural cellulose may react with reagents to give cellulose derivatives, such as carboxymethylcellulose or hydroxypropylmethylcellulose.

[0038] The natural or naturally derived polymer is, for example, chosen from polysaccharides, in particular polysaccharides, preferably water-soluble or water-dispersible. The polymer is, for example, chosen from the group consisting of cellulose, chitosan, heparin, alginate, dextran, a dextran derivative, xanthan gum, starch, a starch derivative, hyaluronic acid, carrageenan, guar gum, pullulan, gellan, pectin, agar, and their derivatives.

[0039] The bark deposited on the hybrid silica core is preferably made of natural or naturally derived polymer(s). A naturally derived polymer may also be described as a natural polymer derivative. The portion of the bark deposited in contact with the hybrid silica core is preferably silica-free. In this case, the synthesis step of the hybrid silica core is followed directly by the deposition of an organic material, preferably an organic polymer (an organic polymer is understood to be a polymer devoid of silicon).

[0040] A person skilled in the art will be able to choose a bark deposition process from among the methods known in the state of the art, a method by physical deposition of a polymer being preferred.

[0041] Alternatively, a chemical deposition can be carried out consisting of synthesizing the bark by reaction of monomers in the presence of the hybrid silica core.

[0042] In a particular embodiment, the process of the invention includes a physical deposition step of the bark, referred to as a “layer-by-layer” deposition, the cohesion of the bark being ensured by electrostatic interaction between a positively charged polymer and a negatively charged polymer. In this embodiment, the bark therefore comprises at least two different polymers, the polymers being superimposed and deposited in successive steps. A “layer-by-layer” process thus comprises the alternating deposition of a layer of a cationic polymer and the deposition of a layer of anionic polymer, the resulting bark being able to comprise at least one layer of cationic polymer and at least one layer of anionic polymer, preferably 2 to 10 layers of cationic polymer and 2 to 10 layers of anionic polymer.

[0043] The cationic polymer can be selected from chitosan, dextran, a dextran ester such as 2-(diethylamino)ethyl dextran, starch, cationic cyclodextrin and cationic cellulose nanocrystals.

[0044] The anionic polymer can be selected from carboxymethylcellulose, chitosan sulfate, dextran sulfate, dextran phosphate, alginate, fucoidan, and cellulose nanocrystals sulfated or oxidized by 2,2,6,6-tetramethyl-l-piperidinyloxyl (TEMPO).

[0045] A first particular embodiment of the invention consists of using the starch / cellulose pair. An aqueous solution of cationic starch and an aqueous suspension of cellulose nanocrystals can be used to form several successive layers, the first layer deposited on the surface of the silica core originating from a polymer with a charge opposite to the surface of the silica core.

[0046] A second particular embodiment of the invention comprises alternating layers of chitosan and carboxymethylcellulose.

[0047] Polymers and deposition conditions are advantageously chosen to obtain a bark that remains stable under the UV irradiation conditions of the third step of the synthesis process of the invention.

[0048] In a layer-by-layer core coating process, hybrid silica nanoparticles can first be mixed with an aqueous solution or suspension of cationic polymer and incubated for the required time, Preferably at room temperature. The incubated nanoparticles coated with a layer of cationic polymer are recovered by centrifugation and washed with water. The same process is repeated with an aqueous solution or suspension of anionic polymer. Alternating layers of cationic and anionic polymer can be repeated until the desired shell thickness is achieved, sufficient to cover the surface of the hybrid silica core. In one particular embodiment, the shell thickness is less than 10 nm, for example, on the order of 4 to 5 nm. The number of cationic polymer layers can be even or odd. The same applies to the number of anionic polymer layers.

[0049] The core-shell nanoparticles obtained at the end of the second step of the synthesis process of the invention are subjected to a third UV treatment step.

[0050] The third UV irradiation step of the core-shell nanoparticles advantageously includes the preparation of an aqueous suspension of the core-shell nanoparticles obtained at the end of the second step of the process of the invention, and UV irradiation of this aqueous suspension.

[0051] The core removal step from the core-bark nanoparticles obtained at the end of the second step of the synthesis process of the invention is essentially free from, or even entirely free from, the addition of an organic solvent, the addition of a strong acid, and a temperature increase likely to cause calcination of the core. Care will also be taken to ensure that the aqueous suspension of core-bark nanoparticles does not contain any molecule likely to modify the structure of the bark during UV irradiation.

[0052] The aqueous suspension of core-shell nanoparticles preferably consists essentially of water and core-shell nanoparticles.

[0053] The core removal step in the process of the invention is carried out at a low temperature, unlike the temperatures used in the prior art. Preferably, the aqueous suspension of nanoparticles is not subjected to a heat source during exposure to UV radiation. The temperature of the aqueous suspension is preferably maintained at a temperature ranging from 20°C to 30°C throughout the irradiation process.

[0054] The pH of the aqueous suspension of the nanoparticles is preferably neutral.

[0055] The UV light source can be chosen by a person skilled in the art, according to the desired wavelength, from among known light sources such as deuterium lamps or UV light-emitting diodes. A particular irradiation protocol involves exposing an aqueous suspension of the core-shell nanoparticles for a period of between 1 and 5 hours, at a wavelength between 340 nm and 390 nm (indicative time values ​​for an initial turbidity of approximately 200 NTU, with an irradiation source located 10 cm from the samples).

[0056] In a preferred embodiment of the present invention, the nanocapsule obtained at the end of the UV irradiation step is hollow, in the case where the core of the core-shell nanoparticles which is based on hybrid silica has been completely disintegrated by the UV rays, and the center of the nanocapsule is empty.

[0057] The invention has as its second object core-shell nanoparticles that can be obtained by the process described above.

[0058] Their size can be between X and X nm, preferably between 250 nm and 550 nm. They have the advantage of being monodisperse, preferably having a polydispersity index ranging from 0.05 to 0.20.

[0059] The nanocapsules can be described as "hollow" when the hybrid silica core has been completely removed after the third UV exposure step. The nanocapsules will be described as "porous" if the hybrid silica core has become porous after the ultraviolet light irradiation step. The pore volume can be measured by any method known to those skilled in the art.

[0060] Within the scope of the invention, the nanocapsules prepared according to the process described above can be loaded with an organic molecule, chosen, for example, from cosmetic actives, therapeutic actives, diagnostic agents, and dermatological actives. The loading of the organic molecule inside the nanocapsules can be carried out in a fourth step, subsequent to the third UV irradiation step described above, once the hybrid silica core has been destroyed or degraded. The nanocapsules of the invention loaded with an organic molecule can thus serve as a carrier for a biological active ingredient.

[0061] A third object of the invention relates to hybrid silica nanoparticles, which can be used as sacrificial cores in the implementation of a nanocapsule preparation process, particularly in the first step of the process of the invention as described above. These hybrid silica nanoparticles can be obtained by reacting a mixture comprising a photolyzable organic compound, an organo-alkoxysilane, a tetra-alkoxysilane, and water.

[0062] The characteristics described in relation to the synthesis process of the invention are applicable to hydride silica nanoparticles.

[0063] The present invention also relates to a cosmetic composition comprising nanocapsules that can be obtained according to the synthesis process described above.

[0064] The cosmetic composition may include, in addition to the nanocapsules, at least one cosmetically acceptable ingredient selected from water, solvents, oils, surfactants, film-forming polymers, waxes, pasty fatty compounds, agents gelling agents, thickening agents, powders such as pigments and fillers, pH adjusters, antioxidants and active molecules.

[0065] Finally, the invention relates to a method of applying nanocapsules that can be obtained according to the synthesis process described above, to keratinous materials such as skin, eyelashes, eyebrows, hair or nails.

[0066] Example 1: Synthesis of hybrid silica nanoparticles comprising a photolyzable organic compound

[0067] 1, Synthesis

[0068] 0.052 g of ACVA (4,4'-Azobis(4-cyanovaleric acid)) is dissolved in 30 mL of absolute ethanol. The mixture is then transferred to a three-necked flask and 0.168 g of APTES ((3-aminopropyl)triethoxysilane) is added. The mixture is stirred magnetically at 25°C for 1 hour. Next, 0.242 g of TEOS (tetraethyl orthosilicate), 80 mL of demineralized water, and 1 mL of 28% ammonia (NH4.OH) are added. Magnetic stirring is stopped, and the mixture is left to react overnight at 25°C. The following morning, the ammonia is washed off by performing three centrifugation cycles (10,000 rpm, 5 min). The mixture is then resuspended in demineralized water to obtain a suspension containing 6 g / L of nanoparticles of silica hydrides. The molar concentrations and molar ratios of the reactants in the water / ethanol solution are given in Tables 1 and 2 below.

[0069] [Table 1] Molar concentrations of reactants Reagents Molar concentrations (mol / L) TEOS 0.010 APTES 0.007 ACVA 0.002 [Table 2] Molar ratios of reactants APTES / ACVA molar ratio 4 (TEOS+APTES) / ACVA molar ratio 10

[0070] 2, Characterization

[0071] The size of the nanoparticles is measured by DLS. The silica nuclei comprising the ACVA compound were measured to have an average diameter of 344 nm with a standard deviation of 32 nm. The average polydispersity index, also measured by DLS, is 0.084. A scanning electron microscopy image of the nanoparticles is shown in [Fig. 1].

[0072] The surface charge of the nanoparticles is determined at different pH values ​​on samples taken without dilution and whose pH is adjusted to the desired value. The zeta potential varies with pH, ​​which will determine the incubation pH of the first bark layer. The results are presented in Table 3.

[0073] [Table 3] Measurement of the zeta potential of hybrid silica nanoparticles pH Zeta (mV) Conductivity (mS / cm) 5.7 26.04 0.1844 7.9 -0.15 0.07 10.2 -39.85 0.32 Example 2: Synthesis of core-shell nanoparticles according to the invention

[0074] Step 1: Coating the hybrid silica cores with a bark

[0075] The shell was assembled on the hybrid silica nanoparticles prepared according to Example 1, using a layer-by-layer technique.

[0076] 1. Synthesis A 1.25 mL sample of the aqueous suspension of hybrid silica nanoparticles (SNPs) prepared according to Example 1 is taken. 1.43 mL of a carboxymethylcellulose solution (CMC 250 kDa, ref: 419311-100G, Aldrich, at 1 g / L in water) is added. Then, 1.3 mL of a 10 g / L NaCl solution is added, and the mixture is made up to 10 mL with 6 mL of deionized water. The pH is adjusted to 5.8, and the mixture is incubated for 40 min to 1 h under magnetic stirring at a controlled temperature of 23.5°C. The excess CMC is washed off by centrifuging the suspension (10,000 rpm, 10 min, 15°C). The supernatant is removed, resuspended in deionized water, and the washing process is repeated. The supernatant is then removed again.

[0077] Add another 7.250 mL of deionized water, along with 1.3 mL of 10 g / L NaCl. For the second layer, add 1.43 mL of a 1 g / L chitosan solution (low molecular weight, 50-190 kDa, in water, solubilization pH = 5.5, ref: 448869-50G, Aldrich). Adjust the pH to 5.7 and incubate for 40 min to 1 h with magnetic stirring at a controlled temperature of 23.5°C. Remove the excess chitosan by centrifugation as described for the previous layer. Repeat this cycle once more to build four layers. The mass concentrations of the reagents and their ratios are shown in Table 4 below.

[0078] [Table 4] Concentrations and mass ratios of reactants Concentratio Concentratio Concentratio Concentratio Ratio Ratio n in Nps (g / L) n in chitosan (g / L) n in CMC (g / L) n NaCl (g / L) mass Nps / polymer mass polymer / NaCl 1 0.143 0.143 1.3 7 0.11

[0079] 2, Characterization The formation of the layers is monitored by measurements of the zeta potential at a pH of approximately 6. The results are presented in Table 5.

[0080] [Table 5] Measurement of the zeta potential of core-shell nanoparticles Nano-object pH measurement Zeta + / - deviation (mV) Hybrid silica nanoparticles (Nps) 6.01 -13.8+ / - 1.8 First layer CMC nanoparticles 6.05 -45.5 + / - 0.2 Second layer Chitosan nanoparticles 6.10 11.8+ / - 0.4

[0081] Step 2: Core degradation under UV irradiation We prepare 10 ml of the core-shell nanoparticles obtained in Step 1. Under magnetic stirring, in a black box, we place the lamp at the same horizontal level as the samples, at a distance of 10 cm. We irradiate for 4.5 h with a UV lamp (Fire Edge FE300® 75xlOAC 365, 345-385 nm, Phasem Techno).

Claims

Demands

1. A process for synthesizing nanocapsules comprising i) a first step of preparing a hybrid silica core by a sol-gel process, incorporating a photolyzable compound during gel formation, ii) a second step of coating the hybrid silica core with an organic bark to obtain core-bark nanoparticles, and iii) a third step of UV irradiation of the core-bark nanoparticles.

2. A synthesis process according to the preceding claim, characterized in that the first step is a sol-gel reaction carried out in the presence of water and performed from an organo-alkoxysilane, a tetra-al-coxysilane and a photolyzable organic compound.

3. A synthesis process according to claim 2, characterized in that the photolyzable organic compound is an azobis compound such as 4,4'-azobis(4-cyanovaleric acid) and the organosilane is an amino-silane such as 3-aminopropyl triethoxysilane.

4. A synthesis process according to claim 2, characterized in that the ratio between the number of moles of the photolyzable compound and the number of moles of the silica precursors (organo-alkoxysilane and tetra-al-coxysilane) ranges from 1 / 11 to 1 / 9, and in that the ratio between the number of moles of the photolyzable compound and the number of moles of the organo-alkoxysilane is fixed in a range from 1 / 5 to 1 / 3.

5. A synthesis process according to claim 1, characterized in that the organic bark comprises at least one organic polymer, preferably natural or of natural origin.

6. A synthesis process according to the preceding claim, characterized in that the natural or naturally derived polymer is selected from polysaccharides, such as, for example, cellulose, chitosan, heparin, alginate, dextran, a dextran derivative, xanthan gum, starch, a starch derivative, hyaluronic acid, carrageenan, guar gum, pullulan, gellan, pectin, agar, and their derivatives.

7. A synthesis process according to the preceding claim, characterized in that a derivative of cellulose is carboxymethylcellulose.

8. Nanocapsules that can be obtained by the process according to any one of the preceding claims.

9. Nanocapsules according to claim 8, characterized in that their size is between 250 nm and 550 nm, and in that their poly- index Dispersion ranges from 0.05 to 0.

20.

10. Cosmetic composition comprising nanocapsules that can be obtained according to the synthesis process of any one of claims 1 to 7.

11. Method of applying to keratin materials nanocapsules that can be obtained according to the synthesis process of any one of claims 1 to 7.

12. Hybrid silica nanoparticles that can be obtained by reacting a mixture comprising a photolyzable organic compound, an organo-alkoxysilane, a tetra-alkoxysilane and water.

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