Composition or medical device comprising oligo(ethylene glycol) based polymers

Abstract

Cosmetic or pharmaceutical composition comprising oligo(ethylene glycol)-based polymers. The present invention relates to a cosmetic or pharmaceutical composition for topical application, said composition comprising a combination of a crosslinked oligo(ethylene glycol)-based polymer in the form of an aqueous dispersion of microgel particles and a non-crosslinked, water-soluble oligo(ethylene glycol)-based polymer. The invention also relates to a method for preparing this composition.

Description

Title of the invention: Composition or medical device comprising oligo(ethylene glycol) based polymers technical field

[0001] The present invention relates to a cosmetic, pharmaceutical composition, or medical device for topical or mucous membrane application, said composition comprising a combination of a crosslinked oligo(ethylene glycol)-based polymer in the form of an aqueous dispersion of colloidal microgel particles and a water-soluble oligo(ethylene glycol)-based polymer. The invention also relates to a method for preparing this composition. Previous art

[0002] In the field of adhesive polymers, the modification of the viscoelastic modulus is mainly achieved by the addition of resins or sticky oils, which require complete miscibility with the polymer (Tse MF, Jacob L. Pressure Sensitive Adhesives Based on VectorR SIS Polymers I. Rheological Model and Adhesive Design Pathways. The Journal of Adhesion. 1996 Apr 1; ​​56(1-4):79-95, and C. Derail, A. Allai, G. Marin, Ph. Tordjeman, Relationship between viscoelastic and peeling properties of model adhesives. Part 1: Cohesive fracture, J. of Adhesion, 61, 123-157, 1997).

[0003] There remains a need to propose a new way of modulating the mechanical properties of cosmetic and pharmaceutical product films intended to be applied to mucous membranes or skin.

[0004] It has been found in the context of the present invention that compositions based on poly(oligo-(ethylene glycol) methacrylate microgels) make it possible to achieve this object.

[0005] The synthesis of aqueous dispersions of such microgels has been described in the literature, in particular in patent applications WO 2016 / 110615 and WO 2019 / 077404, and the publications Boularas et al., Polymer Chem., 2016, 7, 350-363; and Aguirre et al., Polymer Chem., 9, 1155-1159. During the synthesis of these microgels, a by-product is formed, which consists of a water-soluble polymer (WSP), referred to as a free polymer. Upon evaporation of the aqueous solvent, the self-assembly of the purified microgels forms cohesive and elastic films.

[0006] There remains a need for cosmetic products, pharmaceutical products, and medical devices intended for application to the skin or mucous membranes, said films being sufficiently flexible, cohesive, and adhesive to remain in place once applied without breaking, crumbling, or tearing. It is also desirable that these products be removable by hand without tearing. and without leaving any residue on the skin.

[0007] However, the inventors discovered that mixing purified microgels with the free polymer allows for the control and manipulation of the viscoelastic modulus of the films without reducing elongation at break. In particular, the free polymer increases the adhesion of a microgel film without altering its mechanical properties.

[0008] Adding the free polymer at different concentrations allows the rheological and mechanical properties of the films to be controlled and consequently the tack, or in other words the stickiness.

[0009] In the present invention, the films obtained by drying the combination of microgels and the free polymer exhibit particular mechanical properties of elasticity and tackiness. The inventors have surprisingly found that these properties can be modulated according to the microgel-to-polymer mass ratio. The inventors discovered that the chemical composition of the free polymer is very similar to that of the microgels and allows for good compatibility between the two components. Furthermore, the branched and cross-linked structure allows the films obtained from their mixtures to retain their tensile strength.

[0010] By evaporation of the aqueous solvent, the self-assembly of the microgel / polymer mixture forms a film with promising mechanical properties for skin applications: the elastic modulus is low, the deformability is high, and the elongation at break is high. Reformulation with the free polymer potentially allows for the control and manipulation of the viscoelastic modulus of the films without reducing the elongation at break.

[0011] The formation of microgel films with adjustable mechanical properties has never been reported in the literature. In this invention, the variation of the rheological properties of the films is directly achieved through a synthetic by-product, the free polymer. This polymer has the same chemical composition as the microgels and therefore exhibits excellent compatibility with them. This has the advantage of not weakening the self-assembled network of the microgels, resulting in the preservation of tensile strength.

[0012] The addition of the free polymer can induce a variation in the real part of the complex shear modulus (G') between 1xlO3 and 1xlO5 Pa. This makes it possible to obtain films with very pronounced stickiness, ranging from films with no stickiness at all. However, the elongation at break, which reflects the cohesion of the microgel network under very large deformations, does not decrease with the addition of free polymer. Structural characterization of the free polymer by aqueous chromatography reveals a highly branched polymer resembling nanogels, whose structure explains the conservation of the network's strength, which can thus follow the deformations of the skin or mucous membranes without peeling or breaking.

[0013] General description of the invention

[0014] A first object of the invention is a cosmetic composition, a pharmaceutical composition or a medical device each comprising a water-soluble polymer (WSP) and microgel particles, wherein the microgel particles and the water-soluble polymer can be independently obtained by aqueous phase precipitation polymerization of di(ethylene glycol) methyl ether methacrylate, of an oligo(ethylene glycol) methyl ether methacrylate, and of a vinyl monomer bearing a carboxyl group, in the presence of N,N'-methylenebisacrylamide as a crosslinking agent, wherein the ratio between the mass of the water-soluble polymer and the mass of the microgel particles in the dry state is between 0% and 100%.

[0015] According to one embodiment, the ratio between the mass of the water-soluble polymer and the mass of the microgel particles is between 0% and 35%, or between 35% and 100%.

[0016] A second object of the invention is a method for the topical cosmetic treatment of the skin, nails, lips, mucous membranes or hair of a person, said method comprising a first step of applying the cosmetic composition as defined above.

[0017] A third object of the invention is a process for preparing the cosmetic composition, the pharmaceutical composition or the medical device, said process comprising a step of preparing a mixture of microgel particles and a water-soluble polymer, said step comprising:

[0018] - a first step in the preparation of microgel particles,

[0019] - a second step of preparing the water-soluble polymer, and

[0020] - a third step of mixing microgel particles and the soluble polymer in water, the ratio between the mass of the water-soluble polymer and the dry mass of the microgel particles is between 0% and 100%. Description of the figures

[0021] [Fig. 1] Figure 1 is a conformation plot of the radius of gyration as a function of molar mass for MBA-WSP (red), OEGDA-WSP (blue), and PEG35K (black). The WSP is obtained from a synthesis with 2 mol% crosslinking agent. The dashed line represents a power law with an exponent of 0.6. The solid black line fits the MBA-WSP curve according to a power law with an exponent of 0.27.

[0022] [Fig.2] On [Fig.2], the number and mass molecular masses, and the polydispersity index for different WSPs are indicated.

[0023] [Fig.3] Fig.3 represents the curve of the preservation modulus G' and the loss modulus G" as a function of the frequency of an unpurified MBA film and an unpurified OEGDA film with different crosslinking rates: 2% in moles and 8% in moles.

[0024] [Fig.4] Fig.4 is a table providing the mass composition of non-films purified without purification, after synthesis.

[0025] [Fig.5A] Fig.5A represents the extensional viscosity as a function of time of unpurified MBA and OEGDA films with different crosslinking ratios: 2% by mole and 8% by mole.

[0026] [Fig.5B] The [Fig.5B] is the elongation at break for an MBA film and an OEGDA film for different crosslinking densities at 2% in moles and 8% in moles.

[0027] [Fig.6A] Fig.6A represents the storage modulus G' and the loss modulus G" as a function of frequency of a 2.0 mol% OEGDA-MG film with different MG levels.

[0028] [Fig.6B] The [Fig.6B] is the conservation modulus G' and the loss modulus G" as a function of frequency of a 2.0 mole % MBA-MG film with different MG levels.

[0029] [Fig.7] Shown on [Fig.7] are G' (square symbol), G" (triangular symbol) and tan ô (round symbol) as a function of the microgel content at co = 0.01 rad.s *. Solid symbols correspond to OEGDA, hollow symbols correspond to MBA.

[0030] [Fig.8A] [Fig.8A] is the extensional viscosity curve as a function of time for OEGDA-MG films with different MG contents.

[0031] [Fig.8B] The [Fig.8B] is the extensional viscosity curve as a function of time of OEGDA-MG films for different MG contents.

[0032] [Fig.9] Fig.9 is a bar chart representing the elongation at break for an MBA film and an OEGDA film for different MG contents.

[0033] [Fig. 10A] The [Fig. 10A] represents the extensional viscosity curve as a function of time for pure OEGDA-MG films at different film formation temperatures.

[0034] [Fig.1OB] The [Fig.1OB] is a histogram showing the elongation at break values ​​for pure OEGDA-MG films at different film formation temperatures.

[0035] [Fig. 11] Fig. 11 presents two images obtained by AFM atomic force microscopy of the upper surface of OEGDA-MG (left image) and MBA-MG (right image) films.

[0036] [Fig. 12] The [Fig. 12] presents two AFM images of a cross-section of films of OEGDA-MG (left image) and MBA-MG (right image).

[0037] [Fig. 13] Fig. 13 presents two images obtained by AFM atomic force microscopy of the upper surface of OEGDA-MG (left image) and MBA-MG (right image) films subjected to an elongation of 30%.

[0038] [Fig. 14] [Fig. 14] presents AFMs in topographic contrast and images of the LogDMT module: (a) AFM in topographic contrast and (b) LogDMT module for (c) 2% mol MBA-MG films containing 25% MG, (d) AFM in topographic contrast and (e) LogDMT module for 2% mol MBA-MG films containing 50% MG; (f) AFM in topographic contrast and (e) LogDMT module for 2% mol MBA-MG films containing 75% MG.

[0039] Definitions

[0040] It is understood from the meaning of the invention that "microgel particles" are a cross-linked polymer in the form of spherical particles having an average size that can vary from 100 nm to 1000 nm in the dry state (i.e., containing less than 2% water by mass), preferably between 100 nm and 500 nm, from 350 to 450 nm, or even better, 400 nm. The hydrodynamic radial distribution function of the microgels measured at an angle of 60° and at a temperature of 20°C can be less than 1.1.

[0041] The microgel of the invention can be obtained by aqueous phase copolymerization of several monomers. The average size of the microgel particles can vary depending on whether they contain water or not.

[0042] "Microgels," as used in this description, may be in the form of an aqueous dispersion of "microgel particles" or in the form of a film comprising microgel particles as defined above. The microgels may trap active organic molecules for cosmetic or pharmaceutical use. A film comprising microgel particles may have a thickness ranging from 1 micron to 10 millimeters, for example, from 10 microns to 500 microns, from 100 microns to 400 microns, or from 500 microns to 1000 microns. In a particular embodiment, the microgel particles preferably do not comprise any inorganic material.

[0043] It is preferred that the microgel particles be made of organic compounds. The microgel particles do not, for example, contain silica, in particular silica as a support for the cross-linked polymer.

[0044] A "crosslink" is a group (part of a molecule) that links the copolymer chains together. This crosslink originates from a "crosslinking agent" molecule that is mixed with the monomers during the polymerization process of the crosslinked polymer.

[0045] It is understood from the meaning of the invention that a "water-soluble polymer" is a polymer having a radius of gyration at 20°C of 5 nm to 80 nm, for example, from 10 nm to 30 nm. The water-soluble polymer may have an average molecular mass of 1 x 10⁵ g.mol⁻¹ to 1 x 10⁶ g.mol⁻¹. The radius of gyration and the molecular mass can be measured by any method known to those skilled in the art, for example, by size-exclusion chromatography. A water-soluble polymer is distinct from microgel particles: for example, microgel particles They can be identified by atomic force microscopy (AFM) observation of a film made by drying an aqueous dispersion of microgel particles. Conversely, no particles can be detected by AFM observation of films made by drying a water-soluble solution of the polymer.

[0046] The expression "between" excludes, within the meaning of the invention, the numerical limits that follow it. On the other hand, the expression "from ... to" includes the limits mentioned. Detailed description of the invention

[0047] The first object of the invention relates to a cosmetic composition, a pharmaceutical composition, or a medical device, each comprising a water-soluble polymer and microgel particles, said microgel particles having an average diameter of 100 nm to 1000 nm in the dry state,

[0048] wherein the microgel particles and the water-soluble polymer can be independently obtained by aqueous-phase precipitation polymerization of at least the following three monomers, in the presence of a crosslinking agent:

[0049] - di(ethylene glycol) methyl ether methacrylate,

[0050] - an oligo(ethylene glycol) methyl ether methacrylate,

[0051] - a vinyl monomer comprising a carboxyl group,

[0052] where at least one of the two crosslinking agents is N,N'-methylenebisacrylamide, and

[0053] where the ratio between the mass of the water-soluble polymer and the mass of the microgel particles in the dry state is between 0% and 100% by mass,

[0054] where the medical device includes a mixture consisting of the water-soluble polymer, microgels and optionally water, and where the solid content of the cosmetic composition, the solid content of the pharmaceutical composition, and the solid content of said mixture ranges from 1.5% to 100% by mass.

[0055] The solid content may be greater than a percentage chosen from the group consisting of 2%; 3%; 4%; 5%; 10%; 15%; 20%; 25%; 30%; 35%; 40%; 45% and 50% by mass.

[0056] According to one embodiment, the microgel particles and the water-soluble polymer comprise chains having diethylene glycol methacrylate monomer units, oligoethylene glycol methacrylate monomer units comprising 6 to 10 ethylene glycol motifs, methacrylic acid monomer units, and crosslinks. The oligo(ethylene glycol) methyl ether methacrylate preferably comprises 7 to 8 ethylene glycol motifs.

[0057] Oligo(ethylene glycol) methyl ether methacrylate may have a number-average molar mass (Mn) of 400 g / mol to 600 g / mol, preferably 450 to 500 g / mol.

[0058] The vinyl monomer may be a monomer of the formula CR1R2=CR3R4 in which RI, R2, R3 and R4 represent a hydrogen, a halogen or a hydrocarbon group, provided that at least one of the four groups comprises a -COOH or -COO-M+ group, M+ representing a cation. The vinyl monomer is preferably a (meth)acrylic acid monomer.

[0059] The microgel particles and the water-soluble polymer can be independently obtained by aqueous-phase precipitation polymerization of three monomers in the presence of a crosslinking agent. The precipitation polymerization step comprises contacting the three monomers described above and the crosslinking agent in an aqueous phase at a temperature between 40°C and 90°C, preferably around 70°C. The process does not require the presence of a surfactant, such as SDS (sodium dodecyl sulfate), and the polymerization can be initiated by the addition of a water-soluble radical initiator, for example, potassium persulfate (KPS).

[0060] According to one embodiment, the mole fraction of di(ethylene glycol) methyl ether methacrylate is 80% to 90%, the mole fraction of oligo(ethylene glycol) methyl ether methacrylate is 5% to 15%, the mole fraction of the vinyl monomer bearing a carboxyl group is 2% to 8%, and the mole fraction of the crosslinking agent is 0.5% to 10%, the sum of the four mole fractions being equal to 100%. In this description, mole fractions can be defined as the mole fractions of the monomers used to prepare the microgel or the water-soluble polymers. Mole fractions can otherwise be defined as the mole fractions of the monomer units in the microgel or in the water-soluble polymer that were obtained from the reaction between the monomers.

[0061] The mole fraction of the crosslinking agent can be from 0.5% in moles to 10% in moles, from 0.5% in moles to 8% in moles, from 1% in moles to 7% in moles or from 1.5% in moles to 6% in moles.

[0062] The molar ratio (a:b) between di(ethylene glycol) methyl ether methacrylate (a) and oligo(ethylene glycol) methyl ether methacrylate (b) is preferably between 1:1 and 20:1, for example between 5:1 and 10:1.

[0063] The (meth)acrylic acid monomer may have the formula CR1R2=CR3R4 in which RI, R2, R3 and R4 represent a hydrogen, a halogen or a hydrocarbon group, at least one of the four groups comprising a -COOH or -COO-M+ group, M+ representing a cation.

[0064] The (meth)acrylic acid monomer can be chosen from the group consisting of methyl acrylic, methyl methacrylic, ethyl acrylic, ethyl methacrylic, n-butyl acrylic, and n-butyl methacrylic, methacrylic, itaconic or acrylic acids. We prefer methacrylic acid.

[0065] Oligo(ethylene glycol) methyl ether methacrylate may have a molecular mass between 200 g / mol and 600 g / mol, or between 300 g / mol and 550 g / mol or between 450 g / mol and 500 g / mol.

[0066] In a particular embodiment, the mole fraction of di(ethylene glycol) methacrylate monomer units is 80% to 90%, preferably 82% to 86%, the mole fraction of oligo(ethylene glycol) methyl ether methacrylate monomer units is 5% to 15%, preferably 7% to 11%, the mole fraction of (meth)acrylic acid monomer units is 2% to 8%, preferably 3% to 7%, and the mole fraction of the crosslink is 1% to 6% or 1% to 3%.

[0067] According to another embodiment, the crosslinked polymer comprises copolymer chains having diethylene glycol methacrylate monomer units, oligoethylene glycol methacrylate monomer units comprising 4 to 10 ethylene glycol motifs, and methacrylic acid monomer units. The monomer units are preferably: oligo(ethylene glycol) methyl ether methacrylate having 7 or 8 ethylene glycol motifs; and methacrylic acid. The oligo(ethylene glycol) methyl ether methacrylate monomer units may also have 9 ethylene glycol motifs.

[0068] The microgel is obtained by polymerization of at least three monomers in the presence of a first crosslinking agent, and the water-soluble polymer is obtained from the polymerization of at least three monomers in the presence of a second crosslinking agent. The first and / or second crosslinking agent is N,N'-methylenebisacrylamide.

[0069] According to one embodiment, one of the two crosslinking agents has di(meth)acrylate terminal groups and a motif selected from the group consisting of -(CH2-CH2-O)m-CH2-CH2- where n is from 0 to 6, -NH-CH2-NH- and mixtures thereof. The number m is preferably from 3 to 6.

[0070] One of the crosslinking agents is, for example, N,N'-methylenebisacrylamide (MBA), while the other is 1'-(ethylene glycol) dimethacrylate (EGDMA) or an oligo(ethylene glycol) diacrylate (OEGDA). In one embodiment, the first crosslinking agent and the second crosslinking agent are both N,N'-methylenebisacrylamide.

[0071] According to a preferred embodiment, the cosmetic composition, the pharmaceutical composition, and the mixture included in the medical device are in the form of a film comprising microgels obtained with 1.8–2.2 mol% N,N'-methylenebisacrylamide as a crosslinking agent. These films are advantageous because they are very flexible.

[0072] In a particular embodiment, the cosmetic composition, pharmaceutical composition or mixture which is included in the medical device is in the form of a film which has a thickness of 500 microns to 1,000 microns.

[0073] The ratio between the mass of the water-soluble polymer and the mass of the microgel particles is greater than 0% and less than 100%. The ratio may have a lower value, which is selected from the group consisting of 5%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%. The ratio may have a higher value, which is selected from the group consisting of 5%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%.

[0074] In one embodiment, the ratio between the mass of the water-soluble polymer and the mass of the microgel particles is between 0% and 35%. In a second embodiment, the ratio between the mass of the water-soluble polymer and the mass of the microgel particles is between 35% and 100%.

[0075] The cosmetic composition and the pharmaceutical composition can be a liquid, a gel or a solid.

[0076] The cosmetic composition, pharmaceutical composition, or mixture consisting of the water-soluble polymer, microgels, and optionally water, which is included in the medical device, may contain from 50% to 100% by mass of a mixture consisting of microgel particles and water-soluble polymer, and from 0% to 50% by mass of water, the percentages being relative to the mass of the composition and the mass of the microgel particles being the mass of the particles in the dry state. The solids content of the cosmetic composition, the solids content of the pharmaceutical composition, and the solids content of the mixture consisting of the water-soluble polymer, microgels, and optionally water, which is included in the medical device, may be from 50% to 100% by mass.In the case where the composition of the invention is liquid, it can be spread on the skin or mucous membranes and can form a transparent film adhering to the skin or mucous membranes through simple evaporation of water. It is known that the skin has a low elastic modulus and that the applied product must have a modulus comparable to that of the skin so as not to be felt by the user. In this invention, the free polymer acts as a lever to adjust the modulus according to the intended application. During product formulation, the addition of components, such as gelling agents or bioactives, can increase the modulus: it is then possible to add the appropriate proportion of free polymer to reduce it to a target value. The films have high elongation at break regardless of the free polymer content, which is essential for application on the face, for example.

[0077] The composition may comprise from 1% to 100% by mass of microgels. According to one embodiment, the composition comprises from 1% to 50% by mass of microgels relative to the mass of the composition, and from 0.9% to 100% by mass of water relative to the mass of the composition.

[0078] The composition may be in the form of a dispersion of microgels in water. The aqueous dispersion may comprise from 1% to 50% by mass of a mixture consisting of microgels and a water-soluble polymer, based on the mass of the composition, and from 50% to 99% by mass of water, based on the mass of the composition.

[0079] The composition may be in the form of a film having a thickness of 1 micron to 10 millimeters in thickness, comprising from 50% to 100% by mass of a mixture consisting of microgels and a water-soluble polymer, and from 0% to 50% by mass of water, the percentages being expressed relative to the total mass of the composition.

[0080] The films can be produced from an aqueous dispersion comprising the microgel and the water-soluble polymer, by evaporation of the water. The aqueous dispersion is, for example, spread onto a rigid or flexible substrate, where the substrate has a temperature between 20°C and 60°C, even better a temperature of 30°C to 40°C, and even better a temperature of 35°C.

[0081] The films can be formed by a step of placing a dispersion of microgel particles in water and the water-soluble polymer in a mold, and by a step of drying the dispersion. Drying can be achieved by placing the mold at a temperature above ambient temperature, for example, a temperature of 30°C to 60°C.

[0082] The cosmetic composition may include at least one component selected from the group consisting of preservatives, perfumes, emollients, surfactants, oils, biologically active products, pigments and colorants.

[0083] According to the second object of the invention, the process of the invention comprises a first step of preparing microgels, a second step of preparing the water-soluble polymer and a third step of mixing the two.

[0084] The process for preparing a cosmetic composition, a pharmaceutical composition, or a medical device as described above, said process comprising a step of preparing a mixture of microgel particles and a water-soluble polymer, said step comprising a first step and a second step which may be successive, in any order, or simultaneous:

[0085] - said first step being a step of preparing microgel particles, and comprising a step (i) of aqueous phase precipitation polymerization of at least the following three monomers, in the presence of a first crosslinking agent:

[0086] - di(ethylene glycol) methyl ether methacrylate,

[0087] - an oligo(ethylene glycol) methyl ether methacrylate,

[0088] - a vinyl monomer bearing a carboxyl group,

[0089] and a purification step (ii) to recover microgel particles that were obtained at the end of step (i),

[0090] - said second step of preparing the water-soluble polymer comprising a step (a) of polymerization by precipitation in aqueous phase of at least the following three monomers, in the presence of a second crosslinking agent:

[0091] - di(ethylene glycol) methyl ether methacrylate,

[0092] - an oligo(ethylene glycol) methyl ether methacrylate,

[0093] - a vinyl monomer bearing a carboxyl group,

[0094] and a purification step (b) to recover the water-soluble polymer obtained at the end of step (a),

[0095] wherein at least the first or second crosslinking agent is N,N'-methylenebisacrylamide,

[0096] - a third step which follows said first step and said second step, said the third step being a mixing step of a mass of purified microgel particles obtained at the end of said first step, and a mass of water-soluble polymer obtained at the end of said second step,

[0097] where the ratio between the mass of the water-soluble polymer and the dry mass of the microgel particles is between 0% and 100%.

[0098] Step (ii) may include at least one centrifugation / redispersion cycle to separate the precipitate and the supernatant material, and a step for recovering microgel particles from the precipitate.

[0099] Similarly, step (b) may include at least one centrifugation / redispersion cycle to separate the precipitate and the supernatant material, and a step of recovering the water-soluble polymer from the supernatant material.

[0100] According to one embodiment, the first step and the second step are a single step, such that microgel particles and a water-soluble polymer are produced at the same time from the same monomers, wherein the single step comprises at least one centrifugation / redispersion cycle to separate the precipitate and the supernatant material that were obtained from the aqueous phase precipitation polymerization of the monomers, said microgel particles being recovered in the precipitate, and said water-soluble polymer being recovered in the supernatant material.

[0101] In the case where the first and second steps are a single step - the ratio between the mass of the water-soluble polymer in the supernatant and the mass of the microgel particles in the precipitate is a first ratio and, in the third step, the ratio between the mass of the water-soluble polymer and the mass of the microgel particles is a second ratio which is between 0% and 100% and which is different from the first ratio.

[0102] The first crosslinking agent and the second crosslinking agent are preferably both N,N'-methylenebisacrylamide, although one of them may be different from this.

[0103] The invention also relates to a method for topical cosmetic treatment of a person's skin, nails, lips, mucous membranes, or hair, said method comprising a first step of applying a cosmetic composition as described above to the person. The method may include a second step of drying the composition or device that has been applied to the person to obtain a flexible, cohesive, and adhesive film. Examples

[0104] Microgels of poly(oligo-(ethylene glycol) methacrylate), water-soluble polymers, and films comprising a mixture of these microgels and water-soluble polymers were prepared according to the following protocol. Their rheology (linear and non-linear) was studied and their structure was observed by atomic force microscopy (AFM).

[0105] - A) Preparation of microgels (MG), water-soluble polymers (WSP) and films including these starting materials

[0106] Di(ethylene glycol) methyl ether methacrylate (MEO2MA, 95%), oligo(ethylene glycol) methyl ether methacrylate (OEGMA, terminated with 8 EG units with Mn=475 g.mol*), methacrylic acid (MAA), poly(ethylene glycol) diacrylate (OEGDA, Mn=250 g.mol*), N,N-methylenebisacrylamide (MBA), and potassium persulfate (KPS) were purchased from Sigma Aldrich and used as receipts. Purified water from a Millipore Milli-Q system was used.

[0107] Synthesis of microgels, synthesis of WSP and film preparation

[0108] MEO2MA (92.6 mmol), OEGMA (10.3 mmol), and a crosslinking agent (OEGDA or MBA) were dissolved in 930 g of water. The crosslinking agent ratios were set at either 2.0 mol% or 8.0 mol% depending on the total vinyl molecules, corresponding to 2.12 mmol and 9.42 mmol, respectively. The mixture was introduced into the 2 L reactor, and the stirring speed was set at 150 rpm. The reactor was purged with nitrogen for 45 min to remove oxygen at room temperature. MAA (5.41 mmol) was dissolved in 30 g of water and added to the reactor. The mixture was then heated to 70°C. Finally, KPS (0.958 mmol) was dissolved in 40 g of water and added to the reactor to start the reaction. The reaction is then maintained at 70°C for 6 hours.

[0109] A first part of the aqueous suspension comprising MG and WSP is obtained and the films (F6, F6', F7 and F7') are formed.

[0110] A second portion of the aqueous suspension is separated by 3 centrifugation cycles (20,000 rpm, 20 min), where WSP is retained in the aqueous supernatant while MG is found in the precipitate. Films with WSP alone (F5 and F5') and films with MG alone (F1 and F1') are formed as comparative films.

[0111] Films comprising a mixture of WSP and MG in a predetermined ratio are also prepared (F2, F2', F3, F3', F4 and F4'). Film preparation process

[0112] Films were formed by the direct evaporation of water from microgel solutions in a glass bell oven heated to 37°C. It was demonstrated that the formation temperature does not influence the film properties. Silicone molds were used as containers for easy removal of the films after drying. For the rheological experiments, the final film thicknesses were between 500 microns and 1000 microns. All thicknesses below and above these values ​​are nevertheless technically feasible, for example, as small as 500 nm.

[0113] B) Determination of the molar mass of water-soluble polymers (WSP) by size-exclusion chromatography

[0114] - Method: The size exclusion chromatography (SEC) apparatus consists of A set of aqueous columns from Shodex and an Agilent 1260 Iso pump from Agilent Technologies were used. The apparatus was coupled with a Multi-Angle Light Scattering (MALS) detector and a differential refractometer (DR) detector. The MALS detector used was a Dawn Heleos detector from Wyatt Technology. The DR detector was an Optilab T-rEX from Wyatt Technology operating at a laser wavelength of 664 nm. The flow rate was fixed at 0.5 mL / min during the experiment, and the column temperature was fixed at 30°C. The mobile phase consisted of a 0.1 g / mol (8.2 g / L) NaNO3 solution and sodium azide (NaN3) (0.1 mol / L) as the eluent, stabilized with a pH 8 buffer. The mobile phase was filtered to 0.1 µm before use. Water-soluble polymer solutions are prepared at a concentration of 200 ppm in a pH 8 buffer, into which a volume of 100 pL is injected. The solutions are filtered before use at 250 nm to remove any impurities and microgels.

[0115] To interpret the SEC results, the value of the refractive index increment (dn / dc) is experimentally measured on a WYATT Technology Optilab T-rEX refractometer with a laser wavelength of 532 nm. Five WSP solutions are prepared with Milli-Q water at different concentrations (0.97 g L⁻¹; 0.75 g L⁻¹; 0.51 g L⁻¹ and 0.11 g L⁻¹).

[0116] - Results: Size exclusion chromatography makes it possible to determine the molar mass of WSP from a 2 mol% OEGDA synthesis and a Synthesis of 2 mol% MBA. This technique has the advantage of measuring both the molecular mass and the radius of gyration. It thus provides more information regarding the structure of WSP. OEGDA-WSP and MBA-WSP are compared to a linear PEG with an average molecular mass of 35,000 g / mol*. The molar mass and the radius of gyration are related by Flory's theory.

[0117] With a SEC technique, the separation is done by size: larger objects will pass through the column set earlier (= in a smaller elution volume) than smaller objects.

[0118] Figure 1 shows the conformity plot, i.e., the radius of gyration as a function of molecular weight, for OEGDA-WSP, MBA-WSP, and PEG 35K. Figure 2 summarizes the molecular weights and polydispersity index of OEGDA-WSP, MBA-WSP, and PEG 35K. PEG 35K has an average Mw of 34,000 g·mol⁻¹, which validates the reliability of the method used. Because the polymer has a very narrow mass distribution, it is not possible to observe the variation of the radius of gyration as a function of molecular weight. OEGDA-WSP and MBA-WSP share a similar population of molecular weights, ranging from 1 × 10⁴ to 1 × 10⁵ g·mol⁻¹. These polymer chains have an average radius of gyration of around 15-20 nm, indicating a very dense structure. MBA-WSP exhibits a significant proportion of molecular masses, ranging from 1 x 10⁶ g.mol*, which does not appear in the OEGDA chromatogram. These masses reach gyration radii of up to 30 nm. The detection limit of the equipment corresponds to Rg equal to approximately 10 nm and explains the dispersed value for the smallest radii. As mentioned, linear PEG 35K (black dots) exhibits such a narrow mass distribution that it is not possible to fit the gyration radius using a power law. The black line drawn from Rg = 0.6 Mw was therefore added to represent a theoretical linear polymer in a good solvent. Only MBA-WSP was fitted using a power law since it is the population with the clearest and widest variation. The value of the power-law exponent was found to be a = 0.27, which is very close to the theoretical value for dendrimers.The latest result confirms the initial hypothesis that the water-soluble polymer formed during the synthesis is, for both crosslinkers, a hyperbranched polymer with a diameter of 30 to 60 nm.

[0119] C) Spectromechanical characterization of films comprising microgels alone (comparatives), water-soluble polymers alone (comparatives) and films comprising microgels and WSP (invention)

[0120] Certain films are formed from the aqueous suspension comprising MG and WSP which is obtained from the aqueous precipitation polymerization process, before any centrifugation stage.

[0121] F6 - 2% by mole OEGDA: (32% by mass WSP - 68% by mass MG);

[0122] F7 - 8% by mole OEGDA: (22% by mass WSP - 78% by mass MG);

[0123] F6' - 2 mole% MBA: (29% by mass WSP - 71% by mass MG);

[0124] F7' - 8% by mole MBA: (20% by mass WSP - 80% by mass MG);

[0125] Other films are formed by mixing with a controlled ratio of a microgel (MG) and a water-soluble polymer (WSP) which were recovered from the precipitate and supernatant material, after the centrifugation step.

[0126] Fl - 2% by mole OEDGA comparative (0% by mass WSP - 100% by mass MG);

[0127] Fl' - 2% by mole comparative MBA (0% by mass WSP - 100% by mass MG);

[0128] F2 - 2% by mole OEDGA (25% by mass WSP - 75% by mass MG);

[0129] F2' - 2% by mole MBA (25% by mass WSP - 75% by mass MG);

[0130] F3 - 2% by mole OEDGA (50% by mass WSP - 50% by mass MG);

[0131] F3' - 2% by mole MBA (50% by mass WSP - 50% by mass MG);

[0132] F4 - 2% by mole OEDGA (75% by mass WSP - 25% by mass MG);

[0133] F4' - 2 mole% MBA (75% by mass WSP - 25% by mass MG);

[0134] F5 - 2% by mole OEDGA comparative (100% by mass WSP - 0% by mass MG);

[0135] F5' - 2% by mole MBA comparative (100% by mass WSP - 0% by mass MG). 1. Spectromechanical characterization method

[0136] To study the mechanical properties, the films are characterized by linear oscillatory rheology and non-linear extensional rheology on an MCR 302 rheometer from Anton Paar.

[0137] Oscillatory rheology is performed on films approximately 1 mm thick using parallel 8 mm plates at a controlled temperature. Frequency sweeps are carried out at 20°C from 0.01 to 600 rad / s at a constant elongation of 1%, which ensures the linear regime.

[0138] Extensional rheology is performed using a Sentmanat Extension Rheometer (SER) geometry consisting of matched winding drums moving in equal but opposite rotations. The tests are carried out at 20°C. The film dimensions are within the following range: 0.5–1 mm x 1–2 mm x 15–20 mm. Thickness and width are measured before testing using optical microscopy and calipers, respectively. The films are stretched to breakage at a constant elongation rate, also known as the Hencky elongation rate (eH). A minimum of fifty samples is tested for each film type. The extensional viscosity (qE) is measured as a function of time. The logarithmic elongation in the sample, also known as the Hencky eH, is a function of e, the constant elongation rate; t, time; L, the sample length at time t; and L0, the initial sample length. In order to To calculate the elongation at break eR, the constant elongation rate is multiplied by the time to break.

[0139] 2. Spectromechanical characterization of comparative films (Fl: 0% WSP and 100% MG)

[0140] The impact of formation temperature was evaluated by forming purified films at 20°C, 32°C, 37°C, and 60°C. The aim was to assess whether the state of the microgels, i.e., slumped or swollen, impacts the quality of the assembly during film formation. Indeed, during the liquid-to-solid transition, the state of the microgel can play a significant role; that is, microgels swollen below the VPTT would create more intra-entanglements than microgels slumped above the VPTT. The extensional viscosity was measured at 20°C with a constant elongation rate of 0.5 s⁻¹.

[0141] Figure 10 shows the average extensional viscosity for four different formation temperatures. It is clearly observed that the formation temperature does not affect the extensional viscosity or the elongation at break. It is not a parameter governing the mechanical properties of the films. If the microgels are below the VPTT (20°C), in the interval (32°C, 37°C), or above (60°C), the elongation at break remains at 133 ± 2%. The microgel shell appears to retain some mobility at 60°C, which allows the microgels to interpenetrate each other in their collapsed state. Furthermore, the microgel films, once formed, are maintained at 20°C and tested at 20°C. The chains thus have time to relax and reach a similar state of interpenetration, regardless of the formation temperature. 3. Spectromechanical characterization of films (F6 and F7)

[0142] The following four systems were studied: 2 mol% OEGDA, 2 mol% MBA; 8 mol% OEGDA and finally 8 mol% MBA. [Fig. 4] shows the ratio of water-soluble polymer to microgels in the different films that were prepared. 3.1 Linear Rheology: Results

[0143] The dynamic rheological response is compared for the different films in [Fig.3]. Frequency sweeps, with fixed elongation in the linear domain, were carried out at 20°C.

[0144] All the films generally behaved like viscoelastic solids since G' is greater than G" at low frequency values. The films reach a plateau at low frequency values, which is characteristic of chain entanglement in the films (elastic lattice). The transition to the glassy region is observed in all cases by an intersection point of G' and G" at higher frequencies. The storage moduli of 2 mol% OEGDA and 2 mol% MBA are approximately 1 x 10⁵ Pa at 1 Hz (6 rad / s). The films thus exhibit very low tackiness. Indeed, the Dahlquist criterion states that G' would be less than 1 x 10⁵ Pa at 1 Hz for the material exhibits rapid and measurable tackiness.

[0145] The modulus of 8 mol% MBA films increases considerably compared to 2 mol% crosslinking agent, by approximately 1.5 x 10⁶ Pa and 1 x 10⁵ Pa at 1 Hz (6 rad / s), respectively. The increased storage modulus, resulting from the higher crosslinking agent density, leads to a less flexible film that exhibits no stickiness whatsoever.

[0146] An 8 mol% OEGDA film surprisingly exhibits moduli very similar to those of 2 mol% films. This particular behavior could be explained by a higher quantity of water in the film at the time of testing, due to an uncontrolled humidity environment or incomplete drying of the film. 3.2 Extensional Rheology: Results

[0147] Extensional rheology consists of elongating materials in the nonlinear strain range at a constant elongation rate. Uniaxial extension can produce a much higher degree of molecular orientation and stretching than simple tearing. Therefore, extensional rheology is more sensitive to long-chain polymer branching and can be more descriptive than other types of bulk rheological tests. Extensional rheology allows for establishing a relationship with adhesive behavior.

[0148] The extensional viscosity of OEGDA and MBA films for 2 mol% and 8 mol% of crosslinker was measured at 20°C at a constant elongation rate: 0.5 s1. The logarithm of the mean elongation at break eR as well as the ratio LR / L0 were calculated with the following formula: eR = ex tR = In (LR / L0).

[0149] Figure 5 (right-hand image) shows the average extensional viscosity as a function of time for MBA and OEGDA for the two crosslinking ratios. First, the extensional viscosity increases steadily following the linear viscoelastic envelope defined by the slope of 3 times the complex viscosity: 3.q*.

[0150] For elongation values ​​above 40%, the extensional viscosity begins to deviate upwards from the zero-speed shear viscosity. This upward deviation is referred to as elongation-curing and classically appears in chemically crosslinked or physically well-entangled polymers. It is an indicator of the chain branching architecture. Chain entanglements begin to resist extension whenever the chain extensibility limit is approached, causing the network to stiffen. Consequently, the extensional viscosity follows an upward deviation. The occurrence of elongation-curing was expected since the films contained 2 mol% and 8 mol% crosslinking agent, respectively. Elongation-curing was considered a desirable property for improved adhesive performance.It fulfills the typical requirement for an adhesive that fails without leaving any residue. sticky residue on the surface providing cohesion to the network under high deformation.

[0151] The OEGDA and MBA films exhibit similar behavior in the linear region. However, the elongation at break is significantly higher for MBA than for OEGDA, regardless of the crosslinking density, Figure 5 (left image). This indicates that the MBA network withstands higher stress before breaking, although it does not differentiate between the influence of the water-soluble polymer and the microgels. Increasing the crosslinking density leads to lower elongation at break for both crosslinkers. This is because a more crosslinked network cannot stretch as much to accommodate the stress and breaks at a less advanced stage. Denser, more crosslinked particles also tend to interpenetrate less, thus creating a weaker network.

[0152] 4. Spectro-mechanical characterization of films (Fl to F5)

[0153] The formulation consisting of film formation with a controlled ratio of WSP and MG was carried out for films of 2 mol% MBA and 2 mol% OEGDA. The linear oscillatory rheology and linear extensional rheology methods are identical to those described above. 4.1 Linear Rheology: Results

[0154] Frequency scans at 20°C were carried out for the two crosslinkers OEGDA and MBA on the five different formulated films, i.e. with a MG content of 0% by mass to 100% by mass.

[0155] The dynamic rheological response is compared for different MG contents for OEGDA and MBA in Figure 6. It is important to note that all films, regardless of MG content, behaved like viscoelastic solids since G' is greater than G" at low frequencies. Regardless of MG content, all microgel films reached a plateau at low frequencies, indicating the presence of a polymer network. The flow region is not observed, even for films made of 100% WSP. This important result indicates crosslinking and / or branching in the water-soluble polymer. Thus, WSP is not linear and does not flow like thermoplastic polymers (within the parameter ranges explored in this work: frequency, temperature, etc.). The glass transition is observed in all films as an intersection of G' and G" at high frequencies.For both crosslinkers, the crossing does not vary significantly with the addition of WSP. The glass transition thus appears at approximately the same frequency regardless of the amount of WSP. This is not surprising since the glass temperature of a polymer is determined by its molecular structure. As observed in [Fig. 7], the storage and loss moduli (taken in the rubbery plateau at co = 0.01 rad.s*). The shear modulus increases significantly with increasing MG content. MG particles increase the shear modulus, similarly to the fillers that bind a composite. Furthermore, as tan θ approaches infinity, the G" / G' ratio decreases with increasing MG content, indicating that the dissipative response of the films is lower and less pronounced. The ability to shift the shear modulus towards higher or lower values ​​by controlling the MG / WSP ratio is extremely valuable, as it provides a simple lever for adjusting the tackiness or adhesive properties of the films according to the intended application. For both systems, G' is approximately 1 x 10⁵ Pa at 1 Hz: 8.5 x 10⁴ Pa and 1.5 x 10⁵ Pa for OEGDA-MG and MBA-MG, respectively. It is reported that the films exhibit very fine tackiness at 20°C when fully purified. 4.2 Extensional Rheology: Results

[0156] The extensional viscosity for 2 mol% OEGDA and MBA films with different MG contents was measured at 20°C for a constant elongation rate of 0.5 s1. Figure 8 shows the average extensional viscosity as a function of time for MBA and OEGDA for different MG contents.

[0157] For elongation values ​​above 40%, the extensional viscosity begins to deviate upwards from the zero-speed shear viscosity for all formulations. As previously mentioned, this upward deviation is called elongation-curing. The appearance of elongation-curing for 100% MG films is expected since the films contained 2 mol% of a crosslinking agent providing crosslink points to the network. However, it is more surprising to note that all films, including 100% WSP, exhibit elongation-curing. We can therefore assume that the network stiffening is much more related to chemical crosslink points than to physical entanglements of branched chains. As expected, the microgel content has a significant impact on the extensional viscosity values. Indeed, the microgels act as matrix stiffening fillers and increase the G' and G" moduli.As a direct consequence, higher moduli increase the extensional viscosity value.

[0158] However, it follows that the microgel content does not impact either the elongation / hardening or the elongation at break. In the field of future applications, this result is extremely positive since it indicates that the proportion of water-soluble polymer can be modified to adjust the desired modulus according to the application without losing the film's stretching capacity in any case. As observed in [Fig. 9], the logarithmic elongation at break is significantly higher for MBA films than for OEGDA films, regardless of the microgel content. This initially confirms that the microgel network MBA withstands higher stress before fracture than OEGDA particles. This reinforces the assumption of a greater capacity for MBA to form a stronger network, likely due to a looser shell architecture compared to OEGDA-MG. The second important result of [Fig. 9] is that MBA films composed of 100% WSP also exhibit higher elongation at break than OEGDA-WSP films. This corroborates the SEC results, which show a more branched structure in the case of MBA-WSP. D) Microgel film assembly (F1 to F5)

[0159] Method: Topographic images were captured using AFM (Bruker Multi-Mode 8) to analyze the microgel assembly on the film surface. For all scans, the Peak Force QNM Air mode and ScanAsyst Air probes (average spring constant k of 0.4 N·m) were used. Clear cross-sections of microgel films were also prepared to visualize the assembly within the film using a Leica EM UC7 ultra-cryo-microtome and a Leica EM-FC7 cryo-chamber cooled to -80°C. Finally, the films were manually subjected to unidirectional stretching, and images were formed in the stretched state. The elongation was 30%. Results for the films Fl and Fl' comparative

[0160] Atomic force microscopy was performed on the upper surface of films made with 100% microgels (no water-soluble polymer). The microgel particles self-assemble in a near-hexagonal, near-perfect packing, as seen in the topographic contrast images in [Fig. 1 1] (right image) for 2 mol% OEGDA-crosslinked microgels and (left image) for 2 mol% MB A-crosslinked microgels. Unlike conventional latex, the particles do not coalesce but maintain their spherical shape with some interpenetration. The AFM topographic contrast images showed the slightly larger size of the MBA-crosslinked microgels.

[0161] Cross-sections of films were surface-treated by ultra cryomicrotomy and observed by AFM. The topographic contrast images in [Fig. 12] show the settling of spherical particles with localized hexagonal settling. Unlike the deformation of particles that have fallen and dried on a hard wafer, the multiple stacking layers of MG during solvent evaporation have not flattened and remain spherical. A contrast difference of approximately 15 nm between the core and the bark is observed for most microgels in both types of crosslinkers. Even after being formed, the microgel films contain and absorb water from their surroundings. As a result, it can be suggested that the bark, which is much more swollen, is loosely crosslinked and the The heart, which is more hollow, is more reticulated than the bark.

[0162] Microgel films were stretched to achieve 30% elongation, and their upper surfaces were observed by AFM. Figure 13 shows a 5 mm topographic contrast image of A-crosslinked OEGD and A-crosslinked MB microgel films. The stretching direction is parallel to the X-axis. Stretching causes the loss of hexagonal compactness and deformation of the particle network. Gaps appear between the microgels in the direction of deformation. However, it appears that the microgels are not significantly deformed and maintain their spherical shape. It is suggested that, at this elongation, most of the tangled chains of the microgel shell stretch to accommodate the stress, and the dense core is not yet deformed.

[0163] Results of WSP-MG film assembly according to the invention F2 to F4'

[0164] Cross-sections of reformulated films with microgel content controlled by AFM were observed. Figure 14 shows the 2-micron topographic contrast image (a) and the logDMT modulus (b) of 2 wt. MBA-MG films with 25 wt. MG. The logDMT channel shows the stiffest regions in lighter colors and the softest regions in dark colors. As expected, the microgels are much denser than the water-soluble polymer and resemble fillers dispersed in a flexible composite matrix. They do not form aggregates but are not perfectly homogeneously dispersed. Figure 14 shows the 1 mm topographic contrast image (c) and the logDMT modulus (d) of 2 wt. MBA-MG films with 50 wt. MG. The microgels begin to come into contact with each other, but no structured arrangement is observed. In some areas, a depletion of microgel is observed.Figure 14 shows the 500 nm topographic contrast image (e) and the logDMT modulus (f) of MBA-MG films for 75 wt% MG. Similar conclusions can be drawn; the microgels are closer together, but no hexagonal packing arrangement is observed.

[0165] Once again, the core / shell structure is clearly observed, with a distinct modulus gradient between the core and the WSP matrix. The denser, less swollen cores are characterized by hollows, while the shells are more swollen than the cores but slightly denser than the water-soluble polymer, which is characterized by a lower modulus. A very gradual transition is observed between the microgel shell and the water-soluble polymer, suggesting a similar structure and some interpenetration between the two phases. E) Conclusion

[0166] Linear rheology on 2 mol% OEGDA and MB A-crosslinked microgel films demonstrates that the shear modulus value can vary and be The properties of the microgel films are adjusted via the water-soluble polymer content, from 0% to 100%. As a result, a range of films can be formed, from highly sticky to non-sticky, on any substrate simply through water evaporation. These microgel films exhibit interesting mechanical properties under high deformation. Elongation at break reaches up to 60%, demonstrating that these films possess strong cohesion for a simple, spontaneously self-assembling particle network. Furthermore, varying the water-soluble polymer content allows for adjustments to the rheological properties without altering the films' stretching properties. Indeed, all films, regardless of microgel content, exhibit elongation-hardening, a valuable property for adhesives as it ensures film cohesion during detachment.The latest finding suggests that a water-soluble polymer is clearly branched and / or crosslinked, since films composed entirely of it also exhibit elongation-hardening. The elongation at break of A-crosslinked MB films is significantly higher than that of OEGDA-crosslinked films at 2 mol% crosslinker. This correlates with the results on suspension viscosities, which show that A-crosslinked MB particles exhibit higher interaction and tend to form a stronger network. These stronger interactions, likely due to the higher number of chains suspended on the surface, lead to a higher elongation at break when the film is formed, as the microgels are more interpenetrated. Furthermore, the elongation at break decreases for higher crosslinker ratios in a manner similar to how viscosity decreases for dispersions.Denser particles tend to exhibit less interpenetration and form a weaker network than looser, cross-linked particles.

Claims

Demands

1. A composition comprising a water-soluble polymer and microgel particles, said microgel particles having an average size of 100 nm to 1000 nm in the dry state, characterized in that the microgel particles and the water-soluble polymer are independently obtained by aqueous-phase precipitation polymerization of at least the following three monomers, in the presence of a crosslinking agent: - di(ethylene glycol) methyl ether methacrylate, - an oligo(ethylene glycol) methyl ether methacrylate having a number-average molar mass of 400 g / mol to 600 g / mol, - a vinyl monomer comprising a carboxyl group, wherein at least the crosslinking agent used to prepare the microgel particles or the crosslinking agent used to prepare the water-soluble polymer is N,N'-methylenebisacrylamide,and where the ratio between the mass of the water-soluble polymer and the mass of the microgel particles in the dry state is between 0% and 100% by mass, and where the solid content of the composition is from 3% to 100% by mass.

2. Composition according to claim 1, characterized in that the composition contains from 50% to 100% by mass of a mixture consisting of microgel particles and water-soluble polymer, and from 0% to 50% by mass of water, the percentages being relative to the mass of the composition, and the mass of the microgel particles being the mass of the particles in the dry state.

3. Composition according to claim 1 or 2, characterized in that the solid content of the composition is from 50% to 100% by mass.

4. Composition according to any one of the preceding claims, being in the form of a film having a thickness of 500 microns to 1000 microns.

5. Composition according to any one of the preceding claims, characterized in that the radius of gyration of the water-soluble polymer measured by size-exclusion chromatography at 20°C is from 5 nm to 80 nm.

6. Composition according to any one of the preceding claims, characterized in that the water-soluble polymer has an average molecular mass measured by size-exclusion chromatography at 20°C of 1 x 10⁵ g.mol⁻¹ to 1 x 10⁶ g.mol⁻¹.

7. Composition according to any one of the preceding claims, characterized in that the mole fraction of di(ethylene glycol) methyl ether methacrylate is 80% to 90%, the mole fraction of oligo(ethylene glycol) methyl ether methacrylate is 5% to 15%, the mole fraction of the vinyl monomer bearing a carboxyl group is 2% to 8%, and the mole fraction of the crosslinking agent is 0.5% to 10%, the sum of the four mole fractions being equal to 100%.

8. Composition according to any one of the preceding claims, characterized in that the ratio between the mass of the water-soluble polymer and the mass of the microgel particles is between 0% and 35%.

9. Composition according to any one of claims 1 to 7, characterized in that the ratio between the mass of the water-soluble polymer and the mass of the microgel particles is between 35% and 100%.

10. A method for topical cosmetic treatment of the skin, nails, lips, mucous membranes or hair of a person, said method comprising a first step of applying to the person a composition according to any one of claims 1 to 9.

11. A process for preparing a composition according to any one of claims 1 to 9, said process comprising a step of preparing a mixture of microgel particles and a water-soluble polymer, said step comprising a first step and a second step which may be successive in any order, or simultaneous: - said first step being a step of preparing microgel particles, and comprising a step (i) of aqueous-phase precipitation polymerization of at least the following three monomers, in the presence of a first crosslinking agent: - di(ethylene glycol) methyl ether methacrylate, - an oligo(ethylene glycol) methyl ether methacrylate, - a vinyl monomer bearing a carboxyl group, and a step (ii) of purification to recover microgel particles which were obtained at the end of step (i), - said second step of preparing the water-soluble polymer,and comprising a step (a) of aqueous-phase precipitation polymerization of at least the following three monomers, in the presence of a second crosslinking agent: - di(ethylene glycol) methyl ether methacrylate, - an oligo(ethylene glycol) methyl ether methacrylate, - a vinyl monomer bearing a carboxyl group, and a purification step (b) for recovering the water-soluble polymer obtained at the end of step (a), characterized in that at least the first or second crosslinking agent is N,N'-methylenebisacrylamide, - a third step following the first step and said second step, said third step being a mixing step of a mass of purified microgel particles obtained at the end of said first step, and a mass of water-soluble polymer obtained at the end of said second step, - wherein the ratio between the mass of the water-soluble polymer and the dry mass of the microgel particles is between 0% and 100%.

12. A process according to claim 11, characterized in that step (ii) comprises at least one centrifugation / redispersion cycle to separate the precipitate and the supernatant, and a step of recovering microgel particles from the precipitate.

13. A process according to claim 11 or claim 12, characterized in that step (b) comprises at least one centrifugation / redispersion cycle to separate the precipitate and the supernatant material, and a step of recovering the water-soluble polymer from the supernatant material.

14. A process according to claim 11, 12 or 13, characterized in that the first step and the second step are a single step, such that microgel particles and a water-soluble polymer are produced at the same time from the same monomers, wherein the single step comprises at least one centrifugation / redispersion cycle to separate the precipitate and the supernatant material which have been obtained from the aqueous phase precipitation polymerization of the monomers, said microgel particles being recovered in the precipitate, and said water-soluble polymer being recovered in the supernatant material.

15. A process according to claim 14, characterized in that - in the single step - the ratio between the mass of the water-soluble polymer in the supernatant material and the mass of the microgel particles in the precipitate is a first ratio and - in the third step - the ratio between the mass of the water-soluble polymer and the mass of the microgel particles is a second ratio which is between 0% and 100% and which is different from the first ratio.

16. A process according to claim 11, characterized in that the first crosslinking agent and the second crosslinking agent are N,N'-methylenebisacrylamide.

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