The present invention relates to a process, in particular a cosmetic process, for caring for the skin, intended to attenuate wrinkles, comprising the application to the skin of the mixture of a composition comprising a grafted polysaccharide polymer and of a particular crosslinking thiol compound, and to the use of this mixture as a skin tensioning agent.

During the ageing process, various signs appear on the skin, which are very characteristic of this ageing, resulting in particular in a modification of skin structure and functions. The main clinical signs of skin ageing are in particular the appearance of fine lines and deep wrinkles, which increase with age.

It is known practice to treat these signs of ageing using cosmetic or dermatological compositions containing active agents capable of combating ageing, such as ohydroxy acids, β-hydroxy acids and retinoids. These active agents act on wrinkles by eliminating dead skin cells and by accelerating the cell renewal process. However, these active agents have the drawback of only being effective for the treatment of wrinkles after a certain application time. However, it is increasingly sought to obtain an immediate effect of the active agents used, rapidly resulting in smoothing out of wrinkles and fine lines and in the disappearance of the signs of fatigue.

The inventors have discovered that a polysaccharide polymer grafted with (meth)acrylate groups combined with a particular thiol compound, applied to the skin, has a good tensioning effect on the skin and thus makes it possible to immediately attenuate wrinkles on the skin. Furthermore, this tensioning effect exhibits good water resistance, and therefore good persistence with respect to water. The tensioning effect is also resistant to sweat, and to the mechanical stresses created by movement of the skin.

Polymers of hyaluronic acid grafted with (meth)acrylate groups are described in document WO 2007/106738 and the publications J. Burdick et al "Controlled degradation and mechanical behavior photopolymerized hyaluronic acid networks", Biomacromolecules, 2005, 6, pages 386-391 ; Mark Grinstaff "Photocrosslinkable polysaccharides for in situ hydrogel formation", Journal of biomedical materials research, 2001 , volume 55, Issue 2, pages 1 15-121 . They have been used to form hydrogels after crosslinking.

Dextran polymers grafted with methacrylate groups are described in document WO 2010/083039. They are used in combination with riboflavin and arginine or chitosan for forming, after crosslinking under UV exposure or exposure to visible light, hydrogels which are applied to the skin. The article S.H.Kim, "Synthesis and characterization of dextran-methacrylate hydrogels and structural study by SEM" J. Biomed Mater Res , 49 (2005) 517 describes hydrogels obtained by photo-crosslinking after UV exposure of dextran methacrylate. Carrageenans are known for their skin tensioning properties, in particular in document FR-A-2838343.

More specifically, a subject of the present invention is a process, in particular a cosmetic process, for caring for the skin, more particularly facial skin, in particular wrinkled skin, comprising:

either the topical application to the skin of an extemporaneous mixture of a composition, in particular a cosmetic composition, comprising at least one, preferably one, polysaccharide polymer grafted with (meth)acrylate groups and of at least one, preferably one, crosslinking thiol compound having one or more thiol groups;

or the sequential application to the skin of a composition, in particular a cosmetic composition, A comprising at least one, preferably one, polysaccharide polymer grafted with (meth)acrylate groups, followed by the application of at least one, preferably one, crosslinking thiol compound having one or more thiol groups, or of a composition, in particular a cosmetic composition, B containing same.

A subject of the invention is also the use, in particular cosmetic use, as a skin, in particular wrinkled skin, tensioning agent, of a grafted polysaccharide polymer as previously defined, or of a composition, in particular a cosmetic composition, containing same, mixed with the crosslinking thiol compound as previously defined.

A subject of the invention is also a composition, in particular a cosmetic composition, obtained by mixing a composition, in particular a cosmetic composition, comprising a grafted polysaccharide polymer as previously defined and a crosslinking thiol compound as previously defined or a composition, in particular a cosmetic composition, containing same.

A subject of the invention is also a kit comprising a first composition (composition A), which is in particular a cosmetic composition, comprising a grafted polysaccharide polymer as previously defined and a second composition (composition B), which is in particular a cosmetic composition, comprising a crosslinking thiol compound as previously defined, the first and second compositions each being packaged in a distinct packaging assembly.

The composition packaging assembly is, in a known manner, any packaging that is suitable for storing cosmetic compositions (in particular a bottle, tube, spray bottle or aerosol bottle).

Such a kit allows the skin treatment process according to the invention to be performed. The process according to the invention is in particular intended for smoothing out wrinkled human facial and/or body skin, in particular for reducing or effacing wrinkles and/or fine lines on the skin.

The tensioning effect may be characterized by means of an in vitro retraction test as described in Examples 1 to 4.

The term "polysaccharide grafted with (meth)acrylate groups" is intended to mean a polysaccharide of which all or some free hydroxyl groups have been esterified so as to form (meth)acrylate ester groups.

The grafted polysaccharide used according to the invention may be chosen from (meth)acrylate-grafted hyaluronic acid, (meth)acrylate-grafted dextran and (meth)acrylate-grafted carrageenan, such as those described hereinafter.

Advantageously, the (meth)acrylate-grafted polysaccharide has a weight-average molecular weight ranging from 5000 to 1 000 000 daltons, preferably ranging from 10 000 to 500 000 daltons, and even more preferentially ranging from 15 000 to 350 000 daltons.

According to a first embodiment of the process according to the invention, the grafted polysaccharide may be a (meth)acrylate-grafted hyaluronic acid. Hyaluronic acid is a linear glycosaminoglycan composed of repeating D-glucuronic acid and N-acetyl-D-glucosamine units linked together via alternating beta-1 ,4 and beta-1 ,3 glycosidic linkages.

Preferably, the grafted hyaluronic acid polymer has a weight-average molecular weight ranging from 5000 to 1 000 000 daltons, more preferentially ranging from 10 000 to

500 000 daltons, and even more preferentially ranging from 15 000 to 350 000 daltons. The molecular weight can be determined in particular by liquid chromatography, the eluent being 0.1 M sodium chloride and 330 mg/l of sodium azide in water, with dextran as standard, and Wyatt Optilab T-Rex refractometer and Wyatt Dawn-Heleos II light scattering detectors.

Advantageously, the grafted hyaluronic acid polymer has a degree of grafting with (meth)acrylate groups ranging from 10% to 80% or 20% to 80%, preferably ranging from 40% to 70%, and preferentially ranging from 45% to 65%. The degree of grafting corresponds to the mole percentage of hydroxyl groups of the hyaluronic acid which are grafted with a (meth)acrylate group.

By way of example, a degree of grafting of 50% corresponds to 2 acrylate groups grafted onto the 4 hydroxyls of the repeating unit of the hyaluronic acid. The grafting of hyaluronic acid with (meth)acrylate groups results from the presence of a (meth)acrylate ester group formed with the free hydroxyls of hyaluronic acid. Preferably, the hyaluronic acid is grafted with acrylate groups.

The hyaluronic acid grafted with (meth)acrylate groups can be obtained by reaction of the hyaluronic acid with (meth)acrylic anhydride. The reaction is advantageously carried out in a basic aqueous medium, in particular in the presence of an organic or inorganic base such as, for example, sodium hydroxide. Preferably, the reaction is carried out at a temperature ranging from 5 to 10°C, in particular for a period of time ranging from 24 hours to 48 hours.

Various degrees of grafting with the (meth)acrylate groups can be obtained by varying the amount of (meth)acrylic anhydride used proportionally to the amount of hyaluronic acid.

According to a second embodiment of the process according to the invention, the grafted polysaccharide may be a (meth)acrylate-grafted dextran.

Dextran is a branched polysaccharide of d-glucose (dextrose) which has a linear backbone, the glucoses of which are linked to one another by alpha-1 ,6 linkages; it has branched chains consisting of d-glucose linked to one another by alpha-1 ,2 or -1 ,3 or - 1 ,4 linkages.

Preferably, the grafted dextran polymer is a weight-average molecular weight ranging from 10 000 to 1 000 000 daltons, more preferentially ranging from 10 000 to 500 000 daltons, and even more preferentially ranging from 15 000 to 350 000 daltons.

The weight-average molecular weight can in particular be determined by the liquid chromatography by gel permeation or by size exclusion chromatography.

Advantageously, the grafted dextran polymer has a degree of grafting with (meth)acrylate groups ranging from 2% to 70%, preferably ranging from 3% to 65%, and preferentially ranging from 5% to 60%. The degree of grafting corresponds to the mole percentage of hydroxyl groups of the dextran which are grafted with a (meth)acrylate group. By way of example, a degree of grafting of 50% corresponds to 1 .5 acrylate groups grafted onto the 3 hydroxyls of the repeating unit of the dextran.

The grafting of dextran with (meth)acrylate groups results from the presence of a

(meth)acrylate ester group formed with the free hydroxyls of dextran.

Preferably, the dextran is grafted with methacrylate groups.

The dextran grafted with (meth)acrylate groups can be obtained by reaction of the dextran with (meth)acrylic anhydride. The reaction is advantageously carried out in an aprotic polar solvent (example dimethylformamide, N-methylpyrrolidone, N- ethylpyrrolidone), in particular in the presence of a non-nucleophilic organic or inorganic base, for instance tertiary amines (such as triethanolamine). Preferably, the reaction is carried out at a temperature ranging from 20 to 100°C, in particular for a period of time ranging from 1 to 12 hours

Various degrees of grafting with the (meth)acrylic groups can be obtained by varying the amount of (meth)acrylic anhydride used proportionally to the amount of dextran, and also the reaction conditions, such as the reaction temperature and time. According to a third embodiment of the process according to the invention, the grafted polysaccharide may be a (meth)acrylate-grafted carrageenan.

Carrageenans are sulfated polysaccharides which constitute the cell walls of various red algae, from which they can be obtained. Among these red algae, mention may be made, in a non-limiting manner, of Kappaphycus alvarezii, Eucheuma denticulatum, Eucheuma spinosum, Chondrus crispus, Betaphycus gelatinum, Gigartina skottsbergii, Gigartina canaliculata, Sarcothalia crispata, Mazzaella laminaroides, Hypnea musciformis, Mastocarpus stellatus and Iridaea cordata.

They comprise long galactan chains, made up of disaccharide units. These polysaccharides are composed of alternating (1→3) β-D-galactopyranose (G unit) and (1→4) a-galactopyranose (D unit) or 3,6-anhydro-a-galactopyranose (AnGal unit). Each sugar unit can be sulfated one or more times in position 2, 3, 4 or 6. Methyl and pyruvic acid groups and also other sugar units grafted onto the base structures previously described can also be found. The carrageenans were initially subdivided into subfamilies according to their solubility in KCI, then according to the number and position of the sulfate groups and the presence of 3',6'-anhydro bridges on the galactopyranosyl residues. There are at least about 15 carrageenans listed, the structure of which depends on the alga of origin and the extraction method. Among the most common, mention may be made of the carrageenans below:

μ- Carrageenan κ- Carrageenan

(1→3) P-D-galactopyranose-4-sulfate-(l→4) (1→3) P-D-galactopyranose-4-sulfate-(l-

3,6-anhydro-a-D-galactopyranose-6-sulfate anhydro-a-D-galactopyranose

λ- Carrageenan _θ . _Cari . _a g _eenan

3) p-D-galactopyranose-2-sulfate-(l→4)-a-D- _{(1→3) p-D} -galactopyranose-2-sulfate-(l→4) 3, galactopyranose -2,6-d ⁱ sulfate anhydro-a-D-galactopyranose-2-sulfate

These carrageenans are thus often obtained in the form of mixtures of different structures such as, and in a non-limiting manner, mixtures of κβ, κι, κμ forms. The carrageenans that can be used may in particular be chosen from carrageenans of μ, K, v, i, λ and Θ type. Carrageenans that are particularly suitable for implementing the invention are carrageenans of μ, v and λ type. Lambda carrageenan is preferably used. The carrageenans of the present invention can be used in acid form or in salified form. By way of acceptable salts, mention may be made, in a non-limiting manner, of lithium, sodium, potassium, calcium, zinc or ammonium salts.

Preferably, the grafted carrageenan polymer has a weight-average molecular weight ranging from 10 000 to 1 000 000 daltons, more preferentially ranging from 10 000 to 500 000 daltons, and even more preferentially ranging from 15 000 to 350 000 daltons. The molecular weight can be determined in particular by liquid chromatography, the eluent being 0.1 M sodium chloride and 330 mg/l of sodium azide in water, with dextran as standard, and Wyatt Optilab T-Rex refractometer and Wyatt Dawn-Heleos II light scattering detectors.

Advantageously, the grafted carrageenan polymer has a degree of grafting with (meth)acrylate groups ranging from 2% to 60%, preferably ranging from 2% to 50%, and preferentially ranging from 5% to 30%. The degree of grafting corresponds to the mole percentage of hydroxyl groups of the carrageenan which are grafted with a (meth)acrylate group.

By way of example, a degree of grafting of 50% corresponds to 1 .5 acrylate groups grafted onto the 3 hydroxyls of the repeating unit of the carrageenan.

The grafting of the carrageenan with (meth)acrylate groups results from the presence of a (meth)acrylate ester group formed with the free hydroxyls of the carrageenan.

Preferably, the carrageenan is grafted with acrylate groups.

The carrageenan grafted with (meth)acrylate groups can be obtained by reaction of the carrageenan with (meth)acrylic anhydride. The reaction is advantageously carried out in a basic aqueous medium, in particular in the presence of an organic or inorganic base such as, for example, sodium hydroxide. Preferably, the reaction is carried out at a temperature ranging from 5 to 10°C, in particular for a period of time ranging from 24 hours to 48 hours.

R = H or COCH=CH ₂

Various degrees of grafting with the (meth)acrylic groups can be obtained by varying the amount of (meth)acrylic anhydride used proportionally to the amount of

carrageenan.

Advantageously, a carrageenan chosen from μ-carrageenan, λ-carrageenan, v- carrageenans, and preferably λ-carrageenan, is used.

The grafted polysaccharide polymer as previously defined may be present in the composition used according to the invention (in particular composition A) in a content ranging from 0.1 % to 10% by weight, relative to the total weight of the composition, preferably from 0.5% to 10% by weight of active material, preferentially ranging from 1 % to 8% by weight, and more preferentially ranging from 1 % to 6% by weight. Advantageously, the grafted polysaccharide is chosen from acrylate-grafted hyaluronic acid, (meth)acrylate-grafted dextran and acrylate-grafted carrageenan.

The crosslinking thiol used in the invention is a compound comprising one or more thiol groups (SH) and optionally another function capable of reacting with the ethylenic unsaturation of the (meth)acrylate groups grafted onto the polysaccharide, such as a primary or secondary amine function, preferably a primary amine function.

The crosslinking thiol may be a crosslinking polythiol or monothiol as described hereinafter.

The term "polythiol" is intended to mean any compound bearing two or more than two thiol groups SH. It may be a non-polymeric organic molecule bearing two or more than two thiol groups, or a polymer bearing two or more than two thiol groups. The polythiol compound according to the invention must not contain vinyl (C=C) (non- aromatic) or acetylenic (C C) functions. The polythiol compound may be aromatic or heteroaromatic or may contain an aromatic radical. The polythiol compound used according to the invention may also contain one or more heteroatoms chosen from O, N and S and/or one or more functions chosen from ester, ketone, amide, urea and isocyanurate functions. Preferably, the polythiol compound used according to the invention may also contain one or more heteroatoms chosen from O, N and S and/or one or more functions chosen from ester and ketone functions.

According to a first variant, the polythiol compound used according to the invention denotes a non-polymeric organic compound and can be represented by formula (I)

W(SH)n (I) in which n denotes an integer greater than or equal to 2, preferably between 2 and 10, preferably between 2 and 5,

and W denotes a linear or branched or (hetero)cyclic, saturated C ₂ -C ₈ o multivalent (at least divalent) radical, an aromatic radical or a heteroaromatic cyclic radical, it being possible for W to also contain one or more heteroatoms such as O, N or S, and/or one or more functions chosen from ester, ketone, amide or urea functions and/or to be substituted with one or more linear or branched C-I-C-IO alkyl, hydroxyl, amino, (CrC ₆ alkyl) amino, carboxylic, carboxylate, or linear or branched C-I-C-IO alkoxy groups, it being understood that, when the W radical is substituted, the thiol functions can be borne by the substituent(s). The term "cyclic radical" is intended to mean a hydrocarbon-based saturated monocyclic or heterocyclic radical, a saturated or aromatic polycyclic radical, for example biphenyl, or condensed rings, for instance the naphthyl radical.

The molar mass of the compounds of formula (I) is generally between 70 and 1500 g/mol and preferably between 70 and 500 g/mol.

According to a first embodiment, the polythiol compound of formula (I) is such that n=2 (dithiol) and W denotes a linear or branched C ₂ -C ₂ o, preferably C ₂ -Ci ₂ , hydrocarbon- based saturated divalent radical.

According to this embodiment, the polythiol compound of the invention denotes, for example

1 ,2-ethanedithiol, 1 ,2-propanedithiol, 1 ,3-propanedithiol, 1 ,4-butanedithiol, 1 ,6-hexanedithiol, 1 ,7-heptanedithiol, 1 ,8-octanedithiol, 1 ,9-nonanedithiol, 1 ,10-decanedithiol, 1 ,12-dodecanedithiol, 2, 2-dimethyl-1 ,3-propanedithiol, 3- methyl-1 ,5-pentanedithiol, or 2-methyl-1 ,8-octanedithiol. According to a second embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 3 and W denotes a linear or branched C ₃ -C ₂ o, preferably linear or branched C ₂ -Ci ₂ , hydrocarbon-based saturated trivalent radical.

According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from 1 ,1 ,1 -tris(mercaptomethyl)ethane, 2-ethyl-2-mercaptomethyl-1 ,3- propanedithiol, and 1 ,2,3-propanetrithiol.

According to a third embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 2 or 3 and W denotes a linear or branched C ₃ -C ₂ o, preferably linear or branched C ₂ -Ci ₂ , hydrocarbon-based saturated divalent or trivalent radical, said radical containing one or more non-adjacent heteroatom(s) chosen from O and S..

According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from

bis(mercapto(C ₂ -Ci ₂ )alkyl) ethers and sulfides, such as bis(2- mercaptoethyl) ether, bis(2-mercaptoethyl)sulfide, bis(2-mercaptoethylthio-3- mercaptopropane)sulfide,

O bis(2-mercapto((Ci-C ₃ )alkyl)thio) (CrC ₅ )alkanes or bis(2-mercapto((Ci- C ₃ )alkyl)thio) (Ci-C ₅ )mecaptoalkanes, for instance bis(2- mercaptoethylthio)methane, 1 ,2-bis(2-mercaptoethylthio)ethane, 1 ,3-bis(2- mercaptoethylthio)propane, 1 ,2-bis(2-mercaptoethylthio)propanethiol, 1 ,2- bis(2-mercaptoethyl)thio-3-mercaptopropane, or 1 ,2,3-tris(2- mercaptoethylthio)propane.

Preferably, according to this embodiment, the compound (I) is chosen from 1 ,2-bis(2- mercaptoethylthio)propanethiol, 1 ,2,3-tris(2-mercaptoethylthio)propane and tetrakis(2- mercaptoethylthiomethyl)methane.

According to a fourth embodiment, the compound comprising a thiol unit, of formula (I), is such that n denotes an integer greater than or equal to 2 and W denotes a linear or branched C ₃ -C ₂₀ , preferably linear or branched C ₂ -Ci ₂ , hydrocarbon-based saturated multivalent (at least divalent) radical, said radical containing at least one ester function. According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from

esters of polyols (glycols, triols, tetraols, pentaols, hexaols) and of Ci-C ₆ mercaptocarboxylic acid, such as ethylene glycol bis(2-mercaptoacetate), ethylene glycol bis(3-mercaptopropionate), thylene glycol bis(thioglycolate), trimethylolpropane tris(thioglycolate), trimethylolpropane tris(beta- mercaptopropionate), pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis(beta-mercaptopropionate), dipentaerylthritol hexakis(beta- mercaptoproprionate), trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(2- mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutanate), and dipentaerythritol hex-3- mercaptopropionate. Preferably, according to this embodiment, the compound comprising a thiol unit is chosen from trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3- mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutanate) and dipentaerythritol hex-3-mercaptopropionate.

Particularly preferably, the compound comprising a thiol unit is pentaerythritol tetrakis(3- mercaptopropionate).

According to a fifth embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 4 and W denotes a branched C ₄ -C ₂ o, preferably C ₈ -Ci ₄ , hydrocarbon-based saturated tetravalent radical interrupted with one or more non-adjacent sulfur atoms. According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from tetrakis(2-mercaptoethylthiomethyl)methane and bis-(2-mercaptoethylthio- 3-mercaptopropane)sulfide.

According to a sixth embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 2 and W denotes a hydrocarbon-based cyclic divalent radical optionally containing one or more non-adjacent sulfur atoms, optionally substituted with one or more linear or branched C-I-C-IO alkyl radicals.

According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from 1 ,4-cyclohexanedithiol, 1 ,4-bis(mercaptomethyl)cyclohexane, 1 ,1 - cyclohexanedithiol, 1 ,2-cyclohexanedithiol, 1 ,1 -bis(mercaptomethyl)cyclohexane, and 2,5-dimercapto-1 ,4-dithiane.

According to a seventh embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 3 and W denotes a substituted isocyanurate-type cyclic radical.

According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from polythiols of the isocyanurate class, described in patents US 3 676 440 and US 201 1 023 0585, such as tris((mercaptopropionyloxy)ethyl)isocyanurate.

According to this embodiment, the compound comprising a thiol unit denotes tris((mercaptopropionyloxy)ethyl)isocyanurate. According to an eighth embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 2 or 3 or 4 and W denotes an aromatic radical optionally substituted with one or more identical or different radicals of C1-C10 alkyl or C1-C10 alkoxy type, it being understood that, when the W radical is substituted, the thiol functions can be borne by the substituent(s). According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from

1 .2- dimercaptobenzene, 1 ,3-dimercaptobenzene,

1 ,4-dimercaptobenzene, 1 ,2-bis(mercaptomethyl)benzene,

1 .3- bis(mercaptomethyl)benzene,

1 ,4-bis(mercaptomethyl)benzene,

1 .2- bis(2-mercaptoethyl)benzene,

1 .3- bis(2-mercaptoethyl)benzene,

1 .4- bis(2-mercaptoethyl)benzene,

1 ,2-bis(2-mercaptoethyleneoxy)benzene,

1 ,3-bis(2-mercaptoethyleneoxy)benzene,

1 ,4-bis(2-mercaptoethyleneoxy)benzene,

1 .2.3- trimercaptobenzene,

1 .2.4- trimercaptobenzene,

1 .3.5- trimercaptobenzene,

1 ,2,3-tris(mercaptomethyl)benzene,

1 .2.4- tris(mercaptomethyl)benzene,

1 .3.5- tris(mercaptomethyl)benzene,

1 .2.3- tris(2-mercaptoethyl)benzene,

1 .2.4- tris(2-mercaptoethyl)benzene,

1 ,3,5-tris(2-mercaptoethyl)benzene,

1 .2.3- tris(2-mercaptoethyleneoxy)benzene,

1 .2.4- tris(2-mercaptoethyleneoxy)benzene,

1 .3.5- tris(2-mercaptoethyleneoxy)benzene,

1 .2.3.4- tetramercaptobenzene,

1 ,2,3,5-tetramercaptobenzene,

1 .2.4.5- tetramercaptobenzene,

1 .2.3.4- tetrakis(mercaptomethyl)benzene,

1 .2.3.5- tetrakis(mercaptomethyl)benzene,

1 ,2,4,5-tetrakis(mercaptomethyl)benzene,

1 ,2,3,4-tetrakis(2-mercaptoethyl)benzene,

1 ,2,3,5-tetrakis(2-mercaptoethyl)benzene,

1 ,2,4,5-tetrakis(2-mercaptoethyl)benzene,

1 .2.3.4- tetrakis(2-mercaptoethyleneoxy)benzene,

1 .2.3.5- tetrakis(2-mercaptoethyleneoxy)benzene,

1 ,2,4,5-tetrakis(2-mercaptoethyleneoxy)benzene,

2,2'-dimercaptobiphenyl, 4,4'-dimercaptobiphenyl,

4,4'-dimercaptobibenzyl,

2,5-toluenedithiol,

3.4- toluenedithiol,

1 ,4-naphthalenedithiol,

1 .5- naphthalenedithiol,

2.6- naphthalenedithiol,

2.7- naphthalenedithiol,

2,4-dimethylbenzene-1 ,3-dithiol,

4,5-dimethylbenzene-1 ,3-dithiol,

9,10-anthracenedimethanethiol,

1 .3- bis(2-mercaptoethylthio)benzene,

1 .4- bis(2-mercaptoethylthio)benzene,

1 ,2-bis(2-mercaptoethylthiomethyl)benzene,

1 ,3-bis(2-mercaptoethylthiomethyl)benzene,

1 ,4-bis(2-mercaptoethylthiomethyl)benzene,

1 .2.3- tris(2-mercaptoethylthio)benzene,

1 .2.4- tris(2-mercaptoethylthio)benzene,

1 .3.5- tris(2-mercaptoethylthio)benzene,

1 ,2,3,4-tetrakis(2-mercaptoethylthio)benzene,

1 ,2,3,5-tetrakis(2-mercaptoethylthio)benzene,

1 ,2,4,5-tetrakis(2-mercaptoethylthio)benzene,

3,4-thiophenedithiol. According to this embodiment, the compound (I) is chosen from 1 ,2,3- trimercaptobenzene, 1 ,2,4-trimercaptobenzene, 1 ,3,5-trimercaptobenzene, 1 ,2,3- tris(mercaptomethyl)benzene, 1 ,2,4-tris(mercaptomethyl)benzene, 1 ,3,5- tris(mercaptomethyl)benzene, 1 ,2,3-tris(2-mercaptoethyl)benzene, 1 ,2,4-tris(2- mercaptoethyl)benzene, 1 ,3,5-tris(2-mercaptoethyl)benzene, 1 ,2,3-tris(2- mercaptoethyleneoxy)benzene, 1 ,2,4-tris(2-mercaptoethyleneoxy)benzene, 1 ,3,5-tris(2- mercaptoethyleneoxy)benzene, 1 ,2,3,4-tetramercaptobenzene, 1 ,2,3,5- tetramercaptobenzene, 1 ,2,4,5-tetramercaptobenzene, 1 ,2,3,4- tetrakis(mercaptomethyl)benzene, 1 ,2,3,5-tetrakis(mercaptomethyl)benzene, 1 ,2,4,5- tetrakis(mercaptomethyl)benzene, 1 ,2,3,4-tetrakis(2-mercaptoethyl)benzene, 1 ,2,3,5- tetrakis(2-mercaptoethyl)benzene, 1 ,2,4,5-tetrakis(2-mercaptoethyl)benzene, 1 ,2,3,4- tetrakis(2-mercaptoethyleneoxy)benzene, 1 ,2,3,5-tetrakis(2- mercaptoethyleneoxy)benzene, 1 ,2,4,5-tetrakis(2-mercaptoethyleneoxy)benzene, 1 ,2,3- tris(2-mercaptoethylthio)benzene, 1 ,2,4-tris(2-mercaptoethylthio)benzene, 1 ,3,5-tris(2- mercaptoethylthio)benzene, 1 ,2,3,4-tetrakis(2-mercaptoethylthio)benzene, 1 ,2,3,5- tetrakis(2-mercaptoethylthio benzene, 1 ,2,4,5-tetrakis(2-mercaptoethylthio)benzene and 3,4-thiophenedithiol. According to a ninth embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 2 or 3 or 4 and W denotes a triglyceride of a fatty acid or a vegetable oil, optionally substituted, it being understood that, when the W radical is substituted, the thiol functions can be borne by the substituent(s).

According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from triglycerides of fatty acids or vegetable oils modified with thiol groups by chemical reaction, for instance thiolated soybean oils and hydroxylated and thiolated soybean oils, in particular the polymercaptan® products from the company Chevron Phillips, such as polymercaptan 358 (mercaptanized soybean oil) and polymercaptan 407 (mercapto hydroxy soybean oil).

Polymercaptan 358

According to a tenth embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 2 and W denotes a C ₂ -C ₆ hydrocarbon-based saturated divalent radical substituted with one or more hydroxyl groups.

According to this embodiment, the compound comprising a thiol unit can be chosen, for example, from dithiothreitol and 2,3-dimercapto-1 -propanol.

According to an eleventh embodiment, the compound comprising a thiol unit, of formula (I), is such that n = 2 and W denotes a C ₂ -C ₆ hydrocarbon-based saturated divalent radical substituted with one or more carboxylic acid groups or carboxylate groups (C ₂ -C ₅ ester group).

According to this embodiment, the compound comprising a thiol unit, of formula (I), may be meso-2,3-dimercaptosuccinic acid or Ci-C ₄ alcohol esters thereof.

According to this first variant, the compounds of formula (I) for which n denotes an integer ranging from 2 to 4 will be preferred.

Preferably, according to this variant, the compounds of formula (I) are chosen from the compounds of the fourth embodiment, such as, in particular, trimethylolpropane tris(2- mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutanate) or dipentaerythritol hex-3- mercaptopropionate, and more particularly pentaerythritol tetrakis(3- mercaptopropionate); or from the compounds of the tenth embodiment, such as, in particular, dithiothreitol. Particularly preferably, according to this variant, the compounds of formula (I) denote pentaerythritol tetrakis(3-mercaptopropionate), or dithiothreitol.

According to a second variant, the polythiol compound used according to the invention denotes a polymeric compound and can be represented by formula (II) POL(SH)n (II)

in which n denotes an integer greater than or equal to 5, preferably between 5 and 5000, preferably between 5 and 1000,

and POL denotes a multivalent (at least pentavalent) carbon-based or silicone polymeric radical, it being possible for POL to also contain one or more heteroatoms such as O, N or S, and/or one or more functions chosen from ester, ketone, amide, urea and carbamate functions, and/or to be substituted with one or more linear or branched C-I-C-IO alkyl or linear or branched C-I-C-IO alkoxy groups, it being understood that, when POL is substituted, the thiol functions can be borne by the substituent(s). The molar mass of the compounds of formula (I I) is generally between 500 and 400 000 g/mol and preferably between 500 and 150 000 g/mol.

POL can denote a multivalent radical of homopolymer or copolymer type;

POL can denote a polymeric radical of star, comb, brush or dendritic type.

The POL radical may be of natural origin (such as polysaccharides, peptides) or synthetic origin (such as acrylic polymers, polyesters, polyglycols).

The thiol functions (-SH) may be end and/or pendant groups.

According to a first embodiment, the thiolated compound of formula (I I) is such that POL denotes a hydrocarbon-based polymeric radical.

As an example, mention may be made of the polymers described in the following articles: Polymers containing groups of biological activity, CG Overberger et al, Polytechnic Institute of Brooklyn, http://pac.iupac.org/publications/pac/pdf/1962/pdf/0402x0521 .pdf and Mercaptan-containing polymers, Advances in Polymer Science Volume 15, 1974, pp 61 -90.

In particular, mention may be made of the compounds comprising a thiol unit, of formula (II), such as poly(vinylmercaptan), poly(4-mercaptostyrene), poly(vinylbenzylmercaptan), poly(4-mercaptostyrene)-co-poly(methyl methacrylate), and also polymers containing amide functions in the polymer, such as poly(thiolated hexamethylene adipamide). The compounds of formula (II) also denote proteins and peptides with thiol units, for instance the structures re resented in the following table:

The thiolated compound of formula (II) also denotes the compounds of formula (II) such that POL denotes a radical termed dendrimer or polymer which is branched or hyperbranched, and the thiol groups are end groups. As examples, mention may be made of the polymers described in the article Progress in Organic Coatings, Volume 63, Issue 1 , July 2008, Pages 100-109.

As an example of the synthesis of such polymers, mention may be made of the synthesis described in said article, where the Boltorn H40 polymer is converted into a thiolated polymer of formula (II) according to the scheme below:

The structure of the thiolated polymer (II) obtained is given below:

The compound comprising a thiol unit, of formula (II), may also denote a hyperbranched or dendritic polymer modified with thiol functions, as described in application FR 2 761 691 . Polymers of polypropylene ether glycol bis(beta-mercaptopropionate) type can also be used. They are prepared from polypropylene ether glycol (e.g., Pluracol P201 , Wyandotte Chemical Corp.) and beta-mercaptopropionic acid by esterification reaction and are known to those skilled in the art.

Some polymers comprising a thiol unit, of formula (II), are also commercially available, such as the Thiocure® products from the company Bruno Brock, Thiocure® ETTMP 1300 (Ethoxylated-Trimethylolpropane Tri-3-Mercaptopropionate (CAS# 345352-19-4) and Thiocure® ETTMP 700 (Ethoxylated-Trimethylolpropane Tri-3-Mercaptopropionate (CAS# 345352-19-4);

According to a second embodiment, the compound of formula (II) is such that POL denotes a silicone-based polymeric radical.

Among the polythiol inorganic polymers, mention may be made of silicone polythiols.

The silicone polythiols are in particular polydimethylsiloxanes comprising two or more than two thiol groups such as, for example, the SMS-022, SMS-042 and SMS-992 products sold by the company Gelest Inc.

The crosslinking thiol may also be a monothiol compound comprising another function capable of reacting with the ethylenic unsaturation of the (meth)acrylate groups grafted onto the polysaccharide, such as a primary or secondary amine function, preferably a primary amine function.

The crosslinking thiol may in particular be an aminothiol, in particular a compound of formula (III):

(HS)-L-(NHR)b (III)

in which b denotes an integer ranging from 1 to 5, preferably ranging from 1 to 3 and more preferentially equal to 1 .

L denotes a linear or branched or (hetero)cyclic, saturated C ₂ -C ₈ o multivalent (at least divalent) radical, an aromatic radical or a heteroaromatic cyclic radical, it being possible for W to also contain one or more non-adjacent heteroatoms such as O, N or S, and/or one or more functions chosen from ester, ketone, amide, urea and carbamate functions, preferably ester and ketone functions, and/or to be substituted with one or more linear or branched C1-C1 ₀ alkyl, hydroxyl, carboxylic, carboxylate, or linear or branched C1-C1 ₀ alkoxy groups, it being understood that, when the W radical is substituted, the thiol functions can be borne by the substituent(s);

R denotes a hydrogen atom or a Ci-C ₆ alkyl, or CH ₃ CO- or C ₂ H ₅ -CO- radical, and preferably a hydrogen atom.

As aminothiol compound, mention may be made of cysteamine, N-acetyl cysteamine, cysteine, N-acetyl cysteine, homocysteine, the compounds of formula

HS-(CH2)n-NH-(CH2)m-NH, n and m being integers ranging from 1 to 4,

ortho-aminothiophenol, meta-aminothiophenol and para-aminothiophenol.

Preferably, the crosslinking thiol is chosen from cysteamine, dithiothreitol, and pentaerythritol tetra(3-mercaptopropionate). Preferentially, the crosslinking thiol is cysteamine.

Preferably, the process according to the invention is carried out with hyaluronic acid grafted with acrylate groups and cysteamine.

Advantageously, the composition (in particular composition B) comprising the crosslinking thiol used in the process according to the invention is an aqueous composition having a pH ranging from 5 to 10.5, preferably ranging from 6 to 9, and preferentially ranging from 7 to 8.5.

According to one embodiment of the process according to the invention, an extemporaneous mixture of the polysaccharide polymer grafted with (meth)acrylate groups and of a crosslinking thiol compound is prepared and the mixture is applied to the skin. It is also possible to carry out a sequential application to the skin, on the one hand, of the saccharide polymer grafted with (meth)acrylate groups and, on the other hand, of the crosslinking thiol compound. Advantageously, the thiol compound used in the process according to the invention is used according to a thiol compound/grafted-polysaccharide (meth)acrylate group mole ratio ranging from 0.01 to 10, preferably ranging from 0.01 to 5.

The thiol compound may be present in composition B used according to the invention in a content ranging from 0.1 % to 100% by weight, relative to the total weight of the composition, and preferably ranging from 1 % to 10% by weight.

The crosslinking thiol compound in contact with the polysaccharide grafted with (meth)acrylate groups reacts with the ethylenic unsaturations of the (meth)acrylate groups grafted onto the polysaccharide so as to form thio bonds with the end carbon of the ethylenic unsaturation of the (meth)acrylate group (this reaction is known as the Michael reaction).

Examples of this reaction are illustrated with dextran (meth)acrylate in the following schemes:

When the grafted dextran comprises methacrylate groups, a catalyst can be used in the presence of the thiol compound. This catalyst makes it possible to obtain good reactivity of the thiol compound on the ethylenic unsaturation of the methacrylate group.

The catalyst can be chosen from the catalysts described in the articles Tetrahedron Letters 48 (2007), pages 141 -143, and Tetrahedron Letters 46 (2005), pages 8329-8331 , and also in the articles cited in these two articles.

As an example of a catalyst, mention may be made of Lewis acids, such as boric acid, aluminium chloride or cerium chloride, and also phosphines, such as trimethylphosphine (trialkylphosphine), phenyldimethylphosphine (dialkylarylphosphine), diphenylmethylphosphine (alkyldiarylphosphine), triphenylphosphine (triarylphosphine), tricarboxyethylphosphine, and the oxide equivalents. The compositions used according to the invention are generally suitable for topical application to the skin and thus generally comprise a physiologically acceptable medium, i.e. a medium that is compatible with the skin and/or skin appendages. It is preferably a cosmetically acceptable medium, i.e. a medium which has a pleasant colour, odour and feel and which does not cause any unacceptable discomfort (stinging, tautness or redness) liable to discourage the consumer from using this composition.

The compositions according to the invention may be in any galenic form conventionally used for a topical application and especially in the form of dispersions of aqueous gel or lotion type, emulsions of liquid or semi-liquid consistency of the milk type, obtained by dispersing a fatty phase in an aqueous phase (O/W) or vice versa (W/O), or suspensions or emulsions of soft, semi-solid or solid consistency of the cream or gel type, or alternatively multiple emulsions (W/O/W or 0/W/O), microemulsions, vesicular dispersions of ionic and/or non-ionic type, or wax/aqueous phase dispersions. These compositions are prepared according to the usual methods.

According to one preferred embodiment of the invention, the compositions are in the form of an O/W emulsion or an aqueous gel.

Advantageously, the compositions used according to the invention comprise water, in particular in a content which can range from 10% to 99% by weight and preferably ranging from 50% to 99% by weight, relative to the total weight of the composition. The compositions used according to the invention may also contain one or more adjuvants commonly used in the cosmetics field, such as emulsifiers, preservatives, sequestering agents, fragrances, thickeners, oils, waxes or film-forming polymers.

Needless to say, those skilled in the art will take care to select this or these optional additional compound(s), and/or the amount thereof, such that the properties of the composition according to the invention are not, or are not substantially, adversely affected by the envisaged addition.

According to a first embodiment of the process according to the invention, an extemporaneous mixture of a composition, in particular a cosmetic composition, comprising the (meth)acrylate-grafted polysaccharide polymer and of a crosslinking thiol compound, as previously described, is applied to the skin. The extemporaneous mixture is advantageously prepared less than 5 minutes before it is applied to the skin, and preferably less than 3 minutes.

According to a second embodiment of the process according to the invention, the composition, in particular cosmetic composition, comprising the (meth)acrylate-grafted polysaccharide polymer is first applied to the skin, then the crosslinking thiol compound or a cosmetic composition containing same is applied. The application of the crosslinking thiol compound can be carried out after a time of between 5 minutes and one hour after having applied the grafted polysaccharide polymer. The application of the cosmetic composition used according to the invention is carried out according to the usual techniques, for example by application (in particular of creams, gels, sera or lotions) to the skin intended to be treated, in particular facial and/or neck skin, especially the skin of the area around the eyes. In the context of this process, the composition may, for example, be a care composition.

The invention will now be described with reference to the examples that follow, which are given as non-limiting illustrations.

Synthesis example 1 (polymer 1 ): Hyaluronic acid 60%-functionalized with acrylic anhydride In a thermostated reactor, 5 g of hyaluronic acid (Hyacare® 50 from Evonik) were dissolved in 100 ml of water and the mixture was maintained at a temperature of 7°C, then 14.8 g of acrylic anhydride were added dropwise over the course of approximately 2 min. The pH was adjusted to 7.7 by slowly adding (over the course of approximately one hour) sodium hydroxide at 30% in water (7 M). The mixture was left to react for 24 hours. The mixture obtained was purified by dialysis (polymer in 150 ml of water, 3.3% by weight) on a Spectra/Por® 15 kDa membrane for 5 days in 5 litres of water (water changed 4 times, i.e. 20 litres in total), then the mixture of the purified fraction was lyophilized by freezing with a bath of dry ice + acetone at -80°C, then by placing the frozen mixture in a lyophilization apparatus for 4 days. 2.5 g of a white solid were obtained.

Analyses:

¹ H NMR D ₂ 0: 2.45 (7.36/3) OH units functionalized for 4 OH units available.

The hyaluronic acid obtained is 60%-functionalized with acrylate groups.

Synthesis example 2 (polymer 2): Dextran 33%-functionalized with methacrylate groups 10 g of dextran (sold under the reference 406261000 by the company Acros) were suspended in 40 ml of a lithium chloride/dimethylformamide mixture (at 10% by weight of LiCI) and the suspension was heated to 100°C. 20 ml of the lithium chloride/dimethylformamide mixture were added until complete dissolution of the dextran. The mixture was then cooled to 80°C, then 0.56 g of triethanolamine was added, the mixture was stirred for 15 minutes at 80°C, then 8.55 g of methacrylic anhydride were slowly added (10 minutes). The mixture was left to stir for 5 hours at 70°C and was then left to return to ambient temperature (25°C). The reaction mixture was then poured into 150 ml of isopropanol, stirred for 1 hour and then filtered. 1 1 .8 g of a white solid were obtained. Analyses:

¹ H NMR D ₂ 0: 1 OH unit functionalized for 3 OH units available.

The dextran obtained is 33%-functionalized with acrylate groups.

Synthesis example 3 (polymer 3): Dextran 50%-functionalized with methacrylate groups

10 g of dextran (sold under the reference 406261000 by the company Acros) were suspended in 40 ml of a lithium chloride/dimethylformamide mixture (at 10% by weight of LiCI) and the suspension was heated to 100°C. 20 ml of the lithium chloride/dimethylformamide mixture were added until complete dissolution of the dextran. The mixture was then cooled to 80°C, then 0.56 g of triethanolamine was added, the mixture was stirred for 15 minutes at 80°C, then a 8.55 g of methacrylic anhydride were slowly added (10 minutes). The mixture was left to stir for 5 hours at 80°C and was then left to return to ambient temperature (25°C). The reaction mixture was then poured into 150 ml of isopropanol, stirred for 1 hour and then filtered. 13.4 g of a white solid were obtained. Analyses:

¹ H NMR D ₂ 0: 1 .5 OH units functionalized for 3 OH units available.

The dextran obtained is 50%-functionalized with methacrylate groups. Synthesis example 4 (polymer 4): Carrageenan 15%-functionalized with acrylic anhydride

In a thermostated reactor, 5 g of carrageenan (lambda form) (Satiagum UTC 10 from Cargill) were dissolved in 100 ml of water and the mixture was maintained at a temperature of 7°C, then 10.7 g of acrylic anhydride were added dropwise over the course of approximately 2 min. The pH was adjusted to 7.7 by slowly adding (over the course of approximately one hour) sodium hydroxide at 30% in water (7 M). The mixture was left to react for 24 hours.

The mixture obtained was purified by dialysis (polymer in 150 ml of water, 3.3% by weight) on a Spectra/Por® 15 kDa membrane for 5 days in 5 litres of water (water changed 4 times, i.e. 20 litres in total), then the mixture of the purified fraction was lyophilized by freezing with a bath of dry ice + acetone at -80°C, then by placing the frozen mixture in a lyophilization apparatus for 4 days.

3.7 g of a white solid were obtained.

Analyses:

¹ H NMR D ₂ 0: 0.44 OH unit functionalized for 3 OH units available.

The carrageenan obtained is 10%-functionalized with acrylate groups. Examples 1 to 4: Demonstration of the tensioning effect of mixtures of polymers with a thiol

The tensioning effect of the polymers of Example 1 was evaluated by means of an in vitro retraction test. This test consists in comparing, in vitro, the tensioning capacity of the mixture of polymer and thiol to be evaluated relative to a reference tensioning polymer: Hybridur ^® 875 polymer dispersion from Air Products (aqueous dispersion at 40% by weight of particles of an interpenetrated network of polyurethane and acrylic polymers).

The mixture of polymer and thiol to be evaluated was deposited on a nitrile rubber strip cut from a glove sold under the reference Safeskin Nitrile Critical No. 038846 by the company Dominique Dutscher SA, having a surface area of 3.5 cm ² , stretched taut beforehand on a support. The mixture of polyol and thiol was deposited on the elastomer strip, by depositing 1 .8 mg (of solids) of polymer.

26 μΙ of an aqueous solution containing 7% AM of Hybridur ^® 875 polymer are thus deposited on a nitrile rubber strip so as to thus obtain a reference tensioning strip. 104 μΙ of the mixture containing 1 .75% AM of acrylate-grafted hyaluronic acid and the thiol were deposited on another strip.

After drying for 24 hours (overnight) at ambient temperature (25°C), the curving

(retraction) of the strip treated with the mixture is observed in comparison with that obtained with the control (Hybridur ^® 875).

An aqueous solution containing 1 % by weight of cysteamine was prepared.

The solution of acrylate-grafted hyaluronic acid (at 3.50% AM) and the solution of cysteamine were then mixed in the proportions indicated in the table hereinafter, and then an amount of the prepared mixture was deposited on the nitrile rubber strips.

With the polymer of Example

The tensioning effect obtained was measured according to the protocol previously described. The water resistance of the tensioning effect was then evaluated by immersing the rubber strips treated with the polymer to be evaluated in water at ambient temperature (25°C) for 10 minutes.

The results obtained show that the mixtures of hyaluronic acid and cysteamine (Ex 1 a, 1 b, 1 c, 1 d) make it possible to obtain a good tensioning effect that is persistent with respect to water. Example 5

Demonstration of the tensioning effect of mixtures of polymer and thiol

The tensioning effect of the polymer of Example 3 mixed with a thiol was evaluated by means of an in vitro retraction test. This test consists in comparing, in vitro, the tensioning capacity of the mixture of polymer + thiol to be evaluated, relative to a reference tensioning polymer: Hybridur ^® 875 polymer dispersion from Air Products (aqueous dispersion at 40% by weight of particles of an interpenetrated network of polyurethane and acrylic polymers). The polymer to be evaluated was deposited on a nitrile rubber strip cut from a glove sold under the reference Safeskin Nitrile Critical No. 038846 by the company Dominique Dutscher SA, having a surface area of 3.5 cm ² , stretched taut beforehand on a support. An aqueous solution containing 7% AM of Hybridur ^® 875 polymer was thus deposited on a nitrile rubber strip so as to thus obtain a reference tensioning strip.

A mixture containing the polymer and the thiol according to the amounts described in the table hereinafter is deposited on another strip.

After drying overnight (12 hours) at ambient temperature (22°C / 45% relative humidity), the curving (retraction) of the strip treated with the polymers was observed in comparison with that obtained with the control (Hybridur ^® 875).

The persistence of the tensioning effect (i.e. the retaining of the tensioning effect in the face of perspiration or washing) was evaluated by rinsing the nitrile strips with a 0.9 M aqueous NaCI solution (10 ml of the saline solution are projected onto the strip at a distance of 5 cm using a pipette). The strip was left to dry for 3 hours and the tensioning effect (the curving (retraction) of the strip) was again observed, comparing it with the effect observed before rinsing. The following solutions were prepared and immediately applied (26 μΙ of the final solution) to the strips.

The following results were obtained

The result obtained with the methacrylate-grafted dextran of Example 2 without thiol (Example 2) shows that it exhibits a good tensioning effect, but the latter is not persistent with respect to water. On the other hand, with treatment with a thiol such as dithiothreitol (Example 2a), the tensioning effect of the polymer after rinsing does not show any change compared with the tensioning effect before rinsing. The treatment with the thiol compound therefore makes it possible to obtain a persistent tensioning effect.

Examples 6 to 13:

Demonstration of the tensioning effect in basecoat application with polymer and topcoat application with thiol The tensioning effect of the polymers of Examples 1 to 4 was evaluated according to the in vitro retraction test described in the previous example, with the same tensioning polymer reference.

An aqueous solution of the polymer to be evaluated was deposited on an elastomer strip according to the amount indicated in the table hereinafter. After waiting for 5 minutes, the aqueous solution containing the thiol was then applied.

The following applications were carried out:

The following results were obtained

Example Tensioning effect Tensioning effect after before persistence test persistence test reference less

1 Same as reference less

1 a' Same as reference No change

1 b' Same as reference No change

2 Same as reference less

2a' Same as reference No change

2b' Same as reference No change

3 Same as reference less

3a' Same as reference No change

3b' Same as reference No change

4 Same as reference less

4a' Same as reference No change

4b' Same as reference No change

The results obtained with the acrylate-grafted hyaluronic acid P1 (Example 1 ), the methacrylate-grafted dextran P2, P3 (Examples 2 and 3), and the acrylate-grafted carrageenan P4 without thiol shows that these polymers have a good tensioning effect, but the latter is not persistent with respect to water. On the other hand, with post- treatment with a thiol such as dithiothreitol (Examples 1 a', 2a', 3a', 4a') or pentaerythritol tetra(3-mercaptopropionate) (Examples 1 b', 2b', 3b', 4b'), the tensioning effect of the polymers after rinsing does not show any change compared with the tensioning effect before rinsing. The post-treatment with the thiol compound therefore makes it possible to obtain a persistent tensioning effect.

Example 14:

An anti-wrinkle gel having the following composition is prepared:

- polymer of Example 1 g

- hydroxyethylcellulose (Natrosol® 250 HHR CS from Ashland) 0.5 g

- Preservatives qs

- Water qs 100 g

A similar composition is also prepared using the polymer of Example 2.

Just before the application to the skin, 1 g of an aqueous solution containing 1 % by weight of cysteamine, relative to the total weight of the solution, is added to the gel. The composition obtained, as a mixture with cysteamine, applied to the face (approximately 20 mg of composition per cm ² of skin treated) makes it possible to effectively smooth out the wrinkles.

Example 15:

A basecoat gel having the following composition is prepared:

- polymer of Example 1 3.5 g

- Polyacrylamidomethylpropanesulfonic acid partially

neutralized with aqueous ammonia and highly crosslinked

(Hostacerin AMPS ^® from Clariant) 2 g

- Preservatives qs

- Water qs 100 g A similar composition is also prepared using the polymer of Example 2.

The gel obtained is applied to wrinkled facial skin (approximately 20 mg of the composition per cm ² of skin treated). An aqueous solution (topcoat) containing 0.5% by weight of cysteamine is then applied to the treated area according to the following weight criteria: 26 μΙ of basecoat gel and either 2.6 μΙ or 10.6 μΙ of topcoat solution.

After drying, the application of the 2 compositions to the face makes it possible to effectively smooth out the wrinkles.

Example 16:

An anti-wrinkle gel having the following composition is prepared:

- polymer of Example 1 g - hydroxyethylcellulose (Natrosol® 250 HHR CS from Ashland) 0.5 g

- Preservatives qs

- Water qs 100 g

A similar composition is also prepared using the polymer of Example 2.

Just before the application to the skin, added to the gel are 10 g of an aqueous solution containing 5% by weight of dithiothreitol, pH adjusted to 8 with aqueous ammonia.

The composition obtained, as a mixture with dithiothreitol, applied to the face (approximately 20 mg of composition per cm ² of skin treated) makes it possible to effectively smooth out the wrinkles. Example 17: An anti-wrinkle basecoat gel having the following composition is prepared:

- polymer of Example 1 1 g

- hydroxyethylcellulose (Natrosol® 250 HHR CS from Ashland) 0.5 g

- Preservatives qs

- Water qs 100 g

A similar composition is also prepared using the polymer of Example 2.

The gel obtained is applied to wrinkled facial skin (approximately 20 mg of the composition per cm ² of skin treated). An aqueous gel (topcoat) having the following composition is then applied to the treated area:

Dithiothreitol 5 g

Hydroxyethylcellulose (Natrosol® 250 HHR CS from Ashland) 0.5 g

Preservative qs

Fragrance qs

Aqueous ammonia qs pH 8

Water qs 100 g

After drying, the application of the 2 compositions to the face makes it possible to effectively smooth out the wrinkles.

Example 18:

An anti-wrinkle gel having the following composition is prepared:

- polymer of Example 3 1 g - hydroxyethylcellulose (Natrosol® 250 HHR CS from Ashland) 0.5 g

- Preservatives qs

- Water qs 100 g

A similar composition is also prepared using the polymer of Example 4. Just before the application to the skin, 10 g of an ethanolic solution containing 10% by weight of pentaerythritol tetra(3-mercaptopropionate) are added to the gel.

The composition obtained, as a mixture with pentaerythritol tetra(3-mercaptopropionate), applied to the face, makes it possible to effectively smooth out the wrinkles.