WO2007057452A1 - Cosmetic use of tensing agents to improve the homeostasis of the skin and/or the radiance of the complexion - Google Patents

Abstract

The present invention relates in particular to the cosmetic use of an effective amount of at least one tensing agent as an agent intended to promote the homeostasis of the skin and/or the radiance of the complexion. The invention likewise relates to a cosmetic method of treatment of dull and/or poorly defined complexion which comprises the topical application to people exhibiting a dull and/or poorly defined complexion of a composition comprising an effective amount of at least one tensing agent.

Description

Cosmetic use of tensing agents to improve the homeostasis of the skin and/or the radiance of the complexion

The present invention relates to the field of skincare and is directed in particular to improving the appearance of the skin and/or the complexion.

It relates in particular to the cosmetic use of an effective amount of at least one tensing agent as an agent intended to promote the homeostasis of the skin and/or the radiance of the complexion.

The invention likewise relates to a cosmetic method of treatment of dull and/or poorly defined complexion which comprises the topical application to people exhibiting a dull and/or poorly defined complexion of a composition comprising an effective amount of at least one tensing agent.

The skin constitutes a physical barrier between the body and its environment. It is composed of two tissues: the epidermis and the dermis.

The epidermis is a keratinizing multi-layered epithelium which undergoes continual renewal.

Keratinocytes make up the primary epidermal cell population and are responsible for maintaining the epithelial structure and its barrier function. The epidermis rests on an acellular basal membrane, called the dermoepidermal junction, which ensures cohesion with the dermis.

The epidermis is composed of a number of strata of cells, the deepest of which is the basal stratum, which is composed of undifferentiated cells. Over time these cells will undergo differentiation and will migrate towards the surface of the epidermis, thereby making up the different epidermal strata, until, at the surface of the epidermis, they will form the corneocytes, which are dead cells which are removed by desquamation. This surface loss is compensated by the migration of cells from the basal stratum towards the surface of the epidermis. The process is one of continuous renewal of the skin.

The dermis is an elastic and compressible conjunctive support tissue of mesodermal origin and consists primarily of fibroblasts and an extracellular matrix which is composed of fibrous proteins (collagens and elastin) and non- fibrous proteins (proteoglycans and glycoproteins) . The dermis is a feeder tissue for the epidermis, but also plays a fundamental part in the development and growth of the epidermis, and also in its differentiation. The fibroblasts and the extracellular matrix also influence the mechanical properties of the skin, particularly its elasticity and firmness .

The homeostasis of the skin, and in particular of the epidermis, results from a finely regulated balance between the processes of proliferation and differentiation of the cells of the skin. These proliferation and differentiation processes are perfectly regulated: they participate in the renewal and/or regeneration of the skin and lead to the maintenance of a constant skin thickness, and in particular a constant epidermal thickness. This homeostasis of the skin is also involved in maintaining the mechanical properties of the skin.

However, this homeostasis of the skin can be affected by certain physiological factors (age, menopause, hormones, etc.) or environmental factors (UV stress, pollution, oxidizing stress, irritant stress, etc.). The regenerative potential of the epidermis becomes less great: the cells of the basal layer divide less actively, which leads in particular to a slowdown and/or decrease in epidermal renewal. Consequently, cellular renewal no longer compensates for the loss of the cells removed at the surface, leading to atrophy of the epidermis and/or to a decrease in the thickness of the skin and/or a loss of elasticity and/or firmness of the skin.

The alterations in epidermal homeostasis are also manifested in a dull and/or poorly defined appearance to the complexion of the skin.

This phenomenon may be accentuated by the menopause: women complain of their skin tightening and becoming dry, or even of the appearance of xerosis. The hormonal deficits associated with the menopause are accompanied in particular by a drop in metabolic activity, which can result in a decrease in the proliferation of the keratinocytes and in an increase in epidermal differentiation.

The need is understood, therefore, to have agents capable of promoting the homeostasis of the skin in order to maintain and/or increase the thickness of the skin and thus to maintain and/or improve the mechanical properties of the skin and/or to promote radiance in the complexion.

The prior art discloses the use of soluble cosmetic agents for promoting cellular renewal. They include, for example, retinoic acid derivatives, and especially retinol, also known as vitamin A, and esterified derivatives of retinol, which have the effect of promoting proliferation of the keratinocytes and of inhibiting their differentiation, thereby making it possible to stimulate epidermal renewal, to increase the thickness of the epidermis and/or to promote radiance in the complexion.

The soluble cosmetic agents act classically via a bond to a receptor which initiates intracellular responses, leading to a regulation of the expression of proteins which are involved in the processes of epidermal proliferation and/or differentiation. This is termed a direct 'biological' effect.

The Applicant has now shown, surprisingly and unexpectedly, that an improvement in the homeostasis of the skin and/or in the radiance of the complexion can be obtained via a biomechanical effect provided by the topical application of an effective amount of cosmetic agents, especially tensing agents.

The Applicant has shown in effect that the topical application of an effective amount of tensing agents, such as acrylic copolymers, to a model of reconstructed skin had the effect of modulating the expression of proteins involved in the homeostasis of the skin.

By 'biomechanical effect' according to the invention is meant the capacity of a cosmetic agent, and in particular of a tensing agent, to induce a biological response in the cells of the epidermis and/or dermis, via a mechanical effect which is effective at the surface of the skin {stratum corneum) .

By 'mechanical effect which is effective at the surface of the skin' is meant the capacity of a cosmetic agent to induce biologically effective mechanical tensions, i.e. mechanical tensions capable of transmitting a mechanical perturbation from cell to cell or via the extracellular matrix, and involving the activation of mechanoreceptors which are present on the membranes of said cells. These cells are referred to as 'biologically sensitive to mechanical tensions': interest attaches in particular to the cells of the epidermis and dermis, and especially to the keratino- cytes and fibroblasts.

These mechanical tensions, in contrast to conventional stimulation by soluble molecules of the kind used hitherto, have the effect of modifying, via membrane receptors or 'mechanoreceptors', an equilibrium which is established between the extracellular matrix and a cell, or between two adjacent cells.

The mechanical tensions are transmitted in the cell in the form of biochemical signals via membrane receptors or mechanoreceptors .

These mechanoreceptors are membrane receptors which are sensitive to mechanical tensions, in other words membrane receptors capable of inducing an intracellular biological response in response to a mechanical perturbation. They include the integrins (Pommerenke et al., Eur J Cell Biol 1996 Jun_; 70(2): 157-64), PECAMl receptors (Fujiwara et al . , Cell struct funct 2001 Feb; 26(1): 11-17) or else PDGF growth factor receptors (Li et al . , Cell Signal 2000 JuI; 12(7): 435- 45) .

The tensions, by inducing mechanical perturbation of these receptors, in a first step trigger activation of multiple second messengers. The tensions activate, in particular, protein tyrosine kinase (PTK) , protein kinase C (PKC), the G proteins rac and cdc42, or induce the release of calcium flows. The activation of these various signalling pathways leads to the activation of protein kinases from a single family, the MAPkinases, Erkl, Erk2 and p38. The MAPKs, once activated, induce the activation of specific transcriptional factors which regulate the expression of numerous genes involved in the homeostasis of keratinocytes . These activation mechanisms are, moreover, well regulated: in the course of tensions, in particular, Erk induces the expression of MAPK phosphatases, which are known to inhibit Erk. This process allows the cells to control the signals induced by the tensions, and to prevent pathological hyperproliferation of the keratinocytes. To the knowledge of the Applicant there has never to date been any description or suggestion of improving epidermal homeostasis and/or the radiance of the complexion by the topical application to the skin of an effective amount of a cosmetic agent having a biomechanical effect, in particular a tensing agent.

The prior art has disclosed the use of tensing agents to obtain a superficial and immediate visual effect of smoothing of the microrelief of the skin, particularly smoothing of wrinkles and fine lines. These agents are described as being capable of forming a film which causes the retraction of the stratum corneum, which is the surface, horny layer of the epidermis. The cosmetic or dermatological use of such polymer systems for attenuating the alterations in the microrelief of the skin that are associated with age is described in patent application WO 98/29091. Other tensing agents consist of dispersions of inorganic colloidal particles, particularly silica, as described in patent applications FR-A-2 823 113, FR-2 843 024 and FR-2 659 551 or in patents US-3,819,825 and US-4 , 777 , 041 , for example. Further tensing agents are mixed silicates such as those described in patent application FR-2 816 315.

To the knowledge of the Applicant, however, there has never to date been any description of a biological effect of the tensors, and in particular of their capacity to regulate the expression of proteins involved in the homeostasis of the skin, or of their use to promote the homeostasis of the skin and/or to improve the radiance of the complexion and/or to improve the mechanical properties of the skin.

The invention thus provides in particular for the cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to promote the homeostasis of the skin.

In particular, the effective amount of at least one tensing agent is intended to promote the homeostasis of the epidermis.

By 'effective amount of tensing agent' which can be used in accordance with the invention is meant, in particular, an amount sufficient to obtain the required biological effect of the tensors in the context of the present invention, namely, in particular, an effect on the regulation of the expression of genes involved in the homeostasis of the skin.

This effective amount or effective dose can be evaluated, for example, by a DNA array method as described in the illustrative examples below, the general principle of which is as follows:

different doses of tensing agents are applied to cells in culture or to a model of epidermis and/or of reconstructed skin;

the mRNAs are extracted from said treated or untreated (control) cells and a 'reverse' transcription is carried out using, for example, oligo dT and a P33- labelled deoxynucleotide triphosphate, to give labelled target cDNA sequences;

these target cDNA sequences are hybridized on dedicated minichips containing DNAs specific for the markers that are involved in the physiology of the cells of the skin, and in particular in the homeostasis of the skin (called 'cDNA probes'); after washing, the amount of labelled target sequences is measured, and is compared with the control in order to evaluate the variation of expression of the target genes that is induced by the topical application of said tensing agent, relative to the control;

subsequently a selection is made of the effective doses or amounts for which a variation is obtained in the expression of genes involved in the proliferation (increase) and/or differentiation

(decrease) in the cells of the skin relative to an

(untreated) control. Advantageously, a selection is made of the effective doses for which a decrease is obtained in the expression of genes involved in the differentiation of keratinocytes (e.g. corneodesmosin, loricrin, suprabasin) and/or an increase in genes involved in the regeneration of the skin (e.g. cytokeratins) relative to a control, preferably a variation in the expression by a factor of 2 or more relative to the control.

The amount of tensing agent present in the cosmetic compositions according to the invention ranges from 0.1% to 30% by weight of active ingredient relative to the total weight of the composition. Preference will be given to using an effective amount ranging from 1% to 30% by weight of active ingredient relative to the total weight of the composition, preferably from 4% to 20% by weight of active ingredient relative to the total weight of the composition, and in particular an effective amount of between 6% and 10% by weight of active ingredient relative to the total weight of the composition.

By "active ingredient" the intention is to exclude the medium in which the tensing agent is optionally solubilized or in dispersion in its commercial form, as for example in the case of dispersions of colloidal particles .

The invention likewise provides for the cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to prevent and/or reduce the alteration in the homeostasis of the skin that is induced by environmental stresses.

By 'environmental stresses' are meant in particular, in accordance with the invention, UV radiation, pollution, oxidizing stress or irritant stress.

The invention likewise provides for the cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to: increase the thickness of the skin, particularly the thickness of the epidermis, and/or promote the radiance of the complexion, and/or - promote and/or improve the mechanical properties of the skin, in particular to promote and/or improve the elasticity and/or firmness of the skin.

According to one embodiment the invention provides for the cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of 1% to 30% by weight, relative to the total weight of the composition, of at least one tensing agent selected from vegetable or animal proteins and their hydrolysates ; polysaccharides of natural origin selected from carrageenans, agars, gellans, alginates and pectins,- synthetic polymers; and mixtures thereof, for promoting and/or improving the elasticity and/or firmness of the skin.

The effective amount of at least one tensing agent present in the composition is intended to reduce the processes of epidermal differentiation and/or to promote the regeneration and/or renewal of the skin.

The biological effect of the tensors demonstrated by the Applicant is a durable biological effect, in contrast to an immediate visible effect which has been known to date for tensing agents.

The durable or remanent effect obtained on the homeostasis of the skin may be optimized by daily application of a composition according to the invention.

The effective amount of at least one tensing agent, applied to the surface layers of the skin, is intended in particular to regulate the expression of genes involved in the homeostasis of the skin via the transmission of mechanical tensions involving the activation of mechanoreceptors .

By "tensing agent" that can be used in accordance with the invention is meant a compound liable to have a tensing effect, in other words able to stretch the skin.

Generally speaking, a tensing agent, according to the invention, refers to any compounds which are soluble or dispersible in water at a temperature ranging from 25⁰C to 5O⁰C at a concentration of 7% by weight in water or at the maximum concentration at which they form a medium of homogeneous appearance, and which at this concentration of 7% or at this maximum concentration in water produce a retraction of more than 15% in the test described below. The maximum concentration at which they form a medium having a homogeneous appearance is determined to ± 10% and preferably to ± 5%.

By 'medium having a homogeneous appearance' is meant a medium which does not exhibit aggregates visible to the naked eye .

To determine said maximum concentration, the tensing agent is added gradually to water, with stirring using a deflocculator device, at a temperature ranging from

25⁰C to 5O⁰C, and then the mixture is kept with stirring for an hour. Inspection then takes place after

24 hours to determine whether the mixture thus prepared has a homogeneous appearance (absence of aggregates visible to the naked eye) .

The tensing effect may be characterized by an in vitro retraction test.

Beforehand, and as described above, a homogeneous mixture of the tensing agent is prepared in water, at the concentration of 7% by weight or at the maximum concentration defined above.

30 μl of the homogeneous mixture are placed on a rectangular test specimen (10 x 40 mm, hence having an initial width W₀ of 10 mm) of elastomer having a modulus of 20 MPa and a thickness of 100 μm.

After 3 h of drying at 22 + 3⁰C and 40 ± 10% relative humidity (RH) , the elastomer test specimen exhibits a retracted width, recorded as W_3h, owing to the tension exerted by the applied tensing agent.

The tensing effect (TE) of said agent is then quantified as follows: ^NTE' = (W₀ - W_3h/W₀ ) x 100 in % where Wo = initial width, 10 mm and W_3h = width after 3 h of drying

The tensing agent may be selected from:

a) animal or vegetable proteins and their hydrolysates; b) polysaccharides of natural origin; c) mixed silicates,- d) colloidal particles of inorganic fillers,- e) synthetic polymers; and mixture of these.

A person skilled in the art will know how the select, from the chemical categories listed above, the materials conforming to the tensing test as described above .

These various categories of tensing agents will now be described.

a) Vegetable proteins and their hydrolysates

Examples of vegetable proteins and vegetable protein hydrolysates which can be used as tensing agents in accordance with the invention comprise proteins and protein hydrolysates of maize, rye, wheat, buckwheat, sesame, spelt, tobacco, pea, bean, lentil, soya, almond and lupin.

Animal proteins which can be used in accordance with the invention include, in particular, the proteins extracted from silk, milk, whey and egg.

b) Polysaccharides of natural origin

The polysaccharides of natural origin which are suitable for formulating compositions in accordance with the invention are any polysaccharides of natural origin that are capable of forming gels of either thermoreversible or crosslinked type.

Preference will be given to using polysaccharides capable of forming thermoreversible gels. By thermoreversible is meant that the gel state of these polymer solutions is obtained reversibly once the solution has been cooled below the gelling temperature, which is a characteristic of the polysaccharide used.

A first class of polysaccharides of natural origin which can be used in the present invention is composed of the carrageenans and more particularly of kappa- carrageenan and iota-carrageenan. These are linear polysaccharides which are present in certain red algae. They are composed of alternating β-1,3 and Ot- 1,4 galactose residues, it being possible for many galactose residues to be sulphated. This class of polysaccharides is described in chapter 3 of the book "Food Gels" edited by Peter HARRIS, Elsevier 1989.

Another class of polysaccharides which can be used is composed of the agars . These are also polymers extracted from red algae, and are composed of alternating 1 , 4-L-galactose and 1, 3-D-galactose residues. This class of polysaccharides is also described in chapter 1 of the book "Food Gels" mentioned above.

A third class of polysaccharides is composed of polysaccharides of bacterial origin, which are called gellans. These are polysaccharides composed of an alternation of glucose, glucuronic acid and rhamnose residues. These gellans are described in particular in chapter 6 of the book "Food Gels" mentioned above. Finally, in the case of polysaccharides forming gels of crosslinked type, induced in particular by addition of salts, mention will be made of the polysaccharides belonging to the class of the alginates and the pectins .

These tensing polysaccharides may be present in the form of microgels as described in patent application FR 2 829 025 or not.

It is also possible to make mention of tensing systems comprising: a polysaccharide and a polyhydroxylated moisturizing agent, such as the system described in patent application FR 2 828 810; a polysaccharide of pullulan type, as described in patent US 6,703,027; a polysaccharide of Biopolymer B16 type, as described in patent US 5,175,279.

c) Mixed silicates

Another class of tensing agents which can be used in accordance with the invention is composed of mixed silicates. By this expression are meant all of the silicates of natural or synthetic origin which contain at least two different cations selected from alkali metals (for example Na, Li, K) or alkaline-earth metals (for example Be, Mg, Ca) and transition metals.

Preference is given to using phyllosilicates, namely silicates having a structure in which the SiO₄ tetra- hedra are organized in sheets between which the metal cations are enclosed.

One class of silicates that is particularly preferred as tensing agents is that of the laponites. Laponites are magnesium lithium sodium silicates which have a layer structure similar to that of montmorillonites . Laponite is the synthetic form of the natural mineral known as hectorite. Use may be made, for example, of the laponite sold under the name Laponite XLS or Laponite XLG by Rockwood.

d) Colloidal particles of mineral filler

By "colloidal particles" are meant particles in dispersion in an aqueous, aqueous-alcoholic or alcoholic medium, preferably an aqueous medium, which have a number-average diameter of between 0.1 and 100 nm, preferably between 3 and 30 nm.

The colloidal particles according to the invention have no thickening property in water, alcohol, oil and all other solvents. At a concentration greater than or equal to 15% by weight in water, the viscosity of the solutions thus obtained is less than 0.05 Pa . s for a shear rate of 10 s^"1. The measurements are made at 25⁰C using a Haake RheoStress RS150 rheometer in cone/plate configuration, the measurements of the measuring cone being as follows: 60 mm diameter and 2° angle.

These particles are generally prepared by a sol-gel process and are therefore different in particular from particles of fumed silica, which undergo agglomeration in water to form larger aggregates.

The colloidal particles of mineral filler which can be used in accordance with the invention are generally selected from colloidal particles of silica, cerium oxide, zirconium oxide, alumina, calcium carbonate, barium sulphate, calcium sulphate, zinc oxide and titanium dioxide, colloidal particles of platinum, mixed colloidal particles such as, for example, titanium dioxides with one or more coatings, such as titanium dioxide with a silica coating. In the composition according to the invention preference will be given to using colloidal silicas or colloidal silica-alumina composite particles. Colloidal particles of silica

By colloidal silicas are meant, for the purposes of this application, colloidal particles of silica in dispersion in an aqueous, aqueous-alcoholic or alcoholic medium. The colloidal particles of silica have a diameter ranging from 0.1 to 100 nm and preferably from 3 to 30 nm. These particles are present in the form of aqueous dispersions and do not have any thickening property in water, alcohol, oil and all other solvents. At a concentration greater than or equal to 15% by weight in water, the viscosity of the solutions thus obtained is less than 0.05 Pa . s for a shear rate of 10 s^"1. The measurements are made at 25⁰C using a Haake RheoStress RS150 rheometer in cone/plate configuration, the measurements of the measuring cone being as follows: 60 mm diameter and 2° angle.

Colloidal silicas which can be used in the composition according to the invention include, for example, those sold by Catalysts & Chemicals under the names Cosmo S-40 and Cosmo S-50.

Colloidal silica-alumina composite particles

The colloidal particles of mineral fillers which can be used according to the invention may also be selected from colloidal silica-alumina composite particles. By silica-alumina composite is meant particles of silica in which atoms of aluminium have been partly substituted for atoms of silica. By colloidal particles are meant, for the purposes of this application, colloidal particles in dispersion in an aqueous, aqueous-alcoholic or alcoholic medium. The colloidal silica-alumina composite particles have a diameter ranging from 0.1 to 100 nm and preferably from 3 to 30 nm. These particles are present in the form of aqueous dispersions and do not have any thickening property in water, alcohol, oil and all other solvents. At a concentration greater than or equal to 15% by weight in water, the viscosity of the solutions thus obtained is less than 0.05 Pa . s for a shear rate of 10 s^"1. The measurements are made at 25⁰C using a Haake RheoStress RS150 rheometer in cone/plate configuration, the measurements of the measuring cone being as follows: 60 mm diameter and 2° angle.

At a pH of 7, the colloidal silica-alumina composite particles according to the invention have a zeta potential of less than -20 mV and preferably less than -25 mV. The measurements are made at 25⁰C using a Coulter Scientific Instrument DELSA 440SX apparatus.

Colloidal silica-alumina composite particles which can be used in the compositions according to the invention include, for example, those sold by Grace under the names Ludox AM, Ludox AM-X 6021, Ludox HSA and Ludox TMA.

e) Synthetic polymers

The synthetic polymers used according to the invention may be in solution or in suspension in a polar or apolar (latex) liquid, particularly in aqueous solution or aqueous dispersion, or in a dry form which is redispersible in a cosmetic solvent.

The synthetic polymers which can be used as a tensing agent may be selected from: polycondensates, especially polyurethanes,- - acrylic polymers; graft silicone polymers; water-soluble or water-dispersible polymers containing water-soluble or water-dispersible units and LCST units.

The synthetic polymers according to the invention may in particular be selected from interpenetrating polymer networks (IPNs) . These polymers may take the form, in particular, of random linear copolymers, of interpenetrating polymer networks (IPNs) , of polycondensates, of graft silicone polymer and of block polymer. Irrespective of its nature, the synthetic polymeric tensing agent may have a weight-average mass Mw ranging from 3000 to 1 000 000 Da.

Random linear copolymers The random linear copolymers which are tensors in the sense of the present invention are selected from random copolymers having a linear ethylenic main chain with a molecular weight of less than 600 000 Da (g/mol) , preferably a weight-average molecular weight of between 15 000 and 600 000 g/mol, and contain at least 70% of a monomer with a glass transition temperature, Tg, greater than 4O⁰C (preferably > 6O⁰C) whose corresponding homopolymer is insoluble in water at 25⁰C, and at least one ionic hydrophilic monomer. This copolymer may also contain a non-majority monomer with a Tg less than 4O⁰C.

These copolymers generally exhibit an overall glass transition temperature greater than or equal to 45⁰C.

Preference is given to all copolymers composed of:

• 70% to 90% by weight of at least one aryl or alkyl acrylate and (or) at least one aryl or alkyl methacrylate cited in the list below and (or) styrene

• 10% to 30% by weight of (meth) acrylic acid.

List of preferred alkyl (meth) acrylates : benzyl acrylate, cyclohexyl acrylate, tert-butyl acrylate, isobornyl acrylate and norbornyl acrylate, methyl, ethyl, isobutyl, cyclohexyl, benzyl, tert-butyl, isobornyl and norbornyl methacrylate, preferably methyl methacrylate and cyclohexyl methacrylate. Among the abovementioned polymers preference will be given particularly to: copolymers of methyl methacrylate/methacrylic acid; copolymers of methyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of methyl methacrylate; copolymers of ethyl methacrylate/methacrylic acid; copolymers of ethyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of ethyl methacrylate; copolymers of isobutyl methacrylate/methacrylic acid; copolymers of isobutyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of isobutyl methacrylate; - copolymers of benzyl methacrylate/methacrylic acid; copolymers of benzyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of benzyl methacrylate; copolymers of benzyl acrylate/methacrylic acid; copolymers of benzyl acrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of benzyl acrylate; copolymers of cyclohexyl methacrylate/ methacrylic acid; copolymers of cyclohexyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of cyclohexyl methacrylate; copolymers of cyclohexyl acrylate/methacrylic acid; copolymers of cyclohexyl acrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of cyclohexyl acrylate; copolymers of tert-butyl methacrylate/ methacrylic acid; copolymers of tert-butyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of tert-butyl methacrylate ; copolymers of tert-butyl acrylate/methacrylic acid; copolymers of tert-butyl acrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of tert-butyl acrylate; copolymers of isobornyl methacrylate/ methacrylic acid; copolymers of isobornyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of isobornyl methacrylate ; copolymers of isobornyl acrylate/methacrylic acid; copolymers of isobornyl acrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of isobornyl acrylate; copolymers of norbornyl methacrylate/ methacrylic acid; copolymers of norbornyl methacrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of norbornyl methacrylate; copolymers of norbornyl acrylate/methacrylic acid; copolymers of norbornyl acrylate/acrylic acid, said copolymers containing between 70% and 90% by weight of norbornyl acrylate; and - copolymers of styrene/methacrylic acid; copolymers of styrene/acrylic acid, said copolymers containing between 70% and 90% by weight of styrene.

The copolymers in accordance with the present invention are in the form of a dispersion in a polar liquid. These copolymers are dispersed in water after neutralization with a base.

Interpenetrating polymers or IPNs An "interpenetrating polymer network" for the purposes of the present invention means a mixture of two inter- meshed polymers obtained by simultaneous polymerization and/or crosslinking of two types of monomers, the resulting mixture having a single glass transition temperature. Examples of IPNs that are suitable for employment in the present invention, and the process for preparing them, are described in patents US 6,139,322 and US 6,465,001, for example. Preferably the IPN according to the invention comprises at least one acrylic polymer and, more preferably, it further comprises at least one polyurethane or a copolymer of vinylidene fluoride and hexafluoropropylene . According to one preferred embodiment the IPN according to the invention comprises a polyurethane and an acrylic polymer. IPNs of this kind are in particular those of the Hybridur series which are available commercially from Air Products. One particularly preferred IPN is in the form of an aqueous dispersion of particles having a weight-average size of between 90 and 110 nm and a number-average size of approximately 80 nm. This IPN preferably has a glass transition temperature, Tg, which ranges from approximately -6O⁰C to +100⁰C. An IPN of this type is sold in particular by Air Products under the trade name Hybridur 875. Other IPNs suitable for use in the present invention are referenced Hybridur X01602 and Hybridur 580.

Other IPNs suitable for employment in the present invention include IPNs composed of a mixture of a polyurethane with a copolymer of vinylidene fluoride and hexafluoropropylene . These IPNs can be prepared in particular as described in patent US 5,349,003. As a variant, they are available commercially in the form of a colloidal dispersion in water, in a ratio of the fluoro copolymer to the acrylic polymer of between 70:30 and 75:25, under the trade names KYNAR RC-10, 147 and KYNAR RC-10, 151 from ATOFINA.

Polycondensate

According to a second variant the composition may comprise as synthetic polymeric tensing agent at least one polycondensate . Polymers in the form of polycondensates having a tensing effect have been described in particular in patent application WO 98/29092.

Polycondensates include polyurethanes, especially anionic, cationic, nonionic or amphoteric polyurethanes, polyurethane-acrylics, polyurethane- polyvinylpyrrolidones, polyester-polyurethanes, polyether-polyurethanes, polyureas, and mixtures thereof .

The polyurethane may be, for example, a polyurethane, polyurea/urethane or polyurea copolymer which is aliphatic, cycloaliphatic or aromatic and comprises, alone or in a mixture, - at least one sequence originating from a linear or branched aliphatic and/or cycloaliphatic and/or aromatic polyester, and/or at least one sequence originating from an aliphatic and/or cycloaliphatic and/or aromatic polyether, and/or at least one sequence containing fluorinated groups .

The polyurethanes may also be obtained from branched or unbranched polyesters or from alkyds containing mobile hydrogens that are modified by reaction with a diisocyanate and a difunctional organic compound (for example a dihydro, diamino or hydroxyamino compound) , further containing alternatively a carboxylic acid or carboxylate group, or a sulphonic acid or sulphonate group, or else a neutralizable tertiary amine group or a quaternary ammonium group. Mention may also be made of polyesters, polyester amides, fatty-chain polyesters, polyamides, and epoxy ester resins.

In order to form a polyurethane, mention may be made, as a monomer which carries an anionic group and can be used in polycondensation, of dimethylolpropionic acid, trimellitic acid or a derivative, such as trimellitic anhydride, the sodium salt of the acid

3-sulphopentanediol , or the sodium salt of 5-sulpho- 1, 3-benzenedicarboxylic acid.

The polycondensates include the polymers sold under the trade names Avalure UR410, Avalure UR405, Avalure UR460 by Noveon, and under the trade names Neorez R974, Neorez R981 and Neorez R970 by Avecia.

Mention may also be made of combinations of polymers, such as polyurethanes having a degree of shrinkage of less than or equal to 20% and acrylic polymers having a degree of shrinkage of less than or equal to 20%, which are described in patent application WO 2005067884.

Graft silicone polymer

Among the synthetic polymeric tensing agents used in the composition according to the invention, mention may be made, as a variant, of graft silicone polymers in particular, as defined in patent application EP-1038519. The polymer in question may more particularly be a polymer comprising a main chain of silicone or polysiloxane (Si-O- polymer) on which is grafted, within said chain and, optionally, at at least one of its ends, at least one organic group not containing silicone.

The polymers having a polysiloxane backbone grafted with non- silicone organic monomers according to the invention may be existing commercial products or may be obtained by any means known to a person skilled in the art, in particular by reaction between (i) a starting silicone correctly functionalized on one or more of its silicon atoms and (ii) a non- silicone organic compound which is itself correctly functionalized by a function which is capable of reacting with the functional group or groups carried by said silicone, thereby forming a covalent bond; a classic example of such a reaction is the hydrosilylation reaction between ≡Si-H groups and vinylic groups CH₂=CH-, or else the reaction between thiofunctional groups -SH and the same vinylic groups.

Examples of polymers having a polysiloxane backbone grafted with non- silicone organic monomers that are suitable for an implementation of the present invention, and their particular method of preparation, are described in particular in patent applications EP-A-0582152, WO 93/23009 and WO 95/03776, the teachings of which are included in their entirety in the present description as non-limitative references.

According to one particularly preferred embodiment of the present invention the silicone polymer that is employed, having a polysiloxane backbone grafted with non-silicone organic monomers, is the result of free- radical copolymerization between, on the one hand, at least one non-silicone anionic organic monomer containing ethylenic unsaturation and/or a non-silicone hydrophobic organic monomer containing ethylenic unsaturation and, on the other hand, a silicone having in its chain at least one functional group capable of reacting with said ethylenic unsaturations of said non- silicone monomers, thereby forming a covalent bond, and particularly thio-functional groups.

According to the present invention said ethylenically unsaturated anionic monomers are preferably selected, alone or in mixtures, from linear or branched unsaturated carboxylic acids which optionally are partly or totally neutralized in the form of a salt, it being possible for this or these unsaturated carboxylic acids to be, more particularly, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, fumaric acid and crotonic acid. The salts that are suitable are, in particular, alkali metal salts, alkaline-earth metal salts and ammonium salts. It will be noted that, likewise, in the final graft silicone polymer, the anionic organic group which constitutes the result of the free-radical

(homo) polymerization of at least one anionic monomer of unsaturated carboxylic acid type may, after reaction, be neutralized with a base (sodium hydroxide solution, aqueous ammonia, etc.) in order to bring it into the form of a salt .

According to the present invention the ethylenically unsaturated hydrophobic monomers are preferably selected, alone or in mixtures, from esters of acrylic acid with alkanols and/or esters of methacrylic acid with alkanols. The alkanols are preferably Ci-Ci₈ and more particularly Ci-Ci₂. The preferred monomers are selected from the group consisting of isooctyl (meth) acrylate, isononyl (meth) acrylate, 2-ethylhexyl

(meth) acrylate, lauryl (meth) acrylate, isopentyl

(meth) acrylate, n-butyl (meth) acrylate, isobutyl

(meth) acrylate, methyl (meth) acrylate, tert-butyl

(meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate or mixtures thereof.

One class of silicone polymers having a polysiloxane backbone grafted with non- silicone organic monomers that is particularly suitable for the implementation of the present invention is composed of silicone polymers containing in their structure the unit of formula (I) below:

in which the radicals Gi, identical or different, represent hydrogen or a Ci-Ci₀ alkyl radical or else a phenyl radical; the radicals G₂, identical or different, represent a Ci-Ci₀ alkylene group,- G₃ represents a polymeric residue resulting from the

(homo) polymerization of at least one ethylenically unsaturated anionic monomer; G₄ represents a polymeric residue resulting from the (homo) polymerization of at least one ethylenically unsaturated hydrophobic monomer; m and n are, independently of one another, 0 or 1; a is an integer ranging from 0 to 50; b is an integer which can be between 10 and 350; and c is an integer ranging from 0 to 50, with the proviso that one of parameters a and c is different from 0.

Preferably the unit of formula (I) above has at least one, and more preferably all, of the following features :

- the radicals d denote a Ci-Ci₀ alkyl radical;

- n is non-zero, and the radicals G₂ represent a divalent Ci-C₃ radical; - G₃ represents a polymeric radical resulting from the

(homo) polymerization of at least one ethylenically unsaturated carboxylic acid monomer, preferably acrylic acid and/or methacrylic acid;

- G₄ represents a polymeric radical resulting from the (homo) polymerization of at least one Ci-Ci₀ alkyl

(meth) acrylate monomer.

Examples of graft silicone polymers conforming to the formula (I) are therefore, in particular, polydimethyl- siloxanes (PDMSs) grafted via a thiopropylene linker with polymeric units of poly (meth) acrylic acid type and/or polyalkyl, especially Ci-C₃, or even Ci, alkyl

(meth) acrylate type.

These polymers are referenced under the CTFA name

"polysilicone-8" .

One preferred example of a graft silicone polymer is the polysilicone-8 (CTFA name) which is a polydimethyl- siloxane grafted via a thiopropylene linker with mixed polymer units of poly (meth) acrylic acid type and of polyalkyl, especially Ci-C₃, or even Ci, alkyl

(meth) acrylate type.

The polymer in question may therefore be a propyl- thio (polymethyl acrylate/methyl methacrylate/methacrylic acid) -grafted polydimethylsiloxane or a propyl - thio (polymethyl acrylate)-, propylthio (polymethyl methacrylate) - and propylthio (polymethacrylic acid)- grafted polydimethylsiloxane . As a variant it may be a propylthio (polyisobutyl methacrylate) - and propyl - thio (polymethacrylic acid) -grafted polydimethylsiloxane. Preference is given to using a propyl - thio (polymethyl acrylate) /methyl methacrylate/ methacrylic acid) -grafted polydimethylsiloxane.

A polymer of this type is available in particular under the trade name VS 80 or VS 70 (at 10% in water) or LO 21 (in powder form) from 3M.

Preferably the number-average molecular mass of the silicone polymers having a polysiloxane backbone grafted with non- silicone organic monomers of the invention varies from 10 000 to 1 000 000 approximately and more preferably from 10 000 to 100 000 approximately .

Star polymer According to yet another possibility, the synthetic polymeric tensing agent which can be used in the composition according to the invention may comprise at least one polymer of "star" structure, represented by the following formula (I) :

A- [(Ml)pl - (M2)p2 .... (Mi)pj]n (I)

in which:

A represents a multifunctional centre, of functionality "n" , n being an integer greater than 2, in particular greater than 5 ;

[(Ml)pl - (M2)p2 .... (Mi)pj] represents a polymeric chain, also called a branch, which is composed of polymerized monomers Mi, which are identical or different, having a polymerization index pj , each branch being identical or different, and being grafted covalently onto said centre A; i is greater than or equal to 1, and pj is greater than or equal to 2 ; said polymer comprising one or more monomers Mi whose corresponding homopolymer exhibits a Tg of greater than or equal to approximately 1O⁰C, preferably greater than or equal to 15⁰C, and more preferably greater than or equal to 2O⁰C; and this or these monomers Mi being present in a minimum amount of approximately 45% by weight, preferably in an amount varying between 55% and 99% by weight, and more preferably between 75% and 90% by weight, relative to the total weight of the entirety of the monomers of the final polymer. These polymers, and the process for preparing them, are described in particular in document EP 1 043 345.

Block polymer As a variant, the synthetic polymeric tensing agents which can be used in the composition according to the invention may be block polystyrene (PS) -polyethyl acrylate (PEA) polymers.

Very generally, a block copolymer is a polymer composed of at least two distinct homopolymers composed solely of monomers A and B respectively. Thus the blocks according to the invention are, respectively, polystyrene (PS) and polyethyl acrylate (PEA) blocks.

In the context of this variant, the polymer may be a triblock polymer of type PS-PEA-PS or else a multiblock polymer of type PS-[PEA-PSJn, or PEA-[PS-PEAJn, where n is a positive integer and is preferably 1. Advantageously these block polymers are linear copolymers. The molecular weight of this polymer is preferably greater than 10 000 daltons, and more preferably greater than 50 000 daltons. The ratio by weight of the PS and PEA monomers may be defined such that PS/PEA is greater than 1 and preferably such that PS/PEA is greater than 5.

Mention may be made of the triblock polymer PS (30 000)- PEA(IO 000) -PS (30 000), which is most particularly suitable for the implementation of the invention. This particularly advantageous block copolymer is a triblock copolymer comprising: a first block containing units deriving from styrene, having a number-average molecular mass of 30 000 g/mol; a second block composed of units deriving from ethyl acrylate, having a number-average molecular mass of 10 000 g/mol; - a third block containing units deriving from styrene, having a number-average molecular mass of 30 000 g/mol.

A copolymer conforming to the definition given above may be a copolymer for which the first block and/or the third block and, preferably, the first block and the third block comprise, in addition to the units deriving from styrene, units deriving from methacrylic acid, for example, in a mass ratio (styrene/methacrylic acid) of 98/2.

The synthetic copolymers used according to the invention may also, as a variant, be composed of a random polystyrene polyethyl acrylate copolymer. The ratio by weight of the PS and PEA monomers is defined such that PS/PEA > 1 and preferably such that PS/PEA > 5.

Alternatively the tensing polymers according to the invention may also be selected from vinyl derivatives such as polyvinyl alcohols and polyvinylpyrrolidones, either in block or else in random form.

Finally, synthetic polymers which are appropriate may be water-soluble or water-dispersible polymers containing water-soluble or water-dispersible units and containing LCST units, said LCST units exhibiting, in particular, a separation temperature in water of 5 to 4O⁰C at a mass concentration of 1%. This type of polymer is more fully described in patent application FR 2 819 429.

Preferably the tensing agent used according to the invention is selected from: vegetable or animal proteins and their hydrolysates,- polysaccharides of natural origin; synthetic polymers of polycondensate or graft silicone polymer type.

More preferably still, use will be made of a graft silicone polymer.

The tensing agent will be present in the composition in an amount effective for obtaining the required biological effect in accordance with the invention.

By way of example the tensing agent may be included in the composition according to the invention in an amount ranging from 0.01% to 30% by weight of active ingredient, preferably from 1% to 30% by weight of active ingredient, relative to the total weight of the composition.

In particular it will be possible to use an effective amount of tensing agent ranging from 2% to 30% by weight, in particular from 3% to 20%, preferably from 4% to 20% by weight of active ingredient relative to the total weight of the composition, for example an amount between 6% and 10% by weight of active ingredient relative to the total weight of the composition.

According to one particular embodiment an effective amount of tensing agent will be used of 3% to 20%, in particular from 3% to 7% by weight of active ingredient relative to the total weight of the composition. By "active ingredient" the intention is to exclude the medium in which the tensing agent is optionally solubilized or in dispersion in its commercial form, as for example in the case of dispersions of colloidal particles.

The composition according to the invention comprises a physiologically acceptable medium, in other words a medium which is compatible with the skin of the face and/or body. It is preferably a cosmetically acceptable medium, in other words a medium which has a colour, odour and feel that are pleasant and which does not give rise to any unacceptable discomfort (stinging, tautness, redness) that might dissuade the consumer from using this composition.

The composition according to the invention may be a bodycare or facial -care composition or a makeup composition.

The composition according to the invention may be in any of the formulated forms conventionally used for topical application, and particularly in the form of dispersions of the aqueous gel or lotion type, emulsions with a liquid or semi-liquid consistency of the milk type, obtained by dispersing a fatty phase in an aqueous phase (0/W) or conversely (W/0) , or of suspensions or emulsions with a soft, semi-solid or solid consistency, of cream or gel type, or in the form of a serum or stick, or else of multiple emulsions (W/O/W or 0/W/O) . These compositions are prepared in accordance with the customary methods.

Oils which can be used in the composition according to the invention include the following: hydrocarbon oils of animal origin, such as perhydrosqualene ; hydrocarbon oils of vegetable origin, such as liquid triglycerides of fatty acids containing 4 to 10 carbon atoms, or else, for example, vegetable oils such as apricot kernel oil and shea butter oil; synthetic esters and ethers, especially those of fatty acids, such as the oils of formulae R¹COOR² and R¹OR² in which R¹ represents the residue of a fatty acid containing 8 to 29 carbon atoms and R² represents a branched or unbranched hydrocarbon chain containing 3 to 30 carbon atoms,- linear or branched hydrocarbons of mineral or synthetic origin, such as volatile or non-volatile liquid paraffins and derivatives thereof, isohexadecane, isododecane, Vaseline, polydecenes, hydrogenated polyisobutene such as Parleam^® oil; natural or synthetic essential oils,- - branched fatty alcohols having 8 to 26 carbon atoms, such as octyldodecanol ; partially hydrocarbon-modified and/or silicone- modified fluoro oils like those described in document JP-A-2-295912; - silicone oils such as volatile or non-volatile polydimethylsiloxanes (PDMSs) having a linear or cyclic silicone chain which are liquid or pasty at ambient temperature, especially cyclopolydimethylsiloxanes

(cyclomethicones) such as cyclohexasiloxane and cyclo- pentasiloxane,- polydimethylsiloxanes containing alkyl, alkoxy or phenyl groups pendantly or at the end of a silicone chain, these groups having 2 to 24 carbon atoms,- phenyl silicones such as phenyltrimethicones, phenyldimethicones, phenyltrimethylsiloxydiphenyl- siloxanes, diphenyldimethicones, diphenylmethyl- diphenyltrisiloxanes, 2-phenylethyl trimethylsiloxy- silicates, and polymethylphenylsiloxanes,- and mixtures thereof .

The other fatty substances which may be present in the oily phase are, for example, fatty acids containing 8 to 30 carbon atoms, such as stearic acid, lauric acid, palmitic acid and oleic acid; linear fatty alcohols such as cetyl alcohol and/or stearyl alcohol; pasty fatty substances such as lanolin; waxes,- and gums such as silicone gums (dimethiconol) .

These fatty substances may be selected variously by the skilled worker in order to prepare a composition having the desired properties of, for example, consistency or texture.

This composition may further comprise various adjuvants commonly used in the field of cosmetology, such as emulsifiers, including esters of fatty acids and of polyethylene glycol, esters of fatty acid and of sorbitan which are optionally polyoxyethylenated, polyoxyethylenated fatty alcohols and the esters or ethers of fatty acid and of sugars such as sucrose or glucose; fillers,- preservatives; sequestrants,- fragrances; and thickeners and/or gelling agents, such as homopolymers and copolymers of acrylic acid, homopolymers and copolymers of acrylamide and/or of 2-acrylamido-2-methylpropanesulphonic acid (AMPS), modified AMPS (Aristoflex LNC and SNC) products, and xanthan gum.

Fillers include, for example, particles of polyamide (Nylon) in spherical or microfibre form,- microspheres of polymethyl methacrylate,- ethylene-acrylate copolymer powders; expanded powders such as hollow microspheres and, in particular, the microspheres formed from a terpolymer of vinylidene chloride, acrylonitrile and methacrylate which are sold under the name Expancel,- powders of natural organic materials such as powders of starch, particularly of maize starch, wheat starch or rice starch, crosslinked or non-crosslinked, such as powders of starch crosslinked with octenylsuccinic anhydride; silicone resin microbeads such as those sold under the name Tospearl by Toshiba Silicone,- silica,- metal oxides such as titanium dioxide or zinc oxide,- mica,- hollow hemispherical particles of silicone such as NLK506 sold by Takemoto Oil and Fat,- and mixtures thereof .

The skilled worker will of course take care to select this or these optional additional compounds and/or their amount in such a way that the advantageous properties of the composition according to the invention are not, or not substantially, adversely affected by the intended addition.

The composition according to the invention is applied in accordance with the typical techniques, for example by application of creams, gels, serums or lotions to the skin it is intended to treat, in particular the skin of the body, face and/or neck.

The invention further provides a cosmetic method of treatment of dull and/or poorly defined complexion, characterized in that a composition comprising, in a physiologically acceptable medium, an effective amount of at least one tensing agent is applied to people having a dull and/or poorly defined complexion.

Likewise included in the context of the invention is a cosmetic method of treatment of soft and/or flaccid skin, characterized in that a composition comprising, in a physiologically acceptable medium, an effective amount of at least one tensing agent is applied to people having soft and/or flaccid skin or to areas of the body exhibiting a loss of elasticity and/or firmness.

In particular it will be possible to apply the composition to the face, the stomach and the thighs.

Advantageously, and in order to obtain a remanent effect over time of the tensing agents on the homeostasis of the skin, it will be possible to apply the composition according to the invention daily, in the morning and/or the evening. The invention will now be described with reference to the following examples, which are given by way of illustration and not of limitation. In these examples, unless indicated to the contrary, the amounts are expressed in weight percentages.

EXAMPLES

EXAMPLE 1: Demonstration of the biological effects of the tensors

a) Effect on the differential expression of genes The biological effects of the tensing agents were demonstrated after application to Episkin reconstructed epidermides .

Culture conditions of reconstructed epidermides The Episkin reconstructed epidermides used were obtained at d 15. They were placed in a maintenance medium for 8 hours. They were then transferred to a DMEM/Ham F12 medium devoid of EGF, of pituitary extract and of foetal calf serum. The epidermides were placed in this medium for 24 hours in order to equilibrate.

Preparation of the tensor: ethylenic copolymer of methyl methacrylate/methacrylic acid copolymer type Step 1: Synthesis of the polymer A jacketed 2 1 reactor was charged with 1 g of Trigonox 21S (tert-butyl peroxy-2-ethylhexanoate) and 200 g of methyl ethyl ketone. The mixture was heated at reflux for 1 h. After I h a mixture of 170 g of methyl methacrylate and 30 g of methacrylic acid was added dropwise over a time of I h. The colourless mixture became viscous. Heating was interrupted 6 h after the addition of the monomers.

Composition by NMR: methyl methacrylate 85.1%, methacrylic acid 14.9% Mass by GPC in THF (polystyrene standards): Mw = 98772; Mn = 61261; Mw = 105698 Ip = 1.7

Step 2 : Dispersion of the polymer in water The above reaction mixture was admixed with 200 g of methyl ethyl ketone and heated to 6O⁰C. 30.86 g of 2-amino-2-methylpropanol and 1200 g of water were added dropwise. The volatile solvents were evaporated by heating to 100⁰C. This gave a transparent yellow aqueous dispersion.

One hundred microlitres of an aqueous dispersion of this ethylenic copolymer were then applied to the Episkins in this culture medium and left in contact with the epidermides for 24 hours in a chamber thermostated at 37⁰C and 40% relative humidity. At the end of this period, the epidermides were withdrawn and extracted for the cDNA array studies .

Dedicated analysis by minichips

Gene expression analysis was performed by using standard DNA arrays that were dedicated to the search and adapted for screening. These minichips were produced on a nylon support by fixing marker- specific cDNAs involved in the regulation of the physiology of keratinocytes . The analysis is performed by an in-house optimized and miniaturized technique based on the use of mRNA and of labelling with phosphorus 33 (P33) .

Schematically, the mRNAs of the cells were extracted and purified with the aid of trireagent, the mRNA of each culture is "reverse" transcribed using oligo dT and a P33- labelled deoxynucleotide triphosphate. Multiple cDNA "target" labelled sequences were therefore produced for each Episkin^® reconstructed epidermis. These targets were then hybridized, under optimized conditions, with cDNA "probes" in excess, fixed on the membranes. After washing, the quantity of labelled target is visualized by autoradiography and by direct counting on a Phosphorlmager . The membranes are analysed by the Imagequant software.

The results are expressed in relative expression units.

The levels of expression were corrected 1) for the average background noise present on each membrane and

2) for the differences in labelling intensity of the different probes used. This correction is carried out on the basis of differences in labelling intensity of the reference genes. The average of the counting results of "housekeeping gene" markers, whose expression is generally considered to be stable, was taken as a reference for quantifying, relatively, the expression of the other markers.

The significance limit was set at 180% of the untreated control for a stimulating effect and at 50% of the control for a repressive effect.

Results

Modulation of the expression of genes involved in the differentiation of keratinocytes :

The ethylenic copolymer tested reduced the expression of a number of proteins which make up the stratum corneum, such as corneodesmosin and loricrin, by a factor of two, and suprabasin by a factor of 3, which suggests that the copolymer diminishes the process of terminal differentiation.

The acrylic copolymer increases, moreover, the expression of a number of proteins of the intermediate filaments of the cytoskeleton, the cytokeratins, which are found in particular in foetal epitheliums and regenerative epitheliums. After 24 h of treatment, the expression of cytokeratins 1 is increased by a factor of 10 and the expression of cytokeratin 19 is increased by a factor of 3. These two cytokeratins, although present in adult epidermides, have been described as being expressed in many types of epithelial tissues, in particular in non-stratified epitheliums and also foetal epitheliums (Haake et al . , Exp Cell Res., 1997 Feb 25; 231(1): 83-95). Also increased is the expression of cytokeratin 2E/A, by a factor of 10: this cytokeratin 2 has been described as being expressed both in an adult epidermis and in a foetal epidermis. Finally, the expression of cytokeratin 6 is increased by a factor of 4. This cytokeratin 6 has been described as being overexpressed in regenerative epidermides, particularly in the course of cicatrization (Mazzalupo et al . , 2003 Feb; 226(2): 356-65), which suggests that, in the course of the tensions provided by the application of the acrylic copolymer, the epidermides adopt features of regenerative epidermides. The ethylenic copolymer according to the invention reduces the expression of complexes necessary for the process of differentiation of keratinocytes, such as SPRL, also called LEPlO, by a factor of 5, and in the case of SPRL6 by a factor of 2.

In parallel with this, these results show that the copolymer increases the expression of CRBPl, which is involved in the cellular response to retinol, by a factor of 3, which suggests that the tensions are able to sensitize the cells to retinol.

Modulation of the expression of TGFb.

The expression of TGFb is increased by a factor of 4. This cytokine increases the expression of all of the fibrillar collagens and also of the plasminogen activator of type I, PAIl, and reduces the expression of a number of enzymes involved in the degradation of the extracellular matrix, the metalloproteinases .

In the course of the tensions caused by the acrylic latex it will be possible for the induced TGFb to diffuse to the level of the dermis and thus to induce tissue repair. The increase in the expression of TGFb by the tensions may be considered as a testament to the sensitivity of the cells to the tensions brought about by the acrylic latex tensor. Increase in the response of cells to environmental stresses

The ethylenic copolymer increased the expression of the chaperone protein HSP90A by a factor of 10. HSP90A proteins play a fundamental part during the process of maturing of the proteins. They regulate the conformation of kinase or of transcription factors and, consequently, control their activity and their degradation.

The totality of these data show that the mechanical tensions applied via an effective amount of the tensing agent according to the invention are sensed by the keratinocytes as a stimulus which leads to a slowdown in the process of differentiation of the epidermis,- the modulation of the expression of the genes cited above appears to show, moreover, that the epidermis acquires a regenerative epidermal phenotype . These results indicate that topical application of an effective amount of at least one tensing agent makes it possible to promote the homeostasis of the skin and thus to increase the thickness of the skin and/or improve the mechanical properties of the skin and/or promote the radiance of the complexion.

Moreover, the increase of the expression of HSP90 suggests that the tensions will reinforce the capacity of the epidermis to combat the alteration of the homeostasis of the skin that is induced by environmental stresses.

EXAMPLE 2 : Demonstration of an effect of the tensors on the radiance of the complexion

A serum is prepared comprising the ethylenic copolymer described in Example 1 :

A- Water 50.45 g

Ammonium polyacryldimethyltauramide (Hostacerine AMPS) 2.0O g Preservatives 0.85 g

B- Ethylenic copolymer of Example 1

(7% dispersion in water) 46.70 g

The lightening and homogenizing effects and also the cosmetic aspects of this serum were evaluated on a panel of 6 subjects having normal/mixed skin. Following application of this serum in the evening for one month, a less poorly defined complexion was observed.

These results show that the biomechanical effect provided by the topical application of tensors to the skin, which is manifested in a reduction in epidermal differentiation and/or an increase in the regenerative power of the epidermis, makes it possible to enhance the appearance of the skin and in particular the radiance of the complexion.

Claims

1. Cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to promote the homeostasis of the skin.

2. Use according to Claim 1, characterized in that the effective amount of at least one tensing agent is intended to promote the homeostasis of the epidermis.

3. Cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to prevent and/or reduce the alteration in the homeostasis of the skin that is induced by environmental stresses.

4. Cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to increase the thickness of the skin.

5. Cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to promote the radiance of the complexion.

6. Cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of an effective amount of at least one tensing agent as an agent intended to promote and/or improve the mechanical properties of the skin.

7. Use according to Claim 6, characterized in that the effective amount of at least one tensing agent is intended to promote and/or improve the elasticity and/or firmness of the skin.

8. Cosmetic use, in a composition for topical application to the skin, containing a physiologically acceptable medium, of 1% to 30% by weight, relative to the total weight of the composition, of at least one tensing agent selected from vegetable or animal proteins and their hydrolysates ; polysaccharides of natural origin selected from carrageenans, agars, gellans, alginates and pectins,- synthetic polymers; and mixtures thereof, for promoting and/or improving the elasticity and/or firmness of the skin.

9. Use according to any one of the preceding claims, characterized in that the effective amount of at least one tensing agent is intended to reduce the processes of epidermal differentiation and/or to promote the regeneration and/or renewal of the skin.

10. Use according to any one of the preceding claims, characterized in that the effect of the tensing agent on the homeostasis of the skin and/or on the thickness of the skin and/or on the radiance of the complexion and/or on the mechanical properties of the skin is a durable biological effect.

11. Use according to any one of the preceding claims, characterized in that the effective amount of at least one tensing agent, applied to the surface layers of the skin, is intended to regulate the expression of genes involved in the homeostasis of the skin via the transmission of mechanical tensions involving the activation of mechanoreceptors .

12. Use according to any one of the preceding claims, characterized in that the said tensing agent is selected from synthetic polymers, animal or vegetable proteins, polysaccharides of natural origin and mixtures thereof .

13. Use according to Claim 12, characterized in that the synthetic polymer is selected from silicone polymers having a polysiloxane backbone grafted with non-silicone organic monomers.

14. Use according to the preceding claim, characterized in that the silicone polymer comprises in its structure the unit of formula (I) below:

in which the radicals d, identical or different, represent hydrogen or a Ci-Ci₀ alkyl radical or else a phenyl radical; the radicals G₂, identical or different, represent a Ci-Ci₀ alkylene group,- G₃ represents a polymeric residue resulting from the (homo) polymerization of at least one ethylenically unsaturated anionic monomer; G₄ represents a polymeric residue resulting from the

(homo) polymerization of at least one ethylenically unsaturated hydrophobic monomer; m and n are, independently of one another, 0 or 1; a is an integer ranging from 0 to 50; b is an integer which can be between 10 and 350; and c is an integer ranging from 0 to 50, with the proviso that one of the parameters a and c is different from 0.

15. Use according to the preceding claim, characterized in that the unit of formula (I) has at least one, and more preferably all, of the following features : - the radicals Gi denote a Ci-Ci₀ alkyl radical; - n is non-zero, and the radicals G₂ represent a divalent Ci-C₃ radical;

- G₃ represents a polymeric radical resulting from the (homo) polymerization of at least one ethylenically unsaturated carboxylic acid monomer, preferably acrylic acid and/or methacrylic acid;

- G₄ represents a polymeric radical resulting from the (homo) polymerization of at least one Ci-Ci₀ alkyl (meth) acrylate monomer.

16. Use according to either of Claims 14 and 15, characterized in that the graft silicone polymers corresponding to the formula (I) are polydimethyl- siloxanes (PDMSs) grafted via a thiopropylene linker with polymeric units of poly (meth) acrylic acid type and/or of polyalkyl, especially Ci-C₃, or even Ci, alkyl (meth) acrylate type.

17. Use according to one of Claims 13 to 16, characterized in that the graft silicone polymer is a propylthio (polymethyl acrylate/methyl methacrylate/ methacrylic acid) -grafted polydimethylsiloxane .

18. Use according to any one of the preceding claims, characterized in that the said tensing agent is present in the composition in an amount ranging from 1% to 30% by weight of active ingredient relative to the total weight of the composition.

19. Use according to any one of the preceding claims, characterized in that the said tensing agent is present in the composition in an amount ranging from 2% to 30% of active ingredient by weight relative to the total weight of the composition.

20. Use according to any one of the preceding claims, characterized in that said tensing agent is present in the composition in an amount ranging from 3% to 20% by weight of active ingredient relative to the total weight of the composition.

21. Cosmetic method of treatment of dull and/or poorly defined complexion, characterized in that a composition comprising, in a physiologically acceptable medium, an effective amount of at least one tensing agent is applied to people having a dull and/or poorly defined complexion.

22. Cosmetic method of treatment of soft and/or flaccid skin, characterized in that a composition comprising, in a physiologically acceptable medium, an effective amount of at least one tensing agent is applied to people having soft and/or flaccid skin or to the areas of the body exhibiting a loss of elasticity and/or firmness.