according to a first aspect , the invention relates to a method comprising at least the administering by injection to a patient in need thereof : ( a ) at least an efficient amount of hyaluronic acid or a salt thereof ; and ( b ) at least an efficient amount of mepivacaine or a salt thereof as anesthetic agent , said mepivacaine being administered before or concurrently with the hyaluronic acid . the inventors have indeed found that a method according to the invention may constitute a viable alternative to current methods for in particular preventing and / or treating the surface appearance of the skin which consider the implementation of hyaluronic acid with lidocaine but also ( i ) for treating sites of deficiencies and defects in gingival architecture and contour and bony tissue , ( ii ) for ophthalmic intraocular surgeries , ( ii ) for the regeneration of the cartilage and ( iv ) in the treatment of arthritis . firstly , in contrast to lidocaine , mepivacaine do not displays significant vasodilatory properties than lidocaine . furthermore , mepivacaine has a pka of 7 , 6 whereas lidocaine has a pka of 7 . 9 . therefore , mepivacaine having a pka lower than lidocaine , it displays a better lipid solubility which improves its diffusion through lipid barriers . therefore , due to the fact that mepivacaine may be absorbed more rapidly than lidocaine , mepivacaine is therefore appropriate to better prevent a painful sensation during the injection . but above all , the inventors have unexpectedly observed than a filler compositions according to the invention , i . e including mepivacaine as anesthetic agent , may be sterilized without significantly affecting the stability of the gel of hyaluronic acid . it is indeed known than the gels of hyaluronic acid are particularly sensible to the heat treatment like required for their sterilization and that this low stability may be increased by the presence of further materials like the anesthetic agent . unexpectedly , this indesirable phenomenon is significantly lowered with mepicavaine comparatively to lidocaine , as shown in the following examples 1 and 2 . in addition , the inventors have shown that a composition according to the invention further complies with the requirements in terms of stability in time , as hereinafter shown in example 3 . according to the inventors , the manifestation of these above - mentioned advantageous effects within soft tissue filler compositions comprising hyaluronic acid was not known . preferably , the hyaluronic acid or a salt thereof is administered concurrently with the mepivacaine or a salt thereof . preferably , the administering by injection is an intraepidermal and / or intradermal and / or subcutaneous injection . however it may be also administered by a gingival , articular and . intraocular road . as above - mentioned hyaluronic acid ( also called hyaluronan or hyaluronate ) is a linear non - sulfated glycosaminoglycan composed of repeating units of d - glucuronic acid and n - acetyl - d - glucosamine ( tamrni r ., agren u m ., tuhkanen al , tammi m . hyaluronan metabolism in skin . progress in histochemistry & amp ; cytochemistry 29 ( 2 ): 1 .- 81 , 1994 ). in the skin , hyaluronic acid is primarily synthesized by dermal fibroblasts and epidermal keratinocytes ( tammi r ., cited above ). through its residues bearing a negative charge , hyaluronic acid acts as a water pump for maintaining the elasticity of the skin . as above - mentioned , the present invention considers the implementation of hyaluronic acid as such but also a salt thereof therefore , the hyaluronic acid in accordance with the invention may be more particularly chosen from physiologically acceptable salts such as the sodium salt , the potassium salt , the zinc salt , the silver salt and mixtures thereof , preferably the sodium salt . preferably , the hyaluronic acid according to the invention has a high average molecular weight , preferably ranging from 50 000 to 10 000 000 daltons , preferably from 500 000 to 4 000 000 daltons . one particularly preferred salt of hyaluronic acid is sodium hyaluronate ( naha ). as above - mentioned , hyaluronic acid is administered by injection in an effective amount . an “ effective amount ” of hyaluronic acid is an appropriate amount to obtain the desired technical effect , notably to have a visible result on the surface appearance of the skin . in particular , an effective amount of hyaluronic acid is an appropriate amount of hyaluronic acid for a good filling of volume defects of the skin , and in particular the filling of wrinkles . adjusting the amount of hyaluronic acid falls within the competence of a person skilled in the art . advantageously , the hyaluronic acid or a salt thereof in a method according to the invention is present in a solution . in this regard , an effective amount of hyaluronic acid may range from 0 . 1 to 5 % by weight , preferably from 1 to 3 % by weight , relative to the total weight of said solution comprising the hyaluronic acid or a salt thereof . according to a particular embodiment , the hyaluronic acid may be present under an uncrosslinked form . for the purpose of the present invention , the term “ uncrosslinked ” or “ non - crosslinked ” is understood in the context of the present invention to mean a gel of hyaluronic acid which is not crosslinked or slightly crosslinked , that is to say a gel having a phase - shift angle δ , measured under dynamic rheology conditions at 1 hz , that is greater than 40 ° when subjected to a stress above 1 pa . according to another particular embodiment , the hyaluronic acid may be present under a crosslinked form . according to another particular embodiment , the hyaluronic acid may be present under crosslinked and non - crosslinked forms . in this regard , the weight ratio “ crosslinked hyaluronic acid / non - crosslinked hyaluronic acid ” is preferably greater than 1 . according to a particular embodiment , the solution comprising the hyaluronic acid and being intended to be administered may comprise : from 50 % to 99 % by weight , more preferably 70 % to 95 % by weight of hyaluronic acid present in the form of a crosslinked gel , from 1 % to 50 % by weight , preferably 5 % to 30 % by weight , of hyaluronic acid present in the free form or a physiologically acceptable salt thereof , the ratio between the weight of the crosslinked hyaluronic acid gel and the weight of the free hyaluronic acid being between 1 : 1 and 1 : 0 . 02 . when the hyaluronic acid is crosslinked , said crosslinked hyaluronic acid has preferably a degree of modification ranging from 0 . 1 to 20 %, preferably from 0 . 4 to 10 %. by “ degree of modification ” is meant , in the sense of the present invention , the ratio between the number of moles of crosslinking agent attached to the hyaluronic acid and the number of moles of hyaluronic acid forming said crosslinked hyaluronic acid gel . this value may be measured by a nmr analysis 1d 1h of the crosslinked gel . by “ number of moles of hyaluronic acid ” is meant the number of moles of repeating disaccharide units of the hyaluronic acid , a disaccharide unit being composed of d - glucuronic acid and d - n - acetylglucosamine linked together by alternated beta - 1 , 4 and beta - 1 , 3 glycosidic bonds . this degree of modification may be notably appreciated as disclosed herein after . thus , the characterizing of the degree of modification of the hyaluronic acid is carried out by spectroscopy by nmr ( spectrometer bruker avance 1 operating at 400 mhz ( 1 h )). for bdde , the degree of modification is obtained by integrating the signal of 1 h nmr n - acetyl group ( δ ≈ 2 ppm ) present in the hyaluronic acid and a signal present in the crosslinking agent ( two — ch2 - groups , δ ≈ 1 . 6 ppm ). the ratio of integrals of these two signals ( crosslinking agent / naha ) relates to the degree of modification , after correcting the number of protons attached to each signal . the term “ crosslinking agent ” is understood to mean any compound capable of inducing a crosslinking between the various chains of the hyaluronic acid . the choice of this crosslinking agent clearly falls within the competence of a person skilled in the art . a crosslinking agent in accordance with the invention may be chosen from difunctional or multifunctional epoxy crosslinking agents but also polyamines like for example hexamethylenediamine ( nmda ) or endogeneous polyamines . by “ endogenous polyamine ” within the meaning of the present invention is meant a polyamine naturally present in living organisms and particularly the human body . as representative of endogenous polyamines , may be especially mentioned those cited in eukaryotes animals , such as the putrescine ( or 1 , 4 - diaminobutane ), the spermidine ( or 1 , 8 - diamino - 5 - azaoctane ) and the spermine ( 1 , 12 - diamino - 5 , 9 - diazadodecane ), preferably the spermine . more particularly , a crosslinking agent according to the present invention may be preferably selected from the group consisting of 1 , 4 - butanediol diglycidyl ether ( bdde ), 1 , 4 - bis ( 2 , 3 - epoxypropoxy ) butane , 1 , 4 - bisglycidyloxybutane , 1 , 2 - bis ( 2 , 3 - epoxypropoxy ) ethylene and 1 -( 2 , 3 - epoxypropyl )- 2 , 3 - epoxycyclohexane , an endogenous polyamine , and mixtures thereof . preferably , a crosslinking agent according to the invention is 1 , 4 - butartediol diglycidyl ether ( bdde ). in the particular embodiment wherein the crosslinking agent is a polyamine , and more particularly an endogenous polyamine , the coupling reaction with the hyaluronic acid may be carried out in the presence of at least one activator , and the case arising associated with at least one auxiliary coupling , in this regard , the activator may be selected from water - soluble carbodiimides such as 1 - ethyl - 3 -( 3 - dimethylaminopropyl ) carbodiimide ( edc ), 1 - ethyl - 3 -( 3 - 25 trimethylaminopropyl ) carbodiimide hydrochloride ( etc ), 1 - cyclohexyl - 3 -( 2 - morphilinoethyl ) carbodiimide ( cmc ) and a salt thereof , and mixtures thereof , preferably is represented by the edc . regarding the coupling auxiliary , when it is present , it may be selected from n - hydroxy succinimide ( nhs ), n - hydroxybenzotriazole ( hobt ), 3 , 4 - dihydro - 3 - hydroxy - 4 - oxo - 1 , 2 , 3 - benzotriazole ( hoobt ), 1 - hydroxy - 7 - 7azabenzotriazole ( hat ) and n - hydroxysylfosuccinimide ( sulfo nhs ), and mixtures thereof , preferably is represented by the hobt . an “ effective amount ” of crosslinking agent is an appropriate amount to obtain an appropriate degree of crosslinking of hyaluronic acid . adjusting the amount of crosslinking agent falls within the competence of a person skilled in the art . advantageously , an effective amount of crosslinking agent may range from 0 . 05 to 15 % by weight relative to the total weight of the hyaluronic acid or a salt thereof . advantageously , when the hyaluronic acid is crosslinked , and when the crosslinking agent is bdde , the amount in mole ratio of nbdde / n hyaluronic acid may range between 0 . 01 and 0 . 5 , preferably between 0 . 04 and 0 . 25 . an anesthetic agent according to the present invention has the particular advantage to reduce or eliminate the pain sensation experienced by the patient during and / or following the injection . moreover , an anesthetic agent according to the present invention is chosen among compounds which do not raise risk of incompatibility with other compounds used in a composition according to the invention , especially with hyaluronic acid . as above - mentioned , an anesthetic agent according to the present invention is mepivacaine , or a salt thereof . the mepivacaine is a local anesthetic of the amino - amids family of the formula ( i ): the mepivacaine is notably sold under the name carbocaine ® by the company cook - waite . the mepivacaine is a molecule having a good stability . its main degradation product is 2 , 6 - dimethylaniline . mepivacaine is a molecule containing a chiral center ( asymmetric carbon ). thus , there are the r and s enantiomers . in the following examples , it is considered the racemic mixture of the two forms of mepivacaine . preferably , the mepivacaine is under a salt form , and more particularly the salt of mepivacaine is chlorhydrate mepivacaine . as above - mentioned , the mepivacaine or a salt thereof is administered by injection in an effective amount . an “ effective amount ” of mepivacaine or a salt thereof is an appropriate amount to effectively reduce or eliminate the pain sensation experienced by the patient during and / or following the injection . adjusting the amount of mepivacaine or a salt thereof falls within the competence of a person skilled in the art . advantageously , the mepivacaine or a salt thereof in a method according to the invention is present in a solution . in this regard , an effective amount of the mepivacaine or a salt thereof may range from 0 . 05 to 3 % by weight relative to the weight of the solution comprising said mepivacaine or a salt thereof . the method may further comprises the administration , the case arising joint to the mepivacaine , of at least one additional anesthetic agent or a salt thereof different from the mepivacaine . this further anesthetic agent may be in particular selected from ambucaine , amolanone , amylocaine , benoxinate , benzocaine , betoxycaine , biphenamine , bupivacaine , butacaine , butamben , butanilicaine , butethamine , butoxycaïne , carticaïne , chloroprocaine , cocaethylene , cocaine , cyclométhycaïne , dibucaine , dimëthysoquine , dimethocaine , diperodone , dycyclonine , ecgonidine , ecgonine , ethyl chloride , etidocaine , beta - eucaine , euprocine fenalcomine , formocaïne , hexylcaine , hydroxytétracaïne , isobutyl p - aminobenzoate , leucinocaine mesylate , levoxadrol , lidocaine , meprylcaïne , metabutoxycaïne , methyl chloride , myrtecaïne , naepaïne , octacaïne , orthocaïne , oxethazaine , parethoxycaine , phénacaïne , phenol , piperocaine , piridocaïne , polidocanol , prarnoxine , prilocaine , procaine , propanocaïne , proparacaine , propipocaïne , propoxycaine , pseudococaine , pyrrocaïnc , ropivacaine , salicyl alcohol , tetracaine , tolycaïne , frimécaïne , zolamine , or a salt thereof , and a mixture thereof . preferably , this additional anesthetic agent is lidocaine or a salt thereof . according to a first embodiment , the additional anesthetic agent is administered alone , previous to the hyaluronic acid and the mepivacaine or a salt thereof . according to a second embodiment , the additional anesthetic agent is administered together with the mepivacaine or a salt thereof , previous to the hyaluronic acid or a salt thereof . according to a third embodiment , the additional anesthetic agent is administered together with the mepivacaine or a salt thereof and the hyaluronic acid or a salt thereof . in the specific embodiment where both anesthetic agents are contained in a same composition , they may be present therein in a ratio “ mepivacaine / lidocaine ” 1 : 1 , preferably a ratio 1 : 0 . 1 . according to a particular embodiment , the method according to the invention may further comprise at least a step of administering by injection to said patient of ( c ) at least a balanced salt solution , concurrently with said hyaluronic acid and / or mepivacaine , preferably with mepivacaine . the implementation of this balanced salt solution is particularly interesting in that it allows still reducing the injection pain ( see farley j . s . et al ., regional anesthesia a ., 1994 , vol , 19 : 48 ). preferably , said balanced salt solution is a phosphate buffered saline , and more particularly is a phosphate buffered saline and particularly a kh 2 po 4 / k 2 hpo 4 saline buffer . according to a particular embodiment , said balanced salt solution may further comprise at least one compound selected from the group consisting of an alpha - lipoic acid ; n - acetyl - l - cysteine ; reduced glutathion ; amino acid such as l - arginine , l - isoleucine , l - leucine , monohydrated l - lysine , glycine , l - valine , l - threonine , l - proline ; pyridoxine hydrochloride ; dehydrated zinc acetate ; pentahydrates copper sulphate , and mixture thereof . as above - mentioned , the present invention also relates to a sterile and injectable composition , in particular a soft filler composition , comprising an effective amount of at least hyaluronic acid or a salt thereof and including an effective amount of at least mepivacaine or a salt thereof as anesthetic agent . by “ sterile ”, in the sense of the present invention , is meant an environment capable of guaranteeing to the considered compounds in a composition according to the invention safety requirements for the administration routes such as above - mentioned , notably into or through the skin . indeed , for obvious reasons , it is essential that a composition according to the invention be devoid of any contaminant body capable of initiating an undesirable side reaction at the host organism , the hyaluronic acid , the crosslinking agent , and the anesthetic agent ( s ) are such as above - mentioned . regarding the hyaluronic acid , a composition according to the invention may comprise from 0 . 1 to 5 % by weight , preferably from 1 to 3 % by weight of hyaluronic acid , relative to the total weight of said composition . according to a particular embodiment , as above - mentioned , the hyaluronic acid may be present in crosslinked and non - crosslinked forms . in this regard , the ratio “ crosslinked hyaluronic acid / non - crosslinked hyaluronic acid ” is preferably greater than 1 . from 50 % to 99 % by weight , more preferably 70 % to 95 % by weight of hyaluronic acid present in the form of a crosslinked gel , from 1 % to 50 % by weight , preferably 5 % to 30 % by weight of hyaluronic acid present in a non - crosslinked form , the ratio between the weight of the crosslinked hyaluronic acid gel and the weight of the non - crosslinked hyaluronic acid being between 1 : 1 and 1 : 0 . 02 . regarding the anesthetic agent ( s ), a composition according to the invention may comprise from 0 . 01 % to 5 % by weight , preferably from 0 . 05 % to 3 % by weight of anesthetic agent ( s ), based on the total weight of said composition . by its injectable character , a composition according to the invention necessarily comprises a physiologically acceptable medium . a “ physiologically acceptable medium ” means a medium devoid of toxicity and compatible with the injection and / or the application of the composition such as considered in the present invention . the composition may comprise a solvent or a mixture of physiologically acceptable solvents . as an aqueous medium suitable for the invention , may be for example mentioned water . as isotonic agents suitable for the preparation of a composition according to the invention , it may be mentioned sugars and sodium chloride . according to a particular embodiment , a composition according to the invention may further comprise at least a balanced salt solution such as above - mentioned . according to a particular embodiment , a composition according to the invention may further comprise at least one compound selected from the group consisting of an alpha - lipoic acid ; n - acetyl - l - cysteine ; reduced glutathion ; amino acid such as l - arginine , l - isoleucine , l - leucine , monohydrated l - lysine , glycine , l - valine , l - threonine , l - proline ; pyridoxine hydrochloride ; dehydrated zinc acetate ; pentahydrates copper sulphate , and mixture thereof . a composition according to the invention may comprise , in addition to the above - mentioned compounds , at least one additional compound compatible with use in the field of soft tissue filler composition compositions . in this regard , additional compounds which may be implemented in a composition according to the invention may be chosen from copper salt , alpha - lipoie acid , acetylated derivative of cysteine or mixture thereof . the amounts of these additional compounds depend on the nature of the compound in question , the desired effect , and the destination of the composition according to the invention . a composition further comprising at least one copper salt may preferably comprises said copper salt in an amount ranging from 0 . 1 to 50 ppm based on the total weight of said composition . a composition further comprising at least one alpha - lipoic acid preferably comprises said alpha - lipoic acid in an amount ranging from 0 . 5 to 10 , 000 ppm , preferably from 5 to 100 ppm of alpha - lipoic acid , based on the total weight of said composition , a composition further comprising at least one acetylated derivative of cysteine preferably comprises said acetylated derivative of cysteine in an amount ranging from 0 . 5 to 10 , 000 ppm based on the total weight of said composition . among the other additional compounds which may be used in the present invention , may be mentioned antioxidants , amino acids , vitamins , minerals , nucleic acids , co - enzymes , adrenal derivatives , and mixtures thereof , said additional compounds being distinct from those indicated above . as an antioxidant , it may be mentioned glutathione , ellagic acid , spermine , resveratrol , retinol , l - carnitine , polyols , polyphenols , flavonols , theaflavins , catechins , caffeine , ubiquinol , ubiquinone , and mixture thereof . as amino acid , there may be mentioned arginine , isoleucine , leucine , lysine , glycine , valine , threonine , proline , methionine , histidine , phenylalanine , tryptophan , and mixture thereof . as vitamins and their derivatives , may be mentioned vitamins e , a , c , b , especially vitamins b6 , b8 , b4 , b5 , b9 , b7 , b12 , and pyridoxine better . as minerals , mention may in particular be made of zinc salts , magnesium salts , calcium salts , potassium salts , manganese salts , sodium salts , and mixtures thereof . as nucleic acids , may be mentioned in particular the derivatives of adenosine , cytidine , guanosine , thymidine , the cytodinc and mixture thereof . as co - enzymes , may be cited coenzyme q10 , coa , nad , nadp , and mixtures thereof . in addition , a composition according to the invention may further comprise any excipient commonly used in the technical field , such as for example mono - and / or di - hydrated dihydrogenophosphate sodium and sodium chloride , in physiological concentrations . the amounts of additional active agents and / or excipients of course depend on the nature of the compound in question , the desired effect , and the destination of the composition according to the invention . according to a particular embodiment , a composition according to the invention may have a complex viscosity η * of between about 5 pa · s and about 450 pa · s when measured at about 1 hz . according to a particular embodiment , a composition according to the invention made up of crosslinked hyaluronic acid may have a viscosity between 200 and 2000 pa · s , preferably between 1000 and 1800 pa · s . the viscoelastic properties of a composition according to the invention may be measured using a rheometer ( notably haake rs6000 ) with a cone / plate geometry ( 1 ° cone angle / 35 mm diameter plate ). a strain scan is carried out and the elastic modulus g ′ ( in pa ) and the phase - shift angle 5 ( in )° are measured for a stress of 5 pa . method for preparing a sterile and injectable composition according to the invention as above - mentioned , the present invention also relates to a method of preparing a sterile and injectable composition , more particularly a soft tissue filler composition , the method comprising at least the steps of : a ) providing at least one gel of a hyaluronic acid or a salt thereof , said hyaluronic acid being selected under a crosslinked hyaluronic acid form , a non - crosslinked hyaluronic acid foam or a mixture thereof ; b ) adding to said gel of hyaluronic acid at least mepivacaine or a salt thereof as anesthetic agent ; and according to a preferred embodiment , the mepivacaine or a salt thereof is added to an injectable form of hyaluronic acid . in other words , the gel of hyaluronic acid considered in step a ) already exhibits a concentration in hyaluronic acid , in crosslinking agent residues if presents , and physiological and / or ph conditions which are compatible with an injectable use , in particular in the fields of the applications considered above . by this way , the risks affecting the stability of the hyaluronic acid in the mixture hyaluronic acid and mepivacaine by imposing additional purification steps , such as above - defined , are significantly reduced . the mixture advantageously undergoes only one sterilization step . this step is preferably carried out on the mixture already packaged in its delivery device , usually a syringe , as herein after defined . advantageously , the sterilization is carried out at a temperature ranging from 120 to 140 ° c . in particular , the sterilization step can be performed in an autoclave ( moist heat ) t ° c .≧ 121 ° c ., to obtain a f 0 & gt ; 15 ( sterilizing value ). in this regard , and as above - mentioned , a composition according to the invention is particularly advantageous in that it displays a very interesting high resistance to this sterilization step . indeed , as shown in the examples 1 and 2 , the loss of g ′ generated by sterilization for a composition according to the invention is less than for a composition comprising lidocaine instead of mepivacaine . according to a particular embodiment , the method for preparing a gel of hyaluronic acid according to the invention may further comprise a step d ) consisting of adding an additional anesthetic agent or a salt thereof , different from the mepivacaine or a salt thereof , such as above - mentioned , preferably lidocaine or a salt thereof , said step d ) being carried out before , simultaneously and / or after the step b ). when the gel considered in step a ) comprises a crosslinked hyaluronic acid form , this last may be obtained beforehand from an uncrosslinked form of hyaluronic acid . the reticulation may be performed by a conventional way with at least one crosslinking agent , such above - mentioned . the aqueous mixture comprising the crosslinking agent and the hyaluronic acid to crosslink is advantageously homogenized before performing the crosslinking . the purpose of this operation is more particularly for the hyaluronic acid or a salt thereof in the aqueous medium to be hydrated and homogenized perfectly and thus to help to optimize the properties of the gel of hyaluronic acid expected . this step of homogenization is more important when the hyaluronic acid has a high molecular weight , because the hydration of such a compound tends to result in the formation of a high - viscosity solution within which the appearance of agglomerates is commonly observed . the purpose of this operation is also intended to homogenize perfectly the crosslinking agent within the mixture so as to subsequently assure a homogeneous crosslinking reaction . the homogenization is considered to be satisfactory when the solution obtained is uniformly coloured , with no agglomerates , and has a uniform viscosity . the homogenization may advantageously be carried out under mild operating conditions so as to prevent degradation of the hyaluronic acid chains . the duration of this homogenization step depends on the nature of the hyaluronic acid or a salt thereof , and more particularly the molecular weight and the concentration thereof , on the operation conditions within the aqueous medium and on the homogenizing device used , generally a device which allows a soft mechanical agitation . preferably , a homogenization step may take place over a time of less than 200 minutes , preferably less than 150 minutes , or even between 15 and 100 minutes . the purpose of the crosslinking reaction is to create bridges between the hyaluronic acid chains making it possible to obtain a dense solid three - dimensional network from a viscous solution . the particular conditions to be adopted in order to stimulate the crosslinking reaction may depend on the molecular weight of the hyaluronic acid , on the aqueous medium and on the nature of the crosslinking agent . in general , this reticulation may be achieved by bringing the mixture comprising the non crosslinked hyaluronic acid and at least one crosslinking agent as above - mentioned , into contact with a triggering element , or stimulant , such as , for example by heating or exposure to uv , or even by bringing said mixture into contact with a material of the catalyst type . the choice of such a triggering element falls within the general knowledge of a person skilled in the art . in the context of the present invention , this triggering element is advantageously represented by an increase in temperature imposed on the mixture “ non - crosslinked hyaluronic acid / aqueous medium / crosslinking agent ”. a particularly suitable temperature for the crosslinking reaction is between 35 ° c . and 60 ° c ., preferably between 45 and 55 ° c ., and better still between 48 and 52 ° c . the degree of crosslinking also depends on the crosslinking time and of the temperature imposed on the mixture “ non - crosslinked hyaluronic acid / aqueous medium / crosslinking agent ”. the longer the time is , the higher the degree of crosslinking will be , with however an optimum not to be exceeded without running the risk of degrading the hyaluronic acid . thus , at a temperature ranging from 35 ° c . and 60 ° c ., the crosslinking reaction may be carried out over a time ranging from 30 to 300 minutes , preferably 100 to 200 minutes , and better still 150 to 190 minutes . preferably , the crosslinking conditions are adjusted to obtain a degree of crosslinking such that the gel of crosslinked hyaluronic acid formed is a viscous , viscoelastic gel , or even a solid gel . stopping the crosslinking reaction requires exposing the crosslinked gel or , during crosslinking , even the receptacle containing it , to conditions propitious for stopping the crosslinking or else to conditions capable of stopping the formation of bonds between the various hyaluronic acid chains . for example , with regard to the thermal conditions that will be applied to stimulate the crosslinking process , the crosslinking may be stopped : by simply removing the receptacle from the thermostatted bath and cooling it until it returns to room temperature ; by placing the receptacle in a bath of cold water , preferably at a temperature below room temperature , until the temperature within said receptacle is close to room temperature ; or even by extracting the gel from said receptacle . according to a particular embodiment , the homogenization and crosslinking may be carried out within a hermetic cavity delimited at least partially by a deformable wall , preferably made within a deformable pouch , which may be deformed at least manually by palpation , such as described notably in wo 2010 / 131175 . the gel obtained at the end of the crosslinking step cannot in general be injected directly , in particular because of its high hyaluronic acid concentration and / or of the possible presence of crosslinking agent residues or else because of its physiological and / or ph conditions incompatible with use in the fields of applications considered above . furthermore , some gels may especially have too high a stiffness to be injected as such into a patient . therefore , several additional steps , known to those skilled in the art , can be carried out to obtain an injectable hydrogel . more particularly , a step of neutralizing and expanding this gel is required in order to give it its implant qualities . the chains of the hyaluronic acid network are then stretched and hydrated , while the ph is brought to that of the dermis . a step of protecting and redensifying the gel can also be carried out for further improving the qualities of the implant , according to the know - how of a person skilled in the art . the gel must be physiologically formulated by virtue of the presence of salts in equivalent amounts to those of the medium injected . for even higher purity , an additional purification step may also be carried out . advantageously , the mepivacaine or salt thereof and , the case arising , additional anesthetic agent ( s ), is / are added at the end of this protocol of preparation of an injectable form of hyaluronic acid , just before the step of sterilization , such as above - defined . according to a particular embodiment , the hydrogel added of mepicacaine and optionally of additional anesthetic agent ( s ), may be used to fill syringes under controlled atmosphere conditions , said syringes then possibly undergoing a sterilization step , preferably a thermal sterilization step such as above - defined . a composition according to the invention can be injected using any of the known methods in the art . particularly , a composition of the invention may be administered by means of an injection device suitable for intraepidermal and / or intradermally and / or subcutaneously . a composition of the invention may also be administered by means of an injection device suitable for gingival , articular and / or intraocular regions . the injection device , notably when a composition of the invention is administered by means of an injection device suitable for intraepidermal and / or intradermally and / or subcutaneously , may be selected from a syringe , a set of microsyringes , a laser device , a hydraulic device , an injection gun , a needleless injection device , a rolling with microneedles . preferably , the injection device may be selected from a syringe or a set of microsyringe . in an alternative embodiment , the injection device can be adapted to the technique of mesotherapy . mesotherapy is a treatment technique by intraepidermal and / or intradermally and / or subcutaneously actives ) product ( s ). the administration intraepidermal and / or intradermally and / or subcutaneously according to the invention is to inject a composition of the invention in an epidermal region , dermo - epidermal and / or dermal . the injection device may comprise any conventionally used injection such as hypodermic needle or cannula . a needle or a cannula according to the invention can have a diameter ranging between 18 and 34 g , preferably 25 to 32 g , and a length varying from 4 to 70 mm , preferably 4 to 25 mm . advantageously , the needle or cannula is associated with a syringe or other device capable of delivering through the needle or cannula said injectable composition . according to one embodiment , a catheter may be inserted between the needle / cannula and syringe . in known manner , the syringe can be operated manually by the practitioner or by a syringe holder as guns . throughout the description , including the claims , the expression “ comprising a ” should be understood as being synonymous with “ comprising at least one ” unless specifically stated otherwise . the expressions “ between . . . and . . . ” and “ ranging from . . . to . . . ” should be understood to mean that the limits are inclusive , unless specified otherwise . the following examples and figures are presented by way of non - limiting illustration of the invention . the protocol herein after defined regarding the measure of the viscoelastic properties of a composition apply for the following examples . the viscoelastic properties of a composition are measured using a rheometer ( haake rs6000 ) with a cone / plate geometry ( 1 ° cone angle / 35 mm diameter plate ). a strain scan is carried out and the elastic modulus g ′ ( in pa ) and the phase - shift angle δ ( in °) are measured for a stress of 5 pa . protocol of preparing a composition according to the invention implementing a non crosslinked hyaluronic acid and analysis regarding its stability to the sterilization 3 g of hyaluronic acid ( 1 . 5 mda ,) and 197 g of a phosphate buffer ( as defined in fr 2 979 539 ) are mixed . 1 . tridimensional homogenization of the mixture “ hyaluronic acid + phosphate buffer ” at room temperature in an airtight container ( nalgene jar ) for a minimum of 20 hours ; 2 . separating the obtained non - crosslinked gel into 2 equivalent fractions ( called hereinafter fractions a1 and a2 ); 3 . regarding fraction a1 , adding to gel 1 % by weight of a solution of mepivacaine ( 30 % by weight in phosphate buffer medium ) and 0 . 4 % by weight of a solution of naoh 1 % ; or 4 . regarding fraction a2 , adding to gel 1 % by weight of a solution of lidocaine ( 30 % by weight in phosphate buffer medium ) and 0 . 4 % by weight off solution of naoh 1 %; and 5 . homogenization , packaging in syringes lml for injection , and autoclaving ( f 0 & gt ; 15 ). tables below gives the values of the elastic moduli g ′ ( in pa ) of the hydrogels obtained and of the extrusion force f ( n ). the loss in sterilization for g ′ at f = 5 hz is calculated as follows : ( 103 . 3 - 45 . 0 )/ 103 . 3 = 56 . 4 ( en %) in view of the above , it therefore appears that the stability to the sterilization step of a composition comprising uncrosslinked hyaluronic acid is at least equivalent with mepivacaine than with lidocaine . protocol of preparing a composition according to the invention implementing crosslinked and non crosslinked hyaluronic acid and analysis regarding its stability to the sterilization 8 g of hyaluronic acid ( 4mda ), 58 . 7 g of sodium hydroxide ( naoh ) 1 % and 0 . 6 g of butanediol diglycidyl ether ( bdde ) are implemented . the crosslinking reaction is induced by an incubation for 3 hours at 52 ° c . 1 . homogenization of the mixture “ hyaluronic acid + naoh 1 %” at room temperature in an airtight and deformable container ( pouch such as considered in the patent application wo 2010 / 131175 ) during about 1h30 so as to obtain a perfectly homogeneous viscous solution ; 2 . adding the crosslinking agent ( bdde ) into the receptacle and new homogenization at room temperature for about 20 min ; 3 . incubation for 3 hours at 52 ° c . of the receptacle containing the viscous solution of “ hyaluronic acid / sodium hydroxide 1 %/ bdde ” so as to initiate the crosslinking step ; 4 , neutralization , swelling and homogenizing the obtained solid ( solution of crosslinked hyaluronic acid ) in a phosphate buffer ( as defined in fr 2 979 539 ), and adding a non - crosslinked gel containing 4 g of ha 4 mda and 668 g of supplemented phosphate buffer , so as to obtain a hydrogel having 11 mg / g in hyaluronic acid , at ph around neutrality ; 5 . purification by dialysis during 48 hours , and then collecting the purified gel in a tank homogenization ; 6 . sieving of the whole gel ( 230 μm ); 7 . separation of the collected gel into two fractions ( fraction b1 and b2 ); 8 . incorporation to the gel of i % by weight of a solution of mepivacaine ( 30 % by weight in medium phosphate buffer ) and of 0 . 4 % by weight of a solution of naoh 1 % (= fraction b1 ); 9 . incorporation to the gel of 1 % by weight of a solution of lidocaine ( 30 % by weight in medium phosphate buffer ) and of 0 . 4 % by weight of a solution of naoh 1 % (= fraction b2 ); 10 . homogenization , packaging in syringes 1 ml , for injection and sterilization . tables below gives the values of the elastic modulus g ′ ( in pa ) of the hydrogels obtained and of the extrusion force f ( n ). in view of the above , it therefore appears that the stability to the sterilization step of a composition comprising crosslinked and uncrosslinked hyaluronic acid is at least equivalent with mepivacaine than with lidocaine . protocol of preparing a composition according to the invention implementing crosslinked and non crosslinked hvaluronic acid and analysis regarding its stability in time 10 g of hyaluronic acid ( 1 . 5 mda ,) 73 g of sodium hydroxide 1 % and 0 . 9 g of butanediol diglycidyl ether ( bdde ) are mixed . then , the crosslinking reaction is induced by incubation for 3 hours at 52 ° c . 1 . homogenizing the mixture at room temperature “ hyaluronic acid + sodium hydroxide 1 %, in an airtight and deformable container ( pocket ) for about 1h30 to obtain a perfectly homogeneous viscous solution ; 2 . adding the crosslinking agent ( bdde ) into the container and further homogenization at room temperature for about 20 min ; 3 . incubation for 3 hours at 52 ° c . of the receptacle containing the viscous solution of hyaluronic acid / sodium hydroxide 1 %/ bdde so as to initiate the crosslinking step ; 4 . neutralization , swelling and homogenizing the obtained solid ( solution of crosslinked hyaluronic acid ) in a phosphate buffer containing 2 g of non - crosslinked hyaluronic acid ( 1 . 5 mda ), so as to obtain a hydrogel at 25 mg / g of hyaluronic acid at ph close to neutrality ; 5 . purification by dialysis ( during 48 hours ), and then collecting the purified gel in a degassing vessel / homogenization ; 6 . incorporation in the gel of 1 % by weight of a solution of mepivacaine ( 30 % by weight in a phosphate buffer medium ) and of 0 . 4 % by weight of a naoh solution 1 %; 7 . homogenization , degassing , packaging in syringes lml for injection and sterilization ( f 0 & gt ; 15 ). table below gives the values of the phase - shift angle δ (°) and the extrusion force , the results obtained 19 months after the date of manufacture of the gel are equivalent to those obtained initially , and thus demonstrate the stability of the gel . the disclosure of all publications cited above are expressly incorporated herein by reference , each in its entirety , to the same extent as if each were incorporated by reference individually . the disclosure of all publications cited above are expressly incorporated herein by reference , each in its entirety , to the same extent as if each were incorporated by reference individually . it is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described , and all statements of the scope of the invention which , as a matter of language , might be said to fall therebetween .
compositions and methods for the surface appearance of the skin a subject are provided . an injectable composition comprising at least hyaluronic acid or a salt thereof ; and an effective amount of at least mepivacaine or a salt thereof are provided . the hyaluronic acid optionally has an average molecular weight ranging from 50 , 000 to 10 , 000 , 000 daltons , and may be crosslinked hyaluronic acids , non - crosslinked hyaluronic acids , or a combination , in some embodiments . the compositions and methods of the present invention are useful for treating and preventing the cutaneous signs of chronological aging and / or induced by external factors such as stress , air pollution , tobacco or prolonged exposure to ultraviolet exposure , impaired surface appearance of the skin , impaired viscoelastic or biomechanical properties of the skin , and / or the long - lasting filling of volume defects of the skin .