method for evaluating the rheological characteristics of a gel

Abstract

Method for evaluating the rheological characteristics of a gel. The invention relates to a method for evaluating the rheological characteristics of at least one gel, consisting of determining the extent of the plastic domain in stress ζc-ζp and in strain γC-γP, said determination being carried out according to the steps of: subjecting at least one sample of at least one gel to oscillatory mechanical stresses at a fixed frequency, determining and plotting the curves of the elastic modulus G' and the viscous modulus G'' as a function of strain and stress, determining ζc and γC at the point of intersection Xc of the curves G' and G'' in stress and strain, determining ζp and γp by fixing an arbitrary value of G' (G'x) which will be defined as the entry value in the plastic domain and, calculating ζc-ζp and γC-γP.

Description

Title of the invention: Method for evaluating the rheological characteristics of a gel

[0001] The invention relates to a method for evaluating the rheological characteristics of a gel, in particular a hyaluronic acid-based hydrogel, allowing in particular the differentiation of comparable products in terms of use or recommendations for use.

[0002] Such gels may be hydrogels used as injectable gels in cosmetic surgery, gels usable in the field of joint treatments or gels used in medical applications such as wound healing or as devices for releasing and diffusing pharmaceutical active ingredients. In the context of this application, a number of definitions are recalled below.

[0003] The gel, according to the IUPAC (International Union of Pure and Applied Chemistry) is described as a non-fluid colloidal network or a polymer network which is extended throughout its volume by a fluid.

[0004] Among gels, hydrogels are distinguished, defined as polymeric gels consisting of a three-dimensional network made up of at least one polymer capable of absorbing a large quantity of water or aqueous solution and which exhibit particular rheological properties, especially in terms of viscosity and viscoelasticity.

[0005] In a gel or hydrogel, said network may be formed by chemical crosslinking through the creation of bonds between polymer chains, these bonds being covalent bonds. Said network may also be obtained by transient physical interactions, for example ionic, hydrophobic, or hydrogen bonds.

[0006] Rheological characteristics or rheological properties are the physical characteristics that allow the study of the deformation and flow of matter under the application of a stress.

[0007] Regarding the rheological characteristics determined for hydrogels, we can mention the elastic modulus G' and the viscous modulus G”. These data are obtained by subjecting a sample to a low-amplitude fixed strain frequency scan (in the linear domain) which is a method well known to those skilled in the art.

[0008] However, these frequency scans are comparable to static photographs of the networks and are not sufficient to predict and / or determine the dynamic behavior of the gels under different in-vivo stresses or deformations. and to differentiate and compare products.

[0009] However, the evaluation of the rheological characteristics of a gel is essential during product development because it allows limiting the number of laboratory tests to evaluate the performance of gels and making choices without having to systematically resort to in vivo tests.

[0010] Furthermore, the evaluation of the rheological characteristics of a gel makes it possible to facilitate the development of new types of gels and to work on the properties of the gel to obtain the desired result according to the different applications.

[0011] In the prior art, methods for evaluating the rheological characteristics of injectable gels complementary to the determination of the elastic modulus G' and viscous modulus G'' have been described.

[0012] For example, in Teoxane patent EP3274685B1, a method for evaluating the rheological characteristics of an injectable gel is disclosed. This method relates to a method for measuring the area under the G' curve between two arbitrarily determined measurement limits, in order to provide an indication of the gel's mechanical strength, that is, its ability to maintain its structure over a wide range of values. However, to differentiate between two gels that have a similar "integral score," this score being dependent on the choice of integration limits and the integration method, another parameter must be measured in addition. This is the "creep measurement," which is a quantity associated with immediate or time-dependent elastic and viscous deformation.

[0013] In patent application WO2018 / 104426 filed in the name of Nestlé Skin Health, a method for evaluating the rheological characteristics of an injectable gel is disclosed. This method is based on the measurement of a parameter called flexibility. This physical parameter is evaluated by measuring the stress at the point where the amplitude sweep crosses between the elastic modulus G' and the viscous modulus G”.

[0014] Thus, these methods allow us to complement the classic measurements of elasticity / stiffness and viscosity, but they do not allow us to measure and study the behavior of the hydrogel subjected to stresses and / or deformations in the plastic domain.

[0015] The present invention makes it possible to measure and study the behavior of the hydrogel subjected to stresses and / or deformations in the plastic domain and consists of a method for evaluating the rheological characteristics of at least one gel, consisting of determining the resistance range, said resistance range being defined by the difference çc -çp, i.e. the extent of the plastic domain in stress and the malleability range, said malleability range being defined by the difference yc-Yp, i.e. the extent of the plastic domain in deformation.

[0016] Fig. 1 is a schematic representation of revolutions of the viscous modules and elastic of a gel sample subjected to a deformation and / or stress scan and linearity domains noted LI, plastic PL and spreading ET.

[0017] The elastic modulus G' is an intrinsic property of a material, in this case a gel, defined by the ratio of stress to elastic strain. The elastic modulus is expressed in Pascals.

[0018] The viscous modulus G'' or dissipation modulus is a physical quantity that characterizes viscous behavior related to the capacity to dissipate elastic stress. The viscous modulus is expressed in Pascals.

[0019] The ratio of the viscous modulus to the elastic modulus is defined as the mechanical loss factor, denoted tan ô.

[0020] The deformation scanning allows the dynamic study of G' and G'' as a function of the deformation for a fixed oscillation frequency.

[0021] The stress sweep allows the dynamic study as a function of the stress for a fixed frequency.

[0022] As illustrated in [Fig. 1], the linearity domain is the domain in which the gel is not affected by the stress; it is considered at rest, i.e., G' is considered constant. This domain, denoted LI in the diagram, corresponds to the domain delimited by the origin value of the x-axis and the value P on the x-axis.

[0023] The spreading domain is the domain in which the frost exhibits a complete disruption of the network. As illustrated in [fig.1], this domain, denoted ET on the diagram, corresponds to the domain beyond the value C on the x-axis.

[0024] The plastic domain is the domain in which the gel is malleable and exhibits rearrangements at the level of locally broken physical bonds.

[0025] As illustrated in [fig.1], the beginning and end limits of the plastic domain, noted PL on the diagram, are represented respectively by the points P and C on the x-axis and this domain.

[0026] The point P is determined arbitrarily when the value of the elastic modulus G' has decreased by x%.

[0027] As illustrated in [fig.1], its value is determined on the x-axis when G' is equal to G'p.

[0028] As illustrated in [fig.1], point C represents the value of the abscissas at the point of intersection of the curves of G' and G” at a fixed oscillation frequency. This point of intersection is denoted Xc in [fig.1].

[0029] During the constraint sweep, the points P and C shown in [fig.l] respectively designate the variables çc and çp, expressed in Pascal.

[0030] During the strain scan, points P and C shown in [Fig. 1] denote the variables yp and yc respectively. These variables are expressed as % strain and are dimensionless.

[0031] The resistance range can be defined as the interval of forces that can be applied to the gel to deform it without permanently damaging its structure. Beyond this range, the gel has lost its integrity. It will be determined by the extent of the plastic stress domain, namely by the value of the difference between yc and çp.

[0032] This resistance range makes it possible to quantify the gel's resistance to the stresses and forces to which it is subjected in vivo, for example in moving lips or in a joint. It will allow us to assess the gel's ability to break and fragment under external pressure.

[0033] The malleability range can be defined as the gel's ability to deform and be molded while retaining its initial rheological characteristics. It will be determined by the extent of the plastic deformation range, namely by the value of the difference between Yc and Yp.

[0034] The malleability range will allow us to assess the product's adaptability and responsiveness to the dynamics and movements of surrounding tissues. It will also allow us to predict the product's ability to be "molded" according to the need and the indication.

[0035] The present invention is a method for evaluating the rheological characteristics of at least one gel, consisting of determining the extent of the plastic domain in stress yc-çp and strain Yc-Yp, said determination being carried out according to the steps of: - subjecting at least one sample of at least one gel to oscillatory mechanical stresses at a fixed frequency, - determination and plotting of the curves of the elastic modulus G' and the viscous modulus G” as a function of deformation and stress, - determination of yc and Yc at the point of intersection (Xc) of the curves G' and G'' in stress and strain, - determination of çp and yp by fixing an arbitrary value of G' (G'p) which will be defined as the input value in the plastic domain and, - calculation of yc -çp and Yc-Yp-

[0036] In one embodiment, the oscillatory mechanical constraints are implemented by an amplitude sweep.

[0037] In one embodiment, amplitude sweep refers to both strain sweep and stress sweep.

[0038] In one embodiment, the arbitrary value of G' is defined as the value for which the elastic modulus G' has decreased by at most 15% compared to the value of G' at the plateau of the linear domain, denoted G'p.

[0039] The minimum percentage decrease in the elastic modulus G' is dependent on the sensitivity of the measurements taken which is less than or equal to 5%.

[0040] In one embodiment, the arbitrary value of G' is defined as the value for which the elastic modulus G' has decreased by 5 to 15% compared to the value of G' at the plateau of the linear domain, denoted G'p.

[0041] In one embodiment, the arbitrary value of G' is defined as the value for which the elastic modulus G' has decreased by 5 to 10% compared to the value of G' at the plateau of the linear domain, denoted G'p.

[0042] In one embodiment, the arbitrary value of G' is defined as the value for which the elastic modulus G' has decreased by 5% compared to the value of G' at the plateau of the linear domain, denoted G'p in stress and strain.

[0043] In one embodiment, the arbitrary value of G' is defined as the value for which the elastic modulus G' has decreased by 7.5% compared to the value of G' at the plateau of the linear domain, denoted G'p in stress and strain.

[0044] In a preferred embodiment, the arbitrary value of G' is defined as the value for which the elastic modulus G' has decreased by 10% compared to the value of G' at the plateau of the linear domain, denoted G'p in stress and strain.

[0045] In one embodiment, the frequency set during the deformation and / or stress sweep is between 0.1 and 10 Hz.

[0046] In one embodiment, the frequency set during the deformation and / or stress sweep is between 0.5 and 5 Hz. In another embodiment, the frequency set during the deformation and / or stress sweep is between 0.1 and 5 Hz.

[0047] In one embodiment, the frequency set during the deformation and / or stress sweep is between 0.1 and 3 Hz.

[0048] In one embodiment, the frequency set during the deformation and / or stress sweep is between 0.5 and 3 Hz.

[0049] In one embodiment, the frequency set during the strain and stress sweep is between 0.7 and 2.5 Hz.

[0050] In one embodiment, the frequency set during the deformation and / or stress sweep is equal to 0.1 Hz.

[0051] In one embodiment, the frequency set during the deformation and / or stress sweep is equal to 0.5 Hz.

[0052] In one embodiment, the frequency set during the deformation and / or stress sweep is equal to 0.7 Hz.

[0053] In one embodiment, the frequency set during the deformation and / or stress sweep is equal to 1 Hz.

[0054] In one embodiment, the frequency set during the deformation and / or stress sweep is equal to 2.5 Hz.

[0055] In one embodiment, the frequency set during the strain and stress sweep is equal to 3 Hz.

[0056] In one embodiment, the frequency set during the deformation and / or stress sweep is equal to 5 Hz.

[0057] In one embodiment, the sample whose rheological properties are studied by applying the process is a gel.

[0058] In one embodiment said gel is chosen from the group comprising hydrogels, silicone gels (for example a polydimethylsiloxane gel), acrylic gels (for example from polymethyl methacrylate particles), polyacrylamide gels.

[0059] In one embodiment, the gel whose rheological properties are studied by applying the process according to the invention is a hydrogel.

[0060] In one embodiment, said hydrogel is selected from the group comprising: polysaccharides, polyacrylamides, polyvinyl alcohol, polylactic acid, polyglycolic acid, poly(lactic-co-glycolic acids), poloxamers, polyethylene glycol, poly(N-isopropylacrylamide), gelatin and collagen, alone or in mixtures

[0061] In one embodiment, said hydrogel is selected from the group of polysaccharides comprising dextran, cellulose, starch and modified starches, cyclodextrins and their derivatives, cellulose derivatives (in particular hydroxypropylcellulose, hydroxypropylmethylcellulose, ethylmethylcellulose, carboxymethylcellulose), alginic acid, xanthan gum, carrageenan, chitosan, agarose, pectin, glycosaminoglycans (GAGs) and their biologically acceptable salts, alone or in mixture.

[0062] In one embodiment, said polysaccharide is chosen from the group of glycosaminoglycans (GAGs), such as chondroitin, keratan, heparin, heparosan or hyaluronic acid, and their biologically acceptable salts, alone or in mixture.

[0063] In one embodiment, said polysaccharide is hyaluronic acid, or one of its biologically acceptable salts, alone or in mixture.

[0064] In one embodiment, said polysaccharide is hyaluronic acid.

[0065] In one embodiment, said polysaccharide is hyaluronic acid or one of of its salts, alone or in mixtures.

[0066] In one embodiment, said polysaccharide is hyaluronic acid in the form of sodium or potassium salt.

[0067] In one embodiment, said polysaccharide is hyaluronic acid in the form of sodium salt.

[0068] In one embodiment, said polysaccharide is cross-linked hyaluronic acid or one of its salts, alone or in a mixture.

[0069] In one embodiment, said polysaccharide is crosslinked hyaluronic acid or one of its salts, alone or in mixture, and in that said crosslinking is carried out by means of at least one crosslinking agent.

[0070] In one embodiment, said polysaccharide is crosslinked hyaluronic acid or one of its salts, alone or in mixture, and in that said crosslinking is carried out by means of at least one bi- or polyfunctional crosslinking agent.

[0071] In one embodiment, said at least one crosslinking agent is selected from the group consisting of ethyleneglycoldiglycidyl ether, butanedioldiglycidyl ether (BDDE), polyglycerolpolyglycidyl ether, polyethyleneglycoldiglycidyl ether, polypropyleneglycoldiglycidyl ether, a bis- or polyepoxy such as 1,2,3,4-diepoxybutane or 1,2,7,8-diepoxyoctane, a dialkylsulfone, divinylsulfone, formaldehyde, epichlorohydrin or glutaraldehyde, carbodiimides such as, for example, l-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC), trimetaphosphates, such as, for example, sodium trimetaphosphate, calcium trimetaphosphate, or even barium trimetaphosphate.

[0072] In one embodiment, said at least one crosslinking agent is chosen from the group consisting of ethyleneglycoldiglycidyl ether, butanedioldiglycidyl ether (BDDE), polyglycerolpolyglycidyl ether, polyethylene-glycoldiglycidyl ether, polypropyleneglycoldiglycidyl ether, a bis- or polyepoxy such as 1,2,3,4-diepoxybutane or 1,2,7,8-diepoxyoctane, trimeta-phosphates, such as sodium trimetaphosphate, calcium trimetaphosphate, or barium trimetaphosphate.

[0073] In one embodiment, said polysaccharide is co-crosslinked hyaluronic acid or one of its salts, alone or in a mixture.

[0074] In one embodiment, said polysaccharide is chemically modified hyaluronic acid by substitution, crosslinked or non-crosslinked, or one of its salts, alone or in mixture.

[0075] In one embodiment, said polysaccharide is doubly cross-linked hyaluronic acid as described in patent application WO2000 / 046253 in the name of Fermentech medical limited.

[0076] In one embodiment, said polysaccharide is a mixture of hyaluronic acids, or one of their salts, crosslinked and non-crosslinked.

[0077] In one embodiment, said polysaccharide is a cross-linked mixture of hyaluronic acids, or one of their salts.

[0078] In one embodiment, said polysaccharide is a cross-linked mixture of hyaluronic acids, or one of their salts, such as that described in the patent application WO2009 / 071697 on behalf of the plaintiff.

[0079] In one embodiment, said polysaccharide is a mixture of hyaluronic acids, obtained by mixing several hyaluronic acids, or one of their salts, of different molecular masses prior to their cross-linking, as described in patent application WO2004092222 in the name of Cornéal industrie.

[0080] In one embodiment, said polysaccharide is hyaluronic acid or one of its salts, substituted by a group providing lipophilic or hydrating properties, such as, for example, substituted hyaluronic acids as described in patent application FR2983483 filed by the applicant. This application describes a process for the simultaneous substitution and crosslinking of a polysaccharide via its hydroxyl groups in an aqueous phase, characterized in that it comprises the following steps: (i) a polysaccharide is placed in an aqueous medium, (ii) it is brought into contact with at least one precursor of a substituent, (iii) it is brought into contact with a crosslinking agent, and (iv) the substituted and crosslinked polysaccharide is obtained and isolated.

[0081] In one embodiment, said polysaccharide is hyaluronic acid or one of its salts, grafted with glycerol, for example as described in application WO2017162676 in the name of MERZ.

[0082] In one embodiment, said gel further comprises at least one active ingredient selected from the group consisting of local anesthetics, vitamin C derivatives, anti-inflammatories, polyols, and mixtures thereof.

[0083] In one embodiment, said gel further comprises at least one local anesthetic selected from the group consisting of lidocaine, mepivacaine, and mixtures thereof.

[0084] In one embodiment, at least one local anesthetic is present at a local anesthetic concentration of between 0.1 and 5%, relative to the total mass of said gel.

[0085] In one embodiment, said gel further comprises at least one anti-inflammatory chosen from the group consisting of steroidal and non-steroidal anti-inflammatories.

[0086] In one embodiment, said at least one anti-inflammatory drug is chosen from the group consisting of steroidal anti-inflammatory drugs (such as, for example, dexamethasone, prednisolone, corticosterone, budesonide, sulfasalazine, mesalamine, cetirizine, diphenhydramine, antipyrine, methyl salicylate, loratadine, thymol, carvacrol, bisabolol, allantoin, eucalyptol, phenazone (antipyrine), propyphenazone) and non-steroidal anti-inflammatory drugs (such as, for example, ibuprofen, naproxen, fenoprofen, ketoprofen, flurbiprofen, oxaprozin, indomethacin, sulindac, etodolac, ketorolac, the diclofenac, nabumetone, the piroxicam, meloxicam, tenoxicam, droxicam, lornoxicam, isoxicam, mefenamic acid, meclofenamic acid, flufenamic acid, tolfenamic acid, celecoxib, rofecoxib, valdecoxib, parecoxib, lumiracoxib, etoricoxib, firocoxib, or sucrose octasulfate and / or its salts). In one embodiment, the process for preparing a formulation comprising at least one crosslinked polymer obtained according to the process of the invention further comprises at least one step of adding at least one polyol selected from the group consisting of mannitol, sorbitol, glycerol, maltitol, lactitol, and erythritol.

[0087] In one embodiment, said gel further comprises at least one polyol selected from the group consisting of mannitol, sorbitol and glycerol.

[0088] In one embodiment, at least one polyol is present at a polyol concentration between 0.1 mg / ml and 50 mg / ml, relative to the total mass of said gel.

[0089] In one embodiment, the molecular mass mw of at least one hyaluronic acid before crosslinking is within a range of 0.01 MDa and 5 MDa.

[0090] In one embodiment, the molecular mass mw of at least one hyaluronic acid before crosslinking is within a range of 0.1 MDa and 3.5 MDa.

[0091] In one embodiment, the molecular mass mw of at least one hyaluronic acid before crosslinking is within a range of 1 MDa and 3 MDa.

[0092] In one embodiment, the molecular mass mw of at least one hyaluronic acid before crosslinking is 1 MDa.

[0093] In one embodiment, the molecular mass mw of at least one hyaluronic acid before crosslinking is 3 MDa.

[0094] In one embodiment, the concentration of hyaluronic acid [HA] is between 2 mg / g and 50 mg / g of total weight of said hydrogel.

[0095] In one embodiment, the concentration of hyaluronic acid [HA] is between 4 mg / g and 40 mg / g of total weight of said hydrogel.

[0096] In one embodiment, the concentration of hyaluronic acid [HA] is between 5 mg / g and 30 mg / g of total weight of said hydrogel.

[0097] In one embodiment, the concentration of hyaluronic acid [HA] is between 10 mg / g and 30 mg / g of total weight of said hydrogel.

[0098] In one embodiment, the concentration of hyaluronic acid [HA] is 20 mg / g of total weight of said hydrogel.

[0099] The applications of gels whose rheological properties are studied by applying the process according to the invention are applications aimed at creating volumes, applying mechanical stresses and creating physiological barriers.

[0100] Among the applications targeted, medical applications are of interest; for example, injections to replace deficient biological fluids, for example in joints to replace synovial fluid, injection following a Surgery to prevent peritoneal adhesions, periurethral injections to treat incontinence, and injections following presbyopia surgery are all examples of cosmetic applications.

[0101] The applications targeted are more particularly those commonly used in the context of injectable viscoelastics and polysaccharides used or potentially usable in the following pathologies or treatments: - cosmetic injections on the face: for filling wrinkles, skin defects or for volumizing (cheekbones, chin, lips); - volumizing injections on the body: calf size augmentation, breast and buttock augmentation, G-spot augmentation, vaginoplasty, vaginal lip reconstruction, penis size augmentation; - in joint surgery and in dental surgery for filling periodontal pockets for example. - treatment of osteoarthritis, injection into the joint as a replacement or supplement for deficient synovial fluid; - periurethral injection for the treatment of urinary incontinence due to sphincter insufficiency; - post-surgical injection to prevent peritoneal adhesions in particular - injection following presbyopia surgery via scleral incisions with laser; - injection into the vitreous cavity; - injection during cataract surgery; - injection for the treatment of cases of vaginal dryness; - injection into the genitals. - for filling fine, medium or deep wrinkles, and to be injected with fine diameter needles (27 Gauge for example); - as a volumizer with injection using larger diameter needles, 22 to 26 Gauge for example, and longer (30 to 40 mm for example); in this case, its cohesive nature will ensure that it remains in place at the injection site.

[0102] These examples of use are by no means limiting because the gels studied according to the process of the invention have many applications such as for example: - filling volumes; - to generate spaces within certain tissues, thereby promoting their optimal functioning; - to replace deficient physiological fluids.

[0103] The present invention also includes a method for comparing and differentiating gels comprising the steps of: - Determination, according to the method of the invention described above, of the resistance range of gels, said resistance range being defined by the difference çc -çp; i.e., the extent of the plastic stress domain, - determination, according to the method of the invention described above, of the malleability range of gels, said malleability range being defined by the difference Yc-Yp; i.e., the extent of the plastic deformation domain, - use of resistance range values ​​and malleability range values, in order to compare and differentiate gels.

[0104] In one embodiment, the comparison method includes the use, in combination with the use of the strength range values ​​and the malleability range values, of the elastic modulus G', viscous modulus G”, delta (ô) and tangent ô values.

[0105] In one embodiment, the hydrogel comparison process allows a complete range of hydrogels from the same manufacturer to be compared based on one or more parameters defined above.

[0106] In one embodiment, the hydrogel comparison method allows a range of filler gels from the same manufacturer to be compared based on one or more parameters defined above.

[0107] In one embodiment, the hydrogel comparison method allows a range of facial volumizing gels from the same manufacturer to be compared based on one or more parameters defined above.

[0108] In one embodiment, the hydrogel comparison process allows a complete range of hydrogels from different manufacturers to be compared based on one or more parameters defined above.

[0109] In one embodiment, the hydrogel comparison method allows a range of filler gels from different manufacturers to be compared based on one or more parameters defined above.

[0110] In one embodiment, the hydrogel comparison method allows a range of facial volumizing gels from different manufacturers to be compared based on one or more parameters defined above. Brief description of the drawings

[0111] Fig. 1 is a schematic representation of revolutions of the viscous and elastic moduli of a gel sample subjected to a deformation and / or stress sweep and of the linearity domains denoted LI, plastic PL and spreading ET.

[0112] Figs. 2, 3, 7, 10 and 13 are representations of the extent of the plastic domain under stress of different formulas with T in Pa on the abscissa and FO on the ordinates.

[0113] Figs. 4, 5, 8, 11 and 14 are representations of the extent of the plastic deformation domain of different formulas with y in (%) on the abscissa and FO on the ordinate.

[0114] Figs. 6, 9 and 12 are representations of the elastic moduli G' in Pa at 1Hz of different products.

[0115] Examples

[0116] The measurements are carried out on the DHR-2 imposed stress rheometer (TA Instruments) using a 2° 40mm cone-plane geometry at 25°C.

[0117] The viscoelastic parameters are evaluated through a strain sweep carried out from 0.1 to 1000% strain at a frequency of 1Hz. The value of the elastic and viscous moduli G' and G” at the frequency 1Hz corresponds to that of the elastic and viscous moduli in the linear domain.

[0118] For all examples, G'p is the value of G' for which the elastic modulus has decreased by 10% compared to the value of G' at the plateau of the linear domain.

[0119] Example 1:

[0120] The table below presents the rheological parameters measured, according to the process of the invention, of a non-crosslinked hyaluronic acid gel. [Tables 1] Product g' ei Hz (Pa) G" # 1Hz (Pa) tanS @ 1 Hz Vp (%) Çp (Pa) Ce (Ps) A-Yp (%) (Pa) A 1100 319 D.29 36 375 192 813 15S 439 B 7SS 344 0.44 40 322 230 863 190,541

[0121] This non-crosslinked hyaluronic acid gel was prepared by dissolving sodium hyaluronate of molecular mass 3 MDa at a concentration of 30 mg / mL in PB S buffer.

[0122] The process according to the invention made it possible to evaluate the rheological parameters of the gel before and after the gel sterilization step.

[0123] In this example, the gel before the sterilization step is denoted A and the gel after the sterilization step is denoted B.

[0124] In the table above, a variation in rheological parameters can be observed during of the hyaluronic acid gel sterilization step. An increase in the malleability range and a decrease in the resistance range are noted during this sterilization step.

[0125] Example 2:

[0126] The table below presents the rheological parameters measured, according to the process of the invention, of a KartilageCross® gel (intra-articular injection) marketed by Laboratoires Vivacy. [Tables 2] Product G! @ 1Hz (Pa) G” 1Hz (Pa) tanS @ 1 Hz.

[0127] In the context of this example, KartilageCross gel marketed by Laboratoires VIVACY is rated C.

[0128] The process according to the invention made it possible to measure and evaluate the classic rheological parameters of the C gel such as the elastic modulus and the viscous modulus.

[0129] In addition, the process according to the invention made it possible to measure rheological parameters such as the malleability range and the resistance range of the C gel.

[0130] These parameters make it possible in particular to complete the study of the behavior of the C gel.

[0131] Example 3:

[0132] The table below presents the measured rheological parameters, according to the process of the invention, of two gel formulations. Vapor Stenlization Product G' (P3) G" ©1Hz (Pa) Y» (%) (Pa) V (%) & (Pa) y -yp (%) Ce <p (Pa) Non D 367 43 54 183 417 540 363 358 E 379 39 51 176 384 511 333 334 Fç- 9min D 311 44 57 164 494 542 436 378 E 284 40 64 167 508 529 444 362 D 282 42 64 167 538 544 474 377 E 238 37 64 140 595 527 531 387 D 242 41 84 143 619 559 555 415 Fo-46,Smin E 171 31 64 101 768 560 703 458

[0133] The first is a formulation made according to the process described in patent EP231108 with incorporation of mannitol (noted D in the table above).

[0134] The second is a formulation made according to the process in patent EP231108 without incorporation of mannitol (noted E in the table above).

[0135] The process according to the invention made it possible to evaluate the rheological parameters of these two formulations at different sterilizing values ​​Fo= 9min; Fo=20.5min and Fo =46.5min.

[0136] As a reminder, the sterilizing value is expressed in units of time and allows the effect of a sterilizing treatment to be quantified.

[0137] In the table above, it can be seen that the elastic modulus of formulations D and E decreases during the sterilization step.

[0138] On the other hand, as illustrated in [fig.2] and [fig.3], the resistance range parameter increases during the sterilization of formulations D and E.

[0139] As illustrated in [fig.4] and [fig.5], the extent of the malleability range increases significantly during the sterilization process of formulations D and E.

[0140] Example 4:

[0141] The table below presents the rheological parameters measured, according to the process of the invention, of two different gels. Product G! @ 1Hz (Pa) G" @ 1Hz(Pa) tanS © 1Hz YP (%) (p (Pa) yc (%} (Pa) yc-yp (%) Cc-Cp (Pa) F 25 0.12 18 31 128 112 112 81 H 204 33 0.16 SI 95 309 253 258 15S

[0142] The first is the product Juvederm Volbella (with lidocaine) marketed by the company Allergan. In the context of this example, the Volbella product is designated F.

[0143] The second is the Special Lips product from the Stylage range marketed by Laboratoires Vivacy. In this example, the Special Lips product is denoted H.

[0144] As illustrated in [fig.6], gels F and H have similar elastic moduli G'.

[0145] They also exhibit neighboring viscous moduli G”.

[0146] On the other hand, the extent of the resistance range and the malleability range allow us to distinguish between the two products.

[0147] As illustrated in [fig.7], the resistance range of product H is twice as extensive as that of product F, it is also shifted in translation towards higher values ​​of T in such a way that there is practically no overlap of the resistance ranges.

[0148] Also in [fig.8], it is observed that the malleability range of product H is twice as extensive as that of product F, it is also shifted in translation towards higher values ​​of T but a significant overlap of the resistance ranges is preserved.

[0149] In conclusion, the process according to the invention made it possible to differentiate two gels with similar elastic and viscous moduli.

[0150] Example 5: The table below presents the rheological parameters measured, according to the process of the invention, of three different Restylane gels Product G' @ IHe (Ps) G" @ 1Hz (Pa) Tans @ IHe ¥P (¾} CP yc (%) Ce CM (Pa) ¥■. ■ VP (%) I 262.5 26..01 32 77 631 664 587 599 J 160 25 0.16 64 94 942 679 585 878 K 168 25 0.15 64 98 874 666 562 810

[0151] The first is the Restylane Defyne product marketed by the company Galderma. In this example, the Restylane Defyne product is denoted I.

[0152] The second is the Restylane Volyme product marketed by the company Galderma. In the context of this example, the Restylane Volyme product is denoted J.

[0153] The third is the Restylane Kysse product marketed by the company Galderma. In this example, the Restylane Kysse product is denoted K.

[0154] As illustrated in [fig.9], gels J and K have similar elastic moduli G' while the elastic modulus of gel I is different.

[0155] In contrast, gels I, J and K have similar viscous moduli G”.

[0156] As shown in [fig.10], the resistance range of gels I and J is almost- identical and is of the same order of magnitude for gel K.

[0157] As shown in the figure [fig.l 1], it can be observed that the range of malleability differs according to the nature of the products I, J and K.

[0158] In the context of this example, the process according to the invention made it possible to differentiate two gels with similar elastic and viscous moduli (J and K).

[0159] In conclusion, the method according to the invention made it possible to evaluate the rheological parameters of commercial gels and to differentiate two gels with similar elastic and viscous moduli.

[0160] Example 6:

[0161] The table below presents the rheological parameters measured, according to the process of the invention, of two different gels. LG' 1Hz (Pa) SG 1Hz (Pa) 4 yp (%) 101 Çp vc (Pa) (%) 46 § 346 Ce (Pa)) 90 yc -yp Ce - Cp (%) | (Pa) 245 | 44 M 71 5 90 58 I 442 158 352 | 100

[0162] The 2% non-sterile bovine gelatin solution, denoted L, was obtained from "high bloom" type gelatin after dissolution in purified water, homogenization by vortexing and then heating to 37°C for 15 minutes, followed by further homogenization and finally cooling to room temperature.

[0163] The 2% non-sterile porcine gelatin solution, denoted M, was obtained from "high bloom" type gelatin after dissolution in purified water, homogenization by vortexing and then heating to 37°C for 15 minutes, followed by further homogenization and finally cooling to room temperature.

[0164] As illustrated in [fig.12], the gels L and M have similar elastic moduli G'.

[0165] They also exhibit similar viscous moduli G”.

[0166] As illustrated in [fig. 13], the resistance range of product M is twice as extensive as that of product L and is also shifted in translation towards higher values ​​of T but a significant overlap of the resistance ranges is maintained.

[0167] Also in [fig. 14], it is observed that the malleability range of product M is more extensive than that of product L.

[0168] These parameters make it possible in particular to complete the study of the behavior of L and M gels.

[0169] In conclusion, the process according to the invention made it possible to evaluate and compare the rheological parameters of gelatin gels such as L and M gels.

Claims

Claims

1. Method for evaluating the rheological characteristics of at least one gel, consisting of determining the extent of the plastic domain in stress çc -Çp and in deformation Yc-Yp, said determination being carried out according to the steps of: - subjecting at least one sample of at least one gel to oscillatory mechanical stresses at a fixed frequency, - determining and plotting the curves of the elastic modulus G' and the viscous modulus G' ' as a function of the deformation and the stress, - determining çc and Yc at the point of intersection Xc of the curves G' and G' ' in stress and deformation, - determining çp and yp by fixing an arbitrary value of G' (G'x) which will be defined as the entry value in the plastic domain and, - calculating çc -çp and Yc-Yp-

2. Method according to claim 1, characterized in that the oscillatory mechanical constraints are implemented by an amplitude sweep.

3. Method according to claim 2, characterized in that the amplitude scan is a deformation and / or stress scan.

4. Method according to claim 1 and 2, characterized in that the arbitrary value of G' is defined as the value for which the elastic modulus G' has decreased by at most 15% compared to the value of G' at the plateau of the linear domain.

5. Method according to any one of the preceding claims, characterized in that the fixed frequency is between 0.1 and 10 Hz.

6. Method according to any one of the preceding claims, characterized in that the fixed frequency is equal to 1 Hz.

7. Method according to any one of the preceding claims, characterized in that it is implemented by the use of a rheometer connected to a control unit to carry out the measurements and calculations.

8. A method according to any preceding claim, in that the gel is a hydrogel.

9. A method according to any preceding claim, in that

10.

11.

12. that the hydrogel consists of at least one polysaccharide chosen from the group comprising: hyaluronic acid, heparosan, keratan, heparin, cellulose, cellulose derivatives (in particular hydroxypropylcellulose, hydroxypropylmethylcellulose, ethylmethylcellulose, carboxymethylcellulose), alginic acid, xanthan, carrageenan, chitosan, chondroitin, heparosan, and their biologically acceptable salts, alone or as a mixture. A method according to any one of the preceding claims, in that the gel consists of hyaluronic acid. A method according to any preceding claim, in that the gel is an injectable gel. Method for comparing and differentiating gels comprising the steps of: - determination according to the method of claim 1 of the resistance range of gels, said resistance range being defined by the difference çc -çp; i.e. the extent of the plastic domain under stress, - determination according to the method of claim 1 of the malleability of gels, said malleability range being defined by the difference yc-Yp; i.e. the extent of the plastic domain in deformation, - use of the parameters defined above in order to compare and differentiate the gels.

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