FR3085953A1 - HYDROGEL PARTICLES OF STIMULABLE BIPHILIC POLYMERS FOR STABILIZING WATER-IN-WATER EMULSIONS - Google Patents

Abstract

The present invention relates to hydrogel particles consisting of a copolymer of at least one polysaccharide and at least one heat-sensitive polymer. It also relates to their use for the stabilization of a water-in-water emulsion, as well as said corresponding water-in-water emulsions.

Description

HYDROGEL PARTICLES OF STIMULABLE BIPHILIC POLYMERS FOR STABILIZING WATER-IN-WATER EMULSIONS

The present invention relates to hydrogel particles of stimulable polymers and their use for the stabilization of water-in-water emulsions. It also relates to the emulsions thus obtained.

Many aqueous ternary systems containing two types of polymers exhibit a liquid-liquid phase separation between a phase rich in polymer A and a phase rich in polymer B (WJ Frith, Advances in Colloid and Interface Science, 2010, 161,48-60 ). Among the known examples, the water-dextran-polyethylene oxide (POE) systems (D. Forciniti, CK Hall and MR Kula, Fluid Phase Equilibria, 1991, 61, 243-262) or water-dextran-gelatin ( MW Edelman, E. van der Linden, E. de Hoog and RH Tromp, Biomacromolecules, 2001, 2, 1148-1154). These systems are interesting from the point of view of applications because they make it possible to sequester certain molecules of interest in one of the phases, in particular certain proteins or DNA (JP Douliez, N. Martin, C. Gaillard, T. Beneyton, JC Baret, S. Mann, L. Beven, Angew. Chem. Int. Ed., 2017, 3689). These systems have very low interfacial tension (G. Balakrishnan, T. Nicolai, L. Benyahia and D. Durand, Langmuir, 2012, 28, 59215926). They can be mixed temporarily but demix over time, unless one of the two phases is gelled (I. Capron, S. Costeux and M. Djabourov, Rheologica Acta, 2001, 40, 441-456). A more general approach would be to preserve the dispersed state from one aqueous phase to the other in the liquid state by adding surfactants.

Unlike water-oil emulsions, these water-in-water emulsions are difficult to stabilize. In fact, not only do adequate chemistry surfactants not exist - biphilic surfactants should be designed - but small molecules cannot stabilize water-in-water emulsions because the correlation length is less than that of polymer solutions . Proteins or particles at interfaces can constitute an alternative (T. Nicolai and B. Murray, Food Hydrocolloids, 2017, 68, 157-163; J. Esquena, Current Opinion in Colloid & Interface Science, 2016, 25, 109-119 ).

However, to date, no compound has made it possible to obtain water-in-water emulsions stable at dilution. In addition, no system has yet made it possible to control the direction of the emulsion and its temperature stability.

The present invention therefore aims to provide a system adapted to allow stabilization of water-in-water emulsions, and this for a satisfactory duration, in particular for at least 3 months.

The present invention also aims to provide water-water emulsions stable over time, but also having dilution stability for a satisfactory duration, in particular for at least 1 month.

The present invention also aims to provide water-water emulsions stable over time and which can be destabilized as a function of an external stimulus such as temperature.

Another object of the invention consists in providing aqueous systems, obtained by simple mixing, at low shear rate, based on capsules of controlled size, stable over time and at dilution, and which can be destroyed on demand, by application of an external stimulus such as temperature.

Another object of the invention is to provide a system for encapsulating water-soluble molecules, including fragile molecules such as proteins, enzymes or nucleic acids such as DNA.

Thus, the present invention relates to a hydrogel particle, in particular a nanogel, consisting of a copolymer of at least one polysaccharide and at least one heat-sensitive polymer.

According to one embodiment, the copolymer according to the invention contains from 10% to 50% by weight of polysaccharide and from 50% to 90% by weight of heat-sensitive polymer.

According to one embodiment, the copolymer according to the invention is a copolymer with two distinct units: a polysaccharide and a heat-sensitive polymer.

Preferably, the two polymers are chemically crosslinked, at least partially, and form a swollen network of water.

According to the invention, the term "heat-sensitive polymer" designates a polymer which exhibits a drastic and discontinuous change in its physical properties with temperature. In particular, this term designates polymers with LCST (critical lower solubility temperature) or UCST (critical upper solubility temperature). These polymers are specific polymers whose solubility in water is modified above or below a certain temperature. These are polymers with a critical temperature (or cloud point) defining their zone of solubility in water. This temperature is called LOST (Lower Critical Solution Temperature) when above this temperature, the polymer loses its solubility in water and becomes soluble in water below this critical temperature. In the case where the polymer becomes soluble above a critical temperature, this is designated by the acronym UCST (Upper Critical Solution Temperature).

According to one embodiment, the heat-sensitive polymer is an LCST polymer.

Preferably, the heat-sensitive polymer is chosen from the group consisting of N-alkyl-substituted polyacrylamides such as poly (N-isopropylacrylamide), poly (N-isopropylmethacrylamide) or poly (N-ethylacrylamide), poly ((2dimethylamino) ethyl methacrylate), oligoethylene glycol side chain poly (methacrylates), poly (N-vinylcaprolactam), poly (vinyl methyl ether), poly (2-alkyl-2-oxazoline), Poly (propylene oxide) and their mixtures.

The heat-sensitive polymer can also be chosen from the group consisting of copolymers of acrylamide and acrylonitrile, homopolymers of methacrylamide, polymers with ureido derivative such as poly (allylamine) -copoly (allylurea) and zwittterionic polymers , such as poly (sulfobetaine) s or poly (phosphorylcholine) s, and mixtures thereof.

According to a preferred embodiment, the heat-sensitive polymer is poly (N-isopropylacrylamide).

According to one embodiment, the polysaccharide according to the invention is at least difunctional, that is to say that it is substituted by at least two functional groups. According to the invention, the term “functional group” designates a group carrying a chemical function, in particular chosen from methacrylate, acrylate, vinyl, acrylamide, methacrylamide, maleimide, vinyl sulfone, acrylonitrile, azide and amine functions.

Preferably, the polysaccharide according to the invention has a degree of substitution (DS) of between 2% and 30% by moles.

The degree of substitution is defined as the molar ratio between the grafted functional groups, in particular the grafted methacrylate functions, and the repeat unit of the polysaccharide, here namely dextran. It can be measured by NMR (Nuclear Magnetic Resonance) of the proton, by integrating vinyl protons (5.8 and 6.25 ppm) and those of anomeric dextran (5 ppm).

Preferably, the polysaccharide is chosen from the group consisting of hyaluronic acid, heparosan, chondroitin, chondroitin sulfate, heparin, heparan sulfate, alginate, pectin , dextran, dextrin, pullulan, glycogen and mixtures thereof.

Preferably, the polysaccharide is dextran, in particular functionalized, in particular substituted by at least two methacrylate groups.

According to the invention, said particles are networks of polymer swollen with solvent. The network is continuous through the particle, we can then speak of "full" particles. Generally, the particles contain more solvent than polymer. The particles according to the invention can also be designated as colloidal hydrogel particles.

The hydrogel or nanogel particles according to the invention preferably have a diameter of between 10 nm and 10 μm.

The present invention also relates to a series of hydrogel or nanogel particles as defined above.

Thus, the present invention is based on a new class of particles, consisting of copolymers, one of the entities having an affinity for the aqueous phase containing a polymer A and the other having an affinity for the aqueous phase containing a polymer B These copolymers are qualified as doublehydrophilic or biphilic.

The present invention also relates to the use of at least one hydrogel or nanogel particle as defined above, for the stabilization of a water-in-water emulsion.

When the particles of the invention, consisting of copolymers, of which one of the entities has an affinity for the aqueous phase containing a polymer A (polA) and the other has an affinity for the aqueous phase containing a polymer B (polB) , are added to the ternary water-polA-polB mixture, they are preferably placed at the interface between the two incompatible aqueous phases and stabilize drops of A-in-B or B-in-A depending on whether the particles prefer to be dispersed in the phase rich in B or in the phase rich in A respectively. This preference results from the composition of the copolymer and from its structure.

The present invention also relates to a water-in-water emulsion, comprising a dispersed aqueous phase containing a polymer A and a continuous aqueous phase containing a polymer B, and further comprising, at the interface of these two phases, particles of hydrogel or nanogel as defined above.

According to one embodiment, the concentration of polymers A and B in the continuous and dispersed aqueous phases is between 0.1% and 80% by mass relative to the mass of continuous or dispersed aqueous phase, respectively.

According to one embodiment, the concentration of the particles is between 0.005% and 30% by mass relative to the mass of emulsion.

The present invention also relates to a water-in-water emulsion as defined above, the dispersed aqueous phase of which is formed of at least one capsule comprising a core containing polymer A and a shell of hydrogel or nanogel particles. as defined above.

According to one embodiment, in water-in-water emulsions as defined above, the polymer A is a water-soluble polymer which may have a phase separation with B. Such a polymer can be chosen from the class of polysaccharides (dextran , chitosan, guar ...), proteins (casein, globular proteins ...), oligopeptides, nucleic acids (DNA, RNA) or synthetic polymers (POE, PPO, acrylates, ...) for example.

According to one embodiment, in water-in-water emulsions as defined above, in which the polymer B is a water-soluble polymer which can have a phase separation with A. Such a polymer can be chosen from the class of polysaccharides (dextran, chitosan, guar ...), proteins (casein, globular proteins ...), oligopeptides, nucleic acids (DNA, RNA) and synthetic polymers (POE, PPO, acrylates, ...) by example.

According to one embodiment, when one of the two polymers of the particle has a critical temperature of solution, low for example (LOST), that is to say that it is soluble at low temperature in water but precipitates for at a temperature above the LOST, the copolymer particles pass from the swollen state at a temperature below the LOST to contracted beyond the LOST. The dispersibility of the particles in A or B is also a function of the swelling state of the particle.

If the particles have an affinity for A at low temperature, the emulsions of B-in-A will be stable at low temperature. A rise in temperature beyond the LOST causes destabilization of the emulsion. If the emulsion is produced at high temperature, the emulsions from A to B will be stable. A decrease in temperature below the LOST causes destabilization of the emulsion.

According to one embodiment, when one of the two polymers is a UCST polymer, that is to say that it is soluble at high temperature in water but precipitates for a temperature below the UCST, the particles of copolymers pass from the contracted state at a temperature lower than the UCST to swollen beyond the UCST.

If the particles have an affinity for A at high temperature, the emulsions of B-in-A will be stable at high temperature. A decrease in temperature above the UCST causes destabilization of the emulsion. If the emulsion is made at low temperature, the emulsions from A to B will be stable. A decrease in temperature beyond the UCST causes destabilization of the emulsion.

Thus, the present invention is advantageous in that it is possible to modify the direction of the emulsion obtained in a simple manner. Indeed, the direction of the emulsion obtained differs depending on whether one is below the solubility temperature of the heat-sensitive polymer according to the invention or above. For example, using an LCST polymer at low temperature, the aqueous phase containing polysaccharides will be the dispersed phase while at high temperature it will become the continuous phase. Thus, it is possible to choose the direction of the emulsion by adapting the phase transition temperature of the hydrogels or nanogels to the chosen use temperature.

In addition, the above-mentioned water-in-water emulsions, stabilized at low temperature, can be destabilized on demand by increasing the temperature above the solubility temperature of the LCST polymer.

Finally, the emulsions according to the invention are stable at dilution, which is generally impossible for water-in-water emulsions because the dilution causes the reduction of the interfacial tension between the two phases rich in A and B and ends up at high dilution, to bring the polymers back to the monophasic field.

The present invention also relates to a method making it possible to change the direction of the abovementioned emulsions, by means of a temperature change, as described below.

For example, by modifying the temperature, it is possible to transform a water-in-water emulsion, comprising a dispersed aqueous phase containing a polymer A and a continuous aqueous phase containing a polymer B, into a water-in-water emulsion, comprising a dispersed aqueous phase containing a polymer B and a continuous aqueous phase containing a polymer A.

The present invention also relates to a polymer capsule, comprising:

- a core containing an aqueous phase and at least one polymer A; and

- a bark of hydrogel or nanogel particles as defined above, said bark completely encapsulating said heart at its periphery.

Preferably, these capsules have a size of between 0.1 μm and 1000 μm, preferably between 500 nm and 100 μm.

The present invention also relates to the use of a capsule as defined above for the encapsulation of water-soluble molecules, in particular chosen from proteins, enzymes or nucleic acids such as DNA or RNA.

Such capsules thus allow the encapsulation of food, cosmetic or pharmaceutical assets.

In particular, these capsules can be used for the encapsulation of dyes, pigments, quantum dots, fluorescent markers, vitamins, peptides, oligonucleotides, antibiotics, hormones, anticancer agents or sun filters.

According to one embodiment, the heart of said capsules also comprises an active ingredient.

As an active ingredient, one can for example quote any water-soluble active ingredient with a partition coefficient different from 1. According to the invention, said active ingredient will be in the dispersed phase. The state of the hydrogel will be chosen so as to orient the direction of the emulsion so that the phase in which the active ingredient is dissolved becomes the dispersed phase.

Thus, as explained above, the present invention provides a means of encapsulating fragile water-soluble molecules. In particular, in a process of separation of liquid-liquid phases in an aqueous medium, the latter have a greater affinity for one aqueous phase of polymers than for the other. By adapting the conditions, they can therefore be localized selectively in the dispersed phase. If the dispersed phase drops are sufficiently stable, they can be concentrated without the risk of coalescing or diluted without dislocating. It is therefore possible to transport these fragile molecules, while protecting them from the outside environment via the capsule.

The hydrogel or nanogel capsule can then be destroyed by the application of a simple stimulus such as temperature. The formation process used is not deleterious for fragile molecules since the mechanical agitation remains moderate and the stability rests solely on physical processes (no reactivity, no change of environment such as pH or temperature).

FIGURES

Figure 1: TEM image (transmission electron microscopy) of 1 ’nanogels (see Table 1 below)

Figure 2: Influence of the DS of dextran in nanogels on the evolution of their diameter as a function of temperature. Example for nanogels of composition containing 37% by mass of dextran-MA (dextran-methacrylate), with different rates of substitution of dextran.

Figure 3: Stability of emulsions produced from different nanogels for compositions containing 75% dextran aqueous phase and 25% PEO phase (left) and 25% dextran aqueous phase and 75% PEO phase comparison between t = 0 (high) and t = 1 day (low), at room temperature. For each series, R is the reference without nanogel, 0 the emulsion stabilized by pNIPAM nanoparticles without dextran, 1,2 and 3 are stabilized by nanogels

1,2 and 3 respectively (see table 1).

Figure 4: Dextran-in-POE emulsion with 0.04% m of 1 ′ fluorescent nanogels after 3 days at 25 ° C.

Figure 5: Inverse of the diameter of the drops as a function of the amount of nanogels for dextran-in-POE emulsions (1 ’nanogels) at 25 ° C.

Figure 6: Influence of the nanogel concentration on the stability of dextran-in-PEO emulsions stabilized by T nanogels (37% by mass of dextran DS 10), at 25 ° C. Temporal monitoring of the transrrittance of emulsions subjected to a centrifugal force of 300g (t = 2 min, 6 min, 33 h). The emulsions contain 0, 0.01%, 0.04% and 0.08% by weight in nanogels.

Figure 7: Influence of the nanogel concentration on the stability of PEO-in-dextran emulsions stabilized by 1 ’nanogels (37% m of dextran DS 10), at 50 ° C. Temporal monitoring of the transmittance of emulsions subjected to a centrifugal force of 300g (t = 6 min, 33h). The emulsions contain 0, 0.01%, 0.04%, 0.08% and 0.12% by weight of nanogels.

Figure 8: Behavior of dextran-in-PEO emulsions stabilized by T nanogels at 20 ° C following dilutions ranging from 1 to 5 times the initial volume of the emulsion. Temporal monitoring of the transmittance of emulsions under normal gravity.

The emulsions contain 0.1% by weight of nanogels.

EXAMPLES

Example 1: Preparation of particles according to the invention

New nanoparticles made of copolymers of pNIPAM and dextran are synthesized. For this, dextran is functionalized by methacrylate patterns.

Dextran-methacrylate (Dex-MA) is obtained by reaction of methacrylic anhydride with the hydroxyls of dextran, in DMF / water medium (Pitarresi, G .; Pierro, P .; Palumbo, FS; Tripodo, G .; Giammona , G. Biomacromolecules 2006, 7, 1302-1310; Auzely, dx.doi.org/10.1021/bm300324m | Biomacromolecules') according to the following diagram:

CH, CHa

pH = 8-9,

methacrylic anhydride water / DMF

For example, to obtain a substitution rate of 10%, dextran (40 kg / mol, Sigma-Aldrich) is introduced into 175 mL of water / DMF 7/3 mixture to which 2 g of methacrylic anhydride is added . The pH is maintained between 8 and 9 by additions of 0.5 M NaOH for 4 h at 4 ° C. At the end of the reaction, the medium is dialyzed via a dialysis membrane (cutoff threshold 3500 g / mol) for 6 days, changing the water at least once a day. The solution is then lyophilized. The substitution rate (DS), defined as the molar ratio between the grafted methacrylate functions and the repeat unit of dextran, is determined by proton NMR by integrating vinyl protons (5.8 and 6.25 ppm) and those of anomeric dextran ( 5 ppm). DS ranging from 5 to 40% of the dextran chain is obtained by modifying the concentration of methacrylic anhydride.

The pNIPAM-Dex particles are synthesized by precipitation polymerization. NIPAM (796 mg) and dex-MA (between 10 and 37% by mass compared to NIPAM) are dissolved in 95 mL of deionized water. The medium is heated to 70 ° C and degassed. Then potassium persulfate β7 mg in 5 mL) is introduced to initiate the polymerization. After about ten minutes, the medium becomes turbid, indicating the nucleation of the particles. The reaction is carried out for 4 h. In the case of the synthesis of fluorescent particles, fluorescein-Omethacrylate (0.1% mol. With respect to NIPAM) is introduced into the solution, at the same time as NIPAM.

The particles from the synthesis are filtered and then dialyzed for at least 6 days using a dialysis membrane with a cut-off threshold of 100 kDa. The particles are of uniform size, as evidenced by their analysis in the dry state by transmission electron microscopy (TEM Tecnai Biotwin (120 kV)) (Figure 1). The diameter of the particles d _H is measured by dynamic light scattering (Zetasizer Nano S90, Malvern Instruments) equipped with a He-Ne laser at 90 ° incidence relative to the detector. It is reported in Table 1 for different particle compositions. The evolution of the diameter of the particles as a function of the temperature is given in Figure 2. The nanogels are swollen at low temperature and contract for a temperature above 32 ° C, corresponding to the LCST of pNIPAM.

Table 1: Examples of nanogels obtained for different compositions. Each synthesis uses a defined quantity of NIPAM, of Dex-MA whose degree of substitution (DS) varies. All contents are given for 100 mL of water. The amount of initiator, potassium persulfate, is 2.5 mM. The dextran of molar mass Mn = 40 kDa is used. The compositions of the resulting nanogels are determined by ¹ H NMR. After purification by dialysis, the level of solid (dry extract, expressed in% m.) Is measured by weighing after evaporation of the aqueous phase.

NIPAM (g) DS Dex-MA (g) d _H (nm) T = 20 ° C d _H (nm) T = 40 ° C Dry extract (% m) 1 0.796 10 0.292 160 100 0.65 2 0.796 2 0.292 150 80 0.37 3 0.796 10 0.079 200 100 0.34 1 ’ 0.796 10 0.292 240 160 1.22

Example 2: Preparation of ternary systems

The emulsions were prepared with solutions containing for one a mass fraction of poly (ethylene oxide) POE (Sigma-Aldrich), of average molar mass by mass of 200,000 g / mol, and for the other a mass fraction of dextran (Sigma-Aldrich), of mass-average molar mass of between 450,000 and 650,000 g / mol. All solutions are obtained with milli-Q water with a resistivity of 18.2 18Ω-cm.

Two stock solutions are prepared in advance. The POE solution has a concentration of 10% by mass and the dextran solution is 20% by mass. The POE powder containing silica particles, these were removed by passing the POE solutions to the centrifuge for 4 h at 50,000 g.

These solutions were prepared by weighing each solution, then stirred for 24 hours before use to ensure their homogeneity. The stock solution of dextran was obtained for example by weighing 20 g of polymer and then making up to 100 g total by adding milli-Q water.

The emulsions are produced by mixing a volume ratio of 75% / 25% of each phase. A first system contains a volume fraction of 75% of the phase rich in POE and 25% of the phase rich in dextran. For the 75% by volume POE system, the masses of dextran and POE are 4% and 6% respectively. After phase separation, the concentration of the phase rich in POE is 15.8% and that in dextran is 8.2%.

The nanogels in solution are added to the mixture, so as to obtain a maximum of 0.12% by mass of nanogels in the total mixture. The dilution ability was tested by adding up to 5 times the volume of the emulsion in water equivalent.

The emulsions were then mixed in the Fisherbrand shaker for 10 s. It was verified that the strength and the agitation time had no influence on the behavior of the emulsions.

Example 3 Emulsions Made at Room Temperature

The tests carried out with the various nanogels are shown in Figure 3.

Only the emulsion whose continuous phase is PEO with nanogel 1 is stable over one day. The PEO phase being less dense than the dextran phase, it creams during the phase separation.

The tests in Figure 3 show that:

1) Nanogels containing the greatest amount of dextran better stabilize emulsions;

2) The dextran-in-PEO system is stable while the PEO-dansdextran system is unstable;

3) Whatever their composition, the particles tend to migrate in the PEO phase after destabilization.

Emulsions are produced with a batch of nanogels containing 37% DexMA of DS 10, into which a fluorescent comonomer (Fluorescein O-methacrylate, 0.1% mol relative to NIPAM) has been introduced. The preparation of the emulsions with the addition of particles is carried out as described in Example 2. The emulsions are observed under a confocal microscope. It is clear that nanogels are placed on the surface of the drops, thus forming capsules. These capsules containing dextran, heavier than POE, sediment under the effect of gravity, concentrate but they remain intact while being in contact (Figure 4). Their size changes little over time. It varies by around 30% over the first 3 days and then stabilizes. The drops are therefore very resistant to storage.

It should also be noted that the size of the drops is a function of the quantity of particles (Figure 5). The linear evolution of the inverse of the diameter as a function of the quantity of particles is a signature characteristic of the limited coalescence of Pickering emulsions. From a practical point of view, this phenomenon constitutes a lever to control the size of the drops and therefore of the capsules.

The mechanical stability of dextran-in-PEO emulsions is evaluated by subjecting the emulsions to a centrifugal force. The LUMIsizer® gives the simultaneous analysis of the transmittance as a function of the altitude in a tube, it makes it possible to probe the phenomena of creaming / sedimentation, as well as coalescence with force and centrifugal and temperature controlled. Thus a weak transmittance translates a turbid phase and therefore the existence of drops. They can be located in a small area after sedimentation / creaming. A high transmittance over the whole height means that the sample has out of phase or that the interfaces have disappeared by coalescence.

Figure 6 shows the evolution of this signal for emulsions stabilized by nanogel 1 ’, used at different concentrations. For concentrations greater than 0.04% by mass, the persistence of a turbidity at the bottom of the tube after a very long centrifugation (33 h) at 300 g testifies to a great resistance of the drops to coalescence under mechanical stress.

Thus, emulsions stabilized by nanogels having a composition of 37% m. in DS 10 dextran, provide great emulsion stability. The comparison of lots 1 and 1 ′, of the same composition but of different size, show that this stability is all the greater the higher the size of the nanogels.

EXAMPLE 4 Phase Reversal of the Emulsions

The same emulsions as in the previous section underwent the same treatment with LUMiSizer® but at 50 ° C. There is an inversion of behavior with respect to ambient temperature, as with particles 1 ’.

Thus, dextran-in-POE emulsions are not very stable. POEin-dextran emulsions, on the other hand, are very stable (Figure 7).

The results obtained therefore show that temperature is a lever for modulating the affinity of the nanogel for one of the aqueous phases. The direction of the water-in-water emulsion stabilized by nanogels is dictated by the preference of the particles for one or the other of the phases. The emulsions produced are extremely stable at the temperature considered. A fortiori, the emulsions can be destabilized by the application of a stimulus which reduces the affinity of the particles for the continuous phase and causes their dispersion in the dispersed phase.

Example 5: Stability at dilution

A POE / dextran emulsion (75% / 25%) was prepared by adding 0.1% m of 5 particles 1 ’.

As stated above, this system has shown unprecedented stability at room temperature. After 1 day of stabilization of the system, the emulsions were diluted 1 to 5 times by adding water.

The emulsions are then observed over a period of 1 week.

ίο The quantification of this stability to the dilution of the emulsions was carried out on the LUMiReader®, the equivalent of the LUMiSizer® but working at 1g, so no additional mechanical stress or any disturbance is inflicted on the emulsions (Figure 8). It appears that a dilution up to 5 times does not affect the stability of the emulsions even after a week after dilution. It is the first water-in-water system that has shown such dilution stability to date.

Claims (10)

1. Hydrogel particle consisting of a copolymer of at least one polysaccharide and at least one heat-sensitive polymer. 2. A hydrogel particle according to claim 1, in which the copolymer contains from 10% to 50% by weight of polysaccharide and from 50% to 90% by weight of heat-sensitive polymer. 3. Hydrogel particle according to claim 1 or 2, wherein the polysaccharide is chosen from the group consisting of hyaluronic acid, heparosan, chondroitin, chondroitin sulfate, heparin, sulfate heparan, alginate, pectin, dextran, dextrin, pullulan, glycogen and mixtures thereof. 4. Hydrogel particle according to any one of claims 1 to 3, in which the heat-sensitive polymer is chosen from the group consisting of N-alkyl-substituted polyacrylamides such as poly (N-isopropylacrylamide), poly (N-isopropylmethacrylamide) ) or poly (N-ethylacrylamide), poly ((2dimethylamino) ethyl methacrylate), poly (methacrylates) with oligoethylene glycol side chain, poly (N-vinylcaprolactam), poly (vinyl methyl ether), poly ( 2-alkyl-2-oxazoline), Poly (propylene oxide), copolymers of acrylamide and acrylonitrile, homopolymers of methacrylamide, polymers with ureido derivative such as poly (allylamine) -co-poly (allylurea) and its derivatives, zwitterionic polymers, such as poly (sulfobetaine) s or poly (phosphorylcholine) s, and mixtures thereof. 5. Hydrogel particle according to any one of claims 1 to 4, whose diameter is between 10 nm and 10 pm. 6. A series of hydrogel particles according to any one of claims 1 to 5. 7. Use of at least one hydrogel particle according to any one of claims 1 to 5, for the stabilization of a water-in-water emulsion. 8. Water-in-water emulsion, comprising a dispersed aqueous phase containing a polymer A and a continuous aqueous phase containing a polymer B, and further comprising, at the interface of these two phases, hydrogel particles 5 according to any one of claims 1 to 5. 9. Polymer capsule, comprising: - a core containing an aqueous phase and at least one polymer A; and - a bark of hydrogel particles according to any one of claims 1 to 5, said bark completely encapsulating said heart at its periphery. 10. Use of a capsule according to claim 9 for the encapsulation of water-soluble molecules, in particular chosen from proteins, enzymes or nucleic acids such as DNA or RNA.