Responsive hydrophilic microgel stabilized water-in-water pickering emulsion and method of making the same

Abstract

The application discloses a kind of responsive hydrophilic microgel stabilized water-in-water Pickering emulsion and preparation method thereof, belong to colloid and interface chemistry technical field.The application provides a kind of stimulus-responsive poly (N-isopropyl acrylamide-co-dimethylaminoethyl methacrylate) -dextran microgel (PND-DEX) stabilized water-in-water Pickering emulsion and preparation method thereof.The application is with PEG and DEX as two phases, PND-DEX is emulsifier, and a new type of water-in-water Pickering emulsion is prepared, has good pH, salt ion tolerance and responsiveness.

Description

Technical Field

[0001] This invention relates to a responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion and its preparation method, belonging to the field of colloid and interface chemistry technology. Background Technology

[0002] Water-in-water emulsions, also known as aqueous two-phase emulsions, are formed by dispersing two water-soluble substances that are immiscible at certain concentrations. Compared to traditional oil-water emulsions, both the inner and outer phases of a water-in-water emulsion are hydrophilic and contain no organic reagents, exhibiting excellent biocompatibility and environmental friendliness. They have attracted widespread attention in fields such as active ingredient encapsulation, providing reaction conditions for microreactors, and bioengineering.

[0003] Water-in-water emulsions are characterized by extremely low interfacial tension and large interfacial thickness, making it difficult for small molecules such as surfactants used in conventional oil-water emulsions to adsorb at the water-water interface, thus stabilizing water-in-water emulsions is challenging. Pickering emulsions can provide spatial protection and shielding by adsorbing a layer of particles at the interface, forming one or more protective layers, thereby preventing droplet aggregation, coalescence, and deformation, and achieving emulsion stabilization. Current research on water-in-water emulsions focuses on this. Currently, the Pickering particles used to stabilize water-in-water emulsions can be broadly classified into: block copolymers polymerized from monomers with different affinities; and colloidal particles represented by silica, cellulose nanocrystals, polydopamine, and microgels.

[0004] Microgels are colloidal particles with a size ranging from nanometer to micrometer, possessing a three-dimensional cross-linked network structure, and capable of swelling in solvents (mostly water). Their structure is a flexible and compressible cross-linked polymer network. Unlike rigid solid particles, the core advantage of microgels lies in their swelling and responsiveness. Their size, modulus, and interfacial properties can undergo significant and reversible changes with environmental factors such as temperature and pH, thus allowing for intelligent control of emulsions. They are ideal materials for constructing water-in-water emulsion systems.

[0005] Currently, most microgels used to stabilize water-in-water picking emulsions are protein microgels, especially whey protein. This is due to their excellent biocompatibility and availability, as well as their peptide nature, which makes them easy to prepare and reproducible. However, both whey protein and gelatin, being biomaterials, have limitations in terms of pH, temperature, and ionic strength, thus restricting the range of emulsion formation. In contrast, chemical synthesis is also an important source of microgels, and by using appropriate raw materials and synthetic methods, it is possible to maintain good biocompatibility while meeting the requirements for stabilizing water-in-water emulsions under different conditions.

[0006] Currently, N-isopropylacrylamide microgels co-modified with dextran (DEX) and acrylic acid (AA) are used to stabilize water-in-water emulsions. The stability of these emulsions is affected by both pH and temperature. While the addition of AA groups introduces a pH response, the increase in negative charge also enhances charge repulsion. At low pH, the microgels become too hydrophilic, leading to weakened emulsion stability. Therefore, salts need to be added to shield the charge and enhance emulsion stability.

[0007] Therefore, developing a method for preparing microgels and emulsions that can form emulsions at low pH and have responsiveness would not only satisfy the biocompatibility requirements of water-in-water emulsions but also fully leverage the tunable advantages of microgels, thus expanding the application of microgels in water-in-water emulsions. Summary of the Invention

[0008] To address the aforementioned problems, this invention uses dimethylaminoethyl methacrylate (DMAEMA), which can be protonated to generate a positive charge, instead of AA groups. This reduces the charge repulsion of the microgel, eliminates salt dependence, and forms a stable water-in-water emulsion under acidic conditions. This invention provides a stimulus-responsive poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel (PND-DEX) stable water-in-water Pickering emulsion and its preparation method. A novel water-in-water Pickering emulsion is prepared using PEG and DEX as two phases and PND-DEX as an emulsifier.

[0009] The first objective of this invention is to provide a method for preparing a responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion, comprising the steps of: (1) N-isopropylacrylamide, dimethylaminoethyl methacrylate and methacrylate-modified dextran were dissolved in water, and potassium persulfate was added after reflux under nitrogen. The mixture was magnetically stirred to obtain a mixture. The mixture was dialyzed and freeze-dried to prepare poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel. (2) Poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel was dispersed in water to obtain a microgel dispersion; PEG 20k and DEX 500k were added to the microgel dispersion, and the mixture was mixed evenly and homogenized to obtain a water-in-water Pickering emulsion with responsive hydrophilic microgel stability.

[0010] In one embodiment, in step (1), the ratio of N-isopropylacrylamide, dimethylaminoethyl methacrylate, methacrylate-modified dextran, and water is 0.2~0.8 g: 1.0~0.3 g: 0.2~0.8 g: 80~120 mL; Optionally, in step (1), the reflux condensation is performed at 65~75 ℃ for 240~360 min; Optionally, in step (2), the ratio of PEG 20k, DEX 500k, poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel to water is 0.3~1.0 g: 0.1~0.5 g: 0.0025~0.02 g; : 4.5~3.5 g.

[0011] In one embodiment, the amount of potassium persulfate added in step (1) is 0.02~0.1 wt% of the total system mass.

[0012] In one embodiment, in step (1), dialysis is performed using a dialysis bag with a molecular weight of 80,000 to 120,000, for 7 to 10 days, with the deionized water being replaced every 8 to 12 hours.

[0013] In one implementation, in step (2), homogenization is performed at 12k~13k rpm for 2~3 min.

[0014] In one embodiment, the method for preparing methacrylate-modified dextran is as follows: DEX 70000 was dissolved in water, N,N-dimethylformamide was added and stirred; then methacrylic anhydride was added, the pH was adjusted, and the reaction was carried out to obtain a reaction solution; the reaction solution was dialyzed and freeze-dried to obtain methacrylate-modified dextran; Optionally, the ratio of DEX 70000, N,N-dimethylformamide, methacrylic anhydride and water is 5 g: 50 mL: 2~5 g: 80~120 mL.

[0015] In one implementation, the pH is adjusted to 8-9.

[0016] In one implementation, the reaction is carried out by cooling to 4°C and reacting for 4-6 hours.

[0017] In one embodiment, in step (2), PEG 20k and DEX 500k are added to the microgel dispersion and mixed evenly. Then, active substances can be added further and homogenized to obtain a water-in-water Pickering emulsion with responsive hydrophilic microgel encapsulated with active substances.

[0018] In one embodiment, the active ingredients include water-soluble active ingredients such as hydrolyzed collagen, hydroxytyrosol, and 2-phenylbenzimidazole-5-sulfonic acid, as well as water-soluble sunscreen agents.

[0019] A third objective of this invention is to provide a water-in-water Pickering emulsion with responsive hydrophilic microgels prepared by any of the methods described above.

[0020] A fourth object of the present invention is to provide the application of any of the above-described responsive hydrophilic microgel-stabilized water-in-water Pickering emulsions in the preparation of cosmetics, pharmaceuticals, and food.

[0021] A fifth object of the present invention is to provide a cosmetic product containing the above-described responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion.

[0022] In one embodiment, the cosmetic includes sunscreen lotion, serum, etc.

[0023] A sixth object of the present invention is to provide a medicine comprising the above-described responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion.

[0024] The seventh objective of this invention is to provide a method for improving the performance of water-in-water Pickering emulsions, the performance including stability under low pH conditions, pH responsiveness, salt ion responsiveness, and temperature responsiveness, wherein the water-in-water Pickering emulsion is prepared using methacrylate-modified dextran, comprising the steps of: (1) N-isopropylacrylamide, dimethylaminoethyl methacrylate and methacrylate-modified dextran were dissolved in water, and potassium persulfate was added after reflux under nitrogen. The mixture was magnetically stirred to obtain a mixture. The mixture was dialyzed and freeze-dried to prepare poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel. (2) Poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel was dispersed in water to obtain a microgel dispersion; PEG 20k and DEX 500k were added to the microgel dispersion, and the mixture was mixed evenly and homogenized to obtain a water-in-water Pickering emulsion with responsive hydrophilic microgel stability.

[0025] In one embodiment, in step (1), the ratio of N-isopropylacrylamide, dimethylaminoethyl methacrylate, methacrylate-modified dextran, and water is 0.6~1:0.1~0.2 g:0.2~0.4 g:100 mL; Optionally, in step (1), the reflux condensation is performed at 60~80 ℃ for 240~300 min; Optionally, in step (2), the ratio of PEG 20k, DEX 500k, poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel to water is 0.3~0.5 g: 0.1~0.2 g: 0.0015~0.003 g: 4.5 g.

[0026] In one embodiment, in step (1), the ratio of N-isopropylacrylamide, dimethylaminoethyl methacrylate, methacrylate-modified dextran, and water is 0.8 g: 0.2 g: 0.3 g: 100 mL; Optionally, in step (1), the reflux condensation is performed at 70 °C for 240 min; Optionally, in step (2), the ratio of PEG 20k, DEX 500k, poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel to water is 0.35 g: 0.15 g: 0.0025 g: 4.5 g.

[0027] In one embodiment, the amount of potassium persulfate added in step (1) is 0.02~0.05 wt% of the total system mass; Optionally, the amount of potassium persulfate added is 0.03 wt% of the total system mass.

[0028] In one implementation, dialysis in step (1) is performed using a dialysis bag with a molecular weight of 100,000, for 7 days, with the deionized water being changed every 12 hours.

[0029] In one implementation, in step (2), homogenization is performed at 12k rpm for 3 min.

[0030] In one embodiment, the method for preparing methacrylate-modified dextran is as follows: DEX 70000 was dissolved in water, N,N-dimethylformamide was added and stirred; then methacrylic anhydride was added, the pH was adjusted, and the reaction was carried out to obtain a reaction solution; the reaction solution was dialyzed and freeze-dried to obtain methacrylate-modified dextran; Optionally, the ratio of DEX 70000, N,N-dimethylformamide, methacrylic anhydride and water is 4~6 g:50 mL:1~3 g:100 mL.

[0031] Optionally, the ratio of DEX 70000, N,N-dimethylformamide, methacrylic anhydride and water is 5 g: 50 mL: 2 g: 100 mL.

[0032] In one implementation, the pH is adjusted to 8-9.

[0033] In one implementation, the reaction is carried out by cooling to 4°C and reacting for 4-6 hours.

[0034] In one embodiment, in step (2), PEG 20k and DEX 500k are added to the microgel dispersion and mixed evenly. Then, active substances can be added further and homogenized to obtain a water-in-water Pickering emulsion with responsive hydrophilic microgel encapsulated with active substances.

[0035] In one embodiment, the active ingredients include water-soluble active ingredients such as hydrolyzed collagen, hydroxytyrosol, and 2-phenylbenzimidazole-5-sulfonic acid, as well as water-soluble sunscreen agents.

[0036] Beneficial effects of the present invention (1) The poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel-stabilized water-in-water Pickering emulsion described in this invention is a novel method for stabilizing water-in-water emulsions. The preparation method provided by this invention is simple and easy to operate, low in cost, and has low dependence on organic solvents. It has pH-responsive capabilities, achieving excellent ability to demulsify under alkaline conditions and re-emulsify under acidic conditions.

[0037] (2) This invention is the first to apply the responsive microgel formed by the copolymerization of N-isopropylacrylamide and dimethylaminoethyl methacrylate to water-in-water emulsion. It has good environmental friendliness and biocompatibility and can be applied to active ingredient encapsulation and delivery, biomineralization and other fields. It has good application prospects in cosmetics, pharmaceuticals, food and other industries. Attached Figure Description

[0038] Figure 1 The 1H NMR spectrum of the prepared poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel; Figure 2 Digital photographs of the appearance of the prepared DEX 500K / PEG 20k emulsion; Figure 3 Microscopic images of droplets in the prepared DEX 500K / PEG 20k emulsion under a super depth-of-field microscope; Figure 4 The image shows a microscopic view of an emulsion prepared by staining PEG 20000 with Rhodamine B under an upright fluorescence microscope. Figure 5 Microscopic images of droplets in an emulsion placed at room temperature for 3 days under a super depth-of-field microscope; Figure 6 Microscopic images of droplets in emulsions under ultra-depth-of-field microscopes with different emulsifier concentrations; Figure 7 Microscopic images of emulsions with different two-phase composition ratios prepared by staining PEG 20000 with Rhodamine B, observed under an upright fluorescence microscope. Figure 8Microscopic images of droplets in emulsion systems with different pH values ​​under a super depth-of-field microscope; Figure 9 Microscopic images of droplets under a super depth-of-field microscope at different ionic intensities of the emulsion; Figure 10 Digital photographs showing the appearance of the two synthesized microgels in aqueous solution under the same ionic strength; Figure 11 Digital photographs of the appearance of the prepared water-in-water emulsion under acid-base cycling; Figure 12 Digital photographs of the appearance of the emulsion at 25°C and 45°C; Figure 13 This is a microscopic image of bovine serum albumin stained with isothiocyanate and encapsulated in an emulsion under an upright fluorescence microscope. Detailed Implementation

[0039] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0040] Raw materials used in the examples: Dextran 70000 was purchased from Shanghai Titan Technology Co., Ltd., CAS number 9004-54-0; Polyethylene glycol 20k was purchased from Beijing Innocare Technology Co., Ltd., CAS number 25322-68-3; Rhodamine B was purchased from Adamas (Shanghai) Chemical Reagent Co., Ltd., CAS No. 81-88-9; N,N-Dimethylformamide was purchased from Shanghai Titan Technology Co., Ltd., CAS No. 68-12-2; 500kg of dextran was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., CAS No. 9004-54-0; N-Isopropylacrylamide was purchased from: TCI Chemical Industry Development Co., Ltd., CAS No. 2210-25-5; Dimethylaminoethyl methacrylate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS number 2867-47-2.

[0041] Test method: 1. NMR detection methods for DEX-MA and PND-DEX: The product was dissolved in deuterium water, freeze-dried, and placed in an NMR tube. The proton NMR spectrum was then detected using an NMR spectrometer.

[0042] 2. Method for detecting emulsion particle size: Take 10 μL of emulsion and drop it onto a glass slide. Use a super depth-of-field microscope to observe the morphology of the droplet and take pictures. Use NanoMeasurer software to count the size of the emulsion particles.

[0043] 3. Methods for identifying emulsion types: The enriched PEG phase was stained with Rhodamine B, and PND-DEX was stained with fluorescein isothiocyanate. After preparing the emulsion, 10 μL of the emulsion was dropped onto a glass slide and the droplet morphology was observed and photographed using an upright fluorescence microscope.

[0044] Example 1: Preparation of a water-in-water Pickering emulsion using poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel 1. Preparation of methacrylate-modified dextran, the steps are as follows: (1) Weigh 5 g of DEX 70000 and dissolve it in 100 mL of ultrapure water, and lower the temperature to 4℃; after the dextran is completely dissolved, add 50 mL of N,N-dimethylformamide and stir at 4℃ (500 rpm) for 4 h; finally add 2 g of methacrylic anhydride, adjust the pH to 8~9, react for 4 h, and obtain the reaction solution; The pH value was measured every half hour during the period, and the pH value was stabilized at 8-9 by adding 1wt% sodium hydroxide aqueous solution. (2) The reaction solution was placed in a dialysis bag with a molecular weight of 3500 and dialyzed in deionized water for 7 days. The deionized water was changed every 12 hours during the period. After the dialysis was completed, the solution was freeze-dried to obtain methacrylate-modified dextran (DEX-MA).

[0045] 2. Preparation of poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel (PND-DEX): The steps are as follows: (1) Weigh 0.792 g N-isopropylacrylamide, 0.279 g dimethylaminoethyl methacrylate and 0.2376 g DEX-MA and dissolve them in 100 mL of ultrapure water. Use nitrogen to remove oxygen from the system. After refluxing at 70 °C for 30 min, add 0.003 g potassium persulfate. Keep the system unchanged and react for 4 h under magnetic stirring (600 rpm) (the molar ratio of N-isopropylacrylamide and dimethylaminoethyl methacrylate is 4:1, and the amount of DEX-MA added is 30% of the mass of N-isopropylacrylamide) to obtain a mixture. (2) The mixture was placed in a dialysis bag with a molecular weight of 100,000 and dialyzed in deionized water for 7 days. The deionized water was changed every 12 hours during the period. After dialysis, the mixture was freeze-dried to obtain poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel (PND-DEX).

[0046] PND-DEX is a white, flocculent granule that showed no significant changes after 30 days of storage at room temperature. Its proton NMR spectrum is as follows: Figure 1 As shown, the specific values ​​are as follows: δ 3.80 – 3.66 (m, 3H), 3.66 – 3.28 (m, 3H), 2.83 (d, J = 17.7 Hz, 3H), 2.07 (s, 1H), 1.91 (d, J = 43.1 Hz, 3H), 1.43 (s, 6H), 1.12 –0.86 (m, 18H). 3. Preparation of DEX / PEG water-in-water emulsion Pickering emulsion, the steps are as follows: (1) Weigh 0.0025 g of PND-DEX (0.05 wt% of the total mass of water, PEG 20k and DEX 500k) and disperse it in 4.5 g of ultrapure water. Sonicate for 1 min to obtain a microgel dispersion. (2) Weigh 0.35 g PEG 20k and 0.15 g DEX 500k (mass ratio 7:3) and dissolve them in the above microgel dispersion. Vortex for 3 min to fully dissolve and mix them. Then, use a high-speed dispersion homogenizer to homogenize at 12000 rpm for 3 min to prepare DEX / PEG water-in-water Pickering emulsion.

[0047] The appearance of DEX / PEG water-in-water Pickering emulsion is as follows: Figure 2 As shown.

[0048] 4. Emulsion property testing (1) Particle size The DEX / PEG water-in-water Pickering emulsion prepared in step 3 was used, and the droplet morphology was observed using a super depth-of-field microscope. The droplet size was statistically analyzed using Nano Measurer 1.2 software. The results are as follows: Figure 3 As shown, the results indicate that the emulsion particle size is 15 μm and the particle size distribution is uniform.

[0049] (2) Emulsion type In step (2) of 3, 10 μL of Rhodamine B was added before homogenization to stain the PEG-rich phase. The staining agent concentration was 0.1 wt%. The remaining steps were the same as in 3. The prepared DEX / PEG water-in-water Pickering emulsion was observed under an upright fluorescence microscope with an excitation wavelength of 546 nm.

[0050] The results are as follows Figure 4As shown, the results indicate that the internal phase of the emulsion is black and the external phase is red, indicating that the prepared emulsion is a PEG-rich continuous phase and a DEX-rich dispersed phase.

[0051] (3) Long-term stability test Take 3 of the prepared DEX / PEG water-in-water Pickering emulsion and place it at room temperature for 2 days, during which time the appearance and microstructure of the emulsion are observed.

[0052] The results are as follows Figure 5 As shown, the results indicate that the number of emulsion droplets decreases with increasing time, and the emulsion droplets basically disappear after 72 h.

[0053] Example 2: Changing the concentration of PND-DEX microgel emulsifier Based on Example 1, the amount of PND-DEX used in step (1) of step 3 was changed to 0.005 g, 0.0075 g, and 0.010 g, respectively. The remaining steps were the same as in Example 1, and emulsions containing different concentrations of emulsifiers were prepared.

[0054] The microstructure of the emulsion droplets was observed using a super depth-of-field 3D microscope. The results are as follows: Figure 6 As shown, when the addition amount is 0.005 g (0.1 wt% of the total mass), the average particle size of the emulsion droplets is the largest, which is 16.6 μm. The size of the emulsion droplets decreases with the increase of particle concentration.

[0055] Example 3: Changing the composition ratio of the two phases Based on Example 1, the amount of PND-DEX microgel added was 0.005 g, and the mass ratio of DEX 500k to PEG 20k was changed to 3.55:6.88, 7.11:5.16, 10.65:3.44, and 14.21:1.73, respectively. Water-in-water emulsions with different two-phase compositions were prepared by staining with Rhodamine B, and their microstructures were observed using an upright fluorescence microscope.

[0056] The results are as follows Figure 7 As shown, the emulsion stability is highest when PEG 20k:DEX 500K = 7:3. With changes in the mass ratio of the two phases, the emulsion type gradually changes, and the stability tends to decrease with decreasing polyethylene glycol mass. After PEG 20k:DEX500K = 7.1:5.16, the emulsion changes from DEX-in-PEG to PEG-in-DEX.

[0057] Example 4: Emulsion Performance Testing Based on Example 1, a DEX / PEG water-in-water Pickering emulsion was prepared by adding 0.005 g of PND-DEX microgel and using PEG 20k:DEX 500K = 7:3. The performance was tested as follows: 1. Emulsion properties at different pH levels The pH of the emulsion was adjusted to 3, 5, 7, and 9 using 6 mol / L HCl aqueous solution and sodium hydroxide solid, and its microstructure was observed using a super depth-of-field three-dimensional microscope.

[0058] The results are as follows Figure 8 As shown, the stability of the emulsion is affected by pH. The emulsion is stable at pH 3 and 5, but unstable at pH 7 and 9, where the droplets rapidly coalesce and then break down and disappear.

[0059] 2. Emulsion properties under different ionic strengths The ionic strength of emulsions was controlled using NaCl particles. 50 mM and 100 mM NaCl particles were added to the emulsions, and the microstructure of the emulsions was observed using a super depth-of-field three-dimensional microscope.

[0060] like Figure 9 As shown, increasing the ionic strength of an emulsion leads to a destructive decrease in its stability. Compared to 50 mM, the addition of 100 mM NaCl causes almost complete demulsification. Therefore, when the NaCl concentration exceeds a certain value, the emulsion becomes unstable and rapidly separates into phases.

[0061] 3. pH responsiveness The pH of the emulsion was adjusted to pH 3 and pH 9 using 6 mol / L HCl aqueous solution and sodium hydroxide solid, and then circulated. Its microstructure was observed using a super depth-of-field three-dimensional microscope.

[0062] The results are as follows Figure 11 As shown, the emulsion can form when it is acidic. When the pH of the system becomes 9, the emulsion breaks down rapidly. After the emulsion system is brought back to acidic, the emulsion can be homogenized again to form an emulsion again. The cycle can be repeated at least 5 times.

[0063] The above demonstrates that PND-DEX-stabilized DEX / PEG emulsions exhibit pH responsiveness.

[0064] 4. Temperature Response The prepared emulsions were placed in environments of 25℃ and 45℃ for stability experiments, and their microstructure was observed using a super depth-of-field three-dimensional microscope.

[0065] The results are as follows Figure 12 As shown, the increase in temperature will accelerate the demulsification of the emulsion and destroy its stability. The precipitation of the DEX-rich phase can be clearly observed at 45°C.

[0066] Comparative Example 1: Comparison of microgels containing DEX and those without DEX under a certain ionic strength Based on Example 1, N,N-methylenebisacrylamide was used to replace DEX-MA in step (1) of 3, while keeping the other steps the same, to prepare microgel PND.

[0067] Microgel PND and PND-DEX prepared in Example 1 were respectively prepared into aqueous solutions (0.2 wt%), and then equal amounts of NaCl were added to them and the pH was further adjusted (0.1 g NaCl, pH3 and pH9).

[0068] The results are as follows Figure 10 As shown, the results indicate that a large amount of white flocculent precipitate appeared in the aqueous solution of PND microgel, while the aqueous solution of PND-DEX microgel showed no significant change. This suggests that the addition of dextran enhanced the anti-ion ability of the microgel to a certain extent.

[0069] Comparative Example 2: Comparison of the ability of microgels containing DEX and those without DEX to stabilize water-in-water emulsions Water-in-water emulsions were prepared using the microgel PND obtained in Comparative Example 1 and the PND-DEX obtained in Example 1, respectively, according to the method in Example 1.

[0070] The results showed that, at the same microgel concentration, PND microgels could not stabilize water-in-water emulsions with dextran and polyethylene glycol as the two phases.

[0071] Example 8: Encapsulation of bovine serum albumin using a microgel-stabilized water-in-water Pickering emulsion The encapsulation effect of DEX / PEG water-in-water Pickering emulsion on bovine serum albumin was determined by the following steps: (1) Dissolve BSA in sodium carbonate-sodium bicarbonate buffer (0.1 mol·L⁻¹) -1 In a solution at pH 9.0, the concentration was adjusted to 2 mg / mL. -1 ; Dissolve fluorescein isothiocyanate (FITC) in dimethyl sulfoxide (DMSO) to a concentration of 1 mg·mL. -1 ; Add 50 μL of the above FITC solution to 1 mL of BSA solution (add 5 μL at a time, shake and mix well until the total volume reaches 50 μL), and stir at 4°C. o After being incubated overnight in the dark at C, the solution was dialyzed until no residual FITC was exudated, yielding a BSA fluorescent solution. (2) Weigh 0.005 g of PND-DEX (0.1 wt% of total mass) and disperse it in 4.5 g of ultrapure water. Sonicate for 1 min to obtain a microgel dispersion. (3) Weigh 0.35 g of PEG 20k and 0.15 g of DEX 500k (mass ratio 7:3) and dissolve them in the above microgel dispersion. Vortex for 3 min to ensure complete dissolution and mixing. Then add BSA fluorescent solution and homogenize at 12000 rpm for 3 min using a high-speed homogenizer to prepare a DEX / PEG water-in-water Pickering emulsion encapsulating bovine serum albumin. The results are as follows: Figure 13 As shown.

[0072] Example 9: Application of DEX / PEG water-in-water Pickering emulsion in the preparation of cosmetics The microgel prepared in Example 1 was used to prepare cosmetics, as follows: (1) Weigh 0.0025g of microgel and disperse it in 4.5g of ultrapure water, and sonicate for 1 min to obtain microgel dispersion.

[0073] (2) Weigh 0.35 g of PEG 20k and 0.15 g of DEX 500k (mass ratio of 7:3) and dissolve them in the above microgel dispersion. Vortex for 3 min to fully dissolve and mix them. Then add the water-soluble sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid and vortex for another 2 min to initially disperse the water-soluble sunscreen agent. Finally, use a high-speed dispersion homogenizer to homogenize at 12000 rpm for 3 min to prepare an oil-free sunscreen lotion.

[0074] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion, characterized in that, Including the following steps: (1) N-isopropylacrylamide, dimethylaminoethyl methacrylate and methacrylate-modified dextran were dissolved in water, and potassium persulfate was added after reflux under nitrogen. The mixture was magnetically stirred to obtain a mixture. The mixture was dialyzed and freeze-dried to prepare poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel. (2) Poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel was dispersed in water to obtain a microgel dispersion; polyethylene glycol 20k (PEG 20k) and dextran 500k (DEX 500k) were added to the microgel dispersion and mixed evenly and homogenized to obtain a water-in-water Pickering emulsion with responsive hydrophilic microgel stability.

2. The method according to claim 1, characterized in that, In step (1), the ratio of N-isopropylacrylamide, dimethylaminoethyl methacrylate, methacrylate-modified dextran, and water is 0.2~0.8 g : 1.0~0.3 g : 0.2~0.8 g : 80~120 mL; Optionally, in step (1), the reflux condensation is performed at 65~75 ℃ for 240~360 min; Optionally, in step (2), the ratio of PEG 20k, DEX 500k, poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel and water is 0.3~1.0 g: 0.1~0.5 g: 0.0025~0.02 g: 4.5~3.5 g.

3. The method according to claim 1, characterized in that, The preparation method of methacrylate-modified dextran is as follows: DEX 70k was dissolved in water, N,N-dimethylformamide was added and stirred; then methacrylic anhydride was added, the pH was adjusted, and the reaction was carried out to obtain a reaction solution; the reaction solution was dialyzed and freeze-dried to obtain methacrylate-modified dextran; Optionally, the ratio of DEX 70000, N,N-dimethylformamide, methacrylic anhydride and water is 5 g: 50 mL: 2~5 g: 80~120 mL.

4. The method according to claim 1, characterized in that, In step (2), PEG20k and DEX 500k are added to the microgel dispersion and mixed evenly. Then, active substances can be added further and homogenized to obtain a water-in-water Pickering emulsion with responsive hydrophilic microgel encapsulated with active substances.

5. The method according to claim 7, characterized in that, The active ingredients include bovine serum albumin, hydrolyzed collagen, hydroxytyrosol, and 2-phenylbenzimidazole-5-sulfonic acid.

6. The responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion prepared by the method according to any one of claims 1 to 5.

7. The application of the responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion according to claim 6 in the preparation of cosmetics, pharmaceuticals, and food.

8. A cosmetic product, characterized in that, The cosmetic contains the responsive hydrophilic microgel-stabilized water-in-water Pickering emulsion as described in claim 6.

9. A medicine, characterized in that, The drug contains the water-in-water Pickering emulsion stabilized by the responsive hydrophilic microgel as described in claim 6.

10. A method for improving the performance of water-in-water Pickering emulsions, said performance including stability under low pH conditions, pH responsiveness, salt ion responsiveness, and temperature responsiveness, characterized in that, The preparation of a water-in-water Pickering emulsion using methacrylate-modified dextran includes the following steps: (1) N-isopropylacrylamide, dimethylaminoethyl methacrylate and methacrylate-modified dextran were dissolved in water, and potassium persulfate was added after reflux under nitrogen. The mixture was magnetically stirred to obtain a mixture. The mixture was dialyzed and freeze-dried to prepare poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel. (2) Poly(N-isopropylacrylamide-co-dimethylaminoethyl methacrylate)-dextran microgel was dispersed in water to obtain a microgel dispersion; PEG 20k and DEX 500k were added to the microgel dispersion, and the mixture was mixed evenly and homogenized to obtain a water-in-water Pickering emulsion with responsive hydrophilic microgel stability.

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