Microcapsules, their preparation and use

Abstract

The application provides a microcapsule and preparation and application thereof. The microcapsule comprises a core layer and a shell layer in a volume ratio of 3.4-3.8:0.8-1.2; wherein the core layer comprises 8wt%-12wt% of polyvinyl alcohol (PVA), 4wt%-6wt% of a density enhancer and 0.1wt%-0.3wt% of an active substance, and the balance is water; and the shell layer comprises an elastomer precursor, a curing agent and silicone oil in a mass ratio of 9-11:0.8-1.2:2.5-3. The microcapsule of the application can completely release the active ingredient within a few milliseconds, and the release process has a strong mechanical stimulation intensity on the surrounding environment. When applied in the field of medicines and cosmetics, the microcapsule can further improve the absorption efficiency of the active ingredient; and when applied in the field of food, the microcapsule can provide a unique sensory experience.

Description

Technical Field

[0001] This invention belongs to the field of microcapsule preparation technology. More specifically, it relates to a microcapsule, its preparation, and its application. Background Technology

[0002] Microencapsulation is a technology that encapsulates trace amounts of substances within polymer films, providing miniature packaging for storing solids, liquids, and gases. Specifically, it involves completely encapsulating a target substance (core or inner phase) with a continuous film (wall or outer phase) of various natural or synthetic polymer compounds without compromising its original chemical properties. The substance's function is then gradually revealed through external stimuli or sustained-release mechanisms, or the capsule wall acts as a shield to protect the core material.

[0003] Currently, microcapsules are widely used in cosmetics, pharmaceuticals, and food. In cosmetics, microcapsules are typically added to products such as toners, lotions, serums, creams, masks, foundations, eyeshadows, and powders. This is primarily to encapsulate active ingredients using microencapsulation technology, preventing interference between various components and improving the stability of active ingredients. In pharmaceuticals, microcapsules are used to prevent the inactivation of active ingredients, mask unpleasant odors, provide sustained-release, controlled-release, or targeted effects, or reduce incompatibilities in compound formulations. In food, microcapsules are typically used to better integrate natural flavorings and bioactive substances into food systems while maintaining their bioactivity.

[0004] To achieve rapid release of active ingredients from microcapsules, self-rupturing or self-exploding microcapsules have emerged. However, since most microcapsules rely on the slow diffusion of active ingredients rather than rapid convection during the release process, their release rate is limited, and complete release can take several seconds or even minutes. For example, existing microcapsules with polyelectrolyte membranes require several seconds to release the active ingredient, and the rupture process is mild, resulting in weak mechanical stimulation of the surrounding environment. Therefore, they cannot further promote the absorption of active ingredients or provide a unique sensory experience through ultra-fast release and mechanical stimulation. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a microcapsule that can completely release active ingredients within milliseconds, and the release process generates strong mechanical stimulation to the surrounding environment. When applied to the pharmaceutical and cosmetic fields, it can further improve the absorption efficiency of active ingredients, and when applied to the food field, it can provide a unique sensory experience.

[0006] The primary objective of this invention is to provide a microcapsule.

[0007] A second objective of this invention is to provide a method for preparing the aforementioned microcapsules.

[0008] A third objective of this invention is to provide the application of the above-described microcapsules in the fields of cosmetics, pharmaceuticals, and / or food.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution:

[0010] The present invention provides a microcapsule comprising a core layer and a shell layer in a volume ratio of 3.4–3.8:0.8–1.2;

[0011] The core layer contains 8wt%–12wt% polyvinyl alcohol (PVA), 4wt%–6wt% density enhancer, and 0.1wt%–0.3wt% active ingredient, with the balance being water; the shell layer contains an elastomer precursor, curing agent, and silicone oil in a mass ratio of 9–11:0.8–1.2:2.5–3.

[0012] The microcapsules of this invention not only maintain high mechanical stability without mechanical stress, effectively preserving the active ingredient within the cavity without leakage, but also completely release the active ingredient within milliseconds when mechanical pressure exceeds the critical stress for microcapsule rupture. Furthermore, the release process generates a strong mechanical stimulus to the surrounding environment. In pharmaceuticals and cosmetics, this further enhances the absorption efficiency of active ingredients, while in the food industry, it provides a unique sensory experience. The microcapsules of this invention are highly perceptible to both touch and sight. Because the microcapsules are soft and elastic, they leave no foreign body residue after rupture, preventing user discomfort and enhancing the visual aesthetic value of the final product.

[0013] Preferably, the volume ratio of the core layer to the shell layer is 3.6:1.

[0014] Preferably, the core layer comprises 10 wt% PVA, 5 wt% density enhancer, and 0.2 wt% active ingredient, with the balance being water.

[0015] Preferably, the shell layer comprises an elastomer precursor, a curing agent, and silicone oil in a mass ratio of 10:1:2.75. After curing, the elastomer precursor forms an elastic shell, which can effectively preserve the active ingredient within the inner cavity of the microcapsule.

[0016] Preferably, the osmotic pressure of the core layer is adjusted by an osmotic pressure regulator, such as a sodium chloride solution, most preferably a sodium chloride solution of 1 to 1.1 mol / L.

[0017] Preferably, the osmotic pressure of the core layer is 2200-2280 mOSM / L, and most preferably 2240 mOSM / L.

[0018] Preferably, the density enhancer is one or more of sucrose, glucose, maltose, fructose, glycerol or PEG, with sucrose being the most preferred.

[0019] Preferably, the elastomer precursor is polydimethylsiloxane (PDMS). PDMS has a sufficiently low viscosity, making it suitable for microfluidic operations, and after curing, it can provide a stable elastomer for microcapsules; moreover, both PDMS and silicone oil have excellent biocompatibility, making them suitable as raw materials for cosmetics, pharmaceuticals, and food.

[0020] Preferably, the curing agent is a reagent that can cure elastomer precursors, such as a reagent that can cure PDMS, and more preferably a reagent that can cure PDMS within 2.5 to 3.5 hours at 45 to 55°C.

[0021] Preferably, the expansion degree α of the microcapsule is greater than 1.63, and most preferably it is 2.53 to 3.59.

[0022] The term "expansion degree" refers to the volume ratio of an expanded microcapsule to an unexpanded microcapsule. Expanded microcapsules maintain the integrity and mechanical properties of their elastic shell even without mechanical stress, thus safely storing the active ingredient within the cavity without leakage. When the deformation exceeds the mechanical rupture threshold of the elastic shell (e.g., when applying or chewing a product containing microcapsules, the mechanical pressure on the elastic shell exceeds the critical stress for microcapsule rupture), the microcapsule ruptures, violently releasing the active ingredient from the core layer within milliseconds. This mechanically stimulates the surrounding environment, restores the stress-free state, and the rapid retraction of the elastic shell converts its elastic potential energy into significant mechanical energy, generating a strong mechanical stimulus to the surrounding environment. In pharmaceuticals and cosmetics, this can further enhance the absorption efficiency of active ingredients; in the food industry, it can provide a unique sensory experience. The critical strain and stress causing microcapsule rupture decrease with increasing expansion degree of the elastic shell. Furthermore, the higher the expansion degree of the elastic shell, the faster the microcapsule release rate and the greater the mechanical stimulus to the surrounding environment.

[0023] The present invention also provides a method for preparing the above-mentioned microcapsules, wherein a double emulsion droplet is first prepared by a microfluidic device, and then the microcapsules are obtained by heat treatment.

[0024] Preferably, the microfluidic device includes an injection capillary, a collection capillary, and an outermost square capillary. The injection capillary and the collection capillary are inserted from both sides of the square capillary and spaced apart to form an emulsification zone. The ends of the injection capillary and the collection capillary within the emulsification zone are both tapered.

[0025] The microfluidic device of this invention consists of glass capillaries. The injection capillary and the collection capillary can be cylindrical capillaries, and the tapered ends of the injection capillary and the collection capillary are arranged coaxially opposite each other, forming a tip-to-tip structure in the square capillary. Using this device, microcapsules can be prepared with more uniform size.

[0026] More preferably, the core material is injected through an injection capillary, the shell material is injected through the gap between the injection capillary and the square capillary, and the continuous phase is injected through the gap between the collection capillary and the square capillary; the continuous phase raw material contains 8wt% to 12wt% PVA (most preferably 10wt%), with the balance being water.

[0027] More preferably, the flow rates of the core material, shell material, and continuous phase are 170–180 μL / h, 170–180 μL / h, and 5800–6200 μL / h, respectively, with the most preferred values ​​being 175 μL / h, 175 μL / h, and 6000 μL / h, and the flow rates are controlled by an injection pump.

[0028] Preferably, the heat treatment involves heating at 45–55°C for 2.5–3.5 hours, and most preferably at 50°C for 3 hours. The heat treatment is to solidify the elastomeric precursor in the shell material, forming a semi-permeable elastic shell, thereby obtaining a core-shell structured microcapsule.

[0029] More preferably, the heat treatment is performed simultaneously with stirring, such as at a speed of 130–170 r / min. Stirring can prevent the double emulsion droplets from agglomerating due to hydrophobicity and better avoid uneven shell thickness caused by gravity.

[0030] Preferably, after the heat treatment, the microcapsules are further expanded.

[0031] More preferably, the expansion treatment method involves transferring the microcapsules to an aqueous solution containing 1.5 wt% to 2.5 wt% PVA (preferably 2 wt%), and adjusting the osmotic pressure of the aqueous solution to achieve an expansion degree of α > 1.63 (e.g., using a 110–130 mmol / L sodium chloride solution). Since the osmotic pressure of the aqueous solution is much lower than that of the microcapsule core, water will flow inward, causing the microcapsules to expand due to the osmotic pressure difference. The degree of expansion is determined by the balance between the osmotic pressure difference and the shell wall tension. The expanded microcapsules have a low coefficient of variation (CV), indicating that the microcapsules are highly monodisperse and have a relatively uniform particle size.

[0032] The microcapsules of this invention not only maintain high mechanical stability without mechanical stress, effectively preserving the active ingredient within the cavity without leakage, thus serving as an excellent carrier for active ingredient delivery; but also completely release the active ingredient within milliseconds when mechanical pressure exceeds the critical stress for microcapsule rupture, with a strong mechanical stimulation to the surrounding environment during the release process. In the pharmaceutical and cosmetic fields, this further enhances the absorption efficiency of active ingredients, while in the food field, it provides a unique sensory experience. Therefore, the application of the aforementioned microcapsules in the cosmetic, pharmaceutical, and / or food fields should be within the scope of protection of this invention.

[0033] The present invention has the following beneficial effects:

[0034] The microcapsules of this invention not only maintain high mechanical stability without mechanical stress, effectively preserving the active ingredient within the cavity without leakage, but also completely release the active ingredient within milliseconds when mechanical pressure exceeds the critical stress for microcapsule rupture. Furthermore, the release process generates a strong mechanical stimulus to the surrounding environment. When applied to pharmaceuticals and cosmetics, this can further enhance the absorption efficiency of active ingredients, while in the food industry, it can provide a unique sensory experience. Therefore, the microcapsules of this invention serve as an excellent carrier for delivering active ingredients, suitable for the preparation of cosmetics, pharmaceuticals, and food. Attached Figure Description

[0035] Figure 1 a shows a schematic diagram and an optical microscope image of the formation of dual emulsion droplets in a microfluidic device; Figure 1 b is an optical microscope image of the S5 double emulsion droplet; Figure 1 c is a schematic diagram of the S6 microcapsule preparation process; Figure 1 d is a scanning electron microscope image of the microcapsules obtained from S6.

[0036] Figure 2 a is a schematic diagram of the entire process of a microcapsule going from not expanding to expanding to being compressed and bursting; Figure 2 b shows an optical microscope image of the microcapsule before it expands and a photograph of the balloon before it is inflated; Figure 2 c shows an optical microscope image of the microcapsule after expansion and a photograph of the balloon after inflation; Figure 2 d shows an optical microscope image of the microcapsule being compressed by a glass slide and a photograph of the balloon being squeezed. Figure 2 e shows an optical microscope image of the microcapsule after it bursts and a photograph of the balloon after it bursts.

[0037] Figure 3 a is a schematic diagram of the mechanical test of the microcapsules; Figure 3 b is an optical image of the deformation process of the microcapsule under different displacements; Figure 3 c represents the force-displacement curves of the microcapsules being compressed and relaxed under different displacements; Figure 3Threshold strain and stress diagrams for the bursting of 12 independent microcapsules with d = 2.53; Figure 3 e is a still image captured by a high-speed camera of the microcapsule bursting.

[0038] Figure 4 a represents the compressive force-strain curves of the microcapsules under different degrees of expansion; Figure 4 b is an electron micrograph of the deformation process of the microcapsules with α values ​​of 1 and 3.59; Figure 4 c is a bar chart of average strain versus expansion degree; Figure 4 d is a bar chart showing the stress and expansion degree during microcapsule rupture; Figure 4 e is a graph showing the effect of expansion degree on bursting time and mechanical potential energy generated by expansion; Figure 4 f represents the force-strain curves of freshly prepared microcapsules and microcapsules stored for 5 months; Figure 4 g represents the average strain and stress diagrams at the bursting of freshly made microcapsules and microcapsules stored for 5 months. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0040] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0041] Example 1: Preparation of Microcapsules

[0042] S1. Preparation of core layer material: Prepare an aqueous solution containing 10 wt% PVA (87%–89% hydrolyzed, weight average molecular weight 13,000–23,000), 5 wt% sucrose (Sigma-Aldrich), and 0.2 wt% green food coloring agent (representative active ingredient), and adjust its osmotic pressure to 2240 mOSM / L with 1 mol / L sodium chloride solution (Junsei).

[0043] S2. Preparation of shell material: PDMS (Sylgard 184, Dow Chemical), curing agent (Sylgard 184, Dow Chemical) and silicone oil (viscosity approximately 20 mPa·s, Sigma-Aldrich) were mixed at a mass ratio of 10:1:2.75.

[0044] S3. Preparation of the continuous phase: Prepare an aqueous solution containing 10 wt% PVA;

[0045] S4. Fabrication of the microfluidic device: Prepare two cylindrical glass capillaries (1B100F-6, World Precision Instruments) and one square glass capillary. Use a needle puller (P97, Sutter Instruments) to... (Instrument) Two cylindrical glass capillaries were drawn into a tapered shape at one end, and then the tapered capillaries were sanded to the required orifice diameter (100 μm for the injection capillary and 200 μm for the collection capillary). The injection capillary was then treated with octadecyltrimethoxysilane (Sigma-Aldrich) to make its surface hydrophobic, and the collection capillary was treated with 2-[methoxy(polyoxyethylene)propyl]trimethoxysilane (Gelest, Inc.) to make its surface hydrophilic. After treatment for 30 min, the injection capillary was cleaned with isopropanol and the collection capillary was cleaned with distilled water. After complete drying, the injection capillary and the collection capillary were inserted from both sides of a square capillary (1.05 mm inner diameter, Atlantic International Technologies) and spaced apart to form an emulsification zone, and arranged coaxially opposite each other with a 100 μm tip-to-tip distance.

[0046] S5. Preparation of the dual emulsion droplets: The core material obtained in S1 was injected through an injection capillary, the shell material obtained in S2 was injected through the gap between the injection capillary and the square capillary, and the continuous phase obtained in S3 was injected through the gap between the collection capillary and the square capillary. The flow rates of the core material, shell material and continuous phase were set to 175 μL / h, 175 μL / h and 6000 μL / h, respectively, using an injection pump (Legato 100, KD Scientific). (At this time, the average diameter of the dual emulsion droplets was 199 μm, the coefficient of variation (CV) was 1.8%, and the shell thickness was 7.8 μm).

[0047] S6. Preparation of microcapsules: The double emulsion droplets obtained in S5 were collected in a small bottle and placed in a water bath at 50℃ and 150r / min for 3h to solidify the PDMS shell.

[0048] The formation process of double emulsion droplets in a microfluidic device was observed using an inverted optical microscope (Eclipse TS100, Nikon) and a high-speed camera (Phantom v7.3, Vision Research Inc.), and a schematic diagram of the principle of double emulsion droplet formation in the microfluidic device was drawn, as shown below. Figure 1 As shown in Figure a; then, the S5 double emulsion droplet was observed using an inverted optical microscope, and the resulting optical microscope image is shown in Figure a. Figure 1 As shown in b, the dual emulsion droplets effectively encapsulate the contents (green food coloring agent) within the inner cavity; a schematic diagram of the S6 microcapsule preparation process is shown below. Figure 1 As shown in c; the scanning electron microscope image of the microcapsules obtained in S6 is shown in Figure 6. Figure 1 As shown in d, the microcapsules are uniform in size.

[0049] The microcapsules obtained from S6 were transferred to an aqueous solution containing 2 wt% PVA. The osmotic pressure of the aqueous solution was adjusted to 250 mOsm / L using a 120 mmol / L sodium chloride solution, so that the microcapsules were positioned at an osmotic pressure difference ΔC of 1990 mOsm / L. –1 In the environment, microcapsules undergo osmotic expansion (at which point the average diameter of the microcapsules is 306 μm, the coefficient of variation (CV) is 0.8%, and the shell thickness is 1 μm). They are then compressed using a pair of glass slides, inducing the microcapsules to burst and rapidly release their contents (green food coloring). A schematic diagram of this process is shown below. Figure 2 As shown in Figure a. Furthermore, the process was observed using an optical microscope, and the corresponding balloon states were used to better explain this process, resulting in the following... Figure 2 Images of microcapsule changes from b to 2e and corresponding balloon images, where... Figure 2 b shows an optical microscope image of the microcapsules obtained in S6 (in their uninflated state) and a photograph of the balloon in its normal state (uninflated). (The inset in the upper right corner is a photograph of a vial containing the uninflated microcapsules.) Figure 2 c shows an optical microscope image of the microcapsules after expansion and a photograph of the inflated balloon. Figure 2 d shows an optical microscope image of the microcapsules compressed by a glass slide and a photograph of the balloon being squeezed. Figure 2 e shows an optical microscope image of the microcapsules after they burst and a photograph of the balloon after it bursts (the inset in the upper right corner shows a photograph of a vial containing the burst microcapsules). This indicates that from... Figure 2 b's unexpanded state changes to Figure 2 During the bursting process of e, the microcapsule releases its contents (green food coloring agent) from its inner cavity.

[0050] Example 2: Preparation of Microcapsules

[0051] S1. Preparation of core layer material: Prepare an aqueous solution containing 8wt% PVA, 6wt% sucrose and 0.1wt% green food coloring agent, and adjust its osmotic pressure to 2280 mOSM / L with 1.1mol / L sodium chloride solution;

[0052] S2. Preparation of shell material: PDMS, curing agent and silicone oil are mixed in a mass ratio of 11:1.2:2.5;

[0053] S3. Preparation of the continuous phase: Prepare an aqueous solution containing 8 wt% PVA;

[0054] S4 and S5 are the same as in Example 1, except that the flow rates of the core material, shell material and continuous phase are set to 170 μL / h, 170 μL / h and 6200 μL / h, respectively.

[0055] S6. Preparation of microcapsules: The double emulsion droplets obtained in S5 were collected in a small bottle and incubated in a water bath at 45℃ and 170r / min for 3.5h.

[0056] Example 3: Preparation of Microcapsules

[0057] S1. Preparation of core layer material: Prepare an aqueous solution containing 12wt% PVA, 4wt% sucrose and 0.3wt% green food coloring agent, and adjust its osmotic pressure to 2200 mOSM / L with 1mol / L sodium chloride solution;

[0058] S2. Preparation of shell material: Mix PDMS, curing agent and silicone oil at a mass ratio of 9:0.8:3;

[0059] S3. Preparation of the continuous phase: Prepare an aqueous solution containing 12 wt% PVA;

[0060] S4 and S5 are the same as in Example 1, except that the flow rates of the core material, shell material and continuous phase are set to 180 μL / h, 180 μL / h and 5800 μL / h, respectively.

[0061] S6. Preparation of microcapsules: The double emulsion droplets obtained in S5 were collected in a small bottle and incubated in a water bath at 55℃ and 130r / min for 2.5h.

[0062] Test Example 1: Mechanical Properties of Microcapsule Shells

[0063] The expanded microcapsules maintain the integrity and mechanical properties of their elastic shell even without mechanical stress, thus safely storing the active ingredient within the cavity without leakage. When the deformation exceeds the mechanical breakage threshold of the elastic shell, the microcapsule bursts, violently releasing the active ingredient from the core layer within milliseconds, mechanically stimulating the surrounding environment. To quantitatively study its mechanical response, mechanical tests were conducted on individual microcapsules, as illustrated in the schematic diagram. Figure 3 As shown in Figure a, after the expanded microcapsules were compressed by mechanical force, the mechanical force was removed, and it was observed whether the microcapsules could return to their original shape.

[0064] The microcapsules obtained in S6 of Example 1 were transferred to an aqueous solution containing 2 wt% PVA, and the osmotic pressure difference ΔC of the aqueous solution was adjusted to 1740 mOs / ml using sodium chloride solution. –1The microcapsules underwent osmotic expansion, resulting in microcapsules with a diameter of 271 μm, a shell thickness of 4 μm, and an expansion degree α of 2.53. The microcapsules were then completely immersed in water, and the deformation was observed using a camera while the forces required for compression and relaxation were measured. The compression-relaxation rate was also measured. Set to 1.4 μm s -1 (equivalent to strain rate) It is 0.005s -1 This is to eliminate the dynamic effects of compression.

[0065] A single microcapsule was compressed and relaxed for four cycles, while the maximum displacement was increased from d = 125 μm to 150 μm, 175 μm, and 190 μm. Optical images of the microcapsule deformation process are shown below. Figure 3 As shown in b, the force-displacement curves for compression and relaxation (the horizontal axis represents the lateral displacement change of the microcapsule) are as follows: Figure 3 As shown in c. It can be seen that: (1) when the microcapsule is at the maximum displacement of d = 125 μm or the strain of ε = 0.447, it exhibits insignificant hysteresis. After one cycle of compression and relaxation, the microcapsule completely recovers its spherical shape; and the force-displacement curve during compression coincides with the force-displacement curve during relaxation; (2) when the microcapsule is at d = 150 μm (ε = 0.536) or d = 175 μm (ε = 0.625), after one cycle of compression and relaxation, the microcapsule does not completely recover its original spherical shape. Figure 3 (b) The dashed line represents the original spherical outline, and it can be seen that the relaxed microcapsule deviates from the original outline. Furthermore, the force-displacement curve during compression and the force-displacement curve during relaxation exhibit hysteresis, and the slope of both curves increases with the increase of vertical displacement. This is because under a large vertical displacement, the microcapsule needs to maintain its original internal volume in order to prevent leakage of active material, and thus naturally stretches more along the lateral direction. (3) When the microcapsule is at d = 190 μm (ε = 0.661), after one cycle of compression and relaxation, the microcapsule instantly shrinks back to the unexpanded state, and cracks in the outer shell of the microcapsule can be clearly observed. Before ejection, the compressive force is F. pop =89.2mN, which, when divided by the contact area between the microcapsule and the parallel plate, is converted into a stress of 0.491MPa. This indicates that the expanded microcapsules exhibit elastic deformation under pressure within the range of d≤125μm; under pressure within the range of d=150~175μm, plastic deformation occurs due to the lateral strain of the microcapsule shell exceeding the yield point, but the shell integrity is still maintained, preventing leakage of the green food coloring; under pressure within the range of d≥190μm, the lateral strain of the microcapsule shell exceeds the rupture point, causing the shell to rupture and release the green food coloring from the core layer.

[0066] The mechanical properties of the microcapsules obtained in S6 of Examples 2-3 were tested using the same method. The results were found to be similar to those of Example 1, indicating that the microcapsules of the present invention can maintain the integrity of the shell and prevent leakage of the core active material even under pressure in the range of d≤175μm.

[0067] Test Example 2: Ultrafast Release of Active Ingredients from Microcapsules

[0068] The microcapsules obtained in S6 of Example 1 were transferred to an aqueous solution containing 2 wt% PVA. The osmotic pressure of the aqueous solution was adjusted to 500 mOsm / L using a 120 mmol / L sodium chloride solution, so that the microcapsules were in an osmotic pressure difference ΔC of 1740 mOsm / L. –1 The microcapsules underwent permeable expansion in the environment, resulting in a diameter of 271 μm, a shell thickness of 4 μm, and an expansion degree α of 2.53.

[0069] Twelve independent microcapsules were dispensed at 0.05 s. -1 The microcapsules were compressed at the equivalent strain rate until they burst, and the threshold strain and stress were measured. The results are as follows: Figure 3 As shown in d (the horizontal line represents the average value), it can be seen that the average threshold strain ε leading to microcapsule rupture is... pop =0.75, stress 0.43MPa, strain ε pop The cv value is 10%, and the cv value of stress is 47%.

[0070] To measure the timescale of microcapsule bursting and investigate how microcapsules recover from their uninflated state, this test case used a pair of glass slides to compress the microcapsules while simultaneously observing them with a high-speed camera. The results are as follows: Figure 3 As shown in Figure e (when compression begins at t = 0 ms), it can be seen that: (1) the expanded microcapsule deforms into a disk shape under compression and ruptures at the thinnest point exceeding the threshold strain; (2) within t = 0 to 0.33 ms, the microcapsule contracts significantly and violently ejects water from its cavity; (3) within t = 0.33 to 1 ms, the microcapsule contracts further and water is rapidly ejected from its cavity; the ejection gradually stops at 1.67 ms. This indicates that the microcapsule of the present invention can achieve ultra-fast release of active ingredients within one millisecond under a certain external force.

[0071] The same method was used to test the ultrafast release of active ingredients in the microcapsules obtained in S6 of Examples 2-3. The results were found to be close to those of Example 1, indicating that the microcapsules of the present invention can achieve ultrafast release of active ingredients within one millisecond under a certain external force.

[0072] Test Example 3: The effect of the expansion degree of the elastic shell of the microcapsule on the mechanical stimulation generated by bursting.

[0073] After the microcapsules expand, their outer shell stretches, making them more sensitive to external mechanical stress. Upon rupture, the elastic potential energy within the microcapsules (including energy generated by osmotic expansion and compression deformation) is converted into mechanical potential energy, providing mechanical stimulation to the surrounding environment. To quantitatively study the effect of the degree of microcapsule expansion on its mechanical response, in this test example, the microcapsules obtained in S6 of Example 1 were transferred to an aqueous solution containing 2 wt% PVA. Five microcapsules were adjusted to different degrees of expansion using sodium chloride solutions of varying concentrations: 1, 1.34, 1.63, 2.53, and 3.59. The expansion was then measured at 0.05 s⁻¹. -1 Equivalent variable rate compression.

[0074] The obtained compressive force-strain curve is as follows Figure 4 As shown in Figure a (the bursting moment is indicated by an arrow), electron micrographs of the microcapsule deformation process with α values ​​of 1 and 3.59 are shown below. Figure 4 As shown in b (from uncompressed to compressed to bursting to removal of compressive force), the bar chart shows the average strain versus the degree of expansion. Figure 4 As shown in Figure c, the bar chart of stress versus expansion during bursting is as follows: Figure 4 As shown in Figure d, the effect of expansion degree on burst time / water jet cycle (measured by monitoring ejection behavior with a high-speed camera) and the mechanical potential energy converted from the elastic potential energy stored by the expansion of the microcapsules is shown in the figure. Figure 4 As shown in e.

[0075] It can be seen that: (1) for microcapsules with α≤1.34, the force does not decrease upon bursting; for microcapsules with α≥1.63, the force suddenly decreases upon bursting due to the ejection of water from the cavity; (2) when α=3.59, the strain ε during bursting is... pop =0.561, force F pop =47.2mN, the microcapsules rapidly shrink back to their original size and shape before expansion; (3) when the α value increases from 1 to 1.63, the average strain of the microcapsules during bursting increases from ε pop = 0.900 decreases slightly to 0.877; when the α value increases to 3.59, the average strain of the microcapsules during bursting decreases sharply to ε. pop=0.633; (4) When the value of α increases from 1 to 3.59, the average stress (force divided by contact area) of the microcapsule during bursting gradually decreases from 1.82 MPa to 0.39 MPa, indicating that the higher the degree of expansion, the more sensitive the microcapsule is to the external mechanical stress during bursting, and the degree of expansion significantly changes the dynamics of bursting; (5) When α = 1, the water injection cycle is as high as 184 ms, indicating that the release rate is not very fast without shell expansion; when α = 1.34, the rapid water injection cycle is 8.68 ms; when α = 3.59, The rapid water injection cycle is 1.45 ms; (6) The bursting time decreases as α increases, and the mechanical power generated by the permeation expansion of the microcapsule increases sharply as α increases; when α = 3.59, the mechanical power generated by the permeation expansion is 947 μW, which is 148 times that when α = 1.34; (7) The mechanical potential energy released by the bursting of the microcapsule is much greater than that generated by the permeation expansion alone, because the expanded microcapsule will be further deformed under compression, and the compression deformation will also generate mechanical potential energy, so that the microcapsule stores more elastic potential energy when bursting. This indicates that when the expansion degree of the microcapsule α ≥ 1.34, preferably ≥ 1.63, especially when α is 2.53 to 3.59, under the condition that the mechanical pressure exceeds the critical stress of the microcapsule bursting, the microcapsule can completely release the active ingredient within a few milliseconds, and the release process has a strong mechanical stimulation intensity on the surrounding environment. When applied to the pharmaceutical and cosmetic fields, it can further improve the absorption efficiency of the active ingredient, and when applied to the food field, it can provide a unique sensory experience.

[0076] The same method was used to test the effect of the expansion degree of the elastic shell of the microcapsule obtained in S6 of Examples 2-3 on the mechanical stimulation generated by the burst. The results showed that the results were close to those of Example 1, indicating that the microcapsules of the present invention can completely release the active ingredients within a few milliseconds when the mechanical pressure exceeds the critical stress for microcapsule bursting, and the release process has a strong mechanical stimulation intensity on the surrounding environment. When applied to the pharmaceutical and cosmetic fields, it can further improve the absorption efficiency of the active ingredients, and when applied to the food field, it can provide a unique sensory experience.

[0077] Test Example 4: Stability of mechanical stimulation generated by microcapsule rupture

[0078] Microcapsules with α = 2.53 prepared according to the method of Test Example 2 were stored at 25°C for 5 months and then compressed with the same strain as expanded microcapsules prepared by the same method.

[0079] The obtained force-strain curve is as follows Figure 4 As shown in f (the moment of bursting is indicated by an arrow), the average strain and stress measurement results are as follows: Figure 4As shown in g, the results of microcapsules stored for 5 months are similar to those of freshly prepared expanded microcapsules, with no significant difference. This indicates that when the external force strain on the expanded microcapsules is below the yield point, the deformation is perfectly elastic, and long-term storage does not change the mechanical properties of the shell. That is, even after long-term storage, they can still generate strong mechanical stimulation to the surrounding environment upon bursting, which can further enhance the absorption efficiency of active ingredients or provide a unique sensory experience, demonstrating excellent stability.

[0080] The stability of the mechanical stimulation generated by the bursting of the microcapsules obtained in S6 of Examples 2-3 was tested using the same method. The results were found to be similar to those of Example 1, indicating that the mechanical properties of the outer shell of the microcapsules of the present invention do not change during long-term storage. That is, after long-term storage, they can still generate strong mechanical stimulation to the surrounding environment when they burst, which can further improve the absorption efficiency of active ingredients or provide a unique sensory experience, and have excellent stability.

[0081] Test Example 5: Sensory Experience of Using Microcapsules

[0082] The microcapsules obtained in S6 of Example 1 were transferred to an aqueous solution containing 2 wt% PVA. The microcapsules were then osmotically swelled using sodium chloride solution, resulting in microcapsules with a diameter of 795 μm and a swelling degree α of 3.59. The microcapsules were then applied to the skin and gently rubbed back and forth with a finger for 15 cycles (shear rate approximately 2.5 cm / s). -1 The study found that the microcapsules are very soft and elastic, providing a comfortable touch to the skin. Friction causes the microcapsules to burst, which not only releases the green food coloring agent (active substance) very quickly, but also allows the skin to feel the mechanical energy generated by the burst. Furthermore, the burst does not leave any foreign body sensation on the skin.

[0083] The sensory experience of the microcapsules obtained in S6 of Examples 2-3 was tested using the same method. The results were similar to those of Example 1, indicating that the microcapsules of the present invention can not only release green food coloring agents (active substances) at an ultra-fast speed, but also allow the skin to feel the mechanical energy generated by the bursting, and will not leave any residual foreign body sensation on the skin after bursting.

[0084] In summary, the microcapsules of this invention not only maintain high mechanical stability without mechanical stress, effectively preserving the active ingredient within the cavity without leakage, but also completely release the active ingredient within milliseconds when mechanical pressure exceeds the critical stress for microcapsule rupture. Furthermore, the release process generates strong mechanical stimulation to the surrounding environment. When applied to pharmaceuticals and cosmetics, this can further enhance the absorption efficiency of active ingredients, while in the food industry, it can provide a unique sensory experience. Therefore, the microcapsules of this invention serve as an excellent carrier for delivering active ingredients, suitable for the preparation of cosmetics, pharmaceuticals, and food.

[0085] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A microcapsule, characterized in that, It contains a core and shell with a volume ratio of 3.4–3.8:0.8–1.2; The core layer comprises 8wt%–12wt% polyvinyl alcohol, 4wt%–6wt% density enhancer, and 0.1wt%–0.3wt% active ingredient, with the balance being water; the shell layer comprises PDMS, curing agent, and silicone oil in a mass ratio of 9–11:0.8–1.2:2.5–3; the density enhancer is sucrose; the expansion degree α of the microcapsule is ≥1.

34. The microcapsules are prepared by first preparing double emulsion droplets using a microfluidic device, followed by heat treatment and then expansion treatment to obtain microcapsules.

2. The microcapsule according to claim 1, characterized in that, The curing agent is a reagent that can cure PDMS.

3. The microcapsule according to claim 1, characterized in that, The expansion degree α of the microcapsule is greater than 1.

63.

4. The microcapsule according to claim 1, characterized in that, The microfluidic device includes an injection capillary, a collection capillary, and an outermost square capillary. The injection capillary and the collection capillary are inserted from both sides of the square capillary and spaced apart to form an emulsification zone. The ends of the injection capillary and the collection capillary within the emulsification zone are both tapered.

5. The microcapsule according to claim 4, characterized in that, The core material is injected through an injection capillary, the shell material is injected through the gap between the injection capillary and the square capillary, and the continuous phase is injected through the gap between the collection capillary and the square capillary.

6. The microcapsule according to claim 1, characterized in that, The heat treatment is performed by heating at 45–55 °C for 2.5–3.5 h.

7. The use of the microcapsules according to any one of claims 1 to 6 in the fields of cosmetics, pharmaceuticals and / or food.

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