Microneedle patch provided with porous microneedles, and method for manufacturing said microneedle patch

Abstract

[Problem] To provide a microneedle patch having porous microneedles capable of collecting and storing interstitial fluid, and a method for manufacturing the microneedle patch. [Solution] Provided is a microneedle patch with porous microneedles and an absorbent material capable of absorbing interstitial fluid, wherein the microneedles and the absorbent material are integrated.

Description

Microneedle patch with porous microneedles and method for manufacturing the same

[0001] The present invention relates to a microneedle patch comprising porous microneedles and a method for manufacturing the microneedle patch.

[0002] Preventive medicine is becoming increasingly important due to factors such as an aging society and the rise in lifestyle-related diseases. In today's technologically advanced world, early detection and appropriate treatment of diseases can prevent the condition from worsening and can significantly contribute to improving people's quality of life and survival rates after the disease is discovered.

[0003] Biomarker analysis is one method for early detection. This involves collecting biological fluids such as blood or tissues and examining components that indicate physiological characteristics in order to evaluate the state and progression of a disease. Blood is widely used for collecting biological fluids, but the method of collection, subcutaneous injection, is painful and invasive, and requires medical professionals to perform the collection. Therefore, alternative methods for collecting biological fluids are needed.

[0004] Although urine and tears are other biological fluids that can be collected besides blood, interstitial fluid is considered particularly effective for biomarker analysis (Non-patent Document 1). Interstitial fluid is tissue fluid that seeps from blood vessels into cells and is present in the skin. The components contained in interstitial fluid are similar to those in serum and plasma, and it has attracted attention as a biological fluid that can replace blood (Non-patent Document 2).

[0005] There are various methods for collecting interstitial fluid, but microneedle extraction has been particularly well-researched. Microneedles allow for the collection of interstitial fluid from the skin without reaching nerves or blood vessels, resulting in minimal pain and invasiveness. Porous microneedles, in particular, utilize capillary force to collect interstitial fluid due to their porous needles, enabling rapid collection. However, conventional porous microneedle patches are interstitial fluid collection systems that simply stack a microneedle array and filter paper. While they can diagnose even minute amounts, they are limited to on-site diagnosis and monitoring of diseases that require minute amounts of interstitial fluid. Therefore, creating a patch that can collect, store, and transport interstitial fluid regardless of the collection site would enable analysis at specialized institutions and expand the potential for biomarker analysis using interstitial fluid. However, such an interstitial fluid collection system has yet to be realized.

[0006] J. Heikenfeld et al, "Accessing analytes in biofluids for peripheral biochemical monitoring," Nature Biotechnology, vol. 37(4), pp. 407-419, 2019.PR Miller et al, "Extraction and biomolecular analysis of dermal interstitial fluid collected with hollow microneedles," Communications Biology, vol. 1(1), 173, 2018.

[0007] An object of the present invention is to provide a microneedle patch having porous microneedles that enable the collection and storage of interstitial fluid, and a method for manufacturing such a microneedle patch. Another object of the present invention is to provide a microneedle patch having porous microneedles that have greater strength than conventional porous microneedles, and a method for manufacturing such a microneedle patch.

[0008] After extensive research, the inventors discovered that the above-mentioned problems can be solved by a microneedle patch that integrates a dual structure of porous microneedles and an absorbent material capable of absorbing interstitial fluid, and thus completed the present invention. Furthermore, the inventors discovered that by using monodisperse fine particles of a biodegradable material with a uniform particle size, it is possible to provide a microneedle patch equipped with porous microneedles that have greater strength than conventional porous microneedles, and thus completed the present invention.

[0009] That is, the present invention has the following configurations. [1] A microneedle patch comprising porous microneedles and an absorbent material capable of absorbing interstitial fluid, the microneedles and the absorbent material being integrated. [2] The microneedle patch according to [1], wherein the microneedles are formed by bonding microspheres of a biodegradable material to each other to form a network of interconnected pores. [3] The microneedle patch according to any one of [1] to [2], wherein the biodegradable material includes at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG (polyethylene glycol), polyhydroxybutyric acid, and ethyl cellulose. [4] The microneedle patch according to any one of [1] to [3], wherein the microneedles are surface-modified with ethanol which may contain a hydrophilic substance. [5] The microneedle patch according to any one of [1] to [4], further comprising a microneedle substrate, the microneedles being bonded to the microneedle substrate. [6] A microneedle patch comprising porous microneedles and an absorbent material capable of absorbing interstitial fluid, wherein the microneedles are formed by thermally bonding monodisperse microparticles made of a biodegradable material. [7] The microneedle patch according to [6], wherein the monodisperse microparticles are prepared using microfluidics. [8] The microneedle patch according to [6] or [7], wherein the monodisperse microparticles are a mixture of two or more types of monodisperse microparticles having different average particle sizes. [9] The microneedle patch according to any one of [6] to [8], wherein the biodegradable material contains at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG (polyethylene glycol), polyhydroxybutyric acid, and ethyl cellulose.

[10] The microneedle patch according to any one of [6] to [9], wherein the microneedles are surface-modified with ethanol or the like which may contain a hydrophilic substance.

[11] The microneedle patch according to any one of [6] to

[10] , wherein the microneedles and the absorbent material are integrated.

[12] The microneedle patch according to any one of [6] to

[11] , further comprising a microneedle substrate, the microneedles being bonded to the microneedle substrate.

[13] A method for manufacturing a microneedle patch, comprising: (a) pouring a biodegradable material microsphere solution or suspension containing biodegradable material microspheres into a female mold; (b) placing an absorbent material capable of absorbing interstitial fluid on the mold into which the solution or suspension has been poured; and (c) drying the solution or suspension and the absorbent material, and then baking the resulting mixture at a predetermined temperature.

[14] The manufacturing method according to

[13] , comprising pouring the solution or suspension into the female mold and then removing a portion of the solution or suspension.

[15] The manufacturing method according to

[13] or

[14] , wherein the biodegradable material microsphere solution or suspension is prepared by preparing a solution A by dissolving a biodegradable material in an organic solvent, mixing the solution A with an aqueous solution containing a surfactant, evaporating the organic solvent, and stirring.

[16] The manufacturing method according to any one of

[13] to

[15] , wherein the microneedle patch has the microneedles and the absorbent material integrated together.

[17] The microneedle patch obtained by the manufacturing method according to any one of

[13] to

[16] .

[18] The manufacturing method of a microneedle patch, comprising: (a) filling a female mold with monodisperse microparticles of a biodegradable material; (b) placing an absorbent material capable of absorbing interstitial fluid on the mold filled with the monodisperse microparticles; and (c) thermally bonding the monodisperse microparticles.

[19] The manufacturing method according to

[18] , wherein the monodisperse microparticles are obtained from microdroplets generated using microfluidics technology.

[20] The manufacturing method according to

[18] or

[19] , wherein the monodisperse microparticles are a mixture of two or more types of monodisperse microparticles having different average particle diameters.

[21] A microneedle patch obtained by the manufacturing method according to any one of

[18] to

[20] .

[0010] The present invention can provide a microneedle patch equipped with porous microneedles that enable collection and storage of interstitial fluid. The present invention can also provide a method for easily manufacturing such a microneedle patch. The present invention can also provide a microneedle patch equipped with porous microneedles that have greater strength than conventional porous microneedles. The present invention can also provide a method for easily manufacturing such a microneedle patch.

[0011] 1 shows a schematic diagram of a method for preparing monodisperse microparticles of biodegradable material by a flow focusing method. 2 shows a schematic diagram of a non-limiting example of a method for preparing microneedles 2 of the present invention using monodisperse microparticles. 3 shows a schematic diagram of the fabrication process of the microneedle patch of the present invention in Example 1. 4 shows a cross-sectional view of the microneedle patch fabricated in Example 1. 5 shows microneedle patches fabricated for each set parameter. 6 shows patches (a), (b), (c), and (d) after puncturing for 5 minutes (left photo: needle side, right photo: absorbent side). 7 shows a schematic diagram of generating microdroplets using microfluidic technology. 8 shows a schematic diagram of a method for fabricating porous MNs using PLA microspheres. 9 shows SEM images of PLA microspheres with different diameters. 10 shows optical microscope images of microneedles fabricated in Example 2. 11 shows the extracted volume and porosity of MNs fabricated using microspheres of different sizes in Example 2. Modes for carrying out the invention

[0012] <Microneedle Patch of Embodiment 1> One embodiment of the present invention is a microneedle patch comprising porous microneedles and an absorbent material capable of absorbing interstitial fluid, the microneedles and the absorbent material being integrated together (hereinafter also referred to as the "microneedle patch of embodiment 1"). Hereinafter, the microneedle patch of embodiment 1 will be described in detail for each component.

[0013] 1. Microneedles (1) Structure and Properties of Microneedles The microneedles used in the microneedle patch of embodiment 1 (hereinafter also referred to as "microneedles of embodiment 1") are porous and are mainly made of a biodegradable material.

[0014] The biodegradable material constituting the microneedle of embodiment 1 includes at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide), PEG (polyethylene glycol), polyhydroxybutyric acid, and ethyl cellulose. The microneedle of embodiment 1 may be composed solely of the biodegradable material, or may contain trace amounts of raw materials used in the method for producing the microneedle of embodiment 1 described below (e.g., polyvinyl alcohol, methyl cellulose, sorbitan fatty acid esters, sorbitan monooleate, surfactants such as sodium dodecyl sulfate and hexadecyltrimethylammonium bromide), or other additives (e.g., carboxymethylcellulose (CMC), hyaluronic acid), to the extent that the function of the microneedle of embodiment 1 is not impaired. Furthermore, at least a portion of the microneedle of embodiment 1 may be coated with a coating agent so as not to impair its function. Materials commonly used in this technical field (e.g., CMC, hyaluronic acid, etc.) can be used as the coating agent.

[0015] As the microneedle of embodiment 1, various manufacturing methods, for example, microneedles obtained by the salt leaching method described in Japanese Patent No. 7129720 can be used, but it is preferable to use microneedles obtained by the microsphere method developed by the inventors' previous research (details of which are described in International Publication No. 2023 / 021665). That is, the microneedle of embodiment 1 is preferably formed from a microsphere of a biodegradable material. Specifically, the microneedle of embodiment 1 is preferably manufactured using a microsphere of a biodegradable material.

[0016] As used herein, the term "microsphere" refers to spherical fine particles having an average particle size on the order of μm (preferably 1 to 100 μm, more preferably 5 to 30 μm, and even more preferably 10 to 20 μm). The average particle size is usually determined by measurement using an optical microscope.

[0017] In the microneedle of embodiment 1, preferably, microspheres of a biodegradable material are bonded to each other to form a network of interconnected pores. In the salt-leaching method using water-soluble particles such as sodium chloride, a biodegradable material and water-soluble particles are typically mixed, the mixture is filled into a dispenser or the like, droplets are ejected, and the mixture is shaped into a microneedle. The mixture is then immersed in water to dissolve the water-soluble particles. When the water-soluble particles are removed, the sites where the water-soluble particles were present become voids, resulting in a porous microneedle (see, for example, WO 2019 / 176126). In contrast, microneedles manufactured by the microsphere method involve injecting a solution of microspheres of a biodegradable material into a female mold and drying to obtain a microneedle precursor, which is then heated to approximately 150 to 250°C to bond the microspheres to each other, forming a network of interconnected (communicating) continuous pores. This results in a robust pore structure in the microneedle of embodiment 1.

[0018] In the microneedle of embodiment 1, it is not necessary for all microspheres to be bonded to each other, but it is preferable that the microspheres constituting the microneedle precursor are in a state where they can be confirmed to be bonded to each other by heating using an electron microscope or the like.

[0019] The porosity of the microneedle of embodiment 1 is usually 10 to 40%, preferably 20 to 30%. Here, the porosity is measured by the following procedure, comparing the mass before and after fluid extraction using a water absorption method using a porous membrane (see P. Liu, et al., J Mater Chem B, 2020). First, the dry mass (W ｄｒｙThe mass is then measured immediately and the W ｗｅｔ Record as Calculate the porosity using the following formula:

[0020]

[0021] In formula (1), ρ ｐ is the density of the biodegradable material, ρ ０ is the density of DI water (1.0 g / cm ３ )

[0022] Absorption volume is one indicator of water absorption capacity, and the absorption volume of the microneedle of embodiment 1 is usually 10 to 150 μL, preferably 60 to 120 μL. Here, the absorption volume is measured by puncturing a microneedle array in which 169 porous PLA MNs are arranged upright in a 1% agarose gel, removing it from the gel after 2 minutes, and measuring its weight.

[0023] The microneedle of embodiment 1 typically has an absorption rate of 0.01 to 0.3 μL / min, preferably 0.2 to 0.3 μL / min, per MN. The absorption rate is measured by puncturing a microneedle array of 169 porous PLA MNs upright in a 1% agarose gel, removing the MN from the gel after 2 minutes, and measuring its weight.

[0024] (2) Shape of the microneedle of embodiment 1 The shape of the microneedle of embodiment 1 can be an approximately conical shape, an approximately pyramidal shape, or the like, but a polygonal shape (e.g., an approximately pyramidal shape) is preferred because it penetrates the skin more easily than an approximately conical shape.

[0025] The diameter of the tip of the microneedle of embodiment 1 is usually 10 μm to 60 μm. The diameter or maximum dimension of the base is, for example, about 50 μm to 800 μm. The height of the microneedle determines the depth of penetration into the skin. In the microneedle of the present invention, the diameter is preferably 300 μm or more and 1500 μm or less, taking into consideration that it can reach the dermis without stimulating pain sensation.

[0026] When multiple microneedles are provided, the smaller the spacing is, the better for absorbing the interstitial fluid sample, and spacing of 500 to 5000 μm is preferred.

[0027] Regarding the angle of the tip of the microneedle in embodiment 1, a larger angle increases the mechanical strength, but a larger tip angle also increases the force required for penetration. A tip angle of 15 to 30° is preferred, as the force required for the microneedle to penetrate is less than 0.2 N.

[0028] (3) Surface Modification of Microneedles of Embodiment 1 In another preferred aspect of the present invention, the microneedles of embodiment 1 are surface-modified. That is, since biodegradable materials such as polylactic acid (PLA) are not hydrophilic, porous microneedles are usually hydrophilized by plasma treatment before use. However, this does not necessarily mean that the interior of the porous needle can be hydrophilized, and plasma treatment alone will cause the surface properties to be lost over time. The present inventors have investigated this issue and found that surface modification of porous microneedles with ethanol, which may contain a hydrophilic substance such as ethanol or a PEG-ethanol solution (i.e., an ethanol solution containing a hydrophilic substance such as ethanol or PEG), can result in extremely high absorption capacity. Solvents such as ethanol can be completely evaporated by drying at an elevated temperature. As explained above, the microneedles of embodiment 1 may be at least partially coated with a coating agent without impairing their function, but the coating with a coating agent is intended to harden the microneedles so that they can be pierced into the skin, whereas the surface treatment with ethanol or the like in this embodiment is intended to increase the absorbency of the porous microneedles with a very simple operation. That is, one aspect of the present invention is a microneedle patch in which the microneedles of embodiment 1 are surface-modified with ethanol which may contain a hydrophilic substance.

[0029] (4) Microneedle Array The microneedles of embodiment 1 can themselves be provided on an absorbent material capable of absorbing interstitial fluid, which will be described later.

[0030] Furthermore, a plurality of microneedles according to embodiment 1 can be erected on a microneedle substrate to form a microneedle array, which can be joined to an absorbent material capable of absorbing interstitial fluid. That is, in another aspect of the present invention, the microneedles according to embodiment 1 are a microneedle array in which a plurality of microneedles are erected on a microneedle substrate (hereinafter also referred to as the "microneedle array of embodiment 1").

[0031] In the microneedle array of embodiment 1, the microneedles can be arranged vertically and horizontally as desired. The spacing between the microneedles is preferably small in order to absorb samples of interstitial fluid, and is preferably 500 to 5000 μm.

[0032] The microneedle substrate may be formed from the same material as the microneedles, or may be formed from a different material.

[0033] In one embodiment, the microneedle substrate is made of a film or a hydrocolloid film containing at least one of polylactic acid resin, polyvinyl alcohol resin, polymethyl methacrylate resin, and polyurethane resin.

[0034] In another embodiment, the microneedle substrate is formed from a biodegradable material. The biodegradable material includes at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG (polyethylene glycol), polyhydroxybutyric acid, and ethyl cellulose. In one preferred embodiment, the microneedle substrate is formed from the same biodegradable material as the microneedles, and the two are integrally configured.

[0035] Furthermore, the microneedles of embodiment 2 described below, i.e., microneedles formed by thermally bonding monodisperse fine particles of a biodegradable material, can also be suitably used as the microneedles used in the microneedle patch of embodiment 1.

[0063] to

[0091] of this specification provide a detailed explanation of the microneedles of embodiment 2, and the descriptions therein regarding the structure, properties, and shape of the microneedles of embodiment 2, the surface modification of the microneedles of embodiment 2, and the microneedle array can also be applied to the microneedles used in the microneedle patch of embodiment 1. The microneedle patch of embodiment 2 has higher strength than conventional techniques, and its use makes it possible to provide the microneedle patch of embodiment 1 equipped with high-strength microneedles.

[0036] That is, in another preferred embodiment of the microneedle patch of embodiment 1, the porous microneedles are formed by thermally bonding monodisperse microparticles made of a biodegradable material. In another preferred embodiment of the microneedle patch of embodiment 1, the monodisperse microparticles are prepared using microfluidics technology. In another preferred embodiment of the microneedle patch of embodiment 1, the monodisperse microparticles are a mixture of two or more types of monodisperse microparticles with different average particle sizes. In another preferred embodiment of the microneedle patch of embodiment 1, the microneedles used in embodiment 2 are surface-modified with ethanol or the like, which may contain a hydrophilic substance. The details of each of the above-mentioned configurations are described in detail in paragraphs

[0063] to

[0091] of this specification.

[0037] 2. Absorbent capable of absorbing interstitial fluid The absorbent capable of absorbing interstitial fluid used in the microneedle patch of embodiment 1 (hereinafter also referred to as "absorbent used in embodiment 1") is an absorbent with a relatively high flow rate and absorption capacity. Examples of such absorbent materials include filter paper or nonwoven fabrics made from materials selected from the group consisting of glass fiber, cellulose, polyester, polyethylene, rayon, acrylic resin, polyvinyl alcohol, polypropylene, nylon, biodegradable polymers, and combinations of any two or more of these. These filter papers or nonwoven fabrics may contain a binder.

[0038] Examples of filter paper made from glass fiber include, for example, the glass fiber filter paper used in Whatman (trademark) lateral flow immunoassays. Examples of nonwoven fabrics made from glass fiber include, for example, glass paper from Oji F-Tex Co., Ltd. Here, filter paper and nonwoven fabric made from glass fiber refer to filter paper and nonwoven fabric obtained using glass fiber as a raw material (material). The same applies to other materials. Examples of filter paper made from cellulose include, for example, filter paper made from one or more materials selected from the group consisting of regenerated cellulose (RC), cellulose acetate (CA), cellulose mixed esters, nitrocellulose, etc. Examples of nonwoven fabrics made from cellulose include, for example, cotton nonwoven fabrics. Examples of filter paper made from polyester include, for example, the polyester filter paper used in Whatman (trademark) lateral flow immunoassays. Examples of nonwoven fabrics made from polyester include, for example, polyester long-fiber nonwoven fabric from Toyobo MC Co., Ltd. Examples of filter paper made from polyethylene include filter paper from Toho Separator Co., Ltd. Examples of nonwoven fabrics made from polyethylene include polyethylene spunbond nonwoven fabrics from Maeda Kosen Co., Ltd. Examples of filter paper made from rayon include filter paper from Toho Separator Co., Ltd. Examples of nonwoven fabrics made from rayon include rayon nonwoven fabrics from Kuraray Kuraflex Co., Ltd. Examples of filter paper made from acrylic resin include acrylic pulp filter paper from Asaka Filter Paper Co., Ltd. Examples of nonwoven fabrics made from acrylic resin include acrylic fiber nonwoven fabrics from Nippon Exlan Kogyo Co., Ltd. Examples of filter paper made from polypropylene include polypropylene filters from Merck Co., Ltd. Examples of nonwoven fabrics made from polypropylene include polypropylene nonwoven wipers from Nippon Paper Crecia Co., Ltd. Examples of filter paper made from nylon include polypropylene filters from Merck Co., Ltd.An example of a filter paper made from a biodegradable polymer is a PVA sponge sheet manufactured by Aion Corporation.

[0039] The absorbent material used in embodiment 1 may be filter paper or nonwoven fabric made from a combination of any two or more materials selected from the group consisting of glass fiber, cellulose, polyester, polyethylene, rayon, acrylic resin, polyvinyl alcohol, polypropylene, nylon, and biodegradable polymers. The filter paper or nonwoven fabric used as the absorbent material in embodiment 1 may contain a binder. Examples of binders include polyvinyl alcohol. The absorbent material used in embodiment 1 may also be obtained by combining two or more types of filter paper or nonwoven fabric made from materials selected from the group consisting of glass fiber, cellulose, polyester, polyethylene, rayon, acrylic resin, polyvinyl alcohol, polypropylene, nylon, biodegradable polymers, and combinations of any two or more of these. In this case, the absorbent obtained by combining two or more types of filter paper or nonwoven fabric may contain a binder. Examples of binders include cellulose-based additives and silk fibroin. Note that lactose, polyol, povidone, starch, and polysaccharide binders are undesirable as they may affect future measurements of biomarkers.

[0040] The thickness of the absorbent material used in embodiment 1 is preferably 100 to 999 μm.

[0041] 3. Microneedle Patch (1) Structure of the Microneedle Patch of Embodiment 1 The microneedle patch of embodiment 1 has a structure comprising porous microneedles and an absorbent material capable of absorbing interstitial fluid, with the microneedles and the absorbent material being integrated together. The integration of the microneedles and the absorbent material enables rapid collection of interstitial fluid by the microneedles.

[0042] In the microneedle patch of embodiment 1, the microneedles themselves can be provided on the absorbent material to form an integrated structure. Furthermore, in the microneedle patch of embodiment 1, a microneedle array in which a plurality of microneedles are erected on a microneedle substrate can be provided on the absorbent material to form an integrated structure. In the microneedle patch of embodiment 1, the absorbent material and the microneedles are in close contact with each other, thereby improving water absorption and water absorption efficiency and reducing uneven water absorption.

[0043] In the microneedle patch of embodiment 1, the absorbent material is preferably separable from the microneedles or microneedle array, thereby enabling the microneedle patch of embodiment 1 to collect and store interstitial fluid for biomarker analysis, and also transport the interstitial fluid via the separated absorbent material for analysis at a specialized institution.

[0044] <Method 1 for manufacturing a microneedle patch of the present invention> Another embodiment of the present invention is a method for manufacturing a microneedle patch, comprising: (a) a step of injecting a biodegradable microsphere solution or suspension containing microspheres of a biodegradable material into a female mold; (b) a step of placing an absorbent material capable of absorbing interstitial fluid on the mold into which the solution or suspension has been injected; and (c) a step of drying the solution or suspension and the absorbent material, followed by baking at a predetermined temperature (hereinafter also referred to as "method 1 for manufacturing the present invention").

[0045] The biodegradable material includes at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG, polyhydroxybutyric acid, and ethyl cellulose.

[0046] The particle size of the biodegradable microspheres is preferably 5 to 30 μm, which is preferable in terms of achieving both mechanical strength and fluid performance.

[0047] The solution or suspension of biodegradable microspheres refers to a liquid in which biodegradable microspheres are dissolved or dispersed in water or an organic solvent, preferably a suspension of biodegradable microspheres, and more preferably a suspension in which biodegradable microspheres are dispersed in water.

[0048] In the manufacturing method 1 of the present invention, the biodegradable material microsphere solution is preferably prepared by preparing a solution A in which the biodegradable material is dissolved in an organic solvent, mixing the solution A with an aqueous solution containing a surfactant, and then evaporating the organic solvent.

[0049] The organic solvent is not particularly limited as long as it dissolves the biodegradable material, and examples thereof include dichloromethane and acetone.

[0050] The concentration of the biodegradable material in solution A is, for example, 5 to 10% (w / v).

[0051] The surfactant is preferably polyvinyl alcohol (PVA), CMC (carboxymethyl cellulose), or the like. These surfactants can reduce the surface tension of the solution obtained by mixing Solution A with an aqueous solution and stabilize the resulting microspheres. In addition, Solution A and / or the aqueous solution containing the surfactant may contain other additives (e.g., carboxymethyl cellulose (CMC), hyaluronic acid) to the extent that the functionality of the resulting porous microneedles is not impaired.

[0052] The solution obtained by mixing Solution A with the aqueous solution can be stirred at about room temperature at 500 to 1500 ppm using a magnetic stirrer or the like to evaporate the organic solvent.

[0053] In step (a), a solution or suspension of biodegradable microspheres is injected into a female mold. The mold used here is a female micromold prepared from a metal master mold consisting of multiple microneedles, and its material is preferably polydimethylsiloxane (PDMS), SUS, or the like. The shape and size of the microneedles of the metal master mold can be appropriately determined to match the shape and size of the desired microneedles.

[0054] The mold may have only the template shape of the microneedle to be prepared. The female micromold can have a desired number of cavities corresponding to the template shape of the microneedle. Furthermore, the female micromold can be appropriately provided with cavities, for example, vertically and horizontally. The spacing between cavities is usually 500 to 5000 μm, preferably 1000 to 3000 μm.

[0055] Furthermore, the cavity can have a shape in which a microneedle substrate and multiple microneedles are bonded together. Since manufacturing method 1 of the present invention produces a microneedle patch in which microneedles and an absorbent material are integrated, it is preferable to provide a cavity (hollow) having a shape including a space for arranging the absorbent material above the microneedle template shape. In this case, a microneedle array in which multiple microneedles are bonded to the microneedle substrate and arranged upright can be obtained. The micromold itself can have a desired number of cavities. Furthermore, the cavities in the micromold itself can be appropriately arranged vertically and horizontally. The spacing between the cavities is preferably 500 to 5000 μm.

[0056] After injecting a solution or suspension of biodegradable microspheres into the cavity of the female mold, it is preferable to degas the cavity by leaving it in a vacuum or applying centrifugal force, thereby filling the cavity with the microspheres.

[0057] Next, in step (b), an absorbent material capable of absorbing interstitial fluid is placed on top of the mold into which the solution or suspension of biodegradable microspheres has been poured. Details of the absorbent material capable of absorbing interstitial fluid are the same as those described for the absorbent material usable in the microneedle patch of embodiment 1 above. Here, in this specification, "placing an absorbent material capable of absorbing interstitial fluid on top of the mold into which the solution or suspension of biodegradable microspheres has been poured" means placing the absorbent material on top of the solution or suspension of biodegradable microspheres poured into the female mold so that the absorbent material is in contact with the solution or suspension. After degassing and filling the cavity with microspheres, the method preferably includes a step of removing a portion of the solution or suspension (supernatant) before placing the absorbent material capable of absorbing interstitial fluid on top of the mold. Removing the supernatant of the solution or suspension removes surfactants such as PVA, shortening the distance between the absorbent material and the needles made of biodegradable material, thereby reducing the inhibition of moisture transfer from the needles to the absorbent material. Furthermore, by placing the absorbent material on a mold, it is possible to make the absorbent material absorb the solution in advance and then dry it, thereby making the absorbent material and the microneedle array adhere to each other.

[0058] The amount of the microsphere solution or suspension (supernatant) to be removed is preferably 60% to 70% of the solution or suspension, and the absorbent material is preferably placed on the mold immediately after removing the microsphere solution or suspension (supernatant) and before the water has completely evaporated within two hours after removal.

[0059] In step (c), the solution or suspension of biodegradable microspheres is dried to evaporate the water, solvent, and dispersant. The drying method can be temperature-controlled by providing piping within the female micromold, or the entire micromold can be placed in a dryer such as a convection oven for drying. The drying temperature is preferably 25 to 100°C, and the drying time can be appropriately determined, but is typically 1 to 24 hours.

[0060] After drying, water evaporates from the solution or suspension of biodegradable material microspheres, yielding unfired microneedles (also called "microneedle precursors") composed of biodegradable material microspheres. At this stage, the microneedle precursors may be removed from the mold and subjected to the next step (firing). Alternatively, at this stage, the microneedle precursors may be left in the mold and subjected to the next heating step without being removed from the mold.

[0061] In step (c), the microneedle precursor is heated at a predetermined temperature. In the microneedle precursor, the individual microspheres maintain their shape and are not bonded to one another. In manufacturing method 1 of the present invention, the microneedle precursor is heated at a high temperature to bond the microspheres to one another. The heating temperature must be such that the microspheres deform and bond to one another, and varies depending on the type of biodegradable resin. For example, in the case of polylactic acid, the temperature is preferably 170 to 200°C, more preferably 170 to 190°C. In the case of polyglycolic acid, the temperature is preferably 170 to 250°C. In the case of poly(lactide-co-glycolide) copolymer, the temperature is preferably 50 to 200°C. In the case of PEG, the temperature is preferably 30 to 200°C. In the case of polyhydroxybutyric acid, the temperature is preferably 100 to 200°C. In the case of ethyl cellulose, the temperature is preferably 80 to 300°C. The drying time is, for example, 1 to 24 hours.

[0062] The porous microneedles obtained by the above-described manufacturing method 1 of the present invention have a structure in which the microspheres are partially in a liquid phase or rubber state and bonded to each other, thereby forming a network of interconnected (communicating) continuous pores, thereby forming a robust pore structure. Furthermore, the microneedle patch obtained by manufacturing method 1 of the present invention preferably has a structure in which the porous microneedles (i.e., the microneedles of embodiment 1) and the absorbent material are integrated, and has high mechanical strength. Furthermore, the close contact of the absorbent material with the needle improves water absorption and water absorption efficiency, and improves water absorption unevenness. That is, in manufacturing method 1 of the present invention, the microneedles and the absorbent material are integrated in the obtained microneedle patch. Another aspect of the present invention is a microneedle patch obtained by manufacturing method 1 of the present invention.

[0063] <Microneedle patch of embodiment 2> Another embodiment of the present invention is a microneedle patch comprising porous microneedles and an absorbent material capable of absorbing interstitial fluid, the microneedles being formed by thermally bonding monodisperse microparticles of a biodegradable material (hereinafter also referred to as the "microneedle patch of embodiment 2").

[0064] In the microneedle patch of embodiment 2, it is important that the porous microneedles are formed by thermally bonding monodisperse fine particles of a biodegradable material. As a result, the microneedle patch of embodiment 2 is provided with microneedles that have higher strength than conventional techniques. Hereinafter, the porous microneedles provided in the microneedle patch of embodiment 2 will also be referred to as "microneedles of embodiment 2."

[0065] 1. Microneedle of Embodiment 2 (1) Structure and Characteristics of Microneedle of Embodiment 2 In the microneedle of Embodiment 2, preferably, monodisperse microparticles of a biodegradable material are prepared using microfluidic technology. More specifically, the monodisperse microparticles of a biodegradable material are obtained from microdroplets generated using microfluidic technology. Here, "monodisperse microparticles of a biodegradable material" refers to microparticles of a biodegradable material having a uniform particle size. Furthermore, the particle size (diameter) dispersity of the monodisperse microparticles is preferably within ±7-8% of the average particle size, more preferably within ±5% of the average particle size. Here, the particle size dispersity is calculated by dividing the standard deviation of the diameter distribution by the arithmetic mean. When microneedles are manufactured from microparticles of a biodegradable material having such a uniform particle size, high strength microneedles can be obtained with the expected porosity and a uniform porosity distribution throughout the needle surface and interior. Furthermore, because the particles are uniform, there is little performance variation between the resulting microneedles' lots.

[0066] The biodegradable material constituting the microneedle of embodiment 2 includes at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide), PEG, polyhydroxybutyric acid, and ethyl cellulose. The microneedle of embodiment 2 may be composed solely of the biodegradable material, or may contain trace amounts of raw materials used in the method for producing the microneedle of embodiment 2 (e.g., polyvinyl alcohol, methyl cellulose, sorbitan fatty acid esters, sorbitan monooleate, surfactants such as sodium dodecyl sulfate and hexadecyltrimethylammonium bromide), or other additives (e.g., carboxymethylcellulose (CMC), hyaluronic acid), as long as the function of the microneedle is not impaired. Furthermore, the microneedle of embodiment 2 may be at least partially coated with a coating agent so as not to impair its function. Materials commonly used in this technical field (e.g., CMC, hyaluronic acid, etc.) can be used as the coating agent.

[0067] Monodisperse fine particles of a biodegradable material that can be suitably used in the production of the microneedles of embodiment 2 can be preferably obtained by the following preparation method, but is not limited to this.

[0068] Monodisperse microparticles of biodegradable materials can be produced using microfluidic technology, particularly droplet microfluidic technology. More specifically, microdroplets with uniform diameters can be prepared by a flow focusing method using a microchannel, resulting in monodisperse microparticles of biodegradable materials.

[0069] The upper part of Figure 1 shows a schematic diagram of a method for preparing monodisperse microparticles of a biodegradable material by the flow focusing method. A biodegradable material dissolved in an organic solvent or the like is introduced into a microfluidic chip as the dispersed phase, and an aqueous solution of a polymer or the like can be used as the continuous phase. Here, it is preferable to use an aqueous solution of a polymer or the like that functions as a surfactant to prevent the aggregation of droplets of the biodegradable material. The flow rate ratio of the dispersed phase (Q ｄ ) is fixed, and the flow rate ratio of the continuous phase (Q ｃ The droplet size can be controlled by changing the temperature. The droplets are collected in a container containing deionized water, and the organic solvent in the droplets is removed by dispersing it in a sufficient amount of water. The solvent is then evaporated, solidifying the biodegradable material particles. The particles are then collected by centrifugation and washed about five times with deionized water.

[0070] The lower part of Figure 1 shows an example in which biodegradable polylactic acid (PLA) dissolved in dichloromethane (DCM) was introduced into a microfluidic chip as the dispersed phase, and an aqueous polyvinyl alcohol (PVA) solution was used as the continuous phase. To prepare monodisperse microparticles of biodegradable materials using the flow focusing method, ethyl acetate (EA) or the like can also be used as the dispersed phase solvent, and sodium dodecyl sulfate (SDS) or the like can also be used as the continuous phase solvent.

[0071] The microneedles of embodiment 2 can be obtained by filling a female mold with monodisperse microparticles of a biodegradable material prepared by the flow focusing method as described above and thermally bonding the monodisperse microparticles. Figure 2 shows a schematic diagram of a non-limiting example of a method for preparing microneedles of embodiment 2 using monodisperse microparticles. The monodisperse microparticles can be directly filled into a female mold (such as a PDMS mold), or a solution containing the monodisperse microparticles can be filled into the female mold. The solvent in this case is, for example, deionized water, pure water, etc.

[0072] When filling a female mold (such as a PDMS mold) with the solution containing the monodisperse microparticles, a vacuum may be applied to remove air bubbles so that the microparticles can be filled to the tip of the mold. Alternatively, another PDMS sheet or the like may be placed on top of the female mold filled with the monodisperse microparticles and pressed to help fill the tip of the mold with the microparticles.

[0073] The step of thermally bonding (thermal joining) the monodisperse microparticles is preferably carried out using a convection oven. Pressure can be applied by placing a preheated metal block from above. Thermal bonding can be carried out by heat treatment at 120 to 180°C for 0.5 to 1.5 hours, and may also be carried out under vacuum.

[0074] In the microneedle of embodiment 2, the pore size distribution of the porous structure can be changed by changing the diameter of the microspheres, thereby adjusting the extraction ability of the porous microneedle.

[0075] The average diameter of the monodisperse microparticles used in preparing the microneedles of embodiment 2 is preferably 1 to 40 μm, more preferably 5 to 30 μm, and even more preferably 5 to 20 μm. When the diameter of the monodisperse microparticles is within this range, it is possible to increase the absorption efficiency. Furthermore, as described above, the degree of dispersion of the particle size (diameter) of the monodisperse microparticles is preferably within ±7 to 8% of the average particle size, more preferably within ±5% of the average particle size.

[0076] In another aspect of the present invention, the monodisperse microparticles used in preparing the microneedles of embodiment 2 are a combination or mixture of two or more types of monodisperse microparticles with different average particle sizes (average diameters). By using two or more types of monodisperse microparticles with such uniform particle sizes, it is possible to improve absorption efficiency. Basically, the smaller the particle size, such as from 30 μm to 20, 10, or 5 μm, the stronger the capillary force and the higher the absorption efficiency. However, in the particle size range of 5 μm to 20 μm, by using a mixture of two or more types of monodisperse microparticles, it is possible to increase the frequency of interparticle voids forming a network, and the overall void ratio and void volume inside the needle.

[0077] Examples of combinations of two or more types of monodisperse microparticles with uniform particle diameters include a mixture of monodisperse microparticles made of a biodegradable material with an average particle diameter of 10 μm and monodisperse microparticles made of a biodegradable material with an average particle diameter of 20 μm, and a mixture of monodisperse microparticles made of a biodegradable material with an average particle diameter of 5 μm and monodisperse microparticles made of a biodegradable material with an average particle diameter of 10 μm.

[0078] The porosity of the microneedles of embodiment 2 is usually 30 to 80%, preferably 45 to 55%. Here, the porosity is measured in the same manner as described for the microneedles of embodiment 1.

[0079] The microneedle of embodiment 2 has an absorption volume of typically 1 to 10 μL, preferably 7.5 to 9 μL. Here, the absorption volume is measured by puncturing a microneedle array with 25 porous PLA MNs standing upright in 1% agarose gel with a force of 5 N, removing it from the gel after 1 minute, and measuring its weight.

[0080] The microneedle of embodiment 2 typically has an absorption rate of 0.05 to 0.35 μL / min, preferably 0.3 to 0.35 μL / min, per MN. The absorption rate is measured by puncturing a microneedle array with 25 porous PLA MNs upright in 1% agarose gel with a force of 5 N, removing the array from the gel after 1 minute, and measuring its weight.

[0081] (2) Shape of the microneedle of embodiment 2 The shape of the microneedle of embodiment 2 can be an approximately conical shape, an approximately pyramidal shape, or the like, but a polygonal shape (e.g., an approximately pyramidal shape) is preferred because it penetrates the skin more easily than an approximately conical shape.

[0082] The diameter of the tip of the microneedle of embodiment 2 is usually 10 μm to 50 μm. The diameter or maximum dimension of the base is, for example, about 50 μm to 800 μm. The height of the microneedle determines the depth of penetration into the skin. In the microneedle of the present invention, the diameter is preferably 300 μm or more and 1500 μm or less, taking into consideration that it can reach the dermis without stimulating pain sensation.

[0083] When multiple microneedles are provided, the smaller the spacing is, the better for absorbing the interstitial fluid sample, and spacing of 500 to 2000 μm is preferred.

[0084] Regarding the angle of the tip of the microneedle of embodiment 2, a larger angle increases the mechanical strength, but a larger tip angle increases the force required for penetration. A tip angle of 15 to 30° is preferable, as the force required for the microneedle to penetrate is less than 0.1 N.

[0085] (3) Surface Modification of Microneedles of Embodiment 2 In another preferred aspect of the present invention, the microneedles of embodiment 2 are surface-modified. As described above, the inventors have conducted research and found that surface modification of porous microneedles with ethanol, which may contain a hydrophilic substance such as ethanol or a PEG-ethanol solution (i.e., an ethanol solution containing a hydrophilic substance such as ethanol or PEG), results in extremely high absorption. The solvent, such as ethanol, may be completely evaporated by drying at an elevated temperature. As explained above, the microneedles of embodiment 2 may be at least partially coated with a coating agent without impairing their function. While the coating agent is intended to harden the microneedles for piercing the skin, the surface treatment with ethanol or the like in this embodiment is intended to increase the absorption capacity of the porous microneedles with a very simple procedure. That is, one aspect of the present invention is a microneedle patch in which the microneedles of embodiment 2 are surface-modified with ethanol, which may contain a hydrophilic substance.

[0086] (4) Microneedle Array The microneedles of embodiment 2 can themselves be provided on an absorbent material capable of absorbing interstitial fluid, which will be described later.

[0087] Furthermore, a plurality of microneedles according to embodiment 2 can be erected on a microneedle substrate to form a microneedle array, which can be joined to an absorbent material capable of absorbing interstitial fluid. That is, in another aspect of the present invention, the microneedles according to embodiment 2 are a microneedle array in which a plurality of microneedles are erected on a microneedle substrate (hereinafter also referred to as the "microneedle array of embodiment 2").

[0088] In the microneedle array of embodiment 2, the microneedles can be arranged vertically and horizontally as desired. The spacing between the microneedles is preferably small in order to absorb samples of interstitial fluid, and is preferably 500 to 2000 μm.

[0089] The microneedle substrate may be formed from the same material as the microneedles, or may be formed from a different material.

[0090] In one embodiment, the microneedle substrate is made of a film or a hydrocolloid film containing at least one of polylactic acid resin, polyvinyl alcohol resin, polymethyl methacrylate resin, and polyurethane resin.

[0091] In another embodiment, the microneedle substrate is formed from a biodegradable material. The biodegradable material includes at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG, polyhydroxybutyric acid, and ethyl cellulose. In one preferred embodiment, the microneedle substrate is formed from the same biodegradable material as the microneedles, and the two are integrally configured.

[0092] 2. Absorbent capable of absorbing interstitial fluid The absorbent capable of absorbing interstitial fluid used in the microneedle patch of embodiment 2 (hereinafter also referred to as "absorbent used in embodiment 2") is an absorbent with a relatively high flow rate and absorption capacity. Examples of such absorbent materials include filter paper or nonwoven fabrics made from materials selected from the group consisting of glass fiber, cellulose, polyester, polyethylene, rayon, acrylic resin, polyvinyl alcohol, polypropylene, nylon, biodegradable polymers, and combinations of any two or more of these. These filter papers or nonwoven fabrics may contain a binder.

[0093] Examples of filter paper made from glass fiber, nonwoven fabric made from glass fiber, filter paper made from cellulose, nonwoven fabric made from cellulose, filter paper made from polyester, nonwoven fabric made from polyester, filter paper made from polyethylene, nonwoven fabric made from polyethylene, filter paper made from rayon, nonwoven fabric made from rayon, filter paper made from acrylic resin, nonwoven fabric made from acrylic resin, filter paper made from polyvinyl alcohol, nonwoven fabric made from polyvinyl alcohol, filter paper made from polypropylene, nonwoven fabric made from polypropylene, filter paper made from nylon, filter paper made from biodegradable polymers, etc. are as described in detail for the absorbent material used in embodiment 1.

[0094] The absorbent material used in embodiment 2 may be filter paper or nonwoven fabric made from a combination of any two or more materials selected from the group consisting of glass fiber, cellulose, polyester, polyethylene, rayon, acrylic resin, polyvinyl alcohol, polypropylene, nylon, and biodegradable polymers. The filter paper or nonwoven fabric used as the absorbent material in embodiment 2 may contain a binder. Examples of binders include polyvinyl alcohol. The absorbent material used in embodiment 2 may also be obtained by combining two or more types of filter paper or nonwoven fabric made from materials selected from the group consisting of glass fiber, cellulose, polyester, polyethylene, rayon, acrylic resin, polyvinyl alcohol, polypropylene, nylon, biodegradable polymers, and combinations of any two or more of these. In this case, the absorbent obtained by combining two or more types of filter paper or nonwoven fabric may contain a binder. Examples of binders include cellulose-based additives and silk fibroin. Note that lactose, polyol, povidone, starch, and polysaccharide binders are undesirable as they may affect future measurements of biomarkers.

[0095] The thickness of the absorbent material used in embodiment 2 is preferably 100 to 999 μm.

[0096] 3. Microneedle Patch of Embodiment 2 (1) Structure of the Microneedle Patch of Embodiment 2 The microneedle patch of embodiment 2 comprises the microneedle of embodiment 2 and an absorbent material capable of absorbing interstitial fluid.

[0097] In the microneedle patch of embodiment 2, the microneedle or microneedle array of embodiment 2 may be adhered to the absorbent material. The adhesion can be achieved by adhesion using an adhesive or by pressure bonding.

[0098] The microneedle patch of embodiment 2 preferably has a structure in which the microneedles of embodiment 2 and the absorbent material are integrated. By integrating the microneedles of embodiment 2 and the absorbent material, rapid collection of interstitial fluid by the microneedles becomes possible.

[0099] In the microneedle patch of embodiment 2, the microneedles themselves can be provided on the absorbent material to form an integrated structure. Furthermore, in the microneedle patch of embodiment 2, a microneedle array in which a plurality of microneedles are erected on a microneedle substrate can be provided on the absorbent material to form an integrated structure. In the microneedle patch of embodiment 2, the absorbent material is in close contact with the microneedles, thereby improving water absorption and water absorption efficiency and improving uneven water absorption. The integration of the microneedles of embodiment 2 and the absorbent material can be achieved by directly molding the microneedles of embodiment 2 into the absorbent material.

[0100] In the microneedle patch of embodiment 2, the absorbent material is preferably separable from the microneedles or microneedle array, thereby enabling the microneedle patch of embodiment 2 to collect and store interstitial fluid for biomarker analysis, and also transport the interstitial fluid via the separated absorbent material, enabling analysis at a specialized institution.

[0101] <Method for manufacturing a microneedle patch according to the present invention, 2> Another embodiment of the present invention is a method for manufacturing a microneedle patch, comprising the steps of: (a) filling a female mold with monodisperse microparticles made of a biodegradable material; (b) placing an absorbent material capable of absorbing interstitial fluid on top of the mold filled with the monodisperse microparticles; and (c) thermally bonding the monodisperse microparticles (hereinafter also referred to as "method for manufacturing a microneedle patch according to the present invention").

[0102] The details of the biodegradable material, the female mold, and the absorbent material capable of absorbing interstitial fluid used in Production Method 2 of the present invention are as described in detail in Production Method 1 of the present invention.

[0103] The monodisperse microparticles of biodegradable material used in Production Method 2 of the present invention can be produced using microfluidic technology, particularly droplet microfluidic technology. That is, in Production Method 2 of the present invention, the monodisperse microparticles of biodegradable material are preferably obtained from microdroplets generated using microfluidic technology. More preferably, the monodisperse microparticles of biodegradable material used in Production Method 2 of the present invention are preferably prepared by a flow focusing method using a microchannel. Details of the method for preparing monodisperse microparticles of biodegradable material using the flow focusing method are as described in detail for the microneedle 2 of the present invention.

[0104] In one embodiment of Production Method 2 of the present invention, the monodisperse microparticles of a biodegradable material are prepared by a flow focusing method in which biodegradable polylactic acid (PLA) dissolved in dichloromethane (DCM) is introduced into a microfluidic chip as a dispersed phase, and an aqueous polyvinyl alcohol (PVA) solution is used as a continuous phase.

[0105] In one embodiment of Production Method 2 of the present invention, the monodisperse fine particles of a biodegradable material are a combination or mixture of two or more types of monodisperse fine particles having different average particle sizes.

[0106] In step (a) of manufacturing method 2 of the present invention, preferably, monodisperse microparticles of a biodegradable material prepared by the flow focusing method as described above are filled into a female mold. Here, the monodisperse microparticles can be filled directly into the female mold, or a solution containing the monodisperse microparticles can be filled into the female mold. Examples of solvents used in this case include deionized water and pure water. Furthermore, in this specification, "placing an absorbent material capable of absorbing interstitial fluid on a mold filled with monodisperse microparticles of a biodegradable material" means placing the absorbent material on the monodisperse microparticles or the solution containing the monodisperse microparticles filled into the female mold so that the absorbent material is in contact with the monodisperse microparticles or the solution containing the monodisperse microparticles.

[0107] When the solution containing the monodisperse microparticles is filled into the female mold, a vacuum may be applied to remove air bubbles so that the microparticles can be filled into the tip of the mold. Alternatively, another PDMS sheet or the like may be placed on top of the female mold filled with the monodisperse microparticles and pressed to help the microparticles fill into the tip of the mold.

[0108] Next, in step (b), an absorbent capable of absorbing interstitial fluid is placed on top of the mold filled with monodisperse microparticles of a biodegradable material. When filling a female mold with a solution containing dispersed microparticles, it is preferable to include a step of degassing the cavity, filling the cavity with the solution, and then removing a portion of the solution (supernatant) before placing the absorbent capable of absorbing interstitial fluid on top of the mold. Removing the supernatant reduces the distance between the absorbent and the needles made of a biodegradable material, thereby reducing the inhibition of moisture transfer from the needles to the absorbent. Furthermore, by placing the absorbent on top of the mold, the absorbent can be allowed to absorb the solution in advance and then dried, thereby allowing the absorbent and the microneedle array to adhere to each other.

[0109] The step (c) of thermally bonding (thermal joining) the monodisperse microparticles is preferably carried out using a convection oven. Pressure can be applied by placing a preheated metal block from above. Regarding the thermal bonding conditions, low temperatures do not provide enough energy for the polymer chains to diffuse across the interface between the microspheres, which has low bond strength, while high temperatures tend to melt the microspheres and reduce the extraction efficiency of the microneedle array. Insufficient pressure makes it difficult to maintain close contact between the microspheres during bonding. Furthermore, high pressure tends to cause excessive deformation of the thermoplastic microspheres, resulting in loss of inter-pore connectivity. Thermal bonding is preferably carried out by heat treatment at 120-180°C for 0.5-1.5 hours, and a pressure of 10-20 kPa is preferably applied.

[0110] In the microneedle patch obtained by the above-described manufacturing method 2 of the present invention, the microneedles are manufactured using fine particles of a biodegradable material having a uniform particle size, thereby enabling the production of high-strength microneedles. Furthermore, because the particles are uniform, the performance difference between the obtained microneedles and the resulting lot is small. Furthermore, the microneedle patch obtained by manufacturing method 2 of the present invention preferably has a structure in which the porous microneedles (i.e., the microneedles of embodiment 2) and an absorbent material are integrated, and has high mechanical strength. Furthermore, the close contact of the absorbent material with the needle improves water absorption and water absorption efficiency, and improves water absorption unevenness. In other words, in one aspect of manufacturing method 2 of the present invention, the microneedles and the absorbent material are integrated in the obtained microneedle patch. In other words, another aspect of the present invention is a microneedle patch obtained by manufacturing method 2 of the present invention.

[0111] [Example 1] Preparation of microneedle patch 1 of the present invention Microneedles were prepared based on the single emulsion method described in International Publication WO 2023 / 021665. A schematic diagram of the preparation process is shown in Figure 3. First, a female needle mold made of polydimethylsiloxane (PDMS) was prepared using a mold. The mold had 13 x 13 needles with a height of 800 μm arranged on a 15 mm x 15 mm substrate. A mixture of PDMS and curing agent was poured onto the mold, degassed, and then cured in an oven at 90 ° C to prepare a female mold.

[0112] Next, a polylactic acid (PLA) solution was prepared as the material for the microneedle array. PLA is biodegradable, minimizing the risk to human health if the needles break. First, 50 mL of a 5% polyvinyl alcohol (PVA) aqueous solution was poured with 1.0 g of PLA dissolved in 15 mL of dichloromethane (DCM). The mixture was then stirred at room temperature for 6 hours to evaporate the organic phase, the DCM. Here, the PVA acts as a surfactant, creating PLA particles. It is known that the particle size of PLA is affected by the ratio of DCM to PLA (L. Bao et al., "Anti-SARS-CoV-2 IgM / IgG antibody detection using a patch sensor containing porous microneedles and a paper-based immunoassay," Scientific Reports, vol. 12(1), 10693, 2022). When a PLA solution was prepared by dissolving 1.0 g of PLA in 15 mL of DCM, the average particle size in a given area was 9.9 ± 5.3 μm.

[0113] The PLA solution was then poured into the female mold. Conventional methods involve degassing the mold and drying it for 48 hours. In our proposed method, a certain amount of the PLA solution's supernatant is removed after degassing, and the absorbent material is then placed on the mold immediately or after a certain period of time. The purpose of removing the PLA solution's supernatant is to reduce the obstruction of water transfer from the needles to the absorbent material by removing the PVA and shortening the distance between the absorbent material and the PLA needles. The absorbent material is then placed on the mold to allow the absorbent material to absorb the solution and then dry, thereby ensuring close contact between the absorbent material and the microneedle array. We tested two different PLA solution volumes: 900 μL and 800 μL. We also tested two different timings for placing the absorbent material: immediately after removing the PLA solution and two hours afterward.

[0114] The absorbent material was glass fiber filter paper, which is used in Whatman™ lateral flow immunoassays. The glass fiber material was chosen because it has a relatively high flow rate and absorption capacity, making it suitable for rapid interstitial fluid collection using microneedles. The PLA solution was then poured into a female mold, dried for 12 hours, and baked in an oven at 170°C for 30 minutes.

[0115] The fabricated microneedle patch is shown in Figures 4 and 5. The needles (white in the actual photograph) and substrate in Figure 4 are made of PLA, and after the PVA is absorbed into the filter paper, it is baked and changes color to a dark color (brown in the actual photograph). In this way, the absorbent material and the microneedle array are integrated. However, some needle detachment was observed, exposing the filter paper at the puncture surface.

[0116] Next, a water absorption experiment was conducted using a 1% agarose gel stained with 0.05% rhodamine B as a skin model. For the experiment, aluminum foil was used to cover the microneedle patch integrated with the absorbent material, allowing only the needle to penetrate the aluminum foil and puncture the gel. The aluminum foil was used to prevent water absorption into the patch from any other location than the needle. A weight was then applied from above with a pressure of 2.5 kPa to puncture the gel, and the patch was left to stand for 5 minutes before examining whether or not water was absorbed (Figure 6). Water absorption was confirmed in all microneedle patches, and differences in water absorption patterns were also observed depending on the amount of PLA solution removed.

[0117] Of the four patches in each photograph in Figure 6, (a) and (c) were prepared by removing 900 μL of PLA solution, and (b) and (d) were prepared by removing 800 μL of PLA solution. Looking at the absorbent side, it can be seen that both patches were absorbed and that the dyed water reached the absorbent.

[0118] Example 2: Preparation of Microneedle 2 of the Present Invention (1) Preparation Method Uniform microdroplets were generated by a flow focusing method using microfluidic technology as shown in Figure 7. PLA was dissolved in dichloromethane (1%, w / w) as the dispersed phase, and the continuous phase was an aqueous solution of polyvinyl alcohol (PVA) (5%, w / w). PVA served as a surfactant to prevent droplets from coalescing. The flow rate of the dispersed phase was fixed, and the flow rate of the continuous phase was adjusted to generate microdroplets of different diameters.

[0119] The resulting droplets were then passed through a water-filled outlet to induce solvent removal of the DCM. The PLA microspheres were collected by centrifugation and rinsed several times with deionized water to remove residual PVA. The PLA microspheres were then packed into a PDMS female mold made from a metal master mold, and another piece of PDMS sheet was placed on top and pressed to help the microspheres pack into the tip of the mold. The thermal bonding process was carried out using a convection oven, with pressure provided by a preheated metal block. Finally, a porous microneedle (MN) array was fabricated and peeled off from the PDMS mold. Figure 8 shows a schematic diagram of the fabrication method for porous MNs using PLA microspheres. The porous structure was achieved by packing and bonding PLA microspheres together. Because the needle pores originate from the voids between the microspheres, varying the diameter of the microspheres can alter the pore size distribution of the porous structure and tune the extraction capacity of the porous MN array.

[0120] (2) Evaluation Results Uniform microdroplets with diameters ranging from 30 μm to 150 μm were generated by a dropwise method using a microfluidic chip. After solvent removal from microdroplets with different diameters, PLA microspheres with diameters ranging from 10 to 40 μm were obtained. The shrinkage rate of the microsphere diameter relative to the initial droplet diameter generated using a dispersed phase of 1% PLA / DCM solution was 28.05% (R ２ = 0.99). The shrinkage ratio can be varied by changing the concentration of the dispersed phase during droplet generation to produce microspheres with a wider range of diameters. SEM images of PLA microspheres with different diameters are shown in Figure 9. Figure 9 (a) shows monodisperse microspheres with diameters of 10 μm, (b) shows 20 μm, (c) shows 30 μm, and (d) shows 40 μm. The scale bar is 20 μm. The coefficient of variation of the microsphere diameters was less than 5%, indicating that the microsphere sizes were highly monodisperse.

[0121] The resulting microspheres were thermally bonded using a convection oven. The bonding parameters, including temperature, pressure, and time, were adjusted to provide sufficient bond strength between the microspheres while limiting deformation of the thermoplastic PLA microspheres during bonding. It was found that low temperatures could not provide enough energy for the polymer chains to diffuse across the interface between the microspheres, which had low bond strength, while high temperatures caused the microspheres to melt, reducing the extraction efficiency of the MN array. In terms of pressure, insufficient pressure could not maintain intimate contact between the microspheres during bonding. Furthermore, excessive deformation of the thermoplastic microspheres under high pressure led to loss of inter-pore connectivity. Finally, the thermal bonding conditions were set to 140 °C and 15 kPa and held for 60 minutes to bond the microspheres together, followed by peeling the MN array from the PDMS mold. Optical microscope images of the fabricated MNs are shown in Figure 10. The 5 × 5 MNs on the patch had a pyramidal shape with an average length of 1060 μm and a base width of 596 μm (Figure 10).

[0122] The extraction ability of the fabricated MNs was tested using a skin model made of 1% agarose gel. The MN array was penetrated into the skin model covered with aluminum foil. Extraction was maintained for 5 minutes, and the weight of the MN array was measured before and after extraction to calculate the extracted volume of the sample fluid. As a result, a porous MN array made of 20 μm diameter microspheres extracted 7.9 μL of sample liquid in 5 minutes. Furthermore, the extraction ability of the porous MNs decreased when larger microspheres were used or as the MNs were fabricated. Figure 11 shows the extraction volume and porosity of MNs fabricated using microspheres of different sizes.

[0123] The porosity of the fabricated MNs was tested using a method based on Archimedes' principle. The open porosity value was close to the total porosity value, indicating that nearly all pores in the MN arrays were interconnected. The continuous network of interconnected channels within the needles was attributed to optimized bonding conditions that prevented pores from pinching off during fabrication. The porosity of the MN arrays was 53% and remained constant with increasing microsphere size, which was considered reasonable. Because the packing density of equal spheres is independent of sphere size, the fraction of pores in the MN arrays does not change regardless of how the microsphere size changes, as long as they are monodisperse.

[0124] To measure the pore size distribution of porous MNs, the porous MNs were first filled with UV-curable resin under vacuum. After solidification under UV exposure, cross-sections of the porous MNs with resin-filled pores were obtained by grinding using sandpaper attached to a stage controller. The pore size distribution was evaluated by measuring the distance between adjacent microspheres on the same plane using SEM observation. The average pore size was approximately 36% of the microsphere size, and it was found that the pore size distribution broadened as the microsphere diameter increased.

Claims

1. A microneedle patch comprising porous microneedles and an absorbent material capable of absorbing interstitial fluid, the microneedles and the absorbent material being integrated together.

2. The microneedle patch of claim 1, wherein the microneedles are microspheres of a biodegradable material bonded together to form a network of interconnected pores.

3. The microneedle patch of claim 1, wherein the biodegradable material comprises at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG (polyethylene glycol), polyhydroxybutyric acid, and ethyl cellulose.

4. The microneedle patch according to claim 1, wherein the microneedles are surface-modified with ethanol which may contain a hydrophilic substance.

5. The microneedle patch of claim 1, further comprising a microneedle substrate, the microneedles being bonded to the microneedle substrate.

6. A microneedle patch comprising porous microneedles and an absorbent material capable of absorbing interstitial fluid, wherein the microneedles are formed by thermally bonding monodisperse microparticles of a biodegradable material.

7. The microneedle patch according to claim 6, wherein the monodisperse microparticles are prepared using microfluidic technology.

8. The microneedle patch according to claim 6, wherein the monodisperse microparticles are a mixture of two or more types of monodisperse microparticles having different average particle sizes.

9. The microneedle patch of claim 6, wherein the biodegradable material includes at least one of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG (polyethylene glycol), polyhydroxybutyric acid, and ethyl cellulose.

10. The microneedle patch according to claim 6, wherein the microneedles are surface-modified with ethanol or the like which may contain a hydrophilic substance.

11. The microneedle patch of claim 6, wherein the microneedles and absorbent material are integrated.

12. The microneedle patch of claim 6, further comprising a microneedle substrate, the microneedles being bonded to the microneedle substrate.

13. A method for manufacturing a microneedle patch, comprising: (a) injecting a biodegradable microsphere solution or suspension containing microspheres of a biodegradable material into a female mold; (b) placing an absorbent material capable of absorbing interstitial fluid on top of the mold into which the solution or suspension has been injected; and (c) drying the solution or suspension and the absorbent material, and then baking them at a predetermined temperature.

14. The method of claim 13, further comprising the step of removing a portion of the solution or suspension after the solution or suspension has been poured into the negative mold.

15. The manufacturing method described in claim 13, wherein the biodegradable material microsphere solution or suspension is prepared by preparing solution A by dissolving the biodegradable material in an organic solvent, mixing solution A with an aqueous solution containing a surfactant, and then evaporating the organic solvent and stirring.

16. The manufacturing method according to claim 13, wherein the microneedles and the absorbent material are integrated in the microneedle patch.

17. A microneedle patch obtained by the manufacturing method according to any one of claims 13 to 16.

18. A method for manufacturing a microneedle patch, comprising: (a) filling a female mold with monodisperse microparticles of a biodegradable material; (b) placing an absorbent material capable of absorbing interstitial fluid on top of the mold filled with the monodisperse microparticles; and (c) thermally bonding the monodisperse microparticles.

19. The method of claim 18, wherein the monodisperse microparticles are obtained from microdroplets generated using microfluidic technology.

20. The method of manufacturing according to claim 18, wherein the monodisperse fine particles are a mixture of two or more types of monodisperse fine particles having different average particle sizes.

21. A microneedle patch obtained by the manufacturing method according to any one of claims 18 to 20.

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