Porous microneedle manufacturing method

Abstract

[Problem] To provide a porous microneedle capable of collecting a body fluid. [Solution] Provided is a porous microneedle including a water-soluble material and microspheres of a biodegradable material, wherein: the microspheres of the biodegradable material are bonded to each other to form a network of interconnected pores; the microneedle may comprise a microneedle substrate including the microspheres and the water-soluble material; and the volume ratio of the water-soluble material and the biodegradalbe material is 1:2 to 3.

Description

Method for manufacturing porous microneedles

[0001] The present invention relates to a porous microneedle, a microneedle patch including the same, and a method for manufacturing the microneedle.

[0002] In recent years, many point-of-care testing (POCT) devices have been developed that enable rapid and convenient disease testing and diagnosis and health monitoring. To live a healthy life, it is essential to monitor biomarkers, such as blood glucose levels and cholesterol levels, which are closely related to lifestyle-related diseases. Conventional testing and diagnosis require blood samples to be collected using a syringe or urine or tear samples to measure multiple biomarkers. However, using a syringe involves pain and bleeding with each measurement, placing a significant burden on the patient. Furthermore, urine and tear samples have a large margin of error compared to the biological information in the blood, resulting in unreliable measurements.

[0003] On the other hand, interstitial fluid present in the skin has attracted attention as a promising alternative sample to blood for measuring biomarkers because it has a composition similar to that of plasma. However, a method for extracting interstitial fluid has not yet been established, and a simple and minimally invasive method for extracting interstitial fluid is needed.

[0004] Microneedles, which have a shorter and thinner needle structure than conventional injection needles, have attracted attention as a painless, minimally invasive biosensor device. Microneedle (MN) arrays are an effective approach for puncturing the dermis layer to painlessly extract interstitial fluid, and biodegradable polymer MNs with a porous structure have attracted considerable attention in recent years. However, various challenges remain for practical application, such as complex processing, time-consuming manufacturing, and difficulty in obtaining sufficient mechanical strength (e.g., strength that allows easy penetration into the skin).

[0005] The present inventors have discovered that porous microneedles can be produced by heat treatment of microspheres of a biodegradable polymer such as polylactic acid, and that the porous microneedles thus obtained have high mechanical strength (Patent Document 1). In the single emulsion method discovered by the present inventors, when molding porous microneedles formed from a biodegradable polymer such as polylactic acid (PLA) and a surfactant (water-soluble material) such as polyvinyl alcohol (PVA), the PLA particles accumulate and a PVA solution penetrates into the gaps between them. When dried, the adhesive PVA bonds the PLA particles together, allowing the shape to be maintained even after demolding. Furthermore, during the heating process, the entire microneedle can be exposed to ambient temperature, which has the advantage of allowing for uniform heating.

[0006] However, when actually producing microneedles using the above-mentioned single emulsion method, it was necessary to gradually change the amount of materials and the manufacturing process to find the optimal conditions, so if the conditions changed, it was necessary to adjust the amount of materials from scratch. Furthermore, even if optimization was possible, it was only possible under one condition, and if the length and number of needles, the thickness of the microneedle substrate, etc. were different, it was necessary to adjust the amount of materials such as PLA and PVA from scratch and repeat prototyping and evaluation, which was inefficient. Furthermore, since the optimal ratio of the amount of biodegradable material such as PLA and the amount of water-soluble material such as PVA that allows efficient collection of body fluids was not clear, it was difficult to stably prepare porous microneedles that could efficiently collect body fluids.

[0007] International Publication No. 2023 / 021665

[0008] An object of the present invention is to provide a porous microneedle capable of collecting body fluids. Another object of the present invention is to provide a microneedle composed of a water-soluble material and a biodegradable material in an optimal ratio.

[0009] The present inventors have investigated the above-mentioned problems in the production of porous microneedles using the single emulsion method and found that the cause is practical optimization in which conditions are changed little by little, and that in order to theoretically optimize the process, it is necessary to clarify the deposition state of the particles of biodegradable material such as PLA and the water-soluble material such as PVA that make up the porous microneedle. They also found that by setting the volume ratio of the water-soluble material to the biodegradable material within a specific range, an optimal deposition distance from the needle tip of the microneedle to the particles of biodegradable material and the water-soluble material can be obtained.

[0010] Furthermore, the present inventors have discovered that by treating porous microneedles obtained by the single emulsion method under specific conditions, porous microneedles from which water-soluble materials have been removed can be obtained, and that these microneedles have a higher collection ability than conventional porous microneedles.

[0011] That is, the present invention has the following configurations. [1] A porous microneedle comprising microspheres of a biodegradable material and a water-soluble material, wherein the microspheres of the biodegradable material are bonded to one another to form a network of interconnected pores, and the microneedle may comprise a microneedle substrate comprising the microspheres and a water-soluble material, wherein the volume ratio of the water-soluble material to the biodegradable material is 1:2 to 3. [2] The microneedle according to [1], wherein the water-soluble material fills the voids between the microsphere particles from the tip to the base of the microneedle (here, if the microneedle comprises the microneedle substrate, from the tip to the base of the microneedle). [3] The microneedle according to [1] or [2], wherein the biodegradable material comprises at least one selected from the group consisting of polylactic acid (PLA), polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG copolymer, polyhydroxybutyric acid, and ethyl cellulose. [4] The microneedle according to any one of [1] to [3], wherein the water-soluble material is polyvinyl alcohol (PVA), CMC (carboxymethyl cellulose), or starch. [5] A microneedle patch comprising the porous microneedle according to any one of [1] to [4]. [6] A method for producing a porous microneedle or a porous microneedle array, comprising the steps of: (a) preparing solution A by dissolving a biodegradable material in an organic solvent, mixing solution A with an aqueous solution containing a water-soluble material, and stirring the mixture to prepare a biodegradable material microsphere solution or suspension containing microspheres of the biodegradable material; (b) pouring the solution or suspension into a female mold; (c) drying the solution or suspension to obtain a microneedle precursor or a microneedle array precursor; and (d) heating the microneedle precursor at a predetermined temperature to partially turn the microspheres into a liquid phase or a rubbery state and bond them to each other, wherein the volume ratio of the water-soluble material to the biodegradable material in the obtained porous microneedle or porous microneedle array is 1:2 to 3.[7] The manufacturing method according to [6], wherein the biodegradable material comprises at least one selected from the group consisting of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG copolymer, polyhydroxybutyric acid, and ethyl cellulose. [8] The manufacturing method according to [6] or [7], wherein the water-soluble material is polyvinyl alcohol (PVA), CMC (carboxymethyl cellulose), or starch. [9] The method according to any one of [6] to [8], wherein the drying of the solution or suspension in step (c) is carried out by natural drying, a pressure drying treatment in which the solution or suspension is dried while applying pressure, or a combination thereof.

[10] The manufacturing method according to [9], wherein in step (c), after natural drying of the solution or suspension, a pressure drying treatment in which the solution or suspension is dried while applying pressure is carried out to obtain a microneedle precursor or a microneedle array precursor.

[11] The manufacturing method according to [9], wherein in step (c), a pressure drying treatment in which the solution or suspension is dried while applying pressure is carried out to obtain a microneedle precursor or a microneedle array precursor.

[12] A porous microneedle or a porous microneedle array obtained by the manufacturing method according to any one of [6] to

[11] .

[13] A method for manufacturing a porous microneedle or a porous microneedle array from which the water-soluble material has been removed, comprising the steps of: (a) preparing a solution A by dissolving a biodegradable material in an organic solvent, and mixing and stirring the solution A with an aqueous solution containing a water-soluble material to prepare a biodegradable material microsphere solution or suspension containing microspheres of the biodegradable material, (b) pouring the solution or suspension into a female mold, (c) drying the solution or suspension to obtain a microneedle precursor or a microneedle array precursor, (d) heating the microneedle precursor at a predetermined temperature to cause the microspheres to partially become liquid or rubbery and bond to each other, thereby obtaining a porous microneedle or a porous microneedle array, and (e) treating the porous microneedle or porous microneedle array obtained in step (d) with water.

[14] The manufacturing method according to

[13] , which comprises, after step (e), a step (f) of heating the porous microneedles or porous microneedle array treated with water at a temperature below the temperature at which the biodegradable material begins to melt near its melting point.

[15] The manufacturing method according to

[14] , wherein in step (e), the temperature at which the porous microneedles or porous microneedle array is treated with water is 20 to 60°C.

[16] The method according to any one of

[13] to

[15] , wherein the drying of the solution or suspension in step (c) is carried out by natural drying, a pressurized drying treatment in which the solution or suspension is dried while applying pressure, or a combination thereof.

[17] The manufacturing method according to

[16] , wherein in step (c), the solution or suspension is natural dried and then a pressurized drying treatment in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

[18] The manufacturing method according to

[16] , wherein in step (c), a pressure drying treatment is performed in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

[19] A porous microneedle or porous microneedle array substantially free of water-soluble materials, obtained by the manufacturing method according to any one of

[13] to

[18] .

[20] A porous microneedle formed from microspheres of a biodegradable material, wherein the microspheres of the biodegradable material are bonded to each other to form a network of interconnected pores, and the microneedle is substantially free of water-soluble materials.

[21] The microneedle according to

[20] , having an absorption volume of 8 to 150 μL.

[22] The microneedle according to

[20] or

[21] , having a mechanical strength (breaking strength) of 0.1 to 0.5 N.

[23] A microneedle patch comprising the porous microneedle according to any one of

[20] to

[22] .

[0012] The microneedles and microneedle arrays (details will be described later) according to the first embodiment of the present invention are composed of a water-soluble material and a biodegradable material in an optimal ratio, making it possible to provide porous microneedles that can efficiently collect body fluids. Furthermore, the method for manufacturing a microneedle (or a microneedle array) according to the first embodiment of the present invention can provide microneedles composed of a water-soluble material and a biodegradable material in an optimal ratio. In the method for manufacturing a microneedle (or a microneedle array) according to the first embodiment of the present invention, by appropriately adjusting the ratio of the water-soluble material and the biodegradable material at the start of manufacturing, microneedles with stable performance can be manufactured, and therefore the method can also be used for mass production of microneedles.

[0013] The manufacturing method according to the second embodiment of the present invention (described in detail below) can provide porous microneedles or porous microneedle arrays from which water-soluble material has been removed. Furthermore, the microneedles and microneedle arrays from which water-soluble material has been removed according to the second embodiment of the present invention can have a higher collection ability than conventional porous microneedles.

[0014] As a typical example of the single emulsion method, a non-limiting schematic diagram of a method for manufacturing porous microneedles using PLA and PVA is shown. Various morphologies (structures) of PLA particles and PVA inside porous microneedles obtained by the single emulsion method using PLA and PVA are shown. A 3D-CAD model of densely deposited PLA particles is shown for a porous microneedle obtained by the single emulsion method using PLA and PVA. A line graph of the model of a porous microneedle obtained by the single emulsion method using PLA and PVA is shown, with the x-axis representing the distance from the needle tip and the y-axis representing the volume, divided into (1) the range of distance from the needle tip where PLA particles are deposited and (2) the range where only PVA is present. In Example 1, a table and figure are shown in which a simulation was conducted on the amount of material layered on a microneedle array with a needle height of 1200 μm. In Example 1, when the PLA content is entered into the table form shown in Figure 5, the result is reflected in each cell of 1.0 mL to 0.5 mL of 5% (w / v) PVA solution. In Example 1, a repeating "pattern shape" is extracted from a dense collection of PLA microparticles with the same diameter of 11 μm, and the volume of the PLA microparticles and voids is compared. In Example 1, a schematic diagram is shown in which a 3D model of the recess of the female mold of the MAP is created and the volume is confirmed in 10 μm increments from 0 μm to 1620 μm from the needle tip. In Example 1, the result of creating a list of the entire MAP volume at the distance from the needle tip is shown. In Example 1, the result of creating a list of the entire MAP volume at the distance from the needle tip is shown. In Example 1, the result of creating a list of the entire MAP volume at the distance from the needle tip is shown. In Example 1, the result of creating a list of the entire MAP volume at the distance from the needle tip is shown. In Example 1, the result of creating a graph of the transition of the PLA volume and PVA volume (when the injection amount is 1.0 mL) is shown on the vertical axis and the horizontal axis, respectively. This shows the results of graphing the transitions in Example 1, with the distance from the needle tip on the horizontal axis and the PLA volume and PVA volume (when the injection amount is 1.0 to 0.5 mL) on the vertical axis. This shows a graph of the PLA volume and PVA volume versus the distance from the needle tip when the needle length is 300 μm and the PLA content is 100 mg in Example 1. This shows a stacked image of the MNs cross section obtained by the simulation of Example 1.1 shows a non-limiting schematic diagram of a method for producing porous PLA microneedles from which PVA has been removed according to the present invention. 2 shows evaluation results of the porous PLA microneedles from which PVA has been removed obtained in Example 2. 3 shows non-limiting schematic diagrams illustrating the detailed structure of microneedles due to differences in the drying process, for cases where only natural drying is performed and cases where natural drying and pressure drying treatment using a pressure vessel are performed in Production Methods 1 and 2 of the present invention. 4 shows a non-limiting schematic diagram of a case where pressure drying treatment using a pressure vessel is performed in step (c) in a method for producing porous PLA microneedles from which PVA has been removed according to the present invention (Example 3). 5 shows a schematic diagram of pressure drying using the pressure vessel used in Example 3. 6 shows a non-limiting schematic diagram of a case where only pressure drying treatment using a pressure vessel is performed in step (c) in a method for producing porous PLA microneedles from which PVA has been removed according to the present invention (Example 4).

[0015] I. First Embodiment of the Present Invention One aspect of the first embodiment of the present invention is a porous microneedle comprising microspheres of a biodegradable material and a water-soluble material, wherein the microspheres of the biodegradable material are bonded to one another to form a network of interconnected pores, and the microneedle may comprise a microneedle substrate comprising the microspheres and a water-soluble material, wherein the volume ratio of the water-soluble material to the biodegradable material is 1:2 to 3 (hereinafter also referred to as "microneedle 1 of the present invention").

[0016] Another aspect of the first embodiment of the present invention is a method for producing porous microneedles or porous microneedle arrays, comprising the steps of: (a) preparing solution A by dissolving a biodegradable material in an organic solvent, mixing solution A with an aqueous solution containing a water-soluble material, and stirring the mixture to prepare a biodegradable material microsphere solution or suspension containing microspheres of the biodegradable material; (b) pouring the solution or suspension into a female mold; (c) drying the solution or suspension to obtain a microneedle precursor or a microneedle array precursor; and (d) heating the microneedle precursor at a predetermined temperature to partially turn the microspheres into a liquid phase or a rubbery state and bond them to each other, wherein the volume ratio of the water-soluble material to the biodegradable material is 1:2 to 3 (hereinafter also referred to as "production method 1 of the present invention").

[0017] Hereinafter, a microneedle 1 of the present invention and a manufacturing method 1 of the present invention will be described in detail for a first embodiment of the present invention.

[0018] 1. Microneedle 1 of the Present Invention (1) Structure and Characteristics of the Microneedle The microneedle 1 of the present invention is a porous microneedle containing microspheres of a biodegradable material and a water-soluble material, and is characterized in that the volume ratio of the water-soluble material to the biodegradable material is 1:2 to 3.

[0019] While not intending to be bound by theory, the present inventors have discovered that the single emulsion method, when forming porous microneedles formed from a biodegradable polymer such as polylactic acid (PLA) and a surfactant (water-soluble material) such as polyvinyl alcohol (PVA), accumulates PLA particles, and a PVA solution penetrates into the gaps between them. When dried, the adhesive PVA bonds the PLA particles together, allowing them to maintain their shape even after demolding. Furthermore, during the heating process, the entire microneedle can be exposed to ambient temperature, which has the advantage of allowing for uniform heating. As a typical example of the single emulsion method disclosed in Patent Document 1, a non-limiting schematic diagram of a method for manufacturing porous microneedles using PLA and PVA is shown in Figure 1. However, when actually producing microneedles using the single emulsion method, it was necessary to gradually change the amount of materials and the manufacturing process to find the optimal conditions, and therefore, if the conditions changed, it was necessary to adjust the amount of materials from scratch. Furthermore, even if optimization was possible, it was only possible under one condition; if the length or number of needles, or the thickness of the microneedle substrate, etc. were different, it was necessary to adjust the amount of materials such as PLA or PVA from scratch and repeat the prototyping and evaluation, which was inefficient.

[0020] For example, in porous microneedles obtained by the single emulsion method using PLA and PVA, the PLA, which has a melting point of 170°C, is coated with PVA, which has a higher melting point. Therefore, the PLA particles are heated to 180°C, slightly higher than the melting point of the PLA, to partially transform them into a liquid or rubbery state, thereby bonding them together. However, the optimal ratio of PLA and PVA amounts required for efficient collection of body fluids has not been clearly determined. Therefore, if the amount of PVA is too low relative to the amount of PLA particles, the PVA cannot coat the PLA particles on the backside of the microneedle. When heated to 180°C, above the melting point of the PLA, the uncoated PLA particles melt, blocking the pore network (capillaries) and preventing collection of body fluids (see the right diagram in Figure 2). Furthermore, if the amount of PVA is too high relative to the amount of PLA particles, a PVA-only layer forms covering the PLA particle deposition layer on the backside of the microneedle, making it difficult for the body fluid to dissolve the PLA, making it difficult to collect samples in a short time. A thick PVA-only layer also makes it difficult for heat to reach the PLA particles inside the backside. While the needle side reaches a temperature where the PLA particles are partially in a liquid or rubbery state and bonded to each other, the backside does not reach a temperature where the PLA particles are partially in a liquid or rubbery state and bonded to each other, resulting in uneven heating (see the left side of Figure 2). Furthermore, the water-soluble PVA dissolves in the body fluid during puncture and is absorbed along with the biomarkers in the body fluid, which may affect the analytical results depending on the biomarker. Furthermore, because the time it takes for the PVA to dissolve is added to the time required for body fluid collection, even though the method is already fast, there is a need for further time reduction.

[0021] Thus, in the method for producing porous microneedles (porous MNs) using the single emulsion method, the optimal ratio of the amount of biodegradable material such as PLA and the amount of water-soluble material such as PVA was not clearly defined, making it difficult to stably prepare porous microneedles capable of efficiently collecting body fluids. The inventors discovered that this was due to practical optimization in which conditions were changed little by little, and that in order to theoretically optimize the porous microneedles, it was necessary to clarify the deposition state of the particles of biodegradable material such as PLA and the water-soluble material such as PVA.

[0022] Therefore, the inventors first created a model of porous microneedles obtained by the single emulsion method using PLA and PVA, in which PLA particles were densely deposited, using 3D-CAD. From the pattern shape, they confirmed the volume ratio of the pattern shape, PLA particles, and voids between the particles, and found it to be 1:0.7404:0.2596 (see Figure 3, Examples). This indicates that the volume ratio of PLA to PVA is 2.85:1 (3:1 by mass) (Figure 3).

[0023]

[0024] Furthermore, a bar graph was created to display the line graph in the shape of a needle, with the distance from the needle tip on the x-axis and the volume on the y-axis (see Example, Figure 13). A simulation was then created using the calculated volume ratio, and the optimized content was input. After subtracting the blade weight and inputting the PVA amount again, it was confirmed that the PLA and PVA deposition amounts were equal. Note that the blade here primarily refers to the precipitated PVA, which will be described later.

[0025] In this way, the inventors have studied the optimization of the material ratio using porous microneedles formed from PLA particles and PVA as an example, and have found that even if the needle height and number of the porous MNs, the thickness of the microneedle substrate, etc. are different, the volume ratio of water-soluble material to biodegradable material in the finished MNs is 1:2 to 3, preferably 1:2.85 (weight ratio is "1:3").

[0026] Due to PVA's surface activity, when PLA particles and a PVA solution are mixed and poured into a female mold, a thin PVA skin precipitates on the side of the recess in the female mold during the drying process. Note that "precipitation" here includes the evaporation of water by drying, leaving PVA behind. The precipitated thin PVA skin is PVA that spreads and solidifies on the side of the recess in the female mold. The thin PVA skin can form around the entire periphery of the side of the female mold. The precipitated PVA may contain other components (e.g., biodegradable materials such as PLA, carboxymethylcellulose (CMC), and hyaluronic acid). Since the precipitated PVA is unnecessary in the final product state, it can be discarded. By measuring the weight of the precipitated PVA and adding it to the amount of PVA initially poured into the female mold, the resulting mixture of PVA and PLA particles will have a volume ratio of 1:2-3, preferably 1:2.85, and a mass ratio of 1:3. In this way, taking into account the amount of PVA discarded during production, it is also possible to calculate the optimal amounts of PLA and PVA materials at the start of production. The precipitated PVA can be discarded by separating the portion containing the precipitated PVA from the microneedle. The separated material may contain other components (e.g., PLA, carboxymethyl cellulose (CMC), hyaluronic acid). Separation can be performed, for example, by cutting with a blade. The mixed portion of PVA and PLA particles in the microneedle (precursor) obtained by this separation has a volume ratio of 1:2 to 3, preferably 1:2.85, and a mass ratio of 1:3. The weight of the PVA or PLA contained in the separated material can be measured and added as feedback to the weight of the PVA or PLA of the resulting microneedle to calculate the amount of PVA or PLA to be initially injected into the female mold. Alternatively, the weight of the separated material may be considered the weight of PVA and added as feedback to the weight of the PVA or PLA of the resulting microneedle.

[0027] In the microneedle 1 of the present invention, the biodegradable material includes at least one selected from the group consisting of polylactic acid (PLA), polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG copolymer, polyhydroxybutyric acid, and ethyl cellulose. The biodegradable material is preferably polylactic acid or polyglycolic acid, and more preferably polylactic acid.

[0028] In the microneedle 1 of the present invention, the water-soluble material is polyvinyl alcohol (PVA), CMC (carboxymethyl cellulose), or starch, and preferably polyvinyl alcohol.

[0029] The microneedle 1 of the present invention may be provided with a microneedle substrate. That is, the microneedle 1 of the present invention can also be used as a microneedle array in which a plurality of microneedles of the present invention are erected on a microneedle substrate. That is, in another aspect of the present invention, the microneedle of the present invention is a microneedle array in which a plurality of microneedles are erected on a microneedle substrate (hereinafter also referred to as "microneedle array 1 of the present invention").

[0030] Because the microneedle 1 and the microneedle array 1 of the present invention are themselves porous, the microneedle array of the present invention can also be used as a microneedle array patch or patch-type body fluid collection system without using an absorbent material such as filter paper. The microneedle 1 of the present invention can also be provided on an absorbent material capable of absorbing interstitial fluid and used as a microneedle array patch or patch-type body fluid collection system. The microneedle array 1 of the present invention can also be joined to an absorbent material capable of absorbing interstitial fluid and used as a microneedle patch or patch-type body fluid collection system.

[0031] In the microneedle array 1 of the present invention, the microneedles can be arranged vertically and horizontally as desired. The spacing between the microneedles is preferably small in order to absorb the intercellular fluid sample, and is preferably 500 to 2000 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 copolymer, polyhydroxybutyric acid, and ethyl cellulose. In one preferred embodiment, the microneedle substrate is formed from the same biodegradable and water-soluble material as the microneedles, and the two are integrally formed.

[0035] In the microneedle 1 of the present invention, the water-soluble material fills the gaps between the microsphere particles from the tip to the bottom of the microneedle (here, in the case where the microneedle has a microneedle substrate formed from a biodegradable material and a water-soluble material, from the tip to the bottom of the microneedle). Furthermore, if the water-soluble material is adhesive PVA or the like, the PVA plays a role in fixing (maintaining) the positions (spacing) between particles of the biodegradable material such as PLA.

[0036] In the microneedle 1 of the present invention, by determining the optimal volume ratio of the final amount of biodegradable material particles to the amount of water-soluble material, if the amount of water-soluble material such as PVA is small relative to the amount of biodegradable material particles, a layer of only the biodegradable material will accumulate on the microneedle, the biodegradable material particles will not be coated with the water-soluble material, and when heated at a temperature above the melting point of the biodegradable material, the biodegradable material particles that are not coated will dissolve and block the pore network (capillaries), making it impossible to collect body fluids.Furthermore, if the amount of water-soluble material is large relative to the amount of biodegradable material particles, a single layer of water-soluble material will occur that covers the deposited layer of biodegradable material particles, and it will take time for body fluids to dissolve the biodegradable material, making it difficult to collect body fluids in a short time. Furthermore, if the biodegradable material monolayer is thick, it becomes difficult for heat to reach the biodegradable material particles inside the back surface side, and when the needle side reaches a temperature at which the biodegradable material particles are partially put into a liquid or rubbery state and bonded to each other, the back surface side has not yet reached a temperature at which the biodegradable material particles are partially put into a liquid or rubbery state and bonded to each other, which solves the problem of uneven heating. Note that the formation of a monolayer of water-soluble material (e.g., a monolayer of PVA) is not prohibited in the microneedle of the present invention.

[0037] The microneedle 1 of the present invention may be composed only of the above-mentioned biodegradable material and water-soluble material, or may contain other additives (e.g., carboxymethyl cellulose (CMC), hyaluronic acid) as trace components to the extent that the function of the microneedle of the present invention is not impaired. Furthermore, the microneedle 1 of the present invention 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.

[0038] The porosity of the microneedle 1 of the present invention 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 ｄｒｙ The mass is then measured immediately and the W ｗｅｔ Record as Calculate the porosity using the following formula:

[0039]

[0040] 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 )

[0041] The microneedle 1 of the present invention has excellent water absorption capacity, such as water absorption speed. When the microneedle precursor is heated at a high temperature, the microspheres are partially transformed into a liquid phase or rubbery state by the heat treatment, and bond to form a strong interconnected micropore network, which allows efficient extraction of interstitial skin fluid by capillary force.

[0042] Absorption volume is one indicator of water absorption capacity, and the absorption volume of the microneedle 1 of the present invention is usually 8 to 150 μL, preferably 20 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 to 2% agarose gel, removing it from the gel after 2 minutes, and measuring its weight.

[0043] The microneedle 1 of the present invention has an absorption rate of typically 0.01 to 0.3 μL / min per MN, preferably 0.2 to 0.3 μL / min. The absorption rate is measured by puncturing a microneedle array in which 169 porous PLA MNs are arranged upright in a 1 to 2% agarose gel, removing the microneedle array from the gel after 2 minutes, and measuring its weight.

[0044] The microneedle 1 of the present invention has a strength such that the load at the yield point measured under the following conditions is 0.1 N or more, preferably 0.3 N or more. Conditions: A compressive load is applied to the microneedle alone in the axial direction, and the load at the yield point obtained from the load-displacement curve is measured as the breaking strength. The microneedle of the present invention has such high mechanical strength, which makes it possible to realize the inspection device of the present invention.

[0045] (2) Shape of the microneedle The shape of the microneedle 1 of the present invention 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.

[0046] The diameter of the tip of the microneedle 1 of the present invention 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 to 2500 μm inclusive, taking into account that it reaches the dermis, and more preferably 300 μm to 1500 μm inclusive, taking into account that it does not stimulate pain sensations.

[0047] 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.

[0048] Regarding the angle of the tip of the microneedle of the present invention, 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 preferable, as the force required for the microneedle to penetrate is less than 0.1 N.

[0049] Embodiment 1 of the present invention includes a microneedle patch comprising the microneedle 1 of the present invention and / or the microneedle array 1 of the present invention (hereinafter also referred to as the "microneedle patch 1 of the present invention"). Furthermore, the microneedle 1 of the present invention and / or the microneedle array 1 of the present invention may further be provided with filter paper as a means for storing collected interstitial fluid. The filter paper may be provided with a sensor that detects a biomarker from the stored interstitial fluid.

[0050] 2. Manufacturing Method 1 of the Present Invention One aspect of Embodiment 1 of the present invention is a method for manufacturing porous microneedles or porous microneedle arrays, comprising the steps of: (a) preparing solution A by dissolving a biodegradable material in an organic solvent, mixing solution A with an aqueous solution containing a water-soluble material, and stirring the mixture to prepare a biodegradable material microsphere solution or suspension containing microspheres of the biodegradable material; (b) pouring the solution or suspension into a female mold; (c) drying the solution or suspension to obtain a microneedle precursor or a microneedle array precursor; and (d) heating the microneedle precursor at a predetermined temperature to partially convert the microspheres into a liquid phase or a rubbery state and bond them to each other, wherein the volume ratio of the water-soluble material to the biodegradable material in the obtained porous microneedles or porous microneedle array is 1:2 to 3.

[0051] The biodegradable material includes at least one selected from the group consisting of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG copolymer, polyhydroxybutyric acid, and ethyl cellulose, and is preferably polylactic acid or polyglycolic acid, and more preferably polylactic acid.

[0052] The water-soluble material is polyvinyl alcohol (PVA), CMC (carboxymethyl cellulose), or starch, and preferably polyvinyl alcohol.

[0053] 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.

[0054] 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.

[0055] The organic solvent is not particularly limited as long as it dissolves the biodegradable material, and examples thereof include dichloromethane and acetone.

[0056] The concentration of the biodegradable material in solution A is, for example, 0.05 to 0.1% (w / v).

[0057] Solution A and / or the aqueous solution containing the water-soluble material 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.

[0058] 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.

[0059] In step (b), 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.

[0060] The mold may have only the template shape of the microneedle to be prepared. In this case, a single microneedle can be obtained. The mold can also be provided with a cavity having a shape in which a microneedle substrate and multiple microneedles are bonded to each other. In this case, a microneedle array can be obtained in which multiple microneedles are bonded to the microneedle substrate and arranged upright. The micromold itself can have a desired number of cavities. The cavities in the micromold itself can also be appropriately arranged vertically and horizontally. The spacing between the cavities is preferably 500 to 2000 μm.

[0061] After injecting a solution or suspension of biodegradable microspheres into the cavity of the female mold, it is preferable to place the mold in a vacuum or apply centrifugal force to pack or deposit the microspheres in the cavity.

[0062] 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 20 to 100°C, and the drying time can be appropriately determined, but is typically 1 to 48 hours.

[0063] In addition, in step (c), the method for drying the solution or suspension of biodegradable material microspheres can be carried out by natural drying, a pressurized drying process in which the solution or suspension is dried while applying pressure, or a combination of these.

[0064] The above drying method can be selected arbitrarily, but in particular, when manufacturing microneedles with a large height (needle height) (for example, a needle height of 800 μm or more, which may vary slightly depending on the manufacturing conditions), it is preferable to use a pressurized drying process or a combination of natural drying and pressurized drying process. By using these drying methods, it is possible to obtain microneedles with suppressed bending of the needle tip, even when the needle height of the microneedle is large.

[0065] While not intending to be bound by theory, Figure 16 shows non-limiting schematic diagrams illustrating the detailed structure of microneedles depending on the drying process, when only natural drying is performed, and when natural drying and pressurized drying using a pressure vessel are performed. In the drying process (c), when a solution or suspension of biodegradable material microspheres is only natural dried, microspheres such as PLA microparticles are stacked by gravity, and the gaps are filled with a water-soluble material such as PVA, which is thought to fix the microparticles after drying (see the left diagram in the upper part of Figure 16). In this case, the gaps filled with the water-soluble material are relatively large, and in the heating process (d) after the process (c), the microsphere particles are partially converted to a liquid phase or rubbery state and bonded to each other, which is thought to slightly reduce the gaps, but most of the gaps are maintained. Furthermore, in the second embodiment of the present invention described below, even when the microneedle is heated after the water-soluble material is removed and then again after the water-soluble material is removed, relatively large gaps remain between the microsphere particles. The presence of gaps between such relatively large microsphere particles (including gaps filled with the water-soluble material and gaps remaining after the water-soluble material has been removed) is not particularly problematic when the microneedle needle height is small, but as the needle height increases, the needle tip becomes more prone to bending. In contrast, when a pressurized drying process is performed in the drying step (c) to dry a solution or suspension of biodegradable material microspheres while applying pressure, or when a combination of natural drying and pressurized drying is performed, after the microspheres such as PLA microparticles are stacked by gravity, the pressure pushes in the solution of water-soluble material such as PVA, thereby pushing in each microparticle, and further the pressure pushes in the microparticles themselves, resulting in a dense structure, where the water-soluble material such as PVA in the gaps dries and fixes the microparticles (see the left diagram in the lower part of Figure 16). In this case, the gaps filled with the water-soluble material are small, and in the heating step (d) after step (c), the microsphere particles partially become liquid or rubbery and bond to each other, which is thought to further reduce the gaps.

[0066] In one preferred embodiment of manufacturing method 1 of the present invention, in step (c), the solution or suspension is naturally dried, and then subjected to a pressurized drying process in which the solution or suspension is dried while applying pressure, thereby obtaining a microneedle precursor or a microneedle array precursor.

[0067] In another preferred embodiment of the manufacturing method 1 of the present invention, in step (c), a pressure drying treatment is carried out in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

[0068] It is preferable to use a pressure vessel for pressure drying. When drying in a pressure vessel, if the vessel is sealed, water vapor generated during drying cannot escape to the outside of the vessel, making drying impossible. Therefore, it is preferable to use an air leak, which allows water vapor to be discharged outside the pressure vessel.

[0069] When pressure drying is performed using a pressure vessel, the drying time is preferably about 72 to 96 hours at room temperature. Furthermore, when natural drying and pressure drying using a pressure vessel are combined, natural drying is preferably performed for about 18 to 24 hours at room temperature, and pressure drying using a pressure vessel (preferably with air leakage) is preferably performed for about 24 to 36 hours. This drying time makes it possible to produce microneedles with a uniform structure and small interstices between the microsphere particles.

[0070] The pressure inside the pressure vessel is preferably in the range of more than 0.1 MPa to 0.5 MPa, but from the viewpoint of a balance with the promotion of drying, it is more preferably around 0.2 MPa. The pressure inside the pressure vessel can be adjusted by changing the pressure of the air introduced by the compressor.

[0071] Furthermore, when pressure drying is performed using a pressure vessel, it is preferable to install a cover so that it partially or entirely covers the female mold into which the biodegradable microsphere solution or suspension has been poured. This prevents the microneedles from being directly subjected to the air pressure from the compressor, allowing for the production of uniform microneedles without being affected by air pressure that can vary depending on the position within the mold. Placing silica gel inside the pressure vessel can also speed up the drying time.

[0072] After drying, water evaporates from the solution or suspension of biodegradable material microspheres to obtain a microneedle precursor or a microneedle array precursor composed of biodegradable material microspheres. At this stage, the microneedle precursor may be removed from the mold and subjected to the next step (d). Alternatively, at this stage, the microneedle precursor may be left in the mold and subjected to the heating step of the next step (d).

[0073] In step (d), the microneedle precursor is heated at a predetermined temperature. In the microneedle precursor, the individual microspheres retain their original shape and are not bonded to one another. In the manufacturing method of the present invention, the microneedle precursor or microneedle array 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 copolymer, 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 heating time is, for example, 10 to 120 minutes.

[0074] The porous microneedles obtained by the manufacturing method of the present invention described above have microspheres that are partially in a liquid or rubbery state and bonded to each other, forming a network of interconnected (communicating) continuous pores, thereby forming a robust pore structure.

[0075] In manufacturing method 1 of the present invention, the volume ratio of water-soluble material particles to biodegradable material particles in the obtained porous microneedles or porous microneedle array is 1:2 to 3. In manufacturing method 1 of the present invention, the "obtained porous microneedles or porous microneedle array" refers to the porous microneedles or porous microneedle array obtained through the heating step of step (d) (i.e., the porous microneedles or porous microneedle array obtained by manufacturing method 1 of the present invention). Here, the optimal amounts of water-soluble material and biodegradable material at the start of manufacturing are calculated taking into account the amounts of water-soluble material and biodegradable material discarded during manufacturing. For example, when the water-soluble material is PVA, due to its surface activity, PLA precipitates on the side surfaces of the recesses in the female mold during the drying process after mixing and injecting biodegradable material particles and a PVA solution into the female mold. The precipitated PVA is not needed in the finished product and is therefore discarded, but the weight of the precipitated PVA is measured and fed back and added to the amount of PVA initially injected into the female mold, so that the mixture of PVA and biodegradable material particles in the finished product is adjusted to a volume ratio of 1:2 to 3, preferably 1:2.85 (mass ratio of 1:3).

[0076] An example of a method for calculating the optimal amounts of water-soluble material and biodegradable material at the start of production is described below for porous microneedles formed from PLA particles and PVA. The procedure is as follows: 1. Determine the height of the microneedle to be produced (microneedle needle height + microneedle substrate thickness).

[0077] 2. Using simulation, input the amount of PLA so that the thickness of the back layer (microneedle substrate) that is considered necessary for the PLA fine particles to constitute is obtained. For example, find the amount of PLA so that the stacked height of the PLA is the same as the height of the microneedle to be manufactured.

[0078] 3. Next, the amount of PVA contained is input into the simulation so that the ratio of PVA amount to PLA amount is 1:2 (weight ratio), and the position of the PVA accumulation amount relative to the accumulation amount of PLA microparticles is confirmed. For example, when the PVA amount is input, the PVA accumulation height displayed on the map is checked to see if it is the same as, higher than, or lower than the PLA stacking height, and the PVA amount is determined.

[0079] 4. A prototype microneedle is fabricated under the above conditions to confirm that the pore network of the microneedle is not collapsed. (Conditions such as strength, absorption volume, and the presence or absence of a PVA-only layer may also be confirmed.) After the microneedle has dried, the weight of the part (also called the "wing") cut off from the microneedle, including the thin PVA skin that has actually precipitated (or formed) on the side of the recess in the female mold, is measured, and the weight of this wing (most of which is PVA) is fed back to the initially determined amount of PVA to adjust it to the appropriate amount.

[0080] In this way, the optimum volume ratio between the water-soluble material and the biodegradable material at the start of production can be determined.

[0081] As a non-limiting example, consider a case where the needle height is 800 μm, the microneedle substrate thickness is 150 μm, and there is only one cavity (recess) in the female mold. The amounts of PLA and PVA required to fill this cavity are 30 mg of PLA, 25 mg of PVA, and 15 mg of blade weight. Since the blade is composed almost entirely of PVA, the amount of PVA remaining in the microneedle is 10 mg. The weight ratio of PVA:PLA at the start of production is 2.5:3. This is the ratio of the microneedle (precursor) in the process prior to the separation process of the PVA (precipitated PVA) that will be separated later. After the separation process of the precipitated PVA, the volume ratio of PVA:PLA in the microneedle (precursor) obtained is 1:2-3. After the heating process, the volume ratio of PVA:PLA in the microneedle obtained is 1:2-3.

[0082] Another aspect of the present invention is a porous microneedle or porous microneedle array obtained by manufacturing method 1 of the present invention. Also, embodiment 1 of the present invention includes a microneedle patch comprising porous microneedles and / or a porous microneedle array obtained by manufacturing method 1 of the present invention (hereinafter also referred to as "microneedle patch 1A of the present invention").

[0083] By using the microneedle patch 1 or 1A of the present invention, interstitial fluid can be collected in place of a blood collection needle, and the operation is painless and simple. Furthermore, the microneedle patch 1 or 1A of the present invention can be integrated with a sensor as a medical device, making it possible to detect various biomarkers.

[0084] The manufacturing method 1 of the present invention can be used to manufacture microneedles. Furthermore, since the manufacturing method 1 of the present invention can manufacture microneedles with stable performance, the manufacturing method 1 of the present invention can also be used for mass production of microneedles. The microneedle 1 of the present invention and / or the microneedle array 1 of the present invention can also be used for drug delivery.

[0085] II. Second embodiment of the present invention One aspect of the second embodiment of the present invention is a method for producing porous microneedles or porous microneedle arrays from which the water-soluble material has been removed, comprising the steps of: (a) preparing solution A by dissolving a biodegradable material in an organic solvent, mixing solution A with an aqueous solution containing a water-soluble material, and stirring the mixture to prepare a biodegradable material microsphere solution or suspension containing microspheres of the biodegradable material; (b) pouring the solution or suspension into a female mold; (c) drying the solution or suspension to obtain a microneedle precursor or a microneedle array precursor; (d) heating the microneedle precursor at a predetermined temperature to partially convert the microspheres into a liquid phase or rubbery state and bond them to each other to obtain a porous microneedle or a porous microneedle array; and (e) treating the porous microneedles or porous microneedle array obtained in step (d) with water (hereinafter also referred to as "production method 2 of the present invention").

[0086] 1. Manufacturing Method 2 of the Present Invention By manufacturing method 2 of the present invention, it is possible to manufacture porous microneedles or porous microneedle arrays from which water-soluble materials have been removed.

[0087] Steps (a) to (d) in Production Method 2 of the present invention are basically the same as steps (a) to (d) in Production Method 1 of the present invention. However, in Production Method 2 of the present invention, the volume ratio of the water-soluble material to the biodegradable material in the porous microneedle or porous microneedle array obtained through the heating step of step (d) does not need to be 1:2-3, but the volume ratio is preferably 1:2-3, and more preferably 1:2.85 (1:3 in mass ratio).

[0088] In the manufacturing method 2 of the present invention, in step (c), the method for drying the solution or suspension of biodegradable material microspheres can be carried out by natural drying, a pressurized drying process in which the solution or suspension is dried while applying pressure, or a combination of these.

[0089] The above drying method can be selected arbitrarily, but in particular, when manufacturing microneedles with a large height (needle height) (for example, a needle height of 800 μm or more, which may vary slightly depending on the manufacturing conditions), it is preferable to use a pressurized drying process or a combination of natural drying and pressurized drying. By using these drying methods, it is possible to obtain microneedles with suppressed bending of the needle tip even when the needle height of the microneedle is large. The reason for this is as described in detail in Manufacturing Method 1 of the present invention.

[0090] In one preferred embodiment of manufacturing method 2 of the present invention, in step (c), the solution or suspension is naturally dried, and then a pressurized drying process is carried out in which the solution or suspension is dried while applying pressure, thereby obtaining a microneedle precursor or a microneedle array precursor.

[0091] In another preferred embodiment of the manufacturing method 2 of the present invention, in step (c), a pressure drying treatment is carried out in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

[0092] It is preferable to use a pressure vessel for pressure drying. When drying in a pressure vessel, if the vessel is sealed, water vapor generated during drying cannot escape, making drying impossible. Therefore, it is preferable to have an air leak, which allows water vapor to be discharged outside the pressure vessel.

[0093] When pressure drying is performed using a pressure vessel, the drying time is preferably about 72 to 96 hours at room temperature. Furthermore, when natural drying and pressure drying using a pressure vessel are combined, natural drying is preferably performed for about 18 to 24 hours at room temperature, and pressure drying using a pressure vessel (preferably with air leakage) is preferably performed for about 24 to 36 hours. This drying time makes it possible to produce microneedles with a uniform structure and small interstices between the microsphere particles.

[0094] The pressure inside the pressure vessel is preferably in the range of more than 0.1 MPa to 0.5 MPa, but from the viewpoint of a balance with the promotion of drying, it is more preferably around 0.2 MPa. The pressure inside the pressure vessel can be adjusted by changing the pressure of the air introduced by the compressor.

[0095] Furthermore, when pressure drying is performed using a pressure vessel, it is preferable to install a cover so that it partially or entirely covers the female mold into which the biodegradable microsphere solution or suspension has been poured. This prevents the microneedles from being directly subjected to the air pressure from the compressor, allowing for the production of uniform microneedles without being affected by air pressure that can vary depending on the position within the mold. Placing silica gel inside the pressure vessel can also speed up the drying time.

[0096] In step (e) of manufacturing method 2 of the present invention, the porous microneedles or porous microneedle array obtained in step (d) is treated with water. The treatment with water can be carried out, for example, by immersing (saturating) the porous microneedles or porous microneedle array in a hot bath. By treating the porous microneedles or porous microneedle array with water, the water-soluble material dissolves in water, thereby obtaining porous microneedles or porous microneedle arrays from which the water-soluble material has been removed.

[0097] The water treatment temperature (preferably the immersion temperature) is desirably a temperature that is unlikely to affect the biodegradable material, and is desirably a temperature below the glass transition point. When the biodegradable material is PLA, the glass transition temperature of PLA is 50 to 60°C, so a temperature below the glass transition point, 20 to 60°C, is desirable. The water treatment can be carried out for a predetermined period of time; for example, the water treatment (preferably the immersion in water) can be carried out for 20 to 60 minutes.

[0098] In manufacturing method 2 of the present invention, the volume ratio of the voids from which the water-soluble material has been removed to the biodegradable material in the porous microneedle or porous microneedle array obtained by further undergoing step (e) is preferably 1:2 to 3, and more preferably 1:2.85 (1:3 in mass ratio).

[0099] In manufacturing method 2 of the present invention, following step (e), a further step (f) can be included in which the water-treated porous microneedles or porous microneedle array (i.e., the porous microneedles or porous microneedle array from which the water-soluble material has been removed) is heated. The heating temperature is preferably near the melting point of the biodegradable material, and when the biodegradable material is PLA, it is preferably 160°C or lower. This heating temperature may be slightly lower than the heating temperature in the first heating step.

[0100] In the manufacturing method 2 of the present invention, porous microneedles or porous microneedle arrays from which the water-soluble material has been removed can be obtained by treating with water without undergoing the above-mentioned reheating step. On the other hand, if the removal of the water-soluble material reduces the mechanical strength of the microneedles, in the manufacturing method 2 of the present invention, after removing the water-soluble material from the porous microneedles or porous microneedle array, the microneedles are heated to slightly deform the biodegradable material and increase the bonding strength between the biodegradable material particles, thereby achieving a high yield while maintaining mechanical strength. Removing the water-soluble material makes it easier for the biodegradable material particles to bond together. Furthermore, since the heating temperature is near the melting point of the biodegradable material, the biodegradable material particles do not completely melt, and the biodegradable material particles bond together while maintaining the pore network (capillaries), thereby providing mechanical strength.

[0101] In manufacturing method 2 of the present invention, the volume ratio of the voids from which the water-soluble material has been removed to the biodegradable material in the porous microneedle or porous microneedle array obtained by further undergoing step (f) is preferably 1:2 to 3, and more preferably 1:2.85 (1:3 in mass ratio).

[0102] Another aspect of the second embodiment of the present invention is a porous microneedle or porous microneedle array that is substantially free of water-soluble materials, obtained by Production Method 2 of the present invention.

[0103] Another aspect of the second embodiment of the present invention is a porous microneedle formed from microspheres of a biodegradable material, in which the microspheres of the biodegradable material are bonded to one another to form a network of interconnected pores, and which is substantially free of water-soluble materials (hereinafter also referred to as "microneedle 2 of the present invention").

[0104] The microneedle 2 of the present invention may be provided with a microneedle substrate. That is, the microneedle 2 of the present invention can also be used as a microneedle array in which a plurality of microneedles of the present invention are erected on a microneedle substrate. That is, in another aspect of the present invention, the microneedle 2 of the present invention is a microneedle array in which a plurality of microneedles are erected on a microneedle substrate (hereinafter also referred to as "microneedle array 2 of the present invention"). Details of the microneedle substrate, shape, etc. of the microneedle array 2 of the present invention are the same as those described in detail for the microneedle array 1 of the present invention.

[0105] The microneedle 2 of the present invention preferably has an absorption volume of 8 to 150 μL. The absorption volume varies depending on the volume of the microneedle. For example, if the volume of the biodegradable material is 80 mm ３ In this case, the theoretical absorption volume is 28.07 mm ３ This corresponds to an absorbed amount of 28.07 μL. The absorbed volume can be measured by inserting a microneedle array of 289 porous PLA MNs into a 1% to 2% agarose gel, removing it from the gel after 2 minutes, and measuring its weight.

[0106] Furthermore, the absorption volume is approximately equal to the volume of the (removed) water-soluble material in the resulting microneedle, and is also approximately equal to the volume of the non-biodegradable material portion. Furthermore, the volume of the continuous pore network is approximately equal to the volume of the water-soluble material. Therefore, when the volume ratio of the water-soluble material to the biodegradable material is 1:2-3, the volume ratio of the absorption volume to the biodegradable material is 1:2-3. The absorption volume can also be determined by the porosity measurement method described above.

[0107] The microneedle 2 of the present invention preferably has a mechanical strength (breaking strength) of 100 mN to 500 mN (0.1 to 0.5 N), more preferably 100 mN to 300 mN (0.1 to 0.3 N).

[0108] Another aspect of the second embodiment of the present invention is a microneedle patch (hereinafter also referred to as "microneedle patch 2 of the present invention") comprising a microneedle 2 of the present invention or a microneedle array 2 of the present invention, and an absorbent material capable of absorbing interstitial fluid.

[0109] The absorbent material capable of absorbing interstitial fluid, the structure of the microneedle patch, etc. in the microneedle patch 2 of the present invention are the same as those described in detail for the microneedle patch 1 of the present invention.

[0110] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0111] Example 1 A simulation was performed using the table and diagram shown in Figure 5 to determine the material layering amount of a MAP (microneedle array patch (meaning a microneedle patch equipped with a microneedle array)) with a needle height of 1200 μm. Here, a MAP layering diagram was displayed for a material preparation in which the PLA content was constant even when the injection amount of 5% (w / t) PVA solution was changed from 1.0 to 0.5 mL. The calculation flow and calculation form are described in detail below.

[0112] 1-1. Calculation of Volume (1) When the PLA content is entered in the table form shown in Figure 5, it is reflected in each cell of 1.0 mL to 0.5 mL of the 5% (w / v) PVA solution (see Figure 6). (2) The densities of PLA and PVA were entered. (3) The PLA volume and PVA volume for each injection amount were calculated using the formula "Volume = Mass (content) ÷ Density."

[0113] 1-2. Volume ratio of voids in PLA microparticles (microspheres) (4) Repeated "pattern shapes" were extracted from a densely packed mass of PLA microparticles with the same diameter of 11 μm, and the volume of the PLA microparticles and voids was compared (see Figure 7). Comparing the case where PLA microparticles were poured into a female mold with the case where dissolved resin (not microparticles) was poured, the deposition distance from the needle tip was equal when an amount of PLA microparticles 0.7404 times the amount of dissolved resin was poured. Because PVA fills the voids in the PLA microparticles, the deposition distance from the needle tip was equal when an amount of PVA 0.2596 times the amount of dissolved resin was poured.

[0114] 1-3. Calculating the volume of the entire MAP using 3D CAD (5) A 3D model of the female recess of the MAP was created, and the volume was confirmed in 10 μm increments from 0 μm to 1620 μm at the needle tip (see Figure 8). Here, numerical calculations alone may not be able to accurately calculate volume ratios, etc., depending on the shape of the microneedle. However, using a 3D-CAD model has the advantage of being able to calculate the volume regardless of the shape, whether the outer shape is elliptical or curved. The volume can also be calculated using methods other than the 3D model (for example, a formula).

[0115] 1-4. Create a table of the volume of the entire MAP at the distance from the needle tip. (6) A table of volumes was created every 10 μm from the needle tip, along with the PLA and PVA volumes at that time. (7) Since the PLA to PVA volume ratio is "0.7404:0.2596" from "1-2. Volume ratio of voids in PLA microparticles," the entire MAP volume was set to "0.7404 times the volume of the entire MAP" (preprocessing). (8) Because there is an upper limit to the amount of PLA, when the volume increases and reaches the upper limit, an IF function is used to prevent it from exceeding the upper limit [Upper limit setting]. = IF (PLA volume [pretreatment] < PLA volume upper limit, PLA volume [pretreatment], PLA volume upper limit) (9) PVA volume [pretreatment 1] is the "total MAP volume minus PLA volume [pretreatment]" (10) PVA volume [pretreatment 2] is the "total MAP volume minus PLA volume [upper limit setting]" (11) Since there is an upper limit to the amount of PVA, when the volume increases and reaches the upper limit, the IF function is used to prevent it from exceeding the upper limit [upper limit setting] = IF (PVA volume [pretreatment 2] < PVA volume upper limit, PVA volume [pretreatment 2], PVA volume upper limit) ... 6 types from 1.0 mL to 0.5 mL A list of the total MAP volume at the distance from the needle tip is shown in Figure 9.

[0116] 1-5. Calculating the thickness of the backlayer and the thickness of the PVA layer only Here, the backlayer thickness refers to the thickness of the microneedle substrate. (12) The distance from the needle tip to the PLA back surface is read using the INDEX function as the distance from the needle tip when the PLA volume [upper limit setting] first reaches its maximum value. =INDEX(distance from needle tip, MATCH(MAX(PLA volume [upper limit setting]), PLA volume [upper limit setting], 0), 1) (13) The distance from the needle tip to the PVA back surface is read using the INDEX function from the distance from the needle tip when the PVA volume [upper limit setting] first reaches its maximum value and the volume of the entire MAP. =INDEX (distance from needle tip: total MAP volume, MATCH (MAX (PVA volume [upper limit setting]), PVA volume [upper limit setting], 0), 1) ... 6 types from 1.0 mL to 0.5 mL (14) The distance from the needle tip to the backside of the backlayer is read using the INDEX function as the distance from the needle tip when the PVA volume [upper limit setting] first reaches its maximum value. = MAX (distance from needle tip to PLA back surface: distance from needle tip to PVA back surface) (15) The thickness of the backlayer was displayed as the distance from the needle tip to the back surface of the backlayer minus the needle height of 1,200 μm, and if there was no backlayer, it was displayed as “none.” = IF (distance from needle tip to back surface of the backlayer – needle length <= 0, “none,” distance from needle tip to back surface of the backlayer – needle length) (16) The thickness of the PVA layer alone was calculated using the IF function by subtracting the distance from the needle tip to the PVA back surface from the distance from the needle tip to the PLA back surface. If the PLA back surface was higher and the value was less than zero, it was displayed as “none” because there was no PVA layer alone. = IF (distance from needle tip to PVA back surface - distance from needle tip to PLA back surface <= 0, "none", distance from needle tip to PVA back surface - distance from needle tip to PLA back surface) The results of calculating the thickness of the backlayer and the thickness of the PVA layer alone are shown in Table 1 below.

[0117]

[0118] 1-6. Changes in PLA volume and PVA volume versus distance from the needle tip (17) The changes were plotted as a graph with the distance from the needle tip on the horizontal axis and the PLA volume and PVA volume (at an injection volume of 1.0 mL) on the vertical axis (see Figure 10).

[0119] (18) The changes were plotted as a graph with the distance from the needle tip on the horizontal axis and the PLA volume and PVA volume (injection volumes of 1.0 to 0.5 mL) on the vertical axis (see Figure 11).

[0120] FIG. 12 shows a graph of the PLA volume and PVA volume versus the distance from the needle tip when the needle length is 300 μm and the PLA content is 100 mg.

[0121] 1-7. Layered image of MNs cross section (19) The graph in "1-6. Changes in PLA volume and PVA volume as a function of distance from the needle tip" was converted into a layered image that is easy to understand intuitively. ⇒ By creating and overlaying four types of layers, a layered image of the MAP cross section was expressed (see Figure 13).

[0122] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0123] 1. Materials Polylactic acid (PLA): MAGIX PLA 30 Clear (Mutoh Industries) Polyvinyl alcohol: 363073-500G (SIGMA-ALDRICH) Dichloromethane: 135-02446 (Fujifilm Wako Pure Chemical Industries)

[0124] 2. Experimental equipment Optical microscope: Stemi305 (Carl Zeiss) Optical microscope (microsphere observation): IX71 (OLYMPUS) Force measurement: MX2-500N-FA-V45 (IMADA) Vacuum application: vacuum desiccator (SANPLATEC); oil rotary vacuum pump GLS-051 (ULVAC) Electronic balance: SECURA 125-1SJP (Sartorius) Hot plate: hot plate / stirrer LSH-4D (AS ONE) Constant temperature dryer: OFP-300V (AS ONE) Desiccator: DCD-PSPS (AS ONE)

[0125] Example 2: Preparation of 300 μm Porous Microneedles Using Polylactic Acid Microspheres Porous PLA microneedles were prepared using polylactic acid (PLA) microspheres according to the procedure described in the schematic diagram of the porous microneedle preparation method of the present invention shown in the upper and middle sections of Figure 14. As shown in Figure 14 (top), a 6.7% (w / v) PLA solution was prepared as an organic phase in dichloromethane (DCM). The organic phase was then mixed with an aqueous phase containing 5% (w / v) polyvinyl alcohol (PVA) as a water-soluble material and stirred at 1000 rpm for 6 hours, resulting in PLA microspheres in the PVA solution.

[0126] Once the PLA microspheres were formed, their spherical shape could be stably maintained in the ambient environment. The diameter of the microspheres was 15.5±6.9 μm. The diameter of the microspheres was measured by optical microscopy.

[0127] The PLA microsphere solution was then injected into a PDMS female mold prepared from a metal master mold consisting of 289 pyramidal microneedles, each 300 μm long. A vacuum was then applied to fill the cavity with the microsphere solution. The entire mold was then placed in a desiccator at 20°C and 20% RH for 36 hours to allow the water to evaporate naturally. The mold was then released from the PDMS female mold, and the edges (such as the blades) were cut off. The microspheres were then heat-treated at 180°C for 30 minutes to bond together.

[0128] Next, in order to remove the PVA, the microneedles were placed in water on a hot plate set at 60°C for 20 minutes to dissolve the PVA into the water.

[0129] Finally, the microspheres were heated for 30 minutes at 160°C, a temperature at which PLA begins to melt, near its melting point. This reheating strengthened the bond between the microspheres, which had been weakened when the PVA was removed in the previous step.

[0130] Furthermore, plasma treatment was performed to improve the hydrophilicity of the microneedle surface (see Figure 15).

[0131] Evaluation of porous PLA microneedles after PVA removal: Shape and dimensions. The measured dimensions were 261.3 ± 4.8 μm and 10.3 ± 0.7 μm (n = 5). The fabrication results showed that the shape and sharp tip were maintained after heat treatment, but the MN height and tip diameter were slightly reduced. The shrinkage was attributed to the deformation and bonding of PLA microspheres inside the MNs.

[0132] The absorption capacity of PVA-removed porous PLA microneedles was investigated using 2% (w / v) agarose gel coated with aluminum foil, which mimics human skin. A 100 g force was applied to the MN array, and the agarose gel was allowed to penetrate for 5 minutes. The absorption volume was 14 ± 1 μL (n = 4).

[0133] The strength of the microneedles was measured using a force measuring device and found to be 0.2 N to 0.3 N (n=8).

[0134] Example 3: Preparation of 800 μm needle-height porous microneedles using polylactic acid microspheres (1) The method of Example 2 was partially modified to prepare porous microneedles with a needle height of 800 μm. Porous PLA microneedles were prepared using polylactic acid (PLA) microspheres according to the procedure described in the schematic diagram of the porous microneedle preparation method of the present invention shown in the upper and middle sections of Figure 17. As shown in Figure 17 (top), a 6.7% (w / v) PLA solution was prepared as an organic phase in dichloromethane (DCM). The organic phase was then mixed with an aqueous phase containing 5% (w / v) polyvinyl alcohol (PVA) as a water-soluble material, and the mixture was stirred at 1000 rpm for 6 hours, resulting in PLA microspheres in the PVA solution.

[0135] Once the PLA microspheres were formed, their spherical shape could be stably maintained in the ambient environment. The diameter of the microspheres was 15.5±6.9 μm. The diameter of the microspheres was measured by optical microscopy.

[0136] Next, the PLA microsphere solution was injected into a PDMS female mold prepared from a metal master mold consisting of 81 pyramidal microneedles, each 800 μm long. A vacuum was then applied to fill the cavity with the microsphere solution. The entire mold was then placed in a desiccator at 30°C and 20% RH for 24 hours to allow the moisture to evaporate. The entire mold was then placed in a pressure vessel and left at 20°C and 0.2 MPa for 24 hours to allow the moisture to evaporate. The drying process in Example 3 differs from that in Example 2. To promote drying within the pressure vessel, the pressure vessel was pressurized to 0.3 MPa, while an air leak of 0.1 MPa was used to maintain the pressure within the vessel at 0.2 MPa. Figure 18 shows a schematic diagram of the pressure drying process using the pressure vessel used in this example. The mold was then released from the PDMS female mold, and the edges (such as the blades) were cut off. A heat treatment of 180° C. was then applied for 30 minutes to bond the microspheres together.

[0137] Next, in order to remove the PVA, the microneedles were placed in water on a hot plate set at 60°C for 20 minutes to dissolve the PVA into the water.

[0138] Finally, the microspheres were heated for 30 minutes at 160°C, a temperature at which PLA begins to melt, near its melting point. This reheating strengthened the bond between the microspheres, which had been weakened when the PVA was removed in the previous step.

[0139] Furthermore, plasma treatment was performed to improve the hydrophilicity of the microneedle surface (see Figure 15).

[0140] Evaluation of porous PLA microneedles after PVA removal: Shape and dimensions. The measured dimensions were 719.3 ± 6.8 μm and 19.2 ± 1.0 μm (n = 5). The fabrication results showed that the shape and sharp tip were maintained after heat treatment, but the MN height and tip diameter were slightly reduced. The shrinkage was attributed to the deformation and bonding of PLA microspheres inside the MNs.

[0141] Absorption capacity of PVA-removed porous PLA microneedles was investigated using 2% (w / v) agarose gel coated with aluminum foil, which mimics human skin. A 100 g force was applied to the MN array, and the agarose gel was allowed to penetrate for 5 minutes. The absorbed volume was 17 ± 1 μL (n = 4).

[0142] The strength of the microneedles was measured using a force measuring device and found to be 0.2 N to 0.3 N (n=8).

[0143] Example 4: Preparation of 800 μm Porous Microneedles Using Polylactic Acid Microspheres (2) The method of Example 2 was partially modified to prepare porous microneedles with a needle height of 800 μm. Porous PLA microneedles were prepared using polylactic acid (PLA) microspheres according to the procedure described in the schematic diagram of the porous microneedle preparation method of the present invention shown in the upper and middle sections of Figure 19. As shown in Figure 19 (top), a 6.7% (w / v) PLA solution was prepared as an organic phase in dichloromethane (DCM). The organic phase was then mixed with an aqueous phase containing 5% (w / v) polyvinyl alcohol (PVA) as a water-soluble material, and the mixture was stirred at 1000 rpm for 6 hours, resulting in PLA microspheres in the PVA solution.

[0144] Once the PLA microspheres were formed, their spherical shape could be stably maintained in the ambient environment. The diameter of the microspheres was 15.5±6.9 μm. The diameter of the microspheres was measured by optical microscopy.

[0145] Next, the PLA microsphere solution was injected into a PDMS female mold prepared from a metal master mold consisting of 81 pyramidal microneedles, each 800 μm long. A vacuum was then applied to fill the cavity with the microsphere solution. The entire mold was then placed in a pressure vessel and left at 20°C and 0.2 MPa for 96 hours to evaporate the water. The drying process in Example 4 differs from that in Example 2. To accelerate drying within the pressure vessel, the pressure vessel was pressurized to 0.3 MPa while an air leak of 0.1 MPa was introduced to maintain the pressure within the vessel at 0.2 MPa. Figure 18 shows a schematic diagram of the pressure drying process using the pressure vessel used in this example. The mold was then released from the PDMS female mold, and the edges (such as the wings) were cut. A heat treatment at 180°C for 30 minutes was then applied to bond the microspheres to each other.

[0146] Next, in order to remove the PVA, the microneedles were placed in water on a hot plate set at 60°C for 20 minutes to dissolve the PVA into the water.

[0147] Finally, the microspheres were heated for 30 minutes at 160°C, a temperature at which PLA begins to melt, near its melting point. This reheating strengthened the bond between the microspheres, which had been weakened when the PVA was removed in the previous step.

[0148] Furthermore, plasma treatment was performed to improve the hydrophilicity of the microneedle surface (see Figure 15).

[0149] Evaluation of porous PLA microneedles after PVA removal: Shape and dimensions. The measured dimensions were 713.6 ± 16.2 μm and 23.1 ± 4.5 μm (n = 5). The fabrication results showed that the shape and sharp tip were maintained after heat treatment, but the MN height and tip diameter were slightly reduced. The shrinkage was attributed to the deformation and bonding of PLA microspheres inside the MNs.

[0150] The absorption capacity of PVA-removed porous PLA microneedles was investigated using 2% (w / v) agarose gel coated with aluminum foil, which mimics human skin. A 100 g force was applied to the MN array, and the agarose gel was allowed to penetrate for 5 minutes. The absorption volume was 12.5 ± 1.5 μL (n = 4).

[0151] The strength of the microneedles was measured using a force measuring device and found to be 0.2 N to 0.3 N (n=8).

Claims

1. A porous microneedle comprising microspheres of a biodegradable material and a water-soluble material, wherein the microspheres of the biodegradable material are bonded to one another to form a network of interconnected pores, and the microneedle may comprise a microneedle substrate comprising the microspheres and a water-soluble material, wherein the volume ratio of the water-soluble material to the biodegradable material is 1:2-3.

2. A microneedle as described in claim 1, wherein a water-soluble material fills the gaps between the microsphere particles from the tip to the bottom of the microneedle (or, if the microneedle has a microneedle substrate, from the tip to the bottom of the microneedle substrate).

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

4. The microneedle of claim 1, wherein the water-soluble material is polyvinyl alcohol (PVA), CMC (carboxymethyl cellulose), or starch.

5. A microneedle patch comprising the porous microneedles according to any one of claims 1 to 4.

6. A method for producing porous microneedles or porous microneedle arrays, comprising the steps of: (a) preparing solution A by dissolving a biodegradable material in an organic solvent, mixing said solution A with an aqueous solution containing a water-soluble material, and stirring to prepare a biodegradable material microsphere solution or suspension containing microspheres of the biodegradable material; (b) pouring said solution or suspension into a female mold; (c) drying said solution or suspension to obtain a microneedle precursor or a microneedle array precursor; and (d) heating said microneedle precursor at a predetermined temperature to partially turn the microspheres into a liquid phase or rubbery state and bond them to each other, wherein the volume ratio of water-soluble material to biodegradable material in the resulting porous microneedles or porous microneedle arrays is 1:2-3.

7. The manufacturing method of claim 6, wherein the biodegradable material comprises at least one selected from the group consisting of polylactic acid, polyglycolic acid, poly(lactide-co-glycolide) copolymer, PEG copolymer, polyhydroxybutyric acid, and ethyl cellulose.

8. The manufacturing method according to claim 6, wherein the water-soluble material is polyvinyl alcohol (PVA), CMC (carboxymethyl cellulose), or starch.

9. The method according to claim 6, wherein the drying of the solution or suspension in step (c) is carried out by natural drying, pressure drying in which the solution or suspension is dried while applying pressure, or a combination thereof.

10. The manufacturing method described in claim 9, wherein in step (c), after the solution or suspension is naturally dried, a pressure drying process is carried out in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

11. The manufacturing method according to claim 9, wherein in step (c), a pressure drying process is carried out in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

12. A porous microneedle or porous microneedle array obtained by the manufacturing method according to any one of claims 6 to 11.

13. A method for producing porous microneedles or porous microneedle arrays from which water-soluble material has been removed, comprising the steps of: (a) preparing solution A by dissolving a biodegradable material in an organic solvent, mixing solution A with an aqueous solution containing a water-soluble material, and stirring the mixture to prepare a biodegradable material microsphere solution or suspension containing microspheres of the biodegradable material; (b) pouring the solution or suspension into a female mold; (c) drying the solution or suspension to obtain a microneedle precursor or a microneedle array precursor; (d) heating the microneedle precursor at a predetermined temperature to cause the microspheres to partially become liquid or rubbery and bond to each other, thereby obtaining a porous microneedle or a porous microneedle array; and (e) treating the porous microneedles or porous microneedle array obtained in step (d) with water.

14. The manufacturing method according to claim 13, comprising, after step (e), a step (f) of heating the water-treated porous microneedles or porous microneedle array to a temperature below the temperature at which the biodegradable material begins to melt, near the melting point of the biodegradable material.

15. The manufacturing method according to claim 13, wherein in step (e), the temperature at which the porous microneedles or porous microneedle array is treated with water is 20 to 60°C.

16. The method according to claim 13, wherein the drying of the solution or suspension in step (c) is carried out by natural drying, pressure drying in which the solution or suspension is dried while applying pressure, or a combination thereof.

17. The manufacturing method described in claim 16, wherein in step (c), after the solution or suspension is naturally dried, a pressure drying process is carried out in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

18. The manufacturing method described in claim 16, wherein in step (c), a pressure drying process is performed in which the solution or suspension is dried while applying pressure to obtain a microneedle precursor or a microneedle array precursor.

19. A porous microneedle or porous microneedle array substantially free of water-soluble materials, obtained by the manufacturing method according to any one of claims 13 to 18.

20. A porous microneedle formed from microspheres of a biodegradable material, the microspheres of the biodegradable material being bonded to one another to form a network of interconnected pores, the microneedle being substantially free of water-soluble materials.

21. The microneedle according to claim 20, wherein the absorption volume is 8 to 150 μL.

22. The microneedle according to claim 20, having a mechanical strength (breaking strength) of 0.1 to 0.5 N.

23. A microneedle patch comprising the porous microneedles according to any one of claims 20 to 22.

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