Assembled microneedle mold and method for manufacturing microneedles using the same

Abstract

The present disclosure relates to an assembly type microneedle mold and a method for manufacturing microneedles using the same, comprising: a mold plate including a microneedle shape protruding in an upward direction; and a plurality of separated microneedle pins; wherein the mold plate includes a plurality of slots into which the needle portions of the microneedle pins can be inserted. Specifically, the present disclosure relates to an assembly type microneedle mold capable of producing various molds by freely combining microneedle tips of various sizes and lengths on the mold plate.

Description

Technology Field

[0001] The present disclosure relates to an assembly type microneedle mold and a method for manufacturing microneedles using the same. Background Technology

[0002] The current global microneedle market is worth 865.5 billion won and is steadily increasing. Microneedles are a technology that uses tiny needles hundreds of micrometers in length to penetrate the stratum corneum of the skin and reach the epidermis and dermis layers to deliver drugs painlessly, or to create bioelectrodes with superior performance compared to surface electrodes.

[0003] However, existing microneedle manufacturing methods primarily involve mass production using molds of fixed shapes. This traditional mold manufacturing method has the following problems.

[0004] First, the cost of manufacturing molds is very high, and this cost increases even further, especially when producing microneedle tips with complex shapes. Second, since molds must be reused once manufactured, it is difficult to change or improve the design of microneedles; therefore, new molds must be manufactured to produce new types of microneedles. This results in additional time and costs being consumed in the process of modifying molds or manufacturing additional molds.

[0005] Furthermore, as the demand for microneedles with various shapes and functions increases, there is a growing need for flexible production systems capable of manufacturing microneedles in diverse ways. Particularly in the medical and biomedical fields, the shapes and functions of microneedles required vary, necessitating technical solutions capable of producing various types of microneedles to meet these demands. However, existing mold systems have the disadvantage of requiring the continuous production of new molds to satisfy these requirements, which entails significant costs and time consumption. While 3D printing technology has been proposed as an alternative, current commercial 3D printers are unsuitable for the precise fabrication of microneedle tips due to limitations in resolution and durability. These technical limitations are acting as a significant factor hindering the growth of the microneedle industry. The problem to be solved

[0006] The present disclosure is devised to solve the above-mentioned problems, and according to one aspect of the present disclosure, it provides a microneedle mold capable of assembling various shapes by arranging and assembling microneedle pins on a plate, and a method for manufacturing microneedles using the same. means of solving the problem

[0007] The present disclosure provides an assembly type microneedle mold comprising: a mold plate having a microneedle base portion shape protruding in an upward direction; and a plurality of separated microneedle pins; wherein the mold plate includes a plurality of slots into which the needle portions of the microneedle pins can be inserted, and the microneedle pins are detachably attachable to the mold plate.

[0008] In one embodiment of the present disclosure, the mold plate may include a plurality of slots ranging from 25 (5x5) to 900 (30x30) arranged regularly per unit area (1cm x 1cm).

[0009] In one embodiment of the present disclosure, the microneedle pin may comprise a pillar portion; and a microneedle needle portion.

[0010] In one embodiment of the present disclosure, the height of the micro-needle needle portion may be 100 μm to 1,500 μm.

[0011] In one embodiment of the present disclosure, the aspect ratio of the microneedle needle portion may be in the range of 1:1 to 1:20.

[0012] In one embodiment of the present disclosure, the angle of the tip of the needle portion of the microneedle pin may be 30° or more.

[0013] In one embodiment of the present disclosure, the microneedle needle portion may have a tip selected from the group consisting of a cone, a triangular pyramid, a square pyramid, a pentagonal pyramid, a hexagonal pyramid, and a polygonal pyramid.

[0014] In one embodiment of the present disclosure, a method for manufacturing a microneedle intaglio mold can be provided, comprising: a step of preparing a first mold by assembling microneedle pins on a mold plate using the aforementioned assembly type microneedle mold; and a step of forming a microneedle mold having the same intaglio shape as the first mold using a first polymer material.

[0015] In one embodiment of the present disclosure, a first mold may be formed by assembling microneedle pins, each having the same length and size of the tip portion, onto a mold plate.

[0016] In one embodiment of the present disclosure, one or more types of microneedle pins with different lengths and sizes of tip portions may be assembled on a mold plate to form a first mold.

[0017] In one embodiment of the present disclosure, a primary mold may be formed by combining a microneedle tip in a slanted multi-array shape with a mold plate.

[0018] In one embodiment of the present disclosure, the first polymer material may be one or more selected from the group consisting of silicone-based polymers or polyurethanes.

[0019] In one embodiment of the present disclosure, a microneedle intaglio mold manufactured according to the microneedle manufacturing method described above may be provided.

[0020] In another embodiment of the present disclosure, a method for manufacturing microneedles is provided, comprising: a step of preparing the aforementioned microneedle intaglio mold; a step of injecting a second polymer material into the microneedle intaglio mold; a vacuum placement step in which the mold into which the second polymer material has been injected is placed in a vacuum; a microneedle array curing step in which the second polymer material injected into the microneedle mold placed in the vacuum is cured; and a step of separating the cured microneedle array.

[0021] In one embodiment of the present disclosure, the second polymer material may be selected from the group consisting of a polymer solution in which an active ingredient for therapeutic purposes is dissolved in a biocompatible polymer, a polyimide polymer, and a shape memory polymer.

[0022] In one embodiment of the present disclosure, the step of forming a conductive layer by coating a metal electrode or a conductive polymer on the surface of the separated microneedles may be further included. Effects of the invention

[0023] An assembled microneedle mold according to one embodiment of the present disclosure can produce multiple primary molds by assembling microneedle pins of a design having a desired size or shape onto a mold plate as needed.

[0024] An assembled microneedle mold according to one embodiment of the present disclosure can provide a microneedle mold including a sharp microneedle tip than performing a conventional 3D process.

[0025] A manufacturing method using an assembly-type microneedle mold according to one embodiment of the present disclosure can provide the effect of manufacturing microneedles with complex shapes in a short time and at low cost.

[0026] A manufacturing method using an assembled microneedle mold according to one embodiment of the present disclosure can improve skin penetration ability by making the microneedle tip sharp. Brief explanation of the drawing

[0027] Figure 1 shows the upper side view (a) and the rear side view (b) of an assembled microneedle mold plate. FIG. 2 illustrates the column portion (22) and needle portion (21) of a microneedle pin. Figure 3 illustrates an A-type microneedle pin of one embodiment. Figure 4 illustrates a B-type microneedle pin of one embodiment. Figure 5 illustrates a C-type microneedle pin of one embodiment. Figure 6 illustrates a D-type microneedle pin of one embodiment. FIG. 7 shows an upper side view (a) and a lower side view (b) of a plate with microneedle pins attached to the back surface of one embodiment. Figure 8 illustrates a schematic diagram of an inclined microneedle with microneedle pins of different lengths and sizes attached to a plate. Figure 9 is a schematic diagram showing microneedle pins arranged on a plate. Figure 10 illustrates a side view of microneedle pins of different lengths and sizes attached to a plate. FIG. 11 illustrates a microneedle manufactured using the assembled microneedle mold of the present disclosure. Specific details for implementing the invention

[0028] The advantages and features of the present disclosure and the methods for achieving them will become clear by referring to the embodiments described in detail below. However, the present disclosure is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present disclosure is complete and to fully inform those skilled in the art of the scope of the invention, and the present disclosure is defined only by the scope of the claims.

[0029] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which this disclosure pertains.

[0030] Unless otherwise specifically indicated, the singular form of a term used in this specification may be interpreted to include the plural form.

[0031] The numerical ranges used herein include lower and upper limits and all values ​​within the range, increments logically derived from the form and width of the defined range, all of which are limited values, and all possible combinations of upper and lower limits of the numerical range defined in different forms. Unless otherwise specifically defined in the specification of this disclosure, values ​​outside the numerical range that may occur due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0032] As used in this specification, "comprising" is an open description equivalent to expressions such as "comprising," "containing," "having," and "characteristics," and does not exclude elements, materials, or processes not additionally listed.

[0033] As mentioned in this specification, 'tip diameter' refers to the longest side of the cross-section of the insertion end, but may refer to the diameter if the cross-section is circular,

[0034] As mentioned in this specification, the 'tip' of a microneedle refers to the outermost portion of the leading edge that first contacts the skin when the microneedle is applied to the skin. Alternatively, it refers to a portion of the same shape of an assembled microneedle mold for forming it.

[0035] The 'aspect ratio' mentioned in this specification refers to the ratio of the height to the base of the needle portion of the microneedle pin.

[0036] The 'base' mentioned in this specification can be verified by measuring the length of the base of the needle portion of the microneedle pin.

[0037] Hereinafter, the assembly type microneedle mold of the present disclosure and the method for manufacturing microneedles using the same will be described in detail. However, this is merely illustrative and the present disclosure is not limited to the specific embodiments described illustratively.

[0038] Conventional microneedle molds have the disadvantage that they cannot be modified once produced and consume a lot of time and cost for production. Although a 3D printing process was introduced to solve this problem, there is a problem that it is difficult to produce precise molds due to the low resolution of 3D printers. To solve this problem, the inventor of the present disclosure devised an assembly-type microneedle mold that can produce various molds by freely combining microneedle tips of various sizes and lengths on a mold plate.

[0039] The present disclosure provides an assembled microneedle mold comprising: a mold plate having a microneedle base portion shape protruding in an upward direction; and a plurality of separated microneedle pins; wherein the mold plate includes a plurality of slots into which the needle portions of the microneedle pins can be inserted.

[0040] Here, the mold plate may include the shape of a base portion, which is the part of the microneedle shape excluding the needle portion as shown in FIG. 1, and is the part where the microneedle is not inserted into the skin. The shape of the base portion shown in FIG. 1 is exemplary and is not limited thereto. The base portion includes a slot for inserting the needle portion of the microneedle pin.

[0041] In addition, as shown in FIG. 1, the back surface of the mold plate may further include a fixing device for inserting and fixing microneedle pins. Accordingly, the microneedle pins can be freely attached and detached from the slots of the mold plate, allowing for various arrangements as needed. Therefore, while conventional microneedle molds cannot be modified or deformed after manufacturing, the modular microneedle mold of the present disclosure allows for mold deformation by attaching and detaching microneedle pins of various shapes as needed.

[0042] Specifically, the above-described assembly type microneedle mold may be used as a primary mold for forming a microneedle intaglio mold. Accordingly, the assembly type microneedle mold has the advantage of being able to produce multiple primary molds by assembling microneedle pins of a design with a desired size or shape onto a mold plate as needed. Therefore, by using the assembly type microneedle mold of the present disclosure, which can be assembled into various forms, as a primary mold, there is an advantage of being able to produce various microneedle intaglio molds and microneedles at a low cost and in a short period of time.

[0043] Hereinafter, an assembled microneedle mold according to an example of the present disclosure will be described in detail with reference to FIGS. 1 to 10. However, since the configuration of FIGS. 1 to 10 is merely one embodiment, it should be understood that any modification of the form or substitution of components is included within the scope that does not impair the scope of the rights of the present disclosure.

[0044] According to one embodiment of the present disclosure, the mold plate may include a plurality of slots ranging from 1 (1x1) to 900 (30x30) arranged regularly per unit area (1cm x 1cm).

[0045] Since different microneedle pins are inserted into the microneedle slots, a microneedle mold with various arrangements of microneedle tips can be produced. Specifically, as shown in FIG. 8, they can be arranged in a slanted array, and as shown in FIG. 9, the number of microneedle pins to be inserted can be appropriately selected and assembled.

[0046] According to one embodiment of the present disclosure, the microneedle pin can be appropriately selected and used by a person skilled in the art as long as it is made of a material that is hard enough to have good machinability and durability, such as high-speed steel or stainless steel.

[0047] When microneedle pins are manufactured from materials such as high-speed steel, the microneedles possess high durability, which offers the advantage of enabling the repeated production of microneedle intaglio molds, such as silicone-based molds like PDMS and Ecoflex.

[0048] According to one embodiment of the present disclosure, the microneedle pin may include a pillar portion; and a needle portion.

[0049] Specifically, as disclosed in FIG. 2, the microneedle pin includes a column portion (22), and the end of the pin includes a needle portion (21). As shown in FIG. 7, the microneedle pin can be assembled by inserting it into the plate from the back of the plate through a slot in the plate and in the direction of the plate upward. One microneedle pin may be assembled for each slot of the mold plate, and the inserted microneedle pins may be assembled with the same or different lengths and sizes of the needle portions.

[0050] According to one embodiment of the present disclosure, the slot of the mold plate may be larger than the size of the bottom surface of the needle portion of the microneedle pin so that the needle portion of the microneedle pin can be inserted. Additionally, the size of the bottom surface of the column portion of the microneedle pin may be larger than the diameter of the slot. Accordingly, by referring to the section view of FIG. 4, it can be seen that only the needle portion of the microneedle pin is inserted in the upward direction of the plate to form an assembled shape.

[0051] According to one embodiment of the present disclosure, the height of the microneedle needle portion may be 100 μm to 1,500 μm, but is not necessarily limited thereto.

[0052] Specifically, if the length of the needle tip of the microneedle is long, the manufactured microneedle can be used for muscle tissue treatment and stimulation, and if the length of the microneedle is short, the manufactured microneedle can be used for skin or tissue treatment and stimulation near the skin surface. Therefore, a person skilled in the art can assemble a microneedle mold by appropriately selecting the height of the needle tip of the microneedle pin according to the intended use of the microneedle to be manufactured.

[0053] In one embodiment of the present disclosure, the aspect ratio of the microneedle pin needle portion may be 1:1 to 1:20.

[0054] Specifically, the aspect ratio of the pin needle portion may be in the range of 1:1 to 1:18, 1:1 to 1:16, 1:1 to 1:14, or 1:1 to 1:12. More specifically, the aspect ratio of the pin needle portion may be in the range of 1:1 to 1:10, 1:2 to 1:10, or 1:3 to 1:10, and more specifically, in the range of 1:4 to 1:10, but is not necessarily limited thereto. A person skilled in the art can appropriately select the aspect ratio of the microneedle pin according to the purpose, application, and material of the microneedle to be manufactured.

[0055] If the aspect ratio is less than 1, microneedles manufactured in a blunt shape may have difficulty perforating the skin, and if it is greater than 10, microneedles may easily break or bend, making it difficult to perforate the skin.

[0056] In one embodiment of the present disclosure, the angle of the tip of the needle portion may be 30° or more. More specifically, it may be 30° or more, 35° or more, or 40° or more. More specifically, it may be 30° or more and 60° or less.

[0057] Since the angle of the above-mentioned tip satisfies the above range, the microneedle tip is sharply formed, allowing the manufactured microneedle to puncture the skin without pain.

[0058] According to one embodiment of the present disclosure, the microneedle needle portion may have a tip selected from the group consisting of a cone, a triangular pyramid, a square pyramid, a pentagonal pyramid, a hexagonal pyramid, and a polygonal pyramid, but is not necessarily limited thereto. Specifically, if it has a tip in the shape of a cone or a square pyramid, a microneedle with high insertion ability into the skin can be manufactured.

[0059] In addition, the microneedle needle portion may not form a step in the middle, or may form one, two, or three steps in the middle, and the microneedle tip portion may be solid or include a hollow portion, but is not necessarily limited thereto.

[0060] Such an assembled microneedle mold is used as a primary mold for forming a microneedle intaglio mold, and microneedle pins of various sizes and lengths can be assembled in various arrangements on a mold plate.

[0061] Therefore, there is an advantage in that various shapes of intaglio microneedle molds can be produced using a single primary mold, and in particular, there is an advantage in easily manufacturing complex shapes such as inclined multi-channels. In addition, the modular microneedle mold has durability, allowing for the repeated production of microneedle intaglio molds made of materials such as silicone. Furthermore, while conventional methods of forming the primary mold using a 3D printing process resulted in the microneedle tip portion appearing blunt due to low resolution, microneedles produced using the modular microneedle mold of the present disclosure have sharp tips, which can improve skin penetration ability.

[0063] Hereinafter, a method for manufacturing a microneedle intaglio mold using the assembly type microneedle mold of the present disclosure will be described in detail, and the tip length, size, and aspect ratio of the microneedle pin are the same as those described above.

[0064] The present disclosure provides a method for manufacturing a microneedle intaglio mold, comprising: a step of preparing a first mold by assembling microneedle pins on a mold plate using the aforementioned assembly-type microneedle mold; and a step of forming a microneedle mold having the same intaglio shape as the first mold by using a first polymer material.

[0065] In one embodiment of the present disclosure, a first mold may be formed by assembling microneedle pins, each having the same length and size of the tip portion, onto a mold plate.

[0066] In one embodiment of the present disclosure, a first mold may be formed by assembling microneedle pins with different lengths and sizes of their tips onto a mold plate.

[0067] In addition, a primary mold may be formed by combining microneedle tips in a slanted multi-array shape with a mold plate, as exemplarily illustrated in Figures 8 (a), (b), and (c).

[0068] The arrangement method of the microneedle pins of such an assembled microneedle mold is not limited to this, and a person skilled in the art can produce a primary mold by appropriately selecting the arrangement method as needed, taking into account the intended use and the area of ​​use.

[0069] The step of forming a microneedle mold having the same intaglio shape as the first mold can involve placing the first mold into a container containing a polymer material, and forming a microneedle intaglio mold by injecting a polymer material into the container containing the first mold.

[0070] According to one embodiment of the present disclosure, the polymer material may be one or more selected from the group consisting of silicone-based polymers or polyurethanes. More specifically, the polymer material may be polydimethylsiloxane (PDMS), but is not necessarily limited thereto.

[0071] A microneedle mold having the same intaglio shape as the primary mold can be manufactured using a primary polymer material with the primary mold having the above-mentioned sharp tip portion.

[0072] Various types of micro-needles can be manufactured using the various types of micro-needle intaglio molds manufactured above.

[0073] According to one embodiment of the present disclosure, a method for manufacturing microneedles is provided, comprising: a step of preparing a microneedle intaglio mold as described above; a step of injecting a second polymer material into the microneedle intaglio mold; a vacuum placement step in which the mold into which the second polymer material has been injected is placed in a vacuum; a microneedle array curing step in which the second polymer material injected into the microneedle mold placed in the vacuum is cured; and a step of separating the cured microneedle array.

[0074] The above vacuum placement step allows the second polymer material to easily fill up to the end of the intaglio mold without external pressure because the mold into which the second polymer is injected is placed in a vacuum, thereby enabling the manufacture of microneedles having the same shape as the first mold.

[0075] In one embodiment of the present disclosure, the second polymer material may be a polymer solution in which an active ingredient for therapeutic purposes is dissolved in a biocompatible polymer. The microneedles prepared as described above are soluble microneedles, and may follow a method in which a drug is released as the microneedles, composed of a biodegradable material, decompose within the body. When the biodegradable polymer is used, the microneedle curing step may be degassing and drying in a vacuum atmosphere at room temperature.

[0076] In one embodiment of the present disclosure, the second polymer material may be a polyimide polymer or a shape memory polymer.

[0077] When the second polymer material used is a polyimide polymer or a shape-memory polymer, the curing step of the microneedle array may include a UV curing or hard-baking step. Specifically, it may include a primary curing step in which it is cured by irradiation with ultraviolet light, and a secondary curing step in which it is cured by being placed in an oven. Accordingly, the second polymer can be completely cured through the primary and secondary curing processes, and a person skilled in the art can appropriately select and perform the UV irradiation time, exposure time, and hard baking temperature and time. Additionally, if the second polymer is a shape-memory polymer, shape-memory properties can be designed during the curing step.

[0078] Accordingly, the mold into which the second polymer is injected can undergo the processes of first curing, second curing, and third curing so that the second polymer can be completely cured, and accordingly, the second polymer can be completely separated from the mold into which the second polymer is injected so that a microneedle having the same shape as the mold can be produced.

[0079] According to one embodiment of the present disclosure, the method may further include the step of forming a conductive layer by coating a metal electrode or a conductive polymer on the surface of the separated microneedles.

[0080] The metal and conductive polymer mentioned above can be appropriately selected and used by a person skilled in the art, and the coating method may form a conductive layer on the surface of the microneedle using one or more methods selected from the group consisting of spin coating, spray coating, inkjet printing, and dip coating, but is not necessarily limited to the coating method mentioned above.

[0081] In addition, conductive microneedles can be fabricated by utilizing a conductive polymer. The conductive polymer can be prepared by mixing a conductive polymer, such as PEDOT:PSS or MXene, with a base polymer, such as polyurethane, SEBS (Styrene-Ethylene-Butylene-Styrene), or a shape memory polymer. Specifically, it may be a solution of PEDOT:PSS and polyurethane mixed in an appropriate ratio, but is not necessarily limited thereto.

[0082] Since the above microneedles are conductive, they can be inserted into the skin to measure biosignals such as electrocardiograms, electromyograms, electroencephalograms, and nerve conductions of the body, and can also be used for electroporation to inject drugs.

[0083] Accordingly, the microneedle manufacturing method of the present disclosure can manufacture microneedles with sharp microneedle tips, and can manufacture microneedles including multiple channels with the same or different lengths and sizes of each needle through a simple process.

[0084] Although embodiments of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention may be implemented in other specific forms without changing its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. Explanation of the symbols

[0085] 1: Mold plate 2: Microneedle pin 21: Needle portion of the microneedle pin 22: Pillar part of the microneedle pin

Claims

Claim 1 An assembly type microneedle mold comprising: a mold plate including a microneedle base portion shape protruding in an upward direction; and a plurality of separated microneedle pins; wherein the mold plate includes a plurality of slots into which the needle portions of the microneedle pins can be inserted, and the microneedle pins are detachably attachable to the mold plate. Claim 2 In claim 1, the mold plate comprises a plurality of slots ranging from 25 (5x5) to 900 (30x30) regularly arranged per unit area (1cm x 1cm), forming an assembled microneedle mold. Claim 3 An assembled microneedle mold according to claim 1, wherein the microneedle pin comprises a pillar portion; and a microneedle needle portion. Claim 4 An assembled microneedle mold according to claim 1, wherein the height of the microneedle needle portion is 0.4 mm to 1.2 mm. Claim 5 An assembled microneedle mold according to claim 1, wherein the aspect ratio of the microneedle needle portion is 1:1 to 1:

20. Claim 6 An assembled microneedle mold according to claim 1, wherein the angle of the tip of the needle portion of the microneedle pin is 30° or more. Claim 7 An assembled microneedle mold according to claim 1, wherein the microneedle needle portion has a tip selected from the group consisting of a cone, a triangular pyramid, a square pyramid, a pentagonal pyramid, a hexagonal pyramid, and a polygonal pyramid. Claim 8 A method for manufacturing a microneedle intaglio mold, comprising: a step of preparing a primary mold by assembling microneedle pins on a mold plate using an assembly-type microneedle mold according to claim 1; and a step of forming a microneedle mold having the same intaglio shape as the primary mold using a first polymer material. Claim 9 A method for manufacturing a microneedle intaglio mold according to claim 8, wherein a first mold is formed by assembling microneedle pins, each having the same length and size of the tip portion, onto a mold plate. Claim 10 A method for manufacturing a microneedle intaglio mold according to claim 8, wherein one or more types of microneedle pins with different lengths and sizes of tip portions are assembled on a mold plate to form a first mold. Claim 11 A method for manufacturing a microneedle intaglio mold according to claim 10, wherein a primary mold is formed by combining a microneedle tip in a slanted multi-array form with a mold plate. Claim 12 A method for manufacturing a microneedle intaglio mold according to claim 8, wherein the first polymer material is one or more selected from the group consisting of silicone-based polymers or polyurethane. Claim 13 A microneedle intaglio mold manufactured according to any one of paragraphs 8 to 12. Claim 14 A method for manufacturing microneedles comprising: a step of preparing a microneedle intaglio mold according to claim 13; a step of injecting a second polymer material into the microneedle intaglio mold; a vacuum placement step in which the mold into which the second polymer material has been injected is placed in a vacuum; a microneedle array curing step in which the second polymer material injected into the microneedle mold placed in the vacuum is cured; and a step of separating the cured microneedle array. Claim 15 A method for manufacturing microneedles according to claim 14, wherein the second polymer material is selected from the group consisting of a polymer solution in which the active ingredient for therapeutic purposes is dissolved in a biocompatible polymer, a polyimide polymer, and a shape memory polymer. Claim 16 A method for manufacturing microneedles according to claim 15, further comprising the step of forming a conductive layer by coating a metal electrode or a conductive polymer on the surface of the separated microneedles.

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