JP2014051579A - Method for manufacturing dried silk fibroin porous body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient method for manufacturing a dried silk fibroin porous body capable of easily retaining the shape of the silk fibroin porous body and capable of largely shortening the drying time.SOLUTION: The method for manufacturing a dried silk fibroin porous body comprises: a step (1) of freezing a silk fibroin aqueous solution or a silk fibroin porous body containing water; and a step (2) of retaining the freezed silk fibroin aqueous solution or the freezed silk fibroin porous body on an air permeable base material to dry them under reduced pressure.

Description

  The present invention relates to a method for producing a dry silk fibroin porous material.

Porous materials that can be made using biological materials such as proteins and saccharides are used in medical fields such as wound dressings and sustained-release drugs, daily necessities such as disposable diapers and sanitary products, and living places such as microorganisms and bacteria. Wide range of industries such as water purification field that can be used as a support, cosmetic / esthetic field for esthetic salon and personal use, cell culture support and tissue regeneration support in tissue engineering and regenerative medical engineering Used in the field.
As biologically-derived substances constituting these porous bodies, saccharides such as cellulose and chitin, and protein groups such as collagen, keratin, and silk fibroin are known.

Among these biologically derived substances, collagen has often been used as a protein, but it has become very difficult to utilize bovine-derived collagen after the occurrence of the BSE problem. Keratin can be obtained from wool and feathers, but there is a problem in obtaining raw materials and it is difficult to use it industrially. For wool, the raw material price is soaring and there is no market for feathers, so it is not possible to obtain the raw material. On the other hand, silk fibroin has the feature that it can be expected to be supplied stably from the viewpoint of obtaining raw materials, and the price is also stable, making it easy to use industrially.
Silk fibroin has a long track record of being used as a surgical suture in addition to clothing applications, and is currently used as an additive for food and cosmetics. It can be used in the field of application of such a porous body.

There are several reports on the technique for producing silk fibroin porous materials. For example, Patent Document 1 discloses a method for producing a silk fibroin porous material having excellent mechanical properties. According to Patent Document 1, the porous body is manufactured through the following steps.
First, a silk fibroin solution in which 0.1 to 5% by mass of an aliphatic carboxylic acid is added to a silk fibroin aqueous solution having a concentration of 1 to 12% by mass is prepared, and the solution is poured into a mold or the like. A silk fibroin porous material can be obtained by placing it in a low-temperature thermostatic bath at 0 ° C. and freezing it over 2 hours, followed by thawing.

  Since the obtained silk fibroin porous body contains an aliphatic carboxylic acid, if it is necessary to remove the aliphatic carboxylic acid depending on the application, the porous body is immersed in pure water. The aliphatic carboxylic acid is removed from the silk fibroin porous material to obtain a wet silk fibroin porous material.

  In Patent Document 2, a mixed solution obtained by adding 0.1 to 1% by volume of glycerin to a fibroin aqueous solution having a concentration of 0.5 to 3% by mass is placed in a flat bottom container having a depth of about 0.5 to 4 mm. , Freeze the plate at a temperature of −40 to −15 ° C. for 3 to 20 hours to produce a plate-like material, take out the plate-like material from the container, hang it vertically with a clip etc., and both sides are the same A method of freeze-drying for about 60 to 100 hours at a temperature of −40 to −15 ° C. while being exposed to air under conditions is disclosed.

International Publication No. 2010/116994 Pamphlet JP 2011-173963 A

  However, Patent Document 1 does not mention a specific embodiment of the drying method, or mention a drying method that requires a short drying time while maintaining the shape of the porous body. In Patent Document 2, the drying time is as long as about 60 to 100 hours, and the shape is difficult to maintain.

  Therefore, an object of the present invention is to provide an efficient method for producing a dried silk fibroin porous body, which can easily maintain the shape of the silk fibroin porous body and can greatly reduce the drying time.

As a result of intensive studies to achieve the above problems, the present inventors have found that the problems can be solved by the following invention.
That is, the gist of the present invention is as follows.

1. Step (1) of freezing silk fibroin aqueous solution or silk fibroin porous material containing water, and holding the frozen silk fibroin aqueous solution or silk fibroin porous material on a breathable substrate and drying under reduced pressure The manufacturing method of the dry silk fibroin porous body which has the process (2) to make.
2. 2. The production method according to 1 above, wherein the silk fibroin aqueous solution or the silk fibroin porous material containing water further contains a water-soluble organic solvent.
3. Furthermore, the manufacturing method of said 1 or 2 which has the process (3) of heating the said air permeable base material.

  According to the method for producing a dried silk fibroin porous body of the present invention, a dried silk fibroin porous body can be efficiently obtained in a short drying time while easily maintaining the shape of the porous body.

It is the schematic which shows the drying apparatus which can be used by this invention. It is detail drawing which shows the air permeable tray part of the drying apparatus which can be used by this invention. It is a schematic diagram explaining (DELTA) H / L calculated in evaluation of the shape maintenance of an Example. It is a schematic diagram explaining the shrinkage | contraction rate computed in evaluation of the shape maintenance of an Example.

<Step (1)>
Step (1) is a step of freezing the silk fibroin aqueous solution or the silk fibroin porous material containing water.
The silk fibroin porous material can be obtained, for example, by the following production method. First, an aqueous silk fibroin solution is prepared. You may add additives, such as aliphatic carboxylic acid and an organic solvent, to this silk fibroin aqueous solution. Here, the silk fibroin may be any one as long as it is produced from silkworms such as rabbits, wild silkworms, and tengu, and the manufacturing method thereof is not limited. The concentration of silk fibroin in the silk fibroin aqueous solution is preferably such a concentration as 0.1 to 40% by mass from the viewpoint of producing a porous body having sufficient strength, and 0.5 to 20% by mass. It is more preferable that it is 1-12 mass%.

  The additive is preferably an aliphatic carboxylic acid. As the aliphatic carboxylic acid, a saturated or unsaturated monocarboxylic acid, dicarboxylic acid or tricarboxylic acid having preferably 1 to 6 carbon atoms, more preferably 3 to 5 carbon atoms can be preferably used. For example, formic acid, acetic acid Preferred examples include unsaturated monocarboxylic acids such as propionic acid, butyric acid, lactic acid, acrylic acid, and 2-butenoic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, and fumaric acid. Two or more kinds can be used in combination. The content of the aliphatic carboxylic acid in the silk fibroin solution is preferably 0.01 to 18% by volume, from 0.1 to 5% by volume, from the viewpoint of producing a porous body having sufficient strength. More preferably, it is more preferably 0.5 to 4% by volume.

  Next, the silk fibroin aqueous solution is poured into a mold or a container and allowed to stand in a low-temperature thermostat (freezer) to obtain a frozen silk fibroin aqueous solution (hereinafter sometimes referred to as freezing). Here, in the frozen state, it is presumed that a silk fibroin porous body is formed, and frozen water or the like is present in the pores of the porous body. Therefore, in this specification, the frozen silk fibroin aqueous solution may be called "frozen silk fibroin porous body." The temperature in the low-temperature thermostatic chamber is preferably a temperature at which the silk fibroin aqueous solution is frozen, preferably about -1 to -40 ° C, more preferably about -5 to -40 ° C, and further preferably about -10 to -30 ° C. The freezing time is preferably 2 hours or longer, and more preferably 4 hours or longer so that the silk fibroin solution can be sufficiently frozen and kept in a frozen state for a certain period of time.

  What is necessary is just to select a type | mold or a container suitably according to a desired shape, For example, it can be set as the shape according to the objective, such as plate shape, block shape, tubular shape, spherical shape. In the manufacturing method of this invention, it is preferable that it is plate-shaped from a viewpoint that it can dry efficiently, The width and depth are about 10-1000 mm, and the thickness is about 0.1-50 mm.

  When the frozen silk fibroin porous material contains an additive that hardly evaporates such as an aliphatic carboxylic acid, it is necessary to remove the additive depending on the application. As a method for removing additives such as aliphatic carboxylic acid, for example, a frozen silk fibroin porous material is melted and immersed or washed in pure water to thereby remove the aliphatic carboxylic acid from the silk fibroin porous material. Etc. and the silk fibroin aqueous solution remaining in the pores can be removed. In this way, a silk fibroin porous body containing water (wet silk fibroin porous body) containing water and an additive that hardly evaporates such as aliphatic carboxylic acid is substantially obtained. In this invention, this can be left still in a low temperature thermostat (freezer), and it can also be set as the frozen silk fibroin porous body of the process (1). The melting method is not particularly limited, and examples include natural melting and storage in a thermostatic bath.

  In the present invention, it is preferable that a water-soluble organic solvent is further included when the silk fibroin aqueous solution is prepared. That is, the organic solvent described as the additive preferably contains the water-soluble organic solvent. In addition, when using a silk fibroin porous material containing water (wet silk fibroin porous material) from which the additive that hardly evaporates is substantially removed, it is preferable to further include a water-soluble organic solvent. By containing the water-soluble organic solvent, shape retention is facilitated, and the silk fibroin porous material that has been efficiently frozen can be dried in a short drying time. The silk fibroin porous material containing water and a water-soluble organic solvent is obtained by immersing the silk fibroin porous material containing water in a water-soluble organic solvent or a mixed solvent containing water and a water-soluble organic solvent. can get.

  The water-soluble organic solvent used here can be used without limitation as long as it is generally recognized as water-soluble, but has water-solubility and a lower boiling point or freezing point than water. Is preferred. As such a water-soluble organic solvent, alcohols such as methanol, ethanol and isopropyl alcohol are preferably exemplified. Moreover, these alcohols are preferable also in the point which does not give the bad influence that a silk fibroin is decomposed | disassembled. These water-soluble organic solvents may be used alone or in combination of two or more.

When the water-soluble organic solvent is used, the content of the water-soluble organic solvent in the mixed solvent containing water and the water-soluble organic solvent is appropriately selected depending on the freezing temperature condition, and the freezing point of the mixed solvent is higher than the freezing temperature. It is preferable. For example, when ethanol is employed as the water-soluble organic solvent and frozen at a temperature of −20 to −25 ° C., the ethanol content is such that the freezing point of the mixed solvent is −2 to −19 ° C. The content is preferably such that the freezing point is -5 to -15 ° C, and more preferably the content is such that the freezing point is -8 to -12 ° C. That is, the freezing point of the mixed solvent is preferably about 1 to 23 ° C higher than the freezing temperature, more preferably 5 to 15 ° C, and further preferably 5 to 10 ° C.
Moreover, when using the mixed solvent containing water and a water-soluble organic solvent, as content of the water-soluble organic solvent in this mixed solvent, it is preferable that it is about 5-30 mass%, More preferably, it is 5-25 mass. %. When the content of the water-soluble organic solvent is within the above range, the shape can be easily maintained, and the silk fibroin porous material that has been efficiently frozen can be dried in a short drying time.

  As a temperature condition for freezing the water obtained as described above, preferably a silk fibroin porous material further containing a water-soluble organic solvent, about -1 to -40 ° C is preferable, and about -10 to -40 ° C. More preferably, about −20 to −25 ° C. is more preferable. Moreover, although freezing time is about 0.5 to 24 hours, 0.5 to 12 hours are preferable from a viewpoint of productivity. By keeping the freezing temperature condition and freezing time within the above ranges, the silk fibroin porous material that has been efficiently frozen can be efficiently dried in a short drying time while easily retaining the shape of the silk fibroin porous material. Can do.

<Step (2)>
Step (2) is a step of holding the frozen silk fibroin aqueous solution or silk fibroin porous material obtained by the above step (1) on a breathable substrate and drying it under reduced pressure.
The breathable base material is a base material used for drying efficiently while maintaining the shape of the silk fibroin porous material obtained in the above step (1). Preferable types include a punched metal, a punched metal, an expanded metal, and a wire mesh such as a plain weave wire mesh, a twill wire mesh, and a crimp wire mesh, and a plain weave wire mesh is more preferable. A wire mesh is also preferable from the viewpoint of shape retention.
Preferred examples of the material include iron, aluminum, and stainless steel, and stainless steel is preferable.

The porosity of the breathable substrate is preferably 50% or more, more preferably 50 to 85%, and still more preferably 70 to 85%. Here, the porosity is a hole area ratio when punching metal is used as the air-permeable base material, and is a space ratio when adopting a metal mesh as the air-permeable base material. Moreover, when employ | adopting an expanded metal as an air permeable base material, what has an aperture | opening comparable as the porosity of a punching metal is preferable. Moreover, 0.1-5 mm is preferable, as for the wire diameter of a wire mesh, More preferably, it is 0.1-2 mm, More preferably, it is 0.2-1.5 mm.
The breathable base material used in the present invention is a base material having air permeability by having an aperture ratio and a space ratio in the above range, and by using such a breathable base material, It is easy to maintain the shape without warping of the porous body, and it is possible to dry the silk fibroin porous body that has been efficiently frozen in a short drying time.

The breathable substrate used in the present invention may be the above-described substrate alone, for example, an outer layer for supporting the entire weight of the silk fibroin porous body, and the porous body. In order to protect the surface state, a breathable multilayer substrate such as a breathable two-layer substrate having a two-layer structure having at least an inner layer in direct contact with the porous body is preferable. Moreover, as a breathable multilayer base material, you may take the structure of three or more layers as needed.
In this case, the outer layer and the inner layer may use the same breathable substrate or different breathable substrates, but use a fine mesh (a large mesh) for the inner layer substrate, It is preferable to use a coarser mesh (small mesh) than the inner layer base material for the outer layer. For example, when a wire mesh is adopted as the base material, the inner layer is preferably about 8 to 40 mesh, more preferably 8 to 20 mesh, and the outer layer is preferably about 1 to 10 mesh, more preferably. 2-6 mesh.
In the present invention, when the breathable base material is a breathable multilayer base material as described above, shape retention is facilitated, and the silk fibroin porous material that has been efficiently frozen is dried in a short drying time. Furthermore, the surface state of the silk fibroin porous material can be made favorable.

  The pressure reduction conditions in the step (2) are not particularly limited, but are preferably 5 to 500 Pa, more preferably 5 to 200 Pa from the viewpoint of efficiently drying the silk fibroin porous material in a short drying time. It is.

The production method of the present invention preferably further includes a step (3) of heating the silk fibroin porous body. This is because the silk fibroin porous material that has been frozen efficiently can be dried in a shorter drying time. In the step (2), when the mixed solvent contained in the silk fibroin porous material is dried, the drying rate is increased when the mixed solvent is sublimated. Therefore, by heating the porous body, sublimation heat necessary for sublimation can be supplied to the porous body, so that the drying rate can be further increased. From such a viewpoint, the step (3) is preferably performed in the step (2).
As heating temperature, it is preferable that it is 15-100 degreeC, More preferably, it is 40-80 degreeC.

  Step (2) and step (3) can be performed using, for example, a drying apparatus as shown in FIG. A drying apparatus 10 shown in FIG. 1 includes a breathable base material receiving jig 12 and a breathable base material receiving jig 12 disposed on a breathable base material receiving jig 12 in a vacuum chamber 11, and the breathable base material receiving jig 12. 12, an upper heating plate 14 and a lower heating plate 15 are installed. And the silk fibroin porous body 20 frozen by the process (1) is hold | maintained on the air permeable base material 13, and is dried.

  When step (3) is not applied in the present invention, a heating plate may not be used. Further, the upper heating plate 14 and the lower heating plate 15 may be used at the same time, or only one of them may be used, and the heating plate heating temperature may be the same or different. May be. Further, a heating plate that can freely set the temperature rising pattern is preferably employed.

  As shown in FIG. 1, the breathable base material 13 may be provided so as to cover the lower and side surfaces of the frozen silk fibroin porous body. FIG. 2 shows details of the breathable substrate receiving jig 12, the breathable substrate 13, the breathable substrate inner layer 13a and the breathable substrate outer layer 13b, and the details of the frozen silk fibroin porous body 20 portion. FIG. As shown in FIG. 2, when the breathable base material 13 has a multilayer structure, a spacer can be provided between the base materials from the viewpoint of drying more efficiently. FIG. 1 shows an embodiment in which the breathable base material 13 is provided with a lower part and a side surface of a frozen silk fibroin porous body. For example, the upper part of the frozen silk fibroin porous body is also covered, that is, You may provide so that the whole surface of the frozen silk fibroin porous body may be covered. By providing so as to cover the entire surface, it can be dried more uniformly.

The dried silk fibroin porous material obtained by the production method of the present invention is substantially free of moisture. As described above, the silk fibroin porous material is obtained by freezing a silk fibroin aqueous solution, melting it if necessary, and immersing it in ultrapure water, so that water or the like is usually present in the pores. . Therefore, the dried silk fibroin porous material obtained by the production method of the present invention is a silk fibroin porous material that does not go through the steps specified in the production method of the present invention, and the amount of water etc. present in the pores. The state will be different.
Further, when the dried silk fibroin porous material obtained by the production method of the present invention is taken out of the drying apparatus and placed in the atmosphere, it may absorb about 10%. This moisture absorption is a phenomenon that occurs in the same manner as long as it is a silk fibroin porous material obtained by any other manufacturing method. However, the dried silk fibroin porous material obtained by the production method of the present invention is a silk fibroin porous material in which water or the like is present in the pores even when moisture is absorbed. The state will be different in terms of the amount of.

  EXAMPLES The present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

(Evaluation method)
(1) Evaluation of shape retention (evaluation of warpage)
The warp of the silk fibroin porous material obtained in the examples and comparative examples was calculated by calculating the ratio ΔH / L between the in-plane step ΔH and the width L of the porous material shown in FIG. When it was less than 1, it was evaluated as “no warp”, and when ΔH / L was 0.1 or more, it was evaluated as “warp”.
(2) Evaluation of shape retention (evaluation of shrinkage rate)
About the silk fibroin porous body obtained by the Example and the comparative example, the shrinkage | contraction rate of each dimension of the width L, depth W, and thickness H of the silk fibroin porous body shown by FIG. 4 is computed by the following numerical formula. To do. If all dimensions were less than 10%, it was judged as ◯, and if any one dimension was 10% or more, it was judged as x.
Shrinkage rate (%) = ((size before drying−size after drying) / size before drying) × 100

Production Example 1: Production of Silk Fibroin Porous Material A (Preparation of Silk Fibroin Aqueous Solution)
Silk fibroin aqueous solution is prepared by dissolving silk fibroin powder (KB Selen Co., Ltd., trade name: “Fibroin IM”) in 9M lithium bromide aqueous solution. Obtained by repeating. The obtained silk fibroin aqueous solution was air-dried in a dialysis tube and concentrated. An acetic acid aqueous solution was added as an additive to the concentrated solution to prepare a silk fibroin aqueous solution having a silk fibroin concentration of 3% by mass and an acetic acid concentration of 2% by volume.
(Manufacture of silk fibroin porous material)
This silk fibroin aqueous solution was poured into a mold (inside size; 150 mm × 220 mm × 10 mm) made of an aluminum plate, and stored in a freezer (manufactured by EYELA, NCB-3300).
(Freezing condition)
For freezing, the freezer is cooled to -5 ° C in advance, and a mold containing silk fibroin aqueous solution is put into the freezer and held for 2 hours. After cooling to -25 ° C, the temperature is kept at that temperature for 5 hours. Retained.
The frozen sample is returned to room temperature by natural thawing, then removed from the mold, immersed in ultrapure water, and the acetic acid used is removed by replacing the ultrapure water twice a day for 3 days to contain water. A silk fibroin porous material A was obtained.

Production Example 2: Production of Silk Fibroin Porous Material B In the silk fibroin porous material obtained in Production Example 1, a mixed solvent containing 7.5% by mass of ethanol and water was immersed in water and a water-soluble organic solvent. A silk fibroin porous material B containing was obtained.

Production Example 3: Production of Silk Fibroin Porous Material C A silk fibroin porous material obtained in Production Example 1 was immersed in a mixed solvent containing 15% by mass of ethanol and water, and silk containing water and a water-soluble organic solvent. Fibroin porous material C was obtained.

Example 1
The silk fibroin porous material A containing water obtained in Production Example 1 was kept in a freezer previously cooled to −25 ° C. for 2 hours and frozen. 47. Place the frozen silk fibroin porous material A on the breathable substrate of the drying apparatus shown in FIG. 1, set the pressure in the drying apparatus to 30 Pa, and set the temperature of the upper and lower heating plates to 25 ° C .; Drying was completed in 5 hours. The end of drying was the time when the temperature in the silk fibroin porous body reached 20 ° C. As the breathable substrate, a breathable two-layer substrate in which a breathable substrate inner layer was placed on the breathable substrate outer layer shown in Table 1 was used. The evaluation results are shown in Table 2.

Example 2
In Example 2, the silk fibroin porous material A was dried in the same manner as in Example 1 except that the temperature of the upper and lower heating plates was set to 40 ° C., and the drying was completed in 40.5 hours. The results of evaluation are shown in Table 2.

Example 3
In Example 3, the silk fibroin porous body B was obtained in the same manner as in Example 1 except that the silk fibroin porous body A obtained in Production Example 1 was changed to the silk fibroin porous body B obtained in Production Example 2. Was dried, drying was completed in 42.2 hours. The results of evaluation are shown in Table 2.

Example 4
In Example 4, a silk fibroin porous material was obtained in the same manner as in Example 1 except that the silk fibroin porous material A obtained in Production Example 1 was replaced with the silk fibroin porous material C obtained in Production Example 3. When C was dried, drying was completed in 34.8 hours. The results of evaluation are shown in Table 2.

Example 5
The silk fibroin porous material C obtained in Production Example 3 is placed on the breathable substrate of the drying device shown in FIG. 1, the pressure in the drying device is 30 Pa, and the temperature of the upper and lower heating plates is 40 ° C. When set and dried, drying was completed in 30 hours. The results of evaluation are shown in Table 2.

Comparative Example 1
In Example 1, the silk fibroin porous material A was dried in the same manner as in Example 1 except that the breathable base material was replaced with an aluminum plate. The drying was completed in 71.5 hours, and warping occurred. did. Further, the shrinkage rate was 10% or more. The results of evaluation are shown in Table 2.

Comparative Example 2
The silk fibroin porous material A obtained in Production Example 1 is placed in a low-temperature thermostatic chamber capable of decompressing a clip, which is separately installed in the drying apparatus shown in FIG. When the temperature was set to 25 ° C. and dried, drying was completed in 50 hours, and the upper end sandwiched between the clips was locally deformed. Further, the shrinkage rate was 10% or more. The evaluation results are shown in Table 2.

* 1, This is the concentration of the water-soluble organic solvent in the mixed solvent when the silk fibroin porous material is immersed in the mixed solvent. “-” Indicates that the silk fibroin porous material is not immersed in the mixed solvent.

  From the results of the above Examples 1 to 5, according to the production method of the present invention, there is no warpage, and since the shrinkage rate is small, the shape can be easily maintained, and the drying time can be greatly shortened. In particular, it was confirmed that a dried silk fibroin porous material could be obtained. On the other hand, in Comparative Example 1 in which no breathable substrate was used, warpage occurred, the shrinkage rate was large, the shape could not be maintained, and the drying time was long. In Comparative Example 2 in which the upper end of the silk fibroin porous body was sandwiched between a clip and hung and dried, it was confirmed that the portion sandwiched between the clips was locally deformed, the contraction rate was large, and the shape could not be maintained.

  According to the method for producing a dried silk fibroin porous body of the present invention, a dried silk fibroin porous body can be efficiently obtained in a short drying time while easily maintaining the shape of the porous body. The dried silk fibroin porous material obtained by the production method of the present invention is used in medical fields such as wound dressings, drug sustained-release carriers, hemostatic sponges, daily necessities such as disposable diapers and organizing articles, tissue optics and regenerative medical engineering. The present invention can be applied to various industries such as cell culture supports, tissue regeneration supports, and supports for living organisms such as microorganisms and bacteria in the field of water purification and the environment.

DESCRIPTION OF SYMBOLS 10 Drying apparatus 11 Vacuum chamber 12 Breathable base material receiving jig 13 Breathable base material 13a Breathable base material inner layer 13b Breathable base material outer layer 14 Upper heating plate 15 Lower heating plate 20 Silk fibroin porous body

Claims (8)

  Step (1) of freezing silk fibroin aqueous solution or silk fibroin porous material containing water, and holding the frozen silk fibroin aqueous solution or silk fibroin porous material on a breathable substrate and drying under reduced pressure The manufacturing method of the dry silk fibroin porous body which has the process (2) to make.   The manufacturing method according to claim 1, wherein the silk fibroin aqueous solution or the silk fibroin porous material containing water further contains a water-soluble organic solvent.   The production method according to claim 2, wherein the water-soluble organic solvent is at least one selected from methanol, ethanol, and isopropyl alcohol.   The production method according to claim 2 or 3, wherein a content of the water-soluble organic solvent in the mixed solvent containing water and the water-soluble organic solvent is 5 to 30% by mass.   The manufacturing method according to any one of claims 1 to 4, wherein a porosity of the breathable substrate is 50 to 85%.   The method according to any one of claims 1 to 5, wherein the silk fibroin porous body is plate-shaped.   Furthermore, the manufacturing method in any one of Claims 1-6 which has the process (3) of heating the said air permeable base material.   The manufacturing method according to claim 7, wherein the heating is performed at 15 to 100 ° C.