Gel containing bagworm silk and method for producing the same

Abstract

To provide a new application technology for bagworm silk.SOLUTION: Provided is a gel containing bagworm silk and water.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a gel containing bagworm silk and a method for producing the same.

Background Art

[0002] Silk derived from bagworms (bagworm silk), which is a general term for the larvae of moths belonging to the family Psychidae of the order Lepidoptera, has mechanically superior properties to silkworm silk and spider silk. For example, with respect to the elastic modulus, the bagworm silk of Eumeta minuscula is 3.5 times that of silkworm silk and 2.5 times that of the spider silk of Nephila clavata, and it exhibits very high strength (Non-Patent Documents 1 and 2).

[0003] In terms of breeding, bagworms also have advantages over silkworms. For example, silkworms generally belong to species of the genus Morus (mulberry), and as an example, they feed only on fresh leaves of Morus bombycis, Morus alba, Morus Ihou, etc. Therefore, the breeding area and breeding time depend on the supply area of mulberry leaves and the leaf-opening period of mulberry trees. On the other hand, bagworms are polyphagous, have low specificity for food leaves, and can feed on the leaves of many different tree species. Therefore, it is easy to obtain food leaves, and the breeding area can be chosen freely. Also, depending on the species, evergreen tree leaves can also be used as food leaves, so unlike deciduous mulberry trees, food leaves can be supplied throughout the year. Moreover, since bagworms are smaller in size than silkworms, a breeding space equal to or smaller than that of silkworms is sufficient, and mass breeding is also easy. Therefore, the breeding cost can be significantly reduced compared to silkworms.

[0004] Also, in terms of productivity, bagworms have advantages over silkworms. For example, silkworms spin silk in large quantities only during cocoon formation, and cocoon formation is carried out simultaneously by all larvae. Therefore, there is a problem that the silk harvesting periods overlap and the labor period becomes concentrated. On the other hand, bagworms repeatedly spin silk during nest building and movement throughout the larval stage. Therefore, there is an advantage that the labor period can be dispersed by artificially adjusting the silk harvesting period.

[0005] As described above, since the silkworm silk has properties that exceed those of conventional animal fibers and also has many advantages in terms of production, it is expected to be an environmentally friendly alternative material for silk (Non-Patent Document 2). And, for example, applications to fiber-reinforced composite materials combined with other polymers have been reported (Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the conventional application technology of silkworm silk has only utilized the properties of silkworm silk as fibers. Therefore, an object of the present invention is to provide a new application technology for silkworm silk.

Means for Solving the Problems

[0009] Therefore, the inventor of the present invention studied to change the silkworm silk into other forms instead of the fibrous form. As a result, quite unexpectedly, by heating and then cooling a dispersion or aqueous solution containing silkworm silk and adjusting the water content as necessary, a hydrogel (silkworm silk hydrogel) can be easily formed. The obtained hydrogel is excellent in stability and moldability and can be used in various technical fields. Thus, the present invention was completed.

[0010] That is, the present invention provides the following inventions [1] to [6]. [1] A gel containing (i) minomushi silk thread and (ii) water (hereinafter, sometimes abbreviated as minomushi silk thread-containing hydrogel). [2] The minomushi silk thread-containing hydrogel according to [1], wherein the water content is 80% by mass or more and 99.99% by mass or less in the total amount of the gel. [3] The minomushi silk thread-containing hydrogel according to [1] or [2], further containing one or more components selected from gel-forming polymers, saccharides, sugar alcohols, alcohols, polyhydric alcohols, water-soluble polymers, and basic substances. [4] The minomushi silk thread-containing hydrogel according to [1], wherein the minomushi silk thread is a silk thread spun by Eumeta japonica, Eumeta minuscula, or Nipponopsyche fuscescens. [5] Foods, pharmaceuticals, cosmetics, biomaterials, cushioning materials, elastic materials, fishing tackle, medical devices, industrial materials, and sanitary materials containing the minomushi silk thread-containing hydrogel according to any one of [1] to [4]. [6] A method for producing the minomushi silk thread-containing hydrogel according to any one of [1] to [3], characterized by heating the minomushi silk thread-containing aqueous solution to 50°C or higher and then cooling it.

Advantages of the Invention

[0011] The minomushi silk thread-containing hydrogel of the present invention is a hydrogel formed by a minomushi silk thread having an extremely high elastic modulus and strength and water molecules, and its strength and the like can also be changed, and it can be used in a wide range of fields such as foods, pharmaceuticals, cosmetics, biomaterials, cushioning materials, elastic materials, fishing tackle, medical devices, industrial materials, and sanitary materials.

Brief Description of the Drawings

[0012]

Figure 1

Modes for Carrying Out the Invention

[0013] The present invention relates to a caseworm silk hydrogel, and one aspect thereof is a caseworm silk hydrogel containing (i) caseworm silk and (ii) water.

[0014] In the present specification, a gel refers to a solid among colloids of a liquid dispersion medium. Since it is solid, it has the property of not flowing like a gas or a liquid. Therefore, a substance having thixotropy, which shows fluidity when subjected to shear stress and loses fluidity in a stationary state, is a gel. In the present specification, a hydrogel is a colloid in which the dispersion medium is water and which is solid. Specifically, it is in a state where a polymer in a network form has taken in a large amount of water. The caseworm silk hydrogel is a gel in a state where caseworm silk has taken in a large amount of water.

[0015] The main component constituting the hydrogel of the present invention is caseworm silk, which is silk (caseworm silk) derived from caseworms, which is a general term for the larvae of moths belonging to the family Psychidae of the order Lepidoptera. More specifically, it is a protein-based silk spun by the larvae of caseworms.

[0016] The Psychidae family includes genera such as Acanthopsyche, Anatolopsyche, Bacotia, Bambalina, Canephora, Chalioides, Dahlica, Diplodoma, Eumeta, Eumasia, Kozhantshikovia, Mahasena, Nipponopsyche, Paranarychia, Proutia, Psyche, Pteroma, Siederia, Striglocyrbasia, Taleporia, Theriodopteryx, Trigonodoma, etc. The bagworms referred to in this specification can be species belonging to any of these genera. Specific examples of Psychidae species include Eumeta japonica, Eumeta minuscula, and Nipponopsyche fuscescens. The age of the larvae can be any age from the first instar to the last instar. However, for the purpose of obtaining thicker and longer bagworm silk, larger bagworms are preferred. For example, among the same species, the last instar larvae are more preferred, and among males and females, larger females are preferred. Also, within the Psychidae family, larger species are more preferred. Therefore, Eumeta japonica and Eumeta minuscula are suitable species as bagworms.

[0017] As used herein, "silk thread" refers to a thread derived from an insect, which is a protein-based thread spun by insect larvae or adults for purposes such as nest building, movement, fixation, cocoon spinning, and prey capture. When simply referred to as silk thread in this specification, it means bagworm silk thread unless otherwise specified.

[0018] The bagworm silk thread of this specification includes single fibers, spun fibers, and aggregated fibers. A "single fiber" is the smallest unit filament that constitutes a fiber component and is also called a monofilament. Single fibers are mainly composed of fibroin-like proteins. Bagworm silk thread is spun as a bifilament in its natural state and usually does not exist as a single fiber. However, through a refining process, the adhesive substance can be removed to obtain single fibers.

[0019] The "silk-spun fiber" refers to the silk thread in the state where the silkworm has spun the silk. The silk-spun fiber of the silkworm is composed of a filament of a pair of two single fibers. This form is based on the form in which two single fibers ejected from the silk-spinning orifices located on the left and right sides of the silkworm during silk spinning are joined by a sericin-like adhesive substance. In addition, when described together with "silk spinning" as in "silk thread spun by the silkworm" or "spinning the silkworm silk thread" in this specification, it shall generally mean the silk-spun fiber.

[0020] The "aggregate fiber" refers to a fiber composed of a plurality of fiber bundles, also called a multifilament. It is a so-called raw silk, which is generally composed of a plurality of single fibers, but in this specification, it also includes cases composed of a plurality of single fibers and silk-spun fibers, or a plurality of silk-spun fibers. The aggregate fiber in this specification shall mean an aggregate fiber composed only of silkworm silk thread. The aggregate fiber is twisted through a twisting process to become a stronger silk thread. However, the aggregate fiber in this specification includes not only the twisted yarn fiber but also the untwisted yarn fiber that exhibits a soft and smooth texture.

[0021] There are support silk threads and nest silk threads in the silkworm silk thread. The "support silk thread" is the silk thread that the silkworm spins prior to moving, and has a function as a support to prevent it from falling from branches, leaves, etc. during movement. The silkworm usually uses this support silk thread as a foothold and moves in the advancing direction while hooking the claws of both legs. The support silk thread is spun in a zigzag pattern so that the silkworm can easily hook its left and right legs and also disperse the fixing part of the silk thread and the load on the silk thread to the left and right. On the other hand, the "nest silk thread" is the silk thread that constitutes the nest and is spun to sew together leaf pieces and branch pieces or to make the inner wall of the nest, which is the living area, into a comfortable environment. Generally, the support silk thread is thicker and more mechanically tough than the nest silk thread.

[0022] The method for obtaining the silkworm silk thread is not particularly limited, but it is preferably produced by the method described in Japanese Patent Application Laid-Open No. 2018-197415, for example. In addition, the modified silkworm silk thread ejected by the genetically modified silkworm described in International Publication No. 2018 / 074403 can also be used.

[0023] As described in Non-Patent Documents 1 and 2, the silk fiber of the bombardier beetle has a special amino acid sequence and a highly ordered hierarchical structure. By having such a special amino acid sequence and a highly ordered hierarchical structure, it becomes a fiber having excellent elastic modulus and strength. The silk fiber of the bombardier beetle is composed of a fibril hierarchical structure with nanofibrils composed of a repeating long-period structure of a crystalline phase and an amorphous phase as a basic unit. The repeating unit of the primary structure is about 160 residues, which is about five times longer than that of spider silk. The most characteristic feature of the silk fiber of the bombardier beetle is that it has a hybrid type that combines both the polyalanine sequence and the Gly-Gly-X (X is Ala, Tyr, etc.) sequence, which are characteristics of spider silk, and the Gly-X (X is Ala, Ser, etc.), which is a characteristic of silkworm silk. The number of amino acid residues in the crystalline phase is considered to be 67 residues, which is several times longer than that of other silks (for example, the silk of the Antheraea mylitta), and the length of the period (long period) of the crystalline phase and the amorphous phase, which serves as a measure of the length of the crystalline phase, is also several times longer than that of other silks. In the formation of the hydrogel, it is considered that regions where such a crystalline phase is easily formed form a physical cross-linking structure, and it is considered that the formation of a firm cross-linking structure affects the strength of the gel. It is considered that water molecules during hydrogel formation gather in the amorphous region. As described above, the repeating unit of the primary structure is 160 residues, and 67 of them form the crystalline phase, so the amorphous phase is about 90 residues. It is considered that water molecules gather in this 90-residue amorphous region.

[0024] The hydrogel of the silk fiber of the bombardier beetle of the present invention contains water as a solvent or a dispersion medium. The water content in the gel may be an amount that can form a gel at 25°C under atmospheric pressure, and can be appropriately adjusted according to the strength, function, etc. of the target hydrogel, and also according to the characteristics of other additives. From the perspective of forming a gel at 25 °C under atmospheric pressure, the water content in the hydrogel is preferably 80% by mass or more and 99.99% by mass or less in the total amount of the gel. Further, it is more preferably 85% by mass or more, still more preferably 90% by mass or more, and even more preferably 95% by mass or more. Also, it is more preferably 99.95% by mass or less, still more preferably 99.9% by mass or less, and even more preferably 99.5% by mass or less. In addition, the mass ratio (a / b) of the silk worm silk (a) to water (b) varies depending on the strength and function of the hydrogel, and also on the characteristics of other additives, etc., but is preferably 0.0001 or more and 0.1765 or less, more preferably 0.0005 or more and 0.1111 or less, and still more preferably 0.005 or more and 0.0417 or less.

[0025] To prepare an aqueous solution containing silk worm silk, in addition to water, an aqueous solvent that is advantageous for dissolving the silk worm silk can also be used. Examples of the aqueous solvent include solutions obtained by dissolving a neutral salt in water, such as copper - ethylenediamine aqueous solution, copper hydroxide - ammonia aqueous solution, copper hydroxide - alkali - glycerin aqueous solution, lithium bromide aqueous solution, calcium chloride aqueous solution, magnesium chloride aqueous solution, zinc chloride aqueous solution, calcium nitrate aqueous solution, magnesium nitrate aqueous solution, zinc nitrate aqueous solution, calcium thiocyanate aqueous solution, magnesium thiocyanate aqueous solution, zinc thiocyanate aqueous solution, sodium thiocyanate aqueous solution, lithium thiocyanate aqueous solution, urea aqueous solution, sodium dodecyl sulfate aqueous solution, etc. Note that an aqueous alcohol obtained by mixing a lower alcohol such as methanol or ethanol with water can also be used. Also, from the perspective of dissolving the silk worm silk, for example, organic solvents such as hexafluoroacetone, dichloroacetic acid, trifluoroacetic acid, hexafluoroisopropanol, hexafluoroacetone, and formic acid may be used. In the silk worm silk hydrogel of the present invention, in addition to the silk worm silk as the solute / dispersed substance and water as the solvent / dispersion medium, various additives can be contained in consideration of the strength of the hydrogel, the functions and characteristics desired to be imparted, etc. Examples of additives that can be included are components with high affinity for minomushi silk and water, gel-forming polymers, saccharides, sugar alcohols, alcohols, polyhydric alcohols, water-soluble polymers, plasticizers, basic compounds such as organic bases and inorganic bases, and pigments. Examples of gel-forming polymers include synthetic polymers such as poly(meth)acrylic acid, poly(meth)acrylate, carboxyvinyl polymer, polyvinyl chloride, polyvinyl acetate, and salts thereof, cellulose derivatives, and natural polymers such as polysaccharides (agar, gelatin, carrageenan, pectin, gellan gum, xanthan gum, locust bean gum, tamarind seed gum, curdlan, etc.). Examples of saccharides include monosaccharides, oligosaccharides, and oligosaccharides. Examples of sugar alcohols include erythritol, lactitol, maltitol, mannitol, sorbitol, and xylitol. Examples of alcohols include ethanol, isopropanol, and butanol. Examples of polyhydric alcohols include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerin, polyglycerin, butylene glycol, and polybutylene glycol. Examples of water-soluble polymers include polyvinyl alcohol. Examples of plasticizers include triacetin, triethylene glycol diacetate, tributyl acetylcitrate, dibutyl sebacate, epoxidized soybean oil, phthalic acid esters, and adipic acid esters. Basic compounds such as organic bases and inorganic bases act as crosslinking agents for acidic polymers such as polyacrylic acid. Examples of pigments include Food Red No. 2, Food Red No. 3, Food Red No. 40, Food Red No. 102, Food Red No. 106, Food Yellow No. 4, Food Yellow No. 5, Food Blue No. 1, Food Blue No. 2, caramel, etc.

[0026] Since these other components have different effects on the hydrogel of the present invention depending on their types, their contents vary greatly, but are preferably 0.5% by mass or more and 60% by mass or less, more preferably 1% by mass or more and 45% by mass or less, and even more preferably 5% by mass or more and 30% by mass or less, based on the total amount of the gel. The minotermite silk-containing hydrogel of the present invention can be easily produced, for example, by heating an aqueous solution or aqueous dispersion containing minotermite silk (hereinafter, the aqueous solution or aqueous dispersion containing minotermite silk may be abbreviated as an aqueous solution containing minotermite silk) to 50°C or higher and then cooling it. If necessary, the aqueous solution containing minotermite silk may be subjected to a concentration treatment such as dialysis or ultrafiltration before heating. In the method for producing the minotermite silk-containing hydrogel of the present invention, first, an aqueous solution or dispersion containing minotermite silk is prepared. The aqueous solution containing minotermite silk can be produced by adding a sufficient amount of water to minotermite silk and, if necessary, an additive. The additive may be added simultaneously with water or separately. The heating temperature of the aqueous solution containing minotermite silk is preferably 50°C or higher, more preferably 60°C or higher. The upper limit of the heating temperature may be 100°C or higher, and is preferably 130°C or lower in consideration of industrial productivity. Regarding the heating conditions, if the concentration of minotermite silk changes significantly during the gelation stage of the aqueous solution containing minotermite silk, it becomes difficult to obtain a gel having the desired properties. Therefore, it is preferable to set the conditions to prevent evaporation of water during gelation and to allow the passage of water molecules inside and outside the solution or gel. Considering such conditions, it is preferable to fill the aqueous solution containing minotermite silk into a container (mold) with a certain degree of water permeability restriction and heat it. The container (mold) for heating is not particularly limited, and examples include a dialysis membrane container, a low-density polyethylene container, and a metal container. Also, the heating may be performed by heating in water or heating in air. After sufficient gelation is confirmed, the minotermite silk-containing hydrogel of the present invention can be obtained by cooling to 15 - 25°C. Also, for example, when the container is a dialysis membrane, the water content in the gel can be adjusted by appropriately changing the solvent of the external liquid of the container. Incidentally, since no gel was obtained even after heating an aqueous solution of silkworm silk for a long time (heating at 80 °C for 500 minutes) and then cooling, the method for producing the gel containing mealworm silk of the present invention is industrially advantageous. In producing the mealworm silk-containing hydrogel of the present invention, not only mealworm silk but also proteins having the amino acid sequence constituting the mealworm silk and those having an amino acid sequence in which one or more amino acids of the amino acid sequence are deleted, added and / or substituted based on known methods can be used.

[0027] If other components (additives) such as polyvinyl alcohol and agar are added to the aqueous solution containing mealworm silk, heated to 50 °C or higher and cooled, a composite hydrogel of mealworm silk, polyvinyl alcohol and agar can be obtained. The obtained hydrogel is soft but maintains its shape and has the property of being resilient. At this time, if a dialysis membrane is used as the container, there is little evaporation of water and no adhesion deformation to the container occurs.

[0028] The mealworm silk-containing hydrogel of the present invention can also obtain a thixotropic gel that is solid at 15 to 25 °C but has fluidity when a shearing force is applied by adjusting the moisture and other components (additives) added during gelation. Such a gel can be used as pharmaceuticals, cosmetics, foods, etc. Moreover, it can also be made into a solid and elastic hydrogel. Such a gel can be used as foods, cosmetics, biomaterials, cushioning materials, elastic materials, fishing tools, medical devices, industrial materials, sanitary materials (such as diapers), etc.

Examples

[0029] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0030] Example 1 As the minotaur silk thread, the scaffold silk thread of the minotaur was used and scoured in a 0.02 M aqueous sodium carbonate solution heated to 90 °C for 30 minutes. 40 mg of the scoured minotaur silk thread was dissolved in a saturated lithium thiocyanate aqueous solution heated to 70 °C for 60 minutes, then placed in a cellulose dialysis tube and dialyzed using 2 liters of ultrapure water as the external dialysis solution. The dialysis temperature was set at 4 °C, and the external dialysis solution was exchanged 4 times in total at a frequency of 2 times a day. The concentration of the prepared minotaur silk thread aqueous solution was calculated to be 1.2% by mass through the measurement of the dry weight. The obtained minotaur silk thread aqueous solution was placed in a cellulose dialysis tube and air-dried and concentrated to prepare a 2% by mass minotaur silk thread aqueous solution. The obtained aqueous solution was sealed in a dialysis tube and heated in a warm bath at 38 °C to 80 °C. Table 1 shows the relationship between the heating time and gelation. From Table 1, it was found that the minotaur silk thread-containing aqueous solution easily gels when heated to 50 °C or higher. Note that the 2% by mass silkworm silk thread aqueous solution did not gel even when heated at 80 °C for 500 minutes.

[0031]

Table 1

[0032] Example 2 The 2% by mass minotaur silk thread aqueous solution was sealed in a dialysis membrane, a low-density polyethylene (LDPE) membrane, and a sealed container (sample tube with lid), or placed in an open container (petri dish), heated for 20 minutes under the conditions shown in Table 2, and the state of the resulting gel was observed. Note that the heating in water and the drying oven were set at 80 °C. The dry heat treatment was heated in a dry heat sterilizer set at 80 °C for 20 minutes, and the autoclave treatment was heated at 121 °C for 20 minutes. The results are shown in Table 2. From Table 2, it can be seen that the heating conditions are good when there is permeability of water molecules inside and outside the membrane (container) while preventing the evaporation of moisture during gelation.

[0033]

Table 2

[0034] Example 3 In the same manner as in Example 1, 1 mL of an aqueous solution of minomushi silk thread prepared to 0.005, 0.01, 0.05, 0.07, 0.1, 0.5, 0.75, 1, 2, 4, 5, 6, 7% by mass was sealed in an 8 / 32 dialysis membrane together with air bubbles and heated in hot water at 90 °C for 15 minutes. After heating, the gelation was determined based on the movement of the air bubbles when the dialysis membrane was inverted, and then the dialysis membrane was cut open to evaluate the form of the gel. The degree of gelation was determined by the movement of the air bubbles enclosed in the dialysis membrane. The evaluation criteria are as follows. ×: No change from before heating could be confirmed. △: The movement was slightly slower than before gelation. ○: The movement was slower than before gelation. ◎: The movement of the air bubbles stopped in the gel or the air bubbles did not move. The results are shown in Table 3.

[0035]

Table 3

[0036] Example 4 1 mL of a 10% by mass aqueous solution of polyvinyl alcohol and 100 mg of agar were placed in a 5 mL sample tube and dispersed by strong stirring with a vortex mixer. 1 mL of a 2% by mass aqueous solution of minomushi silk thread was added and mixed uniformly by pipetting. The mixed solution was sealed in a dialysis membrane, immersed in a water bath at 90 °C and heated for 30 minutes, and then transferred to a saturated aqueous boric acid solution heated at 90 °C and heated for 30 minutes. Moisture was removed, and after cooling at 4 °C for 5 minutes, the dialysis membrane was cut open to recover the gel. The surface smoothness, shape stability, and appearance of the obtained gel were evaluated. The surface smoothness was evaluated by the roughness of the gel surface and whether peeling occurred. The shape stability was evaluated by whether the shape of the dialysis membrane container was maintained and whether the adhered part to the membrane peeled off. The appearance was evaluated by transparency, gloss, etc. The results are shown in Fig. 1.

[0037] As shown in Fig. 1, a composite hydrogel of minomushi silk yarn, polyvinyl alcohol, and agar was obtained, and its surface smoothness, shape stability, and appearance were all good. Also, when placed in a dialysis membrane and heated in water, polyvinyl alcohol did not elute. Since it was placed in a dialysis membrane and contacted with borax water, excess water escaped from the gel, causing the membrane to shrink and tighten. A gel structure was formed through three steps: gelation of minomushi silk yarn → gelation of polyvinyl alcohol → gelation of agar.

[0038] Test Example 1 Comparison of Physical Properties between Minomushi Silk Yarn Gel and Silkworm Silk Hydrogel Similar to minomushi, a test was conducted to compare the physical properties of a hydrogel containing silkworm silk yarn, which is a silk-spinning insect, with the minomushi silk yarn hydrogel of the present invention. In the same manner as in Example 1, a 2% by mass aqueous solution of minomushi silk yarn and a 2% by mass aqueous solution of silkworm silk yarn were prepared, and 2 mL of each was sealed in an 8 / 32 dialysis membrane. The obtained dialysis membrane was placed in a 50 mL tube containing 40 mL of ultrapure water preheated at 100 °C in a dry thermo unit and heated to cause gelation. The treatment was continued until gelation occurred by heating in water, and when the length of the gel reached 10 mm, it was cut, and a uniaxial compression test was carried out (load cell: 50 N, plunger: φ23 mm, pedestal set at Z = 0, and the position where F>0.03 N was taken as the height of the gel and measured at a compression rate of 1 mm / min until 70%. n = 9). The compressive elastic modulus was calculated from the stress and strain at a strain of 0.05 - 0.25%, and the results until the first fracture occurred in the gel are shown in Table 4.

[0039]

Table 4

[0040] It was revealed that the minomushi silk yarn hydrogel had extremely excellent physical properties, with a compressive elastic modulus: 0.8 times, toughness: 6.0 times, fracture displacement: 2.3 times, and compressive fracture stress: 3.7 times compared to the silkworm silk yarn hydrogel.

Claims

**Claim 1** A hydrogel agent containing minomushi silk thread. **Claim 2** The hydrogel agent according to Claim 1, wherein the minomushi silk thread is the silk spun by Eumeta japonica, Eumeta minuscula or Nipponopsyche fuscescens.

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