JP6011963B2 - Multilayer cellulose airgel and method for producing the same - Google Patents

Description

  The present invention relates to a multilayer cellulose airgel and a method for producing the same.

  Airgels and hydrogels containing cellulose fibers (hereinafter also referred to as “cellulose aerogels” and “cellulose hydrogels”) are attracting attention as industrial materials, medical materials, and edible materials. Cellulose hydrogel is a gel in which water is retained in pores (holes) in a three-dimensional network structure of cellulose fibers, and cellulose airgel is obtained by replacing this water with air. Furthermore, when the air in the airgel is replaced with water again, a cellulose hydrogel is obtained.

  Cellulose hydrogel is obtained by culturing cellulose-producing bacteria. For example, Patent Document 1 discloses that a cellulose hydrogel is obtained by stationary culture of cellulose-producing bacteria at 30 ° C. for 5 to 10 days. The cellulose hydrogel thus obtained usually has a single layer structure.

  In addition, a cellulose hydrogel having a multilayer structure in which layers having high fiber density and layers having low fiber density are alternately laminated is also known. For example, “Natadecoko” included in “Halohalo” manufactured by Ministop Co., Ltd. and “Natadecoko wrapping (light)” manufactured by Dole Co., Ltd. are commercially available.

JP 2006-241450 A

  The cellulose hydrogel having a multilayer structure is industrially useful because it may be able to impart high functionality by taking advantage of the characteristics of each layer. Therefore, the inventors preliminarily examined commercially available multilayer cellulose hydrogels, and found that these had many variations in the layer structure. This is presumably because a commercially available multilayered cellulose hydrogel is produced by culturing cellulose-producing bacteria in a natural environment, so that the layer structure is not easily controlled. Specifically, these multilayer cellulose hydrogels are usually produced in Southeast Asian regions such as Thailand and the Philippines. The average annual temperature in Thailand is almost the same every month, with a maximum temperature of 30-32 ° C and a minimum temperature of 24-25 ° C. The average daily maximum temperature in the Philippines is 31 ° C, and the average minimum temperature is 24 ° C. For this reason, bacteria have high activity and a high fiber density layer is produced in daytime high temperature (29 to 32 ° C) culture, and bacteria have low activity and low fiber density layer in low temperature culture at night (24 to 25 ° C). Produced. However, since the temperature is left to nature, the fluctuation range is large. The high temperature culture and the low temperature culture are repeated at a cycle of about 12 hours, but it varies depending on the time. Therefore, it has been difficult to obtain a multilayer cellulose hydrogel having a precisely controlled structure by the conventional method.

  In view of the above circumstances, an object of the present invention is to provide a method for producing a multilayer cellulose hydrogel capable of controlling the structure more accurately.

As a result of repeated studies on solving the problems, the inventors have found that the above problems can be solved by culturing cellulose-producing bacteria at a specific temperature, and the present invention has been completed. That is, the said subject is solved by the following this invention.
[1] A step of culturing a cellulose-producing bacterium at 23 to 40 ° C. to form a first hydrogel layer having a low fiber density, and (B) culturing a cellulose-producing bacterium at 10 ° C. or more and less than 23 ° C. And forming a second hydrogel layer having a fiber density higher than that of the first hydrogel layer,
A method for producing a multilayer hydrogel in which three or more layers of the first hydrogel layer and the second hydrogel layer are alternately laminated.
[2] The average fiber bundle distance determined by the following method of the first hydrogel layer is 3.5 to 5 μm, the average pore diameter determined by the following method is 0.9 to 5 μm,
In the second hydrogel layer, the distance between the average fiber bundles is 0.1 μm or more and less than 3 μm, and the average pore diameter is 0.3 to 0.9 μm:
[Measuring method of distance between average fiber bundles] The multilayer cellulose hydrogel obtained by the method described in [1] is dried to obtain an airgel, and the airgel is cut in a direction perpendicular to the laminated surface, and is present in a layered form. Measure and average multiple shortest distances between layers of fiber bundles,
Method of measuring average pore diameter: Observe the surface of the airgel, measure the diameter of a plurality of pores, and average]
A multilayer hydrogel obtained by the method described in [1] above.
[3] R1 defined below of the first hydrogel layer is 0.05 or more and less than 0.50,
R2 defined below of the second hydrogel layer is 0.50 to 1.2,
R1 (%) = D1 / W1 × 100
D1: Mass at the time of drying of the first hydrogel layer W1: Mass at the time of saturated water absorption of the first hydrogel layer R2 (%) = D2 / W2 × 100
D2: Mass of the second hydrogel layer upon drying W2: Mass of the second hydrogel layer upon saturated water absorption Multilayer hydrogel obtained by the method described in [1] above.

  The present invention can provide a method for producing a multilayer cellulose hydrogel whose structure can be controlled more accurately.

Overview of cellulose hydrogel Diagram showing processing method Diagram showing processing method SEM image of the surface of multilayer cellulose airgel obtained in the present invention SEM image of cut surface of multilayer cellulose airgel obtained in the present invention SEM image of the surface of commercially available two-layer cellulose airgel SEM image of cut surface of commercially available two-layer cellulose airgel SEM image of the surface of commercially available multilayer cellulose airgel SEM image of cut surface of commercially available multilayer cellulose airgel Diagram showing the expansion rate of cellulose airgel

Hereinafter, the present invention will be described in detail. In the present invention, “to” includes values at both ends thereof.
1. Method for producing cellulose hydrogel (1) Step A
In step A, the cellulose-producing bacterium is cultured at 23 to 40 ° C. to form a first hydrogel layer having a low fiber density. The cellulose-producing bacterium is a bacterium that produces cellulose by culturing, and examples thereof include acetic acid bacteria. Known strains may be used as the acetic acid bacterium, and examples of the strain include ATCC 23769, ATCC 10245, ATCC 35959, ATCC 10821, ATCC 7000017, Acetobacter xylinum FF-88 (FERM BP-4407) and the like.

  A known medium can be used as the medium, for example, an agar-like solid medium or a liquid medium (culture solution) can be used. Examples of the culture solution include a culture solution containing corn steep liquor and fructose as main components and having a pH adjusted to about 5.

  The culture temperature is 23-40 ° C. By culturing at this temperature, cellulose-producing bacteria produce cellulose hydrogel. Considering ease of temperature setting, cost, and the like, the culture temperature in Step A is preferably 23 to 33 ° C, more preferably 25 to 32 ° C, and further preferably 26 to 31 ° C.

  The culture time may be appropriately adjusted in order to obtain a desired layer thickness, but is preferably 12 hours to 60 days, preferably 3 days to 22 days, and more preferably 4 days to 10 days. The culture is preferably stationary culture.

(2) Process B
In step B, the cellulose-producing bacterium is cultured at 10 ° C. or more and less than 23 ° C. By culturing cellulose-producing bacteria at this temperature, a second hydrogel layer having a fiber density higher than that of the first hydrogel layer is formed. In general, the higher the temperature, the higher the bacterial activity, and therefore the fiber density of the resulting layer is also considered to be higher. In the present invention, by culturing at a lower temperature than in step A, Get.

  Although this reason is not limited, it thinks as follows. Generally, when cellulose-producing bacteria are cultured, the bacteria move randomly while exhaling cellulose. When the culture temperature is appropriate, the bacteria actively move and grow. For this reason, although the quantity of the cellulose fiber produced is large, since the movement distance of bacteria is also large, the fiber density per unit volume becomes low and a low fiber density layer is obtained. However, when the culture temperature is low, the motility of the bacterium is reduced, so that the range of the bacterium's behavior is narrowed, and the bacterium grows without changing its position so much. For this reason, bacteria grow in a certain limited place and produce cellulose, so that the fiber density per unit volume is increased and a high fiber density layer is obtained.

  In addition, by culturing at a low temperature of 10 ° C. or more and less than 23 ° C., the activity of acetic acid bacteria is not lowered, but the activity of other bacteria is lowered, so that impurities in the gel can be reduced or the medium is less likely to corrode. There are advantages.

In order to express this effect better, the low temperature culture temperature is preferably 15 to 20 ° C, more preferably 17 to 19 ° C. The culture time is the same as that for high-temperature culture.
By performing steps A and B alternately, the first hydrogel layer and the second hydrogel layer are alternately stacked. In order to manufacture efficiently, it is preferable to perform the process A and B continuously. In addition, if the outermost layer of the obtained cellulose hydrogel is a second hydrogel layer having a high fiber density, the strength and shape stability of the gel will be good, so step B is performed first, and then steps A and B It is more preferable to repeat step B and finally carry out step B.

(3) Post-treatment A cellulose hydrogel can be obtained by subjecting the cultured medium to a known post-treatment. For example, a cellulose hydrogel can be obtained by taking out the product from the medium and then removing the bacteria by washing with water and alkali treatment.

2. Cellulose hydrogel Cellulose hydrogel is a gel formed by holding water in pores (holes) in a three-dimensional network structure of cellulose fibers. An example of the cellulose hydrogel obtained in the present invention is shown in FIG. In FIG. 1, 10 is a first hydrogel layer, and 20 is a second hydrogel layer. Since the second hydrogel layer has high strength and rigidity, the outermost layer of the multilayer cellulose hydrogel is preferably the second hydrogel layer from the viewpoint of shape stability. In the present specification, the outermost layer is described as the second hydrogel layer unless otherwise specified. Moreover, although FIG. 1 has shown the cellulose hydrogel of 3 layer structure, the number of layers of the multilayer cellulose hydrogel obtained by this invention should just be three or more, and about 3-11 and 3-7 are preferable.

(1) First hydrogel layer The first hydrogel layer is a layer having a lower fiber density than the second hydrogel layer. The layer can be specified by drying the cellulose hydrogel to obtain a cellulose airgel, observing the surface or fracture surface of the cellulose airgel with an electron microscope or the like, and measuring the pore diameter. In the cellulose airgel, a layer having a large pore diameter corresponds to the first hydrogel layer, and a layer having a small pore diameter corresponds to the second hydrogel layer. Or a cellulose hydrogel is observed and a layer can be specified by transparency. In this case, the layer with high transparency is the first hydrogel layer, and the layer with low transparency is the second hydrogel layer.

  The fiber density range of the first hydrogel layer is not particularly limited, but the average pore diameter is preferably 0.9 to 5 μm. The average pore diameter is measured as follows. 1) The multilayer cellulose hydrogel is immersed in water at room temperature (20 to 25 ° C.) for 16 to 24 hours, and then freeze-dried to obtain a cellulose airgel. 2) The diameter of pores (holes) observed when the surface of the cellulose airgel is observed with an electron microscope or the like is measured. When the pore is not a circle, the major axis and the minor axis are measured, and the average is taken as the pore diameter. 3) The pore diameter is measured for a plurality of pores and averaged.

  The fiber density in the airgel layer is also affected by the average distance between fiber bundles measured as follows. Usually, a cellulose hydrogel is produced in the form of a thin sheet-like cellulose hydrogel, and then the sheet-like gel is laminated to form a cellulose hydrogel having a certain size. As described above, when a cellulose hydrogel is produced using cellulose-producing bacteria, the sheet-like gel is usually laminated on the liquid phase side in parallel to the liquid surface. Therefore, in the cellulose hydrogel, fiber bundles in which cellulose fibers are gathered are present in layers. The shortest distance between the fiber bundles is referred to as an inter-fiber bundle distance, and an average of the inter-fiber bundle distances obtained by measuring and averaging the inter-fiber bundle distances for a plurality of fiber bundles. The average fiber bundle distance is an index of fiber density, and the fiber density decreases as the average fiber bundle distance increases. The average distance between the fiber bundles of the first hydrogel layer is preferably 3.5 to 5 μm. The average distance between fiber bundles is measured as follows. 1) A cellulose airgel is obtained by the above-mentioned method. 2) Using a cutter or the like, cut the cellulose airgel perpendicular to the laminated surface. 3) The cut surface is observed with an electron microscope or the like, and the shortest distance between the layers of the fiber bundles existing in layers is measured. 4) Measure and average the distances for multiple layers.

In addition, the fiber density can also be evaluated by a dry mass method in which a dry mass R per unit mass of cellulose hydrogel is calculated. Specifically, R (%) is defined by D / W × 100. D is the mass when the hydrogel is dried, and W is the mass when the hydrogel is saturated with water. If D is a mass D1 when the first hydrogel layer is dried and W is a mass W1 when the first hydrogel layer is saturated, water absorption R, that is, R1 is obtained. Saturated water absorption is the time when water absorption is saturated when gel is absorbed in a normal state (room temperature and atmospheric pressure). Moreover, the time of hydrogel drying means that the hydrogel is completely dried to become an airgel in an absolutely dry state. Specifically, W1 and D1 are obtained as follows.
1) The first hydrogel layer is specified by the method described above.
2) A sample is taken from the first hydrogel layer.
3) After soaking the sample in water at room temperature overnight, the mass is weighed to determine the saturated water absorption mass W1.
4) After drying the sample obtained in 3), the mass is weighed to determine the dry mass D1.

  The weighing is preferably measured to the order of 0.1 mg using a precision balance. Drying may be performed by hot air drying, freeze drying, natural drying, or the like, but hot air drying is preferable in consideration of drying efficiency. When dividing | segmenting a 1st hydrogel layer and a 2nd hydrogel layer, it is preferable to cut | disconnect using a cutter etc. so that a gel may not be crushed.

  The smaller R is the first hydrogel layer (low density layer), and the larger R is the second hydrogel layer (high density layer). R1 is preferably 0.05 or more and less than 0.50.

(2) Second hydrogel layer The second hydrogel layer has a higher fiber density than the first hydrogel layer. The range of the fiber density of the second hydrogel layer is not particularly limited, but the average pore diameter is preferably 0.3 to 0.9 μm, and more preferably 0.6 to 0.9 μm. Since the preferable average pore diameter of the first hydrogel layer is 0.9 to 5 μm, it overlaps the upper limit (0.9 μm) of the preferable average pore diameter of the second hydrogel layer. However, the average pore diameter of the first airgel layer is always larger than the average pore diameter of the second airgel layer, and the above description does not mean that both values are the same.

The average distance between fiber bundles of the second hydrogel layer is preferably 0.1 μm or more and less than 3 μm.
The cellulose hydrogel of the present invention has a relatively small average interfiber bundle distance in both the first hydrogel layer and the second hydrogel layer. For this reason, when the cellulose hydrogel of the present invention is edible, it has an excellent texture with a unique lump.

  Further, R in the second hydrogel layer, that is, R2 is obtained in the same manner as R1. R2 is preferably 0.50 to 1.2. From the above, in the cellulose hydrogel of the present invention, R1: R2 is preferably “0.05 or more and less than 0.50”: “0.50 to 1.2”.

(3) Shape and dimension Although the shape of the cellulose hydrogel obtained by this invention is not limited, from a handleability etc., a substantially cube or a substantially rectangular parallelepiped is preferable. A substantially cube is a shape that conforms to a cube. For example, the substantially cube includes a cube having a shape in which an angle between a vertex and a surface is slightly deviated from a right angle, or a rounded shape, and a cube whose sides are substantially parallel. The same applies to a substantially rectangular parallelepiped. In this case, from the viewpoint of handleability, it is preferable that the main surfaces of the first hydrogel layer and the second hydrogel layer are substantially parallel to the bottom surface of the approximately cubic or approximately cuboid. The main surface is a main surface of each layer and is a surface on which other layers are laminated. The cellulose hydrogel obtained in the present invention may be formed into a substantially cubic shape or a substantially rectangular parallelepiped shape by cutting or the like. The substantially rectangular parallelepiped includes a plate-like shape in which the length of one side is shorter than the other side. The plate shape is thicker than the aforementioned sheet obtained by culturing bacteria and is different from the sheet.

  Although the dimension of the cellulose hydrogel used by this invention is not specifically limited, When handling property etc. are considered, it is preferable that the length of one side is 0.5-2.0 cm, and is 1.0-1.8 cm. It is more preferable.

(4) Layer thickness In the present invention, since the thickness of the first hydrogel layer and the second hydrogel layer can be controlled as desired, functionality can be imparted to the cellulose hydrogel or the cellulose aerogel prepared therefrom. For example, cellulose aerogel is useful as a water-absorbing material, but when the first hydrogel layer is thickened or the number of first hydrogel layers is increased, a cellulose airgel having a high water absorption rate is obtained. In addition, when the cellulose airgel is compressed, it is possible to delay the return of the shape at the time of restoration (the expansion rate can be reduced). Such a property is necessary when used as a medical material such as a liquid absorbing material at the time of surgery. However, when the second hydrogel layer is thickened or the number of second hydrogel layers is increased, the expansion coefficient is further increased. Reduced cellulose airgel is obtained.

  As described above, functionality can be imparted to the cellulose hydrogel by changing the thickness of the layer, but the thickness of each layer is preferably 1 to 8 mm, and more preferably 2 to 4 mm.

3. Cellulose aerogel (1) Preparation method 1) Drying Cellulose aerogel can be prepared by drying the cellulose hydrogel. In the cellulose airgel, the layer derived from the first hydrogel layer is referred to as a first airgel layer, and the layer derived from the second hydrogel layer is referred to as a second airgel layer. Examples of the drying method include freeze-drying, reduced-pressure drying, supercritical liquid drying, and subcritical liquid drying. Freeze-drying is drying performed by freezing water and sublimating. In the present invention, it is preferable to freeze-dry at a low temperature of 50 ° C. or lower under reduced pressure in order to avoid gel degradation. Specifically, it is preferable to freeze-dry at a temperature of −50 to −40 ° C. under a pressure of 15 to 25 Pa.

Vacuum drying is a drying that removes water under reduced pressure. In this invention, it is preferable to dry at the temperature of -40-100 degreeC under the pressure of 25 Pa-0.1 MPa.
Supercritical liquid drying is a method in which a solvent solution is heated by being supercritical or higher and then dried by gently discharging solvent vapor out of the system. Subcritical liquid drying is a method in which a solvent solution is brought into a subcritical state where the temperature and pressure are slightly lower than those of the supercritical state, and the solvent vapor is discharged out of the system.

  In the present invention, it is preferable to replace water in the cellulose hydrogel as it is or with ethanol, methanol, carbon dioxide or the like, and dry water or ethanol with supercritical liquid drying or subcritical liquid drying. The critical temperature and pressure are as shown below. For example, when ethanol is used, supercritical liquid drying can be performed at 6.38 MPa and 243 ° C.

In the case of drying as it is without replacing water, it is preferable to carry out in a subcritical state because cellulose may be decomposed in a supercritical state. For example, it is preferable to set the temperature to 100 ° C. or higher at atmospheric pressure and to a temperature of 374.15 ° C. (647.30 K) or lower at 22.12 MPa.
Carbon dioxide: 304.1 (K), 7.38 (MPa)
Water: 647.3 (K), 22.12 (MPa)
Methanol: 512.6 (K), 8.09 (MPa)
Ethanol: 513.9 (K), 6.14 (MPa)
Acetone: 508.1 (K), 4.70 (MPa)
Although drying time can be suitably adjusted with a dry state, it is preferable to carry out for about 24 to 72 hours.

2) Pretreatment for drying However, if the cellulose hydrogel is simply dried, defects such as cracks in the cellulose hydrogel may occur. The reason for this is that the water present inside the cellulose hydrogel may undergo volume expansion during drying, and the strain generated thereby destroys the surface of the cellulose hydrogel that has already been dried and reduced in strength. it is conceivable that. In order to solve this problem, the inventors have developed a method of coating the surface of cellulose hydrogel with water before drying (see Japanese Patent Application No. 2010-020455). Therefore, it is preferable to perform drying in the same manner in the present invention.

  In the present invention, instead of coating the surface of the cellulose hydrogel with water, the cellulose hydrogel may be immersed in an aqueous solution containing a disaccharide such as maltose. When such an aqueous solution is used, not only the breakage of the cellulose hydrogel during drying is prevented, but also the restoration rate and texture when obtaining the restored cellulose hydrogel are improved. Maltose is a disaccharide in which two α-glucoses are linked by α1-4 glycosidic bonds. In addition, sucrose (sucrose) or lactose (lactose) may be used as the disaccharide. The concentration range is preferably 0.001 to 1% by mass, more preferably 0.01 to 0.5% by mass, further preferably 0.1 to 0.5% by mass, and more preferably 0.2 to 0.3% by mass. Further preferred is 0.22 to 0.27% by mass.

  Since maltose is contained as a main component in the starch syrup, in the present invention, it is preferable to use an aqueous solution containing starch syrup as the aqueous solution containing maltose. Mizuame is an edible sweetener containing glucose and dextrin in addition to the main component maltose. Using water candy can improve the surface gloss. The concentration of the syrup aqueous solution is adjusted so that the concentration of maltose contained in the aqueous solution falls within the above range. However, since other components are contained in the starch candy, it becomes difficult to penetrate into the gel when the concentration of the starch candy increases. Therefore, from this viewpoint, the starch candy concentration is preferably 0.01 to 0.25% by mass.

  Moreover, as an aqueous solution containing maltose, an aqueous solution obtained by further diluting 10 to 1000 times an aqueous solution obtained by dissolving 2 to 10 g of starch syrup and 10 to 20 mL of gelatin in 30 mL of water may be used. Gelatin is an induced protein obtained by boiling collagen in water.

By immersing the cellulose hydrogel in the aqueous solution for 1 to 24 hours, the aqueous solution penetrates into the cellulose hydrogel. The temperature during immersion is preferably room temperature.
The reason why the texture and appearance of the regenerated cellulose hydrogel are improved by using such an aqueous solution is not limited, but is presumed as follows. Since disaccharides such as maltose have a chemical structure similar to cellulose and have a low molecular weight, they easily penetrate into the cellulose hydrogel. And since disaccharide has good affinity with a cellulose fiber, it exists between cellulose fibers also at the time of drying. For this reason, if there is no maltose, the cellulose fibers are strongly bound to each other by drying, but the fact that the cellulose fibers are strongly bound to each other by the disaccharide is reduced. As a result, when the water is absorbed again to obtain the restored cellulose hydrogel, the network structure of the original cellulose fiber is easily reproduced. Further, when the disaccharide is infiltrated into the cellulose hydrogel, an aqueous solution having a relatively low concentration is used in the present invention. Since the concentration is low, capillary action is likely to occur and the disaccharide is more easily penetrated into the cellulose hydrogel.

  In addition, gelatin used in combination with disaccharides is considered to act to reinforce the outer shell of cellulose hydrogel because of its high molecular weight. However, since gelatin is also used as an aqueous solution having a relatively low concentration as described above, the cellulose hydrogel is not completely coated, so that it is considered that the texture is not lowered.

  In addition, instead of coating the cellulose hydrogel, 30 to 50% by volume of the cellulose hydrogel may be subjected to drying in a state of being immersed in water or the aqueous solution.

(2) Processing The cellulose aerogel may be subjected to processing such as cutting. When cellulose aerogel is absorbed and a cellulose hydrogel is obtained again, the restorability can be enhanced by the processing. The restorability will be described in detail later, but the restorability is an index indicating how close the restored cellulose hydrogel is to the original cellulose hydrogel.

1) Incision processing As the incision processing, i) a plurality of incisions 1 having a depth x are provided in parallel on either the long side or the short side on the surface of the second airgel layer constituting the outermost layer, or ii) depth It is preferable to provide a plurality of cuts 1 having a length x parallel to one of the long side and the short side, and to provide a plurality of cuts 2 having a depth x in parallel to the other side. The process of i) is also called “parallel cut”, and the process of ii) is also called “cross cut”. FIG. 2 shows a cellulose airgel subjected to such processing. FIG. 2 (a) is a cellulose airgel subjected to a parallel cut, and FIG. 2 (b) is a cellulose airgel subjected to a cross cut. In FIG. 2, reference numeral 30 denotes a cut 1, and s <b> 1 is a side 1 (length is L <b> 1) parallel to the cut 1. Reference numeral 32 denotes a cut 2, and s 2 denotes a side 2 (length is L 2) parallel to the cut 2. In FIG. 2, the display of the first airgel layer and the second airgel layer is omitted.

  The depth x of the cut is L (= (long side + short side), the average length of the long side and the short side of the surface where the cut of the substantially cube or the substantially rectangular parallelepiped (hereinafter also referred to as “substantially cube” or the like) is provided. Side) / 2), the length is 0.02L to 0.1L. Specifically, about 0.5-1 mm is preferable.

  Moreover, it is preferable that the minimum angle made by the depth direction of a notch and the surface which provides a notch is 15-90 degrees. If the angle is about 15 to 30 °, the cut may be provided without damaging the cellulose airgel.

  Thus, the cellulose airgel excellent in the recoverability is obtained by processing the surface of the second airgel layer constituting the outermost layer. The reason for this is not limited, but the second airgel layer has a high fiber density, so the pore diameter is small and water does not easily permeate. However, it is presumed that the above-described processing facilitates water permeation. In order to exhibit this effect more fully, the length of the cut 1 is preferably 70 to 100% of the length L1 of the side 1 parallel to the cut. Moreover, as for the space | interval of the adjacent notches 1, L1 / 5-L1 / 100 are preferable. Specifically, about 5 to 100 are preferably provided on one surface. In this case, it is preferable that the notches 1 are provided at unequal intervals as much as possible. The same applies to the cut 2. When the cuts are provided at regular intervals so as to have periodicity, the surface may be difficult to wet due to the so-called lotus leaf effect, and water may not easily penetrate.

  The means for providing the cut is not limited. For example, a notch may be provided using a cutter or a razor. Further, this cutting process may be performed on other five surfaces such as a substantially cube.

2) Through perforation processing In addition to the above-described cutting processing, the cellulose airgel may be subjected to through perforation processing. The through drilling process is to provide a hole that passes through the center of a surface such as a substantially cube and penetrates to the center of the opposing surface. This hole makes it easier for water to penetrate into the cellulose airgel. FIG. 3 (a) shows a cellulose airgel that has been perforated. In FIG. 3A, reference numeral 40 denotes a through hole.

  For the perforation, a known material may be used. For example, it is preferable to use a needle having a diameter of 0.3 to 1 mm. Further, the through drilling process may be performed on six surfaces such as a substantially cube.

3) Non-penetrating perforation process In addition to the above-described cutting process, the cellulose airgel may be subjected to non-penetrating perforation process. The non-penetrating drilling process is to provide a hole that does not penetrate from a surface such as a substantially cubic body to a facing surface. FIG. 3 (b) shows a cellulose airgel that has been perforated. In FIG. 3B, reference numeral 42 denotes a non-through hole. The minimum angle formed by the depth direction of the non-through hole 42 and the surface where the non-through hole 42 is provided is preferably 75 to 90 °.

  The depth of the hole is preferably 10 to 70% of the distance M between the facing surfaces. The number of holes not penetrating is preferably about 2 to 20. The non-through drilling process is preferably performed using, for example, a needle having a diameter of 0.3 to 1 mm. Further, the non-penetrating drilling process may be performed on six surfaces such as a substantially cube.

4) Deep cutting process In addition to the said cutting process, you may give a deep cutting process to a cellulose airgel. Deep cutting is a deep cutting with a depth of 0.5M to 0.7M (where M is the distance between the opposing surfaces) on two opposing faces such as a substantially cube, where both deep cuttings are cellulose. It is to provide one by one so as not to bond in the airgel. This deep cutting makes it easier for water to penetrate into the cellulose airgel. FIG. 3C shows a cellulose airgel that has been deep-cut. In FIG. 3C, 44 is a deep cut. In this case, the minimum angle formed by the deep cut and the surface on which the deep cut is provided is preferably 75 to 90 °, and more preferably 85 to 90 °. Further, the position on the z-axis at which the deep cut is provided is preferably 0.25Z to 0.33Z, where Z is the length of the side (s3) in the z-axis direction in FIG.

  If the width of the deep cut (the length in the y-axis direction in FIG. 3 (c)) is excessively long, the strength of the cellulose airgel may be reduced, so the width of the cut is the short side of the surface on which the cut is provided. And 50 to 70% of the average length L of the long side is preferable. The means for providing the deep cutting is as described in the cutting process.

5) Combination of processing The processing described in the above 1) to 4) may be arbitrarily combined. In particular, it is preferable to apply the processes 1) to 3) to 6 surfaces such as a substantially cubic body and the 4) process to 2 surfaces facing each other, because a cellulose airgel having extremely excellent restoration properties can be obtained. This processing is sometimes referred to as “S processing”.

6) Significance of processing cellulose aerogel In the present invention, it is preferable to process a cellulose aerogel, that is, a gel in a dry state. When the cellulose hydrogel is processed and dried, the cellulose fibers in the vicinity of the processed part are excessively adhered during drying. Adherent cellulose fibers are not easily loosened at the time of water absorption, so that the effect of improving the water absorption rate by processing is offset and it is difficult to obtain satisfactory restoration. However, when the cellulose gel after drying is processed, the cellulose fibers in the vicinity of the processed portion do not excessively adhere to each other, so that excellent resilience can be achieved.

4). Restoration hydrogel (1) Preparation method (restoration method)
The cellulose aerogel prepared from the cellulose hydrogel obtained in the present invention (hereinafter also referred to as “cellulose aerogel obtained in the present invention”) can be made into a restored hydrogel by absorbing water. The temperature at this time is preferably 0 to 100 ° C. Water absorption can be performed by immersing the cellulose hydrogel of the present invention in water or an aqueous solution at the above temperature. Examples of the aqueous solution include an aqueous sugar solution, an aqueous solution containing inorganic ions (mineral components), carbonated water, and broth. In the conventional cellulose aerogel, it was necessary to immerse in hot water in order to quickly restore the hydrogel, but the cellulose aerogel obtained in the present invention is cold water (preferably 4 to 30 ° C., more preferably 10 ˜30 ° C.).

  Although the time to immerse can be selected in 1 minute-24 hours, the cellulose airgel obtained by this invention can achieve a high restoration rate especially also in about 3 minutes of immersion.

(2) Restorability Restorability is an index representing how close the shape and properties of the restored cellulose hydrogel are to the original cellulose hydrogel. Restorability can be evaluated using the restoration rate. The restoration rate is defined by the mass of the restored cellulose hydrogel / the mass of the cellulose airgel. The cellulose airgel obtained in the present invention preferably has a recovery rate (also referred to as “3-minute recovery rate”) of 60% or more when immersed in water for 3 minutes.

  The restorability can also be evaluated by visually observing the white residue of the restored cellulose hydrogel. The “white residue” is a portion that appears white because water does not penetrate.

[Example 1]
(1) Preparation of cellulose hydrogel and cellulose airgel Acetic acid bacteria (strain ATCC 23769) were prepared as cellulose-producing bacteria. For liquid medium, corn steep liquor (manufactured by Sigma Aldrich, trade name Corn Step Liquid) 10 mL, fructose 20 g, (NH ₄ ) ₂ SO ₄ 1,65 g, KH ₂ PO ₄ 0.5 g, MgSO ₄ .7H ₂ O 125.0 mg, vitamin mixture 5.0 mL, and salt mixture 5.0 mL were prepared.

  The vitamin mixture is inositol 2.0 mg / L, D-Chiro nicotinic acid 0.4 mg / L, pyridoxine hydrochloride 0.4 mg / L, thiamine hydrochloride 0.4 mg / L, calcium pantothenate 0.2 mg / L, riboflavin It was a mixed solution of 0.2 mg / L, p-aminobenzoic acid 0.2 mg / L, folic acid 0.002 mg / L, biotin 0.002 mg / L, and each reagent was manufactured by Wako Pure Chemical Industries, Ltd.

The salt mixture was CaCl ₂ · 2H ₂ O 14.7 mg / L, FeSO ₄ · 7H ₂ O 3.6 mg / L, Na ₂ MoO ₄ · 2H ₂ O 2.42 mg / L, ZnSO ₄ · 7H ₂ O 1. It was a mixed solution of 73 mg / L, MnSO ₄ · 5H ₂ O 1.39 mg / L, CuSO ₄ · 5H ₂ O 0.05 mg / L, and each reagent was manufactured by Wako Pure Chemical Industries, Ltd.

  Ingredients other than the vitamin mixture were dissolved in distilled water to prepare a 500 mL aqueous solution. NaOH was added to the aqueous solution to adjust the pH to 5, followed by autoclave sterilization (at 121 ° C. for 20 minutes). Subsequently, the aqueous solution was cooled to room temperature, and then a vitamin mixture treated by filtration sterilization (manufactured by Sartorius steady Biotech, trade name Minisart RC15, pore size 0.20 μm was used as a filter) was added.

  Culturing was performed in a 15 mL falcon tube. The culture temperature was changed to 18 ° C. and 29 ° C. every 5 days for a total of 30 days. This gave a 1 cm thick gel.

  The gel was immersed in water and treated with an autoclave at 105 ° C. for 20 minutes. Next, autoclave treatment was performed 10 times at 105 ° C. for 20 minutes using 0.1 N NaOH instead of water. Further, using water, autoclaving was performed at 105 ° C. for 20 minutes, and washing was sufficiently performed to remove alkali.

  The obtained cellulose hydrogel was put into a 10 mL beaker so that the gas phase at the time of culture was below and the layer was horizontal. Distilled water was put into the beaker so that half of the gel was immersed in water, and freeze-drying was performed for 48 hours (Fukuoka, manufactured by Tokyo Science Instruments Co., Ltd., −40 to 50 ° C., 15 to 25 Pa).

  The gel thus obtained was a total of three transparent layers (first hydrogel layer) produced by 29 ° C. culture and three cloudy layers (second hydrogel layer) produced by 18 ° C. culture. It had a multilayer structure consisting of 6 layers.

  The cellulose hydrogel thus obtained was immersed in water overnight at room temperature. The soaked cellulose hydrogel was freeze-dried for 48 hours to obtain a cellulose airgel. The surfaces of the first hydrogel layer and the second hydrogel layer of the cellulose airgel were observed with a scanning electron microscope (JSM-5200, manufactured by JEOL Ltd.) (FIG. 4). The pore diameter was observed from an electron microscope image. Specifically, the portion indicated by the arrow in FIG. 4 was recognized as the pore diameter, and the pore diameter was measured for a plurality of pores. The average pore diameters of the first hydrogel layer and the second hydrogel layer were 1.0 μm and 0.90 μm, respectively. Furthermore, the cellulose airgel was cut | disconnected in the surface perpendicular | vertical to the lamination | stacking surface using the razor (Kaishin razor Co., Ltd. product, long pattern gold alpha). The fracture surface was observed with a scanning electron microscope (FIG. 5). The average distance between fiber bundles was measured from an electron microscope image. Specifically, a portion indicated by an arrow in FIG. 5 was recognized as an interlayer distance, and a plurality of interlayer distances were measured. The average fiber bundle distances of the first hydrogel layer and the second hydrogel layer were 3.78 μm and 1.15 μm, respectively.

  Moreover, R was calculated | required about each layer as above-mentioned. The values of R1 and R2 were 0.28% and 0.90%, respectively.

(2) Restoration of cellulose airgel The cellulose airgel prepared in the above (1) was cut with a razor to form a cube having a side of about 1 cm. At this time, the laminated surface was made parallel to the bottom surface. The cellulose airgel thus obtained was fully immersed in water at 25 ° C., and the restoration rate after 3 minutes was measured. As described above, the restoration rate was obtained from the mass of the restored cellulose hydrogel / the mass of the cellulose airgel. The mass was measured using a chemical balance (Cal Zeiss). As a result, the recovery rate (recovery rate at 3 minutes) was 0.35.

(3) Restoration of processed cellulose aerogel The above-mentioned cross-cut processing was applied to the surface of the six surfaces of the cubic cellulose aerogel obtained in (1) above using a razor (manufactured by Kaiken Razor Co., Ltd., long pattern gold alpha). The depth of cut was 0.5 to 1 mm, and the number of cuts was 100 per side (50 cuts 1 and 50 cuts 2). The minimum angle formed by the depth direction of the cuts 1 and 2 and the surface provided with the cuts was about 90 °.

  Next, the 6th surface of the cellulose airgel is subjected to the above-described through-piercing process using a sewing needle (diameter 0.71 mm), and further, the above-described non-through-hole drilling is performed using a sewing needle (diameter 0.53 mm). Processed. The number of non-through holes was 20 per surface, and the depth was 1 to 5 mm. The minimum angle formed by the depth direction of the non-through hole and the surface provided with the hole was about 90 °.

  Further, as shown in FIG. 3 (c), one deep cut having a depth of 8 mm and a length of 14 mm is made by using a scalpel (Dispomes No. 10 manufactured by ASONE CORPORATION) on two opposing surfaces of the cellulose airgel. Each was provided perpendicular to the surface. The shortest distance between the deep-cut main surface and the cellulose airgel surface parallel to the main surface was 0.3 mm.

  The cellulose airgel processed in this manner was fully immersed in water at 25 ° C., and the restoration rate after 3 minutes was measured. As a result, the recovery rate (restoration rate at 3 minutes) was 0.7. Furthermore, when the restoration rate after 60 minutes (the restoration rate at 60 minutes) was measured, it was 8.0.

[Comparative Example 1]
A cellulose hydrogel was prepared in the same manner as (1) of Example 1 except that the culture condition was a single condition for 20 days at 28 ° C. The obtained cellulose hydrogel was a gel in which a cloudy part and a transparent part were laminated in two layers. The part produced by the medium exposed to the air corresponded to the second hydrogel layer, and the part produced by the medium present in the culture medium corresponded to the first hydrogel layer. Each layer was evaluated in the same manner as in Example 1. The average pore diameter in the second hydrogel layer was 0.2 μm (FIG. 6 b), and the average inter-fiber bundle distance was 5 μm (FIG. 7 b). The average pore diameter in the first hydrogel layer was 1 μm (FIG. 6 a), and the average interfiber bundle distance was 8 μm (FIG. 7 a). The values of R1 and R2 were 0.29% and 0.52%, respectively.

  The cellulose hydrogel thus obtained was dried in the same manner as in Example 1 to obtain a cellulose airgel. About the obtained cellulose airgel, the restoration rate was evaluated like (2) of Example 1 without processing. As a result, the 3-minute recovery rate was 0.28.

  Moreover, about the obtained cellulose airgel, when the restoration rate was evaluated after processing like (3) of Example 1, the 3-minute restoration rate was 0.55.

[Comparative Example 2]
A rectangular parallelepiped cellulose hydrogel (Natadecoko included in “Halohalo” manufactured by Ministop Co., Ltd.) having a vertical and horizontal side of 1.4 cm and a height of 1.8 cm was prepared. Impurities were removed from the Nata de Coco, and after sufficient washing with water, it was washed 10 times with hot water at 100 ° C. The nata de coco was dried in the same manner as in Example 1 to obtain a cellulose airgel.

  The cellulose airgel is formed of two first airgel layers and three second airgel layers. Each layer has a thickness of about 3.1 mm for the first airgel and 3.6 mm for the second airgel layer. . The average pore diameter in the second hydrogel layer was 0.2 μm (FIG. 8 b), and the average inter-fiber bundle distance was 3.5 μm (FIG. 9 b). The average pore diameter in the first hydrogel layer was 0.4 μm (FIG. 8 a), and the average fiber bundle distance was 4 μm (FIG. 9 a). The values of R1 and R2 were 0.45% and 1.0%, respectively.

  The cellulose hydrogel was dried in the same manner as in Example 1 and further processed to obtain a cellulose airgel. About the obtained cellulose airgel, the restoration rate was evaluated like (2) of Example 1. As a result, the 3-minute recovery rate was 0.68. Further, the 60-minute restoration rate was measured and found to be 7.0.

[Example 2]
(1) Preparation of Cellulose Hydrogel and Cellulose Airgel The culture conditions were the same as in (1) of Example 1 except that the culture conditions were 18 ° C for 10 days, then 29 ° C for 10 days, and then 18 ° C for 10 days. To obtain a three-layer cellulose hydrogel. The values of R1 and R2 were 0.28% and 0.90%, respectively.

(2) Expansion rate The cellulose airgel is placed in a press machine (manufactured by ASONE Co., Ltd., 1 ton high pressure jack) so that the laminated surface and the press plate are parallel to each other at room temperature for 30 seconds at a pressure of 7 MPa. And pressed. The cellulose airgel after pressing was fully immersed in water at 25 ° C., and the change with time in thickness (t ₁ ) was determined. The expansion rate (t ₁ / t ₀ ) was measured from the ratio between t ₁ and the thickness t ₀ of the cellulose airgel after pressing.

[Example 3]
Three-layer cellulose processed in the same manner as (1) and (3) of Example 1 except that the culture conditions were 29 ° C. for 10 days, then 18 ° C. for 10 days, and then 29 ° C. for 10 days. A hydrogel was obtained. The values of R1 and R2 were 0.40% and 0.90%, respectively. With respect to the processed cellulose airgel, the expansion coefficient was evaluated in the same manner as in Example 2.

[Comparative Example 3]
A cellulose hydrogel was prepared in the same manner as (1) of Example 1 except that the culture condition was a single condition at 29 ° C. for 30 days. Cellulose airgel was prepared from the cellulose hydrogel, and the expansion rate was evaluated in the same manner as in Example 2 (2).

[Comparative Example 4]
A cellulose hydrogel was prepared in the same manner as (1) of Example 1 except that the culture condition was a single condition for 30 days at 18 ° C. Cellulose airgel was prepared from the cellulose hydrogel, and the expansion rate was evaluated in the same manner as in Example 2 (2).

  The results of Examples 2-3 and Comparative Examples 3-4 are shown in FIG. It is clear that the cellulose airgel of the present invention can moderately reduce the restoration rate. Thus, the cellulose airgel which can reduce a restoration | restoration rate moderately is useful as medical materials, such as the amount of liquid absorbers for surgery, since it can suppress rapid expansion | swelling.

10 1st hydrogel layer 20 2nd hydrogel layer 30 Notch 1
s1 Side 1 parallel to notch 1
32 depth of cut 2
s2 Side 2 parallel to notch 2
40 through hole 42 non-through hole 44 deep cut s3 side

Claims (4)

(A) a step of culturing a cellulose-producing bacterium at 23 to 40 ° C. to form a first hydrogel layer having a low fiber density, and (B) culturing the cellulose-producing bacterium at 10 ° C. or more and less than 23 ° C. Forming a second hydrogel layer having a higher fiber density than the first hydrogel layer;
A method for producing a multilayer hydrogel in which three or more layers of the first hydrogel layer and the second hydrogel layer are alternately laminated.   The manufacturing method of Claim 1 whose temperature in the said process (A) is 25-32 degreeC, and whose temperature in the said process (B) is 15-20 degreeC.   The manufacturing method of Claim 1 or 2 whose culture | cultivation time in the said process (A) and (B) is 12 hours-60 days, respectively.   The manufacturing method of Claim 1 or 2 whose culture | cultivation time in the said process (A) and (B) is 3 to 22 days, respectively.