JP6205723B2 - Porous material and porous sheet - Google Patents

Description

  The present invention relates to a porous material and a porous sheet obtained using a silk fibroin porous material.

Porous materials made using biological materials such as proteins and saccharides are used in medical fields such as wound dressings and drug sustained-release carriers, daily necessities such as disposable diapers and sanitary products, and living places such as microorganisms and bacteria. It is expected to be used as a support, and in the water purification field, cosmetics and esthetics for the purpose of moisturizing by use in esthetic salons and individuals, and cell culture supports and tissue regeneration supports in tissue engineering and regenerative medical engineering. It can be used in a wide range of fields.
Protein groups such as saccharides such as cellulose and chitin, collagen, keratin, and silk fibroin are known as biologically-derived substances constituting the porous body. Among these, silk fibroin is industrially used from the viewpoint of stable supply of raw materials and price stability. Furthermore, it has a track record of being used as a surgical suture for a long time other than clothing, and has recently been used as an additive for foods and cosmetics. Since silk fibroin has no problem with respect to safety to the human body, its use for porous materials has been studied.
There are several reports on the technique for producing silk fibroin porous materials. For example, a method in which a silk fibroin aqueous solution is rapidly frozen and then immersed in a crystallization solvent and melted and crystallized at the same time (Patent Document 1). (Patent Document 2), a method of producing a porous material by adding a small amount of a water-soluble organic solvent to a silk fibroin aqueous solution, and then freezing and melting for a certain time to obtain a silk fibroin porous material. Yes (Patent Document 3).

JP-A-8-41097 JP 2006-249115 A Japanese Patent No. 3412014

Biomacromolecules, 6, 3100-3106 (2005)

The porous body prepared by the above method is soft in a wet state containing water, but is brittle in a dry state where water is removed by drying such as freeze drying, and it is inferior in workability and appearance due to generation of cracks. was there.
An object of the present invention is to provide a silk fibroin porous material and a silk fibroin porous sheet which are soft even in a dry state and excellent in appearance after drying and slice processability.

As a result of intensive studies to achieve the above problems, the present inventor has found that the problems can be solved by the following invention.
[1] A porous material in which the silk fibroin porous material contains a hydroxyl group-containing compound having a molecular weight of 1,000 or less.
[2] The porous material according to [1], wherein the content of the hydroxyl group-containing compound is 0.1 to 300% by mass with respect to the total amount of the silk fibroin porous body.
[3] The hydroxyl group-containing compound is selected from glycerin, polyglycerin, polyethylene glycol, triethyl citrate, lactic acid, polyvinyl alcohol, propylene glycol, butylene glycol, alcohol, glycerin fatty acid ester, polyglycerin fatty acid ester, and sorbitan fatty acid ester. The porous material according to [1] or [2], which is at least one kind.
[4] A porous sheet made of the porous material according to any one of [1] to [3] and having a thickness of 0.1 to 50 mm.

  The porous material and the porous sheet according to the present invention are soft even in a dry state, and are excellent in appearance after drying and slice processability.

2 is a photograph showing the appearance after drying of the porous material produced in Example 1. FIG. 2 is a photograph showing the appearance of a porous sheet obtained by slicing the porous material produced in Example 1. FIG. 2 is a photograph showing the appearance of a porous material produced in Comparative Example 1 after drying. 4 is a photograph showing the appearance of a porous sheet obtained by slicing the porous material produced in Comparative Example 1. FIG. 5 is a photograph showing the appearance after drying of the porous material produced in Comparative Example 2. 5 is a photograph showing the appearance of a porous sheet obtained by slicing the porous material produced in Comparative Example 2. FIG.

  In the porous material according to the present invention, the silk fibroin porous material comprises a hydroxyl group-containing compound having a molecular weight of 1,000 or less. That is, in the porous material of the present invention, the silk fibroin porous body holds the hydroxyl group-containing compound.

The hydroxyl group-containing compound may be any compound having one or more hydroxyl groups per molecule, preferably having 1 to 10 hydroxyl groups per molecule, and more preferably having 1 to 4 hydroxyl groups per molecule. preferable.
Further, the molecular weight of the hydroxyl group-containing compound is 1000 or less, preferably 800 or less, and more preferably 500 or less.
Specific examples of the hydroxyl group-containing compound include glycerin, polyglycerin, polyethylene glycol, triethyl citrate, lactic acid, polyvinyl alcohol, propylene glycol, butylene glycol, alcohol, glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, and the like. Of these, one or more of them can be used. Among these, glycerin, polyethylene glycol, triethyl citrate, polyglycerin, lactic acid, propylene glycol, and butylene glycol are particularly preferable from the viewpoints of handling properties, slicing workability, and safety.

  The porous material according to the present invention preferably contains 0.01 to 500% by mass, more preferably 5 to 300% by mass of the hydroxyl group-containing compound, based on the total amount of the silk fibroin porous material. It is more preferable to contain ~ 250 mass%. When the content of the hydroxyl group-containing compound relative to the total amount of the silk fibroin porous material is less than 0.01% by mass, the porous material of the present invention tends to be brittle in a dry state, easily broken during slicing, and poor in handling properties. If it exceeds 500 mass%, the tack of the surface of the porous material becomes strong, and it tends to be wound around the roll during slicing, and the handling property tends to be lowered.

The silk fibroin used as a raw material for the silk fibroin porous material may be any one as long as it is produced from silkworms such as rabbits, wild silkworms, and tengu. The silk fibroin porous material can be obtained from a silk fibroin solution, but when dissolved in water, silk fibroin has poor solubility in water and is difficult to dissolve directly in water. As a method for obtaining a silk fibroin aqueous solution, any known method may be used, but a method in which silk fibroin is dissolved in a high concentration lithium bromide aqueous solution, followed by desalting by dialysis and concentration by air drying is simple.
The method for producing the silk fibroin porous material used in the present invention is not limited. For example, the silk fibroin porous material is obtained by rapidly freezing a silk fibroin aqueous solution and then immersing it in a crystallization solvent and simultaneously proceeding with melting and crystallization ( Patent Document 1), a technique for producing a porous body by maintaining a frozen state for a long time after freezing a silk fibroin aqueous solution (Patent Document 2), after adding a small amount of a water-soluble organic solvent to the silk fibroin aqueous solution A technique (Patent Document 3) for obtaining a porous body by freezing and thawing for a certain time is mentioned.

In addition, the silk fibroin porous material used in the present invention is preferably produced by adding a specific additive to a silk fibroin aqueous solution, freezing the aqueous solution, and then thawing it.
In the production of the silk fibroin porous material, the concentration of silk fibroin is preferably 0.1 to 40% by mass, more preferably 0.5 to 20% by mass in the silk fibroin solution, and 1.0% More preferably, it is -12 mass%. By setting within this range, a silk fibroin porous body having sufficient strength can be efficiently produced.

  Examples of the additive include aliphatic carboxylic acids and amino acids. Although there is no restriction | limiting in particular as an additive, A water-soluble thing is preferable and the thing with the high solubility to water is more preferable. Moreover, as an aliphatic carboxylic acid used in manufacture of a silk fibroin porous body, that whose pKa is 5.0 or less is preferable, the thing of 3.0-5.0 is more preferable, and 3.5-5. Even more preferred is zero.

  As the aliphatic carboxylic acid, for example, a saturated or unsaturated monocarboxylic acid, dicarboxylic acid or tricarboxylic acid having 1 to 6 carbon atoms can be preferably used. For example, formic acid, acetic acid, propionic acid, butyric acid, succinic acid Lactic acid, acrylic acid, 2-butenoic acid, 3-butenoic acid and the like. These aliphatic carboxylic acids can be used alone or in combination of two or more.

The amino acid is not particularly limited, and examples thereof include monoaminocarboxylic acids such as valine, leucine, isoleucine, glycine, alanine, serine, threonine, and methionine, and monoaminodicarboxylic acids (acidic amino acids) such as aspartic acid and glutamic acid. Examples include aliphatic amino acids, aromatic amino acids such as phenylalanine, and amino acids having a heterocyclic ring such as hydroxyproline. Among these, acidic amino acids and oxyamino acids such as hydroxyproline, serine, and threonine are preferable from the viewpoint of easy shape adjustment. . From the same viewpoint, monoaminocarboxylic acid is more preferable among acidic amino acids, aspartic acid and glutamic acid are particularly preferable, and hydroxyproline is more preferable among oxyamino acids. These amino acids can be used alone or in combination of two or more.
In addition, there are L-type and D-type optical isomers of amino acids, but when L-type and D-type are used, there is no difference in the resulting porous material, so which amino acid is used. Also good.

  When the additive is used in the silk fibroin aqueous solution, the content of the additive is preferably 0.1 to 18% by mass, more preferably 0.1 to 5.0% by mass, More preferably, it is 4.0 mass%. By setting within this range, a porous body having sufficient strength can be produced. Moreover, if it is 18 mass% or less, when leaving the silk fibroin solution which added the aliphatic carboxylic acid and / or the acidic amino acid to the silk fibroin aqueous solution, the solution is hard to be gelled, and the silk fibroin porous material having a stable and good quality. A mass is obtained. Moreover, it is preferable that content of an amino acid is 1-500 mass% with respect to silk fibroin, It is more preferable that it is 5-50 mass%, It is further more preferable that it is 10-30 mass%.

The silk fibroin porous material to which the additive is added can be produced by pouring the silk fibroin solution to which the additive is added into a mold or container, freezing it in a low-temperature thermostatic bath, and then thawing it. it can. The freezing temperature is not particularly limited as long as the silk fibroin solution containing the additive is frozen, but is preferably about −10 to −30 ° C. Further, the freezing time is preferably 4 hours or more at a predetermined freezing temperature so that it can be sufficiently frozen and kept in a frozen state for a certain time.
As a method of freezing, the silk fibroin solution may be frozen to a freezing temperature all at once, but once it is kept at about −5 ° C. for about 2 hours to be in a supercooled state and then lowered to the freezing temperature. Freezing is preferable for obtaining a porous body having high mechanical strength. The structure and strength of the porous body can be controlled to some extent by adjusting the time taken from −5 ° C. to the freezing temperature.
Thereafter, the silk fibroin porous material is obtained by thawing the frozen silk fibroin solution. The melting method is not particularly limited, and examples include natural melting and a method of holding in a thermostatic bath.

  The resulting silk fibroin porous material contains an additive, but if it is necessary to remove the additive depending on the application, remove the additive from the silk fibroin porous material by an appropriate method. Can be used. For example, the simplest method is to immerse the silk fibroin porous material in pure water to remove the additive. Or it is possible to remove an additive and a water | moisture content simultaneously by freeze-drying a porous body.

  The silk fibroin porous material has a sponge-like porous structure. Normally, this silk fibroin porous material contains water unless it is removed by freeze-drying or the like. is there. In addition, a dried silk fibroin porous material can be obtained by freeze-drying the silk fibroin porous material.

  This silk fibroin porous material can be made into a shape suitable for the purpose, such as a film shape, a sheet shape, a block shape, a tubular shape, a spherical shape, etc., by appropriately selecting a mold and a container for producing the silk fibroin porous material. . There are no restrictions on the shape or container of the silk fibroin solution so long as it does not flow out, and the material used is a material with high thermal conductivity such as iron, stainless steel, aluminum, gold, silver, or copper. It is preferable from the viewpoint of obtaining a silk fibroin porous body having a uniform structure. In addition, the thickness of the mold or the wall of the container is preferably 0.5 mm or more from the viewpoint of its function and deformation due to expansion during freezing, etc., and is easy to handle and efficient in cooling. More preferably, the thickness is 1 to 3 mm.

Moreover, the mold | type and container used here can provide a sheet | seat in the inner wall surface which contact | connects the silk fibroin solution inside for the purpose of controlling the structure and thickness of the said film layer.
As the sheet, a sheet made of a fluororesin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), or Preferable examples include release-treated sheets made of polyethylene terephthalate (PET) or polypropylene (PP). When these sheets are used, a smooth film layer with few pores can be obtained. In addition, when it is not desired to provide a film layer, a sheet having a rough surface such as filter paper can be provided. About adoption of these sheets, what is necessary is just to select suitably according to the use of a porous body.
In addition, it is preferable to use a sheet having a thickness of 1 mm or less that hardly inhibits heat conduction.

  This silk fibroin porous body may be subjected to a cutting process or a cutting process after the melting step described above. When making a silk fibroin porous body into a sheet shape, when making a porous body consisting only of a porous layer, in addition to selecting the material of the container, the surface structure is selected by cutting the film layer be able to. Specifically, for example, a block-shaped mold or container in which a sheet such as a Teflon sheet is provided on the inner wall surface is taken out from the mold or container, and then the four side film layers are removed to remove the porous layer. A porous body consisting only of a porous layer can be obtained by cutting or excising a portion. Alternatively, a porous body having a film layer only on one surface can be obtained by using a mold or a container in which a sheet such as a Teflon sheet is provided on one inner surface and a filter paper is provided on the other inner surface.

  The method of incorporating the hydroxyl group-containing compound into the silk fibroin porous material is not particularly limited.When producing the silk fibroin porous material, the method of blending it into the silk fibroin solution or the preparation of the silk fibroin porous material, You may make it soak in the solution containing the hydroxyl-containing compound of the grade to immerse. Although the immersion time is not particularly defined, if the immersion time is short, the amount of the hydroxyl group-containing compound introduced into the silk fibroin porous material may be reduced.

The porous sheet which concerns on this invention consists of the said porous material, The film thickness is 0.01-300 mm, It is preferable that it is 0.01-100 mm, It is more preferable that it is 0.1-50 mm. preferable.
The porous sheet can be easily produced by slicing the porous material.

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

Example 1
(Preparation of silk fibroin solution)
Silk fibroin aqueous solution is prepared by dissolving silk fibroin powder (KB Selen, trade name: “Silk Powder IM”) in 9M lithium bromide aqueous solution, removing insoluble matter by centrifugation, and dialysis against ultrapure water. It was obtained by repeating. The obtained silk fibroin aqueous solution was air-dried in a dialysis tube and concentrated. Acetic acid was added as an additive to the concentrated solution to prepare a silk fibroin solution having a silk fibroin concentration of 30 g / L and an acetic acid concentration of 2% by volume.

(Manufacture of silk fibroin porous material)
The silk fibroin solution is poured into a mold (inside size: 400 mm × 300 mm × 20 mm, 60 mm × 30 mm × 10 mm, 100 mm × 10 mm × 10 mm) made of an aluminum plate, and placed in a low temperature constant temperature bath (NCB-3300 manufactured by EYELA). It left still at -1 degreeC for 10 hours.
Thereafter, the low-temperature thermostat is cooled to -1 ° C in advance, and a mold containing the silk fibroin solution is put into the low-temperature thermostat, and then cooled to -20 ° C at a rate of 3 ° C / hour. And frozen for 5 hours.
The frozen sample was returned to room temperature by natural thawing, then removed from the mold, immersed in ultrapure water, and the acetic acid used was removed by exchanging the ultrapure water twice a day for 3 days. Then, the dry mass of the silk fibroin porous body which freeze-dried and produced with the type | mold of internal diameter 60mmx30mmx10mm was measured.

(Introduction of hydroxyl-containing compound)
A 5% by volume glycerin aqueous solution was prepared so that the entire silk fibroin porous material produced as described above was immersed, and was immersed for 24 hours, and then lyophilized to obtain a porous material. . Further, the dry mass of the porous material after lyophilization was measured.
The mass ratio of the hydroxyl group-containing compound in the porous material was calculated by the following equation, assuming that the amount of the hydroxyl group-containing compound was divided by the amount of the silk fibroin porous material after drying.
((Dry mass of porous material after introduction of hydroxyl group compound)-(dry mass of silk fibroin porous body before introduction of hydroxyl group-containing compound)) / (dry mass of silk fibroin porous body before introduction of hydroxyl group-containing compound) )

About the porous material obtained by making it above, the external appearance after drying and slicing workability were evaluated as shown below. The evaluation results are shown in Table 1.
(Appearance after drying)
The appearance of the porous material after drying was observed, and the presence or absence of cracks and the state of the appearance were evaluated so that they could be recognized visually (width 0.3 mm or more, length 2 mm or more). If there was even one crack, it was rated as “x”, and when there was no crack but the porous material had appearance abnormalities such as precipitates, it was evaluated as Δ, and when there were no cracks or abnormal appearance, it was determined as “◯”.
(Slicing workability)
The porous material after drying was sliced using a slicing device (manufactured by Kitajima Machine Knife) so that the thickness after slicing was about 1 mm. The case where the sheet or the porous body was broken at the time of slicing was determined as “x”, and the case where there was no crack was determined as “◯”.

Examples 2-30 and Comparative Examples 1-7
In Example 1, the concentration of glycerin was set to the concentration described in Table 1, or the solution or dispersion described in Table 1 was used at the concentration described in Table 1 instead of the glycerin solution. Obtained a porous material in the same manner as in Example 1. Table 1 also shows the evaluation results of the appearance after drying and the slice processability.

  From Examples 1 to 30, the porous material of the present invention in which the silk fibroin porous material contains a hydroxyl group-containing compound having a molecular weight of 1,000 or less is excellent in appearance after drying and slice processability. On the other hand, from Comparative Examples 1 to 7, a compound containing no hydroxyl group or a material containing a hydroxyl group-containing compound having a molecular weight higher than 1,000 is cracked after drying, abnormal in appearance, or sliced. Sometimes cracks occurred.

PEG: Polyethylene glycol PGL: Polyglycerin TEC: Triethyl citrate DMSO: Dimethyl sulfoxide PVA: Polyvinyl alcohol

  The porous material of the present invention can be widely applied to the cosmetics and esthetic fields, and is extremely useful as a face mask adapted to the shape of the face. In addition, medical fields such as wound dressings, sustained drug carriers, hemostatic sponges, daily necessities such as disposable diapers and sanitary products, cell culture supports and tissue regeneration supports in tissue engineering and regenerative medical engineering, water purification applications and environmental fields The present invention can be applied to various industries such as a support that becomes a place of residence for microorganisms and bacteria.

Claims (1)

  Silk fibroin aqueous solution is frozen and thawed to produce a silk fibroin porous material. A total amount of the silk fibroin porous material of the hydroxyl group-containing compound is immersed in an aqueous solution containing a hydroxyl group-containing compound having a molecular weight of 1,000 or less selected from fatty acid esters, polyglycerin fatty acid esters, and sorbitan fatty acid esters. The manufacturing method of the porous material which makes content with respect to 28-300 mass%.