JPH02109570A - Silkfibroin-containing molding - Google Patents

Abstract

PURPOSE:To provide the above molding which has resilience and the strength to withstand use, utilizes the characteristics of silkfibroin, is usable adequately for various medical materials and biochemical materials and is improved in dimensional stability to underwater heat by forming the molding of a mixture composed of the silkfibroin and a synthetic high-polymer material. CONSTITUTION:The silkfibroin is dissolved into a thick aq. soln. of calcium chloride (usually 40 to 50% concn.) or dissolved in an aq. soln. of a neutral salt such as satd. aq. soln. of lithium bromide after removing sericin in case of a raw material in which the sericin is contained. This soln. is dialyzed by a semipermeable membrane such as cellophane film to remove the salt. The resulted aq. silkfibroin soln. and an aq. soln. or emulsion of the synthetic high- polymer material are mixed. This liquid mixture is used and is molded by a proper means meeting the desired molding form and if necessary, the molding is heat treated at 200 to 230 deg.C or is immersed into lower alcohol in order to assure insolubilization.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to molded articles containing silk fibroin, which is a substance constituting the protein fibers of silk obtained from silkworms, which are used in the medical and biochemical fields, for example. It relates to molded products that can be used as various materials.

Conventional technology Silk is an animal fiber that has been widely used for textiles since ancient times, but in recent years, research has focused on the physical and biochemical properties of silk cells and applied them to medical and biochemical materials. is being carried out.

One silk fiber that makes up the cocoon of a silkworm contains two fibroins (Plbroln), which are substances that make up protein fibers.
and sericin (Serl), a gluey substance that envelops its surface.
cln), and the so-called silk thread is made by removing sericin from cocoon silk and raw silk by scouring, but the fibroin of this silk thread, or silk fibroin, is dissolved in an aqueous solution of neutral salts such as calcium chloride and lithium bromide. Silk fibroin can be dissolved and dialyzed to obtain an aqueous silk fibroin solution, and a membrane or film can be formed from this aqueous solution by appropriate means. Silk fibroin itself has the ability to immobilize enzymes, and is known to have high oxygen permeability in the form of membranes and films mentioned above, as well as selective ion permeability and absorbability. As suggested by its use in surgical sutures, it is non-toxic and has excellent compatibility with living organisms.

Therefore, silk fibroin is expected to be used as a material for various medical and biochemical materials that utilize the above properties, such as enzyme-immobilized membranes, dialysis membranes, artificial blood vessels, artificial skin, artificial corneas, contact lenses, and pharmaceutical capsules. There is.

Problems to be Solved by the Invention However, when silk fibroin is made into a membrane or film, it does not exhibit the flexibility and elasticity of the original silk thread, and is extremely brittle and has poor mechanical strength. There are problems in that the film easily breaks and breaks when bent during handling, and it becomes difficult to separate the film from the substrate when the film is formed using the casting method. This is the biggest factor preventing its practical application as a material or biochemical material. In addition, the dimensions of the swollen body change due to changes in the heat in the water, resulting in lack of stability.

In light of the above circumstances, this invention has flexibility and strength that can withstand use, can be suitably used for various medical materials and biochemical materials that utilize the characteristics of silk fibroin, and is dimensionally stable against heat in water. The purpose of the present invention is to provide a molded product containing silk fibroin that has the properties of silk fibroin.

Means for Solving the Problems In order to achieve the above object, the inventors have conducted intensive research and found that by creating a molded product made of a mixture of silk fibroin and a synthetic polymer substance, the original properties of silk fibroin can be improved. It was discovered that this material has good flexibility and strength without deteriorating its physical and biochemical properties, and can be used satisfactorily in the form of a membrane or film, leading to the completion of this invention. Ta.

That is, the present invention relates to a silk fibroin-containing molded article made of a mixture of silk fibroin and a synthetic polymeric substance.

In this invention, the above-mentioned polymer substance is polyvinyl alcohol, the polyvinyl alcohol is made of a polymer having a syndiotact dyad content of 45% or more, and the molded product is in the form of a membrane or film. Each of these is a preferred embodiment.

Detailed Structure and Function of the Invention The type of synthetic component substance to be mixed with silk fibroin is not particularly limited; however, since the silk fibroin is obtained as an aqueous solution within the membrane, water-soluble resins and polymers that can be formed into an emulsion form may be used. suitable.

Examples of the above-mentioned water-soluble resins include polyvinyl alcohol (hereinafter abbreviated as PVA), cellulose-based water-soluble resins such as hydroxyethyl cellulose, water-soluble acrylic resins,
Various polymers such as water-soluble melamine resin can be used, but among these, PVA has a particularly good affinity with silk fibroin and gives good flexibility to the molded product.

In addition, since PVA has hydroxyl groups and hydrogen bonded to the carbon atoms in its main chain, it has heterotact, isotact, and syndiotact stereoisomerism, and the properties of molded products differ depending on the degree of stereoregularity. For molded products using PVA with a high syndiotact dyad content (hereinafter abbreviated as 5-PVA), such as those derived from trifluorovinyl acetate, the most common heterotact derived from vinyl acetate Atactic PVA with a lot of
(hereinafter abbreviated as a-PVA) has the advantage of having higher water resistance and superior strength than molded products using a-PVA. In particular, molded products using 5-PVA with syndiotact dyad content in the range of 45% or more are hydrophilic, but
It is stable in water up to temperatures of 0°C or higher, hardly eluting, and the degree of swelling remains constant regardless of the water temperature, so it dislikes applications that require dimensional stability and activity fluctuations due to temperature. It also shows excellent suitability for various purposes. In addition, 5-PVA whose dyad content in syndiotact is higher than 60% is difficult to use in terms of handling and mixing with silk fibroin because an aqueous solution thereof is very likely to gel. However, gelation depends on the concentration of PVA, so if the concentration is low, 60
Can be used with 96 or higher.

On the other hand, in a molded product using a-PVA, the a-P of the molded product is
The higher the VA ratio and the higher the temperature of the water in contact, the easier it is to elute, but this elution can be prevented or suppressed by applying heat treatment, formalization, freezing/thawing cycle treatment, etc., so there is no problem depending on the application. Can be used. These treatments also improve strength.

In addition, the degree of polymerization of PVA is preferably 500 or more for both 5-PVA5a-PVA.

The polymeric substances that can be formed into the emulsion form include:
Various types of products containing acrylic acid, methacrylic acid, and their alkyl esters as monomer components, such as acrylic-styrene copolymers, acrylic-vinyl acetate copolymers, acrylic-vinylidene chloride copolymers, and acrylic homopolymers. Examples include acrylic polymers.

The raw materials for silk fibroin are not limited to high-quality cocoon, raw silk, and silk thread, but also their scraps, used and disused silk thread, and silk outer material, as well as the liquid in the silk glands within the silkworm body. is also available.

In order to produce the molded article of the present invention, silk fibroin is removed from raw materials containing sericin by well-known means, and then a concentrated aqueous acid solution of calcium chloride (usually 40 to 50%
Silk fibroin is dissolved in an aqueous solution of a neutral salt such as 0% concentration) or a saturated aqueous solution of lithium bromide, and this solution is dialyzed with a semipermeable membrane such as a cellophane membrane to remove the salt, and the resulting silk fibroin aqueous solution is synthesized. The mixture is mixed with an aqueous solution or emulsion of a polymeric substance, and the mixture is molded by an appropriate means depending on the desired shape of the molded product. If necessary, heat treatment at 100 to 230°C or What is necessary is to immerse it in a lower alcohol. In addition, it is preferable to use a low-concentration aqueous solution or to mix the rainwater solution at a temperature of 50° C. or higher to avoid gelation. In addition, when using PVA as a synthetic polymer substance, it is necessary to be careful about stirring since its aqueous solution tends to precipitate when stirred. However, even at room temperature, it is possible to mix the solution immediately after preparing the solution before gelling.

To obtain a molded product in the form of a membrane or film, the above-mentioned mixture is usually cast onto a flat plate surface such as a glass plate, water as a solvent is evaporated to form a film, and this membrane or film is cast onto the flat plate surface. A so-called cast method is used in which the film is peeled off from above. In addition,
In this case, if a water-volatile liquid agent such as silicone oil is applied as a release agent on the flat plate surface in advance, peeling becomes easy. Alternatively, a non-aqueous polymer film may be formed in advance on the flat plate surface, a mixed solution may be poured onto this membrane to form a film, and both films may be peeled off as one from the flat plate surface and then separated from each other. good. Generally, films with a thickness of 5 μm or more can be produced by such casting methods, but ultra-thin films with a thickness of 1 μm or less can also be produced using the soap bubble method or the frame method (for example, a patent for a single 5-PVA film: JP-A-1983-1993). 144305).

The mixing ratio of silk fibroin and synthetic polymer material is
The weight ratio of the former/latter is preferably about 2/8 to 8/2; if the ratio of silk fibroin is too low, its properties will not be fully expressed, and on the other hand, if the ratio of the synthetic polymer substance is too low, The molded product lacks flexibility and strength, making it impossible to achieve the intended purpose.

The molded product thus obtained has excellent flexibility, high mechanical strength, and even in the form of a membrane or film, it is tough and resistant to breakage - it also has considerable elongation, and also has silk fibroin's inherent enzyme fixation ability. It has oxygen permeability, selective ion permeability and adsorptivity, and also exhibits good biocompatibility, is stable in the pH range of 2 to 11, and has excellent light resistance, making it similar to silk fibroin single molded products. It has various advantages in that it does not easily cause yellowing. In particular, PvA
The mixture of fibroin and silk fibroin swells with water, but
Since the degree of expansion is constant and does not depend on the temperature of the water,
It is also highly suitable for applications that require dimensional stability and applications that dislike fluctuations in activity due to temperature.

Therefore, molded products in membrane or film form include enzyme-immobilized membranes, selective ion permeable membranes such as dialysis membranes, various separation membranes, soft contact lens materials, biocompatible membranes such as artificial blood vessels, artificial skin, and artificial corneas, and pharmaceutical capsules. It can be used for various materials such as medical and biochemical fields, and can also be used as a desalting treatment agent, as a raw material when used as beads, molded products in various forms, and powder. It can also be expected to be applied as a waste liquid treatment agent, a carrier for biochemical reactions, etc.

Example Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Using the cocoon of domestic silkworm as a raw material, sericin was removed with Marselle soap, and the obtained dried silk thread 0.429 was immersed in a 9.3 molar lithium bromide aqueous solution and dissolved using a hot water bath. Thereafter, the solution was centrifuged, and the resulting solution was dialyzed for 2 days in a cellophane tube to remove lithium bromide, thereby preparing an aqueous silk fibroin solution with a concentration of 1°397/dΩ.

Next, 5-PVA derived from vinyl trifluoroacetate (121 degree 2720, syndiotact dyad content 55%) was added to this aqueous solution and heated to about 130°C in an autoclave with water to obtain a concentration of 1. .49g/d
Q's-PVA aqueous solution was mixed with silk fibroin/PV
A is mixed at room temperature so that the weight ratio (solid content) is 1/1, and the resulting mixture is applied to the surface of a glass plate that has been coated with silicone oil in advance to a dry film thickness of about 10 μm. A silk fibroin-PVA mixed film was prepared by peeling the dried film from the glass plate.

Example 2 A silk fibroin-PVA mixed film was produced in the same manner as in Example 1, except that the casting onto a glass plate was set so that the dry film thickness was about 30 μm.

Example 3 Strained silk fibroin-P in the same manner as in Example 2 except that the weight ratio of silk fibroin/PVA was 1/2.
A VA mixed film was produced.

Comparative Example A single silk fibroin membrane was prepared in the same manner as in Example 2 using only an aqueous solution of silk fibroin. In addition,
A similar attempt was made to prepare a thin silk fibroin-only film corresponding to Example 1, but the film broke when peeled from the glass plate, and a satisfactory film could not be obtained.

For each of the four films obtained in Examples 1 to 3 and Comparative Example above, the film thickness was measured, as well as Young's modulus, breaking strength, elongation, and light resistance (25°C, 7 days of sunlight exposure). When tested, the results shown in the table below were obtained. In addition, all the numerical values in the table are the average of the measured values of four membranes, and the elongation shows the value at break. Moreover, Young's modulus is a value calculated by the following formula from the test results of stress-strain characteristics described later.

GPa = 109 N/m - 109 K'l/ms2 In addition, the films obtained in each of the above Examples and Comparative Examples were
Sample pieces were cut to a size of 0 #llll x 21111, and both ends of each sample piece were glued to both sides of a U-shaped supporting paperboard.The base of this supporting paperboard was cut and used for thin film. Tensile tester (product name 70M1 manufactured by Shinko Tsushinsha)
The stress-strain characteristics of each sample piece were measured under the condition that the distance between both pieces of supporting paperboard was expanded at a rate of 10 mII/min. The result is the first
As shown in the figure. In addition, the curve A1 in the figure corresponds to the sample piece of Example 1, A2 corresponds to the sample piece of Example 2, A3 corresponds to the sample piece of Example 3, and B corresponds to the sample piece of the comparative example.

From the results shown in the above table and FIG. 1, the silk fibroin-PVA mixed membrane according to the present invention is more flexible and extremely strong than the silk fibroin-only membrane, and
It can be seen that it also has excellent light resistance.

On the other hand, the NaCΩ permeability of the mixed membrane before the methanol treatment in Example 3 was examined by conductivity measurement. The results are shown in FIG. 2 together with the same permeability of a 5-PVA single membrane having approximately the same thickness. Curve C in the figure shows the characteristics of the mixed film of Example 3, and the curved line shows the characteristics of the 5-PVA single film.

From the results shown in FIG. 2, it can be seen that the silk fibroin-PVA mixed membrane exhibits higher electrolyte permeability than the 5-PVA membrane alone, and is excellent as a dialysis membrane or various separation membranes.

Effects of the Invention Since the silk fibroin-containing molded article of the present invention is composed of a mixture of silk fibroin and a synthetic polymer substance,
It has excellent flexibility and strength, and has physical and biochemical properties inherent to silk fibroin, such as enzyme immobilization ability, oxygen permeability, selective ion permeability, and absorbability.
It also has good biocompatibility and can be suitably used in various materials that utilize the above characteristics, including medical materials and biochemical materials.

In addition, when PVA is used as the synthetic polymer material, in addition to its great flexibility imparting effect, it has good affinity with silk fibroin and forms a sea-island-like microphase-separated structure. The molded product is flexible, has excellent quality, and has particularly good biocompatibility. Furthermore, this Pv
By using a polymer having a syndiotact content of 50% or more as A, a molded product with better water resistance and strength can be provided.

Furthermore, when the molded product is in the form of a membrane or film, there is an advantage that the flexibility and strength improvement effects of the present invention are maximized.

[Brief explanation of the drawing]

FIG. 1 is a stress-strain characteristic diagram of molded products of Examples 1 to 3 of the present invention and a comparative example, and FIG. 2 is an electrolyte permeation characteristic diagram of molded products of Example 3 and a reference example. That's all (@／,) 1st figure (minutes) 2nd figure

Claims (4)

[Claims] (1) A silk fibroin-containing molded article made of a mixture of silk fibroin and a synthetic polymer substance. (2) The silk fibroin-containing molded article according to claim (1), wherein the synthetic polymeric substance is polyvinyl alcohol. (3) The silk fibroin-containing molded article according to claim (2), wherein the polyvinyl alcohol comprises a polymer having a syndiotact dyad content of 45% or more. (4) Claim (1) formed in the form of a membrane or film
The silk fibroin-containing molded article according to any one of (3) to (3).