JPH0760087A - Environmentally response drug sustained release control membrane - Google Patents

Abstract

PURPOSE:To obtain an environmentally response drug sustained release control membrane excellent in mechanical strength, showing high safety against a human body, having no problem even when scattered over a farm because of microbial biodegradability and gentle to a human being or the globe by using a water-insoluble silk fibroin membrane containing a crystalline substance. CONSTITUTION:An environmentally resposive drug sustained release control membrane is obtained by forming a membrane from an aq. soln. of silk fibroin to crystallize the same, make a crystals contained in the membrane and make the membrane water-insoluble. When the drug sustained release control membrane is formed by crystallizing a silk fibroin membrane, at the degree of crystallization thereof the membrane can contain 10-60wt.% of moisture. This environmentally responsive drug sustained control membrane becomes drug sustained release properties or drug hardly sustained release properties by changing the pH of the aq. soln. brought into contact with the silk fibroin membrane. This function is developed because silk fibroin has a polar group such as an amino group because of protein and the degree of dissociation of the polar group is changed by pH.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an environmentally responsive drug sustained release control film comprising silk fibroin.

[0002]

2. Description of the Related Art Recently, various polymer membranes have been developed and applied to various fields by utilizing their gas permeable membrane, water vapor permeability and solute permeability. Among these polymer membranes, those having drug permeability have been applied to the sustained release of pharmaceuticals, agricultural chemicals, fertilizers and the like. It is desirable that the administration of pharmaceuticals and the spraying of pesticides and fertilizers be the minimum necessary from the viewpoints of reducing side effects and environmental pollution. Conventionally known drug sustained-release membranes are membranes that have the property of always releasing the drug at a constant rate, but the release cannot be stopped even when the sustained-release of the drug becomes unnecessary. There is a problem. Therefore, the development of a membrane that has a mechanism to release the drug only when the drug is needed and to stop the drug release when it is no longer needed, that is, a film in which the drug release is controlled ON-OFF with environmental changes (stimulation). Is desired.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an environment-responsive drug sustained release control film made of a new material, which does not have the above problems.

[0004]

The present inventor has completed the present invention as a result of intensive studies to solve the above-mentioned problems. According to the present invention, there is provided an environment-responsive drug sustained-release control film comprising a silk fibroin film, which contains a crystalline substance and is water-insoluble.

The environmentally responsive drug sustained-release control film of the present invention is obtained by forming an aqueous silk fibroin solution to obtain a silk fibroin film. This film is amorphous and water-soluble. In the present invention, this film is crystallized, and a crystalline substance is contained in the film to make it water-insoluble. Crystallization of the silk fibroin film can be performed using a poor solvent for silk fibroin, such as ethanol or methanol.

The silk fibroin used as a raw material may be derived from domestic silkworms or wild silkworms. As the silk fibroin solution, liquid silk fibroin extracted from the silk gland in the silkworm silkworm body can be used, or a solution of silk fibroin regenerated from raw silk can be used.

The crystallization treatment of the silk fibroin film can be carried out by immersing the silk fibroin film in a mixed solution of a solvent and water and then drying it.
In this case, the controlled drug sustained release performance of the membrane can be changed by changing the composition, temperature, and treatment time of the mixed solution. The drying temperature is 5 to 80 ° C. In the present invention, when the silk fibroin film is crystallized to form a controlled drug release film, its crystallinity is at least 10%, preferably 15%.
It is preferable to specify it in the range of 50%.

The environment-responsive drug sustained-release control membrane of the present invention means a membrane whose drug permeation function changes in response to environmental changes (stimulation). Specifically, the pH of the aqueous solution in contact with the silk fibroin membrane is changed, whereby the drug is easily or slowly released. To express such a function, silk fibroin has a polar group such as amino group, carboxyl group, imidazole group, hydroxyl group, and guanidino group because silk fibroin is a protein, and these polar groups change the dissociation degree depending on pH, And the interaction between these polar groups and the polar groups of the drug itself.

Examples of the drug include drugs such as antineoplastic agents, vitamins and disinfectants, pesticides such as antibacterial agents and insecticides, fertilizers and pigments.

The shape of the film is flat, capsule-shaped,
It includes various shapes such as spherical shape and cylindrical shape, and has a function as a partition wall that isolates the drug from the outside world.

[0011]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 Silk fibroin was mixed with CaCl ₂ : C ₂ H ₅ OH: H ₂ O = 1:
It was dissolved in a mixed solution of 2: 8 (molar ratio) at 70 ° C. for 2 hours. After filtering the dissolved aqueous fibroin solution,
The filtrate was dialyzed against ion-exchanged water through a cellulose semipermeable membrane for 3 days. The concentrated fibroin solution was cast on a polystyrene dish and dried at 30 ° C. for about 48 hours to form a film. The thickness of the film was about 27 μm. Further, these prepared membranes were treated in a 75% aqueous methanol solution for 15 minutes. The crystallinity of this film was 18% according to the X-ray diffraction method.

The membrane was immersed in an aqueous solution of various pH values for 3 days and dried in a vacuum dryer at 76 ° C. for 24 hours to measure the water content. As a result, the water content depends on the pH,
33.9% (pH 3), 32.3% (pH 5), 29.
It was 9% (pH 6) and 32.6% (pH 8).

5-Fluorouracil (abbreviation 5FU) and Vitamin C, which are used as drugs, as antineoplastic agents
(Abbreviated name Vc), resorcin (abbreviated name Res) which is a disinfectant or dermatological agent, sodium phenolsulfonate (abbreviated name SPS) which is a preservative, and benzyltrimethylammonium chloride (abbreviated name BTAC) which is a disinfectant were used.

A two-chamber cell is used as a membrane permeation measuring device,
A membrane is sandwiched between both cells, an aqueous solution of a drug having a concentration C ₀ of 10 ⁻³ mol / l is put in the right cell, and pure water is put in the left cell. Remove 3.4 ml of pure water solution every hour,
Absorbance was measured by an ultraviolet spectrophotometer in order to measure the concentration C _d of the transmitted drug. The drug concentration was determined by a conversion curve of absorbance ABS and drug concentration prepared in advance. The same amount of pure water as the extracted aqueous solution was supplied to the left cell. The measurement was carried out for 8 hours, the measurement temperature was 25 ° C., and the effective diameter of the film was 30 mm. In the permeation experiments at various pHs, the pH value of the aqueous solution was adjusted using HCl or NaOH so that the pH concentrations on both sides of the cell were the same at the start of the experiment.

The isoelectric point of this membrane is about pH = 4.5, below the isoelectric point the membrane is a weakly positively charged membrane, and above the isoelectric point the membrane is a weakly negatively charged membrane. Permeation curves of various drugs are shown in FIG. The concentration of each drug increased linearly with time, but the permeation rate of each drug was different.

The permeation coefficient P, which represents the ease of drug penetration, was calculated by the following equation. P = Vd (ΔC _d / Δt) S (C ₀ −C _d ).

S: area of membrane, V: volume of water on low concentration side,
d: film thickness ΔC _d / Δt: change in concentration of the low-concentration solution per unit time (gradient of straight line in FIG. 1)

The permeation coefficient measured under various pH values is shown in FIG.
Shown in. In SPS, since it becomes an anion in water, the permeation coefficient remarkably decreased with the increase of pH. On the other hand, in BTAC, since it becomes a cation in water, the tendency opposite to that of SPS was observed. Since Res is a neutral molecule in the pH range tested, the permeation coefficient was almost constant regardless of changes in pH. The permeation coefficient of 5FU was almost the same in acidic and neutral, but it decreased at about pH = 7.0 or higher. pH 7
The significant decrease in the transmission coefficient of 5FU is due to the fact that 5FU has negatively charged groups (pK _a = 8.0). Vc had a relatively large permeability coefficient when it was acidic (pH <4.5), but dropped sharply when pH> 4.5. P of Vc
This is because K _a is 4.25 and Vc comes to have a negatively charged group.

As described above, a drug having a positively charged group is less likely to be gradually released as it becomes more acidic, whereas a drug having a negatively charged group is less likely to be slowly released as it becomes more alkaline. Alternatively, the membrane sustained release rate of various drugs having negatively charged groups can be changed by changing the pH of the aqueous solution.

Example 2 A silk fibroin membrane was prepared in the same manner as in Example 1, the membrane was sandwiched between both cells of a membrane permeation measuring device, and the drug BTAC having a concentration of 10 ⁻³ mol / l was placed in the cell on the right side. Pour the aqueous solution and pure water into the left cell. In order to measure the concentration of the drug penetrated, instead of withdrawing the solution every hour in Example 1, the concentration of the drug in the cell on the left side was directly measured with an ultraviolet spectrophotometer equipped with an optical fiber. Figure 3 after starting the measurement
As shown in, the drug concentration was increased. After 15 minutes, 0.4 ml of 0.1 M hydrochloric acid was added to the cell on the left side to adjust the pH to 3.9, and the increase in the drug concentration stopped. After 30 minutes, 0.5 ml of 0.1 M sodium hydroxide was added to the left cell, and pH = 7.
At 2, the drug concentration started to increase again. I was able to repeat this many times. That is, the sustained release rate of the drug could be controlled to be ON-OFF in response to the environment (pH) change.

Example 3 An experiment was conducted in the same manner as in Example 2 except that SPS was used instead of the drug BTAC of Example 2. As shown in FIG. 4, pH =
Although the drug penetrated in 3.7 to 3.9, pH = 6.8 to
At 7.1, the permeation rate decreased. Further, when the same experiment was performed by changing the right side cell pH opposite to that of Example 2, the
As shown in (4), the drug permeated at pH = 3.5 to 3.9, but the drug permeation almost stopped at pH = 8.4 to 8.9.

Example 4 When 5FU was used in place of the drug BTAC of Example 2 and the same experiment as in Example 2 was carried out, pH =
The drug penetrated at 6.9-7.3, but pH = 8.9-
At 9.1 drug penetration ceased.

Example 5 10 mg of silk fibroin membrane (film thickness 0.028 mm when dried) prepared in the same manner as in Example 1 was immersed in 1 ml (100 times amount) of carminic acid solution and heated at 80 ° C. for 30 minutes. The solution of carminic acid, which is an edible pigment, is 100g of 1g carcass dead.
It was prepared by extracting the dye with 100 ml of water for 30 minutes at 100 ° C. and filtering, and 1% of acetic acid was added to the solution.

The membrane treated by the above procedure was taken out and an elution experiment was carried out using four kinds of buffer solutions pH 3.7, 5.8, 7.4 and 8.8. An acetic acid-sodium hydroxide buffer solution was used for pH 3.7, a phosphate buffer solution was used for pH 5.8 and pH 7.4, and a pyrophosphate buffer solution was used for pH 8.8. Add each of the carminic acid-containing membranes to 3 ml of buffer (300 times volume),
While stirring with a stirrer, the ultraviolet absorption intensity of carminic acid at 450 nm on the acidic side and 550 nm on the alkaline side was measured over time. After a sufficient time has elapsed, take out all the carminic acid contained in the membrane and measure the absorbance,
The total elution amount was determined. FIG. 7 shows the results of the elution experiment of carminic acid in four kinds of buffer solutions. The elution rate was represented by setting the ultraviolet absorption intensity of the total elution amount of each dyed film to 100%. On the alkaline side, elution was fast and almost equilibrium was reached at an elution rate of 95% or more, but the elution rate was suppressed as the pH was lower.

This is because carminic acid has a carboxyl group, and this silk fibroin film has an isoelectric point (pH
It is considered that these behaviors are largely attributed to the fact that the higher the pH is, the more negative charges the alkaline side than 4.5), and the lower the pH, the more positive charges the acidic side. It was revealed that the silk fibroin membrane is promising as a pH environment-responsive controlled release controlled drug membrane.

[0027]

The environmentally responsive drug sustained-release control film of the present invention not only exhibits an excellent drug sustained-release function, but also has excellent mechanical strength and high safety to the human body, as well as microorganisms and the like. Since it is biodegraded by, there is no problem even if it is sprayed on the farm.

The following can be considered as specific examples of practical use of the environment-responsive drug sustained release control film of the present invention. When the pH of the wastewater of the sewerage is neutral, various bacteria and the like are easily propagated, so that a disinfectant is required. However, as described in Example 1, the disinfectant (for example, a cation in water like BTAC) is used in the present invention. Released from silk fibroin membrane. On the other hand, if the pH of the wastewater becomes acidic, the bacteria will not propagate, so the release of the disinfectant becomes unnecessary, and the release of the disinfectant stops as described in Example 2.

[0029]

[Brief description of drawings]

[Fig. 1] Relationship between concentration of permeated drug and time

FIG. 2 pH dependence of permeation coefficient

FIG. 3: pH of solution in left cell and permeated drug (BT
Relationship between AC) concentration and time

FIG. 4: pH of solution in left cell and permeated drug (SP
Relationship between S) concentration and time

FIG. 5: pH of solution in right cell and permeated drug (SP
Relationship between S) concentration and time

FIG. 6: pH of solution in left cell and permeated drug (5F
Relationship between U) concentration and time

FIG. 7: Time course of elution rate of carminic acid in various buffer solutions

Claims (2)

[Claims] 1. An environmentally responsive drug sustained-release control film comprising a silk fibroin film, which contains a crystalline substance and is water-insoluble. 2. The environment-responsive controlled-release drug release film according to claim 1, wherein the film contains 10 to 60% by weight of water.