JP2711119B2 - Volume changeable microcapsules by electrical stimulation - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polymer capable of responding to an electric stimulus by applying an external voltage, and more particularly to a microcapsule capable of contracting volume by the electric stimulus.

(Prior Art) In recent years, the demand for incorporating a sophisticated movement function of a living body into an engineering system has been increasing with the rapid development of high-performance robots and system control methods. However, in the case of simulating the kinetic function and mechanical energy generation mechanism in a living body, when a so-called rigid material mainly composed of a conventional metal is used, its ability and application range are naturally limited.

There is a need to develop active soft-body machines and soft-materials that do the work, mainly based on hydrous polymer gels as found in living muscle. Active soft machines with telescopic functions are not only new types of power systems for robots, manipulations and actuators that are closer to biological movements, but also biocomputer elements, switching, biomechanochemical elements, biosensors, etc. It can be a new functional material with a very wide range of applications, such as organ materials, motor center replacement systems, artificial limbs, assistive devices, information transmission for sensory impaired persons, biofeedback, mechanothermal, and visual substitute systems. In the case where these soft machines are systematized and used as highly controlled materials, there has been a strong demand for the development of soft machines that operate directly in connection with externally controlled electronic devices such as electrical stimulation and palaces. However, to date, there has been virtually no such system.

Conventionally, this type of conversion method involves reversing the ionization state of the electrolyte membrane by immersing a polymer electrolyte membrane such as polyacrylic acid or phosphorylated polyvinyl alcohol in water and alternately adding an acid and an alkali substance thereto. Energy conversion by a pH change, which causes the polymer electrolyte membrane to expand and contract by changing the pH, has already been known. However, the above energy conversion method has the following disadvantages.

(1) Since the range of expansion and contraction of the polymer electrolyte membrane due to the pH change is small, the efficiency of energy conversion and form exchange is low.

(2) Since the expansion and contraction of the polymer electrolyte membrane depends on the diffusion rate of the acid and alkali substances into the electrolyte membrane, the expansion and contraction response of the electrolyte membrane is slow, and the energy conversion speed is slow.

(3) An acid and an alkali substance are alternately added to the polymer electrolyte membrane to expand and contract. If this operation is repeated, a large amount of salt is generated in the immersion liquid, and the energy conversion ability of the electrolyte membrane is significantly impaired. Is done. Therefore, the immersion liquid has to be changed frequently.

Such a polymer reaction system that converts into a mechanical energy by utilizing a chemical reaction of a water-containing polymer is generally known as a mechanochemical reaction or a mechanochemical system. (1) Energy conversion system by ion exchange (2) Chelate formation 〃 (3) Redox reaction 〃 (4) Phase transition (Toyoichi Tanaka, Science, March 1981) No. 80-95
(5) Formation of polymer aggregates 〃 (6) Stereoisomerization reaction 〃 etc. are known, for example, detailed information on [Functional polymers] (Kyoritsu Publishing) and [Polymer aggregates] (Academic Society Publishing Center) Have been described. All of the above mechanochemical systems have low conversion efficiency, low response speed, accumulation of reaction products, poor reproducibility, as well as those based on pH changes.
There are drawbacks such as difficulty in controlling the reaction.

The present inventors have conducted intensive studies to improve the above-mentioned drawbacks, and as a result, proposed a material capable of being deformed and stretched by external electrical stimulation by using a specific polymer having a charge as Japanese Patent Application Laid-Open No. 61-71683. did. However, the stretching speed was still low here, and it was still far from practical use. Further, as stimulus-responsive microcapsules, those capable of breaking down and dissolving by pressure, friction, heat, water, etc. to release the contents or exhibit various functions have been conventionally known. Electrically stimulating microcapsules that change the contraction volume upon stimulation have not been proposed yet.

(Problems to be Solved by the Invention) An object of the present invention is to provide a microcapsule capable of contracting volume by electrical stimulation. In particular, it is an object of the present invention to provide a microcapsule using a polymer whose volume can be contracted by electrical stimulation.

(Means for Solving the Problems) The present invention is a microcapsule made of a polymer electrolyte that can be contracted by electrical stimulation.

The polymer used in the present invention needs to have a charge. The charge is, for example, polyacrylic acid, polymethacrylic acid, polyphosphoric acid, poly2-acrylamide-
Positively charged synthetic polymers such as 2-methylpropanesulfonic acid, ionized negatively charged synthetic polymers such as polyglutamic acid, polyvinyl pyridine, polyvinyl benzyl trimethyl ammonium salt, polyaion such as polyxyl viologen, and polylysine. Such as a polymer can be mentioned.

Further, it may be a copolymer with a nonionic monomer containing the above-mentioned polymer electrolyte as one component, such as methyl methacrylate, isoprene, vinyl chloride, acrylonitrile, styrene and the like. Saccharides such as agar, cellulose sulfate, carrageenan, collagen, casein, gelatin, etc., proteins or derivatives thereof may be used. Further, these synthetic or natural polymers may form complexes with polyvalent metal salts such as copper, chromium, cobalt, calcium, or form a salt bond with sodium, potassium, rubidium, monovalent metal ions, or have the opposite sign. A salt with a polymer, a so-called polyion complex or an interpolymer complex may be used. And polyacrylamide,
Hydroxylethyl methacrylate, starch. Even a non-charged polymer such as cellulose may be mixed with the above-mentioned various metal salts by any method to prepare a charged polymer substance. In short, it is necessary that the system contains a charge in a system containing a high-molecular substance regardless of the amount thereof, always or depending on conditions.

These polymer substances are subjected to a gelling agent, a cross-linking agent, or an appropriate insolubilization treatment, if necessary, as long as they have a shape retention ability.

Microcapsules can be produced by a conventionally known method such as an interfacial polymerization method, a phase separation method using coacervation, a dry coating method, a melt dispersion coating method, an air dispersion coating method, a spray method, and the like. Preferably, an interfacial polymerization method and a phase separation method are used. In the interfacial polymerization method, a polymer can be formed from a monomer or a prepolymer. In the phase separation method, a microcapsule is formed from a prepolymer or polymer solution. The crosslinking agent is added and crosslinked at the time of forming the microcapsules or after the formation of the microcapsules.

The size of the microcapsules and the thickness of the capsule wall used in the present invention are not particularly limited, but the size is usually 1 μm or more, preferably several μm to several hundred μm, but the size can be arbitrarily determined depending on the purpose. .

In order to generate electric charge, the microcapsules may be used in a state of being hydrated or swelled in a suitable solvent such as alcohol or acetone in some cases. Further, in order to control the charge state, salts such as sodium chloride, calcium chloride, and calcium sulfate, electrolytes such as sulfuric acid, acetic acid, sodium hydroxide, and aqueous ammonia, and various organic solvents can be mixed. Its hydrated state, solvated state,
The swelling state of the mechanochemical polymer is affected by the charge density and the like, and therefore the deformation response and the converted mechanical energy are affected. The degree of water swelling of microcapsules is
Usually 500 times, preferably 5 to 300 times, more preferably 10 to 100 times
It is twice. If the water swelling degree is more than 500 times, the mechanical strength and deformation force at the time of swelling are too weak, and if it is less than 5 times, the deformation speed and deformation amount are small.

The microcapsules of the present invention can be contracted by applying electrical stimulation to the microcapsules directly or indirectly through an electrolyte solution. As the electrical stimulation, any of AC / DC and Palace current can be applied, but DC is preferred. The electric potential may be applied to the gel through an appropriate electrode. Examples of the electrodes include a pair of platinum (plate or wire), carbon, and a transparent electrode (ITO, NESA). Of course, a suitable iron plate, an aluminum thin film, or a metal deposited film of gold or the like may be used.

The applied potential only needs to be equal to or higher than the electrolysis voltage of water,
Usually, it is 2.5 V or more, preferably 4 V or more. Current is usually 0.
It is at least 01 mA / cm ² , preferably 0.1 to 1 A / cm ² . The larger the current is, the higher the rate of volume change is, but it is not preferable because the electrolyte is electrolyzed.

Upon application of an electric potential, these materials generally shrink, in which case the mechanochemical material is hydrated (solvated).
In the state, the shrinkage phenomenon accompanied by dehydration (desolvation) accompanying the shrinkage becomes remarkable and quick in proportion to the applied potential and the magnitude of the current flowing through the substance. The shrinkage is generally as high as a fraction of a hundredth of the original volume. When the applied voltage is large, the deformation speed is large,
Electrolysis of the electrolyte occurs, which is not preferable. When the potential is removed, the contraction stops immediately, but when the potential is applied again, the deformation phenomenon resumes. After contracting by applying a potential for a certain period of time, if the microcapsules are brought into contact with the original solution, such as water, the contracted microcapsules absorb water and return to the original volume, so they repeatedly expand and contract as many times as possible. Can be repeated. Since the deformation rate and the deformation speed are proportional to the current value, the larger the amount of ions in the substance, the larger the size and the smaller the size in an organic solvent such as alcohol.

The temperature and pH at which the deformation behavior is performed are not particularly limited. The molecular weight of the polymer substance is also arbitrary. It is deformed only by the presence of water in addition to a charged polymer substance, and an organic solvent for causing a so-called phase transition phenomenon is not necessarily required in addition to water.

In order for the nuclear material in the microcapsule to enter and exit the capsule due to the volume change due to electrical stimulation, the size of the nuclear material must be smaller than the polymer network forming the shell of the capsule. The size of the polymer network can be controlled using a crosslinking agent or the like. Alternatively, the nuclear substance can be released by contraction and destruction of the microcapsules by electrical stimulation.

 Hereinafter, preferred embodiments of the present invention will be summarized.

B) The microcapsule according to claim 1, wherein the electric stimulus is a DC voltage.

(B) The microcapsule according to claim 1, wherein a DC current of at least 0.01 mA / cm ² flows when a voltage is applied.

(C) The microcapsule according to claim 1 or 2, wherein the volume change is proportional to the electric current.

D) The microcapsule according to claim 1, wherein the polymer electrolyte is a crosslinked polymer.

E) The microcapsule according to claim 1, wherein the polymer electrolyte is a cationic polymer or an anionic polymer.

(F) The microcapsule according to claim 1 or 8, wherein the polymer electrolyte is a salt of an anionic polymer.

G) The microcapsule according to claim 1, 8 or 9, wherein the polymer electrolyte is a salt of an anionic polymer and a strong base.

(H) The microcapsule according to claim 1, wherein the polymer electrolyte is an ampholyte polymer.

The microcapsules according to claim 1, wherein the water swelling degree of the polymer electrolyte is 10 to 1000 times.

(Effects of the Invention) According to the present invention, a microcapsule that shrinks at an arbitrary place or in a situation other than the function of a conventional microcapsule has been made possible. For example, a drug, a dye, etc. are added to the inside of a microcapsule, and the internal filler is simply applied with a voltage without depending on heat, pressure, mechanical friction, dissolution in water or a chemical solution like a conventional microcapsule, It is very useful, for example, it can be freely released from the microcapsule in any shape at any place.

(Example) Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 1.5 g of acrylamide (Amm), 2-acrylamide-2
1.5 g of methylpropanesulfonic acid and 0.3 g of NN'methylenebisacrylamide were dissolved in water to prepare a 30 g aqueous solution, which was mixed with 30 g of a 5% gelatin aqueous solution. Next, 0.2 g of isopropyl peroxide was dissolved in 140 ml of cyclohexane, and a monomer-containing aqueous solution was added dropwise with sufficient stirring to prepare a water-in-oil (W / O) emulsion. Stirring was continued for 5 hours to allow interfacial polymerization. After washing with cyclohexane, water-containing AMPS-Co-Amm wall microcapsules were obtained. The average diameter of the capsule was 1.9 mm, the average diameter of the nuclear material was 1.5 mm, and the water content of the shell component was about 20 times. A conductive film was stuck on a glass plate of 2.5 cm × 7.5 cm, and an adhesive tape having a thickness of 0.3 mm cut out to 1.5 × 1.5 cm was further formed to form an electrode. A microcapsule equilibrated and swollen in water was placed on the cut-out portion, and a change in capsule weight was measured while applying a DC voltage of 2.5 V or 4 V. The capsules lost weight over time, but at about a 45% reduction rate, the capsules broke and water flowed out. During this time, the capsule wall contracted. It is considered that shrinkage failure of the capsule occurs when the shrinkage rate of the shell component increases and the release rate of the nuclear material cannot keep up with it.

Claims (1)

(57) [Claims] 1. A microcapsule comprising a polymer electrolyte capable of contracting volume by application of a voltage.