JP4682712B2 - Polymer actuator - Google Patents

Description

  The present invention relates to a polymer actuator using a stimulus-responsive high-strength hydrogel.

  Conventionally, practical application of robots has attracted attention in various fields such as care support, dangerous work, and entertainment. A robot applied to these uses is required to have a large number of joints (movable parts) like an animal and to enable complicated movement.

Conventionally, a magnetic rotary motor has been used as an actuator for driving the movable part, but it has a disadvantage that the weight of the constituent material increases because of the metal. Since the actuator weight becomes a load when the movable part is operated, if a heavy actuator is used, a large output is required. On the other hand, a large output actuator is large and heavy.
In addition, when using a magnetic rotary motor, a speed reducer for adjusting to the required rotational speed and torque is required, and the performance of the gear used for this speed reducer is gradually deteriorated due to wear. Therefore, there is a problem that it is difficult to ensure reliability.
An ultrasonic motor capable of obtaining high torque at low speed does not require a speed reducer, but it is also made of a metal material, so that its weight increases and the same problem as described above occurs.

In view of the problems as described above, in recent years, a polymer actuator made of a polymer material that is light and flexible is beginning to attract attention.
Known polymer actuators include, for example, polymer piezoelectric elements using polyvinylidene fluoride, conductive polymer actuators using electronically conductive polymers, gel actuators using polymer gels, and the like. .

  Among the above gel actuators, polymer hydrogel actuators using water-swelling polymer gels in particular are based on the fact that the polymer hydrogel changes its volume in response to the surrounding temperature, ionic strength, pH and other environments. is there. The displacement amount is as large as 30 to 50%, and exhibits performance comparable to that of living skeletal muscle.

However, when the volume change depends on the temperature, high-speed control is difficult for both heating and cooling.
In addition, when depending on the ion concentration, it is necessary to dispose an electric field solution around the polymer hydrogel, and for the control to forcibly replace it with a pump or the like. Is also not suitable for a small and lightweight system.

On the other hand, when a pH-responsive polymer hydrogel is applied, the pH can be controlled by exchanging the surrounding solution, and can also be changed using an electrochemical reaction.
In other words, when a voltage is applied between electrodes disposed in the aqueous solution around the electrolyte solution, hydrogen ions and hydroxide ions are consumed due to electrode reaction, or the concentration associated with the formation of an electric double layer on the electrode surface. A gradient can be generated, and the pH in the vicinity of the electrode can be changed. By utilizing this phenomenon, the pH-responsive hydrogel can be controlled and driven by electricity.
In particular, the electrode is embedded in the hydrogel, and the hydrogel used is paired with an acidic polymer gel on the anode and a basic polymer gel on the cathode, so that the same expansion and contraction as in living skeletal muscles can be achieved by electrical control and electrical drive. It is known that operation can be obtained (for example, refer to Patent Document 1 below).

JP 2004-188523 A

  By the way, when constructing an actuator using the expansion and contraction of the stimulus-responsive hydrogel, it is important to efficiently transfer the mechanical energy resulting from the expansion and contraction of the stimulus-responsive hydrogel to the power point of the operating machine. It becomes.

  However, when the stimulus-responsive hydrogel is directly joined to the operating machine's power point using a hard adhesive such as general-purpose epoxy resin, the stimulus-responsive hydrogel near the joint location expands due to the drag received from the joint location. In addition, the stress cannot be shrunk, and internal stress and strain are accumulated between the parts that can expand and contract, and in the worst case, the stimulus-responsive hydrogel is broken.

  In view of the above-described problems, when a material having elasticity is applied as an adhesive and bonded, the accumulation of internal stress and internal strain can be reduced. In addition to causing loss and delay when transferring the mechanical energy generated by the gel to the power point of the operating machine, the adhesive side may be broken.

  Therefore, in the present invention, in view of the problems of the prior art as described above, there is provided a polymer actuator capable of efficiently taking out mechanical energy without causing breakage of a stimulus-responsive hydrogel or a force point joint. It was.

  In the present invention, in the polymer actuator including the stimulus-responsive hydrogel that swells and gels by absorbing moisture and changes the degree of swelling and volume by the stimulus, a part of the stimulus-responsive hydrogel is at least It is embedded and bonded to the outer shell having a structure in which two or more layers are laminated, and among the layers constituting the outer shell, the Young's modulus of the material constituting the inner layer bonded to the stimulus-responsive hydrogel is other than The Young's modulus of the material constituting the layer is lower than the Young's modulus of the stimulus-responsive hydrogel.

  According to the present invention, a part of the stimulus-responsive hydrogel is embedded and bonded to the outer shell having a multilayer structure, and the Young's modulus of the inner layer of the outer shell bonded to the hydrogel is determined from the Young's modulus of the other layers. And lower than the Young's modulus of the stimulus-responsive hydrogel, the material of the inner layer joined to the hydrogel allows expansion / contraction of the stimulus-responsive hydrogel at the joint due to elastic deformation. Because the other layers of the outer shell material function to suppress the breakage of the inner layer material joined to the stimulus responsive hydrogel, the stimulus responsive hydrogel and the force point joint break. Can be avoided, and mechanical energy can be extracted efficiently.

  Hereinafter, specific embodiments of the polymer actuator of the present invention will be described with reference to the drawings, but the present invention is not limited to the examples shown below.

  The polymer actuator of the present invention is provided with a stimulus-responsive hydrogel whose degree of swelling and volume changes by stimulation, and a part of the stimulus-responsive hydrogel is laminated at least in two or more layers. The material that constitutes the other layer is the Young's modulus of the material that constitutes the inner layer that is joined to the stimuli-responsive hydrogel among the layers that constitute the outer shell and is embedded and joined to the outer shell having the above structure. The Young's modulus is lower than the Young's modulus of the stimulus-responsive hydrogel.

In the following, preferred examples of the polymer actuator of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.
In FIG. 1, the schematic block diagram of the polymer actuator 1 of this invention is shown.

In the polymer actuator 10 of FIG. 1, both end portions of a stimulus-responsive hydrogel 1 having a so-called long shape are embedded and joined to the outer shell 2.
The shape of the polymer actuator 10 may be any of a rod shape, a column shape, a strip shape, and the like.
The outer shell 2 existing in the buried joint 11 of the polymer actuator 10 has a two-layered structure composed of the buried joint inner layer 3 and the buried joint outer layer 4. However, the present invention is not limited to this, and a multilayer structure of three or more layers may be used.
Hereinafter, each part which comprises the polymer actuator 10 is demonstrated.

The stimulus-responsive hydrogel 1 is a so-called stimulus-responsive hydrogel material whose swelling degree changes in response to the surrounding environment such as temperature and ion concentration.
In particular, the ion concentration can be easily controlled by placing a predetermined solution around it and changing it or changing it using an electrochemical reaction. Specifically, it uses a power supply and a control circuit. This is preferable because high-speed control is possible.

Examples of stimuli-responsive hydrogel materials whose swelling degree changes in response to ion concentration include carboxylic acid, phosphoric acid, sulfonic acid, primary amine, secondary amine, tertiary amine, and quaternary ammonium in the molecule. And polymers having an ionic functional group such as
Specifically, acrylic acid, methacrylic acid, vinyl acetic acid, maleic acid, methacryloyloxyethyl phosphoric acid, vinyl sulfonic acid, styrene sulfonic acid, vinyl pyridine, vinyl aniline, vinyl imidazole, aminoethyl acrylate, methylaminoethyl acrylate, Dimethylaminoethyl acrylate, ethylaminoethyl acrylate, ethylmethylaminoethyl acrylate, diethylaminoethyl acrylate, aminoethyl methacrylate, methylaminoethyl methacrylate, dimethylaminoethyl methacrylate, ethylaminoethyl methacrylate, ethylmethylaminoethyl methacrylate, diethylaminoethyl methacrylate, amino Propyl acrylate, methylaminopropyl acrylate, dimethylaminopropyl Pyracrylate, ethylaminopropyl acrylate, ethylmethylaminopropyl acrylate, diethylaminopropyl acrylate, aminopropyl methacrylate, methylaminopropyl methacrylate, dimethylaminopropyl methacrylate, ethylaminopropyl methacrylate, ethylmethylaminopropyl methacrylate, diethylaminopropyl methacrylate, dimethylaminoethyl Polymers such as acrylamide, dimethylaminopropylacrylamide, acryloyloxyethyltrimethylammonium salt and the like can be mentioned.
In the molecule or between the molecules, a cross-link may be formed as needed, the various materials may be used alone, or a plurality of types of copolymers or a mixture may be used.
Further, a water-insoluble polymer may be added as a reinforcing agent.

Next, the outer shell 2 in which the stimulus-responsive hydrogel is embedded and bonded will be described.
The outer shell 2 can be formed of a conventionally known structural material such as a predetermined polymer, ceramic, or metal.
The outer shell 2 is assumed to have a multilayer structure of two or more layers, and among the multiple layers constituting the outer shell 2, the Young's modulus of the inner layer side material is lower than the Young's modulus of the material of the other layers, and It is assumed that the Young's modulus of the stimulus-responsive hydrogel 1 is equal to or lower than that.
For example, as shown in FIG. 1, when the outer shell 2 has a two-layer structure, the Young's modulus E ₁ of the buried joint inner layer 3 joined to the stimuli-responsive hydrogel 1 and the Young's modulus E ₂ of the buried joint outer layer 4. And the Young's modulus E ₃ of the stimulus-responsive hydrogel, a relationship of E ₂ > E ₁ ≦ E ₃ is established.

  The outer shell 2 may have a multilayer structure of three or more layers. In such a case, the inner layer 3 of the innermost buried joint to be bonded to the stimulus-responsive hydrogel 1 has a lower Young's modulus than the stimulus-responsive hydrogel. The materials are selected so that the other layers have higher Young's modulus toward the outside.

Since the stimulus-responsive hydrogel 1 performs expansion / contraction operations in water or an aqueous solution in which a predetermined solute is dissolved, the material of the stimulus-responsive hydrogel is stable in mechanical properties against water. A material having a high water solubility, water absorption, and low water swellability is preferable.
In addition, when a slip occurs at the joint between the stimulus-responsive hydrogel 1 and the innermost buried joint inner layer 3 constituting the outer shell 2, sufficient force and displacement can be taken out as the polymer actuator 10. For this reason, at least the innermost layer is preferably made of a material having high adhesiveness and tackiness.

However, if the Young's modulus E ₁ of the buried joint inner layer 3 is too low, the buried joint inner layer 3 is elastically deformed to absorb the force and displacement when the stimulus-responsive hydrogel 1 is expanded. Therefore, the Young's modulus E ₁ of the buried joint inner layer 3 is preferably in the range of 10 to 100% with respect to the Young's modulus of the stimulus-responsive hydrogel 1.

The case where the long stimulus-responsive hydrogel 1 as shown in FIG. 1 is applied and the dimensional change in the longitudinal direction is used as the expansion / contraction displacement will be described.
For example, a predetermined electrode is provided in the stimulus-responsive hydrogel 1.
The electrodes are connected to a predetermined power source, but the conductive portion that electrically connects them may be embedded in the outer shell 2. In addition, when a metal wire is used for such a conductive portion, current and voltage to be transmitted to the electrode may be lost unless the metal wire is insulated, but the metal wire is embedded in the outer shell 2. This eliminates the need for separate insulation coating.
Furthermore, by embedding a metal wire in the outer shell 2, when the stimulus-responsive hydrogel 1 expands or contracts, the metal wire contacts or clings to the stimulus-responsive hydrogel 1. Can be avoided, and mutual damage can be effectively prevented.

As described above, by installing the outer shell 2 having two or more layers that specify the Young's modulus at the end of the long stimulus-responsive hydrogel 1, the length of the stimulus-responsive hydrogel 1 is increased. The expansion / contraction force in the vertical direction and the vertical direction is absorbed by the material of the innermost layer of the outer shell 2, and the buried joint outer layer 4 made of a material having a high Young's modulus becomes the material of the buried joint inner layer 3. Since the deformation is suppressed, the breakage of the power point joint can be effectively suppressed, and the expansion / contraction displacement can be taken out efficiently.
Further, since the volume of the outer shell 2 does not change when the actuator expands and contracts, it can be directly joined to the power point of the operating machine like a tendon in a living skeletal muscle.

  An example in which a specific sample of the polymer actuator according to the present invention was prepared and operated will be described below.

〔Example〕
In this example, a polymer actuator 20 having a configuration as shown in FIG. 2 was produced.
First, DMF (dimethylformamide) is used as a non-aqueous solvent, 5 ml of DMF, 1 ml of acrylic acid (AA) as a monomer of stimuli-responsive polymer, N, N′-methylenebisacrylamide (BIS) 0 as a crosslinking agent .1 g, 0.01 g of 2,2′-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 0.712 g of polyvinylidene fluoride (PVdF) having a molecular weight of 270,000 as a water-insoluble polymer are dissolved to prepare an organogel precursor A body solution was obtained.
Next, the organogel precursor solution obtained as described above is poured into a glass tube having an inner diameter of 1.5 mm, both ends of the glass tube are sealed with rubber stoppers, and heated to 60 ° C. Gelation was performed.
After gelation, the rubber stopper was removed from the glass tube, and the organogel together with the glass tube was dried by heating at 60 ° C. under reduced pressure to remove DMF to obtain a rod-shaped dry gel.
Next, a low density polyethylene (LDPE) tube having an inner diameter of 1.5 mm filled with a flexible epoxy resin before curing and sealed at one end by heat fusion is prepared.
Next, both ends of the rod-shaped dry gel obtained as described above were inserted into the tube to cure the flexible epoxy resin.
By the above operation, a rod-shaped dry gel having LDPE tubes bonded to both ends is obtained. This is immersed in ion-exchanged water to swell, and further washed repeatedly using ion-exchanged water. A rod-like pH-responsive hydrogel 21 having a two-layer outer shell 22 of both ends at a flexible epoxy resin layer 23 as a joint inner layer and an LDPE layer 24 as an embedded joint outer layer was obtained.
When the Young's modulus of the applied material was measured, it was pH-responsive hydrogel (E ₃ ): 20 MPa, flexible epoxy resin (E ₁ ): 15 MPa, and LDPE (E ₂ ): 1 GPa.
That is, the relationship E ₂ > E ₁ ≦ E ₃ is established.

  A polymer actuator 20 having a double-layered outer shell 22 of a flexible epoxy resin layer 23 and an LDPE layer 24 at both ends of a rod-like pH-responsive hydrogel produced as described above is prepared by using a 50 mN-NaOH aqueous solution. After repeating the operation of immersing and expanding in 50 mN-HCl and then shrinking, the pH-responsive hydrogel, flexible epoxy resin, and LDPE were not broken, and the two-layer outer shell It was confirmed that the pH-responsive hydrogel was kept stretched and stretched in a good state.

[Comparative Example 1]
In this example, a polymer actuator 30 configured as shown in FIG. 3 was produced.
A rod-like pH-responsive hydrogel 21 was obtained by the same process as in the above example.
Next, a low density polyethylene (LDPE) tube having an inner diameter of 1.5 mm filled with a flexible epoxy resin before curing and sealed at one end by heat fusion was prepared.
Next, both ends of the rod-shaped dry gel obtained as described above were inserted into the tube to cure the flexible epoxy resin.
After the flexible epoxy resin was cured, only the LDPE tube was excised to obtain a rod-shaped dry gel in which the flexible epoxy resin was bonded to both ends.
This is immersed in ion-exchanged water to swell, and further washed repeatedly with ion-exchanged water, whereby a rod-like pH-responsive hydrogel 21 having outer shells 22 of a single layer structure of a flexible epoxy resin layer 23 at both ends. was gotten.
When the Young's modulus of the applied material was measured, the pH-responsive hydrogel was 20 MPa, and the flexible epoxy resin layer was 15 MPa.

  A rod-like pH-responsive hydrogel having a single-layered outer shell 22 of the flexible epoxy resin layer 23 at both ends is immersed in a 50 mN-NaOH aqueous solution to expand, and then immersed in 50 mN-HCl to shrink. When the operation was repeated, the flexible epoxy resin layer 23 was cracked and fractured during the pH-responsive hydrogel expansion, and was separated from the pH-responsive hydrogel.

[Comparative Example 2]
In this example, a polymer actuator 40 configured as shown in FIG. 4 was produced.
A rod-like pH-responsive hydrogel 21 was obtained by the same process as in the above example.
Next, a low density polyethylene (LDPE) tube having an inner diameter of 1.5 mm filled with an epoxy resin before curing and sealed at one end by heat fusion was prepared.
Next, both ends of the rod-shaped dry gel obtained as described above were inserted into the tube to cure the epoxy resin.
After curing the epoxy resin, only the LDPE tube was excised to obtain a rod-shaped dry gel having an epoxy resin bonded to both ends.
This is immersed in ion-exchanged water to swell, and further washed repeatedly with ion-exchanged water, whereby a rod-like pH-responsive hydrogel 21 having an outer shell 22 of a single layer structure of the epoxy resin layer 25 at both ends is obtained. It was.
When the Young's modulus of the applied material was measured, it was pH-responsive hydrogel: 20 MPa and epoxy resin layer: 2 GPa.

  The rod-like pH-responsive hydrogel having the single-layered outer shell 22 of the epoxy resin layer 25 at both ends is immersed in a 50 mN-NaOH aqueous solution to be expanded, and then immersed in 50 mN-HCl to be contracted. When repeated, the pH responsive hydrogel 21 near the embedded boundary with the epoxy resin was cracked and fractured during expansion of the pH responsive hydrogel.

As apparent from the results of Examples, the Young's modulus E ₁ of the embedded joint portion inside layer 23 of the outer shell 22 bonded to the stimuli-responsive hydrogels, and the Young's modulus E ₂ of the buried junction portion outside layer 24, stimulus response When the relationship of E ₂ > E ₁ ≦ E ₃ is established between the Young's modulus E ₃ of the heat-sensitive hydrogel, the material of the inner layer 23 joined to the stimulus-responsive hydrogel 21 is elastically deformed. Thus, the stimulation-responsive hydrogel 21 at the joint is allowed to expand / contract, and the outer layer 24 suppresses the breakage of the material of the inner layer 23 joined to the stimulus-responsive hydrogel 21. Breakage did not occur in the gel 21 or the power point joint, and the mechanical energy could be taken out efficiently.
On the other hand, in Comparative Example 1, the elastic deformation of the flexible epoxy resin layer 23 bonded to the stimulus responsive hydrogel 21 allows expansion / contraction of the stimulus responsive hydrogel 21 in the bonded portion. Since there is no outer layer that suppresses deformation of the flexible epoxy resin 23, the flexible epoxy resin layer 23 has been cracked and broken.
In Comparative Example 2, since the Young's modulus of the epoxy resin layer 25 bonded to the stimulus-responsive hydrogel 21 is high, the expansion / contraction of the stimulus-responsive hydrogel 21 at the bonded portion is not allowed, and the pH response When the functional hydrogel 21 expands, it cracks and breaks.

The schematic block diagram of the polymer actuator of this invention is shown. The schematic block diagram of the polymer actuator of an Example is shown. The schematic block diagram of the polymer actuator of the comparative example 1 is shown. The schematic block diagram of the polymer actuator of the comparative example 2 is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stimulus responsive hydrogel, 2, 22 ... Outer shell, 3 ... Embedded joint inner layer, 4 ... Embedded joint outer layer, 10 ... Polymer actuator, 11 ... Embedded joint, 20, 30 , 40 …… Polymer actuator, 21 …… pH responsive hydrogel, 23 …… Flexible epoxy resin layer, 24 …… Low density polyethylene (LDPE) layer, 25 …… Epoxy resin layer

Claims (3)

A polymer actuator comprising a stimulus-responsive hydrogel that swells and gels by absorbing moisture, and that changes in swelling and volume upon stimulation,
A part of the stimuli-responsive hydrogel is embedded and bonded to an outer shell having a structure in which at least two layers are laminated,
Of the layers constituting the outer shell, the Young's modulus of the material constituting the inner layer bonded to the stimulus-responsive hydrogel is lower than the Young's modulus of the material constituting the other layer, and the stimulus A polymer actuator having a Young's modulus lower than that of a responsive hydrogel. The stimulus-responsive hydrogel is assumed to have a long shape,
2. The polymer actuator according to claim 1, wherein both ends of the stimulus-responsive hydrogel in the longitudinal direction are embedded and joined to the outer shell. In the stimulus-responsive hydrogel, an electrode for generating stimulus for the stimulus-responsive hydrogel is provided,
3. The polymer actuator according to claim 1, wherein a conductive portion that electrically connects the electrode and a power source that sends an electric machine to the electrode is embedded in the outer shell.

Images