Method for producing gel-metal composite

Abstract

This method for producing a gel-metal composite involves: a step for providing, on one surface of a solid substrate, a mask seal having an opening part; a step for forming a release layer on an exposed part exposed in the opening part on the one surface of the solid substrate; a step for forming a metal thin film on the exposed part via the release layer by coating the exposed part with a metal; a step for removing the mask seal from the one surface of the solid substrate; a step for activating a surface of the metal thin film on the side opposite to the release layer to perform a surface activation treatment, with the surface on the opposite side as a surface to be adhesion-activated; a step for providing a hydrogel so as to cover the one surface of the solid substrate and the adhesion-activated surface of the metal thin film; and a step for peeling the metal thin film and the hydrogel from the one surface of the solid substrate.

Description

Method for producing gel-metal composite

[0001] The present invention relates to a method for producing a gel-metal composite.

[0002] Hydrogels are polymeric materials that contain large amounts of liquid, and have characteristics similar to biological tissues, such as high water content and flexibility. Metals have characteristics such as high conductivity, high rigidity, and catalytic activity. Therefore, gel-metal composites, which are composite materials of hydrogels and metals, possess the characteristics of both hydrogels and metals. Gel-metal composites are expected to be applied to soft electronics and materials engineering, such as the creation of electronic devices by metal wiring on hydrogels and the creation of anisotropic soft materials by increasing the local elastic modulus of the metal attachment area.

[0003] As a method for producing a gel-metal composite, for example, a method of introducing an adhesive into the composite interface between a hydrogel and a metal is known (see, for example, Non-Patent Document 1).

[0004] In the field of soft electronics, a method is known in which a composite material of an elastomer material and a metal is produced by transferring a metal thin film formed on a solid substrate onto an elastomer material without using an adhesive (see, for example, Non-Patent Document 2).

[0005] Shiyuan Wei, Rongkang Yin, Tao Tang, Yingxiao Wu, Yang Liu, Puxin Wang, Kai Wang, Ming Mei, Ruqiang Zou, Xiaojie Duan, “Gas-Permeable, Irritation-Free, Transparent Hydrogel Contact Lens Devices with Metal-Coated Nanofiber Mesh for Eye Interfacing”, ACS Nano 2019,13,7920-7929.MATTHEW A.MEITL,ZHENG-TAO ZHU,VIPAN KUMAR,KEON JAE LEE,XUE FENG,YONGGANG Y.HUANG,ILESANMI ADESIDA,RALPH G.NUZZO,JOHN A.ROGERS,“Transfer printing by kinetic control of adhesion to an elastomeric stamp”,Nature Materials,5(1),33-38,(2006).

[0006] To simplify the manufacturing process of gel-metal composites, it is desirable to directly bond the composite interface between the hydrogel and metal, but because the hydrogel contains water, it is difficult to directly bond the hydrogel and metal.

[0007] In view of the above circumstances, an object of the present invention is to provide a technique that enables a metal thin film to be directly attached to any desired portion of the surface of a hydrogel, regardless of the type of material.

[0008] One aspect of the present invention is a method for producing a gel-metal composite, comprising the steps of: providing a mask seal having an opening on one surface of a solid substrate; forming a release layer on an exposed portion of the one surface of the solid substrate that is exposed in the opening; coating the exposed portion with a metal and forming a metal thin film on the exposed portion via the release layer; removing the mask seal from the one surface of the solid substrate; performing a surface activation treatment on the surface of the metal thin film opposite the release layer to make the opposite surface an adhesion-activated surface; providing a hydrogel so as to cover the one surface of the solid substrate and the adhesion-activated surface of the metal thin film; and peeling the metal thin film and the hydrogel from the one surface of the solid substrate.

[0009] According to the present invention, it is possible to directly attach a metal thin film to any desired portion of the surface of a hydrogel, regardless of the type of material.

[0010] 1 is a cross-sectional view schematically showing a gel-metal composite according to one embodiment of the present invention. 2 is a cross-sectional view schematically showing a method for producing a gel-metal composite according to one embodiment of the present invention. 3 is a cross-sectional view schematically showing a method for producing a gel-metal composite according to one embodiment of the present invention. 4 is a cross-sectional view schematically showing a method for producing a gel-metal composite according to one embodiment of the present invention. 5 is a cross-sectional view schematically showing a method for producing a gel-metal composite according to one embodiment of the present invention. 6 is a cross-sectional view schematically showing a method for producing a gel-metal composite according to one embodiment of the present invention. 7 is a cross-sectional view schematically showing a method for producing a gel-metal composite according to one embodiment of the present invention. 8 is a cross-sectional view schematically showing a method for producing a gel-metal composite according to one embodiment of the present invention. 9 is a photograph of an acrylamide gel-platinum composite obtained in an example. 10 is a photograph of an acrylamide gel-platinum composite obtained in a comparative example.

[0011] The present invention will be described below based on preferred embodiments with reference to the drawings, but the present invention is not limited to these embodiments. Note that the drawings used in the following description may show essential parts enlarged for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0012] [Gel-metal composite] Fig. 1 is a cross-sectional view schematically showing a gel-metal composite according to one embodiment of the present invention. As shown in Fig. 1, the gel-metal composite 1 of this embodiment has a hydrogel 2 and a metal thin film 3 formed on one surface 2a of the hydrogel 2.

[0013] The hydrogel 2 and the metal thin film 3 are directly bonded at their composite interface without the use of an adhesive. Specifically, the hydrogel 2 and the metal thin film 3 are bonded via an adhesion activation surface 3a formed on the surface of the metal thin film 3 that comes into contact with the hydrogel 2.

[0014] The hydrogel 2 is not particularly limited, but examples thereof include hydrogels composed of synthetic polymers such as polyacrylamide and polyvinyl alcohol, and biopolymers such as gelatin and alginic acid. Other examples of the hydrogel 2 include copolymer gels such as a combination of acrylamide and aminophenylboronic acid, and gels having an interpenetrating network structure such as a combination of polyvinyl alcohol and polyaniline. Other examples of the hydrogel 2 include functional gels in which gold nanoparticles or carbon nanotubes are supported on the aforementioned gels.

[0015] There are no particular limitations on the metal that constitutes the thin metal film 3, but metals with high chemical stability are preferred, such as gold and platinum.

[0016] The adhesion-activated surface 3a of the metal thin film 3 is a surface in which the adhesiveness of the metal thin film 3 has been activated by a surface activation treatment described below. Specifically, the adhesion-activated surface 3a is a surface that has been made hydrophilic by a plasma treatment.

[0017] The thin metal film 3 may be divided into small pieces on one surface 2a of the hydrogel 2. This increases the surface area of ​​the thin metal film 3.

[0018] According to the gel-metal composite 1 of this embodiment, by providing a metal thin film 3 on a portion of one surface 2a of the hydrogel 2, it becomes possible to apply electrical stimulation or receive electrical signals using the hydrogel 2, thereby enabling use as a soft electronics substrate. Furthermore, the gel-metal composite 1 of this embodiment can be used as an electrically operable cell culture substrate because it allows localized electrical stimulation or reception of electrical signals to the hydrogel 2.

[0019] The gel-metal composite 1 according to this embodiment is unlikely to experience peeling of the metal thin film 3 due to frictional forces on the surface or expansion and contraction of the hydrogel 2, and therefore can be treated as a highly reliable composite. Furthermore, because the thickness of the metal thin film 3 can be reduced to a few nanometers, the metal thin film 3 can be provided in a very small area on one surface 2a of the hydrogel 2. Furthermore, because the hydrogel 2 and the metal thin film 3 are directly bonded without the use of an adhesive, material design that takes advantage of the transparency of the hydrogel 2 and the metal thin film 3 becomes possible. The gel-metal composite 1 according to this embodiment has a metal thin film 3 with a high elastic modulus (on the order of GPa) provided on the surface of the hydrogel 2 with a low elastic modulus (on the order of kPa), and therefore can be used as a soft material that undergoes characteristic deformation due to the difference in the mechanical properties of the metal thin film 3 and the hydrogel 2.

[0020] [Method for manufacturing gel-metal composite] A method for manufacturing a gel-metal composite according to one embodiment of the present invention includes the steps of providing a mask seal having an opening on one surface of a solid substrate (hereinafter referred to as the "first step"), forming a release layer on an exposed portion of one surface of the solid substrate that is exposed in the opening (hereinafter referred to as the "second step"), applying a metal coating to the exposed portion and forming a metal thin film on the exposed portion via the release layer (hereinafter referred to as the "third step"), removing the mask seal from one surface of the solid substrate (hereinafter referred to as the "fourth step"), activating the surface of the metal thin film opposite the release layer to perform a surface activation treatment that makes the opposite surface an adhesion-activated surface (hereinafter referred to as the "fifth step"), providing a hydrogel so as to cover one surface of the solid substrate and the adhesion-activated surface of the metal thin film (hereinafter referred to as the "sixth step"), and peeling the metal thin film and the hydrogel from one surface of the solid substrate (hereinafter referred to as the "seventh step").

[0021] 2 to 7 are cross-sectional views that schematically show a method for producing a gel-metal composite according to one embodiment of the present invention.

[0022] 2, in the first step, a solid substrate 11 is prepared to determine the surface shape and metal portion of the gel-metal composite. The solid substrate 11 is not particularly limited, but may be, for example, glass or a polymer film.

[0023] Next, as shown in FIG. 2, a mask seal 12 having an opening 12a is attached to the portion of one surface 11a of the solid substrate 11 where no metal thin film is to be provided.

[0024] [Second Step] As shown in FIG. 2, in the second step, a release layer 13 is formed on an exposed portion 11b of one surface 11a of the solid substrate 11 that is exposed in the opening 12a of the mask seal 12.

[0025] The release layer 13 is not particularly limited, but is preferably composed of at least one selected from alginate gel, agarose, copper, silver, and polymethyl methacrylate. Alginate gel dissolves due to differences in binding constants, and therefore can be easily removed from the first surface 11a of the solid substrate 11. Agarose dissolves due to temperature, and therefore can be easily removed from the first surface 11a of the solid substrate 11. Copper dissolves electrochemically, and therefore can be easily removed from the first surface 11a of the solid substrate 11. Silver dissolves electrochemically, and therefore can be easily removed from the first surface 11a of the solid substrate 11. Polymethyl methacrylate dissolves in certain solvents, and therefore can be easily removed from the first surface 11a of the solid substrate 11.

[0026] The method for forming the release layer 13 is not particularly limited, but a method can be used in which a solution or dispersion containing the components that make up the release layer 13 is applied to the exposed portion 11b to form a coating film, and then the coating film is dried.

[0027] 3, in the third step, the exposed portion 11b is coated with a metal, and a thin metal film 14 is formed on the exposed portion 11b via a release layer 13. The method for forming the thin metal film 14 on the exposed portion 11b may be a sputtering method or a vapor deposition method.

[0028] [Fourth Step] As shown in FIG. 4, in the fourth step, the mask seal 12 is removed from the one surface 11 a of the solid substrate 11 .

[0029] [Fifth Step] As shown in FIG. 4, in the fifth step, a surface activation process is performed to activate the surface (one surface) 14a of the metal thin film 14 opposite the release layer 13, making the one surface 14a an adhesion-activated surface (see FIG. 5).

[0030] The surface activation treatment is not particularly limited, but for example, oxygen plasma treatment on the surface 14a of the thin metal film 14 can provide an activated surface for adhesion, enabling strong adhesion. Also, surface treatment on the surface 14a of the thin metal film 14 that exposes methacryl groups through thiol bonds with the noble metal can enable strong adhesion through gelation starting from the exposed methacryl groups.

[0031] [Sixth Step] As shown in FIG. 6, in the sixth step, a hydrogel 15 is provided so as to cover the one surface 11 a of the solid substrate 11 and the adhesion activation surface (one surface) 14 a of the metal thin film 14 .

[0032] The method for providing the hydrogel 15 is not particularly limited, and any of the following methods can be used: a method in which a gel precursor solution is dropped onto one surface 11 a of the solid substrate 11 and one surface 14 a of the thin metal film 14, and the gel precursor solution is gelled on the spot by light irradiation or the like; or a method in which a gel prepared elsewhere is swelled to a desired swelling ratio and then placed on one surface 11 a of the solid substrate 11 and one surface 14 a of the thin metal film 14.

[0033] 7 , in the sixth step, the metal thin film 14 and the hydrogel 15 are peeled off from the one surface 11a of the solid substrate 11. Because the metal thin film 14 is formed on the one surface 11a of the solid substrate 11 via the release layer 13, the metal thin film 14 and the hydrogel 15 can be easily peeled off from the one surface 11a of the solid substrate 11. To peel off the metal thin film 14 and the hydrogel 15 from the one surface 11a of the solid substrate 11, for example, a laminate consisting of the solid substrate 11 / release layer 13 / metal thin film 14 / hydrogel 15 is immersed in a solution to dissolve the release layer 13. The solution is not particularly limited, but for example, an ethylenediaminetetraacetic acid solution or the like can be used.

[0034] "Eighth Step" The method for producing a gel-metal composite of this embodiment may include a step (eighth step) of peeling the release layer 13 from the metal thin film 14.

[0035] Through the above steps, the gel-metal composite 1 of the above embodiment is obtained.

[0036] The surface of the thin metal film 3 of the gel-metal composite 1 obtained by the method for producing a gel-metal composite of this embodiment is connected to an electrode and electrolytic plating is performed, thereby making it possible to increase the thickness of the thin metal film 3. Furthermore, the thickness of the thin metal film 3 can be increased by performing electroless plating on the surface of the thin metal film 3 of the gel-metal composite 1 obtained by the method for producing a gel-metal composite of this embodiment.

[0037] Furthermore, by arranging two gel-metal composites 1 so that their respective hydrogels 2 are in contact with each other, and sandwiching these gel-metal composites 1 in the thickness direction and performing dry adhesion, a film-like hydrogel having metal thin films 3 on both sides can be obtained.

[0038] Furthermore, by forming a hydrogel on the metal thin film 3 of the gel-metal composite 1, a hydrogel with the metal thin film 3 embedded therein can be obtained.

[0039] By selecting the material of the solid substrate 11 or by performing a surface treatment, the interaction between the solid substrate 11 and the hydrogel 15 can be reduced, thereby facilitating the peeling of the metal thin film 14 from the solid substrate 11 .

[0040] According to the method for producing a gel-metal composite of this embodiment, the metal thin film 14 and the hydrogel 15 are directly bonded to each other, which makes production easy, and the strong adhesion makes it possible to obtain a gel-metal composite 1 that is highly stable against external invasion.

[0041] According to the method for producing a gel-metal composite of this embodiment, by providing a thin metal film 14 on one surface of a swellable hydrogel 15 before it swells, the swelling of the hydrogel 15 causes the thin metal film 14 to be divided into small pieces, increasing the surface area of ​​the thin metal film 14. This improves the metal catalytic activity of the thin metal film 14 and maintains the permeability of the hydrogel 15, resulting in a gel-metal composite 1 that functions as a substrate surface having both the material properties of the thin metal film 14 and the hydrogel 15. On the other hand, if a metal is attached to the surface of the swollen hydrogel 15, electricity can be passed through the gel-metal composite 1 in liquid via the metal.

[0042] According to the method for producing a gel-metal composite of this embodiment, a thin metal film 14 with a high elastic modulus (on the order of GPa) is provided only at an arbitrary location on the surface of a hydrogel 15 with a low elastic modulus (on the order of kPa), thereby obtaining a gel-metal composite 1 that can be used as a soft material that undergoes characteristic deformation due to the difference in mechanical properties between the thin metal film 14 and the hydrogel 15.

[0043] According to the method for producing a gel-metal composite of this embodiment, since it is composed of only steps that allow multiple processes to be performed simultaneously, such as forming the metal thin film 14, it is easy to scale up the production of the gel-metal composite 1.

[0044] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0045] [Example] As an example of a gel-metal composite, an acrylamide gel-platinum composite having an acrylamide gel as the hydrogel and a platinum thin film as the metal thin film will be described.

[0046] "Preparation of Acrylamide Gel-Platinum Composite" A mask seal was attached to one side of a solid glass substrate, exposing the metal-attached area (exposed glass area). Next, sodium alginate was applied to the exposed glass area by spin coating. The sodium alginate-coated glass substrate was then immersed in a calcium ion solution to form an alginate gel on the exposed glass area. Platinum was then sputtered through the alginate gel onto the exposed glass area, forming a platinum thin film on the entire surface of the glass substrate. The mask seal was then removed to obtain a laminate consisting of a platinum thin film / alginate gel / glass substrate. Next, one side of the glass substrate and one side of the platinum thin film were treated with oxygen plasma to activate one side of the platinum thin film, making it an adhesively activated surface. Next, a gel precursor solution containing acrylamide as a monomer, bisacrylamide as a crosslinker, and lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate as a polymerization initiator was prepared, and the gel precursor solution was dripped onto the platinum thin film and glass substrate in the laminate. Next, the gel precursor solution was polymerized by ultraviolet irradiation with diffusion restricted by the spacers on both ends of the glass substrate and the cover glass on top, resulting in a laminate consisting of acrylamide gel / platinum thin film / alginate gel / glass substrate. Next, the laminate consisting of acrylamide gel / platinum thin film / alginate gel / glass substrate was immersed in an ethylenediaminetetraacetic acid solution to dissolve the alginate gel and obtain a gel-platinum composite separated from the glass substrate. A photograph of the resulting acrylamide gel-platinum composite is shown in Figure 8. As shown in Figure 8, the platinum thin film formed on the exposed glass surface was transferred to the acrylamide gel.

[0047] Comparative Example: "Preparation of an Acrylamide Gel-Platinum Composite" Platinum was sputtered without using a mask seal to form a platinum thin film over the entire surface of a glass substrate, yielding a laminate consisting of a platinum thin film, alginate gel, and glass substrate. Next, the same gel precursor solution as in the Example was dripped onto the laminate, covering the platinum thin film and glass substrate. The gel precursor solution was then polymerized by ultraviolet irradiation, with diffusion restricted by spacers on both ends of the glass substrate and a cover glass on the top surface, yielding a laminate consisting of an acrylamide gel, platinum thin film, alginate gel, and glass substrate. The acrylamide gel, platinum thin film, alginate gel, and glass substrate laminate was then immersed in an ethylenediaminetetraacetic acid solution to dissolve the alginate gel and separate it from the glass substrate, yielding a gel-platinum composite. A photograph of the resulting acrylamide gel-platinum composite is shown in Figure 9. As shown in Figure 9, a platinum thin film was transferred to the entire surface of the acrylamide gel.

[0048] The gel-metal composite according to the present invention is useful as a soft material that takes advantage of the high electrical conductivity, catalytic properties, and high rigidity of metals, and is widely applicable to fields such as soft electronics and materials engineering.

[0049] REFERENCE SIGNS LIST 1 Gel-metal composite 2 Hydrogel 3 Metal thin film 11 Solid substrate 12 Mask seal 13 Release layer 14 Metal thin film 15 Hydrogel

Claims

1. A method for producing a gel-metal composite, comprising the steps of: providing a mask seal having an opening on one surface of a solid substrate; forming a release layer on an exposed portion of the one surface of the solid substrate that is exposed in the opening; coating the exposed portion with a metal and forming a metal thin film on the exposed portion with the release layer interposed therebetween; removing the mask seal from the one surface of the solid substrate; performing a surface activation process of activating a surface of the metal thin film opposite the release layer to make the opposite surface an adhesion-activated surface; providing a hydrogel so as to cover the one surface of the solid substrate and the adhesion-activated surface of the metal thin film; and peeling off the metal thin film and the hydrogel from the one surface of the solid substrate.

2. The method for producing a gel-metal composite according to claim 1, further comprising the step of peeling the release layer from the thin metal film.

3. The method for producing a gel-metal composite according to claim 1, wherein the release layer is composed of at least one material selected from the group consisting of alginate gel, agarose, copper, silver, and polymethyl methacrylate.

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