Laser-formed conductive hydrogel with enhanced adhesion to substrate

Abstract

The present invention relates to a method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion. Particularly, the method may comprise the steps of: preparing a transparent polymer substrate; forming a conductive polymer layer including a first polymer and a second polymer on one surface of the substrate; forming a conductive hydrogel pattern on the substrate by irradiating a laser from the rear surface of the substrate toward the conductive polymer layer; and washing and removing the conductive polymer layer.

Description

Laser-formed conductive hydrogels with enhanced bonding to substrates

[0001] The present invention relates to a conductive hydrogel.

[0002]

[0003] Conductive hydrogels possess soft mechanical properties and can retain large amounts of water, making them ideal for a variety of electrolyte-driven electronic devices. They are particularly promising as electrode materials for electrophysiological signal measurement devices capable of transmitting and receiving signals via body electrolytes. However, their use in humid environments can weaken their bonding to the substrate, leading to cracking or delamination, a critical issue hindering their commercialization.

[0004] Applying special surface treatment techniques to the substrate is commonly used to improve the bonding strength of conductive hydrogels to the substrate. Previously, a technique was reported to roughen the substrate surface to increase the contact area between the conductive hydrogel and the substrate. However, this technique is limited to certain substrates and requires significant processing costs and time.

[0005] Furthermore, the development of soft bio-implantable devices requires the use of polymer-based substrates. However, previously reported techniques have limitations in their application to soft substrates. Furthermore, the development of microdevices using conductive hydrogels requires selective surface treatment, necessitating the production of expensive micromolds or masks.

[0006] Therefore, there is an urgent need to develop a technology that can pattern high-resolution patterns on soft substrates while improving the substrate adhesion of conductive hydrogels so that they can be used for long periods in wet environments.

[0007]

[0008] The present invention is intended to solve the above-described conventional problems and to provide a patterning method capable of improving the bonding strength of a conductive hydrogel to a substrate.

[0009] In addition, the present invention aims to provide a method capable of patterning on a soft conductive hydrogel at high resolution.

[0010]

[0011] A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion according to one embodiment of the present invention may include the steps of: preparing a transparent polymer substrate; forming a conductive polymer layer including a first polymer and a second polymer on one surface of the substrate; irradiating a laser toward the conductive polymer layer from a back surface of the substrate to form a conductive hydrogel pattern on the substrate; and washing and removing the conductive polymer layer.

[0012] According to one embodiment, in the step of forming a conductive hydrogel pattern on the substrate by irradiating a laser toward the conductive polymer layer from the back surface of the substrate, welding may be performed at the bonding surface of the substrate and the conductive hydrogel pattern.

[0013] In one embodiment, the first polymer may be more hydrophobic than the second polymer.

[0014] In one embodiment, the substrate may include at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), thermo-plastic polyurethane (TPU), styrene-butadiene-styrene (SBS) and styrene-ethylene-butylene-styrene (SEBS), Polyacrylamide, Poly(acrylic acid), polyethylene glycol dimethacrylate, polyvinyl alcohol, Gelatin, Silk, Chitosan, Alginate, Collagen, and Cellulose.

[0015] According to one embodiment, the conductive polymer layer may include at least one selected from the group consisting of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), PEDOT:ToS, PEDOT, Polyaniline (PANI), PANI:PSS, Sulfonated polyaniline, and Polypyrrole (PPY).

[0016] In one embodiment, the conductive polymer layer may include particles having a region divided into a central first polymer-rich domain and an outer second polymer-rich domain.

[0017] According to one embodiment, the step of forming a conductive hydrogel on the substrate by irradiating a laser toward the conductive polymer layer from the back surface of the substrate may cause phase separation on a molecular scale in the conductive polymer layer and strengthen the bonding force between the first polymer-rich domain and the substrate.

[0018] According to one embodiment, the conductive polymer layer has a better visible light absorption capacity than the substrate, and in the step of irradiating a laser from the back surface of the substrate toward the conductive polymer layer to form a conductive hydrogel on the substrate, the intensity of the irradiated laser may be 150 mW to 300 mW.

[0019] According to one embodiment, the step of washing and removing the conductive polymer layer may be to wash the conductive polymer layer with a hydrophilic solvent to remove the conductive polymer layer in an area that has not been patterned by a laser.

[0020] According to one embodiment, the method further comprises a step of post-treating to increase the electrical conductivity of the conductive hydrogel; wherein the step of post-treating may be treating the conductive hydrogel with one or more selected from the group consisting of ethylene glycol (EG), polyethylene glycol, ethanol, methanol, sulfuric acid, hydrochloric acid, hydrofluoric acid, and DMSO.

[0021] In another embodiment, a conductive hydrogel having excellent substrate adhesion comprises: a transparent polymer substrate; a patterned hydrogel layer formed on one surface of the transparent polymer substrate; wherein the hydrogel layer comprises first and second polymers, and may be a first polymer-rich domain.

[0022] According to one embodiment, the cross-section of the interface where the substrate and the hydrogel layer come into contact may have a wavy shape.

[0023] In one embodiment, the conductive hydrogel layer may have a hydrophobic water barrier formed on its surface.

[0024] In one embodiment, the conductive hydrogel layer may include a pattern having a width of 1 μm to 20 μm.

[0025] In one embodiment, the conductive hydrogel layer may have a higher aspect ratio in terms of thickness to width.

[0026] In one embodiment, the interior of the conductive hydrogel layer may include a first polymer-rich domain, and the first polymer-rich domain located closer to the substrate may form a stronger bond with each other than the first polymer-rich domain located farther from the substrate.

[0027] In one embodiment, the conductive hydrogel layer may block moisture permeation and may include crystals of irregular size.

[0028] According to one embodiment, the conductive hydrogel may be manufactured by a manufacturing method according to one embodiment of the present invention.

[0029] A bio-implantable device comprising a conductive hydrogel according to another embodiment may comprise a conductive hydrogel according to one embodiment of the present invention.

[0030] A wearable sensor comprising a conductive hydrogel according to another embodiment may comprise a conductive hydrogel according to one embodiment of the present invention.

[0031]

[0032] The present invention has the effect of significantly improving bonding strength by inducing direct bonding of a conductive polymer to a substrate by irradiating a laser.

[0033] In addition, the present invention has the effect of performing high-resolution patterning in micro units using a laser on a flexible conductive hydrogel.

[0034] However, the effects of the present invention are not limited to the effects described above, and include all effects naturally implemented due to the various configurations proposed in the present invention.

[0035]

[0036] FIG. 1 is a schematic diagram (a) and a cross-sectional view (b) of each step showing a method for manufacturing a conductive hydrogel pattern according to one embodiment of the present invention.

[0037] Figure 2a is a graph showing the temperature and concentrated location of the photothermal energy of the laser according to the irradiation direction of the laser.

[0038] Figure 2b is a photograph showing the process of testing the bonding strength of the pattern after patterning in each investigation direction.

[0039] Figure 3a is a graph showing the temperature distribution when a laser is irradiated on the substrate and the conductive polymer layer.

[0040] Figure 3b is a graph (a) showing the temperature distribution at four points, a graph (b) showing the maximum temperature distribution in the X-axis direction, and a graph (c) showing the maximum temperature distribution in the Z-axis direction.

[0041] FIG. 4 is a photograph (a) showing the results of a bonding test of a conductive hydrogel patterned by a conventional method, a photograph (b) showing the results of a bonding test of a conductive hydrogel patterned by a laser according to an embodiment of the present invention, and a SEM image (c) showing a cross-sectional view of the interface between a substrate and a conductive polymer layer in an area where a pattern was formed by a laser.

[0042] Figure 5 is a graph (a) showing the conductivity of a conductive hydrogel according to each manufacturing step and a graph (b) showing the conductivity of a conductive hydrogel according to laser intensity.

[0043] Figure 6 is a TEM image (a) showing the surface of a conductive hydrogel patterned with a laser and a TEM image (b) showing the surface of a conductive hydrogel after post-processing.

[0044] Figure 7 is a schematic diagram (a) showing the difference in phase separation in the thickness direction at the interface of a conductive polymer layer and an AFM phase image (b) of a hydrophobic region and a hydrophilic region according to the difference in phase separation.

[0045] Figure 8a is a photograph (a) of a hydrogel neural probe containing a conductive hydrogel, a photograph (b) of an experiment in which the conductive hydrogel was applied to a rat brain, and a graph (c) showing the action potential of a rat brain according to a physiological state collected through the hydrogel neural probe.

[0046] Figure 8b is a photograph of a stretchable, serpentine-shaped hydrogel microelectrode inserted into a rat heart (a), photographs of the used hydrogel microelectrode before and after washing (b), and a photograph of the washed hydrogel microelectrode reinserted (c).

[0047]

[0048] The embodiments of the present invention are provided for the purpose of illustrating the technical concept of the present invention. The scope of the rights of the present invention is not limited to the embodiments presented below or the specific descriptions of these embodiments.

[0049] All technical and scientific terms used in this invention, unless otherwise defined, have the meanings commonly understood by those skilled in the art to which this invention pertains. All terms used in this invention have been selected for the purpose of more clearly explaining the invention and are not intended to limit the scope of the rights provided for in this invention.

[0050] Expressions such as “comprising,” “having,” and the like used in the present invention should be understood as open-ended terms that imply the possibility of including other embodiments, unless otherwise stated in the phrase or sentence in which the expression is included.

[0051] The singular expressions described in the present invention may include plural meanings unless otherwise stated, and this also applies to the singular expressions described in the claims.

[0052]

[0053] The present invention relates to a method for performing high-resolution patterning on a flexible conductive polymer layer using a laser, while solving the problem of weakened adhesion between the substrate and the conductive polymer layer in a wet environment, resulting in separation. The method utilizes the phase separation phenomenon of the conductive polymer layer that occurs when the photothermal energy of the laser is absorbed, and thus a conductive hydrogel with improved adhesion to the substrate does not separate even in a wet environment, and the formed pattern can be stably maintained.

[0054] The inventors of the present invention, after extensive research on lasers and polymer materials, discovered a phase separation phenomenon that occurs when a laser is irradiated on a conductive polymer, and named the patterning technology that can significantly improve the bonding strength between a conductive polymer layer and a substrate through the phase separation phenomenon laser-induced phase separation and adhesion (LIPSA).

[0055]

[0056] A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion according to one embodiment of the present invention may include the steps of: preparing a transparent polymer substrate (101); forming a conductive polymer layer (102) including a first polymer and a second polymer on one surface of the substrate; irradiating a laser toward the conductive polymer layer from a back surface of the substrate to form a conductive hydrogel pattern on the substrate; and washing and removing the conductive polymer layer.

[0057] FIG. 1 is a schematic diagram (a) and a cross-sectional view (b) of each step showing a method for manufacturing a conductive hydrogel pattern according to one embodiment of the present invention.

[0058] According to one embodiment, the substrate (101) may include at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), thermo-plastic polyurethane (TPU), styrene-butadiene-styrene (SBS), styrene-ethylene-butylene-styrene (SEBS), polyacrylamide, poly(acrylic acid), polyethylene glycol dimethacrylate, polyvinyl alcohol, gelatin, silk, chitosan, alginate, collagen, and cellulose. The substrate is not limited in type in the present invention as long as it is a transparent material that can transmit a laser, in addition to the above-described polymers.

[0059] The substrate may be formed of a transparent material having light transmittance, so that when a laser is irradiated toward the substrate, the laser may pass through the transparent substrate. The substrate may preferably include PET, which is a material having high light transmittance and flexibility.

[0060] The substrate may be formed to a thickness of 10 μm to 500 μm. If the substrate thickness is less than 10 μm, the substrate may be formed too thin, which may weaken the durability of the conductive hydrogel. If the substrate thickness exceeds 500 μm, the flexibility of the conductive hydrogel may decrease or the laser transmittance may be reduced, which may not be suitable. Preferably, the substrate may be formed to a thickness of 20 μm to 100 μm.

[0061]

[0062] The above conductive polymer layer (102) may include at least one selected from the group consisting of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), PEDOT:ToS, PEDOT, Polyaniline (PANI), PANI:PSS, Sulfonated polyaniline, and Polypyrrole (PPY).

[0063] According to one embodiment, the conductive polymer layer may include PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)) and may have a thickness of several micrometers or more. The PEDOT:PSS has high electrical conductivity, flexibility, and electrochemical stability, and thus may be preferably included in the conductive polymer layer.

[0064] According to one embodiment, the conductive polymer layer may be a mixture of one or more conductive materials selected from PEDOT:PSS, PANI, and PPY and one or more soft insulators selected from TPU, PU, ​​SEBS, Alginate, and Gelatin.

[0065] In one embodiment, the soft insulator may be a mixture of one of CNT and Metal nanomaterials and one or more of TPU, PU, ​​SEBS, Alginate, and Gelatin.

[0066] The conductive polymer layer may have lower transparency than the substrate and thus higher visible light absorption capability than the substrate. The conductive polymer layer may be composed of a material that has high transparency when the thickness is thin, but as the thickness increases, the transparency decreases and the visible light absorption capability increases. For example, a thin PEDOT:PSS layer has high transparency when it is thin, but as the thickness increases, the transparency decreases and the color gradually changes to blue or dark black, so that the degree of absorption of photothermal energy of a laser can further increase.

[0067] The thickness of the conductive polymer layer may be 100 nm to 50 μm. When the thickness of the conductive polymer layer is less than 100 nm, the transparency of the conductive polymer layer may be high, and thus the absorption of photothermal energy of the laser for phase separation and improved adhesion to the substrate may not be sufficient. When the thickness of the conductive polymer layer exceeds 50 μm, the photothermal energy of the laser may not be sufficiently transmitted in the thickness direction of the conductive polymer layer, and thus the phase separation phenomenon of the conductive polymer layer may not occur effectively or the aspect ratio may become too large, causing a problem of the micro-pattern collapsing. The thickness of the conductive polymer layer may preferably be 1 μm to 20 μm.

[0068] The conductive polymer layer may be formed on one surface of the substrate by one or more of drop-casting, spin-coating, spray-coating, dip coating, stencil printing, inkjet printing, and 3D printing. When the conductive polymer layer is formed by drop-casting or spin-coating, it may be uniformly formed with a fine thickness.

[0069] In one embodiment, the conductive polymer layer may include particles having regions separated by a central first polymer-rich domain and an outer second polymer-rich domain. This separation of regions may be derived from the properties of each polymer included in the conductive polymer.

[0070] The conductive polymer layer may include particles having a core-shell structure comprising a first polymer and a second polymer. In this case, when the core portion and the shell portion clearly absorb the photothermal energy of the laser, a phase separation phenomenon may occur in which the first polymer and the second polymer are separated. Due to the phase separation phenomenon, a first polymer-rich domain and a second polymer-rich domain may be formed.

[0071] In one embodiment, the first polymer may be more hydrophobic than the second polymer. When the phase separation phenomenon occurs, the first polymer-rich domain may exhibit hydrophobic characteristics, and the second polymer-rich domain may exhibit hydrophilic characteristics.

[0072] For example, PEDOT:PSS can form a structure in which a PEDOT having electrically conductive and hydrophobic properties is located at the center, and a PSS having hydrophilic properties surrounds the central PEDOT. When PEDOT:PSS is phase separated, the central PEDOT-rich domain can exhibit hydrophobic properties, and the peripheral PSS-rich domains can exhibit hydrophilic properties.

[0073]

[0074] According to one embodiment, in the step of forming a conductive hydrogel pattern on the substrate by irradiating a laser toward the conductive polymer layer from the back surface of the substrate, welding may be performed at the bonding surface of the substrate and the conductive hydrogel pattern.

[0075] Figure 2a is a graph showing the temperature and concentrated location of the photothermal energy of the laser according to the irradiation direction of the laser.

[0076] Figure 2b is a photograph showing the process of testing the bonding strength of the pattern after patterning in each investigation direction.

[0077] When a conductive polymer layer is formed on one side of the substrate, the laser may be irradiated to the back side of the substrate where the conductive polymer layer is not formed.

[0078] When the laser is irradiated in the front scanning direction on one side of the conductive polymer layer formed, the photothermal energy of the laser can be mostly absorbed in the conductive polymer layer having high visible light absorption. Therefore, the phase separation phenomenon of the conductive polymer due to the laser strongly occurs on the surface of the conductive polymer layer where the laser is incident, and the photothermal energy of the laser may not be conducted to the substrate due to low conductivity as it is absorbed inside the conductive polymer layer. As a result, the phase separation phenomenon due to the laser may be weak or hardly occur at the interface where the substrate and the conductive polymer layer come into contact, and thus may not affect the bonding strength of the substrate and the conductive polymer layer.

[0079] According to one embodiment, the step of forming a conductive hydrogel on the substrate by irradiating a laser toward the conductive polymer layer from the back surface of the substrate may cause phase separation on a molecular scale in the conductive polymer layer and strengthen the bonding force between the first polymer-rich domain and the substrate.

[0080] When a laser is irradiated from the backside scanning direction on the back surface of the substrate where the conductive polymer layer is not formed, the laser can pass through the transparent substrate and thus reach the interface between the substrate and the conductive polymer layer. In this case, a thermodynamic environment is created at the interface due to the photothermal energy of the laser, and the phase separation phenomenon of the conductive polymer can be most strongly exhibited as the photothermal energy is absorbed at the interface.

[0081] At the above interface, a phase separation phenomenon occurs in which the first polymer and the second polymer of the conductive polymer layer are separated, and a hydrophobic first polymer-rich domain can be formed. Since the first polymer-rich domain forms a mechanical interlocking structure and a bonding region at the interface, the interfacial bonding strength between the substrate and the conductive polymer layer can be significantly improved. As a result, a conductive hydrogel with significantly improved adhesion to the substrate can be formed.

[0082] As described above, the inventors of the present invention focus on the fact that by focusing the photothermal energy of a laser on the interface between a transparent substrate and a conductive polymer layer, phase separation of the conductive polymer at the interface is induced, thereby forming a direct bond between the substrate and the conductive polymer layer, thereby significantly improving the bonding strength of the two materials.

[0083]

[0084] According to one embodiment, the conductive polymer layer has a better visible light absorption capacity than the substrate, and in the step of irradiating a laser from the back surface of the substrate toward the conductive polymer layer to form a conductive hydrogel on the substrate, the intensity of the irradiated laser may be 150 mW to 300 mW.

[0085] If the intensity of the laser is lower than 150 mW, the phase separation phenomenon of the conductive polymer due to the laser may not sufficiently occur. If the intensity of the laser is higher than 300 mW, the conductive polymer may be carbonized due to the excessive photothermal energy of the laser, which may actually reduce the conductivity. The intensity of the laser may preferably be 200 mW to 280 mW.

[0086] According to one embodiment, the step of washing and removing the conductive polymer layer may be to wash the conductive polymer layer with a hydrophilic solvent to remove the conductive polymer layer in an area that has not been patterned by a laser.

[0087] The area where the conductive hydrogel pattern is formed by irradiating the laser can have improved interfacial bonding strength due to the phase separation of the conductive polymer, and a hydrophobic first polymer-rich domain can be formed. On the other hand, the conductive polymer layer in the area where the pattern is not formed can be easily separated from the substrate when washed with a hydrophilic solvent because the first polymer is surrounded by a second polymer exhibiting hydrophilic properties. The hydrophilic solvent is not particularly limited, but may be, for example, water.

[0088] The conductive polymer layer in the above-mentioned non-patterned region can be removed by impregnating it with a hydrophilic solvent or by applying an external force while impregnated with a hydrophilic solvent. As a result, a conductive hydrogel bonded to the substrate can be obtained only in the patterned region.

[0089] The method for manufacturing the above conductive hydrogel can have the advantages of forming a high-resolution pattern with only a simple laser irradiation process, easily removing an area where a pattern is not formed, and obtaining a conductive hydrogel with enhanced bonding strength to a substrate.

[0090]

[0091] According to one embodiment, the method further comprises a step of post-treating to increase the electrical conductivity of the conductive hydrogel; wherein the step of post-treating may be treating the conductive hydrogel with at least one selected from the group consisting of ethylene glycol (EG), polyethylene glycol, ethanol, methanol, sulfuric acid, hydrochloric acid, hydrofluoric acid, and DMSO. Preferably, the step of post-treating may be treating the conductive hydrogel with at least one selected from the group consisting of ethylene glycol (EG) and sulfuric acid.

[0092] The above post-treatment step may be performed by immersing the conductive hydrogel in the post-treatment solution for 20 to 60 minutes. Preferably, the conductive hydrogel may be immersed in the solution for 20 to 40 minutes.

[0093] The phase separation phenomenon of the conductive polymer due to the photothermal energy of the laser is most strongly observed at the interface between the substrate and the conductive polymer layer onto which the laser is incident, and the phase separation phenomenon may be weaker as the photothermal energy of the laser spreads unevenly in the thickness direction of the conductive polymer away from the interface. Accordingly, in the part where the phase separation phenomenon is strongly observed, the first polymer-rich domains may be strongly connected, but in the part where the phase separation phenomenon is weak, the first polymer-rich domains may be weakly connected.

[0094] Since the portion where the first polymer-rich domains are weakly connected has lower electrical conductivity than the portion where the first polymer-rich domains are strongly connected, a post-processing step can be performed to improve electrical conductivity by supplementing the interconnection of the weakly connected first polymer-rich domains.

[0095] The portions of the first polymer-rich domains where the first polymer-rich domains are weakly connected may include relatively large aggregates of the first polymer-rich domains and sporadically scattered aggregates of the second polymer-rich domains. Such irregular shapes may appear because the photothermal energy of the laser is unevenly distributed in the thickness direction of the conductive polymer layer. Since the second polymer-rich domains are weakly connected to each other through hydrogen bonds, and hydrogen bonds are vulnerable to moisture, the aggregates of the second polymer-rich domains may act as a factor that reduces mechanical properties such as bonding strength and moisture stability in a wet environment.

[0096] The above post-processing step has the effect of improving the electrical conductivity of the conductive hydrogel as a result of increasing the connection of the first polymer-rich domain, dissolving the aggregation of the second polymer-rich domain, reducing the size of the aggregation, and forming it uniformly.

[0097]

[0098] In another embodiment, a conductive hydrogel having excellent substrate adhesion comprises: a transparent polymer substrate; a patterned hydrogel layer formed on one surface of the transparent polymer substrate; wherein the hydrogel layer comprises first and second polymers, and may be a first polymer-rich domain.

[0099] The hydrogel layer may be formed by phase separation of the polymer of the conductive polymer layer as described above while absorbing the photothermal energy of the laser. Due to the phase separation phenomenon, the hydrogel layer may include a first polymer-rich domain and have improved interfacial bonding strength with the substrate.

[0100] According to one embodiment, the cross-section of the interface where the substrate and the hydrogel layer come into contact may have a wavy shape.

[0101] The above interface is a region where the photothermal energy of the laser is concentrated upon incident laser light, and the surface may be irregularly deformed due to the phase separation phenomenon of the conductive polymer. For example, the surface may be formed into a wave shape with curves. For example, the surface may include a spot-welded region where the two materials of the substrate and the conductive polymer layer are bonded and fused. Through the deformed surface, the contact area between the substrate and the hydrogel layer is expanded, which may affect the improved adhesion between the substrate and the hydrogel layer.

[0102] In one embodiment, the interior of the conductive hydrogel layer may include a first polymer-rich domain, and the first polymer-rich domain located closer to the substrate may form a stronger bond with each other than the first polymer-rich domain located farther from the substrate.

[0103] In one embodiment, the conductive hydrogel layer may have a hydrophobic water barrier formed on its surface.

[0104] Figure 7 is a schematic diagram (a) showing the difference in phase separation in the thickness direction at the interface of a conductive polymer layer and an AFM phase image (b) of a hydrophobic region and a hydrophilic region according to the difference in phase separation.

[0105] The phase separation phenomenon of the conductive polymer may become weaker as the distance from the interface between the substrate and the conductive polymer layer in the thickness direction increases due to the diffusion of photothermal energy. Accordingly, the region where the phase separation phenomenon is strong may be where the first polymer-rich domains are strongly connected, whereas the region where the phase separation phenomenon is weak may be where the first polymer-rich domains are weakly connected. Due to this difference in the degree of phase separation, the region near the interface and the region far from the interface may exhibit different characteristics.

[0106] The conductive hydrogel layer may include a hydrophobic region (water-inhibiting region) located close to the interface where the phase separation phenomenon strongly occurs, and a hydrophilic region (water-absorbing region) located far from the interface in the thickness direction where the phase separation phenomenon weakly occurs.

[0107] The hydrophobic region exhibits enhanced hydrophobic properties by strongly connecting the first polymer-rich domains, thereby effectively preventing moisture penetration. For example, a PET substrate and a conductive polymer layer including PEDOT:PSS may be bonded via hydrogen bonds, but the hydrogen bonds can be easily affected by moisture. However, since the hydrophobic region can effectively prevent water from penetrating between the substrate and the conductive hydrogel layer, it acts as an element that strengthens the bonding strength between the substrate and the conductive hydrogel layer, thereby improving the adhesion to the substrate.

[0108] On the other hand, the hydrophilic region is relatively weakly connected to the first polymer-rich domain, allowing moisture to penetrate into the conductive hydrogel layer, and the penetrated moisture is retained within the hydrogel layer, thereby exhibiting hydrogel properties. Accordingly, the conductive hydrogel layer can have the property of containing a large amount of moisture while maintaining stable adhesion to the substrate in a wet environment.

[0109]

[0110] In one embodiment, the conductive hydrogel layer may include a pattern having a width of 1 μm to 20 μm.

[0111] The conductive hydrogel layer may include a high-resolution pattern formed by irradiating a laser. The pattern may be formed to have a fine width with a single laser irradiation process. Preferably, the conductive hydrogel layer may include a pattern having a width of 1 μm to 10 μm, and more preferably, a pattern having a width of 1 μm to 5 μm.

[0112] In one embodiment, the conductive hydrogel layer may have a higher aspect ratio in terms of thickness to width.

[0113]

[0114] The pattern of the conductive hydrogel layer may be formed by a larger thickness-to-width ratio of the pattern because the photothermal energy of the laser is absorbed in the thickness direction of the conductive polymer layer. Through a pattern having a higher aspect ratio of thickness-to-width as described above, the area capable of retaining moisture can be expanded while maintaining a fine width.

[0115] The width-to-thickness ratio of the above pattern can be formed to be 1:0.1 to 1:5, and preferably 1:1 to 1:25. The above aspect ratio can be maintained even when the conductive hydrogel contains moisture and swells, so that the fine pattern structure can be maintained.

[0116] In one embodiment, the conductive hydrogel may be manufactured using a manufacturing method according to one embodiment of the present invention. Through this manufacturing method, a precisely patterned conductive hydrogel pattern can be formed simply by controlling laser irradiation conditions without the introduction of separate patterning techniques. Furthermore, by utilizing the phase separation phenomenon of the conductive polymer to form a conductive hydrogel layer with enhanced bonding strength to a substrate, a conductive hydrogel that can be maintained for a long period of time in a wet environment can be formed.

[0117]

[0118] The present invention is described in more detail through the following examples. However, these examples are intended to illustrate some experimental methods and configurations of the present invention, and the scope of the present invention is not limited to these examples.

[0119]

[0120] Manufacturing Example 1: Preparation of substrate and conductive polymer layer

[0121] A PEDOT:PSS aqueous solution (1.0 wt% to 1.3 wt%, Clevios PH1000, Heraeus Electronic Materials) was prepared by filtering it through a filter having a pore size of 0.45 μm. The PEDOT:PSS aqueous solution was coated on a polymer substrate including PET by a drop-casting method and dried at room temperature, thereby preparing a PEDOT:PSS conductive polymer layer formed to a thickness of 5 μm on a 50 μm thick PET substrate.

[0122]

[0123] Experimental Example 1: Pattern formation according to laser irradiation direction

[0124] In order to evaluate the bonding strength with the substrate according to the direction of laser irradiation, a 532 nm laser beam was irradiated in different directions to the substrate and conductive polymer layer manufactured according to Manufacturing Example 1 to form a pattern. The laser beam was irradiated in the front direction (frontside scanning) or backside scanning to the structure in which the conductive polymer layer was laminated on the substrate.

[0125] Figure 2a is a graph showing the temperature and concentrated location of the photothermal energy of the laser according to the irradiation direction of the laser.

[0126] Figure 2b is a photograph showing the process of testing the bonding strength of the pattern after patterning in each investigation direction.

[0127] When the laser was irradiated in the front direction, the photothermal energy of the laser was concentrated on the PEDOT:PSS layer with high visible light absorption, and the photothermal energy of the laser reaching the PET substrate was limited.

[0128] On the other hand, when the laser was irradiated in the rear direction, the laser was able to pass through the transparent PET substrate and enter the PEDOT:PSS layer, and as a result, it was confirmed that the photothermal energy of the laser was concentrated at the interface where the substrate and the conductive polymer layer were in contact.

[0129] The conductive hydrogels, each patterned in the front or back direction, were immersed in water and rubbed by hand to test their bonding strength in a wet environment. While the pattern of the conductive hydrogel patterned in the front direction was largely lost after applying an external force, the pattern of the conductive hydrogel patterned in the back direction was confirmed to be maintained.

[0130] Through the above results, it was confirmed that irradiating the laser in the rear direction so that the photothermal energy can be concentrated at the interface between the substrate and the conductive polymer layer through the transparent substrate can effectively improve the bonding strength of the interface.

[0131] Heat transfer simulations were performed to indirectly measure the extent to which phase separation occurs due to the photothermal energy of the laser when the laser is irradiated in the rear direction.

[0132] Figure 3a is a graph showing the temperature distribution when a laser is irradiated on the substrate and the conductive polymer layer.

[0133] Figure 3b is a graph (a) showing the temperature distribution at four points, a graph (b) showing the maximum temperature distribution in the X-axis direction, and a graph (c) showing the maximum temperature distribution in the Z-axis direction.

[0134] It was confirmed that the temperature at the central point (position 1) located at the interface between the substrate and the conductive polymer layer, where the laser's photothermal energy is concentrated, is the highest, and that the temperature decreases as it moves away from the central point in the X-axis and Z-axis directions. In addition, it was confirmed that the laser's photothermal energy is transmitted from the interface to a thickness of 72% of the conductive polymer layer in the Z-axis direction parallel to the direction in which the laser is irradiated.

[0135] Through the above results, it was possible to infer that phase separation of the conductive polymer layer is strong at the interface where the photothermal energy of the laser is concentrated and in the area close to the interface, and phase separation is weak in the area relatively far from the interface where the photothermal energy is weakly transmitted.

[0136]

[0137] Manufacturing Example 2: Manufacturing and post-processing of conductive hydrogel

[0138] The conductive hydrogel, patterned with a 532 nm laser, was immersed in water to remove the unpatterned region. After washing, the conductive hydrogel was dried on a 60°C hot plate. The dried hydrogel was immersed in an ethylene glycol solution for 30 minutes and washed several times with ethanol and water.

[0139]

[0140] Comparative Example 1: Conductive hydrogel patterned by screen printing

[0141] As a comparative example, a conductive hydrogel was prepared by forming a pattern on a PEDOT:PSS polymer layer using one of the following methods: screen printing, 3D printing, inkjet printing, spray printing, and photolithography.

[0142]

[0143] Experimental Example 2: Evaluation of Adhesion and Electrical Conductivity of Conductive Hydrogels

[0144] To test the bonding strength of the conductive hydrogel post-treated with ethylene glycol according to Manufacturing Example 2 and the conductive hydrogel patterned by screen printing according to Comparative Example 1, each hydrogel was immersed in water for 30 minutes and then taken out for examination.

[0145] FIG. 4 is a photograph (a) showing the results of a bonding test of a conductive hydrogel patterned by a conventional method, a photograph (b) showing the results of a bonding test of a conductive hydrogel patterned by a laser according to an embodiment of the present invention, and a SEM image (c) showing a cross-sectional view of the interface between a substrate and a conductive polymer layer in an area where a pattern was formed by a laser.

[0146] In Comparative Example 1, where the conductive hydrogel was patterned using the conventional screen-printing method, it was confirmed that the terminal portion of the pattern was lost when the conductive hydrogel was taken out after being immersed in water. In addition, in the case of Comparative Example 1, where the pattern was formed using a method other than screen printing, it was confirmed that part of the pattern was lost when the conductive hydrogel was taken out after being immersed in water. On the other hand, it was confirmed that the conductive hydrogel, where the pattern was formed using a laser, was maintained without any portion of the pattern being lost even when taken out after being immersed in water.

[0147] A cross-sectional SEM image of the area where the pattern was formed by the laser confirmed that the interface between the substrate and the conductive polymer layer in the area where the pattern was formed exhibited a wavy shape. In addition, it was confirmed that a portion of the interface exhibited a spot-welded shape. It was confirmed that this change was caused by the phase separation phenomenon that occurred when the conductive polymer layer absorbed the photothermal energy of the laser.

[0148]

[0149] The electrical conductivity of a conductive hydrogel patterned with a laser was evaluated after post-processing.

[0150] Figure 5 is a graph (a) showing the conductivity of a conductive hydrogel according to each manufacturing step and a graph (b) showing the conductivity of a conductive hydrogel according to laser intensity.

[0151] The conductivity of the conductive hydrogel was 0.03 S cm before patterning by laser. -1 In , after the pattern was formed, 394 S cm -1 was significantly improved, and after post-treatment with ethylene glycol solution, it reached 543 S cm -1 It was confirmed that the electrical conductivity of the patterned conductive hydrogel could be further improved through the above post-processing step.

[0152] As the laser intensity increases, the phase separation of the conductive polymer becomes stronger, so it was confirmed that the conductivity of the conductive hydrogel improves as the laser intensity increases. When the laser intensity is 250 mW, the conductivity of the conductive hydrogel is 101.4 S cm -1 , and the moisture content was 81.6%, showing the most excellent moisture absorption ability (hygroscopicity). However, at 280 mW intensity, it was confirmed that excessive laser energy carbonized PEDOT:PSS, which actually reduced the conductivity.

[0153]

[0154] Experimental Example 3: Moisture Blocking and Absorption Effects of Conductive Hydrogels

[0155] In one embodiment, the conductive hydrogel layer may block moisture permeation and may include crystals of irregular size.

[0156] Figure 6 is a TEM image (a) showing the surface of a conductive hydrogel patterned with a laser and a TEM image (b) showing the surface of a conductive hydrogel after post-processing.

[0157] TEM images confirmed that relatively large first polymer-rich domain aggregates were formed in areas where the conductive polymer phase separation was weak. However, after post-treatment with an ethylene glycol solution, the scattered second polymer-rich domain aggregates disappeared, and the size of the first polymer-rich domain aggregates decreased and were uniformly deformed.

[0158] Therefore, it was confirmed that the post-processing step changed the crystal size of the patterned region and enhanced the electrical conductivity by strengthening the connection of the first polymer-rich domain of the conductive hydrogel.

[0159] Figure 7 is a schematic diagram (a) showing the difference in phase separation in the thickness direction at the interface of a conductive polymer layer, and an AFM phase image (b) of a hydrophobic region and a hydrophilic region according to the difference in phase separation.

[0160] As described above, the hydrophobic region of a conductive polymer, where phase separation is strongly evident, can block moisture and enhance adhesion to the substrate. Conversely, the hydrophilic region, where phase separation is weak, can exhibit hydrogel properties capable of absorbing and retaining moisture.

[0161] When the hydrophobic and hydrophilic regions were photographed using Atomic Force Microscopy (AFM), it was confirmed that the hydrophilic region contained relatively small-sized PEDOT grains surrounded by PSS, whereas the hydrophobic region formed large grains of PEDOT that were separated from the PSS and strongly connected.

[0162]

[0163] Experimental Example 4: Bio-implantable device containing conductive hydrogel

[0164] A bio-implantable device comprising a conductive hydrogel according to another embodiment may comprise a conductive hydrogel according to one embodiment of the present invention.

[0165] A wearable sensor comprising a conductive hydrogel according to another embodiment may comprise a conductive hydrogel according to one embodiment of the present invention.

[0166] When the long-term stability of the conductive hydrogel with enhanced bonding to the substrate of the present invention was tested in a wet environment immersed in water, it was confirmed that the conductive hydrogel pattern remained intact and undamaged for over 8 months. Accordingly, the conductive hydrogel was confirmed to have the potential to be applied to bio-implantable devices that require long-term stability in a wet environment.

[0167] The conductive hydrogel was washed to remove harmful ethylene glycol residues, and a high-resolution implantable neural probe with a line width of 60 μm and a pitch of 120 μm was fabricated. Sixteen PEDOT:PSS hydrogel electrodes were patterned on a PET substrate, and a thin PDMS layer was formed as a skin-coating for encapsulation. The flexible neural probe fabricated as described above was inserted into the somatosensory cortex region of a rat.

[0168] Figure 8a is a photograph (a) of a hydrogel neural probe containing a conductive hydrogel, a photograph (b) of an experiment in which the conductive hydrogel was applied to a rat brain, and a graph (c) showing the action potential of a rat brain according to a physiological state collected through the hydrogel neural probe.

[0169] Figure 8b is a photograph of a stretchable, serpentine-shaped hydrogel microelectrode inserted into a rat heart (a), photographs of the used hydrogel microelectrode before and after washing (b), and a photograph of the washed hydrogel microelectrode reinserted (c).

[0170] When the action potential of the rat brain was measured under various physiological conditions after inserting the neural probe, a distinct spike was observed on the graph. Since the neural probe was inserted into the body and measured without abnormalities for over three weeks, the long-term stability and biocompatibility of the hydrogel neural probe were confirmed.

[0171] We demonstrated that hydrogel microelectrodes, fabricated with a stretchable, serpentine shape, collected cardiac signals when inserted into a rat heart. The hydrogel microelectrodes were thoroughly cleaned using ultrasonication after use, and were confirmed to function well and collect signals without any abnormalities when reinserted into the body.

[0172] Through this, it was confirmed that the neural probe and microelectrode including the conductive hydrogel can be utilized as a bio-implantable device and also as a wearable sensor.

[0173]

[0174] The above description is merely an illustrative example of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the technical idea of ​​the present invention, and the scope of the technical idea of ​​the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

Claims

1. Step of preparing a transparent polymer substrate; A step of forming a conductive polymer layer including a first polymer and a second polymer on one surface of the substrate; A step of forming a conductive hydrogel pattern on the substrate by irradiating a laser toward the conductive polymer layer on the back surface of the substrate; and A step of washing and removing the conductive polymer layer; including; A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

2. In paragraph 1, A step of forming a conductive hydrogel pattern on the substrate by irradiating a laser toward the conductive polymer layer on the back surface of the substrate; Welding is performed at the joint surface of the substrate and the conductive hydrogel pattern. A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

3. In paragraph 1, The first polymer is more hydrophobic than the second polymer, A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

4. In paragraph 1, The substrate comprises at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), thermo-plastic polyurethane (TPU), styrene-butadiene-styrene (SBS) and styrene-ethylene-butylene-styrene (SEBS), Polyacrylamide, Poly(acrylic acid), polyethylene glycol dimethacrylate, polyvinyl alcohol, Gelatin, Silk, Chitosan, Alginate, Collagen, and Cellulose. A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

5. In paragraph 1, The conductive polymer layer comprises at least one selected from the group consisting of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), PEDOT:ToS, PEDOT, Polyaniline(PANI), PANI:PSS, Sulfonated polyaniline and Polypyrrole(PPY). A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

6. In paragraph 1, The conductive polymer layer comprises particles having a region divided into a first polymer-rich domain in the center and a second polymer-rich domain in the outer edge. A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

7. In paragraph 1, A step of forming a conductive hydrogel on the substrate by irradiating a laser toward the conductive polymer layer on the back surface of the substrate; In the conductive polymer layer, molecular-scale phase separation occurs, and the bonding strength between the first polymer-rich domain and the substrate is strengthened. A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

8. In paragraph 1, The conductive polymer layer has a better visible light absorption capacity than the substrate, A step of forming a conductive hydrogel on the substrate by irradiating a laser toward the conductive polymer layer on the back surface of the substrate; wherein the intensity of the laser irradiated is 150 mW to 300 mW. A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

9. In paragraph 1, A step of washing and removing the conductive polymer layer; The conductive polymer layer is washed with a hydrophilic solvent to remove the conductive polymer layer in the area that is not patterned by the laser. A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

10. In paragraph 1, A step of post-processing to increase the electrical conductivity of the conductive hydrogel is further included; The above post-processing step is to treat the conductive hydrogel with one or more selected from the group consisting of ethylene glycol (EG), polyethylene glycol, ethanol, methanol, sulfuric acid, hydrochloric acid, hydrofluoric acid, and DMSO. A method for manufacturing a conductive hydrogel pattern having excellent substrate adhesion.

11. Transparent polymer substrate; A patterned hydrogel layer formed on one side of the transparent polymer substrate; The hydrogel layer comprises first and second polymers, wherein the first polymer is a rich domain. Conductive hydrogel with excellent substrate adhesion.

12. In paragraph 11, The cross-section of the interface where the substrate and the hydrogel layer come into contact has a wavy shape. Conductive hydrogel with excellent substrate adhesion.

13. In paragraph 11, The conductive hydrogel layer has a hydrophobic water barrier film formed on its surface. Conductive hydrogel with excellent substrate adhesion.

14. In paragraph 11, The conductive hydrogel layer comprises a pattern having a width of 1 μm to 20 μm, Conductive hydrogel with excellent substrate adhesion.

15. In paragraph 14, The conductive hydrogel layer has a higher aspect ratio in terms of thickness to width, Conductive hydrogel with excellent substrate adhesion.

16. In paragraph 11, The interior of the conductive hydrogel layer comprises a first polymer-rich domain, The first polymer-rich domain located close to the substrate forms a stronger bond with each other than the first polymer-rich domain located far from the substrate. Conductive hydrogel with excellent substrate adhesion.

17. In paragraph 11, The conductive hydrogel layer blocks moisture penetration and contains crystals of irregular size. Conductive hydrogel with excellent substrate adhesion.

18. In paragraph 11, The above conductive hydrogel is, Manufactured by the manufacturing method of Article 1, Conductive hydrogel with excellent substrate adhesion.

19. A conductive hydrogel comprising any one of claims 11 to 18, A bio-implantable device comprising a conductive hydrogel.

20. A conductive hydrogel comprising any one of claims 11 to 18. A wearable sensor comprising a conductive hydrogel.

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