A bilayer hydrogel actuator and a method for preparing the same

Abstract

The present application relates to a kind of double-layer hydrogel driver and its preparation method, the double-layer hydrogel driver has high interface toughness.It is with double network (Double Network, referred to as DN) structure of hydrogel for the double-layer hydrogel driver, the material characteristics of first layer using gelatin (Gelatin) cooling gel as first monomer, constructs first network, realizes controllable double-layer structure, with N-hydroxyethyl acrylamide (HEAA) as second monomer, constructs second network, the mechanical property of obtained Gelatin / PHEAA double network hydrogel is excellent, therefore improve the overall mechanical property of driver;Second layer constructs poly (N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) (P (NIPAM-co-HEAA)) temperature-sensitive hydrogel, when the outside temperature is higher than its low critical solution temperature (LCST), it can quickly produce response;Meanwhile, due to synchronous polymerization double-layer hydrogel, molecular penetration of gel-gel interface, high molecular chain intertangling, form local topological network structure, greatly enhance the interface toughness of double-layer hydrogel driver, improve the stability of driver, can realize repeated use.

Description

TECHNICAL FIELD

[0001] The present patent application belongs to the field of high polymer material chemistry, and particularly relates to a double-layer hydrogel actuator and a preparation method thereof. BACKGROUND

[0002] Stimuli-responsive hydrogel is a kind of high polymer material with three-dimensional network structure formed by monomer molecules through chemical or physical cross-linking method, and can respond to various physical, chemical, biological and other changes in the external environment by sensing and self-working. Traditional stimuli-responsive hydrogel can only change in volume or color under the external stimulus. In recent years, researchers introduce anisotropic structure in the preparation process of hydrogel actuator, and through the asymmetric water absorption and dehydration in the hydrogel, the hydrogel can bend in a specific direction, thereby attracting the attention of domestic and foreign scholars to the hydrogel actuator.

[0003] At present, the anisotropic structure of the hydrogel actuator mainly includes double-layer structure, gradient structure, patterned structure and oriented structure. Among them, the double-layer hydrogel actuator is the most widely studied, which is composed of two layers of hydrogels with different water absorption and swelling degrees. When subjected to external stimulus, one layer of hydrogel changes in volume, while the other layer of hydrogel does not change. This difference makes the double-layer hydrogel bend. In order to weaken the internal unbalanced volume change, internal stress is generated in the hydrogel, and then more complex deformation is evolved. However, in the prior art, due to the anisotropic structure characteristics of the double-layer hydrogel, the deformation of each layer of gel is different, the interfacial toughness of the double-layer hydrogel actuator is poor, the gel-gel is easy to separate, the hydrogel actuator is layered, and loses the ability to quickly respond to external stimuli. SUMMARY

[0004] In view of this, one of the purposes of the present patent application is to provide a double-layer hydrogel actuator with high interfacial toughness. Another purpose of the present patent application is to provide a preparation method of the double-layer hydrogel actuator, which simplifies the preparation process of the double-layer hydrogel actuator, thereby greatly improving the interfacial toughness of the double-layer hydrogel actuator.

[0005] In one aspect, the present patent application provides a double-layer hydrogel actuator, which comprises: a first layer of hydrogel and a second layer of hydrogel, the first layer of hydrogel is a double-network hydrogel, the double-network hydrogel comprises a first network composed of gelatin cooling glue and a second network composed of N-hydroxyethyl acrylamide; the second layer of hydrogel is a poly(N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) temperature-sensitive hydrogel constructed by N-isopropyl acrylamide and N-hydroxyethyl acrylamide.

[0006] According to the double-layer hydrogel driver of the present patent application, preferably, the first layer hydrogel is composed of the following mass fractions of substances: 6% to 15% gelatin (Gelatin), 45% to 75% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of HEAA, and the balance being water.

[0007] According to the double-layer hydrogel driver of the present patent application, preferably, the second layer hydrogel is composed of the following mass fractions of substances: 25% to 45% N-isopropyl acrylamide (NIPAM), 10% to 40% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of NIPAM and HEAA, N,N'-methylenebisacrylamide (MBA) added in an amount of 1 mol% of NIPAM, and the balance being water.

[0008] Further, the double-layer hydrogel driver of the present patent application is composed of the following mass fractions of substances:

[0009] First layer hydrogel: 12% gelatin (Gelatin), 60% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of HEAA, and the balance being water;

[0010] Second layer hydrogel: 30% N-isopropyl acrylamide (NIPAM), 25% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of NIPAM and HEAA, N,N'-methylenebisacrylamide (MBA) added in an amount of 1 mol% of NIPAM, and the balance being water.

[0011] In another aspect, the present patent application provides a preparation method of the above-mentioned double-layer hydrogel driver, comprising the following steps:

[0012] S1: respectively weigh appropriate amounts of gelatin (Gelatin), N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959), and water into a glass bottle, and after stirring at room temperature, a pre-polymer solution A is obtained;

[0013] S2: Take appropriate amount of N-isopropyl acrylamide (NIPAM), N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959), N, N'-methylene bisacrylamide (MBA) and add water to dissolve in a glass bottle to obtain a prepolymer solution B;

[0014] S3: Pour the prepolymer solution A obtained in step S1 into an assembled mold and cool it;

[0015] S4: Inject the prepolymer solution B obtained in step S2 into the upper cavity of the mold cavity of the prepolymer solution A cooled in step S3, and stand still to obtain a double-layer hydrogel prepolymer solution C;

[0016] S5: Place the double-layer hydrogel prepolymer solution C obtained in step S4 under an ultraviolet lamp to polymerize and obtain a double-layer hydrogel actuator.

[0017] Further, the preparation method of the double-layer hydrogel actuator of the present patent application, the step "S1: Take appropriate amount of gelatin (Gelatin), N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) and water, and dissolve them in a glass bottle, and stir at room temperature to obtain a prepolymer solution A", includes:

[0018] Take 1.2g 12wt% of gelatin (Gelatin), 6g 60wt% of N-hydroxyethyl acrylamide (HEAA), 0.1169g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (the amount added is 1mol% of HEAA), and then add 2.8g of water to dissolve in a glass bottle, and stir at room temperature for 15-30 minutes to obtain a prepolymer solution A.

[0019] Further, the preparation method of the double-layer hydrogel driver of the patent application, the step "S2, respectively, take N-isopropyl acrylamide (NIPAM) 1.2-4.8 g 10-40 wt%, N-hydroxyethyl acrylamide (HEAA) 1.2-3 g 10-25 wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl benzophenone (I2959) 0.0472-0.1536 g (the amount of 1 mol% of NIPAM and HEAA is added), N, N'-methylene bisacrylamide (MBA) 0.0163-0.0654 g (the amount of 1 mol% of NIPAM is added), then add 4.2-9.6 g H2O to a glass bottle, stir at 20℃ for 15-30 minutes, and obtain the prepolymer solution B" includes: respectively, take N-isopropyl acrylamide (NIPAM) 1.2-4.8 g 10-40 wt%, N-hydroxyethyl acrylamide (HEAA) 1.2-3 g 10-25 wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl benzophenone (I2959) 0.0472-0.1536 g (the amount of 1 mol% of NIPAM and HEAA is added), N, N'-methylene bisacrylamide (MBA) 0.0163-0.0654 g (the amount of 1 mol% of NIPAM is added), then add 4.2-9.6 g H2O to a glass bottle, stir at 20℃ for 15-30 minutes, and obtain the prepolymer solution B.

[0020] Further, the preparation method of the double-layer hydrogel driver of the patent application, the standing in step S4 is specifically standing at room temperature for 10-20 minutes.

[0021] Further, the preparation method of the double-layer hydrogel driver of the patent application, the step "S5, the double-layer hydrogel prepolymer C obtained in step S4 is placed under ultraviolet lamp for polymerization to obtain a double-layer hydrogel driver" includes: the double-layer hydrogel prepolymer C obtained in step S4 is placed under an 8W ultraviolet lamp for polymerization for 0.5-1.0 hours to obtain a double-layer hydrogel driver.

[0022] Further, the preparation method of the double-layer hydrogel driver of the patent application, the step "S5, the double-layer hydrogel prepolymer C obtained in step S4 is placed under ultraviolet lamp for polymerization to obtain a double-layer hydrogel driver" includes: the double-layer hydrogel prepolymer C obtained in step S4 is placed under an 8W ultraviolet lamp for polymerization for 0.5-1.0 hours to obtain a double-layer hydrogel driver.

[0023] The patent application provides a double-layer hydrogel driver and a preparation method thereof, and the double-layer hydrogel driver has high interface toughness. The double-layer hydrogel driver adopts a hydrogel with a double network (DN) structure, a first layer of the driver uses the material property of gelatin (Gelatin) cooling gelatinization as a first monomer to construct a first network, realizes controllable double-layer structure, uses N-hydroxyethyl acrylamide (HEAA) as a second monomer to construct a second network, and the obtained Gelatin / PHEAA double network hydrogel has excellent mechanical properties, and therefore the overall mechanical properties of the driver are improved; a second layer constructs a poly (N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) (P (NIPAM-co-HEAA)) temperature-sensitive hydrogel, which can rapidly respond when the external temperature is higher than a lower critical solution temperature (LCST); meanwhile, due to the synchronous polymerization of the double-layer hydrogel, molecular penetration at a gel-gel interface, and intertangling of polymer chains, a local topological network structure is formed, the interface toughness of the double-layer hydrogel driver is greatly enhanced, the stability of the driver is improved, and the driver can be repeatedly used.

[0024] Additional aspects and advantages of the patent application will be in part apparent and in part pointed out hereinafter in the description. BRIEF DESCRIPTION OF DRAWINGS

[0025] The above and / or additional aspects and advantages of the patent application will become apparent and be readily appreciated from the following description, including the drawings, in which:

[0026] Figure 1 is a step flow chart of the preparation method of the double-layer hydrogel driver in an embodiment of the patent application.

[0027] Figure 2 is a schematic diagram of step S1 in the preparation method of the double-layer hydrogel driver in another embodiment of the patent application.

[0028] Figure 3 is a schematic diagram of step S2 in the preparation method of the double-layer hydrogel driver in another embodiment of the patent application.

[0029] Figure 4 is a step flow chart of the preparation method of the double-layer hydrogel driver in another embodiment of the patent application.

[0030] Figure 5 is a synthesis schematic diagram of the double-layer hydrogel driver in an embodiment of the patent application.

[0031] Figure 6 is an SEM characterization diagram of the double-layer structure of the double-layer hydrogel driver in an embodiment of the patent application.

[0032] Figure 7 is a stress-strain curve of the double-layer hydrogel actuator in the embodiments of the present patent application.

[0033] Figure 8 is an interface toughness curve of the double-layer hydrogel actuator in the embodiments of the present patent application.

[0034] Figure 9 is a driving effect diagram of the double-layer hydrogel actuator in the embodiments of the present patent application.

[0035] Figure 10 is a schematic diagram of a mold used in the preparation of the double-layer hydrogel actuator in the embodiments of the present patent application. DETAILED DESCRIPTION

[0036] The embodiments of the present patent application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the present patent application and should not be regarded as limiting the scope of the present patent application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0037] It should be noted that:

[0038] In the present patent application, all the embodiments and preferred embodiments mentioned in the present text can be combined with each other to form new technical solutions, if not otherwise specified.

[0039] In the present patent application, the percentage (%) or the part refers to the percentage by weight or the parts by weight of the composition, if not otherwise specified.

[0040] In the present patent application, the components or preferred components involved can be combined with each other to form new technical solutions, if not otherwise specified.

[0041] In the present patent application, unless otherwise specified, the numerical range "a~b" represents a shorthand notation for any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "6~15" represents that all the real numbers between "6~15" have been listed in the present text, and "6~15" is only a shorthand notation for these numerical combinations.

[0042] The "range" disclosed in the present patent application in the form of lower limit and upper limit can be one or more lower limits, and one or more upper limits, respectively.

[0043] In the present patent application, unless otherwise specified, each reaction or operation step can be carried out sequentially or according to the sequence. Preferably, the reaction method in the present text is carried out sequentially.

[0044] Unless otherwise indicated, the professional and scientific terms used herein have the same meaning as those familiar to one skilled in the art. In addition, any method or material similar or equivalent to those described can also be applied to the present patent application.

[0045] In contemporary science, the double-layer hydrogel driver is the most widely studied, which is composed of two layers of hydrogels with different water absorption and swelling degrees. One layer may have a stimulus response ability while the other layer does not have a stimulus response ability, or both layers may have different stimulus response abilities. When subjected to external stimuli, one layer of hydrogel changes in volume, while the other layer of hydrogel does not change. This difference enables the double-layer hydrogel to bend. In order to weaken the internal imbalance of volume change, internal stress is generated in the hydrogel, which further evolves into more complex deformation. However, due to the anisotropic structural characteristics of the double-layer hydrogel, the deformation of each layer of gel is different, the interfacial toughness of the hydrogel in the double-layer driver is poor, the gel-gel is easy to separate, the double-layer hydrogel driver appears to be layered, and loses the ability to quickly respond to external stimuli.

[0046] In view of the poor interfacial toughness and easy delamination of the double-layer hydrogel driver, the existing technology mainly introduces other substances (such as nanoclay) into the gel, uses hydrogen bond and other physical interactions to strengthen the interfacial toughness (Li J, et al. ACS Applied Materials & Interfaces, 2020, 12(49), 55290-55298.); or add supramolecular glue, which is bonded at the interface, and use the host-guest interaction between the gel and the supramolecular glue to enhance the interfacial toughness (Ma C, et al. Advanced Functional Materials, 2018, 28(7), 1704568.). However, these methods all use two-step polymerization or in-situ polymerization, which is complicated and complex in actual operation process. The step-by-step polymerization of the hydrogel layer is greatly affected by environmental factors, which can easily reduce its interfacial toughness. Since the gel has not been formed, in-situ polymerization needs to be performed on the surface of the first layer of hydrogel, and the interface of the double-layer hydrogel is difficult to control, making it difficult to achieve the ideal double-layer effect.

[0047] Referring to Figure 5 and Figure 6According to an aspect of the present patent application, the present patent application provides a high interfacial toughness double-layer hydrogel actuator. The double-layer hydrogel actuator comprises a first layer of hydrogel and a second layer of hydrogel, wherein the first layer of hydrogel is a double-network hydrogel comprising a first network of gelatin cooling gelation and a second network of N-hydroxyethyl acrylamide; and the second layer of hydrogel is a poly(N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) temperature-sensitive hydrogel constructed by N-isopropyl acrylamide and N-hydroxyethyl acrylamide. The double-layer hydrogel actuator in the present patent application adopts a hydrogel with a double-network (DN) structure. The first layer selects two monomers of gelatin (Gelatin) and N-hydroxyethyl acrylamide (HEAA). The material properties of gelatin (Gelatin) cooling gelation are used as the first monomer to construct the first network, realizing a controllable double-layer structure. That is, gelatin can form a gel after heating, dissolving and cooling. The first network is constructed by using the property of gelatin cooling gelation. Therefore, the first network composed of gelatin gives the first layer of hydrogel a fixed shape, which can be distinguished from the second layer of hydrogel prepolymer liquid. In addition, N-hydroxyethyl acrylamide (HEAA) has not formed a polymer network because it has not been subjected to ultraviolet (UV) irradiation. The first layer is not completely gelled. While constructing the double-layer structure, it does not affect the molecular penetration of the second layer of hydrogel prepolymer liquid at the interface. Thus, a controllable double-layer structure can be realized. N-hydroxyethyl acrylamide (HEAA) is used as the second network. The obtained gelatin / poly(N-hydroxyethyl acrylamide) (Gelatin / PHEAA) double-network hydrogel has excellent mechanical properties, thus improving the overall mechanical properties of the actuator. The second layer constructs a poly(N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) (P(NIPAM-co-HEAA)) temperature-sensitive hydrogel, which can rapidly respond when the external temperature is higher than its low critical solution temperature (LCST). At the same time, due to the simultaneous polymerization of the double-layer hydrogel, the molecular penetration of the gel-gel interface, and the entanglement of the polymer chains with each other, a local topological network structure is formed, greatly enhancing the interfacial toughness of the double-layer hydrogel actuator, improving the stability of the actuator, and enabling repeated use.

[0048] In some embodiments of the present patent application, the first layer hydrogel of the double-layer hydrogel actuator is composed of the following mass fractions of substances: 6% to 15% gelatin (Gelatin), 45% to 75% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of HEAA, and the balance being water. More preferably, the first layer hydrogel of the double-layer hydrogel actuator is composed of the following mass fractions of substances: 10% to 13% gelatin (Gelatin), 50% to 70% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of HEAA, and the balance being water. Controlling the mass fractions of gelatin (Gelatin) and N-hydroxyethyl acrylamide (HEAA) in the first layer hydrogel to the above ranges can ensure that the first layer utilizes the material properties of gelatin (Gelatin) to cool and gel, builds a first network, and realizes a controllable double-layer structure, and uses N-hydroxyethyl acrylamide (HEAA) as a second network, and the obtained Gelatin / PHEAA double-network hydrogel has excellent mechanical properties.

[0049] In some embodiments of the present patent application, the second layer hydrogel of the double-layer hydrogel actuator is composed of the following mass fractions of substances: 25% to 45% N-isopropyl acrylamide (NIPAM), 10% to 40% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of NIPAM and HEAA, and N,N'-methylenebisacrylamide (MBA) added in an amount of 1 mol% of NIPAM, and the balance being water. More preferably, the second layer hydrogel of the double-layer hydrogel actuator is composed of the following mass fractions of substances: 28% to 40% N-isopropyl acrylamide (NIPAM), 10% to 25% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of NIPAM and HEAA, and N,N'-methylenebisacrylamide (MBA) added in an amount of 1 mol% of NIPAM, and the balance being water. Controlling the mass fractions of N-isopropyl acrylamide (NIPAM) and N-hydroxyethyl acrylamide (HEAA) in the second layer hydrogel to the above ranges can enable the second layer to build a poly(N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) (P(NIPAM-co-HEAA)) temperature-sensitive hydrogel, which can rapidly respond when the external temperature is higher than its lower critical solution temperature, as shown in Figure 9

[0050] ​In some embodiments of the present patent application, the double-layer hydrogel actuator is composed of the following mass fractions of substances: the first layer of hydrogel: 12% gelatin, 60% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of HEAA, and the balance being water; the second layer of hydrogel: 30% N-isopropyl acrylamide (NIPAM), 25% N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of NIPAM and HEAA, N,N'-methylenebisacrylamide (MBA) added in an amount of 1 mol% of NIPAM, and the balance being water. The tensile stress of the double-layer hydrogel actuator composed of the above different mass fractions of substances is 241.45 KPa (see Figure 7 ), the tensile strain is 336.40%, and the maximum interfacial toughness is up to 550.11 J / m 2 , as shown in Figure 8 .

[0051] The following is to illustrate that the interfacial toughness of the double-layer hydrogel actuator composed of different mass fractions of substances is different in different embodiments.

[0052] Embodiment 1

[0053] The double-layer hydrogel actuator in this embodiment, abbreviated as HEAA 10 , is composed of the following mass fractions of substances:

[0054] The first layer of hydrogel: gelatin (Gelatin) 12%, N-hydroxyethyl acrylamide (HEAA) 60%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of HEAA, and the balance being water;

[0055] The second layer of hydrogel: N-isopropyl acrylamide (NIPAM) 30%, N-hydroxyethyl acrylamide (HEAA) 10%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) added in an amount of 1 mol% of NIPAM and HEAA, N,N'-methylenebisacrylamide (MBA) added in an amount of 1 mol% of NIPAM, and the balance being H2O.

[0056] It can be measured through experiments that the tensile stress of the double-layer hydrogel actuator in this embodiment is 105.83 KPa (see Figure 7 ), the tensile strain is 298.45%, and the maximum interfacial toughness is 69.48 J / m 2 , as shown in Figure 8 .

[0057] Example 2

[0058] The double-layer hydrogel actuator in this example is abbreviated as HEAA 15 , which is composed of the following mass fractions of substances:

[0059] The first layer of hydrogel: gelatin (Gelatin) 12%, N-hydroxyethyl acrylamide (HEAA) 60%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (added amount is 1 mol% of HEAA), and the balance is water;

[0060] The second layer of hydrogel: N-isopropyl acrylamide (NIPAM) 30%, N-hydroxyethyl acrylamide (HEAA) 15%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (added amount is 1 mol% of NIPAM and HEAA), N,N'-methylene bisacrylamide (MBA) (added amount is 1 mol% of NIPAM), and the balance is water.

[0061] Through experiments, it can be measured that the tensile stress of the double-layer hydrogel actuator in this example is 130.93 KPa (see Figure 7 ), the tensile strain is 225.11%, and the maximum interfacial toughness is 90.59 J / m 2 , as shown in Figure 8 .

[0062] Example 3

[0063] The double-layer hydrogel actuator in this example is abbreviated as HEAA 20 , which is composed of the following mass fractions of substances:

[0064] The first layer of hydrogel: gelatin (Gelatin) 12%, N-hydroxyethyl acrylamide (HEAA) 60%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (added amount is 1 mol% of HEAA), and the balance is water;

[0065] The second layer of hydrogel: N-isopropyl acrylamide (NIPAM) 30%, N-hydroxyethyl acrylamide (HEAA) 20%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (added amount is 1 mol% of NIPAM and HEAA), N,N'-methylene bisacrylamide (MBA) (added amount is 1 mol% of NIPAM), and the balance is water.

[0066] Through experiments, it can be measured that the tensile stress of the double-layer hydrogel actuator in this example is 123.69 KPa (see Figure 7), the tensile strain is 344.52%, and the maximum interfacial toughness is 296.10 J / m 2 As shown in Figure 8 .

[0067] Example 4

[0068] The double-layer hydrogel actuator in this example is abbreviated as HEAA 25 , and is composed of the following mass fractions of substances:

[0069] The first layer of hydrogel: gelatin (Gelatin) 12%, N-hydroxyethyl acrylamide (HEAA) 60%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (added amount is HEAA 1 mol%), and the balance is water;

[0070] The second layer of hydrogel: N-isopropyl acrylamide (NIPAM) 30%, N-hydroxyethyl acrylamide (HEAA) 25%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (added amount is NIPAM and HEAA 1 mol%), N,N'-methylenebisacrylamide (MBA) (added amount is 1 mol% of NIPAM), and the balance is water.

[0071] Through experiments, it can be measured that the tensile stress of the double-layer hydrogel actuator in this example is 241.45 KPa (see Figure 7 ), the tensile strain is 336.40%, and the maximum interfacial toughness is 550.11 J / m 2 As shown in Figure 8 .

[0072] Example 5

[0073] The double-layer hydrogel actuator is composed of the following mass fractions of substances:

[0074] The first hydrogel layer consists of 12% gelatin, 60% N-hydroxyethyl acrylamide (HEAA), and 1 mol% 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (I2959), with the remainder being water. The second hydrogel layer consists of 40% N-isopropylacrylamide (NIPAM), 20% N-hydroxyethylacrylamide (HEAA), 1 mol% 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (I2959), and 1 mol% NIPAM and HEAA, with the remainder being water. This embodiment describes the formulation for a bilayer hydrogel actuator dynamometer experiment. The optimal concentration of N-hydroxyethylacrylamide (HEAA) was selected, and the concentration of N-isopropylacrylamide (NIPAM) was increased to 40%, maximizing the actuator's dynamism while maintaining mechanical properties.

[0075] like Figure 9 As shown, the bilayer hydrogel actuator can achieve different degrees of actuation effect under different temperature environments. It can respond to external stimuli within 30 seconds, and as the ambient temperature gradually increases from 80℃ to 100℃, the bilayer hydrogel actuator in this patent application can respond and bend within just 30 seconds. The degree of bending increases with the response time from 30 seconds to 15 minutes and then to 60 minutes, eventually forming a continuous ring. Throughout the bending process, the bilayer hydrogel actuator does not delaminate. Therefore, the bilayer hydrogel actuator in this patent application achieves satisfactory results by maintaining high interfacial toughness while ensuring rapid actuation capability.

[0076] In addition, such as Figure 5 , Figure 6 As shown, the Gelatin / PHEAA-P (NIPAM-co-HEAA) bilayer hydrogel actuator exhibits a distinct layered structure; see details below. Figure 6 The SEM images clearly show the bilayer structure of the gel. The upper and lower gel layers have significantly different pores and morphologies. These pores and morphologies are mainly related to the crosslinking density of the gel polymer chains, indicating that the two gel layers have different network structures. The pores and morphology at the interface exhibit characteristics of both the upper and lower gel layers, suggesting the formation of a topologically entangled polymer network at the interface. Stress-strain curves ( Figure 7 The results show that the maximum tensile stress of the bilayer hydrogel is 241.45 kPa and the maximum strain is 344.52%; meanwhile, the interfacial toughness curve ( Figure 8 This indicates that the maximum interfacial toughness of the gel-gel interface is 550.11 J / m. 2 .

[0077] According to a second aspect of the present patent application, the present patent application also provides a preparation method of the above-mentioned double-layer hydrogel Figure 1 ), which is simple in operation and easy to obtain a double-layer structure, has driving ability, can ensure the interface toughness, and will not separate in the actual application process. The preparation method of the present patent application comprises the following steps:

[0078] S1 Take appropriate amounts of gelatin (Gelatin), N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl propiophenone (I2959) and water into a glass bottle, and stir at room temperature to obtain a pre-polymer solution A;

[0079] S2 Take appropriate amounts of N-isopropyl acrylamide (NIPAM), N-hydroxyethyl acrylamide (HEAA), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl propiophenone (I2959), and N,N'-methylene bisacrylamide (MBA) into a glass bottle, and stir to obtain a pre-polymer solution B;

[0080] S3 Pour the pre-polymer solution A obtained in step S1 into the assembled mold and cool it;

[0081] S4 Inject the pre-polymer solution B obtained in step S2 into the cavity of the upper layer of the pre-polymer solution A in the mold after cooling in step S3, and stand still to obtain a double-layer hydrogel pre-polymer solution C;

[0082] S5 Place the double-layer hydrogel pre-polymer solution C obtained in step S4 under an ultraviolet lamp to polymerize and obtain a double-layer hydrogel driver.

[0083] In this method, since the double-layer hydrogel is polymerized synchronously, the molecular penetration of the gel-gel interface, the intertangling of the polymer chains, and the formation of a local topological network structure greatly enhance the interface toughness of the double-layer hydrogel driver, improve the stability of the driver, and enable repeated use.

[0084] In addition, the gelatin (Gelatin) in the prepolymer solution A in steps S3 and S4 in the method can be cooled into a gel, and the N-hydroxyethyl acrylamide (HEAA) is not gelled, which ensures the double-layer structure of the gel, and the standing causes the molecular penetration at the interface. In step S5, the N-hydroxyethyl acrylamide (HEAA) which is not gelled is polymerized into a gel synchronously with the prepolymer solution B under ultraviolet light, and the penetrated molecules form a topological entangled gel network at the interface. Step S5 can be explained as follows: under ultraviolet light, the polymer monomers form polymer chains, which are crosslinked with each other to form a hydrogel network. The penetration of the macromolecules at the gel-gel interface causes the entanglement of the interface macromolecular chains, forming a local topological gel network, which provides a certain binding force at the gel-gel interface, making the double-layer hydrogel more closely combined. In the 90° peeling experiment, in order to peel off the double-layer gel, a larger force is needed to destroy the topological network, thereby enhancing the interface toughness.

[0085] Reference Figure 2 In some embodiments of the present patent application, the step S1 in the preparation method of the double-layer hydrogel driver of the present patent application comprises: weighing gelatin (Gelatin) 1.2 g 12wt%, N-hydroxyethyl acrylamide (HEAA) 6 g 60wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl propiophenone (I2959) 0.1169 g (the amount added is 1 mol% of HEAA), and then adding 2.8 g of water into a glass bottle, stirring at room temperature for 15-30 minutes to obtain a prepolymer solution A. In this way, the first layer hydrogel of the double-layer hydrogel driver can utilize the material properties of the gelatin (Gelatin) which is cooled into a gel, construct the first network, realize the controllable double-layer structure, use N-hydroxyethyl acrylamide (HEAA) as the second monomer, construct the second network, and the obtained Gelatin / PHEAA double-network hydrogel has excellent mechanical properties, thereby improving the overall mechanical properties of the driver.

[0086] Reference Figure 3In some embodiments of the present application, step S2 in the preparation method of the double-layer hydrogel actuator of the present application comprises: weighing N-isopropyl acrylamide (NIPAM) 1.2-4.8 g 10-40 wt%, N-hydroxyethyl acrylamide (HEAA) 1.2-3 g 10-25 wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) 0.0472-0.1536 g (added amount is 1 mol% of NIPAM and HEAA), N,N'-methylenebisacrylamide (MBA) 0.0163-0.0654 g (added amount is 1 mol% of NIPAM), and then adding 4.2-9.6 g H2O into a glass bottle, stirring at 20°C for 15-30 min to obtain a prepolymer solution B. In this way, the second layer of the double-layer hydrogel actuator constructs a poly(N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) (P(NIPAM-co-HEAA)) temperature-sensitive hydrogel that can rapidly respond when the external temperature is higher than its lower critical solution temperature (LCST).

[0087] As shown in Figure 4 In some embodiments of the present application, the preparation method of the double-layer hydrogel actuator comprises the following steps:

[0088] S1 weighing gelatin (Gelatin) 1.2 g 12 wt%, N-hydroxyethyl acrylamide (HEAA) 6 g 60 wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) 0.1169 g (added amount is 1 mol% of HEAA), and then adding 2.8 g H2O into a glass bottle, stirring at room temperature for 15-30 min to obtain a prepolymer solution A;

[0089] S2 weighing N-isopropyl acrylamide (NIPAM) 1.2-4.8 g 10-40 wt%, N-hydroxyethyl acrylamide (HEAA) 1.2-3 g 10-25 wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) 0.0472-0.1536 g (added amount is 1 mol% of NIPAM and HEAA), N,N'-methylenebisacrylamide (MBA) 0.0163-0.0654 g (added amount is 1 mol% of NIPAM), and then adding 4.2-9.6 g H2O into a glass bottle, stirring at 20°C for 15-30 min to obtain a prepolymer solution B;

[0090] S3 pouring the prepolymer solution A obtained in step S1 into the assembled mold, sealing the mold after cooling at 20°C for 20-30 min;

[0091] S4 injects the prepolymer liquid B obtained in step S2 into the mold cavity of the upper layer of the prepolymer liquid A cooled in step S3, and stands still at room temperature for 10-20 min to obtain a double-layer hydrogel prepolymer liquid C;

[0092] S5 polymerizes the double-layer hydrogel prepolymer liquid C obtained in step S4 under an 8W ultraviolet lamp at 20°C for 0.5-1.0 h to obtain a double-layer hydrogel actuator.

[0093] In some other embodiments, the assembled mold used in the preparation of the double-layer hydrogel actuator of the present patent application is as shown in Figure 10

[0094] The preparation method of the double-layer hydrogel actuator of the present patent application simplifies the preparation process of the double-layer hydrogel actuator by using the method of synchronous polymerization, fully guarantees the double-layer structure, and forms a topologically entangled polymer network at the interface of the double-layer hydrogel through molecular penetration between the gel-gel interfaces and high molecular chain mutual entanglement, thereby greatly improving the interface toughness of the double-layer hydrogel actuator, thus improving the stability of the actuator and enabling repeated use.

[0095] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0096] Although several embodiments of the present patent application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the claims and their equivalents.​

Claims

1. A bilayer hydrogel actuator, characterized by, Comprising: A first layer hydrogel, the first layer hydrogel being a double network hydrogel, the double network hydrogel comprising a first network of gelatin cooling gelatinization and a second network of N-hydroxyethyl acrylamide, the first layer hydrogel being composed of the following mass percentage (wt%) raw materials: 6wt%-15wt% gelatin, 45wt%-75wt% N-hydroxyethyl acrylamide, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 added in an amount of 1mol% of HEAA, and the balance being water; A second layer hydrogel, the second layer hydrogel being a poly(N-isopropyl acrylamide-co-N-hydroxyethyl acrylamide) temperature-sensitive hydrogel constructed of N-isopropyl acrylamide and N-hydroxyethyl acrylamide, the second layer hydrogel being composed of the following mass percentage (wt%) raw materials: 10wt%-45wt% N-isopropyl acrylamide, 10wt%-40wt% N-hydroxyethyl acrylamide, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 added in an amount of 1mol% of NIPAM and HEAA, N,N'-methylenebisacrylamide MBA added in an amount of 1mol% of NIPAM, and the balance being water; The preparation method of the double-layer hydrogel driver comprises the following steps: S1, respectively, a suitable amount of gelatin, N-hydroxyethyl acrylamide, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 and water are dissolved in a glass bottle, and after stirring at room temperature, a prepolymer solution A is obtained; S2, respectively, a suitable amount of N-isopropyl acrylamide, N-hydroxyethyl acrylamide, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959, N,N'-methylenebisacrylamide MBA, and then water are dissolved in a glass bottle and stirred to obtain a prepolymer solution B; S3, the prepolymer solution A obtained in step S1 is poured into an assembled mold and cooled; S4, the prepolymer solution B obtained in step S2 is injected into the cavity of the mold on the upper layer of the prepolymer solution A cooled in step S3, and is left to stand to obtain a double-layer hydrogel prepolymer solution C; S5, the double-layer hydrogel prepolymer solution C obtained in step S4 is placed under an ultraviolet lamp for polymerization to obtain a double-layer hydrogel driver.

2. The dual-layer hydrogel actuator of claim 1, wherein, The double-layer hydrogel driver is composed of the following mass percentage (wt%) raw materials: The first layer hydrogel: 12wt% gelatin, 60wt% N-hydroxyethyl acrylamide, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 added in an amount of 1mol% of HEAA, and the balance being water; Second layer hydrogel: 30wt% N-isopropyl acrylamide NIPAM, 25wt% N-hydroxyethyl acrylamide HEAA, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 added in an amount of 1mol% of NIPAM and HEAA, N,N'-methylene bisacrylamide MBA added in an amount of 1mol% of NIPAM, and the rest being water.

3. The method of claim 1 or 2, wherein the double-layer hydrogel actuator is prepared by the steps of: The method comprises the following steps: S1 respectively weigh appropriate amount of gelatin Gelatin, N-hydroxyethyl acrylamide HEAA, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 and water into a glass bottle, and after stirring at room temperature, a prepolymer solution A is obtained; S2 respectively weigh appropriate amount of N-isopropyl acrylamide NIPAM, N-hydroxyethyl acrylamide HEAA, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959, and N,N'-methylene bisacrylamide MBA, and then add water into a glass bottle and stir to obtain a prepolymer solution B; S3 pour the prepolymer solution A obtained in step S1 into an assembled mold and cool; S4 inject the prepolymer solution B obtained in step S2 into the cavity of the mold on the upper layer of the prepolymer solution A cooled in step S3, and stand still to obtain a double-layer hydrogel prepolymer solution C; S5 place the double-layer hydrogel prepolymer solution C obtained in step S4 under an ultraviolet lamp to polymerize, and obtain a double-layer hydrogel actuator.

4. The method for preparing the bilayer hydrogel actuator as described in claim 3, characterized in that, The step S1 comprises: S1 respectively weigh appropriate amount of gelatin Gelatin, N-hydroxyethyl acrylamide HEAA, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 and water into a glass bottle, and after stirring at room temperature, a prepolymer solution A is obtained; 5. The method for preparing the bilayer hydrogel actuator as described in claim 3, characterized in that, The step S2 comprises: respectively weigh N-isopropyl acrylamide NIPAM 1.2-4.8g 10-40wt%, N-hydroxyethyl acrylamide HEAA 1.2-3g 10-25wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 added in an amount of 1mol% of NIPAM and HEAA, N,N'-methylene bisacrylamide MBA added in an amount of 1mol% of NIPAM, and then add 4.2-9.6g H2O into a glass bottle and stir at 20°C for 15-30 minutes to obtain a prepolymer solution B.

6. The method for preparing the bilayer hydrogel actuator as described in claim 3, characterized in that, The standing in the step S4 is specifically standing still at room temperature for 10-20 minutes.

7. The method for preparing the bilayer hydrogel actuator as described in claim 3, characterized in that, The method comprises the following steps: S1 respectively weigh appropriate amount of gelatin Gelatin, N-hydroxyethyl acrylamide HEAA, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 and water into a glass bottle, and after stirring at room temperature, a prepolymer solution A is obtained; S1 respectively weigh appropriate amount of gelatin Gelatin, N-hydroxyethyl acrylamide HEAA, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone I2959 and water into a glass bottle, and after stirring at room temperature, a prepolymer solution A is obtained; S2 respectively take N-isopropyl acrylamide NIPAM 1.2~4.8g 10~40wt%, N-hydroxyethyl acrylamide HEAA 1.2~3g 10~25wt%, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl benzophenone I2959 is added to the amount of 1mol% of NIPAM and HEAA, N,N'-methylene bisacrylamide MBA is added to the amount of 1mol% of NIPAM, then 4.2~9.6g water is dissolved in a glass bottle, stirred at 20℃ for 15~30min, to obtain the prepolymer liquid B; S3 pour the prepolymer liquid A obtained in step S1 into the assembled mold, cool at 20℃ for 20~30min, then seal the mold; S4 inject the prepolymer liquid B obtained in step S2 into the upper cavity of the mold of the prepolymer liquid A cooled in step S3, and stand at room temperature for 10~20min to obtain a double-layer hydrogel prepolymer liquid C; S5 place the double-layer hydrogel prepolymer liquid C obtained in step S4 under an 8W ultraviolet lamp at 20℃ for 0.5~1.0h to obtain a double-layer hydrogel drive.

Images