Intrinsic anti-freezing hydrogel as well as preparation method and application thereof

Abstract

The invention provides intrinsic anti-freezing hydrogel as well as a preparation method and application thereof. The preparation method of the intrinsic anti-freezing hydrogel comprises the step of introducing the polymer with the reverse thermal gel property into a hydrogel system to obtain the intrinsic anti-freezing hydrogel. The invention provides a new strategy for realizing'intrinsic freezing resistance 'of the hydrogel by introducing intelligent macromolecules with reverse thermal gel properties without depending on additional micromolecular antifreeze agents.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrogel, in particular to an intrinsic anti-freezing hydrogel and a preparation method and application thereof. BACKGROUND

[0002] Hydrogel is a kind of polymer material with three-dimensional network structure, which is concerned in the field of flexible strain sensor due to its excellent flexibility, stretchability and conductivity. However, the traditional hydrogel is prone to freezing, and its mechanical properties will degrade at very low temperature, which seriously limits its practical application in low temperature environment.

[0003] Therefore, to improve the anti-freezing performance of hydrogel material, mainly can be realized by reducing its freezing point and inhibiting water molecule crystallization. Among them, the freezing point can be reduced by adding cryoprotective agents such as polyols and ionic compounds; and the strategy of inhibiting water molecule crystallization includes reducing the free water content in hydrogel, introducing nucleation inhibitor, and enhancing the restraining effect of polymer network on water molecules to inhibit ice crystal formation.

[0004] However, in the conductive hydrogel system, high concentration of organic salt can give good ion conductivity and anti-freezing property to the hydrogel, but it may damage its mechanical properties; ionic liquid is limited in practical application in wearable electronic devices due to its high toxicity and high cost; in addition, small molecule reagents such as glycerol will inevitably leak due to physical mixing in the polymer network, which will affect the repeated use performance of hydrogel devices. At present, the preparation of pure polymer hydrogel without any anti-freezing additives and with intrinsic anti-freezing performance is considered as the key direction to solve the above problems.

[0005] Regarding the intrinsic anti-freezing hydrogel, researchers have carried out relevant exploration, and the core mechanism is to introduce dense hydrogen bond groups in the polymer chain segment. These functional groups can interact with water molecules through hydrogen bonds, destroy the original hydrogen bond network between water molecules, inhibit the ordered arrangement of water molecules in the environment below zero, effectively prevent ice crystal formation, and finally give the hydrogel anti-freezing performance. For example, Zheng et al. designed an ethyl glycol derivative crosslinker with more hydrogen bond sites, which successfully delayed the freezing time of the hydrogel without adding antifreeze; Wu et al. prepared a supramolecular hydrogel with intrinsic anti-freezing property by polymerization of monomer acrylamide and methyl methacrylate. Even if it is immersed in liquid nitrogen, the dense hydrogen bond interaction can still keep the hydrogel transparent. In the currently reported anti-freezing hydrogel system, there is still a common situation of relying on small molecule crosslinking agent or small molecule functional unit, which can easily lead to insufficient long-term stability of the hydrogel, and further restrict the improvement of its anti-freezing durability and mechanical properties. Therefore, it is urgent to design a new type of intrinsic anti-freezing hydrogel with macromolecular structure as the core to break through the bottleneck of the existing technology. SUMMARY

[0006] The present application aims at the problem that small molecules in the prior art easily lead to insufficient long-term stability of hydrogel, and provides an intrinsic anti-freezing hydrogel as well as a preparation method and application thereof.

[0007] The technical method of the present application is as follows: The preparation method of the intrinsic anti-freezing hydrogel comprises: introducing a reverse thermal gelation property polymer into a hydrogel system to obtain the intrinsic anti-freezing hydrogel.

[0008] The reverse thermal gelation property polymer is poloxamer. Further, the type of the poloxamer is 407.

[0009] The base material of the hydrogel system comprises one or more of acrylic acid, hydroxyethyl methacrylate, acrylamide, sodium alginate, chitosan, and carboxymethyl cellulose.

[0010] Further, when the base material of the hydrogel system is selected from one or more of acrylic acid, acrylamide, sodium alginate, chitosan, and carboxymethyl cellulose, the step of introducing the reverse thermal gelation property polymer into the hydrogel system comprises: stirring the base material of the hydrogel system, sodium dodecyl sulfate, a poloxamer 407 aqueous solution, N,N'-methylenebisacrylamide, and a photoinitiator uniformly to obtain a hydrogel precursor solution; and irradiating the gel precursor solution under ultraviolet light to obtain the intrinsic anti-freezing hydrogel. Further, the mass ratio of the base material of the hydrogel system, the sodium dodecyl sulfate, the poloxamer 407 aqueous solution, the N,N'-methylenebisacrylamide, and the photoinitiator is 1-6:0-0.05:1-10:0-0.05:0.01-0.05. The irradiation under ultraviolet light comprises: the wavelength of the ultraviolet light is 220-370 nm, preferably 365 nm, and the light irradiation time is 0.1-4 h. The concentration of the poloxamer 407 aqueous solution is 20%-40%.

[0011] Further, when the base material of the hydrogel system is selected from one or more of hydroxyethyl acrylate, acrylamide, sodium alginate, chitosan, carboxymethyl cellulose, the step of introducing the reverse thermal gelation property polymer into the hydrogel system comprises: stirring the base material of the hydrogel system, the poloxamer 407 aqueous solution, cetyltrimethylammonium bromide, lauryl methacrylate uniformly to obtain a hydrogel precursor solution; irradiating the hydrogel precursor solution under ultraviolet light to obtain the intrinsic anti-freezing hydrogel. Further, the mass ratio of the base material of the hydrogel system, the poloxamer 407 aqueous solution, cetyltrimethylammonium bromide, lauryl methacrylate and the photoinitiator is: 1-6: 1-10: 0-0.4: 0-0.1: 0.01-0.05. The ultraviolet light irradiation conditions comprise: the wavelength of the ultraviolet light is 220-370 nm, preferably 365 nm, and the light irradiation time is 0.1-4 h. The concentration of the poloxamer 407 aqueous solution is 20%-40%.

[0012] The application further provides an intrinsic anti-freezing hydrogel prepared by the above-mentioned method.

[0013] The application further provides an application of the intrinsic anti-freezing hydrogel to a flexible electronic device.

[0014] The application has the following beneficial effects: I. The application proposes a new strategy for realizing intrinsic anti-freezing of hydrogel by introducing intelligent macromolecules with reverse thermal gelation property instead of relying on additional small-molecule anti-freezing agents. Specifically, the polymer with reverse thermal gelation property can destroy the regular hydrogen bond network of water at the molecular level by virtue of its unique amphiphilic structure and special interaction with water molecules, thereby realizing intrinsic anti-freezing of the hydrogel.

[0015] II. The hydrogel material prepared by the application expands the application boundary of hydrogel materials by aiming at the actual needs of flexible electronic devices in extreme environments such as severe cold. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Schematic diagram of the reverse thermal gelation property hydrogel; Figure 2 Preparation process diagram of Example 1; Figure 3 PAA (x) -P407 (y) @SDS (z) Tensile curve, toughness and elastic modulus diagram of the hydrogel; wherein, Figure 3 (a) is a tensile curve diagram of the hydrogel after polymerization of acrylic acid and 40wt% poloxamer 407 aqueous solution in different proportions; Figure 3(b) Tensile curves of hydrogels with different sodium dodecyl sulfate content; Figure 3 (c) Tensile curves of hydrogels prepared with different content of MBA crosslinker; Figure 4 PAA (2) -40% P407 (4) @ SDS 0.02 Hydrogel performance chart; wherein, Figure 4 PAA (2) -40% P407 (4) @ SDS 0.02 Hydrogel adhesion to different substrates (plastic, rubber, glass, weight, ceramic) and to human skin schematic diagram; Figure 4 (b) Schematic diagram of lap shear test; Figure 4 PAA (2) -40% P407 (4) @ SDS 0.02 Hydrogel adhesion strength determination chart to different substrates (paper, wood, plastic, glass); Figure 4 PAA (2) -40% P407 (4) @ SDS 0.02 Hydrogel repeated adhesion behavior chart to different substrates (paper, wood, plastic, glass); Figure 5 Temperature performance chart of hydrogels after poloxamer 407 aqueous solution with different mass fraction (20%, 30%, 40%) and acrylic acid polymerization; wherein, Figure 5 (a) Comparison chart of hydrogels after poloxamer 407 aqueous solution with different mass fraction (20%, 30%, 40%) and acrylic acid polymerization before and after being frozen in-20 ℃ refrigerator for 2h; Figure 5 (b) DSC chart of hydrogels after poloxamer 407 aqueous solution with different mass fraction (20%, 30%, 40%) and acrylic acid polymerization in temperature range of-60-25 ℃; Figure 6 Performance chart of hydrogels after poloxamer 407 aqueous solution with different mass fraction and P-HEMA polymerization; wherein, Figure 6 (a) Stress-strain curve chart of hydrogels after poloxamer 407 aqueous solution with different mass fraction and P-HEMA polymerization; Figure 6 (b) Stress-strain curve chart of hydrogels after 40 wt% poloxamer 407 aqueous solution with different proportion and P-HEMA polymerization; Figure 6 (c) Stress-strain curve chart of hydrogels after adding different mass ratio of LMA / CTAB; Figure 7The temperature performance diagram of the hydrogel after HEMA polymerization with P407 aqueous solution of different mass fractions (20wt%, 30wt%, 40wt%); Figure 7 (a) The picture of the hydrogel after HEMA polymerization with P407 aqueous solution of different mass fractions (20wt%, 30wt%, 40wt%) before and after freezing in the refrigerator for 2h; Figure 7 (b) The DSC result diagram of the hydrogel after HEMA polymerization with P407 aqueous solution of different mass fractions (20wt%, 30wt%, 40wt%) in the temperature range of-60 ℃-25 ℃; Figure 8 The resistance signal change diagram of the hydrogel for monitoring the human body; wherein, Figure 8 (a) The resistance signal change diagram of the hydrogel for monitoring the human elbow; Figure 8 (b) The resistance signal change diagram of the hydrogel for monitoring the human finger; Figure 8 (c) The resistance signal change diagram of the hydrogel for monitoring the human wrist bending; Figure 8 (d) The resistance signal change diagram of the hydrogel for monitoring the human smile; Figure 8 (e) The resistance signal change diagram of the hydrogel for monitoring the human raising eyebrows; Figure 8 (f) The resistance signal change diagram of the hydrogel for monitoring the human swallowing; Figure 9 The Morse code diagram; wherein, Figure 9 (a) The Morse code table; Figure 9 (b) The schematic diagram of the Morse code corresponding to the point and line of the different degrees of finger bending; Figure 10 The signal recognition letter diagram output by the hydrogel sensor; wherein, Figure 10 (a) The diagram of recognizing different letters "A", "B", "C" by the signal output by the hydrogel sensor; Figure 10 (b) The diagram of recognizing different letters "x", "y", "z" by the signal output by the hydrogel sensor; Figure 10 (c) The diagram of recognizing different letters "0", "3" by the signal output by the hydrogel sensor; Figure 10 (d) The diagram of recognizing different letters "6", "8" by the signal output by the hydrogel sensor; Figure 11 The diagram of recognizing different text information by the signal output by the HEMA (2) -40%P407 (3) @L1C2 hydrogel sensor; wherein, Figure 11 (a) The diagram of recognizing different text information by the signal output by the HEMA (2) -40%P407 (3)L1C2 hydrogel sensor output signal identifies "H", "U", "T" figure; Figure 11 (b) by HEMA (2) -40% P407 (3) L1C2 hydrogel sensor output signal identifies "C", "O", "L", "D" figure; Figure 11 (c) by HEMA (2) -40% P407 (3) L1C2 hydrogel sensor output signal identifies "S", "O", "S" figure; Figure 11 (d) by HEMA (2) -40% P407 (3) L1C2 hydrogel sensor output signal identifies "H", "E", "L", "P" figure. DETAILED DESCRIPTION

[0017] The present application will be further described in conjunction with experimental examples and specific embodiments. However, it should not be understood that the scope of the above-mentioned subject matter of the present application is limited to the following examples, and any technology realized based on the content of the present application falls within the scope of the present application.

[0018] The concept of the present application: reverse thermal gelation property hydrogel material exhibits unique temperature dependence: liquid at low temperature, and gel at high temperature. As shown in Figure 1 low temperature environment, the hydrophilic fragments or groups in the material will combine with water molecules and dissolve in the solution; when the temperature rises, the molecular chain dehydrates, and then aggregates to form a gel through hydrophobic interaction. This kind of material realizes the characteristics of low-temperature dissolution and high-temperature gelation by regulating the dynamic balance of hydrophilic-hydrophobic interaction. Because it is in liquid state at low temperature, it can guarantee good flowability, which is highly consistent with the demand of hydrogel for antifreeze performance: liquid state is conducive to maintaining the flexibility of hydrogel and ensuring the normal play of its functions. Therefore, the inventors believe that introducing polymers with reverse thermal gelation property into the hydrogel system is of great significance for preparing high-performance antifreeze hydrogel, and will also provide a new strategy for solving the antifreeze problem of hydrogel.

[0019] In a first aspect, the present application provides a preparation method of intrinsic antifreeze hydrogel, which comprises: introducing a polymer with reverse thermal gelation property into a hydrogel system to obtain an intrinsic antifreeze hydrogel.

[0020] In an embodiment, the base material of the hydrogel system comprises one or more of acrylic acid (AA), hydroxyethyl methacrylate (HEMA), acrylamide (AM), sodium alginate (CA), chitosan (CS), carboxymethyl cellulose (CMC). Here, the hydrogel base material is the basis of the network that constitutes the hydrogel, endows it with excellent mechanical properties, and enables the hydrogel system to be functionalized, such as electrically conductive, adhesive, self-healing, etc.

[0021] In an embodiment, the inverse thermogelling property polymer is poloxamer. Further, the type of poloxamer is 407. Poloxamers of the present application are a typical inverse thermogelling hydrogel material. They are amphiphilic triblock copolymers composed of polyethylene oxide (PEO) and polypropylene oxide (PPO) in different proportions. Poloxamer 407 (P407) is a type of poloxamer with a PEO / PPO ratio of 7:3, which has good water solubility. At low temperature (<4℃), it is a flowable liquid. As the temperature increases, its viscosity increases sharply, and at body temperature it forms a semi-solid gel. This behavior is due to the fact that P407 has better solubility in cold water than in hot water. At lower temperatures, P407 exists in the solution in monomer form. As the temperature increases, the hydrophobic interaction increases, causing the PPO segment to dehydrate. Then, P407 self-assembles into spherical micelles, with PPO forming the core and PEO forming the shell. As the temperature further increases, the micelles stack in an orderly manner, promoting gel formation. The unique inverse thermogelling properties, non-toxicity and biocompatibility of P407 make it have wide application prospects in the fields of drug delivery and biomedicine.

[0022] In an embodiment, when the base material of the hydrogel system is selected from one or more of acrylic acid, acrylamide, sodium alginate, chitosan, carboxymethyl cellulose, the step of introducing the inverse thermogelling property polymer into the hydrogel system comprises: stirring the base material of the hydrogel system, sodium dodecyl sulfate (SDS), poloxamer 407 aqueous solution (P407), N,N'-methylenebisacrylamide (MBA) and photoinitiator to obtain a hydrogel precursor solution; irradiating the gel precursor solution under ultraviolet light to obtain an intrinsic freeze-resistant hydrogel. For example, the base material of the gel system can be acrylic acid, acrylamide, acrylic acid / sodium alginate / chitosan / carboxymethyl cellulose.

[0023] Here, the acrylic acid and sodium dodecyl sulfate are stirred and mixed until completely uniform, then the poloxamer 407 aqueous solution, methacrylic acid, and photoinitiator are added and stirred until completely mixed to obtain a hydrogel precursor solution. The mass ratio of the base material of the hydrogel system, the sodium dodecyl sulfate, the poloxamer 407 aqueous solution, the N,N'-methylenebisacrylamide, and the photoinitiator is 1-6:0-0.05:1-10:0-0.05:0.01-0.05. The conditions for irradiation under ultraviolet light include: the wavelength of the ultraviolet light is 220-370 nm, and the light irradiation time is 0.1-4 h. The concentration of the poloxamer 407 aqueous solution is 20%-40%.

[0024] In an embodiment, when the base material of the hydrogel system is selected from one or more of hydroxyethyl acrylate, acrylamide, sodium alginate, chitosan, and carboxymethyl cellulose, the base material of the hydrogel system, the poloxamer 407 aqueous solution (P407), cetyltrimethylammonium bromide (CTAB), and lauryl methacrylate (LMA) are stirred and mixed until uniform to obtain a hydrogel precursor solution; the hydrogel precursor solution is irradiated under ultraviolet light to obtain an intrinsic antifreeze hydrogel. The conditions for irradiation under ultraviolet light include: the wavelength of the ultraviolet light is 360-370 nm, preferably 365 nm, and the light irradiation time is 0.1-4 h. The concentration of the poloxamer 407 aqueous solution is 20%-40%.

[0025] In a second aspect, the present application also provides an intrinsic antifreeze hydrogel, which is obtained by the above-mentioned method for preparing an intrinsic antifreeze hydrogel.

[0026] In a third aspect, the present application also provides the use of an intrinsic antifreeze hydrogel in a flexible electronic device. Here, the flexible electronic device includes a pressure sensor, a strain sensor, and the like.

[0027] In the present application, all the raw materials for preparation are commercially available products well known to those skilled in the art, unless otherwise specified.

[0028] Example 1 The present embodiment provides a method for preparing an intrinsic antifreeze hydrogel, which includes the following steps: Step 1: Prepare a 40% P407 aqueous solution in advance; Step 2: Stir and mix AA and SDS until completely uniform, then add the P407 aqueous solution, MBA, and photoinitiator and stir until completely mixed to obtain a hydrogel precursor solution; wherein AA: 4 g, SDS: 0.02 g, 40% P407: 4 g, MBA: 0.02 g, and photoinitiator: 0.04 g.

[0029] Step 3: The hydrogel precursor solution was left to stand to remove air bubbles, then the hydrogel precursor solution was poured into the mold and irradiated under a 10 W ultraviolet lamp at 365 nm for 2 h (or a 50 W ultraviolet lamp for 10 min) to obtain the target hydrogel PAA(x)-P407(y)@SDSz, wherein x, y and z respectively represent the mass of AA, P407 and SDS.

[0030] The role of this embodiment AA is to provide a framework for the hydrogel and endow it with viscosity. The solubility of P407 at low temperature endows the hydrogel with antifreeze performance. SDS can form mixed micelles with P407, thereby endowing it with electrical conductivity and enhancing the mechanical properties. The preparation process is as shown in Figure 2 .

[0031] In summary, the hydrogel prepared in this embodiment has good mechanical properties (breaking strain 1254.91%, breaking stress 224 KPa) and adhesion ability, and can be firmly attached to various substrates, while having excellent low-temperature antifreeze performance. The hydrogel can be used as a strain sensor to capture subtle human movements, and as a writing sensor to identify different symbolic handwriting, and still maintains excellent flexibility and electrical conductivity under low-temperature conditions (-20°C).

[0032] In this embodiment, as shown in Table 1, the concentration of P407 can be adjusted in the range of 20%~40%, and the effects of key parameters such as P407 concentration, AA and SDS ratio, and crosslinking density on the network structure and performance of the hydrogel are systematically studied.

[0033] Table 1 PAA (x) -P407 (y) @SDS (z) Detailed preparation ratio of hydrogel The effects of the ratio of different materials on the mechanical properties of the hydrogel were investigated. First, the content of the poloxamer 407 aqueous solution, the stress-strain curves of the hydrogel after polymerization of acrylic acid with different proportions of 40 wt% poloxamer 407 aqueous solution are as shown in Figure 3 a, with the increase of the proportion of poloxamer 407 aqueous solution, the elongation of the hydrogel also gradually increases, because the micelles formed by poloxamer 407 can form hydrogen bonding with the polyacrylic acid segment, enhancing the tensile properties of the hydrogel. When the mass ratio of acrylic acid to 40 wt% poloxamer 407 aqueous solution is 2:4, the tensile properties of the hydrogel are best, and when the content of poloxamer 407 is further increased, the over-crosslinked polymer network will limit the movement of the molecular chain, resulting in a decrease in the elongation of the hydrogel. Considering the comprehensive mechanical properties of the material, we selected PAA(2)-40%P407(4) hydrogel for further proportion adjustment.

[0034] Next, we explored the effect of the content of sodium dodecyl sulfate on the mechanical properties of the material. The stress-strain curves of hydrogels with different contents of sodium dodecyl sulfate are shown in Figure 3 b. The addition of a small amount of sodium dodecyl sulfate can effectively improve the mechanical properties of the material. This is because the poloxamer 407 and sodium dodecyl sulfate form Plouonic-rich SDS mixed micelles after mixing. Compared with single poloxamer 407 micelles, the prepared hydrogel has better mechanical properties. However, too much sodium dodecyl sulfate dispersed in the hydrogel will affect the mechanical properties of the material. Therefore, we selected PAA (2) -40%P407 (4) @SDS 0.02 The preparation ratio of the hydrogel is optimal, and the corresponding tensile strain is 1254.91%, and the stress is 224 KPa.

[0035] We also adjusted the content of the crosslinking agent MBA of the material. When MBA = 0.001, the material has the best stress and strain ( Figure 3 c). Too high crosslinking density limits the elongation of the material.

[0036] PAA (2) -40%P407 (4) @SDS 0.02 The hydrogel has rich hydrogen bonding interactions and has good adhesion to various substrates such as plastic, rubber, glass, weights, ceramics, etc. It can also be attached to human skin, as shown in Figure 4 a, showing its advantages as a flexible strain sensor. The adhesion performance of the hydrogel was further quantified by lap shear testing, Figure 4 b is a schematic diagram of lap shear testing. The hydrogel was placed between two identical substrates to measure the adhesion strength. The results are shown in Figure 4 c. Under the same contact area, the adhesion of the hydrogel to paper, glass, plastic, and paper is in the order of paper > wood > plastic > glass. After repeated adhesion, the adhesion performance of the hydrogel did not decrease significantly ( Figure 4 d). The adhesion of the hydrogel to plastic is due to hydrogen bonding and hydrophobic interactions, while the adhesion to paper, wood, and glass is due to the rich hydrogen bonding interactions within the hydrogel. PAA (2) -40%P407 (4) @SDS 0.02 The firm, durable, and repeatable adhesion of the hydrogel can achieve more comfortable contact and help accurately monitor the generation of subtle signals, making the hydrogel have more extensive sensor application scenarios.

[0037] In order to explore whether the addition of poloxamer 407 can make the hydrogel have anti-freezing ability, the mass ratio of acrylic acid to poloxamer 407 aqueous solution is fixed at 2:4, the hydrogel after polymerization of acrylic acid and poloxamer 407 aqueous solution with different mass fractions (20wt%, 30wt%, 40wt%) is placed in a refrigerator at-20℃ for 2h, and differential scanning calorimetry (DSC) is used to study the quantitative relationship between the content of poloxamer 407 and the anti-freezing ability of the hydrogel. The schematic diagram of the hydrogel after polymerization of poloxamer 407 aqueous solution with different mass fractions before and after being placed in the refrigerator for 2h is shown in FIGS. a and b. Figure 5 As can be seen from the figures, when the mass fraction of poloxamer 407 aqueous solution is 20wt%, the hydrogel after polymerization turns white after being frozen in the refrigerator, and with the increase of the content of poloxamer 407, the appearance of the hydrogel after freezing still remains transparent, and DSC (b) shows that the cold crystallization peak of the hydrogel gradually decreases with the increase of the content of poloxamer 407, and even disappears. The results show that the addition of poloxamer 407 can effectively prevent water molecules from crystallizing at low temperature, so that the hydrogel shows anti-freezing property. Figure 5

[0038] Example 2 The present embodiment provides a preparation method of intrinsic anti-freezing hydrogel, comprising the following steps: Step 1: prepare 40% P407 aqueous solution in advance; Step 2: mix a certain mass of HEMA, CTAB and LMA until completely uniform, then add a certain mass fraction of P407 aqueous solution and photoinitiator and stir until completely mixed to obtain a hydrogel precursor solution; wherein HEMA: 4g, CTAB: 0.1g, LMA: 0.05g, photoinitiator: 0.04g, 40% P407: 6g.

[0039] Step 3: let the hydrogel precursor solution stand to remove bubbles, then pour the hydrogel precursor solution into a mold and irradiate under a 365nm 10W ultraviolet lamp for 1h to obtain the target hydrogel HEMA-P407@LC.

[0040] In the present embodiment, CTAB and LMA are combined as hydrophobic crosslinking points to enhance the mechanical properties and conductivity of the hydrogel.

[0041] ​The hydrogel exhibits good mechanical properties (fracture strain of 539.36%, fracture stress of 328.68 KPa) and electrical conductivity (GF = 2.27 in the strain range of 0-100%) and still retains good transmission ability at low temperature (-20 ℃). The hydrogel can be used as a flexible strain sensor to monitor the movement of different parts of the human body. The hydrogel sensor is combined with Morse code to simulate the transmission of simple information at low temperature.

[0042] Among them, as shown in Table 2, the effects of key parameters such as P407 concentration, HEMA, CTAB and LMA ratio, crosslinking density, etc. on the network structure (micro-morphology, pore size distribution) of the hydrogel are systematically studied.

[0043] Table 2. HEMA (a)- R%P407 (b) @ L x C y Detailed preparation ratio of hydrogel A series of tensile tests were performed on the hydrogels with different component ratios using a universal testing machine to demonstrate the effects of various structures on mechanical properties.

[0044] First, the content of poloxamer 407 and the effect of P-HEMA were analyzed. The stress-strain curves of the hydrogels after polymerization of poloxamer 407 aqueous solution with different mass fractions and P-HEMA in different proportions are shown in Figure 6 a. When the mass fraction of poloxamer 407 aqueous solution is increased to 40 wt%, the mechanical properties of the hydrogel are greatly improved, and the stress-strain increases from 78.98 KPa, 134.80% (HEMA (2) -20%P407 (3) ) to 213.86 KPa, 457.16% (HEMA (2) -40%P407 (3) ).

[0045] Further, the ratio of 40 wt% poloxamer 407 aqueous solution and P-HEMA is discussed. The stress-strain curves of the hydrogels after polymerization of 40 wt% poloxamer 407 aqueous solution and HEMA in different proportions are tested, as shown in Figure 6As shown in b, it can be seen that as the content of poloxamer 407 in HEMA gradually increases, the polymerized hydrogel first shows a trend of increasing elongation at break and decreasing tensile strength. Subsequently, both elongation at break and tensile strength decrease simultaneously. This indicates that the addition of an appropriate amount of poloxamer 407 can increase the extensibility of the hydrogel. However, an excessive proportion of poloxamer 407 aqueous solution will cause both elongation at break and tensile strength of the hydrogel to decrease simultaneously, thus damaging the mechanical properties of the hydrogel. Therefore, based on a comprehensive consideration of mechanical properties, a hydrogel with a ratio of 2:3 of HEMA and 40% poloxamer 407 aqueous solution was selected for subsequent testing. Its elongation at break was 457.91%, and its tensile strength was 213.44 kPa.

[0046] To improve the mechanical properties of the material, CTAB and LMA are added to the hydrogel. The hydrophobic LMA groups and the cationic surfactant CTAB can form micelles through hydrophobic interactions, increasing the number and density of hydrophobic crosslinking points. When the LMA / CTAB mass ratio increases, the elongation at break and the tensile strength of the hydrogel first increase and then decrease. Figure 6 c) When the mass ratio of LMA / CTAB is 1:2, the elongation at break of the hydrogel is 539.36% and the tensile strength is 328.68 kPa. However, the presence of excessive CTAB will reduce the local hydrophobic concentration and hinder the hydrophobic crosslinking strength. Therefore, when the mass ratio of LMA / CTAB is further increased, the mechanical properties of the hydrogel will decrease.

[0047] Based on the analysis of the above results, we selected HEMA. (2) -40%P407 (3) Further application research will be conducted on the @L1C2 hydrogel.

[0048] Low-temperature freezing observation and DSC testing demonstrated that the addition of an appropriate amount of poloxamer 407 imparted freeze-thaw resistance to the polymer PHEMA. Figure 7 As shown, with a constant HEMA mass fraction, different amounts of poloxamer 407 aqueous solution (20wt%, 30wt%, 40wt%) were used to prepare corresponding gels, and their appearance after being frozen for 2 hours was observed. Figure 7 As can be seen from Figure a, the hydrogel polymerized with a 20 wt% poloxamer 407 aqueous solution turned into a white and opaque color after freezing, while the hydrogel polymerized with a 30 wt% poloxamer 407 aqueous solution remained transparent after freezing for 2 hours. Figure 7The DSC test results of b further verified the difference between the melting and crystallization temperatures. The DSC curve of the hydrogel after polymerization of 20wt% poloxamer 407 aqueous solution showed a melting peak at -8.3 ℃, and a cold crystallization peak at -39.4 ℃. The melting peak of the hydrogel after polymerization of HEMA with 30wt% poloxamer 407 aqueous solution shifted from -8.3 ℃ to -9.6 ℃, and a thermal crystallization peak at -48.0 ℃ appeared. When the concentration of poloxamer 407 aqueous solution increased to 40wt%, only a melting peak at -16.5 ℃ appeared in the DSC curve, and no crystallization peak appeared, so the appearance of the hydrogel remained transparent after freezing for 2h, and no ice crystals existed. In subsequent studies, 40wt% poloxamer 407 aqueous solution was selected.

[0049] As shown in Figure 8 , the hydrogel can reflect the large range of joint movements of the human body such as elbow, finger, wrist bending, and the resistance change value of the hydrogel increases during the bending process, and the resistance returns to the initial value after straightening. During the same movement process, the amplitude of the resistance change value of the hydrogel remains basically consistent. The hydrogel can also monitor the subtle changes of human body movements such as smiling, raising eyebrows, and throat swallowing, and shows unique and stable waveforms. As a strain sensor, the hydrogel shows high sensitivity and stability, and has great potential in human health and movement monitoring.

[0050] The international Morse code general table is shown in Figure 9 a. The figure lists the Morse code representation of each letter and number in detail. Since each letter and symbol is a unique signal composed of dots, lines and pauses in between, simple information can be transmitted very quickly by controlling the time of finger bending. The triangular electrical signal formed by quickly bending the finger is defined as "·" in Morse code, and the rectangular electrical signal output by staying longer is represented by "—" in Morse code. By changing the electrical signal generated by finger bending, information output and decoding encryption are realized, as shown in Figure 9 b.

[0051] As shown in Figure 10 a, the letter "A" in Morse code is composed of a short signal "·" and a long signal "—". During the transmission process, the hydrogel is only fixed on the finger, and the letter "A" information can be easily transmitted by simply bending the finger once quickly and then slowly bending the finger once. By controlling the pause time during transmission, the same information can be accurately conveyed multiple times. The same applies to different letters and numbers Figure 10 b-d).

[0052] As shown in Figure 11As shown, for example, by arranging different letters, it is possible to communicate information such as "HUT" for injured, "HELP" for help, "SOS" for first aid, "COLD" for cold, and the like, in this way sending out a distress signal, seeking help from others.

[0053] While embodiments of the present application have been shown and described, it is to be understood that the embodiments described are merely divergences of the principles and spirit of the present application and that numerous modifications, changes, substitutions, and alterations can be made thereto without departing from the spirit and scope of the present application as defined by the appended claims and their equivalents.

Claims

1. A method for preparing an intrinsic antifreeze hydrogel, characterized by, The preparation method comprises: introducing a reverse thermal gel property polymer into a hydrogel system to obtain an intrinsic anti-freezing hydrogel.

2. The production method according to claim 1, characterized by, The reverse thermal gel property polymer is a poloxamer.

3. The production method according to claim 2, characterized by, The poloxamer is poloxamer 407.

4. The production method according to claim 3, characterized by, The base material of the hydrogel system comprises one or more of acrylic acid, hydroxyethyl methacrylate, acrylamide, sodium alginate, chitosan, and carboxymethyl cellulose.

5. The production method according to claim 4, characterized by, When the base material of the hydrogel system is selected from one or more of acrylic acid, acrylamide, sodium alginate, chitosan, and carboxymethyl cellulose, the step of introducing the reverse thermal gel property polymer into the hydrogel system comprises: stirring the base material of the hydrogel system, sodium dodecyl sulfate, a poloxamer 407 aqueous solution, N,N'-methylenebisacrylamide, and a photoinitiator uniformly to obtain a hydrogel precursor solution; irradiating the hydrogel precursor solution under ultraviolet light to obtain the intrinsic anti-freezing hydrogel.

6. The production method according to claim 5, wherein The mass ratio of the base material of the hydrogel system, sodium dodecyl sulfate, the poloxamer 407 aqueous solution, N,N'-methylenebisacrylamide, and the photoinitiator is 1-6:0-0.05:1-10:0-0.05:0.01-0.

05.

7. The preparation method according to claim 5, characterized in that, The irradiation under ultraviolet light comprises: the wavelength of the ultraviolet light is 220-370 nm, and the irradiation time is 0.1-4 h.

8. The preparation method according to claim 4, characterized in that, When the base material of the hydrogel system is selected from one or more of hydroxyethyl methacrylate, acrylamide, sodium alginate, chitosan, and carboxymethyl cellulose, the step of introducing the reverse thermal gel property polymer into the hydrogel system comprises: stirring the base material of the hydrogel system, a poloxamer 407 aqueous solution, cetyltrimethylammonium bromide, and lauryl methacrylate uniformly to obtain a hydrogel precursor solution; irradiating the hydrogel precursor solution under ultraviolet light to obtain the intrinsic anti-freezing hydrogel.

9. An intrinsic antifreeze hydrogel characterized in that, The intrinsic anti-freezing hydrogel is obtained by the preparation method of the intrinsic anti-freezing hydrogel according to any one of claims 1-8.

10. Use of the intrinsic anti-freezing hydrogel according to claim 9 on a flexible electronic device.

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