CN112300412A

CN112300412A - Ionic hydrogel and preparation method thereof

Info

Publication number: CN112300412A
Application number: CN202011294231.XA
Authority: CN
Inventors: 胡宁; 文杰; 宁慧铭; 唐佳
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2020-11-18
Filing date: 2020-11-18
Publication date: 2021-02-02
Anticipated expiration: 2040-11-18
Also published as: CN112300412B

Abstract

The invention provides an ionic hydrogel and a preparation method thereof, and the ionic hydrogel comprises the following steps: preparing hydroxyapatite nanowire slurry; adding tannic acid into the prepared hydroxyapatite nanowire slurry, adjusting the pH value of the solution to be alkalescent, and stirring to obtain a hydroxyapatite nanowire suspension wrapped by tannic acid; adding ethylene glycol, PVA and aluminum trichloride into the tannin-coated hydroxyapatite nanowire suspension, uniformly mixing, stirring the mixture at 90-100 ℃ until the PVA is completely dissolved, and then sequentially freezing and thawing the mixture for 2-5 times in a circulating freeze-thaw mode to obtain the nano-particle. The gel can effectively solve the problems of poor freezing resistance, poor ultraviolet resistance, poor mechanical property, simple sensing function and short service life of the existing hydrogel.

Description

Ionic hydrogel and preparation method thereof

Technical Field

The invention belongs to the technical field of ionic hydrogel, and particularly relates to ionic hydrogel and a preparation method thereof.

Background

Ionic hydrogels are considered to be a strong candidate for replacing biomass-capable skin. It has similar functions as human skin, for example being able to sense different types of forces (tension and pressure) and temperature changes. In addition, it has functions not possessed by human skin, such as: the ability to sense ultrasonic and humidity changes, and the ability to photochromize. In the field of ionic hydrogel, hydrogel has gradually become a hot point of research at home and abroad.

However, at present, the ionic hydrogel has the following defects:

1. under normal temperature and humidity, the hydrogel is easy to dehydrate, so that long-term effective work can not be carried out when the hydrogel is in contact with the outside;

2. under a low-temperature environment, free water in the hydrogel is easy to freeze;

3. the transparent hydrogel often lacks the function of ultraviolet shielding, and limits the application of the transparent hydrogel in certain special environments, such as plateau, high altitude or space areas with strong ultraviolet;

4. the sensing function is simple, i.e. it usually responds to only one physical quantity and not to a plurality of physical quantities.

5. The mechanical properties are poor and usually cannot withstand high tensile deformation or compressive stress.

Therefore, it is important to develop a highly conductive hydrogel which is antifreezing at low temperature, ultraviolet resistant, good in mechanical properties, multi-mode sensing performance and capable of working effectively for a long time.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides the ionic hydrogel and the preparation method thereof, and the method can effectively solve the problems of poor freezing resistance, poor ultraviolet resistance, poor mechanical property, simple sensing function and short effective service life of the conventional hydrogel.

In order to achieve the purpose, the technical scheme adopted by the invention for solving the technical problems is as follows:

a preparation method of ionic hydrogel comprises the following steps:

(1) preparing hydroxyapatite nanowire slurry;

(2) adding water and tannic acid into the hydroxyapatite nanowire slurry prepared in the step (1), adjusting the pH value of the solution to be alkalescent, and stirring to obtain a hydroxyapatite nanowire suspension wrapped by tannic acid;

(3) adding ethylene glycol, PVA and aluminum trichloride into the tannin-coated hydroxyapatite nanowire suspension in the step (2), uniformly mixing, stirring the mixture at 90-100 ℃ until PVA is completely dissolved, freezing the mixture, then unfreezing, and performing cyclic freeze thawing for 2-5 times to obtain the tannin-coated hydroxyapatite nanowire suspension.

In the scheme, the tannic acid is coated on the surface of the hydroxyapatite nanowire, and the tannin has strong hydrophilicity, so that the hydroxyapatite nanowire coated with the tannic acid shows good uniform distribution in water, and great help is brought to the improvement of the mechanical property of the hydrogel; the tannic acid with a proper nano size is coated on the hydroxyapatite nanowire, so that ultraviolet rays with a shorter wavelength can be reflected, visible light with a longer wavelength is allowed to pass through, the ultraviolet rays can be reflected, and the transparency is realized; the special catechol group of the tannic acid has an absorption effect on ultraviolet light waves and can play an anti-ultraviolet role; tannic acid and metal ion Al³⁺Has chelating effect to make metal ions Al³⁺The hydrogel can be uniformly distributed in a binary solvent, so that the conductivity of the hydrogel is improved; and metal ion Al³⁺The sensor can move more quickly in a molecular level ion water channel formed by glycol molecules and water molecules, so that the sensitivity of strain sensing is greatly improved.

Further, the specific operation process in the step (1) is as follows: mixing oleic acid, methanol and deionized water to obtain a mixed solution, respectively dropwise adding a sodium hydroxide solution, an anhydrous calcium chloride solution and a disodium hydrogen phosphate dihydrate solution into the mixed solution under the stirring condition, then reacting the final mixture at the temperature of 150 ℃ and 200 ℃ to obtain a hydrothermal product, respectively washing the hydrothermal product with ethanol and deionized water, and then carrying out constant weight until the concentration is 3-4mgmL^-1And (4) preparing.

Further, the weight was constant to a concentration of 3.44mgmL^-1。

In the scheme, the hydroxyapatite prepared by the method is of a nanowire structure, the mechanical strength of the hydrogel can be improved by the structure, and meanwhile, the method is simple and convenient to operate, can be used for mass production, and is low in production cost.

Furthermore, the volume ratio of the oleic acid to the methanol to the deionized water is 6-8:3-5: 8-10.

Further, the volume ratio of oleic acid, methanol and deionized water was 7:4: 9.

Further, the adding amount of the tannic acid in the step (2) is equal to the weight of the hydroxyapatite nanowire slurry.

In the scheme, the same amount of tannic acid is added, so that the tannic acid is uniformly distributed on the surface of the hydroxyapatite nanowire.

Further, the pH value is adjusted to 7.5-8.5 by using a 1M Tris buffer solution in the step (2).

Further, the pH value was adjusted to 8.0 with a buffer of 1M Tris buffer in step (2).

In the scheme, the hydroxyapatite nanowire and the tannic acid react under the alkalescent condition, and the tannic acid can be oxidized and deposited on the surface of the hydroxyapatite nanowire, so that the tannic acid is coated.

Further, the stirring time in the step (2) is 4-7 h.

Further, the stirring time in the step (2) is 5 hours.

In the scheme, the stirring reaction is carried out for 4-7h, so that the reaction between the tannic acid and the hydroxyapatite nanowire is more thorough, and the tannic acid is more completely oxidized and deposited on the surface of the tannin.

Furthermore, the adding amount of the ethylene glycol in the step (3) is equal to the volume of water in the suspension, the adding amount of the PVA is 2-6 wt% of the mass of the tannin-coated hydroxyapatite nanowire, and the molar concentration of the aluminum trichloride in the suspension is 0.08-0.2M after the aluminum trichloride is added.

Further, the adding amount of PVA in the step (3) is 4 wt% of the mass of the tannin-coated hydroxyapatite nanowire, and the molar concentration of aluminum trichloride in the suspension after the aluminum trichloride is added is 0.1M.

Further, in the step (3), freezing for 20-25h at-30 to-40 ℃ and unfreezing at room temperature.

Further, in the step (3), the freeze thawing is performed for 3 times in a circulating way.

In the scheme, in the process of freezing at the temperature of-30 to-40 ℃ and unfreezing at room temperature, the crystalline domain of the polyvinyl alcohol is improved, so that the mechanical property of the ionic skin is improved.

The beneficial effects produced by the invention are as follows: the network structure formed by polyvinyl alcohol in the ionic hydrogel is used as a matrix structure of the hydrogel to provide basic mechanical properties for the ionic skin, the hydroxyapatite nanowire coated with tannic acid is a nano-enhanced filler and also forms a network structure, and a large number of hydrogen bonds can be formed among the hydroxyapatite nanowire coated with tannic acid, PVA and ethylene glycol, so that strong interaction exists between the hydroxyapatite nanowire network coated with tannic acid and the PVA network, and the overall mechanical properties of the ionic skin can be improved by improving the formed network.

The tannic acid is coated on the surface of the hydroxyapatite nanowire, and the tannic acid has hydrophilicity, so that the dispersion uniformity of the hydroxyapatite nanowire in a matrix network structure can be improved, and the overall mechanical property of the hydrogel is further improved.

Because the hydroxyapatite nano-wires have a reflection effect on ultraviolet rays with short wavelengths but cannot block visible light with long wavelengths, according to the size effect, the ionic skin can reflect the ultraviolet rays and transmit the visible light, and because tannic acid has a strong absorption effect on ultraviolet light waves, the anti-ultraviolet capability of the ionic hydrogel is further improved; .

Al in aluminum trichloride³⁺Higher valence state and stronger conductivity, and can provide free moving Al for hydrogel system³⁺As an ion conductor, the sensing performance of the ion skin is further improved; the strong hydrogen bond action among glycol, water and polyvinyl alcohol in the reaction system ensures that the system has the performances of high temperature moisture preservation and low temperature freeze prevention, and simultaneously, the molecular level formed by the separation of glycol moleculesThe ion water channel enables the ion skin to have higher sensitivity in a larger strain range.

Drawings

FIG. 1 is a graph of visible spectral transmittance of a hydrogel;

FIG. 2 is a graph of hydrogel UV spectral transmittance;

FIG. 3 is a histogram of the transmission of three 1.5mm thick hydrogels at the 365nm and 550nm spectral bands;

FIG. 4 is a diagram of hydrogel performance in a live mouse;

FIG. 5 is a micrograph of mouse skin tissue after UV irradiation;

FIG. 6 is a graph showing the weight change of three hydrogels;

FIG. 7 is a graph of the heat flow change for three hydrogels;

FIG. 8 is a graph demonstrating the use of hydrogel as a resistance variable wire at-30 ℃;

FIG. 9 is a diagram of hydrogel performance in a live mouse;

FIG. 10 is a micrograph of mouse skin tissue after freezing;

FIG. 11 is a graph of tensile stress-strain curves for different hydrogels;

FIG. 12 is a graph of mean and standard deviation of tensile stress and tensile strain;

FIG. 13 is a graph of the mean and standard deviation of the elastic modulus and toughness values;

FIG. 14 is a graph of compressive stress-strain curves for different hydrogels;

FIG. 15 hydrogel relative rate of change of resistance versus strain graph;

FIG. 16 is a graph of resistance change at 50% strain;

FIG. 17 is a graph of the time response at 50% tensile strain;

FIG. 18 is a graph of relative rate of change of capacitance versus pressure for a pressure sensor;

FIG. 19 is a graph of relative rate of resistance change versus temperature for a temperature sensor;

FIG. 20 is a tensile strain response diagram of a human finger joint demonstration;

FIG. 21 is a tensile strain sensing diagram of a human arm joint demonstration;

FIG. 22 is a tensile strain sensing diagram of a human knee joint demonstration;

FIG. 23 is a drawing strain response diagram at micro-puff;

FIG. 24 is a graph of tensile strain response with wide mouth;

fig. 25 is a drawing of tensile strain induction graphs of different tones o;

FIG. 26 is a graph of tensile strain response during blinking;

FIG. 27 is a graph showing the induction of tensile strain at the time of frown.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings.

Example 1

An ionic hydrogel, the preparation method of which comprises the following steps:

(1) the preparation method of the hydroxyapatite nanowire slurry comprises the following specific operation processes: mixing 21mL of oleic acid, 12mL of methanol and 27mL of deionized water to obtain a mixed solution, respectively dropwise adding a sodium hydroxide solution (2.1g, 30mL), an anhydrous calcium chloride solution (0.67g, 24mL) and a disodium hydrogen phosphate dihydrate solution (1.87g, 36mL) into the mixed solution under the stirring condition of 500rpm, continuously dropwise adding the next solution at intervals of 20min after each dropwise adding of one solution, then reacting the final mixture at the constant temperature of 180 ℃ for 24h to obtain a hydrothermal product, respectively washing the hydrothermal product for 3 times by using ethanol and deionized water, and then carrying out constant weight until the concentration is 3.44mgmL^-1And (4) preparing;

(2) adding water into the hydroxyapatite nanowire slurry prepared in the step (1) to 15ml, then adding tannic acid with the same weight as the hydroxyapatite nanowire slurry, adjusting the pH value of the solution to 8.0 by using 1M Tris buffer solution, and stirring for 4 hours to obtain a tannic acid-coated hydroxyapatite nanowire suspension;

(3) adding 15ml of ethylene glycol, 80mmol of PVA and 3mmol of aluminum trichloride into the tannin-coated hydroxyapatite nanowire suspension in the step (2), uniformly mixing, stirring the mixture at 90 ℃ until the PVA is completely dissolved, freezing the mixture at-30 ℃ for 22h, then unfreezing at room temperature, and performing cyclic freeze-thaw for 3 times to obtain the tannin-coated hydroxyapatite nanowire suspension.

Example 2

(2) adding water into the hydroxyapatite nanowire slurry prepared in the step (1) to 15ml, then adding tannic acid with the same weight as the hydroxyapatite nanowire slurry, adjusting the pH value of the solution to 7.5 by using 1M Tris buffer solution, and stirring for 6 hours to obtain a tannic acid-coated hydroxyapatite nanowire suspension;

(3) adding 15ml of ethylene glycol, 80mmol of PVA and 3mmol of aluminum trichloride into the tannin-coated hydroxyapatite nanowire suspension in the step (2), uniformly mixing, stirring the mixture at 100 ℃ until the PVA is completely dissolved, freezing the mixture at-35 ℃ for 24h, then unfreezing at room temperature, and performing cyclic freeze-thaw for 2 times to obtain the tannin-coated hydroxyapatite nanowire suspension.

Example 3

(1) the preparation method of the hydroxyapatite nanowire slurry comprises the following specific operation processes: mixing 21mL of oleic acid, 12mL of methanol and 27mL of deionized water to obtain a mixed solution, respectively dropwise adding a sodium hydroxide solution (2.1g, 30mL), an anhydrous calcium chloride solution (0.67g, 24mL) and a disodium hydrogen phosphate dihydrate solution (1.87g, 36mL) into the mixed solution under the stirring condition of 500rpm, and after one solution is dropwise added, continuously dropwise adding the next solution at intervals of 20minReacting the final mixture at 180 ℃ for 24h to obtain a hydrothermal product, washing the hydrothermal product with ethanol and deionized water for 3 times respectively, and then carrying out constant weight until the concentration is 3.44mgmL^-1And (4) preparing;

(2) adding water into the hydroxyapatite nanowire slurry prepared in the step (1) to 15ml, then adding tannic acid with the same weight as the hydroxyapatite nanowire slurry, adjusting the pH value of the solution to 8.5 by using 1M Tris buffer solution, and stirring for 5 hours to obtain a tannic acid-coated hydroxyapatite nanowire suspension;

(3) adding 15ml of ethylene glycol, 80mmol of PVA and 3mmol of aluminum trichloride into the tannin-coated hydroxyapatite nanowire suspension in the step (2), uniformly mixing, stirring the mixture at 95 ℃ until the PVA is completely dissolved, freezing the mixture at-40 ℃ for 20h, then unfreezing at room temperature, and performing cyclic freeze-thaw for 4 times to obtain the tannin-coated hydroxyapatite nanowire suspension.

Comparative example 1

adding 80mmol of PVA and 3mmol of aluminum trichloride into the hydroxyapatite nanowire suspension, uniformly mixing, stirring the mixture at 95 ℃ until the PVA is completely dissolved, freezing the mixture at-40 ℃ for 20h, then unfreezing at room temperature, and carrying out cyclic freeze-thawing for 4 times to obtain the hydroxyapatite nanowire suspension.

Comparative example 2

adding 15ml of ethylene glycol, 80mmol of PVA and 3mmol of aluminum trichloride into the hydroxyapatite nanowire suspension, uniformly mixing, stirring the mixture at 95 ℃ until the PVA is completely dissolved, freezing the mixture at-40 ℃ for 20h, then unfreezing at room temperature, and carrying out cyclic freeze-thaw for 4 times to obtain the hydroxyapatite nanowire suspension.

Test examples

Taking example 1 as an example, the performance test of the hydrogels in example 1, comparative example 1 and comparative example 2 is as follows:

1. ultraviolet ray filtering capability test: the hydrogels of example 1, comparative example 1 and comparative example 2 were tested for uv filtering ability by the following procedure: the ultraviolet transmittance and the visible light transmittance of the PVA (W), the PVA (W/EG) and the TA @ HAP NWs-PVA (W/EG) hydrogel are measured by an ultraviolet-visible-near infrared spectrophotometer (Shimadzu UV-3600), and the transparency and the ultraviolet resistance of the PVA-based hydrogel are characterized. Each set of samples had a thickness of 1.5mm and a wavelength range of 200nm to 780 nm. The specific test results are shown in FIGS. 1-5.

As can be seen from FIG. 1, the transmittances of the hydrogels PVA (W), PVA (EG/W) and TA @ HAP NWs-PVA (EG/W) for the characteristic wavelength of 550nm were 40%, 89%, 60%, respectively. Although the TA @ HAP NWs-PVA (EG/W) hydrogel showed a decrease in transmittance as compared with the PVA (EG/W) hydrogel, it was generally a transparent hydrogel.

As can be seen from FIG. 2, the UV filtering properties of the TA @ HAP NWs-PVA (EG/W) hydrogel are very strong, reflecting almost all UV light, relative to the PVA (W) and PVA (EG/W) hydrogels. This property of reflecting ultraviolet light and transmitting visible light is derived from the microscopic properties of the TA @ HAP NWs filler. Although TA @ HAP NWs are essentially not transparent, they are suitably nanoscale in size. It has a reflective effect on shorter wavelength ultraviolet light but is not able to block longer wavelength visible light.

As can be seen from FIG. 4, in the demonstration of the hydrogel as the ultraviolet-proof dressing for the live mice, two adjacent areas were first selected on the back of BALB/C mice, the hydrogel dressing protection area of the experimental group and the unprotected area of the control group were respectively divided, and the hydrogel in example 1 and the hydrogel in comparative example 1 were respectively coated in the protection area. Next, an ultraviolet lamp (40mW cm)^-2365nm) were irradiated for 1h on the area of the experimental group and the control group, respectively. Finally, the experimental group and the control group were subjected to visual observation and tissue section analysis. The absence of abnormalities in the areas protected by the hydrogel dressing was visually observed in the visual observation of the experimental and control groups, while the skin in the unprotected areas was visibly burned.

As can be seen from fig. 5, the skin structure of the experimental group is complete and clear; the cells are clearly divided; the cell components and the number are moderate; the epidermis layer, the dermis layer and the basal layer are tightly connected. The control group has obvious skin fracture and damage, and local continuity is interrupted; the thickness of the horny layer is increased, nucleus contraction and deformation can be seen occasionally, neutrophil infiltration can be seen occasionally in the dermal layer, and collagen fibers appearing in the transparent layer are locally broken, the integrity is damaged, and the continuity is interrupted. In summary, TA @ HAP NWs-PVA (EG/W) hydrogels having excellent UV-filtering ability and transparency are more suitable for "ionized skin" and for use in UV-filtering skin dressings.

2. And (4) moisture retention performance test: the hydrogels prepared in example 1, comparative example 1 and comparative example 2 were tested for their moisturizing properties by the following procedure: PVA (W), PVA (W/EG), and TA @ HAP NWs-PVA (W/EG) hydrogels (2 cm in diameter, 1cm in thickness) of the same shape were placed in a constant temperature and humidity chamber for 10 days. To simulate human body temperature and dry environment, the temperature was set at 37 ℃ and humidity was 40%. The hydrogel was weighed daily for a fixed period of time. The specific test results are shown in fig. 6.

As can be observed from the moisture retention curves of FIG. 6, the water loss weights of the PVA (W/EG) hydrogel and the 4 wt% TA @ HAP NWs-PVA (W/EG) hydrogel at day 4 were in a converged state; PVA (W/EG) at day 10 had a high weight retention of 71 wt%, and 4 wt% TA @ HAP NWs-PVA (W/EG) also had a high weight retention of 72 wt%; whereas the PVA (W) hydrogel appeared to converge on day 2, with only a low weight retention of 15 wt% on day 10. The reason for this high moisture retention at high temperatures and in extremely dry environments is that many strong hydrogen bonds are formed between PVA, EG and water molecules. Under the interaction, water locking effect is generated, free water molecules can be ensured not to be easily evaporated, and meanwhile, the strong hydrogen bonds can inhibit the free water from freezing at low temperature. In conclusion, the moisture retention of TA @ HAP NWs-PVA (W/EG) is significantly improved compared to conventional hydrogels.

3. And (3) testing the anti-freezing performance: the hydrogels prepared in example 1, comparative example 1 and comparative example 2 were tested for freezing resistance by the following procedure: the freezing temperatures of PVA (W), PVA (W/EG) and TA @ HAP NWs-PVA (W/EG) hydrogels were determined by differential scanning calorimetry (NETZSCCH DSC 214). The temperature of the sample was reduced from 30 ℃ to-100 ℃ at a rate of 5 ℃ min-1 under a nitrogen atmosphere. The test results are shown in FIGS. 7-10.

As can be seen from FIG. 7, the PVA (W) hydrogel exhibited an exothermic peak at-21 ℃ in the range of 30 ℃ to-100 ℃ due to free water coagulation. The PVA (EG/W) hydrogel and the TA @ HAP NWs-PVA (EG/W) hydrogel do not have any exothermic peak, and the PVA and the TA @ HAP NWs-PVA all have excellent frost resistance.

As can be seen from FIG. 8, in the anti-freezing demonstration, at-30 ℃, the TA @ HAP NWs-PVA (EG/W) hydrogel can still be used as a variable resistance wire, and the brightness of the LED lamp is gradually darkened with the increase of strain. These all indicate that the TA @ HAP NWs-PVA (EG/W) hydrogel still has good electrochemical properties at extremely low temperatures.

As can be seen from fig. 9, in the demonstration of the live mice as the antifreeze dressing, two adjacent areas were first selected on the back of Sprague Dawley (SD) white rats, the protected areas were divided into the hydrogel dressing areas of the experimental group and the unprotected areas of the control group, and the hydrogels of example 1 and comparative example 1 were applied on the protected areas, respectively. Second, two stainless steel plates, previously cooled in liquid nitrogen, were placed on the areas of the experimental group and the control group, respectively, and left for 1 min. Finally, the experimental group and the control group were subjected to visual observation and tissue section analysis. The absence of abnormalities in the areas protected by the hydrogel dressing was visually observed in the visual observations of the experimental and control groups, whereas the skin in the unprotected areas was visibly frostbitten.

As can be seen from fig. 10, histological section analysis of this revealed that the area protected with the hydrogel dressing had a continuous intact epidermal layer, tightly connected collagen fibers and evenly distributed hair follicles; the unprotected area has locally thinned and interrupted cuticle layer, damaged and broken collagen fiber in the dermis, damaged hair follicle (elliptical area), etc. In conclusion, the TA @ HAP NWs-PVA (EG/W) hydrogel having excellent freezing resistance can be used in an extremely low temperature environment without adversely affecting mechanical properties and electrochemical properties, and can be applied to an anti-freezing dressing.

4. And (3) testing mechanical properties: for instance, a pair of fruitsThe mechanical properties of the hydrogel in example 1, the hydrogels with different PVA concentrations prepared according to the method in example 1, the hydrogel in comparative example 1 and the hydrogel in comparative example 2 were tested, and the specific test procedures were as follows: mechanical testing of all samples was performed using a universal testing machine (EZ-LX, Shimadzu, Japan) with 100N or 5000N load cells. The length, width and thickness of the tensile specimen were 50 mm. times.10 mm. times.0.15 mm. The gauge length of the test is 15mm, and the stretching speed is 20mmmin^-1. The diameter and thickness of the compressed sample were both 2cm × 1cm, and the compression rate was 5mm min^-1. The tensile or compressive stress is calculated by dividing the force (F) by the cross-sectional area (A)

Toughness is defined by the area integral of the stress-strain curve. The test results are shown in FIGS. 11-14.

As can be seen from FIGS. 11-13, in a certain range (0 wt% to 4 wt%), the tensile strength, tensile strain and toughness of the hydrogel increased with increasing TA @ HAP NWs content; whereas, when the amount exceeds 4% by weight, the tensile strength, tensile strain and toughness of the hydrogel tend to be opposite. I.e., ultimate tensile strength (0.36MPa), ultimate tensile strain (480%) and toughness (937.403 KJm%) at 4 wt% TA @ HAP NWs content^-3) A maximum value is reached. The ultimate tensile strength, ultimate tensile strain and toughness were increased by 100%, 180% and 330% respectively, relative to pure PVA (EG/W) hydrogels. Furthermore, while the tensile modulus of the hydrogel decreased with increasing TA @ HAP NWs content, at 4 wt% TA @ HAP NWs content, the tensile modulus was 80 KPa. The modulus value still meets the requirement of the required Young modulus of human skin. In short, the TA @ HAP NWs filler can significantly improve the mechanical properties of PVA-based hydrogels. This improvement may be associated with the formation of a number of hydrogen bonds between the TA @ HAP NWs, PVA and EG, and therefore an interaction between the TA @ HAP NWs network and the PVA network. Because a double-network structure is formed, energy applied from the outside is cooperatively dissipated, and the mechanical property is greatly improved.

As can be seen from FIG. 14, the same conclusion can be drawn in the stress-strain relationship plot in the compression test, that is, the compressive strength (80% compressive strain) reaches a maximum (1.90MPa) at a 4 wt% TA @ HAP NWs content. At a 4 wt% TA @ HAP NWs content, the most significant is the tensile and compressive properties.

5. Sensitivity testing of hydrogels for sensor applications: the hydrogel in the example 1 is prepared into a sensor, and the sensitivity of the sensor is tested, wherein the specific test process is as follows: in the strain sensing experiment, UTM machine was used for 20mm min^-1The stretching rate of (a) stretches the hydrogel-based sensor unidirectionally. In the pressure sensing experiment, the hydrogel-based sensor was compressed using a UTM machine at a compression rate of 1mm min^-1. In temperature sensing experiments, a high and low temperature environmental test chamber (DELATA 903) was used to control the test temperature of hydrogel-based sensors. The strain sensitivity of a hydrogel-based sensor is calculated by the strain coefficient (GF), which is defined as the ratio of the rate of change of the relative resistance to the applied strain.

GF＝[(R-R₀)/R₀]/s

In the formula, R₀The initial resistance, R the real time resistance, and ε the applied strain.

Likewise, the sensitivity of a pressure sensor is defined by the ratio of the rate of change of relative capacitance to the applied pressure.

S＝[(C-C₀)/C₀]/σ

C₀Initial capacitance, C real-time capacitance, and σ applied compressive stress.

Meanwhile, the sensitivity of the temperature sensor is determined by the ratio of the relative resistance change rate to the ambient temperature₀)/R]/T

Wherein is R₀Initial resistance, R is the real-time resistance, and T is the ambient temperature. The test results are shown in FIGS. 15-19.

It can be seen from fig. 15 that the relative resistance change rate becomes larger with the increase of strain (maximum strain is 350%), and is in a linear proportional relationship (linearity R)²＝0.99003)。

As can be seen from FIG. 16, at a strain of 50%, the stretching rate is 100mmmin^-1In this case, the TA @ HAP NWs-PVA (EG/W) hydrogel-based strain sensor was able to operate stably for 6000s (300 cycles), indicating its excellent stability.

As can be seen from fig. 17, a time response of 51ms for loading and 59ms for unloading can be obtained in the 50% tensile strain-time curve and the corresponding resistance-time curve. This value is almost half of the time response of human skin (generally, the time response of human skin is about 100 ms), which is enough to show that the TA @ HAP NWs-PVA (EG/W) hydrogel has rapid signal responsiveness, and is expected to be a substitute for the human skin sensing function.

As can be seen from FIG. 18, the sensitivity of the pressure sensor is 0.0085kPa^-1Linear R²Is 0.99086. These results indicate that the TA @ HAP NWs-PVA (EG/W) hydrogel can be used for pressure detection and has high linearity and sensitivity.

As can be seen from FIG. 19, the temperature sensitivity was calculated to be 0.00536 deg.C^-1And a degree of linearity R²0.99367. Although the hydrogel-based temperature sensor gradually melts when the temperature exceeds 80 c, so that the sensor loses its original function, it is sufficient for daily use. Therefore TA @ HAP

NWs-PVA (EG/W) hydrogel based temperature sensors have great potential in the temperature sensor field.

6. The hydrogel as a sensor is used for sensitivity test of human body, the hydrogel in the embodiment 1 is respectively placed on different parts of human body, and the relative resistance change is detected, and the specific result is shown in figures 20-27.

By taking 20-27, the A @ HAP NWs-PVA (EG/W) hydrogel tensile strain sensor has excellent performance in detecting large strains of human finger joints, elbows, knees and the like. It can recognize the bending of finger joints and elbows at 45 °, 90 ° and 180 °. At the same time, it is also able to identify the half-flexion state and the full-flexion state of the knee (maintained in flexion state 3 s). It can also be used to detect facial micro-expression changes such as micro-mouth, macro-mouth, different pitch "o" sound, blinking, frowning and anger.

Claims

1. A preparation method of ionic hydrogel is characterized by comprising the following steps:

(1) preparing hydroxyapatite nanowire slurry;

(2) adding tannic acid into the hydroxyapatite nanowire slurry prepared in the step (1), adjusting the pH value of the solution to be alkalescent, and stirring to obtain a hydroxyapatite nanowire suspension wrapped by tannic acid;

(3) adding ethylene glycol, PVA and aluminum trichloride into the tannin-coated hydroxyapatite nanowire suspension in the step (2), uniformly mixing, stirring the mixture at 90-100 ℃ until PVA is completely dissolved, then sequentially freezing and thawing the mixture, and performing cyclic freeze-thawing for 2-5 times to obtain the tannin-coated hydroxyapatite nanowire suspension.

2. The method for preparing ionic hydrogel according to claim 1, wherein the specific operation process in the step (1) is as follows: mixing oleic acid, methanol and deionized water to obtain a mixed solution, respectively dropwise adding a sodium hydroxide solution, an anhydrous calcium chloride solution and a disodium hydrogen phosphate dihydrate solution into the mixed solution under the stirring condition, then reacting the final mixture at the temperature of 150-200 ℃ to obtain a hydrothermal product, and respectively washing the hydrothermal product with ethanol and deionized water to obtain the catalyst.

3. The method of claim 2, wherein the volume ratio of oleic acid, methanol and deionized water is 6-8:3-5: 8-10.

4. The method for preparing an ionic hydrogel according to claim 1, wherein the amount of the tannic acid added in the step (2) is equal to the weight of the hydroxyapatite nanowire slurry.

5. The method of preparing an ionic hydrogel according to claim 1, wherein the pH is adjusted to 7.5 to 8.5 in step (2).

6. The method of claim 1, wherein the stirring time in step (2) is 4 to 7 hours.

7. The method for preparing ionic hydrogel according to claim 1, wherein the amount of ethylene glycol added in step (3) is equal to the volume of water in the suspension, the amount of PVA added is 2-6 wt% of the mass of the tannin-coated hydroxyapatite nanowire, and the molar concentration of aluminum trichloride in the suspension after the aluminum trichloride is added is 0.08-0.2M.

8. The method for preparing ionic hydrogel according to claim 1, wherein in the step (3), the ionic hydrogel is frozen at-30 to-40 ℃ for 20-25h and then thawed at room temperature.

9. The method of claim 1, wherein the step (3) is performed by 3 cycles of freeze-thawing.

10. An ionic hydrogel prepared by the method of any one of claims 1 to 9.