Preparation of sprayable phase change hydrogel and application of sprayable phase change hydrogel in bionic skin

Abstract

The invention aims to disclose a preparation method of sprayable phase change hydrogel and application of the sprayable phase change hydrogel in the field of robot bionic skin. In order to solve the problems that existing hydrogel is insufficient in mechanical property, low in transformation temperature, high in interface impedance, limited in industrial large-scale spraying and the like, a non-covalent cross-linking enhancement strategy is provided by introducing two-dimensional Ti3C2Tx MXene nanosheets into a gelatin matrix. MXene and gelatin synergistically stabilize a triple helix biological molecular structure through hydrogen bonds, ionic bonds and electrostatic interaction, so that the phase transition temperature of the composite hydrogel (GM hydrogel) is increased from 35 DEG C to 44 DEG C, and the mechanical strength of the composite hydrogel is remarkably improved. The hydrogel has solution sprayability and in-situ gelation characteristics, can form a super-conformal seamless interface with the skin / robot surface, can be widely applied to electronic skin, human-computer interaction interfaces and medical monitoring equipment, and provides a new way for industrial scale manufacturing of flexible bionic sensors.

Description

Technical Field

[0001] The object of the present invention is to improve the thermal conversion temperature of phase change hydrogels and the application of robotic bionic skin through non-covalent interaction enhancement strategies. Specifically, it involves generating hydrogen bonds and coordination interactions between MXene nanosheets containing rich functional groups and gelatin hydrogels. The resulting hydrogels have high mechanical properties, electrical conductivity, and low interfacial impedance. In addition, the reversible transition of this temperature-responsive solution-hydrogel provides a new solution for the large-scale preparation of robotic skin by spraying method, enabling it to be more widely used in robotic bionic skin. Background Art

[0002] As a natural biosensing interface, the surface area of the human skin can reach about 2 square meters, and it realizes the interactive perception and neurocognitive processing of a wide range of environmental information through the multimodal mechanoreceptor network distributed therein. Bionic skin electronic devices developed based on the principle of bionics are committed to replicating the unique sensing function of the skin in bionic robots. They can serve as the core sensing layer of bionic robot skin and also promote the breakthrough development of a new generation of bioelectronic devices in fields such as personalized medical monitoring. However, existing bionic skin electronic devices usually have problems such as poor interface contact, high interface impedance, and imperfect compliance, resulting in limited sensory functions. It is worth noting that the phase change hydrogel material system exhibits unique liquid-solid reversible phase change characteristics, and its dynamic phase change behavior endows the material with two core advantages: (1) through the synergistic effect of sprayability and in-situ gelation, it can effectively achieve high conformal contact and continuous compliant fitting with the human skin (especially in multi-hairy or wrinkled areas); (2) based on the liquid coating and processing characteristics, the material exhibits excellent large-scale processing adaptability, providing an innovative technical route for the industrial-level manufacturing of high-performance bionic robot skin devices. Summary of the Invention

[0003] The object of the present invention is to improve the temperature tolerance by enhancing the thermal conversion ability of phase change hydrogels through non-covalent interactions, and then to achieve wide applications in bionic robot skin electronic devices by spraying and other means.

[0004] To achieve the above object, the design idea of the present invention is as follows:

[0005] By introducing MXene flakes with rich surface functional groups into the gelatin-based phase change hydrogel (GM), the formation of reversible non-covalent crosslinks (such as hydrogen bonds) is promoted to stabilize the triple-helix biomolecules in gelatin and increase the transition temperature of the GM hydrogel. In addition, other additives such as borax are added to generate additional hydrogen bonds and electrostatic interactions, further strengthening the gelatin-MXene network. The performance of the gelatin-based phase change hydrogel obtained by the above method is significantly improved. The transition temperature of the GM hydrogel increases from about 35 °C to 44 °C, which is higher than the human skin temperature, demonstrating its potential in the application of robotic bionic skin sensors.

[0006] From the perspective of practical applications, we designed a commercial portable heating device to achieve the transition of the phase change hydrogel from the gel state to the liquid state in a portable manner. It can establish a highly conformal contact and seamless electronic interface with the bionic robot through in-situ gelation after spraying, laying a good foundation for the preparation of the new generation of robotic bionic skin.

[0007] Advantages of the present invention:

[0008] The GM hydrogel prepared in the present invention forms various types of non-covalent interactions (such as hydrogen bonds, ionic bonds, and electrostatic interactions) by introducing MXene nanosheets with rich surface functional groups (-F, -O, -OH) into the phase change hydrogel matrix. It increases the phase transition temperature and enables the hydrogel to have high mechanical properties, high electrical conductivity, and low interfacial impedance. It is widely used in the large-scale preparation of robotic bionic skin and other aspects through methods such as spraying in-situ gelation. At the same time, a commercial portable heating device is self-made, which can quickly achieve the transition from the gel state to the liquid state through thermal induction, laying a good foundation for the preparation of the new generation of robotic bionic skin. Description of the Drawings

[0009] Figure 1 Schematic diagram of the large-scale preparation of robotic bionic skin by spraying method and its application in the present invention.

[0010] Figure 2 Thermal conversion mechanism diagram of the GM phase change hydrogel in the present invention.

[0011] Figure 3 Device diagram for the solid-liquid transition of the hydrogel realized by a commercial portable heating device.

[0012] Figure 4 Rheological characterization of hydrogel solutions with different formulations under temperature scanning from 75 °C to 10 °C in the present invention.

[0013] Figure 5 Photos and infrared camera images of the GM hydrogel prepared in the present invention at high temperature (55 °C) and room temperature (25 °C).

[0014] Figure 6 Photographs of the GM hydrogel directly sprayed and in-situ formed on (A) a flat surface and (B) the wrinkled part of human skin, and (C) the GM hydrogel made into the desired shape.

[0015] Figure 7 Photograph images of the GM phase change hydrogel prepared by the present invention in the original state and the stretched state.

[0016] Figure 8 Cyclic adhesion test of the GM hydrogel prepared by the present invention in-situ generated on the bendable part (such as joints) of human skin.

[0017] Figure 9 Stress-strain curves of the GM hydrogels prepared by the present invention with different MXene contents (0 wt%, 0.05 wt%, 0.05 wt%, 0.1 wt% and 0.4 wt%).

[0018] Figure 10 Stress-strain curves of the adhesion test of the GM hydrogel prepared by the present invention on different substrate materials.

[0019] Figure 11 (A) Sensitivity of the GM hydrogel-based sensor and (B) change of ΔR / R0 under different strains prepared by the present invention.

[0020] Figure 12 Properties of the GM hydrogel of the present invention as a robot skin sensor. (A) Schematic diagram of the GM-based strain sensor and tactile sensor on the robot finger. (B) Photograph of the robot hand covered with the sensor grasping a balloon, and (C) corresponding responses of the strain sensor and tactile sensor covered on the robot hand. Detailed implementation mode

[0021] 1. Synthesis of MXene nanosheets

[0022] The "MILD" method reported in the literature was used to etch the MAX phase to obtain Ti3C2Tx MXene nanosheets. Briefly, 1 g of LiF was added to 16 mL of HCl solution (9 M). Then 1 g of Ti3AlC2 MAX phase was slowly added to the above solution, and then moderately stirred (≈350 rpm) at 45 °C for 30 h. After the reaction, the obtained solution was washed with deionized water until the pH of the supernatant reached ≈6. The obtained multi-layer MXene was centrifugally washed three times with deionized water at 10,000 rpm for 30 min each time. After vigorous shaking, the layered large-sized MXene was collected by centrifugation at 1500 rpm.

[0023] 2. Preparation of GM hydrogel

[0024] Here, the GM hydrogel containing 0.1 wt% MXene (relative to gelatin) was prepared as follows: First, 2.5 g of gelatin was dissolved in a binary solvent system of water (28 mL) / glycerol (8 g), and mechanically stirred at 55 °C for 2 h to form a homogeneous gelatin solution. Then, 2.5 mg of MXene was added, and the mixture was stirred for 10 min. Next, 1.5 g of borax and 0.35 g of anhydrous calcium chloride were added, and then stirred for another 10 min to obtain a homogeneous mixed solution. For comparison, hydrogels with different MXene weight percentages (wt%) were prepared using the same method, named GM-X, where X represents the weight percentage of MXene relative to gelatin.

[0025] 3. From the perspective of practical applications, we designed a commercially available heating device, as shown in the present invention Figure 3 to achieve the thermally induced transition of the hydrogel to liquid in a portable manner. Through this heating device, the GM phase change hydrogel can be quickly transformed from the gel state to the liquid state, and can be coated into the desired shape by spraying or coating, etc., as shown in the present invention Figure 6 , Figure 8. And it grows in situ gelation on the human skin, and by virtue of the fluidity and in situ gelation ability of the GM solution, it ensures good adhesion and close contact between the obtained hydrogel and the irregular skin surface.

[0026] 4. Rheological test of GM hydrogel

[0027] The rheological properties of the phase change hydrogel were characterized by a rheometer, and the storage modulus G' and loss modulus G" before and after the introduction of MXene were obtained. The G' and G" of gelatin and GM hydrogel both decreased with the increase of temperature. Correspondingly, the tanδ (G" / G') values of gelatin and GM hydrogel increased to more than 1 at ~35 °C and 44 °C respectively, indicating their thermal phase transition from the gel state to the liquid state, as shown in the present invention Figure 4 shown. In addition, the photos of the GM hydrogel taken at high temperature and room temperature and the corresponding infrared camera images show that the hydrogel turns into a liquid state at 55 °C, while maintaining a stable gel state at 25 °C, which proves its reversible phase change ability with temperature, as shown in the present invention Figure 5 shown.

[0028] 5. Tensile and adhesion tests

[0029] The mechanical properties were measured using a universal material tester. For the tensile test, the prepared phase change hydrogel liquid was transferred into a polytetrafluoroethylene mold, and gel samples were prepared according to the specification of (50×10×3 mm). Five tests were conducted, and the average value and standard deviation were recorded. The tensile speed of all samples was 20 mm / min. Thanks to the interfacial non-covalent interactions, the GM hydrogel exhibited excellent mechanical and adhesive properties. Although all GM hydrogels added with MXene showed better mechanical properties, the GM hydrogel with 0.1 wt% MXene content showed the best mechanical strength, with a tensile stress of 70 kPa. As shown in the present invention Figure 9 As shown Figure 7 in the present invention

[0030] The adhesion performance was obtained through the gel peeling test. The hydrogel and the test substrate were placed on a rectangular bracket with dimensions of 5 cm x 4 cm. The adhesion force was recorded using a universal tensile testing machine while the bracket was gradually lifted at a speed of 10 mm min -1 until the hydrogel was completely detached from the skin. Different materials were used as the test substrates to compare the adhesion strength of the hydrogel surface on different substrates. As shown in the present invention Figure 10 As shown, the GM hydrogel showed strong adhesion to the surfaces of various inorganic substrate materials, including PET film, glass, paper, porcelain, rubber, and metal, indicating that they can be coated and then firmly attached to the robot skeleton.

[0031] 6. Electrochemical sensing characteristics

[0032] The relative resistance change (ΔR / R0) of the hydrogel under different strains and pressures was measured using a universal material tester in combination with an electrochemical workstation. The response time of the stretching and recovery processes was evaluated through the hysteresis response of impedance (R) to strain (ε). For the strain sensor, two conductive wires were connected to both sides of the gel (50×10×3 mm) to form an ion conductor assembly, as shown in the present invention Figure 11 (A). The sensitivity of the strain sensor is related to its gauge factor (GF), which can be obtained from the slope of the relative resistance change (ΔR / R0)-strain (ε) curve. At the same time, as shown in the present invention Figure 11 (B), the relative resistance change (ΔR / R0) showed a proportional increase with the increase in the degree of tensile strain.

[0033] 7. Robot bionic skin performance test

[0034] As shown in the present invention Figure 12As shown, the GM hydrogel-based e-skin can be used as a stress sensor (coated on the tip of the robot finger) and a tactile sensor (attached to the joint of the robot finger). The sensors assembled in the robot finger are wirelessly controlled by volunteers using a somatosensory glove, enabling the detection of subtle stress changes when grasping a soft balloon. The electrical response signals of the demonstrated tactile and strain sensors show different changes when different fingers touch the balloon, demonstrating the potential of the sensors in intelligent touch sensing and pressure localization in robot bionic skin.

Claims

1. A method for enhancing a reversible phase change hydrogel by non-covalent crosslinking and its application in a bionic skin of a robot, characterized in that: Enhance the thermal conversion ability of phase change hydrogels through non-covalent interactions to improve temperature tolerance, and enable the wide application of phase change hydrogels in robot bionic skin electronic devices by means such as spraying. Introduce MXene flakes into gelatin-based hydrogels, and utilize the hydrogen bonding and coordination interactions generated between MXene nanosheets with rich functional groups and gelatin hydrogels. The obtained hydrogels have high temperature tolerance, high mechanical properties, electrical conductivity, and low interfacial impedance. Design A commercially available heating device to achieve the transformation of phase change hydrogels from the gel state to the liquid state in a portable manner, and establish a highly conformal contact and seamless electronic interface with bionic robots through in-situ gelation after spraying, laying a good foundation for the preparation of a new generation of robot bionic skin.

2. The method for preparing a high temperature-responsive phase change hydrogel according to claim 1, characterized in that: Introduce MXene flakes with rich surface functional groups into gelatin-based phase change hydrogels to promote the formation of reversible non-covalent crosslinks (such as hydrogen bonds) to stabilize the triple-helix biomolecules in gelatin and increase the transition temperature of GM hydrogels. In addition, other additives such as borax are added to generate additional hydrogen bonds and electrostatic interactions, further strengthening the gelatin-MXene network. The performance of the gelatin-based phase change hydrogels obtained by the above method has been significantly improved. The transition temperature of the GM hydrogels has increased from about 35 °C to 44 °C, which is higher than the human skin temperature.

3. The preparation of a commercially available portable heating device according to claim 1, characterized in that: The commercially available portable heating device can achieve the transformation of phase change hydrogels from the gel state to the liquid state within 30 seconds.

4. The method for preparing a non-covalently crosslinked enhanced reversible phase change hydrogel according to claims 1 to 2, characterized in that: The optimal concentration of MXene flakes with rich surface functional groups is 2.5 mg.

5. The method for preparing a non-covalently crosslinked enhanced reversible phase change hydrogel according to claims 1 to 2, characterized in that: The optimal tensile stress of the GM hydrogel is 70 kPa, and the maximum tensile strain reaches 300%.

6. The method for preparing a non-covalently crosslinked enhanced reversible phase change hydrogel according to claims 1 to 2, characterized in that: The thermal transition temperature of the phase change hydrogel increases to 44 °C.

7. The method for preparing a non-covalently crosslinked enhanced reversible phase change hydrogel according to claims 1 to 3, characterized in that: The GM hydrogel is coated into the desired shape by means such as spraying or coating and grows on the human skin through in-situ gelation.

8. The method for preparing a non-covalently crosslinked enhanced reversible phase change hydrogel according to any one of claims 1 to 2, characterized in that: The said phase change hydrogels exhibit strong adhesion to the surfaces of various inorganic substrate materials, indicating that they can be coated and then firmly attached to the robot skeleton.

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