Double-layer hydrogel capable of identifying pressure distribution as well as preparation method and application of double-layer hydrogel

Abstract

The invention discloses double-layer hydrogel capable of recognizing pressure distribution and a preparation method and application thereof, and relates to the field of intelligent flexible materials.The preparation method comprises the steps that epsilon-CL, glycerin and stannous octoate are added into a three-necked flask, and after stirring reaction is finished, a product is dried and collected; gPCL and MAA are fully mixed in a three-necked flask, a reaction solution is subjected to vacuum drying, and a target product GPCL-MA is obtained; the preparation method comprises the following steps: dissolving acrylic acid, acrylamide, glycerol, a gelatin solution, an N, N '-methylene bisacrylamide solution and a photoinitiator Irgacure 2959 in deionized water to form a solution A; the preparation method comprises the following steps: adding butyl acrylate, hydroxyethyl acrylate, GPCL-MA and Irgacure 2959 into ethyl acetate EA to prepare a uniform solution B; and pouring the solution A into a mold, adding the solution B, and irradiating the mixed solution by using an ultraviolet curing machine equipped with an LED lamp to obtain the PAAMG hydrogel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of intelligent flexible material preparation, and particularly relates to a double-layer hydrogel for pressure distribution recognition and a preparation method and application thereof. BACKGROUND

[0002] In recent years, artificial wearable devices have attracted much attention and developed rapidly, and are applied in the fields of flexible robots, implantable sensors, electronic / ion skin and health monitoring. Wearable devices are usually composed of three units: sensing materials, signal conversion modules and signal processing circuits. Among them, sensing materials play a key role in detecting mechanical stimuli and determining device performance. Traditional rigid materials, such as carbon-based compounds and semiconductors, have high reliability and strong bearing capacity, but their inherent rigidity, poor compatibility with the skin and discomfort during long-term use greatly limit their applicability in continuous body monitoring. In contrast, conductive hydrogels have become a promising candidate material for flexible sensors due to their softness, good conductivity, tissue-like modulus and excellent biocompatibility. Their excellent flexibility and stretchability enable them to be seamlessly integrated with biological tissues, achieving precise real-time tracking of human motion; the excellent conductivity enables efficient conversion of motion signals into analyzable electrical signal output, highlighting the great potential of hydrogels as the next generation of wearable device materials. However, traditional hydrogels have a dense hydrophilic network structure, which is prone to swelling in humid environments and dehydrating in dry environments. This instability leads to a significant decrease in mechanical properties and reduces sensing reliability. In addition, in dry conditions, hydrogels become hard and have poor surface wettability, which not only reduces the adhesion strength but also increases the risk of falling off, thereby affecting the long-term functionality of the device. These limitations severely restrict the application of traditional hydrogel-based wearable sensors in complex environments, therefore, developing anti-drying hydrogels is crucial to ensure the safety of use in underwater activities and other scenarios.

[0003] In the early stage, the main method to improve the anti-dehydration performance of hydrogels was to introduce polyols such as glycerol Gly, ethylene glycol EG or sorbitol, to form "bound water" by increasing hydrogen bonding with water molecules. For example, Wu et al. developed a new room temperature humidity hydrogel sensor composed of k-carrageenan / PAM, which used a water-ethylene glycol / glycerol binary solvent system and exhibited significantly enhanced anti-drying ability, stability and sensitivity in humidity detection.

[0004] In addition, the strategy of using high salt concentration to reduce the saturation vapor pressure of the water phase has also shown good prospects in reducing the drying of hydrogels. Yang et al. prepared a conductive PMS hydrogel by in-situ free radical polymerization combined with subsequent LiCl immersion process, which had excellent mechanical strength and ultra-low drying rate at 65℃.

[0005] Zhang et al. reported a multifunctional hydrogel composed of sodium p-styrenesulfonate (SSS) and ionic liquid [BMIM]Cl, in which the ionic SSS-[BMIM]Cl system not only enables the hydrogel to maintain sensing adaptability in a wide temperature range of -25 to 75 °C, but also endows it with elasticity, self-healing and conductive properties. However, the introduction of salt may cause the hydrogel to have poor adhesion or mechanical brittleness / softening problems due to the Hofmeister effect, which may cause the monitoring range to be mismatched. Therefore, designing a hydrogel with excellent adhesion performance and excellent anti-drying performance is still a key goal to be achieved in this field.

[0006] Wearable devices based on hydrogels bring hope for the development of the next generation of electronic devices, but it is still a big challenge to simultaneously achieve strong adhesion, long-term stability and reliable sensing performance.

[0007] Conventional hydrogels without special design usually lack sufficient self-adhesion and often need external auxiliary means such as bandages, adhesive tapes or 3M products to be fixed on the skin. In recent years, researchers have made a lot of research and important progress in the field of adhesive materials, such as enhancing adhesion by introducing monomers or functional groups into the hydrogel network, including chemical modification (such as coupling of gelatin methacrylate (GelMA) microspheres with polydopamine (PDA)), surface treatment (such as using sodium periodate (NaIO4) as an oxidizing agent on the surface of the adherend), mussel-inspired interfacial action (such as catechol-grafted polyacrylic acid (catechol-g-PAA)), and polymer chain design (such as combination of hydrophilic and hydrophobic segments). Although these methods can improve adhesion, the accompanying changes in composition may inadvertently change the mechanical strength of the hydrogel and compromise its thermal stability, electrochemical responsiveness and other key properties. Inspired by the feature of lacquer tree paint that it can adhere to the surface of objects by hand pressing at room temperature, pressure sensitive adhesives (PSAs) emerged as a special class of adhesives - only external pressure is needed to form a strong interfacial bond. Its unique viscoelasticity enables it to have liquid-like flowability, surface wettability and solid-like cohesive strength, allowing reversible adhesion; and no residue when peeled off, naturally with reusability. These characteristics make PSAs a key material in advanced applications, including biomedical devices, flexible electronic products, and other fields that require reversible, durable and clean adhesion. Therefore, in practical applications, there is an urgent need for a simple and reliable method to prepare a hydrogel with excellent adhesion and anti-drying performance SUMMARY

[0008] The technical problems solved: In view of the deficiencies of the prior art, the poor compatibility of traditional rigid materials with the skin and the discomfort after long-term use are solved, the traditional hydrogel has a dense hydrophilic network structure, which is easy to absorb water and swell in a humid environment, and easy to dehydrate in a dry environment, resulting in a significant decrease in mechanical properties and a decrease in sensing reliability. In dry conditions, the hydrogel will become hard and the surface wettability will become poor, not only reducing the adhesion strength, but also increasing the risk of falling off, thereby affecting the long-term functionality of the device. The introduction of salt causes the adhesion of the hydrogel to be poor or the mechanical brittleness / softening problem to occur, thereby possibly causing the monitoring range to be mismatched and other difficult problems. A simple one-step strategy is proposed, and a double-layer hydrogel integrating a hydrogel layer and a pressure-sensitive adhesive layer is constructed, effectively solving the problems of weak adhesion and poor stability of traditional hydrogel sensors.

[0009] The purpose of the application is to provide a double-layer hydrogel for pressure distribution recognition and its preparation method and application. The upper hydrogel is composed of poly(AM-AA), glycerol and gelatin, and has good flexibility and stretchability. The lower pressure-sensitive adhesive layer is based on poly(BA-HEA) and GPCL-MA, which can ensure that the hydrogel forms strong and reversible adhesion with various substrates. Due to the integration of multiple hydrogen bonds and the helical structure of gelatin, the obtained poly(AA-AM-MBA)-gelatin(PAAMG) hydrogel has excellent dry resistance and excellent mechanical properties. This synergistic double-layer design realizes strong interfacial bonding through PSA penetration, while retaining the flexibility and multifunctionality of the hydrogel, avoiding the problem of sacrificing mechanical and sensing performance for simply improving adhesion. By using PAAMG hydrogel as a sensor module, it can accurately detect movements from subtle finger movements to large amplitude bending movements such as elbow and knee movements. Moreover, thanks to its excellent adhesion, the hydrogel can also transmit Morse code as a communication device. The pressure mapping array containing 4x4 sensing units is attached to the robot gripper for tactile operation experiments on balloons and bottles, which confirms the reliable performance of the device in the field of robot sensing, and provides a new idea for the design of intelligent wearable sensors and robot devices with tactile perception. Technical scheme

[0010] To achieve the above-mentioned purpose, the following technical solutions are adopted in the present application: A preparation method of a double-layer hydrogel for pressure distribution recognition, comprising the following steps: Step S10, preparation of glycerol-polycaprolactone methacrylic anhydride GPCL-MA, specifically as follows: Step S11: Under nitrogen protection, ε-CL 29-31 g, glycerol 1.11-1.13 g and stannous octoate 0.2-0.4 g are added to a three-necked flask in a mass ratio, and stirred at 140℃ for 24 h. After the reaction is completed, the obtained glycerol-caprolactone GPCL product is dried and collected. Step S12, preparation of GPCL-MA by one-step reaction: 19-21 g of GPCL and 4-6 g of MAA were mixed in a three-necked flask according to the mass ratio, and reacted at 130 °C for 7 h under a nitrogen atmosphere. The transparent reaction solution was dried in a vacuum oven at 40 °C to remove unreacted methacrylic acid, and the target product GPCL-MA was obtained. Step S20, preparation of PAAMG hydrogel, as follows: Step S21: 0.5-2.5 parts of acrylic acid AA, 0.05-0.5 parts of acrylamide AM, 0-0.5 parts of glycerol Gly, 0.01-1.5 parts of a 20% gelatin solution, 0.05-0.15 parts of a 1.2% N,N'-methylenebisacrylamide MBA solution, and 0.01-0.03 parts of a photoinitiator Irgacure 2959 were dissolved in 1-3 parts of deionized water to form solution A, which was stirred at room temperature for 30 min until completely dissolved; Step S22: 0.1-0.5 parts of butyl acrylate BA, 0.1-0.4 parts of hydroxyethyl acrylate HEA, 0.1-0.3 parts of GPCL-MA, and 0.01-0.03 parts of Irgacure 2959 were added to 0.1-0.5 parts of ethyl acetate EA to prepare a uniform solution B; Step S23: 40-60 parts of solution A were first poured into a mold, and then 60-40 parts of solution B were added. Due to the difference in density between water and ethyl acetate, the mixed solution will automatically stratify. Then, a UV curing machine equipped with an LED lamp was used to irradiate the mixed solution with ultraviolet light for 15 min to obtain the PAAMG hydrogel.

[0011] Preferably, the mass ratio of ε-CL, glycerol and stannous octoate in step S11 is 30.0 g: 1.12 g: 0.3 g.

[0012] Preferably, the molar ratio of ε-CL, glycerol and stannous octoate in step S11 is 0.26 mol: 12.4 mmol: 0.74 mmol.

[0013] Preferably, the mass ratio of GPCL to MAA in step S12 is 20.0 g: 5.0 g.

[0014] Preferably, in the step S21, 1 part of acrylic acid AA, 0.15 parts of acrylamide AM, 0.3 parts of glycerol Gly, 0.01 parts of a gelatin solution with a mass fraction of 20%, 0.1 parts of an N,N'-methylenebisacrylamide MBA solution with a mass fraction of 1.2%, and 0.01 parts of a photoinitiator Irgacure 2959 are dissolved in 1 part of deionized water, and stirred at room temperature for 30 min until completely dissolved to form a solution A.

[0015] Preferably, in the step S22, 0.5 parts of butyl acrylate BA, 0.3 parts of hydroxyethyl acrylate HEA, 0.2 parts of GPCL-MA, and 0.01 parts of Irgacure 2959 are added into 0.3 parts of ethyl acetate EA to prepare a uniform solution B.

[0016] Preferably, in the step S23, the ultraviolet energy of the ultraviolet curing machine is 200 mW / cm 2 , the wavelength is 365 nm; 50 parts of the solution A is first poured into a mold, and then 50 parts of the solution B is added.

[0017] A pressure distribution recognition double-layer hydrogel prepared by any of the above preparation methods.

[0018] The application also discloses application of the pressure distribution recognition double-layer hydrogel prepared by any of the above preparation methods in a wearable electronic device.

[0019] The application also discloses application of the pressure distribution recognition double-layer hydrogel prepared by any of the above preparation methods in a flexible robot.

[0020] The principle of the application is: based on a one-step strategy of water-oil phase separation, a double-layer hydrogel structure is constructed, which combines a poly(acrylamide-acrylic acid)-gelatin sensing layer and a pressure sensitive adhesive PSA substrate; the upper layer hydrogel is enhanced by hydrogen bonds and gelatin helical structures, and has flexibility, mechanical strength and dry resistance; and the lower layer is a pressure sensitive adhesive layer composed of poly(butyl acrylate-hydroxyethyl acrylate) and glycerol-poly-caprolactone methacrylic anhydride GPCL-MA, which can ensure strong and reversible adhesion of the hydrogel to various surfaces, and the double-layer structure realizes stable interface combination without losing sensitivity, and can accurately detect various human movements from slight finger bending to large amplitude joint activities; the excellent adhesion also enables the hydrogel to serve as a communication interface, transmits Morse code through controllable finger movements, integrates a 4x4 pressure mapping array into a robot gripper, and enables the robot gripper to have a tactile feedback function and can distinguish between soft and hard objects such as balloons and bottles.

[0021] The application provides a pressure distribution recognition double-layer hydrogel, a preparation method and application thereof, and has the following beneficial effects: 1. The pressure distribution recognition double-layer hydrogel of the present application has broad application potential in the fields of wearable electronic devices, health monitoring and intelligent robots, and also opens up new directions for the development of intelligent interfaces, advanced human-computer interaction and adaptive flexible robot systems.

[0022] 2. The prepared PAAMG hydrogel exhibits excellent mechanical strength (27.3 kPa), dry resistance (water loss rate 11%) and tensile property (548%).

[0023] 3. The PAAMG hydrogel can withstand environmental fluctuations without significant loss of performance, and is suitable for outdoor wearable devices. Compared with traditional conductive polymer sensors, the PAAMG hydrogel exhibits higher sensitivity in a wide strain range, and the PAAMG hydrogel sensor can be seamlessly applied to human motion monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a design and preparation of the pressure distribution recognition double-layer hydrogel of the present application and its potential application as a flexible pressure sensor, wherein a is a schematic diagram of the preparation method of the PAAMG hydrogel; b is a chemical structure diagram of the monomer and gelatin component of the hydrogel layer; c is a chemical structure diagram of the monomer and GPCL-MA of the pressure-sensitive adhesive layer; d is an adhesion performance diagram of the PAAMG hydrogel with a pressure-sensitive adhesive layer on the skin; e is a schematic diagram of the penetration process of the pressure-sensitive adhesive; f is a diagram of the in vivo application and wireless data transmission of the PAAMG sensor array; g is a pressure mapping diagram of the robot gripper adaptively operating the balloon and the bottle; Figure 2 is a structure characterization and gelation process diagram of the PAAMG hydrogel, wherein a is an energy 200 mW / cm 2 FTIR spectra of the pressure-sensitive adhesive layer and the hydrogel layer at 1635 cm -1 under different ultraviolet polymerization times; b is an energy 200 mW / cm 2 FTIR spectra of the pressure-sensitive adhesive layer and the hydrogel layer at 985 cm -1 under different ultraviolet polymerization times; c is a two-dimensional correlation synchronous spectrogram based on real-time FTIR spectra of the pressure-sensitive adhesive layer and the hydrogel layer at 1635 cm -1 ; d is a two-dimensional correlation synchronous spectrogram based on real-time FTIR spectra of the pressure-sensitive adhesive layer and the hydrogel layer at 985 cm -1 ; e is a monomer conversion rate diagram under an ultraviolet energy of 200 mW / cm 2 ; f is an XPS analysis and SEM diagram of the freeze-dried PAAMG hydrogel; g is an EDS spectrogram of the PAAMG hydrogel; h is a mappings diagram of carbon, oxygen and nitrogen elements in the hydrogel layer; Figure 3Figures are the adhesion characterization of PAAMG gel, where a is the schematic of molecular structure and interaction in the hydrogel and PSA network; b is the schematic of mechanical interlocking and micro-anchoring mechanism of PSAs on substrates; c is the SEM images and 3D surface topography of PSA layer before (I) and after (II) pressure adhesion on skin; d is the DSC curves of PSAs with different BA content; e is the adhesion strength of PSAs on different substrates; f is the adhesion strength of hydrogel layer on different substrates; g is the comparison of adhesion strength of hydrogel layer and PSA layer on different substrates; h is the real picture of PSA layer adhesion on various substrates; i is the comparison of adhesion strength of PSA layer on pig skin in several literatures; Figure 4 Figures are the mechanical characterization of PAAMG gel, where a is the schematic and SEM images showing the state of traditional gel and PAAMG gel network under 200 gram weight; b is the stress-strain curves of gel with different gelatin content; c is the maximum strain and stress of gel with different gelatin content; d is the toughness and Young's modulus of gel with different gelatin content; f is the schematic of network deformation and chain scission under strain; g is the stress-strain curves of gel with different glycerol content; h is the maximum strain and stress of gel with different glycerol content; i is the toughness and Young's modulus of gel with different glycerol content; j is the schematic of gelatin and H2O interaction; k is the H2O loss rate of gel with different glycerol-gelatin ratio; l is the effect of 60 °C and -25 °C treatment on the retention of maximum tensile strain; Figure 5 Figures are the sensing performance of PAAMG hydrogel, where a is the current-voltage curves of hydrogel under different strain; b is the resistance change and gauge factor of hydrogel under different tensile strain; c is the resistance change of repeated tensile cycles under different strain; d is the resistance change under different weight load; e is the response time of hydrogel under 150 g weight; f is the response time of hydrogel under 50% strain; g is the resistance change of hydrogel when elbow is bent; h is the resistance change of hydrogel when finger is bent at different angle; i is the resistance change of hydrogel when knee is bent; j is the hydrogel integrated into a sign language recognition device, installed on the human finger joint; k is the language recognition based on finger movement of hydrogel sensor: "AUST" and "SOS" in Morse code; l is the application of PAAMG hydrogel as a pressure-sensitive switch control device; Figure 6Figure 1 is a wireless detection application diagram of PAAMG hydrogel sensing array, wherein a is the hardware diagram of PAAMG hydrogel sensing array; b is the real-time pressure response mapping of sensing array under 200 g load, c is the real-time pressure mapping of sensing array when grabbing a bottle, d is the spatially resolved pressure mapping when loading hexagonal and circular objects, e is the spatially resolved pressure mapping when loading circular and triangular objects, f is the integration diagram of hydrogel sensing array and smart gripper, g is the real-time pressure distribution mapping of gripper when grabbing a bottle, h is the real-time pressure distribution mapping of gripper when grabbing a balloon. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present application are described below, and it should be understood that the preferred embodiments described herein are used to illustrate and explain the present application, and are not intended to limit the present application.

[0026] The raw materials of the present application are all commercially available.

[0027] Acrylamide (AM, purity 99.9%), acrylic acid (AA, purity 98%), ε-caprolactone (ε-CL, purity 99%), glycerol (Gly, purity 99.5%), stannous octoate (Sn (Oct) 2, purity 95%), methacrylic anhydride (MAA, purity 94%), N,N'-methylenebisacrylamide (MBA, purity 99%), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959, purity 98%) were purchased from Shanghai Aladdin Reagent Co., Ltd. (China); sodium chloride (NaCl, purity 99.5%), sodium sulfate (Na2SO4, purity 99%), butyl acrylate (BA, purity 99%), hydroxyethyl acrylate (HEA, purity 96%) and ethyl acetate (EA) were purchased from Sigma-Aldrich (China); fish skin gelatin (gel strength ≥ 50 g Bloom) was purchased from J&K Chemical Co., Ltd. (China); ultrafiltration deionized water (DIW, resistivity 18.2 MΩ·cm) was prepared by a Milli-Q water system (USA). All chemical reagents were used directly without further purification.

[0028] Example 1, a preparation method of a double-layer hydrogel for pressure distribution recognition, comprising the following steps: Step S10, preparation of glycerol-poly-caprolactone-methacrylic anhydride GPCL-MA, specifically as follows: Step S11: Under nitrogen protection, ε-CL 30 g, glycerol 1.12 g and stannous octoate 0.3 g were added into a three-necked flask in a mass ratio, stirred at 140℃ for 24 h, and after the reaction was completed, the obtained glycerol-caprolactone GPCL product was dried and collected; Step S12, preparation of GPCL-MA by one-step reaction: 20 g of GPCL and 5 g of MAA were mixed in a three-necked flask in a mass ratio, reacted at 130℃ for 7 h under nitrogen atmosphere, and the transparent reaction liquid was dried in a vacuum oven at 40℃ to remove unreacted methacrylic acid to obtain the target product GPCL-MA; Step S20, preparation of pressure distribution-identified double-layer hydrogel, as follows: Step S21: Acrylic acid AA 1 part, acrylamide AM 0.15 part, glycerol Gly 0.3 part, gelatin solution with a mass fraction of 20% 0.01 part, N,N'-methylenebisacrylamide MBA solution with a mass fraction of 1.2% 0.1 part and photoinitiator Irgacure 2959 0.01 part were dissolved in deionized water 1 part in a mass fraction ratio, stirred at room temperature for 30 min to completely dissolve, forming solution A; Step S22: Butyl acrylate BA 0.5 part, hydroxyethyl acrylate HEA 0.3 part, GPCL-MA 0.2 part and Irgacure 2959 0.01 part were added into ethyl acetate EA 0.3 part, and a uniform solution B was prepared; Step S23: Solution A 50 parts was first poured into a mold, and then solution B 50 parts was added, due to the density difference between water and ethyl acetate, the mixed solution would automatically stratify; then the mixed solution was subjected to 15 min ultraviolet irradiation using a UV curing machine equipped with an LED lamp, the ultraviolet energy of the UV curing machine was 200 mW / cm 2 , wavelength 365 nm; pressure distribution-identified double-layer hydrogel was obtained.

[0029] Characterization methods: Fourier transform infrared spectroscopy FTIR: a Thermo Scientific infrared spectrometer was used to analyze the structure of the pressure distribution-identified double-layer hydrogel in the range of 500-4000 cm -1 ; Scanning electron microscope SEM: a scanning electron microscope of Carl Zeiss AG, Oberkochen, Germany was used to observe the microstructure and morphology of the hydrogel; Nuclear magnetic resonance hydrogen spectrum 1H NMR: The test was performed on a Bruker AVANCE II 500 nuclear magnetic resonance instrument in Germany, using CDCl3 as the solvent; Laser confocal microscope: The three-dimensional optical morphology of the hydrogel surface was analyzed by means of a KC-X1000 laser spectrum confocal microscope of Kathmatic, China; X-ray photoelectron spectroscopy XPS: The chemical composition of the hydrogel surface was characterized by an ESCALAB Xi+ photoelectron spectrometer of Thermo Fisher, USA; Differential scanning calorimetry DSC: The thermal properties of the hydrogel were analyzed by using a NETZSCH 209 differential scanning calorimeter of Perkin Elmer, USA, under a nitrogen atmosphere, at a temperature rising rate of 5 K / min, from -20°C.

[0030] Monomer conversion rate determination: The monomer conversion rate in the UV polymerization process was monitored by the attenuation of the carbon-carbon double bond C=C characteristic vibration peak at 1635 cm -1 and the methylene =C-H torsional vibration peak at 985 cm -1 ; The peak area at 1635 cm -1 was calculated according to the following formula (1), and the calculation method of the peak at 985 cm -1 was the same: .

[0031] wherein and represent the peak areas at 1635 cm -1 and 1720 cm -1 after UV polymerization, respectively; and represent the peak areas before UV polymerization. The C=O peak was used as an internal standard.

[0032] Example 2, Adhesion performance test: According to the ASTM F2458-05 standard, the adhesion strength of the PAAMG hydrogel on different surface energy substrates was evaluated by using a lap shear mode on an AGS-X universal testing machine of Shimadzu, Japan. The test used a 50 N load sensor, and the stretching rate was 50 mm / min. The hydrogel sample with a size of 20 mm x 20 mm was placed at the interface of two identical substrates, and the adhesion strength was calculated according to the maximum force required to separate the bonded surfaces. To ensure data reliability, each test was repeated 5 times.

[0033] Example 3, Mechanical property testing: The stress-strain behavior of PAMG hydrogel was evaluated using an AGS-X universal testing machine (50 N load sensor). The sample was stretched at a constant rate of 100 mm / min, and the tensile strain was calculated from the relative length change. The tensile stress was defined as the maximum value at fracture. The Young's modulus was obtained from the slope of the initial linear segment (5%-15%) of the stress-strain curve, and the toughness was determined by the area under the integral stress-strain curve. Each test was repeated 5 times to ensure repeatability. Electrical measurements: Conductivity and strain sensing performance were characterized using an electrochemical workstation (CHI-920, CHInstruments). The resistance change under deformation was recorded, and the strain factor GF was calculated according to formulas (2) and (3), respectively: In the formula, R0 is the initial resistance of the hydrogel, and R is the real-time resistance of the hydrogel when it is stretched. In the formula, R0 is the initial resistance of the hydrogel, R is the real-time resistance of the hydrogel when stretched, and ε is the strain that the hydrogel withstands.

[0034] Results and Discussion: Design principles and preparation of PAAMG hydrogels: A bilayer PAAMG hydrogel was prepared via a one-step UV polymerization method, which can simultaneously form a hydrogel matrix and a pressure-sensitive adhesive layer, such as... Figure 1 As shown in Figure a, this integrated structure achieves excellent overall performance through the synergistic effect between the two layers, and the one-step design does not require a complex multi-layer assembly process, which makes it possible for large-scale and efficient fabrication.

[0035] The upper hydrogel layer consists of AM, AA, and MBA, with gelatin added to enhance biocompatibility, such as... Figure 1 As shown in Figure b, AM and AA form a hydrophilic polymer backbone, giving the hydrogel flexibility and water retention; MBA provides crosslinking sites to stabilize the network structure; and gelatin contributes a semi-crystalline backbone containing helical domains, which enhances the toughness and elasticity of the hydrogel through reversible hydrogen bonding.

[0036] The lower PSAs layer is composed of a copolymer of BA and HEA and is crosslinked with GPCL-MA, such as... Figure 1 As shown in Figure c, the hydroxyl groups introduced by HEA not only improve the compatibility with the hydrogel layer, but also enhance the adhesion of the hydrogel to various substrates; BA has excellent wettability, which can improve the interfacial adhesion and bonding effect; GPCL-MA, as a multifunctional crosslinking agent, has both ester bonds and degradable flexible segments, which can not only adjust the mechanical softness of the pressure-sensitive adhesive layer, but also penetrate into the micro-protrusion structure on the substrate surface.

[0037] Through the above molecular design, the PSAs layer realizes the close interface combination with the hydrogel layer and the external substrate, ensuring that the double-layer structure has good mechanical durability, strong cohesion and stable external adhesion. As shown in FIG. 6a, Figure 1 FIG. 6b shows the adhesion performance of the PAAMG hydrogel, wherein the PSAs layer can form a strong bond with the skin surface without additional adhesive, and can maintain the structural integrity during the peeling process, which is crucial for wearable applications that need to be attached to the skin for a long time.

[0038] To explain its adhesion mechanism, the present application proposes an adhesion process based on penetration, as shown in FIG. 6c, Figure 1 When the PSAs layer is in contact with the substrate, its polymer chains will penetrate into the micro-convex structure on the surface of the substrate, and form a close van der Waals force and hydrogen bond through HEA. This penetration process is beneficial to efficient load transfer at the interface, reducing stress concentration, thereby ensuring that the hydrogel can still maintain excellent adhesion stability under dynamic movement.

[0039] To verify the application potential of the PAAMG hydrogel in the field of wearable electronics, it is integrated into a pressure sensor array, as shown in FIG. 6d, Figure 1 The device is composed by sandwiching the PAAMG hydrogel between copper electrodes, and the electrodes are wrapped with 3M adhesive. Among them, the PAAMG hydrogel serves as a pressure-sensitive unit, which can convert deformation into resistance signals; the pressure-sensitive adhesive layer ensures the reliable adhesion of the hydrogel to the electrode, ensuring stable signal output during movement. The sensor array is connected with a microcontroller unit (MCU) equipped with wireless data transmission function, which can realize real-time monitoring of pressure distribution.

[0040] In addition to the wearable field, the PAAMG hydrogel is also integrated into a flexible robot gripper as a tactile sensing element, as shown in FIG. 6e, Figure 1 The sensor can detect and distinguish the clamping force applied when clamping objects with different stiffness and geometric shapes such as balloons and bottles. The real-time pressure mapping results confirm that the PAAMG hydrogel can adapt to irregular surfaces, so that the gripper will not damage fragile objects during delicate operations. In these fields, both adhesion and sensing performance are indispensable.

[0041] Example 4, characterization and gelation process of PAAMG hydrogel: The successful preparation of the PAAMG hydrogel depends on the precise control of polymerization kinetics, internal structure and interface compatibility. In the infrared spectrum of the GPCL, 3436 cm -1 from the -OH group of glycerol, while 1720 cm -1 is attributed to the C=O group of ε-CL. In addition, the peak at 3436 cm -1 corresponds to the -OH of GPCL, while 2932 cm -1and 2860 cm -1 The band at 1154 cm⁻¹ is attributed to the stretching vibrations of -CH₂ and -CH₃. -1 The peak at 1630 cm⁻¹ originates from the COC group. MAA at 1630 cm⁻¹... -1 The sample exhibits a characteristic C=C stretching vibration peak. In GPCL-MA, the -OH peak disappears, and a new C=C peak appears, confirming its successful preparation.

[0042] To monitor the polymerization kinetics of the PSAs layer in PAAMG, FTIR spectra at different UV polymerization times were recorded, such as... Figure 2 As shown in Figure a, at 1635 cm -1 The disappearance of the C=C characteristic vibration peak indicates the gradual consumption of AM, AA monomers, and MBA, confirming the successful formation of the network structure. In particular, the complete disappearance of this characteristic peak at 6 minutes of polymerization time demonstrates that this time is sufficient to complete the polymerization of the hydrogel layer.

[0043] Similarly, the hydrogel layer of PAAMG also exhibited significant spectral changes during UV polymerization, such as... Figure 2 As shown in b, 985cm -1 The characteristic absorption peak attributable to the =CH torsional vibration gradually weakens with prolonged UV irradiation, reflecting the consumption of BA and HEA monomers. Importantly, the shortest polymerization time (7 min) for the hydrogel layer is similar to that of the PSAs layer, enabling the simultaneous preparation of both layers using a one-step strategy. This rapid polymerization characteristic is beneficial for large-scale production, while ensuring structural homogeneity and shortening processing time. This rapid polymerization is advantageous for large-scale production, ensuring structural homogeneity while minimizing processing time.

[0044] Two-dimensional correlation spectroscopy (2D-COS) was obtained through in-situ polymerization time-dependent FTIR measurements. Analysis of synchronous and asynchronous spectra is as follows: Figure 2 c and Figure 2 As shown in d, it reveals that at 1635 cm -1 and 985 cm -1 There are two distinct peaks. According to Noda's rule, the order of response of different functional groups to polymerization time is: for the PSAs layer, it is δ(C-OH, 1533cm). -1 →ν(C=C,1635cm) -1 →ν(C=O,1667cm) -1 For the hydrogel layer, it is γ (carboxyl group, C-OH, 884cm). -1 )→τ(=CH2,985cm -1 )→ν(CN,1089cm -1These results indicate that although the two layers undergo independent and well-defined polymerization processes, they still exhibit good compatibility at the interface.

[0045] like Figure 2 As shown in Figure e, the monomer conversion rate was further investigated. The hydrogel layer achieved 76.4% monomer conversion within 6 min, and the conversion rate was close to complete (98.8%) after 10 min. The pressure-sensitive adhesive layer achieved a conversion rate of 78.2% at 7 min and reached complete conversion at 13 min. The similar polymerization kinetics of the two layers ensured the balance of polymer growth, avoided interfacial mismatch problems, and helped improve the mechanical stability of the bilayer system.

[0046] like Figure 2 As shown in Figure f, X-ray photoelectron spectroscopy (XPS) analysis revealed the detailed chemical composition of each layer: the spectrum of the hydrogel layer showed the presence of C, O, and N elements, and the high-resolution C1s spectrum showed characteristic peaks corresponding to carbon-oxygen double bonds (C=O, 287.8 eV), carbon-nitrogen bonds (CN, 285.6 eV), and carbon-carbon / carbon-hydrogen bonds (CC (H), 284.8 eV), confirming the successful combination of acrylamide (AM), acrylic acid (AA), and gelatin; while the pressure-sensitive adhesive layer contained only carbon and oxygen elements, consistent with the acrylate formulation, and the characteristic peaks of carbon-oxygen double bonds (C=O, 287.6 eV) and carbon-carbon / carbon-hydrogen bonds (CC / H, 284.8 eV) in its C1s spectrum verified the presence of ester functional groups in BA, HEA, and GPCL-MA. Scanning electron microscopy (SEM) images reveal that the hydrogel layer exhibits a porous, interconnected network structure, which facilitates ion transport and mechanical flexibility while providing interaction sites for reversible hydrogen bonding. The PSAs layer, on the other hand, has a denser and smoother structure, which promotes interfacial adhesion and strong bonding. Cross-sectional SEM images of the bilayer structure clearly show a distinct boundary between the two layers, but without obvious interfacial gaps, indicating a strong interfacial bond and structural integrity. This complementary morphological feature reflects the rational design of the bilayer system: the hydrogel layer ensures sensing performance, while the PSAs layer ensures adhesion.

[0047] Energy dispersive spectroscopy (EDS) further confirmed that the nitrogen content of the hydrogel layer was higher than that of the pressure-sensitive adhesive layer, such as... Figure 2 As described in section g, the pressure-sensitive adhesive layer contains no nitrogen and has the same composition as the acrylate; while the hydrogel layer is rich in nitrogen, reflecting the contributions of AM and gelatin. Elemental mappings images are shown below. Figure 2 As shown in Figure h, the above results are further verified, showing that carbon, nitrogen, and oxygen elements are evenly distributed in the hydrogel layer.

[0048] Example 5, Adhesion properties of PAAMG hydrogel: At the molecular level, the adhesion mechanism of pressure-sensitive adhesives stems from the synergistic effect of hydrogen bonding and hydrophobic association within their network, such as...Figure 3 As shown in Figure a, PSAs are cross-linked from poly(BA-co-HEA) and GPCL-MA, with both hydroxyl and alkyl groups present in their matrix. The HEA-derived hydroxyl groups can form hydrogen bonds with functional groups on the substrate surface, while the hydrophobic alkyl segments increase the interfacial adhesion area and enhance van der Waals interactions. The ester bonds and flexible aliphatic chains provided by the GPCL-MA cross-linking agent allow the pressure-sensitive adhesive chains to rearrange and anchor in the raised structures on the substrate surface. For the hydrogel, AA and AM constitute a flexible basic network; gelatin, with its multifunctional groups, forms effective hydrogen bonds with surrounding H2O, -OH, and -NH2, constructing a dual-network hydrogel. These reversible hydrogen bonding interactions further enhance the mechanical properties of the hydrogel.

[0049] In addition to molecular-level interactions, when pressure is applied, the soft pressure-sensitive adhesive penetrates into the nanoscale irregular structure of the substrate surface, forming a microscopic anchoring effect that hinders peeling. Figure 3 As shown in Figure b, the pressure-sensitive adhesive maintains interfacial adhesion even after the external force is removed, and can maintain stable adhesion even under mechanical stress or hydration conditions. This interfacial anchoring effect is further supported by hydrogen bonding, hydrophobic association, and electrostatic attraction, ensuring long-term adhesion.

[0050] like Figure 3 As shown in Figure c, SEM and 3D surface morphology analysis were used to observe the surface morphology of PSAs at different stages of adhesion. Before adhesion, the PSAs surface was relatively smooth and uniform; after contact with skin and application of pressure, the surface became significantly irregular and wrinkled. This change was further confirmed by 3D surface imaging, which showed that the average surface height increased from 2 μm before adhesion to 15 μm after adhesion. These results demonstrate the excellent adhesion mechanism of PSAs and provide support for the surface micro-anchoring hypothesis.

[0051] like Figure 3 As shown in Figure d, the glass transition temperature T of PSAs increases with increasing BA content. g Significantly reduced: When the BA content increased from 0.1 wt% to 0.5 wt%, T g The temperature dropped from 6.5℃ to 8.1℃. The lower Tg means increased chain flexibility, allowing PSAs molecules to penetrate the interface more easily, thereby improving adhesion compliance and energy dissipation.

[0052] The adhesion ability of PAAMG hydrogels was systematically evaluated on various substrates, such as... Figure 3 China and Figure 3As described in section f, the results show that the pressure-sensitive adhesive layer exhibits excellent adhesion strength on a wide range of substrates from high to low surface energy, including aluminum, stainless steel, pigskin, polypropylene (PP), and polytetrafluoroethylene (PTFE). With increasing BA content, the adhesion strength of PSAs gradually increases, reaching a maximum of 37.68 kPa on aluminum substrates; even on PTFE substrates, the adhesion strength of PSAs reaches 6.46 kPa, highlighting its excellent interfacial adaptability and superior adhesion ability. In contrast, the adhesion performance of the hydrogel layer shows the opposite trend. Although its adhesion increases with increasing gelatin content, its maximum adhesion strength on aluminum is limited to 7.56 kPa. This difference stems from the unique adhesion mechanism of hydrogels. Gelatin molecular chains rich in -NH2 and -COOH functional groups form numerous electrostatic interactions and hydrogen bonds with the substrate surface. These interactions mainly operate at the molecular level, contributing little to macroscopic adhesion.

[0053] like Figure 3 As shown in Figure g, the maximum adhesion strength on different substrates further demonstrates the wide adaptability of PAAMG hydrogel. The PSAs layer exhibits strong adhesion to a variety of surfaces (aluminum: 37.68 kPa, stainless steel: 21.12 kPa, pigskin: 22.89 kPa, PP: 13.94 kPa, PTFE: 6.46 kPa), while the hydrogel layer alone shows limited adhesion (aluminum: 7.56 kPa, stainless steel: 11.86 kPa, pigskin: 17.98 kPa, PP: 4.82 kPa, PTFE: 3.38 kPa).

[0054] like Figure 3 As shown in Figure h, to demonstrate adhesion properties on other substrates, PAAMG hydrogel was applied to a variety of surfaces, including wood, glass, copper, PET, PVC, PMMA, PC, and ceramics. The results showed strong interfacial adhesion without delamination on all substrates, confirming the excellent adhesion of PAAMG hydrogel to a variety of substrates.

[0055] The maximum adhesion strength of various hydrogel-based sensors on pigskin was compared, such as... Figure 3 As shown in Figure i, PAAMG hydrogel exhibits superior adhesion strength compared to most hydrogels reported in the literature.

[0056] Example 6, Mechanical properties and anti-drying properties of PAMG hydrogel: Hydrogels used in flexible wearable applications need to achieve a delicate balance between stiffness, elasticity, and toughness to ensure both mechanical stability and interfacial adhesion. For example... Figure 4As shown in Figure a, the composition and microstructure of hydrogels determine their mechanical behavior: for example, traditional PAM hydrogels exhibit rigid and brittle mechanical properties due to their covalent cross-linking and low chain segment flexibility, resulting in a dense microstructure with small pores. However, by controlling the content of glycerol and gelatin, reversible hydrogen bonds and chain entanglements can be introduced to form a more open interconnected porous network. This structural adjustment can enhance stress dissipation and allow reversible deformation, giving the hydrogel stretchability, softness, and toughness.

[0057] The effect of the glycerol / gelatin ratio on the mechanical properties of PAMG hydrogels was systematically investigated, such as... Figure 4 As shown in b, and Figure 4 As shown in Figure c, with increasing gelatin content, the strain of the hydrogel doubled from 273% to 548%; while when the glycerol:gelatin ratio was 0.3:1, the stress gradually decreased from 59.2 kPa to 44.9 kPa. This result can be explained by the following: the increased gelatin content leads to a decrease in cross-linking density and a weakening of load-bearing capacity; simultaneously, the longer and more flexible molecular chains, combined with additional physical cross-linking points, promote segment slippage and remodeling during stretching, thereby enhancing energy absorption and increasing strain. Figure 4 As shown in Figure d, the effect of gelatin on the toughness and Young's modulus of the hydrogel is as follows: the toughness steadily increases with increasing gelatin content, reaching a maximum of 13.67 kJ / m. 3 Meanwhile, Young's modulus decreased significantly from 38 kPa to 12.5 kPa. This trend is attributed to the fact that while the helical chains of gelatin effectively dissipate stress and adapt to deformation, the relatively weak hydrogen bonding creates a softer network structure. This structure is prone to deformation under low stress, ultimately leading to a decrease in Young's modulus. Figure 4 As shown in Figure e, PAAMG hydrogel can quickly recover its original shape without damage after being punctured or cut, demonstrating excellent toughness and flexibility. This overall performance indicates that PAAMG hydrogel has great potential in durable applications requiring repeated deformation. Figure 4 As shown in Figure f, the deformation mechanism of PAAMG hydrogel is as follows: when an external force is applied, the P(AM-AA) chains initially extend, while weak interactions such as hydrogen bonds dissipate energy. As deformation intensifies, the gelatin helical chains further unwind, accompanied by continuous breaking and reconstruction of reversible bonds, preventing sudden breakage and improving toughness. Under extreme tension, the covalently cross-linked P(AM-AA) network breaks first, while the gelatin chains can still maintain deformation through molecular slip and rearrangement, thus achieving higher toughness and strain. This multi-scale mechanism combining reversible rearrangement and covalent interactions is key to the excellent tensile strength and durability of PAAMG hydrogel.

[0058] like Figure 4 Zhongg and Figure 4As shown in Figure h, the effect of glycerol content on the mechanical properties of PAAMG hydrogel is significant. With increasing glycerol content, the strain of the hydrogel increases significantly from 311% to 548%, while the stress decreases from 75.21 kPa to 44.12 kPa. This behavior can be attributed to the role of glycerol in weakening the hydrogen bonds between polymer chains, thereby reducing the crosslinking density and network stiffness. Furthermore, glycerol acts as a plasticizer, enhancing the fluidity of the molecular chains, making the network more adaptable to stretching and deformation. Figure 4 As described in section i, consistent with the trend influenced by gelatin, the Young's modulus decreased from 20.3 kPa to 12.5 kPa. Importantly, the PAAMG hydrogel exhibited the highest toughness of 12.77 kJ / m at a glycerol:gelatin ratio of 0.3:1. 3 This highlights the crucial role of glycerol in optimizing mechanical properties.

[0059] At 60°C, a dense network of hydrogen bonds forms between gelatin and H2O. These abundant hydrogen bonds effectively anchor H2O within the hydrogel matrix, restricting its flowability and inhibiting evaporation. This molecular interaction not only reduces water loss but also enhances the long-term water retention and mechanical stability of the PAAMG hydrogel, which is crucial for maintaining the functional integrity of the hydrogel under high-temperature conditions.

[0060] like Figure 4 Figure k shows the moisture loss of PAAMG hydrogels with different glycerol / gelatin ratios over 30 days. The moisture loss rates of hydrogels containing only glycerol and only gelatin were 46.8% and 58.7%, respectively, while the PAAMG hydrogel with a glycerol:gelatin ratio of 0.3:1 showed only an 11% moisture loss rate. These results indicate that glycerol and gelatin not only act as mechanical property modifiers but also impart anti-drying properties to the hydrogels, ensuring their long-term durability at room temperature.

[0061] Besides resistance to drying, thermal stability and freeze resistance are also crucial for hydrogel-based sensors. PAAMG hydrogels were treated with 60 °C drying and -25 °C freezing for 24 h, respectively. Figure 5 As shown in Figure 1, the PAAMG hydrogel with a glycerol:gelatin ratio of 0.3:1 retained over 70% and 69.1% of its maximum tensile strain after both treatments; while the hydrogel containing only glycerol or gelatin showed a significant decrease in tensile strain. This result confirms that PAAMG hydrogels can withstand environmental fluctuations without significant performance loss, making them suitable for outdoor wearable devices.

[0062] Example 7, Sensing performance of PAAMG hydrogel: The combination of NaCl and the polymer network endows PAAMG hydrogels with excellent electrical conductivity and tunable strain sensing properties. For example...Figure 5 As shown in Figure a, the current-voltage curves exhibit high linearity and symmetry within the strain range of 0-400%, confirming the stable ohmic properties and efficient charge transport capability of the PAAMG hydrogel. Notably, the slope of the curve gradually decreases with increasing strain, indicating an increase in resistance at high strain. This correlation between strain and current lays the foundation for reliable strain sensing performance.

[0063] The conductivity of the top hydrogel layer reaches 0.099 S / m, while the conductivity of the PSAs layer is only 0.00025 S / m, indicating that the PSAs layer does not affect the sensing capability of the hydrogel layer. Figure 5 As shown in Figure b, the PAAMG hydrogel exhibits three distinct linear strain factor (GF) regions, with GF values ​​of 1.73, 2.64, 3.25, and 4.49 in the corresponding strain ranges of 0%-100%, 100%-200%, 200%-300%, 300%-400%, and 400%-500%, respectively. The increase in GF value under large strain indicates that microstructural rearrangements such as chain extension and partial bond dissociation amplify the resistive response. Compared with traditional conductive polymer sensors, the PAAMG hydrogel exhibits higher sensitivity over a wide strain range.

[0064] Strain detection experiments further confirmed the repeatability of the sensor, such as Figure 5 As shown in Figure c, when the strain increases to 200%, 300%, and 400%, respectively, the rate of change of resistance increases accordingly, and the baseline drift is minimal, indicating that the hysteresis effect is negligible. In addition to strain detection, this hydrogel sensor also exhibits excellent pressure sensitivity. Figure 5 As shown in Figure d, when 100g, 150g, and 200g weight loads are applied, the resistance changes in a stepwise manner, clearly distinguishing minute pressure differences. Under repeated loading conditions, the sensor outputs a fast and stable electrical signal, indicating its quantitative force monitoring capability. The hydrogel exhibits rapid response and recovery characteristics during loading, such as... Figure 5 As shown in Figure e, under a 150 g load, the resistance change occurs immediately with a response time of 500 ms; it fully recovers within 300 ms after unloading. Similarly, under 50% strain, as... Figure 5 As shown in Figure f, the PAAMG hydrogel consistently maintains a fast response (400 ms) and recovery (300 ms). The hydrogel's excellent flexibility and extensibility make it ideal for monitoring human joint motion in wearable sensing applications. Figure 5 As shown in Figure g, repeated elbow flexion produces periodic resistance changes, accurately reflecting the motion state, and the signal does not attenuate after multiple cycles. Similarly, as... Figure 5As shown in Figure h, the resistance response of the finger at different bending angles of 30°, 60°, and 90° is clear and exhibits excellent reproducibility in repeated tests. Furthermore, the sensor maintains reliable performance even under significant joint deformation, such as stable resistance changes during continuous knee flexion. Figure 5 As shown in Figure i, this sensor can effectively convert various human movements into electrical signals, covering deformation monitoring from minute to large magnitudes.

[0065] like Figure 5 As shown in Figure j, this hydrogel is integrated into a sign language recognition device and installed at the joint of a human finger. When the finger is bent from 45° to 90°, the hydrogel undergoes stretching deformation, generating a high-resistance output, corresponding to the "long dash (-)" in Morse code; conversely, when the finger returns to 0°, compression deformation reduces the resistance, corresponding to the "dot (・)". Through this mechanism, users can transmit information based on the Morse code system simply by bending their fingers. Figure 6 As shown in Figure k, the volunteer successfully conveyed specific messages such as "SOS" and "AUST," indicating the device's potential application in assisting personal expression and conveying urgent needs. The sensor was coupled with a programmable LED display, achieving practical integration into the functional circuitry, as shown in Figure k. Figure 6 As shown in Figure 1, the hydrogel sensor acts as a dynamic switch to control the illumination state of the LED matrix displaying "AUST". When there is no load, the display remains lit. When mechanical pressure is applied to the hydrogel, the circuit is immediately interrupted and the LEDs turn off. This verification application highlights the application potential of hydrogel in smart wearable systems such as information display, security verification, and interactive devices.

[0066] Example 8, Practical application of PAAMG hydrogel sensing array: To expand the practicality of hydrogel sensors in intelligent wireless applications, an integrated system was designed to achieve real-time signal acquisition, transmission, and feedback, such as... Figure 6 As shown in Figure a, the system comprises three core components: a PAAMG hydrogel-based pressure sensor, a Bluetooth signal processing module, and a signal system. The PAAMG hydrogel detects external stimuli such as pressure and deformation, converting them into changes in electrical resistance. These signals are processed and wirelessly transmitted to a remote device via the Bluetooth module. The real-time data is reconstructed into a 3D graph for visualization. This framework establishes a seamless path from mechanical input to digital output, demonstrating the feasibility of hydrogel-based sensors in smart, connected electronic devices.

[0067] like Figure 6The spatial sensing capability of the PAAMG hydrogel array was verified by local pressure detection, as shown in FIG. 5B: a 200 g weight load was applied to the sensor array, and the resulting local resistance change was captured and reconstructed into a pressure map. This distribution clearly reflected the location and size of the applied pressure, indicating that the sensor had high sensitivity and resolution. This direct correspondence between local mechanical input and electrical signal output highlighted the ability of the hydrogel as a pressure mapping array, enabling real-time identification of spatially distributed forces. In addition to local force detection, the PAAMG hydrogel sensor also demonstrated strong adaptability in dynamic physiological motion tracking. For example, when the sensor was attached to the palm and a bottle was grasped, as shown in FIG. 5C: Figure 6 As shown in FIG. 5C, the sensor effectively captured the resistance fluctuations associated with the grasping action; the real-time mapping data showed a stable spatial distribution output, accurately reflecting the amplitude and direction of the motion. This high-precision dynamic bending detection capability indicated that the PAAMG hydrogel sensor could be seamlessly applied to human motion monitoring.

[0068] To further evaluate the discrimination ability of the hydrogel array, objects of different shapes were placed on the sensor surface, as shown in FIG. 5D: Figure 6 As shown in FIG. 5D, when a hexagon and a circular object were loaded simultaneously, unique spatial resistance distributions were generated, and the reconstructed bar graph accurately distinguished between the two contact geometries; similarly, the combination of a circular and a triangular object also produced distinguishable unique outputs, as shown in FIG. 5E: Figure 6 As shown in FIG. 5E, the PAAMG hydrogel sensor array was not limited to simple force detection, but could also recognize contact patterns with specific geometries. In the field of robotics, the PAAMG hydrogel sensor array was integrated into a smart gripper, as shown in FIG. 5F: Figure 6 As shown in FIG. 5F, the hydrogel sensing unit was carefully arranged on the inner surface of the gripper fingers, allowing force to be perceived through direct contact during object manipulation. Using the smart gripper equipped with the PAAMG hydrogel array, objects of different stiffness and geometry were tested: as shown in FIG. 5G: ​ As shown in FIG. 5G, when a rigid bottle was grasped, the resistance heat map showed significant changes in the contact area, reflecting the distribution of clamping force on the sensing array; in contrast, when a soft and deformable balloon was held, as shown in FIG. 5H: ​ As shown in FIG. 5H, the resistance response was lower in intensity but more extensive in distribution, which was consistent with the softness and surface adaptability of the balloon. This sensor not only recognized the presence of an object, but also distinguished the stiffness and mechanical properties of the object— a key characteristic for robots to manipulate various objects.

[0069] In summary, the one-step strategy of this application constructs a double-layer hydrogel combining the flexible poly(AM-AA)-gelatin-based hydrogel with the robust PSA layer, effectively solving the problems of weak adhesion and poor stability of traditional hydrogel sensors. Benefiting from the synergistic effect of multiple hydrogen bonds and the helical structure of gelatin, the prepared PAAMG hydrogel exhibits excellent mechanical strength (27.3 kPa), anti-drying property (water loss rate 11%) and tensile property (548%). The double-layer structure realizes strong interfacial bonding through the penetration of pressure-sensitive adhesive, while avoiding the trade-off between adhesion enhancement and sensing performance. With these characteristics, the PAAMG hydrogel has high sensitivity detection capability for human motion from subtle finger movements to large-scale joint bending, and excellent adhesion ensures its stable operation under dynamic conditions. In addition, the reliable signal output of the hydrogel supports advanced applications such as Morse code information transmission and real-time pressure mapping. The successful integration of a 4×4 sensing array into a robot gripper realizes the tactile recognition of balloons and bottles, further highlighting the potential of hydrogels in the field of intelligent robots and human-machine interaction. Overall, this study provides a new design paradigm for double-layer hydrogels with adhesion and multifunctionality, and provides broad opportunities for the development of next-generation wearable electronic devices, health monitoring and robotic tactile systems.

[0070] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a pressure distribution identification bilayer hydrogel, characterized in that, Includes the following steps: Step S10, the preparation of glycerol-polycaprolactone methacrylic anhydride GPCL-MA, is as follows: Step S11: Under nitrogen protection, add 29-31g of ε-CL, 1.11-1.13g of glycerol and 0.2-0.4g of stannous octoate to a three-necked flask according to the mass ratio, and stir the reaction at 140℃ for 24 h. After the reaction is completed, dry the obtained glycerol-caprolactone GPCL product and collect it. Step S12, GPCL-MA is prepared by one-step reaction: 19-21 g of GPCL and 4-6 g of MAA are thoroughly mixed in a three-necked flask according to the mass ratio, and reacted at 130°C for 7 h under a nitrogen atmosphere. The transparent reaction solution is dried in a vacuum oven at 40°C to remove unreacted methacrylic acid and obtain the target product GPCL-MA. Step S20, the preparation of PAAMG hydrogel, is as follows: Step S21: Dissolve 0.5-2.5 parts of acrylic acid AA, 0.05-0.5 parts of acrylamide AM, 0.05-0.5 parts of glycerol Gly, 0.01-1.5 parts of 20% gelatin solution, 0.05-0.15 parts of 1.2% N,N'-methylenebisacrylamide MBA solution, and 0.01-0.03 parts of photoinitiator Irgacure 2959 in 1-3 parts of deionized water according to the following mass ratios. Stir at room temperature for 30 min until completely dissolved to form solution A. Step S22: Add 0.1-0.5 parts of butyl acrylate BA, 0.1-0.4 parts of hydroxyethyl acrylate HEA, 0.1-0.3 parts of GPCL-MA and 0.01-0.03 parts of Irgacure 2959 to 0.1-0.5 parts of ethyl acetate EA according to the mass ratio to prepare a homogeneous solution B; Step S23: Pour 40-60 parts of solution A into the mold according to the volume ratio, then add 60-40 parts of solution B. Due to the density difference between water and ethyl acetate, the mixed solution will automatically separate into layers. The mixed solution was then irradiated with UV light for 15 minutes using a UV curing machine equipped with LED lights to obtain a bilayer hydrogel with pressure distribution identification.

2. The method for preparing a pressure distribution identification bilayer hydrogel according to claim 1, characterized in that: In step S11, the mass ratio of ε-CL, glycerol, and stannous octanoate is 30.0 g: 1.12 g: 0.3 g.

3. The method for preparing a pressure distribution identification bilayer hydrogel according to claim 1, characterized in that: In step S11, the molar ratio of ε-CL, glycerol, and stannous octanoate is 0.26 mol: 12.4 mmol: 0.74 mmol.

4. The method for preparing a pressure distribution identification bilayer hydrogel according to claim 1, characterized in that: In step S12, the mass ratio of GPCL to MAA is 20.0 g: 5.0 g.

5. The method for preparing a pressure distribution identification bilayer hydrogel according to claim 1, characterized in that: In step S21, 1 part of acrylic acid AA, 0.15 parts of acrylamide AM, 0.3 parts of glycerol Gly, 0.01 parts of 20% gelatin solution, 0.1 parts of 1.2% N,N'-methylenebisacrylamide MBA solution, and 0.01 parts of photoinitiator Irgacure 2959 are dissolved in 1 part of deionized water according to the following mass ratios. The solution is stirred at room temperature for 30 minutes until completely dissolved to form solution A.

6. The method for preparing a pressure distribution identification bilayer hydrogel according to claim 1, characterized in that: In step S22, 0.5 parts of butyl acrylate BA, 0.3 parts of hydroxyethyl acrylate HEA, 0.2 parts of GPCL-MA and 0.01 parts of Irgacure 2959 are added to 0.3 parts of ethyl acetate EA according to the mass ratio to prepare a homogeneous solution B.

7. The method for preparing a pressure distribution identification bilayer hydrogel according to claim 1, characterized in that: In step S23, the UV energy of the UV curing machine is 200mW / cm². 2 The wavelength is 365 nm. According to the volume ratio, first pour 50 parts of solution A into the mold, and then add 50 parts of solution B.

8. A pressure distribution identification bilayer hydrogel prepared by any one of the preparation methods of claims 1-7.

9. The application of a pressure distribution identification bilayer hydrogel prepared by any one of claims 1-7 in wearable electronic devices.

10. The application of a pressure distribution identification bilayer hydrogel prepared by any one of claims 1-7 in a flexible robot.

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