Relaxation type pressure ion hydrogel sensor and preparation method thereof, self-driven flexible wearable hand rehabilitation evaluation system

Abstract

The application provides a relaxation type pressure ion hydrogel sensor and a preparation method thereof and a self-driven flexible wearable hand rehabilitation evaluation system, and belongs to the flexible wearable device field; solves the problem that the existing hand movement sensing technology mainly evaluates according to a single signal or a complete continuous waveform in a loading stage, and is difficult to characterize the speed and recovery state in the hand stretching, unloading and active relaxation process; the application utilizes the different ion migration and relaxation behaviors of the pressure ion hydrogel in the loading and unloading processes, so that the sensor generates a first polarity positive peak when the hand is bent or pressed, generates an opposite polarity reverse peak when the hand is stretched or unloaded, and utilizes the amplitude of the reverse peak, whether it can be distinguished and the time relationship between the reverse peak and the positive peak to evaluate the finger bending amplitude, stress state, action speed, stretching state and active relaxation ability; the application can be used for hand fine movement monitoring and active rehabilitation evaluation.

Description

Technical Field

[0001] This application relates to the field of self-driven piezoelectric sensing and hand rehabilitation assessment technology, and in particular to a relaxor-type piezoelectric hydrogel sensor and its preparation method, and a self-driven flexible wearable hand rehabilitation assessment system. Background Technology

[0002] Stroke, Parkinson's disease, and other central motor neuron disorders can lead to a decline in finger dexterity, motor coordination, and muscle control. Hand rehabilitation training, through repeated performance of bending, extending, grasping, and relaxing movements, provides continuous and objective assessment of the degree of completion, speed, and relaxation state of these movements. This helps to understand the patient's hand motor function and rehabilitation progress.

[0003] Traditional hand rehabilitation assessments primarily rely on observation by rehabilitation therapists, scale scoring, or muscle strength measurements. These methods suffer from high subjectivity, difficulty in continuously recording micro-joint movements, and inconvenience for home-based rehabilitation monitoring. Therefore, developing wearable sensing technologies capable of real-time, objective, and quantitative evaluation of hand movement is of great significance. Flexible wearable sensors, characterized by their softness, flexibility, and ease of attachment to joints or deformed areas, have been used for joint movement and rehabilitation training monitoring. For hand rehabilitation assessments, sensors typically need to be attached to finger joints or moving parts of the hand, providing a stable response to bending, extension, and grasping movements. If sensors require a continuous external power supply or complex power supply structures, it not only increases the burden of wearing them but also hinders portable monitoring during natural hand movements. Therefore, self-driven flexible sensors that can directly convert hand mechanical movements into electrical signals have high application value in wearable hand rehabilitation assessments.

[0004] Ionic hydrogels contain a large number of migratable ions. When subjected to external pressure, anions and cations migrate asymmetrically due to their different migration abilities, generating a pressure ion voltage or current. This allows for the conversion of mechanical stimulation into electrical signals without the need for an external excitation power source, making them suitable for constructing self-powered wearable sensors. However, existing pressure ion sensors typically employ isotropic or randomly distributed polymer networks, resulting in disordered ion migration paths. Their output primarily relies on a single peak generated during the pressure loading phase to determine pressure magnitude, bending angle, or movement intensity. Once the pressure is released, ions gradually diffuse along random paths and return to equilibrium, making it difficult to form a stable and distinguishable reverse signal. Furthermore, in hand rehabilitation, patients not only need to perform finger flexion or grasping but also control finger extension and active relaxation. Current technologies struggle to distinguish between rapid and slow hand unloading and to quantify active relaxation capabilities. Especially when monitoring multiple fingers simultaneously, continuously acquiring and processing complete waveforms from each channel increases the burden of data storage, transmission, and analysis, limiting their application in dynamic assessment of hand rehabilitation. Therefore, it is necessary to develop a self-driven flexible wearable hand rehabilitation assessment system based on the characteristics of relaxor-type bipolar piezo-ion response. This system should generate a positive piezo-ion signal during hand bending or compression, and a reverse transient piezo-ion signal during hand extension or unloading, forming a loading-unloading bipolar piezo-ion signal. Based on the positive peak, reverse peak, and time characteristics, the system can characterize the finger bending amplitude, force state, movement speed, extension state, and active relaxation ability, providing objective electrical signal evidence for fine hand movement monitoring and active rehabilitation assessment. Summary of the Invention

[0005] To address the limitations of existing hand motion sensing technologies, which primarily rely on single signals or complete continuous waveforms during the loading phase and struggle to characterize the speed and recovery state during hand extension, unloading, and active relaxation, this application proposes a relaxor-type piezoelectric hydrogel sensor and its fabrication method, along with a self-driven flexible wearable hand rehabilitation assessment system. This system utilizes the ion migration, elastic recovery, and ion relaxation behavior of anisotropic piezoelectric hydrogels with directional ion transport channels during hand bending, compression, extension, or unloading to generate a loading-unloading bipolar piezoelectric signal. Based on the positive peak, negative peak, and temporal characteristics, it achieves rehabilitation assessment of finger flexion amplitude, force state, movement speed, extension state, and active relaxation ability. Simultaneously, by leveraging the positive peak, negative peak, and temporal characteristics of the bipolar piezoelectric signal, it enables real-time monitoring and quantitative assessment of finger flexion amplitude, movement speed, extension state, and active relaxation ability, reducing reliance on the storage, transmission, and analysis of complete continuous waveforms for each signal channel.

[0006] The technical solution adopted in this application is: a relaxor-type ion hydrogel sensor, including anisotropic ion hydrogel, a first electrode, a second electrode and a flexible encapsulation layer, wherein the anisotropic ion hydrogel includes a polymer network, a solvent and cations and anions dispersed in the solvent, the polymer network is arranged in a predetermined direction to form a directional ion transport channel inside the anisotropic ion hydrogel, and the first electrode and the second electrode are respectively connected to two signal acquisition areas of the anisotropic ion hydrogel; The relaxable piezoelectric hydrogel sensor is attached to finger joints or moving parts of the hand, or to other parts of the hand that bend, extend, are compressed, or undergo local deformation with slight joint movements. When the hand is bent or compressed, the cations and anions in the relaxable piezoelectric hydrogel sensor undergo asymmetric migration under the action of a pressure gradient and generate a piezoelectric signal of the first polarity. The first polarity piezoelectric signal has a positive peak. When the hand is extended or unloaded, the anisotropic ionic hydrogel in the relaxable piezoelectric hydrogel sensor undergoes elastic recovery and ionic relaxation, and generates a reverse transient piezoelectric signal with the opposite polarity to the first polarity. The reverse transient piezoelectric signal has a reverse peak, thus forming a loading-unloading bipolar piezoelectric signal.

[0007] Furthermore, the amplitude, time characteristics, and whether a distinguishable reverse peak is formed are related to the rate of hand extension or unloading. When the unloading time experienced by hand extension or unloading is less than the ion relaxation characteristic time of the anisotropic ionic hydrogel, the reverse transient pressure ion signal forms a distinguishable reverse peak. When the unloading time experienced by hand extension or unloading is greater than or equal to the ion relaxation characteristic time, the amplitude of the reverse peak decreases or no distinguishable reverse peak is formed. The amplitude of the reverse peak increases with the increase of unloading speed or unloading acceleration.

[0008] Furthermore, the anisotropic ionic hydrogel undergoes orientation treatment, which makes its ion transport capacity along the orientation direction higher than that perpendicular to the orientation direction, and makes the reverse peak generated during hand extension or unloading easier to distinguish compared to the unoriented ionic hydrogel.

[0009] Furthermore, the polymer network is composed of polyvinyl alcohol; the solvent includes at least two of water, dimethyl sulfoxide, and glycerol; the cations and anions are provided by one or more ionic salts of sodium chloride, lithium chloride, potassium iodide, and sodium sulfate, wherein the concentration of the ionic salt is 0.1~0.3 mol / L.

[0010] Furthermore, the thickness of the anisotropic ionic hydrogel is 1~3mm, and the distance between the first electrode and the second electrode is 5~10mm.

[0011] A method for preparing a relaxor-type piezoelectric hydrogel sensor includes the following steps: a) Add the polymer to the first solvent, heat and stir to obtain a polymer solution; b) Dissolve the ionic salt in a second solvent to obtain an ionic solution, and mix the ionic solution with a polymer solution to obtain an ionic hydrogel precursor; c) Defoaming and gelation treatment of the ion hydrogel precursor to obtain the ion hydrogel; d) Orient the ionic hydrogel so that the polymer network is aligned in a predetermined direction to obtain anisotropic ionic hydrogel with oriented ion transport channels; e) The first electrode and the second electrode are placed in the two signal acquisition areas of the anisotropic ion hydrogel and encapsulated with a flexible encapsulation layer to obtain a relaxor-type pressure ion sensor.

[0012] Further, in step a), polyvinyl alcohol is added to dimethyl sulfoxide and heated and stirred at 80~100℃; in step b), ionic salt and glycerol are dissolved in water and mixed with the polyvinyl alcohol solution; in step c), the ionic hydrogel precursor is degassed and injected into a mold, and frozen at -80~-20℃ for 6~24h; in step d), the ionic hydrogel is subjected to 50~150 cycles of stretching along a fixed direction.

[0013] A self-driven flexible wearable hand rehabilitation assessment system includes at least one relaxable piezoelectric hydrogel sensor, a signal acquisition module, a feature analysis module, and a motion state assessment and feedback module. The relaxable piezoelectric hydrogel sensor is attached to different finger joints or hand movement sites, or to other parts of the hand that bend, extend, are compressed, or undergo local deformation with slight joint movements, and is connected to independent signal channels. The signal acquisition module acquires the piezoelectric voltage signal output by the relaxable piezoelectric hydrogel sensor. The feature analysis module extracts the positive peak amplitude, negative peak amplitude, interpeak time between the positive and negative peaks, and the presence or absence of the negative peak from the piezoelectric voltage signal. The motion state assessment and feedback module characterizes the finger bending amplitude or force state based on the positive peak amplitude, determines the movement speed, extension state, and active relaxation ability based on the negative peak amplitude, the presence or absence of the negative peak, and the interpeak time, and outputs the hand rehabilitation assessment results.

[0014] Furthermore, the feature analysis module is used to perform baseline calibration and extreme value identification on the pressure ion voltage signal, determine the first polarity voltage extreme value that appears during the bending or pressing of the hand as the positive peak, determine the voltage extreme value that appears during the stretching or unloading of the hand and is opposite to the first polarity as the reverse peak, and determine the difference between the time when the positive peak reaches its extreme value and the time when the reverse peak reaches its extreme value as the interpeak time.

[0015] Furthermore, the finger movement state assessment and feedback module uses the positive peak amplitude, negative peak amplitude, interpeak time, and the presence or absence of negative peaks of each signal channel as rehabilitation assessment inputs. Based on the positive peak amplitude, it generates assessment results of finger flexion amplitude or force state. Based on the negative peak amplitude and the presence or absence of negative peaks, it generates assessment results of finger extension state and active relaxation ability. Based on the assessment results of multiple consecutive hand movements, it generates rehabilitation scores and rehabilitation progress information.

[0016] The advantages of this application compared to existing technologies are as follows: The relaxor-type ionized hydrogel sensor prepared in this application can self-drive the output of ionized voltage signals under the action of hand mechanical movements, without the need for an external excitation power supply. This application not only utilizes the positive peak during the loading phase to characterize the hand's bending or stress state, but also utilizes the reverse peak generated by elastic recovery and ion relaxation during the unloading phase to characterize the hand's extension and relaxation process, achieving simultaneous evaluation of both the loading and unloading phases. This application utilizes the relationship between unloading time and ion relaxation characteristic time to form a distinguishable reverse peak during rapid unloading, while the reverse peak weakens or becomes indistinguishable during slow unloading, thus providing an electrical signal basis for distinguishing different unloading states and evaluating active relaxation ability. This application performs rehabilitation assessment by extracting the amplitude of the positive peak, the amplitude of the reverse peak, the interpeak time, and the presence or absence of the reverse peak, reducing the need for repeated storage and analysis of complete continuous waveforms, and is suitable for multi-channel, real-time hand rehabilitation monitoring. This application utilizes anisotropic ionized hydrogels with directional ion transport channels to guide ion migration and relaxation, making the reverse peak during the unloading phase easier to identify, which is beneficial for improving the distinguishability of the assessment of extension and active relaxation states. This application utilizes anisotropic ionized hydrogels with directional ion transport channels to guide ion migration and relaxation, making the reverse peak during the unloading phase easier to identify and improving the discriminability of extension and active relaxation state assessments. The relaxor-type piezoelectric hydrogel sensor of this application requires no external voltage or current excitation during signal generation and can be attached to finger joints and localized deformed areas of the hand, making it suitable for portable, wearable, and home-based hand rehabilitation assessments. By setting multiple independent signal channels, the loading-unloading bipolar piezoelectric response of different fingers can be obtained separately, enabling quantitative assessment of multi-finger movement status, rehabilitation scores, and rehabilitation progress.

[0017] The main difference between the relaxor-type piezoelectric hydrogel sensor of this application and existing piezoelectric sensors lies in that this application does not merely utilize a single piezoelectric signal generated during the pressure loading phase to characterize pressure magnitude, bending degree, or movement intensity. Instead, it further utilizes the reverse transient piezoelectric signal generated by the elastic recovery and ion relaxation of the hydrogel during hand extension or unloading, forming a loading-unloading bipolar piezoelectric response. By extracting the positive peak amplitude, reverse peak amplitude, interpeak time, and the presence or absence of the reverse peak, the finger bending or force state, movement speed, extension state, and active relaxation ability can be characterized, respectively. In particular, when the unloading speed decreases, the reverse peak weakens or does not form a distinguishable reverse peak, thereby enabling the identification of different unloading and relaxation states. Compared with methods relying on complete continuous waveforms for analysis, this application uses finite peak values ​​and time characteristics for rehabilitation assessment, which reduces the burden of storing, transmitting, and analyzing multi-channel signals, providing objective evidence for fine hand movement monitoring and active rehabilitation assessment, and has good application prospects in the fields of self-driven flexible wearable sensing and rehabilitation medicine. Attached Figure Description

[0018] The following description, in conjunction with the accompanying drawings, further illustrates this application: Figure 1 This is a schematic diagram of the overall structure of the relaxor-type pressure ion sensor of this application; Figure 2 This is a schematic diagram illustrating the working principle of the relaxor-type pressure ion sensor and hand rehabilitation assessment system of this application; Figure 3 Schematic diagrams of the relaxed-type piezo-ion sensor prepared by the method of this application before and after orientation; Figure 4 Scanning electron microscope (SEM) images of the structure of the relaxor-type piezo-ion sensor prepared by the method of this application before and after orientation; Figure 5 The tensile stress-strain curves of the gel before and after orientation of the relaxor-type piezo-ion sensor prepared by the method of this application; Figure 6 Graphs showing the changes in water content of the relaxor-type piezo-ion sensor prepared by the method of this application under different temperatures / days and with and without encapsulation. Figure 7 Voltage response diagrams before and after orientation of the relaxor-type piezo-ion sensor prepared by the method of this application; Figure 8 The voltage response diagrams of the relaxor-type piezo-ion sensor prepared by the method of this application at different unloading rates and accelerations; Figure 9 Cyclic response diagram of the relaxor-type piezo-ion sensor prepared by the method of this application; Figure 10 This is a closed-loop evaluation flowchart for the relaxor-type pressure ion sensor and hand rehabilitation assessment system of this application; Figure 11 This is a multi-finger rehabilitation voltage response diagram of the relaxor-type pressure ion sensor and hand rehabilitation assessment system of this application. Detailed Implementation

[0019] like Figures 1 to 11 As shown, this application provides a relaxorable piezoelectric hydrogel sensor, which includes anisotropic ionic hydrogel, a first electrode, a second electrode, and a flexible encapsulation layer. The anisotropic ionic hydrogel includes a polymer network, a solvent, and cations and anions dispersed in the solvent. The polymer network is arranged along a predetermined direction, forming directional ion transport channels within the ionic hydrogel. The first electrode and the second electrode are respectively connected to two signal acquisition areas of the anisotropic ionic hydrogel.

[0020] Relaxable piezoelectric hydrogel sensors can be attached to finger joints or other parts of the hand that bend, extend, are compressed, or undergo localized deformation with slight joint movements. During the generation of piezoelectric signals by the relaxable piezoelectric hydrogel sensor, no external voltage or current excitation is required. When the hand bends or is compressed, a pressure gradient forms between the compressed and uncompressed areas. Cations and anions migrate asymmetrically due to their different migration abilities, generating a piezoelectric signal of the first polarity between the first and second electrodes, which has a positive peak. When the hand extends or is unloaded, the anisotropic ion hydrogel elastically recovers, and cations and anions relax and migrate along directional ion transport channels. When the hand extends or is unloaded quickly, the ion distribution cannot quickly return to equilibrium, resulting in the accumulation of reverse charge in the signal acquisition area and generating a reverse transient piezoelectric signal opposite to the first polarity. When the hand extends or is unloaded slowly, the ions gradually return to equilibrium, the reverse transient piezoelectric signal weakens or disappears, and has a reverse peak. The positive and reverse transient pressure ion signals of the first polarity together constitute the load-unload bipolar pressure ion signal. The amplitude, temporal characteristics, and whether a distinguishable reverse peak forms are related to the rate of hand extension or unloading. When the unloading time experienced by hand extension or unloading is less than the ion relaxation characteristic time of the anisotropic ionized hydrogel, the ion distribution cannot fully recover equilibrium during unloading, and a distinguishable reverse peak forms in the reverse transient pressure ion signal. When the unloading time experienced by hand extension or unloading is greater than or equal to the ion relaxation characteristic time of the anisotropic ionized hydrogel, the ions gradually recover equilibrium during unloading, and the amplitude of the reverse peak decreases or no distinguishable reverse peak forms. The amplitude of the reverse peak increases with increasing unloading speed or unloading acceleration.

[0021] In a preferred embodiment, the anisotropic ionic hydrogel is oriented to increase its ion transport capacity along the orientation direction compared to the direction perpendicular to the orientation, and to make the reverse peaks generated during hand extension or unloading more easily distinguishable compared to unoriented ionic hydrogels. Orientation treatments include one or more of directional stretching, cyclic stretching, directional freezing, shear orientation, or template induction.

[0022] In a preferred embodiment, the polymer network is composed of polyvinyl alcohol, the solvent includes at least two of water, dimethyl sulfoxide and glycerol, the cations and anions are provided by one or more of sodium chloride, lithium chloride, potassium iodide and sodium sulfate, the ionic salt is sodium chloride with a concentration of 0.1~0.3 mol / L, and the flexible encapsulation layer is a polyurethane film.

[0023] In a preferred embodiment, the first electrode and the second electrode are copper electrodes, the thickness of the anisotropic ionic hydrogel is 1~3mm, and the distance between the first electrode and the second electrode is 5~10mm.

[0024] This application also provides a method for preparing a relaxor-type ion-hydrogel sensor, including the preparation of an ion-hydrogel precursor, gelation treatment, orientation treatment, and electrode assembly and encapsulation: a) Add the polymer to the first solvent, heat and stir to obtain a polymer solution; b) Dissolve the ionic salt in a second solvent to obtain an ionic solution, and mix the ionic solution with a polymer solution to obtain an ionic hydrogel precursor; c) Defoaming and gelation treatment of the ion hydrogel precursor to obtain the ion hydrogel; d) Orient the ionic hydrogel so that the polymer network is aligned in a predetermined direction to obtain anisotropic ionic hydrogel with oriented ion transport channels; e) The first electrode and the second electrode are placed in the two signal acquisition areas of the anisotropic ion hydrogel and encapsulated with a flexible encapsulation layer to obtain a relaxor-type pressure ion sensor.

[0025] In a preferred embodiment, polyvinyl alcohol is added to dimethyl sulfoxide and heated and stirred at 80~100°C; ionic salt and glycerol are dissolved in water and mixed with the polyvinyl alcohol solution; the resulting precursor is degassed and injected into a mold, frozen at -80~-20°C for 6~24h to form an ionic hydrogel, and then stretched 50~150 times along a fixed direction to form an anisotropic orientation network.

[0026] This application also provides a self-driven flexible wearable hand rehabilitation assessment system, which includes at least one relaxable piezoelectric hydrogel sensor, a signal acquisition module, a feature analysis module, and a motion state assessment and feedback module. The number of relaxable piezoelectric hydrogel sensors is preferably 1 to 5. Multiple relaxable piezoelectric hydrogel sensors are respectively attached to different finger joints or hand movement sites, or to other parts of the hand that bend, extend, are compressed, or undergo local deformation with slight joint movements, and are respectively connected to independent signal channels. The signal acquisition module acquires load-unload bipolar piezoelectric signals generated by different fingers or different hand sites. The feature analysis module performs baseline calibration and extreme value identification on the piezoelectric signals, determining the first polarity voltage extreme value appearing during hand bending or compression as the positive peak, and determining the voltage extreme value opposite to the first polarity appearing during hand extension or unloading as the reverse peak, and extracting the positive peak amplitude, reverse peak amplitude, the presence of the reverse peak, and the interpeak time for each signal channel. The interpeak time is the time difference between the moment the positive peak reaches its extreme value and the moment the negative peak reaches its extreme value. The motion state assessment and feedback module generates assessment results for the corresponding finger's flexion amplitude, force state, movement speed, extension state, and active relaxation ability based on the characteristic analysis results of each signal channel. It also generates a rehabilitation score and rehabilitation progress information based on the assessment results of multiple consecutive hand movements. Specifically, the positive peak amplitude represents the finger's flexion amplitude or force state, while the negative peak amplitude and its presence or absence represent the finger's extension state and active relaxation ability. The movement speed is determined by combining the interpeak time, and the hand rehabilitation assessment results are output.

[0027] This application utilizes the positive peak, negative peak, and time characteristics in bipolar pressure ion signals to achieve real-time monitoring and quantitative evaluation of finger bending amplitude, movement speed, extension state, and active relaxation ability, reducing reliance on the storage, transmission, and analysis of complete and continuous waveforms of each signal channel.

[0028] The present application will now be further described with reference to the accompanying drawings.

[0029] This application provides a self-driven flexible wearable hand rehabilitation assessment system based on the characteristics of relaxor-type bipolar piezoelectric response. The aim is to address the shortcomings of existing hand motion sensing technologies, which primarily rely on single signals or complete continuous waveforms during the loading phase. These technologies struggle to effectively characterize the speed and recovery state during hand extension, unloading, and active relaxation, and also suffer from the significant burden of storing, transmitting, and analyzing multi-channel continuous waveforms. The system includes at least one relaxor-type piezoelectric hydrogel sensor, a signal acquisition module, a feature analysis module, and a motion state assessment and feedback module. The relaxor-type piezoelectric hydrogel sensor is attached to the finger joints or other parts of the hand that undergo bending, extension, compression, or localized deformation with slight joint movements. Figure 1 Hand movements cause mechanical deformation in the sensor. During signal generation, the sensor converts this mechanical deformation into a pressure-ion voltage signal without external voltage or current excitation. In this embodiment, the "loading phase" refers to the process where bending, pressing, or grasping the hand subjects the sensor to compression, bending, or localized pressure; the "unloading phase" refers to the process where extending, releasing, or relaxing the hand reduces or removes the mechanical force applied to the sensor. The first polarity voltage extreme value formed during the loading phase is called the positive peak; the voltage extreme value opposite to the first polarity generated by the elastic recovery and ion relaxation of the hydrogel during the unloading phase is called the reverse peak. The positive and reverse peaks together constitute the loading-unloading bipolar pressure-ion response. Figure 2 In this embodiment, a "distinguished reverse peak" refers to a reverse voltage extreme value whose amplitude is higher than the baseline fluctuation or the lowest identifiable level of the signal acquisition module, and can be distinguished from the baseline recovery process. When the reverse peak is lower than the lowest identifiable level, it is considered that no distinguishable reverse peak has been formed. "Ion relaxation characteristic time" refers to the characteristic time corresponding to the recovery of ions inside the hydrogel from a non-equilibrium distribution state formed after loading to an equilibrium state under given hydrogel composition, device size, and environmental conditions. The ion relaxation characteristic time can be determined by the reverse peak response under different unloading times. The pressure ion signal is directly induced by hand mechanical movements. The sensor does not require an external excitation power supply during signal generation and can be used as a self-driven wearable sensing unit for hand rehabilitation assessment. Based on the amplitude, polarity change, and time characteristics of this bipolar signal, real-time characterization of finger flexion amplitude, movement speed, extension state, and active relaxation ability can be further realized, providing objective basis for monitoring the movement state, assessing rehabilitation progress, and adjusting feedback during hand rehabilitation training.

[0030] Example 1: Fabrication and performance characterization of a relaxor-type piezoelectric hydrogel sensor The specific steps are as follows: Step 1: Add 6g of polyvinyl alcohol to 25mL of dimethyl sulfoxide, heat and stir at 95℃ until the polyvinyl alcohol is completely dissolved to obtain a homogeneous polymer solution.

[0031] Step 2: Add sodium chloride and an appropriate amount of glycerol to 25 mL of deionized water and stir thoroughly to obtain an ionic solution. The preferred concentration of sodium chloride is 0.2 mol / L. Mix the ionic solution with the polymer solution, inject the mixture into a mold, and freeze at -20°C for 12 hours to obtain a piezoelectric hydrogel.

[0032] Step 3: The ionized hydrogel is subjected to 100 cycles of stretching along a fixed direction, causing the polymer chains to gradually align along the stretching direction, forming an anisotropic ionized hydrogel with oriented ion transport channels. The orientation process and the microstructure before and after orientation are shown below. Figure 3 and Figure 4 As shown.

[0033] Step 4: Cut the anisotropic ion hydrogel to the required size and place copper electrodes in its two signal acquisition areas. The hydrogel thickness is preferably 1.5 mm, and the spacing between the two electrodes is preferably 7 mm. Encapsulate with a polyurethane film to obtain a relaxor-type ion hydrogel sensor. Perform tensile tests on the ion hydrogel before and after orientation; the resulting stress-strain curves are shown below. Figure 5 As shown; the water content change of the ionized hydrogel before and after encapsulation was tested, and the results are as follows. Figure 6 As shown. Test results indicate that orientation treatment transforms the polymer network from a random distribution to an alignment along a predetermined direction. The resulting anisotropic network provides directional transport channels for ions while maintaining good flexibility, tensile properties, and elastic recovery. Polyurethane film encapsulation reduces moisture evaporation, improves the sensor's environmental stability, and facilitates wearable monitoring by attaching the sensor to finger joints or hand movement areas. The material dosage, processing temperature, processing time, number of stretching cycles, and device dimensions in this embodiment are exemplary parameters and can be adjusted within the scope defined in this specification.

[0034] Example 2: Load-Unload Bipolar Response and Unloading Rate Test The sensor prepared in Example 1 was fixed on the test platform, and local pressure loading and unloading were performed between the two electrodes, while the output voltage was collected.

[0035] During pressure loading, anions and cations within the hydrogel undergo asymmetric migration under the pressure gradient, generating a positive peak of the first polarity. During pressure unloading, the hydrogel elastically recovers, and ions relax and migrate along directional transport channels. When pressure is rapidly unloaded, the ion distribution cannot quickly return to equilibrium, leading to a transient accumulation of reverse charge near the electrodes, resulting in a reverse voltage peak. When pressure is slowly unloaded, the ions have sufficient time to return to equilibrium, and the reverse voltage peak weakens or disappears. This reverse transient pressure-ion signal can correspond to the dynamic recovery state during hand extension or unloading processes, such as... Figure 7 As shown.

[0036] Keeping the loading conditions basically consistent, change the unloading time experienced during pressure relief and record the changes in the reverse peak, such as... Figure 8 As shown in the figure, when the unloading speed is fast, the ion distribution cannot recover to equilibrium in time, forming a significant reverse peak; as the unloading time increases, the amplitude of the reverse peak gradually decreases. Repeated loading-unloading tests were performed on the sensor, and the results are as follows. Figure 9 As shown, during multiple cycles, the positive and negative peaks maintained a stable polarity change, indicating that the sensor prepared in this application can be used for continuous hand movement monitoring.

[0037] In this embodiment, a distinct reverse peak is observed when the unloading time is less than 1 second; when the unloading time is greater than 10 seconds, the reverse peak is significantly weakened or indistinguishable. Therefore, the sensor can form a distinguishable self-driven bipolar pressure ion response using the forward peak during the loading phase and the reverse peak during the unloading phase without the need for an external excitation power supply. The above times are the test results of this embodiment; the actual judgment threshold can be determined based on the hydrogel composition, device size, and test conditions.

[0038] Example 3: Feature Extraction of Bipolar Pyro-ion Signals Connect the output of the relaxor-type piezoelectric hydrogel sensor to the signal acquisition module. For example... Figure 10 As shown, the signal acquisition module acquires the pressure-ion voltage signal between the two electrodes of the sensor at a predetermined sampling frequency and transmits the obtained voltage signal to the feature analysis module. The feature analysis module first performs baseline calibration on the acquired voltage signal to reduce the impact of initial potential shift and slow baseline drift on peak identification.

[0039] During the loading phase corresponding to hand bending or pressure, the voltage extreme value of the first polarity is identified as the positive peak, and the amplitude of the positive peak and the time when the positive peak reaches its extreme value are recorded. During the unloading phase corresponding to hand extension or unloading, the voltage extreme value opposite to the first polarity is identified. When the voltage extreme value is higher than the minimum identifiable level of the system, it is identified as a distinguishable reverse peak, and the amplitude of the reverse peak and the time when the reverse peak reaches its extreme value are recorded; when the voltage change of the opposite polarity is lower than the minimum identifiable level, the reverse peak state is identified as no distinguishable reverse peak has been formed.

[0040] The time difference between the moment when the positive peak reaches its extreme value and the moment when the negative peak reaches its extreme value is defined as the interpeak time.

[0041] When a distinguishable reverse peak is formed, the feature analysis module outputs the amplitude of the forward peak, the amplitude of the reverse peak, the interpeak time, and the presence status of the reverse peak. When no distinguishable reverse peak is formed, the feature analysis module outputs the amplitude of the forward peak, the state in which the reverse peak is not distinguishable, and the corresponding unloading status information.

[0042] In other embodiments, the feature analysis module may also extract the duration, peak width, rise time, fall time, or signal recovery time of the positive or negative peaks to assist in evaluating the hand movement status. However, the additional parameters do not affect the basic technical solution of this application for evaluation using positive peaks, negative peaks, and inter-peak times.

[0043] Example 4: Hand Rehabilitation Assessment System for Single and Multiple Fingers One to five relaxable piezoelectric hydrogel sensors prepared in Example 1 were attached to the finger joints or other deformed areas of the hand to be evaluated. One sensor was used for single-finger evaluation, while for multi-finger evaluation, each sensor was connected to an independent signal channel. The subject sequentially performed finger flexion, holding, extension, and relaxation movements, and the signal acquisition module collected the loading-unloading bipolar piezoelectric signals output by each sensor.

[0044] A positive peak is generated when the finger is bent or compressed, and a negative peak is generated when the finger is extended or unloaded. The negative peak is more obvious during rapid extension, and weakens or disappears during slow extension or slow relaxation. The feature analysis module performs baseline calibration and extreme value identification on the signals of each channel, and extracts the amplitude of the positive peak, the amplitude of the negative peak, the interpeak time between the positive and negative peaks, and the presence or absence of the negative peak.

[0045] The motion state assessment and feedback module evaluates the flexion range or force state of the corresponding finger based on the positive peak amplitude, assesses the extension state and active relaxation ability based on the negative peak amplitude and the presence or absence of the negative peak, and evaluates the movement speed or rhythm by combining the interpeak time and negative peak characteristics. In multi-finger assessment, each signal channel generates assessment results for the corresponding finger to reflect the movement differences between different fingers.

[0046] like Figure 11 As shown, based on the characteristic analysis results of multiple consecutive hand movements, assessment results of flexion state, extension state, movement speed, and active relaxation ability can be generated, and further, rehabilitation scores and rehabilitation progress information can be generated. The assessment results can be fed back through display, sound, vibration, or indicator lights for monitoring the hand rehabilitation training status. Furthermore, patients or rehabilitation therapists can determine whether the current movement meets the training requirements of slow relaxation based on the rehabilitation score and changes in the reverse signal, and adjust the training movements accordingly, thereby achieving real-time monitoring and closed-loop feedback of the hand rehabilitation process.

[0047] Example 5: Evaluation Method for Reducing Dependence on Complete Waveform Processing During continuous hand rehabilitation monitoring, the signal acquisition module continues to sample the sensor output signal to ensure that positive and negative peaks can be identified. The signal processing module performs baseline calibration, peak identification, and time feature extraction on the acquired voltage signal.

[0048] After peak identification is completed, the motion state assessment and feedback module mainly uses the positive peak amplitude, negative peak amplitude, inter-peak time, and the presence or absence of the negative peak as input for rehabilitation assessment, without needing to repeatedly call all continuous sampling points of each channel in each assessment. For multiple sensors and multiple consecutive movements, the data to be compared and transmitted can mainly consist of the peak value and time parameters of each channel, thereby reducing the data processing requirements of complete continuous waveforms in subsequent assessment, display, or remote transmission.

[0049] It should be noted that this implementation method does not completely stop the acquisition of the original waveform, but rather reduces the reliance of subsequent rehabilitation assessments on repeated storage, transmission and analysis of the complete waveform by extracting limited characteristic parameters that can reflect the loading, unloading and ion relaxation processes.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A relaxor-type piezoelectric hydrogel sensor, characterized in that: The device includes an anisotropic ionic hydrogel, a first electrode, a second electrode, and a flexible encapsulation layer. The anisotropic ionic hydrogel includes a polymer network, a solvent, and cations and anions dispersed in the solvent. The polymer network is arranged in a predetermined direction to form directional ion transport channels inside the anisotropic ionic hydrogel. The first electrode and the second electrode are respectively connected to two signal acquisition areas of the anisotropic ionic hydrogel. The relaxable piezoelectric hydrogel sensor is attached to finger joints or moving parts of the hand, or to other parts of the hand that bend, extend, are compressed, or undergo local deformation with slight joint movements. When the hand is bent or compressed, the cations and anions in the relaxable piezoelectric hydrogel sensor undergo asymmetric migration under the action of a pressure gradient and generate a piezoelectric signal of the first polarity. The first polarity piezoelectric signal has a positive peak. When the hand is extended or unloaded, the anisotropic ionic hydrogel in the relaxable piezoelectric hydrogel sensor undergoes elastic recovery and ionic relaxation, and generates a reverse transient piezoelectric signal with the opposite polarity to the first polarity. The reverse transient piezoelectric signal has a reverse peak, thus forming a loading-unloading bipolar piezoelectric signal.

2. The relaxor-type piezoelectric hydrogel sensor according to claim 1, characterized in that: The amplitude, time characteristics, and whether a distinguishable reverse peak is formed are related to the rate of hand extension or unloading. When the unloading time experienced by hand extension or unloading is less than the ion relaxation characteristic time of the anisotropic ionic hydrogel, the reverse transient pressure ion signal forms a distinguishable reverse peak. When the unloading time experienced by hand extension or unloading is greater than or equal to the ion relaxation characteristic time, the amplitude of the reverse peak decreases or no distinguishable reverse peak is formed. The amplitude of the reverse peak increases with the increase of unloading speed or unloading acceleration.

3. The relaxor-type piezoelectric hydrogel sensor according to claim 1, characterized in that: The anisotropic ionic hydrogel is oriented to make its ion transport capacity along the orientation direction higher than that perpendicular to the orientation direction, and to make the reverse peak generated during hand extension or unloading easier to distinguish compared to the unoriented ionic hydrogel.

4. The relaxor-type piezoelectric hydrogel sensor according to claim 3, characterized in that: The polymer network is composed of polyvinyl alcohol; the solvent includes at least two of water, dimethyl sulfoxide and glycerol, and the cations and anions are provided by one or more ionic salts of sodium chloride, lithium chloride, potassium iodide and sodium sulfate, wherein the concentration of the ionic salt is 0.1~0.3 mol / L.

5. A relaxor-type piezoelectric hydrogel sensor according to claim 1, characterized in that: The thickness of the anisotropic ionic hydrogel is 1~3mm, and the distance between the first electrode and the second electrode is 5~10mm.

6. A method for preparing a relaxor-type piezoelectric hydrogel sensor as described in any one of claims 1-5, characterized in that: Includes the following steps: a) Add the polymer to the first solvent, heat and stir to obtain a polymer solution; b) Dissolve the ionic salt in a second solvent to obtain an ionic solution, and mix the ionic solution with a polymer solution to obtain an ionic hydrogel precursor; c) Defoaming and gelation treatment of the ion hydrogel precursor to obtain the ion hydrogel; d) Orient the ionic hydrogel so that the polymer network is aligned in a predetermined direction to obtain anisotropic ionic hydrogel with oriented ion transport channels; e) The first electrode and the second electrode are placed in the two signal acquisition areas of the anisotropic ion hydrogel and encapsulated with a flexible encapsulation layer to obtain a relaxor-type pressure ion sensor.

7. The method for preparing a relaxor-type piezoelectric hydrogel sensor according to claim 6, characterized in that: In step a), polyvinyl alcohol is added to dimethyl sulfoxide and heated and stirred at 80~100℃; in step b), ionic salt and glycerol are dissolved in water and mixed with the polyvinyl alcohol solution; in step c), the ionic hydrogel precursor is degassed and injected into a mold, and frozen at -80~-20℃ for 6~24h; in step d), the ionic hydrogel is subjected to 50~150 cycles of stretching along a fixed direction.

8. A self-driven flexible wearable hand rehabilitation assessment system, characterized in that: The device includes at least one relaxable piezoelectric hydrogel sensor as described in any one of claims 1-5, a signal acquisition module, a feature analysis module, and a motion state assessment and feedback module. The relaxable piezoelectric hydrogel sensor is attached to different finger joints or hand movement sites, or to other parts of the hand that bend, extend, are compressed, or undergo local deformation with slight joint movements, and is connected to independent signal channels. The signal acquisition module is used to acquire the piezoelectric voltage signal output by the relaxable piezoelectric hydrogel sensor. The feature analysis module is used to extract the positive peak amplitude, the negative peak amplitude, the interpeak time between the positive and negative peaks, and the presence or absence of the negative peak from the piezoelectric voltage signal. The motion state assessment and feedback module is used to characterize the finger bending amplitude or force state based on the positive peak amplitude, and to determine the movement speed, extension state, and active relaxation ability based on the negative peak amplitude, the presence or absence of the negative peak, and the interpeak time, and outputs the hand rehabilitation assessment results.

9. The self-driven flexible wearable hand rehabilitation assessment system according to claim 8, characterized in that: The feature analysis module is used to perform baseline calibration and extreme value identification on the pressure ion voltage signal. The first polarity voltage extreme value that appears during the bending or pressing of the hand is determined as the positive peak, and the voltage extreme value that appears during the stretching or unloading of the hand and is opposite to the first polarity is determined as the reverse peak. The difference between the time when the positive peak reaches its extreme value and the time when the reverse peak reaches its extreme value is determined as the interpeak time.

10. The self-driven flexible wearable hand rehabilitation assessment system according to claim 8, characterized in that: The finger movement state assessment and feedback module uses the positive peak amplitude, negative peak amplitude, interpeak time, and presence / absence of negative peaks of each signal channel as rehabilitation assessment inputs. Based on the positive peak amplitude, it generates assessment results of finger flexion amplitude or force state. Based on the negative peak amplitude and presence / absence of negative peaks, it generates assessment results of finger extension state and active relaxation ability. Based on the assessment results of multiple consecutive hand movements, it generates rehabilitation scores and rehabilitation progress information.

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