Organohydrogel‐Based Soft SEMG Electrodes for Algorithm‐Assisted Gesture Recognition

Epidermal electronics that can monitor physiological signals such as surface electromyogram (sEMG) signals attract widespread attentions in personalized healthcare, human–machine interfaces (HMI) and virtual/augmented reality (AR/VR). However, conventional electromyographic electrodes suffer from skin discomfort, susceptibility to motion artifact interference, and short service lifetime. Here, an organohydrogel‐based sEMG electrode endows with high conductivity, low modulus and long‐term stability is developed by doping partially reduced graphene oxide (pRGO) into highly cross‐linked organohydrogel network. The as‐fabricated polyacrylamide/sodium alginate/tannic acid/partially reduced graphene oxide (PAM/SA/TA/pRGO) organohydrogel possesses farewell conductivity (4.22 S m−1) while preserving tissue‐like compliance (Young's modulus ≈32 KPa), excellent stretchability (≈600%), high adhesion as well as superior anti‐drying properties. In addition, a stretchable sEMG electrode for long‐term reliable service is fabricated via immobilizing the organohydrogel electrodes onto a flexible very high bond (VHB) substrate. As a result, the integrated electrodes show high signal‐to‐noise ratio (SNR) (35.15 db) comparable to that of the commercial electrodes. Furthermore, with assistance of deep learning, the proposed sEMG electrodes obtain high identification accuracy of 97.11% in distinguishing sophisticated gestures. This system can be further exploited for real‐time tele‐operations and offers broad prospects in human–machine immersive interactive application.


Introduction
[9] Effectively recording sEMG signals through the skin is valuable for rehabilitation training, [10] clinical disease diagnosis, [11] human-machine interfaces, [12][13][14] etc. Particularly, with the rise of concepts such as virtual reality, [15] digital twins and metaverse, [16][17][18] gesture recognition systems that can be applied for human intentions to control hardware or remote operation have garnered great attentions. [19,20]SEMG-based gesture capture devices provide a selection for gesture recognition due to the correspondence between muscle signals and movements. [21]However, current electromyographic detection devices generally use dry electrodes or disposable patch electrodes to transfer physiological signals from the human body to external devices, suffering from limitations inherent to these electrodes. [22]Rigid dry electrodes are mechanically mismatched with the skin and are susceptible to motion artifacts attributing to relative interfacial sliding during movements. [23,24]To alleviate this, the electrodes are required to be fixed tightly on the arm, which results in discomforts during wearing.
Although commercial disposable electrodes use a gel layer to reduce impedance between the electrodes and the skin, [25] the gel is prone to dehydration, which deteriorates the quality of the signal.They also need to be mounted onto the skin by a nonwoven fabric layer brushed with glue and are not suitable for long-time usage. [26]Besides, the separate electrodes are timeconsuming to assemble and disassemble.[29][30] They are considered as great candidates for epidermal electrodes owing to their good biocompatibility, [31,32] and skin-like modulus. [33,34]However, there is a contradiction in integrating superior performance of high conductivity, conformable contact with skin and water retention concurrently. [35,36]Hydrogels primarily rely on the incorporation of conductive polymers (e.g., polystyrene sulfonate (PEDOT:PSS), [37,38] polypyrrole (PPy), polyaniline (PANi)), conductive nanofillers (e.g., carbon nanotubes (CNTs), graphene, MXenes, silver nanowire), [39][40][41] or ionic ions [42] to improve their conductivity. [43,44]The mechanical softness may be compromised due to the loading of high-stiffness additives, and the conductive components tend to agglomerate into clusters. [45,46]For example, Li et al. [47] employed in situ aggregation and densification techniques to construct a compact double-network hydrogel, aiming to enhance the electrical conductivity and mechanical properties of PEDOT:PSS gel.Nevertheless, the resulting modulus is still relatively high (460 KPa), and the mechanical performance remains insufficient (150%).Although ion hydrogels can maintain a relatively low modulus, their conductivity are often poor. [48,49]Moreover, to endow the hydrogels with water-retaining properties, alcohol-based solutions are generally added or used for post soaking the hydrogels to form organohydrogels. [50,51] Sun et al. [52] demonstrated an environment tolerant organohydrogel by replacing the partial water with the glycerol, which, however, sacrificed the ionic conductivity of the hydrogels.Various strategies have been devoted to addressing this tradeoff.[55] Deep eutectic solvents (DESs), eliminating many problems of traditional hydrogels such as water evaporation and biological incompatibility, have emerged as a potential alternative to ILs. [56,57] For example, Picchio et al. [58] exploited choline chloride/glycerol deep eutectic solvent to obtain conductive and biocompatible eutectogels, but its ionic conductivity performance is still unsatisfactory.Wu et al. [59,60] found that introducing the Hofmeister effect and electrostatic interaction can enhance the conductivity of organohydrogels.However, the conductivity still drops by an order of magnitude after soaking.Therefore, it is highly desirable to exploit an anti-drying hydrogel with high conductivity and skin-like low elastic moduli to achieve high-quality sEMG signals.
In this article, a rapidly fabricated organohydrogel with high performance is proposed as sEMG electrode.By adding sodium chloride and embedding partially reduced graphene oxide into an ultra-low modulus polyacrylamide/sodium alginate/tannic acid (PAM/SA/TA) network, the organohydrogel is compatible with good conductivity of 4.22 S m −1 , low modulus (32 KPa) and excellent water retention capacity.Subsequently, three organohydrogels are integrated on a VHB substrate for ease-of-use, while maintaining the soft flexibility of the overall device.The resulting integrated organohydrogel electrodes present a high signalto-noise ratio of 35.15 db.Finally, sEMG signals from the wrist and forearm were collected by these integrated electrodes for gesture recognition with the help of the machine learning.As a result, it realizes a 97.11% recognition accuracy in classifying 10 hand motions.This gesture recognition system potentially paves the way for human-machine immersive interactions in real-time teleoperation scenarios.

Structure and Design Principle of the Organohydrogel
The cross-linked polymer structure of the PAM/SA/TA/pRGO organohydrogel based on both covalent and non-covalent net-works is shown in Figure 1a.The two types of networks endow hydrogel with a suitable elasticity and reliable mechanical properties.In this system, simply by stirring precursor aqueous solutions after adding catalyst and initiator, the hydrogel can quickly polymerization in situ without the need for UV irradiation or heating.This process is demonstrated in Figure S1 (Supporting Information).
As the epidermal electrodes are attached onto the skin, biocompatibility of this organohydrogel is highly significant for long-time wearable applications.Polyacrylamide (PAM), sodium alginate (SA) and tannic acid (TA) are all biocompatible materials that widely used in medical products.][63] The abundant hydrogen bonds in the polymer networks enable both the selfhealing ability and the self-adhesive property of this hydrogel (Figure 1b). [62,64]Owing to these properties, this organohydrogel composite can be conformally attached onto the skin and low contact impedance between skin and electrodes is ensured (Figure 1c).
To improve the conductivity, NaCl solution was dispersed into the above-mentioned mixture, during which the electrostatic interactions inside the hydrogel were strengthened. [59]Moreover, the salting out effect of NaCl can promote the entanglement of polymer chains and improve its mechanical properties. [62]In addition, the electrical conductivity of this hydrogel can be further improved by conductive fillers, such as graphene and carbon nanotubes. [65]The partially reduced graphene oxide (pRGO) was selected as a suitable filler due to the abundant oxygen-containing groups, which is conducive to homogeneous dispersion while obtaining good electrical conductivity.
Figure S2 (Supporting Information) shows the Raman spectra of graphene oxide (GO) and partially reduced graphene oxide (pRGO).The Raman spectra of carbon materials exhibits two characteristic peaks, namely the D-and G-band, located around 1340 cm −1 and 1580 cm −1 , respectively.As the D-band represents carbon atomic structural defects and the G-band represents lattice vibrations, the intensity ratio of the D-and G-band (R = ID/IG) can be used to evaluate the structural integrity and crystal quality of graphene samples.The content of oxygen containing functional groups on the surface of graphene oxide decreases after reduction, leading to an increase in edge effects and disorderliness, thereby increasing the intensity ratio value.Compared to the Raman results of GO, the R value of pRGO increases from 0.895 to 0.949, indicating the existence of pRGO. [66]The porous structure of the obtained organohydrogel composite was also observed by SEM images, which indicates the good permeability for on-skin applications (Figure 1d,e).

Mechanical Properties
The skin undergoes a certain degree of bending and deformation during the movement, especially at joint areas (Figure 2a), which shows high requirements on the modulus and elasticity of the epidermal electrodes.The organohydrogel is soft and highly elastic to be stretched to 400% (Figure 2b).The mechanical properties of PAM/SA, PAM/SA/TA and PAM/SA/TA/pRGO organohydrogels with varying pRGO contents (Figure S3, Supporting Information) were exhibited in Figure 2c.Compared with PAM/SA, the introducing of TA contributes to ultra-low Young's modulus (12.612KPa) and higher stretchability (851%).This phenomenon results from the higher non-covalent bonds than covalent bonds in the network.Figure 2d illustrates an increase in Young's modulus and a decrease in stretchability with the increased content of the pRGO, because the volumetric loading of pRGO will enhance the stiffness of the hydrogel.It is clear to observe that the obtained organohydrogel with higher concentration of pRGO shows higher tensile strength, but lower tensile range due to the structure defects led by doping materials.Considering for conformal attachment of this organohydrogel on curved skin, lower modulus (32 KPa) of PAM/SA/TA/pRGO, as well as good stretchability (599%) can be obtained at a suitable filling concentration of pRGO (0.18%). of PAM/SA organohydrogel and PAM/SA/TA/pRGO organohydrogels with different pRGO content (0%, 0.06%, 0.12%, 0.18%, 0.24%).d) The modulus, strength and fracture strain of above organohydrogels.e) Loading-unloading cycles (300% strain, 5 cycles) of PAM/SA/TA/pRGO organohydrogel with 0.18% pRGO.Sample size, n = 3. f) Loading-unloading cycles (400% strain, 10 cycles) of PAM/SA/TA/pRGO organohydrogel with 0.12% pRGO.g) Cyclic tensile loading-unloading curves at diverse strains (100%, 200%, 300%, and 400%) of PAM/SA/TA/pRGO organohydrogel with 0.18% pRGO.h) The loading-unloading curves at 300% strain of PAM/SA/TA/pRGO organohydrogel with different pRGO content.
In addition, the electrodes have a demand for high elasticity to adapt to the stretching-recovery of the skin.The reversible noncovalent bonds in the network act as sacrificial bonds to provide energy dissipation and protect the covalent network, allowing the PAM/SA/TA organohydrogel for excellent mechanical properties and recovery ability to be conformally attached on the skin (Figure S4, Supporting Information).During the cyclic tensile tests, a hysteresis loop is observed in the first cycle (Figure 2e,f), while the subsequent continuous stretching cycles are almost overlapped, indicating the energy dissipation and good resilience of the organohydrogel.Figure 2g denotes multiple-stage cyclic tensile loading-unloading tests.There is no obvious hysteresis loop in the stress-strain curve at 100% tensile strain.During the subsequent continuous loading-unloading cycles, the hysteresis is more obviously observed due to the fractures of non-covalent bonds in the network under large deformation.The addition of pRGO will affect the mechanical properties of the organohydro-gel and the loading-unloading curves of organohydrogels with different pRGO concentrations at 300% strain are summarized in Figure 2h.The evident hysteresis of pRGO-loaded organohydrogel is attributed to the inner structure defects.The high stretchability, low modulus, and good elasticity of organohydrogel enable it a good match for human skin, laying a foundation for effective monitoring of electromyographic signals.

Conductivity
The conductivity of the organohydrogel is principally related to the content of NaCl and pRGO.Figures 3a and S5 (Supporting Information) illustrate that the resistance changes as a function of NaCl concentration in PAM/SA/TA organohydrogel.The decreasing of resistance gradually reaches saturation at 6% of NaCl concentration as shown in the enlarged view in Figure 3a due to the limited mobility of ions in narrow space.In this case, the 6% concentration of NaCl was used in the synthesis of organohydrogel.Figure 3b shows the conductivity of organohydrogel with different concentrations of pRGO.It is worth noting that the conductivity first decreases as pRGO content increases and then significantly increases when the concentration reaches about 0.1%.This phenomenon may result from the inability of low concentration pRGO to form a conductive network, which instead af-fects the migration of ions.When partial conductive path formed by uniformly dispersed pRGO, the conductivity improves observably.Moreover, the addition of pRGO renders organohydrogel certain electronic conductivity, which is beneficial for signal transduction with external electronic equipment.To verify this concept, the metal electrodes were placed at both ends of organohydrogels and detected the phase angle at different pRGO contents.With the increasing pRGO content, the phase angle in the low-frequency range decreases slightly (Figure 3c), which illustrates the lower proportion of capacitive components and could bring about better signal fidelity.Additionally, organohydrogel electrodes require long-term conductance stability for actual applications.Thus, we further soaked the organohydrogel into glycerol-water binary solvents to obtain better water retention ability.As shown in Figure 3d, the freshly prepared hydrogel possesses high conductivity of 4.22 S m −1 and the conductivity decreases to 0.94 S m −1 after soaking.Satisfactorily, the resulting organohydrogel exhibits good conductance stability, with no significant decline in conductivity after one week and two months.The effect of temperature change on the conductivity was also studied in the range of 15-40 °C in Figure S6 (Supporting Information).The conductivity remains relatively consistent within the temperature range of 15-25 °C.However, there is a noticeable increase in conductivity at 30 °C, followed by a slight decrease after 30 °C.This may be attributed to the fact that heating promotes the migration rate of ions within the organohydrogel while intensifies the dehydration when the temperature exceeds 30 °C.Therefore, the organohydrogel can exhibit better conductivity on the surface of the human skin.

Adhesive Property
The abundant hydroxyl groups in tannic acid and glycerol endow the organohydrogel with excellent adhesion properties.The organohydrogel served as an adhesive layer to be attached on a steel ruler and was adhered steadily to lift the boxes with weights of 60 and 100 g without falling (Figure 3e).Relying on its good mechanical compliance and elasticity, the organohydrogel attached on a finger and wrist shows conformally deformations under different motions (Figure 3f,g).By connecting the PAM/SA/TA/pRGO organohydrogel into a circuit to substitute part of the wire (Figure 3h), the blue light-emitting diode (LED) was lit up successfully.The LED was extinguished as the organohydrogel was cut into two parts and restored to the same brightness when the separated parts were retouched together.This test presents a comprehensive performance about conductivity and adhesion of the organohydrogel.The lap-shear tests of the organohydrogel sandwiched by different substrates (Figure 3i; Figure S7, Supporting Information) were performed to quantify the adhesion performance.The organohydrogel exhibites good adhesion to paper, copper, steel, rubber, and glass.The self-adhesive property and good biocompatibility of the organohydrogel enable it to be attached to the skin for a long time without irritation.To verify its skin-friendliness, organohydrogel electrodes and commercial electrodes were adhered to the skin for 1 h and then removed.As shown in Figure 3j, no evident allergic reactions were found on the skin attached by the organohydrogel electrode but a slight indentation was observed on the skin attached by the conventional electrode.

Integrated Organohydrogel Electrodes for sEMG Recording
Since sEMG signal acquisition relies on differential circuits, two differential electrodes and one reference electrode are required for measuring the signal.For multi-channel sEMG signal acquisitions, the assembly and disassembly of the discrete electrodes are time-consuming.The inconsistent distance between the electrodes would also have an influence on the sEMG signals.We integrated three organohydrogel electrodes (6% NaCl and 0.18% pRGO) together to develop a sEMG electrode (Figure 4a).Each organohydrogel was cut into a size of 20 × 20 × 1 mm.VHB was exploited as the flexible substrate to maintain the overall flexibility of the electrode, and three holes were punched on it at an interval of 25 mm to install metal buttons to connect to external circuits.Meanwhile, the substrate also plays a role in alleviating water evaporation.The substrate and organohydrogel electrodes were glued together by ethyl cyanoacrylate and paraffin liquid to make the electrode more robust.The thicknesses of the substrates affect the supportability and elasticity of the integrated sEMG electrode, this was verified by tensile tests (Figure 4b; Figure S8, Supporting Information).The 0.5 mm VHB exhibits excellent stretchability and relatively low modulus, making it more suitable for the integrated sEMG electrode.Compared to the original organohydrogel, the organohydrogelsubstrate represents increased modulus and similar stretchability (Figure 4c).The overall stretchability can be maintained at around 300% when organohydrogels were fixed onto the substrate (Figure S9, Supporting Information).
The integrated organohydrogel electrodes (Figure 4d) can detect hand movements by adhering them on the arm (Figure 4e) and present good monitoring capability.The commercial Ag/AgCl electrodes and integrated organohydrogel electrodes were attached on the forearm, respectively.The corresponding sEMG signals of clenching and relaxing the fist are shown in Figure 4f.Compared with the commercial electrodes (SNR = 25.36 db), the integrated organohydrogel electrodes have a higher signal-to-noise ratio (SNR = 35.15db).Furthermore, the organohydrogel electrodes have a smaller background noise when we bent five fingers respectively and consequently displayed finger movements more clearly (Figure 4g), which demonstrates its superiority in detecting subtle movements.To verify durable performance of the integrated organohydrogel electrodes, they were placed at ambient condition for 60 days.The SNR kept well after 60 days of placement (Figure 4h,i).Besides, we studied the anti-interference capability by stretching and squeezing the skin surrounding the electrodes while monitoring the sEMG signal.The commercial electrodes brought about significant noise signal, while the integrated organohydrogel electrodes maintained a smoother signal curve due to their robust and conformal contact with the skin (Figure 4j).

Application on Gesture Recognition
The integrated organohydrogel electrodes can obtain high-quality sEMG signals, which can be utilized for complicated gesture predictions.We defined a custom gesture dataset that includes 10 types of hand motions, consisting of 4 wrist gestures and 6 finger gestures, as shown in Figure 5a.These gesture types encompass most frequently used motions in daily life.The sEMG measurement was conducted on the finger or wrist skin using a 6-channel sEMG device, which mainly consists of differential amplification circuits to process and amplify signals, as well as filtering circuits to extract useful signals, to obtain more information regarding the gestures.One group is distributed on the wrist, which contains more information about finger motions.The extensor pollicis longus muscle independently controls the movements of the while the flexor muscles and extensor muscles coordinate the flexion and extension of the other digits.The other group is distributed on the forearm, which mainly reflects the movements of wrist.The sEMG signals of the above 10 gestures are shown in Figure 5b.Attribute to the reasonable electrode arrangement, there are differences in signal patterns when performing different gestures.
However, the four fingers (except the thumb) are controlled by the same series of muscles.There will inevitably be finger motions with similar signals, which hinders the exact discrimination of the gestures.Therefore, to accurately distinguish similar finger motion signals, we processed the signals based on their characteristics.Afterward, we leveraged a neural network based on Convolutional Neural Network (CNN) framework for recognition.A dataset of above 10 gestures was collected and was first normal-ized to improve the generalization ability.Then different labels were added to the data of different gestures.To facilitate data processing, analysis and modeling, the sliding window technique is used to divide the time-domain data into multiple sub-sequences and project them onto a 2D spatiotemporal space.The sliding window size is set to 32 and the stride is 16, maintaining a 50% repetition rate.75% of the processed data were severed as training signals and the CNN model classifier then decoded the input signal (25%) for gesture recognition.The algorithm framework is shown in Figure S10 (Supporting Information).The model consists of two convolutional layers and each sub-network includes the convolution function, the batch normalization layer, the activation function, the dropout layer, and the max pooling layer.Specifically, the Spatial Dropout2D layer can effectively prevent overfitting problems by randomly dropping feature map channels.Meanwhile, the early stopping callback function is also set to stop training when the performance of the model no longer improves, which also avoids the overfitting.Finally, the output recognition results were obtained through a fully connected layer and normalization exponential function.
The recognition results for these 10 gestures are shown in Figure 5c, with a recognition accuracy of 97.11%.All gestures show an accuracy of over 90%.The high recognition for elaborate gestures endows the possibility of remotely control tasks based on hand gestures, involving intelligent robotics, work assistance and dangerous mission execution remotely.

Conclusion
In summary, we report a flexible sEMG electrode for gesture recognition based on PAM/SA/TA/pRGO organohydrogel.The addition of pRGO to the ultra-low modulus PAM/SA/TA organohydrogel coordinates the trade-off between the conductivity, mechanical properties and water retention.The fabricated PAM/SA/TA/pRGO organohydrogel interface can perfectly conformal to skin and record sEMG signals reliably.It maintains stable conductivity (about 0.94 S m −1 ) over 60 days at ambient condition.After assembling the organohydrogel electrodes with flexible substrate, a high signal-to-noise ratio of 35.15 db was achieved.By leveraging the machine learning algorithm, it realizes successful classifications of 10 hand motions with a superior accuracy of 97.11%.Due to comfortable wearability and high SNR performance, the integrated system shows high potentials in human-machine immersive interactive applications.
Preparation of pRGO: Initially, dopamine (DA) was added into NaOH aqueous solution (pH = 11) and magnetically stirred for 20 min.Then, GO suspension liquid (weight ratio of GO to PDA was 2.5:1) was dispersed in PDA solution with consecutive stirring for 5 min to regulate the reduction process of GO.
Synthesis of PAM/SA/TA/pRGO Organohydrogel: According to the pRGO concentration, deionized (DI) water was added to dilute above pRGO solution containing 50 mg pRGO to 10 g.Afterward, 3 g glycerol, 1.2 g sodium chloride, 0.035 g tannic acid, 0.5 g sodium alginate, 3.6 g acrylamide and 0.0132 g MBAA were added into it.The resulting mixture was stirred on a magnetic stirrer until all the components were dissolved.Then, 0.0578 g APS and 38 l of TEMED were added as the initiator and catalyst.The obtained precursor solution was quickly injected into a mold (75 × 50 × 1 mm).After the hydrogel was gelatinized, it was taken out and soaked in the glycerol-water binary solvents for 2 h to obtain the PAM/SA/TA/pRGO organohydrogel.PAM/SA and PAM/SA/TA organohydrogels were prepared in the same way after removing the TA, pRGO and pRGO, respectively.
Fabrication of the Integrated Organohydrogel Electrode: The PAM/SA/TA/pRGO organohydrogel was cut into 2 × 2 cm pieces and the 0.5 mm thick VHB was cut into 10 × 3 cm size.The VHB was punched three small holes evenly at 25 mm intervals and three metal buttons were installed on it.Then, ethyl cyanoacrylate and paraffin liquid were applied as adhesion agents between the organohydrogels and metal buttons.
Characterization and Measurements: The surface morphology images of organohydrogels were characterized by a scanning electron microscope (SEM) (JSM-IT500A, JEOL, Japan) at an accelerating voltage of 15 kV.
Raman analysis was carried out by a laser confocal Raman microscope (vis-NIR-XU, Nanophoton Corporation, Japan), with 532 nm excitation laser and a scanning range of 500-2500 cm −1 .
The mechanical properties were measured by an electronic universal testing machine (E43.104,MTS, America).The dumbbell shape (100 mm in total length, 5 mm in inner width, and 20 mm in gauge length) samples were stretched at a rate of 50 mm min −1 .
The adhesive strength of the PAM/SA/TA/pRGO organohydrogel was performed by lap-shear tests using an electronic universal testing machine (MTS-E43.104,MTS, America) at a speed of 5 mm min −1 .During the tests, the organohydrogel (20 mm × 20 mm × 1 mm) was sandwiched between two paper, copper sheets, steel sheets, rubber sheets and glass sheets, respectively.
The impedance spectroscopy of the organohydrogel was tested by a spectrum analyzer (Bode 100, XiaMen General Electronic Measurement Co., Ltd, China) in the frequency range from 1 to 500 Hz.The resistance of the PAM/SA/TA/pRGO organohydrogels with different pRGO content was measured by a digital multimeter.The conductance () was calculated as Equation ( 1): where L, S, and R represent the length, cross-sectional area, and resistance values.Three organohydrogel or commercial electrodes were attached on the flexor carpi ulnaris muscle as two test electrodes and a reference electrode, respectively.The sEMG signals were recorded by a six-channel EMG sensor (WuXi BoRunYin Technology Co., Ltd, China) while clenching the fist or flexing fingers for 1-2 s.And SNR was obtained from Equation (2): SNR = 10log 10 P S P N (2)   where P S and P N represent the average power of signal and background respectively, and were estimated by calculating the variance of the signal and background noise.
Statistical Analysis: The pre-processing of data included conversion of distance-strain and tension-stress, calculation of conductivity, shear strength and signal-to-noise ratio, as well as removal of outliers in gesture dataset.The corresponding formulas are provided in the respective sections.Use python to identify gesture data that exceeds the average value by 1000 times as outliers and remove them.Variables are expressed as mean ± SD.Sample sizes (n) for each statistical analysis are 3 and are indicated in the corresponding figure legend.The software used for the statistical analysis is OriginLab.
Ethics Approval and Consent to Participate: Human involved in the gesture recognition validation has provided informed consent, and the study protocol was approved by the ethical committee of College of Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University.The operator in the gesture recognition experiment was Y. Xu and L. Deng, two of the co-authors, who had given their approval to publish these results and images.

Figure 1 .
Figure 1.Design and principle of PAM/SA/TA/pRGO organohydrogel.a) Synthesis process and chemical structures of PAM/SA/TA/pRGO organohydrogel.The inset shows the covalent and non-covalent cross-linking of the organohydrogel.b) The schematic illustration of self-adhesion and the adhesion mechanisms with skin.c) Schematic illustration of PAM/SA/TA/pRGO organohydrogels employed as electrodes and the equivalent circuit of tissue/organohydrogel interfaces for sEMG monitoring.d,e) SEM images of cross sections of PAM/SA/TA/pRGO organohydrogel.

Figure 3 .
Figure 3.The electrical and adhesive properties of the organohydrogel.a) Impedance of PAM/SA/TA organohydrogels with different NaCl content.Sample size, n = 3. b) Conductivity of PAM/SA/TA/pRGO organohydrogels with different pRGO concentrations at 6% NaCl.c) Phase angle versus frequency of organohydrogels with different pRGO contents.d) Changes of the conductivity of PAM/SA/TA/pRGO organohydrogel before and after soaking in glycerol and stored at ambient condition over two months.Sample size, n = 3. e) Photographs of the organohydrogel adhered to objects of various materials and weights.Scale bars: 1 cm.f,g) The PAM/SA/TA/pRGO organohydrogels made a conformal adhesion to digital joints and wrist joints.Scale bars: 1 cm.h) Photos of the luminous LED using the organohydrogel as a conductor and the extinguished and relumined LED after cutting and connecting the organohydrogel.i) The adhesion strength of organohydrogels on different substrates.Sample size, n = 3. j) Photograph of the Ag-AgCl electrode and organohydrogel attached on the skin for 1 h.Scale bars: 1 cm.

Figure 4 .
Figure 4. Structure and characteristics of the integrated organohydrogel electrode.a) Schematic illustration of the integrated organohydrogel electrode.b) The tensile stress-strain curves of different VHB thickness.c) The tensile stress-strain curves of 0.5 mm VHB substrate, organohydrogel, and substrate-organohydrogel hybrids.d) Photographs of the integrated organohydrogel electrode.Scale bars: 1 cm.e) Photographs of the integrated organohydrogel electrode attached to the skin.Scale bars: 1 cm.f) sEMG signals detected by the commercial electrodes and organohydrogel electrodes.g) Tiny sEMG signals detected by the commercial electrodes and organohydrogel electrodes.h) Durable performance of the interlocking organohydrogel electrodes for detection of sEMG signal.i) Tiny sEMG signals detected by the organohydrogel electrodes over 60 days.j) sEMG signals subjected to external force recorded by the commercial electrodes and organohydrogel electrodes.

Figure 5 .
Figure 5. Hand motion dataset and application for gesture recognition.a) Photographs showing the 10 categories of hand motions.b) Photos of the arrangement of integrated organohydrogel electrodes attached to the arm.c) Example sEMG signals recorded by the integrated organohydrogel electrodes when performing above 10 gestures.d) Confusion matrix for classifying the ten hand motions.