Hydrogel-based Strain Sensors Research Articles

A high-adhesive and sensitive hydrogel with interpenetrating and interlocking networked structure for efficient biological signal monitoring

Smart flexible sensing materials and devices for wearable health monitoring are considered as prospective and promising areas in healthcare that are currently in high demand in the market. Conductive hydrogel-based sensors, which closely resemble human tissue, encounter notable challenges in attaining high electronic conduction, robust mechanical properties, biocompatibility, and intimate tissue adhesion simultaneously. In this work, a poly(2-acrylamide-2-methylpropane sulfonic acid-co-acrylamide)/bacterial cellulose (P(AMPS-co-AM)/BC) hydrogel with a particular interpenetrating and interlocking networked structure is reported. This hydrogel possesses all the mentioned intriguing properties plus easy degradability. It is realized by utilizing the interaction between amino, amide, and sulfonic groups on polymer molecular chains and polyhydroxy groups on bacterial cellulose. This hydrogel exhibits high strength (1.28 MPa) and tensile strain (525 %), remarkable tissue adhesion (697 kPa), exceptional antibacterial property and low cytotoxicity. Furthermore, it can degrade in the natural environment when exposed to UV light irradiation. The hydrogel-based strain sensors have demonstrated efficient human motion detection with a broad strain detection range (0–360 %) and a high sensitivity (GF = 11.36). Moreover, this hydrogel can be assembled into Triboelectric Nanogenerator for monitoring biological signals. This work presents a new avenue for human-machine interaction and electronic robotic skins.

Stretchable, self-adhesion and durable polyacrylamide/polyvinylalcohol dual-network hydrogel for flexible supercapacitor and wearable sensor

Conductive hydrogels show great promise in the field of flexible electronics, but traditional hydrogels have some problems such as poor environmental tolerance, being easy to damage and not being durable. In this work, polyacrylamide (PAM) was used as the main network, and polyvinylalcohol (PVA) was added to construct a dual network hydrogel. Simultaneously, LiTFSI was added to improve hydrogel ionic conductivity, and multiple interionic and intermolecular interactions formed within the gel, significantly improving the gel's mechanical properties and durability. The area specific capacitance of the hydrogel-based supercapacitor is 383.4 mF cm−2, and it still maintains a high cycle life of 90.35 % after 10,000 cycles. The hydrogel-based strain sensor shows fatigue resistance, rapid recovery after 400 stretches, high sensitivity (GF = 3.83 at 300–400 %), and the ability to detect human motion. Therefore, the multi-functional properties of PAM/PVA/LiTFSI hydrogels are expected to play a demonstration role in a new generation of flexible electronic products.

Anti-Freezing and Ultrasensitive Zwitterionic Betaine Hydrogel-Based Strain Sensor for Motion Monitoring and Human-Machine Interaction.

Ultrasensitive and reliable conductive hydrogels are significant in the construction of human-machine twinning systems. However, in extremely cold environments, freezing severely limits the application of hydrogel-based sensors. Herein, building on biomimetics, a zwitterionic hydrogel was elaborated for human-machine interaction employing multichemical bonding synergies and experimental signal analyses. The covalent bonds, hydrogen bonds, and electrostatic interactions construct a dense double network structure favorable for stress dispersion and hydrogen bond regeneration. In particular, zwitterions and ionic conductors maintained excellent strain response (99 ms) and electrical sensitivity (gauge factor = 14.52) in the dense hydrogel structure while immobilizing water molecules to enhance the weather resistance (-68 °C). Inspired by the high sensitivity, zwitterionic hydrogel-based strain sensors and remote-control gloves were designed by analyzing the experimental signals, demonstrating promising potential applications within specialized flexible materials and human-machine symbiotic systems.

Versatile and recyclable double-network PVA/cellulose hydrogels for strain sensors and triboelectric nanogenerators under harsh conditions

Versatile and recyclable conductive hydrogels with long-term environmental adaptability and mechanical stability have attracted tremendous attention in wearable smart electronics. Here, double-network (DN) polyvinyl alcohol (PVA)/cellulose hydrogels were constructed after introducing a conductive rigid cellulose/Zn2+/Ca2+ network into a soft PVA/borax network. The resultant hydrogels possessed good mechanical and self-adhesive properties, along with transparency, recyclability, and remarkable resistance to freezing. They showed 30-day non-drying properties due to the presence of hygroscopic salts through a dynamic moisture adsorption and desorption process. Dehydrated hydrogels can return to their original states via self-regeneration under high relative humidity. Hydrogel-based strain sensors retained good sensitivity and a wide sensing range during the wide working temperature ranging from −40 °C to 50 °C and after recycling. Additionally, conductive hydrogels were integrated into triboelectric nanogenerators (TENGs) functioning as energy harvesters for powering electronics. TENGs retained stable electrical outputs even under harsh conditions and after recycling. Hydrogels were also assembled into flexible self-powered biomechanical sensors and tactile sensors. Thermally reversible interactions in composite hydrogels enabled their good recyclability, thereby reducing economic costs and environmental impacts caused by e-wastes. This work demonstrates the great potential of versatile and recyclable hydrogels with good environmental and mechanical stability in wearable smart electronics under harsh conditions.

Using chitosan nanofibers to simultaneously improve the toughness and sensing performance of chitosan-based ionic conductive hydrogels

Conductive hydrogels, especially polysaccharide-based ionic conductive hydrogels, have received increasing interest in the field of wearable sensors due to their similarity to human skin. Nevertheless, it is still a challenging task to simultaneously prepare a self-healed and adhesive conductive hydrogel with good toughness, temperature tolerance and high sensing performance, especially with high sensitivity and a low detection limit. Herein, we developed a new strategy to improve the toughness and sensing performance of a multifunctional conductive hydrogel by simultaneously using dissolved chitosan (CS) and solid chitosan nanofibers (CSFs) to induce the formation of hierarchical polymeric networks in the hydrogel. The tensile strength and elongation at break of the hydrogel could be improved from 70.3 kPa and 1005 % to 173.9 kPa and 1477 %, respectively, simply by introducing CSFs to the hydrogel, and its self-healing, adhesive and antibacterial properties were effectively retained. When serving as a resistive sensing material, the introduction of CSFs increased the gauge factor of the hydrogel-based strain sensor from 8.25 to 14.27. Moreover, the hydrogel-based strain sensor showed an ultralow detection limit of 0.2 %, excellent durability and stability (1000 cycles) and could be used to detect various human activities. In addition, the hydrogel prepared by using a water-glycerol binary solvent system showed temperature-tolerant performance and possessed adequate sensitivity when serving as a resistive sensing material. Therefore, this work provides a new way to prepare multifunctional conductive hydrogels with good toughness, sensing performance and temperature tolerance to expand the application range of hydrogel-based strain sensors.

Using chitosan nanofibers to synergistically construct a highly stretchable multi-functional liquid mental-based hydrogel for assembling strain sensor with high sensitivity and broad working range

Liquid metal (LM) microdroplets have garnered significant interest as conductive materials for initiating free radical polymerization in the development of conductive hydrogels suited for strain sensors. However, crafting multi-functional conductive hydrogels that boast both high stretchability and superior sensing capabilities remains as a challenge. In this study, we have successfully synthesized LM-based conductive hydrogels characterized by remarkable stretchability and sensing performance employing acrylic acid (AA) to evenly distribute chitosan nanofibers (CSFs) and to subsequently catalyze the free radical polymerization of AA. The resultant polymer network was crosslinked within situ polyacrylic acid (PAA), facilitated by Ga3+ in conjunction with guar gum (GG)-stabilized Ga droplets. The strategic interplay between the rigid, and protonated CSFs and the pliable PAA matrix, coupled with the ionic crosslinking of Ga3+, endows the resulting GG-Ga-CSF-PAA hydrogel with high stretchability (3700 %), ultrafast self-healing, robust moldability, and strong adhesiveness. When deployed as a strain sensing material, this hydrogel exhibits a high gauge factor (38.8), a minimal detection threshold, enduring durability, and a broad operational range. This versatility enables the hydrogel-based strain sensor to monitor a wide spectrum of human motions. Remarkably, the hydrogel maintains its stretchability and sensing efficacy under extreme temperatures after a simple glycerol solution treatment.

A Sensory Soft Robotic Gripper Capable of Learning-Based Object Recognition and Force-Controlled Grasping

Soft robotic grippers possess high structural compliance and adaptability, allowing them to grasp objects with unknown and irregular shapes and sizes. To enable more dexterous manipulation, soft sensors that are similar in mechanical properties to common elastomer materials are desired to be integrated into soft grippers. In this paper, we develop ionic hydrogel-based strain and tactile sensors and integrate these sensors into a three-finger soft gripper for learning-based object recognition and force-controlled grasping. Such hydrogel-based sensors have excellent conductivity, high stretchability and toughness, good ambient stability, and unique antifreezing property; they can be readily attached to a soft gripper at desired locations for strain and tactile sensing. By using a deep-learning model, the sensory soft gripper is demonstrated to be capable of grasping and recognizing objects at both room and freezing temperatures, and achieving close to 100% recognition accuracy for ten typical objects. Moreover, the capacitive tactile feedback of the gripper is utilized to develop a closed-loop force controller and realize force-controlled grasping of fragile or highly deformable objects. A new slip detection and compensation strategy is also proposed and validated for the sensory gripper for adjusting the grasping force in real time upon detecting slippage. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —The multimodal sensation of a soft robotic gripper could enrich its grasping functionalities and improve its manipulation performance. This research integrates novel antifreezing ionic hydrogel-based strain and tactile sensors into a three-finger soft robotic gripper for learning-based object recognition and force-controlled grasping. Constructed from a highly stretchable, ambient-stable, and antifreezing ionic hydrogel, the strain and tactile sensors can be readily integrated at the desired locations on the soft gripper, and can reliably operate at both ambient and freezing temperatures with excellent mechanical and electrical properties. Based on the feedback of the strain and tactile sensors, a deep learning model is employed to enable high-accuracy object recognition while grasping, which can be useful for manipulation in vision-free environments. Closed-loop force control and slip compensation strategies are also demonstrated for reliably grasping fragile/deformable objects and handling slip events during the manipulation of heavy objects. The sensory soft gripper and the associated object recognition and force control methods could find practical applications in a variety of robotic manipulation tasks.

Low-hysteresis and highly linear sensors based on environmentally stable, adhesive, and antibacterial hydrogels

Ionic hydrogels (PVA-PA-E/M hydrogels) with high adhesive strength, good environmental stability, excellent antibacterial properties, and high conductivity. The hydrogel-based strain sensor exhibited low hysteresis and high linearity simultaneously.

Fabrication of anti-freezing and self-healing nanocomposite hydrogels based on phytic acid and cellulose nanocrystals for high strain sensing applications.

For hydrogel-based flexible sensors, it is a challenge to enhance the stability at sub-zero temperatures while maintaining good self-healing properties. Herein, an anti-freezing nanocomposite hydrogel with self-healing properties and conductivity was designed by introducing cellulose nanocrystals (CNCs) and phytic acid (PA). The CNCs were grafted with polypyrrole (PPy) by chemical oxidation, which were used as the nanoparticle reinforcement phase to reinforce the mechanical strength of hydrogels (851.8%). PA as a biomass material could form strong hydrogen bond interactions with H2O molecules, endowing hydrogels with prominent anti-freezing properties. Based on the non-covalent interactions, the self-healing rate of the hydrogels reached 92.9% at -15 °C as the content of PA was 40.0 wt%. Hydrogel-based strain sensors displayed high sensitivity (GF = 0.75), rapid response time (350 ms), good conductivity (3.1 S m-1) and stability at -15 °C. Various human movements could be detected by using them, including small (smile and frown) and large changes (elbow and knee bending). This work provides a promising method for the development of flexible wearable sensors that work stably in frigid environments.

Multifunctional organohydrogel via the synergy of dialdehyde starch and glycerol for motion monitoring and sign language recognition

Conductive hydrogel which belongs to a type of soft materials has recently become promising candidate for flexible electronics application. However, it remains difficult for conductive hydrogel-based strain sensors to achieve the organic unity of large stretchability, high conductivity, self-healing, anti-freezing, anti-drying and transparency. Herein, a multifunctional conductive organohydrogel with all of the above superiorities is prepared by crosslinking polyacrylamide (PAM) with dialdehyde starch (DAS) in glycerol-water binary solvent. Attributing to the synergy of abundant hydrogen bonding and Schiff base interactions caused by introducing glycerol and dialdehyde starch, respectively, the organohydrogel achieved balanced mechanical and electrical properties. Besides, the addition of glycerol promoted the water-locking effects, making the organohydrogel retain the superior mechanical properties and conductivity even at extreme conditions. The resultant organohydrogel strain sensor exhibits desirable sensing performance with high sensitivity (GF = 6.07) over a wide strain range (0–697 %), enabling the accurate monitoring of subtle body motions even at −30 °C. On the basis, a hand gesture monitor system based on the organohydrogel sensors arrays is constructed using machine learning method, achieving a considerable sign language recognition rate of 100 %, and thus providing convenience for communications between the hearing or speaking-impaired and general person.

Injection-on-Skin Granular Adhesive for Interactive Human-Machine Interface.

Realization of interactive human-machine interfaces (iHMI) is improved with development of soft tissue-like strain sensors beyond hard robotic exosuits, potentially allowing cognitive behavior therapy and physical rehabilitation for patients with brain disorders. Here, this study reports on a strain-sensitive granular adhesive inspired by the core-shell architectures of natural basil seeds for iHMI as well as human-metaverse interfacing. The granular adhesive sensor consists of easily fragmented hydropellets as a core and tissue-adhesive catecholamine layers as a shell, satisfying great on-skin injectability, ionic-electrical conductivity, and sensitive resistance changes through reversible yet robust cohesion among the hydropellets. Particularly, it is found that the ionic-electrical self-doping of the catecholamine shell on hydrosurfaces leads to a compact ion density of the materials. Based on these physical and electrical properties of the sensor, it is demonstrated that successful iHMI integration with a robot arm in both real and virtual environments enables robotic control by finger gesture and haptic feedback. This study expresses benefits of using granular hydrogel-based strain sensors for implementing on-skin writable bioelectronics and their bridging into the metaverse world.

Developing a carbon composite hydrogel with a highly conductive network to improve strain sensing performance

Both carbon aerogels and conductive hydrogels have provoked immense research interest as flexible sensing materials. However, conventional carbon aerogels show limited stretchability, while conductive hydrogels generally show limited conductivity. Herein, we develop a carbon composite hydrogel with a highly conductive network by encapsulating a cellulose fiber-derived carbon aerogel with a liquid metal-based conductive hydrogel formed by the in situ free radical polymerization of acrylic acid. The as-prepared carbon composite hydrogel inherits its high conductivity from the cellulose fiber-derived carbon aerogel and its good stretchability, adhesion and self-healing properties from the liquid metal-based hydrogel. Moreover, the carbon composite hydrogel possesses a high tensile strength and toughness due to the rigid network of the carbon aerogel. When serving as the tensile strain sensing material, the carbon composite hydrogel shows a very high sensitivity (gauge factor = 13.1 in the strain range of 400–500%), ultralow detection limit (0.1%), quick response and recovery time (166 ms at the strain of 1%) and excellent durability (1000 cycles under at 10% and 100% strains). In addition, the carbon composite hydrogel can obtain good temperature tolerance, adapt to high humidity and sustain its good sensing performance at low and high temperatures simply by coating a layer of glycerin on its surface. This work broadens the prospects for the design and preparation of conductive hydrogel-based strain sensors, and it facilitates their application in monitoring the biomedical signals of humans.

A multifunctional hydrogel-based strain sensor and triboelectric nanogenerator for running monitoring and energy harvesting

Recently, flexible wearable electronics for human running posture monitoring and human energy harvesting have attracted widespread attention. Hence, we design a mixed type conductive hydrogel based on polyvinyl alcohol, cotton paper, graphite oxide, and MXene, named PCGM hydrogel. Furthermore, the PCGM hydrogel can act as the PCGM-based strain sensor and triboelectric nanogenerator (P-TENG) for running posture monitoring and mechanical energy harvesting. The PCGM-based strain sensor has two sensing linear regions: The pressure sensitivity is 0.0164 kPa−1 in the low pressure region (0–16 kPa), whereas it is 0.002 86 kPa−1 in the high pressure region (16–120 kPa). To achieve comprehensive health monitoring of runners, the PCGM-based strain sensors can be installed on human joints and facial skin to monitor human posture and facial expressions. The PCGM hydrogel can be combined with a polytetrafluoroethylene film to form a P-TENG device for mechanical energy harvesting. The P-TENG maximum output power can reach 135 µW with a 30 MΩ load. The short-circuit current (Isc), open-circuit voltage (Voc), and transfer charge (Qsc) of P-TENG can reach 10.36 µA, 229.85 V, and 49.24 nC, respectively. This research provides an effective approach for human-running motion monitoring by using multifunctional flexible devices.

Fully Physically Crosslinked Conductive Hydrogel with Ultrastretchability, Transparency, and Self-Healing Properties for Strain Sensors.

Currently, conductive hydrogels have received great attention as flexible strain sensors. However, the preparation of such sensors with integrated stretchability, transparency, and self-healing properties into one gel through a simple method still remains a huge challenge. Here, a fully physically crosslinked double network hydrogel was developed based on poly(hydroxyethyl acrylamide) (PHEAA) and κ-carrageenan (Car). The driving forces for physical gelation were hydrogen bonds, ion bonding, and electrostatic interactions. The resultant PHEAA-Car hydrogel displayed stretchability (1145%) and optical transparency (92%). Meanwhile, the PHEAA-Car hydrogel exhibited a self-healing property at 25 °C. Additionally, the PHEAA-Car hydrogel-based strain sensor could monitor different joint movements. Based on the above functions, the PHEAA-Car hydrogel can be applied in flexible strain sensors.

Transparent, High Stretchable, Environmental Tolerance, and Excellent Sensitivity Hydrogel for Flexible Sensors and Capacitive Pens.

The prospect of ionic conductive hydrogels in multifunctional sensors has generated widespread scientific interest. The new generation of flexible materials should be combined with superior mechanical properties, high conductivity, transparency, sensitivity, good self-restoring fatigue properties, and other multifunctional characteristics, while the current materials are difficult to meet these requirements. Herein, we prepared poly(acrylamide-acrylic acid) (P(AM-AA))/gelatin/glycerol-Al3+ (PG1G2A) ionic conducting hydrogel by one-pot polymerization under UV light. The prepared PG1G2A ionic conductive hydrogel had high tensile strength (539.18 kPa), excellent tensile property (1412.96%), good fast self-recovery and fatigue resistance, high transparency (>80%), excellent moisturizing, and antifreezing/drying properties. In addition, the ionic conductive hydrogel-based strain sensor can respond to mechanical stimulation and generate accurate, stable, and recyclable electrical signals, with excellent sensitivity (GF 5.81). In addition, the PG1G2A hydrogel could be used as flexible wearable devices for monitoring multiple strain and subtle movements of different body parts at different temperatures. Interestingly, the PG1G2A hydrogel capacitive pen embedded in the mold can be used to write and draw on the screen of a phone or tablet. This new multifunctional ionic conducting hydrogel shows broad application prospects in E-skin, motion monitoring, and human-computer interaction in extreme environments.

MXene-Induced Flexible, Water-Retention, Semi-Interpenetrating Network Hydrogel for Ultra-Stable Strain Sensors with Real-Time Gesture Recognition.

As water-saturated polymer networks, hydrogels are a growing family of soft materials that have recently become promising candidates for flexible electronics application. However, it remains still difficult for hydrogel-based strain sensors to achieve the organic unity of mechanical properties, electrical conductivity, and water retention. To address this challenge, based on the template, the excellent properties of MXene nanoflakes (rich surface functional groups, high specific surface area, hydrophilicity, and conductivity) are fully utilized in this study to prepare the P(AA-co-AM)/MXene@PDADMAC semi-interpenetrating network (semi-IPN) hydrogel. The proposed hydrogel continues to exhibit excellent strain response and flexibility after 30 days of storage at room temperature, and its performance do not decrease after 1100 cycles. Considering these characteristics, a hydrogel-based device for converting sign language into Chinese characters is successfully developed and optimized using machine learning. Therefore, this study provides novel insight and application directions for hydrogel families.

Highly sensitive, super high stretchable hydrogel strain sensor with underwater repeated adhesion and rapid healing

Traditional hydrogel-based strain sensors do not work well under water due to extreme swelling and poor adhesion to substrates in water-rich conditions. Inspired by the jellyfish tentacles, a super stretchable dual crosslinked hydrogel was prepared as a motion sensor underwater. The hydrogel contained a cationic surfactant, hexadecyl trimethyl ammonium bromide (CTAB), that crosslinked with hydrophobic lauryl methacrylate (LMA) units in an AA-LMA copolymer. Al3+ ions also coordinated with carboxyl groups in PAA chains and amino groups on chitosan (CS) to form ionic crosslink points. The formed hydrogel exhibited excellent anti-swelling characteristics, superior tensile properties (≈3000%), and rapid self-healing performance. Due to the complementary effects of electrostatic interactions and dynamic chemical bond formation, the hydrogel efficiently and repeatably adhered to various biological tissues, such as hogskin and shrimp, in aquatic environments. Moreover, the hydrogel-based strain sensor showed high sensitivity (GF = 2.04) over a wide sensing range from 0 to 1000% strain with high stability in air and water. The prepared materials' unique performance further expands their application prospects in flexible wearable devices, anti-counterfeiting recognition, and other fields in environmental conditions.

Ion-based double network hydrogel with compressive, conductive, and sensing properties for sports monitoring

Conductive hydrogel, as a promising candidate material, is ideal for multifunctional strain sensors due to its similarity to biological tissues. It offers good wearability and high-precision information acquisition. However, fabricating conductive hydrogel-based strain sensors with both superior mechanical and conductive properties remains challenging. In this study, a compressive and conductive strain sensor based on multi-dynamic interactions is fabricated through a simple strategy. The strategy exploits hydrogen bonding and ionic ligand bonding by using nanocellulose reinforced poly(acrylic acid) hydrogels impregnated with the Fe3+ solution to prepare a double-network hydrogel. The prepared PAA/CNF–Fe3+ double-network hydrogel exhibited excellent properties, including extraordinary performance compressive stress (2.96 MPa) and remarkable electrical conductivity (6.34 S/m). With these advantages, the PAA/CNF–Fe3+ double network hydrogel was developed to be an attractive strain flexible sensor with cyclic stability (150 cycles) and good strain sensitivity (GF = 2.87). In addition, the PAA/CNF–Fe3+ hydrogel flexible sensor can be used as an electronic skin to accurately discriminate subtle and large body movements. Given the simple strategy, double network structure, and satisfactory functionality, the PAA/CNF–Fe3+ hydrogel provides a new sustainable and multifunctional development strategy that can be applied in the field of strain sensors and medical detection.

Road Narrow-Inspired Strain Concentration to Wide-Range-Tunable Gauge Factor of Ionic Hydrogel Strain Sensor.

The application of stretchable strain sensors in human movement recognition, health monitoring, and soft robotics has attracted wide attention. Compared with traditional electronic conductors, stretchable ionic hydrogels are more attractive to organization-like soft electronic devices yet suffer poor sensitivity due to limited ion conduction modulation caused by their intrinsic soft chain network. This paper proposes a strategy to modulate ion transport behavior by geometry-induced strain concentration to adjust and improve the sensitivity of ionic hydrogel-based strain sensors (IHSS). Inspired by the phenomenon of vehicles slowing down and changing lanes when the road narrows, the strain redistribution of ionic hydrogel is optimized by structural and mechanical parameters to produce a strain-induced resistance boost. As a result, the gauge factor of the IHSS is continuously tunable from 1.31 to 9.21 in the strain range of 0-100%, which breaks through the theoretical limit of homogeneous strain-distributed ionic hydrogels and ensures a linear electromechanical response simultaneously. Overall, this study offers a universal route to modulate the ion transport behavior of ionic hydrogels mechanically, resulting in a tunable sensitivity for IHSS to better serve different application scenarios, such as health monitoring and human-machine interface.

Electrical conductivities and sensing mechanisms of low-temperature 3D printing conductive hydrogels with good sensitivity

Flexible strain sensors are core components of wearable strain sensors, and they have attracted much attention because of their applications for electronic skin and monitors of human activity. However, hydrogel-based strain sensors are greatly limited by the trade-offs between mechanical performance, electrical sensing properties and diverse structures. In this paper, we present a facile approach for preparing conductive hydrogels with good mechanical properties, outstanding electrical sensing properties and complex structures. First, a low-temperature 3D printer was designed and fabricated in this laboratory to prepare lignosulfonate/poly(vinyl alcohol) hydrogels with complex structures. The hydrogels with a 30° angle between adjacent layers showed the best optimal tensile properties. Then, extremely thin and dense silver layers were prepared by reducing silver on their surfaces using a two-step immersion process to obtain electrical sensing functionality. The process of preparing layers of reduced silver was carefully analyzed according to the Lamer model, and the resulting silver layers showed relatively high conductivity of 8571 S/cm. By changing the print path angles of the upper surface, hydrogels were prepared with different sensitivities and strain ranges. The maximum sensitivity and widest strain range were 177.65 and 0–55%, respectively. The corresponding hydrogels showed durable sensing performances in various tensile strain and long-term cyclic loading and relaxation tests. The sensing mechanisms of the hydrogels were the opening and closing of microcracks in the silver layers located in the print paths and the gaps between adjacent print paths. The sensors composed of conductive hydrogels successfully detected subtle vibrations in strains and various human activities, indicating their great potential for applications in monitors for human health and soft robotics.