Repeatable Adhesion Research Articles

Catechol-free ternary random copolymers for strong and repeatable underwater adhesion

Ternary random copolymers consisting of chemical features of nonphenolic aromatic groups, cations, and polar side chains enabled excellent underwater adhesion.

Microtemplated Electrowetting for Fabrication of Shape‐Controllable Microdomes in Extruded Microsucker Arrays toward Octopus‐Inspired Dry/Wet Adhesion

AbstractInspired by the prominent adhesion ability of octopus suckers, many dry/wet adhesives with specific micro‐structure have been fabricated for applications in smart robots, manipulators, and medical treatments. However, the reported octopus‐inspired adhesive patches are either suction‐assistant without tight‐sealing, or suction‐sealed but inefficient under both dry/wet environments. Here, a microtemplated electrowetting method is developed for the fabrication of reversible dry/wet adhesive pads consisting of extruded microsuckers with suction‐enhanced microdomes and sealing‐ring tips. The mechanism toward the morphology regulation of microdomes illustrates the uneven electrohydrodynamic force on the liquid–air interface that changes the liquid meniscus and achieves the precise regulation of the microdomes curvature ratio (from 0.45 to 0.74). The tip spacing can be controlled (from 0 to 50 µm) by using different templates. Theoretical and experimental insights into the mechanism of the microdomes morphology and the tip spacing on adhesion are discussed. With optimized microdomes and maximized sealing‐tips, this adhesive patch generates strong and repeatable adhesion on a silicon wafer in both air (≈ 86 kPa) and underwater (≈ 61 kPa) environments. Besides, considerable adhesion to the rough surfaces are also revealed. Its adhesion ability is demonstrated with stable transportation of various objects under air/underwater environments, providing a potential application in cross‐media operation.

Dynamic cross-linked polyurethane hot-melt adhesive with high biomass content and high adhesive strength simultaneously

Polyurethane hot-melt adhesives (PU-HMAs) have been widely used due to their outstanding advantages, however, the high dependence on non-renewable petrochemical resources has limited their green and sustainable development. It is still a challenge to achieve high adhesive strength and high biomass content of PU-HMAs simultaneously. Herein, a bio-based dynamically cross-linked polyurethane hot-melt adhesive (DPU) was constructed by the bio-based vanillin oxime (VO) and soybean oil polyol (SBOH), along with polytetrahydrofuran (PTMG) and isophorone diisocyanate (IPDI). The highest lap shear strength of the DPU adhesive reached up to 6.55 ± 0.88 MPa only after 30 min curing, while the biomass content reached 25 wt% of the total mass, which is significantly higher than that of previous reports. Especially, the oxime group of VO reacts with isocyanates to form the reversible oxime-carbamate covalent bonds, which endows the adhesive with excellent self-healing and repeatable adhesion properties. The lap shear strength remained at 5.56 ± 0.89 MPa after 7 complete breaking-repairing cycles, which exceeded 80 % of the initial lap shear strength. Moreover, the DPU adhesive also displayed excellent resistance to low temperatures and solvents, and better adaptability on different substrate surfaces than commercial PU-HMA Lubrizol-5173 and Loctite-3542. Therefore, this work provided a new route for developing high-performance and self-healing bio-based PU-HMAs.

An anti-swelling, strong and flexible wood-based composite hydrogel as strain sensor

General flexible conductive hydrogels are excellent candidate as strain-sensor. However, they were usually suffered by high water-absorbing and low mechanical properties. Herein, by introducing delignified wood skeleton into polyacrylamide hydrogel, wood-based composite hydrogels (WCH) with low-swelling and high strength were successfully obtained. The fracture tensile strength of the WCH can reach as high as 19.8 MPa along the longitudinal direction of wood and 2.7 MPa along the transverse direction, which originated from the intrinsic structure of wood skeleton. After water-soaking, size and weight of the WCH increased by only 9 % and 42 %, much less than that of the pristine PAM hydrogel (70 % and 383 %). Based on finite element analysis, wood skeleton structure disperses the swelling stress, which was conducive to reduce the water-swelling of hydrogels. The WCH also showed high adhesion to polar substrates (28.55 kPa to paper) and repeatable adhesion properties. Moreover, the WCH sensors demonstrated stable strain sensitivity, which could monitor bending and pressing. The as-prepared WCH will be promising in broaden the application field of flexible conductive hydrogels as strain-sensors. This work also provides a simple method of balsa wood to new multi-functional and smart applications.

Bio-Inspired Instant Underwater Adhesive Hydrogel Sensors.

Underwater adhesion plays an essential role in soft electronics for the underwater interface. Although hydrogel-based electronics are of great interest, because of their versatility, water molecules prevent hydrogels from adhering to substrates, thus bottlenecking further applications. Herein, inspired by the barnacle proteins, MXene/PHMP hydrogels with strong repeatable underwater adhesion are developed through the random copolymerization of 2-phenoxyethyl acrylate, 2-methoxyethyl acrylate, and N-(2-hydroxyethyl) acrylamide with the presence of MXene nanosheets. The hydrogels are mechanically tough (elastic modulus of 32 kPa, fracture stress of 0.11 MPa), and 2-phenoxyethyl acrylate (PEA) with aromatic groups endows the hydrogel with nonswelling property and prevents water molecules from invading the adhesive interface, rendering the hydrogels an outstanding adhesive behavior toward various substrates (including glass, iron, polyethylene terephthalate (PET), porcine). Besides, dynamic physical interactions allow for instant and repeatable underwater adhesion. Furthermore, the MXene/PHMP hydrogels exhibit a high conductivity (0.016 S/m), fast responsiveness, and superior sensitivity as a strain sensor (gauge factor = 7.17 at 200%-500% strain) and pressure sensor (0.63 kPa-1 at 0-70 kPa). The underwater applications of bionic hydrogel-based sensors have been demonstrated, such as human motion, pressure sensing, and holding objects. It is anticipated that the instant and repeatable underwater adhesive hydrogel-based sensors extend the underwater applications of hydrogel electronics.

Catch bond-inspired hydrogels with repeatable and loading rate-sensitive specific adhesion.

Biological receptor-ligand adhesion governed by mammalian cells involves a series of mechanochemical processes that can realize reversible, loading rate-dependent specific interfacial bonding, and even exhibit a counterintuitive behavior called catch bonds that tend to have much longer lifetimes when larger pulling forces are applied. Inspired by these catch bonds, we designed a hydrogen bonding-meditated hydrogel made from acrylic acid-N-acryloyl glycinamide (AA-NAGA) copolymers and tannic acids (TA), which formed repeatable specific adhesion to polar surfaces in an ultra-fast and robust way, but hardly adhered to nonpolar materials. It demonstrated up to five-fold increase in shear adhesive strength and interfacial adhesive toughness with external loading rates varying from 5 to 500 mm min−1. With a mechanochemical coupling model based on Monte Carlo simulations, we quantitatively revealed the nonlinear dependence of rate-sensitive interfacial adhesion on external loading, which was in good agreement with the experimental data. Likewise, the developed hydrogels were biocompatible, possessed antioxidant and antibacterial properties and promoted wound healing. This work not only reports a stimuli-responsive hydrogel adhesive suitable for multiple biomedical applications, but also offers an innovative strategy for bionic designs of smart hydrogels with loading rate-sensitive specific adhesion for various emerging areas including flexible electronics and soft robotics.

Transparent, highly stretchable, adhesive, and sensitive ionic conductive hydrogel strain sensor for human motion monitoring

Due to the flexibility, ductility and tensile properties, hydrogel is considered as promising candidates for the new generation of wearable flexible devices. However, it is still a challenge to endow multiple functions such as excellent conductivity, high stretchability, self-healing, self-adhesion, and biocompatibility in one hydrogel network. Herein, a two-step method was used to prepare multifunctional transparent tannic acid/sodium alginate/polyacrylic acid/carboxymethyl cellulose/aluminum trichloride (SA/TA/PAA/CMC/Al(III)) hydrogels with high stretchability, toughness, adhesion, and conductivity. This hydrogel can adhere to various substrates both organic and inorganic materials. The highest adhesion strength of the hydrogels to the iron sheet reaches 22.33 kPa with the fracture stress being 0.16 MPa and the toughness 1.01 MJ/m3. Moreover, the hydrogel exhibited repeatable and durable adhesion to human skin and could be peeled off completely without any residual, irritation or allergic reactions. Additionally, the hydrogels also have good repetitive adhesion and strain sensitivity. It was demonstrated that both large-scale and small-scale movements of the human body could be monitored by directly attached to various parts of the human body by the self-adhesion. This work provides a new prospect for the design of the biocompatible hydrogels with transparent, stretchable, self-adhesive, and strain-sensitive properties for potential applications in wearable electronic sensors.

Interface interaction-mediated design of tough and conductive MXene-composited polymer hydrogel with high stretchability and low hysteresis for high-performance multiple sensing

Conductive hydrogels based on two-dimensional (2D) nanomaterials, MXene, have emerged as promising materials for flexible wearable sensors. In these applications, the integration of high toughness, ultrastretchability, low hysteresis, self-adhesiveness, and multiple sensory functions into one gel is essential. However, serious issues, such as easy restacking and inevitable oxidation of MXene nanosheets in aqueous media and weak interfacial bindings between MXene and the gel network, make it almost impossible to achieve the multiple performances mentioned above. Here we present a conductive MXene-composited polymer (MCP) hydrogel by incorporating gelatin-modified MXene into polyacrylamide (PAAm) hydrogel for the fabrication of multifunctional sensors. The presence of gelatin not only greatly improves the stability of the MXene nanosheets by forming a protective sheath, but also largely enhances the interfacial interactions between the MXene and the hydrogel network as molecular glues. Thus, the MCP hydrogel exhibits a high strength (430 kPa), remarkable stretchability (1100%), low hysteresis (<10% at 500% cyclic tensile), and excellent repeatable adhesion. The resultant MCP hydrogel-based versatile sensors display a high strain sensitivity with a broad working range (gauge factor (GF) = 8.83, up to 1000%), realizing the detection of various human motions. Moreover, the prepared sensors possess superior thermosensitive capacities (1.110/°C) for the measurement of body temperature. This strategy opens horizons to designing high-performance MXene-based hydrogels for advanced sensing platforms.

Tissue-nanoengineered hyperbranched polymer based multifunctional hydrogels as flexible “wounped treatment-health monitoring” bioelectronic implant

Conductive hydrogels with arisen bioelectronics have shown enormous potential for the integration of real-time monitoring of the injury motion activities and therapeutic effects under electrical stimulation coupled with curative multifunctionality. Herein, inspired by natural skin, a tissue-nanoengineered hyperbranched polymer based multifunctional hydrogels (CHHCMgel) with mechanically flexible, antibacterial, electroactive, bio-adhesive, self-healable and hemostatic features was manufactured through integrative crosslinking and bio-compositing strategy of hyperbranched polyglycidyl ether to incorporate the functional building blocks of biocompatible chitosan/human-like collagen composites along with conductive MXene sheets and Gr (Graphene). Owing to the natural features and reconstructed 3D crosslinked double-network of the based constituents, the proposed CHHCMgel possessed all the desirable multi-functional properties, including adjustable mechanical and bioelectroactive characteristics, fast gelation time, self-healing ability, and repeatable adhesion. Moreover, CHHCMgel exhibited high biocompatibility and extensive antibacterial activity. In vitro and in vivo experiments showed that the CHHCMgel can undergo real-time monitoring of large-scale human motion and simultaneously have significant comprehensive therapeutic effects on the hemostatic efficacy, cell proliferation, and further skin wound healing under specific electrical stimulation, substantiating that the proposed CHHCMgel scaffold can be used in full-thickness dermal wound healing with great potential as a new-type flexible "wound treatment-health monitoring" bioelectronic implant.

Smart Antifreeze Hydrogels with Abundant Hydrogen Bonding for Conductive Flexible Sensors.

Recently, flexible sensors based on conductive hydrogels have been widely used in human health monitoring, human movement detection and soft robotics due to their excellent flexibility, high water content, good biocompatibility. However, traditional conductive hydrogels tend to freeze and lose their flexibility at low temperature, which greatly limits their application in a low temperature environment. Herein, according to the mechanism that multi−hydrogen bonds can inhibit ice crystal formation by forming hydrogen bonds with water molecules, we used butanediol (BD) and N−hydroxyethyl acrylamide (HEAA) monomer with a multi−hydrogen bond structure to construct LiCl/p(HEAA−co−BD) conductive hydrogel with antifreeze property. The results indicated that the prepared LiCl/p(HEAA−co−BD) conductive hydrogel showed excellent antifreeze property with a low freeze point of −85.6 °C. Therefore, even at −40 °C, the hydrogel can still stretch up to 400% with a tensile stress of ~450 KPa. Moreover, the hydrogel exhibited repeatable adhesion property (~30 KPa), which was attributed to the existence of multiple hydrogen bonds. Furthermore, a simple flexible sensor was fabricated by using LiCl/p(HEAA−co−BD) conductive hydrogel to detect compression and stretching responses. The sensor had excellent sensitivity and could monitor human body movement.

Osteichthyes skin-inspired tough and sticky composite hydrogels for dynamic adhesive dressings

Development of biomimetic hydrogel-based wound dressing is highly desirable for addressing life-threatening infectious skin injuries but has proved to be extremely challenging. However, poor tissue adhesive performance, stretchability and difficult fixation lead to conventional wound dressings failing to adapt to dynamic wounds with high-frequency movement or special fluctuant positions. Herein, we present a new biomimetic natural-synthetical combination by integrating Osteichthyes-extracted gelatins into hydrophilic polymeric networks to form unique tough, adhesive, self-healable composite hydrogels. The resultant Gelatin/PHEAA hydrogel without any growth factors/fungicides has high mechanical strength (∼1.0 MPa), high interfacial toughness (>1000 J/m2), and remarkable antifouling activity, enabling the hydrogel to effectively inhibit bacterial proliferation and promote the wound healing. Moreover, due to the abundant hydrogen bonds in composite crosslinked networks, the Gelatin/PHEAA hydrogels maintain high, repeatable adhesion even in high dynamic cases, regardless of wet or dry environments and the types of solid nonporous substrates. Further in vitro and in vivo full-thickness skin defect model confirms that the Osteichthyes-extracted proteins can accelerate collagen deposition and vascular regeneration, leading to a faster wound closure efficiency. Ultimately, we believe that the designed tough Gelatin/PHEAA hydrogels can be high-value candidates for managing rapid wound healing, while the proposed structural biomimetic combination can inspire researchers to design more interesting and effective biomaterials for clinical translation and health care.

Bioinspired Cationic-Aromatic Copolymer for Strong and Reversible Underwater Adhesion

Developing new underwater glue adhesives with robust and repeatable adhesion to various surfaces is promising and useful in marine life and medical treatments. In this work, we developed a novel glue based on a copolymer with a cation-co-aromatic sequence where the cationic units contain both catechol and positively charged sites. The glue consists of a crosslinked copolymer of poly(2-hydroxy-3-phenoxypropyl acrylate-co-3-(5-(3,4 dihydroxyphenyl)-4-oxo-3 N-pentyl)imidazolium) bromide in dimethyl sulfoxide. Solidification of the glue, triggered by contact with water, undergoes a coacervation stage and causes a drastic growth of its mechanical properties over time. The glue demonstrates fast-developing, strong, and repeatable underwater adhesion to different materials and can maintain its strength for a long time. The adhesion strength tends to increase with the surface energy of the substrate material, to a maximum value of 160 kPa found in plywood. Experiments conducted in aqueous media with different pH and ionic strengths, including physiological conditions and seawater, showed an even stronger adhesion than that evolved in deionized water. Thus, the developed glue is a promising candidate for use in marine life, tissue adhesives, and other freshwater and saline water applications.

Highly Sensitive and Robust Polysaccharide-Based Composite Hydrogel Sensor Integrated with Underwater Repeatable Self-Adhesion and Rapid Self-Healing for Human Motion Detection.

Tough, biocompatible, and conductive hydrogel-based strain sensors are attractive in the fields of human motion detection and wearable electronics, whereas it is still a great challenge to simultaneously integrate underwater adhesion and self-healing properties into one hydrogel sensor. Here, a highly stretchable, sensitive, and multifunctional polysaccharide-based dual-network hydrogel sensor was constructed using dialdehyde carboxymethyl cellulose (DCMC), chitosan (CS), poly(acrylic acid) (PAA), and aluminum ions (Al3+). The obtained DCMC/CS/PAA (DCP) composite hydrogels exhibit robust mechanical strength and good adhesive and self-healing properties, due to the reversible dynamic chemical bonds and physical interactions such as Schiff base bonds and metal coordination. The conductivity of hydrogel is 2.6 S/m, and the sensitivity (gauge factor (GF)) is up to 15.56. Notably, the DCP hydrogel shows excellent underwater repeatable adhesion to animal tissues and good self-healing properties in water (self-healing rate > 90%, self-healing time < 10 min). The DCP hydrogel strain sensor can sensitively monitor human motion including finger bending, smiling, and wrist pulse, and it can steadily detect human movement underwater. This work is expected to provide a new strategy for the design of high-performance intelligent sensors, particularly for applications in wet and underwater environments.

PVA/gelatin/β-CD-based rapid self-healing supramolecular dual-network conductive hydrogel as bidirectional strain sensor

Hydrogel-based flexible sensors have exhibited great application prospect in the fields of e-skin, movement monitoring and human-computer interaction. Nevertheless, it is still a difficult problem to construct the biomass-based hydrogel sensors with considerable mechanical property, biocompatibility, self-healing property, sensitivity, self-adhesion and fatigue resistance. Herein, a gelatin-based dual-network (DN) hydrogel sensor with multiple dynamic crosslinking was successfully fabricated, in which the dynamic Schiff base bonds between gelatin and an aldehyde-containing supramolecular crosslinker (PCD-Fc-CHO) formed by the host-guest complexing of β-cyclodextrin (β-CD) to ferrocene (Fc) were used to construct the first network of the hydrogel, while the reversible borate ester bonds of PVA with borax were utilized to establish the second network. Meantime, carbon nanotubes (CNTs) were added to endow the gelatin-based DN hydrogel with good conductivity and improved mechanical property. The prepared gelatin-based DN hydrogel possesses favorable ductility (1200%), biocompatibility, double self-healing (HE = 96%), high sensitivity (GF = 6.4), self-adhesion (repeatable adhesion), dual stimuli-responsiveness (pH and oxidation), plasticity and fatigue resistance. The DN hydrogel-based strain sensor can not only monitor various human body (e.g. fingers, knees, speech, etc.) movements and vital signs (pulse), but also monitor in vitro the breathing movements of pig lungs. Interestingly, the self-healed gelatin-based DN hydrogel sensor can also be reused, and its monitoring ability is basically the same as the original hydrogel. This work puts forward a new strategy for the construction of multiple dynamically cross-linked biomass-based self-healing hydrogels as multifunctional wearable flexible sensors.

Chitin/Ca solvent-based conductive and stretchable organohydrogel with anti-freezing and anti-drying

Conductive hydrogel flexible sensors have attracted considerable research interest because of their good conductivity, flexibility, and biocompatibility. However, conventional hydrogels suffer from dehydration under ambient environments and freezing at low temperatures. Herein, we prepared a chitin/polyacrylamide organohydrogel with highly stretchable, anti-freezing, and anti-drying properties. This organohydrogel was creatively prepared by one-step radical polymerization in the chitin and calcium chloride/methanol (Ca solvent) aqueous solution. Benefiting from the chitin/Ca solvent system, the organohydrogel shows relatively high stretchability (improve ~5 times), excellent anti-freezing (up to −80 °C) upon long-term storage, and anti-drying (67 days under normal environment) performance. What's more, the reversible noncovalent bonds in the organohydrogel endow it with repeatable multi-purpose adhesion and rapid self-healing, while the abundant free ions grant it good conductivity to be a flexible sensor. Therefore, it is promising that this chitin-based conductive organohydrogel with multifunctionality would provide wide application scopes of flexible electronic devices.

Simple Preparation of a Waterborne Polyurethane Crosslinked Hydrogel Adhesive With Satisfactory Mechanical Properties and Adhesion Properties.

Waterborne polyurethane has been proven to be an ideal additive for the preparation of hydrogels with excellent mechanical properties. This work reports that a satisfactory adhesion of acrylamide hydrogels can be obtained by introducing a large amount of waterborne polyurethane into system. A series of polyurethane hydrogels was prepared by using one-pot method with acrylamide monomer and 2-hydroxymethyl methacrylate end-modified waterborne polyurethane emulsion. The hydrogels exhibit good strength (greater than 30 KPa), wide range of adjustable strain (200%–800%), and excellent compression fatigue resistance. The performance improvement is attributed to the fact that the polyurethane emulsion containing double bonds provides chemical crosslinking and forms polyurethane microregions due to hydrophilic and hydrophobic interactions. The hydrogel shows extensive and repeatable adhesion on diverse substrates. This simple preparation method through polyurethane crosslinked hydrogels is expected to become a low-cost and efficient preparation strategy for hydrogel adhesives.

Tough, Instant, and Repeatable Adhesion of Self-Healable Elastomers to Diverse Soft and Hard Surfaces.

Repeatability and high adhesion toughness are usually contradictory for common polymer adhesives. Repeatability requires temporary interactions between the adhesive and the substrate, while high adhesion toughness is usually achieved by permanent bonding. Integrating these two features into one adhesive system is still a daunting challenge. Here, the development of a series of viscoelastic elastomers composed of a soft and hard segment is reported, which exhibit tough, instant, yet repeatable adhesion to a variety of soft and hard surfaces. Such a combination of mutually exclusive properties is attributed to the synergy of high mobility of polymer chains and massive viscoelastic dissipation of the elastomers around the interface. By optimizing the relaxation time and mechanical dissipation, the resulting adhesives can achieve a tough yet repeatable adhesion toughness above 2000 J m−2, superior to the best‐in‐class commercial adhesives. Numerous acrylate monomers are proven applicable to the preparation of such adhesives, validating the universality of the fabrication method. The application of these elastomers as adhesive and protective layers in soft electronics by virtue of their universal and tough adhesion to various soft and hard substrates is also demonstrated.

Hydrogel adhesive formed via multiple chemical interactions: from persistent wet adhesion to rapid hemostasis.

To date, the robust and durable adhesion capability of hydrogel adhesives in wet environments remains a huge challenge. Herein, a physicochemically double-network crosslinked hydrogel matrix was prepared by mixing acrylic acid (AAc), chitosan (CS) and tannic acid (TA) as the main components and the subsequent in situ polymerization of AAc. The abundant reactive sites on the surface of the hydrogel matrix facilitate rapid, strong and repeatable adhesion to different surfaces of engineering solids and biological tissues in an aquatic environment. The formation of amide covalent bonds resulting from the addition of the bridging agent further expands the long-term application of the hydrogel in tissue repair, and the constructed hydrogel-tissue adhesive interface still has robust adhesion energy after soaking in a physiological environment for up to one month. Moreover, the hydrogel showed fantastic hemostatic performance due to its characteristics of platelet adhesion and high burst pressure. Overall, the persistent adhesion and excellent cytocompatibility of the hydrogel adhesive make it potentially applicable in medical adhesives.

Nature-Inspired Hydrogel Network for Efficient Tissue-Specific Underwater Adhesive.

Underwater adhesives with efficient, selective, and repeatable adhesion are urgently needed for biomedical applications. Catechol-containing hydrogel adhesives have aroused much interest, but the design of specific underwater adhesives to biotic surfaces is still a challenge. Here we report a facile way that recapitulates the adhesion mechanism of mussel and sea gooseberry for the development of robust and specific hydrogel adhesives. With an exquisite design of chemical bonding, catechol chemistry, and electrostatic interaction, the hydrogel consisting of poly(acrylic acid) grafted with N-hydroxysuccinimide ester (PAA-NHS ester), tea polyphenol (TP), chitosan (CS), and Al3+ exhibited fast, specific, and repeatable underwater adhesion to various biological tissues, such as porcine skin, intestine, liver, and shrimp. Furthermore, nanofibers-hydrogel composite (NF-HG) was prepared via the wicking effect of curcumin-loaded electrospun nanofibers. The NF-HG exhibited pH-responsive color changing properties, sustained drug release, and good cell viability, which made it suitable as a novel wound healing material. This strategy may provide great inspiration for designing multifunctional specific underwater adhesives.

Tough, Repeatedly Adhesive, Cyclic Compression-Stable, and Conductive Dual-Network Hydrogel Sensors for Human Health Monitoring

Hydrogel-based flexible wearable devices have attracted wide attention from researchers due to their great potential application in human–computer interaction, electronic skin, and disease diagnosis. However, the preparation of conductive hydrogels integrating good biocompatibility, excellent mechanical (tensile and compressible) properties, self-adhesive properties, cyclic stretching, and compression stability remains a challenge. By the Schiff base reaction between dialdehyde carboxymethyl cellulose and amino gelatin to form the first layer of the network and by the free-radical polymerization of acrylic acid to form the second layer of the network, a multifunctional conductive dual-network (DN) hydrogel strain sensor was prepared. The composite DN hydrogel has excellent compression properties (the strength reached to 0.12 MPa when the hydrogel was compressed to 50% of its original height), good cyclic compression (≥10 000 times), repeatable adhesion (≥10 times), reliable electrical conductivity, and high sensitivity (gauge factor = 8.1). The biocompatible hydrogel can be used not only to monitor human body movement but also to detect the breathing movement of simulated pig lungs in vitro. Furthermore, the conductive hydrogel was creatively made into a plantar pressure sensor similar to an insole to monitor the stress on the sole of a flatfoot patient, providing a new potential material for flatfoot detection and correction.