In-situ Preparation of Excellent Temperature Response Hydrogels with SA/PAM/PPy System and its Application in Motion Monitoring

In-situ Preparation of Excellent Temperature Response Hydrogels with SA/PAM/PPy System and its Application in Motion Monitoring | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article In-situ Preparation of Excellent Temperature Response Hydrogels with SA/PAM/PPy System and its Application in Motion Monitoring Qiao feng Wei, Liang Li, Xiaowen Cheng, Yuan zeng, Yongqiang wang, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7742823/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Accurate and continuous monitoring of human body temperature is a core function of smart wearable temperature sensors. However, fabricating temperature sensors with high sensitivity and rapid response remains a challenge. Here, using the natural polysaccharide sodium alginate (SA), acrylamide (AM), and in-situ polymerization of polypyrrole (PPy), a conductive hydrogel (SA/PAM/PPy) was synthetized. It is indicated that as the pyrrole concentration increases the conductivity of hydrogel enhances from 21.3 to 67.7 mS/cm. The temperature sensitivity of hydrogels vary with temperature intervals. In 10–30℃ range, the temperature coefficient of resistance ( TCR ) is -1.22%/℃, increasing to -3.70%/℃ in 30–50℃ range, aligning with human body temperatures. The hydrogels also demonstrate superior responsiveness, with the temperature rise/drop response times of 0.1185 / 0.1957 s, respectively, with excellent cycling stability, maintaining stable electrical signals during multiple cycles in 25–40℃. Its application in running exercises enables effective monitoring of body temperature changes across different speeds. Overall, the developed hydrogels not only sense temperature variations but also align closely with human body temperature ranges, showing great potential in smart wearable technology. Human body temperature Temperature-sensitive property Conductive hydrogel Adhesion Elasticity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Human body temperature serves as a crucial indicator of human health, reflecting the body's internal physiological processes, chemical dynamics, and emotional state[ 1 , 2 ]. Traditional thermometers fail to meet the specific requirements of temperature monitoring devices for intelligent wearable applications, especially in terms of softness, elasticity, adhesion, and structural stability during physical activities. Consequently, the development of flexible and intelligent temperature sensors has become a critical topic of research. Hydrogels are three-dimensional crosslinked network polymers. Their high water retention[ 3 ], flexibility[ 4 ], biocompatibility[ 5 ], and tunability[ 6 ] make them suitable for multifunctional sensors[ 7 ], medical dressings[ 8 , 9 ], and information storage[ 10 ]. Moreover, incorporating conductive materials during hydrogel synthesis imparts electrical conductivity. This enables conductive hydrogels to convert temperature[ 11 ], pressure[ 12 ], and biological signals[ 13 ] into electrical signals, making them the preferred material for temperature sensors. There exist various temperature sensing mechanisms, including conductive temperature variation, thermal expansion and contraction, and phase change principles. Hydrogels, enriched with functional substances that alter resistance[ 11 , 14 ], color[ 15 – 17 ], phase, or swelling[ 18 , 19 ] in response to temperature changes, can enable continuous, real-time, and precise temperature sensing. Hydrogel smart sensors have been widely applied in electronic skin[ 20 ], human-computer interaction[ 21 , 22 ], and soft robotics[ 23 , 24 ]. Compared with rigid sensors, hydrogel sensors offer advantages such as adaptability to complex environments[ 25 ], skin conformability[ 26 ], and high accuracy[ 27 ], showing significant potential for practical applications. For instance, Shi et al.[ 28 ] developed a hydrogel temperature sensor material with high thermal sensitivity (exhibiting volume change within seconds of temperature variation) by forming a phytanic acid crosslinked hydrogel within a poly(N-isopropylacrylamide) matrix. Additionally, Ge et al.[ 29 ] prepared polyaniline (PAA-PANI) hydrogels, which demonstrated good temperature sensitivity (with a resistance temperature coefficient of -1.6%/℃) and high temperature resolution (2.7 ℃). Temperature sensors are subjected to mechanical stress during operation, requiring good tensile, elastic, and toughness properties. Therefore, their mechanical performance and durability are crucial. Zeng et al.[ 4 ] made a dual-network hydrogel using sodium alginate (SA) and acrylamide (AM) as raw materials and adding different amounts of chitosan (CS) to boost the hydrogel's toughness, revealing its strength/elongation at break up to 0.249 MPa /1635.65% with excellent recovery ability under 200% constant-elongation cyclic stretching. Yang et al.[ 30 ]added CS when preparing hydrogels, then the chitosan-based composite hydrogels post-crosslinked with a polyvalent anion solution, forming a rigid CS ionic network, greatly improving the hydrogels' elastic modulus, tensile strength, and fracture energy. Sensitivity, a key indicator for temperature sensors, can be optimized by adjusting the type or content of conductive substances in hydrogels. Zhang et al.[ 25 ] added LiCl and glycerol to hydrogel to broaden its temperature sensing range. However, the sensitivity kept low, with resistance temperature coefficients of -0.87%/℃ (20–50℃) and − 0.19%/℃(50–80℃). Similarly, Liu et al.[ 31 ] used an ionic liquid (1-ethyl-3-methylimidazolium chloride) and water binary solvent system to prepare hydrogels, presenting resistance temperature coefficients of -1.845%/℃ (10–50℃) and − 0.7134%/℃ (50–80℃), indicating a wide sensing range but still low sensitivity.Another important evaluation index is the sensitive temperature coupling interval and responsiveness. The heat transfer process in materials inevitably causes a time lag in temperature sensing. Reducing this lag or enhancing responsiveness, especially in narrower temperature intervals, is a research priority. At present, the hydrogel temperature sensor has a wide sensing range. However, few of them couples to the human body temperature range, cannot fully meet the application requirements. Therefore, developing hydrogel temperature sensors with high sensitivity, good responsiveness, and specific coupling to human body temperature changes is highly necessary. Human body essentially functions as a biological thermostat, with its temperature typically fluctuating between 30℃ and 50℃ due to varying physiological conditions. Therefore, the hydrogel sensor developed here is designed to exhibit adequate sensitivity and responsiveness within this specific temperature interval. In this work, natural polysaccharide sodium alginate (SA) and acrylamide (AM) are employed as monomers for hydrogel synthesis. The hydrogels are immersed in pyrrole (Py) monomer solutions of varying concentrations to undergo in-situ polymerization. By adjusting the concentration of polypyrrole within the hydrogel, the electrical conductivity is systematically investigated. Additionally, the temperature-sensitive characteristics of hydrogels are examined using instantaneous temperature-varying photothermal materials. This approach aims to develop a hydrogel sensor that is highly responsive and specifically coupled to human body temperature range, making it suitable for human body temperature monitoring. 2. Experimental section 2.1 Experimental Materials Acrylamide (AM, AR) and N,N-methylenebisacrylamide (MBAA, AR) were obtained from Tianjin Komeo Chemical Reagent Co. Ltd. Sodium alginate (SA, CP) was acquired from Sinopharm Chemical Reagent Co. Ltd. Ammonium persulfate (APS, AR) was purchased from Tianjin Wind Ship Chemical Reagent Science and Technology Co. Ltd. Chitosan (CS, AR), N,N,N',N'-Tetramethylethylenediamine (TEMED, AR), pyrrole (Py, AR), and anhydrous ferric chloride (FeCl 3 , AR) were supplied by Shanghai McLean Biochemical Science and Technology Co. Ltd. The instantaneous temperature-varying photothermal material[ 32 ] (polydimethylsiloxane doped graphene coated on polyethylene film, with a temperature range of 10–80℃ and a heating rate of 0.35–0.59℃/s) was self-made. 2.2 Preparation of Temperature-Sensitive Hydrogels 2.2.1 Preparation of SA/PAM Hydrogel Firstly, accurately weigh 7.2 g of acrylamide (AM) and 0.6 g of sodium alginate (SA), transfer them to a reagent bottle, and add 52.2 g of deionised water. Stir the mixture using a digital temperature- controlled magnetic stirrer (MS-H-Pro+, Dragon LAB, Germany) until they are completely dissolved. Then, sequentially add 0.027 g of ammonium persulfate (APS), 0.009 g of N,N-methylenebisacrylamide (MBAA), and 0.39 g of chitosan (CS) to the solution, and stir thoroughly until fully dissolved. Next, dropwise add 0.015 g of N,N,N',N'-Tetramethylethylenediamine (TEMED) to the solution and stir well. After that, transfer the resulting solution to a PTFE template and place it into a vacuum drying oven (DZF-6090, Shanghai Jinghong Experimental Equipment Co., Ltd.) at 60℃ for 40 minutes to allow the solution to gel. Finally, take out the template and expose it to a self-made airtight ultraviolet lamp for 120 minutes to complete the preparation of SA/PAM hydrogel. 2.2.2 Preparation of SA/PAM/PPy Hydrogels Firstly, prepare Py monomer solutions at concentrations of 10%, 40%, 70%, and 100%. Immerse the SA/PAM hydrogels in each concentration of Py monomer solution for 24 hours at a low temperature of 2–5℃. Then, remove the hydrogels and place them in a sealed bag, storing them at 5 ℃ or below for approximately 3 hours to allow Py monomer to penetrate into the hydrogels. Next, weigh and dissolve 0.6475 mol·L − 1 FeCl 3 in deionised water, stirring until completely dissolved. Immerse the hydrogels in FeCl 3 solution at 5℃ for 12 hours to initiate the polymerization of Py monomers, in-situ polymerization forming polypyrrole (PPy). This process yields the SA/PAM/PPy hydrogels, specifically designated as SA/PAM/PPy (10), SA/PAM/PPy (40), SA/PAM/PPy (70), and SA/PAM/PPy (100). 2.3 Characterisation 2.3.1 SEM and EDS Analysis The prepared hydrogels were freeze-dried using a freeze-dryer (ALPHA 1–4 LD plus, Christ, Germany). Subsequently, selected dried samples were fractured in liquid nitrogen. The surface morphology and elemental distribution were then characterized using field emission scanning electron microscopy (TM3000, Hitachi Ltd., Japan). Prior to imaging, samples were sputter-coated with gold for 100 seconds. Observations were conducted at an accelerating voltage of 20 kV. 2.3.2 Moisture Content (Mc) Test The hydrogel samples were first subject to freeze-drying. The moisture content was determined using the formula: Mc = ( M p - M b )/ M p , where M p is the mass of the sample before freeze-drying and M b is the mass after freeze-drying. 2.3.3 FTIR and X-ray Diffraction (XRD) Analysis For FTIR analysis, 1–2 mg of the freeze-dried sample was mixed with a small amount of potassium bromide, ground into a fine powder, and then pressed into a uniformly light-transmitting sheet. The sample's characteristic peaks were recorded using a Fourier-transform infrared spectrometer (Tensor37, Bruker, Germany). For XRD analysis, freeze-dried samples (2×2 cm) were used to examine the composition and crystal structure of the composite hydrogels. A X-ray diffractometer (Rigaku Ultima IV, Rigaku Co., Ltd., Japan) was employed with settings of 40 kV voltage, 40 mA current, and a 2θ scanning range of 10°-90°, at a rate of 2°/min. 2.3.4 Thermal Stability Analysis For thermal stability assessment, approximately 5–6 mg of the freeze-dried hydrogel samples were accurately weighed and placed in a crucible. The samples were then analyzed using a thermogravimetric analyzer (STA-449-F5 Jupiter, NETZSCH GmbH, Germany). The analysis was performed in a nitrogen atmosphere, with a flow rate of 20 mL·min − 1 . The temperature was increased at a constant rate of 10 ℃/min, and the mass loss of the samples was recorded over a temperature range of 35–700 ℃. 2.3.5 Mechanical Properties and Adhesion Assessment A universal testing machine (AI-7000S1, High Speed Rail Technology Co., Ltd.) was employed to evaluate the tensile fracture, cyclic tensile behavior, and elastic recovery of hydrogels. Stress-strain curves were obtained by conducting tensile tests on samples with dimensions of 80 mm in length, 10 mm in width, and 5 mm in thickness. The tests were performed at a speed of 100 mm·min − 1 with a fixture distance of 40 mm. For cyclic tensile tests, constant elongation parameters were set at 25%, 50%, and 100% to perform tensile cycling tests. Elastic recovery was calculated based on the recovery of deformation from one cyclic tensile test at a constant elongation of 50%. The bending stiffness of hydrogel was determined using a self-constructed 30° trapezoidal ramp. A steel ruler was launched at a uniform speed, driving the sample to launch synchronously until the sample contacted the ramp due to its self-weight. The bending stiffness was calculated using the formula B = 9.8 w *(0.594* l 0 ) 3 *10 − 5 , where w is the sample's weight per square meter (g·m − 2 ) and l 0 is the length of the steel ruler extending out in centimeters. The adhesion of hydrogel to different substrates, including glass, PE plastic films and copper sheet, was assessed using a lap-shear tensile test conducted with the tensile tester. The adhesion strength was calculated by dividing the maximum load by the contact area. 2.3.6 Electrical Conductivity and Temperature Coefficient of Resistance The sample's resistance was measured by attaching thin copper wires to both ends of a 1 cm×4 cm sample, which was connected to an instant temperature-varying photothermal material and linked to a 2400 digital source meter (Girish Technology Co., Ltd., USA) in a two-wire configuration, with a clamping voltage of 80 V and an output current of 0.1 mA. The temperature of the photothermal material was raised using a xenon lamp (PLS-SXE300+), and the temperature was monitored via an infrared camera (Ti32, Fluke, USA). The distance between the xenon lamp and the photothermal material was 66 cm, with a current of 13 A and a light power density of 1 kW·m − 2 , maintaining the temperature between 10℃ and 50℃. The electrical conductivity ( σ ) was calculated using σ = ρ −1 , where ρ is the resistivity in Ω·m, determined by ρ = ( R * S )/ L ( S is the cross-sectional area in m 2 , and L is the conductor length in m). The temperature coefficient of resistance ( TCR , %/℃) was calculated as TCR =[( R - R 0 )/ R 0 *100%]/ ΔT , where R is the resistance at the measured temperature, R 0 is the initial resistance, and ΔT is the temperature change. 3. Results and Discussions 3.1 Morphological Characteristics and Water Content Analysis Figure 1 (a ~ d) and Fig. S1 (a) presents the SEM images of SA/PAM/PPy hydrogels after freeze- drying. Fig. S1 reveals the microscopic morphology of SA/PAM, showing a porous structure surrounded by particles. These pores facilitate to penetrate PPy macromolecules, as well as Fe 3+ and Fe 2+ , into hydrogels. Figure 1 (a)~(d) display the SEM images of SA/PAM/PPy hydrogels. A porous and interpenetrating network structure is obviously evident on the hydrogel surfaces. This structure arises from the crosslinking of PAM with SA and the interpenetration of amide bonds crosslinked by CS and SA. Small spherical particles aggregated on the hydrogel surface indicate that PPy macromolecules are distributed both on the surface and within the network of hydrogel. As the PPy concentration increases from 10% to 100%, the pores on hydrogel surface gradually decrease in size. At low PPy concentrations, fewer PPy enter the hydrogel, resulting in incomplete conductive pathways in SA/PAM/PPy (10) while SA/PAM/PPy (100) showing significant PPy aggregation. However, at moderate PPy concentrations, no particle aggregation, and the conductive pathways within hydrogel are more complete, which is beneficial for the hydrogel's conductivity and temperature-sensitive properties. Figure 1 (e ~ h) presents the distribution of Fe element in SA/PAM/PPy hydrogel, which indirectly indicates the distribution of PPy within hydrogel. As the PPy concentration increases, the Fe content also increases. In SA/PAM/PPy (10), some regions show no Fe distribution due to low Fe 2+ levels. In contrast, SA/PAM/PPy (40) and SA/PAM/PPy (70) exhibit more uniform Fe distributions. However, in SA/PAM/PPy (100), certain areas appear darker, likely due to PPy aggregation. This aligns with the SEM images in Fig. 1 (a ~ d). The temperature-sensitive properties of hydrogels do not simply enhance with increasing PPy concentration but may vary across different temperature ranges. Hydrogels possess high water retention properties, and their water content significantly influences the toughness, mechanical properties, electrical conductivity, and temperature-sensitive characteristics of hydrogel. Fig. S1 (b) presents the water content of SA/PAM/PPy hydrogel. Immersion of hydrogel in a Py solution leads to the incorporation of both Py molecules and water molecules. At low Py concentrations, this incorporation increases the hydrogel's conductivity and water content. However, when immersed in higher-concentration Py solutions, the number of Py molecules entering the hydrogel increases, while the number of water molecules decreases. This alters the ratio of PPy to water molecules within hydrogel. As the PPy content rises, the water content tends to decrease. This variation in water content not only impacts the electrical conductivity but also results in SA/PAM/PPy hydrogel exhibiting distinct temperature-sensitive properties across different temperature intervals. 3.2 Chemical Structure Analysis Figure 2 (a) depicts the FTIR spectra of SA/PAM/PPy hydrogel. The peaks at 3452 cm − 1 and 1655 cm − 1 are attributed to N-H stretching and C = O stretching vibrations of amide bonds, confirming the successful crosslinking of PAM with SA and CS with SA to form amide linkages (-CO-NH-), which constitute the network structure of SA/PAM hydrogel. As the incorporation of Py, the characteristic peaks near 3500 cm − 1 associated with intermolecular hydrogen bonding become more pronounced, indicating the formation of physical crosslinks between PPy and SA, as well as between PPy and CS through hydrogen bonds, thereby enhancing the mechanical properties of the SA/PAM/PPy hydrogels. As the Py concentration increases, the peak near 1650 cm − 1 , corresponding to the C = C vibration of the pyrrole ring, becomes more evident. The peak at 580 cm − 1 , related to the out-of-plane bending vibration of C-H present in SA, PAM, and PPy, also intensifies with increasing Py concentration and the rising C-H content in hydrogel. The introduction of PPy does not alter the functional groups of SA/PAM hydrogel, preserving its network structure. This structure provides an excellent pathway for the transport of macromolecules and ions within hydrogel, thereby laying the foundation for improving the electrical conductivity and temperature-sensitive properties of hydrogel. Figure 2 (b) and Fig. S2 presents the XRD spectra of SA/PAM/PPy hydrogel. Figure 2 (b) shows that SA/PAM spectrum features a pronounced peak near 25°, attributed to the formation of amide bonds between SA and PAM, as well as between SA and CS. This crosslinking enhances the regularity of the hydrogel's internal network, leading to a high degree of crystallinity. In Fig. S2, after PPy incorporation, a broadened characteristic peak appears between 20° and 30°, which widens with increasing PPy concentration. This is due to PPy's irregular chemical structure, which is less prone to crystallization. At higher concentrations, PPy macromolecules cluster within hydrogel, altering the conductive pathways. Consequently, the SA/PAM/PPy hydrogel exhibits varying temperature-sensitive properties across different temperature ranges. Figure 2 (b) and Fig. S2 presents the XRD spectra of SA/PAM/PPy hydrogel. Figure 2 (b) shows that SA/PAM spectrum features a pronounced peak near 25°, attributed to the formation of amide bonds between SA and PAM, as well as between SA and CS. This crosslinking enhances the regularity of the hydrogel's internal network, leading to a high degree of crystallinity. In Fig. S2, after PPy incorporation, a broadened characteristic peak appears between 20° and 30°, which widens with increasing PPy concentration. This is due to PPy's irregular chemical structure, which is less prone to crystallization. At higher concentrations, PPy macromolecules cluster within hydrogel, altering the conductive pathways. Consequently, the SA/PAM/PPy hydrogel exhibits varying temperature-sensitive properties across different temperature ranges. 3.3 Thermal Stability Analysis Figure 3 presents the TG and DTG curves of SA/PAM/PPy hydrogel, illustrating its thermal degradation in four distinct stages. Initially, between 35℃ and 147℃, the mass loss is predominantly due to water evaporation. Subsequently, from 147℃ to 230℃, the mass loss is attributed to the decomposition of side chains within the hydrogel's macromolecules, releasing small molecules such as NH 3 and CO 2 . In the temperature range of 230℃ to 430℃, the degradation is primarily characterized by the breaking of the macromolecular backbone. This involves the breakage of SA and PPy macromolecular segments, generating small molecules like CO 2 , Py, hydrogen cyanide (HCN), ammonia (NH 3 ), CO, and others, which contribute to the weight loss. Finally, between 430℃ and 700℃, the process is dominated by the carbonization and oxidation of residual materials, during which the mass changes are relatively minimal. Table S1 presents the thermal decomposition data of SA/PAM/PPy hydrogel. After incorporating PPy into SA/PAM hydrogel, the initial decomposition temperature, the temperature of the maximum weight loss rate, and the residual carbon rate at 700℃ all increase. This is because PPy exhibit high thermal stability, maintaining structural integrity at elevated temperatures and protecting the macromolecular main chain from degradation, thereby delaying its fracture.Specifically, SA/PAM/PPy (70) shows the highest initial decomposition temperature. As observed in Fig. 1 (d), when the PPy concentration is 70%, PPy are more uniformly distributed within hydrogel, enhancing its thermal stability. Although SA/PAM/PPy (100) contains the highest amount of PPy macromolecules and thus has the highest residual carbon rate, the thermal stability of hydrogel is optimized at a PPy concentration of 70%. Overall, the SA/PAM/PPy hydrogel demonstrates improved thermal stability. 3.4 Mechanical Properties and Adhesion of Hydrogels The mechanical properties and adhesion of hydrogels are crucial for temperature-sensitive sensor applications. Figure 4 (a) presents the stress-strain curves of SA/PAM/PPy hydrogels. The addition of PPy to SA/PAM hydrogel reduces its mechanical properties, primarily due to the rigidity of PPy. As the PPy concentration increases, the mechanical properties of the conductive hydrogel first increase and then decrease. SA/PAM/PPy (70) exhibits a maximum tensile stress of 0.248 MPa, which is equivalent to SA/PAM. At this concentration, the intertwined macromolecular network in the hydrogel is enhanced, and the mechanical properties and conductivity are improved. However, SA/PAM/PPy (100) shows decreased mechanical properties, as shown in Fig. 1 . When the concentration of PPy reached 70%, its distribution in the hydrogel is more uniform. At the concentration of 100% PPy, the internal pores of hydrogel shrink, and the aggregation of PPy becomes more serious, which introduces obvious defects, leading to the decline of mechanical properties. The bending stiffness of hydrogels was assessed using the ramp method, and the results are presented in Fig. 4 (b). As shown, the bending stiffness increases with higher PPy concentrations, which is attributed to the rigidity of PPy. SA/PAM/PPy(10) exhibits the lowest bending stiffness due to its higher water content. As PPy increase in hydrogel, the softness decreases. SA/PAM/PPy (10) contains relatively less PPy, thus maintaining better softness. The elasticity of hydrogels was evaluated by the elastic recovery rate after one stretching cycle at a constant 50% elongation (Fig. 4 (c)). The elastic recovery rate decreases with increasing PPy concentration but remains above 85% for all samples, indicating that the SA/PAM/PPy hydrogels possess good elasticity.To evaluate the durability of SA/PAM/PPy hydrogel, it underwent 30 cycles of tensile testing. Figure 4 (d) and Fig. S3(a ~ c) shows that after 30 cycles, the overlap of the hysteresis loops is high under different constant tensile parameters. This demonstrates that SA/PAM/PPy hydrogel has excellent durability, meeting the requirements for use as a temperature sensor. In addition to elasticity and flexibility, adhesion is also crucial for the practical application of hydrogels as human body temperature sensors. The adhesion was characterised by the shear stress of SA/PAM/PPy hydrogel on different substrates across multiple cycles, as shown in Fig. 4 (e ~ f) and Fig. S3(d). SA/PAM hydrogel exhibits the highest shear stress, attributed to hydrogen bonding between chitosan and the substrate surface. However, the shear stress of the conductive SA/PAM/PPy hydrogel decreases, likely due to PPy aggregation on the hydrogel surface, which increases surface roughness, reduces contact area with the substrate, and thus lowers adhesion.After 10 adhesion cycles, the shear stress of the PPy-containing hydrogel decreases only slightly, whereas a significant reduction is observed in the hydrogel without PPy. This indicates that SA/PAM/PPy hydrogel maintains better adhesion and durability, making it more suitable for practical applications as a temperature sensor. 3.5 Electrical Conductivity of the Hydrogel Figure 5 (a) illustrates the relationship between the electrical conductivity of SA/PAM/PPy hydrogel and the concentration of PPy. The incorporation of PPy into the hydrogel significantly enhances its conductivity. PPy particles penetrate the hydrogel's three-dimensional porous structure, forming electron or ion transport channels due to their high intrinsic conductivity. The dispersion of PPy within the hydrogel and the interactions between PPy macromolecules, whether in series, parallel, or aggregated configurations, will create a finite-scale conductive network. When the PPy concentration exceeds a critical threshold, an infinite-scale network may form, triggering a percolation effect that brings the composite's conductivity close to that of pure PPy[ 33 ]. Additionally, during the polymerization of Py, Fe 3+ ions enter the hydrogel, with some participating in the reaction and being reduced to Fe 2+ , while unreacted Fe 3+ remains free within the hydrogel. The presence of both Fe 3+ and Fe 2+ further elevates the hydrogel's conductivity. Within the conductive hydrogel, conductive mode can be classified into contact or non-contact. Contact conductivity arises from direct interactions between PPy macromolecules, enabling electron or ion transfer. Non-contact conductivity, however, relies on the tunnelling effect between PPy macromolecules. When the distance between non-contact PPy macromolecules meets the tunnelling conditions, electrons or ions can traverse the conductive network through this quantum mechanical process[ 34 ]. The interplay of these two conductive modes forms the conductive network of the hydrogel. Figure 5 (a) illustrates the relationship between the electrical conductivity of SA/PAM/PPy hydrogel and the PPy concentration. When the PPy concentration is low (e.g., 10%), the distance between macromolecules is relatively large, and only tunneling conductivity occurs, resulting in lower conductivity. As the PPy concentration increases, the contact between PPy macromolecules becomes more frequent, enhancing contact conductivity and improving the conductive pathways, thereby leading to a rapid increase in conductivity. Specifically, increasing the PPy concentration from 10% to 70% raises the conductivity from 21.3 mS·cm − 1 to 67.7 mS·cm − 1 . However, when the PPy concentration exceeds 70% and continues to increase, the conductivity tends to stabilize. This indicates that the conductive pathways and networks within the hydrogel are well-constructed, and further increasing the PPy concentration does not significantly enhance conductivity. Additionally, at 100% PPy concentration, severe aggregation of PPy macromolecules disrupts the internal conductive pathways, resulting in a slight decrease in conductivity. The resistance-temperature curve of the hydrogel is shown in Fig. 5 (b). The hydrogel's resistance decreases with increasing temperature, exhibiting an obvious inflection point near 30℃. After this inflection point, the slope of the resistance temperature curve is significantly higher than before. This behavior is attributed to the combined presence of PPy conductive material and conductive ions (including Na + from SA and Fe 2+ /Fe 3+ generated during PPy polymerization). At lower temperatures (10–30℃), the movement of PPy macromolecules and ions is slower, resulting in smaller resistance changes with temperature. When the temperature rises above 30℃, the migration rate of Na + , Fe 2+ , and Fe 3+ ions accelerates, and the movement of PPy macromolecules intensifies. This leads to larger resistance changes and increased conductivity. The formation of the inflection point is primarily determined by the migration rate of the conductive ions. 3.6 Hydrogel Temperature Sensing Sensitivity The sensitivity of a temperature-sensitive hydrogel is characterized by its temperature coefficient of resistance (TCR), determined from the slope of the hydrogel's resistance change rate versus temperature curve. A larger absolute TCR value indicates better sensitivity and vice versa. Figure 6(b) presents the resistance change rate curve of SA/PAM/PPy hydrogel across the 10–50℃ temperature range. The conductive hydrogel's resistance change rate exhibits a pattern similar to the resistance-temperature variation, with an inflection point whose position varies with PPy content. The TCR is calculated from the slope of the resistance change rate curve in the 10–50℃ range. The inflection points for different conductive hydrogels occur at 28, 26, 26, 32, and 26℃, respectively, possibly influenced by PPy macromolecular and conductive ion distribution.To better match the application requirements of the temperature-sensitive hydrogel, the temperature interval is split based on the inflection point on the resistivity change rate curve. Figure 6(c) and 6(d) show the resistivity change rate curves in the 10–30℃ and 30–50℃ intervals, respectively. TCR values for these intervals are calculated and presented in Table 1 .From Fig. 6(c)(d) and Table 1 , the slopes of the resistance change rate curves vary in different temperature intervals, showing interval-dependent sensitivity. The TCR ranges from − 0.16%/℃ to -1.22%/℃ in 10–30℃ and from − 0.49%/℃ to -3.70%/℃ in 30–50℃, indicating higher sensitivity in the latter interval, making these hydrogels suitable for human body temperature monitoring. Additionally, the slope of the hydrogel's resistance change rate is related to its PPy concentration. When the PPy concentration is 70%, the hydrogel exhibits TCR values of -1.22%/℃ (10–30℃) and − 3.70%/℃ (30–50℃), showing high sensitivity across both intervals. . As shown in Fig. 6(a), The responsiveness of SA/PAM/PPy hydrogel to temperature changes was evaluated by controlling the switching time of the xenon lamp. The response time for rapid temperature increase and decrease was characterized by monitoring the resistance change of the hydrogel. The xenon lamp was activated for a set duration to induce rapid temperature increases, followed by deactivation to cause rapid cooling. This cycle was repeated several times to observe the temperature changes of the photothermal material and the corresponding electrical signal variations of SA/PAM/PPy hydrogel. The results, presented in Fig. 6(e), show that the resistivity change of SA/PAM/PPy hydrogel exhibits stable cyclic variations between 25 and 40 ℃. The temperature increase response time ranged from 0.1185 to 3.4297 s, while the temperature decrease response time ranged from 0.1957 to 1.9335 s. These short response times indicate excellent temperature responsiveness. Notably, SA/PAM/PPy(70) demonstrated the shortest response times of 0.1185 s for heating and 0.1957 s for cooling, as shown in Fig. 6(f) and Fig. S4. These results confirm that SA/PAM/PPy hydrogel possesses high sensitivity, responsiveness, and cyclic stability, making it suitable for accurate and continuous monitoring of human body temperature Table 1 Temperature coefficients of resistance for SA/PAM hydrogels across various temperature ranges. Sample 10℃−30℃ 30℃−50℃ TCR(%/℃) R 2 TCR(%/℃) R 2 SA/PAM -0.16 0.98 -0.49 0.98 SA/PAM/PPy(10) -0.49 0.94 -2.18 0.99 SA/PAM/PPy(40) -0.68 0.95 -2.70 0.98 SA/PAM/PPy(70) -1.22 0.96 -3.70 0.98 SA/PAM/PPy(100) -0.63 0.98 -2.21 0.99 3.7 Application of Temperature-Sensitive Hydrogels in Human Motion Monitoring As shown in Fig. 7 (a), The SA/PAM/PPy(70) hydrogel sensor was integrated into the armpit region of a human body via conductive copper wires, and its resistance response characteristics were investigated during both stationary and motion states (running speeds: 4–10 km/h). As shown in Fig. 7 (b), the sensor's resistance fluctuates in both states. The larger frequency and amplitude of resistance oscillations during motion are related to the dynamic equilibrium of body temperature, reflecting the hydrogel's good responsiveness to temperature changes. From Fig. 7 (c), the stationary state resistance (111.88 Ω) is higher than that in the motion state. In the motion state, the resistance decreases with increasing running speed, corresponding to resistances of 89.07 Ω, 79.19 Ω, and 64.04 Ω at speeds of 4, 8, and 10 km/h, respectively. This trend is attributed to the different amounts of body heat released during various exercise intensities, leading to different body temperatures, corresponding to Fig. 5 (b), specifically 38℃, 39℃, and 39.5℃. These results indicate that the conductive hydrogel can effectively monitor body temperature changes across different exercise states, offering a promising strategy for developing wearable health monitoring systems. 4. Conclusion SA/PAM hydrogels with good mechanical properties were synthetized from SA, AM, and CS, and electrically conductive hydrogels were formed by in-situ polymerisation of PPy through immersion in Py and FeCl 3 solutions. The conductivity of the hydrogel was found to be related to the PPy content, reaching up to 67.7 mS·cm − 1 . The hydrogel exhibited different temperature-sensitive properties in different temperature intervals. Notably, the SA/PAM/PPy (70) hydrogel demonstrated significantly higher sensitivity to temperature changes within 30–50℃ ( TCR = -3.70%/℃) compared to 10–30℃ ( TCR = -1.22%/℃), showing good coupling with human body temperature. It also showed excellent responsiveness (temperature rise response time of 0.1185 s, temperature drop response time of 0.1957 s) and cycling stability (stable electrical signal output during multiple cycles from 25 to 40℃). When applied to running exercises, it could monitor body temperature changes under different speed conditions, achieving accurate, real-time, and continuous monitoring. In summary, the SA/PAM/PPy hydrogel shows great application potential in the field of smart wearables. Declarations Acknowledgements We thank the platform provided by Collaborative Innovation Center of Advanced Textile Equipment. Author contributions Qiaofeng Wei: conceptualization, investigation, writing-original draft. Liang Li: conceptualization, methodology, validation. Xiaowen Cheng: investigation, validation. Yuan Zeng: investigation. Yongqiang Wang: Data Curation, Guangguo Tian: formal analysis. Shuping Liu and Xilin Liao: supervision, Validation. Shujing Li: funding acquisition, resources. Rangtong Liu: conceptualization, writing-review & editing. Funding This work was supported by Key Scientific Research Projects of Higher Education Institutions in Henan Province (grant numbers 25A540001,2.25); Postgraduate Education Reform and Quality Improvement Project of Henan Province (grant numbers YJS2022JC20, 2022); National Key R&D Program of China (grant numbers 2017YFB0309100, 2017); and Collaborative Innovation Center of Advanced Textile Equipment. Data Availability Data will be made available on request from the authors. 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Nanomaterials Nanatechnol. 11 , 18479804211011384 (2021). http://doi.org/10.1177/18479804211011384 Additional Declarations No competing interests reported. Supplementary Files SupportingInformation.docx Supplementary information Supporting Information to this article can be found in the submitted materials. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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13:10:13","extension":"png","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1249474,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/d29955327dab51dfe66b403c.png"},{"id":93686718,"identity":"65c9cc12-2c45-48ed-a484-80e81eba2f8e","added_by":"auto","created_at":"2025-10-16 13:18:14","extension":"xml","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":119887,"visible":true,"origin":"","legend":"","description":"","filename":"22947e4a37c64844ba3a7183d870fd241structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/83e3605a28befe1b9b343f8e.xml"},{"id":93686368,"identity":"6847ab6c-3938-40a2-b8fc-313c96830b92","added_by":"auto","created_at":"2025-10-16 13:10:14","extension":"html","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":129719,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/216e2595703c0c5db8591fe9.html"},{"id":93686365,"identity":"7fb5f99b-dc66-42c3-8f57-49bc4d7ab3ce","added_by":"auto","created_at":"2025-10-16 13:10:13","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":47857940,"visible":true,"origin":"","legend":"\u003cp\u003e(a~d) SEM images of SA/PAM/PPy hydrogel. (e~h) EDS analysis of Fe element distribution in SA/PAM/PPy hydrogel.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/e42521fff637e0b0379abda7.png"},{"id":93686716,"identity":"66f53c04-d0d1-498a-aad5-89c24a459a90","added_by":"auto","created_at":"2025-10-16 13:18:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":6602860,"visible":true,"origin":"","legend":"\u003cp\u003e(a) FTIR spectra of SA/PAM/PPy hydrogel. (b) XRD patterns of SA/PAM versus SA/PAM/PPy (100).\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/7eff9a0be28081945ec25245.png"},{"id":93686717,"identity":"7ac22f73-991f-40ac-84b7-42993d79ac25","added_by":"auto","created_at":"2025-10-16 13:18:13","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":9735664,"visible":true,"origin":"","legend":"\u003cp\u003eThermal analysis of SA/PAM/PPy hydrogel. (a) TG curve; (b) DTG curve.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/d25377498a157ede38b4d29f.png"},{"id":93686359,"identity":"4785713c-12da-4f91-acae-cce285e2eb7d","added_by":"auto","created_at":"2025-10-16 13:10:13","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":20610666,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical properties and adhesion of SA/PAM/PPy hydrogels. (a) Stress-strain curve. (b) Bending stiffness. (c) Elastic recovery rate curves. (d) Cyclic tensile curves of SA/PAM/PPy (70) hydrogels. (e,f) Adhesion comparison of SA/PAM/PPy hydrogels on different substrates.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/e45e88eac971d1ef2a6756bf.png"},{"id":93686357,"identity":"8d14bf1d-afa6-434f-9385-a2d6779000b1","added_by":"auto","created_at":"2025-10-16 13:10:13","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":3738639,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Conductivity variation of SA/PAM/PPy hydrogel. (b) Resistance variation of SA/PAM/PPy (70) with temperature.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/bc0c6ffb1f05465faa5830f2.png"},{"id":93686719,"identity":"c4564680-11ef-4b7a-ae59-0c98eb2dc1ff","added_by":"auto","created_at":"2025-10-16 13:18:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":27540667,"visible":true,"origin":"","legend":"\u003cp\u003eSA/PAM/PPy hydrogel sensor characterization. (a) Temperature sensitivity and responsiveness test. (b~d) Resistance change rate curves in different temperature intervals. (e) Resistance change rate curves during cyclic temperature changes of 25-40℃. (f) Responsiveness of SA/PAM/PPy (70).\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/c25db81ca5b3d15fc3b3f3ce.png"},{"id":93686377,"identity":"32c9e7a7-372a-4816-ad0b-5676f3dedc11","added_by":"auto","created_at":"2025-10-16 13:10:15","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":13373295,"visible":true,"origin":"","legend":"\u003cp\u003eMotion monitoring using SA/PAM/PPy hydrogel sensor: (a) Human motion monitoring experiment; (b) Resistance changes at different motion speeds; (c) Average resistance during rest and at different motion speeds.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/b25c64c943ec8234addfffc1.png"},{"id":94598019,"identity":"e3e25baf-2601-4324-a760-104aea7ffff3","added_by":"auto","created_at":"2025-10-28 18:50:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":91921508,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/5af40807-48f4-40ee-9c3e-0f117455a0ce.pdf"},{"id":93686353,"identity":"f7b53fc7-314b-4d1a-a59a-44c4c5935eeb","added_by":"auto","created_at":"2025-10-16 13:10:13","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1264826,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSupplementary information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupporting Information to this article can be found in the submitted materials.\u003c/p\u003e","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7742823/v1/058944f4287722e8b2bd3d33.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"In-situ Preparation of Excellent Temperature Response Hydrogels with SA/PAM/PPy System and its Application in Motion Monitoring","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHuman body temperature serves as a crucial indicator of human health, reflecting the body's internal physiological processes, chemical dynamics, and emotional state[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Traditional thermometers fail to meet the specific requirements of temperature monitoring devices for intelligent wearable applications, especially in terms of softness, elasticity, adhesion, and structural stability during physical activities. Consequently, the development of flexible and intelligent temperature sensors has become a critical topic of research.\u003c/p\u003e\u003cp\u003eHydrogels are three-dimensional crosslinked network polymers. Their high water retention[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], flexibility[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], biocompatibility[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], and tunability[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] make them suitable for multifunctional sensors[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], medical dressings[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and information storage[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Moreover, incorporating conductive materials during hydrogel synthesis imparts electrical conductivity. This enables conductive hydrogels to convert temperature[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], pressure[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], and biological signals[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] into electrical signals, making them the preferred material for temperature sensors.\u003c/p\u003e\u003cp\u003eThere exist various temperature sensing mechanisms, including conductive temperature variation, thermal expansion and contraction, and phase change principles. Hydrogels, enriched with functional substances that alter resistance[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], color[\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], phase, or swelling[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] in response to temperature changes, can enable continuous, real-time, and precise temperature sensing. Hydrogel smart sensors have been widely applied in electronic skin[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], human-computer interaction[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], and soft robotics[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Compared with rigid sensors, hydrogel sensors offer advantages such as adaptability to complex environments[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], skin conformability[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], and high accuracy[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], showing significant potential for practical applications. For instance, Shi et al.[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] developed a hydrogel temperature sensor material with high thermal sensitivity (exhibiting volume change within seconds of temperature variation) by forming a phytanic acid crosslinked hydrogel within a poly(N-isopropylacrylamide) matrix. Additionally, Ge et al.[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] prepared polyaniline (PAA-PANI) hydrogels, which demonstrated good temperature sensitivity (with a resistance temperature coefficient of -1.6%/℃) and high temperature resolution (2.7 ℃).\u003c/p\u003e\u003cp\u003eTemperature sensors are subjected to mechanical stress during operation, requiring good tensile, elastic, and toughness properties. Therefore, their mechanical performance and durability are crucial. Zeng et al.[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] made a dual-network hydrogel using sodium alginate (SA) and acrylamide (AM) as raw materials and adding different amounts of chitosan (CS) to boost the hydrogel's toughness, revealing its strength/elongation at break up to 0.249 MPa /1635.65% with excellent recovery ability under 200% constant-elongation cyclic stretching. Yang et al.[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]added CS when preparing hydrogels, then the chitosan-based composite hydrogels post-crosslinked with a polyvalent anion solution, forming a rigid CS ionic network, greatly improving the hydrogels' elastic modulus, tensile strength, and fracture energy.\u003c/p\u003e\u003cp\u003eSensitivity, a key indicator for temperature sensors, can be optimized by adjusting the type or content of conductive substances in hydrogels. Zhang et al.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] added LiCl and glycerol to hydrogel to broaden its temperature sensing range. However, the sensitivity kept low, with resistance temperature coefficients of -0.87%/℃ (20\u0026ndash;50℃) and \u0026minus;\u0026thinsp;0.19%/℃(50\u0026ndash;80℃). Similarly, Liu et al.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] used an ionic liquid (1-ethyl-3-methylimidazolium chloride) and water binary solvent system to prepare hydrogels, presenting resistance temperature coefficients of -1.845%/℃ (10\u0026ndash;50℃) and \u0026minus;\u0026thinsp;0.7134%/℃ (50\u0026ndash;80℃), indicating a wide sensing range but still low sensitivity.Another important evaluation index is the sensitive temperature coupling interval and responsiveness. The heat transfer process in materials inevitably causes a time lag in temperature sensing. Reducing this lag or enhancing responsiveness, especially in narrower temperature intervals, is a research priority. At present, the hydrogel temperature sensor has a wide sensing range. However, few of them couples to the human body temperature range, cannot fully meet the application requirements. Therefore, developing hydrogel temperature sensors with high sensitivity, good responsiveness, and specific coupling to human body temperature changes is highly necessary.\u003c/p\u003e\u003cp\u003eHuman body essentially functions as a biological thermostat, with its temperature typically fluctuating between 30℃ and 50℃ due to varying physiological conditions. Therefore, the hydrogel sensor developed here is designed to exhibit adequate sensitivity and responsiveness within this specific temperature interval. In this work, natural polysaccharide sodium alginate (SA) and acrylamide (AM) are employed as monomers for hydrogel synthesis. The hydrogels are immersed in pyrrole (Py) monomer solutions of varying concentrations to undergo in-situ polymerization. By adjusting the concentration of polypyrrole within the hydrogel, the electrical conductivity is systematically investigated. Additionally, the temperature-sensitive characteristics of hydrogels are examined using instantaneous temperature-varying photothermal materials. This approach aims to develop a hydrogel sensor that is highly responsive and specifically coupled to human body temperature range, making it suitable for human body temperature monitoring.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Experimental Materials\u003c/h2\u003e\u003cp\u003eAcrylamide (AM, AR) and N,N-methylenebisacrylamide (MBAA, AR) were obtained from Tianjin Komeo Chemical Reagent Co. Ltd. Sodium alginate (SA, CP) was acquired from Sinopharm Chemical Reagent Co. Ltd. Ammonium persulfate (APS, AR) was purchased from Tianjin Wind Ship Chemical Reagent Science and Technology Co. Ltd. Chitosan (CS, AR), N,N,N',N'-Tetramethylethylenediamine (TEMED, AR), pyrrole (Py, AR), and anhydrous ferric chloride (FeCl\u003csub\u003e3\u003c/sub\u003e, AR) were supplied by Shanghai McLean Biochemical Science and Technology Co. Ltd. The instantaneous temperature-varying photothermal material[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] (polydimethylsiloxane doped graphene coated on polyethylene film, with a temperature range of 10\u0026ndash;80℃ and a heating rate of 0.35\u0026ndash;0.59℃/s) was self-made.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Preparation of Temperature-Sensitive Hydrogels\u003c/h2\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1 Preparation of SA/PAM Hydrogel\u003c/h2\u003e\u003cp\u003eFirstly, accurately weigh 7.2 g of acrylamide (AM) and 0.6 g of sodium alginate (SA), transfer them to a reagent bottle, and add 52.2 g of deionised water. Stir the mixture using a digital temperature- controlled magnetic stirrer (MS-H-Pro+, Dragon LAB, Germany) until they are completely dissolved. Then, sequentially add 0.027 g of ammonium persulfate (APS), 0.009 g of N,N-methylenebisacrylamide (MBAA), and 0.39 g of chitosan (CS) to the solution, and stir thoroughly until fully dissolved. Next, dropwise add 0.015 g of N,N,N',N'-Tetramethylethylenediamine (TEMED) to the solution and stir well. After that, transfer the resulting solution to a PTFE template and place it into a vacuum drying oven (DZF-6090, Shanghai Jinghong Experimental Equipment Co., Ltd.) at 60℃ for 40 minutes to allow the solution to gel. Finally, take out the template and expose it to a self-made airtight ultraviolet lamp for 120 minutes to complete the preparation of SA/PAM hydrogel.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2 Preparation of SA/PAM/PPy Hydrogels\u003c/h2\u003e\u003cp\u003eFirstly, prepare Py monomer solutions at concentrations of 10%, 40%, 70%, and 100%. Immerse the SA/PAM hydrogels in each concentration of Py monomer solution for 24 hours at a low temperature of 2\u0026ndash;5℃. Then, remove the hydrogels and place them in a sealed bag, storing them at 5 ℃ or below for approximately 3 hours to allow Py monomer to penetrate into the hydrogels. Next, weigh and dissolve 0.6475 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e FeCl\u003csub\u003e3\u003c/sub\u003e in deionised water, stirring until completely dissolved. Immerse the hydrogels in FeCl\u003csub\u003e3\u003c/sub\u003e solution at 5℃ for 12 hours to initiate the polymerization of Py monomers, in-situ polymerization forming polypyrrole (PPy). This process yields the SA/PAM/PPy hydrogels, specifically designated as SA/PAM/PPy (10), SA/PAM/PPy (40), SA/PAM/PPy (70), and SA/PAM/PPy (100).\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Characterisation\u003c/h2\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e2.3.1 SEM and EDS Analysis\u003c/h2\u003e\u003cp\u003eThe prepared hydrogels were freeze-dried using a freeze-dryer (ALPHA 1\u0026ndash;4 LD plus, Christ, Germany). Subsequently, selected dried samples were fractured in liquid nitrogen. The surface morphology and elemental distribution were then characterized using field emission scanning electron microscopy (TM3000, Hitachi Ltd., Japan). Prior to imaging, samples were sputter-coated with gold for 100 seconds. Observations were conducted at an accelerating voltage of 20 kV.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e2.3.2 Moisture Content (Mc) Test\u003c/h2\u003e\u003cp\u003eThe hydrogel samples were first subject to freeze-drying. The moisture content was determined using the formula: \u003cem\u003eMc\u003c/em\u003e = (\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e-\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sub\u003e)/\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e, where \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e is the mass of the sample before freeze-drying and \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sub\u003e is the mass after freeze-drying.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e2.3.3 FTIR and X-ray Diffraction (XRD) Analysis\u003c/h2\u003e\u003cp\u003eFor FTIR analysis, 1\u0026ndash;2 mg of the freeze-dried sample was mixed with a small amount of potassium bromide, ground into a fine powder, and then pressed into a uniformly light-transmitting sheet. The sample's characteristic peaks were recorded using a Fourier-transform infrared spectrometer (Tensor37, Bruker, Germany).\u003c/p\u003e\u003cp\u003eFor XRD analysis, freeze-dried samples (2\u0026times;2 cm) were used to examine the composition and crystal structure of the composite hydrogels. A X-ray diffractometer (Rigaku Ultima IV, Rigaku Co., Ltd., Japan) was employed with settings of 40 kV voltage, 40 mA current, and a 2θ scanning range of 10\u0026deg;-90\u0026deg;, at a rate of 2\u0026deg;/min.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e2.3.4 Thermal Stability Analysis\u003c/h2\u003e\u003cp\u003eFor thermal stability assessment, approximately 5\u0026ndash;6 mg of the freeze-dried hydrogel samples were accurately weighed and placed in a crucible. The samples were then analyzed using a thermogravimetric analyzer (STA-449-F5 Jupiter, NETZSCH GmbH, Germany). The analysis was performed in a nitrogen atmosphere, with a flow rate of 20 mL\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The temperature was increased at a constant rate of 10 ℃/min, and the mass loss of the samples was recorded over a temperature range of 35\u0026ndash;700 ℃.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e2.3.5 Mechanical Properties and Adhesion Assessment\u003c/h2\u003e\u003cp\u003eA universal testing machine (AI-7000S1, High Speed Rail Technology Co., Ltd.) was employed to evaluate the tensile fracture, cyclic tensile behavior, and elastic recovery of hydrogels. Stress-strain curves were obtained by conducting tensile tests on samples with dimensions of 80 mm in length, 10 mm in width, and 5 mm in thickness. The tests were performed at a speed of 100 mm\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a fixture distance of 40 mm.\u003c/p\u003e\u003cp\u003eFor cyclic tensile tests, constant elongation parameters were set at 25%, 50%, and 100% to perform tensile cycling tests. Elastic recovery was calculated based on the recovery of deformation from one cyclic tensile test at a constant elongation of 50%.\u003c/p\u003e\u003cp\u003eThe bending stiffness of hydrogel was determined using a self-constructed 30\u0026deg; trapezoidal ramp. A steel ruler was launched at a uniform speed, driving the sample to launch synchronously until the sample contacted the ramp due to its self-weight. The bending stiffness was calculated using the formula \u003cem\u003eB\u003c/em\u003e\u0026thinsp;=\u0026thinsp;9.8\u003cem\u003ew\u003c/em\u003e*(0.594*\u003cem\u003el\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e)\u003csup\u003e3\u003c/sup\u003e*10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e, where \u003cem\u003ew\u003c/em\u003e is the sample's weight per square meter (g\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) and \u003cem\u003el\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e is the length of the steel ruler extending out in centimeters.\u003c/p\u003e\u003cp\u003eThe adhesion of hydrogel to different substrates, including glass, PE plastic films and copper sheet, was assessed using a lap-shear tensile test conducted with the tensile tester. The adhesion strength was calculated by dividing the maximum load by the contact area.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\u003ch2\u003e2.3.6 Electrical Conductivity and Temperature Coefficient of Resistance\u003c/h2\u003e\u003cp\u003eThe sample's resistance was measured by attaching thin copper wires to both ends of a 1 cm\u0026times;4 cm sample, which was connected to an instant temperature-varying photothermal material and linked to a 2400 digital source meter (Girish Technology Co., Ltd., USA) in a two-wire configuration, with a clamping voltage of 80 V and an output current of 0.1 mA.\u003c/p\u003e\u003cp\u003eThe temperature of the photothermal material was raised using a xenon lamp (PLS-SXE300+), and the temperature was monitored via an infrared camera (Ti32, Fluke, USA). The distance between the xenon lamp and the photothermal material was 66 cm, with a current of 13 A and a light power density of 1 kW\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, maintaining the temperature between 10℃ and 50℃.\u003c/p\u003e\u003cp\u003eThe electrical conductivity (\u003cem\u003eσ\u003c/em\u003e) was calculated using \u003cem\u003eσ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eρ\u003c/em\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e, where \u003cem\u003eρ\u003c/em\u003e is the resistivity in Ω\u0026middot;m, determined by \u003cem\u003eρ\u003c/em\u003e = (\u003cem\u003eR\u003c/em\u003e*\u003cem\u003eS\u003c/em\u003e)/\u003cem\u003eL\u003c/em\u003e (\u003cem\u003eS\u003c/em\u003e is the cross-sectional area in m\u003csup\u003e2\u003c/sup\u003e, and \u003cem\u003eL\u003c/em\u003e is the conductor length in m). The temperature coefficient of resistance (\u003cem\u003eTCR\u003c/em\u003e, %/℃) was calculated as \u003cem\u003eTCR\u003c/em\u003e=[(\u003cem\u003eR\u003c/em\u003e-\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e)/\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e*100%]/\u003cem\u003eΔT\u003c/em\u003e, where \u003cem\u003eR\u003c/em\u003e is the resistance at the measured temperature, \u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e is the initial resistance, and \u003cem\u003eΔT\u003c/em\u003e is the temperature change.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Results and Discussions","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Morphological Characteristics and Water Content Analysis\u003c/h2\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a\u0026thinsp;~\u0026thinsp;d) and Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e(a) presents the SEM images of SA/PAM/PPy hydrogels after freeze- drying. Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e reveals the microscopic morphology of SA/PAM, showing a porous structure surrounded by particles. These pores facilitate to penetrate PPy macromolecules, as well as Fe\u003csup\u003e3+\u003c/sup\u003e and Fe\u003csup\u003e2+\u003c/sup\u003e, into hydrogels. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a)~(d) display the SEM images of SA/PAM/PPy hydrogels. A porous and interpenetrating network structure is obviously evident on the hydrogel surfaces. This structure arises from the crosslinking of PAM with SA and the interpenetration of amide bonds crosslinked by CS and SA. Small spherical particles aggregated on the hydrogel surface indicate that PPy macromolecules are distributed both on the surface and within the network of hydrogel. As the PPy concentration increases from 10% to 100%, the pores on hydrogel surface gradually decrease in size. At low PPy concentrations, fewer PPy enter the hydrogel, resulting in incomplete conductive pathways in SA/PAM/PPy (10) while SA/PAM/PPy (100) showing significant PPy aggregation. However, at moderate PPy concentrations, no particle aggregation, and the conductive pathways within hydrogel are more complete, which is beneficial for the hydrogel's conductivity and temperature-sensitive properties.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(e\u0026thinsp;~\u0026thinsp;h) presents the distribution of Fe element in SA/PAM/PPy hydrogel, which indirectly indicates the distribution of PPy within hydrogel. As the PPy concentration increases, the Fe content also increases. In SA/PAM/PPy (10), some regions show no Fe distribution due to low Fe\u003csup\u003e2+\u003c/sup\u003e levels. In contrast, SA/PAM/PPy (40) and SA/PAM/PPy (70) exhibit more uniform Fe distributions. However, in SA/PAM/PPy (100), certain areas appear darker, likely due to PPy aggregation. This aligns with the SEM images in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a\u0026thinsp;~\u0026thinsp;d). The temperature-sensitive properties of hydrogels do not simply enhance with increasing PPy concentration but may vary across different temperature ranges.\u003c/p\u003e\u003cp\u003eHydrogels possess high water retention properties, and their water content significantly influences the toughness, mechanical properties, electrical conductivity, and temperature-sensitive characteristics of hydrogel. Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e(b) presents the water content of SA/PAM/PPy hydrogel. Immersion of hydrogel in a Py solution leads to the incorporation of both Py molecules and water molecules. At low Py concentrations, this incorporation increases the hydrogel's conductivity and water content. However, when immersed in higher-concentration Py solutions, the number of Py molecules entering the hydrogel increases, while the number of water molecules decreases. This alters the ratio of PPy to water molecules within hydrogel. As the PPy content rises, the water content tends to decrease. This variation in water content not only impacts the electrical conductivity but also results in SA/PAM/PPy hydrogel exhibiting distinct temperature-sensitive properties across different temperature intervals.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Chemical Structure Analysis\u003c/h2\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) depicts the FTIR spectra of SA/PAM/PPy hydrogel. The peaks at 3452 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1655 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to N-H stretching and C\u0026thinsp;=\u0026thinsp;O stretching vibrations of amide bonds, confirming the successful crosslinking of PAM with SA and CS with SA to form amide linkages (-CO-NH-), which constitute the network structure of SA/PAM hydrogel. As the incorporation of Py, the characteristic peaks near 3500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e associated with intermolecular hydrogen bonding become more pronounced, indicating the formation of physical crosslinks between PPy and SA, as well as between PPy and CS through hydrogen bonds, thereby enhancing the mechanical properties of the SA/PAM/PPy hydrogels. As the Py concentration increases, the peak near 1650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to the C\u0026thinsp;=\u0026thinsp;C vibration of the pyrrole ring, becomes more evident. The peak at 580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, related to the out-of-plane bending vibration of C-H present in SA, PAM, and PPy, also intensifies with increasing Py concentration and the rising C-H content in hydrogel. The introduction of PPy does not alter the functional groups of SA/PAM hydrogel, preserving its network structure. This structure provides an excellent pathway for the transport of macromolecules and ions within hydrogel, thereby laying the foundation for improving the electrical conductivity and temperature-sensitive properties of hydrogel.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) and Fig. S2 presents the XRD spectra of SA/PAM/PPy hydrogel. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) shows that SA/PAM spectrum features a pronounced peak near 25\u0026deg;, attributed to the formation of amide bonds between SA and PAM, as well as between SA and CS. This crosslinking enhances the regularity of the hydrogel's internal network, leading to a high degree of crystallinity. In Fig. S2, after PPy incorporation, a broadened characteristic peak appears between 20\u0026deg; and 30\u0026deg;, which widens with increasing PPy concentration. This is due to PPy's irregular chemical structure, which is less prone to crystallization. At higher concentrations, PPy macromolecules cluster within hydrogel, altering the conductive pathways. Consequently, the SA/PAM/PPy hydrogel exhibits varying temperature-sensitive properties across different temperature ranges.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) and Fig. S2 presents the XRD spectra of SA/PAM/PPy hydrogel. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) shows that SA/PAM spectrum features a pronounced peak near 25\u0026deg;, attributed to the formation of amide bonds between SA and PAM, as well as between SA and CS. This crosslinking enhances the regularity of the hydrogel's internal network, leading to a high degree of crystallinity. In Fig. S2, after PPy incorporation, a broadened characteristic peak appears between 20\u0026deg; and 30\u0026deg;, which widens with increasing PPy concentration. This is due to PPy's irregular chemical structure, which is less prone to crystallization. At higher concentrations, PPy macromolecules cluster within hydrogel, altering the conductive pathways. Consequently, the SA/PAM/PPy hydrogel exhibits varying temperature-sensitive properties across different temperature ranges.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Thermal Stability Analysis\u003c/h2\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the TG and DTG curves of SA/PAM/PPy hydrogel, illustrating its thermal degradation in four distinct stages. Initially, between 35℃ and 147℃, the mass loss is predominantly due to water evaporation. Subsequently, from 147℃ to 230℃, the mass loss is attributed to the decomposition of side chains within the hydrogel's macromolecules, releasing small molecules such as NH\u003csub\u003e3\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the temperature range of 230℃ to 430℃, the degradation is primarily characterized by the breaking of the macromolecular backbone. This involves the breakage of SA and PPy macromolecular segments, generating small molecules like CO\u003csub\u003e2\u003c/sub\u003e, Py, hydrogen cyanide (HCN), ammonia (NH\u003csub\u003e3\u003c/sub\u003e), CO, and others, which contribute to the weight loss. Finally, between 430℃ and 700℃, the process is dominated by the carbonization and oxidation of residual materials, during which the mass changes are relatively minimal.\u003c/p\u003e\u003cp\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e presents the thermal decomposition data of SA/PAM/PPy hydrogel. After incorporating PPy into SA/PAM hydrogel, the initial decomposition temperature, the temperature of the maximum weight loss rate, and the residual carbon rate at 700℃ all increase. This is because PPy exhibit high thermal stability, maintaining structural integrity at elevated temperatures and protecting the macromolecular main chain from degradation, thereby delaying its fracture.Specifically, SA/PAM/PPy (70) shows the highest initial decomposition temperature. As observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d), when the PPy concentration is 70%, PPy are more uniformly distributed within hydrogel, enhancing its thermal stability. Although SA/PAM/PPy (100) contains the highest amount of PPy macromolecules and thus has the highest residual carbon rate, the thermal stability of hydrogel is optimized at a PPy concentration of 70%. Overall, the SA/PAM/PPy hydrogel demonstrates improved thermal stability.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Mechanical Properties and Adhesion of Hydrogels\u003c/h2\u003e\u003cp\u003eThe mechanical properties and adhesion of hydrogels are crucial for temperature-sensitive sensor applications. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a) presents the stress-strain curves of SA/PAM/PPy hydrogels. The addition of PPy to SA/PAM hydrogel reduces its mechanical properties, primarily due to the rigidity of PPy. As the PPy concentration increases, the mechanical properties of the conductive hydrogel first increase and then decrease. SA/PAM/PPy (70) exhibits a maximum tensile stress of 0.248 MPa, which is equivalent to SA/PAM. At this concentration, the intertwined macromolecular network in the hydrogel is enhanced, and the mechanical properties and conductivity are improved. However, SA/PAM/PPy (100) shows decreased mechanical properties, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. When the concentration of PPy reached 70%, its distribution in the hydrogel is more uniform. At the concentration of 100% PPy, the internal pores of hydrogel shrink, and the aggregation of PPy becomes more serious, which introduces obvious defects, leading to the decline of mechanical properties.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe bending stiffness of hydrogels was assessed using the ramp method, and the results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b). As shown, the bending stiffness increases with higher PPy concentrations, which is attributed to the rigidity of PPy. SA/PAM/PPy(10) exhibits the lowest bending stiffness due to its higher water content. As PPy increase in hydrogel, the softness decreases. SA/PAM/PPy (10) contains relatively less PPy, thus maintaining better softness.\u003c/p\u003e\u003cp\u003eThe elasticity of hydrogels was evaluated by the elastic recovery rate after one stretching cycle at a constant 50% elongation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c)). The elastic recovery rate decreases with increasing PPy concentration but remains above 85% for all samples, indicating that the SA/PAM/PPy hydrogels possess good elasticity.To evaluate the durability of SA/PAM/PPy hydrogel, it underwent 30 cycles of tensile testing. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d) and Fig. S3(a\u0026thinsp;~\u0026thinsp;c) shows that after 30 cycles, the overlap of the hysteresis loops is high under different constant tensile parameters. This demonstrates that SA/PAM/PPy hydrogel has excellent durability, meeting the requirements for use as a temperature sensor.\u003c/p\u003e\u003cp\u003eIn addition to elasticity and flexibility, adhesion is also crucial for the practical application of hydrogels as human body temperature sensors. The adhesion was characterised by the shear stress of SA/PAM/PPy hydrogel on different substrates across multiple cycles, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(e\u0026thinsp;~\u0026thinsp;f) and Fig. S3(d). SA/PAM hydrogel exhibits the highest shear stress, attributed to hydrogen bonding between chitosan and the substrate surface. However, the shear stress of the conductive SA/PAM/PPy hydrogel decreases, likely due to PPy aggregation on the hydrogel surface, which increases surface roughness, reduces contact area with the substrate, and thus lowers adhesion.After 10 adhesion cycles, the shear stress of the PPy-containing hydrogel decreases only slightly, whereas a significant reduction is observed in the hydrogel without PPy. This indicates that SA/PAM/PPy hydrogel maintains better adhesion and durability, making it more suitable for practical applications as a temperature sensor.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Electrical Conductivity of the Hydrogel\u003c/h2\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) illustrates the relationship between the electrical conductivity of SA/PAM/PPy hydrogel and the concentration of PPy. The incorporation of PPy into the hydrogel significantly enhances its conductivity. PPy particles penetrate the hydrogel's three-dimensional porous structure, forming electron or ion transport channels due to their high intrinsic conductivity. The dispersion of PPy within the hydrogel and the interactions between PPy macromolecules, whether in series, parallel, or aggregated configurations, will create a finite-scale conductive network. When the PPy concentration exceeds a critical threshold, an infinite-scale network may form, triggering a percolation effect that brings the composite's conductivity close to that of pure PPy[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Additionally, during the polymerization of Py, Fe\u003csup\u003e3+\u003c/sup\u003e ions enter the hydrogel, with some participating in the reaction and being reduced to Fe\u003csup\u003e2+\u003c/sup\u003e, while unreacted Fe\u003csup\u003e3+\u003c/sup\u003e remains free within the hydrogel. The presence of both Fe\u003csup\u003e3+\u003c/sup\u003e and Fe\u003csup\u003e2+\u003c/sup\u003e further elevates the hydrogel's conductivity.\u003c/p\u003e\u003cp\u003eWithin the conductive hydrogel, conductive mode can be classified into contact or non-contact. Contact conductivity arises from direct interactions between PPy macromolecules, enabling electron or ion transfer. Non-contact conductivity, however, relies on the tunnelling effect between PPy macromolecules. When the distance between non-contact PPy macromolecules meets the tunnelling conditions, electrons or ions can traverse the conductive network through this quantum mechanical process[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The interplay of these two conductive modes forms the conductive network of the hydrogel.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) illustrates the relationship between the electrical conductivity of SA/PAM/PPy hydrogel and the PPy concentration. When the PPy concentration is low (e.g., 10%), the distance between macromolecules is relatively large, and only tunneling conductivity occurs, resulting in lower conductivity. As the PPy concentration increases, the contact between PPy macromolecules becomes more frequent, enhancing contact conductivity and improving the conductive pathways, thereby leading to a rapid increase in conductivity. Specifically, increasing the PPy concentration from 10% to 70% raises the conductivity from 21.3 mS\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 67.7 mS\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. However, when the PPy concentration exceeds 70% and continues to increase, the conductivity tends to stabilize. This indicates that the conductive pathways and networks within the hydrogel are well-constructed, and further increasing the PPy concentration does not significantly enhance conductivity. Additionally, at 100% PPy concentration, severe aggregation of PPy macromolecules disrupts the internal conductive pathways, resulting in a slight decrease in conductivity.\u003c/p\u003e\u003cp\u003eThe resistance-temperature curve of the hydrogel is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b). The hydrogel's resistance decreases with increasing temperature, exhibiting an obvious inflection point near 30℃. After this inflection point, the slope of the resistance temperature curve is significantly higher than before. This behavior is attributed to the combined presence of PPy conductive material and conductive ions (including Na\u003csup\u003e+\u003c/sup\u003e from SA and Fe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e generated during PPy polymerization). At lower temperatures (10\u0026ndash;30℃), the movement of PPy macromolecules and ions is slower, resulting in smaller resistance changes with temperature. When the temperature rises above 30℃, the migration rate of Na\u003csup\u003e+\u003c/sup\u003e, Fe\u003csup\u003e2+\u003c/sup\u003e, and Fe\u003csup\u003e3+\u003c/sup\u003e ions accelerates, and the movement of PPy macromolecules intensifies. This leads to larger resistance changes and increased conductivity. The formation of the inflection point is primarily determined by the migration rate of the conductive ions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003e3.6 Hydrogel Temperature Sensing Sensitivity\u003c/h2\u003e\u003cp\u003eThe sensitivity of a temperature-sensitive hydrogel is characterized by its temperature coefficient of resistance (TCR), determined from the slope of the hydrogel's resistance change rate versus temperature curve. A larger absolute TCR value indicates better sensitivity and vice versa.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;6(b) presents the resistance change rate curve of SA/PAM/PPy hydrogel across the 10\u0026ndash;50℃ temperature range. The conductive hydrogel's resistance change rate exhibits a pattern similar to the resistance-temperature variation, with an inflection point whose position varies with PPy content. The TCR is calculated from the slope of the resistance change rate curve in the 10\u0026ndash;50℃ range. The inflection points for different conductive hydrogels occur at 28, 26, 26, 32, and 26℃, respectively, possibly influenced by PPy macromolecular and conductive ion distribution.To better match the application requirements of the temperature-sensitive hydrogel, the temperature interval is split based on the inflection point on the resistivity change rate curve. Figure\u0026nbsp;6(c) and 6(d) show the resistivity change rate curves in the 10\u0026ndash;30℃ and 30\u0026ndash;50℃ intervals, respectively. TCR values for these intervals are calculated and presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.From Fig.\u0026nbsp;6(c)(d) and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the slopes of the resistance change rate curves vary in different temperature intervals, showing interval-dependent sensitivity. The TCR ranges from \u0026minus;\u0026thinsp;0.16%/℃ to -1.22%/℃ in 10\u0026ndash;30℃ and from \u0026minus;\u0026thinsp;0.49%/℃ to -3.70%/℃ in 30\u0026ndash;50℃, indicating higher sensitivity in the latter interval, making these hydrogels suitable for human body temperature monitoring. Additionally, the slope of the hydrogel's resistance change rate is related to its PPy concentration. When the PPy concentration is 70%, the hydrogel exhibits TCR values of -1.22%/℃ (10\u0026ndash;30℃) and \u0026minus;\u0026thinsp;3.70%/℃ (30\u0026ndash;50℃), showing high sensitivity across both intervals.\u003c/p\u003e\u003cp\u003e.\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;6(a), The responsiveness of SA/PAM/PPy hydrogel to temperature changes was evaluated by controlling the switching time of the xenon lamp. The response time for rapid temperature increase and decrease was characterized by monitoring the resistance change of the hydrogel. The xenon lamp was activated for a set duration to induce rapid temperature increases, followed by deactivation to cause rapid cooling. This cycle was repeated several times to observe the temperature changes of the photothermal material and the corresponding electrical signal variations of SA/PAM/PPy hydrogel. The results, presented in Fig.\u0026nbsp;6(e), show that the resistivity change of SA/PAM/PPy hydrogel exhibits stable cyclic variations between 25 and 40 ℃. The temperature increase response time ranged from 0.1185 to 3.4297 s, while the temperature decrease response time ranged from 0.1957 to 1.9335 s. These short response times indicate excellent temperature responsiveness. Notably, SA/PAM/PPy(70) demonstrated the shortest response times of 0.1185 s for heating and 0.1957 s for cooling, as shown in Fig.\u0026nbsp;6(f) and Fig. S4. These results confirm that SA/PAM/PPy hydrogel possesses high sensitivity, responsiveness, and cyclic stability, making it suitable for accurate and continuous monitoring of human body temperature\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eTemperature coefficients of resistance for SA/PAM hydrogels across various temperature ranges.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e10℃\u0026minus;30℃\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e30℃\u0026minus;50℃\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTCR(%/℃)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eTCR(%/℃)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSA/PAM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.98\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSA/PAM/PPy(10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-2.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSA/PAM/PPy(40)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.68\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-2.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.98\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSA/PAM/PPy(70)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-1.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-3.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.98\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSA/PAM/PPy(100)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-0.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-2.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.99\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\u003ch2\u003e3.7 Application of Temperature-Sensitive Hydrogels in Human Motion Monitoring\u003c/h2\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a), The SA/PAM/PPy(70) hydrogel sensor was integrated into the armpit region of a human body via conductive copper wires, and its resistance response characteristics were investigated during both stationary and motion states (running speeds: 4\u0026ndash;10 km/h). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b), the sensor's resistance fluctuates in both states. The larger frequency and amplitude of resistance oscillations during motion are related to the dynamic equilibrium of body temperature, reflecting the hydrogel's good responsiveness to temperature changes.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c), the stationary state resistance (111.88 Ω) is higher than that in the motion state. In the motion state, the resistance decreases with increasing running speed, corresponding to resistances of 89.07 Ω, 79.19 Ω, and 64.04 Ω at speeds of 4, 8, and 10 km/h, respectively. This trend is attributed to the different amounts of body heat released during various exercise intensities, leading to different body temperatures, corresponding to Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b), specifically 38℃, 39℃, and 39.5℃. These results indicate that the conductive hydrogel can effectively monitor body temperature changes across different exercise states, offering a promising strategy for developing wearable health monitoring systems.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eSA/PAM hydrogels with good mechanical properties were synthetized from SA, AM, and CS, and electrically conductive hydrogels were formed by in-situ polymerisation of PPy through immersion in Py and FeCl\u003csub\u003e3\u003c/sub\u003e solutions. The conductivity of the hydrogel was found to be related to the PPy content, reaching up to 67.7 mS\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The hydrogel exhibited different temperature-sensitive properties in different temperature intervals. Notably, the SA/PAM/PPy (70) hydrogel demonstrated significantly higher sensitivity to temperature changes within 30\u0026ndash;50℃ (\u003cem\u003eTCR\u003c/em\u003e= -3.70%/℃) compared to 10\u0026ndash;30℃ (\u003cem\u003eTCR\u003c/em\u003e= -1.22%/℃), showing good coupling with human body temperature. It also showed excellent responsiveness (temperature rise response time of 0.1185 s, temperature drop response time of 0.1957 s) and cycling stability (stable electrical signal output during multiple cycles from 25 to 40℃). When applied to running exercises, it could monitor body temperature changes under different speed conditions, achieving accurate, real-time, and continuous monitoring. In summary, the SA/PAM/PPy hydrogel shows great application potential in the field of smart wearables.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eWe thank the platform provided by Collaborative Innovation Center of Advanced Textile Equipment.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQiaofeng Wei: conceptualization, investigation, writing-original draft. Liang Li: conceptualization, methodology, validation. Xiaowen Cheng: investigation, validation. Yuan Zeng: investigation. Yongqiang Wang: Data Curation, Guangguo Tian: formal analysis. Shuping Liu and Xilin Liao: supervision, Validation. Shujing Li: funding acquisition, resources. Rangtong Liu: conceptualization, writing-review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Key Scientific Research Projects of Higher Education Institutions in Henan Province (grant numbers 25A540001,2.25); Postgraduate Education Reform and Quality Improvement Project of Henan Province (grant numbers YJS2022JC20, 2022); National Key R\u0026amp;D Program of China (grant numbers 2017YFB0309100, 2017); and Collaborative Innovation Center of Advanced Textile Equipment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request from the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest or competing interests:\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical statement:\u0026nbsp;\u003c/strong\u003eAll experiments involving the human body followed the ethical guidelines of the World Medical Association. The volunteer who participated in the human motion monitoring test was the co-authors of this paper (Xiaowen Cheng), and the gender of the volunteers had no effect on the research results. Human motion monitoring test are voluntary. The informed consent has been obtained for experimentation with human subiects.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eT.Q. Trung, H.S. Le, T.M.L. Dang, S. Ju, N.E. Lee, Freestanding, Fiber-Based, Wearable Temperature Sensor with Tunable Thermal Index for Healthcare Monitoring. Adv. Healthc. Mater. \u003cb\u003e7\u003c/b\u003e, 1800074 (2018). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://doi.org/10.1002/adhm.201800074\u003c/span\u003e\u003cspan address=\"10.1002/adhm.201800074\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eC. Zhu, A. Chortos, Y. Wang, R. Pfattner, T. 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Nanomaterials Nanatechnol. \u003cb\u003e11\u003c/b\u003e, 18479804211011384 (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://doi.org/10.1177/18479804211011384\u003c/span\u003e\u003cspan address=\"10.1177/18479804211011384\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Human body temperature, Temperature-sensitive property, Conductive hydrogel, Adhesion, Elasticity","lastPublishedDoi":"10.21203/rs.3.rs-7742823/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7742823/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAccurate and continuous monitoring of human body temperature is a core function of smart wearable temperature sensors. However, fabricating temperature sensors with high sensitivity and rapid response remains a challenge. Here, using the natural polysaccharide sodium alginate (SA), acrylamide (AM), and in-situ polymerization of polypyrrole (PPy), a conductive hydrogel (SA/PAM/PPy) was synthetized. It is indicated that as the pyrrole concentration increases the conductivity of hydrogel enhances from 21.3 to 67.7 mS/cm. The temperature sensitivity of hydrogels vary with temperature intervals. In 10\u0026ndash;30℃ range, the temperature coefficient of resistance (\u003cem\u003eTCR\u003c/em\u003e) is -1.22%/℃, increasing to -3.70%/℃ in 30\u0026ndash;50℃ range, aligning with human body temperatures. The hydrogels also demonstrate superior responsiveness, with the temperature rise/drop response times of 0.1185 / 0.1957 s, respectively, with excellent cycling stability, maintaining stable electrical signals during multiple cycles in 25\u0026ndash;40℃. Its application in running exercises enables effective monitoring of body temperature changes across different speeds. Overall, the developed hydrogels not only sense temperature variations but also align closely with human body temperature ranges, showing great potential in smart wearable technology.\u003c/p\u003e","manuscriptTitle":"In-situ Preparation of Excellent Temperature Response Hydrogels with SA/PAM/PPy System and its Application in Motion Monitoring","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-16 13:10:08","doi":"10.21203/rs.3.rs-7742823/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"40dba8ea-f34c-453e-bf4c-95f803d0f01e","owner":[],"postedDate":"October 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-28T18:04:41+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-16 13:10:08","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7742823","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7742823","identity":"rs-7742823","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}