A highly stretchable, self-adhesive, antimicrobial conductive hydrogel with guar gum/acrylic acid/MXene@AgNPs for multifunctional wearable sensors and electromagnetic interference shielding

Abstract

Multifunctional conductive hydrogels have attracted extensive attention in the fields of biomedicine and health monitoring. However, integrating excellent stretchability, self-adhesion, sensitive sensing, electromagnetic interference (EMI) shielding, and antibacterial properties into conductive hydrogels for wearable sensor applications remains a significant challenge. In this study, a multifunctional conductive hydrogel (GAMA) was prepared by incorporating MXene@Ag nanoparticles (AgNPs) as conductive fillers, which were uniformly dispersed within a dual-network structure of guar gum/acrylic acid. Serving as conductive agents, reinforcing fillers, and antibacterial components, MXene@AgNPs enable the GAMA hydrogel to achieve multifunctional integration and balanced performance. The GAMA hydrogel exhibits outstanding mechanical performance with a tensile strength of 97 kPa and elongation at a break of 850%, self-adhesion (21.5 kPa), and high conductivity (14.04 mS cm^-1). Additionally, we employed this hydrogel as a flexible strain sensor to monitor human motion, achieving high sensitivity (gauge factor (GF) of 6.48 at 300% strain). The in situ synthesis of AgNPs on MXene nanosheets enhances polarization and interfacial losses of electromagnetic waves, endowing the hydrogel with an EMI shielding effectiveness of 34.5 dB. Furthermore, comprehensive biocompatibility evaluations confirm its excellent antibacterial performance, hemocompatibility, and cytocompatibility. Therefore, these properties endow the multifunctional GAMA hydrogel with great potential for applications in wearable sensors for human motion monitoring and EMI shielding.

Fig. 1. Schematic illustration for the fabrication of the GAMA hydrogel.

Fig. 2. Material characterizations of GAMA hydrogels. Cross-sectional SEM images of freeze-dried (a) GA hydrogel, (b) GAM hydrogel, and (c) GAMA₂ hydrogel. (d) Elemental mapping images of GAMA₂ hydrogel. (e) XRD patterns of MXene@AgNPs, pure GA, GAM, GAMA₂ hydrogels. (f) FTIR spectra of pure GA, GAM, and GAMA₂ hydrogels. (g) XPS spectra of MXene, GA, GAM, GAMA₂ hydrogels. (h) C 1s, and (i) O 1s High-resolution XPS spectra GAMA₂ hydrogel.

Fig. 3. Mechanical properties of the hydrogels. (a) Stress–strain curves, (b) tensile strain and tensile toughness values, and (c) toughness and modulus of elasticity values of hydrogels with different conductive fillers. (d) Hysteresis curves for 10 stretching–releasing cycles at a strain of 300%. (e) Compressive stress–strain curves of hydrogels with different conductive fillers. (f) Loading and unloading cycle compression curves of GAMA₂ hydrogel after 10 cycles at a strain of 70%. Optical photos of (g) large stretching, (h) compressing and recovering.

Fig. 4. Adhesion properties of hydrogels. (a) Adhesive performance of the GAMA₂ hydrogel to various substrate surfaces at room temperature. (b) The adhesion strength of GAM hydrogel to various substrates. (c) The adhesion strength of hydrogels with different conductive fillers to different substrates. (d) Schematic of the lap shear test. (e) Adhesion mechanisms to various substrates.

Fig. 5. EMI shielding performance of hydrogels. (a) Electrical conductivity of hydrogels. (b) EMI SE_T of different hydrogels in the frequency range of 8.2–12.4 GHz. (c) The SE_R, SE_A, and SE_T of different hydrogels at 12.4 GHz. (d) R–A–T coefficients of different hydrogels. (e) Scheme showing the EMI shielding mechanism.

Fig. 6. Sensing performance of the GAMA₂ hydrogel sensor. (a) GF of the GAMA₂ hydrogel sensor at different strains. (b) Real-time response signals of the GAMA₂ hydrogel sensor toward large strains (50%, 100%, 150%, and 200%). (c) Real-time response signals of the GAMA₂ hydrogel sensor toward subtle strains (5%, 10%, 20%, and 30%). Resistance responses of the sensor toward: (d) finger bending at different angles (0°, 30°, 60°, and 90°); (e) voice recognition speaking “ni hao”; (f) continuous finger bending and (g) continuous bending of the wrist.

Fig. 7. Antibacterial performance of the GAMA₂ hydrogel. (a) Photographs of the flat colony counting method for GA, GAM and GAMA₂ hydrogels against E. coli and S. aureus. (b) Antibacterial rate of the hydrogels against E. coli. (c) Antibacterial rate of the hydrogels against S. aureus.

Fig. 8. Biocompatibility of GAMA₂ hydrogel. (a) Cell viability detected by CCK-8 assay after 24 h of treatment. (b) Hemolysis ratio analysis.