# A Novel Polyacrylamide/Sodium Alginate/Polypyrrole Composite Hydrogel for Fabricating Flexible Sensors for Wearable Health Monitoring

## TL;DR

A new conductive hydrogel is developed with high strength, conductivity, and adhesion for flexible sensors in wearable health monitoring.

## Contribution

The ASP hydrogel integrates a double-network architecture with in situ polypyrrole formation for balanced mechanical and electrical properties.

## Key findings

- The ASP hydrogel has a fracture strength of 2.95 MPa, significantly higher than PAM and PAM–SA hydrogels.
- The hydrogel exhibits stable electrical conductivity and reproducible strain-dependent responses.
- Dynamic metal–phenolic coordination and hydrogen bonding provide self-healing and strong adhesion to substrates.

## Abstract

Conductive hydrogels that simultaneously exhibit high mechanical robustness, reliable electrical conductivity, and interfacial adhesion are highly desirable for flexible sensing applications; however, achieving these properties in a single system remains challenging due to intrinsic structure–property trade-offs. Herein, a multifunctional conductive hydrogel (ASP hydrogel) is developed based on a polyacrylamide (PAM)/sodium alginate (SA) double-network architecture using a gallic acid (GA)–Fe3+–pyrrole (Py) coupling strategy. In this design, GA provides metal-coordination sites for Fe3+, while Fe3+ simultaneously serves as an oxidant to trigger the in situ polymerization of pyrrole, enabling the homogeneous integration of polypyrrole (PPy) conductive networks within the hydrogel matrix. The resulting ASP hydrogel exhibits a markedly enhanced fracture strength of 2.95 MPa compared with PAM (0.26 MPa) and PAM–SA (0.22 MPa) hydrogels, together with stable electrical conductivity and reproducible strain-dependent electrical responses. Moreover, the introduction of dynamic metal–phenolic coordination and hydrogen-bonding interactions endows the hydrogel with intrinsic self-healing capability and strong adhesion to diverse substrates. Rather than relying on simple filler incorporation, this work demonstrates an integrated network design that balances mechanical strength, conductivity, and adhesion, providing a versatile material platform for flexible strain sensors and wearable electronics.