Melamine foam-based nanocomposite hydrogel with self-adhesion and antibacterial activity for pressure sensing

Hydrogel-based sensing materials, known for their excellent flexibility and efficient signal transduction capabilities, have attracted significant attention in flexible electronics. However, the limited compression strength and single functionality of conventional strain-sensing hydrogels severely restrict their broader application. Herein, we report the development of a multifunctional nanocomposite pressure-sensing hydrogel featuring self-adhesion and antibacterial activity, synthesized via a two-step polymerization process. The polypyrrole (PPy) nanoparticles are first grown on melamine foam (MF) via oxidative polymerization to form MF@PPy. Subsequently, a polydopamine (PDA)-polyacrylamide (PAM) network is then polymerized within the porous MF@PPy structure to obtain the MF@PPy/PDA-PAM hydrogel. Compared to the pure PDA-PAM hydrogel, the compressive strain is significantly enhanced from 36% to 64%, owing to the resilient MF@PPy skeleton. Additionally, the incorporation of the adhesive PDA-PAM network endows the nanocomposite hydrogel with robust and repeatable adhesion to various substrates including steel, wood, paper, plastic, rubber, and glass with a maximum adhesion strength of 36.8 kPa. Furthermore, the nanocomposite hydrogel exhibits outstanding antibacterial performance, achieving bacterial survival rates of 1% against Escherichia coli (E. coli) and 8% against Staphylococcus aureus (S. aureus). Last but not least, it also shows an ionic conductivity of 12 mS cm^-1 and a highly sensitive response at low pressures (0.3 kPa). This work presents a pressure-sensitive hydrogel sensor that integrates self-adhesion and antibacterial activity for real-time monitoring of human physiological activities, offering valuable insights for the development of multifunctional soft sensors.