Zirconium ion ligand Cross-Linked carbon nanotubes and leather collagen fibers for Flexible, Stable, and highly efficient underwater sensors

Flexible sensing materials have recently found widespread applications in integrating various underwater sensors. In this study, we adopted oil-tanned sheepskin as a "structural template" and harnessed its distinctive three-dimensional collagen fiber network. By leveraging the coordination complexation of zirconium ions (Zr4+), we brided collagen fibers with carbon nanotubes (CNTs) to enhance the bonding fastness of the two. We finally constructed a double cross-linked network to produce a new flexible conductive leather called CNTs@Zr@OTL. This material is the basis for preparing leather bio-based piezoresistive sensors (LBPS) and further developing leather biosensing systems (LBS). Experimental outcomes revealed that when CNTs were employed at a concentration of 8.5 %, CNTs@Zr@OTL exhibited an electrical resistivity of approximately 7.4 Ω·cm and a shrinkage temperature of around 74.5 °C. Furthermore, this material demonstrated remarkable characteristics, including 24-hour biodegradability, a broad sensing range (20 %-120 %), and high sensitivity (with response and recovery times of 300 ms and 100 ms, respectively). Based on multiple cross-linked networks, we propose for the first time the underwater sensing mechanism of "Submarine Tunnel" to achieve strong stability in the water environment. Finally, we simulated the LBPS's response to minor external stimuli, including rainwater exposure, multiangle reactions, and water depth sensitivity. By interfacing with wireless modules and mobile phones, the LBS enabled the execution of emergency SOS signals, highlighting its potential applications in underwater motion monitoring and urgent rescue operations.