Bionic double-network hydrogel nanocomposites reinforced with carboxylated carbon nanotubes: a comprehensive mechanical and tribological study for low friction applications

This study first investigates the influence of precursor concentration on the properties of negatively charged poly (vinyl alcohol) (PVA)/poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) hydrogels using a Box–Behnken experimental design to optimize tribological, mechanical, and water content performance. Subsequently, carboxylated carbon nanotubes (CNT-COOH) were incorporated into the dual-network hydrogel to mimic the negatively charged structure of natural cartilage. Fourier transform infrared spectroscopy (FTIR) confirmed successful polymerization, while scanning electron microscopy (SEM) revealed a porous three-dimensional network structure. The optimized hydrogels exhibited an equilibrium swelling ratio of up to 1785%. Mechanical testing demonstrated improved tensile strength (TS) at intermediate CNT concentrations, with a maximum elongation at break of 229%. Tribological measurements under physiological conditions showed excellent lubrication performance, with a low coefficient of friction (COF) of approximately 0.0336 and enhanced wear resistance. Long-term friction testing (7200 cycles) indicated stable lubrication behavior with minimal surface damage. These results demonstrate that the PVA/PAMPS/CNT-COOH nanocomposite hydrogel exhibits tunable swelling behavior, enhanced mechanical resilience, and superior lubrication performance, making it a promising biomimetic material for underwater and bio-lubrication applications. Graphical