Optimizing the d-band center of Pd/CoPcS-Ti3C2Tx to enhance SOD/CAT-mimicking activities in the treatment of osteoarthritis

The development and pathogenesis of osteoarthritis (OA) are closely related to the redox imbalance caused by the overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the inflammatory microenvironment. Herein, we developed Pd/CoPcS-Ti3C2Tx nanozymes combining cobalt sulfonated phthalocyanine (CoPcS) and titanium carbide (Ti3C2Tx) nanosheets by noncovalent π-π conjugation for loading of ultrafine Pd nanoclusters, as the superoxide dismutase (SOD) and catalase (CAT) mimics for OA therapy. The electron donor CoPcS-Ti3C2Tx facilitated electron transfer to Pd, effectively modulating the d-band center of Pd close to the Fermi energy level, which enhanced the adsorption energy of free radicals and decreased reaction energy barriers. As expected, Pd/CoPcS-Ti3C2Tx nanozymes had a lower electron escape work function than Ti3C2Tx, with improved photothermal conversion efficiency (49.1%) and enzyme catalytic activity. Experiments in vitro demonstrated that the SOD/CAT-mimicking Pd/CoPcS-Ti3C2Tx antioxidant system effectively eliminated ROS and RNS, inhibited inflammatory factors, restored mitochondrial function, and prevented energy deficiency, leading to a reduction in chondrocyte apoptosis. Particularly, near-infrared (NIR) radiation further enhanced the effects. In vivo studies proved the potent preventative effect of Pd/CoPcS-Ti3C2Tx on OA progression as well as its biosafety. This study is expected to provide a promising strategy for designing highly active nanozymes for the treatment of inflammatory diseases.