Fig. 1

Schematic illustration of application of WPV-CuO NPs in OA therapy. Ultrasmall CuO NPs were modified with dual-targeted (COL2 favoring cartilage penetration and MSC favoring MSC recruitment) peptides, which were spaced with an MMP-2-sensitive sequence. After intraarticular injection into OA joint (a), WPV-CuO NPs actively targeted cartilage. b Abundant MMP-2 in the OA microenvironment cleared the outer COL2-targeting sequence (c) and exposed the inner MSC-targeting sequence to attract joint-resident MSCs (d). Directed by CuO NPs, MSCs could differentiate into chondrocytes (e), leading to successful repair of cartilage and reduction in joint destruction