A novel MRI contrast agent NaGdF4@PEG-CLS@MMP-13 NPs for detecting articular cartilage injury.

Early detection of cartilage injuries is crucial due to their limited self-repair capacity and risk of joint dysfunction. Conventional contrast agents like gadolinium-diethylenetriamine-pentaacetic acid (Gd-DTPA) offer low specificity and T1 relaxivity (r1), limiting MRI application. This study introduces NaGdF4 nanoparticles (NPs) modified with polyethylene glycol (PEG) and cholesterol (CLS) to enhance hydrophilicity and lipophilicity. Targeting is achieved using a matrix metalloproteinase-13 (MMP13) cartilage-binding peptide. NaGdF4@PEG-CLS@MMP13 CBP NPs demonstrate an increased r1 value (8.07 mM-1 s-1) compared to NaGdF4@PEG-CLS NPs (6.65 mM-1 s-1) and Gd-DTPA (3.01 mM-1 s-1), enabling deeper cartilage penetration and stronger cartilage affinity. Two hours post-injection, these NPs improved the signal-to-noise ratio at injury sites by 2.4-fold over pre-injection values. Biocompatibility was confirmed with no adverse effects in blood or organs, and the NPs were metabolized in kidneys and liver, with excretion via urine. This study supports NaGdF4@PEG-CLS@MMP13 CBP NPs as an effective MRI contrast agent, enhancing early detection of cartilage injuries.