Figure 2.

Enzyme-responsive biomaterials for OA treatment: (A) Schematic illustration of the synthesis and working mechanism of MMP-13 and pH responsive theranostic MRC-PPL@PSO nano-micelles for osteoarthritis ²². High expression of MMP-13 in OA joints generates fluorescent signals by cleaving sensitive peptides to release Cy5.5. In addition, the low pH environment moderates the release of PSO in micelles to treat cartilage inflammation. Copyright 2020, BMC. (B) Schematic illustration of the CMFn@HCQ as a cartilage-targeting and MMP-13/pH dual-stimuli activatable theranostic nanoprobe for in vivo MMP-13 imaging and precision therapy of osteoarthritis ⁷³. Ferritin in the CMFn@HCQ nanocage dissociates in an acidic environment to release HCQ. Simultaneously, MMP-13 severs the short peptide that connects the burster and the free NIR dye can visualize the concentration of disease progressing MMP-13 in OA. Copyright 2019, Elsevier. (C) In vivo fluorescence imaging of the major organs and bilateral joints 21 days after MRC-PPL joint cavity injection ²². Copyright 2020, BMC. (D) Bioresponsive microspheres for delivery of the anti-inflammatory cytokines in osteoarthritis ⁷⁵. Gelatin microspheres are degraded by the rate of catabolic factors produced by OA microenvironment cells to release IL-4, IL-10 and IL-13 to reduce chondrocyte inflammation. Copyright 2019, Wiley.