A time-programmed therapy for enhanced cartilage regeneration in immunocompetent animals

• Time-programmed nanoparticles deliver IM and Mn for cartilage repair. • Sequential, pH-responsive release matches the biological repair timeline. • Reduces joint inflammation and promotes anti-inflammatory macrophage polarization. • Enhances chondrogenesis and deposits key cartilage matrix components. • Enables robust cartilage regeneration in an immunocompetent rabbit model. Stem cell-based cartilage regeneration remains a major clinical challenge due to the need for temporally coordinated immunomodulation and chondrogenic induction. This study designed a composite G5-IM/Mn nanoparticle system by covalently conjugating the anti-inflammatory drug indomethacin (IM) onto the surface of fifth-generation poly(amidoamine) (G5) dendrimers and encapsulating chondrogenic manganese ions (Mn) within their internal cavities. The G5-IM/Mn nanoparticles enable the rapid release of IM followed by sustained release of Mn, precisely matching the temporal requirements for inflammation control and subsequent chondrogenesis. In vitro studies demonstrated that G5-IM/Mn nanoparticles exerted significant anti-inflammatory effects. These nanoparticles were further incorporated into a GelMA hydrogel to fabricate a GelMA@G5-IM/Mn system. Moreover, experiments showed that the bone marrow stem cell (BMSC)-loaded GelMA@G5-IM/Mn system exhibited excellent biocompatibility and significantly upregulated the expression of chondrogenic markers, including SOX9, ACAN, and Col2a1 . In a rabbit subcutaneous implantation model, the BMSC-loaded GelMA@G5-IM/Mn system markedly reduced CD3 + and CD68 + inflammatory cell infiltration. Furthermore, it enhanced collagen type II expression and cartilage matrix deposition. Biochemical analyses revealed increased glycosaminoglycan and collagen II content, as well as improved Young’s modulus in the GelMA@G5-IM/Mn group. In summary, this time-programmed G5-IM/Mn nanoparticle system first establishes an immuno-favorable microenvironment and subsequently promotes robust cartilage regeneration.