Novel 3D-printing bilayer GelMA-based hydrogel containing BP, β-TCP and exosomes for cartilage-bone integrated repair.

The integrated repair of cartilage and bone involves the migration and differentiation of cells, which has always been a difficult problem to be solved. We utilize the natural biomaterial gelatin to construct gelatin methacryloyl (GelMA), a hydrogel scaffold with high cell affinity. GelMA is mixed with different components to print a bi-layer porous hydrogel scaffold with different modulus and composition in upper and lower layers through 3D printing technology. The upper scaffold adds black phosphorus (BP) and human umbilical cord mesenchymal stem cells (hUMSCs) exosomes in GelMA, which has a relatively lower elastic modulus and is conducive to the differentiation of BMSCs into cartilage. In the lower scaffold, in addition to BP and hUMSCs exosomes, β-tricalcium phosphate (β-TCP), which has osteoconductive and osteoinductive effects, is added to GelMA. The addition of β-TCP significantly enhances the elastic modulus of the hydrogel scaffold, which is conducive to the osteogenic differentiation of BMSCs. In vitro experiments have confirmed that the bi-layer scaffolds can promote osteogenesis and chondrogenic differentiation respectively. And in the rabbit cartilage-bone injury model, MRI and micro-CT results show that the 3D printed bi-layer GelMA composite scaffold has a repair effect close to normal tissue.