Self-healing silk fibroin–gelatin–based 3D-printed bilayer scaffolds with stable interface and bidirectional lineage control for osteochondral regeneration

The osteochondral interface—characterized by a steep gradient in both composition and mechanical properties—remains one of the most challenging anatomical sites to regenerate. Reconstructing this spatially complex heterogeneity continues to confound conventional osteochondral grafts. Although multilayer scaffolds are widely adopted, interfacial delamination frequently compromises repair outcomes. Here, we report a self-healing, physically crosslinked silk fibroin–based 3D-printing ink that incorporates gelatin and nano-hydroxyapatite for the fabrication of bilayer scaffolds with robust interfacial bonding. By tuning ultrasonication time of silk fibroin and gelatin content, the ink exhibits exceptional printability and cytocompatibility, enabling >90% post-printing cell viability. Leveraging a dual-nozzle alternating-print strategy, we generated bilayer constructs that display a stable interface and layerspecific mechanical heterogeneity. Both upper- and lower-layer inks possess good self-healing capacity, eliminating delamination and yielding a monolithic scaffold. Functional analyses revealed significant upregulation of the chondrogenic marker type II collagen in the upper layer and the osteogenic marker RUNX2 in the lower layer, achieving bidirectional lineage instruction required for osteochondral regeneration. This silk/gelatin-based, physically crosslinked, integrative bilayer scaffold offers a promising therapeutic platform for osteochondral defect repair.