Digital light processing 3D bioprinting of collagen-based gradient osteochondral scaffold for cartilage-bone regeneration

Osteochondral defects pose a significant clinical challenge, requiring the regeneration of both articular cartilage and subchondral bone across a continuous gradient of composition and mechanical properties. Here, we present BioGraOstO, a digital light processing (DLP)-based 3D bioprinted scaffold for constructing biomimetic osteochondral organoids with precisely graded architectures. Three photo-crosslinkable, cell-laden bioinks were engineered to emulate native osteochondral zones: methacrylated type II collagen and hyaluronic acid for hyaline cartilage (HyaC); 30 % mineralized methacrylated type I collagen for calcified cartilage (CalC); and 60 % mineralized methacrylated type I collagen and hyaluronic acid for subchondral bone (SubB). Sequential DLP bioprinting produced multilayered constructs with well-integrated organic-inorganic interfaces, a modulus spanning 1.35–17.29 kPa, minimal swelling (<10 %), and programmable biodegradation over 15 days. The organoids supported region-specific chondrogenic and osteogenic differentiation of bone marrow–derived mesenchymal stem cells (BMSCs) in vitro , confirmed by histology, immunofluorescence, and gene expression. In a rat osteochondral defect model, BioGraOstO implants achieved near-complete restoration of cartilage and subchondral bone within 12 weeks, significantly outperforming acellular scaffolds. This study establishes a versatile and clinically translatable strategy for osteochondral regeneration, leveraging high-resolution DLP bioprinting, graded biomimetic bioinks, and integrated organoid functionality, offering a promising approach for joint repair and next-generation tissue engineering.