Structurally defined cartilaginous MEW-assembloids for critical-size long bone healing

Bone defects exceeding a critical size pose significant clinical challenges due to their inability to heal spontaneously. Traditional treatments including autografts and synthetic implants, are often suffer from limitations such as donor site morbidity, infection risk, and poor integration. This study explores a novel approach using MEW-assembloid which combine Melt electrowriting (MEW) scaffolds with cartilaginous microtissues to enhance bone healing. Here, we fabricated bucket-shaped MEW scaffolds (OMesh and CMesh) to optimize microtissue retention and integration, with the OMesh design showing effective shape retention after microtissue seeding. To adapt the scaffold dimensions for in vivo implantation, we introduced elongated MEW (EMesh) based on the OMesh design, forming EMesh-assembloid. These constructs were evaluated for their ability to undergo endochondral ossification and mineralization in subcutaneous implants. Additionally, tubular MEW scaffolds were also created as stabilizers around EMesh-assembloid for orthotopic implantation and showed substantial new bone formation and nearly full defect bridging in a critical-sized mouse tibia defect model after 8 weeks. Our results indicates that MEW-assembloid offer a robust strategy for tissue engineering, enhancing the structural and functional integration of implants, and providing an innovation solution for the repair and regeneration of critical bone defects, potentially advancing clinical treatments for bone regeneration.