A bioprinted periosteum organoid enables functional repair of critical-sized bone defects.

The periosteum is an essential yet often neglected regulator of bone regeneration, and its loss represents a major barrier to healing critical-sized bone defects. Existing periosteum-mimicking strategies rely primarily on static architectures or exogenous factor delivery and fail to reconstruct a living periosteal interface. Here, we introduce an organoid-based approach for engineering functional periosteum organoids capable of restoring periosteal identity and regulatory function. A bioprinted GelMA/SilMA interpenetrating composite hydrogel integrated with black phosphorus nanosheets is developed to create a mechanically stable and bioactive microenvironment that supports osteogenic-angiogenic self-organization. Under three-dimensional culture, the constructs exhibit the potential to form periosteum organoids, with coordinated osteogenic differentiation and pro-angiogenic niche formation. Following in vivo conditioning, the constructs develop into periosteum organoids that exhibit dense collagen-rich fibrous architecture, pronounced periostin expression, enrichment of osteogenic lineage cells, and stabilized microvasculature, closely recapitulating the structural and functional hallmarks of native periosteum. When applied to a critical-sized rat calvarial defect model, the periosteum organoids significantly enhance bone regeneration, improve trabecular microarchitecture, reconstruct a functional periosteal interface, and rebalance bone remodeling without detectable systemic toxicity. This work establishes periosteum organoids as a living regenerative interface for skeletal repair and provides a new organoid-based paradigm for functional periosteal reconstruction in large bone defects.