Hybrid Biofabrication of a Hierarchically Organized Periosteum‐Inspired In Vitro Platform

The periosteum is a hierarchically organized, vascularized membrane essential for skeletal maintenance and regeneration, yet in vitro models that reproduce its compartmentalized and multicellular architecture remain limited. In this study, we present a hierarchically organized, periosteum‐inspired in vitro platform fabricated by integrating melt electrowriting (MEW) with extrusion‐based 3D bioprinting. The platform integrates a human osteoblast‐laden plasma‐containing alginate/methylcellulose hydrogel compartment, a configurable MEW‐PCL microfibrous interface, and an endothelial cell–fibroblast‐laden fibrin/gelatin hydrogel compartment. MEW scaffold architectures and compartment‐specific bioink–cell configurations were screened based on their ability to support osteogenic maturation‐associated readouts and CD31 + endothelial cell organization. The resulting tri‐layer construct maintained high cytocompatibility and structural integrity during culture for up to 49 days. The osteogenic compartment supported osteogenic differentiation‐associated readouts and mineralized matrix deposition, while the endothelial cell‐containing compartment supported interconnected CD31 + endothelial cell organization accompanied by endothelial cell‐associated gene expression. Overall, this hybrid MEW–3D bioprinted platform provides an engineerable in vitro model for periosteum‐inspired tissue modeling, biomaterial screening, and investigation of osteogenic and endothelial cell‐associated processes under controlled conditions.