Innovative 3D-bioprinted microfibers in calcium phosphate cement platform with Nell-1 to activate nerve-bone axis for synergistic bone, vasculature, and nanofibrous nerve regeneration.

Critical-sized bone defects remain a persistent clinical challenge, primarily because conventional scaffolds fail to reproduce the nanofibrous neurovascular architecture that underlies functional bone regeneration. Here, we present a breakthrough 3D-bioprinted platform combining alginate microfibers (aMF) laden with human periodontal ligament stem cells (hPDLSCs) and a calcium phosphate cement (CPC) matrix, creating a hybrid environment that bridges mechanical stability with nanofibrous neurovascular guidance. This platform is engineered for the spatiotemporal delivery of Nell-1, which uniquely activates a novel "nerve-bone" axis. Nell-1 engagement initiates a CYFIP1-mediated CGRP-β3 tubulin cascade that amplifies neurovascular and bone crosstalk. A dual-phase release profile emerges as a critical design feature, with early signaling creating a favorable microenvironment for neurovascular infiltration, and then sustain signaling over time. Together, these phases synergistically enhance osteogenesis by a 2-fold increase, angiogenesis by a 3-fold increase, and innervation by a 2-fold increase. When tested in rat cranial defects, our construct outperformed controls by doubling bone and nerve regeneration while tripling vascular density, thereby achieving unprecedented healing rates compared to existing approaches. Mechanistically, we redefine Nell-1 as a dual osteo-neurogenic regulator, leveraging endogenous stem cells to drive structural and functional repair. This 3D-bioprinted microfiber-in-CPC system advances beyond passive scaffolds by dynamically coupling structural support with bioactive signaling, offering a transformative strategy for neuro-vascularized bone reconstruction.