3D printed scaffolds regulated by neural-bone metabolic coupling promote bone unit regeneration

The bone unit (BU) is a multicellular functional unit composed of neuromodulatory networks, bone tissue, and functional blood vessels. As a functional extension of bone regeneration, the BU coordinates neural signal, regeneration of the circulatory network and remodeling of the bone matrix through the neural-bone metabolic coupling mechanism. Currently, effective strategies are lacking to remodel the homeostasis of the neural-bone metabolic coupling, which in turn leads to impaired BU regeneration. Here, we constructed a 3D-printed biomimetic hydrogel scaffold, GGMN-GSE, to synergistically couple nerve-bone metabolism and restore BU regeneration through electrophysiological microenvironment reconstruction and functional cell recruitment. The GGMN layer (Grooved GelMA@MXene@NGF) incorporates conductive MXene to emulate periosteal electrophysiology and features biomimetic microgrooves to guide neural orientation, collectively modulating neural-bone metabolic coupling. The GSE layer (GelMA@SVVYGLR-E7), engineered with a dual-targeting peptide, recruits BMSCs/EPCs to supply functional cells while remodeling the vasculo-osseous regenerative niche, synergistically driving osteogenic regeneration. In vitro, the GGMN-GSE scaffold promoted nerve fiber regeneration and induced secretion of neuropeptides such as CGRP, GHRH, and VIP, and activated Calcrl, Ghr, Vipr, and other receptors on the surface of BMSCs, driving BU regeneration. This effect was mediated by neural-bone metabolic coupling through the PI3K-Akt/STAT5 signaling axis. In vivo, compared with the control group, the density of CGRP+ nerves in the GGMN-GSE group increased by 2.9-fold, the density of CD31+ blood vessels in the GGMN-GSE group increased by 1.8-fold, the area of the neogenetic bone matrix expanded by 3.6-fold, and the BV/TV reached 97.1 % in the CT. Confocal analysis of rat calvarial defects established that GGMN-GSE scaffolds exclusively promoted synergistic 3D co-localization of neural networks, functionalized vasculature, and osseous tissue, which drove multi-scale BU regeneration. The 3D-printed scaffolds fabricated in this study effectively remodel neural-bone metabolic coupling homeostasis to treat critical bone defects.