3D Printed Microsphere-Hydrogel Scaffold Facilitates Restoration of Reinnervation in Bone Regeneration through Programmable Release of NGF/BMP-2 Mimetic Peptides

Reinnervation is of great significance for bone regeneration and remodeling. Although great progress has been made in bone tissue engineering, reconstruction of neural networks is still a challenge and leads to limited osteogenesis. Nerve growth factor (NGF) guides the innervation in the early stage of bone healing, and bone morphogenetic proteins (BMPs) are continuously expressed during the bone healing process that can induce osteogenic differentiation. A microsphere-hydrogel scaffold mimicking the dynamic performance of NGF and BMPs in a timely manner is designed and constructed via 3D printing. The scaffold enables rapid release of NGF mimetic peptide and long-lasting sustained release of BMP-2 mimetic peptide, which aims at restoring innervation. The rapid release of NGF mimetic peptide could significantly promote migration of RSC96 and axon elongation of pheochromocytoma cells in vitro. Meanwhile, co-delivery of NGF/BMP-2 mimetic peptides could synergistically enhance osteogenic differentiation of bone marrow mesenchymal stem cells mediated by calcitonin gene-related peptide (CGRP)-dependent signaling pathway. Moreover, the scaffold accelerates neural network reconstruction and effectively improves new bone regeneration in vivo. In conclusion, this 3D printed microsphere-hydrogel scaffold could simulate the temporal release profile of natural growth factors, and provide a promising strategy for innervated bone regeneration.