Functionalized magnetic hydrogel encapsulation of human dental follicle stem cells under a static magnetic field enhances multi-site bone regeneration

Abstract Repairing large-scale craniomaxillofacial bone defects is hindered by a limited availability of stem-cell sources and a low osteogenic efficiency. To address these challenges, Fe3O4 nanoparticles were modified with methacrylic anhydride (MAA), which helped to introduce photopolymerizable methacryloyl groups, resulting in MAA–Fe3O4 nanoparticles that exhibit excellent magnetic properties and colloidal stability. These nanoparticles were incorporated into gelatin methacryloyl (GelMA) and covalently crosslinked to form an injectable, photocurable GelMA–Fe3O4 magnetic composite hydrogel. This hydrogel provided a three-dimensional culture microenvironment for human dental follicle stem cells (hDFSCs), and upon encapsulation, osteogenesis was significantly enhanced under a 100 mT static magnetic field (SMF). In vitro, GelMA–Fe3O4 hydrogels demonstrated increased porosity and improved mechanical properties, thereby significantly promoting hDFSCs proliferation, adhesion and spreading. Additionally, under SMF exposure, the expression of osteogenesis-related genes and proteins, including alkaline phosphatase (ALP), Runx2, Col-I and OPN, was significantly upregulated. In a rat calvarial defect model, bone mineralization centers with multi-site distribution were observed in the GelMA–Fe3O4 + SMF group as early as 4 weeks postoperatively, leading to high-quality defect repair. The limitations of traditional ‘peripheral-to-center’ unidirectional repair were overcome by this model of synchronous multi-site osteogenesis, maximizing bone regeneration with a minimal number of stem cells and providing an efficient, controllable tissue-engineering strategy for the clinical treatment of craniomaxillofacial bone defects.