Functionalized Magnetic Hydrogel Encapsulation of Human Dental Follicle Stem Cells under a Static Magnetic Field Enhances Multi-site Bone Regeneration

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 provides a three-dimensional (3D) 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 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.