Assembling Nanofibrous Microspheres Into 3D Matrices for Alveolar Bone Regeneration

Objectives: Alveolar bone regeneration generally needs the guidance of biomaterials. Injectable biomaterials are attractive for the regeneration of irregular shapes of alveolar bone defects. As a new type of injectable biomaterials, functional microspheres possess advantageous features compared to other injectable biomaterials (e.g., hydrogels). However, one limitation is the migration of microspheres outside the defective area, leading to the risk of potential adverse events. In this work, we prepared nanofibrous and photo-crosslinkable functional gelatin-based microspheres as a new type of injectable biomaterials and used them for alveolar bone regeneration. Photo-crosslinkable double bonds on the nanofibrous microsphere surfaces assembled the microspheres into well-defined 3D matrices, thus preventing microsphere migration. In addition, a bone forming peptide (BFP) was loaded to enhance its osteoinductivity.
Methods: BFP was encapsulated into calcium phosphate (CaP) nanoparticles, which were subsequently added to gelatin methacryloyl (GelMA) solution. Then adding solution mixture was added in mineral oil to form a microemulsion. A thermally induced phase separation (TIPS) process was induced by pouring the mixture into isopropanol/hexane/ethanol mixture. The obtained microspheres were crosslinked at 4°C for 24 h to stabilize the nanofibrous microspheres. The microspheres were washed, sieved, and lyophilized. To form well-defined 3D matrices, the microspheres were stacked and photo-crosslinked with UV light irradiation. The mechanical properties, encapsulation efficiency, BFP release, biocompatibility, and mechanical stability were measured.
Results: GelMA microspheres composed of gelatin nanofibers (diameter of approximately 63-90µm) were fabricated. Photo-crosslinking of the microspheres under a mild condition (e.g., under the condition of 100 mW/cm² UV intensity and a time of 30 seconds) formed a stable microsphere-based 3D matrix. The biomimetic matrix promoted bone marrow stem cell adhesion, migration, and proliferation. Furthermore, photo-crosslinking effectively prevented microsphere migration.
Conclusions: The biomimetic 3D matrix assembled from nanofibrous GelMA microspheres serves as a promising cell carriers and drug-delivery vehicles for alveolar bone regeneration.