3D-printed GelMA-Alginate microsphere scaffold with staged dual-growth factor release for enhanced bone regeneration

The process of bone regeneration is inherently complex, relying on the precise regulation of multiple growth factors. However, when bone defects exceed a critical size, this delicate regulatory balance is disrupted, severely hindering new bone formation. In this study, we developed a bioengineered scaffold with staged growth factor release capabilities to promote efficient bone repair, constructed by integrating gelatin methacryloyl (GelMA) with embedded alginate microspheres (AM). Through microfluidic technologies and 3D printing, AM were fabricated and integrated into the GelMA matrix to fabricate the composite scaffold, which not only maintains structural integrity but also enables gradient-controlled release of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2). This design ensures uniform bioactivity of the printed constructs, optimizing conditions for bone regeneration. In vitro experiments demonstrated that the scaffold exhibited an initial burst release of VEGF, followed by a sustained, prolonged release of BMP-2 mimicking the natural sequential processes of tissue vascularization and subsequent osteogenesis. Upon <i>in vivo</i> implantation, the scaffold has demonstrated the ability to effectively repair a critical-sized cranial defect in a rat model within a 12-week period. These findings highlight that the bioink-printed construct, through its spatiotemporally coordinated delivery of VEGF and BMP-2, effectively stimulates bone regeneration. The staged growth factor-releasing 3D printed scaffold offers a promising therapeutic strategy, particularly for treating large-scale bone defects, by significantly enhancing the efficiency of bone defect repair.