Effects of graded pore size distribution structure on enhancing mechanical and biological properties of 3D printed biphase calcium phosphate scaffolds

The pore architecture of the scaffold used to repair bone defects plays a crucial role in bone regeneration. Optimizing the macropore configuration is a practical method for enhancing the mechanical and biological performance of bone scaffolds. Herein, biphasic calcium phosphate (BCP) scaffolds with different graded macropore architectures were designed and fabricated precisely using the vat polymerization (VPP) technique. The BCP porous scaffolds featured structures with a graded macropore size distribution from the periphery to center in radical direction. After sintered, the actual pore size of scaffolds decreased. The P600 scaffold with uniform pore size served as the control group, and its pore size after sintering was 414.49 μm. Our results showed that the P700-900 scaffold (417.39-530.43 μm) had higher compressive strength and porosity. Additionally, BCP graded porous scaffolds had faster biodegradation rates and accelerated the formation of bioactive apatite in simulated body fluid (SBF). All scaffolds showed excellent biocompatibility and promoted osteogenic differentiation in vitro. Graded porous scaffolds facilitated the transition of M1 to M2 macrophages, which is beneficial for bone regeneration. In vivo, micro-CT and histological analyses indicated that more bone was formed in the P600 scaffold at 4 weeks after implantation into rabbit femoral condyle defects, but the amount of new bone in the P500-900 graded porous scaffold (252.17-524.64 μm) was the highest at 8 weeks, attributed to reduced bone resorption. Our findings demonstrated that BCP scaffolds with a graded macropore wide distribution (P500-900 scaffold) have excellent potential in bone regeneration for bone regeneration in clinical bone defect repair. The present study offers a promising strategy to optimize the pore architecture of bone scaffolds to enhance their performance and accelerate their clinical applications.