Selective Laser-Melted Radially Graded Fe-35Mn Scaffolds: Microstructure, Mechanical Properties, Degradation Behavior, and Sustained Release of Human Bone Morphogenetic Protein-2.

Radially graded porous architectures offer advantages over uniformly porous structures in meeting the heterogeneous mechanical and biological requirements of complex bone defects. In this study, the radially graded Fe-35Mn scaffolds based on Gyroid unit cells were successfully manufactured using selective laser melting and subsequently functionalized by vacuum impregnation with human bone morphogenetic protein-2 (BMP-2)-loaded chitosan. The Fe-35Mn scaffolds exhibit a well-interconnected porous structure with ∼53-66% porosity and an average pore size ranging from ∼138 to 483 μm. The microstructure is dominated by γ-austenite with a minor fraction of ε-martensite. The radially graded Fe-35Mn scaffolds possess elastic moduli of 2.4-3.5 GPa and compressive yield strengths of 40.9-67.7 MPa, comparable to those of cortical bone and favorable for minimizing stress shielding while maintaining sufficient load-bearing capacity. The degradation rates of the porous scaffolds in simulated body fluid decrease with immersion time, reaching approximately 0.14-0.23 mm·year-1 after 28 days, which is moderately higher than that of the dense Fe-35Mn alloy (∼0.092 mm·year-1). Moreover, the BMP-2-loaded scaffolds display a biphasic release behavior, characterized by an initial burst release up to 168 h followed by a slower, sustained release from 168 to 456 h. Overall, these results demonstrate that radially graded porous Fe-35Mn scaffolds combine favorable mechanical compatibility, tunable biodegradation, and sustained growth factor delivery, highlighting their potential as biodegradable load-bearing scaffolds for bone regeneration.