Selective Laser-Melted Radially Graded Fe-35Mn Scaffolds: Microstructure, Mechanical Properties, Degradation...

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.