Shape optimization of orthopedic porous scaffolds to enhance mechanical performance

Polymeric bone scaffolds are supposed to temporarily bear the external mechanical forces applied to the injured area. The implanted scaffolds should satisfy both mechanical and cell-proliferation requirements. In this study, to design an optimum scaffold structure from mechanical and cell growth perspectives, a new scaffold structure named MFCC (Modified Face Centered Cubic) is introduced, which is based on the Face Centered Cubic (FCC) arrangement of spherical pores. The geometric parameters of the scaffold structure are optimized to increase the stiffness of the scaffolds with 70%, 75%, and 80% porosities. The optimized MFCC scaffolds satisfy the cell growth requirements and show greater elastic modulus compared to regular OCS (Orthogonal Cylindrical Struts) scaffolds. For validation, the designed scaffolds made by the finite element optimization process were 3D printed, tested and compared with the OCS scaffolds. The results show that the gradual cross-section variation of the spheres in the optimized scaffold reduces the stress concentration and distributes the applied mechanical loads more uniformly compared to OCS scaffolds. Moreover, from the cell growth perspective, a spherical pore with a concave surface provides a better surface for the proliferation of cells. The optimized MFCC scaffolds are stiffer in small strains and have a greater apparent yield stress compared to the OCS scaffolds at the same porosity. The enhancement in the stiffness of the scaffold is shape attributed and is independent of the material used. Therefore, the same percentage increase in the stiffness is achievable for a broad range of materials. The presented new design with improved stiffness helps to enhance the quality of load-bearing scaffolds.