Effect of porosity variation strategy on the performance of functionally graded Ti-6Al-4V scaffolds for bone tissue engineering

Abstract

Functionally graded scaffold (FGS) is designed to mimic the morphology, mechanical and biological properties of natural bone closely. Porosity variation strategy between different regions in FGS plays a crucial role in influencing its mechanical and biological performance. A combination of modeling tool and scripting language can effectively enhance the ability to optimize FGS designs. This study was aimed at determining the effect of porosity variation strategy on the mechanical performance and permeability of the as-built and as-heat-treated FGSs. Ti-6Al-4V FGSs with sizes of 10×10×15 mm and diamond lattice structures were designed and fabricated by means of selective laser melting. A wide range of porosities in the FGSs (38~75%) were achieved by applying six different porosity variation strategies. The elastic modulus (3.7~5.7 GPa) and yield strength (27.1~84.7 MPa) of the as-built FGSs were found to vary between the corresponding mechanical properties of cancellous bone and cortical bone. Heat treatment reduced the strengths by 13~56%. Porosity variation strategy strongly affected the deformation behavior and failure mechanisms of the FGSs. The sigmoid function-controlled FGSs showed gradual failure behavior and

Clinical, industrial, and research perspectives on powder bed fusion additively manufactured metal implants

“…Under compression, sequential collapse of layers prior to full densification of structures has been observed in graded lattices, both with linear and curved gradients in density, with no significant difference in the mechanical response to static and dynamic compression testing [113,114]. The degree of densification between layer failures can be modified, as demonstrated by structures using sigmoidal density gradients [115]. This may reduce the risk of a catastrophic collapse of multiple layers of a lattice.…”

Additive Manufacturing of Customized Metallic Orthopedic Implants: Materials, Structures, and Surface Modifications

“…However, this work only considers the mechanical properties of the implant. Furthermore, Zhang et al [128,129] explored a A series of gradient implant structures can be obtained by applying the common gradient lattice structure, such as the polyhedral gradient structures and the gradient minimal surface structures. The polyhedral structure has a simple topology, and its gradient strategy is easier than the surface structure.…”

“…However, this work only considers the mechanical properties of the implant. Furthermore, Zhang et al [128,129] explored a more complex diamond lattice gradient strategy, achieving a gradient structure implant with rational permeability and mechanical properties.…”

“…Ti-6Al-4V/SLM [127][128][129] Obvious anisotropy; excellent energy absorption; appropriate modulus; good permeability.…”

Reviewing recently developed technologies to direct cell activity through the control of pore size: From the macro‐ to the nanoscale

“…Hence, scaffold pores with controllable diameters over multiple length scales were developed to mimic complex living hierarchical structures. For instance, several studies investigated human bone topological features to resemble its unique hierarchical structure at different scales (Yuan et al, ; Zhang, Fang, Xing, Liu, & Zhou, ). Pore size affects the response of the hosting cells in a different way (Loh & Choong, ): nanopores (<300 nm in size; Cox & Dunand, ; Merhie, Salerno, Toccafondi, & Dante, ) promotes cell adhesion increasing the surface area, micropores (0.3–100 μm in size; Cox & Dunand, ; Sherborne, Owen, Reilly, & Claeyssens, ) enhance the permeability of the scaffold and facilitate cell migration while macropores (>100 μm in size; Bruzauskait, Bironaite, Bagdonas, Bernotiene, ; Salerno, Guarnieri, Iannone, Zeppetelli, & Netti, ; Zopf, Flanagan, Mitsak, Brennan, & Hollister, ) provide space for vascularization and tissue ingrowth, favor gas diffusion, nutrients supply, and waste removal (Figure ).…”