Mechanical Properties and In Vitro Behavior of Additively Manufactured and Functionally Graded Ti6Al4V Porous Scaffolds

Abstract

Abstract:Functionally graded lattice structures produced by additive manufacturing are promising for bone tissue engineering. Spatial variations in their porosity are reported to vary the stiffness and make it comparable to cortical or trabecular bone. However, the interplay between the mechanical properties and biological response of functionally graded lattices is less clear. Here we show that by designing continuous gradient structures and studying their mechanical and biological properties simultaneously, orthopedic implant design can be improved and guidelines can be established. Our continuous gradient structures were generated by gradually changing the strut diameter of a body centered cubic (BCC) unit cell. This approach enables a smooth transition between unit cell layers and minimizes the effect of stress discontinuity within the scaffold. Scaffolds were fabricated using selective laser melting (SLM) and underwent mechanical and in vitro biological testing. Our results indicate that optimal gradient structures should possess small pores in their core (~900 µm) to increase their mechanical strength whilst large pores (~1100 µm) should be utilized in their outer surface to enhance cell penetration and proliferation. We suggest this approach could be widely used in the design of orthopedic implants to maximize both the mechanical and biological properties of the implant.

Additively manufactured functionally graded biodegradable porous zinc

“…61 From surface visualization and cross-sectional imaging, MG-63 cells appeared to be evenly distributed along the periphery as well as within the core region of the specimens, without showing any obvious design-related differences. It is in agreement with the results obtained by other researchers who analyzed pre-osteoblasts in graded Ti-6Al-4V scaffolds, 62 in comparison with cell distribution in graded polymer 3D scaffolds. 63 Of note, cell seeding efficiency was above 70% (i.e., 70% cells attached to the Zn surface) for all the three porous Zn scaffold designs, but a slightly higher efficacy in the group S04 was noticed, as compared to S03.…”

Trabecular-like Ti-6Al-4V scaffolds for orthopedic: fabrication by selective laser melting and in vitro biocompatibility

“…[46][47][48], the human cancellous bone has a Young's modulus range of MPa, which was in the same stiffness level as the cancellous bone but had more excellent stress resistance ability similar to cortical bone. Compared to the gradient regular porous structure [49][50][51] , though they both consisted of pores with varied size, the gradient regular porous structure had obvious gradient phenomenon in mechanical behavior. And the irregular porous structure studied in this work presented a mechanical behavior like homogeneous porous structure with more reasonable match in modulus and strength.…”

“…This was because that the scaffolds with the full irregularity of 0.5 had random porous architecture consisting of pores with a relatively wide size distribution and varied shapes. As with gradient regular porous structure [51,64] , under the premise of providing sufficient nutrients and oxygen, it would make cells exposed to more diversified mechanical stimuli, enhancing osteoblast differentiation. This result was also in accordance with the viewpoints of Lv et al [65] and Cheng at al.…”

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

“…For example, Choy et al [123] proposed two cubic and honeycomb gradient lattice structures by using the rod diameter variation strategy. Onal et al [9] designed two BCC structures with density gradient changes by varying the rod diameter; the structures are beneficial to cell diffusion and proliferation and can maximize the mechanical and biological properties of the implant. Moreover, for the diamond lattice structure, Dumas et al [127] successfully applied its gradient structure to a partially porous femoral stem.…”

“…In order to avoid the phenomenon of "stress shielding" [5], the implant requires mechanical properties such as Young's modulus and strength compatible with the bone. For solid metals, the mechanical properties are higher than the mechanical parameters of the bone, resulting in the mismatch in modulus, thereby causing the "stress shielding", which can be easily solved by using a porous metal material, the topological configuration and relative density of which can be adjusted to meet the mechanical and biological functional requirements of the implant [6][7][8][9]. (3) Appropriate morphological structure and structural processability.…”