Functionally Graded Ti‐6Al‐4V Meshes with High Strength and Energy Absorption

Abstract

Titanium and its alloys with open cellular structures such as mesh and foam are characterized by low Young's modulus similar to that of human bone. Moreover, they provide the space required for bone tissue in-growth. These characteristics render them suitable for use as an implant. [1] However, to ensure long-term endurance and the ability to withstand abrupt impact fracture, the artificial cellular materials are expected to possess adequate strength in conjunction with high energy absorption capability. [2,3] As regard bone ingrowth, recent studies indicated that cellular structures need to have high porosity, but such structures generally lack adequate mechanical strength and energy absorption, [4,5] These mutually opposing requirements of high porosity and mechanical strength in conjunction with high energy absorption have hindered the application of cellular structure as biomedical devices.Thus, to alleviate the aforementioned demerits of cellular structures, graded/gradient cellular titanium and titanium alloys structures are considered appropriate. If we can optimize the distribution of pore size, pore morphology, and relative density, the open cellular structures will exhibit a combination of high porosity and high strength, optimized in-growth of tissues, and the ability to withstand varying mechanical stress at specific regions. [6][7][8] Recent efforts were directed in fabricating functionally graded cellular titanium alloys, with the possibility for consideration in biomedical applications. [9][10][11] Additive manufacturing process using electron beam melting (EBM) technique has been recently developed to fabricate titanium alloy cellular mesh and foam structures. [12,13] The approach provides accurate control of internal pore architecture and complex-shapes, and thereby provides the opportunity to tailor and fabricate bulk functionally graded cellular structures and elucidate their mechanical behavior. In the study presented here, graded/gradient Ti-6Al-4V mesh structures were fabricated by EBM with the objective to elucidate compressive deformation behavior, Young's modulus, strength, and the underlying deformation mechanisms. It is demonstrated that through appropriate design of graded/gradient cellular mesh structure with high strength and high energy, absorption combination can be fabricated, which have mechanical properties superior to those previously reported for uniform metallic cellular structures. Figure 1 is a computer-aided design (CAD) model for reticulated mesh with radial dual-density. The unit cell of the mesh is rhombic dodecahedron (Figure 1a). The macroscopic images of these graded meshes are presented in Figure 1f. Scanning electron microscopy (SEM) studies suggested that the strut thickness of mesh was %500 mm (Figure 1f). In a manner similar to previous studies, the strut surfaces were rough, [14] and the mesh struts had acicular microstructure consisting primarily of a 0 -martensite and a small amount of b-phase (Figure 1f) because of rapid cooling experienced by the thin isola...

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

“…In recent years, additively manufactured gradient structures for tissue engineering have been studied [37][38][39]41,44,64,65]; however these studies either focused on the mechanical properties or biological response independently. In this work, the biological and mechanical responses were assessed simultaneously allowing us to study the overall impact of the designed geometry of the scaffolds.…”

“…A number of studies have investigated the mechanical or biological response of metallic-based gradient porous designs produced by additive manufacturing [37][38][39][40][41][42][43][44][45]. The majority of these studies focused on gradient structures generated by abrupt changes between layers based on change in strut diameter or unit cell volume.…”

“…The majority of these studies focused on gradient structures generated by abrupt changes between layers based on change in strut diameter or unit cell volume. For instance, Li et al [37] studied the deformation behavior of radial dual-density rhombic dodecahedron Ti6Al4V scaffolds fabricated by EBM. They achieved radial dual-density by altering the rhombic dodecahedron unit volume between two layers which resulted in discontinuity between layers.…”

“…They concluded that continuous variation between layers are ideal to minimize the stress concentration at the interface. Nune et al [38,39] investigated the osteoblastic functions of the scaffolds designed using Li et al [37] work, based on gradient rhombic dodecahedron created by changing the unit volume between layers. Although their work showed promising results on cellular activity when cells were seeded from large pore side (1000 µm), there was no complementary study on the mechanical properties and therefore the adverse effect of discontinuity between layers on the mechanical properties were not covered.…”

Advancements in three-dimensional titanium alloy mesh scaffolds fabricated by electron beam melting for biomedical devices: mechanical and biological aspects

“…It is absolutely essential that cellular structures are characterized by adequate strength and ductility combination in conjunction with the ability to absorb high energy [1]. In this regard, a complex structure mimicking bone involving graded/gradient Ti-6Al-4V mesh structure using EBM was fabricated [82]. It was observed that graded and uniform mesh structures had an elastic regime up to the peak stress, followed by a plateau region, where the stress fluctuated (Fig.…”