Page 126 - IJB-8-1

Compression Failure of Trabecular Tantalum Scaffolds
1. Introduction mechanical properties. Wauthle et al. applied LPBF
[5]
to fabricated porous Ta scaffolds comprising of rhombic
Porous tantalum (Ta) scaffolds have attracted immense dodecahedron unit cells for the 1 time. Compression tests
st
interest in bone tissue engineering owing to their and biological evaluation suggested that these scaffolds
excellent physicochemical and biological properties, exhibited desirable mechanical properties and enhanced
including outstanding corrosion resistance, excellent osteogenesis and osteointegration. Wang et al. fabricated
[7]
ductility, non-cytotoxicity, and superior bioactivity and porous Ta scaffolds with diamond unit cells by LPBF and
biocompatibility [1-3] . Numerous biological studies in vitro
and in vivo have confirmed that Ta scaffolds can effectively achieved good osteointegration performance through
[9]
promote osteoblast adhesion, proliferation, differentiation, animal experiments. Guo et al. compared the biological
performance of porous Ta scaffolds with that of porous
and mineralization, and have superior osteoconductivity, Ti6Al4V scaffolds fabricated by LPBF and reported
osteointegration, and vascularization [4-7] . Furthermore, that porous Ta scaffolds showed better biocompatibility
the in vitro biological performance and in vivo bone
ingrowth of Ta scaffolds are superior compared to those and osteointegration than porous Ti6Al4V scaffolds.
of Ti6Al4V scaffolds [8,9] . Therefore, porous Ta scaffolds Therefore, AM, especially LPBF-based AM, is expected
are considered the promising third-generation bone repair to become the mainstream fabrication method for porous
materials. At present, major challenges in the development Ta scaffolds in the future.
of porous Ta scaffolds are fabrication, structural design The trabecular lattice is an irregular structure, which
and optimization. has attracted great interest in bone tissue engineering
Ta processing is hampered by the high melting due to the similarity of its micro-architecture to that of
temperature of Ta (2996°C) . Porous Ta scaffolds are a natural bone and good interconnectivity suitable for
[10]
[23]
typically fabricated by chemical vapor deposition (CVD), bone implants. Liu et al. designed a trabecular bone
powder metallurgy (PM), and additive manufacturing structure derived from micro-computed tomography
(AM). In CVD, a Ta coating is deposited on a low- images of cancellous bone and fabricated trabecular
density vitreous carbon skeleton by a chemical reaction to porous titanium (Ti) scaffolds by LPBF, achieving a
prepare porous Ta scaffolds . Since the CVD-fabricated good match of morphological accuracy and mechanical
[11]
[24]
porous Ta acetabular cup was introduced (Trabecular properties to those of the natural bone. Wang et al.
Metal , Zimmer, Warsaw, IN, USA) in the early 2000s, constructed controllable irregular structures based on the
TM
commercially available CVD-fabricated porous Ta Voronoi–Tessellation method and fabricated trabecular
implants have been applied to bone defect repair and porous Ti6Al4V scaffolds with predictable porosity and
bone disease treatment with excellent clinical results [12-14] . mechanical behavior by LPBF. However, studies on
However, this technique is complicated and expensive trabecular porous Ta scaffolds fabricated by AM were
with poor control over the porous structure and outer rarely reported. In our laboratory, we have successfully
geometry to fabricate patient-specific and anatomically fabricated trabecular porous Ta scaffolds using LPBF
matching implants. Using PM, porous Ta scaffolds are and investigated their pore structure characteristics and
[25]
manufactured by removing space-holding materials comprehensive mechanical properties . However,
through high-temperature sintering or dissolution [15-17] . mechanical behavior evaluation is required prior to their
However, PM-fabricated porous Ta scaffolds present deployment in clinical research.
closed or isolated pores, resulting in poor interconnectivity In this work, we used LPBF-based AM to fabricate
and osteointegration . Compared with CVD and PM, AM innovative trabecular Ta scaffolds with various porosities
[2]
is a more versatile and effective technology to customize (65%, 75%, and 85%). Morphological evaluation was
porous bone implants with complicated geometries that conducted to analyze the microstructural characteristics
match anatomical shapes and meet personalized treatment of as-prepared samples. The mechanical behavior and
requirements. Laser powder bed fusion (LPBF), an AM material failure mechanism of AM trabecular Ta scaffolds
technology, employs high-energy lasers to selectively were investigated by compression testing, finite element
melt the pre-laid metal powder on the build platform analysis (FEA), and microscopic observations.
layer by layer according to a pre-designed CAD model
to manufacture fully dense functional parts with complex 2. Materials and methods
geometries and well-designed open porous structures [18-20] . 2.1. Design and manufacturing
LPBF allows rapid fabrication of parts with complex
geometries and relatively high mechanical performance A stochastic porous structure based on Voronoi tessellation
directly from powders without the time-consuming mold was designed by the Grasshopper plug-in in Rhinoceros
design process [21,22] . Due to its high precision, LPBF has 6.0 (Robert McNeel and Associates, Seattle, WA, USA)
recently been used to fabricate Ta-based structures with and was saved in the STL format. First, we constructed a
controllable porosity/pore geometry and predictable three-dimensional (3D) Voronoi diagram with randomly-

112 International Journal of Bioprinting (2022)–Volume 8, Issue 1