Page 128 - IJB-8-1

Compression Failure of Trabecular Tantalum Scaffolds
Guangdong, China) at room temperature (25°C). Relative Inc., Oberkochen, Germany) before metallographic
density was calculated by dividing the actual weight (W ) sample preparation.
1
by the theoretical weight (W ) of the macrovolume using
2
a theoretical density (16.6 g/cm ) of pure Ta. The porosity (2) Metallographic sample preparation
2
of scaffolds was obtained using the formula as follows: Post-compressive AM trabecular Ta scaffolds were
prepared to metallographic specimens through the
 W  vacuum pressure impregnation resin (VPIR) method .
[28]
Porosity(%) = 1 − 1  ×100 (1) Twenty gram of acrylic powder (G90500, Gaopin


W 
Precision Instrument Co., Ltd., Kunshan, Jiangsu, China)
2
The microstructural characteristics of AM- and 40 ml liquid hardener (G90400, Gaopin Precision
fabricated porous Ta scaffolds were visualized using hot Instrument Co., Ltd., Kunshan, Jiangsu, China) were
field emission scanning electron microscopy (FESEM) mixed and stirred uniformly at room temperature (25°C).
(MERLIN Compact, Carl Zeiss Inc., Oberkochen, Metallographic inlay molds (φ20 mm × H20 mm) were
Germany) equipped with energy-dispersive X-ray used to prepare metallographic specimens. Vacuum
spectroscopy (EDS), which was used to ascertain the defoaming (SIE-MIX80, SIENOX Co., Ltd., Guangzhou,
chemical compositions of the samples. Guangdong, China) was employed to exhaust the air
that remained in porous Ta scaffolds, making the resin
2.3. Mechanical testing solution fully infiltrate into the pores of scaffolds. Then,

To evaluate the mechanical properties of AM- the metallographic specimens were placed at room
fabricated cylindrical trabecular Ta scaffolds (φ10 mm temperature for 12 h to complete resin solidification. In
× H10 mm), 6 samples (n = 6) from each group (65%, addition, an uncompressed porous Ta metallographic
75%, and 85%) were subjected to uniaxial static sample was prepared for each porosity as the control
compression testing at room temperature (25°C). group.
Compression tests were performed in accordance with
ISO 13314:2011 (mechanical testing of metals-ductility (3) Grinding and polishing
testing-compression test for porous and cellular Grinding and polishing of as-prepared metallographic
metals) using mechanical testing machine (max. 5 kN, specimens were conducted by a metallographic sample
Instron 4301, Instron Company, Norwood, MA, USA) grinding and polishing machine (YMP-2B, Metallurgical
equipped with an extensometer (YSJ50/5-ZC, Suzhou Equipment Co., Ltd., Shanghai, China) with a sandpaper
Shenghui Precision Instrument Technology Co., Ltd., diameter of 230 mm. Metallographic specimens were
Suzhou, Jiangsu, China). A constant deformation rate ground using 100, 200, 400, 800, 1200, 1500, and 2000
of 0.5 mm/min was applied during compression tests. SiC papers and then polished by diamond suspensions with
Each specimen was compressed to 50% strain to sizes of 5, 2, and 0.5 μm. To achieve the same polished
obtain stress–strain curves. The elastic modulus (E) cross section, 3 metallographic specimens of each porosity
as the gradient of the straight line was calculated from were ground under an identical extent and direction.
the linear deformation region at the beginning of the The schematic of porous Ta metallographic sample
compressive stress–strain curve. The compressive 0.2% preparation is presented in Figure 2. The morphological
offset stress was identified from the stress–strain curve characterizations of the metallographic specimens were
as the yield strength (σ ). observed by electron backscattered diffraction (EBSD,
y
2.4. Experimental study of compressive behavior Carl Zeiss Inc., Oberkochen, Germany).
and material failure 2.5. FEA
(1) Static compression testing FEA was performed to simulate the mechanical behaviors

To obtain the initial stages of trabecular Ta scaffolds after of trabecular Ta scaffolds under quasi-static compressive
collapse under static compressive loading, 10%, 15%, loading by Abaqus/CAE 2020 (Dassault Systemes
and 20% strain were set for specimens with 65%, 75%, Simulia Co., Johnston, RI, USA). Considering the
and 85% porosities, respectively. Two specimens of each simulation efficiency and required accuracy, a 5 mm ×
porosity (annealed and unannealed) were prepared for 5 mm (diameter × height) model with the same porous
compression tests with an identical strain. Compression structure characteristics as the as-fabricated samples were
tests were performed under the same equipment and applied in this simulation. Ten-node quadratic tetrahedron
deformation rate as mechanical tests described above. (C3D10) with an element size of 0.08 mm was chosen to
Post-compressive microstructures of all samples were mesh this FEA model, and material properties were set
observed by hot FESEM (MERLIN Compact, Carl Zeiss according to pure Ta, consisting of an elastic modulus of

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