Pore size, external shape, and internal complexity of additively manufactured porous titanium scaffolds are three primary determinants of cell viability and structural strength of scaffolds in bone tissue engineering. To obtain an optimal design with the combination of all three determinants, four scaffolds each with a unique topology (external geometry and internal structure) were designed and varied the pore sizes of each scaffold 3 times. For each topology, scaffolds with pore sizes of 300, 400, and 500 µm were designed. All designed scaffolds were additively manufactured in material Ti6Al4V by the direct metal laser melting machine. Compression test was conducted on the scaffolds to assure meeting minimum compressive strength of human bone. The effects of pore size and topology on the cell viability of the scaffolds were analyzed. The 12 scaffolds were ultrasonically cleaned and seeded with NIH3T3 cells. Each scaffold was seeded with 1 million cells. After 32 days of culturing, the cells were fixed for their three-dimensional architecture preservation and to obtain scanning electron microscope images.
An experimental investigation was carried out to examine the seismic behaviour of three lightly reinforced concrete walls with openings subjected to reversed cyclic loading. The three specimens consisted of one solid wall as the control specimen while the other two walls were detailed with regular or irregular openings. The test results indicate that all three specimens eventually failed when the outermost reinforcing bars fractured while the concrete in the compression zone crushed and spalled severely near the base. The specimen with five openings had ultimate strength and stiffness degradation similar to the control specimen. The specimen with nine openings had a lower ultimate strength but exhibited higher ductility, slower stiffness degradation and a more significant shear contribution than the control specimen. Furthermore, strut-and-tie models were developed to predict the ultimate strength of walls with openings. The results obtained from the strut-and-tie models were found to be consistent with the experimentally observed results.
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