MgAl₂O₄ spinel mesh with micro-features of 410 and 250 μm unit cell length and rib thickness, respectively, was three-dimensional (3D) printed and sintered followed by Hot Isostatic Pressing (HIPing). A stable colloidal dispersion of spinel in polymer-water solution was prepared and 3D-printed using a 30-gauge needle (∼100 μm inner diameter) on a regenHU 3D-Discovery bioprinter. Samples were characterized for their density and microstructure. Samples with near theoretical density after HIPing was subjected to mechanical property evaluation such as hardness by Vickers indentation and elastic modulus using nanoindentation technique. Microstructure of sintered samples across the ribs have shown graded grain structure with finer grains near the edges (0.7 μm average) with occasional porosity and coarser grains toward the center of the rib (5.2 μm average). HIPing resulted in substantial grain growth and the average grain size was found to be 10.9 μm (with a variation in the grain size of 2.2 μm along the edges and 13.1 μm at the center of the rib) exhibiting close packed and dense microstructure. Finer grains toward the edges may probably be due to the flow behavior during printing process and lower distribution of the powder loading along the edges resulting in low green density. This relatively higher porosity pining the grain growth under the extremely low heating rate employed for the controlled shrinkage to maintain the integrity of the sample. 3D printed samples after HIPing exhibited a density of 3.57 g/cc and hardness of 12.95 GPa, which are at par with the samples processed through conventional ceramic processing techniques. Nanoindentation studies employing maximum load of 45 mN with depth have shown an elastic modulus of 238 ± 15 GPa. MgAl₂O₄ spinel mesh 3D printed in this study is a potential prospective candidate that can be explored for cranioplasty procedures and other biomedical applications.

中文翻译：

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MgAl2O4尖晶石网格的3D打印和通过无压烧结和热等静压致密化

具有分别为410和250μm晶胞长度和肋厚度的微观特征的MgAl ₂ O ₄尖晶石网格通过三维(3D)打印和烧结，然后进行热等静压(HIPing)。制备了尖晶石在聚合物水溶液中的稳定胶体分散体，并使用 30 号针（内径约 100 μm）在 regenHU 3D-Discovery 生物打印机上进行 3D 打印。对样品的密度和微观结构进行了表征。对热等静压处理后具有接近理论密度的样品进行机械性能评估，例如通过维氏压痕技术评估硬度，并使用纳米压痕技术评估弹性模量。肋上烧结样品的微观结构显示出分级晶粒结构，边缘附近有较细的晶粒（平均 0.7 μm），偶尔有孔隙，肋中心的晶粒较粗（平均 5.2 μm）。HIPing 导致显着的晶粒生长，平均晶粒尺寸为 10.9 μm（沿边缘的晶粒尺寸变化为 2.2 μm，肋中心的晶粒尺寸变化为 13.1 μm），呈现出密排且致密的微观结构。朝向边缘的更细的颗粒可能是由于印刷过程中的流动行为以及沿边缘的粉末负载分布较低导致生坯密度较低。这种相对较高的孔隙率在极低的加热速率下抑制晶粒生长，以控制收缩以保持样品的完整性。HIPing 后的 3D 打印样品的密度为 3.57 g/cc，硬度为 12.95 GPa，与通过传统陶瓷加工技术加工的样品相当。采用 45 mN 最大载荷和深度的纳米压痕研究显示弹性模量为 238 ± 15 GPa。本研究中 3D 打印的MgAl ₂ O ₄尖晶石网是一种潜在的候选材料，可用于颅骨成形术和其他生物医学应用。