Residual powder is a defect in powder bed fusion-based additive manufacturing (3D printing), and it is difficult to completely remove it from as-printed materials. In addition, it is not necessary to apply 3D printed implants with residual powder in the clinic. The immunological response triggered by the residual powder is an important area of study in medical research. To further understand the possible immunological reactions and hidden dangers caused by residual powders in vivo, this study compared the immunological reactions and osteolysis caused by typical powders for four implant materials: 316 L stainless steel, CoCrMo, CP-Ti, and Ti-6Al-4V (particle size range of 15–45 μm), in a mouse skull model. Furthermore, the possible immunological responses and bone regeneration induced by the four 3D printed implants with residual powder in a rat femur model were compared. In the mouse skull model, it was found that the 316L-S, CoCrMo-S, and especially the 316L-M powders, upregulated the expression of pro-inflammatory factors, increased the ratio of RANKL/OPG, and activated more functional osteoclasts, resulting in more severe bone resorption compared with those in other groups. In the rat femur model, which is more suitable for clinical practice, there is no bone resorption in implants with residual powders, but they show good bone regeneration and integration ability because of their original roughness. The results indicate that the expressions of inflammatory cytokines in all experimental groups were the same as those in the control group, showing good biological safety. The results answered some critical questions related to additively manufactured medical materials in vivo and indicated that as-printed implants may have great potential in future clinical applications.

Graphical Abstract

中文翻译：

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残留的 3D 打印金属粉末对免疫反应和骨再生的影响：体内研究

残留粉末是基于粉末床熔融的增材制造（3D打印）的缺陷，并且很难从打印材料中完全去除它。此外，没有必要在临床上应用残留粉末的3D打印植入物。残留粉末引发的免疫反应是医学研究的一个重要研究领域。为了进一步了解残留粉末在体内可能引起的免疫反应和隐患，本研究比较了4种植入材料：316L不锈钢、CoCrMo、CP-Ti和Ti-6Al-典型粉末引起的免疫反应和骨溶解。 4V（颗粒尺寸范围为 15–45 μm），在小鼠头骨模型中。此外，比较了四种带有残留粉末的 3D 打印植入物在大鼠股骨模型中诱导的可能的免疫反应和骨再生。在小鼠颅骨模型中，发现316L-S、CoCrMo-S，尤其是316L-M粉末上调促炎因子的表达，增加RANKL/OPG的比率，并激活更多功能性破骨细胞，与其他组相比，导致更严重的骨吸收。在更适合临床的大鼠股骨模型中，残留粉末的植入物没有出现骨吸收，但由于其原有的粗糙度而表现出良好的骨再生和整合能力。结果表明,各实验组炎症细胞因子的表达量与对照组相同, 显示出良好的生物安全性。结果回答了与体内增材制造医疗材料相关的一些关键问题，并表明打印的植入物在未来的临床应用中可能具有巨大的潜力。

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