Nickel–titanium (NiTi) alloys have shown promise for a variety of biomedical applications because of their unique properties of shape memory, superelasticity, and low modulus of elasticity (Young's modulus). Nevertheless, NiTi bulk components cannot be easily machined (e.g., CNC, rolling, grinding, casting, or press molding) due to their thermomechanical sensitivity as well as inherent superelasticity and shape memory. Thus, powder bed fusion (PBF) additive manufacturing has been used to successfully fabricate NiTi medical devices that match the geometric and mechanical needs of a particular patient's condition. However, NiTi PBF fabrication leaves unmelted particles from the source powder adhered to external surfaces, which cause minor dimensional inaccuracy, increase the risk of mechanical failure, and once loose, may irritate or inflame surrounding tissues. Therefore, there is a need to develop a chemical polishing (cleaning) technique to remove unmelted powder from the surfaces of PBF-fabricated implants, especially from inner surfaces that are difficult to access with mechanical polishing tools. This technique is especially useful for highly porous devices printed at high resolution. In this study, a chemical polishing method utilizing HF/HNO₃ solution was used to remove loosely attached (i.e., unmelted) powder particles from surfaces of porous, skeletal fixation plates manufactured by PBF AM. It was observed that 7 min of polishing in an HF/HNO₃ solution comprising 7.5 HF: 50 HNO₃: 42.5 H₂O enabled successful removal of all relatively loose and unmelted powder particles. A microcomputed tomography study examination found that the volumetric accuracy of the polished skeletal fixation plates was ±10% compared with the computer-aided design (CAD) model from which it was rendered. This postprocessing chemical polishing protocol is also likely to be useful for removing loose powder, while maintaining CAD model accuracy and mechanical stability for other complexly shaped, porous, three-dimensional (3D), printed NiTi devices.

中文翻译：

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增材制造的多孔镍钛骨骼固定板的化学抛光

镍钛 (NiTi) 合金因其独特的形状记忆、超弹性和低弹性模量（杨氏模量）特性，在各种生物医学应用中展现出广阔的前景。然而，镍钛块状部件由于其热机械敏感性以及固有的超弹性和形状记忆性而不易加工（例如数控、轧制、磨削、铸造或压制成型）。因此，粉末床熔融 (PBF) 增材制造已被用于成功制造符合特定患者病情的几何和机械需求的镍钛医疗设备。然而，NiTi PBF 制造会使源粉末中未熔化的颗粒粘附在外表面，这会导致微小的尺寸误差，增加机械故障的风险，并且一旦松动，可能会刺激或引起周围组织发炎。因此，需要开发一种化学抛光（清洁）技术来去除 PBF 制造的植入物表面未熔化的粉末，特别是机械抛光工具难以触及的内表面。该技术对于以高分辨率打印的高多孔器件特别有用。_{在本研究中，使用HF/HNO 3}溶液的化学抛光方法去除PBF AM 制造的多孔骨骼固定板表面上松散附着（即未熔化）的粉末颗粒。据观察，在包含7.5 HF:50 HNO ₃ :42.5 H _{2 O的HF/HNO 3}溶液中抛光7分钟能够成功去除所有相对松散且未熔化的粉末颗粒。一项微型计算机断层扫描研究检查发现，与渲染的计算机辅助设计 (CAD) 模型相比，抛光骨骼固定板的体积精度为 ±10%。这种后处理化学抛光方案也可能有助于去除松散的粉末，同时保持其他复杂形状、多孔、三维 (3D) 打印 NiTi 器件的 CAD 模型精度和机械稳定性。