Bansiddhi A, Dunand D C
Department of Materials Science and Engineering, Northwestern University, Cook Hall 2220 Campus Drive Evanston, IL 60208, USA.
Acta Biomater. 2008 Nov;4(6):1996-2007. doi: 10.1016/j.actbio.2008.06.005. Epub 2008 Jun 27.
NiTi foams were created with a structure (32-36% open pores 70-400 microm in size) and mechanical properties (4-25 GPa stiffness, >1000 MPa compressive strength, >42% compressive ductility, and shape-memory strains up to 4%) useful for bone implant applications. A mixture of NiTi and NaCl powders was hot-isostatically pressed at 950 and 1065 degrees C and the NaCl phase was then dissolved in water. The resulting NiTi foams show interconnected pores that replicate the shape and size of the NaCl powders, indicating that NiTi powders densified significantly before NaCl melted at 801 degrees C. Densifying NiTi or other metal powders above the melting point of the space-holder permits the use of NaCl, with the following advantages compared with higher-melting, solid space-holders such as oxides and fluorides used to date: (i) no temperature limit for densification; (ii) lower cost; (iii) greater flexibility in powder (and thus pore) shape; (iv) faster dissolution; (v) reduced metal corrosion during dissolution; (vi) lower toxicity if space-holder residues remain in the foam.
镍钛泡沫材料具有适合骨植入应用的结构（32 - 36%的开孔，尺寸为70 - 400微米）和机械性能（4 - 25吉帕的刚度、>1000兆帕的抗压强度、>42%的压缩延展性以及高达4%的形状记忆应变）。将镍钛粉末和氯化钠粉末的混合物在950和1065摄氏度下进行热等静压，然后将氯化钠相溶解于水中。所得的镍钛泡沫材料呈现出相互连通的孔隙，这些孔隙复制了氯化钠粉末的形状和尺寸，这表明镍钛粉末在氯化钠于801摄氏度熔化之前就已显著致密化。在空间支撑体的熔点以上对镍钛或其他金属粉末进行致密化处理，使得能够使用氯化钠，与迄今使用的诸如氧化物和氟化物等高熔点固体空间支撑体相比，具有以下优点：（i）致密化无温度限制；（ii）成本更低；（iii）在粉末（进而孔隙）形状方面具有更大的灵活性；（iv）溶解速度更快；（v）溶解过程中金属腐蚀减少；（vi）如果空间支撑体残留物残留在泡沫材料中，毒性更低。
