McEntire Bryan J, Enomoto Yuto, Zhu Wenliang, Boffelli Marco, Marin Elia, Pezzotti Giuseppe
AMEDICA Corporation, 1885 West 2100, South Salt Lake City, UT 84119, USA.
Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8126 Kyoto, Japan.
J Mech Behav Biomed Mater. 2016 Feb;54:346-59. doi: 10.1016/j.jmbbm.2015.08.044. Epub 2015 Sep 12.
Raman microprobe-assisted indentation, a micromechanics method validated in a companion paper, was used to compare the surface toughening behaviors of silicon nitride (Si3N4) and alumina-based bioceramics employed in joint arthroplasty (i.e., monolithic alumina, Al2O3, and yttria-stabilized zirconia (ZrO2)-toughened alumina, ZTA). Quantitative assessments of microscopic stress fields both ahead and behind the tip of Vickers indentation cracks propagated under increasing indentation loads were systematically made using a Raman microprobe with spatial resolution on the order of a single micrometer. Concurrently, crack opening displacement (COD) profiles were monitored on the same microcracks screened by Raman spectroscopy. The Raman eye clearly visualized different mechanisms operative in toughening Si3N4 and ZTA bioceramics (i.e., crack-face bridging and ZrO2 polymorphic transformation, respectively) as compared to the brittle behavior of monolithic Al2O3. Moreover, emphasis was placed on assessing not only the effectiveness but also the durability of such toughening effects when the biomaterials were aged in a hydrothermal environment. A significant degree of embrittlement at the biomaterial surface was recorded in the transformation-toughened ZTA, with the surface toughness reduced by exposure to the hydrothermal environment. Conversely, the Si3N4 biomaterial experienced a surface toughness value independent of hydrothermal attack. Crack-face bridging thus appears to be a durable surface toughening mechanism for biomaterials in joint arthroplasty.
拉曼微探针辅助压痕是一种在配套论文中得到验证的微力学方法，用于比较关节置换术中使用的氮化硅（Si3N4）和氧化铝基生物陶瓷（即整体氧化铝、Al2O3以及氧化钇稳定氧化锆（ZrO2）增韧氧化铝、ZTA）的表面增韧行为。使用空间分辨率约为一微米的拉曼微探针，系统地对在不断增加的压痕载荷下扩展的维氏压痕裂纹尖端前方和后方的微观应力场进行了定量评估。同时，在通过拉曼光谱筛选出的相同微裂纹上监测裂纹开口位移（COD）曲线。与整体Al2O3的脆性行为相比，拉曼观察清楚地显示了增韧Si3N4和ZTA生物陶瓷中起作用的不同机制（分别为裂纹面桥接和ZrO2多晶型转变）。此外，重点不仅放在评估这种增韧效果的有效性上，还放在评估生物材料在水热环境中老化时这种增韧效果的耐久性上。在相变增韧的ZTA中记录到生物材料表面有显著程度的脆化，其表面韧性因暴露于水热环境而降低。相反，Si3N4生物材料的表面韧性值与水热侵蚀无关。因此，裂纹面桥接似乎是关节置换术中生物材料一种持久的表面增韧机制。
