Puppulin Leonardo, Negra Sara Della, Sugano Nobuhiko, Sbaizero Orfeo, Pezzotti Giuseppe
Department of Molecular Cell Physiology, Kyoto Prefectural University of Medicine, Kamigyo-ku Hirokoji agaru, Kawaramachi-dori, 602-8566 Kyoto, Japan.
Department of Industrial Engineering and Information Technology University of Trieste, 34128 Trieste, Italy.
J Mech Behav Biomed Mater. 2016 Jan;53:414-426. doi: 10.1016/j.jmbbm.2015.08.035. Epub 2015 Sep 8.
Single-step and three-step irradiated and annealed ultra-high molecular weight polyethylene (UHMWPE) hip liners have been studied by means of Raman spectroscopy (RS) and Fourier transform infrared spectroscopy (FT-IR), in order to clarify the microstructural modifications induced by in vitro oxidative degradation and wear. These spectroscopic techniques enabled us to measure profiles of oxidation index (OI), crystalline (αc), amorphous (αa), and third phase (αb) fractions along the subsurface of the acetabular cups as a function of in vitro oxidation time or after standard testing in hip simulator. Microtomed sections of the liners after accelerated aging (ASTM F2003-02) showed that oxidation profiles developed differently during the first two weeks, while all samples aged longer than 2 weeks revealed OI increasing with lower rates. The initial oxidation of the single-step-annealed material was higher than the one retrieved from the 3-step-annealed material and showed a peak of OI located at a depth of ~1mm below the exposed surface. The profiles of αc, calculated from the same sample cross-sections, followed trends similar to the respective OI profiles, which enabled a phenomenological (but quantitative) correlation between oxidation and crystallization processes to be obtained. Wear simulation under edge loading conditions was conducted on series of four samples of the above two types of irradiated and annealed materials, and for two different liner thicknesses (5.9 and 7.9 mm). The wear rates calculated at the end of the test were very low for all samples (max 2.08 mm(3)/mc for the thinner liners of the single-step irradiated and annealed material). The results indicated that there was a statistically significant increase in both wear rate and volume loss only for the thinner single-step irradiated and annealed liners. Surface analyses by Raman spectroscopy revealed distinct gradients of crystallinity, amorphous, and third phase fractions along the in-depth axis. In both types of UHMWPE materials, the worn area showed an increase of crystallinity at the expense of the third phase. Differences in crystallinity profiles observed at the wear zone of liners with different thicknesses were correlated to the higher contact stress experienced by thinner liners.
通过拉曼光谱（RS）和傅里叶变换红外光谱（FT-IR）对单步和三步辐照及退火的超高分子量聚乙烯（UHMWPE）髋臼内衬进行了研究，以阐明体外氧化降解和磨损引起的微观结构变化。这些光谱技术使我们能够测量髋臼杯亚表面的氧化指数（OI）、结晶度（αc）、非晶度（αa）和第三相（αb）分数随体外氧化时间或在髋关节模拟器中进行标准测试后的变化情况。加速老化（ASTM F2003-02）后髋臼内衬的切片显示，在前两周氧化分布的发展有所不同，而所有老化时间超过2周的样品的OI增长速率较低。单步退火材料的初始氧化程度高于三步退火材料，且OI峰值位于暴露表面下方约1mm深处。从相同样品横截面计算出的αc分布趋势与各自的OI分布相似，从而能够建立氧化与结晶过程之间的现象学（但定量）相关性。对上述两种辐照和退火材料的四个样品系列以及两种不同内衬厚度（5.9和7.9mm）进行了边缘加载条件下的磨损模拟。测试结束时计算出的所有样品的磨损率都非常低（单步辐照和退火材料较薄内衬的最大磨损率为2.08 mm(3)/mc）。结果表明，仅较薄的单步辐照和退火内衬的磨损率和体积损失在统计学上有显著增加。拉曼光谱进行的表面分析揭示了沿深度轴的结晶度、非晶度和第三相分数的明显梯度。在两种UHMWPE材料中，磨损区域的结晶度增加，第三相减少。在不同厚度内衬的磨损区域观察到的结晶度分布差异与较薄内衬所承受的较高接触应力相关。
