Pöllänen Raimo, Tikkanen Anna-Maria, Lammi Mikko J, Lappalainen Reijo
BioMater Center, University of Eastern Finland, Kuopio, Finland.
J Appl Biomater Biomech. 2011 Jan-Apr;9(1):47-53. doi: 10.5301/JABB.2011.6472.
New methodology for long-term (270 h) biomechanical testing with living cartilage was developed. Polyurethane (PU) implant material was compared with stainless steel and reference samples in static unconfined compressive loading conditions on cartilage to provide a basis for dynamic testing of novel PU implant materials under conditions that simulate an articulating human knee joint.
Custom-made tools and techniques were developed to prepare cylindrical samples from bovine patella with cartilage including subchondral bone. Specific incubator cups with static loading setups for a culture incubator were manufactured to keep bovine cartilage explants alive in cell culture conditions under unconfined static compressive loading (0.25 MPa) for 270 h (11.25 d). Four loading conditions of cartilage were studied: free (FREE), restrained minimal loading (RESTR), loading with a metal plate (MEW) and loading with polyurethane (PUW).
After static loading for 270 h, cartilage biomechanical tests indicated clear differences between the groups in frequency dependent dynamic stiffness curves. Surprisingly, the PU curves were closest to the FREE sample curves. Those with load and direct contact with metal (MEW) became significantly stiffer, while restrained samples became softer. Significant differences (p<0.05, Mann-Whitney's U test) in cell vitality between samples from various groups could be seen in fluorescein diacetate (FDA) and propidium iodide (PI) stained samples by confocal microscopic analysis. The approximate mean percentages of living cells after 270 hours cultivation were: FREE 87%, MEW 3%, PUW 35%, and RESTR 66%. Test results indicate that it is possible to keep cartilage cells alive in cell culture incubator conditions for two weeks period under a 0.25 MPa unconfined static loading. The FREE samples were most successful and cells loaded with PU were more vital than cells loaded with metal.
Based on the results, PU seems to be more compatible material than surgical steel in contact with living cartilage. Because of a large variation in the quality of bovine cartilage material from different animals, special care is necessary when selecting specimens to guarantee reliable and reproducible results.
开发了一种用于对活软骨进行长期（270小时）生物力学测试的新方法。在软骨的静态无侧限压缩加载条件下，将聚氨酯（PU）植入材料与不锈钢及参考样品进行比较，为在模拟人体膝关节活动的条件下对新型PU植入材料进行动态测试提供依据。
开发了定制工具和技术，以从带有软骨（包括软骨下骨）的牛髌骨制备圆柱形样品。制造了用于培养箱的带有静态加载装置的特定培养杯，以使牛软骨外植体在无侧限静态压缩加载（0.25MPa）下于细胞培养条件下存活270小时（11.25天）。研究了软骨的四种加载条件：自由（FREE）、受限最小加载（RESTR）、用金属板加载（MEW）和用聚氨酯加载（PUW）。
在静态加载270小时后，软骨生物力学测试表明，各实验组在频率依赖性动态刚度曲线方面存在明显差异。令人惊讶的是，PU曲线最接近FREE样品曲线。那些受到加载并与金属直接接触（MEW）的样品变得明显更硬，而受限样品则变得更软。通过共聚焦显微镜分析，在荧光素二乙酸酯（FDA）和碘化丙啶（PI）染色的样品中，可以看到不同组样品之间细胞活力存在显著差异（p<0.05，曼-惠特尼U检验）。培养270小时后活细胞的近似平均百分比为：FREE 87%，MEW 3%，PUW 35%，RESTR 66%。测试结果表明，在0.25MPa无侧限静态加载下，有可能在细胞培养箱条件下使软骨细胞存活两周。FREE样品最为成功，加载PU的细胞比加载金属的细胞更具活力。
基于这些结果，在与活软骨接触时，PU似乎是比外科手术用钢更具相容性的材料。由于不同动物的牛软骨材料质量差异很大，在选择标本时需要特别小心，以确保结果可靠且可重复。
