Geometric shapes of tissue-engineered cartilage exert effects on mechanical behaviors of a defected area

doi:10.3969/j.issn.2095-4344.0819

Abstract

Abstract:

BACKGROUND: Uncertainty of repairing articular cartilage defects is highly associated with the mechanical behaviors of the defected area, and the mechanical environment varies with the defect shape, depth and load.
OBJECTIVE: To study the mechanical behaviors of articular cartilage defects under physiological load by finite element analysis.
METHODS: The axisymmetric model of articular cartilage injury and repair based on transversely isotropy was established using ABAQUS software. The mechanical behaviors of the defect zone repaired with different repair shapes (cylindrical, frustum of a cone, orthorhombic prism, elliptical column) and depths of tissue-engineered cartilage under compressive load were analyzed.
RESULTS AND CONCLUSION: The simulation results showed that there were significant differences in the mechanical behaviors of the defect area repaired with tissue-engineered cartilage in different shapes and depths. The stress concentration was the most obvious at the middle-layer defect repair, and the stress distribution was more reasonable at the deep (whole) layer defect repair. Furthermore, the distribution of the stress field and the liquid flow field at the cylinder-shaped tissue-engineered cartilage repair was the closest to the normal cartilage. That is to say, the tissue-engineered cartilage in cylinder or frustum-cone shape is recommended to repair cartilage defect. Importantly, the middle-layer repair is inadvisable.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: Cartilage, Numerical Analysis, Computer-Assisted, Stress, Mechanical, Tissue Engineering

CLC Number:

R318

Zhao Yong-zheng1, 2, Liu Hai-ying1, 2, Zhang Chun-qiu1, 2, Hu Ya-hui1, 2. Geometric shapes of tissue-engineered cartilage exert effects on mechanical behaviors of a defected area[J]. Chinese Journal of Tissue Engineering Research, 2018, 22(16): 2489-2495.

Figures/Tables 4

2 模拟结果分析 Simulation analysis 通过对修复区整体的Mises应力、液相流场的分布，选定路径(path1)上各点随层深的应力、流速的变化，及指定点(位置一)的孔隙压力随时间的变化情况进行分析。研究弹性模量为0.3 MPa、松比为0.2的TEC修复不同缺损形状、缺损深度的宿主软骨时修复区的力学环境，从而确定适于临床修复的TEC构形指标。由于工程化TEC相比于宿主软骨劣质的力学性能，使得修复区力学环境奇异化，因此，本文选取了宿主软骨内距修复边界为0.5 mm的路径path1，及修复边界上位置一处的一点，便于比较构形参数对修复区各力学环境参数的影响，如图6。 2.1 不同修复深度对修复区力学行为的影响 2.1.1 Mises应力分析为探求修复层深对修复区力学环境的影响，本文首先选取圆柱形TEC进行分析，当压缩量为10%时，不同层深缺损修复的Mises应力云图，如图7所示。从图中可见，浅表层、中间层和深层缺损修复时，应力集中都发生在底部粘合交界处的正下方，另外深层修复时，TEC与宿主软骨侧面粘合交界处下半部分应力也开始逐渐增大，如图7A-C；全层缺损修复时，在侧面粘合交界处下部出现应力集中，如图7D，该现象与文献[11]中，当滚子滑到修复位置时的结果接近。对于宿主软骨，应力极值随着修复深度的增减逐渐减小，如图8所示，而对于TEC来说，中间层修复时应力极值最大。综合比较而言，深层或全层缺损益于修复区整体受力。 2.1.2 位置一处孔隙压力变化当载荷作用在软骨上时，软骨内液体压力瞬间增大以承担外载荷，使固体基质免受高应力破坏，随着液体在软骨内流动，载荷逐渐过渡到由固相承担，直至平衡。文中截取加载前20 s，研究位置一处在不同缺损修复深度时孔隙压力的变化曲线，如图9。与无损软骨相比，TEC植入会降低基质的孔隙压力值即液相的承载能力，且随着软骨缺损修复深度增加，孔压值减小的越多，修复效果会越差。中间层、深层和全层缺损修复软骨孔压值相差不大，由前文分析知中间层修复极值应力最大，故若患者软骨为表层以下缺损，可考虑把缺损延伸到深层和全层。 2.2 不同修复形状对修复区力学行为的影响研究表明不同层深缺损修复均改变了软骨修复区的力学环境，而中间层缺损修复时应力奇异化现象最显著，接下来探讨不同修复形状对中间层缺损修复区力学行为的影响。 2.2.1 Mises应力分析数值模拟研究了不同截面形状TEC修复中间层缺损时修复区的Mises应力分布，见图10。图10A为半径2 mm、高0.8 mm圆柱；图10B为底面半径 2 mm、侧面轮廓线与垂线夹角为10°的圆台；图10C、D为短半轴2 mm、长半轴2.5 mm的椭圆柱；图10E为4 mm× 4 mm×0.8 mm正四棱柱；10F为无缺损情况。可见，TEC与宿主软骨在底侧粘合处均出现应力极值。底部粘合界面处宿主软骨应力大于TEC，表层粘合界面处TEC应力大于"

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