组织工程软骨植入缺损后修复区力学特性分析

目的利用组织工程技术建立体外软骨缺损实验模型,研究修复区人工软骨和宿主软骨的力学特性。方法采用一种琼脂糖凝胶作为人工软骨,制作猪软骨深层缺损,在缺损处仿临床植入人工软骨,用生物胶黏接,建立组织工程修复膝关节软骨缺损的体外模型;在压缩载荷作用下,通过数字图像相关技术研究组织工程软骨植入缺损后修复区即刻力学行为。结果压缩过程中界面处没有出现开裂现象,压缩分别为软骨层厚度的3.5%、5.6%、7.04%和9.0%时获得了修复区中间层应变分布图和应变变化曲线。压缩量从3.5%增加到9%时,在垂直软骨面方向上宿主软骨最大压应变增加75.9%,人工软骨最大拉应变增加226.99%;在平行软骨表面方向,交界面处最大拉应变增加116.9%,增加量远高于宿主软骨区和人工软骨区;对于修复区剪应变,随着压缩量增加交界处剪应变方向发生相反的改变。结论软骨组织工程修复缺损效果有很大的不确定性,这与修复区的力学环境有关。组织工程软骨植入缺损后,修复区受到复杂应变状态,随着压缩量增加,界面处、宿主软骨、人工软骨都发生较大的应变变化,界面处垂直软骨面方向的应变由压应变可转化为拉应变,平行软骨表面方向的拉应变有显著增加,交界处剪应变方向甚至发生了相反的改变,而且剪应力数值迅速增加。这种复杂应变状态造成修复区细胞力学环境的较大变化,还可能引起界面的开裂,影响缺损修复过程,这些力学环境变化应受到临床治疗的重视。

Mechanical properties ofinstantly repaired articular cartilage defects by tissue engineering

Objective To investigate the mechanical properties of both artificial cartilage and host cartilage by establishing the in vitro model of tissue engineered cartilage for repairing defects. Methods The agarose gel as an artificial cartilage was implanted in a deep cartilage defect connected with biological adhesive to set up the in vitro model of tissue engineered articular cartilage defects. Under the compression load, the instant mechanical behavior of the repair area was studied using the digital image correlation technology. Results There was no cracking phenomenon occurred at the interface during the compression process. The Strain distributions at middle layer of the repair area were obtained when the cartilage thickness appeared changes with 3.5%, 5.6%, 7.04% and 9.0% by the compression, respectively. When the compressing change increased from 3.5% to 9%, the maximum compressive strain of host cartilage was increased by 75.9%, and the maximum tensile strain of artificial cartilage was increased by 226.99% in the vertical direction of cartilage surface. In the direction parallel with cartilage surface, the maximum tensile strain at the interface was increased by 116.9%, and the increment was far more than that at the host cartilage area and artificial cartilage area. For shear strain at the repair area, the direction of shear strain at the interface changed oppositely with the compression increasing. Conclusions The repair effect of tissue engineered cartilage was uncertain due to the mechanical environment of the repair area. After the tissue engineered cartilage was implanted in the defect, the repair area was under the influence of complex strain states. The strains changed greatly at the interface both with the host cartilage and artificial cartilage as the compression increasing. The strain in the vertical direction of cartilage surface at the interface might change from compressive stain to tensile strain, which was significantly increased in the direction parallel with cartilage surface. The strain direction at the interface could even be changed oppositely, and the shear strain appeared rapidly increase. The complex strain states lead to such great changes in mechanical environment of the defect area, and may cause cracking at the interface, and even further affect the repair process. Therefore, attention should be given to this complex mechanical environment during cartilage defect repair process in clinical treatment.