Measurement of mechanical properties of vascular smooth muscle and blood vessel wall as a model of functional materials

为了估计血管壁上平滑肌细胞（SMCs）的力学环境，我们测量了SMCs的力学性能及其在壁上的微观残余应力和应变：我们用原始的拉伸测试仪测量了刚从培养基中分离出来的SMCs的准静态拉伸性能，发现它们的力学性能与细胞内肌动蛋白丝（AFs）密切相关。我们还测量了它们的应力松弛特性，发现应力松弛过程可以分为两个阶段：以一分钟为时间常数的快速被动松弛阶段和以一小时为时间常数的缓慢主动阶段。然后，我们建立了一种方法来阐明由同心层的SMCs和弹性层板（ELs）组成的主动脉壁的微观力学环境。为了估计el和SMCs在体内状态下的应力，我们从10 μm厚的主动脉壁切片上酶解分离el，以获得它们的拉伸性能。隔离后，el的波纹几乎消失，表明el的波纹是由于其压缩残余应变引起的屈曲。在拉伸试验中，根据核长度估计了SMCs的残余应力和应变。组织中恢复核长度所需的拉应力及其伴随应变作为微观残余应力和应变，分别为10 kPa和23%。根据本研究获得的数据和均匀主动脉壁的应变分布计算el和SMCs的体内应力。它们是墙体平均环向应力的80-40%。造成这种不一致的原因可能是1)SMCs的力学性能是在完全松弛状态下测量的，2)没有考虑胶原纤维。

To estimate mechanical environment of smooth muscle cells (SMCs) in the vessel wall, we measured mechanical properties of SMCs and their microscopic residual stress and strains in the wall : We measured quasi-static tensile properties of SMCs freshly isolated from the media with our original tensile tester to find that their mechanical properties have a close correlation with intracellular actin filaments (AFs). We also measured their stress relaxation properties to find that stress relaxation process could be separated into two phases : fast passive relaxation phase with a time constant in the order of a minute and slow active phase with a time constant in the order of an hour. Then, we established a method to elucidate microscopic mechanical environment for the aortic walls composed of concentric layers of SMCs and elastic laminas (ELs). To estimate stresses in the ELs and SMCs in the in vivo state, ELs were isolated enzymatically from 10-μm-thick slices of aortic walls to obtain their tensile properties. Upon isolation, corrugation of the ELs almost disappeared, indicating that the corrugation was buckling of the ELs due to their compressive residual strain. Residual stress and strain in the SMCs were estimated in their tensile test by referring to their nuclear length. Tensile stress required to restore the nuclear length in tissue and its concomitant strain was obtained as microscopic residual stress and strain and was found to be 10 kPa and 23%, respectively. In vivo stresses in the ELs and SMCs were calculated from data obtained in the present study and strain distribution obtained for homogeneous aortic wall. They were 80-40% of the mean hoop stress of the wall. Such inconsistency might be caused because 1) mechanical properties of SMCs were measured under fully relaxed state, and 2) collagen fibers were not taken into consideration.