细胞迁移中的边缘束缚现象的实验与理论研究

细胞在体内处于一个三维（3D）的微环境中，细胞微环境对于维持正常生理状态和疾病的发生与发展都具有重要作用。其中，微环境中的几何形貌对细胞迁移过程中的细胞粘附、细胞形状和细胞骨架等都有显著的影响，然而，其背后的机制仍在探索中。

本文利用光刻技术制备了聚二甲基硅氧烷微槽基底，然后将新生大鼠心肌细胞、人骨肉瘤细胞（MG63）与成纤维细胞种植在凹槽基底上，并对细胞进行免疫荧光染色与活细胞成像实验。从实验中观察到距离边界5 μm以内的细胞均沿着边界伸长，与边界对齐，具有较大的长宽比，面积相对较小。在MG63活细胞成像中观察到在边界附近的细胞倾向于沿着边界迁移。而一开始不在边界附近的细胞，伸展和迁移的方向没有特定性。

在前人的接触引导实验中使用的几何形貌大多数是微槽基底，细胞在宽度为20～60 μm的双侧壁凹槽内沿着凹槽伸长和迁移。这类实验现象可以简单地解释为细胞受到双侧壁的空间限制的结果。在本实验中使用了宽度约为150 μm的凹槽，这比单个细胞的尺寸大很多，因此双边限制不再成立。令人惊讶的是，本实验发现位于凹槽边缘的细胞，虽然只受到单侧壁的影响，但是仍然沿着边缘伸长和迁移。这与直觉相悖，因为细胞可以从边缘迁移到开放区域。我们称该实验结果为细胞迁移中的边缘束缚现象。

我们对该现象的解释如下：当圆形细胞开始伸展时，边界的几何引导打破了细胞的圆形对称性，根据弹性力学分析，黏着斑的牵引力在细胞的两端附近达到极值；假设黏着斑的力、片状足伸出和应力纤维空间取向之间存在正反馈，细胞将在两端进一步伸长，并沿边缘迁移。

弹性力学的分析是利用有限元计算完成的，在边界处的细胞形状被设置成3D条状，本构关系设置成横观各向异性，细胞骨架上施加“温度应变”来模拟应力纤维的主动收缩。仿真结果显示细胞与基底接触的边界上的支反力由中间向两侧逐渐增加。另外，当长轴与其他方向的刚度比值增大时，细胞横观各向异性将会更加明显，这也会导致牵引力变得更加集中在两端。

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