Development of a micro tensile tester for the in-process monitoring of cell structure

在这项为期3年的研究中，我们开发了一种微型拉伸测试仪，可以测量单个分离细胞的拉伸性能，同时观察拉伸过程中细胞内结构的变化。将细胞的两端用玻璃微量移液管（3- 15 mm，I.D.）用细胞粘合剂（Cell-Tak）包被，用电动操作器（MMS-77，Shimadzu）移动一个移液管，以在显微镜（BX 50 WI，Olympus）下拉伸细胞。通过另一移液管的悬臂部分的偏转来测量施加到细胞的力。为了获得其清晰的图像，在正置显微镜下用水浸物镜观察细胞。为了使细胞操作更容易，显微镜的载物台被固定，物镜被移动以调整焦点。采用组织块法（P6-7）获得的牛主动脉平滑肌细胞（BASMs）和酶分散法获得的大鼠主动脉平滑肌细胞（RASMs）在37℃的生理盐溶液中用该测试仪成功拉伸，以获得其拉伸性能。不同拉伸速率下的拉伸实验表明，当应变速率大于4%/s时，电池的初始弹性模量与应变速率呈显著正相关。在0.2- 4%/s的应变速率下，BASMs和RASMs的弹性模量分别约为3 kPa和12 kPa。由于细胞制备方法的差异，认为BASM和RASM分别显示合成和收缩表型。收缩细胞比合成细胞含有更多的收缩蛋白。收缩蛋白质可能比细胞质硬。因此，收缩细胞可能比合成细胞更硬。在本研究中，BASMs和RASMs的机械性能的差异可能是由于两种细胞标本的表型差异。

In this 3-year study, we have developed a micro tensile tester to measure tensile properties of a single isolated cell and to observe change in intracellular structure during stretching simultaneously. Both ends of the cell were aspirated with glass micropipettes (3-15mm in I.D.) coated with cellular adhesive (Cell-Tak), and one pipette was moved with an electrical manipulator (MMS-77, Shimadzu) to stretch the cell under a microscope (BX50WI, Olympus). The force applied to the cell was measured by the deflection of a cantilever part of the other pipette. To obtain its clear image, the cell was observed with water immersion objectives under the upright microscope. To make cell manipulation easier, the stage of the microscope was fixed and the objectives were moved to adjust the focus. Bovine aortic smooth muscle cells (BASMs) obtained by the explant method (P6-7) and rat aortic smooth muscle cells (RASMs) obtained by the enzymatic dispersion method were successfully stretched with the tester under a physiological salt solution at 37℃ to obtain their tensile properties. Tensile tests of BASMs at various stretch rate show that initial elastic modulus of the cell have a significant positive correlation with the strain rate over 4 %/s. Elastic modulus of BASMs and RASMs were about 3 kPa and about 12kPa, respectively under the strain rate of 0.2-4 %/s. Due to the difference in the cell preparation method, BASMs and RASMs are considered to show synthetic and contractile phenotype, respectively. Contractile cells contain much more contractile proteins than synthetic cells. Contractile proteins may be stiffer than cytoplasm. Contractile cells may thus be stiffer than synthetic cells. The difference in the mechanical properties of BASMs and RASMs in the present study may be due to the difference in the phenotype of the two cell specimens.