A novel micro tensile tester with feed-back control for viscoelastic analysis of single isolated smooth muscle cells

A novel micro tensile tester was developed to measure the viscoelastic properties of single isolated cells. A specimen cell was held with two glass micropipettes, the tips of which were coated with a urethane resin adhesive. One pipette was rigid and fixed in position, and the other was deflectable and could be moved by a laboratory-made piezoelectric actuator to stretch the specimen. The actuator was made of an originally designed lever mechanism which can magnify the deformation of conventional piezoceramic actuator and allowed for sufficient displacement up to 150 μm. The distance between the two pipette tips was obtained by real-time image processing and kept constant following stepwise stretching with an accuracy of ±0.1 μm by changing the voltage applied to the piezoceramics under feed-back control. The force applied to the cell was measured by the deflection of a cantilever part of the deflectable pipette. The stress relaxation test was performed for cultured rat aortic smooth muscle cells. The cells were stretched by 75% and their length was kept constant. Viscoelastic analysis with a standard linear solid showed that the relaxation time constant of the isolated smooth muscle cells was 250 ± 42 s (n = 8, mean ± S.E.M.) which was over six times longer than that reported for vascular endothelial cells and fibroblasts.