Theoretical model to predict membrane strain magnitude. (A) Initial and final position of stretching device (1st row) and flexible membrane (2nd row); equations describing membrane area in each position (3rd row); a: radius of circular stretchable area; b: radius of inner circle where cells can be visualized; h: distance made by the flange (item#4 of Figure 1); c: radius of a hypothetical new circle corresponding to the area of the stretched membrane in the final position (Equation (1)). The relative increment of c/a can be calculated by Equation (2). Equation (3) indicates the percentage of radial strain applied (RSA) to the membrane. (B) The distances between 10 pairs of cells were measured in each orientation (horizontal, vertical and diagonal) in 4 different microscope fields. Data are expressed as means ± SE. Predicted RSA respect to h (from Equation (2) and (3)) is also plot in the graph. (C) Relationship between thread turns and cell area change (%). The areas of 15 cells were measured in four different microcope fields. Data are expressed as means ± SE. The predicted substrate area change (%) is also plot in the graph. (D) Representative image of phase contrast micrographs (magnification 200×) of HC11 cells attached to silicone membranes. Silicone membranes were progressively subjected to 0% (upper panel), 20% (middle panel) and 30% (lower panel) RSA and the same field is shown in each panel. At each RSA, the arrow points out a loosely attached cell, while the arrowhead shows a well attached one. On the left, contours of cells identified on the right are depicted. Relationship between thread-turns and RSA: 1 turn = 0.54 mm.