Strain profiles for circular cell culture plates containing flexible surfaces employed to mechanically deform cells in vitro

Abstract

Cells in the body are constantly subjected to cyclic mechanical deformation involving tension, compression, or shear strain or all three. A mechanical loading system which deforms cultured cells in vitro was analyzed in order to quantify the deformation or strain to which the cells are subjected. The dynamic system utilizes vacuum pressure to deform a circular silicone rubber substrate on which cells are cultured. These thick circular growth surfaces or plates are formed in the bottoms of the wells of 6-well culture plates. An axisymmetric model was formulated and analyzed using rectangular hyperelastic elements in a finite element analysis (FEA) software package. The thick circular plate has some disadvantages such as difficulty in observing cells and a nonhomogeneous strain profile which is maximum at the periphery and minimal at the center. A thinner circular surface (a thin plate) was also investigated in order to provide a more homogeneous strain profile. The radial strain on the thick circular plate, as determined by FEA, was nonlinear with a peak strain value of 0.30 (vacuum pressure of 22 kPa) about three-quarters of the distance from the center to the edge. In contrast, the radial strain of the thin circular plate was moderately constant across the surface. The circumferential strain for both of these models was less than the radial strain except for the center where they are equal. Avian tendon cells were cultured on the surface of a thick plate and exposed to cyclic strains for 24 h at a rate of 0.17 Hz and observed for cellular alignment. In a second experiment, embryonic avian cardiac myocytes were stretched at 0.25 Hz for 72 h and DNA synthesis was analyzed. The avian tendon cells were aligned perpendicular to the radial strain at the cell plate periphery, and the embryonic myocytes displayed a 1.9 increase in DNA synthesis. For investigators utilizing the in vitro cell deformation system, the FEA results for the thick plate surface provide a basis for relating biological effects, such as cell alignment, to a particular point on the strain gradient. However, when the entire cell sheet is collected to quantify a cellular process such as DNA synthesis, the value obtained represents an average response of the high- and low-strain zones unless discrete areas of the gradient are collected separately. Use of the thin plate substratum will provide a more uniform strain field and thus more homogeneously responding cells for biochemical studies.