STRAIN PROFILES FOR CIRCULAR CELL-CULTURE PLATES CONTAINING FLEXIBLE SURFACES EMPLOYED TO MECHANICALLY DEFORM CELLS IN-VITRO

Cells in the body are constantly subjected to cyclic mechanical deform ation involving tension, compression, or shear strain or all three. A mechanical loading system which deforms cultured cells in vitro was an alyzed in order to quantify the deformation or strain to which the cel ls are subjected. The dynamic system utilizes vacuum pressure to defor m a circular silicone rubber substrate on which cells are cultured. Th ese thick circular growth surfaces or plates are formed in the bottoms of the wells of 6-well culture plates. An axisymmetric model was form ulated and analyzed using rectangular hyperelastic elements in a finit e element analysis (FEA) software package. The thick circular plate ha s some disadvantages such as difficulty in observing cells and a nonho mogeneous strain profile which is maximum at the periphery and minimal at the center. A thinner circular surface (a thin plate) was also inv estigated in order to provide a more homogeneous strain profile. The r adial strain on the thick circular plate, as determined by FEA, was no nlinear with a peak strain value of 0.30 (vacuum pressure of 22 kPa) a bout three-quarters of the distance from the center to the edge. In co ntrast, the radial strain of the thin circular plate was moderately co nstant across the surface. The circumferential strain for both of thes e models was less than the radial strain except for the center where t hey are equal. Avian tendon cells were cultured on the surface of a th ick 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 syn thesis was analyzed. The avian tendon cells were aligned perpendicular to the radial strain at the cell plate periphery, and the embryonic m yocytes displayed a 1.9 increase in DNA synthesis. For investigators u tilizing 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 cellula r process such as DNA synthesis, the value obtained represents an aver age response of the high- and low-strain zones unless discrete areas o f the gradient are collected separately. Use of the thin plate substra tum will provide a more uniform strain field and thus more homogeneous ly responding cells for biochemical studies.