CYCLIC STRETCHING OF HUMAN OSTEOBLASTS AFFECTS PROLIFERATION AND METABOLISM - A NEW EXPERIMENTAL-METHOD AND ITS APPLICATION

We developed an experimental system to stimulate cell cultures by unif orm and cyclic biaxial strain of the cell culture surface. The studies reported here were designed to determine the uniformity of the strain distribution, the suitability of the surface for the growth of human osteoblasts, and the effects of strain magnitude on cell proliferation and alkaline phosphatase (AP) activity. Subconfluent cell cultures we re grown in rectangular silicone dishes that were stretched cyclically (1 Hz) in the long axis by an electromechanical apparatus that contro lled peak stretch and cycle frequency. We applied cyclic strains (1.0, 2.4, 5.3, and 8.8% surface strains) for 15 minutes per day on 3 conse cutive days. Phase contrast microscopy confirmed the transfer of dish surface strain to the cells. Stretching of the dish resulted in a homo geneous strain distribution that deviated approximately 0.05% from the applied strain. In comparison with plastic dishes, there was a 20% re duction of cell proliferation on the silicone substrate whereas morpho logy, AP activity, and total protein content of the cells were similar . The proliferation of human osteoblasts was increased significantly ( 16.4-100%) by 1% strains, although higher strain magnitudes had lesser (nonsignificant) effects or decreased the mitotic activity of the cel ls. AP and lactate dehydrogenase activities were not influenced signif icantly by cyclic strains. This study demonstrates that the cell stret ching system is suitable for the investigation of the effects of well defined cyclic strains.