Effects of repetitive and short time strain in human bone marrow stromal cells.

For the long-term objective to engineer a functional bone construct, we applied unidirectional cyclic mechanical strain to human bone marrow stromal cells. Two strain regimes were applied comprising single and repetitive strain, respectively. For the single strain, we applied 15 and 60 min of mechanical load (1 Hz, 5% elongation). Increased proliferation and type I collagen levels were detected after 15- and 60-min load accompanied by increased type III collagen production after 60 min of strain. To study a possible amplification of effects, long time strain on 3 consecutive days, with every day 8 h strain duration, was applied in order to induce persistent and evident cellular reactions. Furthermore, an increased calcification was observed. The observed changes were not associated with changes in p38, extracellular signal regulated kinase or c-jun N-terminal kinase activation (Western Blot). In conclusion, application of a single strain period of up to 60 min is not sufficient to induce persistent cellular reactions. Fifteen minutes seems to induce beneficial effects, whereas 60 min of strain induces collagen type III (as a sign of scar formation). Repetition of strain (3 x 8 h) induced enhanced differentiation without detrimental side effects.