Atomic force microscopy can be used to mechanically stimulate osteoblasts and evaluate cellular strain distributions

In this study, atomic force microscopy (AFM) was used to mechanically stimulate primary osteoblasts. In response to mechanical force applied by the AFM, the indented cell increased its intracellular calcium concentration. The material properties of the cell could be estimated and the membrane strains calculated. We proceeded to validate this technique experimentally and a 20% error was found between the predicted and the measured diameter of indentation. We also determined the strain distributions within the cell that result from AFM indentation using a simple finite element model. This enabled us to formulate hypotheses as to the mechanism through which cells may sense the applied mechanical strains. Finally, we report the effect of the Poisson ratio and the cell thickness on the strain distributions. Varying the Poisson ratio did not change the order of magnitude of the strains; whereas the cellular thickness dramatically changed the order of magnitude of the cellular strains. We conclude that AFM can be used for controlled mechanical stimulation of osteoblasts and that cellular strain distributions can be computed with a good accuracy when the cell is indented in its highest part.