Engineering the geometrical shape of mesenchymal stromal cells through defined cyclic stretch regimens.

Stem cells have been predicted to improve disease outcomes and patient lives. Steering stem cell fate - through controlling cell shape - may substantially accelerate progress towards this goal. As mesenchymal stromal cells (MSCs) are continuously exposed in vivo to a dynamically changing biomechanical environment, we hypothesized that exogenous forces can be applied for engineering a variety of significantly different MSC shapes. We applied specific cyclic stretch regimens to human MSCs and quantitatively measured the resulting cell shape, alignment, and expression of smooth muscle (SMC) differentiation markers, as those have been associated with elongated morphology. As proof of principle, a range of different shapes, alignments, and correlating SMC marker levels were generated by varying strain, length, and repetition of stretch. However, the major determinant of biomechanically engineering cellular shape was the repetition of a chosen stretch regimen, indicating that the engineered shape and associated differentiation were complex non-linear processes relying on sustained biomechanical stimulation. Thus, forces are key regulators of stem cell shape and the targeted engineering of specific MSC shapes through biomechanical forces represents a novel mechanobiology concept that could exploit naturally occurring in vivo forces for improving stem cell fate in clinical regenerative therapies.