The role of mechanical forces is crucial for stem cell adhesion, viability, proliferation, self-renewal, and differentiation. The relationship between the natural extracellular matrix mechanics and cell behavior is dynamic, such as compressive stress from skeletal muscle contraction. Thus, relatively little is known about how stem cells respond to reversibly dynamic mechanical stimulation (RD-MS) in a 3D fiber network. Here, thermosensitive electrospun microfibrous cross-linked hydrogels are investigated from variants of polycaprolactone and poly(N-isopropylacrylamide) in which the mechanosensing can be in situ thermo-induced switched from stiff (37 degrees C) to soft (25 degrees C) for multiple cycles. It is found that human mesenchymal stem cells seeded in bioengineered fibrillar microenvironments with multicyclic RD-MS result in an increased cell spreading area and polarization. This 3D cell shape deformation can ultimately alter the intracellular signaling related to the differentiation. Combining with mechanosensing computer simulations, a positive correlation between the elongated morphology and the cycles of RD-MS is predicted, suggesting that the cell polarization is proportional to dynamic changes of local stiffness and geometric fiber density of the fiber network. This study reveals RD-MS as a key design parameter for biomaterial scaffolds as well to control cell behavior in tissue engineering applications.