On the other hand, contrary to our observations from 3T3 fibroblasts, the F-actin expression of hLFs was not changed by exposure to cyclic stretching (Figure ). It has been reported that the pre-stress experienced by the cells, defined as the cytoskeletal tension under static conditions (proportional to the material stiffness), can affect the stability of actin fibers upon stretching. High cellular pre-stress is associated with the depolymerization of actin fibers upon cyclic stretching, while low pre-stress induces reinforcement. Following this logic, the stiffness of the hydrogels used for the 3T3 and hLF experiments could influence the F-actin expression within the cells, with a more pronounced reduction in the F-actin expression for the cells stretched on the stiffer material (5% GelMA). The 3T3 fibroblasts stretched on the stiffer hydrogels (5% GelMA)