Fibroblast alignment is governed by stiffness interfaces in hydrogels

Transitions in mechanical properties between different tissue extracellular matrices are common in the body and influence cellular orientation. For example, in teeth, the abrupt transition between soft dental pulp (∼5 kPa) and stiff dentin (>100 kPa) directs the alignment of odontoblasts. In this study, hydrogels with defined mechanical transitions were used to evaluate the phenotypic response of fibroblasts to soft/soft (3/3 kPa) or soft/stiff (3/200 kPa) interfaces. Near the soft/soft interface, fibroblasts aligned in a parallel-like fashion to the interface (11° angle), compared to the more perpendicular fashion (69° angle to the interface) observed at the soft-stiff interface. Notably, regions of alignment also showed an increased proportion of alpha smooth muscle actin (αSMA)-positive cells, indicating myofibroblast differentiation in response to the mechanical transition. These findings demonstrate that introduction of an interface as a biomaterial mechanical modification, without changes to the biochemical environment, is enough to alter cellular bioactivity.