Growing evidences support the notion that cells respond to mechanical signals from the local
extracellular matrix. Epidermal homeostasis is therefore intrinsically linked to the mechanical properties provided by its underlying conjunctive tissues: the dermis and the hypodermis. In fact, stiffness changes may regulate how the skin behaves in both physiological and pathological circumstances. However, the mechanistic clues remain unclear.
Using a step boundary in rigidity from 1 to 24 kPa compared to plastic (MPa), we studied whether and how substrate stiffness influences primary human keratinocyte behaviour. We took advantages of primary human keratinocytes growing polyacrylamide gels in which the concentration of bis-acrylamide crosslinking sets the elastic modulus while adhesion is allowed by functionalization of the gel surface with type I collagen.
We first determined a range of rigidities, from 1 kPa to 24kPa, that can modulate keratinocytes morphology. We then showed that on 3 kPa polyacrylamide gel, keratinocytes exhibited the best differentiation ability among all other rigidities. We also observed that below 3 kPa cells were not spread out, resulting in proliferation arrest. Our results demonstrate the influence of mechanical substrate on epidermal cell behaviour, particularly in a narrow range of substrate rigidities (around 3kPa). This may pave the way to new strategies to alter cellular responses to dermis mechanical property alterations involved during ageing or skin disorders.

Optimal primary human keratinocyte behaviour in a narrow range of substrate rigidities