Neuronal adhesion and differentiation driven by nanoscale surface free-energy gradients.

Recent results indicate that, in addition to chemical, spatial and mechanical cues, substrate physical cues such as gradients in surface energy may also impact cell functions, such as neuronal differentiation of PC12 cells. However, it remains to be determined what surface effect is the most critical in triggering PC12 cell differentiation. Here we show that, beyond continuously probing the surface energy landscape of their environment, PC12 cells are highly sensitive to nanoscale chemical heterogeneities. Self-assembled monolayers of alkylsiloxanes on glass were used as a culture substrate. By changing the structure, ordering and chemical nature of the monolayer, the surface energy distribution is altered. While both well-ordered CH(3) terminated substrates and bare glass (OH terminated) substrates did not favor PC12 cell adhesion, PC12 cells seeded on highly disordered CH(3)/OH substrates underwent enhanced adhesion and prompt neuritogenesis by 48 h of culture, without nerve growth factor treatment. These data illustrate that surface free-energy gradients, generated by nanoscale chemical heterogeneities, are critical to biological processes such as nerve regeneration on biomaterials.