Oxygen Plasma Etching of Silk Fibroin Alters Surface Stiffness: A Cell-Substrate Interaction Study

Oxygen plasma etching was used to treat silk fibroin (SF). The plasma exposure removed a significant amount of SF but left behind most surface properties close to their original state. However, nano-indenter measurements revealed a substantial increase in surface modulus of swollen SF from 62 to 500 kPa. This allowed oxygen plasma etching as a potential tool to investigate the impact of surface stiffness on cell-substrate interaction. Mouse fibroblasts (L929) and human mesenchymal stem cells (hMSC) were employed as distinct model cases. In vitro results revealed that the increased stiffness of plasma-treated SF affected only L929 adhesion, not hMSC. L929 cell attachment and spreading were better on the stiffer surface than the untreated surface, while hMSC could spread well on all SF surfaces.