Surface Stability of Azobenzene-Based Thin Films in Aqueous Environment: Light-Controllable Underwater Blistering

Azobenzene-based light-responsive thin films are emerging as appealing candidates for smart cell-culture substrates. Their attraction lies in the fact that they can be reversibly photo-patterned, providing a route for dynamically mimicking the remodeling of the extracellular matrix. However, since the cells need to be cultured in aqueous environment, a key parameter in the layout of any biological application is the stability of the surface underwater. In this work, the authors perform a detailed investigation on the surface stability of azobenzene-based thin films in water and in a biologically relevant aqueous medium in which surface blistering occurs, as a result of water-material interaction. The phenomenon arises due to film delamination, and it can be prevented by changing the underlying substrate, by an additional coating layer, or by photo-induced control over the film permeability. It is also shown that the blister orientation can be controlled with polarized light. Furthermore, a simple model based on osmotic pressure is proposed to explain the blister formation. These findings provide a comprehensive overview of the interaction between water and the photo-responsive film surface, pertinent for engineering biomaterials with enhanced dynamic control over the cell-material interface.