Photoswitched Cell Adhesion on Azobenzene-Containing Self-Assembled Films.

Stimuli-responsive surfaces that can regulate and control cell adhesion have attracted much attention for their great potential in diverse biomedical applications. Unlike for pH- and temperature-responsive surfaces, the process of photoswitching requires no additional input of chemicals or thermal energy. In this work, two different photoresponsive azobenzene films are synthesized by chemisorption and electrostatic layer-by-layer (LbL) assembly techniques. The LbL film exhibits a relatively loose packing of azobenzene chromophores compared with the chemisorbed film. The changes in trans/cis isomer ratio of the azobenzene moiety and the corresponding wettability of the LbL films are larger than those of the chemisorbed films under UV light irradiation. The tendency for cell adhesion on the LbL films decreases markedly after UV light irradiation, whereas adhesion on the chemisorbed films decreases only slightly, because the azobenzene chromophores stay densely packed. Interestingly, the tendency for cell adhesion can be considerably increased on rough substrates, the roughness being introduced by use of photolithography and inductively coupled plasma deep etching techniques. For the chemisorbed films on rough substrates, the amount of cells that adhere also changes slightly after UV light irradiation, whereas, the amount of cells that adhere to LbL films on rough substrates decreases significantly.