Nanostructured and Photoswitchable Biointerfaces for Controlling Cell Adhesion
I present two novel approaches to control cell adhesion. The first provides a static spatial control while the other offers a reversible dynamic control. The first is enabled by a biocompatible microstructured interface that accommodates an additional pattern of ordered gold nanoparticles. This was obtained using both photolithography and Micelle Nanolithography. The superposition of the two structures to generate a so-called micronanostructure allows to obtain different interparticle spacings on adjacent segments of the substrate. The second approach allows a rapid, reversible and dynamic way of controlling cell adhesion. The switching was fulfilled using two different surface chemistries, both of which are based on light-responsive RGD-functionalized azobenzene molecules that are immobilized on glass substrates alongside a monolayer of polyethylene glycol (PEG). Azobenzenes are able to switch reversibly between two isomeric states, trans and cis, upon light exposure. The first type modulates cell adhesion through UV illumination, which switches trans isomer to cis and thus immersing RGD in PEG. A subsequent illumination with visible light switches cis back to trans and makes RGD available again for binding. This shows reversible adhesion as confirmed by atomic force spectroscopy studies. The other surface chemistry is based on push-pull azobenzenes. These offer an intriguing method that allows the system to be set reversibly between two phases using a single wavelength within the visible spectrum. The first phase is a state of rapid trans/cis switching of the push-pull azobenzene that takes place during exposure to a 530 nm light, which induces an oscillation of the azobenzene. The second phase is set once the light is switched off, which seizes the oscillation of the push-pull azobenzene and leads to a resetting of trans. This oscillation reinforced cell adhesion forces and increased the gene expression of proteins involved in focal adhesion clusters.
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