A photoresponsive soft interface reversibly controls wettability and cell adhesion by conformational changes in a spiropyran-conjugated amphiphilic block copolymer

The functionalities of soft interfaces including cell adhesion can be enhanced by dynamic conversion of polymer properties and movement via external stimuli. Light is a superior stimulus, and various surfaces modified with photoreactive molecules have been prepared. However, in most of these studies, the surface properties are irreversibly changed due to photo-degradation, and reversible adhesion and collection of cells is not feasible. In this study, we developed a photoresponsive polymer soft interface that was able to spatiotemporally control wettability, cell adhesion, and detachment in a reversible manner. Spiropyran molecules were introduced into the hydrophobic block of an amphiphilic diblock copolymer consisting of poly(methyl methacrylate) and polyethylene glycol, and the monomer unit numbers of these components were optimized. The copolymer was immobilized on a glass substrate as a nanofilm. With alternating irradiation using UV and visible light, the surface exhibited reversible changes in hydrophobicity and hydrophilicity, and the direction of change was opposite to the polarity change in photo-isomerization of spiropyran. We also achieved photo-control of effective cell adhesion and detachment with sequential irradiation with UV and visible light. These remarkable functions could be ascribed to conformational changes triggered by photo-isomerization of spiropyran. This photoresponsive polymer soft interface may have applications as a powerful tool in biological studies by facilitating sequential changes in wettability and bioaffinity. Statement of Significance We developed a photoresponsive polymer soft interface, which was able to spatiotemporally control wettability and cell adhesion/detachment in a reversible manner, by introducing spiropyran into the hydrophobic block of an amphiphilic diblock copolymer. With alternating irradiation using UV and visible light, the surface exhibited unique reversible wettability changes; the direction of hydrophobicity and hydrophilicity change was opposite to the polarity change in spiropyran photo-isomerization. Light-dependent reversible control of spatiotemporal cell adhesion and detachment was also achieved with sequential UV (adhesion) and visible light irradiation (detachment). Cell detachment using noncytotoxic visible light was realized for the first time. Cell-patterning capability stably lasted for 25 days. This photoresponsive surface could be applied to fabrication of engineered tissues comprised of several cellular species.