Masato Ueda 1 , Chika Fujita 1 , Masahiko Ikeda 1
1 Kansai University Suita Japan
Several techniques have been employed to attach/detach cells to/from a substrate. Cells cultured on a substrate are generally detached from the substrate into a sheet by the destruction of protein between the cells and the substrate using enzymes such as trypsin. However, the enzymes also damage the adhesion molecules among the cells.
Anatase-type TiO2 is an n-type semiconductor with an energy band gap of Eg=3.2 eV, which displays a relatively high photocatalytic activity under light irradiation at wavelengths of λ<380 nm. When an n-type semiconductor is immersed in an aqueous solution, an up-hill potential gradient is produced towards the surface in the conduction and the valence bands. Under ultraviolet (UV) irradiation, electrons and holes are formed in the conduction and the valence band, respectively. These photogenerated charges are then spatially separated by the potential gradient. This phenomenon can be regarded as photocurrent, electromotive force, or redox reaction.
The purpose of this work was to fabricate photo-responsive cell culture vessels using TiO2 and to investigate adhesion/proliferation behaviors of cells on them. Following three types of vessels were fabricated: (a) TiO2 film/Ti, (b) TiO2 film/SiO2 and (c) Ti/TiO2 film/Hanks’ solution/SiO2. In the vessels of (b) and (c), light was irradiated from back-side of the vessels.
TiO2 films were prepared on commercial purity Ti plates or SiO2 plates by the combined chemical-hydrothermal treatment or a general sol-gel method using titanium tetraisopropoxide, respectively. Primary osteoblasts were seeded on the vessels and then incubated at 37 °C. During the incubation, the light irradiation was performed intermittently or continuously.
Basically the number of cells monotonically increased with incubation periods on both Ti and TiO2 under darkness. The intermittent light irradiation promoted the adhesion of cells on the surface in the vessel of (a). The formation of Ti-OH groups on the TiO2 seems to be facilitated by the UV irradiation. In contrast, the cells decreased under continuous light irradiation. Direct UV irradiation is known to damage to the cells. The decrease was significant in the TiO2, not in the Ti. The cells might be additionally received some sort of stimulus from the surface of TiO2. In the vessel of (b), the cells are not exposed to UV since it is completely absorbed by the TiO2 layer. However, the cell adhesion was suppressed by light irradiation; it might be due to generated photocurrent or hydroxyl radicals on the surface of TiO2. On the other hand, the cell adhesion was also suppressed by continuous light irradiation in the vessel of (c). The cells adhered under dark could be detached by light irradiation in the vessels of (b) and (c), though the efficiency was not so high. These results imply that the adhesion/proliferation/detachment behaviors of cells can be controlled by the photocatalytic reaction of TiO2 and the irradiation patterns.