Light-induced Protein Desorption On TiO₂Nanodots And Its Application In Cell Harvest

Protein adsorption happens at the very initially on biomaterial surfaces when they are in contact with body. The adsorption greatly influences on subsequent cell responses as well as biological performances of biomaterials. Recently, the emerge of intelligent switchable materials allows us to control protein adsorption dynamically via field stimulation, light-responsive biomaterials is one of the best candidates in this frontier research area.In this thesis, to utilize light-responsive TiO2nanodot films as a nanostructured surface, we focused on changing behaviors of protein adsorption status on TiO2nanodots under UV365illumination and the mechanism of the behavior, and the application of the behavior in cell harvest. The main results are as follows:A phase-separation-induced self-assembly process was adopted to prepare a TiO2nanodot gel film on a substrate with adjustable size and density. Subsequently, the gel film could be transformed to an amorphous TiO2dot film under a hydrothermal treatment (100-140℃for2h), and to an anatase T1O2dot film by500℃heat-treatment. Both the amorphous and anatase TiO2nanodot films showed high light adsorption and conversion from a good hydrophobic surface to a highly hydrophilic one after UV365illumination. Zeta potential on anatase TiO2nanodot film showed more negative shift than that on amorphous one after UV365illumination.When BSA adsorbed on the both films, the adsorption status of BSA was multilayer type on anatase TiO2nanodots, while monolayer type on amorphous TiO2nanodots. The difference is attributed to that more defects existing on amorphous TiO2nanodot surface lead to more surface hydroxyl groups which have great attraction to the-NH3+groups on BSA molecule to result in more negatively charged outer surface of the surface-bound proteins. The negatively charged surface hinders electrostatically further BSA adsorption because BSA molecules in solution are also negatively charged.The multilayer BSA adsorbed on anatase TiO2nanodots could be desorbed by UV365illumination, and it was found that the surface-bound proteins were not desorbed. Fn proteins could be subsequently adsorbed onto BSA on amorphous TiO2, and also the Fn could be desorbed by UV365illumination although BSA on amorphous TiO2nanodots had no light-induced desorption phenomenon due to its monolayer adsorption.The light-induced protein desorption is mainly attributed to the changes in the adsorption conformation of surface-bound protein on anatase TiO2nanodots after UV365illumination. The illumination increases-OH groups on TiO2nanodot surface, the increase could enhance the electrostatic attraction to-NH3+groups on surface-bound proteins, and decrease the exposed—NH3+groups on outer surface of surface-bound protein, making the outer surface become less positively charged and even negatively charged. Subsequently, the previous electrostatic interactions between surface-bound proteins and outer-layer proteins in multilayer type adsorption are affected. When the change in the adsorption conformation of surface-bound proteins has enough large, the outer surface of surface-bound protein becomes negatively charged, the outer-layer proteins will desorb because of an electrostatic repulsion. The conformation of surface-bound protein on amorphous TiO2nanodots was also found to change too. Other light-responsive semiconductors and proteins also demonstrated the light-induced protein adsorption phenomenon, and these strongly supported the above mechanism establishement.When the light-induced protein desorption was utilized in cell harvest, different cells could be rapidly detached from anatase TiO2nanodot film after20min UV365illumination with detachment rate above90%. The detached cells had good viability. Also cell sheet could be obtained by8min UV365illumination with good viability and functionalization. Cells on amorphous TiO2nanodot film could detach, but the detachment rate was lower than that on anatase TiO2nanodot film. The cell sheets obtained by light-induced cell harvest method had good repairing results in promoting osteogenesis and skin regeneration. These results proved that light-induced cell harvest from TiO2nanodot film is very convenient and safety, and also has promising application in tissue engineering.The thesis research originally demonstrates a TiO2light-induced protein desorption effect, soundly clarifies the mechanism of the effect, and successfully applies the effect to cell harvest. These are great helpful to gain insight into understanding of the interaction between material and protein.