Preparation Of Graphene-based Light Responsive Surface And Its Cellular Responses

Surface characteristics could effectively regulate the interaction between surface of biomaterial and cells.Surface potential plays a key role in these interactions.The surface potential can determine the fate of targeted proteins and cells,and presents great promising applications for controlling the cell’s behavior.However,how to regulate cell’s behavior through surface potential and understanding the corresponding mechanism,remain challenges for biomaterial researches and applications.In this dissertation,uniform and patterned surface potentials were implanted,and the effect on cell’s responses and the mechanism behind were revealed.With light illumination,the light-induced surface potential distributions on the surface of single-layer graphene（Gr）/titanium dioxide（TiO₂）films,Gr/silicon（Si）and Gr/TiO₂/p-Si were investigated.Light-generated charges of Gr/TiO₂ films for cells detachment,and the effect of surface potentials on the surface of Gr/Si and Gr/TiO₂/p-Si for regulating rat bone marrow mesenchymal stem cells（BMSCs）behavior（adhesion,proliferation,differentiation）were studied.Moreover,the mechanism of the interaction between light-induced surface potential and cell’s reaction were also investigated and discussed.The main results are as follows:1.Gr/TiO₂ films with light-controlled positive/negative charge for cell harvesting applicationGr was transferred with the assisted of polylactic acid（PLA）,the transferred Gr has a clean surface,few lattice defects,and maintained single-layer structure.TiO₂nanodots（TN）was prepared on the surface of SiO₂ substrate by sol-gel and phase-separated self-assembly method,then covered with the transferred Gr to obtained a Gr/TN film.The obtained Gr/TN film shows good responsiveness to ultraviolet（UV）and visible light.Under UV light illumination,negative charges accumulated on the surface of Gr/TN film,and resulted a negative surface potential change.Under visible light illumination,positive charges accumulated on the surface of Gr/TN film,and resulted a positive surface potential change.After 365 nm UV or 450 nm visible light irradiation for 20 minutes,several types of cells could be detached from the surface effectively,and the highest cell detachment ratio reaches about 95%.The mechanism of such a cell detachment is contributed to light illumination generates charges accumulation,which,in turn,changes the conformation of the extracellular matrix protein molecules adsorbed to a more disordered state,and eventually leads to the cells detachment.Such UV and visible light responsive Gr/TiO₂ film could be a good candidate for a surface with light-induced cell detachment property.2.Gr/Si-promoted osteogenic differentiation of BMSCs through light-indcued surface potentialSchottky junction formed at interface of Gr and Si,under visible light illumination,for Gr/n-Si,positive charges tend to accumulate on the surface of Gr;for Gr/p-Si,negative charges tend to accumulate on the surface of Gr.On the surface of Gr/Si,the light-induced surface potential had no significant effects on cells adhesion,proliferation,and morphology for BMSCs,but it could promote osteogenic differentiation significantly.The effect of light-induced surface potential promoted osteogenic differentiation on Gr/Si could be attributed to the activation of the voltage-gated Ca²⁺channels by surface potentials,leading to the accumulation of Ca²⁺in cells.On the other hand,light-generated charges on the surface could also affect BMSCs differentiation through the promotion or inhibition of the adsorption of osteogenic growth factors.Such light-induced surface potential promoted osteogenic differentiation of BMSCs on Gr/Si may have great potential application for biomedical materials or devices for bone regeneration.3.Controllable nanozone surface potential regulating osteogenic differentiation of BMSCsTiO₂ nanodots films were prepared by a sol-gel and phase-separated self-assembly method on the surface of p-Si,and then Gr was transferred to the surface of TiO₂/p-Si with the assisted of PLA to obtained Gr/TiO₂/p-Si.The density and size of TiO₂nanodots could be adjusted through controlling the content of TBOT in the precursor.The transferred Gr maintained a good lattice and single-layer structure.Moreover,Gr has a good binding with TiO₂ and Si,and shows good responsiveness to both UV and visible light.Under visible light illumination,Gr/TiO₂/p-Si exhibited varied nanozone or microzone surface potentials distribution,depending on the size of TiO₂ nanodots.Gr/TiO₂/p-Si shows good biocompatibility under visible light illumination,although the reduced filopodias of BMSCs was observed,no significant effects for cells adhesion and proliferation were observed.Moreover,the controllable nanozone surface potential inhibited BMSCs osteogenic differentiation,and the inhibition effect reinforced with the increase of the zone size.In this thesis,the light-induced surface potentials with uniform morphology and heterogeneous distribution of nanozone surface potential were obtained.The effects of such surfaces on cells adhesion,proliferation,differentiation and detachment behavior were explored,and the possible mechanism between light-induced surface potential and cellular behavior were explored.It will help in understanding of surface potential to regulate cell’s reaction and its potential application.