Controlling cell behaviors is important issue in biomedicine. Because cells are generally sensitive to the surrounding environment, manipulations of chemical functional groups at cell-surface interfaces and the physical structure interacting with cells are easy method to modulate cell behaviors. Recently, nanomaterials also have been actively used for regulating cell behaviors as a gene delivery carrier. Therefore, we try to modulate cell behaviors as follows.
First, we examine the development of primary neurons on thoroughly controlled chemical functional groups to investigate effects of surface charges on neuronal behaviors. Negatively charged surfaces presenting carboxylate ($COO^-$) or sulfonate ($SO_3^-$) groups prove beneficial to neuronal behavior, in spite of their supposed repulsive electrostatic interactions with cellular membranes. The adhesion and survival of primary hippocampal neurons on negatively charged surfaces are comparable to or slightly better than of those on positively charged (poly-D-lysine-coated) surfaces, and neuritogenesis and neurite outgrowth are accelerated on $COO^-$ and $SO_3^-$ surfaces. Moreover, such favorable influences of the negatively charged surfaces are only seen in neurons, but not for astrocytes. To induce synergistic effects of chemical functional groups and nanotopograpy, we introduce chemical functional groups into nanogrooves. We are eventually able to modulate not only neurite extension but also neurite directionality. These results indicate that the in vitro developmental behavior of primary hippocampal neurons is sophisticatedly modulated by angstrom-sized differences in chemical structure or the charge density of the surface, and not by simple electrostatic interactions.
Second, we manipulate cellular responses by using gene delivery technique based on surface charges and structural effects of nanomaterials. We synthesize monodispersed mesoporous silica nanoparticles (MMSNs) possessing very large pores (> 15 nm) to apply the nanoparticles to plasmid DNA delivery to human cells. The aminated MMSNs with large pores provide cationic pores large enough to load plasmids inside and outside of the particles and readily enter into cells without supplementary polymers such as cationic dendrimers. Furthermore, MMSNs with large pores can efficiently protect plasmids from nuclease-mediated degradation and show much higher transfection efficiency of the plasmids encoding luciferase and green fluorescent protein (pLuc, pGFP) compared to MMSNs with small pores (~ 2 nm).
Third, we protect cells from exogenous substances (toxic hydrophobic molecules, nanoparticles, and nucleic acids such as siRNA, and plasmid DNA) by using micro-sized graphene oxide (GO) that exhibits a sheet-like structure. The cytoprotective effect of GO against the internalization of extracellular materials enables spatial control over gene transfection through region-selective gene delivery only into GO-untreated cells, and not into the GO-treated cells.