We developed herein an original electron emission device that can stably operate in the atmosphere. The important features of the device are that the energy of electrons is as extremely small as several eV, the emission current in the atmosphere is as large as several μA/cm2, and the durability is of several hundred hours. These characteristics are obtained by an original device structure based on a 1 μm-thick Ag nanoparticle/polymer composite layer. The electron emission device does not require a strong electric field in the space between the emitter and the collector as required for discharge or plasma. The physical mechanism of electron emission is a mixture of field emission according to the Fowler–Nordheim plot and electron emission caused by breakdown. The energy of the emitted electrons depends on the applied voltage and can be controlled. The electrons emitted from the device can generate various ions and radicals.

In this report we demonstrate the effect of a novel electron emission-based cell culture device on the proliferation and differentiation of pre-osteoblastic MC3T3-E1 cells. Our device has an electron emission element that allows, for the first time, stable emission of electrons into an atmosphere. Atmospheric electrons react with gas molecules to generate radicals and negative ions, which induce a variety of biochemical reactions in the attached cell culture system. In this study, we demonstrated the effect of this new electron emission-based cell culture device on cell proliferation and differentiation using pre-osteoblastic MC3T3-E1 cells. Electron emission stimulation (EES) was applied directly to culture medium containing plated cells, after which the number of living cells, the mRNA levels of osteogenesis-related genes, and the alkaline phosphatase (ALP) activity were evaluated. The growth rate of EES-exposed cells increased by approximately 20% in comparison with unexposed control cells. We also found the mRNA levels of osteogenic specific genes such as collagen type I α-1, core-binding factor α-1, and osteocalcin to be up-regulated following EES. ALP activity, a marker for osteogenic activity, was significantly enhanced in EES-treated cells. Furthermore, reactive oxygen species generated by EES were measured to determine their effect on MC3T3-E1 cells. These results suggest that our new electron emission-based cell culture device, while providing a relatively weak stimulus in comparison with atmospheric plasma systems, promotes cell proliferation and differentiation. This system is expected to find application in regenerative medicine, specifically in relation to bone regeneration.