The control of neural cell-to-cell interactions through non-contact electrical field stimulation using graphene electrodes Chaejeong Heo a , Jeongwan Yoo b , Siyoung Lee a , Areum Jo b , Susie Jung b , Hyosun Yoo a , Young Hee Lee a, * , Minah Suh b, ** a Department of Energy Science, Department of Physics, Sungkyunkwan Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea b Department of Biological Science, System Neuroscience Laboratory, Sungkyunkwan University, Suwon 440-746, South Korea article info Article history: Received 19 August 2010 Accepted 29 August 2010 Available online 28 September 2010 Keywords: Electrical stimulation Electrode Biocompatibility Cell adhesion Cell morphology abstract Electric field stimulation has become one of the most promising therapies for a variety of neurological diseases. However, the safety and effectiveness of the stimulator are critical in determining the outcome. Because there are few safe and effective in vivo and/or in vitro stimulator devices, we demonstrate a method that allows for non-contact electric field stimulation with a specific strength that is able to control cell-to-cell interaction in vitro. Graphene, a form of graphite, and polyethylene terephthalate (PET) was used to create a non-cytotoxic in vitro graphene/PET film stimulator. A transient non-contact electric field was produced by charge-balanced biphasic stimuli through the graphene/PET film elec- trodes and applied to cultured neural cells. We found that weak electric field stimulation (pulse duration of 10 s) as low as 4.5 mV/mm for 32 min was particularly effective in shaping cell-to-cell interaction. Under weak electric field stimulation, we observed a significant increase in the number of cells forming new cell-to-cell couplings and in the number of cells strengthening existing cell-to-cell couplings. The underlying mechanism of the altered cellular interactions may be related to an altered regulation of the endogenous cytoskeletal proteins fibronectin, actin, and vinculin. In conclusion, this technique may open a new therapeutic approach for augmenting cell-to-cell coupling in cell transplantation therapy in the central nervous system. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Neurons conduct incoming or outgoing signals through synaptic coupling and/or gap junctions (i.e., electrical coupling). Both synaptic coupling and electrical coupling play a critical role in shaping neuronal function but these connections can be transient [1e4]. To make the coupling stronger, various attempts have been made to find novel ways to facilitate coupling [5]. In particular, aiding contact between cells is a crucial beginning step of neural cell coupling. It has been reported that various types of electrical stimulation can regulate cell physiological activities such as division, migration, differentiation and cell death [6e9]. Because of its noninvasiveness, electrical stimulation has been used in promoting healing for spinal cord repair and cancer therapy [10e13]. Moreover, direct current (DC) injection methods can dramatically induce a neural cell to align perpendicular to the direction of the applied electrical field. DC stimulation also induces axonal outgrowth toward the cathode with axons aligning with the direction of current flow [14]. Most of these cellular changes, however, occur by chronic exposure to DC electric field and may result in potential cellular damage to the underlying cells or tissue [15,16]. Therefore, in order to minimize cellular damage following electrical stimulation, it is necessary to develop an effective electrical stimulator that has a non-cytotoxic substrate that can serve as a stable interface between the stimu- lator and the cells [17,18]. Recently, nanocarbon materials such as carbon nanotubes and graphene have been considered to be new effective electrode materials with high conductivity. Graphene, a two-dimensional (2D) form of graphite, has high transmittance and excellent conductivity [19]. Recently developed large-area graphene has been applied to flexible thin film transistors [20] and touch panel electrodes [21e23]. In addition, polyethylene terephthalate (PET) is a well-known transparent polymer that is a non-cytotoxic material used in catheters for medical surgery [24]. * Corresponding author. Tel.: þ 82 31 299 6507; fax: þ 82 31 299 6505. ** Corresponding author. Tel.: þ 82 31 299 4496; fax: þ 82 31 299 4506. E-mail addresses: leeyoung@skku.edu (Y.H. Lee), minahsuh@skku.edu (M. Suh). Contents lists available at ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2010.08.095 Biomaterials 32 (2011) 19e27