Research Article www.acsami.org
Organic Photovoltaics and Bioelectrodes Providing Electrical Stimulation for PC12 Cell Differentiation and Neurite Outgrowth Yu-Sheng Hsiao,*,† Yan-Hao Liao,‡ Huan-Lin Chen,† Peilin Chen,§ and Fang-Chung Chen*,‡ †
Department of Materials Engineering, Ming Chi University of Technology, 84 Gunjuan Road, Taishan, New Taipei City 243 Taiwan Department of Photonics, National Chiao Tung University, 1001 University Road, Hsinchu 30010 Taiwan § Research Center for Applied Sciences, Academia Sinica, 128 Sec. 2, Academia Road, Taipei 11529 Taiwan ‡
S Supporting Information *
ABSTRACT: Current bioelectronic medicines for neurological therapies generally involve treatment with a bioelectronic system comprising a power supply unit and a bioelectrode device. Further integration of wireless and self-powered units is of practical importance for implantable bioelectronics. In this study, we developed biocompatible organic photovoltaics (OPVs) for serving as wireless electrical power supply units that can be operated under illumination with near-infrared (NIR) light, and organic bioelectronic interface (OBEI) electrode devices as neural stimulation electrodes. The OPV/OBEI integrated system is capable to provide electrical stimulation (ES) as a means of enhancing neuron-like PC12 cell differentiation and neurite outgrowth. For the OPV design, we prepared devices incorporating two photoactive material systemsβ-carotene/N,N′-dioctyl-3,4,9,10-perylenedicarboximide (β-carotene/PTCDI-C8) and poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM)that exhibited open circuit voltages of 0.11 and 0.49 V, respectively, under NIR light LED (NLED) illumination. Then, we connected OBEI devices with different electrode gaps, incorporating biocompatible poly(hydroxymethylated-3,4-ethylenedioxythiophene), to OPVs to precisely tailor the direct current electric field conditions during the culturing of PC12 cells. This NIR light-driven OPV/OBEI system could be engineered to provide tunable control over the electric field (from 220 to 980 mV mm−1) to promote 64% enhancement in the neurite length, direct the neurite orientation on chips, or both. The OPV/OBEI integrated systems under NIR illumination appear to function as effective power delivery platforms that should meet the requirements for wirelessly offering medical ES to a portion of the nervous system; they might also be a key technology for the development of next-generation implantable bioelectronics. KEYWORDS: bioelectronic medicines, wireless, organic photovoltaics, organic bioelectronic interfaces, electrical stimulation
1. INTRODUCTION Bioelectronic medicine, a new class of interventional therapy, has many facets: the application of electrical stimulation (ES) in neuroscience,1−5 the monitoring of electrical signals as a means of understanding biological activities,6−8 the closed-loop electrical control over drug release,9−12 and, when combined with circulating tumor cell (CTC) liquid biopsies, a technology for cancer research.13−16 In particular, implanted organic bioelectronics have recently gained considerable interest because the organic electronic materials possess many unique properties, including good biocompatibility, low toxicity, and ability to adjust the strain mismatch between soft tissues and rigid electronics, thereby meeting clinical requirements.3,12,17 Various π-conjugated conducting materials, including poly(3,4ethylenedioxythiophene) (PEDOT), poly(3-hexylthiophene2,5-diyl) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and perylene derivatives, have been integrated into bioelectronic devices.12,17−19 For examples, PEDOT-based bioelectronic interface (BEI) electrodes have served as communication layers to enhance ion/electron transport © 2016 American Chemical Society
properties between biological and electronic systems; perylene-based organic field-effect transistors (OFETs) have served as analog and digital interfaces for bidirectional stimulation and recording of neurons; P3HT-based organic photovoltaics (OPVs) have also served as wireless electrical power supply units for biomedical applications.20 BEI electrodes and power supply units are the two core components of implanted bioelectronic devices for directly operated therapeutic intervention systems. For example, deep brain stimulation (DBS) devices, consisting of a batterypowered neurostimulator and lead units (e.g., BEI electrodes), can be used to provide long-term effective therapies with ES for treatment-resistant movement and affective disorders (e.g., Parkinson’s disease, essential tremors, dystonia, chronic pain, major depression, and obsessive behavior).21 However, battery replacement for the DBS devices is generally required after Received: January 24, 2016 Accepted: March 21, 2016 Published: March 21, 2016 9275
DOI: 10.1021/acsami.6b00916 ACS Appl. Mater. Interfaces 2016, 8, 9275−9284
Research Article
ACS Applied Materials & Interfaces
Figure 1. Schematic representation of an OPV/OBEI integrated system for exerting an ES effect on PC12 cells. (a) Device architecture of OBEIs with different electrode gaps. (b) Device architecture of a β-carotene/PTCDI-C8-based OPV (OPV-1). (c) Device architecture of a P3HT:PCBM− based OPV (OPV-2). (d) Photograph of the OPV/OBEI integrated systems: OPV setup was outside the cell culture incubator under illumination with a white light LED (WLED) and a NIR light LED (NLED); (inset) OBEI device setup in a conventional cell culture incubator.
employing ES for neuron-like PC12 cell differentiation and neurite outgrowth behavior (Figure 1).
approximately 10 months of operation. In addition, there can be surgical risks associated with battery replacement. Thus, the challenge remains to develop wireless systems as power delivery units in bioelectronic devices that are simple to operate and prevent bacterial influx.22−24 Nerve stimulation for neuronal cells/tissues might become an acceptable and promising modality for controlling and treating various diseases and disorders. Although the working mechanism of nerve stimulation is not fully understood, various approaches (e.g., electrical, optical, chemical, magnetic) are available for neural stimulation.25−28 Among these methods, the relatively reliable ES techniques appear to be promising for various biomedical applications because electrical signals on chips are highly controlled and quantifiable. Electrophysiology has revealed that the electric field strength (mV mm−1) can be tailored through changing the two-electrode gap distance; therefore, optimized ES conditions for neuronal outgrowth can be obtained readily by changing the voltage and distance between the two electrodes. In addition, PEDOT-coated electrodes can further enhance protein (e.g., neuron growth factor or fibronectin) adsorption and ensure the redistribution of ion homeostasis or polarized receptors at cell surfaces through charge injection when using PEDOT-based BEIs.4 Furthermore, biocompatible poly(hydroxymethylated-3,4-ethylenedioxythiophene) (PEDOT−OH) coatings might lead to more effective recording and stimulating, due to their low impedance,29,30 as well as improved cell adhesion on electrodes. We have previously found that the general architecture of a P3HT:PCBM-based active layer of OPVs exhibits a noticeable NIR photovoltaic response originating from the long-wavelength absorption of the charge transfer (CT) states, thereby directly converting 980 nm light into electrical power. Due to the high transparency of biological tissues toward NIR photons, the OPVs might serve as a promising electrical source for biomedical treatments. To the best of our knowledge, however, the practical application of OPV-based power delivery units under NIR illumination has not yet been widely realized for the direct application of ES effects in biological systems. Accordingly, in this study, we developed biocompatible OPV devices, using low-toxicity β-carotene and perylene materials as the active layers,31 and investigated the integration level between OPVs and OBEIs to explore the possibility of NIR photon−driven ES through the OPV devices as a means of
2. EXPERIMENTAL METHODS 2.1. OPV Device Fabrication. The OPV devices were fabricated on patterned indium tin oxide (ITO) glasses (
