Contents lists available at ScienceDirect Nano Energy journal homepage: www.elsevier.com/locate/nanoen Development of battery-free neural interface and modulated control of tibialis anterior muscle via common peroneal nerve based on triboelectric nanogenerators (TENGs) Sanghoon Lee a,b,c,d , Hao Wang a,b,c,d , Qiongfeng Shi a,b,c,d , Lokesh Dhakar a,c , Jiahui Wang a,b , Nitish V. Thakor b,e,f , Shih-Cheng Yen a,b,c , Chengkuo Lee a,b,c,d,e, ⁎ a Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Singapore b Singapore Institute for Neurotechnology (SINAPSE), National University of Singapore, Singapore 117456, Singapore c Center for Intelligent Sensors and MEMS, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Singapore d NUS Suzhou Research Institute (NUSRI), Suzhou, Industrial Park, Suzhou 215123, PR China e Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore 117456, Singapore f Johns Hopkins University, Biomedical Engineering, Baltimore, MD 21205, USA ARTICLE INFO Keywords: Flexible electronics e-Skin Implantable bioelectronics Neural interface Selective stimulation Triboelectric nanogenerator (TENG) ABSTRACT Flexible and stretchable electronics, also known as e-skin, have been a technology to create diversified sensors and wearable devices. Implantable bioelectronics have recently been recognized as a promising research field to modulate biological signals and treat many diseases and pathological conditions. The marriage of two technologies gives us a new cutting-edge research area, i.e., implantable flexible electronics. While strain sensors, ECG sensors, pH sensors, temperature sensors and LED chips have been integrated together as a novel platform for measuring physiological signals, one of critical challenges for long-term use of such devices is a reliable power source with sound output power. To support operation of the implantable bioelectronics, triboelectric nanogenerators (TENGs) have recently been explored, as a promising technology to harvest energy, as the concept of scavenging human body energy into useful electrical power. In this work, we investigate stacked TENGs with output voltage of 160 V p-p and a short circuit current of 6.7 μA as a potential power source for neural stimulation using flexible and adjustable neural interfaces. To advance a generic design of flexible neural interfaces which is good at sciatic nerve recording and stimulation, we optimize a new flexible sling electrode and successfully achieve neural signal recording with different amplitudes and latencies. More importantly, successful selective stimulation achieved in this work proves that the flexible sling electrode is a good generic neural interface. We demonstrate direct stimulation of a sciatic nerve and a common peroneal nerve in rats by the TENGs connected with the suggested interface and a pair of Pt/Ir wires, respectively, while monitoring muscle signals. The muscle contraction can be controlled by the operation of the TENGs. This prove-concept result indicates that this technology could be the way of realizing battery-free wearable neuromodulators in the future. 1. Introduction Implantable bioelectronics have recently emerged as a powerful way to monitor biological signals and treat diseases such as pace- makers, deep brain stimulators, and neuromodulators [1–3]. The enormous progress attributed to the development of flexible/stretch- able electronics, which enables the integration of various kinds of bio- sensors, actuators and energy storage elements, has opened up a new research field [4–8]. Meanwhile, using e-skin technology to craft soft and stretchable implantable/wearable medical devices, it has also provided a better interface to the human organs, blood vessels and neural branches. By using these flexible implantable bioelectronics to achieve more sensitive and accurate bio-signal recording and stimula- tion, we have new ways of enabling electroceuticals [9–11]. One of critical challenges for long-term use of such devices is a reliable power source with sound output power. Some feasible solutions have been investigated including external energy sources, which are out of body and provides energy to the devices via wired [3] and wireless [12–14] communication, and implantable batteries that normally require recharge or replacement [15,16]. The concept of scavenging human http://dx.doi.org/10.1016/j.nanoen.2016.12.038 Received 23 October 2016; Received in revised form 17 December 2016; Accepted 17 December 2016 ⁎ Corresponding author at: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Singapore. E-mail address: elelc@nus.edu.sg (C. Lee). Nano Energy 33 (2017) 1–11 Available online 10 January 2017 2211-2855/ © 2017 Elsevier Ltd. All rights reserved. MARK