© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 wileyonlinelibrary.com COMMUNICATION Biocompatible Nanogenerators through High Piezoelectric Coefficient 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 Nanowires for In-Vivo Applications Miaomiao Yuan, Li Cheng, Qi Xu, Weiwei Wu, Suo Bai, Long Gu, Zhe Wang, Jun Lu, Huanping Li, Yong Qin,* Tao Jing,* and Zhong Lin Wang* M. Yuan, [+] L. Cheng, [+] Q. Xu, W. Wu, S. Bai, L. Gu, Z. Wang, Y. Qin Institute of Nanoscience and Nanotechnology School of Physical Science and Technology Lanzhou University Lanzhou 730000, China E-mail: qinyong@lzu.edu.cn M. Yuan, J. Lu, H. Li, T. Jing Institute of Pathogenic Biology School of Basic Medical Sciences Lanzhou University 730000, China E-mail: jtao@lzu.edu.cn M. Yuan, Y. Qin, T. Jing The Research Institute of Biomedical Nanotechnology School of Basic Medical Sciences Lanzhou University Lanzhou 730000, China Y. Qin, Z. L. Wang Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 100085, China E-mail: zhong.wang@mse.gatech.edu Z. L. Wang School of Materials Science and Engineering Georgia Institute of Technology Atlanta, Georgia 30332–0245, USA DOI: 10.1002/adma.201402868 cost, inconvenience to the patients and potential radiation effect. [10] In a case of the thermoelectric power generator, it is necessary to have a large temperature gradient, which is impos- sible inside human body. Therefore, it is extremely urgent to develop new techniques for effective and sustainable power supplies. Fortunately, there is abundant and natural in vivo biomechanical energy, such as bone strain, acceleration during locomotion, motion of respiration and heart contraction. If these mechanical energies can be harvested, it will contribute greatly to solving the challenge of powering IMDs. The nanogenerators (NGs) as an emerging energy con- vertor, [11,12] which can convert tiny mechanical energy in the environment such as low frequency movement, [13,14] air flowing, [15] animal’s motion [16] and heart beating [17] into elec- trical energy, have attracted much attention in recent years. NGs can be effectively integrated with the micro/nano-scale functional devices to form a self-powered system. This has been proven practicable via self-powered pH sensor, UV sensor, small liquid crystal display, commercial laser diode, pressure/speed sensor, environmental sensor and so on. [18–24] After generating electricity with rabbit quadriceps, [25] the piezoelectric NG shows the great potential to be further integrated with IMDs to form a self-powered system. Furthermore, piezoelectric NGs have been implemented in animals’ bodies to harvest energy from the motion of different organisms such as heart, lung and dia- phragm. [26] More importantly, comparing with the other energy technologies such as battery, NG can power the IMDs for quite long time because it can continuously convert the mechanical movements into electricity. As for the application of powering IMDs, the in vivo biocompatibility of NG is a big concern. Therefore, developing a kind of biocompatible NG with high performance is critically important. Although ZnO has a good biocompatibility, [27] due to the relatively low piezoelectric coef- ficient, the output power of ZnO based NGs is relatively low, which limits their applications in powering some in vivo elec- trical devices. The conventional high piezoelectric coefficient materials are dominated by the lead zirconatetitanate (PZT) family. However, the Pb toxicity causes severe pollution to the environment during the synthesis process and the hazard to human body, which hinders the applications of Pb-based mate- rials for IMDs. Thus it is urgent to search for materials with high piezoelectric coefficient and good biocompatibility. As an emerging lead-free piezoelectric material, 0.5Ba(Zr 0.2 Ti 0.8 )O 3 - 0.5(Ba 0.7 Ca 0.3 )TiO 3 (BZT-BCT) has a piezoelectric coefficient (∼620 pC/N) [28] that can be compared with the conventional Implantable medical devices (IMDs) have been widely used for therapies and may serve as functional devices to detect, prevent and cure many diseases challenging human life. [1–7] Among all factors affecting the performance of an IMD, a power source is indispensable for its operation, which is now becoming a major technological difficulty for sustainable operation of the IMD. Although several technologies such as battery, electromagnetic induction [8] and thermoelectric devices [9] have been explored, there are still many bottlenecks for them to power IMDs. Up to now, lithium batteries have been widely used to power the IMDs, but due to their limited capacity and lifetime, the patients are required to have surgeries to replace the depleted battery once a while, which is not only a painful process but also a high risky surgical procedure. As for the wireless power transmission technology, the energy is transferred between in vitro and in vivo coils or wires by electromagnetic wave or ultra- sonic, which has a relatively low efficiency, high equipment [+] These authors contributed equally to this work. Adv. Mater. 2014, DOI: 10.1002/adma.201402868 www.advmat.de www.MaterialsViews.com