COMMUNICATION © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com (1 of 8) 1606453 Microtopography-Guided Conductive Patterns of Liquid- Driven Graphene Nanoplatelet Networks for Stretchable and Skin-Conformal Sensor Array Youngjin Park, Jongwon Shim, Suyeon Jeong, Gi-Ra Yi, Heeyeop Chae, Jong Wook Bae, Sang Ouk Kim,* and Changhyun Pang* DOI: 10.1002/adma.201606453 Wearable and implantable devices aiming at biomedical diag- nosis or therapy have been developed by integrating multiple functions, [1,2] such as high bendability or stretchability, [3,4] transparency, [5,6] conformal contacts on biosurfaces, [7,8] and low Flexible thin-film sensors have been developed for practical uses in invasive or noninvasive cost-effective healthcare devices, which requires high sensitivity, stretchability, biocompatibility, skin/organ-conformity, and often transparency. Graphene nanoplatelets can be spontaneously assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar sub- strates via a convective Marangoni force in a highly controlled manner. Based on this versatile graphene assembled film preparation, a thin, stretchable and skin-conformal sensor array (144 pixels) is fabricated having microtopo- graphy-guided, graphene-based, conductive patterns embedded without any complicated processes. The electrically controlled sensor array for mapping spatial distributions (144 pixels) shows high sensitivity (maximum gauge factor ≈1697), skin-like stretchability (<48%), high cyclic stability or durability (over 10 5 cycles), and the signal amplification (≈5.25 times) via structure- assisted intimate-contacts between the device and rough skin. Furthermore, given the thin-film programmable architecture and mechanical deformability of the sensor, a human skin-conformal sensor is demonstrated with a wire- less transmitter for expeditious diagnosis of cardiovascular and cardiac illnesses, which is capable of monitoring various amplified pulse-waveforms and evolved into a mechanical/thermal-sensitive electric rubber-balloon and an electronic blood-vessel. The microtopography-guided and self-assembled conductive patterns offer highly promising methodology and tool for next-gen- eration biomedical devices and various flexible/stretchable (wearable) devices. Y. Park, Prof. G.-R. Yi, Prof. H. Chae, Prof. J. W. Bae, Prof. C. Pang School of Chemical Engineering Sungkyunkwan University (SKKU) Suwon 440-746, Republic of Korea E-mail: chpang@skku.edu Prof. J. Shim Department of Applied Chemistry Dongduk Women’s University Seoul 02748, Republic of Korea S. Jeong, Prof. C. Pang SKKU Advanced Institute of Nanotechnology Sungkyunkwan University (SKKU) Suwon 440-746, Republic of Korea Prof. S. O. Kim National Creative Research Initiative Center for Multi-Dimensional Directed Nanoscale Assembly Department of Materials Science and Engineering KI for the Nanocentury KAIST, Daejeon 34141, Republic of Korea E-mail: sangouk.kim@kaist.ac.kr Prof. C. Pang Samsung Advanced Institute of Health Science & Technology Sungkyunkwan University (SKKU) Suwon 440-746, Republic of Korea map-resolution without cross-talk, [9] and many others. In advanced multifunctional devices, it is one of the critical issues to develop noninvasive diagnostic and thera- peutic technique or minimize invasiveness if necessary. To this end, ultrathin-layer devices with active or passive electronic components are required to be flexible and also attached onto the rough surfaces of skin and other nonplanar objects. [10–12] Recently, for intimate contacts between the device and human, skin-conformal devices having thermoresponsive microneedles or microhairy structures on thin flexible or stretchable supporting layer have been reported, where the physical activity data on various spots on skin are monitored and amplified including temperature, humidity, glucose, pH, and various tiny pulsations (e.g., radial artery, carotid, and even jugular vein). [8,13] Despite remark- able advances in skin- or organ-attachable devices, challenging issues still remain for implementing those in the real-world market. For instance, the fabrication of sensor array embedded in skin-attachable and implantable devices are still compli- cated and costly due to the multistep litho- graphic processes. Moreover, since most sensing elements for sensor array are composed of metal-based microstructures, [14] hybrid composites with nanowires, [13,15] or pristine graphene sheets, [7] fabrication process also requires ultravacuum and high temperature (e.g., chemical/physical Adv. Mater. 2017, 1606453 www.advancedsciencenews.com www.advmat.de