Oliver Graudejus, Arizona State University
Ingrid Graz, Johannes Kepler University
Ivan Minev, EPFL
Tsuyoshi Sekitani, Osaka University
Symposium Support Aldrich Materials Science
Morrell Instrument Company Inc.
LL2/II2: Joint Session: Neural Interfacing I
Tuesday PM, April 07, 2015
Park Central Hotel, 2nd Floor, Metropolitan II
2:30 AM - *LL2.01/ll2.01
Optimizing the Charge Transport and Mechanical Properties of Functionalized Polythiophene Copolymers for Biomedical Device Interfaces
David C. Martin 1 Liangqi Ouyang 1 Bin Wei 1 Jing Qu 1 Jinglin Liu 1 Whirang Cho 1 Minsoo Kim 1 Chin-Chen Kuo 1
1The University of Delaware Newark United StatesShow Abstract
We are continuing to investigate the molecular design, electrochemical synthesis, and characterization of functionalized polythiophene copolymers based on poly(3,4-ethylene dioxythiophene) (PEDOT) and poly(3,4-propylene dioxythiophene) (PProDOT). Our most recent efforts have focused on the use of multifunctional monomers for introducing controlled amounts of crosslinking and branching and for promoting adhesion with solid inorganic substrates and specific interactions with soft living tissue. By introducing various amounts of these comonomers, we have created families of materials with tailored electronic and ionic charge transport and mechanical properties. We will specifically discuss the use of a tri-functional EDOT monomer 1,3,5-tri[2-(3,4-ethylenedioxythienyl)]-benzene (EPh), an amine-functionalized EDOT (EDOT-amine), and a multiply ProDOT-modified polyhedral oligomeric silsequioxane (POSS). The structure and properties of these functionalized copolymers were determined using UV/Vis, FTIR, and NMR spectroscopy; optical and electron microscopy; and cyclic voltammetry and electrochemical impedance spectroscopy (EIS).
3:00 AM - LL2.02/II2.02
Auxetic Micropatterning of a Cell Adhesive-Conductive Composite for Cardiac Tissue Engineering
Michaella Kapnisi 1 2 3 Damia Mawad 1 2 3 Dilshani Rathnayake-Arachchige 4 Paul Conway 4 Molly Stevens 1 2 3
1Imperial College London London United Kingdom2Imperial College London London United Kingdom3Imperial College London London United Kingdom4Loughborough University Loughborough United KingdomShow Abstract
Cardiac patches are a highly promising tissue engineering solution, to treat one of the most common cardiovascular diseases, myocardial infarction . Conductive polymers are of particular interest as scaffolds for cardiac tissue engineering, primarily for their potential ability to transport the electrical pulses which are vital to the contractions of the heart. However, they need further manipulation in order to impart the properties necessary of a cardiac tissue scaffold , . Herein the need for improved mechanical and topological properties, particularly the anisotropy of stiffness, is addressed by the auxetic micropatterning of a cardiac patch. Auxetic materials are those with a negative Poisson&’s ratio, they expand laterally when stretched longitudinally. The negative Poisson&’s ratio can also explain the other distinctive properties of auxetic materials, such as shear resistance, indentation resistance and anisotropy, which make it appealing as a possible feature of biomaterials . A thin layer of a cell adhesive was successfully micropatterned with a re-entrant honeycomb design by excimer laser microablation. The high precision of this pattern is maintained upon coating and crosslinking with a conductive polymer layer. The micropatterned samples, both before and after coating have been characterised by optical microscopy, scanning electron microscopy and x-ray photoelectron spectroscopy. The ability to control the porosity, effective stiffness and anisotropy of the cardiac patch, by modifying pattern dimensions, has been confirmed by mechanical tests. In addition, measurements for the mode of fracture, stress, effective stiffness and anisotropy have been compared to finite element analysis models. In vitro cell studies have also been conducted to demonstrate the level of support, adhesion and alignment of cardiac cells on the patches. Hence it can be seen, that through the incorporation of an auxetic micropattern, a material&’s properties&’ can be directed to more closely match those of native cardiac tissue, which in turn could lead to improved scaffold design for cardiac tissue engineering.
 A. Silvestri, M. Boffito, S. Sartori, and G. Ciardelli, “Biomimetic materials and scaffolds for myocardial tissue regeneration.,” Macromol. Biosci., vol. 13, no. 8, pp. 984-1019, 2013.
 J. G. Hardy, J. Y. Lee, and C. E. Schmidt, “Biomimetic conducting polymer-based tissue scaffolds.,” Curr. Opin. Biotechnol., vol. 24, pp. 1-8, 2013.
 E. S. Place, N. D. Evans, and M. M. Stevens, “Complexity in biomaterials for tissue engineering.,” Nat. Mater., vol. 8, no. 6, pp. 457-70, 2009.
 K. E. Evans and A. Alderson, “Auxetic Materials: Functional Materials and Structures from Lateral Thinking!,” Adv. Mater., vol. 12, no. 9, pp. 617-628, 2000.
3:15 AM - *LL2.03/II2.03
Conducting Polymers: Stretchable Polymeric Neural Electrode Array
Liang Guo 1
1The Ohio State University Columbus United StatesShow Abstract
Conducting polymers are often employed as coatings on smooth metal electrodes to improve the electrode performance with respect to the signal-to-noise ratio (SNR) for neural recording, charge-injection capacity for neural stimulation, and inducement of neural growth for electrode-tissue integration. However, adhesion of conducting polymer coatings on metal electrodes is poor, making the coating less durable and the electrical property of the electrode less stable. Moreover, conventional conducting polymers have relative low conductance, preventing their direct use as the electrode and lead material; and they are brittle, making it difficult for flexible neural electrodes to incorporate conducting polymer coatings.
We have developed a new polypyrrole/polyol-borate composite film with concurrent excellent electrical and mechanical properties. We further developed a method to fabricate a stretchable multielectrode array, directly, using this new material as the sole conductor for both electrodes and leads, in contrast with the conventional approach of incorporating conducting polymers only through coating on non-stretchable metal electrodes. The resulting stretchable polymeric multielectrode array (SPMEA) was stretchable up to 22.84% uniaxial tensile strain with minimal losses in electrical conductivity. Electrochemical testing revealed the SPMEA&’s impressive advantage for recording local field neural potentials and for epimysial stimulation of denervated skeletal muscles.
As a neural interface engineer, I would also like to compare the compliant neural interfacing technology to other technologies, such as optogenetics, radiogenetics, and even a living neural interface that is currently under development in our lab.
4:15 AM - *LL2.04/II2.04
Interfacing with the Brain Using Organic Electronics
George G. Malliaras 1
1Ecole des Mines Gardanne FranceShow Abstract
Implantable electrodes are being used for diagnostic purposes, for brain-machine interfaces, and for delivering electrical stimulation to alleviate the symptoms of diseases such as Parkinson&’s. The field of organic electronics made available devices with a unique combination of attractive properties, including mixed ionic/electronic conduction, mechanical flexibility, enhanced biocompatibility, and capability for drug delivery. I will present examples of organic electrodes, transistors and other devices for recording and stimulation of brain activity and discuss how they can improve our understanding of brain physiology and pathology, and how they can be used to deliver new therapies.
4:45 AM - LL2.05/II2.05
Frequency-Based Pressure Sensors for Neural Interfacing
Benjamin Tee 1 Alex Chortos 1 Andre Berndt 1 Ariane Tom 1 Allister McGuire 1 Kevin Tien 3 Huiliang Wang 1 Bianxiao Cui 1 Tse Nga Ng 2 Karl Deisseroth 1 Zhenan Bao 1
1Stanford University Stanford United States2Palo Alto Research Ctr Sunnyvale United States3Columbia University New York United StatesShow Abstract
Active and multifunctional prosthetics could provide amputees with improved quality of life by restoring the sense of touch that is so essential to many human experiences. In order to make active prosthetics a reality, fabricated sensors must be able to communicate information about stimuli to the nervous system of the wearer. Consequently, sensing systems must be developed that produce signals that can be interpreted by the nervous system. Mechanoreceptor cells in humans transduce a force signal into a frequency signal, and the frequency is reflective of the magnitude of the force. We have created an artificial mechanoreceptor system that mimics the frequency-based force sensing properties of human skin by integrating a resistive pressure sensor with a ring oscillator. The use of printed organic ring oscillators is important for future applications in large area, low cost sensor skins. The pressure sensor functions based on the contact-area dependent tunneling resistance between a counter electrode and a micropatterned composite of CNTs and insulating polymer. The pressure sensors were optimized to function in the appropriate impedance range to facilitate the frequency-dependent operation of the oscillators. The oscillators are operated at biologically-relevant frequencies in the range from 0 to ~200 Hz. By controlling the concentration of CNTs, the pressure sensing range can be widely tuned. This can be used to mimic the different sensitivities of mechanoreceptors located in different parts of the body. By using switch-like pressure sensors with a large pressure threshold, the devices can mimic pain receptors, which act as switch-like sensors that turn on at large pressure values. The frequency signal of the sensors was used to stimulate mouse neurons using an optoelectronic approach. There was a direct correspondence between the frequency of the sensor and the resulting frequency of action potentials in the neurons. These simple, neutrally-interfaced pressure sensors are a substantial step toward the development of cost effective active prosthetics.
5:00 AM - *LL2.06/II2.06
Freestanding Conductive Hydrogels for Soft, Flexible Organic Bionics
Rylie Green 1
1The University of New South Wales Sydney AustraliaShow Abstract
Soft, flexible electrode arrays have been proposed for improving the chronic performance of bioelectronic devices. Conducting polymers (CP) are the technology of choice for producing soft electrode coatings [1, 2]. Despite CPs being softer than conventional metal electrodes, brittle and friable mechanical properties have limited their use. As such, researchers have studied copolymers of CPs with flexible materials such as hydrogels [3, 4]. Although approaches have been developed for fabricating such copolymer electrode coatings, the integration of CPs within hydrogels remains suboptimal . Furthermore, most of these approaches require electropolymerisation of the CP from an underlying substrate, which limits them to being coatings rather than freestanding electrode arrays. This research explored the fabrication of freestanding conductive hydrogels (CHs) by seeding hydrogels with chains of pre-synthesised CP. The dispersed CP chains were hypothesised to provide nucleation sites, from which subsequent CP could be electropolymerised.
Chemically synthesised poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) was dispersed within a 20 wt% poly(vinyl alcohol) (PVA) solution at 0.01, 0.05, 0.1 and 0.5 wt%. PEDOT:PSS is a dispersion of polymer chains, and cannot meet the fast charge transfer requirements of medical electrodes . The hydrogels were crosslinked by photopolymerisation and then PEDOT was electropolymerised through the PVA-PEDOT:PSS at 0.5 mA/cm2. The electrical properties and physical appearance of the gels were analysed at varied time points between 10 and 160 mins of electrodeposition.
Nucleation and growth of CP through the PEDOT:PSS loaded PVA was macroscopically observed (opaque blue particulate was seen) at the highest loading after only 10 min of electropolymerisation. No CP was observed in the lower loadings even at 160 min. The 0.5 wt% PEDOT:PSS loaded PVA, showed a significant increase in CSC from 3.8 mC/cm2 at 0 min to 16 mC/cm2 at 160 min. There was also a statistically significant decrease in the impedance at 1Hz with the average impedance magnitude decreasing from 1990 Omega; to 715 Omega;.
These studies demonstrate that nucleation and CP growth within an insulative material can be achieved through secondary nucleation, being the use of a CP chain from which subsequent CP can grow. Loading the PVA with 0.5 wt% PEDOT:PSS enabled the fabrication of a free-standing, electroactive material, but this was time consuming and the electroactivity achieved was still relatively low compared to other CP materials. Future work will explore loading the hydrogel with a higher percentage of PEDOT:PSS.
 R.A. Green, et al, Biomaterials, 29 (2008) 3393-3399.
 G.G. Wallace, G.M. Spinks, Soft Matter, 3 (2007) 665-671.
 S. Sekine, Y. et al, Journal of the American Chemical Society, 132 (2010) 13174-13175.
 R.A. Green, et al, Macromol Biosci, 12 (2012).
 L. Basiricograve;, et al, Organic Electronics, 13 (2012) 244-248.
5:30 AM - LL2.07/II2.07
Photochemical Sub-Micron Patterning of Organic and Carbon-Based Materials for High-Density Flexible Electronics
Jaekyun Kim 1 Myung-Gil Kim 2 Sangho Jo 1 Jingu Kang 1 Jaehyun Kim 1 Jeong-Wan Jo 1 Juhyuk Moon 3 Yong-Young Noh 4 Yong-Hoon Kim 5 6 Sung Kyu Park 1
1Chung-Ang University Seoul Korea (the Republic of)2Chung-Ang University Seoul Korea (the Republic of)3Stony Brook University Stony Brook United States4Dongguk University Seoul Korea (the Republic of)5Sungkyunkwan University Suwon Korea (the Republic of)6Sungkyunkwan University Suwon Korea (the Republic of)Show Abstract
The recent developement of high performance organic and carbon-based materials demonstrated charge carrier mobility and conductivity over 10 cm2V-1s-1 and 103-104 Scm-1, respectively, which outperform industrial standard materials such as amorphous silicon and indium-tin-oxide. Although these outstanding electrical properties from the soft matters envision them as promising building blocks for next generation flexible electronics, reliable and scalable fine-patterning technology should be also accompanied toward realization of high-density and multi-functional soft electronics. Typically, a proper isolation/patterning of the functional materials is required to suppress parasitic and off current, leading to less cross-talk between neighboring devices and minimum power consumption in the high density integrated systems. For patterning the soft materials, fluorinated photoresist using an orthogonal solvent, pre-patterned self-assembled monolayers, and various direct printing techniques have been reported, however, several drawbacks such as the process complexity, limited choice of materials, low throughput, and resolution limit have been problematic for industrial realization. Here, we report a facile and general route to achieve scalable high-resolution (sub-micron) patterning of organic and carbon-based materials for device and material integrations via a photochemically induced molecular disordering. Upon deep ultraviolet (DUV) irradiation, the soft matters underwent dissociation of specific chemical bonds within molecules as well as loss of inter-molecular ordering, transforming them into non-functional state. Spatially-selective DUV irradiation enables large arrays of patterned functional devices on a substrate. Utilizing this patterning approach, various organic and carbon-based thin-film-transistors were fabricated demonstrating well-defined active material isolation (current on/off ratio: >107) and minimized parasitic current (~pA), and low-power consumption integrated circuits on both rigid and flexible substrates without compromising their individual device performance.
5:45 AM - LL2.08/II2.08
Protein-Based Protonic Transistors
David D. Ordinario 1 Long Phan 1 Jonah-Micah D. Jocson 1 Tam Nguyen 1 Yegor Van Dyke 1 Alon Gorodetsky 1 Emil Karshalev 1
1University of California, Irvine Irvine United StatesShow Abstract
Ionic transistors from organic and biological materials represent an emerging class of soft and flexible devices for bioelectronics applications. Within this context, protonic transistors are exciting targets for further research and development, despite the fact that they have received relatively little attention to date. Such devices represent a natural choice for interfacing rugged traditional electronics and biological systems due to the ubiquity of proton transport and transfer phenomena in biology. Recently, we have fabricated and characterized protonic transistors from the cephalopod structural protein reflectin.1 We have investigated these devices with standard electrical and electrochemical techniques, discovering that they exhibit performance comparable to the best protonic transistors.1 We have also developed simple strategies for improving the performance of our protein-based transistors by altering their active layer geometry and integrating them with flexible substrates. Overall, our findings may hold significance for a broad range of conformable biomedical and bioelectrochemical devices.
1. Ordinario, D. D.; Phan, L.; Walkup IV, W. G.; Jocson, J.-M.; Karshalev, E.; Hüsken, N.; Gorodetsky, A. A. Bulk protonic conduction in a cephalopod structural protein. Nat. Chem. 2014,6, 596-602.
LL3: Poster Session: Organic and Stretchable Bioelectronics
Tuesday PM, April 07, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - LL3.01
Microscale Mechanical Testing of Electrochemically Polymerized Poly(3,4-ethylene dioxythiophene) (PEDOT) Thin Films by In-Situ FIB/SEM
Chin-Chen Kuo 1 Fei Deng 1 David C. Martin 1
1University of Delaware Newark United StatesShow Abstract
PEDOT is a conjugated polymer that is of considerable interest for use in neural interfaces. However, in certain cases delamination and cracking of PEDOT-based coatings has been observed after extended implantations in vivo. Therefore, more detailed information about the mechanical properties of PEDOT films is needed. However it is difficult to obtain free-standing thin films of sufficient size to do extensive mechanical testing. A variety of indirect methods have been used to estimate PEDOT film mechanics such as nanoindentation or Atomic Force Microscopy Quantitative Nanomechanical analysis (AFM QNM). Here, we describe a novel method of testing the tensile properties of individual PEDOT thin films using the manipulating probe and capacitive force sensor inside the sample chamber of a Zeiss Auriga 60 Focused Ion Beam / Scanning Electron Microscope (FIB/SEM). The typical sample cross section was 0.7 um x 1.5 um, with gage length of ~5 um. Our results reveal that tensile modulus of electrochemically deposited PEDOT thin films is ~5 GPa, and the tensile strength is ~170 MPa.
9:00 AM - LL3.02
Facile Fabrication of Wavy Ag Nanowire Network for Stretchable Transparent Electrodes
Jun Beom Pyo 1 Byoung Soo Kim 1 2 Tae Ann Kim 1 Hyun-Chul Park 1 Jong Hyuk Park 1 Jonghwi Lee 2 Sang-Soo Lee 1
1Korea Institute of Science and Technology Seoul Korea (the Republic of)2Chung-Ang University Seoul Korea (the Republic of)Show Abstract
Ag nanowire networks are considered one of the strong candidates for stretchable transparent conductor which are essential components in many of the stretchable electronics. Therefore, there have been many studies to control Ag nanowire alignment, create composites, change interfaces of substrates and more to increase the stability in conductivity under applied strains. Here we present a facile fabrication process that creates networks of wavy Ag nanowires. Strains up to 30% were applied to measure changes in resistances and cyclic tests were also conducted to analyze stability of the samples both of which tests resulted enhanced performances in the samples made using our transfer process. Scanning electron microscope (SEM) and optical microscope were utilized to analyze and understand the creation of wavy structure. Images of wavy nanowires being stretched and released to its original curved shape were acquired which support their improved performances. Developed electrodes were directly applied to dielectric elastomer actuators to further analyze their structural benefits. We anticipate that the method that we have developed could potentially be used for creating wavy structures in other metal nanowires for various applications.
9:00 AM - LL3.03
Metrology of Organic Electronics using Elastomeric Substrates: Beyond the Tensile Modulus
Adam Printz 1 Andrew S.-C. Chiang 1 Suchol Savagatrup 1 Daniel Rodriquez 1 Darren J. Lipomi 1
1University of California, San Diego La Jolla United StatesShow Abstract
Reducing mechanical degradation in organic electronics is of critical importance to create robust devices which can survive roll-to-roll manufacturing, as well as repetitive strains applied during use in portable, outdoor, and wearable applications. In applications where devices undergo these repetitious strains, plastic deformation is frequently undesirable. However, the difficulties in fabricating and manipulating free-standing thin films pose a barrier to measuring the mechanical properties of these films. The buckling technique—in which the wavelength of sinusoidal buckles on elastomeric substrates is correlated to the tensile modulus of thin films—has been frequently utilized in the literature. However, the tensile modulus only describes how a material behaves under strain while it is still in the elastic regime. To gain a more complete understanding of how stretchable organic semiconductors are, we developed an extension of the buckling technique to determine the elastic limit of thin films. By iteratively straining (increasing the strain upon each iteration) and relaxing the film on an elastomeric substrate, we could determine the elastic limit by observing the onset of sinusoidal buckles in the film in the relaxed state. Utilizing this technique, we found a positive correlation in the elastic limit of poly(3-alklythiophene)s (P3ATs) with increasing alkyl side-chain length as well as increasing film thickness. This simple technique to determine the strain devices can accommodate before plastically deforming will inform the design and selection of appropriate materials for portable, wearable, and outdoor applications.
9:00 AM - LL3.04
Uniformly Interconnected Silver Nanowire Network for Transparent and Stretchable Heater
Sukjoon Hong 1 Habeom Lee 1 Jinhwan Lee 1 Junyeob Yeo 1 Seungyong Han 1 Young Duk Suh 1 Hyunjin Moon 1 Jinhyeong Kwon 1 Seung Hwan Ko 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Currently, intensive researches are ongoing for developing innovative electronics that can be bent, folded and even stretched, and it is a very exciting moment for both industry and academia as the demands on these devices are rapidly increasing due to the explosive growth of wearable devices and bio-integrable electronics. The realization of stretchable electronics has been considered to be very challenging, but the investigations on the nanowires (NWs) revealed that they can exhibit outstanding stretchability and mechanical robustness at the micro-scale, while at the same time diverse configurations and structures such as conductive percolation network are introduced to boost these properties at the macro-scale to produce large-area stretchable devices.
In this study, as one of the potential applications in soft electronics, we report bio-compatible, transparent and stretchable heater based on solution processed silver (Ag) NW percolation network. Ag NW percolation network has been received a great amount of attention as it can exhibit both high optical transmittance and low sheet resistance even at significant strain. We utilize the Ag NW percolation network as a heater by inducing an electrically driven Joule heating. For the fabrication of the transparent and stretchable heater, uniform Ag NWs are firstly synthesized by a conventional polyol process and transferred to a thin Polydimethylsiloxane (PDMS) film by vacuum filtration process. The vacuum filtration transfer provides not only homogeneously dispersed Ag NW on the PDMS film, but also the effect of mechanical pressing of the Ag NW junctions as the pressure is applied between Ag NW percolation network and the target PDMS film. As a result, the Ag NW percolation network prepared by the vacuum filtration transfer exhibits superb electrical conductivity even without any thermal treatment. By applying a constant bias voltage, we confirmed that the proposed heater successfully operates at 50 % strain, which is considered to be sufficient for general wearable applications.
As PDMS shows good conformal coverage and fine biocompatibility, the proposed transparent and stretchable heater can be directly applied to wide range of applications. As a proof-of-concept design, we attach the proposed heater on vial and human wrist to confirm its operation under various deformation and physical disturbances.
9:00 AM - LL3.05
Direct Printing of Stretchable Strain Sensor Based on Silver Nanowires (Ag NWs)/PDMS Composite
Hyungdong Lee 1 Baekhoon Seong 1 Doyoung Byun 1
1Sungkyunkwan University Suwon Korea (the Republic of)Show Abstract
In this study, we fabricated stretchable Silver nanowries (Ag NWs)/PDMS composite strain sensor with arbitrary micro-pattern electrodes using dispensing nozzle printing. In order to find mechanically stable electrode design, we proposed two types of electrodes such as a series of rings and diamonds shape pattern. Also, we investigated that the electrical resistance of patterned line could be modified according to the printing condition such as speed of nozzle. Through the static simulation about the two geometries to compare proper pattern when strain sensor was stretched. As a results, we obtained highly stretchable strain sensor (up to 60 % strain) with suitable electrode design. Based on experimental results, the authors are expect that directly drawn electronic skin (E-skin) via printing method can be fabricated with multifunctional sensing abilities in the near future.
9:00 AM - LL3.06
Ink Composition of PEG Filler Inks for Printed 3D Microfluidic Devices
Owen Hildreth 1 Christopher Lefky 1 Avinash Mamidanna 1 Jignesh Vanjaria 1
1Arizona State University Tempe United StatesShow Abstract
The ability to directly print a 3D microfluidic device and sensor using the equivalent of a home printer is a very attractive technology for rapidly deploying chemical and biological sensors. One of the challenges of printing a 3D microfluidic device is removing the “filler” material that is used to define the future microfluidic channel. In this work we examine the use of common Poly(Ethylene Glycol) (PEG) ink as a phase-change filler material with Polydimethylsiloxane (PDMS) ink acting as a printed matrix material. The printed PEG is solid near room temperature and undergoes a phase-change at mild temperatures enabling the filler to be simply “pushed” out of the microfluidic device. This ink combination allows us to print a fully functioning microfluidic device from a 3D Computer Aided Design (CAD) file using drop-on-demand printing techniques.
This work examines how PEG and PDMS molecular weight, ink composition, solvent type, print viscosity, jetting parameters, and substrate temperature impact printed feature resolution. Computational models and experiments show how PEG melt viscosity impacts both directly driven flow channel clearing along with pocket clearing where diffusion is required to completely remove the filler material from a “dead-end” reservoir. A simple chemical detector is exampled by printing metal electrodes using metal-reactive inks. Overall, this work demonstrates a simple method to fabricate 3D microfluidic devices using readily available drop-on-demand printing techniques and helps bring the concept of at-home device fabrication one step closer to reality.
9:00 AM - LL3.07
Hybrid Substrate Structure for Strain-Free and Readily Stretchable Electronic Circuits
Chan Woo Park 1 Bock Soon Na 1 Soon Won Jung 1 Ji-Young Oh 1 Sang Seok Lee 1 Jae Bon Koo 1
1Electronics and Telecommunications Research Institute Daejeon Korea (the Republic of)Show Abstract
We propose a new structure of the substrate for fabricating stretchable electronic circuits, which provides well-controlled wavy and stretchable regions for interconnects and flat and rigid areas for active devices, respectively. Although many approaches have been demonstrated to be very successful in realizing highly stretchable electronic circuits, it is still difficult to achieve high reliability and reproducibility for more practical, especially large-area applications. For overcoming the inherent drawbacks of previous technologies based on pre-stretching and transfer processes, a new strategy is required for obtaining highly stretchable interconnects with no pre-stretching step, while completely suppressing the deformation within active device areas. In the present work, we demonstrate a new approach employing a hybrid structure for polyimide substrates, where thick-and-flat islands are located within a thin-and-wavy layer. For achieving the hybrid structure, we first prepared a wavy Si substrate with a water-soluble sacrificial layer on it, and coated and cured a thin (~600nm thick) polyimide layer so that the wavy surface profile could be maintained. After additionally coating and pattering a thick (~9mu;m thick) polyimide layer by photolithography and wet etching processes, we could obtain a hybrid substrate with thick-and-flat islands with tapered sidewalls on the thin-and-wavy layer. After forming various types of active devices (organic or oxide thin film transistors) and metal interconnects (Al or Au) within the island and wavy region, respectively, the whole circuit was transferred to a stretchable sheet by casting a silicone elastomer onto the substrate and dissolving the sacrificial layer. At this state, even when the whole circuit was stretched up to ~40%, the strain within the thick island region remained nearly 0%, while most strain was compensated by the deformation of the wavy interconnecting area. Such observation can be attributed to large difference in the local stiffness of the thick and thin polyimide areas. It was also observed that the transistors and interconnects still maintained proper functions under highly stretched conditions, which implies that the simultaneous control of local stiffness and surface profile can enhance the circuit stretchability effectively. As the whole circuit can be fabricated by conventional processes which are completely compatible with existing flexible circuit technologies, the present technique is also desired to be readily applicable for practical systems.
This research was funded by the MSIP(Ministry of Science, ICT & Future Planning), Korea in the ICT R&D Program (The core technology development of light and space adaptable energy-saving I/O platform for future advertising service).
9:00 AM - LL3.08
Stretchable Dynamic Acoustic Devices with Elastic Flat Spiral Voice Coil of Liquid Metal
Sang Woo Jin 1 Soo Yeong Hong 1 Heun Park 1 Yura Jeong 1 Jeong Sook Ha 2
1Korea University Seoul Korea (the Republic of)2Korea Univ Seoul Korea (the Republic of)Show Abstract
Considering the dramatic need of various wearable and body-attached devices, it will be very useful to develop stretchable acoustic devices applicable to them. Until now, however, the research and the fabrication of the acoustic devices remained flexible, mainly because of the limited materials of the operating component, such as rigid metal wire of voice coil.
In this work, we report on the fabrication of the stretchable dynamic acoustic devices of actuator/sensor using elastic flat polymer matrix with embedded spiral microchannel filled with liquid metal that exhibits stable electric and mechanical properties under applied uniaxial strain of up to 50%.
The stretchable acoustic device is composed of the deformable liquid metal voice coil on which neodymium magnet is attached. To fabricate the liquid metal voice coil, we prepared SU-8 mold with embossed spiral pattern via photolithography and poured the mixtures of elastic polymers (PDMS & Ecoflex) on the SU-8 mold. The use of the liquid metal Galinstan makes the stretching of the voice coil possible by providing electrical stability under mechanical deformation.
Because of the principles of the dynamic acoustic devices, it can perform as both acoustic actuator and sensor simultaneously. If the device is once fed by audio frequency electric currents, liquid metal voice coil generates mechanical vibration by creating alternate magnetic field that interacts with neodymium magnet, and emits acoustic wave. On the other hand, if the device is fed by external acoustic vibration, the vibrating interaction between neodymium magnet and liquid metal voice coil generates audio frequency electric currents which can be recorded by commercial computer programs.
To demonstrate the acoustic performance of the device, we carried out frequency-response test by applying audio frequency sine wave sweep signal from 100 Hz to 22 kHz. As an acoustic actuator, it generates audio frequency acoustic wave and shows stable performance under uniaxial strain of up to 50% and biaxial strain of up to 30%. As an acoustic sensor, it detects external audio frequency vibration and generates acoustic frequency electric current, also shows stable performance under the 50% uniaxial strain. To show the performance of the device more eidetically, we played and recorded pop song through the device, and both demonstration is also conducted under uniaxial strain respectively. Such acoustic device invented in this study has an enormous potential for their application as a stretchable, wearable and bio-implantable acoustic sensor and actuator electronics.
9:00 AM - LL3.09
Stretchable Galvanic Skin Response Monitoring Electronic Textile
Peter Haddad 1 2 Amir Servati 1 2 Saeid Soltanian 1 Frank Ko 2 Peyman Servati 1
1University of British Columbia Vancouver Canada2University of British Columbia Vancouver CanadaShow Abstract
Measurement of galvanic skin response (GSR) is critical for the evaluation of tissue dehydration as well as sweating as an indicator to assess the autonomic nervous system (ANS). Therefore, the monitoring of the electrodermal response could have many clinical applications in different fields including neurology psychiatry, emergency medicine and also in pharmaceutical research. The main obstacle for using this well-established physiological fact for the real clinical application is the lack of stretchable and wearable sensing systems that could be used for long-time monitoring purposes. Although the GSR measurement has been widely used for decades, the commercial electrodes suffer from several drawbacks such as lack of comfortability and stability for prolonged measurements. This work presents a novel nanofibrous electronic textile suitable for monitoring of skin conductance that can be used for wearable wireless health monitoring applications. Several moisture sensitive and skin conductance sensors are integrated in the form of a stretchable wearable textile that can enable intimate and conformal contact with the skin of patients and be used for accurate monitoring of skin moisture and conductance. The stability of sensors are studied by prolonged GSR measurements for up to four hours. The effect of mechanical deformation on the performance of the sensors are examined by testing the sensors subjected to successive bending up to 1000 cycles. The repeatability and reliability of the sensors were also investigated. The fabricated sensors provide a fast response, stable and accurate performance compared to the commercial sensors. The nanofibrous electrodes are promising candidates for GSR measurement sensors due to their unique mechanical and electrical characteristics owing to their particular structural and material properties which results in high conductivity, high surface area and high flexibility.
LL1/II1: Joint Session: Soft E-Skins
Tuesday AM, April 07, 2015
Park Central Hotel, 2nd Floor, Metropolitan II
9:30 AM - *LL1.01/II1.01
Ultraflexible Organic Devices and Sensors for Biomedical Applications
Takao Someya 1 2 Tomoyuki Yokota 1 2 Sungwon Lee 1 2 Martin Kaltenbrunner 1 2 Tsuyoshi Sekitani 1 2 3 Masaki Sekino 1 2
1University of Tokyo Tokyo Japan2Japan Science and Technology Agency (JST) Tokyo Japan3Osaka University Osaka JapanShow Abstract
Soft electronic materials that enhance compatibility with living tissues have attracted much attention in the field of electronics. Conventional electronics that are manufactured on rigid substrates with high controllability exhibit electric performances; however, when they are pressed against biological tissues, they cause biological reaction or discomfort. It is desirable that the contact surfaces of bio information sensing are to be made of soft materials. From this view point, building integrated circuits or sensors on plastic or rubber substrates, called flexible and stretchable electronics, have been intensively investigated. Especially, by reducing the total thickness of a bio information sensing system, bending strain is reduced, allowing the system to achieve incredibly small minimum bending radius. In fact, we have fabricated, on one micron thick plastic film, an organic thin film transistor (OTFT), an organic photovoltaics (OPV), and an organic light emitting diode (OLED), and have confirmed their excellent mechanical durability. Furthermore, besides the above mentioned organic devices, pressure and temperature sensors are also integrated on ultrathin plastic foils (total thickness of these devices are as thin as a few tens micrometers) achieving amazing conformability. In this talk, we will report recent progress of flexible organic thin-film devices and sensors. Those electronic devices are utilized for measuring biological signals such as body temperature, electromyogram (EMG) and/or electrocardiogram (ECG). We also address remarkable stability of these devices in physiological conditions. Finally, their outlook and future prospect in the field of biomedical applications will also be described.
10:00 AM - LL1.02/II1.02
Organic Bioelectronic Devices from Ion-Conducting Tough Edible Hydrogels
Dominik Benz 1 Alex Keller 1 Marc In het Panhuis 1
1University of Wollongong Wollongong AustraliaShow Abstract
New applications of hydrogels such as soft robotics and cartilage tissue scaffolds require hydrogels with enhanced mechanical performance, which has stimulated an investigation into how hydrogels may be made electrically conducting, tougher and more enduring. This will open up application of these tough conducting materials as pressure and strain sensors for electronic skin devices for monitoring biological function.
In this presentation, I will describe our approach to the fabrication and characteristics of sensor devices based on electronically active soft materials (consisting of the edible biopolymers gellan gum and gelatin). Gellan gum and gelatin are versatile ingredients in well-known food products such as the commercially available product Aeroplane Jelly. These polymer are combined into ionic-covalent entanglement (ICE) gels consisting of ionically cross-linked gellan gum and covalently cross-linked gelatin networks. These ICE gels exhibit suitable mechanically and electrical characteristics for device applications. In addition, I will demonstrate that ICE gels can be prepared in a “one-pot” synthesis approach which facilitates their processing into devices through additive manufacturing (3D printing). Finally, I will present our understanding of the mechanical robust and electrical behaviour, and discuss the properties of the strain and pressure sensors in detail.
10:15 AM - LL1.03/II1.03
Skin-Inspired Imperceptible Plastic Electronic Wrap
Michael Drack 1 Ingrid Graz 1 Tsuyoshi Sekitani 2 Takao Someya 2 Martin Kaltenbrunner 1 Siegfried Bauer 1
1Johannes Kepler University Linz Austria2The University of Tokyo Tokyo JapanShow Abstract
Electronics becomes highly conformable, with the prospect to fit to randomly shaped 3D-objects like skin, an area of research that is booming, evolving from laboratory curiosity to practical implementations. Here we describe a skin-spired electronic platform for highly stretchable interconnects with stretch independent electrical conductivity. With a total thickness below 2µm our electronic foil is practically imperceptible. In conjunction with a stretchable carrier, gold, and copper conductors with a resistivity close to that of the bulk metals are unimpaired by mechanical cycling up to 50% strain for up to 1000 cycles. These stretchable conductors can be readily combined with off-the-shelf electronic items to form stretchable LED stripes that remain functional when stretching up to 240% strain and twisting by 720°. In addition we demonstrate a hybrid 2D biaxial stretchable LED network that is readily stretched to 2.5 times its initial area repeatedly. Conducting polymer electrodes extend the concept of imperceptible electronics to transparent devices. The developed technology platform marks first steps towards imperceptible electronic devices that camouflage their presence with potential applications in mobile appliances, sports, health care, food and environmental quality monitoring.
10:30 AM - LL1.04/II1.04
Stretchable Electronic Skin Based on Distributed Flexion and Pressure Sensors Mounted on a Textile Glove
Aaron P. Gerratt 1 Hadrien O. Michaud 1 Stephanie P. Lacour 1
1EPFL Lausanne SwitzerlandShow Abstract
We demonstrate a wearable tactile skin fitted to a human or robotic hand. Strain, proprioceptive-like, sensors cover the dorsal side of the fingers while pressure sensors are distributed along the inner side of the fingers. We manufacture the electronic skin combining conventional microfabrication techniques and rapid prototyping tools. Stretchable gold thin films on silicone are used to form parallel plate capacitive sensors with soft, compressible foam as dielectric layer. The same metal film technology is used to define stretchable resistive flexion sensors on a silicone substrate, which are then interconnected with highly conductive, strain insensitive liquid metal printed wires. An array of six pressure sensors is mounted on the palmar side of a textile glove, covering the entire length of the finger. Two flexion sensors are mounted on the dorsal side of the glove, one on top of the metacarpophalangeal joint and one on top of the proximal interphalangeal joint. Total thickness of the pressure-sensing layer (including sensor nodes, shielding, interconnects, and encapsulation) is less than 1.4 mm while the flexion-sensing layer is 0.5 mm thin. The sensors are read out in real time at 20 Hz using commercial microelectronic components.
Sensitivity of the foam-based pressure sensors is between 0.1 and 0.001 kPa-1 over a 0 to 405 kPa range, which corresponds to standard forces exerted by a human hand, and can withstand uniaxial tensile strains to 30%. Flexion sensors exhibit a linear response to joint&’s rotation with a sensitivity of more than 0.75 rad-1. The sensors were mounted on a textile glove and were used to monitor the manipulation of hard and soft objects. We also included our system in a closed sensory feedback loop to reach and maintain a defined pressure when grasping an object. These sensors work toward enabling generalized tactile sensing in robotic and prosthetic applications.
10:45 AM - LL1.05/II1.05
Imperceptible Perovskite Solar Cells with 30W/g Specific Weight
Martin Kaltenbrunner 1 Getachew Adam Workneh 2 Lucia Nicoleta Leonat 2 Matthew Schuette White 2 Markus Clark Scharber 2 Niyazi Serdar Sariciftci 2 Siegfried Bauer 1
1Johannes Kepler University Linz Austria2Johannes Kepler University Linz AustriaShow Abstract
Flexibility, compliance and weight will turn out to be key metrics for future electronic appliances and power supplies. Imperceptible plastic electronic wraps integrate nanometer thin film active components on sub-2-mu;m polymer foils and create devices unmatched in mechanical flexibility, stretchability and weight.
Organometallic halide perovskites are capable of delivering very high power per weight when fabricated on ultrathin substrates, an important metric for wearable and ultraportable electronics, for remote sensing, powering electronic skins or for space applications.
Here we demonstrate methods to fabricate perovskite solar cells on 1.4mu;m thick PET substrates with 12% power conversion efficiency and a record high solar cell specific weight of 30W/g. The solar cells are less than 2mu;m in total thickness and can be bent into radii smaller than 50mu;m. Our devices are fabricated from solution in ambient air at temperatures below 120°C to ensure process compatibility with ultrathin polymer foil substrates. Their unique mechanical properties are achieved with an all ITO/FTO free device architecture that does not require titanium oxide interlayers and avoids high sintering temperatures typically employed for rigid devices on glass substrates. These potentially low cost power sources conform to arbitrary shapes and are expected to provide electrical energy wherever high specific power is critical, as in next generation ultra light portables, wearables, small-scale autonomous robots, electronic and robotic sensor skins or space technologies.
The authors acknowledge funding from the Wittgenstein award and the ERC advanced investigators grant “Soft Map”.
11:30 AM - *LL1.06/II1.06
Skin-Inspired Electronics from Organic Materials
Zhenan Bao 1
1Stanford University Stanford United StatesShow Abstract
In this talk, I will present our recent progress in developing skin-inspired electronics in terms of materials and applications.
12:00 PM - LL1.07/II1.07
Intrinsically Stretchable Organic Semiconductors for Wearable Electronics
Darren J. Lipomi 1 Suchol Savagatrup 2 Timothy F. O'Connor 1 Kirtana Rajan 2
1University of California, San Diego La Jolla United States2University of California, San Diego La Jolla United StatesShow Abstract
This talk will describe our group&’s efforts to use intrinsically—“molecularly”—stretchable electronic materials in wearable applications. Organic semiconductors have a wide range of mechanical behavior, which will significantly affect the ability of these materials to form conformal chemical interfaces with biological structures. There is also an apparent competition between good electronic properties and favorable mechanical properties. That is, state-of-the-art organic semiconductors tend to be stiff and brittle. We have developed several approaches based on molecular design, processing, and the use of plasticizers that can maximize semiconducting performance and mechanical softness. Mechanical measurements, combined with spectroscopic characterization of solid-state microstructure, inform our design of materials, while finite-element modeling is used to design device layouts and measure mechanical forces when deformed in operational environments. Applications include the first skin-mounted organic solar cell, all-elastomeric transistors, and a sensing “glove” that can be used to translate manual motions—e.g., sign language—into electronic signals for individuals with sensory impairment or for consumer electronic devices.
12:15 PM - LL1.08/II1.08
Ultra-Conformable, Submicrometer Free-Standing OTFTs Operating at Low Voltages
Alessandra Zucca 2 Piero Cosseddu 2 3 Stefano Lai 3 Francesco Greco 1 Virgilio Mattoli 1 Annalisa Bonfiglio 3 2
1Istituto Italiano di Tecnologia Pontedera Italy2S3 nanoStructures and bioSystems at Surfaces, CNR-INFM Cagliari Italy3University of Cagliari Cagliari ItalyShow Abstract
In this work we report on the fabrication of highly flexible, ultra-conformable free-standing organic thin film transistors (OTFTs) operating at low voltages. We have tested several sub-micrometer, free-standing plastic substrates, on which low voltage organic TFTs and inverters have been fabricated. At first, an aluminum gate electrode is patterned on the ultrathin substrate by standard photolithography, and afterwards the sample is baked overnight in order to obtain an ultrathin Al2O3 layer acting as first gate dielectric. In order to obtain a high performing nanometric gate dielectric, a 80 nm thick Parylene C film is deposited over the whole structure. Finally, on top of this structure gold source and drain are fabricated by a self-alignment process  in order to dramatically reduce the overlapping between source and drain electrodes with the underneath gate electrode, thus lowering the parasitic capacitances. Two different organic semiconductors have been employed, namely p-type TIPS-Pentacene and n-type N1400, both deposited from liquid phase.
Thanks to the high capacitance coupling induced by the ultrathin hybrid double-layer insulating film, such devices can be operated at ultra-low voltages, as low as 2V, showing hole mobility up to 0.4 cm2/Vs (electron mobility up to 1x10-2 cm2/Vs), Ion/Ioff up to 105 and remarkably low leakage currents (100 pA).
Full swing complementary inverters have been also fabricated, showing low noise margins and gains up to 20. Thanks to the properly engineered self-aligned structure, these devices are also characterized by a very good frequency response, with a cut-off frequency usually ranging around 100 kHz.
The fabricated structure is highly robust to mechanical stress: devices can be bent down to bending radii as small as 150 um without giving evidence of any significant variation of their electrical properties. In fact, since the electrical response of OTFTs to mechanical deformation is mainly related to the surface strain induced by the device substrate in the active layer, these effects are dramatically reduced (by orders of magnitude) by using ultra-thin free-standing substrates. Thanks to the extreme flexibility of the proposed structure and their ultra-conformability, such patterned films can be easily transferred on whatever kind of structure like paper, fabric, or 3D structures representing a step forward to the realization of highly flexible, compliant electronics particularly suited for smart wearable systems.
 S. Lai, P. Cosseddu, G.C. Gazzadi, M. Barbaro e A. Bonfiglio, Org. Electr. 14, 754-761 (2013)
12:30 PM - LL1.09/II1.09
Modularized Epidermal RF Energy Harvester with Releasable Interconnect and Matching Components
YuHao Liu 1 Xian Huang 2 John A. Rogers 1
1University of Illinois at Urbana Champaign Urbana United States2Missouri University of Science and Technology Rolla United StatesShow Abstract
Spontaneously coated epidermal electronics systems (EES) have demonstrated their unique advantages in healthcare and human-machine interface. These EES largely rely on external power supplies, which limit their convenience and mobility. Here, we introduce an epidermal radio frequency (RF) energy scavenger system based on ultrathin passive and active electronic components. This flexible and stretchable system offers tunable system parameters and stable performance under mechanical deformation. It can harvest environmental RF power directly and support the operation of microscale light-emitting diodes ( mu;-LEDs) and simple radio circuits, eliminating the need for external power sources that present in conventional medical sensors and most EES. A modularization process divides the system into several components based on their functions and fabrication requirements. Series of impedance matching LC circuits provides tunability to overall circuit efficiency. Each component is separately fabricated and tested before transfer-printing on a soft elastomer to enhance yield and the overall system performance. Here we report systematic characterization of individual components and overall system performance in various dielectric environments (air, skin, and wet sponge). In addition, we demonstrate long distance, wireless powering of mu;-LED in air and on skin. Infra-red thermal analysis is utilized to evaluate impedance matching efficiency and heat distribution on the device. The system is verified to be fully operational under IEEE regulation&’s maximum permissible exposure for RF energy. The cold-welded metal interface between interconnects is investigated by focus ion beaming milling and scanning electron microscopy. The results suggest a robust wireless epidermal system for RF power harvesting and represent important progress in developing self-supported mobile healthcare systems.
12:45 PM - LL1.10/II1.10
Stretchable ECG Electrodes with Printed Silver Nano-Ink
Jiseok Kim 1 Woo Soo Kim 1
1Simon Fraser University Surrey CanadaShow Abstract
Electrocardiagraphy (ECG) is widely used to diagnose abnormal rhythms of the heart and other cardiovascular diseases non-invasively. Electrical impulses go through the heart with heartbeats and an ECG device detects small changes in electric field on the skin above the heart by the electrical impulses during heartbeats. ECG electrodes' tight attachment to the skin is a key function for reliable transmission of electrical signals from the skin to the electrodes with low impedance between skin and the electrodes. Thus, an electrically conductive gel is usually used on the ECG electrodes to remove gaps between skin and the electrodes. However, it is inconvenient for patients to apply and remove the conductive gel every time.
In this study, we develop stretchable and attachable ECG electrodes by utilizing printed metal nano-ink-based stretchable electrodes, which enables conformal contact to the skin without any conductive gel. The stretchable electrode is fabricated as a strain-relief pattern of thin silver electrodes shaped with crossing horseshoes is printed on a stretchable substrate via direct stamping of silver nano-ink. Conformal contact of the fabricated stretchable ECG electrodes to the chest allows for clear electrical signal from the heart. For a future study, wireless connection to the stretchable ECG device could be established, and then, even a simple self-diagnosis by an electrocardiogram obtained through the stretchable ECG system would be possible for smart phone applications.
[Ref] Jiseok Kim and Woo Soo Kim, " Stretching Silver: Printed Metallic Nano Inks in Stretchable Conductor Applications", IEEE Nanotechnology Magazine, 8 (2014).
Oliver Graudejus, Arizona State University
Ingrid Graz, Johannes Kepler University
Ivan Minev, EPFL
Tsuyoshi Sekitani, Osaka University
Symposium Support Aldrich Materials Science
Morrell Instrument Company Inc.
LL5: Stretchable Electronic Materials for Transducers, Biosensors and Optical Devices I
Wednesday PM, April 08, 2015
Park Central Hotel, 2nd Floor, Metropolitan II
2:30 AM - *LL5.01
3D Printing of Soft Electronics and Sensors
Jennifer A. Lewis 1
1Harvard University Cambridge United StatesShow Abstract
The ability to pattern functional materials in planar and three-dimensional forms is of critical importance for several emerging applications. We have developed a multimaterial 3D printing platform that enables the rapid design and fabrication of soft functional devices in arbitrary shapes without the need for expensive tooling, dies, or lithographic masks. In this talk, I will describe our recent efforts to create soft, stretchable electronics and sensors for applications ranging from wearable sensors to intelligent biochips.
3:00 AM - LL5.02
Nanofibrillated Cellulose and Single-Walled Carbon Nanotube Films for High Performance Transparent, Conductive and Flexible Electronics
Antti Kaskela 2 Matti Toivonen 2 Olli Ikkala 2 Esko I. Kauppinen 1
1Aalto University Espoo Finland2Department of Applied Physics, Aalto University Espoo FinlandShow Abstract
Nanofibrillated cellulose (NFC) is a fibrillar nanomaterial that has drawn significant attention due to its excellent mechanical properties and transparency among other interesting properties. Highly transparent NFC films were prepared by solvent casting from an aqueous suspension from which aggregates and poorly fibrillated material were removed by centrifugation, leading to excellent optical transparency and clarity. The NFC films were used as transparent substrates for high performance floating catalyst CVD synthesized single-walled carbon nanotube (SWCNT) networks. The NFC-SWCNT hybrid material fabricated by simple room-temperature press-transfer process , exhibits excellent transparent conductive film performance, with with sheet resistance of 100 Ohm/sq. at 77 % without any chemical doping, while offering superior flexibility compared to commercially available transparent conductors such as ITO-on-polymer. The mechanical characteristics of the NFC-SWCNT hybrid, especially its high ultimate tensile strength, compare favorably with conventional polymers such as PET. Additionally, biocompatibility and intrinsic porosity of the NFC-SWCNT hybrid material can enable unique applications of this novel hybrid material in bioelectronics.
 A. Kaskela, A. G. Nasibulin, M. Y. Timmermans, B. Aitchison, A. Papadimitratos, Y. Tian, Z. Zhu, H. Jiang, D. P. Brown, A. Zakhidov, and E. I. Kauppinen, “Aerosol-Synthesized SWCNT Networks with Tunable Conductivity and Transparency by a Dry Transfer Technique,” Nano Lett., vol. 10, no. 11, pp. 4349-4355, Nov. 2010.
3:15 AM - LL5.03
Triggered Poly(phthalaldehyde) for Transient Electronics
Hector Lopez Hernandez 2 Seung-Kyun Kang 2 Olivia P. Lee 2 Suk-Won Hwang 4 Joshua A. Kaitz 2 Chan Woo Park 2 Bora Inci 3 Nancy R. Sottos 1 John A. Rogers 3 Jeffrey S Moore 3 Scott R. White 3
1Univ of Illinois-Urbana-Champaign Urbana United States2University of Illinois at Urbana Champaign Urbana United States3University of Illinois Urbana United States4KU-KIST Graduate School of Converging Science and Technology Seoul Korea (the Republic of)Show Abstract
Traditional electronics systems are designed for long term stability. In contrast, transient electronics are designed to operate for user-defined life times and then physically degrade. This new paradigm in the design of electronic systems is predicated on the degradation behaviors of the materials used in device fabrication. The development of a new class of degradable substrates that can be triggered to degrade at controlled rates by exposure to a variety of environmental stimuli (e.g. mechanical stress, UV light, pH) would enable new applications in a variety of industries.
In this work, we present a photodegradable transient substrate made of cyclic poly(phthalaldehyde) (PPA) doped with a photo-acid generator (PAG). Exposing the substrate to UV light generates acid through reaction of the PAG which promotes the cleavage of the acetal backbone of PPA, leading to rapid film degradation. We monitored the degradation of the film&’s storage modulus using dynamic mechanical analysis (DMA) and the depolymerization of the film using Fourier transform infrared spectroscopy (FTIR). Results demonstrate that the polymer degrades into monomer and that the degradation rate is controlled by varying the concentration of PAG and the intensity of the UV source.
Additionally, electronic transistors, diodes, and resistors were fabricated from magnesium (Mg) and silicon nano-membranes using our newly designed substrate. A combination of transfer-printing and electron-beam evaporation were used to demonstrate lithographic compatibility. We demonstrate electronic transience of a Mg resistor in as fast as 20 minutes with substantial physical degradation of the electronic package in 72 hours.
3:30 AM - LL5.04
Changes in Resistance of a Stretchable Interconnect Upon Bending
Oliver Graudejus 1 2 Teng Li 4 Jian Cheng 4 James Abbas 3 2
1Arizona State University Tempe United States2Arizona State University Tempe United States3Arizona State University Tempe United States4Univ of Maryland College Park United StatesShow Abstract
Microcracked gold films on elastomeric substrates can function as stretchable, conformal interconnects and electrodes. In these stretchable interconnects and electrodes, the gold film is sandwiched between two layers of an elastomeric substrate, such as silicone. Experimental evidence shows that the resistance upon bending changes depending on three factors: the direction of the bending, the distance of the film from the neutral plane, and the bending radius. The combination of the first two factors determines whether gold film is (i) compressed, (ii) stretched, or (iii) neither compressed nor stretched. Specifically, the resistance of the gold interconnects decreases upon bending when the film is on the compressed side of the neutral plane, and increases when the film on the stretched side of the neutral plane. In both cases, the magnitude of the change in resistance increases with distance from the neutral plane, but the decrease in resistance in compression is much smaller than the increase in resistance in tension. When the film is on the neutral plane (i.e., the film is neither stretched nor compressed), its resistance does not change upon bending. Furthermore, the resistance increase is significantly higher for smaller bending radii when the film is in tension, but the resistance decrease is nearly independent of the bending radius when the film is in compression. A model of the mechanics of the propagation of microcracks in the gold film is presented to offer additional understanding of the changes in resistance upon bending. Together, these results can provide guidance on the most suitable placement of the gold film within the stretchable interconnect/electrode to meet the requirements of a specific application.
3:45 AM - LL5.05
Dichroic Mechano-Responsive Nanocomposites: Reversible Alignment of Gold Nanorods Embedded in Elastomer Matrix
Moritz Tebbe 1 Holger Pletsch 2 Martin Dulle 3 Andreas Fery 1 Stephan Foerster 3 Andreas Greiner 2 Seema Agarwal 2
1University of Bayreuth Bayreuth Germany2University of Bayreuth Bayreuth Germany3University of Bayreuth Bayreuth GermanyShow Abstract
There is a high potential of reversible mechano-responsive and flexible nanocomposite materials based on plasmonic nanoparticles for various applications such as flexible sensors, flexible electronics and optical filters.
However, homogenous incorporation of noble metal nanoparticles in elastomers preserving their unique optical properties remains a challenge. Some efforts have been done to transfer gold nanorods into thermoplastic polymers such as PVA to induce uniaxial orientation by thermoplastic deformation resulting in optically anisotropy.[4, 5] These kinds of nanocomposites are however ultimately fixed to one alignment constitution in which the alignment degree cannot be altered by external stimuli.
Here, we present a thermoplastic elastomer, incorporated with anisotropic gold nanoparticles (Au NRs) with high AuNR filling fractions (2 wt%). In an easy and scalable ligand exchange process, CTAB-stabilized gold nanorods (AuNR@CTAB) were first functionalized with a telechelic thiolated ABA tri-block co-oligomer precursor containing isoprene and styrene. The resulting highly filled viscous nanocomposite material is either directly physically cross-linked or embedded in a matrix consisting of a thermoplastic elastomer. The final plasmonic elastomeric material was studied with respect to its strain responsive reversible structure-property relationships using UV-Vis-NIR spectroscopy with polarized incident light and small angle x-ray scattering (SAXS). Indeed, the nanocomposites show reversible strain induced alignment of gold nanorods along with high optical anisotropy characterized by a strong polarization dependent decrease in extinction.
As a consequence from its anisotropic optical properties, the resulting flexible nanocomposite material can be used as a simple strain sensor or as a mechano-responsive filter where elongation renders the material dichroic.
1. Segev-Bar, M. and H. Haick, ACS Nano, 2013. 7(10): p. 8366-8378.
2. Kim, Y., et al., Nature, 2013. 500(7460): p. 59-63.
3. Wilson, O., G.J. Wilson, and P. Mulvaney, Advanced Materials, 2002. 14(13-14): p. 1000-1004.
4. Pérez-Juste, J., et al., Advanced Functional Materials, 2005. 15(7): p. 1065-1071.
5. van der Zande, B.M.I., et al., The Journal of Physical Chemistry B, 1999. 103(28): p. 5761-5767.
6. Vigderman, L. and E.R. Zubarev, Chemistry of Materials, 2013. 25(8): p. 1450-1457.
7. Pletsch, H., M.J. Schnepf, and S. Agarwal, Chemistry of Materials, 2014
4:30 AM - *LL5.06
Diffraction Gratings with Optical Power Based on Stretchable Elastomeric Nanocomposites for a Widespread Exploitation of Hyperspectral Imaging
Marco Potenza 1 Cristian Ghisleri 2 Luca Ravagnan 2 Paolo Milani 1
1University of Milano Milan Italy2Wise srl Milano ItalyShow Abstract
Deformable optical elements (lenses, mirrors and gratings) are fundamental ingredients for the fabrication of compact, inexpensive and portable devices based on adaptive optics. In particular the use of tunable gratings based on stretchable reflective substrates could revolutionize the design of optical miniature spectrometers and widen significantly their field of applications.
Here we present and discuss an effective approach to the fabrication of nanocomposite-based deformable and stretchable optical systems by means of Supersonic Cluster Beam Implantation (SCBI) of metal nanoparticles in PDMS . A beam of electrically neutral nanoparticles, accelerated by a pressure difference and focused with a very low divergence by aerodynamical effects, is directed towards the polymeric substrate and gain sufficient kinetic energy to get implanted. The extremely good resilience of the nanoparticles layer embedded in the polymer upon deformation of the so obtained nanocomposite allows to maintain extremely good optical performances upon substantial deformation of the material and a large number of deformation cycles . Stretchable reflective optical gratings can be easily fabricated by supersonic cluster beam implantation in PDMS .
Optical power can be imposed on stretchable gratings by sticking them onto curved surfaces, provided that the diffraction properties are preserved. Experimental results confirm the effectiveness of this solution, which eventually enables to get gratings with strong optical power in an extremely simple and very cheap way.
In force of this solution it is straightforward to realize very small optical devices for spectral analysis. This opens completely new perspectives for hyperspectral imaging , a field which is currently limited in widespread use by the need of the integration of many optical elements in small packages . Using stretchable elements with optical power, a single grating could be exploited together with any low-cost imaging device and a medium computation capability for the fabrication and integration of portable and user-friendly hyperspectral devices.
 C. Ghisleri et al., Laser & Photon. Rev. 7, 1020 (2013)
 C. Ghisleri et al., Appl. Phys. Lett. 104, 061910 (2014)
 D. Bannon, Nature Photonics 3, 627 (2009)
 C.P. Warren, et al., Opt. Eng. 51, 111720 (2012)
5:00 AM - LL5.07
Flexible Conductive Au Films through Direct Reduction of a Soluble Gold Complex
Raz Jelinek 1 T.P. Vinod 1
1Ben Gurion University Beer Sheva IsraelShow Abstract
Construction of transparent, conductive films on bent and non-planar substrates is a fundamental objective in the emerging field of "flexible electronics". We present a new strategy for creating conductive and transparent films in 2-D and 3-D, based upon incubation of water-soluble gold thiocyanate with amine-displaying surfaces, producing spontaneous of crystalline, metallic Au coating. Notably, no external reducing agents were needed to initiate or promote formation of the metallic Au films; in essence, the thiocyanate ligands provide the means for surface targeting of the complex, guide the Au crystallization process, and, importantly, donate the reducing electrons. The Au films exhibit unique “nano-ribbon” morphology which allow significant light transmittance. We show that the generic technology can be employed for generating transparent conductive coatings on a variety of substrate materials in both two dimensional (flat) as well as three dimensional surfaces.
- “Patterned transparent conductive Au films through direct reduction of gold thiocyanate”, Ahiud Morag, Natalya Froumin, Dimitry Mogiliansky, Vladimir Ezersky, Edith Beilis, Shachar Richter, Raz Jelinek, Advanced Functional Materials, 2013, 23, 5663-5668.
- “Flexible conductive surfaces via "bottom-up" gold nanotechnology”, T.P. Vinod and Raz Jelinek, ACS Applied Materials and Interfaces2014, 6, 3341-3346.
5:15 AM - LL5.08
1D/2D-Based Transparent and Stretchable Thin Film Transistors
Sang Hoon Chae 1 Young Hee Lee 1 2
1CINAP, SKKU Suwon-si Korea (the Republic of)2Sungkyunkwan Univ Suwon Korea (the Republic of)Show Abstract
Although 1D carbon nanotubes (CNTs) show semiconducting and metallic properties depending on the chirality and recent achievement of separation of semiconducting nanotubes, small portion of metallic nanotubes and short length of the separated semiconducting nanotubes still limit the use of CNTs for thin film transistors. The newly developed 2D large-area graphene by chemical vapor deposition opens the new possibility of their use to switching devices but still limited by the gapless Dirac cone. Motivated by this, semiconducting 2D layered structures, for example, transition metal dichalcogenides (TMD), have been successfully synthesized recently and demonstrate unusual electronic and optical properties. We will show a recent progress on how these materials including their hybrids have been evolved for switching devices with strong emphasis on transparency, flexibility and stretchability for future soft electronics.
Firstly, we report the fabrication of highly stretchable and transparent field-effect transistors combining graphene/single-walled carbon nanotube (SWCNT) electrodes and a SWCNT-network channel with a geometrically wrinkled inorganic dielectric layer. The resulting 1D/2D hybrid devices exhibited an excellent on/off ratio of ~105, a high mobility of ~40thinsp;cm2thinsp;Vminus;1thinsp;sminus;1 and a low operating voltage of less than 1thinsp;V. Importantly, because of the wrinkled dielectric layer, the transistors retained performance under strains as high as 20% without appreciable leakage current increases or physical degradation.
Secondly, we report the fabrication of new TFTs using only 2D materials. All components of TFTs are consist of 2D materials (graphene, TMD, boron nitride (BN)), and fabricated TFTs are also highly stretchable and transparent. Aside from carbon, other classes of 2D materials and their stacked structure are promising in the field of soft electronics when a superior electrical/mechanical property is required.
5:30 AM - LL5.09
Compact Single Channel Two-Liquid Hyperelastic Capacitive Strain Sensor
Shanliangzi Liu 1 Xiaoda Sun 1 Konrad Rykaczewski 1
1Arizona State University Tempe United StatesShow Abstract
Applications of liquid metal microfluidic devices include soft robotics, biomedical devices, and flexible electronics. Currently two types of liquid metal based strain sensors exist: single microchannel resistive and two microchannel capacitive sensors. To achieve a sensible output, both of these types of sensors currently require microchannels with length on the order of a few centimeters. With winding channel geometry, these sensors typically have a footprint of about a square centimeter. To address this issue, we developed a compact two liquid single straight channel capacitive strain sensor. The device consists of a dielectric liquid sandwiched between two liquid metal electrodes within a single channel. Fabricating of this capacitor with a liquid dielectric instead of PDMS enables capacitance increase through selection of high permittivity liquids. We demonstrate that use of water and glycerol instead of silicone as the dielectric material can increase the device capacitance by factor of five. Furthermore, this device only has a footprint of a few square millimeters. We discuss the effect of channel diameter, dielectric spacing, interfacial meniscus shape, and oxide shell on device capacitance as well as response to strain.
5:45 AM - LL5.10
Microfluidic Heterojunction Sensors Having High Deformability
Hiroki Ota 1 Kevin Chen 1 Yongjing Lin 1 Hiroshi Shiraki 1 Daisuke Kiriya 1 Zhibin Yu 1 Tae-Jun Ha 1 Ali Javey 1
1University of California, Berkeley Berkeley United StatesShow Abstract
Electronic devices and sensors which exhibit large amounts of mechanical deformability have many applications such as in smart wallpapers and human-machine interfaces for prosthetics. In this regard, tremendous advancements have been made in engineering solid-state electronic materials and devices on elastic substrates. Recently, sensors based on using liquid active components embedded within soft elastomeric substrates have shown much promise for such applications as liquids present the ultimate limit in deformability.
One limiting factor in the fabrication of more sophisticated liquid based sensors is the inability to combine multiple liquids into one device due to intermixing. Through proper design of the liquid-liquid junction, we enabled heterojunction confinement without intermixing. As a proof of concept, we utilize multiple ionic liquids as the active sensing liquid to sense different stimuli including temperature, humidity, and oxygen gas sensing, with excellent performance characteristics even when under deformation.
The device was fabricated by photolithography techniques using PDMS as the substrate, eutectic GaInSn as electrodes and an ionic liquid as a sensing material. To prevent intermixing of the liquids, they were connected via “junction channels” 30 mu;m width and 150 mu;m length. The maximum width of the junction channels without intermixing is limited to 250 mu;m due to capillary forces. The sensor showed highly structural stability to mechanical deformation. In order to conduct electrical measurements, a constant phase element-based equivalent circuit of the device was constructed from the result of a Nyquist plot.
The sensor showed stable sensitivity to temperature without hysteresis as shown with a 0.039/°C increase in conductivity, which is quite high compared to other reports. The conductance and capacitance increase by 0.13 and 0.08 respectively as the device undergoes 30% uniaxial stretch perpendicular to the axis of the junction channels, which is low compared to the temperature sensitivity. We also show proof of concept for humidity and oxygen gas sensing using three kinds of ionic liquids, [EMIM][Otf], [BMIM][PF6], and [BMPYR][NTf2]. The sensitivity of each ionic liquid to humidity and oxygen differed depending on the ionic liquid. For each type of stimuli, the sensing can be optimized by choosing the proper ionic liquid. In the future, multiple liquid heterojunction sensors, each with a different ionic liquid may be multiplexed into a fully integrated system to sense different stimuli with calibrated response.
 H. Ota, K. Chen, Y. Lin, H. Shiraki, D. Kiriya, Z. Yu, T.-J. Ha, and A. Javey,: “Highly-deformable liquid-state heterojunction sensors.” Nature Communications, 5(5032), 2014
LL6: Poster Session: Electronic Skins/Neural interfaces
Wednesday PM, April 08, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - LL6.01
In-Fiber Polymer Composite Electrodes for Neural Recording
Benjamin Grena 1 2 3 Xiaoting Jia 1 2 3 Yuanyuan Guo 2 Seongjun Park 1 2 4 Yoel Fink 1 2 3 Polina Anikeeva 1 2
1Massachusetts Institute of Technology Cambridge United States2Massachusetts Institute of Technology Cambridge United States3Massachusetts Institute of Technology Cambridge United States4Massachusetts Institute of Technology Cambridge United StatesShow Abstract
The most commonly used electrophysiological probes for neural signal recording are based on materials with elastic moduli significantly exceeding those of neural tissues. This mismatch in mechanical properties prevents such devices from probing arbitrary locations in the brain without causing significant damage to the tissues. In addition, shear-induced inflammations limit the ability of using such probes for long-term experiments. Flexible electronics devices also exist, but currently these devices are mostly limited to probing the surface of the brain. Scalable fabrication methods of flexible electrodes that would mimic the brain compliance and be capable of deep brain recording are still largely unexplored. Here, we present a new pathway for the fabrication of electrophysiological probes, based on custom-made composite polymer electrodes drawn into thin and flexible fibers. We first produce electrically conductive bulk composite electrodes by mixing either carbon black or graphite in a polymer binder, through conventional methods such as solution-casting or melt-processing. Then we incorporate such electrodes in a polycarbonate cladding, and draw the material into a fiber through the preform-to-fiber thermal drawing method. This process enables us to produce flexible fibers with thicknesses lower than 300 µm, containing conductive polymer composite electrode with sizes down to 10 µm. The use of polymer composites enables additional control over the materials properties. We investigate the effects of the filler material and volume fraction over the DC conductivity and the Young&’s modulus of the resulting fiber. We additionally study the effects of the same parameters on the AC impedance of our devices, a critical parameter in neural recording. Lastly, we demonstrate that we can use our fibers to measure neural activity. Our ability to optimize the electrical and mechanical properties of our electrodes offers a great advantage over silicon or metal-based probes, and paves the way towards more complex flexible fiber neural probes.
9:00 AM - LL6.02
Flexible All-Polymer Multimodal Fibers for Integrated Optogenetics
Seongjun Park 1 2 Xiaoting Jia 2 3 Benjamin Grena 2 3 Yuanyuan Guo 2 3 Yoel Fink 2 3 Polina Anikeeva 2 3
1Massachusetts Institute of Technology Cambridge United States2Massachusetts Institute of Technology Cambridge United States3Massachusetts Institute of Technology Cambridge United StatesShow Abstract
Developing multifunctional devices for stimulating and probing neural tissue is important to the study of information processing as well as pathologies of the nervous system. With the invention of optogenetics it became possible to uniquely optically identify specific cells types via expression of light-sensitive proteins, opsins, of bacterial and archeal origin. Since optogenetic experiments typically rely on viral delivery of opsin genes and require visible light, an invasive two-step surgery is often employed to inject the viral vector solution and then implant an optical fiber and a neural recording device.
Here we report an approach that enables optogenetic study of neural circuits with minimal mechanical invasiveness. Our approach relies on all-polymer fiber-based neural probes, which incorporate six recording electrodes, optical waveguide core, and two microfluidic channels for viral delivery. These devices are produced via thermal drawing process, which is compatible with a broad palette of polymer materials allowing for combination of a transparent optical core and cladding with conductive polymer electrodes within an integrated structure. Our multimodal fiber probes based on polycarbonates, cyclic olefins and conductive polyethylene composites exhibit outer dimensions of <300 µm, while individual recording electrodes have dimensions 20-40 µm thus reducing the damage to the surrounding tissue. Furthermore, all-polymer architecture yields low flexural moduli and permits operation of all three modalities under 90° bending angles.
We show that our flexible multimodal fiber probes allow for simultaneous recording and optical stimulation of neural activity. Furthermore, the same device is used for injection of viral vectors, such as adeno-associated viruses (AAVs) commonly used for delivery of opsin genes in vivo. This technology offers a flexible integrated alternative to multi-step surgeries required for optogenetic mapping of brain function.
9:00 AM - LL6.03
Engineering Neural Probes from Multimaterial Fibers by Selective Etching
Christina Tringides 1 Andres Canales 1 Polina Anikeeva 1 2
1Massachusetts Institute of Technology Cambridge United States2Massachusetts Institute of Technology Cambridge United StatesShow Abstract
The ability to chronically record electrical activity from single neurons enables mapping of the brain, spinal cord and peripheral nerve circuits. This is essential to develop effective therapies for debilitating disorders of the nervous system. Neural tissues, however, impose stringent design constraints on the electronic interfaces with neurons, which, if not followed, lead to glial scarring. This irreversible foreign body response is thought to isolate electrodes from neurons, resulting in recordings with low signal-to-noise ratio (SNR). Based on the results from biocompatibility studies, we hypothesize that small, flexible and chemically inert implants will minimize the tissue response to the implanted probe. The improved biocompatibility should lead to recordings with high SNR over long periods of time.
To address the neural probe design challenges, we use thermal drawing process (TDP), which allows us to reduce macroscopic multimaterial templates into hundreds of meters of fibers with microscale features. Consecutive TDP steps can be used to draw down polymer-metal composite fibers to produce dense arrays of recording microelectrodes, each with a diameter of approximately 5 mu;m. While TDP allows for fabrication of flexible devices with micron features, the final geometry is limited by the fundamental axial symmetry of the fiber as well as dimensions required for stable thermal drawing.
To overcome both of these limitations, we have developed a combinatorial approach that uses multi-layer fiber design and incorporates polymers with orthogonal solubilities. In particular, sacrificial claddings of polyphenylsulfone (PPSU) or polycarbonate (PC) can be introduced into fibers with a polyetherimide (PEI) or cyclic olefin copolymer (COC) matrix, respectively. Selective etching of these claddings yields neural probes with diameters of less than 100 mu;m inaccessible with TDP alone. This process can be extended to other polymers, such as polymethylmethacrylate (PMMA), that are soluble in more common solvents, such as acetone. The use of these polymers gives additional flexibility in the final probe geometries, allowing for less invasive implants. Selective etching can also be applied to metals and combined with electrodeposition. This could improve biocompatibility of the electrode interface with neurons by electroplating individual electrodes with materials such as gold or iridium oxide.
9:00 AM - LL6.04
A Flexible Electronic Bandage with Micro-Device Arrays for Wound Management
Tianbai Xu 1 Xiaozhi Wang 1
1Zhejiang University Hangzhou ChinaShow Abstract
When a body is physically injured, specifically when a wound on the skin is formed, medical treatment is needed to prevent the condition from worsening. Wound management aims at managing and accelerating the healing of an acute, chronic or surgical wound. The bandage is an old though the most common used medical material in both slight and severe wound management. It is consisted of several functional layers, usually including an absorbent layer for wound exudate, antimicrobial barrier dressing, and a low adhesive layer to keep the bandage from adhering to the wound. In addition, cryotherapy and thermotherapy are often used to ease aches from the wound, although current medical devices cannot deliver accurate temperature control in a small and specific area.
Here we firstly demonstrate a “band-aids” like flexible electronic bandage in which multiple wound healing techniques including micro-area temperature management, wound exudate absorption and electrical field assisted cell migration healing are integrated.
The smart bandage is built on the bendable substrate of polyimide, spin-coated with a layer of patterned PEGDA hydrogel for wound exudate absorption. The micro-area temperature management and electrical field assisted healing are achieved in arrays with each pixel of 1mm2 by micro-fabrication techniques. The temperature management array is composed of thermoelectric micro-coolers and resistive micro-heaters. Each pixel in the array has eight thermoelectric junctions connected in series, fabricated by sputtering Te and Bi thin films, as well as a micro-heater consisting of the Cr-Au thin films. Several device structures are designed and compared to obtain better thermal conduction on one side and thermal isolation on the other side. The AC electrical field is generated by separate micro-electrodes to perform the cell migration healing treatment.
The temperature of the bandage could be tuned from 18#8451; to 50#8451; at room temperature of 23#8451;. And the temperature distribution could be adjusted to conform to the shape of the wound by independently turning on or off each cooler and heater in the array to inhibit the bacteria growth and to host an optimal temperature for wound healing. The hydrogel absorbent layer ensured the suitable humidity around the microenvironment of the wound. The practical protecting effect was shown by detailed biological characterizations. The wound healing time was accelerated by micro-electrodes arrays as well, which promoted the cell migration across the wound. It could attach to human skin easily due to the patterned high surface area on the substrate.
In this work, smart bandage with adjustable recovery patterns designed for precise wound management is proposed. Compared to traditional bandage materials, this electronics-integrated medical material shows great potentials in many occasions requiring intensive professional wound cares such as the battlefield, sport field and so on.
9:00 AM - LL6.05
Flexible Bio Probe and Sensors for Biomedical Applications
Sungwon Lee 1 Yusuke Inoue 1 Dongmin Kim 2 Amir Reuveny 1 Kazunori Kuribara 1 Tomoyuki Yokota 2 Tsuyoshi Sekitani 2 Yusuke Abe 2 Takao Someya 2
1The University of Tokyo Tokyo Japan2University of Tokyo Tokyo JapanShow Abstract
It is crucial to establish stable, soft, and nonallergic contacts between the biological tissue and the electrode from the devices as well as the good performance to precisely measure bio signal. It has been difficult to form a stable interface, especially when the surface of the biological tissue is wet and/or the tissue exhibits motion. So we suggest one simple way to solve the difficulty by designing and fabricating stress-absorbing electronic devices that can adhere to wet and complex surfaces and allow for reliable, relatively long-term electronic measurements of vital signals. A multielectrode array (MEA) is manufactured on an ultrathin polymeric substrate show how this design can absorb the stress under extreme deformation. The surface of each electrode is coated with a photo patternable adhesive gel. The MEA could be attached to the surface of a moving body, resulting in good conformal contact for more than 3 h. Furthermore, arrays of highly sensitive, stretchable strain sensors are fabricated using a similar electronic design. These could be attached on human skin to detect the strain induced by the motion of the joint.
9:00 AM - LL6.06
Printed Strain and Temperature Sensors for Multi-Functional Artificial Electronic Whisker
Kuniharu Takei 1 Shingo Harada 1 Wataru Honda 1 Takayuki Arie 1 Seiji Akita 1
1Osaka Prefecture University Berkeley United StatesShow Abstract
Artificial electronics are of great interests in diverse applications such as robotics. In fact, there are a variety of demonstrations including artificial electronic eye (e-eye), e-skin, and e-nose. Due to animal/human mimicking devices, these devices need to be on a macroscale flexible substrate. Considering the device cost, macroscale, and economical fabrication technique such as a printing method is another key factor in addition to improving the functionality and performance. Here, we report fully-printed strain and temperature sensors on a user-defined flexible substrate for the application of ultralight and compact artificial electronic whisker (e-whisker) for robots as an example.
For strain sensor, silver nanoparticle (AgNP) ink and carbon nanotube (CNT) ink were mixed (8:10 wt% ratio) and printed on a flexible substrate via a screen printer. For temperature sensor, conductive polymer (PEDOT:PSS) and CNT ink were used with 10:1 wt% ratio. To show different patterning method, the ink was first spin-coated, and the film was then patterned by using a laser cutter tool. Both strain and temperature sensor films were cured at 70°C for 1 hour.
Printed strain sensor is first characterized. By reading the electrical resistance change of AgNP-CNT film, strength and directions of strain (i.e. tensile and compressive) can be determined. The maximum sensitivity was ~59 %/Pa, and the device in terms of mechanical reliability was stable at least 200 bending cycles. Importantly, the composition ratio of inks can readily tune the sensitivity depending on the applications. Next, for temperature sensor, linear resistance change was observed up to 50 °C with the sensitivity of ~0.6 %/°C. For the integration of both sensors, we confirmed the selectivity of each sensor that is high enough to distinguish strain and temperature (strain sensitivity of temperature sensor ~0.02 %/Pa and temperature sensitivity of strain sensor ~0.03 %/°C).
Finally, we integrated strain and temperature sensors and formed 5 whisker array to map spatial and temperature distributions by scanning an object like an animal whiskers. As the results, three-dimensional spatial and temperature mapping can be successfully conducted with a scan speed of 0.6 mm/s. Based on the results, the strain sensor on a flexible substrate can monitor at least 200 µm height difference. By changing the whisker design such as length and thickness of flexible substrate (here we used 100 µm thickness and 10 mm length), we experimentally confirmed that the sensitivity can be tuned, resulting in that height resolution can be improved if needed.
In summary, we developed the fully-printed high sensitive strain and temperature sensor and demonstrated e-whisker applications. The technique to fabricate highly sensitive sensors on a user-defined substrate using only printing methods should lead the future flexible and wearable electronics.
9:00 AM - LL6.07
Wearable and Highly Stretchable Strain Sensors Using Fragmentized Graphene Networks
Yura Jeong 1 Heun Park 1 Sang Woo Jin 2 Soo Yeong Hong 1 Jeong Sook Ha 1 2
1Korea Univ Seoul Korea (the Republic of)2Korea University Seoul Korea (the Republic of)Show Abstract
Various soft electronics using flexible polymers and carbon based materials have been demonstrated recently. Many of those devices are eventually expected to be in the form of clothing and to operate along the human body. Above all, strain sensors which can detect various human motions have gained attraction in the realization of wearable electronics.
Here, we report on the fabrication of wearable and highly stretchable strain sensors by using fragmentized graphene networks (graphene foams) and PDMS elastomer composite. Graphene foams (GFs) with interconnected porous microstructure have attained lots of attention because of their high specific surface area combined with excellent mechanical and electrical properties of graphene. GF/PDMS composite was proved to have good flexibility and stretchability, however it has limitations as materials for a strain sensor since the change in the resistance with the applied strain is not significantly outstanding. In this work, we fragmentized GF grown via chemical vapor deposition into few hundred micro-sized branches using a vortex mixer with isopropyl alcohol in order to fully utilize the specific area of the porous microstructure. Although the whole interconnection was broken, the three-dimensional structure of the GF was conserved. When the GF fragments/PDMS composite was stretched, the contact resistance of the fragments changed and the sensitivity of the sensor could be enhanced since the reorganized fractured graphene branches densely contact with each other, as a result. Our strain sensors are capable of sensing minimal strain down-to 0.1% as well as high strain up-to100% with high durability over 1000 cycles and their gauge factors are tunable in the range of 2.4 to 13 depending on the amount of the GF fragments. Also, the devices can be fabricated in various sizes with simple processes.
We could detect various human motions such as pulse, elbow and finger movements by attaching our sensor onto the human skin. The gloves integrated with the strain sensors and LEDs could visualize finger motions through the change of the light intensity. Moreover, we demonstrated stretchable touch sensor array embedded with LEDs which can be used as electronic skin.
9:00 AM - LL6.08
Stretchable and Highly Sensitive Pressure Sensor Array using Elastomeric Micropillars and Conductive Polymer Nanofibers
Heun Park 1 Yura Jeong 1 Junyeong Yun 1 Soo Yeong Hong 1 Sang Woo Jin 1 Jeong Sook Ha 1
1Korea University Seoul Korea (the Republic of)Show Abstract
Recently, the research on the artificial skin has been actively performed due to its potential applications in sensing physical properties such as tactility, distortion, and temperature. Natural skin receives tactile sensation via detecting the pressure distribution with excellent pressure sensitivity. In order to mimic such tactile sensation of natural skin, artificial skin needs to be equipped with stretchable pressure sensors of high sensitivity over a wide range of pressure: Stretchable sensor enables a conformal detection along with the movement of human body.
In this work, we demonstrate the stretchable and highly sensitive pressure sensor array that employs electrodes of Au-coated polydimethylsiloxane (PDMS) micropillars and polyaniline (PANI) nanofibers on deformable polymer substrate, in which their contact resistance changes with applied pressure. PDMS micropillars were fabricated for increasing the contact area by using the patterned mold of SU-8 photoresist and then coated with e-beam evaporated Ti/Au thin film. PANI nanofibers were grown on polyethylene terephthalate (PET) film by potentiodynamic deposition.
The fabricated pressure sensor showed high sensitivity of 1.79 kPa-1 in low pressure region of < 0.3 kPa and 0.04 kPa-1 in high pressure range of >2kPa, respectively, where the response was very fast to have a response time of 50 ms. Of particular interest, it could also detect a very low pressure applied by a rice grain of 20 Pa. With this pressure sensor attached directly above the artery of the neck, the change in pulse before and after exercise could be reliably distinguished.
In order to be used as artificial tactile sensor, it is required to have stable sensing of pressure under applied strain such as bending, twisting, and stretching. We have fabricated the 5x5 array of the pressure sensors on a specially designed deformable substrate, where the strain applied to each pressure sensor was minimized: The deformable substrate consists of rigid PDMS islands where the pressure sensors are attached and soft thin mixed film of Ecoflex and PDMS between the PDMS islands. Liquid metal interconnects of Galinstan were embedded in the thin polymer film for electrical connection between the pressure sensors. Under biaxial stretching up-to 30%, the distribution of pressure was successfully measured to confirm its possible application as tactile sensors for artificial skin, wearable electronic device and robotics.
9:00 AM - LL6.09
Deformable Microsystem for In Situ Cure Degree Monitoring of GFRP(Glass Fibre Reinforced Plastic)
Yang Yang 1 2 3 Gabriele Chiesura 2 Thomas Vervust 1 2 3 Frederick Bossuyt 1 2 3 Geert Luyckx 2 Markus Kaufmann 4 Joris Degrieck 2 Jan Vanfleteren 1 2 3
1Center for Microsystems Technology Ghent Belgium2Ghent University Ghent Belgium3IMEC Leuven Belgium4Sirris Leuven-Gent Composites Application Lab Leuven BelgiumShow Abstract
The composites industry is becoming a valid alternative to many traditional heavy metal industries because of the high specific stiffness of composite materials over the more classical construction metals. Because of the continuous growth of the composites industry with new materials and complex shapes, a method to optimize the production process is imposed. As such the different manufacturing stages (e.g. the injection of resin, the curing and post curing stage) of a composite component can be understood to increase the quality of the produced part while reducing manufacturing costs (less scrap, energy and material reduction).
In this work, the current progress of the Self Sensing Composite project on the in situ cure degree monitoring of glass fibre reinforced plastic is shown. By controlling the curing phase one can obtain a superior quality component and, as a consequence, will increase the reliability and optimize the design of the part, leading to a decrease of the lifecycle cost (i.e. maintenance costs, material costs, design costs). Two strategies are followed, firstly, the embedding of a capacitive-sensor-based deformable microsystem in the composite material, and secondly, the installation of the deformable microsystem in the production mould of the composite part. In the former case, the embedded microsystem can later on be used to sense the ageing effects of composites in operation as well.
The research leading to these results has received funding from the Flemish Agency for Innovation by Science and Technology (IWT) - through the program for Strategic Basic Research (SBO) under grant agreement n° 120024 (Self Sensing Composites).
9:00 AM - LL6.10
Piezo-Resistive Pressure Sensor Arrays with Photo-Thermally Reduced Graphene Oxide
Rouzbeh Kazemzadeh 1 Woo Soo Kim 1
1Simon Fraser University Surrey CanadaShow Abstract
Pressure sensors or touch sensors are popular components to detect the changes of forces (per unit area) applying on objects for the applications such as human touch/pressure detection, or touch screen pads. The pressure sensor material needs to have proper electrical properties as well as being transparent and mechanically durable for fore-mentioned applications. Graphene has been used as piezoresistive sensing materials with really superior electrical and mechanical properties. Considering the unique electro-mechanical properties of graphene; thin film sensors based on graphene could be conductive and transparent with acceptable sensitivity.
Here, we report a highly sensitive pressure sensor array fabricated with photo-thermally reduced graphene oxide (r-GO). Non-conductive GO thin film is converted into conductive (~ 104S/m) thin layer by fast and precisely designed laser scribing method to generate pressure sensors with sensitivity of 19mV/kPa. The fabricated piezoresistive pressure sensor shows the pressure-sensitivity of 19mV/kPa which is superior to the previously reported MEMS-based pressure sensors' sensitivity with capacitive-type MEMS-based pressure sensor:0.001 mV/kPa. And it is similar with the other highly sensitive diaphragm type piezoresistive MEMS-based sensor with sensitivity 37.5 mV/kPa, or carbon nano tube (CNT)-based sensor's sensitivity as 10 mV/kPa. The fabricated array is easily attachable on any surface for monitoring applied forces or pressure and maintains excellent electrical conductivity under high mechanical stress and thus holds promise for durable sensors.
R. Kazemzadeh, Kimbal Andersen, Lazarus Motha and W.S. Kim “Highly Sensitive Pressure Sensor Array with Photo-thermally Reduced Graphene Oxide” under review in IEEE Electron Device Letters (2015)
9:00 AM - LL6.11
Instrumented Shoe Insole with Printed Pressure Sensors
Lazarus Motha 1 Jiseok Kim 1 Woo Soo Kim 1
1Simon Fraser University Surrey CanadaShow Abstract
Measurement and analysis of plantar pressure caused by contact between human body and external environment is of importance because this pressure directly affects human body. Accordingly, analysis of plantar pressure has been used for many applications including footwear design, performance improvement and injury prevention of sports players, clinical gait analysis and diagnosis of foot-related diseases such as diabetic ulceration, plantar fasciitis and arthritis. Among plantar pressure sensing systems, the in-shoe system can conveniently provide real-life value of plantar pressure because it is meant to measure the pressure inside the shoes.
We demonstrate in this study, an instrumented soft insole embedded with printed inter-digitated capacitive pressure sensors for measurement and analysis of plantar pressure. Unlike the conventional mode of pressure sensing of interdigitated capacitors in which change in dimension of electrodes by external pressure leads to variation of capacitance, for this study, the change in capacitance is entirely led by variation of relative permittivity of the surrounding dielectric medium with applied pressure. For reliable measurement, capacitance is changed into voltage with the assistance of a simple capacitance-to-voltage converter. The measured sensitivity of the sensor is 4-5 V/MPa with high linearity in the pressure exerted by human weight. The sensors are placed at three high-pressure regions, hind-foot, mid-foot, and fore-foot, and plantar pressure is successfully registered for various foot postures.
[Ref] J. Kim, K. Wubs, B. S. Bae and W.S. Kim*, “Direct Stamping of Silver Nanoparticles toward Residue-free Thick Electrode ” Sci. Technol. Adv. Mater.13, pp. 035004 (2012).
9:00 AM - LL6.12
Fabrication of Stretchable Oxide Semiconductor TFT Backplane
Jihun Park 1 Mijung Kim 1 Jang-Ung Park 1
1UNIST (Ulsan National Institute of Science and Technology) Ulsan Korea (the Republic of)Show Abstract
Nowadays, the need of human-friendly devices is increased because the performance of devices has been already saturated. Therefore, a lot of researchers have started the study associated with stretchable electronics or wearable electronics. However, ordinary electronics are brittle, so that they cannot be used as wearable ones. Thus, stretchability has to been applied into conventional devices in order to realize human-friendly electronics in improving the convenience for human. To accomplish this goal, many research results or methods have been presented during the last decade. The most typical one is the transfer method. While this transfer method is very easy, it has to be accompanied the transfer of devices onto pre-strained substrate which has problems relevant low yield and size limitation.
Here, we demonstrate a fabrication process of stretchable oxide semiconductor TFT backplane which does not include any transfer process. For this aim, we applied two systems. To explain, the first system is a hybrid substrate. This substrate contains both rigid and soft areas to limit strain at specific regions. Thanks to this hybrid substrate, materials used in conventional electronics can be also exploited. The hybrid substrate exhibits not only substantial mechanical property (stable until 100%), but also high transparency (~ 97%) simultaneously. The second system is a stretchable conductor that plays a role as interconnects. This stretchable conductor is employed to tolerate mechanical strain on the soft regions. In detail, the produced one also shows superb mechanical and electrical property at the same time. In addition, its conductivity maintains during stretching test.
By using these systems and methodology, we can demonstrate stretchable active matrix based on oxide semiconductor which shows general electrical properties (mobilities, on/off ratio, etc.). According to these properties, this stretchable TFT backplane can be adapted on existing devices like the backplane of displays immediately. As a result, we believe that this fabrication process presents a promising strategy toward stretchable and wearable electronics.
9:00 AM - LL6.13
A Wearable and Multimodal Carbon Nanotube Sensor Skin Fabric Beyond Human Skin
So Young Kim 1 Sang-Sik Park 1 Han Wool Park 1 Young Jin Jeong 1 Do Hwan Kim 1
1Soongsil University Seoul Korea (the Republic of)Show Abstract
Human-adaptive, stretchable artificial skin has recently attracted tremendous interest because of its unique capability of detecting subtle stimuli changes, which may come out its potential applications in wearable health monitoring, sensitive tactile information display, prosthetics, and multifunctional robot skin. In particular, the development of an artificial skin with multimodal sensing capabilities as well as high sensitivity is desired to more plausibly emulate human skin. Moreover, effectively combining the chemical/biological detection with tactile sensing into a single pixel remains a challenging task to augment a sensor skin beyond the capabilities of human skin, whereas this has not been explored.
In this talk, we describe a highly sensitive, wearable, and multimodal sensor skin fabric based on hierarchically assembled elastic and highly conductive carbon nanotube (CNT) microfibers, which is capable of simultaneously detecting versatile external subtle stimuli into a single pixel. We utilized piezocapacitive-type device architecture that consists of highly stretchable CNT microfiber circuitry incorporated with stretchable elastomer dielectric of Ecoflex, where CNT microfibers were aligned to allow point-to-point overlap for implementing high sensitivity as well as high spatial resolution of the sensors. Based on this kind of capacitive sensory system, we could successfully demonstrate the highly sensitive and reliable tactile sensor arrays to allow position detection under even ultralow pressure of 0.4Pa and exhibit fast response time of 63ms. In particular, multimodal output electric signals can be effectively manipulated as a change of resistance or capacitance under mechanical deformations (including pressure and flexion), touch, temperature change, and even chemical variables with different dipole moments.
We believe that elastic CNT microfiber fabric skin will be an effective way to implement human-interactive smart robots capable of recognizing the robot-human-environment interface and in-situ human monitoring capable of biologically detecting some fluidic markers as well as tactile stimuli.
9:00 AM - LL6.14
User-Interactive and Color-Tunable Electronic Skin
Ho-Hsiu Chou 1 Alex Chortos 2 Amanda Kim Nguyen 3 John To 1 Jianguo Mei 1 Tadanori Kurosawa 1 Zhenan Bao 1 2
1Stanford University Stanford United States2Stanford University Stanford United States3Stanford University Stanford United StatesShow Abstract
Human skin is the largest organ of our body. It provides a remarkable network of highly sensitive diverse sensors, such as those for tactile sensing, health monitoring, and temperature sensing, that are able to convert mechanical stimuli into physiological signals, which are then interpreted by the brain. Because skin has numerous potential applications, scientists are now exploring the field of electronic skin (e-skin), dreaming to mimic the properties of skin and create novel applications. Besides human skin, the animal and insect skins exhibit many amazing functions. For example, chameleon skin is famous for its color-changing abilities. A chameleon can control its pigment cells and change its coloration for purposes of camouflage, temperature maintenance, and communication, which has inspired scientists to develop biomimetic applications through various approaches. However, previous studies only demonstrated this color changing ability without integrating the most crucial function of e-skin#8213;tactile sensing.
Herein, we present a user-interactive and color-tunable e-skin that enables not only detecting but also distinguishing various pressure forces through real-time absorption change. In addition, the different pressure forces accompanied with corresponding absorption bands in the system demonstrate that skin color can be controlled through applying various pressure forces; on the other hand, the controllable skin color change can be utilized to identify various pressures. Stretchable and ultrathin carbon-based electrochromic devices, and the tunable resistance and tunable switching range of pressure sensors were compliantly integrated in this study. This is the first demonstration of camouflaging e-skin with tactile sensing control. The e-skin integrated color-tunable properties and a tactile sensing ability that incorporates diverse functionalities, and we believe that it will meet diverse applications in health monitoring, interactive and wearable devices, military applications, artificial prosthetics, and smart robots.
9:00 AM - LL6.15
Micro Patterned Silver Nanowire-PDMS Composite
Flurin Stauffer 1 Vincent Martinez 1 Mohammed Adagunodo 2 Janos Voeroes 1 Alexandre Larmagnac 1
1Laboratory of Biosensors and Bioelectronics, ETH Zurich Zurich Switzerland2Biomedical Engineering, University of Bern Bern SwitzerlandShow Abstract
In the last decade, significant progress has been made towards stretchable electronics. Conductive elastomers have interesting properties for use in diverse conformal devices for monitoring, diagnosing and therapeutic purposes in medicine, e.g. human motion sensors [1,2] and stretchable multielectrode arrays (MEAs) for electrical stimulation . Until now our focus have been on developing stretchable MEAs which can withstand a rat&’s movement when the MEA is implanted in the spinal canal for epidural spinal cord stimulation. This requires that the conductive material can maintain impedances below 10k#8486; (< 20 #8486;/sq) for strains as high as 50%. Furthermore, the implanted material composite needs to be biocompatible, mechanically robust and stable over several months in vivo. To match the mechanical properties of biological tissue we use polydimethylsiloxane (PDMS) that has a Young&’s modulus around 1 MPa and is biocompatible. Stretchable MEAs based on conductive PDMS have been successfully and chronically implanted in spinalized rats for epidural spinal cord stimulation . However, the electrode density of the implant is limited by the fabrication method and the electromechanical properties of the material.
Novel nano-composites as silver nanowire (AgNW) networks embedded in PDMS have been shown to be promising for use as highly conductive elastomers as well as in strain sensing applications [2,5]. Our presented work focuses on photolithographically micro patterned AgNW networks embedded in PDMS for miniaturizing stretchable MEAs as well as producing highly sensitive strain sensors.
We investigate the electrical response of micropatterned AgNW structures under mechanical stress by conducting uniaxial tensile and fatigue tests. We can tailor the electromechanical properties by adapting our microfabrication process to tackle both electrode and strain sensing applications. We explore possibilities and limitations of this approach by controlling track dimensions in all three dimensions as well as other material property parameters to tailor the electromechanical response of the nano-composite material.
Our approach of photolithographically micro patterned AgNW networks embedded in PDMS can improve limitations in current implants both in terms of its electromechanical material property as well as in terms of electrode dimensions and potentially enable fabrication of miniaturized stretchable MEAs. Furthermore, by adapting our fabrication method, we can tailor the electromechanical properties of the nanocomposite for use in strain sensing applications with high sensitivity over high deformations.
 Yamada, T. et al., Nat. Nanotechnol., 6, 296-301 (2011).
 Amjadi, M. et al., ACS nano, 8(5), 5154-63 (2014).
 Van den Brand, R. et al., Science, 336(6085), 1182-5 (2012).
 Larmagnac, A. et al., IFMBE Proceedings, 37, 1180-8 (2012).
 Xu, F. & Zhu, Y., Advanced materials, 24(37), 5117-22 (2012).
9:00 AM - LL6.16
Wearable Resistance Type Strain Sensor Based on Long Silver Nanowires Synthesized by One Step Polyol Method
Teppei Araki 1 Katsunari Sato 2 Tohru Sugahara 1 Jinting Jiu 1 Tsuyoshi Sekitani 1 Katsuaki Suganuma 1
1Osaka Univ Osaka Japan2Nara Womenrsquo;s University Nara JapanShow Abstract
Sensors integrating to clothing system provide many advantages as they are personal, comfortable, close to the body and used almost anywhere and anytime, therefore, are now increasing demand for health care and human-robot interface. Resistance type strain sensor is a simple sensor by detecting correlation between electrical resistance and deformation and obtaining corresponding information of human motions. The sensor fabricated with metal fillers and stretchable binder has mechanical flexibility for wear comfort and shows low electrical resistivity with reduce power consumption. However, the electrical resistance of the sensor was not stable as the sensor held at same strain due to stress relaxation of the binder. In order to remove the effect of binder, high aspect ratio of metal filler, i.e. nanowire, was required to make electrical network without binder on clothes composed by similar yarn with large openings and roughness. Here, we developed long silver nanowires up to 400 micrometer in a length by one step polyol method and demonstrated resistance type strain sensor on clothes. Long silver nanowires were synthesized by the reduction of silver nitrate in the presence of polyvinylpyrrolidone and reduction agent in ethylene glycol. After the reaction, the solutions were washed by water/ethanol and mounted as conductive tracks on a several kinds of clothes by thermal transfer method. The conductive tracks performed as the strain sensor correlated with electrical resistance during elongation and contraction. It is noted that less change of electrical resistance was found during keeping at same strain due to the matching of long metal filler and clothing yarn. The detailed performances of the resistance type sensor will be presented in the meeting.
9:00 AM - LL6.17
Stretchable Organic Memory
Ying-Chih Lai 1 Yi-Chuan Huang 2 Tai-Yuan Lin 2 Chun-Yu Chang 3 Wei-Fang Su 3 Yang-Fang Chen 1 Fang-Chi Hsu 3
1National Taiwan University Taipei Taiwan2National Taiwan Ocean University Keelung Taiwan3National Taiwan University Taipei TaiwanShow Abstract
A stretchable organic digital information storage device has been demonstrated, which enables to advance the development of future smart and digital stretchable electronic systems. The stretchable organic memory with a buckled structure was configured by the mechanical flexible and elastic graphene bottom electrode and polymer compound. The current-voltage curve of the wrinkled memory showed the electrical bistability with typical write-once-read-many-times (WORM) memory features and a high ON/OFF current ratio of ~105. Even under repetitive stretching, the stretchable organic memory exhibited excellent electrical switching functions and memory effects. We believe this the first proof-of-concept presentation of the stretchable organic nonvolatile memory may progress the development for information storage device in various stretchable electronic applications,such as stretchable display, wearable computer and artificial skin.
9:00 AM - LL6.19
Fabrication of Stretchable Transparent Antenna Using Novel Wavy Ag Nanowire Network Electrode
Byoung Soo Kim 1 2 Jun Beom Pyo 1 Keun Young Shin 1 Jong Hyuk Park 1 Jonghwi Lee 2 Sang-Soo Lee 1
1Korea Institute of Science and Technology Seoul Korea (the Republic of)2Chung-Ang University Seoul Korea (the Republic of)Show Abstract
Stretchable transparent antenna is an important part for wireless system of wearable electronics. Flexible antennas are fabricated by printing or etching conductive materials but these antennas are not stretchable. Recently, there are several attempts to fabricate stretchable antennas using carbon based materials such as CNT, graphene and metal nanowires. Among these materials, Ag nanowires are promising candidates with their electrical and mechanical properties. Although there have been efforts in enhancing the stretching performance of antenna, attempts to create stretchable architectures are rare. In here, we present the facile fabrication of wavy nanowire network as stretchable electrode material for antenna. Fabricated wavy nanowire network electrodes are applied to stretchable transparent antenna. To construct wavy Ag nanowire electrode, filtered Ag nanowires are floated on water and then subsequently compressing the floated Ag nanowire network. After transferring the compressed Ag nanowire network to flexible substrate, we have successfully produced stretchable transparent micro strip antenna patch. Radiating properties of the wavy nanowire antenna are superior to straight nanowire antenna under tensile strain because the wavy structures can be reversibly stretched and compressed large extent without nanowires fracture. We believe the proposed novel fabrication technique that produced wavy nanowire network antenna is applicable to other types of stretchable antennas with different patterns and is possible to be integrated into previous studies to create synergistic effects.
9:00 AM - LL6.20
Soft Hydrogel-Skin Interfaces for EKG Heart Monitoring Devices
Timothy W Shay 1 Michael Dickey 1 Orlin D Velev 1
1NC State University Raleigh United StatesShow Abstract
Wearable biosensors could reduce hospital and clinic visits while lowering costs associated with staffing and equipment. These sensors require means of continuous skin interfacing and sampling. We use hydrogels as a biomimetic interface for early prototypes of wearable health monitoring devices. The goals include constructing new electrocardiogram (EKG) electrodes utilizing our hydrogels and EGaIn, a eutectic liquid metal alloy, to create a truly flexible electrode. A low impedance electrode is needed to obtain a strong heart&’s electrical signal from the body for an EKG. A potentiostatic electrochemical impedance test method has been created. On this basis, we can measure both the hydrogel resistivity as well as the impedance of the hydrogel-EGaIn interface. The inclusion of ionizable groups into the hydrogel matrix directly reduces the electrical resistance. The hydrogel-EGaIn interface has a large impedance at low frequencies, where the EKG signal exists. It was believed that this is due to the presence of an oxide skin on the EGaIn. The oxide skin on EGaIn can be removed by adding acid or base. Creating hydrogels that are acidic or basic enable the construction of lower interface impedances by removing this oxide skin. Although both acid and base remove the oxide skin, a high ionic strength is still required to decrease the low frequency impedance. This hydrogel-EGaIn system was successfully modeled with an RRC circuit. Low impedance hydrogels were utilized to create a prototype soft electrode which successfully sampled an EKG signal. These hydrogel based flexible EKG electrodes will later be implemented into a sweat capture device operating under the principles of osmotic and capillary pressure. This provides the multifunctionality needed for future biosensors.
9:00 AM - LL6.21
Optically Directed Mesoscale Assembly and Patterning of Hybrid Nanomaterials for Flexible Electronics
Subramanian Sankaranarayanan 1
1Argonne National Lab Lemont United StatesShow Abstract
Synthesis of conductive mesoscale structures is essential for developing low-cost, energy efficient, flexible and lightweight devices for next-generation micro and nano- electronics. Despite the wide variety of electronic materials available including soft organic materials such as conducting polymers, carbon nanotubes, as well as inorganic materials such as metals and semiconductors, the creation of high-conductivity and high-resolution microcircuits in high aspect ratio layouts is a major challenge. Conventional electronics is based on solid inorganic materials with very high conductivities (sim;103-105 S/cm) but with limited mechanical robustness and flexibility. Moreover, the substrates used for flexible electronics are also not compatible with the high temperature processing generally needed for forming metal circuits. Recent attention has therefore focused on using organic materials such as polymers and carbon-based materials as the conduction medium. In the field of organic electronics, however, typical conductivities of soft organic materials are sim;10minus;6 S/cm, limiting their practical implementation in electronics. We report the directed, colloidal synthesis of conductive organic-inorganic hybrid mesoscale structures. The technique is simple but allows hierarchical assembly and patterning of hybrid materials. We use a focused laser spot to direct colloidal assembly of nanoparticles (NPs) into electrically conductive organic-inorganic hybrid mesoscale filaments with arbitrary permanent patterns on a glass surface. High aspect ratio structures are fabricated with high deposition rate from colloids containing carbon and gold NPs, as well as other NP types. Growth mechanisms elucidated through finite element and kinetic Monte Carlo calculations suggest that this optically directed mesoscale assembly and patterning (ODMAP) operates through optical trapping, convective fluid flow, and chemical interactions forcing NPs to fuse near the laser focus and to continuously grow as the spot is moved along the glass-colloid interface. The synthesized filaments exhibit high ohmic con- ductivities, sim;430 S/cm, which is supported by non-equilibrium Green&’s function based density functional theory calculations. As ODMAP is applicable to other types of NPs and can be inte- grated with existing fabrication processes, it represents a simple and economical route to realize a variety of large-area electronic devices.
LL4: Neural Interfaces II
Wednesday AM, April 08, 2015
Park Central Hotel, 2nd Floor, Metropolitan II
9:30 AM - *LL4.01
Chronic, Elastomer-Based, Multimodal Neural Implants
Stephanie P. Lacour 1
1EPFL Lausanne SwitzerlandShow Abstract
The nervous system is a complex mechanical system. Neural tissues are mechanically heterogeneous and viscoelastic with typical elastic modulus E in the 1-100kPa range. Furthermore neural tissues reversibly deform during daily living activities: changes in posture and free movement may reversibly extend the spinal cord, by tens of percent; breathing induces physiologic motion of the brain. In contrast, most electrode implants are rigid.
We developed a neuroprosthesis with mechanical properties mimicking those of dura mater, one of the components of the nervous system. Dura mater (E ~ 100kPa) acts as a protective membrane for the brain and spinal cord and plays a major functional role in their stability and mechanical integrity. The neuroprosthesis is soft, manufactured with silicone, stretchable thin metal film and elastic platinum-silicone composite. It integrates an electrode array for stimulation and recording of brain and/or spinal tissue, and microfluidic channels for local drug delivery.
The implant is soft enough to be surgically inserted in the sub-dural space (below the natural dura mater) of the spinal cord. After 4 to 6 weeks in vivo, we observed unprecedented biointegration of the implant with the tissue. We further used the soft technology to pioneer a chronic electrochemical neuroprosthesis implanted in the spinal subdural space, deliver locally electrochemical neuromodulation that restored walking in rats with paralyzing spinal cord injury.
10:00 AM - LL4.02
Optical Control and Neural Recording in the Spinal Cord In Vivo using Integrated Polymer Waveguides and Carbon Nanoparticle Composites
Chi Lu 1 Ulrich Paul Froriep 1 Andres Canales 1 Jennifer Selvidge 1 Polina Anikeeva 1
1Massachusetts Institute of Technology Cambridge United StatesShow Abstract
In the past decades, significant progress has been made in the neural stimulation and recording technologies. Nevertheless, the majority of the devices available to date have been developed to primarily interface with brain circuits, and there is a technological gap for neural recording and modulation in the spinal cord. This is potentially due to the complex neurophysiology, and inhomogeneous and flexible structure of the spinal cord that impede the development of neural probes and future spinal neuroprosthetics. The latter may, in principle, allow for restoration of motor and sensory functions in paralyzed patients. Advances in optical neural interrogation tools have recently enabled cell-specific neural stimulation compatible with concomitant recording of neural activity. Thus it is highly advantageous to create flexible multifunctional neural probes that can conform to the spinal cord geometry and mechanical properties, while providing optical stimulation and neural recording.
We mimic the fibrous and flexible structure of the spinal cord and fabricate all-polymer fiber probes that consist of a polycarbonate waveguide and carbon nanoparticle polymer composite electrodes. The polymer fiber probes exhibit low-loss light transmission 0.5-2 dB/cm even under repeated deformation at bending radii < 1 mm. The conductive polymer composite electrodes exhibit tip impedance 1-3 MOmega; suitable to record single neuron activity. The mechanical properties of the integrated devices match those of biological tissues, which is difficult to achieve with traditional electrode materials such as metals or doped silicon. We demonstrate the utility our devices for recording and optical stimulation in the spinal cord of transgenic mice expressing the light sensitive protein channelrhodopsin 2 (ChR2). Furthermore, we find that optical stimulation of the spinal cord with the polymer fiber probes induces on-demand limb movements. Finally, we illustrate that the modest dimensions 50-100 µm and high flexibility of our devices permit chronic implantation into mouse spinal cords with minimal damage to the neural tissue.
10:15 AM - LL4.03
Flexible Electrode Arrays of Penetrating Electrodes
Theodore Ng 1 Samuel Maloney 1 Benjamin Nearingburg 1 Walied Moussa 1 Vivian Mushahwar 1 Anastasia Leila Elias 1
1University of Alberta Edmonton CanadaShow Abstract
A variety of sophisticated neural interfaces have been developed to communicate electrically with the central and peripheral nervous systems to restore function after disease or injury. Micro- and nanoscaled devices are of particular interest to allow specific targeting of small areas, allowing communication with small groups of cells. To reach cells deep beneath the surface of the tissue, penetrating electrodes may be required. Despite the outstanding clinical potential of a variety of neural interfaces, the applicability of these devices remains limited by the failure of the neural interface over time. Failure is due in part to the foreign body inflammatory response to implanted devices (glial scarring), which creates an insulating barrier between electrodes and neural tissue. The mechanical mismatch between stiff devices and soft tissue contributes to this response, particularly during motion. Soft devices, mimicking the mechanical properties of neural tissue, are therefore desired, provided that they are also both suitably stiff to enable insertion, and conductive for stimulation or recording. In study, we describe flexible electrode arrays consisting of penetrating Pt-Ir microwire electrodes connected by a soft, biocompatible silicone elastomer base. Individual Pt-Ir microwires (10s of µm in diameter) have been shown previously to carry large current densities (~10s of µC/cm2) while causing minimal glial scar formation. Using a surrogate tissue model, we demonstrate that our arrays can deform with the tissue as it is elongated, undergoing behavior similar to individual microwires. Stiff-base arrays, by comparison, impede the deformation of the surrogate tissue. Our finite element modeling shows that under deformation, higher levels of stress developed at the electrode-tissue interface when the electrodes are connected by a stiffer rather than less rigid base. We explore different methods for fabricating arrays of penetrating electrodes connected by flexible bases. In one method, individual microwires, which comprise a continuous lead wire and electrode, are first arranged in a rapid prototyped mold, and the elastomer is then set in the mold to form the base. This approach reduces the number of points at which the device can undergo mechanical failure due to separation of the conducting wires. In another approach, micropatterning gold or conductive ink traces are formed and encapsulated on flexible elastomer substrates, and penetrating microwires and lead wires are then connected to the patterned surfaces. This design allows superior mechanical isolation of the lead wires from the penetrating electrodes. Advantages and challenges associated with each of these methods will be reviewed in this presentation. Our work focuses on devices for use in the spinal cord (which undergoes significant deformation during daily motion) but our designs could easily be adapted for use in the brain or peripheral nervous system.
10:30 AM - LL4.04
Design Guidelines for Soft Neural Implants
Arthur Hirsch 1 Ivan Minev 1 Qihan Liu 2 Zhigang Suo 2 Stephanie P. Lacour 1
1EPFL Lausanne Switzerland2Harvard University Cambridge United StatesShow Abstract
There are an increasing number of evidences indicating the mechanical mismatch between neural tissues and implantable electrodes contribute to their poor long-term biocompatibility. In an effort to improve this heterogeneous interface, flexible and conformable bioelectronics implement electrodes on ultra-thin polymers and elastomers rather than silicon. While matching the geometry and surface contour of the neural tissues is important, one should also consider the mechanical dynamic response of the tissue. For example, the spinal cord stretches and flexes during daily activities.
We have developed a mechanical model of the spinal cord in order to define the most appropriate geometrical and mechanical parameters of implants designed to conform the surface of the delicate tissue. The spinal cord surrogate is composed of an artificial dura mater and spinal tissues, fabricated from silicone and gelatin hydrogel, respectively. The model can flex to controlled bending radii, and stretch reversibly to cover the entire range of physiologically relevant spinal movement. We inserted two types of implants in the subdural space of the spinal cord model: a plastic (polyimide based) implant and an elastic (silicone based) implant.
We quantified the spinal cord deformation upon bending and stretching of the model. Upon bending, the polyimide implant wrinkles thus induces local compressions along the hydrogel core (i.e. the spinal cord). In contrast, the silicone implant does not affect the smoothness of simulated spinal tissues. When the model is stretched, the stiff implant slides relative to the hydrogel core, whereas the soft implant elongates together with the entire spinal cord.
These results suggest soft, elastic materials are better suited to interface with the delicate neural tissues.
10:45 AM - LL4.05
Thermally Drawn Minimally Invasive Probes for High-Density Neurophysiology
Andres Canales 2 Ulrich Paul Froriep 3 4 Ryan A Koppes 3 Christina Myra Tringides 1 Yoel Fink 2 3 Polina Anikeeva 2 3
1Massachusetts Institute of Technology Cambridge United States2Massachusetts Institute of Technology Cambridge United States3Massachusetts Institute of Technology Cambridge United States4Massachusetts Institute of Technology Cambridge United StatesShow Abstract
The multiplicity of brain signaling modalities and their high spatial resolution impose a challenging barrier to high-density mapping neural circuits in vivo. Existing neural probes are limited in their long-term utility due to decreasing signal-to-noise ratio (SNR) and the number of separable neuronal units, caused by glial scarring and cell death surrounding the device. It has been hypothesized that this neural probe failure stems from a mismatch in elastic moduli between the neural tissue and the neural probes. Incorporation of additional modalities such as optical waveguides or drug-delivery channels is expected to further aggravate the foreign body response to neural probes.
We developed minimally invasive neural probes by employing a thermal drawing process, commonly used in the photonics industry, which allows straight forward integration of multiple materials and geometries into a single probe. In this process we apply heat under controlled stress to a macroscopic template of the final probe to reduce its size (30-200 times) until the desired diameter is reached. By performing multiple thermal drawing steps, the reduction factor is increased exponentially. By combining polymers and low-melting temperature metals and alloys in defined arrangements we fabricated flexible probes that facilitate high-density mapping of brain circuits. Our probes incorporate up to several tens of tin or tin-indium alloy electrodes, each as low as 5 µm in diameter, with defined inter-electrode spacing. Hollow channels and polymer waveguides can be incorporated within the same structure to enable pharmacological or optogenetic neural interrogation.
We fabricated flexible, high-density fiber probes as thin as 80 µm in diameter (comparable to size and flexibility of a human hair). These devices enabled chronic recording of well-isolated action potentials in freely moving mice with average SNR=13. In a comprehensive three-months long histological study we found that these flexible fiber probes produce minimal foreign body response in the mouse brain as indicated by negligible accumulation of glia, astrocytes and macrophages and minimal blood-brain barrier breach. We show that the high-density fiber probes exhibit higher biocompatibility than the best-performing existing neural electrodes.
11:30 AM - LL4.06
In-Situ Polymerization of Poly(3, 4-ethylenedioxythiophene) (PEDOT) in Agarose Hydrogels for Neural Recording
Chin-Chen Kuo 1 Gabriel Szczepanek 2 Unnati Patel 2 Liangqi Ouyang 1 Amy Griffin 3 David C. Martin 1 2
1University of Delaware Newark United States2University of Delaware Newark United States3University of Delaware Newark United StatesShow Abstract