Martin Kaltenbrunner, Johannes Kepler University
Michael Dickey, North Carolina State University
Christoph Keplinger, University of Colorado Boulder
Rebecca Kramer, Purdue University
Heraeus Holding GmbH
SM4.1/SM1.1/SM3.1: Joint Session I
Mohammad Reza Abidian
Tuesday AM, April 18, 2017
PCC North, 100 Level, Room 121 AB
11:30 AM - *SM4.1.01/SM1.1.01/SM3.1.01
Nano-Bioelectronics: From Biological Sensor Chips to Cyborg Tissues and Seamless Brain-Electronics Implants
Charles Lieber 1 , Jae-hyun Lee 1 Show Abstract
1 , Harvard University, Cambridge, Massachusetts, United States
Nanoscale materials enable unique opportunities at the interface between the physical and life sciences, for example, by integrating nanoelectronic devices with cells and/or tissue to make possible communication at the length scales relevant to biological function. In this presentation, I will present an overview of bioelectronics, including general questions, primary research results, and future opportunities. First, general questions and issues for developing electronic devices for biological sensors through implants will be introduced. Second, transistor-based nanoelectronic chip-based platforms will be introduced and selected studies detection of biological analytes as well as neuron and cardiac cell action potentials will be briefly reviewed. Third, the design and implementation of new nanoelectronic probes capable of intracellular recording and stimulation at scales heretofore not possible with existing techniques will be discussed, including applications in neuroscience and the prospects of biologically-targeting of nanoscale devices. Fourth, a new concept will be introduced for seamless three-dimensional integration of addressable networks of multi-functional devices in engineered tissue, and exemplified with studies of cyborg cardiac tissue. Last, an ‘out-of-the-box’ approach for seamlessly merging nanoelectronic arrays with brain using syringe-injectable polymer-like mesh electronics will be discussed, including quantitative studies demonstrating unprecedented absence of tissue immune response and stable recording at the single neuron/neural circuit level for more than a year. Finally, the prospects for broad-ranging applications in the life sciences as the distinction between electronic and living systems is blurred in the future will be discussed, as well as future challenges.
12:00 PM - *SM4.1.02/SM1.1.02/SM3.1.02
Soft Wearable Robots Improve Walking Function and Economy after Stroke and Grasping Function after Spinal Cord Injury
Conor Walsh 1 Show Abstract
1 , Harvard School of Engineering, Cambridge, Massachusetts, United States
Stroke-induced hemiparetic gait is characteristically slow and metabolically-expensive. Conventional rehabilitation efforts have had limited effectiveness in restoring normal walking behavior, often relying on gait compensations for the limited gains observed. We sought to determine if a unilateral, soft wearable robot (exosuit) designed to supplement the paretic limb’s residual ability to generate forward propulsion and ground clearance during walking could facilitate more normal walking behavior after stroke. Herein, we evaluate the effects of walking with an exosuit actively assisting the paretic limb of nine individuals in the chronic phase of stroke recovery compared to walking with an exosuit unpowered. Spinal cord injury patients often lose the ability to grasp objects and their poor hand function limits their ability to perform activities of daily living. We sought to determine if lightweight, fabric-based soft fluidic actuators would be capable of applying sufficient assistance when integrated into a glove to improve grasping functions. Herein, we evaluate the effects of grasping when wearing the glove of five individuals who have suffered a spinal cord injury and compared to their baseline ability.
SM4.2/SM1.2/SM3.2: Joint Session II: Bioelectronics
Mohammad Reza Abidian
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 121 AB
2:30 PM - *SM4.2.01/SM1.2.01/SM3.2.01
Skin-Inspired Materials, Devices and Applications
Zhenan Bao 1 Show Abstract
1 , Stanford University, Stanford, California, United States
In this talk, I will discuss fabrication of skin-inspired devices and related applications in bioelectronics and robotics.
3:00 PM - *SM4.2.02/SM1.2.02/SM3.2.02
Biocompatible Gel Electrodes and Ultraflexible Organic Devices for Implantable Electronics
Takao Someya 1 , Tsuyoshi Sekitani 2 , Sungwon Lee 3 , Tomoyuki Yokota 1 Show Abstract
1 Electrical and Electronic Engineering and Information Systems, University of Tokyo, Tokyo Japan, 2 The Institute of Scientific and Industrial Research, Osaka University, Osaka Japan, 3 , Daegu Gyeongbuk Institute of Science and Technology, Daegu Korea (the Republic of)
We report recent progress of ultraflexible organic photonic and electronic devices for implantable electronics. In particular, we describe the fabrication of different organic devices such as organic thin-film transistors (OTFTs), organic photodetectors (OPDs), and organic light-emitting diodes (OLEDs) that are manufactured on ultrathin plastic film with the thickness of 1 μm. We also fabricate two types of gels that are patterned on the surface of ultrathin film devices for implantable applications. First, by designing and fabricating smart, stress-absorbing electronic devices with sticky gels that can adhere to wet and complex tissue surfaces, we realize reliable, long-term measurements of vital signals. We fabricated a multielectrode array, which can be attached to the surface of a rat heart, resulting in good conformal contact. Second, a biocompatible highly conductive gel composite comprising multi-walled carbon nanotube-dispersed sheet with an aqueous hydrogel. By using gel composites, we fabricated an ultrathin organic active matrix amplifier on a 1-μm-thick polyethylene-naphthalate film to amplify weak biosignals. This work is financially supported by JST/ERATO Bio-harmonized electronics project.
3:30 PM - *SM4.2.03/SM1.2.03/SM3.2.03
Interfacing with the Brain Using Organic Electronics
George Malliaras 1 Show Abstract
1 , ENSM Saint-Etienne, Gardanne France
One of the most important scientific and technological frontiers of our time lies in the interface between electronics and the human brain. It promises to help elucidate aspects of the brain’s working mechanism and deliver new tools for diagnosis and treatment of a host of pathologies including epilepsy and Parkinson’s disease. The field of organic electronics has made available materials with a unique combination of attractive properties, including mechanical flexibility, mixed ionic/electronic conduction, enhanced biocompatibility, and capability for drug delivery. I will present examples of organic-based devices for recording and stimulation of brain activity, highlighting the connection between materials properties and device performance. I will show that organic electronic materials provide unparalleled opportunities to design devices that improve our understanding of brain physiology and pathology, and can be used to deliver new therapies.
4:30 PM - *SM4.2.04/SM1.2.04/SM3.2.04
Materials and Devices Designs for Flexible, Active Electronic Interfaces to the Brain and the Heart
John Rogers 1 Show Abstract
1 , Northwestern University, Evanston, Illinois, United States
Advanced capabilities in electrical recording and stimulation are essential to the treatment of heart rhythm diseases and brain disorders and to progress in cardiac and brain science. The most sophisticated technologies for this purpose utilize geometrically conformal, active electronics that achieve high speed, high resolution electrophysiological mapping through direct measurement interfaces to adjacent, contacting tissues. Unfortunately, slow penetration of biofluids through the materials of the surface layers and/or through localized defects in them prevent chronic modes of use. Here we present advances in materials for ultrathin biofluid barriers and in actively multiplexed device designs for capacitive signal detection that, together, enable flexible electronic devices with stable, long-term operational capabilities as full implants. Systematic studies, including accelerated in vitro testing that suggests lifetimes of several decades, reveal the fundamental materials considerations and highlight the practical advantages of such platforms. High resolution mapping of cardiac function in Langendorff hearts and of brain activity in live animal models demonstrates the capabilities, with quantitative validation against control measurements. The results establish pathways for use of flexible electronics as long-term implants, with important implications for basic scientific study and future clinical use.
5:00 PM - *SM4.2.05/SM1.2.05/SM3.2.05
Conformal, Microfabricated Electrode Array for Optimization of Spectral Content in the Auditory Brainstem Implant (ABI)
Amelie Guex 1 , Ariel Hight 2 , Daniel Lee 2 , M. Brown 2 , Stephanie Lacour 1 Show Abstract
1 , Ecole Polytechnique Federale de Lausanne, Switzerland, Lausanne Switzerland, 2 , Harvard Medical School, Boston, Massachusetts, United States
The auditory brainstem implant (ABI) is a neuroprosthesis that provides sound sensations to patients who cannot benefit from a cochlear implant (CI) by stimulating the cochlear nucleus (CN) surface, the first auditory processing nucleus in the central nervous system. Compared to the CI however, ABI users lag behind in speech comprehension, which may be due to the poor spatial resolution of its stimulating channels leading to a low spectral resolution.
In this study, we test whether using a flexible microfabricated electrode array with high channel resolution and small contacts (100 µm diameter) coated with conducting polymer PEDOT:PSS can provide significant spectral information, and how the presentation of stimulus current can be optimized (e.g. monopolar or bipolar stimulation, distance and angle between the two electrodes of a pair). Using a rat model of the ABI, we place the electrode array along the length of the dorsal cochlear nucleus (DCN) surface to selectively stimulate different locations, and we record evoked activity along the tonotopic axis of the inferior colliculus (IC), an auditory structure located in the midbrain, to measure the resolution of evoked tonotopic cues.
Initially, we found high variability in the pattern of evoked activity but upon further analysis found two components that revealed tonotopic cues. Specifically, we found that there was a common pattern of evoked activity across all electrodes that masks tonotopic cues, and that early latency spikes following each stimulus pulse are more tonotopic than later spikes. While focusing our analysis on tonotopic cues, we found minimal measured differences between monopolar vs. bipolar stimulation, but found that small inter-electrode distances were better than large ones. These results suggest that modifications in the electrode design, particularly an increase in the density of stimulation electrode sites, could ultimately improve tonotopic cues for ABI users.
5:30 PM - *SM4.2.06/SM1.2.06/SM3.2.06
Interfacing Neurons with Electronic Devices
Andreas Offenhaeusser 1 Show Abstract
1 , Forschungszentrum Juelich, Juelich Germany
A challenging issue in Neuroscience is tightly monitoring and controlling of the functionality of neural networks. Direct interfacing of devices based on inorganic and organic semiconductor and (non conventional) electrode material with nerve cells and brain tissue open novel perspective for multifunctional electrophysiological tools in vitro and in vivo with high spatiotemporal resolution and improved sensitivity.
We aim for the fabrication of chip-based sensors that enable an efficient neuro-electronic interface towards precise recording of cellular signals. Within this framework, we have developed a variety of microelectrode array (MEA) designs that enable non-invasive, parallel, multi-site recording of action potentials from primary neurons and cardiomyocyte-like HL-1 cell line. We have modified standard planar 64 electrode MEA design with different geometries ranging from nanometer-sized cavities that allow for cellular protrusion into the sensor to mushroom-shaped 3D electrodes. Furthermore, we investigate various field-effect transistor (FET) designs ranging from silicon nanowires to graphene. Recently we could demonstrate successful interfacing of electrogeneic cells with fully printed and flexible MEA and flexible graphene FETs.
Martin Kaltenbrunner, Johannes Kepler University
Michael Dickey, North Carolina State University
Christoph Keplinger, University of Colorado Boulder
Rebecca Kramer, Purdue University
Heraeus Holding GmbH
SM4.3: Soft and Flexible Electronics
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 121 B
9:15 AM - SM4.3.01
Inkjet-Printed Electrodes Fabricated on Various Substrates for Cutaneous Electrophysiological Applications
Timothee Roberts 1 2 , Eloise Bihar 3 2 , Mohamed Saadaoui 4 , Thierry Herve 2 , George Malliaras 3 , Jozina De Graaf 1 Show Abstract
1 , Institut des Sciences du Mouvement, Marseille France, 2 , Microvitae Technologies, Meyreuil, PACA, France, 3 BEL, EMSE, Gardanne, PACA, France, 4 PS2, EMSE, Gardanne, PACA, France
Electrophysiology, health and welfare are domains in need for custom, multi-site, long-term lasting electrodes. In order to fit these needs, specific substrates are required such as strong, thin and flexible substrates (e.g., Polyimide1 or Paper2), or soft and stretchable ones (e.g., fabric3). We used PEDOT: PSS for its biocompatibility, softness and electrical properties, and solid ionic gels for their abilities to ensure a stable and efficient contact in cutaneous applications.
In the present project we focused on electrode fabrication and characterization. We used an inkjet-printer being an easy method to customize low cost biomedical electrodes for ECG and EMG applications. The selected materials were PEDOT: PSS and Cholinium-based ion gel. We inkjet-printed the successive layers on a broad range of substrates such as paper, tights, fabric and tattoo paper. We evaluated the performance of these electrodes using electro-chemical impedance measurements and by the analysis of electro-physiological recordings such as electrocardiogram and electromyogram.
The electrodes displayed high quality recordings, similar to the ones acquired with the state-of-the-art electrodes. The electrochemical impedance of PEDOT: PSS electrodes were measured to be between one and two order of magnitude higher than commercial electrodes. However, the addition of solid gel lowered the impedance to the level of commercial ones. The electrodes deposited on tights have been subjected to stretching cycles and appeared to still display a normalized resistance of 1.036 after 50 cycles of 30% strain, reflecting insensitivity of electrical properties to mechanical deformations. The sensitivity to motion artifacts has been evaluated showing a good stability of solid gel for small motions. The signal to noise ratio from ECG measurement of PEDOT: PSS electrodes were measured to be around 12dB which remained stable for few months.
Our results demonstrate that inkjet-printing is a versatile, low cost and precise tool for producing high quality electrodes with, if necessary complex and customizable designs, for electrophysiological applications.
1 Roberts T., De Graaf JB, Nicol C, Hervé T, Fiocchi M, Sanaur S (2016). Flexible Inkjet-Printed Multielectrode Arrays for Neuromuscular Cartography.Advanced Healthcare Materials
2 Bihar E, Roberts T, Saadaoui M, Hervé T, De Graaf JB, Malliaras G. Inkjet Printed PEDOT:PSS electrodes for ECG measurements on paper. In review
3 Bihar E, Roberts T, Ismailova E, Saadaoui M, Isik M, Sanchez-Sanchez A, Mecerreyes D, Hervé T, De Graaf JB, Malliaras G. Fully printed electrodes on stretchable textiles for long-term electrophysiological measurements. In review
9:30 AM - SM4.3.02
Wearable Paper-Based Sensors for Green Electronics
Xinqin Liao 1 , Qingliang Liao 1 , Yue Zhang 1 Show Abstract
1 , University of Science and Technology Beijing, Beijing China
As wearable electronic devices (WEDs) are often characterized by their requirement for being able to be quickly replaced and disposed of, discarding used WEDs is a waste disposal issue that cannot be disregarded in our living environment. Therefore the development of green electronics is a welcome proposition. Paper-based substrate is a novel material platform with unique and obvious virtues including flexibility, lightweight, ease of recycling/disposal and cost efficiency.
In general, flexible and wearable sensing devices are typically complex and manufactured by complicated producing processes with a number of circuits or intricate layered matrix arrays, leading to energy intensive consumption while limiting their wide applications. By developing highly efficient, scalable and low cost fabrication schemes, paper-based strain sensors are attractive candidates for promoting the advancement of science and technology.
Herein, we demonstrate that the application of pencil-on-paper (PoP) method, stencil printing, hydrothermal process and direct-current (DC) sputtering method can be expanded even further to crucial flexible sensing devices. We evaluated the repeatability of bending-unbending and the robustness of the bending strain sensors under strain loading. In the bending-simulations, the strain sensors can respond to micro-shape changes and allow to be used to variously monitor structural change and even human motion by facilitated and effective designs. These performances of the sensors attain and even surpass the properties of recent sensing devices with subtle design of materials and device architectures. The fabrication methods may further develop portable, environmentally friendly, and economical lab-on-paper applications and offer valuable methods to fabricate other multifunctional devices.
9:45 AM - *SM4.3.03
Concealed Electronics and Photonics
Siegfried Bauer 1 Show Abstract
1 , Johannes Kepler Univ-Linz, Linz Austria
We are at the brink of a fascinating technological society: Imagine science fiction turning into reality via an evolution of technologies that is blurring the lines between the physical, digital and biological spheres. Think of living organisms: they distribute perception and proprioception throughout their body by seamlessly blending mechanical, electrical and chemical systems in a way that enables them to perform complex tasks. Eating a strawberry is intuitive and amazingly simple, but necessitates the almost invisible operation of the whole somatosensory system. As scientists we are inspired both by this apparent simplicity and by the true complexity of biology, and we dream to mimic nature by creating a world with concealed technology virtually embedded anywhere, increasing comfort, safety and quality of everyday life. Just a decade ago such a vision was not much more than pie in the sky, with hesitant approaches towards soft electronics and photonics. Today, this particular field of soft matter science became a distinct and booming area, briefly reviewed in this talk. A tour d’horizon through most recent developments is given, starting from ultra-flexible electronics and proceeding to imperceptible and transient electronic and photonic systems. Electronics and photonics drive innovation in society, and future products from this soft revolution in electronics will form seamless links between living beings and the digital world. Prospect for applications of such a pluripotent “soft” technology platform is bright, ranging from smart systems for buildings, automotive and many more, to mobile health, sports and well-being.
10:15 AM - SM4.3.04
A Soft Prosthetic Hand—Synthetic Remapping of Softness and Roughness Enabled by Stretchable Optical Sensors and Displays
Shuo Li 1 , Hedan Bai 2 , Yaqi Tu 1 , Huichan Zhao 2 , Robert Shepherd 2 1 Show Abstract
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York, United States
Recent advances in fluidic elastomer actuators demonstrate new potentials in the field of wearable soft robots for healthcare implementations. Hand prosthetics, in particular, has gained emerging interests as they can provide safe assistance in everyday tasks to those who suffer the loss of dexterity. To better realize its functionalities, conventional sensors lack the material compatibility with highly extensible soft actuator. Moreover, the sophistication of collected signals greatly exceeds our routine cognitive capabilities. This work reported here presents an integrated hand prosthetics that provides haptic perception and sensory feedback via simple indications. Stretchable optical sensors can independently detect softness and roughness of an object; integrated electronics extracts digital signals from photodetector and manipulate the output light intensity of embedded stretchable displays to synthetically remap those perceptions. The results show potential capabilities in assistive training for hospital care and at-home rehabilitation.
10:30 AM - *SM4.3.06
Soft Gel Electrodes and Organic Amplification Circuits for Bio-Signal Monitoring Systems
Tsuyoshi Sekitani 1 Show Abstract
1 , Osaka University, Osaka Japan
We demonstrate the fabrication of wearable and implantable bio-signal monitoring systems, whose measurement accuracy is 0.2 μV, and weight is 20 g. This system comprises biocompatible, multichannel, soft gel electrodes with Ag-nanowire-based elastic conductors, organic amplification circuits, Si-LSI platform (AD converter, CPU, wireless communication module), and a thin-film Li-ion battery. This soft gel electrode exhibits elastic modulus less than 100 kPa and conductivity greater than 1000 S/cm. It maintains high conductivity even during stretching more than 100%. Upon implantation into a living hypodermal tissue for four weeks, it showed a small foreign-body reaction compared with widely used metal electrodes. Capitalizing on the multi-functional gel electrodes, we fabricated an ultrathin and mechanically flexible organic amplifier on a 1.2-μm-thick polyethylene–naphthalate film to amplify weak biosignals. Small input voltage for 10 µVpp at 3 Hz sine wave is amplified to 10 mVpp, which means the voltage gain is 60 dB (amplification factor is 1000). The large voltage gain is quite beneficial for detecting small biological signals. The soft electrodes and organic amplification circuit were integrated to thin Si-LSI platform (weight: 15 g, thickness: 4 mm) to realize wireless measurements of electroencephalogram (brain wave) from a forehead. Furthermore, we have measured electrooculogram (EOG), electrocardiogram (ECG), electrocorticogram (ECoG) that are easily spread over an uneven tissue and organs.
11:30 AM - *SM4.3.07
Flexible and Printed Organic TFT Devices and their Potential Applications
Shizuo Tokito 1 Show Abstract
1 , Yamagata University, Yamagata Japan
Recently, smart labels and wearable biosensors based on thin-film transistor (TFT) devices fabricated on thin plastic film substrates with various printing processes are attracting significant attention in research and development. In particular, TFT devices based on organic semiconductors (OSC) can be fabricated at low temperatures and are more compatible with plastic film substrates and printing methods than inorganic semiconductors. Here, we will report briefly on printable materials, printed OTFT devices and their potential application to TFT arrays and integrated circuits as well as biosensors.
We developed Ag nanoparticle ink that was optimized for organic TFT applications. Finely patterned Ag lines with a low resistivity could be obtained by inkjet printing and thermal sintering or photonic sintering. We adopted newly developed p-type OSC material based on dithienobenzodithiophene derivative (DTBDT), which is soluble in common organic solvents and highly crystalline. High mobility over 3 cm2/Vs and high on/off current ratio of 107 were obtained in a typical bottom-contact top-gate OTFT device. N-type OSC material, TU series, based on benzobisthiadiazole moiety was also developed. A mobility of 2 cm2/Vs was demonstrated in a top-contact bottom gate device structure.
Printed OTFT arrays (30x30) were successfully fabricated employing DTBDT on plastic film substrates. By optimizing the semiconducting layer crystal growth, excellent p-type electrical performance with a high mobility of 1.9 cm2/Vs and high on/off current ratios over 107 were achieved. Exceptional uniformities of device characteristics were also observed within in the array. Ultra-thin OTFT devices can also be fabricated using ultra-thin Parylene films. The resulting ultra-thin printed OTFT devices and inverter circuits were extremely lightweight, flexible and compressible.
One of the important applications of OTFT devices is integrated circuits for RFID and microprocessor. We successfully fabricated pseudo-CMOS inverters using the p-type OTFTs, as well as NAND logic gates that exhibited ideal characteristics at a low voltage operation. Very high gains over 250 were obtained in the printed pseudo-CMOS inverters. Of course, real CMOS inverter using both p-type and n-type OSC materials are significantly important for the integrated circuit fabrication. We proposed stacked TFT structure for the CMOS inverter and fabricated using our n-type OSC material (TU-3) and commonly used p-type OSC material (diF-TES-ADT). Good switching characteristics were observed and a high gain was obtained at an operating voltage of 10 V. Based on this CMOS inverter a three –stage ring oscillator and D-flip flop circuits were also fabricated on a ultra-thin substrate based on Parylene film. In order to realize very shot-channel OTFT devices and more integrated circuits we have employed the reverse offset printing method and obtained good characteristics in the printed CMOS inverters.
12:00 PM - SM4.3.08
All-Solution-Processed Stretchable Transistor Arrays Based on Polymer Semiconductor and Dielectric
Sihong Wang 1 , Francisco Molina-Lopez 1 , Jia Liu 1 , Jie Xu 1 , Jong Won Chung 1 , Zhenan Bao 1 Show Abstract
1 Department of Chemical Engineering, Stanford University, Stanford, California, United States
The next generation of consumable electronics and biomedical devices feature more intimate integration with human bodies and tissues, which makes the development of stretchable electronics that can function under straining highly desirable. Besides the device structural engineering approaches, the realization of stretchable electronics based on the development of intrinsically stretchable electronic materials could offer a number of important advantages, including larger strain tolerance, higher device density and simpler fabrication. In order to construct stretchable circuits and functional systems utilizing the intrinsically stretchable materials, the fabrication technology of stretchable transistor array is critically important. With polymer as the primary material system for the intrinsically stretchable semiconductors and dielectrics, the traditional fabrication processes for Si-electronics are not compatible. In this work, we developed the first all-solution-processed fabrication strategy that gives the first stretchable transistor array based on polymer semiconductor and dielectrics. This innovative fabrication process gives the record-high device density, a yield almost 100%, and little performance variation among individual devices. With the intrinsic stretchability of the semiconductor and the strain-engineering design, this array can keep its original performance without any degradation under a large strain up to 100%. In order to reveal its practical applicability in the development of next-generation electronics, this stretchable transistor array is further utilized as the backplane in a constructed stretchable active-matrix LED array display. In another demonstration, prototypes of stretchable logic circuits have been realized based on this stretchable transistor array. With the fabrication process reported here, future-developed intrinsically stretchable semiconductors and dielectrics can be combined to generate transistor arrays with even higher stretchability and robustness. Moreover, the nature of all-solution-processing makes this fabrication strategy scalable and cost-effective for the industrialization.
12:15 PM - SM4.3.09
Towards Non-Invasive Biochemical Monitoring—Utilizing Hydrogels and Paper Microfluidics to Create a Wearable Sweat Sensing Platform
Timothy Shay 1 , Orlin Velev 1 , Michael Dickey 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
The use of wearable devices in healthcare can greatly benefit from the development of new microfluidic sampling methods for sensing biomarkers in sweat. Therefore, we aim to develop a wearable platform for non-invasive microfluidic sweat sampling. A combination of hydrogels and paper microfluidics will be used to pump and draw sweat from the surface of the skin. Paper microfluidics have been commonly used in single use biochemical tests, where a bio-fluid is wicked into a paper strip on which sensing is performed. We have created a method in which paper can be used to continually wick fluids for upwards of ten days. This allows for paper microfluidics to be used in a long-term continual manner for sweat wicking and sensing. During periods of low sweat rate, hydrogels will passively pump sweat towards the paper microfluidic strip using osmotic pressure differences created with the body. By combining hydrogels with a paper microfluidic network, we seek to create a soft matter platform that is non-invasive and capable of pumping sweat from the body with no power requirement. Biochemical sensors (glucose and lactate) will interface with the paper microfluidics to enable continual sensing. We will first demonstrate the use of this platform in a lab setting utilizing a water permeable dialysis membrane as a skin mimic. We will also present the results of an ongoing IRB study where testing is being performed on human subjects.
12:30 PM - *SM4.3.10
Tailoring Organic Electronic Materials for Bioelectronics—A Case for Biosensors
Sahika Inal 1 2 Show Abstract
1 Biological and Environmental Science & Engineering, KAUST, Thuwal Saudi Arabia, 2 Department of Bioelectronics, CMP-EMSE, Gardanne France
Organic electronic materials have the potential to impact greatly on applications in biology, where electrical signals are used to interact with biological systems. Sensors that allow for electrical read-out of disease markers, and implants/stimulators used for the detection and treatment of pathological cellular activity are only a few examples of what this technology can offer. In addition to their soft mechanical properties, a feature that makes organics attractive for biological applications is their mixed electronic/ionic conductivity. Mixed conductivity enables state-of-the-art devices such as the organic electrochemical transistor (OECT), an amplifying transducer that uses an organic film as the channel.
Poly(3,4- ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) has been a prototype material for OECTs, mostly due to its chemical stability. There is, however, room for improving the channel material for better performing and specialized OECTs for targeted applications. In this work, I will show a comprehensive study on the thin film properties of conjugated polymers that are operated in the accumulation mode and evaluate how systematic chemical modifications can impact the device performance. Highlighting the materials properties that enable enhanced ion-to-electron transduction, we design n-type and p-type OECTs for sensing clinically relevant biomarkers with improved sensitivity. We investigate two distinct biosensing regimes, based on enzymatic reactions and redistribution of ions following specific binding events at the polymer/electrolyte interface. Tailoring the devices for each regime, this work provides an understanding of materials-device performance relations for the development of low-cost, rapid, label free point of care assays.
SM4.4: Soft Power Generation and Storage
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 121 B
2:30 PM - *SM4.4.01
Ultrathin Optoelectronic Devices—Light-Weight and Extreme Flexibility
Matthew White 1 2 , Martin Kaltenbrunner 3 Show Abstract
1 Department of Physics, University of Vermont, Burlington, Vermont, United States, 2 Materials Science Program, University of Vermont, Burlington, Vermont, United States, 3 Soft Matter Physics, Johannes Kepler University, Linz Austria
Solution-processed semiconductor devices, including perovskite and organic photovoltaics and organic LEDs, are inherently thin-film technologies. Therefore. low-weight and flexibility are natural advantages. However, common substrate materials are over 300 times thicker than the active device materials. Therefore, the mechanical properties of weight and flexibility are entirely determined by the substrate. We present the use of a 1.4 μm PET foil substrate material to demonstrate ultrathin solar cells and LEDs. This allows continuous operation of devices under extreme deformation. We can crumple the films, bend them to radius of under 10 µm, and even stick them to elastomeric tape to form stretchable polymer-based LEDs, and organic, and perovskite solar cells. The mechanical flexibility renders the devices perfectly compatible with elastomeric surfaces, necessary for integration with biological tissues such as human skin. Their weight becomes negligible (only 4 - 5 g/m2), resulting in ultrathin solar cells with the highest specific weight (W/kg) of any photovoltaic technology.
3:00 PM - SM4.4.02
High Efficiency and Stable Polymer Solar Cells on Ultra-Flexible Substrate
Kenjiro Fukuda 1 2 , Hiroaki Jinno 1 , Xiaomin Xu 1 , Yasuhito Suzuki 1 , Itaru Osaka 1 , Kazuo Takimiya 1 , Takao Someya 1 3 Show Abstract
1 , RIKEN, Saitama Japan, 2 , JST PRESTO, Saitama Japan, 3 , The University of Tokyo, Tokyo Japan
Novel electrical power sources that are compatible with textiles or clothes are playing a key role in the recent internet-of-things (IoT) applications. Among kinds of solar cells, bulk-heterojunction polymer solar cells have garnered significant attention because they possess great potentials for making large-area, light-weight and flexible devices. Here we report ultrathin, stretchable, high performance, and air-stable polymer solar cells. The combination of stable active layers and inverted architecture enabled reduced total thickness to 3 μm with high power conversion efficiency (PCE) of 7.4% and air stability (remained more than 50% after 30 days) in addition to the excellent strechability of 67%.
The polymer solar cells were fabricated on a 1-μm-thick parylene film. An ITO was sputtered on a 1-μm-thick parylene film with a 500-nm-thick epoxy planarization layer. To form a zinc oxide buffer layer, zinc acetate dehydrate dissolved in 2-methoxyethanol and ethanolamine solution was spin-coated and then the substrates were annealed at 180°C. A blend solution of a D–A polymer with quaterthiophene and naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NTz) (PNTz4T)  and PCBM was spin-coated to form an active layer. Molybdenum oxide and silver were evaporated as a top interlayer and an electrode. Finally the 1-μm-thick parylene was deposited to form encapsulation layer. The maximum processing temperature employed was 180 °C, which was compatible with the other flexible films.
The freestanding (delaminated from the supporting glasses) solar cells exhibited a maximum PCE of 4.3% under a one-sun illumination. The air-stable polymer active layer and the inverted structures realized ultrathin OPVs with long-term stability. The PCE value of the freestanding devices after 720 h (30 days) remained at 54% of the initial value. The mechanical stability of the fabricated OPVs was evaluated by applying a compressive strain . The devices were fully functional even when 67% compressive strain was applied to them. A stress cycle was also applied to the devices. The device performance remained practically unchanged after the first cycle. The changes in the PCE amounted to 1.6% after 20 full cycles.
 V. Vohra et al. Nat. Photon. 9, 403 (2015).
 M. Kaltenbrunner et al. Nature 499, 458 (2013).
3:15 PM - SM4.4.03
Subcutaneous Flexible Solar Cells for Supplying Electrical Power to Medical Implants
Kwangsun Song 1 , Jongho Lee 1 Show Abstract
1 , Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
As the population has been rapidly aging in the world, humans have the opportunity to use the various biomedical implants in order to take care of functionally deteriorated organs in the human body. Because the implants only rely on the battery whose electricity is finite, the discharged battery has to be replaced every 5-8 years through surgical operation which causes psychological and physical stress to patients. To resolve this problem, alternative approaches using mechanical movements, electrochemical reactions, wireless power transmissions and others have been studied for the decades. However, they need more effort to improve the electrical power density, biocompatibility and lifetime. Here we suggest the new concept to generate and supply the sustainable electric power in the human body with subcutaneously implantable solar cells. The dual junction solar cells array (GaInP/GaAs, thickness: ~ 5.7 μm) was separated from the original wafer after etching the release layer and transfer-printed on the flexible polyimide (PI) film (~12.5 μm). The microcells were interconnected by thin metal layers (Ti: 20 nm/Au: 300 nm) with sputtering deposition systems. Finally, the IPV device were multiply encapsulated with transparent and biocompatible materials (SU-8, NOA). The measurement of the electrical property of the IPV device begins with preparing animal models (hairless mouse: SKH1-Hrhr). The IPV devices were inserted under the skin of the hairless mouse through simple dermatology surgery. We assessed the electrical properties including short circuit current (Isc), open circuit voltage (Voc), fill factor (FF) and power density under standard test conditions (AM1.5G, 100mW/cm2). The IPV device with flexibility properly worked without any degradation after bending with a radius of ~1.75 mm. Under the mouse skin, the IPV device generated high electric power (~9.5 mW/cm2) that was comparable with previous results. The custom-built pacemaker, integrated with the IPV device and a rechargeable battery, operated with electricity by IPV device or the recharged battery by the IPV device. The subdermally implanted self-powered pacemaker could pace the heart of the mouse under bradycardia state. In conclusion, we confirmed that the flexible IPV device can generate high electric energy under the skin and demonstrated the feasibility to supply sustainable electricity to commercial medical implants without periodic operations. The efforts to improve the problem related to electrical energy in the human body should enable the use of the various implantable Bioelectronics to assist or communicate with the internal organs in real time.
4:30 PM - SM4.4.04
Denys Makarov 1 , Gilbert Santiago Canon Bermudez 1 , Tetiana Voitsekhivska 1 , Jin Ge 1 , Juergen Fassbender 1 Show Abstract
1 , Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden Germany
Augmented reality gadgets are becoming common for our information intensive society assisting us to acquire and process the data. Although impressive in the realization and demonstrations, the obvious drawback of the state-of-the-art augmented and virtual reality devices relying on optical detection systems is their bulkiness, energy inefficiency and the stringent requirement for an operator to be at the line of sight of the device.
We envision that prospective augmented reality systems will strongly benefit from the recent developments in compliant on-skin electronics [1-3]. The fabrication of highly conformable gadgets requires the realization of the electronic replica of the exteroceptive sensory system of humans as well as calls for the acquiring new perception skills beyond those prescribed by the evolution. The representative example of the missing exteroceptive sense of humans is the magnetoception, which allows some of the mammals but not humans perceiving the location in space or directions based on the detection of magnetic fields. The first crucial step towards the realization of this vision was accomplished with the development of interactive magnetosensitive skins [4-6]. The key enabler for this technology is the shapeable  –namely, flexible [5,6], stretchable [8,9] and imperceptible – magnetic field sensorics.
Here, we present the first on-skin gadgets, which replicate our natural proprioceptive sensory ability of detecting the motion. The technology is put forth to realize distributed arrays of magnetic field sensors on ultra-thin polymeric foils. The sensors are multiplexed using a highly compact multiplexer based on silicon-gate 125 nm CMOS technology, which is integrated as a part of a compliant gadget relying on the rigid island approach . Relying on this magnetically enabled electronic proprioception, we visualize the bodily motion and demonstrate the touchless manipulation of virtual objects for augmented reality systems.
Those highly conformable interactive devices possess great potential to extend the portfolio of tasks, which can be performed in virtual or augmented reality. The integration of gadgets in imperceptible electronic skins will open not only exciting possibilities for business or gaming industry but is also beneficial for safety and security applications, where the somatic manipulation of objects, e.g. turning regulation knobs located in a restricted environment is undesirable or even prohibited.
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3. M. Kaltenbrunner et al., Nature 499, 458 (2013).
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5. M. Melzer et al., Adv. Mater. 27, 1274 (2015).
6. N. Münzenrieder et al., Adv. Electron. Mater. 2, 1600188 (2016).
7. D. Makarov et al., Appl. Phys. Rev. 3, 011101 (2016).
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10. D. H. Kim et al., Adv. Mater. 21, 3703 (2009).
4:45 PM - SM4.4.05
Compliant On-Skin Compass for Artificial Magnetoception
Gilbert Santiago Canon Bermudez 1 , Juergen Fassbender 1 , Denys Makarov 1 Show Abstract
1 , Helmholtz-Zentrum Dresden Rossendorf, Dresden Germany
Flexible electronics has inspired novel concepts like electronic skins [1-3] equipped with e.g. pressure  and temperature  sensing capabilities, which could potentially replicate the 5 empirical senses of humans. Very recently, magnetosensitive skins [6-8] enabled by shapeable magnetoelectronics  were reported, allowing humans to perceive magnetic fields, which is beyond the senses developed during the evolution.
Magnetoception for humans, i.e., the ability to detect and respond to magnetic fields, has been a subject of debate and dreams since the early days of navigation when sailors used compasses to orient themselves with respect to earth’s magnetic field. Sailors of old times often had compass rose tattoos to “enable” magnetoception, assuring success and luck in their trips [10,11].
Here, we present a technology platform to turn these dreams into a functional on-skin compass system. The highly compliant compasses are prepared on 6-µm-thick polymeric foils and rely on the anisotropic magnetoresistance (AMR) effect in magnetic thin film sensors. The response of these sensors is tailored to be linear and possess maximum sensitivity around the earth’s magnetic field by using a barber pole  configuration and preconditioned via a Wheatstone bridge arrangement. In a barber pole configuration, conductive slabs with a 45 degrees tilt are fabricated on top of Permalloy sensing stripes to force the current to flow skewed with respect to the easy axis of the stripes. By defining the tilt angle and properly adjusting the inter-slab separation, the magnetic field dependence of the AMR on the stripes becomes even and linear around zero.
We envision that this on-skin compass can enable humans to electronically emulate the magnetoceptive sense which some mammals possess naturally . Thereby, allowing us to orient ourselves with respect to earth’s magnetic field ubiquitously. This feat could open new possibilities to support research efforts on biomagnetic orientation and novel magnetic interactive devices. In the latter case, the applications span a plethora of tasks from virtual or augmented reality systems to touchless security systems and magnetic tags.
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5:00 PM -
5:15 PM - SM4.4.07
High Power, Tough Battery with Integrated Stretchable Circuit
Gerald Kettlgruber 1 , Richard Moser 1 , Michael Drack 1 , Robert Pichler 1 , Daniela Wirthl 1 , Florian Hartmann 1 , Doris Danninger 1 , Martin Kaltenbrunner 1 , Siegfried Bauer 1 Show Abstract
1 Soft Matter Physics, Johannes Kepler University Linz, Linz Austria
Energy density is a key metric when powering mobile devices and plays a crucial role for autonomous soft systems ranging from robotics to wearables and implants. All mobile, untethered applications require a reliable power source that withstands stretching and twisting while operating, ideally with low internal resistance and high power density. To achieve this, we redesigned our pioneering approach towards stretchable batteries [1,2] from scratch and demonstrate a tough, soft battery that can be stretched to over 50% and withstands twisting by 90 degrees without detrimental impact on performance. On the contrary, due to a new design, the battery even improves its performance when deformed - the short circuit current increases from 160 mA to 220 mA when stretched by 50%. The new, stacked design of anode, cathode and electrolyte containing hydrogels drastically improves performance and energy density. We achieve this by using a tough hydrogel separator with high ionic conductivity, strongly bond to the soft encapsulating matrix. This architecture drastically reduces ionic pathways and enables superior use of active materials, leading to a continuous discharge capacity at 5 mA of 2.1 mAh/cm2. Demonstrating the feasibility of our new stretchable batteries, we use them to power stretchable, imperceptible circuits bearing several SMD LEDs, a step up converter and various passive components. The whole soft assembly, including battery and electronics, endures severe mechanical deformation during during operation. This soft energy storage platform opens up a cornucopia of applications, from mobile health to consumer electronics and soft robotics.
5:30 PM - SM4.4.08
Flexible and Stretchable Batteries with Concept of Geometric Design
In-Suk Choi 1 Show Abstract
1 , Korea Institute of Science and Technology (KIST), Seoul Korea (the Republic of)
Developing reliable and robust flexible/stretchable batteries is core to realize the ultimate full flexible/stretchable devices. Taking a cue from geometric design, we introduced simple design concepts that significantly enhance flexibility and stretchability of batteries. Geometric design influenced by differential geometry, fractal geometry and cellular automata) provides us many examples of the formation of delicate and, detailed patterns leading to the effective distribution of stresses. Instead of complex structure design, the simple juxtaposition of unit design by putting the array of cut and holes can lead to simple, cheap and easily processed flexible and stretchable batteries. We believe that geometrical modulation by controlled size, shape, and symmetry adds another dimension unleashing the limitation of conventional design space of flexible and stretchable batteries.
5:45 PM - SM4.4.09
Highly Stretchable and Self-Powered Conformal Electronic Skin
Ying-Chih Lai 1 2 , Jianan Deng 2 , Simiao Niu 2 , Wenbo Peng 2 , Changsheng Wu 2 , Ruiyuan Liu 2 , Zhen Wen 2 , Zhong Lin Wang 2 3 Show Abstract
1 , National Chung Hsing University, Taipei Taiwan, 2 , Georgia Institute of Technology, Atlanta, Georgia, United States, 3 , Beijing Institute of Nanoenergy and Nanosystems, Beijing China
Power source is an important issue in soft and self-autonomous electronic skins. In this study, a mechanically tolerable, resilient and self-powered electronic skin has been demonstrated the capability of producing electricity from the touch energy. The self-powered electronic skin was fabricated by the composed of intrinsically stretchable materials, endowing it excellent toleratability to various kinds of extreme deformations, including ominidirectional stretch, twist, and fold. The outstanding mechanical properities render the soft electronic skin to be able to fully wrap on various kinds of objects with irregular shapes. By extracting energy from the motion of touch, the newly-designed electronic skin can sense touch without the need of extrernal powered source. Utilizing the outstanding mechanical tolerance and self-powered features, a highly conformable and fully-autonomous user-interactive e-skin system with visually human-readable signals was demonstrated. The presented system is highly conformal and promising to long-term uses with self-supporting energy. It is believed the newly-designed electronic skin can path a way for self-sufficient electronic-skin applications.
SM4.5: Poster Session I
Wednesday PM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - SM4.5.01
Skin-Inspired Haptic Memory Arrays with Electrically Reconfigurable Architecture
Geng Chen 1 , Bowen Zhu 1 , Xiaodong Chen 1 Show Abstract
1 , Nanyang Technological University, Singapore Singapore
Sensory memory is the process by which the human body retains the sensations of interaction with human body after the external stimuli ceased, thus helping humans describe the physical quantities in their environment and manipulate objects in daily activities. Skin, the largest organ in the human body, comprises a variety of sensory receptors and provides significant sensation information such as force, pain, shape, and texture. Skin perceives external stimuli and conveys the sensory information to the brain through afferent neurons to form haptic memory, allowing humans to remember the impressions of the stimuli applied on the skin. Skin-inspired haptic-memory devices, which can retain pressure information after the removel of external pressure by virtue of the nonvolatile nature of the memory devices, are achieved. The pressure distribution could be detected and recorded by introducing memory devices arrays, and the spatial resolution can be further improved by increasing the densities of device pixels to emulate the sensation of highly sensitive body sites like fingertips. The rise of haptic memory devices delivers a guide for designing and integrating future sensing and memory devices to mimic other sensory memory functions of humans, such as iconic and echoic memory, thus opening new avenues for the advancement of next-generation high-performance sensing systems for applications in electronic skins and humanoid robots, as well as human–machine interfaces.
9:00 PM - SM4.5.02
Printed, Stretchable Zinc-Silver Batteries for Wearable Electronics
Rajan Kumar 1 , Jae Wook 1 , Lu Yin 1 , Jung Min 1 , Y. Shirley Meng 1 , Joseph Wang 1 Show Abstract
1 , University of California, San Diego, La Jolla, California, United States
While several stretchable batteries utilizing either deterministic or random composite architectures have been described, none have been fabricated using inexpensive printing technologies. Here we printed a highly stretchable Zn-Ag2O battery by incorporating polystyrene-block-polyisoprene-block-polystyrene (SIS) as a hyperelastic binder for custom-made printable inks. The remarkable mechanical properties of the SIS binder lead to an all-printed, stretchable Zn-Ag2O rechargeable battery with a ~2.5 mAh cm-2 reversible capacity density even after multiple iterations of 100% stretching. This battery offers the highest reversible capacity and discharge current density for intrinsically stretchable batteries reported to date. The electrochemical and mechanical properties are characterized under different strain conditions. The new stress-enduring printable inks pave ways for further developing printable, stretchable electronics for the wide range of wearable applications.
9:00 PM - SM4.5.03
Skin-Like, Transparent and Flexible Tactile Sensor Based on Graphene Films for Human-Machine Interfaces
Minxuan Xu 1 , Junjie Qi 1 , Yue Zhang 1 Show Abstract
1 , University of Science and Technology Beijing, Beijing China
Tactile sensing, which can reflect the displacement of touch, is considered to be an essential function for electronic skin to mimic the natural skin. Here we report a novel tactile sensor with good sensitivity, excellent durability and fast response based on highly flexible and transparent conductor layers. The tactile device is simple in terms structure consisted a pair of compliant conductive plates, which were adhered the graphene films(GFs) on the surface layer of the polyethylene terepthalate(PET) substrate, and a transparent elastic adhesive sandwiched between the electrodes. The as-assembled tactile sensors can reflect one-dimensional (1D) touch tactile . And the resistance of the device is linearly related to the tactile of touch. Notably, the rate of resistance change is up to 420% when the displacement changed 25mm. The tactile sensor features a highly sensitivity of 0.143 mm-1, a long lifetime of 14 000 cyclic loading tests, and fast response of 0.3 ms. Furthermore, the electrical signals of the tactile sensors are almost irrelevant to the interference signals such as vertical displacement, stress magnitude, stress acting area and bending strain. This rational design of innovative materials and devices present a great potential for electronic devices to completely replace the unique tough sensing properties of human skin.
9:00 PM - SM4.5.04
Wearable Strain Sensor Based on Carbonized Silk Fabric for Full-Range Human Motion Detection
Chunya Wang 1 , Yingying Zhang 1 Show Abstract
1 Department of Chemistry, Tsinghua University, Beijing China
Flexible and wearable strain sensors have explosively evolved for their great potentiality in human motion detection, personalized health monitoring and smart human-machine interaction. Particularly, resistive-type strain sensors, which are typically composed of electrically conductive sensing elements coupled with flexible polymer substrates, have been widely investigated in virtue of their relatively simple read-out systems and high flexibility. Herein, we reported a novel commercial silk plain-woven fabric based resistive-type wearable strain sensors which showed superior sensing performance and tremendous potential applications in monitoring both vigorous (e.g. jumping, marching, jogging, bending and rotation of joints) and subtle human activities (e.g. facial expression, pulse, respiration and phonation). Through a simple thermal treatment process, commercial silk woven fabric could be converted to be carbonized woven fabric which kept the woven structure and possessed high flexibility and electrical conductivity, rendering its possibility as strain sensing element. The carbonized woven fabric also maintained the hierarchical structure of which the weft yarns were composed of parallel fibers and the warp yarns were composed of twisted fibers, which endowed the carbonized fabric based strain sensor with combined superiority of large tolerable strain (>500% strain), high sensitivity (gauge factor of 9.6 for strain within 250%) and 37.5 for strain of 250–500%), fast response (<70 ms) and remarkable durability (10 000 cycles). To the best of our knowledge, it is the first time to utilize carbonized woven fabrics as sensing elements by taking advantage of the chemical structure as well as the unique woven and hierarchical structures of mass-produced fabrics. Besides, the concept could be readily extended to other woven fabrics made of cotton, modal or other materials, paving a new way for the low cost and scalable fabrication of wearable strain sensors.
 T. Q. Trung, N. E. Lee, Adv. Mater. 2016, DOI: 10.1002/adma.201504244.
 M. Amjadi, K. U. Kyung, I. Park, M. Sitti, Adv. Funct. Mater. 2016, 26, 1678–1698.
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9:00 PM - SM4.5.06
Ultrasensitive and Transparent Electronic Skin Based on Carbonized Silk Nanofibers
Qi Wang 1 , Yingying Zhang 1 Show Abstract
1 , Tsinghua University, Beijing China
Recent years have witnessed the explosive development of electronic skin (E-skin). An emerging development in E-skin focuses on highly sensitive, low-cost and wearable pressure sensors. To date, most of the reported highly sensitive flexible pressure sensors are fabricated using nanomaterials (such as carbon nanotubes, graphene, and metal nanowires and nanoparticles) as the active materials and microstructured polydimethylsiloxane (PDMS) films as the substrates, limiting their wide practical applications due to the unknown biotoxicity of nanomaterials and the complicated and costly fabrication process.
Natural biomaterials have offered lasting inspirations and are attractive building blocks for fabricating flexible and biosustainable electronics. Silk fibroin (SF) is a natural protein which has recently drawn great attention for applications in flexible electronics. To date, the application of SF in flexible electronics is largely limited in being used as the flexible substrates since natural SF is not electrically conductive. Actually, SF can transform into highly conductive N-doped sp2-hybridized graphitic structures through a simple carbonization process.
In this work, we demonstrated the fabrication of ultrasensitive and transparent pressure sensors based on ultrathin carbonized SF nanofiber membranes and unstructured PDMS films through a cost-effective and large-scale capable approach. Due to the unique N-doped carbon nanofiber interconnected structure, the obtained skin-like pressure sensor demonstrates an ultrahigh sensitivity of 34.47 kPa−1 for a broad pressure range, an ultra-low detection limit of 0.8 Pa, a rapid response time of <16.7 ms, and an excellent durability and stability over >10,000 cycles, exhibiting comprehensive superiority over previously reported pressure sensors. Based on its superior performance, the applications of our flexible pressure sensor in monitoring human physiological signals, sensing subtle touch, and detecting spatial distribution of pressure were demonstrated.
To the best of our knowledge, this is the first report on utilizing N-doped carbon nanofibers derived from natural biomaterials to fabricate highly sensitive and transparent skin-like flexible sensors. This strategy may be also used on other nanofibers derived from natural materials, paves a new way for the low cost and large scale fabrication of biocompatible skin-like flexible sensors with superior performance.
9:00 PM - SM4.5.07
Skin-Mountable Multichannel Surface Electromyography Sensor for Controlling Home Electronics
Namyun Kim 1 , Jongho Lee 1 Show Abstract
1 , Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Wearable electronics are spotlighted in both research and commercial fields due to various potential applications including continuous healthcare monitoring, drug delivery system, human-machine interface, and energy harvester. In recent researches, to develop comfortable and reliable sensors for wearable electronics, numerous flexible and stretchable electronics designs are suggested. Among these designs, ultrathin film electronics or conductive elastomer sensors are drawing huge attention for their mechanical properties and high sensitivity. Although the designs provide flexible, stretchable characteristics and stable contact between skin and sensors, most of the presented sensors are single-channel, covering a small area, or easily damaged after repeated use. In this paper, we report stretchable multichannel surface electromyography (EMG) sensor that enables high stretchability (>30%), multichannel EMG signal detection from multiple muscles with one sensor array, and reliable signal detection while repetitive use.
EMG signal detection is chosen to realize human-machine interface application which the user can actively control commercial electronic devices using the sensor. The sensor design consists of contact electrodes, electrical interconnects, and supporting frames. Interconnects and frames have different serpentine structure dimensions to control stiffness and compliance independently. With proposed design, the sensor can easily stretch and compress resulting stable electrical properties and physical contact between the electrode and skin while actual use. Surrounding frames have higher mechanical properties that can support the sensor array while handling and cleaning process even without any substrate. We verified the concept of the sensor by experiments including mechanical and electrical properties measurement, repetitive EMG signal detection, and showed an illustrative demonstration on controlling home electronics using the sensor array.
9:00 PM - SM4.5.08
A Core-Shell Structured Mechanically Robust and Electrically Conductive Solid-Phase Via for Stretchable Electronics
Eunho Oh 1 2 , Junghwan Byun 1 2 , Byeongmoon Lee 1 2 , Sangwoo Kim 1 2 , Yongtaek Hong 1 2 Show Abstract
1 Department of Electrical and Computer Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Inter-University Semiconductor Research Center, Seoul National University, Seoul Korea (the Republic of)
There has been great progress of stretchable electronics, from a simple stretchable electrode to a multi-functional healthcare system, in multidisciplinary areas of science and industrial technology. Due to its nearly boundless potential as commercial products for healthcare monitoring, soft robotics, or a novel user interface, most conventional electrical devices or components such as organic light emitting diodes, thin film transistors, sensors, and even photovoltaic solar cells have been tried as stretchable electronic devices.
To integrate stretchable devices and interconnects as multi-functional stretchable circuits, however, only two-dimensional arrangement of circuit elements has been insufficient for implementation of well-defined stretchable systems. In the case of conventional printed circuit boards (PCBs), a via, which is also known as “vertical interconnect access”, is widely used to implement stacked or double-sided circuit on a board. But in the case of stretchable electronics, studies for the electrically conductive and mechanically robust via technology was insufficient.
In this research, we report a mechanically robust core-shell structured via through the stretchable elastomer substrate without drilling and filling process. By strongly patterned magnetic field, a core-shell structure was spontaneously formed by the movement of magnetic particles toward center in silicone resin. Remnant silicone resin act as a rigid island that prevents the conductive core from the deformation, achieving greater mechanical stability as a vertical interconnect. The initial resistance of a core-shell via was changed only 1.4 times in 80% strain. Conductivity of optimized via was in the order of 1.5 S/m for our nickel particles, but is capable of improvement by considering other conductive materials. With this fabrication process, via-embedded free-standing stretchable substrate was directly obtained without any drilling and filling process for the vias. Also, this process was compatible with printing process, by directly printing a circuit on the as-prepared via-embedded stretchable substrate.
This work was supported by the Center for Advanced Soft-Electronics funded by the Ministry of Science, ICT and Future Planning as Global Frontier Project (CASE-2015M3A6A5065309), and the Brain Korea 21 Plus Project in 2017.
9:00 PM - SM4.5.09
Stretchable and Multimodal all Graphene Electronic Skin
Qijun Sun 1 , Donghae Ho 2 , Jeong Ho Cho 2 Show Abstract
1 , Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing China, 2 , SAINT, Seoul Korea (the Republic of)
Here, we developed a transparent and stretchable all-graphene multifunctional E-skin sensor matrix. Three different functional sensors were included in this matrix: humidity, thermal, and pressure sensors, and were judiciously integrated into a layer-by-layer geometry through a simple lamination process. CVD-grown graphene was used to form the electrodes and interconnects for these three sensors, whereas GO and rGO were used as the active sensing materials for the humidity and temperature sensors, respectively. The top polydimethylsiloxane(PDMS) substrate, which bore the GO humidity sensor array, was laminated in a crisscross fashion onto the top of the bottom PDMS substrate, which bore the rGO temperature sensor array. The arrays were prepared to have the same geometry. The top PDMS substrate sandwiched between two CVD-graphene electrodes acted as an active layer for the capacitive pressure and strain sensors. Together, the sensors monitored a variety of daily life sensations (e.g., a hot wind blowing, breathing, and finger touching) with excellent sensitivity. Each sensor in the matrix exhibited simplex sensing performance: it was only sensitive to its specific stimulation and gave no response to other stimulations. The three sensors in the matrix detected external stimuli simultaneously and relayed independent electrical signals. 2D color mappings of the simultaneous multifunctional sensing were collected. The device architecture developed here for use as a multifunctional E-skin sensor matrix not only avoided the preparation of several materials separately; it enabled sensor integration using a simple lamination method.
9:00 PM - SM4.5.10
Thin Carbon Nanotubes/Nickel Sulfide Composite as Binder-Free and Flexible High Performance Lithium-Ion Batteries Anode
Hao Liu 1 , Peng Fan 1 , Libing Liao 1 Show Abstract
1 , China University of Geoscience-Beijing, Beijing China
Thin, flexible lithium-ion batteries, which are promising power sources for flexible and wearable electronic devices, have attracted great attention in recent years. Making flexible anode with good mechanical and electrochemical properties is an essential and important to realize flexible lithium-ion batteries. In present work, binder-free hybrid, i.e., carbon nanotubes (CNTs)/nickel sulfide (NiSx) composite, has been fabricated using pulsed electrodeposition. Here, in order to meet both requirements for good flexibility and high capacity, flexible carbon nanotubes paper was employed as current collector due to its good electrical and mechanical characteristics; nickel sulfide was selected as battery material due to its high capacity and low cost. The thin hybrid electrode (less than 20 micrometer) showed excellent flexibility and good electrochemical performances. For example, the flexible hybrid electrode exhibited high specific capacities of ~800 mA h/g at charging rate of 0.1 C, while the capacities were ~460 mA h/g at higher rate of 1.0 C. In addition, the capacities cycled at charging rate of 0.5 C were maintained at ~550 mAh/g after 50 cycles, indicating its good cycling performance. Therefore, the CNTs/NiSx hybrid composite showed promising application as a binder-free, flexible anode material in flexible lithium-ion batteries.
9:00 PM - SM4.5.11
Wrinkled Nitrile Rubber Films for Stretchable Ultra-Sensitive Respiration Sensors
Yaodong Guan 1 , Luyao Song 1 , Yajun Sun 1 , Yan Yu 1 , Lei Ye 1 , Jianfeng Zang 1 Show Abstract
1 School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan China
Health informatics that deals with the acquisition, transmission, processing, storage, retrieval, and use of health information, has emerged as an active area of interdisciplinary research [1,2]. Breath sensors that can distinguish abnormalities in breath patterns can ascertain the basic human body conditions during sleep, exercise, sports and surgery play a significant role in healthcare system and have attracted more and more attentions [3-8]. Whitesides group reported a breath sensor capable of measuring the rate of respiration of a person, by detecting the difference in moisture adsorbed on paper from inhaled and exhaled air . Yoon et al. reported another breath sensor relying on a temporarily condensed water layer that is instantly formed on the surface of an oxidized substrate from exhaled breath and that quickly disappears owing to evaporation . These new findings indicated that insulate films can be used as highly functional sensing materials. However, the sensors based on paper or oxidized substrate are not stretchable, and the capability to distinguish different intensities of respiration is limited. So, although diverse approaches have been attempted, implementing wearable, stretchable, precise and stable breathing sensors is still demanded for practical applications.
Here we present a simple approach employing the wrinkled nitrile rubber films to detect the human respiration, both breath rate and intensity. The three-dimensional wrinkled structure of nitrile rubber films could significantly increase the capability to distinguish different intensities of respiration, with an average intensity ratio of 16 times for strong breath over weak breath signal. These sensors also show fast response (within 1 second), high sensitivity, and can be stretched by 100% with stable breath sensing property. Because of the high capability to distinguish respiration intensity, our respiration sensors are favorable to the urgent healthcare monitoring applications such as disease intervention, systematic data fusion framework, etc., in the near future.
1. A. Chortos, et al., Nat. Mater. 15, 937 (2016).
2. Y. Khan, et al., Adv. Mater. 28, 4373 (2016).
3. F. Güder, et al., Angew. Chem. Int. Ed. 55, 5727 (2016).
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6. G. Konvalina, et al., Acc. Chem. Res. 47, 66 (2014).
7. H. Haick, et al., Chem. Soc. Rev. 43, 1423 (2014).
8. G. Peng, et al., Nat. Nanotechnol. 4, 669 (2009).
9:00 PM - SM4.5.12
Capillary Force Induced Cold Welding in Silver-Nanowire-Based Flexible Transparent Electrodes
Yuan Liu 1 , Chuanfei Guo 2 , Zhifeng Ren 1 Show Abstract
1 Department of Physics and Texas Center for Superconductivity (TcSUH), University of Houston, Houston, Texas, United States, 2 Department of Materials Science & Engineering, South University of Science & Technology of China, Shenzhen, Guangdong, China
Silver nanowire (AgNW) films have been studied as the most promising flexible transparent electrodes (FTEs) for flexible optoelectronics. The wire-wire junction resistance in the AgNW film is a critical parameter to the electrical performance, and several techniques of nanowelding or soldering have been reported to reduce the wire-wire junction resistance. However, these methods require either specific facilities or additional materials as the “solder”, and often have adverse effects on the AgNW film or substrate. In this study, we show that at nanoscale, capillary force is a powerful driving force that can effectively induce the self-limited cold-welding of wire-wire junctions for AgNWs. The capillary-force-induced welding can be simply achieved by applying moisture on the AgNW film, without any technical support like the addition of materials or the use of specific facilities.
The moisture-treated AgNW films exhibit a significant decrease in sheet resistance, but negligible changes in transparency. We have also demonstrated that this method is effective to heal damaged AgNW films of wearable electronics, and can be conveniently performed not only indoors but also outdoors where technical support is often unavailable. The capillary force based method may also be useful in the welding of other metal NWs, the fabrication of nanostructures and smart assemblies for versatile flexible optoelectronic applications.
9:00 PM - SM4.5.13
Viscoelastic Effects on Piezoelectric Performance of Soft Piezoelectric Nanocomposites
Jing Li 1 2 3 , Ugur Erturun 4 , Zeyu Zhu 1 2 5 , James West 1 4 , Sung Kang 1 2 Show Abstract
1 Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 Hopkins Extreme Materials Institute, Johns Hopkins University, Baltimore, Maryland, United States, 3 Hubei Key Laboratory of Advanced Technology for Automotive Components, Wuhan University of Technology, Wuhan China, 4 Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 5 Institute of Robotics, Shanghai Jiao Tong University, Shanghai China
There is a significant growth on the use of soft energy harvesters for low power applications such as healthcare devices and self-powered electronics. Polymer-based piezoelectric composite made of a polymeric matrix and piezoelectric particles with conductive additives is an attractive material that enables use of piezoelectricity in a broad range of applications. As the matrix that consists the major portion of piezocomposites is made of viscoelastic materials, it is expected that both elastic and viscous characteristic of the matrix will contribute to the piezoelectric response of the piezocomposite. However, there is limited understanding of the viscoelasticity of the matrix on the piezoelectric performance of piezocomposites. We synthesized piezocomposites based on polydimethylsiloxane matrix, BaTiO3 nanoparticles and multi-walled carbon nanotubes conductive additives. The viscoelastic properties of the piezocomposites were controlled by changing the ratio between monomer and cross-linker of the polymer matrix. Then, we measured the piezoelectric properties of the composites by both quasi-static and dynamic methods. We found that the quasi-static piezoelectric coefficients (d33) of the softest specimen was ~120 pC/N, while the hardest one was ~62 pC/N. The results suggest that softer matrices enhance the energy harvesting performance because they can result in larger deformation for a given load. Moreover, from dynamic mechanical analysis, we found the piezoelectric responses from the piezocomposites are dependent on the loss modulus as well as the storage modulus. For instance, at 40 Hz and 50 Hz the storage moduli of the softest specimen are ~0.625 MPa and ~0.485 MPa, while the loss moduli are ~0.108 MPa and ~0.151 MPa, respectively. As the piezocomposites with less viscous loss can transfer mechanical energy more efficiently to piezoelectric particles, the dynamic piezoelectric coefficient (d33) measured at 40 Hz (~53 pC/N) was larger than that at 50Hz (~47 pC/N) even though it has a larger storage modulus. The results demonstrate that viscoelastic properties of the piezocomposite play important roles in the resulting piezoelectric outputs. Based on these findings, we can further enhance the energy harvesting performance of soft energy harvesters by harnessing the viscoelastic contribution of piezocomposites.
9:00 PM - SM4.5.14
Soft Electrical Conductor Based on PEDOT:PSS-Metal Nanowire Hybrid Nanocomposites/Acrylamide Organogels
Seung-Min Lim 1 , Yoo-Yong Lee 1 , Jung-Kwon Yang 1 , Seok Hyeon Gwon 1 , Gwang Mook Choi 1 , Jeong-Yun Sun 1 , Young-chang Joo 1 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of)
One of the promising strategy to solve mechanical and biocompatibility issues in current wearable electronics is using soft gel material based conductors, which called conductive gels. Conductive gels are polymeric materials that contain conductive polymers as a conducting components in highly cross-linkable matrix polymers. As the mechanical property of gel is similar to that biological tissues, conductive gels have a potential to applied to skin attachable and bio-implantable devices such as electronic skins, bio-sensors and electro-stimulated drug delivery devices.
However, in spite of their excellent mechanical compliance with bio system, conductive gels still suffer from poor electrical performance for the practical use because the electrical conductivity of conducting polymer is quite lower than that of metallic materials. Therefore, it is essential to focus on the enhancement of the electrical percolation of conducting components in gel matrix by material design.
In this study, we introduce the Ag nanowire for the conducing component in gel matrix to improve the electrical percolation network of conducing polymers. Hybrid nanocomposites of poly(3,4-ethylene-dioxythiophene) poly(4-styrenesulphonate) (PEDOT:PSS)/Ag Nanowire were implemented by freeze drying the mixture of PEDOT:PSS solution and water based AgNW solution. From the microscopic analysis, uniformly dispersed structure of AgNW mesh in PEDOT:PSS matrix was observed. When they embedded in acrylamide organogel which includes ethylene glycol solvent, the electrical conductivity of hybrid-gel can be rapidly enhanced by several orders rather than that of only using PEDOT:PSS as Ag nanowire forms effective percolation network in the PEDOT:PSS polymeric paths. Moreover, during the cyclic tensile deformation with 100 % strain, the conductivity of hybrid-organogel was well maintained and even improved, which can be caused by the ordering of Ag nanowire during the repeated deformation. The fabricated gel conductors which have great mechanical and electrical performance can be applied to realization of future wearable and bio-medical devices.
9:00 PM - SM4.5.15
Highly Stretchable Polymer Semiconductor Films through Nanoconfinement Effect
Sihong Wang 1 , Jie Xu 1 , Zhenan Bao 1 Show Abstract
1 Department of Chemical Engineering, Stanford University, Stanford, California, United States
Soft or conformable wearable electronics depend on stretchable semiconductors but existing ones typically sacrifice charge-transport mobility to achieve stretchability. Here, we present a concept based on nanoconfinement effect of polymers to significantly improve the stretchability of polymer semiconductors, without affecting its charge transport mobility. Our fabricated semiconducting film can be stretched up to 100% strain without affecting its mobility, through which a record-high mobility of 1.32 cm2/Vs has been achieved at 100% strain, the value raveling that of amorphous silicon. Consequently, our fabricated fully stretchable transistor device also has very high stretchability in both directions to the charge transport channel, again measured at a record high mobility value of 0.55 cm2/Vs at 100% strain. We proceed to demonstrate this transistor device as a finger-wearable driver circuit for a LED. Furthermore, this versatile methodology was extended to four other semiconducting conjugated polymers with significant improvement in stretchabilility, which brings the mobilities of three resulting films over 1 cm2/Vs at 100% strain. Because of high versatility on different semiconducting polymers, our nanoconfinement concept could be utilized to impart high stretchability onto any molecular-engineered high-performance conjugated polymers that are developed in the future. 
 J. Xu+, S. Wang+, Z. Bao, et al. Highly Stretchable Polymer Semiconductor Films through the Nanoconfinement Effect. Science. 355, 59-64, 2017.
9:00 PM - SM4.5.16
Mechanical Metamaterial Based Highly Sensitive Stretchable Strain Sensors
Ying Jiang 1 , Xiaodong Chen 1 Show Abstract
1 , Nanyang Technological University, Singapore Singapore
Stretchable, skin-mounted and wearable strain sensors are vital for body-attachable or implantable sensory platform, soft robotic system, virtual reality equipment and so forth. Recently, several types of stretchable strain sensors have been proposed, with conductive nanomaterials as active layer, and stretchable polymers as supporting substrate. However, the achievable sensitivity remains limited, and the method to improve the sensitivity is restricted in exchanging materials for active layer/supporting substrate.
Herein, we report a radically new strategy: mechanical metamaterial-based configuration to enormously enhance the sensitivity of stretchable strain sensors. Our strategy can be applied to any present thin-film-based stretchable strain sensors. By employing carbon nanotube coffee ring effect, we demonstrate that the sensitivity reflected by the gauge factor reaches ~800 under 30% strain with good linearity, corresponding to a 2,500 % improvement over non-metamaterial ones ( ~30).
Mechanical metamaterials achieve counterintuitive mechanical properties, attributable to their artificial structures rather than composition. The mechanical metamaterial-based configuration we employed reduced Poisson’s ratio of the stretchable strain sensor, which changes 1D strain to 2D strain. Therefore, 2D strain leads to elongation of microcracks in active layer, proved by SEM, and causing a 2,500 % improvement of gauge factor. Numerical simulation based on finite element analysis shows that introduction of mechanical metamaterial-based configuration causes microcracks elongation, which agrees well with SEM results. Another simulation calculated electrical resistance changing tendency under strain, which are calculated by pixels in frames of SEM images. The simulated result suggests that resistance change under strain increases because of microcracks elongation, thus enhances the gauge factor. Also, cycling test proves good durability. The size of mechanical metamaterial-based configuration can be scaled up/down depending on applied position of stretchable strain sensor, or be arranged into array for larger coverage of area. Physiological signals and microfluidic flow rate are recorded precisely using this highly sensitive stretchable strain sensor, manifesting its immense potential for emerging human-interactive and other possible applications.
9:00 PM - SM4.5.17
Stretchable Silver-Polymer Composite Based Interdigitated Sensor for Capacitive Strain Sensing
Jignesh Vanjaria 1 , Todd Houghton 1 , Hongbin Yu 1 Show Abstract
1 , Arizona State University, Tempe, Arizona, United States
Detection of human body motion presents both unique challenges and opportunities for next-generation human-machine interfaces. It is anticipated that future motion sensing technologies will likely be soft, stretchy, and flexible. Capacitance-based motion sensors provide numerous advantages when paired with elastic materials. They are physically robust, can be made into various shapes, and have the potential to be manufactured at low cost. Here, we present a stretchable capacitance sensor which utilized a highly conductive silver-polymer composite developed by our lab group.
The sensor used an interdigitated comb pattern for capacitance detection, where each tooth of the comb was filled with silver-polymer composite. A commercially available silicon elastomer called Ecoflex® served as both the dielectric material and substrate. The silver-polymer composite was prepared by dispersing silver flakes into a mixture of polyvinyl alcohol, poly(3,4-ethyl-ene-dioxythiophene) (PEDOT): Poly(styrene sulfonic acid) (PSS), and phosphoric acid. Strains up to 55% were measured using the sensor, and an appreciable change in capacitance relative to the strain was observed.
A detailed outline of the sensor construction process will be presented. Electrical and mechanical performance will also be discussed.
9:00 PM - SM4.5.18
A Novel Fiber-Based Stretchy Sensor
Qiao Li 1 , Xin Ding 1 , Lina Zhang 1 , Jiamei Zeng 1 , Xiaobao Jiang 1 Show Abstract
1 , Donghua University, Shanghai China
Next-to-skin sensors play significant roles in medical electronic devices, and are indispensible in wearable electronics that works in repeatedly large deformation in tensile, bending, and shear modes and in three dimensions. This paper conducts a systematic investigation into a fiber-based stretchy sensor for three-dimensional surfaces, whose satisfactory electro-mechanical behaviors potentially initiate vast applications such as continuous, long-term health monitoring system, human-machine interface, as well as artificially electronic skin.
The fiber sensor was created by coating conductive materials into an elastic fiber/yarn. The elastic fiber/yarn was chosen from a series of elastic fibers, whose mechanical behavior was compared and analyzed. Fabrication of the fiber sensor was divided into two steps: firstly, the conductive material was coated into pre-stretched elastic fiber; then, the elastic fiber was heated after relaxation. The electro-mechanical performance proves high sensitivity and low hysteresis, opening up vast applications in healthcare products.
9:00 PM - SM4.5.19
Flexible Vertical GaAs Solar Cells by Using Interlayer Adhesiveless Transfer-Printing
Juho Kim 1 , Jongho Lee 1 Show Abstract
1 , Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
The interests and the commercial potential on wearable and health care devices lead to increased research into flexible electronics and related fields. These electronics often require sustainable and flexible power sources to be used in wireless form and to endure the extreme bending accompanied during their general use. One promising approach is utilizing flexible III-V compound solar cells which have high energy conversion efficiency. To enable flexible III-V compound solar cells, property of thin film that thinner devices undergo less strain when bent are exploited with the transfer-printing technology. In the transfer printing process, thin inorganic solar cells are picked up from an original substrate using elastomeric stamps and placed onto a flexible receiver substrate with aids of interlayer adhesives. But the interlayer adhesives increase thermal or electrical resistance between the devices and substrate, which forces to use lateral form having thick contact layers for bottom electrodes.
In this study, the interlayer adhesiveless transfer-printing technology to realize flexible vertical GaAs solar cell is described. In the transfer-printing process, covering the flexible vertical solar cells with a layer of removable photoresist is involved instead of the interlayer adhesive. The photoresist overlayer improves a yield in low-pressure cold-welding process by spreading and forming one overlayer piece. Therefore, the transfer-printing technology enables direct printing and electrical interconnection on metal surfaces of flexible film substrates without the interlayer adhesive and the thick contact layers for the bottom electrodes in lateral form. And the vertical structure recycles reflected photons by means of bottom electrodes, thus improving energy conversion efficiency.
Experimental results on electrical properties with four different types of GaAs solar cells indicate that the flexible vertical GaAs solar cells, at only a quarter of the thickness of similarly designed lateral solar cells, generate a level of electric power similar to that of thicker lateral cells. The experimental results of mechanical properties along with the theoretical analysis show that there is no performance degradation even after bending down to a radius of curvature of 1.4 mm and the ultra-thin vertical-type solar microcells are durable under repetitive extreme bending. Thus, the fabricated flexible vertical GaAs solar cells are suitable and useful for use in wearable electronics.
9:00 PM - SM4.5.20
Adhesiveless Transfer Printing Assisted by Controllable Bending Radius of a Flat Elastomeric Stamp
Sungbum Cho 1 , Jongho Lee 1 2 Show Abstract
1 Mechanical Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of), 2 Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Fabricating complex micro electronic devices such as wearable or implantable devices need to integrate the devices onto unconventional substrates. However, if the adhesive is used when placing the electronic devices onto the substrate at the interlayer of the devices and the substrates, processing temperature should be controlled and electrical or thermal resistance at the interface may increase. This presentation suggests a simple but effective transfer printing method that does not require an interlayer adhesive. Controlling the bending radius of a flat elastomeric stamp determines the result of picking up or printing of micro semiconductor plates. The capability of switching adhesion enables transferring the micro semiconductor plates onto rigid, curvilinear, or flexible substrates without the interlayer adhesive. Theoretical and experimental studies support the mechanism of the suggested method.
Martin Kaltenbrunner, Johannes Kepler University
Michael Dickey, North Carolina State University
Christoph Keplinger, University of Colorado Boulder
Rebecca Kramer, Purdue University
Heraeus Holding GmbH
SM4.6: Soft Robotics—Manufacturing, Design, Materials and Applications
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 121 B
9:00 AM - SM4.6.01
Autonomous Locomotion of Polymer Films Coupled to Stimuli Gradients
Benjamin Treml 1 2 , Ruel McKenzie 2 , David Wang 1 2 , Andrew Gillman 1 2 , Michael Kuhn 1 2 , Phil Buskohl 2 , Loon-Seng Tan 2 , Richard Vaia 2 Show Abstract
1 , UES, Dayton, Ohio, United States, 2 , Air Force Research Laboratory, Dayton, Ohio, United States
Adaptive soft materials change size or shape in response to external stimuli, enabling critical components of sensors, actuators, and soft robotics. Autonomous locomotion requires adaptivity, as well as energy harvesting and internal transduction of potential to kinetic energy to occur in the same material. Typically considered a biotic process, continuous locomotion has recently been reported for a few composites films containing a hygroscopic polymer in the presence of a non-uniform humidity environment. In these monolithic films the material is the machine, which performs the process of gathering, storing, and releasing energy continuously during locomotion. We use commercial nylon films, which combine significant hygroscopic expansion (up to 8% strain) with robust mechanical properties (E~0.1-1 GPa), as an experimental platform to demonstrate that control of the local humidity environment can be used to control the material and produce stable deformation, oscillation and locomotion. During stable deformation, films are able to lift 4X their mass. Based on estimates of the chemical potential energy resource available as well as the potential energy stored during locomotion, we determine the efficiency of locomotion to be around 0.1%, comparable to the metabolic efficiency of insects of similar mass (~40 mg). This improved understanding of the material-stimulus coupling enables a design-development-implementation framework for advanced stimuli responsive soft materials.
9:15 AM - SM4.6.02
A 3D Fabrication Method for Soft Robots and Organ Phantoms
Tian Qiu 1 , Stefano Palagi 1 , Andrew Mark 1 , Fabian Adams 1 2 , Peer Fischer 1 Show Abstract
1 , Max Planck Institute for Intelligent Systems, Stuttgart Germany, 2 Department of Urology, University Medical Center Freiburg, Freiburg Germany
Soft materials are promising in robotics  and applications in biomedical engineering. While a number of fabrication schemes can be used to pattern soft polymers in 2D, it is still challenging to obtain functional 3D structures using soft materials. Recent advances in 3D printing present opportunities to directly write polymers in 3D, however, this limits the choice of printing materials, typically limits the resolution, and often means that a supporting material needs to be removed in an additional step.
Here, we report a fabrication method that integrates 3D printing and micro-molding. A negative mold is 3D printed with two removable materials: one serves as the supporting material during printing and can be dissolved after printing; the other one is the printing material that forms a negative mold and that can also be dissolved after molding. Liquid polymer materials are injected in the 3D printed negative mold under vacuum and solidified. Finally, the negative mold is dissolved by rinsing with ethanol and water. This procedure enables the fabrication of arbitrary 3D shapes with hundred-micrometer resolution, and allows for a wide choice of soft materials, including biomimetic hydrogels. The fabrication method intrinsically allows the mixing of micro/nanomaterials and thus can be used to obtain unique physical properties.
We demonstrated the versatility of the fabrication method with two applications: A soft robot and a soft organ model. The robot combines an auxetic metamaterial with a normal material  to allow a simplified tube-crawling robot. Using the fabrication technique we present, we are able to shrink the size of the soft robot down to the millimeter scale. In addition, we also show how the fabrication method can be used to make ~10 cm organ phantoms that reproduce anatomical features with ~600 µm accuracy. Realistic organ phantoms may eventually lead to an effective way to evaluate surgical procedures and allow the in vitro testing of biomedical devices.
 S. Palagi, A.G. Mark, S.Y. Reigh, et al. Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots. Nature Materials 15, 647-53 (2016).
 A.G. Mark, S. Palagi, T. Qiu, et al. Auxetic metamaterial simplifies soft robot design. IEEE International Conference on Robotics and Automation (ICRA), 4951-6 (2016).
 F. Adams, T. Qiu, A.G. Mark, et al. Soft 3D-printed phantom of the human kidney with collecting system. Under revision.
9:30 AM - *SM4.6.03
Elastomeric Robots via Additive Manufacturing: Actuation, Sensing, and Visual Interfaces
Robert Shepherd 1 Show Abstract
1 , Cornell University, Ithaca, New York, United States
Synthetic replicas of natural muscle do not exist, though there are some interesting routes towards that goal. In lieu of this technology, we must use artificial muscle that behaves differently than the ratcheting mechanism of biological muscle. We have chosen to use fluidically powered, poroelastic foam actuators that we mold into the form of bioinspired robots. To enable haptic and kinesthetic sense in these robots we ‘innervate’ them with stretchable strain sensors based on optical waveguides. Using this basic strategy, we have formed tentacle, squid mantle, human hand, and even human heart like robots. Finally, we have developed dynamic display interfaces that match the mechanical properties of the elastomeric robots.I will present methods for fabricating these devices, both molding and 3D printing, and their integration into robots.
10:00 AM - SM4.6.04
Stereolithography 3D Printing of Highly Extensible Silicones for Soft Robotics
Thomas Wallin 1 , James Pikul 1 , Robert Shepherd 1 , Jeremy Odent 1 Show Abstract
1 , Cornell University, Ithaca, New York, United States
Stereolithography (SLA) is an additive manufacturing technique that can rapidly fabricate intricate architectures with micron-sized features. However, until very recently, resins that met the processing requirements of SLA only produced brittle polymer networks limiting applications to rigid objects. We report the SLA of polydimethylsiloxane (PDMS) by using a novel step-wise polymerization reaction and a custom 3D printer. By controlling the crosslink density and degree of polymerization, we can produce soft, highly extensible silicone structures. This new-found capability to manufacture truly elastomeric devices of arbitrary geometry offers the potential to improve the performance and capabilities of soft robots. To illustrate this, we fabricate: (i.) synthetic antagonist muscles, (ii.) a soft robotic fish, and (iii.) a tentacle-like gripper. These monolithic, compliant devices display remarkable fatigue resistance at large actuation amplitudes, rapid actuation speeds, and complex actuation states. We further modified the pre-polymers to include novel functionalities that introduce self-healing behavior, improve conductivity, and increase biocompatibility in these printed devices.
10:15 AM - SM4.6.05
3D Printed Soft Materials for Sensors and Actuators across Multiple Length Scales
Michal Soreni-Harari 1 , Dinesh Patel 2 , Ryan St. Pierre 1 , Caroline McCue 1 , Hongyu Guo 3 , Zhihong Nie 3 , Shlomo Magdassi 2 , Sarah Bergbreiter 1 Show Abstract
1 Department of Mechanical Engineering, Institute for Systems Research, University of Maryland, College Park, Maryland, United States, 2 Casali Center for Applied Chemistry, Institute of Chemistry, The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem Israel, 3 Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States
Miniaturization of small-scale robots and wearable sensors necessitates the development of 3D fabrication methods and adoption of soft materials for compliance and dynamic range. For example, compliant legs can enhance locomotion in small, legged robots. Soft materials with large strains can improve range in soft, wearable sensors.
An additional challenge in the development of functional components is the introduction of magnetic properties and electrical conductivity to the soft material. Integrating materials with multiple functionalities in the 3D printed parts can further enhance the performance of the resulting components.
We are developing a tool box, comprised of several polymers including elastomeric and soft conductive materials, compatible with advanced fabrication processes, including direct ink and laser writing to cover multiple length scales.
Here, we describe the high resolution 3D printing of a PDMS-like material using two photon polymerization for the study of small-scale actuators and sensors. We also present progress toward sensors and actuators using these soft materials at multiple length scales (microns to centimeters).
10:30 AM - SM4.6.06
A New Class of Soft Microrobotic Components Assembled from Magnetically Interacting Metallo-Dielectric Microcubes
Koohee Han 1 2 , C. Shields 1 2 3 , Bhuvnesh Bharti 1 4 , Gabriel Lopez 2 5 , Paulo Arratia 6 , Orlin Velev 1 2 Show Abstract
1 Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 , Research Triangle Materials Research Science and Engineering Center, Durham, North Carolina, United States, 3 Department of Biomedical Engineering, Duke University, Durham, North Carolina, United States, 4 Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, Louisiana, United States, 5 Department of Chemical and Biological Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 6 Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
The primary challenges in making soft robots on the micron scale include finding means for their construction (either via top-down or bottom-up approaches), remote supply of energy, and directional navigation. We show how polymeric, cube-shaped microparticles with a cobalt (Co) patch along one face can be used in the assembly of a new class of soft robotic components that can be dynamically reconfigured and spatially maneuvered using external magnetic fields. These Co patches attain a magnetic polarization by the application of an external magnetic field, leading to the assembly of chain-like clusters. The key feature of such multi-cube chains is that, once assembled, each Co patch stores magnetic energy, introducing a directional interaction as well as preserving an assembled sequence even after the field is removed. Importantly the residual magnetic polarization of the Co patches guides the multi-cube clusters to spontaneously self-fold into configurations which can be analyzed on the basis of the classical theory of dipolar interactions. Upon reapplication of the external magnetic field, specific sequences of clusters revert to their original stretched configuration by co-aligning the Co patches in the direction of the field. Consequently, the dynamic and reversible reconfiguration of the assembled clusters is achieved on-demand by switching between the states of dipole-field-dominated interaction and residual dipole-dipole-dominated attraction where the folding pattern of the soft robotic assembly is encoded by the sequence of cubes within the clusters. The discovery of this reversible on-demand reconfiguration provides us with a broad range of microscale manipulation tools. We will present two representative classes of soft robots based on such active matter. The first is microbot prototypes – multi-cube clusters with specific sequences that can be reversibly actuated, reoriented and spatially maneuvered by multiple fields that are capable of capturing and transporting microscale objects (e.g., biological cells). The second type of active microcluster is self-propelling swimmers – single-hinged reconfigurable clusters that propel in non-Newtonian fluids by generating the local viscosity gradient through time-asymmetric reciprocal motions (e.g., rapid opening and slow closing). We will discuss the future potential of such field-driven microbot assemblies for soft matter manipulation on the microscale.
10:45 AM - SM4.6.07
Printable Robots—Self-Assembled Function during Inkjet Printing
Rebecca Kramer 1 Show Abstract
1 School of Mechanical Engineering, Purdue University, West Lafayatte, Indiana, United States
As a drop of liquid evaporates on a solid surface, the particles within form a deposit. Due to the myriad of physical and chemical processes involved during evaporation, the structure of this deposit can vary greatly, ranging from simple ring formations like those seen in coffee drops, to more complex morphologies such as fractal patterns. Of these possible outcomes, a strikingly uniform deposit may be formed by mixing together two co-solvents. In our recent work, we have ascribed this outcome to a hybrid self-assembly process that leverages both particle−fluid interactions to carry the particles to the drop surface and particle−interface interactions to assemble the particles into a uniform film. In this talk, I will demonstrate how we have used this self-assembly process to print soft (flexible, stretchable) sensors and electronics via inkjet printing. Furthermore, I will discuss how the printable self-assembly process is transferrable to other substrates and functional inks, and how it may be used to develop inkjet printable robots.
11:30 AM - *SM4.6.08
Micro-Patterned Materials to Enable In Vivo Robotic Capsule Endoscope Locomotion
Mark Rentschler 1 Show Abstract
1 , University of Colorado, Boulder, Colorado, United States
The state-of-the-art technology for deep gastrointestinal (GI) tract exploration is a capsule endoscope (CE). Capsule endoscopes are pill-sized devices that provide visual feedback of the GI tract as they move passively through the patient. These passive devices could benefit from a mobility system enabling maneuverability and controllability. Potential benefits of a robotic capsule endoscope (RCE) include faster travel speeds, ability to maintain an anchored position, reaction force generation for biopsy, and decreased capsule retention. The objective of this research is to understand how micro-patterned materials can be used to enable in vivo robot locomotion for surgical applications. Both tractive and adhesive properties are studied as a micro-patterned material that exhibits high traction with low adhesion is considered ideal for this application. The design of a three degree-of-freedom automated traction measurement (ATM) platform for quantitative evaluation of traction is presented along with work of adhesion and work of separation methods for a non-conventional geometry. Work of adhesion and work of separation are characteristic properties of a contact interface which describe the amount of energy per unit area required to adhere or separate two contacting substrates, respectively. In this work, the experimental and data analysis procedures which allow the contact interface between a soft synthetic tissue and a smooth or micro-patterned polydimethylsiloxane (PDMS) substrate to be characterized in terms of these characteristic parameters, is presented. Due to physical geometry limitations (i.e., wrapping micro-pillars around a spherical indenter, extremely soft substrate compared to micro-pillars), the experimental contact geometry chosen for this study differs from conventional test geometries. Therefore, finite element modeling is used to develop correction factors specific to the experimental contact geometry used in this work. An empirical model for traction force as a function of slip ratio, robot speed and weight for micro-patterned PDMS on synthetic tissue is developed using data collected from the ATM platform. The model is then used to predict traction force at different slip ratios, speeds and weights, and is verified experimentally. A work of adhesion was directly extracted from experimental data while the work of separation was estimated based on experimental results. These values are compared to other theoretical calculations for validation. The results of this work indicate that the micro-patterned PDMS substrate significantly decreases both the work of adhesion and work of separation as compared to a smooth PDMS substrate when in contact with a soft synthetic tissue substrate. Going forward, understanding how model parameters influence tread performance will improve future RCE mobility systems as these models of traction, adhesion and separation can be used to optimize micro-patterned material designs for in vivo mobility.
12:00 PM - SM4.6.09
Compliant, Buckled-Foam Pneumatic Actuators and Application in a Patient-Specific Cardiac Assist Device
Benjamin Mac Murray 1 , Robert Shepherd 2 , Thomas Wallin 1 Show Abstract
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York, United States
Open-celled elastomer foams have enabled many new fluidically inflated, soft machine designs. Because these foams are cast as a liquid into 3D shapes that inherently contain an open-celled inflation pathway, they make possible a variety of bioinspired geometries without complex molding or assembly. Currently a key limitation of these foam materials is their modest ultimate elongation which limits the extent of fluidic actuation and ultimately their utility as soft machines.
Here, we have addressed this limitation by exploring the first use of buckled foam actuators for pneumatically powered machines. In compressing these foams, we imparted residual strains that can aid in extending the overall displacement in tension prior to failure. We performed X-ray micro-computed tomography imaging to visualize these residual strains as buckling of the foam cell walls. When we integrated these compressed foams in inflatable actuators, the buckled foams exhibited augmented actuation over non-compressed foams by providing either more force or a larger displacement at a given pressure. We attributed the augmented actuation to both the foam’s asymmetric stress-strain behavior in compression and tension and a reduced strain hardening effect.
As a demonstration of the utility of these buckled foam actuators, we designed and fabricated a unique Direct Cardiac Compression (DCC) device. These biomedical devices are a type of implanted, mechanical circulatory support that apply pressure to the exterior of the heart to aid in blood flow. In our device, the high porosity of the foam actuators allowed rapid inflation and deflation cycling at physiological rates (90 beats per minute). By buckling the foam actuators, we achieved a large volume displacement upon inflation (ΔV ~ 70 mL per chamber) from an initially thin device thickness (d ~ 15 mm). Finally, because the major components of the device were liquid-processable elastomers and foams, we demonstrated that the device can be fabricated in a patient-specific shape using custom 3D printed molds designed from standard clinical imaging data. In ex-vivo tests, the device formed a tight fit surrounding a model porcine heart and pumped fluid at physiologically relevant frequencies. Additionally, we have demonstrated the use of real-time electrocardiography (ECG) measurements to control the inflation rate of the device.
12:15 PM - SM4.6.10
Multifunctional Soft-Robotic Skin for Medical Applications
Deepak Ganta 1 , Rolando Villanueva 1 , Miguel Hernandez 1 , Jose Jara 1 Show Abstract
1 , Texas A&M International University, Laredo, Texas, United States
Wearable skin-like materials have potential to transform how inexpensive electromechanical
systems were developed and the way medicine is practiced. The key challenge of soft materials
remain in their ability to both integrate and replicate the complex geometry of the human body parts. Another challenge being the ionic liquid sensors integrated inside the artificial skin responding like blood or even better. Pneumatic actuation currently under investigation by several groups has limited applications beyond grasping and moving objects, especially in the medical field which require minimally invasive, inexpensive, and in-home treatment methods. We need the soft robot to look and respond like humans.
To overcome these limitations, we have investigated inexpensive skin-like materials, developed artificial skin from 3D printed molds, encapsulated ionic liquid inside the skin and further be able to control movement using wireless methods. We have developed two methods in that direction. In the first method, we have chosen inexpensive and readily available materials such as carbon, glycerin, and Epson salt and the final mixture or product behaves and looks like expensive commercially available gallium and indium ionic fluid. We were able to design the artificial skin with multiple channels, 3D print them using skin-like materials such as silicone, and integrated the channels filled with ionic fluid inside the skin. By varying the ratio of the materials used we were able to control the electrical properties, in particular, the resistance of the skin from 1-3 kilo- ohm. The skin was also subjected high strain, stress, and ambient temperature changes, to determine mechanical and thermal properties.
In the second method to demonstrate wireless actuation, we developed Electroactive Polymer (EAP) skin actuators. In our EAP actuator design, we encapsulated carbon conductive grease and electrically conductive particles inside the DS10 (dragon skin 10) polymer. Upon fabrication of EAP actuators, electrical measurements such as conductivity were measured. The actuation was observed with increase in the surface area of EAP, under the influence of high voltages ~1 kV. Several challenges in this approach will be discussed. This soft robotic skin with multifunctionality will advance the soft robotic field and should revolutionize the way medicine is practiced.
12:30 PM - *SM4.6.11
Towards a Continuous Sensory Experience and Autonomic Nervous System for Soft Robots
Iain Anderson 1 3 2 , E.F. Markus Henke 1 , Andreas Tairych 1 , Katherine Wilson 1 Show Abstract
1 Biomimetics Laboratory, University of Auckland, Auckland New Zealand, 3 Engineering Science, University of Auckland, Auckland New Zealand, 2 , Stretchsense Ltd., Auckland New Zealand
We humans are a continuum of sensor and soft autonomous actuator. At any position on our skin we can sense touch contact. Control is local and autonomous: we never need to think about digesting a meal, our next heartbeat, or the peristaltic contractions of our bowel. Sensory neurons are fully integrated with skin and muscle cells and in communication with local neural ganglia that provide control and pace-making roles. These few examples provide design principles and goals that we as soft roboticists should seek to emulate. These include 1) continuous sensory feedback, 2) coupling strain feedback to electrical activity and 3) integrated local pace-making for controlling actuator groups. Multifunctional dielectric elastomer devices offer a way for emulating these capabilities.
For our first goal, the near continuous strain sensing of skin, we can exploit the typically high electrical resistance on the electrodes of DE sensors. A thin sheet of DE material with two dielectric elastomer sensory layers back to back can be treated as a two-dimensional (2D) array of parallel capacitor sets; a 2D transmission line. A frequency rich sensing signal sent into each layer can then be used to deduce localized pressure or stretch to in a 2D soft sensory skin.
Coupling active strain with electrical activity (goal #2) can be achieved using piezoresistive dielectric elastomer switches (DESs). These directly switch charge flow on and off with stretch. They can be used to influence the actuation of dielectric elastomer actuators (DEAs). Like the sensors, DEAs electrically resemble stretchable capacitors. Electric charge that is placed on the electrode surfaces can, under the influence of Maxwell pressure, produce in-plane expansion and through thickness contraction of the DEA. So grouping the two together DES and DEA in the same structure can be used for the construction of autonomous self-controlling mechanisms. One of these is a mechano-electrical oscillator. This is constructed from an odd number of inverters, each assembled from a DES and a DEA. The oscillator can be used for distributing electrical charge directly to DEA with a controllable period. This has been demonstrated as a driving mechanism for DEA enabled crawling and wing flapping robots.
This synergy distributed sensing, along with charge based actuation and stretch controlled charge gating opens the door for a new class of robotic devices that have little or no hard electronics.
SM4.7: Soft Robotics—Actuators, Sensors, Materials and Mechanics
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 121 B
2:30 PM - *SM4.7.01
Hydrogel Robots—High-Speed, High-Force and Opto-Sonically Camouflaged
Xuanhe Zhao 1 Show Abstract
1 Soft Active Materials Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Sea animals such as leptocephali develop tissues and organs composed of active transparent hydrogels to achieve agile motions and natural camouflage in water. Hydrogel-based actuators and robots that can imitate the capabilities of leptocephali will enable new applications in diverse fields. However, existing hydrogel actuators, mostly swelling-driven, are intrinsically low-speed and/or low-force; and optically and sonically transparent underwater robots have not been achieved yet. Here we show that hydraulic actuations of robust transparent hydrogel structures can give soft actuators and robots that are high-speed, high-force, and optically and sonically invisible in water. We invent a simple process capable of fabricating complicated hydraulic hydrogel actuators with robust bodies and interfaces. We demonstrate that the agile and transparent hydrogel robots can perform functions including swimming, kicking rubber-balls and even catching a live fish in water.
3:00 PM - SM4.7.02
4D Printing Spatiotemporal Material Gradients in Ionic Hydrogel Soft Actuators
Brittany Rauzan 1 , Joselle McCracken 1 , Jacob Kjellman 1 , Simon Rogers 2 , Ralph Nuzzo 1 Show Abstract
1 Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Patterning ionotropic material gradients within a structure is foundational for assembly of 4D (dynamic 3D) soft actuators. We report 3D printing to pattern complex, doubly responsive (spatial and temporal) ionic, soft actuators. Our approach uses an ink that can be tailored with viscosifying agent, multivalent salts, small molecules, and nanoparticles to create chemo-mechanical gradients. We spatially pattern intricate, local gradients within a structure that are selectively actuated with a programmed electromagnetic field.
3:15 PM - SM4.7.03
Stimuli-Induced Bi-Directional Hydrogel Unimorph Actuators
Shanliangzi Liu 1 , Elisa Boatti 2 , Katia Bertoldi 2 , Rebecca Kramer 1 Show Abstract
1 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States, 2 John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
The desire to create soft, compliant structures inspired by nature has increased interests in the development of soft robotics, where various kinds of materials have been explored as actuators. As a class of stimuli-responsive materials, hydrogel networks are capable of large volume changes with reversible swelling and deswelling in response to environmental stimuli such as temperature, pH, electric and magnetic fields, etc. Hydrogel composites made of heterogeneous materials are able to construct 3D shape changing structures by undergoing inhomogeneous deformations such as bending, twisting, and buckling. However, these systems require a complicated fabrication process and an external stimulus. In this talk, we report stimuli-induced bi-directional hydrogel unimorph actuators that can produce considerable bending curvature change while swelling in aqueous solutions. Composed of polyacrylamide (PAAm) hydrogel, which can swell to 16 times its original size, bonded to polydimethylsiloxane (PDMS) elastomer, which does not swell in water, the actuators tend to bend towards one direction after swelling and bend in an opposite direction when fully dried without any delamination observed after 25 cycles. We revise an existing bonding method by using both chemical and mechanical approaches and quantify the interfacial toughness between two materials by peel tests. We also demonstrate that stress developed by water intake into the hydrogel is not able to break the bonding between hydrogel and PDMS in 24hrs. Additionally, we observe the bending behaviours of hydrogel unimorphs in water and prove that the response rates and curvatures can be tuned by the relative thickness of the two layers and predicted by analytic and FEA models. Lastly, several 3D shape changing structures are explored.
3:30 PM - *SM4.7.04
Embracing Instabilities to Achieve Function in Soft Structures
Katia Bertoldi 1 Show Abstract
1 , Harvard University, Cambridge, Massachusetts, United States
The use of soft materials has led to the development of soft devices that have the potential to be more robust, adaptable, and safer for human interaction than traditional rigid systems. Moroever, altough the geometrical non-linearities and instabilities that typically arise in these systems complicate the design process, exactly these non-linearities make the systems inherently capable of rich behavior. Here, I will focus on a specific class of such soft systems: highly non-linear periodic and elastic structures comprising bistable elements. First, I will show that these structures, although made of purely elastic materials, can act as energy-absorbing materials. Second, I will demonstrate, that although made of highly dissipative soft materials, they can support stable propagation of nonlinear transition waves along their length. Altogether, the proposed techniques and case studies can inform simplified routes for the design of soft structures with new mode of functionality over a wide range of length scales.
4:30 PM - *SM4.7.05
Dielectric Elastomers Actuators for Soft High-Force Grippers
Herbert Shea 1 Show Abstract
1 , EPFL, Neuchatel Switzerland
Picking up a raw egg, a half-filled water balloon, or a playing card is trivial for a child, but presents a major challenge for conventional robotic grippers. Using soft actuators allows solving this difficult robotics task in an elegant manner, but requires fast, high force, distributed actuation. We present two types of 10 cm long compliant grippers capable of the manipulation tasks listed above, based on Dielectric Elastomer Actuators (DEA), a class of stretchable electromechanically active polymers that combines very high strains, high force density, and low power consumption.
Our first approach combines electroadhesion with DEA actuation. The DEA provides mN-level bending forces, providing the ability to conform to extremely fragile and deformable objects. The electroadhesion provides over 1N shear force per square cm, enabling the manipulation of objects weighing 60x more than the gripper. The use of low-viscoelasticity materials allows fast operation (100 ms to close the fingers). The compliant gripper conforms to the shape of nearly any object, requiring no a-priori knowledge of its shape, and allows simple on-off control input to achieve complex shapes.
Our second approach has many of the same advantages, and combines shape memory polymers (SMP) with DEAs. We used a conductive SMP composite as the electrode for our DEA gripper. SMPs have a phase transition near room temperature in which change their stiffness by up to three orders of magnitude, from 1 GPa below the glass transition temperature to approximately 1 MPa just above it. The SMP electrodes make the DEA rigid when at room temperature, thus offering a good holding force. Applying Joule heating softens the SMP electrodes, thus enabling DEA actuation. Cooling locks in the actuated position. We used this technique to individually address multiple actuator elements on a single gripper, enabling independent actuation of multiple segments.
5:00 PM - SM4.7.06
High Performance, Electrically Powered, Soft Actuators that Self-Heal
Christoph Keplinger 1 Show Abstract
1 , University of Colorado at Boulder, Boulder, Colorado, United States
Soft robots predominantly rely on pneumatic or fluidic actuators, which limit speed and efficiency. Electrically powered muscle-like actuators, such as dielectric elastomer actuators (DEAs) offer high performance actuation, but they come with their own challenges. Being driven by high electric fields, they are prone to failure by dielectric breakdown and electrical ageing. DEAs are also hard to scale up to deliver high forces, as large areas of dielectric are required (e.g. in stack actuators), which are much more likely to experience premature electrical failure, following the Weibull distribution for dielectric breakdown.
Here a series of advances is presented, that promise to overcome important limitations of electrically powered soft actuators, including I) a highly stretchable self-healing elastomer, that autonomously heals from severe mechanical damage, II) a transparent, self-healing, ionically conductive elastomer that can be used to electrically activate soft electrostatic actuators, III) a new class of versatile, reliable, self-healing muscle-like soft actuators, that use an electro-hydraulic mechanism to combine the strength of fluidic and electrostatic actuators, and IV) a new type of soft electrostatic actuator that linearly contracts upon activation with voltage.
5:15 PM - SM4.7.07
Rapidly Actuated Shape Changing Surfaces Using Circumferentially Constrained Elastomeric Membranes
James Pikul 2 1 , Itai Cohen 1 , Robert Shepherd 2 Show Abstract
2 Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York, United States, 1 Physics, Cornell University, Ithaca, New York, United States
Cuttlefish, and other cephalopods, can rapidly actuate local regions of their skin (papillae) to produce textures that camouflage into their environment. Engineers and scientists have used a variety of soft materials (hydrogels, electroactive polymers, shape memory polymers, and elastomers for examples) to replicate the texture changing capabilities of cephalopods, but current technologies suffer from a lack of geometric control (typically Gaussian, but not mean curvature control), low actuation rate, or applicability at a specific length scale.
Here we present pneumatically actuated elastomeric membranes with tailored moduli that are programmed to achieve a wide variety of shapes. We demonstrate this by developing 0.1 m2 areas of artificial camouflage with deployable textures that mimic the shape of cephalopod papillae and other organic materials. The membranes can be fully inflated in less than 1 second at 2 - 5 psi. We overcome the primary challenge of achieving targeted shape control in soft materials by controlling the radial and circumferential strain. The circumferential strain is constrained by integrating radially symmetric hoops of high modulus non-woven fabric into the elastomeric membrane (typically Ecoflex 00-10 silicone), which restricts the membrane to vertical displacement, instead of vertical and radial displacement. This simplifies the membrane deformation mechanics and directly relates the slope of the displaced membrane to the local radial strain. The volume fraction of the high modulus fabric controls the radial strain. Using this technique, we can achieve prescribed shapes with positive, zero, and negative Gaussian curvature, as well as branched and hierarchical shapes. Non-woven fabrics provide a high in plane modulus, out of plane flexibility, homogeneity, and porosity, which improves adhesion between the fabric and silicone. A laser cutter patterned the fabric sheets into uncured silicone, shaped by 3-D printed molds. The fabrication method allows shapes to be patterned over large areas, enabling a variety of applications from camouflage to shape changing displays and human-machine interfaces.
5:30 PM - SM4.7.08
Actuation of Elastomeric Surfaces for the Micromanipulation and Assembly of Solid Particles and Liquid Pre-Polymer Droplets
T.P. Vinod 1 , John Bowen 1 , Stephen Morin 1 Show Abstract
1 , University of Nebraska Lincoln, Lincoln, Nebraska, United States
The rational manipulation and assembly of micron-scale building blocks to fabricate extended micro/mesostructures is challenging using existing techniques, especially when many (e.g., 103 – 106) objects, various liquid and/or solid precursors, and a range of length scales (e.g., mm – cm) are involved. Despite progress in microactuation and the directed assembly of materials, methods capable of addressing such limitations remain elusive. In response, we are investigating scalable techniques that use the precise mechanical actuation of elastic substrates to manipulate and assemble large numbers of building blocks—micro/nanoscale particles and droplets—rationally and simultaneously. Specifically, we organized particles and/or pre-polymer droplets on the surface of functionalized elastomeric polymers (e.g., silicone films decorated with hydrophilic moieties), and, through mechanical actuation of the polymer support, controlled the microscale position (in 2D space) and morphology of the blocks/droplets, enabling their precise manipulation into desired configurations. When subjected to the appropriate secondary chemical/physical processing (e.g., photopolymerization or annealing), the organized particle/droplet precursors can be converted into permanent assemblies of the required shapes, sizes, and periodicities. We could then release these assemblies from the elastic “assembly” substrate for use and/or for subsequent rounds of assembly. Following this approach we demonstrated the fabrication of many (>106) polymeric microstructures (e.g., hard assemblies based on polystyrene and soft assemblies based on polyacrylamide gels) simultaneously and their elaboration into mesoscopic structures using simple actuation of centimeter-scale elastomeric devices. We believe this approach, and extensions of it, will enable significant advances in the assembly of functional structures from a compositionally diverse range of microscale (and potentially nanoscale) building blocks relevant to numerous fields (e.g., micromanufacturing, nanotechnology, optoelectronics, etc.).
5:45 PM - SM4.7.09
Soft Multi-Modal Sensor—Bend, Stretch, Pressure, Touch and Proximity Using a Gel Electrode Array
Mirza Sarwar 1 , Justin Wyss 1 , Claire Preston 1 , Thomas Searle 1 , Shahriar Mirabbasi 1 , John Madden 1 Show Abstract
1 Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia, Canada
Soft wearable devices undergo bend and stretch in response to human movement. In this work we address the sensing challenge of discriminating between these natural environmental effects and the human tactile interaction. We demonstrate the simultaneous detection of proximity, light touch, pressure and stretch. The decoupling of the effects of a deformation from a touch/proximity is achieved by using two different capacitive effects. (1) Stretch/pressure gives rise to a reduction of thickness of the dielectric that increases the sensor capacitance between parallel plate sense electrodes. (2) In mutual capacitance sensing a finger in proximity or lightly touching the surface of the sensor results in a decrease in coupling of fringe electric fields between the sense electrodes thereby reducing the sensor capacitance. In this second case the fields influenced are external to the device, while in the former they are internal. A 4 x 4 array of deformable electrodes is constructed that features both the internal and external coupling in the form of perpendicularly running strips of polyacrylamide hydrogel, 4 mm x 50 mm x 400 mm, spaced 4 mm apart. These are separated and surrounded by Ecoflex soft silicone dielectric material. The hydrogel is ionically conductive due to the introduction of NaCl during the polymerization phase. The sensor is highly stretchable (~300% strain) and generates a proportional change in capacitance with strain (capacitive gauge factor ~1). Light touch at the surface results in a 10% decrease in capacitance while firm pressure on the sensor increases the capacitance (20% dC/Co for ~200 kPa). The capacitance map generated for a sensor array is used to distinguish between light touches, pressure, bend and stretch, as is required to reconstruct the surface shape and local environment following a combination of interactions and deformations.
SM4.8: Poster Session II
Thursday PM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - SM4.8.01
Soft Robotic Hand with Fiber Reinforced Actuators for Hand Rehabilitation
Deepak Ganta 1 , Rolando Villanueva 1 , Jose Jara 1 , Carlos Guzman 1 Show Abstract
1 , Texas A&M University, Laredo, Texas, United States
It has been reported in the Americans with Disabilities 2010 report that millions of people suffer from disabilities especially with hand. These disabilities were the result of a wide variety of conditions for ex. paralysis, surgery, stress, heart stroke, arthritis, and trauma. The existing methods of conventional therapy are expensive, invasive, and time-consuming, and require several clinical visits. The existing methods also lack round the clock monitoring, with a lengthy time for patient recovery.
To overcome these limitations, we developed reliable and cost effective soft actuators. The complex motions and structure of human fingers including the palm were matched with 3D soft actuator designs. Finally, the models designed using AutoCAD were 3D printed with home-built 3D printer using an appropriate skin like materials. The mold you design will impact the behavior of your actuator. In this study, we developed a semi -cylindrical shaped actuator. This particular shape was compared for efficiency and it required less pressure to achieve the same radial angle. Fabricating the actuator for fingers involves inner skin fabrication, strain limiting fiber reinforcement, outer skin fabrication, and finally sealing of the actuator. The palm is fabricated from different materials such as DS (Dragon Skin) 30 strong enough to hold the five fingers and we used Elastosil, DS 10 and DS 20 for the finger actuators. Replicating the ulnar nerves and tendons inside the hand, the finger actuators were connected by air valves providing pneumatic actuation from a compact fluidic control board, integrate with the hand.
We tested the actuation at various air pressures demonstrating relaxed state prior to actuation and flexed during actuation varying the pressure from 0-200 psi. The force exerted by the actuator is measured and Force vs. Pressure data is obtained for various components of the hand and compared, as pressure were varied from 0-100 psi. Further with the aid of the fluidic control board, we were able to actuate all the fingers simultaneously and perform simple tasks such as lifting and grasping of objects. We also tested methods to improve human- machine interactions by remotely monitoring the movement of the hand using graphical user interface on the smartphone and inexpensive Radio frequency ID stickers. In the near future, human trials will be performed under collaboration with the TAMIU school of nursing.
9:00 PM - SM4.8.02
Fabrication and Characterization of BaTiO3/PVDF Nanocomposites Using FDM 3D Printing Technology
Hoejin Kim 1 , Fernando Torres 1 , Tzu-Liang (Bill) Tseng 1 , Yirong Lin 1 Show Abstract
1 , University of Texas at El Paso, El Paso, Texas, United States
This work presents a novel fabrication process to prepare homogeneous dispersion of BaTiO3/polyvinylidene fluoride (BaTiO3/PVDF) nanocomposites with in-situ poling process using fused deposition modeling 3D printing technique. The nanocomposites integrate the functional property (piezo-, pyro-, and dielectric) of BaTiO3 and flexibility and lightweight of PVDF. Traditionally, the simple yet effective way to fabricate the nanocomposites is a solvent-cast method, compared with spin-coating and hot-embossing. However, this method has a disadvantage in heterogeneous dispersion of BaTiO3 nanoparticles (NPs) in PVDF matrix due to agglomeration during drying process. This heterogeneous dispersion could weaken piezoelectric and mechanical properties. Herein, fused deposition modeling (FDM) 3D printing technique was utilized for homogeneous dispersion and alleviate agglomeration of BaTiO3 nanoparticles in PVDF through two processes: filament extrusion and 3D printing. In addition, in-situ poling process was integrated during 3D printing process to simplify post-processing requirement. Thermal poling was processed to further enhance piezoelectric response of the BaTiO3/PVDF nanocpmposites. It is found that 3D printed BaTiO3/PVDF showed more than twice higher piezoelectric response increase than solvent-cast ones.
9:00 PM - SM4.8.03
Reversible Actuation of Soft Liquid Metal Plugs in Microfluidic Systems Using Low Voltages
Ishan Joshipura 1 , Yash Patil 1 , Alexander Johnson 1 , Michael Dickey 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
Integrating liquid metals with other low modulus materials, such as elastomers and gels, imparts high electrical conductivity into a composite without altering its mechanical properties. Combined, these materials form ‘softer than skin’ systems that are well-suited for forming conformal interfaces and ultra-compliant soft electronics. This work characterizes the behavior of a eutectic alloy of gallium and indium (75% Ga, 25% In, by weight, ‘EGaIn’) in response to electric fields. The metal remains a liquid at room temperature (M.P., 15.5 oC) and has low toxicity. These fluidic metals are injectable into microfluidic systems, fibers, and capillary networks. Once injected, the metal remains in its place because of the adhesive nature of its thin native oxide. Preventing the oxide adhesion within microchannels enables reversible actuation of EGaIn. Actuating liquid metals may be useful for soft actuators, reconfigurable optical displays, frequency tunable antennas, and other opto-fluidic technologies.
This work studies methods to reversibly move droplets of EGaIn through microchannels using low voltages. Pre-wetting the channels with an aqueous solution prior to injecting the metal prevents oxide adhesion; the water forms an interfacial ‘slip-layer’ between the metal and channel wall. Thereafter, an applied electric field (~10-20 V/m) actuates the liquid metal by establishing a gradient of surface tension; this effect is known as continuous electrowetting (CEW). Although CEW has been utilized before with mercury, which is toxic, the presence of a Ga oxide complicates CEW behavior. This work compares the electro-hydrodynamic behavior of EGaIn with and without the presence of an oxide ‘skin’. Optical microscopy and electrochemical measurements characterize the movement of EGaIn droplets under a variety of conditions. Specifically, we elucidate the influence of the electrolyte (i.e., composition, pH, and viscosity) on the metal-electrolyte interface. In addition, thin film interference characterizes the thickness and dynamics of the interfacial slip-layer of water. However, evaporation of water may cause the slip-layer to disappear and impede CEW. Therefore, this work explores novel microfabrication strategies to design interfaces that prevent oxide adhesion. These interfaces form alternative slip-layers, which also renders microfluidic channels with self-healing and self-cleaning abilities. In addition, these interfaces may be useful for the transport of chemical or biological samples within three-dimensional microfluidic devices and vascular networks using low voltages.
9:00 PM - SM4.8.04
Purifying Nanomaterials Using AC Dielectrophoresis for Flexible Electronic and Energy Harvesting Applications
Roshan Plamthottam 2 1 , Nathan Palmquist 2 1 , Kevin Li 2 1 , Nathan Smith 2 1 , Samuel Rosenthal 2 3 , Robert Cammarata 2 1 , Stephen Farias 2 1 Show Abstract
2 , NanoDirect LLC, Baltimore, Maryland, United States, 1 Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 3 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, United States
Flexible electronic materials have the potential to open the doors to a wide range of industrial and commercial applications. Electronic skins that exhibit high degrees of deformation can be used in various health monitoring devices, flexible displays, and energy conversion technologies. These materials can potentially assist in the production of clean energy via flexible solar cells. Many applications require the use of optically transparent materials as well as flexible circuitry. Flexible and printed electronic components are often manufactured using nanoparticulate inks including metal nanospheres, metal nanowires, carbon nanotubes, graphene, and other oxide and semiconducting nanomaterials. These materials are often difficult to produce in a bulk, purified form and are typically manufactured with significant quantities of nanoparticle byproduct materials that deviate from the desired electrical and structural properties. It is therefore necessary to separate and isolate desired nanomaterials from undesirable byproducts before using these materials for flexible electronic fabrication.
We have developed a novel and scalable nanoparticle isolation process using AC dielectrophoresis (DEP). The magnitude and direction of each particles’ velocity is determined by the physical and electrical properties of each particle. This allows for particles of different size, shape, and conductivity to be concentrated to different regions within a nanoparticle suspension. This technique is demonstrated for silver nanoparticles, carbon nanotubes, and oxide nanomaterials. Separation via DEP promises to be more effective than other conventional methods such as gravitational settling or centrifugation, as our experiments showed that it can be achieved in a continuous-flow system with high processing rates. Our system also leaves the desired particle undamaged where other techniques, like centrifugation, can induce significant defects in the nanomaterials. Analysis of the separated materials is presented with microscopy and spectroscopy results.
9:00 PM - SM4.8.05
Soft Microactuator for Minimally Invasive Surgery
Jun Kameoka 1 2 , Sina Baghbani Kordmahale 1 Show Abstract
1 Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, 2 Department of Medicine, Jikei Medical School of Tokyo, Tokyo Japan
Silicon or shape memory alloy (SMA) has been used as base material for micro actuator devices. Silicon based micro actuators include complicated comb drive structures, gears and cranks that are normally actuated by electro static force. SMA micro actuators also have complicated microstructures, and are actuated via shear force subjected to external heat. Both actuator devices require high cost fabrication process, and are not designed for handling soft materials such as biological objects. Hard material characteristics of actuators sometimes damage biological cells and tissues. In this paper, we have developed a low cost and simple design for soft micro actuators. These soft micro actuators have demonstrated ability to grip millimeter or sub millimeter scale soft objects without any damages, which paves the way for future applications on minimally invasive surgery. The designed gripper is consisted of three layers, a microgripper surface, a pneumatic layer and a bottom layer. Two micro scale columns made of polydimethylsiloxane (PDMS) are located on the surface layer. The hydraulic reservoir on the actuation layer is located under the columns. Air suction from the hydraulic reservoir induces the concave deformation of the gripper surface layer. And as a result, two columns are bent to opposite directions to grip a small object between them. In this paper, we report the discovery of two columns demonstrating identical bending motions and having linear bending angle relation. The overall benefit of the device with simple design and soft material coupled with low fabrication cost and ease of use will make it ideal candidate for minimally invasive surgery and other delicate and biologically oriented applications.
9:00 PM - SM4.8.06
Interface Contact Mechanics for Highly Functional Flexible/Stretchable Sensors
Yan Yu 1 Show Abstract
1 , Huazhong University of Science and Technology, Wuhan China
Interface contact mechanics are very important for flexible/stretchable electronics, having influence both on fabrication process and device performance [1-3]. Herein, we present our recent research results in interface contact mechanics for highly functional flexible/stretchable sensors.
(1) Flexible strain sensors that have high sensitivity (high gauge factor) under tiny strain could be useful in diverse applications requiring ultrahigh displacement sensitivity, such as microstrain detection in artificial vessels, weak motions, human-computer interactions, etc., [4-7].
Using the different micro-contact condition during friction progress, we proposed a frictional direct writing approach to obtain flexible strain sensors that can detect tiny strain (0.1%～0.5%) with high gauge factor (300～30000).
(2) Highly sensitive strain sensors typically responded to the applied strain with high nonlinearity and low stretchability, leading to the challenge of strain sensors with both high linear range and highly sensitivity [5-8].
Through structure designs which confine the interface deformation, we developed stretchable strain sensors with both high gauge factor (>50) and high linear range (100%) by friction-transfer approach.
(3) Respiration sensors that can be weaved or integrated into clothing, accessories, and the living environment, such that health information can be acquired seamlessly and pervasively in daily living, play a significant role in healthcare system and attracts more and more attention [9, 10].
Based on the surface tension and capillary forces in the water/insulate interface, we prepared a series of respiration sensors based on variety of insulate materials. These flexible/stretchable respiration sensors have an average intensity ratio of 10 times (or higher) for strong breath over weak breath signal, and rapid response (up to 2 Hz).
(4) The optical transparency of sensors would provide a way to realize a new class of human-interface devices for real-life applications, attracting substantial research interests in transparent sensors [7, 8].
By applying classical friction and wear effects into 2D materials fabrication, we proposed a soft friction method for transfer-free production of 2D materials on various substrates, leading to the fabrication of transparent strain sensors and transparent humidity sensors [11, 12].
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2. Z. Suo, MRS Bull. 37, 218 (2012).
3. J. A. Rogers, et al., Science 327, 1603 (2010).
4. D. Kang, et al., Nature 516, 222 (2014).
5. T. Quang, et al., Adv. Mater. 28, 4338 (2016).
6. M. Amjadi, et al., Adv. Funct. Mater. 26, 1678 (2016).
7. H. Jang, et al., Adv. Mater. 28, 41 (2016).
8. S. Yao, et al., Adv. Mater. 27, 1480 (2015).
9. G. Konvalina, et al., Acc. Chem. Res. 47, 66 (2014).
10. H. Haick, et al., Chem. Soc. Rev. 43, 1423 (2014).
11. S. Jiang, et a., Sci. Rep. 6, 19313 (2016).
12. Y. Yu, et al., Sci. Rep. 3, 2697 (2013).
9:00 PM - SM4.8.07
Mechanically Tunable Elastomeric Hydrogels Made from Melt-Fabricated Photoreactive Block Copolymer Micelles
Nabila Huq 1 , Travis Bailey 1 Show Abstract
1 , Colorado State University, Fort Collins, Colorado, United States
Recently, our group has developed a range of novel elastomeric hydrogels using thermoplastic elastomer (TPE) design concepts. These materials have been traditionally formed using two-component blends of AB diblock and ABA triblock copolymer, molecularly designed to self-assemble into spherical (micelle-like) domains in the melt. Vitrification or chemical fixation of the micelle cores (A blocks) followed by swelling in aqueous media leads to an elastic network of spheres tethered through the population of bridging ABA triblock copolymer chains in the blend. The concentration of ABA triblock copolymer used has a strong influence on the mechanical properties exhibited by the resulting hydrogels formed. We have built on this framework by replacing AB diblock in the traditional blend with a photoreactive AB diblock copolymer (AB-p). This construct provides flexibility to install specific concentrations of ABA triblock copolymer tethering molecules at any point in the fabrication process as well as at any location on the gel simply through intensity-controlled, spatially directed irradiation with UV light. Increasing UV exposure time results in greater ABA triblock concentrations and thus reinforcement in the area of exposure. In this presentation we explore the influence of patterned triblock copolymer installation on shape, surface topography, and mechanical properties of the resulting hydrogels.
9:00 PM - SM4.8.08
Omnidirectional Soft Elasticity in Homeotropically Aligned Liquid Crystal Elastomers
Anesia Auguste 1 , Nicholas Godman 2 , Tyler Guin 2 , Timothy White 1 Show Abstract
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 , Azimuth Corporation, Beavercreek, Ohio, United States
Liquid crystal elastomers (LCE) contain rod-like rigid units (mesogens) within the polymer backbone or side chain which exhibit and maintain orientational or positional order. At appropriate crosslink densities, these materials have glass transition temperature (Tg) below room temperature. The mobility of these mesogens in the elastomeric state allows for large stimuli-induced shape and/or optical changes which can be used in aerospace applications, optics, or medicine. The mechanical response of LCEs in the planar orientation to an applied load are anisotropic and sensitive to the direction of the applied force with respect to the director. When the director is perpendicular to the applied force, the material exhibits ‘soft’ elasticity, where the material deforms at nearly constant stress due to the mesogens in the macromolecular units realigning to the stretching direction. If the director is aligned with the stretching direction, the material behaves much like a classical rubber. Here, we explore the ‘soft’ elasticity of homeotropically aligned LCEs in which the mesogens are aligned normal to the substrate. This orientation enables and allows for ‘omnidirectional’ soft elasticity in which the LCE exhibits nonlinear elasticity in any and all deformation directions. By using ink-jet printing to localize regions of homeotropic and planar orientation, we can prepare designer elastomers with distinct elastic properties, which may find use in flexible hybrid devices.
9:00 PM - SM4.8.09
Geometric Design of Mechanically Tunable Soft Composite Materials
Young-Joo Lee 1 , Jeong Ho Lee 1 , Gwang Mook Choi 1 , In-Suk Choi 2 , Young-chang Joo 1 Show Abstract
1 , Seoul National University, Seoul, SE, Korea (the Republic of), 2 , Korea Institute of Science and Technology, Seoul Korea (the Democratic People's Republic of)
In the present work, we propose a new method for tuning the elastic modulus and Poisson’s ratio of soft materials by geometric design of composite materials. Devices are growing soft, satisfying the increasing demands of attachable, epidermal electronics. Elastomers such as PDMS, Ecoflex, rubbers, and hydrogels are conventionally used as substrate or packaging materials to realize soft electronics. However, mechanical mismatch, which comes from the difference of elastic modulus and Poisson’s ratio, has been an issue to induce surface instability at the heterogeneous material interface such as wrinkling or buckling, degrading the performance of devices. Therefore, modulating the elastic properties such as modulus and Poisson’s ratio of soft material substrate is a key challenge to achieve soft electronics.
Here, we are able to modulate the modulus and Poisson’s ratio of soft materials by using geometrical design of composite materials. Combination of computational and analytical modeling provides a guidance of materials design with various soft materials, leading us tunable modulus and negative Poisson’s ratio. To prove our new composite design concept, we fabricated 100 μm-thick soft composite substrate with polyurethane(PU) and Ecoflex. Systematic change in composite design of matrix and filler increased modulus of soft composite materials from 0.01 MPa to 2.31 MPa, and Poisson’s ratio dramatically decreased from 0.49 to -0.25. Our proposed strategy could provide an easy way to expand the variety of application for mechanical engineering of soft materials.
9:00 PM - SM4.8.10
Monodisperse Core-Shell Microcapsules for Acid-Responsive Release of Hydrophobic Agents
Mostafa Yourdkhani 1 , Shijia Tang 1 2 , Nancy Sottos 1 2 , Jeffrey Moore 1 3 , Scott White 1 4 Show Abstract
1 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Urbana, Illinois, United States, 3 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Polymer microcapsules are of great interest for isolation, protection, and controlled delivery of active core materials in various applications ranging from drug delivery to self-healing materials. Encapsulated contents can be released from microcapsules in response to various environmental stimuli (triggering events), including mechanical rupture, temperature, pH variations, and light irradiation. Here, we present an efficient microencapsulation technique based on emulsion solvent evaporation method to fabricate stimuli-responsive microcapsules with hydrophobic core contents. Flow-focusing microfluidic devices were utilized to produce oil-in-water (O/W) template emulsion droplets for the formation of microcapsules. Upon the collection of emulsion droplets, the organic solvent was extracted and evaporated to form microcapsules with a core-shell structure. This method produces microcapsules with a high loading efficiency, monodisperse size distribution, good capsule morphology and barrier properties.
In this work, we used cyclic poly(phthalaldehyde) (cPPA), a low-ceiling temperature (Tc) metastable polymer, as the shell wall material to enable the triggered-release of core contents from microcapsules. cPPA undergoes rapid depolymerization upon backbone bond cleavage by several environmental triggers, including temperature and acidic conditions. Hence, depolymerization of the shell polymer leads to a rapid loss in the mechanical integrity of the shell wall, providing on-demand delivery of the encapsulated contents. Stimuli-responsiveness of fabricated microcapsules was determined by measuring their release profile in various acidic conditions. We demonstrate the ability to tune microcapsules size by adjusting the flow rates of the two solutions within the microfluidic device. Fabricated microcapsules are beneficial in applications which require autonomous release of active payloads without any mechanical damage, such as autonomic corrosion inhibition.
9:00 PM - SM4.8.11
3D Microstructured Flexible Molds via Direct Laser Lithography for the Functional Patterning of Soft Materials
Omar Tricinci 1 , Irene Bernardeschi 1 , Virgilio Mattoli 1 , Lucia Beccai 1 Show Abstract
1 Center for Micro-BioRobotics, Istituto Italiano di Tecnologia, Pontedera, Pisa, Italy
In recent years soft robotics has emerged as a new approach in which the robot body (i.e. physical structure and constituting materials) acquires a major role for negotiating tasks and interacting with the environment.1 Three-dimensionally micropatterned surfaces are attracting increasing interest owing to the potential of mimicking natural morphologies at the microscale and nanoscale.2 Indeed, properly designed polymeric soft materials can create original solutions for soft robotics, since shape and spatial organization can add peculiar functionalities to the entire material.
In this work we employed direct laser lithography (DLL) for the fabrication of flexible molds with complex 3D features that allow the patterning of soft moldable materials. With DLL it is possible to create arbitrarily complex 3D designs (e.g. reentrant geometries), with high spatial resolution3, not achievable with standard methods, which usually require multiple lithographic steps. The combination of having a deformable material and an ad hoc 3D design is the key to endow new functionalities to the surface of a bulk material, like gripping and trapping, useful to create new ways for soft robots to gently interact with the external environment.
Molds, fabricated in a positive photoresist (AZ9260) on flexible Mylar sheets, can conform to curved surfaces, allowing an integrated approach in the fabrication process: it is possible to directly fabricate 3D modeled flexible materials with truly 3D surface micropatterns in a single molding step. Several shapes were designed in order to investigate the potentiality of the presented technique, obtaining 3D microstructures in polydimethylsiloxane (PDMS).
We fabricated hollow truncated hemispheres with nominal diameter 33 μm, height 15 μm and aperture diameter 15 μm and microgrippers, consisting of couples of sloping trapezoidal arms with major and minor bases of 20 and 10 μm lengths, 9 μm height and a bottom to top decreasing thickness of 3.6 μm at the base.
The hyperelastic behavior of PDMS allowed us to deform the 3D architectures, demonstrating the possibility of fabricating surfaces with soft gripping and trapping capabilities. Furthermore, we built hemispheres and microgrippers on the surface of a PDMS solid cylinder in a single molding step, showing that integration in a bulk material can be easily achieved.
Finally, we fabricated extended or very tiny structures, like microchannels of 150 μm length and 10 μm diameters and crossed arches of thickness of 2.5 μm and several diameters.
The proposed micromolding technique proved to be effective in terms of resolutions and reproducibility, and it can also be applied to any moldable material.
(1) Kim, S. et al.; Trends Biotechnol. 2013, 31, 287–294.
(2) Bhushan, B.; Philos. Trans. R. Soc. Lond. Math. Phys. Eng. Sci. 2009, 367, 1445–1486.
(3) Sun, H.-B. et al.; NMR - 3D Analysis - Photopolymerization; Advances in Polymer Science; Springer Berlin Heidelberg, 2006, 169–273.
9:00 PM - SM4.8.12
Flower Blossom-Inspired Soft Morphing Structures
Min-Woo Han 1 , Sung-Hoon Ahn 1 Show Abstract
1 Department of Mechanical & Aerospace Engineering, Seoul National University, Seoul Korea (the Republic of)
The hygroscopic swelling plays an important role in the transformation of the plant geometry such as the unfolding of the seed capsule. This cellular expansion based on passive actuation has been conducted for completing the life cycle of plants that achieve the macroscopic shape change or variation of their mechanical properties. In order to design and demonstrate the flower blossom, the unit cell-based looping architectures were developed for soft morphing structures made of the phase transformation materials. The design and fabrication of the morphing flowers using the methodology for looping architecture and their blooming motions were demonstrated by using Joule heating. Each petal has its own loop patterns for the creation of a variety of morphing motions, including three-dimensional volumetric change in complex stereotactic models. By controlling the electric current to each petal, different types of flower blossoms were realized.
Martin Kaltenbrunner, Johannes Kepler University
Michael Dickey, North Carolina State University
Christoph Keplinger, University of Colorado Boulder
Rebecca Kramer, Purdue University
Heraeus Holding GmbH
SM4.9: Soft Systems and Liquid-Metal Embedded Soft Structures
Friday AM, April 21, 2017
PCC North, 100 Level, Room 121 B
9:00 AM - SM4.9.01
Smart Garments for Joint Position Analysis
Massimo Totaro 1 , Chiara Lucarotti 1 , Alessio Mondini 1 , Jesus Ortiz 1 , Lucia Beccai 1 Show Abstract
1 , Istituto Italiano di Tecnologia, Pontedera Italy
Advancements in soft materials, with compliances and extensibilities not allowed by rigid components, open new perspectives for the facile integration of wearable sensors into garments for human motion detection, health monitoring, rehabilitation, etc.  where it is essential to conform to the body unobtrusively. Indeed several soft sensors were reported [2, 3]. However, the majority of them were first developed as separate components  with limitations in terms of integration, conformability, and robustness; or they were mainly resistive-based [5, 6]. Some of them were affected by hysteresis, low sensitivity and low accuracy , while other issues regard complex microfabrication technologies, and lack of reliability of the conductive materials (i.e. liquid metals) used for both electrodes and connections . Here we present two types of smart garments embedding electrotextile-based capacitive strain sensors for joint motion analysis: a sensorized kneepad able to reveal the knee bending angle; and, an anklet for dorsi/plantar flexion and prono/supination monitoring. The fabrication process is simple, low cost, and yields robust devices. The kneepad has three strain sensors (one central and two lateral), while the anklet integrates five sensors (three in front and two in the back). Each sensor is assembled layer-by-layer directly onto the garment to achieve a complete integrated, robust and electrically shielded solution. It consists of one central electrode and two ground layers made of stretchable conductive fabric extensible up to 350%, and two silicone elastomeric films in between as dielectrics. This three-electrode configuration minimizes proximity effects, further reduced by shielded connections to the customized electronics (that is based on a capacitive to digital converter with 0.25 fF resolution, a 32-bit PIC µcontroller, and a RF module to transmit data wirelessly to a PC). With respect to previous works [4-6], complex mechanical stimuli can be discriminated with high accuracy because of the redundant number of sensors per garment and of their specific layouts. For instance, the kneepad can decouple strain and pressure due to accidental contacts, while with the smart anklet 3D movements can be reconstructed. Preliminary measurements, with an optical tracking system used for correlating the sensor signals to the joint bending angle, demonstrate that the smart kneepad is able to detect angles over 90°, and suggest the possibility to distinguish between the two DoFs relative to dorsi/plantar flexion and prono/supination movements in the human ankle.
1. Veltink P.H. et al., IEEE Eng. in Med. and Biol. Mag., 2010. 29(3): p. 37-43.
2. Amjadi M. et al., ACS Nano, 2014. 8(5): p. 5154-5163.
3. Gong S. et al., Nat. Comm., 2014. 5: p. 3132.
4. Jang H. et al, Adv. Mat., 2016. 28(22): p. 4184-4202.
5. Lorussi F. et al., IEEE Sensors Jour., 2004. 4(6): p. 807-818.
6. Mengüç Y. et al., The Int. Journ. of Robotics Research, 2014. 33(14): p. 1748-1764.
9:15 AM - SM4.9.02
Design, Mechanics and Fabrication of 3D Helix Coil Interconnection for Extremely Stretchable Biomedical Devices
Kyung In Jang 1 , John Rogers 2 Show Abstract
1 Robotics Engineering, DGIST, Daegu Korea (the Republic of), 2 Center for Bio-Integrated Electronics, Departments of Materials Science and Engineering, Biomedical Engineering, Chemistry, Mechanical Engineering, Electrical Engineering and Computer Science, Neurological Surgery, Simpson Querrey Institute for BioNanotechnology, McCormick School of Engineering and Feinberg School of Medicine, Northwestern University, Evanston, Illinois, United States
Coils are made of elastic materials formed into the shape of helixes which return to their natural length when unloaded. With its unique geometrical formation, the helix coil structure is considered as one of the most stretchable forms among all kinds of shapes in man-made systems and nature. However, since the conventional N/MEMS has been well-established only for planar and rigid substrate, new manufacturing strategies needs to be developed by shifting many aspects in processing mechanisms, structural design, mechanics, and tools. In this research, Firstly, we employed the new fabrication process and coil mechanics to archive an extreme level of elastic stretchability, which cannot be accomplished with existing technologies. Compared to typical 2D filamentary serpentines fully bonded onto soft planar elastomeric substrates, the proposed 3D helix structures are designed to be uniformly bent with compressive buckling with minimally defined bonding sites. The constructed helix coil interconnections can be naturally deformed along the coil direction under tensile stress with minimal stress concentration. As a result, these structures exhibit extreme elastic stretchability up to ~150%. Secondly, we conducted extremely stretchable biomedical devices by applying 3D coil as electrical interconnects to system circuit. To ensure uniform stretchability across the system, large scale non-linear FEM simulation and systematic optimization were employed. Successful demonstrations including electrophysiological signal sensing and motion tracking present challenging, but still practical potentials for advanced biomedical applications.
9:30 AM - *SM4.9.03
R2R-Nanoimprint Lithography on the Long Run for Fabrication of Hierarchical Microfluidic Structures on Large and Flexible Plastic Films
Barbara Stadlober 1 , Dieter Nees 1 , Ursula Palfinger 1 , Stephan Ruttloff 1 , Johannes Goetz 1 , Anja Haase 1 , Michael Suppan 1 , Ladislav Kuna 1 Show Abstract
1 , Joanneum Research, Weiz Austria
R2R-nanoimprint lithography has proven as a very powerful tool to realize hierarchical structures on large areas of flexible substrates at medium to high throughput. Such roller-imprinted microstructures with nanoscale features are essential for many applications based on biomimicry and fluid dynamics. Accordingly, the drag resistance of objects moving fast in fluids can be controlled by hierarchical structures on flexible substrates attached to their surfaces and on the other hand the wettability of fluids on hierarchically patterned surfaces can be tuned from superhydrophobic to spontaneous wettability. The latter is a property that can be exploited for ink and fluid transport, microfluidics, and multilevel patterning.
This paper introduces R2R-UV-Nanoimprint Lithography for the combined micro- and nanopatterning of proprietary UV-curable liquid resist layers thus aiming for the creation of large-area film surfaces with controlled wettability. We demonstrate the fast and reliable fabrication of microfluidic devices for lab-on-chip devices and embedded metal patterns and verify our results by simulation and quantitative measurements of the fluid dynamics. Moreover, the long-term stability of the R2R-UV-NIL process w.r.t. durability of the applied polymer and Ni stamps and of the resist materials and structures will be discussed. Finally, new findings about pattern reproduction fidelity and UV-induced polymer shrinkage in thiol-ene imprint resist systems will be presented both for flat and roller-based imprinting. The paper is supported by the H2020 project R2R Biofluidics under the Award No. 646260 and by the national FFG project MoMiFlu@Foil (No. 844726).
10:00 AM - SM4.9.04
Camouflage Materials Inspired by Cephalopods
Erica Leung 1 , Long Phan 1 , Chengyi Xu 1 , Alon Gorodetsky 1 Show Abstract
1 , University of California, Irvine, Irvine, California, United States
The unique skin structure of cephalopods endows them with remarkable dynamic camouflage capabilities. Such abilities are partially enabled by optically-active intracellular ultrastructures in part comprised of the cephalopod structural protein reflectin. By drawing inspiration from these ultrastructures, we have begun to develop new types of biomimetic camouflage materials. To date, we have optimized strategies for the production of reflectins in multi-gram quantities and for the manufacture of reflectin-based coatings on both rigid and soft support substrates. We have also validated the dynamic functionality of these coatings by showing that chemical stimuli tune their reflectance over a ~ 600 nm range and that mechanical stimuli shift their reflectance from the visible to the near infrared. These findings represent a key step towards wearable, biomimetic color-changing technologies both for everyday use and for stealth applications.
10:15 AM - SM4.9.05
A Flexible Sensor Analog to Human Skin Via Air-Configured Motile Electronic Whiskers
Jonathan Reeder 1 , Tong Kang 1 , Sarah Rains 1 , Walter Voit 1 Show Abstract
1 , University of Texas at Dallas, Richardson, Texas, United States
We demonstrate a sensing analog to human skin comprised of electronic whiskers which encompass the ability to sense temperature, proximity, material stiffness, microscale texture and nanoscale texture. This development is driven by a novel fabrication technique for transforming arrays of planar electronics on plastic substrates into 3D shapes using warm air. By heating a shape memory polymer substrate above its glass transition temperature, deformation of predefined sections of the substrate are deformed out of plane in its softened state. Gold strain gages patterned atop the substrate are therefore assembled into 3D space. Deformations of the cantilever tips as small as 5 µm can be sensed, enabling a variety of distinct sensing modes including proximity, texture mapping, surface roughness, temperature, material stiffness. An extraordinary wide range of surface topology features can be sensed, from 50 nm changes in surface roughness to height changes up to 500 µm. The shape memory properties of the substrate enable reversible assembly and flattening, mimicking the whisking functionality of vibrissae in nature.
Thiol-click polymer substrates are synthesized with a glass transition of 55 °C and 3x3 arrays of SMP cantilevers (150 µm x 2mm) are laser machined into the substrate. The application of 70 °C air from the backside of the substrate softens the substrate two orders of magnitude and forces the array of cantilevers out-of-plane to angles reaching 80° from the substrate surface, as determined by the air flow rate and substrate thickness. The shape fixing properties of the substrate allow the deformed, out-of-plane state to be “locked in” by cooling to room temperature. The relationship between deployment angle and both substrate thickness and air flow rate is shown for ranges of 25-125 µm and 1-30 LPM, respectively. Photolithographically defined strain gages patterned at the hinges of the cantilevers enable tracking of the angular deflection of the 3x3 array of flanges.
10:30 AM - *SM4.9.06
Fabrication of Fixed-Shape Soft Smart Objects by Thermoplastic Forming of Flat Stretchable Circuits
Andres Vasquez Quintero 1 , Jan Vanfleteren 1 , Frederick Bossuyt 1 , Bart Plovie 1 , Rik Verplancke 1 , Herbert De Smet 1 Show Abstract
1 , imec Ghent University, Gent-Zwijnaarde Belgium
There is a growing interest in soft smart structures with embedded sensors and electronics. Although mechanically soft and easily deformable, in some applications these objects should take a predetermined shape when no other external forces than gravity are acting on them. Examples of such objects are smart lenses or smart shoe insoles. In this contribution we will present technologies for the production of such fixed-shape soft smart objects. A stretchable sensor and electronics circuit is first produced on a flat carrier using conventional thin-film or PCB (printed circuit board) technology, also including the assembly of the components. Fabrication on flat carriers makes these technologies suitable for future transfer to an industrial environment. The circuit is subsequently embedded in one or more thermoplastic polymers, and the obtained flat circuit is finally formed from flat to its final 3D shape using a thermoforming step. The stretchability of the electrical connections between components guarantees maintained functionality of the circuit after deformation. Using this technology principle smart lenses were built with embedded active (Si chip) and passive (antenna) components. The contribution will describe in further detail the technologies used, the smart lens electrical and mechanical design flow, as well as the characteristics of the obtained smart lenses.
11:30 AM - *SM4.9.07
Liquid-Metal Embedded Elastomers—Microfluidics, Colloids, and Microelectronics Interfacing
Carmel Majidi 1 Show Abstract
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Elastomers that are embedded with liquid metal (LM) inclusions can be tailored to exhibit a broad range of electrical, thermal, and mechanical properties. Efforts over the past decade have primarily focused on microfluidic channels of Ga-based LM alloys that are sealed in a soft elastomer and function as highly deformable electrical wiring. More recently, there has been interest in elastomers embedded with a dispersion or percolating network of LM inclusions. In contrast to the deterministically-patterned LM microfluidic architectures, these LM-embedded elastomer (LMEE) composites are statistically homogenous and exhibit effective medium properties at the mesoscale. Eutectic Ga-In (EGaIn) and Ga-In-Sn (Galinstan) alloys are typically used as the liquid metal due to their high electrical conductivity, low viscosity, non-toxicity, and the self-passivating formation of an oxide skin (Ga2O3) that enables emulsification and wetting to non-metallic materials. Because they are liquid-phase at room temperature, these alloys have virtually no influence on the mechanics of the surrounding elastomer medium. This allows the resulting soft microfluidic system to exhibit a unique and extraordinary combination of features not seen in other heterogeneous material compositions. These include the electrical and thermal properties of metals and the robust mechanics of soft hyperelastic solids. In this talk, I will review recent experimental and theoretical studies of this unique class of soft material architectures and identify current technical challenges and opportunities for further advancement within the field. I’ll also highlight several applications in which they can have a potentially transformative impact, especially in the domains of wearable computing and physical human-machine interaction.
12:00 PM - SM4.9.08
3D Printing of Flexible and Stretchable Electronic Devices via Direct-Writing of Liquid Metals
Dishit Parekh 1 , Collin Ladd 1 , Michael Dickey 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
Flexible electronics are devices that can be bent, folded, stretched, or conformed regardless of their material composition without losing the electronic functionality. These electronics are employed in healthcare – designing stretchable electronic skins or lightweight smart sensors conformal to human body for biomonitoring and energy harvesting applications. Despite their increasing demands, only a handful of these devices have been commercialized due to the lack of novel functional materials available along with the complex fabrication mechanisms needed to process them. Unlike conventional silicon-based microelectronics manufacturing that is limited to rigid wafers, flexible electronics need to be incorporated onto plastics, paper, fibers and even biological tissues – necessitating low temperature processing. In addition, these devices need to be inexpensive and customizable according to an individual’s body needs with short manufacturing lead times. In 2014, TIME Magazine heralded 3D printing – the process of joining materials to make objects from 3D model data, usually layer upon layer – as one of the 25 best inventions of all-time signifying that it can lead to a decentralized and highly customizable manufacturing technique in the future. Current methods for 3D printing metals tend to be prohibitively expensive, and use energy-intensive lasers at high sintering temperatures in excess of 800°C. Secondly, they need vacuum-like pressures to avoid oxidation while handling metal nanoparticles, leading to porosity in finished parts, low resolution and poor electrical conductivity, apart from having slow printing speeds. Finally, the operating procedures are impossible to integrate with various polymeric, organic, soft and biological materials. We present a simple approach that utilizes low melting point alloys that offer the electrical and thermal benefits of various metals like gallium and indium, combined with the ease of printing due to its low viscosity. Despite having high surface tension, these metals build mechanically stable structures due to the formation of a thin surface oxide. The oxide skin forms spontaneously in presence of air allowing us to direct-write planar as well as free-standing, out-of-plane conductive microstructures at room temperature, down to a resolution of ~10 microns, on-demand, using a pneumatic dispensing robot at relatively low pressures. We have demonstrated rapid prototyping of functional electronics such as flexible and stretchable antennas for defense communications, consumer-friendly electronic devices like inductive power coils for wireless charging of smartphones, and wearable thermoelectric generators for energy-harvesting applications. We have also exhibited the patterning of 3D multilayered microchannels with vasculature using liquid metals as a sacrificial template at room temperature, that can be embedded in lab-on-a-chip devices to enable inexpensive fabrication of personalized healthcare sensors.
12:15 PM - SM4.9.09
Liquid Metal Switches for Environmentally Responsive Electronics
R. Adam Bilodeau 1 , Dmitry Zemlyanov 1 , Rebecca Kramer 1 Show Abstract
1 , Purdue University, West Lafayette, Indiana, United States
Through their high conductivity and inherent malleability, room-temperature liquid metals hold great potential for creating reconfigurable electronics and circuitry. Emerging methods for patterning gallium-based room temperature liquid metals onto substrates are being thoroughly investigated, and even more effort is being invested into basic reconfiguration of the metal post patterning. Despite this, a major hurtle in liquid metal reconfiguration comes from post-morphological fixity: currently there are no techniques to fix the liquid metal into its new form. In this talk, we present environmentally controlled, fully reversible, wetting-dewetting transitions of liquid metal droplets: work that points toward full circuit reconfiguration and repinning of liquid metals using purely chemical stimuli. We attribute the transitions to the removal, formation, and transformation of droplet surface oxide. We compare the use of highly acidic hydrochloric acid (HCl) and highly alkaline sodium hydroxide (NaOH) in removing the oxide to release pinned droplets, with no mechanical perturbation of the liquid metal droplets. Although both etchant solutions result in high contact angles between the droplet and the substrate, NaOH achieves this result at a rate that is orders of magnitudes faster than HCl. To subsequently re-pin droplets that have been removed from a substrate, we explore the use of neutral distilled water in re-growing the oxide and manipulating the contact area of the liquid metal droplet on the surface. We demonstrate that this allows for fully removed droplets to completely re-adhere to the substrate, even after droplet translation. The talk concludes with a demonstration of an immediate application of this technique, in which an electrical circuit is opened and closed repeatedly to create liquid metal switches that are controlled by purely environmental stimuli.
12:30 PM - SM4.9.10
Self Actuation of Liquid Metals in Ionic Imbalance of Aqueous Electrolytes
Ali Zavabeti 1 , Torben Daeneke 1 , Kourosh Kalantar-zadeh 1 Show Abstract
1 , RMIT University, Melbourne, Victoria, Australia
Smart, soft and small entities with self-actuation ability will form the foundation of the future stretchable and reconfigurable electronics, soft sensors, artificial biological systems and autonomous microfluidics components.
Gallium based liquid metal alloys feature some of the largest surface tensions of any room temperature liquid material. Hence they are efficient materials to be used for surface tension driven self-actuation mechanisms. Gallium alloys are not harmful to human health and the environment. Therefore, they are suitable candidates to be safely used in research environments and practical applications. Eutectic alloys of gallium such as EGaIn or GaInSn have negligible vapor pressure thus can be used in commercial micro/nano analysis instruments which require vacuum compatibility.
In a novel approach, we have constructed fully soft-component fluidic frameworks in which the self-actuation of liquid metals is induced by changing the ionic contents of their surrounding aqueous electrolytes. When the liquid metal is placed in an aqueous electrolyte environment featuring a concentration imbalance, an asymmetrical Electrical Double Layer (EDL) spontaneously forms on its surface. This surface EDL stores capacitive energy in the form of accumulated charges involving both the conductive core of the liquid metal and the electrolytes of the aqueous solution. This stored energy, in accordance with Lippmann’s equation, is then converted to mechanical energy leading to deformation and surface tangential flow.
We have fully investigated, modeled and characterized these dynamics under different aqueous electrolyte ionic imbalance conditions. We have shown several key applications of this framework such as autonomous soft switch, self propulsion and pumping ability without the need for an external source of electrical potential. We have determined the conditions leading to maximum self-propulsion velocities of a liquid metal droplet inside a fluidic channel and adjusted it by changing pH gradients as well as salt concentration imbalances.
Zavabeti, A. et al. Ionic imbalance induced self-propulsion of liquid metals. Nat. Commun. 7:12402 doi: 10.1038/ncomms12402 (2016).
12:45 PM - SM4.9.11
Facile Patterning Methods for Liquid Metal Soft Electronics
Yiliang Lin 1 , Jan Genzer 1 , Michael Dickey 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
Metals that are liquid at room temperature attract attention due to their fluidity and soft nature. To date, gallium and its alloys have been utilized for soft electronics, such as antennas, stretchable wires and reconfigurable circuits due to their low melting point and low toxicity.
In this talk, we will discuss several new methods to pattern these metals into useful structures. For example, we report a facile way to produce liquid metal nanoparticles via probe sonication. The nanoparticles could be embedded into elastomer matrices as insulating films yet can be locally mechanically sintered into conductive paths at room temperature. In this manner, arbitrary conductive patterns can be obtained by using a writing stylus. We utilize mechanically sinterable nanoparticles for soft circuit boards and pressure-stimulus antennas with frequency-shifting properties. We also report a simple fabrication method to draw conductive wires at room temperature by stretching polymer substrates with liquid metal droplets. The diameter narrows with strain as expected from geometrical principles and conservation of mass. Various geometries, including parallel, core-shell, branched and helix structures, are feasible. Furthermore, the resulting wires can be soft and stretchable or rigid, depending on the nature of the substrate. Finally, we also report a new protocol to pattern liquid metal into microfluidic channels. Compared to injection, it fills channels with a smaller density of defects in complex geometries with features as small as a few microns. Developing new patterning and fabrication technologies for liquid metal opens up new opportunities for constructing stretchable electronics, metallic microfluidic components, and conductors for soft robotics and sensors.
SM4.10: Soft Structures and Emerging Applications
Friday PM, April 21, 2017
PCC North, 100 Level, Room 121 B
2:30 PM - SM4.10.01
Soft Elastomers with Ionic Liquid-Filled Cavities as Strain Isolating Substrates for Wearable Electronics
Matt Pharr 1 , Yinji Ma 2 , Yonggang Huang 2 , John Rogers 2 Show Abstract
1 , Texas A&M University, College Station, Texas, United States, 2 , Northwestern University, Evanston, Illinois, United States
Managing the mechanical mismatch between hard semiconductor components and soft biological tissues represents a key challenge in the development of advanced forms of wearable electronic devices. An ultra-low modulus material or a liquid that surrounds the electronics and resides in a thin elastomeric shell provides a strain-isolation effect that not only enhances the wearability but also the range of stretchability in suitably designed devices. The results presented here build on these concepts by (1) replacing traditional liquids explored in the past, which have some non-negligible vapor pressure and finite permeability through the encapsulating elastomers, with ionic liquids to eliminate any possibility for leakage or evaporation, and (2) positioning the liquid between the electronics and the skin, within an enclosed, elastomeric microfluidic space, but not in direct contact with the active elements of the system, to avoid any negative consequences on electronic performance. Combined experimental and theoretical results establish the strain-isolating effects of this system, and the considerations that dictate mechanical collapse of the fluid-filled cavity. Examples in skin-mounted wearable include wireless sensors for measuring temperature and wired systems for recording mechano-acoustic responses.
2:45 PM - SM4.10.02
Strain-Dependent and Hysteretic Resistance of Stretchable Carbon Nanotube Electrodes under Cyclic Loadings
Lihua Jin 1 , Alex Chortos 2 , Christian Linder 2 , Zhenan Bao 2 , Wei Cai 2 Show Abstract
1 , University of California, Los Angeles, Los Angeles, California, United States, 2 , Stanford University, Stanford, California, United States
The increasing demands of human-machine integration require stretchable electronic devices in novel technologies, such as biomedical devices and wearable electronics. However, electronic materials, such as carbon nanotubes (CNTs), are not intrinsically stretchable. Percolating networks of CNTs offer a generic mechanism to realize stretchability of electronic materials: CNTs can reorient and slide under large strain. This morphological change of CNT networks under strain further leads to the evolution of their electrical property. To better develop stretchable CNT devices, it is important to establish the relationship of loading, morphology, and electrical property for CNT networks.
In this work, we investigate the effect of cyclic loadings on the resistance and morphology of stretchable CNT electrodes, by combining coarse grained molecular static (CGMS) simulation, experiment, and analytical modeling. Experimentally, a CNT electrode spray coated on the surface of a stretchable substrate is subject to cyclic stretching with the maximal strain sequentially increasing. The resistance of the electrode in both stretching and transverse directions increases during the loading, while it remains almost a constant during the unloading, forming a hysteresis between the loading and unloading. When the sample is reloaded, the resistance stays at the same constant value before the previous maximal strain is reached, and increases again with the strain when the loading exceeds the previous maximal strain.
To understand the strain-dependent and hysteretic resistance of stretchable CNT electrodes, we have developed a CGMS method to simulate the morphological change of CNT networks under loading and unloading cycles. Then we calculate the evolution of the resistance for different CNT configurations, by modeling a network of nanotube resistances and contact resistances. We find that during stretching, the CNTs reorient to the stretching direction. As the strain increases, the nanotubes slide between each other, and the resistance of the network increases. During the unloading, the CNTs buckle due to the compression, and the resistance of the network almost remains a constant. The evolution of the resistance obtained by the CGMS method shows quantitative agreement with the performed experimental results. This agreement allows us to successfully identify the key microstructural parameter that captures the correlation between the morphology and the electrical resistance of CNT networks. Based on this understanding, we have further developed an analytical model to describe the evolution of the resistance of CNT electrodes under arbitrary loadings. This combined approach enables us to design stretchable CNT devices with optimized properties.
3:00 PM - SM4.10.03
Highly-Stretchable 3D-Architected Mechanical Metamaterials
Qiming Wang 1 Show Abstract
1 , University Southern California, Los Angeles, California, United States
Soft materials featuring both 3D free-form architectures and high stretchability are highly desirable for a number of engineering applications ranging from cushion modulators, soft robots to stretchable electronics; however, both the manufacturing and fundamental mechanics are largely elusive. Here, we overcome the manufacturing difficulties and report a class of mechanical metamaterials that not only features 3D free-form lattice architectures but also poses ultrahigh reversible stretchability (strain>414%), 4 times higher than that of the existing counterparts with the similar complexity of 3D architectures. The microarchitected metamaterials, made of highly stretchable elastomers, are realized through an additive manufacturing technique, projection microstereolithography, and its postprocessing. With the fabricated metamaterials, we reveal their exotic mechanical behaviors: Under large-strain tension, their moduli follow a linear scaling relationship with their densities regardless of architecture types, in sharp contrast to the architecture-dependent modulus power-law of the existing engineering materials; under large-strain compression, they present tunable negative-stiffness that enables ultrahigh energy absorption efficiencies. To harness their extraordinary stretchability and microstructures, we demonstrate that the metamaterials open a number of application avenues in lightweight and flexible structure connectors, ultraefficient dampers, 3D meshed rehabilitation structures and stretchable electronics with designed 3D anisotropic conductivity.
3:15 PM - SM4.10.04
Fabric Sensory Sleeves for State Estimation of Soft Structures
Michelle Yuen 1 , John McCaw 1 , Edward White 1 , Henry Tonoyan 2 , Maria Telleria 2 , Rebecca Kramer 1 Show Abstract
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Otherlab Pneubotics, San Francisco, California, United States
Soft structures experience continuous deformations throughout their body. One approach to estimating the state of a soft structure (i.e., proprioception) is by measuring surface strains, which requires arrays of flexible and stretchable sensors. This talk will focus on the fabrication and testing of stretchable fabric sleeves embedded with elastic strain sensor arrays for state reconstruction of two soft joints: a human limb and a pneumatically-actuated soft robot manipulator. The strain sensors are stretchable parallel-plate capacitors, composed of conductive composite electrodes and a silicone elastomer dielectric. The conductive composite is made of silicone elastomer and expanded intercalated graphite (EIG), an analog of graphene. Using these two materials, the sensors are either screenprinted or directly written into the fabric sleeve, which contrasts the approach of pre-fabricating sensors and subsequently attaching them to a host. These approaches both eliminate the additional integration step of attaching the sensors to the fabric substrate and provide a very robust mechanical interface between the sensors and the fabric. We demonstrate the capabilities of the sensor-embedded fabric sleeve by determining the joint angle and end effector position of both a human limb and a soft pneumatic joint, with emphasis on the reliability of the sensors and their robustness to variations in the processing steps. Furthermore, we show that the sensory sleeve is capable of capturing more complex system states, such as surface buckling and non-constant curvatures along linkages and joints.
3:30 PM - *SM4.10.05
Molecularly Stretchable Electronics for Energy and Healthcare
Darren Lipomi 1 Show Abstract
1 , University of California, San Diego, La Jolla, California, United States
The term “plastic electronics” masks the wide range of mechanical behavior possessed by films of π-conjugated (semiconducting) small molecules and polymers. Such materials are promising for biosensors, large-area displays, low-energy lighting, and low-cost photovoltaic modules. There is also an apparent trade-off between electronic performance and mechanical compliance in films of some of the best-performing semiconducting polymers, which fracture at tensile strains not significantly greater than those at which conventional inorganic semiconductors fail. The design of intrinsically deformable electronic materials—i.e., imagine a semiconducting rubber band—would facilitate roll-to-roll production, mechanical robustness for potable applications, and conformal bonding to curved surfaces. This seminar describes my group’s efforts to understand and control the structural parameters that influence the mechanical properties of π-conjugated polymers. The techniques we employ include synthetic chemistry, spectroscopy and microstructural characterization, computation from the molecular to continuum level, and electrical measurements of devices. A complex picture emerges for the interplay between molecular structure, the way the process of solidification influences the morphology, and how molecular structure and morphology combine to produce a film with a given modulus, elastic range, ductility, and toughness. We are also exploring ways to introduce other properties into organic semiconductors that are inspired by biological tissue. That is, not just elasticity and toughness, but also biodegradability and the capacity for self-repair. The seminar will also touch on our use of self-assembled metallic nanoislands on graphene for ultra-sensitive mechanical sensing using piezoresistive and “piezoplasmonic” mechanisms. The applications for these materials are in detecting human motion and measuring the mechanics of cardiac and musculoskeletal cells. My group is broadly interested in the intersection of soft materials and human touch for virtual and augmented reality, and I will briefly mention our work in these areas.
4:30 PM - SM4.10.06
Superporous Intelligent Hydrogels for Environmentally Adaptive Building Skins
Shane Smith 1 Show Abstract
1 , University of Arizona, Tucson, Arizona, United States
This work explores responsive hydrophilic polymers for convergent functions of climate control with architectural material systems. In buildings, the transition across exterior and interior space occurs through the envelope, which is an enclosure system that mediates heat, light, air and moisture transfer functions. Conventional building envelopes are typically constructed to form a barrier that insulates and hermetically separates outdoor and indoor conditions. The dynamic environmental responses of superporous intelligent hydrogels are shown to be beneficial at the interior layer of a double-skin glazing system for building envelope applications. If the hydrogels are integral to the building envelope system, then various environmental functions (such as natural daylighting, heat transfer, airflow and moisture control) can be achieved through integrated actuators to result in improved building energy performance.
Specifically, polyacrylamide gels are fabricated by pouring the liquid phase polymer into 3D printed scaffold matrices prior to room temperature or UV gelation. The resultant superporous translucent gel is then integrated into either transparent elastomeric laser-cut fabrics or slump-formed glass modules. The composite embodiments subsequently emulate bio-analytical functions when embedded microbore-tube water channels and polyamide thermo-foils serve as actuators for swelling and deswelling kinetics respectively. Each prototype is conceived in response to hot-arid climate contexts. One prototype is a high heat capacitance daylighting and evaporative cooling system, while the second prototype is a lightweight ventilation cooling and daylighting system.
Initial prototypes are inserted into an environmental test-bed that is consequently divided into two chambers to represent an outdoor and indoor condition. The input chamber includes controllable heat and light elements that affect the dynamics of the hydrogel system. The output chamber on the opposite side of the prototype division includes temperature, humidity and photo sensors that are connected to an Arduino board for data collection. Dependent upon the environmental conditions of chamber two, a control program actuates either an electric charge to induce evaporation of moisture from the gels, or a small hydro-pump to saturate the gels with water.
The initial results provide average rates for sorption-desorption kinetics and correlations between saturation loading and visible transmittance. Future work includes integration of physical test data into building-scale energy performance simulations and hygrothermal transfer numerical analysis for building envelope compositions, as well as additional hydrogel composites for microbial sensing and semiconductor properties. The current work demonstrates a highly promising application of soft-skin membranes for much needed reductions in energy consumption within the building sector.
4:45 PM - SM4.10.07
Fully-Printed, Double-Side Integrated High-Speed Stretchable Digital Logic Circuits for Self-Computable Electronic Skin
Junghwan Byun 1 2 , Eunho Oh 1 2 , Byeongmoon Lee 1 2 , Sangwoo Kim 1 2 , Yongtaek Hong 1 2 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Inter-University Semiconductor Research Center, Seoul Korea (the Republic of)
Recently, remarkable strategies in materials, mechanics, devices, and their system-level design that can be rendered in stretchable formats have been exploited. Due to the softness and body compliance, advanced capabilities likely in intimate, noninvasive, continuous measurement of vital signals in human body and adaptable locomotion in soft machines have been introduced in the emerging fields of chronic diagnostics and soft robotics. Despite meaningful works for in vivo, in vitro measurements of various bio-, robotic-signals obtained from sensory networks integrated in a stretchable form, however, well-refined data processing and analyzing of such enormous signals are hindered without externally connected bulky wires nor low quality wireless communication process (available operating distance ~1 cm). Consequently, compared to “in-system” computation, only an indirect way of analysis that limits the system performance and user-activated feedback has been addressed.
In this work, we report fully-printed, high-speed (~1 MHz), self-computable electronic skin where dozens of tiny logic devices are highly integrated by means of double-side integration in conjunction with well-developed stretchable via technology. Scalable architectures of embedded printed rigid islands provide optimized stress-free areas in both sides (top, bottom) of the soft, engineered substrate simultaneously; thereby safely preventing active logic devices from unpredictable skin-like deformation. Magnetically self-assembled Ni/silicone core-shell structures that can be site-selectively formed by a drop-on-demand printing process function as stretchable, mechanically robust vias; stably linking the both sides of electronic circuits together with inkjet-printed stretchable Ag interconnects. Based on the prestrain-induced gradual strain-absorbing design, inkjet-printed stretchable Ag interconnects fulfills a sufficient level of conductivity (~9 x 104 S/cm), stretchability (~50%), cyclic property (> 1000) to stably operate the large-area logic circuits. As a fundamental building block of digital computer, 4-bit parallel-in-series-out shift register (10 NAND gates, 4 D flip flops) and BCD to 7-segment programmable logic array (PLA) (32 logic gates) are demonstrated in a double-side printed form, providing evidence for potential self-computable stretchable systems.
This work was supported by the Center for Advanced Soft-Electronics funded by the Ministry of Science, ICT and Future Planning as Global Frontier Project (CASE-2015M3A6A5065309), and the Brain Korea 21 Plus Project in 2017.
5:00 PM - SM4.10.08
Metamorphic Stretchable Electronics
Shantonu Biswas 1 , Andreas Schoeberl 1 , Mahsa Mozafari 1 , Joerg Pezoldt 1 , Thomas Stauden 1 , Heiko Jacobs 1 Show Abstract
1 , Technical University Ilmenau, Ilmenau Germany
We report a novel method to produce stretchable printed circuit boards that is compatible with standard industrial manufacturing processes. Different from most reports the approach delays the use of the stretchable rubber support to the end of the processing sequence. Specifically, the entire circuit containing interconnects, unpackaged chips or chip-scale packaged surface mount devices (SMDs) are fabricated on a hard carrier. This facilitates high temperature processing, automated mounting, and precision alignment. Moreover, it enables “on-hard” carrier functionality tests, which are critical to determine correct functionality and a comparison of the performance metrics after the circuit is released. Application of the rubber support, release, and stretchability tests are last.
As an application, the concept of metamorphic electronics is demonstrated. Our demonstrators are inflatable electronic structures and contain arrays with packaged SMDs and bare dies integrating light emitting diodes (LEDs) and transistors within a rubber matrix. As a third application a stretchable metamorphic microphones array has been presented for the first time. The test structures morph from planar, to spherical, to cone like topologies.
5:15 PM - SM4.10.09
Heat and pH Activated Fibrillar Adhesives
Hosain Bagheri 1 , Subbarao Raikar 1 , Douglas Elson 1 , Qing Wang 1 , Alex Gendt 1 , Ivana Ninkovic 1 , Ximin He 1 , Hamid Marvi 1 Show Abstract
1 , Arizona State University, Tempe, Arizona, United States
Switchable adhesives have been developed for applications that require varying states of adhesive strength. This research has explored a novel effective adhesion switching approach, using a stimuli-responsive hydrogel as an active component to reconfigure the embedded fibrillar structures and thus, rapidly and precisely control their adhesion states. In particular, changing the pH and/or temperature of the hydrogel causes the material to bend/unbend the fibers and switch adhesion off/on. Projection lithography is utilized to fabricate polymeric fibers embedded in a hydrogel with carefully designed effective stiffness of the fibers. The adhesive strength of the fibrillar structure is characterized by measuring the normal pull-off force exerted by the fibers onto an indenter. The switching ratio is then determined by dividing the pull-off force of the “on” state by that of the “off” state. The switching ratio can be used to determine if the material may perform as an effective switchable adhesive. Such adhesives can be used for different industrial and space applications such as pick and place or robotic locomotion.
5:30 PM - SM4.10.10
Highly Stretchable, Twisted, Conductive Tubules for Robotics, Electronics, and Healthcare Applications
Thanh Nho Do 1 , Yon Visell 1 Show Abstract
1 , California NanoSystems Institute, Goleta, California, United States
Stretchable and flexible multifunctional electronic components, including sensors and actuators, have received increasing attention in robotics, electronics, wearable, and healthcare applications. Despite advances, it has remained challenging to design analogs of electronic components to be highly stretchable, to be efficient to fabricate, and to provide control over electronic performance. Here, we describe highly stretchable sensors and interconnects formed from thin, twisted conductive tubules. These devices consist of liquid metal alloy conductor (eutectic gallium indium, eGaIn), which we inject into fine, hollow core, highly stretchable (>400%) elastomer filaments. The filaments are fabricated using a simple roller coating process. Through a twisting and pretensioning procedure, we demonstrate that it is possible to control the mechanical performance and electronic sensitivity of these devices. In experiments, we have evaluated the mechanical and electronic capabilities of these devices, and have prototyped their applications for the design of stretchable electronics and wearable sensing applications. These twisted conductive tubules provide a novel, low cost solution for high performance stretchable electronic with broad potential applications to emerging products of high economic and societal significance.
5:45 PM - SM4.10.11
Soft Electronics with Hard Performance: Morphology and Geometry Engineering of In-Plane Crystalline Silicon Nanowires for Highly Stretchable Electronics
Linwei Yu 1 2 , Zhaoguo Xue 1 , Yaolong Zhao 1 , Junzhuan Wang 1 , Jun Xu 1 , Kunji Chen 1 , Pere Roca i Cabarrocas 2
1 , Nanjing University, Nanjing China, 2 , LPICM, Ecole Polyt