System Integration of Flexible and Multifunctional Thin Film Sensors for Structural Health Monitoring

Greater information is needed on the state of civil infrastructure to ensure public safety and cost-efficient management. Lack of infrastructure investment and foreseeable funding challenges mandate a more intelligent approach to future maintenance of infrastructure systems. Much of the technology currently utilized to assess structural performance is based on discrete sensors. While such sensors can provide valuable data, they can lack sufficient resolution to accurately identify damage through inverse methods. Alternatively, technologies have shown promise for distributed, direct damage detection with flexible thin film and multifunctional polymer-nanocomposite materials. However, challenges remain as significant past work has focused on material optimization as opposed to sensing systems for damage detection. This dissertation offers novel methods for direct and distributed strain sensing by providing a fabrication methodology for broadly enabling thin film sensing technologies in structural health monitoring (SHM) applications. This fabrication methodology is presented initially as a set of materials and processes which are illustrated in analog circuit primitive forms including flexible, thin film capacitors, resistors, and inductors. Three sensing systems addressing specific SHM challenges are developed from this base of components and processes as specific illustrations of the broader fabrication approach. The first system developed is a fully integrated strain sensing system designed to enable the use of multifunctional materials in sensing applications. This is achieved through the development of an optimized fabrication approach applicable to many multifunctional materials. A layer-by-layer (LbL) deposited nanocomposite is incorporated with a lithography process to produce a sensing system. To illustrate the process, a strain sensing platform consisting of a nanocomposite film within an amplified Wheatstone bridge circuit is presented. The study reveals the material process is highly repeatable to produce fully integrated strain sensors with high linearity and sensitivity. The thin film strain sensors are robust and are capable of high strain measurements beyond 3,000 μϵ. The second system developed is an array of resistive distributed strain sensors and an associated algorithm to provide an alternative to electrical impedance tomography for spatial strain sensing. An LbL deposited polymer composite thin film is utilized as the piezoresistive sensing material. An inverse algorithm is presented and utilized for determining the resistance of array elements by electrically stimulating boundary nodes. Two polymer nanocomposite arrays are strain tested under cyclic loading. Both arrays functioned as networks of strain sensors confirming the viability of the approach and computational benefits for SHM. The third system developed is a thin film wireless threshold strain sensor for measuring strain in implanted and embedded applications. The wireless sensing system is comprised of two thin film, inductor-capacitor circuits, one of which included a fuse element. The sensor is fabricated on polyimide with metal layers used to pattern inductive antennas and a strain sensitive parallel plate capacitor. A titanium thin film fuse is designed to fail, or have a large resistance increase, when a strain threshold is exceeded. Three prototype systems are interrogated wirelessly while under increasing tensile strain. One of two sensor resonant peaks disappear at a strain threshold as designed, validating the sensing approach and thin film form for use in SHM systems. The fuse approach provides a platform for various systems and sensing elements. The reference peak remains intact and is used for continuous real-time strain sensing with a sensitivity of 0.5 and a noise floor below 50 microstrain.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144183/1/arburt_1.pd

Fabrication of Flexible Hybrid Circuits in Parylene

In recent years, with the increasing research interest in personalized medicine, new and disruptive technologies such as the Internet of Things (IoT) and flexible wearable electronics have emerged and have become trending topics in the scientific community. Despite consistent progress in the area of fully flexible electronics, these continue to reveal some restrictions, which can be overcome by traditional silicon integrated circuits (ICs). The combination between these technologies generated the new concept of flexible hybrid electronics (FHE) igniting a new generation of wearable health monitoring systems. This thesis reports a new way to the use parylene C as substrate, dielectric and encap- sulation layers to accommodate silicon ICs, surface mounted devices (SMDs) and thin metal layers, in order to create flexible and conformable double layered hybrid sensing membranes for body temperature monitoring, one of the most relevant physiological pa- rameters upon a medical diagnosis, since it’s among the main indicators for inflammation and infection. To achieve the thin metal and parylene C layers, thin-film microfabrica- tion techniques were employed and corroborated by superficial, electrical and structural characterization techniques. In addition the establishment of an electrical connection by the integration of silicon ICs and SMDs onto the thin metal layer was successfully tested using a low-temperature solder paste and a reflow oven, which reproduced a previously inputted time-temperature profile. Furthermore, this thesis analyses the repercussions of this integration procedure on the peel off process. Throughout this work, commercial body temperature measuring circuits were used as inspiration for the temperature sensing circuits developed. The interface between the produced membranes and their respective microcontrollers was also tested, although no temperature measurements were obtained due to parylene’s performance as a dielectric. The successful production of a fully functional flexible and conformable double layered hybrid sensing membrane could propel the adaptation of other rigid health monitoring electronics to FHE membranes, further engraving this technology into people’s daily lives.Com o crescente interesse na pesquisa em medicina personalizada, novas tecnologias como a Internet of Things (IoT) e a eletrónica flexível, surgiram e tornaram-se tópicos de tendência na comunidade científica. Apesar dos progressos na área da eletrónica totalmente flexível, continuam a existir algumas restrições, que podem ser superadas pelos circuitos integrados de silício (ICs) tradicionais. A junção entre estas tecnologias gerou um novo conceito de eletrónica híbrida flexível (FHE) dando início a uma nova geração de sistemas de monitorização de saúde. Esta tese aborda uma forma inovadora de usar parileno C como substrato, dielétrico e camada de encapsulamento para acomodar ICs de silício, surface mounted devices (SMDs) e camadas metálicas finas, a fim de criar circuitos em membranas híbridas de dupla camada flexíveis e conformáveis para monitorização da temperatura corporal, um dos parâmetros fisiológicos com maior relevância aquando do diagnóstico, uma vez que é um dos principais indicadores de infeções e inflamações. Para obter as camadas finas de metal e parileno C, foram empregues técnicas de microfabricação de filmes finos, corroboradas por caracterizações superficiais, elétricas e estruturais. Utilizando uma pasta de solda de baixa temperatura e um forno de refluxo, reproduzindo um perfil de tempo-temperatura, foi desenvolvido um protocolo para a conexão e integração de ICs na fina camada de metal. São ainda apresentados resultados relativos às implicações deste processo no método do peel off. Os circuitos desenvolvidos durante esta tese tiveram por base circuitos comerciais que medem a temperamtura corporal. Apesar da interface entre as membranas produzidas e os seus respetivos microcontroladores ter sido testada, não foi possível medir a temperatura com os circuitos desenvolvidos devido à performance do parileno como dielétrico. A produção bem-sucedida de uma membrana híbrida de dupla camada, flexível e conformável, totalmente funcional pode impulsionar a adaptação de outros equipamentos rígidos de monitorização de saúde para membranas híbridas flexíveis, inserindo ainda mais esta tecnologia na vida quotidiana

WiForceSticker: Batteryless, Thin Sticker-like Flexible Force Sensor

Any two objects in contact with each other exert a force that could be simply due to gravity or mechanical contact, such as a robotic arm gripping an object or even the contact between two bones at our knee joints. The ability to naturally measure and monitor these contact forces allows a plethora of applications from warehouse management (detect faulty packages based on weights) to robotics (making a robotic arms' grip as sensitive as human skin) and healthcare (knee-implants). It is challenging to design a ubiquitous force sensor that can be used naturally for all these applications. First, the sensor should be small enough to fit in narrow spaces. Next, we don't want to lay cumbersome cables to read the force values from the sensors. Finally, we need to have a battery-free design to meet the in-vivo applications. We develop WiForceSticker, a wireless, battery-free, sticker-like force sensor that can be ubiquitously deployed on any surface, such as all warehouse packages, robotic arms, and knee joints. WiForceSticker first designs a tiny $4$~mm~$\times$~$2$~mm~$\times$~$0.4$~mm capacitative sensor design equipped with a $10$~mm~$\times$~$10$~mm antenna designed on a flexible PCB substrate. Secondly, it introduces a new mechanism to transduce the force information on ambient RF radiations that can be read by a remotely located reader wirelessly without requiring any battery or active components at the force sensor, by interfacing the sensors with COTS RFID systems. The sensor can detect forces in the range of $0$-$6$~N with sensing accuracy of $<0.5$~N across multiple testing environments and evaluated with over $10,000$ varying force level presses on the sensor. We also showcase two application case studies with our designed sensors, weighing warehouse packages and sensing forces applied by bone joints

Design, characterization and validation of integrated bioelectronics for cellular studies: from inkjet-printed sensors to organic actuators

Mención Internacional en el título de doctorAdvances in bioinspired and biomimetic electronics have enabled coupling engineering devices to biological systems with unprecedented integration levels. Major efforts, however, have been devoted to interface malleable electronic devices externally to the organs and tissues. A promising alternative is embedding electronics into living tissues/organs or, turning the concept inside out, lading electronic devices with soft living matters which may accomplish remote monitoring and control of tissue’s functions from within. This endeavor may unleash the ability to engineer “living electronics” for regenerative medicine and biomedical applications. In this context, it remains a challenge to insert electronic devices efficiently with living cells in a way that there are minimal adverse reactions in the biological host while the electronics maintaining the engineered functionalities. In addition, investigating in real-time and with minimal invasion the long-term responses of biological systems that are brought in contact with such bioelectronic devices is desirable. In this work we introduce the development (design, fabrication and characterization) and validation of sensors and actuators mechanically soft and compliant to cells able to properly operate embedded into a cell culture environment, specifically of a cell line of human epithelial keratinocytes. For the development of the sensors we propose moving from conventional microtechnology approaches to techniques compatible with bioprinting in a way to support the eventual fabrication of tissues and electronic sensors in a single hybrid plataform simultaneously. For the actuators we explore the use of electroactive, organic, printing-compatible polymers to induce cellular responses as a drug-free alternative to the classic chemical route in a way to gain eventual control of biological behaviors electronically. In particular, the presented work introduces inkjet-printed interdigitated electrodes to monitor label-freely and non-invasively cellular migration, proliferation and cell-sensor adhesions of epidermal cells (HaCaT cells) using impedance spectroscopy and the effects of (dynamic) mechanical stimulation on proliferation, migration and morphology of keratinocytes by varying the magnitude, frequency and duration of mechanical stimuli exploiting the developed biocompatible actuator. The results of this thesis contribute to the envision of three-dimensional laboratory-growth tissues with built-in electronics, paving exciting avenues towards the idea of living smart cyborg-skin substitutes.En los útimos años los avances en el desarrollo de dispositivos electrónicos diseñados imitando las propiedades de sistemas vivos han logrado acoplar sistemas electrónicos y órganos/tejidos biológicos con un nivel de integración sin precedentes. Convencionalmente, la forma en que estos sistemas bioelectrónicos son integrados con órganos o tejidos ha sido a través del contacto superficial entre ambos sistemas, es decir acoplando la electrónica externamente al tejido. Lamentablemente estas aproximaciones no contemplan escenarios donde ha habido una pérdida o daño del tejido con el cual interactuar, como es el caso de daños en la piel debido a quemaduras, úlceras u otras lesiones genéticas o producidas. Una alternativa prometedora para ingeniería de tejidos y medicina regenerativa, y en particular para implantes de piel, es embeber la electrónica dentro del tejido, o presentado de otra manera, cargar el sistema electrónico con células vivas y tejidos fabricados por ingeniería de tejidos como parte innata del propio dispositivo. Este concepto permitiría no solo una monitorización remota y un control basado en señalizaciones eléctricas (sin químicos) de tejidos biológicos fabricados mediante técnicas de bioingeniería desde dentro del propio tejido, sino también la fabricación de una “electrónica viva”, biológica y eléctricamente funcional. En este contexto, es un desafío insertar de manera eficiente dispositivos electrónicos con células vivas sin desencadenar reacciones adversas en el sistema biológico receptor ni en el sistema electrónico diseñado. Además, es deseable monitorizar en tiempo real y de manera mínimamente invasiva las respuestas de dichos sistemas biológicos que se han añadido a tales dispositivos bioelectrónicos. En este trabajo presentamos el desarrollo (diseño, fabricación y caracterización) y validación de sensores y actuadores mecánicamente suaves y compatibles con células capaces de funcionar correctamente dentro de un entorno de cultivo celular, específicamente de una línea celular de células epiteliales humanas. Para el desarrollo de los sensores hemos propuesto utilizar técnicas compatibles con la bioimpresión, alejándonos de la micro fabricación tradicionalmente usada para la manufactura de sensores electrónicos, con el objetivo a largo plazo de promover la fabricación de los tejidos y los sensores electrónicos simultáneamente en un mismo sistema de impresión híbrido. Para el desarrollo de los actuadores hemos explorado el uso de polímeros electroactivos y compatibles con impresión y hemos investigado el efecto de estímulos mecánicos dinámicos en respuestas celulares con el objetivo a largo plazo de autoinducir comportamientos biológicos controlados de forma electrónica. En concreto, este trabajo presenta sensores basados en electrodos interdigitados impresos por inyección de tinta para monitorear la migración celular, proliferación y adhesiones célula-sustrato de una línea celular de células epiteliales humanas (HaCaT) en tiempo real y de manera no invasiva mediante espectroscopía de impedancia. Por otro lado, este trabajo presenta actuadores biocompatibles basados en el polímero piezoeléctrico fluoruro de poli vinilideno y ha investigado los efectos de estimular mecánicamente células epiteliales en relación con la proliferación, migración y morfología celular mediante variaciones dinámicas de la magnitud, frecuencia y duración de estímulos mecánicos explotando el actuador biocompatible propuesto. Ambos sistemas presentados como resultado de esta tesis doctoral contribuyen al desarrollo de tejidos 3D con electrónica incorporada, promoviendo una investigación hacia la fabricación de sustitutos equivalentes de piel mitad orgánica mitad electrónica como tejidos funcionales biónicos inteligentes.The main works presented in this thesis have been conducted in the facilities of the Universidad Carlos III de Madrid with support from the program Formación del Profesorado Universitario FPU015/06208 granted by Spanish Ministry of Education, Culture and Sports. Some of the work has been also developed in the facilities of the Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (IZM) and University of Applied Sciences (HTW) in Berlin, under the supervision of Prof. Dr. Ing. H-D. Ngo during a research visit funded by the Mobility Fellows Program by the Spanish Ministry of Education, Culture, and Sports. This work has been developed in the framework of the projects BIOPIELTEC-CM (P2018/BAA-4480), funded by Comunidad de Madrid, and PARAQUA (TEC2017-86271-R) funded by Ministerio de Ciencia e Innovación.Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidente: José Antonio García Souto.- Secretario: Carlos Elvira Pujalte.- Vocal: María Dimak

From wearable towards epidermal computing : soft wearable devices for rich interaction on the skin

Human skin provides a large, always available, and easy to access real-estate for interaction. Recent advances in new materials, electronics, and human-computer interaction have led to the emergence of electronic devices that reside directly on the user's skin. These conformal devices, referred to as Epidermal Devices, have mechanical properties compatible with human skin: they are very thin, often thinner than human hair; they elastically deform when the body is moving, and stretch with the user's skin. Firstly, this thesis provides a conceptual understanding of Epidermal Devices in the HCI literature. We compare and contrast them with other technical approaches that enable novel on-skin interactions. Then, through a multi-disciplinary analysis of Epidermal Devices, we identify the design goals and challenges that need to be addressed for advancing this emerging research area in HCI. Following this, our fundamental empirical research investigated how epidermal devices of different rigidity levels affect passive and active tactile perception. Generally, a correlation was found between the device rigidity and tactile sensitivity thresholds as well as roughness discrimination ability. Based on these findings, we derive design recommendations for realizing epidermal devices. Secondly, this thesis contributes novel Epidermal Devices that enable rich on-body interaction. SkinMarks contributes to the fabrication and design of novel Epidermal Devices that are highly skin-conformal and enable touch, squeeze, and bend sensing with co-located visual output. These devices can be deployed on highly challenging body locations, enabling novel interaction techniques and expanding the design space of on-body interaction. Multi-Touch Skin enables high-resolution multi-touch input on the body. We present the first non-rectangular and high-resolution multi-touch sensor overlays for use on skin and introduce a design tool that generates such sensors in custom shapes and sizes. Empirical results from two technical evaluations confirm that the sensor achieves a high signal-to-noise ratio on the body under various grounding conditions and has a high spatial accuracy even when subjected to strong deformations. Thirdly, Epidermal Devices are in contact with the skin, they offer opportunities for sensing rich physiological signals from the body. To leverage this unique property, this thesis presents rapid fabrication and computational design techniques for realizing Multi-Modal Epidermal Devices that can measure multiple physiological signals from the human body. Devices fabricated through these techniques can measure ECG (Electrocardiogram), EMG (Electromyogram), and EDA (Electro-Dermal Activity). We also contribute a computational design and optimization method based on underlying human anatomical models to create optimized device designs that provide an optimal trade-off between physiological signal acquisition capability and device size. The graphical tool allows for easily specifying design preferences and to visually analyze the generated designs in real-time, enabling designer-in-the-loop optimization. Experimental results show high quantitative agreement between the prediction of the optimizer and experimentally collected physiological data. Finally, taking a multi-disciplinary perspective, we outline the roadmap for future research in this area by highlighting the next important steps, opportunities, and challenges. Taken together, this thesis contributes towards a holistic understanding of Epidermal Devices}: it provides an empirical and conceptual understanding as well as technical insights through contributions in DIY (Do-It-Yourself), rapid fabrication, and computational design techniques.Die menschliche Haut bietet eine große, stets verfügbare und leicht zugängliche Fläche für Interaktion. Jüngste Fortschritte in den Bereichen Materialwissenschaft, Elektronik und Mensch-Computer-Interaktion (Human-Computer-Interaction, HCI) [so that you can later use the Englisch abbreviation] haben zur Entwicklung elektronischer Geräte geführt, die sich direkt auf der Haut des Benutzers befinden. Diese sogenannten Epidermisgeräte haben mechanische Eigenschaften, die mit der menschlichen Haut kompatibel sind: Sie sind sehr dünn, oft dünner als ein menschliches Haar; sie verformen sich elastisch, wenn sich der Körper bewegt, und dehnen sich mit der Haut des Benutzers. Diese Thesis bietet, erstens, ein konzeptionelles Verständnis von Epidermisgeräten in der HCI-Literatur. Wir vergleichen sie mit anderen technischen Ansätzen, die neuartige Interaktionen auf der Haut ermöglichen. Dann identifizieren wir durch eine multidisziplinäre Analyse von Epidermisgeräten die Designziele und Herausforderungen, die angegangen werden müssen, um diesen aufstrebenden Forschungsbereich voranzubringen. Im Anschluss daran untersuchten wir in unserer empirischen Grundlagenforschung, wie epidermale Geräte unterschiedlicher Steifigkeit die passive und aktive taktile Wahrnehmung beeinflussen. Im Allgemeinen wurde eine Korrelation zwischen der Steifigkeit des Geräts und den taktilen Empfindlichkeitsschwellen sowie der Fähigkeit zur Rauheitsunterscheidung festgestellt. Basierend auf diesen Ergebnissen leiten wir Designempfehlungen für die Realisierung epidermaler Geräte ab. Zweitens trägt diese Thesis zu neuartigen Epidermisgeräten bei, die eine reichhaltige Interaktion am Körper ermöglichen. SkinMarks trägt zur Herstellung und zum Design neuartiger Epidermisgeräte bei, die hochgradig an die Haut angepasst sind und Berührungs-, Quetsch- und Biegesensoren mit gleichzeitiger visueller Ausgabe ermöglichen. Diese Geräte können an sehr schwierigen Körperstellen eingesetzt werden, ermöglichen neuartige Interaktionstechniken und erweitern den Designraum für die Interaktion am Körper. Multi-Touch Skin ermöglicht hochauflösende Multi-Touch-Eingaben am Körper. Wir präsentieren die ersten nicht-rechteckigen und hochauflösenden Multi-Touch-Sensor-Overlays zur Verwendung auf der Haut und stellen ein Design-Tool vor, das solche Sensoren in benutzerdefinierten Formen und Größen erzeugt. Empirische Ergebnisse aus zwei technischen Evaluierungen bestätigen, dass der Sensor auf dem Körper unter verschiedenen Bedingungen ein hohes Signal-Rausch-Verhältnis erreicht und eine hohe räumliche Auflösung aufweist, selbst wenn er starken Verformungen ausgesetzt ist. Drittens, da Epidermisgeräte in Kontakt mit der Haut stehen, bieten sie die Möglichkeit, reichhaltige physiologische Signale des Körpers zu erfassen. Um diese einzigartige Eigenschaft zu nutzen, werden in dieser Arbeit Techniken zur schnellen Herstellung und zum computergestützten Design von multimodalen Epidermisgeräten vorgestellt, die mehrere physiologische Signale des menschlichen Körpers messen können. Die mit diesen Techniken hergestellten Geräte können EKG (Elektrokardiogramm), EMG (Elektromyogramm) und EDA (elektrodermale Aktivität) messen. Darüber hinaus stellen wir eine computergestützte Design- und Optimierungsmethode vor, die auf den zugrunde liegenden anatomischen Modellen des Menschen basiert, um optimierte Gerätedesigns zu erstellen. Diese Designs bieten einen optimalen Kompromiss zwischen der Fähigkeit zur Erfassung physiologischer Signale und der Größe des Geräts. Das grafische Tool ermöglicht die einfache Festlegung von Designpräferenzen und die visuelle Analyse der generierten Designs in Echtzeit, was eine Optimierung durch den Designer im laufenden Betrieb ermöglicht. Experimentelle Ergebnisse zeigen eine hohe quantitative Übereinstimmung zwischen den Vorhersagen des Optimierers und den experimentell erfassten physiologischen Daten. Schließlich skizzieren wir aus einer multidisziplinären Perspektive einen Fahrplan für zukünftige Forschung in diesem Bereich, indem wir die nächsten wichtigen Schritte, Möglichkeiten und Herausforderungen hervorheben. Insgesamt trägt diese Arbeit zu einem ganzheitlichen Verständnis von Epidermisgeräten bei: Sie liefert ein empirisches und konzeptionelles Verständnis sowie technische Einblicke durch Beiträge zu DIY (Do-It-Yourself), schneller Fertigung und computergestützten Entwurfstechniken

Mechanical Design and Analysis: High-Precision Microcontact Printhead for Roll-to-Roll Printing of Flexible Electronics

Flexible electronics have demonstrated potential in a wide range of applications including wearable sensors, photovoltaics, medical devices and more, due to their properties of extreme adaptability while also being lightweight and highly robust. The main challenge standing in the way of progress in this field is the difficulty of large-scale manufacturing of these flexible electronics compared to their rigid counterparts. Microcontact printing is a form of soft lithography in which an elastomeric stamp is used to transfer sub-micron scale surface patterns onto a flexible substrate via ink monolayers. The integration of microcontact printing into a roll-to-roll (R2R) system will enable continuous printing of flexible electronics and scale it up for massive manufacturing. The proposed thesis outlines a novel mechanical design for a microcontact printer which utilizes flexural motion stages with integrated position and force sensors to control the print process on a R2R system. The printhead is designed to fit the available space on the pre-installed UMass Amherst Intelligent Sensing Laboratory test table and breadboard. The R2R system includes motorized rollers for winding/unwinding the PET (polyethylene terephthalate) web substrate, and idler rollers for guiding a web through the print system. As the central element to this design, two matching plate flexures are designed on the two ends of the printer roller to control the tilting and positioning of the print roller. Flexure mechanisms rely on bending and torsion of flexible elements: this allows them to achieve much higher precision in positioning compared to conventional mechanisms which rely on surface interaction between multiple moving parts. The print resolution target for this design is 500 nm (linewidth), based on current state-of-the-art designs [1, 2]. In the initial version of the printhead design, a total of 33 parts are custom fabricated for assembly and installation in the R2R system lab setup. These include everything from the components of the print roller, specially adapted air-bearing mounts, support structures, and connectors. The design and 4 fabrication process for every component is outlined here along with the functionality, as every component was designed with the system objectives and constraints in mind. Using SolidWorks simulation, FEA (finite element analysis) is performed for every part of the assembly that is subjected to stress in the real system, so that predictions can be made about the displacement of the motion stages and the frequency of vibration. These predictions are evaluated by comparation with the experimental results from tests conducted on the real system hardware and used to assess the quality of the fabricated assembly. The work performed in this thesis enables advancements in the assembly of an updated, optimized R2R system and has led to an experimentally functioning lab setup that is ripe for further improvements. Completion and calibration of this augmented R2R system will, in future, enable UMass Amherst in-house production of large-area flexible electronics which may be used in a wide range of applications, including medical sensors, solar cells, displays, and more. In addition to microcontact printing, this R2R system may also be applied to nanoimprint lithography, another contact-based print method, or integrated with inkjet printing, a non-contact method

Conformable transistors for bioelectronics

The diversity of network disruptions that occur in patients with neuropsychiatric disorders creates a strong demand for personalized medicine. Such approaches often take the form of implantable bioelectronic devices that are capable of monitoring pathophysiological activity for identifying biomarkers to allow for local and responsive delivery of intervention. They are also required to transmit this data outside of the body for evaluation of the treatment’s efficacy. However, the ability to perform these demanding electronic functions in the complex physiological environment with minimum disruption to the biological tissue remains a big challenge. An optimal fully implantable bioelectronic device would require each component from the front-end to the data transmission to be conformable and biocompatible. For this reason, organic material-based conformable electronics are ideal candidates for components of bioelectronic circuits due to their inherent flexibility, and soft nature. In this work, first an organic mixed-conducting particulate composite material (MCP) able to form functional electronic components and non-invasively acquire high–spatiotemporal resolution electrophysiological signals by directly interfacing human skin is presented. Secondly, we introduce organic electrochemical internal ion-gated transistors (IGTs) as a high-density, high-amplification sensing component as well as a low leakage, high-speed processing unit. Finally, a novel wireless, battery-free strategy for electrophysiological signal acquisition, processing, and transmission that employs IGTs and an ionic communication circuit (IC) is introduced. We show that the wirelessly-powered IGTs are able to acquire and modulate neurophysiological data in-vivo and transmit them transdermally, eliminating the need for any hard Si-based electronics in the implant

Flexible stretchable electronics for sport and wellbeing applications

Wearable electronics are becoming increasingly widespread in modern society. Though these devices are intended to be worn, integrated into clothing and other everyday objects, the technologies and processes used to manufacture them is no different than those that manufacture laptops and mobile phones. Many of these devices are intended to monitor the user’s health, activity and general wellbeing, within clinical, recreational and assistive environments. Consequently, the inherent incompatibility of these rigid devices with the soft, elastic structure of the human body can in some cases can be uncomfortable and inconvenient for everyday life. For devices to take the step from a ‘wearable’ to an ‘invisible’, a drastic rethinking of electronics manufacturing is required.The fundamental aim of this research is to establish parameters of usefulness and an array of materials with complimentary processes that would assist in transitioning devices to long term almost invisible items that can assist in improving the health of the wearer. In order to approach this problem, a novel architecture was devised that utilised PDMS as a substrate and microfluid channels of Galinstan liquid alloy for interconnects. CO2 laser machining was investigated as a means of creating channels and vias on PDMS substrates. Trace speeds and laser power outputs were investigated in order to find an optimal combination. The results displayed upper limits for power densities; where surpassing this limit resulted in poor repeatability and surface finish. It was found that there was an optimal set of trace speeds that ranged from approximately 120mm/s to 190mm/s that resulted in the most reliable and repeatable performance. Due to the complex nature of a materials variable energy absorption properties, it is not possible to quantify a single optimal parameter set.To understand the performance of these devices in situ, finite element analysis was employed to model deformations that such a device could experience. The aims here were to investigate the bond strength required to prevent delamination, between the silicon-PDMS and PDMS-PDMS bonds, in addition to the stress applied to the silicone die during these deformations. Based upon the applied loads the required bond strengths would need to be at least ~65kPa to maintain PDMS-PDMS adhesion during these tests, while stress on the silicone-PDMS adhesion required an expected v higher ~160kPa, both of which are within the reach of existing bonding techniques that are capable of withstanding a pressure of ~600kPa before failure occurs. Stress on the silicon die did not exceed ~7.8 MPa during simulation, which is well below the fracture stress.By developing knowledge about how various components of such a system will respond during use and under stress, it allows future engineers to make informed design decisions and develop better more resilient products.</div