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The next generation of biomedical tools requires reshapeable electronics to closely interface with biological tissues. This will offer unique mechanical properties and the ability to conform to irregular geometries while being robust and lightweight. Such devices can be achieved with soft materials and thin-film structures that are able to reshape on demand. However, reshaping at the submillimeter scale remains a challenging task. Herein, shape-controlled microscale devices are demonstrated that integrate electronic sensors and electroactive polymer actuators. The fast and biocompatible actuators are capable of actively reshaping the device into flat or curved geometries. The curvature and position of the devices are monitored with strain or magnetic sensors. The sensor signals are used in a closed feedback loop to control the actuators. The devices are wafer-scale microfabricated resulting in multiple functional units capable of grasping, holding, and releasing biological tissues, as demonstrated with a neuronal bundle.

Les polymères ferroélectriques et plus récemment les matériaux électrostrictifs ont attiré l’attention de la communauté scientifique en raison de leur capacité de conversion d’une excitation électrique en une réponse mécanique et vice versa. La synergie entre les propriétés électro actives de ces polymères et leurs propriétés physico-chimiques intrinsèques (souplesse, légèreté, grande résistance mécanique, facilité de mise en œuvre etc.) en font des candidats de choix pour des applications de types capteurs et actionneurs souples. Cette thèse vise à déterminer de façon systématique le comportement électromécanique des terpolymères P (fluorure de vinylidène-trifluoréthylène-chlorotrifluoroéthylène) [P (VDF-TrFE-CTFE)] par des techniques de cristallisation et de technologies additives et entend étendre ces terpolymères à l'application des dispositifs de type capteur de force électromécanique. L'influence du traitement thermique sur la réponse électromécanique et la microstructure des terpolymères a d'abord été étudiée. Il a été mis en évidence que la déformation électrostrictive transversale S31 pour chaque terpolymère traité thermiquement suit une loi quadratique avec le champ électrique. Par ailleurs il a été démontré que la déflexion d’un actionneur unimorphe est maximisée pour une fraction de phase cristalline de 39,3%. La dynamique moléculaire des terpolymères cristallisés a également été étudiée par spectroscopie diélectrique à large bande. Une dynamique segmentaire contrainte a été observée dans le terpolymère contenant la fraction cristalline la plus élevée pour laquelle une distribution étroite du temps de relaxation a été mise en évidence. En outre, il a été démontré que l’ajout d’agent plastifiant permet d’augmenter de manière significative la réponse électromécanique des terpolymères fluorés, ouvrant la voie vers de nouveaux matériaux électrostrictifs hautes performances fonctionnant sous faible champ électrique. De plus, la réponse diélectrique et électromécanique accrue du terpolymère dopé a été étudiée par microscope à force atomique et spectroscopie diélectrique dynamique. Ces analyses ont permis de lier l’augmentation de la réponse électromécanique de ces mélanges à un effet de polarisation interfaciale intensifié lors de l’augmentation de mobilité moléculaire de la phase amorphe rigide de ces terpolymères fluorés. Enfin, des dispositifs électromécaniques basés sur le polymère ferroélectrique P (VDF-TrFE) et le terpolymère électrostrictif P (VDF-TrFE-CTFE) ont été élaborés. Un procédé de fabrication additive utilisant la technologie d'impression jet d'encre a permis de concevoir et valider la faisabilité de réalisation de capteurs de force dynamique. Il a alors été démontré que les propriétés pseudo-piézoélectriques du terpolymère électrostrictif sont équivalentes à celles du copolymère ferroélectrique pour un faible champ électrique de biais de 7,5 V /μ / Electromechanical coupling effect has been paid the increasing attention due to ability to realize conversion between electric excitation and mechanical response and vice versa. Thanks to their flexibility, light weight, relatively low mechanical strength, ease of processability into large-area films, and ability to be molded into desirable geometric dimensions, polymers materials which possess an electromechanical coupling effect have been emerging recently. This thesis aims to systematically determine the electromechanical behavior of the P(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] terpolymers via crystallization and additive technology approaches and intend to extend such terpolymers to the electromechanical force sensor devices application. The influence of the thermal processing on the electromechanical response and microstructure of the terpolymers were firstly investigated. Cantilever unimorph bending measurement found the tip displacement δ and transverse strain S_31 for each thermally treated terpolymer followed a quadratic correlation with the electric field. δ was maximized at a 39.3% crystal content, instead of S_31 peaking at lowest crystal content, showing an exponential decay against the crystal fraction increasing. The dynamics of crystallized terpolymers were additionally studied via broadband dielectric spectroscopy. Constrained segmental dynamics was observed in the terpolymer containing the highest crystal fraction for which a narrow relaxation time distribution was found. Moreover, the enhanced dielectric and electromechanical response of DEHP doped terpolymer were interpreted via morphology microstructure and molecular mobility analysis. Interfacial polarization shifted to the high frequency by one decade because of dopant DEHP. Finally, electromechanical devices based on ferroelectric P(VDF-TrFE) and electrostrictive P(VDF-TrFE-CTFE) towards the dynamic force sensor implementation were designed and fabricated via inkjet printing technology. The bias electric field for terpolymer sensor was much lower than the poling electric field for a copolymer sensor. And the piezoelectric properties equivalent to the corresponding copolymer sensor can be obtained for a bias as low as 7.5 V/μ

Ces dernières années, les capteurs embarqués ont gagné en précision, fiabilité et robustesse, tout en se miniaturisant. Ces capteurs sont largement utilisés dans le domaine médical et sportif pour récolter toutes sortes de données physiologiques. Développer des générateurs d’énergie qui convertissent l’énergie mécanique ambiante en électricité constitue une voie très intéressante afin de rendre ces capteurs autonomes.Dans ce contexte, en 2013, un premier générateur souple autonome d’énergie a été développé au sein de notre équipe au G2Elab en collaboration avec le laboratoire LaMCoS. Ce générateur est conçu à partir d’élastomères électroactifs, basés sur la déformation de matériaux souples (polyacrylates, silicones) incorporés entre deux électrodes déformables et fonctionnent suivant un mode électrostatique. Ces structures présentent l’avantage d’être légères, peu chères, souples et elles peuvent être fabriquées suivant des géométries complexes. De plus, elles fonctionnent dans des gammes de fréquence basses (<100 Hz), les rendant ainsi attractives pour la récupération et la conversion d’énergie mécanique ambiante.L’objectif de ce travail de thèse était d’optimiser ce générateur pour en faire un générateur de seconde génération plus performant en terme d’énergie récupérée, beaucoup plus adaptable sur le corps humain et avec une durée de vie accrue. Pour atteindre ces différents critères, la conception et la réalisation de nouveaux dispositifs alternatifs hybridés pour des générateurs autonomes ont également été menées.Pour cela, la première étape a consisté à chercher un nouveau matériau pouvant remplacer le téflon comme électret dans la structure. Cet électret joue le rôle de réservoir de charges pour la polarisation du générateur fonctionnant en mode électrostatique. Le choix s’est porté sur plusieurs familles de poly(p-xylylene) plus communément appelées parylènes. Le fait de pouvoir les déposer dans un procédé CVD sur des géométries complexes et de façon très conforme a justifié ce choix. Le comportement temporel du potentiel de surface développé par ces électrets après une décharge couronne a été analysé en fonction du type et de l’épaisseur de parylène et du potentiel initial de charge. Cela a permis d’évaluer les potentialités en électret de ces matériaux et de mieux cerner la dynamique des charges électriques dans un environnement proche de l’application (sous contrainte mécanique) et pour des conditions plus extrêmes en température. Ces travaux ont permis de valider des parylènes fluorés comme d’excellents électrets (tests réalisés sur 1.5 an) tant en potentiel positif que négatif.La seconde étape s’est focalisée dans la conception de structures développant une architecture qui optimise les couplages électromécaniques au sein des matériaux constituant le générateur souple d’énergie. Dans ce but, et avec l’appui de modélisations que nous avons réalisées pour définir les géométries optimales de nos structures pour maximiser la puissance produite en sortie, deux principes de fonctionnement se sont dégagés : le premier fait appel à des électrets et il est ainsi en étroite continuité de l’étude précédente ; le second utilise des matériaux piézoélectriques (PZT et PVDF) comme source de polarisation ouvrant ainsi une nouvelle voie prometteuse de générateurs autonomes embarqués. Pour ces différentes structures, des prototypes de taille centimétrique ont été réalisés et caractérisés avec pour but final d’être insérés au niveau du genou pour récupérer la déformation mécanique lors de la marche ou de la course à pied. / Over the last years, wearable sensors have gained in accuracy and precision, while following the demands of miniaturization and lower power consumption. Scavenging human kinetic energy to produce electricity is an attractive alternative for the power supply of these low-power-consumption devices. E-textiles for health-monitoring or biomedical implants are some of the possible applications that could benefit from a self-powering system.In this context, in 2013, a first prototype of soft and autonomous energy scavenger was developed by our research group through the collaboration between LaMCoS and G2Elab laboratories. This electrostatic generator was based on the dielectric elastomers generators (DEGs) technology, which relies on the mechanical deformation of a thin layer of dielectric material (acrylic or silicone) sandwiched between two compliant electrodes. The main advantages of this technology are their low-cost, compliance, light-weight and adaptability to complex shapes. In addition, they can work on a large scale of temperatures and frequencies (<100Hz), which make them interesting to harvest and convert ambient mechanical vibrations.The objectives of this work were focused on the first prototype optimization to realize a second-generation device with higher energy output, suitability for wearable applications and lifetime and to conceive new alternatives hybrid devices for autonomous DEGs.To these aims, the first stage of the study consisted in the investigation of new conformant electret materials (representing the charges reservoir for electrostatic generator polarization) replacing Teflon in the scavenger structure. Different variants of poly(p-xylylene) polymers, better known with the commercial name of Parylene, were tested as new potential electret materials, mainly due to their highly conformability and possibility of CVD-deposition on complex shapes. The surface potential decays (SPD) on electrets formed by corona discharge method were monitored over time for different Parylene variants, samples thicknesses and charging voltages. These characterizations were aimed to evaluate the performance of Parylene electrets and to monitor the charge dynamic under mechanical conditions close to the final applications and under harsher environmental temperatures. As a result of these tests, fluorinated Parylenes showed excellent long-term charge retention performance (over 1.5 years) both for positive and negative charges.The second part of the work consisted in the realization of optimized structures realizing the electromechanical coupling of the two different electroactive materials constituting the soft electrostatic generator. For this aim, two different working modes were developed: the first one employs electret materials as polarization source, with the aim of optimizing the first hybrid device conceived in the previous study; the second one is made of piezoelectric materials (PZT and PVDF) as DEGs polarization sources, opening a new promising solution for autonomous wearable generators. Through numerical simulations, geometry optimization was performed with the aim of increasing the power output of the devices. Beneath, for the different structures, centimeter scale prototypes were realized and characterized with the final aim to be integrated at human knee level to exploit the mechanical deformation given by human body while walking.

<p dir="ltr">The present work expands the state of the art in the design of soft actuators and flexible sensors manufactured through fused deposition modelling (FDM) and direct ink writing (DIW). The first design consisted of flexible sensors for rehabilitation. Three different designs were tested and compared according to their sensitivity and accuracy. The flexible sensor successfully responded to deformation by changing its resistance. The first design of soft actuator was the Closed Dual Pneumatic Bellow Actuator. The soft actuator was manufactured using FDM and included an inner chamber in which the input air flows through and produces the actuation. The actuator also included dielectric electroactive polymer (DEAP) that showed response to pressure between the actuator and the object to be grasped. The electrodes of the DEAP were manufactured using commercial conductive TPU. A second soft actuator was designed with a circular shape and embedded DEAP. The electrodes in the DEAP consisted of conductive carbon grease. Previous tests were performed to assess the functionality of a DEAP structure using conductive carbon grease. The DEAP showed an increase in capacitance as pressure was applied on one side of the structure parallel to the electrodes and computational simulations validated such response. Future work using the sensors and actuators presented includes the implementation of a closed-loop system to the soft actuators, using the readouts of the sensors to adjust the input pressure and apply precise pressure on objects. The flexible sensor for rehabilitation has the potential to be implemented in each of the fingers of the hand and use the data to characterize the movement of the hand under different configurations providing feedback to patients in task-oriented therapy.</p>

La Fabrication Additive (FA) est un procédé de fabrication qui a commencé à se développer dans les années 80 et qui atteint actuellement une maturité qui lui permet d’être utilisé de manière rentable et fonctionnelle par les industriels. La fabrication additive est définie comme étant le procédé de mise en forme d’une pièce par ajout de matière, à l’opposé de la mise en forme traditionnelle par enlèvement de matière (usinage). Cette nouvelle technologie est une réelle révolution et permet de relever de nouveaux défis technologiques sans précédent. Que ce soit sur un axe matériau ou plus largement dans le cadre de l’usine du futur, la fabrication additive est un réel levier de croissance, mais de nombreux travaux de recherche sont encore à mener afin de perfectionner cette nouvelle technologie. C’est autour de cette problématique que les travaux de thèses se sont focalisés avec un accent sur l’intégration de matériaux électroactifs pour la réalisation de fonction mécatronique tirant profit des procédés de Fabrication Additive. Les actions de recherche montrent que la fabrication additive de matériaux électroactifs sera de plus en plus employée pour la réalisation de fonctions mécatroniques hybrides qui combineront à la fois la structure mécanique, des circuits intégrés en silicium, des pistes conductrices et des matériaux couplés imprimés, intégrant ainsi des fonctionnalités, telles que des capteurs, des affichages ou des sources d’énergie. Les travaux montrent le potentiel applicatif autour du contrôle de santé des structures en composites, mais aussi du contrôle de forme d’instrument pour la chirurgie. Pour arriver au développement de ces dispositifs, les points suivants ont été développés autour des matériaux électroactifs et de leurs règles d’intégrations et d’optimisation. / Additive Manufacturing (FA) is a manufacturing process that began to develop in the 1980s and is now mature enough to be used in a cost-effective and functional way by manufacturers. Additive manufacturing is defined as the process of shaping a part by adding material, as opposed to traditional shaping by material removal (machining). This new technology is a real revolution and enables us to meet new unprecedented technological challenges. Whether on a material axis or more widely as part of the plant of the future, additive manufacturing is a real growth driver, but many research work is yet to be conducted to perfect this new technology. It is around this issue that the work of theses focused with a focus on the integration of electroactive materials for the realization of mechatronics function taking advantage of Additive Manufacturing processes. Research shows that additive manufacturing of electroactive materials will be increasingly used for the realization of hybrid mechatronic functions that will combine both the mechanical structure, silicon integrated circuits, conductive tracks and printed coupled materials, integrating as well as features, such as sensors, displays or power sources. The work shows the potential application around the health control of composite structures, but also the instrument shape control for surgery. To arrive at the development of these devices, the following points have been developed around electroactive materials and their integration and optimization rules.

This work is inspired by the peculiar behavior of the natural systems, namely the ability to produce self-sustained oscillations in the level of tens of Hertz in constant ambient conditions. This feature is one of the key signatures prescribed to living organisms. The firing rate of neuronal cells, a pulsating heart, or the beating of cilia and flagella are among many biological examples that possess amazing functionalities and unprecedented intelligence solely relying on bio-electro-chemical processes. Exploring shapeable polymeric technologies, new self-oscillating artificial microsystems were developed within this thesis. These microsystems rely on the novel nonlinear architecture that exhibits a negative differential resistance (NDR) within the parametric response that enables periodic oscillations. These systems are made of polymers and metals and were microfabricated in a planar fashion. The electrochemically deposited ionic electroactive polymers act as actuators of the system. Upon the self-assembly process, due to the interlayer strains, the planar device transforms into a three-dimensional soft nonlinear system that is able to perform self-sustained relaxation oscillations when subjected to a constant electric field while consuming extremely low powers (as low as several microwatts). The parameters of these systems were tuned for a high oscillation amplitude and frequency. This electro-mechanical parametric relaxation oscillator (EMPRO) can generate a rhythmic motion at stroke frequencies that are biologically relevant reaching up to ~95 Hz. The EMPRO oscillations at high frequencies generate a flow in the surrounding liquid, which was observed in the form of vortices around the micro actuators. This flow was further studied in ex-vivo conditions by measuring Doppler shifts of ultrasound waves. The EMPRO was made autonomous by integrating an electrochemical voltaic cell. Four different electrochemical batteries were tested to match the power consumption of the EMPRO system and electrochemical compatibility of the surrounding media. An Ag-Mg primary cell was then integrated with the EMPRO for autonomous operation without the need for external power sources, cables or controllers. This biomimicking self-powered self-sustaining oscillating microsystem is envisioned to be useful in novel application scenarios operating at low Reynolds numbers in biologically relevant conditions. Furthermore, as the system is electromechanical in nature, it could be integrated with electronic components such as sensors and communication devices in the next generation of autonomous microsystems.:  Table of contents Acronyms 7 1 Introduction 8 1.1 Motivation 9 1.2 Objectives 9 1.3 Thesis organization 10 2 Background 12 2.1 A brief review on nonlinear self-oscillation 12 2.2 Self-oscillating biological systems 13 2.3 Stimuli responsive materials 15 2.3.1 Electroactive polymers in electrochemical cells 16 2.3.2 Sources of electrical field for electroactive polymers 24 2.4 Self-oscillating synthetic systems 27 2.5 Movement in low Reynolds number regime 33 3 Materials and methods 38 3.1 Deposition methods 38 3.1.1 Photolithography 38 3.1.2 Plasma sputtering 41 3.1.3 Atomic layer deposition 42 3.1.4 Electrochemical polymerization 44 3.2 Shapeable polymeric platform technology 46 3.2.1 Sacrificial layer 46 3.2.2 Hydrogel swelling layer 47 3.2.3 Polyimide reinforcing layer 48 3.3 Characterization methods 49 3.3.1 Profilometry 49 3.3.2 Scanning electron and focused ion beam microscopy 50 3.3.3 Cyclic Voltammetry 52 3.3.4 Ultrasound and Doppler shift measurements 53 4 Electromechanical Parametric Relaxation Oscillators (EMPROs) 56 4.1 Relaxation oscillation in EMPROs 56 4.2 Theory of EMPRO relaxation oscillations 61 4.3 Realization of EMPROs 67 4.3.1 Design parameters of EMPROs 67 4.3.2 EMPRO on-chip battery integration 71 4.4 Fabrication of autonomous EMPROs 76 5 EMPRO performances 84 5.1 Externally biased EMPROs 84 5.2 Autonomous EMPROs 95 6 Conclusions and outlook 98 6.1 Outlook 99 Bibliography i List of Figures and Tables xi Versicherung xiii Acknowledgements xiv Scientific publications and contributions xvi Theses xvii Curriculum Vitae xix

Future robotic systems will be pervasive technologies operating autonomously in unknown spaces that are shared with humans. Such complex interactions make it compulsory for them to be lightweight, soft, and efficient in a way to guarantee safety, robustness and long-term operation. This set of qualities can be achieved using soft multipurpose systems that combine, integrate and commute between conventional electromechanical and fluidic drives, as well as harvest energy during inactive actuation phases for increased energy efficiency. Recent research work has shown that dielectric fluids with specific properties, can be combined with stretchable or flexible shell structures made of polymeric dielectric/electrode composite films, to implement a novel type of soft electrically-driven fluidic transducers with self-healing and self-sensing capabilities that take the name of Liquid-based Electro-Active Polymer transducers (LEAPs). These devices are similar to dielectric elastomer transducers in regards to their electrostatic working principle, but they can potentially produce larger displacements due to their lower mechanical stiffness. In this thesis a novel electrostatic transducer is presented; the transducer is made of thin polymer films and liquid dielectrics, combined with rigid stiffening elements to form a circular electrostatic bellow muscle (EBM) unit capable of out-of-plane contraction. These units are easy to manufacture and can be arranged in arrays and stacks that can be employed as contractile artificial muscles, pumps for fluid-driven soft robots, or as energy harvesters. As artificial muscles, EBMs of 20 - 40 millimeters in diameter can exert forces of up to 6 newtons, lift loads over a hundred times their own weight, and reach contractions of over 40 per cent with strain rates over 1200 per cents per second, with a bandwidth over 10 Hz. As pump drivers, EBMs produce flow rates of up 0.63 liters per minute and maximum pressure head of 6 kilopascals, whereas as generators, they reach a conversion efficiency close to 20 per cent. The compact shape, low cost, simple assembling procedure, high reliability and large contractions make the EBM a promising technology for high-performance robotic systems.