abstract: Ordered buckling of stiff films on elastomeric substrates has many applications in the field of stretchable electronics. Mechanics plays a very important role in such systems. A full three dimensional finite element analysis studying the pattern of wrinkles formed on a stiff film bonded to a compliant substrate under the action of a compressive force has been widely studied. For thin films, this wrinkling pattern is usually sinusoidal, and for wide films the pattern depends on loading conditions. The present study establishes a relationship between the effect of the load applied at an angle to the stiff film. A systematic experimental and analytical study of these systems has been presented in the present study. The study is performed for two different loading conditions, one with the compressive force applied parallel to the film and the other with an angle included between the application of the force and the alignment of the stiff film. A geometric model closely resembling the experimental specimen studied is created and a three dimensional finite element analysis is carried out using ABAQUS (Version 6.7). The objective of the finite element simulations is to validate the results of the experimental study to be corresponding to the minimum total energy of the system. It also helps to establish a relation between the parameters of the buckling profile and the parameters (elastic and dimensional parameters) of the system. Two methods of non-linear analysis namely, the Newton-Raphson method and Arc-Length method are used. It is found that the Arc-Length method is the most cost effective in terms of total simulation time for large models (higher number of elements).The convergence of the results is affected by a variety of factors like the dimensional parameters of the substrate, mesh density of the model, length of the substrate and the film, the angle included. For narrow silicon films the buckling profile is observed to be sinusoidal and perpendicular to the direction of the silicon film. As the angle increases in wider stiff films the buckling profile is seen to transit from being perpendicular to the direction of the film to being perpendicular to the direction of the application of the pre-stress. This study improves and expands the application of the stiff film buckling to an angled loading condition. / Dissertation/Thesis / M.S. Mechanical Engineering 2010

abstract: Flexible conducting materials have been in the forefront of a rapidly transforming electronics industry, focusing on wearable devices for a variety of applications in recent times. Over the past few decades, bulky, rigid devices have been replaced with a surging demand for thin, flexible, light weight, ultra-portable yet high performance electronics. The interconnects available in the market today only satisfy a few of the desirable characteristics, making it necessary to compromise one feature over another. In this thesis, a method to prepare a thin, flexible, and stretchable inter-connect is presented with improved conductivity compared to previous achievements. It satisfies most mechanical and electrical conditions desired in the wearable electronics industry. The conducting composite, prepared with the widely available, low cost silicon-based organic polymer - polydimethylsiloxane (PDMS) and silver (Ag), is sandwiched between two cured PDMS layers. These protective layers improve the mechanical stability of the inter-connect. The structure can be stretched up to 120% of its original length which can further be enhanced to over 250% by cutting it into a serpentine shape without compromising its electrical stability. The inter-connect, around 500 µm thick, can be integrated into thin electronic packaging. The synthesis process of the composite material, along with its electrical and mechanical and properties are presented in detail. Testing methods and results for mechanical and electrical stability are also illustrated over extensive flexing and stretching cycles. The materials put into test, along with conductive silver (Ag) - polydimethylsiloxane (PDMS) composite in a sandwich structure, are copper foils, copper coated polyimide (PI) and aluminum (Al) coated polyethylene terephthalate (PET). / Dissertation/Thesis / Masters Thesis Electrical Engineering 2020

Electronic skin (e-skin) materials have gained a wide range of attention due to their multiple applications in different areas, including soft robotics, skin attachable electronics, prosthetics, and health care. These materials are required to emulate tactile perceptions and sense the surrounding environments while maintaining properties such as flexibility and stretchability. Current e-skin fabrication techniques, such as photolithography, screen printing, lamination, and laser reducing, have limitations in terms of costs and manufacturing scalability, which ultimately preventing e-skin widespread usage. In this work, we introduce conductive stretchable 3D printable skin-like nanocomposite material. Our nanocomposite is easily 3D printed, cost-effective, and actively senses physical stimuli, such as strain and pressure, which gave them the potential to be used in prosthetics, skin-attachable electronics, and soft robotics applications. Using the conductive properties of carbon nanofibers, alongside a polymeric matrix based on Smooth-on platinum cured silicone and crosslinked PDMS, we can obtain a flexible and stretchable material that resembles human skin and can conduct electricity. A great advantage in our composite is the ability to tune its mechanical properties to fit the desired application area through varying PDMS's chain lengths and composition ratios in the nanocomposite. Also, the interconnecting network of micrometer-long nanofibers allows the measurement of resistivity changes upon physical stimuli, granting the nanocomposite sensing abilities. Moreover, we explored and optimized 3D printing of the nanocomposite material, which offering simplicity and versatility for fabricating complex 3D structures at lower costs.

The development of wearable devices to monitor biosignals and collect real-time data from biological systems at all scales from cellular to organ level has played a significant role in the field of medical engineering. The current coronavirus disease 2019 (COVID-19) pandemic has further increased the demand for remote monitoring and smart healthcare where patient data can be also be accessed from a remote distance. Recent efforts to integrate wearable devices with artificial intelligence and machine learning have transformed conventional healthcare into smart healthcare, which requires reliable and robust recording data. The biomedical devices that are mechanically stretchable and compliant have provided the capability to form a seamless interface with the curvilinear, soft surface of tissues and body, enabling accurate, continuous acquisition of physical and electrophysiological signals. This dissertation presents a comprehensive set of functional materials, design principles, and fabrication strategies to develop mechanically stretchable and compliant biomedical devices tailored for various applications, including (1) a stretchable sensor patch enabling the continuous monitoring of swallowing function from the submental/facial area for the telerehabilitation of patients with dysphagia, (2) a human hand-like sensory glove for advanced control of prosthetic hands, (3) a mechanically compliant manipulator for the non-invasive handling of delicate biomaterials and bioelectronics, and (4) a stretchable sensors embedded inside a tissue scaffold enabling the continuous monitoring of cellular electrophysiological behavior with high spatiotemporal resolution.<br>

<p>By using flexible and stretchable materials in place of fixed components, soft robots can materially adapt or change to their environment, providing built-in safeties for robotic operation around humans or fragile, delicate objects. And yet, building a robot out of only soft and flexible materials can be a significant challenge depending on the tasks that the robot needs to perform, for example if the robot were to need to exert higher forces (even temporarily) or self-report its current state (as it deforms unexpectedly around external objects). Thus, the appeal of multifunctional materials for soft robots, wherein the materials used to build the body of the robot also provide actuation, sensing, or even simply electrical connections, all while maintaining the original vision of environmental adaptability or safe interactions. Multifunctional material systems are explored throughout the body of this dissertation in three ways: (1) Sensor integration into high strain actuators for state estimation and closed-loop control. (2) Simplified control of multifunctional material systems by enabling multiple functions through a single input stimulus (<i>i.e.</i>, only requiring one source of input power). (3) Presenting a solution for the open challenge of controlling both well established and newly developed thermally-responsive soft robotic materials through an on-body, high strain, uniform, Joule-heating energy source. Notably, these explorations are not isolated from each other as, for example, work towards creating a new material for thermal control also facilitated embedded sensory feedback. The work presented in this dissertation paves a way forward for multifunctional material integration, towards the end-goal of full-functioning soft robots, as well as (more broadly) design methodologies for other safety-forward or adaptability-forward technologies.</p>

The proposed study develops a framework that can accurately capture and model input and output variables for multidisciplinary systems to mitigate the computational cost when uncertainties are involved. The dimension of the random input variables is reduced depending on the degree of correlation calculated by relative entropy. Feature extraction methods; namely Principal Component Analysis (PCA), the Auto-Encoder (AE) algorithm are developed when the input variables are highly correlated. The Independent Features Test (IndFeaT) is implemented as the feature selection method if the correlation is low to select a critical subset of model features. Moreover, Artificial Neural Network (ANN) including Probabilistic Neural Network (PNN) is integrated into the framework to correctly capture the complex response behavior of the multidisciplinary system with low computational cost. The efficacy of the proposed method is demonstrated with electro-mechanical engineering examples including a solder joint and stretchable patch antenna examples.

The advancement of technologies that interface with electrically excitable tissues, such as the cortex and muscle, has the potential to lend greater mobility to the disabled, and facilitate the study of the central and peripheral nervous systems. Myoelectric interfaces are currently limited in their signal fidelity, spatial resolution, and interfacial area. Such interfaces are either implanted in muscle or applied to the surface of the muscle or skin. Thus far, the former technology has been limited in its applications due to the stiffness (several orders of magnitude greater than muscle) of its substrates, such as silicon and polyimide, whereas the latter technology suffers from poor spatial resolution and signal quality due to the physical separation between the electrodes and the signal source. We have developed a stretchable microneedle electrode array (sMEA) that can function while stretching and flexing with muscle tissue, thereby enabling multi-site muscle stimulation and electromyography (EMG) measurement across a large interfacial area. The scope of this research encompassed: (i) the development of a stretchable and flexible array of penetrating electrodes for the purposes of stimulating and measuring the electrical activity of excitable tissue, (ii) the characterization of the electrical, mechanical, and biocompatibility properties of this electrode array, (iii) the measurement of regional electrical activity of muscle via the electrode array, (iv) the study of the effect of spatially distributed stimulation of muscle on the fatigue and ripple of muscle contractions, and (v) the assessment of the extent to which the stretch response of electrically stimulated muscle behaves in a physiological manner.

This thesis presents a melt electrospinning technique to fabricate highly porous and controllable poly (ε-caprolactone) (PCL) microfibers for tissue engineering applications and rehabilitation applications. Electrospinning without solvents via melt methods may be an attractive approach to tissue engineering of cell constructs where solvent accumulation or toxicity is an issue. This method is also able to produce microfibers with controllable parameters. However, the fiber diameters resulting from melt electrospinning processes are relatively large when compared to the fibers from solution electrospinning. The typical microfiber diameter from melt electrospinning was reported to be approximately 0.1mm. In order to further develop the melt electrospinning technique, we focused on the design of a melt electrospinning setup based on numerical analysis using the Solidworks 2013 simulation package and practically established a melt electrospinning setup and thermal control system for accurate experiments. One of main purposes of this thesis is the build-up of mathematical modeling to control and predict the electrospun microfiber via a more intricate understanding of their parameters such as the nozzle diameter, applied voltage, distance between the nozzle and counter electrode, temperature, flow rate, linear transitional speed, among others. The model is composed of three parts: 1) melt electrospinning process modeling, 2) fibrous helix movement modeling, and 3) build-up of microfibers modeling. The melt electrospinning process model describes an electric field, the shape of jet’s continuously changing shape, and how the polymer melt is stretched into a Taylor cone and a straight jet. The fibrous helix movement model describes movement of electrospun microfibers influenced by Lorentz force, which moves along the helix pattern. Lastly, the build-up microfiber modeling describes the accumulation of the extruded microfibers on both flat and round counter electrodes based on the physical forces involved. These models are verified by experimental data from our own customized melt electrospinning setup. Moreover, the fabricated scaffolds are tested by seeding neural progenitors derived from murine R1 embryonic stem cell lines and it demonstrates the potential of scaffolds for tissue engineering applications. To increase cell attachment and proliferation, highly porous microfibers are fabricated by combination of melt electrospinning and particulate leaching technique. Finally, auxetic stretchable PCL force sensors are fabricated by melt electrospinning for hand rehabilitation. These stretchable sensors can be used to measure applied external loads or displacement and are also attachable to various substrates. We have attempted to apply the sensors to real human hand in order to prove their functionality. / Graduate / jko@me.uvic.ca

Electronic platforms that are able to re-shape and assume different geometries are attractive for the advancing biomedical technologies, where the re-shaping feature increases the adaptability and compliance of the electronic platform to the human body. In this thesis, we present a serpentine-honeycomb reconfigurable electronic platform that has the ability to reconfigure into five different geometries: quatrefoil, ellipse, diamond, star and one irregular geometry. We show the fabrication processes of the serpentine-honeycomb reconfigurable platform in a micro-scale, using amorphous silicon, and in a macro-scale using polydimethylsiloxane (PDMS). The chosen materials are biocompatible, where the silicon was selected due to its superior electrical properties while the PDMS was selected due to its unique mechanical properties. We study the tensile strain for both fabricated-versions of the design and we demonstrate their reconfiguring capabilities. The resulting reconfiguring capabilities of the serpentine-honeycomb reconfigurable platform broaden the innovation opportunity for wearable electronics, implantable electronics and soft robotics.

abstract: Electronic devices based on various stimuli responsive polymers are anticipated to have great potential for applications in innovative electronics due to their inherent intelligence and flexibility. However, the electronic properties of these soft materials are poor and the applications have been limited due to their weak compatibility with functional materials. Therefore, the integration of stimuli responsive polymers with other functional materials like Silicon is strongly demanded. Here, we present successful strategies to integrate environmentally sensitive hydrogels with Silicon, a typical high-performance electronic material, and demonstrate the intelligent and stretchable capability of this system. The goal of this project is to develop integrated smart devices comprising of soft stimuli responsive polymeric-substrates with conventional semiconductor materials such as Silicon, which can respond to various external stimuli like pH, temperature, light etc. Specifically, these devices combine the merits of high quality crystalline semiconductor materials and the mechanical flexibility/stretchability of polymers. Our innovative system consists of ultra-thin Silicon ribbons bonded to an intelligently stretchable substrate which is intended to interpret and exert environmental signals and provide the desired stress relief. As one of the specific examples, we chose as a substrate the standard thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel with fast response and large deformation. In order to make the surface of the hydrogel waterproof and smooth for high-quality Silicon transfer, we introduced an intermediate layer of poly(dimethylsiloxane) (PDMS) between the substrate and the Silicon ribbons. The optical microscope results have shown that the system enables stiff Silicon ribbons to become adaptive and drivable by the soft environmentally sensitive substrate. Furthermore, we pioneered the development of complex geometries with two different methods: one is using stereolithography to electronically control the patterns and build up their profiles layer by layer; the other is integrating different multifunctional polymers. In this report, we have designed a bilayer structure comprising of a PNIPAAm hydrogel and a hybrid hydrogel of N-isopropylacrylamide (NIPAAm) and acrylic acid (AA). Typical variable curvatures can be obtained by the hydrogels with different dimensional expansion. These structures hold interesting possibilities in the design of electronic devices with tunable curvature. / Dissertation/Thesis / M.S. Chemical Engineering 2012