Printing of wirelessly rechargeable solid-state supercapacitors for soft, smart contact lenses with continuous operations

Recent advances in smart contact lenses are essential to the realization of medical applications and vision imaging for augmented reality through wireless communication systems. However, previous research on smart contact lenses has been driven by a wired system or wireless power transfer with temporal and spatial restrictions, which can limit their continuous use and require energy storage devices. Also, the rigidity, heat, and large sizes of conventional batteries are not suitable for the soft, smart contact lens. Here, we describe a human pilot trial of a soft, smart contact lens with a wirelessly rechargeable, solid-state supercapacitor for continuous operation. After printing the supercapacitor, all device components (antenna, rectifier, and light-emitting diode) are fully integrated with stretchable structures for this soft lens without obstructing vision. The good reliability against thermal and electromagnetic radiations and the results of the in vivo tests provide the substantial promise of future smart contact lenses

High-resolution 3D direct-write prototyping for healthcare applications

The healthcare sector has much to benefit from the vast array of novelties erupting from the manufacturing world. 3D printing (additive manufacturing) is amongst the most promising recent inventions with much research concentrated around the various approaches of 3D printing and applying this effectively in the health sector. Amongst these methods, the direct-write assembly approach is a promising candidate for rapid prototyping and manufacturing of miniaturised medical devices/sensors and in particular, miniaturised flexible capacitive pressure sensors. Microstructuring the dielectric medium of capacitive pressure sensors enhances the sensitivity of the capacitive pressure sensor. The structuring has been predominantly achieved with photolithography and similar subtractive approaches. In this project high-resolution 3D direct write printing was used to fabricate structured dielectric mediums for capacitive pressure sensors. This involved the development and rheological characterisation of printability-tuned water soluble polyvinyl pyrrolidone (PVP) based inks (10%-30% polymer content) for stable high-resolution 3D printing. These inks were used to print water soluble micromoulds that were filled and cured with otherwise difficult to structure low G’ materials like PDMS. Our approach essentially decouples ink synthesis from printability at the micrometre scale. The developed micro moulding approach was employed for printing pyramidal micro moulds, that were used as templates for fabricating pyramid structured dielectric mediums for capacitive pressure sensing. The power of the approach was used to alter the microstructures and reap enhanced pressure sensing characteristics for effective miniaturised capacitive pressure sensors. A pressure sensing ring – that could be worn by doctors and surgeons – was prototyped with our approach and employed successfully to monitor in real-time the radial pulse signal of a 29 year old male volunteer. The print resolution of the inks was enhanced by formulating and rheologically characterising a PVP/PVDF polymer blend ink that would wet the printing nozzle less due to the hydrophobicity of the PVDF

Multifunctional vertical interconnections of multilayered flexible substrates for miniaturised POCT devices

Point-of-care testing (POCT) is an emerging technology which can lead to an eruptive change of lifestyle and medication of population against the traditional medical laboratory. Since living organisms are intrinsically flexible and malleable, the flexible substrate is a necessity for successful integration of electronics in biological systems that do not cause discomfort during prolonged use. Isotropic conductive adhesives (ICAs) are attractive to wearable POCT devices because ICAs are environmentally friendly and allow a lower processing temperature than soldering which protects heat-sensitive components. Vertical interconnections and optical interconnections are considered as the technologies to realise the miniaturised high-performance devices for the future applications. This thesis focused on the multifunctional integration to enable both electrical and optical vertical interconnections through one via hole that can be fabricated in flexible substrates. The functional properties of the via and their response to the external loadings which are likely encountered in the POCT devices are the primary concerns of this PhD project. In this thesis, the research of curing effect on via performance was first conducted by studying the relationship between curing conditions and material properties. Based on differential scanning calorimetry (DSC) analysis results, two-parameter autocatalytic model (Sestak-Berggren model) was established as the most suitable curing process description of our typical ICA composed of epoxy-based binders and Ag filler particles. A link between curing conditions and the mechanical properties of ICAs was established based on the DMA experiments. A series of test vehicles containing vias filled with ICAs were cured under varying conditions. The electrical resistance of the ICA filled vias were measured before testing and in real time during thermal cycling tests, damp heat tests and bending tests. A simplified model was derived to represent rivet-shaped vias in the flexible printed circuit boards (FPCBs) based on the assumption of homogenous ICAs. An equation was thus proposed to evaluate the resistance of the model. Vias with different cap sizes were also tested, and the equation was validated. Those samples were divided into three groups for thermal cycling test, damp heat ageing test and bending test. Finite element analysis (FEA) was used to aid better understanding of the electrical conduction mechanisms. Based on theoretical equation and simulation model, the fistula-shape ICA via was fabricated in flexible PCB. Its hollow nature provides the space for integrations of optical or fluidic circuits. Resistance measurements and reliability tests proved that carefully designed and manufactured small bores in vias did not comprise the performance. Test vehicles with optoelectrical vias were made through two different approaches to prove the feasibility of multifunctional vertical interconnections in flexible substrates. A case study was carried out on reflection Photoplethysmography (rPPG) sensors manufacturing, using a specially designed optoelectronic system. ICA-based low-temperature manufacture processes were developed to enable the integration of these flexible but delicate substrates and components. In the manufacturing routes, a modified stencil printing setup, which merges two printing-curing steps (vias forming and components bonding) into one step, was developed to save both time and energy. The assembled probes showed the outstanding performance in functional and physiological tests. The results from this thesis are anticipated to facilitate the understanding of ICA via conduction mechanism and provide an applicable tool to optimise the design and manufacturing of optoelectrical vias

Self-Assembled Porous-Reinforcement Microstructure-Based Flexible Triboelectric Patch for Remote Healthcare.

Realizing real-time monitoring of physiological signals is vital for preventing and treating chronic diseases in elderly individuals. However, wearable sensors with low power consumption and high sensitivity to both weak physiological signals and large mechanical stimuli remain challenges. Here, a flexible triboelectric patch (FTEP) based on porous-reinforcement microstructures for remote health monitoring has been reported. The porous-reinforcement microstructure is constructed by the self-assembly of silicone rubber adhering to the porous framework of the PU sponge. The mechanical properties of the FTEP can be regulated by the concentrations of silicone rubber dilution. For pressure sensing, its sensitivity can be effectively improved fivefold compared to the device with a solid dielectric layer, reaching 5.93 kPa-1 under a pressure range of 0-5 kPa. In addition, the FTEP has a wide detection range up to 50 kPa with a sensitivity of 0.21 kPa-1. The porous microstructure makes the FTEP ultra-sensitive to external pressure, and the reinforcements endow the device with a greater deformation limit in a wide detection range. Finally, a novel concept of the wearable Internet of Healthcare (IoH) system for real-time physiological signal monitoring has been proposed, which could provide real-time physiological information for ambulatory personalized healthcare monitoring

Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors

This reprint is a collection of the Special Issue "Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors" published in Nanomaterials, which includes one editorial, six novel research articles and four review articles, showcasing the very recent advances in energy-harvesting and self-powered sensing technologies. With its broad coverage of innovations in transducing/sensing mechanisms, material and structural designs, system integration and applications, as well as the timely reviews of the progress in energy harvesting and self-powered sensing technologies, this reprint could give readers an excellent overview of the challenges, opportunities, advancements and development trends of this rapidly evolving field

Development and Testing of an Implantable Perfusion and Oxygenation Sensor for Liver Transplant Monitoring

Since the first successful liver transplant in 1968 the surgery has become very common and 6,291 patients received liver transplants in 2010 in the United States. However, the monitoring methods used post-surgery, in the recovery phase, are still very basic and rely mainly on blood tests and looking for unusual symptoms. Complications are usually detected after the organ is substantially damaged which poses a risk to the patients’ life. This dissertation presents the development and testing of an implantable sensor that can potentially be used to monitor the transplant continuously and transmit the information wirelessly to the medical staff for timely intervention. Such a sensor could have a great effect on survival and reduction of retransplantation rates. The presented sensor employs near infrared spectroscopy to measure perfusion changes, arterial oxygenation and venous oxygenation in the parenchyma of the liver tissue and the supplying vessels. Light at three different wavelengths (735-, 805- and 940-nm) is shined on the tissue and the diffuse reflectance is collected via a photodetector. The collected signals can be transmitted wirelessly to an external unit for processing and display. In this dissertation, different perfusion and oxygenation monitoring techniques are reviewed and the instrumentation of an NIRS based wireless sensor is introduced. A phantom that mimics the anatomy of the liver and its optical and mechanical properties is presented. The processing methods to extract the information of interest from the diffuse reflectance are described in details. Finally, results from in vitro phantom experiments, ex vivo perfused livers and in vivo porcine studies are presented. The first in vivo wireless monitoring of hepatic perfusion and oxygenation levels is reported. The studies show that the sensor can track perfusion changes with a resolution of 0.1 mL/min/g of tissue. The possibility of tracking oxygen saturation changes is also shown as well as the ability to separate them from perfusion changes. Combining results from the pulsatile wave and DC levels, venous and arterial oxygen saturation changes were tracked with a resolution of 1.39% and 2.19% respectively. In conclusion, optical spectroscopy is shown to track perfusion, and arterial and venous oxygenation in tissue. In particular, the method was tested on hepatic and intestinal tissue

Highly Sensitive Soft Foam Sensors for Wearable Applications

Due to people’s increasing desire for body health monitoring, the needs of knowing humans’ body parameters and transferring them to analyzable and understandable signals become increasingly attractive and significant. The present body-sign measurement devices are still bulky medical devices used in settings such as clinics or hospitals, which are accurate, but expensive and cannot achieve the personalization of usage targets and the monitoring of real-time body parameters. Many commercial wearable devices can provide some of the body indexes, such as the smartwatch providing the pulse/heartbeat information, but cannot give accurate and reliable data, and the data could be influenced by the user’s movement and the loose wearing habit, either. In this way, developing next-generation wearable devices combining good wearable experience and accuracy is gathering increasing attention. The aim of this study is to develop a high-performance pressure/strain sensor with the requirements of comfortable to wear, and having great electromechanical behaviour to convert the physiological signal to an analyzable signal

Flexible Electrode Array System for Sweat Analysis in Vitro Information

Sweat is a kind of liquid secreted to the body surface by human sweat glands, and its composition is highly related to the physiological state of the human body. Flexible wearable devices can dynamically monitor the change of sweat composition and the state of motion in real-time, which makes it become an important means for clinical and physiological research. In this thesis, a sensing system based on the flexible electrode array, which mainly includes a flexible electrode array and portable signal acquisition and processing system module, is designed and used for dynamic sweat detection. The system is characterized by high sensitivity, high selectivity, and repeatability, enabling online sweat composition analysis in vitro or wearable situations. Flexible electrode array mainly includes ion-selective electrodes (ISEs), enzyme electrodes, and reference electrodes. The ISEs include sodium and potassium selective electrodes. Enzyme electrodes include glucose and lactate oxidase electrodes. Reference electrodes are two pseudo-Ag/AgCl reference electrodes, both of which also act as counter electrodes. Signal acquisition and processing module mainly include voltage signal amplification, current signal amplification, filtering, signal selection, and A/D conversion circuit. This thesis studies the response characteristics of the electrode array to four kinds of sweat components. The sensitivity of ISEs and enzyme electrodes can be obtained by using an electrochemical workstation: The voltage response sensitivity of potassium ISE is 60.8 mV/lg[c(K+)]; The voltage response sensitivity of sodium ISE is 45.9 mV/lg[c(Na+)]; The current response sensitivity of glucose oxidase electrode is 2.28 μA·L/mmol; The current response sensitivity of lactate oxidase electrode is 45 nA·L/mmol. At the same time, the selectivity of ISEs is studied, and the experiment shows that both potassium and sodium ISE have a good anti-interference ability with low sensitivity against temperature. The sensitivity of potassium, sodium, glucose and lactate electrodes can still maintain a good linear relationship and meet the sensitivity requirements by using the portable signal acquisition and processing system. Combined with the "Clip Plate Method", sodium ion, glucose, and lactate of sweat sample collected from sportive volunteers are measured and analyzed, and the detecting of oxygen saturation and heart rate is also carried out in real-time, through which it can be found that the composition of sweat will change with the motion state and individual differences, providing a reference for the follow-up single targeted detection. In the thesis, a new type of enzyme electrode based on viologen compounds is developed, which has simple technological process and good stability, and the current response sensitivity of glucose and lactate oxidase electrode based on sulfhydryl viologen is measured as -0.234 μA·L/mmol and -41.7 nA·L/mmol, which shows improved linearity and stability compared with conventional enzyme electrode

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Department of Energy EngineeringElectronic skins (e-skins) enabling to detect various mechanical/chemical stimuli and environmental conditions by converting into various electrical and optical signals have attracted much attentions for various fields including wearable electronics, intelligent/medical robotics, healthcare monitoring devices, and haptic interfaces. Conventional e-skins have been widely used for the realization of these applications, however it is still considered that new e-skins with enhanced sensor performances (i.e. sensitivity, flexibility, multifunctionality, etc.) should be developed. In accordance with these demands, two approaches to explore novel functional materials or to modify device architectures have been introduced for enhancing sensor performance and acquiring multifunctional sensing capabilities. Firstly, a synthesis of multifunctional materials combined with conductive fillers (carbon nanotube, graphene oxide) and functional polymer matrix (i.e. ferroelectric polymer, elastomer) can provide the multimodal sensing capability of various stimuli and stretchability. Secondly, controlling design of device structures into various micro/nanostructures enables a significant improvement on sensing capabilities of e-skins with sensitivity and multidirectional force sensing, resulting from structural advantages such as large surface area, effective stress propagation, and anisotropic deformation. Therefore, a demonstration of e-skin combined with the functional composites and uniquely designed microstructures can offer a powerful platform to realize ideal sensor systems for next generation applications such as wearable electronics, healthcare devices, acoustic sensor, and haptic interface devices. In this thesis, we introduce the novel multifunctional and high performance electronic skins combined with various types of composite materials and nature-inspired 3D microstructures. Firstly, Chapter 1 briefly introduces various types of e-skins and the latest research trends of microstructured e-skins and summarizes the key components for their promising application fields. In chapters 2 and 3, mimicked by interlocking system between epidermal and dermal layers in human skin, we demonstrate the piezoresistive e-skins based on CNT/PDMS composite materials with interlocked microdome arrays for great pressure sensitivity and multidirectional force sensing capabilities. In chapter 4, we conduct in-depth study on giant tunneling piezoresistance in interlocking system and investigate systematically on the geometrical effect of microstructures on multidirectional force sensitivity and selectivity in interlocking sensor systems. In chapter 5, we demonstrate the ferroelectric e-skin that can detect and discriminate the static/dynamic touches and temperature inspired by multi-stimuli detection of various mechanoreceptors in human skin. Using the multifunctional sensing capabilities, we demonstrated our e-skin to the temperature-dependent pressure monitoring of artery vessel, high-precision acoustic sound detection, and surface texture recognition of various surfaces. In chapter 6, we demonstrate the linear and wide range pressure sensor with multilayered composite films having interlocked microdomes. In chapter 7, we present a new-concept of e-skin based on mechanochromic polymer and porous structures for overcoming limitations in conventional mechanochromic systems with low mechanochromic performances and limited stretchability. In addition, our mechanochromic e-skins enable the dual-mode detection of static and dynamic forces without any external power. Our e-skins based on functional composites and uniquely designed microstructures can provide a solid platform for next generation eskin in wearable electronics, humanoid robotics, flexible sensors, and wearable medical diagnostic systems.clos