Wireless sEMG System with a Microneedle-Based High-Density Electrode Array on a Flexible Substrate

Surface electromyography (sEMG) signals reflect muscle contraction and hence, can provide information regarding a user's movement intention. High-density sEMG systems have been proposed to measure muscle activity in small areas and to estimate complex motion using spatial patterns. However, conventional systems based on wet electrodes have several limitations. For example, the electrolyte enclosed in wet electrodes restricts spatial resolution, and these conventional bulky systems limit natural movements. In this paper, a microneedle-based high-density electrode array on a circuit integrated flexible substrate for sEMG is proposed. Microneedles allow for high spatial resolution without requiring conductive substances, and flexible substrates guarantee stable skin-electrode contact. Moreover, a compact signal processing system is integrated with the electrode array. Therefore, sEMG measurements are comfortable to the user and do not interfere with the movement. The system performance was demonstrated by testing its operation and estimating motion using a Gaussian mixture model-based, simplified 2D spatial pattern.111Ysciescopu

Systematic review of textile-based electrodes for long-term and continuous surface electromyography recording

This systematic review concerns the use of smart textiles enabled applications based on myoelectric activity. Electromyography (EMG) is the technique for recording and evaluating electric signals related to muscle activity (myoelectric). EMG is a well-established technique that provides a wealth of information for clinical diagnosis, monitoring, and treatment. Introducing sensor systems that allow for ubiquitous monitoring of health conditions using textile integrated solutions not only opens possibilities for ambulatory, long-term, and continuous health monitoring outside the hospital, but also for autonomous self-administration. Textile-based electrodes have demonstrated potential as a fully operational alternative to \u27standard\u27 Ag/AgCl electrodes for recording surface electromyography (sEMG) signals. As a substitute for Ag/AgCl electrodes fastened to the skin by taping or pre-gluing adhesive, textile-based electrodes have the advantages of being soft, flexible, and air permeable; thus, they have advantages in medicine and health monitoring, especially when self-administration, real-time, and long-term monitoring is required. Such advances have been achieved through various smart textile techniques; for instance, adding functions in textiles, including fibers, yarns, and fabrics, and various methods for incorporating functionality into textiles, such as knitting, weaving, embroidery, and coating. In this work, we reviewed articles from a textile perspective to provide an overview of sEMG applications enabled by smart textile strategies. The overview is based on a literature evaluation of 41 articles published in both peer-reviewed journals and conference proceedings focusing on electrode materials, fabrication methods, construction, and sEMG applications. We introduce four textile integration levels to further describe the various textile electrode sEMG applications reported in the reviewed literature. We conclude with suggestions for future work along with recommendations for the reporting of essential benchmarking information in current and future textile electrode applications

Tutorial. Surface EMG detection, conditioning and pre-processing: Best practices

This tutorial is aimed primarily to non-engineers, using or planning to use surface electromyography (sEMG) as an assessment tool for muscle evaluation in the prevention, monitoring, assessment and rehabilitation fields. The main purpose is to explain basic concepts related to: (a) signal detection (electrodes, electrode–skin interface, noise, ECG and power line interference), (b) basic signal properties, such as amplitude and bandwidth, (c) parameters of the front-end amplifier (input impedance, noise, CMRR, bandwidth, etc.), (d) techniques for interference and artifact reduction, (e) signal filtering, (f) sampling and (g) A/D conversion, These concepts are addressed and discussed, with examples. The second purpose is to outline best practices and provide general guidelines for proper signal detection, conditioning and A/D conversion, aimed to clinical operators and biomedical engineers. Issues related to the sEMG origin and to electrode size, interelectrode distance and location, have been discussed in a previous tutorial. Issues related to signal processing for information extraction will be discussed in a subsequent tutorial

Engineering Novel High-Resolution Bioelectronic Interfaces From Mxene Nanomaterials

At the interface between Man and Machine are electrode technologies. Using recording electrodes, it is possible to observe and monitor the activity of neurons or nervous tissue, affording us with an understanding of the basic dynamics underlying behavior and disease. By interacting with the nervous system through stimulating electrodes, it is possible to impact brain function, or evoke muscle activation and coordination, paving the way for treatments to severe neurological and neuromuscular disorders. However, despite the exciting promises of electrode technologies, current state-of-the-art platforms feature stiff and high-impedance materials, which are incompatible with soft biological tissue. Additionally, many current technologies suffer from shorter lifetimes than may be desirable for a truly chronic implant or wearable health monitoring device. Recently, there has been a shift in focus towards two-dimensional nanocarbons as alternative materials for superior electrode technologies. This comes as a result of the enhanced flexibility, biocompatibility, and electronic and electrochemical properties that most carbon-based nanomaterials exhibit. In particular, the 2D nanomaterial titanium carbide MXene (Ti3C2Tx) has very recently shown great promise for a variety of biomedical applications. However, the long-term stability of Ti3C2Tx has not been fully explored, and it is still unknown whether Ti3C2Tx can be used for chronic bioelectronic applications. Accordingly, in this thesis, I address and explore the key advantages of Ti3C2Tx for biopotential sensing, with a particular emphasis on validating this unique material for chronic recording studies. First, I demonstrate the superior advantages of Ti3C2Tx for direct recording of biopotential signals at the skin level in humans. Second, I define the long-term stability of Ti3C2Tx MXene in dried film form, and explore modifications in synthesis and film assembly to improve the material’s lifetime. Third, I fabricate and validate Ti3C2Tx-based epidermal sensors that exhibit comparable recording capabilities to state-of-the-art clinical electrodes, firmly establishing Ti3C2Tx electrode technologies for future, chronic experiments. The processing and fabrication methods developed herein translate into mature technologies with unique properties that are comparable to state-of-the-art designs, thereby offering a novel bioelectronic platform with the potential to benefit a variety of fields in both the research and clinical settings

Epidermal sensors for monitoring skin physiology

Wearable sensors are revolutionizing personalised healthcare and have continuously progressed over the years in both research and commercialization. However, most efforts on wearable sensors have been focused on tracking movement, spatial position and continuous monitoring of vital signs such as heart rate or respiration rate. Recently, there is a demand to obtain biochemical information from the body using wearables. This demand stems from an individuals’ desire for improved personal health awareness as well as the drive for doctors to continuously obtain medical information for a patients’ disease management. Epidermal sensors are a sub-class of wearable sensors that can intimately integrate with skin and have the potential for monitoring physical changes as well as detecting biomarkers within skin that can be related to human health. The holy grail for these types of sensors is to achieve continuous real-time monitoring of the state of an individual and the development of these sensors are paving the way towards personalised healthcare. However, skin is highly anisotropic which makes it challenging to keep epidermal sensors in consistent contact with skin. It is important that these sensors remain in contact with skin in order to measure its electrical properties and acquire high fidelity signals. The key objective of this thesis is to develop thin conformable, stretchable epidermal sensors for tracking changes in skin physiology. The initial iteration of the screen printed epidermal sensor comprised of a flexible silver film. Impedance spectroscopy was used to understand the electrical signals generated on skin and it was used to measure relative changes due to varying water content. However, this iteration was more suited for single use. The next chapters explore different ink formulations and adherence methodologies to enhance the epidermal sensors adherence to skin. Impedance spectroscopy was used to characterise the electrical signals from these different epidermal sensor iterations, while tensile testing and on-body assessment was used to characterise its mechanical properties. The final chapter focused on investigating the use of phenyl boronic acid (PBA) functionalized hydrogels to modify the epidermal sensor with responsive hydrogel materials to enable chemical sensing of analytes relevant to skin physiology. Impedance spectroscopy was used to characterise and understand the electrical signals generated by the binding interaction of the PBA and analytes using the sensor. Overall, the work demonstrates the challenges of developing these epidermal sensors as well as presenting their potential for continuous monitoring of human skin in the future

Enhancing the longevity and functionality of Ti-Ag dry electrodes for remote biomedical applications: a comprehensive study

This study aims to evaluate the lifespan of Ti-Ag dry electrodes prepared using flexible polytetrafluoroethylene (PTFE) substrates. Following previous studies, the electrodes were designed to be integrated into wearables for remote electromyography (EMG) monitoring and electrical stimulation (FES) therapy. Four types of Ti-Ag electrodes were prepared by DC magnetron sputtering, using a pure-Ti target doped with a growing number of Ag pellets. After extensive characterization of their chemical composition and (micro)structural evolution, the Ti-Ag electrodes were immersed in an artificial sweat solution (standard ISO-3160-2) at 37 °C with constant stirring. Results revealed that all the Ti-Ag electrodes maintained their integrity and functionality for 24 h. Although there was a notable increase in electrical resistivity beyond this timeframe, the acquisition and transmission of (bio)signals remained viable for electrodes with Ag/Ti ratios below 0.23. However, electrodes with higher Ag content (Ag/Ti = 0.31) became insulators after 7 days of immersion due to excessive Ag release into the sweat solution. This study concludes that higher Ag/Ti atomic ratios result in heightened corrosion processes on the electrode’s surface, consequently diminishing their lifespan despite the advantages of incorporating Ag into their composition. This research highlights the critical importance of evaluating electrode longevity, especially in remote biomedical applications like smart wearables, where electrode performance over time is crucial for reliable and sustained monitoring and stimulation.This research was funded by the European Regional Development Fund (ERDF) through the Operational Programme for Competitiveness and Internationalization (COMPETE 2020) under Portugal 2020, in the framework of the NanoStim (POCI-01-0247-FEDER-045908) and NanoID (NORTE-01-0247-FEDER-046985) Projects

A Hybrid-Powered Wireless System for Multiple Biopotential Monitoring

Chronic diseases are the top cause of human death in the United States and worldwide. A huge amount of healthcare costs is spent on chronic diseases every year. The high medical cost on these chronic diseases facilitates the transformation from in-hospital to out-of-hospital healthcare. The out-of-hospital scenarios require comfortability and mobility along with quality healthcare. Wearable electronics for well-being management provide good solutions for out-of-hospital healthcare. Long-term health monitoring is a practical and effective way in healthcare to prevent and diagnose chronic diseases. Wearable devices for long-term biopotential monitoring are impressive trends for out-of-hospital health monitoring. The biopotential signals in long-term monitoring provide essential information for various human physiological conditions and are usually used for chronic diseases diagnosis. This study aims to develop a hybrid-powered wireless wearable system for long-term monitoring of multiple biopotentials. For the biopotential monitoring, the non-contact electrodes are deployed in the wireless wearable system to provide high-level comfortability and flexibility for daily use. For providing the hybrid power, an alternative mechanism to harvest human motion energy, triboelectric energy harvesting, has been applied along with the battery to supply energy for long-term monitoring. For power management, an SSHI rectifying strategy associated with triboelectric energy harvester design has been proposed to provide a new perspective on designing TEHs by considering their capacitance concurrently. Multiple biopotentials, including ECG, EMG, and EEG, have been monitored to validate the performance of the wireless wearable system. With the investigations and studies in this project, the wearable system for biopotential monitoring will be more practical and can be applied in the real-life scenarios to increase the economic benefits for the health-related wearable devices

Digital CMOS ISFET architectures and algorithmic methods for point-of-care diagnostics

Over the past decade, the surge of infectious diseases outbreaks across the globe is redefining how healthcare is provided and delivered to patients, with a clear trend towards distributed diagnosis at the Point-of-Care (PoC). In this context, Ion-Sensitive Field Effect Transistors (ISFETs) fabricated on standard CMOS technology have emerged as a promising solution to achieve a precise, deliverable and inexpensive platform that could be deployed worldwide to provide a rapid diagnosis of infectious diseases. This thesis presents advancements for the future of ISFET-based PoC diagnostic platforms, proposing and implementing a set of hardware and software methodologies to overcome its main challenges and enhance its sensing capabilities. The first part of this thesis focuses on novel hardware architectures that enable direct integration with computational capabilities while providing pixel programmability and adaptability required to overcome pressing challenges on ISFET-based PoC platforms. This section explores oscillator-based ISFET architectures, a set of sensing front-ends that encodes the chemical information on the duty cycle of a PWM signal. Two initial architectures are proposed and fabricated in AMS 0.35um, confirming multiple degrees of programmability and potential for multi-sensing. One of these architectures is optimised to create a dual-sensing pixel capable of sensing both temperature and chemical information on the same spatial point while modulating this information simultaneously on a single waveform. This dual-sensing capability, verified in silico using TSMC 0.18um process, is vital for DNA-based diagnosis where protocols such as LAMP or PCR require precise thermal control. The COVID-19 pandemic highlighted the need for a deliverable diagnosis that perform nucleic acid amplification tests at the PoC, requiring minimal footprint by integrating sensing and computational capabilities. In response to this challenge, a paradigm shift is proposed, advocating for integrating all elements of the portable diagnostic platform under a single piece of silicon, realising a ``Diagnosis-on-a-Chip". This approach is enabled by a novel Digital ISFET Pixel that integrates both ADC and memory with sensing elements on each pixel, enhancing its parallelism. Furthermore, this architecture removes the need for external instrumentation or memories and facilitates its integration with computational capabilities on-chip, such as the proposed ARM Cortex M3 system. These computational capabilities need to be complemented with software methods that enable sensing enhancement and new applications using ISFET arrays. The second part of this thesis is devoted to these methods. Leveraging the programmability capabilities available on oscillator-based architectures, various digital signal processing algorithms are implemented to overcome the most urgent ISFET non-idealities, such as trapped charge, drift and chemical noise. These methods enable fast trapped charge cancellation and enhanced dynamic range through real-time drift compensation, achieving over 36 hours of continuous monitoring without pixel saturation. Furthermore, the recent development of data-driven models and software methods open a wide range of opportunities for ISFET sensing and beyond. In the last section of this thesis, two examples of these opportunities are explored: the optimisation of image compression algorithms on chemical images generated by an ultra-high frame-rate ISFET array; and a proposed paradigm shift on surface Electromyography (sEMG) signals, moving from data-harvesting to information-focused sensing. These examples represent an initial step forward on a journey towards a new generation of miniaturised, precise and efficient sensors for PoC diagnostics.Open Acces