Comparison of silver-plated nylon (Ag/PA66) e-textile and Ag/AgCl electrodes for bioelectrical impedance analysis (BIA)

Recently, researchers have adapted Bioelectrical Impedance Analysis (BIA) as a new approach to objectively monitor wounds. They have indicated various BIA parameters associated to specific wound types can be linked to wound healing through trend analysis relative to time. However, these studies are conducted using wet electrodes which have been identified as possessing several shortcomings, such as unstable measurements. Thus, the adaption of e-textile electrodes has become an area of interest in measuring biosignals. E-textile electrodes are known to possess a significantly large polarization impedance (Zp) that potentially influences these biosignal measurements. In this study we aim to identify the suitability of e-textile electrodes to monitor wounds using BIA methodologies. By adapting suggested methodologies conducted in-vivo from previous studies, we used an ex-vivo model to observe the behaviour of e-textile electrodes relative to time. This was compared to common clinical wet electrodes, specifically Ag/AgCl. The objective of this study was to identify the BIA parameters that can be used to monitor wounds with e-textile electrodes. By analysing the BIA parameters relative to time, we observed the influence of Zp on these parameters.Peer ReviewedPostprint (author's final draft

Bioimpedance spectroscopy - can it be used as a tool for monitoring fluid shifts in burns?

Large fluid shifts and oedema are features of burn injuries. Oedema hampers burn wound healing and is directly related to the size and depth of the burn. The degree of oedema in burns covers a broad spectrum: Minor burns cause localised or peripheral oedema, whilst major burns may result in a systemic inflammatory response which can be life threatening and necessitates formal fluid resuscitation. Acute burn fluid resuscitation is paramount in decreasing patient morbidity and mortality but can contribute to already large amounts of oedema. There is currently no single clinically applicable, non-invasive and accurate outcome measure to titrate fluid volumes in acute burns or monitor the effect of treatments on oedema (in minor and major burns). Bioimpedance spectroscopy (BIS) has emerged as a possible solution to these challenges. It can measure body fluid compartments and thus fluid volume changes over time providing a sensitive non-invasive device to estimate resuscitation requirements and oedema change and is emerging as a measure of wound healing. This series of studies therefore aimed to 1) address the potential barriers to use of BIS in the burns population, 2) determine if BIS provides an accurate measure of whole body/systemic fluid volume change and 3) localised burn wound oedema changes, as applied across the spectrum of burn severity, and 4) determine if BIS can monitor wound healing in minor burns. The studies therefore investigated novel whole body and localised electrode positions in the presence of open and dressed wounds, using repeated measures over time in minor and major burns. The key novel findings arising from the research series include: 1) alternate electrode placements are interchangeable with standardised placement for the measurement of whole body resistance, extracellular and total body fluid volumes in specified dressing conditions. Therefore BIS can be utilised to monitor changes in fluid shifts when wounds preclude the manufacturer’s standard placement of electrodes in the presence of burn wounds, 2) BIS is a reliable method of monitoring fluid in any dressing condition and electrode position with no systematic bias indicated in both major and minor burns, 3) In both minor and major burns, BIS is a valid indicator of net fluid shifts and oedema change, if dressing condition is adjusted for using the developed algorithms or calculator and 4) BIS resistance variables, R0 and Rinf, can be used to monitor wound healing in minor limb burns as an adjunct to standard practice

Flexible Electrodes for Smart Bandages: Feasibility Exploration

Flexible electrodes are revolutionizing the field of wearable health-monitoring and therapeutic devices by enabling the production of large, lightweight, and thin gadgets. These electrodes are incredibly beneficial for collecting bioelectric signals from the human body. They offer stable, high-quality signals while ensuring breathability and skin-friendly contact. Products for which flexible electrodes are actively being developed include innovative wearable devices, portable medical equipment, and brain-computer interfaces. Wearable medical devices necessitate the integration of electrodes, power sources, and microcontroller chips. Flexible electrodes offer several advantages, namely, flexibility, comfort, biocompatibility, and superior signal quality. Flexible electrodes made using conductive ink and a polyurethane film with an adhesive layer are capable of long-term monitoring while maintaining high signal quality. The primary objective of this study is to refine the design of flexible electrodes used in wearable health-monitoring and therapeutic devices. By fabricating micro-perforated structures with various aperture sizes and spacings and applying silver ink on Z-conductive electrodes, the aim is to identify the optimal combination of aperture size and spacing. To this end, a measuring and fitting process is employed. We discovered that Z-conductive electrodes with a hole spacing of 0.28 mm exhibited the lowest impedance values in the low-frequency range of 5 kHz-50 kHz. Comparatively, holes with a spacing of 0.4 mm had the lowest impedance in the high-frequency range of 100-500 kHz. These findings may facilitate future mass production efforts for our industrial partner, Ti2 Pty Ltd. This research contributes to innovation in wearable medical technologies by enhancing the performance of flexible electrodes, thereby improving the quality of biometric signal collection and the comfortability of wearable devices

Characterization of printable electrical sensors applied to cellular cultures

Impedance biosensors have turned in a special interest as label-free and low cost platforms for real time detection of biological phenomena. The objective of this study was to characterize a given model of an interdigitated electrode sensor (model 1) manufactured by inkjet printing technology over a flexible substrate (PET). This characterization was applied to HaCaT cellular cultures at different confluences in order to distinguish an impedance response first associated with the cellular presence and then proportional to the cellular confluence of such presence. With this aim in mind, impedance spectroscopy principle was employed as the main analysis method. From the empirical impedance response, electrical equivalent circuits were obtained by fitting the empirical values with theoretical circuit’s elements. In addition, inverted and scanning electron microscopes were used in order to visualize the whole process, as a way of ensuring that the electrical changes recorded had a real and relevant biological meaning. Three different conditions were tested over the sensor: culture medium without cells, HaCaT epithelial cells seeded over the sensor at 40% of confluence and at 80% of confluence. Impedance responses were recorded each 2 h during 36 h. Results obtained showed that at some point the cellular presence changed the equivalent electrical circuit when compared with the control measurements performed without cells. This change in the circuit has been associated with the cellular attachment of the cells on the IDE, which, as it was later confirmed by the visualization of the cellular culture, has been identified to take place from 22 h on and coincides with the presence of an additional time constant in the electrical circuit. Moreover, the constant phase element of such equivalent circuits was compared for the three conditions, obtaining that its variation is inversely proportional to the area covered by the cells on the sensor. The main drawback encountered during the process was the noise coming at low frequencies that compromise the measurement from 0,1 Hz to 10 Hz. In conclusion, this work has been useful to prove that IDEs can provide an impedance response associated to cellular presence. Based on the main findings, another setup to reduce the noise was proposed (solution design: model 2) and tested for the following experiments, reporting good results.Ingeniería Biomédica (Plan 2010

Developing a real time sensing system to monitor bacteria in wound dressings

Infection control is a key aspect of wound management strategies. Infection results in chemical imbalances and inflammation in the wound and may lead to prolonged healing times and degradation of the wound surface. Frequent changing of wound dressings may result in damage to healing tissues and an increased risk of infection. This paper presents the first results from a monitoring system that is being developed to detect presence and growth of bacteria in real time. It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time. As wounds can produce large volumes of exudate, the initial system reported here was developed to test for the presence of bacteria in suspension. Impedance was measured using disposable silver-silver chloride electrodes. The bacteria Staphylococcus aureus were chosen for the study as a species commonly isolated from wounds. The growth of bacteria was confirmed by plate counting methods and the impedance data were analysed for discernible differences in the impedance profiles to distinguish the absence and/or presence of bacteria. The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities. However, the presence of the silver-silver chloride electrodes tended to inhibit the growth of bacteria. These results indicate that there is potential to create a real time infection monitor for wounds based upon impedance sensing

The detection and prediction of surgical site infections using multi-modal sensors and machine learning: Results in an animal model

IntroductionSurgical Site Infection (SSI) is a common healthcare-associated infection that imposes a considerable clinical and economic burden on healthcare systems. Advances in wearable sensors and digital technologies have unlocked the potential for the early detection and diagnosis of SSI, which can help reduce this healthcare burden and lower SSI-associated mortality rates.MethodsIn this study, we evaluated the ability of a multi-modal bio-signal system to predict current and developing superficial incisional infection in a porcine model infected with Methicillin Susceptible Staphylococcus Aureus (MSSA) using a bagged, stacked, and balanced ensemble logistic regression machine learning model.ResultsResults demonstrated that the expression levels of individual biomarkers (i.e., peri-wound tissue oxygen saturation, temperature, and bioimpedance) differed between non-infected and infected wounds across the study period, with cross-correlation analysis indicating that a change in bio-signal expression occurred 24 to 31 hours before this change was reflected by clinical wound scoring methods employed by trained veterinarians. Moreover, the multi-modal ensemble model indicated acceptable discriminability to detect the presence of a current superficial incisional SSI (AUC = 0.77), to predict an SSI 24 hours in advance of veterinarian-based SSI diagnosis (AUC = 0.80), and to predict an SSI 48 hours in advance of veterinarian-based SSI diagnosis (AUC = 0.74).DiscussionIn sum, the results of the current study indicate that non-invasive multi-modal sensor and signal analysis systems have the potential to detect and predict superficial incisional SSIs in porcine subjects under experimental conditions

Bioimpedance sensors: a tutorial

Electrical bioimpedance entails the measurement of the electrical properties of tissues as a function of frequency. It is thus a spectroscopic technique. It has been applied in a plethora of biomedical applications for diagnostic and monitoring purposes. In this tutorial, the basics of electrical bioimpedance sensor design will be discussed. The electrode/electrolyte interface is thoroughly described, as well as methods for its modelling with equivalent circuits and computational tools. The design optimization and modelling of bipolar and tetrapolar bioimpedance sensors is presented in detail, based on the sensitivity theorem. Analytical and numerical modelling approaches for electric field simulations based on conformal mapping, point electrode approximations and the finite element method (FEM) are also elaborated. Finally, current trends on bioimpedance sensors are discussed followed by an overview of instrumentation methods for bioimpedance measurements, covering aspects of voltage signal excitations, current sources, voltage measurement front-end topologies and methods for computing the electrical impedance

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