A hybrid microfluidic platform for energy harvesting based on piezoelectricity and reverse electrowetting for wearable biosensors

The continuous monitoring of human biomarkers in wearable biosensors requires constant energy supply and the usage of batteries introduces a number of limitations. A self-rechargeable biosensor would prove to be beneficial and vital in a timely medical diagnosis and prevention of health implications. This study explores the proof of concept of a novel microfluidics platform of simultaneous harvesting energy from an arterial wall pulsation through piezoelectricity and from the reverse electrowetting on dielectric (REWOD) phenomenon. Both physical principles are successfully employed in conventional designs as separate actuating and sensory units, yet their combined incorporation is often overlooked. A designed hybrid droplet microfluidics platform utilizes piezoelectric films to react to perturbations caused by pulsation of arteries and to press down droplets while electrodes around the microchannel collect energy from deformed droplets. This hybrid approach allows enhanced energy harvesting. A commercial multi-physics based Computational Fluid Dynamics (COMSOL) software was used to verify the posited hypothesis and to carry out a set of time-varying flow simulations with parametric variation of a number of physical and geometrical parameters. As a result, the interrelations between various physical parameters of the designed system, such as viscosity, surface tension, flow velocity, frequency and amplitude of pressure variations occurring on microchannel walls, droplet properties, droplet number and distribution, wetting and de-wetting frequency etc, were investigated and correlated with the produced electrical generation aiming towards its maximisation. The design and control of microfluidic parameters are highly important for the optimised performance of the prototype device. Furthermore, based on the analysis and quantification of the extracted energy results, a number of design recommendations are provided and a forecast of potential applications and innovations such as wearable and implantable biosensors, continuous monitoring of medical conditions for personalized medicine is outlined

Recent Advances in Energy Harvesting from the Human Body for Biomedical Applications

Energy harvesters serve as continuous and long-lasting sources of energy that can be integrated into wearable and implantable sensors and biomedical devices. This review paper presents the current progress, the challenges, the advantages, the disadvantages and the future trends of energy harvesters which can harvest energy from various sources from the human body. The most used types of energy are chemical; thermal and biomechanical and each group is represented by several nano-generators. Chemical energy can be harvested with a help of microbial and enzymatic biofuel cells, thermal energy is collected via thermal and pyroelectric nano-generators, biomechanical energy can be scavenged with piezoelectric and triboelectric materials, electromagnetic and electrostatic generators and photovoltaic effect allows scavenging of light energy. Their operating principles, power ratings, features, materials, and designs are presented. There are different ways of extracting the maximum energy and current trends and approaches in nanogenerator designs are discussed. The ever-growing interest in this field is linked to a larger role of wearable electronics in the future. Possible directions of future development are outlined; and practical biomedical applications of energy harvesters for glucose sensors, oximeters and pacemakers are presented. Based on the increasingly accumulated literature, there are continuous promising improvements which are anticipated to lead to portable and implantable devices without the requirement for batteries

A hybrid piezoelectric and electrostatic energy harvester for scavenging arterial pulsations

Implantable and wearable biomedical devices suffer from a limited lifespan of on-board batteries which require change causing physical discomfort. In order to overcome this, various energy harvesters have been developed as the human body possesses several types of energy available for scavenging through appropriately designed energy harvesting devices, while the cardiovascular system in particular represents a constant reliable source of mechanical energy from vibration. Most conventional energy harvesters exploit only a single phenomenon, such piezo- or triboelectricity, thus producing reduced power density. As an improvement, hybridisation of energy harvesters intends to negate this drawback by simultaneously scavenging energy by multiple harvesters. In the present work, the reverse electrowetting on dielectric (REWOD) phenomenon is combined with the piezoelectric effect in a proof-of-concept hybrid harvester for scavenging biomechanical energy from arterial or other type pulsations. A mathematical model of the harvester was developed; and, an investigation using computational fluid dynamics simulations was carried out using the COMSOL Multiphysics software. The effect of the materials of piezoelectric film and geometrical features of the harvester on parameters such as the displacement, the frequency of pulsations and the energy produced were studied. An experimental setup that could model the time-varying pressures and displacements caused from arterial pulsations was designed and the characteristics of the produced piezoelectrical energy were analysed. A comparison between experimental and computational data was carried out demonstrating a good agreement. The dependencies between geometrical parameters and electrical output were determined and recommendations on piezoelectric materials and design solutions were provided

Computational and Experimental Investigation of Microfluidic Chamber Designs for DNA Biosensors

A critical characteristic for continuous monitoring using DNA biosensors is the design of the microfluidics system used for sample manipulation, effective and rapid reaction and an ultra-low detection limit of the analyte. The selection of the appropriate geometrical design and control of microfluidic parameters are highly important for the optimum performance. In the present study, a number of different shapes of microchambers are designed and computationally assessed using a Multiphysics software. Flow parameters such as pressure drop, and shear rates are compared. Three-dimensional printing was used to construct the designs and an experimental investigation is underway for the validation of the computational results

A 3D-Printed Piezoelectric Microdevice for Human Energy Harvesting for Wearable Biosensors

The human body is a source of multiple types of energy, such as mechanical, thermal and biochemical, which can be scavenged through appropriate technological means. Mechanical vibrations originating from contraction and expansion of the radial artery represent a reliable source of displacement to be picked up and exploited by a harvester. The continuous monitoring of physiological biomarkers is an essential part of the timely and accurate diagnosis of a disease with subsequent medical treatment, and wearable biosensors are increasingly utilized for biomedical data acquisition of important biomarkers. However, they rely on batteries and their replacement introduces a discontinuity in measured signals, which could be critical for the patients and also causes discomfort. In the present work, the research into a novel 3D-printed wearable energy harvesting platform for scavenging energy from arterial pulsations via a piezoelectric material is described. An elastic thermoplastic polyurethane (TPU) film, which forms an air chamber between the skin and the piezoelectric disc electrode, was introduced to provide better adsorption to the skin, prevent damage to the piezoelectric disc and electrically isolate components in the platform from the human body. Computational fluid dynamics in the framework of COMSOL Multiphysics 6.1 software was employed to perform a series of coupled time-varying simulations of the interaction among a number of associated physical phenomena. The mathematical model of the harvester was investigated computationally, and quantification of the output energy and power parameters was used for comparisons. A prototype wearable platform enclosure was designed and manufactured using fused filament fabrication (FFF). The influence of the piezoelectric disc material and its diameter on the electrical output were studied and various geometrical parameters of the enclosure and the TPU film were optimized based on theoretical and empirical data. Physiological data, such as interdependency between the harvester skin fit and voltage output, were obtained

A hybrid piezoelectric and electrostatic energy harvester for scavenging arterial pulsations

Implantable and wearable biomedical devices suffer from a limited lifespan of on-board batteries which results in a requirement to change the battery or the device itself causing additional physical discomfort. In order to overcome this, various energy harvesters have been developed. The human body possesses several types of energy available for scavenging through appropriately designed energy harvesting devices, while cardiovascular system in particular represents a constant reliable source of mechanical energy from vibration. Most conventional energy harvesters exploit only a single phenomenon, such piezo- or triboelectricity, thus producing reduced power density. As an improvement, hybridisation of energy harvesters intends to negate this drawback by simultaneously scavenging energy by multiple harvesters. In the present work, the reverse electrowetting on dielectric (REWOD) phenomenon is combined with the piezoelectric effect in a proof-of-concept hybrid harvester for scavenging biomechanical energy from arterial or other type pulsations. A mathematical model of the harvester was developed, and a computational investigation using CFD, and fluid-structure interaction simulations were carried out using the COMSOL Multiphysics software. The effect of the materials of piezoelectric film and geometrical features of the harvester on parameters such as the displacement, the frequency of pulsations and the energy produced were studied. An experimental setup that could imitate the displacements caused from arterial pulsations was designed and the produced electrical energy characteristics were analysed. A comparison between experimental and computational data was carried out and demonstrated a good agreement. Dependencies between geometrical parameters and electrical output were obtained, recommendation on piezoelectric materials and design solutions were provided

A 3D printed wearable piezoelectric platform for energy harvesting from artery pulsation

Continuous monitoring of physiological biomarkers is an essential part of timely and accurate diagnosis of a disease with subsequent medical treatment towards personalised medicine. Wearable biosensors are used for biomedical data acquisition of important biomarkers, these devices rely on batteries. Battery replacement introduces a discontinuity in measured signals which could be critical for the patients and also causes discomfort. Human body is a source of multiple types of energies, such as mechanical, thermal, and biochemical, all of which can be scavenged. Mechanical vibrations originating from contraction and expansion of the radial artery represents a reliable source of displacement to be picked up by a harvester. In present work a 3D printed wearable platform for scavenging energy of arterial pulsations via a piezoelectric material is described. To provide better adsorption to the skin, prevent damage to the piezoelectric disc and electrically isolate components in the platform from the human body, an elastic thermoplastic polyurethane (TPU) film, which forms an air gap between the skin and the piezoelectric disc electrode, was introduced. Computational fluid dynamics in the framework of a Multiphysics software was employed to conduct a series of coupled physics phenomena simulations. The mathematical model of the harvester was studied, and output energy parameters were obtained. A prototype wearable platform enclosure was designed and manufactured with fused deposition modelling. Influence of the piezoelectric disc material and diameter on the output were studied, geometrical parameters of the enclosure and TPU film were optimised based on theoretical and empirical data. Physiological data, such interdependency between the harvester skin fit and voltage output, were obtained. Further study regarding the hybridisation of the developed energy harvester was provided

Arterial pulsations as an energy source for a hybrid piezoelectric/electrostatic energy microharvester

Human cardiovascular system represents an effective pumping mechanism that produces pulsations. Their energy can be picked up with the help of energy microharvesters. These are bioelectronic microdevices which transduce input energy into electrical power. This work focuses on hybridisation of piezoelectric effect and reverse electrowetting on dielectric phenomenon (REWOD). Mathematical modelling was used for the proposed energy harvester design validation. Piezoelectric harvester exciter was designed for investigation of different parameters such as chamber height, pulsation amplitude, piezoelectric disc diameter and material. Empirical data were compared to computational results. Hybrid harvester design recommendations were formulated

A Hybrid Piezoelectric and Reverse Electrowetting Energy Harvester for Wearable Biosensors

Wearable biosensors play a critical role for healthcare monitoring. However, reliance of biosensors on batteries has serious drawbacks. Although the human body energy can be converted into electricity with energy harvesters. Hybridization of multiple energy harvesters is a prominent trend to increase the power output. In this work a hybrid piezoelectric and reverse electrowetting (REWOD) energy harvester is proposed. The main principle of working is based on the presence of electrical double layer in REWOD component and the coupling with a piezoelectric nanogenerator via an electret. The proposed energy harvester design was tested numerically and in a series of experiments