Review
Progress and challenges in fabrication of wearable sensors for health monitoring

https://doi.org/10.1016/j.sna.2020.112105Get rights and content

Abstract

Rapid development in sensor technology, has led to fabrication of high-performance wearable sensors with application in human health monitoring. As human health is an utmost importance issue, various high-tech equipment has been developed to use in continuous health monitoring. The favorable properties of wearable sensors, make them an appropriate choice in medical applications. In this context, wearable sensors designed, produced and utilized in human health care systems which can facilitate diseases diagnosis. Depend on the type of sensor, a specific parameter such as heart beat, pressure, and temperature can be monitored and measured. This review attempts to summarize the progress and challenges in fabrication of wearable sensors for human health monitoring. In this context, applications of wearable sensors are divided into (a) biophysical tracking, (b) biochemical monitoring, and (c) detection of real-time data. Moreover, details of medical wearable sensors are outlined. In this regard, types of sensors, their materials and fabrication processes are explained. Finally, performance and current challenges in this field are briefly discussed. The documented analysis and discussion in this paper show the advantages and limitations in this field, and also highlight needs for next researches. This review confirmed that the emergence of wearable sensors has opened new horizons for human health monitoring.

Introduction

Engineering sciences and their principles have found essential roles in medicine. In today's society, applications of engineering techniques have tied to human healthcare. In this context, advances in electronics can overcome the limitations. In fact, applications of different sensors in human healthcare is a promising approach to solving various problems in this field.

Different wearable sensors have gained significant interest over the past few years. Wearable sensors can be defined as devices which can be worn by humans to track human health. Based on the advances in fabrication of sensors, wearable health sensors have been developed for several purposes [1], [2], [3]. In this regard, various wearable sensors have been fabricated to recognize different disease [4]. For instance, in [5] human motion was monitored via a wearable sensor. In detail, a flexible graphene film was utilized in fabrication of a strain sensor to detect human motion for medical applications. The produced wearable strain sensor was encapsulated with nylon fabric, and its resistance and conductivity were tested. Consequently, a good performance of the sensor was reported. More recently, a wireless wearable sensor was developed to monitor tooth fracture [6]. Indeed, the graphite was used in the wearable bio-tooth sensor and it was coated with resin. The produced sensor was able to diagnose different motions, such as drinking, chewing, and speaking. The sensor was tested on several patients to determine oral activities. The documented results indicated promising diagnostic method.

Using wearable sensor in monitoring of health status of human body was one of the earliest developments in this type of sensor in several years ago [7]. Later, at the beginning of the current century a wearable sensor was developed for continuous monitoring beat-to-beat pulsation [8]. A comprehensive history of wearable sensors is presented in [9]. However, advances in electronics, has led to new class of electronic devices. Indeed, different attempts have been made toward wearable electronics over the years [10], [11], [12]. It is noteworthy that there are different detection principles, such as strain, force, displacement, tactile, and pressure. In [13] a wearable fabric tactile sensor was produced. Later, in [14] a force sensor was produced to use in a wearable system. In RMIT University at Melbourne, researchers have worked on electronic skin which can be considered as a part of health care [15]. Wearable sensors can be divided to two main groups: (a) physical, and (b) electrochemical. As it has been documented in Grand View Research Inc., wearable sensors market worth will reach $ 2.86 Billion by 2025 [16]. This indicates the interest in wearable sensors which cover several branch of science and technology. However, as described in [17], wearable electrochemical sensors attracted less attention than physical detectors in wearable device during the last decade.

Wearable sensors can be used not only by the people with reduced access to doctors, but also during the recovery period. Hospitalization is expensive and wearable sensors can provide continuous monitoring of health parameters without visiting hospitals frequently. However, there are limitations in real-time monitoring of parameters in each wearable sensors. Therefore, different types of sensors are needed to measure various health parameters. Over the years, different fabrication process have been develop to produce this family of sensor for health care, detection of pathogens, and clinical purposes [18], [19], [20]. Advances in microelectronics and nanomaterials provide a wide range of scenarios for development of wearable health monitoring systems. As pressure variation can show deteriorating actions, pressure monitoring has been considered in different wearable health sensors. However, monitoring human body conditions including wrist pulse, heart and breath rate, temperature, and motion have been performed by wearable and flexible sensors.

In the current study, we have surveyed and divided applications of wearable sensors into (a) biophysical tracking, (b) biochemical monitoring, and (c) detection of real-time data. In this study, the documented researches have been analyzed based on application of these three sub-domains of human health monitoring. Owing to the promising applications of wearable sensors in health care, we believe that it is expedient to present a comprehensive and concise review of this topic. The main objective of this review is to summarize, explain and compare recent advances in fabrication of wearable sensors in healthcare. Moreover, challenges and summary of current issues are presented. The rest of this papers is organized as follows, where the next section describes usage of wearable sensors in health monitoring. Section 3 presents current progress in wearable sensors. Performance and challenges are summarized in Section 4. The conclusion has been presented in Section 5.

Section snippets

Wearable sensors in health monitoring

Developments of wearable and flexible sensors for disease forecasting and health monitoring and have been significantly increased in the past few years [21]. In this context, fabricated wearable sensors have been placed on chest or wrist to record or detect different important physiological parameters. These sensors are able to inform the users whenever there is an abnormal condition. This can protect human health by providing time to do preventive measures.

In order to obtain higher

Engineering issues in wearable health sensors

Technological development of wearable sensors depend on a wide variety of engineering aspects, such as material science, engineering design, fabrication processes, and assembly technology. Herein, we briefly discuss materials and fabrication processes of wearable health sensors in the following subsections.

Performance and challenges

In this section, key parameters in performance of wearable sensors and some challenging issues are briefly presented. The key metrics in evaluation of wearable sensors are as follows:

  • -

    Stretchability: is an important parameter in assessment of wearable sensors. Stretchability is defined by the Young's modulus of the sensor obtained from tensile test (E = /), where σ and ε are stress and corresponding strain, respectively. Generally, stretchability is reported by the maximum strain which can

Conclusions

Based on the innovations, wearable sensors have been developed as portable electronic equipment that play important role in the field of human health monitoring. Wearable health sensors have garnered increasing attention owing to their potential in providing reliable measurements. In this respect, various systems have been proposed to measure different human health parameters. This paper presents recent developments in fabrication of wearable sensors in biophysical and biochemical monitoring

Conflict of interest

None declared.

Acknowledgments

The first author would like to acknowledge the Exist-GS program for the research project “Node 4.0” (Exist-GS 03EGSNW668) which has been funded by the Federal Ministry of Economics and Energy (BMWi) and the European Social Fund (ESF).

Dr.-Ing. Sara Nasiri is a postdoctoral research associate at the Department of Electrical Engineering & Computer Science at the University of Siegen, Germany. She got her Ph.D. in computer science from the University of Siegen in 2018. She is also the co-founder and leader of Node 4.0 project, a startup for intelligent system integration solutions in Industry 4.0. Her research interests include application of artificial intelligence techniques with a special focus on an integration of knowledge

References (191)

  • Y. Li et al.

    Flexible and wearable healthcare sensors for visual reality health-monitoring

    Nano Energy

    (2019)
  • M.M. Hassan et al.

    A robust human activity recognition system using smartphone sensors and deep learning

    Future Gener. Comput. Syst.

    (2018)
  • S. Chernbumroong et al.

    A practical multi-sensor activity recognition system for home-based care

    Decis. Support Syst.

    (2014)
  • P. Fayyaz Shahandashti et al.

    Highly conformable stretchable dry electrodes based on inexpensive flex substrate for long-term biopotential (EMG/ECG) monitoring

    Sens. Actuators A

    (2019)
  • A.D. De Vore et al.

    The future of wearables in heart failure patients

    JACC: Heart Fail.

    (2019)
  • S. Chen et al.

    Hierarchical elastomer tuned self-powered pressure sensor for wearable multifunctional cardiovascular electronics

    Nano Energy

    (2020)
  • Y. Zeng et al.

    Positive temperature coefficient thermistors based on carbon nanotube/polymer composites

    Sci. Rep.

    (2014)
  • R. Sun et al.

    Novel sensing technology in fall risk assessment in older adults: a systematic review

    BMC Geriatrics

    (2018)
  • M. Patel et al.

    Wearable inertial sensors to measure gait and posture characteristic differences in older adult fallers and non-fallers: a scoping review

    Gait Posture

    (2020)
  • P. Bet et al.

    Fall detection and fall risk assessment in older person using wearable sensors: a systematic review

    Int. J. Med. Inform.

    (2019)
  • J. Zhang et al.

    Highly stretchable and self-healable MXene/polyvinyl alcohol hydrogel electrode for wearable capacitive electronic skin

    Adv. Electron. Mater.

    (2019)
  • X. Chen et al.

    Flexible one-structure arched triboelectric nanogenerator based on common electrode for high efficiency energy harvesting and self-powered motion sensing

    AIP Adv.

    (2018)
  • Y.T. Jao et al.

    A textile-based triboelectric nanogenerator with humidity-resistant output characteristic and its applications in self-powered healthcare sensors

    Nano Energy

    (2018)
  • M.S. Rasel et al.

    An impedance tunable and highly efficient triboelectric nanogenerator for large-scale, ultra-sensitive pressure sensing applications

    Nano Energy

    (2018)
  • W. Choi et al.

    Stretchable triboelectric multimodal tactile interface simultaneously recognizing various dynamic body motions

    Nano Energy

    (2019)
  • L. Sun et al.

    Ionogel-based, highly stretchable, transparent, durable triboelectric nanogenerators for energy harvesting and motion sensing over a wide temperature range

    Nano Energy

    (2019)
  • S. Aziz et al.

    Smart-fabric sensor composed of single-walled carbon nanotubes containing binary polymer composites for health monitoring

    Compos. Sci. Technol.

    (2018)
  • H. Sun et al.

    Highly stretchable, transparent, and bio-friendly strain sensor based on self-recovery ionic-covalent hydrogels for human motion monitoring

    Macromol. Mater. Eng.

    (2019)
  • T. Li et al.

    A flexible strain sensor based on CNTs/PDMS microspheresfor human motion detection

    Sens. Actuators A

    (2020)
  • P. Kassal et al.

    Wireless chemical sensors and biosensors: a review

    Sens. Actuators B

    (2018)
  • A. Turner

    Biosensors: then and now

    Trends Biotechnol.

    (2013)
  • A.J. Bandodkar et al.

    Non-invasive wearable electrochemicalsensors: a review

    Trends Biotechnol.

    (2014)
  • Y. Jiao et al.

    Wearable graphene sensors with microfluidic liquid metal wiring for structural health monitoring and human body motion sensing

    IEEE Sens. J.

    (2016)
  • S. Rhee et al.

    Artifact-resistant power-efficient design of finger-ring plethysmographic sensors

    IEEE Trans. Biomed. Eng.

    (2001)
  • J. Heikenfeld et al.

    Wearable sensors: modalities, challenges, and prospects

    Lab Chip

    (2018)
  • P. Gutruf et al.

    Stretchable gas and UV sensors towards wearable electronics

  • P. Gutruf et al.

    Transparent functional oxide stretchable electronics: micro-tectonics enabled high strain electrodes

    NPG Asia Mater.

    (2015)
  • Y. Hasegawa et al.

    Fabrication of a wearable fabric tactile sensor produced by artificial hollow fiber

    J. Micromech. Microeng.

    (2008)
  • S. Kitamura et al.

    Cylinder-shaped thermal inertial force sensor for wearable fabric sensor systems

    Proceedings of the 16th International Solid-State Sensors, Actuators and Microsystems Conference, Beijing, China

    (2011)
  • Stretchable and Wearable Electronics and Sensors. http://www.functionalmaterials.info (Accessed 08 March...
  • Wearable Sensors Market Worth. http://www.grandviewresearch.com/press-release/wearable-sensors-market (Accessed 12...
  • J.R. Windmiller et al.

    Wearable electrochemical sensors and biosensors: a review

    Electroanalysis

    (2012)
  • M. Ahmed et al.

    MEMS force sensor in a flexible substrate using nichrome piezoresistors

    IEEE Sens. J.

    (2013)
  • J. Rogers et al.

    Wearable bioelectronics: opportunities for chemistry

    Acc. Chem. Res.

    (2019)
  • S. Ramasamy et al.

    Wearable sensors for ECG measurement: a review

    Sens. Rev.

    (2018)
  • M. Georgu et al.

    Recognizing hand and finger gestures with IMU based motion and EMG based muscle activity sensing

  • A.R. Anwary et al.

    An automatic gait feature extraction method for identifying gait asymmetry using wearable sensors

    Sensors

    (2018)
  • H. Gjoreski et al.

    Activity/posture recognition using wearable sensors placed on different body locations

  • J. Parkka et al.

    Activity classification using realistic data from wearable sensors

    IEEE Trans. Inform. Technol. Biomed.

    (2006)
  • M. Georgu et al.

    From smart to deep robust activity recognition on smart watches using deep learning

  • Cited by (149)

    View all citing articles on Scopus

    Dr.-Ing. Sara Nasiri is a postdoctoral research associate at the Department of Electrical Engineering & Computer Science at the University of Siegen, Germany. She got her Ph.D. in computer science from the University of Siegen in 2018. She is also the co-founder and leader of Node 4.0 project, a startup for intelligent system integration solutions in Industry 4.0. Her research interests include application of artificial intelligence techniques with a special focus on an integration of knowledge based methods (e.g., CBR) in the medical and mechanical engineering systems.

    Dr.-Ing. Mohammad Reza Khosravani is a postdoctoral research fellow in the Department of Mechanical Engineering at the University of Siegen, Germany. He earned his Ph.D. degree in mechanical engineering from University of Siegen, with emphasis on fracture mechanics. His research interests include mechanical behavior of materials at high strain rates, additive manufacturing, mechanics of composite materials, 3D-printed sensors, and applications of artificial intelligence in fracture mechanics.

    View full text