REVIEW 1800008 (1 of 14) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advmattechnol.de Survey on Textile Electrode Technologies for Electrocardiographic (ECG) Monitoring, from Metal Wires to Polymers Danilo Pani,* Andrea Achilli, and Annalisa Bonfiglio DOI: 10.1002/admt.201800008 Wearable devices and smart textiles also represent target technologies in the military sector, [3] even though healthcare remains the most interesting market, potentially enabling the development of new healthcare system models ensuring significant cost reductions. Nevertheless, this market is also the most challenging one, with several barriers, [4] regulatory issues, [5] and blurred boundaries between consumer health wearables and medical devices accepted in clinical practice, which leads the patients to make improper med- ical use of the data generated by their devices. [6] Incontrovertibly, different cat- egories of subjects (from neonates to elderly), including patients with specific health conditions, could achieve substan- tial benefits using wearable devices. [7,8] The market of wearables and smart textiles is research- driven, as demonstrated by the high number of projects in the field funded by the European Commission in the framework of the Horizon 2020 program (Table 1) compared to those in the 6th and 7th framework programmes. [9] This survey aims to present the main characteristics of the current wearable and smart textile technologies developed for electrocardiographic (ECG) signal monitoring, with a spe- cial focus on electrodes, which currently represents the most critical aspect to deal with, and the approaches to their char- acterization. The research interest for this specific aspect is demonstrated by the exponentially growing number of publica- tions on textile electrodes resulting from the Scopus database (www.scopus.com) (Figure 1). Remarkably, the same trend can be observed for other keywords, such as wearable, monitoring, and human. [10] A more detailed analysis of the research fields associated with these publications revealed that the largest part of these works belonged to engineering (22%), material sci- ence (15%), and chemistry or chemical engineering (22%) and related to the development of these devices. Meanwhile, only 7% of the publications were a medical journal, reflecting the current limitations of such technologies for clinical application. The survey is organized as follows: Section 2 briefly presents the main aspects of wearable devices, smart materials and tex- tiles to highlight the key features that textile electrodes must have to represent valuable alternatives to traditional solutions for biopotential monitoring; Section 3.4 presents an over- view of the textile electrode technologies for ECG recordings, Wearable technologies represent the new frontier of vital sign monitoring in different applications, from fitness to health. With the progressive min- iaturization of the electronic components, enabling the implementation of portable and hand-held acquisition and recording devices, the research focus has shifted toward the development of effective and unobtrusive textile electrodes. These electrodes can represent an alternative to the Ag/AgCl dis- posable gelled electrodes usually adopted in clinical practice. This survey pre- sents the main requirements for these electrodes, with a particular emphasis on those conceived for electrocardiographic signals, and the main challenges to be faced. An overview of the main materials and fabrication technologies presented so far in the scientific literature for this purpose is also given. The pieces of evidence resulting from the test of these electrodes clearly reveal the virtues and vices of current technologies, prospectively opening to their use in smart garments for real application scenarios. Dr. D. Pani, A. Achilli, Prof. A. Bonfiglio DIEE Department of Electrical and Electronic Engineering University of Cagliari Piazza d’Armi, 09123 Cagliari, Italy E-mail: pani@diee.unica.it The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admt.201800008. Textile Electrocardiographic Electrodes 1. Introduction The interest in wearable devices and smart textiles is continu- ously growing, fostered by the growth of the research in the field and by the continuous introduction of novel products in the market. In 2016, IDTechEx (www.idtechex.com) depicted the wearable technology sector as a market with great opportu- nities of expansion and expected to reach 51.6 billion USD by 2022. This compound annual growth rate of 15.5% is caused by the involvement of the big companies in the sector, such as Google, Apple, Adidas, Nike, Samsung, and Intel. [1] Con- sidering an estimated number of 3 billion wearable sensors by 2025, the fast growth is associated with the introduction of consumer products (e.g., smart wrist-wears for wellness, fitness, health, and fashion applications) on the market along with a growing popularity of the Internet of things and connected devices. [2] Adv. Mater. Technol. 2018, 1800008