What do your clothes say about you and your surroundings? Current trends in textile developments

Introduction

Technical textiles and intelligent materials are revolutionising our clothing by introducing new functions such as sensing, actuating and wireless communications. By introducing sensing elements to textiles it is possible to provide on-demand information regarding the wearer in an innocuous manner. These "smart" textiles allow the wearer's health to be monitored while also detecting hazardous situations in their environment. Such garments may be used to monitor well-being and safety in extreme conditions experienced by military or security services. These garments may also be found in the home, providing citizens with a personalised healthcare system targeting prevention and early detection of illness. This is changing the conventional healthcare approach where physicians are only privy to “snap-shots” of the individual’s health through sporadic surgery visits.

Research in this field to date has focused primarily on physical sensors and transducers, i.e. they convert physical properties into electrical signals. Wearable sensors have been developed to measure signals such as body temperature, electro-cardiogram, electromyogram, and breathing rhythm. These developments are already reaching the marketplace, such as the Smartshirt by Sensatex™ [1]and the Life Shirt® system by Vivometrics®[2]. However, for a greater contextual awareness, the introduction of chemical and bio-sensors will be needed to provide supplementary information regarding our well-being. Textile-based chemical sensors are currently being developed to monitor the health status of the individual and also to detect potential threats within the environment. This research is carried out within two EU projects - BioTex [3]and ProeTex[4]. These are a follow-on from previous studies in physiological monitoring, MyHeart and WEALTHY[5], and form part of the EU roadmap in wearable technologies, shown in Figure 1. The aim of Biotex is to look inwards to the body’s health through analysis of body fluids such as sweat, blood and wound exudate. ProeTex monitors the surrounding atmosphere for hazardous gases such as carbon monoxide.

Textile/Sensor Integration

Seamless integration of the sensing elements into the textile is imperative. There is often a major stumbling block in creating an electronic blend of brittle silicon circuitry with soft and flexible fabrics. Developing any type of wearable sensor must ensure that the look and feel of the textile is maintained. A garment will not be useful unless it retains the usual tactile, flexible and comfortable properties of clothing. Much work in the field of smart clothing features conventional electronics overlaid onto a textile substrate and yields problems of connections, bulkiness, wearability and washability. To do this textile techniques must be considered when integrating the new functionalities. Manipulation at the nano-scale is a very desirable approach, and this may be carried out at fibre spinning level, during yarn/fabric formations or at the finishing stage. [6]

The implementation of chemical and bio-sensors has been slow in comparison to the prevalence of transducers due to the number of issues involved by their tricky integration. Chemical and bio-sensors by their nature are complex systems; they possess in addition to a transduction platform, a highly selective and reactive layer which must be exposed to the target sample in order for the reaction to occur. Thus, the sample must be delivered to the sensor, so sample movement on the textile is highly important. These chemical and biological reactions occur at the micro level and can be influenced through manipulation of the molecules attached. Because of the highly reactive nature of these sensing layers, it is possible that they will change their properties over time. Therefore, in order to be confident in the signal that is generated by the chemical or bio-sensors, compensation for these changes must be considered. This is done, either by regenerating the reactive surface so that an identical surface is available for each measurement or by performing calibrations to determine the behaviour of the system. Either option will increase the complexity of the sensor by introducing the need for reagents, fluid movement procedures or adaptable materials that can be activated or pacified on demand.

Integration of the sensor into the textile interface depends on the state of the sample being monitored. If the sensor is detecting the external environment, e.g. acidic gas plumes, the sample is likely to be volatile, whereas if the sensor is monitoring the body’s physiology e.g. sweat analysis, fluid must be delivered to the sensor. In the case of body fluids, sample collection and delivery ideally should be incorporated within the layers of the garment, whereas external gaseous sampling requires the sensor to be positioned at the outer edge of the garment interface, where contact between the sensor and the sample will be optimal. The sensor itself must be robust, miniature, flexible, washable and ideally textile-based. The overall assembly of sensor must be safe for the wearer’s health. Non-toxic or hazardous chemicals must be avoided or well isolated from the wearer.

The BioTex and Proetex projects are tackling these issues, by developing textile based sensors and designing specifically for wearable applications. Fitting to a person necessitates a new way of thinking, and human factors play a major issue in terms of design, and also in data analysis. Effects such as motion on the signal integrity must also be considered. The human body’s physiology is not always straightforward or fully understood and there is wide difference between individuals. It is hoped that this approach, with wearable continuous sensing, will provide further insight into the body’s physiology, assessing it at work, while also providing a means of early detection of illness.

BioTex – monitoring citizen health

The aim of the EU-supported BioTex project is to perform real-time analysis of various constituents in body fluids, such as sweat and wound exudate. There are three target applications of the BioTex project – sports and human performance, patient monitoring and wound monitoring.

Sports and human performance

Physiological testing can serve as a valuable tool for athletes and coaches to check the athlete’s health and develop individualised training strategies. While laboratory testing may be increasingly widespread there is a great demand for wearable sensors to be used in the field. For effective rehydration strategies it is important not only to replace volume losses, but also electrolytes. The electrolyte composition of sweat is highly variable among individuals; although it might be theoretically optimal to match electrolyte loss with equal quantities in a rehydration drink, this is virtually impossible in a practical situation with current technology and it is impossible to prescribe a general fluid replacement plan that will meet the needs of all athletes[7]. At present, monitoring electrolyte concentrations in sweat is carried out in the laboratory setting using sweat patches. These patches must then be sent away for analysis, an impractical scenario for frequent monitoring. Also, athletes typically estimate their own fluid requirements by weighing themselves before and after exercise sessions, but this does not give an accurate picture of electrolyte balance. BioTex aims to provide real-time feedback regarding electrolyte concentration, sweat rate and pH of sweat in addition to monitoring cardiac and respiratory functions.

Patient monitoring

Wearable sensors, enabling monitoring of long-term and short-term healthcare needs have a huge potential for disease prevention in medicine and for diagnosis. This introduces a continuity of care system where the individual may be assessed in a realistic setting within their natural environment as they partake in daily activities.

This can overcome the problem of infrequent clinical visits that may fail in sampling rare events that may be of important diagnostic importance.

Providing feedback on health and well-being through clothing will allow a patient to take care of his/her own healthcare at home. This is part of the concept of personalised healthcare, empowering the individual to take charge of their own well-being. For healthy subjects, this may help them adopt a healthier lifestyle and thus improve personal performance. If the person is at risk of disease wearable sensors may provide information on their overall well-being and in the occurrence of complications, the wearer may be alerted to contact their physician.[8]

Wound healing monitoring

Another application area the BIOTEX project is targeting is monitoring the wound healing process by measuring the physiological parameters such as growth factors and histamine. The idea is to keep both patients and doctors informed about wound evolution and complications. The sensor will consist in a patch incorporated in a textile (garment or wound dressing) that could be placed in contact with a wound from the first day on allowing monitoring of the injury evolution either in hospital or at home.