The development of a washable and durable smart textile to measure
electrodermal activity for early stress recognition
Authors: Leborgne François , Smits Reon , Gencheva Maya , De Vries Stefan , Meinders Erwin , Cluitmans Pierre , Lee Chris , Kuhlmann Jan-carlos 
Published: February 2023

This paper presents the results of the development of a new sock garment
with integrated electrodes for monitoring physiological signals for stress
detection in people with intellectual disabilities or dementia.
Misunderstood stress-induced behaviours reduce the quality of life of these
individuals and complicate caregiver support and treatment, as the correct
interpretation of these behaviours. One of the physiological parameters most
related to stress is electrodermal activity (EDA). It shows a direct
response to the sympathetic nervous system activation ('fight or flight'
response) in the form of a change in skin electrical properties such as skin
conductance (SC) or skin impedance (SI). The phasic component of EDA is
associated with short-term events and occurs in the presence of stimuli that
control sweat gland activity. Therefore, analysis of this signal can be used
as an indicator of emotional arousal or stress.To continuously measure EDA
on an individual, a comfortable, durable, and easy-to-use carrier is
essential. Current medical electrode patches (carriers) have limited
user-friendliness because of their large shape and risk of skin irritation
during extended use. Besides, the daily disposal of electrode patches would
pose a major supply chain challenge and generate large amounts of medical
waste. Furthermore, depending on the target group, classic wrist sensors may
not be accepted by patients due to their discomfort and removed during
recording. Considering the above limitations, a garment sock with integrated
electrodes was proven to be the most efficient location in terms of signal
quality, comfort, and an optimal alternative to standard medical electrodes.
This allows the electrodes to be applied in one handling while maintaining
permanent spacing and positioning of the electrodes on the skin. This
garment can also be reused several times after regular washing cycles.
Screen printing was chosen as a method for incorporating conductive
electrodes onto garments. Conductive inks can be printed onto the garment
directly or onto a thermoplastic polyurethane (TPU) film, which has been
proven to be a suitable material for this type of integration. Screen
printing onto these films offers both high flexibility and stretchability.
The printing process allows the use of complex designs, such as stacking
layers and printing dielectric insulating layers on top of the conductive
layers. Different types of connectors were studied and designed to convert
this stretchable film into a fixed connector tail with strain relief.
Finally, test prints were made in a lab to validate each material and ink
combination of silver, carbon, and dielectric inks. This aim was to achieve
the desired robustness, and flexibility and to optimise the position of the
sensors to achieve a good balance between patient comfort and good EDA
signal output.The work showed that the use of advanced screen-printing
technologies in the smart sock was the best solution to ensure high wear
comfort while maintaining good signal quality even after repeated use and
washing while maintaining low costs and high flexibility during production.
In addition, the sheet-to-sheet production method proved to be
cost-effective and enabled rapid changes in the material stack and sock
design.