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Textile sensors to measure sweat pH and sweat-rate during exercise


Abstract and Figures

Sweat analysis can provide a valuable insight into a person's well-being. Here we present wearable textile-based sensors that can provide real-time information regarding sweat activity. A pH sensitive dye incorporated into a fabric fluidic system is used to determine sweat pH. To detect the onset of sweat activity a sweat rate sensor is incorporated into a textile substrate. The sensors are integrated into a waistband and controlled by a central unit with wireless connectivity. The use of such sensors for sweat analysis may provide valuable physiological information for applications in sports performance and also in healthcare.
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Textile sensors to measure sweat pH and sweat-rate
during exercise
Shirley Coyle, Deirdre Morris, King-Tong Lau,
Dermot Diamond
CLARITY, NCSR, School of Chemical Sciences
Dublin City University, Dublin 9, Ireland
Nicola Taccini
Smartex s.r.l
56023 Navacchio, Italy
Daniele Costanzo, Pietro Salvo
Centro Interdipartimentale “E. Piaggio”
Università di Pisa, Italy
Fabio Di Francesco
Dipartmento di Chimica e Chimica Industriale
Università di Pisa, Italy
Maria Giovanna Trivella
Istituto di Fisiologia Clinica C.N.R.
Pisa, Italy
Jacque-André Porchet, Jean Luprano
Neuchâtel, Switzerland
Abstract— Sweat analysis can provide a valuable insight into a
person’s well-being. Here we present wearable textile-based
sensors that can provide real-time information regarding sweat
activity. A pH sensitive dye incorporated into a fabric fluidic
system is used to determine sweat pH. To detect the onset of
sweat activity a sweat rate sensor is incorporated into a textile
substrate. The sensors are integrated into a waistband and
controlled by a central unit with wireless connectivity. The use of
such sensors for sweat analysis may provide valuable
physiological information for applications in sports performance
and also in healthcare.
Keywords-sweat analysis, wearable sensors, smart textiles,
personalised healthcare
I. I
The primary purpose of the sweating mechanism is thermo-
regulation. Throughout times of physical exertion sweat rate
is increased in order to avoid a dangerous rise in body
temperature caused by the persons’ increased metabolic rate
[1]. Monitoring sweat composition in real-time can provide
useful physiological information. Sweat analysis is a valuable
diagnostic tool, being the gold standard for Cystic Fibrosis
diagnosis [2]. Physiological monitoring using sweat has the
advantage of being non-invasive and easily accessible there
are many cases where such monitoring is beneficial.
Continuous physiological monitoring of athletes during
training is a vital tool in improving performance while also
assessing the health status of the individual. Athletes must
ensure electrolyte balance and adequate re-hydration after
exercise or risk reduced performance [1, 3]. Re-hydration is a
major part of the recovery process after exercise. It is well
established that performance of exercise in a dehydrated state
is impaired, and that both high-intensity and endurance
activities are affected. There is also an increased risk of heat
illness in individuals who begin exercise in a dehydrated state
[4]. The concentration of electrolytes in sweat varies between
individuals and therefore it would be of great advantage to
develop personalized rehydration strategies depending on fluid
and electrolyte losses. Another scenario where electrolyte
balance is critical is in cases of extreme heat and/or physical
exertion where drinking too much water can lead to
hyponatremia. This is characterized by low levels of sodium
and can result in symptoms such as headache, nausea,
vomiting and muscle cramps. When there is a quick onset of
hyponatremia, for example during prolonged exercise, it can
lead to more severe complications such as seizures, coma,
brain damage and death [5]. Dehydration and electrolyte
balance is not only of vital importance to athletes but can
seriously affect vulnerable populations, e.g. in the elderly
dehydration can cause serious illness and even death
particularly in the event of a heat-wave [6]. Continuous
analysis of sweat may be used to detect changes in sweat
composition and be used as a warning indicator.
It is known that sweat pH and electrolyte concentrations
are closely related [7]. It has also been shown that sweat pH
during exercise will change with the onset of metabolic
alkalosis [8] which means that pH measurements may be used
to relate the build-up of acid in muscle cells during exercise
which leads to muscle fatigue.
While sweat may be easily obtainable, collection and
measurement techniques for analysis can be awkward -
Minor’s method involves covering the skin with starch-iodine
powder that exhibits purple dots when sweat droplets appear
[9]. “Wash-down” techniques involve exercising within a
plastic enclosure to collect sweat and then washing down the
body within the enclosure using de-ionised water at the end of
the exercise trial [10]. These methods are obviously unsuitable
for long-term measurements outside of a laboratory setting.
Parafilm patches have been used to create a capsule on the skin
surface but these may change the sweat composition by
preventing water evaporation which may block sweat gland
ducts and lead to a progressive fall in sweating rates [6].
Bioimpedance measurements have been used to estimate the
amount of water in the body. As a wearable system this is
challenging due to complex circuitry, measurement times [11]
and the effects of movement and electrode placement [12]. to
In the field, the most practical way for athletes to monitor their
sweat loss is to measure changes in body weight pre- and post-
exercise [13]. Therefore it is clear that a method is needed to
collect and analyse sweat in an unobtrusive way in normal
settings, at home, in the gym or on the track to provide real-
time analysis of sweat activity.
In addition to the analysis of sweat composition for such
applications, it is also of benefit to examine sweating patterns,
i.e. sweat rates on different regions of the body. This may be
used to identify autonomic nervous system dysfunction that
may occur due to condition such as diabetes [14]. Monitoring
sweat activity may also be useful in understanding and treating
a condition known as hyperhidrosis which causes excessive
sweating [14].
The aim of this work is to develop textile-based sensors
capable of performing chemical measurements on body fluids.
Sweat must be collected, delivered to the sensor surface and
waste products removed. This paper presents part of the
research carried out during the BIOTEX project, an EU-funded
FP6 project with a consortium of 8 partners, (see www.biotex- The goal has been to create a system that can be
easily integrated into fabric and for the first time perform
chemical sensing within a textile substrate.
A. pH fabric sensor
A textile based platform with fluid handling properties is used
to collect and analyse sweat samples. The design of the device
is shown in Figure 1(b). The system exhibits a passive
pumping mechanism, controlling fluid flow through a fabric
substrate. A fabric fluidic channel is created by screen-
printing an acrylic hydrophobic paste either side of the fabric.
At one end of this channel is a collection “window” where
sweat enters from the skin, at the opposite end of the channel a
super-absorbent (SAB) material is placed to increase the
capillary flow through the fabric and store the collected sweat.
An acquisition layer of moisture wicking fabric is stitched in
place on the skin side of the fabric patch, beneath the sensing
layer. The acquisition layer in contact with the skin helps to
increase the collection capacity of the device.
A pH sensitive dye is immobilised onto the fabric channel
using tetraoctyl ammonium bromide. Sweat pH can range
from pH 4-8, therefore the dye chosen for sweat analysis is
bromocresol purple (BCP, pKa = 6.2) which exhibits a colour
change from yellow to blue over this pH range. A paired
emitter-detector LED configuration is used to quantify the
colour change of the dye. The photo detector is a reverse
biased LED and the discharge time due to stray capacitance is
measured using a microcontroller. This technique has been
discussed previously [15]. This technique is chosen as it is a
low-power digital technique for optical detection and LEDs
are versatile components that may be easily integrated into
textiles. Two LEDs are embedded in silicone to prevent
condensation from sweat and positioned over the fabric
channel using a protective black polymethyl methacrylate
dye Hydrophobic
Optical Detection
Sweat SAB
Opaque cover
dye Hydrophobic
Optical Detection
Sweat SAB
Opaque cover
Figure 1. a) pH sensing patch b) fabric passive pump design
(SAB) placement
Placement for
silicone gasket
Placement area for
additional sensors
pH sensor
55 mm
a) wearable humidity sensor b) textile
arrangement to measure
low sweat rate values
(PMMA) cover held in place by a rubber gasket.
B. Sweat rate sensor
The method used to continuously measure sweat rate is to
derive its value from the gradient of humidity measured by a
pair of wearable humidity sensors at two distances (0.5 and 1.5
cm) from the skin. In cases where sweat rates are low (10-40
h) more accurate estimates can be obtained by increasing
the gradient. In this case, the sensor is modified by inserting a
net fabric (88% polyamide, 12% elastane) between the two
humidity sensors.
Figure 2 shows a humidity sensor and the
latter textile arrangement. The textile membrane is removed when
the measurement range has to be extended up to 1000
h. In
that case, a flexible textile frame is used to place the sensors at
the right positions (Figure 3). Capacitive humidity sensors are
prepared either by vacuum depositing gold electrodes onto
hydrophilic films (polyvinyl alcohol or cellulose acetate
butyrate) or by modifying a commercial device (Philips H1)
which are manufactured by a similar method.
The sensors are held in place using a waistband, designed by
Smartex, which ensures the fabric patch maintains good contact
with the skin during exercise (Figure 3). The waistband
is also
used to block ambient light, which may affect the operation of
the pH sensor. The waistband is made from a moisture
wicking, stretch fabric for comfort with an integrated pocket to
hold the pH sensing patch in place. The use of an elastic fabric
laminated with a hydrophobic membrane prevents the
absorption of sweat from the waistband and the reduction of the
sweat flow through the pump. Hooks and loops fasteners are
used to keep the passive pump and the electronics in place.
This reduces motion effects during exercise.
A second pocket houses the sweat rate sensor. A neoprene
frame makes sure that the right distance between sensors and
skin is maintained, while holes in the pocket allow the water
vapour to diffuse away without obstacles. A reference patch
for pH measurements is also included in the waistband. This is
used to make pH measurements via a Skincheck
pH meter,
which is pressed against the patch at 5 minute intervals.
Reference measurements are taken once the subject is observed
to begin sweating. The waistband is positioned on the subjects
back so that both the pH sensor patch and the reference patch
are to the right of the spine. The sweat rate sensor is positioned
to the left of the spine. This is done to avoid collecting sweat
which runs from the top to the bottom of the back along this
hollow from other parts of the back.
The LED optical detection configuration is controlled by a
central unit developed by CSEM ( The detected
light intensity relating to pH measurements is transferred
wirelessly to a nearby laptop using a Bluetooth communication
module within the central unit. The control unit also interfaces
with the sweat rate sensor by measuring the capacitance of each
humidity sensor. Both pH and sweat rate measurements are
sampled at a rate of 0.2 Hz. The exercise set-up is shown in
Figure 4. The protocol involved indoor cycling in a room at
20°C with relative humidity of 50%. Subjects were asked to
cycle for up to 60 minutes at a self-selected pace.
Results of exercise trials on two healthy male subjects are
shown in Figure 5. Sweat rate is represented by the difference
in capacitance between the two humidity sensors. Sweat rate
data have been normalised and smoothed using a moving
average of 12 points. Figure 6 shows how the sensor signal
follows the variations of the sweat rate measured by a
commercial reference meter (Vapometer, Delfintech) quite
well. The Vapometer is currently used in many fields such as
Sweat Rate sensor
(b) (c)
pH sensor pocket
Reference patch
Figure 3. a) the waistband b-c) details of the housings of the pH sensing
patch and sweat rate sensor
Sweat rate
sensor Control
Figure 4. Experimental set-up, sweat rates sensor is positioned on the
left, the pH textile patch on the right behind the control unit
academic skin research and testing laboratories, personal care
and chemical industries for the measurement of evaporation
The temporal characteristic of sweating pattern is useful for
interpreting the response of the pH sensor. A priming time is
involved before the pH measurements are valid. This involves
the time it takes for the subject to start sweating and for the
sweat to enter the fluidic channel. This varies between
individuals and depends on fitness levels and environmental
conditions. The priming time is also indicated by the
reference measurements as these measurements are taken once
there is adequate sweat on the reference patch to wet the
reference electrode. From the results in Figure 5 this priming
time corresponds to the time taken to reach a constant sweat
rate as measured by the sweat rate sensor. Once the sweat
enters the channel it takes up to 5 minutes before a complete
colour change in the pH sensitive dye is achieved. Sweat pH
is observed to increase as the exercise trial progresses and as
the sweat rate increases. It can be seen that for both trials
there is close agreement between the results of the textile
based pH sensor and those obtained using the reference
method. These data have demonstrated that the performance of
the textile sensor is comparable to the commercial system.
Differences may be attributed to the fact that the pH sensor
and reference patch are sampling sweat from separate regions
of the back [7]. The increase in pH during exercise can be
explained by considering the anatomy of sweat glands and
their operation. Sweat glands have two main components, a
tubular coiled area where the sweat is produced and the duct
through which it reaches the skin surface. The primary sweat,
formed in the secretory coil is near iso-osmotic, with a pH
close to 7, while that excreted onto the skin is hypo-osmotic,
making it acidic. It is thought that this is most likely due to
ductal transport processes, which are dependent on the
physiological condition [8]. The sweat becomes acidic due to
re-absorption processes which occur in the duct. However, as
the subject continues to exercise, the rate at which sweat is
excreted increases, in order to regulate body temperature. This
reduces the amount of time available for re-adsorption
processes and sweat pH increases.
V. D
Sweat is a clear hypotonic, odourless fluid containing
sodium, chloride, potassium, urea, lactate, bicarbonate,
calcium, ammonia, organic and non-organic compounds [16].
Clearly there are many different constituents in sweat that are
inter-related. pH is a useful parameter to measure as every
function of the body is dependent on our bodies maintaining a
precisely balanced pH in order to function correctly. The
enzyme system, as well as the electrical functions of our body,
is dependent on electrolytes. Rehydration after exercise
requires not only replacement of volume losses, but also
replacement of the electrolytes, primarily sodium, lost in the
sweat. Sweat composition not only varies among individuals
but also varies with time during exercise, and is further
influenced by the state of acclimatization [4]. The onset of
significant dehydration is preventable, or at least modifiable,
when hydration protocols are followed to assure all athletes
the most productive and the safest athletic experience [17].
Therefore individual monitoring would enable personalized
rehydration drinks to be prepared for each athlete to meet their
needs. The design of a wearable sweat analysis system has
been demonstrated as a step towards such strategies. Further
trials with a wider variety of subjects in different training
scenarios are needed to further validate the system.
The fabric pH sensor has been demonstrated during indoor
cycling trials. To function it needs an adequate quantity of
sweat entering the patch, which often takes up to 20 minutes
for the person to start to sweat. Simultaneous measurement of
sweat rate is useful to know when the pH readings are valid.
0 10 20 30 40 50 60
Time (min)
pH sensor
0 10 20 30 40 50 60
Sweat rate (a.u.)
pH measurement
0 10 20 30 40 50
Time (min)
pH sensor
0 10 20 30 40 50
Sweat rate (a.u.)
pH measurement
Figure 5.
Results of exercise trials on two healthy volunteers: sweat rate and pH values measured during a 60 minutes effort at self
selected pace
The priming time of the sensor will vary depending on the
individual and their sweating patterns. Future work will aim
to reduce the priming time by reducing the sensor surface area
where a lower quantity of sweat would be required for the
reaction to occur. The dimensions of the current design were
chosen to accommodate the placement of additional sensors on
the channel so that more detailed analysis of sweat
composition could be performed. The work presented here is
just part of work involved in the BIOTEX project that tackles
the issues involved in real-time sweat analysis. To get a
complete picture the overall BIOTEX system includes sodium,
chloride and sweat conductivity sensors along with
measurement of other physiological parameters such as
breathing, heart rate and blood oxygen saturation. The sweat
sensors may provide complimentary signals to ECG and
respiration data which have already been demonstrated using
textile sensors [18, 19] to form a complete wearable healthcare
monitoring garment. By developing textile sensors, the
sensing elements can be easily integrated and distributed
throughout a garment. This means that to study sweating
activity patterns the sweat rate sensors could be placed at
different regions of the body which may assist in diagnosis
and treatment of illnesses affecting the autonomic nervous
system. The great advantage of textile sensors is that they
enable long term monitoring of the wearer at home, in normal
Textile based sensors to measure sweat pH and sweat rate
during exercise have been demonstrated. Further work is
needed to relate the sweat rate measurements with flow rates.
This could provide valuable information to athletes regarding
their rehydration needs and also in clinical applications for
treatment and diagnosis of conditions such as hyperhydrosis.
The temporal response of sweating patterns provided by the
sweat rate sensor has been useful in interpreting the response
of the fabric pH sensor which needs adequate sweat rates to
function effectively. Further work is needed to investigate
other constituents of sweat such as electrolyte concentrations
and also investigation of different training regimes in different
environmental conditions. Analysis of these different
parameters should help to understand the sweating mechanism
and open a new area of research as a non-invasive approach to
physiological measurements.
This area of research is unfortunately lacking due to the
difficulty in sampling sweat. It is hoped that this system will
open a new avenue of research allowing physiologists to
explore the benefits of non-invasive sweat studies. Textile
sensors in contact with the skin offer much promise to provide
novel physiological information. The textile based fluid
handling system that has been developed provides a platform
for implementing wearable biological and chemical sensors.
Garments integrating such textile sensors allow innocuous
monitoring of the health and well-being of their wearers. This
has many applications in sports performance and also in
We gratefully acknowledge the financial support of the
European Union (Biotex FP6-2004-IST-NMP-2) and Science
Foundation Ireland (07/CE/I1147).
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... In detail, 25 mM of Na + and Cl − , 0.45 mM of NH4 + , 1.75 mM of K + and 7.5 mM of lactic acid were injected into a PBS at pH 6. This value was selected because it is the intermediate value of the pH of sweat that can vary from pH 4 to 8 [27]. The concentration of interfering agents was selected in order to simulate the sweat composition. ...
... In detail, 25 mM of Na + and Cl − , 0.45 mM of NH 4 + , 1.75 mM of K + and 7.5 mM of lactic acid were injected into a PBS at pH 6. This value was selected because it is the intermediate value of the pH of sweat that can vary from pH 4 to 8 [27]. The concentration of interfering agents was selected in order to simulate the sweat composition. ...
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Nowadays, we are assisting in the exceptional growth in research relating to the development of wearable devices for sweat analysis. Sweat is a biofluid that contains useful health information and allows a non-invasive, continuous and comfortable collection. For this reason, it is an excellent biofluid for the detection of different analytes. In this work, electrochemical sensors based on polyaniline thin films deposited on the flexible substrate polyethylene terephthalate coated with indium tin oxide were studied. Polyaniline thin films were abstained by the potentiostatic deposition technique, applying a potential of +2 V vs. SCE for 90 s. To improve the sensor performance, the electronic substrate was modified with reduced graphene oxide, obtained at a constant potential of 􀀀0.8 V vs. SCE for 200 s, and then polyaniline thin films were electrodeposited on top of the as-deposited substrate. All samples were characterized by XRD, SEM, EDS, static contact angle and FT-IR/ATR analysis to correlate the physical-chemical features with the performance of the sensors. The obtained electrodes were tested as pH sensors in the range from 2 to 8, showing good behavior, with a sensitivity of 62.3 mV/pH, very close to a Nernstian response, and a reproducibility of 3.8%. Interference tests, in the presence of competing ions, aimed to verify the selectivity, were also performed. Finally, a real sweat sample was collected, and the sweat pH was quantified with both the proposed sensor and a commercial pH meter, showing an excellent concordance.
... Additional tests ( Supplementary Fig. 17) demonstrate the capabilities for chronological sampling from a device mounted on the forehead while home training. The data show increases in the concentration of chloride and the pH level during exercise that are comparable to the results of previous studies 32, 34 . Creatinine (µM) 5 12.5 25 50 Glucose (µM) 12 Sweat rate, f (µl min -1 ) ...
... These values are within the normal range 4 , and the times for filling each μ-RV (volume, 10 μl) are consistent with those obtained using the flow-sensing platform. The increase in pH during exercise is consistent with the results of previous studies 34,35 , originating from the anatomy of sweat glands and their operation. The measurements of glucose concentration are 39.2 and 70.6 μM after ~14 and 23 min of exercising, respectively. ...
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Monitoring the flow rate, cumulative loss and temperature of sweat can provide valuable physiological insights for the diagnosis of thermoregulatory disorders and illnesses related to heat stress. However, obtaining accurate, continuous estimates of these parameters with high temporal resolution remains challenging. Here, we report a platform that can wirelessly measure sweat rate, sweat loss and skin temperature in real time. The approach combines a short, straight fluid passage to capture sweat as it emerges from the skin with a flow sensor that is based on a thermal actuator and precision thermistors, and that is physically isolated from, but thermally coupled to, the sweat. The platform transfers data autonomously using a Bluetooth Low Energy system on a chip. Our approach can also be integrated with advanced microfluidic systems and colorimetric chemical reagents for the measurement of pH and the concentration of chloride, creatinine and glucose in sweat.
... In this case, small fiber nerves lacking myelinated axons produce a durable shift in the ionic balance and pH value of sweat conducts [3,7,8]. Indeed, it has been reported that the pH value of the sweat can vary from 4.5 to 7.0 [9][10][11] due to the damage in the glands [7], sweat-rate [12], and glucose concentration [13]. ...
... Notice that the acid solution corresponds to the case when the peripheral neuropathy is early developed in patients with diabetes [19], producing a durable shift in the ionic balance and pH value of sweat conducts [3,[7][8][9][10][11]. In this condition, glands [7], sweat-rate [12], and glucose concentration [13] can be strongly damaged, therefore, analyzing the metal surfaces that can be in contact with the sweat is very interesting from a corrosion point of view. Additionally, the ASS solution was inoculated with an active inoculum of Escherichia coli BW25113 and Staphylococcus aureus BAA977, separately, which are frequently found on the human skin. ...
AISI 430 stainless steel is an attractive material to be used in the healthcare industry, particularly as a sensor due to its low cost, corrosion resistance, as well as being Ni-free. AISI 430 was evaluated in an artificial sweat solution with the presence of Escherichia coli, and Staphylococcus aureus. Surface microbial analyses did not reveal colonization of bacteria on metallic surfaces, even when bacteria adhesion was investigated in a Müeller-Hinton solution. However, by electrochemical techniques, the AISI 430 surfaces demonstrated clear signs of corrosion mainly in a sterile medium after two weeks of exposure.
... Generally, diverse properties can be detected by an analysis of the human sweat, such as glucose, lactate, ascorbic acid [15], but also pH value and sweat rate during exercises [127]. Moreover, pH value measurements can be performed, for example, by conductive PEDOT:PSS coated fibers with an additional functionalization with bromothymol blue dye, as presented by Possanzini et al. [128]. ...
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... (2009) presented a colorimetric optical sensor to monitor sweat activity in real-time and pH-sensitive bromocresol purple dye was incorporated into a fabric fluidic system using tetraoctyl ammonium bromide [308]. The fabric fluidic channel was created by screen printing an acrylic hydrophobic paste on both sides of the fabric. ...
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Electrodes fabricated on a flexible substrate are a revolutionary development in wearable health monitoring due to their lightweight, breathability, comfort, and flexibility to conform to the curvilinear body shape. Different metallic thin-film and plastic-based substrates lack comfort for long-term monitoring applications. However, the insulating nature of different polymer, fiber, and textile substrates requires the deposition of conductive materials to render interactive functionality to substrates. Besides, the high porosity and flexibility of fiber and textile substrates pose a great challenge for the homogenous deposition of active materials. Printing is an excellent process to produce a flexible conductive textile electrode for wearable health monitoring applications due to its low cost and scalability. This article critically reviews the current state of the art of different textile architectures as a substrate for the deposition of conductive nanomaterials. Furthermore, recent progress in various printing processes of nanomaterials, challenges of printing nanomaterials on textiles, and their health monitoring applications are described systematically. Graphical Abstract
... Continuous measurements of hydration level through sweat sensing would be of importance to several population groups, including athletes, military personnel, elderly people, and medical patients, and would serve as an early dehydration warning to prevent injury, illness, or death. (Coyle et al. 2009;Baker 2017;Alizadeh et al. 2018;Seshadri et al. 2019). Therefore, it is of great interest to develop a scalable, adaptable, and disposable microfluidic valve for sweat collection. ...
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Skin-compatible microfluidic valving systems with on-demand sweat capture are necessary to understand the temporal variation of biomarkers. Here, we demonstrate solution-based electrowetting valves with rapid actuation integrated into a flexible microfluidic sweat collection patch. The valve is produced by inkjet-printing a pair of silver electrodes with spacings of 0.2–2 mm and modifying the downstream electrode with a hydrophobic self-assembled monolayer. To complete the valve, a microfluidic channel is fabricated from laser ablation of adhesive layers and pressed over the silver electrodes. Artificial perspiration is driven by capillary action within the channel until stopped by the electrowetting valve. A low voltage is applied to the electrodes, decreasing the surface energy of the hydrophobic monolayer and allowing the fluid front to continue through the microchannel. Statistical analysis demonstrated that applied voltage, and not electrode spacing, influenced valve actuation time, with 17 ± 8 s for 4 V and 40 ± 16 s for 1 V. Inkjet-printing conditions were also optimized to achieve a valve fluid retention time of 9 h. Using four electrowetting valves, an integrated wearable device is designed for artificial perspiration collection through valve actuation at distinct time points over 40 min. Finally, these inexpensive, user-friendly, and disposable electrowetting valves offer exciting opportunities for non-invasive point-of-care sweat monitoring.
... Many studies have shown the composition of human sweat varies substantially among individuals (Taylor and Machado-Moreira, 2013). Changes in ion concentration (Ranchordas et al., 2017) and pH value (Coyle et al., 2009) might affect the outcomes of a pressure sensing system. While the resistance of the fluid in the microchannel increases, it is also a proportional change when detecting resistance results, interfering in the determination of which paired electrodes have been connected. ...
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Sweat-based wearable devices have attracted increasing attention by providing abundant physiological information and continuous measurement through noninvasive healthcare monitoring. Sweat pressure generated via sweat glands to the skin surface associated with osmotic effects may help to elucidate such parameters as physiological conditions and psychological factors. This study introduces a wearable device for measuring secretion sweat pressure through noninvasive, continuous monitoring. Secretion pressure is detected by a microfluidic chip that shows the resistance variance from a paired electrode pattern and transfers digital signals to a smartphone for real-time display. A human study demonstrates this measurement with different exercise activities, showing the pressure ranges from 1.3 to 2.5 kPa. This device is user-friendly and applicable to exercise training and personal health care. The convenience and easy-to-wear characteristics of this device may establish a foundation for future research investigating sweat physiology and personal health care.
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Background: Kickboxing is a combat sport with high demands on fitness and coordination skills. Scientific research shows that kickboxing fights induce substantial physiological stress. Therefore, it is important to determine the body composition of athletes before competitions and to analyze the skin temperature and skin pH during the fight. Methods: This study aimed to determine the body composition, skin temperature, and skin pH in kickboxers during a fight according to K1 rules. A total of 24 kickboxers (age range: 19 to 28 years) competing in a local K1 kickboxing league participated in the present study. Results: Changes in skin temperature and pH were observed and significant correlations were found between body composition and weight category. Conclusions: Changes in skin temperature and pH were demonstrated after each round of the bout. Level of body fat and muscle tissue significantly correlates with technical-tactical skills of the K1 athletes studied.
Wearable electrochemical sensors have attracted tremendous attention in recent years. Significant progress has been achieved, particularly in device integration. Most wearable devices are integrated on thin-film polymer, however, less attention is paid to the sweat flow at human-device interfaces, which is of great significance for continuous real-time analysis and long-term skin comfort. Here, we reported a low-cost, freestanding and disposable highly integrated sensing paper (HIS paper) for real-time analysis of sweat. By using a simple printing process, the HIS paper combining hydrophobic protecting wax, conducting electrodes, and the incorporated MXene/methylene blue (Ti3C2Tx/MB) active materials was assembled. In particular, the printed paper was folded into a multi-layer structure, in which a reasonable designed three-dimensional (3D) sweat diffusion path is established by connecting the hydrophilic regions of each layer, providing efficient pathways for the collection and diffusion of sweat along the vertical direction of the folded HIS paper. More importantly, the independent 3D position of three-electrode facilitates the decoration and fixation of enzymes, as well as the accessibility of electrolytes. In addition, a dual-channel electrochemical sensor that can simultaneously detect glucose and lactate with sensitivity of 2.4 nA μM⁻¹ and 0.49 μA mM⁻¹ respectively was produced based on the HIS paper. This HIS paper provides a miniaturized, low-cost and flexible solution for a range of biochemical platforms, including wearable bioelectronics.
Recent data. - Restoration of water and electrolyte balance is an essential part of the recovery process after exercise that results in sweat loss. Ingestion of plain water results in a fall in plasma sodium concentration and osmolality, reducing the drive to drink and stimulating urine output. Addition of sodium and potassium to rehydration fluids will decrease urine output in the hours after rehydration. Because of urine losses, subjects are in net negative fluid balance throughout the recovery period, unless the volume ingested exceeds the loss. Urine output is inversely proportional to the sodium concentration of the ingested fluid. Ingestion of large volumes of fluid is not effective in maintaining positive fluid balance without electrolyte replacement. Ingestion of solid food together with plain water is effective in maintaining fluid balance if the electrolyte content is adequate. Addition of alcohol to ingested fluids has little effect in concentrations of 1 % or 2%, but there is a tendency for a diuretic effect that becomes significant at an alcohol concentration of about 4%. Ad libitum intake is strongly influenced by palatability. Conclusion. - Rehydration will only be achieved if a volume of fluid in excess of the sweat loss is ingested together with sufficient electrolytes.
The aim of this paper is to give brief information on recent developments and trends in biomedical sensors. We also tried to reveal the close correlation between biomedical sensors and smart (intelligent) textiles. We emphasized on the concept of wearable, as we have considered this notion the transition zone between the contemporary biomedical sensors and smart (intelligent) textiles.
A disco photometer which was an optical sensing array based on multiple LEDs was constructed for colorimetric analysis. This approach has been used to analyse single dyes and dye mixtures containing up to three dye components. This technique made use of the inherent well-defined LED emission band to provide selectivity for chromophors, which have equally well-defined absorbance band to give very good analytical data. The results showed that this LED array configuration could be used to reduce the complexity of data obtained from the mixtures and also improve the quality of the output.
Conference Paper
Bioimpedance spectroscopy (BIS) enables the determination of the human body composition (e.g. fat content, water content). From this data, it is possible to draw conclusions about the person’s health condition. The measurement is carried out with at least four electrodes placed on the body. Nowadays, positioning and wiring of the electrodes can only been conducted by qualified personnel. Even the latest systems on the market are uncomfortable to wear and their use for mobile purposes is highly limited. The commercial BIS electrodes, not suitable for a long term use, may cause allergic reactions. Textile integration plays a role not just concerning the manufacturing of long term electrodes, but also concerning the integration of cables and other electrical components into a wearable and comfortable application. In this article, a portable BIS system combined with textile electrodes is presented as a possible future application. The first validation results of the portable BIS-device and textile electrodes are analysed and the suitability of application is discussed in order to develop a wearable bioimpedance spectroscopy system.
Athletes are encouraged to begin exercise well hydrated and to consume sufficient amounts of appropriate fluids during exercise to limit water and salt deficits. Available evidence suggests that many athletes begin exercise already dehydrated to some degree, and although most fail to drink enough to match sweat losses, some drink too much and a few develop hyponatremia. Some simple advice can help athletes assess their hydration status and develop a personalized hydration strategy that takes account of exercise, environment, and individual needs. Preexercise hydration status can be assessed from urine frequency and volume, with additional information from urine color, specific gravity, or osmolality. Change in hydration during exercise can be estimated from the change in body mass that occurs during a bout of exercise. Sweat rate can be estimated if fluid intake and urinary losses are also measured. Sweat salt losses can be determined by collection and analysis of sweat samples, but athletes losing large amounts of salt are likely to be aware of the taste of salt in sweat and the development of salt crusts on skin and clothing where sweat has evaporated. An appropriate drinking strategy will take account of preexercise hydration status and of fluid, electrolyte, and substrate needs before, during, and after a period of exercise. Strategies will vary greatly between individuals and will also be influenced by environmental conditions, competition regulations, and other factors.
Despite recent progress in eccrine sweat gland physiology, simple, safe and reliable methods of visualizing local and generalized sweating are not available for clinicians and physiologists. We developed a simple one-step method for visualizing sweating that requires only soluble starch previously treated with iodine. When the powder is sprayed on the skin, sweat droplets are visualized as discrete dark purple dots. Since visualized dots are easily wiped off without staining the skin, sweating patterns can be obtained consecutively on the same skin site. The method is far superior to the classical Minor's method and is useful for clinical diagnosis of disorders of sweating and for visualization of the total body sweating for physiological studies. Two simple devices for spraying powder also have been presented.
When sweat rates are sufficiently elevated, i.e., in high ambient temperatures or during exercise, due to potential losses of sweat by runoff, the whole body washdown technique of sweat collection is considered invalid in all but low humidity environments. This paper describes a modification of this technique that makes its use possible in moderate to high humidity environments. During exercise, sweat loss by runoff was minimized by maximizing evaporation of sweat (subjects wore little clothing and electric fans were utilized) and by drying the surface of the body when sweat became excessive (with small hand towels). Sweat rate was calculated from weight changes with appropriate corrections. Total sweat content and concentration of urea N were determined from the rinsings of the body, hand towels, and clothing. To validate this procedure, runoff sweat that was not collected was estimated from the weight change of collecting towels positioned under a bicycle ergometer. Eight subjects exercised at approximately 60% VO2max for 30 min in 22.6 degrees +/- 0.46 degrees C (means +/- SD) and 66.1% +/- 2.34% RH. Volume of sweat secreted was 581 +/- 31 ml (1.162 +/- .062 l X h-1; means +/- SE). Sweat content of the collecting towels (corrected for evaporation loss) was 4.675 ml (0.8%) of total sweat rate), indicating that it is possible to prevent significant sweat loss with this procedure. Moreover, we have found that this procedure can be employed with little difficulty at exercise intensities up to approximately 75% VO2max, in RH of approximately 70%, and with sweat rates as high as 1.65 l X h-1.(ABSTRACT TRUNCATED AT 250 WORDS)
Previous methods used to collect human sweat for electrolyte analysis have been criticized because they involve only regional sampling or because of methodological problems associated with whole body-washdown techniques. An improved method for collection of whole body sweat from exercising subjects is described. It involved construction of a plastic frame that supports a large plastic bag within which the subject exercises. The subject and the equipment are washed with distilled, deionized water before exercise begins. After exercise is completed, the subject and equipment are again washed with water containing a marker not present in sweat (ammonium sulfate). Total sweat loss is calculated from the change in body mass, and the volume of sweat not evaporated is calculated from dilution of the added marker. Recovery of added water was 102 +/- 2% (SD) of the added volume, and recovery of added electrolytes was 99 +/- 2% for sodium, 98 +/- 9% for potassium, and 101 +/- 4% for chloride. Repeated trials (n = 4) on five subjects to establish the reproducibility of the method gave a coefficient of variation of 17 +/- 5% for sodium, 23 +/- 6% for potassium, and 15 +/- 6% for chloride. These values include the biological variability between trials as well as the error within the method. The biological variability thus appears to be far greater than the methodological error. Normal values for the composition of sweat induced by exercise in a hot, humid environment in healthy young men and women were (in mM) 50.8 +/- 16.5 sodium, 4.8 +/- 1.6 potassium, 1.3 +/- 0.9 calcium, 0.5 +/- 0.5 magnesium, and 46.6 +/- 13.1 chloride.