Design and Development of an E-Textile Mat for Assuring the Comfort of Bedridden Persons
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materials
Article
Design and Development of an E-Textile Mat for Assuring the
Comfort of Bedridden Persons
Daniela Sofronova 1 , Radostina A. Angelova 1, * and Yavor Sofronov 2
1 Centre of Competence MIRACle—Mechatronics, Innovation, Robotics, Automation, Clean Technologies,
Laboratory “Intelligent Mechatronic Solutions in the Field of Textiles and Clothing”, Technical University of
Sofia, 1000 Sofia, Bulgaria; dcholeva@tu-sofia.bg
2 Laboratory “CAD/CAM/CAE in Industry”, Technical University of Sofia, 1000 Sofia, Bulgaria;
ysofronov@tu-sofia.bg
* Correspondence: joy_angels@abv.bg
Abstract: An e-textile mat with capacitive textile sensors was designed and manufactured to monitor
body position and prevent decubitus ulcers in the case of bedridden people. The sensors were
incorporated through a process of machine embroidery with electrically conductive threads. A new
production method for the conductive threads is still expected to be developed, resulting in good
conductive properties, high wear resistance and durability. Samples of five variants of motifs
without cross-stitching were studied, and the capacity and electrical resistance were determined
experimentally. A prototype of the e-textile mat was made with a motif showing the best ratio
between the inserted thread and the measured capacity. A hardware solution and a software
application for collecting, processing and visualising the received information were developed. Tests
were performed in real conditions, which clearly showed that the designed e-textile mat could be
successfully applied for non-invasive and continuous control of the position of the human body in a
supine position to prevent decubitus ulcers.
Citation: Sofronova, D.; Angelova,
R.A.; Sofronov, Y. Design and
Keywords: e-textiles; health care; multifunctional textiles; bedridden persons; decubitus ulcers;
Development of an E-Textile Mat for human comfort; body position; textile sensors; conductive threads; monitoring system
Assuring the Comfort of Bedridden
Persons. Materials 2021, 14, 5437.
https://doi.org/10.3390/ma14185437
1. Introduction
Academic Editor: Barbara Simončič
Decubitus ulcers are a severe medical problem that is difficult to treat. They are usually
the result of some tissue nutrition disorder; the most common cause is lying sick for a long
Received: 12 August 2021
time. In places of contact of the body with a hard pad (mattress), the perfusion with the
Accepted: 17 September 2021
tissue’s blood worsens. As a result, its nutrition hampers, leading to the appearance of
Published: 20 September 2021
necrosis and concomitant wound [1]. The main principle for avoiding decubitus ulcers is
prevention, which is expressed in frequent changes in the body position of a bedridden
Publisher’s Note: MDPI stays neutral
patient or the use of an anti-decubitus mattress.
with regard to jurisdictional claims in
The firmness of the mattress, temperature and humidity are the main physico-mechanical
published maps and institutional affil-
iations.
and physiological factors that affect the quality of sleep and the comfort of the body lying in
bed [2]. The use of e-textiles with sensors to monitor body pressure on the mattress has been
investigated in [3,4]. However, the pressure sensors were used to provide information on
the areas with the most active wear for each person, depending on the weight, gender and
sleeping position as well as for the improvement of the mattress’ ergonomics and sleeping
Copyright: © 2021 by the authors.
quality.
Licensee MDPI, Basel, Switzerland.
At present, there are many examples of developed textile sensors [5–13], but few are
This article is an open access article
used to monitor the distribution of pressure and, respectively, hardness, in the process of
distributed under the terms and
operation. In [5], some commercially available systems and devices for beds and cushions
conditions of the Creative Commons
Attribution (CC BY) license (https://
were discussed. It should be mentioned, however, that the price impedes the large-scale
creativecommons.org/licenses/by/
application of these products. The authors of [10] presented technology for smart jacket
4.0/). production. In [12], the possibility of measuring the sitting posture via textile pressure
Materials 2021, 14, 5437. https://doi.org/10.3390/ma14185437 https://www.mdpi.com/journal/materials
Materials 2021, 14, 5437 2 of 11
sensors was investigated. A new resistive pressure sensing principle was applied in [6].
The authors used conductive yarns and different technologies, such as embroidery, hand
sewing, and weaving, for textile sensor production. Textile capacitive pressure sensors
were developed in [7,8]. In [7], foam was used as a layer between the electrodes. In [8], the
3D compressible spacer fabric of Mueller Textil, Germany, was applied, the compressibility
of which affected the sensor’s performance. Some examples for smart textiles production
using the embroidery technique are described in [9]. Detailed analyses of the methods for
obtaining textile pressure control sensors are presented in [14,15].
Various technologies are used to produce e-textiles with sensors, one of which is
machine embroidery of electrically conductive threads [16]. The main advantage of this
technology is that it can change the functionality of a finished traditional textile product in
a less expensive, labour-consuming and time-consuming process.
Our study was dedicated to designing and developing an e-textile mat with textile
sensors, incorporated by embroidery, applied for the movement monitoring of bedridden
people. The continuous data from sensors would give information about the period of
immobility of the individual parts of the body. As a result, the position of a bedridden
person could be regularly changed in situations where a caregiver is not necessarily present
at the bedside or when the medical staff shifts. Communications and programs are also
built to collect and process the data from the sensors and provoke reactions. The designed
e-textile mat could have a great social impact.
2. Materials and Methods
2.1. The Design Idea
The design idea was to incorporate textile capacitive sensors in a thin mat, which
ought to be set under the body of the bedridden person. The sensors should have the
ability to register the movement of the body. The designed mat does not involve the zone
of the head, as, usually, there is a pillow under the head.
The selection of the structure of the e-textile mat was carried out in three main direc-
tions:
• Selection of the sensors and measuring system;
• Selection of the textile system;
• Embedding of the sensors in the textile system through embroidery.
2.2. Sensors and Measuring System
Of the three possible options for choosing the type of textile, sensor-resistive, capacitive
and piezo-resistive–capacitive sensors have been found to be the most suitable for the
design of the e-textile. The capacitive sensors have low power consumption, high accuracy
and a lack of requirements for special equipment and operating conditions. At the same
time, the capacitive sensors are affected by environmental conditions: temperature and
humidity. That is why the MPR121 controller of the capacitive sensors was chosen. The
controller allows continuous and independent calibration of the inputs of each electrode,
i.e., the current data obtained are compared with a base value that changes based on the
variation of the background capacity. In addition, the data sampling rate was 64 ms, and
its sensitivity was high, which significantly improves the capabilities of the filter system.
It is possible to separate each electrode’s touch and release thresholds, which ensures
independence from hysteresis.
Figure 1 illustrates the data flow in the MPR121 capacitive sensors controller. The raw
data outputs run through 3 levels of digital filtering to remove the encountered high- and
low-frequency noises. After the first and second filtering, the result was the immediate
capacitance of each sensing input. The reference value represents the capacitance variation
over a long period caused by environmental changes such as atmospheric moisture and
dirt. The data from the 2nd filter and the reference value were compared, and then the
measured value was presented.
and dirt. The data from the 2nd filter and the reference value were compared, and then
Materials 2021, 14, x FOR PEER REVIEW 3 of 11
the measured value was presented.
Materials 2021, 14, 5437 3 of 11
and dirt. The data from the 2nd filter and the reference value were compared, and then
the measured value was presented.
Figure 1. Data flow in the MPR121 capacitive sensor controller.
The number and location of the sensors were determined according to the critical
areas of the human body where decubitus ulcers occur. They are found in the neck, shoul‐
Figure
Figure1. 1.
ders, DataData
elbow, flow
flowin in
pelvis,thetheMPR121
MPR121
thigh, legscapacitive
capacitive
and heel sensor
[17].controller.
sensor controller. when designing the sensor array,
Therefore,
it was not necessary to fill the entire area of the mat regularly. The location of the sensors
Thenumber
The numberand andlocation
location of of the
thesensors
sensors were determined according to the critical areas
could be tailored to the anatomical featureswereof thedetermined
human body. according to the critical
of the human
areas of Three
the human body where decubitus ulcers occur. They are found in the neck, shoulders,
zonesbody werewherebuilt decubitus
in the designedulcerse‐textile
occur. They
mat are found in
following thestrategy
this neck, shoul‐and the
elbow,
ders, pelvis,
elbow, thigh,
pelvis, legs legs
thigh, and and
heelheel
[17].[17].
Therefore, when
Therefore, designing
when the sensor
designing the array,array,
sensor it was
sizes of the most common human figures (Figure 2). The first two zones contained three
not
it was necessary
notofnecessary to fill the
to fill entire
the area of
entire area the mat
of the regularly.
matthe The
regularly. location
The of the
location could sensors
of the be could
sensors
rows sensors, and the third‐two rows. Thus, designed prototype used by
be
could tailored to
be tailored the anatomical
to the features
anatomical of
features the human body.
individuals with a different build. The of the human
zones with threebody. rows of sensors were located
Three
Three zones
zones were
were built
built ininthe
thedesigned
designede‐textile
e-textilemat
matfollowing
followingthis thisstrategy
strategy andthe the
along the lines of the back and hips. The zone with two rows was along the and line of the
sizes
sizes of the
of theThe most
most common
common human figures (Figure 2). The first two zones contained three
calves. width of thehuman
e‐textilefigures
was 700 (Figure 2). Thecan
mm, which firstbetwo
usedzones contained
in a single bed.three
rows
rows ofof sensors,
sensors, andand thethe third-two
third‐two rows.Thus,
rows. Thus, thethe designed
designed prototype
prototype could
could be be used
used byby
Figure 3 shows a diagram of the designed measuring system, which consisted of tex‐
individuals
individuals with
with a different build. The zones with three rows of sensors were located along
tile sensors (1),amultiplexers
different build. (2), aThe zones (3),
controller witha microcontroller
three rows of sensors (4) and were
a screen located
(5). The
the lines
along of the
thetolines ofback
the and hips.
back The zone
and hips. Theto with with
zone two rows
two was along
rows the line
was along theof theofcalves.
line thethat
need
The width include
of the multiplexers
e-textile was wasmm,
700 due whichthe can
largebe group
used ofasensors
in single which
bed. have data
calves.
mustThe be width
collectedof theande‐textile
processedwassimultaneously
700 mm, whichincan realbetime.
used in a single bed.
Figure 3 shows a diagram of the designed measuring system, which consisted of tex‐
tile sensors (1), multiplexers (2), a controller (3), a microcontroller (4) and a screen (5). The
need to include multiplexers was due to the large group of sensors which have data that
must be collected and processed simultaneously in real time.
Figure 2. Scheme of the sensors’ arrangement.
Figure 2. Scheme of the sensors’ arrangement.
Figure 3 shows a diagram of the designed measuring system, which consisted of
textile sensors (1), multiplexers (2), a controller (3), a microcontroller (4) and a screen (5).
Figure 2. Scheme
The need of the sensors’
to include arrangement.
multiplexers was due to the large group of sensors which have data
that must be collected and processed simultaneously in real time.
Materials 2021, 14, 5437 4 of 11
Materials 2021, 14, x FOR PEER REVIEW 4 of 11
Figure 3. Scheme of the measuring system: 1—sensors, 2—multiplexers, 3—controller, 4—micro‐
Figure 3. Scheme of the measuring system: 1—sensors, 2—multiplexers, 3—controller, 4—
controller, and 5—screen.
microcontroller, and 5—screen.
Themultiplexer
The multiplexerhas hasseveral
severalinputs
inputsand andoneoneoutput.
output.ItItacts
actsasasaacircuit
circuitbreaker,
breaker,where
where
the connection is not mechanical, but is made through an integrated
the connection is not mechanical, but is made through an integrated semiconductor circuit. semiconductor cir‐
cuit.The entire development kit consists of a 12 bit ADC, Raspberry Pi 4 and 5” display. The
The entire
first module development
was the Pi HAT versionkit consists of a 12 bit
of the Adafruit ADC, Raspberry
MPR121 Pi 4 and
capacitive sensor. 5” display.
It measured
65The
× 56first
mm module
2 and had was12the Pi HAT
sensor version
channels. of the
It can Adafruiton
be mounted MPR121 capacitive
a Raspberry Pi 4. sensor. It
measured 65 × 56 mm 2 and had 12 sensor channels. It can be mounted on 2a Raspberry Pi
The Raspberry Pi 4 minicomputer with dimensions of 85 × 56 mm works with
an4. ARM processor. It has 2 GB of memory and multiple interfaces: 2 × micro-HDMI,
TV/AudioThe Raspberry
OUT, 300 mbps Pi 4 minicomputer
ethernet, dual-bandwith dimensions
Wi-Fi, Bluetooth 56 mm2 works
of 855,×micro-SD, 2 × USB with an
3.0,
ARM processor. It has 2 GB of memory and multiple interfaces: 2 ×
2 × USB 2.0, over 20 GPIO ports, I2C, SPI, UART, I2S, CSI, DSI, and USB 3.0 ports and is micro‐HDMI, TV/Au‐
dio OUT,
powered by3005 V.mbps ethernet, dual‐band Wi‐Fi, Bluetooth 5, micro‐SD, 2 × USB 3.0, 2 × USB
2.0, Connecting
over 20 GPIO ports, I2C,
a display SPI,
to the UART, I2S, CSI,
minicomputer makesDSI,
it and USB
easier for3.0
theports and
user to is powered
monitor the
by 5 V.of the measuring system. It is compatible with Raspberry Pi 4.
results
Connecting a display to the minicomputer makes it easier for the user to monitor the
2.3.
results Textile
The of the Phase
measuring system. It is compatible with Raspberry Pi 4.
The textile system, which plays the role of a carrier phase, can be developed from
2.3. The
layers Textile Phase
of different types and thicknesses, which can vary in number. The most important
properties for the upper layer
The textile system, whichofplays
the system
the roleareof ahigh wear
carrier resistance,
phase, can below elongation
developed from
under tensile load, good air permeability, lack of peeling and the possibility
layers of different types and thicknesses, which can vary in number. The most important of trouble-free
machine
propertiesembroidery. The woven
for the upper layer ofmacrostructures
the system are had highbetter
wear performance
resistance, low than the knitted
elongation un‐
macrostructures
der tensile load,ingood terms airofpermeability,
low elongation lackunder tensileand
of peeling load.
theTherefore,
possibilitya woven fabric
of trouble‐free
ofmachine
100% cotton with mass
embroidery. The per unit area
woven of 230 g/m2 was
macrostructures had chosen for the e-textile
better performance than mat.
the knit‐
The requirements for the second layer were good air permeability,
ted macrostructures in terms of low elongation under tensile load. Therefore, a woven good absorption
and lowofcost.
fabric 100% cotton with mass per unit area of 230 g/m2 was chosen for the e‐textile mat.
The requirements for the second layer were good air permeability, good absorption
2.4. Embedding of the Sensors
and low cost.
2.4.1. Machine Embroidering
2.4. From the analysis
Embedding of the motifs applied so far for developing resistive and capacitive
of the Sensors
textile sensors by machine embroidery [6–8,12,13], it was found that the motif’s shape was
2.4.1. Machine Embroidering
usually rectangular, filled with weave stitch line. The weave stitch line (Figure 4) is used in
objectsFrom
wherethe analysisstitches
covering of the motifs applied
are needed socombination
or in far for developing resistive
with other typesand capacitive
of underlay
textile sensors
stitches. Only theby machine
authors ofembroidery [6–8,12,13], [13]
a recent publication it was found five
studied that motifs
the motif’s shapethe
in which was
usually rectangular, filled with weave stitch line. The weave stitch line (Figure
distance between the electrodes was constantly preserved and the length of the conductive 4) is used
in objects
thread was where covering
significantly stitches are needed or in combination with other types of un‐
reduced.
derlay stitches. Only the authors of a recent publication [13] studied five motifs in which
Materials 2021, 14, x FOR PEER REVIEW 5 of 11
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Materials 2021, 14, 5437
the distance between the electrodes was constantly preserved and the length of the 5con‐
of 11
the distance between the electrodes was constantly preserved and the length of the con‐
ductive thread was significantly reduced.
ductive thread was significantly reduced.
Figure 4. Object with a weave stitch line.
Figure4.4.Object
Figure Objectwith
withaaweave
weavestitch
stitchline.
line.
The machine embroidery of the sensors was made with an MB4 Janome machine with
The
Themachine
machine embroidery of of the
thesensors
sensorswas wasmade
made with
with ananMB4MB4 Janome
Janome machine
machine with
one head and four needles. Madeira Germany conductive HC 12 thread was used for the
with
one one
headhead and and
four four needles.
needles. MadeiraMadeira Germany
Germany conductive
conductive HC 12HC 12 thread
thread was for
was used used
the
upper and lower threads. HC 12 is a twisted polyester polyfilament with silver coating, a
for the upper
upper and lowerand threads.
lower threads.
HC 12 isHC 12 is a twisted
a twisted polyesterpolyester polyfilament
polyfilament with silverwith silvera
coating,
linear density of 235 × 2 dtex and an electrical resistance < 100 Ω/m. The main disad‐
coating, a linear of
linear density density
235 × of dtex×and
2 235 2 dtex
an and an electrical
electrical resistance
resistance < 100 < 100 Ω/m.
Ω/m. The main
The main disad‐
vantage of this thread is its durability, which according to [18], is approximately 10 wash‐
disadvantage of this thread is its durability, which according to [18], is
vantage of this thread is its durability, which according to [18], is approximately 10 wash‐approximately 10
ing cycles. The best performance had the stainless‐steel microfibre thread, but there were
washing
ing cycles. cycles.
The The
best best performance
performance had had the stainless-steel
the stainless‐steel microfibre
microfibre thread,thread, but there
but there were
difficulties with its application in machine embroidery.
were difficulties
difficulties withwith its application
its application in machine
in machine embroidery.
embroidery.
A crucial feature of the embroidery of electrically conductive threads is that the work
AAcrucial
crucialfeature
featureofofthetheembroidery
embroideryofofelectrically
electricallyconductive
conductivethreads
threadsisisthat
thatthe
thework
work
process
process isisnot
not interrupted
interrupted due
due to
to the
the fact
factof
of thread
thread break;
break; otherwise,
otherwise, the
the electrical
electrical circuit
circuit
process is not interrupted due to the fact of thread break; otherwise, the electrical circuit
also
alsobreaks. ItItisisalso essential to avoid the accumulation of stitches on top of each other.
alsobreaks.
breaks. It isalso
alsoessential
essentialtotoavoid
avoidthe
theaccumulation
accumulationofofstitches
stitcheson ontop
topofofeach
eachother.
other.
The
The test
testsamples
samples with
with the
theembroidered
embroidered sensors
sensors were
were made
made with
with aa woven
woven macrostruc‐
macrostruc-
The test samples with the embroidered sensors were made with a woven macrostruc‐
ture
turein a twill weave (120 g/m2 2mass per unit area) using a non‐woven macrostructure on
tureininaatwill
twillweave
weave (120
(120g/m
g/m2 mass
massper perunit
unitarea)
area)using
usingaanon-woven
non‐wovenmacrostructure
macrostructureon on
the
thebackside (70 g/m mass
2 2 per unit area).
thebackside
backside(70 (70g/m
g/m2 mass
mass per
per unit
unit area).
area).
2.4.2.
2.4.2.Electrical
ElectricalResistance
Resistanceand andCapacitance
CapacitanceMeasuring
Measuring
2.4.2. Electrical Resistance and Capacitance Measuring
The
Themeasurement
measurementof ofthe
theelectrical
electricalresistance
resistanceand
andcapacitance
capacitancewas
wasconducted
conductedwith
withaa
The measurement of the electrical resistance and capacitance was conducted with a
digital
digitalLCR‐819
LCR-819m mofofGW
GWInstek
Instekwith
withan anaccuracy
accuracyofof0.05%,
0.05%,capacity
capacityrange
rangefrom
from0.00001
0.00001
digital LCR‐819 m of GW Instek with an accuracy of 0.05%, capacity range from 0.00001
pF
pFtoto99.999
99.999nF,
nF, electrical
electricalresistance
resistanceranging
rangingfrom
from 0.00001
0.00001to
to 99.999
99.999 Ω,Ω,and
and measurement
measurement
pF to 99.999 nF, electrical resistance ranging from 0.00001 to 99.999 Ω, and measurement
speed
speedof of68
68ms.
ms.The
Theresistance
resistancewaswasdetermined
determinedininfive
fivezones
zones(1(1to
to5)
5)of
ofthe
the embroidered
embroidered
speed of 68 ms. The resistance was determined in five zones (1 to 5) of the embroidered
element
elementaccording
accordingtotothe
thescheme
schemein inFigure
Figure5.5.
element according to the scheme in Figure 5.
Figure
Figure5.5.Scheme
Schemeforforthe
theelectrical
electricalresistance
resistancemeasurement
measurementofofthe
theembroidered
embroideredelement:
element:starting
startinginin
Figure
zone 1 and5. finishing
Scheme forin the
zoneelectrical
5. resistance measurement of the embroidered element: starting in
zone
zone11and
andfinishing
finishingininzone
zone5.5.
The
Theexperimental
experimentalschemeschemeforforthe
thecapacitance
capacitancemeasurement
measurementisispresented
presentedininFigure
Figure6.6.
The experimental scheme for the capacitance measurement is presented in Figure 6.
The
The first electrode was the embroidered sensor, and the second was a flat parallel end
first electrode was the embroidered sensor, and the second was a flat parallel end
The first electrode was the embroidered sensor, and the second33was a flat parallel end
measure
measuremade
made of of stainless
stainless steel with dimensions 30 30 ×
× 32
32 ××88mm
mm. .3AAstandard
standardtest
testwas
was
measure made of stainless steel with dimensions 30 × 32 × 8 mm . A standard test was
performed
performedat ataa voltage
voltage ofof 11 V and a frequency of 1 kHz.
kHz.
performed at a voltage of 1 V and a frequency of 1 kHz.
Materials 2021, 14, x FOR PEER REVIEW 6 of 11
Materials 2021, 14,
Materials 2021, 14, 5437
x FOR PEER REVIEW 66 of
of 11
11
Figure 6. Scheme for the capacitance measurement.
Figure 6.
Figure Scheme for
6. Scheme for the
the capacitance
capacitance measurement.
measurement.
3.3.Results
ResultsandandDiscussion
Discussion
3. Results and Discussion
3.1.
3.1.Selection
Selectionofofthe
theTextile
TextileSensors
Sensors
3.1. Selection of the Textile Sensors
When
Whenincorporating sensorsusing
incorporating the sensors usingembroidery
embroiderywith with conductive
conductive threads,
threads, it isitcru‐
is
cial When
crucial
to to incorporating
follow
follow specific
specific the sensors using embroidery with conductive threads, it is cru‐
rules:
rules:
cial to follow specific rules:
• Avoid
Avoidoverlapping
overlappingstitches;
stitches;
• Avoid
Minimum overlapping
thread
Minimum thread length; stitches;
length;
• Minimum
Making
Makingthe thread
the motiflength;
motif without
withoutbreaking/cutting
breaking/cuttingthe thethreads.
threads.
Making
Five the
motifs motif
were without
developed breaking/cutting
to incorporate the
the threads.
sensors in the textile systems: concentric
Five motifs were developed to incorporate the sensors in the textile systems: concen‐
Five
circles, motifs
cobweb, were
spiral,developed
five-pointed to incorporate
star and the
Hilbert sensors
curve. in
Theythe textile
were
tric circles, cobweb, spiral, five‐pointed star and Hilbert curve. They were designed systems:
designed concen‐
based on
based
tric
knowncircles, cobweb,
mathematical spiral, five‐pointed
functions and star
fractals and
and Hilbert
observed curve.
work They were
conditions
on known mathematical functions and fractals and observed work conditions with con‐ designed
with based
conductive
on known
threads.
ductive mathematical
These
threads. variants
These havefunctions andnot
not have
variants been fractals
been and
proposed observed
in the
proposed work
literature
in the yet.conditions
The sensor
literature with
yet. The con‐
designs
sensor
ductive
were
designs threads.
madewerewith These variants
3D modelling
made with have notsoftware,
software,
3D modelling beenwhich
after proposed in thethe
thewhich
after literature
embroideries wereyet.created
embroideries The sensor
were with
cre‐
designs
Digitizer were
MB made
V 3.0 with
(Figure 3D7).modelling
ated with Digitizer MB V 3.0 (Figure 7). software, after which the embroideries were cre‐
ated with Digitizer MB V 3.0 (Figure 7).
Figure7.7.Design
Figure Designofofthe
thesensor
sensorpatterns:
patterns:(a)
(a)concentric
concentriccircles;
circles;(b)
(b)cobweb;
cobweb;(c)
(c)five-pointed
five‐pointedstar;
star;(d)
(d)
Figure
spiral;7.(e)Design
Hilbertofcurve.
the sensor patterns: (a) concentric circles; (b) cobweb; (c) five‐pointed star; (d)
spiral; (e)
spiral; (e) Hilbert
Hilbert curve.
curve.
Allmotifs
All motifs were
were designed
designed with
with the
the same
same overall
overallsize
sizeofof2020mm,
mm,which
whichis is
in in
fullfull
ac‐
All motifs
cordance with were
the designedStraight
literature. with the same overall
double‐sided sizeline,
stitch of 20 mm,consumes
which which is in
lessfull ac‐
thread
accordance with the literature. Straight double-sided stitch line, which consumes less
cordance with the literature. Straight double‐sided stitch line, which consumes less thread
Materials 2021, 14, 5437 7 of 11
thread length, was used, with a stitch step of 2 mm. The produced samples with the sensors
are presented in Figure 8. It resulted that only the motif with concentric circles cannot be
made without overlapping the stitches, which is undesirable.
Figure 8. Embroidered textile sensors: (a) concentric circles; (b) cobweb; (c) five-pointed star; (d)
Hilbert curve; (e) spiral.
The results of the measurement of the sensors’ electrical resistance and capacitance in
different patterns are shown in Table 1. The cobweb and five-pointed star were the motifs
with the lowest electrical resistance. The spiral and cobweb motifs showed the highest
capacitance, approximately 20 pF. Since the cobweb motif had a lower electrical resistance
and a lower conductive thread consumption, it was selected for the e-textile mat design.
Table 1. Electrical resistance and capacitance of the sensors in different embroidery patterns.
Concentric Five-Pointed Hilbert
Pattern Cobweb Spiral
Circles Star Curve
Average 3.95 1.65 1.43 2.49 11.28
Electrical resistance, Ω
Standard
0.34 0.20 0.13 0.95 1.25
deviation
Average 15.58 19.28 15.76 25.68 17.5
Capacitance, pF
Standard
0.492 0.207 0.285 0.312 0.303
deviation
Invested thread length, m 1.06 1.10 0.98 1.49 1.06
Capacitance/thread length 14.70 17.53 16.08 17.23 16.51
3.2. Production of the Textile Sensors
The sensors’ incorporation through embroidery required marking the lines on the
fabric along which the sensors would be located. Thus, it was possible to centre the
textile system in the embroidery frame. With the application of an embroidery frame
with the largest dimensions, it was possible to digitise and produce a total of nine sensors
simultaneously. The group of nine sensors had to be centred relative to the zero in the x-
and y-directions (Figure 9).
largest dimensions, it was possible to digitise and produce a total of nine sensors simulta‐
Materials 2021, 14, x FOR PEER REVIEW
neously. The group of nine sensors had to be centred relative to the zero in the x‐ and8 of y‐11
directions (Figure 9).
Figure 10 presents the embroidered textile sensors for body position. Because the
Materials 2021, 14, 5437 8 of 11
photo was
largest taken at anitangle,
dimensions, the rows
was possible to of embroidered
digitise image
and produce sensors
a total seemsensors
of nine to be located
simulta‐
atneously.
an angle,The
resulting
group in
of image distortion.
nine sensors had to be centred relative to the zero in the x‐ and y‐
directions (Figure 9).
Figure 10 presents the embroidered textile sensors for body position. Because the
photo was taken at an angle, the rows of embroidered image sensors seem to be located
at an angle, resulting in image distortion.
Figure 9.
Figure Thedevelopment
9. The development of
of aa program
program for
for the
the sensors’
sensors’ incorporation
incorporation with
with Digitizer
Digitizer MB.
MB.
Figure 10 presents the embroidered textile sensors for body position. Because the
photo was taken at an angle, the rows of embroidered image sensors seem to be located at
an angle, resulting in image distortion.
Figure 9. The development of a program for the sensors’ incorporation with Digitizer MB.
Figure 10. The e‐textile mat with the embroidered textile sensors.
When incorporating the sensors, a certain length of the upper thread (approximately
15–20 cm) was left free to be connected with the flat ribbon cable passing from the reverse
side of the
Figure 10.mat. The ribbon
The e‐textile cablethe
mat with passed throughtextile
embroidered the entire width of the product, ensuring
sensors.
Figure 10. The e-textile mat with the embroidered textile sensors.
that an equal length of conductive thread was used for each sensor. Figure 11 shows an
imageWhen of theincorporating
When connected sensors
incorporating with the
thesensors,
the sensors, flat
a acertainribbon
certain cable
length
length using
ofofthe
theupper a cable
upper lug.
thread
thread The width of
(approximately
(approximately
the ribbon
15–20 cm) cable
was was
left consistent
free to be with
connectedthe number
with the of
flatsensors
ribbon
15–20 cm) was left free to be connected with the flat ribbon cable passing from the in the
cable three
passing groups.
from The
the ap‐
reverse
reverse
plication
sideofofthe
side ofmat.
the amat.
second
The layer
Theribbon
ribbon incable
the mat
cable ensured
passed
passed the preservation
through
through theentire
the entirewidthof the
width comfort
ofofthe andensuring
theproduct,
product, stability
ensuring
of thean
that
that product
an equal (to
equallength avoid
length the mat’s wrinkle
ofofconductive
conductive threadwas
thread when
wasused thefor
used body
foreachturns)
each during
sensor.
sensor. Figure
Figure operation.
1111shows
showsAn
anan
ethylene‐vinyl
of the acetate
connected (EVA) foam
sensors could
with the also
flat be used
ribbon for
cablea second
image of the connected sensors with the flat ribbon cable using a cable lug. The widthof
image using a mat
cablelayer.
lug. The width
ofthe
theribbon
ribboncablecablewas wasconsistent
consistentwith withthe thenumber
number ofofsensors
sensors inin
thethethree
threegroups.
groups. The ap‐
The
plication of a second layer in the mat ensured the preservation
application of a second layer in the mat ensured the preservation of the comfort and of the comfort and stability
of the product
stability (to avoid
of the product the mat’s
(to avoid wrinkle
the mat’s whenwhen
wrinkle the body
the bodyturns) during
turns) duringoperation. An
operation.
Anethylene‐vinyl
ethylene-vinyl acetate
acetate (EVA)
(EVA) foam
foam could
could also
also bebeused
used forfor
a second
a second matmatlayer.
layer.
Materials 2021, 14, 5437 9 of 11
Materials 2021,
Materials 2021, 14,
14, xx FOR
FOR PEER
PEER REVIEW
REVIEW 99 of
of 11
11
Figure 11.
Figure 11. The
The reverse
reverse side
side of
of the
the e‐textile
e‐textile mat
mat with
with the
the embroidered
embroidered textile
textile sensors.
sensors.
Figure 11. The reverse side of the e-textile mat with the embroidered textile sensors.
3.3.The
3.3.
3.3. TheSoftware
The SoftwareConnection
Software Connection
Connection
Partofof
Part
Part ofthe
theproject
the projectwas
project wasdeveloping
was developingspecific
developing specificsoftware
specific software(application)
software (application)for
(application) forcontrol
for controlofof
control ofthethe
the
multiplexers,
multiplexers, collecting
collecting the
thedata
data from
from the
the controller
controller of the
of the capacitive
capacitive
multiplexers, collecting the data from the controller of the capacitive sensors and sending sensors
sensors and
and sending
sending
them
theminin
them inaaaprotocol
protocolon
protocol on aaa serial
on port. The
serial port. Theapplication
The applicationwas
application wascreated
was createdin
created inin the
thethe processing
processing
processing envi-
environ‐
environ‐
ronment
ment for for visualisation
visualisation of of
the the results.
results. A A
moremore straightforward
straightforward interface
interface
ment for visualisation of the results. A more straightforward interface was offered to sim‐ was was offered
offered to to
sim‐
simplify
plify the
plify the
the data data reading
data reading
reading by by
by thethe user.
the user.
user. A A mesh
A mesh
mesh of of squares
of squares (visualising
squares (visualising
(visualising the the sensors)
the sensors) was
sensors) was used,
was used,
used,
which
whichchanged
which changedfrom
changed fromblack
from blackfor
black forthe
for thepassive
the passivesensors
passive sensorstoto
sensors tolight
lightgreen
light greenfor
green forthe
for theactive.
the active.The
active. Thedepth
The depth
depth
ofof
ofthe
thegreen
the greencolour
green colourvaried
colour variedaccording
varied accordingtoto
according tothe
thechange
the changeinin
change inthe
thecapacitance,
the capacitance,which
capacitance, whichrepresented
which represented
represented
the
thepressure
pressure that
thatthe
theperson
person exerted
exerted onon the
thesensors.
sensors. Therefore,
Therefore,
the pressure that the person exerted on the sensors. Therefore, it shows that the ititshows
shows that the
that theair
airgap
air gap
gap
between the
between the
between body
the body and
body and the
and the sensors
the sensors decreased
sensors decreased
decreased or or the
or the overlapping
the overlapping
overlapping area area increased.
area increased. This
increased. This way,
This way,
way,
the
theuser
the user(caregiver,
user (caregiver,
(caregiver, medical
medical
medical staff) could
staff)
staff) could
couldbe informed
be informed
be informedabout the bedridden
about
about the bedridden
the bedridden person’s position,
person’s
person’s posi‐
posi‐
which
tion, had not
tion, which
which had
hadbeen
notchanged.
not been changed.
been changed.
To
Toverify
verify the
thedata
data obtained
obtained from
fromthe thesensors,
sensors,experimental
experimentalstudies studieswere wereperformed
performed
To verify the data obtained from the sensors, experimental studies were performed
with
with ananindividual
individual inintwo
two postures,
postures, essential
essential for
forthe
the human
human body
body inina asupine
supine position:
position:
with an individual in two postures, essential for the human body in a supine position:
posture one,
posture one, on
one, on the
on the back
the back (Figure
back (Figure 12),
(Figure 12), and
12), and posture
and posture two,
posture two, in
two, in a sideways
in aa sideways pose.
sideways pose. pose.
posture
Figure 12.
Figure 12. The
The experimental
experimental setup
setup for
for the
the measurement
measurement with
with the
the e‐textile
e‐textile mat.
mat.
Figure 12. The experimental setup for the measurement with the e-textile mat.
Thesensor
The
The sensor
sensor readings
readings
readings were
were
were displayed
displayed
displayed on the
on
on the the screen
screen
screen ofRaspberry
of
of the the Raspberry
the Raspberry Pi 44 minicom‐
Pi minicom‐
Pi 4 minicomputer.
puter.
puter.
The The squares
The squares
squares with
with thewith the darkest
the darkest
darkest colour corresponded
colour corresponded
colour corresponded to the passive
to the passive
to the passive sensors,sensors,
sensors, and those
andwith
and those those
with
lighter lighter
with lighter
ones toones
ones to
the to the activated
the activated
activated ones.
ones. ones. The motives
The motives
The motives that were
that were
that were obtained
obtained
obtained in the
intwo
in the two
the two postures
postures
postures of
of human
of
the the human
the human
bodybody
body are presented
are presented
are presented in Figure
in Figure
in Figure 13.
13. 13.Materials 2021, 14, 5437 10 of 11
Materials 2021, 14, x FOR PEER REVIEW 10 of 11
Figure 13. Results from the measurements: (a) back posture; (b) sideways posture.
Figure 13. Results from the measurements: (a) back posture; (b) sideways posture.
Thesoftware
The softwaremakes
makes itit possible
possible to
to set
setaatime
timeinterval forfor
interval which
whichthethe
sensors move
sensors from
move
one shade to another. Thus, the user could determine whether the bedridden
from one shade to another. Thus, the user could determine whether the bedridden person person has
performed movements of the torso and lower and upper limbs. At this
has performed movements of the torso and lower and upper limbs. At this stage, it stage, it is impos‐
issible to accurately
impossible determine
to accurately the pressure
determine values invalues
the pressure the separate zones, aszones,
in the separate the capacitive
as the
sensors are
capacitive influenced
sensors not onlynot
are influenced by the
onlyhardness of the mattress
by the hardness used forused
of the mattress the for
testthe
buttest
also
byalso
but the environmental conditions.
by the environmental However,
conditions. the presence
However, of reference
the presence valuesvalues
of reference of theofsensor
the
controller
sensor beforebefore
controller each measurement eliminates
each measurement the influence
eliminates of theofenvironment.
the influence the environment.
4.4.Conclusions
Conclusions
The
Thedesign
design andanddevelopment
development of aofprototype
a prototypeof an
ofe-textile mat mat
an e‐textile withwith
textile sensors
textile for
sensors
avoiding decubitus
for avoiding ulcersulcers
decubitus in bedridden persons
in bedridden were presented.
persons The developed
were presented. monitoring
The developed mon‐
system
itoringand software
system allowed real-time
and software monitoring
allowed real‐time of the body
monitoring position.
of the The sensor
body position. Thewas
sen‐
produced with silver-coated conductive thread, which has a good
sor was produced with silver‐coated conductive thread, which has a good sewability.sewability.
Five
Fivevariants
variantsof of
thethe
pattern for for
pattern the the
textile sensor
textile werewere
sensor developed, and their
developed, and capacitance
their capaci‐
was
tance was measured. The best performance had the design with cobweb,capacitance
measured. The best performance had the design with cobweb, with a of
with a capaci‐
19.28
tancepF,ofand it was
19.28 pF, andusedit for
wasthe smart
used for mat production.
the smart mat production.
Future
Future work in this direction could be expandedbybyincluding
work in this direction could be expanded includinga agroup
groupofofsensors
sensors(at(at
least
least two rows of three sensors each) in the head area. It is also possible to lookfor
two rows of three sensors each) in the head area. It is also possible to look forother
other
software solutions for visualisation of the
software solutions for visualisation of the results results
WeWe hope
hopethat ourour
that work willwill
work encourage
encourage the development
the development of similar devices
of similar in the field,
devices in the
which would increase the comfort of the bedridden persons and help their
field, which would increase the comfort of the bedridden persons and help their caregiv‐ caregivers’ per-
formance.
ers’ performance.
Author Contributions: Conceptualisation, R.A.A. and D.S.; methodology, D.S.; software, Y.S.; valida-
Author Contributions: Conceptualisation, R.A.A. and D.S.; methodology, D.S.; software, Y.S.; vali‐
tion, D.S. and Y.S.; formal analysis, D.S.; investigation, D.S.; resources, R.A.A.; data curation, D.S.;
dation, D.S. and Y.S.; formal analysis, D.S.; investigation, D.S.; resources, R.A.A.; data curation, D.S.;
writing—original draft preparation, D.S.; writing—review and editing, R.A.A.; visualisation, D.S.,
writing—original draft preparation, D.S.; writing—review and editing, R.A.A.; visualisation, D.S.,
R.A.A. and Y.S.; project administration, R.A.A.; funding acquisition, R.A.A. All authors have read
R.A.A. and Y.S.; project administration, R.A.A.; funding acquisition, R.A.A. All authors have read
and agreed to the published version of the manuscript.
and agreed to the published version of the manuscript.
Funding:The
Funding: Thestudy
study and the APC
and the APCwas
wasfunded
fundedbyby Project
Project BG05M20P001-1.002-0011
BG05M20P001-1.002-0011 “Centre
“Centre of
of Com‐
Competence MIRACle—Mechatronics, Innovation, Robotics, Automation, Clean Technologies”,
petence MIRACle—Mechatronics, Innovation, Robotics, Automation, Clean Technologies”, Labor‐
Laboratory 3.4 “Intelligent
atory 3.4 “Intelligent Mechatronic
Mechatronic Solutions
Solutions in Field
in the the Field of Textiles
of Textiles andand Clothing”.
Clothing”.
Institutional Review
Institutional Board
Review Statement:Not
Statement:
Board Notapplicable.
applicable.
Informed Consent
Informed Statement:Not
Statement:
Consent Notapplicable.
applicable.
Data
DataAvailability
AvailabilityStatement: Not
Statement: applicable.
Not applicable.
Conflicts
Conflictsofof
Interest: The
Interest: authors
The declare
authors nono
declare conflict of of
conflict interest.
interest.Materials 2021, 14, 5437 11 of 11
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