high-sensitivity-and-extreme-environment-resistant-sensors-based-on-pedot-pss-pva-hydrogel-fibers-for-physiological

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High-Sensitivity and Extreme Environment-Resistant Sensors Based
on PEDOT:PSS@PVA Hydrogel Fibers for Physiological Monitoring
Wanhui Shi, Ziwei Wang, Hua Song, Yunzhen Chang,* Wenjing Hou,* Yanping Li, and Gaoyi Han*
Cite This: ACS Appl. Mater. Interfaces 2022, 14, 35114−35125 Read Online
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ABSTRACT: The rapid development of flexible electronic devices
has caused a boom in researching flexible sensors based on
hydrogels, but most of the flexible sensors can only work at room
temperature, and they are difficult to adapt to extremely cold or dry
environments. Here, the flexible hydrogel fibers (PEDOT:PSS@
PVA) with excellent resistance to extreme environments have been
prepared by adding glycerin (GL) to the mixture of poly(vinyl
alcohol) (PVA) and poly 3,4-dioxyethylene thiophene:polystyrene
sulfonic acid (PEDOT:PSS) because GL molecules can form
dynamic hydrogen bonds with an elastic matrix of PVA molecules.
It is found that the prepared sensor exhibits very good flexibility
and mechanical strength, and the ultimate tensile strength can
reach up to 13.76 MPa when the elongation at break is 519.9%.
Furthermore, the hydrogel fibers possess excellent water retention performance and low-temperature resistance. After being placed
in the atmospheric environment for 1 year, the sensor still shows good flexibility. At a low temperature of −60 °C, the sensor can
stably endure 1000 repeated stretches and shrinks (10% elongation). In addition to the response to a large strain, this fiber sensor
can also detect extremely small strains as low as 0.01%. It is proved that complex human movements such as knuckle bending,
vocalization, pulse, and others can be monitored perfectly by this fiber sensor. The above results mean that the PEDOT:PSS@PVA
fiber sensor has great application prospects in physiological monitoring.
KEYWORDS: PEDOT:PSS, poly(vinyl alcohol), antidrying, antifreezing, strain sensor
■ INTRODUCTION
The explosive growth of the Internet and big data has laid a
solid foundation for the rapid development of wearable
electronic devices.1,2 At present, the common wearable devices
mainly include smart glasses,3 watches,4 sports bracelets,5 and
others,6,7 and are mainly used in human healthcare and
human-machine interfaces.8 However, these wearable devices
mainly use metal or ceramic sensors that are uncomfortable
because of the rigidity and brittleness of the used materials.
Therefore it is urgent to develop sensors that are highly skin fit
with the body to enhance people’s physical comfort.9 Recently,
flexible and stretchable sensors have attracted widespread
attention due to their extensive deformability and somato-
sensory comfort.
Usually, a flexible sensor is composed of flexible substrates
and a conductive material, where the flexible matrix
contributes to stretchability, and the conductive material
serves signal responses. Based on the fabric,10,11 rubber,12 and
poly(dimethylsiloxane) (PDMS),13,14 many flexible sensors
have been constructed using carbon nanotubes, graphene,
metallic nanomaterials, and carbon black as the conductive
component, but they exhibit such problems as limited
stretchability, poor air permeability, and biocompatibility.
Currently, conductive hydrogels have attracted researchers’
attention due to their excellent stretchability, good biocompat-
ibility, and extremely high shape plasticity. For example, Wang
et al.15 have introduced sodium caseinate and reduced
graphene oxide (rGO) into a polyacrylamide hydrogel to
prepare an SC/rGO/PAAm hydrogel strain sensor for
detection of humans’ larger activities such as joint motion.
However, the sensitivity of this kind of sensor is limited and
cannot recognize small movements. By covalent cross-linking
of MBA and P(AAM-AAc) polymer chains, strain sensors
based on Amy/poly(acrylamide−acrylic acid) polymer net-
work hydrogels have been prepared16 and show significantly
improved sensitivity and can detect various physical activities
of human beings. However, the hydrogel-based sensors still
exhibit problems such as poor water retention to overcome
Received: May 28, 2022
Accepted: July 11, 2022
Published: July 21, 2022
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© 2022 American Chemical Society
35114
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ACS Appl. Mater. Interfaces 2022, 14, 35114−35125
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https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Wanhui+Shi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
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dryness, which indicates that they can only work at room
temperature with relatively high humidity.
On the other hand, if someone walks from a warm and
humid indoor to a cold and dry outdoor in winter, the sudden
change in the environment may cause the sensor not to work
normally. To solve this problem, glycerin (GL) is introduced
into the hydrogels to improve the water retention and
antifreezing of the hydrogel-based sensors.17−20 The reason
is that GL has a high boiling point and can form hydrogen
bonds with water molecules, which will not only reduce the
freezing point of water but also prevent the volatilization of
water. Recently, Ma et al. have prepared a double-layer
antifreezing hydrogel-based sensor using polyvinyl alcohol
(PVA)−GL hydrogel as a nonconductive layer and polyaniline
(PANI)-doped PVA−GL as the core of the conductive
material for signal responses,18 therefore, the sensor can be
used within the temperature range of −20 to 20 °C. An
organic−inorganic polyacrylamide/montmorillonite/carbon
nanotube organohydrogel (MMCOH) sensor has also been
prepared using a convenient solvent replacement strategy,
which has excellent sensing performance and can maintain
flexibility at low temperatures.21 But the freeze tolerance of the
sensor is only verified by freezing at −60 °C for several
minutes and its properties are tested after being thawed at
room temperature. Therefore, it is still necessary to develop a
high-sensitivitystrain sensor that can stably detect the strains
of the human body under extreme conditions.
Here, we use the PVA hydrogel that is dynamically cross-
linked by GL as the stretchable matrix, PEDOT:PSS as the
conductive substance to prepare the PEDOT:PSS@PVA fiber-
based hydrogel strain sensor with excellent sensitivity to small
strains, and antidrying and antifreezing performances. Inside
the hydrogel, PVA molecular chains will be cross-linked by GL
molecules through dynamic hydrogen bonds to form a three-
dimensional (3D) network structure, which can improve the
stretchability and mechanical properties of the hydrogel, and
meantime, the GL molecules can form hydrogen bonds with
water molecules to reduce the volatilization of water and
improve water retention. On the other hand, the PEDOT:PSS
component is evenly dispersed or wrapped in the PVA network
to form a 3D conductive network to ensure the ultrahigh
sensitivity of the strain sensor. Furthermore, the addition of
rigid particles (compared with PVA molecules, PEDOT:PSS
has more rigidity due to the conjugated structure) will improve
the mechanical strength of the fiber through the intermolecular
interaction of hardness and softness. Through the above
interactions, the PEDOT:PSS@PVA hydrogel fiber strain
sensor can detect an extremely small strain of 0.01%, and the
ultimate tensile strength can reach up to 13.76 MPa while the
elongation at break is 519.9%. Surprisingly, the sensor also
exhibits excellent stability and freezing resistance, under
extremely cold conditions of −60 °C, and the ΔR/R0 value
does not change significantly after 1000 cycles under a 10%
repeated strain; and the hydrogel fiber is still flexible after one
year’s placement in an atmospheric environment.
■ EXPERIMENTAL SECTION
Reagents and Materials. PEDOT:PSS (CLEVIOS PH 1000)
was purchased from Heraeus Clevios GmbH and stored in a
refrigerator to maintain a storage environment of 5−10 °C. PVA-1750
and GL were purchased from Hengxing Chemical Reagent Co. Ltd.
All other reagents used in this work were of analytical grade.
Preparation of the PEDOT:PSS@PVA Hydrogel Fiber. Certain
amounts of GL (0, 0.05, 0.08, 0.10, 0.15, and 0.20 g) were added into
200 μL of deionized water to form GL aqueous solutions. Powders of
PVA (1.0 g) were soaked in 9.0 g of deionized water to swell for 30
min at 60 °C, and then heated to 90 °C until they were completely
dissolved under continuous stirring, and finally cooled to room
temperature for use. Subsequently, PEDOT:PSS solution (1.0 mL)
was added to 0.5 g of PVA solution (10.0 wt %), and after being
mixed evenly, the GL solution with a certain concentration was added
into the mixture. The blue mixture was continually stirred until it
became uniform. Then, the uniform mixture was injected into glass
capillaries with an inner diameter of about 1000 μm using a syringe.
The capillaries containing the mixture were transferred into a
refrigerator (−20 °C) to freeze the mixture for 4 h, and then the
capillaries were taken out and thawed at room temperature. After the
samples were repeatedly frozen and thawed for five cycles, the blue
hydrogel fibers were drawn from the capillaries and hung on a
horizontally suspended glass rod for 1 night to obtain PEDOT:PSS@
PVA hydrogel fibers. The hydrogel fibers were named PEDOT: PSS@
PVA-X (X = 0, 1, 2, 3, 4, and 5) according to the amount of GL added
(0, 0.05, 0.08, 0.10, 0.15, and 0.20 g).
The hydrogel fibers were cut into about 3.0 cm pieces to construct
the strain sensors. Two thin copper wires were used as leads to closely
contact both ends of the fiber, and the connection points between the
copper wire and the fiber ends were fixed with copper foil that was
fixed with conductive silver glue. The other end of the copper wire
that was not in contact with the hydrogel fiber was connected to a
testing instrument for various tests.
Characterization and Measurements. The morphologies of the
composites were observed using a field emission scan electron
microscope (JSM-6701F, JEOL) operating at 5 kV. The infrared
spectra of the samples were directly recorded using an attenuated total
reflection Fourier transform infrared spectrometer (ATR-FTIR,
Nicolet iS50R, USA) at 400−4000 cm−1 with a resolution of 2
cm−1. The X-ray diffraction (XRD) patterns were obtained using a
Rigaku Ultimate IV diffractometer with Cu Ka radiation at a scan
speed of 5° min−1 with a step size of 0.02°. The Raman spectra were
recorded with a confocal Raman spectroscope (HORIBA 550) with
an incident laser of 532 nm. X-ray photoelectron spectra (XPS) were
obtained using a Kratos Analytical Ltd AXIS Ultra with an Al Kα
excitation source. Thermogravimetric analysis (TGA) was performed
in a N2 atmosphere and at a heating rate of 10 °C min−1 from 25 to
600 °C (SETSYS Evolution TGA 16/18, France). The electrical
signals of all of the samples were measured in real time using a
potentiostatic method on an electrochemical workstation (CHI 660E,
Chenhua, China). Strain-sensing characteristics were conducted on a
microcomputer-controlled electronic universal material testing
machine (CTM9050, Xieqiang, China) at 25 °C. During the
mechanical test, the samples were kept at a length of 50.0 mm
between the two test fixtures. The smallest test displacement accuracy
of the instrument was about 1.0 μm. When the strain was less than
1.0%, the stretching rate was set to be about 5.0 mm min−1; while the
strain was larger than 1.0%, the stretching rate was set to be 50.0 mm
min−1. During the test of cyclic stability, the strain was set to be
10.0%, and the stretching rate was about 50 mm min−1, so the test
frequency was about one cycle every 12 seconds.
■ RESULTS AND DISCUSSION
Using the general preparation process for hydrogel fibers
shown in Figure 1, the antifreezing conductive hydrogel fibers
(PEDOT:PSS@PVA) with high mechanical strength are
achieved through dynamic cross-linking between PVA
molecular chains and GL molecules. In the hydrogel fiber,
the PEDOT:PSS acts as the conductive active material, while
the GL molecules play the roles of cross-linking, antirefriger-
ant, and a water-retaining agent. A GL molecule contains
multiple hydroxyl groups and has a high boiling point, so it has
a strong binding ability to water due to the formation of
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hydrogen bonds with water. Furthermore, the hydroxyl groups
of GL can form dynamic hydrogen bonds with the hydroxyl
functional groups on the PVA molecular chain to achieve
interchain cross-linking of the polymer. What we need to
emphasize here is that freezing plays an important role. If there
is no freezing process, the hydrogel cannot be formed in the
selected composition (Figure S1). The role played by the
freezing process can be explained as follows: during the
freezing process, the ice first forms on the surface of the sample
and the ice surface acts as the rigid shell; and when the ice
crystals grow continuously, some parts of the PVA molecular
chains are squeezed closely to form crystalline regions because
the squeezing effect of ice reduces the distance between the
chains of PVA and leads to the formation of a crystalline
region. In addition to the extrusion, the generated ice crystal
occupies the space of the original PVA chains and acts as a
template to make the PVA matrix form a 3D network structure.
Therefore, the PVA hydrogel now contains a crystalline region
and an amorphous region, which gives the hydrogel elasticity
and strength. On the other hand, water freezing also increases
the chance for the interaction between PVA molecular chains
and GL molecules, which promotes the formation of hydrogen
bonds between GL molecules and PVA molecules. At the same
time, the PEDOT:PSS component will be uniformly dispersed
into the network structuredue to the interaction among the
molecules. Through the repeated freezing and thawing cycles,
more and more crystalline regions among PVA molecules will
be formed, and more hydrogen bonds between GL and PVA
molecules will be formed too, so the hydrogel’s strength is
enhanced. After the composite fibers have been drawn out of
the capillary, the moisture is evaporated in the atmospheric
environment to obtain the flexible PEDT:PSS@PVA con-
ductive hydrogel fibers. It is notable that the evaporation of
water in this stage will not affect the porous structure of the
fibers because the 3D network has formed and the PVA can
not dissolve into the water at room temperature, but the pore
size will become smaller than before. Furthermore, the specific
strength of the fibers will increase because the diameter of the
fiber decreases.
The SEM image in Figure 2A shows a diameter of about 240
μm for a PEDOT:PSS @PVA-5 fiber; some cracks are
Figure 1. Schematic illustration for the fabrication process of a
PEDOT:PSS@PVA-based hydrogel fiber sensor.
Figure 2. SEM images of the PEDOT:PSS@PVA-5 fiber surface (A, B) and cross-sectional surface (C, D), and the back-scattered electron images
and elemental mappings of C, O, and S on the cross section of the PEDOT:PSS@PVA-5 fiber (E).
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dispersed on the fiber’s surface (Figure 2B), the crack length is
about more than 10 microns, and the width of the slit ranges
from hundreds of nanometers to several micrometers. The
SEM image of the cross section in Figure 2C shows a nearly
circular shape, and the cross-sectional surface appears a bit
rough. From the SEM image with large magnification (Figure
2D), one can find that many pores of the size of microns are
scattered on the surface. Compared with the crack-shaped
pores on the surface of the fiber, the pores on the cross-
sectional surface are irregular, which means that the micro-
structure of the fiber has a certain orientation that has
originated from the preparation process. According to the
structural features shown in Figure 2B and D, we can deduce
that the hydrogel fiber exhibits 3D porous network
architectures. To clarify the distribution information of
PEDOT:PSS in the fiber, elemental mappings of C, O, and S
are determined (Figure 2E). It is found that the distribution of
C, O, and S is uniform, which proves that PEDOT:PSS is
distributed not only on the surface of the composite fiber but
also evenly in the entire PVA matrix, and that the
interpenetrating network of PEDOT:PSS and PVA has been
formed.
Since the hydrogel fiber can be formed within a certain range
of GL amounts, we can control the fiber’s internal structure by
adjusting the added amount of GL. From the SEM images of
the PEDOT:PSS@PVA-0 fiber (Figures S2A and S3A), the
surface of the fiber is very coarse, and the cross-sectional
surface exhibits a corrugated structure, almost no pore is
observed, and the structure is dense. When a small amount of
GL is added, the surface of the PEDOT:PSS@PVA-1 fiber is
not so rough compared with PEDOT:PSS@PVA-0, and some
small holes are found (Figures S2B and S3B), indicating that
part of PVA has been cross-linked with GL molecules. When
the amount of GL increases continuously, a large number of
foldlike structures appear inside the fiber (Figure S2C), and
the roughness of the fiber surface (Figure S3C) becomes lower
than that of the PEDOT:PSS@PVA-0 fiber. When the addition
amount of GL is 0.1 g, the interior presents a 3D convex fold
structure, and the surface roughness is further reduced (Figures
S2D and S3D); as the amount of GL increases further, the
degree of cross-linking of PVA increases more, and a 3D
network structure appears inside the fiber (Figures S2E and
S3E). When the content of GL reaches 0.2 g, the 3D structure
inside the fiber is more obvious, the distribution of pores is
more uniform (Figure S2F), and the surface of the fiber
becomes the smoothest (Figure S3F). However, when the
added GL amount further increases to 0.3 g, the mixture
cannot form the hydrogel fiber, regardless of what freeze−thaw
cycle it goes through (Figure S4).
The evolution of the fiber structure with the added amount
of GL can be explained as follows: in the hydrogel fiber, GL
acts as a cross-linking agent based on dynamic hydrogen
bonds, and it will act with the PVA chains and PEDOT:PSS.
When the GL content is low, the PEDOT:PSS particles
interact with PVA and GL molecules,22 but PEDOT:PSS can
not be evenly dispersed into the matrix, which causes the fiber
surface to be rough. With the increase of the GL content,
enough GL molecules can interact with PVA chains and
PEDOT:PSS species. The degree of cross-linking in the matrix
is increased, so the PVA molecular chain gradually forms a 3D
network structure, and PEDOT:PSS can be evenly dispersed in
the matrix. Therefore, as the amount of GL added increases to
0.2 g, the surface of the fibers becomes smoother. However,
when the GL content reaches 0.3 g in the mixture, the content
of the hydroxyl group of GL molecules is 0.010 mol. Under
this condition, the content of the hydroxyl group for PVA
Figure 3. Raman spectra (A) and XRD patterns (B) of pure PVA, PVA/GL, PEDOT:PSS @PVA-0, and PEDOT:PSS@PVA-5 fibers; whole XPS
spectrum of the PEDOT:PSSS@PVA-5 fiber (C) and the C 1s XPS (D).
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molecules is only 0.0011 mol, and the GL molecules are
sufficiently enough to surround all of the PVA molecules. On
the other hand, GL in water also acts as an antifreezing agent,
so that the sample with an added amount of 0.3 g cannot be
frozen at a temperature of −20 °C. For the above reasons, the
3D network structure cannot be formed.
The Raman spectra (Figure 3A) show three main peak
regionsfor pure PVA and PVA/GL hydrogel fibers. The
characteristic scattering peaks ranging from 838 to 1065 cm−1
are attributed to the scattering peak of the C−C and C−O
stretching and bending vibrations of PVA.23 The peak located
at about 1434 cm−1 originates from the C−H and O−H
bending vibrations. The strong peak at 2905 cm−1 is assigned
to the symmetrical vibrations of −CH2− in PVA.24 However,
some peaks related to the groups of PVA (for example the
peaks at 838 to 1065 and 2905 cm−1) have become weak or
disappeared when PEDOT:PSS is added into the fibers, while
peaks related to PEDOT are observed, for instance, the peak at
1486 cm−1 in the spectra of PEDOT:PSS@PV-0 and
PEDOT:PSS@PV-5 is assigned to the stretching vibrations
of Cα = Cβ on the five-member thiophene ring of PEDOT.25
The XRD pattern (Figure 3B) of pure PVA exhibits a broad
peak at 22° and a very weak peak at 9.7°, which is assigned to
the crystalline region of the PVA molecule. However, the
broad peaks for PVA/GL and PEDOT:PSS@PVA-5 fibers are
slightly shifted to the left compared with pure PVA, which is
caused by the interaction between GL or PEDOT:PSS and
PVA molecular chains and increases the stacking distance of
the PVA crystalline regions.26 With the increase of GL in the
fibers, the peak located at about 22° has a similar left shift
(Figure S5), meaning that the GL molecules can also increase
the stacking distance of the PVA chains.
The XPS spectrum of the PEDOT:PSS@PVA-5 fiber
(Figure 3C) reveals that the elements of C, O, and S coexist
in the hydrogel fiber, and the S element comes from the
PEDOT:PSS component. The high-resolution C 1s XPS
spectrum can be deconvoluted by the peaks centered at
284.60 eV (C−C), 286.06 eV (C−OH), and 288.68 eV (C�
O). The incomplete hydrolysis of poly(vinyl acetate) in the
process of preparing PVA leads to the existence of carbonyl
groups.27 In addition, as shown in FTIR spectra (Figure S6),
the peaks at 1509 and 1189 cm−1 of the PEDOT:PSS@PVA-5
fiber are attributed to the sulfonic acid groups of PSS,28 and
the peaks at 1021 and 920 cm−1 may have resulted from the
hydrogen bonding between the O−H of PVA and GL.29−31
The water content and the thermal stability of the fibers are
also evaluated. According to the TG profiles shown in Figure
4A, it can be seen that the water content in the pure PVA
hydrogel fiber is about 1.0%, while the PEDOT:PSS@PVA-0
fiber shows a similar result. The water content in the PVA/GL
hydrogel fiber significantly increases to about 13.5%, while in
the PEDOT:PSS@PVA-5 fiber, it increases to 13.8%,
indicating that GL molecules in the composite can greatly
increase the water retention in the hydrogel fiber. The thermal
decomposition process of the pure PVA fiber can be mainly
divided into three stages. The first weight loss in the
temperature region of 30−100 °C can be attributed to the
loss of free water molecules. The second weight loss at 250 °C
is related to the stage during which the −OH groups on the
PVA molecular chain are completely removed and most of the
main chains are decomposed. The third weight loss stage at
425 °C is caused by the complete decomposition of the PVA
molecular backbone. Compared with the pure PVA sample, it
is found that the thermal stability of the PEDOT:PSS@PVA-0
fiber is significantly improved, which may be due to the
formation of hydrogen bonds between the sulfonic acid groups
on PEDOT:PSS and the −OH groups on PVA, which
enhances the intermolecular interaction force.28 But the lowest
thermostability of PVA/GL can be attributed to the GL
addition. For PEDOT:PSS@PVA-5 fibers, it also loses free
water molecules at 30−100 °C, and in the temperature range
of 100−600 °C, its weight loss is between PVA and PVA/GL
samples. As shown in Figure 4B, compared with PVA fibers,
the DTG curves of PVA/GL and PEDOT:PSS@PVA-5
samples show a new peak at 200 °C, which are caused by
the volatilization of GL. As the amount of GL increases, the
mass fraction of PVA decreases in the hydrogel fibers, and the
decomposition peak of PVA at 250 °C is covered by the weight
loss peak of GL (Figure S7).
The fiber of PVA will harden due to the water loss after
being placed in the atmospheric conditions for a few days.
After PEDOT:PSS@PVA-(0−5) fibers have been placed in the
atmospheric environment for 10 days, it is found that the
length shrinkage rate for all of the fibers with added GL is
smaller than PEDOT:PSS@PVA-0 (Figure S8). Furthermore,
the more GL is added to the composite, the smaller the fiber
length shrinkage becomes; therefore, PEDOT:PSS@PVA-5
has the largest length. This phenomenon shows that the
PEDOT:PSS@PVA-5 fiber has the best performance for water
retention, which is consistent with the TG test results (Figure
4). It is surprised to find that the PEDOT:PSS@PVA-5 fiber
still maintains excellent flexibility after being placed in the air
for 1 year (Figure S9), demonstrating that the flexibility has
been significantly improved by appropriate GL addition.
The mechanical properties, electrical properties, and
sensitivity are essential indicators for flexible strain sensors.
Figure 4. TG (A) and DTG (B) curves of pure PVA, PVA/GL, PEDOT:PSS@PVA-0, and PEDOT:PSS@PVA-5 hydrogel fibers.
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The plots of stress versus the strain degree (Figure 5A) reveal
that the ultimate tensile strength of the pure PVA fiber is 8.8
MPa with 283.9% of elongation at break, while the ultimate
tensile strength of the PEDOT:PSS@PVA-0 fiber is more than
4 times (38.1 MPa) of the PVA fiber, but the elongation at
break (160.8%) is reduced to nearly half of the PVA fiber’s.
Obviously, addition of PEDOT:PSS in the PVA matrix can
increase the tensile strength of the composite. The reason may
be that PVA is a flexible chain polymer, its low strength and
high elongation can be attributed to the easy sliding between
chain molecules under force. However, the introduction of
PEDOT:PSS (its conjugate system makes it rigid compared
with PVA) will provide a rigid segment to the matrix of linear
molecular chains. Through the interactions of hydrogen bonds
Figure 5. Stress−strain curves of pure PVA, PEDOT:PSS@PVA-0, and PEDOT:PSS@ PVA-5 fibers (A), and the relative resistance change-strain
curve of the PEDOT:PSS@PVA-5 fiber (B).
Figure 6. Strain−stress curves of the PEDOT:PSS@PVA-5 fiber sensor at a strain of 0.01−10% (A) and 10−130% (B), and the ΔR/R0 value of the
PEDOT:PSS@PVA-5 fiber sensor under 0.01−1.0% (C), 10−60% (D), and 70−130% (E) strain cycle tests.
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and the π-dipole interaction between the rigid and flexible
molecules, the system containing rigid and flexible components
will be constructed uniformly, which is conducive to better
disperse the loaded force along the fiber axis, so that the fiber’s
tensile strength at break is significantly enhanced. However,
the mutual sliding between PVA chains is limited by the added
PEDOT:PSS rigid molecule modules due to the winding effect
of flexible PVA molecules on rigid PEDOT units, which results
in a poor elongation for PEDOT:PSS@PVA-0 compared with
the pure PVA fiber.32
The ultimate tensile strength of the PEDOT:PSS@PVA-5
fiber can reach 13.8 MPa with 519.9% of elongation at break,
which is better than the PVA fiber but the tensile strength at
break is lower than that of the PEDOT:PSS@ PVA-0 fiber. To
understand the effect of GL molecules on the tensile strength
of the composite fibers, the mechanical behaviors of
PEDOT:PSS@ PVA-X (X = 1−5) are compared with each
other (Figure S10). It is found that both the ultimate tensile
strength and elongation at break for all of the samples are
larger than those for the PVA fiber, and increase with the
increment of added GL in the composites. From the DTG
curves shown in Figure S7B, one can find that the temperature
of the second weight loss stage for the fibers decreases as the
added GL in the composite increases due to the generation of
Figure 7. Various stability tests for the fibrous sensor. The resistance of PEDOT: PSS@PVA-5 fibers that are placed at room temperature for 2 h
and 10 days (A), the resistance of PEDOT: PSS@PVA-5 fiber at 25 and −60 °C (B), and the ΔR/R0 for 3000 stretch-and-release cycles of strain
variation from 0 to 10% at 25 °C (C), and −60 °C (D).
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hydrogen bonds. Combining the results of mechanical
properties and DTG curves, we can infer the following
conclusions: the sample of PEDOT:PSS@PVA-0 increases the
mechanical strength but decreases the elongation at break
compared with the pure PVA fiber due to the addition of the
rigid component of PEDOT:PSS. However, when the GL
molecules are added to the composite, the interaction between
the component of PEDOT:PSS and PVA will be decreased due
to the competition of GL molecules because the GL molecules
can also interact with PVA and PEDOT:PSS molecules in the
system, which leads to the strength of PEDOT:PSS@ PVA-
(1−5) smaller than that of PEDOT:PSS@PVA-0. On the
other hand, with the increase of GL in the composite, the
formed hydrogen bonds between PVA and GL molecules
increase to form the network structure, so the mechanical
strength of PEDOT:PSS@PVA-(1−5) is larger than that of the
pure PVA fiber; furthermore, a large number of dynamic
hydrogen bonds are formed in the system because of the
presence of GL, which is also beneficial to enhance the
stretchability of the material. Therefore, the elongation at
break for PEDOT:PSS@PVA-(1−5) is larger than pure PVA
and PEDOT:PSS@PVA-0 fibers, and the elongation at break
increases with the increased addition of GL.
The excellent flexibility and mechanical properties have laid
a good foundation for the application of the PEDOT:PSS@
PVA-5 hydrogel fiber as a strain sensor. The relative resistance
change during the stretching process has been monitored and
the result is shown in Figure 5B. During the stretching process,
the ΔR/R0 values increase as the strain increases. This may be
due to the deformation or even destruction of the 3D
conductive network during the strain process. The PE-
DOT:PSS rigid component is wrapped in a flexible network
of PVA cross-linked with GL. In the process of a small strain,
the PVA molecular chains slip, which increases the distance
among the conductive particles wrapped in it, which makes the
resistance of the sensor increase. The PVA polymer chain and
GL are cross-linked by hydrogen bonds between molecules;
when the strain continues to increase, the hydrogen bonds
between PVA molecules are partially broken, and the distance
between PEDOT:PSS particles continues to increase, which
will make the resistance of the device further increase. The
gauge factor (GF) is an important parameter to evaluate the
sensitivity of the sensor. It is calculated to find that the GF
value increases from 0.5 to 5.4 with strain from 0 to 130%,
which demonstrates that strain-related responsivity can be used
in a wide working strain.
At the same time, the reversibility and sensing performance
of the sensor under different strains have been evaluated by
testing the conductivity under the stepwise cyclic tensile
deformation conditions. The strain−stress curves at 0.01−
130% strain form a closed hysteresis loop (Figure 6A,B). Based
on Figure 6A, it is found that the curves corresponding to the
loaded process and the unloaded process almost coincide at a
small strain of 0.01−0.1%. But according to the enlarged figure
shown on the left of Figure 6A, one can find the closed
hysteresis loops during the loaded and the unloaded process,
but the hysteresis area is very small, meaning that the fibers
mainly undergo elastic deformation with the rupture of an
extremely small amount of hydrogen bonds, which results in
light hysteresis losses.13 The rapid increase of the hysteresis
areas above 1.0% strain indicates that the energy can be
efficiently dissipated to enhance the toughness and damage
tolerance of the elastomer.33,34 Superior to other samples of
PEDOT:PSS@PVA (Figure S11), PEDOT:PSS@PVA-5 can
respond to the minimum strain of 0.01%. As shown in Figure
6C−E, the PEDOT:PSS@PVA-5 fiber sensor shows an
obvious resistance response even if the strain is as low as
0.01%, and it also has a good electrical signal response at a
large strain of 130%. In addition, in the strain range of 0.01−
130%, the ΔR/R0 values increase with the increase of the
applied tensile strain, and the signal almost completely
recovers to the original value during the unloading process,
demonstrating the excellent strain-sensing stability and
reversibility of the sensor in a wide strain working range.
The above advantages mean a promising application prospect
for the PEDOT:PSS @PVA hydrogel fiber sensor for
monitoring the human physiological characteristics.
The stability of the material resistance is critical to the
sensor. According to Figures S12 and S13, one can find that
PEDOT:PSS@PVA-5 has a relatively low resistance, and the
electrical resistance of PEDOT:PSS@PVA-5 will reach stable
values within 2 h when it is taken out of the capillary tube.
Furthermore, it is interesting to find that the resistance of the
PEDOT:PSS@PVA-5 fiber is about 6.8 MΩ (Figure 7A)
before and after being placed in an atmospheric environment
for 10 days, which corresponds to a conductivity of about
0.00163 S cm−1; one can also find that the resistance of
PEDOT: PSS@PVA-5 has almost no change after it has dried
for 2 h and 10 days. However, the monitored resistance of
PEDOT:PSS@PVA-5 (Figure 7B) is found to be increased to
about 7.0 MΩ at a low temperature of −60 °C, which is
obviously higher than that at room temperature and is in line
with the semiconductor properties of PEDOT.35,36 The
tolerance to repeated stretching of the sensoris tested at 25
°C after the sensor has been placed for 10 days in an
atmospheric environment (Figure 7C). In the testing process,
the strain deformation is limited to 10%, and the strain rate is
kept at 50 mm min−1. It is clear that the change of ΔR/R0 is
almost invisible within the testing 3000 cycles. From the inset
figures in Figure 7C, one can find that the shape of the plot of
ΔR/R0 versus cyclic number (curve of the stretch-recovery)
after 2800 cycles is almost the same as that of the first 200th
cycle. Moreover, the surface morphology (Figure S14) shows
that PEDOT:PSS@PVA-5 fibers after 3000 cycles at 10%
strain do not change significantly compared with their original
state (no more cracks appearing), which indicates that the 3D
structure in PEDOT:PSS@PVA-5 fibers is very stable and
shows excellent durability. However, the orientation texture
has been seen in the stretching direction appears, which
indicates that the 3D structure is severely deformed or even
destroyed when the fiber has been stretched to fracture. In
addition, the performances of the PEDOT:PSS@PVA-5 fiber
sensors are also investigated in harsh circumstances to verify
their environmental tolerance. As shown in Video S1, after
being placed at −60 °C for 8 min, the PEDOT:PSS@PVA-5
fiber is not frozen hard, but it shows excellent flexibility and
stretchability. At the low temperature of −60 °C, the sensor
still displays satisfactory repeatability when the strain
deformation is limited to 10% (Figure 7D). Within 1000
cycles, we find that the response of ΔR/R0 to the stretch-
recovery process is almost not changed. The above test results
prove that the PEDOT:PSS@PVA-5 fiber sensor has an
excellent performance in sensitivity, recoverability, cycle life,
and resistance to extreme environments.
The properties of some anti-freezing sensors have been
summarized in Table 1. On comparison, it is found that
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although PAAM-based sensors37−40 have better stretchability
and their sensitivity is significantly lower. However, the
elongation at break of the PVA-based sensor is significantly
lower than that of the former, but the minimum temperature
tolerance is significantly increased.18,41−43 It is notable that the
tensile strength of these two kinds of sensors is less than 1.0
MPa. The tensile strength of our PEDOT:PSS@PVA fiber
sensor is about 26 times that of PEDOT/PVA-based sensors.43
Besides, the sensitivity of 0.01% is significantly higher than
those sensors reported recently15,27,37−47 although the
PEDOT:PSS@ PVA-5 hydrogel fiber has a smaller elongation
than some sensor materials.15,37,39,42,44 These excellent proper-
ties show that it could be used for physiological monitoring of
various human activities.
We mount the fiber sensor on the back of the hand to
monitor the grip-extension movement of the hand. With the
action of making a fist, ΔR/R0 increases rapidly, and the
resistance remains the same when the fist is kept, and when the
hand is opened, the ΔR/R0 value returns to the original state
(Figure 8A). The fast grip-extension process of the hand can
also be recorded by the sensor. Furthermore, the sensor has
also been assembled to the finger joints to accurately track the
precise movements of the hand (Figure 8B). The sensor has
presented an excellent function feature as a wearable sensor to
detect complex human movements.
The sensor can be also used to monitor tiny movements of
the throat (Figure 9A) if it is adhered to a volunteer’s throat.
When the throat swallows regularly, the sensor can reflect the
throat movement in a timely manner (Figure 9B).
Furthermore, the sensor can also recognize the strong and
weak pronunciations of letters such as A and B (Figure 9C,D).
At the same time, the sensor’s ability to monitor the
pronunciation of words in the throat has also been tested
(Figure 9E,F). For example, different words like YES and NO
show different curve shapes. The sensor can even distinguish
the difference in tone, the louder the sound, the more obvious
the ΔR/R0 changes get.
Compared with the movements of the hand and finger, the
human pulse movement has a tiny deformation, and
monitoring this kind of movement needs a highly sensitive
sensor. Since PEDOT:PSS@PVA-5 has high sensitivity, we fix
the sensor on the wrist of an adult woman to try to monitor
her body pulse. According to the curves shown in Figure 10, it
is surprising to find that small signals are regularly distributed
on the large signals, which are arranged regularly. The small
signals are attributed to the body pulse beats, and the large
signals come from the movements caused by breathing.
Furthermore, one can easily find that there are significant
systolic pressure peak P1 and diastolic pressure peak P2 in a
single pulse waveform. It is notable that the periodicity and
stability of the signals are not stable due to the difference in the
amplitude of each breath of the volunteer. The above test data
correspond to the condition of an adult woman with 14
breaths and 72 pulse beats per minute.
■ CONCLUSIONS
A flexible hydrogel fiber sensor with excellent characteristics of
biocompatibility, mechanical property, sensitivity, and cycle
Table 1. Examples of Recently Published Sensors and Their Material Properties
sensor material stretchability (%) tensile strength (MPa) sensitivity (%) the lowest temperature (°C) ref
Ca-GG/PAAm-ZP 1349 0.410 20 −40 37
(EMImAc)/H2O/KCl 277 0.450 −50 38
DN-Cit 692 5.560 10 −50 39
PNIPAM-MWNT 87 0.027 25 40
Eg-DN 950 0.5 −18 41
PVA/B-GL-H/PPY 990.5 0.462 −20 42
PVA-GL-PAni 420 0.035 −20 18
PEDOT/PVA 400 0.397 −70 43
PDMS/(CB+CNTs)/EB 996.5 3.7 10 25 44
SC/rGO/PAAm 1100 0.027 0.1 25 15
PPy@PVA film 309.5 45.35 0.1 25 27
PC-hydrogel 277 0.450 10 25 45
PVA/SA/MXene 263 0.392 0.2 25 46
RGO/PU fiber 20 0.1 25 47
PEDOT:PSS@PVA 519.9 13.76 0.01 −60 our work
Figure 8. Demonstration of the sensor for monitoring human activities, fist−palm (A) and knuckle bending (B).
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stability has been prepared by repeating the freezing−thawing
of the mixture of PVA, PEDOT:PSS, and GL. Their excellent
properties are attributed to the dynamic cross-linked hydrogen
bonds between GL and the elastic matrix of PVA. The exciting
antidrying and antifreezing performances of the PE-
DOT:PSS@PVA-5 sensor are endowed with the hydrogen
bond between GL and water molecules, so that the sensor can
not only work under an atmospheric environment but also can
stably cycle 1000 times at −60 °C. In addition, this fiber sensor
can detect extremely small strains as low as 0.01%, and thus
can monitor humans’ complex movements, such as knuckle
bending, vocalization, pulse, and others. The strategy
developed for fabricating conductive hydrogel fibers by simply
mixing the components will open a new simple route for
Figure 9. Photograph of a fiber sensor attached to the throat (A), relative resistance signals for swallowing actions (B), and differentsounds (C−F).
Figure 10. Respiratory and pulse signals of an adult female at rest within 1 min.
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making high-sensitivity strain sensors that can be used in
extreme environments.
■ ASSOCIATED CONTENT
*sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acsami.2c09556.
Photos of the conductive hydrogels before and after
freezing; cross-sectional SEM images; SEM images of
the PEDOT:PSS@PVA fiber; photos of samples with
different glycerol contents; FTIR spectra; TG and DTG
curves; stress−strain curve; the resistive response of
PEDOT:PSS@PVA-(1, 2, 3, and 4); resistance-content
of the glycerin curve; weight-time curve; resistance-
content of the water curve; and the photograph of the
PEDOT:PSS@PVA fiber (PDF)
Demo video of flexibility and stretchability of the
PEDOT:PSS@PVA-5 fiber at −60 °C (MP4)
■ AUTHOR INFORMATION
Corresponding Authors
Yunzhen Chang − Institute of Molecular Science, Key
Laboratory of Materials for Energy Conversion and Storage
of Shanxi Province, Key Laboratory of Chemical Biology and
Molecular Engineering of Education Ministry, Shanxi
University, Taiyuan 030006, China; Phone: +86-351-
7010699; Email: changyunzhen@sxu.edu.cn; Fax: +86-
351-7016358
Wenjing Hou − Institute of Molecular Science, Key Laboratory
of Materials for Energy Conversion and Storage of Shanxi
Province, Key Laboratory of Chemical Biology and Molecular
Engineering of Education Ministry, Shanxi University,
Taiyuan 030006, China; Email: houwenjing@sxu.edu.cn
Gaoyi Han − Institute of Molecular Science, Key Laboratory of
Materials for Energy Conversion and Storage of Shanxi
Province, Key Laboratory of Chemical Biology and Molecular
Engineering of Education Ministry, Shanxi University,
Taiyuan 030006, China; orcid.org/0000-0002-7019-
3392; Email: han_gaoyis@sxu.edu.cn
Authors
Wanhui Shi − Institute of Molecular Science, Key Laboratory
of Materials for Energy Conversion and Storage of Shanxi
Province, Key Laboratory of Chemical Biology and Molecular
Engineering of Education Ministry, Shanxi University,
Taiyuan 030006, China; orcid.org/0000-0002-5588-
2296
Ziwei Wang − Institute of Molecular Science, Key Laboratory
of Materials for Energy Conversion and Storage of Shanxi
Province, Key Laboratory of Chemical Biology and Molecular
Engineering of Education Ministry, Shanxi University,
Taiyuan 030006, China
Hua Song − School of Foreign Languages, Shanxi University,
Taiyuan 030006, China
Yanping Li − Institute of Molecular Science, Key Laboratory of
Materials for Energy Conversion and Storage of Shanxi
Province, Key Laboratory of Chemical Biology and Molecular
Engineering of Education Ministry, Shanxi University,
Taiyuan 030006, China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acsami.2c09556
Author Contributions
W.S. and G.H. directed and designed the project; W.S. and
Z.W. performed the experiments; W.S. wrote the paper with
the support of G.H., H.S., Y.C., W.H., and Y.L., and all authors
contributed to the general discussions.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work was supported by the National Natural Science
Foundation of China (U21A6004, U21A20172, 21574076, and
61804091), the Science and Technology Major Project of
Shanxi (No. 202101030201022), and the Fundamental
Research Program of Shanxi Province (202103021223019).
■ REFERENCES
(1) Ye, Y. H.; Zhang, Y. F.; Chen, Y.; Han, X. H.; Jiang, F. Cellulose
Nanofibrils Enhanced, Strong, Stretchable, Freezing-Tolerant Ionic
Conductive Organohydrogel for Multi-Functional Sensors. Adv. Funct.
Mater. 2020, 30, No. 2003430.
(2) Chen, S.; Zeng, S. H.; Liu, S. Q.; Liu, H. Z.; Zheng, R. Z.; et al. A
Biomimetic Interface with High Adhesion, Tailorable Modulus for
On-Skin Sensors, and Low-Power Actuators. Chem. Mater. 2019, 31,
8708−8716.
(3) Chen, R.; Zhang, Z. C.; Deng, K.; Wang, D. H.; Ke, H. M.; Cai,
L.; Chang, C. W.; Pan, T. R. Blink-sensing glasses: A Flexible
Iontronic Sensing Wearable for Continuous Blink Monitoring. iScience
2021, 24, No. 102399.
(4) Wile, D. J.; Ranawaya, R.; Kiss, Z. H. Smart Watch
Accelerometry for Analysis and Diagnosis of Tremor. J. Neurosci.
Methods 2014, 230, 1−4.
(5) Hu, J.; Wang, J. J.; Xie, H. Q. Wearable Bracelets with Variable
Sampling Frequency for Measuring Multiple Physiological Parameter
of Human. Comput. Commun. 2020, 161, 257−265.
(6) Wu, P. C.; Fu, J. Z.; Xu, Y. T.; He, Y. Liquid Metal Microgels for
Three-Dimensional Printing of Smart Electronic Clothes. ACS Appl.
Mater. Interfaces 2022, 14, 13458−13467.
(7) Wang, I. J.; Chang, W. T.; Wu, W. T.; Lin, B. S. Applying
Noncontact Sensing Technology in the Customized Product Design
of Smart Clothes Based on Anthropometry. Sensors 2021, 21,
No. 7978.
(8) Lim, H. R.; Kim, H. S.; Qazi, R.; Kwon, Y. T.; Jeong, J. W.; Yeo,
W. H. vanced Soft Materials, Sensor Integrations, and Applications of
Wearable Flexible Hybrid Electronics in Healthcare, Energy, and
Environment. Adv. Mater. 2020, 32, No. 1901924.
(9) Kazem, N.; Tess, H.; Carmel, M. Soft Multifunctional
Composites and Emulsions with Liquid Metals. Adv. Mater. 2017,
29, 1605985−1605999.
(10) Yin, B.; Wen, Y. W.; Hong, T.; Xie, Z. S.; Yuan, G. L.; Ji, Q. M.;
Jia, H. B. Highly Stretchable, Ultrasensitive, and Wearable Strain
Sensors Based on Facilely Prepared Reduced Graphene Oxide Woven
Fabrics in an Ethanol Flame. ACS Appl. Mater. Interfaces 2017, 9,
32054−32064.
(11) Yang, Z.; Pang, Y.; Han, X. L.; Yang, Y. F.; Ling, J.; Jian, M. Q.;
Zhang, Y. G.; Yang, Y.; Ren, T. L. Graphene Textile Strain Sensor
with Negative Resistance Variation for Human Motion Detection.
ACS Nano. 2018, 12, 9134−9141.
(12) Boland, C. S.; Khan, U.; Backes, C.; O’Neill, A.; McCauley, J.;
Duane, S.; Shanker, R.; Liu, Y.; Jurewicz, I.; Dalton, A. B.; Coleman, J.
N. Sensitive, High-Strain, High-Rate Bodily Motion Sensors Based on
GrapheneRubber Composites. ACS Nano. 2014, 8, 8819−8830.
(13) Wang, X. H.; Zhan, S. N.; Lu, Z. Y.; Li, J.; Yang, X.; Qiao, Y. N.;
Men, Y. F.; Sun, J. Q. Healable, Recyclable, and Mechanically Tough
Polyurethane Elastomers with Exceptional Damage Tolerance. Adv.
Mater. 2020, 32, No. 2005759.
(14) Yang, Z.; Wang, D. Y.; Pang, Y.; Li, Y. X.; Wang, Q.; Zhang, T.
Y.; Wang, J. B.; Liu, X.; Yang, Y. Y.; Jian, J. M.; Jian, M. Q.; Zhang, Y.
ACS Applied Materials & Interfaces www.acsami.org Research Article
https://doi.org/10.1021/acsami.2c09556
ACS Appl. Mater. Interfaces 2022, 14, 35114−35125
35124
https://pubs.acs.org/doi/10.1021/acsami.2c09556?goto=supporting-info
https://pubs.acs.org/doi/suppl/10.1021/acsami.2c09556/suppl_file/am2c09556_si_001.pdf
https://pubs.acs.org/doi/suppl/10.1021/acsami.2c09556/suppl_file/am2c09556_si_002.mp4
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yunzhen+Chang"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
mailto:changyunzhen@sxu.edu.cn
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Wenjing+Hou"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
mailto:houwenjing@sxu.edu.cn
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Gaoyi+Han"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdfhttps://orcid.org/0000-0002-7019-3392
https://orcid.org/0000-0002-7019-3392
mailto:han_gaoyis@sxu.edu.cn
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Wanhui+Shi"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
https://orcid.org/0000-0002-5588-2296
https://orcid.org/0000-0002-5588-2296
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Ziwei+Wang"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Hua+Song"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Yanping+Li"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
https://pubs.acs.org/doi/10.1021/acsami.2c09556?ref=pdf
https://doi.org/10.1002/adfm.202003430
https://doi.org/10.1002/adfm.202003430
https://doi.org/10.1002/adfm.202003430
https://doi.org/10.1021/acs.chemmater.9b02274?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.chemmater.9b02274?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.chemmater.9b02274?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.isci.2021.102399
https://doi.org/10.1016/j.isci.2021.102399
https://doi.org/10.1016/j.jneumeth.2014.04.021
https://doi.org/10.1016/j.jneumeth.2014.04.021
https://doi.org/10.1016/j.comcom.2020.07.043
https://doi.org/10.1016/j.comcom.2020.07.043
https://doi.org/10.1016/j.comcom.2020.07.043
https://doi.org/10.1021/acsami.1c22975?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.1c22975?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.3390/s21237978
https://doi.org/10.3390/s21237978
https://doi.org/10.3390/s21237978
https://doi.org/10.1002/adma.201901924
https://doi.org/10.1002/adma.201901924
https://doi.org/10.1002/adma.201901924
https://doi.org/10.1002/adma.201605985
https://doi.org/10.1002/adma.201605985
https://doi.org/10.1021/acsami.7b09652?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.7b09652?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.7b09652?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsnano.8b03391?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsnano.8b03391?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/nn503454h?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/nn503454h?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1002/adma.202005759
https://doi.org/10.1002/adma.202005759
www.acsami.org?ref=pdf
https://doi.org/10.1021/acsami.2c09556?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
Y.; Yang, Y.; Ren, T. L. Simultaneously Detecting Subtle and Intensive
Human Motions Based on a Silver Nanoparticles Bridged Graphene
Strain Sensor. ACS Appl. Mater. Interfaces 2018, 10, 3948−3954.
(15) Wang, Y.; Gao, G. H.; Ren, X. Y. Graphene Assisted Ion-
Conductive Hydrogel with Super Sensitivity for Strain Sensor.
Polymer 2021, 215, 123340−123349.
(16) Kong, L. S.; Gao, Z. J.; Li, X. Y.; Gao, G. H. An Amylopectin-
Enabled Skin-Mounted Hydrogel Wearable Sensor. J. Mater. Chem. B
2021, 9, 1082−1089.
(17) Han, L.; Liu, K. Z.; Wang, M. H.; Wang, K. F.; Fang, L. M.;
Chen, H. T.; Zhou, J.; Lu, X. Mussel-Inspired Adhesive and
Conductive Hydrogel with Long-Lasting Moisture and Extreme
Temperature Tolerance. Adv. Funct. Mater. 2018, 28, 1704195−
1704207.
(18) Ma, Y.; Gao, Y.; Liu, L.; Ren, X. Y.; Gao, G. H. Skin-
Contactable and Antifreezing Strain Sensors Based on Bilayer
Hydrogels. Chem. Mater. 2020, 32, 8938−8946.
(19) Chen, H.; Ren, X.; Gao, G. Skin-Inspired Gels with Toughness,
Antifreezing, Conductivity, and Remoldability. ACS Appl. Mater.
Interfaces 2019, 11, 28336−28345.
(20) Kozlowska, J.; Pauter, K.; Sionkowska, A. Carrageenan-based
Hydrogels: Effect of Sorbitol and Glycerin on The Stability, Swelling
and Mechanical Properties. Poly Test. 2018, 67, 7−11.
(21) Sun, H. L.; Zhao, Y.; Jiao, S. L.; Wang, C. F.; Jia, Y. P.; Dai, K.;
Zheng, G. Q.; Liu, C. T.; Wan, P. B.; Shen, C. Y. Environment
Tolerant Conductive Nanocomposite Organohydrogels as Flexible
Strain Sensors and Power Sources for Sustainable Electronics. Adv.
Funct. Mater. 2021, 31, No. 2101696.
(22) Ko, Y. S.; Kim, J. H.; Jeong, H. Y.; Kwon, G.; Kim, D. B.; Ku,
M. H.; Yang, J.; Yamauchi, Y.; Kim, H. Y.; Lee, C. H.; You, J.
Antibacterial Poly (3,4-Ethylenedioxythiophene):Poly(Styrene-Sulfo-
nate)/Agarose Nanocomposite Hydrogels with Thermo-Processabil-
ity and Self-Healing. Carbohydr. Polym. 2019, 203, 26−34.
(23) Jo, B. W.; Park, S. K.; Kim, D. K. Mechanical Properties of
Nano-MMT Reinforced Polymer Composite and Polymer Concrete.
Constr. Build. Mater. 2008, 22, 14−20.
(24) Nandakumar, P.; Vijayan, C.; Rajalakshmi, M.; Arora, A. K.;
Murti, Y. V. G. S. Raman Spectra of Cds Nanocrystals in Nafion:
Longitudinal Optical and Confined Acoustic Phonon Modes. Phys. E
2001, 11, 377−384.
(25) Klem, M. D. S.; Morais, R. M.; Goncalves Rubira, R. J.; Alves,
N. Paper-based Supercapacitor with Screen-Printed Poly (3, 4-
Ethylene Dioxythiophene)-Poly (Styrene Sulfonate)/Multiwall Car-
bon Nanotube Films Actuating Both as Electrodes and Current
Collectors. Thin Solid Films 2019, 669, 96−102.
(26) Dai, L. X.; Li, J.; Yamada, E. Effect of Glycerin on Structure
Transition of PVA/SF Blends. J. Appl. Polym. Sci. 2002, 86, 2342−
2347.
(27) Shi, W. H.; Han, G. Y.; Chang, Y. Z.; Song, H.; Hou, W. J.;
Chen, Q. Using Stretchable PPy@PVA Composites as a High-
Sensitivity Strain Sensor To Monitor Minute Motion. ACS Appl.
Mater. Interfaces 2020, 12, 45373−45382.
(28) Wang, X. Y.; Feng, G. Y.; Li, M. J.; Ge, M. Q. Effect of
PEDOT:PSS Content on Structure and Properties of PEDOT:PSS/
Poly(Vinyl Alcohol) Composite Fiber. Polym Bull. 2019, 76, 2097−
2111.
(29) Nguyen, N. T.; Liu, J. H. A Green Method for in Situ Synthesis
of Poly(vinyl Alcohol)/chitosan Hydrogel Thin Films with Entrapped
Silver Nanoparticles. J. Taiwan Inst. Chem. E 2014, 45, 2827−2833.
(30) Mathew, S.; Snigdha, S.; Mathew, J.; Radhakrishnan, E. K.
Poly(vinyl Alcohol): Montmorillonite: Boiled Rice Water (Starch)
Blend Film Reinforced with Silver Nanoparticles; Characterization
and Antibacterial Properties. Appl. Clay Sci. 2018, 161, 464−473.
(31) Rolim, W. R.; Joana, C. P.; Debora, L. S. R.; Bruna, A. L.;
Mônica, H. M. N.; Felipe, N. A.; Christiane, B. L.; Marcelo, B.; Ana
Carolina, S.; Amedea, B. S. Antimicrobial Activity and Cytotoxicity to
Tumor Cells of Nitric Oxide Donor and Silver Nanoparticles
Containing PVA/PEG Films for Topical Applications. ACS Appl.
Mater. Interfaces 2019, 11, 6589−6604.
(32) Wang, X. Y.; Ge, M. Q.; Feng, G. Y. The Effects of DMSO on
Structure and Properties of PVA/PEDOT:PSS Blend Fiber. Fibers
Polym. 2015, 16, 2578−2585.
(33) Shi, W.; Lynd, N. A.; Montarnal, D.; Luo, Y. D.; Fredrickson,
G. H.; Kramer, E. J.; Ntaras, C.; Avgeropoulos, A.; Hexemer, A.
Toward Strong Thermoplastic Elastomers with Asymmetric Mik-
toarm Block Copolymer Architectures. Macromolecules 2014, 47,
2037−2043.
(34) Yoshida, S.; Ejima, H.; Yoshie, N. Tough Elastomers with
Superior Self-Recoverability Induced by Bioinspired Multiphase
Design. Adv. Funct. Mater. 2017, 27, 1701670−1701679.
(35) Pathak, C. S.; Singh, J. P.; Singh, R. Preparation of Novel
Graphene-PEDOT:PSS Nanocomposite Films and Fabrication of
Heterojunction Diodes with n-Si. Chem. Phys. Lett. 2018, 694, 75−81.
(36) Zhou, J.; Anjum, D. H.; Chen, L.; Xu, X. Z.; Ventura, I. A.;
Jiang, L.; Gilles Lubineau, G. The Temperature-dependent Micro-
structure of PEDOT/PSS Films: Insights From Morphological,
Mechanical and Electrical Analyses. J. Mater. Chem. C 2014, 2,
9903−9910.
(37) Jiao, Q.; Cao, ll.; Zhao, Z. J.; Zhang, H.; Li, J. J.; Wei, Y. P.
Zwitterionic Hydrogel with High Transparency, Ultrastretchability,
and Remarkable Freezing Resistance for Wearable Strain Sensors.
Biomacromolecules 2021, 22, 1220−1230.
(38) Wang, W. Q.; Yizhuo Liu, Y. Z.; Shiqiang Wang,S. Q.; Xuemei
Fu, X. M.; Tiancheng Zhao, T. C.; Xin Chen, X.; Zhengzhong Shao,
Z. Z. Physically Cross-Linked Silk Fibroin-Based Tough Hydrogel
Electrolyte with Exceptional Water Retention and Freezing Tolerance.
ACS Appl. Mater. Interfaces 2020, 12, 25353−25362.
(39) Yang, Y. Y.; Yang, Y. T.; Cao, Y. X.; Wang, X.; Chen, Y. R.; Liu,
H. Y.; Gao, Y. F.; Wang, J. F.; Liu, C.; Wang, W. J.; Yu, J. K.; Wu, D.
C. Anti-freezing, Resilient And Tough Hydrogels for Sensitive and
Large-Range Strain and Pressure Sensors. Chem. Eng. J. 2021, 403,
126431−126445.
(40) Liu, J. W.; Fan, X. H.; Tao, Y. F.; Deng, C. S.; Yu, K. W.;
Zhang, W. G.; Deng, L. M.; Xiong, W. Two-Step Freezing
Polymerization Method for Efficient Synthesis of High-Performance
Stimuli-Responsive Hydrogels. ACS Omega 2020, 5, 5921−5930.
(41) Wu, J.; Wu, Z. X.; Lu, X.; Han, S. J.; Yang, B. R.; Gui, X. C.;
Tao, K.; Miao, J. M.; Liu, C. Ultrastretchable and Stable Strain
Sensors Based on Antifreezing and Self-Healing Ionic Organo-
hydrogels for Human Motion Monitoring. ACS Appl. Mater. Interfaces
2019, 11, 9405−9414.
(42) Zhang, W.; Wen, J. Y.; Ma, M. G.; Li, M. F.; Peng, F.; Bian, J.
Anti-freezing, Water-retaining, Conductive, and Strain-Sensitive
Hemicellulose/Polypyrrole Composite Hydrogels for Flexible Sen-
sors. J. Mater. Res. Technol. 2021, 14, 555−566.
(43) Peng, Y. J.; Yan, B.; Li, Y. S.; Lan, J.; Shi, L. Y.; Ran, R.
Antifreeze and Moisturizing High Conductivity PEDOT/PVA
Hydrogels for Wearable Motion Sensor. J. Mater. Sci. 2020, 55,
1280−1291.
(44) Li, S. S.; Xu, R.; Wang, J. S.; Yang, Y. P.; Fu, Q.; Pan, C. X.
Ultra-stretchable, Super-hydrophobic and High-Conductive Compo-
site for Wearable Strain Sensors with High Sensitivity. J. Colloid
Interface Sci. 2022, 617, 372−382.
(45) Gu, Z. D.; Xu, Y. C.; Chen, L.; Fang, R. C.; Rong, Q. F.; Jin, X.;
Jiang, L.; Liu, M. J. Macroporous Conductive Hydrogels with Fatigue
Resistance as Strain Sensor for Human Motion Monitoring.
Macromol. Mater. Eng. 2018, 303, 1800339−1800347.
(46) Wang, T. T.; Wang, J. Q.; Li, Z. P.; Yue, M. Q.; Qing, X. L.;
Zhang, P. X.; Xiaozhu, Liao.; Fan, Z. J.; Yang, S. R. PVA/SA/MXene
Dual-network Conductive Hydrogelfor Wearable Sensor to Monitor
Human Motions. J. Appl. Polym. Sci. 2022, 139, 51627−51637.
(47) Chen, Y.; Zhang, Y. Y.; Song, F.; Zhang, H. Y.; Zhang, Q. K.;
Xu, J.; Wang, H. P.; Ke, F. Graphene Decorated Fiber for Wearable
Strain Sensor with High Sensitivity at Tiny Strain. Adv. Mater.
Technol. 2021, 6, 2100421−2100430.
ACS Applied Materials & Interfaces www.acsami.org Research Article
https://doi.org/10.1021/acsami.2c09556
ACS Appl. Mater. Interfaces 2022, 14, 35114−35125
35125
https://doi.org/10.1021/acsami.7b16284?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.7b16284?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.7b16284?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.polymer.2020.123340
https://doi.org/10.1016/j.polymer.2020.123340
https://doi.org/10.1039/D0TB02460K
https://doi.org/10.1039/D0TB02460K
https://doi.org/10.1002/adfm.201704195
https://doi.org/10.1002/adfm.201704195
https://doi.org/10.1002/adfm.201704195
https://doi.org/10.1021/acs.chemmater.0c02919?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.chemmater.0c02919?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.chemmater.0c02919?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.9b11032?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.9b11032?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.polymertesting.2018.02.016
https://doi.org/10.1016/j.polymertesting.2018.02.016
https://doi.org/10.1016/j.polymertesting.2018.02.016
https://doi.org/10.1002/adfm.202101696
https://doi.org/10.1002/adfm.202101696
https://doi.org/10.1002/adfm.202101696
https://doi.org/10.1016/j.carbpol.2018.09.026
https://doi.org/10.1016/j.carbpol.2018.09.026
https://doi.org/10.1016/j.carbpol.2018.09.026
https://doi.org/10.1016/j.conbuildmat.2007.02.009
https://doi.org/10.1016/j.conbuildmat.2007.02.009
https://doi.org/10.1016/S1386-9477(01)00157-6
https://doi.org/10.1016/S1386-9477(01)00157-6
https://doi.org/10.1016/j.tsf.2018.10.029
https://doi.org/10.1016/j.tsf.2018.10.029
https://doi.org/10.1016/j.tsf.2018.10.029
https://doi.org/10.1016/j.tsf.2018.10.029
https://doi.org/10.1002/app.11260
https://doi.org/10.1002/app.11260
https://doi.org/10.1021/acsami.0c14503?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.0c14503?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1007/s00289-018-2459-y
https://doi.org/10.1007/s00289-018-2459-y
https://doi.org/10.1007/s00289-018-2459-y
https://doi.org/10.1016/j.jtice.2014.06.017
https://doi.org/10.1016/j.jtice.2014.06.017
https://doi.org/10.1016/j.jtice.2014.06.017
https://doi.org/10.1016/j.clay.2018.05.009
https://doi.org/10.1016/j.clay.2018.05.009
https://doi.org/10.1016/j.clay.2018.05.009
https://doi.org/10.1021/acsami.8b19021?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.8b19021?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.8b19021?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1007/s12221-015-5616-z
https://doi.org/10.1007/s12221-015-5616-z
https://doi.org/10.1021/ma402566g?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/ma402566g?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1002/adfm.201701670
https://doi.org/10.1002/adfm.201701670
https://doi.org/10.1002/adfm.201701670
https://doi.org/10.1016/j.cplett.2018.01.049
https://doi.org/10.1016/j.cplett.2018.01.049
https://doi.org/10.1016/j.cplett.2018.01.049
https://doi.org/10.1039/C4TC01593B
https://doi.org/10.1039/C4TC01593B
https://doi.org/10.1039/C4TC01593B
https://doi.org/10.1021/acs.biomac.0c01724?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.biomac.0c01724?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.0c07558?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.0c07558?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.cej.2020.126431
https://doi.org/10.1016/j.cej.2020.126431
https://doi.org/10.1021/acsomega.9b04224?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsomega.9b04224?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsomega.9b04224?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.8b20267?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.8b20267?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acsami.8b20267?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.jmrt.2021.06.088
https://doi.org/10.1016/j.jmrt.2021.06.088
https://doi.org/10.1016/j.jmrt.2021.06.088
https://doi.org/10.1007/s10853-019-04101-7
https://doi.org/10.1007/s10853-019-04101-7
https://doi.org/10.1016/j.jcis.2022.03.020
https://doi.org/10.1016/j.jcis.2022.03.020
https://doi.org/10.1002/mame.201800339
https://doi.org/10.1002/mame.201800339
https://doi.org/10.1002/app.51627
https://doi.org/10.1002/app.51627
https://doi.org/10.1002/app.51627
https://doi.org/10.1002/admt.202100421
https://doi.org/10.1002/admt.202100421
www.acsami.org?ref=pdf
https://doi.org/10.1021/acsami.2c09556?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as