printable smart pattern for multifunctional energy ...functional fibers (i.e., fibertronics) in...
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Article
Printable Smart Pattern for MultifunctionalEnergy-Management E-Textile
Mingchao Zhang, Mingyu Zhao,
Muqiang Jian, ..., Xiao Liang,
Junyi Zhai, Yingying Zhang
[email protected] (J.Z.)
[email protected] (Y.Z.)
HIGHLIGHTS
A large scalable strategy for
fabrication of fibertronics for
smart E-textile
Printing of sheath-core fibers
using a 3D printer equipped with a
coaxial spinneret
Printing of various aesthetic smart
patterns on textile
Energy-harvesting textile
composed of silk-sheathed
carbon nanotube fibers
A facile one-step fabrication of coaxial fiber-based smart patterns for E-textile
through 3D printing equipped with a coaxial spinneret is reported. Versatile smart
textiles for different purposes can be fabricated by selecting different materials in
construction of the coaxial layers. Examples such as silk energy-harvesting textile
and energy-storage textile with superior performance are demonstrated.
Zhang et al., Matter 1, 1–12
July 10, 2019 ª 2019 Elsevier Inc.
https://doi.org/10.1016/j.matt.2019.02.003
Article
Printable Smart Pattern for MultifunctionalEnergy-Management E-TextileMingchao Zhang,1,2 Mingyu Zhao,1,2 Muqiang Jian,1,2 Chunya Wang,1,2 Aifang Yu,3,4 Zhe Yin,1,2
Xiaoping Liang,1,2 HuiminWang,1,2 Kailun Xia,1,2 Xiao Liang,1,2 Junyi Zhai,3,4,* and Yingying Zhang1,2,5,*
Progress and Potential
E-textiles, inheriting tradition
merits of textiles with
incorporated electric
components, have drawn great
attention in recent years.
However, the attachment of rigid
and bulky electronics on textile
will severely deteriorate the
breathability and flexibility of the
textile. Alternatively, integrating
functional fibers in traditional
fabrics is a versatile and promising
approach while keeping the
intrinsic merits of fabrics.
SUMMARY
Electronic textile (E-textile) has drawn tremendous attention with the develop-
ment of flexible and wearable electronics in recent years. Herein, we report
the direct printing of E-textile composed of core-sheath fibers by employing
a 3D printer equipped with a coaxial spinneret. Customer-designed core-
sheath fiber-based patterns can be printed on textile for various purposes.
For demonstration, we used carbon nanotubes (CNTs) as a conductive core
and silk fibroin (SF) as a dielectric sheath, and fabricated a CNTs@SF core-
sheath fiber-based smart pattern, which was further used as a triboelectricity
nanogenerator textile. The smart textile could harvest biomechanical energy
from human motion and achieve a power density as high as 18 mW/m2.
We also demonstrated the printing of a supercapacitor textile for energy
storage. The direct printing of smart patterns on textile may contribute
to the large-scale production of self-sustainable E-textile with integrated
electronics.
Nevertheless, a practical
approach to integrate smart fibers
with textile is still lacking. Here, we
report a facile one-step
fabricating process for core-
sheath fiber-based smart patterns
on textile for E-textile, which are
realized by a coaxial spinneret-
equipped 3D printer. The printed
smart pattern on textile, which is
demonstrated for energy
management and other
applications, is beyond the
conventionally aesthetic purpose
or trademark identification of
patterns, paving the way for facile
fabrication of E-textile with
various integrated electronics.
INTRODUCTION
Electronic textile (E-textile), which refers to textile or fabric with integrated digital
components,1 has the potential to have characteristics inherited from traditional
fabrics, such as softness, breathability, and stretchability,2 beyond the desired
electronic functions. However, the attachment of rigid electronics on textile will
severely deteriorate its breathability and flexibility.3 Alternatively, incorporation
functional fibers (i.e., fibertronics) in common fabrics is a versatile and promising
way to obtain E-textile while keeping the aforementioned merits of fabrics.4
Thus, developing techniques to fabricate smart fibers with built-in or add-on
electronic functionality attracts significant attention.5 Nevertheless, imparting
desired functions to highly deformable fibers remains a significant technical
challenge.1
On the other hand, practical approaches to integrate smart fibers with textile are still
lacking. The fabrication of fibertronics and their assemblies into fabric are usually
carried out in separate procedures, which is arduous and time consuming.6–9 For
example, a recent work reported the fabrication of an organic light-emitting diode
(LED) fiber through multi-step dip-coating and thermal deposition, followed by be-
ing sewn into fabrics.7 A functional circuitry on cotton yarns was reported by coating
a layer of aluminum using dip-coating and a layer of polymer by chemical vapor
deposition, following by being woven into fabrics.8 Although these approaches
are effective, the processes are still complex and arduous. Therefore, facile or
even one-step fabrication processes of fibertronics, which have potential for mass
production, are highly desirable.
Matter 1, 1–12, July 10, 2019 ª 2019 Elsevier Inc. 1
Recently, 3D printing has rapidly developed into an important state-of-the-art
additive manufacturing technology.10–13 In particular, a 3D printing technique
based on direct ink writing was proved to be an efficient approach to fabricate
fiber-based architectures for soft robotics,10 smart composites,11 and stretchable
electronics.12 Currently a single-axial spinneret is usually used for 3D printing,13
restricting the material choice and structure design of the printed architectures.
We foresee that the introduction of the multi-axial spinneret will greatly widen
the capability of 3D printing techniques, especially for fabrication of multifunc-
tional fibers and smart textile.
Here, we report the one-step fabrication of fiber-based smart patterns for E-textile
through a 3D printer equipped with a coaxial spinneret. The patterns consisted of
core-sheath fibers, which were extruded from a coaxial spinneret and were directly
printed on textile by a 3D printer. The precursor materials for the sheath and the core
fibers could be facilely selected depending on different purposes, enabling the
fabrication of versatile functional E-textiles. As a proof of concept, we used carbon
nanotubes (CNTs) as the core fiber and silk fibroin (SF) as the sheath layer, and
printed core-sheath fiber-based patterns on textile. We further demonstrated the
excellent performance of the obtained smart textile while serving as a triboelectricity
nanogenerator to harvest mechanical energy from human motion. A smart superca-
pacitor textile for energy storage was also demonstrated. The direct printing of
smart patterns on textile enables the facile fabrication of E-textile with various inte-
grated electronics.
1Key Laboratory of Organic Optoelectronics andMolecular Engineering of the Ministry ofEducation, Department of Chemistry, TsinghuaUniversity, Beijing 100084, P. R. China
2Center for Nano andMicroMechanics, School ofAerospace Engineering, Tsinghua University,Beijing 100084, P. R. China
3Beijing Institute of Nanoenergy andNanosystems, Chinese Academy of Science,Beijing 100083, P. R. China
4School of Nanoscience and Technology,University of Chinese Academy of Sciences,Beijing, 100049, P. R. China
5Lead Contact
*Correspondence: [email protected] (J.Z.),[email protected] (Y.Z.)
https://doi.org/10.1016/j.matt.2019.02.003
RESULTS AND DISCUSSION
3D Printing of Smart Patterns on Textile
Figure 1A illustrates the printing of core-sheath fiber-based patterns on fabrics us-
ing a 3D printer equipped with a coaxial spinneret. Two injection syringes contain-
ing different inks were connected to a coaxial spinneret, which was fixed on a 3D
printer. Inks containing various materials can be selected depending on the
desired functions of the final power devices. The flexibility, biocompatibility, and
waterproofness of the sheath materials should be considered for practical applica-
tions of E-textile. For demonstration purposes, we used CNT aqueous solution as
the core ink and SF solution as the sheath ink. On this basis, we fabricated an
E-textile that can harvest mechanical energy of human body motion for wearable
energy-management purposes. The CNT ink from the inner spinneret and the SF
ink from the outer spinneret were synchronously injected to form core-sheath
structured fibers. Due to the different cross-sectional areas of the inner and outer
spinneret, different feeding rates of CNT and SF inks were applied to ensure a
similar flow rate of both inks. To ensure the formation of continuous and robust fi-
bers on textile, the moving speed of the coaxial spinneret must match the
extruding rate of the fiber.
Various flexible customer-designed patterns composed of core-sheath functional
fibers can be printed onto fabrics for smart E-textile by controlling the moving
path of the coaxial spinneret using a programmed procedure (Figures 1B and
1C). Figure 1C and its insets show examples of the as-obtained patterns, which
contain Chinese characters meaning PRINTING with hollow structures, English
letters spelling SILK with solid lines, and a pigeon with hollow structures. As shown
in Figure 1D, the obtained smart textile showed good flexibility against twisting
and folding, which was realized based on the good flexibility and robustness of
the printed patterns. The versatility of this approach and the good flexibility of
2 Matter 1, 1–12, July 10, 2019
Figure 1. Direct Printing of Core-Sheath Fiber-Based Patterns on Fabrics for Energy-Management Smart Textile
(A) Schematic illustration showing the 3D printing process using a coaxial spinneret.
(B) Photograph of the 3D printing process.
(C) Photographs of customer-designed patterns on textile, including English letters of SILK, a pattern of a pigeon, and Chinese characters of PRINTING.
(D) A smart textile under twisting and folding, showing its high flexibility.
the printed structures encourage the application of this technique in fabrication of
various smart textiles.
Printing Inks and Their Rheological Properties
To ensure the successful printing of continuous and uniform core-sheath fibers on
textile, the uniformity and rheological properties of the printing inks should be
controlled and adjusted. For example, we studied the process to prepare the SF
ink and the CNT ink, which was essential for the printing of CNTs@SF core-sheath
fibers for the fabrication of a nanogenerator textile. The SF ink was employed to
construct the dielectric sheath of the fiber, and the CNT ink was used to fabricate
the conductive core of the fiber. For the construction of the sheath layer, silkworm
silk was chosen due to its top-level position in the triboelectric series, superior me-
chanical properties, and good biocompatibility when particularly used in wearable
devices.14–16 Figure 2A shows the SF ink, which was prepared by dissolving de-
gummed silk cocoons in a formic acid/CaCl2 solution (for details see Experimental
Procedures). It takes only a fewminutes to obtain a stable and viscous ink when using
the formic acid/CaCl2 solution, whereas it requires arduous and time-consuming
dissolution and dialysis process using other typical dissolution systems such as
CaCl2/ethanol/H2O or LiBr/H2O.17 Moreover, the calcium ions in the resulting fibers
tend to bind with water molecules in air, facilitating achievement of good flexibility
of the printed architectures.18
Matter 1, 1–12, July 10, 2019 3
Figure 2. Printing Inks and Their Rheological Properties
(A) Photographs of silk cocoons and the obtained SF ink.
(B) Optical image showing the SF microfibrils in the SF ink.
(C) Photograph showing the highly injectable SF ink.
(D) Photographs of CNT powder and the CNT ink.
(E) TEM image showing the good dispersion of CNTs.
(F) TEM image of a multiwall carbon nanotube wrapped by polymer on its outer wall; the inset is a zoomed-in image.
(G) Apparent viscosity as a function of shear rate of the CNT and SF inks.
(H) Storage (G0) and loss (G00) modulus as a function of shear stress of the CNT and SF inks.
(I) Photograph of a free-standing CNTs@SF core-sheath fiber after being extruded, showing good spinnability of both inks.
It is noteworthy that this dissolution system could partially dissolve SF fibers into
microfibrils with a diameter of several micrometers (Figures 2B and S1). The confor-
mation of the secondary structure of SF in natural silk fibers could be largely main-
tained, leading to good mechanical properties and water resistance of the printed
structures. This can be evidenced by Raman spectroscopy (Figure S2A). According
to the deconvolution of the amide I region (1,600–1,700 cm�1), the secondary struc-
ture elements of SF with a b-sheet structure content in the regenerated SF fiber ob-
tained from the formic acid/CaCl2 system was estimated to be 53.3%, which is close
to that of the degummed natural silk (57.3%) (Figures S2B and S2C; Table S1).19 In
contrast, the b-sheet structure content obtained from the CaCl2/ethanol/H2O
4 Matter 1, 1–12, July 10, 2019
system was dramatically reduced to 23.3% (Figure S2D). As shown in Figures 2C and
S3, the SF ink extruded from a spinneret under mild extruding forces can solidify
quickly in air and form a self-standing long filament, showing its potential as printing
ink. The mechanical performance of the as-obtained SF fiber (Figure S4) was obvi-
ously better than that of SF fibers obtained from other dissolution systems20 in as-
pects of modulus, breaking stress, strain at breaking, and toughness, indicating its
suitability as robust building blocks for wearable electronics.
Regarding the CNT ink, a good dispersion of the CNTs in the solution is very impor-
tant in enabling a smooth flow when being extruded as well as the formation of a
continuous and conductive core fiber. To this end, CNT powder was dispersed in
an aqueous solution with SDS as the surfactant and polyvinyl acetate (PVA) as a vis-
cosity regulation agent (Figure 2D). The obtained CNT ink showed good uniformity.
Figure 2E shows a transmission electron microscopy (TEM) image of the dispersed
CNTs, exhibiting no observed coagulation. Figure 2F shows a magnified TEM image
of a CNT coated with a polymer layer. Entangled polymer chains can physically
adhere on the outer wall of the CNT, which brings steric hindrance against the strong
p-p stacking and hydrophilic interactions among CNTs, thus enabling good disper-
sion of the CNTs in the ink.
The rheological nature of the SF and CNT inks are also very important factors influ-
encing the quality of the printed fibers on textile. A certain rheological property of
the printing ink is required to ensure a smooth flow to achieve a continuous core-
sheath fiber with good shape fidelity. As shown in Figure 2G, the apparent viscosities
of the SF and CNT inks reduce alongside the increase of shear rates, displaying a
typical shear-thinning behavior. These curves indicate that both SF and CNT inks
have a flow behavior at high shear rates and a solid-like state at rest. Besides, the
SF ink possesses a larger viscosity than the CNT ink, indicating that higher extrusion
stress is required for the SF ink.
Figure 2H displays the storage (G0) and loss (G00) modulus of the SF and CNT inks as a
function of shear stress. The G0 values of both inks exhibit plateaus at low shear
stresses and are larger than the G00, indicating their solid-like behavior at low
stresses.21 After a yield point of �25 Pa for the CNT ink and �150 Pa for the SF
ink, their G0 drops sharply and falls below G00, indicating that both inks behave like
viscous liquids under high shear stresses. The shear stresses during extrusion are
orders of magnitude higher than the yield point stresses of both inks, thus allowing
a smooth flow through the spinneret.21 Once the inks are extruded from the spin-
neret the applied stresses disappear, leading to the formation of solid-like filaments.
The shear-thinning behavior under extrusion and the capability of keeping good
shape fidelity after extrusion of both inks are prerequisites for the formation of
stable, robust, and even free-standing core-sheath structures using the printing
technique (Figure 2I).
Structure of the Core-Sheath Fiber
The morphologies and structures of the CNTs@SF core-sheath fiber were investi-
gated. The core-sheath fibers printed on textile have a diameter of �500 mm
(Figure 3A). The conductive CNT core has a width of �200 mm and is closely encap-
sulated by the SF sheath (Figure 3B). Figure 3C shows the cross-section of the fiber
on a textile, exhibiting distinct areas of the CNT core and the SF sheath. As shown in
Figure 3D, there are entangled CNTs in the core area, enabling an electrical conduc-
tivity of 2.1 3 10�2 S/cm. Moreover, the printed structures on the textile can resist
the peeling force using common adhesive tapes (e.g., Scotch tape, polyimide
Matter 1, 1–12, July 10, 2019 5
Figure 3. Structure and Morphology of the as-obtained CNTs@SF Core-Sheath Fibers on Textile
(A) Scanning electron microscopy (SEM) image of top-view of a core-sheath fiber on textile.
(B) Optical image of top-view of a core-sheath fiber on textile.
(C) SEM image of cross-section of a core-sheath fiber on textile.
(D) SEM image of cross-section of a fiber showing the CNT core.
tape) (Video S1 and Figure S5), indicating the strong interaction between the sub-
strate fabric and the printed core-sheath fibers. In addition the printed fibers are
waterproof (Figure S6), which can be ascribed to the encapsulation of the b-sheet-
rich SF sheath. These results prove the successful construction of CNTs@SF fibers
on textiles, which can be used to fabricate smart patterns beyond traditionally
aesthetic purposes and integrated into fabrics for E-textile.
3D-Printed Energy-Harvesting Textile
For demonstration purposes, a CNTs@SF core-sheath fiber-based pattern printed
on a conventional fabric was used as an E-textile for harvesting biomechanical en-
ergy of human body motion (for details see Experimental Procedures). The basic
working mechanism, which is illustrated in Figure 4A, is based on the coupling effect
of contact electrification and electrostatic induction. The printed SF pattern and a
polyethylene terephthalate (PET) film were chosen as the triboelectric pair. The SF
has a strong ability to lose electrons and the PET tends to gain electrons. Therefore,
the contact/separation of the two parts will generate a variable dipole moment,
leading to the flow of electrons between the two electrodes. We investigated the
performance of a pattern composed of parallel CNTs@SF core-sheath fibers on
textile for energy harvesting (Figure S7). This can generate a short-circuit current
(Isc) peak of 1.4 mA and an open-circuit voltage (Voc) peak of 15 V at a displacement
speed of 10 cm/s, as shown in Figure 4B. In addition, the power density peak can
reach a maximum value of 18 mW/m2 at an external resistance load of 4 MU
(Figure 4C).
Furthermore, the outputs of the different patterns under different contacting/sepa-
rating speeds with PET films were investigated. A pattern of gridline on textile (Fig-
ure 4D) showed that output Voc peaks increased from 30 to 55 V as the displacement
6 Matter 1, 1–12, July 10, 2019
Figure 4. Performance of the 3D-Printed Energy-Harvesting Textile
(A) Schematic illustration of the working mechanism of the smart textile.
(B) Typical output open-circuit voltage (Voc) and short-circuit current (Isc) of a parallel-line pattern on textile (9 3 9 cm, with a spacing of 2 mm).
(C) Output Isc density and power density as a function of resistance of the 3D-printed smart textile.
(D) Schematic illustration of a gridline pattern (9 3 9 cm, with a spacing of 2 mm) on textile.
(E and F) Output Voc (E) and Isc (F) of a gridline pattern on the textile while contacting/separating with a PET film at different displacement speeds (5, 8,
10, 13, 15, and 18 cm/s).
speeds increased from 5 to 18 cm/s (Figure 4E). At the same time, the output Isc peak
also increased from 1.0 to 7.0 mA with the increase of the displacement speeds (Fig-
ure 4F), indicating that a high displacement speed leads to a high output of current.
For comparison, the pattern of parallel core-sheath fibers on textile (Figure S7) only
generated Voc peaks from 14 to 17 V and Isc peaks from 0.4 to 2.7 mA as the displace-
ment speeds increased from 5 to 18 cm/s (Figure S8). These results can be inter-
preted by considering the fact that a pattern with a larger effective area brings about
greater electron transfer to achieve a higher output voltage and current. In addition,
the long-term performance of the printed textile was explored, which showed stable
results during 15,000 cycles of loading/unloading (Figure S9), indicating its good
mechanical durability and stability. Compared with recently reported silk-based
triboelectric nanogenerators,22,23 the printed textile in this work showed obviously
higher output power.
3D-Printed Energy-Storage Textile
We also demonstrated the direct printing of supercapacitors on fabrics for energy-
storage textile using the 3D printing technique with a coaxial spinneret. The
Matter 1, 1–12, July 10, 2019 7
designed smart pattern for supercapacitor was composed of two core-sheath fiber
electrodes on textile (for details see Experimental Procedures and schematic
illustration in Figure S10). Its electrochemical performance was measured through
a cyclic voltammetry (CV) method at scanning rates from 5 to 100 mV/s (Fig-
ure S11A). The quasi-rectangular curves of these CV curves indicate the good
electrochemical double-layer capacitance properties of the smart pattern.24 The
galvanostatic charge/discharge (GCD) curves (Figure S11B) at different current
density are close to triangular shapes, indicating good charge transportation
across the two fiber electrodes. According to the GCD curves, the areal capaci-
tance of the smart pattern was calculated to be 26.42 mF/cm2 at a current density
of 0.42 mA/cm2, and the corresponding areal energy density and areal power
density were 0.33 mWh/cm2 and 31.85 mW/cm2, respectively. The stability of the
supercapacitor under mechanical deformation was also investigated. The GCD
curves measured under different bending degrees up to 150� are similar to each
other (Figure S12), indicating the good flexibility and superior stability of the
energy-storage textile. In addition, apart from the aforementioned CNTs@SF
and CNTs@SCC structures, other versatile materials-based structures, such as gra-
phene oxide@SF and reduced graphene oxide@SF structures, can also be printed
(Figure S13).
3D-Printed Energy-Management Textile for Smart Clothes
The smart patterns can be directly printed or integrated into clothes/garments for
wearable energy-management systems. As a proof of concept, smart patterns
were printed on different parts of clothes to harvest biomechanical energy
from the movement of the human body, such as walking and running (Figure 5A;
Videos S2 and S3). The touching/separating of the smart pattern with an opposite
PET film on the underarm sleeve induced by moving the arms can generate
an alternating current. Figure 5Ai shows the typical alternating current with a
maximal Isc peak of �1.8 mA/cm2. For practical applications, a bridge rectifier
was usually employed to convert the alternating current to direct current for further
applications (see the rectifying circuit diagram shown in Figure 5Aii). Figure 5Aiii
shows the rectified Isc. The collected energy can be stored in capacitors for
later uses.
Next, the performance of the energy-management textile at different displacement
speeds to charge capacitors was investigated. As the displacement speeds
increased from 2 to 18 cm/s, the required time to charge a 3.3-mF capacitor to a
voltage of 3 V shortened from �130 s to �10 s (Figure 5B). Capacitors with different
capacitances were charged at a fixed displacement speed of 13 cm/s. As shown in
Figure 5C, a capacitor with larger capacitance required a longer time to reach 5 V.
The energy stored in the capacitors could be used to drive small electronic devices.
For examples, 14 LED bulbs could be lit up using the smart pattern power system
(Figure 5Di). Besides, the printed power textile could also drive an electrical watch
(Figure 5Dii) and an electrical timer (Figure S14). These results not only show the
potential applications of the printed E-textile for wearable energy-management
systems, but also indicate the feasibility of the directly printed E-textile for smart
clothes.
Conclusion
In summary, we reported the direct printing of core-sheath fiber-based smart pat-
terns for energy-management E-textile. By selecting different inks for the sheath
and core layer of the coaxial spinneret on the 3D printer, versatile energy-manage-
ment smart textile can be fabricated. For our demonstration, we used CNT ink and
8 Matter 1, 1–12, July 10, 2019
Figure 5. Application of the 3D-Printed E-Textile for Energy Management
(A) Schematic illustration showing smart clothes for energy management and its performance. Inset (i) shows the output Isc density of a smart gridline
pattern printed on the underarm sleeve of a shirt generated by an arm moving. Inset (ii) is the rectifying circuit diagram of the power system. Inset (iii)
shows the rectified output Isc density of the smart pattern.
(B) Charging curves of a capacitor (3.3 mF) charged using the smart pattern displaced at different speeds.
(C) Charging curves of different capacitances charged using the smart pattern with a displacement speed of 13 cm/s.
(D) Photographs showing LEDs and an electrical watch driven by the power generated by the 3D-printed E-textile.
SF ink and directly printed coaxial CNTs@SF fiber-based patterns on textile. The uni-
formity and rheological properties of both inks were investigated to meet the re-
quirements for direct ink writing based a 3D printing technique. The good dispersion
of the CNTs in aqueous solution ensured a smooth flow for making the continuous
and conductive core fiber. SF microfibrils in the SF solution, prepared by partially
dissolving natural silk fibers using formic acid/CaCl2 solution, can retain the second-
ary structure of the protein molecule in natural silk fibers, thus enabling the good
mechanical properties and water resistance of the printed structures. In our demon-
stration, we showed that the obtained CNTs@SF fiber-based smart textile could har-
vest mechanical energy of human motion and achieve a maximal power density of
18 mW/m2. The direct printing of supercapacitors on fabrics for an energy-storage
textile, which showed a capacitance of 26.42 mF/cm2 at a current density of
0.42 mA/cm2, was also demonstrated. Apart from fabrication of energy-manage-
ment systems, this strategy may also be applied to the fabrication of other wearable
electronics such as flexible sensors, electric antennas, and other functional circuits,
merely by designing the printing-ink combinations. We hope that the direct printing
of smart patterns on textile, which is beyond the conventionally aesthetic purpose or
trademark identification of patterns, paves the way for the facile fabrication of
E-textile with various integrated electronics, holding great promise for practical
applications.
Matter 1, 1–12, July 10, 2019 9
EXPERIMENTAL PROCEDURES
Preparation of SF Ink
For the printing of the triboelectricity nanogenerator, SF ink was employed for
the dielectric sheath. Silk cocoon from Bombyx mori silkworm was cut into small
pieces and put into boiling water with 5 wt % NaHCO3 to degum for half an
hour. The degummed procedure was repeated twice. CaCl2 (0.22 g) was dissolved
in 5 mL of formic acid to form a solution, and 2.0 g of degummed silk fibers was
then mixed into the solution to form SF ink using a Speed Mixer for 10 min at
3,500 rpm.
Preparation of CNT Ink
CNT aqueous ink was used for the conductive core of the fiber. Multiwall carbon
nanotubes (MWCNTs, with diameters of 50–150 nm and lengths of 10–30 um)
were added into SDS dispersed aqueous solution at an MWCNT/SDS/H2O ratio of
300 mg:300 mg:10 mL, followed by ultrasonic treatment for 30 min. Ten milliliters
of PVA/H3PO4, which was used as a polymer dispersant and a viscosity regulation
agent, was then added. The PVA/H3PO4 was obtained according to a previously re-
ported procedure.24 In brief, 1 g of PVA was added to 10 mL of deionized water at
90�C under moderate stirring until totally dissolved, followed by cooling to room
temperature for further use, and thereafter 1 mL of H3PO4 was added and the solu-
tion was stirred for 30 min. Finally the obtained CNT solution was stirred at 90�C for
about 60 min for evaporation to obtain the CNT ink with a favorable rheological
property (with a solid content of �30%–40%).
3D Printing of Energy-Harvesting Textile
The CNTs@SF core-sheath fiber was extruded from a coaxial spinneret and printed
into designed patterns on textile using a 3D printer (Anycubic I3 MEGA). Two injec-
tion syringes, containing CNT ink and SF ink, respectively, were connected to the
inner (diameter: 260 mm) and outer (diameter: 840 mm) channels of a coaxial spin-
neret, respectively. The coaxial spinneret was then fixed onto a 3D printer. The
CNT and SF inks were synchronously injected to form CNTs@SF core-sheath
conductive fibers. The feeding rates of the inner and outer nozzle were kept at
10 mL/h and 25 mL/h. By exquisitely controlling the print path of the coaxial spin-
neret at a rate of 20 mm/s using a programmed procedure, customized patterns
composed of the CNTs@SF core-sheath conductive fibers were directly printed
onto the fabric substrate.
3D Printing of Energy-Storage Textile
For the energy-storage textile, the fabrication procedure was the same as that for the
energy-harvesting textile with the exception that the sheath of the printed fiber was
sodium carboxymethyl cellulose, which serves as a solid-state electrolyte and a flex-
ible buffering layer against mechanical deformation. The gap between two individ-
ual core-sheath fiber electrodes was then filled with PVA/H3PO4 gel to work as the
solid-state electrolyte for the supercapacitor. Lastly, polydimethylsiloxane was
used to encapsulate the printed supercapacitor.
Characterization of Materials
The dispersion of the CNTs in the CNT ink was investigated using a field-emission
transmission electron microscope (JEOL, JEM2012F) by dropping the ink on a
copper grid. The rheological properties of the CNT and SF inks were characterized
using a rheometer (Anton Paar, MCR301). Themorphology of CNTs@SF core-sheath
fiber was characterized using a scanning electron microscope (Zeiss, Merlin) and an
optical microscope (Leica, DMi8 S).
10 Matter 1, 1–12, July 10, 2019
Performance Measurement of the E-Textile
All the measurements of the E-textile were carried out in ambient conditions with a
relative humidity of 20% and a temperature of 25�C. The open-circuit voltage of the
energy-harvesting textile wearable triboelectricity nanogenerator was measured
using an electrometer (Keithley, 6517B). The short-circuit current of the wearable
triboelectricity nanogeneratorwas recordedby a low-noise current preamplifier (Stan-
fordResearch Systems, SR570). Theenergy-harvesting textilewasdrivenby amechan-
ical linear motor (Linmot, E1100) with a constant acceleration of 50 m/s2 and a
displacement distance of 10 cm. The electrochemical performance of supercapacitor
was measured by an electrochemical workstation (RST5200, China). The specific areal
capacitance (C) was calculated fromGCD curves using the equationC =it
AV, where I is
the discharge current, t is the discharge time, V is the discharge window, and A is sur-
face area of the fibers in the overlapping portion (the circumference of the cross-sec-
tion of the CNT multiplied by the length of fibers in the overlapping portion). Energy
density (E) of the supercapacitor was calculated according to E = C,V2=8, and the
average-power density (P) of the supercapacitor was obtained according to P =E=t.
SUPPLEMENTAL INFORMATION
Supplemental Information can be found online at https://doi.org/10.1016/j.matt.
2019.02.003.
ACKNOWLEDGMENTS
This work was financially supported by the National Natural Science Foundation of
China (51672153), the National Key Basic Research and Development Program
(2016YFA0200103), and the National Program for Support of Top-notch Young
Professionals.
AUTHOR CONTRIBUTIONS
Y.Z. supervised the project. M. Zhang designed and performed most of the experi-
ment with the help from the other authors. M. Zhao, M.J., C.W., Z.Y., Xiaoping Liang,
H.W., K.X., and Xiao Liang participated in parts of the experiments. A.Y. and J.Z.
contributed to the measurement of energy-harvesting textile. M. Zhang and Y.Z.
co-wrote the manuscript with feedback from all authors.
DECLARATION OF INTERESTS
A China patent application (CN201810073665) has been filed, with Y.Z. and M.
Zhang as inventors, covering the coaxial spinneret-equipped 3D printing technique
for E-textiles described herein. The authors declare no competing interests.
Received: December 24, 2018
Revised: February 18, 2019
Accepted: February 25, 2019
Published: March 27, 2019
REFERENCES
1. Zeng,W., Shu, L., Li, Q., Chen, S.,Wang, F., andTao, X.M. (2014). Fiber-based wearableelectronics: a review of materials, fabrication,devices, and applications. Adv. Mater. 26,5310–5336.
2. Lai, Y.C., Deng, J., Zhang, S.L., Niu, S., Guo, H.,and Wang, Z.L. (2017). Single-thread-based
wearable and highly stretchable triboelectricnanogenerators and their applications in cloth-based self-powered human-interactive andbiomedical sensing. Adv. Funct. Mater. 27,1604462.
3. Pu, X., Hu, W., and Wang, Z.L. (2018). Towardwearable self-charging power systems: the
integration of energy-harvesting and storagedevices. Small 14, 1702817.
4. Chen, J., Huang, Y., Zhang, N., Zou, H., Liu, R.,Tao, C., Fan, X., and Wang, Z.L. (2016). Micro-cable structured textile for simultaneouslyharvesting solar and mechanical energy. Nat.Energy 1, 16138.
Matter 1, 1–12, July 10, 2019 11
5. Lee, J., Kwon, H., Seo, J., Shin, S., Koo, J.H.,Pang, C., Son, S., Kim, J.H., Jang, Y.H., andKim, D.E. (2015). Conductive fiber-basedultrasensitive textile pressure sensor forwearable electronics. Adv. Mater. 27, 2433–2439.
6. Liang, G., Yi, M., Hu, H., Ding, K., Wang, L.,Zeng, H., Tang, J., Liao, L., Nan, C., and He, Y.(2017). Coaxial-structured weavable andwearable electroluminescent fibers. Adv.Electron. Mater. 3, 1700401.
7. Kwon, S., Kim, H., Choi, S., Jeong, E.G., Kim,D., Lee, S., Lee, H.S., Seo, Y.C., and Choi, K.C.(2017). Weavable and highly efficient organiclight-emitting fibers for wearable electronics:a scalable, low-temperature process. NanoLett. 18, 347–356.
8. Bae, H., Jang, B.C., Park, H., Jung, S.H., Lee,H.M., Park, J.Y., Jeon, S.B., Son, G., Tcho, I.W.,and Yu, K. (2017). Functional circuitry oncommercial fabric via textile-compatiblenanoscale film coating process for fibertronics.Nano Lett. 17, 6443–6452.
9. Lv, J., Jeerapan, I., Tehrani, F., Yin, L., Silva-Lopez, C.A., Jang, J.-H., Joshuia, D., Shah, R.,Liang, Y., and Xie, L. (2018). Sweat-basedwearable energy harvesting-storage hybridtextile devices. Energy Environ. Sci. 11, 3431–3442.
10. Zarek, M., Layani, M., Cooperstein, I., Sachyani,E., Cohn, D., and Magdassi, S. (2016). 3Dprinting of shape memory polymers for flexibleelectronic devices. Adv. Mater. 28, 4449–4454.
12 Matter 1, 1–12, July 10, 2019
11. Xiao, Y., He, L., and Che, J. (2012). An effectiveapproach for the fabrication of reinforcedcomposite hydrogel engineered with SWNTs,polypyrrole and PEGDA hydrogel. J. Mater.Chem. 22, 8076–8082.
12. Muth, J.T., Vogt, D.M., Truby, R.L., Menguc, Y.,Kolesky, D.B., Wood, R.J., and Lewis, J.A.(2014). Embedded 3D printing of strain sensorswithin highly stretchable elastomers. Adv.Mater. 26, 6307–6312.
13. Chen, S., Huang, T., Zuo, H., Qian, S., Guo, Y.,Sun, L., Lei, D., Wu, Q., Zhu, B., and He, C.(2018). A single integrated 3D-printing processcustomizes elastic and sustainable triboelectricnanogenerators for wearable electronics. Adv.Funct. Mater. 28, 1805108.
14. Ren, J., Liu, Y., Kaplan, D.L., and Ling, S. (2019).Interplay of structure and mechanics in silk/carbon nanocomposites. MRS Bull. 44, 53–58.
15. Yin, Z., Jian, M., Wang, C., Xia, K., Liu, Z., Wang,Q., Zhang, M., Wang, H., Liang, X., Liang, X.,et al. (2018). Splash-resistant and light-weightsilk-sheathed wires for textile electronics. NanoLett. 18, 7085–7091.
16. Zheng, K., Zhong, J., Qi, Z., Ling, S., andKaplan, D.L. (2018). Isolation of silkmesostructures for electronic andenvironmental applications. Adv. Funct. Mater.28, 1806380.
17. Rockwood, D.N., Preda, R.C., Yucel, T., Wang,X., Lovett, M.L., and Kaplan, D.L. (2011).Materials fabrication from Bombyx mori silkfibroin. Nat. Protoc. 6, 1612.
18. Ling, S., Zhang, Q., Kaplan, D.L., Omenetto, F.,Buehler, M.J., and Qin, Z. (2016). Printing ofstretchable silk membranes for strainmeasurements. Lab Chip 16, 2459–2466.
19. Du, N., Yang, Z., Liu, X.Y., Li, Y., and Xu, H.Y.(2011). Structural origin of the strain-hardeningof spider silk. Adv. Funct. Mater. 21, 772–778.
20. Wei, W., Zhang, Y., Zhao, Y., Shao, H., and Hu,X. (2012). Studies on the post-treatment of thedry-spun fibers from regenerated silk fibroinsolution: post-treatment agent and method.Mater. Des. 36, 816–822.
21. Li, Y., Gao, T., Yang, Z., Chen, C., Luo, W.,Song, J., Hitz, E., Jia, C., Zhou, Y., and Liu, B.(2017). 3D-printed, all-in-one evaporator forhigh-efficiency solar steam generation under 1sun illumination. Adv. Mater. 29, 1700981.
22. Kim, H.J., Kim, J.H., Jun, K.W., Kim, J.H.,Seung, W.C., Kwon, O.H., Park, J.Y., Kim, S.W.,and Oh, I.K. (2016). Silk nanofiber-networkedbio-triboelectric generator: silk Bio-TEG. Adv.Energy Mater. 6, 1502329.
23. Zhang, X.S., Brugger, J., and Kim, B. (2016).A silk-fibroin-based transparent triboelectricgenerator suitable for autonomous sensornetwork. Nano Energy 20, 37–47.
24. Ma, Y., Li, P., Sedloff, J.W., Zhang, X., Zhang,H., and Liu, J. (2015). Conductive graphenefibers for wire-shaped supercapacitorsstrengthened by unfunctionalized few-walledcarbon nanotubes. ACS Nano 9, 1352–1359.