High-Performance Electronic Cloth for Facilitating the Rehabilitation of

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Research Article Cite This: ACS Appl. Mater. Interfaces 2019, 11, 22722−22729

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High-Performance Electronic Cloth for Facilitating the Rehabilitation of Human Joints Fan Wu,†,‡,§,∥,⊥ Congju Li,*,†,‡,§,∥ Ran Cao,†,‡,§,∥,⊥ and Xinyu Du†,‡,§,∥ †

School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China Beijing Key Laboratory of Resource-Oriented Treatment of Industrial Pollutants, Beijing 100083, China § Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China ∥ School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China Downloaded via BUFFALO STATE on July 24, 2019 at 07:29:37 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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ABSTRACT: The concern about easily characterizing the conditions of human joints to facilitate rehabilitation during recovery training has been out of sight, even though it is acknowledged that timely recovering functions of injured joints is a must. To facilitate the situation to be addressed, a stretchable, air-permeable electronic cloth (SApEC) was fabricated by electrostatic spinning and hot-pressing. The SApEC consists of conductiveelastic fabric Ag and composite nanofibrous membrane (CNFM) with components of poly(vinylidene fluoride-co-hexa-fluoropropyiene) and thermoplastic urethane. The electronic cloth not only owns chemical stability and ultralight weight, but scavenges triboelectric signals from joint movements. These characters allow the SApEC to be an easy and convenient indicator to indicate the activity of joints, when users get rehabilitation training in non-hospital places. With the assistance of several electronic components, the SApEC could control alarms, such as a warning lamp. This favorable ability allows the SApEC to make alerts, once users face any accidents again, like sudden fall or heart failure. Given the advantages mentioned above, it is reasonable to believe that the SApEC has a promising prospect in portable and wearable electronics, involving indicating rehabilitation of joints and keeping an eye on users’ safety. KEYWORDS: electrostatic spinning, stretchability, air permeability, joints indicating, wireless sensing

1. INTRODUCTION It is universally acknowledged that human joints always play an indispensable role in people’s lives, including driving a car, writing a letter, or brushing teeth. Unfortunately, there are numerous chances to deprive human joints of functions, such as the results of accidents, the health problems induced by aging, or provocation from malignant diseases.1−3 Considering the importance of human joints, it is completely significant to explore and develop some devices used to indicate the conditions of injured joints during rehabilitation training. Yet, the attention paid to this issue is not as much as it should be which urges more effort to be made to cope with it. Recently, the increasing requirement of devices with portability, sustainability, miniaturization, and flexibility has encouraged triboelectric devices (TEDs) to become an eyecatching topic because of their self-power for micro-/ nanosystems.4,5 Various TEDs with different functions and their derivatives have been applied to a range of areas.6−9 Merging a rotary-blade-based TED and a rotating electromagnetic device, for example, Wang et al. achieved a hybrid device which could detect the speed of wind.10 A multitude of researchers have been motivated to develop superior TEDs and widen their uses because of their strong points, embracing high outputs, effective designability, and long stability.11−13 Following that, the devices and systems being compatible with © 2019 American Chemical Society

people’s skin and based on TEDs are also increasingly noticed. Dong and his co-workers developed a skin-inspired TED which could sense mechanical stimuli.14 It showed perfect flexibility with the assistant of the silicone rubber elastomer. The multifunctional e-skin detecting multiple environmental factors, such as temperature, relative humidity, and ultraviolet light, has been completely considered for stretchability and comfort to human skin using the stretchable and conformable matrix network.15 The merits and demerits of these TEDs given above motivate more effort to be devoted to TED optimization. Thanks to its advantages in mass production, easy operation, and low cost; electrostatic spinning (ESS) as a preparation method of materials has been applied widely to a variety of industries.16−21 Moreover, ESS is a feasible way to attain special materials with favorable breathability, and this makes ESS become one of the best choices to manufacture functional materials.22−24 Focusing on indicating rehabilitation conditions of injured joints and using the strengths of TEDs and ESS, herein, a stretchable, air-permeable, electronic cloth (SApEC) based on Received: March 19, 2019 Accepted: May 31, 2019 Published: May 31, 2019 22722

DOI: 10.1021/acsami.9b04860 ACS Appl. Mater. Interfaces 2019, 11, 22722−22729

Research Article

ACS Applied Materials & Interfaces the single-electrode structure has been fabricated, which was made of the composite nanofiber membrane (CNFM) and conductive-elastic cloth Ag. The CNFM fabricated via ESS is a complex material, from poly(vinylidene fluoride-co-hexafluoropropyiene) (P(VDF−HFP)) and thermoplastic urethane (TPU). Integrating CNFM and cloth Ag with hot pressing (HP), the ultralight and chemically resistant SApEC owns some pleasant performances presented in the following part. It has also been proved that the SApEC could successfully indicate the recovery conditions of injured joints. With several electronics for signal processing, a SApEC wireless sensing system (SWSS) has been designed. The SWSS could generate alarms, and once the injured gets into trouble again, such as suddenly fall or heart failure. These aggregable features of the SApEC offer the possibility that it would hold a promising application in wearable and portable electronics, such as indicating rehabilitation conditions of injured joints and keeping an eye on users’ safety.

2. RESULTS AND DISCUSSION Considering the electroactive property and tensility of composite materials, P(VDF−HFP) and TPU were chosen

Figure 2. Comparison of various nanofiber membranes in stretchability and air permeability as well as the stretchability of the SApEC. (a) Comparison of nanofiber membranes of P(VDF−HFP), TPU, and P. + T. (0.6 + 0.6) in elongation at break. (b) Influence of the type and thickness of materials on the air permeability of materials. (c) Illustration of the elongation at break and tensile strength of the SApEC to indicate the stretchability of the electronic cloth.

Table 1. Information About the Flow Rates of Solutions of P(VDF−HTP) and TPU To Attain Materials 1−7 and Their Thickness materials material material material material material material material

the flow rate of P(VDF−HFP) solution (mL/h)

the flow rate of TPU solution (ml/h)

thickness of material (μm)

0.6 0 0.6 0.6 0.3 0.3 0.3

0 0.6 0.6 0.3 0.6 0.6 0.6

12 14 20 14 23 28 46

1 2 3 4 5 6 7

Table 2. Different Sizes of SApECs Used Different Parts of Hand name

Figure 1. Fabrication, picture, work mechanism, and potential distribution simulations of the SApEC. (a) Schematic diagram of manufacturing the SApEC through ESS and HP. (b) Photograph of the SApEC. (c) Work mechanism of the single-electrode structure SApEC based on the vertical contact separation. (d) Potential distribution simulations of SApEC during the working stage in Figure 1c.

to attain the CNFM.25−28 As Figure 1a shows, after acquiring the CNFM through ESS, HP was applied to prepare the SApEC as shown in Figure 1b. More information about the preparation is presented in the Experimental Section. The SApEC was classified as a single-electrode structure,29 based

cloth Ag (cm2)

CNFM (cm2)

another friction layer 2 × 2 cm2 copper foil no

the SApEC

2×2

3×3

the SApEC for the test in elongation at break thumb forefinger middle finger ring finger little finger metacarpophalangeal joint wrist elbow joint

8×2

9×3

5.6 5.6 5.6 5.6 5.6 20 15.5 23

× × × × × × × ×

1 1 1 1 1 2 5 4

7 7 7 7 7 22 18 25

× × × × × × × ×

2 2 2 2 2 3.3 3.3 5

skin skin skin skin skin skin skin skin

on vertical contact and separation.12,30,31 Consequently, skin and CNFM playing the roles of positive and negative triboelectric layers, respectively, generated equal and opposite 22723

DOI: 10.1021/acsami.9b04860 ACS Appl. Mater. Interfaces 2019, 11, 22722−22729

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P(VDF−HFP) nanofibrous membrane was up to 75.3%, which was only one-third of that of the TPU nanofibrous membrane, reaching 226.7%. Compared to the P(VDF−HFP) nanofibrous membrane, the P. + T. (0.6 + 0.6) nanofiber membrane made a dramatic enhancement that the ε of the latter was over two times than that of the former. Upon above outcomes, further investigations about nanofiber membrane air permeability (A-p) were implemented. Figure 2b exhibits that flow rates of solutions and membrane thickness had a crucial influence on A-p of materials. The information about the flow rates of solutions of P(VDF−HFP) and TPU to attain materials 1−7 and their thickness has been listed in Table 1. Compared to material 1 [P(VDF−HFP) nanofiber membrane], 2 (TPU nanofiber membrane) and 3 [P. + T. (0.6 + 0.6)], with the same flow rate (0.6 mL/h) and spinning time (4 h), the TPU film (material 2) owned the best breathability among three materials. The A-p of the TPU film was followed by materials 3 and 1. The results could be explained by the compactness of material 2 smaller than that of material 1 in Figure S1a−c. The diameter of the single fiber of material 2 is about two times larger than that of material 1, and this means that the voids of material 2 is larger than that of material 1. The fact that caused the compactness of material 1 was larger than that of material 2. As for material 3, the existence of TPU nanofibers offered numerous larger void structures, while the attendance of P(VDF−HFP) nanofibers could cover those voids and restrict the development of the openness. Thus, the A-p of material 3 was between material 1 and 2. It could be predictable that the more the content of P(VDF−HFP) was given, the worse the A-p of complex materials would be. This prediction has been proved by materials 3, 4, and 5. Material 4 was marked as P. + T. (0.6 + 0.3) and material 5, 6, 7 as P. + T. (0.6 + 0.3) (the thickness of materials 5−7 is different from each other). When the flow rates of solutions of P(VDF−HFP) and TPU were enforced at the speeds of 0.6 mL/h and 0.3 mL/h, the A-p of material 4 largely depended on the content of P(VDF−HFP). The breathability of material 4 was up to 60 mm/s, just a bit higher than that of P(VDF−HFP) (54 mm/s). While the speeds were 0.3 and 0.6 mL/h, respectively, the breathability of material 5 achieved the first place among these three materials. The A-p of material 5 was just approximately 10 mm/s lower than that of the TPU; meanwhile, the thickness of material 5 was larger than that of the TPU nanofiber membrane (material 2). Because the diameter of the single fiber of TPU is larger than that of the P(VDF−HFP) single fiber, the former tends to make the CNFM thicker, but the latter represents a reverse tendency with the same ESS time. Besides, the cover-up of P(VDF−HFP) fibers could affect the void structures of TPU fibers. To optimize a better structure, a systematic investigation on various combinations of spinning solution flow rates has been carried out. Comparing the A-p of materials 5, 6, and 7, the A-p of the complex material inclined to decrease over the thickness of the complex material increase. Based on these results, material 5 is the best choice among all composite nanofibrous membranes to manufacture the stretchable and air-permeable electronic cloth (SApEC). The scanning electron microscopy (SEM) image of material 5 is shown in Figure S1d. In addition, the elongation of SApEC made of material 5 and conductive-elastic cloth Ag is characterized in Figure 2c. The ε and largest tensile strength of the SApEC reached to 216.7% and 28.8 N, respectively, which means the

Figure 3. Demonstration of the SApEC chemical stability. (a) Photograph of the SApECs submerged into deionized water, anhydrous alcohol, and aqueous solutions of HCl and NaOH at a concentration of 0.1 mol/L. (b) SEM image of the original SApEC and the photo of the original one (the inset). (c−f) SEM images of SApECs after being soaked into deionized water, anhydrous alcohol, and aqueous solutions of HCl and NaOH.

charges after several cycles of contact and separation in Figure 1c(i). When the skin got gradually close to the CNFM, electrons from the earth started to flow to the CNFM via an external lead and cloth Ag and balance the potential difference between skin and CNFM [Figure 1c(ii)]. Meanwhile, a pulse current, whose direction was opposite to the flow of electrons, was produced. When two triboelectric layers contacted each other completely, there would be no current at all, because charges on these two surfaces were neutralized, in Figure 1c(iii). Conversely, when the skin was gradually away from the CNFM, positive charges would flow spontaneously from the CNFM to ground, generating a reverse pulse current [Figure 1c(iv)]. Figure 1c(i−iv) represents a complete cycle, whose potential distribution simulations are displayed in Figure 1d(i− iv) with COMSOL software. Some time and effort were systematically spent acquiring the CNFM, although it was convinced that consolidating two excellent materials is one of the right ways to achieve materials with outstanding properties. The same flow rate (0.6 mL/h) of solutions of P(VDF−HFP) and TPU was carried out during the whole ESS process; then, a stretchable composite membrane combining nanofibers of P(VDF−HFP) and TPU was achieved. The same flow rate of solutions of P(VDF− HFP) and TPU with 0.6 mL/h is defined as P. + T. (0.6 + 0.6), and the nanofiber membrane attained by this flow rate is marked as material 3 or P. + T. (0.6 + 0.6). In Figure 2a, the breaking elongations (ε) of nanofibrous membranes of P(VDF−HFP), TPU, and the P. + T. (0.6 + 0.6) were compared. The breaking elongation is defined as ε=

( Δl l × 100%), where Δl and l represent the difference

between the lengths of membranes in ultimate and original states, as well as the original lengths of materials. The ε of the 22724

DOI: 10.1021/acsami.9b04860 ACS Appl. Mater. Interfaces 2019, 11, 22722−22729

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Figure 4. Triboelectricity features of the SApEC. (a−c) Fundamental property in short-circuit current, open-circuit voltage, and transferred charges of the SApEC. (d,e) Current and voltage of the SApEC at different working frequencies. (f) Behavior of the SApEC at different extra resistance loadings. (g) Long output stability of the SApEC.

SApEC holds satisfied stretchability. All the sizes of SApECs used in the experiment are listed in Table 2. Because of the agreeable chemical stability of P(VDF−HFP) and TPU,28,32−35 there is no difficulty in assuming that the SApEC could possess the same ability too. To figure it out, several SApECs were soaked into deionized water, anhydrous alcohol, and aqueous solutions of HCl and NaOH at a concentration of 0.1 mol/L, respectively (Figure 3a). After being soaked for 4 days, the appearances of those electronic clothes changed little. Comparing the SEM images of the original device and the SApECs treated by awful circumstances (Figure 3b−f), it was a clear indication that there was little damage to both inside and outside of these SApECs. The result indicated clearly that the SApEC could protect itself from severe environment. The resistance of the SApEC to deionized water, ethylalcohol, acid, and base is allowed by the existence of the C−F bond of P(VDF−HFP) and the −NH−COO− bond of TPU.36−38 Besides, several SApECs have also been submerged into n-hexane, acetic acid, ethylene glycol, and isopropanol, and the SEM images (Figure S2) of those SApECs indicated that there were little changes to the surface of cloth Ag and the CNFM. This means that the SApEC could also resist to damage of those agents. It is the existence of the C−F bond and −NH−COO− bond as well as the implementation of ESS that allow that the CNFM possesses

outstanding hydrophobicity (the water contact angle of the CNFM was 124°)39,40 in Figure S3. The fundamental studies of the simple electronic cloth have also been conducted. In Figure 4a,b, the outputs of shortcircuit current and open-circuit voltage of SApEC were acquired with the assistance of a linear motor at a frequency of 1.75 Hz. The transferred charges (Figure 4c) were attained by the equation of Q = ∫ I dt, where Q, I, and t represent transferred charges, short-circuit current, and time, respectively. During measurement, human skin was simulated via 2 × 2 cm2 copper foil. As the graphs illustrate, those outputs were up to 1 μA, 28 V, and 10 nC, separately. The signals under different frequencies (1.25−1.98 Hz) were also investigated (Figure 4d,e). When frequency increased from 1.23 to 1.98 Hz, the short-circuit current, open-circuit voltage, and transferred charges (Figure S4) appeared with some elevation. This phenomenon was caused by the enhancement of virtual contact-separation area under the periodic pressure of the linear motor. After being impacted continually by the linear motor, the compactness of the CNFM on the surface of the SApEC got elevated, but simultaneously, the A-p of the CNFM had declined in Figure S5a−c. In Figure 4f, the performance of the SApEC under different external loadings was explored. After the current gained a peak value of 1.045 μA with an extra resistance load of 105 Ω, a dramatic drop appeared over the 22725

DOI: 10.1021/acsami.9b04860 ACS Appl. Mater. Interfaces 2019, 11, 22722−22729

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Figure 5. Indication of the SApEC indicating the states of joints of different gestures. (a−d) Photos of different gestures to simulate the conditions of injured joints during recovering training. (e−h) Exhibition of indicating signals of SApECs attached to proximal interphalangeal joints during those different gestures. From bottom to top, the curves belong to the proximal interphalangeal joints of the thumb, forefinger, middle finger, ring finger, and little finger, respectively. (i−l) Output signals of SApECs, indicating the proximal interphalangeal joint and distal interphalangeal joint during each finger straightening and bending without including the thumb.

whole fingers fully and bending them without changing the state of the palm. The results (Figure 5e−h) of simultaneously indicating all the proximal interphalangeal joints in different movements have illustrated that the shapes and values of each finger-joint signal curve differed from each other. This disclosed that the SApEC was reliable to indicate the flexibility of joints. This would be beneficial to establish more suitable proposals for recovering functions of hand joints during training. Each separate signal curve of detecting each finger alternately straightening and bending is demonstrated in Figure S6a−e. These illustrations mean that SApECs attached to each proximal interphalangeal joint have indeed generated distinct signals. Video S1 shows the real-time capacity of the SApEC in indicating alternate spreading-bending all fingers is offered. Besides, the indication of arm joints has also been explored, including the metacarpophalangeal joint, wrist, and elbow joint in Figure S7. The research on indicating the proximal interphalangeal joint and distal interphalangeal joint when each finger got straightened and bent, not including thumb, has been implemented (Figure 5i−l). These are notable examples demonstrating the practicability of the SApEC as a simple monitor to indicate joint conditions during training. The pleasant behavior given above proves that the SApEC holds the ability to manifest the situations of joint recovering. This means that it could be used as an indicator during recovery training. Also, the ultralight weight of the SApEC is shown in Figure S8.

loading increase. The power density slowly rose at first, then soared at the range of 107 to 2 × 108 Ω and grew gently to a maximum value of 179 mW/m2 under an outer load of 7 × 108 Ω. Then, the power density began to decline. Thus, the optimal outer load resistance of the SApEC that could meet the maximum power density is 7 × 108 Ω. To confirm the feasibility of the SApEC, its long stability has been accomplished at a frequency of 1.75 Hz in Figure 4g. After running continuously for approximately 10 250 s, the shortcircuit current of the SApEC had little remarkable fluctuation. This outcome demonstrates the long stability of the electronic cloth and agreeable feasibility. Those features about stretchability, air permeability, chemical resistance, and stable signal output enable SApEC to have a wide potential application in wearable and portable electronics.41,42 To further exploit the uses of the electronic cloth, SApECs with different areas were manufactured, whose sizes were listed in Table 2. Each SAPEC corresponding to each finger was attached to the proximal interphalangeal joint of researcher’s left hand and various gestures pictured in Figure 5a−d were made to simulate the health status of joints during recovery training. These four movements included the following: (1) alternately straightening all fingers and bringing them together; (2) alternately straightening all fingers and bending them into a fist; (3) keeping the thumb straight, alternately stretching out the rest of fingers and bending them; (4) alternately spreading 22726

DOI: 10.1021/acsami.9b04860 ACS Appl. Mater. Interfaces 2019, 11, 22722−22729

Research Article

ACS Applied Materials & Interfaces

Figure 6. Diagrammatic sketch and signal changes of the SWSS and the photos of electronic modules involved in the SWSS. (a) Diagrammatic sketch of the SWSS realizing wireless sensing by converting signals. (b) Signal changes of the SWSS during indicating forefinger flexion. From bottom to top, the curves belong to the original voltage (Ori. V.), the amplified and conversed voltage (Amp. V.) and the trigger voltage, (Tri. V.), respectively. (c) Photos of electronic elements involved in the SWSS: the AD 623 instruction amplifier, the latching relay, the emitter and the receiver, in order.

3. CONCLUSIONS To conclude, utilizing ESS, a special composite nanofiber membrane (CNFM) with components of P(VDF−HFP) and TPU was achieved. Combining HP, a stretchable and airpermeable electric cloth (SApEC) made of CFNM and conductive-elastic cloth Ag has been realized. The SApEC owns outstanding stretchability, air permeability, chemical stability, and ultralight weight. Because of the merits of this electric cloth in triboelectricity, the SApEC not only holds the ability to obtain triboelectric signals from body movements but also is available to indicate conditions of human joints during recovering. Furthermore, with the help of signal-processing electronics, the SWSS was achieved, and the advantage of the SApEC in wearable and portable fields has been further optimized. As a wireless sensor, the SApEC could generate alarms once any accident has happened to SApEC users again, such as sudden fall or heart failure. Based on those desirable functions of the electronic cloth, it is believed that the SApEC would embrace a wide range of applications from rehabilitation therapy to users’ safety.

Inspired by previous works about wireless sensing of Li’s group,31,43 a wireless sensing system consisting of the SApEC with several electronic modules for signal processing, SWSS, offered SApEC more portable capacity. Through the procedure revealed in Figure 6a, the row signals (original voltage, Ori. V.) generated from indicating the forefinger flexion with SApEC were amplified and converted by an instrument amplifier. After amplification and conversion, the changed signals (amplified and conversed voltage, Amp. V.) were sent to a latching relay creating and transmitting the converted signals to an emitter. In the end, the emitter established and delivered regularly the triggering signals (trigger voltage, Tri. V.) to a receiver controlling the states of an alarm such as an alert light bulb (Video S2). The signal changes of three processes are illustrated in Figure 6b. From bottom to top, the curves were in the order: Ori. V., Amp. V., and Tri. V. Figure 6c shows electronic modules involved in the SWSS, embracing the instrument amplifier, the latching relay, the emitter, and the receiver, in order. In order to smoothly change signals, the SApEC was connected to the instrument amplifier in parallel, and the latching relay followed by the emitter in series connection was connected to the instrument amplifier in series. The receiver was connected to the alarm in series. Also, the circuit diagram is indicated in Figure S9. In the above order, the circuit ensured that once the SApEC generated pulse signals, the alarm could respond to pulse signals. Thereby, the excellent response of each course could make sure when users got into trouble again, such as sudden fall or heart failure, they could make alarms. This feature of SWSS permits that the SApEC would be better applied to wearable and portable electronics, especially to rehabilitation training and users’ safety.

4. EXPERIMENTAL SECTION 4.1. Fabrication of CNFM. The granules of P(VDF−HFP) (average Mw ≈ 400 000, bought from Aldrich Chemical Co., Inc) and TPU (bought from Foshan City Heifer Plastic Co, Ltd) were dissolved, respectively, in a 10 mL mixture of N,N-dimethylformamide and acetone (1:1) and a 10 mL mixture of N,Ndimethylformamide and dichloromethane (5:1) to form solutions of 24.44 wt % and 18.76 wt %. These two solutions were decanted into two clean injectors, separately. Later, the voltage of 20 kV was simultaneously exerted on the needles of these two syringes during the whole electrospinning. Afterward, the nanofiber membrane gained 22727

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ACS Applied Materials & Interfaces from ESS was placed into the vacuum oven for 4 h at 80 °C. Ultimately, the CNFM was realized. 4.2. Realization of SApEC. With the aid of protective coating (conductive-elastic cloth Ag, which was 4 times bigger than the CNFM needed and bought from Yantai Kangkang Textile Science & Technology Co., Ltd), the cloth Ag (the one used to fabricate the SApEC) and the above CNFM (placed under the cloth Ag) were compressed into a unity at 170 °C, 20 s. Later, another piece of the CNFM was placed on the unity, and an extra lead was inserted between the second CNFM and the first unity. The pressure was given to the whole with the same time and temperature. Eventually, the SApEC was obtained. 4.3. Achievement of SWSS. The original signals were generated by triboelectricity between the CNFM and skin during every action of the forefinger proximal interphalangeal joint. Then, the original signals were amplified and converted with the AD 623 instruction amplifier, transmitting the amplified and converted signals to the latching relay. The converted signals gained by the relay were immediately sent to the emitter, forming the trigger signals. After that, the receiver connected with an alarm in series could control the states of the alarm. Once the signals from the SApEC appeared, alarms could occur. 4.4. Characterization and Electrical Measurement. All SEM images were taken with Hitachi SU8020. All open-circuit voltage and short-circuit current of SApEC were measured by a Keithley electrometer system (Keithley 6514). All measurements about air permeability of nanofiber membranes were taken via Textest AG (FX 3300) at a size of 5 cm2 and a pressure of 300 Pa. All scaling about thickness of nanofiber membranes were gained through a thickness tester (CHY-CA). The contact angle was demonstrated by an XGCAM contact angle meter. All indication signals were acquired through National Instruments NI TB-4300. All tests about elongation at break were gained by an Auto Tensile Tester (XLM-50N).

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the Central Universities (no. 06500100), the “Ten thousand plan”-National High-level personnel of special support program, and the “Thousands Talents” Program for Pioneer Researcher and His Innovation Team, China.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b04860. Indication of real-time capacity of the SApEC (AVI) SApEC establishing and delivering regularly signals to a receiver controlling the states of an alarm such as an alert light bulb via the SApEC wireless sensing system (AVI) SEM images, contact angle, transferred charges, illustration of SApECs, indication of arm joints via the SApEC, and the circuit diagram of the SApEC wireless sensing system (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], [email protected]. ORCID

Congju Li: 0000-0001-6030-7002 Author Contributions ⊥

F.W. and C.L. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (NSFC nos. 51503005, 21703010, and 21274006), National Key R&D Project from Minister of Science and Technology (2016YFA0202702), the Programs for Beijing Science and Technology Leading Talent (grant no. Z161100004916168), the Fundamental Research Funds for 22728

DOI: 10.1021/acsami.9b04860 ACS Appl. Mater. Interfaces 2019, 11, 22722−22729

Research Article

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