Highly Sensitive Flexible Piezoresistive Pressure Sensor Developed

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Surfaces, Interfaces, and Applications

Highly Sensitive Flexible Piezoresistive Pressure Sensor Developed Using Biomimetically Textured Porous Materials Tingting Zhao, Tongkuai Li, Longlong Chen, Li Yuan, Xifeng Li, and Jianhua Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b09265 • Publication Date (Web): 10 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019

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ACS Applied Materials & Interfaces

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Highly Sensitive Flexible Piezoresistive Pressure

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Sensor Developed Using Biomimetically Textured

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Porous Materials

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Tingting Zhao, Tongkuai Li, Longlong Chen, Li Yuan, Xifeng Li and Jianhua Zhang*

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Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai

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University, Shanghai, 200072, China

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KEYWORDS: pressure sensors, hybrid porous-microstructures, sensitivities, bio-inspired, pore

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resistances

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ABSTRACT

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In recent times, high-performance flexible pressure sensors that can be fabricated in an

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environmentally friendly and low-cost manner have received considerable attention owing to

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their potential applications in wearable health monitors and intelligent soft robotics. This paper

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proposes a highly sensitive flexible piezoresistive pressure sensor based on hybrid porous

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microstructures that can be designed and fabricated using a bio-inspired and low-cost approach

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employing the Epipremnum aureum leaf and sugar as the template. The sensitivity and detection

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limit of the obtained pressure sensor can be as high and low as 83.9 kPa−1 (< 140 Pa) and 0.5 Pa,

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respectively. According to the mechanism and simulation analyses, the hybrid porous

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microstructures lower the effective elastic modulus of the sensor and introduce an additional

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pore resistance, which increases the contact area and conductive path with loads, thereby

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contributing to the high sensitivity that exceeds that of traditional microstructured pressure

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sensors. Real-time monitoring of human physiological signals such as finger pressing, voice

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vibration, swallowing activity, and wrist pulse is demonstrated for the proposed device. The high

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performance and easy fabrication of the hybrid porous microstructured sensor can encourage the

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development of a novel approach for the design and fabrication of future pressure sensors.

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1. INTRODUCTION

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Presently, flexible pressure sensors are receiving significant attentions owing to their potential

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applications in future wearable health monitors, human–machine interfaces, and electronic skins

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[1-4].

The working principle of a pressure sensor involves the conversion of mechanical stimuli [5],

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into electrical signals based on a variety of sensing mechanisms, such as piezoresistivity

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capacitance

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sensors have been widely adopted because of their simple device structure, easy signal

13

processing, and relatively low energy consumption in operation

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piezoresistive pressure sensors have been designed and fabricated by exploiting various materials,

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structures, and processes

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sensitivity and low limit of detection (LOD), which can be fabricated in an environmentally

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friendly and low-cost manner, are highly desired for practical applications, for instance, to

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monitor subtle pressures induced by small-scale activities such as a gentle touches, heartbeats,

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and respiration.

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The typical structure of a piezoresistive pressure sensor consists of two opposing elastomer

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substrates coated with active conductive electrodes. Under the stimuli of an applied pressure, the

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two elastomers come into contact to form conduction paths, and this process transduces the

23

applied pressure into a change in resistance [13]. Thus, the performance of a flexible piezoresistive

24

pressure sensor depends on the variation of the conductive paths as pressure, which is

[6],

piezoelectricity

[10-12].

[7],

and triboelectricity

[8].

In particular, piezoresistive pressure

[9].

Several types of

Despite their promising capacities, pressure sensors with a high


2

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determined by the deformation behavior of both the conducting electrodes and elastomer

2

substrates and the number of conductive paths. Recently developed nanomaterials with excellent

3

mechanical flexibility, including graphene, carbon nanotubes, metal particles, and nanowires

4

have been intensively investigated and demonstrated as active electrode materials

5

Polydimethylsiloxane (PDMS) is the elastomer generally employed in pressure sensors because

6

of its superior mechanical flexibility, compatibility, and optical properties

7

the variation of conductive paths of a pressure sensor further, PDMS has been prepared by

8

employing several types of surface microstructures, including microdomes,[16] micropyramid,[17]

9

hollow-spheres,[18] and bionic microstructures[19–21].

[3, 14, 15].

[3, 4].

To increase

10

Such microstructures can contribute to the realization of a higher sensitivity and lower limit of

11

detection because the contact surface areas, namely, the conductive paths in these cases, increase

12

rapidly owing to the presence of stress concentration in the low-pressure regime. Many

13

microstructure-based piezoresistive pressure sensors have been designed and successfully

14

demonstrated. However, regardless of the fabrication methods being used to prepare

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microstructures, current pressure sensors based on microstructures are developed with the

16

objective of increasing the surface conductive paths to improve the performance of the sensors.

17

With increase in the pressure, the sensitivity of sensors based on microstructures is limited by the

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rapid saturation of the surface conductive paths under the build-up of stress in the pre-existing

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contact area. Therefore, further increasing the number of conductive paths as the pressure is the

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key to improve the sensitivity of microstructured-PDMS-based pressure sensors.

21

Porous elastomers composed of electrode materials can provide more conductive paths because

22

several pores exist in the bulk elastomers

23

composed of active materials has been explored for enhancing the sensitivity. For example, Pang

[22,23].

In recent times, the use of porous PDMS


3


[24]

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et al.

demonstrated a piezoresistive pressure sensor with a graphene porous network (GPN)

2

combined with PDMS using nickel foam as the template. Because of the pores in the GPN, the

3

composite exhibited a maximum sensitivity (0.09 kPa−1) for a pressure of up to 1000 kPa.

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Rinaldi et al. [25] fabricated a pressure sensor with a sensitivity of 0.23kPa−1 corresponding to an

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applied pressure of 70 kPa. However, although pressure sensors based on porous elastomers

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exhibit certain sensitivity in a wide pressure range owing to the considerable increase in the

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number of conductive paths in the bulk, the pre-existing space between the pores hinders their

8

sensitivity in the low-pressure regime. Therefore, the integration of the microstructure and

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porous structure can not only solve the bottleneck problems of limited sensitivity in current

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microstructured sensors, but also improve the low sensitivity of the porous sensor, by

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introducing pore conductive paths on the basis of surface conductive paths. Meanwhile, the

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introduction of pores can reduce the effective Young’s modulus of PDMS, thereby improving the

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deformation behavior of the PDMS which can also enhance the sensor performance. For example,

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Chen et al.

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microstructure (HPM), and the device demonstrated a high sensitivity of 35.7 kPa−1 in the low-

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pressure regime, as compared to the microstructured sensor based on the mechanism in which

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the pores decrease the effective Young’s modulus of PDMS. Yang et al.

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flexible capacitive pressure sensor consisting of porous pyramid dielectric layer, which

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drastically increased the sensitivity to 44.5 kPa−1 in the pressure range 0). Notably, the contact fraction (red) of the HPM-model was larger than that

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of the M-model, indicating that the contact area variation was relevant to the porosity. Next,

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HPM models with different porosities were established by changing the pore size. Figure 4d

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shows the 𝜑 values as a function of the applied pressure for models with different porosities. 𝜑

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demonstrates a rapid increase in the low-pressure regime and becomes saturated as the pressure

[31,32],

the contact model between two films with HPM structures could be


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increases. Furthermore, φ increases with increase in the porosity. This could be explained by the

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fact that the porous structures decreased the effective elastic modulus of the PDMS, leading to

3

more easy deformation of the films. Figure 4e shows the relationship between the stress and

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strain for PDMS blocks with four porosities. We found that the PDMS block with the higher

5

porosity had the smallest effective Young's modulus.

6

Next, by introducing the simulated results of the φ value (shown in Figure 4d) into Equation (2),

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the dimensionless current, I%, could be obtained as the function of the dimensionless load P/Pmax

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for the HPM- (ξ = 0.15) and M-based (ξ=0) sensors, where Pmax denotes the maximum load

9

applied in the FEA simulation, as shown in Figure 4f. Although the saturated contact area in the

10

same load case varied slightly among the four samples with different porosities (see Figure 4d),

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the output current at the large load range as well as the sensitivity at the small load range of the

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HPM-sensor (red circles) was enhanced significantly compared to that of the M-sensor (blue

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square), which was in good agreement with the experimental results shown in Figure 3b. This

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could be considered compelling evidence for the essential role of the additional pore resistance in

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enhancing the overall performance of the device. However, as the load increased further and 𝜑

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attained its maximum value, the proposed model seemed to fail to predict the current response to

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the applied load for both the HPM-based and M-based sensors, which still had sensitivities of

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approximately 0.4 kPa−1 and 0.12 kPa−1, respectively. This aspect was not unexpected because

19

although complete contact between the two surfaces could be achieved at a scale approximately

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equal to the dimension of the microstructures (the proposed model was established at this scale),

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contact at smaller scale could be further established with increase in the applied load; however,

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this aspect was not the focus of this study and was thus not considered in the established model.

23

In summary, the high performance of the proposed hybrid porous microstructure-based sensor


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resulted from two aspects: First, the combined action of the microstructures and porous

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structures further increased the contact area under the pressure due to the reduction in the

3

effective Young’s modulus. Second, and more importantly, the porous structures introduced an

4

additional pore resistance that behaved in parallel with the surface resistance, leading to the

5

enhancement of the conductivity as well as the sensitivity with increase in the load.

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Figure 4. Working mechanism of the sensor based on hybrid porous microstructures. (a) Schematic

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illustrations of circuit models of the sensor. The surface resistance was the sum of contact resistance (Rc) and

9

film resistance (Rf) connected in series. (b) Schematic illustrations for the M-model with 0 % porosity and

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HPM-model with a porosity of 15 %. (c) Process of change in the contact area of the M-model and HPM-

11

model with a porosity of 15% under the same pressure (contact is built at places where the contact pressure >

12

0). (d) Change in contact area of M-model and HPM-model with different porosities in response to the applied

13

pressure in FEA modeling. (e) Simulation results indicating the stress–strain curve of the M-model and HPM-


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model with different porosities. (f) Calculated results for the current variation versus applied pressure for M-

2

model and HPM-model with a porosity of 15 %.

3 4

2.4 Sensor Applications

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This section elaborates on the applications of the flexible pressure sensor based on HPM-

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PDMS/MWCNTs films, which could be realized owing to the high sensitivity and low LOD of

7

the sensor. As shown in Figure 5a, with a cyclical pressing force applied on the pressure sensor

8

using a finger, the device demonstrated a prompt and repeatable response with an essentially

9

constant value of change in current. The flexible pressure sensor could also be applied in voice

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recognition. As shown in Figure 5b, a pressure-sensor device was attached to the neck of a

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speaker directly. When the speaker spoke different words such as “Shanghai University” and

12

“pressure sensor” repeatedly, the output current signal changed correspondingly, indicating that

13

the device was able to discriminate the voice through the vibration patterns. The proposed

14

flexible pressure sensor could also be potentially applied to wearable electronics for real-time

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health monitoring. The treatment for nasopharynx cancer via X-rays can damage the normal

16

laryngeal tissue owing to the motion of the throat during the surgery [33,34]. Thus, monitoring the

17

swallowing activity in real-time during surgery could provide important feedback information

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for treatment. When the proposed sensor device was attached onto the skin of the throat, it could

19

accurately respond to the motion of the throat, as shown in Figure 5c. Further, the wrist pulse

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waveform can provide useful and valuable information for some diseases such as cardiovascular

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diseases

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medical tape (inset in Figure 5d). Figure 5d shows the real-time recording of the pulse signals by

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the device, indicating that the corresponding heart rate was ≈75 beats min−1. By amplifying one

24

of the pulse signals, a typical pulse waveform in which three peaks, including those for the

[35,36].

We attached the device onto the radial artery of an adult human wrist by using


16

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percussion wave (P1) and diastolic wave (P2) could be clearly identified, as illustrated in Figure

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5e. Furthermore, the HPM-based pressure sensor was attached to a wrist and employed to detect

3

the gripping and opening activity of the palm reliably (Figure 5f), which could be useful for

4

physical training. As shown in Figure 5g, the Morse code of six characters, such as “HYBRID”,

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was input by touching the pressure sensor, and the corresponding current output was observed.

6

These results highlight the promising potential of the flexible pressure sensor in wearable

7

medical electronic applications.

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Figure 5. Real-time recording of current changes for detecting (a) pressing force applied by repeated finger

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touching, (b) acoustic vibration (Inset: Photograph of the pressure sensor attached onto the neck of a speaker),

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(c) swallowing activity (Inset: Photograph of the pressure sensor attached onto the neck of a speaker), (d) wrist

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pulses (inset: Photograph of a sensor device attached onto a wrist). (e) Magnified view of a single pulse in (d).


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(f) Sensing performance of the pressure sensor for detecting the gripping and opening activity of the human

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palm (Inset: Photograph of a sensor attached onto a wrist), and (g) Morse code for “HYBRID” produced by

3

touching the sensors.

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3. CONCLUSION

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This paper proposes a flexible piezoresistive pressure sensor based on hybrid porous

7

microstructures fabricated via a bio-inspired and low-cost approach. The micropatterned contact

8

surface was prepared by replicating the natural Epipremnum aureum leaves, and the porous

9

structure was formed using sugar as the template. The hybrid porous microstructure combines

10

the advantages of hybrid structures, which increase the contact area due to stress concentration

11

and reduce Young’s modulus, and the porous structure, which introduces additional pore

12

resistance. Consequently, the pressure sensor had a high sensitivity and low LOD. The obtained

13

flexible pressure sensor exhibited a high sensitivity of 83.9 kPa−1 at an applied pressure < 140 Pa,

14

which was considerably higher than those of the microstructured sensor and porous-structured

15

sensor. Furthermore, the HPM sensor exhibited a low LOD of less than 0.5 Pa, while

16

demonstrating excellent stability (>28000 cycles). These aspects enabled the proposed flexible

17

pressure sensor to detect finger pressing, voice vibration, swallowing activity, and wrist pulses.

18

Considering the high performance and ease of fabrication of the device, the proposed sensor

19

could be a promising candidate for application in artificial intelligence and smart medical

20

electronics.

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EXPERIMENTAL SECTION


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Materials. The SYLGARD 184 silicone elastomer base and curing agent were provided by Dow

2

Corning Co. Ltd. The MWCNTs were supplied by XF NANO, INC. The MWCNTs had a

3

diameter of more than 50 nm and length of 10−20 μm. The sugar particles as a soluble medium

4

with sizes in the range of 10–100 μm were obtained by grinding the purchased sugar using a

5

commercial grinder.

6

Fabrication of hybrid porous microstructured PDMS (HPM-PDMS) film. Four glass sheets

7

were enclosed on a glass board to form a glass container for casting the PDMS. Fresh E. aureum

8

leaves were selected and cut into a rectangle shape, and subsequently cleaned using deionized

9

water. Next, the leaves were blow dried with compressed air and fixed inside the prepared glass

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container using double-sided adhesive tape. Sugar particles were used to cover the entire

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container. The PDMS prepolymer mixed with the curing agent in a weight ratio of 10:1 was

12

poured into the sugar particles and then degassed, followed by curing at 65 ℃ for 4 h.

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Subsequently, the cured sugar/PDMS composite film was peeled from the leaves and immersed

14

into 60 ℃ water to remove the sugar particles. Finally, the samples were dried at 65 ℃ for 4 h.

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The microstructured PDMS (M-PDMS) and porous PDMS (P-PDMS) film were prepared using

16

the same procedure as that described above, just without sugars and leaves, respectively.

17

Fabrication of pressure sensor based on HPM-PDMS film. The as-prepared HPM PDMS

18

films were immersed in an MWCNT water solution (9.8 wt%) and stirred for 1 h; the films were

19

then dried at 60 ℃ in air. On each of the HPM-PDMS/MWCNT composite films, a copper wire

20

was attached at the side using conductive adhesive tapes to serve as an electrode. Two HPM-

21

PDMS films coated with MWCNTs (2×2 cm2) were placed face-to-face to construct a pressure

22

sensor. It should be noted that the conductive adhesive tapes in each film should not touch the


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conductive part of the other film. The M-PDMS- and P-PDMS-based pressure sensors were

2

prepared using the same procedures.

3

Characterization. A digital microscope (KEYENCE, VHX-5000) was used to acquire the 3D

4

morphology data of E. aureum leaves for 3D modeling and simulation. A scanning electron

5

microscope (Hitachi S-4800) was used to characterize the surface morphology of the prepared

6

samples. Pressure loading was performed with a mechanical performance testing system (ZQ,

7

990-6), and the electrical properties of the pressure sensor were characterized by using a digital

8

source meter (Keithley 4200). The dynamic pressure response test was performed using a sweep

9

signal generator (DH-1301), vibration exciter (DH40020), and acquisition analyzer (DH5992N),

10

which were provided by Donghua Testing Technology Co. Ltd.

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ASSOCIATED CONTENT

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Supporting Information

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Supporting Information is available free of charge on the ACS Publications website.

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The 3D digital microscope image of protuberances on the E. aureum leaves; The optical images

16

of sugar particles before and after grinding; I–V curves of HPM-PDMS-based sensor under

17

static pressure; The dynamic response of pressure sensor to different frequencies; The

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corresponding response time and releasing time of the pressure sensor under the pressure of 4

19

KPa; The limit of detection of the pressure-sensor (20 mg, 0.5 Pa); A plot and table showing the

20

sensitivity and the limit of detection of the mentioned piezoresistive pressure sensors in the paper;

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The resistance model development process; The calculation of the porosity; The FEA modeling

22

process.

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AUTHOR INFORMATION

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Corresponding Author


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*E-mail: [email protected]

2

ORCID

3

Jianhua Zhang: 0000-0001-8061-1861

4 5

ACKNOWLEDGMENT

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This work was partially supported by the National Natural Science Foundation of China (No.

7

51805311), the National Science Fund for Distinguished Young Scholars under Grant (No.

8

51725505), the National Key R&D Plan under Grant (No. 2017YFB0404703), the Postdoctoral

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innovative talent program (No. BX20180184), the China Postdoctoral Science Foundation

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funded project (No. 2018M640374).

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REFERENCES

13

(1) Zang, Y.; Zhang, F.; Di, C.; Zhu, D. Advances of flexible pressure sensors toward artificial

14

intelligence and health care applications. Mater. Horiz. 2015, 2, 140.

15

(2) Trung, T. Q.; Lee, N. Flexible and Stretchable Physical Sensor Integrated Platforms for

16

Wearable Human-Activity Monitoring and Personal Healthcare. Adv. Mater. 2016, 28, 4338-

17

4372.

18

(3) Wang, Z.;Guo, S.; Li, H.; Wang, B.; Sun, Y.; Xu, Z.; Chen, X.; Wu, K.; Zhang, X.; Xing, F.;

19

Li, L.; Hu, W.The Semiconductor/Conductor Interface Piezoresistive Effect in an Organic

20

Transistor for Highly Sensitive Pressure Sensors. Adv. Mater. 2019, 31, 1805630.

21

(4) Yang, T.; Xie, D.; Li, Z.; Zhu, H. Recent advances in wearable tactile sensors: Materials,

22

sensing mechanisms, and device performance. Mater. Sci. Eng. R 2017, 115, 1-37.


21


Page 22 of 32

1

(5) Li, T.; Chen, L.; Yang, X.; Chen, Xin.; Zhang, Z.; Zhao, T.; Li, X.; Zhang, J. A flexible

2

pressure sensor based on an MXene–textile network structure. J. Mater. Chem. C 2019, 7, 1022-

3

1027.

4

(6) Lee, K.; Lee, J.; Kim, G.; Kim, Y.; Kang, S.; Cho, S.; Kim, S.; Kim, J.; Lee, W.; Kim, D.;

5

Kang, S.; Kim, D.; Lee, T.; Shim, W. Rough-Surface-Enabled Capacitive Pressure Sensorswith

6

3D Touch Capability. Small 2017, 13, 1700368.

7

(7) Wang, B.; Liu, C.; Xiao, Y.; Zhong, J.; Li, W.; Cheng, Y.; Hu, B.; Huang, L.; Zhou, J.

8

Ultrasensitive cellular fluorocarbon piezoelectret pressure sensor for selfpowered human

9

physiological monitoring. Nano Energy 2017, 32, 42-49.

10

(8) Askari H.; Saadatnia, Z.; Asadi, E.; Khajepour, A.; Khamesee, M. B.; Zu, J. A flexible

11

hybridized electromagnetic-triboelectric multi-purpose selfpowered sensor. Nano Energy 2018,

12

45, 319-329.

13

(9) Wang, X.; Dong, L.; Zhang, H.; Yu, R.; Pan, C.; Wang, Z. Recent Progress in Electronic

14

Skin. Adv. Sci. 2015, 2, 1500169

15

(10) Tao, L.; Zhang, K.; Tian, H.; Liu, Y.; Wang, D.; Chen, Y.; Yang, Y.; Ren, T. Graphene-

16

Paper Pressure Sensor for Detecting Human Motions. ACS Nano 2017, 11, 8790-8795.

17

(11) Bae, G. Y.; Pak, S. W.; Kim, D.; Lee, G.; Kim, D. H.; Chung, Y.; Cho, K. Linearly and

18

Highly Pressure-Sensitive Electronic Skin Based on a Bioinspired Hierarchical Structural Array.

19

Adv. Mater. 2016, 28, 5300-5306.


22

Page 23 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

(12) Liu, M.; Pu, X.; Jiang, C.; Liu, T.; Huang, X.; Chen, L.; Du, C.; Sun, J.; Hu, W.; Wang, Z.

2

Large-Area All-Textile Pressure Sensors for Monitoring Human Motion and Physiological

3

Signals. Adv. Mater. 2017, 29, 1703700.

4

(13) Shu, Y.; Tian, H.; Yang, Y.; Li, C.; Cui, Y.; Mi, W.; Li, Y.; Wang, Z.; Deng, N.; Peng, B.;

5

Ren, T. Surface-modified piezoresistive nanocomposite flexible pressure sensors with high

6

sensitivity and wide linearity. Nanoscale 2015, 7, 8636-8644.

7

(14) Shi, J.; Wang, L.; Dai, Z.; Zhao, L.; Du, M.; Li, H.; Fang, Y. Multiscale Hierarchical Design

8

of a Flexible Piezoresistive Pressure Sensor with High Sensitivity and Wide Linearity Range.

9

Small 2018, 1800819.

10

(15) Jian, M.; Xia, K.; Wang ,Q.; Yin, Z.; Wang, H.; Wang, C.; Xie, H.; Zhang, M.; Zhang, Y.

11

Flexible and Highly Sensitive Pressure Sensors Based on Bionic Hierarchical Structures. Adv.

12

Funct. Mater. 2017, 27, 1606066.

13

(16) Park, J.; Lee, Y.; Hong, J.; Ha, M.; Jung, Y.; Lim, H.; Kim, S. Y.; Ko, H. Giant Tunneling

14

Piezoresistance of Composite Elastomers with Interlocked Microdome Arrays for Ultrasensitive

15

and Multimodal Electronic Skins. ACS Nano 2014, 8, 4689-4697.

16

(17) Li, H.; Wu, K.; Xu, Z.; Wang, Z.; Meng, Y.; Li, L.. Ultrahigh-Sensitivity Piezoresistive

17

Pressure Sensors for Detection of Tiny Pressure. ACS Appl. Mater. Interfaces 2018, 10,

18

20826−20834.

19

(18) Pan, L.; Chortos, A.; Yu, G.; Wang, Y.; Isaacson, S.; Allen, R.; Shi, Y.; Dauskardt, R.; Bao,

20

Z. An ultra-sensitive resistive pressure sensor based on hollow-sphere microstructure induced

21

elasticity in conducting polymer film. Nat. Commun. 2014, 5, 3002.


23


Page 24 of 32

1

(19) Nie, P.; Wang, R.; Xu, X.; Cheng, Y.; Wang, X.; Shi, L.; Sun, J. High-Performance

2

Piezoresistive Electronic Skin with Bionic Hierarchical Microstructure and Microcracks. ACS

3

Appl. Mater. Interfaces 2017, 9, 14911-14919.

4

(20) Xia, K.; Wang, C.; Jian, M.; Wang, Q.; Zhang, Y. CVD growth of fingerprint-like patterned

5

3D grapheme film for an ultrasensitive pressure sensor. Nano Research 2018, 11, 1124-1134.

6

(21) Su, B.; Gong, S.; Ma, Z.; Yap, L. W.; Cheng W. Mimosa-Inspired Design of a Flexible

7

Pressure Sensor with Touch Sensitivity. Small 2015, 11, 1886-1891.

8

(22) Kang, S.; Lee, J.; Lee, S.; Kim, S.; Kim, J.; Algadi, H.; Al-Sayari, S.; Kim, D.; Kim, D.; Lee,

9

T. Highly Sensitive Pressure Sensor Based on Bioinspired Porous Structure for Real-Time

10

Tactile Sensing. Adv. Electron. Mater. 2016, 2, 1600356.

11

(23) Wu, S.; Zhang, J.; Ladani, R. B.; Ravindran, A. R.; Mouritz, A. P.; Kinloch, A. J.; Wang, C.

12

H. Novel Electrically Conductive Porous PDMS/Carbon Nanofiber Composites for Deformable

13

Strain Sensors and Conductors. ACS Appl. Mater. Interfaces 2017, 9, 14207-14215.

14

(24) Pang, Y.; Tian, H.; Tao, L.; Li, Y.; Wang, X.; Deng, N.; Yang, Yi.; Ren, T. Flexible, Highly

15

Sensitive, and Wearable Pressure and Strain Sensors with Graphene Porous Network Structure.

16

ACS Appl. Mater. Interfaces 2016, 8, 26458-26462.

17

(25) Rinaldi, A.; Tamburrano, A.; Fortunato, M.; Sarto, M. S. A Flexible and Highly Sensitive

18

Pressure Sensor Based on a PDMS Foam Coated with Graphene Nanoplatelets. Sensors 2016, 16,

19

2148.


24

Page 25 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

(26) Chen, H.; Song, Y.; Guo, H.; Miao, L.; Chen, X.; Su, Z.; Zhang, H. Hybrid porous micro

2

structured finger skin inspired self-powered electronic skin system for pressure sensing and

3

sliding detection. Nano Energy 2018, 51, 496-503.

4

(27) Yang, J.; Kim, J.; Oh, J.; Kwon, S.; Sim, J.; Kim, D.; Choi, H.; Park, S. Microstructured

5

Porous Pyramid-Based Ultrahigh Sensitive Pressure Sensor Insensitive to Strain and

6

Temperature. ACS Appl. Mater. Interfaces 2019, 11, 19472−19480.

7

(28) Tian, H.; Shu, Y.; Wang, X.; Mohammad, M. A.; Bie, Z.; Xie, Q.; Li, C.; Mi, W.; Yang, Y.;

8

Ren, T. A Graphene-Based Resistive Pressure Sensor with Record-High Sensitivity in a Wide

9

Pressure Range. Sci. Rep. 2015, 5, 8603.

10

(29) Holm, R. Electrical Contacts, 4th ed. Springer, New York, 1967, 9-16.

11

(30) GREENWOOD, J. A. Constriction resistance and the real area of contact. BRIT. J. APPL.

12

PHYS. 1966, 17, 1621-1632.

13

(31) Pastewka, L.; Robbins, M. O. Contact between rough surfaces and a criterion for

14

macroscopic adhesion. Proc. Natl. Acad. Sci. U.S.A 2014, 111, 3298-3303.

15

(32) Peia, L.; Hyunb, S.; Molinaria, J. F.; Robbins, M. O. Finite element modeling of elasto-

16

plastic contact between rough surfaces. J. Mech. Phys. Solids 2005, 53, 2385-2409.

17

(33) Markkanen-Leppa¨nen, M.; Isotalo, E.; Ma¨kitie, A. A.; Rorarius, E.; Asko-Seljavaara, S.;

18

Pessi, T.; Suominen, E.; Haapanen, M. Swallowing after free-flap reconstruction in patients with

19

oral and pharyngeal cancer. Oral Oncology 2006, 42, 501-509.

20

(34) MITTAL, B. B.; PAULOSKI, B. R.; HARAF, D. J.; PELZER, H. J.; ARGIRIS, A.;

21

VOKES, E. E.; RADEMAKER, A.; LOGEMANN, J. A. SWALLOWING DYSFUNCTION—

22

PREVENTATIVE AND REHABILITATION STRATEGIES IN PATIENTS WITH HEAD-

23

AND-NECK

CANCERS

TREATED

WITH

SURGERY,

RADIOTHERAPY,

AND


25


Page 26 of 32

1

CHEMOTHERAPY: A CRITICAL REVIEW. Int. J. Radiation Oncology Biol. Phys. 2003, 57,

2

1219-1230.

3

(35) Pang, C.; Koo, J.; Nguyen, A.; Caves, J. M.; Kim, M.; Chortos, A.; Kim, K.; Wang, P. J.;

4

Tok, J. B.-H.; Bao, Z. Highly Skin-Conformal Microhairy Sensor for Pulse Signal Amplifi cation.

5

Adv. Mater. 2015, 27, 634-640.

6

(36) Yang, T.; Jiang, X.; Zhong, Y.; Zhao, X.; Lin, S.; Li, J.; Li, X.; Xu, J.; Li, Z.; Zhu, H. A

7

Wearable and Highly Sensitive Graphene Strain Sensor for Precise Home-Based Pulse Wave

8

Monitoring. ACS Sens. 2017, 2, 967-974.

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Figure 1. Fabrication process of the pressure sensor based on hybrid porous microstructure PDMS. (a) Schematic of the fabrication process of the pressure sensor. Top views of optical images of an E. aureum leaf (inset) under scale bars of (b) 1000 μm (c) 100 μm. (d) SEM image of the M-PDMS film. Scale bar: 100 μm. (e) Line profiles of microstructures on the M-PDMS film in the 3D digital microscope image (inset). (f) SEM image of the HPM-PDMS. Scale bar: 100 μm. (g) SEM image of cross-sectional view of the HPM-PDMS film. Scale bar: 400 μm. 200x179mm (300 x 300 DPI)


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Figure 2. (a) SEM image of the HPM-PDMS film covered with MWCNT film. Scale bar: 100 μm. (inset: Photograph of the flexible pressure sensor. Scale bar: 1 cm). (b) SEM image of the cross-sectional view of HPM-PDMS film covered with MWCNT film. Scale bar: 100 μm. (c) Enlarged SEM image of (b). Scale bar: 10 μm. (inset: Enlarged SEM image of the MWCNT coating in (c). Scale bar: 500 μm) 198x46mm (300 x 300 DPI)



Figure 3. (a) Sensitivity of the HPM-PDMS- (black squares), M-PDMS- (blue triangles) and P-PDMS (red circles)-based pressure sensors. (b) The magnified image of purple dotted box in (a). (c) Repeated real-time responses to pressures of 0.2, 1, and 4 kPa for the HPM-PDMS-based sensor. d) Real-time response of the sensor to a pressure of 200 Pa. The insets show the response time and recovery time upon loading and unloading. (e) Stability of the sensor tested for 29, 000 cycles at an applied frequency of 1 Hz; the insets show the output signal under different numbers of cycles. 165x79mm (300 x 300 DPI)


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Figure 4. Working mechanism of the sensor based on hybrid porous microstructures. (a) Schematic illustrations of circuit models of the sensor. The surface resistance was the sum of contact resistance (Rc) and film resistance (Rf) connected in series. (b) Schematic illustrations for the M-model with 0 % porosity and HPM-model with a porosity of 15 %. (c) Process of change in the contact area of the M-model and HPMmodel with a porosity of 15% under the same pressure (contact is built at places where the contact pressure > 0). (d) Change in contact area of M-model and HPM-model with different porosities in response to the applied pressure in FEA modeling. (e) Simulation results indicating the stress–strain curve of the M-model and HPM-model with different porosities. (f) Calculated results for the current variation versus applied pressure for M-model and HPM-model with a porosity of 15 %. 160x113mm (300 x 300 DPI)



Figure 5. Real-time recording of current changes for detecting (a) pressing force applied by repeated finger touching, (b) acoustic vibration (Inset: Photograph of the pressure sensor attached onto the neck of a speaker), (c) swallowing activity (Inset: Photograph of the pressure sensor attached onto the neck of a speaker), (d) wrist pulses (inset: Photograph of a sensor device attached onto a wrist). (e) Magnified view of a single pulse in (d). (f) Sensing performance of the pressure sensor for detecting the gripping and opening activity of the human palm (Inset: Photograph of a sensor attached onto a wrist), and (g) Morse code for “HYBRID” produced by touching the sensors. 159x124mm (300 x 300 DPI)


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Highly Sensitive Flexible Piezoresistive Pressure Sensor Developed

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