An ultra-stretchable, highly sensitive and biocompatible capacitive strain sensor from an ionic nanocomposite for on-skin monitoring

Xu, Haihua; Lv, Ying; Qiu, Dexing; Zhou, Yongjin; Zeng, Haoxuan; Chu, Yican

doi:10.1039/c8nr08589g

Cited by 149 publications

(124 citation statements)

References 60 publications

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“…The obtained value was 1.61 ± 0.01 for the sensor with the auxetic structure, and 0.86 ± 0.02 for that without the auxetic structure, thus indicating that it increased by 1.9 times for the former sensor (Figure 4C). The sensitivity 1.61 obtained in this study is lower than those reported in the other studies: 3.05 (Nur et al, 2018) and 165 (Xu et al, 2019). However, the current design of the sensor is only to validate the concept of this study and it can potentially be optimized for achieving better performance.…”

Section: Resultsmentioning

confidence: 53%

“…Nur et al have developed a sensor with electrodes made from wrinkled gold films and have shown sensitivity of 3.05 with maximum strain of 140% (Nur et al, 2018). Xu et al have demonstrated that a nano composite membrane consisting of ionic hydrogels and silver nano fibers, exhibits a large change of the capacitance between the electrodes, placed at the edges of the membrane (Xu et al, 2019). In their study, the sensitivity is reported to be 165 with maximum strain of 1,000%.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity Improvement of Highly Stretchable Capacitive Strain Sensors by Hierarchical Auxetic Structures

2019

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Highly stretchable sensors that can detect large strains are useful in deformable systems, such as soft robots and wearable devices. For stretchable strain sensors, two types of sensing methods exist, namely, resistive and capacitive. Capacitive sensing has several advantages over the resistive type, such as high linearity, repeatability, and low hysteresis. However, the sensitivity (gauge factor) of capacitive strain sensors is theoretically limited to 1, which is much lower than that of the resistive-type sensors. The objective of this study is to improve the sensitivity of highly stretchable capacitive strain sensors by integrating hierarchical auxetic structures into them. Auxetic structures have a negative Poisson's ratio that causes increase in change in capacitance with applied strains, and thereby improving sensitivity. In order to prove this concept, we fabricate and characterize two sensor samples with planar dimensions 60 mm × 16 mm. The samples have an acrylic elastomer (3M, VHB 4905) as the dielectric layer and a liquid metal (eutectic gallium-indium) for electrodes. On both sides of the sensor samples, hierarchical auxetic structures made of a silicone elastomer (Dow Corning, Sylgard 184) are attached. The samples are tested under strains up to 50% and the experimental results show that the sensitivity of the sensor with the auxetic structure exceeds the theoretical limit. In addition, it is observed that the sensitivity of this sensor is roughly two times higher than that of a sensor without the auxetic structure, while maintaining high linearity (R 2 = 0.995), repeatability (≥10 4 cycles), and low hysteresis.

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Section: Resultsmentioning

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Sensitivity Improvement of Highly Stretchable Capacitive Strain Sensors by Hierarchical Auxetic Structures

2019

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“…Secondly, as a result of the use of a dry adhesive substrate for creating robust, conformal contact between sensor and skin, even a slight strain from a pulse at~1.5 beat per second could be clearly detected by the sensor (Figure 4c). Each pulse cycle recorded at the wrist included (i) a peak corresponding to the precussion wave, (ii) a relative steady section originating from the diastolic wave, and (iii) a minor dicrotic notch [45]. The pulse measurement could also be made at other body locations, including the radial and ulnar arteries (see Figure S12 for anatomical locations of radial and ulnar arteries; testing graphs are shown in Figure 4c,d).…”

Section: Application Of the Strain Sensor As Health Monitor Electronmentioning

confidence: 99%

A Multifunctional Wearable Device with a Graphene/Silver Nanowire Nanocomposite for Highly Sensitive Strain Sensing and Drug Delivery

Shi

Liu

Kopecki

et al. 2019

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Advances in wearable, highly sensitive and multifunctional strain sensors open up new opportunities for the development of wearable human interface devices for various applications such as health monitoring, smart robotics and wearable therapy. Herein, we present a simple and cost-effective method to fabricate a multifunctional strain sensor consisting of a skin-mountable dry adhesive substrate, a robust sensing component and a transdermal drug delivery system. The sensor has high piezoresisitivity to monitor real-time signals from finger bending to ulnar pulse. A transdermal drug delivery system consisting of polylactic-co-glycolic acid nanoparticles and a chitosan matrix is integrated into the sensor and is able to release the nanoparticles into the stratum corneum at a depth of~60 µm. Our approach to the design of multifunctional strain sensors will lead to the development of cost-effective and well-integrated multifunctional wearable devices. C 2019, 5, 17 2 of 16the development of mobile devices where increasing functionalities are being integrated into single devices, multifunctional wearable devices [2,10,11] open new tech logical possibilities in areas such as human-machine interaction, health monitoring and drug delivery [12]. For example, a single device might be fabricated which can simultaneously deliver drugs and monitor the physiological response. Despite the clear promise of such multifunctional wearable devices, further improvements related to the fabrication process and cost-effectiveness are needed for their adoption.In terms of materials selection, there have been various approaches utilizing nanomaterials (e.g., silver nanowires [13], carbon nanotubes [14] and chemical vapor deposition (CVD) graphene [15]) as sensing components and elastomeric polymers or textiles as flexible and stretchable substrates [16,17]. Graphene nanoplatelets (GnPs) have been widely used in various polymer nanocomposites because of their superior electrical and mechanical properties [18][19][20]. Each GnP is typically 2-5 nm in thickness and may contain 3-10 graphene layers [21]. Upon reaching the percolation threshold in a matrix, the individual GnP forms a physically connected network where the overall resistance of the nanocomposites becomes limited by the interlayer contact resistance of the GnPs [4,22]. A strategy to reduce the contact resistance is to combine GnPs with silver nanowires (AgNWs). AgNWs employed in this work are around 40 nm in diameter and 20-60 µm in length. Under low strain, nanowires might change wave amplitudes and slide across each other, thus facilitating and maintaining a conducting network to accommodate the strain [23].Transdermal drug delivery is a promising drug delivery strategy to complement the limitations of traditional oral-and injectable-based methods. Transdermal drug delivery might potentially realize convenient and painless drug delivery and a sustained release profile with reduced side effects [24]. Advances in nanotechnology have led to the development of drug nanocarriers whi...

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“…Stretchable strain sensors are widely used to obtain mechanical feedback from the soft interfaces of various fields: health care, rehabilitation monitoring, human–machine interaction, soft robotics, and mass measurement . Generally, these sensors are used to measure large strains (>2%) of objects . During stretching, force applied on sensor interacts with produced strain, and it is necessary to measure the exact value of the interacting force like in the case of joint bending .…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10][11] Generally, these sensors are used to measure large strains (>2%) of objects. [12][13][14] During stretching, force applied on sensor interacts with produced strain, and it is necessary to measure the exact value of the interacting force like in the case of joint bending. [15,16] Wide-range force detection sensors are crucial for soft robots lifting variable loads and rehabilitation training of patients having broken joints.…”

Section: Introductionmentioning

confidence: 99%

A Stretchable Capacitive Strain Sensor Having Adjustable Elastic Modulus Capability for Wide‐Range Force Detection

et al. 2019

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Stretchable strain sensors are important components of soft robotics, rehabilitation assistance, and human health monitoring systems. However, strain sensors capable of wide‐range force detection with adjustable modulus facilities are highly desirable to obtain mechanical feedback in various scenarios. Herein, a stretchable capacitive strain sensor capable of adjustable modulus and wide‐range force detection is reported. The sensor consists of two liquid metals (LMs) filled thermoplastic elastomer (TPE) tubes encapsulated in flexible silicone. The adjustable modulus capability of the sensor is attained by mounting the sensor with springs of different elastic coefficients. During electromechanical tests, the elastic coefficient‐dependent adjustable modulus is obtained in the range of 0.78–10.3 MPa. After optimizing the performance, a sensor capable of wide force‐sensing range (0.07–74 N), high cyclic stability (>3500 cycles), with low hysteresis, good linearity, and fast response time (<50 ms) is achieved. Finally, a digital display system is developed to display the amount of detected force during the loading of the sensor, which confirms the great capability of the sensor to be applied in joint rehabilitation and soft robotic fields.

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An ultra-stretchable, highly sensitive and biocompatible capacitive strain sensor from an ionic nanocomposite for on-skin monitoring

Abstract: An ultra-stretchable and highly-sensitive strain sensor was reported, which can monitor pulse, electrocardiograph, breath, finger motions and emotion changes.

Cited by 149 publications

References 60 publications

Sensitivity Improvement of Highly Stretchable Capacitive Strain Sensors by Hierarchical Auxetic Structures

Sensitivity Improvement of Highly Stretchable Capacitive Strain Sensors by Hierarchical Auxetic Structures

A Multifunctional Wearable Device with a Graphene/Silver Nanowire Nanocomposite for Highly Sensitive Strain Sensing and Drug Delivery

A Stretchable Capacitive Strain Sensor Having Adjustable Elastic Modulus Capability for Wide‐Range Force Detection

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