Carbon Nanotube Polydimethylsiloxane Research Articles

Broadband All-Optical Plane-Wave Ultrasound Imaging System Based on a Fabry-Perot Scanner.

A broadband all-optical plane-wave ultrasound imaging system for high-resolution 3-D imaging of biological tissues is presented. The system is based on a planar Fabry-Perot (FP) scanner for ultrasound detection and the photoacoustic generation of ultrasound in a carbon-nanotube-polydimethylsiloxane (CNT-PDMS) composite film. The FP sensor head was coated with the CNT-PDMS film which acts as an ultrasound transmitting layer for pulse-echo imaging. Exciting the CNT-PDMS coating with nanosecond laser pulses generated monopolar plane-wave ultrasound pulses with MPa-range peak pressures and a -6-dB bandwidth of 22 MHz, which were transmitted into the target. The resulting scattered acoustic field was detected across a 15 mm ×15 mm scan area with a step size of 100 [Formula: see text] and an optically defined element size of [Formula: see text]. The -3-dB bandwidth of the sensor was 30 MHz. A 3-D image of the scatterer distribution was then recovered using a k -space reconstruction algorithm. To obtain a measure of spatial resolution, the instrument line-spread function (LSF) was measured as a function of position. At the center of the scan area, the depth-dependent lateral LSF ranged from 46 to 65 [Formula: see text] for depths between 1 and 12 mm. The vertical LSF was independent of position and measured to be [Formula: see text] over the entire field of view. To demonstrate the ability of the system to provide high-resolution 3-D images, phantoms with well-defined scattering structures of arbitrary geometry were imaged. To demonstrate its suitability for imaging biological tissues, phantoms with similar impedance mismatches, sound speed and scattering properties to those present in the tissue, and ex vivo tissue samples were imaged. Compared with conventional piezoelectric-based ultrasound scanners, this approach offers the potential for improved image quality and higher resolution for superficial tissue imaging. Since the FP scanner is capable of high-resolution 3-D photoacoustic imaging of in vivo biological tissues, the system could ultimately be developed into an instrument for dual-mode all-optical ultrasound and photoacoustic imaging.

Large-Area, Crosstalk-Free, Flexible Tactile Sensor Matrix Pixelated by Mesh Layers.

Tactile sensor arrays have attracted considerable attention for their use in diverse applications, such as advanced robotics and interactive human-machine interfaces. However, conventional tactile sensor arrays suffer from electrical crosstalk caused by current leakages between the tactile cells. The approaches that have been proposed thus far to overcome this issue require complex rectifier circuits or a serial fabrication process. This article reports a flexible tactile sensor array fabricated through a batch process using a mesh. A carbon nanotube-polydimethylsiloxane composite is used to form an array of sensing cells in the mesh through a simple "dip-coating" process and is cured into a concave shape. The contact area between the electrode and the composite changes significantly under pressure, resulting in an excellent sensitivity (5.61 kPa-1) over a wide range of pressure up to 600 kPa. The mesh separates the composite into the arranged sensing cells to prevent the electrical connection between adjacent cells and simultaneously connects each cell mechanically. Additionally, the sensor shows superior durability compared with previously reported tactile sensors because the mesh acts as a support beam. Furthermore, the tactile sensor array is successfully utilized as a Braille reader via information processing based on machine learning.

Plasma-jet-induced programmable wettability on stretchable carbon nanotube films

Stretchable surfaces with site-selective and degree-controlled wettability are indispensable for various applications ranging from self-cleaning to droplet manipulation and drag reduction; however, superwettable surfaces or patterns with robust stretchability are seldom demonstrated to date. To address such challenging issue, herein, we proposed a facile approach to programmatically realize extreme wetting-contrast patterning of stretchable carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) using atmospheric micro-plasma jet (μPJ). The μPJ had been used to engineer both superhydrophobicity and superhydrophilicity through exploiting surface hierarchical roughness under a shielding nitrogen gas and oxygenic functional groups in atmosphere, respectively, tailoring the water contact angles from ~160° to <10° ultimately. The as-prepared superhydrophobic, conductive surfaces could bear tensile strain even up to 100% and demonstrated no noticeable wettability deterioration after 1000 cyclic stretching from ε = 0% to ε = 50%. And they also presented a distinguished enduring stability in terms of exposure to air and even extreme acidic/alkaline aqueous droplets. As the randomly entangled CNTs film could respond to tensile strain, the superhydrophobic films had been successfully applied to water-repellent epidermal sensors. And hydrophilic patterns had been fabricated on the superhydrophobic surfaces as well. It can be envisioned that a variety of novel applications ranging from water/blood-repellent human-machine interfaces to in-plane microfluidic can be implemented via this powerful wettability regulation paradigm.

Highly sensitive and flexible wearable pressure sensor with dielectric elastomer and carbon nanotube electrodes

Wearable sensors for tracking human body motion are being increasingly applied in medical systems and are considered important components of human–machine interfaces. This study proposes a flexible sandwich-like capacitive pressure sensor that consists of carbon nanotube–polydimethylsiloxane (CNT–PDMS) composite electrodes and a porous polymer dielectric layer.CNT yarn and polymer materials help fabricate a pressure sensor without complex patterns, easily and quickly. The dielectric layer is made of a porous polymer to improve the sensor sensitivity. The high porosity of the dielectric layer increases its deformation under pressure and enhances the sensitivity (to approximately 5.6 kPa−1 (%)) even under low pressures (< 5 kPa). The sensitivity of the sensor varies according to the density of porosity and dielectric permittivity of the dielectric layer.Owing to the high porosity of the dielectric layer and flexibility of the CNT yarn, the capacitive pressure sensor proposed in this study exhibits good performance in detecting even a slight change in stimulus. The proposed pressure sensor can be applied in wearable applications such as human-friendly interfaces and sensitive electronic skins.

Skin-Inspired Humidity and Pressure Sensor with a Wrinkle-on-Sponge Structure.

Sensors with multifunctions have attracted great attention for their extensive application value, among which humidity sensing and pressure sensing are necessary to electronics undoubtedly because of the complex physical environment we live in. Inspired by the structure of skin, in this article, we design a new method to combine wrinkle structure with porous sponge structure and achieve a novel, flexible, compressible, and bifunctional sensor based on carbon nanotube-polydimethylsiloxane (CNT-PDMS) with functions of humidity sensing and pressure sensing. The performance of the humidity sensing part can be controlled by the ultraviolet and ozone (UVO) treatment time and CNT concentration, while the sensitivity of the pressure sensing part can be controlled by the CNT concentration and grinding time of sugar granules. The bifunctional sensor can easily sense approaching and touching of a hand, which shows great potential of alarming and protecting some electronics. Moreover, the bifunctional sensor can also be used in detecting human joint motions and breath conditions as a wearable and flexible health monitor.

Flexible Tactile Electronic Skin Sensor with 3D Force Detection Based on Porous CNTs/PDMS Nanocomposites

HighlightsFlexible sensitive carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) nanocomposite with novel double-side rough porous structure was proposed by simple manufacturing methods.Three-dimensional (3D) force tactile electronic skin sensor based on CNTs/PDMS nanocompositions exhibited high sensitivity, good consistency and fast response.A promising strategy for low-cost multi-functional detection in human body monitoring and intelligent robot grasping applications was provided.

Conductive and flexible multi‐walled carbon nanotube/polydimethylsiloxane composites made with naphthalene/toluene mixture

ABSTRACTConventional conductive materials face challenges when utilizing them for flexible and wearable electronics and soft robotics. Carbon nanotube/polydimethylsiloxane (CNT/PDMS) composites are a promising alternative to the conventional hard conductors because they are light and can realize large deformation. To date, well dispersion of CNTs into PDMS to increase conductivity while maintaining flexibility remains challenging. We aimed at developing highly electrically conductive and flexible multi‐walled carbon nanotube/PDMS (MWCNT/PDMS) composites. To this end, we proposed a method to enhance the dispersion of MWCNTs into PDMS using naphthalene and toluene. Our results showed that the addition of naphthalene and toluene into the composites improved dispersion of the MWCNTs and increased the direct current (DC) electrical conductivity. We also found that the morphology of primary aggregates of the MWCNTs influenced the DC electrical conductivity of the composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48167.

Piezo-impedance response of carbon nanotube/polydimethylsiloxane nanocomposites

Advanced physical sensors based on carbon nanotube/polydimethylsiloxane (CNT/PDMS) nanocomposites have recently attracted much attention for potential applications such as wearable and flexible electronic devices. In this work, a CNT/PDMS sponge was fabricated and their capacitive as well as resistive response was investigated by impedance characterization with an equivalent circuit model. The newly defined gauge factor, which considers simultaneously both the piezocapacitive and piezoresistive effects of CNT/PDMS sponge sensors, showed a significantly improved sensitivity. This work provides important information for a better understanding of CNT/PDMS nanocomposites and their sensing performance.

A conductive cell-imprinted substrate based on CNT-PDMS composite.

Cell function regulation is influenced by continuous biochemical and biophysical signal exchange within the body. Substrates with nano/micro-scaled topographies that mimic the physiological niche are widely applied for tissue engineering applications. As the cartilage niche is composed of several stimulating factors, a multifunctional substrate providing topographical features while having the capability of electrical stimulation is presented. Herein, we demonstrate a biocompatible and conductive chondrocyte cell-imprinted substrate using polydimethylsiloxane (PDMS) and carbon nanotubes (CNTs) as conductive fillers. Unlike the conventional silicon wafers or structural photoresist masters used for molding, cell surface topographical replication is challenging as biological cells showed extremely sensitive to chemical solvent residues during molding. The composite showed no significant difference compared with PDMS with regard to cytotoxicity, whereas an enhanced cell adhesion was observed on the conductive composite's surface. Integration of nanomaterials into the cell seeding scaffolds can make tissue regeneration process more efficient.

Photoacoustic Energy Sensor for Nanosecond Optical Pulse Measurement.

We demonstrate a photoacoustic sensor capable of measuring high-energy nanosecond optical pulses in terms of temporal width and energy fluence per pulse. This was achieved by using a hybrid combination of a carbon nanotube-polydimethylsiloxane (CNT-PDMS)-based photoacoustic transmitter (i.e., light-to-sound converter) and a piezoelectric receiver (i.e., sound detector). In this photoacoustic energy sensor (PES), input pulsed optical energy is heavily absorbed by the CNT-PDMS composite film and then efficiently converted into an ultrasonic output. The output ultrasonic pulse is then measured and analyzed to retrieve the input optical characteristics. We quantitatively compared the PES performance with that of a commercial thermal energy meter. Due to the efficient energy transduction and sensing mechanism of the hybrid structure, the minimum-measurable pulsed optical energy was significantly lowered, ~157 nJ/cm2, corresponding to 1/760 of the reference pyroelectric detector. Moreover, despite the limited acoustic frequency bandwidth of the piezoelectric receiver, laser pulse widths over a range of 6–130 ns could be measured with a linear relationship to the ultrasound pulse width of 22–153 ns. As CNT has a wide electromagnetic absorption spectrum, the proposed pulsed sensor system can be extensively applied to high-energy pulse measurement over visible through terahertz spectral ranges.

Sandpaper-molded wearable pressure sensor for electronic skins

Wearable pressure sensors fabricated with sandpaper-molded carbon nanotube-polydimethylsiloxane (CNT-PDMS) electrodes are developed for electronic skins. Compared to the lithography method, widely adopted to prepare pressure sensors based on microstructures, the sandpaper molding method is much more cost-effective and scalable. The microhumps templated from the sandpaper are suggested to amplify the external stimuli during device deformation, leading to an improved sensitivity that is ∼20 times of the one without microstructures. Moreover, the detectable range of the sandpaper –molded device covers pressures from 5.0 Pa to 50.0 kPa, with a stimuli-response time around 0.19 s and a cycling stability more than 5000 cycles. The sandpaper-molded devices have been explored for external stimuli detection such as pressing, bending and twisting, and human health monitoring including phonation and pulsing.

Electrically Conductive Polymer Nanocomposites for 3D Printing

Recently, 3D printing has been used to print functional conductive microstructures for sensors [1] and other microelectromechanical applications [2,3]. In addition, micromolding [4] and micropatterning [5], including large scale micropattering on flexible substrates [6] have been accomplished using conductive nanocomposites. These conductive nanocomposites comprised multi-walled carbon nanotubes dispersed in crosslinked poly(dimethylsiloxane). A particular disadvantage of this conductive nanocomposite is the multistep, time-consuming preparation process. In addition, there is little understanding of the relationship between the preparation process and the functional properties of the composite. Therefore, here we focus on this more fundamental issue — the effect of the processing on the properties. In this study, poly(acrylonitorile butadiene styrene) (ABS) is chosen as the matrix polymer because it is already widely used in 3D printing. For reasons to be elaborated upon later, multi-walled carbon nanotubes (MWCNTs) were chosen as the conductive filler. Several nanocomposites were prepared by dispersing various concentrations of MWCNTs in ABS using two different methods: melt blending and solution casting. In melt blending, shear deformation of the molten material is used to disperse the filler in the matrix. This deformation can orient the nanotubes. In contrast, solution casting is expected to randomly disperse the nanotubes. In addition, the degree of dispersion of the nanocomposite produced by the two methods need not be identical. To understand the effect of the shear deformation, we measured the conductivity of the nanocomposites prepared by the two methods. For both preparation methods, addition of a small quantity of MWCNT (0.25 weight%), increased the conductivity by several orders of magnitude. Upon further addition of MWCNT, the conductivity of the melt-blended samples increased more rapidly than that of the solution cast samples such that beyond approximately 1 weight% of MWCNT, the conductivity of the melt-blended samples was almost two orders of magnitude higher than that of the solution cast samples. We also compared two ABS polymers with different acrylonitirle contents, but the measured conductivity was not significantly different. In order to understand the difference between the two methods of preparation, we investigated the linear rheology of the nanocomposites. For 0.25 and 0.5 weight% of MWCNT, the storage and the loss moduli of the nanocomposites were essentially similar to that of the matrix polymer. Upon increasing the concentration of MWCNT, the material progressively exhibits solid-like characteristics at low frequencies. These findings suggest that nanocomposites with a low concentration of MWCNTs can be used even in narrow nozzle 3D printers in current use. However, the maximum MWCNT concentration is limited by the more solid-like behaviour seen at progressively higher concentrations. In 3D printing, the molten sample is forced through a nozzle under pressure. This is similar to the pressure-driven flow through a capillary tube. Therefore, to understand the effect of the flow through the nozzle on the conductivity of the material after printing, we extruded the prepared composites through a capillary tube and compared the conductivities of the resulting samples. The conductivities before and after capillary extrusion were not significantly different. This suggests that the process of 3D printing itself does not significantly alter the conductivity characteristics of the material used for printing. In summary, we have achieved an increase in conductivity of several orders of magnitude without significantly altering the rheology of the nanocomposite. Therefore, we expect that such materials can be used in conventional 3D printers, even in the case of narrow nozzles. While the conductivity obtained is still several orders of magnitude smaller than that of metals and hence not sufficient for applications such as circuits, the conductivity is sufficient for applications including electromagnetic shielding and electrostatic discharge. [1] S. Guo, X. Yang, M.-C. Heuzey, and D. Therriault, "3D printing of a multifunctional nanocomposite helical liquid sensor" Nanoscale, 7, 6451–6456 (2015). doi: 10.1039/C5NR00278H [2] A. Khosla, "Nanoparticle-doped electrically-conducting polymers for flexible nano-micro systems" The Electrochemical Society Interface, 21, 67-20 (2012). doi: 10.1149/2.F04123-4if [3] Khosla, A. (2011). "Micropatternable multifunctional nanocomposite polymers for flexible soft MEMS applications" (Doctoral dissertation, Applied Science: School of Engineering Science). http://summit.sfu.ca/item/12017 [4] A. Khosla, B.L. Gray, "Preparation, characterization and micromolding of multi-walled carbon nanotube polydimethylsiloxane conducting nanocomposite polymer" Materials Letters, 63, 1203-1206 (2009). doi: 10.1016/j.matlet.2009.02.043 [5] A. Khosla, B. L. Gray, "Preparation, micro-patterning and electrical characterization of functionalized carbon-nanotube polydimethylsiloxane nanocomposite polymer" Macromol. Symp., 297, 210–218 (2010). doi:10.1002/masy.200900165 [6] A. Khosla, D. Hilbich, C. Drewbrook, D. Chung, B. L. Gray, "Large scale micropatterning of multi-walled carbon nanotube/polydimethylsiloxane nanocomposite polymer on highly flexible 12×24 inch substrates" Proc. SPIE 7926, Micromachining and Microfabrication Process Technology XVI, 79260L (2011); doi:10.1117/12.876738.

Flexible Conductive Composite Integrated with Personal Earphone for Wireless, Real-Time Monitoring of Electrophysiological Signs.

We introduce optimized elastomeric conductive electrodes using a mixture of silver nanowires (AgNWs) with carbon nanotubes/polydimethylsiloxane (CNTs/PDMS), to build a portable earphone type of wearable system that is designed to enable recording electrophysiological activities as well as listening to music at the same time. A custom-built, plastic frame integrated with soft, deformable fabric-based memory foam of earmuffs facilitates essential electronic components, such as conductive elastomers, metal strips, signal transducers and a speaker. Such platform incorporates with accessory cables to attain wireless, real-time monitoring of electrical potentials whose information can be displayed on a cell phone during outdoor activities and music appreciation. Careful evaluations on experimental results reveal that the performance of fabricated dry electrodes are comparable to that of commercial wet electrodes, and position-dependent signal behaviors provide a route toward accomplishing maximized signal quality. This research offers a facile approach for a wearable healthcare monitor via integration of soft electronic constituents with personal belongings.

Virtual reality training for assembly of hybrid medical devices

Skill training in the medical device manufacturing industry is essential to optimize and expedite the efficiency level of new workers. This process, however, gives rise to many underlying issues such as contamination and safety risks, long training period, high skill and experience requirements of operators, and greater training costs. In this paper, we proposed and evaluated a novel virtual reality (VR) training system for the assembly of hybrid medical devices. The proposed system, which is an integration of Artificial Intelligence (AI), VR and gaming concepts, is self-adaptive and autonomous. This enables the training to take place in a virtual workcell environment without the supervision of a physical trainer. In this system, a sequential framework is proposed and utilized to enhance the training through its various “game” levels of familiarity-building processes. A type of hybrid medical device: carbon nanotubes-polydimethylsiloxane (CNT-PDMS) based artificial trachea prosthesis is used as a case study in this paper to demonstrate the effectiveness of the proposed system. Evaluation results with quantitative and qualitative comparisons demonstrated that our proposed training method has significant advantages over common VR training and conventional training methods. The proposed system has addressed the underlying training issues for hybrid medical device assembly by providing trainees with effective, efficient, risk-free and low cost training.

Highly sensitive strain sensors based on fragmentized carbon nanotube/polydimethylsiloxane composites

Wearable strain sensors based on nanomaterial/elastomer composites have potential applications in flexible electronic skin, human motion detection, human–machine interfaces, etc. In this research, a type of high performance strain sensors has been developed using fragmentized carbon nanotube/polydimethylsiloxane (CNT/PDMS) composites. The CNT/PDMS composites were ground into fragments, and a liquid-induced densification method was used to fabricate the strain sensors. The strain sensors showed high sensitivity with gauge factors (GFs) larger than 200 and a broad strain detection range up to 80%, much higher than those strain sensors based on unfragmentized CNT/PDMS composites (GF < 1). The enhanced sensitivity of the strain sensors is ascribed to the sliding of individual fragmentized-CNT/PDMS-composite particles during mechanical deformation, which causes significant resistance change in the strain sensors. The strain sensors can differentiate mechanical stimuli and monitor various human body motions, such as bending of the fingers, human breathing, and blood pulsing.

Highly Stretchable Supercapacitors Enabled by Interwoven CNTs Partially Embedded in PDMS

We present flexible and stretchable supercapacitors composed of interwoven carbon nanotubes (CNTs) embedded in polydimethylsiloxane (PDMS) substrates. CNTs are grown using atmospheric-pressure chemical vapor deposition (APCVD) on a Si/SiO2 substrate and then partially embedded into PDMS. This unique process permits a rapid and facile integration of the interwoven CNT–PDMS structure as a flexible and stretchable supercapacitor electrode with a high level of integrity under various strains. The electrochemical properties of the supercapacitors are measured in 30% KOH solution and with a poly(vinyl alcohol) (PVA)–KOH gel electrolyte (i.e., all-solid-state flexible supercapacitor). The measured capacitance of the supercapacitor is 0.6 mF/cm2 in 30% KOH solution and is 0.3 mF/cm2 with a PVA–KOH gel electrolyte at a scan rate of 100 mV/s, showing a consistent performance under stretching from 0% to 200% and bending/twisting angles from 0° to 180°. The stretching test is performed for 200 cycles from 0% to 100%,...

Through-needle all-optical ultrasound imaging in vivo: a preclinical swine study

High-frequency ultrasound imaging can provide exquisite visualizations of tissue to guide minimally invasive procedures. Here, we demonstrate that an all-optical ultrasound transducer, through which light guided by optical fibers is used to generate and receive ultrasound, is suitable for real-time invasive medical imaging in vivo. Broad-bandwidth ultrasound generation was achieved through the photoacoustic excitation of a multiwalled carbon nanotube-polydimethylsiloxane composite coating on the distal end of a 300-μm multi-mode optical fiber by a pulsed laser. The interrogation of a high-finesse Fabry–Pérot cavity on a single-mode optical fiber by a wavelength-tunable continuous-wave laser was applied for ultrasound reception. This transducer was integrated within a custom inner transseptal needle (diameter 1.08 mm; length 78 cm) that included a metallic septum to acoustically isolate the two optical fibers. The use of this needle within the beating heart of a pig provided unprecedented real-time views (50 Hz scan rate) of cardiac tissue (depth: 2.5 cm; axial resolution: 64 μm) and revealed the critical anatomical structures required to safely perform a transseptal crossing: the right and left atrial walls, the right atrial appendage, and the limbus fossae ovalis. This new paradigm will allow ultrasound imaging to be integrated into a broad range of minimally invasive devices in different clinical contexts.

Electrically Conductive Polymer Nanocomposites for 3D Printing

Three-dimensional (3D) printing technology provides a simple and reasonably fast method to produce complex structures and hence is widely used in rapid prototyping. In addition, due to its ease of use and cost-effectiveness, the technology offers immense scope for personalization. Recently, there has been great interest in using 3D printing to print functional conductive microstructures for use as sensors [1] and for other microelectromechanical applications [2,3]. Past successes include using conductive nanocomposites for micromolding [4] and micropatterning [5]. In fact, large scale micropatterning on flexible substrates has been demonstrated [6]. The nanocomposites were prepared by mixing multi-walled carbon nanotubes in poly(dimethylsiloxane) and then crosslinking the linear polymer. In spite the aforementioned successes, this particular nanocomposite has some disadvantages. For one, it is not easy to prepare. Therefore, there is significant scope for improvement if effective use of the processing-properties-performace triad can be mastered. However, much remains to be understood even in the realm of materials design. Therefore, here we step back and focus on a more fundamental issue — the link between the processing undergone by a material intended for use in 3D printing and its effect on various properties. As it is already widely used, poly(acrylonitrile butadiene styrene) was chosen as the matrix polymer. To render the material electrically conductive, multi-walled carbon nanotubes (MWCNTs) were introduced at several concentrations. The polymer and the carbon nanotubes were blended and the nanocomposites prepared by three different methods: solvent casting, melt mixing and capillary extrusion. Solvent casting was unlikely to significantly orient the carbon nanotubes and hence was expected to function as the control. Melt mixing uses mostly shear deformations to disperse the carbon nanotubes in the sample. In capillary extrusion, in addition to shear flow, the sample also experiences significant elongational deformation. Therefore, these three methods are expected to yield polymer nanocomposites with different orientations of the carbon nanotubes and/or agglomerates and consequently, produce nanocomposites with different physical properties. The mechanical and electrical properties of the nanocomposites prepared by the three methods were compared. The structure and morphology of the nanocomposites were investigated by various techniques and several structural parameters that quantify the structure were measured. It was found that certain structural parameters were sensitive to the processing method used to prepare the samples. It will be argued that the aforementioned structural parameters can provide one route to rationally connect the processing method to the properties of the nanocomposite produced. [1] S. Guo, X. Yang, M.-C. Heuzey, and D. Therriault, "3D printing of a multifunctional nanocomposite helical liquid sensor" Nanoscale, 7, 6451–6456 (2015). doi: 10.1039/C5NR00278H[2] A. Khosla, "Nanoparticle-doped electrically-conducting polymers for flexible nano-micro systems" The Electrochemical Society Interface, 21, 67-20 (2012). doi: 10.1149/2.F04123-4if[3] Khosla, A. (2011). "Micropatternable multifunctional nanocomposite polymers for flexible soft MEMS applications" (Doctoral dissertation, Applied Science: School of Engineering Science). http://summit.sfu.ca/item/12017[4] A. Khosla, B.L. Gray, "Preparation, characterization and micromolding of multi-walled carbon nanotube polydimethylsiloxane conducting nanocomposite polymer" Materials Letters, 63, 1203-1206 (2009). doi: 10.1016/j.matlet.2009.02.043[5] A. Khosla, B. L. Gray, "Preparation, micro-patterning and electrical characterization of functionalized carbon-nanotube polydimethylsiloxane nanocomposite polymer" Macromol. Symp., 297, 210–218 (2010). doi:10.1002/masy.200900165[6] A. Khosla, D. Hilbich, C. Drewbrook, D. Chung, B. L. Gray, "Large scale micropatterning of multi-walled carbon nanotube/polydimethylsiloxane nanocomposite polymer on highly flexible 12×24 inch substrates" Proc. SPIE 7926, Micromachining and Microfabrication Process Technology XVI, 79260L (2011); doi:10.1117/12.876738.

Highly Compressible Integrated Supercapacitor-Piezoresistance-Sensor System with CNT-PDMS Sponge for Health Monitoring.

Rapid improvement of wearable electronics stimulates the demands for the matched functional devices and energy storage devices. Meanwhile, wearable microsystem requires every parts possessing high compressibility to accommodate large-scale mechanical deformations and complex conditions. In this work, a general carbon nanotube-polydimethylsiloxane (CNT-PDMS) sponge electrode is fabricated as the elementary component of the compressible system. CNT-PDMS sponge performs high sensitivity as a piezoresistance sensor, which is capable of detecting stress repeatedly and owns great electrochemical performance as a compressible supercapacitor which maintains stably under compressive strains, respectively. Assembled with the piezoresistance sensor and the compressible supercapacitor, such highly compressible integrated system can power and modulate the low-power electronic devices reliably. More importantly, attached to the epidermal skin or clothes, it can detect human motions, ranging from speech recognition to breathing record, thus showing feasibility in real-time health monitor and human-machine interfaces.

Fingertip-inspired electronic skin based on triboelectric sliding sensing and porous piezoresistive pressure detection

Fingertip is the region with the largest density of mechanoreceptors in human body. Inspired by its complicated anatomical structure, we design a fingertip-like electronic skin (e-skin) that can simultaneously detect the movements from lateral and vertical directions. The device includes three parts that correspond to fingerprint, epidermis and dermis of the human being, respectively. The fabricated double spiral carbon nanotube-polydimethylsiloxane (CNT-PDMS) electrodes and substrate mimic the structure of fingerprint and epidermis, respectively. Based on triboelectrification effect, the double spiral CNT-PDMS electrodes can generate alternating voltage with different frequencies when sliding across different rough surfaces, which behaves like fast adapting (FA) in real skin. Porous CNT-PDMS is used for detecting pressure, mimicking the function of slow adapting (SA) and the structure of dermis. A cost efficient way to fabricated porous CNT-PDMS is adopted and it can modulate the porosity and resistance at the same time, which provides a way to modulate its sensitivity. With the help of both sliding sensing and pressure sensing, this device can execute many complicated tasks such as differentiating roughness of surfaces and holding-releasing execution, which greatly expands the application fields of e-skin.