Quantitative mapping of tissue mechanical properties is essential for understanding disease progression and guiding therapeutic interventions. However, conventional techniques are constrained by limited spatial coverage and poor mechanical compliance between rigid probes and soft biological tissues. Here, we report an adjustable magnetic tweezer microsystem that actuates a 1 mm vegetable oil-based ferrofluid droplet for in situ mechanical measurement with high spatial coverage and accuracy. The system features a tunable workspace (9-80 mm) that enables two operational modes: large-scale magnetic field gradients for droplet navigation and localized uniform fields for controlled deformation. The ferrofluid's fluid-like compliance facilitates soft-soft interaction with tissue, reducing artifacts from probe stiffness mismatch. Quantitative tests across sucrose solutions (0.8-83 mPa·s) and agar gels (0.4-142 kPa) showed agreement with viscometer and indentation standards (with all errors under 10%, except for the case with 1 mPa·s viscosity, where the Brownian motion at the low viscosity affects the accuracy). The method was further validated in biological tissue, demonstrating 1.6% deviation from reference measurements. This integrated ferrofluid-magnetic tweezer platform provides a minimally invasive, compliance-matched approach for viscoelastic characterization of soft materials and tissues.

Multimodal physiological monitoring using in-ear devices is an excellent solution for nonintrusive and noninvasive health monitoring. However, the small size of the ear canal, variation in its morphology in different individuals, and ear wax introduce challenges such as a non-conformal interface between the sensors and the skin due to the complex ear canal geometry, device fitting issues, biofouling blockage layers, hearing blockage by the device and discomfort. Here, we report a multimodal self-cleansing, in-ear nonintrusive and configurable electronic (SCIENCE) device which adapts to various canal geometries and performs active wax cleaning at the sensor-canal interfaces. Triggered by immersing the sensor in water, the small cylindrical device with a diameter of 2 mm expands once in the ear, and it converts to a spindle shape with a center diameter that can reach 9 mm, thus leading to adaptive contact with the ear canal and forming a stable sensor-canal interface. The proposed in-ear device was also endowed with wax cleaning capability to automatically break the biofouling barrier and decrease the sensor-skin interface impedance by 20%. SCIENCE is integrated with miniaturized circuits and enables simultaneous mobile and wireless recording of electroencephalography (EEG), electrocardiography (ECG), and core body temperature.

This work introduces a novel method for recording electrophysiological signals and sensing physiological events using an optical tattoo sensor (OTS), eliminating the need for integrating electronics on the skin. Traditional sensors face challenges due to the mechanical mismatch between rigid silicon-based circuits and soft, stretchable sensors, leading to poor performance and interface failures. The OTS, which can be applied as a conventional temporary tattoo, eliminates scattered light from beneath the skin. When used with a handheld speckle sensing device, it improves signal-to-noise ratio and stability in capturing physiological activities beneath the skin. Using the tattoo assisted portable optical sensing system, different types of electrophysiological signal recording and physiological events sensing, including electrocardiography (ECG), electromyography (EMG), seismocardiography (SCG), respiration rate, and pulses, are performed. A shallow neural network is developed to convert the detected skin motions into electrophysiological signals such as ECG. The electrophysiological recording using OTS shows consistency with electrically measured signals.

Advancement of truly stretchable wireless circuits is crucial for the development of high-fidelity wearables for health monitoring, human-machine interfaces and body-sensor network applications. Reported stretchable wireless circuits are capable of reliable functioning under tensile strain of up to 30%, which is not sufficient for applications on the parts of the body with greater deformation. Here, a novel strategy is reported for forming highly stretchable interconnects, namely electrical metamaterial-based interconnect (EMI), that can be integrated with electronic components to develop complex stretchable circuits for various applications including wearables. EMIs are 3D microfluidic channels embedded in hyperelastic polymers, filled with liquid metal, gallium indium (GaIn). Unlike other metal conductors and liquid metal-based interconnects reported so far, EMI shows metamaterial-like property of reduction of its electrical resistance under strain. Using EMIs a highly stretchable wireless electrocardiography wearable is developed that functions reliably under up to 100% strain. The circuit includes amplifiers, filters, Bluetooth components, and a rechargeable battery and attaches to soft sensor patches via magnetic connectors. The use of the soft and stretchable circuit with the Young's modulus of 0.65 MPa along with soft sensors results in minimizing the motion artifacts significantly making it ideal for reliable long-term health monitoring.

Here we report a soft and stretchable surface-modified carbon nano tube (CNT)/silicone oil (SO)/polydimethylsiloxane (PDMS) sensor for biological signal recording. Silver nano particles were used to modify the surface of the sensor, improve its interface with the skin and reduce electrode-skin interface impedance (ESII). Our results show that adding a layer of silver nanoparticles at sensor surface decreases the ESII by 30% and increases the signal-to-nose ratio (SNR) from 21 dB to 29 dB. The sensor is easy to apply, comfortable to wear and reusable and it was fabricated using our developed scalable, time-and-cost-effective method.

During recent years, stretchable and flexible sensors for wearable application have gained a lot of interest, but one of the grand challenges that yet to be addressed is the interface between the soft and stretchable sensor and the hard and rigid circuits. The mechanical mismatch between soft sensors and hard connectors to external circuits makes the interface prone to quick failure under mechanical strain and deformation.Here, we report a soft piezoresistive posture sensor made of a hetero-phase nanocomposite with the stretchable connector-sensor interface for the robust sensing of the posture. The hetero-phase nanocomposite is made of Gallium-indium (GaIn) in the liquid phase, carbon nano tube (CNT) and polydimethylsiloxane (PDMS) in the solid phase. The sensor with the Young's modulus of 158 kPa shows comparable mechanical softness to the skin, which is essential for accurate sensing. Further, we developed liquid metal (LM) based stretchable connections between the soft sensor and the connectors to the external circuit to enable the stable operation of the sensor under deformation. The developed posture sensor has a gauge factor (GF) of 0.815 under 20 % and 0.32 between 20 % and 60 % of applied tensile strain. The sensor was successfully used for sensing of the posture with the sensitivity of 1 % change in its electrical resistance per 10 degrees of neck tilting and strain sensitivity of 2 % of applied strain. The fabrication of the CNT-LM-PDMS posture sensor employed a scalable and cost-effective process. The presented stretchable connection is a solution that can be applied to many soft and stretchable wearable sensors and circuit interfaces with various physiological sensing applications.

Recently electronic tattoo sensors have attracted immense interest for health monitoring mainly due to their higher sensing performance than conventional dry sensors, owing to the ultra-low thickness which results in their conformability to the skin. However, their performance is worse than wet sensors. Further, these electronic tattoo sensors are not durable and reusable when free-standing because of their low thickness and being too delicate. Here, we report a remarkably high-performance freestanding, reusable, ultrathin and ultra-soft electronic tattoo sensor made of parylene-hydrogel double layer system with high water retention over extended periods that can be used for the extended period of 6 months. The hydrogel electronic tattoo (HET) sensors consist of electrically conductive self-adhesive hydrogel with a thickness of 20 µm and Young’s modulus of only 31 kPa at 37 °C, allowing for ultra-conformal contact to the skin microscopic features. Our HET sensors are fabricated using a scalable cost-effective method on ordinary tattoo papers and are laminated on the skin like temporary tattoos and were used for electrophysiological signals recording such as electrocardiography (ECG), electromyography (EMG), and skin hydration, temperature sensing. The HET sensors, for the first time, show 234% lower sensor-skin interface impedance (SSII) and significantly lower susceptibility to motion than gold standard medical grade silver/silver chloride wet gel electrodes which are known to have the lowest SSII and susceptibility to motion. Further, the low HET-skin interface impedance leads to a considerably larger signal amplitude and signal-to-noise ratio (SNR) of the electrophysiological signals recorded using HET sensors in comparison with those obtained using gold standard medical grade silver/silver chloride wet gel electrodes. The SNR of some types of electrophysiological signals such as EMG recorded using HET is up to 19 dB higher than gold standard medical grade electrodes due to higher signal amplitude, significantly lower susceptibility of HET to motion and lower motion artifacts. Also, the HET sensor is the first free-standing ultrathin tattoo sensor that can be transferred from the skin to tattoo paper and vice versa many times and the electrophysiological sensing quality remained high during repeated use for over 6 months.

Significant developments have been made in the field of wearable healthcare by utilizing soft materials for the construction of electronic sensors. However, the lack of adaptability to complex topologies, such as ear canal, results in inadequate sensing performance. Here, we report an in-ear physiological sensor with mechanical adaptability, which softens upon contact with the ear canal's skin, thus reducing the sensor-skin mechanical mismatch and interface impedance. An efficient strategy of mechanical adjustment and switching is exploited to increase the softness of the device, leading to a significant decrease in Young's modulus from 30.5 MPa of thermoplastic polyurethane (TPU) to 0.86 MPa of TPU/Ecoflex foam (TEF).The mechanical adaptability at body temperature endows the in-ear device improved device-canal contact area and interface stability. As a result, the TEF-based in-ear device demonstrates reliable sensing, low motion artifact, and high comfort in electroencephalography (EEG) and core body temperature sensing. High quality EEG signals of alpha, beta, delta, and gamma are measured during different activities. Moreover, the TEF-based in-ear device exhibits high reusability for over 4 months, which makes it suitable for long-term healthcare monitoring.

Here, we report an effective method of modifying the mechanical stiffness of thermoplastic polyurethane (TPU)/carbon black (CB) nanocomposite to improve the quality of electrocardiography (ECG) by reducing electrode-skin interface impedance and consequently increasing the signal-to-noise ratio (SNR). Our results show the liquid blending of silicon-based monomer (Ecoflex A) and TPU before polymerization reduces the Young’ modulus of TPU/CB nanocomposite by 33% and the electrode-skin interface impedance of it by 38% and increases the SNR of ECG signals recorded using it by 15% in dB.

Carbon nanotube (CNT)-based nanocomposites have found applications in making sensors for various types of physiological sensing. However, the sensors’ fabrication process is usually complex, multistep, and requires longtime mixing and hazardous solvents that can be harmful to the environment. Here, we report a flexible dry silver (Ag)/CNT/polydimethylsiloxane (PDMS) nanocomposite-based sensor made by a solvent-free, low-temperature, time-effective, and simple approach for electrophysiological recording. By mechanical compression and thermal treatment of Ag/CNT, a connected conductive network of the fillers was formed, after which the PDMS was added as a polymer matrix. The CNTs make a continuous network for electrons transport, endowing the nanocomposite with high electrical conductivity, mechanical strength, and durability. This process is solvent-free and does not require a high temperature or complex mixing procedure. The sensor shows high flexibility and good conductivity. High-quality electroencephalography (EEG) and electrooculography (EOG) were performed using fabricated dry sensors. Our results show that the Ag/CNT/PDMS sensor has comparable skin–sensor interface impedance with commercial Ag/AgCl-coated dry electrodes, better performance for noninvasive electrophysiological signal recording, and a higher signal-to-noise ratio (SNR) even after 8 months of storage. The SNR of electrophysiological signal recording was measured to be 26.83 dB for our developed sensors versus 25.23 dB for commercial Ag/AgCl-coated dry electrodes. Our process of compress-heating the functional fillers provides a universal approach to fabricate various types of nanocomposites with different nanofillers and desired electrical and mechanical properties.

Here, we report an ultrasoft extra long-lasting, reusable hydrogel-based sensor that enables high-quality electrophysiological recording with low-motion artifacts. The developed sensor can be used and stored in an ambient environment for months before being reused. The developed sensor is made of a self-adhesive electrical-conductivity-enhanced ultrasoft hydrogel mounted in an Ecoflex-based frame. The hydrogel’s conductivity was enhanced by incorporating polypyrrole (PPy), resulting in a conductivity of 0.25 S m−1. Young’s modulus of the sensor is only 12.9 kPa, and it is stretchable up to 190%. The sensor was successfully used for electrocardiography (ECG) and electromyography (EMG). Our results indicate that using the developed hydrogel-based sensor, the signal-to-noise ratio of recorded electrophysiological signals was improved in comparison to that when medical-grade silver/silver chloride (Ag/AgCl) wet gel electrodes were used (33.55 dB in comparison to 22.16 dB). Due to the ultra-softness, high stretchability, and self-adhesion of the developed sensor, it can conform to the skin and, therefore, shows low susceptibility to motion. In addition, the sensor shows no sign of irritation or allergic reaction, which usually occurs after long-term wearing of medical-grade Ag/AgCl wet gel electrodes on the skin. Further, the sensor is fabricated using a low-cost and scalable fabrication process.

Electroencephalography has garnered interest for applications in mobile healthcare, human–machine interfaces, and Internet of Things. Conventional electroencephalography relies on wet and dry electrodes. Despite favorable interface impedance of wet electrodes and skin, the application of a large amount of gel at their interface with skin limits the electroencephalography spatial resolution, increases the risk of shorting between electrodes, and makes them unsuited for long‐term mobile recording. In contrast, dry electrodes are better suited for long‐term recordings but susceptible to motion artifacts. In addition, both wet and dry electrodes are non‐adhesive to the hairy scalp and mechanical support, or chemical adhesives are used to hold them in place. Herein, a conical microstructure array (CMSA) based sensor made of carbon nanotube‐polydimethylsiloxane composite is reported. The CMSA sensor is fabricated using the innovative, cost‐effective, and scalable method of viscosity‐controlled dip‐pull process. The sensor adheres to the hairy scalp by generating negative pressure in its conical microstructures when it is pressed against scalp. Aided by the application of a trace amount of gel, CMSA sensor establishes good electrical contact with the skin, enabling its applications in mobile electroencephalography over extended periods. Notably, the signal quality of CMSA sensors is comparable to that of medical‐grade wet gel electrodes.

EDITORIAL article Front. Nanotechnol., 25 April 2022Sec. Nanomaterials Volume 4 - 2022 | https://doi.org/10.3389/fnano.2022.886586

Electrocardiography (ECG) is a primary tool for diagnosis of various types of disease and disorders such as arrhythmias, coronary heart disease, heart attack, mental disorders, etc. Reliable wearable ECG devices can be a valuable tool in early diagnosis and effective treatment of such disease and disorders. Convention wearable ECG sensor-systems are rigid, bulky, expensive, and the recorded ECG signals using these wearable devices lack required accuracy for medical diagnosis mainly due to motion artifacts that is originated from slippage of sensors on skin and/or instable interface between the soft sensor and the rigid electronic circuits. Here, we report a low-modulus, soft and stretchable wearable electrocardiography (ECG) sensor-system patch which enables continuous and long-term recording of ECG signals with minimal motion artifacts. This system consists of two reusable, detachable-attachable patches: sensor patch and circuit patch, as shown in Figure 1a. The reusable multi-wall carbon nanotube (MWCNT) based sensor patch is fabricated on stretchable elastomer substrate by our developed cost and time-effective method. Reusable, front-end and wireless circuit patch is made by integration of the off-the-shelf integrated circuit components with three-dimensional (3D) stretchable-deformable interconnects (SDI). SDIs are 3D springs of liquid metal (EGaIn). Unlike other reported liquid metal based interconnects, SDI has been designed in 3D form to increase the stretchability and make it low-modulus and robust to deformations in all directions. The stretchability of SDI structure is beyond 500% (the limit of our measurement system) without any negligible change in electrical resistivity of the interconnects. With less than 1% change in the resistance of SDIs after 50,000 cycles of applied tensile strain of 200%, the SDI structure ensures reliable stretchability and durability of the circuit patch for long-term electrocardiography. The sensor patch is soft, stretchable and it is fabricated using a low-cost scalable method. This soft and stretchable ECG sensor-system shows comparable performance with respect to medical grade Ag/AgCl wet gel electrodes. Our CNT-PDMS sensors shows low electrode-skin interface impedance and low susceptibility to motion artifact which similar of it in medical grade Ag/AgCl wet gel sensors (Fig. 1b). Further, it is waterproof, reusable and comfortable to wear. The circuit patch includes a rechargeable battery and ECG signals is wirelessly sent to a personal device such as cellphone, tablet and laptop through Bluetooth low energy (BLE) and it is displayed in real-time (Fig. 1c) Our developed sensor-system is a multi-use platform which can be applied for the detection of EMG, EEG or EOG signals. Figure 1

Here we report a low-modulus, low-motion-artifact (LMLMA) sensor for electrocardiography (ECG) recording. Motion artifacts are one of the most prominent issues of both wet and dry electrophysiological electrodes/sensors. Our soft and stretchable LMLMA sensor shows significantly lower motion artifacts than gold-standard medical grade Ag/ AgCI electrodes This sensor is easy to use, comfortable to wear, waterproof, and fabricated using a low-cost, time-effective, and scalable method. LMLMA sensor is connected to our developed soft and stretchable wearable wireless circuit for long-term mobile ECG recording on personal devices.

As performant and well-established as conventional silicon-based electronics have become, the era of wearable electronics and the Internet-of-Things has created a demand for robust electronic devices that can conform to the surfaces of the human body. Whereas the mechanical mismatch between rigid silicon electronics and the human body represents a fundamental limit to conventional non-invasive health sensing, wearable electronics and electrodes that can conform to the microscopic features of the skin 1,2 can circumvent most of the motion artifacts inherent to conventional, rigid sensing devices, and facilitate continuous health monitoring as is required for modern, more proactive healthcare. Unfortunately, without addressing this fundamental mechanical incompatibility, devices that leverage the high density of transistors available in rigid silicon-based integrated circuits are handicapped by how well they can maintain contact with the body, and consequently are prone to failure at the sensor-circuit interface. The extraordinary properties of two-dimensional materials pose a unique opportunity for addressing this mechanical mismatch. Their unusual mechanical strength combined with their ultimate thinness, optical transparency, and favorable electronic transport properties 3 makes them ideal candidates for the next generation of highly conformable wearable electronics free of the constraints of a rigid silicon circuit board—however, minimizing local strain in the vicinity of the active devices to ensure reliable operation remains a priority. Using a design informed by finite element method (FEM) simulations, our proposed strain-neutralizing 2D transistors are configured to resist applied strains on the order of the 30% strains human skin can withstand by redistributing strain away from active regions. Tight binding simulations of the transistor channels helps with further compensation of residual strain in the active regions, alongside careful consideration of materials and device architecture during fabrication. Together, these considerations help realize the possibility of fully integrated strain-neutralized 2D transistors compatible with state-of-the-art conformable wearable sensors. [1]S. Kabiri Ameri et al., “Graphene electronic tattoo sensors,” ACS Nano, 11, 7634–7641, 2017. [2] S. Kabiri Ameri et al., “ Imperceptible electrooculography graphene sensor system for human–robot interface ”, npj 2D Materials and Applications, 2, 1-7, 2018. [3] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, “The electronic properties of graphene,” Rev. Mod. Phys. , vol. 81, no. 1, pp. 109–162, Jan. 2009, doi: 10.1103/RevModPhys.81.109 .

Numerous fields of science and technology, including healthcare, robotics and bioelectronics, have begun to switch their research direction from developing 'high-end, high-cost' tools towards 'high-end, low-cost' solutions. Graphene electronic tattoos (GETs), whose fabrication protocol is discussed in this work, are ideal building blocks of future wearable technology due to their outstanding electromechanical properties. The GETs are composed of high-quality, large-scale graphene that is transferred onto tattoo paper, resulting in an electronic device that is applied onto skin like a temporary tattoo. Here, we provide a comprehensive GET fabrication protocol, starting from graphene growth and ending with integration onto human skin. The methodology presented is unique since it utilizes high-quality electronic-grade graphene, while the processing is done by using low-cost and off-the-shelf methods, such as a mechanical cutter plotter. The GETs can be either used in combination with advanced scientific equipment to perform precision experiments, or with low-cost electrophysiology boards, to conduct similar operations from home. In this protocol, we showcase how GETs can be applied onto the human body and how they can be used to obtain a variety of biopotentials, including electroencephalogram (brain waves), electrocardiogram (heart activity), electromyogram (muscle activity), as well as monitoring of body temperature and hydration. With graphene available from commercial sources, the whole protocol consumes ~3 h of labor and does not require highly trained personnel. The protocol described in this work can be readily replicated in simple laboratories, including high school facilities.

The ability to fabricate incredibly sophisticated integrated circuits at low cost rendered modern electronics more affordable, efficient, and functional. This monumental advance in technology would usher in the age of the Internet-of-things and transform wearable electronics from a largely academic pursuit into an everyday reality around which a robust and rapidly growing industry has formed. However, even the highly connected wearable electronics of today leave much to be desired with respect to their compatibility with soft tissues such as skin. More specifically, the poor compliance of the rigid, silicon-based integrated circuits conventionally used in the construction of these devices with the soft, curvilinear surfaces of the human body can result in high impedances at the skin-sensor interface which in turn contribute to low signal-to-noise ratios as well as poor sensitivity and accuracy. Motion artifacts originating from the poor conformability of such devices only exacerbate these problems. This mechanical mismatch represents a significant hurdle in the effort to move away from the conventional reactive approach to healthcare towards a more proactive approach that leverages ‘truly’ wearable sensors to improve health outcomes. Transistors are the building blocks upon which the vast majority of modern electronics are built. Although single transistors can be used to amplify or otherwise control electronic signals using only a small input signal, most of their functionality comes in the form of integrated circuits (ICs) consisting of many connected transistors. Conventional techniques for fabricating ICs exploit the rigidity of the semiconducting silicon substrate to ensure the device performance is consistent throughout the circuit. In contrast, integrated circuits for highly compliant wearable electronics that can conform even to microscopic features of the skin[1,2] face the inherent challenge of maintaining their electrical performance under mechanical deformations. As is the case with most sensors, the front-end circuitry for these devices (responsible for conveying the information contained in the signal – either wirelessly or without wires – to the end user) requires reliable and performant integrated circuits. Of course, integrating soft, ultra-thin sensors with the rigid silicon-based integrated circuits results in a mechanical mismatch with mechanical failure at the interface where the two components meet being the most likely scenario. Instead, here we present an approach which uses two-dimensional (2D) transistors in a specially designed strain-neutralizing configuration which circumvents much of the difficulties associated with the aforementioned mismatch. The extraordinary properties of 2D materials—particularly their excellent mechanical flexibility, ultimate thinness, optical transparency, and favorable transport properties for realizing electronics—make them prime candidates for replacing conventional silicon-based transistor circuits in next-generation wearable applications. Using finite-element analysis we have designed and simulated a compliant, strain-insensitive substrate which can resist uniaxial applied strains upwards of 35%. Moreover, simulations of the electronic band structure of the transistors under applied strain is used to optimize the circuit design and further minimize the effect of strain in the transistors. These electronic and mechanical simulations are used together in the configuration and subsequent fabrication of fully integrated strain-neutralized 2D transistors compatible with state-of-the-art soft stretchable wearable sensors. [1]S. Kabiri Ameri et al., “Graphene electronic tattoo sensors,” ACS Nano, 11, 7634–7641, 2017. [2] S. Kabiri Ameri et al., “Imperceptible electrooculography graphene sensor system for human–robot interface”, npj 2D Materials and Applications, 2, 1-7, 2018.

The recent COVID-19 pandemic has proven that low-cost wireless wearable medical device which offer reliable continuous health monitoring can be extremely valuable and game changing tools in early diagnosis, control and management of contiguous disease. Current commercial wearables are not reliable and accurate enough for medical diagnosis, further they are rigid, bulky, and expensive. Here we present a skin-mounted, low-cost, soft and stretchable wearable electrocardiography (ECG) sensor-system which enables continuous and wireless ECG recording. The ECG sensor-system consists of low-cost, disposable, soft and stretchable, carbon-based electrodes patch; and a reusable, front-end and wireless circuits patch. The sensor patches are made by our developed low-cost scalable manufacturing method of spray-printing, on breathable, conformal, stretchable medical adhesives. The softness and thinness of electrodes patch ensure the conformability of electrodes to skin, maximizes the quality of sensing by decreasing the electrode-skin impedance and consequently improving the signal to noise ratio (SNR) and furthermore offer comfort to users. The reusable ECG circuit patch consists of three-dimensional stretchable/deformable interconnects (SDI) integrated with off-the-shelf integrated circuit components. SDI is made of microfluidic channels filled with liquid metal (LM). Unless other reported liquid metal based interconnects, SDI has been designed in 3D form to increase the stretchability and make it robust to deformations in all three x, y and z axis. The sensor-system is also waterproof and the developed disposable sensors are breathable and more comfortable than commercial wet gel electrodes. The recorded ECG signal can be sent to a personal device such as tablet and laptop wirelessly and be displayed in real-time. The developed sensor-system is a platform that can be applied for the construction of various types of sensor-systems with other sensing capabilities. Figure 1

Realizing flexible strain sensor with high sensitivity and tunable gauge factor is a challenge. To meet this challenge, we report an ionic liquid gated three-dimensional graphene field effect strain sensor. The charge carrier concentration in this 3D graphene is modulated by applied electric field through an all-around self-assembled electrical double layer capacitance formed at the interface of graphene with ionic liquid. Strain causes folding and unfolding of microscopic wrinkles and formation of cracks in the graphene network altering transistor behavior. Mechanical deformation of graphene also alters its bandgap providing inherent strain sensitivity. Use of 3D network results in robust operation since there exists multiple paths for the charge carriers to flow between source and drain terminals. Interestingly, changing the applied bias allows one to tune the gauge factor of this graphene transistor based strain sensor. The current-voltage characteristics of the sensor were measured for different tensile strain values of 0.5% to 35%. Our results show that the sensor maintains its field effect characteristics over a large strain range; moreover it enables up to 68% tunability in the strain gauge factor. We also report cyclic measurements with varied magnitude and frequency showing repeatability and robustness as a highly sensitive strain sensor.