Ultraconformal Skin-Interfaced Sensing Platform for Motion Artifact-Free Monitoring.

Capable of directly capturing various physiological signals from human skin, skin-interfaced bioelectronics has emerged as a promising option for human health monitoring. However, the accuracy and reliability of the measured signals can be greatly affected by body movements or skin deformations (e.g., stretching, wrinkling, and compression). This study presents an ultraconformal, motion artifact-free, and multifunctional skin bioelectronic sensing platform fabricated by a simple and user-friendly laser patterning approach for sensing high-quality human physiological data. The highly conductive membrane based on the room-temperature coalesced Ag/Cu@Cu core-shell nanoparticles in a mixed solution of polymers can partially dissolve and locally deform in the presence of water to form conformal contact with the skin. The resulting sensors to capture improved electrophysiological signals upon various skin deformations and other biophysical signals provide an effective means to monitor health conditions and create human-machine interfaces. The highly conductive and stretchable membrane can also be used as interconnects to connect commercial off-the-shelf chips to allow extended functionalities, and the proof-of-concept demonstration is highlighted in an integrated pulse oximeter. The easy-to-remove feature of the resulting device with water further allows the device to be applied on delicate skin, such as the infant and elderly.

Recent progress in multifunctional, reconfigurable, integrated liquid metal-based stretchable sensors and standalone systems.

Possessing a unique combination of properties that are traditionally contradictory in other natural or synthetical materials, Ga-based liquid metals (LMs) exhibit low mechanical stiffness and flowability like a liquid, with good electrical and thermal conductivity like metal, as well as good biocompatibility and room-temperature phase transformation. These remarkable properties have paved the way for the development of novel reconfigurable or stretchable electronics and devices. Despite these outstanding properties, the easy oxidation, high surface tension, and low rheological viscosity of LMs have presented formidable challenges in high-resolution patterning. To address this challenge, various surface modifications or additives have been employed to tailor the oxidation state, viscosity, and patterning capability of LMs. One effective approach for LM patterning is breaking down LMs into microparticles known as liquid metal particles (LMPs). This facilitates LM patterning using conventional techniques such as stencil, screening, or inkjet printing. Judiciously formulated photo-curable LMP inks or the introduction of an adhesive seed layer combined with a modified lift-off process further provide the micrometer-level LM patterns. Incorporating porous and adhesive substrates in LM-based electronics allows direct interfacing with the skin for robust and long-term monitoring of physiological signals. Combined with self-healing polymers in the form of substrates or composites, LM-based electronics can provide mechanical-robust devices to heal after damage for working in harsh environments. This review provides the latest advances in LM-based composites, fabrication methods, and their novel and unique applications in stretchable or reconfigurable sensors and resulting integrated systems. It is believed that the advancements in LM-based material preparation and high-resolution techniques have opened up opportunities for customized designs of LM-based stretchable sensors, as well as multifunctional, reconfigurable, highly integrated, and even standalone systems.

Monolayer, open-mesh, pristine PEDOT:PSS-based conformal brain implants for fully MRI-compatible neural interfaces.

Understanding brain function is essential for advancing our comprehension of human cognition, behavior, and neurological disorders. Magnetic resonance imaging (MRI) stands out as a powerful tool for exploring brain function, providing detailed insights into its structure and physiology. Combining MRI technology with electrophysiological recording system can enhance the comprehension of brain functionality through synergistic effects. However, the integration of neural implants with MRI technology presents challenges because of its strong electromagnetic (EM) energy during MRI scans. Therefore, MRI-compatible neural implants should facilitate detailed investigation of neural activities and brain functions in real-time in high resolution, without compromising patient safety and imaging quality. Here, we introduce the fully MRI-compatible monolayer open-mesh pristine PEDOT:PSS neural interface. This approach addresses the challenges encountered while using traditional metal-based electrodes in the MRI environment such as induced heat or imaging artifacts. PEDOT:PSS has a diamagnetic property with low electrical conductivity and negative magnetic susceptibility similar to human tissues. Furthermore, by adopting the optimized open-mesh structure, the induced currents generated by EM energy are significantly diminished, leading to optimized MRI compatibility. Through simulations and experiments, our PEDOT:PSS-based open-mesh electrodes showed improved performance in reducing heat generation and eliminating imaging artifacts in an MRI environment. The electrophysiological recording capability was also validated by measuring the local field potential (LFP) from the somatosensory cortex with an in vivo experiment. The development of neural implants with maximized MRI compatibility indicates the possibility of potential tools for future neural diagnostics.

Direct Laser Processing and Functionalizing PI/PDMS Composites for an On-Demand, Programmable, Recyclable Device Platform.

Skin-interfaced high-sensitive biosensing systems to detect electrophysiological and biochemical signals have shown great potential in personal health monitoring and disease management. However, the integration of 3D porous nanostructures for improved sensitivity and various functional composites for signal transduction/processing/transmission often relies on different materials and complex fabrication processes, leading to weak interfaces prone to failure upon fatigue or mechanical deformations. The integrated system also needs additional adhesive to strongly conform to the human skin, which can also cause irritation, alignment issues, and motion artifacts. This work introduces a skin-attachable, reprogrammable, multifunctional, adhesive device patch fabricated by simple and low-cost laser scribing of an adhesive composite with polyimide powders and amine-based ethoxylated polyethylenimine dispersed in the silicone elastomer. The obtained laser-induced graphene in the adhesive composite can be further selectively functionalized with conductive nanomaterials or enzymes for enhanced electrical conductivity or selective sensing of various sweat biomarkers. The possible combination of the sensors for real-time biofluid analysis and electrophysiological signal monitoring with RF energy harvesting and communication promises a standalone stretchable adhesive device platform based on the same material system and fabrication process.

Intelligence Sparse Sensor Network for Automatic Early Evaluation of General Movements in Infants.

General movements (GMs) have been widely used for the early clinical evaluation of infant brain development, allowing immediate evaluation of potential development disorders and timely rehabilitation. The infants' general movements can be captured digitally, but the lack of quantitative assessment and well-trained clinical pediatricians presents an obstacle for many years to achieve wider deployment, especially in low-resource settings. There is a high potential to explore wearable sensors for movement analysis due to outstanding privacy, low cost, and easy-to-use features. This work presents a sparse sensor network with soft wireless IMU devices (SWDs) for automatic early evaluation of general movements in infants. The sparse network consisting of only five sensor nodes (SWDs) with robust mechanical properties and excellent biocompatibility continuously and stably captures full-body motion data. The proof-of-the-concept clinical testing with 23 infants showcases outstanding performance in recognizing neonatal activities, confirming the reliability of the system. Taken together with a tiny machine learning algorithm, the system can automatically identify risky infants based on the GMs, with an accuracy of up to 100% (99.9%). The wearable sparse sensor network with an artificial intelligence-based algorithm facilitates intelligent evaluation of infant brain development and early diagnosis of development disorders.

Closely Packed Stretchable Ultrasound Array Fabricated with Surface Charge Engineering for Contactless Gesture and Materials Detection.

Communication with hand gestures plays a significant role in human-computer interaction by providing an intuitive and natural way for humans to communicate with machines. Ultrasound-based devices have shown promising results in contactless hand gesture recognition without requiring physical contact. However, it is challenging to fabricate a densely packed wearable ultrasound array. Here, a stretchable ultrasound array is demonstrated with closely packed transducer elements fabricated using surface charge engineering between pre-charged 1-3 Lead Zirconate Titanate (PZT) composite and thin polyimide film without using a microscope. The array exhibits excellent ultrasound properties with a wide bandwidth (≈57.1%) and high electromechanical coefficient (≈0.75). The ultrasound array can decipher gestures up to 10 cm in distance by using a contactless triboelectric module and identify materials from the time constant of the exponentially decaying impedance based on their triboelectric properties by utilizing the electrostatic induction phase. The newly proposed metric of the areal-time constant is material-specific and decreases monotonically from a highly positive human body (1.13 m2 s) to negatively charged polydimethylsiloxane (PDMS) (0.02 m2 s) in the triboelectric series. The capability of the closely packed ultrasound array to detect material along with hand gesture interpretation provides an additional dimension in the next-generation human-robot interaction.

Highly Sensitive Wearable Sensor Based on (001)-Orientated TiO2 for Real-Time Electrochemical Detection of Dopamine, Tyrosine, and Paracetamol.

The concentration of dopamine (DA) and tyrosine (Tyr) reflects the condition of patients with Parkinson's disease, whereas moderate paracetamol (PA) can help relieve their pain. Therefore, real-time measurements of these bioanalytes have important clinical implications for patients with Parkinson's disease. However, previous sensors suffer from either limited sensitivity or complex fabrication and integration processes. This work introduces a simple and cost-effective method to prepare high-quality, flexible titanium dioxide (TiO2) thin films with highly reactive (001)-facets. The as-fabricated TiO2 film supported by a carbon cloth electrode (i.e., TiO2-CC) allows excellent electrochemical specificity and sensitivity to DA (1.390 µA µM-1 cm-2), Tyr (0.126 µA µM-1 cm-2), and PA (0.0841 µA µM-1 cm-2). More importantly, accurate DA concentration in varied pH conditions can be obtained by decoupling them within a single differential pulse voltammetry measurement without additional sensing units. The TiO2-CC electrochemical sensor can be integrated into a smart diaper to detect the trace amount of DA or an integrated skin-interfaced patch with microfluidic sampling and wireless transmission units for real-time detection of the sweat Try and PA concentration. The wearable sensor based on TiO2-CC prepared by facile manufacturing methods holds great potential in the daily health monitoring and care of patients with neurological disorders.

Bionic artificial skin with a fully implantable wireless tactile sensory system for wound healing and restoring skin tactile function.

Tactile function is essential for human life as it enables us to recognize texture and respond to external stimuli, including potential threats with sharp objects that may result in punctures or lacerations. Severe skin damage caused by severe burns, skin cancer, chemical accidents, and industrial accidents damage the structure of the skin tissue as well as the nerve system, resulting in permanent tactile sensory dysfunction, which significantly impacts an individual's daily life. Here, we introduce a fully-implantable wireless powered tactile sensory system embedded artificial skin (WTSA), with stable operation, to restore permanently damaged tactile function and promote wound healing for regenerating severely damaged skin. The fabricated WTSA facilitates (i) replacement of severely damaged tactile sensory with broad biocompatibility, (ii) promoting of skin wound healing and regeneration through collagen and fibrin-based artificial skin (CFAS), and (iii) minimization of foreign body reaction via hydrogel coating on neural interface electrodes. Furthermore, the WTSA shows a stable operation as a sensory system as evidenced by the quantitative analysis of leg movement angle and electromyogram (EMG) signals in response to varying intensities of applied pressures.

Skin-Interfaced Bifluidic Paper-Based Device for Quantitative Sweat Analysis.

The erratic, intermittent, and unpredictable nature of sweat production, resulting from physiological or psychological fluctuations, poses intricacies to consistently and accurately sample and evaluate sweat biomarkers. Skin-interfaced microfluidic devices that rely on colorimetric mechanisms for semi-quantitative detection are particularly susceptible to these inaccuracies due to variations in sweat secretion rate or instantaneous volume. This work introduces a skin-interfaced colorimetric bifluidic sweat device with two synchronous channels to quantify sweat rate and biomarkers in real-time, even during uncertain sweat activities. In the proposed bifluidic-distance metric approach, with one channel to measure sweat rate and quantify collected sweat volume, the other channel can provide an accurate analysis of the biomarkers based on the collected sweat volume. The closed channel design also reduces evaporation and resists contamination from the external environment. The feasibility of the device is highlighted in a proof-of-the-concept demonstration to analyze sweat chloride for evaluating hydration status and sweat glucose for assessing glucose levels. The low-cost yet highly accurate device provides opportunities for clinical sweat analysis and disease screening in remote and low-resource settings. The developed device platform can be facilely adapted for the other biomarkers when corresponding colorimetric reagents are exploited.

The effect of a helmet type, home-use low-level light therapy device for chemotherapy-induced alopecia: study protocol for a randomized controlled trial.

BACKGROUND: Alopecia is one of the most common adverse effects of chemotherapy. It reduces the patient's self-esteem and quality of life and the effect of therapy. Scalp cooling is the only verified current method for prevention but success is not guaranteed, particularly after receiving anthracycline-based combinations. Low-level light therapy has been clinically proven to inhibit the progress of androgenic alopecia. A previous study using human subjects shows limited benefits for low-level light therapy for patients who suffer chemotherapy-induced alopecia but an increase in the number of probes and the optimization of light sources may improve the efficacy. This study determines the efficacy of low-level light therapy for the prevention of chemotherapy-induced hair loss for patients with breast cancer using a randomized controlled trial. METHODS: One hundred six eligible breast cancer patients were randomly distributed into a low-level light therapy group and a control group, after receiving chemotherapy. Subjects in the low-level light therapy group received 12 courses of intervention within 4 weeks. Subjects in the control group received no intervention but were closely monitored. The primary outcome is measured as the difference in the hair count in a target area between the baseline and at the end of week 4, as measured using a phototrichogram (Sentra scalp analyzer). The secondary outcomes include the change in hair count at the end of week 1, week 2, and week 3 and hair width at the end of week 1, week 2, week 3, and week 4, as measured using a phototrichogram, and the change in distress, the quality of life, and self-esteem due to chemotherapy-induced alopecia, at the end of week 4, as measured using a questionnaire. DISCUSSION: This study improves cancer patients' quality of life and provides clinical evidence. TRIAL REGISTRATION: Registered at ClinicalTrials.gov- NCT05397457 on 1 June 2022.

A fully integrated, standalone stretchable device platform with in-sensor adaptive machine learning for rehabilitation.

Post-surgical treatments of the human throat often require continuous monitoring of diverse vital and muscle activities. However, wireless, continuous monitoring and analysis of these activities directly from the throat skin have not been developed. Here, we report the design and validation of a fully integrated standalone stretchable device platform that provides wireless measurements and machine learning-based analysis of diverse vibrations and muscle electrical activities from the throat. We demonstrate that the modified composite hydrogel with low contact impedance and reduced adhesion provides high-quality long-term monitoring of local muscle electrical signals. We show that the integrated triaxial broad-band accelerometer also measures large body movements and subtle physiological activities/vibrations. We find that the combined data processed by a 2D-like sequential feature extractor with fully connected neurons facilitates the classification of various motion/speech features at a high accuracy of over 90%, which adapts to the data with noise from motion artifacts or the data from new human subjects. The resulting standalone stretchable device with wireless monitoring and machine learning-based processing capabilities paves the way to design and apply wearable skin-interfaced systems for the remote monitoring and treatment evaluation of various diseases.

A wireless, solar-powered, optoelectronic system for spatial restriction-free long-term optogenetic neuromodulations.

Numerous wireless optogenetic systems have been reported for practical tether-free optogenetics in freely moving animals. However, most devices rely on battery-powered or coil-powered systems requiring periodic battery replacement or bulky, high-cost charging equipment with delicate antenna design. This leads to spatiotemporal constraints, such as limited experimental duration due to battery life or animals' restricted movement within specific areas to maintain wireless power transmission. In this study, we present a wireless, solar-powered, flexible optoelectronic device for neuromodulation of the complete freely behaving subject. This device provides chronic operation without battery replacement or other external settings including impedance matching technique and radio frequency generators. Our device uses high-efficiency, thin InGaP/GaAs tandem flexible photovoltaics to harvest energy from various light sources, which powers Bluetooth system to facilitate long-term, on-demand use. Observation of sustained locomotion behaviors for a month in mice via secondary motor cortex area stimulation demonstrates the notable capabilities of our device, highlighting its potential for space-free neuromodulating applications.

Superhydrophobic, stretchable kirigami pencil-on-paper multifunctional device platform.

Wearable electronics with applications in healthcare, human-machine interfaces, and robotics often explore complex manufacturing procedures and are not disposable. Although the use of conductive pencil patterns on cellulose paper provides inexpensive, disposable sensors, they have limited stretchability and are easily affected by variations in the ambient environment. This work presents the combination of pencil-on-paper with the hydrophobic fumed SiO2 (Hf-SiO2) coating and stretchable kirigami structures from laser cutting to prepare a superhydrophobic, stretchable pencil-on-paper multifunctional sensing platform. The resulting sensor exhibits a large response to NO2 gas at elevated temperature from self-heating, which is minimally affected by the variations in the ambient temperature and relative humidity, as well as mechanical deformations such as bending and stretching states. The integrated temperature sensor and electrodes with the sensing platform can accurately detect temperature and electrophysiological signals to alert for adverse thermal effects and cardiopulmonary diseases. The thermal therapy and electrical stimulation provided by the platform can also deliver effective means to battle against inflammation/infection and treat chronic wounds. The superhydrophobic pencil-onpaper multifunctional device platform provides a low-cost, disposable solution to disease diagnostic confirmation and early treatment for personal and population health.

Direct Laser Writing of the Porous Graphene Foam for Multiplexed Electrochemical Sweat Sensors.

Wearable electrochemical sensors provide means to detect molecular-level information from the biochemical markers in biofluids for physiological health evaluation. However, a high-density array is often required for multiplexed detection of multiple markers in complex biofluids, which is challenging with low-cost fabrication methods. This work reports the low-cost direct laser writing of porous graphene foam as a flexible electrochemical sensor to detect biomarkers and electrolytes in sweat. The resulting electrochemical sensor exhibits high sensitivity and low limit of detection for various biomarkers (e.g., the sensitivity of 6.49/6.87/0.94/0.16 µA µM-1 cm-2 and detection limit of 0.28/0.26/1.43/11.3 µM to uric acid/dopamine/tyrosine/ascorbic acid) in sweat. The results from this work open up opportunities for noninvasive continuous monitoring of gout, hydration status, and drug intake/overdose.

Iontronic pressure sensor with high sensitivity over ultra-broad linear range enabled by laser-induced gradient micro-pyramids.

Despite the extensive developments of flexible capacitive pressure sensors, it is still elusive to simultaneously achieve excellent linearity over a broad pressure range, high sensitivity, and ultrahigh pressure resolution under large pressure preloads. Here, we present a programmable fabrication method for microstructures to integrate an ultrathin ionic layer. The resulting optimized sensor exhibits a sensitivity of 33.7 kPa-1 over a linear range of 1700 kPa, a detection limit of 0.36 Pa, and a pressure resolution of 0.00725% under the pressure of 2000 kPa. Taken together with rapid response/recovery and excellent repeatability, the sensor is applied to subtle pulse detection, interactive robotic hand, and ultrahigh-resolution smart weight scale/chair. The proposed fabrication approaches and design toolkit from this work can also be leveraged to easily tune the pressure sensor performance for varying target applications and open up opportunities to create other iontronic sensors.

Ultrathin Crystalline Silicon Nano and Micro Membranes with High Areal Density for Low-Cost Flexible Electronics.

Ultrathin crystalline silicon is widely used as an active material for high-performance, flexible, and stretchable electronics, from simple passive and active components to complex integrated circuits, due to its excellent electrical and mechanical properties. However, in contrast to conventional silicon wafer-based devices, ultrathin crystalline silicon-based electronics require an expensive and rather complicated fabrication process. Although silicon-on-insulator (SOI) wafers are commonly used to obtain a single layer of crystalline silicon, they are costly and difficult to process. Therefore, as an alternative to SOI wafers-based thin layers, here, a simple transfer method is proposed for printing ultrathin multiple crystalline silicon sheets with thicknesses between 300 nm to 13 µm and high areal density (>90%) from a single mother wafer. Theoretically, the silicon nano/micro membrane can be generated until the mother wafer is completely consumed. In addition, the electronic applications of silicon membranes are successfully demonstrated through the fabrication of a flexible solar cell and flexible NMOS transistor arrays.

Laser Processing of Crumpled Porous Graphene/MXene Nanocomposites for a Standalone Gas Sensing System.

Integrating wearable gas sensors with energy harvesting and storage devices can create self-powered systems for continuous monitoring of gaseous molecules. However, the development is still limited by complex fabrication processes, poor stretchability, and sensitivity. Herein, we report the low-cost and scalable laser scribing of crumpled graphene/MXenes nanocomposite foams to combine stretchable self-charging power units with gas sensors for a fully integrated standalone gas sensing system. The crumpled nanocomposite designed in island-bridge device architecture allows the integrated self-charging unit to efficiently harvest kinetic energy from body movements into stable power with adjustable voltage/current outputs. Meanwhile, given the stretchable gas sensor with a large response of ∼1% ppm-1 and an ultralow detection limit of ∼5 ppb to NO2/NH3, the integrated system provides real-time monitoring of the exhaled human breath and the local air quality. The innovations in materials and structural designs pave the way for the future development of wearable electronics.

Ultra-stretchable and biodegradable elastomers for soft, transient electronics.

As rubber-like elastomers have led to scientific breakthroughs in soft, stretchable characteristics-based wearable, implantable electronic devices or relevant research fields, developments of degradable elastomers with comparable mechanical properties could bring similar technological innovations in transient, bioresorbable electronics or expansion into unexplored areas. Here, we introduce ultra-stretchable, biodegradable elastomers capable of stretching up to ~1600% with outstanding properties in toughness, tear-tolerance, and storage stability, all of which are validated by comprehensive mechanical and biochemical studies. The facile formation of thin films enables the integration of almost any type of electronic device with tunable, suitable adhesive strengths. Conductive elastomers tolerant/sensitive to mechanical deformations highlight possibilities for versatile monitoring/sensing components, particularly the strain-tolerant composites retain high levels of conductivities even under tensile strains of ~550%. Demonstrations of soft electronic grippers and transient, suture-free cardiac jackets could be the cornerstone for sophisticated, multifunctional biodegradable electronics in the fields of soft robots and biomedical implants.

Skin-Interfaced Superhydrophobic Insensible Sweat Sensors for Evaluating Body Thermoregulation and Skin Barrier Functions.

Monitoring sweat rate is vital for estimating sweat loss and accurately measuring biomarkers of interest. Although various optical or electrical sensors have been developed to monitor the sensible sweat rate, the quantification of the insensible sweat rate that is directly related to body thermoregulation and skin barrier functions still remains a challenge. This work introduces a superhydrophobic sweat sensor based on a polyacrylate sodium/MXene composite sandwiched between two superhydrophobic textile layers to continuously measure sweat vapor from insensible sweat with high sensitivity and rapid response. The superhydrophobic textile on a holey thin substrate with reduced stiffness and excellent breathability allows the permeation of sweat vapor, while preventing the sensor from being affected by the external water droplets and internal sensible sweat. Integrating the insensible sweat sensor with a flexible wireless communication and powering module further yields a standalone sensing system to continuously monitor insensible sweat rates at different body locations for diverse application scenarios. Proof-of-concept demonstrations on human subjects showcase the feasibility to continuously evaluate the body's thermoregulation and skin barrier functions for the assessment of thermal comfort, disease conditions, and nervous system activity. The results presented in this work also provide a low-cost device platform to detect other health-relevant biomarkers in the sweat (vapor) as the next-generation sweat sensor for smart healthcare and personalized medicine.