A dual-mode fiber-shaped flexible capacitive strain sensor fabricated by direct ink writing technology for wearable and implantable health monitoring applications

Flexible fiber-shaped strain sensors show tremendous potential in wearable health monitoring and human‒machine interactions due to their compatibility with everyday clothing. However, the conductive and sensitive materials generated by traditional manufacturing methods to fabricate fiber-shaped strain sensors, including sequential coating and solution extrusion, exhibit limited stretchability, resulting in a limited stretch range and potential interface delamination. To address this issue, we fabricate a fiber-shaped flexible capacitive strain sensor (FSFCSS) by direct ink writing technology. Through this technology, we print parallel helical Ag electrodes on the surface of TPU tube fibers and encapsulate them with a high dielectric material BTO@Ecoflex, endowing FSFCSS with excellent dual-mode sensing performance. The FSFCSS can sense dual-model strain, namely, axial tensile strain and radial expansion strain. For axial tensile strain sensing, FSFCSS exhibits a wide detection range of 178%, a significant sensitivity of 0.924, a low detection limit of 0.6%, a low hysteresis coefficient of 1.44%, and outstanding mechanical stability. For radial expansion strain sensing, FSFCSS demonstrates a sensitivity of 0.00086 mmHg-1 and exhibits excellent responsiveness to static and dynamic expansion strain. Furthermore, FSFCSS was combined with a portable data acquisition circuit board for the acquisition of physiological signals and human‒machine interaction in a wearable wireless sensing system. To measure blood pressure and heart rate, FSFCSS was combined with a printed RF coil in series to fabricate a wireless hemodynamic sensor. This work enables simultaneous application in wearable and implantable health monitoring, thereby advancing the development of smart textiles.

Wearable Iontronic FMG for Classification of Muscular Locomotion

Human motion recognition with high accuracy, fast response speed has long been considered an essential component in human-machine interactive activities such as assistive robotics, medical prosthesis, and wearable electronics. This study proposed a novel human lower limb locomotion classification strategy based on flexible supercapacitive iontronic sensors. Benefiting from the ultrahigh sensitivity (up to 1 nF/mmHg) and low activation pressure (less than 3 mmHg) of the supercapacitive iontronic pressure sensor, force myography (FMG) signal was acquired more accurately from 5 iontronic sensors strapped to the thigh (5 percentage point improvement compared with force sensitive resistor (FSR) in low window length). In the experiment with 12 subjects, the real-time classification strategy based on sliding window and SVM model gave an average locomotion classification accuracy of 99% for seven categories, including sitting, standing, walking on level ground, ramp ascent, ramp descent, stair ascent, stair descent. Compared with traditional FSR sensors, the result showed that iontronic sensors improved the classification accuracy by 5 percentage points in the case of short time window. The implementation of the high sensitivity flexible iontronic sensors in the wearable system brings a valuable tool for detecting small human body pressure signals and has great potential to improve the performance of the human-machine interface in rehabilitation and medical applications.

Highly stable flexible pressure sensors with a quasi-homogeneous composition and interlinked interfaces

Electronic skins (e-skins) are devices that can respond to mechanical stimuli and enable robots to perceive their surroundings. A great challenge for existing e-skins is that they may easily fail under extreme mechanical conditions due to their multilayered architecture with mechanical mismatch and weak adhesion between the interlayers. Here we report a flexible pressure sensor with tough interfaces enabled by two strategies: quasi-homogeneous composition that ensures mechanical match of interlayers, and interlinked microconed interface that results in a high interfacial toughness of 390 J·m⁻². The tough interface endows the sensor with exceptional signal stability determined by performing 100,000 cycles of rubbing, and fixing the sensor on a car tread and driving 2.6 km on an asphalt road. The topological interlinks can be further extended to soft robot-sensor integration, enabling a seamless interface between the sensor and robot for highly stable sensing performance during manipulation tasks under complicated mechanical conditions.

E-skins often have poor interfaces that lead to unstable performances. Here, authors report e-skins with a quasi-homogeneous composition and bonded micro-structured interfaces, through which both the sensitivity and stability of the devices are improved.

Electrical Failure Mechanism in Stretchable Thin-Film Conductors

Stretchable thin-film conductors are basic building blocks in advanced flexible and stretchable electronics. Current research mainly focuses on strategies to improve stretchability and widen the range of applications of stretchable conductors. However, stability should not be neglected, and the electrical failure mode is one of the most common stability issues that determines the current range and duration in a circuit. In this work, we report the electrical failure mechanism of stretchable conductors. We find a special failure mode for the stretchable conductors, which can be attributed to the coupling effect between local thermal strains and dynamic resistance changes of the thin film. This creates a vicious circle that significantly differs from traditional conductors. Physical parameters related to this special failure mode are investigated in detail. It is found that this mechanism is applicable to different kinds of stretchable conductors. Based on this finding, we also explore methods to modulate the failure of stretchable conductors. The failure mechanism found here provides a fundamental understanding of the current effect of stretchable circuits and is crucial for designing stable stretchable bioelectrodes and circuits.

Insole-Based Systems for Health Monitoring: Current Solutions and Research Challenges

Wearable health monitoring devices allow for measuring physiological parameters without restricting individuals' daily activities, providing information that is reflective of an individual's health and well-being. However, these systems need to be accurate, power-efficient, unobtrusive and simple to use to enable a reliable, convenient, automatic and ubiquitous means of long-term health monitoring. One such system can be embedded in an insole to obtain physiological data from the plantar aspect of the foot that can be analyzed to gain insight into an individual's health. This manuscript provides a comprehensive review of insole-based sensor systems that measure a variety of parameters useful for overall health monitoring, with a focus on insole-based PPD measurement systems developed in recent years. Existing solutions are reviewed, and several open issues are presented and discussed. The concept of a fully integrated insole-based health monitoring system and considerations for future work are described. By developing a system that is capable of measuring parameters such as PPD, gait characteristics, foot temperature and heart rate, a holistic understanding of an individual's health and well-being can be obtained without interrupting day-to-day activities. The proposed device can have a multitude of applications, such as for pathology detection, tracking medical conditions and analyzing gait characteristics.

Review of Recent Technologies for Tackling COVID-19

The current pandemic caused by the COVID-19 virus requires more effort, experience, and science-sharing to overcome the damage caused by the pathogen. The fast and wide human-to-human transmission of the COVID-19 virus demands a significant role of the newest technologies in the form of local and global computing and information sharing, data privacy, and accurate tests. The advancements of deep neural networks, cloud computing solutions, blockchain technology, and beyond 5G (B5G) communication have contributed to the better management of the COVID-19 impacts on society. This paper reviews recent attempts to tackle the COVID-19 situation using these technological advancements.

HIGH-INTENSITY TRAINING ON PULSE AND DICROTIC WAVEFORM IN CHRONIC DISEASES

ABSTRACT Introduction: The formation and propagation of pulse waves are mainly accomplished by coordinating the heart and the vascular system. The contraction and relaxation of the heart are the sources of pulse waves. The aorta vibrates regularly as the heart contracts. This vibration propagates forward along the elastic blood vessel to form a pulse wave. The pulse wave contains very rich physiological and pathological information about the cardiovascular system. If there is a problem with the heart's structure, it can cause abnormal pulse waveforms. Objective: This article analyzes pulse waveform changes and blood flow during high-intensity interval training. It combines the test results to guide the exercise rehabilitation treatment of patients with chronic diseases. Methods: Pulse waves were collected from subjects under different exercise loads and the characteristics of pulse wave parameters under intermittent exercise were studied. Results: An athlete's pulse wave response is different in the case of high-intensity intermittent exercise. There are differences in the cardiovascular response of patients with different body weights. Conclusion: High-intensity interval training can improve the cardiovascular function of patients with chronic diseases and affect their pulse waveform. Level of evidence II; Therapeutic studies - investigation of treatment results.

Blink-sensing glasses: A flexible iontronic sensing wearable for continuous blink monitoring

Blink reflex has long been considered closely related to physiological states, from which abundant information on ocular health and activities can be revealed. In this study, a smart glasses wearable has been developed, incorporating a flexible and sensitive pressure sensor, to monitor blink patterns by continuously detecting ocular muscular movements, referred to as blink-sensing glasses. By applying the emerging flexible iontronic sensing (FITS) sensor with the sensitivity of 340 pF/mmHg, the skin pressure variations induced by movements of the orbicularis oculi muscles can be monitored in real time. The blink-sensing glasses can successfully capture blink patterns with a high accuracy of 96.3% and have been used to differentiate the blink features from both dry-eye subjects and healthy controls. This device can be potentially used as a new clinical and research monitoring tool for continuous eye blink analysis, while providing patients with high comfortableness in long-term ambulatory and home settings.

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Blink-sensing glasses can capture blink patterns with clinical-grade high accuracy

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A FITS sensor is applied to monitor the blink by detecting the muscle movement

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Blink-sensing glasses can be of potential use to prognose the dry eye

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The glasses are a continuous detection manner with immunity to ambient lights

First Decade of Interfacial Iontronic Sensing: From Droplet Sensors to Artificial Skins

Over the past decade, a brand-new pressure- and tactile-sensing modality, known as iontronic sensing has emerged, utilizing the supercapacitive nature of the electrical double layer (EDL) that occurs at the electrolytic-electronic interface, leading to ultrahigh device sensitivity, high noise immunity, high resolution, high spatial definition, optical transparency, and responses to both static and dynamic stimuli, in addition to thin and flexible device architectures. Together, it offers unique combination of enabling features to tackle the grand challenges in pressure- and tactile-sensing applications, in particular, with recent interest and rapid progress in the development of robotic intelligence, electronic skin, wearable health as well as the internet-of-things, from both academic and industrial communities. A historical perspective of the iontronic sensing discovery, an overview of the fundamental working mechanism along with its device architectures, a survey of the unique material aspects and structural designs dedicated, and finally, a discussion of the newly enabled applications, technical challenges, and future outlooks are provided for this promising sensing modality with implementations. The state-of-the-art developments of the iontronic sensing technology in its first decade are summarized, potentially providing a technical roadmap for the next wave of innovations and breakthroughs in this field.

iWRAP: A Theranostic Wearable Device With Real-Time Vital Monitoring and Auto-Adjustable Compression Level for Venous Thromboembolism

OBJECTIVE

Venous Thromboembolism (VTE) is a commonly underdiagnosed disease with severe consequences and an exceedingly high mortality rate. Conventional compression wraps are devised for therapeutic purpose but lack diagnostic capacity. Recent advances in flexible electronics and wearable technologies offer many possibilities for chronic disease management. In particular, vital signs have been studied to show a strong correlation with the risk of VTE patients. In this study, we aim to develop an intelligent theranostic compression device, referred to as iWRAP, with the built-in capacity of real-time vital sign monitoring together with auto-adjustable compression level.

METHODS

An instantaneous pneumatic feedback control with a high-resolution pressure sensor is integrated to provide a highly stabilized compression level at the prescribed interface pressure for an improved therapeutic outcome. Meanwhile, arterial pulse waveforms extracted from the pressure readings from the smart compression device can be utilized to derive the body vital signs, including heart rate (HR), respiratory rate (RR) and blood pressure (BP).

RESULTS

A reliable delivery of the targeted compression level within ±5% accuracy in the range of 20-60 mmHg has been achieved through the feedback of the interface pressure. Both HR and RR have been measured within clinical-grade accuracies. Moreover, BP estimated using an ALA model has been achieved at low compression levels, which is also within a clinical-acceptable accuracy. The acquired vital information has been instantaneously fit into the clinically acceptable criteria for life-threatening PE risk with timely assessments.

CONCLUSION

The iWRAP has shown the potential to become the first theranostic wearable device with both continuous delivery of accurate and effective compression therapy and real-time monitoring of life-threatening conditions for VTE patients.

Optical difference in the frequency domain to suppress disturbance for wearable electronics

Measurements based on optics offer a wide range of unprecedented opportunities in the biological application due to the noninvasive or non-destructive detection. Wearable skin-like optoelectronic devices, capable of deforming with the human skin, play significant roles in future biomedical engineering such as clinical diagnostics or daily healthcare. However, the detected signals based on light intensity are very sensitive to the light path. The performance degradation of the wearable devices occurs due to device deformation or motion artifact. In this work, we propose the optical difference in the frequency domain of signals for suppressing the disturbance generated by wearable device deformation or motion artifact during the photoplethysmogram (PPG) monitoring. The signal processing is simulated with different input waveforms for analyzing the performance of this method. Then we design and fabricate a wearable optoelectronic device to monitor the PPG signal in the condition of motion artifact and use the optical difference in the frequency domain of signals to suppress irregular disturbance. The proposed method reduced the average error in heart rate estimation from 13.04 beats per minute (bpm) to 3.41 bpm in motion and deformation situations. These consequences open up a new prospect for improving the performance of the wearable optoelectronic devices and precise medical monitoring in the future.

A Review of Smart Technologies Embedded in Shoes

Technological advancements in wearable devices have revolutionized smart shoes. Smart shoes are sometimes referred to as intelligent shoes or computer-based shoes. They are capable of recognizing and recording data from day-to-day activities by the user. Such smart shoes are designed with sensors, vibrating motors, GPS, wireless systems, and various other sensors/actuators for the comfort and benefit of the wearer. In the current manuscript, we are reviewing various technologies that are implemented in smart shoes.

An Instrumented Urethral Catheter with a Distributed Array of Iontronic Force Sensors

This paper develops a novel instrumented urethral catheter with an array of force sensors for measuring the distributed pressure in a human urethra. The catheter and integrated portions of the force sensors are fabricated by the use of 3D printing using a combination of both soft and hard polymer substrates. Other portions of the force sensors consisting of electrodes and electrolytes are fabricated separately and assembled on top of the 3D-printed catheter to create a soft flexible device. The force sensors use a novel supercapacitive (iontronic) sensing mechanism in which the contact area between a pair of electrodes and a paper-based electrolyte changes in response to force. This provides a highly sensitive measure of force that is immune to parasitic noise from liquids. The developed catheter is tested using a force calibration test rig, a cuff-based pressure application device, an extracted bladder and urethra from a sheep and by dipping inside a beaker of water. The force sensors are found to have a sensitivity of 30-50 nF/N, which is 1000 times larger than that of traditional capacitive force sensors. They exhibit negligible capacitance change when dipped completely in water. The pressure cuff tests and the extracted sheep tissue tests also verify the ability of the sensor array to work reliably in providing distributed force measurements. The developed catheter could help diagnose ailments related to urinary incontinence and inadequate urethral closure pressure.