Smart Wearable Devices Research Articles

Porous nanofibers and micro-pyramid structures array for high-performance flexible pressure sensors

Flexible pressure sensors have attracted extensive research interest as smart wearable devices’ core components. However, developing flexible pressure sensors with high sensitivity and wide pressure detection range remains a great challenge. Utilizing electrospinning and mould transfer technology, this paper presents a novel ‘sandwich’ flexible pressure sensor composed of a sensitive layer of poly (lactic acid) (PLA) porous nanofiber network film and electrodes made of polydimethylsiloxane (PDMS) micro-pyramid structure array film. Through ultrasonic treatment, carbon black particles penetrate into the PLA porous nanofiber film, which effectively enhances the conductivity of the PLA film. Due to the complex conductive pathways formed by the ultra-high specific surface area of the PLA porous nanofibers and the three-dimensional amplification structure of the PDMS micro-pyramid arrays, the sensor has a high sensitivity of 54.06 kPa−1, a wide detection range of 0–56 kPa, an ultra-low detection limit of 2.5 Pa and excellent durability (10000 cycles). Impressively, the sensor is able to accurately monitor various physiological activities of the human body in real time, which is believed to be a strong impetus for the development of the next generation of wearable products.

Advances in Wearable Multifunctional Devices Based on Human‐Body Energy Harvesting

AbstractWearable electronics with multi‐functionalities are widely utilized in various domains, including everyday living, healthcare, military training, and sports. Advances in flexible electronic technology, new materials, artificial intelligence technology, and sensor technology have accelerated the rapid development of smart wearable devices toward multifunctional and highly integrated trends. The energy supply technology based on the human‐body energy harvesting method endows wearable, multifunctional electronic devices with sustainable, renewable, and self‐powered characteristics, which proposes a solution strategy for the function expansion and energy supply of wearable devices. Herein, this paper discusses recent research on various methods of harvesting human body energy and wearing parts respectively, focusing on the new materials, structures, and processes involved in the representative studies, as well as the impact on energy harvesting and output, and functional applications. Furthermore, the challenges and obstacles faced in the creation of wearable multifunctional devices based on human self‐sufficiency and propose solution strategies to propel them in order to advance the creation of the next wave of intelligent wearable technology are also discussed.

Skin-Friendly Flexible Ultraviolet Detectors Based on Reversibly Deformable Worm-Like Polymer Nanoparticles.

Flexible ultraviolet (UV) light detection technology has important applications in wearable devices, smart sensors, and other fields and attracts much attention in recent years. However, for most semiconductor-based UV detectors, the elastic modulus between rigid semiconductors and flexible substrates is mismatched, which makes it difficult to fabricate UV detectors that meet the needs of wearable devices. Herein, a fully flexible, large-scale, skin-friendly UV photodetector component centered on photo-responsive worm-like polymer nanoparticles (NPs) is developed, and the resulting device can quantitatively detect UV illumination. Skin-friendly poly(vinyl alcohol) (PVA), amphiphilic azobenzene-containing polymer NPs (AzNPs), and water-soluble ionic liquids (IL) are formed into (AzNPs-IL)/PVA fabrics by electrospinning. There are interactions such as hydrogen bonding among PVA, AzNPs, and IL, which make the material system stable. The UV detector made of the fabric realizes UV sensing through the illuminance-mechanical stress-electrical signal conversion mechanism. It is capable of achieving a response time of 9 s, a detection range of 10-150mW cm-2 , and stability for 1000 cycle tests upon 365nm UV irradiation. Moreover, it has good skin affinity, and the water contact angle of the fabric is only 23.57°, which holds great promise for wearable smart devices.

Appropriate addition power for aphakic infants determined by a smart wearable device Clouclip

ABSTRACT Clinical relevance It is particularly important to perform reasonable and effective optical correction to enable visual development after primary lens removal surgery for congenital cataracts. Aphakic infants need a suitable addition power of prescription (ADD) to help them focus on close visual objects. Background It is challenging to obtain appropriate ADD power for infants due to poor cooperation and lack of subjective feedback. We aimed to determine the appropriate ADD for aphakic infants using a recently developed smart wearable device called Clouclip. Methods The study was a cross-sectional, observational pilot study. Twenty-three aphakic infants (aged from 6 months to 3.5 years) were invited to wear a smart wearable device for 7 days consecutively to monitor the near viewing distance in real life. Viewing habits and its associations with the possible influencing factors were investigated based on the data obtained from the device. Results The average proportion of near viewing time was 77.9% (95% confidence interval (CI) 72.1–83.7%). The average of the median near viewing distance was 23.8 cm (95% CI 20.6 cm-27.0 cm), which corresponded to an ADD of +4.25 D (95% CI + 3.75 D – +4.75 D) spectacle prescription. The height of the child was found to be positively correlated with the median of near viewing distance (r = 0.646, p = 0.001). Age, current ADD, age of cataract extraction surgery and bilaterality or monocularity of the aphakic eyes showed no significant correlation with the aforementioned viewing habits (all p > 0.05). Conclusion By using the novel wearable device, we found the suitable ADD of spectacle prescription for aphakic infants is about +4.25 D. The height of the child was an influencing factor for ADD.

Three-dimensional surface strain sensor based on PDMS/LIG composite film with adjustable electromechanical performance

Flexible strain sensors play a crucial role in health monitoring, smart wearable devices, and human–machine interaction. Three-dimensional surface evaluation methods for strain sensors offer advantages by being closer to actual strain, featuring a larger working range, and being more suitable for multidirectional strain. In this study, a three-dimensional (3D) surface strain sensor based on polydimethylsiloxane/laser-induced graphene (PDMS/LIG) composite films has been developed. The electromechanical properties of this sensor, encompassing 3D strain range and sensitivity, can be adjusted by manipulating laser parameters and LIG patterns. The key to attaining these specific characteristics lies in the intentional design of crack types and orientations on the sensor's surface. Remarkably, the line-vertical (LV) sensor exhibits outstanding sensitivity with a GF of 211.3. The line-parallel (LP) sensor achieves a GF of 115.1. Additionally, it demonstrates a stretching range of 25% and maintains stable performance over an extensive number of strain/release test cycles (more than 3000 cycles). With these advantages, the 3D strain sensor can not only be applied in human activity monitoring but also monitoring pressure within microchannels in microfluidic chips, suggesting promising applications in the health and medical fields.

Epoxy resin reinforced high-performance conductive composite foam with ultra-wide pressure sensing range

Flexible piezoresistive sensors based on conductive polymer composites (CPCs) have shown great potential and application in smart wearable devices, sports and health monitoring. Nevertheless, the practical use of many CPCs pressure sensors is often limited by their narrow monitoring range and low sensitivity. Here, a thermoplastic urethane/ epoxy resin/ carbon nanotubes/ polydopamine/ Ti3C2TX MXene (TPU/EP/CNT/PDA/MXene) composite foam was prepared using the commonly used freeze-drying and impregnation methods. Due to the high strength of the EP/TPU foam matrix and CNT@MXene's internal and external synergistic conductive network, the TECPMF has outstanding mechanical and conductive properties. As a result, the foam pressure sensor has an extremely wide monitoring range (0∼300 kPa) and a sensitivity of 2.42 kPa−1 (0∼5 kPa). Furthermore, the superior performance of the foam provides fast response (100 ms) and outstanding durability of more than 8000 cycles. The piezoresistive TECPMF sensor can be used for real-time monitoring of human movement, as well as the magnitude and position of various pressures and air pressures. These promise to enable a wide range of smart wearable and engineering applications. This work opens up a new avenue for the design of more advanced piezoresistive sensors.

Flexible, hydrophobic, and robust composite films with sandwich structure for electromagnetic interference shielding and Joule heating

Electromagnetic interference (EMI) shielding materials with favorable flexibility, robustness, and multipurpose capabilities are urgently desired for smart wearable devices. Herein, flexible PDMS/cellulose nanofiber/Ag nanowire composite films with sandwich structures were successfully fabricated by a facile method. First, silver nanowires (AgNWs) were uniformly stacked in the upper part of the cellulose gel using a controlled two-step vacuum-assisted filtration; next, AgNWs were tightly embedded in the cellulose matrix by a hot-pressing strategy; finally, a hydrophobic protective layer, PDMS, was introduced. The water contact angle (WCA) of composite films could reach 121°. Compared with uniformly mixed films, AgNWs deposited only on the surface of the matrix allowed the conductivity to reach 381 S/cm at a low weight fraction of AgNWs (6 wt%). Thanks to such excellent conductivity, the composite films exhibited superior EMI shielding effectiveness (49 dB) at only 40 μm thickness, and Joule heating performance, i.e., the surface temperature reached 111.3 °C at 1.5 V driving voltage. It was worth noting that after bending and peeling damage, the WCA and EMI shielding effectiveness of composite films were not significantly impacted due to the hot-pressing strategy and hydrophobic surface protection. The robust composite films show huge application potential in the wearable electronics field.

Graphene Oxide Wrapped VO2 Nanobelts for Calendar‐Life Zn Storage Devices

AbstractAqueous zinc ion batteries (AZIBs) are thought to be emerging energy storage systems due to their features with high safety, low cost, and eco‐friendliness. They possess potential applications in smart grids and wearable devices. However, it is still a challenge to design suitable cathode materials that matches well with anode. Herein, graphene oxide (GO) coated VO2 nanobelts are prepared through a facile hydrothermal route. The Zn//VO2@GO batteries deliver a specific capacity of 323 mA h g−1 at a current density of 0.1 A g−1. It maintains an 88% of capacity retention rate at 5 A g−1 after 1000 times cycling. Moreover, the assembled flexible cells demonstrate excellent mechanical stability under different folding conditions.

Prediction of the efficacy of group cognitive behavioral therapy using heart rate variability based smart wearable devices: a randomized controlled study

BackgroundDepression and anxiety are common and disabling mental health problems in children and young adults. Group cognitive behavioral therapy (GCBT) is considered that an efficient and effective treatment for these significant public health concerns, but not all participants respond equally well. The aim of this study was to examine the predictive ability of heart rate variability (HRV), based on sensor data from consumer-grade wearable devices to detect GCBT effectiveness in early intervention.MethodsIn a study of 33 college students with depression and anxiety, participants were randomly assigned to either GCBT group or a wait-list control (WLC) group. They wore smart wearable devices to measure their physiological activities and signals in daily life. The HRV parameters were calculated and compared between the groups. The study also assessed correlations between participants’ symptoms, HRV, and GCBT outcomes.ResultsThe study showed that participants in GCBT had significant improvement in depression and anxiety symptoms after four weeks. Higher HRV was associated with greater improvement in depressive and anxious symptoms following GCBT. Additionally, HRV played a noteworthy role in determining how effective GCBT was in improve anxiety(P = 0.002) and depression(P = 0.020), and its predictive power remained significant even when considering other factors.ConclusionHRV may be a useful predictor of GCBT treatment efficacy. Identifying predictors of treatment response can help personalize treatment and improve outcomes for individuals with depression and anxiety.Trial registrationThe trial has been retrospectively registered on [22/06/2023] with the registration number [NCT05913349] in the ClinicalTrials.gov.Condensed abstractVariations in heart rate variability (HRV) have been associated with depression and anxiety, but the relationship of baseline HRV to treatment outcome in depression and anxiety is unclear. This study predicted GCBT effectiveness using HRV measured by wearable devices. 33 students with depression and anxiety participated in a trial comparing GCBT and wait-list control. HRV parameters from wearables correlated with symptoms (PHQ, PSS) and GCBT effectiveness. Baseline HRV levels are strongly associated with GCBT treatment outcomes. HRV may serve as a useful predictor of efficacy of GCBT treatment,facilitating personalized treatment approaches for individuals with depression and anxiety.

Applying punching without die to micro-hole array processing

Aluminum alloy (Al6061) sheet micro-hole processing is extensively used in smartphones, tablet PC, and smart wearable devices. The micro-hole processing is commonly performed using laser, micro drilling, micropunching, micro discharge, and chemical etching technologies. Micro-punching technology is characterized by precision and rapid processing, but the precision positioning of the punch head and lower die is one of the major difficulties in micro-hole punching, especially in manufacturing array micro-holes. This study used punching without die technology. This technology uses an array punch head to punch the lower die holes on the base, then performs array micro-hole punching. The experimental results show that a micro-hole array with 37 micro-holes were successfully manufactured and can be reproduced many times. Tapered array micro-holes with a high aspect ratio can be manufactured using this punching without die technology; the micro-hole depth can be 260 μm, the inlet diameter is 116 μm, and the outlet diameter is 25 μm. This study has successfully developed the feasibility of array micro-hole punching technology.

Design and development of a horizontal contact separated (HCS) test setup for measuring the performance of triboelectric nanogenerator for sustainable energy harvesting applications.

Triboelectric nanogenerators (TENGs) can play a pivotal role in harnessing non-utilized reciprocating motion and convert it into electrical energy that can later be stored in a battery or capacitor to power various Internet of Things-based smart electronic and wearable devices. Herein, we designed a cost-effective instrumental test bed focused on investigating the output performance of a horizontal contact separation mode triboelectric nanogenerator by varying the input parameters, such as applied force, motor speed, triboplate separation, and frequency of instrumental setup. The test bed mainly consists of three major parts: (i) application of force, (ii) tapping of TENG sample, and (iii) output parameters measurement. The output performance in terms of open circuit output voltage (VOC), short circuit current (ISC), and power density of polydimethylsiloxane-based TENG was monitored and optimized by varying the input parameters. A low-cost current measuring circuitry using an operational amplifier integrated circuit has been proposed with 92% accuracy. The maximum value of VOC and ISC was observed to be 254V and 31.8 µA at a motor speed of 600rpm, the distance between both the plates was 6mm, the input applied force of 40 N, and the striking frequency of 3Hz. The maximum power density of 2.1 W/m2 was obtained at an input impedance of 8 kΩ. The durability of the test bed as well as the TENG sample was also measured for 25h. The degree of uncertainty was measured for VOC, ISC, and applied force and calculated to be 1.62%, 7.45%, and 6.27%, respectively.

Waste Cotton-Derived Fiber-Based Thermoelectric Aerogel for Wearable and Self-Powered Temperature–Compression Strain Dual-Parameter Sensing

The rapid development of the global economy and population growth are accompanied by the production of numerous waste textiles. This leads to a waste of limited resources and serious environmental pollution problems caused by improper disposal. The rational recycling of wasted textiles and their transformation into high-value-added emerging products, such as smart wearable devices, is fascinating. Here, we propose a novel roadmap for turning waste cotton fabrics into three-dimensional elastic fiber-based thermoelectric aerogels by a one-step lyophilization process with decoupled self-powered temperature–compression strain dual-parameter sensing properties. The thermoelectric aerogel exhibits a fast compression response time of 0.2 s, a relatively high Seebeck coefficient of 43 μV·K−1, and an ultralow thermal conductivity of less than 0.04 W·m−1·K−1. The cross-linking of trimethoxy(methyl)silane (MTMS) and cellulose endowed the aerogel with excellent elasticity, allowing it to be used as a compressive strain sensor for guessing games and facial expression recognition. In addition, based on the thermoelectric effect, the aerogel can perform temperature detection and differentiation in self-powered mode with the output thermal voltage as the stimulus signal. Furthermore, the wearable system, prepared by connecting the aerogel-prepared array device with a wireless transmission module, allows for temperature alerts in a mobile phone application without signal interference due to the compressive strains generated during gripping. Hence, our strategy is significant for reducing global environmental pollution and provides a revelatory path for transforming waste textiles into high-value-added smart wearable devices.

Sustainable Data-Driven Strategies and Active Well-Being: A Case Study

Nowadays the world is characterized by an increasingly aging society. This phenomenon represents a risk for the sustainability of the healthcare system. One of the factors that can accelerate the consequences of the aging process is sedentary behavior. Currently, there is a large availability of wearable smart devices and mobile applications, that can collect data. However, some social and functional problems were observed, therefore we believe that there is great room for improvement (Mincolelli et al., 2018). In addition, the paradigm of the Internet of Things is enabling those applications to share data with other programs and smart devices, which, in turn, can generate an ecosystem of services that can improve the quality of life, not only of the single user, but of many groups of a determined social context. The contribution presents a case study (PLEINAIR project) that focuses specifically on the development of Human-Centered outdoor smart technologies that can adapt themselves to the necessities of people of all ages and abilities in order to encourage them of taking care of their health.

Smart Bracelet Design and Function Improvement

With the increasing development and popularity of smart wearable devices, smart bracelets have become one of the hottest smart devices today. Through a comparative analysis of existing products, this paper proposes improvement strategies in the three main directions of UI and module design, security, and handling of health issues to provide a product that is easier to use and meets the health needs of the elderly. For the direction of UI and module design, it is proposed to add the gesture recognition function and develop it in the direction of non-contact recognition based on the existing technology, and at the same time, use machine learning to achieve personalized recognition. Based on personalized module design, a GPS tracking device is installed to prevent users from being tracked, and a new network module is added to enable users to get in touch with others at a time when they encounter danger in remote areas. Improvement strategies in the security direction include data transmission, storage, and device security. The smart bracelet can use trusted computing for data encryption and storage by adding low-power core and optimizing the data transmission in three paths: local area network (LAN), public network (PN), and the cloud.Regarding health problem processing, it is proposed to achieve fall prevention through scene recognition and optimize the fall detection function through user information. In addition, this paper takes UV irradiation as an example to point out that smart bracelet devices can be added with new indicator detection technology to prevent some diseases. At the same time, a full voice interaction system can be developed to meet the social needs of the elderly.

PASSO Project: Design of a Smart System Using Biofeedback to Train People with Parkinson’s Disease

This paper describes the design process of a smart system monitoring and training the gait and posture of people with Parkinson’s disease. The project aimed to develop an innovative mHealth system and validate it in a laboratory context. The designed solution is supposed to help people in postponing the rise of the most impairing symptoms and prolong autonomy. The project was divided into three main design cycles regarding respectively the design and test of sensory signals, the smart wearable devices transmitting them, and the system interface. The multidisciplinary team involved in the project followed a User-Centered methodology, involving users in the design process to improve the system’s usability and accessibility. The adopted methodological strategy led to satisfactory results and proved to be particularly suitable for multidisciplinary design processes involving both human and technological factors related to the development of smart systems targeted to niche users.

Laser etching of on-chip ultra-high stability flexible micro MnO2//Zn batteries

Micro zinc batteries have great potential in fields such as smart clothing, wearable devices, and implantable medical devices, due to their high-energy density and biocompatibility, etc. However, the side reactions in Zn anode have limited their lifespan. Here we design a high stable fork-finger-shaped electrode using laser etching to obtain MnO2//Zn flexible miniature zinc ion batteries. And then, a carbon slurry is introduced to inhibit hydrogen evolution to suppress the detachment of the zinc anode. Compared with Au/PET interface, the PET/C interface had lower water retention and higher hydrogen evolution production barrier based on first-principles calculation. The interdigital electrode based on PET/C/Au had good stability. The micro MnO2–Zn flexible battery showed high specific capacity of 0.091 mAh/cm2 at 0.1 mA. After 5000 cycles at 0.5 mA, the capacity retention rate reached 83.6%. This study of interdigital electrode by laser etching brings an inspired universal pathway to fabricate a reversible Zn anode for micro-zinc storage systems.

Application of Traditional Method and Smart Wearable Devices in Monitoring Physical Fitness: A Comparative Study

Application of Traditional Method and Smart Wearable Devices in Monitoring Physical Fitness: A Comparative Study

High-Performance Piezoelectric Nanogenerator of BTO-PVDF Nanofibers for Wearable Sensing.

Piezoelectric nanogenerator (PENG) produces stable electrical signals in response to external mechanical stimuli and holds promise in the fields of flexible sensors and smart wearable devices. In practice, a high-performance PENG with a straightforward structure and exceptional reliability is deeply desired. This study optimally synthesizes piezoelectric composites comprising polyvinylidene fluoride (PVDF) incorporated with barium titanate (BTO) nanoparticles (NPs) and fabricated a PENG with heightened sensitivity by using the electrospinning technique. The polar β-phase content of the dual-optimized BTO-PVDF (barium titanate and polyvinylidene fluoride) electrospun fiber reaches up to 82.39%. In the bending mode, it achieves a remarkable maximum open-circuit voltage of 19.152V, a transferred charge of 8.058 nC, and an output voltage per unit area of 2.128Vcm- 2. Under vertical pressure conditions, the BP-PENG exhibits an impressive voltage of 12.361V while the force is 2.156 N, demonstrating a notable pressure sensing sensitivity of 5.159VkPa-1, with an excellent linear relationship. Furthermore, the BP-PENG displays sensitive sensing features in monitoring hand movements. The sensitive response and high performance make it promising for applications in human motion monitoring and smart wearable devices.

Seamless Integration of Conducting Hydrogels in Daily Life: From Preparation to Wearable Application.

Conductive hydrogels (CHs) have received significant attention for use in wearable devices because they retain their softness and flexibility while maintaining high conductivity. CHs are well suited for applications in skin-contact electronics and biomedical devices owing to their high biocompatibility and conformality. Although highly conductive hydrogels for smart wearable devices are extensively researched, a detailed summary of the outstanding results of CHs is required for a comprehensive understanding. In this review, the recent progress in the preparation and fabrication of CHs is summarized for smart wearable devices. Improvements in the mechanical, electrical, and functional properties of high-performance wearable devices are also discussed. Furthermore, recent examples of innovative and highly functional devices based on CHs that can be seamlessly integrated into daily lives are reviewed.

Structurally engineered 3D porous graphene based phase change composite with highly efficient multi-energy conversion and versatile applications

Micro-nano encapsulation strategy combining three-dimensional (3D) porous carriers and phase change materials (PCMs) has been widely investigated due to its structure stability, high efficiency, and designability. However, the current 3D scaffolds suffering from structure regularity are hard to meet the urgent requirements of high energy conversion efficiency and versatile applications. Herein, a 3D porous graphene scaffold (2LrGO@LIG), which is fabricated from polybenzoxazine/graphene oxide (GO) composite using laser irradiation that structurally engineers a gully-shaped surface and a 3D overlapped graphene networks, was employed for PCMs encapsulation. The addition of GO is proved to enhance the quality of produced laser induced graphene (LIG), which could also be reduced into laser-reduced graphene oxide (LrGO) and connect the adjacent LIGs as thermal bridges. As a consequence, the obtained phase change composite (2LrGO@LIG/MA) showed photo-thermal and electro-thermal conversion efficiency of 94.1 % and 99.1 %, respectively. In addition, benefiting from the surface hydrophobicity (135°), high energy storage density (167.7 J/g) and electrical conductivity (307.9 S/m), 2LrGO@LIG/MA also demonstrated great potential in smart building materials and wearable electronic devices. This study provides a facile method for designing advanced PCM composites with multi-energy conversion capacity and application versatility.