Wearable and Flexible Sensor Devices: Recent Advances in Designs, Fabrication Methods, and Applications

Jawli A., Nabi G., Huang Z.

Multiparametric ultrasound (mpUS) enhances prostate cancer (PCa) diagnosis by using multiple imaging modalities. Tissue-mimicking materials (TMM) phantoms, favoured over animal models for ethical and consistency reasons, were created using polyvinyl alcohol (PVA) with varying molecular weights (Mw). Methods: Four PVA samples, varying in Mw with constant concertation, were mixed with glycerol, silicon carbide (SiC), and aluminium oxide (Al2O3). Phantoms with varying depth and inclusion sizes were created and tested using shear-wave elastography (SWE). An mpUS phantom was developed to mimic prostate tissue, including isoechoic and hypoechoic inclusions and vessels. The phantom was scanned using supersonic ultrasound, strain elastography, and Doppler ultrasound. Validation was performed using radical prostatectomy data and shear-wave elastography. Results: The acoustic properties varied with enhancers like glycerol and Al2O3. Low Mw PVA samples had a speed of sound ranging from 1547.50 ± 2 to 1553.70 ± 2.2 m/s and attenuation of 0.61 ± 0.062 to 0.63 ± 0.05 dB/cm/MHz. High Mw PVA samples ranged from 1555 ± 2.82 to 1566 ± 4.5 m/s and 0.71 ± 0.02 to 0.73 ± 0.046 dB/cm/MHz. Young’s modulus ranged from 11 ± 2 to 82.3 ± 0.5 kPa across 1 to 10 freeze-thaw cycles. Inclusion size, depth, and interaction statistically affect the SWE measurements with p-value = 0.056327, p-value = 8.0039 × 10−8, and p-value = 0.057089, respectively. SWE showed isoechoic inclusions, prostate tissue, and surrounding tissue only. The Doppler velocity was measured in three different inner diameters. Conclusion: PVA mixed with enhancer materials creates an mpUS phantom with properties that mimic normal and abnormal prostate tissue, blood vessels, and soft tissue, facilitating advanced diagnostic training and validation.

Wang Z., Yi N., Zheng Z., Zhou J., Zhou P., Zheng C., Chen H., Shen G., Weng M.

Yang J., Liu Y., Morgan P.L.

Since the concept of Industry 5.0 was proposed, the emphasis on human–machine​ interaction (HMI) in industrial scenarios has continued to increase. HMI is part of the factory's development towards Industry 5.0, mainly because HMI can help realise the human-centric vision. At the same time, to achieve the sustainable and resilient goals proposed by Industry 5.0, green, smart, and more advanced technologies are also considered important driving factors for factories to achieve Industry 5.0. Human-centric smart manufacturing (HCSM) factories that integrate HMI with advanced technologies are expected to become the paradigm of future manufacturing. Therefore, it is necessary to discuss technologies and research directions that may promote the implementation of HCSM in the future. In a smart factory, HMI signals will go through the process of being collected by sensors, processed, transmitted to the data analysis centre and output to complete the interaction. Based on this process, we divide HMI into four parts: sensor and hardware, data processing, transmission mechanism, and interaction and collaboration. Through a systematic literature review process, this article evaluates and summarises the current research and technologies in the HMI field and categorises them into four parts of the HMI process. Since the current usage scenarios of some technologies are relatively limited, the introduction focuses on the possible applications and problems they face. Finally, the opportunities and challenges of HMI for Industry 5.0 and HCSM are revealed and discussed.

Huang Y., Tao Y., Wang Y.

Four-dimensional-printed smart materials have a wide range of applications in areas such as biomedicine, aerospace, and soft robotics. Among 3D printing technologies, fused deposition molding (FDM) is economical, simple, and apply to thermoplastics. Cross-linked polyethylene (XLPE) forms a stable chemical cross-linking structure and shows good shape-memory properties, but the sample is not soluble or fusible, which makes it hard to be applied in FDM printing. Therefore, in this work, a new idea of printing followed by irradiation was developed to prepare 4D-printed XLPE. First, low-density polyethylene (LDPE) was used to print the products using FDM technology and then cross-linked by gamma irradiation was used. The printing parameters were optimized, and the gel content, mechanical properties, and shape-memory behaviors were characterized. After gamma irradiation, the samples showed no new peak in FTIR spectra. And the samples exhibited good shape-memory capabilities. Increasing the irradiation dose increased the cross-linking degree and tensile strength and improved the shape-memory properties. However, it also decreased the elongation at break, and it did not affect the crystallization or melting behaviors of LDPE. With 120 kGy of irradiation, the shape recovery and fixity ratios (Rr and Rf) of the samples were 97.69% and 98.65%, respectively. After eight cycles, Rr and Rf remained at 96.30% and 97.76%, respectively, indicating excellent shape-memory performance.

Hasson A.M., Patel R.D., Sissoko C.A., Brattain L., Dion G.R.

AbstractObjectivesWith rapid advances in ultrasound‐guided procedures, there is an unmet need for echogenic phantoms with sufficient anatomical details for artificial intelligence and ultrasound‐guided device testing. We developed a method for creating neck phantoms for novel otolaryngology‐related device testing. To achieve accurate representation of the anatomy, we utilized CT scans and 3D printing technology to create customized agar molds, thus providing high‐fidelity yet cost‐effective tools.MethodsBased on previous studies, the key components in our neck phantom include the cervical vertebrae, trachea, common carotid arteries, internal jugular veins, thyroid gland, and surrounding soft tissue. Open‐source image analysis software were employed to process CT data to generate high fidelity 3D models of the target structures. Resin molds were 3D printed and filled with various agar mixtures to mimic anatomical echogenicity.ResultsFollowing the method proposed, we successfully assembled the neck phantom which provided a detailed representation of the target structures. To evaluate the results, ultrasound data was collected on the phantom and living tissue and analyzed with ImageJ. We were able to demonstrate echogenicity comparable to that of living tissue.ConclusionThe proposed method for building neck phantoms with detailed anatomical features offers a valuable, detailed, low‐cost tool for medical training and device testing in otolaryngology, particularly for novel devices that involve artificial intelligence (AI) guidance and robotic‐based needle insertion. Additional anatomical refinements and validation studies could further enhance the consistency and accuracy, thus paving the way for future advancements in ultrasound training and research, and ultimately benefiting patient care and safety.

Zheng F., Jiang H., Yang X., Guo J., Sun L., Guo Y., Xu H., Yao M.

Wearable health monitoring technologies have garnered extensive public attention, leading to significant economic and societal impacts. These advancements have prompted changes in medical practices and personal lifestyles. Among these innovations, flexible gas sensing systems have become crucial devices in wearable technology, capable of detecting various stimuli associated with exhaled biomarkers or specific environments. In recent years, there have been substantial advancements in the commercialization and research of flexible gas sensors. In the realm of health monitoring, research has primarily focused on flexibility, biocompatibility, low power consumption, miniaturization, and integration. This study provides a summary of the latest developments and advantages of smart wearable health monitoring systems based on flexible gas sensors in practical electronic applications. Additionally, it outlines various strategies for wearable health sensing systems, such as flexibility/stretchability, biocompatibility, self-healing, low power consumption, and self-powering. Furthermore, the potential applications of wearable gas sensing systems in healthcare are briefly discussed. The conclusion presents challenges and prospects in this field.

Bai Y., Meng H., Li Z.

The energy harvesting technology based on piezoelectricity promises to achieve a self-powered mode for portable medical electronic devices. Piezoelectric materials as crucial components in electromechanical applications, have extensively been utilized in portable medical electronic devices. Especially, Degradable piezoelectric biomaterials have received much attention in the medical field due to their excellent biocompatibility and biosafety. This minireview mainly summarizes types and structural characteristics of degradable piezoelectric biomaterials from degradable piezoelectric small molecule crystals to piezoelectric polymers. Afterward, medical applications are briefly introduced, including energy harvester and sensor, actuator and transducer, and tissue engineering scaffold. Finally, from a material perspective, some challenges currently faced by degradable piezoelectric biomaterials are proposed.

Feng J., Ao H., Cao P., Yang T., Xing B.

A patterned, stretchable, and fully elastomeric multiwalled carbon nanotube (MWCNT)/silver nanowire (Ag NW)/silicone rubber (SR) composite have been developed.

Mohamadbeigi N., Shooshtari L., Fardindoost S., Vafaiee M., Iraji zad A., Mohammadpour R.

AbstractRespiration stands as a vital process reflecting physiological and pathological human health status. Exhaled breath analysis offers a facile, non-invasive, swift, and cost-effective approach for diagnosing and monitoring diseases by detecting concentration changes of specific biomarkers. In this study, we employed Polyethylene oxide/copper (I) oxide composite nanofibers (PCNFs), synthesized via the electrospinning method as the sensing material to measure ethanol levels (1–200 ppm) in an exhaled breath simulator environment. The integrated contact-separation triboelectric nanogenerator was utilized to power the self-powered PCNFs exhaled breath sensor. The PCNFs-based gas sensor demonstrates promising results with values of 0.9 and 3.2 for detecting 5 ppm and 200 ppm ethanol, respectively, in the presence of interfering gas at 90% relative humidity (RH). Notably, the sensor displayed remarkable ethanol selectivity, with ratios of 10:1 to methanol and 25:1 to acetone. Response and recovery times for 200 ppm ethanol at 90 RH% were rapid, at 2.7 s and 5.8 s, respectively. The PCNFs-based exhaled breath sensor demonstrated consistent and stable performance in practical conditions, showcasing its potential for integration into wearable devices. This self-powered breath sensor enabling continuous monitoring of lung cancer symptoms and facilitating compliance checks with legal alcohol consumption limits.

Dai Z., Lei M., Ding S., Zhou Q., Ji B., Wang M., Zhou B.

AbstractThe current generation of wearable sensors often experiences signal interference and external corrosion, leading to device degradation and failure. To address these challenges, the biomimetic superhydrophobic approach has been developed, which offers self‐cleaning, low adhesion, corrosion resistance, anti‐interference, and other properties. Such surfaces possess hierarchical nanostructures and low surface energy, resulting in a smaller contact area with the skin or external environment. Liquid droplets can even become suspended outside the flexible electronics, reducing the risk of pollution and signal interference, which contributes to the long‐term stability of the device in complex environments. Additionally, the coupling of superhydrophobic surfaces and flexible electronics can potentially enhance the device performance due to their large specific surface area and low surface energy. However, the fragility of layered textures in various scenarios and the lack of standardized evaluation and testing methods limit the industrial production of superhydrophobic wearable sensors. This review provides an overview of recent research on superhydrophobic flexible wearable sensors, including the fabrication methodology, evaluation, and specific application targets. The processing, performance, and characteristics of superhydrophobic surfaces are discussed, as well as the working mechanisms and potential challenges of superhydrophobic flexible electronics. Moreover, evaluation strategies for application‐oriented superhydrophobic surfaces are presented.

Kazanskiy N.L., Khonina S.N., Butt M.A.

According to the age-old adage, while eyes are often considered the gateway to the soul, they might also provide insights into a more pragmatic aspect of our health: blood sugar levels. This potential breakthrough could be realized through the development of smart contact lenses (SCLs). Although contact lenses were first developed for eyesight correction, new uses have recently become available. In the near future, it might be possible to monitor a variety of ocular and systemic disorders using contact lens sensors. Within the realm of glaucoma, SCLs present a novel prospect, offering a potentially superior avenue compared to traditional management techniques. These lenses introduce the possibility of non-invasive and continuous monitoring of intraocular pressure (IOP) while also enabling the personalized administration of medication as and when needed. This convergence holds great promise for advancing glaucoma care. In this review, recent developments in SCLs, including their potential applications, such as IOP and glucose monitoring, are briefly discussed.

Sreejith S., Joseph L.M., Kollem S., Vijumon V.T., Ajayan J.

For many years, environmental issues caused by huge volume of non-degradable medical as well as electronic waste remains as a major concern. In order to mitigate this issue, eco-friendly sensors have been developed from biocompatible and biodegradable materials which naturally degrade into physiological environment without causing any environmental issues. These sensors have also emerged as an attractive alternative to conventional non-degradable sensors in both non-invasive and invasive health monitoring. They also provide unique opportunity for continuous health-monitoring via wearable sensors, in vivo sensing and in temporal medical implants. Implantable BD-SENs (biodegradable sensors) prevent the need for re-operation and also reduce chronic inflammatory responses. In this article a comprehensive overview of different biodegradable materials used in the fabrication of these BD-SENs, degradation mechanism, degradation-time and their applications has been presented. Also this article critically analyse different biodegradable wearable sensors, implantable BD-SENs as well as their recent developments.

Jeerapan I., Khumngern S.

Tu J., Wang M., Li W., Su J., Li Y., Lv Z., Li H., Feng X., Chen X.

Multiple types of sensory information are detected and integrated to improve perceptual accuracy and sensitivity in biological cognition. However, current studies on electronic skin (e-skin) systems have mainly focused on the optimization of the modality-specific data acquisition and processing. Endowing e-skins with the abilities of multimodal sensing and even perception that can achieve high-level perception behaviors has been insufficiently explored. Moreover, the perception progress of multisensory e-skin systems is faced with challenges at both device and software levels. Here, we provide a perspective on the multisensory fusion of e-skins. The recent progress in e-skins realizing multimodal sensing is reviewed, followed by bottom-up and top-down multimodal perception. With the deepening understanding of neuroscience and the rapid advance of novel algorithms and devices, multimodal perception function becomes possible and will promote the development of highly intelligent e-skin systems.

Cai X., Xiao Y., Zhang B., Yang Y., Wang J., Chen H., Shen G.

AbstractMXene materials emerge as promising candidates for energy harvesting and storage application. In this study, the effect of the surface chemistry on the work function of MXenes, which determines the performance of MXene‐based triboelectric nanogenerator (TENG), is elucidated. First‐principles calculations reveal that the surface functional group greatly influences MXene work function: OH termination reduces the work function with respect to that of bare surface, while F and Cl increase it. Then, work functions are experimentally determined by Kelvin probe force microscopy. The MXene prepared by gentle etching at 40 °C for 48 h (GE40/48) has the largest work function. Furthermore, an electron‐cloud potential‐well model is established to explain the mechanism of electron emission‐dominated charge transfer and assemble a triboelectric device to verify experimentally its conclusions. It is found that GE40/48 has the best performance with a 281 V open‐circuit voltage, 9.7 µA short‐current current, and storing 1.019 µC of charge, which is consistent with the model. Last, a patterned TENG is demonstrated for self‐powered human–machine interaction application. This finding enhances the understanding of the inherent mechanism between the surface structure and the output performance of MXene‐based TENG, which can be applied to other TENG based on 2D materials.

Zhou Y., Wang Q., Xiang T., Chen X.

Zhao X., Liu Y., Li A., Chen J.

Manohar B.A., Devaraj J., Maheswaran C., Pugalenthi S.

This study seeks to automate the Rapid Entire Body Assessment (REBA) in dentistry with Artificial Intelligence (AI) technologies, notably MediaPipe, to improve accuracy and obviate the necessity for expert judgment. This research utilizes time-synchronized videos and averages across frames to mitigate mistakes resulting from visual occlusion and over- or underestimation, respectively. The REBA scores of the observed dentists were evaluated and compared with the conventional single image-based method. Among the evaluated dentists, 83% of dentists are at high risk, and the other 17% of dentists are at very high risk, requiring solutions to lower their REBA scores and prevent musculoskeletal disorders (MSDs). The individual REBA point profiles differed, necessitating a collective study through response surface methodology (RSM) utilizing Design Expert software. The RSM model exhibited substantial results, as indicated by R2 = 0.9055 and p = < 0.0001 values. A linear regression equation was established, and contour graphs depicted the relative variation of REBA points. The optimized REBA score profile establishes a maximum attainable threshold for dentists, directing them towards the lower scores. This streamlined contour functions as a design restriction for creating ergonomic solutions in dental practice.