Wireless Human-Machine Interface Based on Artificial Bionic Skin with Damage Reconfiguration and Multisensing Capabilities

Portable and Self-Powered Sensing AI-Enabled Mask for Emotional Recognition in Virtual Reality

With the increasing development of metaverse and human-computer interaction (HMI) technologies, artificial intelligence (AI) applications in virtual reality (VR) environments are receiving significant attention. This study presents a self-sensing facial recognition mask (FRM) utilizing triboelectric nanogenerators (TENG) and machine learning algorithms to enhance user immersion and interaction. Various TENG negative electrode materials are evaluated to improve sensor performance, and the efficacy of a single sensor is confirmed. For accurate facial movement and emotion detection, different machine learning algorithms are assessed, leading to the selection of an advanced data processing method with a two-layer long short-term memory model, which achieves 99.87% accuracy. The practical applications of the FRM system in virtual reality, including psychotherapy and HMI scenarios, are validated through mathematical models. Additionally, a digital twin-based monitoring platform is developed using 5G, database, and visualization technologies to oversee the user status. Overall, these innovative approaches overcome the limitations of existing face recognition technologies, including environmental interference and high cost, compared with other facial recognition technologies.

Flexible Strain Sensors with Ultra-High Sensitivity and Wide Range Enabled by Crack-Modulated Electrical Pathways

This study presents a breakthrough in flexible strain sensor technology with the development of an ultra-high sensitivity and wide-range sensor, addressing the critical challenge of reconciling sensitivity with measurement range. Inspired by the structure of bamboo slips, we introduce a novel approach that utilises liquid metal to modulate the electrical pathways within a cracked platinum fabric electrode. The resulting sensor demonstrates a gauge factor greater than 108 and a strain measurement capability exceeding 100%. The integration of patterned liquid metal enables customisable tuning of the sensor's response, while the porous fabric structure ensures superior comfort and air permeability for the wearer. Our design not only optimises the sensor's performance but also enhances the electrical stability that is essential for practical applications. Through systematic investigation, we reveal the intrinsic mechanisms governing the sensor's response, offering valuable insights for the design of wearable strain sensors. The sensor's exceptional performance across a spectrum of applications, from micro-strain to large-strain detection, highlights its potential for a wide range of real-world uses, demonstrating a significant advancement in the field of flexible electronics.

A high-sensitivity flexible bionic tentacle sensor for multidimensional force sensing and autonomous obstacle avoidance applications

Bionic tentacle sensors are important in various fields, including obstacle avoidance, human‒machine interfaces, and soft robotics. However, most traditional tentacle sensors are based on rigid substrates, resulting in difficulty in detecting multidirectional forces originating from the external environment, which limits their application in complex environments. Herein, we proposed a high-sensitivity flexible bionic tentacle sensors (FBTSs). Specifically, the FBTS featured an ultrahigh sensitivity of 37.6 N-1 and an ultralow detection limit of 2.4 mN, which benefited from the design of a whisker-like signal amplifier and crossbeam architecture. Moreover, the FBTS exhibited favorable linearity (R2 = 0.98) and remarkable durability (more than 5000 cycles). This was determined according to the improvement in the uniformity of the sensing layer through a high-shear dispersion process. In addition, the FBTS could accurately distinguish the direction of external stimuli, resulting in the FBTS achieving roughness recognition, wind speed detection and autonomous obstacle avoidance. In particular, the ability of autonomous obstacle avoidance was suitably demonstrated by leading a bionic rat through a maze with the FBTS. Notably, the proposed FBTS could be widely applied in tactile sensing, orientation perception, and obstacle avoidance.

Advances in Piezoelectret Materials-Based Bidirectional Haptic Communication Devices

Bidirectional haptic communication devices accelerate the revolution of virtual/augmented reality and flexible/wearable electronics. As an emerging kind of flexible piezoelectric materials, piezoelectret materials can effortlessly convert mechanical force into electrical signals and respond to electrical fields in a deformation manner, exhibiting enormous potential in the construction of bidirectional haptic communication devices. Existing reviews on piezoelectret materials primarily focus on flexible energy harvesters and sensors, and the recent development of piezoelectret-based bidirectional haptic communication devices has not been comprehensively reviewed. Herein, a comprehensive overview of the materials construction, along with the recent advances in bidirectional haptic communication devices, is provided. First, the development timeline, key characteristics, and various fabrication methods of piezoelectret materials are introduced. Subsequently, following the underlying mechanisms of bidirectional electromechanical signal conversion of piezoelectret, strategies to improve the d33 coefficients of materials are proposed. The principles of haptic perception and feedback are also highlighted, and representative works and progress in this area are summarized. Finally, the challenges and opportunities associated with improving the overall practicability of piezoelectret materials-based bidirectional haptic communication devices are discussed.

Ultra-stretchable, adhesive, fatigue resistance, and anti-freezing conductive hydrogel based on gelatin/guar gum and liquid metal for dual-sensory flexible sensor and all-in-one supercapacitors

Benefiting from the tissue-like mechanical properties, conductive hydrogels have emerged as a promising candidate for manufacturing wearable electronics. However, the high water content within hydrogels will inevitably freeze at subzero temperature, causing a degradation or loss of functionality, which severely prevent their practical application in wearable electronics. Herein, an anti-freezing hydrogel integrating high conductivity, superior stretchability, and robust adhesion was fabricated by dissolving choline chloride and gallium in gelatin/guar gum network using borax as the cross-linker. Based on the synergistic effect of dynamic borate ester bonds and hydrogen bonds, the hydrogel exhibited rapid self-healing property and excellent fatigue resistance. Profiting from these fascinating characteristics, the hydrogel was assembled as strain sensor to precisely detect various human activities with high strain sensitivity and fast response time. Meanwhile, the hydrogel was demonstrated high sensitivity and rapid response to temperature, which can be used as thermal sensor to monitor temperature. Moreover, the conductive hydrogel was encapsulated into supercapacitors with high areal capacitance and favorable cycle stability. Importantly, the flexible sensor and supercapacitors still maintain stable sensing performance and good electrochemical performance even at subzero temperature. Therefore, our work broaden hydrogels application in intelligent wearable devices and energy storage in extreme environments.

Haptic Sensing and Feedback Techniques toward Virtual Reality

Haptic interactions between human and machines are essential for information acquisition and object manipulation. In virtual reality (VR) system, the haptic sensing device can gather information to construct virtual elements, while the haptic feedback part can transfer feedbacks to human with virtual tactile sensation. Therefore, exploring high-performance haptic sensing and feedback interface imparts closed-loop haptic interaction to VR system. This review summarizes state-of-the-art VR-related haptic sensing and feedback techniques based on the hardware parts. For the haptic sensor, we focus on mechanism scope (piezoresistive, capacitive, piezoelectric, and triboelectric) and introduce force sensor, gesture translation, and touch identification in the functional view. In terms of the haptic feedbacks, methodologies including mechanical, electrical, and elastic actuators are surveyed. In addition, the interactive application of virtual control, immersive entertainment, and medical rehabilitation is also summarized. The challenges of virtual haptic interactions are given including the accuracy, durability, and technical conflicts of the sensing devices, bottlenecks of various feedbacks, as well as the closed-loop interaction system. Besides, the prospects are outlined in artificial intelligence of things, wise information technology of medicine, and multimedia VR areas.

An approach to the dermatological classification of histopathological skin images using a hybridized CNN-DenseNet model

This research addresses the challenge of automating skin disease diagnosis using dermatoscopic images. The primary issue lies in accurately classifying pigmented skin lesions, which traditionally rely on manual assessment by dermatologists and are prone to subjectivity and time consumption. By integrating a hybrid CNN-DenseNet model, this study aimed to overcome the complexities of differentiating various skin diseases and automating the diagnostic process effectively. Our methodology involved rigorous data preprocessing, exploratory data analysis, normalization, and label encoding. Techniques such as model hybridization, batch normalization and data fitting were employed to optimize the model architecture and data fitting. Initial iterations of our convolutional neural network (CNN) model achieved an accuracy of 76.22% on the test data and 75.69% on the validation data. Recognizing the need for improvement, the model was hybridized with DenseNet architecture and ResNet architecture was implemented for feature extraction and then further trained on the HAM10000 and PAD-UFES-20 datasets. Overall, our efforts resulted in a hybrid model that demonstrated an impressive accuracy of 95.7% on the HAM10000 dataset and 91.07% on the PAD-UFES-20 dataset. In comparison to recently published works, our model stands out because of its potential to effectively diagnose skin diseases such as melanocytic nevi, melanoma, benign keratosis-like lesions, basal cell carcinoma, actinic keratoses, vascular lesions, and dermatofibroma, all of which rival the diagnostic accuracy of real-world clinical specialists but also offer customization potential for more nuanced clinical uses.

Bioinspired nanoplatforms for human-machine interfaces: Recent progress in materials and device applications

The panoramic characteristics of human-machine interfaces (HMIs) have prompted the needs to update the biotechnology community with the recent trends, developments, and future research direction toward next-generation bioelectronics. Bioinspired materials are promising for integrating various bioelectronic devices to realize HMIs. With the advancement of scientific biotechnology, state-of-the-art bioelectronic applications have been extensively investigated to improve the quality of life by developing and integrating bioinspired nanoplatforms in HMIs. This review highlights recent trends and developments in the field of biotechnology based on bioinspired nanoplatforms by demonstrating recently explored materials and cutting-edge device applications. Section 1 introduces the recent trends and developments of bioinspired nanomaterials for HMIs. Section 2 reviews various flexible, wearable, biocompatible, and biodegradable nanoplatforms for bioinspired applications. Section 3 furnishes recently explored substrates as carriers for advanced nanomaterials in developing HMIs. Section 4 addresses recently invented biomimetic neuroelectronic, nanointerfaces, biointerfaces, and nano/microfluidic wearable bioelectronic devices for various HMI applications, such as healthcare, biopotential monitoring, and body fluid monitoring. Section 5 outlines designing and engineering of bioinspired sensors for HMIs. Finally, the challenges and opportunities for next-generation bioinspired nanoplatforms in extending the potential on HMIs are discussed for a near-future scenario. We believe this review can stimulate the integration of bioinspired nanoplatforms into the HMIs in addition to wearable electronic skin and health-monitoring devices while addressing prevailing and future healthcare and material-related problems in biotechnologies.

Highly Flexible, Self-Bonding, Self-Healing, and Conductive Soft Pressure Sensors Based on Dicarboxylic Cellulose Nanofiber Hydrogels

Conductive hydrogels have gained a great deal of interest in the flexible electronics industry because of their remarkable inherent properties. However, a significant challenge remains for balancing hydrogel's conductivity, self-healing, and strength properties. Herein, double network ionic hydrogels were fabricated by concurrently introducing borax into dicarboxylic cellulose nanofiber (DCNFs) and polyacrylamide (PAM) hydrogels. The incorporation of borax provided a superabsorbent feature to the PAM/DCNF hydrogels (without borax) with the equilibrium water absorption rate increased from 552 to 1800% after 42 h. The compressive strength of the prepared hydrogel was 935 kPa compared to 132 kPa for the PAM hydrogel, with high cycling stability (stable after 1000 compression cycles with 50% strain). The hydrogel pressure sensor had a very sensitive response (gauge factor = 1.36) in the strain range from 10 to 80%, which made it possible to detect mechanical motion accurately and reliably. The developed hydrogels with high-performance, environmentally friendly properties are promising for use in future artificial skin and human-machine interface applications.

Simple and Rapid Way to a Multifunctionally Conductive Hydrogel for Wearable Strain Sensors

Conductive hydrogels have gained increasing attention in the field of wearable smart devices. However, it remains a big challenge to develop a multifunctionally conductive hydrogel in a rapid and facile way. Herein, a conductive tannic acid-iron/poly (acrylic acid) hydrogel was synthesized within 30 s at ambient temperature by the tannic acid-iron (TA@Fe3+)-mediated dynamic catalytic system. The TA@Fe3+ dynamic redox autocatalytic pair could efficiently activate the ammonium persulfate to initiate the free-radical polymerization, allowing the gelation to occur easily and rapidly. The resulting hydrogel exhibited enhanced stretchability (3560%), conductivity (33.58 S/m), and strain sensitivity (gauge factor = 2.11). When damaged, it could be self-healed through the dynamic and reversible coordination bonds between the Fe3+ and COO- groups in the hydrogel network. Interestingly, the resulting hydrogel could act as a strain sensor to monitor various human motions including the huge movement of deformations (knuckle, wrist) and subtle motions (smiling, breathing) in real time due to its enhanced self-adhesion, good conductivity, and improved strain sensitivity. Also, the obtained hydrogel exhibited efficient electromagnetic interference (EMI) shielding performance with an EMI shielding effectiveness value of 24.5 dB in the X-band (8.2-12.4 GHz). Additionally, it displayed antibacterial properties, with the help of the activity of TA.

Self-Powered Multifunctional Organic Hydrogel Based on Poly(acrylic acid-N-isopropylacrylamide) for Flexible Sensing Devices

Human-machine interactions, medical monitoring, and flexible robots stimulate interest in hydrogel sensing devices. However, developing hydrogel sensors with multifunctions such as good mechanics, electroconductivity, resistance to solvent volatility as well as freezing, self-adhesion, and independence on external power supply remains a challenge. In the work, a poly(acrylic acid-N-isopropylacrylamide) P(AA-NIPAm) organic hydrogel loading LiCl is prepared by ultraviolet cross-linking in ethylene glycol/H₂O. The organic hydrogel exhibits favorable mechanical properties such as an elongation of break at 700% and a breaking strength of 20 KPa, can adhere to various substrates, and resists frost and solvent volatility. Especially, it possesses an excellent conductivity of 8.51 S/m. The organic hydrogel shows wide strain sensitivity based on resistance change, and the gauge factor reaches 5.84 in the range of 300-700%. It has short responsive and recuperative time and is still stable within 1000 rounds. Moreover, the organic hydrogel is also assembled into a self-powered device in which the open-circuit voltage is 0.74 V. The device can transform external stimuli such as stretching or compressing into the output current change, so it detects human motion effectively in real time. The work provides a perspective for electrical sensing engineering.

Reinforcement of Nanocomposite Hydrogel with Dialdehyde Cellulose Nanofibrils via Physical and Double Network Crosslinking Synergies

Preparation of tough and high-strength hydrogels for water plugging in oil fields with an easy-scalable method is still considered to be a challenge. In this study, dialdehyde cellulose nanofibril (DA-CNF) prepared by sodium periodate oxidation, polyamine, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with sulfonate groups and Acrylamide (AM) as raw materials, CNF reinforced nanocomposite hydrogels were prepared in one step by in-situ polymerization. The tensile strength, and texture stability of the obtained nanocomposite hydrogel were determined. The results showed that the tensile strength and toughness of the obtained nanocomposite hydrogel increased four times compared with control sample due to physical and chemical double crosslinking synergies. Moreover, the texture intensity of DA-CNFs reinforced hydrogel still maintains high stability and strength performance under high salinity conditions. Therefore, DA-CNF reinforced hydrogel has potential application value in both normal and high-salinity environments in oil recovery.

Design and Analysis of a Hybrid Displacement Amplifier Supporting a High-Performance Piezo Jet Dispenser

In this study, a compliant amplifier powered by a piezoelectric stack is designed to meet high-performance dispensing operation requirements. By studying the issue of low frequency bandwidth on the traditional bridge-type amplifier mechanism, we propose a displacement amplifier mechanism, hybrid bridge-lever-bridge (HBLB), that enhances its dynamic performance by combining the traditional bridge-type and lever mechanism. A guiding beam is added to further improve its output stiffness with a guaranteed large amplification ratio. An analytical model has been developed to describe the full elastic deformation behavior of the HBLB mechanism that considers the lateral displacement loss of the input end, followed by a verification through a finite element analysis (FEA). Results revealed that the working principle of the HBLB optimizes the structural parameters using the finite element method. Finally, a prototype of the displacement amplifier was fabricated for performance tests. Static and dynamic test results revealed that the proposed mechanism can reach a travel range of 223.2 μm, and the frequency bandwidth is 1.184 kHz, which meets the requirements of a high-performance piezo jet dispenser.

Modeling of Shunted Piezoelectrics and Enhancement of Vibration Suppression through an Auxetic Interface

In this study, a new technique is presented for enhancing the vibration suppression of shunted piezoelectrics by using an auxetic composite layer. Finite element models have been created to simulate the dynamic behavior of the piezoelectric composite beam. In particular, 2D FE and 3D FE models have been created by simulating the shunt as a passive controller and their results are compared. Furthermore, a parametric analysis is presented of the circuit elements, i.e., the resistors, inductors, and capacitors and of the auxetic material, i.e., the thickness. It was found that the proposed modification by adding an auxetic layer of a considerable thickness enhances the electromechanical coupling and indirectly influences the vibration control of the whole structure. However, the use of 3D modeling is necessary to study this auxetic enhancement.

Hybrid Systems of Nanofibers and Polymeric Nanoparticles for Biological Application and Delivery Systems

Nanomedicine is a new discipline resulting from the combination of nanotechnology and biomedicine. Nanomedicine has contributed to the development of new and improved treatments, diagnoses, and therapies. In this field, nanoparticles have notable importance due to their unique properties and characteristics, which are useful in different applications, including tissue engineering, biomarkers, and drug delivery systems. Electrospinning is a versatile technique used to produce fibrous mats. The high surface area of the electrospun mats makes them suitable for applications in fields using nanoparticles. Electrospun mats are used for tissue engineering, wound dressing, water-treatment filters, biosensors, nanocomposites, medical implants, protective clothing materials, cosmetics, and drug delivery systems. The combination of nanoparticles with nanofibers creates hybrid systems that acquire properties that differ from their components' characteristics. By utilizing nanoparticles and nanofibers composed of dissimilar polymers, the two synergize to improve the overall performance of electrospinning mats and nanoparticles. This review summarizes the hybrid systems of polymeric nanoparticles and polymeric nanofibers, critically analyzing how the combination improves the properties of the materials and contributes to the reduction of some disadvantages found in nanometric devices and systems.