Hydrogel-Based Sensors for Human-Machine Interaction

Advancements in Binary Solvent-Assisted Hydrogel Composites for Wearable Sensing Applications

The advancement of wearable sensing technologies has been pivotal in revolutionizing healthcare, environmental monitoring, and personal fitness. Among the diverse materials employed in these technologies, multifunctional hydrogel composites have emerged as critical components due to their unique properties, including high water content, flexibility, and biocompatibility. This review provides a comprehensive overview of the state-of-the-art in binary solvent-assisted hydrogel composites for wearable sensing applications. It begins by defining hydrogel composites and their essential attributes for wearable sensors, specifically focusing on binary solvent-assisted methods that enhance their performance and functionality. The review then delves into the applications of these composites in health monitoring, environmental detection, and sports and fitness, highlighting their role in advancing wearable technologies. Despite their promising features, there are significant challenges related to durability, sensitivity, and integration that need to be addressed to fully exploit these materials in wearable devices. This review discusses these challenges and presents potential solutions, including the development of new materials, improvement in fabrication processes, and strategies for achieving multifunctionality and sustainable design. Looking forward, the paper outlines future directions for research in this field, emphasizing the need for innovative materials and technologies that can lead to more effective, reliable, and eco-friendly wearable sensors. This review aims to inspire further research and development in the field of wearable sensing, paving the way for new applications and advancements in healthcare, environmental monitoring, and personal fitness technologies.

Conducting polymer hydrogels based on supramolecular strategies for wearable sensors

Conductive polymer hydrogels (CPHs) are gaining considerable attention in developing wearable electronics due to their unique combination of high conductivity and softness. However, in the absence of interactions, the incompatibility between hydrophobic conductive polymers (CPs) and hydrophilic polymer networks gives rise to inadequate bonding between CPs and hydrogel matrices, thereby significantly impairing the mechanical and electrical properties of CPHs and constraining their utility in wearable electronic sensors. Therefore, to endow CPHs with good performance, it is necessary to ensure a stable and robust combination between the hydrogel network and CPs. Encouragingly, recent research has demonstrated that incorporating supramolecular interactions into CPHs enhances the polymer network interaction, improving overall CPH performance. However, a comprehensive review focusing on supramolecular CPH (SCPH) for wearable sensing applications is currently lacking. This review provides a summary of the typical supramolecular strategies employed in the development of high-performance CPHs and elucidates the properties of SCPHs that are closely associated with wearable sensors. Moreover, the review discusses the fabrication methods and classification of SCPH sensors, while also exploring the latest application scenarios for SCPH wearable sensors. Finally, it discusses the challenges of SCPH sensors and offers suggestions for future advancements.

Cutting-Edge Hydrogel Technologies in Tissue Engineering and Biosensing: An Updated Review

Hydrogels, known for their unique ability to retain large amounts of water, have emerged as pivotal materials in both tissue engineering and biosensing applications. This review provides an updated and comprehensive examination of cutting-edge hydrogel technologies and their multifaceted roles in these fields. Initially, the chemical composition and intrinsic properties of both natural and synthetic hydrogels are discussed, highlighting their biocompatibility and biodegradability. The manuscript then probes into innovative scaffold designs and fabrication techniques such as 3D printing, electrospinning, and self-assembly methods, emphasizing their applications in regenerating bone, cartilage, skin, and neural tissues. In the realm of biosensing, hydrogels' responsive nature is explored through their integration into optical, electrochemical, and piezoelectric sensors. These sensors are instrumental in medical diagnostics for glucose monitoring, pathogen detection, and biomarker identification, as well as in environmental and industrial applications like pollution and food quality monitoring. Furthermore, the review explores cross-disciplinary innovations, including the use of hydrogels in wearable devices, and hybrid systems, and their potential in personalized medicine. By addressing current challenges and future directions, this review aims to underscore the transformative impact of hydrogel technologies in advancing healthcare and industrial practices, thereby providing a vital resource for researchers and practitioners in the field.

An interfacial host-guest inclusion complex regulated supramolecular nanocomposite hydrogel showing tunable mechanical strength, self-healing, strain sensitivity and NIR responsiveness

The development of supramolecular nanocomposite hydrogels with good mechanical properties and multifunctional characteristics remains challenging. The reinforced role of interfacial weak interactions is important for the mechanical properties of nanocomposite hydrogels. Here, a dynamic host-guest inclusion complex from the host molecule CB[7] and guest units was employed to prepare Fe3O4 hybrid supramolecular nanocomposite hydrogels. The results show that the as-obtained hydrogel with a porous structure was prepared. The CB[7]-modified Fe3O4 (Fe3O4@CB[7]) nanoparticles severed as a cross-linker for fabricating the hydrogel's network. By changing the Fe3O4@CB[7] content, their tensile stress ranged from 0.102 to 0.403 MPa and their compression stress ranged (70% compression strain) from 0.059 to 0.775 MPa. By changing the guest units, their tensile stress ranged from 0.3 MPa to 0.403 MPa. The self-healing efficiency of the hydrogels was 99% after 48 h at room temperature. The as-obtained hydrogels with strain sensitivity can be applied for detecting the movement of an elbow and finger. The supramolecular hydrogel exhibits NIR responsiveness, self-healing, injectability, tunable mechanical strength and conductive ability, and can be used in flexible electronics.

From Fluorescence-Transfer-Lightening-Printing-Assisted Conductive Adhesive Nanocomposite Hydrogels toward Wearable Interactive Optical Information-Electronic Strain Sensors

The interactive flexible device, which monitors the human motion in optical and electrical synergistic modes, has attracted growing attention recently. The incorporation of information attribute within the optical signal is deemed advantageous for improving the interactive efficiency. Therefore, the development of wearable optical information-electronic strain sensors holds substantial promise, but integrating and synergizing various functions and realizing strain-mediated information transformation keep challenging. Herein, an amylopectin (AP) modified nanoclay/polyacrylamide-based nanocomposite (NC) hydrogel and an aggregation-induced-emission-active ink are fabricated. Through the fluorescence-transfer printing of the ink onto the hydrogel film in different strains with nested multiple symbolic information, a wearable interactive fluorescent information-electronic strain sensor is developed. In the sensor, the nanoclay plays a synergistic "one-stone-three-birds" role, contributing to "lightening" fluorescence (≈80 times emission intensity enhancement), ionic conductivity, and excellent stretchability (>1000%). The sensor has high biocompatibility, resilience (elastic recovery ratio: 97.8%), and strain sensitivity (gauge factor (GF): 10.9). Additionally, the AP endows the sensor with skin adhesiveness. The sensor can achieve electrical monitoring of human joint movements while displaying interactive fluorescent information transformation. This research poses an efficient strategy to develop multifunctional materials and provides a general platform for achieving next-generation interactive devices with prospective applications in wearable devices, human-machine interfaces, and artificial intelligence.