Tissue adhesive hydrogel bioelectronics

Advances in polysaccharide-based conductive hydrogel for flexible electronics

Polysaccharides, being the most abundant natural polymers, play a pivotal role in the development of hydrogel materials. Polysaccharide-based conductive hydrogels have found extensive applications in flexible electronics due to their excellent conductivity and biocompatibility. This review highlights recent advancements in this area, starting with an overview of polysaccharide materials such as chitosan, cellulose, starch, cyclodextrin, alginate, hyaluronic acid, and agarose. It then explores different classifications of conductive hydrogels: ionic conductive, electronic conductive, and ionic-electronic composite types. The review also covers key characteristics of these hydrogels, including mechanical properties, self-healing, adhesion, structural color, antibacterial, responsiveness, biocompatibility and anti-swelling. Representative applications, such as flexible sensors, triboelectric nanogenerators, supercapacitors, and flexible electronic wound dressings, are summarized. Finally, the review addresses current challenges and provides guidance for future research, aiming to advance the field of polysaccharide-based conductive hydrogels in flexible electronics.

Physical stimuli-responsive polymeric patches for healthcare

Many chronic diseases have become severe public health problems with the development of society. A safe and efficient healthcare method is to utilize physical stimulus-responsive polymer patches, which may respond to physical stimuli, including light, electric current, temperature, magnetic field, mechanical force, and ultrasound. Under certain physical stimuli, these patches have been widely used in therapy for diabetes, cancer, wounds, hair loss, obesity, and heart diseases since they could realize controllable treatment and reduce the risks of side effects. This review sketches the design principles of polymer patches, including composition, properties, and performances. Besides, control methods of using different kinds of physical stimuli were introduced. Then, the fabrication methods and characterization of patches were explored. Furthermore, recent applications of these patches in the biomedical field were demonstrated. Finally, we discussed the challenges and prospects for its clinical translation. We anticipate that physical stimulus-responsive polymer patches will open up new avenues for healthcare by acting as a platform with multiple functions.

Advances in Adhesive Materials for Oral and Maxillofacial Soft Tissue Diseases

Oral diseases represent a prevalent global health burden, profoundly affecting patients' quality of life. Given the involvement of oral mucosa and muscles in diverse physiological functions, coupled with clinical aesthetics considerations, repairing oral and maxillofacial soft tissue defects poses a formidable challenge. Wet-adhesive materials are regarded as promising oral repair materials due to their unique advantages in easily overcoming physical and biological barriers in the oral cavity. This review first introduces the intricate wet-state environment prevalent in the oral cavity, meticulously explaining the fundamental physical and chemical adhesion mechanisms that underpin adhesive materials. It then comprehensively summarizes the diverse types of adhesives utilized in stomatology, encompassing polysaccharide, protein, and synthetic polymer adhesive materials. The review further evaluates the latest research advancements in utilizing these materials to treat various oral and maxillofacial soft tissue diseases, including oral mucosal diseases, periodontitis, peri-implantitis, oral and maxillofacial skin defects, and maxillofacial tumors. Finally, it also highlights the promising future prospects and pivotal challenges related to stomatology application of multifunctional adhesive materials.

Design and in vitro/in vivo evaluation of chitosan-polyvinyl alcohol copolymer material cross-linked by dynamic borate ester covalent for pregabalin film-forming delivery system

This research introduced a novel polymer synthesized by combining chitosan and modified polyvinyl alcohol, cross-linked with boric acid using dynamic covalent bonds. The polymer was developed to formulate a pregabalin Film-forming system (FFS) for treating postherpetic neuralgia via topical application, showcasing notable skin adhesion and drug delivery properites. The chitosan-boric acid-modified polyvinyl alcohol polymer was analyzed using NMR, FTIR. The exceptional features of the optimized FFS were evaluated through rheometer, Differential scanning calorimetry (Tg = 45.98 °C), contact angle (θ = 78.62°). The elongation (60.05 ± 3.67 %), cohesion (56.94 ± 4.65 MPa) and skin adhesion (58.12 ± 2.99 kPa) of chitosan-boric acid-modified polyvinyl alcohol were found to be 5.2, 6.8, and 8.3 times higher than those of the pure chitosan film, attributed to the double network structure formed by the cross-linked reversible dynamic covalent bond. The optimized pregabalin FFS exhibited increased in vitro (86.25 ± 1.87 μg/g) and in vivo (100.42 ± 7.44 μg/g) skin retention amounts compared to in vivo oral administration (28.43 ± 4.61 μg/g). In summary, the utilization of borate ester dynamic covalent bonds in developing chitosan-based film-forming polymer proved beneficial in improving skin adhesion and topical therapeutic effectiveness, thereby mitigating the risk of systemic side effects associated with oral administration.

Thermal responsive sodium alginate/polyacrylamide/poly (N-isopropylacrylamide) ionic hydrogel composite via seeding calcium carbonate microparticles for the engineering of ultrasensitive wearable sensors

The design of polyelectrolyte hydrogel with unique tensile and adhesive properties which can be applied across disciplines has gradually become a popular trend. However, the phenomenon of global warming and the emergence of extreme weather, it still faces some urgent problems that should be solved, such as the optimal utilization of polyelectrolyte hydrogel across a wide range of temperatures. Herein, a wide temperature sensitivity and conductivity hydrogel based on sodium alginate, acrylamide and N-isopropylacrylamide was constructed, which exhibited excellent adhesion and temperature conductivity. It is worth noting that after the inclusion of CaCO3 and NaCl in the hydrogel, the hydrogel showed excellent tensile properties (fracture strain >2000 %). Within a wide temperature range (-15-50 °C), it exhibits exceptional electrical conductivity (2.75 S ∗ m-1) and sensitivity (GF = 8.76 under high strain). This innovative intelligent polyelectrolyte hydrogel provides suitable strategy for flexible sensors, smart wearable devices and medical monitoring equipment.

Advancements of Biomacromolecular Hydrogel Applications in Food Nutrition and Health

Hydrogels exhibit remarkable degradability, biocompatibility and functionality, which position them as highly promising materials for applications within the food and pharmaceutical industries. Although many relevant studies on hydrogels have been reported in the chemical industry, materials, and other fields, there have been few reviews on their potential applications in food nutrition and human health. This study aims to address this gap by reviewing the functional properties of hydrogels and assessing their value in terms of food nutrition and human health. The use of hydrogels in preserving bioactive ingredients, food packaging and food distribution is delved into specifically in this review. Hydrogels can serve as cutting-edge materials for food packaging and delivery, ensuring the preservation of nutritional activity within food products, facilitating targeted delivery of bioactive compounds and regulating the digestion and absorption processes in the human body, thereby promoting human health. Moreover, hydrogels find applications in in vitro cell and tissue culture, human tissue repair, as well as chronic disease prevention and treatment. These broad applications have attracted great attention in the fields of human food nutrition and health. Ultimately, this paper serves as a valuable reference for further utilization and exploration of hydrogels in these respective fields.

Supramolecular Conductive Hydrogels for Tissue Engineering Applications

Owing to their unique attributes, including reversibility, specificity, directionality, and tunability, supramolecular biomaterials have evolved as an excellent alternative to conventional biomaterials like polymers, ceramics, and metals. Supramolecular hydrogels, in particular, have garnered significant interest because their fibrous architecture, high water content, and interconnected 3D network resemble the extracellular matrix to some extent. Consequently, supramolecular hydrogels have been used to develop biomaterials for tissue engineering. Supramolecular conductive hydrogels combine the advantages of supramolecular soft materials with the electrical properties of metals, making them highly relevant for electrogenic tissue engineering. Given the versatile applications of these hydrogels, it is essential to periodically review high-quality research in this area. In this review, we focus on recent advances in supramolecular conductive hydrogels, particularly their applications in tissue engineering. We discuss the conductive components of these hydrogels and highlight notable reports on their use in cardiac, skin, and neural tissue engineering. Additionally, we outline potential future developments in this field.

Calcium-Based Mineralized Hydrogels for Temporary Reinforcement and Conservation of Ancient Ivory Relics

Ancient ivory serves as an important witness of time and historical events, offering highly significant insights into the fields of paleontology, mineralogy, materials science, and geochemistry. However, ancient ivory has undergone groundwater corrosion and has a loose porous structure and reduced mechanical strength due to being buried for a long time. Therefore, the temporary reinforcement and preservation of ancient ivory artifacts are a well-known challenge. A methodology was presented in this article for the synthesis of calcium-based mineralized hydrogels (Ca-gel), which possess controllable adhesive strength, beneficial compatibility, environmentally friendly and noninvasive protection, as well as efficient and rapid adhesion for ancient ivory cultural relics. By manipulating the various components of Ca-gel, it was possible to achieve a controllable gel time and gel state. Additionally, the hydrogel possessing a substantial water content has the potential to establish a humid environment suitable for the preservation of ancient ivory, thereby overcoming the challenges associated with water loss and weathering that may arise during excavation processes. It is noteworthy that Ca-gel possessed universality and temporary adhesive properties that could be employed in the temporary reinforcement of cultural relics from different materials. A method has been proposed in this study to facilitate the temporary reinforcement process while ensuring the protection of authenticity, integrity, and continuity for cultural relics.

Hydrogel-based therapeutic strategies for spinal cord injury repair: Recent advances and future prospects

Spinal cord injury (SCI) is a debilitating condition that can result in significant functional impairment and loss of quality of life. There is a growing interest in developing new therapies for SCI, and hydrogel-based multimodal therapeutic strategies have emerged as a promising approach. They offer several advantages for SCI repair, including biocompatibility, tunable mechanical properties, low immunogenicity, and the ability to deliver therapeutic agents. This article provides an overview of the recent advances in hydrogel-based therapy strategies for SCI repair, particularly within the past three years. We summarize the SCI hydrogels with varied characteristics such as phase-change hydrogels, self-healing hydrogel, oriented fibers hydrogel, and self-assembled microspheres hydrogel, as well as different functional hydrogels such as conductive hydrogels, stimuli-responsive hydrogels, adhesive hydrogel, antioxidant hydrogel, sustained-release hydrogel, etc. The composition, preparation, and therapeutic effect of these hydrogels are briefly discussed and comprehensively evaluated. In the end, the future development of hydrogels in SCI repair is prospected to inspire more researchers to invest in this promising field.

Application of Organic Gel on Skin Realized by Hydrogel/Organic Gel Adhesion

Diversity in solvent selection bestows the organic gel with appealing characteristics embracing antidrying, anti-icing, and antifouling abilities. However, organic gel, subjected to the "toxic" inherent property of solvent, is not able to be manipulated on skin. Herein, introducing the hydrogel layer amid organic gel and skin is envisaged to realize application of organic gel on skin. Hydrogel, inserted as the medium layer, works for the coupling role between skin and organic gel, also avoids the direct contact of organic gel toward skin. First, hydrogel system composed of acrylic acid is fabricated, meanwhile organic gel is prepared employing 2-hydroxyethyl methacrylate, ethylene glycol (EG) as solvent. Organic gel is able to adhere to hydrogel by hydrogen bonding resulting from carboxyl groups of polyacrylic acid chains and hydroxyl groups occurring on 2-hydroxyethyl methacrylate or EG. Additionally, hydrogen bonding enables the hydrogel to be firmly attached to skin, thus organic gel/hydrogel/skin assembly is produced. The further application of organic gel is exploited by incorporating stimuli-responsive dyes including spiropyran and rhodamine derivative.

A Review of Conductive Hydrogel-Based Wearable Temperature Sensors

Conductive hydrogel has garnered significant attention as an emergent candidate for diverse wearable sensors, owing to its remarkable and tailorable properties such as flexibility, biocompatibility, and strong electrical conductivity. These attributes make it highly suitable for various wearable sensor applications (e.g., biophysical, bioelectrical, and biochemical sensors) that can monitor human health conditions and provide timely interventions. Among these applications, conductive hydrogel-based wearable temperature sensors are especially important for healthcare and disease surveillance. This review aims to provide a comprehensive overview of conductive hydrogel-based wearable temperature sensors. First, this work summarizes different types of conductive fillers-based hydrogel, highlighting their recent developments and advantages as wearable temperature sensors. Next, this work discusses the sensing characteristics of conductive hydrogel-based wearable temperature sensors, focusing on sensitivity, dynamic stability, stretchability, and signal output. Then, state-of-the-art applications are introduced, ranging from body temperature detection and wound temperature detection to disease monitoring. Finally, this work identifies the remaining challenges and prospects facing this field. By addressing these challenges with potential solutions, this review hopes to shed some light on future research and innovations in this promising field.

A selective frequency damping and Janus adhesive hydrogel as bioelectronic interfaces for clinical trials

Maintaining stillness is essential for accurate bioelectrical signal acquisition, but dynamic noise from breathing remains unavoidable. Isotropic adhesives are often used as bioelectronic interfaces to ensure signal fidelity, but they can leave irreversible residues, compromising device accuracy. We propose a hydrogel with selective frequency damping and asymmetric adhesion as a bioelectronic interface. This hydrogel mitigates dynamic noise from breathing, with a damping effect in the breathing frequency range 60 times greater than at other frequencies. It also exhibits an asymmetric adhesion difference of up to 537 times, preventing residues. By homogenizing ion distribution, extending Debye length, and densifying the electric field, the hydrogel ensures stable signal transmission over 10,000 cycles. Additionally, it can non-invasively diagnose otitis media with higher sensitivity than invasive probes and has been effective in clinical polysomnography monitoring, aiding in the diagnosis of obstructive sleep apnea.

Multifunctional Conductive Hydrogel Interface for Bioelectronic Recording and Stimulation

The past few decades have witnessed the rapid advancement and broad applications of flexible bioelectronics, in wearable and implantable electronics, brain-computer interfaces, neural science and technology, clinical diagnosis, treatment, etc. It is noteworthy that soft and elastic conductive hydrogels, owing to their multiple similarities with biological tissues in terms of mechanics, electronics, water-rich, and biological functions, have successfully bridged the gap between rigid electronics and soft biology. Multifunctional hydrogel bioelectronics, emerging as a new generation of promising material candidates, have authentically established highly compatible and reliable, high-quality bioelectronic interfaces, particularly in bioelectronic recording and stimulation. This review summarizes the material basis and design principles involved in constructing hydrogel bioelectronic interfaces, and systematically discusses the fundamental mechanism and unique advantages in bioelectrical interfacing with the biological surface. Furthermore, an overview of the state-of-the-art manufacturing strategies for hydrogel bioelectronic interfaces with enhanced biocompatibility and integration with the biological system is presented. This review finally exemplifies the unprecedented advancement and impetus toward bioelectronic recording and stimulation, especially in implantable and integrated hydrogel bioelectronic systems, and concludes with a perspective expectation for hydrogel bioelectronics in clinical and biomedical applications.

A Universal Biocompatible and Multifunctional Solid Electrolyte in p-Type and n-Type Organic Electrochemical Transistors for Complementary Circuits and Bioelectronic Interfaces

The development of soft and flexible devices for collection of bioelectrical signals is gaining momentum for wearable and implantable applications. Among these devices, organic electrochemical transistors (OECTs) stand out due to their low operating voltage and large signal amplification capable of transducing weak biological signals. While liquid electrolytes have demonstrated efficacy in OECTs, they limit its operating temperature and pose challenges for electronic packaging due to potential leakage. Conversely, solid electrolytes offer advantages such as mechanical flexibility, robustness against environmental factors, and ability to bridge the interface between rigid dry electronics systems and soft wet biological tissues. However, few systems have demonstrated generality and compatibility with a wide range of state-of-the-art organic mixed ionic-electronic conductors (OMIECs). This paper introduces a highly stretchable, flexible, biocompatible, self-healable gelatin-based solid-state electrolyte, compatible with both p- and n-type OMIEC channels while maintaining high performance and excellent stability. Furthermore, this nonvolatile electrolyte is stable up to 120 °C and exhibits high ionic conductivity even in dry environment. Additionally, an OECT-based complementary inverter with a record-high normalized-gain of 228 V-1 and a corresponding ultralow static power consumption of 1 nW is demonstrated. These advancements pave the way for versatile applications ranging from bioelectronics to power-efficient implants.

Recent Advances in Natural-Polymer-Based Hydrogels for Body Movement and Biomedical Monitoring

In recent years, the interest in medical monitoring for human health has been rapidly increasing due to widespread concern. Hydrogels are widely used in medical monitoring and other fields due to their excellent mechanical properties, electrical conductivity and adhesion. However, some of the non-degradable materials in hydrogels may cause some environmental damage and resource waste. Therefore, organic renewable natural polymers with excellent properties of biocompatibility, biodegradability, low cost and non-toxicity are expected to serve as an alternative to those non-degradable materials, and also provide a broad application prospect for the development of natural-polymer-based hydrogels as flexible electronic devices. This paper reviews the progress of research on many different types of natural-polymer-based hydrogels such as proteins and polysaccharides. The applications of natural-polymer-based hydrogels in body movement detection and biomedical monitoring are then discussed. Finally, the present challenges and future prospects of natural polymer-based hydrogels are summarized.

Bioelectronics for electrical stimulation: materials, devices and biomedical applications

Bioelectronics is a hot research topic, yet an important tool, as it facilitates the creation of advanced medical devices that interact with biological systems to effectively diagnose, monitor and treat a broad spectrum of health conditions. Electrical stimulation (ES) is a pivotal technique in bioelectronics, offering a precise, non-pharmacological means to modulate and control biological processes across molecular, cellular, tissue, and organ levels. This method holds the potential to restore or enhance physiological functions compromised by diseases or injuries by integrating sophisticated electrical signals, device interfaces, and designs tailored to specific biological mechanisms. This review explains the mechanisms by which ES influences cellular behaviors, introduces the essential stimulation principles, discusses the performance requirements for optimal ES systems, and highlights the representative applications. From this review, we can realize the potential of ES based bioelectronics in therapy, regenerative medicine and rehabilitation engineering technologies, ranging from tissue engineering to neurological technologies, and the modulation of cardiovascular and cognitive functions. This review underscores the versatility of ES in various biomedical contexts and emphasizes the need to adapt to complex biological and clinical landscapes it addresses.

Natural polymer starch-based materials for flexible electronic sensor development: A review of recent progress

In response to the burgeoning interest in the development of highly conformable and resilient flexible electronic sensors capable of transducing diverse physical stimuli, this review investigates the pivotal role of natural polymers, specifically those derived from starch, in crafting sustainable and biocompatible sensing materials. Expounding on cutting-edge research, the exploration delves into innovative strategies employed to leverage the distinctive attributes of starch in conjunction with other polymers for the fabrication of advanced sensors. The comprehensive discussion encompasses a spectrum of starch-based materials, spanning all-starch-based gels to starch-based soft composites, meticulously scrutinizing their applications in constructing resistive, capacitive, piezoelectric, and triboelectric sensors. These intricately designed sensors exhibit proficiency in detecting an array of stimuli, including strain, temperature, humidity, liquids, and enzymes, thereby playing a pivotal role in the continuous and non-invasive monitoring of human body motions, physiological signals, and environmental conditions. The review highlights the intricate interplay between material properties, sensor design, and sensing performance, emphasizing the unique advantages conferred by starch-based materials, such as self-adhesiveness, self-healability, and re-processibility facilitated by dynamic bonding. In conclusion, the paper outlines current challenges and future research opportunities in this evolving field, offering valuable insights for prospective investigations.

Optimizing Silver Paste Conductivity with Controlled Convection for Nanowrinkle Growth

Conductive silver paste plays a crucial role as an interconnecting material between electrodes and circuits in electronic circuits and solar cells. The quality of the silver paste is greatly influenced by the preparation of the conductive-phase silver powder and the sintering process. This study investigated the impact of fluid dynamics on the preparation of silver powder. Combined with X-ray diffractometer characterization and molecular dynamics simulation, the formation mechanism of wrinkled silver powder was explained. The wrinkled silver powder replaced the traditional smooth spherical silver powder, and the point contact between the smooth silver powder turned into a line and surface contact. After mixing and sintering with the micrometer flake silver powder, the electrical conductivity and sintering morphology of the silver paste were improved. Compared with the silver content of conventional silver paste (≥75 wt %), the silver paste of (9.23 ± 0.68) × 10-6 Ω cm can be prepared by curing at 250 °C for 45 min when wrinkled powder/flake powder = 1:1 and silver paste content was only 66.7%. This research work provides a new idea for the morphology control of submicrometer silver powder, which has important applications in the field of low-temperature silver paste for new N-type batteries.

Dual network composite hydrogels with robust antibacterial and antifouling capabilities for efficient wound healing

Wound dressings play a critical role in the wound healing process; however, conventional dressings often address singular functions, lacking versatility in meeting diverse wound healing requirements. Herein, dual-network, multifunctional hydrogels (PSA/CS-GA) have been designed and synthesized through a one-pot approach. The in vitro and in vivo experiments demonstrate that the optimized hydrogels have exceptional antifouling properties, potent antibacterial effects and rapid hemostatic capabilities. Notably, in a full-thickness rat wound model, the hydrogel group displays a remarkable wound healing rate exceeding 95% on day 10, surpassing both the control group and the commercial 3M group. Furthermore, the hydrogels exert an anti-inflammatory effect by reducing inflammatory factors interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α), enhance the release of the vascular endothelial growth factor (VEGF) to promote blood vessel proliferation, and augment collagen deposition in the wound, thus effectively accelerating wound healing in vivo. These innovative hydrogels present a novel and highly effective approach to wound healing.

Biocompatible Tough Ionogels with Reversible Supramolecular Adhesion

Cohesive and interfacial adhesion energies are difficult to balance to obtain reversible adhesives with both high mechanical strength and high adhesion strength, although various methods have been extensively investigated. Here, a biocompatible citric acid/L-(-)-carnitine (CAC)-based ionic liquid was developed as a solvent to prepare tough and high adhesion strength ionogels for reversible engineered and biological adhesives. The prepared ionogels exhibited good mechanical properties, including tensile strength (14.4 MPa), Young's modulus (48.1 MPa), toughness (115.2 MJ m-3), and high adhesion strength on the glass substrate (24.4 MPa). Furthermore, the ionogels can form mechanically matched tough adhesion at the interface of wet biological tissues (interfacial toughness about 191 J m-2) and can be detached by saline solution on demand, thus extending potential applications in various clinical scenarios such as wound adhesion and nondestructive transfer of organs.

Self-Healing Hydrogel Bioelectronics

Hydrogels have emerged as powerful building blocks to develop various soft bioelectronics because of their tissue-like mechanical properties, superior bio-compatibility, the ability to conduct both electrons and ions, and multiple stimuli-responsiveness. However, hydrogels are vulnerable to mechanical damage, which limits their usage in developing durable hydrogel-based bioelectronics. Self-healing hydrogels aim to endow bioelectronics with the property of repairing specific functions after mechanical failure, thus improving their durability, reliability, and longevity. This review discusses recent advances in self-healing hydrogels, from the self-healing mechanisms, material chemistry, and strategies for multiple properties improvement of hydrogel materials, to the design, fabrication, and applications of various hydrogel-based bioelectronics, including wearable physical and biochemical sensors, supercapacitors, flexible display devices, triboelectric nanogenerators (TENGs), implantable bioelectronics, etc. Furthermore, the persisting challenges hampering the development of self-healing hydrogel bioelectronics and their prospects are proposed. This review is expected to expedite the research and applications of self-healing hydrogels for various self-healing bioelectronics.

Advances in Stimuli-Responsive Chitosan Hydrogels for Drug Delivery Systems

Sustainable and controllable drug transport is one of the most efficient ways of disease treatment. Due to high biocompatibility, good biodegradability, and low costs, chitosan and its derivatives are widely used in biomedical fields. Specifically, chitosan hydrogel enables drugs to pass through biological barriers because of their abundant amino and hydroxyl groups that can interact with human tissues. Moreover, the multi-responsive nature (pH, temperature, ions strength, and magnetic field, etc.) of chitosan hydrogels makes precise drug release a possibility. Here, the synthesis methods, modification strategies, stimuli-responsive mechanisms of chitosan-based hydrogels, and their recent progress in drug delivery are summarized. Chitosan hydrogels that carry and release drugs through subcutaneous (dealing with wound dressing), oral (dealing with gastrointestinal tract), and facial (dealing with ophthalmic, ear, and brain) are reviewed. Finally, challenges toward clinic application and the future prospects of stimuli-responsive chitosan-based hydrogels are indicated.

Mussel-inspired chitin nanofiber adherable hydrogel sensor with interpenetrating network and great fatigue resistance for motion and acoustics monitoring

A method for grafting dopamine onto TEMPO-oxidized chitin nanofibers (TOChN) was developed, achieving a surface grafting rate of 54 % through the EDC/NHS reaction. This process resulted in the formation of dopamine-grafted TOChN (TOChN-DA). Subsequently, an adherent, highly sensitive, fatigue-resistant conductive PAM/TOChN-PDA/Fe3+ (PTPF) hydrogel was successfully synthesized based on the composition of polyacrylamide (PAM) and TOChN-DA, which exhibited good cell compatibility, a tensile strength of 89.42 kPa, and a high adhesion strength of 62.56 kPa with 1.2 wt% TOChN-DA. Notably, the PTPF hydrogel showed stable adherence to various surfaces, such as rubber, copper, and human skin. Specifically, the addition of FeCl3 contributed to a multifunctional design in the PTPF interpenetrating network (IPN) hydrogel, endowing it with conductivity, cohesion, and antioxidant properties, which facilitated sensitive motion and acoustics monitoring. Moreover, the PTPF hydrogel demonstrated exceptional fatigue resistance and sensing stability, maintaining performance at 50 % strain over 1000 cycles. These attributes render the PTPF hydrogel a promising candidate for advanced biosensors in medical and athletic applications.

Gallic acid: design of a pyrogallol-containing hydrogel and its biomedical applications

Polyphenol hydrogels have garnered widespread attention due to their excellent adhesion, antioxidant, and antibacterial properties. Gallic acid (GA) is a typical derivative of pyrogallol that is used as a hydrogel crosslinker or bioactive additive and can be used to make multifunctional hydrogels with properties superior to those of widely studied catechol hydrogels. Furthermore, compared to polymeric tannic acid, gallic acid is more suitable for chemical modification, thus broadening its range of applications. This review focuses on multifunctional hydrogels containing GA, aiming to inspire researchers in future biomaterial design. We first revealed the interaction mechanisms between GA molecules and between GA and polymers, analyzed the characteristics GA imparts to hydrogels and compared GA hydrogels with hydrogels containing catechol. Subsequently, in this paper, various methods of integrating GA into hydrogels and the applications of GA in biomedicine are discussed, finally assessing the current limitations and future development potential of GA. In summary, GA, a natural small molecule polyphenol with excellent functionality and diverse interaction modes, has great potential in the field of biomedical hydrogels.

Self-adhesive wearable poly (vinyl alcohol)-based hybrid biofuel cell powered by human bio-fluids

Advancement of wearable microelectronics demands their power source with continuous energy supply, skin-integration and miniaturization. In light of poly (vinyl alcohol) (PVA) hydrogel with nontoxicity, good biocompatibility and low cost, an advanced wearable PVA-based hybrid biofuel cells (HBFCs) with high self-adhesiveness was developed. Through the reaction between PVA molecules and succinic anhydride (SAA), the carboxylated PVA (PVA/SAA) was obtained, and by incorporation with PDA as crosslinker, the self-adhesive PVA/SAA-DA hydrogel electrolytes formed by dual covalent and hydrogen bonding. With increasing SAA and PDA content, the pore size decreased, and a uniform and dense network formed, endowing the hydrogel with a relatively high absorption capacity of PBS solution of lactate as cell fuel. Meanwhile the various functional groups of hydrogel, including catechol, quinone, amino and hydroxyl groups, contributed to impressive tissue adhesion strength against pigskin under dry and wet conditions. The PVA/SAA-DA hydrogel displayed high conductive property, and the integrated PVA-based HBFC generated open circuit voltage of 0.50 V and maximum power density of 128.76 μW/cm2 in 20 mM lactate solution, which was optimized to be 0.57 V/224.85 μW/cm2 when the pore size was enlarged. The power retention reached above 70% in one week, showing long-term stability of HBFC. The PVA-based HBFC was further adhered to human skin without extra adhesive tapes to scavenge human sweat as biofuel, and the maximum power density reached 85.34 μW/cm2, while by connected with a DC-DC converter, the HBFC could power watch, exhibiting promising application potentials as wearable electronic device to provide bioelectricity.

Strong and tough polysaccharide organohydrogels for strain, humidity and temperature sensors

To avoid the potential toxicity of monomer residues in synthetic polymer based organohydrogels, natural polysaccharide-based organohydrogels are expected to be used in multi-functional wearable sensory systems, but most of them have unsatisfactory stiffness, strength and fracture toughness. Herein, a cooking and soaking strategy is proposed to prepare novel natural polysaccharide-based organohydrogels possessing outstanding stiffness, strength, toughness, freezing resistance, heating resistance and long-term durability. The agar organohydrogel exhibits a fracture stress of 3.3 MPa, a Young's modulus of 2.26 MPa and a fracture toughness of 14.8 kJ m-2, the κ-carrageenan organohydrogel exhibits a fracture stress of 3.3 MPa, a Young's modulus of 4.34 MPa and a fracture toughness of 11.0 kJ m-2, and the gellan organohydrogel exhibits a fracture stress of 1.2 MPa, a Young's modulus of 2.81 MPa and a fracture toughness of 5.4 kJ m-2. Furthermore, the agar organohydrogels are assembled into multi-functional wearable sensors by introducing NaCl as a conducting agent exhibiting responses to strain (5-150%), temperature (-15 to 60 °C) and humidity (11-97%), and possessing exceptional multi-sensory capabilities. Therefore, the developed strategy has shown a new pathway towards strengthening polysaccharide-based organohydrogels with potential for application in wearable sensory systems.

Flexible and Stretchable Light-Emitting Diodes and Photodetectors for Human-Centric Optoelectronics

Optoelectronic devices with unconventional form factors, such as flexible and stretchable light-emitting or photoresponsive devices, are core elements for the next-generation human-centric optoelectronics. For instance, these deformable devices can be utilized as closely fitted wearable sensors to acquire precise biosignals that are subsequently uploaded to the cloud for immediate examination and diagnosis, and also can be used for vision systems for human-interactive robotics. Their inception was propelled by breakthroughs in novel optoelectronic material technologies and device blueprinting methodologies, endowing flexibility and mechanical resilience to conventional rigid optoelectronic devices. This paper reviews the advancements in such soft optoelectronic device technologies, honing in on various materials, manufacturing techniques, and device design strategies. We will first highlight the general approaches for flexible and stretchable device fabrication, including the appropriate material selection for the substrate, electrodes, and insulation layers. We will then focus on the materials for flexible and stretchable light-emitting diodes, their device integration strategies, and representative application examples. Next, we will move on to the materials for flexible and stretchable photodetectors, highlighting the state-of-the-art materials and device fabrication methods, followed by their representative application examples. At the end, a brief summary will be given, and the potential challenges for further development of functional devices will be discussed as a conclusion.

A 3D printable tissue adhesive

Tissue adhesives are promising alternatives to sutures and staples for joining tissues, sealing defects, and immobilizing devices. However, existing adhesives mostly take the forms of glues or hydrogels, which offer limited versatility. We report a direct-ink-write 3D printable tissue adhesive which can be used to fabricate bioadhesive patches and devices with programmable architectures, unlocking new potential for application-specific designs. The adhesive is conformable and stretchable, achieves robust adhesion with wet tissues within seconds, and exhibits favorable biocompatibility. In vivo rat trachea and colon defect models demonstrate the fluid-tight tissue sealing capability of the printed patches, which maintained adhesion over 4 weeks. Moreover, incorporation of a blood-repelling hydrophobic matrix enables the printed patches to seal actively bleeding tissues. Beyond wound closure, the 3D printable adhesive has broad applicability across various tissue-interfacing devices, highlighted through representative proof-of-concept designs. Together, this platform offers a promising strategy toward developing advanced tissue adhesive technologies.

Fabrication of highly stretchable salt and solvent blended PEDOT:PSS/PVA free-standing films: non-linear to linear electrical conduction response

Nowadays, ductile and conducting polymeric materials are highly utilizable in the realm of stretchable organic electronics. Here, mechanically ductile and electrically conducting free-standing films are fabricated by blending different solvents such as dimethyl sulfoxide (DMSO), diethylene glycol (DEG) and N,N-dimethylformamide (DMF), and salts such as silver nitrate (AgNO3), zinc chloride (ZnCl2), copper chloride (CuCl2) and indium chloride (InCl3) with the homogeneous solution of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and poly(vinyl alcohol) (PVA) through solution casting method. The presence of salt modifies the PEDOT conformation from benzoid to quinoid, and induces the evolution of different morphologies. ZnCl2 or AgNO3 blended films have lower surface roughness and good miscibility with polymers, while CuCl2 or InCl3 blended films have relatively higher surface roughness as well as irregularly distributed surface morphology. Some crystalline domains are also formed due to the salt agglomeration. The presence of salt inside PEDOT:PSS/PVA/solvent system changes the current-voltage response from non-linear to linear. Among all the films, zinc salt blended PEDOT:PSS/PVA/DMSO, PEDOT:PSS/PVA/DEG and PEDOT:PSS/PVA/DMF films have higher conductivity, and zinc salt blended PEDOT:PSS/PVA/DEG film shows the highest conductivity of 0.041 ± 0.0014 S cm-1, while silver salt blended PEDOT:PSS/PVA/DMSO, PEDOT:PSS/PVA/DEG and PEDOT:PSS/PVA/DMF films have higher elongation at break, and silver salt blended PEDOT:PSS/PVA/DMSO film shows the highest elongation at break of 670 ± 31%. Both the charge carriers, i.e., electrons and ions, contribute to the electrical conduction, and the presence of hydrogen bonds and ionic interactions among PEDOT+, PSS-, PVA, residual solvent, salt cations and anions modifies the film behaviours. Among all the films, ZnCl2 blended PEDOT:PSS/PVA/DMSO film offers relatively superior behaviours having higher conductivity (0.025 ± 0.0013 S cm-1) and elongation at break (517 ± 15%), and therefore can have potential applications in the fields of wearable devices, bioelectronics, etc.

A "Mesh Scaffold" that regulates the mechanical properties and restricts the phase transition-induced volume change of the PNIPAM-based hydrogel for wearable sensors

Poly(N-isopropylacrylamide) (PNIPAM) is capable of improving the reversibility and responsiveness of flexible electronics. However, its phase transition-induced volume variation and poor adhesiveness remain limitations for expending its applications. Herein, a pressure-sensitive adhesive (PSA), which is a type of mesh scaffold, is constructed inside the network of PNIPAM, providing the hydrogel with a constant volume in response to different temperatures, in situ tunable mechanical properties, and superior adhesiveness. The reversible density of the mesh scaffold adjusts the aggregation state of the hydrogel chains, whereupon it is capable of changing its mechanical modulus from 6.7 kPa to 45.3 kPa. This mechanical mechanism contributes to hydrogel-based flexible devices for multiple applications, especially in pressure-related sensors. The mesh scaffold restricts the phase-transition-induced volume variation, which allows the hydrogel sensor to stably monitor the external pressure at various temperatures. The high adhesion enables the effective interfacial interaction with the skin, avoiding the loss of sensing signals during the detection of human body movements. When it is assembled into an electronic device, it can transmit information and recognize sign language via Morse code. Thus, herein, we report a hydrogel sensor that is promising for pressure detection in temperature-unstable environments, especially for managing the health of patients who require emergency medical care through sign language recognition.

Peptide Stereochemistry Effects from pKa-Shift to Gold Nanoparticle Templating in a Supramolecular Hydrogel

The divergent supramolecular behavior of a series of tripeptide stereoisomers was elucidated through spectroscopic, microscopic, crystallographic, and computational techniques. Only two epimers were able to effectively self-organize into amphipathic structures, leading to supramolecular hydrogels or crystals, respectively. Despite the similarity between the two peptides' turn conformations, stereoconfiguration led to different abilities to engage in intramolecular hydrogen bonding. Self-assembly further shifted the pKa value of the C-terminal side chain. As a result, across the pH range 4-6, only one epimer predominated sufficiently as a zwitterion to reach the critical molar fraction, allowing gelation. By contrast, the differing pKa values and higher dipole moment of the other epimer favored crystallization. The four stereoisomers were further tested for gold nanoparticle (AuNP) formation, with the supramolecular hydrogel being the key to control and stabilize AuNPs, yielding a nanocomposite that catalyzed the photodegradation of a dye. Importantly, the AuNP formation occurred without the use of reductants other than the peptide, and the redox chemistry was investigated by LC-MS, NMR, and infrared scattering-type near field optical microscopy (IR s-SNOM). This study provides important insights for the rational design of simple peptides as minimalistic and green building blocks for functional nanocomposites.

Hydrogel Loaded with Components for Therapeutic Applications in Hypertrophic Scars and Keloids

Hypertrophic scars and keloids are common fibroproliferative diseases following injury. Patients with pathologic scars suffer from impaired quality of life and psychological health due to appearance disfiguration, itch, pain, and movement disorders. Recently, the advancement of hydrogels in biomedical fields has brought a variety of novel materials, methods and therapeutic targets for treating hypertrophic scars and keloids, which exhibit broad prospects. This review has summarized current research on hydrogels and loaded components used in preventing and treating hypertrophic scars and keloids. These hydrogels attenuate keloid and hypertrophic scar formation and progression by loading organic chemicals, drugs, or bioactive molecules (such as growth factors, genes, proteins/peptides, and stem cells/exosomes). Among them, smart hydrogels (a very promising method for loading many types of bioactive components) are currently favoured by researchers. In addition, combining hydrogels and current therapy (such as laser or radiation therapy, etc.) could improve the treatment of hypertrophic scars and keloids. Then, the difficulties and limitations of the current research and possible suggestions for improvement are listed. Moreover, we also propose novel strategies for facilitating the construction of target multifunctional hydrogels in the future.

A 10-micrometer-thick nanomesh-reinforced gas-permeable hydrogel skin sensor for long-term electrophysiological monitoring

Hydrogel-enabled skin bioelectronics that can continuously monitor health for extended periods is crucial for early disease detection and treatment. However, it is challenging to engineer ultrathin gas-permeable hydrogel sensors that can self-adhere to the human skin for long-term daily use (>1 week). Here, we present a ~10-micrometer-thick polyurethane nanomesh-reinforced gas-permeable hydrogel sensor that can self-adhere to the human skin for continuous and high-quality electrophysiological monitoring for 8 days under daily life conditions. This research involves two key steps: (i) material design by gelatin-based thermal-dependent phase change hydrogels and (ii) robust thinness geometry achieved through nanomesh reinforcement. The resulting ultrathin hydrogels exhibit a thickness of ~10 micrometers with superior mechanical robustness, high skin adhesion, gas permeability, and anti-drying performance. To highlight the potential applications in early disease detection and treatment that leverage the collective features, we demonstrate the use of ultrathin gas-permeable hydrogels for long-term, continuous high-precision electrophysiological monitoring under daily life conditions up to 8 days.

Multifunctional chitosan-based gel sponge with efficient antibacterial, hemostasis and strong adhesion

Developing wound dressings with solid adhesive properties that enable efficient, painless hemostasis and prevent wound infection remain a huge challenge. Herein, the tris(hydroxymethyl) methyl glycine-modified chitosan derivative (CTMG) was prepared and freeze-dried after simply adjusting the concentration of CTMG to obtain the chitosan-based gel sponge with desired multi-hollow structure, special antibacterial and biocompatibility. The adhesion strength on porcine skin was impressive up to 113 KPa, much higher than fibrin glue. It can withstand the pressure that far exceeds blood pressure. CTMG exhibits bacteriostatic abilities as demonstrated in a bacteriostatic assay, and alongside biocompatibility, as shown in cytotoxicity and hemolytic assays. Moreover, CTMG gel sponge showed hemostatic properties in both in vivo and in vitro hemostasis experiments. During an experiment on liver hemorrhage in rats, CTMG gel sponge proved to be more effective in controlling bleeding than other hemostatic sponges available on the market, indicating its promising hemostatic properties. CTMG gel sponge possesses the potential to function as a wound dressing and hemostatic material, making it suitable for various clinical applications.

A multifunctional sensor for real-time monitoring and pro-healing of frostbite wounds

Flexible epidermal sensors based on conductive hydrogels hold great promise for various applications, such as wearable electronics and personal healthcare monitoring. However, the integration of conductive hydrogel epidermal sensors into multiple applications remains challenging. In this study, a multifunctional PAAm/PEG/hydrolyzed keratin (Hereinafter referred to as HK)/MXene conductive hydrogel (PPHM hydrogel) was designed as a high-performance therapeutic all-in-one epidermal sensor. This sensor not only accelerates wound healing but also provides wearable human-computer interaction. The developed sensor possesses highly sensitive sensing properties (Gauge Factor = 4.82 at high strain), strong mechanical tensile properties (capable of achieving a maximum elongation at break of 600 %), rapid self-healing capability, stable self-adhesive capability, biocompatibility, freeze resistance at -20 °C, and adjustable photo-thermal conversion capability. This therapeutic all-in-one sensor can sensitively monitor human movements, enabling the detection of small electrophysiological signals for diagnosing relevant activities and diseases. Furthermore, using a rat frostbite model, we demonstrated that the composite hydrogel sensor can serve as an effective wound dressing to accelerate the healing process. This study serves as a valuable reference for the development of multifunctional flexible epidermal sensors for personal smart health monitoring. STATEMENT OF SIGNIFICANCE: Accelerated wound healing reduces the risk of wound infection, and conductive hydrogel-based sensors can monitor physiological signals. The multifunctional application of conductive hydrogel sensors combined with wound diagnostic and therapeutic capabilities can meet personalized medical requirements for wound healing and sensor monitoring. The aim of this study is to develop a multifunctional hydrogel patch. The multifunctional hydrogel can be assembled into a flexible wearable high-performance diagnostic and therapeutic integrated sensor that can effectively accelerate the healing of frostbite wounds and satisfy the real-time monitoring of multi-application scenarios. We expect that this study will inform efforts to integrate wound therapy and sensor monitoring.

Conductive, water-retaining and knittable hydrogel fiber from xanthan gum and aniline tetramer modified-polysaccharide for strain and pressure sensors

Herein, we explored strategies for defoaming and controllable adjustment of spinnable and mechanical properties of polyanion polysaccharide-based hydrogels to fabricate conductive, water-retaining, and knittable hydrogel fibers for next-generation flexible electronics. Xanthan gum (XG) and aniline tetramer modified-polysaccharide (TMAT38) were crosslinked with sodium trimetaphosphate (STMP) and subsequently by Fe3+/Fe2+ ions coordination to prepare conductive and spinnable hydrogels. Polypropylene glycol was introduced as chemical antifoam, and solvent displacement method was adopted to improve mechanical and water-retaining properties. The glycerol-immersed XG5-TMAT38-STMP-Fe3+/CA-PPG hydrogel exhibited conductivity of 3.55×10-3-27.30×10-3 S/cm, storage modulus at linear viscoelastic region of 573 Pa-1717 Pa and self-healing percentage of 100 %-108 %. The 2 h glycerol-immersed hydrogel fibers with good flexibility, moisture retention and freezing tolerance were ready to bend and knit into fabrics. The hydrogel fiber braid possessed better conductivity, reliability and durability than the single hydrogel fiber as strain sensors. The hydrogel fiber fabric perceived tiny vibration triggered by swallowing, speaking and writing with good sensitivity and reproducibility. Furthermore, a three-component model was developed to evaluate response sensitivity and recoverability of the hydrogel fiber fabric-based pressure sensors, which facilitated understanding transient response of polymer-based hydrogel strain and pressure sensors.

A Nature-Inspired Versatile Bio-Adhesive

The application of most hydrogel bio-adhesives is greatly limited due to their high swelling, low underwater adhesion, and single function. Herein, a spatial multi-level physical-chemical and bio-inspired in-situ bonding strategy is proposed, to develop a multifunctional hydrogel bio-glue using polyglutamic acid (PGA), tyramine hydrochloride (TYR), and tannic acid (TA) as precursors and 4-(4,6-dimethoxytriazine-2-yl) -4-methylmorpholine hydrochloride(DMTMM) as condensation agent, which is used for tissue adhesion, hemostasis and repair. By introducing TYR and TA into the PGA chain, it is demonstrated that not only can the strong adhesion of bio-glue to the surface of various fresh tissues and wet materials be realized through the synergistic effect of spatial multi-level physical and chemical bonding, but also this glue can be endowed with the functions of anti-oxidation and hemostasis. The excellent performance of such bio-glue in the repair of the wound, liver, and cartilage is achieved, showing a great potential in clinical application for such bio-glue. This study will open up a brand-new avenue for the development of multifunctional hydrogel biological adhesive.

Cancer Immunotherapy Using Bioengineered Micro/Nano Structured Hydrogels

Hydrogels, a class of materials with a 3D network structure, are widely used in various applications of therapeutic delivery, particularly cancer therapy. Micro and nanogels as miniaturized structures of the bioengineered hydrogels may provide extensive benefits over the common hydrogels in encapsulation and controlled release of small molecular drugs, macromolecular therapeutics, and even cells. Cancer immunotherapy is rapidly developing, and micro/nanostructured hydrogels have gained wide attention regarding their engineered payload release properties that enhance systemic anticancer immunity. Additionally, they are a great candidate due to their local administration properties with a focus on local immune cell manipulation in favor of active and passive immunotherapies. Although applied locally, such micro/nanostructured can also activate systemic antitumor immune responses by releasing nanovaccines safely and effectively inhibiting tumor metastasis and recurrence. However, such hydrogels are mostly used as locally administered carriers to stimulate the immune cells by releasing tumor lysate, drugs, or nanovaccines. In this review, the latest developments in cancer immunotherapy are summarized using micro/nanostructured hydrogels with a particular emphasis on their function depending on the administration route. Moreover, the potential for clinical translation of these hydrogel-based cancer immunotherapies is also discussed.

Extracellular Matrix-Mimetic Immunomodulatory Hydrogel for Accelerating Wound Healing

Macrophages play a crucial role in the complete processes of tissue repair and regeneration, and the activation of M2 polarization is an effective approach to provide a pro-regenerative immune microenvironment. Natural extracellular matrix (ECM) has the capability to modulate macrophage activities via its molecular, physical, and mechanical properties. Inspired by this, an ECM-mimetic hydrogel strategy to modulate macrophages via its dynamic structural characteristics and bioactive cell adhesion sites is proposed. The LZM-SC/SS hydrogel is in situ formed through the amidation reaction between lysozyme (LZM), 4-arm-PEG-SC, and 4-arm-PEG-SS, where LZM provides DGR tripeptide for cell adhesion, 4-arm-PEG-SS provides succinyl ester for dynamic hydrolysis, and 4-arm-PEG-SC balances the stability and dynamics of the network. In vitro and subcutaneous tests indicate the dynamic structural evolution and cell adhesion capacity promotes macrophage movement and M2 polarization synergistically. Comprehensive bioinformatic analysis further confirms the immunomodulatory ability, and reveals a significant correlation between M2 polarization and cell adhesion. A full-thickness wound model is employed to validate the induced M2 polarization, vessel development, and accelerated healing by LZM-SC/SS. This study represents a pioneering exploration of macrophage modulation by biomaterials' structures and components rather than drug or cytokines and provides new strategies to promote tissue repair and regeneration.

Chitosan-based mussel-inspired hydrogel for rapid self-healing and high adhesion of tissue adhesion and wound dressings

The hydrogel wound dressing with self-healing and adhesive property can provide better protection to the wound and prolong the service life of the material. Inspired by mussels, a high-adhesion, injectable, self-healing and antibacterial hydrogel was designed in this study. The lysine (Lys) and the catechol compound 3,4-dihydroxyphenylacetic acid (DOPAC) were grafted onto chitosan (CS). The presence of catechol group endows the hydrogel strong adhesion and antioxidation. In the experiment of wound healing in vitro, the hydrogel can adhere to the wound surface and promote wound heal. In addition, it has been proved the hydrogel has good antibacterial properties against S. aureus and E. coli. The treatment of CLD hydrogel, the degree of wound inflammation was significantly alleviated. The levels of TNF-α, IL-1β, IL-6 and TGF-β1 were reduced from 39.8379 %, 31.6768 %, 32.1015 % and 38.4911 % to 18.5931 %, 12.2275 %, 13.0524 % and 16.9959 %, respectively. And the levels of PDGFD and CD31 were increased from 35.6054 %, 21.7394 % to 51.8555 %, 43.9326 %, respectively. These results indicated that the CLD hydrogel has a good ability to promote angiogenesis, thickening of skin and epithelial structures.

Chitosan-Based Self-Healing Hydrogel: From Fabrication to Biomedical Application

Biocompatible self-healing hydrogels are new-generation smart soft materials that hold great promise in biomedical fields. Chitosan-based self-healing hydrogels, mainly prepared via dynamic imine bonds, have attracted broad attention due to their mild preparation conditions, excellent biocompatibility, and self-recovery ability under a physiological environment. In this review, we present a comprehensive overview of the design and fabrication of chitosan-based self-healing hydrogels, and summarize their biomedical applications in tissue regeneration, customized drug delivery, smart biosensors, and three/four dimensional (3D/4D) printing. Finally, we will discuss the challenges and future perspectives for the development of chitosan-based self-healing hydrogels in the biomedical field.

Konjac glucomannan-based hydrogels with health-promoting effects for potential edible electronics applications: A mini-review

Konjac glucomannan (KGM), a dietary fiber hydrocolloid polysaccharide isolated from Amorphophallus konjac tubers, has potential applications in various fields. However, the use of KGM-based hydrogels has mainly focused on the food, biomedical, and water treatment industries. KGM possesses several health benefits and could be a promising candidate for use in edible electronics. This paper presents the first review of KGM-based hydrogels as edible electronics and their potential health benefits. The paper initially focuses on the health-promoting effects of KGM-based hydrogels, such as prebiotic effects, antiobesity, antioxidant, and antibacterial properties. Then, it discusses the feasible design strategies for KGM-based hydrogels as edible electronics, considering their flexibility, mechanical properties, response to stimuli, degradability aspects, their role as electronic device components, and the retention period of the devices. Finally, this review outlines future directions for developing KGM-based hydrogels for use in edible electronics.

Bioadhesive polymer semiconductors and transistors for intimate biointerfaces

The use of bioelectronic devices relies on direct contact with soft biotissues. For transistor-type bioelectronic devices, the semiconductors that need to have direct interfacing with biotissues for effective signal transduction do not adhere well with wet tissues, thereby limiting the stability and conformability at the interface. We report a bioadhesive polymer semiconductor through a double-network structure formed by a bioadhesive brush polymer and a redox-active semiconducting polymer. The resulting semiconducting film can form rapid and strong adhesion with wet tissue surfaces together with high charge-carrier mobility of ~1 square centimeter per volt per second, high stretchability, and good biocompatibility. Further fabrication of a fully bioadhesive transistor sensor enabled us to produce high-quality and stable electrophysiological recordings on an isolated rat heart and in vivo rat muscles.

Controlling C2C12 Cytotoxicity on Liquid Metal Embedded Elastomer (LMEE)

Liquid metal embedded elastomers (LMEEs) are highly stretchable composites comprising microscopic droplets of eutectic gallium-indium (EGaIn) liquid metal embedded in a soft rubber matrix. They have a unique combination of mechanical, electrical, and thermal properties that make them attractive for potential applications in flexible electronics, thermal management, wearable computing, and soft robotics. However, the use of LMEEs in direct contact with human tissue or organs requires an understanding of their biocompatibility and cell cytotoxicity. In this study, the cytotoxicity of C2C12 cells in contact with LMEE composites composed of EGaIn droplets embedded with a polydimethylsiloxane (PDMS) matrix is investigated. In particular, the influence of EGaIn volume ratio and shear mixing time during synthesis on cell proliferation and viability is examined. The special case of electrically-conductive LMEE composites in which a percolating network of EGaIn droplets is created through "mechanical sintering" is also examined. This study in C2C12 cytotoxicity represents a first step in determining whether LMEE is safe for use in implantable biomedical devices and biohybrid systems.

Hydrogel-Based Bioelectronics and Their Applications in Health Monitoring

Flexible bioelectronics exhibit promising potential for health monitoring, owing to their soft and stretchable nature. However, the simultaneous improvement of mechanical properties, biocompatibility, and signal-to-noise ratio of these devices for health monitoring poses a significant challenge. Hydrogels, with their loose three-dimensional network structure that encapsulates massive amounts of water, are a potential solution. Through the incorporation of polymers or conductive fillers into the hydrogel and special preparation methods, hydrogels can achieve a unification of excellent properties such as mechanical properties, self-healing, adhesion, and biocompatibility, making them a hot material for health monitoring bioelectronics. Currently, hydrogel-based bioelectronics can be used to fabricate flexible bioelectronics for motion, bioelectric, and biomolecular acquisition for human health monitoring and further clinical applications. This review focuses on materials, devices, and applications for hydrogel-based bioelectronics. The main material properties and research advances of hydrogels for health monitoring bioelectronics are summarized firstly. Then, we provide a focused discussion on hydrogel-based bioelectronics for health monitoring, which are classified as skin-attachable, implantable, or semi-implantable depending on the depth of penetration and the location of the device. Finally, future challenges and opportunities of hydrogel-based bioelectronics for health monitoring are envisioned.

Role of nano-hydrogels coated exosomes in bone tissue repair

With the development of nanotechnology, nanomaterials are widely applied in different areas. Some nanomaterials are designed to be biocompatible and can be used in the medical field, playing an important role in disease treatment. Exosomes are nanoscale vesicles with a diameter of 30-200 nm. Studies have shown that exosomes have the effect of angiogenesis, tissue (skin, tendon, cartilage, et al.) repair and reconstruction. Nano-hydrogels are hydrogels with a diameter of 200 nm or less and can be used as the carrier to transport the exosomes into the body. Some orthopedic diseases, such as bone defects and bone infections, are difficult to handle. The emergence of nano-hydrogels coated exosomes may provide a new idea to solve these problems, improving the prognosis of patients. This review summarizes the function of nano-hydrogels coated exosomes in bone tissue repair, intending to illustrate the potential use and application of nano-hydrogels coated exosomes in bone disease.

Near-Infrared Light-Responsive Hydrogels for Highly Flexible Bionic Photosensors

Soft biological tissues perform various functions. Sensory nerves bring sensations of light, voice, touch, pain, or temperature variation to the central nervous system. Animal senses have inspired tremendous sensors for biomedical applications. Following the same principle as photosensitive nerves, we design flexible ionic hydrogels to achieve a biologic photosensor. The photosensor allows responding to near-infrared light, which is converted into a sensory electric signal that can communicate with nerve cells. Furthermore, with adjustable thermal and/or electrical signal outputs, it provides abundant tools for biological regulation. The tunable photosensitive performances, high flexibility, and low cost endow the photosensor with widespread applications ranging from neural prosthetics to human-machine interfacing systems.

Bio-Inspired Homogeneous Conductive Hydrogel with Flexibility and Adhesiveness for Information Transmission and Sign Language Recognition

The wearable electronic technique is increasingly becoming an effective approach to overcoming the communication obstacles between signers and non-signers. However, the efficacy of conducting hydrogels currently proposed as flexible sensor devices is hindered by their poor processability and matrix mismatch, which frequently results in adhesion failure at the combined interfaces and deterioration of mechanical and electrochemical performance. Herein, we propose a hydrogel composed of a rigid matrix in which the hydrophobic and aggregated polyaniline was homogeneously embedded, while quaternate-functionalized nucleobase moieties endowed the flexible network with adhesiveness. Accordingly, the resulting hydrogel with chitosan-graft-polyaniline (chi-g-PANI) copolymers exhibited a promising conductivity (4.8 S·m^-1) because of the uniformly dispersed polyaniline components and a high strain strength (0.84 MPa) because of the chain entanglement of chitosan after soaking. In addition, the modified adenine molecules not only realized synchronization in improving the stretchability (up to 1303%) and exhibiting a skin-like elastic modulus (≈184 kPa), but also provided a durable interfacial contact with various materials. The hydrogel was further fabricated into a strain-monitoring sensor for information encryption and sign language transmission based on its sensing stability and strain sensitivity of up to 2.77. The developed wearable sign language interpreting system provides an innovative strategy to assist auditory or speech-impaired people in communicating with non-signers using visual-gestural patterns including body movements and facial expressions.

Injectable Conductive Hydrogels with Tunable Degradability as Novel Implantable Bioelectrodes

Bioelectrodes have been developed to efficiently mediate electrical signals of biological systems as stimulators and recording devices. Recently, conductive hydrogels have garnered great attention as emerging materials for bioelectrode applications because they can permit intimate/conformal contact with living tissues and tissue-like softness. However, administration and control over the in vivo lifetime of bioelectrodes remain challenges. Here, injectable conductive hydrogels (ICHs) with tunable degradability as implantable bioelectrodes are developed. ICHs were constructed via thiol-ene reactions using poly(ethylene glycol)-tetrathiol and thiol-functionalized reduced graphene oxide with either hydrolyzable poly(ethylene glycol)-diacrylate or stable poly(ethylene glycol)-dimaleimide, the resultant hydrogels of which are degradable and nondegradable, respectively. The ICH electrodes had conductivities of 21-22 mS cm^-1 and Young's moduli of 15-17 kPa, and showed excellent cell and tissue compatibility. The hydrolyzable conductive hydrogels disappeared 3 days after in vivo administration, while the stable conductive hydrogels maintained their shapes for up to 7 days. Our proof-of-concept studies reveal that electromyography signals with significantly improved sensitivity from rats could be obtained from the injected ICH electrodes compared to skin electrodes and injected nonconductive hydrogel electrodes. The ICHs, offering convenience in use, controllable degradation and excellent signal transmission, will have great potential to develop various bioelectronics devices.