Conductive and Tough Hydrogels Based on Biopolymer Molecular Templates for Controlling in Situ Formation of Polypyrrole Nanorods

From lab to wearables: Innovations in multifunctional hydrogel chemistry for next-generation bioelectronic devices

Functional hydrogels have emerged as foundational materials in diagnostics, therapy, and wearable devices, owing to their high stretchability, flexibility, sensing, and outstanding biocompatibility. Their significance stems from their resemblance to biological tissue and their exceptional versatility in electrical, mechanical, and biofunctional engineering, positioning themselves as a bridge between living organisms and electronic systems, paving the way for the development of highly compatible, efficient, and stable interfaces. These multifaceted capability revolutionizes the essence of hydrogel-based wearable devices, distinguishing them from conventional biomedical devices in real-world practical applications. In this comprehensive review, we first discuss the fundamental chemistry of hydrogels, elucidating their distinct properties and functionalities. Subsequently, we examine the applications of these bioelectronics within the human body, unveiling their transformative potential in diagnostics, therapy, and human-machine interfaces (HMI) in real wearable bioelectronics. This exploration serves as a scientific compass for researchers navigating the interdisciplinary landscape of chemistry, materials science, and bioelectronics.

Electroactive Nanomaterials for the Prevention and Treatment of Heart Failure: From Materials and Mechanisms to Applications

Heart failure (HF) represents a cardiovascular disease that significantly threatens global well-being and quality of life. Electroactive nanomaterials, characterized by their distinctive physical and chemical properties, emerge as promising candidates for HF prevention and management. This review comprehensively examines electroactive nanomaterials and their applications in HF intervention. It presents the definition, classification, and intrinsic characteristics of conductive, piezoelectric, and triboelectric nanomaterials, emphasizing their mechanical robustness, electrical conductivity, and piezoelectric coefficients. The review elucidates their applications and mechanisms: 1) early detection and diagnosis, employing nanomaterial-based sensors for real-time cardiac health monitoring; 2) cardiac tissue repair and regeneration, providing mechanical, chemical, and electrical stimuli for tissue restoration; 3) localized administration of bioactive biomolecules, genes, or pharmacotherapeutic agents, using nanomaterials as advanced drug delivery systems; and 4) electrical stimulation therapies, leveraging their properties for innovative pacemaker and neurostimulation technologies. Challenges in clinical translation, such as biocompatibility, stability, and scalability, are discussed, along with future prospects and potential innovations, including multifunctional and stimuli-responsive nanomaterials for precise HF therapies. This review encapsulates current research and future directions concerning the use of electroactive nanomaterials in HF prevention and management, highlighting their potential to innovating in cardiovascular medicine.

Facile One-Pot Preparation of Polypyrrole-Incorporated Conductive Hydrogels for Human Motion Sensing

Conductive hydrogels have been widely used in soft robotics, as well as skin-attached and implantable bioelectronic devices. Among the candidates of conductive fillers, conductive polymers have become popular due to their intrinsic conductivity, high biocompatibility, and mechanical flexibility. However, it is still a challenge to construct conductive polymer-incorporated hydrogels with a good performance using a facile method. Herein, we present a simple method for the one-pot preparation of conductive polymer-incorporated hydrogels involving rapid photocuring of the hydrogel template followed by slow in situ polymerization of pyrrole. Due to the use of a milder oxidant, hydrogen peroxide, for polypyrrole synthesis, the photocuring of the hydrogel template and the growing of polypyrrole proceeded in an orderly manner, making it possible to prepare conductive polymer-incorporated hydrogels in one pot. The preparation process is facile and extensible. Moreover, the obtained hydrogels exhibit a series of properties suitable for biomedical strain sensors, including good conductivity (2.49 mS/cm), high stretchability (>200%), and a low Young's modulus (~30 kPa) that is compatible with human skin.

A wearable iontophoresis enables dual-responsive transdermal delivery for atopic dermatitis treatment

Atopic dermatitis is a chronic, inflammation skin disease that remains a major public health challenge. The current drug-loading hydrogel dressings offer numerous benefits with enhanced loading capacity and a moist-rich environment. However, their development is still limited by the accessibility of a suitable driven source outside the clinical environment for precise control over transdermal delivery kinetics. Here, we prepare a sulfonated poly(3,4-ethylenedioxythiophene) (PEDOT) polyelectrolyte hydrogel drug reservoir that responds to different stimuli-both endogenous cue (body temperature) and exogenous cue (electrical stimulation), for wearable on-demand transdermal delivery with enhanced efficacy. Functioned as both the drug reservoir and cathode in a Zn battery-powered iontophoresis patch, this dual-responsive hydrogel achieves high drug release efficiency (68.4 %) at 37 °C. Evaluation in hairless mouse skin demonstrates the efficacy of this technology by facilitating transdermal transport of 12.2 μg cm-2 dexamethasone phosphate when discharged with a 103 Ω external resistor for 3 h. The Zn battery-driven iontophoresis results in an effective treatment of atopic dermatitis, displaying reductions in epidermal thickness, mast cell infiltration inhibition, and a decrease in IgE levels. This work provides a new treatment modality for chronic epidermal diseases that require precise drug delivery in a non-invasive way.

MXene-coated piezoelectric poly-L-lactic acid membrane accelerates wound healing by biomimicking low-voltage electrical pulses

Electrical stimulation therapy is effective in promoting wound healing by rescuing the decreased endogenous electrical field, where self-powered and miniaturized devices such as nanogenerators become the emerging trends. While high-voltage and unidirectional electric field may pose thermal effect and damage to the skin, nanogenerators with lower voltages, pulsed or bidirectional currents, and less invasive electrodes are preferred. Herein, we construct a polydopamine (PDA)-modified poly-L-lactic acid (PLLA) /MXene (PDMP/MXene) nanofibrous composite membrane that generates piezoelectric voltages matching the transepithelial potential (TEP) to accelerate wound healing. PDA coating not only enhances the piezoelectricity of PLLA by dipole attraction and alignment, but also increases its hydrophilicity and facilitates subsequent MXene adhesion for electrical conductivity and stability in physiological environment. When applied as wound dressings in mice, the PDMP/MXene membranes act as a nanogenerators with reduced internal resistances and satisfactory piezoelectric performances that resemble bioelectric potentials (~10 mV) responding to physical activities. The membrane significantly accelerates wound closure by facilitating fibroblast migration, collagen deposition and angiogenesis, and suppressing the expression of inflammatory responses. This piezoelectric fibrous membrane therefore provides a convenient solution for speeding up wound healing by sustained low voltage mimicking bioelectricity, better cell affinity.

Conductive Polymer-Based Hydrogels for Wearable Electrochemical Biosensors

Hydrogels are gaining popularity for use in wearable electronics owing to their inherent biomimetic characteristics, flexible physicochemical properties, and excellent biocompatibility. Among various hydrogels, conductive polymer-based hydrogels (CP HGs) have emerged as excellent candidates for future wearable sensor designs. These hydrogels can attain desired properties through various tuning strategies extending from molecular design to microstructural configuration. However, significant challenges remain, such as the limited strain-sensing range, significant hysteresis of sensing signals, dehydration-induced functional failure, and surface/interfacial malfunction during manufacturing/processing. This review summarizes the recent developments in polymer-hydrogel-based wearable electrochemical biosensors over the past five years. Initially serving as carriers for biomolecules, polymer-hydrogel-based sensors have advanced to encompass a wider range of applications, including the development of non-enzymatic sensors facilitated by the integration of nanomaterials such as metals, metal oxides, and carbon-based materials. Beyond the numerous existing reports that primarily focus on biomolecule detection, we extend the scope to include the fabrication of nanocomposite conductive polymer hydrogels and explore their varied conductivity mechanisms in electrochemical sensing applications. This comprehensive evaluation is instrumental in determining the readiness of these polymer hydrogels for point-of-care translation and state-of-the-art applications in wearable electrochemical sensing technology.

Free-standing and flexible polyvinyl alcohol-sodium alginate-polypyrrole electrodes based on interpenetrating network hydrogels

Flexible supercapacitors (FSCs) have attracted much attention due to their strong mechanical flexibility, wearability and portability, which greatly rely on the employed flexible electrodes. The conductive polymer hydrogels with excellent flexibility, processability and capacitive performance are one of the most promising candidates, which are still limited by their poor mechanical properties. Constructing robust interpenetrating polymer networks (IPN) is an effective approach to promote their mechanical properties. Herein, interpenetrating polyvinyl alcohol (PVA)-sodium alginate (SA)-polypyrrole (PPy) hydrogels are prepared by the freeze-thaw and in-situ polymerization method. The IPN structure composed of PVA and SA not only enhances the mechanical properties of hydrogels, but also provides substantial active sites for electrochemical reactions. Moreover, the hydrogen-bonding interaction between different components in the PVA-SA-PPy hydrogel boosts the charge/ion transfer. The optimal PVA-SA-PPy hydrogels show an elongation at break of 380 %, a tensile strength of 1.5 MPa, and a specific capacitance of 2646 mF cm-2 at 2 mA cm-2. The symmetric PVA-SA-PPy FSCs show an energy density of 96.7 μWh cm-2 at a power density of 999.9 μW cm-2, and the capacitance retention is 66.3 % after 10,000 cycles. These exceptional mechanical and electrochemical properties make the PVA-SA-PPy hydrogels a promising candidate for FSCs.

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.

Gel-Based Triboelectric Nanogenerators for Flexible Sensing: Principles, Properties, and Applications

The rapid development of the Internet of Things and artificial intelligence technologies has increased the need for wearable, portable, and self-powered flexible sensing devices. Triboelectric nanogenerators (TENGs) based on gel materials (with excellent conductivity, mechanical tunability, environmental adaptability, and biocompatibility) are considered an advanced approach for developing a new generation of flexible sensors. This review comprehensively summarizes the recent advances in gel-based TENGs for flexible sensors, covering their principles, properties, and applications. Based on the development requirements for flexible sensors, the working mechanism of gel-based TENGs and the characteristic advantages of gels are introduced. Design strategies for the performance optimization of hydrogel-, organogel-, and aerogel-based TENGs are systematically summarized. In addition, the applications of gel-based TENGs in human motion sensing, tactile sensing, health monitoring, environmental monitoring, human-machine interaction, and other related fields are summarized. Finally, the challenges of gel-based TENGs for flexible sensing are discussed, and feasible strategies are proposed to guide future research.

3D Printing Silk Fibroin/Polyacrylamide Triple-Network Composite Hydrogels with Stretchability, Conductivity, and Strain-Sensing Ability as Bionic Electronic Skins

Electronic skins have received increasing attention due to their great application potential in wearable electronics. Meanwhile, tremendous efforts are still needed for the fabrication of multifunctional composite hydrogels with complex structures for electronic skins via simple methods. In this work, a novel three-dimensional (3D) printing composite hydrogel with stretchability, conductivity, and strain-sensing ability is produced using a one-step photocuring method to achieve a dual-signal response of the electronic skin. The composite hydrogel exhibits a triple-network structure composed of silk microfibers (SMF), regenerated silk fibroin (RSF), and polyacrylamide (PAM). The establishment of triple networks is based on the electrostatic interaction between SMF and RSF, as well as the chemically cross-linked RSF and PAM. Thanks to its specific structure and components, the composite hydrogel possesses enhanced mechanical properties (elastic modulus of 140 kPa, compressive stress of 21 MPa, and compression modulus of 600 kPa) and 3D printability while retaining stretchability and flexibility. The interaction between negatively charged SMF and cations in phosphate-buffered saline endows the composite hydrogel with good conductivity and strain-sensing ability after immersion in a low-concentration (10 mM) salt solution. Moreover, the 3D printing composite hydrogel scaffold successfully realizes real-time monitoring. Therefore, the proposed hydrogel-based ionic sensor is promising for skin tissue engineering, real-time monitoring, soft robotics, and human-machine interfaces.

Smart materials for flexible electronics and devices: hydrogel

In recent years, flexible conductive materials have attracted considerable attention for their potential use in flexible energy storage devices, touch panels, sensors, memristors, and other applications. The outstanding flexibility, electricity, and tunable mechanical properties of hydrogels make them ideal conductive materials for flexible electronic devices. Various synthetic strategies have been developed to produce conductive and environmentally friendly hydrogels for high-performance flexible electronics. In this review, we discuss the state-of-the-art applications of hydrogels in flexible electronics, such as energy storage, touch panels, memristor devices, and sensors like temperature, gas, humidity, chemical, strain, and textile sensors, and the latest synthesis methods of hydrogels. Describe the process of fabricating sensors as well. Finally, we discussed the challenges and future research avenues for flexible and portable electronic devices based on hydrogels.

Antibacterial conductive polyacrylamide/quaternary ammonium chitosan hydrogel for electromagnetic interference shielding and strain sensing

The utilization of biomass-based conductive polymer hydrogels in wearable electronics holds great promise for advancing performance and sustainability. An interpenetrating network of polyacrylamide/2-hydroxypropyltrimethyl ammonium chloride chitosan (PAM/HACC) was firstly obtained through thermal-initiation polymerization of AM monomers in the presence of HACC. The positively charged groups on HACC provide strong electrostatic interactions and hydrogen bonding with the PAM polymer chains, leading to improved mechanical strength and stability of the hydrogel network. Subsequently, the PAM/HACC networks served as the skeletons for the in-situ polymerization of polypyrrole (PPy), and then the resulting conductive hydrogel demonstrated stable electromagnetic shielding performance (40 dB), high sensitivity for strain sensing (gauge factor = 2.56). Moreover, the incorporation of quaternary ammonium chitosan into PAM hydrogels enhances their antimicrobial activity, making them more suitable for applications in bacterial contamination or low-temperature environments. This conductive hydrogel, with its versatility and excellent mechanical properties, shows great potential in applications such as electronic skin and flexible/wearable electronics.

Biomedical applications of stimuli-responsive "smart" interpenetrating polymer network hydrogels

In recent years, owing to the ongoing advancements in polymer materials, hydrogels have found increasing applications in the biomedical domain, notably in the realm of stimuli-responsive "smart" hydrogels. Nonetheless, conventional single-network stimuli-responsive "smart" hydrogels frequently exhibit deficiencies, including low mechanical strength, limited biocompatibility, and extended response times. In response, researchers have addressed these challenges by introducing a second network to create stimuli-responsive "smart" Interpenetrating Polymer Network (IPN) hydrogels. The mechanical strength of the material can be significantly improved due to the topological entanglement and physical interactions within the interpenetrating structure. Simultaneously, combining different network structures enhances the biocompatibility and stimulus responsiveness of the gel, endowing it with unique properties such as cell adhesion, conductivity, hemostasis/antioxidation, and color-changing capabilities. This article primarily aims to elucidate the stimulus-inducing factors in stimuli-responsive "smart" IPN hydrogels, the impact of the gels on cell behaviors and their biomedical application range. Additionally, we also offer an in-depth exposition of their categorization, mechanisms, performance characteristics, and related aspects. This review furnishes a comprehensive assessment and outlook for the advancement of stimuli-responsive "smart" IPN hydrogels within the biomedical arena. We believe that, as the biomedical field increasingly demands novel materials featuring improved mechanical properties, robust biocompatibility, and heightened stimulus responsiveness, stimuli-responsive "smart" IPN hydrogels will hold substantial promise for wide-ranging applications in this domain.

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

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

Three-Dimensional Printing of Hydrogels for Flexible Sensors: A Review

The remarkable flexibility and heightened sensitivity of flexible sensors have drawn significant attention, setting them apart from traditional sensor technology. Within this domain, hydrogels-3D crosslinked networks of hydrophilic polymers-emerge as a leading material for the new generation of flexible sensors, thanks to their unique material properties. These include structural versatility, which imparts traits like adhesiveness and self-healing capabilities. Traditional templating-based methods fall short of tailor-made applications in crafting flexible sensors. In contrast, 3D printing technology stands out with its superior fabrication precision, cost-effectiveness, and satisfactory production efficiency, making it a more suitable approach than templating-based strategies. This review spotlights the latest hydrogel-based flexible sensors developed through 3D printing. It begins by categorizing hydrogels and outlining various 3D-printing techniques. It then focuses on a range of flexible sensors-including those for strain, pressure, pH, temperature, and biosensors-detailing their fabrication methods and applications. Furthermore, it explores the sensing mechanisms and concludes with an analysis of existing challenges and prospects for future research breakthroughs in this field.

Tough Hydrogels for Load-Bearing Applications

Tough hydrogels have emerged as a promising class of materials to target load-bearing applications, where the material has to resist multiple cycles of extreme mechanical impact. A variety of chemical interactions and network architectures are used to enhance the mechanical properties and fracture mechanics of hydrogels making them stiffer and tougher. In recent years, the mechanical properties of tough, high-performance hydrogels have been benchmarked, however, this is often incomplete as important variables like water content are largely ignored. In this review, the aim is to clarify the reported mechanical properties of state-of-the-art tough hydrogels by providing a comprehensive library of fracture and mechanical property data. First, common methods for mechanical characterization of such high-performance hydrogels are introduced. Then, various modes of energy dissipation to obtain tough hydrogels are discussed and used to categorize the individual datasets helping to asses the material's (fracture) mechanical properties. Finally, current applications are considered, tough high-performance hydrogels are compared with existing materials, and promising future opportunities are discussed.

Sodium carboxymethyl cellulose and MXene reinforced multifunctional conductive hydrogels for multimodal sensors and flexible supercapacitors

With the growing demand for eco-friendly materials in wearable smart electronic devices, renewable, biocompatible, and low-cost hydrogels based on natural polymers have attracted much attention. Cellulose, as one of the renewable and degradable natural polymers, shows great potential in wearable smart electronic devices. Multifunctional conductive cellulose-based hydrogels are designed for flexible electronic devices by adding sodium carboxymethyl cellulose and MXene into polyacrylic acid networks. The multifunctional hydrogels possess excellent mechanical property (stress: 310 kPa; strain: 1127 %), toughness (206.67 KJ m-3), conductivity (1.09 ± 0.12 S m-1) and adhesion (82.19 ± 3.65 kPa). The multifunctional conductive hydrogels serve as strain sensors (Gauge Factor (GF) = 5.79, 0-700 % strain; GF = 14.0, 700-900 % strain; GF = 40.36, 900-1000 % strain; response time: 300 ms; recovery time: 200 ms) and temperature sensors (Temperature coefficient of resistance (TCR) = 2.5755 °C-1 at 35 °C- 60 °C). The sensor detects human activities with clear and steady signals. A distributed array of flexible sensors is created to measure the magnitude and distribution of pressure and a hydrogel-based flexible touch keyboard is also fabricated to recognize writing trajectories, pressures and speeds. Furthermore, a flexible hydrogel-based supercapacitor powers the LED and exhibits good cyclic stability over 15,000 charge-discharge cycles.

Stimuli-Responsive 3D Printable Conductive Hydrogel: A Step toward Regulating Macrophage Polarization and Wound Healing

Conductive hydrogels (CHs) are promising alternatives for electrical stimulation of cells and tissues in biomedical engineering. Wound healing and immunomodulation are complex processes that involve multiple cell types and signaling pathways. 3D printable conductive hydrogels have emerged as an innovative approach to promote wound healing and modulate immune responses. CHs can facilitate electrical and mechanical stimuli, which can be beneficial for altering cellular metabolism and enhancing the efficiency of the delivery of therapeutic molecules. This review summarizes the recent advances in 3D printable conductive hydrogels for wound healing and their effect on macrophage polarization. This report also discusses the properties of various conductive materials that can be used to fabricate hydrogels to stimulate immune responses. Furthermore, this review highlights the challenges and limitations of using 3D printable CHs for future material discovery. Overall, 3D printable conductive hydrogels hold excellent potential for accelerating wound healing and immune responses, which can lead to the development of new therapeutic strategies for skin and immune-related diseases.

A highly sensitive and anti-freezing conductive strain sensor based on polypyrrole/cellulose nanofiber crosslinked polyvinyl alcohol hydrogel for human motion detection

Electro-conductive hydrogels emerge as a stretchable conductive materials with diverse applications in the synthesis of flexible strain sensors. However, the high-water content and low cross-links density cause them to be mechanically destroyed and freeze at subzero temperatures, limiting their practical applications. Herein, we report a one-pot strategy by co-incorporating cellulose nanofiber (CNF), Poly pyrrole (PPy) and glycerol with polyvinyl alcohol (PVA) to prepare hydrogel. The addition of PPy endowed the hydrogel with good conductivity (∼0.034 S/m) compared to the no PPy@CNF group (∼0.0095 S/m), the conductivity was increased by 257.9 %. The hydrogel exhibits comparable ionic conductivity at -18 °C as it does at room temperature. It's attributed to the glycerol as a cryoprotectant and the formation of hydrated [Zn(H2O)n]2+ ions via strong interaction between Zn2+ and water molecules. Moreover, the cellulose nanofiber intrinsically assembled into unique hierarchical structures allow for strong hydrogen bonds between adjacent cellulose and PPy polymer chains, greatly improve the mechanical strength (stress∼0.65 MPa, strain∼301 %) and excellent viscoelasticity (G'max ∼ 82.7 KPa). This novel PPy@CNF-PVA hydrogel exhibits extremely high Gauge factor (GF) of 2.84 and shows excellent sensitivity, repeatability and stability. Therefore, the hydrogel can serve as reliable and stable strain sensor which shows excellent responsiveness in human activities monitoration.

Conductive and Eco-friendly Biomaterials-based Hydrogels for Noninvasive Epidermal Sensors: A Review

As noninvasive wearable electronic devices, epidermal sensors enable continuous, real-time, and remote monitoring of various human physiological parameters. Conductive biomaterials-based hydrogels as sensor matrix materials have good biocompatibility, biodegradability, and efficient stimulus response capabilities and are widely applied in motion monitoring, healthcare, and human-machine interaction. However, biomass hydrogel-based epidermal sensing devices still need excellent mechanical properties, prolonged stability, multifunctionality, and extensive practicality. Therefore, this paper reviews the common biomass hydrogel materials for epidermal sensing (proteins, polysaccharides, polyphenols, etc.) and the various types of noninvasive sensing devices (strain/pressure sensors, temperature sensors, glucose sensors, electrocardiograms, etc.). Moreover, this review focuses on the strategies of scholars to enhance sensor properties, such as strength, conductivity, stability, adhesion, and self-healing ability. This work will guide the preparation and optimization of high-performance biomaterials-based hydrogel epidermal sensors.

Implantable Nerve Conduit Made of a Self-Powered Microneedle Patch for Sciatic Nerve Repair

Peripheral nerve defects, particularly those of a larger size, pose a significant challenge in clinical practice due to their limited regenerative capacity. To tackle this challenge, an advanced self-powered enzyme-linked microneedle (MN) nerve conduit is designed and fabricated. This innovative conduit is composed of anodic and cathodic MN arrays, which contain glucose oxidase (GOx) and horseradish peroxidase (HRP) encapsulated in ZIF-8 nanoparticles, respectively. Through an enzymatic cascade reaction, this MN nerve conduit generates microcurrents that stimulate the regeneration of muscles, blood vessels, and nerve fibers innervated by the sciatic nerve, eventually accelerating the repair of sciatic nerve injury. It is clear that this self-powered MN nerve conduit will revolutionize traditional treatment methods for sciatic nerve injury and find widespread application in the field of nerve tissue repair.

Strong, Tough, and Anti-Swelling Supramolecular Conductive Hydrogels for Amphibious Motion Sensors

Conductive polymer hydrogels (CPHs) are widely employed in emerging flexible electronic devices because they possess both the electrical conductivity of conductors and the mechanical properties of hydrogels. However, the poor compatibility between conductive polymers and the hydrogel matrix, as well as the swelling behavior in humid environments, greatly compromises the mechanical and electrical properties of CPHs, limiting their applications in wearable electronic devices. Herein, a supramolecular strategy to develop a strong and tough CPH with excellent anti-swelling properties by incorporating hydrogen, coordination bonds, and cation-π interactions between a rigid conducting polymer and a soft hydrogel matrix is reported. Benefiting from the effective interactions between the polymer networks, the obtained supramolecular hydrogel has homogeneous structural integrity, exhibiting remarkable tensile strength (1.63 MPa), superior elongation at break (453%), and remarkable toughness (5.5 MJ m-3 ). As a strain sensor, the hydrogel possesses high electrical conductivity (2.16 S m-1 ), a wide strain linear detection range (0-400%), and excellent sensitivity (gauge factor = 4.1), sufficient to monitor human activities with different strain windows. Furthermore, this hydrogel with high swelling resistance has been successfully applied to underwater sensors for monitoring frog swimming and underwater communication. These results reveal new possibilities for amphibious applications of wearable sensors.

A Self-Powered Hydrogel/Nanogenerator System Accelerates Wound Healing by Electricity-Triggered On-Demand Phosphatase and Tensin Homologue (PTEN) Inhibition

Electrical stimulation therapy (EST) has been established as an effective strategy to accelerate wound healing by stimulating cell proliferation and migration, ultimately promoting re-epithelialization and vascularization, two key processes that significantly influence the rate of wound healing. Phosphatase and tensin homologue (PTEN), a widely expressed protein in somatic cells, works as a "brake" regulating cell differentiation, proliferation, and migration. Given that this "brake" also works in cell electrical responses, there is a hypothesis that PTEN inhibition may amplify the efficacy of EST in wound treatment. However, long-term inhibition of PTEN may result in DNA damage and reduce DNA repair, which poses a significant challenge to the safe use of PTEN inhibitors. To address this issue, we developed a system that combines PTEN inhibitor loaded electro-responsive hydrogel (BPV@PCP) with a wearable direct current pulse piezoelectric nanogenerator (PENG). The PENG converts the rat's motions into electric fields that synchronously charge the wound edge tissue and BPV@PCP. Electric field intensity was lower when the rat was quiet or anesthetized, which is insufficient to trigger an effective PTEN inhibitor release. However, when the rat was in action, the electric field intensity exceeded 625 mV/mm, resulting in a rapid drug release. This on-demand PTEN inhibition accelerated wound healing by amplifying cell electric responsiveness while avoiding negative effects associated with continuous overinhibition of PTEN. Notably, this system improves vascularization not only by improving endothelial cell electric responsiveness but also through the paracrine pathway, in which electrical stimulation and PTEN inhibition synergically promote VEGF secretion.

MXene-enhanced ePatch with antibacterial activity for wound healing

Prudent wound-healing strategies hold great potential in expediting tissue renovation and regeneration. Despite the widespread adoption of hydrogels as preferred carriers for wound healing patches, achieving optimal mechanical compatibility and superior wound performance remains a formidable challenge. Consequently, meticulous attention must be given to the formulation of hydrogel structure and materials design to overcome these hurdles. In response, we have developed an ePatch composed of polyacrylamide (PAAM) as the primary hydrogel structure, augmented with MXene, silver nanowires (AgNWs), and resveratrol to act as sustained-release agents, structural enhancers, and antibacterial agents, respectively. Notably, the ePatch exhibited exceptional wound-fitting capabilities and impressive mechanical stretchability (with a relative standard deviation [RSD] of only 1.36% after 55 stretches) and Young's modulus. In contrast to the commercial 3M Tegaderm, the ePatch demonstrated superior wound healing properties, with the inclusion of MXene into PAAM/AgNWs playing a pivotal role in expanding the ePatch's potential use across various interconnected fields.

Advances in the Preparation of Tough Conductive Hydrogels for Flexible Sensors

The rapid development of tough conductive hydrogels has led to considerable progress in the fields of tissue engineering, soft robots, flexible electronics, etc. Compared to other kinds of traditional sensing materials, tough conductive hydrogels have advantages in flexibility, stretchability and biocompatibility due to their biological structures. Numerous hydrogel flexible sensors have been developed based on specific demands for practical applications. This review focuses on tough conductive hydrogels for flexible sensors. Representative tactics to construct tough hydrogels and strategies to fulfill conductivity, which are of significance to fabricating tough conductive hydrogels, are briefly reviewed. Then, diverse tough conductive hydrogels are presented and discussed. Additionally, recent advancements in flexible sensors assembled with different tough conductive hydrogels as well as various designed structures and their sensing performances are demonstrated in detail. Applications, including the wearable skins, bionic muscles and robotic systems of these hydrogel-based flexible sensors with resistive and capacitive modes are discussed. Some perspectives on tough conductive hydrogels for flexible sensors are also stated at the end. This review will provide a comprehensive understanding of tough conductive hydrogels and will offer clues to researchers who have interests in pursuing flexible sensors.

A Bioinspired Self-Healing Conductive Hydrogel Promoting Peripheral Nerve Regeneration

The development of self-healing conductive hydrogels is critical in electroactive nerve tissue engineering. Typical conductive materials such as polypyrrole (PPy) are commonly used to fabricate artificial nerve conduits. Moreover, the field of tissue engineering has advanced toward the use of products such as hyaluronic acid (HA) hydrogels. Although HA-modified PPy films are prepared for various biological applications, the cell-matrix interaction mechanisms remain poorly understood; furthermore, there are no reports on HA-modified PPy-injectable self-healing hydrogels for peripheral nerve repair. Therefore, in this study, a self-healing electroconductive hydrogel (HASPy) from HA, cystamine (Cys), and pyrrole-1-propionic acid (Py-COOH), with injectability, biodegradability, biocompatibility, and nerve-regenerative capacity is constructed. The hydrogel directly targets interleukin 17 receptor A (IL-17RA) and promotes the expression of genes and proteins relevant to Schwann cell myelination mainly by activating the interleukin 17 (IL-17) signaling pathway. The hydrogel is injected directly into the rat sciatic nerve-crush injury sites to investigate its capacity for nerve regeneration in vivo and is found to promote functional recovery and remyelination. This study may help in understanding the mechanism of cell-matrix interactions and provide new insights into the potential use of HASPy hydrogel as an advanced scaffold for neural regeneration.

Highly conductive and tough polyacrylamide/sodium alginate hydrogel with uniformly distributed polypyrrole nanospheres for wearable strain sensors

Conductive hydrogels have attracted widespread attention because of their integrated characteristics of being stretchable, deformable, adhesive, self-healable, and conductive. Herein, we report a highly conductive and tough double-network hydrogel based on a double cross-linked polyacrylamide (PAAM) and sodium alginate (SA) network with conducting polypyrrole nanospheres (PPy NSs) uniformly distributed in the network (PAAM-SA-PPy NSs). SA was employed as a soft template for synthesis of PPy NSs and distribution of PPy NSs uniformly in the hydrogel matrix to construct SA-PPy conductive network. The PAAM-SA-PPy NS hydrogel exhibited both high electrical conductivity (6.44 S/m) and excellent mechanical properties (tensile strength of 560 kPa at 870 %), as along as high toughness, high biocompatibility, good self-healing and adhesion properties. The assembled strain sensors showed high sensitivity and a wide sensing range (a gauge factor of 1.89 for 0-400 % strain and 4.53 for 400-800 % strain, respectively), as well as fast responsiveness and reliable stability. When used as a wearable strain sensor, it was able to monitor a series of physical signals from human large-scale joint motions and subtle muscle movements. This work provides a new strategy for the development of electronic skins and flexible strain sensors.

Stimuli-responsive dynamic hydrogels: design, properties and tissue engineering applications

The field of tissue engineering and regenerative medicine has been evolving at a rapid pace with numerous novel and interesting biomaterials being reported. Hydrogels have come a long way in this regard and have been proven to be an excellent choice for tissue regeneration. This could be due to their innate properties such as water retention, and ability to carry and deliver a multitude of therapeutic and regenerative elements to aid in better outcomes. Over the past few decades, hydrogels have been developed into an active and attractive system that can respond to various stimuli, thereby presenting a wider control over the delivery of the therapeutic agents to the intended site in a spatiotemporal manner. Researchers have developed hydrogels that respond dynamically to a multitude of external as well as internal stimuli such as mechanics, thermal energy, light, electric field, ultrasonics, tissue pH, and enzyme levels, to name a few. This review gives a brief overview of the recent developments in such hydrogel systems which respond dynamically to various stimuli, some of the interesting fabrication strategies, and their application in cardiac, bone, and neural tissue engineering.

Polyacrylate-graft-polypyrrole Copolymer as Intrinsically Elastic Electrodes for Stretchable Supercapacitors

Constructing elastic electrodes with high mechanical and electrochemical stability remains a challenge in developing flexible supercapacitors. Instability of elastic composite electrodes stems from detachment of noncovalently associated electroactive components from elastic substrates under cyclic deformations. Herein, a novel all-organic copolymer consisting of polypyrrole grafted from a polyacrylate elastomer is proposed as elastic electrodes for stretchable supercapacitors. The single copolymer is obtained by graft polymerization in the swollen state, characterized by a wrinkled polypyrrole coating covalently attached on an elastic core. The copolymer is intrinsically elastic and maintains structural integrity under bending, twisting, and stretching deformations to ensure stable electrochemical performance. In addition, the grafted polypyrrole aggregates densely under the constraint of the backbone and gives a competitive conductivity of 41.6 S cm-1. A stretchable supercapacitor is constructed using the copolymer as electrodes and an acid hydrogel as an electrolyte, resulting in a specific capacitance of 430 mF cm-2. The supercapacitor delivers a capacitance retention of 100% after 1000 stretching-releasing cycles, exhibiting mechanical and electrochemical reliability under elastic deformations.

Magnetic chitosan hydrogel induces neuronal differentiation of neural stem cells by activating RAS-dependent signal cascade

Our aim was to modulate magnetic cues to influence the differentiation of neural stem cell (NSC) into neuron during nerve repair and to explore corresponding mechanisms. Here, a magnetic hydrogel composed of chitosan matrices and magnetic nanoparticles (MNPs) with different content was prepared as the magnetic-stimulation platform to apply intrinsically-present magnetic cue and externally-applied magnetic field to NSC grown on the hydrogel. The MNP content had regulatory effects on neuronal differentiation and the MNPs-50 samples exhibited the best neuronal potential and appropriate biocompatibility in vitro, as well as accelerated the subsequent neuronal regeneration in vivo. Remarkably, the use of proteomics analysis parsed the underlying mechanism of magnetic cue-mediated neuronal differentiation form the perspective of protein corona and intracellular signal transduction. The intrinsically-present magnetic cues in hydrogel contributed to the activation of intracellular RAS-dependent signal cascades, thus facilitating neuronal differentiation. Magnetic cue-dependent changes in NSCs benefited from the upregulation of adsorbed proteins related to "neuronal differentiation", "cell-cell interaction", "receptor", "protein activation cascade", and "protein kinase activity" in the protein corona. Additionally, magnetic hydrogel acted cooperatively with the exterior magnetic field, showing further improving neurogenesis. The findings clarified the mechanism for magnetic cue-mediated neuronal differentiation, coupling protein corona and intracellular signal transduction.

Application of Conductive Hydrogels on Spinal Cord Injury Repair: A Review

Spinal cord injury (SCI) causes severe motor or sensory damage that leads to long-term disabilities due to disruption of electrical conduction in neuronal pathways. Despite current clinical therapies being used to limit the propagation of cell or tissue damage, the need for neuroregenerative therapies remains. Conductive hydrogels have been considered a promising neuroregenerative therapy due to their ability to provide a pro-regenerative microenvironment and flexible structure, which conforms to a complex SCI lesion. Furthermore, their conductivity can be utilized for noninvasive electrical signaling in dictating neuronal cell behavior. However, the ability of hydrogels to guide directional axon growth to reach the distal end for complete nerve reconnection remains a critical challenge. In this Review, we highlight recent advances in conductive hydrogels, including the incorporation of conductive materials, fabrication techniques, and cross-linking interactions. We also discuss important characteristics for designing conductive hydrogels for directional growth and regenerative therapy. We propose insights into electrical conductivity properties in a hydrogel that could be implemented as guidance for directional cell growth for SCI applications. Specifically, we highlight the practical implications of recent findings in the field, including the potential for conductive hydrogels to be used in clinical applications. We conclude that conductive hydrogels are a promising neuroregenerative therapy for SCI and that further research is needed to optimize their design and application.

Antibacterial Conductive Collagen-Based Hydrogels for Accelerated Full-Thickness Wound Healing

Antibacterial conductive hydrogels have been extensively utilized in tissue repair and regeneration on account of their unique electrochemical performances and advantages of anti-pathogenic bacterial infection. Here, multi-functional collagen-based hydrogels (CHLY) with adhesivity, conductivity, and antibacterial and antioxidant activities were developed by introducing cysteine-modified ε-poly(l-lysine) (ε-PL-SH) and in situ-polymerized polypyrrole (PPy) nanoparticles to induce full-thickness wound healing. CHLY hydrogels have a low swelling ratio, good compressive strength, and viscoelasticity due to chemical crosslinking, chelation, physical interaction, and nano-reinforcements in the matrix network of hydrogels. CHLY hydrogels possess excellent tissue adhesion ability, low cytotoxicity, enhanced cell migration ability, and good blood coagulation performance without causing hemolysis. Interestingly, the chemical conjugation of ε-PL-SH in the hydrogel matrix gives hydrogels an inherently robust and broad-spectrum antibacterial activity, while the introduction of PPy endows hydrogels with superior free radical scavenging capacity and good electroactivity. Significantly, CHLY hydrogels have advantages in alleviating persistent inflammatory response as well as promoting angiogenesis, epidermis regeneration, and orderly collagen deposition at the wound sites through their multi-functional synergies, thus effectively accelerating full-thickness wound healing and improving wound healing quality. Overall, our developed multi-functional collagen-based hydrogel dressing demonstrates promising application prospects in the field of tissue engineering to induce skin regeneration.

Double-Network Chitosan-Based Hydrogels with Improved Mechanical, Conductive, Antimicrobial, and Antibiofouling Properties

In recent years, the antimicrobial activity of chitosan-based hydrogels has been at the forefront of research in wound healing and the prevention of medical device contamination. Anti-infective therapy is a serious challenge given the increasing prevalence of bacterial resistance to antibiotics as well as their ability to form biofilms. Unfortunately, hydrogel resistance and biocompatibility do not always meet the demands of biomedical applications. As a result, the development of double-network hydrogels could be a solution to these issues. This review discusses the most recent techniques for creating double-network chitosan-based hydrogels with improved structural and functional properties. The applications of these hydrogels are also discussed in terms of tissue recovery after injuries, wound infection prevention, and biofouling of medical devices and surfaces for pharmaceutical and medical applications.

Iontophoresis-driven microneedle patch for the active transdermal delivery of vaccine macromolecules

COVID-19 has seriously threatened public health, and transdermal vaccination is an effective way to prevent pathogen infection. Microneedles (MNs) can damage the stratum corneum to allow passive diffusion of vaccine macromolecules, but the delivery efficiency is low, while iontophoresis can actively promote transdermal delivery but fails to transport vaccine macromolecules due to the barrier of the stratum corneum. Herein, we developed a wearable iontophoresis-driven MN patch and its iontophoresis-driven device for active and efficient transdermal vaccine macromolecule delivery. Polyacrylamide/chitosan hydrogels with good biocompatibility, excellent conductivity, high elasticity, and a large loading capacity were prepared as the key component for vaccine storage and active iontophoresis. The transdermal vaccine delivery strategy of the iontophoresis-driven MN patch is "press and poke, iontophoresis-driven delivery, and immune response". We demonstrated that the synergistic effect of MN puncture and iontophoresis significantly promoted transdermal vaccine delivery efficiency. In vitro experiments showed that the amount of ovalbumin delivered transdermally using the iontophoresis-driven MN patch could be controlled by the iontophoresis current. In vivo immunization studies in BALB/c mice demonstrated that transdermal inoculation of ovalbumin using an iontophoresis-driven MN patch induced an effective immune response that was even stronger than that of traditional intramuscular injection. Moreover, there was little concern about the biosafety of the iontophoresis-driven MN patch. This delivery system has a low cost, is user-friendly, and displays active delivery, showing great potential for vaccine self-administration at home.

Conductive hydrogels for tissue repair

Conductive hydrogels (CHs) combine the biomimetic properties of hydrogels with the physiological and electrochemical properties of conductive materials, and have attracted extensive attention in the past few years. In addition, CHs have high conductivity and electrochemical redox properties and can be used to detect electrical signals generated in biological systems and conduct electrical stimulation to regulate the activities and functions of cells including cell migration, cell proliferation, and cell differentiation. These properties give CHs unique advantages in tissue repair. However, the current review of CHs is mostly focused on their applications as biosensors. Therefore, this article reviewed the new progress of CHs in tissue repair including nerve tissue regeneration, muscle tissue regeneration, skin tissue regeneration and bone tissue regeneration in the past five years. We first introduced the design and synthesis of different types of CHs such as carbon-based CHs, conductive polymer-based CHs, metal-based CHs, ionic CHs, and composite CHs, and the types and mechanisms of tissue repair promoted by CHs including anti-bacterial, antioxidant and anti-inflammatory properties, stimulus response and intelligent delivery, real-time monitoring, and promoted cell proliferation and tissue repair related pathway activation, which provides a useful reference for further preparation of bio-safer and more efficient CHs used in tissue regeneration.

Fabrication and desired properties of conductive hydrogel dressings for wound healing

Conductive hydrogels are platforms recognized as constituting promising materials for tissue engineering applications. This is because such conductive hydrogels are characterized by the inherent conductivity properties while retaining favorable biocompatibility and mechanical properties. These conductive hydrogels can be particularly useful in enhancing wound healing since their favorable conductivity can promote the transport of essential ions for wound healing via the imposition of a so-called transepithelial potential. Other valuable properties of these conductive hydrogels, such as wound monitoring, stimuli-response etc., are also discussed in this study. Crucially, the properties of conductive hydrogels, such as 3D printability and monitoring properties, suggest the possibility of its use as an alternative wound dressing to traditional dressings such as bandages. This review, therefore, seeks to comprehensively explore the functionality of conductive hydrogels in wound healing, types of conductive hydrogels and their preparation strategies and crucial properties of hydrogels. This review will also assess the limitations of conductive hydrogels and future perspectives, with an emphasis on the development trend for conductive hydrogel uses in wound dressing fabrication for subsequent clinical applications.

Electroactive injectable hydrogel based on oxidized sodium alginate and carboxymethyl chitosan for wound healing

Electroactive hydrogel is of great significance in restoring wound currents, promoting cell proliferation, and accelerating the wound healing process. However, the poor dispersity and underlying toxicity of electronic conductive fillers and high concentration of ionic conductors in traditional electroactive hydrogel limited its application in medical care. Herein, an electroactive oxidized sodium alginate/carboxymethyl chitosan/silver nanoparticles (OSA/CMCS/AgNPs) hydrogel was constructed with no additional conductive fillers or synthesized conductive polymers being added, in which the dynamic imine bonds were rapidly formed between aldehyde groups in OSA and amino groups in CMCS, and AgNPs were further in situ formed by UV irradiation. The electroactive hydrogel exhibited the injectable property, strong self-healing ability, excellent biocompatibility, and high antibacterial activities. Moreover, the electroactive hydrogel can significantly promote the proliferation of L929 cells under electrical stimulation. Furthermore, the electroactive hydrogel was proved to significantly accelerate the wound healing process in the full-thickness skin defect model, exhibiting anti-inflammation, promoting the fibroblasts proliferation, angiogenesis, and collagen deposition under electrical stimulation. In summary, the current work explored a novel strategy to construct the polysaccharides-based electroactive hydrogel with good biocompatibility and multi-functions, which is promising to be used in deep wound treatment.

An integrated Mg battery-powered iontophoresis patch for efficient and controllable transdermal drug delivery

Wearable transdermal iontophoresis eliminating the need for external power sources offers advantages for patient-comfort when deploying epidermal diseases treatments. However, current self-powered iontophoresis based on energy harvesters is limited to support efficient therapeutic administration over the long-term operation, owing to the low and inconsistent energy supply. Here we propose a simplified wearable iontophoresis patch with a built-in Mg battery for efficient and controllable transdermal delivery. This system decreases the system complexity and form factors by using viologen-based hydrogels as an integrated drug reservoir and cathode material, eliminating the conventional interface impedance between the electrode and drug reservoir. The redox-active polyelectrolyte hydrogel offers a high energy density of 3.57 mWh cm^-2, and an optimal bioelectronic interface with ultra-soft nature and low tissue-interface impedance. The delivery dosage can be readily manipulated by tuning the viologen hydrogel and the iontophoresis stimulation mode. This iontophoresis patch demonstrates an effective treatment of an imiquimod-induced psoriasis mouse. Considering the advantages of being a reliable and efficient energy supply, simplified configuration, and optimal electrical skin-device interface, this battery-powered iontophoresis may provide a new non-invasive treatment for chronic epidermal diseases.

Green approaches for extraction, chemical modification and processing of marine polysaccharides for biomedical applications

Over the past few decades, natural-origin polysaccharides have received increasing attention across different fields of application, including biomedicine and biotechnology, because of their specific physicochemical and biological properties that have afforded the fabrication of a plethora of multifunctional devices for healthcare applications. More recently, marine raw materials from fisheries and aquaculture have emerged as a highly sustainable approach to convert marine biomass into added-value polysaccharides for human benefit. Nowadays, significant efforts have been made to combine such circular bio-based approach with cost-effective and environmentally-friendly technologies that enable the isolation of marine-origin polysaccharides up to the final construction of a biomedical device, thus developing an entirely sustainable pipeline. In this regard, the present review intends to provide an up-to-date outlook on the current green extraction methodologies of marine-origin polysaccharides and their molecular engineering toolbox for designing a multitude of biomaterial platforms for healthcare. Furthermore, we discuss how to foster circular bio-based approaches to pursue the further development of added-value biomedical devices, while preserving the marine ecosystem.

Design strategies for adhesive hydrogels with natural antibacterial agents as wound dressings: Status and trends

The wound healing process is usually susceptible to different bacterial infections due to the complex physiological environment, which significantly impairs wound healing. The topical application of antibiotics is not desirable for wound healing because the excessive use of antibiotics might cause bacteria to develop resistance and even the production of super bacteria, posing significant harm to human well-being. Wound dressings based on adhesive, biocompatible, and multi-functional hydrogels with natural antibacterial agents have been widely recognized as effective wound treatments. Hydrogels, which are three-dimensional (3D) polymer networks cross-linked through physical interactions or covalent bonds, are promising for topical antibacterial applications because of their excellent adhesion, antibacterial properties, and biocompatibility. To further improve the healing performance of hydrogels, various modification methods have been developed with superior biocompatibility, antibacterial activity, mechanical properties, and wound repair capabilities. This review summarizes hundreds of typical studies on various ingredients, preparation methods, antibacterial mechanisms, and internal antibacterial factors to understand adhesive hydrogels with natural antibacterial agents for wound dressings. Additionally, we provide prospects for adhesive and antibacterial hydrogels in biomedical applications and clinical research.

Polypyrrole Nanomaterials: Structure, Preparation and Application

In the past decade, nanostructured polypyrrole (PPy) has been widely studied because of its many specific properties, which have obvious advantages over bulk-structured PPy. This review outlines the main structures, preparation methods, physicochemical properties, potential applications, and future prospects of PPy nanomaterials. The preparation approaches include the soft micellar template method, hard physical template method and templateless method. Due to their excellent electrical conductivity, biocompatibility, environmental stability and reversible redox properties, PPy nanomaterials have potential applications in the fields of energy storage, biomedicine, sensors, adsorption and impurity removal, electromagnetic shielding, and corrosion resistant. Finally, the current difficulties and future opportunities in this research area are discussed.

Natural Glycyrrhizic Acid-Tailored Homogeneous Conductive Polyaniline Hydrogel as a Flexible Strain Sensor

Polyaniline (PANi) hydrogels often exhibit highly mechanical and electrochemical properties, which have received extensive attention in the fields of batteries, supercapacitors, and sensors. However, the shortcomings such as hydrophobicity and easy aggregation of PANi frequently result in deterioration of mechanical and electrochemical performance of PANi hydrogels. Here, a bifunctional natural product, glycyrrhizic acid (GL), is utilized to prepare the homogeneous conductive PANi hydrogel, because GL not only can assemble into supramolecular hydrogel as the biocompatible matrix but also can salinize aniline monomers to facilitate the polymerization in situ to form uniformly dispersed PANi within GL matrix. Accordingly, the resulting GL/PANi hydrogel shows the Tyndall effect caused by the nanoclusters entangled by nanofibers and exhibits an improved storage modulus G' (3.2 kPa) and loss modulus G″ (0.9 kPa), as well as the expected conductivity (0.17 S·m^-1). In addition, the GL/PANi hydrogel is further reinforced by blending poly(vinyl alcohol) (PVA) for the required strength and stretchability as a flexible strain sensor. The results reveal that the obtained PVA/GL/PANi hydrogel has a fracture stress of 693 kPa at an elongation of 329%, with a fracture toughness of 82 MJ·m^-3 and Young's modulus of 47.9 kPa. Its gauge factor (GF) is measured to be 2.5 at lower strain (<130%) and up to 4.3 at larger strain (>130%). This good sensitivity and sensing stability make the PVA/GL/PANi hydrogel effectively monitor relevant human motion detections. Our work provides an innovative strategy to manufacture the homogeneous conductive PANi hydrogel for high-performance soft electronic devices.

Antibacterial Conductive UV-Blocking Adhesion Hydrogel Dressing with Mild On-Demand Removability Accelerated Drug-Resistant Bacteria-Infected Wound Healing

The on-demand replacement of multifunctional hydrogel wound dressings helps to avoid bacterial colonization, and the on-demand painless peeling of tissue adhesive hydrogels on the wound site remains a major challenge to be solved. In this work, we design and develop a series of multifunctional dynamic Schiff base network hydrogels composed of cystamine-modified hyaluronic acid, benzaldehyde-functionalized poly(ethylene glycol)-co-poly(glycerol sebacate), and polydopamine@polypyrrole nanocomposite (PDA@PPy) with mild on-demand removability to enhance drug-resistant bacteria-infected wound healing. These hydrogels exhibited ideal injectable and self-healing properties, excellent tissue adhesion, in vivo hemostasis, good antioxidation, and conductivity. PDA@PPy inspired by melanin endows hydrogels with excellent antioxidant capacity, UV-blocking ability, and photothermal anti-infection ability. Based on the dynamic oxidation-reduction response of disulfide bonds inspired by the dissociation of the tertiary spatial structure transformation of poly-polypeptide chains, these hydrogels can achieve rapid painless on-demand removal under mild conditions by adding dithiothreitol. These multifunctional hydrogels significantly promoted collagen deposition and angiogenesis in the MRSA-infected full-thickness skin repair experiment. All the results showed that these multifunctional hydrogels with painless on-demand removal property showed great potential in clinical treatment of infected wounds.

Recent Developments and Implementations of Conductive Polymer-Based Flexible Devices in Sensing Applications

Flexible sensing devices have attracted significant attention for various applications, such as medical devices, environmental monitoring, and healthcare. Numerous materials have been used to fabricate flexible sensing devices and improve their sensing performance in terms of their electrical and mechanical properties. Among the studied materials, conductive polymers are promising candidates for next-generation flexible, stretchable, and wearable electronic devices because of their outstanding characteristics, such as flexibility, light weight, and non-toxicity. Understanding the interesting properties of conductive polymers and the solution-based deposition processes and patterning technologies used for conductive polymer device fabrication is necessary to develop appropriate and highly effective flexible sensors. The present review provides scientific evidence for promising strategies for fabricating conductive polymer-based flexible sensors. Specifically, the outstanding nature of the structures, conductivity, and synthesis methods of some of the main conductive polymers are discussed. Furthermore, conventional and innovative technologies for preparing conductive polymer thin films in flexible sensors are identified and evaluated, as are the potential applications of these sensors in environmental and human health monitoring.

Bacterial Growth-Induced Tobramycin Smart Release Self-Healing Hydrogel for Pseudomonas aeruginosa-Infected Burn Wound Healing

Burns are a common health problem worldwide and are highly susceptible to bacterial infections that are difficult to handle with ordinary wound dressings. Therefore, burn wound repair is extremely challenging in clinical practice. Herein, a series of self-healing hydrogels (QCS/OD/TOB/PPY@PDA) with good electrical conductivity and antioxidant activity were prepared on the basis of quaternized chitosan (QCS), oxidized dextran (OD), tobramycin (TOB), and polydopamine-coated polypyrrole nanowires (PPY@PDA NWs). These Schiff base cross-links between the aminoglycoside antibiotic TOB and OD enable TOB to be slowly released and responsive to pH. Interestingly, the acidic substances during the bacteria growth process can induce the on-demand release of TOB, avoiding the abuse of antibiotics. The antibacterial results showed that the QCS/OD/TOB/PPY@PDA9 hydrogel could kill high concentrations of Pseudomonas aeruginosa (PA), Staphylococcus aureus, and Escherichia coli in a short time and showed a bactericidal effect for up to 11 days in an agar plate diffusion experiment, while showing good in vivo antibacterial activity. Excellent and long-lasting antibacterial properties make it suitable for severely infected wounds. Furthermore, the incorporation of PPY@PDA endowed the hydrogel with near-infrared (NIR) irradiation assisted bactericidal activity of drug-resistant bacteria, conductivity, and antioxidant activity. Most importantly, in the PA-infected burn wound model, the QCS/OD/TOB/PPY@PDA9 hydrogel more effectively controlled wound inflammation levels and promoted collagen deposition, vascular generation, and earlier wound closure compared to Tegaderm dressings. Therefore, the TOB smart release hydrogels with on-demand delivery are extremely advantageous for bacterial-infected burn wound healing.

Promotion of right ventricular outflow tract reconstruction using a novel cardiac patch incorporated with hypoxia-pretreated urine-derived stem cells

Approximately 25% of patients with congenital heart disease require implantation of patches to repair. However, most of the currently available patches are made of inert materials with unmatched electrical conductivity and mechanical properties, which may lead to an increased risk for arrhythmia and heart failure. In this study, we have developed a novel Polyurethane/Small intestinal submucosa patch (PSP) with mechanical and electrical properties similar to those of the native myocardial tissue, and assessed its feasibility for the reconstruction of right ventricular outflow tract. A right ventricular outflow tract reconstruction model was constructed in 40 rabbits. Compared with commercially available bovine pericardium patch, the PSP patch has shown better histocompatibility and biodegradability, in addition with significantly improved cardiac function. To tackle the significant fibrosis and relatively poor vascularization during tissue remodeling, we have further developed a bioactive patch by incorporating the PSP composites with urine-derived stem cells (USCs) which were pretreated with hypoxia. The results showed that the hypoxia-pretreated bioactive patch could significantly inhibit fibrosis and promote vascularization and muscularization, resulting in better right heart function. Our findings suggested that the PSP patch combined with hypoxia-pretreated USCs may provide a better strategy for the treatment of congenital heart disease.

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A novel cardiac patch (PSP) with mechanical and electrical properties similar to native myocardium.

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PSP patch improved cardiac function in right ventricular outflow tract reconstruction model.

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Hypoxia pretreated USCs combined PSP patch promoted vascularization and inhibited fibrosis.