Controlled tough bioadhesion mediated by ultrasound

Immunomodulatory bioadhesive technologies

Bioadhesives have found significant use in medicine and engineering, particularly for wound care, tissue engineering, and surgical applications. Compared to traditional wound closure methods such as sutures and staples, bioadhesives offer advantages, including reduced tissue damage, enhanced healing, and ease of implementation. Recent progress highlights the synergy of bioadhesives and immunoengineering strategies, leading to immunomodulatory bioadhesives capable of modulating immune responses at local sites where bioadhesives are applied. They foster favorable therapeutic outcomes such as reduced inflammation in wounds and implants or enhanced local immune responses to improve cancer therapy efficacy. The dual functionalities of bioadhesion and immunomodulation benefit wound management, tissue regeneration, implantable medical devices, and post-surgical cancer management. This review delves into the interplay between bioadhesion and immunomodulation, highlighting the mechanobiological coupling involved. Key areas of focus include the modulation of immune responses through chemical and physical strategies, as well as the application of these bioadhesives in wound healing and cancer treatment. Discussed are remaining challenges such as achieving long-term stability and effectiveness, necessitating further research to fully harness the clinical potential of immunomodulatory bioadhesives.

A double network composite hydrogel with enhanced transdermal delivery by ultrasound for endometrial injury repair and fertility recovery

Endometrial injury and resulting female infertility pose significant clinical challenges due to the notable shortcomings of traditional treatments. Herein, we proposed a double network composite hydrogel, CSMA-RC-Zn-PNS, which forms a physical barrier on damaged tissue through photo-crosslinking while enabling sustained release of the active ingredient PNS. Based on this, we developed a combined strategy to enhance transdermal delivery efficiency using ultrasound cavitation. In vitro experiments demonstrated that CSMA-RC-Zn-PNS exhibits excellent biosafety, biodegradability, and promotes cell proliferation, migration, and tube formation, along with antioxidant and antibacterial properties. In a rat endometrial injury model, the ultrasound cavitation effect was demonstrated to enhance transdermal delivery efficiency, and the ability of CSMA-RC-Zn-PNS to promote endometrial regeneration, anti-fibrosis and fertility restoration was verified. Overall, this strategy combining CSMA-RC-Zn-PNS hydrogel and ultrasound treatment shows promising applications in endometrial regeneration and female reproductive health.

Probiotic domestication and engineering enable one-shot treatment for bladder mucosal repair

The bladder mucosa is an important blood-urine barrier in the human body, its destruction can lead to distressing cystitis. Traditional treatment approaches often require frequent catheterization and intravesical instillation of hyaluronic acid (HA), which greatly reduces patient compliance and therapeutic efficacy. Herein, we develop a probiotic-based one-shot therapy to repair bladder mucosa with improved convenience, efficacy, and biosafety. To this end, a high-biocompatible probiotic strain is engineered to secrete high-molecular-weight HA controlled by ultrasound stimulation. Meanwhile, a bacterium acclimation-inspired strategy to select bacterial cells targeting the site of bladder inflammation is also proposed. With just one-shot intravesical administration, these engineered bacteria can strongly adhere to the damaged bladder epithelium, continuously secrete HA, and stimulate the formation of protective living engineered materials on the bladder. Consequently, varying therapeutic efficacies in damaged murine model, such as reporting the site of inflammation within 28 days, accelerating mucosal repair (such as significantly increased expression of tight junction proteins occludin-1 and ZO-1), modulating innate immune reactions (such as pro-inflammatory factor levels decreased by about 50 %), and even recovering animal motion behaviors, are realized, achieving an improved therapeutic effect without detectable adverse effects.

Hydrogel adhesives for tissue recovery

Hydrogel adhesives (HAs) are promising and rewarding tools for improving tissue therapy management. Such HAs had excellent properties and potential applications in biological tissues, such as suture replacement, long-term administration, and hemostatic sealing. In this review, the common designs and the latest progress of HAs based on various methodologies are systematically concluded. Thereafter, how to deal with interfacial water to form a robust wet adhesion and how to balance the adhesion and non-adhesion are underlined. This review also provides a brief description of gelation strategies and raw materials. Finally, the potentials of wound healing, hemostatic sealing, controlled drug delivery, and the current applications in dermal, dental, ocular, cardiac, stomach, and bone tissues are discussed. The comprehensive insight in this review will inspire more novel and practical HAs in the future.

Thermo-responsive and phase-separated hydrogels for cardiac arrhythmia diagnosis with deep learning algorithms

Adhesive epidermal hydrogel electrodes are essential for achieving robust signal transduction and cardiac arrhythmia diagnosis, but detachment of conventional adhesive dressings easily causes secondary damage to delicate wound tissues due to lack of programmable capability of changed adhesion. Herein, we developed hydrogel-based skin-interfacing electrodes capable of on-demand programmable adhesion and detachment to capture electrocardiogram signals for diagnosing cardiac arrhythmia. This was achieved by integrating dynamic multiscale contact and coordinated regulation through temperature-mediated switchable hydrogen bond interactions in phase-separated smart hydrogels. Through micro-scale regulation of adhesive molecules and meso-scale modulation of the modulus, the hydrogel electrodes can be rapidly transited between a slippery state (adhesion ∼1.3 N/m) and a sticky one (adhesion ∼110 N/m) during its peeling from skin. This achieves an 84.5-fold increase of on/off adhesive energy (or reducing the adhesion at the skin interface by 98%) at low temperatures compared to normal skin temperature. A real-time cloud platform was developed by integrating hydrogel electrodes, enabling remote electrocardiogram (ECG) monitoring. For clinical applications, such developed skin sensing platform effectively captured cardiac activities in patients with eight common arrhythmias, achieving by the recorded high-fidelity and analyzable electrical signals. With the assistance of deep learning algorithms, we demonstrated a wearable cardiac arrhythmia intelligent diagnosis system which enables real-time conversion of the collected ECG data into diagnostic evaluations with a recognition accuracy of 98.5%.

Robust Supramolecular Adhesives Based on Natural Small Molecules Through Hydrogen Bonding

The environmental persistence and widespread application of conventional polymer adhesives raise critical concerns regarding network design complexity and long-term residue accumulation. Herein, we present a water-soluble supramolecular adhesive synthesized from natural small molecules. Unlike traditional polymer networks relying on weak intermolecular forces, this system establishes a robust ordered architecture through dynamic disulfide bond ring-opening polymerization and carboxylate ion electrostatic interactions. Water-soluble hexamethylenetetramine (HMTA) strategically increases hydrogen-bonding site density while stabilizing the network topology, efficiently reducing chain entanglement. These synergistic effects endow the material with strong adhesion capability even at minimal usage (∼0.4 mg/cm2), achieving a maximum adhesion strength capable of supporting up to 107 times its weight while maintaining considerable resistance to various environmental factors, including thermal extremes (-80°C to 120°C) and exposure to organic solvents. This supramolecular design paradigm offers an eco-friendly alternative to conventional polymeric adhesives.

Lithium Bond-Mediated Molecular Cascade Hydrogel for Injury-Free and Repositionable Adhesive Bioelectronic Interfaces

Flexible bioelectronic interfaces with adhesive properties are essential for advancing modern medicine and human-machine interactions. However, achieving both stable adhesion and non-damaging detachment remains a significant challenge. In this study, a lithium bond-mediated molecular cascade hydrogel (LMCH) for bioelectronic interfaces is designed, which facilitates robust adhesion at the tissue level and permits atraumatic detachment for repositioning as required. By integrating the adhesive properties of the molecular cascade structure with the elastic characteristics of the hydrogel interface, the LMCH interface not only achieved a high adhesion strength (197 J m-2) on the skin, but also significantly extended the cracking cycles on the tissue surface during the peeling process from 4 to 380, marking an enhancement of nearly two orders of magnitude. Furthermore, with Young's modulus similar to that of human tissue (25 kPa), exceptional stretchability (1080%), and high ionic conductivity (7.14 S m-1), the LMCH interface demonstrates outstanding tissue compatibility, biocompatibility, and stable detection capabilities for electrocardiogram (ECG) and electromyogram (EMG) signals. This study presents new insights and potential for advancing bioelectronics and implantable interface technologies.

Hydrogel tissue adhesive: Adhesion strategy and application

Hydrogel tissue adhesives have emerged as a promising alternative to conventional wound closure methods such as sutures and staples due to their operational simplicity demonstrated biocompatibility and capacity for multifunctional integration. However, complex and variable tissue microenvironments and dynamic adhesion surfaces still challenge the actual adhesion performance of adhesives, especially natural polymer-based adhesives. In addition, to expand the application of adhesives in biomedical fields, there is an urgent need to further improve tissue adhesion performance through composition design, adhesion mechanism research and bioeffect development. This review focuses on the adhesive properties of adhesives and their applications in biomedical fields. Adhesion-cohesion equilibria, forms of adhesion failure, methods for improving cohesion and various interfacial adhesion mechanisms are presented. Moreover, practical biomedical applications of tissue adhesives are reviewed, focusing on skin, heart, stomach, liver, and cornea. Finally, this review looks ahead to a new generation of multi-functional, strong adhesion tissue adhesives, in the hope of providing inspiration to those working in the field.

A Microphase Separation-Driven Supramolecular Tissue Adhesive with Instantaneous Dry/Wet Adhesion, Alcohol-Triggered Debonding, and Antibacterial Hemostasis

Tissue adhesives are promising materials for expeditious hemorrhage control, while it remains a grand challenge to engineer a superior formulation with instantaneous adhesion, on-demand debonding, and the integration of multiple desirable properties such as antibacterial and hemostatic capabilities. Herein, a multifunctional supramolecular tissue adhesive based on guanidinium-modified polydimethylsiloxane (PDMS) is introduced, driven by a reversible microphase separation mechanism. By optimizing the content of guanidinium ions, precise control over cohesive strength, adhesion, and wettability is achieved, resulting in strong instantaneous adhesion under both dry and wet conditions. Notably, the supramolecular nature of the adhesive allows for convenient on-demand removal using medical-grade alcohol, offering a critical advantage for easy debonding. Additionally, the adhesive exhibits remarkable antimicrobial properties while maintaining excellent biocompatibility and hemocompatibility. Its underwater injectability supports minimally invasive surgical procedures. Furthermore, the adhesive's ability to incorporate solid particles enhances its versatility, particularly for the development of drug-embedded bioadhesives. This work addresses key challenges in tissue adhesive design via a microphase separation-driven working principle, thereby opening promising new avenues for the development of advanced bioadhesives with tailored properties and enhanced surgical and wound care outcomes.

Ultrasound Cavitation Enables Rapid, Initiator-Free Fabrication of Tough Anti-Freezing Hydrogels

Hydrogels are often synthesized with thermal or photo-initiated gelation, leaving alternative energy sources less explored. While ultrasound has been used for polymer synthesis and mechanochemistry, its application through cavitation for hydrogel synthesis as a constructive force is rare, and the underlying sonochemical mechanisms are poorly understood. Here, the application and mechanism of ultrasound cavitation for rapid, initiator-free, and oxygen-tolerant fabrication of tough anti-freezing hydrogels is reported. By incorporating polyol solvents and interpenetrating polymers into the gelling solution, radical generation is amplified and network formation is enhanced. Using tough polyacrylamide-alginate hydrogels as a model system, rapid gelation (as fast as 2 minutes) and high fracture toughness (up to 600 J m- 2) is demonstrated. By varying ultrasound intensity, crosslinker-to-monomer ratio, and glycerol concentration, the synthesis-structure-property relation is established for the resulting sonogels and the underlying mechanism is uncovered using combined molecular, optical, and mechanical testing techniques. The coupling of gelation and convection under ultrasound results in sonogels with unique structural and mechanical properties. Additionally, the fabrication of hydrogel constructs is demonstrated using both non-focused and high-intensity focused ultrasound. This work establishes a foundation for ultrasound-driven sono-fabrication and highlights new avenues in soft materials, advanced manufacturing, bioadhesives, and tissue engineering.

Mechanical Compatibility in Stitch Configuration and Sensor Adhesion for High-Fidelity Pulse Wave Monitoring

Wearable electronics can achieve high-fidelity monitoring of pulse waveforms on the body surface enabling early diagnosis of cardiovascular diseases (CVDs). Textile-based wearable devices offer advantages in terms of high permeability and comfort. However, knitted strain sensors struggle to capture small-range deformation signals due to stress dissipation during friction and slip of yarns within the textiles. They are optimized for mechanical adaptability and adhesive capability. In this work, the stitch configurations of knitted structure are adjusted to optimize the energy dissipation ratio during deformation and waveform fitting performance. These electric-mechanical results enabled the selection of the most suitable knitted structure for the clinical diagnosis. On the other hand, the sensor's adhesion is optimized with respect to electrical-force-strain coupling and energy transfer efficiency at the interface between skin and sensor. The balance between the storage modulus and loss modulus are adjusted via the crosslinking degree of the polyacrylamide (PAAm) hydrogel network. As a result, the optimized knitted sensor enables stable collection of pulse waveforms from the radial and dorsalis pedis arteries. In human patient evaluations, the knitting-based strain sensor can distinguish patients with different potential CVD risks through extracted characteristic indicators.

Synergistically Toughening Non-Neutral Polyampholyte Hydrogels by Ionic and Coordination Bonds at Low Metal-Ion Contents

Polyampholyte (PA) hydrogels, composed of charged hydrophilic networks with both positive and negative groups, have attracted great attention due to the unique structure and excellent antifouling properties. Yet, the superhydrophilicity usually makes non-neutral PA (n-PA) gels highly swollen and mechanically very weak in aqueous environments, severely limiting their applications. Herein metal-coordination bonds are designed to introduce to synergistically toughen n-PA hydrogels with ionic bonds via a secondary equilibrium strategy. In the design, as-prepared n-PA gels are dialyzed in metal-ion solutions and deionized water in sequence to achieve the tough gels. Through this strategy, the weak n-PA gels can be significantly toughened by the synergy of ionic and metal-coordination bonds. A systematic study indicates that both the molar ratio of oppositely charged monomers and the metal-ion concentration affect the mechanical enhancements clearly. The universality of the proposed strategy is further proved by selecting different gel systems and multivalent metal ions. Notably, low metal-ion concentrations (≤0.1 m) of dialysis solutions can enable synergistic toughening. Theoretical models are also adopted to disclose the toughening mechanism. This work not only expands the understanding on the fabrication of strong and tough PA hydrogels but also provides some insights for PA gels in electrolyte solutions.

Bioinspired hierarchical porous tough adhesive to promote sealing of high-pressure bleeding

Timely and stable sealing of uncontrolled high-pressure hemorrhage in emergency situations outside surgical units remains a major clinical challenge, contributing to the high mortality rate associated with trauma. The currently widely used hemostatic bioadhesives are ineffective for hemorrhage from major arteries and the heart due to the absence of biologically compatible flexible structures capable of simultaneously ensuring conformal tough adhesion and biomechanical support. Here, inspired by the principle of chromatin assembly, we present a tissue-conformable tough matrix for robust sealing of severe bleeding. This hierarchical matrix is fabricated through a phase separation process, which involves the in-situ formation of nanoporous aggregates within a microporous double-network (DN) matrix. The dispersed aggregates disrupt the rigid physical crosslinking of the original DN matrix and function as a dissipative component, enabling the aggregate-based DN (aggDN) matrix to efficiently dissipate energy during stress and achieve improved conformal attachment to soft tissues. Subsequently, pre-activated bridging polymers facilitate rapid interfacial bonding between the matrix and tissue surfaces. They synergistically withstand considerable hydraulic pressure of approximately 700 mmHg and demonstrate exceptional tissue adhesion and sealing in rat cardiac and canine aortic hemorrhages, outperforming the commercially available bioadhesives. Our findings present a promising biomimetic strategy for engineering biomechanically compatible and tough adhesive hydrogels, facilitating prompt and effective treatment of hemorrhagic wounds.

Supramolecular interactions-driven aggregation to prepare lipoic acid-bioadhesives for seawater-immersed wounds

Seawater-immersed wounds can be threatened by high pH, high permeability and infection, which may lead to the development of chronic wounds. The present study develops an aggregation strategy for the rapid preparation of α-lipoic acid (LA)-based bioadhesives at room temperature with strong and underwater adhesion for emergency treatment of trauma in maritime activities. The bioadhesives are fabricated from the aggregation of LA, MXene and Ag+ through their supramolecular interactions, which can be rapidly formed in mild environments, showing strong interface adhesion without adhesive failure caused by depolymerization, while exhibiting mechanical self-reinforcing. To further improve the adhesive strength, the formation of MXene/Ag+/LA interactions was integrated into poly(2-hydroxyethyl methacrylate) (pHEMA) electrospinning to manufacture electrospun film with the adhesion strength as high as 2 MPa. The bioadhesives are sensitive to alkaline environments and can lead to deprotonation of LA. The released H+ can instantly adjust the pH of weakly alkaline seawater-immersed wounds to normal pH, while deprotonated LA is released into wounds to exert anti-inflammatory functions. Together with antibacterial property, bioadhesives applied to seawater-immersed wounds provide stable barrier protection and correct adverse microenvironment, promoting wound healing.

Integrating Hydrogels and Biomedical Plastics via In Situ Physical Entanglements and Covalent Bonding

Both rigid plastics and soft hydrogels find ample applications in engineering and medicine but bear their own disadvantages that limit their broader applications. Bonding these mechanically dissimilar materials may resolve these limitations, preserve their advantages, and offer new opportunities as biointerfaces. Here, a robust adhesion strategy is proposed to integrate highly entangled tough hydrogels and diverse plastics with high interfacial adhesion energy and strength. Systemic investigations on the effects of hydrogel monomer content and crosslink fraction revealed the significant contributions of both polymer physical entanglements and interfacial covalent bonding. This hybrid engineering strategy also enables the plastic-hydrogel composite to attenuate foreign body response caused by pristine rigid plastics in vivo in mice. This versatile materials engineering approach may be broadly applicable to other polymer-based devices commonly used in regenerative medicine and surgical robotics.

Emerging Wearable Acoustic Sensing Technologies

Sound signals not only serve as the primary communication medium but also find application in fields such as medical diagnosis and fault detection. With public healthcare resources increasingly under pressure, and challenges faced by disabled individuals on a daily basis, solutions that facilitate low-cost private healthcare hold considerable promise. Acoustic methods have been widely studied because of their lower technical complexity compared to other medical solutions, as well as the high safety threshold of the human body to acoustic energy. Furthermore, with the recent development of artificial intelligence technology applied to speech recognition, speech recognition devices, and systems capable of assisting disabled individuals in interacting with scenes are constantly being updated. This review meticulously summarizes the sensing mechanisms, materials, structural design, and multidisciplinary applications of wearable acoustic devices applied to human health and human-computer interaction. Further, the advantages and disadvantages of the different approaches used in flexible acoustic devices in various fields are examined. Finally, the current challenges and a roadmap for future research are analyzed based on existing research progress to achieve more comprehensive and personalized healthcare.

A natural gelatin/casein hydrogel with on-demand adhesion via chitosan solution for wound healing

Adhesive hydrogels have been widely studied as wound dressings due to their excellent biocompatibility and biological activity. However, most designed hydrogels still exist limitations including potentially toxic monomer, complex preparation process and non-degradable property. Here, a natural and degradable gelatin/casein hydrogel was prepared by enzymatic cross-linking. The hydrogel could adhere to tissue on-demand with the mediation of chitosan (CS) solution. It was found that the adhesion strength of hydrogel could be controlled by adjusting gelatin/casein ratio, EDC&NHS concentration, CS concentration, glycerol content and crosslinking degree. To further expand the applicability of hydrogels, the degradation and drug release rate of hydrogels could be modulated by changing transglutaminase (TG) concentration. Moreover, tetracycline hydrochloride (TH) was loaded into hydrogel as a drug model, which endowed hydrogel with good antibacterial properties. It was shown that the 0.03 % TH hydrogel had excellent blood compatibility and cell compatibility, and can promote the healing of infected wounds in mice. This research provides a new natural adhesive hydrogel for biomedical engineering field.

Cilia-Mimic Locomotion of Magnetic Colloidal Collectives Enhanced by Low-Intensity Ultrasound for Thrombolytic Drug Penetration

Rapid thrombolysis is very important to reduce complications caused by vascular blockage. A promising approach for improving thrombolysis efficiency is utilizing the permanent magnetically actuated locomotion of nanorobots. However, the thrombolytic drug transportation efficiency is challenged by in-plane rotating locomotion and the insufficient drug penetration limits further improvement of thrombolysis. Inspired by ciliary movement for cargo transportation in human body, in this study, cilia-mimic locomotion of magnetic colloidal collectives is realized under torque-force vortex magnetic field (TFV-MF) by a designed rotating permanent magnet assembly. This cilia-mimic locomotion mode can generate more disturbances to the fluids to improve thrombolytic drug transportation and the increased height and area of colloidal collectives boosted the imaging capability. In addition, low-intensity ultrasound is applied to enhance colloids infiltration by producing the fiber breakage and inducing erythrocyte deformation. In vitro thrombolytic experiments demonstrate that the thrombolysis efficiency increased by 16.2 times compared with that of pure tissue plasminogen activator (tPA) treatments. Furthermore, in vivo rat models of femoral vein thrombosis confirmed that this approach can achieve blood flow recanalization more quickly. The proposed cilia-mimic locomotion of magnetic colloidal collectives combined with low-intensity ultrasound irradiation mode provides a new insight of therapeutic interventions for vascular thrombus by enhancing drug penetration.

Bio-Inspired Highly Stretchable and Ultrafast Autonomous Self-Healing Supramolecular Hydrogel for Multifunctional Durable Self-Powered Wearable Devices

As skin bioelectronics advances, hydrogel wearable devices have broadened perspectives in environment sensing and health monitoring. However, their application is severely hampered by poor mechanical and self-healing properties, environmental sensitivity, and limited sensory functions. Herein, inspired by the hierarchical structure and unique cross-linking mechanism of hagfish slime, a self-powered supramolecular hydrogel is hereby reported, featuring high stretchability (>2800% strain), ultrafast autonomous self-healing capabilities (electrical healing time: 0.3 s), high self-adhesiveness (adhesion strength: 6.92 kPa), injectability, ease of shaping, antimicrobial properties, and biocompatibility. It is observed that by embedding with the highly hygroscopic salt LiCl in supramolecular hydrogel, the hydrogel not only showed excellent electrical conductivity but also presented favorable anti-freezing and water retention properties in extremely cold environments and natural settings. Given these attributes, the hydrogel served as a multifunctional durable self-powered wearable device with high sensitivity (gauge factor: 3.68), fast response time (160 ms), low detection limit, and frequency sensitivity. Moreover, the multifunctional applicability of this supramolecular hydrogel is further demonstrated in long-term cold environments sensing, remote medical communication, and underwater communication. Overall, these findings pave the way for the sustainable development of hydrogel-based wearable devices that are self-powered, durable, and offer high performance, environmental adaptability, and multi-sensory capabilities.

The current research status of immobilized lipase performance and its potential for application in food are developing toward green and healthy direction: A review

Immobilized lipases have received great attention in food, environment, medicine, and other fields due to their easy separation, high stability (temperature, pH), and high storage properties. After immobilization, lipase transforms from a homogeneous to a heterogeneous state, making it easier to recover from the reaction substrate and achieve recycling, which is in line with the concept of green chemistry and reduces protein contamination in the product. There are various materials for enzyme immobilization, including polysaccharides from natural sources, inorganic compounds, carbon nanotubes, metal-organic framework materials, and so forth. Magnetic immobilization carriers have been widely studied due to their ability to achieve separation by adding a magnetic field. Its immobilization method can be simply divided into two categories: physical action (adsorption, embedding) and chemical binding (covalent, cross-linking). Some studies mainly discuss the immobilization support materials, immobilization methods, and applications of immobilized lipases in food. On this basis, our review also focuses on the changes in crosslinking agents for immobilized lipases, different methods to promote immobilization, new trends in the study of immobilized lipases, and proposes prospects for immobilized lipase research in the food industry.

Recent Development of Fibrous Hydrogels: Properties, Applications and Perspectives

Fibrous hydrogels (FGs), characterized by a 3D network structure made from prefabricated fibers, fibrils and polymeric materials, have emerged as significant materials in numerous fields. However, the challenge of balancing mechanical properties and functions hinders their further development. This article reviews the main advantages of FGs, including enhanced mechanical properties, high conductivity, high antimicrobial and anti-inflammatory properties, stimulus responsiveness, and an extracellular matrix (ECM)-like structure. It also discusses the influence of assembly methods, such as fiber cross-linking, interfacial treatments of fibers with hydrogel matrices, and supramolecular assembly, on the diverse functionalities of FGs. Furthermore, the mechanisms for improving the performance of the above five aspects are discussed, such as creating ion carrier channels for conductivity, in situ gelation of drugs to enhance antibacterial and anti-inflammatory properties, and entanglement and hydrophobic interactions between fibers, resulting in ECM-like structured FGs. In addition, this review addresses the application of FGs in sensors, dressings, and tissue scaffolds based on the synergistic effects of optimizing the performance. Finally, challenges and future applications of FGs are discussed, providing a theoretical foundation and new insights for the design and application of cutting-edge FGs.

Multifunctional Adhesive Hydrogels: From Design to Biomedical Applications

Adhesive hydrogels characterized by structural properties similar to the extracellular matrix, excellent biocompatibility, controlled degradation, and tunable mechanical properties have demonstrated significant potential in biomedical applications, including tissue engineering, biosensors, and drug delivery systems. These hydrogels exhibit remarkable adhesion to target substrates and can be rationally engineered to meet specific requirements. In recent decades, adhesive hydrogels have experienced significant advancements driven by the introduction of numerous multifunctional design strategies. This review initially summarizes the chemical bond-based design strategies for tissue adhesion, encompassing static covalent bonds, dynamic covalent bonds, and non-covalent interactions. Subsequently, the multiple functionalities imparted by these diverse design strategies, including highly stretchable and tough performances, responsiveness to microenvironments, anti-freezing/heating properties, conductivity, antibacterial activity, and hemostatic properties are discussed. In addition, recent advances in the biomedical applications of adhesive hydrogels, focusing on tissue repair, drug delivery, medical devices, and wearable sensors are reviewed. Finally, the current challenges are highlighted and future trends in this rapidly evolving field are discussed.

Hydrogel Fibers-Based Biointerfacing

The unique 1D structure of fibers offers intriguing attributes, including a high length-to-diameter ratio, miniatured size, light-weight, and flexibility, making them suitable for various biomedical applications, such as health monitoring, disease treatment, and minimally invasive surgeries. However, traditional fiber devices, typically composed of rigid, dry, and non-living materials, are intrinsically different from the soft, wet, and living essence of biological tissues, thereby posing grand challenges for long-term, reliable, and seamless interfacing with biological systems. Hydrogel fibers have recently emerged as a promising candidate, in light of their similarity to biological tissues in mechanical, chemical and biological aspects, as well as distinct fiber geometry. In this review, a comprehensive overview of recent progress in hydrogel fibers-based biointerfacing technology is provided. It thoroughly summarizes the manufacturing strategy and functional design, especially for hydrogel fibers with distinct optical and electron conductive performance, as well as responsiveness to triggers including thermal, magnetic field and ultrasonic wave, etc. Such unique attributes enable various biomedical applications, which are also examined in detail. Future challenges and potential directions, including biosafety, long-term reliability, sterilization, multi-modalities integration and intelligent therapeutic systems, are raised. This review will serve as a valuable resource for further advancement and implementation as next-generation biointerfacing technology.

Tough and Functional Hydrogel Coating by Electrostatic Spraying

Hydrogel coatings impart superior surface properties to materials, but their application on large and complicated substrates is hindered by two challenges: limited wetting conditions and intricate curing processes. To overcome the challenges, lyophilized adhesive hydrogel powders (LAHPs) are developed, which consist of poly(acrylic acid-co-3-(trimethoxysilyl)propyl methacrylate) crosslinked with chitosan. These powders are electrostatic sprayed onto substrates to address wetting issues and rehydrated to form bulk hydrogel coatings to circumvent curing challenges. This approach enables the application of hydrogel coatings with a smooth surface and adjustable thickness on various materials, irrespective of category, geometry, or size. The coatings exhibit remarkable mechanical properties (strength of 2.62 MPa, elastic modulus of 6.84 MPa, and stretchability exceeding 3 folds) and robust adhesion (adhesion energy ≈900 J m-2) through a three-step bonding process involving electrostatic attraction, hydrogen bonding, and covalent bonding. Notably, these coatings confer multiple functional attributes to the substrate, including lubricity, hydrophilicity, nucleation inhibition, and pH-responsive actuation. Moreover, incorporating LAHPs with functional agents or rehydrating with functional solutions opens possibilities for diverse functional hydrogel coatings, such as thermal responsiveness and NH3 indication. Leveraging the virtues of simplicity, flexibility, convenience, and broad applicability, this strategy presents an enticing pathway for the widespread applications of hydrogel coatings.

Design Strategy, On-Demand Control, and Biomedical Engineering Applications of Wet Adhesion

The adhesion of tissues to external devices is fundamental to numerous critical applications in biomedical engineering, including tissue and organ repair, bioelectronic interfaces, adhesive robotics, wearable electronics, biomedical sensing and actuation, as well as medical monitoring, treatment, and healthcare. A key challenge in this context is that tissues are typically situated in aqueous and dynamic environments, which poses a bottleneck to further advancements in these fields. Wet adhesion technology (WAT) presents an effective solution to this issue. In this review, we summarize the three major design strategies and control methods of wet adhesion, comprehensively and systematically introducing the latest applications and advancements of WAT in the field of biomedical engineering. First, single adhesion mechanism under the frameworks of the three design strategies is systematically introduced. Second, control methods for adhesion are comprehensively summarized, including spatiotemporal control, detachment control, and reversible adhesion control. Third, a systematic summary and discussion of the latest applications of WAT in biomedical engineering research and education were presented, with a particular focus on innovative applications such as tissue-electronic interface devices, ingestible devices, end-effector components, in vivo medical microrobots, and medical instruments and equipment. Finally, opportunities and challenges encountered in the design and development of wet adhesives with advanced adhesive performance and application prospects are discussed.

An Environmentally Stable, Biocompatible, and Multilayered Wound Dressing Film with Reversible and Strong Adhesion

Reversible adhesives for wound care improve patient experiences by permitting reuse and minimizing further tissue injury. Existing reversible bandages are vulnerable to water and can undergo unwanted deformation during removal and readdressing procedures. Here, a biocompatible, multilayered, reversible wound dressing film that conforms to skin and is waterproof is designed. The inner layer is capable of instant adhesion to various substrates upon activation of the dynamic boronic ester bonds by water; intermediate hydrogel layer and outer silicone backing layer can enhance the dressing's elasticity and load distribution for adhesion, and the silicone outer layer protects the dressing from exposure to water. The adhesive layer is found to be biocompatible with mouse skin. Skin injuries on the mouse skin heal more rapidly with the film compared to no dressing controls. Evaluations of the film on skin of freshly euthanized minipigs corroborate the findings in the mouse model. The film remains attached to skins without delamination despite subjecting to various degrees of deformation. Exposure to water softens the film to allow removal from the skin without pulling any hair off. The multilayered design considers soft mechanics in each layer and will offer new insights to improve wound dressing performance and patient comfort.

Highly conductive and sensitive alginate hydrogel strain sensors fabricated using near-field electrohydrodynamic direct-writing process

Hydrogel flexible sensors have attracted considerable attention because of their wearability, biocompatibility, and precision signal transmission capability. However, the hydrogel strain sensors fabricated by conventional printing or hand-injection methods have difficulty balancing their mechanical strength and sensing characteristics, limiting the application of hydrogel strain sensors. Herein, polyvinyl alcohol and polyacrylamide were loosely crosslinked with sodium alginate through chemical cross-linking. Subsequently, MXene nanosheets were introduced for doping, the crosslinked hydrogel conductive network was constructed, and the hydrogel strain sensors were fabricated using the electrohydrodynamic (EHD) printing method. The ions in the EHD-printed hydrogel undergo directional movement under an externally enhanced electric field, causing the formation of more uniform and dense porous conductive networks inside the hydrogel, and high electrical conductivity (0.49 S m-1) is obtained. These hydrogel strain sensors have excellent mechanical properties (tensile strength: 0.17 MPa at 787 % strain), high sensitivity (gauge factor: 1.54 at 0-100 % strain), and low detection limits (1 % strain). Furthermore, demonstrations of real-time Morse code tapping information transmission, handwriting recognition during writing, and human physiological behavior monitoring demonstrations using the fabricated sensors indicate that the EHD-printed hydrogel strain sensor method has significant potential for wearable devices and human-computer interaction applications.

A Mg Battery-Integrated Bioelectronic Patch Provides Efficient Electrochemical Stimulations for Wound Healing

Bioelectronic patches hold promise for patient-comfort wound healing providing simplified clinical operation. Currently, they face paramount challenges in establishing long-term effective electronic interfaces with targeted cells and tissues due to the inconsistent energy output and high bio interface impedance. Here a new electrochemical stimulation technology is reported, using a simple wound patch, which integrates the efficient generation and delivery of stimulation. This is realized by employing a hydrogel bioelectronic interface as an active component in an integrated power source (i.e., Mg battery). The Mg battery enhances fibroblast functions (proliferation, migration, and growth factor secretion) and regulates macrophage phenotype (promoting regenerative polarization and down-regulating pro-inflammatory cytokines), by providing an electric field and the ability to control the cellular microenvironment through chemical release. This bioelectronic patch shows an effective and accelerated wound closure by guiding epithelial migration, mediating immune response, and promoting vasculogenesis. This new electrochemical-mediated therapy may provide a new avenue for user-friendly wound management as well as a platform for fundamental insights into cell stimulation.

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.

Penetration enhancers strengthen tough hydrogel bioadhesion and modulate locoregional drug delivery

The human body possesses natural barriers, such as skin and mucosa, which limit the effective delivery of therapeutics and integration of medical devices to target tissues. Various strategies have been deployed to breach these barriers mechanically, chemically, or electronically. The development of various penetration enhancers (PEs) offers a promising solution due to their ability to increase tissue permeability using readily available reagents. However, existing PE-mediated delivery methods often rely on weak gel or liquid drug formulations, which are not ideal for sustained local delivery. Hydrogel adhesives that can seamlessly interface biological tissues with controlled drug delivery could potentially resolve these issues. Here, we demonstrate that tough adhesion between drug-laden hydrogels and biological tissue (e.g. skin and tumours) can lead to effective local delivery of drugs deep into targeted tissues by leveraging the enhanced tissue penetration mediated by PEs. The drug release profile of the hydrogel adhesives can be fine-tuned by further engineering the nanocomposite hydrogel matrix to elute chemotherapeutics from 2 weeks to 2 months. Using a 3D tumour spheroid model, we demonstrated that PEs increased the cancer-killing effectiveness of doxorubicin by facilitating its delivery into tumour microtissues. Therefore, the proposed tough bioadhesion and drug delivery strategy modulated by PEs holds promise as a platform technique to develop next-generation wearable and implantable devices for cancer management and regenerative medicine.

3D printed multi-coupled bioinspired skin-electronic interfaces with enhanced adhesion for monitoring and treatment

Skin-electronic interfaces have broad applications in fields such as diagnostics, therapy, health monitoring, and smart wearables. However, they face various challenges in practical use. For instance, in wet environments, the cohesion of the material may be compromised, and under dynamic conditions, maintaining conformal adhesion becomes difficult, leading to reduced sensitivity and fidelity of electrical signal transmission. The key scientific issue lies in forming a stable and tight mechanical-electronic coupling at the tissue-electronic interface. Here, inspired by octopus sucker structures and snail mucus, we propose a strategy for hydrogel skin-electronic interfaces based on multi-coupled bioinspired adhesion and introduce an ultrasound (US)-mediated interfacial toughness enhancement mechanism. Ultimately, using digital light processing micro-nano additive manufacturing technology (DLP 3D), we have developed a multifunctional, diagnostic-therapeutic integrated patch (PAMS). This patch exhibits moderate water swelling properties, a maximum deformation of up to 460%, high sensitivity (GF = 4.73), and tough and controllable bioadhesion (shear strength increased by 109.29%). Apart from outstanding mechanical and electronic properties, the patch also demonstrates good biocompatibility, anti-bacterial properties, photothermal properties, and resistance to freezing at -20 °C. Experimental results show that this skin-electronic interface can sensitively monitor temperature, motion, and electrocardiogram signals. Utilizing a rat frostbite model, we have demonstrated that this skin-electronic interface can effectively accelerate the wound healing process as a wound patch. This research offers a promising strategy for improving the performance of bioelectronic devices, sensor-based educational reforms and personalized diagnostics and therapeutics in the future. STATEMENT OF SIGNIFICANCE: Establishing stable and tight mechanical-electronic coupling at the tissue-electronic interface is essential for the diverse applications of bioelectronic devices. This study aims to develop a multifunctional, diagnostic-therapeutic integrated hydrogel skin-electronic interface patch with enhanced interfacial toughness. The patch is based on a multi-coupled bioinspired adhesive-enhanced mechanism, allowing for personalized 3D printing customization. It can be used as a high-performance diagnostic-therapeutic sensor and effectively promote frostbite wound healing. We anticipate that this research will provide new insights for constructing the next generation of multifunctional integrated high-performance bioelectronic interfaces.

Mechanical Regulation of Polymer Gels

The mechanical properties of polymer gels devote to emerging devices and machines in fields such as biomedical engineering, flexible bioelectronics, biomimetic actuators, and energy harvesters. Coupling network architectures and interactions has been explored to regulate supportive mechanical characteristics of polymer gels; however, systematic reviews correlating mechanics to interaction forces at the molecular and structural levels remain absent in the field. This review highlights the molecular engineering and structural engineering of polymer gel mechanics and a comprehensive mechanistic understanding of mechanical regulation. Molecular engineering alters molecular architecture and manipulates functional groups/moieties at the molecular level, introducing various interactions and permanent or reversible dynamic bonds as the dissipative energy. Molecular engineering usually uses monomers, cross-linkers, chains, and other additives. Structural engineering utilizes casting methods, solvent phase regulation, mechanochemistry, macromolecule chemical reactions, and biomanufacturing technology to construct and tailor the topological network structures, or heterogeneous modulus compositions. We envision that the perfect combination of molecular and structural engineering may provide a fresh view to extend exciting new perspectives of this burgeoning field. This review also summarizes recent representative applications of polymer gels with excellent mechanical properties. Conclusions and perspectives are also provided from five aspects of concise summary, mechanical mechanism, biofabrication methods, upgraded applications, and synergistic methodology.

Mussel-Bioinspired Lignin Adhesive for Wearable Bioelectrodes

As a natural "binder," lignin fixes cellulose in plants to foster growth and longevity. However, isolated lignin has a poor binding ability, which limits its biomedical applications. In this study, inspired by mussel adhesive proteins, acidic/basic amino acids (AAs) are introduced in alkali lignin (AL) to form ionic-π/spatial correlation interactions, followed by demethylation to create catechol residues for enhanced adhesion activity. Atomic force microscopy reveals that catechol residues are the primary adhesion structures, with basic AAs exhibiting superior synergistic effects compared to acidic AAs. Demethylated lysine-grafted AL exhibits the strongest adhesion force toward skin tissue. Molecular dynamic simulation and density functional theory calculations indicate that adhesion against skin tissue mainly results from hydrogen bonds and cation-π interactions, with the adhesion mechanism being based on the Gibbs free energy of the Schiff base reaction. In summary, a biomimetic electrode based on lignin inspired by mussel adhesive proteins is prepared; the presented method offers a straightforward strategy for the development of biomimetic adhesives. Furthermore, this mussel-inspired adhesive can be used as a wearable bioelectrode in biomedical applications.

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.

Hydrogels: a promising therapeutic platform for inflammatory skin diseases treatment

Inflammatory skin diseases, such as psoriasis and atopic dermatitis, pose significant health challenges due to their long-lasting nature, potential for serious complications, and significant health risks, which requires treatments that are both effective and exhibit minimal side effects. Hydrogels offer an innovative solution due to their biocompatibility, tunability, controlled drug delivery capabilities, enhanced treatment adherence and minimized side effects risk. This review explores the mechanisms that guide the design of hydrogel therapeutic platforms from multiple perspectives, focusing on the components of hydrogels, their adjustable physical and chemical properties, and their interactions with cells and drugs to underscore their clinical potential. We also examine various therapeutic agents for psoriasis and atopic dermatitis that can be integrated into hydrogels, including traditional drugs, novel compounds targeting oxidative stress, small molecule drugs, biologics, and emerging therapies, offering insights into their mechanisms and advantages. Additionally, we review clinical trial data to evaluate the effectiveness and safety of hydrogel-based treatments in managing psoriasis and atopic dermatitis under complex disease conditions. Lastly, we discuss the current challenges and future opportunities for hydrogel therapeutics in treating psoriasis and atopic dermatitis, such as improving skin barrier penetration and developing multifunctional hydrogels, and highlight emerging opportunities to enhance long-term safety and stability.

Composite Hydrogel Sealants for Annulus Fibrosus Repair

Intervertebral disc (IVD) herniation is a leading cause of disability and lower back pain, causing enormous socioeconomic burdens. The standard of care for disc herniation is nucleotomy, which alleviates pain but does not repair the annulus fibrosus (AF) defect nor recover the biomechanical function of the disc. Existing bioadhesives for AF repair are limited by insufficient adhesion and significant mechanical and geometrical mismatch with the AF tissue, resulting in the recurrence of protrusion or detachment of bioadhesives. Here, we report a composite hydrogel sealant constructed from a composite of a three-dimensional (3D)-printed thermoplastic polyurethane (TPU) mesh and tough hydrogel. We tailored the fiber angle and volume fraction of the TPU mesh design to match the angle-ply structure and mechanical properties of native AF. Also, we proposed and tested three types of geometrical design of the composite hydrogel sealant to match the defect shape and size. Our results show that the sealant could mimic native AF in terms of the elastic modulus, flexural modulus, and fracture toughness and form strong adhesion with the human AF tissue. The bovine IVD tests show the effectiveness of the composite hydrogel sealant for AF repair and biomechanics recovery and for preventing herniation with its heightened stiffness and superior adhesion. By harnessing the combined capabilities of 3D printing and bioadhesives, these composite hydrogel sealants demonstrate promising potential for diverse applications in tissue repair and regeneration.

Additive manufacturing of highly entangled polymer networks

Incorporation of polymer chain entanglements within a single network can synergistically improve stiffness and toughness, yet attaining such dense entanglements through vat photopolymerization additive manufacturing [e.g., digital light processing (DLP)] remains elusive. We report a facile strategy that combines light and dark polymerization to allow constituent polymer chains to densely entangle as they form within printed structures. This generalizable approach reaches high monomer conversion at room temperature without the need for additional stimuli, such as light or heat after printing, and enables additive manufacturing of highly entangled hydrogels and elastomers that exhibit fourfold- to sevenfold-higher extension energies in comparison to that of traditional DLP. We used this method to print high-resolution and multimaterial structures with features such as spatially programmed adhesion to wet tissues.

Chemically Programmed Hydrogels for Spatiotemporal Modulation of the Cardiac Pathological Microenvironment

After myocardial infarction (MI), sustained ischemic events induce pathological microenvironments characterized by ischemia-hypoxia, oxidative stress, inflammatory responses, matrix remodeling, and fibrous scarring. Conventional clinical therapies lack spatially targeted and temporally responsive modulation of the infarct microenvironment, leading to limited myocardial repair. Engineered hydrogels have a chemically programmed toolbox for minimally invasive localization of the pathological microenvironment and personalized responsive modulation over different pathological periods. Chemically programmed strategies for crosslinking interactions, interfacial binding, and topological microstructures in hydrogels enable minimally invasive implantation and in situ integration tailored to the myocardium. This enhances substance exchange and signal interactions within the infarcted microenvironment. Programmed responsive polymer networks, intelligent micro/nanoplatforms, and biological therapeutic cues contribute to the formation of microenvironment-modulated hydrogels with precise targeting, spatiotemporal control, and on-demand feedback. Therefore, this review summarizes the features of the MI microenvironment and chemically programmed schemes for hydrogels to conform, integrate, and modulate the cardiac pathological microenvironment. Chemically programmed strategies for oxygen-generating, antioxidant, anti-inflammatory, provascular, and electrointegrated hydrogels to stimulate iterative and translational cardiac tissue engineering are discussed.

Diatomite-incorporated hierarchical scaffolds for osteochondral regeneration

Osteochondral regeneration involves the highly challenging and complex reconstruction of cartilage and subchondral bone. Silicon (Si) ions play a crucial role in bone development. Current research on Si ions mainly focuses on bone repair, by using silicate bioceramics with complex ion compositions. However, it is unclear whether the Si ions have important effect on cartilage regeneration. Developing a scaffold that solely releases Si ions to simultaneously promote subchondral bone repair and stimulate cartilage regeneration is critically important. Diatomite (DE) is a natural diatomaceous sediment that can stably release Si ions, known for its abundant availability, low cost, and environmental friendliness. Herein, a hierarchical osteochondral repair scaffold is uniquely designed by incorporating gradient DE into GelMA hydrogel. The adding DE microparticles provides a specific Si source for controlled Si ions release, which not only promotes osteogenic differentiation of rBMSCs (rabbit bone marrow mesenchymal stem cells) but also enhances proliferation and maturation of chondrocytes. Moreover, DE-incorporated hierarchical scaffolds significantly promoted the regeneration of cartilage and subchondral bone. The study suggests the significant role of Si ions in promoting cartilage regeneration and solidifies their foundational role in enhancing bone repair. Furthermore, it offers an economic and eco-friendly strategy for developing high value-added osteochondral regenerative bioscaffolds from low-value ocean natural materials.

An artificial liquid-liquid phase separation-driven silk fibroin-based adhesive for rapid hemostasis and wound sealing

The powerful adhesion systems of marine organisms have inspired the development of artificial protein-based bioadhesives. However, achieving robust wet adhesion using artificial bioadhesives remains technically challenging because the key element of liquid-liquid phase separation (LLPS)-driven complex coacervation in natural adhesion systems is often ignored. In this study, mimicking the complex coacervation phenomenon of marine organisms, an artificial protein-based adhesive hydrogel (SFG hydrogel) was developed by adopting the LLPS-mediated coacervation of the natural protein silk fibroin (SF) and the anionic surfactant sodium dodecylbenzene sulfonate (SDBS). The assembled SF/SDBS complex coacervate enabled precise spatial positioning and easy self-adjustable deposition on irregular substrate surfaces, allowing for tight contact. Spontaneous liquid-to-solid maturation promoted the phase transition of the SF/SDBS complex coacervate to form the SFG hydrogel in situ, enhancing its bulk cohesiveness and interfacial adhesion. The formed SFG hydrogel exhibited intrinsic advantages as a new type of artificial protein-based adhesive, including good biocompatibility, robust wet adhesion, rapid blood-clotting capacity, and easy operation. In vitro and in vivo experiments demonstrated that the SFG hydrogel not only achieved instant and effective hemostatic sealing of tissue injuries but also promoted wound healing and tissue regeneration, thus advancing its clinical applications. STATEMENT OF SIGNIFICANCE: Marine mussels utilize the liquid-liquid phase separation (LLPS) strategy to induce the supramolecular assembly of mussel foot proteins, which plays a critical role in strong underwater adhesion of mussel foot proteins. Herein, an artificial protein-based adhesive hydrogel (named SFG hydrogel) was reported by adopting the LLPS-mediated coacervation of natural protein silk fibroin (SF) and anionic surfactant sodium dodecylbenzene sulfonate (SDBS). The assembled SFG hydrogel enabled the precise spatial positioning and easy self-adjustable deposition on substrate surfaces with irregularities, allowing tight interfacial adhesion and cohesiveness. The SFG hydrogel not only achieved instant and effective hemostatic sealing of tissue injuries but also promoted wound healing and tissue regeneration, exhibiting intrinsic advantages as a new type of artificial protein-based bioadhesives.

3D Printable Active Hydrogels with Supramolecular Additive-Driven Adaptiveness

Smart hydrogels are a promising candidate for the development of next-generation soft materials due to their stimuli-responsiveness, deformability, and biocompatibility. However, it remains challenging to enable hydrogels to actively adapt to various environmental conditions like living organisms. In this work, supramolecular additives are introduced to the hydrogel matrix to confer environmental adaptiveness. Specifically, their microstructures, swelling behaviors, mechanical properties, and transparency can adapt to external environmental conditions. Moreover, the presence of hydrogen bonding provides the hydrogel with applicable rheological properties for 3D extrusion printing, thus allowing for the facile preparation of thickness-dependent camouflage and multistimuli responsive complex. The environmentally adaptive hydrogel developed in this study offers new approaches for manipulating supramolecular interactions and broadens the capability of smart hydrogels in information security and multifunctional integrated actuation.

Progress in the development of piezoelectric biomaterials for tissue remodeling

Piezoelectric biomaterials have demonstrated significant potential in the past few decades to heal damaged tissue and restore cellular functionalities. Herein, we discuss the role of bioelectricity in tissue remodeling and explore ways to mimic such tissue-like properties in synthetic biomaterials. In the past decade, biomedical engineers have adopted emerging functional biomaterials-based tissue engineering approaches using innovative bioelectronic stimulation protocols based on dynamic stimuli to direct cellular activation, proliferation, and differentiation on engineered biomaterial constructs. The primary focus of this review is to discuss the concepts of piezoelectric energy harvesting, piezoelectric materials, and their application in soft (skin and neural) and hard (dental and bone) tissue regeneration. While discussing the prospective applications as an engineered tissue, an important distinction has been made between piezoceramics, piezopolymers, and their composites. The superiority of piezopolymers over piezoceramics to circumvent issues such as stiffness mismatch, biocompatibility, and biodegradability are highlighted. We aim to provide a comprehensive review of the field and identify opportunities for the future to develop clinically relevant and state-of-the-art biomaterials for personalized and remote health care.

Thermo-growing ion clusters enabled healing strengthening and tough adhesion for highly reliable skin electronics

Self-healing and self-adhesion capacities are essential for many modern applications such as skin-interfaced electronics for improving longevity and reliability. However, the self-healing efficiency and adhesive toughness of most synthetic polymers are limited to their original network, making reliability under dynamic deformation still challenging. Herein, inspired by the growth of living organisms, a highly stretchable supramolecular elastomer based on thermo-responsive ion clusters and a dynamic polysulfide backbone was developed. Attributed to the synergic growth of ion clusters and dynamic exchange of disulfide bonds, the elastomer exhibited unique healing strengthening (healing efficiency >200%) and thermo-enhanced tough adhesion (interfacial toughness >500 J m-2) performances. To prove its practical application in highly reliable skin electronics, we further composited the elastomer with a zwitterion to prepare a highly conductive ionic elastomer and applied it in wearable strain sensing and long-term electrophysiological detection. This work provides a new avenue to realize high reliability in skin interfaced electronics.

Mechanically Controlled Enzymatic Polymerization and Remodeling

In nature, proteins possess the remarkable ability to sense and respond to mechanical forces, thereby triggering various biological events, such as bone remodeling and muscle regeneration. However, in synthetic systems, harnessing the mechanical force to induce material growth still remains a challenge. In this study, we aimed to utilize low-frequency ultrasound (US) to activate horseradish peroxidase (HRP) and catalyze free radical polymerization. Our findings demonstrate the efficacy of this mechano-enzymatic chemistry in rapidly remodeling the properties of materials through cross-linking polymerization and surface coating. The resulting samples exhibited a significant enhancement in tensile strength, elongation, and Young's modulus. Moreover, the hydrophobicity of the surface could be completely switched within just 30 min of US treatment. This work presents a novel approach for incorporating mechanical sensing and rapid remodeling capabilities into materials.

Emerging polymeric materials for treatment of oral diseases: design strategy towards a unique oral environment

Oral diseases are prevalent but challenging diseases owing to the highly movable and wet, microbial and inflammatory environment. Polymeric materials are regarded as one of the most promising biomaterials due to their good compatibility, facile preparation, and flexible design to obtain multifunctionality. Therefore, a variety of strategies have been employed to develop materials with improved therapeutic efficacy by overcoming physicobiological barriers in oral diseases. In this review, we summarize the design strategies of polymeric biomaterials for the treatment of oral diseases. First, we present the unique oral environment including highly movable and wet, microbial and inflammatory environment, which hinders the effective treatment of oral diseases. Second, a series of strategies for designing polymeric materials towards such a unique oral environment are highlighted. For example, multifunctional polymeric materials are armed with wet-adhesive, antimicrobial, and anti-inflammatory functions through advanced chemistry and nanotechnology to effectively treat oral diseases. These are achieved by designing wet-adhesive polymers modified with hydroxy, amine, quinone, and aldehyde groups to provide strong wet-adhesion through hydrogen and covalent bonding, and electrostatic and hydrophobic interactions, by developing antimicrobial polymers including cationic polymers, antimicrobial peptides, and antibiotic-conjugated polymers, and by synthesizing anti-inflammatory polymers with phenolic hydroxy and cysteine groups that function as immunomodulators and electron donors to reactive oxygen species to reduce inflammation. Third, various delivery systems with strong wet-adhesion and enhanced mucosa and biofilm penetration capabilities, such as nanoparticles, hydrogels, patches, and microneedles, are constructed for delivery of antibiotics, immunomodulators, and antioxidants to achieve therapeutic efficacy. Finally, we provide insights into challenges and future development of polymeric materials for oral diseases with promise for clinical translation.

Hydrogen Bonds-Pinned Entanglement Blunting the Interfacial Crack of Hydrogel-Elastomer Hybrids

Anchoring a layer of amorphous hydrogel on an antagonistic elastomer holds potential applications in surface aqueous lubrication. However, the interfacial crack propagation usually occurs under continuous loads for amorphous hydrogel, leading to the failure of hydrogel interface. This work presents a universal strategy to passivate the interfacial cracks by designing a hydrogen bonds-pinned entanglement (Hb-En) structure of amorphous hydrogel on engineering elastomers. The unique Hb-En structure is created by pinning well-tailored entanglements via covalent-like hydrogen bonds, which can amplify the delocalization of interfacial stress concentration and elevate the necessary fracture energy barrier within hydrogel interface. Therefore, the interfacial crack propagation can be suppressed under single and cyclic loads, resulting in a high interfacial toughness over 1650 J m-2 and an excellent interfacial fatigue threshold of 423 J m-2. Such a strategy universally works on blunting the interfacial crack between hydrogel coating and various elastomer materials with arbitrary shapes. The superb fatigue-crack insensitivity at the interface allows for durable aqueous lubrication of hydrogel coating with low friction.

Closely Packed Stretchable Ultrasound Array Fabricated with Surface Charge Engineering for Contactless Gesture and Materials Detection

Communication with hand gestures plays a significant role in human-computer interaction by providing an intuitive and natural way for humans to communicate with machines. Ultrasound-based devices have shown promising results in contactless hand gesture recognition without requiring physical contact. However, it is challenging to fabricate a densely packed wearable ultrasound array. Here, a stretchable ultrasound array is demonstrated with closely packed transducer elements fabricated using surface charge engineering between pre-charged 1-3 Lead Zirconate Titanate (PZT) composite and thin polyimide film without using a microscope. The array exhibits excellent ultrasound properties with a wide bandwidth (≈57.1%) and high electromechanical coefficient (≈0.75). The ultrasound array can decipher gestures up to 10 cm in distance by using a contactless triboelectric module and identify materials from the time constant of the exponentially decaying impedance based on their triboelectric properties by utilizing the electrostatic induction phase. The newly proposed metric of the areal-time constant is material-specific and decreases monotonically from a highly positive human body (1.13 m2 s) to negatively charged polydimethylsiloxane (PDMS) (0.02 m2 s) in the triboelectric series. The capability of the closely packed ultrasound array to detect material along with hand gesture interpretation provides an additional dimension in the next-generation human-robot interaction.

Low-impedance tissue-device interface using homogeneously conductive hydrogels chemically bonded to stretchable bioelectronics

Stretchable bioelectronics has notably contributed to the advancement of continuous health monitoring and point-of-care type health care. However, microscale nonconformal contact and locally dehydrated interface limit performance, especially in dynamic environments. Therefore, hydrogels can be a promising interfacial material for the stretchable bioelectronics due to their unique advantages including tissue-like softness, water-rich property, and biocompatibility. However, there are still practical challenges in terms of their electrical performance, material homogeneity, and monolithic integration with stretchable devices. Here, we report the synthesis of a homogeneously conductive polyacrylamide hydrogel with an exceptionally low impedance (~21 ohms) and a reasonably high conductivity (~24 S/cm) by incorporating polyaniline-decorated poly(3,4-ethylenedioxythiophene:polystyrene). We also establish robust adhesion (interfacial toughness: ~296.7 J/m2) and reliable integration between the conductive hydrogel and the stretchable device through on-device polymerization as well as covalent and hydrogen bonding. These strategies enable the fabrication of a stretchable multichannel sensor array for the high-quality on-skin impedance and pH measurements under in vitro and in vivo circumstances.

Stimuli-Responsive Hydrogel Adhesives for Wound Closure and Tissue Regeneration

Sutures and staplers, as gold standards for clinical wound closure, usually cause secondary tissue injury and require professional technicians and equipment. The noninvasive hydrogel adhesives are used in various biomedical applications, such as wound closure, tissue sealing, and tissue regeneration, due to their remarkable properties. Recently-developed hydrogel adhesives, especially stimuli-responsive hydrogels, have shown great potential owing to their advantages in regulating their performance and functions according to the wound situations or external conditions, thus allowing the wounds to heal gradually. However, comprehensive summary on stimuli-responsive hydrogels as tissue adhesives is rarely reported to date. This review focuses on the advances in the design of various stimuli-responsive hydrogel adhesives over the past decade, including the systems responsive to pH, temperature, photo, and enzymes. Their potential biomedical applications, such as skin closure, cardiovascular and liver hemostasis, and gastrointestinal sealing, are emphasized. Meanwhile, the challenges and future development of stimuli-responsive hydrogel adhesives are discussed. This review aims to provide meaningful insights for the further design of next-generation of hydrogel adhesives for wound closure and tissue regeneration.

An Emerging Era: Conformable Ultrasound Electronics

Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.