A Biocompatible Self-Powered Piezoelectric Poly(vinyl alcohol)-Based Hydrogel for Diabetic Wound Repair

Exogenous electron generation techniques for biomedical applications: Bridging fundamentals and clinical practice

Endogenous bioelectrical signals are quite crucial in biological development, governing processes such as regeneration and disease progression. Exogenous stimulation, which mimics endogenous bioelectrical signals, has demonstrated significant potential to modulate complex biological processes. Consequently, increasing scientific efforts have focused on developing methods to generate exogenous electrons for biological applications, primarily relying on piezoelectric, acoustoelectric, optoelectronic, magnetoelectric, and thermoelectric principles. Given the expanding body of literature on this topic, a systematic and comprehensive review is essential to foster a deeper understanding and facilitate clinical applications of these techniques. This review synthesizes and compares these methods for generating exogenous electrical signals, their underlying principles (e.g., semiconductor deformation, photoexcitation, vibration and relaxation, and charge separation), biological mechanisms, potential clinical applications, and device designs, highlighting their advantages and limitations. By offering a comprehensive perspective on the critical role of exogenous electrons in biological systems, elucidating the principles of various electron-generation techniques, and exploring possible pathways for developing medical devices utilizing exogenous electrons, this review aims to advance the field and support therapeutic innovation.

Electroactive Electrospun Nanofibrous Scaffolds: Innovative Approaches for Improved Skin Wound Healing

The incidence and burden of skin wounds, especially chronic and complex wounds, have a profound impact on healthcare. Effective wound healing strategies require a multidisciplinary approach, and advances in materials science and bioengineering have paved the way for the development of novel wound healing dressing. In this context, electrospun nanofibers can mimic the architecture of the natural extracellular matrix and provide new opportunities for wound healing. Inspired by the bioelectric phenomena in the human body, electrospun nanofibrous scaffolds with electroactive characteristics are gaining widespread attention and gradually emerging. To this end, this review first summarizes the basic process of wound healing, the causes of chronic wounds, and the current status of clinical treatment, highlighting the urgency and importance of wound dressings. Then, the biological effects of electric fields, the preparation materials, and manufacturing techniques of electroactive electrospun nanofibrous (EEN) scaffolds are discussed. The latest progress of EEN scaffolds in enhancing skin wound healing is systematically reviewed, mainly including treatment and monitoring. Finally, the importance of EEN scaffold strategies to enhance wound healing is emphasized, and the challenges and prospects of EEN scaffolds are summarized.

Electrical hydrogel: electrophysiological-based strategy for wound healing

Wound healing remains a significant challenge in clinical practice, driving ongoing exploration of innovative therapeutic approaches. In recent years, electrophysiological-based wound healing strategies have gained considerable attention. Specifically, electrical hydrogels combine the synergistic effects of electrical stimulation and hydrogel properties, offering a range of functional benefits for wound healing, including antibacterial activity, real-time wound monitoring, controlled drug release, and electrical treatment. Despite significant progress made in electrical hydrogel research for wound healing, there is a lack of comprehensive, systematic reviews summarizing this field. In this review, we survey the latest advancements in electrical hydrogel technology. After analyzing the mechanisms of electrical stimulation in promoting wound healing, we establish a novel classification framework for electrical hydrogels based on their operational principles. The review further provides an in-depth evaluation of the therapeutic efficacy of these hydrogels in various types of wounds. Finally, we propose future directions and challenges for the development of electrical hydrogels for wound healing.

Applications of Piezoelectric Materials in Biomedical Engineering

Piezoelectric materials are unique biomedical materials whose asymmetric crystal structures enable them to convert various forms of mechanical energy from the environment, including ultrasound, into electrical or chemical energy. These materials have wide applications in the biomedical field and are gradually becoming a research hotspot in applications such as energy harvesters, biosensors, and tissue engineering. This article first provides a systematic review of the research progress on piezoelectric materials, then outlines frontier strategies for achieving high-performance electrical materials and devices. This article discusses the highly oriented nature of piezoelectric materials mediated by intermolecular forces and explores the applications of piezoelectric implants in biomedicine, including biosensing, energy harvesting, tissue engineering, and disease treatment. Finally, the challenges faced by piezoelectric devices in future research are elaborated.

Ultrasound-induced piezoionic hydrogels with antibacterial and antioxidant properties for promoting infected diabetic wound healing

The effective treatment of infected diabetic wounds remains a major challenge due to bacterial infection and severe oxidative stress. Herein, an antibacterial and antioxidant piezoionic hydrogel (ANDT) is synthesized via a one-pot photocuring process of a precursor solution containing acrylic acid, N-isopropyl acrylamide, quaternary ammonium salt (DPAB), and tannic acid (TA). The ANDT hydrogel exhibits reliable adhesion and appropriate mechanical properties, which can provide a favorable physical barrier. Owing to the introduction of antibacterial DPAB and antioxidant TA, the ANDT hydrogel can reduce inflammation and create an optimal microenvironment for cellular growth. Furthermore, due to the piezoionic effects, the ANDT hydrogel under ultrasound stimulation can generate a biomimetic endogenous electric field to modulate cellular behaviors, thereby achieving an active pro-healing effect. The infected diabetic wound model demonstrates that the ANDT hydrogel combined with ultrasound therapy can effectively reduce inflammation, increase collagen deposition, and promote angiogenesis, thus accelerating the healing process of infected diabetic wounds. This work may provide a promising strategy for developing advanced wound dressing to promote infected diabetic wound healing.

Necklace-Structured PVA Sponges for Fast Bleeding Control in the Punctured Femoral Artery Hemorrhage

Uncontrollable hemorrhage from deep, narrow wounds poses a critical threat to life, as locating the bleeding arteries in such areas is challenging. Rapid bleeding control remains a significant challenge in pre-hospital care. Herein, an injectable hemostatic device filled with disc-like PVA sponges is developed for this objective. The pristine PVA sponge is strung as a necklace-structured sponge loaded in a foldable injector. With a novel retraction mechanism, this self-designed injector precisely deploys hemostatic sponges to deep bleeding sites, surpassing the XStatTM injector in design innovation. The PVA sponges' high porosity and unique porous structure allowed it for rapid shape recovery (<30 s) and good compressive strength. In the punctured wound, the swollen PVA sponges exert high compression to close the bleeding artery, resulting in fast-bleeding control. In the pig groin femoral artery injury model, the PVA sponge treatment resulted in a 100% survival rate during a 2-h hemostasis period, compared to a 33.3% survival rate in the cotton gauze control group. In addition, it can be easily taken out by a simple pulling. The easily applicable and removable necklace-structured PVA sponge is a highly promising hemostat for punctured wounds.

A Heterojunction Piezoelectric Antimicrobial Asymmetric Hydrogel for Dynamic Wound Healing and Monitoring

Dynamic wound care presents significant challenges for conventional dressings due to the complex environment and high-frequency motion associated with such injuries. In this study, a multifunctional photo-crosslinked piezoelectric hydrogel (OAPS) is developed, incorporating heterojunction Se-doped KH570 modified BaTiO3 nanoparticles (Se-BT570 NPs) as a core component, and designed to address antimicrobial and monitoring needs in wound care, particularly at sites with high-frequency movement. The OAPS hydrogel effectively utilizes the inherent high-frequency motion in dynamic wounds, enhancing antimicrobial efficacy and enabling real-time monitoring of wound and human health statuses. This is achieved through the synergistic effects of piezoelectric properties and nano-heterostructures that enable self-driven charge transfer. Such integration allows for dual applications in both diagnosis and treatment. Experimental results demonstrated that the OAPS hydrogel exhibits excellent mechanical strength and adhesive properties, effectively adapting to high-frequency motion. Additionally, the hydrogel can be activated by dynamic wound environments to perform antimicrobial and wound monitoring functions, significantly accelerating the healing of dynamic wounds, with an efficacy rate of 99.75%. This study highlights the potential of piezoelectric nanomaterials in dynamic wound healing, offering a promising strategy for managing complex, dynamic wound care.

A calcitonin gene-related peptide co-crosslinked hydrogel promotes diabetic wound healing by regulating M2 macrophage polarization and angiogenesis

Delayed diabetic wound (DBW) healing is a severe complication of diabetes, characterized notably by peripheral sensory neuropathy. The underlying mechanism of sensory nerves and DBW remain unclear. Here, we demonstrate the role of calcitonin gene-related peptide (CGRP) in regulating epithelialization and angiogenesis in DBW. Subsequently, we design and synthesis a gelatin methacryloyl (GelMA-CGRP) hydrogel that slowly releases CGRP, and evaluated its effect on promoting DBW healing. The results show that CGRP is abnormally downregulated in DBW, and CGRP ablation further delays DBW healing. This is due to the reduced M2 polarization and decreased angiogenesis in the absence of CGRP, whereas local application of GelMA-CGRP accelerates DBW healing. Mechanistic studies indicate that CGRP promotes M2 macrophage polarization by inhibiting the p53 signaling pathway and enhances endothelial cell function, thereby accelerating DBW healing. These findings suggest that CGRP could provide a novel therapeutic approach for diabetic wound treatment. STATEMENT OF SIGNIFICANCE: Current methods for treating diabetic wounds have many limitations. Compared to conventional dressings, hydrogels combined with drugs or biological factors to promote diabetic wound healing have become an important research direction in recent years. This study reveals the key role of CGRP in the pathogenesis of diabetic wounds. The research found that CGRP promotes M2 macrophage polarization and angiogenesis by inhibiting the p53 signaling pathway, thereby promoting diabetic wound healing. We further utilized the carrier properties of GelMA hydrogel to develop a GelMA-CGRP hydrogel material that slowly delivers CGRP and effectively treats diabetic wounds. This material demonstrates strong biocompatibility and antimicrobial properties, offering a novel approach for the treatment of diabetic wounds.

Biocompatible and stretchable chitosan piezoelectric gel with antibacterial capability and motion monitoring function for Achilles tendon rupture treatment

Achilles tendon rupture is a common and serious condition that remains a challenge in the restoration of tendon structure and function. The design and use of high-performance piezoelectric materials serve as an effective solution to enhance repair outcomes, shorten recovery times, and reduce the risk of recurrence. In this study, we prepared a chitosan piezoelectric gel (CSPG) as an organic polymer with excellent biocompatibility, stretchability, and piezoelectric properties as well as excellent antibacterial properties. In vitro experiments showed that CSPG, which induces a piezoelectric effect, can inhibit bacterial growth, promote cell proliferation and migration, upregulate the expression of tendon-related genes, and inhibit the expression of inflammation-related genes. In vivo experiments showed improved outcomes for Achilles tendon repair following CSPG intervention, as evidenced by enhanced animal mobility and improved mechanical test results. In addition, the CSPG exhibited sensory functions capable of monitoring temperature and motion, providing timely feedback on repair efficacy. In summary, this study not only successfully prepared a multifunctional piezoelectric material that can effectively promote Achilles tendon rupture repair and regeneration and control inflammatory response, it also possesses antibacterial and sensing functions, thus offering a new strategy for Achilles tendon rupture repair.

Self-powered biomedical devices: biology, materials, and their interfaces

Integrating biomedical electronic devices holds profound promise for advancements in healthcare and enhancing individuals' quality of life. However, the persistent challenges associated with the traditional batteries' limited lifespan and bulkiness hinder these devices' long-term functionality and consistent power supply. Here, we delve into the biology and material interfaces in self-powered medical devices by summarizing the intrinsic electric demands in humans, analyzing material and biological mechanisms for electricity generation and storage, and discussing the pathways toward self-chargeable powering. As a result, the current challenges in material designs and biological integrations emerged to shape the future directions in advancing self-powered medical devices. This paper calls on the community to integrate biology and material science to develop self-powering medical devices and improve their clinical prospects.

The Influence of DMSO on PVA/PVDF Hydrogel Properties: From Materials to Sensors Applications

This research study aims to explore the synergistic effects of incorporating polyvinylidene fluoride (PVDF) into polyvinyl alcohol (PVA) hydrogels to enhance their suitability for triboelectric sensors applications. The preparation process employs a method of freezing/thawing conducted in dimethyl sulfoxide (DMSO), followed by solvent replacement with water. This approach effectively preserves PVDF in its α phase, eliminating piezoelectric effects and enhancing the hydrogels' mechanical properties. The use of DMSO contributes to reduced pore size, while incorporating PVDF significantly improves the three-dimensional network structure of the hydrogels, resulting in enhanced thermal and chemical resistance. Thorough characterization of the resulting PVA/PVDF composite hydrogels, prepared with varying ratios of PVA to PVDF (10:0, 8:2, and 5:5), was conducted by using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), rheology, and thermogravimetric analysis (TGA). Notably, the composite hydrogels were tested in pressure sensors and human voice sensors, demonstrating their capability to recognize different patterns associated with various letters. The incorporation of PVDF significantly enhanced the signal-to-noise ratio in PVA/PVDF-based sensors compared with those made solely from PVA, highlighting a notable improvement in voice detection. The enhancements were quantified as 56% for "a", 35% for "r", and 47% for "m".

Piezoelectric nanocomposite electrospun dressings: Tailoring mechanics for scar-free wound recovery

Rational wound management and enhancing healing quality are critical in clinical practice. Electrical stimulation therapy (EST) has emerged as a valuable adjunctive treatment due to its safety and cost-effectiveness. Integrating piezoelectric materials into dressings offers a way to miniaturize and personalize electrotherapy, enhancing convenience. To address the impact of physical factors of dressings on wound healing, a nanocomposite piezoelectric electrospun dressing using poly(L-lactic acid) (PLLA) and barium titanate (BaTiO3) was developed. We intentionally exaggerated design flaws to mimic the characteristics of scar extracellular matrix (ECM), including the oriented thick fibers and high Young's modulus. Initially, these dressings promoted fibrosis and hindered functional regeneration. However, when the piezoelectric effect was triggered by ultrasound, the fibrotic phenotype was reversed, leading to scar-free healing with well-regenerated functional structures. This study highlights the significant therapeutic potential of piezoelectric dressings in skin wound treatment and underscores the importance of carefully designing the static physical properties of dressings for optimal efficacy.

Piezoelectric hydrogels for accelerating healing of diverse wound types

The skin, as the body's largest organ, plays a crucial role in protecting against mechanical forces and infections, maintaining fluid balance, and regulating body temperature. Therefore, skin wounds can significantly threaten human health and cause a heavy economic burden on society. Recently, bioelectric fields and electrical stimulation (ES) have been recognized as a promising pathway for modulating tissue engineering and regeneration of wounded skin. However, conventional hydrogel dressing lacks electrical generation capabilities and usually requires external stimuli to initiate the cell regeneration process, and the role of ES in different stages of healing is not fully understood. Therefore, to endow hydrogel-based wound dressings with piezoelectric properties, which can accelerate wound healing and potentially suppress infection via introducing ES, piezoelectric hydrogels (PHs) have emerged recently, combining the advantages of both piezoelectric nanomaterials and hydrogels beneficial for wound healing. Given the scarcity of systematic literature on the application of PHs in wound healing, this paper systematically discusses the principles of the piezoelectric effects, the design and fabrication of PHs, their piezoelectric properties, the way PHs trigger ES and the mechanisms by which they promote wound healing. Additionally, it summarizes the recent applications of PHs in various types of wounds, including traumatic wounds, pressure injuries, diabetic wounds, and infected wounds. Finally, the paper proposes future directions and challenges for the development of PH wound dressings for wound healing.

Synthesis of PVA-Based Hydrogels for Biomedical Applications: Recent Trends and Advances

There is ongoing research for biomedical applications of polyvinyl alcohol (PVA)-based hydrogels; however, the execution of this has not yet been achieved at an appropriate level for commercialization. Advanced perception is necessary for the design and synthesis of suitable materials, such as PVA-based hydrogel for biomedical applications. Among polymers, PVA-based hydrogel has drawn great interest in biomedical applications owing to their attractive potential with characteristics such as good biocompatibility, great mechanical strength, and apposite water content. By designing the suitable synthesis approach and investigating the hydrogel structure, PVA-based hydrogels can attain superb cytocompatibility, flexibility, and antimicrobial activities, signifying that it is a good candidate for tissue engineering and regenerative medicine, drug delivery, wound dressing, contact lenses, and other fields. In this review, we highlight the current progresses on the synthesis of PVA-based hydrogels for biomedical applications explaining their diverse usage across a variety of areas. We explain numerous synthesis techniques and related phenomena for biomedical applications based on these materials. This review may stipulate a wide reference for future acumens of PVA-based hydrogel materials for their extensive applications in biomedical fields.

Two-dimensional nanomaterials: A multifunctional approach for robust for diabetic wound repair

Diabetic wounds pose a clinical challenge due to persistent inflammation, severe bacterial infections, inadequate vascularization, and pronounced oxidative stress. Current therapeutic modalities fail to provide satisfactory outcomes in managing these conditions, resulting in considerable patient distress. Two-dimensional nanomaterials (2DNMs), characterized by their unique nanosheet structures, expansive surface areas, and remarkable physicochemical properties, have garnered considerable attention for their potential in therapeutic applications. Emerging 2DNMs can be loaded with various pharmacological agents, including small molecules, metal ions, and liposomes. Moreover, they can be integrated with various biomaterials such as hydrogels, microneedles, and microspheres, thus demonstrating unprecedented advantages in expediting the healing process of diabetic wounds. Moreover, 2DNMs exhibit exceptional performance characteristics, including high biocompatibility, effective antimicrobial properties, optimal phototherapeutic effects, and enhanced electrostimulation capabilities. These properties enable them to modulate the wound microenvironment, leading to widespread application in tissue repair with remarkable outcomes. This review delineates several emerging 2DNMs, such as graphene and its derivatives, black phosphorus, MXenes, and transition metal dichalcogenides, in the context of diabetic wound repair. Furthermore, it elucidates the translational challenges and future perspectives of 2DNMs in wound healing treatments. Overall, 2DNMs present a highly promising strategy for ameliorating diabetic wounds, thus providing novel avenues for diagnostic and therapeutic strategies in diabetic wound management.

Electrical Stimulating Redox Membrane Incorporated with PVA/Gelatin Nanofiber for Diabetic Wound Healing

Chronic wounds adversely affect the quality of life. Although electrical stimulation has been utilized to treat chronic wounds, there are still limitations to practicing it due to the complicated power system. Herein, an electrostimulating membrane incorporated with electrospun nanofiber (M-sheet) to treat diabetic wounds is developed. Through the screen printing method, the various alternate patterns of both Zn and AgCl on a polyurethane substrate, generating redox-mediated electrical fields are introduced. The antibacterial ability of the patterned membrane against both E. coli and S. aureus is confirmed. Furthermore, the poly(vinyl alcohol) (PVA)/gelatin electrospun fiber is incorporated into the patterned membrane to enhance biocompatibility and maintain the wet condition in the wound environment. The M-sheet can improve cell proliferation and migration in vitro and has an immune regulatory effect by inducing the polarization of macrophage to the M2 phenotype. Finally, when applied to a diabetic skin wound model, the M-sheet displays an accelerated wound healing rate and enhances re-epithelialization, collagen synthesis, and angiogenesis. It suggests that the M-sheet is a simple and portable system for the spontaneous generation of electrical stimulation and has great potential to be used in the practical wound and other tissue engineering applications.

Ingenious Structure Engineering to Enhance Piezoelectricity in Poly(vinylidene fluoride) for Biomedical Applications

The future development of wearable/implantable sensing and medical devices relies on substrates with excellent flexibility, stability, biocompatibility, and self-powered capabilities. Enhancing the energy efficiency and convenience is crucial, and converting external mechanical energy into electrical energy is a promising strategy for long-term advancement. Poly(vinylidene fluoride) (PVDF), known for its piezoelectricity, is an outstanding representative of an electroactive polymer. Ingeniously designed PVDF-based polymers have been fabricated as piezoelectric devices for various applications. Notably, the piezoelectric performance of PVDF-based platforms is determined by their structural characteristics at different scales. This Review highlights how researchers can strategically engineer structures on microscopic, mesoscopic, and macroscopic scales. We discuss advanced research on PVDF-based piezoelectric platforms with diverse structural designs in biomedical sensing, disease diagnosis, and treatment. Ultimately, we try to give perspectives for future development trends of PVDF-based piezoelectric platforms in biomedicine, providing valuable insights for further research.

Macrophage plasticity: signaling pathways, tissue repair, and regeneration

Macrophages are versatile immune cells with remarkable plasticity, enabling them to adapt to diverse tissue microenvironments and perform various functions. Traditionally categorized into classically activated (M1) and alternatively activated (M2) phenotypes, recent advances have revealed a spectrum of macrophage activation states that extend beyond this dichotomy. The complex interplay of signaling pathways, transcriptional regulators, and epigenetic modifications orchestrates macrophage polarization, allowing them to respond to various stimuli dynamically. Here, we provide a comprehensive overview of the signaling cascades governing macrophage plasticity, focusing on the roles of Toll-like receptors, signal transducer and activator of transcription proteins, nuclear receptors, and microRNAs. We also discuss the emerging concepts of macrophage metabolic reprogramming and trained immunity, contributing to their functional adaptability. Macrophage plasticity plays a pivotal role in tissue repair and regeneration, with macrophages coordinating inflammation, angiogenesis, and matrix remodeling to restore tissue homeostasis. By harnessing the potential of macrophage plasticity, novel therapeutic strategies targeting macrophage polarization could be developed for various diseases, including chronic wounds, fibrotic disorders, and inflammatory conditions. Ultimately, a deeper understanding of the molecular mechanisms underpinning macrophage plasticity will pave the way for innovative regenerative medicine and tissue engineering approaches.

Advances and Challenges in Immune-Modulatory Biomaterials for Wound Healing Applications

Wound healing progresses through three distinct stages: inflammation, proliferation, and remodeling. Immune regulation is a central component throughout, crucial for orchestrating inflammatory responses, facilitating tissue repair, and restraining scar tissue formation. Elements such as mitochondria, reactive oxygen species (ROS), macrophages, autophagy, ferroptosis, and cytokines collaboratively shape immune regulation in this healing process. Skin wound dressings, recognized for their ability to augment biomaterials' immunomodulatory characteristics via antimicrobial, antioxidative, pro- or anti-inflammatory, and tissue-regenerative capacities, have garnered heightened attention. Notwithstanding, a lack of comprehensive research addressing how these dressings attain immunomodulatory properties and the mechanisms thereof persists. Hence, this paper pioneers a systematic review of biomaterials, emphasizing immune regulation and their underlying immunological mechanisms. It begins by highlighting the importance of immune regulation in wound healing and the peculiarities and obstacles faced in skin injury recovery. This segment explores the impact of wound metabolism, infections, systemic illnesses, and local immobilization on the immune response during healing. Subsequently, the review examines a spectrum of biomaterials utilized in skin wound therapy, including hydrogels, aerogels, electrospun nanofiber membranes, collagen scaffolds, microneedles, sponges, and 3D-printed constructs. It elaborates on the immunomodulatory approaches employed by these materials, focusing on mitochondrial and ROS modulation, autophagic processes, ferroptosis, macrophage modulation, and the influence of cytokines on wound healing. Acknowledging the challenge of antibiotic resistance, the paper also summarizes promising plant-based alternatives for biomaterial integration, including curcumin. In its concluding sections, the review charts recent advancements and prospects in biomaterials that accelerate skin wound healing via immune modulation. This includes exploring mitochondrial transplantation materials, biomaterial morphology optimization, metal ion incorporation, electrostimulation-enabled immune response control, and the benefits of composite materials in immune-regulatory wound dressings. The ultimate objective is to establish a theoretical foundation and guide future investigations in the realm of skin wound healing and related materials science disciplines.

Targeted delivery of black phosphorus nanosheets by ROS responsive complex hydrogel based on angiogenesis and antioxidant promotes myocardial infarction repair

Myocardial infarction (MI) is one of the leading causes of death. This is attributed to the dramatic changes in the myocardial microenvironment post-MI. Therefore, effective intervention in the early stages of MI is significant for inhibiting its progression and improving cardiac function. Herein, an injectable composite hydrogel scaffold (Gel-pBP@Mg) was developed by integrating magnesium (Mg)-modified black phosphorus nanosheets (pBP@Mg) into a reactive oxygen species-responsive hydrogel (Gel). This loose and porous Gel provides a natural platform for carrying pBP@Mg. In situ, sustained release of pBP@Mg is achieved via responsive ROS degradation in the infarct site. The high ROS reactivity of Black phosphorus nanosheets (BPNSs) can effectively inhibit the progression of oxidative stress in the infarct area and reduce inflammatory response by down-regulating the NF-κB pathway. Additionally, the sustained release of Mg loaded on the surface of BPNSs can effectively promote angiogenesis in MI, which is significant for the long-term prognosis after infarction. Our developed Gel-pBP@Mg effectively blocked infarction progression and improved myocardial function by sustainably inhibiting the "oxidative stress-inflammation" reaction chain and pro-angiogenesis. This study reveals Gel-pBP@Mg composite therapeutic potential in treating MI through In vitro and In vivo studies, providing a promising modality for MI treatment.

Piezoelectric Hydrogels: Hybrid Material Design, Properties, and Biomedical Applications

Hydrogels show great potential in biomedical applications due to their inherent biocompatibility, high water content, and resemblance to the extracellular matrix. However, they lack self-powering capabilities and often necessitate external stimulation to initiate cell regenerative processes. In contrast, piezoelectric materials offer self-powering potential but tend to compromise flexibility. To address this, creating a novel hybrid biomaterial of piezoelectric hydrogels (PHs), which combines the advantageous properties of both materials, offers a systematic solution to the challenges faced by these materials when employed separately. Such innovative material system is expected to broaden the horizons of biomedical applications, such as piezocatalytic medicinal and health monitoring applications, showcasing its adaptability by endowing hydrogels with piezoelectric properties. Unique functionalities, like enabling self-powered capabilities and inducing electrical stimulation that mimics endogenous bioelectricity, can be achieved while retaining hydrogel matrix advantages. Given the limited reported literature on PHs, here recent strategies concerning material design and fabrication, essential properties, and distinctive applications are systematically discussed. The review is concluded by providing perspectives on the remaining challenges and the future outlook for PHs in the biomedical field. As PHs emerge as a rising star, a comprehensive exploration of their potential offers insights into the new hybrid biomaterials.

Polypropylene mesh coated with hyaluronic acid/polyvinyl alcohol composite hydrogel for preventing bowel adhesion

Polypropylene (PP) mesh is the most widely used prosthetic material in hernia repair. However, the efficacy of implanted PP mesh is often compromised by adhesion between viscera and PP mesh. Thus, there is a recognized need for developing an anti-adhesive PP mesh. Here, a composite hydrogel coated PP mesh with the prevention of adhesion after hernia repair was designed. The composite hydrogel coating was prepared from polyvinyl alcohol (PVA) and hyaluronic acid (HA) by using the freezing-thawing (FT) method. To overcome the shortcoming of the long time of the traditional freezing-thawing method, a small molecule 3,4-dihydroxyphenylacetic acid (DHPA) was introduced to promote the formation of composite hydrogel. The as-prepared composite hydrogel coating displayed modulus more closely resembling that of native abdominal wall tissue. In vitro studies illustrated that the resulting meshes showed excellent coating stability, hemocompatibility, and non-cytotoxicity. In vivo experiments using a rat abdominal wall defect model demonstrated that the composite hydrogel coated PP mesh could prevent the formation of adhesion, alleviate the inflammatory response, and reduce the deposition of collagen around the damaged tissue. These disclosed results manifested that the PP mesh coated with HA/PVA composite hydrogel might be a promising application in preventing adhesion for hernia repair.

Engineering Platelet Membrane-Coated Bimetallic MOFs as Biodegradable Nanozymes for Efficient Antibacterial Therapy

Nanocatalytic-based wound therapeutics present a promising strategy for generating reactive oxygen species (ROS) to antipathogen to promote wound healing. However, the full clinical potential of these nanocatalysts is limited by their low reactivity, limited targeting ability, and poor biodegradability in the wound microenvironment. Herein, a bio-organic nanozyme is developed by encapsulating a FeZn-based bimetallic organic framework (MOF) (MIL-88B-Fe/Zn) in platelet membranes (PM@MIL-88B-Fe/Zn) for antimicrobial activity during wound healing. The introduction of Zn in MIL-88B-Fe/Zn modulates the electronic structure of Fe thus accelerating the catalytic kinetics of its peroxidase-like activity to catalytically generate powerful ROS. The platelet membrane coating of MOF innovatively enhanced the interaction between nanoparticles and the biological environment, further developing bacterial-targeted therapy with excellent antibacterial activity against both gram-positive and gram-negative bacteria. Furthermore, this nanozyme markedly suppressed the levels of inflammatory cytokines and promoted angiogenesis in vivo to effectively treat skin surface wounds and accelerate wound healing. PM@MIL-88B-Fe/Zn exhibited superior biodegradability, favourable metabolism and non-toxic accumulation, eliminating concerns regarding side effects from long-term exposure. The high catalytic reactivity, excellent targeting features, and biodegradability of these nanoenzymes developed in this study provide useful insights into the design and synthesis of nanocatalysts/nanozymes for practical biomedical applications.

3D-Printed Piezoelectric Stents for Electricity Generation Driven by Pressure Fluctuation

Vascular stenting is a common procedure used to treat diseased blood vessels by opening the narrowed vessel lumen and restoring blood flow to ischemic tissues in the heart and other organs. In this work, we report a novel piezoelectric stent featuring a zigzag shape fabricated by fused deposition modeling three-dimensional (3D) printing with a built-in electric field. The piezoelectric composite was made of potassium sodium niobite microparticles and poly(vinylidene fluoride-co-hexafluoropropylene), complementing each other with good piezoelectric performance and mechanical resilience. The in situ poling yielded an appreciable piezoelectricity (d33 ∼ 4.2 pC N-1) of the as-printed stents. In vitro testing revealed that materials are nontoxic to vascular cells and have low thrombotic potential. Under stimulated blood pressure fluctuation, the as-printed piezoelectric stent was able to generate peak-to-peak voltage from 0.07 to 0.15 V corresponding to pressure changes from 20 to 120 Psi, giving a sensitivity of 7.02 × 10-4 V Psi-1. Biocompatible piezoelectric stents bring potential opportunities for the real-time monitoring of blood vessels or enabling therapeutic functions.

Hydrogel-based immunoregulation of macrophages for tissue repair and regeneration

The rational design of hydrogel materials to modulate the immune microenvironment has emerged as a pivotal approach in expediting tissue repair and regeneration. Within the immune microenvironment, an array of immune cells exists, with macrophages gaining prominence in the field of tissue repair and regeneration due to their roles in cytokine regulation to promote regeneration, maintain tissue homeostasis, and facilitate repair. Macrophages can be categorized into two types: classically activated M1 (pro-inflammatory) and alternatively activated M2 (anti-inflammatory and pro-repair). By regulating the physical and chemical properties of hydrogels, the phenotypic transformation and cell behavior of macrophages can be effectively controlled, thereby promoting tissue regeneration and repair. A full understanding of the interaction between hydrogels and macrophages can provide new ideas and methods for future tissue engineering and clinical treatment. Therefore, this paper reviews the effects of hydrogel components, hardness, pore size, and surface morphology on cell behaviors such as macrophage proliferation, migration, and phenotypic polarization, and explores the application of hydrogels based on macrophage immune regulation in skin, bone, cartilage, and nerve tissue repair. Finally, the challenges and future prospects of macrophage-based immunomodulatory hydrogels are discussed.

Multifunctional Hydrogel Enhances Inflammatory Control, Antimicrobial Activity, and Oxygenation to Promote Healing in Infectious Wounds

Chronic infected wounds often fail to heal through normal repair mechanisms, and the persistent response of reactive oxygen species (ROS) and inflammation is a major contributing factor to the difficulty in their healing. In this context, we developed an ROS-responsive injectable hydrogel. This hydrogel is composed of ε-polylysine grafted (EPL) with caffeic acid (CA) and hyaluronic acid (HA) grafted with phenylboronic acid (PBA). Before the gelation process, a mixture CaO2@Cur-PDA (CCP) consisting of calcium peroxide (CaO2) coated with polydopamine (PDA) and curcumin (Cur) is embedded into the hydrogel. Under the conditions of chronic refractory wound environments, the hydrogel gradually dissociates. HA mimics the function of the extracellular matrix, while the released caffeic acid-grafted ε-polylysine (CE) effectively eliminates bacteria in the wound vicinity. Additionally, released CA also clears ROS and influences macrophage polarization. Subsequently, CCP further decomposes, releasing Cur, which promotes angiogenesis. This multifunctional hydrogel accelerates the repair of diabetic skin wounds infected with Staphylococcus aureus in vivo and holds promise as a candidate dressing for the healing of chronic refractory wounds.

Remodelers of the vascular microenvironment: The effect of biopolymeric hydrogels on vascular diseases

Vascular disease is the leading health problem worldwide. Vascular microenvironment encompasses diverse cell types, including those within the vascular wall, blood cells, stromal cells, and immune cells. Initiation of the inflammatory state of the vascular microenvironment and changes in its mechanics can profoundly affect vascular homeostasis. Biomedical materials play a crucial role in modern medicine, hydrogels, characterized by their high-water content, have been increasingly utilized as a three-dimensional interaction network. In recent times, the remarkable progress in utilizing hydrogels and understanding vascular microenvironment have enabled the treatment of vascular diseases. In this review, we give an emphasis on the utilization of hydrogels and their advantages in the various vascular diseases including atherosclerosis, aneurysm, vascular ulcers of the lower limbs and myocardial infarction. Further, we highlight the importance and advantages of hydrogels as artificial microenvironments.

Advancements in Bio-inspired Self-Powered Wireless Sensors: Materials, Mechanisms, and Biomedical Applications

The rapid maturation of smart city ecosystems is intimately linked to advances in the Internet of Things (IoT) and self-powered sensing technologies. Central to this evolution are battery-less sensors that are critical for applications such as continuous health monitoring through blood metabolites and vital signs, the recognition of human activity for behavioral analysis, and the operational enhancement of humanoid robots. The focus on biosensors that exploit the human body for energy-spanning wearable, attachable, and implantable variants has intensified, driven by their broad applicability in areas from underwater exploration to biomedical assays and earthquake monitoring. The heart of these sensors lies in their diverse energy harvesting mechanisms, including biofuel cells, and piezoelectric, triboelectric, and pyroelectric nanogenerators. Notwithstanding the wealth of research, the literature still lacks a holistic review that integrates the design challenges and implementation intricacies of such sensors. Our review seeks to fill this gap by thoroughly evaluating energy harvesting strategies from both material and structural perspectives and assessing their roles in powering an array of sensors for myriad uses. This exploration offers a comprehensive outlook on the state of self-powered sensing devices, tackling the nuances of their deployment and highlighting their potential to revolutionize data gathering in autonomous systems. The intent of this review is to chart the current landscape and future prospects, providing a pivotal reference point for ongoing research and innovation in self-powered wireless sensing technologies.

From emerging modalities to advanced applications of hydrogel piezoelectrics based on chitosan, gelatin and related biological macromolecules: A review

The rapid development of functional materials and manufacturing technologies is fostering advances in piezoelectric materials (PEMs). PEMs can convert mechanical energy into electrical energy. Unlike traditional power sources, which need to be replaced and are inconvenient to carry, PEMs have extensive potential applications in smart wearable and implantable devices. However, the application of conventional PEMs is limited by their poor flexibility, low ductility, and susceptibility to fatigue failure. Incorporating hydrogels, which are flexible, stretchable, and self-healing, providing a way to overcome these limitations of PEMs. Hydrogel-based piezoelectric materials (H-PEMs) not only resolve the shortcomings of traditional PEMs but also provide biocompatibility and more promising application potential. This paper summarizes the working principle of H-PEMs. Recent advances in the use of H-PEMs as sensors and in vitro energy harvesting devices for smart wearable devices are described in detail, with emphasis on application scenarios in human body like fingers, wrists, ankles, and feet. In addition, the recent progress of H-PEMs in implantable medical devices, especially the potential applications in human body parts such as bones, skin, and heart, are also elaborated. In addition, challenges and potential improvements in H-PEMs are discussed.

Piezoelectric dressings for advanced wound healing

The treatment of chronic refractory wounds poses significant challenges and threats to both human society and the economy. Existing research studies demonstrate that electrical stimulation fosters cell proliferation and migration and promotes the production of cytokines that expedites the wound healing process. Presently, clinical settings utilize electrical stimulation devices for wound treatment, but these devices often present issues such as limited portability and the necessity for frequent recharging. A cutting-edge wound dressing employing the piezoelectric effect could transform mechanical energy into electrical energy, thereby providing continuous electrical stimulation and accelerating wound healing, effectively addressing these concerns. This review primarily reviews the selection of piezoelectric materials and their application in wound dressing design, offering a succinct overview of these materials and their underlying mechanisms. This study also provides a perspective on the current limitations of piezoelectric wound dressings and the future development of multifunctional dressings harnessing the piezoelectric effect.

Highly Biocompatible Polyester-Based Piezoelectric Elastomer with Antitumor and Antibacterial Activity for Ultrasound-Enhanced Piezoelectric Therapy

Currently, the use of piezoelectric materials to provide sustainable and noninvasive bioelectric stimulation to eradicate tumor cells and accelerate wound healing has raised wide attention. The development of a multifunctional piezoelectric elastomer with the ability to perform in situ tumor therapy as well as wound repair is of paramount importance. However, current piezoelectric materials have a large elastic modulus and limited stretchability, making it difficult to match with the dynamic curvature changes of the wound. Therefore, by copolymerizing lactic acid, butanediol, sebacic acid, and itaconic acid to develop a piezoelectric elastomer (PLBSIE), we construct a new ultrasound-activated PLBSIE-based tumor/wound unified therapeutic platform. Excitedly, it showed outstanding piezoelectric performance and high stretchability, and the separated carrier could react with water to generate highly cytotoxic reactive oxygen species (ROS), contributing to effectively killing tumor cells and eliminating bacteria through piezoelectric therapy. In addition, ultrasound-triggered piezoelectric effects could promote the migration and differentiation of wound-healing-related cells, thus accelerating wound healing. Herein, such a piezoelectric elastomer exerted a critical role in postoperative tumor-induced wound therapy and healing with the merits of possessing multifunctional abilities. Taken together, the developed ultrasound-activated PLBSIE will offer a comprehensive treatment for postoperative osteosarcoma therapy.

A review of the evidence to support electrical stimulation-induced vascularization in engineered tissue

Tissue engineering presents a promising solution for regenerative medicine and the success depends on the supply of oxygen/nutrients to the cells by rapid vascularization. More and more technologies are being developed to facilitate vascularization of engineered tissues. In this review, we indicated that a regulatory system which influences all angiogenesis associated cells to achieve their desired functional state is ideal for the construction of vascularized engineered tissues in vitro. We presented the evidence that electrical stimulation (ES) enhances the synergistic promotion of co-cultured angiogenesis associated cells and its potential regulatory mechanisms, highlighted the potential advantages of a combination of mesenchymal stem cells (MSCs), endothelial cells (ECs) and ES to achieve tissue vascularization, with particular emphasis on the different biological pathways of ES-regulated ECs. Finally, we proposed the future direction of using ES to reconstruct engineered tissue blood vessels, pointed out the potential advantages and disadvantages of ES application on tissue vascularization.

Perspectives on recent advancements in energy harvesting, sensing and bio-medical applications of piezoelectric gels

The development of next-generation bioelectronics, as well as the powering of consumer and medical devices, require power sources that are soft, flexible, extensible, and even biocompatible. Traditional energy storage devices (typically, batteries and supercapacitors) are rigid, unrecyclable, offer short-lifetime, contain hazardous chemicals and possess poor biocompatibility, hindering their utilization in wearable electronics. Therefore, there is a genuine unmet need for a new generation of innovative energy-harvesting materials that are soft, flexible, bio-compatible, and bio-degradable. Piezoelectric gels or PiezoGels are a smart crystalline form of gels with polar ordered structures that belongs to the broader family of piezoelectric material, which generate electricity in response to mechanical stress or deformation. Given that PiezoGels are structurally similar to hydrogels, they offer several advantages including intrinsic chirality, crystallinity, degree of ordered structures, mechanical flexibility, biocompatibility, and biodegradability, emphasizing their potential applications ranging from power generation to bio-medical applications. Herein, we describe recent examples of new functional PiezoGel materials employed for energy harvesting, sensing, and wound dressing applications. First, this review focuses on the principles of piezoelectric generators (PEGs) and the advantages of using hydrogels as PiezoGels in energy and biomedical applications. Next, we provide a detailed discussion on the preparation, functionalization, and fabrication of PiezoGel-PEGs (P-PEGs) for the applications of energy harvesting, sensing and wound healing/dressing. Finally, this review concludes with a discussion of the current challenges and future directions of P-PEGs.

Flexible, Breathable, and Self-Powered Patch Assembled of Electrospun Polymer Triboelectric Layers and Polypyrrole-Coated Electrode for Infected Chronic Wound Healing

Chronic wound healing is often impaired by bacterial infection and weak trans-epithelial potential. Patches with electrical stimulation and bactericidal activity may solve this problem. However, inconvenient power and resistant antibiotics limit their application. Here, we proposed a self-powered and intrinsic bactericidal patch based on a triboelectric nanogenerator (TENG). Electrospun polymer tribo-layers and a chemical vapor-deposited polypyrrole electrode are assembled as the TENG, offering the patch excellent flexibility, breathability, and wettability. Electrical stimulations by harvesting mechanical motions and positive charges on the polypyrrole surface kill over 96% of bacteria due to their synergistic effects on cell membrane disruption. Moreover, the TENG patch promotes infected diabetic rat skin wounds to heal within 2 weeks. Cell culture and animal tests suggest that electrical stimulation enhances gene expression of growth factors for accelerated wound healing. This work provides new insights into the design of wearable and multifunctional electrotherapy devices for chronic wound treatment.