Accelerated Skin Wound Healing by Electrical Stimulation

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.

Innovative Strategies for Hair Regrowth and Skin Visualization

Today, about 50% of men and 15-30% of women are estimated to face hair-related problems, which create a significant psychological burden. Conventional treatments, including drug therapy and transplantation, remain the main strategies for the clinical management of these problems. However, these treatments are hindered by challenges such as drug-induced adverse effects and poor drug penetration due to the skin's barrier. Therefore, various efforts have been undertaken to enhance drug permeation based on the mechanisms of hair regrowth. Notably, understanding the delivery and diffusion of topically administered drugs is essential in hair loss research. This review focuses on the advancement of transdermal strategies for hair regrowth, particularly those involving external stimulation and regeneration (topical administration) as well as microneedles (transdermal delivery). Furthermore, it also describes the natural products that have become alternative agents to prevent hair loss. In addition, given that skin visualization is necessary for hair regrowth as it provides information on drug localization within the skin's structure, this review also discusses skin visualization strategies. Finally, it details the relevant patents and clinical trials in these areas. Together, this review highlights the innovative strategies for skin visualization and hair regrowth, aiming to provide novel ideas to researchers studying hair regrowth in the future.

Conductive fibers for biomedical applications

Bioelectricity has been stated as a key factor in regulating cell activity and tissue function in electroactive tissues. Thus, various biomedical electronic constructs have been developed to interfere with cell behaviors to promote tissue regeneration, or to interface with cells or tissue/organ surfaces to acquire physiological status via electrical signals. Benefiting from the outstanding advantages of flexibility, structural diversity, customizable mechanical properties, and tunable distribution of conductive components, conductive fibers are able to avoid the damage-inducing mechanical mismatch between the construct and the biological environment, in return to ensure stable functioning of such constructs during physiological deformation. Herein, this review starts by presenting current fabrication technologies of conductive fibers including wet spinning, microfluidic spinning, electrospinning and 3D printing as well as surface modification on fibers and fiber assemblies. To provide an update on the biomedical applications of conductive fibers and fiber assemblies, we further elaborate conductive fibrous constructs utilized in tissue engineering and regeneration, implantable healthcare bioelectronics, and wearable healthcare bioelectronics. To conclude, current challenges and future perspectives of biomedical electronic constructs built by conductive fibers are discussed.

Reshaping the Endogenous Electric Field to Boost Wound Repair via Electrogenerative Dressing

The endogenous electric field (EF) generated by transepithelial potential difference plays a decisive role in wound reepithelialization. For patients with large or chronic wounds, negative-pressure wound therapy (NPWT) is the most effective clinical method in inflammation control by continuously removing the necrotic tissues or infected substances, thus creating a proproliferative microenvironment beneficial for wound reepithelialization. However, continuous negative-pressure drainage causes electrolyte loss and weakens the endogenous EF, which in turn hinders wound reepithelialization. Here, an electrogenerative dressing (EGD) is developed by integrating triboelectric nanogenerators with NPWT. By converting the negative-pressure-induced mechanical deformation into electricity, EGD produces a stable and high-safety EF that can trigger a robust epithelial electrotactic response and drive the macrophages toward a reparative M2 phenotype in vitro. Translational medicine studies confirm that EGD completely reshapes the wound EF weakened by NPWT, and promotes wound closure by facilitating an earlier transition of inflammation/proliferation and guiding epithelial migration and proliferation to accelerate reepithelialization. Long-term EGD therapy remarkably advances tissue remodeling with mature epithelium, orderly extracellular matrix, and less scar formation. Compared with the golden standard of NPWT, EGD orchestrates all the essential wound stages in a noninvasive manner, presenting an excellent prospect in clinical wound therapy.

Conductive hydrogels for tissue repair

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

Nanofibrous Scaffolds for Diabetic Wound Healing

Chronic wounds are one of the secondary health complications that develop in individuals who have poorly managed diabetes mellitus. This is often associated with delays in the wound healing process, resulting from long-term uncontrolled blood glucose levels. As such, an appropriate therapeutic approach would be maintaining blood glucose concentration within normal ranges, but this can be quite challenging to achieve. Consequently, diabetic ulcers usually require special medical care to prevent complications such as sepsis, amputation, and deformities, which often develop in these patients. Although several conventional wound dressings, such as hydrogels, gauze, films, and foams, are employed in the treatment of such chronic wounds, nanofibrous scaffolds have gained the attention of researchers because of their flexibility, ability to load a variety of bioactive compounds as single entities or combinations, and large surface area to volume ratio, which provides a biomimetic environment for cell proliferation relative to conventional dressings. Here, we present the current trends on the versatility of nanofibrous scaffolds as novel platforms for the incorporation of bioactive agents suitable for the enhancement of diabetic wound healing.

Biomaterials releasing drug responsively to promote wound healing via regulation of pathological microenvironment

Wound healing is characterized by complex, orchestrated, spatiotemporal dynamic processes. Recent findings demonstrated suitable local microenvironments were necessities for wound healing. Wound microenvironments include various biological, biochemical and physical factors, which are produced and regulated by endogenous biomediators, exogenous drugs, and external environment. Successful drug delivery to wound is complicated, and need to overcome the destroyed blood supply, persistent inflammation and enzymes, spatiotemporal requirements of special supplements, and easy deactivation of drugs. Triggered by various factors from wound microenvironment itself or external elements, stimuli-responsive biomaterials have tremendous advantages of precise drug delivery and release. Here, we discuss recent advances of stimuli-responsive biomaterials to regulate local microenvironments during wound healing, emphasizing on the design and application of different biomaterials which respond to wound biological/biochemical microenvironments (ROS, pH, enzymes, glucose and glutathione), physical microenvironments (mechanical force, temperature, light, ultrasound, magnetic and electric field), and the combination modes. Moreover, several novel promising drug carriers (microbiota, metal-organic frameworks and microneedles) are also discussed.

Bioelectronic microfluidic wound healing: a platform for investigating direct current stimulation of injured cell collectives

Upon cutaneous injury, the human body naturally forms an electric field (EF) that acts as a guidance cue for relevant cellular and tissue repair and reorganization. However, the direct current (DC) flow imparted by this EF can be impacted by a variety of diseases. This work delves into the impact of DC stimulation on both healthy and diabetic in vitro wound healing models of human keratinocytes, the most prevalent cell type of the skin. The culmination of non-metal electrode materials and prudent microfluidic design allowed us to create a compact bioelectronic platform to study the effects of different sustained (12 hours galvanostatic DC) EF configurations on wound closure dynamics. Specifically, we compared if electrotactically closing a wound's gap from one wound edge (i.e., uni-directional EF) is as effective as compared to alternatingly polarizing both the wound's edges (i.e., pseudo-converging EF) as both of these spatial stimulation strategies are fundamental to the eventual translational electrode design and strategy. We found that uni-directional electric guidance cues were superior in group keratinocyte healing dynamics by enhancing the wound closure rate nearly three-fold for both healthy and diabetic-like keratinocyte collectives, compared to their non-stimulated respective controls. The motility-inhibited and diabetic-like keratinocytes regained wound closure rates with uni-directional electrical stimulation (increase from 1.0 to 2.8% h^-1) comparable to their healthy non-stimulated keratinocyte counterparts (3.5% h^-1). Our results bring hope that electrical stimulation delivered in a controlled manner can be a viable pathway to accelerate wound repair, and also by providing a baseline for other researchers trying to find an optimal electrode blueprint for in vivo DC stimulation.

Applications of MXene and its modified materials in skin wound repair

The rapid healing and repair of skin wounds has been receiving much clinical attention. Covering the wound with wound dressing to promote wound healing is currently the main treatment for skin wound repair. However, the performance of wound dressing prepared by a single material is limited and cannot meet the requirements of complex conditions for wound healing. MXene is a new two-dimensional material with electrical conductivity, antibacterial and photothermal properties and other physical and biological properties, which has a wide range of applications in the field of biomedicine. Based on the pathophysiological process of wound healing and the properties of ideal wound dressing, this review will introduce the preparation and modification methods of MXene, systematically summarize and review the application status and mechanism of MXene in skin wound healing, and provide guidance for subsequent researchers to further apply MXene in the design of skin wound dressing.

Enhanced proliferation and migration of fibroblast cells by skin-attachable and self-cleaning triboelectric nanogenerator

Skin wounds are common in accidental injuries, surgical operations, and chronic diseases. The migration and proliferation of fibroblast cells are fundamental to wound healing, which can be promoted by electrical stimulation as a physical therapy modality. Therefore, the development of portable electrical stimulation devices that can be used by patients on-site is an essential need. In the present study, a self-cleaning triboelectric nanogenerator (TENG) has been fabricated for enhancing cell proliferation and migration. The polycaprolactone‑titanium dioxide (PCL/TiO₂₎ and polydimethylsiloxane (PDMS) layers were fabricated via a facile method and used as the electropositive and electronegative pair, respectively. The effect of stimulation time on proliferation and migration of fibroblast cells was investigated. The results demonstrated that when the cells were stimulated once-a-day for 40 min, the cell viability was increased, while a long daily stimulation time has an inhibitory effect. Under electrical stimulation, the cells move toward the middle of the scratch, making the scratch almost invisible. During repeated movements, the prepared TENG connected to a rat skin generated an open-circuit voltage and a short-circuit current around 4 V and 0.2 μA, respectively. The proposed self-powered device can pave the way for a promising therapeutic strategy for patients with chronic wounds.

An Ultrasound-Driven Bioadhesive Triboelectric Nanogenerator for Instant Wound Sealing and Electrically Accelerated Healing in Emergencies

A bioadhesive triboelectric nanogenerator (BA-TENG), as a first-aid rescue for instant and robust wound sealing and ultrasound-driven accelerated wound healing, is designed. This BA-TENG is fabricated with biocompatible materials, and integrates a flexible TENG as the top layer and bioadhesive as the bottom layer, resulting in effective electricity supply and strong sutureless sealing capability on wet tissues. When driven by ultrasound, the BA-TENG can produce a stable voltage of 1.50 V and current of 24.20 µA underwater. The ex vivo porcine colon organ models show that the BA-TENG seals defects instantly (≈5 s) with high interfacial toughness (≈150 J m^-2 ), while the rat bleeding liver incision model confirms that the BA-TENG performs rapid wound closure and hemostasis, reducing the blood loss by about 82%. When applied in living rats, the BA-TENG not only seals skin injuries immediately but also produces a strong electric field (E-field) of about 0.86 kV m^-1 stimulated by ultrasound to accelerate skin wound healing significantly. The in vitro studies confirm that these effects are attributed to the E-field-accelerated cell migration and proliferation. In addition, these TENG adhesives can be applied to not only wound treatment, nerve stimulation and regeneration, and charging batteries in implanted devices.

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

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

Piezoelectric Bioactive Glasses Composite Promotes Angiogenesis by the Synergistic Effect of Wireless Electrical Stimulation and Active Ions

Insufficient angiogenesis frequently occurs after the implantation of orthopedic materials, which greatly increases the risk of bone defect reconstruction failure. Therefore, the development of bone implant with improved angiogenic properties is of great importance. Mimicking the extracellular matrix clues provides a more direct and effective strategy to modulate angiogenesis. Herein, inspired by the bioelectrical characteristics of the bone microenvironment, a piezoelectric bioactive glasses composite (P-KNN/BG) based on the incorporation of polarized potassium sodium niobate is constructed, which could effectively promote angiogenesis. It is found that P-KNN/BG has exceptional wireless electrical stimulation performance and sustained active ions release. In vitro cell experiments reveal that P-KNN/BG enhances endothelial cell adhesion, migration, and differentiation via activating the eNOS/NO signaling pathway, which might be contributed to cell membrane hyperpolarization induced by wireless electrical stimulation increase the influx of active ions into the cells. In vivo chick chorioallantoic membrane experiment demonstrates that P-KNN/BG shows excellent pro-angiogenic capacity and biocompatibility. This work broadens the current understanding of bioactive materials with bionic electrical properties, which brings new insights into the clinical treatment of bone defect repair.

One-Pot Synthesis of Bi2 S3 /TiO2 /rGO Heterostructure with Red Light-Driven Photovoltaic Effect for Remote Electrotherapy-Assisted Wound Repair

The past decades have witnessed the rational design of novel functional nanomaterials and the potential to revolutionize many applications. With the increasing focus on electronic biological processes, novel photovoltaic nanomaterials are highly expectable for empowering new therapeutic strategies such as establishing a link between endogenous electric field (EEF) and electrotherapy. Compared to traditional invasive stimulation, the light-initiating strategy has the advantages of non-invasion, non-power supply, and precise controllability. Whereas, common photoactivated materials require short-wavelength light excitation accompanied by poor tissue penetration and biohazard. Herein, by the construction of p-n heterostructured Bi₂ S₃ /TiO₂ /rGO (BTG) nanoparticles, broadener light absorption and higher light conversion than regular UV excitation are realized. Simultaneously, the photoelectric performance of BTG heterostructure, as well as the synergistic effect of Bi₂ S₃ morphology, are revealed. Besides, the rationally designed biomimetic hydrogel matrix consisting of collagen and hyaluronic acid provides appropriate bioactivity, interface adhesion, mechanical matching, and electron transfer. Therefore, the photovoltaic BTG-loaded matrix provides a platform of light-driven electrical stimulation, coupling the EEF to modulate the electrophysiological and regeneration microenvironment. The implementation of photoelectric stimulation holds broad prospects for non-drug therapy and electrical-related biological process modulation including osseointegration, nerve regeneration, electronic skin, and wound healing.

Dynamically evolving piezoelectric nanocomposites for antibacterial and repair-promoting applications in infected wound healing

Wound healing from bacterial infections is one of the major challenges in the biomedical field. The traditional single administration methods are usually accompanied with side effects or unsatisfactory efficacy. Herein, we design dynamically evolving antibacterial and repair-promoting nanocomposites (NCs) by in situ self-assembling of zeolitic imidazolate framework-8 (ZIF-8) on the surface of barium titanate (BTO), and further loading with a small amount of ciprofloxacin (CIP). The new strategy of combining pH-stimulated drug delivery and ultrasound-controlled sonodyamics has the potential to dynamically evolve in infected wound sites, offering a multifunctional therapy. In vitro study demonstrates that the enhancement generation of reactive oxygen species through the sonodynamic process due to the heterostructures and a small amount of CIP released in an acidic environment are synergistically antibacterial, and the inhibition rate was >99.9%. In addition, reduced sonodynamic effect and Zn²⁺ generated along with the gradual degradation of ZIF-8 simultanously promote cell migration and tissue regeneration. The in vivo study of full-thickness skin wounds in mouse models demonstrate a healing rate of 99.3% could be achieved under the treatment of BTO@ZIF-8/CIP NCs. This work provides a useful improvement in rational design of multi-stimulus-responsive nanomaterials for wound healing. STATEMENT OF SIGNIFICANCE: A novel piezoelectric nanocomposite was proposed to realize sonodynamic therapy and pH-stimulated drug releasing simultaneously in wound healing treatment. The dynamically evolving structure of the piezoelectric nanocomposite in acidic microenvironment has been theoretically and experimentally verified to contribute to a continuous variation of sonodymanic strength, which accompanied with the gradual releasing of drug and biocompatible Zn²⁺effectively balanced antibacterial and repair-promoting effects. Both of the in vitro and in vivo study demonstrated that the strategy could significantly accelerate wound healing, inspiring researchers to optimize the design of multi-stimulus-responsive nanomaterials for various applications in biomedical and biomaterial fields.

A self-powered multifunctional dressing for active infection prevention and accelerated wound healing

Interruption of the wound healing process due to pathogenic infection remains a major health care challenge. The existing methods for wound management require power sources that hinder their utilization outside of clinical settings. Here, a next generation of wearable self-powered wound dressing is developed, which can be activated by diverse stimuli from the patient's body and provide on-demand treatment for both normal and infected wounds. The highly tunable dressing is composed of thermocatalytic bismuth telluride nanoplates (Bi₂Te₃ NPs) functionalized onto carbon fiber fabric electrodes and triggered by the surrounding temperature difference to controllably generate hydrogen peroxide to effectively inhibit bacterial growth at the wound site. The integrated electrodes are connected to a wearable triboelectric nanogenerator (TENG) to provide electrical stimulation for accelerated wound closure by enhancing cellular proliferation, migration, and angiogenesis. The reported self-powered dressing holds great potential in facilitating personalized and user-friendly wound care with improved healing outcomes.

Effects of Electrical Stimulation of the Cell: Wound Healing, Cell Proliferation, Apoptosis, and Signal Transduction

Electrical stimulation of the cell can have a number of different effects depending on the type of cell being stimulated. In general, electrical stimulation can cause the cell to become more active, increase its metabolism, and change its gene expression. For example, if the electrical stimulation is of low intensity and short duration, it may simply cause the cell to depolarize. However, if the electrical stimulation is of high intensity or long duration, it may cause the cell to become hyperpolarized. The electrical stimulation of cells is a process by which an electrical current is applied to cells in order to change their function or behavior. This process can be used to treat various medical conditions and has been shown to be effective in a number of studies. In this perspective, the effects of electrical stimulation on the cell are summarized.

Design and engineering of organ-on-a-chip

Organ-on-a-chip (OOC) is an emerging interdisciplinary technology that reconstitutes the structure, function, and physiology of human tissues as an alternative to conventional preclinical models for drug screening. Over the last decade, substantial progress has been made in mimicking tissue- and organ-level functions on chips through technical advances in biomaterials, stem cell engineering, microengineering, and microfluidic technologies. Structural and engineering constituents, as well as biological components, are critical factors to be considered to reconstitute the tissue function and microenvironment on chips. In this review, we highlight critical engineering technologies for reconstructing the tissue microarchitecture and dynamic spatiotemporal microenvironment in OOCs. We review the technological advances in the field of OOCs for a range of applications, including systemic analysis tools that can be integrated with OOCs, multiorgan-on-chips, and large-scale manufacturing. We then discuss the challenges and future directions for the development of advanced end-user-friendly OOC systems for a wide range of applications.

Light-Programmable Nanocomposite Hydrogel for State-Switchable Wound Healing Promotion and Bacterial Infection Elimination

Developing an ideal wound dressing that not only accelerates wound healing but also eliminates potential bacterial infections remains a difficult balancing act. This work reports the design of a light-programmable sodium alginate nanocomposite hydrogel loaded with BiOCl/polypyrrole (BOC/PPy) nanosheets for state-switchable wound healing promotion and bacterial infection elimination remotely. The nanocomposite hydrogel possesses programmable photoelectric or photothermal conversion due to the expanded light absorption range, optimized electron transmission interface, promoted photo-generated charge separation, and transfer of the BOC/PPy nanosheets. Under white light irradiation state, the nanocomposite hydrogel induces human umbilical vein endothelial cells migration and angiogenesis, and accelerates the healing efficiency of mouse skin in vivo. Under near-infrared light irradiation state, the nanocomposite hydrogel presents superior antibacterial capability in vitro, and reaches an antibacterial rate of 99.1% for Staphylococcus aureus infected skin wound in vivo. This light-programmable nanocomposite hydrogel provides an on-demand resolution of biological state-switching to balance wound healing and elimination of bacterial infection.

Assisted biomimetic electrostimulation therapy can improve the clinical pregnancy rate of patients with abnormal endometrial receptivity undergoing frozen-thawed embryo transfer cycles

This study aimed to explore whether assisted biomimetic electrostimulation (BES) therapy can improve clinical outcomes in patients with abnormal endometrial receptivity undergoing frozen-thawed embryo transfer (FET) cycles. We retrospectively collected data from 132 patients who underwent FET cycles and divided them into the BES (n = 86) and non-BES (NBES) groups (n = 46). The clinical pregnancy rate (55.8 vs. 37.0%), biochemical pregnancy rate (59.3 vs. 41.3%), and live birth rate (44.2 vs. 23.9%) of the BES group were significantly higher than those of the NBES group (p < 0.05). No significant difference between the two groups was observed in endometrial thickness at FET day, embryo implantation rate, and early abortion rate (p > 0.05). The logistic regression analysis indicated that blastocyst transfer (adjusted OR = 3.617; 1.337-9.783; p = 0.011) and BES (adjusted OR = 2.398; 1.094-5.256; p = 0.029) were positively associated with the clinical pregnancy rate. These results suggested that assisted BES therapy can improve clinical outcomes in patients with diseases affecting endometrial receptivity.Impact statementWhat is already known on this subject? Biomimetic electrostimulation (BES) therapy can increase endometrial thickness in patients with thin endometria undergoing embryo transfers and to some extent improve their clinical outcomes.What do the results of this study add? Assisted BES therapy can improve clinical pregnancy rates in patients with abnormal endometrial receptivity undergoing FET cycles (55.8 vs. 37.0%, p = 0.039). After adjusting for covariates, BES was still positively associated with the clinical pregnancy rate (adjusted OR = 2.398; 1.094-5.256; p = 0.029).What are the implications of these findings for clinical practice and/or further research? BES therapy can improve endometrial receptivity. Further studies are needed to understand its specific mechanisms.

Improved pharmacodynamics of epidermal growth factor via microneedles-based self-powered transcutaneous electrical stimulation

Epidermal growth factor is an excellent drug for promoting wound healing; however, its conventional administration strategies are associated with pharmacodynamic challenges, such as low transdermal permeability, reduction, and receptor desensitization. Here, we develop a microneedle-based self-powered transcutaneous electrical stimulation system (mn-STESS) by integrating a sliding free-standing triboelectric nanogenerator with a microneedle patch to achieve improved epidermal growth factor pharmacodynamics. We show that the mn-STESS facilitates drug penetration and utilization by using microneedles to pierce the stratum corneum. More importantly, we find that it converts the mechanical energy of finger sliding into electricity and mediates transcutaneous electrical stimulation through microneedles. We demonstrate that the electrical stimulation applied by mn-STESS acts as an "adjuvant" that suppresses the reduction of epidermal growth factor by glutathione and upregulates its receptor expression in keratinocyte cells, successfully compensating for receptor desensitization. Collectively, this work highlights the promise of self-powered electrical adjuvants in improving drug pharmacodynamics, creating combinatorial therapeutic strategies for traditional drugs.

The 3D printed conductive grooved topography hydrogel combined with electrical stimulation for synergistically enhancing wound healing of dermal fibroblast cells

Patients with extensive cutaneous damage resulting from poor wound healing often have other comorbidities such as diabetes that may lead to impaired skin functions and scar formation. Many recent studies have shown that the application of electrical stimulation (ES) to cutaneous lesions significantly improves skin regeneration via activation of AKT intracellular signaling cascades and secretion of regeneration-related growth factors. In this study, we fabricated varying concentrations of gelatin-methacrylate (GelMa) hydrogels with poly(3,4-ethylenedioxythiophene) (PEDOT): polystyrene sulfonate (PSS), which is a conductive material commonly used in tissue engineering due to its efficiency among conductive thermo-elastic materials. The results showed successful modification of PEDOT:PSS with GelMa while retaining the original structural characteristics of the GelMa hydrogels. In addition, the incorporation of PEDOT:PSS increased the interactions between both the materials, thus leading to enhanced mechanical strength, improved swelling ratio, and decreased hydrophilicity of the scaffolds. Our GelMa/PEDOT:PSS scaffolds were designed to have micro-grooves on the surfaces of the scaffolds for the purpose of directional guiding. In addition, our scaffolds were shown to have excellent electrical conductivity, thus leading to enhanced cellular proliferation and directional migration and orientation of human dermal fibroblasts. In vivo studies revealed that the GelMa/PEDOT:PSS scaffolds with electrical stimulation were able to induce full skin thickness regeneration, as seen from the various stainings. These results indicate the potential of GelMa/PEDOT:PSS as an electro-conductive biomaterial for future skin regeneration applications.

Wireless-Powered Electrical Bandage Contact Lens for Facilitating Corneal Wound Healing

Corneal injury can lead to severe vision impairment or even blindness. Although numerous methods are developed to accelerate corneal wound healing, most of them are passive treatments that rarely participate in controlling endogenous cell behaviors or are incompatible with nontransparent bandage. In this work, a wireless-powered electrical bandage contact lens (EBCL) is developed to generate a localized external electric field to accelerate corneal wound healing and vision recovery. The wireless electrical stimulation circuit employed a flower-shaped layout design that can be compactly integrated on bandage contact lens without blocking the vision. The role of the external electric field in promoting corneal wound healing is examined in vitro, where the responses of directional migration and corneal cells alignment to the electric field are observed. The RNA sequencing (RNA-seq) analysis indicates that the electrical stimulation can participate in controlling cell division, proliferation, and migration. Furthermore, the wireless EBCL is demonstrated to accelerate the completed recovery of corneal wounds on rabbits' eyes by electrical stimulation, while the control group exhibits delayed recovery and obvious corneal defects. As a new generation of intelligent device, the wireless and patient-friendly EBCL can provide a promising therapeutic strategy for ocular diseases.

Microcurrent Reverses Cigarette Smoke-Induced Angiogenesis Impairment in Human Keratinocytes In Vitro

Cigarette smoking (CS) leads to several adverse health effects, including diseases, disabilities, and even death. Post-operative and trauma patients who smoke have an increased risk for complications, such as delayed bone or wound healing. In clinical trials, microcurrent (MC) has been shown to be a safe, non-invasive, and effective way to accelerate wound healing. Our study aimed to investigate if MC with the strength of 100 μA may be beneficial in treating CS-related healing impairment, especially in regard to angiogenesis. In this study, we investigated the effect of human keratinocyte cells (HaCaT) on angiogenesis after 72 h of cigarette smoke extract (CSE) exposure in the presence or absence of 100 μA MC. Cell viability and proliferation were evaluated by resazurin conversion, Sulforhodamine B, and Calcein-AM/Hoechst 33342 staining; the pro-angiogenic potential of HaCaT cells was evaluated by tube formation assay and angiogenesis array assay; signaling pathway alterations were investigated using Western blot. Constant exposure for 72 h to a 100 μA MC enhanced the angiogenic ability of HaCaT cells, which was mediated through the PI3K-Akt signaling pathway. In conclusion, the current data indicate that 100 μA MC may support wound healing in smoking patients by enhancing angiogenesis.

Emerging Development of Auto-Charging Sensors for Respiration Monitoring

In recent years, the development of biomedical monitoring systems, including respiration monitoring systems, has been accelerated. Wearable and implantable medical devices are becoming increasingly important in the diagnosis and management of disease and illness. Respiration can be monitored using a variety of biosensors and systems. Auto-charged sensors have a number of advantages, including low cost, ease of preparation, design flexibility, and a wide range of applications. It is possible to use the auto-charged sensors to directly convert mechanical energy from the airflow into electricity. The ability to monitor and diagnose one's own health is a major goal of auto-charged sensors and systems. Respiratory disease model output signals have not been thoroughly investigated and clearly understood. As a result, figuring out their exact interrelationship is a difficult and important research question. This review summarized recent developments in auto-charged respiratory sensors and systems in terms of their device principle, output property, detecting index, and so on. Researchers with an interest in auto-charged sensors can use the information presented here to better understand the difficulties and opportunities that lie ahead.

Reduced Graphene Oxide-Extracellular Matrix Scaffolds as a Multifunctional and Highly Biocompatible Nanocomposite for Wound Healing: Insights into Characterization and Electroconductive Potential

The development of novel regenerative technologies based on the implementation of natural extracellular matrix (ECM), or individual components of ECM combined with multifunctional nanomaterials such as graphene oxide and reduced graphene oxide, has demonstrated remarkable results in wound healing and tissue engineering. However, the synthesis of these nanocomposites involves great challenges related to maintaining the biocompatibility with a simultaneous improvement in their functionalities. Based on that, in this research we developed novel nanoengineered ECM-scaffolds formed by mixing small intestinal submucosa (SIS) with graphene oxide (GO)/reduced graphene oxide (rGO) to improve electrical conductivity while maintaining remarkable biocompatibility. For this, decellularized SIS was combined with GO to form the scaffold precursor for subsequent lyophilization, chemically crosslinking and in situ reduction. The obtained GO and rGO were characterized via Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), electrical conductivity testing and atomic force microscopy (AFM). The results confirm the suitable synthesis of GO, the effective reduction to rGO and the significant increase in the electrical conductivity (more than four orders of magnitude higher than bare GO). In addition, the graphene oxide/reduced graphene oxide-SIS scaffolds were characterized via Raman spectroscopy, FTIR, TGA, SEM, porosity assay (higher than 97.5% in all cases) and protein secondary structural analysis. Moreover, the biocompatibility of scaffolds was studied by standardized assays of hemolysis activity (less than 0.5%), platelet activation and deposition, and cell viability in Vero, HaCat and HFF-1 cells (higher than 90% for all evaluated cell lines on the different scaffolds). The obtained results confirm the remarkable biocompatibility, as supported by high hemocompatibility, low cytotoxicity and no negative impact on platelet activation and deposition. Finally, structural characteristics such as pore size and interconnectivity as well as superior cell attachment abilities also corroborated the potential of the developed nanoengineered ECM-scaffolds as a multifunctional nanoplatform for application in regenerative medicine and tissue engineering.

Recent advances and trends in the applications of MXene nanomaterials for tissue engineering and regeneration

MXene, as a new two-dimensional nanomaterial, is endowed with lots of particular properties, such as large surface area, excellent conductivity, biocompatibility, biodegradability, hydrophilicity, antibacterial activity, and so on. In the past few years, MXene nanomaterials have become a rising star in biomedical fields including biological imaging, tumor diagnosis, biosensor, and tissue engineering. In this review, we sum up the recent applications of MXene nanomaterials in the field of tissue engineering and regeneration. First, we briefly introduced the synthesis and surface modification engineering of MXene. Then we focused on the application and development of MXene and MXene-based composites in skin, bone, nerve and heart tissue engineering. Uniquely, we also paid attention to some research on MXene with few achievements at present but might become a new trend in tissue engineering and regeneration in the future. Finally, this paper will also discuss several challenges faced by MXene nanomaterials in the clinical application of tissue engineering.

Bioelectric fields coordinate wound contraction and re-epithelialization process to accelerate wound healing via promoting myofibroblast transformation

Electric fields (EFs) are thought to play a decisive role in wound healing. However, most studies focused on the effects of EF on single species of cells in vitro. Here, we aimed to investigate the coordination function of EFs on wound healing. Using a bamamini pig whole-layer wound model, we further evaluated the potential of EFs as a treatment modality by applying continuous and stable EF to the wound, and we found that EF promoted wound contraction and re-epithelialization in vivo, which accelerated wound healing. In vitro, we found that EFs significantly promoted the collective migration of HaCaT cells, guided HSF cells rearrangement, and promoted collagen secretion and myofibroblast transformation, and the electrotaxis of HaCaT cells was significantly enhanced on the collagen substrate and F-actin polarization at the leading edge of the cells was more pronounced. Overall, we determined that EF promotes wound contraction by promoting myofibrillar transformation, while accelerating the formation of collagen substrates, and the substrates could provide a good basis for electric field-guided re-epithelialization. EF may promote wound healing in multiple dimensions interaction and coordinate the whole process of wound healing. These findings provide support for the continued development of EF for wound treatment applications.

Recent Advances in Nano-Formulations for Skin Wound Repair Applications

Skin injuries caused by accidents and acute or chronic diseases place a heavy burden on patients and health care systems. Current treatments mainly depend on preventing infection, debridement, and hemostasis and on supplementing growth factors, but patients will still have scar tissue proliferation or difficulty healing and other problems after treatment. Conventional treatment usually focuses on a single factor or process of wound repair and often ignores the influence of the wound pathological microenvironment on the final healing effect. Therefore, it is of substantial research value to develop multifunctional therapeutic methods that can actively regulate the wound microenvironment and reduce the oxidative stress level at the wound site to promote the repair of skin wounds. In recent years, various bioactive nanomaterials have shown great potential in tissue repair and regeneration due to their properties, including their unique surface interface effect, small size effect, enzyme activity and quantum effect. This review summarizes the mechanisms underlying skin wound repair and the defects in traditional treatment methods. We focus on analyzing the advantages of different types of nanomaterials and comment on their toxicity and side effects when used for skin wound repair.

Implantable Electronic Medicine Enabled by Bioresorbable Microneedles for Wireless Electrotherapy and Drug Delivery

A combined treatment using medication and electrostimulation increases its effectiveness in comparison with one treatment alone. However, the organic integration of two strategies in one miniaturized system for practical usage has seldom been reported. This article reports an implantable electronic medicine based on bioresorbable microneedle devices that is activated wirelessly for electrostimulation and sustainable delivery of anti-inflammatory drugs. The electronic medicine is composed of a radio frequency wireless power transmission system and a drug-loaded microneedle structure, all fabricated with bioresorbable materials. In a rat skeletal muscle injury model, periodic electrostimulation regulates cell behaviors and tissue regeneration while the anti-inflammatory drugs prevent inflammation, which ultimately enhance the skeletal muscle regeneration. Finally, the electronic medicine is fully bioresorbable, excluding the second surgery for device removal.

The Emerging Role of Immune Cells and Targeted Therapeutic Strategies in Diabetic Wounds Healing

Poor wound healing in individuals with diabetes has long plagued clinicians, and immune cells play key roles in the inflammation, proliferation and remodeling that occur in wound healing. When skin integrity is damaged, immune cells migrate to the wound bed through the actions of chemokines and jointly restore tissue homeostasis and barrier function by exerting their respective biological functions. An imbalance of immune cells often leads to ineffective and disordered inflammatory responses. Due to the maladjusted microenvironment, the wound is unable to smoothly transition to the proliferation and remodeling stage, causing it to develop into a chronic refractory wound. However, chronic refractory wounds consistently lead to negative outcomes, such as long treatment cycles, high hospitalization rates, high medical costs, high disability rates, high mortality rates, and many adverse consequences. Therefore, strategies that promote the rational distribution and coordinated development of immune cells during wound healing are very important for the treatment of diabetic wounds (DW). Here, we explored the following aspects by performing a literature review: 1) the current situation of DW and an introduction to the biological functions of immune cells; 2) the role of immune cells in DW; and 3) existing (or undeveloped) therapies targeting immune cells to promote wound healing to provide new ideas for basic research, clinical treatment and nursing of DW.

Electrical Shunting Prevents the Decline of Galvanotaxis After Monophasic Pulsed Microcurrent Stimulation in Human Dermal Fibroblasts

BACKGROUND

Electrical stimulation (ES) therapy is recommended for healing pressure injuries. Monophasic pulsed microcurrent stimulation promotes the migration of human dermal fibroblasts (HDFs) to the cathode, and ES potentially accelerates pressure injury healing. A reverse current is generated after ES in the human body; however, the effects of the electrical shunt in preventing the reverse current from migrating are unclear. Therefore, this study aimed to investigate the effects of an electrical shunt on the migration of HDFs.

METHODS

In the shunt groups, HDFs were electrically stimulated (0, 200, 400, and 600 µA) for 8 hours, and an electrical shunt was used to remove the electricity after ES. HDFs were observed under time-lapse microscopy for 24 hours. The migration ratio toward the cathode was calculated for each dish.

RESULTS

The migration ratio was significantly higher in the 200-µA group than in the other groups. HDFs migrated toward the anode after ES in the non-shunt groups with greater than 400 µA ES; however, HDFs did not migrate toward the anode with electrical shunting.

CONCLUSIONS

A post-ES electrical shunt is important in preventing a decline in the migration effect of ES.

Hybrid nanogenerator based closed-loop self-powered low-level vagus nerve stimulation system for atrial fibrillation treatment

Atrial fibrillation is an "invisible killer" of human health. It often induces high-risk diseases, such as myocardial infarction, stroke, and heart failure. Fortunately, atrial fibrillation can be diagnosed and treated early. Low-level vagus nerve stimulation (LL-VNS) is a promising therapeutic method for atrial fibrillation. However, some fundamental challenges still need to be overcome in terms of flexibility, miniaturization, and long-term service of bioelectric stimulation devices. Here, we designed a closed-loop self-powered LL-VNS system that can monitor the patient's pulse wave status in real time and conduct stimulation impulses automatically during the development of atrial fibrillation. The implant is a hybrid nanogenerator (H-NG), which is flexible, light weight, and simple, even without electronic circuits, components, and batteries. The maximum output of the H-NG was 14.8 V and 17.8 μA (peak to peak). In the in vivo effect verification study, the atrial fibrillation duration significantly decreased by 90% after LL-VNS therapy, and myocardial fibrosis and atrial connexin levels were effectively improved. Notably, the anti-inflammatory effect triggered by mediating the NF-κB and AP-1 pathways in our therapeutic system is observed. Overall, this implantable bioelectronic device is expected to be used for self-powerability, intelligentization, portability for management, and therapy of chronic diseases.

Pine pollen polysaccharides promote cell proliferation and accelerate wound healing by activating the JAK2-STAT3 signaling pathway

Natural medicine can be used to develop wound healing agents due to its excellent characteristics of promoting rapid wound healing. Pine pollen polysaccharides (PPPS), a water-soluble polysaccharide with hydrophilicity and viscosity, which is suitable for the development of wound dressing. The purpose of this study is to explore the role and mechanism of PPPS in the process of wound healing. The results showed that PPPS could accelerate the wound healing, promote cell proliferation, transform the cell cycle from G1 phase to S and G2 phase, and increase the expression of Cyclin B1 in vitro. These effects of PPPS were achieved by activating JAK2-STAT3 signaling pathway. Similarly, PPPS could accelerate the healing of mouse cutaneous wounds, and could promote the growth of chicken embryo chorioallantoic vessels. In conclusion, this study indicates that PPPS is a new promising natural agent for promoting wound healing.

Electrical Stimulation of Acute Fractures: A Narrative Review of Stimulation Protocols and Device Specifications

Orthopedic fractures have a significant impact on patients in the form of economic loss and functional impairment. Beyond the standard methods of reduction and fixation, one adjunct that has been explored since the late 1970s is electrical stimulation. Despite robust evidence for efficacy in the preclinical arena, human trials have mixed results, and this technology is not widely accepted. The purpose of this review is to examine the body of literature supporting electrical stimulation for the purpose of fracture healing in humans with an emphasis on device specifications and stimulation protocols and delineate a minimum reporting checklist for future studies of this type. We have isolated 12 studies that pertain to the administration of electrical stimulation for the purpose of augmenting fracture healing in humans. Of these, one was a direct current electrical stimulation study. Six studies utilized pulsed electromagnetic field therapy and five used capacitive coupling. When examining these studies, the device specifications were heterogenous and often incomplete in what they reported, which rendered studies unrepeatable. The stimulation protocols also varied greatly study to study. To demonstrate efficacy of electrical stimulation for fractures, the authors recommend isolating a fracture type that is prone to nonunion to maximize the electrical stimulation effect, a homogenous study population so as to not dilute the effect of electrical stimulation, and increasing scientific rigor in the form of pre-registration, blinding, and sham controls. Finally, we introduce the critical components of minimum device specification reporting for repeatability of studies of this type.

Advanced Implantable Biomedical Devices Enabled by Triboelectric Nanogenerators

Implantable biomedical devices (IMDs) play essential roles in healthcare. Subject to the limited battery life, IMDs cannot achieve long-term in situ monitoring, diagnosis, and treatment. The proposal and rapid development of triboelectric nanogenerators free IMDs from the shackles of batteries and spawn a self-powered healthcare system. This review aims to overview the development of IMDs based on triboelectric nanogenerators, divided into self-powered biosensors, in vivo energy harvesting devices, and direct electrical stimulation therapy devices. Meanwhile, future challenges and opportunities are discussed according to the development requirements of current-level self-powered IMDs to enhance output performance, develop advanced triboelectric nanogenerators with multifunctional materials, and self-driven close-looped diagnosis and treatment systems.

Accelerated Skin Wound Healing Using Flexible Photovoltaic-Bioelectrode Electrical Stimulation

Owing to the complex and long-term treatment of foot wounds due to diabetes and the limited mobility of patients, advanced clinical surgery often uses wearable flexible devices for auxiliary treatment. Therefore, there is an urgent need for self-powered biomedical devices to reduce the extra weight. We have prepared an electrically stimulated MEMS (Micro Electromechanical System) electrode integrated with wearable OPV (Organic photovoltaic). The wearable OPV is constructed of a bio-affinity PET-ITO substrate and a hundred-nanometer organic layer. Under sunlight and near-infrared light irradiation, a voltage and current are supplied to the MEMS electrode to generate an exogenous lateral electric field directed to the center of the wound. The results of in vitro cell experiments and diabetic skin-relieving biological experiments showed the proliferation of skin fibroblasts and the expression of transforming growth factors increased, and the skin wounds of diabetic mouse healed faster. Our research provides new insights for the clinical treatment of diabetes.

A self-powered wearable brain-machine-interface system for ceasing action

A self-powered wearable brain-machine-interface system with pulse detection and brain stimulation for ceasing action has been realized. The system is composed of (1) a power supply unit that employs a piezoelectric generator and converts the mechanical energy of human daily activities into electricity; (2) a neck pulse biosensor that allows continuous measurements of carotid pulse by using a piezoelectric polyvinylidene fluoride film; (3) a data analysis module that enables a coordinated brain-machine-interface system to output brain stimulation signals; and (4) brain stimulating electrodes linked to the brain that implement behavioral intervention. Demonstration of the system with stimulating electrodes implanted in the periaqueductal gray (PAG) in running mice reveals the great effect of forced ceasing action. The mice stop their running within several seconds when the stimulation signals are sent into the PAG brain region (inducing fear). This self-powered scheme for neural stimulation realizes specific behavioral intervention without any external power supply, thus providing a new concept for future behavior intervention.

A healing promoting wound dressing with tailor-made antibacterial potency employing piezocatalytic processes in multi-functional nanocomposites

Developing a novel antibiotics-free antibacterial strategy is essential for minimizing bacterial resistance. Materials that not only kill bacteria but also promote tissue healing are especially challenging to achieve. Inspired by chemical conversion processes in living organisms, we develop a piezoelectrically active antibacterial device that converts ambient O₂ and H₂O to ROS by piezocatalytic processes. The device is achieved by mounting nanoscopic polypyrrole/carbon nanotube catalyst multilayers onto piezoelectric-dielectric films. Under stimuli by a hand-held massage device, the sterilizing rates for S. aureus and E. coli reach 84.11% and 94.85% after 10 minutes of operation, respectively. The antibacterial substrate at the same time preserves and releases drugs and presents negligible cytotoxicity. Animal experiments demonstrate that daily treatment for 10 minutes using the device effectively accelerates the healing of infected wounds on the backs of mice, promoting hair follicle generation and collagen deposition. We believe that this report provides a novel design approach for antibacterial strategies in medical treatment.

Platelet Deposition Onto Vascular Wall Regulated by Electrical Signal

Platelets deposition at the site of vascular injury is a key event for the arrest of bleeding and for subsequent vascular repair. Therefore, the regulation of platelet deposition onto the injured site during the process of platelet plug formation is an important event. Herein, we showed that electrical signal could regulate the deposition of platelets onto the injured site. On the one hand, the area of platelet deposition was reduced when the cathode of the applied electric field was placed at the injured site beforehand, while it was increased when the anode was at the site. On the other hand, if a cathode was placed at the injured site after the injury, the electrical signal could remove the outer layer of the deposited platelets. Furthermore, an electric field could drive rapid platelet deposition onto the blood vessel wall at the site beneath the anode even in uninjured blood vessels. Platelet deposition could thus be manipulated by externally applied electric field, which might provide a mechanism to drive platelet deposition onto the wall of blood vessels.

A bionic cellulose nanofiber-based nanocage wound dressing for NIR-triggered multiple synergistic therapy of tumors and infected wounds

Tumor recurrence and drug-resistant bacterial infection are the main reasons that wounds heal with difficulty after skin tumor treatment. The near infrared- (NIR-) and pH-responsive, bionic, cellulose nanofiber-based (CNF-based) nanocage wound dressing with biocompatibility, bioviscosity, and shape adaptability is designed for dual NIR-triggered photothermal therapy of tumor and infection-induced wound healing. The wound dressing with the intertwining three dimensional (3D) nanocage network structure is skillfully constructed using NIR-responsive cellulose nanofibers and pH-responsive cellulose nanofibers as the skeleton, which endows the dressing with a high drug-loading capacity of doxorubicin (400 mg·g^-1), and indocyanine green (25 mg·g^-1). Moreover, the NIR- and pH-responsive bionic "On/Off" switches of the dressing enable a controllable and efficient drug release onto the wound area. The dual NIR-triggered wound dressing with excellent photothermal conversion performance possesses good antibacterial properties against Escherichia coli, Staphylococcus aureus, and drug-resistant Staphylococcus aureus. It could effectively eliminate bacterial biofilms and kill A375 tumor cells. Interestingly, the bionic wound dressing with shape adaptability could adapt and treat irregular postoperative skin tumor wounds and drug-resistant bacterial infection via the synergistic therapy of photothermal, photodynamic, and chemotherapy, which provides an ideal strategy for clinical intervention.