Electroactive polymers for tissue regeneration: Developments and perspectives

Fabrication of piezoelectric/conductive composite nerve conduits for peripheral nerve regeneration

Due to the complex regenerative microenvironment after peripheral nerve injury (PNI), developing a piezoelectric/conductive composite nerve guidance conduit (NGC) for repairing nerve defects remains a great challenge. The conductivity and piezoelectricity have been separately demonstrated to enhance the repair of PNI, yet there is a paucity of studies investigating the synergistic effects of both functions. Herein, a piezoelectric/conductive nerve conduit composed of chitosan (CS), reduced graphene oxide (rGO), and poly-L-lactic acid (PLLA) was fabricated, which provided the conductivity, mechanical support and piezoelectricity. Tensile strength, conductivity, antibacterial activity, and cell viability of piezoelectric/conductive composite NGCs were evaluated. Piezoelectric/conductive composite NGCs exhibited electrical signal output capability and conductive performance. Moreover, rGO significantly promoted cell proliferation and adhesion. Overall, the piezoelectric/conductive CS/rGO/PLLA nerve conduit shows great promise as a potential treatment of PNI.

A self-powered sandwich-structured scaffold with dual-electroactive properties to regenerate damaged intervertebral discs after discectomy

Discectomy is the most commonly used surgery in treating herniation-induced nerve compression, but it often destroys the structural integrity and leaves a defect in the intervertebral disc (IVD), leading to re-herniation risk. Considering that electric signals play a crucial role in tissue regeneration, a dual-electroactive scaffold was fabricated to promote the repair effect of the discectomy-left IVD defect. An electroconductive scaffold (G10) was 3D-printed firstly by doping graphene to form electro-osmotic networks in a polycaprolactone (PCL) matrix, then tetragonal barium titanate (T-BT) doped polyvinylidene fluoride (PVDF) fibrous membranes (B5) with piezoelectricity were electrospun on both the upper and lower surfaces of G10 to obtain a sandwich-structured scaffold (G10B5) with both piezoelectric and electroconductive activities. The in vitro experimental results confirmed that the dual-electroactive G10B5 scaffold could well mimic the electroconductive properties of natural IVDs and harvest ambient mechanical energy to produce electrical stimuli, thus recruiting surrounding stem cells. Following implantation in defective IVDs of rats, the dual-electroactive scaffolds could effectively decrease the loss of cells and extracellular matrix (ECM) and maintain the composite cartilage structure of IVDs. The dual-electroactive scaffold with a sandwich structure is proposed here to provide a novel strategy for treating the IVD defects after discectomy and broaden the application of electroactive biomaterials in tissue regeneration.

Polypyrrole-modified gelatin-based hydrogel: A dressing for intestinal perforation treatment with enhanced wound healing and anti-adhesion properties

Intestinal perforation is a serious medical emergency, and traditional surgery often causes adhesion and other complications. Innovative hydrogels improve postoperative care and rehabilitation with their anti-adhesion, antibacterial, and hemostatic properties. We have developed an advanced anti-adhesion hydrogel, AA-A30, composed of polypyrrole-modified gelatin (PPy-GelMA), carboxymethyl chitosan (CMCS), and NHS-functionalized polyethylene glycol (PEG-NHS). This hydrogel is specifically tailored for intestinal perforations. Upon hydrolysis, PEG-NHS forms a protective barrier that effectively prevents adhesion to surrounding normal tissues. Furthermore, the integration of PPy-GelMA significantly extends the degradation duration of the hydrogel, from 24 to 48 h. In a mouse model of intestinal perforation, the AA-A30 hydrogel demonstrated remarkable efficacy in inhibiting inflammation and preventing tissue adhesion by modulating the expression of both inflammatory and tissue adhesion-related factors, such as IL-1β, TNF-α, and the ratio of tPA to PAI-1. These findings underscore the considerable potential of AA-A30 for the therapeutic management of intestinal perforations.

3D-printed Ti3C2/polycaprolactone composite scaffold with a DOPA-SDF1 surface modified for bone repair

Large bone defects are a major clinical challenge in bone reconstructive surgery. 3D printing is a powerful technology that enables the manufacture of custom tissue-engineered scaffolds for bone regeneration. Electrical stimulation (ES) is a treatment method for external bone defects that compensates for damaged internal electrical signals and stimulates cell proliferation and differentiation. In this study, we propose a simple, reliable, and versatile strategy to prepare multifunctional 3D printed scaffold combined with ES for bone defect therapy. Firstly, scaffolds composed of polycaprolactone (PCL) and Ti3C2 were prepared by 3D printing technology, and then a stromal cell derived factor 1 (SDF1) containing DOPA tag was loaded onto the scaffold surface. Ti3C2 was selected as the electrode component because of its excellent electrical conductivity. The selection of DOPA-modified SDF-1(DOPA-SDF1) can improve the material binding ability and exert long-term stem cell recruitment function. The results show that prepared 3D printed scaffold (DOPA-SDF1@PCL#Ti3C2) has good hydrophilicity, electrical conductivity, antibacterial property, biocompatibility and stem cell recruitment ability. Furthermore, the expression of osteogenic specific genes in scaffold surface cells was significantly increased when pulse ES (PES) treatment was applied. The results of tibial plateau defect repair experiment showed that DOPA-SDF1@PCL#Ti3C2 scaffold can significantly promote the formation of new bone and collagen fibres. When the DOPA-SDF1@PCL#Ti3C2 scaffold was used in combination with PES therapy, the bone defect regeneration rate was further improved. This kind of scaffold could provide a new strategy for promoting the healing of large bone injuries and could expand the application of adjuvant therapy such as PES.

Mechano-Responsive Biomaterials for Bone Organoid Construction

Mechanical force is essential for bone development, bone homeostasis, and bone fracture healing. In the past few decades, various biomaterials have been developed to provide mechanical signals that mimic the natural bone microenvironment, thereby promoting bone regeneration. Bone organoids, emerging as a novel research approach, are 3D micro-bone tissues that possess the ability to self-renew and self-organize, exhibiting biomimetic spatial characteristics. Incorporating mechano-responsive biomaterials in the construction of bone organoids presents a promising avenue for simulating the mechanical bone microenvironment. Therefore, this review commences by elucidating the impact of mechanical force on bone health, encompassing both cellular interactions and alterations in bone structure. Furthermore, the most recent applications of mechano-responsive biomaterials within the realm of bone tissue engineering are highlighted. Three different types of mechano-responsive biomaterials are introduced with a focus on their responsive mechanisms, construction strategies, and efficacy in facilitating bone regeneration. Based on a comprehensive overview, the prospective utilization and future challenges of mechano-responsive biomaterials in the construction of bone organoids are discussed. As bone organoid technology advances, these biomaterials are poised to become powerful tools in bone regeneration.

Osteoblastic Differentiation of Human Adipose-Derived Mesenchymal Stem Cells on P3HT Thin Polymer Film

Bone defects restoration has always been an arduous challenge in the orthopedic field due to the limitations of conventional grafts. Bone tissue engineering offers an alternative approach by using biomimetic materials, stem cells, and growth factors that are able to improve the regeneration of bone tissue. Different biomaterials have attracted great interest in BTE applications, including the poly(3-hexylthiofene) (P3HT) conductive polymer, whose primary advantage is its capability to provide a native extracellular matrix-like environment. Based on this evidence, in this study, we evaluated the biological response of human adipose-derived mesenchymal stem cells cultured on P3HT thin polymer film for 14 days. Our results suggest that P3HT represents a good substrate to induce osteogenic differentiation of osteoprogenitor cells, even in the absence of specific inductive growth factors, thus representing a promising strategy for bone regenerative medicine. Therefore, the system provided may offer an innovative platform for next-generation biocompatible materials for regenerative medicine.

Role of Piezoelectricity in Disease Diagnosis and Treatment: A Review

Because of their unique electromechanical coupling response, piezoelectric smart biomaterials demonstrated distinctive capability toward effective, efficient, and quick diagnosis and treatment of a wide range of diseases. Such materials have potentiality to be utilized as wireless therapeutic methods with ultrasonic stimulation, which can be used as self-powered biomedical devices. An emerging advancement in the realm of personalized healthcare involves the utilization of piezoelectric biosensors for a range of therapeutic diagnosis such as diverse physiological signals in the human body, viruses, pathogens, and diseases like neurodegenerative ones, cancer, etc. The combination of piezoelectric nanoparticles with ultrasound has been established as a promising approach in sonodynamic therapy and piezocatalytic therapeutics and provides appealing alternatives for noninvasive treatments for cancer, chronic wounds, neurological diseases, etc. Innovations in implantable medical devices (IMDs), such as implantable piezoelectric energy generator (iPEG), offer significant advantages in improving physiological functioning and ability to power a cardiac pacemaker and restore the heart function. This comprehensive review critically evaluates the role of piezoelectricity in disease diagnosis and treatment, highlighting the implication of piezoelectric smart biomaterials for biomedical devices. It also discusses the potential of piezoelectric materials in healthcare monitoring, tissue engineering, and other medical applications while emphasizing future trends and challenges in the field.

Piezoelectric Scaffolds as Smart Materials for Bone Tissue Engineering

Bone repair and regeneration require physiological cues, including mechanical, electrical, and biochemical activity. Many biomaterials have been investigated as bioactive scaffolds with excellent electrical properties. Amongst biomaterials, piezoelectric materials (PMs) are gaining attention in biomedicine, power harvesting, biomedical devices, and structural health monitoring. PMs have unique properties, such as the ability to affect physiological movements and deliver electrical stimuli to damaged bone or cells without an external power source. The crucial bone property is its piezoelectricity. Bones can generate electrical charges and potential in response to mechanical stimuli, as they influence bone growth and regeneration. Piezoelectric materials respond to human microenvironment stimuli and are an important factor in bone regeneration and repair. This manuscript is an overview of the fundamentals of the materials generating the piezoelectric effect and their influence on bone repair and regeneration. This paper focuses on the state of the art of piezoelectric materials, such as polymers, ceramics, and composites, and their application in bone tissue engineering. We present important information from the point of view of bone tissue engineering. We highlight promising upcoming approaches and new generations of piezoelectric materials.

Highly stretchable nanocomposite piezofibers: a step forward into practical applications in biomedical devices

High-performance biocompatible composite materials are gaining attention for their potential in various fields such as neural tissue scaffolds, bio-implantable devices, energy harvesting, and biomechanical sensors. However, these devices currently face limitations in miniaturization, finite battery lifetimes, fabrication complexity, and rigidity. Hence, there is an urgent need for smart and self-powering soft devices that are easily deployable under physiological conditions. Herein, we present a straightforward and efficient fabrication technique for creating flexible/stretchable fiber-based piezoelectric structures using a hybrid nanocomposite of polyvinylidene fluoride (PVDF), reduced graphene oxide (rGO), and barium-titanium oxide (BT). These nanocomposite fibers are capable of converting biomechanical stimuli into electrical signals across various structural designs (knit, braid, woven, and coil). It was found that a stretchable configuration with higher output voltage (4 V) and a power density (87 μW cm-3) was obtained using nanocomposite coiled fibers or knitted fibers, which are ideal candidates for real-time monitoring of physiological signals. These structures are being proposed for practical transition to the development of the next generation of fiber-based biomedical devices. The cytotoxicity and cytocompatibility of nanocomposite fibers were tested on human mesenchymal stromal cells. The obtained results suggest that the developed fibers can be utilized for smart scaffolds and bio-implantable devices.

Electroconductive cardiac patch based on bioactive PEDOT:PSS hydrogels

Engineering cardiac implants for treating myocardial infarction (MI) has advanced, but challenges persist in mimicking the structural properties and variability of cardiac tissues using traditional bioconstructs and conventional engineering methods. This study introduces a synthetic patch with a bioactive surface designed to swiftly restore functionality to the damaged myocardium. The patch combines a composite, soft, and conductive hydrogel-based on (3,4-ethylenedioxythiophene):polystyrene-sulfonate (PEDOT:PSS) and polyvinyl alcohol (PVA). This cardiac patch exhibits a reasonably high electrical conductivity (40 S/cm) and a stretchability up to 50% of its original length. Our findings reveal its resilience to 10% cyclic stretching at 1 Hz with no loss of conductivity over time. To mediate a strong cell-scaffold adhesion, we biofunctionalize the hydrogel with a N-cadherin mimic peptide, providing the cardiac patch with a bioactive surface. This modification promote increased adherence and proliferation of cardiac fibroblasts (CFbs) while effectively mitigating the formation of bacterial biofilm, particularly against Staphylococcus aureus, a common pathogen responsible for surgical site infections (SSIs). Our study demonstrates the successful development of a structurally validated cardiac patch possessing the desired mechanical, electrical, and biofunctional attributes for effective cardiac recovery. Consequently, this research holds significant promise in alleviating the burden imposed by myocardial infarctions.

High-performance electrically responsive artificial muscle materials for soft robot actuation

Traditional robotic devices are often bulky and rigid, making it difficult for them to adapt to the soft and complex shapes of the human body. In stark contrast, soft robots, as a burgeoning class of robotic technology, showcase exceptional flexibility and adaptability, positioning them as compelling contenders for a diverse array of applications. High-performance electrically responsive artificial muscle materials (ERAMMs), as key driving components of soft robots, can achieve efficient motion and deformation, as well as more flexible and precise robot control, attracting widespread attention. This paper reviews the latest advancements in high-performance ERAMMs and their applications in the field of soft robot actuation, using ionic polymer-metal composites and dielectric elastomers as typical cases. Firstly, the definition, characteristics, and electro-driven working principles of high-performance ERAMMs are introduced. Then, the material design and synthesis, fabrication processes and optimization, as well as characterization and testing methods of the ERAMMs are summarized. Furthermore, various applications of two typical ERAMMs in the field of soft robot actuation are discussed in detail. Finally, the challenges and future directions in current research are analyzed and anticipated. This review paper aims to provide researchers with a reference for understanding the latest research progress in high-performance ERAMMs and to guide the development and application of soft robots. STATEMENT OF SIGNIFICANCE.

Injectable conductive hydrogel remodeling microenvironment and mimicking neuroelectric signal transmission after spinal cord injury

Severe spinal cord injury (SCI) leads to dysregulated neuroinflammation and cell apoptosis, resulting in axonal die-back and the loss of neuroelectric signal transmission. While biocompatible hydrogels are commonly used in SCI repair, they lack the capacity to support neuroelectric transmission. To overcome this limitation, we developed an injectable silk fibroin/ionic liquid (SFMA@IL) conductive hydrogel to assist neuroelectric signal transmission after SCI in this study. The hydrogel can form rapidly in situ under ultraviolet (UV) light. The mechanical supporting and neuro-regenerating properties are provided by silk fibroin (SF), while the conductive capability is provided by the designed ionic liquid (IL). SFMA@IL showed attractive features for SCI repair, such as anti-swelling, conductivity, and injectability. In vivo, SFMA@IL hydrogel used in rats with complete transection injuries was found to remodel the microenvironment, reduce inflammation, and facilitate neuro-fiber outgrowth. The hydrogel also led to a notable decrease in cell apoptosis and the achievement of scar-free wound healing, which saved 45.6 ± 10.8 % of spinal cord tissue in SFMA@IL grafting. Electrophysiological studies in rats with complete transection SCI confirmed SFMA@IL's ability to support sensory neuroelectric transmission, providing strong evidence for its signal transmission function. These findings provide new insights for the development of effective SCI treatments.

3D-Printed Demineralized Bone Matrix-Based Conductive Scaffolds Combined with Electrical Stimulation for Bone Tissue Engineering Applications

Bone is remodeled through a dynamic process facilitated by biophysical cues that support cellular signaling. In healthy bone, signaling pathways are regulated by cells and the extracellular matrix and transmitted via electrical synapses. To this end, combining electrical stimulation (ES) with conductive scaffolding is a promising approach for repairing damaged bone tissue. Therefore, "smart" biomaterials that can provide multifunctionality and facilitate the transfer of electrical cues directly to cells have become increasingly more studied in bone tissue engineering. Herein, 3D-printed electrically conductive composite scaffolds consisting of demineralized bone matrix (DBM) and polycaprolactone (PCL), in combination with ES, for bone regeneration were evaluated for the first time. The conductive composite scaffolds were fabricated and characterized by evaluating mechanical, surface, and electrical properties. The DBM/PCL composites exhibited a higher compressive modulus (107.2 MPa) than that of pristine PCL (62.02 MPa), as well as improved surface properties (i.e., roughness). Scaffold electrical properties were also tuned, with sheet resistance values as low as 4.77 × 105 Ω/sq for our experimental coating of the highest dilution (i.e., 20%). Furthermore, the biocompatibility and osteogenic potential of the conductive composite scaffolds were tested using human mesenchymal stromal cells (hMSCs) both with and without exogenous ES (100 mV/mm for 5 min/day four times/week). In conjunction with ES, the osteogenic differentiation of hMSCs grown on conductive DBM/PCL composite scaffolds was significantly enhanced when compared to those cultured on PCL-only and nonconductive DBM/PCL control scaffolds, as determined through xylenol orange mineral staining and osteogenic protein analysis. Overall, these promising results suggest the potential of this approach for the development of biomimetic hybrid scaffolds for bone tissue engineering applications.

Preparation and Structure-Property Relationship Study of Piezoelectric-Conductive Composite Polymer Nanofiber Materials for Bone Tissue Engineering

This study aimed to develop Janus-, cross-network-, and coaxial-structured piezoelectric-conductive polymer nanofibers through electrospinning to mimic the piezoelectricity of bone and facilitate the conduction of electrical signals in bone tissue repair. These nanofibers were constructed using the piezoelectric polymer polyvinylidene fluoride, and the conductive fillers reduced graphene oxide and polypyrrole. The influence of structural features on the electroactivity of the fibers was also explored. The morphology and components of the various structural samples were characterized using SEM, TEM, and FTIR. The electroactivity of the materials was assessed with a quasi-static d33 meter and the four-probe method. The results revealed that the piezoelectric-conductive phases were successfully integrated. The Janus-structured nanofibers demonstrated the best electroactivity, with a piezoelectric constant d33 of 24.5 pC/N and conductivity of 6.78 × 10-2 S/m. The tensile tests and MIP measurements showed that all samples had porosity levels exceeding 70%. The tensile strength of the Janus and cross-network structures exceeded that of the periosteum (3-4 MPa), with average pore sizes of 1194.36 and 2264.46 nm, respectively. These properties indicated good mechanical performance, allowing material support while preventing fibroblast invasion. The CCK-8 and ALP tests indicated that the Janus-structured samples were biocompatible and significantly promoted the proliferation of MC3T3-E1 cells.

Dynamic regulation of stem cell adhesion and differentiation on degradable piezoelectric poly (L-lactic acid) (PLLA) nanofibers

Degradable piezoelectric materials possess significant potential for application in the realm of bone tissue regeneration. However, the correlation between cell regulation mechanisms and the dynamic variation caused by material degradation has not been explained, hindering the optimization of material design and its in vivo application. Herein, piezoelectric poly (L-lactic acid) (PLLA) nanofibers with different molecular weights (MW) were fabricated, and the effects of their piezoelectric properties, structural morphology, and material products during degradation on the adhesion and osteogenic differentiation of mesenchymal stem cells (MSCs) were investigated. Our results demonstrated that cell adhesion-mediated piezoelectric stimulation could significantly enhance cell spreading, cell orientation, and upregulate the expression of calmodulin, which further triggers downstream signaling cascade to regulate osteogenic differentiation markers of type I collagen and runt-related transcription factor 2. Additionally, during the degradation of the nanofibers, the piezoelectric properties of PLLA weakened, the fibrous structure gradually diminished, and pH levels in the vicinity decreased, which resulting in reduced osteogenic differentiation capability of MSCs. However, nanofibers with higher MW (280 kDa) have the ability to maintain the fibrous morphology and piezoelectricity for a longer time, which can regulate the osteogenic differentiation of stem cells for more than 4 weeks. These findings have provide a new insight to correlate cell behavior with MW and the biodegradability of piezopolymers, which revealed an active method for cell regulation through material optimization for bone tissue engineering in near future.

Electroactive Biomaterials Regulate the Electrophysiological Microenvironment to Promote Bone and Cartilage Tissue Regeneration

The incidence of large bone and articular cartilage defects caused by traumatic injury is increasing worldwide; the tissue regeneration process for these injuries is lengthy due to limited self‐healing ability. Endogenous bioelectrical phenomenon has been well recognized to play an important role in bone and cartilage homeostasis and regeneration. Studies have reported that electrical stimulation (ES) can effectively regulate various biological processes and holds promise as an external intervention to enhance the synthesis of the extracellular matrix, thereby accelerating the process of bone and cartilage regeneration. Hence, electroactive biomaterials have been considered a biomimetic approach to ensure functional recovery by integrating various physiological signals, including electrical, biochemical, and mechanical signals. This review will discuss the role of endogenous bioelectricity in bone and cartilage tissue, as well as the effects of ES on cellular behaviors. Then, recent advances in electroactive materials and their applications in bone and cartilage tissue regeneration are systematically overviewed, with a focus on their advantages and disadvantages as tissue repair materials and performances in the modulation of cell fate. Finally, the significance of mimicking the electrophysiological microenvironment of target tissue is emphasized and future development challenges of electroactive biomaterials for bone and cartilage repair strategies are proposed.

Biodegradable Conducting Polymer-Based Composites for Biomedical Applications-A Review

In recent years, researchers have increasingly directed their focus toward the biomedical field, driven by the goal of engineering polymer systems that possess a unique combination of both electrical conductivity and biodegradability. This convergence of properties holds significant promise, as it addresses a fundamental requirement for biomedical applications: compatibility with biological environments. These polymer systems are viewed as auspicious biomaterials, precisely because they meet this critical criterion. Beyond their biodegradability, these materials offer a range of advantageous characteristics. Their exceptional processability enables facile fabrication into various forms, and their chemical stability ensures reliability in diverse physiological conditions. Moreover, their low production costs make them economically viable options for large-scale applications. Notably, their intrinsic electrical conductivity further distinguishes them, opening up possibilities for applications that demand such functionality. As the focus of this review, a survey into the use of biodegradable conducting polymers in tissue engineering, biomedical implants, and antibacterial applications is conducted.

An Antibacterial, Conductive Nanocomposite Hydrogel Coupled with Electrical Stimulation for Accelerated Wound Healing

Background

Electrical stimulation (ES) can effectively promote skin wound healing; however, single-electrode-based ES strategies are difficult to cover the entire wound area, and the effectiveness of ES is often limited by the inconsistent mechanical properties of the electrode and wound tissue. The above factors may lead to ES treatment is not ideal.

Methods

A multifunctional conductive hydrogel dressing containing methacrylated gelatin (GelMA), Ti3C2 and collagen binding antimicrobial peptides (V-Os) was developed to improve wound management. Ti3C2 was selected as the electrode component due to its excellent electrical conductivity, the modified antimicrobial peptide V-Os could replace traditional antibiotics to suppress bacterial infections, and GelMA hydrogel was used due to its clinical applicability in wound healing.

Results

The results showed that this new hydrogel dressing (GelMA@Ti3C2/V-Os) not only has excellent electrical conductivity and biocompatibility but also has a durable and efficient bactericidal effect. The modified antimicrobial peptides V-Os used were able to bind more closely to GelMA hydrogel to exert long-lasting antibacterial effects. The results of cell experiment showed that the GelMA@Ti3C2/V-Os hydrogel dressing could enhance the effect of current stimulation and significantly improve the migration, proliferation and tissue repair related genes expression of fibroblasts. In vitro experiments results showed that under ES, GelMA@Ti3C2/V-Os hydrogel dressing could promote re-epithelialization, enhance angiogenesis, mediate immune response and prevent wound infection.

Conclusion

This multifunctional nanocomposite hydrogel could provide new strategies for promoting infectious wound healing.

Biomimetic bone-periosteum scaffold for spatiotemporal regulated innervated bone regeneration and therapy of osteosarcoma

The complexity of repairing large segment defects and eradicating residual tumor cell puts the osteosarcoma clinical management challenging. Current biomaterial design often overlooks the crucial role of precisely regulating innervation in bone regeneration. Here, we develop a Germanium Selenium (GeSe) co-doped polylactic acid (PLA) nanofiber membrane-coated tricalcium phosphate bioceramic scaffold (TCP-PLA/GeSe) that mimics the bone-periosteum structure. This biomimetic scaffold offers a dual functionality, combining piezoelectric and photothermal conversion capabilities while remaining biodegradable. When subjected to ultrasound irradiation, the US-electric stimulation of TCP-PLA/GeSe enables spatiotemporal control of neurogenic differentiation. This feature supports early innervation during bone formation, promoting early neurogenic differentiation of Schwann cells (SCs) by increasing intracellular Ca2+ and subsequently activating the PI3K-Akt and Ras signaling pathways. The biomimetic scaffold also demonstrates exceptional osteogenic differentiation potential under ultrasound irradiation. In rabbit model of large segment bone defects, the TCP-PLA/GeSe demonstrates promoted osteogenesis and nerve fibre ingrowth. The combined attributes of high photothermal conversion capacity and the sustained release of anti-tumor selenium from the TCP-PLA/GeSe enable the synergistic eradication of osteosarcoma both in vitro and in vivo. This strategy provides new insights on designing advanced biomaterials of repairing large segment bone defect and osteosarcoma.

In vitro neuronal and glial response to magnetically stimulated piezoelectric poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV)/cobalt ferrite (CFO) microspheres

Polymer biomaterials are being considered for tissue regeneration due to the possibility of resembling different extracellular matrix characteristics. However, most current scaffolds cannot respond to physical-chemical modifications of the cell microenvironment. Stimuli-responsive materials, such as electroactive smart polymers, are increasingly gaining attention once they can produce electrical potentials without external power supplies. The presence of piezoelectricity in human tissues like cartilage and bone highlights the importance of electrical stimulation in physiological conditions. Although poly(vinylidene fluoride) (PVDF) is one of the piezoelectric polymers with the highest piezoelectric response, it is not biodegradable. Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) is a promising copolymer of poly(hydroxybutyrate) (PHB) for tissue engineering and regeneration applications. It offers biodegradability, piezoelectric properties, biocompatibility, and bioactivity, making it a superior option to PVDF for biomedical purposes requiring biodegradability. Magnetoelectric polymer composites can be made by combining magnetostrictive particles and piezoelectric polymers to further tune their properties for tissue regeneration. These composites convert magnetic stimuli into electrical stimuli, generating local electrical potentials for various applications. Cobalt ferrites (CFO) and piezoelectric polymers have been combined and processed into different morphologies, maintaining biocompatibility for tissue engineering. The present work studied how PHBV/CFO microspheres affected neural and glial response in spinal cord cultures. It is expected that the electrical signals generated by these microspheres due to their magnetoelectric nature could aid in tissue regeneration and repair. PHBV/CFO microspheres were not cytotoxic and were able to impact neurite outgrowth and promote neuronal differentiation. Furthermore, PHBV/CFO microspheres led to microglia activation and induced the release of several bioactive molecules. Importantly, magnetically stimulated microspheres ameliorated cell viability after an in vitro ROS-induced lesion of spinal cord cultures, which suggests a beneficial effect on tissue regeneration and repair.

Magnetic field application in bone tissue regeneration: issue current status and prospects for method development

Relevance. Magnets have long been used to treat various diseases, especially in inflammatory processes. According to existing historical data, magnetotherapy was already used in ancient times by the Chinese, Egyptians and Greeks. Different magnetic field strengths affect cells in different ways, with medium-strength magnetic fields being the most widely used. The review presents a brief history and current state of the issue of using a magnetic field in bone tissue regeneration. Modern knowledge about the mechanisms of physiological and reparative regeneration, restoration of bone tissue is clarified, and modern areas of bone tissue engineering are considered, taking into account the characteristics of microcirculation and the effect of a magnetic field on the physiology of bone tissue and reparative regeneration. One of the key findings of the review is that the magnetic field improves bone tissue repair by influencing the metabolic behavior of cells. Studies show that magnetotherapy promotes the activation of cellular processes, accelerates the formation of new bone tissue and improves its quality. It is also noted that the magnetic field has a positive effect on microcirculation, improving the blood supply to tissues and facilitating a better supply of nutrients to the site of injury. This contributes to faster wound healing and early rehabilitation of patients. Conclusion. Magnetotherapy is one of the effective physical and rehabilitation methods of treatment that will become increasingly important in modern medicine. However, further research is needed to better understand the mechanisms of action of a magnetic field on bone tissue and to determine the optimal parameters for its application.

Smart Hydrogels for Tissue Regeneration

The rapid growth in the portion of the aging population has led to a consequent increase in demand for biomedical hydrogels, together with an assortment of challenges that need to be overcome in this field. Smart hydrogels can autonomously sense and respond to the physiological/pathological changes of the tissue microenvironment and continuously adapt the response according to the dynamic spatiotemporal shifts in conditions. This along with other favorable properties, make smart hydrogels excellent materials for employing toward improving the precision of treatment for age-related diseases. The key factor during the smart hydrogel design is on accurately identifying the characteristics of natural tissues and faithfully replicating the composition, structure, and biological functions of these tissues at the molecular level. Such hydrogels can accurately sense distinct physiological and external factors such as temperature and biologically active molecules, so they may in turn actively and promptly adjust their response, by regulating their own biological effects, thereby promoting damaged tissue repair. This review summarizes the design strategies employed in the creation of smart hydrogels, their response mechanisms, as well as their applications in field of tissue engineering; and concludes by briefly discussing the relevant challenges and future prospects.

Preparation of bilayer tissue-engineered polyurethane/poly-L-lactic acid nerve conduits and their in vitro characterization for use in peripheral nerve regeneration

BACKGROUND

Due to loss of peripheral nerve structure and/or function resulting from trauma, accidents, and other causes, peripheral nerve injuries continue to be a major clinical problem. These injuries can cause partial or total loss of sensory, motor, and autonomic capabilities as well as neuropathic pain. PNI affects between 13 and 23 out of every 100,000 people annually in developed countries. Regeneration of damaged nerves and restoration of function after peripheral nerve injury remain significant therapeutic challenges. Although autologous nerve graft transplantation is a viable therapy option in several clinical conditions, donor site morbidity and a lack of donor tissue often hinder full functional recovery. Biomimetic conduits used in tissue engineering to encourage and direct peripheral nerve regeneration by providing a suitable microenvironment for nerve ingrowth are only one example of the cutting-edge methods made possible by this field. Many innate extracellular matrix (ECM) structures of different tissues can be successfully mimicked by nanofibrous scaffolds. Nanofibrous scaffolds can closely mimic the surface structure and morphology of native ECMs of many tissues.

METHODS

In this study, we have produced bilayer nanofibrous nerve conduit based on poly-lactic acid/polyurethane/multiwall carbon nanotube (PLA/PU/MWCNT), for application as composite scaffolds for static nerve tissue engineering. The contact angle was indicated to show the hydrophilicity properties of electrospun nanofibers. The SEM images were analyzed to determine the fiber's diameters, scaffold morphology, and endometrial stem cell adhesion. Moreover, MTT assay and DAPI staining were used to show the viability and proliferation of endometrial stem cells.

RESULTS

The constructed bilayer PLA/PU/MWCNT scaffolds demonstrated the capacity to support cell attachment, and the vitality of samples was assessed using SEM, MTT assay, and DAPI staining technique.

CONCLUSIONS

According to an in vitro study, electrospun bilayer PLA/PU/MWCNT scaffolds can encourage the adhesion and proliferation of human endometrial stem cells (hEnSCs) and create the ideal environment for increasing cell survival.

Controlled Sr(ii) ion release from in situ crosslinking electroactive hydrogels with potential for the treatment of infections

The development of electrochemical stimuli-responsive drug delivery systems is of both academic and industrial interest due to the ease with which it is possible to trigger payload release, providing drug delivery in a controllable manner. Herein, the preparation of in situ forming hydrogels including electroactive polypyrrole nanoparticles (PPy-NPs) where Sr2+ ions are electrochemically loaded for electrically triggered release of Sr2+ ions is reported. The hydrogels were characterized by a variety of techniques including Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), X-ray diffraction (XRD), cyclic voltammetry (CV), etc. The cytocompatibility towards human mesenchymal stem cells (MSCs) and fibroblasts were also studied. The Sr2+ ion loaded PEC-ALD/CS/PPy-NPs hydrogel showed no significant cytotoxicity towards human mesenchymal stem cells (MSCs) and fibroblasts. Sr2+ ions were electrochemically loaded and released from the electroactive hydrogels, and the application of an electrical stimulus enhanced the release of Sr2+ ions from gels by ca. 2-4 fold relative to the passive release control experiment. The antibacterial activity of Sr2+ ions against E. coli and S. aureus was demonstrated in vitro. Although these prototypical examples of Sr2+ loaded electroactive gels don't release sufficient Sr2+ ions to show antibacterial activity against E. coli and S. aureus, we believe future iterations with optimised physical properties of the gels will be capable of doing so.

Current advances in biomaterials for inner ear cell regeneration

Inner ear cell regeneration from stem/progenitor cells provides potential therapeutic strategies for the restoration of sensorineural hearing loss (SNHL), however, the efficiency of regeneration is low and the functions of differentiated cells are not yet mature. Biomaterials have been used in inner ear cell regeneration to construct a more physiologically relevant 3D culture system which mimics the stem cell microenvironment and facilitates cellular interactions. Currently, these biomaterials include hydrogel, conductive materials, magneto-responsive materials, photo-responsive materials, etc. We analyzed the characteristics and described the advantages and limitations of these materials. Furthermore, we reviewed the mechanisms by which biomaterials with different physicochemical properties act on the inner ear cell regeneration and depicted the current status of the material selection based on their characteristics to achieve the reconstruction of the auditory circuits. The application of biomaterials in inner ear cell regeneration offers promising opportunities for the reconstruction of the auditory circuits and the restoration of hearing, yet biomaterials should be strategically explored and combined according to the obstacles to be solved in the inner ear cell regeneration research.

The progression of inorganic nanoparticles and natural products for inflammatory bowel disease

There is a growing body of evidence indicating a close association between inflammatory bowel disease (IBD) and disrupted intestinal homeostasis. Excessive production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), along with an increase in M1 proinflammatory macrophage infiltration during the activation of intestinal inflammation, plays a pivotal role in disrupting intestinal homeostasis in IBD. The overabundance of ROS/RNS can cause intestinal tissue damage and the disruption of crucial gut proteins, which ultimately compromises the integrity of the intestinal barrier. The proliferation of M1 macrophages contributes to an exaggerated immune response, further compromising the intestinal immune barrier. Currently, intestinal nanomaterials have gained widespread attention in the context of IBD due to their notable characteristics, including the ability to specifically target regions of interest, clear excess ROS/RNS, and mimic biological enzymes. In this review, we initially elucidated the gut microenvironment in IBD. Subsequently, we delineate therapeutic strategies involving two distinct types of nanomedicine, namely inorganic nanoparticles and natural product nanomaterials. Finally, we present a comprehensive overview of the promising prospects associated with the application of nanomedicine in future clinical settings for the treatment of IBD (graphic abstract). Different classes of nanomedicine are used to treat IBD. This review primarily elucidates the current etiology of inflammatory bowel disease and explores two prominent nanomaterial-based therapeutic approaches. First, it aims to eliminate excessive reactive oxygen species and reactive nitrogen species. Second, they focus on modulating the polarization of inflammatory macrophages and reducing the proportion of pro-inflammatory macrophages. Additionally, this article delves into the treatment of inflammatory bowel disease using inorganic metal nanomaterials and natural product nanomaterials.

Stimuli-responsive Biomaterials for Tissue Engineering Applications

The use of ''smart materials,'' or ''stimulus responsive'' materials, has proven useful in a variety of fields, including tissue engineering and medication delivery. Many factors, including temperature, pH, redox state, light, and magnetic fields, are being studied for their potential to affect a material's properties, interactions, structure, and/or dimensions. New tissue engineering and drug delivery methods are made possible by the ability of living systems to respond to both external stimuli and their own internal signals) for example, materials composed of stimuliresponsive polymers that self assemble or undergo phase transitions or morphology transformation. The researcher examines the potential of smart materials as controlled drug release vehicles in tissue engineering, aiming to enable the localized regeneration of injured tissue by delivering precisely dosed drugs at precisely timed intervals.

Adhesion of Escherichia coli and Lactobacillus fermentum to Films and Electrospun Fibrous Scaffolds from Composites of Poly(3-hydroxybutyrate) with Magnetic Nanoparticles in a Low-Frequency Magnetic Field

The ability of materials to adhere bacteria on their surface is one of the most important aspects of their development and application in bioengineering. In this work, the effect of the properties of films and electrospun scaffolds made of composite materials based on biosynthetic poly(3-hydroxybutyrate) (PHB) with the addition of magnetite nanoparticles (MNP) and their complex with graphene oxide (MNP/GO) on the adhesion of E. coli and L. fermentum under the influence of a low-frequency magnetic field and without it was investigated. The physicochemical properties (crystallinity; surface hydrophilicity) of the materials were investigated by X-ray structural analysis, differential scanning calorimetry and "drop deposition" methods, and their surface topography was studied by scanning electron and atomic force microscopy. Crystal violet staining made it possible to reveal differences in the surface charge value and to study the adhesion of bacteria to it. It was shown that the differences in physicochemical properties of materials and the manifestation of magnetoactive properties of materials have a multidirectional effect on the adhesion of model microorganisms. Compared to pure PHB, the adhesion of E. coli to PHB-MNP/GO, and for L. fermentum to both composite materials, was higher. In the magnetic field, the adhesion of E. coli increased markedly compared to PHB-MNP/GO, whereas the effect on the adhesion of L. fermentum was reversed and was only evident in samples with PHB-MNP. Thus, the resultant factors enhancing and impairing the substrate binding of Gram-negative E. coli and Gram-positive L. fermentum turned out to be multidirectional, as they probably have different sensitivity to them. The results obtained will allow for the development of materials with externally controlled adhesion of bacteria to them for biotechnology and medicine.

Zwitterionic Conductive Hydrogel-Based Nerve Guidance Conduit Promotes Peripheral Nerve Regeneration in Rats

In recent years, conductive biomaterials have been widely used to enhance peripheral nerve regeneration. However, most biomaterials use electronic conductors to increase the conductivity of materials. As information carriers, electronic conductors always transmit discontinuous electrical signals, while biological systems essentially transmit continuous signals through ions. Herein, an ion-based conductive hydrogel was fabricated by simple copolymerization of the zwitterionic monomer sulfobetin methacrylate and hydroxyethyl methacrylate. Benefiting from the excellent mechanical stability, suitable electrical conductivity, and good cytocompatibility of the zwitterionic hydrogel, the Schwann cells cultured on the hydrogel could grow and proliferate better, and dorsal root ganglian had an increased neurite length. The zwitterionic hydrogel-based nerve guidance conduits were then implanted into a 10 mm sciatic nerve defect model in rats. Morphological analysis and electrophysiological data showed that the grafts achieved a regeneration effect close to that of the autologous nerve. Overall, our developed zwitterionic hydrogel facilitates efficient and efficacious peripheral nerve regeneration by mimicking the electrical and mechanical properties of the extracellular matrix and creating a suitable regeneration microenvironment, providing a new material reserve for the repair of peripheral nerve injury.

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.

Piezoelectric materials for neuroregeneration: a review

The purpose of nerve regeneration via tissue engineering strategies is to create a microenvironment that mimics natural nerve growth for achieving functional recovery. Biomaterial scaffolds offer a promising option for the clinical treatment of large nerve gaps due to the rapid advancement of materials science and regenerative medicine. The design of biomimetic scaffolds should take into account the inherent properties of the nerve and its growth environment, such as stiffness, topography, adhesion, conductivity, and chemical functionality. Various advanced techniques have been employed to develop suitable scaffolds for nerve repair. Since neuronal cells have electrical activity, the transmission of bioelectrical signals is crucial for the functional recovery of nerves. Therefore, an ideal peripheral nerve scaffold should have electrical activity properties similar to those of natural nerves, in addition to a delicate structure. Piezoelectric materials can convert stress changes into electrical signals that can activate different intracellular signaling pathways critical for cell activity and function, which makes them potentially useful for nerve tissue regeneration. However, a comprehensive review of piezoelectric materials for neuroregeneration is still lacking. Thus, this review systematically summarizes the development of piezoelectric materials and their application in the field of nerve regeneration. First, the electrical signals and natural piezoelectricity phenomenon in various organisms are briefly introduced. Second, the most commonly used piezoelectric materials in neural tissue engineering, including biocompatible piezoelectric polymers, inorganic piezoelectric materials, and natural piezoelectric materials, are classified and discussed. Finally, the challenges and future research directions of piezoelectric materials for application in nerve regeneration are proposed.

Bioelectronic medicine potentiates endogenous NSCs for neurodegenerative diseases

Neurodegenerative diseases (NDs) are commonly observed and while no therapy is universally applicable, cell-based therapies are promising. Stem cell transplantation has been investigated, but endogenous neural stem cells (eNSCs), despite their potential, especially with the development of bioelectronic medicine and biomaterials, remain understudied. Here, we compare stem cell transplantation therapy with eNSC-based therapy and summarize the combined use of eNSCs and developing technologies. The rapid development of implantable biomaterials has resulted in electronic stimulation becoming increasingly effective and decreasingly invasive. Thus, the combination of bioelectronic medicine and eNSCs has substantial potential for the treatment of NDs.

Synergistic effects of electroactive antibacterial material and electrical stimulation in enhancing skin tissue regeneration: A next-generation dermal wound dressing

OBJECTIVE

We aimed to develop an electroactive antibacterial material for the treatment of skin wound diseases.

METHOD

To this aim, we modified chitosan (CS), a biocompatible polymer, by coupling it with graphene (rGO) and an antimicrobial polypeptide DOPA-PonG1. The material's effect on skin injury healing was studied in combination with external electrical stimulation (EEM). The structure, surface composition, and hydrophilicity of the modified CS materials were evaluated using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and contact angle measurements. We studied NIH3T3 cells cultured with modified materials and subjected to EEM to assess viability, adhesion, and tissue repair-related gene expression.

RESULTS

SEM data demonstrated that rGO was distributed uniformly on the surface of the CS material, increasing surface roughness, and antimicrobial peptides had minimal impact on surface morphology. FTIR confirmed the uniform distribution of rGO and antibacterial peptides on the material surface. Both rGO and DOPA-PonG1 enhanced the hydrophilicity of CS materials, with rGO also improving tensile strength. The dual modification of CS with rGO and DOPA-PonG1 synergistically increased antibacterial efficacy. Cellular events and gene expression relevant to tissue repair process were enhanced by these modifications. Furthermore, EEM accelerated epidermal regeneration more than the material alone. In a rat skin wound model, DOPA-PonG1@CS/rGO dressing combined with electrical stimulation exhibited accelerated healing of skin defect.

CONCLUSION

Overall, our results demonstrate that CS materials modified with rGO and DOPA-PonG1 have increased hydrophilicity, antibacterial characteristics, and tissue regeneration capacities. This modified material in conjunction with EEM hold promise for the clinical management for dermal wounds.

Biomimetic cell culture for cell adhesive propagation for tissue engineering strategies

Biomimetic cell culture, which involves creating a biomimetic microenvironment for cells in vitro by engineering approaches, has aroused increasing interest given that it maintains the normal cellular phenotype, genotype and functions displayed in vivo. Therefore, it can provide a more precise platform for disease modelling, drug development and regenerative medicine than the conventional plate cell culture. In this review, initially, we discuss the principle of biomimetic cell culture in terms of the spatial microenvironment, chemical microenvironment, and physical microenvironment. Then, the main strategies of biomimetic cell culture and their state-of-the-art progress are summarized. To create a biomimetic microenvironment for cells, a variety of strategies has been developed, ranging from conventional scaffold strategies, such as macroscopic scaffolds, microcarriers, and microgels, to emerging scaffold-free strategies, such as spheroids, organoids, and assembloids, to simulate the native cellular microenvironment. Recently, 3D bioprinting and microfluidic chip technology have been applied as integrative platforms to obtain more complex biomimetic structures. Finally, the challenges in this area are discussed and future directions are discussed to shed some light on the community.

A Review on Electroactive Polymer-Metal Composites: Development and Applications for Tissue Regeneration

Electroactive polymer-metal composites (EAPMCs) have gained significant attention in tissue engineering owing to their exceptional mechanical and electrical properties. EAPMCs develop by combining an electroactive polymer matrix and a conductive metal. The design considerations include choosing an appropriate metal that provides mechanical strength and electrical conductivity and selecting an electroactive polymer that displays biocompatibility and electrical responsiveness. Interface engineering and surface modification techniques are also crucial for enhancing the adhesion and biocompatibility of composites. The potential of EAPMC-based tissue engineering revolves around its ability to promote cellular responses, such as cell adhesion, proliferation, and differentiation, through electrical stimulation. The electrical properties of these composites can be used to mimic natural electrical signals within tissues and organs, thereby aiding tissue regeneration. Furthermore, the mechanical characteristics of the metallic components provide structural reinforcement and can be modified to align with the distinct demands of various tissues. EAPMCs have extraordinary potential as regenerative biomaterials owing to their ability to promote beneficial effects in numerous electrically responsive cells. This study emphasizes the characteristics and applications of EAPMCs in tissue engineering.

How to fix a broken heart-designing biofunctional cues for effective, environmentally-friendly cardiac tissue engineering

Cardiovascular diseases bear strong socioeconomic and ecological impact on the worldwide healthcare system. A large consumption of goods, use of polymer-based cardiovascular biomaterials, and long hospitalization times add up to an extensive carbon footprint on the environment often turning out to be ineffective at healing such cardiovascular diseases. On the other hand, cardiac cell toxicity is among the most severe but common side effect of drugs used to treat numerous diseases from COVID-19 to diabetes, often resulting in the withdrawal of such pharmaceuticals from the market. Currently, most patients that have suffered from cardiovascular disease will never fully recover. All of these factors further contribute to the extensive negative toll pharmaceutical, biotechnological, and biomedical companies have on the environment. Hence, there is a dire need to develop new environmentally-friendly strategies that on the one hand would promise cardiac tissue regeneration after damage and on the other hand would offer solutions for the fast screening of drugs to ensure that they do not cause cardiovascular toxicity. Importantly, both require one thing-a mature, functioning cardiac tissue that can be fabricated in a fast, reliable, and repeatable manner from environmentally friendly biomaterials in the lab. This is not an easy task to complete as numerous approaches have been undertaken, separately and combined, to achieve it. This review gathers such strategies and provides insights into which succeed or fail and what is needed for the field of environmentally-friendly cardiac tissue engineering to prosper.

Functional material-mediated wireless physical stimulation for neuro-modulation and regeneration

Nerve injuries and neurological diseases remain intractable clinical challenges. Despite the advantages of stem cell therapy in treating neurological disorders, uncontrollable cell fates and loss of cell function in vivo are still challenging. Recently, increasing attention has been given to the roles of external physical signals, such as electricity and ultrasound, in regulating stem cell fate as well as activating or inhibiting neuronal activity, which provides new insights for the treatment of neurological disorders. However, direct physical stimulations in vivo are short in accuracy and safety. Functional materials that can absorb energy from a specific physical field exerted in a wireless way and then release another localized physical signal hold great advantages in mediating noninvasive or minimally invasive accurate indirect physical stimulations to promote the therapeutic effect on neurological disorders. In this review, the mechanism by which various physical signals regulate stem cell fate and neuronal activity is summarized. Based on these concepts, the approaches of using functional materials to mediate indirect wireless physical stimulation for neuro-modulation and regeneration are systematically reviewed. We expect that this review will contribute to developing wireless platforms for neural stimulation as an assistance for the treatment of neurological diseases and injuries.

Robust but On-Demand Detachable Wet Tissue Adhesive Hydrogel Enhanced with Modified Tannic Acid

Adhesives with robust but readily detachable wet tissue adhesion are of great significance for wound closure. Polyelectrolyte complex adhesive (PECA) is an important wet tissue adhesive. However, its relatively weak cohesive and adhesive strength cannot satisfy clinical applications. Herein, modified tannic acid (mTA) with a catechol group, a long alkyl hydrophobic chain, and a phenyl group was prepared first, and then, it was mixed with acrylic acid (AA) and polyethylenimine (PEI), followed by UV photopolymerization to make a wet tissue adhesive hydrogel with tough cohesion and adhesion strength. The hydrogel has a strong wet tissue interfacial toughness of ∼1552 J/m2, good mechanical properties (∼7220 kPa cohesive strength, ∼873% strain, and ∼33,370 kJ/m3 toughness), and a bursting pressure of ∼1575 mmHg on wet porcine skin. The hydrogel can realize quick and effective adhesion to various wet biological tissues including porcine skin, liver, kidney, and heart and can be changed easily with triggering urea solution to avoid tissue damage or uncomfortable pain to the patient. This biosafe adhesive hydrogel is very promising for wound closure and may provide new ideas for the design of robust wet tissue adhesives.

A nano-conductive osteogenic hydrogel to locally promote calcium influx for electro-inspired bone defect regeneration

Conductive nano-materials and electrical stimulation (ES) have been recognized as a synergetic therapy for ordinary excitable tissue repair. It is worth noting that hard tissues, such as bone tissue, possess bioelectrical properties as well. However, insufficient attention is paid to the synergetic therapy for bone defect regeneration via conductive biomaterials with ES. Here, a novel nano-conductive hydrogel comprising calcium phosphate-PEDOT:PSS-magnesium titanate-methacrylated alginate (CPM@MA) was synthesized for electro-inspired bone tissue regeneration. The nano-conductive CPM@MA hydrogel has demonstrated excellent electroactivity, biocompatibility, and osteoinductivity. Additionally, it has the potential to enhance cellular functionality by increasing endogenous transforming growth factor-beta1 (TGF-β1) and activating TGF-β/Smad2 signaling pathway. The synergetic therapy could facilitate intracellular calcium enrichment, resulting in a 5.8-fold increase in calcium concentration compared to the control group in the CPM@MA ES + group. The nano-conductive CPM@MA hydrogel with ES could significantly promote electro-inspired bone defect regeneration in vivo, uniquely allowing a full repair of rat femoral defect within 4 weeks histologically and mechanically. These results demonstrate that our synergistic strategy effectively promotes bone restoration, thereby offering potential advancements in the field of electro-inspired hard tissue regeneration using novel nano-materials with ES.

Copper Ion-Modified Germanium Phosphorus Nanosheets Integrated with an Electroactive and Biodegradable Hydrogel for Neuro-Vascularized Bone Regeneration

Severe bone defects accompanied by vascular and peripheral nerve injuries represent a huge orthopedic challenge and are often accompanied by the risk of infection. Thus, biomaterials with antibacterial and neurovascular regeneration properties are highly desirable. Here, a newly designed biohybrid biodegradable hydrogel (GelMA) containing copper ion-modified germanium-phosphorus (GeP) nanosheets, which act as neuro-vascular regeneration and antibacterial agents, is designed. The copper ion modification process serves to improve the stability of the GeP nanosheets and offers a platform for the sustained release of bioactive ions. Study findings show that GelMA/GeP@Cu has effective antibacterial properties. The integrated hydrogel can significantly boost the osteogenic differentiation of bone marrow mesenchymal stem cells, facilitate angiogenesis in human umbilical vein endothelial cells, and up-regulate neural differentiation-related proteins in neural stem cells in vitro. In vivo, in the rat calvarial bone defect mode, the GelMA/GeP@Cu hydrogel is found to enhance angiogenesis and neurogenesis, eventually contributing to bone regeneration. These findings indicate that in the field of bone tissue engineering, GelMA/GeP@Cu can serve as a valuable biomaterial for neuro-vascularized bone regeneration and infection prevention.

Regenerative bioelectronics: A strategic roadmap for precision medicine

In the past few decades, stem cell-based regenerative engineering has demonstrated its significant potential to repair damaged tissues and to restore their functionalities. Despite such advancement in regenerative engineering, the clinical translation remains a major challenge. In the stance of personalized treatment, the recent progress in bioelectronic medicine likewise evolved as another important research domain of larger significance for human healthcare. Over the last several years, our research group has adopted biomaterials-based regenerative engineering strategies using innovative bioelectronic stimulation protocols based on either electric or magnetic stimuli to direct cellular differentiation on engineered biomaterials with a range of elastic stiffness or functional properties (electroactivity/magnetoactivity). In this article, the role of bioelectronics in stem cell-based regenerative engineering has been critically analyzed to stimulate futuristic research in the treatment of degenerative diseases as well as to address some fundamental questions in stem cell biology. Built on the concepts from two independent biomedical research domains (regenerative engineering and bioelectronic medicine), we propose a converging research theme, 'Regenerative Bioelectronics'. Further, a series of recommendations have been put forward to address the current challenges in bridging the gap in stem cell therapy and bioelectronic medicine. Enacting the strategic blueprint of bioelectronic-based regenerative engineering can potentially deliver the unmet clinical needs for treating incurable degenerative diseases.

Extracellular matrix-mimetic electrically conductive nanofibrous scaffolds based on polyaniline-grafted tragacanth gum and poly(vinyl alcohol) for skin tissue engineering application

As pivotal role of scaffold in tissue engineering (TE), the aim of present study was to design and development of extracellular matrix (ECM)-mimetic electrically conductive nanofibrous scaffolds composed of polyaniline-grafted tragacanth gum (TG-g-PANI) and poly(vinyl alcohol) (PVA) with different PANI content for skin tissue engineering (STE) application. The fabricated scaffolds were preliminary evaluated in terms of some physicochemical and biological properties. Cytocompatibility and cells proliferation properties of the scaffolds were examined with the well-known MTT assay, and it was found that the developed scaffolds have proper cytocompatibilities and can enhances the mouse fibroblast L929 cells adhesion as well as proliferation, which confirm their potential for STE applications. Hemocompatibility assay revealed that the hemolysis rate of the fabricated scaffolds were <2 % even at a relatively high concentration (200 μgmL-1) of samples, therefore, these scaffolds can be considered as safe. Human serum albumin (HSA) protein adsorption capacities of the fabricated scaffolds were quantified as 42 and 49 μgmg-1 that represent suitable values for a successful TE. Overall, the fabricated scaffold with 20 wt% of TG-g-PANI showed higher potential in both physicochemical and biological features than scaffold with 30 wt% of mentioned copolymer for STE application.

Advanced surface engineering of titanium materials for biomedical applications: From static modification to dynamic responsive regulation

Titanium (Ti) and its alloys have been widely used as orthopedic implants, because of their favorable mechanical properties, corrosion resistance and biocompatibility. Despite their significant success in various clinical applications, the probability of failure, degradation and revision is undesirably high, especially for the patients with low bone density, insufficient quantity of bone or osteoporosis, which renders the studies on surface modification of Ti still active to further improve clinical results. It is discerned that surface physicochemical properties directly influence and even control the dynamic interaction that subsequently determines the success or rejection of orthopedic implants. Therefore, it is crucial to endow bulk materials with specific surface properties of high bioactivity that can be performed by surface modification to realize the osseointegration. This article first reviews surface characteristics of Ti materials and various conventional surface modification techniques involving mechanical, physical and chemical treatments based on the formation mechanism of the modified coatings. Such conventional methods are able to improve bioactivity of Ti implants, but the surfaces with static state cannot respond to the dynamic biological cascades from the living cells and tissues. Hence, beyond traditional static design, dynamic responsive avenues are then emerging. The dynamic stimuli sources for surface functionalization can originate from environmental triggers or physiological triggers. In short, this review surveys recent developments in the surface engineering of Ti materials, with a specific emphasis on advances in static to dynamic functionality, which provides perspectives for improving bioactivity and biocompatibility of Ti implants.

Filler-Enhanced Piezoelectricity of Poly-L-Lactide and Its Use as a Functional Ultrasound-Activated Biomaterial

Poly-L-lactide (PLLA) offers a unique possibility for processing into biocompatible, biodegradable, and implantable piezoelectric structures. With such properties, PLLA has potential to be used as an advanced tool for mimicking biophysical processes that naturally occur during the self-repair of wounds and damaged tissues, including electrostimulated regeneration. The piezoelectricity of PLLA strongly depends on the possibility of controlling its crystallinity and molecular orientation. Here, it is shown that modifying PLLA with a small amount (1 wt%) of crystalline filler particles with a high aspect ratio, which act as nucleating agents during drawing-induced crystallization, promotes the formation of highly crystalline and oriented PLLA structures. This increases their piezoelectricity, and the filler-modified PLLA films provide a 20-fold larger voltage output than nonmodified PLLA during ultrasound (US)-assisted activation. With 99% PLLA content, the ability of the films to produce reactive oxygen species (ROS) and increase the local temperature during interactions with US is shown to be very low. US-assisted piezostimulation of adherent cells directly attach to their surface (such as skin keratinocytes), stimulate cytoskeleton formation, and as a result cells elongate and orient themselves in a specific direction that align with the direction of PLLA film drawing and PLLA dipole orientation.

Nature-Skin-Derived e-Skin as Versatile "Wound Therapy-Health Monitoring" Bioelectronic Skin-Scaffolds: Skin to Bio-e-Skin

Electronic skins (e-skins) have the potential to turn into breakthroughs in biomedical applications. Herein, a novel acellular dermal matrix (ADM)-based bioelectronic skin (e-ADM) is used to fabricate versatile "wound therapy-health monitoring" tissue-nanoengineered skin scaffolds via a facile "one-pot" bio-compositing strategy to incorporate the conductive carbon nanotubes and self-assembled micro-copper oxide microspheres with a cicada-wing-like rough surface and nanocone microstructure. The e-ADM exhibits robust tensile strength (22 MPa), flexibility, biodegradability, electroactivity, and antibacterial properties. Interestingly, e-ADM exhibits the pH-responsive ability for intelligent command between sterilization and wound repair . Additionally, e-ADM enables accurate real-time monitoring of human activities, providing a novel flexible e-skin sensor to record injury and motions. In vitro and in vivo experiments show that with electrical stimulation, e-ADM could prominently facilitate cell growth and proliferation and further promote full-thickness skin wound healing, providing a comprehensive therapeutic strategy for smart sensing and tissue repair, guiding the development of high-performance "wound therapy-health monitoring" bioelectronic skin-scaffolds.

In situ activation of flexible magnetoelectric membrane enhances bone defect repair

For bone defect repair under co-morbidity conditions, the use of biomaterials that can be non-invasively regulated is highly desirable to avoid further complications and to promote osteogenesis. However, it remains a formidable challenge in clinical applications to achieve efficient osteogenesis with stimuli-responsive materials. Here, we develop polarized CoFe₂O₄@BaTiO₃/poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)] core-shell particle-incorporated composite membranes with high magnetoelectric conversion efficiency for activating bone regeneration. An external magnetic field force conduct on the CoFe₂O₄ core can increase charge density on the BaTiO₃ shell and strengthens the β-phase transition in the P(VDF-TrFE) matrix. This energy conversion increases the membrane surface potential, which hence activates osteogenesis. Skull defect experiments on male rats showed that repeated magnetic field applications on the membranes enhanced bone defect repair, even when osteogenesis repression is elicited by dexamethasone or lipopolysaccharide-induced inflammation. This study provides a strategy of utilizing stimuli-responsive magnetoelectric membranes to efficiently activate osteogenesis in situ.

Stimulation strategies for electrical and magnetic modulation of cells and tissues

Electrical phenomena play an important role in numerous biological processes including cellular signaling, early embryogenesis, tissue repair and remodeling, and growth of organisms. Electrical and magnetic effects have been studied on a variety of stimulation strategies and cell types regarding cellular functions and disease treatments. In this review, we discuss recent advances in using three different stimulation strategies, namely electrical stimulation via conductive and piezoelectric materials as well as magnetic stimulation via magnetic materials, to modulate cell and tissue properties. These three strategies offer distinct stimulation routes given specific material characteristics. This review will evaluate material properties and biological response for these stimulation strategies with respect to their potential applications in neural and musculoskeletal research.

Development of a Pneumatic-Driven Fiber-Shaped Robot Scaffold for Use as a Complex 3D Dynamic Culture System

Cells can sense and respond to different kinds of continuous mechanical strain in the human body. Mechanical stimulation needs to be included within the in vitro culture system to better mimic the existing complexity of in vivo biological systems. Existing commercial dynamic culture systems are generally two-dimensional (2D) which fail to mimic the three-dimensional (3D) native microenvironment. In this study, a pneumatically driven fiber robot has been developed as a platform for 3D dynamic cell culture. The fiber robot can generate tunable contractions upon stimulation. The surface of the fiber robot is formed by a braiding structure, which provides promising surface contact and adequate space for cell culture. An in-house dynamic stimulation using the fiber robot was set up to maintain NIH3T3 cells in a controlled environment. The biocompatibility of the developed dynamic culture systems was analyzed using LIVE/DEAD™ and alamarBlue™ assays. The results showed that the dynamic culture system was able to support cell proliferation with minimal cytotoxicity similar to static cultures. However, we observed a decrease in cell viability in the case of a high strain rate in dynamic cultures. Differences in cell arrangement and proliferation were observed between braided sleeves made of different materials (nylon and ultra-high molecular weight polyethylene). In summary, a simple and cost-effective 3D dynamic culture system has been proposed, which can be easily implemented to study complex biological phenomena in vitro.

Engineering Multi-Scale Organization for Biotic and Organic Abiotic Electroactive Systems

Multi-scale organization of molecular and living components is one of the most critical parameters that regulate charge transport in electroactive systems-whether abiotic, biotic, or hybrid interfaces. In this article, an overview of the current state-of-the-art for controlling molecular order, nanoscale assembly, microstructure domains, and macroscale architectures of electroactive organic interfaces used for biomedical applications is provided. Discussed herein are the leading strategies and challenges to date for engineering the multi-scale organization of electroactive organic materials, including biomolecule-based materials, synthetic conjugated molecules, polymers, and their biohybrid analogs. Importantly, this review provides a unique discussion on how the dependence of conduction phenomena on structural organization is observed for electroactive organic materials, as well as for their living counterparts in electrogenic tissues and biotic-abiotic interfaces. Expansion of fabrication capabilities that enable higher resolution and throughput for the engineering of ordered, patterned, and architecture electroactive systems will significantly impact the future of bioelectronic technologies for medical devices, bioinspired harvesting platforms, and in vitro models of electroactive tissues. In summary, this article presents how ordering at multiple scales is important for modulating transport in both the electroactive organic, abiotic, and living components of bioelectronic systems.

Electrically Triggered Quercetin Release from Polycaprolactone/Bismuth Ferrite Microfibrous Scaffold for Skeletal Muscle Tissue

Skeletal muscle tissue engineering presents a promising avenue to address the limitations pertaining to the regenerative potential of stem cells in case of injury or damage. The objective of this research was to evaluate the effects of utilizing novel microfibrous scaffolds, containing the compound quercetin (Q), on skeletal muscle regeneration. Morphological test results showed us that the combination of bismuth ferrite (BFO), polycaprolactone (PCL), and Q were bonded and well-ordered with each other, and a uniform microfibrous structure was obtained. Antimicrobial susceptibility testing of PCL/BFO/Q was conducted, and microbial reduction was found to be over 90% in the highest concentration of Q-loaded microfibrous scaffolds with the most inhibitory effect on S. aureus strains. Further, biocompatibility was investigated by performing MTT testing, fluorescence testing, and SEM imaging on mesenchymal stem cells (MSCs) to determine whether they could act as suitable microfibrous scaffolds for skeletal muscle tissue engineering. Incremental changes in the concentration of Q led to increased strength and strain, allowing muscles to withstand stretching during the healing process. In addition, electrically conductive microfibrous scaffolds enhanced the drug release capability by revealing that Q can be released significantly more quickly by applying the appropriate electric field, compared with conventional drug-release techniques. These findings suggest a possible use for PCL/BFO/Q microfibrous scaffolds in skeletal muscle regeneration by demonstrating that the combined action of both guidance biomaterials was more successful than Q itself acting alone.