Advances in electrical and magnetic stimulation on nerve regeneration

Cortical Mechanisms Underlying Effects of Repetitive Peripheral Magnetic Stimulation on Dynamic and Static Postural Control in Patients with Chronic Non-Specific Low Back Pain: A Double-Blind Randomized Clinical Trial

INTRODUCTION

Patients with chronic non-specific low back pain (CNLBP) often experience impaired postural control, contributing to pain recurrence. Although repetitive peripheral magnetic stimulation (rPMS) combined with core muscle training (CMT) could improve postural control, its neural mechanism remains unclear. This study aims to investigate the postural control-related cortical mechanism of the effect of rPMS on patients with CNLBP.

METHODS

This unicentric, prospective, randomized, double-blind, controlled trial was conducted in a public hospital from May to December 2023. A total of 40 patients (27 females and 13 males, mean age 29.38 ± 7.72) with CNLBP were randomly assigned to either the rPMS group (real rPMS with CMT) or the sham-rPMS group (sham-rPMS with CMT) for 12 sessions over 4 weeks. The rPMS was applied to the lumbar paravertebral multifidus muscle on the painful side. Pain and disability were quantified using the visual analog scale (VAS) and Oswestry dysfunction index (ODI) pre- and post-intervention. Furthermore, the sway area and velocity of the center of pressure (COP) were measured using a force platform. The cortical activities in 6 regions of interest during 4 tasks (standing with eyes open/closed on a stable/unstable plane) were recorded by functional near-infrared spectroscopy (fNIRS) pre- and post-intervention. The repeated measure ANOVA was applied for statistical analysis. Spearman's correlation was used to determine the relationships between variables.

RESULTS

After the intervention, the rPMS group showed decreased pain intensity (p = 0.001) and sway area (unstable eyes-closed task) (p = 0.046) compared to the sham-rPMS group. Additionally, the rPMS group exhibited increased activation in left primary motor cortex (M1) (p = 0.042) and reduced in left supplementary motor area (SMA) (p = 0.045), whereas the sham-rPMS group showed no significant changes. The increased activation of left M1 was negatively correlated to the reduction of pain intensity (r = - 0.537, p = 0.018) and sway area (r = - 0.500, p = 0.029) under the static balancing task. Furthermore, there was a positive correlation between sway velocity and VAS (r = 0.451, p = 0.046) post-rPMS intervention.

CONCLUSION

Repetitive peripheral magnetic stimulation combined with core muscle training demonstrated better analgesic effects and postural control improvements, compared to sham-stimulation. This may be attributed to the increased activation of the left primary motor cortex.

CLINICAL TRIAL REGISTRATION

The trial was registered on ClinicalTrials.gov (ChiCTR2300070943).

Pulsed electromagnetic field-assisted reduced graphene oxide composite 3D printed nerve scaffold promotes sciatic nerve regeneration in rats

Peripheral nerve injuries can lead to sensory or motor deficits that have a serious impact on a patient's mental health and quality of life. Nevertheless, it remains a major clinical challenge to develop functional nerve conduits as an alternative to autologous grafts. We applied reduced graphene oxide (rGO) as a bioactive conductive material to impart electrophysiological properties to a 3D printed scaffold and the application of a pulsed magnetic field to excite the formation of microcurrents and induce nerve regeneration.In vitrostudies showed that the nerve scaffold and the pulsed magnetic field made no effect on cell survival, increased S-100βprotein expression, enhanced cell adhesion, and increased the expression level of nerve regeneration-related mRNAs.In vivoexperiments suggested that the protocol was effective in promoting nerve regeneration, resulting in functional recovery of sciatic nerves in rats, when they were damaged close to that of the autologous nerve graft, and increased expression of S-100β, NF200, and GAP43. These results indicate that rGO composite nerve scaffolds combined with pulsed magnetic field stimulation have great potential for peripheral nerve rehabilitation.

Strategies for Treating Traumatic Neuromas with Tissue-Engineered Materials

Neuroma, a pathological response to peripheral nerve injury, refers to the abnormal growth of nerve tissue characterized by disorganized axonal proliferation. Commonly occurring after nerve injuries, surgeries, or amputations, this condition leads to the formation of painful nodular structures. Traditional treatment options include surgical excision and pharmacological management, aiming to alleviate symptoms. However, these approaches often offer temporary relief without addressing the underlying regenerative challenges, necessitating the exploration of advanced strategies such as tissue-engineered materials for more comprehensive and effective solutions. In this study, we discussed the etiology, molecular mechanisms, and histological morphology of traumatic neuromas after peripheral nerve injury. Subsequently, we summarized and analyzed current nonsurgical and surgical treatment options, along with their advantages and disadvantages. Additionally, we emphasized recent advancements in treating traumatic neuromas with tissue-engineered material strategies. By integrating biomaterials, growth factors, cell-based approaches, and electrical stimulation, tissue engineering offers a comprehensive solution surpassing mere symptomatic relief, striving for the structural and functional restoration of damaged nerves. In conclusion, the utilization of tissue-engineered materials has the potential to significantly reduce the risk of neuroma recurrence after surgical treatment.

Perspectives on the Novel Multifunctional Nerve Guidance Conduits: From Specific Regenerative Procedures to Motor Function Rebuilding

Peripheral nerve injury potentially destroys the quality of life by inducing functional movement disorders and sensory capacity loss, which results in severe disability and substantial psychological, social, and financial burdens. Autologous nerve grafting has been commonly used as treatment in the clinic; however, its rare donor availability limits its application. A series of artificial nerve guidance conduits (NGCs) with advanced architectures are also proposed to promote injured peripheral nerve regeneration, which is a complicated process from axon sprouting to targeted muscle reinnervation. Therefore, exploring the interactions between sophisticated NGC complexes and versatile cells during each process including axon sprouting, Schwann cell dedifferentiation, nerve myelination, and muscle reinnervation is necessary. This review highlights the contribution of functional NGCs and the influence of microscale biomaterial architecture on biological processes of nerve repair. Progressive NGCs with chemical molecule induction, heterogenous topographical morphology, electroactive, anisotropic assembly microstructure, and self-powered electroactive and magnetic-sensitive NGCs are also collected, and they are expected to be pioneering features in future multifunctional and effective NGCs.

Research advancements on nerve guide conduits for nerve injury repair

Peripheral nerve injury (PNI) is one of the most serious causes of disability and loss of work capacity of younger individuals. Although PNS has a certain degree of regeneration, there are still challenges like disordered growth, neuroma formation, and incomplete regeneration. Regarding the management of PNI, conventional methods such as surgery, pharmacotherapy, and rehabilitative therapy. Treatment strategies vary depending on the severity of the injury. While for the long nerve defect, autologous nerve grafting is commonly recognized as the preferred surgical approach. Nevertheless, due to lack of donor sources, neurological deficits and the low regeneration efficiency of grafted nerves, nerve guide conduits (NGCs) are recognized as a future promising technology in recent years. This review provides a comprehensive overview of current treatments for PNI, and discusses NGCs from different perspectives, such as material, design, fabrication process, and composite function.

Cell metabolism pathways involved in the pathophysiological changes of diabetic peripheral neuropathy

Diabetic peripheral neuropathy is a common complication of diabetes mellitus. Elucidating the pathophysiological metabolic mechanism impels the generation of ideal therapies. However, existing limited treatments for diabetic peripheral neuropathy expose the urgent need for cell metabolism research. Given the lack of comprehensive understanding of energy metabolism changes and related signaling pathways in diabetic peripheral neuropathy, it is essential to explore energy changes and metabolic changes in diabetic peripheral neuropathy to develop suitable treatment methods. This review summarizes the pathophysiological mechanism of diabetic peripheral neuropathy from the perspective of cellular metabolism and the specific interventions for different metabolic pathways to develop effective treatment methods. Various metabolic mechanisms (e.g., polyol, hexosamine, protein kinase C pathway) are associated with diabetic peripheral neuropathy, and researchers are looking for more effective treatments through these pathways.

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.

Adaptive conductive electrotherapeutic scaffolds for enhanced peripheral nerve regeneration and stimulation

BACKGROUND

While peripheral nerve stimulation (PNS) has shown promise in applications ranging from peripheral nerve regeneration to therapeutic organ stimulation, clinical implementation has been impeded by various technological limitations, including surgical placement, lead migration, and atraumatic removal.

METHODS

We describe the design and validation of a platform technology for nerve regeneration and interfacing: adaptive, conductive, and electrotherapeutic scaffolds (ACESs). ACESs are comprised of an alginate/poly-acrylamide interpenetrating network hydrogel optimized for both open surgical and minimally invasive percutaneous approaches.

FINDINGS

In a rodent model of sciatic nerve repair, ACESs significantly improved motor and sensory recovery (p < 0.05), increased muscle mass (p < 0.05), and increased axonogenesis (p < 0.05). Triggered dissolution of ACESs enabled atraumatic, percutaneous removal of leads at forces significantly lower than controls (p < 0.05). In a porcine model, ultrasound-guided percutaneous placement of leads with an injectable ACES near the femoral and cervical vagus nerves facilitated stimulus conduction at significantly greater lengths than saline controls (p < 0.05).

CONCLUSION

Overall, ACESs facilitated lead placement, stabilization, stimulation, and atraumatic removal, enabling therapeutic PNS as demonstrated in small- and large-animal models.

FUNDING

This work was supported by K. Lisa Yang Center for Bionics at MIT.

Evaluation of Possible Side Effects in the Treatment of Urinary Incontinence with Magnetic Stimulation

Background and Objectives: Magnetic stimulation is a type of conservative treatment of urinary incontinence. Our aim was to evaluate the possible side effects of this method. Materials and Methods: We conducted a systematic literature review. The key search terms were urinary incontinence, magnetic stimulation, and female. All known synonyms were used. Results: 255 titles and abstracts were retrieved, and 28 articles met our inclusion criteria. Out of 28 studies, 15 reported no side effects, five reported side effects, and eight did not report anything. There was no significant difference in the incidence of side effects between the sham and active treatment groups. Conclusions: Side effects of magnetic stimulation in comparison to other active treatments are minimal and transient. Among the conservative UI treatment methods, magnetic stimulation is one of the safest methods for the patient and as such a suitable first step in treating UI.

External magnetic field non-invasively stimulates spinal cord regeneration in rat via a magnetic-responsive aligned fibrin hydrogel

Magnetic stimulation is becoming an attractive approach to promote neuroprotection, neurogenesis, axonal regeneration, and functional recovery in both the central nervous system and peripheral nervous system disorders owing to its painless, non-invasive, and deep penetration characteristics. Here, a magnetic-responsive aligned fibrin hydrogel (MAFG) was developed to import and amplify the extrinsic magnetic field (MF) locally to stimulate spinal cord regeneration in combination with the beneficial topographical and biochemical cues of aligned fibrin hydrogel (AFG). Magnetic nanoparticles (MNPs) were embedded uniformly in AFG during electrospinning to endow it magnetic-responsive feature, with saturation magnetization of 21.79 emu g-1. It is found that the MNPs under the MF could enhance cell proliferation and neurotrophin secretion of PC12 cellsin vitro. The MAFG that was implanted into a rat with 2 mm complete transected spinal cord injury (SCI) effectively enhanced neural regeneration and angiogenesis in the lesion area, thus leading to significant recovery of motor function under the MF (MAFG@MF). This study suggests a new multimodal tissue engineering strategy based on multifunctional biomaterials that deliver multimodal regulatory signals with the integration of aligned topography, biochemical cues, and extrinsic MF stimulation for spinal cord regeneration following severe SCI.

Additive manufacturing of peripheral nerve conduits - Fabrication methods, design considerations and clinical challenges

Tissue-engineered nerve guidance conduits (NGCs) are a viable clinical alternative to autografts and allografts and have been widely used to treat peripheral nerve injuries (PNIs). Although these NGCs are successful to some extent, they cannot aid in native regeneration by improving native-equivalent neural innervation or regrowth. Further, NGCs exhibit longer recovery period and high cost limiting their clinical applications. Additive manufacturing (AM) could be an alternative to the existing drawbacks of the conventional NGCs fabrication methods. The emergence of the AM technique has offered ease for developing personalized three-dimensional (3D) neural constructs with intricate features and higher accuracy on a larger scale, replicating the native feature of nerve tissue. This review introduces the structural organization of peripheral nerves, the classification of PNI, and limitations in clinical and conventional nerve scaffold fabrication strategies. The principles and advantages of AM-based techniques, including the combinatorial approaches utilized for manufacturing 3D nerve conduits, are briefly summarized. This review also outlines the crucial parameters, such as the choice of printable biomaterials, 3D microstructural design/model, conductivity, permeability, degradation, mechanical property, and sterilization required to fabricate large-scale additive-manufactured NGCs successfully. Finally, the challenges and future directions toward fabricating the 3D-printed/bioprinted NGCs for clinical translation are also discussed.

Novel Approach of Femur Shortening With Insertion of Expandable Rod to Achieve End-to-End Repair of Sciatic Nerve Laceration

BACKGROUND

Sciatic nerve injuries are challenging for diagnosis and treatment. Particularly in proximally located high-grade injuries, neurorrhaphy often has poor outcomes. Most advocate autologous grafting and some more recently have suggested the value of knee flexion braces to facilitate end-to-end repair.

OBJECTIVE

To describe a case of femur shortening to facilitate tension-free, end-to-end sciatic nerve neurorrhaphy.

METHODS

The patient was a 17-year-old man who was injured by the propeller of a motor boat and suffered a series of lacerations to both lower extremities including transection of his right sciatic nerve in the proximal thigh. After extensive mobilization of the nerve, a greater than 7-cm gap was still present. The patient was treated with femur shortening to facilitate end-to-end coaptation. He subsequently had an expandable rod placed which was lengthened 1 mm per day until his leg length was symmetric.

RESULTS

Within 7 months postoperatively, the patient had an advancing Tinel sign and paresthesias to the dorsum of his foot. Nine months postoperatively, he had early mobility in his plantarflexion.

CONCLUSION

We present a novel method of femur shortening with insertion of an expandable rod to facilitate direct end-to-end and tension-free sciatic nerve neurorrhaphy in a proximally located injury. Furthermore, larger scale and comparative studies are warranted to further explore this and other techniques.

Nanocomposite Hydrogels as Functional Extracellular Matrices

Over recent years, nano-engineered materials have become an important component of artificial extracellular matrices. On one hand, these materials enable static enhancement of the bulk properties of cell scaffolds, for instance, they can alter mechanical properties or electrical conductivity, in order to better mimic the in vivo cell environment. Yet, many nanomaterials also exhibit dynamic, remotely tunable optical, electrical, magnetic, or acoustic properties, and therefore, can be used to non-invasively deliver localized, dynamic stimuli to cells cultured in artificial ECMs in three dimensions. Vice versa, the same, functional nanomaterials, can also report changing environmental conditions-whether or not, as a result of a dynamically applied stimulus-and as such provide means for wireless, long-term monitoring of the cell status inside the culture. In this review article, we present an overview of the technological advances regarding the incorporation of functional nanomaterials in artificial extracellular matrices, highlighting both passive and dynamically tunable nano-engineered components.

Exploring the Physicochemical, Electroactive, and Biodelivery Properties of Metal Nanoparticles on Peripheral Nerve Regeneration

Despite the advances in the regeneration/rehabilitation field of damaged tissues, the functional recovery of peripheral nerves (PNs), especially in a long gap injury, is considered a great medical challenge. Recent progress in nanomedicine has provided great hope for PN regeneration through the strategy of controlling cell behavior by metal nanoparticles individually or loaded on scaffolds/conduits. Despite the confirmed toxicity of metal nanoparticles due to long-term accumulation in nontarget tissues, they play a role in the damaged PN regeneration based on the topography modification of scaffolds/conduits, enhancing neurotrophic factor secretion, the ion flow improvement, and the regulation of electrical signals. Determining the fate of neural progenitor cells would be a major achievement in PN regeneration, which seems to be achievable by metal nanoparticles through altering cell vital approaches and controlling their functions. Therefore, in this literature, an attempt was made to provide an overview of the effective activities of metal nanoparticles on the PN regeneration, until the vital clues of the PN regeneration and how they are changed by metal nanoparticles are revealed to the researcher.

Gelatin Meshes Enriched with Graphene Oxide and Magnetic Nanoparticles Support and Enhance the Proliferation and Neuronal Differentiation of Human Adipose-Derived Stem Cells

The field of tissue engineering is constantly evolving due to the fabrication of novel platforms that promise to stimulate tissue regeneration in the scenario of accidents. Here, we describe the fabrication of fibrous nanostructured substrates based on fish gelatin (FG) and enriched with graphene oxide (GO) and magnetic nanoparticles (MNPs) and demonstrate its biological properties in terms of cell viability and proliferation, cell adhesion, and differentiation. For this purpose, electrospun fibers were fabricated using aqueous precursors containing either only GO and only MNP nanospecies, or both of them within a fish gelatin solution. The obtained materials were investigated in terms of morphology, aqueous media affinity, tensile elasticity, and structural characteristics. The biological evaluation was assessed against adipose-derived stem cells by MTT, LDH, Live/Dead assay, cytoskeleton investigation, and neuronal trans-differentiation. The results indicate an overall good interaction and show that these materials offer a biofriendly environment. A higher concentration of both nanospecies types induced some toxic effects, thus 0.5% GO, MNPs, and GO/MNPs turned out to be the most suitable option for biological testing. Moreover, a successful neuronal differentiation has been shown on these materials, where cells presented a typical neuronal phenotype. This study demonstrates the potential of this scaffold to be further used in tissue engineering applications.

Graphene Family Nanomaterials for Stem Cell Neurogenic Differentiation and Peripheral Nerve Regeneration

Stem cells play a critical role in peripheral nerve regeneration. Nerve scaffolds fabricated by specific materials can help induce the neurogenic differentiation of stem cells. Therefore, it is a potential strategy to enhance therapeutic efficiency. Graphene family nanomaterials are widely applied in repairing peripheral nerves. However, the mechanism underlying the pro-regeneration effects remains elusive. In this review, we first discuss the properties of graphene family nanomaterials, including monolayer and multilayer graphene, few-layer graphene, graphene oxide, reduced graphene oxide, and graphene quantum dots. We also introduce their applications in regulating stem cell differentiation. Then, we review the potential mechanisms of the neurogenic differentiation of stem cells facilitated by the materials. Finally, we discuss the existing challenges in this field to advance the development of nerve biomaterials.

Possible Synergies of Nanomaterial-Assisted Tissue Regeneration in Plasma Medicine: Mechanisms and Safety Concerns

Cold atmospheric plasma and nanomedicine originally emerged as individual domains, but are increasingly applied in combination with each other. Most research is performed in the context of cancer treatment, with only little focus yet on the possible synergies. Many questions remain on the potential of this promising hybrid technology, particularly regarding regenerative medicine and tissue engineering. In this perspective article, we therefore start from the fundamental mechanisms in the individual technologies, in order to envision possible synergies for wound healing and tissue recovery, as well as research strategies to discover and optimize them. Among these strategies, we demonstrate how cold plasmas and nanomaterials can enhance each other's strengths and overcome each other's limitations. The parallels with cancer research, biotechnology and plasma surface modification further serve as inspiration for the envisioned synergies in tissue regeneration. The discovery and optimization of synergies may also be realized based on a profound understanding of the underlying redox- and field-related biological processes. Finally, we emphasize the toxicity concerns in plasma and nanomedicine, which may be partly remediated by their combination, but also partly amplified. A widespread use of standardized protocols and materials is therefore strongly recommended, to ensure both a fast and safe clinical implementation.

Biofeedback electrostimulation for bionic and long-lasting neural modulation

Invasive electrical stimulation (iES) is prone to cause neural stimulus-inertia owing to its excessive accumulation of exogenous charges, thereby resulting in many side effects and even failure of nerve regeneration and functional recovery. Here, a wearable neural iES system is well designed and built for bionic and long-lasting neural modulation. It can automatically yield biomimetic pulsed electrical signals under the driven of respiratory motion. These electrical signals are full of unique physiological synchronization can give biofeedback to respiratory behaviors, self-adjusting with different physiological states of the living body, and thus realizing a dynamic and biological self-matched modulation of voltage-gated calcium channels on the cell membrane. Abundant cellular and animal experimental evidence confirm an effective elimination of neural stimulus-inertia by these bioelectrical signals. An unprecedented nerve regeneration and motor functional reconstruction are achieved in long-segmental peripheral nerve defects, which is equal to the gold standard of nerve repair -- autograft. The wearable neural iES system provides an advanced platform to overcome the common neural stimulus-inertia and gives a broad avenue for personalized iES therapy of nerve injury and neurodegenerative diseases.

Designing wereable neural invasive electrical stimulation system remains a challenge. Here, researchers provide an effective technology platform for the elimination of tricky neural stimulus-inertia using bionic electronic modulation, which is a significant step forward for long-lasting treatment of nervous system diseases.

Enhanced neurogenic differentiation on anisotropically conductive carbon nanotube reinforced polycaprolactone-collagen scaffold by applying direct coupling electrical stimulation

Electrical stimulation is conducive to neural regeneration. Different types of stimuli propagation patterns are required for regenerating cells in peripheral and central nervous systems. Modulation of the pattern of stimuli propagation cannot be achieved through external means. Reinforcing scaffolds, with suitably shaped conductive second phase materials, is a promising option in this regard. The present study has taken the effort of modulating the pattern (arrangement) of reinforced phase, namely multiwalled carbon nanotubes (MWCNT), in a biodegradable scaffold made of PCL-collagen mixture, by applying an external electric field during curing. Because of their extraordinary physical properties, MWCNTs have been selected as nano-reinforcement for this study. The nature of reinforcement affects the electrical conductivity of the scaffold and also determines the type of cell it can support for regeneration. Further, electrical stimulation, applied during incubation, was observed to have a positive influence on differentiating neural cells in vitro. However, the structure of the nano-reinforcement determined the differentiated morphology of the cells. Reinforced MWCNTs being tubes, imparted bipolarity to the cells. Therefore, these scaffolds, coupled with electrical stimulation possess significant potential to be used for directional regeneration of the nerves.

3D Printed Personalized Nerve Guide Conduits for Precision Repair of Peripheral Nerve Defects

The treatment of peripheral nerve defects has always been one of the most challenging clinical practices in neurosurgery. Currently, nerve autograft is the preferred treatment modality for peripheral nerve defects, while the therapy is constantly plagued by the limited donor, loss of donor function, formation of neuroma, nerve distortion or dislocation, and nerve diameter mismatch. To address these clinical issues, the emerged nerve guide conduits (NGCs) are expected to offer effective platforms to repair peripheral nerve defects, especially those with large or complex topological structures. Up to now, numerous technologies are developed for preparing diverse NGCs, such as solvent casting, gas foaming, phase separation, freeze-drying, melt molding, electrospinning, and three-dimensional (3D) printing. 3D printing shows great potential and advantages because it can quickly and accurately manufacture the required NGCs from various natural and synthetic materials. This review introduces the application of personalized 3D printed NGCs for the precision repair of peripheral nerve defects and predicts their future directions.

Multifunctional biomimetic hydrogel based on graphene nanoparticles and sodium alginate for peripheral nerve injury therapy

Peripheral nerve injury (PNI) caused by injury may influence the patients' lifelong mobility unless there is an appropriate treatment. Tissue engineering has become a hot field to replace traditional autologous nerve transplantation due to its low surgical damage and easy-to-industrial advantages. Graphene (GR) is a kind of carbon nanomaterial with good electrical and mechanical properties that satisfy the demand for a good tissue scaffold for nerve regeneration. Herein, a novel and biosafe hydrogel is fabricated by using graphene and sodium alginate (GR-SA) together. This hydrogel not only can mimic the nerve growth microenvironment but also can promote the expression of neurotrophic substances and growth factors. Additionally, GR-SA hydrogel can significantly reduce inflammatory factors. Moreover, the results of both in vitro and in vivo tests demonstrate that GR-SA hydrogel has a promising prospect in PNI regeneration.

Ti3C2Tx MXene-Coated Electrospun PCL Conduits for Enhancing Neurite Regeneration and Angiogenesis

An electrical signal is the key basis of normal physiological function of the nerve, and the stimulation of the electric signal also plays a very special role in the repair process of nerve injury. Electric stimulation is shown to be effective in promoting axonal regeneration and myelination, thereby promoting nerve injury repair. At present, it is considered that electric conduction recovery is a key aspect of regeneration and repair of long nerve defects. Conductive neural scaffolds have attracted more and more attention due to their similar electrical properties and good biocompatibility with normal nerves. Herein, PCL and MXene-PCL nerve guidance conduits (NGCs) were prepared; their effect on nerve regeneration was evaluated in vitro and in vivo. The results show that the NGCs have good biocompatibility in vitro. Furthermore, a sciatic nerve defect model (15 mm) of SD rats was made, and then the fabricated NGCs were implanted. MXene-PCL NGCs show similar results with the autograft in the sciatic function index, electrophysiological examination, angiogenesis, and morphological nerve regeneration. It is possible that the conductive MXene-PCL NGC could transmit physiological neural electric signals, induce angiogenesis, and stimulate nerve regeneration. This paper presents a novel design of MXene-PCL NGC that could transmit self-originated electric stimulation. In the future, it can be combined with other features to promote nerve regeneration.

Multilayered 3-D nanofibrous scaffold with chondroitin sulfate sustained release as dermal substitute

Electrospun nanofibers for skin tissue engineering applications face two main challenges. The low thickness of electrospun mats is the main reason for their weak load-bearing performance at clinical applications and limited cell penetration due to their small pore sizes. We have developed multi-layered nanofibrous 3D (M3DN) scaffolds comprising gelatin, polyvinyl alcohol, and chondroitin sulfate (CS) by an electrospinning method and attaching three electrospun layers via ethanol to cause interface fibers to come in contact with each other. Prepared M3DN scaffolds revealed a sustained CS release profile. The improved mechanical performance, stable release of CS, and penetration capability of the cells and blood vessels through the spaces between layers in the prepared multi-layered nanofibrous scaffolds demonstrate their potential applications in response to the increasing demand for replacement of damaged dermis. The results of animal studies on the dorsal skin of Rat with full-thickness wounds have shown that the reconstruction of full-thickness skin lesions is significantly higher for M3DN scaffolds than a control group (treated with sterile gauze). The amount of epithelization, collagen arrangement, and inflammatory cells (acute and chronic) has been investigated, and their associated results demonstrated that M3DN scaffolds have great potential for full-thickness wound restoration.

Electrospun conductive nanofiber yarns for accelerating mesenchymal stem cells differentiation and maturation into Schwann cell-like cells under a combination of electrical stimulation and chemical induction

Development of multifunctional tube-filling materials is required to improve the performances of the existing nerve guidance conduits (NGCs) in the repair of long-gap peripheral nerve (PN) injuries. In this study, composite nanofiber yarns (NYs) based on poly(p-dioxanone) (PPDO) biopolymer and different concentrations of carbon nanotubes (CNTs) were manufactured by utilizing a modified electrospinning apparatus. We confirmed the successful incorporation of CNTs into the PPDO nanofibers of as-fabricated composite NYs. The PPDO/CNT NYs exhibited similar morphology and structure in comparison with pure PPDO NYs. However, the PPDO/CNT NYs showed obviously enhanced mechanical properties and electrical conductivity compared to PPDO NYs. The biological tests revealed that the addition of CNTs had no negative effects on the cell growth, and proliferation of rabbit Schwann cells (rSCs), but it better maintained the phenotype of rSCs. We also demonstrated that the electrical stimulation (ES) significantly enhanced the differentiation capability of human adipose-derived mesenchymal stem cells (hADMSCs) into SC-like cells (SCLCs) on the PPDO/CNT NYs. More importantly, a unique combination of ES and chemical induction was found to further enhance the maturation of hADMSC-SCLCs on the PPDO/CNT NYs by notably upregulating the expression levels of SC myelination-associated gene markers and increasing the growth factor secretion. Overall, this study showed that our electrically conductive PPDO/CNT composite NYs could provide a beneficial microenvironment for various cell activities, making them an attractive candidate as NGC-infilling substrates for PN regeneration applications. STATEMENT OF SIGNIFICANCE: The morphology, microstructure, and bioelectrical properties of conductive PPDO/CNT NYs have been explored for guiding or controlling cell behaviors. The PPDO/CNT NYs exhibited improved mechanical properties and increased electrical conductivity compared to the CNT-free PPDO NYs. They also presented an obviously enhanced biocompatibility by effectively maintaining the phenotype of rSCs. In addition, when hADMSCs were seeded and cultured on the conductive PPDO/CNT NYs, CI was demonstrated to promote the SC-related growth factor secretion of hADMSCs, and ES was demonstrated to improve the phenotypic maturation of hADMSCs into myelinating SCLCs. Moreover, the combination of CI and ES was found to further synergistically enhance the maturation of hADMSC-SCLCs. The achievement of conductive PPDO/CNT NYs shows potential for application as NGC-infilling substrates for PN regeneration.

Tacrolimus-Induced Neurotrophic Differentiation of Adipose-Derived Stem Cells as Novel Therapeutic Method for Peripheral Nerve Injury

Peripheral nerve injuries (PNIs) are frequent traumatic injuries across the globe. Severe PNIs result in irreversible loss of axons and myelin sheaths and disability of motor and sensory function. Schwann cells can secrete neurotrophic factors and myelinate the injured axons to repair PNIs. However, Schwann cells are hard to harvest and expand in vitro, which limit their clinical use. Adipose-derived stem cells (ADSCs) are easily accessible and have the potential to acquire neurotrophic phenotype under the induction of an established protocol. It has been noticed that Tacrolimus/FK506 promotes peripheral nerve regeneration, despite the mechanism of its pro-neurogenic capacity remains undefined. Herein, we investigated the neurotrophic capacity of ADSCs under the stimulation of tacrolimus. ADSCs were cultured in the induction medium for 18 days to differentiate along the glial lineage and were subjected to FK506 stimulation for the last 3 days. We discovered that FK506 greatly enhanced the neurotrophic phenotype of ADSCs which potentiated the nerve regeneration in a crush injury model. This work explored the novel application of FK506 synergized with ADSCs and thus shed promising light on the treatment of severe PNIs.

Physiologically Self-Regulated, Fully Implantable, Battery-Free System for Peripheral Nerve Restoration

The long-segment peripheral nerve injury (PNI) represents a global medical challenge, leading to incomplete nerve tissue recovery and unsatisfactory functional reconstruction. However, the current electrical stimulation (ES) apparatuses fail perfect nerve repair due to their inability of the variable synchronous self-regulated function with physiological states. It is urgent to develop an implantable ES platform with physiologically adaptive function to provide instantaneous and nerve-preferred ES. Here, a physiologically self-regulated electrical signal is generated by integrating a novel tribo/piezoelectric hybrid nanogenerator with a nanoporous nerve guide conduit to construct a fully implantable neural electrical stimulation (FI-NES) system. The optimal neural ES parameters completely originate from the body itself and are highly self-responsive to different physiological states. The morphological evaluation, representative protein expression level, and functional reconstruction of the regenerated nerves are conducted to assess the PNI recovery process. Evidence shows that the recovery effect of 15 mm length nerve defects under the guidance of the FI-NES system is significantly close to the autograft. The designed FI-NES system provides an effective method for long-term accelerating the recovery of PNI in vivo and is also appropriate for other tissue injury or neurodegenerative diseases.

Two-Dimensional Nanomaterials for Peripheral Nerve Engineering: Recent Advances and Potential Mechanisms

Peripheral nerve tissues possess the ability to regenerate within artificial nerve scaffolds, however, despite the advance of biomaterials that support nerve regeneration, the functional nerve recovery remains unsatisfactory. Importantly, the incorporation of two-dimensional nanomaterials has shown to significantly improve the therapeutic effect of conventional nerve scaffolds. In this review, we examine whether two-dimensional nanomaterials facilitate angiogenesis and thereby promote peripheral nerve regeneration. First, we summarize the major events occurring after peripheral nerve injury. Second, we discuss that the application of two-dimensional nanomaterials for peripheral nerve regeneration strategies by facilitating the formation of new vessels. Then, we analyze the mechanism that the newly-formed capillaries directionally and metabolically support neuronal regeneration. Finally, we prospect that the two-dimensional nanomaterials should be a potential solution to long range peripheral nerve defect. To further enhance the therapeutic effects of two-dimensional nanomaterial, strategies which help remedy the energy deficiency after peripheral nerve injury could be a viable solution.

A low direct electrical signal attenuates oxidative stress and inflammation in septic rats

Electrical stimulation is proposed to exert an antimicrobial effect according to studies performed using bacterial and cell cultures. Therefore, we investigated the effects of electrification on inflammation in septic rats. Twenty-eight male Wistar albino rats were divided into 4 groups: healthy control (C), electrified healthy (E), sepsis (S), and electrified sepsis (SE) groups. Staphylococcus aureus (1 x 109 colonies) in 1 ml of medium was intraperitoneally injected into rats to produce a sepsis model. The rats in the E and SE groups were exposed to a low direct electrical signal (300 Hz and 2.5 volts) for 40 min and 1 and 6 h after bacterial infection. Immediately after the second electrical signal application, blood and tissue samples of the heart, lung, and liver were collected. An antibacterial effect of a low direct electrical signal was observed in the blood of rats. The effects of electrical signals on ameliorating changes in the histological structure of tissues, blood pH, gases, viscosity and cell count, activities of some important enzymes, oxidative stress parameters, inflammation and tissue apoptosis were observed in the SE group compared to the S group. Low direct electrical signal application exerts antibacterial, antioxidant, anti-inflammatory and antiapoptotic effects on septic rats due to the induction of electrolysis in body fluids without producing any tissue damage.

Electric Factors in Wound Healing

Significance: Electric factors such as electric charges, electrodynamic field, skin battery, and interstitial exclusion permeate wound healing physiology and physiopathology from injury to re-epithelialization. The understanding of how electric factors contribute to wound healing and how treatments may interfere with them is fundamental for the development of better strategies for the management of pathological scarring and chronic wounds. Recent Advances: Angiogenesis, cell migration, macrophage activation hemorheology, and microcirculation can interfere and be interfered with electric factors. New treatments with various types of electric currents, laser, light emitting diode, acupuncture, and weak electric fields applied directly on the wound have been developed to improve wound healing. Critical Issues: Despite the basic and clinical development, pathological scars such as keloids and chronic wounds are still a challenge. Future Directions: New treatments can be developed to improve skin wound healing taking into account the influence of electrical charges. Monitoring electrical activity during skin healing and the influence of treatments on hemorheology and microcirculation are examples of how to use knowledge of electrical factors to increase their effectiveness.

Multifunctional Scaffolds and Synergistic Strategies in Tissue Engineering and Regenerative Medicine

The increasing demand for organ replacements in a growing world with an aging population as well as the loss of tissues and organs due to congenital defects, trauma and diseases has resulted in rapidly evolving new approaches for tissue engineering and regenerative medicine (TERM). The extracellular matrix (ECM) is a crucial component in tissues and organs that surrounds and acts as a physical environment for cells. Thus, ECM has become a model guide for the design and fabrication of scaffolds and biomaterials in TERM. However, the fabrication of a tissue/organ replacement or its regeneration is a very complex process and often requires the combination of several strategies such as the development of scaffolds with multiple functionalities and the simultaneous delivery of growth factors, biochemical signals, cells, genes, immunomodulatory agents, and external stimuli. Although the development of multifunctional scaffolds and biomaterials is one of the most studied approaches for TERM, all these strategies can be combined among them to develop novel synergistic approaches for tissue regeneration. In this review we discuss recent advances in which multifunctional scaffolds alone or combined with other strategies have been employed for TERM purposes.

Para-substituted sulfonic acid-doped protonated emeraldine salt nanobuds: a potent neural interface targeting PC12 cell interactions and promotes neuronal cell differentiation

Structural parameters, such as metal-like semiconductor and electrochemical properties of functionalized polyaniline, hold great potential especially for the development of the cell-substrate interface due to its ion/electron transfer ability. We report the one-step synthesis of sulfonic acid-doped polyaniline nanobuds (s-PANINbs) with controlled shape/size under various oxidation potentials. The different oxidation states of s-PANINbs are used to investigate the cell-specific platform for the induction of neuronal networks in PC12 cells, including the growth, proliferation, and differentiation of cells. The unique structure of one-dimensional (1-D) s-PANINbs enhances its intrinsic conductive properties, and facilitates the dispersibility and electrochemical activity via covalent bonding with dopants. The protonated emeraldine salt nanobuds of s-PANINbs synthesized at 0.18 V anodic potential demonstrated low resistivity (∼81.18 mΩ) and charge transfer resistance (∼3253 Ω). The most biologically compatible protonated emeraldine salt was used in vitro to induce PC12 cells associated with neurite outgrowth, contributing to the electrophysiology of neuronal cells under an external electrical stimulation. The western blotting analysis and qRT-PCR results show that β-III Tubulin, synapsin I, and TREK-1 are highly expressed in PC12 cells, confirming their successful differentiation into neural-specific cells. Our approach demonstrates the promising role of the self-standing framework based on the s-PANINbs of the protonated emeraldine salt in peripheral nerve repair for the future in vivo cell-interface.

Crosstalk between Bone and Nerves within Bone

For the past two decades, the function of intrabony nerves on bone has been a subject of intense research, while the function of bone on intrabony nerves is still hidden in the corner. In the present review, the possible crosstalk between bone and intrabony peripheral nerves will be comprehensively analyzed. Peripheral nerves participate in bone development and repair via a host of signals generated through the secretion of neurotransmitters, neuropeptides, axon guidance factors and neurotrophins, with additional contribution from nerve-resident cells. In return, bone contributes to this microenvironmental rendezvous by housing the nerves within its internal milieu to provide mechanical support and a protective shelf. A large ensemble of chemical, mechanical, and electrical cues works in harmony with bone marrow stromal cells in the regulation of intrabony nerves. The crosstalk between bone and nerves is not limited to the physiological state, but also involved in various bone diseases including osteoporosis, osteoarthritis, heterotopic ossification, psychological stress-related bone abnormalities, and bone related tumors. This crosstalk may be harnessed in the design of tissue engineering scaffolds for repair of bone defects or be targeted for treatment of diseases related to bone and peripheral nerves.

Surface-Functionalized Conducting Nanofibers for Electrically Stimulated Neural Cell Function

Strategies involving the inclusion of cell-instructive chemical and topographical cues to smart biomaterials in combination with a suitable physical stimulus may be beneficial to enhance nerve-regeneration rate. In this regard, we investigated the surface functionalization of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)-based electroconductive electrospun nanofibers coupled with externally applied electrical stimulus for accelerated neuronal growth potential. In addition, the voltage-dependent conductive mechanism of the nanofibers was studied in depth to interlink intrinsic conductive properties with electrically stimulated neuronal expressions. Surface functionalization was accomplished using 3-aminopropyltriethoxysilane (APTES) and 1,6-hexanediamine (HDA) as an alternative to costly biomolecule coating (e.g., collagen) for cell adhesion. The nanofibers were uniform, porous, electrically conductive, mechanically strong, and stable under physiological conditions. Surface amination boosted biocompatibility, 3T3 cell adhesion, and spreading, while the neuronal model rat PC12 cell line showed better differentiation on surface-functionalized mats compared to nonfunctionalized mats. When coupled with electrical stimulation (ES), these mats showed comparable or faster neurite formation and elongation than the collagen-coated mats with no-ES conditions. The findings indicate that surface amination in combination with ES may provide an improved strategy to faster nerve regeneration using MEH-PPV-based neural scaffolds.

CNT/Sericin Conductive Nerve Guidance Conduit Promotes Functional Recovery of Transected Peripheral Nerve Injury in a Rat Model

Peripheral nerve injury usually leads to poor outcomes such as painful neuropathies and disabilities. Autogenous nerve grafting is the current gold standard; however, the limited source of a donor nerve remains a problem. Numerous tissue engineering nerve guidance conduits have been developed as substitutes for autografts. However, a few conduits can achieve the reparative effect equivalent to autografts. Here, we report for the development and application of a carbon nanotube (CNT)/sericin nerve conduit with electrical conductivity and suitable mechanical properties for nerve repair. This CNT/sericin conduit possesses favorable properties including biocompatibility, biodegradability, porous microarchitecture, and suitable swelling property. We thus applied this conduit for bridging a 10 mm gap defect of a transected sciatic nerve combined with electrical stimulation (ES) in a rat injury model. By the end of 12 weeks, we observed that the CNT/sericin conduit combined with electrical stimulation could effectively promote both structural repair and functional recovery comparable to those of the autografts, evidenced by the morphological and histological analyses, electrophysiological responses, functional studies, and target muscle reinnervation evaluations. These findings suggest that this electric conductive CNT/sericin conduit combined with electrical stimulation may have the potential to serve as a new alternative for the repair of transected peripheral nerves.