The Effect of Electrical Stimulation on Nerve Regeneration Following Peripheral Nerve Injury

Types of Short-Duration Electrical Stimulation-Induced Efficiency in the Axonal Regeneration and Recovery: Comparative in Vivo Study in Rat Model of Repaired Sciatic Nerve and its Tibial Branch after Transection Injury

The restoration of adequate function and sensation in nerves following an injury is often insufficient. Electrical stimulation (ES) applied during nerve repair can promote axon regeneration, which may enhance the likelihood of successful functional recovery. However, increasing operation time and complexity are associated with limited clinical use of ES. This study aims to better assess whether short-duration ES types (voltage mode vs. current mode) are able to produce enhanced regenerative activity following peripheral nerve repair in rat models. Wistar rats were randomly divided into 3 groups: no ES (control), 30-minute ES with a current pulse, and 30-minute ES with a voltage pulse. All groups underwent sciatic nerve transection and repair using a silicone tube to bridge the 6-mm gap between the stumps. In the 2 groups other than the control, ES was applied after the surgical repair. Outcomes were evaluated using electrophysiology, histology, and serial walking track analysis. Biweekly walking tracks test over 12 weeks revealed that subjects that underwent ES experienced more rapid functional improvement than subjects that underwent repair alone. Electrophysiological analysis of the newly intratubular sciatic nerve at week 12 revealed strong motor function recovery in rats that underwent 30-minute ES. Histologic analysis of the sciatic nerve and its tibial branch at 12 weeks demonstrated robust axon regrowth in all groups. Both types of short-duration ES applied during nerve repair can promote axon regrowth and enhance the chances of successful functional recovery.

Advancements in stimulation therapies for peripheral nerve regeneration

Soft-tissue injuries affecting muscles, nerves, vasculature, tendons, and ligaments often diminish the quality of life due to pain, loss of function, and financial burdens. Both natural healing and surgical interventions can result in scarring, which potentially may impede functional recovery and lead to persistent pain. Scar tissue, characterized by a highly disorganized fibrotic extracellular matrix, may serve as a physical barrier to regeneration and drug delivery. While approaches such as drugs, biomaterials, cells, external stimulation, and other physical forces show promise in mitigating scarring and promoting regenerative healing, their implementation remains limited and challenging. Ultrasound, laser, electrical, and magnetic forms of external stimulation have been utilized to promote soft tissue as well as neural tissue regeneration. After stimulation, neural tissues experience increased proliferation of Schwann cells, secretion of neurotropic factors, production of myelin, and growth of vasculature, all aimed at supporting axon regeneration and innervation. Yet, the outcomes of healing vary depending on the pathophysiology of the damaged nerve, the timing of stimulation following injury, and the specific parameters of stimulation employed. Increased treatment intensity and duration have been noted to hinder the healing process by inducing tissue damage. These stimulation modalities, either alone or in combination with nerve guidance conduits and scaffolds, have been demonstrated to promote healing. However, the literature currently lacks a detailed understanding of the stimulation parameters used for nerve healing applications. In this article, we aim to address this gap by summarizing existing reports and providing an overview of stimulation parameters alongside their associated healing outcomes.

Advances in Exosome-Based Therapies for the Repair of Peripheral Nerve Injuries

Peripheral nerve injuries (PNIs) are the term used to describe injuries that occur to the nerve fibers of the peripheral nervous system (PNS). Such injuries may be caused by trauma, infection, or aberrant immunological response. Although the peripheral nervous system has a limited capacity for self-repair, in cases of severe damage, this process is either interrupted entirely or is only partially completed. The evaluation of variables that promote the repair of peripheral nerves has consistently been a focal point. Exosomes are a subtype of extracellular vesicles that originate from cellular sources and possess abundant proteins, lipids, and nucleic acids, play a critical role in facilitating intercellular communication. Due to their modifiable composition, they possess exceptional capabilities as carriers for therapeutic compounds, including but not limited to mRNAs or microRNAs. Exosome-based therapies have gained significant attention in the treatment of several nervous system diseases due to their advantageous properties, such as low toxicity, high stability, and limited immune system activation. The objective of this review article is to provide an overview of exosome-based treatments that have been developed in recent years for a range of PNIs, including nerve trauma, diabetic neuropathy, amyotrophic lateral sclerosis (ALS), glaucoma, and Guillain-Barre syndrome (GBS). It was concluded that exosomes could provide favorable results in the improvement of peripheral PNIs by facilitating the transfer of regenerative factors. The development of bioengineered exosome therapy for PNIs should be given more attention to enhance the efficacy of exosome treatment for PNIs.

Therapeutic Electrical Stimulation for Surgeons: How it Works and How to Apply it

Electrical stimulation (ES) enhances peripheral nerve inherent regeneration capacity by promoting accelerated axonal outgrowth and selectivity toward appropriate motor and sensory targets. These effects lead to significantly improved functional outcomes and shorter recovery time. Electrical stimulation can be applied intra-operatively or immediately post-operatively. Active clinical trials are looking into additional areas of application, length of stimulation, and functional outcomes.

Combat-related peripheral nerve injuries

Active-duty service members (ADSM) and military Veterans represent a population with increased occupational risk for nerve injuries sustained both during training operations and wartime. Mechanisms of war-related nerve injuries have evolved over time, from the musket ball-related traumas described by S.W. Mitchell to complex blast injuries and toxic exposures sustained during Middle East conflicts in the 21st century. Commonly encountered nerve injury etiologies in this population currently include compression, direct trauma, nutritional deficits, traumatic limb amputation, toxic chemical exposures, or blast-related injuries. Expeditious identification and comprehensive, interdisciplinary treatment of combat-associated neuropathies, as well as prevention of these injuries whenever possible is critical to reduce chronic morbidity and disability for service members and to maintain a well-prepared military. However, diagnosis of a combat-associated nerve injury may be particularly challenging due to comorbid battlefield injuries or delayed presentation of neuropathy from military toxic exposures. Advances in imaging for nerve injury, including MRI and ultrasound, provide useful tools to compliment EMG in establishing a diagnosis of combat-associated nerve injury, particularly in the setting of anatomic disruption or edema. Surgical techniques can improve pain control or restoration of function. In all cases, comprehensive interdisciplinary rehabilitation provides the best framework for optimization of recovery. Further work is needed to prevent combat-associated nerve injuries and promote nerve recovery following injury.

The role of microRNAs in axon regeneration after peripheral nerve injury: a bibliometric analysis

Objective

This study analyzed the current research hotspots and future development trends of the therapeutic effects of microRNA on PNI axonal regeneration through bibliometric methods. Moreover, the current advantages and disadvantages of this field as well as future development prospects are discussed in depth.

Methods

CiteSpace V and VOSviewer were used as bibliometric tools to complete the analysis of the research focus and direction of the published articles. To supplement, sort out, and summarize, we analyzed the research status of the study on the application of microRNAs for axonal regeneration after peripheral nerve injury from 2013 to 2023.

Results

A total of 207 publications were retrieved from the Web of Science database. After exclusion and screening, a final selection of 174 articles that met the research criteria. These 174 articles were authored by a total of 846 individuals, representing 24 countries and 199 institutions. Additionally, this study presents information on the annual publication output, country distribution, top 5 contributing authors, top 5 most cited articles, and top 10 contributing institutions.

Conclusion

As one of the hottest topics today, microRNAs have become the current research hotspot in neural inflammation, neural cell repair and regeneration, neural protection, and functional recovery. With more investment in research in this field, more high-quality articles will be published in both domestic and international outstanding journals, which will bring a new era for the treatment of peripheral nerve injury.

Enhancing regeneration and repair of long-distance peripheral nerve defect injuries with continuous microcurrent electrical nerve stimulation

Introduction

Peripheral nerve injuries, especially those involving long-distance deficits, pose significant challenges in clinical repair. This study explores the potential of continuous microcurrent electrical nerve stimulation (cMENS) as an adjunctive strategy to promote regeneration and repair in such cases.

Methods

The study initially optimized cMENS parameters and assessed its impact on Schwann cell activity, neurotrophic factor secretion, and the nerve regeneration microenvironment. Subsequently, a rat sciatic nerve defect-bridge repair model was employed to evaluate the reparative effects of cMENS as an adjuvant treatment. Functional recovery was assessed through gait analysis, motor function tests, and nerve conduction assessments. Additionally, nerve regeneration and denervated muscle atrophy were observed through histological examination.

Results

The study identified a 10-day regimen of 100uA microcurrent stimulation as optimal. Evaluation focused on Schwann cell activity and the microenvironment, revealing the positive impact of cMENS on maintaining denervated Schwann cell proliferation and enhancing neurotrophic factor secretion. In the rat model of sciatic nerve defect-bridge repair, cMENS demonstrated superior effects compared to control groups, promoting motor function recovery, nerve conduction, and sensory and motor neuron regeneration. Histological examinations revealed enhanced maturation of regenerated nerve fibers and reduced denervated muscle atrophy.

Discussion

While cMENS shows promise as an adjuvant treatment for long-distance nerve defects, future research should explore extended stimulation durations and potential synergies with tissue engineering grafts to improve outcomes. This study contributes comprehensive evidence supporting the efficacy of cMENS in enhancing peripheral nerve regeneration.

Techniques and graft materials for repairing peripheral nerve defects

Peripheral nerve defects refer to damage or destruction occurring in the peripheral nervous system, typically affecting the limbs and face. The current primary approaches to address peripheral nerve defects involve the utilization of autologous nerve transplants or the transplantation of artificial material. Nevertheless, these methods possess certain limitations, such as inadequate availability of donor nerve or unsatisfactory regenerative outcomes post-transplantation. Biomaterials have been extensively studied as an alternative approach to promote the repair of peripheral neve defects. These biomaterials include both natural and synthetic materials. Natural materials consist of collagen, chitosan, and silk, while synthetic materials consist of polyurethane, polylactic acid, and polycaprolactone. Recently, several new neural repair technologies have also been developed, such as nerve regeneration bridging technology, electrical stimulation technology, and stem cell therapy technology. Overall, biomaterials and new neural repair technologies provide new methods and opportunities for repairing peripheral nerve defects. However, these methods still require further research and development to enhance their effectiveness and feasibility.

Brief Electrical Stimulation Promotes Recovery after Surgical Repair of Injured Peripheral Nerves

Injured peripheral nerves regenerate their axons in contrast to those in the central nervous system. Yet, functional recovery after surgical repair is often disappointing. The basis for poor recovery is progressive deterioration with time and distance of the growth capacity of the neurons that lose their contact with targets (chronic axotomy) and the growth support of the chronically denervated Schwann cells (SC) in the distal nerve stumps. Nonetheless, chronically denervated atrophic muscle retains the capacity for reinnervation. Declining electrical activity of motoneurons accompanies the progressive fall in axotomized neuronal and denervated SC expression of regeneration-associated-genes and declining regenerative success. Reduced motoneuronal activity is due to the withdrawal of synaptic contacts from the soma. Exogenous neurotrophic factors that promote nerve regeneration can replace the endogenous factors whose expression declines with time. But the profuse axonal outgrowth they provoke and the difficulties in their delivery hinder their efficacy. Brief (1 h) low-frequency (20 Hz) electrical stimulation (ES) proximal to the injury site promotes the expression of endogenous growth factors and, in turn, dramatically accelerates axon outgrowth and target reinnervation. The latter ES effect has been demonstrated in both rats and humans. A conditioning ES of intact nerve days prior to nerve injury increases axonal outgrowth and regeneration rate. Thereby, this form of ES is amenable for nerve transfer surgeries and end-to-side neurorrhaphies. However, additional surgery for applying the required electrodes may be a hurdle. ES is applicable in all surgeries with excellent outcomes.

Progress in methods for evaluating Schwann cell myelination and axonal growth in peripheral nerve regeneration via scaffolds

Peripheral nerve injury (PNI) is a neurological disorder caused by trauma that is frequently induced by accidents, war, and surgical complications, which is of global significance. The severity of the injury determines the potential for lifelong disability in patients. Artificial nerve scaffolds have been investigated as a powerful tool for promoting optimal regeneration of nerve defects. Over the past few decades, bionic scaffolds have been successfully developed to provide guidance and biological cues to facilitate Schwann cell myelination and orientated axonal growth. Numerous assessment techniques have been employed to investigate the therapeutic efficacy of nerve scaffolds in promoting the growth of Schwann cells and axons upon the bioactivities of distinct scaffolds, which have encouraged a greater understanding of the biological mechanisms involved in peripheral nerve development and regeneration. However, it is still difficult to compare the results from different labs due to the diversity of protocols and the availability of innovative technologies when evaluating the effectiveness of novel artificial scaffolds. Meanwhile, due to the complicated process of peripheral nerve regeneration, several evaluation methods are usually combined in studies on peripheral nerve repair. Herein, we have provided an overview of the evaluation methods used to study the outcomes of scaffold-based therapies for PNI in experimental animal models and especially focus on Schwann cell functions and axonal growth within the regenerated nerve.

Assessment, patient selection, and rehabilitation of nerve transfers

Peripheral nerve injuries are common and can have a devastating effect on physical, psychological, and socioeconomic wellbeing. Peripheral nerve transfers have become the standard of care for many types of peripheral nerve injury due to their superior outcomes relative to conventional techniques. As the indications for, and use of, nerve transfers expand, the importance of pre-operative assessment and post-operative optimization increases. There are two principal advantages of nerve transfers: (1) their ability to shorten the time to reinnervation of muscles undergoing denervation because of peripheral nerve injury; and (2) their specificity in ensuring proximal motor and sensory axons are directed towards appropriate motor and sensory targets. Compared to conventional nerve grafting, nerve transfers offer opportunities to reinnervate muscles affected by cervical spinal cord injury and to augment natural reinnervation potential for very proximal injuries. This article provides a narrative review of the current scientific knowledge and clinical understanding of nerve transfers including peripheral nerve injury assessment and pre- and post-operative electrodiagnostic testing, adjuvant therapies, and post-operative rehabilitation for optimizing nerve transfer outcomes.

Role of Long Non-coding RNA in Nerve Regeneration

Nerve injury can be caused by a variety of factors. It often takes a long time to repair a nerve injury and severe nerve injury is even difficult to heal. Therefore, increasing attention has focused on nerve injury and repair. Long non-coding RNA (lncRNA) is a newly discovered non-coding RNA with a wide range of biological activities. Numerous studies have shown that a variety of lncRNAs undergo changes in expression after nerve injury, indicating that lncRNAs may be involved in various biological processes of nerve repair and regeneration. Herein, we summarize the biological roles of lncRNAs in neurons, glial cells and other cells during nerve injury and regeneration, which will help lncRNAs to be better applied in nerve injury and regeneration in the future.

The Dynamics of Nerve Degeneration and Regeneration in a Healthy Milieu and in Diabetes

Appropriate animal models, mimicking conditions of both health and disease, are needed to understand not only the biology and the physiology of neurons and other cells under normal conditions but also under stress conditions, like nerve injuries and neuropathy. In such conditions, understanding how genes and different factors are activated through the well-orchestrated programs in neurons and other related cells is crucial. Knowledge about key players associated with nerve regeneration intended for axonal outgrowth, migration of Schwann cells with respect to suitable substrates, invasion of macrophages, appropriate conditioning of extracellular matrix, activation of fibroblasts, formation of endothelial cells and blood vessels, and activation of other players in healthy and diabetic conditions is relevant. Appropriate physical and chemical attractions and repulsions are needed for an optimal and directed regeneration and are investigated in various nerve injury and repair/reconstruction models using healthy and diabetic rat models with relevant blood glucose levels. Understanding dynamic processes constantly occurring in neuropathies, like diabetic neuropathy, with concomitant degeneration and regeneration, requires advanced technology and bioinformatics for an integrated view of the behavior of different cell types based on genomics, transcriptomics, proteomics, and imaging at different visualization levels. Single-cell-transcriptional profile analysis of different cells may reveal any heterogeneity among key players in peripheral nerves in health and disease.

Functional Electrical Stimulation in Conjunction With Proprioceptive Neuromuscular Facilitation (PNF) Technique to Improve Upper Limb Function in Traumatic Brachial Plexus Injury: A Case Report

Traumatic brachial plexus injuries (TBPIs) in the adult population are primarily a result of road traffic accidents or falls on a shoulder, which mainly affects the young population. Adult TBPI is a serious incapacitating injury that affects young adults. It decreases the function of upper extremity muscles, which affects social participation and quality of life. Physiotherapy intervention demonstrates its effectiveness in enhancing and maintaining the function of the upper extremity, eventually decreasing the participation restriction and improving quality of life. The proprioceptive neuromuscular facilitation (PNF) technique has been selected as a useful therapeutic option to enhance upper limb function after TBPI. The preceding case report proved the effectiveness of six weeks of functional electrical stimulation in addition to the PNF technique in improving upper limb function after TBPI.

Stem Cell Scaffolds for the Treatment of Spinal Cord Injury-A Review

Spinal cord injury (SCI) is a profoundly debilitating yet common central nervous system condition resulting in significant morbidity and mortality rates. Major causes of SCI encompass traumatic incidences such as motor vehicle accidents, falls, and sports injuries. Present treatment strategies for SCI aim to improve and enhance neurologic functionality. The ability for neural stem cells (NSCs) to differentiate into diverse neural and glial cell precursors has stimulated the investigation of stem cell scaffolds as potential therapeutics for SCI. Various scaffolding modalities including composite materials, natural polymers, synthetic polymers, and hydrogels have been explored. However, most trials remain largely in the preclinical stage, emphasizing the need to further develop and refine these treatment strategies before clinical implementation. In this review, we delve into the physiological processes that underpin NSC differentiation, including substrates and signaling pathways required for axonal regrowth post-injury, and provide an overview of current and emerging stem cell scaffolding platforms for SCI.

Effect of Metformin on the Functional and Electrophysiological Recovery of Crush Injury-Induced Facial Nerve Paralysis in Diabetic Rats

The impact of metformin on the rat facial nerve following crush injury has only occasionally been documented to date. The purpose of the current investigation was to use functional and electrophysiological evaluations to investigate the effects of metformin administration on recovery following crush injury to the rat facial nerve. The rats were randomly divided into four groups: the nonDM/PBS group (n = 4), the nonDM/metformin group (n = 4), the DM/PBS group (n = 4), and the DM/metformin group (n = 4). Diabetes was generated by an intraperitoneal injection of streptozotocin. Facial nerve paralysis was induced by a crush injury 7 days after diabetes induction. The blood glucose levels of the DM/PBS and DM/metformin groups were maintained at over 300 mg/dL, whereas the blood glucose levels of the nonDM/PBS and nonDM/metformin groups were maintained at less than 150 mg/dL. There was no significant difference between the two nonDM groups. In comparison to the PBS group, the metformin group's recurrence of vibrissa fibrillation occurred noticeably sooner over time. The nonDM/metformin group showed the highest recovery rate in the second, third, and fourth weeks post-crush, respectively. The threshold of action potential 4 weeks after crush injury showed that the nonDM/metformin group had a significantly lower mean threshold of MAP compared to other groups. The short-term effect of metformin on the recovery of facial nerve blood flow (FNBF) was significantly increased compared to the DM/PBS group. However, there was no significant difference in FNBF between the nonDM/metformin and nonDM/PBS groups. A diabetic condition promoted a delay in FN regeneration. Metformin is able to accelerate functional recovery in diabetic or nondiabetic FN-injured rats. Further studies using a morphometric or molecular approach are planned to understand the pharmacologic mechanism of metformin.

The effectiveness of photobiomodulation therapy on inferior alveolar nerve injury: A systematic review and META-analysis

OBJECTIVE

The aim of this META-analysis was to evaluate the efficacy of photobiomodulation (PBM) therapy in the treatment of inferior alveolar nerve (IAN) injury due to orthognathic surgeries, extraction of impacted third molars and mandibular fractures.

METHODS AND MATERIALS

A electric search was conducted by a combination of manual search and four electric databases including Pubmed, Embase, Cochrane library and Web of Science, with no limitation on language and publication date. Gray literature was searched in ClinicalTrials.gov and googlescholar. All retrieved articles were imported into ENDNOTE software (version X9) and screened by two independent reviewers. All analysis was performed using the REVMAN software (version 5.3).

RESULTS

Finally, 15 randomized controlled trials met the inclusion criteria for qualitative analysis and 14 for META-analysis from 219 articles. The results showed that PBM therapy had no effect on nerve injury in a short period of time (0-48h, 14 days), but had significant effect over 30 days. However, the effect of photobiomodulation therapy on thermal discrimination was still controversial, most authors supported no significant improvement. By calculating the effective rate of PBM, it was found that there was no significant difference in the onset time of treatment, whether within or over 6 months.

CONCLUSIONS

The results of this META-analysis show that PBM therapy is effective in the treatment of IAN injures no matter it begins early or later. However, due to the limited number of well-designed RCTs and small number of patients in each study, it would be necessary to conduct randomized controlled trials with large sample size, long follow-up time and more standardized treatment and evaluation methods in the future to provide more accurate and clinically meaningful results.