Weak direct current (DC) electric fields as a therapy for spinal cord injuries: review and advancement of the oscillating field stimulator (OFS)

Advances in Material-Assisted Electromagnetic Neural Stimulation

Bioelectricity plays a crucial role in organisms, being closely connected to neural activity and physiological processes. Disruptions in the nervous system can lead to chaotic ionic currents at the injured site, causing disturbances in the local cellular microenvironment, impairing biological pathways, and resulting in a loss of neural functions. Electromagnetic stimulation has the ability to generate internal currents, which can be utilized to counter tissue damage and aid in the restoration of movement in paralyzed limbs. By incorporating implanted materials, electromagnetic stimulation can be targeted more accurately, thereby significantly improving the effectiveness and safety of such interventions. Currently, there have been significant advancements in the development of numerous promising electromagnetic stimulation strategies with diverse materials. This review provides a comprehensive summary of the fundamental theories, neural stimulation modulating materials, material application strategies, and pre-clinical therapeutic effects associated with electromagnetic stimulation for neural repair. It offers a thorough analysis of current techniques that employ materials to enhance electromagnetic stimulation, as well as potential therapeutic strategies for future applications.

Axon-like aligned conductive CNT/GelMA hydrogel fibers combined with electrical stimulation for spinal cord injury recovery

Rehabilitation and regenerative medicine are two promising approaches for spinal cord injury (SCI) recovery, but their combination has been limited. Conductive biomaterials could bridge regenerative scaffolds with electrical stimulation by inducing axon regeneration and supporting physiological electrical signal transmission. Here, we developed aligned conductive hydrogel fibers by incorporating carbon nanotubes (CNTs) into methacrylate acylated gelatin (GelMA) hydrogel via rotating liquid bath electrospinning. The electrospun CNT/GelMA hydrogel fibers mimicked the micro-scale aligned structure, conductivity, and soft mechanical properties of neural axons. For in vitro studies, CNT/GelMA hydrogel fibers supported PC12 cell proliferation and aligned adhesion, which was enhanced by electrical stimulation (ES). Similarly, the combination of aligned CNT/GelMA hydrogel fibers and ES promoted neuronal differentiation and axon-like neurite sprouting in neural stem cells (NSCs). Furthermore, CNT/GelMA hydrogel fibers were transplanted into a T9 transection rat spinal cord injury model for in vivo studies. The results showed that the incorporating CNTs could remain at the injury site with the GelMA fibers biodegraded and improve the conductivity of regenerative tissue. The aligned structure of the hydrogel could induce the neural fibers regeneration, and the ES enhanced the remyelination and axonal regeneration. Behavioral assessments and electrophysiological results suggest that the combination of aligned CNT/GelMA hydrogel fibers and ES could significantly restore motor function in rats. This study demonstrates that conductive aligned CNT/GelMA hydrogel fibers can not only induce neural regeneration as a scaffold but also support ESto promote spinal cord injury recovery. The conductive hydrogel fibers enable merging regenerative medicine and rehabilitation, showing great potential for satisfactory locomotor recovery after SCI.

Efficacy of growth factor gene-modified stem cells for motor function after spinal cord injury in rodents: a systematic review and meta‑analysis

The efficacy of growth factor gene-modified stem cells in treating spinal cord injury (SCI) remains unclear. This study aims to evaluate the effectiveness of growth factor gene-modified stem cells in restoring motor function after SCI. Two reviewers searched four databases, including PubMed, Embase, Web of Science, and Scopus, to identify relevant records. Studies on rodents assessing the efficacy of transplanting growth factor gene-modified stem cells in restoring motor function after SCI were included. The results were reported using the standardized mean difference (SMD) with a 95% confidence interval (95% CI). Analyses showed that growth factor gene-modified stem cell transplantation improved motor function recovery in rodents with SCI compared to the untreated (SMD = 3.98, 95% CI 3.26-4.70, I2 = 86.8%, P < 0.0001) and stem cell (SMD = 2.53, 95% CI 1.93-3.13, I2 = 86.9%, P < 0.0001) groups. Using growth factor gene-modified neural stem/histone cells enhanced treatment efficacy. In addition, the effectiveness increased when viral vectors were employed for gene modification and high transplantation doses were administered during the subacute phase. Stem cells derived from the human umbilical cord exhibited an advantage in motor function recovery. However, the transplantation of growth factor gene-modified stem cells did not significantly improve motor function in male rodents (P = 0.136). Transplantation of growth factor gene-modified stem cells improved motor function in rodents after SCI, but claims of enhanced efficacy should be approached with caution. The safety of gene modification remains a significant concern, requiring additional efforts to enhance its clinical translatability.

Electroacupuncture Relieves HuR/KLF9-Mediated Inflammation to Enhance Neurological Repair after Spinal Cord Injury

Electroacupuncture (EA) is widely applied in clinical therapy for spinal cord injury (SCI). However, the associated molecular mechanism has yet to be elucidated. The current study aimed to investigate the underlying mechanism of EA in neurologic repair after SCI. First, we investigated the role of EA in the neurologic repair of the SCI rat model. The expression levels of human antigen R (HuR) and Krüppel-like factor 9 (KLF9) in spinal cord tissues were quantified after treatment. Second, we conducted bioinformatics analysis, RNA pull-down assays, RNA immunoprecipitation, and luciferase reporter gene assay to verify the binding of HuR and KLF9 mRNA for mRNA stability. Last, HuR inhibitor CMLD-2 was used to verify the enhanced effect of EA on neurologic repair after SCI via the HuR/KLF9 axis. Our data provided convincing evidence that EA facilitated the recovery of neuronal function in SCI rats by reducing apoptosis and inflammation of neurons. We found that EA significantly diminished the SCI-mediated upregulation of HuR, and HuR could bind to the 3' untranslated region of KLF9 mRNA to protect its decay. In addition, a series of in vivo experiments confirmed that CMLD-2 administration increased EA-mediated pain thresholds and motor function in SCI rats. Collectively, the present study showed that EA improved pain thresholds and motor function in SCI rats via impairment of HuR-mediated KLF9 mRNA stabilization, thus providing a better understanding of the regulatory mechanisms regarding EA-mediated neurologic repair after SCI.

Generation of direct current electrical fields as regenerative therapy for spinal cord injury: A review

Electrical stimulation (ES) shows promise as a therapy to promote recovery and regeneration after spinal cord injury. ES therapy establishes beneficial electric fields (EFs) and has been investigated in numerous studies, which date back nearly a century. In this review, we discuss the various engineering approaches available to generate regenerative EFs through direct current electrical stimulation and very low frequency electrical stimulation. We highlight the electrode-tissue interface, which is important for the appropriate choice of electrode material and stimulator circuitry. We discuss how to best estimate and control the generated field, which is an important measure for comparability of studies. Finally, we assess the methods used in these studies to measure functional recovery after the injury and treatment. This work reviews studies in the field of ES therapy with the goal of supporting decisions regarding best stimulation strategy and recovery assessment for future work.

Oscillating field stimulation promotes axon regeneration and locomotor recovery after spinal cord injury

Oscillating field stimulation (OFS) is a potential method for treating spinal cord injury. Although it has been used in spinal cord injury (SCI) therapy in basic and clinical studies, its underlying mechanism and the correlation between its duration and nerve injury repair remain poorly understood. In this study, we established rat models of spinal cord contusion at T10 and then administered 12 weeks of OFS. The results revealed that effectively promotes the recovery of motor function required continuous OFS for more than 6 weeks. The underlying mechanism may be related to the effects of OFS on promoting axon regeneration, inhibiting astrocyte proliferation, and improving the linear arrangement of astrocytes. This study was approved by the Animal Experiments and Experimental Animal Welfare Committee of Capital Medical University (supplemental approval No. AEEI-2021-204) on July 26, 2021.

SIROF stabilized PEDOT/PSS allows biocompatible and reversible direct current stimulation capable of driving electrotaxis in cells

Electrotaxis is a naturally occurring phenomenon in which ionic gradients dictate the directed migration of cells involved in different biological processes such as wound healing, embryonic development, or cancer metastasis. To investigate these processes, direct current (DC) has been used to generate electric fields capable of eliciting an electrotactic response in cells. However, the need for metallic electrodes to deliver said currents has hindered electrotaxis research and the application of DC stimulation as medical therapy. This study aimed to investigate the capability of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) on sputtered iridium oxide film (SIROF) electrodes to generate stable direct currents. The electrochemical properties of PEDOT/PSS allow ions to be released and reabsorbed depending on the polarity of the current flow. SIROF stabilized PEDOT/PSS electrodes demonstrated exceptional stability in voltage and current controlled DC stimulation for periods of up to 12 hours. These electrodes were capable of directing cell migration of the rat prostate cancer cell line MAT-LyLu in a microfluidic chamber without the need for chemical buffers. This material combination shows excellent promise for accelerating electrotaxis research and facilitating the translation of DC stimulation to medical applications thanks to its biocompatibility, ionic charge injection mechanisms, and recharging capabilities in a biological environment.