A review of oscillating field stimulation to treat human spinal cord injury

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.

State of the Art and Current Challenges on Electroactive Biomaterials and Strategies for Neural Tissue Regeneration

The loss or failure of an organ/tissue stands as one of the healthcare system's most prevalent, devastating, and costly challenges. Strategies for neural tissue repair and regeneration have received significant attention due to their particularly strong impact on patients' well-being. Many research efforts are dedicated not only to control the disease symptoms but also to find solutions to repair the damaged tissues. Neural tissue engineering (TE) plays a key role in addressing this problem and significant efforts are being carried out to develop strategies for neural repair treatment. In the last years, active materials allowing to tune cell-materials interaction are being increasingly used, representing a recent paradigm in TE applications. Among the most important stimuli influencing cell behavior are the electrical and mechanical ones. In this way, materials with the ability to provide this kind of stimuli to the neural cells seem to be appropriate to support neural TE. In this scope, this review summarizes the different biomaterials types used for neural TE, highlighting the relevance of using active biomaterials and electrical stimulation. Furthermore, this review provides not only a compilation of the most relevant studies and results but also strategies for novel and more biomimetic approaches for neural TE.

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.

Light Stimulation of Neurons on Organic Photocapacitors Induces Action Potentials with Millisecond Precision

Nongenetic optical control of neurons is a powerful technique to study and manipulate the function of the nervous system. This research has benchmarked the performance of organic electrolytic photocapacitor (OEPC) optoelectronic stimulators at the level of single mammalian cells: human embryonic kidney (HEK) cells with heterologously expressed voltage-gated K+ channels and hippocampal primary neurons. OEPCs act as extracellular stimulation electrodes driven by deep red light. The electrophysiological recordings show that millisecond light stimulation of OEPC shifts conductance-voltage plots of voltage-gated K+ channels by ≈30 mV. Models are described both for understanding the experimental findings at the level of K+ channel kinetics in HEK cells, as well as elucidating interpretation of membrane electrophysiology obtained during stimulation with an electrically floating extracellular photoelectrode. A time-dependent increase in voltage-gated channel conductivity in response to OEPC stimulation is demonstrated. These findings are then carried on to cultured primary hippocampal neurons. It is found that millisecond time-scale optical stimuli trigger repetitive action potentials in these neurons. The findings demonstrate that OEPC devices enable the manipulation of neuronal signaling activities with millisecond precision. OEPCs can therefore be integrated into novel in vitro electrophysiology protocols, and the findings can inspire in vivo applications.

Management of Acute Traumatic Spinal Cord Injury: A Review of the Literature

Traumatic spinal cord injury (TSCI) is a debilitating disease that poses significant functional and economic burden on both the individual and societal levels. Prognosis is dependent on the extent of the spinal injury and the severity of neurological dysfunction. If not treated rapidly, patients with TSCI can suffer further secondary damage and experience escalating disability and complications. It is important to quickly assess the patient to identify the location and severity of injury to make a decision to pursue a surgical and/or conservative management. However, there are many conditions that factor into the management of TSCI patients, ranging from the initial presentation of the patient to long-term care for optimal recovery. Here, we provide a comprehensive review of the etiologies of spinal cord injury and the complications that may arise, and present an algorithm to aid in the management of TSCI.

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.

Electrotaxis-on-Chip to Quantify Neutrophil Migration Towards Electrochemical Gradients

Electric fields are generated in vivo in a variety of physiologic and pathologic settings, including wound healing and immune response to injuries to epithelial barriers (e.g. lung pneumocytes). Immune cells are known to migrate towards both chemical (chemotaxis), physical (mechanotaxis) and electric stimuli (electrotaxis). Electrotaxis is the guided migration of cells along electric fields, and has previously been reported in T-cells and cancer cells. However, there remains a need for engineering tools with high spatial and temporal resolution to quantify EF guided migration. Here we report the development of an electrotaxis-on-chip (ETOC) platform that enables the quantification of dHL-60 cell, a model neutrophil-like cell line, migration toward both electrical and chemoattractant gradients. Neutrophils are the most abundant white blood cells and set the stage for the magnitude of the immune response. Therefore, developing engineering tools to direct neutrophil migration patterns has applications in both infectious disease and inflammatory disorders. The ETOC developed in this study has embedded electrodes and four migration zones connected to a central cell-loading chamber with migration channels [10 µm X 10 µm]. This device enables both parallel and competing chemoattractant and electric fields. We use our novel ETOC platform to investigate dHL-60 cell migration in three biologically relevant conditions: 1) in a DC electric field; 2) parallel chemical gradient and electric fields; and 3) perpendicular chemical gradient and electric field. In this study we used differentiated leukemia cancer cells (dHL60 cells), an accepted model for human peripheral blood neutrophils. We first quantified effects of electric field intensities (0.4V/cm-1V/cm) on dHL-60 cell electrotaxis. Our results show optimal migration at 0.6 V/cm. In the second scenario, we tested whether it was possible to increase dHL-60 cell migration to a bacterial signal [N-formylated peptides (fMLP)] by adding a parallel electric field. Our results show that there was significant increase (6-fold increase) in dHL60 migration toward fMLP and cathode of DC electric field (0.6V/cm, n=4, p-value<0.005) vs. fMLP alone. Finally, we evaluated whether we could decrease or re-direct dHL-60 cell migration away from an inflammatory signal [leukotriene B4 (LTB4)]. The perpendicular electric field significantly decreased migration (2.9-fold decrease) of dHL60s toward LTB4vs. LTB4 alone. Our microfluidic device enabled us to quantify single-cell electrotaxis velocity (7.9 µm/min ± 3.6). The magnitude and direction of the electric field can be more precisely and quickly changed than most other guidance cues such as chemical cues in clinical investigation. A better understanding of EF guided cell migration will enable the development of new EF-based treatments to precisely direct immune cell migration for wound care, infection, and other inflammatory disorders.

Electrophysiological Outcome Measures in Spinal Cord Injury Clinical Trials: A Systematic Review

Background: Electrophysiological measures are being increasingly utilized due to their ability to provide objective measurements with minimal bias and to detect subtle changes with quantitative data on neural function. Heterogeneous reporting of trial outcomes limits effective interstudy comparison and optimization of treatment. Objective: The objective of this systematic review is to describe the reporting of electrophysiological outcome measures in spinal cord injury (SCI) clinical trials in order to inform a subsequent consensus study. Methods: A systematic search of PubMed and EMBASE databases was conducted according to PRISMA guidelines. Adult human SCI clinical trials published in English between January 1, 2008 and September 15, 2018 with at least one electrophysiological outcome measure were eligible. Findings were reviewed by all authors to create a synthesis narrative describing each outcome measure. Results: Sixty-four SCI clinical trials were included in this review. Identified electrophysiological outcomes included electromyography activity (44%), motor evoked potentials (33%), somatosensory evoked potentials (33%), H-reflex (20%), reflex electromyography activity (11%), nerve conduction studies (9%), silent period (3%), contact heat evoked potentials (2%), and sympathetic skin response (2%). Heterogeneity was present in regard to both methods of measurement and reporting of electrophysiological outcome measures. Conclusion: This review demonstrates need for the development of a standardized reporting set for electrophysiological outcome measures. Limitations of this review include exclusion of non-English publications, studies more than 10 years old, and an inability to assess methodological quality of primary studies due to a lack of guidelines on reporting of systematic reviews of outcome measures.

P3HT:Bebq2-Based Photovoltaic Device Enhances Differentiation of hiPSC-Derived Retinal Ganglion Cells

Electric field stimulation is known to affect various cellular processes, including cell fate specification and differentiation, particularly towards neuronal lineages. This makes it a promising therapeutic strategy to stimulate regeneration of neuronal tissues. Retinal ganglion cells (RGCs) is a type of neural cells of the retina responsible for transduction of visual signals from the retina to the brain cortex, and is often degenerated in various blindness-causing retinal diseases. The organic photovoltaic materials such as poly-3-hexylthiophene (P3HT) can generate electric current upon illumination with light of the visible spectrum, and possesses several advantageous properties, including light weight, flexibility and high biocompatibility, which makes them a highly promising tool for electric stimulation of cells in vitro and in vivo. In this study, we tested the ability to generate photocurrent by several formulations of blend (bulk heterojunction) of P3HT (which is electron donor material) with several electron acceptor materials, including Alq3 and bis(10-hydroxybenzo[h]quinolinato)beryllium (Bebq2). We found that the photovoltaic device based on bulk heterojunction of P3HT with Bebq2 could generate photocurrent when illuminated by both green laser and visible spectrum light. We tested the growth and differentiation capacity of human induced pluripotent stem cells (hiPSC)-derived RGCs when grown in interface with such photostimulated device, and found that they were significantly increased. The application of P3HT:Bebq2-formulation of photovoltaic device has a great potential for developments in retinal transplantation, nerve repair and tissue engineering approaches of treatment of retinal degeneration.

Epidural oscillating field stimulation as an effective therapeutic approach in combination therapy for spinal cord injury

BACKGROUND

Traumatic spinal cord injury (SCI) causes partial or total loss of sensory and motor functions. Despite enormous efforts, there is still no effective treatment which might improve patients' neurological status.The application of electric current to the injured spinal cord is known to promote healing and tissue regeneration. The use of this modality in treating the injured spinal cord to improve neurological recovery has been introduced as a potential treatment.

NEW METHOD

Here we describe the method of epidural implantation of a miniature oscillating field (OF) stimulator designed in our laboratory immediately after Th9 spinal compression in Wistar rats. Three groups of animals were analyzed (intact; SCI only; OFS + SCI; n = 8 each). Histological, immunohistological and behavioral analysis were used to show the favorable effect of epidural OF stimulation on axonal regeneration and modulation of astrogliosis.

RESULTS

Our study revealed considerable differences in white matter integrity in animals with an implanted OF stimulator. Moreover, we detected significantly increased numbers of neurofilaments and massive reduction in activated forms of astrocytes in the group of stimulated animals compared to the animals without stimulation.

COMPARISON WITH EXISTING METHOD(S)

Compared with previous research, our study revealed that epidural implantation of an OF stimulator immediately after spinal compression effectively reduced the expression of inflammatory response and suppressed activated astrocyte formation.

CONCLUSIONS

Our finding confirms that implanting an OF stimulator is safe, stable and suitable for future combined therapy which could effectively promote and accelerate regeneration and functional restoration after spinal trauma.

The Role of Direct Current Electric Field-Guided Stem Cell Migration in Neural Regeneration

Effective directional axonal growth and neural cell migration are crucial in the neural regeneration of the central nervous system (CNS). Endogenous currents have been detected in many developing nervous systems. Experiments have demonstrated that applied direct current (DC) electric fields (EFs) can guide axonal growth in vitro, and attempts have been made to enhance the regrowth of damaged spinal cord axons using DC EFs in in vivo experiments. Recent work has revealed that the migration of stem cells and stem cell-derived neural cells can be guided by DC EFs. These studies have raised the possibility that endogenous and applied DC EFs can be used to direct neural tissue regeneration. Although the mechanism of EF-directed axonal growth and cell migration has not been fully understood, studies have shown that the polarization of cell membrane proteins and the activation of intracellular signaling molecules are involved in the process. The application of EFs is a promising biotechnology for regeneration of the CNS.

Nature's Electric Potential: A Systematic Review of the Role of Bioelectricity in Wound Healing and Regenerative Processes in Animals, Humans, and Plants

Natural endogenous voltage gradients not only predict and correlate with growth and development but also drive wound healing and regeneration processes. This review summarizes the existing literature for the nature, sources, and transmission of information-bearing bioelectric signals involved in controlling wound healing and regeneration in animals, humans, and plants. It emerges that some bioelectric characteristics occur ubiquitously in a range of animal and plant species. However, the limits of similarities are probed to give a realistic assessment of future areas to be explored. Major gaps remain in our knowledge of the mechanistic basis for these processes, on which regenerative therapies ultimately depend. In relation to this, it is concluded that the mapping of voltage patterns and the processes generating them is a promising future research focus, to probe three aspects: the role of wound/regeneration currents in relation to morphology; the role of endogenous flux changes in driving wound healing and regeneration; and the mapping of patterns in organisms of extreme longevity, in contrast with the aberrant voltage patterns underlying impaired healing, to inform interventions aimed at restoring them.

Bioelectric Medicine and Devices for the Treatment of Spinal Cord Injury

Recovery of motor control is paramount for patients living with paralysis following spinal cord injury (SCI). While a cure or regenerative intervention remains on the horizon for the treatment of SCI, a number of neuroprosthetic devices have been employed to treat and mitigate the symptoms of paralysis associated with injuries to the spinal column and associated comorbidities. The recent success of epidural stimulation to restore voluntary motor function in the lower limbs of a small cohort of patients has breathed new life into the promise of electric-based medicine. Recently, a number of new organic and inorganic electronic devices have been developed for brain-computer interfaces to bypass the injury, for neurorehabilitation, bladder and bowel control, and the restoration of motor or sensory control. Herein, we discuss the recent advances in neuroprosthetic devices for treating SCI and highlight future design needs for closed-loop device systems.

Electrical stimuli in the central nervous system microenvironment

Electrical stimulation to manipulate the central nervous system (CNS) has been applied as early as the 1750s to produce visual sensations of light. Deep brain stimulation (DBS), cochlear implants, visual prosthetics, and functional electrical stimulation (FES) are being applied in the clinic to treat a wide array of neurological diseases, disorders, and injuries. This review describes the history of electrical stimulation of the CNS microenvironment; recent advances in electrical stimulation of the CNS, including DBS to treat essential tremor, Parkinson's disease, and depression; FES for the treatment of spinal cord injuries; and alternative electrical devices to restore vision and hearing via neuroprosthetics (retinal and cochlear implants). It also discusses the role of electrical cues during development and following injury and, importantly, manipulation of these endogenous cues to support regeneration of neural tissue.

Collective migration exhibits greater sensitivity but slower dynamics of alignment to applied electric fields

During development and disease, cells migrate collectively in response to gradients in physical, chemical and electrical cues. Despite its physiological significance and potential therapeutic applications, electrotactic collective cell movement is relatively less well understood. Here, we analyze the combined effect of intercellular interactions and electric fields on the directional migration of non-transformed mammary epithelial cells, MCF-10A. Our data show that clustered cells exhibit greater sensitivity to applied electric fields but align more slowly than isolated cells. Clustered cells achieve half-maximal directedness with an electric field that is 50% weaker than that required by isolated cells; however, clustered cells take ∼2-4 fold longer to align. This trade-off in greater sensitivity and slower dynamics correlates with the slower speed and intrinsic directedness of collective movement even in the absence of an electric field. Whereas isolated cells exhibit a persistent random walk, the trajectories of clustered cells are more ballistic as evidenced by the superlinear dependence of their mean square displacement on time. Thus, intrinsically-directed, slower clustered cells take longer to redirect and align with an electric field. These findings help to define the operating space and the engineering trade-offs for using electric fields to affect cell movement in biomedical applications.