Electric field stimulation induced neuronal differentiation of filum terminale derived neural progenitor cells

Bioelectronics for electrical stimulation: materials, devices and biomedical applications

Bioelectronics is a hot research topic, yet an important tool, as it facilitates the creation of advanced medical devices that interact with biological systems to effectively diagnose, monitor and treat a broad spectrum of health conditions. Electrical stimulation (ES) is a pivotal technique in bioelectronics, offering a precise, non-pharmacological means to modulate and control biological processes across molecular, cellular, tissue, and organ levels. This method holds the potential to restore or enhance physiological functions compromised by diseases or injuries by integrating sophisticated electrical signals, device interfaces, and designs tailored to specific biological mechanisms. This review explains the mechanisms by which ES influences cellular behaviors, introduces the essential stimulation principles, discusses the performance requirements for optimal ES systems, and highlights the representative applications. From this review, we can realize the potential of ES based bioelectronics in therapy, regenerative medicine and rehabilitation engineering technologies, ranging from tissue engineering to neurological technologies, and the modulation of cardiovascular and cognitive functions. This review underscores the versatility of ES in various biomedical contexts and emphasizes the need to adapt to complex biological and clinical landscapes it addresses.

Agarose disk electroporation method for ex vivo retinal tissue cultured at the air-liquid interface reveals electrical stimulus-induced cell cycle reentry in retinal cells

It is advantageous to culture the ex vivo murine retina along with many other tissue types at the air-liquid interface. However, gene delivery to these cultures can be challenging. Electroporation is a fast and robust method of gene delivery, but typically requires submergence in a liquid buffer to allow electric current flow. We have developed a submergence-free electroporation technique using an agarose disk that allows for efficient gene delivery to the ex vivo murine retina. This method advances our ability to use ex vivo retinal tissue for genetic studies and can easily be adapted for any tissue cultured at an air-liquid interface. We found an increased ability to transfected Muller glia at 14 days ex vivo and an increase in BrdU incorporation in Muller glia following electrical stimulation. Use of this method has revealed valuable insights on the state of ex vivo retinal tissues and the effects of electrical stimulation on retinal cells.

bHLH transcription factors Hes1, Ascl1 and Oligo2 exhibit different expression patterns in the process of physiological electric fields-induced neuronal differentiation

BACKGROUND

Recent studies have shown that the expression of bHLH transcription factors Hes1, Ascl1, and Oligo2 has an oscillating balance in neural stem cells (NSCs) to maintain their self-proliferation and multi-directional differentiation potential. This balance can be disrupted by exogenous stimulation. Our previous work has identified that electrical stimulation could induce neuronal differentiation of mouse NSCs.

METHODS

To further evaluate if physiological electric fields (EFs)-induced neuronal differentiation is related to the expression patterns of bHLH transcription factors Hes1, Ascl1, and Oligo2, mouse embryonic brain NSCs were used to investigate the expression changes of Ascl1, Hes1 and Oligo2 in mRNA and protein levels during EF-induced neuronal differentiation.

RESULTS

Our results showed that NSCs expressed high level of Hes1, while expression of Ascl1 and Oligo2 stayed at very low levels. When NSCs exited proliferation, the expression of Hes1 in differentiated cells began to decrease and oscillated at the low expression level. Oligo2 showed irregular changes in low expression level. EF-stimulation significantly increased the expression of Ascl1 at mRNA and protein levels accompanied by an increased percentage of neuronal differentiation. What's more, over-expression of Hes1 inhibited the neuronal differentiation induced by EFs.

CONCLUSION

EF-stimulation directed neuronal differentiation of NSCs by promoting the continuous accumulation of Ascl1 expression and decreasing the expression of Hes1.

A novel ex vivo assay to define charge-balanced electrical stimulation parameters for neural precursor cell activation in vivo

Endogenous neural stem cells and their progeny (together termed neural precursor cells (NPCs)) are promising candidates to facilitate neuroregeneration. Charge-balanced biphasic monopolar stimulation (BPMP) is a clinically relevant approach that can activate NPCs both in vitro and in vivo. Herein, we established a novel ex vivo stimulation system to optimize the efficacy of BPMP electric field (EF) application in activating endogenous NPCs. Using the ex vivo system, we discerned that cathodal amplitude of 200 μA resulted in the greatest NPC pool expansion and enhanced cathodal migration. Application of the same stimulation parameters in vivo resulted in the same NPC activation in the mouse brain. The design and implementation of the novel ex vivo model bridges the gap between in vitro and in vivo systems, enabling a moderate throughput stimulation system to explore and optimize EF parameters that can be applied to clinically relevant brain injury/disease models.

A Strategy for Magnetic and Electric Stimulation to Enhance Proliferation and Differentiation of NPCs Seeded over PLA Electrospun Membranes

Neural progenitor cells (NPCs) have been shown to serve as an efficient therapeutic strategy in different cell therapy approaches, including spinal cord injury treatment. Despite the reported beneficial effects of NPC transplantation, the low survival and differentiation rates constrain important limitations. Herein, a new methodology has been developed to overcome both limitations by applying a combination of wireless electrical and magnetic stimulation to NPCs seeded on aligned poly(lactic acid) nanofibrous scaffolds for in vitro cell conditioning prior transplantation. Two stimulation patterns were tested and compared, continuous (long stimulus applied once a day) and intermittent (short stimulus applied three times a day). The results show that applied continuous stimulation promotes NPC proliferation and preferential differentiation into oligodendrocytic and neuronal lineages. A neural-like phenotypic induction was observed when compared to unstimulated NPCs. In contrast, intermittent stimulation patterns did not affect NPC proliferation and differentiation to oligodendrocytes or astrocytes morphology with a detrimental effect on neuronal differentiation. This study provides a new approach of using a combination of electric and magnetic stimulation to induce proliferation and further neuronal differentiation, which would improve therapy outcomes in disorders such as spinal cord injury.

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.

Engineering Tissues of the Central Nervous System: Interfacing Conductive Biomaterials with Neural Stem/Progenitor Cells

Conductive biomaterials provide an important control for engineering neural tissues, where electrical stimulation can potentially direct neural stem/progenitor cell (NS/PC) maturation into functional neuronal networks. It is anticipated that stem cell-based therapies to repair damaged central nervous system (CNS) tissues and ex vivo, "tissue chip" models of the CNS and its pathologies will each benefit from the development of biocompatible, biodegradable, and conductive biomaterials. Here, technological advances in conductive biomaterials are reviewed over the past two decades that may facilitate the development of engineered tissues with integrated physiological and electrical functionalities. First, one briefly introduces NS/PCs of the CNS. Then, the significance of incorporating microenvironmental cues, to which NS/PCs are naturally programmed to respond, into biomaterial scaffolds is discussed with a focus on electrical cues. Next, practical design considerations for conductive biomaterials are discussed followed by a review of studies evaluating how conductive biomaterials can be engineered to control NS/PC behavior by mimicking specific functionalities in the CNS microenvironment. Finally, steps researchers can take to move NS/PC-interfacing, conductive materials closer to clinical translation are discussed.

Physiological Electric Field: A Potential Construction Regulator of Human Brain Organoids

Brain organoids can reproduce the regional three-dimensional (3D) tissue structure of human brains, following the in vivo developmental trajectory at the cellular level; therefore, they are considered to present one of the best brain simulation model systems. By briefly summarizing the latest research concerning brain organoid construction methods, the basic principles, and challenges, this review intends to identify the potential role of the physiological electric field (EF) in the construction of brain organoids because of its important regulatory function in neurogenesis. EFs could initiate neural tissue formation, inducing the neuronal differentiation of NSCs, both of which capabilities make it an important element of the in vitro construction of brain organoids. More importantly, by adjusting the stimulation protocol and special/temporal distributions of EFs, neural organoids might be created following a predesigned 3D framework, particularly a specific neural network, because this promotes the orderly growth of neural processes, coordinate neuronal migration and maturation, and stimulate synapse and myelin sheath formation. Thus, the application of EF for constructing brain organoids in a3D matrix could be a promising future direction in neural tissue engineering.

Electrochemically differentiated human MSCs biosensing platform for quantification of nestin and β-III tubulin as whole-cell system

Polydimethylsiloxane (PDMS) on ITO substrate was used to create a well with conducting surface to adhere human mesenchymal stem cells (hMSCs) and provide electrochemical stimulation for inducing their differentiation into neural-like cells. The cells that received electrochemical stimulation did not show any noticeable change in their viability and proliferation. The cell morphology of the differentiated hMSCs adherent on ITO showed outgrowth and elongation in one dimension, resembling neural-like cells. Immunocytochemistry assessment by quantifying the expression of nestin and β-III tubulin also confirmed the differentiation of hMSCs. These differentiated hMSCs adherent on ITO were used as electrochemical biosensing platform for differential pulse voltammetry (DPV) measurement for selectively quantifying cell surface markers expressed by neural stem cells and mature neurons. The variation of nestin antibodies concentrations from 9 μU to 27 μU showed a linear increase in DPV current with a detection sensitivity of ∼28 nA/μU of antibody. Varying concentrations of β-III tubulin antibodies from 30 μU to 210 μU showed a linear increase in DPV current with a detection sensitivity of ∼2.0 nA/μU of antibody. The highest expression level of cell surface marker corresponding to β-III tubulin in total adherent cells on ITO was calculated. It was in the order of 10^-8 U of antibodies/cell, representing the total population of mature neuron cells. This new way of detection may rapidly assess the quantitative expression of cell surface markers/antigens.

Cochlear implant-based electric-acoustic stimulation modulates neural stem cell-derived neural regeneration

Cochlear implantation is considered to be the best therapeutic method for profound sensorineural hearing loss, but insufficient numbers of functional spiral ganglion neurons hinder the clinical effects of cochlear implantation. Stem cell transplantation has the potential to provide novel strategies for spiral ganglion neuron regeneration after injury. However, some obstacles still need to be overcome, such as low survival and uncontrolled differentiation. Several novel technologies show promise for modulating neural stem cell behaviors to address these issues. Here, a device capable of electrical stimulation was designed by combining a cochlear implant with a graphene substrate. Neural stem cells (NSCs) were cultured on the graphene substrate and subjected to electrical stimulation transduced from sound waves detected by the cochlear implant. Cell behaviors were studied, and this device showed good biocompatibility for NSCs. More importantly, electric-acoustic stimulation with higher frequencies and amplitudes induced NSC death and apoptosis, and electric-acoustic stimulation could promote NSCs to proliferate and differentiate into neurons only when low-frequency stimulation was supplied. The present study provides experimental evidence for understanding the regulatory role of electric-acoustic stimulation on NSCs and highlights the potentials of the above-mentioned device in stem cell therapy for hearing loss treatment.

Electric field stimulation for tissue engineering applications

Electric fields are involved in numerous physiological processes, including directional embryonic development and wound healing following injury. To study these processes in vitro and/or to harness electric field stimulation as a biophysical environmental cue for organised tissue engineering strategies various electric field stimulation systems have been developed. These systems are overall similar in design and have been shown to influence morphology, orientation, migration and phenotype of several different cell types. This review discusses different electric field stimulation setups and their effect on cell response.

Theoretical analysis of the electrochemical systems used for the application of direct current/voltage stimuli on cell cultures

Endogenous electric fields drive many essential functions relating to cell proliferation, motion, differentiation and tissue development. They are usually mimicked in vitro by using electrochemical systems to apply direct current or voltage stimuli to cell cultures. The many studies devoted to this topic have given rise to a wide variety of experimental systems, whose results are often difficult to compare. Here, these systems are analysed from an electrochemical standpoint to help harmonize protocols and facilitate optimal understanding of the data produced. The theoretical analysis of single-electrode systems shows the necessity of measuring the Nernst potential of the electrode and of discussing the results on this basis rather than using the value of the potential gradient. The paper then emphasizes the great complexity that can arise when high cell voltage is applied to a single electrode, because of the possible occurrence of anode and cathode sites. An analysis of two-electrode systems leads to the advice to change experimental practices by applying current instead of voltage. It also suggests that the values of electric fields reported so far may have been considerably overestimated in macro-sized devices. It would consequently be wise to revisit this area by testing considerably lower electric field values.

Electrical stimulation as a novel tool for regulating cell behavior in tissue engineering

Recently, electrical stimulation as a physical stimulus draws lots of attention. It shows great potential in disease treatment, wound healing, and mechanism study because of significant experimental performance. Electrical stimulation can activate many intracellular signaling pathways, and influence intracellular microenvironment, as a result, affect cell migration, cell proliferation, and cell differentiation. Electrical stimulation is using in tissue engineering as a novel type of tool in regeneration medicine. Besides, with the advantages of biocompatible conductive materials coming into view, the combination of electrical stimulation with suitable tissue engineered scaffolds can well combine the benefits of both and is ideal for the field of regenerative medicine. In this review, we summarize the various materials and latest technologies to deliver electrical stimulation. The influences of electrical stimulation on cell alignment, migration and its underlying mechanisms are discussed. Then the effect of electrical stimulation on cell proliferation and differentiation are also discussed.

Electrical stimulation affects neural stem cell fate and function in vitro

Electrical stimulation (ES) has been applied in cell culture system to enhance neural stem cell (NSC) proliferation, neuronal differentiation, migration, and integration. According to the mechanism of its function, ES can be classified into induced electrical (EFs) and electromagnetic fields (EMFs). EFs guide axonal growth and induce directional cell migration, whereas EMFs promote neurogenesis and facilitates NSCs to differentiate into functional neurons. Conductive nanomaterials have been used as functional scaffolds to provide mechanical support and biophysical cues in guiding neural cell growth and differentiation and building complex neural tissue patterns. Nanomaterials may have a combined effect of topographical and electrical cues on NSC migration and differentiation. Electrical cues may promote NSC neurogenesis via specific ion channel activation, such as SCN1α and CACNA1C. To accelerate the future application of ES in preclinical research, we summarized the specific setting, such as current frequency, intensity, and stimulation duration used in various ES devices, as well as the nanomaterials involved, in this review with the possible mechanisms elucidated. This review can be used as a checklist for ES work in stem cell research to enhance the translational process of NSCs in clinical application.

Ascl1 Regulates Electric Field-Induced Neuronal Differentiation Through PI3K/Akt Pathway

Directing differentiation of neural stem/progenitor cells (NSCs/NPCs) to produce functional neurons is one of the greatest challenges in regenerative medicine. Our previous paper has confirmed that electrical stimulation has a high efficiency of triggering neuronal differentiation by using isolated filum terminale (FT)-derived NPCs. To further clarify the intrinsic molecular mechanisms, protein-protein interaction (PPI) network analysis was applied to pinpoints novel hubs in electric field (EF)-induced neuronal differentiation. In this study, siRNA transfection of Achaete-scute homolog 1 (Ascl1) in NPCs or NPCs was followed by direct current stimulation at 150 mV/mm. Neuronal differentiation rate and protein expression level were analyzed after 7 or 14 days of electrical stimulation. The data showed that the expression level of Ascl1 was enhanced by electrical stimulation and positively correlated to EF strength. Moreover, we identified that the expression of Ascl1 positively regulated neuronal differentiation of NPCs and can be up-regulated by EF-stimulation through the activation of phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway. Therefore, this study provides new insights into the role of Ascl1 and its relevant PI3K/Akt pathway in regulating of EF-induced neuronal differentiation and pointed out that continuous expression of Ascl1 in NPCs is required for EF-induced neuronal differentiation.

Potential Application of Electrical Stimulation in Stem Cell-Based Treatment against Hearing Loss

Deafness is a common human disease, which is mainly caused by irreversible damage to hair cells and spiral ganglion neurons (SGNs) in the mammalian cochlea. At present, replacement of damaged or missing hair cells and SGNs by stem cell transplantation therapy is an effective treatment. However, the survival rate of stem cell transplantation is low, with uncontrollable differentiation hindering its application. Most researchers have focused on biochemical factors to regulate the growth and differentiation of stem cells, whereas little study has been performed using physical factors. This review intends to illustrate the current problems in stem cell-based treatment against deafness and to introduce electric field stimulation as a physical factor to regulate stem cell behavior and facilitate stem cell therapy to treat hearing loss in the future.