Controlling cell behavior electrically: current views and future potential

Influence of surface peripheral electrical stimulation on nerve regeneration after digital nerve neurorrhaphy: study protocol for a randomized clinical trial

We will study the influence of low intensity and frequency surface peripheral electrical stimulation (PES) on nerve regeneration of digital nerve injuries of the hand after its surgical repair in humans. Participants will be patients with acute traumatic peripheral nerve injury referred to the Hand Surgery Service of the General Hospital of the State of Bahia, a reference service in the state. These patients will undergo surgery followed by PES in the immediate postoperative period. After hospital discharge, they will be followed up on an outpatient basis by researchers, who will remotely supervise a physiotherapy program. Our hypothesis is that PES will positively influence the recovery of sensory function in patients undergoing neurorrhaphy of digital nerves of the hand.

ReBEC registration:  U1111-1259-1998 (12/18/2020)

Glial-Neuronal Interactions in Pathogenesis and Treatment of Spinal Cord Injury

Traumatic spinal cord injury (SCI) elicits an acute inflammatory response which comprises numerous cell populations. It is driven by the immediate response of macrophages and microglia, which triggers activation of genes responsible for the dysregulated microenvironment within the lesion site and in the spinal cord parenchyma immediately adjacent to the lesion. Recently published data indicate that microglia induces astrocyte activation and determines the fate of astrocytes. Conversely, astrocytes have the potency to trigger microglial activation and control their cellular functions. Here we review current information about the release of diverse signaling molecules (pro-inflammatory vs. anti-inflammatory) in individual cell phenotypes (microglia, astrocytes, blood inflammatory cells) in acute and subacute SCI stages, and how they contribute to delayed neuronal death in the surrounding spinal cord tissue which is spared and functional but reactive. In addition, temporal correlation in progressive degeneration of neurons and astrocytes and their functional interactions after SCI are discussed. Finally, the review highlights the time-dependent transformation of reactive microglia and astrocytes into their neuroprotective phenotypes (M2a, M2c and A2) which are crucial for spontaneous post-SCI locomotor recovery. We also provide suggestions on how to modulate the inflammation and discuss key therapeutic approaches leading to better functional outcome after SCI.

Conductive Biomaterials as Bioactive Wound Dressing for Wound Healing and Skin Tissue Engineering

Conductive biomaterials based on conductive polymers, carbon nanomaterials, or conductive inorganic nanomaterials demonstrate great potential in wound healing and skin tissue engineering, owing to the similar conductivity to human skin, good antioxidant and antibacterial activities, electrically controlled drug delivery, and photothermal effect. However, a review highlights the design and application of conductive biomaterials for wound healing and skin tissue engineering is lacking. In this review, the design and fabrication methods of conductive biomaterials with various structural forms including film, nanofiber, membrane, hydrogel, sponge, foam, and acellular dermal matrix for applications in wound healing and skin tissue engineering and the corresponding mechanism in promoting the healing process were summarized. The approaches that conductive biomaterials realize their great value in healing wounds via three main strategies (electrotherapy, wound dressing, and wound assessment) were reviewed. The application of conductive biomaterials as wound dressing when facing different wounds including acute wound and chronic wound (infected wound and diabetic wound) and for wound monitoring is discussed in detail. The challenges and perspectives in designing and developing multifunctional conductive biomaterials are proposed as well.

Electrical aspects of skin as a pathway to engineering skin devices

Skin is one of the indispensable organs for life. The epidermis at the outermost surface provides a permeability barrier to infectious agents, chemicals, and excessive loss of water, while the dermis and subcutaneous tissue mechanically support the structure of the skin and appendages, including hairs and secretory glands. The integrity of the integumentary system is a key for general health, and many techniques have been developed to measure and control this protective function. In contrast, the effective skin barrier is the major obstacle for transdermal delivery and detection. Changes in the electrical properties of skin, such as impedance and ionic activity, is a practical indicator that reflects the structures and functions of the skin. For example, the impedance that reflects the hydration of the skin is measured for quantitative assessment in skincare, and the current generated across a wound is used for the evaluation and control of wound healing. Furthermore, the electrically charged structure of the skin enables transdermal drug delivery and chemical extraction. This paper provides an overview of the electrical aspects of the skin and summarizes current advances in the development of devices based on these features.

Come together: On-chip bioelectric wound closure

There is a growing interest in bioelectric wound treatment and electrotaxis, the process by which cells detect an electric field and orient their migration along its direction, has emerged as a potential cornerstone of the endogenous wound healing response. Despite recognition of the importance of electrotaxis in wound healing, no experimental demonstration to date has shown that the actual closing of a wound can be accelerated solely by the electrotaxis response itself, and in vivo systems are too complex to resolve cell migration from other healing stages such as proliferation and inflammation. This uncertainty has led to a lack of standardization between stimulation methods, model systems, and electrode technology required for device development. In this paper, we present a 'healing-on-chip' approach that is a standardized, low-cost, model for investigating electrically accelerated wound healing. Our device provides a biomimetic convergent field geometry that more closely resembles actual wound fields. We validate this device by using electrical stimulation to close a 1.5 mm gap between two large (30 mm2) layers of primary skin keratinocyte to completely heal the gap twice as quickly as in an unstimulated tissue. This demonstration proves that convergent electrotaxis is both possible and can accelerate healing and offers an accessible 'healing-on-a-chip' platform to explore future bioelectric interfaces.

Development and Utilization of Multifunctional Polymeric Scaffolds for the Regulation of Physical Cellular Microenvironments

Polymeric biomaterials exhibit excellent physicochemical characteristics as a scaffold for cell and tissue engineering applications. Chemical modification of the polymers has been the primary mode of functionalization to enhance biocompatibility and regulate cellular behaviors such as cell adhesion, proliferation, differentiation, and maturation. Due to the complexity of the in vivo cellular microenvironments, however, chemical functionalization alone is usually insufficient to develop functionally mature cells/tissues. Therefore, the multifunctional polymeric scaffolds that enable electrical, mechanical, and/or magnetic stimulation to the cells, have gained research interest in the past decade. Such multifunctional scaffolds are often combined with exogenous stimuli to further enhance the tissue and cell behaviors by dynamically controlling the microenvironments of the cells. Significantly improved cell proliferation and differentiation, as well as tissue functionalities, are frequently observed by applying extrinsic physical stimuli on functional polymeric scaffold systems. In this regard, the present paper discusses the current state-of-the-art functionalized polymeric scaffolds, with an emphasis on electrospun fibers, that modulate the physical cell niche to direct cellular behaviors and subsequent functional tissue development. We will also highlight the incorporation of the extrinsic stimuli to augment or activate the functionalized polymeric scaffold system to dynamically stimulate the cells.

Direct Current Electrical Fields Improve Experimental Wound Healing by Activation of Cytokine Secretion and Erk1/2 Pathway Stimulation

There is growing evidence that cell behaviors can be influenced by the direct current electric fields (EFs). Some behaviors may influence wound healing directly. This study aimed to investigate the effects of EF (200 mV/mm) on immortalized nontumorigenic human epidermal (HaCaT) cells. We established a setup that can transmit an EF and maintain a stable cell culture environment. An EF was applied to HaCaT cells, and scratch-assays were performed as a model of wound healing to observe cell migration. Proliferation was evaluated by mitochondrial activity, total protein, and DNA content. Secretion of healing-associated cytokines was evaluated via cytokine arrays, and Western blot was applied to investigate signaling pathway alterations. Compared with the control group, the migration of cells exposed to EFs significantly increased (p < 0.01). After 7 days, the changes in proliferation also increased significantly (p < 0.05). The cytokine arrays revealed that granulocyte-macrophage colony-stimulating factor (GM-CSF) was the most abundant factor secreted by HaCaT following EF exposure. The signals for phospho-Erk1/2 showed a significant (p < 0.0001) increase following EF exposure. The results demonstrate that exposure of HaCaT cells to EFs has positive effects on migration, proliferation, and cytokine secretion—three important steps in wound healing—and these effects may be partially mediated by activation of the Erk1/2 signaling pathway.

Improving motor neuron-like cell differentiation of hEnSCs by the combination of epothilone B loaded PCL microspheres in optimized 3D collagen hydrogel

Spinal cord regeneration is limited due to various obstacles and complex pathophysiological events after injury. Combination therapy is one approach that recently garnered attention for spinal cord injury (SCI) recovery. A composite of three-dimensional (3D) collagen hydrogel containing epothilone B (EpoB)-loaded polycaprolactone (PCL) microspheres (2.5 ng/mg, 10 ng/mg, and 40 ng/mg EpoB/PCL) were fabricated and optimized to improve motor neuron (MN) differentiation efficacy of human endometrial stem cells (hEnSCs). The microspheres were characterized using liquid chromatography-mass/mass spectrometry (LC-mas/mas) to assess the drug release and scanning electron microscope (SEM) for morphological assessment. hEnSCs were isolated, then characterized by flow cytometry, and seeded on the optimized 3D composite. Based on cell morphology and proliferation, cross-linked collagen hydrogels with and without 2.5 ng/mg EpoB loaded PCL microspheres were selected as the optimized formulations to compare the effect of EpoB release on MN differentiation. After differentiation, the expression of MN markers was estimated by real-time PCR and immunofluorescence (IF). The collagen hydrogel containing the EpoB group had the highest HB9 and ISL-1 expression and the longest neurite elongation. Providing a 3D permissive environment with EpoB, significantly improves MN-like cell differentiation and maturation of hEnSCs and is a promising approach to replace lost neurons after SCI.

Cathodal Transcranial Direct Current Stimulation in Refractory Epilepsy: A Noninvasive Neuromodulation Therapy

SUMMARY

Epilepsy is a chronic disease of the brain that affects individuals of all ages and has a worldwide distribution. According to a 2006 World Health Organization report, 50 million people had epilepsy. Approximately 30% of people with epilepsy have refractory disease despite recent therapeutic developments. Consequently, new treatments are necessary. Transcranial direct current stimulation (tDCS) is a noninvasive method for cortical excitability modulation by subthreshold membrane depolarization or hyperpolarization (cathodal stimulation decreases cortical excitability, whereas anodal stimulation increases it), which has been shown to be safe, economical, and easy to use. The mechanism of action of tDCS is partially understood. Cathodal tDCS in vitro and in vivo animal studies have shown that direct current and cathodal tDCS can successfully induce suppression of epileptiform activity in EEG recordings. Cathodal tDCS has been used in heterogeneous clinical trials in pediatric and adult patients with refractory epilepsy and is well tolerated. A comprehensive review of the clinical trials based on their quality and biases shows evidence that cathodal tDCS in patients with epilepsy is potentially effective. However, additional randomized clinical trials are needed with other etiologies, special populations, additional concomitants therapies, long-term follow-up, and new parameters of stimulation.

Unveiling the morphogenetic code: A new path at the intersection of physical energies and chemical signaling

In this editorial, we discuss the remarkable role of physical energies in the control of cell signaling networks and in the specification of the architectural plan of both somatic and stem cells. In particular, we focus on the biological relevance of bioelectricity in the pattern control that orchestrates both developmental and regenerative pathways. To this end, the narrative starts from the dawn of the first studies on animal electricity, reconsidering the pioneer work of Harold Saxton Burr in the light of the current achievements. We finally discuss the most recent evidence showing that bioelectric signaling is an essential component of the informational processes that control pattern specification during embryogenesis, regeneration, or even malignant transformation. We conclude that there is now mounting evidence for the existence of a Morphogenetic Code, and that deciphering this code may lead to unprecedented opportunities for the development of novel paradigms of cure in regenerative and precision medicine.

Pulsed Electrical Stimulation Enhances Consistency of Directional Migration of Adipose-Derived Stem Cells

Electrical stimulation is a well-known strategy for regulating cell behavior, both in pathological and physiological processes such as wound healing, tissue regeneration, and embryonic development. Electrotaxis is the directional migration of cells toward the cathode or anode when subjected to electrical stimulation. In this study, we investigated the conditions for enhanced directional migration of electrically stimulated adipose-derived stem cells (ADSCs) during prolonged culture, using a customized agar-salt electrotaxis chamber. Exposure of ADSCs to a 1200 μA electric current for 3 h, followed by cessation of stimulation for 6 h and resumed stimulation for a further 3 h, increased directional cell migration toward the anode without inducing cell death. Moreover, Golgi polarization maintained the direction of polarity parallel to the direction of cell movement. Herein, we demonstrated that a pulsed electric current is sufficient to trigger directional migration of ADSCs in long-term culture while maintaining cell viability.

Migration of Human Renal Tubular Epithelial Cells in Response to Physiological Electric Signals

Restoration of proximal tubular cell integrity and function after ischemic injury involves cell migration and proliferation. Endogenous fields are present during embryonic development and wound healing. Electric field (EF)-induced effects on cell migration have been observed in many cell types. This study investigated the effect of physiological direct current EF (dc EF) on the motility of renal epithelial cells. Human renal tubular epithelial (HK-2) and human-derived renal epithelial (HEK-293) cells were exposed to dc EF at physiological magnitude. Cell images were recorded and analyzed using an image analyzer. Cell lysates were used to detect protein expression by western blot. Scratch wounds were created in monolayers of HK-2 cells, and wound areas of cells were measured in response to EF exposure. Cells migrated significantly faster in the presence of an EF and toward the cathode. Application of an EF led to activation of the Erk1/2, p38 MAPK, and Akt signaling pathways. Pharmacological inhibition of Erk1/2, p38 MAPK, and Akt impaired EF-induced migratory responses, such as motility rate and directedness. In addition, exposure of the monolayers to EF enhanced EF-induced HK-2 wound healing. Our results suggest that EFs augment the rate of single renal epithelium migration and induce cell cathodal migration through activation of Erk1/2, p38 MAPK, and Akt signaling. Moreover, exposure of the renal epithelium to EF facilitated closure of in vitro small wounds by enhancing cell migration.

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.

Microscopic Volta potential difference on metallic surface promotes the osteogenic differentiation and proliferation of human mesenchymal stem cells

Endogenous microscopic electric cues play an essential role in bone's remodeling and self-repair. Modulating the extracellular electrical environment, by means of external electric stimulation or changing surface potential of implants, was manifested to facilitate the osteointegration. The microscopic potential difference, originating from heterogeneous microstructures of materials, may mimic the endogenous electric signals to stimulate surrounding cells. In this study, the spark-plasma sintered Ti/Ta hybrid metal was fabricated and utilized to realize a surface microscopic potential difference at the same magnitude as endogenous potentials. Activated by the electric stimulation, the mesenchymal stem cells exhibited the anisotropic and polygonal cellular morphology on the Ti/Ta hybrid metal. The microscopic electric potential difference coordinated the cells proliferation on the subsequent days. Moreover, the results showed that the osteo-lineage differentiation on Ti/Ta hybrid metal were in vitro boosted over the control groups. Tailoring microstructures of material to obtain a reasonable electric microenvironment may be a necessary principle to achieve more favorable cell responses to implants, suggesting an extra degree of freedom in bone-repairing material design.

Electrified microglia: Impact of direct current stimulation on diverse properties of the most versatile brain cell

BACKGROUND

Transcranial direct current stimulation [(t)DCS], modulates cortical excitability and promotes neuroplasticity. Microglia has been identified to respond to electrical currents as well as neuronal activity, but its response to DCS is mostly unknown.

OBJECTIVE

This study addresses effects of DCS applied in vivo to the sensorimotor cortex on physiological microglia properties and neuron-microglia communication.

METHODS

Time lapse in vivo 2-photon microscopy in anaesthetized mice was timely coupled with DCS of the sensorimotor cortex to observe microglia dynamics on a population-based and single cell level. Neuron-microglia communication during DCS was investigated in mice with a functional knock out of the fractalkine receptor CX3CR1. Moreover, the role of voltage gated microglial channels and DCS effects on phagocytosis were studied.

RESULTS

DCS promoted several physiological microglia properties, depending on the glial activation state and stimulation intensity. On a single cell level, process motility was predominantly enhanced in ramified cells whereas horizontal soma movement and galvanotaxis was pronounced in reactive microglia. Blockage of voltage sensitive microglial channels suppressed DCS effects in vivo and in vitro. Microglial motility changes were partially driven by the fractalkine signaling pathway. Moreover, phagocytosis increased after DCS in vitro.

CONCLUSION

Microglia dynamics are rapidly influenced by DCS. This is the first in vivo demonstration of a direct effect of electrical currents on microglia and indirect effects potentially driven by neuronal activity via the fractalkine pathway.

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.

Electroactive Biomaterials and Systems for Cell Fate Determination and Tissue Regeneration: Design and Applications

During natural tissue regeneration, tissue microenvironment and stem cell niche including cell-cell interaction, soluble factors, and extracellular matrix (ECM) provide a train of biochemical and biophysical cues for modulation of cell behaviors and tissue functions. Design of functional biomaterials to mimic the tissue/cell microenvironment have great potentials for tissue regeneration applications. Recently, electroactive biomaterials have drawn increasing attentions not only as scaffolds for cell adhesion and structural support, but also as modulators to regulate cell/tissue behaviors and function, especially for electrically excitable cells and tissues. More importantly, electrostimulation can further modulate a myriad of biological processes, from cell cycle, migration, proliferation and differentiation to neural conduction, muscle contraction, embryogenesis, and tissue regeneration. In this review, endogenous bioelectricity and piezoelectricity are introduced. Then, design rationale of electroactive biomaterials is discussed for imitating dynamic cell microenvironment, as well as their mediated electrostimulation and the applying pathways. Recent advances in electroactive biomaterials are systematically overviewed for modulation of stem cell fate and tissue regeneration, mainly including nerve regeneration, bone tissue engineering, and cardiac tissue engineering. Finally, the significance for simulating the native tissue microenvironment is emphasized and the open challenges and future perspectives of electroactive biomaterials are concluded.

Accelerated Skin Wound Healing by Electrical Stimulation

When the integrity of the skin got damaged, an endogenous electric field will be generated in the wound and a series of physiological reactions will be initiated to close the wound. The existence of the endogenous electric field of the wound has a promoting effect on all stages of wound healing. For wounds that cannot heal on their own, the exogenous electric field can assist the treatment. In this review, the effects of exogenous electrical stimulation on wound healing, such as the inflammation phase, blood flow, cell proliferation and migration, and the wound scarring is overviewed. This article also reviews the new electrical stimulation methods that have emerged in recent years, such as small power supplies, nanogenerators (NGs), and other physical, chemical or biological strategies. These new electrical stimulation methods and devices are safe, low-cost, stable, and small in size. The challenge and perspective are discussed for the future trends of the electrical stimulation treatment in accelerating skin wound healing.

Electrical Stimulation and Conductive Polymers as a Powerful Toolbox for Tailoring Cell Behaviour in vitro

Electrical stimulation (ES) is a well-known method for guiding the behaviour of nerve cells in in vitro systems based on the response of these cells to an electric field. From this perspective, understanding how the electrochemical stimulus can be tuned for the design of a desired cell response is of great importance. Most biomedical studies propose the application of an electrical potential to cell culture arrays while examining the cell response regarding viability, morphology, and gene expression. Conversely, various studies failed to evaluate how the fine physicochemical properties of the materials used for cell culture influence the observed behaviours. Among the various materials used for culturing cells under ES, conductive polymers (CPs) are widely used either in pristine form or in addition to other polymers. CPs themselves do not possess the optimal surface for cell compatibility because of their hydrophobic nature, which leads to poor protein adhesion and, hence, poor bioactivity. Therefore, understanding how to tailor the chemical properties on the material surface will determine the obtention of improved ES platforms. Moreover, the structure of the material, either in a thin film or in porous electrospun scaffolds, also affects the biochemical response and needs to be considered. In this review, we examine how materials based on CPs influence cell behaviour under ES, and we compile the various ES setups and physicochemical properties that affect cell behaviour. This review concerns the culture of various cell types, such as neurons, fibroblasts, osteoblasts, and Schwann cells, and it also covers studies on stem cells prone to ES. To understand the mechanistic behaviour of these devices, we also examine studies presenting a more detailed biomolecular level of interaction. This review aims to guide the design of future ES setups regarding the influence of material properties and electrochemical conditions on the behaviour of in vitro cell studies.

Electrical stimulation for pain reduction in hard-to-heal wound healing

OBJECTIVE

Despite treatment advances over the past 30 years, the societal impact of hard-to-heal wounds is increasingly burdensome. An unresolved issue is wound pain, which can make many treatments, such as compression in venous leg ulcers, intolerable. The aim of this review is to present the evidence and stimulate thinking on the use of electrical stimulation devices as a treatment technology with the potential to reduce pain, improve adherence and thus hard-to-heal wound outcomes.

METHOD

A literature search was conducted for clinical studies up to August 2020 reporting the effects of electrical stimulation devices on wound pain. Devices evoking neuromuscular contraction or direct spinal cord stimulation were excluded.

RESULTS

A total of seven publications (three non-comparative and four randomised trials) were identified with four studies reporting a rapid (within 14 days) reduction in hard-to-heal wound pain. Electrical stimulation is more widely known for accelerated healing and is one of the most evidence-based technologies in wound management, supported by numerous in vitro molecular studies, five meta-analyses, six systematic reviews and 30 randomised controlled trials (RCTs). Despite this wealth of supportive evidence, electrical stimulation has not yet been adopted into everyday practice. Some features of electrical stimulation devices may have hampered adoption in the past.

CONCLUSION

As new, pocket-sized, portable devices allowing convenient patient treatment and better patient adherence become more widely available and studied in larger RCTs, the evidence to date suggests that electrical stimulation should be considered part of the treatment options to address the challenges of managing and treating painful hard-to-heal wounds.

Therapy of pancreatic cancer with alternating electric fields: Limitations of the method

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant tumor with a poor prognosis. More effective treatment options are urgently needed. The use of physical and weak alternating electric fields (TTFields) can inhibit cell division of PDAC carcinoma and is currently being investigated in clinical trials. Here, we analyzed this new physical treatment under non-ideal conditions such as may occur during patient treatment. Three established human PDAC cell lines BxPC-3, gemcitabine-resistant BxPC-3 (BxGem), AsPC-1, and a non-malignant primary pancreatic cell line CRL-4023 were treated with TTFields in vitro. MTT assays, electrical impedance measurement, cell staining with Annexin V/7AAD followed by FACS analysis, digital image analysis and immunohistochemistry were performed. Treatment with TTFields smaller than 0.7 V/cm and field lines in the direction of mitotic spindle orientation significantly inhibited proliferation of all PDAC cells at 150 kHz, but significantly increased viability of AsPC-1 cells at all frequencies between 100 kHz and 300 kHz and that of BxPC-3 and BxGem cells at 250 kHz. Apoptosis or necrosis were not induced. Non-malignant CRL-4023 cells were not affected at 150 kHz. TTFields damaged PDAC cell lines but even favored their viability at very weak field strength and unfavorable frequency or inadequate field direction.

Optic Nerve Regeneration: How Will We Get There?

BACKGROUND

Restoration of vision in patients blinded by advanced optic neuropathies requires technologies that can either 1) salvage damaged and prevent further degeneration of retinal ganglion cells (RGCs), or 2) replace lost RGCs.

EVIDENCE ACQUISITION

Review of scientific literature.

RESULTS

In this article, we discuss the different barriers to cell-replacement based strategies for optic nerve regeneration and provide an update regarding what progress that has been made to overcome them. We also provide an update on current stem cell-based therapies for optic nerve regeneration.

CONCLUSIONS

As neuro-regenerative and cell-transplantation based strategies for optic nerve regeneration continue to be refined, researchers and clinicians will need to work together to determine who will be a good candidate for such therapies.

Recycled algae-based carbon materials as electroconductive 3D printed skeletal muscle tissue engineering scaffolds

Skeletal muscle is an electrically and mechanically active tissue that contains highly oriented, densely packed myofibrils. The tissue has self-regeneration capacity upon injury, which is limited in the cases of volumetric muscle loss. Several regenerative therapies have been developed in order to enhance this capacity, as well as to structurally and mechanically support the defect site during regeneration. Among them, biomimetic approaches that recapitulate the native microenvironment of the tissue in terms of parallel-aligned structure and biophysical signals were shown to be effective. In this study, we have developed 3D printed aligned and electrically active scaffolds in which the electrical conductivity was provided by carbonaceous material (CM) derived from algae-based biomass. The synthesis of this conductive and functional CM consisted of eco-friendly synthesis procedure such as pre-carbonization and multi-walled carbon nanotube (MWCNT) catalysis. CM obtained from biomass via hydrothermal carbonization (CM-03) and its ash form (CM-03K) were doped within poly(ɛ-caprolactone) (PCL) matrix and 3D printed to form scaffolds with aligned fibers for structural biomimicry. Scaffolds were seeded with C2C12 mouse myoblasts and subjected to electrical stimulation during the in vitro culture. Enhanced myotube formation was observed in electroactive groups compared to their non-conductive counterparts and it was observed that myotube formation and myotube maturity were significantly increased for CM-03 group after electrical stimulation. The results have therefore showed that the CM obtained from macroalgae biomass is a promising novel source for the production of the electrically conductive scaffolds for skeletal muscle tissue engineering.

Electricity auto-generating skin patch promotes wound healing process by activation of mechanosensitive ion channels

Electricity constitutes a natural biophysical component that preserves tissue homeostasis and modulates many biological processes, including the repair of damaged tissues. Wound healing involves intricate cellular events, such as inflammation, angiogenesis, matrix synthesis, and epithelialization whereby multiple cell types sense the environmental cues to rebuild the structure and functions. Here, we report that electricity auto-generating glucose-responsive enzymatic-biofuel-cell (EBC) skin patch stimulates the wound healing process. Rat wounded-skin model and in vitro cell cultures showed that EBC accelerated wound healing by modulating inflammation while stimulating angiogenesis, fibroblast fuctionality and matrix synthesis. Of note, EBC-activated cellular bahaviors were linked to the signalings involved with calcium influx, which predominantly dependent on the mechanosensitive ion channels, primarily Piezo1. Inhibition of Piezo1-receptor impaired the EBC-induced key functions of both fibroblasts and endothelial cells in the wound healing. This study highlights the significant roles of electricity played in wound healing through activated mechanosensitive ion channels and the calcium influx, and suggests the possibility of the electricity auto-generating EBC-based skin patch for use as a wound healing device.

Understanding, engineering, and modulating the growth of neural networks: An interdisciplinary approach

A deeper understanding of the brain and its function remains one of the most significant scientific challenges. It not only is required to find cures for a plethora of brain-related diseases and injuries but also opens up possibilities for achieving technological wonders, such as brain-machine interface and highly energy-efficient computing devices. Central to the brain's function is its basic functioning unit (i.e., the neuron). There has been a tremendous effort to understand the underlying mechanisms of neuronal growth on both biochemical and biophysical levels. In the past decade, this increased understanding has led to the possibility of controlling and modulating neuronal growth in vitro through external chemical and physical methods. We provide a detailed overview of the most fundamental aspects of neuronal growth and discuss how researchers are using interdisciplinary ideas to engineer neuronal networks in vitro. We first discuss the biochemical and biophysical mechanisms of neuronal growth as we stress the fact that the biochemical or biophysical processes during neuronal growth are not independent of each other but, rather, are complementary. Next, we discuss how utilizing these fundamental mechanisms can enable control over neuronal growth for advanced neuroengineering and biomedical applications. At the end of this review, we discuss some of the open questions and our perspectives on the challenges and possibilities related to controlling and engineering the growth of neuronal networks, specifically in relation to the materials, substrates, model systems, modulation techniques, data science, and artificial intelligence.

Small Molecule-Protein Hybrid for Voltage Imaging via Quenching of Bioluminescence

We report a small-molecule enzyme pair for optical voltage sensing via quenching of bioluminescence. This quenching bioluminescent voltage indicator, or Q-BOLT, pairs the dark absorbing, voltage-sensitive dipicrylamine with membrane-localized bioluminescence from the luciferase NanoLuc (NLuc). As a result, bioluminescence is quenched through resonance energy transfer (QRET) as a function of membrane potential. Fusion of HaloTag to NLuc creates a two-acceptor bioluminescence resonance energy transfer (BRET) system when a tetramethylrhodamine (TMR) HaloTag ligand is ligated to HaloTag. In this mode, Q-BOLT is capable of providing direct visualization of changes in membrane potential in live cells via three distinct readouts: change in QRET, BRET, and the ratio between bioluminescence emission and BRET. Q-BOLT can provide up to a 29% change in bioluminescence (ΔBL/BL) and >100% ΔBRET/BRET per 100 mV change in HEK 293T cells, without the need for excitation light. In cardiac monolayers derived from human-induced pluripotent stem cells (hiPSCs), Q-BOLT readily reports on membrane potential oscillations. Q-BOLT is the first example of a hybrid small molecule-protein voltage indicator that does not require excitation light and may be useful in contexts where excitation light is limiting.

The design criteria and therapeutic strategy of functional scaffolds for spinal cord injury repair

Spinal cord injury (SCI) remains a therapeutic challenge in clinic. Current drug and cell therapeutics have obtained significant efficacy but are still in the early stages for complete neural and functional recovery. In the past few decades, functional scaffolds (FSs) have been rapidly developed to bridge the lesion and provide a framework for tissue regeneration in SCI repair. Moreover, a FS can act as an adjuvant for locally delivering drugs in the lesion with a designed drug release profile, and supplying a biomimetic environment for implanted cells. In this review, the design criteria of FSs for SCI treatment are summarized according to their biocompatibility, mechanical properties, morphology, architecture, and biodegradability. Subsequently, FSs designed for SCI repair in the scope of drug delivery, cell implantation and combination therapy are introduced, respectively. And how a FS promotes their therapeutic efficacy is analyzed. Finally, the challenges, perspectives, and potential of FSs for SCI treatment are discussed. Hopefully, this review may inspire the future development of potent FSs to facilitate SCI repair in clinic.

Optimizing microenvironment by integrating negative pressure and exogenous electric fields via a flexible porous conductive dressing to accelerate wound healing

Wound healing is a complex and sequential biological process that involves multiple stages. Current treatments for nonhealing or chronic wounds are unsatisfactory as they exert a single effect on one specific activity. Herein, we constructed a silver nanowire (AgNW)-based, three-dimensional (3D), porous foam dressing that is flexible and conductive. This conductive foam dressing was composed of AgNWs modified with a stable hydrophobic coating and porous polyurethane (PU), providing a skeleton to support the 3D conductive networks. The AgNWs-PU foam dressing exhibited favorable biocompatibility, outstanding electrical properties, excellent bending-compression durability, and long-term stability under wet conditions, making it suitable for wound treatment. Via the conductive foam dressing, negative pressure and exogenous wound directional electric fields (EFs) could be integrated for simultaneous implementation, and the artificial jointly constructed microenvironment promoted wound healing in a system. This novel "all-in-one" device presented intrinsic multifunctionality, including the drainage of pus and necrotic tissue, mitigation of inflammation, promotion of cell proliferation, direction of keratinocyte migration, and induction of angiogenesis. An immunohistochemical assay and western blot analysis illustrated that the angiogenesis and cell proliferation pathways in the tissue were significantly activated when this novel therapy was adopted. More importantly, the practical performance of this "all-in-one" device was demonstrated by assessment of full-thickness defect wounds in model pigs. Comparing the percentage of residual wound area after administration of traditional treatment (25.82 ± 3.52%) and the novel treatment (3.07 ± 1.23%) demonstrated the promising applications of this novel treatment in clinical wound healing.

Hydraulic and electric control of cell spheroids

We use a theoretical approach to examine the effect of a radial fluid flow or electric current on the growth and homeostasis of a cell spheroid. Such conditions may be generated by a drain of micrometric diameter. To perform this analysis, we describe the tissue as a continuum. We include active mechanical, electric, and hydraulic components in the tissue material properties. We consider a spherical geometry and study the effect of the drain on the dynamics of the cell aggregate. We show that a steady fluid flow or electric current imposed by the drain could be able to significantly change the spheroid long-time state. In particular, our work suggests that a growing spheroid can systematically be driven to a shrinking state if an appropriate external field is applied. Order-of-magnitude estimates suggest that such fields are of the order of the indigenous ones. Similarities and differences with the case of tumors and embryo development are briefly discussed.

A calcineurin-mediated scaling mechanism that controls a K+-leak channel to regulate morphogen and growth factor transcription

The increase in activity of the two-pore potassium-leak channel Kcnk5b maintains allometric juvenile growth of adult zebrafish appendages. However, it remains unknown how this channel maintains allometric growth and how its bioelectric activity is regulated to scale these anatomical structures. We show the activation of Kcnk5b is sufficient to activate several genes that are part of important development programs. We provide in vivo transplantation evidence that the activation of gene transcription is cell autonomous. We also show that Kcnk5b will induce the expression of different subsets of the tested developmental genes in different cultured mammalian cell lines, which may explain how one electrophysiological stimulus can coordinately regulate the allometric growth of diverse populations of cells in the fin that use different developmental signals. We also provide evidence that the post-translational modification of serine 345 in Kcnk5b by calcineurin regulates channel activity to scale the fin. Thus, we show how an endogenous bioelectric mechanism can be regulated to promote coordinated developmental signaling to generate and scale a vertebrate appendage.

Morphogenic fields: A coming of age

Morphogenesis, the coming-into-being of living organisms, was first described in the 4th century BC by Aristotle, progenitor of biology and embryology. Over the centuries it has been the subject of innumerable commentaries by philosophers, theologians and scientists but no consensus has ever been reached as to its causes. In the late 19th century, along with the emergence of cellular and molecular biology, embryology underwent a renaissance and became a topic of great interest and research. Early on the discipline divided into two opposing factions, those who attempted to explain fetal development on the basis of cellular and molecular mechanisms, and those who invoked the presence of organizing fields. The morphogenic field was first articulated in the early decades of the 20th century by multiple researchers independently of each other. The field became an extremely useful conceptual tool by which to explain a wide range of developmental phenomena. While embryology and genetics originally formed a unified discipline, during the 1930s  40 s geneticists became progressively skeptical of the field notion. The discovery of the DNA structure by Watson and Crick in the early 1950s decisively settled matters and thereafter the two disciplines pursued different lines of inquiry. After World War II embryology and the field concept went into a decades-long decline. By the 1980s an increasing number of scientists began to critically reexamine the morphogenic field concept and it underwent a second renaissance. In this paper I examine the development and evolution of the field concept, both experimentally and conceptually, and highlight the failure of genetic mechanisms to explain morphogenesis. I provide three instances from the medical literature of developmental phenomena which are only explainable on the basis of morphogenic field dynamics and argue that the field concept must be readmitted into mainstream scientific discourse.

Cardio-microcurrent device for chronic heart failure: first-in-human clinical study

AIMS

Most devices for treating ambulatory Class II and III heart failure are linked to electrical pulses. However, a steady electric potential gradient is also necessary for appropriate myocardial performance and may be disturbed by structural heart diseases. We investigated whether chronic application of electrical microcurrent to the heart is feasible and safe and improves cardiac performance. The results of this study should provide guidance for the design of a two-arm, randomized, controlled Phase II trial.

METHODS AND RESULTS

This single-arm, non-randomized pilot study involved 10 patients (9 men; mean age, 62 ± 12 years) at two sites with 6 month follow-up. All patients had New York Heart Association (NYHA) Class III heart failure and non-ischaemic dilated cardiomyopathy, with left ventricular ejection fraction (LVEF) <35%. A device was surgically placed to deliver a constant microcurrent to the heart. The following tests were performed at baseline, at hospital discharge, and at six time points during follow-up: determination of LVEF and left ventricular end-diastolic/end-systolic diameter by echocardiography; the 6 min walk test; and assessment of NYHA classification and quality of life (36-Item Short-Form Health Survey questionnaire). Microcurrent application was feasible and safe; no device-related or treatment-related adverse events occurred. During follow-up, rapid and significant signal of efficacy (P < 0.005) was present with improvements in LVEF, left ventricular end-diastolic diameter, left ventricular end-systolic diameter, and distance walked. For eight patients, NYHA classification improved from Class III to Class I (for seven, as early as 14 days post-operatively); for one, to Class II; and for one, to Class II/III. 36-Item Short-Form Health Survey questionnaire scores also improved highly significantly.

CONCLUSIONS

Chronic application of microcurrent to the heart is feasible and safe and leads to a rapid and lasting improvement in heart function and a near normalization of heart size within days. The NYHA classification and quality of life improve just as rapidly.

Biofuels from Micro-Organisms: Thermodynamic Considerations on the Role of Electrochemical Potential on Micro-Organisms Growth

Biofuels from micro-organisms represents a possible response to the carbon dioxide mitigation. One open problem is to improve their productivity, in terms of biofuels production. To do so, an improvement of the present model of growth and production is required. However, this implies an understanding of the growth spontaneous conditions of the bacteria. In this paper, a thermodynamic approach is developed in order to highlight the fundamental role of the electrochemical potential in bacteria proliferation. Temperature effect on the biosystem behaviour has been pointed out. The results link together the electrochemical potential, the membrane electric potential, the pH gradient through the membrane, and the temperature, with the result of improving the thermodynamic approaches, usually introduced in this topic of research.

Direct Current Electric Stimulation Alters the Frequency and the Distribution of Mitotic Cells in Planarians

Background: The use of direct current electric stimulation (DCS) is an effective strategy to treat disease and enhance body functionality. Thus, treatment with DCS is an attractive biomedical alternative, but the molecular underpinnings remain mostly unknown. The lack of experimental models to dissect the effects of DCS from molecular to organismal levels is an important caveat. Here, we introduce the planarian flatworm Schmidtea mediterranea as a tractable organism for in vivo studies of DCS. We developed an experimental method that facilitates the application of direct current electrical stimulation to the whole planarian body (pDCS). Materials and Methods: Planarian immobilization was achieved by combining treatment with anesthesia, agar embedding, and low temperature via a dedicated thermoelectric cooling unit. Electric currents for pDCS were delivered using pulled glass microelectrodes. The electric potential was supplied through a constant voltage power supply. pDCS was administered up to six hours, and behavioral and molecular effects were measured by using video recordings, immunohistochemistry, and gene expression analysis. Results: The behavioral immobilization effects are reversible, and pDCS resulted in a redistribution of mitotic cells along the mediolateral axis of the planarian body. The pDCS effects were dependent on the polarity of the electric field, which led to either increase in reductions in mitotic densities associated with the time of pDCS. The changes in mitotic cells were consistent with apparent redistribution in gene expression of the stem cell marker smedwi-1. Conclusion: The immobilization technique presented in this work facilitates studies aimed at dissecting the effects of exogenous electric stimulation in the adult body. Treatment with DCS can be administered for varying times, and the consequences evaluated at different levels, including animal behavior, cellular and transcriptional changes. Indeed, treatment with pDCS can alter cellular and transcriptional parameters depending on the polarity of the electric field and duration of the exposure.

Electric field-driven conformational changes in the elastin protein

The formation of aggregates and amyloids, a hallmark of many protein misfolding diseases, depends on many intrinsic and extrinsic factors. Many approaches (in vitro, in vivo, and in silico) have been attempted to inhibit the aggregation process so that the progression of these diseases can be controlled. We investigate the effect of a static electric field (EF; 120 V cm-1 and 200 V cm-1) on the conformational change of elastin protein using light scattering, spectroscopy, and microscopy techniques. Laser light scattering and photoluminescence spectroscopy show the formation of fibrils of unexposed elastin with aging, whereas disruption of fibril formation with EF exposed elastin. The size of EF exposed elastin first increases and exhibits an apex, and subsequently decreases with an increasing time of exposure. We observed that a decrease in the size of EF exposed elastin depends on the strength of the EF, faster decrement at higher EF. FTIR data show that EF modifies elastin protein's secondary structures; it facilitates the interconversion of β-sheets and turns into α-helix structures. The SEM images of unexposed and EF exposed elastin confirms the observation through light scattering and PL techniques. The effect of an EF on protein conformation and amyloids is promising to treat Parkinson's disease, a protein misfolding disease.

Neurobiological After-Effects of Low Intensity Transcranial Electric Stimulation of the Human Nervous System: From Basic Mechanisms to Metaplasticity

Non-invasive low-intensity transcranial electrical stimulation (tES) of the brain is an evolving field that has brought remarkable attention in the past few decades for its ability to directly modulate specific brain functions. Neurobiological after-effects of tES seems to be related to changes in neuronal and synaptic excitability and plasticity, however mechanisms are still far from being elucidated. We aim to review recent results from in vitro and in vivo studies that highlight molecular and cellular mechanisms of transcranial direct (tDCS) and alternating (tACS) current stimulation. Changes in membrane potential and neural synchronization explain the ongoing and short-lasting effects of tES, while changes induced in existing proteins and new protein synthesis is required for long-lasting plastic changes (LTP/LTD). Glial cells, for decades supporting elements, are now considered constitutive part of the synapse and might contribute to the mechanisms of synaptic plasticity. This review brings into focus the neurobiological mechanisms and after-effects of tDCS and tACS from in vitro and in vivo studies, in both animals and humans, highlighting possible pathways for the development of targeted therapeutic applications.

The role of topical timolol in wound healing and the treatment of vascular lesions: A narrative review

Beta-2 adrenergic receptors are the only subgroup of beta-adrenergic receptors expressed in the membrane of large cells, including skin keratinocytes, fibroblasts, and melanocytes. Alterations in the function or concentration of β2 adrenoreceptors related to keratinocytes are associated with some skin conditions. Some findings suggest the role of β2 adrenoreceptors in maintaining the function and integrity of the epidermis. Beta-receptor antagonists can be systemically and topically effective in healing hemangioma, paronychia, vasculitis ulcer, tufted angioma, acute and chronic wounds. Most studies with a strong design on this subject deal with the systemic form, but recently, numerous case and group reports and smaller studies have focused on topical forms, especially topical timolol. The present comprehensive review study surveys the role of topical timolol in acute and chronic wound healing in the field of dermatology.

Effects of electrical biostimulation and silver ions on porcine fibroblast cells

The medical applications of electrical biostimulation and silver ions have been evaluated in laboratory experiments and clinical studies for more than two decades. Their effects on preventing infection and promoting wound healing have been described. However, little is known about the role of electrical biostimulation and/or silver ion on changes in cellular transcriptome dynamics. To our knowledge, few studies have been conducted to investigate the potential of electrical biostimulation and silver ions in cell reprogramming. Besides, it is essential to assess any possible adverse effects or potential benefits of the silver ions on mammalian cells to address its safety concerns and to improve silver medical products. In this study, we investigated transcriptomic changes in porcine fibroblast cells in response to electrical biostimulation in the presence of silver ions. Exposed cells presented distinct morphological changes after treatment, which was mainly due to the exposure of silver ions rather than the electrical current itself. Gene expression analyses suggested that electrical biostimulation and silver ions did not increase the expression of pluripotency genes. Interestingly, a set of genes related to cellular metabolic processes were differentially expressed after cells were exposed to electrically generated silver ions for 21 hours. We found that 2.00 mg/L of electrically generated silver ion caused an increase of ATP generation and an increase of the total pool of NAD⁺ and NADH, while ROS production did not change. Aside from toxic effects, the results reported herein demonstrate the alternative effects of silver ions on mammalian cells, especially an oxidative phosphorylation burst. To our knowledge, this response of mammalian cells to silver ions has not been described previously. Although the function of this burst is not understood, it may lead to alterations in cellular activities such as metabolic remodeling and cell reprogramming, and/or serve an as-yet unknown function in neutralization or detoxification of the silver ions within the cells.

Proximity-induced electrodeformation and membrane capacitance coupling between cells

Membrane capacitance and transmembrane potential are sensitive to the proximity of neighboring biological cells which eventually induces anisotropic perturbation of the local electric field distribution in a cell assembly and/or a tissue. The development of robust and reliable multiphysics approaches is essential to solve the challenge of analyzing proximity-induced capacitance coupling (CC) between cells. In this study, we ask to what extent this CC is a minor perturbation on the individual cells or whether it can fundamentally affect bio-electromechanical cues. A key component of our continuum electromechanical analysis is the consideration of elastic models of cells under steady state electric field excitation to characterize electrodeformation (ED). Analyzing the difference between the ED force for a pair of cells and its counterpart for a single reference cell allows us to determine a separation distance-orientation angle diagram providing evidence of a separation distance beyond which the electrostatic interactions between a pair of biological cells become inconsequential for the ED. An attenuation-amplification transition of ED force in this diagram suggests that anisotropy induced by the orientation angle of the cell pair relative to the applied electric field direction has a significant influence on ED and CC. We furthermore observe that the shape of this diagram changes when extracellular conductivity is varied. The results obtained are then contrasted with the corresponding diagrams of similar cell configurations under an oscillating electric field excitation below and above the α-dispersion frequency. This investigation may provide new opportunities for further assessment of electromechanical properties of engineered tissues.

Advances in Engineering Human Tissue Models

Research in cell biology greatly relies on cell-based in vitro assays and models that facilitate the investigation and understanding of specific biological events and processes under different conditions. The quality of such experimental models and particularly the level at which they represent cell behavior in the native tissue, is of critical importance for our understanding of cell interactions within tissues and organs. Conventionally, in vitro models are based on experimental manipulation of mammalian cells, grown as monolayers on flat, two-dimensional (2D) substrates. Despite the amazing progress and discoveries achieved with flat biology models, our ability to translate biological insights has been limited, since the 2D environment does not reflect the physiological behavior of cells in real tissues. Advances in 3D cell biology and engineering have led to the development of a new generation of cell culture formats that can better recapitulate the in vivo microenvironment, allowing us to examine cells and their interactions in a more biomimetic context. Modern biomedical research has at its disposal novel technological approaches that promote development of more sophisticated and robust tissue engineering in vitro models, including scaffold- or hydrogel-based formats, organotypic cultures, and organs-on-chips. Even though such systems are necessarily simplified to capture a particular range of physiology, their ability to model specific processes of human biology is greatly valued for their potential to close the gap between conventional animal studies and human (patho-) physiology. Here, we review recent advances in 3D biomimetic cultures, focusing on the technological bricks available to develop more physiologically relevant in vitro models of human tissues. By highlighting applications and examples of several physiological and disease models, we identify the limitations and challenges which the field needs to address in order to more effectively incorporate synthetic biomimetic culture platforms into biomedical research.

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 enhances early palatal wound healing in mice

BACKGROUND/OBJECTIVE

Electrical stimulation (ES) has been used to treat chronic wound and other clinical applications, showing favorable results in wound closure. It was hypothesized that ES can present a positive effect on oral mucosa healing. The aim of this study was to investigate the effects of ES during the palatal mucosa early healing process in Swiss mice.

METHODS

Ninety animals were divided into two groups: Control (C; n = 45), which received Sham ES applications, and Test (ES; n = 45), which received ES (100 μA; 9 kHz; 660 mVpp) once a day for 3 days. A full thickness wound was performed with a 1.5 mm diameter biopsy punch in the hard palate. Histologically, the following parameters were evaluated: palatal wound closure and epithelial and connective wound edge distance (EED and CED). Furthermore, IL-1β, IL-6, IL-10 TNF-α, and VEGF cytokine levels were evaluated by multiplex assay. The percentage of collagen fibers was assessed using the polarization method and the Smad proteins using the immunofluorescence method.

RESULTS

Palatal wound closure presented a significant reduction on day 5 in the ES group (p = 0.01). Additionally, both EED and CED were shorter for all time points in the ES group (p < 0.05), and the inflammatory markers IL-6, IL-10, TNF-α, and VEGF were reduced (p < 0.05). There were no differences in collagen fibers and phospho-Smad2 between the groups.

CONCLUSION

ES had a positive effect on early palatal wound closure outcomes, as well as on inflammatory markers.

Electrical stimulation at nanoscale topography boosts neural stem cell neurogenesis through the enhancement of autophagy signaling

Neural stem cells (NSCs) transplantation at the injury site of central nerve system (CNS) makes it possible for neuroregeneration. Long-term cell survival and low proliferation, differentiation, and migration rates of NSCs-graft have been the most challenging aspect on NSCs application. New multichannel electrical stimulation (ES) device was designed to enhance neural stem cells (NSCs) differentiation into mature neurons. Compared to controls, ES at nanoscale topography enhanced the expression of mature neuronal marker, growth of the neurites, concentration of BDNF and electrophysiological activity. RNA sequencing analysis validated that ES promoted NSC-derived neuronal differentiation through enhancing autophagy signaling. Emerging evidences showed that insufficient or excessive autophagy contributes to neurite degeneration. Excessive ES current were able to enhance neuronal autophagy, the neuronal cells showed poor viability, reduced neurite outgrowth and electrophysiological activity. Well-controlled autophagy not only protects against neurodegeneration, but also regulates neurogenesis. Current NSC treatment protocol efficiently enhanced NSC differentiation, maturation and survival through combination of proper ES condition followed by balance of autophagy level in the cell culture system. The successful rate of such protreated NSC at injured CNS site should be significantly improved after transplantation.

Optimization of Electrical Stimulation for Safe and Effective Guidance of Human Cells

Direct current (DC) electrical stimulation has been shown to have remarkable effects on regulating cell behaviors. Translation of this technology to clinical uses, however, has to overcome several obstacles, including Joule heat production, changes in pH and ion concentration, and electrode products that are detrimental to cells. Application of DC voltages in thick tissues where their thickness is >0.8 mm caused significant changes in temperature, pH, and ion concentrations. In this study, we developed a multifield and -chamber electrotaxis chip, and various stimulation schemes to determine effective and safe stimulation strategies to guide the migration of human vascular endothelial cells. The electrotaxis chip with a chamber thickness of 1 mm allows 10 voltages applied in one experiment. DC electric fields caused detrimental effects on cells in a 1 mm chamber that mimicking 3D tissue with a decrease in cell migration speed and an increase in necrosis and apoptosis. Using the chip, we were able to select optimal stimulation schemes that were effective in guiding cells with minimal detrimental effects. This experimental system can be used to determine optimal electrical stimulation schemes for cell migration, survival with minimal detrimental effects on cells, which will facilitate to bring electrical stimulation for in vivo use.

Engineering an Injectable Electroactive Nanohybrid Hydrogel for Boosting Peripheral Nerve Growth and Myelination in Combination with Electrical Stimulation

Electrical stimulation (ES) can be used to manipulate recovery after peripheral nerve injuries. Although biomaterial-based strategies have already been implemented to gain momentum for ES and engineer permissive microenvironments for neural regeneration, the development of biomaterials for specific stimuli-responsive modulation of neural cell properties remains a challenge. Herein, we homogeneously incorporate pristine carbon nanotubes into a functional self-assembling peptide to prepare a hybrid hydrogel with good injectability and conductivity. Two-dimensional (on the surface) and three-dimensional (within the hybrid hydrogel) culturing experiments demonstrate that ES promotes axon outgrowth and Schwann cell (SC) migration away from dorsal root ganglia spheres, further revealing that ES-enhanced interactions between SCs and axons result in improved myelination. Thus, our study not only advances the development of tailor-made materials but also provides useful insights into comprehensive approaches for promoting nerve growth and presents a practical strategy of repairing peripheral nerve injuries.

Osmolarity-independent electrical cues guide rapid response to injury in zebrafish epidermis

The ability of epithelial tissues to heal after injury is essential for animal life, yet the mechanisms by which epithelial cells sense tissue damage are incompletely understood. In aquatic organisms such as zebrafish, osmotic shock following injury is believed to be an early and potent activator of a wound response. We find that, in addition to sensing osmolarity, basal skin cells in zebrafish larvae are also sensitive to changes in the particular ionic composition of their surroundings after wounding, specifically the concentration of sodium chloride in the immediate vicinity of the wound. This sodium chloride-specific wound detection mechanism is independent of cell swelling, and instead is suggestive of a mechanism by which cells sense changes in the transepithelial electrical potential generated by the transport of sodium and chloride ions across the skin. Consistent with this hypothesis, we show that electric fields directly applied within the skin are sufficient to initiate actin polarization and migration of basal cells in their native epithelial context in vivo, even overriding endogenous wound signaling. This suggests that, in order to mount a robust wound response, skin cells respond to both osmotic and electrical perturbations arising from tissue injury.

Long-Range Charge Reorganization as an Allosteric Control Signal in Proteins

A new mechanism of allostery in proteins, based on charge rather than structure, is reported. We demonstrate that dynamic redistribution of charge within a protein can control its function and affect its interaction with a binding partner. In particular, the association of an antibody with its target protein antigen is studied. Dynamic charge shifting within the antibody during its interaction with the antigen is enabled by its binding to a metallic surface that serves as a source for electrons. The kinetics of antibody–antigen association are enhanced when charge redistribution is allowed, even though charge injection happens at a position far from the antigen binding site. This observation points to charge-reorganization allostery, which should be operative in addition or parallel to other mechanisms of allostery, and may explain some current observations on protein interactions.

REAC Cervicobrachial Neuromodulation Treatment of Depression, Anxiety, and Stress During the COVID-19 Pandemic

Introduction

In addition to the effects of coronavirus infection, the Covid-19 pandemic has induced widespread psychosocial distress, which has triggered the onset of anxious and depressive states, reactive to the socio-relational and economic situation induced by the pandemic. Some of our participants showed depressive and anxious attitudes even in the absence of real pictures of depression and anxiety. This phenomenon, combined with mechanisms of emulation and conditioning, can trigger a vicious cycle within interpersonal relationships and promote the administration of unnecessary treatments. Various approaches have been proposed to help populations suffering from psychosocial problems induced by the Covid-19 pandemic, but there is an objective difficulty in treating a large population.

Methods

To contain and reduce this widespread psychosocial unease, in this study we used two radio electric asymmetric conveyer (REAC) technology neuromodulation treatments, neuro postural optimization (NPO) and neuropsychophysical optimization-cervicobrachial (NPPO-CB), aimed at optimizing an individual's response to the effects of environmental stressors. These treatments are quick and easy to administer; therefore, they can be administered to a large cohort of participants in a short time. To evaluate the effects of the REAC NPO and NPPO-CB treatments, the DASS-21 psychometric test was used because it has already been used to test depression, anxiety, and stress during the Covid-19 pandemic.

Results

The results of the study confirm the usefulness of REAC NPO and NPPO-CB treatments in helping participants to have better coping strategies for the environmental pressures and reduce the neuropsychological and behavioral effects induced by the Covid-19 pandemic.

Discussion

The results obtained in this study are consistent with previous clinical studies confirming the usefulness of the treatments to face neuropsychological and behavioral effects induced by exposome pressure.

Modeling the mechanobioelectricity of cell clusters

We propose a continuum finite strain theory for the interplay between the bioelectricity and the poromechanics of a cell cluster. Specifically, we refer to a cluster of closely packed cells, whose mechanics is governed by a polymer network of cytoskeletal filaments joined by anchoring junctions, modeled through compressible hyperelasticity. The cluster is saturated with a solution of water and ions. We account for water and ion transport in the intercellular spaces, between cells through gap junctions, and across cell membranes through aquaporins and ion channels. Water fluxes result from the contributions due to osmosis, electro-osmosis, and water pressure, while ion fluxes encompass electro-diffusive and convective terms. We consider both the cases of permeable and impermeable cluster boundary, the latter simulating the presence of sealing tight junctions. We solve the coupled governing equations for a one-dimensional axisymmetric benchmark through finite elements, thus determining the spatiotemporal evolution of the intracellular and extracellular ion concentrations, setting the membrane potential, and water concentrations, establishing the cluster deformation. When suitably complemented with genetic, biochemical, and growth dynamics, we expect this model to become a useful instrument for investigating specific aspects of developmental mechanobioelectricity.