Measurement of electrical currents emerging during the regeneration of amputated finger tips in children

Wireless control of nerve growth using bipolar electrodes: a new paradigm in electrostimulation

Electrical activity underpins all life, but is most familiar in the nervous system, where long range electrical signalling is essential for function. When this is lost (e.g., traumatic injury) or it becomes inefficient (e.g., demyelination), the use of external fields can compensate for at least some functional deficits. However, its potential to also promote biological repair at the cell level is underplayed despite abundant in vitro evidence for control of neuron growth. This perspective article considers specifically the emerging possibility of achieving cell growth through the interaction of external electric fields using conducting materials as unwired bipolar electrodes, and without intending stimulation of neuron electrical activity to be the primary consequence. The use of a wireless method to create electrical interactions represents a paradigm shift and may allow new applications in vivo where physical wiring is not possible. Within that scheme of thought an evaluation of specific materials and their dynamic responses as bipolar unwired electrodes is summarized and correlated with changes in dynamic nerve growth during stimulation, suggesting possible future schemes to achieve neural growth using bipolar unwired electrodes with specific characteristics. This strategy emphasizes how nerve growth can be encouraged at injury sites wirelessly to induce repair, as opposed to implanting devices that may substitute the neural signals.

Piezoelectric and Triboelectric Nanogenerators for Enhanced Wound Healing

Wound healing is a highly orchestrated biological process characterized by sequential phases involving inflammation, proliferation, and tissue remodeling, and the role of endogenous electrical signals in regulating these phases has been highlighted. Recently, external electrostimulation has been shown to enhance these processes by promoting cell migration, extracellular matrix formation, and growth factor release while suppressing pro-inflammatory signals and reducing the risk of infection. Among the innovative approaches, piezoelectric and triboelectric nanogenerators have emerged as the next generation of flexible and wireless electronics designed for energy harvesting and efficiently converting mechanical energy into electrical power. In this review, we discuss recent advances in the emerging field of nanogenerators for harnessing electrical stimulation to accelerate wound healing. We elucidate the fundamental mechanisms of wound healing and relevant bioelectric physiology, as well as the principles underlying each nanogenerator technology, and review their preclinical applications. In addition, we address the prominent challenges and outline the future prospects for this emerging era of electrical wound-healing devices.

Bioelectric Signaling: Role of Bioelectricity in Directional Cell Migration in Wound Healing

In wound healing, individual cells' behaviors coordinate movement toward the wound center to restore small or large barrier defects. The migration of epithelial cells as a continuous sheet structure is one of the most important processes by which the skin barrier is restored. How such multicellular and tissue level movement is initiated upon injury, coordinated during healing, and stopped when wounds healed has been a research focus for decades. When skin is wounded, the compromised epithelial barrier generates endogenous electric fields (EFs), produced by ion channels and maintained by cell junctions. These EFs are present across wounds, with the cathodal pole at the wound center. Epithelial cells detect minute EFs and migrate directionally in response to electrical signals. It has long been postulated that the naturally occurring EFs facilitate wound healing by guiding cell migration. It is not until recently that experimental evidence has shown that large epithelial sheets of keratinocytes or corneal epithelial cells respond to applied EFs by collective directional migration. Although some of the mechanisms of the collective cell migration are similar to those used by isolated cells, there are unique mechanisms that govern the coordinated movement of the cohesive sheet. We will review the understanding of wound EFs and how epithelial cells and other cells important to wound healing respond to the electric signals individually as well as collectively. Mounting evidence suggests that wound bioelectrical signaling is an important mechanism in healing. Critical understanding and proper exploitation of this mechanism will be important for better wound healing and regeneration.

Bioelectric Potential in Next-Generation Organoids: Electrical Stimulation to Enhance 3D Structures of the Central Nervous System

Pluripotent stem cell-derived organoid models of the central nervous system represent one of the most exciting areas in in vitro tissue engineering. Classically, organoids of the brain, retina and spinal cord have been generated via recapitulation of in vivo developmental cues, including biochemical and biomechanical. However, a lesser studied cue, bioelectricity, has been shown to regulate central nervous system development and function. In particular, electrical stimulation of neural cells has generated some important phenotypes relating to development and differentiation. Emerging techniques in bioengineering and biomaterials utilise electrical stimulation using conductive polymers. However, state-of-the-art pluripotent stem cell technology has not yet merged with this exciting area of bioelectricity. Here, we discuss recent findings in the field of bioelectricity relating to the central nervous system, possible mechanisms, and how electrical stimulation may be utilised as a novel technique to engineer “next-generation” organoids.

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.

Electric Factors in Wound Healing

Significance: Electric factors such as electric charges, electrodynamic field, skin battery, and interstitial exclusion permeate wound healing physiology and physiopathology from injury to re-epithelialization. The understanding of how electric factors contribute to wound healing and how treatments may interfere with them is fundamental for the development of better strategies for the management of pathological scarring and chronic wounds. Recent Advances: Angiogenesis, cell migration, macrophage activation hemorheology, and microcirculation can interfere and be interfered with electric factors. New treatments with various types of electric currents, laser, light emitting diode, acupuncture, and weak electric fields applied directly on the wound have been developed to improve wound healing. Critical Issues: Despite the basic and clinical development, pathological scars such as keloids and chronic wounds are still a challenge. Future Directions: New treatments can be developed to improve skin wound healing taking into account the influence of electrical charges. Monitoring electrical activity during skin healing and the influence of treatments on hemorheology and microcirculation are examples of how to use knowledge of electrical factors to increase their effectiveness.

A Model and Simulation With Therapeutic Device-Protocol Design Implications for Acute and Chronic Wounds

An understanding of healing processes for different tissues and organs, along with the development of appropriate therapeutic devices and treatment protocols, requires an appreciation for the mechanisms-of-action and sequencing of many interconnected chemical, electrical, mechanical, and optical activities. Unfortunately, the substantial contributions that endogenous electrical mechanisms-of-action provide in healing and regulation are often overlooked, resulting in a poor transfer of knowledge from science, to engineering, and finally, to therapy. The wide variety of healing processes, their therapeutic implications, and the devices and protocol designs that are most effective cannot be understood or addressed adequately without an understanding of the endogenous electrical mechanisms-of-action associated with wound healing. Achieving this level of understanding can be enhanced by the use of appropriate models and simulations that are based on physiological/biochemical system response characteristics.

Bio-instructive materials for musculoskeletal regeneration

The prevalence and cost of disorders affecting the musculoskeletal system are predicted to rise significantly in the coming years due to the aging global population and the increase of associated risk factors. Despite being the second largest cause of disability, the clinical options for therapeutic intervention remain limited. The clinical translation of cell-based therapies for the treatment of musculoskeletal disorders faces many challenges including maintenance of cell survival in the harsh in vivo environment and the lack of control over regulating cell phenotype upon implantation. In order to address these challenges, the development of bio-instructive materials to modulate cell behavior has taken center stage as a strategy to increase the therapeutic potential of various cell populations. However, the determination of the necessary cues for a specific application and how these signals should be presented from a biomaterial remains elusive. This review highlights recent biochemical and physical strategies used to engineer bio-instructive materials for the repair of musculoskeletal tissues. There is a particular emphasis on emerging efforts such as the engineering of immunomodulatory and antibacterial materials, as well as the incorporation of these strategies into biofabrication and organ-on-a-chip approaches. STATEMENT OF SIGNIFICANCE: Disorders affecting the musculoskeletal system affect individuals across the lifespan and have a profound effect on mobility and quality of life. While small defects in many tissues can heal successfully, larger defects are often unable to heal or instead heal with inferior quality fibrous tissue and require clinical intervention. Cell-based therapies are a promising option for clinical translation, yet challenges related to maintaining cell survival and instructing cell phenotype upon implantation have limited the success of this approach. Bio-instructive materials provide an exciting opportunity to modulate cell behavior and enhance the efficacy of cell-based approaches for musculoskeletal repair. However, the identification of critical instructive cues and how to present these stimuli is a focus of intense investigation. This review highlights recent biochemical and physical strategies used to engineer bio-instructive materials for the repair of musculoskeletal tissues, while also considering exciting progress in the engineering of immunomodulatory and antibacterial materials.

Disposable Patterned Electroceutical Dressing (PED-10) Is Safe for Treatment of Open Clinical Chronic Wounds

Objective: To evaluate if patterned electroceutical dressing (PED) is safe for human chronic wounds treatment as reported by wound care providers. Approach: This work reports a pilot feasibility study with the primary objective to determine physically observable effects of PED application on host tissue response from a safety evaluation point of view. For this pilot study, patients receiving a lower extremity amputation with at least one open wound on the part to be amputated were enrolled. Patients were identified through the Ohio State University Wexner Medical Center (OSUWMC) based on inclusion and exclusion criteria through prescreening through the Comprehensive Wound Center's (CWC) Limb Preservation Program and wound physicians and/or providers at OSUWMC. Wounds were treated with the PED before amputation surgery. Results: The intent of the study was to identify if PED was safe for clinical application based on visual observations of adverse or lack of adverse events on skin and wound tissue. The pilot testing performed on a small cohort (N = 8) of patients showed that with engineered voltage regulation of current flow to the open wound, the PED can be used with little to no visually observable adverse effects on chronic human skin wounds. Innovation: The PED was developed as a second-generation tunable electroceutical wound care dressing, which could potentially be used to treat wounds with deeper infections compared with current state of the art that treats wounds with treatment zone limited to the surface near topical application. Conclusion: Technology advances in design and fabrication of electroceutical dressings were leveraged to develop a tunable laboratory prototype that could be used as a disposable low-cost electroceutical wound care dressing on chronic wounds. Design revisions of PED-1 (1 kΩ ballast resistor) circumvented previously observed adverse effects on the skin in the vicinity of an open wound. PED-10 (including a 10 kΩ ballast resistor) was well tolerated in the small cohort of patients (N = 8) on whom it was tested, and the observations reported here warrant a larger study to determine the clinical impact on human wound healing and infection control.

The Epidermo-Peritoneal Potential in Patients Treated with Continuous Ambulatory Peritoneal Dialysis

At physiologic pH, S. epidermidis moves along an electrical potential gradient. We measured the epidermo-peritoneal electrical potential (EPP) in 23 end-stage renal failure patients treated with CAPD. There was a negative correlation between the mean EPP and the patient's age (r=0.47, p=0.016), but no correlation between the mean EPP and the duration of treatment (r=0.003, p=0.5). The EPP was greater in those patients with a history of recurrent bacterial peritonitis due to S. epidermidis [median EPP 23 mv (95% confidence limits 16-51)] compared to those with only one or no episodes of bacterial peritonitis due to S. epidermidis infection [11 mv (9-17), p<0.05]. Thus electrical gradients caused by the presence of the CAPD catheter could contribute to colonisation and subsequent infection by skin commensals, by aiding bacterial migration.

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

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

The use of electric, magnetic, and electromagnetic field for directed cell migration and adhesion in regenerative medicine

Directed cell migration and adhesion is essential to embryonic development, tissue formation and wound healing. For decades it has been reported that electric field (EF), magnetic field (MF) and electromagnetic field (EMF) can play important roles in determining cell differentiation, migration, adhesion, and evenwound healing. Combinations of these techniques have revealed new and exciting explanations for how cells move and adhere to surfaces; how the migration of multiple cells are coordinated and regulated; how cellsinteract with neighboring cells, and also to changes in their microenvironment. In some cells, speed and direction are voltage dependent. Data suggests that the use of EF, MF and EMF could advance techniques in regenerative medicine, tissue engineering and wound healing. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:5-16, 2017.

Diabetic cornea wounds produce significantly weaker electric signals that may contribute to impaired healing

Wounds naturally produce electric signals which serve as powerful cues that stimulate and guide cell migration during wound healing. In diabetic patients, impaired wound healing is one of the most challenging complications in diabetes management. A fundamental gap in knowledge is whether diabetic wounds have abnormal electric signaling. Here we used a vibrating probe to demonstrate that diabetic corneas produced significantly weaker wound electric signals than the normal cornea. This was confirmed in three independent animal models of diabetes: db/db, streptozotocin-induced and mice fed a high-fat diet. Spatial measurements illustrated that diabetic cornea wound currents at the wound edge but not wound center were significantly weaker than normal. Time lapse measurements revealed that the electric currents at diabetic corneas lost the normal rising and plateau phases. The abnormal electric signals correlated significantly with impaired wound healing. Immunostaining suggested lower expression of chloride channel 2 and cystic fibrosis transmembrane regulator in diabetic corneal epithelium. Acute high glucose exposure significantly (albeit moderately) reduced electrotaxis of human corneal epithelial cells in vitro, but did not affect the electric currents at cornea wounds. These data suggest that weaker wound electric signals and impaired electrotaxis may contribute to the impaired wound healing in diabetes.

Elucidating the Role of Injury-Induced Electric Fields (EFs) in Regulating the Astrocytic Response to Injury in the Mammalian Central Nervous System

Injury to the vertebrate central nervous system (CNS) induces astrocytes to change their morphology, to increase their rate of proliferation, and to display directional migration to the injury site, all to facilitate repair. These astrocytic responses to injury occur in a clear temporal sequence and, by their intensity and duration, can have both beneficial and detrimental effects on the repair of damaged CNS tissue. Studies on highly regenerative tissues in non-mammalian vertebrates have demonstrated that the intensity of direct-current extracellular electric fields (EFs) at the injury site, which are 50-100 fold greater than in uninjured tissue, represent a potent signal to drive tissue repair. In contrast, a 10-fold EF increase has been measured in many injured mammalian tissues where limited regeneration occurs. As the astrocytic response to CNS injury is crucial to the reparative outcome, we exposed purified rat cortical astrocytes to EF intensities associated with intact and injured mammalian tissues, as well as to those EF intensities measured in regenerating non-mammalian vertebrate tissues, to determine whether EFs may contribute to the astrocytic injury response. Astrocytes exposed to EF intensities associated with uninjured tissue showed little change in their cellular behavior. However, astrocytes exposed to EF intensities associated with injured tissue showed a dramatic increase in migration and proliferation. At EF intensities associated with regenerating non-mammalian vertebrate tissues, these cellular responses were even more robust and included morphological changes consistent with a regenerative phenotype. These findings suggest that endogenous EFs may be a crucial signal for regulating the astrocytic response to injury and that their manipulation may be a novel target for facilitating CNS repair.

Evidence-Based Approach to Advanced Wound Care Products

There is increasing pressure from industry to use advanced wound care products and technologies. Many are very expensive but promise to reduce overall costs associated with wound care. Compelling anecdotal evidence is provided that inevitably shows wounds that failed all other treatments but responded positively to the subject product. Evidence-based medicine is the standard by which physician-scientists must make their clinical care decisions. In an attempt to provide policy makers with the most current evidence on advanced wound care products, the Department of Veteran Affairs conducted an Evidence-based Synthesis Program review of advanced wound care products. This paper suggests how to take this information and apply it to policy to drive evidence-based care to improve outcomes and fiduciary responsibility.

Regeneration, Stem Cells, and Aging in the Tunicate Ciona: Insights from the Oral Siphon

Regeneration studies in the tunicate Ciona intestinalis have recently been focused on the potential of adult stem cells to replace injured tissues and organs during the adult life cycle using the oral siphon (OS) as a model. The OS has oral siphon pigment organs (OPOs) along its rim and an underlying network of muscle fibers in its tube. Different regeneration processes are triggered by OS amputation at the tip, along the tube, or at the base. One process involves the replacement of OPOs without new cell division by direct differentiation of locally deployed stem cells or stem cells that migrate from the branchial sac. Another process involves blastema formation by the migration of progenitor cells produced from branchial sac stem cells. The capacity for complete and accurate OS regeneration declines continuously during the adult life cycle. Finally, after an age threshold is reached, OS regeneration ceases in old animals. The loss of regeneration capacity in old animals involves the depletion of stem cells in the branchial sac, the inability of branchial sac progenitor cells to migrate to the sites of regeneration, and defective oral pigment organ replacement. The significance of the OS model for studying regeneration, stem cells, and aging will be enhanced by the application of molecular methods.

Three-dimensional numerical model of cell morphology during migration in multi-signaling substrates

Cell Migration associated with cell shape changes are of central importance in many biological processes ranging from morphogenesis to metastatic cancer cells. Cell movement is a result of cyclic changes of cell morphology due to effective forces on cell body, leading to periodic fluctuations of the cell length and cell membrane area. It is well-known that the cell can be guided by different effective stimuli such as mechanotaxis, thermotaxis, chemotaxis and/or electrotaxis. Regulation of intracellular mechanics and cell's physical interaction with its substrate rely on control of cell shape during cell migration. In this notion, it is essential to understand how each natural or external stimulus may affect the cell behavior. Therefore, a three-dimensional (3D) computational model is here developed to analyze a free mode of cell shape changes during migration in a multi-signaling micro-environment. This model is based on previous models that are presented by the same authors to study cell migration with a constant spherical cell shape in a multi-signaling substrates and mechanotaxis effect on cell morphology. Using the finite element discrete methodology, the cell is represented by a group of finite elements. The cell motion is modeled by equilibrium of effective forces on cell body such as traction, protrusion, electrostatic and drag forces, where the cell traction force is a function of the cell internal deformations. To study cell behavior in the presence of different stimuli, the model has been employed in different numerical cases. Our findings, which are qualitatively consistent with well-known related experimental observations, indicate that adding a new stimulus to the cell substrate pushes the cell to migrate more directionally in more elongated form towards the more effective stimuli. For instance, the presence of thermotaxis, chemotaxis and electrotaxis can further move the cell centroid towards the corresponding stimulus, respectively, diminishing the mechanotaxis effect. Besides, the stronger stimulus imposes a greater cell elongation and more cell membrane area. The present model not only provides new insights into cell morphology in a multi-signaling micro-environment but also enables us to investigate in more precise way the cell migration in the presence of different stimuli.

A multi-scale feedback control system model for wound healing electrical activity: therapeutic device/protocol implications

Regulation, growth and healing in biological systems involve many interconnected and interdependent processes that include chemical and electrical mechanisms of action. Unfortunately, the significant contributions that electrical events provide are often overlooked; resulting in a poor transfer of knowledge from science, to engineering and finally to therapy. Wound site electrical processes can influence cell migration, fluid transport, cellular signaling events, gene expression, cell differentiation and cell proliferation; affecting both form and function at the cell, tissue and organ levels. Wound healing, and its interrelationships with transport, regeneration, and growth, cannot be understood or therapeutically assisted unless both chemical and electrical activities associated with the healing process are addressed.

The Tunicate CIONA: A Model System for Understanding the Relationship Between Regeneration and Aging

The use of the tunicate Ciona intestinalis as a model system to study the relationship between regeneration and aging is reviewed. Ciona has powerful regeneration capacities, which fade with age. Some additional benefits are-, a relatively short life span, the ability to study regeneration in vitro, the close phylogenetic relationship between tunicates and vertebrates, and the host of molecular tools already established in this system. The neural complex (NC), the oral siphon (OS), and the oral siphon pigment organs (OPO) have high capacities for regeneration. However, these organs show an inverse relationship between rate of regeneration and age. The ability to regenerate a complete OS disappears in the oldest animals of a natural population, probably due to the inability to form a blastema at the wound site. Effects on blastema formation could also be involved in the reduction of NC regeneration capacity. The fidelity of OPO restoration is also compromised by excess differentiation of precursor cells in local siphon niches in the oldest animals. The Ciona model provides a pathway to understand the molecular basis of these phenomena.

V-ATPase proton pumping activity is required for adult zebrafish appendage regeneration

The activity of ion channels and transporters generates ion-specific fluxes that encode electrical and/or chemical signals with biological significance. Even though it is long known that some of those signals are crucial for regeneration, only in recent years the corresponding molecular sources started to be identified using mainly invertebrate or larval vertebrate models. We used adult zebrafish caudal fin as a model to investigate which and how ion transporters affect regeneration in an adult vertebrate model. Through the combined use of biophysical and molecular approaches, we show that V-ATPase activity contributes to a regeneration-specific H+ ef`flux. The onset and intensity of both V-ATPase expression and H+ efflux correlate with the different regeneration rate along the proximal-distal axis. Moreover, we show that V-ATPase inhibition impairs regeneration in adult vertebrate. Notably, the activity of this H+ pump is necessary for aldh1a2 and mkp3 expression, blastema cell proliferation and fin innervation. To the best of our knowledge, this is the first report on the role of V-ATPase during adult vertebrate regeneration.

Computational modelling of multi-cell migration in a multi-signalling substrate

Cell migration is a vital process in many biological phenomena ranging from wound healing to tissue regeneration. Over the past few years, it has been proven that in addition to cell-cell and cell-substrate mechanical interactions (mechanotaxis), cells can be driven by thermal, chemical and/or electrical stimuli. A numerical model was recently presented by the authors to analyse single cell migration in a multi-signalling substrate. That work is here extended to include multi-cell migration due to cell-cell interaction in a multi-signalling substrate under different conditions. This model is based on balancing the forces that act on the cell population in the presence of different guiding cues. Several numerical experiments are presented to illustrate the effect of different stimuli on the trajectory and final location of the cell population within a 3D heterogeneous multi-signalling substrate. Our findings indicate that although multi-cell migration is relatively similar to single cell migration in some aspects, the associated behaviour is very different. For instance, cell-cell interaction may delay single cell migration towards effective cues while increasing the magnitude of the average net cell traction force as well as the local velocity. Besides, the random movement of a cell within a cell population is slightly greater than that of single cell migration. Moreover, higher electrical field strength causes the cell slug to flatten near the cathode. On the other hand, as with single cell migration, the existence of electrotaxis dominates mechanotaxis, moving the cells to the cathode or anode pole located at the free surface. The numerical results here obtained are qualitatively consistent with related experimental works.

Electrical Stimulation of Wound Healing: A Review of Animal Experimental Evidence

Significance: Electrical stimulation (ES) is a therapeutic intervention that may help specialists facilitate wound healing rates. The purpose of this section is to compile the available animal research regarding the effectiveness of ES on the injury potential, healing rate, cellular and molecular proliferation, mechanical properties, and survival rate of skin flaps. Recent Advances: Regardless of the type of ES current and polarity used, most of the animal experimental evidence suggests that application of ES can facilitate wound healing. However, treatment time should be sufficiently long to attain good mechanical strength of regenerated tissue, because tensile strength is not consistent with augmented collagen deposition. ES improves the survival rate and skin blood flow of animal flaps, but clinical studies are needed to substantiate the findings from these animal experiments. Critical Issues: Impaired or delayed healing is a major clinical problem that can lead to wound chronicity. ES with various strategies has been used to facilitate the healing process, but many aspects remain controversial. Despite much research, no consensus exists regarding the detailed effects of ES on wound healing. Nevertheless, ES has been approved by the Center for Medicare and Medicine Services for reimbursement of the treatment of some chronic ulcers. Future Directions: Exogenous ES may promote the directional migration of cells and signaling molecules via electrotaxis; however, its underlying mechanism is still poorly understood. Future studies that further elucidate the mechanisms regulating electrotaxis will be necessary to optimize the use of ES in different wound states.

Electricity and colloidal stability: how charge distribution in the tissue can affects wound healing

The role of endogenous electric fields in wound healing is still not fully understood. Electric fields are of fundamental importance in various biological processes, ranging from embryonic development to disease progression, as described by many investigators in the last century. This hypothesis brings together some relevant literature on the importance of electric fields in physiology and pathology, the theory of biologically closed electric circuits, skin battery (a phenomenon that occurs after skin injury and seems to be involved in tissue repair), the relationship between electric charge and interstitial exclusion, and how skin tissues can be regarded as colloidal systems. The importance of electric charges, as established in the early works on the subject and the relevance of zeta potential and colloid stability are also analyzed, and together bring a new light for the physics involved in the wound repair of all the body tissues.

3D computational modelling of cell migration: a mechano-chemo-thermo-electrotaxis approach

Single cell migration constitutes a fundamental phenomenon involved in many biological events such as wound healing, cancer development and tissue regeneration. Several experiments have demonstrated that, besides the mechanical driving force (mechanotaxis), cell migration may be also influenced by chemical, thermal and/or electrical cues. In this paper, we present an extension of a previous model of the same authors adding the effects of chemotaxis, thermotaxis and electrotaxis to the initial mechanotaxis model of cell migration, allowing us to predict cell migration behaviour under different conditions and substrate properties. The present model is based on the balance of effective forces during cell motility in the presence of the several guiding cues. This model has been applied to several numerical experiments to demonstrate the effect of the different drivers onto the cell path and final location within a certain three-dimensional substrate with heterogeneous properties. Our findings indicate that the presence of the chemotaxis, thermotaxis and/or electrotaxis reduce, in general, the random component of cell movement, being this reduction more important in the case of electrotaxis that can be considered a dominating signal during cell migration (besides the underlying mechanical effects). These results are qualitatively in agreement with well-known experimental ones.

Light-activation of the Archaerhodopsin H(+)-pump reverses age-dependent loss of vertebrate regeneration: sparking system-level controls in vivo

Optogenetics, the regulation of proteins by light, has revolutionized the study of excitable cells, and generated strong interest in the therapeutic potential of this technology for regulating action potentials in neural and muscle cells. However, it is currently unknown whether light-activated channels and pumps will allow control of resting potential in embryonic or regenerating cells in vivo. Abnormalities in ion currents of non-excitable cells are known to play key roles in the etiology of birth defects and cancer. Moreover, changes in transmembrane resting potential initiate Xenopus tadpole tail regeneration, including regrowth of a functioning spinal cord, in tails that have been inhibited by natural inactivity of the endogenous H(+)-V-ATPase pump. However, existing pharmacological and genetic methods allow neither non-invasive control of bioelectric parameters in vivo nor the ability to abrogate signaling at defined time points. Here, we show that light activation of a H(+)-pump can prevent developmental defects and induce regeneration by hyperpolarizing transmembrane potentials. Specifically, light-dependent, Archaerhodopsin-based, H(+)-flux hyperpolarized cells in vivo and thus rescued Xenopus embryos from the craniofacial and patterning abnormalities caused by molecular blockade of endogenous H(+)-flux. Furthermore, light stimulation of Arch for only 2 days after amputation restored regenerative capacity to inhibited tails, inducing cell proliferation, tissue innervation, and upregulation of notch1 and msx1, essential genes in two well-known endogenous regenerative pathways. Electroneutral pH change, induced by expression of the sodium proton exchanger, NHE3, did not rescue regeneration, implicating the hyperpolarizing activity of Archaerhodopsin as the causal factor. The data reveal that hyperpolarization is required only during the first 48 hours post-injury, and that expression in the spinal cord is not necessary for the effect to occur. Our study shows that complex, coordinated sets of stable bioelectric events that alter body patterning-prevention of birth defects and induction of regeneration-can be elicited by the temporal modulation of a single ion current. Furthermore, as optogenetic reagents can be used to achieve that manipulation, the potential for this technology to impact clinical approaches for preventive, therapeutic, and regenerative medicine is extraordinary. We expect this first critical step will lead to an unprecedented expansion of optogenetics in biomedical research and in the probing of novel and fundamental biophysical determinants of growth and form.

Electrical stimulation: a novel tool for tissue engineering

New advances in tissue engineering are being made through the application of different types of electrical stimuli to influence cell proliferation and differentiation. Developments made in the last decade have allowed us to improve the structure and functionality of tissue-engineered products through the use of growth factors, hormones, drugs, physical stimuli, bioreactor use, and two-dimensional (2-D) and three-dimensional (3-D) artificial extracellular matrices (with various material properties and topography). Another potential type of stimulus is electricity, which is important in the physiology and development of the majority of all human tissues. Despite its great potential, its role in tissue regeneration and its ability to influence cell migration, orientation, proliferation, and differentiation has rarely been considered in tissue engineering. This review highlights the importance of endogenous electrical stimulation, gathering the current knowledge on its natural occurrence and role in vivo, discussing the novel methods of delivering this stimulus and examining its cellular and tissue level effects, while evaluating how the technique could benefit the tissue engineering discipline in the future.

Siphon regeneration capacity is compromised during aging in the ascidian Ciona intestinalis

The ascidian Ciona intestinalis has a short life span and powerful regeneration capacities. The regeneration of the oral siphon (OS) involves wound healing, blastema formation, cell proliferation, and replacement of 8 oral pigment organs (OPO), the latter via differentiation and migration of stem/precursor cells from localized niches in the siphon. The restoration of OPO pattern during OS regeneration occurs with a high degree of accuracy through three successive cycles of amputation. It is shown here that oral siphons of the largest and oldest members of a wild Ciona population do not completely regenerate their siphons after amputation. The loss of regeneration capacity was accompanied by reduced cell proliferation. In contrast to arrested OS outgrowth, the stem/precursor cells responsible for OPO replacement "over-differentiate" after OS amputation in the oldest animals, the typical number of OPO is increased from 8 to 12-16, and malformed OPO are produced. Also in contrast to younger animals, the oldest animals of the population show arrested OPO development after two consecutive cycles of amputation and regeneration. We conclude that there is a size and age threshold in Ciona after which the regenerative capacity of the OS is compromised due to effects of aging on cell proliferation.

The electric field near human skin wounds declines with age and provides a noninvasive indicator of wound healing

Due to the transepidermal potential of 15-50 mV, inside positive, an injury current is driven out of all human skin wounds. The flow of this current generates a lateral electric field within the epidermis that is more negative at the wound edge than at regions more lateral from the wound edge. Electric fields in this region could be as large as 40 mV/mm, and electric fields of this magnitude have been shown to stimulate human keratinocyte migration toward the wounded region. After flowing out of the wound, the current returns through the space between the epidermis and stratum corneum, generating a lateral field above the epidermis in the opposite direction. Here, we report the results from the first clinical trial designed to measure this lateral electric field adjacent to human skin wounds noninvasively. Using a new instrument, the Dermacorder®, we found that the mean lateral electric field in the space between the epidermis and stratum corneum adjacent to a lancet wound in 18-25-year-olds is 107-148 mV/mm, 48% larger on average than that in 65-80-year-olds. We also conducted extensive measurements of the lateral electric field adjacent to mouse wounds as they healed and compared this field with histological sections through the wound to determine the correlation between the electric field and the rate of epithelial wound closure. Immediately after wounding, the average lateral electric field was 122 ± 9 mV/mm. When the wound is filled in with a thick, disorganized epidermal layer, the mean field falls to 79 ± 4 mV/mm. Once this epidermis forms a compact structure with only three cell layers, the mean field is 59 ± 5 mV/mm. Thus, the peak-to-peak spatial variation in surface potential is largest in fresh wounds and slowly declines as the wound closes. The rate of wound healing is slightly greater when wounds are kept moist as expected, but we could find no correlation between the amplitude of the electric field and the rate of wound healing.

Electrical signaling in control of ocular cell behaviors

Epithelia of the cornea, lens and retina contain a vast array of ion channels and pumps. Together they produce a polarized flow of ions in and out of cells, as well as across the epithelia. These naturally occurring ion fluxes are essential to the hydration and metabolism of the ocular tissues, especially for the avascular cornea and lens. The directional transport of ions generates electric fields and currents in those tissues. Applied electric fields affect migration, division and proliferation of ocular cells which are important in homeostasis and healing of the ocular tissues. Abnormalities in any of those aspects may underlie many ocular diseases, for example chronic corneal ulcers, posterior capsule opacity after cataract surgery, and retinopathies. Electric field-inducing cellular responses, termed electrical signaling here, therefore may be an unexpected yet powerful mechanism in regulating ocular cell behavior. Both endogenous electric fields and applied electric fields could be exploited to regulate ocular cells. We aim to briefly describe the physiology of the naturally occurring electrical activities in the corneal, lens, and retinal epithelia, to provide experimental evidence of the effects of electric fields on ocular cell behaviors, and to suggest possible clinical implications.

Extracellular electrical fields direct wound healing and regeneration

Endogenous DC electric fields (EFs) are important, fundamental components of development, regeneration, and wound healing. The fields are the result of polarized ion transport and current flow through electrically conductive pathways. Nullification of endogenous EFs with pharmacological agents or applied EFs of opposite polarity disturbs the aforementioned processes, while enhancement increases the rate of wound closure and the extent of regeneration. EFs are applied to humans in the clinic, to provide an overwhelming signal for the enhancement of healing of chronic wounds. Although clinical trials, spanning a course of decades, have shown that applied EFs enhance healing of chronic wounds, the mechanisms by which cells sense and respond to these weak cues remains unknown. EFs are thought to influence many different processes in vivo. However, under more rigorously controlled conditions in vitro, applied EFs induce cellular polarity and direct migration and outgrowth. Here we review the generation of endogenous EFs, the results of their alteration, and the mechanisms by which cells may sense these weak fields. Understanding the mechanisms by which native and applied EFs direct development and repair will enable current and future therapeutic applications to be optimized.

Effect of Ga-As (904nm) and He-Ne (632.8 nm) laser on injury potential of skin full-thickness wound

Injury potential may have a triggering biological role in wound healing. In this study, the effect of photostimulation to promote wound healing and its effect on injury potential was investigated using the Ga-As and He-Ne lasers. In this study, 30 healthy male Sprague-Dawley rats were randomly divided into a control and two laser groups, He-Ne and Ga-As laser. A 2.5 cm craniocaudal full-thickness skin incision was made on each animal's dorsal region. Differential skin surface potential was measured before and immediately after the injury and also up to the 21st day, every other day. Wound surface area was also measured. Immediately after injury, wound potential significantly increased in all three groups. Maximum positive peak of injury potential was greater in Ga-As group compared to He-Ne laser and control groups (P<0.05) and lasting period of maximum positive potential in two laser groups was longer than that in the control group. There were no significant differences between the mean potential of before wounding and after the 15th, 17th, and 19th day in Ga-As, He-Ne, and control group, respectively (P>0.05). On the other hand, Ga-As and He-Ne laser facilitated the normal distribution of skin potential after wounding. These findings demonstrate that Ga-As laser may be more effective on wound closure and on returning the injury potential to normal level than the He-Ne laser.

Effects of physiological electric fields on migration of human dermal fibroblasts

Endogenous electric currents generated instantly at skin wounds direct migration of epithelial cells and are likely to be important in wound healing. Migration of fibroblasts is critical in wound healing. It remains unclear how wound electric fields guide migration of dermal fibroblasts. We report here that mouse skin wounds generated endogenous electric currents for many hours. Human dermal fibroblasts of both primary and cell-line cultures migrated directionally but slowly toward the anode in an electric field of 50-100 mV mm(-1). This is different from keratinocytes, which migrate quickly to the cathode. It took more than 1 hour for dermal fibroblasts to manifest detectable directional migration. Larger field strength (400 mV mm(-1)) was required to induce directional migration within 1 hour after onset of the field. Phosphatidylinositol-3-OH kinase (PI3 kinase) mediates cathode-directed migration of keratinocytes. We tested the role of PI3 kinase in anode-directed migration of fibroblasts. An applied electric field activated PI3 kinase/Akt in dermal fibroblasts. Dermal fibroblasts from p110gamma (a PI3 kinase catalytic subunit) null mice showed significantly decreased directional migration. These results suggest that physiological electric fields may regulate motility of dermal fibroblasts and keratinocytes differently, albeit using similar PI3 kinase-dependent mechanisms.

Electrotherapeutic device/protocol design considerations for visual disease applications

One of the more interesting applications of electrotherapy involves its use in the treatment of visual disease; including retinitis pigmentosa, diabetic retinopathy and macular degeneration. The therapeutic efficacy of electrotherapy is highly dependent upon the incorporation of appropriate design choices for both the electrotherapeutic device and treatment protocol. Electrotherapeutic design drivers include electrode probe-tissue interface, device reliability, operational constraints, treatment protocol procedures, and safety. In FDA guided and FDA supervised clinical studies (FDA pre-IDE numbers 1980275 and 1000038 and FDA IDE number G020106) involving electrotherapeutic intervention for dry macular degeneration, 61% of a 400 patient cohort treated with electrotherapy achieved visual acuity improvements of two lines or more on the Snellen chart. Average electric current intensities in the range of 60 to 125 muA were utilized to achieve this level of therapeutic efficacy. With further improvements in the design of electrotherapeutic device waveforms, frequency selection, treatment protocols and electrode probe configurations; long-term visual acuity improvements of two lines or better on the Snellen chart can be anticipated for more than 60% of the patients who are in the early stages of retinitis pigmentosa, diabetic retinopathy and dry macular degeneration.

Electric currents in Xenopus tadpole tail regeneration

Xenopus laevis tadpoles can regenerate tail, including spinal cord, after partial amputation, but lose this ability during a specific period around stage 45. They regain this ability after stage 45. What happens during this "refractory period" might hold the key to spinal cord regeneration. We hypothesize that electric currents at amputated stumps play significant roles in tail regeneration. We measured electric current at tail stumps following amputation at different developmental stages. Amputation induced large outward currents leaving the stump. In regenerating stumps of stage 40 tadpoles, a remarkable reversal of the current direction occurred around 12-24 h post-amputation, while non-regenerating stumps of stage 45 tadpole maintained outward currents. This reversal of electric current at tail stumps correlates with whether tails regenerate or not (regenerating stage 40-inward current; non-regenerating stage 45-outward current). Reduction of tail stump current using sodium-free solution decreased the rate of regeneration and percentage regeneration. Fin punch wounds healed normally at stages 45 and 48, and in sodium-free solution, suggesting that the absence of tail re-growth at stage 45 is regeneration-specific rather than a general inhibition of wound healing. These data suggest that electric signals might be one of the key players regulating regeneration.

Noninvasive electromagnetic fields on keratinocyte growth and migration

BACKGROUND

Although evidence has shown that very small electrical currents produce a beneficial therapeutic result for wounds, noninvasive electromagnetic field (EMF) therapy has consisted mostly of anecdotal clinical reports, with very few well-controlled laboratory mechanistic studies. In this study, we evaluate the effects and potential mechanisms of a noninvasive EMF device on skin wound repair.

MATERIALS AND METHODS

The effects of noninvasive EMF on keratinocytes and fibroblasts were assessed via proliferation and incisional wound model migration assays. cDNA microarray and RT-PCR were utilized to assess genetic expression changes in keratinocytes after noninvasive EMF treatment.

RESULTS

In vitro analyses with human skin keratinocyte cultures demonstrated that noninvasive EMFs have a strong effect on accelerating keratinocyte migration and a relatively weaker effect on promoting keratinocyte proliferation. The positive effects of noninvasive EMFs on cell migration and proliferation seem keratinocyte-specific without such effects seen on dermal fibroblasts. cDNA microarray and RT-PCR performed revealed increased expression of CRK7 and HOXC8 genes in treated keratinocytes.

CONCLUSIONS

This study suggests that a noninvasive EMF accelerates wound re-epithelialization through a mechanism of promoting keratinocyte migration and proliferation, possibly due to upregulation of CRK7 and HOXC8 genes.

Electrical fields in wound healing-An overriding signal that directs cell migration

Injury that disrupts an epithelial layer instantaneously generates endogenous electric fields (EFs), which were detected at human skin wounds over 150 years ago. Recent researches combining molecular, genetic and imaging techniques have provided significant insights into cellular and molecular responses to this "unconventional" signal. One unexpected finding is that the EFs play an overriding guidance role in directing cell migration in epithelial wound healing. In experimental models where other directional cues (e.g., contact inhibition release, population pressure etc.) are present, electric fields of physiological strength override them and direct cell migration. The electrotaxis or galvanotaxis is mediated by polarized activation of multiple signaling pathways that include PI3 kinases/Pten, membrane growth factor receptors and integrins. Genetic manipulation of PI3 kinase/Pten (Phosphoinositide 3-kinases/phosphatase and tensin homolog) and integrin beta4 demonstrated the importance of those molecules. The electric fields are therefore a fundamental signal that directs cell migration in wound healing. One of the most challenging question is: How do cells sense the very weak electric signals? Clinically, it is highly desirable to develop practical and reliable technologies for wound healing management exploiting the electric signaling.

Imaging the electric field associated with mouse and human skin wounds

We have developed a noninvasive instrument called the bioelectric field imager (BFI) for mapping the electric field between the epidermis and the stratum corneum near wounds in both mouse and human skin. Rather than touching the skin, the BFI vibrates a small metal probe with a displacement of 180 mum in air above the skin to detect the surface potential of the epidermis through capacitative coupling. Here we describe our first application of the BFI measuring the electric field between the stratum corneum and epidermis at the margin of skin wounds in mice. We measured an electric field of 177+/-14 (61) mV/mm immediately upon wounding and the field lines pointed away from the wound in all directions around it. Because the wound current flows immediately upon wounding, this is the first signal indicating skin damage. This electric field is generated at the outer surface of the epidermis by the outward flow of the current of injury. An equal and opposite current must flow within the multilayered epidermis to generate an intraepidermal field with the negative pole at the wound site. Because the current flowing within the multilayered epidermis is spread over a larger area, the current density and subsequent E field generated in that region is expected to be smaller than that measured by the BFI beneath the stratum corneum. The field beneath the stratum corneum typically remained in the 150-200 mV/mm range for 3 days and then began to decline over the next few days, falling to zero once wound healing was complete. The mean wound field strength decreased by 64+/-7% following the application of the sodium channel blocker, amiloride, to the skin near the wound and increased by 82+/-21% following the application of the Cl- channel activator, prostaglandin E2.

Effects of micro-amperage direct current stimulation on injury potential and its relation to wound surface area in guinea pig

INTRODUCTION

it is believed that the exogenous electrical stimulation via improving the natural endogenous bioelectric current, accelerate the wound healing. Up to now, this hypotheses has not been researched in acute surgically wounds.

MATERIALS AND METHODS

Thirty-nine male guinea pigs were randomly divided into one control and two experimental groups (DC anodal group and DC cathodal group). A full thickness skin incision, length of 2.5 cm, was made on the dorsum of each animal The differential surface skin potential was measured before and immediately after the injury and also through the healing process until 21st days.

RESULTS

Only in anodal group, there was not significant difference between the basal initial potential and the wound potential on days of 17, 19 and 21 (p>0.05). On days of 19 and 21, the wound potential decreased higher in anodal group than in control group (p<0.05). Wound surface area in two experimental groups decreased higher in 3rd weeks with respect to control group (p<0.05).

DISCUSSION AND CONCLUSION

Anodal micro-amperage direct current can accelerate bioelectric events of skin wound and return more rapidly the wound potential to its before injury natural level.

Non-invasive measurement of bioelectric currents with a vibrating probe

Small d.c. electrical signals have been detected in many biological systems and often serve important functions in cells and organs. For example, we have recently found that they play a far more important role in directing cell migration in wound healing than previously thought. Here, we describe the manufacture and use of a simplified ultrasensitive vibrating probe system for measuring extracellular electrical currents. This vibrating probe is an insulated, sharpened metal wire with a small platinum-black tip (10-30 microm), which can detect ionic currents in the microA cm(-2) range in physiological saline. The probe is vibrated at about 300 Hz by a piezoelectric bender. In the presence of an ionic current, the probe detects a voltage difference between the extremes of its movement. The basic, low-cost system we describe is readily adaptable to most laboratories interested in measuring physiological electric currents associated with wounds, developing embryos and other biological systems.