Electric field-directed fibroblast locomotion involves cell surface molecular reorganization and is calcium independent

Cell shape and orientation control galvanotactic accuracy

Eukaryotic cells sense and follow electric fields during wound healing and embryogenesis - this is called galvanotaxis. Galvanotaxis is believed to be driven by the redistribution of "sensors" - potentially transmembrane proteins or other molecules - through electrophoresis and electroosmosis. Here, we update our previous model of the limits of galvanotaxis due to the stochasticity of sensor movements to account for cell shape and orientation. Computing the Fisher information shows that, in principle, cells have more information about the electric field direction when their long axis is parallel to the field. However, for weak fields, maximum-likelihood estimators may have lower variability when the cell's long axis is perpendicular to the field. In an alternate possibility, we find that if cells instead estimate the field direction by taking the average of all the sensor locations as its directional cue ("vector sum"), this introduces a bias towards the short axis, an effect not present for isotropic cells. We also explore the possibility that cell elongation arises downstream of sensor redistribution. We argue that if sensors migrate to the cell's rear, the cell will tend to expand perpendicular the field - as is more commonly observed - but if sensors migrate to the front, the cell will tend to elongate parallel to the field.

Effect of Electromagnetic Field on Proliferation and Migration of Fibroblasts and Keratinocytes: Implications in Wound Healing and Regeneration

Proliferation and migration of fibroblasts, keratinocytes, and endothelial cells are key events in the physiological process of wound healing. This process includes different but overlapping stages: hemostasis, inflammatory phase, the proliferative phase, and the remodeling phase. Traumatic brain injury (TBI) is defined as a mechanical insult to the brain from external mechanical force (primary injury), usually followed by the secondary injury including edema, inflammation, excitotoxicity, oxidative stress, or mitochondrial dysfunction. The process of tissue repair following TBI is based on the neuronal-glial interactions, where phagocytosis by microglia plays a crucial role. Low-frequency electromagnetic field (LF-EMF) has been shown to enhance tissue repair after TBI, however, there are limited studies investigating the effects of LF-EMF on the proliferation and migration of keratinocytes, fibroblasts, VSMCs, and endothelial cells in the context of wound healing and on neuronal cells and microglia in relation to healing after TBI. Better understanding of the effects of LF-EMF on the proliferation, migration, and differentiation of these cells is important to enhance tissue healing after injury. This review article comprehensively discussed the effect of EMF/LF-EMF on these cells. Results published by different authors are hardly comparable due to different methodological approach and experimental settings. EMF promotes migration and proliferation of fibroblasts, keratinocytes and endothelial cells (EC), and thus could improve wound healing. The pilot study preformed on a large animal model of TBI suggests anti-inflammatory effects of EMF stimulation following TBI. Therefore, EMF is recognized as a potential therapeutic option to accelerate the wound healing and improve cellular recovery and function after TBI. Nonetheless, future studies are needed to define the optimal parameters of EMF stimulation in terms of frequency or duration of exposure.

Making Sense of Electrical Stimulation: A Meta-analysis for Wound Healing

Electrical stimulation as a mode of external enhancement factor in wound healing has been explored widely. It has proven to have multidimensional effects in wound healing including antibacterial, galvanotaxis, growth factor secretion, proliferation, transdifferentiation, angiogenesis, etc. Despite such vast exploration, this modality has not yet been established as an accepted method for treatment. This article reviews and analyzes the approaches of using electrical stimulation to modulate wound healing and discusses the incoherence in approaches towards reporting the effect of stimulation on the healing process. The analysis starts by discussing various processes adapted in in vitro, in vivo, and clinical practices. Later it is focused on in vitro approaches directed to various stages of wound healing. Based on the analysis, a protocol is put forward for reporting in vitro works in such a way that the outcomes of the experiment are replicable and scalable in other setups. This work proposes a ground of unification for all the in vitro approaches in a more sensible manner, which can be further explored for translating in vitro approaches to complex tissue stimulation to establish electrical stimulation as a controlled clinical method for modulating wound healing.

The dynamics of the electrotactic reaction of mouse 3T3 fibroblasts

The molecular mechanisms behind electrotaxis remain largely unknown, with no identified primary direct current electric field (dcEF) sensor. Two leading hypotheses propose mechanisms involving the redistribution of charged components in the cell membrane (driven by electrophoresis or electroosmosis) and the asymmetric activation of ion channels. To investigate these mechanisms, we studied the dynamics of electrotactic behaviour of mouse 3T3 fibroblasts. We observed that 3T3 fibroblasts exhibit cathodal migration within just 1 min when exposed to physiological dcEF. This rapid response suggests the involvement of ion channels in the cell membrane. Our large-scale screening method identified several ion channel genes as potential key players, including the inwardly rectifying potassium channel Kir4.2. Blocking the Kir channel family with Ba2+ or silencing the Kcnj15 gene, encoding Kir4.2, significantly reduced the directional migration of 3T3 cells. Additionally, the levels of the intracellular regulators of Kir channels, spermine (SPM) and spermidine (SPD), had a significant impact on cell directionality. Interestingly, inhibiting Kir4.2 resulted in the temporary cessation of electrotaxis for approximately 1-2 h before its return. This observation suggests a two-phase mechanism for the electrotaxis of mouse 3T3 fibroblasts, where ion channel activation triggers the initial rapid response to dcEF, and the subsequent redistribution of membrane receptors sustains long-term directional movement. In summary, our study unveils the involvement of Kir channels and proposes a biphasic mechanism to explain the electrotactic behaviour of mouse 3T3 fibroblasts, shedding light on the molecular underpinnings of electrotaxis.

Electrical Stimulation for Wound Healing: Opportunities for E-Textiles

Ulcers and chronic wounds are a large and expensive problem, costing billions of pounds a year and affecting millions of people. Electrical stimulation has been known to have a positive effect on wound healing since the 1960s and this has been confirmed in numerous studies, reducing the time to heal, and the incidence of adverse events such as infections. However, because each study used different parameters for the treatment, inclusion criteria and metrics for quantifying the success, it is currently hard to combine them statistically and gain a true picture of its efficacy. As such, electrical stimulation has not been universally adopted as a recommended treatment for various types of wound. This paper summarises the biological basis for electrical simulation treatment and reviews the clinical evidence for its effectiveness. Notable is the lack of research focused on the electrodes used to deliver electrostimulation treatment. However, a significant amount of work has been conducted on electrodes for other medical applications in the field of e-textiles. This e-textile work is reviewed with a focus on its potential in electrostimulation and proposals are made for future developments to improve future studies and applications for wound healing via electrical stimulation.

Physical limits on galvanotaxis

Eukaryotic cells can polarize and migrate in response to electric fields via "galvanotaxis," which aids wound healing. Experimental evidence suggests cells sense electric fields via molecules on the cell's surface redistributing via electrophoresis and electroosmosis, though the sensing species has not yet been conclusively identified. We develop a model that links sensor redistribution and galvanotaxis using maximum likelihood estimation. Our model predicts a single universal curve for how galvanotactic directionality depends on field strength. We can collapse measurements of galvanotaxis in keratocytes, neural crest cells, and granulocytes to this curve, suggesting that stochasticity due to the finite number of sensors may limit galvanotactic accuracy. We find cells can achieve experimentally observed directionalities with either a few (∼100) highly polarized sensors or many (∼10^{4}) sensors with an ∼6-10% change in concentration across the cell. We also identify additional signatures of galvanotaxis via sensor redistribution, including the presence of a tradeoff between accuracy and variance in cells being controlled by rapidly switching fields. Our approach shows how the physics of noise at the molecular scale can limit cell-scale galvanotaxis, providing important constraints on sensor properties and allowing for new tests to determine the specific molecules underlying galvanotaxis.

Bronchial Fibroblasts from Asthmatic Patients Display Impaired Responsiveness to Direct Current Electric Fields (dcEFs)

Accumulating evidence suggests that an important role is played by electric signals in modifying cell behaviour during developmental, regenerative and pathological processes. However, their role in asthma has not yet been addressed. Bronchial fibroblasts have recently been identified having important roles in asthma development. Therefore, we adapted an experimental approach based on the lineages of human bronchial fibroblasts (HBF) derived from non-asthmatic (NA) donors and asthmatic (AS) patients to elucidate whether their reactivity to direct current electric fields (dcEF) could participate in the asthmatic process. The efficient responsiveness of NA HBF to an electric field in the range of 2-4 V/cm was illustrated based on the perpendicular orientation of long axes of the cells to the field lines and their directional movement towards the anode. These responses were related to the activity of TGF-β signalling, as the electrotaxis and re-orientation of NA HBF polarity was impaired by the inhibitors of canonical and non-canonical TGF-β-dependent pathways. A similar tendency towards perpendicular cell-dcEF orientation was observed for AS HBF. However, their motility remained insensitive to the electric field applied at 2-4 V/cm. Collectively, these observations demonstrate the sensitivity of NA HBF to dcEF, as well as the inter-relations between this parameter and the canonical and non-canonical TGF-β pathways, and the differences between the electrotactic responses of NA and AS HBF point to the possible role of their dcEFs in desensitisation in the asthmatic process. This process may impair the physiologic behaviour of AS HBF functions, including cell motility, ECM deposition, and contractility, thus promoting bronchial wall remodelling, which is a characteristic of bronchial asthma.

Bioelectronic microfluidic wound healing: a platform for investigating direct current stimulation of injured cell collectives

Upon cutaneous injury, the human body naturally forms an electric field (EF) that acts as a guidance cue for relevant cellular and tissue repair and reorganization. However, the direct current (DC) flow imparted by this EF can be impacted by a variety of diseases. This work delves into the impact of DC stimulation on both healthy and diabetic in vitro wound healing models of human keratinocytes, the most prevalent cell type of the skin. The culmination of non-metal electrode materials and prudent microfluidic design allowed us to create a compact bioelectronic platform to study the effects of different sustained (12 hours galvanostatic DC) EF configurations on wound closure dynamics. Specifically, we compared if electrotactically closing a wound's gap from one wound edge (i.e., uni-directional EF) is as effective as compared to alternatingly polarizing both the wound's edges (i.e., pseudo-converging EF) as both of these spatial stimulation strategies are fundamental to the eventual translational electrode design and strategy. We found that uni-directional electric guidance cues were superior in group keratinocyte healing dynamics by enhancing the wound closure rate nearly three-fold for both healthy and diabetic-like keratinocyte collectives, compared to their non-stimulated respective controls. The motility-inhibited and diabetic-like keratinocytes regained wound closure rates with uni-directional electrical stimulation (increase from 1.0 to 2.8% h^-1) comparable to their healthy non-stimulated keratinocyte counterparts (3.5% h^-1). Our results bring hope that electrical stimulation delivered in a controlled manner can be a viable pathway to accelerate wound repair, and also by providing a baseline for other researchers trying to find an optimal electrode blueprint for in vivo DC stimulation.

Effect of Sulfonation Group on Polyaniline Copolymer Scaffolds for Tissue Engineering with Laminin Treatment under Electrical Stimulation

Sulfonated copolyanilines (SPANs), SPAN-40 and SPAN-75, were prepared and applied in this tissue engineering study. SPAN scaffolds (SPANs) and control group polyaniline (PANI) were synthesized by performing oxidative polymerization. To further research the effects of neuron regeneration, PC12 cells were cultured on as-prepared PANI and SPANs with laminin (La) treatment under electrical stimulation. The effects on PC12 cell differentiation were investigated by controlling the amount of sulfonated groups (-SO₃H) in the SPAN chain, the electrical stimulation voltage, and the presence or absence of La coating. The adhesion and proliferation of cells increased with the degree of sulfonation; La and electrical stimulation further promoted neuronal cell differentiation as increased neurite length was demonstrated in the micrograph analyses. In summary, the sulfonated copolyaniline coated with La had the best effect on neuronal differentiation under electrical stimulation, suggesting its potential as a substrate for nerve tissue engineering.

Electric fields regulate cellular elasticity through intracellular Ca2+ concentrations

Cellular elasticity is a key factor related to a broad range of physiological and pathological processes. The elasticity of a single cell has thus emerged as a potential biomarker to characterize the cellular state. Both internal and external stimuli affect cellular elasticity, and changes in elasticity can cause alterations in cellular characteristics or function. The application of electric fields (EFs) is a promising method that can be used to change cellular elasticity; however, the mechanisms underlying its effect remain unknown. Here, we demonstrate EFs-induced elasticity changes in human dermal fibroblasts and discuss the underlying mechanism related to actin polymerization. Cellular elasticity increases after EF (50 mV/mm) stimulation, reaching a maximum at 30 min before decreasing between 30 and 120 min. The cellular elasticity under EF stimulation, regardless of stimulation time, is higher than that of the control. F-actin regulates the elasticity of cells through gelsolin activation. We show changes in intracellular Ca²⁺ caused by EFs, which induced gelsolin activation and F-actin content changes. This result demonstrates a series of processes in which external electrical stimulation conditions regulate cellular elasticity.

Progress in the mechanical modulation of cell functions in tissue engineering

In mammals, mechanics at multiple stages-nucleus to cell to ECM-underlie multiple physiological and pathological functions from its development to reproduction to death. Under this inspiration, substantial research has established the role of multiple aspects of mechanics in regulating fundamental cellular processes, including spreading, migration, growth, proliferation, and differentiation. However, our understanding of how these mechanical mechanisms are orchestrated or tuned at different stages to maintain or restore the healthy environment at the tissue or organ level remains largely a mystery. Over the past few decades, research in the mechanical manipulation of the surrounding environment-known as substrate or matrix or scaffold on which, or within which, cells are seeded-has been exceptionally enriched in the field of tissue engineering and regenerative medicine. To do so, traditional tissue engineering aims at recapitulating key mechanical milestones of native ECM into a substrate for guiding the cell fate and functions towards specific tissue regeneration. Despite tremendous progress, a big puzzle that remains is how the cells compute a host of mechanical cues, such as stiffness (elasticity), viscoelasticity, plasticity, non-linear elasticity, anisotropy, mechanical forces, and mechanical memory, into many biological functions in a cooperative, controlled, and safe manner. High throughput understanding of key cellular decisions as well as associated mechanosensitive downstream signaling pathway(s) for executing these decisions in response to mechanical cues, solo or combined, is essential to address this issue. While many reports have been made towards the progress and understanding of mechanical cues-particularly, substrate bulk stiffness and viscoelasticity-in regulating the cellular responses, a complete picture of mechanical cues is lacking. This review highlights a comprehensive view on the mechanical cues that are linked to modulate many cellular functions and consequent tissue functionality. For a very basic understanding, a brief discussion of the key mechanical players of ECM and the principle of mechanotransduction process is outlined. In addition, this review gathers together the most important data on the stiffness of various cells and ECM components as well as various tissues/organs and proposes an associated link from the mechanical perspective that is not yet reported. Finally, beyond addressing the challenges involved in tuning the interplaying mechanical cues in an independent manner, emerging advances in designing biomaterials for tissue engineering are also explored.

Efficacy and safety of non-surgical short-wave radiofrequency treatment of mild-to-moderate erythematotelangiectatic rosacea: a prospective, open-label pilot study

Although various treatments have been proposed for the management of rosacea, achieving complete remission of persistent erythema remains challenging. Short-wave radiofrequency (SWRF) treatment has been shown to repair skin barriers and reduce chronic inflammation. However, limited studies have evaluated the effectiveness of SWRF treatment for erythematotelangiectatic rosacea (ETR). A prospective, open-label pilot study using SWRF therapy was conducted on 30 patients with mild-to-moderate ETR. During the first stage, the patients underwent a single, full-face treatment and were evaluated before and after the session, as well as on the 7th and 15th day post-treatment. During the second stage, ten treatment sessions were administered, and the patients were evaluated before and after the tenth session, as well as 1 month after the treatment. Adverse events were recorded during each treatment session, and the patients were followed up for 3 months after the last session. Twenty-eight patients completed the entire trial. On the 7th day after the single treatment, the global score (total score of flushing, persistent erythema, and telangiectasia) of ETR improved from 5.23 ± 1.09 to 4.00 ± 0.76 relative to the baseline value (p < 0.05); moreover, the overall treatment satisfaction improved from 7.27 ± 0.89 to 4.90 ± 0.91 (p < 0.05). 1 month after the tenth treatment session, the global score improved from 5.30 ± 1.01 to 3.85 ± 0.93 (p < 0.05), and the overall treatment satisfaction improved from 7.13 ± 0.85 to 5.17 ± 1.19 (p < 0.05). During the 3 month follow-up period, there were two cases of recurrence. Therefore, this report indicates that SWRF might be an effective auxiliary treatment for mild-to-moderate ETR.

Conductive Materials for Healing Wounds: Their Incorporation in Electroactive Wound Dressings, Characterization, and Perspectives

The use of conductive materials to promote the activity of electrically responsive cells is an effective means of accelerating wound healing. This article focuses on recent advancements in conductive materials, with emphasis on overviewing their incorporation with non-conducting polymers to fabricate electroactive wound dressings. The characteristics of these electroactive dressings are deliberated, and the mechanisms on how they accelerate the wound healing process are discussed. Potential directions for the future development of electroactive wound dressings and their potential in monitoring the course of wound healing in vivo concomitantly are also proposed.

Advances in Biodegradable 3D Printed Scaffolds with Carbon-Based Nanomaterials for Bone Regeneration

Bone possesses an inherent capacity to fix itself. However, when a defect larger than a critical size appears, external solutions must be applied. Traditionally, an autograft has been the most used solution in these situations. However, it presents some issues such as donor-site morbidity. In this context, porous biodegradable scaffolds have emerged as an interesting solution. They act as external support for cell growth and degrade when the defect is repaired. For an adequate performance, these scaffolds must meet specific requirements: biocompatibility, interconnected porosity, mechanical properties and biodegradability. To obtain the required porosity, many methods have conventionally been used (e.g., electrospinning, freeze-drying and salt-leaching). However, from the development of additive manufacturing methods a promising solution for this application has been proposed since such methods allow the complete customisation and control of scaffold geometry and porosity. Furthermore, carbon-based nanomaterials present the potential to impart osteoconductivity and antimicrobial properties and reinforce the matrix from a mechanical perspective. These properties make them ideal for use as nanomaterials to improve the properties and performance of scaffolds for bone tissue engineering. This work explores the potential research opportunities and challenges of 3D printed biodegradable composite-based scaffolds containing carbon-based nanomaterials for bone tissue engineering applications.

Blocking exposed PD-L1 elicited by nanosecond pulsed electric field reverses dysfunction of CD8+ T cells in liver cancer

As a promising method for local tumor treatment, nanosecond pulsed electric field (nsPEF) ablation elicits a potent anti-tumor immune response. However, the mechanism of the nsPEF-mediated anti-tumor immune response and its effects on the tumor microenvironment remains unclear. Here, we demonstrated that nsPEF treatment increased the level of membrane PD-L1 in liver cancer cells. Furthermore, nsPEF induced the release of PD-L1-associated extra-cellular vesicles, leading to the dysfunction of CD8⁺ T cells, which could potentially be reversed by PD-L1 blockade. Biological and functional assays also demonstrated that nsPEF treatment resulted in the increased PD-L1 level and dysfunction of infiltrated CD8⁺ T cells in tumor tissues in vivo, indicating the long term antitumor efficacy of nsPEF treatment. A combination of nsPEF treatment and PD-L1 blockade effectively inhibited tumor growth and improved the survival of the tumor-bearing mouse. In conclusion, nsPEF treatment induced the translocation and release of PD-L1 and contributed to the dysfunction of infiltrated CD8⁺ T cells, resulting in tumor progression at later stages. The combination of nsPEF treatment and PD-L1 blockade is a promising therapeutic strategy for liver cancer.

Modeling the cornea in 3-dimensions: Current and future perspectives

The cornea is an avascular, transparent ocular tissue that serves as a refractive and protective structure for the eye. Over 90% of the cornea is composed of a collagenous-rich extracellular matrix within the stroma with the other 10% composed by the corneal epithelium and endothelium layers and their corresponding supporting collagen layers (e.g., Bowman's and Descemet's membranes) at the anterior and posterior cornea, respectively. Due to its prominent role in corneal structure, tissue engineering approaches to model the human cornea in vitro have focused heavily on the cellular and functional properties of the corneal stroma. In this review, we discuss model development in the context of culture dimensionality (e.g., 2-dimensional versus 3-dimensional) and expand on the optical, biomechanical, and cellular functions promoted by the culture microenvironment. We describe current methods to model the human cornea with focus on organotypic approaches, compressed collagen, bioprinting, and self-assembled stromal models. We also expand on co-culture applications with the inclusion of relevant corneal cell types, such as epithelial, stromal keratocyte or fibroblast, endothelial, and neuronal cells. Further advancements in corneal tissue model development will markedly improve our current understanding of corneal wound healing and regeneration.

Cell migration driven by substrate deformation gradients

Identifying the cues followed by cells is key to understand processes as embryonic development, tissue homeostasis, or several pathological conditions. Based on a durotaxis model, it is shown that cells moving on predeformed thin elastic membrane follow the direction of increasing strain of the substrate. This mechanism, straintaxis, does not distinguish the origin of the strain, but the active stresses produce large strains on cells or tissues being used as substrates. Hence, straintaxis is the natural realization of duratoaxis in vivo. Considering a circular geometry for the substrate cells, it is shown that if the annular component of the active stress component increases with the radial distance, cells migrate toward the substrate cell borders. With appropriate estimation for the different parameters, the migration speeds are similar to those obtained in recent experiments (Reig et al 2017 Nat. Commun. 8 15431). In these, during the annual killifish epiboly, deep cells that move in contact with the epithelial enveloping cell layer (EVL), migrate toward the EVL cell borders with speeds of microns per minute.

Mechanical Model for Durotactic Cell Migration

Cell migration is a fundamental process in biological systems, playing an important role for diverse physiological processes. Cells often exhibit directed migration in a specific direction in response to various types of cues. In particular, cells are able to sense the rigidity of surrounding environments and then migrate toward stiffer regions. To understand this mechanosensitive behavior called durotaxis, several computational models have been developed. However, most of the models employed cell decision making to recapitulate durotactic behaviors, significantly limiting insights provided from these studies. In this study, we developed a computational biomechanical model without any cell decision making to illuminate intrinsic mechanisms of durotactic behaviors of cells migrating on a two-dimensional substrate. The model consists of a simplified cell generating contractile forces and a deformable substrate coarse-grained into an irregular triangulated mesh. Using the model, we demonstrated that durotactic behaviors emerge from purely mechanical interactions between the cell and the underlying substrate. We investigated how durotactic migration is regulated by biophysical properties of the substrate, including elasticity, viscosity, and stiffness profile.

Expression of integrins to control migration direction of electrotaxis

Proper control of cell migration is critically important in many biologic processes, such as wound healing, immune surveillance, and development. Much progress has been made in the initiation of cell migration; however, little is known about termination and sometimes directional reversal. During active cell migration, as in wound healing, development, and immune surveillance, the integrin expression profile undergoes drastic changes. Here, we uncovered the extensive regulatory and even opposing roles of integrins in directional cell migration in electric fields (EFs), a potentially important endogenous guidance mechanism. We established cell lines that stably express specific integrins and determined their responses to applied EFs with a high throughput screen. Expression of specific integrins drove cells to migrate to the cathode or to the anode or to lose migration direction. Cells expressing αMβ2, β1, α2, αIIbβ3, and α5 migrated to the cathode, whereas cells expressing β3, α6, and α9 migrated to the anode. Cells expressing α4, αV, and α6β4 lost directional electrotaxis. Manipulation of α9 molecules, one of the molecular directional switches, suggested that the intracellular domain is critical for the directional reversal. These data revealed an unreported role for integrins in controlling stop, go, and reversal activity of directional migration of mammalian cells in EFs, which might ensure that cells reach their final destination with well-controlled speed and direction.-Zhu, K., Takada, Y., Nakajima, K., Sun, Y., Jiang, J., Zhang, Y., Zeng, Q., Takada, Y., Zhao, M. Expression of integrins to control migration direction of electrotaxis.

Electrical Stimulation Activates Fibroblasts through the Elevation of Intracellular Free Ca2+: Potential Mechanism of Pelvic Electrical Stimulation Therapy

Ca²⁺ is an important ion in response to electrical stimulation (ES) and acts as second messenger in the regulation of various physiological processes. Pelvic floor electrical stimulation (PES) is a low-voltage clinical application, available for urinary incontinence (UI) treatment. Fibroblasts, as the main cellular component of vaginal wall and pelvic ligament, play an important role in the maintenance of pelvic health. We studied the effect of ES on fibroblasts in this study. ES was conducted with electrotaxis chambers on L929 fibroblast and the ES parameter was 100 mV/mm×2h. The results showed that ES increased intracellular Ca²⁺ concentration, promoted the expression of PCNA, CyclinB1, and CyclinD1, and increased the proportion of cells in S and G2 phages. After ES, fibroblasts get activated and proliferated. Besides, BAPTA-AM, a membrane permeated chelator for intracellular free Ca²⁺, partially inhibited the effect of ES on fibroblasts activation and proliferation promotion. Furthermore, we elucidated that Ca²⁺, as a second messenger and upstream signal for Smads and Akt signaling, regulated ES-induced nuclear translocation of smad2/3, phosphorylation of smad2/3, Akt, and GSK3β. Finally, we validated the effect of ES on PES mouse model. The results indicated that PES promoted the activation and proliferation of fibroblasts in vivo. In conclusion, we verify that ES can elevate the concentration of intracellular Ca²⁺ and activate its downstream signaling and then promote the activation of fibroblasts, which may be one of the mechanisms of PES therapy.

DC Electric Fields Induce Perpendicular Alignment and Enhanced Migration in Schwann Cell Cultures

Schwann cells (SCs) are PNS glia that play numerous support functions including myelination of axons. After PNS injury, SCs facilitate regeneration by phagocytosing cellular debris and providing physical and biochemical cues to guide axon growth. This reparative phenotype suggests SCs could be critical cellular targets for enhancing nerve regeneration. One method for altering cell morphology and motility is the application of direct current (DC) electric fields (EFs). Endogenous EFs have physiologic relevance during embryogenesis and serve as guidance and polarization cues. While much literature exists on EFs and CNS and PNS neurons, the effects of EFs on SCs have not been extensively studied. In this work, cell alignment, migration, and morphology of rat SCs were measured in response to several EF stimulation regimes including constant DC, 50% duty cycle DC and oscillating DC. SCs were found to re-orient perpendicular to field lines and respond to DC EFs as low as 75 mV/mm. EF exposure promoted directed migration, with travel towards the cathode at a mean rate of 7.5 µm/h. The data highlight the utility of EFs in modulating SC morphology, alignment and migration. Results may have implications for using EFs to attract and realign SCs at the site of PNS trauma.

Mechanisms of invasion and motility of high-grade gliomas in the brain

High-grade gliomas are especially difficult tumors to treat due to their invasive behavior. This has led to extensive research focusing on arresting glioma cell migration. Cell migration involves the sensing of a migratory cue, followed by polarization in the direction of the cue, and reorganization of the actin cytoskeleton to allow for a protrusive leading edge and a contractile trailing edge. Transmission of these forces to produce motility also requires adhesive interactions of the cell with the extracellular microenvironment. In glioma cells, transmembrane receptors such as CD44 and integrins bind the cell to the surrounding extracellular matrix that provides a substrate on which the cell can exert the requisite forces for cell motility. These various essential parts of the migratory machinery are potential targets to halt glioma cell invasion. In this review, we discuss the mechanisms of glioma cell migration and how they may be targeted in anti-invasion therapies.

Calcium influx differentially regulates migration velocity and directedness in response to electric field application

Neural precursor cells (NPCs) respond to externally applied direct current electrical fields (DCEFs) by undergoing rapid and directed migration toward the cathode in a process known as galvanotaxis. It is unknown if the underlying mechanisms of galvanotactic migration is common to non-electrosensitive cells and if so, how NPCs and other galvanotactic cells sense and transduce electrical fields into cellular motility. In this study, we show that distinct aspects of NPC galvanotactic migration: motility (quantified through |velocity|) and directedness, are differentially regulated by calcium. We use low-Ca²⁺ culture conditions; an intracellular Ca²⁺ chelator; and voltage gated calcium channel (VGCC) inhibitors to specific channels expressed on NPCs, to demonstrate the role of Ca²⁺ influx in DCEF-induced NPC migration. Consistent with existing literature, we show Ca²⁺ is involved in F-actin polymerization that lengthens NPC membrane protrusions necessary for cellular motility. However, inhibiting Ca²⁺ results in reduced velocity but has no effect on DCEF-induced directedness. This dissociation between velocity and directedness reveal that these migration parameters can be independently regulated, thus suggesting a parallel process of sensing DCEFs by NPCs.

Reversing the direction of galvanotaxis with controlled increases in boundary layer viscosity

Weak external electric fields (EFs) polarize cellular structure and direct most migrating cells (galvanotaxis) toward the cathode, making it a useful tool during tissue engineering and for healing epidermal wounds. However, the biophysical mechanisms for sensing weak EFs remain elusive. We have reinvestigated the mechanism of cathode-directed water flow (electro-osmosis) in the boundary layer of cells, by reducing it with neutral, viscous polymers. We report that increasing viscosity with low molecular weight polymers decreases cathodal migration and promotes anodal migration in a concentration dependent manner. In contrast, increased viscosity with high molecular weight polymers does not affect directionality. We explain the contradictory results in terms of porosity and hydraulic permeability between the polymers rather than in terms of bulk viscosity. These results provide the first evidence for controlled reversal of galvanotaxis using viscous agents and position the field closer to identifying the putative electric field receptor, a fundamental, outside-in signaling receptor that controls cellular polarity for different cell types.

Electrical stimulation structurally affects the tissues of the rectum and anus of nulliparous rats

Considering that the muscles of the anus perform a critical role in maintaining continence, losses in their structure can negatively affect the physiological control of the intestinal contents. Anorectal electro-stimulation (ARES) has been reported to have a positive effect on the functionality of treated patients, but how ARES affects the structural tissues of the anorectal segment remains unknown. Because the study of how ARES structurally affects human tissues is not possible, this study aimed to clarify these effects in a murine model, which has a similar anorectal segment (structure and physiology) to humans. For the descriptive and comparative study, randomly selected nulliparous adult Wistar rats (n = 5) were submitted to 30 anorectal sessions of ARES with a biphasic current (700 μs, 50 Hz from 2 to 4 mA). After treatment, the animals were euthanized, and the anorectal segments were dissected and processed for histopathological analysis. Our results showed that ARES increased the widths of the mucosal, submucosal and muscle layers of the rectum, as well as the number of leukocytes in the mucosa. ARES also caused hyperplasia of the smooth muscle of the internal anal sphincter and hypertrophy of the external anal sphincter muscle. In conclusion, our results showed that ARES had not only a positive effect on the structure (morphology) of all tissues associated with the rectum and anus but, more importantly, on the structural gain of the muscles (hyperplasia and hypertrophy), which could point to a functional gain of the anal sphincter, reinforcing the applicability of ARES as a non-invasive treatment for anal incontinence.

Electromagnetic Fields and Stem Cell Fate: When Physics Meets Biology

Controlling stem cell (SC) fate is an extremely important topic in the realm of SC research. A variety of different external cues mainly mechanical, chemical, or electrical stimulations individually or in combination have been incorporated to control SC fate. Here, we will deconstruct the probable relationship between the functioning of electromagnetic (EMF) and SC fate of a variety of different SCs. The electromagnetic (EM) nature of the cells is discussed with the emphasis on the effects of EMF on the determinant factors that directly and/or indirectly influence cell fate. Based on the EM effects on a variety of cellular processes, it is believed that EMFs can be engineered to provide a controlled signal with the highest impact on the SC fate decision. Considering the novelty and broad applications of applying EMFs to change SC fate, it is necessary to shed light on many unclear mechanisms underlying this phenomenon.

Electrical Stimulation Increases Random Migration of Human Dermal Fibroblasts

Exogenous electrical stimulation (ES) has been investigated as a therapy for chronic wounds, as the skin produces currents and electrical fields (EFs) during wound healing. ES therapies operate by applying small EFs to the skin to mimic the transepithelial potentials that occur during the granulation phase of wound healing. Here, we investigated the effect of short duration (10 min) ES on the migration of HDFs using various magnitudes of physiologically relevant EFs. We modeled cutaneous injury by culturing HDFs in custom chambers that allowed the application of ES and then performed timelapse microscopy on a standard wound model. Using MATLAB to process cell coordinate data, we determined that the cells were migrating randomly and fit mean squared displacement data to the persistent random walk equation using nonlinear least squares regression analysis. Results indicated that application of 25-100 mV/mm DC EFs to HDFs on either uncoated or FN-coated surfaces demonstrated no significant changes in viability or proliferation. Of significance is that the HDFs increased random migration behavior under some ES conditions even after 10 min, providing a mechanism to enhance wound healing.

Electric field as a potential directional cue in homing of bone marrow-derived mesenchymal stem cells to cutaneous wounds

Bone marrow-derived cells are thought to participate and enhance the healing process contributing to skin cells or releasing regulatory cytokines. Directional cell migration in a weak direct current electric field (DC-EF), known as electrotaxis, may be a way of cell recruitment to the wound site. Here we examined the influence of electric field on bone marrow adherent cells (BMACs) and its potential role as a factor attracting mesenchymal stem cells to cutaneous wounds. We observed that in an external EF, BMAC movement was accelerated and highly directed with distinction of two cell populations migrating toward opposite poles: mesenchymal stem cells migrated toward the cathode, whereas macrophages toward the anode. Analysis of intracellular pathways revealed that macrophage electrotaxis mostly depended on Rho family small GTPases and calcium ions, but interruption of PI3K and Arp2/3 had the most pronounced effect on electrotaxis of MSCs. However, in all cases we observed only a partial decrease in directionality of cell movement after inhibition of certain proteins. Additionally, although we noticed the accumulation of EGFR at the cathodal side of MSCs, it was not involved in electrotaxis. Moreover, the cell reaction to EF was very dynamic with first symptoms occurring within <1min. In conclusion, the physiological DC-EF may act as a factor positioning bone marrow cells within a wound bed and the opposite direction of MSC and macrophage movement did not result either from utilizing different signalling or redistribution of investigated cell surface receptors.

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.

Electrochemical Potential Gradient as a Quantitative in Vitro Test Platform for Cellular Oxidative Stress

Oxidative stress in a biological system is often defined as a redox imbalance within cells or groups of cells within an organism. Reductive-oxidative (redox) imbalances in cellular systems have been implicated in several diseases, such as cancer. To better understand the redox environment within cellular systems, it is important to be able to characterize the relationship between the intensity of the oxidative environment, characterized by redox potential, and the biomolecular consequences of oxidative damage. In this study, we show that an in situ electrochemical potential gradient can serve as a tool to simulate exogenous oxidative stress in surface-attached mammalian cells. A culture plate design, which permits direct imaging and analysis of the cell viability, following exposure to a range of solution redox potentials, was developed. The in vitro oxidative stress test vessel consists of a cell growth flask fitted with two platinum electrodes that support a direct current along the flask bottom. The applied potential span and gradient slope can be controlled by adjusting the constant current magnitude across the vessel with spatially localized media potentials measured with a sliding reference electrode. For example, the viability of Chinese Hamster Ovary cells under a gradient of redox potentials indicated that cell death was initiated at approximately 0.4 V vs. standard hydrogen electrode (SHE) media potential and this potential could be modified with antioxidants. This experimental platform may facilitate studies of oxidative stress characteristics on different types of cells by enabling imaging live cell cultures that have been exposed to a gradient of exogenous redox potentials.

Uniform electric field generation in circular multi-well culture plates using polymeric inserts

Applying uniform electric field (EF) in vitro in the physiological range has been achieved in rectangular shaped microchannels. However, in a circular-shaped device, it is difficult to create uniform EF from two electric potentials due to different electrical resistances originated from the length difference between the diameter of the circle and the length of any parallel chord of the bottom circular chamber where cells are cultured. To address this challenge, we develop a three-dimensional (3D) computer-aided designed (CAD) polymeric insert to create uniform EF in circular shaped multi-well culture plates. A uniform EF with a coefficient of variation (CV) of 1.2% in the 6-well plate can be generated with an effective stimulation area percentage of 69.5%. In particular, NIH/3T3 mouse embryonic fibroblast cells are used to validate the performance of the 3D designed Poly(methyl methacrylate) (PMMA) inserts in a circular-shaped 6-well plate. The CAD based inserts can be easily scaled up (i.e., 100 mm dishes) to further increase effective stimulation area percentages, and also be implemented in commercially available cultureware for a wide variety of EF-related research such as EF-cell interaction and tissue regeneration studies.

Effects of electric fields on human mesenchymal stem cell behaviour and morphology using a novel multichannel device

The intrinsic piezoelectric nature of collagenous-rich tissues, such as bone and cartilage, can result in the production of small, endogenous electric fields (EFs) during applied mechanical stresses. In vivo, these EFs may influence cell migration, a vital component of wound healing. As a result, the application of small external EFs to bone fractures and cutaneous wounds is actively practiced clinically. Due to the significant regenerative potential of stem cells in bone and cartilage healing, and their potential role in the observed improved healing in vivo post applied EFs, using a novel medium throughput device, we investigated the impacts of physiological and aphysiological EFs on human bone marrow-derived mesenchymal stem cells (hBM-MSCs) for up to 15 hours. The applied EFs had significant impacts on hBM-MSC morphology and migration; cells displayed varying degrees of conversion to a highly elongated phenotype dependent on the EF strength, consistent perpendicular alignment to the EF vector, and definitive cathodal migration in response to EF strengths ≥0.5 V cm(-1), with the fastest migration speeds observed at between 1.7 and 3 V cm(-1). We observed variability in hBM-MSC donor-to-donor responses and overall tolerances to applied EFs. This study thus confirms hBM-MSCs are responsive to applied EFs, and their rate of migration towards the cathode is controllable depending on the EF strength, providing new insight into the physiology of hBM-MSCs and possibly a significant opportunity for the utilisation of EFs in directed scaffold colonisation in vitro for tissue engineering applications or in vivo post implantation.

Cell motility regulation on a stepped micro pillar array device (SMPAD) with a discrete stiffness gradient

Our tissues consist of individual cells that respond to the elasticity of their environment, which varies between and within tissues. To better understand mechanically driven cell migration, it is necessary to manipulate the stiffness gradient across a substrate. Here, we have demonstrated a new variant of the microfabricated polymeric pillar array platform that can decouple the stiffness gradient from the ECM protein area. This goal is achieved via a "stepped" micro pillar array device (SMPAD) in which the contact area with the cell was kept constant while the diameter of the pillar bodies was altered to attain the proper mechanical stiffness. Using double-step SU-8 mold fabrication, the diameter of the top of every pillar was kept uniform, whereas that of the bottom was changed, to achieve the desired substrate rigidity. Fibronectin was immobilized on the pillar tops, providing a focal adhesion site for cells. C2C12, HeLa and NIH3T3 cells were cultured on the SMPAD, and the motion of the cells was observed by time-lapse microscopy. Using this simple platform, which produces a purely physical stimulus, we observed that various types of cell behavior are affected by the mechanical stimulus of the environment. We also demonstrated directed cell migration guided by a discrete rigidity gradient by varying stiffness. Interestingly, cell velocity was highest at the highest stiffness. Our approach enables the regulation of the mechanical properties of the polymeric pillar array device and eliminates the effects of the size of the contact area. This technique is a unique tool for studying cellular motion and behavior relative to various stiffness gradients in the environment.

Lamellipodia and Membrane Blebs Drive Efficient Electrotactic Migration of Rat Walker Carcinosarcoma Cells WC 256

The endogenous electric field (EF) may provide an important signal for directional cell migration during wound healing, embryonic development and cancer metastasis but the mechanism of cell electrotaxis is poorly understood. Additionally, there is no research addressing the question on the difference in electrotactic motility of cells representing various strategies of cell movement—specifically blebbing vs. lamellipodial migration. In the current study we constructed a unique experimental model which allowed for the investigation of electrotactic movement of cells of the same origin but representing different modes of cell migration: weakly adherent, spontaneously blebbing (BC) and lamellipodia forming (LC) WC256 cells. We report that both BC and LC sublines show robust cathodal migration in a physiological EF (1–3 V/cm). The directionality of cell movement was completely reversible upon reversing the field polarity. However, the full reversal of cell direction after the change of EF polarity was much faster in the case of BC (10 minutes) than LC cells (30 minutes). We also investigated the distinct requirements for Rac, Cdc42 and Rho pathways and intracellular Ca²⁺ in electrotaxis of WC256 sublines forming different types of cell protrusions. It was found that Rac1 is required for directional movement of LC to a much greater extent than for BC, but Cdc42 and RhoA are more crucial for BC than for LC cells. The inhibition of ROCK did not affect electrotaxis of LC in contrast to BC cells. The results also showed that intracellular Ca²⁺ is essential only for the electrotactic reaction of BC cells. Moreover, inhibition of MLCK and myosin II did not affect the electrotaxis of LC in contrast to BC cells. In conclusion, our results revealed that both lamellipodia and membrane blebs can efficiently drive electrotactic migration of WC 256 carcinosarcoma cells, however directional migration is mediated by different signalling pathways.

Monophasic Pulsed 200-μA Current Promotes Galvanotaxis With Polarization of Actin Filament and Integrin α2β1 in Human Dermal Fibroblasts

OBJECTIVE

The monophasic pulsed microcurrent is used to promote wound healing, and galvanotaxis regulation has been reported as one of the active mechanisms in the promotion of tissue repair with monophasic pulsed microcurrent. However, the optimum monophasic pulsed microcurrent parameters and intracellular changes caused by the monophasic pulsed microcurrent have not been elucidated in human dermal fibroblasts. The purpose of this study was to investigate the optimum intensity for promoting galvanotaxis and the effects of electrical stimulation on integrin α2β1 and actin filaments in human dermal fibroblasts.

METHODS

Human dermal fibroblasts were treated with the monophasic pulsed microcurrent of 0, 100, 200, or 300 μA for 8 hours, and cell migration and cell viability were measured 24 hours after starting monophasic pulsed microcurrent stimulation. Polarization of integrin α2β1 and lamellipodia formation were detected by immunofluorescent staining 10 minutes after starting monophasic pulsed microcurrent stimulation.

RESULTS

The migration toward the cathode was significantly higher in the cells treated with the 200-μA monophasic pulsed microcurrent than in the controls (P < .01) without any change in cell viability; treatment with 300-μA monophasic pulsed microcurrent did not alter the migration ratio. The electrostimulus of 200 μA also promoted integrin α2β1 polarization and lamellipodia formation at the cathode edge (P < .05).

CONCLUSION

The results show that 200 μA is an effective monophasic pulsed microcurrent intensity to promote migration toward the cathode, and this intensity could regulate polarization of migration-related intracellular factors in human dermal fibroblasts.

Electric fields are novel determinants of human macrophage functions

Macrophages are key cells in inflammation and repair, and their activity requires close regulation. The characterization of cues coordinating macrophage function has focused on biologic and soluble mediators, with little known about their responses to physical stimuli, such as the electrical fields that are generated naturally in injured tissue and which accelerate wound healing. To address this gap in understanding, we tested how properties of human monocyte-derived macrophages are regulated by applied electrical fields, similar in strengths to those established naturally. With the use of live-cell video microscopy, we show that macrophage migration is directed anodally by electrical fields as low as 5 mV/mm and is electrical field strength dependent, with effects peaking ∼300 mV/mm. Monocytes, as macrophage precursors, migrate in the opposite, cathodal direction. Strikingly, we show for the first time that electrical fields significantly enhance macrophage phagocytic uptake of a variety of targets, including carboxylate beads, apoptotic neutrophils, and the nominal opportunist pathogen Candida albicans, which engage different classes of surface receptors. These electrical field-induced functional changes are accompanied by clustering of phagocytic receptors, enhanced PI3K and ERK activation, mobilization of intracellular calcium, and actin polarization. Electrical fields also modulate cytokine production selectively and can augment some effects of conventional polarizing stimuli on cytokine secretion. Taken together, electrical signals have been identified as major contributors to the coordination and regulation of important human macrophage functions, including those essential for microbial clearance and healing. Our results open up a new area of research into effects of naturally occurring and clinically applied electrical fields in conditions where macrophage activity is critical.

The Role of Kv1.2 Channel in Electrotaxis Cell Migration

Voltage-gated potassium Kv1.2 channels play pivotal role in maintaining of resting membrane potential and, consequently, regulation of cellular excitability of neurons. Endogenously generated electric field (EF) have been proven as an important regulator for cell migration and tissue repair. The mechanisms of ion channel involvement in EF-induced cell responses are extensively studied but largely are poorly understood. In this study we generated three COS-7 clones with different expression levels of Kv1.2 channel, and confirmed their functional variations with patch clamp analysis. Time-lapse imaging analysis showed that EF-induced cell migration response was Kv1.2 channel expression level depended. Inhibition of Kv1.2 channels with charybdotoxin (ChTX) constrained the sensitivity of COS-7 cells to EF stimulation more than their motility. Immunocytochemistry and pull-down analyses demonstrated association of Kv1.2 channels with actin-binding protein cortactin and its re-localization to the cathode-facing membrane at EF stimulation, which confirms the mechanism of EF-induced directional migration. This study displays that Kv1.2 channels represent an important physiological link in EF-induced cell migration. The described mechanism suggests a potential application of EF which may improve therapeutic performance in curing injuries of neuronal and/or cardiac tissue repair, post operational therapy, and various degenerative syndromes.

Calcium Ion Flow Permeates Cells through SOCs to Promote Cathode-Directed Galvanotaxis

Sensing and responding to endogenous electrical fields are important abilities for cells engaged in processes such as embryogenesis, regeneration and wound healing. Many types of cultured cells have been induced to migrate directionally within electrical fields in vitro using a process known as galvanotaxis. The underlying mechanism by which cells sense electrical fields is unknown. In this study, we assembled a polydimethylsiloxane (PDMS) galvanotaxis system and found that mouse fibroblasts and human prostate cancer PC3 cells migrated to the cathode. By comparing the effects of a pulsed direct current, a constant direct current and an anion-exchange membrane on the directed migration of mouse fibroblasts, we found that these cells responded to the ionic flow in the electrical fields. Taken together, the observed effects of the calcium content of the medium, the function of the store-operated calcium channels (SOCs) and the intracellular calcium content on galvanotaxis indicated that calcium ionic flow from the anode to the cathode within the culture medium permeated the cells through SOCs at the drift velocity, promoting migration toward the cathode. The RTK-PI3K pathway was involved in this process, but the ROCK and MAPK pathways were not. PC3 cells and mouse fibroblasts utilized the same mechanism of galvanotaxis. Together, these results indicated that the signaling pathway responsible for cathode-directed cellular galvanotaxis involved calcium ionic flow from the anode to the cathode within the culture medium, which permeated the cells through SOCs, causing cytoskeletal reorganization via PI3K signaling.

Correlation between cell migration and reactive oxygen species under electric field stimulation

Cell migration is an essential process involved in the development and maintenance of multicellular organisms. Electric fields (EFs) are one of the many physical and chemical factors known to affect cell migration, a phenomenon termed electrotaxis or galvanotaxis. In this paper, a microfluidics chip was developed to study the migration of cells under different electrical and chemical stimuli. This chip is capable of providing four different strengths of EFs in combination with two different chemicals via one simple set of agar salt bridges and Ag/AgCl electrodes. NIH 3T3 fibroblasts were seeded inside this chip to study their migration and reactive oxygen species (ROS) production in response to different EF strengths and the presence of β-lapachone. We found that both the EF and β-lapachone level increased the cell migration rate and the production of ROS in an EF-strength-dependent manner. A strong linear correlation between the cell migration rate and the amount of intracellular ROS suggests that ROS are an intermediate product by which EF and β-lapachone enhance cell migration. Moreover, an anti-oxidant, α-tocopherol, was found to quench the production of ROS, resulting in a decrease in the migration rate.

Opposing Rigidity-Protein Gradients Reverse Fibroblast Durotaxis

The migration of cells is a complex and dynamic process that is governed by several stimuli acting simultaneously. In vivo, cells receive and process a wide range of cues that guide their motion and migratory characteristics such as speed and directionality. The design of biomaterials that can recapitulate the combinatorial signaling environment can aid in understanding how migrating cells respond to more than one stimulus and when one cue dominates over the other. We have designed hydrogel substrates that exhibit opposing rigidity-and collagen gradients. Within the boundaries of the interfacial region, the values for substrate modulus decreased in one direction with a concomitant increase in the concentration of surface-bound collagen. The well-known durotactic migration of fibroblasts was first validated on substrates that only exhibit a gradient in modulus while keeping the concentration of surface-bound collagen constant. Upon increasing the collagen concentration on the low-modulus regions by 4- or 7-fold compared to the high-modulus side of the interface, cells exhibited directed migration toward the soft regions of the substrate. This effect was more pronounced when the surface-bound collagen concentration was 7-fold greater. Cell displacements, areas, cytoskeleton and focal adhesions were investigated on the opposing rigidity-immobilized collagen gradients. These features were affected by the elastic modulus of the substrate as well as the change in protein concentration. In the future, incorporating multiple gradients within a single substrate will lead to a deeper and more comprehensive understanding of cells navigate through the complex in vivo microenvironment.

Segmentation of the Clustered Cells with Optimized Boundary Detection in Negative Phase Contrast Images

Cell image segmentation plays a central role in numerous biology studies and clinical applications. As a result, the development of cell image segmentation algorithms with high robustness and accuracy is attracting more and more attention. In this study, an automated cell image segmentation algorithm is developed to get improved cell image segmentation with respect to cell boundary detection and segmentation of the clustered cells for all cells in the field of view in negative phase contrast images. A new method which combines the thresholding method and edge based active contour method was proposed to optimize cell boundary detection. In order to segment clustered cells, the geographic peaks of cell light intensity were utilized to detect numbers and locations of the clustered cells. In this paper, the working principles of the algorithms are described. The influence of parameters in cell boundary detection and the selection of the threshold value on the final segmentation results are investigated. At last, the proposed algorithm is applied to the negative phase contrast images from different experiments. The performance of the proposed method is evaluated. Results show that the proposed method can achieve optimized cell boundary detection and highly accurate segmentation for clustered cells.

Effects of high voltage pulsed current stimulation with a visible contraction intensity on expression of TGF-β1 and synthesis of type I collagen in wound-induced white rats

[Purpose] This study aimed to examine the expression of transforming growth factor β1 (TGF-β1) and type I collagen by applying high voltage pulsed current stimulation (HVPCS) with a visible contraction intensity to white rats with induced wounds. [Subjects] Thirty-six white rats were used for this study. HVPCS with a non-visible contraction intensity was applied to experimental group I, and HVPCS with a visible contraction intensity was applied to experimental group II. Placebo stimulation was applied to the control group. [Methods] After wounds were triggered, the intervention appropriate for each group was applied. Changes in the size of their wounds and expression of TGF- β1 and type I collagen were measured on the third, fifth, and seventh days. [Results] Comparison of the sizes of the wounds among the groups showed that the most significant decreases were found in experimental group II on the fifth and seventh days. TGF-β1 expression comparison revealed that experimental group II had the most expression on the fifth day. [Conclusion] HVPCS with a visible contraction intensity was effective in promoting wound healing by increasing expression of TGF-β1 and synthesis of type I collagen.

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.

DC electric fields direct breast cancer cell migration, induce EGFR polarization, and increase the intracellular level of calcium ions

Migration of cancer cells leads to invasion of primary tumors to distant organs (i.e., metastasis). Growing number of studies have demonstrated the migration of various cancer cell types directed by applied direct current electric fields (dcEF), i.e., electrotaxis, and suggested its potential implications in metastasis. MDA-MB-231 cell, a human metastatic breast cancer cell line, has been shown to migrate toward the anode of dcEF. Further characterizations of MDA-MB-231 cell electrotaxis and investigation of its underlying signaling mechanisms will lead to a better understanding of electrically guided cancer cell migration and metastasis. Therefore, we quantitatively characterized MDA-MB-231 cell electrotaxis and a few associated signaling events. Using a microfluidic device that can create well-controlled dcEF, we showed the anode-directing migration of MDA-MB-231 cells. In addition, surface staining of epidermal growth factor receptor (EGFR) and confocal microscopy showed the dcEF-induced anodal EGFR polarization in MDA-MB-231 cells. Furthermore, we showed an increase of intracellular calcium ions in MDA-MB-231 cells upon dcEF stimulation. Altogether, our study provided quantitative measurements of electrotactic migration of MDA-MB-231 cells, and demonstrated the electric field-mediated EGFR and calcium signaling events, suggesting their involvement in breast cancer cell electrotaxis.