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

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.

Development of a Cell Culture Chamber for Investigating the Therapeutic Effects of Electrical Stimulation on Neural Growth

Natural electric fields exist throughout the body during development and following injury, and, as such, EFs have the potential to be utilized to guide cell growth and regeneration. Electrical stimulation (ES) can also affect gene expression and other cellular behaviors, including cell migration and proliferation. To investigate the effects of electric fields on cells in vitro, a sterile chamber that delivers electrical stimuli is required. Here, we describe the construction of an ES chamber through the modification of an existing lid of a 6-well cell culture plate. Using human SH-SY5Y neuroblastoma cells, we tested the biocompatibility of materials, such as Araldite®, Tefgel™ and superglue, that were used to secure and maintain platinum electrodes to the cell culture plate lid, and we validated the electrical properties of the constructed ES chamber by calculating the comparable electrical conductivities of phosphate-buffered saline (PBS) and cell culture media from voltage and current measurements obtained from the ES chamber. Various electrical signals and durations of stimulation were tested on SH-SY5Y cells. Although none of the signals caused significant cell death, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays revealed that shorter stimulation times and lower currents minimized negative effects. This design can be easily replicated and can be used to further investigate the therapeutic effects of electrical stimulation on neural cells.

Electro-mechanical coupling directs endothelial activities through intracellular calcium ion deployment

Conversion between mechanical and electrical cues is usually considered unidirectional in cells with cardiomyocytes being an exception. Here, we discover a material-induced external electric field (Eex) triggers an electro-mechanical coupling feedback loop in cells other than cardiomyocytes, human umbilical vein endothelial cells (HUVECs), by opening their mechanosensitive Piezo1 channels. When HUVECs are cultured on patterned piezoelectric materials, the materials generate Eex (confined at the cellular scale) to polarize intracellular calcium ions ([Ca2+]i), forming a built-in electric field (Ein) opposing Eex. Furthermore, the [Ca2+]i polarization stimulates HUVECs to shrink their cytoskeletons, activating Piezo1 channels to induce influx of extracellular Ca2+ that gradually increases Ein to balance Eex. Such an electro-mechanical coupling feedback loop directs pre-angiogenic activities such as alignment, elongation, and migration of HUVECs. Activated calcium dynamics during the coupling further modulate the downstream angiogenesis-inducing eNOS/NO pathway. These findings lay a foundation for developing new ways of electrical stimulation-based disease treatment.

Fiber and Electrical Field Alignment Increases BDNF Expression in SH-SY5Y Cells following Electrical Stimulation

The limited expression of neurotrophic factors that can be included in neural tissue engineering scaffolds is insufficient for sustained neural regeneration. A localized and sustained method of introducing neurotrophic factors is required. We describe our attempt at inducing neuroblastoma cells to express trophic factors following electrical stimulation. Human SH-SY5Y neuroblastoma cells, cultured on polycaprolactone electrospun nanofibers, were electrically stimulated using a 100 mV/mm electric field. Nuclear morphology and brain-derived neurotrophic factor (BDNF) expression were analyzed. Cells were classified based on the type of fiber orientation and the alignment of these fibers in relation to the electric field. Nuclear deformation was mainly influenced by fiber orientation rather than the electrical field. Similarly, fiber orientation also induced BDNF expression. Although electrical field alone had no significant effect on BDNF expression, combining fiber orientation with electrical field resulted in BDNF expression in cells that grew on electrospun fibers that were aligned perpendicular to the electrical field.

Thermosensitive hydrogel carrying extracellular vesicles from adipose-derived stem cells promotes peripheral nerve regeneration after microsurgical repair

Peripheral nerve injuries are commonly occurring traumas of the extremities; functional recovery is hindered by slow nerve regeneration (<1 mm/day) following microsurgical repair and subsequent muscle atrophy. Functional recovery after peripheral nerve repair is highly dependent on local Schwann cell activity and axon regeneration speed. Herein, to promote nerve regeneration, paracrine signals of adipose-derived stem cells were applied in the form of extracellular vesicles (EVs) loaded in a thermosensitive hydrogel (PALDE) that could solidify rapidly and sustain high EV concentration around a repaired nerve during surgery. Cell experiments revealed that PALDE hydrogel markedly promotes Schwann-cell migration and proliferation and axon outgrowth. In a rat sciatic nerve repair model, the PALDE hydrogel increased repaired-nerve conduction efficacy; contraction force of leg muscles innervated by the repaired nerve also recovered. Electromicroscopic examination of downstream nerves indicated that fascicle diameter and myeline thickness in the PALDE group (1.91 ± 0.61 and 1.06 ± 0.40 μm, respectively) were significantly higher than those in PALD and control groups. Thus, this EV-loaded thermosensitive hydrogel is a potential cell-free therapeutic modality to improve peripheral-nerve regeneration, offering sustained and focused EV release around the nerve-injury site to overcome rapid clearance and maintain EV bioactivity in vivo.

The impact of physical, biochemical, and electrical signaling on Schwann cell plasticity

Peripheral nervous system (PNS) injuries are an ongoing health care concern. While autografts and allografts are regarded as the current clinical standard for traumatic injury, there are inherent limitations that suggest alternative remedies should be considered for therapeutic purposes. In recent years, nerve guidance conduits (NGCs) have become increasingly popular as surgical repair devices, with a multitude of various natural and synthetic biomaterials offering potential to enhance the design of conduits or supplant existing technologies entirely. From a cellular perspective, it has become increasingly evident that Schwann cells (SCs), the primary glia of the PNS, are a predominant factor mediating nerve regeneration. Thus, the development of severe nerve trauma therapies requires a deep understanding of how SCs interact with their environment, and how SC microenvironmental cues may be engineered to enhance regeneration. Here we review the most recent advancements in biomaterials development and cell stimulation strategies, with a specific focus on how the microenvironment influences the behavior of SCs and can potentially lead to functional repair. We focus on microenvironmental cues that modulate SC morphology, proliferation, migration, and differentiation to alternative phenotypes. Promotion of regenerative phenotypic responses in SCs and other non-neuronal cells that can augment the regenerative capacity of multiple biomaterials is considered along with innovations and technologies for traumatic injury.

Use of weak DC electric fields to rapidly align mammalian cells

Objective.The ability to modulate cell morphology has clinical relevance in regenerative biology. For example, cells of the skeletal muscle, peripheral nerve and vasculature have specific oriented architectures that emerge from unique structure-function relationships. Methods that can induce similar cell morphologiesin vitrocan be of use in the development of biomimetic constructs for the repair or replacement of damaged tissues. In this work, we demonstrate that direct current (DC) electric fields (EFs) can be used as a tool to globally align cell populationsin vitro. Approach.Using a 2D culture chamber system, we were able to quickly (within hours) align Schwann cells at different culture densities with an application of steady EFs at 200-500 mV mm^-1.Main results.Cellular alignment was perpendicular to the field vector and varied proportionately as a function of field magnitude. In addition, the degree of cellular alignment was also dependent on cellular density. Even well-established Schwann cell monolayers were responsive to the applied DC fields with cells retracting parallel oriented processes (with respect to the imposed field) and re-extending them along the perpendicular axis. When the DC field was removed, monolayers retained the aligned morphology for many days afterwards, likely due to contact inhibition. We further show the method is applicable to other field-responsive cells, such as 3T3 fibroblasts.Significance.The patterned cells provided nanoscale haptotactic cues and can be subsequently used as a basal layer for co-culturing or manipulated for other applications. DC fields represent a rapid, simple, and efficient technique compared to other cell patterning methods such as substrate manipulation.

Mesenchymal stem cell treatment for peripheral nerve injury: a narrative review

Peripheral nerve injuries occur as the result of sudden trauma and lead to reduced quality of life. The peripheral nervous system has an inherent capability to regenerate axons. However, peripheral nerve regeneration following injury is generally slow and incomplete that results in poor functional outcomes such as muscle atrophy. Although conventional surgical procedures for peripheral nerve injuries present many benefits, there are still several limitations including scarring, difficult accessibility to donor nerve, neuroma formation and a need to sacrifice the autologous nerve. For many years, other therapeutic approaches for peripheral nerve injuries have been explored, the most notable being the replacement of Schwann cells, the glial cells responsible for clearing out debris from the site of injury. Introducing cultured Schwann cells to the injured sites showed great benefits in promoting axonal regeneration and functional recovery. However, there are limited sources of Schwann cells for extraction and difficulties in culturing Schwann cells in vitro. Therefore, novel therapeutic avenues that offer maximum benefits for the treatment of peripheral nerve injuries should be investigated. This review focused on strategies using mesenchymal stem cells to promote peripheral nerve regeneration including exosomes of mesenchymal stem cells, nerve engineering using the nerve guidance conduits containing mesenchymal stem cells, and genetically engineered mesenchymal stem cells. We present the current progress of mesenchymal stem cell treatment of peripheral nerve injuries.

Collective cell migration of fibroblasts is affected by horizontal vibration of the cell culture dish

Regulating the collective migration of cells is an important issue in bioengineering. Enhancing or suppressing cell migration and controlling the migration direction is useful for various physiological phenomena such as wound healing. Several methods of migration regulation based on different mechanical stimuli have been reported. While vibrational stimuli, such as sound waves, show promise for regulating migration, the effect of the vibration direction on collective cell migration has not been studied in depth. Therefore, we fabricated a vibrating system that can apply horizontal vibration to a cell culture dish. Here, we evaluated the effect of the vibration direction on the collective migration of fibroblasts in a wound model comprising two culture areas separated by a gap. Results showed that the vibration direction affects the cell migration distance: vibration orthogonal to the gap enhances the collective cell migration distance while vibration parallel to the gap suppresses it. Results also showed that conditions leading to enhanced migration distance were also associated with elevated glucose consumption. Furthermore, under conditions promoting cell migration, the cell nuclei become elongated and oriented orthogonal to the gap. In contrast, under conditions that reduce the migration distance, cell nuclei were oriented to the direction parallel to the gap.

Partial enzyme digestion facilitates regeneration of crushed nerve in rat

Peripheral nerve injury is a life-changing disability with significant socioeconomic consequences. In this rat model, we propose that partial enzyme digestion can facilitate the functional recovery of a crushed nerve. The sciatic nerves were harvested and in vitro cultured with the addition of Liberase to determine the appropriate enzyme amount in the hyaluronic acid (HA) membrane. Then, the sciatic nerve of adult male Sprague-Dawley rats was exposed, crushed, and then treated with partial enzyme digestion (either 0.001 or 0.002 unit/mm² Liberase-HA membrane). The sciatic function index (SFI) for functional recovery of the sciatic nerve was evaluated. After 2 h of in vitro digestion, fascicles and axons were separated from each other, with the cells mobilized. Greater destruction of histology structures occurred in the high enzyme (Liberase-HA membrane at 0.002 unit/mm²) group at 24 h than in the low enzyme (0.001 unit/mm²) group at 48 h. In the SFI evaluation, the improvement in 0.001 unit/mm² Liberase group was significantly better than control and 0.002 unit/mm² Liberase group. Our study demonstrated that appropriate enzyme digestion had a significantly faster and earlier recovery.

Effects of Microstripe Geometry on Guided Cell Migration

Cell migration on material surfaces is a fundament issue in the fields of biomaterials, cell biology, tissue engineering, regenerative medicine, etc. Herein, we aim to guide cell migration by flat microstripes with significant contrast of cell adhesion and varied geometric features of the adhesive stripes. To this end, we designed and fabricated cell-adhesive arginine-glycine-aspartate (RGD) microstripes on the nonfouling poly(ethylene glycol) (PEG) background and examined the microstripe-guided adhesion and migration of a few cell types. The migration of cell clusters adhering on the RGD regions was found to be significantly affected by the widths and arc radiuses of the guided microstripes. The cells migrated fastest on the straight microstripes with width of about 20 μm, which we defined as single file confined migration (SFCM). We also checked the possible left-right asymmetric bias of cell migration guided by combinatory microstripes with alternative wavy and quasi-straight stripes under a given width, and found that the velocity of CCW (counter clockwise) migration was higher than that of CW (clockwise) migration for primary rat mesenchymal stem cells (rMSCs), whereas no left-right asymmetric bias was observed for NIH3T3 (mouse embryonic fibroblast cell line) and Hela (human cervix epithelial carcinoma cell line) cells. Comparison of migration of cells on the nanotopological stripe and smooth surfaces further confirmed the importance of cell orientation coherence for guided cell migration and strengthened the superiority of SFCM.