Bioelectric mechanisms in regeneration: Unique aspects and future perspectives

Multifunctional scaffolds for bone repair following age-related biological decline: Promising prospects for smart biomaterial-driven technologies

The repair of large bone defects due to trauma, disease, and infection can be exceptionally challenging in the elderly. Despite best clinical practice, bone regeneration within contemporary, surgically implanted synthetic scaffolds is often problematic, inconsistent, and insufficient where additional osteobiological support is required to restore bone. Emergent smart multifunctional biomaterials may drive important and dynamic cellular crosstalk that directly targets, signals, stimulates, and promotes an innate bone repair response following age-related biological decline and when in the presence of disease or infection. However, their role remains largely undetermined. By highlighting their mechanism/s and mode/s of action, this review spotlights smart technologies that favorably align in their conceivable ability to directly target and enhance bone repair and thus are highly promising for future discovery for use in the elderly. The four degrees of interactive scaffold smartness are presented, with a focus on bioactive, bioresponsive, and the yet-to-be-developed autonomous scaffold activity. Further, cell- and biomolecular-assisted approaches were excluded, allowing for contemporary examination of the capabilities, demands, vision, and future requisites of next-generation biomaterial-induced technologies only. Data strongly supports that smart scaffolds hold significant promise in the promotion of bone repair in patients with a reduced osteobiological response. Importantly, many techniques have yet to be tested in preclinical models of aging. Thus, greater clarity on their proficiency to counteract the many unresolved challenges within the scope of aging bone is highly warranted and is arguably the next frontier in the field. This review demonstrates that the use of multifunctional smart synthetic scaffolds with an engineered strategy to circumvent the biological insufficiencies associated with aging bone is a viable route for achieving next-generation therapeutic success in the elderly population.

Application and Development of Electrospun Nanofiber Scaffolds for Bone Tissue Engineering

Nanofiber scaffolds have gained significant attention in the field of bone tissue engineering. Electrospinning, a straightforward and efficient technique for producing nanofibers, has been extensively researched. When used in bone tissue engineering scaffolds, electrospun nanofibers with suitable surface properties promote new bone tissue growth and enhance cell adhesion. Recent advancements in electrospinning technology have provided innovative approaches for scaffold fabrication in bone tissue engineering. This review comprehensively examines the utilization of electrospun nanofibers in bone tissue engineering scaffolds and evaluates the relevant literature. The review begins by presenting the fundamental principles and methodologies of electrospinning. It then discusses various materials used in the production of electrospun nanofiber scaffolds for bone tissue engineering, including natural and synthetic polymers, as well as certain inorganic materials. The challenges associated with these materials are also described. The review focuses on novel electrospinning techniques for scaffold construction in bone tissue engineering, such as multilayer nanofibers, multifluid electrospinning, and the integration of electrospinning with other methods. Recent advancements in electrospinning technology have enabled the fabrication of precisely aligned nanofiber scaffolds with nanoscale architectures. These innovative methods also facilitate the fabrication of biomimetic structures, wherein bioactive substances can be incorporated and released in a controlled manner for drug delivery purposes. Moreover, they address issues encountered with traditional electrospun nanofibers, such as mechanical characteristics and biocompatibility. Consequently, the development and implementation of novel electrospinning technologies have revolutionized scaffold fabrication for bone tissue engineering.

Progress in the development of piezoelectric biomaterials for tissue remodeling

Piezoelectric biomaterials have demonstrated significant potential in the past few decades to heal damaged tissue and restore cellular functionalities. Herein, we discuss the role of bioelectricity in tissue remodeling and explore ways to mimic such tissue-like properties in synthetic biomaterials. In the past decade, biomedical engineers have adopted emerging functional biomaterials-based tissue engineering approaches using innovative bioelectronic stimulation protocols based on dynamic stimuli to direct cellular activation, proliferation, and differentiation on engineered biomaterial constructs. The primary focus of this review is to discuss the concepts of piezoelectric energy harvesting, piezoelectric materials, and their application in soft (skin and neural) and hard (dental and bone) tissue regeneration. While discussing the prospective applications as an engineered tissue, an important distinction has been made between piezoceramics, piezopolymers, and their composites. The superiority of piezopolymers over piezoceramics to circumvent issues such as stiffness mismatch, biocompatibility, and biodegradability are highlighted. We aim to provide a comprehensive review of the field and identify opportunities for the future to develop clinically relevant and state-of-the-art biomaterials for personalized and remote health care.

Electrical Stimulation for Immunomodulation

The immune system plays a key role in the development and progression of numerous diseases such as chronic wounds, autoimmune diseases, and various forms of cancer. Hence, controlling the behavior of immune cells has emerged as a promising approach for treating these diseases. Current modalities for immunomodulation focus on chemical based approaches, which while effective have the limitations of nonspecific systemic side effects or requiring invasive delivery approaches to reduce the systemic side effects. Recent advances have unraveled the significance of electrical stimulation as an attractive noninvasive approach to modulate immune cell phenotype and activity. This review provides insights on electrical stimulation strategies employed for regulating the behavior of macrophages, T and B cells, and neutrophils. For obtaining a better understanding, two major types of electrical stimulation sources, conventional and self-powered sources, that have been used for immunomodulation are extensively discussed. Next, the strategies of electrical stimulation that may be applied to cells in vitro and in vivo are discussed, with a focus on conventional and stimuli-responsive self-powered sources. A description of how these strategies influence the polarization, phagocytosis, migration, and differentiation of immune cells is also provided. Finally, recent developments in the use of highly localized and efficient platforms for electrical stimulation based immunomodulation are also highlighted.

Advances in Conductive Hydrogel for Spinal Cord Injury Repair and Regeneration

Spinal cord injury (SCI) treatment represents a major challenge in clinical practice. In recent years, the rapid development of neural tissue engineering technology has provided a new therapeutic approach for spinal cord injury repair. Implanting functionalized electroconductive hydrogels (ECH) in the injury area has been shown to promote axonal regeneration and facilitate the generation of neuronal circuits by reshaping the microenvironment of SCI. ECH not only facilitate intercellular electrical signaling but, when combined with electrical stimulation, enable the transmission of electrical signals to electroactive tissue and activate bioelectric signaling pathways, thereby promoting neural tissue repair. Therefore, the implantation of ECH into damaged tissues can effectively restore physiological functions related to electrical conduction. This article focuses on the dynamic pathophysiological changes in the SCI microenvironment and discusses the mechanisms of electrical stimulation/signal in the process of SCI repair. By examining electrical activity during nerve repair, we provide insights into the mechanisms behind electrical stimulation and signaling during SCI repair. We classify conductive biomaterials, and offer an overview of the current applications and research progress of conductive hydrogels in spinal cord repair and regeneration, aiming to provide a reference for future explorations and developments in spinal cord regeneration strategies.

Agency, Goal-Directed Behavior, and Part-Whole Relationships in Biological Systems

In this essay we aim to present some considerations regarding a minimal but concrete notion of agency and goal-directed behavior that are useful for characterizing biological systems at different scales. These considerations are a particular perspective, bringing together concepts from dynamical systems, combinatorial problem-solving, and connectionist learning with an emphasis on the relationship between parts and wholes. This perspective affords some ways to think about agents that are concrete and quantifiable, and relevant to some important biological issues. Instead of advocating for a strict definition of minimally agential characteristics, we focus on how (even for a modest notion of agency) the agency of a system can be more than the sum of the agency of its parts. We quantify this in terms of the problem-solving competency of a system with respect to resolution of the frustrations between its parts. This requires goal-directed behavior in the sense of delayed gratification, i.e., taking dynamical trajectories that forego short-term gains (or sustain short-term stress or frustration) in favor of long-term gains. In order for this competency to belong to the system (rather than to its parts or given by its construction or design), it can involve distributed systemic knowledge that is acquired through experience, i.e., changes in the organization of the relationships among its parts (without presupposing a system-level reward function for such changes). This conception of agency helps us think about the ways in which cells, organisms, and perhaps other biological scales, can be agential (i.e., more agential than their parts) in a quantifiable sense, without denying that the behavior of the whole depends on the behaviors of the parts in their current organization.

Bioelectric networks: the cognitive glue enabling evolutionary scaling from physiology to mind

Each of us made the remarkable journey from mere matter to mind: starting life as a quiescent oocyte ("just chemistry and physics"), and slowly, gradually, becoming an adult human with complex metacognitive processes, hopes, and dreams. In addition, even though we feel ourselves to be a unified, single Self, distinct from the emergent dynamics of termite mounds and other swarms, the reality is that all intelligence is collective intelligence: each of us consists of a huge number of cells working together to generate a coherent cognitive being with goals, preferences, and memories that belong to the whole and not to its parts. Basal cognition is the quest to understand how Mind scales-how large numbers of competent subunits can work together to become intelligences that expand the scale of their possible goals. Crucially, the remarkable trick of turning homeostatic, cell-level physiological competencies into large-scale behavioral intelligences is not limited to the electrical dynamics of the brain. Evolution was using bioelectric signaling long before neurons and muscles appeared, to solve the problem of creating and repairing complex bodies. In this Perspective, I review the deep symmetry between the intelligence of developmental morphogenesis and that of classical behavior. I describe the highly conserved mechanisms that enable the collective intelligence of cells to implement regulative embryogenesis, regeneration, and cancer suppression. I sketch the story of an evolutionary pivot that repurposed the algorithms and cellular machinery that enable navigation of morphospace into the behavioral navigation of the 3D world which we so readily recognize as intelligence. Understanding the bioelectric dynamics that underlie construction of complex bodies and brains provides an essential path to understanding the natural evolution, and bioengineered design, of diverse intelligences within and beyond the phylogenetic history of Earth.

Physical stimuli-emitting scaffolds: The role of piezoelectricity in tissue regeneration

The imbalance between life expectancy and quality of life is increasing due to the raising prevalence of chronic diseases. Musculoskeletal disorders and chronic wounds affect a growing percentage of people and demand more efficient tools for regenerative medicine. Scaffolds that can better mimic the natural physical stimuli that tissues receive under healthy conditions and during healing may significantly aid the regeneration process. Shape, mechanical properties, pore size and interconnectivity have already been demonstrated to be relevant scaffold features that can determine cell adhesion and differentiation. Much less attention has been paid to scaffolds that can deliver more dynamic physical stimuli, such as electrical signals. Recent developments in the precise measurement of electrical fields in vivo have revealed their key role in cell movement (galvanotaxis), growth, activation of secondary cascades, and differentiation to different lineages in a variety of tissues, not just neural. Piezoelectric scaffolds can mimic the natural bioelectric potentials and gradients in an autonomous way by generating the electric stimuli themselves when subjected to mechanical loads or, if the patient or the tissue lacks mobility, ultrasound irradiation. This review provides an analysis on endogenous bioelectrical signals, recent developments on piezoelectric scaffolds for bone, cartilage, tendon and nerve regeneration, and their main outcomes in vivo. Wound healing with piezoelectric dressings is addressed in the last section with relevant examples of performance in animal models. Results evidence that a fine adjustment of material composition and processing (electrospinning, corona poling, 3D printing, annealing) provides scaffolds that act as true emitters of electrical stimuli that activate endogenous signaling pathways for more efficient and long-term tissue repair.

Epithelial Ca2+ waves triggered by enteric neurons heal the gut

A fundamental and unresolved question in regenerative biology is how tissues return to homeostasis after injury. Answering this question is essential for understanding the etiology of chronic disorders such as inflammatory bowel diseases and cancer. We used the Drosophila midgut to investigate this question and discovered that during regeneration a subpopulation of cholinergic enteric neurons triggers Ca2+ currents among enterocytes to promote return of the epithelium to homeostasis. Specifically, we found that down-regulation of the cholinergic enzyme Acetylcholinesterase in the epithelium enables acetylcholine from defined enteric neurons, referred as ARCENs, to activate nicotinic receptors in enterocytes found near ARCEN-innervations. This activation triggers high Ca2+ influx that spreads in the epithelium through Inx2/Inx7 gap junctions promoting enterocyte maturation followed by reduction of proliferation and inflammation. Disrupting this process causes chronic injury consisting of ion imbalance, Yki activation and increase of inflammatory cytokines together with hyperplasia, reminiscent of inflammatory bowel diseases. Altogether, we found that during gut regeneration the conserved cholinergic pathway facilitates epithelial Ca2+ waves that heal the intestinal epithelium. Our findings demonstrate nerve- and bioelectric-dependent intestinal regeneration which advance the current understanding of how a tissue returns to its homeostatic state after injury and could ultimately help existing therapeutics.

Multiscalar electrical spiking in Schizophyllum commune

Growing colonies of the split-gill fungus Schizophyllum commune show action potential-like spikes of extracellular electrical potential. We analysed several days of electrical activity recording of the fungus and discovered three families of oscillatory patterns. Very slow activity at a scale of hours, slow activity at a scale of 10 min and very fast activity at scale of half-minute. We simulated the spiking behaviour using FitzHugh-Nagume model, uncovered mechanisms of spike shaping. We speculated that spikes of electrical potential might be associated with transportation of nutrients and metabolites.

Advances in protein glycosylation and its role in tissue repair and regeneration

After tissue damage, a series of molecular and cellular events are initiated to promote tissue repair and regeneration to restore its original structure and function. These events include inter-cell communication, cell proliferation, cell migration, extracellular matrix differentiation, and other critical biological processes. Glycosylation is the crucial conservative and universal post-translational modification in all eukaryotic cells [1], with influential roles in intercellular recognition, regulation, signaling, immune response, cellular transformation, and disease development. Studies have shown that abnormally glycosylation of proteins is a well-recognized feature of cancer cells, and specific glycan structures are considered markers of tumor development. There are many studies on gene expression and regulation during tissue repair and regeneration. Still, there needs to be more knowledge of complex carbohydrates' effects on tissue repair and regeneration, such as glycosylation. Here, we present a review of studies investigating protein glycosylation in the tissue repair and regeneration process.

A Comprehensive conceptual and computational dynamics framework for autonomous regeneration of form and function in biological organisms

In biology, regeneration is a mysterious phenomenon that has inspired self-repairing systems, robots, and biobots. It is a collective computational process whereby cells communicate to achieve an anatomical set point and restore original function in regenerated tissue or the whole organism. Despite decades of research, the mechanisms involved in this process are still poorly understood. Likewise, the current algorithms are insufficient to overcome this knowledge barrier and enable advances in regenerative medicine, synthetic biology, and living machines/biobots. We propose a comprehensive conceptual framework for the engine of regeneration with hypotheses for the mechanisms and algorithms of stem cell-mediated regeneration that enables a system like the planarian flatworm to fully restore anatomical (form) and bioelectric (function) homeostasis from any small- or large-scale damage. The framework extends the available regeneration knowledge with novel hypotheses to propose collective intelligent self-repair machines with multi-level feedback neural control systems driven by somatic and stem cells. We computationally implemented the framework to demonstrate the robust recovery of both form and function (anatomical and bioelectric homeostasis) in an in silico worm that, in a simple way, resembles the planarian. In the absence of complete regeneration knowledge, the framework contributes to understanding and generating hypotheses for stem cell mediated form and function regeneration, which may help advance regenerative medicine and synthetic biology. Further, as our framework is a bio-inspired and bio-computing self-repair machine, it may be useful for building self-repair robots/biobots and artificial self-repair systems.

Integrative biology of injury in animals

Mechanical injury is a prevalent challenge in the lives of animals with myriad potential consequences for organisms, including reduced fitness and death. Research on animal injury has focused on many aspects, including the frequency and severity of wounding in wild populations, the short- and long-term consequences of injury at different biological scales, and the variation in the response to injury within or among individuals, species, ontogenies, and environmental contexts. However, relevant research is scattered across diverse biological subdisciplines, and the study of the effects of injury has lacked synthesis and coherence. Furthermore, the depth of knowledge across injury biology is highly uneven in terms of scope and taxonomic coverage: much injury research is biomedical in focus, using mammalian model systems and investigating cellular and molecular processes, while research at organismal and higher scales, research that is explicitly comparative, and research on invertebrate and non-mammalian vertebrate species is less common and often less well integrated into the core body of knowledge about injury. The current state of injury research presents an opportunity to unify conceptually work focusing on a range of relevant questions, to synthesize progress to date, and to identify fruitful avenues for future research. The central aim of this review is to synthesize research concerning the broad range of effects of mechanical injury in animals. We organize reviewed work by four broad and loosely defined levels of biological organization: molecular and cellular effects, physiological and organismal effects, behavioural effects, and ecological and evolutionary effects of injury. Throughout, we highlight the diversity of injury consequences within and among taxonomic groups while emphasizing the gaps in taxonomic coverage, causal understanding, and biological endpoints considered. We additionally discuss the importance of integrating knowledge within and across biological levels, including how initial, localized responses to injury can lead to long-term consequences at the scale of the individual animal and beyond. We also suggest important avenues for future injury biology research, including distinguishing better between related yet distinct injury phenomena, expanding the subjects of injury research to include a greater variety of species, and testing how intrinsic and extrinsic conditions affect the scope and sensitivity of injury responses. It is our hope that this review will not only strengthen understanding of animal injury but will contribute to building a foundation for a more cohesive field of 'injury biology'.

The Role of Low-Frequency Electromagnetic Fields on Mesenchymal Stem Cells Differentiation: A Systematic Review

BACKGROUND

Low-frequency electromagnetic fields (EMFs) influence biological processes. This present study was aimed at the scientific literature on the use of EMFs in the mesenchymal stem cell differentiation process.

MATERIALS AND METHODS

The electronic search was carried out in PubMed and Web of Science, a database with a combination of the sinusoidal and pulsed low- and extremely low-frequency electromagnetic fields stimulation and mesenchymal stem cells differentiation, considering the period of publication until December 2021. The literature search identified 118 references in PubMed and Web of Science of which 46 articles were selected, respectively, according to the eligibility requirements.

CONCLUSION

The analysis of research indicated that EMFs are an easy-to-apply and practical way in cell therapy and tissue engineering when regulation of stem cells is required. Studies have shown that EMFs have positive effects on stem cell differentiation, accelerating its process regardless of the parameters and type of stem cells. However, the exact amplitude, frequency, duration of the electrical field, and application method remain elusive and need more study in future work.

Engineering multicellular living systems-a Keystone Symposia report

The ability to engineer complex multicellular systems has enormous potential to inform our understanding of biological processes and disease and alter the drug development process. Engineering living systems to emulate natural processes or to incorporate new functions relies on a detailed understanding of the biochemical, mechanical, and other cues between cells and between cells and their environment that result in the coordinated action of multicellular systems. On April 3-6, 2022, experts in the field met at the Keystone symposium "Engineering Multicellular Living Systems" to discuss recent advances in understanding how cells cooperate within a multicellular system, as well as recent efforts to engineer systems like organ-on-a-chip models, biological robots, and organoids. Given the similarities and common themes, this meeting was held in conjunction with the symposium "Organoids as Tools for Fundamental Discovery and Translation".

Bioelectric regulation of intestinal stem cells

Proper regulation of ion balance across the intestinal epithelium is essential for physiological functions, while ion imbalance causes intestinal disorders with dire health consequences. Ion channels, pumps, and exchangers are vital for regulating ion movements (i.e., bioelectric currents) that control epithelial absorption and secretion. Recent in vivo studies used the Drosophila gut to identify conserved pathways that link regulators of Ca²⁺, Na⁺ and Cl^- with intestinal stem cell (ISC) proliferation. These studies laid a foundation for using the Drosophila gut to identify conserved proliferative responses triggered by bioelectric regulators. Here, we review these studies, discuss their significance, as well as the advantages of using Drosophila to unravel conserved bioelectrically induced molecular pathways in the intestinal epithelium under physiological, pathophysiological, and regenerative conditions.

Internal Wireless Electrical Stimulation from Piezoelectric Barium Titanate Nanoparticles as a New Strategy for the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive BC subtype with a higher metastatic rate and a worse 5-year survival ratio than the other BC. It is an urgent need to develop a noninvasive treatment with high efficiency to resist TNBC cell proliferation and invasion. Internal wireless electric stimulation (ES) based on piezoelectric materials is an emerging noninvasive strategy, with adjustable ES intensity and excellent biosafety. In this study, three different barium titanate nanoparticles (BTNPs) with different crystal phases and piezoelectric properties were studied. Varying intensities of internal ES were generated from the three BTNPs (i.e., BTO, U-BTO, P-BTO). In vitro tests revealed that the internal ES from BTNPs was efficient at reducing the proliferative potential of cancer cells, particularly BC cells. In vitro experiments on MDA-MB-231, a typical TNBC cell line, further revealed that the internal wireless ES from BTNPs significantly inhibited cell growth and migration up to about 82% and 60%, respectively. In vivo evaluation of MDA-MB-231 tumor-bearing mice indicated that internal ES not only resisted almost 70% tumor growth but also significantly inhibited lung metastasis. More importantly, in vitro and in vivo studies demonstrated a favorable correlation between the anticancer impact and the intensities of ES. The underlying mechanism of MDA-MB-231 cell proliferation and metastasis inhibition caused by internal ES was also investigated. In summary, our results revealed the effect and mechanism of internal ES from piezoelectric nanoparticles on TNBC cell proliferation and migration regulation and proposed a promising noninvasive therapeutic strategy for TNBC with minimal side effects while exhibiting good therapeutic efficiency.

A computational model of organism development and carcinogenesis resulting from cells' bioelectric properties and communication

A sound theory of biological organization is clearly missing for a better interpretation of observational results and faster progress in understanding life complexity. The availability of such a theory represents a fundamental progress in explaining both normal and pathological organism development. The present work introduces a computational implementation of some principles of a theory of organism development, namely that the default state of cells is proliferation and motility, and includes the principle of variation and organization by closure of constraints. In the present model, the bioelectric context of cells and tissue is the field responsible for organization, as it regulates cell proliferation and the level of communication driving the system's evolution. Starting from a depolarized (proliferative) cell, the organism grows to a certain size, limited by the increasingly polarized state after successive proliferation events. The system reaches homeostasis, with a depolarized core (proliferative cells) surrounded by a rim of polarized cells (non-proliferative in this condition). This state is resilient to cell death (random or due to injure) and to limited depolarization (potentially carcinogenic) events. Carcinogenesis is introduced through a localized event (a spot of depolarized cells) or by random depolarization of cells in the tissue, which returns cells to their initial proliferative state. The normalization of the bioelectric condition can reverse this out-of-equilibrium state to a new homeostatic one. This simplified model of embryogenesis, tissue organization and carcinogenesis, based on non-excitable cells' bioelectric properties, can be made more realistic with the introduction of other components, like biochemical fields and mechanical interactions, which are fundamental for a more faithful representation of reality. However, even a simple model can give insight for new approaches in complex systems and suggest new experimental tests, focused in its predictions and interpreted under a new paradigm.

Bioelectric Dysregulation in Cancer Initiation, Promotion, and Progression

Cancer is primarily a disease of dysregulation – both at the genetic level and at the tissue organization level. One way that tissue organization is dysregulated is by changes in the bioelectric regulation of cell signaling pathways. At the basis of bioelectricity lies the cellular membrane potential or V_mem, an intrinsic property associated with any cell. The bioelectric state of cancer cells is different from that of healthy cells, causing a disruption in the cellular signaling pathways. This disruption or dysregulation affects all three processes of carcinogenesis – initiation, promotion, and progression. Another mechanism that facilitates the homeostasis of cell signaling pathways is the production of extracellular vesicles (EVs) by cells. EVs also play a role in carcinogenesis by mediating cellular communication within the tumor microenvironment (TME). Furthermore, the production and release of EVs is altered in cancer. To this end, the change in cell electrical state and in EV production are responsible for the bioelectric dysregulation which occurs during cancer. This paper reviews the bioelectric dysregulation associated with carcinogenesis, including the TME and metastasis. We also look at the major ion channels associated with cancer and current technologies and tools used to detect and manipulate bioelectric properties of cells.

Electrical stimulation to human dermal papilla cells for hair regenerative medicine

Hair follicle dermal papilla cells (DPCs) are specialized mesenchymal cells that play pivotal roles in hair formation, growth, and cycles, and they are considered as a cell source in hair regenerative medicine. Rodent dermal papilla cells have been shown to induce de novo hair follicle generation in the skin of recipients following transplantation, suggesting that dermal papilla cells can reprogram epidermal microenvironments. However, human DPCs (hDPCs) lose their ability to generate de novo hair follicles under conventional culture methods. We investigated the effects of electrical stimulation (ES) on hDPCs to restore the depressed trichogenic activity. We demonstrated that ES with a polypyrrole (PPy)-modified electrode upregulated trichogenic gene expression in hDPCs in vitro, and the activated cells when transplanted into mice generated double the number of hairs compared to that without the ES. Using specific inhibitors, we revealed that the mechanisms behind the electrical activation are associated with voltage-gated ion channels. Further, ES can be adapted for hDPCs from a patient with androgenic alopecia. Thus, this approach is potentially beneficial in preparing hDPCs for hair regenerative medicine.

Perspectives, Measurability and Effects of Non-Contact Biofield-Based Practices: A Narrative Review of Quantitative Research

Practices such as "Reiki", therapeutic touch, healing touch, and external "Qigong" have been regarded as some form of "energy medicine" or "biofield therapy". The biofield concept has been studied and debated by researchers of distinct areas of expertise, and although the phenomenon was sometimes described as physically related to electromagnetics, other factors such as "subtle energy" and focused intention might be involved. These nonconventional practices integrate contact and non-contact techniques, and those dealing with so-called distant healing interventions are perhaps the most difficult to understand and accept. Practitioners describe these so-called nonlocal interventions as involving intentional factors and particular states of consciousness. With a spiritual mindset and a particular state of awareness, compassion is said to work out as a catalyst to produce physiological and physical changes through mechanisms that are still unknown. At the body level, these vegetative changes might be related to individual self-perception variations as part of the body neurovegetative feedback system of regulation. Further mechanisms are difficult to document and measure, and might be more accessible to research by using physical signal detectors, chemical dynamics methods, detectors using biological materials, detectors using living sensors, and detectors using the human body. The growing interest in these practices and the considerable amount of research exploring their effects and clinical applications encouraged this narrative review, which aims to provide an easy to consult partial overview of the history, theory and findings of quantitative research strategies exploring non-contact biofield-based practices. This work also aims to stimulate the reader's mind with the raised hypotheses, catalyzing further research on the subject to confirm or deny the reported outcomes.

Bioelectric signaling as a unique regulator of development and regeneration

It is well known that electrical signals are deeply associated with living entities. Much of our understanding of excitable tissues is derived from studies of specialized cells of neurons or myocytes. However, electric potential is present in all cell types and results from the differential partitioning of ions across membranes. This electrical potential correlates with cell behavior and tissue organization. In recent years, there has been exciting, and broadly unexpected, evidence linking the regulation of development to bioelectric signals. However, experimental modulation of electrical potential can have multifaceted and pleiotropic effects, which makes dissecting the role of electrical signals in development difficult. Here, I review evidence that bioelectric cues play defined instructional roles in orchestrating development and regeneration, and further outline key areas in which to refine our understanding of this signaling mechanism.

Modulation of Human Mesenchymal Stem Cells by Electrical Stimulation Using an Enzymatic Biofuel Cell

Enzymatic biofuel cells (EBFCs) have excellent potential as components in bioelectronic devices, especially as active biointerfaces to regulate stem cell behavior for regenerative medicine applications. However, it remains unclear to what extent EBFC-generated electrical stimulation can regulate the functional behavior of human adipose-derived mesenchymal stem cells (hAD-MSCs) at the morphological and gene expression levels. Herein, we investigated the effect of EBFC-generated electrical stimulation on hAD-MSC cell morphology and gene expression using next-generation RNA sequencing. We tested three different electrical currents, 127 ± 9, 248 ± 15, and 598 ± 75 nA/cm2, in mesenchymal stem cells. We performed transcriptome profiling to analyze the impact of EBFC-derived electrical current on gene expression using next generation sequencing (NGS). We also observed changes in cytoskeleton arrangement and analyzed gene expression that depends on the electrical stimulation. The electrical stimulation of EBFC changes cell morphology through cytoskeleton re-arrangement. In particular, the results of whole transcriptome NGS showed that specific gene clusters were up- or down-regulated depending on the magnitude of applied electrical current of EBFC. In conclusion, this study demonstrates that EBFC-generated electrical stimulation can influence the morphological and gene expression properties of stem cells; such capabilities can be useful for regenerative medicine applications such as bioelectronic devices.

Modulation of the Cell Membrane Potential and Intracellular Protein Transport by High Magnetic Fields

To explore cellular responses to high magnetic fields (HMF), we present a model of the interactions of cells with a homogeneous HMF that accounts for the magnetic force exerted on paramagnetic/diamagnetic species. There are various chemical species inside a living cell, many of which may have large concentration gradients. Thus, when an HMF is applied to a cell, the concentration-gradient magnetic forces act on paramagnetic or diamagnetic species and can either assist or oppose large particle movement through the cytoplasm. We demonstrate possibilities for changing the machinery in living cells with HMFs and predict two new mechanisms for modulating cellular functions with HMFs via (i) changes in the membrane potential and (ii) magnetically assisted intracellular diffusiophoresis of large proteins. By deriving a generalized form for the Nernst equation, we find that an HMF can change the membrane potential of the cell and thus have a significant impact on the properties and biological functionality of cells. The elaborated model provides a universal framework encompassing current studies on controlling cell functions by high static magnetic fields. Bioelectromagnetics. 2021;42:27-36. © 2020 Bioelectromagnetics Society.

Ageing, computation and the evolution of neural regeneration processes

Metazoans gather information from their environments and respond in predictable ways. These computational tasks are achieved with neural networks of varying complexity. Their performance must be reliable over an individual's lifetime while dealing with the shorter lifespan of cells and connection failure-thus rendering ageing a relevant feature. How do computations degrade over an organism's lifespan? How reliable can they remain throughout? We tackle these questions with a multi-objective optimization approach. We demand that digital organisms equipped with neural networks solve a computational task reliably over an extended lifespan. Neural connections are costly (as an associated metabolism in living beings). They also degrade over time, but can be regenerated at some expense. We investigate the simultaneous minimization of both these costs and the computational error. Pareto optimal trade-offs emerge with designs displaying a broad range of solutions: from small networks with high regeneration rate, to large, redundant circuits that regenerate slowly. The organism's lifespan and the external damage act as evolutionary pressures. They improve the exploration of the space of solutions and impose tighter optimality constraints. Large damage rates can also constrain the space of possibilities, forcing the commitment of organisms to unique strategies for neural systems maintenance.

Epithelial tissue geometry directs emergence of bioelectric field and pattern of proliferation

Patterns of proliferation are templated by both gradients of mechanical stress as well as by gradients in membrane voltage (Vm), which is defined as the electric potential difference between the cytoplasm and the extracellular medium. Either gradient could regulate the emergence of the other, or they could arise independently and synergistically affect proliferation within a tissue. Here, we examined the relationship between endogenous patterns of mechanical stress and the generation of bioelectric gradients in mammary epithelial tissues. We observed that the mechanical stress gradients in the tissues presaged gradients in both proliferation and depolarization, consistent with previous reports correlating depolarization with proliferation. Furthermore, disrupting the Vm gradient blocked the emergence of patterned proliferation. We found that the bioelectric gradient formed downstream of mechanical stresses within the tissues and depended on connexin-43 (Cx43) hemichannels, which opened preferentially in cells located in regions of high mechanical stress. Activation of Cx43 hemichannels was necessary for nuclear localization of Yap/Taz and induction of proliferation. Together, these results suggest that mechanotransduction triggers the formation of bioelectric gradients across a tissue, which are further translated into transcriptional changes that template patterns of growth.

The Use of Pulsed Electromagnetic Field to Modulate Inflammation and Improve Tissue Regeneration: A Review

Pulsed electromagnetic field (PEMF) is emerging as innovative treatment for regulation of inflammation, which could have significant effects on tissue regeneration. PEMF modulates inflammatory processes through the regulation of pro- and anti-inflammatory cytokine secretion during different stages of inflammatory response. Consistent outcomes in studies involving animal and human tissue have shown promise for the use of PEMF as an alternative or complementary treatment to pharmaceutical therapies. Thus, PEMF treatment could provide a novel nonpharmaceutical means of modulating inflammation in injured tissues resulting in enhanced functional recovery. This review examines the effect of PEMF on immunomodulatory cells (e.g., mesenchymal stem/stromal cells [MSCs] and macrophages [MΦ]) to better understand the potential for PEMF therapy to modulate inflammatory signaling pathways and improve tissue regeneration. This review cites published data that support the use of PEMF to improve tissue regeneration. Our studies included herein confirm anti-inflammatory effects of PEMF on MSCs and MΦ.

Influence of conductive PEDOT:PSS in a hard tissue scaffold: In vitro and in vivo study

The presence of a conductive component in bone scaffolds can be helpful in facilitating the intracellular electrical signaling among cells as well as improving bone healing when electromagnetic stimulation is applied. In this study, poly(3,4-ethylenedioxythiophene): poly(4-styrene sulfonate) as a biocompatible conductive polymer was incorporated into a hard tissue scaffold made of gelatin (Gel) and bioactive glass. The in vitro results revealed that incorporation of an optimized amount of poly(3,4-ethylenedioxythiophene): poly(4-styrene sulfonate) into the scaffold composition enhanced cell viability more than four times after 14 days incubation, compared to the scaffold without poly(3,4-ethylenedioxythiophene): poly(4-styrene sulfonate). The in vivo studies demonstrated the amount of new bone formation of Gel/bioactive glass/poly(3,4-ethylenedioxythiophene): poly(4-styrene sulfonate) scaffolds was significantly higher than the Gel/bioactive glass scaffolds.

Insights into regeneration tool box: An animal model approach

For ages, regeneration has intrigued countless biologists, clinicians, and biomedical engineers. In recent years, significant progress made in identification and characterization of a regeneration tool kit has helped the scientific community to understand the mechanism(s) involved in regeneration across animal kingdom. These mechanistic insights revealed that evolutionarily conserved pathways like Wnt, Notch, Hedgehog, BMP, and JAK/STAT are involved in regeneration. Furthermore, advancement in high throughput screening approaches like transcriptomic analysis followed by proteomic validations have discovered many novel genes, and regeneration specific enhancers that are specific to highly regenerative species like Hydra, Planaria, Newts, and Zebrafish. Since genetic machinery is highly conserved across the animal kingdom, it is possible to engineer these genes and regeneration specific enhancers in species with limited regeneration properties like Drosophila, and mammals. Since these models are highly versatile and genetically tractable, cross-species comparative studies can generate mechanistic insights in regeneration for animals with long gestation periods e.g. Newts. In addition, it will allow extrapolation of regenerative capabilities from highly regenerative species to animals with low regeneration potential, e.g. mammals. In future, these studies, along with advancement in tissue engineering applications, can have strong implications in the field of regenerative medicine and stem cell biology.

Use Microfluidic Chips to Study the Phototaxis of Lung Cancer Cells

Cell migration is an important process involved in wound healing, tissue development, and so on. Many studies have been conducted to explore how certain chemicals and electric fields induce cell movements in specific directions, which are phenomena termed chemotaxis and electrotaxis, respectively. However, phototaxis, the directional migration of cells or organisms toward or away from light, is rarely investigated due to the difficulty of generating a precise and controllable light gradient. In this study, we designed and fabricated a microfluidic chip for simultaneously culturing cells and generating a blue light gradient for guiding cell migration. A concentration gradient was first established inside this chip, and by illuminating it with a blue light-emitting diode (LED), a blue light gradient was generated underneath. Cell migration in response to this light stimulus was observed. It was found that lung cancer cells migrated to the dark side of the gradient, and the intracellular reactive oxygen species (ROS) was proportional to the intensity of the blue light.

Bioelectricity, Its Fundamentals, Characterization Methodology, and Applications in Nano-Bioprobing and Cancer Diagnosis

Bioelectricity is an essential characteristic of a biological system that has played an important role in medical diagnosis particularly in cancer liquid biopsy. However, its biophysical origin and measurements have presented great challenges in experimental methodologies. For instance, in dynamic cell processes, bioelectricity cannot be accurately determined as a static electrical potential via electrophoresis. Cancer cells fundamentally differ from normal cells by having a much higher rate of glycolysis resulting in net negative charges on cell surfaces. The most recent investigations on cancer cell surface charge that is the direct bio-electrical manifestation of the "Warburg Effect," which can be directly monitored by specially designed nanoprobes, has been provided. The most up-to-date research results from charge-mediated cell targeting are reviewed. Correlations between the cell surface charge and cancer cell metabolism are established based on cell/probe electrostatic interactions. Bioelectricity is utilized not only as an analyte for investigation of the metabolic state of the cancer cells, but also applied in electrostatically and magnetically capturing of the circulating tumor cells from whole blood. Also reviewed is on the isolation of Candida albicans via bioelectricity-driven nanoparticle binding on fungus with surface charges.

Electrical stimulation shifts healing/scarring towards regeneration in a rat limb amputation model

Different species respond differently to severe injury, such as limb loss. In species that regenerate, limb loss is met with complete restoration of the limbs’ form and function, whereas in mammals the amputated limb’s stump heals and scars. In in vitro studies, electrical stimulation (EStim) has been shown to promote cell migration, and osteo- and chondrogenesis. In in vivo studies, after limb amputation, EStim causes significant new bone, cartilage and vessel growth. Here, in a rat model, the stumps of amputated rat limbs were exposed to EStim, and we measured extracellular matrix (ECM) deposition, macrophage distribution, cell proliferation and gene expression changes at early (3 and 7 days) and later stages (28 days). We found that EStim caused differences in ECM deposition, with less condensed collagen fibrils, and modified macrophage response by changing M1 to M2 macrophage ratio. The number of proliferating cells was increased in EStim treated stumps 7 days after amputation, and transcriptome data strongly supported our histological findings, with activated gene pathways known to play key roles in embryonic development and regeneration. In conclusion, our findings support the hypothesis that EStim shifts injury response from healing/scarring towards regeneration. A better understanding of if and how EStim controls these changes, could lead to strategies that replace scarring with regeneration.

Hyperosmolar Potassium (K+) Treatment Suppresses Osteoarthritic Chondrocyte Catabolic and Inflammatory Protein Production in a 3-Dimensional In Vitro Model

OBJECTIVE

The main goal of this study was to provide a proof-of-concept demonstrating that hyperosmolar K⁺ solutions can limit production of catabolic and inflammatory mediators in human osteoarthritic chondrocytes (OACs).

METHODS

A 3-dimensional in vitro model with poly(ethylene glycol) diacrylate (PEGDA) hydrogels was used. Catabolic and pro-inflammatory protein production from encapsulated OACs was assessed following culture for 1 or 7 days in the presence or absence of 80 mM K⁺ gluconate, 80 mM sodium (Na⁺) gluconate, or 160 mM sucrose, each added to culture media (final osmolarity ~490 mOsm).

RESULTS

Relative to untreated controls, OACs treated with hyperosmolar (80 mM Na⁺ gluconate or 160 mM sucrose) solutions produced lower levels of catabolic and inflammatory mediators in a marker- and time-dependent manner (i.e., MMP-9 after 1 day; MCP-1 after 7 days ( P ≤ 0.015)). In contrast, OAC treatment with 80 mM K⁺ gluconate reduced catabolic and inflammatory mediators to a greater extent (both the number of markers and degree of suppression) relative to untreated, Na⁺ gluconate, or sucrose controls (i.e., MMP-3, -9, -13, TIMP-1, MCP-1, and IL-8 after 1 day; MMP-1, -3, -9, -13, TIMP-1, MCP-1, and IL-8 after 7 days ( P ≤ 0.029).

CONCLUSIONS

Hyperosmolar K⁺ solutions are capable of attenuating protein production of catabolic and inflammatory OA markers, providing the proof-of-concept needed for further development of a K⁺-based intra-articular injection for OA treatment. Moreover, K⁺ performed significantly better than Na⁺- or sucrose-based solutions, supporting the application of K⁺ toward improving irrigation solutions for joint surgery.

Repetitive Transcranial Magnetic Stimulation Promotes Neural Stem Cell Proliferation and Differentiation after Intracerebral Hemorrhage in Mice

Repetitive transcranial magnetic stimulation (rTMS) is a physical treatment applied during recovery after intracerebral hemorrhage (ICH). With in vivo and in vitro assays, the present study sought to investigate how rTMS influences neural stem cells (NSCs) after ICH and the possible mechanism. Following a collagenase-induced ICH, adult male C57BL/6 J mice were subjected to rTMS treatment every 24 h for 5 days using the following parameters: frequency, 10 Hz; duration, 2 s; wait time, 5.5 s; 960 trains (500 µV/div, 5 ms/div, default setting). Brain water content and neurobehavioral score were assessed at days 1, 3, and 5 after ICH. The proliferation and differentiation of NSCs were observed using immunofluorescence staining for Nestin, Ki-67, DCX, and GFAP on day 3 after ICH, and rTMS treatment with the same parameters was applied to NSCs in vitro. We found that rTMS significantly reduced brain edema and alleviated neural functional deficits. The mice that underwent ICH recovered faster after rTMS treatment, with apparent proliferation and neuronal differentiation of NSCs and attenuation of glial differentiation and GFAP aggregation. Accordingly, proliferation and neuronal differentiation of isolated NSCs were promoted, while glial differentiation was reduced. In addition, microarray analysis, western blotting assays, and calcium imaging were applied to initially investigate the potential mechanism. Bioinformatics showed that the positive effect of rTMS on NSCs after ICH was largely related to the MAPK signaling pathway, which might be a potential hub signaling pathway under the complex effect exerted by rTMS. The results of the microarray data analysis also revealed that Ca²⁺ might be the connection between physical treatment and the MAPK signaling pathway. These predictions were further identified by western blotting analysis and calcium imaging. Taken together, our findings showed that rTMS after ICH exhibited a restorative effect by enhancing the proliferation and neuronal differentiation of NSCs, potentially through the MAPK signaling pathway.

Selective Serotonin Reuptake Inhibitor Use During Pregnancy and Major Malformations: The Importance of Serotonin for Embryonic Development and the Effect of Serotonin Inhibition on the Occurrence of Malformations

Bioelectric signaling is transduced by neurotransmitter pathways in many cell types. One of the key mediators of bioelectric control mechanisms is serotonin, and its transporter SERT, which is targeted by a broad class of blocker drugs (selective serotonin reuptake inhibitors [SSRIs]). Studies showing an increased risk of multiple malformations associated with gestational use of SSRI have been accumulating but debate remains on whether SSRI as a class has the potential to generate these malformations. This review highlights the importance of serotonin for embryonic development; the effect of serotonin inhibition during early pregnancy on the occurrence of multiple diverse malformations that have been shown to occur in human pregnancies; that the risks outweigh the benefits of SSRI use during gestation in populations of mild to moderately depressed pregnant women, which encompass the majority of pregnant depressed women; and that the malformations seen in human pregnancies constitute a pattern of malformations consistent with the known mechanisms of action of SSRIs. We present at least three mechanisms by which SSRI can affect development. These studies highlight the relevance of basic bioelectric and neurotransmitter mechanism for biomedicine.

Bioelectric Properties of Myogenic Progenitor Cells

Modern stem cell research has mainly focused on protein expression and transcriptional networks. However, transmembrane voltage gradients generated by ion channels and transporters have demonstrated to be powerful regulators of cellular processes. These physiological cues exert influence on cell behaviors ranging from differentiation and proliferation to migration and polarity. Bioelectric signaling is a fundamental element of living systems and an untapped reservoir for new discoveries. Dissecting these mechanisms will allow for novel methods of controlling cell fate and open up new opportunities in biomedicine. This review focuses on the role of ion channels and the resting membrane potential in the proliferation and differentiation of skeletal muscle progenitor cells. In addition, findings relevant to this topic are presented and potential implications for tissue engineering and regenerative medicine are discussed.

Functionalized-ferroelectric-coating-driven enhanced biomineralization and protein-conformation on metallic implants

In the context of bone regeneration, it is important to have platforms that with appropriate stimuli can support the attachment and direct the growth, proliferation and differentiation of cells.

Effects of Ivermectin Exposure on Regeneration of D. dorotocephala Planaria: Exploiting Human-Approved Ion Channel Drugs as Morphoceuticals

Transformative applications in regenerative medicine await increased control of processes implementing repair and remodeling of complex living structures. Recent work reveals ion channel drugs as a powerful toolkit for modulating endogenous bioelectric circuits that control growth and form in vivo and in vitro. It is therefore especially important to develop assays in model systems that will enable the testing of these "morphoceuticals"-compounds with predictable effects on anatomical structure. The regenerative planaria are an ideal model system for this purpose. Several studies have shown a role for bioelectric signaling in planarian regeneration, but these have focused on Dugesia japonica and Schmidtea mediterranea. It is not known how the alterations of ion channel activity would affect regeneration in other species of planaria-an important aspect of building robust computational models of bioelectric circuits. Here, the effect of ivermectin (IVM), a chloride channel opener drug commonly used to combat heartworm is tested, on regeneration in a new species of planaria: Dugesia dorotocephala. Exposure to IVM during regeneration results in patterning abnormalities, such as bifurcated tails with partial heads, as well as delayed regeneration. These data extend our understanding of the effects of human-approved ion channel drugs on regenerative processes.

Optogenetics: the new molecular approach to control functions of neural cells in epilepsy, depression and tumors of the central nervous system

The optogenetic tools have been described as valuable techniques to study neural activity through light stimulation, as well as potential neuromodulator approaches in the management of several central nervous system (CNS) diseases. Since the first bacteriorhodopsin protein described as a single-component light-activated regulator of transmembrane ion flow description, in 1980's, the focus has been on channel proteins for neurobiology; however, the advances in engineering techniques showed involvement changes in cellular biological behavior in several types of proteins involved in cell cytoskeleton regulation, motility and gene expression. Although the use of this technology has been published in many papers, a question still remains regarding real results and potential clinical applicability in CNS diseases, as well as the publications scarcity that systematically analyses the published results. Lastly, the aim of this review is to discuss the experimental results, molecular mechanisms and potential clinical applications of optogenetic tools in epilepsy and depression treatment, as well as its applicability in the treatment of CNS tumors.

Calcium as a signal integrator in developing epithelial tissues

Decoding how tissue properties emerge across multiple spatial and temporal scales from the integration of local signals is a grand challenge in quantitative biology. For example, the collective behavior of epithelial cells is critical for shaping developing embryos. Understanding how epithelial cells interpret a diverse range of local signals to coordinate tissue-level processes requires a systems-level understanding of development. Integration of multiple signaling pathways that specify cell signaling information requires second messengers such as calcium ions. Increasingly, specific roles have been uncovered for calcium signaling throughout development. Calcium signaling regulates many processes including division, migration, death, and differentiation. However, the pleiotropic and ubiquitous nature of calcium signaling implies that many additional functions remain to be discovered. Here we review a selection of recent studies to highlight important insights into how multiple signals are transduced by calcium transients in developing epithelial tissues. Quantitative imaging and computational modeling have provided important insights into how calcium signaling integration occurs. Reverse-engineering the conserved features of signal integration mediated by calcium signaling will enable novel approaches in regenerative medicine and synthetic control of morphogenesis.

Combined treatment with electrical stimulation and insulin-like growth factor-1 promotes bone regeneration in vitro

Electrical stimulation (ES) and insulin-like growth factor-1 (IGF-1) are widely used in bone regeneration because of their osteogenic activity. However, the combined effects of ES and supplemental IGF-1 on the whole bone formation process remain unclear. In this study, fluorescence staining and an MTT assay were first utilized to observe the influence of ES and IGF-1 on MC3T3-E1 cell proliferation and adhesion in vitro. Subsequently, osteogenic differentiation was evaluated by the alkaline phosphatase activity (ALP) and the expression of osteogenic marker genes. In addition, cell mineralization was determined by alizarin red staining and scanning electron microscopy (SEM). We demonstrated that the MC3T3-E1 cell proliferation was significantly higher for treatments combining IGF-1 and ES than for treatments with IGF-1 alone. The combination of IGF-1 and ES increased the MC3T3-E1 cell ALP activity, the expression of osteogenesis-related genes and the calcium deposition with a clear dose-dependent effect. Our data show the synergistic effect of IGF-1 and ES in promoting the proliferation, differentiation and mineralization of MC3T3-E1 cells, which suggests that it would be more effective to combine the proper dose of IGF-1 with ES to promote local bone damage repair and regeneration.

The Bioelectric Code: Reprogramming Cancer and Aging From the Interface of Mechanical and Chemical Microenvironments

Cancer is a complex, heterogeneous group of diseases that can develop through many routes. Broad treatments such as chemotherapy destroy healthy cells in addition to cancerous ones, but more refined strategies that target specific pathways are usually only effective for a limited number of cancer types. This is largely due to the multitude of physiological variables that differ between cells and their surroundings. It is therefore important to understand how nature coordinates these variables into concerted regulation of growth at the tissue scale. The cellular microenvironment might then be manipulated to drive cells toward a desired outcome at the tissue level. One unexpected parameter, cellular membrane voltage (Vm), has been documented to exert control over cellular behavior both in culture and in vivo. Manipulating this fundamental cellular property influences a remarkable array of organism-wide patterning events, producing striking outcomes in both tumorigenesis as well as regeneration. These studies suggest that Vm is not only a key intrinsic cellular property, but also an integral part of the microenvironment that acts in both space and time to guide cellular behavior. As a result, there is considerable interest in manipulating Vm both to treat cancer as well as to regenerate organs damaged or deteriorated during aging. However, such manipulations have produced conflicting outcomes experimentally, which poses a substantial barrier to understanding the fundamentals of bioelectrical reprogramming. Here, we summarize these inconsistencies and discuss how the mechanical microenvironment may impact bioelectric regulation.

Stem Cells, Patterning and Regeneration in Planarians: Self-Organization at the Organismal Scale

The establishment of size and shape remains a fundamental challenge in biological research that planarian flatworms uniquely epitomize. Planarians can regenerate complete and perfectly proportioned animals from tiny and arbitrarily shaped tissue pieces; they continuously renew all organismal cell types from abundant pluripotent stem cells, yet maintain shape and anatomy in the face of constant turnover; they grow when feeding and literally degrow when starving, while scaling form and function over as much as a 40-fold range in body length or an 800-fold change in total cell numbers. This review provides a broad overview of the current understanding of the planarian stem cell system, the mechanisms that pattern the planarian body plan and how the interplay between patterning signals and cell fate choices orchestrates regeneration. What emerges is a conceptual framework for the maintenance and regeneration of the planarian body plan on basis of the interplay between pluripotent stem cells and self-organizing patterns and further, the general utility of planarians as model system for the mechanistic basis of size and shape.

Regeneration Genetics

Understanding how and why animals regenerate complex tissues has the potential to transform regenerative medicine. Here we present an overview of genetic approaches that have recently been applied to dissect mechanisms of regeneration. We describe new advances that relate to central objectives of regeneration biologists researching different tissues and species, focusing mainly on vertebrates. These objectives include defining the cellular sources and key cell behaviors in regenerating tissue, elucidating molecular triggers and brakes for regeneration, and defining the earliest events that control the presence of these molecular factors.

Use of genetically encoded, light-gated ion translocators to control tumorigenesis

It has long been known that the resting potential of tumor cells is depolarized relative to their normal counterparts. More recent work has provided evidence that resting potential is not just a readout of cell state: it regulates cell behavior as well. Thus, the ability to control resting potential in vivo would provide a powerful new tool for the study and treatment of tumors, a tool capable of revealing living-state physiological information impossible to obtain using molecular tools applied to isolated cell components. Here we describe the first use of optogenetics to manipulate ion-flux mediated regulation of membrane potential specifically to prevent and cause regression of oncogene-induced tumors. Injection of mutant-KRAS mRNA induces tumor-like structures with many documented similarities to tumors, in Xenopus tadpoles. We show that expression and activation of either ChR2^D156A, a blue-light activated cation channel, or Arch, a green-light activated proton pump, both of which hyperpolarize cells, significantly lowers the incidence of KRAS tumor formation. Excitingly, we also demonstrate that activation of co-expressed light-activated ion translocators after tumor formation significantly increases the frequency with which the tumors regress in a process called normalization. These data demonstrate an optogenetic approach to dissect the biophysics of cancer. Moreover, they provide proof-of-principle for a novel class of interventions, directed at regulating cell state by targeting physiological regulators that can over-ride the presence of mutations.

Endogenous physical regulation of population density in the freshwater protozoan Paramecium caudatum

Studies confirm physical long-range cell-cell communication, most evidently based on electromagnetic fields. Effects concern induction or inhibition of cell growth. Their natural function is unclear. With the protozoan Paramecium caudatum I tested whether the signals regulate cell density and are electromagnetic. Up to 300 cells/mL, cell growth in clones of this study is decreasingly pronounced. Using cuvettes as chemical barriers enabling physical communication  I  placed 5 indicator cells/mL, the inducer populations, into smaller cuvettes that stand in bigger and contained 50, 100, 200 or 300 cells/mL. Under conditions of total darkness such pairs were mutually exposed for 48 hours. The hypothesis was that indicator cells, too, grow less the more neighbor cells there are. The bigger inducer populations were in the beginning the less they grew. The indicator populations grew accordingly; the more cells they were surrounded by the less they grew. The suppressing neighbors-effect disappeared when inner cuvettes were shielded by graphite known to shield electromagnetic radiation from GHz to PHz, i.e. to absorb energy from microwaves to light. These are the first results demonstrating non-contact physical quorum sensing for cell population density regulation. I assume rules intrinsic to electromagnetic fields interacting with matter and life.