Neuronal electrophysiological function and control of neurite outgrowth on electrospun polymer nanofibers are cell type dependent

Standardizing a method for functional assessment of neural networks in brain organoids

During the last decade brain organoids have emerged as an attractive model system, allowing stem cells to be differentiated into complex 3D models, recapitulating many aspects of human brain development. Whilst many studies have analysed anatomical and cytoarchitectural characteristics of organoids, their functional characterisation has been limited, and highly variable between studies. Standardised, consistent methods for recording functional activity are critical to providing a functional understanding of neuronal networks at the synaptic and network level that can yield useful information about functional network phenotypes in disease and healthy states. In this study we outline a detailed methodology for calcium imaging and Multi-Electrode Array (MEA) recordings in brain organoids. To illustrate the utility of these functional interrogation techniques in uncovering induced differences in neural network activity we applied various stimulating media protocols. We demonstrate overlapping information from the two modalities, with comparable numbers of active cells in the four treatment groups and an increase in synchronous behaviour in BrainPhys treated groups. Further development of analysis pipelines to reveal network level changes in brain organoids will enrich our understanding of network formation and perturbation in these structures, and aid in the future development of drugs that target neurological disorders at the network level.

Electrospun aligned tacrolimus-loaded polycaprolactone biomaterials for peripheral nerve repair

Background: Efficacious repair of peripheral nerve injury is an unmet clinical need. The implantation of biomaterials containing neurotrophic drugs at the injury site could promote nerve regeneration and improve outcomes for patients. Materials & methods: Random and aligned electrospun poly-ε-caprolactone scaffolds containing encapsulated tacrolimus were fabricated, and the gene expression profile of Schwann cells (SCs) cultured on the surface was elucidated. On aligned fibers, the morphology of SCs and primary rat neurons was investigated. Results: Both scaffold types exhibited sustained release of drug, and the gene expression of SCs was modulated by both nanofibrous topography and the presence of tacrolimus. Aligned fibers promoted the alignment of SCs and orientated outgrowth from neurons. Conclusion: Electrospun PCL scaffolds with tacrolimus hold promise for the repair of peripheral nerve injury.

Rapid electrophoretic deposition of biocompatible graphene coatings for high-performance recording neural electrodes

The electrical and biological interfacial properties of invasive electrodes have a significant impact on the performance and longevity of neural recordings in the brain. In this study, we demonstrated rapid electrophoretic deposition and electrochemical reduction of graphene oxide (GO) on metal-based neural electrodes. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and other characterizations confirmed the existence of a uniform and effectively reduced graphene oxide coating. Electrochemically reduced graphene oxide (ErGO) coated Pt/Ir neural electrodes exhibited 15.2-fold increase in charge storage capacity (CSC) and 90% decrease in impedance with only 3.8% increase in electrode diameter. Patch clamp electrophysiology and calcium imaging of primary rat hippocampus neurons cultured on ErGO demonstrated that there was no adverse impact on the functional development of neurons. Immunostaining showed a balanced growth of excitatory and inhibitory neurons, and astrocytes. Acute recordings from the auditory cortex and chronic recordings (19 days) from the somatosensory cortex found ErGO coating improved the performance of neural electrodes in signal-to-noise ratio (SNR) and amplitude of signals. The proposed approach not only provides an in-depth evaluation of the effect of ErGO coating on neural electrodes but also widens the coating methods of commercial neural electrodes.

Biofabrication of poly(l-lactide-co-ε-caprolactone)/silk fibroin scaffold for the application as superb anti-calcification tissue engineered prosthetic valve

In this study, electrospun scaffolds were fabricated by blending poly(l-lactide-co-ε-caprolactone) (PLCL) and silk fibroin (SF) with different ratios, and further the feasibility of electrospun PLCL/SF scaffolds were evaluated for application of tissue engineered heart valve (TEHV). Scanning electron microscopy (SEM) results showed that the surface of PLCL/SF electrospun scaffolds was smooth and uniform while the mechanical properties were appropriate as valve prosthesis. In vitro cytocompatibility evaluation results demonstrated that all of the PLCL/SF electrospun scaffolds were cytocompatible and valvular interstitial cells (VICs) cultured on PLCL/SF scaffolds of 80/20 & 70/30 ratios exhibited the best cytocompatibility. The in vitro osteogenic differentiation of VICs including alkaline phosphatase (ALP) activity and quantitative polymerase chain reaction (qPCR) assays indicated that PLCL/SF scaffolds of 80/20 & 90/10 ratios behaved better anti-calcification ability. In the in vivo calcification evaluation model of rat subdermal implantation, PLCL/SF scaffolds of 80/20 & 90/10 ratios presented better anti-calcification ability, which was consistent with the in vitro results. Moreover, PLCL/SF scaffolds of 80/20 & 70/30 ratios showed significantly enhanced cell infiltration and M2 macrophage with higher CD206+/CD68+ ratio. Collectively, our data demonstrated that electrospun scaffolds with the PLCL/SF ratio of 80/20 hold great potential as TEHV materials.

Graphene Promotes Axon Elongation through Local Stall of Nerve Growth Factor Signaling Endosomes

Several works reported increased differentiation of neuronal cells grown on graphene; however, the molecular mechanism driving axon elongation on this material has remained elusive. Here, we study the axonal transport of nerve growth factor (NGF), the neurotrophin supporting development of peripheral neurons, as a key player in the time course of axonal elongation of dorsal root ganglion neurons on graphene. We find that graphene drastically reduces the number of retrogradely transported NGF vesicles in favor of a stalled population in the first 2 days of culture, in which the boost of axon elongation is observed. This correlates with a mutual charge redistribution, observed via Raman spectroscopy and electrophysiological recordings. Furthermore, ultrastructural analysis indicates a reduced microtubule distance and an elongated axonal topology. Thus, both electrophysiological and structural effects can account for graphene action on neuron development. Unraveling the molecular players underneath this interplay may open new avenues for axon regeneration applications.

Biofabrication for neural tissue engineering applications

Unlike other tissue types, the nervous tissue extends to a wide and complex environment that provides a plurality of different biochemical and topological stimuli, which in turn defines the advanced functions of that tissue. As a consequence of such complexity, the traditional transplantation therapeutic methods are quite ineffective; therefore, the restoration of peripheral and central nervous system injuries has been a continuous scientific challenge. Tissue engineering and regenerative medicine in the nervous system have provided new alternative medical approaches. These methods use external biomaterial supports, known as scaffolds, to create platforms for the cells to migrate to the injury site and repair the tissue. The challenge in neural tissue engineering (NTE) remains the fabrication of scaffolds with precisely controlled, tunable topography, biochemical cues, and surface energy, capable of directing and controlling the function of neuronal cells toward the recovery from neurological disorders and injuries. At the same time, it has been shown that NTE provides the potential to model neurological diseases in vitro, mainly via lab-on-a-chip systems, especially in cases for which it is difficult to obtain suitable animal models. As a consequence of the intense research activity in the field, a variety of synthetic approaches and 3D fabrication methods have been developed for the fabrication of NTE scaffolds, including soft lithography and self-assembly, as well as subtractive (top-down) and additive (bottom-up) manufacturing. This article aims at reviewing the existing research effort in the rapidly growing field related to the development of biomaterial scaffolds and lab-on-a-chip systems for NTE applications. Besides presenting recent advances achieved by NTE strategies, this work also delineates existing limitations and highlights emerging possibilities and future prospects in this field.

Layer-By-Layer: The Case for 3D Bioprinting Neurons to Create Patient-Specific Epilepsy Models

The ability to create three-dimensional (3D) models of brain tissue from patient-derived cells, would open new possibilities in studying the neuropathology of disorders such as epilepsy and schizophrenia. While organoid culture has provided impressive examples of patient-specific models, the generation of organised 3D structures remains a challenge. 3D bioprinting is a rapidly developing technology where living cells, encapsulated in suitable bioink matrices, are printed to form 3D structures. 3D bioprinting may provide the capability to organise neuronal populations in 3D, through layer-by-layer deposition, and thereby recapitulate the complexity of neural tissue. However, printing neuron cells raises particular challenges since the biomaterial environment must be of appropriate softness to allow for the neurite extension, properties which are anathema to building self-supporting 3D structures. Here, we review the topic of 3D bioprinting of neurons, including critical discussions of hardware and bio-ink formulation requirements.

Quantum Sensing in a Physiological-Like Cell Niche Using Fluorescent Nanodiamonds Embedded in Electrospun Polymer Nanofibers

Fluorescent nanodiamonds (fNDs) containing nitrogen vacancy (NV) centers are promising candidates for quantum sensing in biological environments. This work describes the fabrication and implementation of electrospun poly lactic-co-glycolic acid (PLGA) nanofibers embedded with fNDs for optical quantum sensing in an environment, which recapitulates the nanoscale architecture and topography of the cell niche. A protocol that produces uniformly dispersed fNDs within electrospun nanofibers is demonstrated and the resulting fibers are characterized using fluorescent microscopy and scanning electron microscopy (SEM). Optically detected magnetic resonance (ODMR) and longitudinal spin relaxometry results for fNDs and embedded fNDs are compared. A new approach for fast detection of time varying magnetic fields external to the fND embedded nanofibers is demonstrated. ODMR spectra are successfully acquired from a culture of live differentiated neural stem cells functioning as a connected neural network grown on fND embedded nanofibers. This work advances the current state of the art in quantum sensing by providing a versatile sensing platform that can be tailored to produce physiological-like cell niches to replicate biologically relevant growth environments and fast measurement protocols for the detection of co-ordinated endogenous signals from clinically relevant populations of electrically active neuronal circuits.

β3-tripeptides act as sticky ends to self-assemble into a bioscaffold

Peptides comprised entirely of β³-amino acids, commonly referred to as β-foldamers, have been shown to self-assemble into a range of materials. Previously, β-foldamers have been functionalised via various side chain chemistries to introduce function to these materials without perturbation of the self-assembly motif. Here, we show that insertion of both rigid and flexible molecules into the backbone structure of the β-foldamer did not disturb the self-assembly, provided that the molecule is positioned between two β³-tripeptides. These hybrid β³-peptide flanked molecules self-assembled into a range of structures. α-Arginlyglycylaspartic acid (RGD), a commonly used cell attachment motif derived from fibronectin in the extracellular matrix, was incorporated into the peptide sequence in order to form a biomimetic scaffold that would support neuronal cell growth. The RGD-containing sequence formed the desired mesh-like scaffold but did not encourage neuronal growth, possibly due to over-stimulation with RGD. Mixing the RGD peptide with a β-foldamer without the RGD sequence produced a well-defined scaffold that successfully encouraged the growth of neurons and enabled neuronal electrical functionality. These results indicate that β³-tripeptides can form distinct self-assembly units separated by a linker and can form fibrous assemblies. The linkers within the peptide sequence can be composed of a bioactive α-peptide and tuned to provide a biocompatible scaffold.

Bridges of biomaterials promote nigrostriatal pathway regeneration

Repair of central nervous system (CNS) lesions is difficulted by the lack of ability of central axons to regrow, and the blocking by the brain astrocytes to axonal entry. We hypothesized that by using bridges made of porous biomaterial and permissive olfactory ensheathing glia (OEG), we could provide a scaffold to permit restoration of white matter tracts. We implanted porous polycaprolactone (PCL) bridges between the substantia nigra and the striatum in rats, both with and without OEG. We compared the number of tyrosine-hydroxylase positive (TH+) fibers crossing the striatal-graft interface, and the astrocytic and microglial reaction around the grafts, between animals grafted with and without OEG. Although TH+ fibers were found inside the grafts made of PCL alone, there was a greater fiber density inside the graft and at the striatal-graft interface when OEG was cografted. Also, there was less astrocytic and microglial reaction in those animals. These results show that these PCL grafts are able to promote axonal growth along the nigrostriatal pathway, and that cografting of OEG markedly enhances axonal entry inside the grafts, growth within them, and re-entry of axons into the CNS. These results may have implications in the treatment of diseases such as Parkinson's and others associated with lesions of central white matter tracts. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 190-196, 2019.

Three-Dimensional Electroconductive Hyaluronic Acid Hydrogels Incorporated with Carbon Nanotubes and Polypyrrole by Catechol-Mediated Dispersion Enhance Neurogenesis of Human Neural Stem Cells

Electrically conductive hyaluronic acid (HA) hydrogels incorporated with single-walled carbon nanotubes (CNTs) and/or polypyrrole (PPy) were developed to promote differentiation of human neural stem/progenitor cells (hNSPCs). The CNT and PPy nanocomposites, which do not easily disperse in aqueous phases, dispersed well and were efficiently incorporated into catechol-functionalized HA (HA-CA) hydrogels by the oxidative catechol chemistry used for hydrogel cross-linking. The prepared electroconductive HA hydrogels provided dynamic, electrically conductive three-dimensional (3D) extracellular matrix environments that were biocompatible with hNSPCs. The HA-CA hydrogels containing CNT and/or PPy significantly promoted neuronal differentiation of human fetal neural stem cells (hfNSCs) and human induced pluripotent stem cell-derived neural progenitor cells (hiPSC-NPCs) with improved electrophysiological functionality when compared to differentiation of these cells in a bare HA-CA hydrogel without electroconductive motifs. Calcium channel expression was upregulated, depolarization was activated, and intracellular calcium influx was increased in hNSPCs that were differentiated in 3D electroconductive HA-CA hydrogels; these data suggest a potential mechanism for stem cell neurogenesis. Overall, our bioinspired, electroconductive HA hydrogels provide a promising cell-culture platform and tissue-engineering scaffold to improve neuronal regeneration.

3D-Printed pHEMA Materials for Topographical and Biochemical Modulation of Dorsal Root Ganglion Cell Response

Understanding and controlling the interactions occurring between cells and engineered materials are central challenges toward progress in the development of biomedical devices. In this work, we describe materials for direct ink writing (DIW), an extrusion-based type of 3D printing, that embed a custom synthetic protein (RGD-PDL) within the microfilaments of 3D-hydrogel scaffolds to modify these interactions and differentially direct tissue-level organization of complex cell populations in vitro. The RGD-PDL is synthesized by modifying poly-d-lysine (PDL) to varying extents with peptides containing the integrin-binding motif Arg-Gly-Asp (RGD). Compositional gradients of the RGD-PDL presented by both patterned and thin-film poly(2-hydroxyethyl) methacrylate (pHEMA) substrates allow the patterning of cell-growth compliance in a grayscale form. The surface chemistry-dependent guidance of cell growth on the RGD-PDL-modified pHEMA materials is demonstrated using a model NIH-3T3 fibroblast cell line. The formation of a more complex cellular system-organotypic primary murine dorsal root ganglion (DRG)-in culture is also achieved on these scaffolds, where distinctive forms of cell growth and migration guidance are seen depending on their RGD-PDL content and topography. This experimental platform for the study of physicochemical factors on the formation and the reorganization of organotypic cultures offers useful capabilities for studies in tissue engineering, regenerative medicine, and diagnostics.

* A Paradigm for the Evaluation of Tissue-Engineering Biomaterials and Templates

Procedures for the evaluation of tissue-engineering processes, including those used for the testing of the relevant biomaterials, have not been developed in a logical manner. This perspectives paper discusses the limitations of testing regimes and recommends a very different approach. The main emphasis is on the existing methods for assessing the biological safety of these biomaterials, which, it is suggested, are irrelevant for evaluating materials that are intended to facilitate the generation of new tissue. An algorithm is proposed that sets out the pathway from materials design and characterization through to the production of a file that sets out full biocompatibility, functionality, and tissue incorporation data that are suitable for regulatory consideration for first-in-man experiences. Central to this algorithm is the choice of animal models and the real-time monitoring of the implanted construct performance.

Human embryonic stem cell dispersion in electrospun PCL fiber scaffolds by coating with laminin-521 and E-cadherin-Fc

Advances in human pluripotent cell cultivation and differentiation protocols have led to production of stem cell-derived progenitors as a promising cell source for replacement therapy. Three-dimensional (3-D) culture is a better mimic of the natural niche for stem cells and is widely used for disease modeling. Here, we describe a nonaggregate culture system of human embryonic stem cells inside electrospun polycaprolactone (PCL) fiber scaffolds combined with defined extracellular proteins naturally occurring in the stem cell niche. PCL fiber scaffolds coated with recombinant human laminin-521 readily supported initial stem cell attachment and growth from a single-cell suspension. The combination of recombinant E-cadherin-Fc and laminin-521 further improved cell dispersion rendering a uniform cell population. Finally, we showed that the cells cultured in E-cadherin-Fc- and laminin-521-coated PCL scaffolds could differentiate into all three germ layers. Importantly, we provided a chemically defined 3-D system in which pluripotent stem cells grown and differentiated avoiding the formation of cell aggregates. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1226-1236, 2018.

Electrical stimulation enhances the acetylcholine receptors available for neuromuscular junction formation

Neuromuscular junctions (NMJ) are specialized synapses that link motor neurons with muscle fibers. These sites are fundamental to human muscle activity, controlling swallowing and breathing amongst many other vital functions. Study of this synapse formation is an essential area in neuroscience; the understanding of how neurons interact and control their targets during development and regeneration are fundamental questions. Existing data reveals that during initial stages of development neurons target and form synapses driven by biophysical and biochemical cues, and during later stages they require electrical activity to develop their functional interactions. The aim of this study was to investigate the effect of exogenous electrical stimulation (ES) electrodes directly in contact with cells, on the number and size of acetylcholine receptor (AChR) clusters available for NMJ formation. We used a novel in vitro model that utilizes a flexible electrical stimulation system and allows the systematic testing of several stimulation parameters simultaneously as well as the use of alternative electrode materials such as conductive polymers to deliver the stimulation. Functionality of NMJs under our co-culture conditions was demonstrated by monitoring changes in the responses of primary myoblasts to chemical stimulants that specifically target neuronal signaling. Our results suggest that biphasic electrical stimulation at 250Hz, 100μs pulse width and current density of 1mA/cm² for 8h, applied via either gold-coated mylar or the conductive polymer PPy, significantly increased the number and size of AChRs clusters available for NMJ formation. This study supports the beneficial use of direct electrical stimulation as a strategic therapy for neuromuscular disorders.

STATEMENT OF SIGNIFICANCE

The beneficial effects of electrical stimulation (ES) on human cells in vitro and in vivo have long been known. Although the effects of stimulation are clear and the therapeutic benefits are known, no uniform parameters exist with regard to the duration, frequency and amplitude of the ES. To this end, we are answering several important questions on the parameters for ES of nerve and muscle monocultures and co-cultures by probing the effects on the enhancement of acetylcholine receptors (AChR) clustering available for neuromuscular junction formation using a conductive platform. This work opens the possibility to combine electrical stimulus delivered via conductive polymer substrates, from which biomolecules could also be delivered, providing opportunities to further enhance the therapeutic effect.

Electrospun Fibers for Spinal Cord Injury Research and Regeneration

Electrospinning is the process by which a scaffold containing micrometer and nanometer diameter fibers are drawn from a polymer solution or melt using a large voltage gradient between a polymer emitting source and a grounded collector. Ramakrishna and colleagues first investigated electrospun fibers for neural applications in 2004. After this initial study, electrospun fibers are increasingly investigated for neural tissue engineering applications. Electrospun fibers robustly support axonal regeneration within in vivo rodent models of spinal cord injury. These findings suggest the possibility of their eventual use within patients. Indeed, both spinal cord and peripheral nervous system regeneration research over the last several years shows that physical guidance cues induce recovery of limb, respiration, or bladder control in rodent models. Electrospun fibers may be an alternative to the peripheral nerve graft (PNG), because PNG autografts injure the patient and are limited in supply, and allografts risk host rejection. In addition, electrospun fibers can be engineered easily to confront new therapeutic challenges. Fibers can be modified to release therapies locally or can be physically modified to direct neural stem cell differentiation. This review summarizes the major findings and trends in the last decade of research, with a particular focus on spinal cord injury. This review also demonstrates how electrospun fibers can be used to study the central nervous system in vitro.

Impact of Genetic Reduction of NMNAT2 on Chemotherapy-Induced Losses in Cell Viability In Vitro and Peripheral Neuropathy In Vivo

Nicotinamide mononucleotide adenylyl transferases (NMNATs) are essential neuronal maintenance factors postulated to preserve neuronal function and protect against axonal degeneration in various neurodegenerative disease states. We used in vitro and in vivo approaches to assess the impact of NMNAT2 reduction on cellular and physiological functions induced by treatment with a vinca alkaloid (vincristine) and a taxane-based (paclitaxel) chemotherapeutic agent. NMNAT2 null (NMNAT2-/-) mutant mice die at birth and cannot be used to probe functions of NMNAT2 in adult animals. Nonetheless, primary cortical cultures derived from NMNAT2-/- embryos showed reduced cell viability in response to either vincristine or paclitaxel treatment whereas those derived from NMNAT2 heterozygous (NMNAT2+/-) mice were preferentially sensitive to vincristine-induced degeneration. Adult NMNAT2+/- mice, which survive to adulthood, exhibited a 50% reduction of NMNAT2 protein levels in dorsal root ganglia relative to wildtype (WT) mice with no change in levels of other NMNAT isoforms (NMNAT1 or NMNAT3), NMNAT enzyme activity (i.e. NAD/NADH levels) or microtubule associated protein-2 (MAP2) or neurofilament protein levels. We therefore compared the impact of NMNAT2 knockdown on the development and maintenance of chemotherapy-induced peripheral neuropathy induced by vincristine and paclitaxel treatment using NMNAT2+/- and WT mice. NMNAT2+/- did not differ from WT mice in either the development or maintenance of either mechanical or cold allodynia induced by either vincristine or paclitaxel treatment. Intradermal injection of capsaicin, the pungent ingredient in hot chili peppers, produced equivalent hypersensitivity in NMNAT2+/- and WT mice receiving vehicle in lieu of paclitaxel. Capsaicin-evoked hypersensitivity was enhanced by prior paclitaxel treatment but did not differ in either NMNAT2+/- or WT mice. Thus, capsaicin failed to unmask differences in nociceptive behaviors in either paclitaxel-treated or paclitaxel-untreated NMNAT2+/- and WT mice. Moreover, no differences in motor behavior were detected between genotypes in the rotarod test. Our studies do not preclude the possibility that complete knockout of NMNAT2 in a conditional knockout animal could unmask a role for NMNAT2 in protection against detrimental effects of chemotherapeutic treatment.

Electrospun SF/PLCL nanofibrous membrane: a potential scaffold for retinal progenitor cell proliferation and differentiation

Biocompatible polymer scaffolds are promising as potential carriers for the delivery of retinal progenitor cells (RPCs) in cell replacement therapy for the repair of damaged or diseased retinas. The primary goal of the present study was to investigate the effects of blended electrospun nanofibrous membranes of silk fibroin (SF) and poly(L-lactic acid-co-ε-caprolactone) (PLCL), a novel scaffold, on the biological behaviour of RPCs in vitro. To assess the cell-scaffold interaction, RPCs were cultured on SF/PLCL scaffolds for indicated durations. Our data revealed that all the SF/PLCL scaffolds were thoroughly cytocompatible, and the SF:PLCL (1:1) scaffolds yielded the best RPC growth. The in vitro proliferation assays showed that RPCs proliferated more quickly on the SF:PLCL (1:1) than on the other scaffolds and the control. Quantitative polymerase chain reaction (qPCR) and immunocytochemistry analyses demonstrated that RPCs grown on the SF:PLCL (1:1) scaffolds preferentially differentiated toward retinal neurons, including, most interestingly, photoreceptors. In summary, we demonstrated that the SF:PLCL (1:1) scaffolds can not only markedly promote RPC proliferation with cytocompatibility for RPC growth but also robustly enhance RPCs’ differentiation toward specific retinal neurons of interest in vitro, suggesting that SF:PLCL (1:1) scaffolds may have potential applications in retinal cell replacement therapy in the future.