Enhanced GLT-1 mediated glutamate uptake and migration of primary astrocytes directed by fibronectin-coated electrospun poly-L-lactic acid fibers

Nanomaterial payload delivery to central nervous system glia for neural protection and repair

Central nervous system (CNS) glia, including astrocytes, microglia, and oligodendrocytes, play prominent roles in traumatic injury and degenerative disorders. Due to their importance, active pharmaceutical ingredients (APIs) are being developed to modulate CNS glia in order to improve outcomes in traumatic injury and disease. While many of these APIs show promise in vitro, the majority of APIs that are systemically delivered show little penetration through the blood-brain barrier (BBB) or blood-spinal cord barrier (BSCB) and into the CNS, rendering them ineffective. Novel nanomaterials are being developed to deliver APIs into the CNS to modulate glial responses and improve outcomes in injury and disease. Nanomaterials are attractive options as therapies for central nervous system protection and repair in degenerative disorders and traumatic injury due to their intrinsic capabilities in API delivery. Nanomaterials can improve API accumulation in the CNS by increasing permeation through the BBB of systemically delivered APIs, extending the timeline of API release, and interacting biophysically with CNS cell populations due to their mechanical properties and nanoscale architectures. In this review, we present the recent advances in the fields of both locally implanted nanomaterials and systemically administered nanoparticles developed for the delivery of APIs to the CNS that modulate glial activity as a strategy to improve outcomes in traumatic injury and disease. We identify current research gaps and discuss potential developments in the field that will continue to translate the use of glia-targeting nanomaterials to the clinic.

The pathogenesis of DLD-mediated cuproptosis induced spinal cord injury and its regulation on immune microenvironment

Introduction

Spinal cord injury (SCI) is a severe central nervous system injury that leads to significant sensory and motor impairment. Copper, an essential trace element in the human body, plays a vital role in various biological functions and is strictly regulated by copper chaperones and transporters. Cuproptosis, a novel type of metal ion-induced cell death, is distinct from iron deprivation. Copper deprivation is closely associated with mitochondrial metabolism and mediated by protein fatty acid acylation.

Methods

In this study, we investigated the effects of cuproptosis-related genes (CRGs) on disease progression and the immune microenvironment in acute spinal cord injury (ASCI) patients. We obtained the gene expression profiles of peripheral blood leukocytes from ASCI patients using the Gene Expression Omnibus (GEO) database. We performed differential gene analysis, constructed protein-protein interaction networks, conducted weighted gene co-expression network analysis (WGCNA), and built a risk model.

Results

Our analysis revealed that dihydrolipoamide dehydrogenase (DLD), a regulator of copper toxicity, was significantly associated with ASCI, and DLD expression was significantly upregulated after ASCI. Furthermore, gene ontology (GO) enrichment analysis and gene set variation analysis (GSVA) showed abnormal activation of metabolism-related processes. Immune infiltration analysis indicated a significant decrease in T cell numbers in ASCI patients, while M2 macrophage numbers were significantly increased and positively correlated with DLD expression.

Discussion

In summary, our study demonstrated that DLD affects the ASCI immune microenvironment by promoting copper toxicity, leading to increased peripheral M2 macrophage polarization and systemic immunosuppression. Thus, DLD has potential as a promising biomarker for ASCI, providing a foundation for future clinical interventions.

Modulating neuroinflammation through molecular, cellular and biomaterial-based approaches to treat spinal cord injury

The neuroinflammatory response that is elicited after spinal cord injury contributes to both tissue damage and reparative processes. The complex and dynamic cellular and molecular changes within the spinal cord microenvironment result in a functional imbalance of immune cells and their modulatory factors. To facilitate wound healing and repair, it is necessary to manipulate the immunological pathways during neuroinflammation to achieve successful therapeutic interventions. In this review, recent advancements and fresh perspectives on the consequences of neuroinflammation after SCI and modulation of the inflammatory responses through the use of molecular-, cellular-, and biomaterial-based therapies to promote tissue regeneration and functional recovery will be discussed.

Advances in the research of the role of macrophage/microglia polarization-mediated inflammatory response in spinal cord injury

It is often difficult to regain neurological function following spinal cord injury (SCI). Neuroinflammation is thought to be responsible for this failure. Regulating the inflammatory response post-SCI may contribute to the recovery of neurological function. Over the past few decades, studies have found that macrophages/microglia are one of the primary effector cells in the inflammatory response following SCI. Growing evidence has documented that macrophages/microglia are plastic cells that can polarize in response to microenvironmental signals into M1 and M2 macrophages/microglia. M1 produces pro-inflammatory cytokines to induce inflammation and worsen tissue damage, while M2 has anti-inflammatory activities in wound healing and tissue regeneration. Recent studies have indicated that the transition from the M1 to the M2 phenotype of macrophage/microglia supports the regression of inflammation and tissue repair. Here, we will review the role of the inflammatory response and macrophages/microglia in SCI and repair. In addition, we will discuss potential molecular mechanisms that induce macrophage/microglia polarization, with emphasis on neuroprotective therapies that modulate macrophage/microglia polarization, which will provide new insights into therapeutic strategies for SCI.

Smart biomaterials and their potential applications in tissue engineering

Smart biomaterials have been rapidly advancing ever since the concept of tissue engineering was proposed. Interacting with human cells, smart biomaterials can play a key role in novel tissue morphogenesis. Various aspects of biomaterials utilized in or being sought for the goal of encouraging bone regeneration, skin graft engineering, and nerve conduits are discussed in this review. Beginning with bone, this study summarizes all the available bioceramics and materials along with their properties used singly or in conjunction with each other to create scaffolds for bone tissue engineering. A quick overview of the skin-based nanocomposite biomaterials possessing antibacterial properties for wound healing is outlined along with skin regeneration therapies using infrared radiation, electrospinning, and piezoelectricity, which aid in wound healing. Furthermore, a brief overview of bioengineered artificial skin grafts made of various natural and synthetic polymers has been presented. Finally, by examining the interactions between natural and synthetic-based biomaterials and the biological environment, their strengths and drawbacks for constructing peripheral nerve conduits are highlighted. The description of the preclinical outcome of nerve regeneration in injury healed with various natural-based conduits receives special attention. The organic and synthetic worlds collide at the interface of nanomaterials and biological systems, producing a new scientific field including nanomaterial design for tissue engineering.

Active cell capturing for organ-on-a-chip systems: a review

Organ-on-a-chip (OOC) is an emerging technology that has been proposed as a new powerful cell-based tool to imitate the pathophysiological environment of human organs. For most OOC systems, a pivotal step is to culture cells in microfluidic devices. In active cell capturing techniques, external actuators, such as electrokinetic, magnetic, acoustic, and optical forces, or a combination of these forces, can be applied to trap cells after ejecting cell suspension into the microchannel inlet. This review paper distinguishes the characteristics of biomaterials and evaluates microfluidic technology. Besides, various types of OOC and their fabrication techniques are reported and various active cell capture microstructures are analyzed. Furthermore, their constraints, challenges, and future perspectives are provided.

Recent Advances in Cell and Functional Biomaterial Treatment for Spinal Cord Injury

Spinal cord injury (SCI) is a devastating central nervous system disease caused by accidental events, resulting in loss of sensory and motor function. Considering the multiple effects of primary and secondary injuries after spinal cord injury, including oxidative stress, tissue apoptosis, inflammatory response, and neuronal autophagy, it is crucial to understand the underlying pathophysiological mechanisms, local microenvironment changes, and neural tissue functional recovery for preparing novel treatment strategies. Treatment based on cell transplantation has become the forefront of spinal cord injury therapy. The transplanted cells provide physical and nutritional support for the damaged tissue. At the same time, the implantation of biomaterials with specific biological functions at the site of the SCI has also been proved to improve the local inhibitory microenvironment and promote axonal regeneration, etc. The combined transplantation of cells and functional biomaterials for SCI treatment can result in greater neuroprotective and regenerative effects by regulating cell differentiation, enhancing cell survival, and providing physical and directional support for axon regeneration and neural circuit remodeling. This article reviews the pathophysiology of the spinal cord, changes in the microenvironment after injury, and the mechanisms and strategies for spinal cord regeneration and repair. The article will focus on summarizing and discussing the latest intervention models based on cell and functional biomaterial transplantation and the latest progress in combinational therapies in SCI repair. Finally, we propose the future prospects and challenges of current treatment regimens for SCI repair, to provide references for scientists and clinicians to seek better SCI repair strategies in the future.

Poly-l-lysine/Laminin Surface Coating Reverses Glial Cell Mechanosensitivity on Stiffness-Patterned Hydrogels

Brain tissues demonstrate heterogeneous mechanical properties, which evolve with aging and pathologies. The observation in these tissues of smooth to sharp rigidity gradients raises the question of brain cell responses to both different values of rigidity and their spatial variations, in dependence on the surface chemistry they are exposed to. Here, we used recent techniques of hydrogel photopolymerization to achieve stiffness texturing down to micrometer resolution in polyacrylamide hydrogels. We investigated primary neuron adhesion and orientation as well as glial cell proliferative properties on these rigidity-textured hydrogels for two adhesive coatings: fibronectin or poly-l-lysine/laminin. Our main observation is that glial cell adhesion and proliferation is favored on the stiffer regions when the adhesive coating is fibronectin and on the softer ones when it consists of poly-l-lysine/laminin. This behavior was unchanged by the presence or the absence of neuronal cells. In addition, glial cells were not confined by sharp, micron-scaled gradients of rigidity. Our observations suggest that rigidity sensing could involve adhesion-related pathways that profoundly depend on surface chemistry.

Polymeric Fibers as Scaffolds for Spinal Cord Injury: A Systematic Review

Spinal cord injury (SCI) is a complex neurological condition caused by trauma, inflammation, and other diseases, which often leads to permanent changes in strength and sensory function below the injured site. Changes in the microenvironment and secondary injuries continue to pose challenges for nerve repair and recovery after SCI. Recently, there has been progress in the treatment of SCI with the use of scaffolds for neural tissue engineering. Polymeric fibers fabricated by electrospinning have been increasingly used in SCI therapy owing to their biocompatibility, complex porous structure, high porosity, and large specific surface area. Polymer fibers simulate natural extracellular matrix of the nerve fiber and guide axon growth. Moreover, multiple channels of polymer fiber simulate the bundle of nerves. Polymer fibers with porous structure can be used as carriers loaded with drugs, nerve growth factors and cells. As conductive fibers, polymer fibers have electrical stimulation of nerve function. This paper reviews the fabrication, characterization, and application in SCI therapy of polymeric fibers, as well as potential challenges and future perspectives regarding their application.

Advanced approaches to regenerate spinal cord injury: The development of cell and tissue engineering therapy and combinational treatments

Spinal cord injury (SCI) is a central nervous system (CNS) devastate event that is commonly caused by traumatic or non-traumatic events. The reinnervation of spinal cord axons is hampered through a myriad of devices counting on the damaged myelin, inflammation, glial scar, and defective inhibitory molecules. Unfortunately, an effective treatment to completely repair SCI and improve functional recovery has not been found. In this regard, strategies such as using cells, biomaterials, biomolecules, and drugs have been reported to be effective for SCI recovery. Furthermore, recent advances in combinatorial treatments, which address various aspects of SCI pathophysiology, provide optimistic outcomes for spinal cord regeneration. According to the global importance of SCI, the goal of this article review is to provide an overview of the pathophysiology of SCI, with an emphasis on the latest modes of intervention and current advanced approaches for the treatment of SCI, in conjunction with an assessment of combinatorial approaches in preclinical and clinical trials. So, this article can give scientists and clinicians' clues to help them better understand how to construct preclinical and clinical studies that could lead to a breakthrough in spinal cord regeneration.

Research progress, models and simulation of electrospinning technology: a review

In recent years, nanomaterials have aroused extensive research interest in the world's material science community. Electrospinning has the advantages of wide range of available raw materials, simple process, small fiber diameter and high porosity. Electrospinning as a nanomaterial preparation technology with obvious advantages has been studied, such as its influencing parameters, physical models and computer simulation. In this review, the influencing parameters, simulation and models of electrospinning technology are summarized. In addition, the progresses in applications of the technology in biomedicine, energy and catalysis are reported. This technology has many applications in many fields, such as electrospun polymers in various aspects of biomedical engineering. The latest achievements in recent years are summarized, and the existing problems and development trends are analyzed and discussed.

Thermosensitive collagen/fibrinogen gels loaded with decorin suppress lesion site cavitation and promote functional recovery after spinal cord injury

The treatment of spinal cord injury (SCI) is a complex challenge in regenerative medicine, complicated by the low intrinsic capacity of CNS neurons to regenerate their axons and the heterogeneity in size, shape and extent of human injuries. For example, some contusion injuries do not compromise the dura mater and in such cases implantation of preformed scaffolds or drug delivery systems may cause further damage. Injectable in situ thermosensitive scaffolds are therefore a less invasive alternative. In this study, we report the development of a novel, flowable, thermosensitive, injectable drug delivery system comprising bovine collagen (BC) and fibrinogen (FB) that forms a solid BC/FB gel (Gel) immediately upon exposure to physiological conditions and can be used to deliver reparative drugs, such as the naturally occurring anti-inflammatory, anti-scarring agent Decorin, into adult rat spinal cord lesion sites. In dorsal column lesions of adult rats treated with the Gel + Decorin, cavitation was completely suppressed and instead lesion sites became filled with injury-responsive cells and extracellular matrix materials, including collagen and laminin. Decorin increased the intrinsic potential of dorsal root ganglion neurons (DRGN) by increasing their expression of regeneration associated genes (RAGs), enhanced local axon regeneration/sprouting, as evidenced both histologically and by improved electrophysiological, locomotor and sensory function recovery. These results suggest that this drug formulated, injectable hydrogel has the potential to be further studied and translated into the clinic.

Advanced Bio-Based Polymers for Astrocyte Cell Models

The development of in vitro neural tissue analogs is of great interest for many biomedical engineering applications, including the tissue engineering of neural interfaces, treatment of neurodegenerative diseases, and in vitro evaluation of cell-material interactions. Since astrocytes play a crucial role in the regenerative processes of the central nervous system, the development of biomaterials that interact favorably with astrocytes is of great research interest. The sources of human astrocytes, suitable natural biomaterials, guidance scaffolds, and ligand patterned surfaces are discussed in the article. New findings in this field are essential for the future treatment of spinal cord and brain injuries.

Glial Interfaces: Advanced Materials and Devices to Uncover the Role of Astroglial Cells in Brain Function and Dysfunction

Research over the past four decades has highlighted the importance of certain brain cells, called glial cells, and has moved the neurocentric vision of structure, function, and pathology of the nervous system toward a more holistic perspective. In this view, the demand for technologies that are able to target and both selectively monitor and control glial cells is emerging as a challenge across neuroscience, engineering, chemistry, and material science. Frequently neglected or marginally considered as a barrier to be overcome between neural implants and neuronal targets, glial cells, and in particular astrocytes, are increasingly considered as active players in determining the outcomes of device implantation. This review provides a concise overview not only of the previously established but also of the emerging physiological and pathological roles of astrocytes. It also critically discusses the most recent advances in biomaterial interfaces and devices that interact with glial cells and thus have enabled scientists to reach unprecedented insights into the role of astroglial cells in brain function and dysfunction. This work proposes glial interfaces and glial engineering as multidisciplinary fields that have the potential to enable significant advancement of knowledge surrounding cognitive function and acute and chronic neuropathologies.

Electrospun Fiber Scaffolds for Engineering Glial Cell Behavior to Promote Neural Regeneration

Electrospinning is a fabrication technique used to produce nano- or micro- diameter fibers to generate biocompatible, biodegradable scaffolds for tissue engineering applications. Electrospun fiber scaffolds are advantageous for neural regeneration because they mimic the structure of the nervous system extracellular matrix and provide contact guidance for regenerating axons. Glia are non-neuronal regulatory cells that maintain homeostasis in the healthy nervous system and regulate regeneration in the injured nervous system. Electrospun fiber scaffolds offer a wide range of characteristics, such as fiber alignment, diameter, surface nanotopography, and surface chemistry that can be engineered to achieve a desired glial cell response to injury. Further, electrospun fibers can be loaded with drugs, nucleic acids, or proteins to provide the local, sustained release of such therapeutics to alter glial cell phenotype to better support regeneration. This review provides the first comprehensive overview of how electrospun fiber alignment, diameter, surface nanotopography, surface functionalization, and therapeutic delivery affect Schwann cells in the peripheral nervous system and astrocytes, oligodendrocytes, and microglia in the central nervous system both in vitro and in vivo. The information presented can be used to design and optimize electrospun fiber scaffolds to target glial cell response to mitigate nervous system injury and improve regeneration.

Conventional immunomarkers stain a fraction of astrocytes in vitro: A comparison of rat cortical and spinal cord astrocytes in naïve and stimulated cultures

Astrocytes are responsible for a wide variety of essential functions throughout the central nervous system. The protein markers glial fibrillary acidic protein (GFAP), glutamate aspartate transporter (GLAST), glutamate transporter-1 (GLT-1), glutamine synthetase (GS), 10-formyltetrahydrofolate dehydrogenase (ALDH1L1), and the transcription factor SOX9 are routinely used to label astrocytes in primary rodent cultures. However, GLAST, GLT-1, GS, and SOX9 are also produced by microglia and oligodendrocytes and GFAP, GLAST, GLT-1, and GS production levels are affected by astrocyte phenotypic changes associated with reactive astrogliosis. No group has performed a comprehensive immunocytochemical evaluation to quantify the percentage of cells labeled by these markers in vitro, nor compared changes in staining between cortex- and spinal cord-derived cells in naïve and stimulated cultures. Here, we quantified the percentage of cells positively stained for these six markers in astrocyte, microglia, and oligodendrocyte cultures isolated from neonatal rat cortices and spinal cords. Additionally, we incubated the astrocytes with transforming growth factor (TGF)-β1 or TGF-β3 to determine if the labeling of these markers is altered by these stimuli. We found that only SOX9 in cortical cultures and ALDH1L1 in spinal cord cultures labeled more than 75% of the cells in naïve and stimulated astrocyte cultures and stained less than 5% of the cells in microglia and oligodendrocyte cultures. Furthermore, significantly more cortical than spinal cord astrocytes stained for GFAP, GLAST, and ALDH1L1 in naïve cultures, whereas significantly more spinal cord than cortical astrocytes stained for GLAST and GS in TGF-β1-treated cultures. These findings are important as variability in marker staining may lead to misinterpretation of the astrocyte response in cocultures, migration assays, or engineered disease models.

PSA mimetic 5-nonyloxytryptamine protects cerebellar neurons against glutamate induced excitotoxicity: An in vitro perspective

PSA-NCAM is a molecule of therapeutic interest for its key role in promoting neuritogenesis and synaptic plasticity. The current study was aimed to investigate the neuroregenerative potential of 5-nonyloxytryptamine (5-NOT) as PSA mimetic compound against glutamate induced excitotoxicity. 2D and 3D cultures of cerebellar neurons challenged with glutamate were used to ascertain the effect of 5-NOT on neurite outgrowth, migration and expression of neuronal plasticity markers. Glutamate excitotoxicity is one of the major underlying pathological factor responsible for neurodegeneration in various neurological disorders such as trauma, stroke, ischemia, epilepsy and neurodegenerative diseases.5-NOT treatment was observed to promote axonal growth and defasiculation in glutamate challenged neurons as well as promoted the migration of cerebellar neurons in both wound scratched area and cerebellar explant cultures. Further, 5-NOT treatment upregulated the expression of synaptic plasticity and cell survival pathway proteins which showed reduced expression after glutamate induced excitotoxicity. Thus, this preliminary data reveals thatPSA-mimetic,5-NOT may prove to be a potential neuroprotective candidate for neurodegenerative diseases.

TGFβ3 is neuroprotective and alleviates the neurotoxic response induced by aligned poly-l-lactic acid fibers on naïve and activated primary astrocytes

Following spinal cord injury, astrocytes at the site of injury become reactive and exhibit a neurotoxic (A1) phenotype, which leads to neuronal death. In addition, the glial scar, which is composed of reactive astrocytes, acts as a chemical and physical barrier to subsequent axonal regeneration. Biomaterials, specifically electrospun fibers, induce a migratory phenotype of astrocytes and promote regeneration of axons following acute spinal cord injury in preclinical models. However, no study has examined the potential of electrospun fibers or biomaterials in general to modulate neurotoxic (A1) or neuroprotective (A2) astrocytic phenotypes. To assess astrocyte reactivity in response to aligned poly-l-lactic acid microfibers, naïve spinal cord astrocytes or spinal cord astrocytes primed towards the neurotoxic phenotype (A1) were cultured on fibrous scaffolds. Gene expression analysis of the pan-reactive astrocyte makers (GFAP, Lcn2, SerpinA3), A1 specific markers (H2-D1, SerpinG1), and A2 specific makers (Emp1, S100a10) was done using quantitative polymerase chain reaction (qPCR). Electrospun fibers mildly increased the expression of the pan-reactive and A1-specific markers, showing the ability of fibrous materials to induce a more reactive, A1 phenotype. However, when naïve or activated astrocytes were cultured on fibers in the presence of transforming growth factor β3 (TGFβ3), the expression of A1-specific markers was greatly reduced, which in turn improved neuronal survival in culture.

Biomaterial strategies for creating in vitro astrocyte cultures resembling in vivo astrocyte morphologies and phenotypes

Astrocytes are dynamic cells residing in the central nervous system exhibiting many diverse functions. Astrocytes quickly change and present unique phenotypes in response to injury or disease. Here, we briefly summarize recent information regarding astrocyte morphology and function and provide brief insight into their phenotypic changes following injury or disease. We also present the utility of in vitro astrocyte cultures and present recent advances in biomaterial development that enable better recapitulation of their in vivo behavior and morphology.

Porous Silicon Nanoparticles Embedded in Poly(lactic-co-glycolic acid) Nanofiber Scaffolds Deliver Neurotrophic Payloads to Enhance Neuronal Growth

Scaffolds made from biocompatible polymers provide physical cues to direct the extension of neurites and to encourage repair of damaged nerves. The inclusion of neurotrophic payloads in these scaffolds can substantially enhance regrowth and repair processes. However, many promising neurotrophic candidates are excluded from this approach due to incompatibilities with the polymer or with the polymer processing conditions. This work provides one solution to this problem by incorporating porous silicon nanoparticles (pSiNPs) that are pre-loaded with the therapeutic into a polymer scaffold during fabrication. The nanoparticle-drug-polymer hybrids are prepared in the form of oriented poly(lactic-co-glycolic acid) nanofiber scaffolds. We test three different therapeutic payloads: bpV(HOpic), a small molecule inhibitor of phosphatase and tensin homolog (PTEN); an RNA aptamer specific to tropomyosin-related kinase receptor type B (TrkB); and the protein nerve growth factor (NGF). Each therapeutic is loaded using a loading chemistry that is optimized to slow the rate of release of these water-soluble payloads. The drug-loaded pSiNP-nanofiber hybrids release approximately half of their TrkB aptamer, bpV(HOpic), or NGF payload in 2, 10, and >40 days, respectively. The nanofiber hybrids increase neurite extension relative to drug-free control nanofibers in a dorsal root ganglion explant assay.

5-Nonyloxytryptamine oxalate-embedded collagen-laminin scaffolds augment functional recovery after spinal cord injury in mice

Polysialic acid (PSA) is crucial for the induction and maintenance of nervous system plasticity and repair after injury. In order to exploit the immense therapeutic potential of PSA, previous studies have focused on the identification and development of peptide-based or synthetic PSA mimetics. 5-Nonyloxytryptamine (5-NOT) has been previously reported as a PSA-mimicking compound for promoting functional recovery after spinal cord injury in mice. In order to explore the neuroregeneration potential of 5-NOT, the current study was based on a biomaterial approach using collagen-laminin (C/L) scaffolds. In in vitro studies, 5-NOT was observed to promote neurite outgrowth, migration, and fasciculation in cerebellar neuronal cells, whereas in 3D cell cultures it showed more ramification and complex Sholl profiles. 5-NOT promoted the survival and neurite length of cortical neurons when cocultured with glutamate-challenged astrocytes. In in vivo studies, spinal cord compression injury mice were used with immediate application of C/L hydrogels impregnated with 5-NOT. C/L + 5-NOT-treated mice demonstrated ∼75% of motor recovery 14 days after injury. Furthermore, this effect was shown to be dependent on the ERK-MAPK pathway and augmentation of cell survival. Thus, based on a biomaterial approach, our current study provides new insight for 5-NOT-containing hydrogels as a promising candidate to speed up recovery after central nervous system injuries.

Fibronectin Functionalized Electrospun Fibers by Using Benign Solvents: Best Way to Achieve Effective Functionalization

The aim of this study is to demonstrate the feasibility of different functionalization methods for electrospun fibers developed using benign solvents. In particular three different approaches were investigated to achieve the functionalization of poly(epsilon caprolactone) (PCL) electrospun fibers with fibronectin. Protein surface entrapment, chemical functionalization and coaxial electrospinning were performed and compared. Moreover, bilayered scaffolds, with a top patterned and functionalized layer with fibronectin and a randomly oriented not functionalized layer were fabricated, demonstrating the versatility of the use of benign solvents for electrospinning also for the fabrication of complex graded structures. Besides the characterization of the morphology of the obtained scaffolds, ATR-FTIR and ToF-SIMS were used for the surface characterization of the functionalized fibers. Cell adhesion and proliferation were also investigated by using ST-2 cells. Positive results were obtained from all functionalized scaffolds and the most promising results were obtained with bilayered scaffolds, in terms of cells infiltration inside the fibrous structure.

Spinning and Applications of Bioinspired Fiber Systems

Natural fiber systems provide inspirations for artificial fiber spinning and applications. Through a long process of trial and error, great progress has been made in recent years. The natural fiber itself, especially silks, and the formation mechanism are better understood, and some of the essential factors are implemented in artificial spinning methods, benefiting from advanced manufacturing technologies. In addition, fiber-based materials produced via bioinspired spinning methods find an increasingly wide range of biomedical, optoelectronic, and environmental engineering applications. This paper reviews recent developments in the spinning and application of bioinspired fiber systems, introduces natural fiber and spinning processes and artificial spinning methods, and discusses applications of artificial fiber materials. Views on remaining challenges and the perspective on future trends are also proposed.

Biomaterial Approaches to Modulate Reactive Astroglial Response

Over several decades, biomaterial scientists have developed materials to spur axonal regeneration and limit secondary injury and tested these materials within preclinical animal models. Rarely, though, are astrocytes examined comprehensively when biomaterials are placed into the injury site. Astrocytes support neuronal function in the central nervous system. Following an injury, astrocytes undergo reactive gliosis and create a glial scar. The astrocytic glial scar forms a dense barrier which restricts the extension of regenerating axons through the injury site. However, there are several beneficial effects of the glial scar, including helping to reform the blood-brain barrier, limiting the extent of secondary injury, and supporting the health of regenerating axons near the injury site. This review provides a brief introduction to the role of astrocytes in the spinal cord, discusses astrocyte phenotypic changes that occur following injury, and highlights studies that explored astrocyte changes in response to biomaterials tested within in vitro or in vivo environments. Overall, we suggest that in order to improve biomaterial designs for spinal cord injury applications, investigators should more thoroughly consider the astrocyte response to such designs.

The Effect of Electrospun Fiber Diameter on Astrocyte-Mediated Neurite Guidance and Protection

The topography of electrospun fiber scaffolds modifies astrocytes toward in vivo-like morphologies and behaviors. However, little is known about how electrospun fiber diameter influences astrocyte behavior. In this work, aligned fibers with two distinct nanoscale fiber diameters (808 and 386 nm) were prepared, and the astrocyte response was measured over time. Astrocytes on the large diameter fibers showed significantly increased elongation as early as 2 h after seeding and remained significantly more elongated for up to 4 days compared to those on small diameter fibers. Astrocytes extending along larger diameter fibers were better equipped to support long neurite outgrowth from dorsal root ganglia neurons, and neurite outgrowth along these astrocytes was less branched than outgrowth along astrocytes cultured on small diameter fibers. The differences in astrocyte shape observed on the small or large diameter fibers did not translate into differences in GLT-1, GFAP, or GLAST protein expression. Thus, different fiber diameters were unable to influence astrocyte protein expression uniquely. Nevertheless, astrocytes cultured in either small or large fibers significantly increased their expression of GLT-1 compared to astrocytes cultured on nonfiber (film) controls. Fibrous-induced increases in astrocyte GLT-1 expression protected astrocyte/neuron cocultures from toxicity generated by high extracellular glutamate. Alternatively, astrocytes/neurons cultured on films were less able to protect these cells from culture conditions consisting of high glutamate levels. Biomaterials, such as the fibrous materials presented here, may help stimulate astrocytes to increase GLT-1 expression and uptake more glutamate, since astrocytes are less likely to uptake glutamate in neurodegenerative pathologies or following central nervous system injury.

A Programmed Anti-Inflammatory Nanoscaffold (PAIN) as a 3D Tool to Understand the Brain Injury Response

Immunology is the next frontier of nano/biomaterial science research, with the immune system determining the degree of tissue repair. However, the complexity of the inflammatory response represents a significant challenge that is essential to understand for the development of future therapies. Cell-instructive 3D culture environments are critical to improve our understanding of the link between the behavior and morphology of inflammatory cells and to remodel their response to injury. This study has taken two recent high-profile innovations-functional peptide-based hydrogels, and the inclusion of anti-inflammatory agents via coassembly-to make a programmed anti-inflammatory nanoscaffold (PAIN) with unusual and valuable properties that allows tissue-independent switching of the inflammatory cascade. Here, extraordinary durability of the anti-inflammatory agent allows, for the first time, the development of a 3D culture system that maintains the growth and cytoskeletal reorganization of brain tissue, while also facilitating the trophic behavior of brain cells for 22 d in vitro. Notably, this behavior was confirmed within an active scar site due to the unprecedented resilience to the presence of inflammatory cells and enzymes in the brain. Efficacy of the culture system is demonstrated via novel insights about inflammatory cell behavior, which would be impossible to obtain via in vivo experimentation.

Polycaprolactone/polysialic acid hybrid, multifunctional nanofiber scaffolds for treatment of spinal cord injury

Scaffold-based tissue engineering is widely used for spinal cord injury (SCI) treatment by creating supporting and guiding neuronal tissue regeneration. However, how to enhance the axonal regeneration capacity following SCI still remains a challenge. Polysialic acid (PSA), a natural, biodegradable polysaccharide, has been increasingly explored for controlling central nervous system (CNS) development by regulating cell adhesive properties and promoting axonal growth. Here, a polycaprolactone (PCL)/PSA hybrid nanofiber scaffold encapsulating glucocorticoid methylprednisolone (MP) is developed for SCI treatment. Rat models with spinal cord transection is established and the PCL/PSA/MP scaffold is transplanted into lesion area. PCL/PSA/MP scaffold decreases tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) release by inhibiting ionized calcium-binding adapter molecule 1 (Iba1) positive microglia/macrophage activation and reduces apoptosis-associated Caspase-3 protein expression. In addition, the PCL/PSA/MP scaffold inhibits axonal demyelination and glial fibrillary acidic protein (GFAP) expression, increases neurofilament 200 (NF-200) expression and improves functional outcome by Basso, Beattie and Bresnahan (BBB) test. These results demonstrate the therapeutic potential of PSA hybrid nanofiber scaffold in promoting axonal growth and enhancing the functional recovery following SCI.

STATEMENT OF SIGNIFICANCE

Scaffold-based tissue engineering is widely used for spinal cord injury (SCI) treatment by creating supporting and guiding neuronal tissue regeneration. And how to enhance the axonal regeneration capacity following SCI still remains a challenge. Polysialic acid (PSA), a natural, biodegradable polysaccharide, has been increasingly explored for controlling central nervous system (CNS) development by regulating cell adhesive properties and promoting axonal growth. However, in vivo therapeutic effect of PSA scaffolds towards SCI is still lack of evidence and needs to be further explored. In this study, a novel electrospun polycaprolactone/PSA scaffold loaded with methylprednisolone (MP) was developed to achieve efficient therapeutic effects towards SCI. And we believe that it broadens the application of PSA for SCI treatment.

Nano-Architectural Approaches for Improved Intracortical Interface Technologies

Intracortical microelectrodes (IME) are neural devices that initially were designed to function as neuroscience tools to enable researchers to understand the nervous system. Over the years, technology that aids interfacing with the nervous system has allowed the ability to treat patients with a wide range of neurological injuries and diseases. Despite the substantial success that has been demonstrated using IME in neural interface applications, these implants eventually fail due to loss of quality recording signals. Recent strategies to improve interfacing with the nervous system have been inspired by methods that mimic the native tissue. This review focusses on one strategy in particular, nano-architecture, a term we introduce that encompasses the approach of roughening the surface of the implant. Various nano-architecture approaches have been hypothesized to improve the biocompatibility of IMEs, enhance the recording quality, and increase the longevity of the implant. This review will begin by introducing IME technology and discuss the challenges facing the clinical deployment of IME technology. The biological inspiration of nano-architecture approaches will be explained as well as leading fabrication methods used to create nano-architecture and their limitations. A review of the effects of nano-architecture surfaces on neural cells will be examined, depicting the various cellular responses to these modified surfaces in both in vitro and pre-clinical models. The proposed mechanism elucidating the ability of nano-architectures to influence cellular phenotype will be considered. Finally, the frontiers of next generation nano-architecture IMEs will be identified, with perspective given on the future impact of this interfacing approach.

Electrospinning: An enabling nanotechnology platform for drug delivery and regenerative medicine

Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.

Electrospun fiber surface nanotopography influences astrocyte-mediated neurite outgrowth

Aligned, electrospun fiber scaffolds provide topographical guidance for regenerating neurons and glia after central nervous system injury. To date, no study has explored how fiber surface nanotopography affects astrocyte response to fibrous scaffolds. Astrocytes play important roles in the glial scar, the blood brain barrier, and in maintaining homeostasis in the central nervous system. In this study, electrospun poly L-lactic acid fibers were engineered with smooth, pitted, or divoted surface nanotopography. Cortical or spinal cord primary rat astrocytes were cultured on the surfaces for either 1 or 3 d to examine the astrocyte response over time. The results showed that cortical astrocytes were significantly shorter and broader on the pitted and divoted fibers compared to those on smooth fibers. However, spinal cord astrocyte morphology was not significantly altered by the surface features. These findings indicate that astrocytes from unique anatomical locations respond differently to the presence of nanotopography. Western blot results show that the differences in morphology were not associated with significant changes in glial fibrillary acidicprotein (GFAP) or vinculin in either astrocyte population, suggesting that surface pits and divots do not induce a reactive phenotype in either cortical or spinal cord astrocytes. Finally, astrocytes were co-cultured with dorsal root ganglia to determine how the surfaces affected astrocyte-mediated neurite outgrowth. Astrocytes cultured on the fibers for shorter periods of time (1 d) generally supported longer neurite outgrowth. Pitted and divoted fibers restricted spinal cord astrocyte-mediated neurite outgrowth, while smooth fibers increased 3 d spinal cord astrocyte-mediated neurite outgrowth. In total, fiber surface nanotopography can influence astrocyte elongation and influence the capability of astrocytes to direct neurites. Therefore, fiber surface characteristics should be carefully controlled to optimize astrocyte-mediated axonal regeneration.

An in vitro study of non-aligned or aligned electrospun poly(methyl methacrylate) nanofibers as primary rat astrocytes-loading scaffold

After spinal cord injury (SCI), functional regeneration of neurites is hard to achieve due to the existence of glial scar, meanwhile astrocytes are believed important for post injury neuroregeneration, therefore how to handle the contradictory roles of astrocytes remains a problem for better neurogenesis. In this report, aligned electrospun poly(methyl methacrylate) (PMMA) nanofibers were assessed as an astrocytes-loading scaffold in vitro. We found that cell adherence and cell expansion of astrocytes could be supported by PMMA nanofibers, which topographic features could obviously influence the growth manner of astrocytes, and cells on aligned nanofibers finally formed longer and highly aligned processes along the axis of substrate fibers compared with cells cultured on film and non-aligned nanofibers. Regarding the relationship between astrocytes and substratum nanofibers, different topographic feature of substrate nanofibers showed varying degree of impact on cell expansion. On non-aligned nanofibers astrocytes expanded along the orientation of nanofibers early, while on aligned nanofibers astrocytes complied with the cues of nanofibers gradually with time. The results strengthen the rationale that aligned nanofibers could serve as the candidate of implantable scaffold after SCI, and it may relieve the stress of proliferated astrocytes by manipulating the growth pattern of astrocytes through its topographic features.

Using biomaterials to promote pro-regenerative glial phenotypes after nervous system injuries

Trauma to either the central or peripheral nervous system (PNS) often leads to significant loss of function and disability in patients. This high rate of long-term disability is due to the overall limited regenerative potential of nervous tissue, even though the PNS has more regenerative potential than the central nervous system (CNS). The supporting glial cells in the periphery, Schwann cells, are part of the reason for the improved recovery observed in the PNS. In the CNS, the glial populations, astrocytes and oligodendrocytes (OLs), do not have as much potential to promote regeneration and are at times inhibitory to neuronal growth. In particular, the inhibitory roles astrocytes play following trauma has led to a historical focus on neurons and OLs instead of astrocytes. Recently, this focus has shifted as new, regenerative astrocyte phenotypes have been described. From these observations, glial cells clearly play critical roles in native recovery pathways in both the CNS and PNS. This makes the ability to manipulate both transplanted and native glial cell phenotypes a potentially successful strategy to improve nerve injury outcomes. This review focuses on factors that cause glial cells to adopt repair phenotypes and biomaterials that manipulate and/or harness these glial phenotypes.

Biomaterial strategies for limiting the impact of secondary events following spinal cord injury

The nature of traumatic spinal cord injury (SCI) often involves limited recovery and long-term quality of life complications. The initial injury sets off a variety of secondary cascades, which result in an expanded lesion area. Ultimately, the native tissue fails to regenerate. As treatments are developed in the laboratory, the management of this secondary cascade is an important first step in achieving recovery of normal function. Current literature identifies four broad targets for intervention: inflammation, oxidative stress, disruption of the blood-spinal cord barrier, and formation of an inhibitory glial scar. Because of the complex and interconnected nature of these events, strategies that combine multiple therapies together show much promise. Specifically, approaches that rely on biomaterials to perform a variety of functions are generating intense research interest. In this review, we examine each target and discuss how biomaterials are currently used to address them. Overall, we show that there are an impressive amount of biomaterials and combinatorial treatments which show good promise for slowing secondary events and improving outcomes. If more emphasis is placed on growing our understanding of how materials can manage secondary events, treatments for SCI can be designed in an increasingly rational manner, ultimately improving their potential for translation to the clinic.

Glial responses to implanted electrodes in the brain

The use of implants that can electrically stimulate or record electrophysiological or neurochemical activity in nervous tissue is rapidly expanding. Despite remarkable results in clinical studies and increasing market approvals, the mechanisms underlying the therapeutic effects of neuroprosthetic and neuromodulation devices, as well as their side effects and reasons for their failure, remain poorly understood. A major assumption has been that the signal-generating neurons are the only important target cells of neural-interface technologies. However, recent evidence indicates that the supporting glial cells remodel the structure and function of neuronal networks and are an effector of stimulation-based therapy. Here, we reframe the traditional view of glia as a passive barrier, and discuss their role as an active determinant of the outcomes of device implantation. We also discuss the implications that this has on the development of bioelectronic medical devices.

Astrocyte spreading and migration on aggrecan-laminin dot gradients

The surface concentration gradient of two extracellular matrix (ECM) macromolecules was developed to study the migratory and morphological responses of astrocytes to molecular cues typically found in the central nervous system injury environment. The gradient, prepared using microcontact printing, was composed of randomly positioned micrometer-sized dots of aggrecan (AGG) printed on a substrate uniformly coated with laminin (LN). AGG dots were printed in an increasing number along the 1000 μm long and 50 μm wide gradient area which had on each end either a full surface coverage of AGG or LN. Each dot gradient was surrounded by a 100 μm-wide uniform field of AGG printed over laminin. Seeded astrocytes were found to predominantly attach to LN regions on the gradient. Cellular extensions of these cells were longer than the similar processes for cells seeded on uniform substrates of AGG or LN serving as controls. Astrocyte extensions were the largest and spanned a distance of 150 μm when the cells were attached to the mixed AGG+LN patches on the gradient. As evidenced by their increased area and perimeter, the cells extended processes in a stellate fashion upon initial attachment and maintained extensions when seeded in AGG+LN regions but not on uniform laminin controls. The cells migrated short distances, ∼20-35 μm, over 24 h and in doing so preferentially shifted from AGG areas to higher LN surface coverage regions. The results indicated that presenting mixed ECM cues caused astrocytes to sample larger areas of the substrate and made the cells to preferentially relocate to a more permissive ECM region.

Nanofiber Scaffolds as Drug Delivery Systems to Bridge Spinal Cord Injury

The complex pathophysiology of spinal cord injury (SCI) may explain the current lack of an effective therapeutic approach for the regeneration of damaged neuronal cells and the recovery of motor functions. A primary mechanical injury in the spinal cord triggers a cascade of secondary events, which are involved in SCI instauration and progression. The aim of the present review is to provide an overview of the therapeutic neuro-protective and neuro-regenerative approaches, which involve the use of nanofibers as local drug delivery systems. Drugs released by nanofibers aim at preventing the cascade of secondary damage (neuro-protection), whereas nanofibrous structures are intended to re-establish neuronal connectivity through axonal sprouting (neuro-regeneration) promotion, in order to achieve a rapid functional recovery of spinal cord.

Electrospun polymeric micro/nanofibrous scaffolds for long-term drug release and their biomedical applications

Electrospun polymeric micro/nanofibrous scaffolds have been investigated extensively as drug delivery platforms capable of controlled and sustained release of therapeutic agents in situ. Such scaffolds exhibit excellent physicochemical and biological properties and can encapsulate and release various drugs in a controlled fashion. This article reviews recent advances in the design and manufacture of electrospun scaffolds for long-term drug release, placing particular emphasis on polymer selection, types of incorporated drugs and the latest drug-loading techniques. Finally, applications of such devices in traumatic or disease states requiring effective and sustained drug action are discussed and critically appraised in their biomedical context.

Galactose-functionalised PCL nanofibre scaffolds to attenuate inflammatory action of astrocytes in vitro and in vivo

Astrocytes represent an attractive therapeutic target for the treatment of traumatic brain injury in the glial scar, which inhibits functional repair and recovery if persistent. Many biomaterial systems have been investigated for neural tissue engineering applications, including electrospun nanofibres, which are a favourable biomaterial as they can mimic the fibrous architecture of the extracellular matrix, and are conveniently modified to present biologically relevant cues to aid in regeneration. Here, we synthesised a novel galactose-presenting polymer, poly(l-lysine)-lactobionic acid (PLL-LBA), for use in layer-by-layer (LbL) functionalisation of poly(ε-caprolactone) (PCL) nanofibres, to covalently attach galactose moieties to the nanofibre scaffold surface. We have assessed the use of this novel biomaterial system in vitro and in vivo, and have shown, for the first time, the ability of galactose to maintain an attenuated inflammatory profile of astrocytes in culture, and to increase the survival of neurons after traumatic injury, as compared to control PCL nanofibres. This study highlights the importance of galactose in controlling the astrocytic response, and provides a promising biomaterial system to deliver the essential morphological and biological cues to achieve functional repair after traumatic brain injury.

The effect of engineered nanotopography of electrospun microfibers on fiber rigidity and macrophage cytokine production

Currently, it is unknown how the mechanical properties of electrospun fibers, and the presentation of surface nanotopography influence macrophage gene expression and protein production. By further elucidating how specific fiber properties (mechanical properties or surface properties) alter macrophage behavior, it may be possible to create electrospun fiber scaffolds capable of initiating unique cellular and tissue responses. In this study, we determined the elastic modulus and rigidity of fibers with varying topographies created by finely controlling humidity and including a non-solvent during electrospinning. In total,five fiber scaffold types were produced. Analysis of fiber physical properties demonstrated no change in fiber diameter amongst the five different fiber groups. However, the four different fibrous scaffolds with nanopits or divots each possessed different numbers of pits with different nanoscale dimensions. Unpolarized bone marrow derived murine macrophages (M0), macrophages polarized towards a pro-inflammatory phenotype (M1), or macrophages polarized towards anti-inflammatory phenotype (M2b) were placed onto each of the scaffolds and cytokine RNA expression and protein production were analyzed. Specific nanotopographies did not appreciably alter cytokine production from undifferentiated macrophages (M0) or anti-inflammatory macrophages (M2b), but a specific fiber (with many small pits) did increase IL-12 transcript and IL-12 protein production compared to fibers with small divots. When analyzing the mechanical properties between fibers with divots or with many small pits,divoted fibers possessed similar elastic moduli but different stiffness values. In total,we present techniques capable of creating unique electrospun fibers. These unique fibers have varying fiber mechanical characteristics and modestly modulate macrophage cytokine expression.

Neuregulin 1 functionalization of organic fibers for Schwann cell guidance

The repair of peripheral nerve lesions is a clinical problem where the functional recovery is often far from being satisfactory, although peripheral nerves generally retain good potential for regeneration. Here, we develop a novel scaffold approach based on bioactive fibers of poly(ε-caprolactone) where nanotopographical guidance and neuregulin 1 (NRG1) cues are combined. We interface them with rat primary Schwann cells (SCs), the peripheral glial cells that drive initial regeneration of injured nerves, and found that the combination of NRG1 with parallel nano-fibrous topographies is effective in improving SC growth up to 72 h, alignment to fiber topography, and bipolar differentiation, opening original perspectives for nerve repair applications.

Heparin/collagen encapsulating nerve growth factor multilayers coated aligned PLLA nanofibrous scaffolds for nerve tissue engineering

Biomimicing topological structure of natural nerve tissue to direct axon growth and controlling sustained release of moderate neurotrophic factors are extremely propitious to the functional recovery of damaged nervous systems. In this study, the heparin/collagen encapsulating nerve growth factor (NGF) multilayers were coated onto the aligned poly-L-lactide (PLLA) nanofibrous scaffolds via a layer-by-layer (LbL) self-assembly technique to combine biomolecular signals, and physical guidance cues for peripheral nerve regeneration. Scanning electronic microscopy (SEM) revealed that the surface of aligned PLLA nanofibrous scaffolds coated with heparin/collagen multilayers became rougher and appeared some net-like filaments and protuberances in comparison with PLLA nanofibrous scaffolds. The heparin/collagen multilayers did not destroy the alignment of nanofibers. X-ray photoelectron spectroscopy and water contact angles displayed that heparin and collagen were successfully coated onto the aligned PLLA nanofibrous scaffolds and improved its hydrophilicity. Three-dimensional (3 D) confocal microscopy images further demonstrated that collagen, heparin, and NGF were not only coated onto the surface of aligned PLLA nanofibrous scaffolds but also permeated into the inner of scaffolds. Moreover, NGF presented a sustained release for 2 weeks from aligned nanofibrous scaffolds coated with 5.5 bilayers or above and remained good bioactivity. The heparin/collagen encapsulating NGF multilayers coated aligned nanofibrous scaffolds, in particular 5.5 bilayers or above, was more beneficial to Schwann cells (SCs) proliferation and PC12 cells differentiation as well as the SC cytoskeleton and neurite growth along the direction of nanofibrous alignment compared to the aligned PLLA nanofibrous scaffolds. This novel scaffolds combining sustained release of bioactive NGF and aligned nanofibrous topography presented an excellent potential in peripheral nerve regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1900-1910, 2017.

Bioengineered 3D Glial Cell Culture Systems and Applications for Neurodegeneration and Neuroinflammation

Neurodegeneration and neuroinflammation are key features in a range of chronic central nervous system (CNS) diseases such as Alzheimer's and Parkinson's disease, as well as acute conditions like stroke and traumatic brain injury, for which there remains significant unmet clinical need. It is now well recognized that current cell culture methodologies are limited in their ability to recapitulate the cellular environment that is present in vivo, and there is a growing body of evidence to show that three-dimensional (3D) culture systems represent a more physiologically accurate model than traditional two-dimensional (2D) cultures. Given the complexity of the environment from which cells originate, and their various cell-cell and cell-matrix interactions, it is important to develop models that can be controlled and reproducible for drug discovery. 3D cell models have now been developed for almost all CNS cell types, including neurons, astrocytes, microglia, and oligodendrocyte cells. This review will highlight a number of current and emerging techniques for the culture of astrocytes and microglia, glial cell types with a critical role in neurodegenerative and neuroinflammatory conditions. We describe recent advances in glial cell culture using electrospun polymers and hydrogel macromolecules, and highlight how these novel culture environments influence astrocyte and microglial phenotypes in vitro, as compared to traditional 2D systems. These models will be explored to illuminate current trends in the techniques used to create 3D environments for application in research and drug discovery focused on astrocytes and microglial cells.

Poly(l-lactide) melt spun fiber-aligned scaffolds coated with collagen or chitosan for guiding the directional migration of osteoblasts in vitro

PLLA melt spun fiber-aligned scaffolds coated with collagen or chitosan enhance the viability, spreading, alignment and mobility of osteoblasts.

Electrospun Fibers for Drug Delivery after Spinal Cord Injury and the Effects of Drug Incorporation on Fiber Properties

There is currently no cure for individuals with spinal cord injury (SCI). While many promising approaches are being tested in clinical trials, the complexity of SCI limits several of these approaches from aiding complete functional recovery. Several different categories of biomaterials are investigated for their ability to guide axonal regeneration, to deliver proteins or small molecules locally, or to improve the viability of transplanted stem cells. The purpose of this study is to provide a brief overview of SCI, present the different categories of biomaterial scaffolds that direct and guide axonal regeneration, and then focus specifically on electrospun fiber guidance scaffolds. Much like other polymer guidance approaches, electrospun fibers can retain and deliver therapeutic drugs. The experimental section presents new data showing the incorporation of two therapeutic drugs into electrospun poly-L-lactic acid fibers. Two different concentrations of either riluzole or neurotrophin-3 were loaded into the electrospun fibers to examine the effect of drug concentration on the physical characteristics of the fibers (fiber alignment and fiber diameter). Overall, the drugs were successfully incorporated into the fibers and the release was related to the loading concentration. The fiber diameter decreased with the inclusion of the drug, and the decreased diameter was correlated with a decrease in fiber alignment. Subsequently, the study includes considerations for successful incorporation of a therapeutic drug without changing the physical properties of the fibers.

Tissue Engineering Approaches to Modulate the Inflammatory Milieu following Spinal Cord Injury

Tissue engineering strategies have shown promise in promoting healing and regeneration after spinal cord injury (SCI); however, these strategies are limited by inflammation and the immune response. Infiltration of cells of the innate and adaptive immune responses and the inflammation that follows cause secondary damage adjacent to the injury, increased scarring, and a potently inhibitory environment for the regeneration of damaged neurons. While the inflammation that ensues is typically associated with limited regeneration, the immune response is a crucial element in the closing of the blood-brain barrier, minimizing the spread of injury, and initiating healing. This review summarizes the strategies that have been developed to modulate the immune response towards an anti-inflammatory environment that is permissive to the regeneration of neurons, glia, and parenchyma. We focus on the use of biomaterials, biologically active molecules, gene therapy, nanoparticles, and stem cells to modulate the immune response, and illustrate concepts for future therapies. Current clinical treatments for SCI are limited to systemic hypothermia or methylprednisolone, which both act by systemically mitigating the effects of immune response but have marginal efficacy. Herein, we discuss emerging research strategies to further enhance these clinical treatments by directly targeting specific aspects of the immune response.

Aligned PLLA nanofibrous scaffolds coated with graphene oxide for promoting neural cell growth

The graphene oxide (GO) has attracted tremendous attention in biomedical fields. In order to combine the unique physicochemical properties of GO nanosheets with topological structure of aligned nanofibrous scaffolds for nerve regeneration, the GO nanosheets were coated onto aligned and aminolyzed poly-l-lactide (PLLA) nanofibrous scaffolds. Scanning electronic microscopy (SEM) and atomic force microscopy (AFM) revealed that the surface of aligned PLLA nanofibers after being coated with GO became rougher than those of the aligned PLLA and aminolyzed PLLA nanofibrous scaffolds. The GO nanosheets did not destroy the alignment of nanofibers. The characterizations of X-ray photoelectron spectroscopy (XPS) and water contact angle displayed that the aligned PLLA nanofibrous scaffolds were introduced with hydrophilic groups such as NH2, COOH, and OH after aminolysis and GO nanosheets coating, showing better hydrophilicity. The GO-coated and aligned PLLA nanofibrous scaffolds significantly promoted Schwann cells (SCs) proliferation with directed cytoskeleton along the nanofibers compared with the aligned PLLA and aminolyzed PLLA nanofibrous scaffolds. These scaffolds also greatly improved the proliferation of rat pheochromocytoma 12 (PC12) cells, and significantly promoted their differentiation and neurite growth along the nanofibrous alignment in the presence of nerve growth factor (NGF). This type of scaffolds with nanofibrous surface topography and GO nanosheets is expected to show better performance in nerve regeneration.

STATEMENT OF SIGNIFICANCE

Recovery of damaged nerve functions remains a principal clinical challenge in spite of surgical intervention and entubulation. The use of aligned fibrous scaffolds provides suitable microenvironment for nerve cell attachment, proliferation and migration, enhancing the regeneration outcome of nerve tissue. Surface modification is generally required for the synthetic polymeric fibers by laminin, fibronectin and YIGSR peptides to stimulate specific cell functions and neurite outgrowth. Yet these proteins or peptides present the poor processibility, limited availability, and high cost, influencing their application in clinic. In this work, we combined GO nanosheets and topological structure of aligned nanofibrous scaffolds to direct cell migration, proliferation, and differentiation, and to induce neurite outgrowth for nerve regeneration. The GO coating improved several biomedical properties of the aligned PLLA nanofibrous scaffolds including surface roughness, hydrophilicity and promotion of cells/material interactions, which significantly promoted SCs growth and regulated cell orientation, and induced PC12 cells differentiation and neurite growth. The design of this type of structure is of both scientific and technical importance, and possesses broad interest in the fields of biomaterials, tissue engineering and regenerative medicine.

Glial progenitor cell migration promotes CNS axon growth on functionalized electroconducting microfibers

Electroactive systems that promote directional axonal growth and migration of glial progenitor cells (GPC) are needed for the treatment of neurological injuries. We report the functionalization of electroconducting microfibers with multiple biomolecules that synergistically stimulate the proliferation and migration of GPC, which in turn induce axonal elongation from embryonic cerebral cortex neurons. PEDOT doped with poly[(4-styrenesulfonic acid)-co-(maleic acid)] was synthesized on carbon microfibers and used for covalent attachment of molecules to the electroactive surface. The molecular complexes that promoted GPC proliferation and migration, followed by axonal extension, were composed of polylysine, heparin, basic fibroblast growth factor (bFGF), and matricellular proteins; the combination of bFGF with vitronectin or fibronectin being indispensable for sustained glial and axonal growth. The rate of glial-induced axonal elongation was about threefold that of axons growing directly on microfibers functionalized with polylysine alone. Electrical stimuli applied through the microfibers released bFGF and fibronectin from the polymer surface, consequently reducing GPC proliferation and promoting their differentiation into astrocytes, without causing cell detachment or toxicity. These results suggest that functionalized electroactive microfibers may provide a multifunctional tool for controlling neuron-glia interactions and enhancing neural repair.

STATEMENT OF SIGNIFICANCE

We report a multiple surface functionalization strategy for electroconducting microfibers (MFs), in order to promote proliferation and guided migration of glial precursor cells (GPC) and consequently create a permissive substrate for elongation of central nervous system (CNS) axons. GPC divided and migrated extensively on the functionalized MFs, leading to fast elongation of embryonic cerebral cortex axons. The application of electric pulses thorough the MFs controlled glial cell division and differentiation. The functionalized MFs provide an advanced tool for neural tissue engineering and for controlling neuron-glial interactions. CNS axonal growth associated to migratory glial precursors, together with the possibility of directing glial differentiation by electrical stimuli applied through the MFs, open a new research avenue to explore for CNS repair.

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.