Neurotrophin-3-Loaded Multichannel Nanofibrous Scaffolds Promoted Anti-Inflammation, Neuronal Differentiation, and Functional Recovery after Spinal Cord Injury

Nature's Secret Neuro-Regeneration Pathway in Axolotls, Polychaetes and Planarians for Human Therapeutic Target Pathways

Despite significant improvements in the comprehension of neuro-regeneration, restoring nerve injury in humans continues to pose a substantial therapeutic difficulty. In the peripheral nervous system (PNS), the nerve regeneration process after injury relies on Schwann cells. These cells play a crucial role in regulating and releasing different extracellular matrix proteins, including laminin and fibronectin, which are essential for facilitating nerve regeneration. However, during regeneration, the nerve is required to regenerate for a long distance and, subsequently, loses its capacity to facilitate regeneration during this progression. Meanwhile, it has been noted that nerve regeneration has limited capabilities in the central nervous system (CNS) compared to in the PNS. The CNS contains factors that impede the regeneration of axons following injury to the axons. The presence of glial scar formation results from this unfavourable condition, where glial cells accumulate at the injury site, generating a physical and chemical barrier that hinders the regeneration of neurons. In contrast to humans, several species, such as axolotls, polychaetes, and planarians, possess the ability to regenerate their neural systems following amputation. This ability is based on the vast amount of pluripotent stem cells that have the remarkable capacity to differentiate and develop into any cell within their body. Although humans also possess these cells, their numbers are extremely limited. Examining the molecular pathways exhibited by these organisms has the potential to offer a foundational understanding of the human regeneration process. This review provides a concise overview of the molecular pathways involved in axolotl, polychaete, and planarian neuro-regeneration. It has the potential to offer a new perspective on therapeutic approaches for neuro-regeneration in humans.

Amniotic Membrane-Derived Multichannel Hydrogels for Neural Tissue Repair

In the pursuit of advancing neural tissue regeneration, biomaterial scaffolds have emerged as promising candidates, offering potential solutions for nerve disruptions. Among these scaffolds, multichannel hydrogels, characterized by meticulously designed micrometer-scale channels, stand out as instrumental tools for guiding axonal growth and facilitating cellular interactions. This study explores the innovative application of human amniotic membranes modified with methacryloyl domains (AMMA) in neural stem cell (NSC) culture. AMMA hydrogels, possessing a tailored softness resembling the physiological environment, are prepared in the format of multichannel scaffolds to simulate native-like microarchitecture of nerve tracts. Preliminary experiments on AMMA hydrogel films showcase their potential for neural applications, demonstrating robust adhesion, proliferation, and differentiation of NSCs without the need for additional coatings. Transitioning into the 3D realm, the multichannel architecture fosters intricate neuronal networks guiding neurite extension longitudinally. Furthermore, the presence of synaptic vesicles within the cellular arrays suggests the establishment of functional synaptic connections, underscoring the physiological relevance of the developed neuronal networks. This work contributes to the ongoing efforts to find ethical, clinically translatable, and functionally relevant approaches for regenerative neuroscience.

Innovative Strategies in 3D Bioprinting for Spinal Cord Injury Repair

Spinal cord injury (SCI) is a catastrophic condition that disrupts neurons within the spinal cord, leading to severe motor and sensory deficits. While current treatments can alleviate pain, they do not promote neural regeneration or functional recovery. Three-dimensional (3D) bioprinting offers promising solutions for SCI repair by enabling the creation of complex neural tissue constructs. This review provides a comprehensive overview of 3D bioprinting techniques, bioinks, and stem cell applications in SCI repair. Additionally, it highlights recent advancements in 3D bioprinted scaffolds, including the integration of conductive materials, the incorporation of bioactive molecules like neurotrophic factors, drugs, and exosomes, and the design of innovative structures such as multi-channel and axial scaffolds. These innovative strategies in 3D bioprinting can offer a comprehensive approach to optimizing the spinal cord microenvironment, advancing SCI repair. This review highlights a comprehensive understanding of the current state of 3D bioprinting in SCI repair, offering insights into future directions in the field of regenerative medicine.

Advancements in neuroregenerative and neuroprotective therapies for traumatic spinal cord injury

Traumatic spinal cord injuries (SCIs) continue to be a major healthcare concern, with a rising prevalence worldwide. In response to this growing medical challenge, considerable scientific attention has been devoted to developing neuroprotective and neuroregenerative strategies aimed at improving the prognosis and quality of life for individuals with SCIs. This comprehensive review aims to provide an up-to-date and thorough overview of the latest neuroregenerative and neuroprotective therapies currently under investigation. These strategies encompass a multifaceted approach that include neuropharmacological interventions, cell-based therapies, and other promising strategies such as biomaterial scaffolds and neuro-modulation therapies. In addition, the review discusses the importance of acute clinical management, including the role of hemodynamic management as well as timing and technical aspects of surgery as key factors mitigating the secondary injury following SCI. In conclusion, this review underscores the ongoing scientific efforts to enhance patient outcomes and quality of life, focusing on upcoming strategies for the management of traumatic SCI. Each section provides a working knowledge of the fundamental preclinical and patient trials relevant to clinicians while underscoring the pathophysiologic rationale for the therapies.

Biomaterials targeting the microenvironment for spinal cord injury repair: progression and perspectives

Spinal cord injury (SCI) disrupts nerve pathways and affects sensory, motor, and autonomic function. There is currently no effective treatment for SCI. SCI occurs within three temporal periods: acute, subacute, and chronic. In each period there are different alterations in the cells, inflammatory factors, and signaling pathways within the spinal cord. Many biomaterials have been investigated in the treatment of SCI, including hydrogels and fiber scaffolds, and some progress has been made in the treatment of SCI using multiple materials. However, there are limitations when using individual biomaterials in SCI treatment, and these limitations can be significantly improved by combining treatments with stem cells. In order to better understand SCI and to investigate new strategies for its treatment, several combination therapies that include materials combined with cells, drugs, cytokines, etc. are summarized in the current review.

3D hydrogel microfibers promote the differentiation of encapsulated neural stem cells and facilitate neuron protection and axon regrowth after complete transactional spinal cord injury

Spinal cord injury (SCI) can cause permanent impairment to motor or sensory functions. Pre-cultured neural stem cell (NSC) hydrogel scaffolds have emerged as a promising approach to treat SCI by promoting anti-inflammatory effects, axon regrowth, and motor function restoration. Here, in this study, we performed a coaxial extrusion process to fabricate a core-shell hydrogel microfiber with high NSC density in the core portion. Oxidized hyaluronic acid, carboxymethyl chitosan, and matrigel blend were used as a matrix for NSC growth and to facilitate the fabrication process. During thein vitrodifferentiation culture, it was found that NSC microfibers could differentiate into neurons and astrocytes with higher efficiency compared to NSC cultured in petri dishes. Furthermore, duringin vivotransplantation, NSC microfibers were coated with polylactic acid nanosheets by electrospinning for reinforcement. The coated NSC nanofibers exhibited higher anti-inflammatory effect and lesion cavity filling rate compared with the control group. Meanwhile, more neuron- and oligodendrocyte-like cells were visualized at the lesion epicenter. Finally, axon regrowth across the whole lesion site was observed, demonstrating that the microfiber could guide renascent axon regrowth. Experiment results indicate that the NSC microfiber is a promising bioactive treatment for complete SCI treatment with superior outcomes.

Nanotherapeutics for Alleviating Anesthesia-Associated Complications

Current management of anesthesia-associated complications falls short in terms of both efficacy and safety. Nanomaterials with versatile properties and unique nano-bio interactions hold substantial promise as therapeutics for addressing these complications. This review conducts a thorough examination of the existing nanotherapeutics and highlights the strategies for developing prospective nanomedicines to mitigate anesthetics-related toxicity. Initially, general, regional, and local anesthesia along with the commonly used anesthetics and related prevalent side effects are introduced. Furthermore, employing nanotechnology to prevent and alleviate the complications of anesthetics is systematically demonstrated from three aspects, that is, developing 1) safe nano-formulization for anesthetics; 2) nano-antidotes to sequester overdosed anesthetics and alter their pharmacokinetics; 3) nanomedicines with pharmacodynamic activities to treat anesthetics toxicity. Finally, the prospects and challenges facing the clinical translation of nanotherapeutics for anesthesia-related complications are discussed. This work provides a comprehensive roadmap for developing effective nanotherapeutics to prevent and mitigate anesthesia-associated toxicity, which can potentially revolutionize the management of anesthesia complications.

Stem cells in central nervous system diseases: Promising therapeutic strategies

Central nervous system (CNS) diseases are a leading cause of death and disability. Due to CNS neurons have no self-renewal and regenerative ability as they mature, their loss after injury or disease is irreversible and often leads to functional impairments. Unfortunately, therapeutic options for CNS diseases are still limited, and effective treatments for these notorious diseases are warranted to be explored. At present, stem cell therapy has emerged as a potential therapeutic strategy for improving the prognosis of CNS diseases. Accumulating preclinical and clinical evidences have demonstrated that multiple molecular mechanisms, such as cell replacement, immunoregulation and neurotrophic effect, underlie the use of stem cell therapy for CNS diseases. However, several issues have yet to be addressed to support its clinical application. Thus, this review article aims to summarize the role and underlying mechanisms of stem cell therapy in treating CNS diseases. And it is worthy of further evaluation for the potential therapeutic applications of stem cell treatment in CNS disease.

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.

Enhanced Neuron Growth and Electrical Activity by a Supramolecular Netrin-1 Mimetic Nanofiber

Neurotrophic factors are essential not only for guiding the organization of the developing nervous system but also for supporting the survival and growth of neurons after traumatic injury. In the central nervous system (CNS), inhibitory factors and the formation of a glial scar after injury hinder the functional recovery of neurons, requiring exogenous therapies to promote regeneration. Netrin-1, a neurotrophic factor, can initiate axon guidance, outgrowth, and branching, as well as synaptogenesis, through activation of deleted in colorectal cancer (DCC) receptors. We report here the development of a nanofiber-shaped supramolecular mimetic of netrin-1 with monomers that incorporate a cyclic peptide sequence as the bioactive component. The mimetic structure was found to activate the DCC receptor in primary cortical neurons using low molar ratios of the bioactive comonomer. The supramolecular nanofibers enhanced neurite outgrowth and upregulated maturation as well as pre- and postsynaptic markers over time, resulting in differences in electrical activity similar to neurons treated with the recombinant netrin-1 protein. The results suggest the possibility of using the supramolecular structure as a therapeutic to promote regenerative bioactivity in CNS injuries.

Nanomedicine innovations in spinal cord injury management: Bridging the gap

Spinal cord injury (SCI) has devastating effects on a person's physical, social, and professional well-being. It is a life-altering neurological condition that significantly impacts individuals and their caregivers on a socioeconomic level. Recent advancements in medical therapy have greatly improved the diagnosis, stability, survival rates, and overall well-being of SCI patients. However, there are still limited options available for enhancing neurological outcomes in these patients. The complex pathophysiology of SCI, along with the numerous biochemical and physiological changes that occur in the damaged spinal cord, contribute to this gradual improvement. Currently, there are no therapies that offer the possibility of recovery for SCI, although several therapeutic approaches are being developed. However, these therapies are still in the early stages and have not yet demonstrated effectiveness in repairing the damaged fibers, which hinders cellular regeneration and the full restoration of motor and sensory functions. Considering the importance of nanotechnology and tissue engineering in treating neural tissue injuries, this review focuses on the latest advancements in nanotechnology for SCI therapy and tissue healing. It examines research articles from the PubMed database that specifically address SCI in the field of tissue engineering, with an emphasis on nanotechnology as a therapeutic approach. The review evaluates the biomaterials used for treating this condition and the techniques employed to create nanostructured biomaterials.

Antidiabetic Effect of a New Original NT-3 Dipeptide Mimetic

It was previously established that the original dipeptide mimetic of the 4th loop of NT-3, hexamethylenediamide bis-(N-monosuccinyl-L-asparaginyl-L-asparagine) (GTS-301), has a pronounced neuroprotective effect in vitro at concentrations of 10-5-10-12 М. In the present study, experiments on the streptozotocin-induced diabetes model in C57Bl/6 mice showed that GTS-301, when administered intraperitoneally for 32 days at doses of 0.1 and 0.5 mg/kg, has antidiabetic activity manifested in a reduction of hyperglycemia and polydipsia and in an increase in animal survival. The results obtained confirm the concept of the similarity of neurochemical mechanisms underlying the regulation of functions of neurons and β-cells.

Hydrogel-based treatments for spinal cord injuries

Spinal cord injury (SCI) is characterized by damage resulting in dysfunction of the spinal cord. Hydrogels are common biomaterials that play an important role in the treatment of SCI. Hydrogels are biocompatible, and some have electrical conductivity that are compatible with spinal cord tissues. Hydrogels have a high drug-carrying capacity, allowing them to be used for SCI treatment through the loading of various types of active substances, drugs, or cells. We first discuss the basic anatomy and physiology of the human spinal cord and briefly discuss SCI and its treatment. Then, we describe different treatment strategies for SCI. We further discuss the crosslinking methods and classification of hydrogels and detail hydrogel biomaterials prepared using different processing methods for the treatment of SCI. Finally, we analyze the future applications and limitations of hydrogels for SCI. The development of biomaterials opens up new possibilities and options for the treatment of SCI. Thus, our findings will inspire scholars in related fields and promote the development of hydrogel therapy for SCI.

Spinal cord injury: molecular mechanisms and therapeutic interventions

Spinal cord injury (SCI) remains a severe condition with an extremely high disability rate. The challenges of SCI repair include its complex pathological mechanisms and the difficulties of neural regeneration in the central nervous system. In the past few decades, researchers have attempted to completely elucidate the pathological mechanism of SCI and identify effective strategies to promote axon regeneration and neural circuit remodeling, but the results have not been ideal. Recently, new pathological mechanisms of SCI, especially the interactions between immune and neural cell responses, have been revealed by single-cell sequencing and spatial transcriptome analysis. With the development of bioactive materials and stem cells, more attention has been focused on forming intermediate neural networks to promote neural regeneration and neural circuit reconstruction than on promoting axonal regeneration in the corticospinal tract. Furthermore, technologies to control physical parameters such as electricity, magnetism and ultrasound have been constantly innovated and applied in neural cell fate regulation. Among these advanced novel strategies and technologies, stem cell therapy, biomaterial transplantation, and electromagnetic stimulation have entered into the stage of clinical trials, and some of them have already been applied in clinical treatment. In this review, we outline the overall epidemiology and pathophysiology of SCI, expound on the latest research progress related to neural regeneration and circuit reconstruction in detail, and propose future directions for SCI repair and clinical applications.

A hyaluronic acid/silk fibroin/poly-dopamine-coated biomimetic hydrogel scaffold with incorporated neurotrophin-3 for spinal cord injury repair

Bio-factor stimulation is essential for axonal regeneration in the central nervous system. Thus, persistent and efficient factor delivery in the local microenvironment is an ideal strategy for spinal cord injury repair. We developed a biomimetic hydrogel scaffold to load biofactors in situ and release them in a controlled way as a promising therapeutic modality. Hyaluronic acid and silk fibroin were cross-linked as the basement of the scaffolds, and poly-dopamine coating was used to further increase the loading of factors and endow the hydrogel scaffolds with ideal physical and chemical properties and proper biocompatibility. Notably, neurotrophin-3 release from the hydrogel scaffolds was prolonged to 28 days. A spinal cord injury model was constructed for hydrogel scaffold transplantation. After eight weeks, significant NF200-positive nerve fibers were observed extending across the glial scar to the center of the injured area. Due to the release of neurotrophin-3, spinal cord regeneration was enhanced, and the cavity area of the injury graft site and inflammation associated with CD68 positive cells were reduced, which led to a significant improvement in hind limb motor function. The results show that the hyaluronic acid/silk fibroin/poly-dopamine-coated biomimetic hydrogel scaffold achieved locally slow release of neurotrophin-3, thus facilitating the regeneration of injured spinal cord. STATEMENT OF SIGNIFICANCE: Hydrogels have received great attention in spinal cord regeneration. Current research has focused on more efficient and controlled release of bio-factors. Here, we adopted a mussel-inspired strategy to functionalize the hyaluronic acid/silk fibroin hydrogel scaffold to increase the load of neurotrophin-3 and extend the release time. The hydrogel scaffolds have ideal physiochemical properties, proper release rate, and biocompatibility. Owing to the continuous neurotrophin-3 release from implanted scaffolds, cavity formation is reduced, inflammation alleviated, and spinal cord regeneration enhanced, indicating great potential for bio-factor delivery in soft tissue regeneration applications.

Anisotropic 3D scaffolds for spinal cord guided repair: Current concepts

A spinal cord injury (SCI) can be caused by unforeseen events such as a fall, a vehicle accident, a gunshot, or a malignant illness, which has a significant impact on the quality of life of the patient. Due to the limited regenerative potential of the central nervous system (CNS), SCI is one of the most daunting medical challenges of modern medicine. Great advances have been made in tissue engineering and regenerative medicine, which include the transition from two-dimensional (2D) to three-dimensional (3D) biomaterials. Combinatory treatments that use 3D scaffolds may significantly enhance the repair and regeneration of functional neural tissue. In an effort to mimic the chemical and physical properties of neural tissue, scientists are researching the development of the ideal scaffold made of synthetic and/or natural polymers. Moreover, in order to restore the architecture and function of neural networks, 3D scaffolds with anisotropic properties that replicate the native longitudinal orientation of spinal cord nerve fibres are being designed. In an effort to determine if scaffold anisotropy is a crucial property for neural tissue regeneration, this review focuses on the most current technological developments relevant to anisotropic scaffolds for SCI. Special consideration is given to the architectural characteristics of scaffolds containing axially oriented fibres, channels, and pores. By analysing neural cell behaviour in vitro and tissue integration and functional recovery in animal models of SCI, the therapeutic efficacy is evaluated for its successes and limitations.

Neurotrophic Factors as Regenerative Therapy for Neurodegenerative Diseases: Current Status, Challenges and Future Perspectives

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS), spinal cord injury (SCI), and amyotrophic lateral sclerosis (ALS), are characterized by acute or chronic progressive loss of one or several neuronal subtypes. However, despite their increasing prevalence, little progress has been made in successfully treating these diseases. Research has recently focused on neurotrophic factors (NTFs) as potential regenerative therapy for neurodegenerative diseases. Here, we discuss the current state of knowledge, challenges, and future perspectives of NTFs with a direct regenerative effect in chronic inflammatory and degenerative disorders. Various systems for delivery of NTFs, such as stem and immune cells, viral vectors, and biomaterials, have been applied to deliver exogenous NTFs to the central nervous system, with promising results. The challenges that currently need to be overcome include the amount of NTFs delivered, the invasiveness of the delivery route, the blood-brain barrier permeability, and the occurrence of side effects. Nevertheless, it is important to continue research and develop standards for clinical applications. In addition to the use of single NTFs, the complexity of chronic inflammatory and degenerative diseases may require combination therapies targeting multiple pathways or other possibilities using smaller molecules, such as NTF mimetics, for effective treatment.

Glycoprotein non-metastatic melanoma B interacts with epidermal growth factor receptor to regulate neural stem cell survival and differentiation

The functional recovery following spinal cord injury (SCI) remains a challenge clinically. Among the proteins interacted with the glycoprotein non-metastatic melanoma B (GPNMB), epidermal growth factor receptor (EGFR) during activation is able to promote the proliferation of neural stem cells (NSCs) in the spinal cord. We investigated the roles of GPNMB and EGFR in regulating the survival and differentiation of the NSCs. By overexpression and short-hairpin RNA-mediated knockdown of GPNMB in the NSCs, GPNMB promoted cell viability and differentiation by increasing the expressions of βIII tubulin and CNPase (2',3'-cyclic nucleotide 3-phosphodiesterase). Using co-immunoprecipitation, we found that EGFR interacted with GPNMB. Furthermore, EGFR had a similar effect as GPNMB on promoting cell viability and differentiation. Overexpression of EGFR reversed the decrease in viability and differentiation caused by the knockdown of GPNMB, and vice versa. Last but not least, we tested the effect of GPNMB and EGFR on several intracellular pathways and found that GPNMB/EGFR modulated the phosphorylated (p)-c-Jun N-terminal kinase (JNK)1/2/JNK1/2 ratio and the p-nuclear factor κB (NF-κB p65)/NF-κB p65 ratio. In sum, our findings demonstrate the interaction between GPNMB and EGFR that regulates cell bioprocesses, with the hope to provide a new strategy of SCI therapy.

Current Concepts of Biomaterial Scaffolds and Regenerative Therapy for Spinal Cord Injury

Spinal cord injury (SCI) is a catastrophic condition associated with significant neurological deficit and social and financial burdens. It is currently being managed symptomatically, with no real therapeutic strategies available. In recent years, a number of innovative regenerative strategies have emerged and have been continuously investigated in preclinical research and clinical trials. In the near future, several more are expected to come down the translational pipeline. Among ongoing and completed trials are those reporting the use of biomaterial scaffolds. The advancements in biomaterial technology, combined with stem cell therapy or other regenerative therapy, can now accelerate the progress of promising novel therapeutic strategies from bench to bedside. Various types of approaches to regeneration therapy for SCI have been combined with the use of supportive biomaterial scaffolds as a drug and cell delivery system to facilitate favorable cell-material interactions and the supportive effect of neuroprotection. In this review, we summarize some of the most recent insights of preclinical and clinical studies using biomaterial scaffolds in regenerative therapy for SCI and summarized the biomaterial strategies for treatment with simplified results data. One hundred and sixty-eight articles were selected in the present review, in which we focused on biomaterial scaffolds. We conducted our search of articles using PubMed and Medline, a medical database. We used a combination of "Spinal cord injury" and ["Biomaterial", or "Scaffold"] as search terms and searched articles published up until 30 April 2022. Successful future therapies will require these biomaterial scaffolds and other synergistic approaches to address the persistent barriers to regeneration, including glial scarring, the loss of a structural framework, and biocompatibility. This database could serve as a benchmark to progress in future clinical trials for SCI using biomaterial scaffolds.

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.

Combination Therapy Using Nanomaterials and Stem Cells to Treat Spinal Cord Injuries

As a part of the central nervous system, the spinal cord (SC) provides most of the communications between the brain and other parts of the body. Any damage to SC interrupts this communication, leading to serious problems, which may remain for the rest of their life. Due to its significant impact on patients' quality of life and its exorbitant medical costs, SC injury (SCI) is known as one of the most challengeable diseases in the world. Thus, it is critical to introduce highly translatable therapeutic platforms for SCI treatment. So far, different strategies have been introduced, among which utilizing various types of stem cells is one of the most interesting ones. The capability of stem cells to differentiate into several types of cell lines makes them promising candidates for the regeneration of injured tissues. One of the other interesting and novel strategies for SCI treatment is the application of nanomaterials, which could appear as a carrier for therapeutic agents or as a platform for culturing the cells. Combining these two approaches, stem cells and nanomaterials, could provide promising therapeutic strategies for SCI management. Accordingly, in this review we have summarized some of the recent advancements in which the applications of different types of stem cells and nanomaterials, alone and in combination forms, were evaluated for SCI treatment.

Bone Marrow Mesenchymal Stem Cells (BMSCs) Expressing Netrin-1 Alleviates Spinal Cord Injury (SCI)-Induced Inflammation

Spinal cord injury (SCI) is a common central nervous system (CNS) injury. Bone marrow mesenchymal stem cells (BMSCs) transplantation is a potential treatment for traumatic SCI. However, the role and mechanism of BMSCs with high expression of Netrin-1 on the repair and inflammation of spinal cord injury cells remains unclear. Our study intends to assess the effect of BMSCs with high Netrin-1 level on the repair of SCI cells. BMSCs or Netrin-1 transfected BMSCs were co-cultured with mechanically injured nerve cells followed by analysis of the differentiation of BMSCs by light microscope, apoptosis activity, expression of TLR-4 and NF-κB, and the TNF-α and IL-1β content in cell supernatant by ELISA. BMSCs with high Netrin-1 expression promoted the proliferation of BMSCs, inhibited apoptosis, and promoted the differentiation of nerve cells along with increased ALK activity, and the expression of GFAP and BDNF. Co-culture with BMSCs or BMSCs with high Netrin-1 expression increased mechanically damaged nerve cell proliferation, decreased apoptosis, downregulated TLR-4 and NF-κB (P < 0.05) with more significant changes after co-culture with BMSCs with high Netrin-1 expression. In conclusion, Netrin-1 can promote BMSCs proliferation and differentiation, and inhibit apoptosis. By inhibiting inflammation, it can promote damaged nerve cell proliferation and repair.

Hydrogels in Spinal Cord Injury Repair: A Review

Traffic accidents and falling objects are responsible for most spinal cord injuries (SCIs). SCI is characterized by high disability and tends to occur among the young, seriously affecting patients' lives and quality of life. The key aims of repairing SCI include preventing secondary nerve injury, inhibiting glial scarring and inflammatory response, and promoting nerve regeneration. Hydrogels have good biocompatibility and degradability, low immunogenicity, and easy-to-adjust mechanical properties. While providing structural scaffolds for tissues, hydrogels can also be used as slow-release carriers in neural tissue engineering to promote cell proliferation, migration, and differentiation, as well as accelerate the repair of damaged tissue. This review discusses the characteristics of hydrogels and their advantages as delivery vehicles, as well as expounds on the progress made in hydrogel therapy (alone or combined with cells and molecules) to repair SCI. In addition, we discuss the prospects of hydrogels in clinical research and provide new ideas for the treatment of SCI.

Towards 3D Bioprinted Spinal Cord Organoids

Three-dimensional (3D) cultures, so-called organoids, have emerged as an attractive tool for disease modeling and therapeutic innovations. Here, we aim to determine if boundary cap neural crest stem cells (BC) can survive and differentiate in gelatin-based 3D bioprinted bioink scaffolds in order to establish an enabling technology for the fabrication of spinal cord organoids on a chip. BC previously demonstrated the ability to support survival and differentiation of co-implanted or co-cultured cells and supported motor neuron survival in excitotoxically challenged spinal cord slice cultures. We tested different combinations of bioink and cross-linked material, analyzed the survival of BC on the surface and inside the scaffolds, and then tested if human iPSC-derived neural cells (motor neuron precursors and astrocytes) can be printed with the same protocol, which was developed for BC. We showed that this protocol is applicable for human cells. Neural differentiation was more prominent in the peripheral compared to central parts of the printed construct, presumably because of easier access to differentiation-promoting factors in the medium. These findings show that the gelatin-based and enzymatically cross-linked hydrogel is a suitable bioink for building a multicellular, bioprinted spinal cord organoid, but that further measures are still required to achieve uniform neural differentiation.

Neurotrophin-3 and neurotrophin-4: The unsung heroes that lies behind the meninges

Neurotrophin is a growth factor that regulates the development and repair of the nervous system. From all factors, two pioneer groups, the nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF), have been widely explored for their role in disease pathogenesis and potential use as therapeutic agents. Nonetheless, neurotrophin-3 (NT3) and neurotrophin-4 (NT4) also have promising potential, albeit less popular than their counterparts. This review focuses on the latter two factors and their roles in the pathogenesis of brain disorders and potential therapies. An extensive literature search of NT3 and NT4 with their receptors, the TrkB and TrkC on the nervous system were extracted and analyzed. We found that NT3 and NT4 are not only involved in the pathogenesis of some neurodegenerative diseases, but also have promising therapeutic potential on injury- and vascular-related nervous system disease, neuropsychiatry, neurodegeneration and peripheral nerve diseases. In conclusion, the role of NT3 and NT4 should be further emphasized, and more studies could be explored on the potential use of these neurotrophins in the human study.

Electrospun Nanofibers for Manipulating the Soft Tissue Regeneration

Soft tissue damage is a common clinical problem that affects the lives of a large number of patients all over the world. It is of great importance to develop functional...

Construction of a niche-specific spinal white matter-like tissue to promote directional axon regeneration and myelination for rat spinal cord injury repair

Directional axon regeneration and remyelination are crucial for repair of spinal cord injury (SCI), but existing treatments do not effectively promote those processes. Here, we propose a strategy for construction of niche-specific spinal white matter-like tissue (WMLT) using decellularized optic nerve (DON) loaded with neurotrophin-3 (NT-3)-overexpressing oligodendrocyte precursor cells. A rat model with a white matter defect in the dorsal spinal cord of the T10 segment was used. The WMLT transplantation group showed significant improvement in coordinated motor functions compared with the control groups. WMLT transplants integrated well with host spinal cord white matter, effectively addressing several barriers to directional axonal regeneration and myelination during SCI repair. In WMLT, laminin was found to promote development of oligodendroglial lineage (OL) cells by binding to laminin receptors. Interestingly, laminin could also guide linear axon regeneration via interactions with specific integrins on the axon surface. The WMLT developed here utilizes the unique microstructure and bioactive matrix of DON to create a niche rich in laminin, NT-3 and OL cells to achieve significant structural repair of SCI. Our protocol can help to promote research on repair of nerve injury and construction of neural tissues and organoids that form specific cell niches.

Anti-Inflammatory Nanotherapeutics by Targeting Matrix Metalloproteinases for Immunotherapy of Spinal Cord Injury

Neuroinflammation is critically involved in the repair of spinal cord injury (SCI), and macrophages associated with inflammation propel the degeneration or recovery in the pathological process. Currently, efforts have been focused on obtaining efficient therapeutic anti-inflammatory drugs to treat SCI. However, these drugs are still unable to penetrate the blood spinal cord barrier and lack the ability to target lesion areas, resulting in unsatisfactory clinical efficacy. Herein, a polymer-based nanodrug delivery system is constructed to enhance the targeting ability. Because of increased expression of matrix metalloproteinases (MMPs) in injured site after SCI, MMP-responsive molecule, activated cell-penetrating peptides (ACPP), is introduced into the biocompatible polymer PLGA-PEI-mPEG (PPP) to endow the nanoparticles with the ability for diseased tissue-targeting. Meanwhile, etanercept (ET), a clinical anti-inflammation treatment medicine, is loaded on the polymer to regulate the polarization of macrophages, and promote locomotor recovery. The results show that PPP-ACPP nanoparticles possess satisfactory lesion targeting effects. Through inhibited consequential production of proinflammation cytokines and promoted anti-inflammation cytokines, ET@PPP-ACPP could decrease the percentage of M1 macrophages and increase M2 macrophages. As expected, ET@PPP-ACPP accumulates in lesion area and achieves effective treatment of SCI; this confirmed the potential of nano-drug loading systems in SCI immunotherapy.

Repair of spinal cord injury in rats via exosomes from bone mesenchymal stem cells requires sonic hedgehog

Objective

The loss of neural ability leading to subsequent diminishing of motor function and the impairment below the location of the injury is a result of the SCI (Spinal Cord Injury). Among the many therapeutic agents for SCI, the exosomes considered as extracellular vesicles seem to be the most promising. Sonic Hedgehog (Shh) is an exosome-carrying protein. This Study's purpose was to identify whether Shh is required for exosomes from BMSCs (mesenchymal stem cells of the bone) and plays a protective effect on SCI.

Methods

Spinal cord injection with shRNA Shh-adeno associated virus (sh-Shh-AAV) were used to silence Shh. Exosomes were extracted from BMSCs. Rats that had suffered SCI were given intravenous injections of exosomes through the veins of the tail. Immunohistochemistry was used to identify the expression of Shh glycoprotein molecule as well as the expression of Gli-1 (glioma-associated oncogene homolog 1) in the rat spinal cord tissues. Western blot was performed to measure the levels of growth associated protein-43 (GAP-43). The BBB (Basso Beattie Bresnahan) score was used to assess the motor functions of the hind legs. In the same manner, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling or TUNEL and Nissl Staining was deployed to assess the level of regeneration of neurons and assess the level of histopathological damage in the tissues of the Spinal Cord.

Results

In the case of the rats with SCI, the levels of display of Gli-1 and Shh showed dramatic improvement after the BMSCs exosome injections. In comparison to rats with SCI, the subjects of BMSCs exosomes group showed an improvement in their SCI, including a higher BBB score and Nissl body count, increasing GAP-43 expression, along with a much-decreased number of cells that suffered apoptosis. While the exosome effect on Spinal Cord Injury was completely ineffective in rats that had Shh silencing.

Conclusions

Exosomes secreted from BMSCs showed great effectiveness in the SCI healing with a vital involvement of Shh in this repair.

An overview of latest advances in exploring bioactive peptide hydrogels for neural tissue engineering

Neural tissue engineering holds great potential in addressing current challenges faced by medical therapies employed for the functional recovery of the brain. In this context, self-assembling peptides have gained considerable interest owing to their diverse physicochemical properties, which enable them to closely mimic the biophysical characteristics of the native ECM. Additionally, in contrast to synthetic polymers, which lack inherent biological signaling, peptide-based nanomaterials could be easily designed to present essential biological cues to the cells to promote cellular adhesion. Moreover, injectability of these biomaterials further widens their scope in biomedicine. In this context, hydrogels obtained from short bioactive peptide sequences are of particular interest owing to their facile synthesis and highly tunable properties. In spite of their well-known advantages, the exploration of short peptides for neural tissue engineering is still in its infancy and thus detailed discussion is required to evoke interest in this direction. This review provides a general overview of various bioactive hydrogels derived from short peptide sequences explored for neural tissue engineering. The review also discusses the current challenges in translating the benefits of these hydrogels to clinical practices and presents future perspectives regarding the utilization of these hydrogels for advanced biomedical applications.