Modified acellular nerve-delivering PMSCs improve functional recovery in rats after complete spinal cord transection

Graphdiyne-loaded polycaprolactone nanofiber scaffold for peripheral nerve regeneration

Graphdiyne (GDY) is a kind of nanomaterial from the graphene carbon family with excellent physical and chemical properties. Despite some applications in medical engineering, GDY has not been used as an electroactive scaffold for tissue regeneration because of its unclear in vitro and in vivo biosafety profiles. Here, a conductive GDY nanomaterial-loaded polycaprolactone (PCL) scaffold was prepared by electrospinning technique. For the first time, the biocompatibility of GDY-based scaffold was assessed at the cellular and animal levels in a peripheral nerve injury (PNI) model. The findings indicated that the conductive three-dimensional (3D) GDY/PCL nerve guide conduits (NGCs) could significantly improve the proliferation, adhesion and glial expression of Schwann cells (SCs). The conduits were implanted into a rat 10-mm sciatic nerve defect model for 3 months in vivo. The toxicity of scaffolds to the organs was negligible, while the GDY/PCL NGCs significantly promoted myelination and axonal growth by upregulating the expression levels of SC marker (S100 β protein), Myelin basic protein (MBP), and axon regeneration marker (β3-tubulin protein (Tuj1) and neurofilament protein 200 (NF200)). In addition, upregulation of vascular factor expression in GDY/PCL NGC group suggested the potential role in angiogenesis to improve nerve repair by GDY nanomaterials. Our findings provide new perspectives on biocompatibility and effectiveness of GDY nanomaterial scaffold in peripheral nerve regeneration for preclinical application.

Pathophysiology of Spinal Cord Injury and Tissue Engineering Approach for Its Neuronal Regeneration: Current Status and Future Prospects

A spinal cord injury (SCI) is a very debilitating condition causing loss of sensory and motor function as well as multiple organ failures. Current therapeutic options like surgery and pharmacotherapy show positive results but are incapable of providing a complete cure for chronic SCI symptoms. Tissue engineering, including neuroprotective or growth factors, stem cells, and biomaterial scaffolds, grabs attention because of their potential for regeneration and ability to bridge the gap in the injured spinal cord (SC). Preclinical studies with tissue engineering showed functional recovery and neurorestorative effects. Few clinical trials show the safety and efficacy of the tissue engineering approach. However, more studies should be carried out for potential treatment modalities. In this review, we summarize the pathophysiology of SCI and its current treatment modalities, including surgical, pharmacological, and tissue engineering approaches following SCI in preclinical and clinical phases.

Stem Cell Strategies in Promoting Neuronal Regeneration after Spinal Cord Injury: A Systematic Review

Spinal cord injury (SCI) is a devastating condition with a significant medical and socioeconomic impact. To date, no effective treatment is available that can enable neuronal regeneration and recovery of function at the damaged level. This is thought to be due to scar formation, axonal degeneration and a strong inflammatory response inducing a loss of neurons followed by a cascade of events that leads to further spinal cord damage. Many experimental studies demonstrate the therapeutic effect of stem cells in SCI due to their ability to differentiate into neuronal cells and release neurotrophic factors. Therefore, it appears to be a valid strategy to use in the field of regenerative medicine. This review aims to provide an up-to-date summary of the current research status, challenges, and future directions for stem cell therapy in SCI models, providing an overview of this constantly evolving and promising field.

Decellularized extracellular matrix scaffolds: Recent trends and emerging strategies in tissue engineering

The application of scaffolding materials is believed to hold enormous potential for tissue regeneration. Despite the widespread application and rapid advance of several tissue-engineered scaffolds such as natural and synthetic polymer-based scaffolds, they have limited repair capacity due to the difficulties in overcoming the immunogenicity, simulating in-vivo microenvironment, and performing mechanical or biochemical properties similar to native organs/tissues. Fortunately, the emergence of decellularized extracellular matrix (dECM) scaffolds provides an attractive way to overcome these hurdles, which mimic an optimal non-immune environment with native three-dimensional structures and various bioactive components. The consequent cell-seeded construct based on dECM scaffolds, especially stem cell-recellularized construct, is considered an ideal choice for regenerating functional organs/tissues. Herein, we review recent developments in dECM scaffolds and put forward perspectives accordingly, with particular focus on the concept and fabrication of decellularized scaffolds, as well as the application of decellularized scaffolds and their combinations with stem cells (recellularized scaffolds) in tissue engineering, including skin, bone, nerve, heart, along with lung, liver and kidney.

Cell-Free Extracts from Human Fat Tissue with a Hyaluronan-Based Hydrogel Attenuate Inflammation in a Spinal Cord Injury Model through M2 Microglia/Microphage Polarization

Treatment for spinal cord injuries (SCIs) is often ineffective because SCIs result in a loss of nerve tissue, glial scar formation, local ischemia and secondary inflammation. The current promising strategy for SCI is the combination of bioactive materials and cytokines. Bioactive materials support the injured spinal cord, stabilize the morphology, and avoid excessive inflammatory responses. Fat extract (FE) is a cell-free liquid component containing a variety of cytokines extracted from human fat tissue using mechanical methods. In this research, a biocompatible HAMC (hyaluronan and methylcellulose) loaded with FE is used to treat a model of spinal cord contusion in mice. The composite not only inhibits death of neuro- and vascular cells and leads to the preservation of neural and vascular structure, but also modulates the inflammatory phenotype of macrophages in the locally injured region. Specifically, FE promotes the polarization of macrophages from an inflammatory M1 phenotype to an anti-inflammatory M2 phenotype. During the screening of the involved pathways, it is corroborated that activation of the STAT6/Arg-1 signaling pathway is involved in macrophage M2 polarization. In summary, FE is a promising treatment for SCI, as it is easy to obtain, nonimmunogenic, and effective.

Decellularized nerve extracellular matrix/chitosan crosslinked by genipin to prepare a moldable nerve repair material

Decellularized nerve extracellular matrix (NECM) composited with chitosan are moldable materials suitable for spinal cord repair. But the rapid biodegradation of the materials may interrupt neural tissue reconstruction in vivo. To improve the stability of the materials, the materials produced by NECM and chitosan hydrogels were crosslinked by genipine, glutaraldehyde or ultraviolet ray. Physicochemical property, degradation and biocompatibility of materials crosslinked by genipin, glutaraldehyde or ultraviolet ray were evaluated. The scaffold crosslinked by genipin possessed a porous structure, and the porosity ratio was 89.07 + 4.90%, the average diameter of pore was 85.32 + 5.34 μm. The crosslinked degree of the scaffold crosslinked by genipin and glutaraldehyde was 75.13 ± 4.87%, 71.25 ± 5.06% respectively; Uncrosslinked scaffold disintegrated when immerged in distilled water while the scaffold crosslinked by genipin and glutaraldehyde group retained their integrity. The scaffold crosslinked by genipin has better water absorption, water retention and anti-enzymatic hydrolysis ability than the other three groups. Cell cytotoxicity showed that the cytotoxicity of scaffold crosslinked by genipin was lower than that crosslinked by glutaraldehyde. The histocompatibility of scaffold crosslinked by genipin was also better than glutaraldehyde group. More cells grew well in the scaffold crosslinked by genipin when co-cultured with L929 cells. The decellularized nerve extracellular matrix/chitosan scaffold crosslinked by the genipin has good mechanical properties, micro structure and biocompatibility, which is an ideal scaffold for the spinal cord tissue engineering.

Regeneration of the peripheral nerve via multifunctional electrospun scaffolds

Over the last two decades, electrospun scaffolds have proved to be advantageous in the field of nerve tissue regeneration by connecting the cavity among the proximal and distal nerve stumps growth cones and leading to functional recovery after injury. Multifunctional nanofibrous structure of these scaffolds provides enormous potential by combining the advantages of nano-scale topography, and biological science. In these structures, selecting the appropriate materials, designing an optimized structure, modifying the surface to enhance biological functions and neurotrophic factors loading, and native cell-like stem cells should be considered as the essential factors. In this systematic review paper, the fabrication methods for the preparation of aligned nanofibrous scaffolds in yarn or conduit architecture are reviewed. Subsequently, the utilized polymeric materials, including natural, synthetic and blend are presented. Finally, their surface modification techniques, as well as, the recent advances and outcomes of the scaffolds, both in vitro and in vivo, are reviewed and discussed.

An injectable recombinant human milk fat globule-epidermal growth factor 8-loaded copolymer system for spinal cord injury reduces inflammation through NF-κB and neuronal cell death

Spinal cord injury (SCI) is a common disease and a major cause of paralysis, carrying much burden around the world. Despite the progress made with growth factors therapy, the response rate of acute SCI treatment still remains unsatisfactory, due largely to complex and severe inflammatory reactions. Herein, we prepare a MFG-E8-loaded copolymer system-based anti-inflammation therapy for SCI treatment. It is shown that the MFG-E8-loaded copolymer system can decrease pro-inflammatory cytokine expression and neuron death. In a rat model of crush-caused SCI, the copolymer system shows significant therapeutic efficacy by ameliorating inflammation, decreasing fibrotic scar, promoting myelin regeneration and suppressing overall SCI severity.

Mesenchymal Stem Cell-Laden Hydrogel Microfibers for Promoting Nerve Fiber Regeneration in Long-Distance Spinal Cord Transection Injury

Mesenchymal stem cell (MSC)-based regenerative medicine is widely considered as a promising approach for repairing tissue and re-establishing function in spinal cord injury (SCI). However, low survival rate, uncontrollable migration, and differentiation of stem cells after implantation represent major challenges toward the clinical deployment of this approach. In this study, we fabricated three-dimensional MSC-laden microfibers via electrospinning in a rotating cell culture to mimic nerve tissue, control stem cell behavior, and promote integration with the host tissue. The hierarchically aligned fibrin hydrogel was used as the MSC carrier though a rotating method and the aligned fiber structure induced the MSC-aligned adhesion on the surface of the hydrogel to form microscale cell fibers. The MSC-laden microfiber implantation enhanced the donor MSC neural differentiation, encouraged the migration of host neurons into the injury gap and significantly promoted nerve fiber regeneration across the injury site. Abundant GAP-43- and NF-positive nerve fibers were observed to regenerate in the caudal, rostral, and middle sites of the injury position 8 weeks after the surgery. The NF fiber density reached to 29 ± 6 per 0.25 mm² at the middle site, 82 ± 13 per 0.25 mm² at the adjacent caudal site, and 70 ± 23 at the adjacent rostral site. Similarly, motor axons labeled with 5-hydroxytryptamine were significantly regenerated in the injury gap, which was 122 ± 22 at the middle injury site that was beneficial for motor function recovery. Most remarkably, the transplantation of MSC-laden microfibers significantly improved electrophysiological expression and re-established limb motor function. These findings highlight the combination of MSCs with microhydrogel fibers, the use of which may become a promising method for MSC implantation and SCI repair.

Asymmetrical 3D Nanoceria Channel for Severe Neurological Defect Regeneration

Inflammation and oxidative stress are major problems in peripheral nerve injury. Nanoceria can manipulate antioxidant factor expression, stimulate angiogenesis, and assist in axonal regeneration. We fabricate collagen/nanoceria/polycaprolactone (COL/NC/PCL) conduit by asymmetrical three-dimensional manufacture and find that this scaffold successfully improves Schwann cell proliferation, adhesion, and neural expression. In a 15-mm rat sciatic nerve defect model, we further confirm that the COL/NC/PCL conduit markedly alleviates inflammation and oxidative stress, improves microvessel growth, and contributes to functional, electrophysiological, and morphological nerve restoration in the long term. Our findings provide compelling evidence for future research in antioxidant nerve conduit for severe neurological defects.

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Collagen/nanoceria/polycaprolactone conduit was prepared by asymmetrical fabrication

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The scaffold induced proliferation, adhesion, and angiogenesis in nerve repair

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The scaffold alleviated oxidative stress and inflammation in the microenvironment

Scaffold-facilitated locomotor improvement post complete spinal cord injury: Motor axon regeneration versus endogenous neuronal relay formation

Complete transected spinal cord injury (SCI) severely influences the quality of life and mortality rates of animals and patients. In the past decade, many simple and combinatorial therapeutic treatments have been tested in improving locomotor function in animals with this extraordinarily challenging SCI. The potential mechanism for promotion of locomotor function relies either on direct motor axon regeneration through the lesion gap or indirect neuronal relay bridging to functionally reconnect transected spinal stumps. In this review, we first compare the advantages and problems of complete transection SCI animal models with other prevailing SCI models used in motor axon regeneration research. Next, we enumerate some of the popular bio-scaffolds utilized in complete SCI repair in the last decade. Then, the current state of motor axon regeneration as well as its role on locomotor improvement of animals after complete SCI is discussed. Last, the current approach of directing endogenous neuronal relays formation to achieve motor function recovery by well-designed functional bio-scaffolds implantation in complete transected SCI animals is reviewed. Although facilitating neuronal relays formation by bio-scaffolds implantation appears to be more practical and feasible than directing motor axon regeneration in promoting locomotor outcome in animals after complete SCI, there are still challenges in neuronal relays formation, maintaining and debugging for spinal cord regenerative repair.

Incorporating placental tissue in cord blood banking for stem cell transplantation

INTRODUCTION

Human term placenta is comprised of various tissues from which different cells can be obtained, including hematopoietic stem cells and mesenchymal stem/stromal cells (MSCs). Areas covered: This review will discuss the possibility to incorporate placental tissue cells in cord blood banking. It will discuss general features of human placenta, with a brief review of the immune cells at the fetal-maternal interface and the different cell populations isolated from placenta, with a particular focus on MSCs. It will address the question as to why placenta-derived MSCs should be banked with their hematopoietic counterparts. It will discuss clinical trials which are studying safety and efficacy of placenta tissue-derived MSCs in selected diseases, and preclinical studies which have proven their therapeutic properties in other diseases. It will discuss banking of umbilical cord blood and raise several issues for improvement, and the applications of cord blood cells in non-malignant disorders. Expert commentary: Umbilical cord blood banking saves lives worldwide. The concomitant banking of non-hematopoietic cells from placenta, which could be applied therapeutically in the future, alone or in combination to their hematopoietic counterparts, could exploit current banking processes while laying the foundation for clinical trials exploring placenta-derived cell therapies in regenerative medicine.

[Review of the regeneration mechanism of complete spinal cord injury]

Spinal cord injury (SCI), especially the complete SCI, usually results in complete paralysis below the level of the injury and seriously affects the patient's quality of life. SCI repair is still a worldwide medical problem. In the last twenty years, Professor DAI Jianwu and his team pioneered complete SCI model by removing spinal tissue with varied lengths in rodents, canine, and non-human primates to verify therapeutic effect of different repair strategies. Moreover, they also started the first clinical study of functional collagen scaffold on patients with acute complete SCI on January 16th, 2015. This review mainly focusses on the possible mechanisms responsible for complete SCI. In common, recovery of some sensory and motor functions post complete SCI include the following three contributing reasons. ① Regeneration of long ascending and descending axons throughout the lesion site to re-connect the original targets; ② New neural circuits formed in the lesion site by newly generated neurons post injury, which effectively re-connect the transected stumps; ③ The combined effect of ① and ②. The numerous studies have confirmed that neural circuits rebuilt across the injury site by newborn neurons might be the main mechanisms for functional recovery of animals from rodents to dogs. In many SCI model, especially the complete spinal cord transection model, many studies have convincingly demonstrated that the quantity and length of regenerated long descending axons, particularly like CST fibers, are too few to across the lesion site that is millimeters in length to realize motor functional recovery. Hence, it is more feasible in guiding neuronal relays formation by bio-scaffolds implantation than directing long motor axons regeneration in improving motor function of animals with complete spinal cord transection. However, some other issues such as promoting more neuronal relays formation, debugging wrong connections, and maintaining adequate neural circuits for functional recovery are urgent problems to be addressed.

Directing Induced Pluripotent Stem Cell Derived Neural Stem Cell Fate with a Three-Dimensional Biomimetic Hydrogel for Spinal Cord Injury Repair

Current treatment approaches for spinal cord injuries (SCIs) are mainly based on cellular transplantation. Induced pluripotent stem cells (iPSCs) without supply constraints and ethical concerns have emerged as a viable treatment option for repairing neurological disorders. However, the primarily limitations in the neuroregeneration field are uncontrolled cell differentiation, and low cell viability caused by the ischemic environment. The mechanical property of three-dimensional (3D) hydrogel can be easily controlled and shared similar characteristics with nerve tissue, thus promoting cell survival and controlled cell differentiation. We propose the combination of a 3D gelatin methacrylate (GelMA) hydrogel with iPSC-derived NSCs (iNSCs) to promote regeneration after SCI. In vitro, the iNSCs photoencapsulated in the 3D GelMA hydrogel survived and differentiated well, especially in lower-moduli hydrogels. More robust neurite outgrowth and more neuronal differentiation were detected in the soft hydrogel group. To further evaluate the in vivo neuronal regeneration effect of the GelMA hydrogels, a mouse spinal cord transection model was generated. We found that GelMA/iNSC implants significantly promoted functional recovery. Further histological analysis showed that the cavity areas were significantly reduced, and less collagen was deposited in the GelMA/iNSC group. Furthermore, the GelMA and iNSC combined transplantation decreased inflammation by reducing activated macrophages/microglia (CD68-positive cells). Additionally, GelMA/iNSC implantation showed striking therapeutic effects of inhibiting GFAP-positive cells and glial scar formation while simultaneously promoting axonal regeneration. Undoubtedly, use of this 3D hydrogel stem cell-loaded system is a promising therapeutic strategy for SCI repair.