Functional Multichannel Poly(Propylene Fumarate)-Collagen Scaffold with Collagen-Binding Neurotrophic Factor 3 Promotes Neural Regeneration After Transected Spinal Cord Injury

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

The clinical therapeutics for nerve tissue regeneration and functional recovery after spinal cord injury (SCI) are very limited because of the complex biological processes and inhibitory microenvironment. Advanced biomaterials are highly desired to avoid severe secondary damage and provide guidance for axonal regrowth. Multichannel nanofibrous scaffolds were modified with gelatin and cross-linked by genipin. The gelatin-coated nanofibers exhibited strong binding affinity with neurotrophin-3, which underwent a well-controlled release and highly promoted neuronal differentiation and synapse formation of the seeded neural stem cells. The nanofibrous scaffolds fabricated by combinatorial biomaterials were implanted into complete transected spinal cords in rats. Not only were the inflammatory responses and collagen/astrocytic scar formation limited, but the functional neurons and remyelination were facilitated postsurgery, leading to highly improved functional restoration. This nanofibrous scaffold with high specific surface area can be easily modified with biomolecules, which was proven to be effective for nerve regeneration after transected SCI, and provided a springboard for advanced scaffold design in clinical applications.

Tailoring synthetic polymeric biomaterials towards nerve tissue engineering: a review

The nervous system is known as a crucial part of the body and derangement in this system can cause potentially lethal consequences or serious side effects. Unfortunately, the nervous system is unable to rehabilitate damaged regions following seriously debilitating disorders such as stroke, spinal cord injury and brain trauma which, in turn, lead to the reduction of quality of life for the patient. Major challenges in restoring the damaged nervous system are low regenerative capacity and the complexity of physiology system. Synthetic polymeric biomaterials with outstanding properties such as excellent biocompatibility and non-immunogenicity find a wide range of applications in biomedical fields especially neural implants and nerve tissue engineering scaffolds. Despite these advancements, tailoring polymeric biomaterials for design of a desired scaffold is fundamental issue that needs tremendous attention to promote the therapeutic benefits and minimize adverse effects. This review aims to (i) describe the nervous system and related injuries. Then, (ii) nerve tissue engineering strategies are discussed and (iii) physiochemical properties of synthetic polymeric biomaterials systematically highlighted. Moreover, tailoring synthetic polymeric biomaterials for nerve tissue engineering is reviewed.

Three-dimensional bioprinting collagen/silk fibroin scaffold combined with neural stem cells promotes nerve regeneration after spinal cord injury

Many studies have shown that bio-scaffolds have important value for promoting axonal regeneration of injured spinal cord. Indeed, cell transplantation and bio-scaffold implantation are considered to be effective methods for neural regeneration. This study was designed to fabricate a type of three-dimensional collagen/silk fibroin scaffold (3D-CF) with cavities that simulate the anatomy of normal spinal cord. This scaffold allows cell growth in vitro and in vivo. To observe the effects of combined transplantation of neural stem cells (NSCs) and 3D-CF on the repair of spinal cord injury. Forty Sprague-Dawley rats were divided into four groups: sham (only laminectomy was performed), spinal cord injury (transection injury of T10 spinal cord without any transplantation), 3D-CF (3D scaffold was transplanted into the local injured cavity), and 3D-CF + NSCs (3D scaffold co-cultured with NSCs was transplanted into the local injured cavity. Neuroelectrophysiology, imaging, hematoxylin-eosin staining, argentaffin staining, immunofluorescence staining, and western blot assay were performed. Apart from the sham group, neurological scores were significantly higher in the 3D-CF + NSCs group compared with other groups. Moreover, latency of the 3D-CF + NSCs group was significantly reduced, while the amplitude was significantly increased in motor evoked potential tests. The results of magnetic resonance imaging and diffusion tensor imaging showed that both spinal cord continuity and the filling of injury cavity were the best in the 3D-CF + NSCs group. Moreover, regenerative axons were abundant and glial scarring was reduced in the 3D-CF + NSCs group compared with other groups. These results confirm that implantation of 3D-CF combined with NSCs can promote the repair of injured spinal cord. This study was approved by the Institutional Animal Care and Use Committee of People's Armed Police Force Medical Center in 2017 (approval No. 2017-0007.2).

LncRNA Neat1 mediates miR-124-induced activation of Wnt/β-catenin signaling in spinal cord neural progenitor cells

BACKGROUND

Emerging evidence suggests that miR-124 performs important biological functions in neural stem cells (NSCs); it regulates NSC behavior and promotes the differentiation of NSCs into neurons, but the exact molecular mechanism remains unknown. And also, the role of miR-124 during spinal cord injury regeneration is unclear.

MATERIALS AND METHODS

In order to explore the function of miR-124 in neural differentiation, the molecular markers (Tuj1, Map2, and GFAP) correlated with the differentiation of NSCs were detected by immunofluorescence staining both in cultured mouse spinal cord progenitor cells (SC-NPCs) and in spinal cord injury (SCI) animal models. The migration ability and apoptosis of cultured SC-NPCs were also evaluated by Transwell migration assay and TUNEL assay. In addition, the relative expression of lnRNA Neat1- and Wnt/β-catenin signaling-related genes were detected by quantitative real-time PCR.

RESULTS

In this study, we revealed that lncRNA Neat1 is involved in regulating Wnt/β-catenin signaling that is activated by miR-124 in SC-NPCs. LncRNA Neat1 was also found to play an important role in regulating neuronal differentiation, apoptosis, and migration of SC-NPCs. Furthermore, we demonstrated that overexpression of miR-124 resulted in elevated Neat1 expression, accompanied with the functional recovery of locomotion in a mouse model of spinal cord injury.

CONCLUSIONS

Our results confirm the therapeutic effectiveness of miR-124 on the functional recovery of injured spinal cord, supporting the rationale and feasibility of miR-124 for spinal cord injury treatment in future clinical therapy. Furthermore, we concluded that the miR-124-Neat1-Wnt/β-catenin signaling axis is involved in regulating the cell function of SC-NPCs, and this may offer novel therapeutic avenues for future treatment of SCI.

Engineered 3D Polymer and Hydrogel Microenvironments for Cell Culture Applications

The realization of biomimetic microenvironments for cell biology applications such as organ-on-chip, in vitro drug screening, and tissue engineering is one of the most fascinating research areas in the field of bioengineering. The continuous evolution of additive manufacturing techniques provides the tools to engineer these architectures at different scales. Moreover, it is now possible to tailor their biomechanical and topological properties while taking inspiration from the characteristics of the extracellular matrix, the three-dimensional scaffold in which cells proliferate, migrate, and differentiate. In such context, there is therefore a continuous quest for synthetic and nature-derived composite materials that must hold biocompatible, biodegradable, bioactive features and also be compatible with the envisioned fabrication strategy. The structure of the current review is intended to provide to both micro-engineers and cell biologists a comparative overview of the characteristics, advantages, and drawbacks of the major 3D printing techniques, the most promising biomaterials candidates, and the trade-offs that must be considered in order to replicate the properties of natural microenvironments.

Modular Strategies to Build Cell-Free and Cell-Laden Scaffolds towards Bioengineered Tissues and Organs

Engineering three-dimensional (3D) scaffolds for functional tissue and organ regeneration is a major challenge of the tissue engineering (TE) community. Great progress has been made in developing scaffolds to support cells in 3D, and to date, several implantable scaffolds are available for treating damaged and dysfunctional tissues, such as bone, osteochondral, cardiac and nerve. However, recapitulating the complex extracellular matrix (ECM) functions of native tissues is far from being achieved in synthetic scaffolds. Modular TE is an intriguing approach that aims to design and fabricate ECM-mimicking scaffolds by the bottom-up assembly of building blocks with specific composition, morphology and structural properties. This review provides an overview of the main strategies to build synthetic TE scaffolds through bioactive modules assembly and classifies them into two distinct schemes based on microparticles (µPs) or patterned layers. The µPs-based processes section starts describing novel techniques for creating polymeric µPs with desired composition, morphology, size and shape. Later, the discussion focuses on µPs-based scaffolds design principles and processes. In particular, starting from random µPs assembly, we will move to advanced µPs structuring processes, focusing our attention on technological and engineering aspects related to cell-free and cell-laden strategies. The second part of this review article illustrates layer-by-layer modular scaffolds fabrication based on discontinuous, where layers' fabrication and assembly are split, and continuous processes.

Application of stem cells and chitosan in the repair of spinal cord injury

Cytology and histology obstacles have been the main barriers to multiple tissues injury repair. In search of the most promising treatment strategies for spinal cord injury (SCI), stem cell-based transplantation coupled with various materials/technologies have been explored extensively to enhance SCI repair. Chitosan (CS) has demonstrated immense potential for widespread application in the form of scaffolds and micro-particles for SCI repair. The current review summarizes the evidences for stem cell-based transplantation and CS in SCI repair. Stem cells transplantation, which plays a key role in the repair of SCI, mainly results from its neural differentiation potential and neurotrophic effects. Application of CS enhances the survival of grafted stem cells, upregulates the expression level of neurotrophic factors and heightens the neural differentiation of stem cells as well as the functional recovery of spinal cord. Meanwhile, CS can also be exploited as growth factors/RNA carriers to control the release of regenerating molecules which are beneficial to damage spinal cord repair.

Poly(propylene fumarate)-based materials: Synthesis, functionalization, properties, device fabrication and biomedical applications

Poly(propylene fumarate) (PPF) is a biodegradable polymer that has been investigated extensively over the last three decades. It has led many scientists to synthesize and fabricate a variety of PPF-based materials for biomedical applications due to its controllable mechanical properties, tunable degradation and biocompatibility. This review provides a comprehensive overview of the progress made in improving PPF synthesis, resin formulation, crosslinking, device fabrication and post polymerization modification. Further, we highlight the influence of these parameters on biodegradation, biocompatibility, and their use in a number of regenerative medicine applications, especially bone tissue engineering. In particular, the use of 3D printing techniques for the fabrication of PPF-based scaffolds is extensively reviewed. The recent invention of a ring-opening polymerization method affords precise control of PPF molecular mass, molecular mass distribution (Ɖ_M) and viscosity. Low Ɖ_M facilitates time-certain resorption of 3D printed structures. Novel post-polymerization and post-printing functionalization methods have accelerated the expansion of biomedical applications that utilize PPF-based materials. Finally, we shed light on evolving uses of PPF-based materials for orthopedics/bone tissue engineering and other biomedical applications, including its use as a hydrogel for bioprinting.

Fibroadhesive scarring of grafted collagen scaffolds interferes with implant-host neural tissue integration and bridging in experimental spinal cord injury

Severe traumatic spinal cord injury (SCI) results in a devastating and permanent loss of function, and is currently an incurable condition. It is generally accepted that future intervention strategies will require combinational approaches, including bioengineered scaffolds, to support axon growth across tissue scarring and cystic cavitation. Previously, we demonstrated that implantation of a microporous type-I collagen scaffold into an experimental model of SCI was capable of supporting functional recovery in the absence of extensive implant–host neural tissue integration. Here, we demonstrate the reactive host cellular responses that may be detrimental to neural tissue integration after implantation of collagen scaffolds into unilateral resection injuries of the adult rat spinal cord. Immunohistochemistry demonstrated scattered fibroblast-like cell infiltration throughout the scaffolds as well as the presence of variable layers of densely packed cells, the fine processes of which extended along the graft–host interface. Few reactive astroglial or regenerating axonal profiles could be seen traversing this layer. Such encapsulation-type behaviour around bioengineered scaffolds impedes the integration of host neural tissues and reduces the intended bridging role of the implant. Characterization of the cellular and molecular mechanisms underpinning this behaviour will be pivotal in the future design of collagen-based bridging scaffolds intended for regenerative medicine.

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.