Central Nervous System Tissue Engineering Research Articles

Exosomes encapsulated in hydrogels for effective central nervous system drug delivery.

The targeted delivery of pharmacologically active molecules, metabolites, and growth factors to the brain parenchyma has become one of the major challenges following the onset of neurodegeneration and pathological conditions. The therapeutic effect of active biomolecules is significantly impaired after systemic administration in the central nervous system (CNS) because of the blood-brain barrier (BBB). Therefore, the development of novel therapeutic approaches capable of overcoming these limitations is under discussion. Exosomes (Exo) are nano-sized vesicles of endosomal origin that have a high distribution rate in biofluids. Recent advances have introduced Exo as naturally suitable bio-shuttles for the delivery of neurotrophic factors to the brain parenchyma. In recent years, many researchers have attempted to regulate the delivery of Exo to target sites while reducing their removal from circulation. The encapsulation of Exo in natural and synthetic hydrogels offers a valuable strategy to address the limitations of Exo, maintaining their integrity and controlling their release at a desired site. Herein, we highlight the current and novel approaches related to the application of hydrogels for the encapsulation of Exo in the field of CNS tissue engineering.

Production of a Bioink Containing Decellularized Spinal Cord Tissue for 3D Bioprinting.

For the past few years, three-dimensional (3D) bioprinting has emerged as a promising approach in the field of regenerative medicine. This technique allows for the production of 3D scaffolds to support cell transplantation due to its ability to mimic the extracellular environment. One alternative to enhancing cell adhesion, survival, and proliferation is the use of decellularized extracellular matrix as a bioink component. The aim of this study was to produce a bioink using lyophilized rat decellularized spinal cord tissue (DSCT) for 3D bioprinting of nervous tissue. DNA quantification, hematoxylin and eosin and DAPI staining indicated that 1% sodium dodecyl sulfate and 9 h processing were effective in removing the cells from the spinal cord samples. The cell viability assay showed that the decellularized matrix is not cytotoxic for PC12 cells. The hydrogel containing DSCT, alginate, and gelatine used as the base for the bioink has a shear thinning behavior and low G″/G' ratio, allowing for good printability without compromising cell viability after 3D bioprinting. The bioink supported long-term PC12 cell survival, with 93% of live cells 4 weeks after printing, and stimulated the production of laminin-1 and neurofilament-M. This bioink, therefore, represents an easily available biomaterial for central nervous system tissue engineering.

Advances in Management of Spinal Cord Injury Using Stem Cell-derived Extracellular Vesicles: A Review Study.

Spinal cord injury (SCI) is characterized by serious both motor and sensory disability of the limbs below the injured segment. It is the most traumatic disorder among central nervous system (CNS) conditions which not only leads to psychological and physical harm to patients but also results in a dramatic loss in the life quality. Many efforts have been developed to find a therapeutic approach for SCI; however, an effective treatment has not yet been found. The lack of effective treatment approach and rehabilitation of SCI underscores the need to identify novel approaches. Tissue engineering associated with stem cells has been recently introduced as an effective treatment approaches for traumatic SCI. Although, low survival rates, immune rejection, cell dedifferentiation, and tumorigenicity have been addressed for tissue engineering. Regenerative medicine is an interdisciplinary field developing and applying tissue engineering, stem cell (SC) therapy, and SC-derived extracellular vesicle therapy that aims to provide reliable and safe ways to replace injured tissues and organs. The application of mesenchymal stem cells-derived extracellular vesicles (MSC-EVs) has recently attracted attention to improve central nervous system dysfunction such as SCI, mainly by promoting neurogenesis and angiogenesis. In this review article the latest information of SCI improvement using stem cell-derived extracellular vesicles published data in the Web of Science, Scopus, Science Direct and Pub Med databases were collected. The data collected show that MSC-EVs, including exosomes, alone or in combination with scaffolds can can regenerate the injured nerve in SCI. This study summarizes the efficacy of MSC-EVs, including exosomes, alone or in combination with scaffolds in the treatment of SCI and then discusses the therapeutic outcomes observed in SCI experimental models following treatment with MSC-EVs alone or loaded on scaffolds in particular collagen-based scaffolds. The pathological process of SCI being very complex.A complete effective strategy has yet to be found for treatment of SCI in human.Exosomes derived-stem cells alone have great potential for the treatment of SCI.Various biocompatible scaffolds are good drug carriers for SCI treatment.Various biocompatible scaffolds are good carriers for exosomes. Human with spinal cord injury (SCI) show serious motor and sensory disability of the limbs. Since there is no an effective treatment for SCI, researchers are trying to develop and find a new therapeutic approach for SCI. CNS tissue engineering with various stem cells sources as well as their derived extracellular vesicle has been extensively attracted for providing reliable and safe approach for SCI treatment. Extracellular vesicles are lipid bilayer membrane-enclosed organelles containing various biomolecules involved in a variety of complex intercellular communication systems. They are released from all cell types into their surrounding environment and are important vehicles for paracrine The application of stem cells-derived extracellular vesicles (MSC-EVs) has recently attracted attention to improve central nervous system dysfunction such as SCI, mainly by promoting neurogenesis and angiogenesis.

Injectable hydrogels in central nervous system: Unique and novel platforms for promoting extracellular matrix remodeling and tissue engineering.

Repairing central nervous system (CNS) is difficult due to the inability of neurons to recover after damage. A clinically acceptable treatment to promote CNS functional recovery and regeneration is currently unavailable. According to recent studies, injectable hydrogels as biodegradable scaffolds for CNS tissue engineering and regeneration have exceptionally desirable attributes. Hydrogel has a biomimetic structure similar to extracellular matrix, hence has been considered a 3D scaffold for CNS regeneration. An interesting new type of hydrogel, injectable hydrogels, can be injected into target areas with little invasiveness and imitate several aspects of CNS. Injectable hydrogels are being researched as therapeutic agents because they may imitate numerous properties of CNS tissues and hence reduce subsequent injury and regenerate neural tissue. Because of their less adverse effects and cost, easier use and implantation with less pain, and faster regeneration capacity, injectable hydrogels, are more desirable than non-injectable hydrogels. This article discusses the pathophysiology of CNS and the use of several kinds of injectable hydrogels for brain and spinal cord tissue engineering, paying particular emphasis to recent experimental studies.

Chitosan-g-oligo(L,L-lactide) Copolymer Hydrogel Potential for Neural Stem Cell Differentiation.

We evaluated the applicability of chitosan-g-oligo(L,L-lactide) copolymer (CLC) hydrogel for central nervous system tissue engineering. The biomechanical properties of the CLC hydrogel were characterized and its biocompatibility was assessed with neural progenitor cells obtained from two different sources: H9-derived neural stem cells (H9D-NSCs) and directly reprogrammed neural precursor cells (drNPCs). Our study found that the optically transparent CLC hydrogel possessed biomechanical characteristics suitable for culturing human neural stem/precursor cells and was noncytotoxic. When seeded on films prepared from CLC copolymer hydrogel, both H9D-NSC and drNPC adhered well, expanded and exhibited signs of spontaneous differentiation. While H9D-NSC mainly preserved multipotency as shown by a high proportion of Nestin+ and Sox2+ cells and a comparatively lower expression of the neuronal markers βIII-tubulin and MAP2, drNPCs, obtained by direct reprogramming, differentiated more extensively along the neuronal lineage. Our study indicates that the CLC hydrogel may be considered as a substrate for tissue-engineered constructs, applicable for therapy of neurodegenerative diseases. Impact statement We synthetized a chitosan-g-oligo(L,L-lactide) hydrogel that sustained multipotency of embryonic-derived neural stem cells (NSCs) and supported differentiation of directly reprogrammed NSC predominantly along the neuronal lineage. The hydrogel exhibited no cytotoxicity in vitro, both in extraction and contact cytotoxicity tests. When seeded on the hydrogel, both types of NSCs adhered well, expanded, and exhibited signs of spontaneous differentiation. The biomechanical properties of the hydrogel were similar to that of human spinal cord with incised pia mater. These data pave the way for further investigations of the hydrogel toward its applicability in central nervous system tissue engineering.

Advanced 4D-bioprinting technologies for brain tissue modeling and study

ABSTRACTAlthough the process by which the cortical tissues of the brain fold has been the subject of considerable study and debate over the past few decades, a single mechanistic description of the phenomenon has yet to be fully accepted. Rather, two competing explanations of cortical folding have arisen in recent years; known as the axonal tension and the differential tangential expansion models. In the present review, these two models are introduced by analyzing the computational, theoretical, materials-based, and cell studies which have yielded them. Then Four-dimensional bioprinting is presented as a powerful technology which can not only be used to test both models of cortical folding de novo, but can also be used to explore the reciprocal effects that folding associated mechanical stresses may have on neural development. Therein, the fabrication of ‘smart’ tissue models which can accurately simulate the in vivo folding process and recapitulate physiologically relevant stresses are introduced. We also provide a general description of both cortical neurobiology as well as the cellular basis of cortical folding. Our discussion also entails an overview of both 3D and 4D bioprinting technologies, as well as a brief commentary on recent advancements in printed central nervous system tissue engineering.

Injectable hyaluronan-methylcellulose composite hydrogel crosslinked by polyethylene glycol for central nervous system tissue engineering

Spontaneous recovery ability of central nerves has inspired researchers to focus on tissue engineering techniques, especially scaffolds. To obtain a material with an appropriate degrading rate, an injectable composite hydrogel HAMC consisting of hyaluronic acid and methylcellulose was prepared using polyethylene glycol as a cross linker in this study. HAMC combined the advantages of two components to be fast-gelling, injectable, degradable, biocompatible, and it was able to meet some special shape requirement for injured tissue by in-situ forming. Moreover, due to the crosslinking effects polyethylene glycol brought to methylcellulose, the rheological properties and stability of HAMC were greatly improved, which could prolong the residence time of this hydrogel effectively. Cell viability results showed HAMC was cytocompatible for further applications in vivo, and would be a promising choice for neural tissue engineering in the future.

The role of the surface on microglia function: implications for central nervous system tissue engineering.

In tissue engineering, it is well accepted that a scaffold surface has a decisive impact on cell behaviour. Here we focused on microglia-the resident immune cells of the central nervous system (CNS)-and on their response to poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-CL)) fibrous and flat surfaces obtained by electrospinning and solvent cast, respectively. This study aims to provide cues for the design of instructive surfaces that can contribute to the challenging process of CNS regeneration. Cell morphology was evidently affected by the substrate, mirroring the surface main features. Cells cultured on flat substrates presented a round shape, while cells with elongated processes were observed on the electrospun fibres. A higher concentration of the pro-inflammatory cytokine tumour necrosis factor-α was detected in culture media from microglia on fibres. Still, astrogliosis is not exacerbated when astrocytes are cultured in the presence of microglia-conditioned media obtained from cultures in contact with either substrate. Furthermore, a significant percentage of microglia was found to participate in the process of myelin phagocytosis, with the formation of multinucleated giant cells being observed only on films. Altogether, the results presented suggest that microglia in contact with the tested substrates may contribute to the regeneration process, putting forward P(TMC-CL) substrates as supporting matrices for nerve regeneration.

Effects of Biologic Scaffolds on Human Stem Cells and Implications for CNS Tissue Engineering

Biologic scaffolds composed of mammalian extracellular matrix (ECM) promote constructive remodeling of tissues via mechanisms that include the recruitment of endogenous stem/progenitor cells, modulation of the host innate immune response, and influence of cell fate differentiation. Such scaffold materials are typically prepared by decellularization of source tissues and are prepared as sheets, powder, or hydrogels. It is plausible that ECM derived from an anatomically distinct tissue would have unique or specific effects on cells that naturally reside in this same tissue. The present study investigated the in vitro effect of a soluble form of ECM derived from central nervous system (CNS) tissue, specifically the spinal cord or brain, versus ECM derived from a non-CNS tissue; specifically, the urinary bladder on the behavior of neural stem cells (NSCs) and perivascular stem cells. All forms of ECM induce positive, mitogenic, and chemotactic effects at concentrations of approximately 100 μg/mL without affecting stem cell viability. CNS-derived ECMs also showed the ability to differentiate NSCs into neurons as indicted by βIII-tubulin expression in two-dimensional culture and neurite extension on the millimeter scale after 24 days of three-dimensional cultures in an ECM hydrogel. These results suggest that solubilized forms of ECM scaffold materials may facilitate the postinjury healing response in CNS tissues.

Viscoelastic characterization of rat cerebral cortex and type I collagen scaffolds for central nervous system tissue engineering

In the field of tissue engineering and regenerative medicine for the central nervous system, therapeutic strategies may involve implantation of biomaterial scaffolds into the brain. An understanding of the relationship between the brain and the scaffold mechanical properties can help in the selection of a safe and effective biomaterial. This research demonstrates the use of indentation testing along with viscoelastic modeling to characterize and compare mechanical properties of in situ rat cerebral cortex and collagen scaffolds of varying collagen concentration. The stress–relaxation solution for indentation of a viscoelastic material was derived based on a five-element Maxwell model and use of the correspondence principle. Applying the model to experimental stress–relaxation data, the brain was characterized by three shear moduli G1=1.6±0.10 kPa, G2=2.0±0.15 kPa, G3=1.8±0.20 kPa, and two viscosities η2=11.0 ± 0.44 kPa⋅s, η3=148.7 ± 6.70 kPa⋅s, with corresponding relaxation time constants τ1=5.7±0.3 s and τ2=88.4 ± 7.6 s. The brain showed average relaxation of 74% from its peak force during loading to an approximately asymptotic force over a 5 minute hold at constant displacement. Collagen scaffolds generally showed increasing trends in the shear moduli, viscosities, and percentage relaxation with increasing collagen concentration. While the brain had similar stiffness to the 1.0% collagen scaffold during the loading phase, the brain’s relaxation behavior was distinct from all of the scaffolds. Similarities and differences between the mechanical behavior of the brain and collagen scaffolds of varying collagen concentration are discussed in relation to application of biomaterials for regenerative medicine.

Scaffolds for central nervous system tissue engineering

Traumatic injuries to the brain and spinal cord of the central nervous system (CNS) lead to severe and permanent neurological deficits and to date there is no universally accepted treatment. Owing to the profound impact, extensive studies have been carried out aiming at reducing inflammatory responses and overcoming the inhibitory environment in the CNS after injury so as to enhance regeneration. Artificial scaffolds may provide a suitable environment for axonal regeneration and functional recovery, and are of particular importance in cases in which the injury has resulted in a cavitary defect. In this review we discuss development of scaffolds for CNS tissue engineering, focusing on mechanism of CNS injuries, various biomaterials that have been used in studies, and current strategies for designing and fabricating scaffolds.

Central Nervous System Tissue Engineering: Current Considerations and Strategies

Combating neural degeneration from injury or disease is extremely difficult in the brain and spinal cord, i.e. central nervous system (CNS). Unlike the peripheral nerves, CNS neurons are bombarded by

Electrospun polyurethane scaffolds for proliferation and neuronal differentiation of human embryonic stem cells

Adult central nervous system (CNS) tissue has a limited capacity to recover after trauma or disease. Hence, tissue engineering scaffolds intended for CNS repair and rehabilitation have been subject to intense research effort. Electrospun porous scaffolds, mimicking the natural three-dimensional environment of the in vivo extracellular matrix (ECM) and providing physical support, have been identified as promising candidates for CNS tissue engineering. The present study demonstrates in vitro culturing and neuronal differentiation of human embryonic stem cells (hESCs) on electrospun fibrous polyurethane scaffolds. Electrospun scaffolds composed of biocompatible polyurethane resin (Desmopan 9370A, Bayer MaterialScience AG) were prepared with a vertical electrospinning setup. Resulting scaffolds, with a thickness of approximately 150 µm, exhibited high porosity (84%) and a bimodal pore size distribution with peaks at 5–6 and 1 µm. The mean fiber diameter was measured to approximately 360 nm with a standard deviation of 80 nm. The undifferentiated hESC line SA002 (Cellartis AB, Göteborg, Sweden) was seeded and cultured on the produced scaffolds and allowed propagation and then differentiation for up to 47 days. Cultivation of hESC on electrospun fibrous scaffolds proved successful and neuronal differentiation was observed via standard immunocytochemistry. The results indicate that predominantly dopaminergic tyrosine hydroxylase (TH) positive neurons are derived in co-culture with fibrous scaffolds, in comparison to reference cultures under the same differentiation conditions displaying large proportions of GFAP positive cell types. Scanning electron micrographs confirm neurite outgrowth and connection to adjacent cells, as well as cell attachment to individual fibers of the fibrous scaffold. Consequently, electrospun polyurethane scaffolds have been proven feasible as a substrate for hESC propagation and neuronal differentiation. The physical interaction between cells and the fibrous scaffold indicates that these scaffolds provide a three-dimensional physical structure; a potential candidate for neural tissue engineering repair and rehabilitation.

Hyaluronic Acid Hydrogel Modified with Nogo-66 Receptor Antibody and Poly(L-Lysine) Enhancement of Adherence and Survival of Primary Hippocampal Neurons

Hyaluronic acid (HA) hydrogel was modified with poly(L-lysine) (PLL) and Nogo-66 Receptor antibody (antiNgR) to enhance the repair of central nervous system (CNS) injuries. The immobilization of PLL was characterized by X-ray photoelectron spectroscopy (XPS) and the immobilization of antiNgR was studied by immunofluorescence. The cytocompatibility of this modified hydrogel was analyzed by culturing primary hippocampal neurons. The quantity and morphology of the neurons were influenced by different modifications; the primary hippocampal neurons cultured with modified HA hydrogel exhibited multipolar and bipolar morphology were compared with unmodified hydrogel cultures. The number of neurons obtained by culturing with HA hydrogel modified with both PLL and antiNgR was almost twice the number of neurons cultured with HA modified with only PLL or antiNgR. This phenomenon was attributed to the collaborative effect of PLL and antiNgR on the neurons. The characteristics of this new hydrogel system, including pore structure, water absorption, hydrolysis degradation did not change much when compared with the hydrogel modified with PLL or antiNgR, respectively. It is expected that this modified HA hydrogel has potential as a CNS tissue engineering material.