3D Microfibrous Scaffolds Selectively Promotes Proliferation and Glial Differentiation of Adult Neural Stem Cells: A Platform to Tune Cellular Behavior in Neural Tissue Engineering

Metabolically Glycoengineered Neural Stem Cells Boost Neural Repair After Cardiac Arrest

Cardiac arrest (CA)-induced cerebral ischemia remains challenging with high mortality and disability. Neural stem cell (NSC) engrafting is an emerging therapeutic strategy with considerable promise that, unfortunately, is severely compromised by limited cell functionality after in vivo transplantation. This groundbreaking report demonstrates that metabolic glycoengineering (MGE) using the "Ac5ManNTProp (TProp)" monosaccharide analog stimulates the Wnt/β-catenin pathway, improves cell adhesion, and enhances neuronal differentiation in human NSCs in vitro thereby substantially increasing the therapeutic potential of these cells. For the first time, MGE significantly enhances NSC efficacy for treating ischemic brain injury after asphyxia CA in rats. In particular, neurological deficit scores and neurobehavioral tests experience greater improvements when the therapeutic cells are pretreated with TProp than with "stand-alone" NSC therapy. Notably, the TProp-NSC group exhibits significantly stronger neuroprotective functions including enhanced differentiation, synaptic plasticity, and reduced microglia recruitment; furthermore, Wnt pathway agonists and inhibitors demonstrate a pivotal role for Wnt signaling in the process. These findings help establish MGE as a promising avenue for addressing current limitations associated with NSC transplantation via beneficially influencing neural regeneration and synaptic plasticity, thereby offering enhanced therapeutic options to boost brain recovery following global ischemia.

Microfiber Fabricated via Microfluidic Spinning toward Tissue Engineering Applications

Microfibers, a type of long, thin, and flexible material, can be assembled into functional 3D structures by folding, binding, and weaving. As a novel spinning method, combining microfluidic technology and wet spinning, microfluidic spinning technology can precisely control the size, morphology, structure, and composition of the microfibers. Particularly, the process is mild and rapid, which is suitable for preparing microfibers using biocompatible materials and without affecting the viability of cells encapsulated. Furthermore, owing to the controllability of microfluidic spinning, microfibers with well-defined structures (such as hollow structures) will contribute to the exchange of nutrients or guide cell orientation. Thus, this method is often used to fabricate microfibers as cell scaffolds for cell encapsulation or adhesion and can be further applied to biomimetic fibrous tissues. In this review, the focus is on different fiber structures prepared by microfluidic spinning technology, including solid, hollow, and heterogeneous structures, generated from three essential elements: spinning platform, fiber composition, and solidification methods. Furthermore, the application of microfibers is described with different structures in tissue engineering, such as blood vessels, skeletal muscle, bone, nerves, and lung bronchi. Finally, the challenges and future development prospects of microfluidic spinning technology in tissue engineering applications are discussed.

Three-Dimensional Printing of Poly-L-Lactic Acid Composite Scaffolds with Enhanced Bioactivity and Controllable Zn Ion Release Capability by Coupling with Carbon-ZnO

Poly-L-lactic acid (PLLA) has gained great popularity with researchers in regenerative medicine owing to its superior biocompatibility and biodegradability, although its inadequate bioactivity inhibits the further use of PLLA in the field of bone regeneration. Zinc oxide (ZnO) has been utilized to improve the biological performance of biopolymers because of its renowned osteogenic activity. However, ZnO nanoparticles tend to agglomerate in the polymer matrix due to high surface energy, which would lead to the burst release of the Zn ion and, thus, cytotoxicity. In this study, to address this problem, carbon–ZnO (C–ZnO) was first synthesized through the carbonization of ZIF-8. Then, C–ZnO was introduced to PLLA powder before it was manufactured as scaffolds (PLLA/C–ZnO) by a selective laser sintering 3D printing technique. The results showed that the PLLA/C–ZnO scaffold was able to continuously release Zn ions in a reasonable range, which can be attributed to the interaction of Zn–N bonding and the shielding action of the PLLA scaffold. The controlled release of Zn ions from the scaffold further facilitated cell adhesion and proliferation and improved the osteogenic differentiation ability at the same time. In addition, C–ZnO endowed the scaffold with favorable photodynamic antibacterial ability, which was manifested by an efficient antibacterial rate of over 95%.

The Application of Biomaterials in Spinal Cord Injury

The spinal cord and the brain form the central nervous system (CNS), which is the most important part of the body. However, spinal cord injury (SCI) caused by external forces is one of the most difficult types of neurological injury to treat, resulting in reduced or even absent motor, sensory and autonomic functions. It leads to the reduction or even disappearance of motor, sensory and self-organizing nerve functions. Currently, its incidence is increasing each year worldwide. Therefore, the development of treatments for SCI is urgently needed in the clinic. To date, surgery, drug therapy, stem cell transplantation, regenerative medicine, and rehabilitation therapy have been developed for the treatment of SCI. Among them, regenerative biomaterials that use tissue engineering and bioscaffolds to transport cells or drugs to the injured site are considered the most promising option. In this review, we briefly introduce SCI and its molecular mechanism and summarize the application of biomaterials in the repair and regeneration of tissue in various models of SCI. However, there is still limited evidence about the treatment of SCI with biomaterials in the clinic. Finally, this review will provide inspiration and direction for the future study and application of biomaterials in the treatment of SCI.

Microfluidically fabricated fibers containing pancreatic islets and mesenchymal stromal cells improve longevity and sustained normoglycemia in diabetic rats

Type 1 diabetes mellitus is an autoimmune disease characterized by the loss of pancreatic isletβcells. Insulin injections and pancreas transplants are currently available therapies. The former requires daily insulin injections, while the latter is constrained by donor organ availability. Islet transplantation is a promising alternative treatment for type 1 diabetes mellitus that may overcome the limitations of previous techniques. Two challenges, however, must be addressed: limited cell retention as a result of the immune response and limited function of the transplanted cells that survive. To address these problems, we developed a microfluidic technology for a one-step generation of islet-laden fibers to protect them from the immune response. This approach enables continuous generation of microfibers with a diameter suitable for islet encapsulation (275µm). We, then, transplanted islet-laden fibers into diabetic Wistar rats. While islet-laden fibers alone were unable to restore normoglycemia in diabetic rats, adding mesenchymal stromal cells (MSCs) restored normoglycemia for an extended time. It increased the animals' lifespan by up to 75 d. Additionally, it improved the glucose-stimulated response of islets to the point where there was no significant difference between the treatment group and the healthy animals. Additionally, the presence of MSCs suppressed the immune response, as seen by decreased levels of pro-inflammatory cytokines such as tumor necrosis factor-α. Taken together, these fibers including islet and MSCs provide a versatile platform for concurrently improving cell preservation and functioning followingin vivotransplantation.

Biodegradable and Electrically Conductive Melanin-Poly (3-Hydroxybutyrate) 3D Fibrous Scaffolds for Neural Tissue Engineering Applications

Due to the severity of peripheral nerve injuries (PNI) and spinal cord injuries (SCI), treatment options for patients are limited. In this context, biomaterials designed to promote regeneration and reinstate the lost function are being explored. Such biomaterials should be able to mimic the biological, chemical, and physical cues of the extracellular matrix for maximum effectiveness as therapeutic agents. Development of biomaterials with desirable physical, chemical, and electrical properties, however, has proven challenging. Here a novel biomaterial formulation achieved by blending the pigment melanin and the natural polymer Poly-3-hydroxybutyrate (PHB) is proposed. Physio-chemical measurements of electrospun fibers reveal a feature rich surface nano-topography, a semiconducting-nature, and brain-tissue-like poroviscoelastic properties. Resulting fibers improve cell adhesion and growth of mouse sensory and motor neurons, without any observable toxicity. Further, the presence of polar functional groups positively affect the kinetics of fibers degradation at a pH (≈7.4) comparable to that of body fluids. Thus, melanin-PHB blended scaffolds are found to be physio-chemically, electrically, and biologically compatible with neural tissues and could be used as a regenerative modality for neural tissue injuries. A biomaterial for scaffolds intended to promote regeneration of nerve tissue after injury is developed. This biomaterial, obtained by mixing the pigment melanin and the natural polymer PHB, is biodegradable, electrically conductive, and beneficial to the growth of motor and sensory neurons. Thus, it is believed that this biomaterial can be used in the context of healthcare applications.

Tissue-Engineered Models of the Human Brain: State-of-the-Art Analysis and Challenges

Neurological disorders affect billions of people across the world, making the discovery of effective treatments an important challenge. The evaluation of drug efficacy is further complicated because of the lack of in vitro models able to reproduce the complexity of the human brain structure and functions. Some limitations of 2D preclinical models of the human brain have been overcome by the use of 3D cultures such as cell spheroids, organoids and organs-on-chip. However, one of the most promising approaches for mimicking not only cell structure, but also brain architecture, is currently represented by tissue-engineered brain models. Both conventional (particularly electrospinning and salt leaching) and unconventional (particularly bioprinting) techniques have been exploited, making use of natural polymers or combinations between natural and synthetic polymers. Moreover, the use of induced pluripotent stem cells (iPSCs) has allowed the co-culture of different human brain cells (neurons, astrocytes, oligodendrocytes, microglia), helping towards approaching the central nervous system complexity. In this review article, we explain the importance of in vitro brain modeling, and present the main in vitro brain models developed to date, with a special focus on the most recent advancements in tissue-engineered brain models making use of iPSCs. Finally, we critically discuss achievements, main challenges and future perspectives.

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.

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

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

Modified Industrial Three-Dimensional Polylactic Acid Scaffold Cell Chip Promotes the Proliferation and Differentiation of Human Neural Stem Cells

In this study, we fabricated a three-dimensional (3D) scaffold using industrial polylactic acid (PLA), which promoted the proliferation and differentiation of human neural stem cells. An industrial PLA 3D scaffold (IPTS) cell chip with a square-shaped pattern was fabricated via computer-aided design and printed using a fused deposition modeling technique. To improve cell adhesion and cell differentiation, we coated the IPTS cell chip with gold nanoparticles (Au-NPs), nerve growth factor (NGF) protein, an NGF peptide fragment, and sonic hedgehog (SHH) protein. The proliferation of F3.Olig2 neural stem cells was increased in the IPTS cell chips coated with Au-NPs and NGF peptide fragments when compared with that of the cells cultured on non-coated IPTS cell chips. Cells cultured on the IPTS-SHH cell chip also showed high expression of motor neuron cell-specific markers, such as HB9 and TUJ-1. Therefore, we suggest that the newly engineered industrial PLA scaffold is an innovative tool for cell proliferation and motor neuron differentiation.

Behavior of Neural Cells Post Manufacturing and After Prolonged Encapsulation within Conductive Graphene-Laden Alginate Microfibers

Engineering conductive 3D cell scaffoldings offer advantages toward the creation of physiologically relevant platforms with integrated real-time sensing capabilities. Dopaminergic neural cells are encapsulated into graphene-laden alginate microfibers using a microfluidic approach, which is unmatched for creating highly-tunable microfibers. Incorporating graphene increases the conductivity of the alginate microfibers by 148%, creating a similar conductivity to native brain tissue. The cell encapsulation procedure has an efficiency of 50%, and of those cells, ≈30% remain for the entire 6-day observation period. To understand how the microfluidic encapsulation affects cell genetics, tyrosine hydroxylase, tubulin beta 3 class 3, interleukin 1 beta, and tumor necrosis factor alfa are analyzed primarily with real-time reverse transcription-quantitative polymerase chain reaction and secondarily with enzyme-linked immunosorbent assay, immediately after manufacturing, after encapsulation in polymer matrix for 6 days, and after encapsulation in the graphene-polymer composite for 6 days. Preliminary data shows that the manufacturing process and combination with alginate matrix affect the expression of the studied genes immediately after manufacturing. In addition, the introduction of graphene further changes gene expressions. Long-term encapsulation of neural cells in alginate and 6-day exposure to graphene also leads to changes in gene expressions.

Targeted Microfluidic Manufacturing to Mimic Biological Microenvironments: Cell-Encapsulated Hollow Fibers

At present, the blood-brain barrier (BBB) poses a challenge for treating a wide range of central nervous system disorders; reliable BBB models are still needed to understand and manipulate the transfer of molecules into the brain, thereby improving the efficiency of treatments. In this study, hollow, cell-laden microfibers are fabricated and investigated as a starting point for generating BBB models. The genetic effects of the manufacturing process are analyzed to understand the implications of encapsulating cells in this manner. These fibers are created using different manufacturing parameters to understand the effects on wall thickness and overall diameter. Then, dopaminergic rat cells are encapsulated into hollow fibers, which maintained at least 60% live cells throughout the three-day observation period. Lastly, genetic changes tyrosine hydroxylase (TH) and tubulin beta 3 class III (TUBB-3) are investigated to elucidate the effects on cell health and behavior; while the TH levels in encapsulated cells were similar to control cells, showing similar levels of TH synthesis, TUBB-3 was downregulated, indicating lower amounts of cellular neurogenesis.

Constructing 3D Macroporous Microfibrous Scaffolds with a Featured Surface by Heat Welding and Embossing

Three-dimensional (3D) microfibrous scaffolds hold great promise for biomedical applications due to their good mechanical properties and biomimetic structure similar to that of the fibrous natural extracellular matrix. However, the large diameter and smooth surface of microfibers provide limited cues for regulating cell activity and behaviors. In this work, we report a facile heat-welding-and-embossing strategy to develop 3D macroporous microfibrous scaffolds with a featured surface topography. Here, solid monosodium glutamate (MSG) particles with crystalline ridge-like surface features play a key role as templates in both the formation of scaffold pores and the surface embossing of scaffold fibers when short thermoplastic polypropylene microfibers were heat-welded. The embossing process can be programmed by adjusting heating temperatures and MSG/fiber ratios. Compared to traditional 3D microfibrous scaffolds, the as-welded 3D scaffolds show higher compressive strength and modulus. Taking mouse C2C12 myoblasts as a model cell line, the scaffolds with embossed surface features significantly promoted the growth of cells, interactions of cells and scaffolds, and formation of myotubes. The findings indicate that the as-prepared 3D scaffolds are a good platform for cell culture study. The facile strategy can be applied to fabricate different fibrous scaffolds by changing the combination of templates and thermoplastic polymer fibers with a melting temperature lower than that of the template. The obtained insights in this work could provide a guide and inspiration for the design and fabrication of functional 3D fibrous scaffolds.

Neurorepair and Regeneration of the Brain: A Decade of Bioscaffolds and Engineered Microtissue

Repairing the human brain remains a challenge, despite the advances in the knowledge of inflammatory response to injuries and the discovery of adult neurogenesis. After brain injury, the hostile microenvironment and the lack of structural support for neural cell repopulation, anchoring, and synapse formation reduce successful repair chances. In the past decade, we witnessed the rise of studies regarding bioscaffolds’ use as support for neuro repair. A variety of natural and synthetic materials is available and have been used to replace damaged tissue. Bioscaffolds can assume different shapes and may or may not carry a diversity of content, such as stem cells, growth factors, exosomes, and si/miRNA that promote specific therapeutic effects and stimulate brain repair. The use of these external bioscaffolds and the creation of cell platforms provide the basis for tissue engineering. More recently, researchers were able to engineer brain organoids, neural networks, and even 3D printed neural tissue. The challenge in neural tissue engineering remains in the fabrication of scaffolds with precisely controlled topography and biochemical cues capable of directing and controlling neuronal cell fate. The purpose of this review is to highlight the existing research in the growing field of bioscaffolds’ development and neural tissue engineering. Moreover, this review also draws attention to emerging possibilities and prospects in this field.

The application of three-dimensional cell culture in clinical medicine

Three-dimensional cell culture technology is a novel cell culture technology, which can simulate the growth state of cells in vivo by scaffolds or special devices. Cells can form tissues or organs in vitro. It combines some advantages of traditional cell experiments and animal model experiments. Because of its advantages, it is widely used in clinical medical research, including research on stem cell differentiation, research on cell behavior, migration and invasion, study on microenvironment, study on drug sensitivity and radio-sensitivity of tumor cells, etc. In this paper, the evolution and classification of three-dimensional cell culture are reviewed, also the advantages and shortages are compared. The application of three-dimensional cell culture in clinical medicine are summarized to provide an insight into translational medicine.

Biocompatibility of α-Al2O3 Ceramic Substrates with Human Neural Precursor Cells

BACKGROUND

Biocompatible materials-topography could be used for the construction of scaffolds allowing the three-dimensional (3D) organization of human stem cells into functional tissue-like structures with a defined architecture.

METHODS

Structural characterization of an alumina-based substrate was performed through XRD, Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), and wettability measurements. Biocompatibility of the substrate was assessed by measuring the proliferation and differentiation of human neural precursor stem cells (NPCs).

RESULTS

α-Al₂O₃ is a ceramic material with crystallite size of 40 nm; its surface consists of aggregates in the range of 8-22 μm which forms a rough surface in the microscale with 1-8 μm cavities. The non-calcined material has a surface area of 5.5 m²/gr and pore size distribution of 20 nm, which is eliminated in the calcined structure. Thus, the pore network on the surface and the body of the ceramic becomes more water proof, as indicated by wettability measurements. The alumina-based substrate supported the proliferation of human NPCs and their differentiation into functional neurons.

CONCLUSIONS

Our work indicates the potential use of alumina for the construction of 3D engineered biosystems utilizing human neurons. Such systems may be useful for diagnostic purposes, drug testing, or biotechnological applications.

Engraving the Surface of Electrospun Microfibers with Nanoscale Grooves Promotes the Outgrowth of Neurites and the Migration of Schwann Cells

We report a simple method based upon coaxial electrospinning for the fabrication of aligned microfibers engraved with nanoscale grooves to promote neurite outgrowth and cell migration. The success of this method relies on the immiscibility between poly(ϵ-caprolactone) (PCL) and poly(vinyl pyrrolidone) (PVP) in 2,2,2-trifluoroethanol (TFE) for the generation of PVP/TFE pockets on the surface of a PCL jet. The pockets are stretched and elongated along with the jet, eventually resulting in the formation of nanoscale grooves upon the removal of PVP. The presence of nanoscale grooves greatly enhances the outgrowth of neurites from both PC12 cells and chick embryonic dorsal root ganglia (DRG) bodies, as well as the migration of Schwann cells. The enhancements can be maximized by optimizing the dimensions of the grooves for potential use in applications involving neurite extension and wound closure.

Recovery of Encapsulated Adult Neural Progenitor Cells from Microfluidic-Spun Hydrogel Fibers Enhances Proliferation and Neuronal Differentiation

Because of the limitations imposed by traditional two-dimensional (2D) cultures, biomaterials have become a major focus in neural and tissue engineering to study cell behavior in vitro. 2D systems fail to account for interactions between cells and the surrounding environment; these cell-matrix interactions are important to guide cell differentiation and influence cell behavior such as adhesion and migration. Biomaterials provide a unique approach to help mimic the native microenvironment in vivo. In this study, a novel microfluidic technique is used to encapsulate adult rat hippocampal stem/progenitor cells (AHPCs) within alginate-based fibrous hydrogels. To our knowledge, this is the first study to encapsulate AHPCs within a fibrous hydrogel. Alginate-based hydrogels were cultured for 4 days in vitro and recovered to investigate the effects of a 3D environment on the stem cell fate. Post recovery, cells were cultured for an additional 24 or 72 h in vitro before fixing cells to determine if proliferation and neuronal differentiation were impacted after encapsulation. The results indicate that the 3D environment created within a hydrogel is one factor promoting AHPC proliferation and neuronal differentiation (19.1 and 13.5%, respectively); however, this effect is acute. By 72 h post recovery, cells had similar levels of proliferation and neuronal differentiation (10.3 and 8.3%, respectively) compared to the control conditions. Fibrous hydrogels may better mimic the natural micro-environment present in vivo and be used to encapsulate AHPCs, enhancing cell proliferation and selective differentiation. Understanding cell behavior within 3D scaffolds may lead to the development of directed therapies for central nervous system repair and rescue.

Hierarchical Ordered Assembly of Genetically Modifiable Viruses into Nanoridge-in-Microridge Structures

Hierarchically assembled nanomaterials can find a variety of applications in medicine, energy, and electronics. Here, an automatically controlled dip-pulling method is developed and optimized to generate an unprecedented ordered nano-to-micro hierarchical nanoridge-in-microridge (NiM) structure from a bacteria-specific human-safe virus, the filamentous phage with or without genetically displaying a foreign peptide. The NiM structure is pictured as a window blind with each lath (the microridge) made of parallel phage bundles (the nanoridges). It is independent of the substrate materials supporting it. Surprisingly, it can induce the bidirectional differentiation of stem cells into neurons and astrocytes within a short timeframe (only 8 d) not seen before, which is highly desired because both neurons and astrocytes are needed simultaneously in treating neurodegenerative diseases. Since phages can direct tissue regeneration, template materials formation, sense molecules, and build electrodes, the NiM structures displaying different peptides and on varying materials hold promise in many technologically important fields.

Current progress in application of polymeric nanofibers to tissue engineering

Tissue engineering uses a combination of cell biology, chemistry, and biomaterials to fabricate three dimensional (3D) tissues that mimic the architecture of extracellular matrix (ECM) comprising diverse interwoven nanofibrous structure. Among several methods for producing nanofibrous scaffolds, electrospinning has gained intense interest because it can make nanofibers with a porous structure and high specific surface area. The processing and solution parameters of electrospinning can considerably affect the assembly and structural morphology of the fabricated nanofibers. Electrospun nanofibers can be made from natural or synthetic polymers and blending them is a straightforward way to tune the functionality of the nanofibers. Furthermore, the electrospun nanofibers can be functionalized with various surface modification strategies. In this review, we highlight the latest achievements in fabricating electrospun nanofibers and describe various ways to modify the surface and structure of scaffolds to promote their functionality. We also summarize the application of advanced polymeric nanofibrous scaffolds in the regeneration of human bone, cartilage, vascular tissues, and tendons/ligaments.