Differentiation of neuronal stem cells into motor neurons using electrospun poly-L-lactic acid/gelatin scaffold

Pioneering a paradigm shift in tissue engineering and regeneration with polysaccharides and proteins-based scaffolds: A comprehensive review

In the realm of modern medicine, tissue engineering and regeneration stands as a beacon of hope, offering the promise of restoring form and function to damaged or diseased organs and tissues. Central to this revolutionary field are biological macromolecules-nature's own blueprints for regeneration. The growing interest in bio-derived macromolecules and their composites is driven by their environmentally friendly qualities, renewable nature, minimal carbon footprint, and widespread availability in our ecosystem. Capitalizing on these unique attributes, specific composites can be tailored and enhanced for potential utilization in the realm of tissue engineering (TE). This review predominantly concentrates on the present research trends involving TE scaffolds constructed from polysaccharides, proteins and glycosaminoglycans. It provides an overview of the prerequisites, production methods, and TE applications associated with a range of biological macromolecules. Furthermore, it tackles the challenges and opportunities arising from the adoption of these biomaterials in the field of TE. This review also presents a novel perspective on the development of functional biomaterials with broad applicability across various biomedical applications.

Preparation of bilayer tissue-engineered polyurethane/poly-L-lactic acid nerve conduits and their in vitro characterization for use in peripheral nerve regeneration

BACKGROUND

Due to loss of peripheral nerve structure and/or function resulting from trauma, accidents, and other causes, peripheral nerve injuries continue to be a major clinical problem. These injuries can cause partial or total loss of sensory, motor, and autonomic capabilities as well as neuropathic pain. PNI affects between 13 and 23 out of every 100,000 people annually in developed countries. Regeneration of damaged nerves and restoration of function after peripheral nerve injury remain significant therapeutic challenges. Although autologous nerve graft transplantation is a viable therapy option in several clinical conditions, donor site morbidity and a lack of donor tissue often hinder full functional recovery. Biomimetic conduits used in tissue engineering to encourage and direct peripheral nerve regeneration by providing a suitable microenvironment for nerve ingrowth are only one example of the cutting-edge methods made possible by this field. Many innate extracellular matrix (ECM) structures of different tissues can be successfully mimicked by nanofibrous scaffolds. Nanofibrous scaffolds can closely mimic the surface structure and morphology of native ECMs of many tissues.

METHODS

In this study, we have produced bilayer nanofibrous nerve conduit based on poly-lactic acid/polyurethane/multiwall carbon nanotube (PLA/PU/MWCNT), for application as composite scaffolds for static nerve tissue engineering. The contact angle was indicated to show the hydrophilicity properties of electrospun nanofibers. The SEM images were analyzed to determine the fiber's diameters, scaffold morphology, and endometrial stem cell adhesion. Moreover, MTT assay and DAPI staining were used to show the viability and proliferation of endometrial stem cells.

RESULTS

The constructed bilayer PLA/PU/MWCNT scaffolds demonstrated the capacity to support cell attachment, and the vitality of samples was assessed using SEM, MTT assay, and DAPI staining technique.

CONCLUSIONS

According to an in vitro study, electrospun bilayer PLA/PU/MWCNT scaffolds can encourage the adhesion and proliferation of human endometrial stem cells (hEnSCs) and create the ideal environment for increasing cell survival.

Electrical stimulation via repeated biphasic conducting materials for peripheral nerve regeneration

Improved materials for peripheral nerve repair are needed for the advancement of new surgical techniques in fields spanning from oncology to trauma. In this study, we developed bioresorbable materials capable of producing repeated electric field gradients spaced 600 μm apart to assess the impact on neuronal cell growth, and migration. Electrically conductive, biphasic composites comprised of poly (glycerol) sebacate acrylate (PGSA) alone, and doped with poly (pyrrole) (PPy), were prepared to create alternating segments with high and low electrically conductivity. Conductivity measurements demonstrated that 0.05% PPy added to PSA achieved an optimal value of 1.25 × 10-4 S/cm, for subsequent electrical stimulation. Tensile testing and degradation of PPy doped and undoped PGSA determined that 35-40% acrylation of PGSA matched nerve mechanical properties. Both fibroblast and neuronal cells thrived when cultured upon the composite. Biphasic PGSA/PPy sheets seeded with neuronal cells stimulated for with 3 V, 20 Hz demonstrated a 5x cell increase with 1 day of stimulation and up to a 10x cell increase with 3 days stimulation compared to non-stimulated composites. Tubular conduits composed of repeated high and low conductivity materials suitable for implantation in the rat sciatic nerve model for nerve repair were evaluated in vivo and were superior to silicone conduits. These results suggest that biphasic conducting conduits capable of maintaining mechanical properties without inducing compression injuries while generating repeated electric fields are a promising tool for acceleration of peripheral nerve repair to previously untreatable patients.

Biomimetic Hydrogel Applications and Challenges in Bone, Cartilage, and Nerve Repair

Tissue engineering and regenerative medicine is a highly sought-after field for researchers aiming to compensate and repair defective tissues. However, the design and development of suitable scaffold materials with bioactivity for application in tissue repair and regeneration has been a great challenge. In recent years, biomimetic hydrogels have shown great possibilities for use in tissue engineering, where they can tune mechanical properties and biological properties through functional chemical modifications. Also, biomimetic hydrogels provide three-dimensional (3D) network spatial structures that can imitate normal tissue microenvironments and integrate cells, scaffolds, and bioactive substances for tissue repair and regeneration. Despite the growing interest in various hydrogels for biomedical use in previous decades, there are still many aspects of biomimetic hydrogels that need to be understood for biomedical and clinical trial applications. This review systematically describes the preparation of biomimetic hydrogels and their characteristics, and it details the use of biomimetic hydrogels in bone, cartilage, and nerve tissue repair. In addition, this review outlines the application of biomimetic hydrogels in bone, cartilage, and neural tissues regarding drug delivery. In particular, the advantages and shortcomings of biomimetic hydrogels in biomaterial tissue engineering are highlighted, and future research directions are proposed.

Gelatin nanofibers: Recent insights in synthesis, bio-medical applications and limitations

The use of gelatin and gelatin-blend polymers as environmentally safe polymers to synthesis electrospun nanofibers, has caused a revolution in the biomedical field. The development of efficient nanofibers has played a significant role in drug delivery, and for use in advanced scaffolds in regenerative medicine. Gelatin is an exceptional biopolymer, which is highly versatile, despite variations in the processing technology. The electrospinning process is an efficient technique for the manufacture of gelatin electrospun nanofibers (GNFs), as it is simple, efficient, and cost-effective. GNFs have higher porosity with large surface area and biocompatibility, despite that there are some drawbacks. These drawbacks include rapid degradation, poor mechanical strength, and complete dissolution, which limits the use of gelatin electrospun nanofibers in this form for biomedicine. Thus, these fibers need to be cross-linked, in order to control its solubility. This modification caused an improvement in the biological properties of GNFs, which made them suitable candidates for various biomedical applications, such as wound healing, drug delivery, bone regeneration, tubular scaffolding, skin, nerve, kidney, and cardiac tissue engineering. In this review an outline of electrospinning is shown with critical summary of literature evaluated with respect to the various applications of nanofibers-derived gelatin.

Worldwide productivity and research trend of publications concerning electroactive materials and spinal cord injury: A bibliometric study

Purpose: We investigated the current state and trends in the area during the previous 10 years using bibliometric approaches to evaluate the global scientific output of research on electroactive materials and spinal cord injury. Methods: Studies on spinal cord injury in electroactive materials that were published between 2012 and 2022 were located using the Web of science (WOS) datebase. The software programs bibliometrix R-package and CiteSpace were used to do quantitative analyses of annual publications, nation, author, institution, journal source, co-cited references, and keywords. The studies were categorized by the research's main points using a qualitative analysis, and publications having more than 10 citations each year. Results: In the final analysis, 1,330 relevant papers or reviews were included. There is an increased tendency in both the average annual citation rate and the number of publications in the discipline. The United States and the University of Toronto are the countries and institutions that have contributed the most to this discipline, respectively. The majority of authors are from the China and United States. Zhang Y is the author with the most published articles and holds the top position in the cited author h-index species. The journal with the highest number of published articles is "Disability and rehabilitation"; the journal is divided into four main areas including physics, materials, chemistry, molecular, and biology. The keyword analysis revealed a shift in research hotspots from schwann cell, fracture, and urinary disorders to carbon-based materials, functional recovery, and surgery. Analysis of qualitative data revealed that the role and mechanism of injectable conductive hydrogels in spinal cord healing after damage is a hot topic of current study, with the mechanism primarily focusing on the inhibition of oxidative stress (Nrf2) and apoptosis (Casepase 3). Conclusion: Our bibliometric analysis indicates that research on electroactive materials for spinal cord injury remains an active field of study. Moreover, contemporary research is concentrated on carbon-based materials, functional rehabilitation, and surgery.

Regulation of stem cell fate using nanostructure-mediated physical signals

One of the major issues in tissue engineering is regulation of stem cell differentiation toward specific lineages. Unlike biological and chemical signals, physical signals with adjustable properties can be applied to stem cells in a timely and localized manner, thus making them a hot topic for research in the fields of biomaterials, tissue engineering, and cell biology. According to the signals sensed by cells, physical signals used for regulating stem cell fate can be classified into six categories: mechanical, light, thermal, electrical, acoustic, and magnetic. In most cases, external macroscopic physical fields cannot be used to modulate stem cell fate, as only the localized physical signals accepted by the surface receptors can regulate stem cell differentiation via nanoscale fibrin polysaccharide fibers. However, surface receptors related to certain kinds of physical signals are still unknown. Recently, significant progress has been made in the development of functional materials for energy conversion. Consequently, localized physical fields can be produced by absorbing energy from an external physical field and subsequently releasing another type of localized energy through functional nanostructures. Based on the above concepts, we propose a methodology that can be utilized for stem cell engineering and for the regulation of stem cell fate via nanostructure-mediated physical signals. In this review, the combined effect of various approaches and mechanisms of physical signals provides a perspective on stem cell fate promotion by nanostructure-mediated physical signals. We expect that this review will aid the development of remote-controlled and wireless platforms to physically guide stem cell differentiation both in vitro and in vivo, using optimized stimulation parameters and mechanistic investigations while driving the progress of research in the fields of materials science, cell biology, and clinical research.

Perspective Insights to Bio-Nanomaterials for the Treatment of Neurological Disorders

The significance of biomaterials is well appreciated in nanotechnology, and its use has resulted in major advances in biomedical sciences. Although, currently, very little data is available on the clinical trial studies for treatment of neurological conditions, numerous promising advancements have been reported in drug delivery and regenerative therapies which can be applied in clinical practice. Among the commonly reported biomaterials in literature, the self-assembling peptides and hydrogels have been recognized as the most potential candidate for treatment of common neurological conditions such as Alzheimer's, Parkinson's, spinal cord injury, stroke and tumors. The hydrogels, specifically, offer advantages like flexibility and porosity, and mimics the properties of the extracellular matrix of the central nervous system. These factors make them an ideal scaffold for drug delivery through the blood-brain barrier and tissue regeneration (using stem cells). Thus, the use of biomaterials as suitable matrix for therapeutic purposes has emerged as a promising area of neurosciences. In this review, we describe the application of biomaterials, and the current advances, in treatment of statistically common neurological disorders.

A Comparative Analysis of the Structure and Biological Properties of Films and Microfibrous Scaffolds Based on Silk Fibroin

A comparative analysis of the structure and biological properties of silk fibroin constructions was performed. Three groups of constructions were obtained: films obtained by casting an aqueous solution of silk fibroin and electrospun microfibrous scaffolds based on silk fibroin, with the addition of 30% gelatin per total protein weight. The internal structures of the films and single fibers of the microfibrous scaffolds consisted of densely packed globule structures; the surface area to volume ratios and volume porosities of the microfibrous scaffolds were calculated. All constructions were non-toxic for cells and provide high levels of adhesion and proliferation. The high regenerative potential of the constructions was demonstrated in a rat full-thickness skin wound healing model. The constructions accelerated healing by an average of 15 days and can be considered to be promising constructions for various tasks of tissue engineering and regenerative medicine.

Simultaneous Modeling of Young's Modulus, Yield Stress, and Rupture Strain of Gelatin/Cellulose Acetate Microfibrous/Nanofibrous Scaffolds Using RSM

Electrospinning is a promising method to fabricate bioengineered scaffolds, thanks to utilizing various types of biopolymers, flexible structures, and also the diversity of output properties. Mechanical properties are one of the major components of scaffold design to fabricate an efficacious artificial substitute for the natural extracellular matrix. Additionally, fiber orientations, as one of the scaffold structural parameters, could play a crucial role in the application of fabricated fibrous scaffolds. In this study, gelatin was used as a highly biocompatible polymer in blend with cellulose acetate (CA), a polysaccharide, to enhance the achievable range of mechanical characteristics to fabricated fibrous electrospun scaffolds. By altering input variables, such as polymers concentration, weight ratio, and mandrel rotation speed, scaffolds with various mechanical and morphological properties could be achieved. As expected, the electrospun scaffold with a higher mandrel rotation speed shows higher fiber alignment. A wide range of mechanical properties were gained through different values of polymer ratio and total concentration. A general improvement in mechanical strength was observed by increasing the concentration and CA content in the solution, but contradictory effects, such as high viscosity in more concentrated solutions, influenced the mechanical characteristics as well. A response surface method was applied on experimental results in order to describe a continuous variation of Young's modulus, yield stress, and strain at rupture. A full quadratic version of equations with the 95% confidence level was applied for the response modeling. This model would be an aid for engineers to adjust mandrel rotation speed, solution concentration, and gelatin/CA ratio to achieve desired mechanical and structural properties.

Electrical stimulation of neural-differentiating iPSCs on novel coaxial electroconductive nanofibers

Neural tissue engineering strategies are paramount to create fully mature neurons, necessary for new therapeutic strategies for neurological diseases or the creation of reliable in vitro models. Scaffolds can provide physical support for these neurons and enable cues for enhancing neural cell differentiation, such as electrical current. Coaxial electrospinning fibers, designed to fulfill neural cell needs, bring together an electroconductive shell layer (PCL-PANI), able to mediate electrical stimulation of cells cultivated on fibers mesh surface, and a soft core layer (PGS), used to finetune fiber diameter (951 ± 465 nm) and mechanical properties (1.3 ± 0.2 MPa). Those dual functional coaxial fibers are electroconductive (0.063 ± 0.029 S cm-1, stable over 21 days) and biodegradable (72% weigh loss in 12 hours upon human lipase accelerated assay). For the first time, the long-term effects of electrical stimulation on induced neural progenitor cells were studied using such fibers. The results show increase in neural maturation (upregulation of MAP2, NEF-H and SYP), up-regulation of glutamatergic marker genes (VGLUT1 - 15-fold) and voltage-sensitive channels (SCN1α - 12-fold, CACNA1C - 32-fold), and a down-regulation of GABAergic marker (GAD67 - 0.09-fold), as detected by qRT-PCR. Therefore, this study suggest a shift from an inhibitory to an excitatory neural cell profile. This work shows that the PGS/PCL-PANI coaxial fibers here developed have potential applications in neural tissue engineering.

Applications of nanomaterials in tissue engineering

Recent advancement in nanotechnology has brought prominent benefits in tissue engineering, which has been used to repair or reconstruct damaged tissues or organs and design smart drug delivery systems. With numerous applications of nanomaterials in tissue engineering, it is vital to choose appropriate nanomaterials for different tissue engineering applications because of the tissue heterogeneity. Indeed, the use of nanomaterials in tissue engineering is directly determined by the choice. In this review, we mainly introduced the use of nanomaterials in tissue engineering. First, the basic characteristics, preparation and characterization methods of the types of nanomaterials are introduced briefly, followed by a detailed description of the application and research progress of nanomaterials in tissue engineering and drug delivery. Finally, the existing challenges and prospects for future applications of nanomaterials in tissue engineering are discussed.

Scientific description about the types, synthesis, functionalization, characterization application, challenges and prospects of nanomaterials in tissue engineering.

Biomaterials for Neural Tissue Engineering

The therapy of neural nerve injuries that involve the disruption of axonal pathways or axonal tracts has taken a new dimension with the development of tissue engineering techniques. When peripheral nerve injury (PNI), spinal cord injury (SCI), traumatic brain injury (TBI), or neurodegenerative disease occur, the intricate architecture undergoes alterations leading to growth inhibition and loss of guidance through large distance. To improve the limitations of purely cell-based therapies, the neural tissue engineering philosophy has emerged. Efforts are being made to produce an ideal scaffold based on synthetic and natural polymers that match the exact biological and mechanical properties of the tissue. Furthermore, through combining several components (biomaterials, cells, molecules), axonal regrowth is facilitated to obtain a functional recovery of the neural nerve diseases. The main objective of this review is to investigate the recent approaches and applications of neural tissue engineering approaches.

A State-of-the-Art of Functional Scaffolds for 3D Nervous Tissue Regeneration

Exploring and developing multifunctional intelligent biomaterials is crucial to improve next-generation therapies in tissue engineering and regenerative medicine. Recent findings show how distinct characteristics of in situ microenvironment can be mimicked by using different biomaterials. In vivo tissue architecture is characterized by the interconnection between cells and specific components of the extracellular matrix (ECM). Last evidence shows the importance of the structure and composition of the ECM in the development of cellular and molecular techniques, to achieve the best biodegradable and bioactive biomaterial compatible to human physiology. Such biomaterials provide specialized bioactive signals to regulate the surrounding biological habitat, through the progression of wound healing and biomaterial integration. The connection between stem cells and biomaterials stimulate the occurrence of specific modifications in terms of cell properties and fate, influencing then processes such as self-renewal, cell adhesion and differentiation. Recent studies in the field of tissue engineering and regenerative medicine have shown to deal with a broad area of applications, offering the most efficient and suitable strategies to neural repair and regeneration, drawing attention towards the potential use of biomaterials as 3D tools for in vitro neurodevelopment of tissue models, both in physiological and pathological conditions. In this direction, there are several tools supporting cell regeneration, which associate cytokines and other soluble factors delivery through the scaffold, and different approaches considering the features of the biomaterials, for an increased functionalization of the scaffold and for a better promotion of neural proliferation and cells-ECM interplay. In fact, 3D scaffolds need to ensure a progressive and regular delivery of cytokines, growth factors, or biomolecules, and moreover they should serve as a guide and support for injured tissues. It is also possible to create scaffolds with different layers, each one possessing different physical and biochemical aspects, able to provide at the same time organization, support and maintenance of the specific cell phenotype and diversified ECM morphogenesis. Our review summarizes the most recent advancements in functional materials, which are crucial to achieve the best performance and at the same time, to overcome the current limitations in tissue engineering and nervous tissue regeneration.

Natural-Based Biomaterials for Peripheral Nerve Injury Repair

Peripheral nerve injury treatment is a relevant problem because of nerve lesion high incidence and because of unsatisfactory regeneration after severe injuries, thus resulting in a reduced patient's life quality. To repair severe nerve injuries characterized by substance loss and to improve the regeneration outcome at both motor and sensory level, different strategies have been investigated. Although autograft remains the gold standard technique, a growing number of research articles concerning nerve conduit use has been reported in the last years. Nerve conduits aim to overcome autograft disadvantages, but they must satisfy some requirements to be suitable for nerve repair. A universal ideal conduit does not exist, since conduit properties have to be evaluated case by case; nevertheless, because of their high biocompatibility and biodegradability, natural-based biomaterials have great potentiality to be used to produce nerve guides. Although they share many characteristics with synthetic biomaterials, natural-based biomaterials should also be preferable because of their extraction sources; indeed, these biomaterials are obtained from different renewable sources or food waste, thus reducing environmental impact and enhancing sustainability in comparison to synthetic ones. This review reports the strengths and weaknesses of natural-based biomaterials used for manufacturing peripheral nerve conduits, analyzing the interactions between natural-based biomaterials and biological environment. Particular attention was paid to the description of the preclinical outcome of nerve regeneration in injury repaired with the different natural-based conduits.

Palmatine-loaded electrospun poly(ε-caprolactone)/gelatin nanofibrous scaffolds accelerate wound healing and inhibit hypertrophic scar formation in a rabbit ear model

Hypertrophic scar (HS) has been considered as a great concern for patients and a challenging problem for clinicians as it can cause functional debility, cosmetic disfigurement and psychological trauma. Although many methods have been developed to prevent and treat HS, the scarless healing is still a worldwide medical problem. In this study, palmatine-loaded poly(ε-caprolactone)/gelatin nanofibrous scaffolds (PCL/GE/PALs) were fabricated by electrospinning, and their effects on wound healing and HS formation were investigated. These nanofiber mats exhibit good antibacterial and antioxidant activities. In vitro studies indicate PCL/GE/PAL scaffolds can facilitate the adhesion, spreading and proliferation of L929 fibroblasts. In vivo tests demonstrate the full-thickness wounds treated with PCL/GE/PAL scaffolds heal about 3.5 days earlier than those in the control group. Scar elevation index measurements and histological analyses reveal PCL/GE/PAL scaffolds significantly inhibit HS formation, with the decrease in the thickness of dermis and epidermis, the number of fibroblasts, as well as the density of collagen and microvascular. Accelerating wound healing and inhibiting HS formation of these scaffolds are contributed to the sustained release of palmatine. The present work validates the potential use of palmatine-loaded electrospun nanofibrous scaffold PCL/GE/PALs as a functional wound dressing for healing wounds and preventing HS formation.

3D multiphoton lithography using biocompatible polymers with specific mechanical properties

The fabrication of two- and three-dimensional scaffolds mimicking the extracellular matrix and providing cell stimulation is of high importance in biology and material science. We show two new, biocompatible polymers, which can be 3D structured via multiphoton lithography, and determine their mechanical properties. Atomic force microscopy analysis of structures with sub-micron feature sizes reveals Young's modulus values in the 100 MPa range. Assessment of biocompatibility of the new resins was done by cultivating human umbilical vein endothelial cells on two-dimensionally structured substrates for four days. The cell density and presence of apoptotic cells has been quantified.

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.

The Cellular and Molecular Patterns Involved in the Neural Differentiation of Adipose-Derived Stem Cells

Injuries to the nervous system cause serious problems among affected patients by preventing them from the possibility of living a normal life. As this tissue possesses a reduced capacity of self-regeneration currently, lots of different strategies are being developed in order to make the regeneration in the nervous system possible. Among them, tissue engineering and stem cell-based therapies are to date very exploded fields and tremendous progress has been made in this direction. As the two main components of the nervous system, react differently to injuries and behave different during disease, it is clear that two separate regeneration approaches have been taken into consideration during development of treatment. Special attention is constantly given to the potential of adipose-derived stem cells for this kind of application. Due to the fact that they present remarkable properties, they can easily be obtained and have demonstrated that are capable of engaging in neural and glial lineages, adipose-derived stem cells are promising tools for the field of nervous system regeneration. Moreover, new insights into epigenetic control and modifications during the differentiation of adipose-derived stem cells towards the neural liege could provide new methods to maximize the regeneration process. In this review, we summarize the current applications of adipose-derived stem cells for neural regeneration and discuss in-depth molecular patterns involved in the differentiation of adipose-derived stem cells in neuron-like cells and Schwann-like cells.

Design of hydrogel-based scaffolds for the treatment of spinal cord injuries

Hydrogel-based scaffold design approaches for the treatment of spinal cord injuries.

High-Dose Neural Stem/Progenitor Cell Transplantation Increases Engraftment and Neuronal Distribution and Promotes Functional Recovery in Rats after Acutely Severe Spinal Cord Injury

Severe spinal cord injury (SCI) leads to permanent, complete paraplegia and places considerable mental and economic burdens on patients, compared with mild to moderate SCI. However, the dose-related effects of the neural stem/precursor cell (NSPC) transplantation on the injury microenvironment, NSPC survival, axonal growth, neuronal distribution, the composition of neurons, oligodendrocytes, and astrocytes in the lesion area and functional recovery have not yet been quantitatively evaluated in the context of severe SCI. In our study, we acutely transplanted 2.5 × 10⁴ or 1.5 × 10⁵ NSPCs/μl into the site of transection SCI. We found that high-dose NSPC transplantation exerted immunomodulatory and neuroprotective effects in the acute phase of severe SCI. In addition, one week later, a remarkable positive relationship was observed between the transplantation dose and the number of surviving NSPCs in severe SCI. At 8 weeks postgrafting, subjects that received the higher cell dose exhibited abundant nerve regeneration, extensive neuronal distribution, increased proportions of neurons and oligodendrocytes, and nascent functional neural network formation in the lesion area. Notably, a significant functional recovery was also observed. Our data suggest that it is important to consider potential dose-related effects on donor cell survival, neuronal distribution, and locomotor recovery in the development of preclinical NSPC transplantation therapy for severe SCI.

Cross-Linking Strategies for Electrospun Gelatin Scaffolds

Electrospinning is an exceptional technology to fabricate sub-micrometric fiber scaffolds for regenerative medicine applications and to mimic the morphology and the chemistry of the natural extracellular matrix (ECM). Although most synthetic and natural polymers can be electrospun, gelatin frequently represents a material of choice due to the presence of cell-interactive motifs, its wide availability, low cost, easy processability, and biodegradability. However, cross-linking is required to stabilize the structure of the electrospun matrices and avoid gelatin dissolution at body temperature. Different physical and chemical cross-linking protocols have been described to improve electrospun gelatin stability and to preserve the morphological fibrous arrangement of the electrospun gelatin scaffolds. Here, we review the main current strategies. For each method, the cross-linking mechanism and its efficiency, the influence of electrospinning parameters, and the resulting fiber morphology are considered. The main drawbacks as well as the open challenges are also discussed.

Neural regeneration therapies for Alzheimer's and Parkinson's disease-related disorders

Neurodegenerative diseases are devastating mental illnesses without a cure. Alzheimer's disease (AD) characterized by memory loss, multiple cognitive impairments, and changes in personality and behavior. Although tremendous progress has made in understanding the basic biology in disease processes in AD and PD, we still do not have early detectable biomarkers for these diseases. Just in the United States alone, federal and nonfederal funding agencies have spent billions of dollars on clinical trials aimed at finding drugs, but we still do not have a drug or an agent that can slow the AD or PD disease process. One primary reason for this disappointing result may be that the clinical trials enroll patients with AD or PD at advances stages. Although many drugs and agents are tested preclinical and are promising, in human clinical trials, they are mostly ineffective in slowing disease progression. One therapy that has been promising is 'stem cell therapy' based on cell culture and pre-clinical studies. In the few clinical studies that have investigated therapies in clinical trials with AD and PD patients at stage I. The therapies, such as stem cell transplantation - appear to delay the symptoms in AD and PD. The purpose of this article is to describe clinical trials using 1) stem cell transplantation methods in AD and PD mouse models and 2) regenerative medicine in AD and PD mouse models, and 3) the current status of investigating preclinical stem cell transplantation in patients with AD and PD.

Mimicking growth factors: role of small molecule scaffold additives in promoting tissue regeneration and repair

The primary aim of tissue engineering scaffolds is to mimic the in vivo environment and promote tissue growth. In this quest, a number of strategies have been developed such as enhancing cell-material interactions through modulation of scaffold physico-chemical parameters. However, more is required for scaffolds to relate to the cell natural environment. Growth factors (GFs) secreted by cells and extracellular matrix (ECM) are involved in both normal repair and abnormal remodeling. The direct use of GFs on their own or when incorporated within scaffolds represent a number of challenges such as release rate, stability and shelf-life. Small molecules have been proposed as promising alternatives to GFs as they are able to minimize or overcome many shortcomings of GFs, in particular immune response and instability. Despite the promise of small molecules in various TE applications, their direct use is limited by nonspecific adverse effects on non-target tissues and organs. Hence, they have been incorporated within scaffolds to localize their actions and control their release to target sites. However, scanty rationale is available which links the chemical structure of these molecules with their mode of action. We herewith review various small molecules either when used on their own or when incorporated within polymeric carriers/scaffolds for bone, cartilage, neural, adipose and skin tissue regeneration.

Spinning and Applications of Bioinspired Fiber Systems

Natural fiber systems provide inspirations for artificial fiber spinning and applications. Through a long process of trial and error, great progress has been made in recent years. The natural fiber itself, especially silks, and the formation mechanism are better understood, and some of the essential factors are implemented in artificial spinning methods, benefiting from advanced manufacturing technologies. In addition, fiber-based materials produced via bioinspired spinning methods find an increasingly wide range of biomedical, optoelectronic, and environmental engineering applications. This paper reviews recent developments in the spinning and application of bioinspired fiber systems, introduces natural fiber and spinning processes and artificial spinning methods, and discusses applications of artificial fiber materials. Views on remaining challenges and the perspective on future trends are also proposed.

The adsorption of phosphate-buffered saline to model films composed of nanofibrillated cellulose and gelatin

Phosphate-buffered saline (PBS) adsorption on model films composed of gelatin and nanofibrillated celluloses (NFCs) with different aldehyde and carboxyl contents was studied by means of the quartz crystal microbalance with dissipation (QCM-D) technique in this study. The results showed that frequency shift (Δ f) due to PBS adsorption increased with increasing gelatin content to 50% in NFC-containing films. The dissipation shift and adsorption rate of PBS followed the same trend. Model films with NFC-1 having 1.22 mmol/g aldehyde and 0.6 mmol/g carboxyl groups adsorbed more PBS than those consisting of NFC-2 with 0.25 mmol/g aldehyde and 1.15 mmol/g carboxyl groups except for film composed of 50% gelatin. However, adsorption rate of PBS was found to be slower for NFC-1 containing film because the acetal and amidol bonds formed by functional groups in the network of cellulose and gelatin needed more time to let PBS migrate into the films.

Current and novel polymeric biomaterials for neural tissue engineering

The nervous system is a crucial component of the body and damages to this system, either by of injury or disease, can result in serious or potentially lethal consequences. Restoring the damaged nervous system is a great challenge due to the complex physiology system and limited regenerative capacity.Polymers, either synthetic or natural in origin, have been extensively evaluated as a solution for restoring functions in damaged neural tissues. Polymers offer a wide range of versatility, in particular regarding shape and mechanical characteristics, and their biocompatibility is unmatched by other biomaterials, such as metals and ceramics. Several studies have shown that polymers can be shaped into suitable support structures, including nerve conduits, scaffolds, and electrospun matrices, capable of improving the regeneration of damaged neural tissues. In general, natural polymers offer the advantage of better biocompatibility and bioactivity, while synthetic or non-natural polymers have better mechanical properties and structural stability. Often, combinations of the two allow for the development of polymeric conduits able to mimic the native physiological environment of healthy neural tissues and, consequently, regulate cell behaviour and support the regeneration of injured nervous tissues.Currently, most of neural tissue engineering applications are in pre-clinical study, in particular for use in the central nervous system, however collagen polymer conduits aimed at regeneration of peripheral nerves have already been successfully tested in clinical trials.This review highlights different types of natural and synthetic polymers used in neural tissue engineering and their advantages and disadvantages for neural regeneration.

Cellular Response to Surface Morphology: Electrospinning and Computational Modeling

Surface properties of biomaterials, such as chemistry and morphology, have a major role in modulating cellular behavior and therefore impact on the development of high-performance devices for biomedical applications, such as scaffolds for tissue engineering and systems for drug delivery. Opportunely-designed micro- and nanostructures provides a unique way of controlling cell-biomaterial interaction. This mini-review discusses the current research on the use of electrospinning (extrusion of polymer nanofibers upon the application of an electric field) as effective technique to fabricate patterns of micro- and nano-scale resolution, and the corresponding biological studies. The focus is on the effect of morphological cues, including fiber alignment, porosity and surface roughness of electrospun mats, to direct cell migration and to influence cell adhesion, differentiation and proliferation. Experimental studies are combined with computational models that predict and correlate the surface composition of a biomaterial with the response of cells in contact with it. The use of predictive models can facilitate the rational design of new bio-interfaces.

Drug-Loaded Halloysite Nanotube-Reinforced Electrospun Alginate-Based Nanofibrous Scaffolds with Sustained Antimicrobial Protection

Halloysite nanotube (HNT)-reinforced alginate-based nanofibrous scaffolds were successfully fabricated by electrospinning to mimic the natural extracellular matrix (ECM) structure which is beneficial for tissue regeneration. An antiseptic drug, cephalexin (CEF)-loaded HNT, was incorporated into the alginate-based matrix to obtain sustained antimicrobial protection and robust mechanical properties, the key criteria for tissue engineering applications. Electron microscopic imaging and drug release studies revealed that CEF had penetrated into the lumen space of the HNT and also deposited on the outer walls, with a total loading capacity of 30 wt %. Moreover, the diameter of alginate-based nanofibers of the scaffolds ranged from 40 to 522 nm with well-aligned HNTs, resulting in superior mechanical properties. For instance, the addition of 5% (w/w) HNT improved the tensile strength (σ) and elastic modulus by 3-fold and 2-fold, respectively, compared to those of the alginate-based scaffolds without HNT. The fabricated scaffolds exhibited remarkable antimicrobial properties against both Gram-negative and Gram-positive bacteria, and the cytotoxicity studies confirmed the nontoxicity of the fabricated scaffolds. Drug release kinetics showed that CEF inside HNTs diffuses within 24 h and that the diffusion of the drug is delayed by 7 days once the CEF-loaded HNTs are incorporated into the alginate-based nanofibers. These fabricated alginate-based electrospun scaffolds with enhanced mechanical properties and sustained antimicrobial protection hold great potential to be used as artificial ECM scaffolds for tissue engineering applications.

Electrospinning: An enabling nanotechnology platform for drug delivery and regenerative medicine

Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.

Polypyrrole increases branching and neurite extension by Neuro2A cells on PBAT ultrathin fibers

We present a methodology for production and application of electrospun hybrid materials containing commercial polyester (poly (butylene adipate-co-terephthalate; PBAT), and a conductive polymer (polypyrrole; PPy) as scaffold for neuronal growth and differentiation. The physical-chemical properties of the scaffolds and optimization of the electrospinning parameters are presented. The electrospun scaffolds are biocompatible and allow proper adhesion and spread of mesenchymal stem cells (MSCs). Fibers produced with PBAT with or without PPy were used as scaffold for Neuro2a mouse neuroblastoma cells adhesion and differentiation. Neuro2a adhered to PBAT and PBAT/PPy2% scaffolds without laminin coating. However, Neuro2a failed to differentiate in PBAT when stimulated by treatment with retinoic acid (RA), but differentiated in PBAT/PPy2% fibers. We hypothesize that PBAT hydrophobicity inhibited proper spreading and further differentiation, and inhibition was overcome by coating the PBAT fibers with laminin. We conclude that fibers produced with the combination of PBAT and PPy can support neuronal differentiation.

[Effect of cells in the epimysium conduit on the regeneration of peripheral nerve]

Objective

To investigate the effect of cells in the epimysium conduit (EMC) on the regeneration of sciatic nerve of mice.

Methods

The epimysium of the 8-week-old male C57BL/6J enhanced green fluorescent protein (EGFP) mouse was trimmed to a size of 5 mm×3 mm, and prepared in a tubular shape (ie, EMC). Some epimysia were treated with different irradiation doses (0, 15, 20, 25, 30, 35 Gy) to inhibit cells migration. Then the number of migrating cells were counted, and the epimysia with the least migrating cells were selected to prepare EMC. Some epimysia were subjected to decellularization treatment and prepared EMC. HE and Masson staining were used to identify the decellularization effect. Twenty-four C57BL/6J wild-type mice were used to prepare a 3-mm-long sciatic nerve defect of right hind limb model and randomly divided into 3 groups ( n=8). EMC (group A), EMC after cell migration inhibition treatment (group B), and decellularized EMC (group C) were used to repair defects. At 16 weeks after operation, the midline of the regenerating nerve was taken for gross, toluidine blue staining, immunofluorescence staining, and transmission electron microscopy.

Results

At 15 days, the number of migrating cells gradually decreased with the increase of irradiation dose. There was no significant difference between 30 Gy group and 35 Gy group ( P>0.05); there were significant differences between the other groups ( P<0.05). The epimysium after treatment with 35 Gy irradiation dose was selected for the in vivo experiment. After the decellularization of the epimysium, no nucleus was found in the epimysium and the epimysium could be sutured to prepare EMC. At 16 weeks after operation, the nerves in all groups were recanalized. The sciatic nerve was the thickest in group A, followed by group B, and the finest in group C. Immunofluorescence staining showed that the EGFP cells in group A were surrounded by regenerated axons. Toluidine blue staining and transmission electron microscopy observation showed that the number of regenerated axons and the thickness of regenerated myelin sheath in group A were significantly better than those in groups B and C ( P<0.05). There was no significant difference between groups B and C ( P>0.05).

Conclusion

The cellular components of the epimysium participate in and promote the regeneration of the sciatic nerve in mice.

Hydrolytic Degradation and Mechanical Stability of Poly(ε-Caprolactone)/Reduced Graphene Oxide Membranes as Scaffolds for In Vitro Neural Tissue Regeneration

The present work studies the functional behavior of novel poly(ε-caprolactone) (PCL) membranes functionalized with reduced graphene oxide (rGO) nanoplatelets under simulated in vitro culture conditions (phosphate buffer solution (PBS) at 37 °C) during 1 year, in order to elucidate their applicability as scaffolds for in vitro neural regeneration. The morphological, chemical, and DSC results demonstrated that high internal porosity of the membranes facilitated water permeation and procured an accelerated hydrolytic degradation throughout the bulk pathway. Therefore, similar molecular weight reduction, from 80 kDa to 33 kDa for the control PCL, and to 27 kDa for PCL/rGO membranes, at the end of the study, was observed. After 1 year of hydrolytic degradation, though monomers coming from the hydrolytic cleavage of PCL diffused towards the PBS medium, the pH was barely affected, and the rGO nanoplatelets mainly remained in the membranes which envisaged low cytotoxic effect. On the other hand, the presence of rGO nanomaterials accelerated the loss of mechanical stability of the membranes. However, it is envisioned that the gradual degradation of the PCL/rGO membranes could facilitate cells infiltration, interconnectivity, and tissue formation.

Combined Effect of Ultrasound Stimulations and Autoclaving on the Enhancement of Antibacterial Activity of ZnO and SiO₂/ZnO Nanoparticles

This study investigates the antibacterial activity (ABA) of suspensions of pure ZnO nanoparticles (ZnO-NPs) and mesoporous silica doped with ZnO (ZnO-UVM7), as well as electrospun nanofibers containing those nanoparticles. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of these two materials were also determined under the same conditions. The results showed a concentration-dependent effect of antibacterial nanoparticles on the viability of Escherichia coli (E. coli). Moreover, the combination of the stimulations and sterilization considerably enhanced the antimicrobial activity (AMA) of the ZnO suspensions. Poly (lactic acid) (PLA) solutions in 2,2,2-trifluoroethanol (TFE) were mixed with different contents of nanoparticles and spun into nonwoven mats by the electrospinning process. The morphology of the mats was analyzed by scanning electron microscopy (SEM). The amount of nanoparticles contained in the mats was determined by thermogravimetric analysis (TGA). The obtained PLA-based mats showed a fibrous morphology, with an average diameter ranging from 350 to 450 nm, a porosity above 85%, but with the nanoparticles agglomeration on their surface. TGA analysis showed that the loss of ZnO-NPs increased with the increase of ZnO-NPs content in the PLA solutions and reached 79% for 1 wt % of ZnO-NPs, which was mainly due to the aggregation of nanoparticles in solution. The ABA of the obtained PLA mats was evaluated by the dynamic method according to the ASTM standard E2149. The results showed that, above an optimal concentration, the nanoparticle agglomeration reduced the antimicrobial efficiency of PLA mats. These mats have potential features for use as antimicrobial food packaging material.

Influence of topography of nanofibrous scaffolds on functionality of engineered neural tissue

Properly engineered scaffolds combined with functional neurons can be instrumental for the effective repair of the neural tissue. In particular, it is essential to investigate how three-dimensional (3D) systems and topographical features can impact on neuronal activity to obtain engineered functional neural tissues. In this study, polyphenylene sulfone (PPSu) scaffolds constituted by randomly distributed or aligned electrospun nanofibers were fabricated to evaluate the neural activity in 3D culture environments for the first time. The obtained results demonstrated that the nanofibers can successfully support the adhesion and growth of neural stem cells (NSCs) and enhance neuronal differentiation compared to 2D substrates. In addition, NSCs could spread and migrate along the aligned fibers. The percentage of active NSC-derived neurons and the overall network activity in the fibrous substrates were also remarkably enhanced. Finally, the data of neuronal activity showed not only that the neurons cultured on the nanofibers are part of a functional network, but also that their activity increases, and the direction of neural signals can be controlled in the aligned 3D scaffolds.

3D scaffolds for brain tissue regeneration: architectural challenges

Critical analysis of experimental studies on 3D scaffolds for brain tissue engineering.