Carbon nanomaterials for nerve tissue stimulation and regeneration

Graphene and its hybrid nanocomposite: A Metamorphoses elevation in the field of tissue engineering

In this discourse, we delve into the manifold applications of graphene-based nanomaterials (GBNs) in the realm of biomedicine. Graphene, characterized by its two-dimensional planar structure, superconductivity, mechanical robustness, chemical inertness, extensive surface area, and propitious biocompatibility, stands as an exemplary candidate for diverse biomedical utility. Graphene include various distinctive characteristics of its two-dimensional planar structure, enormous surface area, mechanical and chemical stability, high conductivity, and exceptional biocompatibility. We investigate graphene and its diverse derivatives, which include reduced graphene oxides (rGOs), graphene oxides (GOs), and graphene composites, with a focus on elucidating the unique attributes relevant to their biomedical utility. In this review article it highlighted the unique properties of graphene, synthesis methods of graphene and functionalization methods of graphene. In the quest for novel materials to advance regenerative medicine, researchers have increasingly turned their attention to graphene-based materials, which have emerged as a prominent innovation in recent years. Notably, it highlights their applications in the regeneration of various tissues, including nerves, skeletal muscle, bones, skin, cardiac tissue, cartilage, and adipose tissue, as well as their influence on induced pluripotent stem cells, marking significant breakthroughs in the field of regenerative medicine. Additionally, this review article explores future prospects in this evolving area of study.

Graphene-based nanomaterials for peripheral nerve regeneration

Emerging nanotechnologies offer numerous opportunities in the field of regenerative medicine and have been widely explored to design novel scaffolds for the regeneration and stimulation of nerve tissue. In this review, we focus on peripheral nerve regeneration. First, we introduce the biomedical problem and the present status of nerve conduits that can be used to guide, fasten and enhance regeneration. Then, we thoroughly discuss graphene as an emerging candidate in nerve tissue engineering, in light of its chemical, tribological and electrical properties. We introduce the graphene forms commonly used as neural interfaces, briefly review their applications, and discuss their potential toxicity. We then focus on the adoption of graphene in peripheral nervous system applications, a research field that has gained in the last years ever-increasing attention. We discuss the potential integration of graphene in guidance conduits, and critically review graphene interaction not only with peripheral neurons, but also with non-neural cells involved in nerve regeneration; indeed, the latter have recently emerged as central players in modulating the immune and inflammatory response and accelerating the growth of new tissue.

Oxidation-treated carbon nanotube yarns accelerate neurite outgrowth and induce axonal regeneration in peripheral nerve defect

Carbon nanotubes (CNTs) have the potential to promote peripheral nerve regeneration, although with limited capacity and foreign body reaction. This study investigated whether CNTs hydrophilized by oxidation can improve peripheral nerve regeneration and reduce foreign body reactions and inflammation. Three different artificial nerve conduit models were created using CNTs treated with ozone (O group), strong acid (SA group), and untreated (P group). They were implanted into a rat sciatic nerve defect model and evaluated after 8 and 16 weeks. At 16 weeks, the SA group showed significant recovery in functional and electrophysiological evaluations compared with the others. At 8 weeks, histological examination revealed a significant increase in the density of regenerated neurofilament and decreased foreign body giant cells in the SA group compared with the others. Oxidation-treated CNTs improved biocompatibility, induced nerve regeneration, and inhibited foreign-body reactions.

A Bioresorbable and Conductive Scaffold Integrating Silicon Membranes for Peripheral Nerve Regeneration

Peripheral nerve injury represents one of the most common types of traumatic damage, severely impairing motor and sensory functions, and posttraumatic nerve regeneration remains a major challenge. Electrical cues are critical bioactive factors that promote nerve regrowth, and bioartificial scaffolds incorporating conductive materials to enhance the endogenous electrical field have been demonstrated to be effective. The utilization of fully biodegradable scaffolds can eliminate material residues, and circumvent the need for secondary retrieval procedures. Here, a fully bioresorbable and conductive nerve scaffold integrating N-type silicon (Si) membranes is proposed, which can deliver both structural guidance and electrical cues for the repair of nerve defects. The entire scaffold is fully biodegradable, and the introduction of N-type Si can significantly promote the proliferation and production of neurotrophic factors of Schwann cells and enhance the calcium activity of dorsal root ganglion (DRG) neurons. The conductive scaffolds enable accelerated nerve regeneration and motor functional recovery in rodents with sciatic nerve transection injuries. This work sheds light on the advancement of bioresorbable and electrically active materials to achieve desirable neural interfaces and improved therapeutic outcomes, offering essential strategies for regenerative medicine.

How to fix a broken heart-designing biofunctional cues for effective, environmentally-friendly cardiac tissue engineering

Cardiovascular diseases bear strong socioeconomic and ecological impact on the worldwide healthcare system. A large consumption of goods, use of polymer-based cardiovascular biomaterials, and long hospitalization times add up to an extensive carbon footprint on the environment often turning out to be ineffective at healing such cardiovascular diseases. On the other hand, cardiac cell toxicity is among the most severe but common side effect of drugs used to treat numerous diseases from COVID-19 to diabetes, often resulting in the withdrawal of such pharmaceuticals from the market. Currently, most patients that have suffered from cardiovascular disease will never fully recover. All of these factors further contribute to the extensive negative toll pharmaceutical, biotechnological, and biomedical companies have on the environment. Hence, there is a dire need to develop new environmentally-friendly strategies that on the one hand would promise cardiac tissue regeneration after damage and on the other hand would offer solutions for the fast screening of drugs to ensure that they do not cause cardiovascular toxicity. Importantly, both require one thing-a mature, functioning cardiac tissue that can be fabricated in a fast, reliable, and repeatable manner from environmentally friendly biomaterials in the lab. This is not an easy task to complete as numerous approaches have been undertaken, separately and combined, to achieve it. This review gathers such strategies and provides insights into which succeed or fail and what is needed for the field of environmentally-friendly cardiac tissue engineering to prosper.

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.

Surface Area of Graphene Governs Its Neurotoxicity

Due to their unique physicochemical properties, graphene and its derivatives are widely exploited for biomedical applications. It has been shown that graphene may exert different degrees of toxicity in in vivo or in vitro models when administered via different routes and penetrated through physiological barriers, subsequently being distributed within tissues or located within cells. In this study, in vitro neurotoxicity of graphene with different surface areas (150 and 750 m²/g) was examined on dopaminergic neuron model cells. SH-SY5Y cells were treated with graphene possessing two different surface areas (150 and 750 m²/g) in different concentrations between 400 and 3.125 μg/mL, and the cytotoxic and genotoxic effects were investigated. Both sizes of graphene have shown increased cell viability in decreasing concentrations. Cell damage increased with higher surface area. Lactate dehydrogenase (LDH) results have concluded that the viability loss of the cells is not through membrane damage. Neither of the two graphene types showed damage through lipid peroxidation (MDA) oxidative stress pathway. Glutathione (GSH) values increased within the first 24 and 48 h for both types of graphene. This increase suggests that graphene has an antioxidant effect on the SH-SY5Y model neurons. Comet analysis shows that graphene does not show genotoxicity on either surface area. Although there are many studies on graphene and its derivatives on their use with different cells in the literature, there are conflicting results in these studies, and most of the literature is focused on graphene oxide. Among these studies, no study examining the effect of graphene surface areas on the cell was found. Our study contributes to the literature in terms of examining the cytotoxic and genotoxic behavior of graphene with different surface areas.

Lactide and Ethylene Brassylate-Based Thermoplastic Elastomers and Their Nanocomposites with Carbon Nanotubes: Synthesis, Mechanical Properties and Interaction with Astrocytes

Polylactide (PLA) is among the most commonly used polymers for biomedical applications thanks to its biodegradability and cytocompatibility. However, its inherent stiffness and brittleness are clearly inappropriate for the regeneration of soft tissues (e.g., neural tissue), which demands biomaterials with soft and elastomeric behavior capable of resembling the mechanical properties of the native tissue. In this work, both L- and D,L-lactide were copolymerized with ethylene brassylate, a macrolactone that represents a promising alternative to previously studied comonomers (e.g., caprolactone) due to its natural origin. The resulting copolymers showed an elastomeric behavior characterized by relatively low Young's modulus, high elongation at break and high strain recovery capacity. The thermoplastic nature of the resulting copolymers allows the incorporation of nanofillers (i.e., carbon nanotubes) that further enable the modulation of their mechanical properties. Additionally, nanostructured scaffolds were easily fabricated through a thermo-pressing process with the aid of a commercially available silicon stamp, providing geometrical cues for the adhesion and elongation of cells representative of the nervous system (i.e., astrocytes). Accordingly, the lactide and ethylene brassylate-based copolymers synthesized herein represent an interesting formulation for the development of polymeric scaffolds intended to be used in the regeneration of soft tissues, thanks to their adjustable mechanical properties, thermoplastic nature and observed cytocompatibility.

Recent advances and trends in the applications of MXene nanomaterials for tissue engineering and regeneration

MXene, as a new two-dimensional nanomaterial, is endowed with lots of particular properties, such as large surface area, excellent conductivity, biocompatibility, biodegradability, hydrophilicity, antibacterial activity, and so on. In the past few years, MXene nanomaterials have become a rising star in biomedical fields including biological imaging, tumor diagnosis, biosensor, and tissue engineering. In this review, we sum up the recent applications of MXene nanomaterials in the field of tissue engineering and regeneration. First, we briefly introduced the synthesis and surface modification engineering of MXene. Then we focused on the application and development of MXene and MXene-based composites in skin, bone, nerve and heart tissue engineering. Uniquely, we also paid attention to some research on MXene with few achievements at present but might become a new trend in tissue engineering and regeneration in the future. Finally, this paper will also discuss several challenges faced by MXene nanomaterials in the clinical application of tissue engineering.

In-Vitro Evaluation of Novel Polycaprolactone/ Chitosan/ Carbon Nano Tube Scaffold for Tissue Regeneration

BACKGROUND

Many patients lose their organs or tissues due to disease, trauma, or a variety of genetic disorders. Tissue engineering is a multidisciplinary science to regenerate or restore tissue or organ function and an appropriate scaffold is the first and certainly a crucial step in tissue engineering strategies.

OBJECTIVE

The purpose of this study is to fabricate and evaluate the in-vitro response of porous nano Polycaprolactone (PCL)/ chitosan/ multi-wall carbon nanotube (MWCNTs) scaffold for tissue regeneration.

MATERIAL AND METHODS

In this experimental research, a novel scaffold containing MWCNTs in polycaprolactone/chitosan nanofibrous scaffold was synthesized by electrospinning technique.

RESULTS

According to scanning electron microscopy SEM images, by increasing the number of MWCNT in the scaffold by 2%, the average diameter decreased significantly for fabricated scaffolds with 5% MWCNTs. Based on the results, the scaffolds plunged from submicron to nanoscale fibers at about 80 nm. In addition, by adding more MWCNT to the nanofibrous scaffold, the biodegradation rate was decreased by 32%. However, mechanical characterization demonstrates that the higher level of MWCNT increases young modulus by 96%, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay illustrated that MWCNTs could enhance bioactivity and cell- scaffold relationship in addition to alkaline phosphatase (ALP).

CONCLUSION

MWCNT significantly improves the physical and mechanical properties of fabricated scaffolds and in-vitro assessment demonstrated that the prepared nanofibrous scaffold containing 4% MWCNT could be a very useful biocompatible material for tissue engineering.

Combination Therapy Using Nanomaterials and Stem Cells to Treat Spinal Cord Injuries

As a part of the central nervous system, the spinal cord (SC) provides most of the communications between the brain and other parts of the body. Any damage to SC interrupts this communication, leading to serious problems, which may remain for the rest of their life. Due to its significant impact on patients' quality of life and its exorbitant medical costs, SC injury (SCI) is known as one of the most challengeable diseases in the world. Thus, it is critical to introduce highly translatable therapeutic platforms for SCI treatment. So far, different strategies have been introduced, among which utilizing various types of stem cells is one of the most interesting ones. The capability of stem cells to differentiate into several types of cell lines makes them promising candidates for the regeneration of injured tissues. One of the other interesting and novel strategies for SCI treatment is the application of nanomaterials, which could appear as a carrier for therapeutic agents or as a platform for culturing the cells. Combining these two approaches, stem cells and nanomaterials, could provide promising therapeutic strategies for SCI management. Accordingly, in this review we have summarized some of the recent advancements in which the applications of different types of stem cells and nanomaterials, alone and in combination forms, were evaluated for SCI treatment.

Gold nanorods decorated polycaprolactone/cellulose acetate hybrid scaffold for PC12 cells proliferation

Synthetic and natural polymers have recently received considerable attention due to the exclusive potential for supporting the regenerative cellular processes in peripheral nerve injuries (PNIs). Gold nanorods (GNRs) decorated polycaprolactone (PCL)/cellulose acetate (CA) nanocomposite (PCL/CA/GNR) were fabricated via electrospinning to improve PC12 cells attachment and growth or scaffold cues. Transmission electron microscopy (TEM) corroborated the GNR distribution (23 ± 2 nm length and 3/1 Aspect ratio) and suitable average dimension of 800 nm for the fibers; also, scanning electron microscopy (SEM) represented block-free and smooth fibers without perturbation. Because of gold nanorods incorporation, electrical conductivity of PCL/CA/GNR increased ~21%. Water contact angle data emphasized PCL/CA/GNR surface is more wettable that PCL/CA (<90° at 62 s). Real-time PCR technique (RT-PCR) demonstrated overexpression of β-tubulin and microtubule-associated protein 2 (MAP2) on PCL/CA/GNR compared to PCL/CA composite. Additionally, evaluated of the maturation and neurogenic differentiation of PC12 cells emphasized overexpression of nestin and β-tubulin by Immunocytochemistry staining onto PCL/CA/GNR in comparison to PCL/CA composite. Notably, these recently developed hybrid scaffolds could be considered for peripheral nerve injury (PNI) regeneration.

Physical and chemical properties of carbon nanotubes in view of mechanistic neuroscience investigations. Some outlook from condensed matter, materials science and physical chemistry

The open border between non-living and living matter, suggested by increasingly emerging fields of nanoscience interfaced to biological systems, requires a detailed knowledge of nanomaterials properties. An account of the wide spectrum of phenomena, belonging to physical chemistry of interfaces, materials science, solid state physics at the nanoscale and bioelectrochemistry, thus is acquainted for a comprehensive application of carbon nanotubes interphased with neuron cells. This review points out a number of conceptual tools to further address the ongoing advances in coupling neuronal networks with (carbon) nanotube meshworks, and to deepen the basic issues that govern a biological cell or tissue interacting with a nanomaterial. Emphasis is given here to the properties and roles of carbon nanotube systems at relevant spatiotemporal scales of individual molecules, junctions and molecular layers, as well as to the point of view of a condensed matter or materials scientist. Carbon nanotube interactions with blood-brain barrier, drug delivery, biocompatibility and functionalization issues are also regarded.

Neurodegenerative disorders management: state-of-art and prospects of nano-biotechnology

Neurodegenerative disorders (NDs) are highly prevalent among the aging population. It affects primarily the central nervous system (CNS) but the effects are also observed in the peripheral nervous system. Neural degeneration is a progressive loss of structure and function of neurons, which may ultimately involve cell death. Such patients suffer from debilitating memory loss and altered motor coordination which bring up non-affordable and unavoidable socio-economic burdens. Due to the unavailability of specific therapeutics and diagnostics, the necessity to control or manage NDs raised the demand to investigate and develop efficient alternative approaches. Keeping trends and advancements in view, this report describes both state-of-the-art and challenges in nano-biotechnology-based approaches to manage NDs, toward personalized healthcare management. Sincere efforts are being made to customize nano-theragnostics to control: therapeutic cargo packaging, delivery to the brain, nanomedicine of higher efficacy, deep brain stimulation, implanted stimulation, and managing brain cell functioning. These advancements are useful to design future therapy based on the severity of the patient's neurodegenerative disease. However, we observe a lack of knowledge shared among scientists of a variety of expertise to explore this multi-disciplinary research field for NDs management. Consequently, this review will provide a guideline platform that will be useful in developing novel smart nano-therapies by considering the aspects and advantages of nano-biotechnology to manage NDs in a personalized manner. Nano-biotechnology-based approaches have been proposed as effective and affordable alternatives at the clinical level due to recent advancements in nanotechnology-assisted theragnostics, targeted delivery, higher efficacy, and minimal side effects.

Synthesis, structure, and properties of carbon/carbon composites artificial rib for chest wall reconstruction

In this work, braided carbon fiber reinforced carbon matrix composites (3D-C/C composites) are prepared by chemical vapor infiltration process. Their composite structure, mechanical properties, biocompatibility, and in vivo experiments are investigated and compared with those of traditional 2.5D-C/C composites and titanium alloys TC4. The results show that 3D-C/C composites are composed of reinforced braided carbon fiber bundles and pyrolytic carbon matrix and provide 51% open pores with a size larger than 100 μm for tissue adhesion and growth. The Young's modulus of 3D-C/C composites is about 5 GPa, much smaller than those of 2.5D-C/C composites and TC4, while close to the autogenous bone. 3D-C/C composites have a higher tensile strength (167 MPa) and larger elongation (5.0%) than 2.5D-C/C composites (81 MPa and 0.7%), and do not show obvious degradation after 1 × 106 cyclic tensile loading. The 3D-C/C composites display good biocompatibility and have almost no artifacts on CT imaging. The in vivo experiment reveals that 3D-C/C composites artificial ribs implanted in dogs do not show displacement or fracture in 1 year, and there are no obvious proliferation and inflammation in the soft tissues around 3D-C/C composites implant. Our findings demonstrate that 3D-C/C composites are suitable for chest wall reconstruction and present great potentials in artificial bones.

Piezoelectric and Magnetoelectric Scaffolds for Tissue Regeneration and Biomedicine: A Review

Electric fields are ubiquitous throughout the body, playing important role in a multitude of biological processes including osteo-regeneration, cell signaling, nerve regeneration, cardiac function, and DNA replication. An increased understanding of the role of electric fields in the body has led to the development of devices for biomedical applications that incorporate electromagnetic fields as an intrinsically novel functionality (e.g., bioactuators, biosensors, cardiac/neural electrodes, and tissues scaffolds). However, in the majority of the aforementioned devices, an implanted power supply is necessary for operation, and therefore requires highly invasive procedures. Thus, the ability to apply electric fields in a minimally invasive manner to remote areas of the body remains a critical and unmet need. Here, we report on the potential of magnetoelectric (ME)-based composites to overcome this challenge. ME materials are capable of producing localized electric fields in response to an applied magnetic field, which the body is permeable to. Yet, the use of ME materials for biomedical applications is just beginning to be explored. Here, we present on the potential of ME materials to be utilized in biomedical applications. This will be presented alongside current state-of-the-art for in vitro and in vivo electrical stimulation of cells and tissues. We will discuss key findings in the field, while also identifying challenges, such as the synthesis and characterization of biocompatible ME materials, challenges in experimental design, and opportunities for future research that would lead to the increased development of ME biomaterials and their applications.

Design of graphenic nanocomposites containing chitosan and polyethylene glycol for spinal cord injury improvement

Advanced therapeutic strategies include the incorporation of biomaterials, which has been identified as an effective method in treating unsolved diseases, such as spinal cord injury. During the acute phase, cascade responses involving cystic cavitation, fibrous glial scar formation, and myelin-associated dissuasive accumulation occur in the microenvironment of the spinal cord lesion. Graphene oxide (GO)-based materials, due to their extraordinary chemical, electrical and mechanical properties and easy to modify structure, are considered as rising stars in biomaterial and tissue engineering. In order to enhance the biodegradability and biocompatibility of GO, cell proliferation may be appropriately designed and situated at the lesion site. In this study, chitosan (CS) and polyethylene glycol (PEG) were grafted onto GO sheets. CS is a natural non-toxic polymer with good solubility and high biocompatible potential that has been used as an anti-inflammatory and anti-oxidant agent. Furthermore, PEG, a synthetic neuroprotective polymer, was used to develop the pharmacokinetic activity and reduce the toxicity of GO. Herein we report a novel nanocomposite consisting of PEG and CS with a potential advantage in spinal tissue regeneration. The preliminary in vitro study on mesenchymal stem cells (MSCs) has demonstrated that the prepared nanocomposites are not only non-toxic but also increase (by nearly 10%) cell growth. Finally, the use of mixed nanocomposites in the spinal cord injury (SCI) model resulted in good repair and inflammation decline after two weeks, such that walking and functional recovery scores of the hind limbs of mice were improved by an average of 6 points in the treatment group.

Herein we report a novel nanocomposite consisting of PEG and CS with a potential advantage in spinal tissue regeneration.

Advancements in Therapeutics via 3D Printed Multifunctional Architectures from Dispersed 2D Nanomaterial Inks

2D nanomaterials (2DNMs) possess fascinating properties and are found in multifarious devices and applications including energy storage devices, new generation of battery technologies, sensor devices, and more recently in biomedical applications. Their use in biomedical applications such as tissue engineering, photothermal therapy, neural regeneration, and drug delivery has opened new horizons in treatment of age-old ailments. It is also a rapidly developing area of advanced research. A new approach of integrating 3D printing (3DP), a layer-by-layer deposition technique for building structures, along with 2DNM multifunctional inks, has gained considerable attention in recent times, especially in biomedical applications. With the ever-growing demand in healthcare industry for novel, efficient, and rapid technologies for therapeutic treatment methods, 3DP structures of 2DNMs provide vast scope for evolution of a new generation of biomedical devices. Recent advances in 3DP structures of dispersed 2DNM inks with established high-performance biomedical properties are focused on. The advantages of their 3D structures, the sustainable formulation methods of such inks, and their feasible printing methods are also covered. Subsequently, it deals with the therapeutic applications of some already researched 3DP structures of 2DNMs and concludes with highlighting the challenges as well as the future directions of research in this area.

3D Printing and Bioprinting Nerve Conduits for Neural Tissue Engineering

Fabrication of nerve conduits for perfectly repairing or replacing damaged peripheral nerve is an urgent demand worldwide, but it is also a formidable clinical challenge. In the last decade, with the rapid development of manufacture technologies, 3D printing and bioprinting have been becoming remarkable stars in the field of neural engineering. In this review, we explore that the biomaterial inks (hydrogels, thermoplastic, and thermoset polyesters and composite) and bioinks have been selected for 3D printing and bioprinting of peripheral nerve conduits. This review covers 3D manufacturing technologies, including extrusion printing, inkjet printing, stereolithography, and bioprinting with inclusion of cells, bioactive molecules, and drugs. Finally, an outlook on the future directions of 3D printing and 4D printing in customizable nerve therapies is presented.

Graphene Promotes Axon Elongation through Local Stall of Nerve Growth Factor Signaling Endosomes

Several works reported increased differentiation of neuronal cells grown on graphene; however, the molecular mechanism driving axon elongation on this material has remained elusive. Here, we study the axonal transport of nerve growth factor (NGF), the neurotrophin supporting development of peripheral neurons, as a key player in the time course of axonal elongation of dorsal root ganglion neurons on graphene. We find that graphene drastically reduces the number of retrogradely transported NGF vesicles in favor of a stalled population in the first 2 days of culture, in which the boost of axon elongation is observed. This correlates with a mutual charge redistribution, observed via Raman spectroscopy and electrophysiological recordings. Furthermore, ultrastructural analysis indicates a reduced microtubule distance and an elongated axonal topology. Thus, both electrophysiological and structural effects can account for graphene action on neuron development. Unraveling the molecular players underneath this interplay may open new avenues for axon regeneration applications.

Recent Advances in Carbon Nanotubes for Nervous Tissue Regeneration

Regenerative medicine has taken advantage of several nanomaterials for reparation of diseased or damaged tissues in the nervous system involved in memory, cognition, and movement. Electrical, thermal, mechanical, and biocompatibility aspects of carbon-based nanomaterials (nanotubes, graphene, fullerenes, and their derivatives) make them suitable candidates to drive nerve tissue repair and stimulation. This review article focuses on key recent advances on the use of carbon nanotube- (CNT-) based technologies on nerve tissue engineering, outlining how neurons interact with CNT interfaces for promoting neuronal differentiation, growth and network reconstruction. CNTs still represent strong candidates for use in therapies of neurodegenerative pathologies and spinal cord injuries.

Piezoelectric Scaffolds as Smart Materials for Neural Tissue Engineering

Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities, which still lacks an effective treatment. Tissue engineering in the post-injury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for either transplanted or resident cells. Tissue engineering relies on scaffolds for supporting cell differentiation and growth with recent emphasis on stimuli responsive scaffolds, sometimes called smart scaffolds. One of the representatives of this material group is piezoelectric scaffolds, being able to generate electrical charges under mechanical stimulation, which creates a real prospect for using such scaffolds in non-invasive therapy of neural tissue. This paper summarizes the recent knowledge on piezoelectric materials used for tissue engineering, especially neural tissue engineering. The most used materials for tissue engineering strategies are reported together with the main achievements, challenges, and future needs for research and actual therapies. This review provides thus a compilation of the most relevant results and strategies and serves as a starting point for novel research pathways in the most relevant and challenging open questions.

A standard method to synthesize Ag, Ag/Ge, Ag/TiO2, SnO2, and Ag/SnO2 nanomaterials using the HVPG technique

Nanotechnology is growing rapidly in the past few decades with the applications in several fields such as medicine, environment, energy, electronics, automotive, and aerospace. There are many methods used by researchers to synthesize nanomaterial. In this paper, Horizontal Vapor Phase Growth (HVPG) technique was successfully used to synthesize various nanomaterial and nanocomposite materials such as Ag, Ag/Ge, Ag/TiO2, SnO2, and Ag/SnO2. HVPG technique used a one-pot step to synthesize nanomaterials with 100 % purity of the results, affordable cost, and environmentally friendly. The method has two variables; growth temperature and curing time. Changing the variables create different shapes of nanomaterials. It also reported that the technique could be used to synthesize various nanomaterials consists of single or multi-material. This detailed method demonstrates the capability of the HVPG technique to synthesize nanomaterials, not only to grow the single shape of nanomaterials but also allow other nanomaterial shapes to grow in different parameter conditions. •HVPG technique successfully used to synthesize various nanomaterials.•Only 2 parameters used; curing time and growth temperature.•Purity result (100 %) with no pollutant.

Heat-treated carbon coatings on poly (l-lactide) foils for tissue engineering

Carbon-based materials have emerged as promising candidates for a wide variety of biomedical applications, including tissue engineering. We have developed a simple but unique technique for patterning carbon-based substrates in order to control cell adhesion, growth and phenotypic maturation. Carbon films were deposited on PLLA foils from distances of 3 to 7 cm. Subsequent heat-treatment (60 °C, 1 h) created lamellar structures with dimensions decreasing from micro- to nanoscale with increasing deposition distance. All carbon films improved the spreading and proliferation of human osteoblast-like MG 63 cells, and promoted the alignment of these cells along the lamellar structures. Similar alignment was observed in human osteoblast-like Saos-2 cells and in human dermal fibroblasts. Type I collagen fibers produced by Saos-2 cells and fibroblasts were also oriented along the lamellar structures. These structures increased the activity of alkaline phosphatase in Saos-2 cells. Carbon coatings also supported adhesion and growth of vascular endothelial and smooth muscle cells, particularly flatter non-heated carbon films. On these films, the continuity of the endothelial cell layer was better than on heat-treated lamellar surfaces. Heat-treated carbon-coated PLLA is therefore more suitable for bone and skin tissue engineering, while carbon-coated PLLA without heating is more appropriate for vascular tissue engineering.

Response of macrophages and neural cells in contact with reduced graphene oxide microfibers

Graphene-based materials are revealing a great promise for biomedical applications and demonstrating attractiveness for neural repair. In the context of neural tissue damage, the dialogue between neural and immune cells appears critical for driving regeneration, thus making the understanding of their relations pivotal. Herein, the acute response of RAW-264.7 macrophages on nanostructured reduced graphene oxide (rGO) microfibers has been evaluated through the analysis of cell parameters including proliferation, viability, intracellular content of reactive oxygen species, cell cycle, apoptosis, and cell size and complexity. The influence of the direct contact of rGO microfibers on their polarization towards M1 and M2 phenotypes has been studied by analyses of both M1 (CD80) and M2 (CD163) markers and the secretion of the inflammatory cytokines TNF-α and IL-6. Finally, the capability of these rGO microfibers to regulate neural stem cell differentiation has been also evaluated. Findings reveal that rGO microfibers inhibit the proliferation of RAW-264.7 macrophages without affecting their viability and cell cycle profiles. The presence of M1 and M2 macrophages on these microfibers was confirmed after 24 and 48 h, respectively, accompanied by a decrease in TNF-α and an increase in IL-6 cytokine secretion. These rGO microfibers were also able to support the formation of a highly interconnected neural culture composed of both neurons (map2⁺ cells) and glial cells (vimentin⁺ cells). These findings encourage further investigation of these microfibers as attractive biomaterials to interact with immune and neural cells, attempting to support wound healing and tissue repair after implantation.

Nanoscaffolds in promoting regeneration of the peripheral nervous system

The ability to surgically repair peripheral nerve injuries is urgently needed. However, traditional tissue engineering techniques, such as autologous nerve transplantation, have some limitations. Therefore, tissue engineered autologous nerve grafts have become a suitable choice for nerve repair. Novel tissue engineering techniques derived from nanostructured conduits have been shown to be superior to other successful functional neurological structures with different scaffolds in terms of providing the required structures and properties. Additionally, different biomaterials and growth factors have been added to nerve scaffolds to produce unique biological effects that promote nerve regeneration and functional recovery. This review summarizes the application of different nanoscaffolds in peripheral nerve repair and further analyzes how the nanoscaffolds promote peripheral nerve regeneration.

Biomaterial Scaffolds in Regenerative Therapy of the Central Nervous System

The central nervous system (CNS) is the most important section of the nervous system as it regulates the function of various organs. Injury to the CNS causes impairment of neurological functions in corresponding sites and further leads to long-term patient disability. CNS regeneration is difficult because of its poor response to treatment and, to date, no effective therapies have been found to rectify CNS injuries. Biomaterial scaffolds have been applied with promising results in regeneration medicine. They also show great potential in CNS regeneration for tissue repair and functional recovery. Biomaterial scaffolds are applied in CNS regeneration predominantly as hydrogels and biodegradable scaffolds. They can act as cellular supportive scaffolds to facilitate cell infiltration and proliferation. They can also be combined with cell therapy to repair CNS injury. This review discusses the categories and progression of the biomaterial scaffolds that are applied in CNS regeneration.

Peripheral Neuron Survival and Outgrowth on Graphene

Graphene displays properties that make it appealing for neuroregenerative medicine, yet its interaction with peripheral neurons has been scarcely investigated. Here, we culture on graphene two established models for peripheral neurons: PC12 cells and DRG primary neurons. We perform a nano-resolved analysis of polymeric coatings on graphene and combine optical microscopy and viability assays to assess the material cytocompatibility and influence on differentiation. We find that differentiated PC12 cells display a remarkably increased neurite length on graphene (up to 27%) with respect to controls. Notably, DRG primary neurons survive both on bare and coated graphene. They present dense axonal networks on coated graphene, while they form cell islets characterized by dense axonal bundles on uncoated graphene. These findings indicate that graphene holds potential for nerve tissue regeneration and might pave the road to novel concepts of active nerve conduits.

Graphene Based Materials in Neural Tissue Regeneration

Due to its extraordinary features such as large surface area, high electrical conductivity, chemical stability and mechanical properties, graphene attracts great interest in various fields of biomedical sciences including biosensors, cancer therapy, diagnosis and regenerative medicine. The use of graphene-based materials has been of great interest for the design of scaffolds that can promote neural tissue regeneration. Recent studies published over the last few years clearly show that graphene and graphene based materials promote adhesion, proliferation and differentiation of various cells including embryonic stem cells (ESC), neural stem cells (NSC), mesenchymal stem cells (MSC) and induced pluripotent stem cells (iPSC). Therefore graphene based materials are one of the promising nanoplatforms in regenerative medicine for neural tissue injury. With its unique topographic and chemical properties, graphene is used as a scaffold that could provide a bridge between regenerating nerves. More importantly, as a conductive substrate, graphene allows the continuation of electrical conduction between damaged nerve ends. The integration of supportive cells such as glial, neural precursor or stem cells in such a scaffold shows higher regeneration when compared to currently used neural autografts and nerve conduits. This review discusses the details of such studies involving graphene based materials with a special interest on neural stem cells, mesenchymal stem cells or pluripotent stem cells.

Promotion of SH-SY5Y Cell Growth by Gold Nanoparticles Modified with 6-Mercaptopurine and a Neuron-Penetrating Peptide

Much effort has been devoted to the discovery of effective biomaterials for nerve regeneration. Here, we reported a novel application of gold nanoparticles (AuNPs) modified with 6-mercaptopurine (6MP) and a neuron-penetrating peptide (RDP) as a neurophic agent to promote proliferation and neurite growth of human neuroblastoma (SH-SY5Y) cells. When the cells were treated with 6MP-AuNPs-RDP conjugates, they showed higher metabolic activity than the control. Moreover, SH-SY5Y cells were transplanted onto the surface coated with 6MP-AuNPs-RDP to examine the effect of neurite development. It can be concluded that 6MP-AuNPs-RDP attached to the cell surface and then internalized into cells, leading to a significant increase of neurite growth. Even though 6MP-AuNPs-RDP-treated cells were recovered from frozen storage, the cells still maintained constant growth, indicating that the cells have excellent tolerance to 6MP-AuNPs-RDP. The results suggested that the 6MP-AuNPs-RDP had promising potential to be developed as a neurophic nanomaterial for neuronal growth.

Graphene-Derived Materials Interfacing the Spinal Cord: Outstanding in Vitro and in Vivo Findings

The attractiveness of graphene-derived materials (GDMs) for neural applications has fueled their exploration as components of biomaterial interfaces contacting the brain and the spinal cord. In the last years, an increasing body of work has been published on the ability of these materials to create biocompatible and biofunctional substrates able to promote the growth and activity of neural cells in vitro and positively interact with neural tissues when implanted in vivo. Encouraging results in the central nervous tissue might impulse the study of GDMs towards preclinical arena. In this mini-review article, we revise the most relevant literature on the interaction of GDMs with the spinal cord. Studies involving the implantation of these materials in vivo in the injured spinal cord are first discussed, followed by models with spinal cord slides ex vivo and a final description of selected results with neural cells in vitro. A closing debate of the major conclusions of these results is presented to boost the investigation of GDMs in the field.

The application of graphene oxidized combining with decellularized scaffold to repair of sciatic nerve injury in rats

This paper combined the decellularized scaffold of sciatic nerve of rats with graphene oxidized (GO), studied and facilitated the regeneration of sciatic nerve of rats, and provided the basis for the clinical application of nanomaterials. GO was prepared through improving Hammer’s Method. Fourier Infrared Spectrum was used to scan and detect the functional groups in GO of sample by using the pellet method, the microcosmic morphological appearance of GO was observed by using the scanning electron microscope. The GO/decellularized scaffold were prepared and operation bridging of injured sciatic nerve was conducted by using the oscillation mixing method. BL-420F Biofunctional Experiment System was used to detect nerve action potential and the maximum tension value of muscles, and the fiber structure of nerve was observed under H-7650 Transmission Electron Microscope (TEM). Scanning electron microscope observed that GO presented a folded and curly single-layer sheet structure. It was soluble in water through ultrasound, brownish, the Fourier Transform Infrared Spectrometer detected the absorption peaks of carbonyl, hydroxy and carboxy, proving that the surface of GO material had many functional groups containing oxygen. Decellularized scaffold combining with GO was applied to repair injury of sciatic nerve, the nerve action potential, maximum tension value of muscle, wet weight value of gastrocnemius, thickness of gastrocnemius, thickness of myelin sheath and diameter of axon of the decellularized scaffold combining with GO group were obviously higher than the decellularized scaffold group and the self-rotating group, approaching to the normal value. All the data were represented by means ± standard deviation (x¯±s) and processed by adopting SPSS 11.0 software. Comparisons among groups were analyzed by variance, and the comparison of two means was detected by student t. The detection level adopted α = 0.05, when P < 0.05, it could be considered that there were significant differences. GO could combine with the biomaterial-decellularized scaffold to repair the injury of sciatic nerve and facilitate the regeneration of injured nerve. This provided new thoughts and theoretical & experimental bases for nanomaterials to be applied to clinic treatment of repair of nerve injury.

The Horizon of Materiobiology: A Perspective on Material-Guided Cell Behaviors and Tissue Engineering

Although the biological functions of cell and tissue can be regulated by biochemical factors (e.g., growth factors, hormones), the biophysical effects of materials on the regulation of biological activity are receiving more attention. In this Review, we systematically summarize the recent progress on how biomaterials with controllable properties (e.g., compositional/degradable dynamics, mechanical properties, 2D topography, and 3D geometry) can regulate cell behaviors (e.g., cell adhesion, spreading, proliferation, cell alignment, and the differentiation or self-maintenance of stem cells) and tissue/organ functions. How the biophysical features of materials influence tissue/organ regeneration have been elucidated. Current challenges and a perspective on the development of novel materials that can modulate specific biological functions are discussed. The interdependent relationship between biomaterials and biology leads us to propose the concept of "materiobiology", which is a scientific discipline that studies the biological effects of the properties of biomaterials on biological functions at cell, tissue, organ, and the whole organism levels. This Review highlights that it is more important to develop ECM-mimicking biomaterials having a self-regenerative capacity to stimulate tissue regeneration, instead of attempting to recreate the complexity of living tissues or tissue constructs ex vivo. The principles of materiobiology may benefit the development of novel biomaterials providing combinative bioactive cues to activate the migration of stem cells from endogenous reservoirs (i.e., cell niches), stimulate robust and scalable self-healing mechanisms, and unlock the body's innate powers of regeneration.

Efficiency testing of artificial neural networks in predicting the properties of carbon nanomaterials as potential systems for nervous tissue stimulation and regeneration

A new method of predicting the properties of carbon nanomaterials from carbon nanotubes and graphene oxide, using electrophoretic deposition (EPD) on a metal surface, was investigated. The main goal is to obtain the basis for nervous tissue stimulation and regeneration. Because of the many variations of the EPD method, costly and time-consuming experiments are necessary for optimization of the produced systems. To limit such costs and workload, we propose a neural network-based model that can predict the properties of selected carbon nanomaterial systems before they are produced. The choice of neural networks as predictive learning models is based on many studies in the literature that report neural models as good interpretations of real-life processes. The use of a neural network model can reduce experimentation with unpromising methods of systems processing and preparation. Instead, it allows a focus on experiments with these systems, which are promising according to the prediction given by the neural model. The performed tests showed that the proposed method of predictive learning of carbon nanomaterial properties is easy and effective. The experiments showed that the prediction results were consistent with those obtained in the real system.

Biocompatible electrically conductive nanofibers from inorganic-organic shape memory polymers

A porous shape memory scaffold with both biomimetic structures and electrical conductivity properties is highly promising for nerve tissue engineering applications. In this study, a new shape memory polyurethane polymer which consists of inorganic polydimethylsiloxane (PDMS) segments with organic poly(ε-caprolactone) (PCL) segments was synthesized. Based on this poly(PCL/PDMS urethane), a series of electrically conductive nanofibers were electrospun by incorporating different amounts of carbon-black. Our results showed that after adding carbon black into nanofibers, the fiber diameters increased from 399±76 to 619±138nm, the crystallinity decreased from 33 to 25% and the resistivity reduced from 3.6 GΩ/mm to 1.8 kΩ/mm. Carbon black did not significantly influence the shape memory properties of the resulting nanofibers, and all the composite nanofibers exhibited decent shape recovery ratios of >90% and shape fixity ratios of >82% even after 5 thermo-mechanical cycles. PC12 cells were cultured on the shape memory nanofibers and the composite scaffolds showed good biocompatibility by promoting cell-cell interactions. Our study demonstrated that the poly(PCL/PDMS urethane)/carbon-black nanofibers with shape memory properties could be potentially used as smart 4-dimensional (4D) scaffolds for nerve tissue regeneration.

Scaffolds based on hyaluronan and carbon nanotubes gels

Physico-chemical and mechanical properties of hyaluronic acid/carbon nanotubes nanohybrids have been correlated with the proportion of inorganic nanophase and the preparation procedure. The mass fraction of -COOH functionalized carbon nanotubes was varied from 0 to 0.05. Hyaluronic acid was crosslinked with divinyl sulfone to improve its stability in aqueous media and allow its handling as a hydrogel. A series of samples was dried by lyophilization to obtain porous scaffolds whereas another was room-dried allowing the collapse of the hybrid structures. The porosity of the former, together with the tighter packing of hyaluronic acid chains, results in a lower water absorption and lower mechanical properties in the swollen state, because of the easier water diffusion. The presence of even a small amount of carbon nanotubes (mass fraction of 0.05) limits even more the swelling of the matrix, owing probably to hybrid interactions. These nanohybrids do not seem to degrade significantly during 14 days in water or enzymatic medium.

Upconversion Nanoparticles for Bioimaging and Regenerative Medicine

Nanomaterials are proving useful for regenerative medicine in combination with stem cell therapy. Nanoparticles (NPs) can be administrated and targeted to desired tissues or organs and subsequently be used in non-invasive real-time visualization and tracking of cells by means of different imaging techniques, can act as therapeutic agent nanocarriers, and can also serve as scaffolds to guide the growth of new tissue. NPs can be of different chemical nature, such as gold, iron oxide, cadmium selenide, and carbon, and have the potential to be used in regenerative medicine. However, there are still many issues to be solved, such as toxicity, stability, and resident time. Upconversion NPs have relevant properties such as (i) low toxicity, (ii) capability to absorb light in an optical region where absorption in tissues is minimal and penetration is optimal (note they can also be designed to emit in the near-infrared region), and (iii) they can be used in multiplexing and multimodal imaging. An overview on the potentiality of upconversion materials in regenerative medicine is given.

Immunomodulatory and angiogenic responses induced by graphene oxide scaffolds in chronic spinal hemisected rats

Attractive physic-chemical features of graphene oxide (GO) and promising results in vitro with neural cells encourage its exploration for biomedical applications including neural regeneration. Fueled by previous findings at the subacute state, we herein investigate for the first time chronic tissue responses (at 30 days) to 3D scaffolds composed of partially reduced GO (rGO) when implanted in the injured rat spinal cord. These studies aim to define fibrotic, inflammatory and angiogenic changes at the lesion site induced by the chronic implantation of these porous structures. Injured animals receiving no scaffolds show badly structured lesion zones and more cavities than those carrying rGO materials, thus pointing out a significant role of the scaffolds in injury stabilization and sealing. Notably, GFAP(+) cells and pro-regenerative macrophages are evident at their interface. Moreover, rGO scaffolds support angiogenesis around and, more importantly, inside their structure, with abundant and functional new blood vessels in whose proximities inside the scaffolds some regenerated neuronal axons are found. On the contrary, lesion areas without rGO scaffolds show a diminished quantity of blood vessels and no axons at all. These findings provide a foundation for the usefulness of graphene-based materials in the design of novel biomaterials for spinal cord repair and encourage further investigation for the understanding of neural tissue responses to this kind of materials in vivo.

A peroxiredoxin-based proteinaceous scaffold for the growth and differentiation of neuronal cells and tumour stem cells in the absence of prodifferentiation agents

The use of nanoscale materials in the design of scaffolds for CNS tissue is increasing, due to their ability to promote cell adhesion, to mimic an extracellular matrix microenvironment and to interact with neuronal membranes. In this framework, one of the major challenges when using undifferentiated neural cells is how to control the differentiation process. Here we report the characterization of a scaffold based on the self-assembled nanotubes of a mutant of the protein peroxiredoxin (from Schistosoma mansoni or Bos taurus), which allows the growth and differentiation of a model neuronal cell line (SHSY5Y). The results obtained demonstrate that SHSY5Y cells grow without any sign of toxicity and develop a neuronal phenotype, as shown by the expression of neuronal differentiation markers, without the use of any differentiation supplement, even in the presence of serum. The prodifferentiation effect is demonstrated to be dependent on the formation of the protein nanotube, since a wild-type (WT) form of the peroxiredoxin from Schistosoma mansoni does not induce any differentiation. The protein scaffold was also able to induce the spread of glioblastoma cancer stem cells growing in neurospheres and allowing the acquisition of a neuron-like morphology, as well as of immature rat cortical neurons. This protein used here as coating agent may be suggested for the development of scaffolds for tissue regeneration or anti-tumour devices. Copyright © 2016 John Wiley & Sons, Ltd.

Peptide nanostructures in biomedical technology

Nanostructures of peptides have been investigated for biomedical applications due to their unique mechanical and electrical properties in addition to their excellent biocompatibility. Peptides may form fibrils, spheres and tubes in nanoscale depending on the formation conditions. These peptide nanostructures can be used in electrical, medical, dental, and environmental applications. Applications of these nanostructures include, but are not limited to, electronic devices, biosensing, medical imaging and diagnosis, drug delivery, tissue engineering and stem cell research. This review offers a discussion of basic synthesis methods, properties and application of these nanomaterials. The review concludes with recommendations and future directions for peptide nanostructures. WIREs Nanomed Nanobiotechnol 2016, 8:730-743. doi: 10.1002/wnan.1393 For further resources related to this article, please visit the WIREs website.

Thermally sensitive conductive hydrogel using amphiphilic crosslinker self-assembled carbon nanotube to enhance neurite outgrowth and promote spinal cord regeneration

We studied a SWNT–PNIPAAM hydrogel for its potential role in the growth of SH-SY5Y cells and found it can enhance neurite outgrowth when adding electrical stimulation in vitro.

Upconversion Nanoparticles for Bioimaging and Regenerative Medicine

Nanomaterials are proving useful for regenerative medicine in combination with stem cell therapy. Nanoparticles (NPs) can be administrated and targeted to desired tissues or organs and subsequently be used in non-invasive real-time visualization and tracking of cells by means of different imaging techniques, can act as therapeutic agent nanocarriers, and can also serve as scaffolds to guide the growth of new tissue. NPs can be of different chemical nature, such as gold, iron oxide, cadmium selenide, and carbon, and have the potential to be used in regenerative medicine. However, there are still many issues to be solved, such as toxicity, stability, and resident time. Upconversion NPs have relevant properties such as (i) low toxicity, (ii) capability to absorb light in an optical region where absorption in tissues is minimal and penetration is optimal (note they can also be designed to emit in the near-infrared region), and (iii) they can be used in multiplexing and multimodal imaging. An overview on the potentiality of upconversion materials in regenerative medicine is given.