Biofunctionalized carbon nanotubes in neural regeneration: a mini-review

Caffeic acid recarbonization: A green chemistry, sustainable carbon nano material platform to intervene in neurodegeneration induced by emerging contaminants

Environmental agents such as pesticides, weedicides and herbicides (collectively referred to as pesticides) are associated with the onset and pathogenesis of neurodegenerative disorders such as Parkinson's (PD) and Alzheimer's (AD) diseases. The development of blood-brain barrier (BBB)-penetrating therapeutic candidates to both prevent and treat the aforementioned xenotoxicant-induced neurodegenerative disorders remains an unmet need. Here, we examine whether caffeic-acid based Carbon Quantum Dots (CACQDs) can intervene in pesticide-associated onset and progress of the PD phenotype. Pulse-chase fluorescence analyses revealed that CACQDs intervene in the soluble-to-toxic transformation of the amyloid-forming protein model Hen Egg White Lysozyme (HEWL). The sp2-rich CACQDs also scavenged free radicals, a milestone along the PD trajectory. In-vitro, CACQDs introduced into a human neuroblastoma-derived cell line (SH-SY5Y) demonstrated negligible cytotoxicity up to 5 mg/mL and protected the cell line against oxidative stress-induced neuronal injury induced by the pesticide and potent neurotoxin, paraquat. Our findings suggest that the potentially BBB-penetrating CACQDs derived from caffeic acid hold promise for mitigating neurodegenerative disorders associated with environmental pesticides and xenobiotic neurotoxicants. Importantly, CACQDs sourced from coffee, coupled with their facile synthesis, represent a sustainable, green chemistry platform for generating interventional candidates in neurodegeneration.

Biomimetic engineered approaches for neural tissue engineering: Spinal cord injury

The healing process for spinal cord injuries is complex and presents many challenges. Current advances in nerve regeneration are based on promising tissue engineering techniques, However, the chances of success depend on better mimicking the extracellular matrix (ECM) of neural tissue and better supporting neurons in a three-dimensional environment. The ECM provides excellent biological conditions, including desirable morphological features, electrical conductivity, and chemical compositions for neuron attachment, proliferation and function. This review outlines the rationale for developing a construct for neuron regrowth in spinal cord injury using appropriate biomaterials and scaffolding techniques.

Artificial nerve graft constructed by coculture of activated Schwann cells and human hair keratin for repair of peripheral nerve defects

Studies have shown that human hair keratin (HHK) has no antigenicity and excellent mechanical properties. Schwann cells, as unique glial cells in the peripheral nervous system, can be induced by interleukin-1β to secrete nerve growth factor, which promotes neural regeneration. Therefore, HHK with Schwann cells may be a more effective approach to repair nerve defects than HHK without Schwann cells. In this study, we established an artificial nerve graft by loading an HHK skeleton with activated Schwann cells. We found that the longitudinal HHK microfilament structure provided adhesion medium, space and direction for Schwann cells, and promoted Schwann cell growth and nerve fiber regeneration. In addition, interleukin-1β not only activates Schwann cells, but also strengthens their activity and increases the expression of nerve growth factors. Activated Schwann cells activate macrophages, and activated macrophages secrete interleukin-1β, which maintains the activity of Schwann cells. Thus, a beneficial cycle forms and promotes nerve repair. Furthermore, our studies have found that the newly constructed artificial nerve graft promotes the improvements in nerve conduction function and motor function in rats with sciatic nerve injury, and increases the expression of nerve injury repair factors fibroblast growth factor 2 and human transforming growth factor B receptor 2. These findings suggest that this artificial nerve graft effectively repairs peripheral nerve injury.

Fullerenes for the treatment of cancer: an emerging tool

Cancer is a most common cause of mortality globally. Available medicines possess severe side effects owing to their non-specific targeting. Hence, there is a need of an alternative in the healthcare system that should have high efficacy with the least side effects, also having the ability to achieve site-specific targeting and be reproducible. This is possible with the help of fullerenes. Fullerenes are having the unique physicochemical and photosensitizer properties. This article discusses the synthesis, functionalization, mechanism, various properties, and applications of C60 fullerenes in the treatment of cancer. The review article also addresses the various factors influencing the activity of fullerenes including the environmental conditions, toxicity profile, and future prospective.

Photoacoustic Carbon Nanotubes Embedded Silk Scaffolds for Neural Stimulation and Regeneration

Neural interfaces using biocompatible scaffolds provide crucial properties, such as cell adhesion, structural support, and mass transport, for the functional repair of nerve injuries and neurodegenerative diseases. Neural stimulation has also been found to be effective in promoting neural regeneration. This work provides a generalized strategy to integrate photoacoustic (PA) neural stimulation into hydrogel scaffolds using a nanocomposite hydrogel approach. Specifically, polyethylene glycol (PEG)-functionalized carbon nanotubes (CNT), highly efficient photoacoustic agents, are embedded into silk fibroin to form biocompatible and soft photoacoustic materials. We show that these photoacoustic functional scaffolds enable nongenetic activation of neurons with a spatial precision defined by the area of light illumination, promoting neuron regeneration. These CNT/silk scaffolds offered reliable and repeatable photoacoustic neural stimulation, and 94% of photoacoustic-stimulated neurons exhibit a fluorescence change larger than 10% in calcium imaging in the light-illuminated area. The on-demand photoacoustic stimulation increased neurite outgrowth by 1.74-fold in a rat dorsal root ganglion model, when compared to the unstimulated group. We also confirmed that promoted neurite outgrowth by photoacoustic stimulation is associated with an increased concentration of neurotrophic factor (BDNF). As a multifunctional neural scaffold, CNT/silk scaffolds demonstrated nongenetic PA neural stimulation functions and promoted neurite outgrowth, providing an additional method for nonpharmacological neural regeneration.

Regenerative rehabilitation with conductive biomaterials for spinal cord injury

The individual approaches of regenerative medicine efforts alone and rehabilitation efforts alone have not yet fully restored function after severe spinal cord injury (SCI). Regenerative rehabilitation may be leveraged to promote regeneration of the spinal cord tissue, and promote reorganization of the regenerated neural pathways and intact spinal circuits for better functional recovery for SCI. Conductive biomaterials may be a linchpin that empowers the synergy between regenerative medicine and rehabilitation approaches, as electrical stimulation applied to the spinal cord could facilitate neural reorganization. In this review, we discuss current regenerative medicine approaches in clinical trials and the rehabilitation, or neuromodulation, approaches for SCI, along with their respective translational limitations. Furthermore, we review the translational potential, in a surgical context, of conductive biomaterials (e.g., conductive polymers, carbon-based materials, metallic nanoparticle-based materials) as they pertain to SCI. While pre-formed scaffolds may be difficult to translate to human contusion SCIs, injectable composites that contain blended conductive components and can form within the injury may be more translational. However, given that there are currently no in vivo SCI studies that evaluated conductive materials combined with rehabilitation approaches, we discuss several limitations of conductive biomaterials, including demonstrating safety and efficacy, that will need to be addressed in the future for conductive biomaterials to become SCI therapeutics. Even so, the use of conductive biomaterials creates a synergistic opportunity to merge the fields of regenerative medicine and rehabilitation and redefine what regenerative rehabilitation means for the spinal cord. STATEMENT OF SIGNIFICANCE: For spinal cord injury (SCI), the individual approaches of regenerative medicine and rehabilitation are insufficient to fully restore functional recovery; however, the goal of regenerative rehabilitation is to combine these two disparate fields to maximize the functional outcomes. Concepts similar to regenerative rehabilitation for SCI have been discussed in several reviews, but for the first time, this review considers how conductive biomaterials may synergize the two approaches. We cover current regenerative medicine and rehabilitation approaches for SCI, and the translational advantages and disadvantages, in a surgical context, of conductive biomaterials used in biomedical applications that may be additionally applied to SCI. Furthermore, we identify the current limitations and translational challenges for conductive biomaterials before they may become therapeutics for SCI.

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.

Electroresponsive Hydrogels for Therapeutic Applications in the Brain

Electroresponsive hydrogels possess a conducting material component and respond to electric stimulation through reversible absorption and expulsion of water. The high level of hydration, soft elastomeric compliance, biocompatibility, and enhanced electrochemical properties render these hydrogels suitable for implantation in the brain to enhance the transmission of neural electric signals and ion transport. This review provides an overview of critical electroresponsive hydrogel properties for augmenting electric stimulation in the brain. A background on electric stimulation in the brain through electroresponsive hydrogels is provided. Common conducting materials and general techniques to integrate them into hydrogels are briefly discussed. This review focuses on and summarizes advances in electric stimulation of electroconductive hydrogels for therapeutic applications in the brain, such as for controlling delivery of drugs, directing neural stem cell differentiation and neurogenesis, improving neural biosensor capabilities, and enhancing neural electrode-tissue interfaces. The key challenges in each of these applications are discussed and recommendations for future research are also provided.

Thin films of functionalized carbon nanotubes support long-term maintenance and cardio-neuronal differentiation of canine induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are a promising cell source for regenerative medicine. However, their feeder-free maintenance in undifferentiated states remains challenging. In recent past extensive studies have been directed using pristine or functionalized carbon nanotube in tissue engineering. Here we proposed thin films of functionalized carbon nanotubes (OH-single-walled CNTs [SWCNTs] and OH-multiwalled CNTs [MWCNTs]), as alternatives for the feeder-free in vitro culture of canine iPSCs (ciPSCs), considered as the cellular model. The ciPSC colonies could maintain their dome-shaped compactness and other characteristics when propagated on CNT films. Concomitantly, high cell viability and upregulation of pluripotency-associated genes and cell adhesion molecules were observed, further supported by molecular docking. Moreover, CNTs did not have profound toxic effects compared to feeder cultures as evident by cytocompatibility studies. Further, cardiac and neuronal differentiation of ciPSCs was induced on these films to determine their influence on the differentiation process. The cells retained differentiation potential and the nanotopographical features of the substrates provided positive cues to enhance differentiation to both lineages as evident by immunocytochemical staining and marker gene expression. Overall, OH-SWCNT provided better cues, maintained pluripotency, and induced the differentiation of ciPSCs. These results indicate that OH-functionalized CNT films could be used as alternatives for the feeder-free maintenance of ciPSCs towards prospective utilization in regenerative medicine.

Vesicle Impact Electrochemical Cytometry to Determine Carbon Nanotube-Induced Fusion of Intracellular Vesicles

Carbon nanotube (CNT)-modified electrodes are used to obtain new measurements of vesicle content via amperometry. We have investigated the interaction between CNTs and isolated adrenal chromaffin vesicles (as a model) by vesicle impact electrochemical cytometry. Our data show that the presence of CNTs not only significantly increased the vesicular catecholamine number from 2,250,000 ± 112,766 molecules on a bare electrode to 3,880,000 ± 686,573 molecules on CNT/carbon fiber electrodes but also caused an enhancement in the maximum intensity of the current, which implies the existence of strong interactions between vesicle biolayers and CNTs and an altered electroporation process. We suggest that CNTs might perturb and destabilize the membrane structure of intracellular vesicles and cause the aggregation or fusion of vesicles into new vesicles with larger size and higher content. Our findings are consistent with previous computational and experimental results and support the hypothesis that CNTs as a mediator can rearrange the phospholipid bilayer membrane and trigger homotypic fusion of intracellular vesicles.

Electroactive Smart Materials for Neural Tissue Regeneration

Repair in the human nervous system is a complex and intertwined process that offers significant challenges to its study and comprehension. Taking advantage of the progress in fields such as tissue engineering and regenerative medicine, the scientific community has witnessed a strong increase of biomaterial-based approaches for neural tissue regenerative therapies. Electroactive materials, increasingly being used as sensors and actuators, also find application in neurosciences due to their ability to deliver electrical signals to the cells and tissues. The use of electrical signals for repairing impaired neural tissue therefore presents an interesting and innovative approach to bridge the gap between fundamental research and clinical applications in the next few years. In this review, first a general overview of electroactive materials, their historical origin, and characteristics are presented. Then a comprehensive view of the applications of electroactive smart materials for neural tissue regeneration is presented, with particular focus on the context of spinal cord injury and brain repair. Finally, the major challenges of the field are discussed and the main challenges for the near future presented. Overall, it is concluded that electroactive smart materials play an ever-increasing role in neural tissue regeneration, appearing as potentially valuable biomaterials for regenerative purposes.

Self-Assembling Hydrogel Structures for Neural Tissue Repair

Hydrogel materials have been employed as biological scaffolds for tissue regeneration across a wide range of applications. Their versatility and biomimetic properties make them an optimal choice for treating the complex and delicate milieu of neural tissue damage. Aside from finely tailored hydrogel properties, which aim to mimic healthy physiological tissue, a minimally invasive delivery method is essential to prevent off-target and surgery-related complications. The specific class of injectable hydrogels termed self-assembling peptides (SAPs), provide an ideal combination of in situ polymerization combined with versatility for biofunctionlization, tunable physicochemical properties, and high cytocompatibility. This review identifies design criteria for neural scaffolds based upon key cellular interactions with the neural extracellular matrix (ECM), with emphasis on aspects that are reproducible in a biomaterial environment. Examples of the most recent SAPs and modification methods are presented, with a focus on biological, mechanical, and topographical cues. Furthermore, SAP electrical properties and methods to provide appropriate electrical and electrochemical cues are widely discussed, in light of the endogenous electrical activity of neural tissue as well as the clinical effectiveness of stimulation treatments. Recent applications of SAP materials in neural repair and electrical stimulation therapies are highlighted, identifying research gaps in the field of hydrogels for neural regeneration.

In situ photocrosslinkable formulation of nanocomposites based on multi-walled carbon nanotubes and formononetin for potential application in spinal cord injury treatment

Carbon nanotubes (CN) have been studied to treat spinal cord injuries because of its electrical properties and nanometric dimensions. This work aims to develop a photopolymerizable hydrogel containing CN functionalized with an anti-inflammatory molecule to be used in situ on spinal cord injuries. The CN functionalization step was done using the drug (formononetin). The nanocomposites were characterized by morphological analysis, FTIR, Raman Spectroscopy, thermal analysis and cytotoxicity assays (MTT and HET-CAM). The nanocomposites were incorporated into gelatin methacryloyl hydrogel and exposed to UV light for photopolymerization. The volume of the formulation and the UV exposition time were also analyzed. The CN characterization showed that formononetin acted as a functionalization agent. The functionalized CN showed safe characteristics and can be incorporated in photocrosslinkable formulation. The UV exposition time for the formulation photopolymerization was compatible with the cell viability and also occurred in the injury site.

Electric Conductivity on Aligned Nanofibers Facilitates the Transdifferentiation of Mesenchymal Stem Cells into Schwann Cells and Regeneration of Injured Peripheral Nerve

Schwann cells (SCs) are the most promising seed cells for peripheral nerve tissue engineering, but clinical applications are limited by the lack of cell sources. Existing data demonstrate that bone marrow mesenchymal stem cells (BMSCs) can be induced to differentiate into Schwann-like cells and aligned nanofibers can enhance the differentiation. Considering that SCs are living along with the electrical conductive axons, it is hypothesized that conductivity properties may play roles in SCs differentiation and then facilitate nerve regeneration. To verify this hypothesis, amine functionalized multi-walled carbon nanotubes (MWCNTs) are incorporated with polycaprolactone and gelatin to fabricate aligned or random conductive nanofibers by electrospinning. Current data demonstrate that MWCNTs can dramatically increase the electrical conductive properties but do not alter the biocompatibility of the nanofibers. It is found that endowing conductive properties into the aligned nanofibers can significantly enhance their capability to promote the SCs differentiation. Furthermore, the aligned and conductive nanofibers with induced BMSCs can dramatically promote peripheral axonal regeneration. Collectively, the present study demonstrates that the conductive properties in the aligned nanofiber plays significant roles in SCs differentiation and the aligned and conductive nanofibers can be used as a promising scaffold for SCs differentiation and peripheral nerve tissue engineering.

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.

3D printing of electrically conductive hydrogels for tissue engineering and biosensors - A review

Electrically conductive biomaterials are gaining increasing interest owing to their potential to be used in smart, biosensoric and functional tissue-engineered scaffolds and implants. In combination with 3D printing technology, this class of materials might be one of the most advanced approaches towards future medical implants regarding potential functionalities and design possibilities. Conductive hydrogels themselves have been researched for potential sensoric and tissue engineering applications for more than a decade, while the 3D printing of such functional materials is still under early exploration. This review aims to provide a short insight into the most recent developments of 3D printable and electrically conductive hydrogels. It also provides a summary of the last few years of research in this field, with key scope on 3D printing for biomedical applications. The final literature search was conducted in May 2019, with the specific keywords '3D', 'printing', 'conductive', 'hydrogel', 'biocompatible' and combinations of the latter, using advanced search in the databases Scopus®, Web of Science® (Web of Knowledge®) and Google Scholar®. A total of 491 results were gained, while 19 recent publications were identified with the above-mentioned criteria and keywords, which are the studies finally discussed in the paper. The key results have been summarised, and the remaining challenges in the field and the scope for future research activities have been discussed. STATEMENT OF SIGNIFICANCE: Hydrogels are among the most frequently used biomaterials in tissue engineering (TE). A new class of hydrogels, namely, electrically conductive hydrogels (ECHs), has been introduced in recent years. Although ECHs have been comprehensively reviewed in the literature, the combination of ECHs with 3D printing technology has emerged only recently, representing a promising key development toward the fabrication of functional 3D TE constructs. In this review, we cover for the first time the state of the art in the field of 3D printing of ECHs. Previous advances are presented, reviewing the 3D printing technologies utilised, spatial resolution and electrical conductivity values achieved, in addition to discussing the obtained mechanical properties and emerging applications of these materials.

3D printing nano conductive multi-walled carbon nanotube scaffolds for nerve regeneration

OBJECTIVE

Nanomaterials, such as carbon nanotubes (CNTs), have been introduced to modify the surface properties of scaffolds, thus enhancing the interaction between the neural cells and biomaterials. In addition to superior electrical conductivity, CNTs can provide nanoscale structures similar to those present in the natural neural environment. The primary objective of this study is to investigate the proliferative capability and differential potential of neural stem cells (NSCs) seeded on a CNT incorporated scaffold.

APPROACH

Amine functionalized multi-walled carbon nanotubes (MWCNTs) were incorporated with a PEGDA polymer to provide enhanced electrical properties as well as nanofeatures on the surface of the scaffold. A stereolithography 3D printer was employed to fabricate a well-dispersed MWCNT-hydrogel composite neural scaffold with a tunable porous structure. 3D printing allows easy fabrication of complex 3D scaffolds with extremely intricate microarchitectures and controlled porosity.

MAIN RESULTS

Our results showed that MWCNT-incorporated scaffolds promoted neural stem cell proliferation and early neuronal differentiation when compared to those scaffolds without the MWCNTs. Furthermore, biphasic pulse stimulation with 500 µA current promoted neuronal maturity quantified through protein expression analysis by quantitative polymerase chain reaction.

SIGNIFICANCE

Results of this study demonstrated that an electroconductive MWCNT scaffold, coupled with electrical stimulation, may have a synergistic effect on promoting neurite outgrowth for therapeutic application in nerve regeneration.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

Carbon-Based Nanomaterials for Biomedical Applications: A Recent Study

The study of carbon-based nanomaterials (CBNs) for biomedical applications has attracted great attention due to their unique chemical and physical properties including thermal, mechanical, electrical, optical and structural diversity. With the help of these intrinsic properties, CBNs, including carbon nanotubes (CNT), graphene oxide (GO), and graphene quantum dots (GQDs), have been extensively investigated in biomedical applications. This review summarizes the most recent studies in developing of CBNs for various biomedical applications including bio-sensing, drug delivery and cancer therapy.

Ultrafast, asymmetric charge transfer and slow charge recombination in porphyrin/CNT composites demonstrated by time-domain atomistic simulation

The versatile photochemical properties of porphyrin molecules make them excellent candidates for solar energy applications. Carbon nanotubes (CNTs) exhibit superior charge conductivity and have been combined with porphyrins to achieve efficient and ultrafast charge separation. Experiments show that the charge separated state lives less than 10 ps, which is too short for applications. Using real-time time-dependent tight binding density functional theory (DFTB) combined with non-adiabatic molecular dynamics (NAMD), we model photo-induced charge separation and recombination in two porphyrin/CNT composites. Having achieved excellent agreement with the experiment for the electron transfer from the porphyrins to the CNT, we demonstrate that hole transfer can be achieved upon CNT excitation, although in a less efficient way. By exciting the CNT one can extend light harvesting into lower energies of the solar spectrum and increase solar light conversion efficiency. We also show that the charge separated state can live over 1 ns. The two orders of magnitude difference from the experimental lifetime could arise due to the presence of defects or metallic tubes in the samples. The charge separated state is long-lived because the non-adiabatic electron-phonon coupling is very small, less than 1 meV, and the quantum coherence is short, 15-20 fs. The excited states in the isolated porphyrins and CNT live around 100 ps, in agreement with experiments as well. The porphyrin/CNT interaction occurs through the π-electron systems of the two species. The non-radiative relaxation is promoted by both high and low frequency phonons, with higher frequency phonons playing more important roles in electron relaxation than in hole relaxation. Low frequency phonons contribute significantly to the decay of the charge separated state, because they modulate the relative positions of the porphyrins and the CNT. The time-domain atomistic simulations provide a detailed understanding of the charge separation and recombination mechanisms, and generate valuable guidelines for the optimization of photovoltaic efficiency in modern nanoscale materials.

Effective nerve cell modulation by electrical stimulation of carbon nanotube embedded conductive polymeric scaffolds

Biomimetic biomaterials require good biocompatibility and bioactivity to serve as appropriate scaffolds for tissue engineering applications.

Nanotechnology for Neuroscience: Promising Approaches for Diagnostics, Therapeutics and Brain Activity Mapping

Unlocking the secrets of the brain is a task fraught with complexity and challenge - not least due to the intricacy of the circuits involved. With advancements in the scale and precision of scientific technologies, we are increasingly equipped to explore how these components interact to produce a vast range of outputs that constitute function and disease. Here, an insight is offered into key areas in which the marriage of neuroscience and nanotechnology has revolutionized the industry. The evolution of ever more sophisticated nanomaterials culminates in network-operant functionalized agents. In turn, these materials contribute to novel diagnostic and therapeutic strategies, including drug delivery, neuroprotection, neural regeneration, neuroimaging and neurosurgery. Further, the entrance of nanotechnology into future research arenas including optogenetics, molecular/ion sensing and monitoring, and piezoelectric effects is discussed. Finally, considerations in nanoneurotoxicity, the main barrier to clinical translation, are reviewed, and direction for future perspectives is provided.

Repair of nerve injury by implanting prostheses obtained from isogenic acellular nerve segments

INTRODUCTION

When a nerve section with a significant gap occurs, it is necessary to use a prosthesis to suture it. To date an autologous nerve segment graft appears to be the best treatment; but it has several important disadvantages. Our goal is to study the effectiveness of an isogenic acellular nerve prosthesis comparing a simple suture with tubulisation.

MATERIAL AND METHOD

Four groups of Wistar rats were used. The animals in Group 0 served as donors of nerve segments to graft. Group 1 received the implant with an end-to-end suture. In group 2, the implant was sutured inside an ɛ-caprolactone tube. Group 3 received it in a polylactic-co-glycolic acid tube. We evaluated the motor function (sciatic index and step test in motion), and the regeneration length by histological study of regeneration, after a maximum of 3 weeks.

RESULTS

Regeneration was uneven in the three groups. In all groups, there were implants with regenerated nerve fibres at the maximum studied length (15mm) and others where regeneration was scarce. The mean regeneration length was greater in the direct end-to-end suture group (G1), although the regeneration speed was similar in the three groups. Group 1 showed the highest percentage of regeneration, but the variability of results prevents this difference reaching statistical significance. We found no significant differences between the two groups with polymer tubes.

CONCLUSION

For the implantation of isogenic acellular nerve prosthesis, under our experimental conditions, the direct end-to-end suture was more effective than when it isprotected with biopolymer tubes.

Carbon nanotubes stimulate synovial inflammation by inducing systemic pro-inflammatory cytokines

Carbon nanotubes (CNTs) have promising applications in a wide range of biomedical fields, including imaging, drug/gene delivery and other therapeutics; however, the biosafety concerns of CNTs should be addressed. To date, many reports have documented the toxicological effects on the cells, tissue or organs that are in direct contact with the tubes; however, there is limited evidence to unravel the secondary toxicity upon CNT treatment. Moreover, more effort is needed to gain a definitive understanding of the adverse outcome pathway (AOP) for CNTs, and a pragmatic framework for risk assessment has not been established yet. In the current study, we aimed to decipher the secondary toxicity to joints under CNT exposure. We demonstrated that carboxylated multi-wall CNTs (MWCNTs-COOH) significantly provoked systemic pro-inflammatory responses, leading to synovial inflammation within knee joints, as evidenced by the infiltration of pro-inflammatory cells in the synovium and meniscus. Mechanistic studies showed that MWCNTs-COOH stimulated pro-inflammatory effects by activating macrophages, and the secreted pro-inflammatory cytokines primed the synoviocytes and chondrocytes, resulting in enhanced production of a large array of enzymes involved in articular cartilage degeneration, including matrix metalloproteinase (MMP) members and cyclooxygenase (COX) members, and increased enzymatic activity of MMPs was demonstrated. Blockade of the cytokines by antibodies significantly attenuated the production of these enzymes. Our current study thus suggests that there is a novel secondary toxicity of CNTs, namely a new AOP to understand the indirect effects of carbon nanotubes: synovial inflammation due to the alteration of the priming state of synoviocytes and chondrocytes under CNT-induced systemic inflammatory conditions.

Nanomedicine in Central Nervous System (CNS) Disorders: A Present and Future Prospective

Purpose: For the past few decades central nervous system disorders were considered as a major strike on human health and social system of developing countries. The natural therapeutic methods for CNS disorders limited for many patients. Moreover, nanotechnology-based drug delivery to the brain may an exciting and promising platform to overcome the problem of BBB crossing. In this review, first we focused on the role of the blood-brain barrier in drug delivery; and second, we summarized synthesis methods of nanomedicine and their role in different CNS disorder. Method: We reviewed the PubMed databases and extracted several kinds of literature on neuro nanomedicines using keywords, CNS disorders, nanomedicine, and nanotechnology. The inclusion criteria included chemical and green synthesis methods for synthesis of nanoparticles encapsulated drugs and, their in-vivo and in-vitro studies. We excluded nanomedicine gene therapy and nanomaterial in brain imaging. Results: In this review, we tried to identify a highly efficient method for nanomedicine synthesis and their efficacy in neuronal disorders. SLN and PNP encapsulated drugs reported highly efficient by easily crossing BBB. Although, these neuro-nanomedicine play significant role in therapeutics but some metallic nanoparticles reported the adverse effect on developing the brain. Conclusion: Although impressive advancement has made via innovative potential drug development, but their efficacy is still moderate due to limited brain permeability. To overcome this constraint,powerful tool in CNS therapeutic intervention provided by nanotechnology-based drug delivery methods. Due to its small and biofunctionalization characteristics, nanomedicine can easily penetrate and facilitate the drug through the barrier. But still, understanding of their toxicity level, optimization and standardization are a long way to go.

Robust neurite extension following exogenous electrical stimulation within single walled carbon nanotube-composite hydrogels

The use of exogenous electrical stimulation to promote nerve regeneration has achieved only limited success. Conditions impeding optimized outgrowth may arise from inadequate stimulus presentation due to differences in injury geometry or signal attenuation. Implantation of an electrically-conductive biomaterial may mitigate this attenuation and provide a more reproducible signal. In this study, a conductive nanofiller (single-walled carbon nanotubes [SWCNT]) was selected as one possible material to manipulate the bulk electrical properties of a collagen type I-10% Matrigel™ composite hydrogel. Neurite outgrowth within hydrogels (SWCNT or nanofiller-free controls) was characterized to determine if: (1) nanofillers influence neurite extension and (2) electrical stimulation of the nanofiller composite hydrogel enhances neurite outgrowth. Increased SWCNT loading (10-100-μg/mL) resulted in greater bulk conductivity (up to 1.7-fold) with no significant changes to elastic modulus. Neurite outgrowth increased 3.3-fold in 20-μg/mL SWCNT loaded biomaterials relative to the nanofiller-free control. Electrical stimulation promoted greater outgrowth (2.9-fold) within SWCNT-free control. The concurrent presentation of electrical stimulation and SWCNT-loaded biomaterials resulted in a 7.0-fold increase in outgrowth relative to the unstimulated, nanofiller-free controls. Local glia residing within the DRG likely contribute, in part, to the observed increases in outgrowth; but it is unknown which specific nanofiller properties influence neurite extension. Characterization of neuronal behavior in model systems, such as those described here, will aid the rational development of biomaterials as well as the appropriate delivery of electrical stimuli to support nerve repair.

STATEMENT OF SIGNIFICANCE

Novel biomedical devices delivering electrical stimulation are being developed to mitigate symptoms of Parkinson's, treat drug-resistant depression, control movement or enhance verve regeneration. Carbon nanotubes and other novel materials are being explored for novel nano-neuro devices based on their unique properties. Neuronal growth on carbon nanotubes has been studied in 2D since the early 2000s demonstrating increased outgrowth, synapse formation and network activity. In this work, single-walled carbon nanotubes were selected as one possible electrically-conductive material, dispersed within a 3D hydrogel containing primary neurons; extending previous 2D work to 3D to evaluate outgrowth within nanomaterial composites with electrical stimulation. This is the first study to our knowledge that stimulates neurons in 3D composite nanomaterial-laden hydrogels. Examination of electrically conductive biomaterials may serve to promote regrowth following injury or in long term stimulation.

Repairing Peripheral Nerves: Is there a Role for Carbon Nanotubes?

Peripheral nerve injury continues to be a major global health problem that can result in debilitating neurological deficits and neuropathic pain. Current state-of-the-art treatment involves reforming the damaged nerve pathway using a nerve autograft. Engineered nerve repair conduits can provide an alternative to the nerve autograft avoiding the inevitable tissue damage caused at the graft donor site. Commercially available nerve repair conduits are currently only considered suitable for repairing small nerve lesions; the design and performance of engineered conduits requires significant improvements to enable their use for repairing larger nerve defects. Carbon nanotubes (CNTs) are an emerging novel material for biomedical applications currently being developed for a range of therapeutic technologies including scaffolds for engineering and interfacing with neurological tissues. CNTs possess a unique set of physicochemical properties that could be useful within nerve repair conduits. This progress report aims to evaluate and consolidate the current literature pertinent to CNTs as a biomaterial for supporting peripheral nerve regeneration. The report is presented in the context of the state-of-the-art in nerve repair conduit design; outlining how CNTs may enhance the performance of next generation peripheral nerve repair conduits.

Versatile Nanosystem-Based Cancer Theranostics: Design Inspiration and Predetermined Routing

The relevance of personalized medicine, aimed at a more individualized drug therapy, has inspired research into nano-based concerted diagnosis and therapeutics (theranostics). As the intention is to "kill two birds with one stone", scientists have already described the emerging concept as a treasured tailor for the future of cancer therapy, wherein the main idea is to design "smart" nanosystems to concurrently discharge both therapeutic and diagnostic roles. These nanosystems are expected to offer a relatively clearer view of the ingenious cellular trafficking pathway, in-situ diagnosis, and therapeutic efficacy. We herein present a detailed review of versatile nanosystems, with prominent examples of recently developed intelligent delivery strategies which have gained attention in the field of theranostics. These nanotheranostics include various mechanisms programmed in novel platforms to enable predetermined delivery of cargo to specific sites, as well as techniques to overcome the notable challenges involved in the efficacy of theranostics.

Neuron-like differentiation of mesenchymal stem cells on silicon nanowires

The behavior of mammalian cells on vertical nanowire (NW) arrays, including cell spreading and the dynamic distribution of focal adhesions and cytoskeletal proteins, has been intensively studied to extend the implications for cellular manipulations in vitro. Prompted by the result that cells on silicon (Si) NWs showed morphological changes and reduced migration rates, we have explored the transition of mesenchymal stem cells into a neuronal lineage by using SiNWs with varying lengths. When human mesenchymal stem cells (hMSCs) were cultured on the longest SiNWs for 3 days, most of the cells exhibited elongated shapes with neurite-like extensions and dot-like focal adhesions that were prominently observed along with actin filaments. Under these circumstances, the cell motility analyzed by live cell imaging was found to decrease due to the presence of SiNWs. In addition, the slowed growth rate, as well as the reduced population of S phase cells, suggested that the cell cycle was likely arrested in response to the differentiation process. Furthermore, we measured the mRNA levels of several lineage-specific markers to confirm that the SiNWs actually induced neuron-like differentiation of the hMSCs while hampering their osteogenic differentiation. Taken together, our results implied that SiNWs were capable of inducing active reorganization of cellular behaviors, collectively guiding the fate of hMSCs into the neural lineage even in the absence of any inducing reagent.

Carbon Nanotube Nanocomposites with Highly Enhanced Strength and Conductivity for Flexible Electric Circuits

Carbon nanotubes (CNTs) have an important role in nanotechnology due to their unique properties, retaining the inherent material flexibility, superior strength, and electrical conductivity, unless the bottleneck of CNTs persists and the aggregated structure is overcome. Here, we report on the highly enhanced mechanical and electrical properties of the CNT-chitosan nanocomposites through homogeneous dispersion of CNTs into chitosan solution using a high-pressure homogenizer. The optimal condition is a 50% (w/w) chitosan-CNT film, providing about 7 nm thickness of homogeneous chitosan layer on CNTs, a good tensile strength of 51 MPa, high electrical conductivity under 16 Ω/sq, and a stable bending and folding performance. This CNT-chitosan nanocomposite with highly enhanced properties is an amenable material to fabricate structures of various shapes such as films, sensors, and circuits and also enables a simple and cost-effective approach to improve the performance of a device that presents the first flexible and soft electric circuits yet reported using only CNT-chitosan as the conductor.

Carbon-nanotube-interfaced glass fiber scaffold for regeneration of transected sciatic nerve

Carbon nanotubes (CNTs), with their unique and unprecedented properties, have become very popular for the repair of tissues, particularly for those requiring electrical stimuli. Whilst most reports have demonstrated in vitro neural cell responses of the CNTs, few studies have been performed on the in vivo efficacy of CNT-interfaced biomaterials in the repair and regeneration of neural tissues. Thus, we report here for the first time the in vivo functions of CNT-interfaced nerve conduits in the regeneration of transected rat sciatic nerve. Aminated CNTs were chemically tethered onto the surface of aligned phosphate glass microfibers (PGFs) and CNT-interfaced PGFs (CNT-PGFs) were successfully placed into three-dimensional poly(L/D-lactic acid) (PLDLA) tubes. An in vitro study confirmed that neurites of dorsal root ganglion outgrew actively along the aligned CNT-PGFs and that the CNT interfacing significantly increased the maximal neurite length. Sixteen weeks after implantation of a CNT-PGF nerve conduit into the 10 mm gap of a transected rat sciatic nerve, the number of regenerating axons crossing the scaffold, the cross-sectional area of the re-innervated muscles and the electrophysiological findings were all significantly improved by the interfacing with CNTs. This first in vivo effect of using a CNT-interfaced scaffold in the regeneration process of a transected rat sciatic nerve strongly supports the potential use of CNT-interfaced PGFs at the interface between the nerve conduit and peripheral neural tissues.

Nanostructured biointerfacing of metals with carbon nanotube/chitosan hybrids by electrodeposition for cell stimulation and therapeutics delivery

Exploring the biological interfaces of metallic implants has been an important issue in achieving biofunctional success. Here we develop a biointerface with nanotopological features and bioactive composition, comprising a carbon nanotube (CNT) and chitosan (Chi) hybrid, via an electrophoretic deposition (EPD). The physicochemical properties, in vitro biocompatibility, and protein delivering capacity of the decorated nanohybrid layer were investigated, to address its potential usefulness as bone regenerating implants. Over a wide compositional range, the nanostructured hybrid interfaces were successfully formed with varying thicknesses, depending on the electrodeposition parameters. CNT-Chi hybrid interfaces showed a time-sequenced degradation in saline water, and a rapid induction of hydroxyapatite mineral in a simulated body fluid. The nanostructured hybrid substrates stimulated the initial adhesion events of the osteoblastic cells, including cell adhesion rate, spreading behaviors, and expression of adhesive proteins. The nanostructured hybrid interfaces significantly improved the adsorption of protein molecules, which was enabled by the surface charge interaction, and increased surface area of the nanotopology. Furthermore, the incorporated protein was released at a highly sustained rate, profiling a diffusion-controlled pattern over a couple of weeks, suggesting the possible usefulness as a protein delivery device. Collectively, the nanostructured hybrid CNT-Chi layer, implemented by an electrodeposition, is considered a biocompatible, cell-stimulating, and protein-delivering biointerface of metallic implants.

Carbon nanotube-collagen three-dimensional culture of mesenchymal stem cells promotes expression of neural phenotypes and secretion of neurotrophic factors

Microenvironments provided by three-dimensional (3-D) hydrogels mimic native tissue conditions, supplying appropriate physical cues for regulating stem cell behaviors. Here, we focused on carbon nanotubes (CNTs) dispersed within collagen hydrogels to provide 3-D microenvironmental conditions for mesenchymal stem cells (MSCs) in stimulating biological functions for neural regeneration. Small concentrations of CNTs (0.1-1wt.%) did not induce toxicity to MSCs, and even improved the proliferative potential of the cells. MSCs cultured within the CNT-collagen hydrogel expressed considerable levels of neural markers, including GAP43 and βIII tubulin proteins by immunostaining as well as GAP43 and synapse I genes by reverse transcriptase polymerase chain reaction (RT-PCR). Of note was that neurotrophic factors, particularly nerve growth factor and brain derived neurotrophic factor, were significantly promoted by the incorporation of CNTs as confirmed by RT-PCR and Western blot analysis. A model experiment involving neuritogenesis of PC12 cells influenced by those releasing neurotrophic factors from MSCs cultured within the CNT-collagen hydrogel demonstrated the significant enhancement in neurite outgrowth behaviors. Taken together, collagen hydrogel provides excellent 3-D conditions for MSC growth, and a small incorporation of CNTs within the hydrogel significantly stimulates MSC expression of neural markers and secretion of neurotrophic factors.

Aqueous adsorption and removal of organic contaminants by carbon nanotubes

Organic contaminants have become one of the most serious environmental problems, and the removal of organic contaminants (e.g., dyes, pesticides, and pharmaceuticals/drugs) and common industrial organic wastes (e.g., phenols and aromatic amines) from aqueous solutions is of special concern because they are recalcitrant and persistent in the environment. In recent years, carbon nanotubes (CNTs) have been gradually applied to the removal of organic contaminants from wastewater through adsorption processes. This paper reviews recent progress (145 studies published from 2010 to 2013) in the application of CNTs and their composites for the removal of toxic organic pollutants from contaminated water. The paper discusses removal efficiencies and adsorption mechanisms as well as thermodynamics and reaction kinetics. CNTs are predicted to have considerable prospects for wider application to wastewater treatment in the future.

Drug-loading capacity and nuclear targeting of multiwalled carbon nanotubes grafted with anionic amphiphilic copolymers

In this study, three types of hybrid nanotubes (NTs), ie, oxidized multiwalled carbon NTs (COOH MWCNTs), heparin (Hep)-conjugated MWCNTs (Hep MWCNTs), and diblock copolymer polyglycolic acid (PGA)-co-heparin conjugated to MWCNTs (PGA MWCNTs), were synthesized with improved biocompatibility and drug-loading capacity. Hydrophilic Hep substituents on MWCNTs improved biocompatibility and acted as nucleus-sensitive segments on the CNT carrier, whereas the addition of PGA enhanced drug-loading capacity. In the PGA MWCNT system, the amphiphilic copolymer (PGA-Hep) formed micelles on the side walls of CNTs, as confirmed by electron microscopy. The PGA system encapsulated the hydrophobic drug with high efficiency compared to the COOH MWCNT and Hep MWCNT systems. This is because the drug was loaded onto the PGA MWCNTs through hydrophobic forces and onto the CNTs by π-π stacking interactions. Additionally, most of the current drug-carrier designs that target cancer cells release the drug in the lysosome or cytoplasm. However, nuclear-targeted drug release is expected to kill cancer cells more directly and efficiently. In our study, PGA MWCNT carriers effectively delivered the active anticancer drug doxorubicin into targeted nuclei. This study may provide an effective strategy for the development of carbon-based drug carriers for nuclear-targeted drug delivery.