Poly(methacrylic acid)-grafted carbon nanotube scaffolds enhance differentiation of hESCs into neuronal cells

The effect of nanomaterials on embryonic stem cell neural differentiation: a systematic review

BACKGROUND

Humans' nervous system has a limited ability to repair nerve cells, which poses substantial challenges in treating injuries and diseases. Stem cells are identified by the potential to renew their selves and develop into several cell types, making them ideal candidates for cell replacement in injured neurons. Neuronal differentiation of embryonic stem cells in modern medicine is significant. Nanomaterials have distinct advantages in directing stem cell function and tissue regeneration in this field. We attempted in this systematic review to collect data, analyze them, and report results on the effect of nanomaterials on neuronal differentiation of embryonic stem cells.

METHODS

International databases such as PubMed, Scopus, ISI Web of Science, and EMBASE were searched for available articles on the effect of nanomaterials on neuronal differentiation of embryonic stem cells (up to OCTOBER 2023). After that, screening (by title, abstract, and full text), selection, and data extraction were performed. Also, quality assessment was conducted based on the STROBE checklist.

RESULTS

In total, 1507 articles were identified and assessed, and then only 29 articles were found eligible to be included. Nine studies used 0D nanomaterials, ten used 1D nanomaterials, two reported 2D nanomaterials, and eight demonstrated the application of 3D nanomaterials. The main biomaterial in studies was polymer-based composites. Three studies reported the negative effect of nanomaterials on neural differentiation.

CONCLUSION

Neural differentiation is crucial in neurological regenerative medicine. Nanomaterials with different characteristics, particularly those cellular regulating activities and stem cell fate, have much potential in neural tissue engineering. These findings indicate a new understanding of potential applications of physicochemical cues in nerve tissue engineering.

In vitro toxicity of carbon nanotubes: a systematic review

Carbon nanotube (CNT) toxicity-related issues provoke many debates in the scientific community. The controversial and disputable data about toxicity doses, proposed hazard effects, and human health concerns significantly restrict CNT applications in biomedical studies, laboratory practices, and industry, creating a barrier for mankind in the way of understanding how exactly the material behaves in contact with living systems. Raising the toxicity question again, many research groups conclude low toxicity of the material and its potential safeness at some doses for contact with biological systems. To get new momentum for researchers working on the intersection of the biological field and nanomaterials, i.e., CNT materials, we systematically reviewed existing studies with in vitro toxicological data to propose exact doses that yield toxic effects, summarize studied cell types for a more thorough comparison, the impact of incubation time, and applied toxicity tests. Using several criteria and different scientific databases, we identified and analyzed nearly 200 original publications forming a "golden core" of the field to propose safe doses of the material based on a statistical analysis of retrieved data. We also differentiated the impact of various forms of CNTs: on a substrate and in the form of dispersion because in both cases, some studies demonstrated good biocompatibility of CNTs. We revealed that CNTs located on a substrate had negligible impact, i.e., 90% of studies report good viability and cell behavior similar to control, therefore CNTs could be considered as a prospective conductive substrate for cell cultivation. In the case of dispersions, our analysis revealed mean values of dose/incubation time to be 4-5 μg mL-1 h-1, which suggested the material to be a suitable candidate for further studies to get a more in-depth understanding of its properties in biointerfaces and offer CNTs as a promising platform for fundamental studies in targeted drug delivery, chemotherapy, tissue engineering, biosensing fields, etc. We hope that the present systematic review will shed light on the current knowledge about CNT toxicity, indicate "dark" spots and offer possible directions for the subsequent studies based on the demonstrated here tabulated and statistical data of doses, cell models, toxicity tests, viability, etc.

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.

Micro/nanoengineered technologies for human pluripotent stem cells maintenance and differentiation

Human pluripotent stem cells (hPSCs) are a promising source of cells for cell replacement-based therapies as well as modeling human development and diseases in vitro. However, achieving fate control of hPSC with a high yield and specificity remains challenging. The fate specification of hPSCs is regulated by biochemical and biomechanical cues in their environment. Driven by this knowledge, recent exciting advances in micro/nanoengineering have been leveraged to develop a broad range of tools for the generation of extracellular biomechanical and biochemical signals that determine the behavior of hPSCs. In this review, we summarize such micro/nanoengineered technologies for controlling hPSC fate and highlight the role of biochemical and biomechanical cues such as substrate rigidity, surface topography, and cellular confinement in the hPSC-based technologies that are on the horizon.

Carbon Nanotube-Hydrogel Composites Facilitate Neuronal Differentiation While Maintaining Homeostasis of Network Activity

It is often assumed that carbon nanotubes (CNTs) stimulate neuronal differentiation by transferring electrical signals and enhancing neuronal excitability. Given this, CNT-hydrogel composites are regarded as potential materials able to combine high electrical conductivity with biocompatibility, and therefore promote nerve regeneration. However, whether CNT-hydrogel composites actually influence neuronal differentiation and maturation, and how they do so remain elusive. In this study, CNT-hydrogel composites are prepared by in situ polymerization of poly(ethylene glycol) around a preformed CNT meshwork. It is demonstrated that the composites facilitate long-term survival and differentiation of pheochromocytoma 12 cells. Adult neural stem cells cultured on the composites show an increased neuron-to-astrocyte ratio and higher synaptic connectivity. Moreover, primary hippocampal neurons cultured on composites maintain morphological synaptic features as well as their neuronal network activity evaluated by spontaneous calcium oscillations, which are comparable to neurons cultured under control conditions. These results indicate that the composites are promising materials that could indeed facilitate neuronal differentiation while maintaining neuronal homeostasis.

Using Wet Electrospun PCL/Gelatin/CNT Yarns to Fabricate Textile-Based Scaffolds for Vascular Tissue Engineering

Incorporating conductive materials in scaffolds has shown advantages in regulating adhesion, mitigation, and proliferation of electroactive cells for tissue engineering applications. Among various conductive materials, carbon nanotubes (CNTs) have shown great promises in tissue engineering because of their good mechanical properties. However, the broad application of CNTs in tissue engineering is limited by current methods to incorporate CNTs in polymers that require miscible solvents to dissolve CNTs and polymers or CNT surface modification. These methods either limit polymer selections or adversely affect the properties of polymer/CNT composites. Here, we report a novel method to fabricate polymer/CNT composite yarns by electrospinning polycaprolactone/gelatin into a bath of CNT dispersion and extracting electrospun fibers out of the bath. The concentration of CNTs in the bath affects the thermal and mechanical properties and the yarns' degradation behavior. In vitro biological test results show that within a limited range of CNT concentrations in the bath, the yarns exhibit good biocompatibility and the ability to guide cell elongation and alignment. We also report the design and fabrication of a vascular scaffold by knitting the yarns into a textile fabric and combining the textile fabric with gelatin. The scaffold has similar mechanical properties to native vessels and supports cell proliferation. This work demonstrates that the wet electrospun polymer/CNT yarns are good candidates for constructing vascular scaffolds and provides a novel method to incorporate CNTs or other functional materials into biopolymers for tissue engineering applications.

Advances in Biodegradable 3D Printed Scaffolds with Carbon-Based Nanomaterials for Bone Regeneration

Bone possesses an inherent capacity to fix itself. However, when a defect larger than a critical size appears, external solutions must be applied. Traditionally, an autograft has been the most used solution in these situations. However, it presents some issues such as donor-site morbidity. In this context, porous biodegradable scaffolds have emerged as an interesting solution. They act as external support for cell growth and degrade when the defect is repaired. For an adequate performance, these scaffolds must meet specific requirements: biocompatibility, interconnected porosity, mechanical properties and biodegradability. To obtain the required porosity, many methods have conventionally been used (e.g., electrospinning, freeze-drying and salt-leaching). However, from the development of additive manufacturing methods a promising solution for this application has been proposed since such methods allow the complete customisation and control of scaffold geometry and porosity. Furthermore, carbon-based nanomaterials present the potential to impart osteoconductivity and antimicrobial properties and reinforce the matrix from a mechanical perspective. These properties make them ideal for use as nanomaterials to improve the properties and performance of scaffolds for bone tissue engineering. This work explores the potential research opportunities and challenges of 3D printed biodegradable composite-based scaffolds containing carbon-based nanomaterials for bone tissue engineering applications.

Carbon nanostructures as a scaffold for human embryonic stem cell differentiation toward photoreceptor precursors

Carbon nanomaterials have been introduced as a scaffold for various biological applications due to their unique physical and electrical properties. Here we studied carbon nanotubes (CNTs) and carbon nanofibers (CNFs) as scaffold materials for the differentiation of human embryonic stem cells (hESCs) towards photoreceptor precursor cells (PRPs). We report on their cytoxicity, their effect on cell morphology, cell-surface interface and the differentiation process. To this end, hESCs were differentiated into PRPs on carbon nanofibers (CNFs), long horizontal CNTs (LHCNTs), vertically aligned CNTs (VACNTs) or glass (control) surfaces. The differentiated cells were investigated by immunohistochemistry, fluorescence imaging and electron microscopy. Our results revealed that the investigated nanomaterials were not cytotoxic to the cells during the differentiation process. The surface interface effect on the cells was apparent, affecting cell directionality, migration and morphology. Interestingly, cell fate was not dependent on the substrate type, as inferred from the similar dynamics of the loss of pluripotency and the comparable expression levels of the photoreceptor marker Crx for all investigated substrates. These results are important for better understanding the effect of nanomaterial surface interaction with differentiating neural cells in general, and for future use of these materials as scaffolds for differentiating photoreceptors for vision restoration in particular.

Culture of dental pulp stem cells on nanoporous alumina substrates modified by carbon nanotubes

PURPOSE

Alumina substrates are one of the commonly used scaffolds applied in cell culture, but in order to prevent formation of biofilm on the alumina substrate, these substrates are modified with carbon nanotube.

METHODS

The alumina substrate was made by a two-step anodization method and was then modified with carbon nanotubes by simple chemical reaction. The substrates were characterized with FTIR, SEM, EDX, 3D laser scanning digital microscope, contact angle (CA) and surface free energy (SFE). To determine how this modification influences the reduction of biofilm, biofilm of two various bacteria, Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus), were investigated.

RESULTS

The biofilm on the modified substrate decreased due to the presence of carbon nanotubes and increased antibacterial properties. Dental pulp stem cells (DPSCs) were cultured onto flat alumina (FA) and nanoporous alumina-multiwalled carbon nanotubes (NAMC) substrates to examine how the chemical modification and surface topography affects growth of DPSCs.

CONCLUSION

Cell attachment and proliferation were investigated with SEM and Presto Blue assay, and the findings show that the NAMC substrates are suitable for cell culture.

Materials for Neural Differentiation, Trans-Differentiation, and Modeling of Neurological Disease

Neuron regeneration from pluripotent stem cells (PSCs) differentiation or somatic cells trans-differentiation is a promising approach for cell replacement in neurodegenerative diseases and provides a powerful tool for investigating neural development, modeling neurological diseases, and uncovering the mechanisms that underlie diseases. Advancing the materials that are applied in neural differentiation and trans-differentiation promotes the safety, efficiency, and efficacy of neuron regeneration. In the neural differentiation process, matrix materials, either natural or synthetic, not only provide a structural and biochemical support for the monolayer or three-dimensional (3D) cultured cells but also assist in cell adhesion and cell-to-cell communication. They play important roles in directing the differentiation of PSCs into neural cells and modeling neurological diseases. For the trans-differentiation of neural cells, several materials have been used to make the conversion feasible for future therapy. Here, the most current applications of materials for neural differentiation for PSCs, neuronal trans-differentiation, and neurological disease modeling is summarized and discussed.

The Role of Biomaterials in Implantation for Central Nervous System Injury

Permanent deficits that occur in memory, sensation, and cognition can result from central nervous system (CNS) trauma that causes dysfunction and/or unregulated CNS regeneration. Some therapeutic approaches are preferentially applied to the human body. Therefore, cell transplantation, one of the therapeutic strategies, may be used to benefit people. However, poor cell viability and low efficacy are the limitations to cell transplantation strategies. Biomaterials have been widely used in several fields (e.g., triggering cell differentiation, guiding cell migration, improving wound healing, and increasing tissue regeneration) by modulating their characteristics in chemistry, topography, and softness/stiffness for highly flexible application. We reviewed implanted biomaterials to investigate the roles and influences of physical/chemical properties on cell behaviors and applications. With their unique molecular features, biomaterials are delivered in several methods and mixed with transplanted cells, which assists in increasing postimplanted biological substance efficiency on cell survival, host responses, and functional recovery of animal models. Moreover, tracking the routes of these transplanted cells using biomaterials as labeling agents is crucial for addressing their location, distribution, activity, and viability. Here, we provide comprehensive comments and up-to-date research of the application of biomaterials.

NIPAAm-MMA nanoparticle-encapsulated visnagin ameliorates myocardial ischemia/reperfusion injury through the promotion of autophagy and the inhibition of apoptosis

The main method for the treatment of acute myocardial infarction (AMI) is percutaneous coronary intervention; however percutaneous coronary intervention will induce ischemia/reperfusion (IR) injury, resulting in the loss of cardiac function and cardiomyocyte death. An effective drug to target this condition is necessary. N-isopropylacrylamide and methacrylic acid were used to synthesize drug delivery nanoparticles (NP) containing the natural compound visnagin for IR injury treatment. It was demonstrated that NP containing fluorescein isothiocyanate localized to the site of myocardial IR, and that NP-visnagin treatment induced cardioprotection, reducing the size of the MI and ameliorating cardiac dysfunction through the induction of autophagy and the inhibition of apoptosis. In the future, visnagin may be suitable as a drug for IR injury treatment, and NP may be an effective drug delivery system.

Biocompatible chitin/carbon nanotubes composite hydrogels as neuronal growth substrates

In the past decades, extensive studies have demonstrated that carbon nanotubes (CNTs) could promote cell adhesion, proliferation and differentiation of neuronal cells. However, the potential cytotoxicity in biological systems severely restricted the utilization of CNTs as substrates for neural growth. In this study, biocompatible chitin/carbon nanotubes (Ch/CNT) composite hydrogels were developed via blending modified CNTs with chitin solution in 11wt% NaOH/4wt% urea aqueous system, and subsequently regenerating in ethanol. As the CNTs were dispersed homogeneously in chitin matrix and combined with chitin nanofibers to form a compact and neat Ch/CNT nanofibrous network through intermolecular interactions, such as electrostatic interactions, hydrogen bonding and amphiphilic interaction, etc. The tensile strength and elongation at break of the Ch/CNT composite hydrogels were obviously enhanced, and the swelling ratio decreased. In addition, the Ch/CNT hydrogels exhibited good hemocompatibility, biodegradation in vitro and biocompatibility without cytotoxicity and neurotoxicity nature to neuronal and Schwann cells (PC12 cells and RSC96 cells). Especially, the Ch/CNT3 composite hydrogels exhibited significant enhancement of the neuronal cell adhesion, proliferation and neurite outgrowth of neuronal cells with a great increase in both the percentage and the length of neurites. Therefore, we provide a simple and efficient approach to construct the novel Ch/CNT hydrogels as neuronal growth substrates for the potential application in nerve regeneration.

Functionalized carbon nanotubes as suitable scaffold materials for proliferation and differentiation of canine mesenchymal stem cells

In the field of regenerative medicine, numerous potential applications of mesenchymal stem cells (MSCs) can be envisaged, due to their ability to differentiate into a range of tissues on the basis of the substrate on which they grow. With the advances in nanotechnology, carbon nanotubes (CNTs) have been widely explored for use as cell culture substrate in tissue engineering applications. In this study, canine bone marrow-derived MSCs were considered as the cellular model for an in vitro study to elucidate the collective cellular processes, using three different varieties of thin films of functionalized carbon nanotubes (COOH-single-walled CNTs [SWCNTs], COOH-multiwalled CNTs [MWCNTs] and polyethylene glycol [PEG]-SWCNTs), which were spray dried onto preheated cover slips. Cells spread out better on the CNT films, resulting in higher cell surface area and occurrence of filopodia, with parallel orientation of stress fiber bundles. Canine MSCs proliferated at a slower rate on all types of CNT substrates compared to the control, but no decline in cell number was noticed during the study period. Expression of apoptosis-associated genes decreased on the CNT substrates as time progressed. On flow cytometry after AnnexinV-fluorescein isothiocyanate/propidium iodide (PI) staining, total number of apoptotic and necrotic cells remained lower in COOH-functionalized films compared to PEG-functionalized ones. Collectively, these results indicate that COOH-MWCNT substrate provided an environment of low cytotoxicity. Canine MSCs were further induced to differentiate along osteogenic, chondrogenic, and neuronal lineages by culturing under specific differentiation conditions. The cytochemical and immunocytochemical staining results, as well as the expression of the bone marker genes, led us to hypothesize that the COOH-MWCNT substrate acted as a better cue, accelerating the osteogenic differentiation process. However, while chondrogenesis was promoted by COOH-SWCNT, neuronal differentiation was promoted by both COOH-SWNCT and COOH-MWCNT. Taken together, these findings suggest that COOH-functionalized CNTs represent a promising scaffold component for future utilization in the selective differentiation of canine MSCs in regenerative medicine.

In Vitro Evaluation of Biocompatibility of Uncoated Thermally Reduced Graphene and Carbon Nanotube-Loaded PVDF Membranes with Adult Neural Stem Cell-Derived Neurons and Glia

Graphene, graphene-based nanomaterials (GBNs), and carbon nanotubes (CNTs) are being investigated as potential substrates for the growth of neural cells. However, in most in vitro studies, the cells were seeded on these materials coated with various proteins implying that the observed effects on the cells could not solely be attributed to the GBN and CNT properties. Here, we studied the biocompatibility of uncoated thermally reduced graphene (TRG) and poly(vinylidene fluoride) (PVDF) membranes loaded with multi-walled CNTs (MWCNTs) using neural stem cells isolated from the adult mouse olfactory bulb (termed aOBSCs). When aOBSCs were induced to differentiate on coverslips treated with TRG or control materials (polyethyleneimine-PEI and polyornithine plus fibronectin-PLO/F) in a serum-free medium, neurons, astrocytes, and oligodendrocytes were generated in all conditions, indicating that TRG permits the multi-lineage differentiation of aOBSCs. However, the total number of cells was reduced on both PEI and TRG. In a serum-containing medium, aOBSC-derived neurons and oligodendrocytes grown on TRG were more numerous than in controls; the neurons developed synaptic boutons and oligodendrocytes were more branched. In contrast, neurons growing on PVDF membranes had reduced neurite branching, and on MWCNTs-loaded membranes oligodendrocytes were lower in numbers than in controls. Overall, these findings indicate that uncoated TRG may be biocompatible with the generation, differentiation, and maturation of aOBSC-derived neurons and glial cells, implying a potential use for TRG to study functional neuronal networks.

Nanobiomaterials' applications in neurodegenerative diseases

The blood-brain barrier is the interface between the blood and brain, impeding the passage of most circulating cells and molecules, protecting the latter from foreign substances, and maintaining central nervous system homeostasis. However, its restrictive nature constitutes an obstacle, preventing therapeutic drugs from entering the brain. Usually, a large systemic dose is required to achieve pharmacological therapeutic levels in the brain, leading to adverse effects in the body. As a consequence, various strategies are being developed to enhance the amount and concentration of therapeutic compounds in the brain. One such tool is nanotechnology, in which nanostructures that are 1-100 nm are designed to deliver drugs to the brain. In this review, we examine many nanotechnology-based approaches to the treatment of neurodegenerative diseases. The review begins with a brief history of nanotechnology, followed by a discussion of its definition, the properties of most reported nanomaterials, their biocompatibility, the mechanisms of cell-material interactions, and the current status of nanotechnology in treating Alzheimer's, Parkinson's diseases, and amyotrophic lateral sclerosis. Of all strategies to deliver drug to the brain that are used in nanotechnology, drug release systems are the most frequently reported.

The potential of nanoparticles in stem cell differentiation and further therapeutic applications

Tissue regeneration could offer therapeutic advantages for individuals experiencing organ or tissue damage. Recently, advances in nanotechnology have provided various nanomaterials, with a wide range of applications, for modulating stem cell behavior and for further therapeutic applications in tissue regeneration. Defects in cell proliferation and differentiation, a low mechanical strength of scaffolds, and inefficient production of factors that are essential for stem cell differentiation are the current challenges in tissue regeneration. This review provides a brief explanation about the link between nanotechnology and tissue engineering, highlighting the current literature about the interaction between nanoparticles (NPs) and stem cells, the promotional effect of NPs on stem cell differentiation into various lineages, and their possible therapeutic applications. We also tried to describe the mechanism through which NPs regulate the spatial-temporal release and kinetics of vital growth and differentiation factors, enhance stem cell differentiation, and improve culture conditions for in vivo tissue regeneration. The field of nanotechnology is promising and provides novel nanomaterials and methods with valuable clinical applications in the regenerative medicine. Understanding the mechanism, as well as the toxic effects of NPs in stem cell biology will undoubtedly provide valuable insight into their clinical application in the regenerative medicine.

Neuronal commitment of human circulating multipotent cells by carbon nanotube-polymer scaffolds and biomimetic peptides

AIM

We aimed to set up a self-standing, biomimetic scaffold system able to induce and support per se neuronal differentiation of autologous multipotent cells.

MATERIALS & METHODS

We isolated a population of human circulating multipotent cells (hCMCs), and used carbon nanotube/polymer nanocomposite scaffolds to mimic electrical/nanotopographical features of the neural environment, and biomimetic peptides reproducing axon guidance cues from neural proteins.

RESULTS

hCMCs showed high degree of stemness and multidifferentiative potential; stimuli from the scaffolds and biomimetic peptides could induce and boost hCMC differentiation toward neuronal lineage despite the absence of exogenously added, specific growth factors.

CONCLUSION

This work suggests the scaffold-peptides system combined with autologous hCMCs as a functional biomimetic, self-standing prototype for neural regenerative medicine applications.

Bio-inspired Hybrid Carbon Nanotube Muscles

There has been continuous progress in the development for biomedical engineering systems of hybrid muscle generated by combining skeletal muscle and artificial structure. The main factor affecting the actuation performance of hybrid muscle relies on the compatibility between living cells and their muscle scaffolds during cell culture. Here, we developed a hybrid muscle powered by C2C12 skeletal muscle cells based on the functionalized multi-walled carbon nanotubes (MWCNT) sheets coated with poly(3,4-ethylenedioxythiophene) (PEDOT) to achieve biomimetic actuation. This hydrophilic hybrid muscle is physically durable in solution and responds to electric field stimulation with flexible movement. Furthermore, the biomimetic actuation when controlled by electric field stimulation results in movement similar to that of the hornworm by patterned cell culture method. The contraction and relaxation behavior of the PEDOT/MWCNT-based hybrid muscle is similar to that of the single myotube movement, but has faster relaxation kinetics because of the shape-maintenance properties of the freestanding PEDOT/MWCNT sheets in solution. Our development provides the potential possibility for substantial innovation in the next generation of cell-based biohybrid microsystems.

Production of human pluripotent stem cell therapeutics under defined xeno-free conditions: progress and challenges

Recent advances on human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) have brought us closer to the realization of their clinical potential. Nonetheless, tissue engineering and regenerative medicine applications will require the generation of hPSC products well beyond the laboratory scale. This also mandates the production of hPSC therapeutics in fully-defined, xeno-free systems and in a reproducible manner. Toward this goal, we summarize current developments in defined media free of animal-derived components for hPSC culture. Bioinspired and synthetic extracellular matrices for the attachment, growth and differentiation of hPSCs are also reviewed. Given that most progress in xeno-free medium and substrate development has been demonstrated in two-dimensional rather than three dimensional culture systems, translation from the former to the latter poses unique difficulties. These challenges are discussed in the context of cultivation platforms of hPSCs as aggregates, on microcarriers or after encapsulation in biocompatible scaffolds.

Behaviors of stem cells on carbon nanotube

Regulating stem cell microenvironment is one of the essential elements in stem cell culture. Recently, carbon nanotube (CNT) has come into the spotlight as a biomaterial that retains unique properties. Based on its high chemical stability, elasticity, mechanical strength, and electrical conductivity, CNT shows great potential as an application for biomedical substrate. Also, properties of CNT could be further regulated by appropriate chemical modifications of CNT. Recent studies reported that modulating the cellular microenvironment through the use of CNT and chemically modified CNT as cell culture substrates can affect proliferation and differentiation of various types of stem cells. This review summarizes the unique biological effects of CNT on stem cells.

Development and characterization of polyethylene glycol–carbon nanotube hydrogel composite

Polyethylene–glycol–carbon nanotube composite was developed where carbon nanotubes altered the hydrogel mechanical and physical properties and aided neuronal cell viability.

Physical cues of cell culture materials lead the direction of differentiation lineages of pluripotent stem cells

Differentiation methods of hPSCs into specific cell lineages. Differentiation of hPSCsviaEB formation (types AB, A–D) or without EB formation (types E–H).

Optothermally responsive nanocomposite generating mechanical forces for cells enabled by few-walled carbon nanotubes

We have designed and fabricated a nanocomposite substrate that can deliver spatially and temporally defined mechanical forces onto cells. This nanocomposite substrate comprises a 1.5-mm-thick near-infrared (NIR) mechanoresponsive bottom layer of few-walled carbon nanotubes (FWCNTs) that are uniformly distributed and covalently connected to thermally responsive poly(N-isopropylacrylamide) and an approximately 0.15-mm-thick cell-seeding top layer of collagen-functionalized poly(acrylic acid)-co-poly(N-isopropylacrylamide) that interpenetrates into the bottom layer. Covalent coupling of all the components and uniform distribution of FWCNTs lead to a large local mechanoresponse. As an example, 50% change in strain at the point of irradiation on the order of 0.05 Hz can be produced reversibly under NIR stimulation with 0.02 wt % FWCNTs. We have further demonstrated that the mechanical strain imposed by NIR stimulation can be transmitted onto cells. Human fetal hepatocytes change shape with no sign of detrimental effect on cell viability. To the best of our knowledge, this is the first demonstration of a nanocomposite platform that can generate fast and controlled mechanical force to actuate cells. Since the amplitude, location, and timing of force can be controlled remotely with NIR, the nanocomposite substrate offers the potential to provide accurately designed force sequences for tissue engineering.

Stem cell responses to nanotopography

Cells interact with various nanoscaled topographical and biochemical cues in their cellular macromolecular environment. Nanotopography recreates or mimic the cellular macromolecular environment in vitro. The influence of material surface topography on the behavior of adherent cells has been studied. Current techniques enable various kinds of nanopatterned surface to be generated and applied to cells. The purpose of this review is to provide an overview of nanotopography and its surface patterns, and introduce nanotopography effects on cell behavior including cell attachment, proliferation, and cell differentiation with particular emphasis on musculoskeletal regeneration.

Cognitive deficits and decreased locomotor activity induced by single-walled carbon nanotubes and neuroprotective effects of ascorbic acid

Single-walled carbon nanotubes (SWCNTs) have shown increasing promise in the field of biomedicine, especially in applications related to the nervous system. However, there are limited studies available on the neurotoxicity of SWCNTs used in vivo. In this study, neurobehavioral changes caused by SWCNTs in mice and oxidative stress were investigated. The results of ethological analysis (Morris water maze and open-field test), brain histopathological examination, and assessments of oxidative stress (reactive oxygen species [ROS], malondialdehyde [MDA], and glutathione [GSH]), inflammation (nuclear factor κB, tumor necrosis factor α, interleukin-1β), and apoptosis (cysteine-aspartic acid protease 3) in brains showed that 6.25 and 12.50 mg/kg/day SWCNTs in mice could induce cognitive deficits and decreased locomotor activity, brain histopathological alterations, and increased levels of oxidative stress, inflammation, and apoptosis in mouse brains; however, 3.125 mg/kg/day SWCNTs had zero or minor adverse effects in mice, and these effects were blocked by concurrent administration of ascorbic acid. Down-regulation of oxidative stress, inflammation, and apoptosis were proposed to explain the neuroprotective effects of ascorbic acid. This work suggests SWCNTs could induce cognitive deficits and decreased locomotor activity, and provides a strategy to avoid the adverse effects.

Carbon nanotubes in neuroregeneration and repair

In the last decade, we have experienced an increasing interest and an improved understanding of the application of nanotechnology to the nervous system. The aim of such studies is that of developing future strategies for tissue repair to promote functional recovery after brain damage. In this framework, carbon nanotube based technologies are emerging as particularly innovative tools due to the outstanding physical properties of these nanomaterials together with their recently documented ability to interface neuronal circuits, synapses and membranes. This review will discuss the state of the art in carbon nanotube technology applied to the development of devices able to drive nerve tissue repair; we will highlight the most exciting findings addressing the impact of carbon nanotubes in nerve tissue engineering, focusing in particular on neuronal differentiation, growth and network reconstruction.

Chondroitin sulphate-based 3D scaffolds containing MWCNTs for nervous tissue repair

Nervous tissue lesions are an important social concern due to their increasing prevalence and their high sanitary costs. Their treatment still remains a challenge because of the reduced ability of nervous tissue to regenerate, its intrinsic structural and functional complexity and the rapid formation of fibroglial scars inhibiting neural repair. Herein, we show that 3D porous scaffolds made of chondroitin sulphate (CS), a major regulatory component of the nervous tissue, and multi-walled carbon nanotubes (MWCNTs) are selective substrates for the formation of a viable and neuron-enriched network with a transitory low glial content. Scaffolds have been fabricated by using the ice segregation-induced self-assembly technique and cultured with embryonic neural progenitor cells. Cell adhesion, morphology, viability, neuron/glial differentiation, calcium signaling dynamics, and mitochondrial activity have been studied over time on the scaffolds and compared to appropriate 2D control substrates. Our results indicate the formation of viable cultures enriched in neuron cells for up to 20 days, with ability to display calcium transients and active mitochondria, even in the absence of poly-D-lysine coating. A synergistic neural-permissive signaling from both the scaffold structure and its components (i.e., MWCNTs and CS) is suggested as the major responsible factor for these findings. We anticipate that these scaffolds may serve nerve regeneration if implanted in the acute phase after injury, as it is during the first stages of graft implantation when the most critical sequence of phenomena takes place to drive either nervous regeneration or fibroglial scar formation. The temporary glial inhibition found may be, indeed, beneficial for promoting the formation of neuron-enriched circuits at early phases while guaranteeing posterior glial integration to support longer-term neuron survival and activity.

Engineering the human pluripotent stem cell microenvironment to direct cell fate

Human pluripotent stem cells (hPSCs), including both embryonic stem cells and induced pluripotent stem cells, offer a potential cell source for research, drug screening, and regenerative medicine applications due to their unique ability to self-renew or differentiate to any somatic cell type. Before the full potential of hPSCs can be realized, robust protocols must be developed to direct their fate. Cell fate decisions are based on components of the surrounding microenvironment, including soluble factors, substrate or extracellular matrix, cell-cell interactions, mechanical forces, and 2D or 3D architecture. Depending on their spatio-temporal context, these components can signal hPSCs to either self-renew or differentiate to cell types of the ectoderm, mesoderm, or endoderm. Researchers working at the interface of engineering and biology have identified various factors which can affect hPSC fate, often based on lessons from embryonic development, and they have utilized this information to design in vitro niches which can reproducibly direct hPSC fate. This review highlights culture systems that have been engineered to promote self-renewal or differentiation of hPSCs, with a focus on studies that have elucidated the contributions of specific microenvironmental cues in the context of those culture systems. We propose the use of microsystem technologies for high-throughput screening of spatial-temporal presentation of cues, as this has been demonstrated to be a powerful approach for differentiating hPSCs to desired cell types.

Carbon nanomaterials for nerve tissue stimulation and regeneration

Nanotechnology offers new perspectives in the field of innovative medicine, especially for reparation and regeneration of irreversibly damaged or diseased nerve tissues due to lack of effective self-repair mechanisms in the peripheral and central nervous systems (PNS and CNS, respectively) of the human body. Carbon nanomaterials, due to their unique physical, chemical and biological properties, are currently considered as promising candidates for applications in regenerative medicine. This chapter discusses the potential applications of various carbon nanomaterials including carbon nanotubes, nanofibers and graphene for regeneration and stimulation of nerve tissue, as well as in drug delivery systems for nerve disease therapy.

Carbon nanotubes: their potential and pitfalls for bone tissue regeneration and engineering

The extracellular environment which supports cell life is composed of a hierarchy of maintenance, force and regulatory systems which integrate from the nano- through to macroscale. For this reason, strategies to recreate cell supporting environments have been investigating the use of nanocomposite biomaterials. Here, we review the use of carbon nanotubes as part of a bottom-up approach for use in bone tissue engineering. We evaluate the properties of carbon nanotubes in the context of synthetic tissue substrates and contrast them with the nanoscale features of the extracellular environment. Key studies are evaluated with an emphasis on understanding the mechanisms through which carbon nanotubes interact with biological systems. This includes an examination of how the different properties of carbon nanotubes affect tissue growth, how these properties and variation to them might be leveraged in regenerative tissue therapies and how impurities or contaminates affect their toxicity and biological interaction.

FROM THE CLINICAL EDITOR

In this comprehensive review, the authors describe the status and potential applications of carbon nanotubes in bone tissue engineering.

Concise review: carbon nanotechnology: perspectives in stem cell research

Carbon nanotechnology has developed rapidly during the last decade, and carbon allotropes, especially graphene and carbon nanotubes, have already found a wide variety of applications in industry, high-tech fields, biomedicine, and basic science. Electroconductive nanomaterials have attracted great attention from tissue engineers in the design of remotely controlled cell-substrate interfaces. Carbon nanoconstructs are also under extensive investigation by clinical scientists as potential agents in anticancer therapies. Despite the recent progress in human pluripotent stem cell research, only a few attempts to use carbon nanotechnology in the stem cell field have been reported. However, acquired experience with and knowledge of carbon nanomaterials may be efficiently used in the development of future personalized medicine and in tissue engineering.

Are carbon nanotubes a natural solution? Applications in biology and medicine

Carbon nanotubes and materials based on carbon nanotubes have many perceived applications in the field of biomedicine. Several highly promising examples have been highlighted in the literature, ranging from their use as growth substrates or tissue scaffolds to acting as intracellular transporters for various therapeutic and diagnostic agents. In addition, carbon nanotubes have a strong optical absorption in the near-infrared region (in which tissue is transparent), which enables their use for biological imaging applications and photothermal ablation of tumors. Although these advances are potentially game-changing, excitement must be tempered somewhat as several bottlenecks exist. Carbon nanotube-based technologies ultimately have to compete with and out-perform existing technologies in terms of performance and price. Moreover, issues have been highlighted relating to toxicity, which presents an obstacle for the transition from preclinical to clinical use. Although many studies have suggested that well-functionalized carbon nanotubes appear to be safe to the treated animals, mainly rodents, long-term toxicity issues remains to be elucidated. In this report, we systematically highlight some of the most promising biomedical application areas of carbon nanotubes and review the interaction of carbon nanotubes with cultured cells and living organisms with a particular focus on in vivo biodistribution and potential adverse health effects. To conclude, future challenges and prospects of carbon nanotubes for biomedical applications will be addressed.

Carbon-based nanomaterials for tissue engineering

Carbon-based nanomaterials such as graphene sheets and carbon nanotubes possess unique mechanical, electrical, and optical properties that present new opportunities for tissue engineering, a key field for the development of biological alternatives that repair or replace whole or a portion of tissue. Carbon nanomaterials can also provide a similar microenvironment as like a biological extracellular matrix in terms of chemical composition and physical structure, making them a potential candidate for the development of artificial scaffolds. In this review, we summarize recent research advances in the effects of carbon nanomaterial-based substrates on cellular behaviors, including cell adhesion, proliferation, and differentiation into osteo- or neural- lineages. The development of 3D scaffolds based on carbon nanomaterials (or their composites with polymers and inorganic components) is introduced, and the potential of these constructs in tissue engineering, including toxicity issues, is discussed. Future perspectives and emerging challenges are also highlighted.

Gene networks: dissecting pathways in retinal development and disease

During retinal neurogenesis, diverse cellular subtypes originate from multipotent neural progenitors in a spatiotemporal order leading to a highly specialized laminar structure combined with a distinct mosaic architecture. This is driven by the combinatorial action of transcription factors and signaling molecules which specify cell fate and differentiation. The emerging approach of gene network analysis has allowed a better understanding of the functional relationships between genes expressed in the developing retina. For instance, these gene networks have identified transcriptional hubs that have revealed potential targets and pathways for the development of therapeutic options for retinal diseases. Much of the current knowledge has been informed by targeted gene deletion experiments and gain-of-functional analysis. In this review we will provide an update on retinal development gene networks and address the wider implications for future disease therapeutics.

Improved neural differentiation of human mesenchymal stem cells interfaced with carbon nanotube scaffolds

AIM

The authors aimed to investigate the effect of carbon nanotube (CNT)-based extracellular environments on the neural differentiation of human mesenchymal stem cells (hMSCs) when combined with chemical inducers.

MATERIALS & METHODS

CNT-based nanoscaffolds (linear CNT network patterns and CNT bulk network films) were prepared on solid substrates for hMSC culturing. After the hMSCs were differentiated in neural differentiation media for 2 weeks, the authors examined the neural differentiation of the hMSCs using immunocytochemistry and real-time PCR.

RESULTS

The authors found that the linear CNT network patterns could effectively control the cell elongation and nuclear shape of hMSCs during the neural differentiation process, further enhancing neural gene expression compared with the bulk CNT-based films. Moreover, the CNT network films could significantly upregulate the gene expression of voltage-gated ion channels, which should be a key component for the neural activity of differentiated hMSCs.

CONCLUSION

These findings suggest that CNT-based nanoscaffolds can be used as an excellent extracellular nano-/micro-environment for applications requiring effective neural differentiation of stem cells, such as regenerative medicine and tissue engineering.

Nanomaterial scaffolds for stem cell proliferation and differentiation in tissue engineering

Tissue engineering is a clinically driven field and has emerged as a potential alternative to organ transplantation. The cornerstone of successful tissue engineering rests upon two essential elements: cells and scaffolds. Recently, it was found that stem cells have unique capabilities of self-renewal and multilineage differentiation to serve as a versatile cell source, while nanomaterials have lately emerged as promising candidates in producing scaffolds able to better mimic the nanostructure in natural extracellular matrix and to efficiently replace defective tissues. This article, therefore, reviews the key developments in tissue engineering, where the combination of stem cells and nanomaterial scaffolds has been utilized over the past several years. We consider the high potential, as well as the main issues related to the application of stem cells and nanomaterial scaffolds for a range of tissues including bone, cartilage, nerve, liver, eye etc. Promising in vitro results such as efficient attachment, proliferation and differentiation of stem cells have been compiled in a series of examples involving different nanomaterials. Furthermore, the merits of the marriage of stem cells and nanomaterial scaffolds are also demonstrated in vivo, providing early successes to support subsequent clinical investigations. This progress simultaneously drives mechanistic research into the mechanotransduction process responsible for the observations in order to optimize the process further. Current understanding is chiefly reported to involve the interaction of stem cells and the anchoring nanomaterial scaffolds by activating various signaling pathways. Substrate surface characteristics and scaffold bulk properties are also reported to influence not only short term stem cell adhesion, spreading and proliferation, but also longer term lineage differentiation, functionalization and viability. It is expected that the combination of stem cells and nanomaterials will develop into an important tool in tissue engineering for the innovative treatment of many diseases.

Influence of nanomaterials on stem cell differentiation: designing an appropriate nanobiointerface

During the last decade, due to advances in functionalization chemistry, novel nanobiomaterials with applications in tissue engineering and regenerative medicine have been developed. These novel materials with their unique physical and chemical properties are bioactive hierarchical structures that hold great promise for future development of human tissues. Thus, various nanomaterials are currently being intensively explored in the directed differentiation of stem cells, the design of novel bioactive scaffolds, and new research avenues towards tissue regeneration. This paper illustrates the latest achievements in the applications of nanotechnology in tissue engineering in the field of regenerative medicine.

Micro-/nano-engineered cellular responses for soft tissue engineering and biomedical applications

The development of biomedical devices and reconstruction of functional ex vivo tissues often requires the need to fabricate biomimetic surfaces with features of sub-micrometer precision. This can be achieved with the advancements in micro-/nano-engineering techniques, allowing researchers to manipulate a plethora of cellular behaviors at the cell-biomaterial interface. Systematic studies conducted on these 2D engineered surfaces have unraveled numerous novel findings that can potentially be integrated as part of the design consideration for future 2D and 3D biomaterials and will no doubt greatly benefit tissue engineering. In this review, recent developments detailing the use of micro-/nano-engineering techniques to direct cellular orientation and function pertinent to soft tissue engineering will be highlighted. Particularly, this article aims to provide valuable insights into distinctive cell interactions and reactions to controlled surfaces, which can be exploited to understand the mechanisms of cell growth on micro-/nano-engineered interfaces, and to harness this knowledge to optimize the performance of 3D artificial soft tissue grafts and biomedical applications.

Carbon nanotubes in neural interfacing applications

Carbon nanotubes (CNT) are remarkable materials with a simple and inert molecular structure that gives rise to a range of potentially valuable physical and electronic properties, including high aspect ratio, high mechanical strength and excellent electrical conductivity. This review summarizes recent research on the application of CNT-based materials to study and control cells of the nervous system. It includes the use of CNT as cell culture substrates, to create patterned surfaces and to study cell-matrix interactions. It also summarizes recent investigations of CNT toxicity, particularly as related to neural cells. The application of CNT-based materials to directing the differentiation of progenitor and stem cells toward neural lineages is also discussed. The emphasis is on how CNT surface chemistry and nanotopography can be altered, and how such changes can affect neural cell function. This knowledge can be applied to creating improved neural interfaces and devices, as well as providing new approaches to neural tissue engineering and regeneration.