Carbon nanotubes and mesenchymal stem cells: biocompatibility, proliferation and differentiation

Nanomaterial-Based Scaffolds for Tissue Engineering Applications: A Review on Graphene, Carbon Nanotubes and Nanocellulose

Nanoscale biomaterials have garnered immense interest in the scientific community in the recent decade. This review specifically focuses on the application of three nanomaterials, i.e., graphene and its derivatives (graphene oxide, reduced graphene oxide), carbon nanotubes (CNTs) and nanocellulose (cellulose nanocrystals or CNCs and cellulose nanofibers or CNFs), in regenerating different types of tissues, including skin, cartilage, nerve, muscle and bone. Their excellent inherent (and tunable) physical, chemical, mechanical, electrical, thermal and optical properties make them suitable for a wide range of biomedical applications, including but not limited to diagnostics, therapeutics, biosensing, bioimaging, drug and gene delivery, tissue engineering and regenerative medicine. A state-of-the-art literature review of composite tissue scaffolds fabricated using these nanomaterials is provided, including the unique physicochemical properties and mechanisms that induce cell adhesion, growth, and differentiation into specific tissues. In addition, in vitro and in vivo cytotoxic effects and biodegradation behavior of these nanomaterials are presented. We also discuss challenges and gaps that still exist and need to be addressed in future research before clinical translation of these promising nanomaterials can be realized in a safe, efficacious, and economical manner.

Nanomaterial-Based Scaffolds for Tissue Engineering Applications: A Review on Graphene, Carbon Nanotubes and Nanocellulose

Nanoscale biomaterials have garnered immense interest in the scientific community in the recent decade. This review specifically focuses on the application of three nanomaterials, i.e., graphene and its derivatives (graphene oxide, reduced graphene oxide), carbon nanotubes (CNTs) and nanocellulose (cellulose nanocrystals or CNCs and cellulose nanofibers or CNFs), in regenerating different types of tissues, including skin, cartilage, nerve, muscle and bone. Their excellent inherent (and tunable) physical, chemical, mechanical, electrical, thermal and optical properties make them suitable for a wide range of biomedical applications, including but not limited to diagnostics, therapeutics, biosensing, bioimaging, drug and gene delivery, tissue engineering and regenerative medicine. A state-of-the-art literature review of composite tissue scaffolds fabricated using these nanomaterials is provided, including the unique physicochemical properties and mechanisms that induce cell adhesion, growth, and differentiation into specific tissues. In addition, in vitro and in vivo cytotoxic effects and biodegradation behavior of these nanomaterials are presented. We also discuss challenges and gaps that still exist and need to be addressed in future research before clinical translation of these promising nanomaterials can be realized in a safe, efficacious, and economical manner.

Inorganic Nanoparticles-Based Systems in Biomedical Applications of Stem Cells: Opportunities and Challenges

Stem cells (SC) are a kind of cells with self renewing ability and multipotent differentiation, which can differentiate into many types of cells such as osteoblast, chondrocyte, neurocyte to treat disease like osteoporosis, osteoarthritis and Alzheimer's disease. Despite the development of novel methods for inducing cell differentiation, the inefficiency and complexity of controlling differentiation of stem cells remain a serious challenge, which necessary to develop a new and alternative approach for effectively controlling the direction of stem cell differentiation in vitro and in vivo in stem cells therapy. Recent advancement in nanotechnology for developing a new class of inorganic nanoparticles that exhibit unique chemical and physical properties holds promise for the treatment of stem cells. Over the last decade, inorganic nanoparticle-based approaches against stem cells have been directed toward developing nanoparticles with drug delivery, or utilizing nanoparticles for controlled cell behaviors, and applying nanoparticles for inducing cell differentiation directly. In addition, a strategy to functionalize inorganic nanoparticles as a nanoprobe towards enhanced penetration through near-infrared light or nuclear magnetic resonance has been receiving considerable interest by means of long-term tracking stem cell in vivo. This review summarizes and highlights the recent development of these inorganic nanoparticle-based approaches as potential therapeutics for controlling differentiation of stem cells and so on for stem cell therapy, along with current opportunities and challenges that need to be overcome for their successful clinical translation.

Impact of Nanotechnology on Differentiation and Augmentation of Stem Cells for Liver Therapy

The liver is one of the crucial organs of the body that performs hundreds of chemical reactions needed by the body to survive. It is also the largest gland of the body. The liver has multiple functions, including the synthesis of chemicals, metabolism of nutrients, and removal of toxins. It also acts as a storage unit. The liver has a unique ability to regenerate itself, but it can lead to permanent damage if the injury is beyond recovery. The only possible treatment of severe liver damage is liver transplant which is a costly procedure and has several other drawbacks. Therefore, attention has been shifted towards the use of stem cells that have shown the ability to differentiate into hepatocytes. Among the numerous kinds of stem cells (SCs), the mesenchymal stem cells (MSCs) are the most famous. Various studies suggest that an MSC transplant can repair liver function, improve the signs and symptoms, and increase the chances of survival. This review discusses the impact of combining stem cell therapy with nanotechnology. By integrating stem cell science and nanotechnology, the information about stem cell differentiation and regulation will increase, resulting in a better comprehension of stem cell-based treatment strategies. The augmentation of SCs with nanoparticles has been shown to boost the effect of stem cell-based therapy. Also, the function of green nanoparticles in liver therapies is discussed.

Engineered nanoparticles toxicity on adipose tissue derived mesenchymal stem cells: A preliminary investigation

Nanoscience and nanotechnologies have recently gained importance in several fields, such as industry and medicine. A big issue of the increasing application of nanomaterials is the poor literature regarding their potential toxicity in humans and animals. Recently, adult stem cells have been proposed as putative targets of nanoparticles (NPs). This study aims to investigate the effects of zerovalent-metallic NPs on isolated and amplified equine Adipose tissue derived Mesenchymal Stem Cells (eAdMSCs). Cells were treated with Cobalt (Co-), Iron (Fe-), and Nickel (Ni-) nanoparticles (NPs) at different concentrations and were characterized for the cytotoxic and genotoxic effects of exposure. Treatment with NPs resulted in reduced cell viability and proliferative capability in comparison with untreated cells. However, this did not influence eAdMSCs potency, as treated cells were able to differentiate towards the adipogenic and osteogenic lineages. Ni- and Fe-NPs showed cytoplasmic localization, while Co-NPs entered the nucleus and mitochondria, suggesting a potential genotoxic activity. Regarding p53 expression, it was enhanced in the first 48 h after treatments, with a drastic reduction of expression within 72 h. Higher p53 expression was reported in the case of Co-NP treatment, suggesting the tumorigenic potential of these NPs. Telomerase activity was enhanced by Fe- and Ni-NP treatments in a concentration- and time-dependent way. This was not true for Co-NP treated samples, suggesting a reduced replicative capacity of eAdMSCs upon Co-NP exposure. The present study is a preliminary investigation of the influence exerted by NPs on eAdMSC physiological activity in terms of cytotoxic and genotoxic effects. The present results revealed eAdMSC physiology to be strongly influenced by NPs in a dose-, time- and NP-dependent way.

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.

Three-dimensional, biomimetic electrospun scaffolds reinforced with carbon nanotubes for temporomandibular joint disc regeneration

Temporomandibular disorder (TMD) remained a huge clinical challenge, with high prevalence but limited, unstable, and only palliative therapeutic methods available. As one of the most vulnerable sites implicated in TMD, the temporomandibular joint disc (TMJD) displayed a complicated microstructure, region-specific fibrocartilaginous distribution, and poor regenerative property, which all further hindered its functional regeneration. To address the problem, with versatile and relatively simple electrospinning (ELS) technique, our study successfully fabricated a biomimetic, three-dimensional poly (ϵ-caprolactone) (PCL)/polylactide (PLA)/carbon nanotubes (CNTs) disc scaffold, whose biconcave gross anatomy and regionally anisotropic microstructure recapitulating those of the native disc. As in vitro results validated the superior mechanical, bioactive, and regenerative properties of the biomimetic scaffolds with optimal CNTs reinforcement, we further performed in vivo experiments. After verifying its biocompatibility and ectopic fibrochondrogenicity in nude mice subcutaneous implantation models, the scaffolds guided disc regeneration and subchondral bone protection were also confirmed orthotopically in rabbits TMJD defected areas, implying the pivotal role of morphological cues in contact-guided tissue regeneration. In conclusion, our work represents a significant advancement in complex, inhomogeneous tissue engineering, providing promising clinical solutions to intractable TMD ailments. STATEMENT OF SIGNIFICANCE: Complex tissue regeneration remains a huge scientific and clinical challenge. Although frequently implicated in temporomandibular joint disorder (TMD), functional regeneration of injured temporomandibular joint disc (TMJD) is extremely hard to achieve, mainly because of the complex anatomy and microstructure with regionally variant, anisotropic fiber alignments in the native disc. In this study, we developed the biomimetic electrospun scaffold with optimal CNTs reinforcement and regionally anisotropic fiber orientations. The excellent mechanical and bioactive properties were confirmed both in vitro and in vivo, effectively promoting defected discs regeneration in rabbits. Besides demonstrating the crucial role of morphological biomimicry in tissue engineering, our work also presents a feasible clinical solution for complex tissue regeneration.

Micro- and nanotechnology in biomedical engineering for cartilage tissue regeneration in osteoarthritis

Osteoarthritis, which typically arises from aging, traumatic injury, or obesity, is the most common form of arthritis, which usually leads to malfunction of the joints and requires medical interventions due to the poor self-healing capacity of articular cartilage. However, currently used medical treatment modalities have reported, at least in part, disappointing and frustrating results for patients with osteoarthritis. Recent progress in the design and fabrication of tissue-engineered microscale/nanoscale platforms, which arises from the convergence of stem cell research and nanotechnology methods, has shown promising results in the administration of new and efficient options for treating osteochondral lesions. This paper presents an overview of the recent advances in osteochondral tissue engineering resulting from the application of micro- and nanotechnology approaches in the structure of biomaterials, including biological and microscale/nanoscale topographical cues, microspheres, nanoparticles, nanofibers, and nanotubes.

Advantages and prospects of stem cells in nanotoxicology

Nanomaterials have been widely used in many fields, especially in biomedical and stem cell therapy. However, the potential risks associated with nanomaterials applications are also gradually increasing. Therefore, effective and robust toxicology models are critical to evaluate the developmental toxicity of nanomaterials. The development of stem cell research provides a new idea of developmental toxicology. Recently, many researchers actively investigated the effects of nanomaterials with different sizes and surface modifications on various stem cells (such as embryonic stem cells (ESCs), adult stem cells, etc.) to study the toxic effects and toxic mechanisms. In this review, we summarized the effects of nanomaterials on the proliferation and differentiation of ESCs, mesenchymal stem cells and neural stem cells. Moreover, we discussed the advantages of stem cells in nanotoxicology compared with other cell lines. Finally, combined with the latest research methods and new molecular mechanisms, we analyzed the application of stem cells in nanotoxicology.

Mesenchymal stem cell-based nanoparticles and scaffolds in regenerative medicine

Mesenchymal stem cells (MSCs) are adult stem cells owing to their regenerative potential and multilineage potency. MSCs have wide-scale applications either in their native cellular form or in conjugation with specific biomaterials as nanocomposites. Majorly, these natural or synthetic biomaterials are being used in the form of metallic and non-metallic nanoparticles (NPs) to encapsulate MSCs within hydrogels like alginate or chitosan or drug cargo loading into MSCs. In contrast, nanofibers of polymer scaffolds such as polycaprolactone (PCL), poly-lactic-co-glycolic acid (PLGA), poly-L-lactic acid (PLLA), silk fibroin, collagen, chitosan, alginate, hyaluronic acid (HA), and cellulose are used to support or grow MSCs directly on it. These MSCs based nanotherapies have application in multiple domains of biomedicine including wound healing, bone and cartilage engineering, cardiac disorders, and neurological disorders. This study focused on current approaches of MSCs-based therapies and has been divided into two major sections. The first section elaborates on MSC-based nano-therapies and their plausible applications including exosome engineering and NPs encapsulation. The following section focuses on the various MSC-based scaffold approaches in tissue engineering. Conclusively, this review mainly focused on MSC-based nanocomposite's current approaches and compared their advantages and limitations for building effective regenerative medicines.

Cytocompatibility of carboxylated multi-wall carbon nanotubes in stem cells from human exfoliated deciduous teeth

Carboxylated multi-wall carbon nanotube (MWCNT-COOH) presents unique properties due to nanoscale dimensions and permits a broad range of applications in different fields, such as bone tissue engineering and regenerative medicine. However, the cytocompatibility of MWCNT-COOH with human stem cells is poorly understood. Thus, studies elucidating how MWCNT-COOH affects human stem cell viability are essential to a safer application of nanotechnologies. Using stem cells from the human exfoliated deciduous teeth model, we have evaluated the effects of MWCNT-COOH on cell viability, oxidative cell stress, and DNA integrity. Results demonstrated that despite the decreased metabolism of mitochondria, MWCNT-COOH had no toxicity against stem cells. Cells maintained viability after MWCNT-COOH exposure. MWCNT-COOH did not alter the superoxide dismutase activity and did not cause genotoxic effects. The present findings are relevant to the potential application of MWCNT-COOH in the tissue engineering and regenerative medicine fields.

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.

Electroactive Biomaterials and Systems for Cell Fate Determination and Tissue Regeneration: Design and Applications

During natural tissue regeneration, tissue microenvironment and stem cell niche including cell-cell interaction, soluble factors, and extracellular matrix (ECM) provide a train of biochemical and biophysical cues for modulation of cell behaviors and tissue functions. Design of functional biomaterials to mimic the tissue/cell microenvironment have great potentials for tissue regeneration applications. Recently, electroactive biomaterials have drawn increasing attentions not only as scaffolds for cell adhesion and structural support, but also as modulators to regulate cell/tissue behaviors and function, especially for electrically excitable cells and tissues. More importantly, electrostimulation can further modulate a myriad of biological processes, from cell cycle, migration, proliferation and differentiation to neural conduction, muscle contraction, embryogenesis, and tissue regeneration. In this review, endogenous bioelectricity and piezoelectricity are introduced. Then, design rationale of electroactive biomaterials is discussed for imitating dynamic cell microenvironment, as well as their mediated electrostimulation and the applying pathways. Recent advances in electroactive biomaterials are systematically overviewed for modulation of stem cell fate and tissue regeneration, mainly including nerve regeneration, bone tissue engineering, and cardiac tissue engineering. Finally, the significance for simulating the native tissue microenvironment is emphasized and the open challenges and future perspectives of electroactive biomaterials are concluded.

Nanomaterials and Stem Cell Differentiation Potential: An Overview of Biological Aspects and Biomedical Efficacy

Nanoparticles (NPs) due to their medical applications are widely used. Accordingly, the use of mesenchymal stem cells is one of the most important alternatives in tissue engineering field. NPs play effective roles in stem cells proliferation and differentiation. The combination of NPs and tissue regeneration by stem cells has created new therapeutic approach towards humanity. Of note, the physicochemical properties of NPs determine their biological function. Interestingly, various mechanisms such as modulation of signaling pathways and generation of reactive oxygen species, are involved in NPs-induced cellular proliferation and differentiation. This review summarized the types of nanomaterials effective on stem cell differentiation, the physicochemical features, biomedical application of these materials and relationship between nanomaterials and environment.

In vitro propagation and cardiac differentiation of canine induced pluripotent stem cells on carbon nanotube substrates

Induced pluripotent stem cells (iPSCs) have attracted an interest for personalized cell based therapy along with various other applications. There have been few studies that effective nanomaterial based scaffolds act as alternative to the commonly used feeder dependent in vitro maintenance of iPSCs. The present study provides the fundamental information on ex vivo behavior of canine iPSC (ciPSCs) maintained on carboxylic acid (COOH) functionalized single-walled carbon nanotubes (COOH-SWCNTs) and multi-walled carbon nanotubes (COOH-MWCNTs) substrates. Here in we evaluated the comparative colony morphology, propagation, characterization, cytocompatibility and differentiation capability of ciPSC cultured on MEF feeder taken as control, and COOH-SWCNTs and COOH-MWCNTs substrates. We observed a healthy growth of ciPSCs on both the types of carbon nanotubes (CNTs) similar to feeder. The ciPSC colonies grown on both CNTs were positive for alkaline phosphatase staining and expressed pluripotent markers with notable significance. Further, the ciPSC colonies grew on these CNTs retained the in vitro differentiation ability into three germ layers as well as cardiac cell. Cytotoxicity analysis revealed that (COOH) functionalized CNTs provided a culture condition of low cytotoxicity. The results of the present study indicated that (COOH) functionalized CNTs could be used as xeno-free substrate to support the maintenance of iPSCs.

Carbon-based Nanomaterials and Curcumin: A Review of Biosensing Applications

Curcumin, the main active constituent of turmeric (Curcuma longa L.), is a naturally occurring phenolic compound with a wide variety of pharmacological activities. Although it has multiple pharmaceutical properties, its bioavailability and industrial usage are hindered due to rapid hydrolysis and low water solubility. Due to the growing market of curcumin, exact determination of curcumin in trade and human biological samples is important for monitoring therapeutic actions. Different nanomaterials have been suggested for sensing curcumin; and in this case, carbon-based nanomaterials (CNMs) are one of the most outstanding developments in nanomedicine, biosensing, and regenerative medicine. There are a considerable number of reports which have shown interesting potential of CNMs-based biosensors in the sensitive and selective detection of curcumin. Therefore, this review aims to increase understanding the interaction of curcumin with CNMs in the context of biosensing.

Nanobiohybrids: Materials approaches for bioaugmentation

Nanobiohybrids, synthesized by integrating functional nanomaterials with living systems, have emerged as an exciting branch of research at the interface of materials engineering and biological science. Nanobiohybrids use synthetic nanomaterials to impart organisms with emergent properties outside their scope of evolution. Consequently, they endow new or augmented properties that are either innate or exogenous, such as enhanced tolerance against stress, programmed metabolism and proliferation, artificial photosynthesis, or conductivity. Advances in new materials design and processing technologies made it possible to tailor the physicochemical properties of the nanomaterials coupled with the biological systems. To date, many different types of nanomaterials have been integrated with various biological systems from simple biomolecules to complex multicellular organisms. Here, we provide a critical overview of recent developments of nanobiohybrids that enable new or augmented biological functions that show promise in high-tech applications across many disciplines, including energy harvesting, biocatalysis, biosensing, medicine, and robotics.

Dense carbon-nanotube coating scaffolds stimulate osteogenic differentiation of mesenchymal stem cells

Carbon nanotubes (CNTs) have desirable mechanical properties for use as biomaterials in orthopedic and dental area such as bone- and tooth- substitutes. Here, we demonstrate that a glass surface densely coated with single-walled carbon nanotubes (SWNTs) stimulate the osteogenic differentiation of rat bone marrow mesenchymal stem cells (MSCs). MSCs incubated on SWNT- and multi-walled carbon nanotube (MWNT)-coated glass showed high activities of alkaline phosphatase that are markers for early stage osteogenic differentiation. Expression of Bmp2, Runx2, and Alpl of MSCs showed high level in the early stage for MSC incubation on SWNT- and MWNT-coated surfaces, but only the cells on the SWNT-coated glass showed high expression levels of Bglap (Osteocalcin). The cells on the SWNT-coated glass also contained the most calcium, and their calcium deposits had long needle-shaped crystals. SWNT coating at high density could be part of a new scaffold for bone regeneration.

The rationale and emergence of electroconductive biomaterial scaffolds in cardiac tissue engineering

The human heart possesses minimal regenerative potential, which can often lead to chronic heart failure following myocardial infarction. Despite the successes of assistive support devices and pharmacological therapies, only a whole heart transplantation can sufficiently address heart failure. Engineered scaffolds, implantable patches, and injectable hydrogels are among the most promising solutions to restore cardiac function and coax regeneration; however, current biomaterials have yet to achieve ideal tissue regeneration and adequate integration due a mismatch of material physicochemical properties. Conductive fillers such as graphene, carbon nanotubes, metallic nanoparticles, and MXenes and conjugated polymers such as polyaniline, polypyrrole, and poly(3,4-ethylendioxythiophene) can possibly achieve optimal electrical conductivities for cardiac applications with appropriate suitability for tissue engineering approaches. Many studies have focused on the use of these materials in multiple fields, with promising effects on the regeneration of electrically active biological tissues such as orthopedic, neural, and cardiac tissue. In this review, we critically discuss the role of heart electrophysiology and the rationale toward the use of electroconductive biomaterials for cardiac tissue engineering. We present the emerging applications of these smart materials to create supportive platforms and discuss the crucial role that electrical stimulation has been shown to exert in maturation of cardiac progenitor cells.

In vitro proliferation and differentiation of canine bone marrow derived mesenchymal stem cells over hydroxyl functionalized CNT substrates

Nanotopography of culture substrate acts as a positive cue in cell-biomaterial based tissue regeneration. Considering the potentiality of carbon nanotubes (CNTs) this study was designed to evaluate its two functionalized form by an in vitro culture condition using canine mesenchymal stem cells as cellular model. Cells were isolated and its behaviour, proliferation and differentiation processes were elucidated onto CNT substrates. Beside the variations in cellular behaviour it was remarkably noted that even though proliferation was reduced but osteogenic and chondrogenic differentiation was enhanced over multi-walled CNTs, whereas neuronal differentiation was better supported by single walled CNTs as evidenced by our cytochemical, immunocytochemical, gene expression and flow cytometry assays. The former one was noticed more cytocompatible by our different apoptosis studies. The outcome of these experiments collectively indicated that hydroxylated functionalized CNTs could be a potential scaffold constituent for future experimentations as well as for the application in regenerative medicine.

Fabrication of Surfactant-Dispersed HiPco Single-Walled Carbon Nanotube-Based Alginate Hydrogel Composites as Cellular Products

In this study, we designed, synthesized, and characterized ultrahigh purity single-walled carbon nanotube (SWCNT)-alginate hydrogel composites. Among the parameters of importance in the formation of an alginate-based hydrogel composite with single-walled carbon nanotubes, are their varying degrees of purity, their particulate agglomeration and their dose-dependent correlation to cell viability, all of which have an impact on the resultant composite’s efficiency and effectiveness towards cell-therapy. To promote their homogenous dispersion by preventing agglomeration of the SWCNT, three different surfactants-sodium dodecyl sulfate (SDS-anionic), cetyltrimethylammonium bromide (CTAB-cationic), and Pluronic F108 (nonionic)-were utilized. After mixing of the SWCNT-surfactant with alginate, the mixtures were cross-linked using divalent calcium ions and characterized using Raman spectroscopy. Rheometric analysis showed an increase in complex viscosity, loss, and storage moduli of the SWCNT composite gels in comparison with pure alginate gels. Scanning electron microscopy revealed the presence of a well-distributed porous structure, and all SWCNT-gel composites depicted enhanced electrical conductivity with respect to alginate gels. To characterize their biocompatibility, cardiomyocytes were cultured atop these SWCNT-gels. Results comprehensively implied that Pluronic F108 was most efficient in preventing agglomeration of the SWCNTs in the alginate matrix, leading to a stable scaffold formation without posing any toxicity to the cells.

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.

Versatile Biomaterial Platform Enriched with Graphene Oxide and Carbon Nanotubes for Multiple Tissue Engineering Applications

Carbon-based nanomaterials, such as graphene oxide (GO) or carbon nanotubes (CNTs) are currently used in various medical applications due to their positive influence on biocompatibility, adhesion, proliferation, and differentiation, as well as their contribution to modulating cell behavior in response to nanomaterial substrates. In this context, in this study, novel flexible membranes based on cellulose acetate (CA) enriched with CNT and GO in different percentages were tested for their versatility to be used as substrates for soft or hard tissue engineering (TE), namely, for their ability to support human adipose-derived stem cells (hASCs) adhesion during adipogenic or osteogenic differentiation. For this purpose, differentiation markers were assessed both at gene and protein levels, while histological staining was performed to show the evolution of the processes in response to CA-CNT-GO substrates. Micro-CT analysis indicated porous morphologies with open and interconnected voids. A slightly lower total porosity was obtained for the samples filled with the highest amount of GO and CNTs, but thicker walls, larger and more uniform pores were obtained, providing beneficial effects on cell behavior and increased mechanical stability. The addition of 1 wt% GO and CNT to the biocomposites enhanced hASCs adhesion and cytoskeleton formation. The evolution of both adipogenic and osteogenic differentiation processes was found to be augmented proportionally to the GO-CNT concentration. In conclusion, CA-CNT-GO biomaterials displayed good properties and versatility as platforms for cell differentiation with potential as future implantable materials in TE applications.

Labeling Stem Cells with a New Hybrid Bismuth/Carbon Nanotube Contrast Agent for X-Ray Imaging

The poor retention and survival of cells after transplantation to solid tissue represent a major obstacle for the effectiveness of stem cell-based therapies. The ability to track stem cells in vivo can lead to a better understanding of the biodistribution of transplanted cells, in addition to improving the analysis of stem cell therapies' outcomes. Here, we described the use of a carbon nanotube-based contrast agent (CA) for X-ray computed tomography (CT) imaging as an intracellular CA to label bone marrow-derived mesenchymal stem cells (MSCs). Porcine MSCs were labeled without observed cytotoxicity. The CA consists of a hybrid material containing ultra-short single-walled carbon nanotubes (20-80 nm in length, US-tubes) and Bi(III) oxo-salicylate clusters which contain four Bi³⁺ ions per cluster (Bi₄C). The CA is thus abbreviated as Bi₄C@US-tubes.

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.

Advanced biomedical applications of carbon nanotube

With advances in nanotechnology, the applications of nanomaterial are developing widely and greatly. The characteristic properties of carbon nanotubes (CNTs) make them the most selective candidate for various multi-functional applications. The greater surface area of the CNTs in addition to the capability to manipulate the surfaces and dimensions has provided greater potential for this nanomaterial. The CNTs possess greater potential for applications in biomedicine due to their vital electrical, chemical, thermal, and mechanical properties. The unique properties of CNT are exploited for numerous applications in the biomedical field. They are useful in both therapeutic and diagnostic applications. They form novel carrier systems which are also capable of site-specific delivery of therapeutic agents. In addition, CNTs are of potential application in biosensing. Many recently reported advanced systems of CNT could be exploited for their immense potential in biomedicine in the future.

Biomimetic Carbon Fiber Systems Engineering: A Modular Design Strategy To Generate Biofunctional Composites from Graphene and Carbon Nanofibers

Carbon-based fibrous scaffolds are highly attractive for all biomaterial applications that require electrical conductivity. It is additionally advantageous if such materials resembled the structural and biochemical features of the natural extracellular environment. Here, we show a novel modular design strategy to engineer biomimetic carbon fiber-based scaffolds. Highly porous ceramic zinc oxide (ZnO) microstructures serve as three-dimensional (3D) sacrificial templates and are infiltrated with carbon nanotubes (CNTs) or graphene dispersions. Once the CNTs and graphene coat the ZnO template, the ZnO is either removed by hydrolysis or converted into carbon by chemical vapor deposition. The resulting 3D carbon scaffolds are both hierarchically ordered and free-standing. The properties of the microfibrous scaffolds were tailored with a high porosity (up to 93%), a high Young's modulus (ca. 0.027-22 MPa), and an electrical conductivity of ca. 0.1-330 S/m, as well as different surface compositions. Cell viability, fibroblast proliferation rate and protein adsorption rate assays have shown that the generated scaffolds are biocompatible and have a high protein adsorption capacity (up to 77.32 ± 6.95 mg/cm3) so that they are able to resemble the extracellular matrix not only structurally but also biochemically. The scaffolds also allow for the successful growth and adhesion of fibroblast cells, showing that we provide a novel, highly scalable modular design strategy to generate biocompatible carbon fiber systems that mimic the extracellular matrix with the additional feature of conductivity.

Migration of mesenchymal stem cells tethered with carbon nanotubes under a chemotactic gradient

Carbon nanotubes (CNTs) have been extensively studied for photothermal ablation of malignant cells due to their ability to absorb near-infrared (NIR) laser light and convert it to thermal energy for the lysis of tumor cells. Functionalizing CNTs with tumor-targeting moieties can facilitate the delivery to tumor sites. Instead of using targeting moieties, mesenchymal stem cells (MSCs) have been considered as vehicles to deliver therapeutic agents to cancer cells. In this study, the effects of attaching CNTs to MSCs on cell migration in response to a chemotactic gradient were investigated. Multiwalled carbon nanotubes (MWCNTs) were functionalized with streptavidin–fluorescein isothiocyanate (SA–FITC). The surface of human MSCs was biotinylated by culturing MSCs with biotin–lipid containing medium. CNTs were then attached on the outer cell membrane of biotinylated MSCs through SA–biotin binding. Fluorescence microscopy confirmed CNTs were located on the surface of MSCs. Various amounts of CNTs anchored on the membrane of MSCs were used to examine the effects of CNTs on MSC proliferation and migration. Our transwell migration assay showed that 4.26 ng CNT per cell is the threshold value that would not affect the migration speed of CNT-tagged MSCs toward the established gradient of chemoattractant SDF-1α.

Chemotactic migration of biotinylated mesenchymal stem cells tethered with streptavidin-functionalized carbon nanotubes.

Recent review of the effect of nanomaterials on stem cells

The field of stem-cell-therapy offers considerable promise as a means of delivering new treatments for a wide range of diseases. Recent progress in nanotechnology has stimulated the development of multifunctional nanomaterials (NMs) for stem-cell-therapy. Several clinical trials based on the use of NMs are currently underway for stem-cell-therapy purposes, such as drug/gene delivery and imaging. However, the interactions between NMs and stem cells are far from being completed, and the effects of the NMs on cellular behavior need critical evaluation. In this review, the interactions between several types of mostly used NMs and stem cells, and their associated possible mechanisms are systematically discussed, with specific emphasis on the possible differentiation effects induced by NMs. It is expected that the enhanced understanding of NM-stem cell interactions will facilitate biomaterial design for stem-cell-therapy and regenerative medicine applications.

Two-dimensional material-based bionano platforms to control mesenchymal stem cell differentiation

Background

In the past decade, stem cells, with their ability to differentiate into various types of cells, have been proven to be resourceful in regenerative medicine and tissue engineering. Despite the ability to repair damaged parts of organs and tissues, the use of stem cells still entails several limitations, such as low differentiation efficiency and difficulties in guiding differentiation. To address these limitations, nanotechnology approaches have been recently implemented in stem cell research. It has been discovered that stem cells, in combination with carbon-based functional materials, show enhanced regenerative performances in varying biophysical conditions. In particular, several studies have reported solutions to the conventional quandaries in biomedical engineering, using synergetic effects of nanohybrid materials, as well as further development of technologies to recover from diverse health conditions such as bone fracture and strokes.

Main text

In this review, we discuss several prior studies regarding the application of various nanomaterials in controlling the behavior of stem cells. We focus on the potential of different types of nanomaterials, such as two-dimensional materials, gold nanoparticles, and three-dimensional nanohybrid composites, to control the differentiation of human mesenchymal stem cells (hMSCs). These materials have been found to affect stem cell functions via the adsorption of growth/differentiation factors on the surfaces of nanomaterials and the activation of signaling pathways that are mostly related to cell adhesion and differentiation (e.g., FAK, Smad, Erk, and Wnt).

Conclusion

Controlling stem cell differentiation using biophysical factors, especially the use of nanohybrid materials to functionalize underlying substrates wherein the cells attach and grow, is a promising strategy to achieve cells of interest in a highly efficient manner. We hope that this review will facilitate the use of other types of newly discovered and/or synthesized nanomaterials (e.g., metal transition dichalcogenides, non-toxic quantum dots, and metal oxide frameworks) for stem cell-based regenerative therapies.

Three-Dimensional Graphene-RGD Peptide Nanoisland Composites That Enhance the Osteogenesis of Human Adipose-Derived Mesenchymal Stem Cells

Graphene derivatives have immense potential in stem cell research. Here, we report a three-dimensional graphene/arginine-glycine-aspartic acid (RGD) peptide nanoisland composite effective in guiding the osteogenesis of human adipose-derived mesenchymal stem cells (ADSCs). Amine-modified silica nanoparticles (SiNPs) were uniformly coated onto an indium tin oxide electrode (ITO), followed by graphene oxide (GO) encapsulation and electrochemical deposition of gold nanoparticles. A RGD–MAP–C peptide, with a triple-branched repeating RGD sequence and a terminal cysteine, was self-assembled onto the gold nanoparticles, generating the final three-dimensional graphene–RGD peptide nanoisland composite. We generated substrates with various gold nanoparticle–RGD peptide cluster densities, and found that the platform with the maximal number of clusters was most suitable for ADSC adhesion and spreading. Remarkably, the same platform was also highly efficient at guiding ADSC osteogenesis compared with other substrates, based on gene expression (alkaline phosphatase (ALP), runt-related transcription factor 2), enzyme activity (ALP), and calcium deposition. ADSCs induced to differentiate into osteoblasts showed higher calcium accumulations after 14–21 days than when grown on typical GO-SiNP complexes, suggesting that the platform can accelerate ADSC osteoblastic differentiation. The results demonstrate that a three-dimensional graphene–RGD peptide nanoisland composite can efficiently derive osteoblasts from mesenchymal stem cells.

Porous Electrospun Fibers with Self-Sealing Functionality: An Enabling Strategy for Trapping Biomacromolecules

Stimuli-responsive porous polymer materials have promising biomedical application due to their ability to trap and release biomacromolecules. In this work, a class of highly porous electrospun fibers is designed using polylactide as the polymer matrix and poly(ethylene oxide) as a porogen. Carbon nanotubes (CNTs) with different concentrations are further impregnated onto the fibers to achieve self-sealing functionality induced by photothermal conversion upon light irradiation. The fibers with 0.4 mg mL-1 of CNTs exhibit the optimum encapsulation efficiency of model biomacromolecules such as dextran, bovine serum albumin, and nucleic acids, although their photothermal conversion ability is slightly lower than the fibers with 0.8 mg mL-1 of CNTs. Interestingly, reversible reopening of the surface pores is accomplished with the degradation of PLA, affording a further possibility for sustained release of biomacromolecules after encapsulation. Effects of CNT loading on fiber morphology, structure, thermal/mechanical properties, degradation, and cell viability are also investigated. This novel class of porous electrospun fibers with self-sealing capability has great potential to serve as an enabling strategy for trapping/release of biomacromolecules with promising applications in, for example, preventing inflammatory diseases by scavenging cytokines from interstitial body fluids.

Nanomaterials modulate stem cell differentiation: biological interaction and underlying mechanisms

Stem cells are unspecialized cells that have the potential for self-renewal and differentiation into more specialized cell types. The chemical and physical properties of surrounding microenvironment contribute to the growth and differentiation of stem cells and consequently play crucial roles in the regulation of stem cells’ fate. Nanomaterials hold great promise in biological and biomedical fields owing to their unique properties, such as controllable particle size, facile synthesis, large surface-to-volume ratio, tunable surface chemistry, and biocompatibility. Over the recent years, accumulating evidence has shown that nanomaterials can facilitate stem cell proliferation and differentiation, and great effort is undertaken to explore their possible modulating manners and mechanisms on stem cell differentiation. In present review, we summarize recent progress in the regulating potential of various nanomaterials on stem cell differentiation and discuss the possible cell uptake, biological interaction and underlying mechanisms.

Evaluating the biological risk of functionalized multiwalled carbon nanotubes and functionalized oxygen-doped multiwalled carbon nanotubes as possible toxic, carcinogenic, and embryotoxic agents

Carbon nanotubes (CNTs) have been a focus of attention due to their possible applications in medicine, by serving as scaffolds for cell growth and proliferation and improving mesenchymal cell transplantation and engraftment. The emphasis on the benefits of CNTs has been offset by the ample debate on the safety of nanotechnologies. In this study, we determine whether functionalized multiwalled CNTs (fMWCNTs) and functionalized oxygen-doped multiwalled CNTs (fCOxs) have toxic effects on rat mesenchymal stem cells (MSCs) in vitro by analyzing morphology and cell proliferation and, using in vivo models, whether they are able to transform MSCs in cancer cells or induce embryotoxicity. Our results demonstrate that there are statistically significant differences in cell proliferation and the cell cycle of MSCs in culture. We identified dramatic changes in cells that were treated with fMWCNTs. Our evaluation of the transformation to cancer cells and cytotoxicity process showed little effect. However, we found a severe embryotoxicity in chicken embryos that were treated with fMWCNTs, while fCOxs seem to exert cardioembryotoxicity and a discrete teratogenicity. Furthermore, it seems that the time of contact plays an important role during cell transformation and embryotoxicity. A single contact with fMWCNTs is not sufficient to transform cells in a short time; an exposure of fMWCNTs for 2 weeks led to cell transformation risk and cardioembryotoxicity effects.

When stem cells meet graphene: Opportunities and challenges in regenerative medicine

Recent advances in stem cell research and nanotechnology have significantly influenced the landscape of tissue engineering and regenerative medicine. Precise and reproducible control of the fate of stem cells and their lineage specification have, therefore, become more crucial than ever for the success of stem cell-based technologies. Extensive research has been geared towards developing materials that are capable of mimicking the physiological microenvironment of stem cells and at the same time, controlling their eventual fate. An interesting example of these materials is two-dimensional graphene and its related derivatives. A high specific surface area coupled with superior chemical stability, biocompatibility, and flexibility in functionalization render graphene-based nanomaterials one of the most exciting platforms for tissue engineering and regenerative medicine applications, especially for stem cell growth, proliferation, and differentiation. In this review, we discuss the love-hate relationship between stem cells and graphene-based nanomaterials in tissue engineering and regenerative medicine. We first discuss the role and importance of stem cells in tissue engineering and regenerative medicine. We then highlight the use of nanomaterials for stem cell control, the interaction between stem cells and graphene nanomaterials as well as their biocompatibility, biodistribution, and biodegradability considerations. We also offer our perspectives on the various challenges and opportunities facing the use of graphene and its derivatives for stem cell growth and differentiation.

Carbon nanotube, graphene and boron nitride nanotube reinforced bioactive ceramics for bone repair

The high brittleness and low strength of bioactive ceramics have severely restricted their application in bone repair despite the fact that they have been regarded as one of the most promising biomaterials. In the last few years, low-dimensional nanomaterials (LDNs), including carbon nanotubes, graphene and boron nitride nanotubes, have gained increasing attention owing to their favorable biocompatibility, large surface specific area and super mechanical properties. These qualities make LDNs potential nanofillers in reinforcing bioactive ceramics. In this review, the types, characteristics and applications of the commonly used LDNs in ceramic composites are summarized. In addition, the fabrication methods for LDNs/ceramic composites, such as hot pressing, spark plasma sintering and selective laser sintering, are systematically reviewed and compared. Emphases are placed on how to obtain the uniform dispersion of LDNs in a ceramic matrix and maintain the structural stability of LDNs during the high-temperature fabrication process of ceramics. The reinforcing mechanisms of LDNs in ceramic composites are then discussed in-depth. The in vitro and in vivo studies of LDNs/ceramic in bone repair are also summarized and discussed. Finally, new developments and potential applications of LDNs/ceramic composites are further discussed with reference to experimental and theoretical studies.

STATEMENT OF SIGNIFICANCE

Despite bioactive ceramics having been regarded as promising biomaterials, their high brittleness and low strength severely restrict their application in bone scaffolds. In recent years, low-dimensional nanomaterials (LDNs), including carbon nanotubes, graphene and boron nitride nanotubes, have shown great potential in reinforcing bioactive ceramics owing to their unique structures and properties. However, so far it has been difficult to maintain the structural stability of LDNs during fabrication of LDNs/ceramic composites, due to the lengthy, high-temperature process involved. This review presents a comprehensive overview of the developments and applications of LDNs in bioactive ceramics. The newly-developed fabrication methods for LDNs/ceramic composites, the reinforcing mechanisms and the in vitro and in vivo performance of LDNs are also summarized and discussed in detail.

Carbon nanotubes gathered onto silica particles lose their biomimetic properties with the cytoskeleton becoming biocompatible

Carbon nanotubes (CNTs) are likely to transform the therapeutic and diagnostic fields in biomedicine during the coming years. However, the fragmented vision of their side effects and toxicity in humans has proscribed their use as nanomedicines. Most studies agree that biocompatibility depends on the state of aggregation/dispersion of CNTs under physiological conditions, but conclusions are confusing so far. This study designs an experimental setup to investigate the cytotoxic effect of individualized multiwalled CNTs compared to that of identical nanotubes assembled on submicrometric structures. Our results demonstrate how CNT cytotoxicity is directly dependent on the nanotube dispersion at a given dosage. When CNTs are gathered onto silica templates, they do not interfere with cell proliferation or survival becoming highly compatible. These results support the hypothesis that CNT cytotoxicity is due to the biomimetics of these nanomaterials with the intracellular nanofilaments. These findings provide major clues for the development of innocuous CNT-containing nanodevices and nanomedicines.

Composite electrospun nanofibers of reduced graphene oxide grafted with poly(3-dodecylthiophene) and poly(3-thiophene ethanol) and blended with polycaprolactone

In this paper, an effective method was employed for preparation of nanofibers using conducting polymer-functionalized reduced graphene oxide (rGO). First, graphene oxide (GO) was obtained from graphite by Hommer method. GO was reduced to rGO by NaBH₄ and covalently functionalized with a 3-thiophene acetic acid (TAA) by an esterification reaction to reach 3-thiophene acetic acid-functionalized reduced graphene oxide macromonomer (rGO-f-TAAM). Afterward, rGO-f-TAAM was copolymerized with 3-dodecylthiophene (3DDT) and 3-thiophene ethanol (3TEt) to yield rGO-f-TAA-co-PDDT (rGO-g-PDDT) and rGO-f-TAA-co-P3TEt (rGO-g-PTEt), which were confirmed by Fourier transform infrared spectra. The grafted materials depicted better electrochemical properties and superior solubilities in organic solvents compared to GO and rGO. The soluble rGO-g-PDDT and rGO-g-PTEt composites blended with polycaprolactone were fabricated by electrospinning, and then cytotoxicity, hydrophilicity, biodegradability and mechanical properties were investigated. The grafted rGO composites exhibited a good electroactivity behavior, mainly because of the enhanced electrochemical performance. The electrospun nanofibers underwent degradation about 7 wt% after 40 days, and the fabricated scaffolds were not able to induce cytotoxicity in mouse osteoblast MC3T3-E1 cells. The soluble conducting composites developed in this study are utilizable in the fabrication of nanofibers with tissue engineering application.