Bone cell proliferation on carbon nanotubes

Acceleration of Bone Regeneration in Critical-Size Defect Using BMP-9-Loaded nHA/ColI/MWCNTs Scaffolds Seeded with Bone Marrow Mesenchymal Stem Cells

Biocompatible scaffolding materials play an important role in bone tissue engineering. This study sought to develop and characterize a nano-hydroxyapatite (nHA)/collagen I (ColI)/multi-walled carbon nanotube (MWCNT) composite scaffold loaded with recombinant bone morphogenetic protein-9 (BMP-9) for bone tissue engineering by in vitro and in vivo experiments. The composite nHA/ColI/MWCNT scaffolds were fabricated at various concentrations of MWCNTs (0.5, 1, and 1.5% wt) by blending and freeze drying. The porosity, swelling rate, water absorption rate, mechanical properties, and biocompatibility of scaffolds were measured. After loading with BMP-9, bone marrow mesenchymal stem cells (BMMSCs) were seeded to evaluate their characteristics in vitro and in a critical sized defect in Sprague-Dawley rats in vivo. It was shown that the 1% MWCNT group was the most suitable for bone tissue engineering. Our results demonstrated that scaffolds loaded with BMP-9 promoted differentiation of BMMSCs into osteoblasts in vitro and induced more bone formation in vivo. To conclude, nHA/ColI/MWCNT scaffolds loaded with BMP-9 possess high biocompatibility and osteogenesis and are a good candidate for use in bone tissue engineering.

The use of functionalized carbon xerogels in cells growth

In the present study carbon xerogels are used for the first time to study the fibroblast cell growth. For that, carbon xerogel microspheres are synthesized and thereafter functionalized with carbon nanofibers followed by the 1,3-dipolar cycloaddition of azomethine ylides (the so called "Prato reaction") or the addition of aryl diazonium salts (the so called "Tour reaction") to improve its wettability. The presence of nanofibers produces a huge improvement of the functionalization degree (59 versus 372 μmol/g for pristine carbon spheres and carbon spheres with 30% of carbon nanofibers, respectively) in spite of the blockage of the carbon spheres porosity caused after the nanofibers growth. This improvement was explained on the base of the increase of the number of probable active sites for the addition reactions (CC bonds) and the accessibility to these active sites (accessible surface area) by the presence of nanofibers. These high functionalization degrees reflect a promising potential of these materials in biomedical applications. Toxicity results obtained using a fibroblast cell line showed that samples are biocompatible for this kind of cells and that the presence of carbon fibers on the surface of the spheres increases the cells proliferation in a high extend reaching in some case values around 150% regarding the control. This study evidences that carbon aerogels could be interesting materials in biological applications, an unexplored field for this type of materials, being biocompatible, favouring the proliferation of cells and achieving high functionalization degrees.

Carbon Nanotubes and Graphene as Nanoreinforcements in Metallic Biomaterials: a Review

Current challenges in existing metallic biomaterials encourage undertaking research in the development of novel materials for biomedical applications. This paper critically reviews the potential of carbon nanotubes (CNT) and graphene as nanoreinforcements in metallic biomaterials for bone tissue engineering. Unique and remarkable mechanical, electrical, and biological properties of these carbon nanomaterials allow their use as secondary-phase reinforcements in monolithic biomaterials. The nanoscale dimensions and extraordinarily large surface areas of CNT and graphene make them suitable materials for purposeful reaction with living organisms. However, the cytocompatibility of CNT and graphene is still a controversial issue that impedes advances in utilizing these promising materials in clinical orthopedic applications. The interaction of CNT and graphene with biological systems including proteins, nucleic acids, and human cells is critically reviewed to assess their cytocompatibity in vitro and in vivo. It is revealed that composites reinforced with CNT and graphene show enhanced adhesion of osteoblast cells, which subsequently promotes bone tissue formation in vivo. This potential is expected to pave the way for developing ground-breaking technologies in regenerative medicine and bone tissue engineering. In addition, current progress and future research directions are highlighted for the development of CNT and graphene reinforced implants for bone tissue engineering.

Biocompatibility Characteristics of Titanium Coated with Multi Walled Carbon Nanotubes-Hydroxyapatite Nanocomposites

Multi walled carbon nanotubes-hydroxyapatite (MWCNTs-HA) with various contents of MWCNTs was synthesized using the sol-gel method. MWCNTs-HA composites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). HA particles were generated on the surface of MWCNT. Produced MWCNTs-HA nanocomposites were coated on pure titanium (PT). Characteristic of the titanium coated MWCNTs-HA was evaluated by field-emission scanning electron microscopy (FE-SEM) and XRD. The results show that the titanium surface was covered with MWCNTs-HA nanoparticles and MWCNTs help form the crystalized hydroxyapatite. Furthermore, the MWCNTs-HA coated titanium was investigated for in vitro cellular responses. Cell proliferation and differentiation were improved on the surface of MWCNT-HA coated titanium.

Nanopharmaceuticals and nanomedicines currently on the market: challenges and opportunities

There has been a revolution in nanotechnology and nanomedicine. Since 1980, there has been a remarkable increase in approved nano-based pharmaceutical products. These novel nano-based systems can either be therapeutic agents themselves, or else act as vehicles to carry different active pharmaceutical agents into specific parts of the body. Currently marketed nanostructures include nanocrystals, liposomes and lipid nanoparticles, PEGylated polymeric nanodrugs, other polymers, protein-based nanoparticles and metal-based nanoparticles. A range of issues must be addressed in the development of these nanostructures. Ethics, market size, possibility of market failure, costs and commercial development, are some topics which are on the table to be discussed. After passing all the ethical and biological assessments, and satisfying the investors as to future profitability, only a handful of these nanoformulations, successfully obtained marketing approval. We survey the range of nanomedicines that have received regulatory approval and are marketed. We discuss ethics, costs, commercial development and possible market failure. We estimate the global nanomedicine market size and future growth. Our goal is to summarize the different approved nanoformulations on the market, and briefly cover the challenges and future outlook.

Balancing biofunctional and biomechanical properties using porous titanium reinforced by carbon nanotubes

Despite the well-known advantages of the titanium-based implant systems, they still lack an optimal balance between biofunctionality and mechanical strength, especially regarding the modulation of cellular response and a desired implant osseointegration. In this work, we fabricated a nanocomposite based on porous commercially pure grade 4 titanium (c.p. Ti) reinforced with carbon nanotubes (CNT) at 5% and 10% w/w, with the aim of obtaining a nanocomposite with lower stiffness compared to traditional titanium-based implants and with the mechanical strength and bioactivity owed by the CNT. Results obtained by scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy characterization showed that the CNT dispersed and incorporated into the porous c.p. Ti matrix. Interestingly, CNT were associated with a higher twining within neighbor Ti grains, which was indeed consistent with an increased in nano-hardness. Biological evaluation by MTT and Comet assay revealed that the nanocomposites did not induce genotoxicity and cytotoxicity on two different cells lines despite the presence of nickel at the surface. Accordingly, a purification step would be required before these CNT can be used for biomedical applications. Our results indicate that incorporation of CNT into porous c.p. Ti is a promising avenue to achieve an adequate balance between biofunctionality and mechanical strength in Ti-based scaffolds for tissue replacement. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 719-731, 2019.

Clinical Applications of Carbon Nanomaterials in Diagnostics and Therapy

Nanomaterials have the potential to improve how patients are clinically treated and diagnosed. While there are a number of nanomaterials that can be used toward improved drug delivery and imaging, how these nanomaterials confer an advantage over other nanomaterials, as well as current clinical approaches is often application or disease specific. How the unique properties of carbon nanomaterials, such as nanodiamonds, carbon nanotubes, carbon nanofibers, graphene, and graphene oxides, make them promising nanomaterials for a wide range of clinical applications are discussed herein, including treating chemoresistant cancer, enhancing magnetic resonance imaging, and improving tissue regeneration and stem cell banking, among others. Additionally, the strategies for further improving drug delivery and imaging by carbon nanomaterials are reviewed, such as inducing endothelial leakiness as well as applying artificial intelligence toward designing optimal nanoparticle-based drug combination delivery. While the clinical application of carbon nanomaterials is still an emerging field of research, there is substantial preclinical evidence of the translational potential of carbon nanomaterials. Early clinically trial studies are highlighted, further supporting the use of carbon nanomaterials in clinical applications for both drug delivery and imaging.

Nanostructures: between natural environment and medical practice

Nanoparticles (NPs) are small structures under 100 nm in dimension. Interrelationships among the morphological parameters and toxicity of NPs have been the focus of several investigations that assessed potential health risk in environmentally-exposed subjects and the realistic uses of NPs in medical practice. In the current review, we provide a summary of the cellular mechanisms of membrane-mediated transport, including old and novel molecules that transport nanostructures across cellular membranes. The effects of geochemical exposure to natural NPs are evaluated through epidemiological data and cancerous pathways activated by Fe2+ NPs. Specifically, we discuss screening for papillary thyroid carcinomas in the inhabitants of the Sicilian volcanic area surrounding Mount Etna to compare the incidence of thyroid carcinoma in this population. Lastly, considering the increased production of carbon nanotubes (CNTs), we examine the toxicity and potential use of these engineered NPs in drug delivery of an extensive amount of therapeutic and imaging molecules (theranosis) that can be conjugated to CNTs.

Enhanced Tribological and Bacterial Resistance of Carbon Nanotube with Ceria- and Silver-Incorporated Hydroxyapatite Biocoating

Pertaining to real-life applications (by scaling up) of hydroxyapatite (HA)-based materials, herein is a study illustrating the role of carbon nanotube (CNT) reinforcement with ceria (CeO₂) and silver (Ag) in HA on titanium alloy (TiAl6V4) substrate, utilizing the plasma-spraying processing technique, is presented. When compared with pure HA coating enhanced hardness (from 2.5 to 5.8 GPa), elastic modulus (from 110 to 171 GPa), and fracture toughness (from 0.7 to 2.2 MPa·m^1/2) elicited a reduced wear rate from 55.3 × 10⁻⁵ mm³·N⁻¹·m⁻¹ to 2.1 × 10⁻⁵ mm³·N⁻¹·m⁻¹ in HA-CNT-CeO₂-Ag. Besides, an order of magnitude lower Archard’s wear constant and a 41% decreased shear stress by for HA-CNT-CeO₂-Ag coating depicted the effect of higher hardness and modulus of a material to control its wear phenomenon. Antibacterial property of 46% (bactericidal) is ascribed to Ag in addition to CNT-CeO₂ in HA. Nonetheless, the composite coating also portrayed exaggerated L929 fibroblast cell growth (4.8 times more than HA), which was visualized as flat and elongated cells with multiple filopodial protrusions. Hence, synthesis of a material with enhanced mechanical integrity resulting in tribological resistance and cytocompatible efficacy was achieved, thereupon making HA-CNT-CeO₂-Ag a scalable potent material for real-life load-bearing implantable bio-coating.

In vitro assessment of neurotoxicity and neuroinflammation of homemade MWCNTs

Multi walled carbon nanotubes (MWCNTs) activate pathways involved in cytotoxicity, genotoxicity and inflammation. Inhaled MWCNTs are translocated to extra pulmonary organs and their hydrophobicity allows them to cross the blood-brain barrier (BBB). Further exposure of central nervous system (CNS) occurs via olfactory neurons. Using differentiated SH-SY5Y, we studied the neurotoxicity and neuroinflammation of pristine and functionalised MWCNTs. ROS overproduction was dose- and time-dependent (P<0.01) and was related to mitochondrial impairment, DNA damage and decreased viability (P<0.05). Transcript levels of TNFα, IL-1β and IL-6 increased, as confirmed by an ELISA test. Raman spectra were acquired to assess MWCNT-cells interactions. The almost superimposable pro-oxidant activity of both CNTs could be imputable to excessive lengths with regard to the pristine MWCNTs and to the eroded surface, causing increased reactivity, with regard to functionalised MWCNTs. Considering the ease with which lightweight MWCNTs aerosolize and the increased production, the results underlined the potential onset of neurodegenerative diseases, due to unintentional MWCNT exposure.

Modeling of the interaction between osteoblasts and biocompatible substrates as a function of adhesion strength

A goal of current implantology research is to design devices that induce controlled, guided, and rapid healing. Nanoscale structured substrates [e.g., titania nanotubes (TNTs) or carbon nanotubes (CNTs)] dramatically improve the functions of conventional biomaterials. The present investigation evaluated the behavior of osteoblasts cells cultured on smooth and nanostructured substrates, by measuring osteoblasts specific biomarkers [alkaline phosphatase (AP) and total protein] and cells adhesion strength to substrates, followed by semi-empirical modeling to predict the experimental results. Findings were in total agreement with the current state of the art. The proliferation, as well as the AP and total protein levels were higher on the nanostructure phases (TNTs, CNTs) comparing to the smooth ones (plastic and pure titanium). Cells adhesion strength measured was found higher on the nanostructured materials. This coincided with a higher value of proteins which are directly implicated in the process of adherence. Results were accurately predicted through the Viscoelastic Hybrid Interphase Model. A gradual adherence of bone cells to implants using multilayered biomaterials that involve biodegradable polymeric films and a nanoscale modification of titanium surface is suggested to improve performance through an interphase-mediated osteointegration of orthopedic implants. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 621-628, 2018.

The development of collagen based composite scaffolds for bone regeneration

Bone is consisted of bone matrix, cells and bioactive factors, and bone matrix is the combination of inorganic minerals and organic polymers. Type I collagen fibril made of five triple-helical collagen chains is the main organic polymer in bone matrix. It plays an important role in the bone formation and remodeling process. Moreover, collagen is one of the most commonly used scaffold materials for bone tissue engineering due to its excellent biocompatibility and biodegradability. However, the low mechanical strength and osteoinductivity of collagen limit its wider applications in bone regeneration field. By incorporating different biomaterials, the properties such as porosity, structural stability, osteoinductivity, osteogenicity of collagen matrixes can be largely improved. This review summarizes and categorizes different kinds of biomaterials including bioceramic, carbon and polymer materials used as components to fabricate collagen based composite scaffolds for bone regeneration. Moreover, the possible directions of future research and development in this field are also proposed.

•

Materials to incorporate collagen scaffolds for bone regeneration are summarized.

•

Bioceramics, carbon and polymer materials can increase the mechanical properties and osteogenesis.

•

The limitation of collagen based materials is analyzed and the prospects of future research are presented.

Enhancement of Bone Healing by Local Administration of Carbon Nanotubes Functionalized with Sodium Hyaluronate in Rat Tibiae

It has been reported that carbon nanotubes (CNTs) serve as nucleation sites for the deposition of bone matrix and cell proliferation. Here, we evaluated the effects of multi-walled CNTs (MWCNTs) on bone repair of rat tibiae. Furthermore, because sodium hyaluronate (HY) accelerates bone restoration, we associated CNTs with HY (HY-MWCNTs) in an attempt to boost bone repair. The bone defect was created by a 1.6-mm-diameter drill. After 7 and 14 days, tibiae were processed for histological and morphometric analyses. Immunohistochemistry was used to evaluate the expression of vascular endothelial growth factor (VEGF) in bone defects. Expression of osteocalcin (OCN), bone morphogenetic protein-2 (BMP-2), and collagen I (Col I) was assessed by real-time PCR. Histomorphometric analysis showed a similar increase in the percentage of bone trabeculae in tibia bone defects treated with HY and HY-MWCNTs, and both groups presented more organized and thicker bone trabeculae than nontreated defects. Tibiae treated with MWCNTs or HY- MWCNTs showed a higher expression of VEGF. Treatment with MWCNTs or HY-MWCNTs increased the expression of molecules involved in the bone repair process, such as OCN and BMP-2. Also, HY- and MWCNT-treated tibiae had an increased expression of Col I. Thus, it is tempting to conclude that CNTs associated or not with other materials such as HY emerged as a promising biomaterial for bone tissue engineering.

Three-dimensional wet-electrospun poly(lactic acid)/multi-wall carbon nanotubes scaffold induces differentiation of human menstrual blood-derived stem cells into germ-like cells

Infertility caused by the disruption or absence of germ cells is a major and largely incurable medical problem. Germ cells (i.e., sperm or egg) play a key role in the transmission of genetic and epigenetic information across generations. Generation of gametes derived in vitro from stem cells hold promising prospects which could potentially help infertile men and women. Menstrual blood-derived stem cells are a unique stem cell source. Evidence suggests that menstrual blood-derived stem cells exhibit a multi-lineage potential and have attracted extensive attention in regenerative medicine. To maintain the three-dimensional structure of natural extra cellular matrices in vitro, scaffolds can do this favor and mimic a microenvironment for cell proliferation and differentiation. According to previous studies, poly(lactic acid) and multi-wall carbon nanotubes have been introduced as novel and promising biomaterials for the proliferation and differentiation of stem cells. Some cell types have been successfully grown on a matrix containing carbon nanotubes in tissue engineering but there is no report for this material to support stem cells differentiation into germ cells lineage. This study designed a 3D wet-electrospun poly(lactic acid) and poly(lactic acid)/multi-wall carbon nanotubes composite scaffold to compare infiltration, proliferation, and differentiation potential of menstrual blood-derived stem cells toward germ cell lineage with 2D culture. Our primary data revealed that the fabricated scaffold has mechanical and biological suitable qualities for supporting and attachments of stem cells. The differentiated menstrual blood-derived stem cells tracking in scaffolds using scanning electron microscopy confirmed cell attachment, aggregation, and distribution on the porous scaffold. Based on the differentiation assay by RT-PCR analysis, stem cells and germ-like cells markers were expressed in 3D groups as well as 2D one. It seems that poly(lactic acid)/multi-wall carbon nanotubes scaffold-seeded menstrual blood-derived stem cells could be viewed as a novel, safe, and accessible construct for these cells, as they enhance germ-like generation from menstrual blood-derived stem cells.

Carbon Nanotube Reinforced Collagen/Hydroxyapatite Scaffolds Improve Bone Tissue Formation In Vitro and In Vivo

Current bone regeneration strategies faced major challenges in fabricating the bionic scaffolds with nano-structure, constituents and mechanical features of native bone. In this study, we developed a new porous scaffold by adding the multi-walled carbon nanotube (MWCNT) into collagen (Col)/hydroxyapatite (HA) composites. Data showed that 0.5%CNT/Col/HA (0.5%CNT) group was approximately tenfolds stiffer than Col-HA, and it was superior in promoting bone marrow mesenchymal stem proliferation and spreading, mRNA and protein expressions of bone sialoprotein (BSP) and osteocalcin (OCN) than Col-HA group. Moreover, we utilized 0.5%CNT composite to repair the rat calvarial defects (8 mm diameter) in vivo, and observed the new bone formation by 3D reconstruction of micro CT, HE and Masson staining, and BSP, OCN by immunohistochemical analysis. Results showed that newly formed bone in 0.5%CNT group was significantly higher than that in Col-HA group at 12 weeks. These findings highlighted a promising strategy in healing of large area bone defect with MWCNT added into the Col-HA scaffold as they possessed the combined effects of mechanical strength and osteogenicity.

Biomedical applications of nanotechnology

The ability to investigate substances at the molecular level has boosted the search for materials with outstanding properties for use in medicine. The application of these novel materials has generated the new research field of nanobiotechnology, which plays a central role in disease diagnosis, drug design and delivery, and implants. In this review, we provide an overview of the use of metallic and metal oxide nanoparticles, carbon-nanotubes, liposomes, and nanopatterned flat surfaces for specific biomedical applications. The chemical and physical properties of the surface of these materials allow their use in diagnosis, biosensing and bioimaging devices, drug delivery systems, and bone substitute implants. The toxicology of these particles is also discussed in the light of a new field referred to as nanotoxicology that studies the surface effects emerging from nanostructured materials.

Multi-walled carbon nanotubes act as a chemokine and recruit macrophages by activating the PLC/IP3/CRAC channel signaling pathway

The impact of nanomaterials on immune cells is gaining attention but is not well documented. Here, we report a novel stimulating effect of carboxylated multi-walled carbon nanotubes (c-MWCNTs) on the migration of macrophages and uncover the underlying mechanisms, especially the upstream signaling, using a series of techniques including transwell migration assay, patch clamp, ELISA and confocal microscopy. c-MWCNTs dramatically stimulated the migration of RAW264.7 macrophages when endocytosed, and this effect was abolished by inhibiting phospholipase C (PLC) with U-73122, antagonizing the IP3 receptor with 2-APB, and blocking calcium release-activated calcium (CRAC) channels with SK&F96365. c-MWCNTs directly activated PLC and increased the IP3 level and [Ca²⁺]_i level in RAW264.7 cells, promoted the translocation of the ER-resident stromal interaction molecule 1 (STIM1) towards the membranous calcium release-activated calcium channel modulator 1 (Orai1), and increased CRAC current densities in both RAW264.7 cells and HEK293 cells stably expressing the CRAC channel subunits Orai1 and STIM1. c-MWCNTs also induced dramatic spatial polarization of KCa3.1 channels in the RAW264.7 cells. We conclude that c-MWCNT is an activator of PLC and strongly recruits macrophages via the PLC/IP3/CRAC channel signaling cascade. These novel findings may provide a fundamental basis for the impact of MWCNTs on the immune system.

BIOPHYSICAL HEAT TRANSFER STUDY FOR THE CONTRACTION AND EXPANSION OF MUSCLES WITH MULTI-WALL CARBON NANOTUBES

The present investigation is associated with the contemporary study of viscous flow in a vertical tube with temperature dependent viscosity. The main flow problem has been modeled using cylindrical coordinates and flow equations are simplified to ordinary differential equations using longwave length and low Reynold's number approximation and exact solutions have been obtained for velocity, pressure gradient and temperature. Results acquired are discussed graphically for better understanding. It is seen that with an increment in the Grashof number, the velocity of the governing fluids start to decrease significantly and pressure gradient is higher for pure water as compared to multi-walled carbon nanotubes (MWCNTs) due to low density. As the specific heat is very high for pure water as compared to the multi-wall CNTs, it rise temperature of the muscles for the case of pure water as compared to the MWCNTs. Furthermore, it is noted that the trapped bolus starts to decrease in size as the buoyancy forces are dominant as compared to viscous force.

Nano-carbohydrates: Synthesis and application in genetics, biotechnology, and medicine

Combining nanoparticles with carbohydrate has triggered an exponential growth of research activities for the design of novel functional bionanomaterials, nano-carbohydrates. Recent advances in versatile synthesis of glycosylated nanoparticles have paved the way towards diverse biomedical applications. The accessibility of a wide variety of these structured nanosystems, in terms of shape, size, and organization around stable nanoparticles, has readily contributed to their development and application in nanomedicine. Glycosylated gold nanoparticles, glycosylated quantum dots, fullerenes, single-wall nanotubes, and self-assembled glyconanoparticles using amphiphilic glycopolymers or glycodendrimers have received considerable attention for their application in powerful imaging, therapeutic, and biodiagnostic devices. Recently, nano-carbohydrates were used for different types of microarrays to detect proteins and nucleic acids.

Long-term release of antibiotics by carbon nanotube-coated titanium alloy surfaces diminish biofilm formation by Staphylococcus epidermidis

Bacterial biofilms cause a considerable amount of prosthetic joint infections every year, resulting in morbidity and expensive revision surgery. To address this problem, surface modifications of implant materials such as carbon nanotube (CNT) coatings have been investigated in the past years. CNTs are biologically compatible and can be utilized as drug delivery systems. In this study, multi-walled carbon nanotube (MWCNT) coated TiAl6V4 titanium alloy discs were fabricated and impregnated with Rifampicin, and tested for their ability to prevent biofilm formation over a period of ten days. Agar plate-based assays were employed to assess the antimicrobial activity of these surfaces against Staphylococcus epidermidis. It was shown that vertically aligned MWCNTs were more stable against attrition on rough surfaces than on polished TiAl6V4 surfaces. Discs with coated surfaces caused a significant inhibition of biofilm formation for up to five days. Therefore, MWCNT-modified surfaces may be effective against pathogenic biofilm formation on endoprostheses.

Carbon nanotubes: a novel material for multifaceted applications in human healthcare

Remarkable advances achieved in modern material technology, especially in device fabrication, have facilitated diverse materials to expand the list of their application fields.

Carbon Nanostructures in Bone Tissue Engineering

BACKGROUND

Recent advances in developing biocompatible materials for treating bone loss or defects have dramatically changed clinicians' reconstructive armory. Current clinically available reconstructive options have certain advantages, but also several drawbacks that prevent them from gaining universal acceptance. A wide range of synthetic and natural biomaterials is being used to develop tissue-engineered bone. Many of these materials are currently in the clinical trial stage.

METHODS

A selective literature review was performed for carbon nanostructure composites in bone tissue engineering.

RESULTS

Incorporation of carbon nanostructures significantly improves the mechanical properties of various biomaterials to mimic that of natural bone. Recently, carbon-modified biomaterials for bone tissue engineering have been extensively investigated to potentially revolutionize biomaterials for bone regeneration.

CONCLUSION

This review summarizes the chemical and biophysical properties of carbon nanostructures and discusses their functionality in bone tissue regeneration.

Cell studies of hybridized carbon nanofibers containing bioactive glass nanoparticles using bone mesenchymal stromal cells

Bone regeneration required suitable scaffolding materials to support the proliferation and osteogenic differentiation of bone-related cells. In this study, a kind of hybridized nanofibrous scaffold material (CNF/BG) was prepared by incorporating bioactive glass (BG) nanoparticles into carbon nanofibers (CNF) via the combination of BG sol-gel and polyacrylonitrile (PAN) electrospinning, followed by carbonization. Three types (49 s, 68 s and 86 s) of BG nanoparticles were incorporated. To understand the mechanism of CNF/BG hybrids exerting osteogenic effects, bone marrow mesenchymal stromal cells (BMSCs) were cultured directly on these hybrids (contact culture) or cultured in transwell chambers in the presence of these materials (non-contact culture). The contributions of ion release and contact effect on cell proliferation and osteogenic differentiation were able to be correlated. It was found that the ionic dissolution products had limited effect on cell proliferation, while they were able to enhance osteogenic differentiation of BMSCs in comparison with pure CNF. Differently, the proliferation and osteogenic differentiation were both significantly promoted in the contact culture. In both cases, CNF/BG(68 s) showed the strongest ability in influencing cell behaviors due to its fastest release rate of soluble silicium-relating ions. The synergistic effect of CNF and BG would make CNF/BG hybrids promising substrates for bone repairing.

In vitro evaluation of osteoblast responses to carbon nanotube-coated titanium surfaces

BACKGROUND

The effects of surface roughness and carboxyl functionalization of multi-walled carbon nanotubes (MWCNTs) mixed with collagen coated onto titanium (Ti) substrates on MC3T3-E1 osteoblasts were evaluated.

METHODS

The proliferation, differentiation, and matrix mineralization were investigated using (1) smooth-surfaced Ti discs, (2) Ti discs coated with collagen and MWCNT (Ti-MWCNT), and (3) Ti discs coated with collagen and MWCNT-COOH (Ti-MWCNT-COOH) for applications in orthodontic mini screw implants (MSIs). The coatings were uniform when analyzed using scanning electron microscopy (SEM), and surface roughness was evaluated by surface profilometry that demonstrated similar surface roughness (R a , mean ± SD) in the MWCNT (0.83 ± 0.02 μm) and MWCNT-COOH (0.84 ± 0.01 μm) groups. MTT (3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide) assay was performed after days 1, 3, and 7 to assess proliferation. Alkaline phosphatase (ALP)-specific activity was assessed after day 7 to quantify differentiation. Alizarin red staining was measured after day 28 to quantify matrix mineralization. All data were analyzed with JMP Pro11 software (SAS, USA) with a statistical significance of p  < 0.05.

RESULTS

Surface profilometry demonstrated similar surface roughness (R a , mean ± SD) in the MWCNT (0.83 ± 0.02 μm) and MWCNT-COOH (0.84 ± 0.01 μm) groups. On day 7, ALP assay showed that MWCNT-COOH (mean ± SD 0.98 ± 0.26 U/μg of protein) enhanced cell differentiation when compared to the uncoated group (p = 0.05). Alizarin red staining after 28 days of cell culture revealed that MWCNT-COOH (mean ± SD 1.5 ± 0.2 OD405) increased (p = 0.03) matrix mineralization when compared to the uncoated group (0.9 ± 0.09 OD405).

CONCLUSIONS

This study showed that coatings containing MWCNT-COOH (increased hydrophilic surface chemistry) influence osteoblast proliferation, differentiation, and matrix mineralization and should be further studied for applications in orthodontic MSIs.

Immune response in hamsters immunised with a recombinant fragment of LigA from Leptospira interrogans, associated with carrier molecules

Immunisation with the C-terminal region of leptospiral immunoglobulin-like A protein (LigANI) has shown promising results against leptospirosis. We evaluated the humoral immune response and protection induced by LigANI associated with carboxyl multi-walled carbon nanotubes (COOH-MWCNTs), CpG oligodeoxynucleotides (CpG ODNs), or Alhydrogel. Animals immunised with CpG ODNs were unable to develop a humoral immune response, whereas immunisation with LigANI and COOH-MWCNTs produced a high level of IgG antibodies, similar to that with LigANI and Alhydrogel, but it was not protective. The use of carbon nanotubes as an adjuvant in subunit vaccines against leptospirosis is a novel approach for improving specific IgG production.

Self-Assembled Heterojunction Carbon Nanotubes Synergizing with Photoimmobilized IGF-1 Inhibit Cellular Senescence

Synthesis of artificial and functional structures for bone tissue engineering has been well recognized but the associated cell senescence issue remains much less concerned so far. In this work, surface-modified polycaprolactone-polylactic acid scaffolds using self-assembled heterojunction carbon nanotubes (sh-CNTs) combined with insulin-like growth factor-1 are synthesized and a series of structural and biological characterizations are carried out, with particular attention to cell senescence mechanism. It is revealed that the modified scaffolds can up-regulate the expressions of alkaline phosphates and bone morphogenetic proteins while down-regulate the expressions of senescence-related proteins in mesenchymal stem cells, demonstrating the highly preferred anti-senescence functionality of the sh-CNTs modified scaffolds in bone tissue engineering. Furthermore, it is also found that with sh-CNTs, scaffolds can accelerate bone healing with extremely low toxicity in vivo.

Development of functionalized multi-walled carbon-nanotube-based alginate hydrogels for enabling biomimetic technologies

Alginate is a hydrogel commonly used for cell culture by ionically crosslinking in the presence of divalent Ca(2+) ions. However these alginate gels are mechanically unstable, not permitting their use as scaffolds to engineer robust biological bone, breast, cardiac or tumor tissues. This issue can be addressed via encapsulation of multi-walled carbon nanotubes (MWCNT) serving as a reinforcing phase while being dispersed in a continuous phase of alginate. We hypothesized that adding functionalized MWCNT to alginate, would yield composite gels with distinctively different mechanical, physical and biological characteristics in comparison to alginate alone. Resultant MWCNT-alginate gels were porous, and showed significantly less degradation after 14 days compared to alginate alone. In vitro cell-studies showed enhanced HeLa cell adhesion and proliferation on the MWCNT-alginate compared to alginate. The extent of cell proliferation was greater when cultured atop 1 and 3 mg/ml MWCNT-alginate; although all MWCNT-alginates lead to enhanced cell cluster formation compared to alginate alone. Among all the MWCNT-alginates, the 1 mg/ml gels showed significantly greater stiffness compared to all other cases. These results provide an important basis for the development of the MWCNT-alginates as novel substrates for cell culture applications, cell therapy and tissue engineering.

Prion like behavior of HSA-hydroxylated MWCNT interface

Carbon nanotubes (CNTs) with unique and outstanding properties were expected to revolutionize various aspects of the biomedical sector. Interaction studies of proteins with functionalized CNTs would shed light on their toxicological aspects upon entering the human body. Hyperchromicity of the UV-Visible spectra and declining fluorescence potential of HSA on interaction with CNTs suggested ground state complex to exist between them. Synchronous and 3D spectral features of CNT-HSA system proposed their possible binding site to occur nearby Trp and Tyr residues. FTIR and FT-Raman spectra showed a shift in the amide band region that proportionate the possible alteration to occur in the alpha-helical structures. CD far and near spectra showed loss of alpha-helical structures and shift in the Trp position of the polypeptide backbone. CNT's UV and FTIR band showed shift on interaction with HSA, which conveys the possible aggregation of CNTs in the presence of protein. The promoting role of CNTs against HSA fibril formation has been confirmed by spectroscopic and microscopic evaluations. Secondary conformational changes, besides the existence of increased beta-sheet structures of HSA amyloid fibrils, remain similar to the amyloid behavior of Prion protein. Hence, HSA fibril-CNT interface predominates the possible mechanism for several amyloid-related disorders concerning their toxic accumulations in the body.

Titania nanotubes for orchestrating osteogenesis at the bone-implant interface

Titanium implants can fail due to inappropriate biomechanics at the bone-implant interface that leads to suboptimal osseointegration. Titania nanotubes (TNTs) fabricated on Ti implants by the electrochemical process have emerged as a promising modification strategy to facilitate osseointegration. TNTs enable augmentation of bone cell functions at the bone-implant interface and can be tailored to incorporate multiple functionalities including the loading of active biomolecules into the nanotubes to target anabolic processes in bone conditions such as osteoporotic fractures. Advanced functions can be introduced, including biopolymers, nanoparticles and electrical stimulation to release growth factors in a desired manner. This review describes the application of TNTs for enhancing osteogenesis at the bone-implant interface, as an alternative approach to systemic delivery of therapeutic agents.

Mussel-inspired PEGylated carbon nanotubes: biocompatibility evaluation and drug delivery applications

Carbon nanotubes (CNTs) have been widely examined for biomedical applications. However, surface functionalization of CNTs with polymers is often required to improve their application performance. To obtain these CNT-based polymer nanocomposites, surface-initiated polymerization strategies are generally adopted. However, all of these methods rely on the surface oxidation of CNTs, which is a rather complex and time-consuming procedure, and involves hazardous reagents. In this work, a facile and efficient bio-inspired strategy was developed for surface PEGylation of CNTs via a combination of mussel-inspired chemistry and the Michael addition reaction. The potential biomedical applications of these PEGylated CNTs were evaluated for intracellular delivery of a normally used anticancer drug (Doxorubicin hydrochloride). Two steps were involved in this strategy, which included the surface coating of CNTs with polydopamine (PDA) through self-polymerization of dopamine, and a Michael addition reaction between the PDA-coated CNTs (CNT-PDA) and amino-functionalized polymers, which were obtained by free radical polymerization using poly(ethylene glycol) methyl methacrylate and N-(3-aminopropyl) methacrylamide as monomers. Results suggested that these PEGylated CNTs are well dispersed in aqueous solution and showed improved biocompatibility toward cancer cells. On the other hand, we also demonstrated that DOX can be effectively loaded on these PEGylated CNTs and delivered into cells for cancer treatment. More importantly, this strategy can also be utilized for surface modification of many other materials with different polymers due to the strong and universal adhesion of PDA and designability of polymerization. Therefore, this method should be of great interest for the fabrication of multifunctional nanocomposites for biomedical applications.

Tartrate Resistant Acid Phosphatase Assisted Degradation of Single-Wall Carbon Nanotubes (SWCNTs)

In this study, we explored the capability of tartrate resistant acid phosphatase (TRAcP), a bone resorption marker, to degrade carboxylated single-walled carbon nanotubes (C-SWCNTs). Optical observations and Raman and high-resolution transmission electron microscopy studies show that the enzyme contributes to the degradation of C-SWCNTs, although the degradation is not complete. Molecular modeling implemented to investigate the binding sites for carboxylated and pristine SWCNTs to TRAcP elucidate the varying proximity of SWCNTs to the binuclear iron active site and the active site residues of TRAcP, which is clearly dependent upon the degree of carboxylation introduced into the SWCNT model. The modeling results presented provide justification to the propensity of TRAcP to degrade the C-SWCNTs alluding to the possibility of C-SWCNTs to be used as a potential degradable biomaterial for use in therapeutic applications of mineralized tissue related conditions.

Multi and single walled carbon nanotubes: effects on cell responses and biomineralization of osteoblasts cultures

The use of carbon nanotubes (CNTs) on the development of biomaterials has been motivated by their excellent mechanical properties that could improve synthetic bone materials. However, the toxicity of CNTs on the tissue/implant interface and their influence on the biomineralization process have some contradictions. We investigated the influence of CNTs on osteoblasts plated on titanium (Ti) discs or plastic surfaces. We evaluated osteoblasts viability, alkaline phosphatase (ALP) activity, and mineralized matrix formation in the different phases of osteoblasts growth in the presence of single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs). An increase in osteoblasts viability was observed at the 21st day for both CNTs on plastic surface, while viability increased for MWCNTs at the 7th and 14th days and at the 7th day for SWCNTs on Ti discs compared to control. ALP activity increased at the 14th and 21st days for MWCNTs on plastic surfaces. For cells incubated with SWCNTs, an increase in ALP activity at the 7th day for plastic surface and at the 14th day for both materials (plastic and Ti) was observed. The mineralized matrix formation increased at the 21st day on plastic surface with SWCNTs, and at the 14th and 21st days for both CNTs on Ti discs. In conclusion, both SWCNTs and MWCNTs are not toxic to osteoblasts at concentrations up to 5 × 10(-5) and 1.3 × 10(-2) mg/mL, respectively, either in Ti discs or plastic surfaces. In the long term, the cells grown in contact with both CNTs and Ti presented better results regarding bone-like nodules formation.