Bone cell proliferation on carbon nanotubes

Interfacing carbon nanotubes with living mammalian cells and cytotoxicity issues

The unique structures and properties of carbon nanotubes (CNTs) have attracted extensive investigations for many applications, such as those in the field of biomedical materials and devices, biosensors, drug delivery, and tissue engineering. Anticipated large-scale productions for numerous diversified applications of CNTs might adversely affect the environment and human health. For successful applications in the biomedical field, the issue of interfacing between CNTs and mammalian cells in vitro needs to be addressed before in vivo studies can be carried out systematically. We review the important studies pertaining to the internalization of CNTs into the cells and the culturing of cells on the CNT-based scaffold or support materials. The review will focus on the description of a variety of factors affecting CNT cytotoxicity: type of CNTs, impurities, lengths of CNTs, aspect ratios, dispersion, chemical modification, and assaying methods of cytotoxicity.

Bone formation on carbon nanotube composite

The effects of a layer-by-layer assembled carbon nanotube composite (CNT-comp) on osteoblasts in vitro and bone tissue in vivo in rats were studied. The effects of CNT-comp on osteoblasts were compared against the effects by commercially pure titanium (cpTi) and tissue culture dishes. Cell proliferation on the CNT-comp and cpTi were similar. However, cell differentiation, measured by alkaline phosphatase activity and matrix mineralization, was better on the CNT-comp. When implanted in critical-sized rat calvarial defect, the CNT-comp permitted bone formation and bone repair without signs of rejection or inflammation. These data indicate that CNT-comp may be a promising substrate for use as a bone implant or as a scaffold for tissue engineering.

A cross-linking model for estimating Young's modulus of artificial bone tissue grown on carbon nanotube scaffold

Carbon nanotubes (CNTs) provide a suitable environment for growth and proliferation of bone cells. The elastic properties exhibited by CNTs can enhance mechanical characteristics of bone mineral phase, hydroxyapatite (HAp), precipitated on such a scaffold. In this article, a simplified model for estimating the axial Young's modulus of a representative volume element (RVE) of CNT-HAp composite is presented. The model is based on the idea of HAp formation on functionalized sites on CNTs as cross-links between HAp matrix and CNT. Modeling results show that the reinforcement role contributed by CNT in the RVE causes a significant increase in the Young's modulus of the composite material which is a direct consequence of transferring stresses from the HAp matrix to the CNT through the cross-links. Similar conclusions may be suggested regarding the improvement of overall mechanical properties of the material. The prediction made by the model lies reasonably well within the limits proposed by conventional Rule-of-Mixtures, and sliding below Voigt's model. The Young's modulus predicted by the model lies adjacent to the Hashin-Shtrikman upper bound as a function of the RVE length (or equivalently CNT aspect ratio). The model simulation indicates that an increase in the CNT aspect ratio and/or number of cross-links in the RVE, results in the prediction to move closer to the estimation made by Voigt as the assumption of perfect bonding between composite phases is approached.

In vitro calcification of chemically functionalized carbon nanotubes

Bone is composed of two phases. The organic phase is made of collagen fibrils assembled in broad fibers acting as a template for mineralization. The mineral phase comprises hydroxyapatite (HAP) crystals grown between and inside the collagen fibers. We have developed a biomimetic material using functionalized carbon nanotubes as scaffold to initiate in vitro mineralization. Biomimetic formation of HAP was performed on single-walled carbon nanotubes (SWCNTs) which have been grafted with carboxylic groups. Two types of nanotubes, HiPco(R) and Carbon Solutions(R), were oxidized via various acidic processes, leading to five different groups of carboxylated nanotubes, fully characterized by physical methods (thermogravimetric analysis, attenuated total reflectance infrared spectroscopy and X-ray photoelectron spectroscopy). All samples were dispersed in ultra-pure water and incubated for 2weeks in a synthetic body fluid, in order to induce the calcification of the SWCNTs. Scanning electron microscopy (SEM) and energy-dispersive X-ray analysis studies showed that Ca(2+) and PO(4)(3-) ions were deposited as round-shaped nodules (calcospherites) on the carboxylated SWCNTs. Fourier transform infrared and Raman spectroscopic studies confirmed the HAP formation, and image analysis made on SEM pictures showed that calcospherites and carboxylated SWCNTs were packed together. The size of calcospherites thus obtained in vitro from the HiPco(R) series was close to that issued from calcospherites observed in vivo. Functionalization of SWCNTs with carboxylic groups confers the capacity to induce calcification similar to woven bone.

Chitosan composites for bone tissue engineering--an overview

Bone contains considerable amounts of minerals and proteins. Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] is one of the most stable forms of calcium phosphate and it occurs in bones as major component (60 to 65%), along with other materials including collagen, chondroitin sulfate, keratin sulfate and lipids. In recent years, significant progress has been made in organ transplantation, surgical reconstruction and the use of artificial protheses to treat the loss or failure of an organ or bone tissue. Chitosan has played a major role in bone tissue engineering over the last two decades, being a natural polymer obtained from chitin, which forms a major component of crustacean exoskeleton. In recent years, considerable attention has been given to chitosan composite materials and their applications in the field of bone tissue engineering due to its minimal foreign body reactions, an intrinsic antibacterial nature, biocompatibility, biodegradability, and the ability to be molded into various geometries and forms such as porous structures, suitable for cell ingrowth and osteoconduction. The composite of chitosan including hydroxyapatite is very popular because of the biodegradability and biocompatibility in nature. Recently, grafted chitosan natural polymer with carbon nanotubes has been incorporated to increase the mechanical strength of these composites. Chitosan composites are thus emerging as potential materials for artificial bone and bone regeneration in tissue engineering. Herein, the preparation, mechanical properties, chemical interactions and in vitro activity of chitosan composites for bone tissue engineering will be discussed.

MWCNTs as reinforcing agent to the hap-gel nanocomposite for artificial bone grafting

The essence of this investigation is to explore MWCNTs as reinforcing agents to strengthen Hap-Gel nanocomposites for artificial bone grafting applications without significantly compromising their biocompatibility. Hap-Gelatin composites, reinforced with various proportions of MWCNTs, were synthesized to optimize the MWCNT content in the composites which yield commendable improvement in the strength. The morphological studies reveal that the MWCNTs act as templates for nucleation of Hap crystals. The biocompatibility of MWCNT reinforced Hap-Gelatin composites were evaluated in animal model through the histopathological investigation of tissues from skin, kidney, and liver. On histopathological examination, no noticeable alteration due to toxicity was found for lower concentration of MWCNTs. Mild reversible changes in the liver and tubular damage in kidney have been observed for higher concentration (4 wt % of MWCNTs). It can be inferred from the findings that MWCNTs, in proportions less than 4%, can successfully be used to reinforce the Hap-Gel nanocomposite to improve its mechanical properties. However, how safe would these CNT reinforced bone implants would be when used for prolonged period in actual physiological conditions needs to be investigated further.

Transmission electron microscopic observation of cells cultured on multiwalled carbon nanotube-coated sponges

The cell structure and interface between cultured cells and a multiwalled carbon nanotube (MWCNT)-coated sponge (MWCNT-coated sponge) were observed by transmission electron microscopy (TEM). Moreover, the atomic structure of MWCNTs that entered the cells was also examined by means of high-resolution TEM (HRTEM). MWCNTs were observed in the cytoplasm, and a few MWCNTs were recognized in the cell nuclei. Those MWCNTs maintained their structure there. Subcellular organelles did not appear to be different from those on the collagen sponge despite the cellular uptake of MWCNTs.

Carbon Nanotubes: A Solution for Processing Smart Biomaterials

In the recent years the driving force for technological change in many respects has shifted towards the design and process of materials that offer a set of responses to external stimuli or environmental conditions. These materials are called “smart materials”. Such responses are designed to fulfil the range of scenarios to which a material or structure may be exposed providing them with a particular functionality. These materials are not only useful because of their structural, chemical, physical or mechanical properties; they can also perform an action within a process. It has been described that smart structures exhibit one or more of the following features; they can act as sensors or actuators within a structural material or bonded in the surface; or they have controllable capabilities that permit to respond to the stimuli according to a prescribed function. These materials become intelligent when they have the ability to respond intelligently and autonomously to changing conditions. There are lots of possibilities within the term functional “smart materials” but in all of them, the term is used to describe systems which respond to a stimulus in a useful and predictable manner. Nowadays it is widely known the useful capability of, piezoelectric, electro-optic, magnetic, electro-mechanic materials, etc…that respond to stimuli such as, electric or magnetic fields, stress, temperature, moisture or pH. These multifunctional character and capability of biomaterials makes them suitable for a big number of applications in every order of human activity, from photochromic lenses for sunglasses to military and aerospace uses. They are already a big part of the market in the engineering industry.

Aluminum nanoparticles enhance anticancer immune response induced by tumor cell vaccine

The application of nanomaterial in cancer treatment is promising and intriguing. Anti-tumor immunotherapy has the potential to significantly improve the prognosis of cancer treatment, though the efficacy of immunotherapy generally needs further improvement. One way to improve the efficacy is using immune adjuvants, but the adjuvants for anticancer immunotherapy have to be more potent than for prophylactic vaccines. Here, we report that compared to conventional alum adjuvant, aluminum oxide nanoparticles (nano-alum) may further enhance the anticancer effects of an immunotherapy that employs tumor cell vaccine (TCV). The average tumor size tends to be lower in animals that receive the combinational treatment of nano-alum and TCV. The anticancer cytotoxicity by the lymphocytes was also significantly higher in the treatment group that received both TCV and nano-alum. These results suggest that nano-alum may potentially serve as a potent immune adjuvant and have prospective applications in anticancer immunotherapy.

Two-dimensional diffusion-ordered NMR spectroscopy as a tool for monitoring functionalized carbon nanotube purification and composition

Functionalized carbon nanotube (CNT) derivatives are currently under thorough investigation in different biomedical investigations. In this field of research, the composition of sample either in terms of covalently attached or physisorbed moieties can greatly affect the observed results and hamper the comparison between different studies. Therefore, the availability of a fast and reliable analytical technique to assess both the type of interaction (covalent vs noncovalent) and the composition of CNT conjugates is of great importance. Here we describe that the two-dimensional diffusion-ordered (DOSY) NMR spectroscopy is extremely useful to discriminate between conjugated and unconjugated polyethylene glycol groups in samples obtained by condensation with oxidized single-walled carbon nanotubes (SWNTs). This fast and nondestructive technique allows us to follow the removal of unconjugated polyethylene glycol chains during the purification. In particular, DOSY analysis reveal that about 1/3 (wt %) of the polyethylene glycol used for the condensation remained physisorbed to functionalized SWNTs after dialysis. Complete elimination of physisorbed polyethylene glycol was achieved using diafiltration.

Current investigations into carbon nanotubes for biomedical application

The nano-dimensionality of nature has logically given rise to the interest in using nanomaterials in the biomedical field. Currently, a lot of investigations into carbon nanotubes (CNTs), as one of the typical nanomaterials, are being made for biomedical application. In this review, five parts, such as cellular functions induced by CNTs, apatite formation on CNTs, CNT-based tissue engineering scaffold, functionalized CNTs for the delivery of genes and drugs and CNT-based biosensors, are stated, which might indicate that CNTs, with a range of unique properties, appear suited as a biomaterial and may become a useful tool for tissue engineering. However, everything has two parts and CNTs is not an exception. There are still concerns about cytotoxicity and biodegradation of CNTs. Chemical fictionalization may be one of the effective ways to improve the 'disadvantages' and utilize the 'advantages' of CNTs. One of their 'disadvantages', unbiodegradable property, may be utilized by creating monitors in in vivo-engineered tissues or nanosized CNT-based biosensors. Other promising research points, for example proteins adsorbed on CNTs, use of CNTs in combination with other biomaterials to achieve the goals of tissue engineering, mineralization of CNTs and standard toxicological tests for CNTs, are also described in the conclusion and perspectives part.

Empirical study of unipolar and bipolar configurations using high resolution single multi-walled carbon nanotube electrodes for electrophysiological probing of electrically excitable cells

Identifying the neurophysiological basis underlying learning and memory in the mammalian central nervous system requires the development of biocompatible, high resolution, low electrode impedance electrophysiological probes; however, physically, electrode impedance will always be finite and, at times, large. Herein, we demonstrate through experiments performed on frog sartorius muscle that single multi-walled carbon nanotube electrode (sMWNT electrode) geometry and placement are two degrees of freedom that can improve biocompatibility of the probe and counteract the detrimental effects of MWNT/electrolyte interface impedance on the stimulation efficiency and signal-to-noise ratio (SNR). We show that high aspect ratio dependent electric field enhancement at the MWNT tip can boost stimulation efficiency. Derivation of the sMWNT electrode's electrical equivalent indicates that, at low stimulus voltage regimes below 1 V, current conduction is mediated by charge fluctuation in the double layer obviating electrolysis of water, which is potentially toxic to pH sensitive biological tissue. Despite the accompanying increase in electrode impedance, a pair of closely spaced sMWNT electrodes in a two probe (bipolar) configuration maintains biocompatibility and enhances stimulation efficiency and SNR compared to the single probe (unipolar) configuration. For stimulus voltages below 1 V, the electrical equivalent verifies that current conduction in the two probe configuration still proceeds via charge fluctuation in the double layer. As an extracellular stimulation electrode, the two sMWNT electrodes comprise a current dipole that concentrates the electric field and the current density in a smaller region of sartorius; consequently, the bipolar configuration can elicit muscle fiber twitching at low voltages that preclude electrolysis of water. When recording field potentials, the bipolar configuration subtracts the potential between two points allowing for the detection of higher signal amplitudes. As a result, SNR is improved. These results indicate that use of the high aspect ratio MWNT in a bipolar configuration can achieve a biocompatible electrode that offers enhanced stimulation efficiency and higher SNR.

Electronic anabolic steroid recognition with carbon nanotube field-effect transistors

A proof of concept of the electronic detection of two anabolic steroids, stanozolol (Stz) and methylboldenone (MB), was carried out using two specific antibodies and arrays of carbon nanotube field-effect transistors (CNTFETs). Antibodies specific for Stz and MB were prepared and immobilized on the carbon nanotubes (CNTs) using two different approaches: direct noncovalent bonding of antibodies to the devices and bonding the antibodies covalently to a polymer previously attached to the CNTFETs. The results indicated that CNTFETs bonded to specific antibodies covalently or noncovalently are able to detect the presence of steroids. Statistically significant changes in the threshold voltage and drain current were registered in the transistors, allowing the steroids to be recognized. On the other hand, it was determined that the specific antibodies do not detect other steroids other than Stz and MB, such as nandrolone (ND) because, in this case, statistically significant changes in the transistors were not detected. The polymer prevents the aggregation of antibodies on the electrodes and decreases the transistor hysteresis. Nevertheless, it is not able to avoid the nonspecific adsorption of streptavidin, meaning that nonspecific adsorption on CNTs remains a problem and that this methodology is only useful for purified samples. Regarding the detection mechanism, in addition to charge transfer, Schottky barrier, SB, modification, and scattering potential reported by other authors, an electron/hole trapping mechanism leading to hysteresis modification has been determined. The presence of polymer seems to hinder the modulation of the electrode-CNT contact.

Multi-walled carbon nanotubes affect drug transport across cell membrane in rat astrocytes

The impact of carbon nanotubes on the cell membrane is an aspect of particular importance and interest in the study of carbon nanotubes' interactions with living systems. One of the many functions of the cell membrane is to execute substance transport into and out of the cell. We investigated the influence of multi-walled carbon nanotubes (MWCNTs) on the transport of several compounds across in the cell membrane of rat astrocytes using flow cytometry. These compounds are fluorescein diacetate, carboxyfluorescein diacetate, rhodamine 123 and doxorubicin, which are prosubstrate/substrates of multidrug transporter proteins. Results showed that MWCNTs significantly inhibited cellular uptake of doxorubicin but not the other drugs and the mode of loading made a significant difference in doxorubicin uptake. Retention of fluorescein, carboxyfluorescein and rhodamine 123 was remarkably higher in MWCNT-exposed cells after an efflux period. A kinetics study also demonstrated slower efflux of intracellular fluorescein and rhodamine 123. Data presented in this paper suggest that MWCNTs could affect drug transport across cell membranes. The implications of the findings are discussed.

Maximizing safe design of engineered nanomaterials: the NIH and NIEHS research perspective

Estimating potential risk of an emerging technology as its products are being developed offers the greatest potential for success of the technology. The National Nanotechnology Initiative was launched in 2000 to provide a federal framework to support safe and responsible development of nanotechnology.Within this framework, the National Institutes of Health (NIH) focuses resources and expertise on both the biomedical applications of nanotechnology and the possibility of adverse health effects, or implications research. NIH developed the NanoHealth and Safety Enterprise Initiative by identifying shared research needs across the nanotechnology applications and implications research communities to create an integrated research strategy to maximize resources and expedite the development of engineered nanomaterials (ENM) that are safe by design. The central goal of this program is to decipher the fundamental principles of ENM interactions with biological systems that are relevant to human exposure and physiological response. Program components include materials science, basic biology, pathobiology, and informatics, as well as a cross-disciplinary training program for new nanotechnology scientists. The magnitude of this program will be best supported by flexible, dynamic funding and research mechanisms including the formation of public-private partnerships that span the expertise and interests of government, industry, academia, public interest, and other stakeholders. It is through such innovative, integrated, and cross-disciplinary programs that the full promise of nanotechnology may be realized while ensuring that this emerging field does not succumb to hidden perils.

Characterization of carbon nanotube (MWCNT) containing P(3HB)/bioactive glass composites for tissue engineering applications

Poly(3-hydroxybutyrate) (P(3HB)) composites with bioactive glass particles and multiwall carbon nanotubes (MWCNTs) were prepared and used to identify whether the electrical properties of MWCNTs can be used to detect the bioactivity of P(3HB)/bioactive glass composites. The presence of MWCNTs (2-7 wt.%) increased the surface roughness of the composites. The presence of MWCNTs in low quantity enhanced MG-63 osteoblast-like cell attachment and proliferation compared to composites with higher concentration of MWCNTs. Current-voltage measurements demonstrated that the electrical resistance of the composites containing bioactive glass particles decreased over a 45-day immersion period in SBF, whereas composites without bioactive glass showed no significant change over the same period.

Multidomain peptides as single-walled carbon nanotube surfactants in cell culture

We present a series of short, multidomain peptides as biocompatible solubilizing agents of single-walled carbon nanotubes (SWCNTs). These peptides are organized into an ABA block motif, where the A block is composed of charged amino acids, such as glutamic acid, and the B block is composed of alternating hydrophilic and hydrophobic residues. The hydrophobic amino acid residues interact with SWCNT sidewalls, while the hydrophilic residues interact primarily with water in an aqueous solution. When many peptides assemble along the length of the nanotube, it becomes effectively encapsulated within a peptide nanofiber. This noncovalent interaction between the peptide and the nanotube solubilizes SWCNTs while keeping the electronic structure of the nanotube intact, thereby preserving the optical and electrical properties that make SWCNTs promising for use in biological applications. To assess the toxicity of these peptide coatings, they were added to cultures of NIH 3T3 mouse fibroblasts and the effect on cell viability was measured. Toxicity was found to be far lower than for ionic surfactants typically used for SWCNT suspension and similar to Pluronics. The near-IR fluorescence intensity of SWCNTs in peptide suspensions was comparable to that in Pluronics. Five surfactants were tested for their effect on the proliferation of NIH 3T3 cells with and without SWCNTs. Although some differences were observed among surfactants, in no case did the presence of SWCNTs make a statistically significant difference. Based on their ability to solubilize SWCNTs, the fluorescence of the suspended tubes, their minimal impact on cell viability, and their potential for easy chemical modification, multidomain peptides have been found to have excellent potential as a biocompatible surfactant for suspension of SWCNTs.

Carbon nanotubes are able to penetrate plant seed coat and dramatically affect seed germination and plant growth

Carbon nanotubes (CNTs) were found to penetrate tomato seeds and affect their germination and growth rates. The germination was found to be dramatically higher for seeds that germinated on medium containing CNTs (10-40 mug/mL) compared to control. Analytical methods indicated that the CNTs are able to penetrate the thick seed coat and support water uptake inside seeds, a process which can affect seed germination and growth of tomato seedlings.

Cell behaviors on polysaccharide-wrapped single-wall carbon nanotubes: a quantitative study of the surface properties of biomimetic nanofibrous scaffolds

Natural polysaccharides such as amylose (AMY), alginate sodium (ALG), and chitosan (CHI) have been noncovalently wrapped onto single-wall carbon nanotubes (SWCNTs) to give a series of SWCNT scaffolds, termed as AMY-SWCNT, ALG-SWCNT, CHI-SWCNT, and CHI/ALG-SWCNT scaffolds. Compared to purified SWCNTs and oxidized SWCNTs, the polysaccharide-wrapped SWCNTs can well mimic nanofibrous extracellular matrix and significantly enhance cell adhesion and proliferation. The surface properties of the SWCNT scaffolds, such as functional groups, surface charge, and hydrophilicity, can all directly influence the protein adsorption and lead to changes in cellular FAK expression, thus affect the mammalian cell morphology and proliferation. By quantitatively studying the surface properties of these SWCNT scaffolds, it can be concluded that relatively positively charged hydrophilic scaffolds that bear -OH groups can remarkably promote cell growth. Considering all properties, the relatively electrical neutral and hydrophilic AMY-SWCNT scaffolds bearing only -OH groups are able to sustain the highest cell viability after 72 h culturing.

Carbon nanofibers and carbon nanotubes in regenerative medicine

Carbon nanotubes and carbon nanofibers have long been investigated for applications in composite structural materials, semiconductor devices, and sensors. With the recent well-documented ability to chemically modify nanofibrous carbon materials to improve their solubility and biocompatibility properties: a whole new class of bioactive carbon nanostructures has been created for biological applications. This review focuses on the latest applications of carbon nanofibers and carbon nanotubes in regenerative medicine.

Induction of aneuploidy by single-walled carbon nanotubes

Engineered carbon nanotubes are newly emerging manufactured particles with potential applications in electronics, computers, aerospace, and medicine. The low density and small size of these biologically persistent particles makes respiratory exposures to workers likely during the production or use of commercial products. The narrow diameter and great length of single-walled carbon nanotubes (SWCNT) suggest the potential to interact with critical biological structures. To examine the potential of nanotubes to induce genetic damage in normal lung cells, cultured primary and immortalized human airway epithelial cells were exposed to SWCNT or a positive control, vanadium pentoxide. After 24 hr of exposure to either SWCNT or vanadium pentoxide, fragmented centrosomes, multiple mitotic spindle poles, anaphase bridges, and aneuploid chromosome number were observed. Confocal microscopy demonstrated nanotubes within the nucleus that were in association with cellular and mitotic tubulin as well as the chromatin. Our results are the first to report disruption of the mitotic spindle by SWCNT. The nanotube bundles are similar to the size of microtubules that form the mitotic spindle and may be incorporated into the mitotic spindle apparatus.

Mechanical and in vitro biological performances of hydroxyapatite-carbon nanotube composite coatings deposited on Ti by aerosol deposition

Hydroxyapatite (HA)-carbon nanotube (CNT) composite coatings on Ti plate, produced by aerosol deposition using HA-CNT powders, were developed for biomedical applications. For the deposition process HA-CNT powder mixtures with CNT contents of 1 and 3 wt.% were used. Dense coatings with a thickness of 5 microm were fabricated, irrespective of the content of CNTs. No pores or microcracks were observed in the coatings. The coatings had good adhesion to the substrate, exhibiting a high adhesion strength, ranging from 27.3 to 29.0 MPa. Microstructural observation using field-emission gun scanning electron microscopy and transmission electron microscopy showed that CNTs with a typical tubular structure were found in the HA-CNT composite coatings. Nanoindentation tests revealed that the mechanical properties, such as the hardness and elastic modulus, were significantly improved by the addition of the CNTs to the HA coating. In addition, the proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 pre-osteoblast cells grown on the HA-CNT composite coatings were higher than those on the bare Ti and pure HA coating. The ALP activity of the composite coatings considerably improved as the CNT content increased. These results suggest that CNTs would be an effective reinforcing agent to enhance both the mechanical and biological performances of HA coatings.

Effect of carbon nanotubes on cellular functions in vitro

Carbon nanotubes (CNTs) have been shown to affect cell behavior. But how and why the CNTs affect potential differentiation of the attached cells has not been largely known. In this study, multiwalled carbon nanotubes (MWNTs) and graphite (GP) were pressed as compacts. Higher ability of CNTs to adsorb proteins, compared with GP, was shown. Myoblastic mouse cells (C2C12) were cultured and the cell responses to the two kinds of compacts were compared in vitro. Meanwhile, we used cell culture on the culture plate as a control. During the conventional culture, significantly better cell attachment, proliferation, and differentiation of cells on the MWNTs were found. To confirm the hypothesis that the larger amount of protein adsorbed on the CNTs was crucial for this, we made the compacts adsorb more proteins in culture medium with 50% fetal bovine serum (FBS) before cell culture. With the adsorption of the proteins in advance, the increments of the total-protein/DNA and alkaline phosphatase (ALP)/DNA for the MWNTs was respectively as about 11 times and 18 times as the increments of those for GP and the control at both day 4 and day 7. Therefore, the CNTs might induce cellular functions by adsorbing more proteins, which indicated that the CNTs might be a candidate for scaffold material for tissue engineering.

Bioglass-based scaffolds with carbon nanotube coating for bone tissue engineering

Highly porous 45S5 Bioglass-based foam scaffolds were coated with multi-walled carbon nanotubes (CNT) by electrophoretic deposition (EPD) technique. By placing the scaffolds in between the two electrodes of the EPD cell, a CNT coating of up to 1 mum thickness was achieved on the surface throughout the whole three dimensional (3D) matrix. A 0.5 wt% CNT aqueous suspension was used and EPD was carried out at 2.8 V for 10 mins. The compression strength of this CNT/Bioglass composite was measured to be 0.70 MPa. Moreover the increased electrical conductivity of the composite with CNT coating was confirmed. The scaffolds have the potential for applications in bone tissue engineering due to the high bioactivity, nano-roughness in 3D and electrical conductivity provided by the addition of CNT.

Modeling the Instability of Carbon Nanotubes: From Continuum Mechanics to Molecular Dynamics

A hybrid continuum mechanics and molecular mechanics model is developed in this paper to predict the critical strain, stress, and buckling load of the inelastic buckling of carbon nanotubes. With the proposed model, the beamlike and shell-like buckling behavior of carbon nanotubes can be analyzed in a unified approach. The buckling solutions from the hybrid model are verified from molecular dynamics simulations via the MATERIALS STUDIO software package and from available research findings. The existence of the optimum diameter, at which the buckling load reaches its maximum, and the correlation of the diameter with the length of carbon nanotubes, as predicted by Liew et al. (2004, “Nanomechanics of Single and Multiwalled Carbon Nanotubes,” Phys. Rev. B, 69(11), pp. 115429), are uncovered by the hybrid model. The simplicity and effectiveness of the proposed model are not only able to reveal the chiral and size-dependent buckling solutions for carbon nanotubes, but also enable a thorough understanding of the stability behavior of carbon nanotubes in potential applications.

A thin carbon-fiber web as a scaffold for bone-tissue regeneration

Due to the rapid progress being made in tissue regeneration therapy, biomaterials used as scaffolds are expected to play an important role in future clinical application. We report the development of a 3D web (sheet) consisting of high-purity carbon fibers in a nanoscale structure. When the thin carbon-fiber web (TCFW) and recombinant human bone morphogenetic protein 2 (rhBMP-2) composite is implanted in the murine back muscle, new ectopic bone is formed, and the values of the bone mineral content and bone mineral density are significantly higher than those obtained with a collagen sheet. Observation of the interface between the carbon fibers and bone matrix reveal that the fibers are directly integrated into the bone matrix, indicating high bone-tissue compatibility. Further, the rhBMP-2/TCFW composite repairs a critical-size bone defect within a short time period. These results suggest that the TCFW functions as an effective scaffold material and will play an important role in tissue regeneration in the future.

Toxicity induced enhanced extracellular matrix production in osteoblastic cells cultured on single-walled carbon nanotube networks

A central effort in biomedical research concerns the development of materials for sustaining and controlling cell growth. Carbon nanotube based substrates have been shown to support the growth of different kinds of cells (Hu et al 2004 Nano Lett. 4 507-11; Kalbacova et al 2006 Phys. Status Solidi b 13 243; Zanello et al 2006 Nano Lett. 6 562-7); however the underlying molecular mechanisms remain poorly defined. To address the fundamental question of mechanisms by which nanotubes promote bone mitosis and histogenesis, primary calvariae osteoblastic cells were grown on single-walled carbon nanotube thin film (SWNT) substrates. Using a combination of biochemical and optical techniques we demonstrate here that SWNT networks promote cell development through two distinct steps. Initially, SWNTs are absorbed in a process that resembles endocytosis, inducing acute toxicity. Nanotube-mediated cell destruction, however, induces a release of endogenous factors that act to boost the activity of the surviving cells by stimulating the synthesis of extracellular matrix.

The role of nanomedicine in growing tissues

Nanomedicine (a division of nanotechnology) is an interdisciplinary research field incorporating biology, chemistry, engineering and medicine with the intention to improve disease prevention, diagnosis, and treatment. Specifically, there have been great strides made in using nanomedicine to enhance the functions of cells necessary to regenerate a diverse number of tissues (such as bone, blood vessels, the bladder, teeth, the nervous system, and the heart to name a few). Traditional (micron-structured or nano-smooth) implants suffer from: (i) infection, (ii) inflammation, and (iii) insufficient prolonged bonding between the implanted material and surrounding tissue. To date, such conventional implants have been improved by implementing nanotopographical features on their surfaces. In this review paper, the application of nanomaterials to regenerate numerous organs (including, as specific examples, bone, neural, and bladder tissues) will be presented with necessary future directions highlighted for the field of nanomedicine to progress.

Carbon nanotubes promote neuron differentiation from human embryonic stem cells

Human embryonic stem cells (hESCs) hold great promise for regenerative medicine and transplantation therapy due to their self-renewal and pluripotent properties. We report that 2D thin film scaffolds composed of biocompatible polymer grafted carbon nanotubes (CNTs), can selectively differentiate human embryonic stem cells into neuron cells while maintaining excellent cell viability. According to fluorescence image analysis, neuron differentiation efficiency of poly(acrylic acid) grafted CNT thin films is significant greater than that on poly(acrylic acid) thin films. When compared with the conventional poly-L-ornithine surfaces, a standard substratum commonly used for neuron culture, this new type thin film scaffold shows enhanced neuron differentiation. No noticeable cytotoxic effect difference has been detected between these two surfaces. The surface analysis and cell adhesion study have suggested that CNT-based surfaces can enhance protein adsorption and cell attachment. This finding indicates that CNT-based materials are excellent candidates for hESCs' neuron differentiation.

Adapting collagen/CNT matrix in directing hESC differentiation

The lineage selection in human embryonic stem cell (hESC) differentiation relies on both the growth factors and small molecules in the media and the physical characteristics of the micro-environment. In this work, we utilized various materials, including the collagen-carbon nanotube (collagen/CNT) composite material, as cell culture matrices to examine the impact of matrix properties on hESC differentiation. Our AFM analysis indicated that the collagen/CNT formed rigid fibril bundles, which polarized the growth and differentiation of hESCs, resulting in more than 90% of the cells to the ectodermal lineage in Day 3 in the media commonly used for spontaneous differentiation. We also observed the differentiated cells followed the coarse alignment of the collagen/CNT matrix. The research not only revealed the responsiveness of hESCs to matrix properties, but also provided a simple yet efficient way to direct the hESC differentiation, and imposed the potential of forming neural-cell based bio-devices for further applications.

Multiwalled carbon nanotubes specifically inhibit osteoclast differentiation and function

Since attention has been paid to the use of multiwalled carbon nanotubes (MWCNTs) as biomaterials in contact with bone, it is critical to understand the reaction of bone cells to MWCNTs. We show that MWCNTs inhibit osteoclastic bone resorption in vivo and that MWCNTs inhibit osteoclastic differentiation and suppressed a transcription factor essential for osteoclastogenesis in vitro. These results suggest that MWCNTs have beneficial effects on bones when they are used as biomaterials.

Carbon nanotubes: biomaterial applications

There is increasing interest in the unique biological and medical properties of carbon nanotubes (CNTs), and it is expected that biomaterials incorporating CNTs will be developed for clinical use. There has been a great deal of progress in improving the various properties of CNTs for use in biomaterials and for promotion of tissue regeneration as scaffold materials. The effects of CNTs on cells and tissues are extremely important for their use in biomaterials. This tutorial review clarifies the current state of knowledge in the interdisciplinary field of CNT-based nanobiotechnology to determine whether CNTs may be useful in biomaterials. Future perspectives in this rapidly developing field will also be discussed.