This invention is a means of delivering a drug, or payload, to cells using non-covalent associations of the payload with nano-engineered scaffolds; specifically, functionalized single-walled carbon nanotubes (SWNTs) and their derivatives where the payload is effectively sequestered by the nanotube's addends and then delivered to the site (often interior of a cell) of interest. Polyethylene glycol (PEG) and other water-soluble organic molecules have been shown to greatly enhance the solubility of SWNTs in water. PEG groups and other water-solubilizing addends can act to sequester (sponge) molecules and deliver them into cells. Using PEG that, when attached to the SWNTs, the SWNT/PEG matrix will enter cells has been demonstrated. This was visualized by the addition of fluorescein isothiocyanate (FITC) to the SWNT/PEG matrix. Control studies showed that both FITC alone and FITC/PEG did not enter the cells. These observations suggest that the FITC is highly associated with the SWNT/PEG matrix that brings the FITC into the cells, allowing visualization of SWNTs in cells. The FITC is not covalently attached, because extended dialysis in hot DMF will remove all fluorescence quickly (one week). However, prolonged dialysis in water (1-2 months) will only slowly diminish the fluorescence. This demonstrates that the SWNT/PEG matrix solubilizes the FITC by sequestering it from the surrounding water and into the more solubilizing organic environment of the SWNT/PEG matrix of this type. This can be extended for the sequestering of other molecules such as drugs with PEG and other surfactants.

Elastomers are reinforced with functionalized, single-walled carbon nanotubes (SWNTs) giving them high-breaking strain levels and low densities. Cross-linked elastomers are prepared using amine-terminated, poly(dimethylsiloxane) (PDMS), with an average molecular weight of 5,000 daltons, and a functionalized SWNT. Cross-link densities, estimated on the basis of swelling data in toluene (a dispersing solvent) indicated that the polymer underwent cross-linking at the ends of the chains. This thermally initiated cross-linking was found to occur only in the presence of the aryl alcohol functionalized SWNTs. The cross-link could have been via a hydrogen-bonding mechanism between the amine and the free hydroxyl group, or via attack of the amine on the ester linage to form an amide. Tensile properties examined at room temperature indicate a three-fold increase in the tensile modulus of the elastomer, with rupture and failure of the elastomer occurring at a strain of 6.5.

Single-walled carbon nanotube (SWCNT) fibers were engineered to become a scaffold for the storage of hydrogen. Carbon nanotube fibers were swollen in oleum (fuming sulfuric acid), and organic spacer groups were covalently linked between the nanotubes using diazonium functionalization chemistry to provide 3-dimensional (3-D) frameworks for the adsorption of hydrogen molecules. These 3-D nanoengineered fibers physisorb twice as much hydrogen per unit surface area as do typical macroporous carbon materials. These fiber-based systems can have high density, and combined with the outstanding thermal conductivity of carbon nanotubes, this points a way toward solving the volumetric and heat-transfer constraints that limit some other hydrogen-storage supports.

Injectable nanocomposites made of biodegradable poly(propylene fumarate) and the crosslinking agent propylene fumarate-diacrylate as well as each of three forms of single-walled carbon nanotubes (SWNTs) were evaluated for their in vitro cytotoxicity. Unreacted components, crosslinked networks, and degradation products of the nanocomposites were investigated for their effects on cell viability using a fibroblast cell line in vitro. The results did not reveal any in vitro cytotoxicity for purified SWNTs, SWNTs functionalized with 4-tert-butylphenylene, and ultra-short SWNTs at 1- 100 microg/mL concentrations. Moreover, nearly 100% cell viability was observed on all crosslinked nanocomposites and cell attachment on their surfaces was comparable with that on tissue culture polystyrene. The degradation products of the nanocomposites displayed a dose-dependent adverse effect on cells, which was partially due to increased osmolarity by the conditions of accelerated degradation and could be overcome at diluted concentrations. These results demonstrate that all three tested nanocomposites have favorable cytocompatibility for potential use as scaffolds for bone tissue engineering applications.

A method has been developed for creating bulk quantities of water-soluble single-walled carbon nanotubes (SWNTs) that contain multifunctional, acid-sensitive addends. Utilizing aryl diazonium salts, the repetitive functionalization protocol can yield multifunctional SWNTs containing moieties that would not be stable to the harsh oleum functionalization conditions used previously. The presence of multifunctionality on the SWNTs has been confirmed using Raman spectroscopy, thermal gravimetric analysis, and X-ray photoelectron spectroscopy.

"Hairy nano-objects" are hybrid nanostructures comprising a core surrounded by a "hairlike" corona of flexible polymer chains, the role of which is typically to improve the solubility of the core material or to improve its dispersability and adhesion in other polymer matrices. Both aspects could be particularly useful with carbon nanotubes, especially in their applications as reinforcing agents. The controlled synthesis of hairy carbon nanotubes is accomplished by chemical modification with 2-bromopropionate followed by extension with poly(n-butyl acrylate) through atom transfer radical polymerization. The obtained hairy nanotubes are visualized at nearly molecular resolution with tapping-mode atomic force microscopy, providing insight into the uniformity of grafted chain lengths and grafting density. The grafting densities vary from approximately 1.0-10.0 chains nm(-1) along the nanotubes. Such a wide range of grafting density may indicate some chemical heterogeneity along and between the nanotubes; it may be also an indication of the challenges associated with carrying out chemical modification of nano-objects having high tendency to aggregate.

The cytotoxic response of cells in culture is dependant on the degree of functionalization of the single-walled carbon nanotube (SWNT). After characterizing a set of water-dispersible SWNTs, we performed in vitro cytotoxicity screens on cultured human dermal fibroblasts (HDF). The SWNT samples used in this exposure include SWNT-phenyl-SO3H and SWNT-phenyl-SO3Na (six samples with carbon/-phenyl-SO3X ratios of 18, 41, and 80), SWNT-phenyl-(COOH)2 (one sample with carbon/-phenyl-(COOH)2 ratio of 23), and underivatized SWNT stabilized in 1% Pluronic F108. We have found that as the degree of sidewall functionalization increases, the SWNT sample becomes less cytotoxic. Further, sidewall functionalized SWNT samples are substantially less cytotoxic than surfactant stabilized SWNTs. Even though cell death did not exceed 50% for cells dosed with sidewall functionalized SWNTs, optical and atomic force microscopies show direct contact between cellular membranes and water-dispersible SWNTs; i.e. the SWNTs in aqueous suspension precipitate out and selectively deposit on the membrane.

Organic triazene compounds are stable precursors to diazonium salts for functionalizing single-wall carbon nanotubes (SWNTs) in aqueous media. This method is particularly useful when a target molecule has functionality that will not tolerate diazotization conditions. We illustrate this by detailing the synthesis of a biotin-containing triazene followed by reaction with SWNTs.

We have investigated the dispersion of single-walled carbon nanotubes (SWNTs) and functionalized SWNTs (F-SWNTs) in the unsaturated, biodegradable polymer poly(propylene fumarate) (PPF) and examined the rheological properties of un-cross-linked nanocomposite formulations as well as the electrical and mechanical properties of cross-linked nanocomposites. F-SWNTs were produced from individual SWNTs by a diazonium-based method and dispersed better than unmodified SWNTs in both un-cross-linked and cross-linked PPF matrix. Cross-linked nanocomposites with F-SWNTs were superior to those with unmodified SWNTs in terms of their mechanical properties. Specifically, nanocomposites with 0.1 wt % F-SWNTs loading resulted in a 3-fold increase in both compressive modulus and flexural modulus and a 2-fold increase in both compressive offset yield strength and flexural strength when compared to pure PPF networks, whereas the use of 0.1 wt % SWNTs gained less than 37% mechanical reinforcement. These extraordinary mechanical enhancements considered together with Raman scattering and sol fraction measurements indicate strong SWNT-PPF interactions and increased cross-linking densities resulting in effective load transfer. With enhanced mechanical properties and capabilities of in situ injection and cross-linking, these SWNT/polymer nanocomposites hold significant implications for the fabrication of bone tissue engineering scaffolds.

Single-walled carbon nanotubes (SWNTs) have unique mechanical, electrical, and optical properties and can be easily chemically modified; features that make them excellent candidate materials for applications as sensors and stimulators in neuronal tissue engineering. The purpose of this study was to demonstrate that SWNTs can support neuronal attachment and growth, that simple chemical modifications can be employed to control cell growth, that SWNTs do not interfere with ongoing neuronal function, and that neurons can be electrically coupled to SWNTs. Growth and attachment of the neuroblastoma*glioma NG108, a model neuronal cell, was assessed on unmodified SWNT substrates or substrates from SWNTs modified with 4-benzoic acid or 4-tert-butylphenyl functional groups using a simple functionalization method. SWNT films support cell growth, but at a reduced level compared to tissue culture-treated polystyrene. The order of viability and cell attachment was tissue culture treated polystyrene > SWNTs > 4-tert-butylphenyl-functionalized SWNTs > 4-benzoic acid-functionalized SWNTs. Decreased cell growth after culture on untreated (non adherent) polystyrene suggested that cell attachment was a critical determinant of proliferation and cell growth on SWNTs. Fluorescence and scanning electron microscopy revealed decreased neurite outgrowth in NG108 grown on SWNT substrates. We are also among the first groups to demonstrate electrical coupling of SWNTs and neurons by demonstrating that NG108 and rat primary peripheral neurons showed robust voltage-activated currents when electrically stimulated through transparent, conductive SWNT films. Our data suggest that SWNTs are flexible resource materials for tissue engineering application involving electrically excitable tissues such as muscles and nerves.

This work investigated the effects of the use of a surfactant or the functionalization of single-walled carbon nanotubes (SWNTs) on their dispersion in uncrosslinked poly(propylene fumarate) (PPF) and the mechanical reinforcement of crosslinked composites as a function of the SWNT concentration. Rheological measurements showed good dispersion of SWNTs in uncrosslinked PPF at low concentrations of 0.05 wt% and SWNT aggregation for higher concentrations for all formulations examined. Mechanical testing demonstrated significant reinforcement in the compressive and flexural mechanical properties of crosslinked nanocomposites which peaked for low SWNT concentrations of the order of 0.05 wt%. For example, a 74% increase was recorded for the compressive modulus and a 69% increase for the flexural modulus of nanocomposites with functionalized SWNTs at a 0.05 wt% loading. Nevertheless, this reinforcement was not related to the use of a surfactant or the functionalization of the SWNTs tested. Scanning electron microscopy examinations of fractured nanocomposite surfaces revealed the formation of SWNT aggregates at higher concentrations corroborating the rheological and mechanical data. These results suggest that the dispersion of individual SWNTs in a uncrosslinked formulation is pivotal to the development of injectable nanocomposites for bone tissue engineering applications.