Patent Application
20120315301
The invention relates to nanomaterials comprising carbon nanotubes that exhibit new morphologies, and/or solubility that make them particularly suitable for use as drug or gene delivery systems. The nanomaterials comprise carbon nanotubes (CNTs), dendritic or linear-dendritic polymers or copolymers, and/or metal nanoparticles.
Due to their unique thermal, optical and chemical properties, carbon nanotubes, CNTs, have been intensively explored for biological and biomedical applications in the past few years [1-7]. They are able to transport therapeutic agents to tumors by “covalent” and “non-covalent” methods effectively. In the covalent method therapeutic agents are attached to their surface through chemical bonds while in the non-covalent method they are encapsulated in their cavity or loaded on their surface [8-12]. Their ability to cross the cell membranes besides the mentioned properties promises them as novel devices for cancer imaging and therapy [13-17]. However poor water solubility and low functionality are two major factors that limit the application of CNTs in the administration step and dominate their toxicity, biocompatibility, blood circulation time and biological properties [18-19]. Since safety and biocompatibility of CNTs is still under question and variety of research works are reported in this case [20-21], development of the new strategies to improve their water solubility and functionality is important [22]. However functionalization of CNTs changes their shape and conformation significantly [23]. While shape and size of nanomaterials—and especially CNTs—based drug delivery systems affect their toxicity efficiently [24, 25], investigation of the interrelation of functionalization, conformation and biocompatibility of CNTs can be important. Based on our research works, hydrophilic dendritic polymers not only rise the functionality, biocompatibility and water solubility of CNTs but also change their conformations dramatically [26].
A new method to improve both functionality and water solubility of CNT or CNT/metal hybrid nanomaterials using linear-dendritic copolymers without damaging their structure has been also reported. Linear-dendritic copolymers are hybrid nanomaterials consisting of linear and dendritic blocks [28-32]. Polyethylene glycol, PEG, is a well-studied and used polymer not only to synthesis variety of linear-dendritic copolymers but also to improve the process ability, water solubility and long blood circulation of CNTs through non-covalent interactions [33-38]. Hence supramolecular interactions between the PEG block of a linear-dendritic copolymers and CNTs leads to water soluble and high functional hybrid nanomaterials. PCA-PEG-PCA copolymers are biocompatible, water soluble and high functional ABA type linear-dendritic copolymers that has been synthesized and characterized and their potential as nanocarriers for drug delivery has been investigated previously [39-40].
One embodiment provides a nanomaterial comprising carbon nanotubes and having a new morphology, such as a morphology selected from liposome-like, vesicle-type, circle-type, spherical, etc., induced by supramolecular chemistry of the nanomaterial. In some embodiments, the nanomaterial exhibits a liposome or liposome-like morphology. In other embodiments, the nanomaterial exhibits a spherical or circle-type morphology. In some embodiments, the material has a core/shell structure based on carbon nanotubes. In some embodiments, the material is carbon nanotubes nanospheres.
Another embodiment provides a nanomaterial comprised of carbon nanotubes and polymers or copolymers, such as dendritic or linear-dendritic polymers or copolymers, and/or metal nanoparticles (“hybrid nanomaterials”). In some embodiments, the nanomaterial exhibits a vesicle-type morphology.
Another embodiment provides a nanomaterial comprised of carbon nanotubes and dendritic or linear-dendritic polymers or copolymers. In some embodiments the nanomaterial exhibits improved water solubility and/or functionality as compared to a material comprised only of carbon nanotubes. In some embodiments, the polymers or copolymers comprise functional groups, such as a large number of functional groups. In some embodiments, the functional groups are disposed on the surface of the nanomaterial. In other embodiments the functional groups are disposed within a cavity of the nanomaterial, such as within the cavity of a liposome-like structure.
Another embodiment provides carrier systems for transferring molecules or macromolecules (for example, drug or gene delivery systems) comprising a hybrid nanomaterial as described herein, e.g., comprising carbon nanotubes and dendritic or linear-dendritic polymers or copolymers and/or metal nanoparticles.
Another embodiment provides hybrid nanomaterials with supramolecular interactions and covalent linkages between carbon nanotubes (CNT) and dendritic or linear-dendritic polymers or copolymers. In some embodiments, the hybrid nanomaterials include a multi-walled carbon nanotube (MWCNT), single-walled carbon nanotube (SWCNT), opened carbon nanotube and/or a carbon nanotube decorated with metal nanoparticles. In some embodiments, the surfaces of the carbon nanotubes are decorated with nanoparticles or nanomaterials. In some embodiments, the carbon nanotubes are decorated by metal nanoparticles such as Fe, Mn, Ni, Co, Cr, Pt, and alloys thereof. In some embodiments, the metal nanoparticles decorated carbon nanotube are superparamagnetic. In some embodiments of the linear-dendritic polymers, the linear segment is a linear polymer or copolymer and the dendritic segment is a dendron, dendrimer or a hyperbranched polymer or their derivations. In some embodiments, the polymers or copolymers of the linear and dendritic segments are synthetic (such as polyethylene glycol, polyglycerol and polycitric acid) or natural macromolecules (such as starch and polylysine) or biomolecules (such as DNA, RNA and proteins).
Also provided are methods of making the nanomaterials described herein.
The present invention will be better understood in view of the following non-limiting figures, wherein:
Before explaining the disclosed embodiment of the present invention in detail it is to be understood that the invention is not limited in scope by the specific embodiment described herein, which are intended for the purpose of exemplification only.
The present invention relates to the preparation of novel hybrid nanomaterials comprised of carbon nanotubes (CNTs) and polymers or copolymers, or comprised of CNTs and metal nanoparticles, or comprised of CNTs, polymers or copolymers, and metal nanoparticles (collectively, “hybrid nanomaterials”). The polymers or copolymers may be dendritic or linear-dendritic (with linear segments and dendritic segments).
Supramolecular interactions between carbon nanotubes and linear-dendritic polymers or copolymers led to formation of liposome-like nanotube structures (LLNs). That is, the hybrid nanomaterials may form structures with liposome-like or vesicle-type morphologies, including spherical structures. The hybrid nanomaterials are useful, for example, as carrier systems for transferring molecules or macromolecules, such as drug or gene delivery systems.
As used herein, carbon nanotubes include multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), pristine carbon nanotubes, opened carbon nanotubes and metal nanoparticle decorated carbon nanotubes, and derivatives thereof.
As used herein, dendritic or linear-dendritic polymers and copolymers contain linear and dendritic segments. The linear and dendritic segments comprise linear polymers or copolymers, and dendron, dendrimer or a hyperbranched polymer and their derivations, respectively. In some embodiments of the linear-dendritic polymers, the linear segment is a linear polymer or copolymer and the dendritic segment is a dendron, dendrimer or a hyperbranched polymer or their derivations. In some embodiments, the polymers or copolymers are synthetic (such as polyethylene glycol, polyglycerol and polycitric acid) or natural macromolecules (such as starch and polylysine) or biomolecules (such as DNA, RNA and proteins). In some embodiments, the polymers or copolymers are hydrphillic.
Embodiments of the present invention provide a simple approach to obtain high functional and water soluble liposome like or vesicle-type hybrid nanomaterials, such as compared to a material comprised only of carbon nanotubes. For example, in some embodiments, the polymers or copolymers comprise functional groups, such as a large number of functional groups. In some embodiments, the functional groups are disposed on the surface of the nanomaterial. In other embodiments the functional groups are disposed within a cavity of the nanomaterial, such as within the cavity of a liposome-like structure.
In some embodiments, the invention provides carbon nanotubes with high functionality and/pr water solubility having morphologies of carbon nanotubes (CNTs) using dendritic or linear-dendritic polymers and copolymers.
In some embodiments, the surfaces of the carbon nanotubes are decorated with nanoparticles or nanomaterials. In some embodiments, the carbon nanotubes are decorated by metal nanoparticles such as Fe, Mn, Ni, Co, Cr, Pt, and alloys thereof. In some embodiments, the metal nanoparticles decorated carbon nanotube are superparamagnetic. By “decorated” means that nanoparticles or nanomaterials are deposited or attached onto the surface of the carbon nanotubes.
Conjugation of the paclitaxol molecules to the end functional groups of a hyperbranched poly(citric acid) grafted onto the surface of multi-walled carbon nanotubes (MWCNTs) leads to LLNs [27]. The main reason to form LLNs from MWCNT-graft-polycitric acid is non-covalent interactions between the functional groups of the grafted hyperbranched polymer and looping the carbon nanotubes to avoid interactions with water molecules.
According to exemplary implementations of the present invention for example, Fe2O3 nanoparticles, γ-Fe2O3NP, were deposited onto the surface of multi walled carbon nanotubes to obtain CNT/γ-Fe2O3NP hybrid nanomaterials. Non-covalent interactions between linear-dendritic copolymers and CNT/γ-Fe2O3NP hybrid nanomaterials led to the formation of a liposome-like or vesicle-type structure, making the hybrid nanomaterials useful as new drug delivery systems.
Simple mixing and sonicating of MWCNTs and linear-dendritic copolymers led to their aqueous solutions that were stable over several months.
When linear-dendritic copolymers were used to modify CNTs, it was found that they changed their conformation from linear to packed state and led to LLNs. Another significant result was that, the geometry of LLNs depended on the type of dendritic blocks of linear-dendritic copolymers and their functional groups.
In spite of the PAMAM-PEG-PAMAM linear-dendritic copolymers, LLNs resulted from the non-covalent interactions between MWCNTs and PCA-PEG-PCA linear-dendritic copolymers (PCA-PEG-PCA/MWCNTs) were containing an empty cavity (
Comparison the SEM images of the acid treatment MWCNTs and PG-PEG-PG/MWCNT LLNs shows that carbon nanotubes are covered by linear-dendritic copolymers and they are not in their extended conformation (
Interactions between the end functional groups of the sheet-like assemblies wrapped around the MWCNTs then lead to the LLNs (
Spectroscopy data show that the carbonyl functional groups of the dendritic blocks of PAMAM-PEG-PAMAM and PCA-PEG-PCA linear-dendritic copolymers dominate their non-covalent interactions with the surface of carbon nanotubes.
Two absorbance bands corresponded to the acidic and esteric carbonyl functional groups of PCA blocks of PCA-PEG-PCA linear-dendritic copolymers are exhibited at 1700 and 1740 cm−1 respectively. In the IR spectra of PCA-PEG-PCA/MWCNT LLNs both absorbance bands are shifted toward lower frequencies proving that there is strong interactions between PCA blocks and MWCNTs. On the other hand intensity of the absorbance band of the esteric carbonyl functional groups is decreased significantly, due to the reduced polarity of these groups. Both observations confirm the electron transferring from MWCNT to the C═O bonds. Absorbance band of the aliphatic C—H bonds is shifted toward higher frequencies confirming that —CH2—O— bonds of PEG are also interacting with MWCNTs.
Comparison of the 1H NMR spectra of PCA-PEG-PCA linear-dendritic copolymers and PCA-PEG-PCA/MWCNT LLNs shows that peak surface area of protons of PEG and methylene groups of PCA blocks do not change upon non-covalent interactions with the surface of MWCNTs. Therefore it can be deduced that the etheric bonds of PEG and C—C bonds of PCA blocks are either equally interacting with the MWCNT or do not have a significant interaction with the surface of MWCNTs. Peak surface area of protons of both PEG and PCA blocks decreased significantly upon coordination of cisplatin (CDDP) molecules to the carboxyl functional groups of PCA-PEG-PCA linear-dendritic copolymers. This result prove that conjugation of CDDP molecules to linear-dendritic copolymers increase interactions between PEG and PCA blocks and MWCNT which is in agreement with the last result founded by the IR spectra.
Intensity of the absorbance bands corresponded to the carbonyl functional groups of PAMAM-PEG-PAMAM linear-dendritic copolymer decrease intensively upon non-covalent interactions with MWCNTs confirming that the polarity of the carbonyl functional groups of PAMAM-PEG-PAMAM linear-dendritic copolymer diminish after staking on MWCNTs. This result can be assigned to the electron transferring from the π system of the MWCNT to the carbonyl functional groups of PAMAM-PEG-PAMAM linear-dendritic copolymer (
Based on spectroscopy data it can be suggested that interactions between the π bonds of the carbonyl functional groups of linear-dendritic copolymers and π system of carbon nanotubes is the main driving force to stake linear-dendritic copolymers onto the surface of carbon nanotubes. In order to investigate this suggestion, 2-chloro-4,6-diphenyl-1,3,5 triazine was synthesized and conjugated to the amino functional groups of the second generation of PAMAM-PEG-PAMAM linear-dendritic copolymer and obtained copolymer (PAMAM-1) was interacted with the MWCNTs (Scheme 1).
AFM images show that PAMAM-1 are staked onto the surface of carbon nanotube intensively (
PG-PEG-PG linear-dendritic copolymer does not have carbonyl functional groups or any functional group containing π bonds to interact with the conjugated π system of carbon nanotubes. However spectroscopy data, thermal analysis and visual observations show that they interact with the surface of MWCNTs strongly.
Carboxyl functional groups (—OH and carbonyl) of MWCNTs and hydroxyl functional groups of polyglycerol shift toward lower and higher frequencies respectively, proving that interactions between these functional groups have critical role in the interactions between MWCNTs and PG-PEG-PG linear-dendritic copolymers (
Interactions between MWCNTs and PG-PEG-PG linear-dendritic copolymer causes a broadening in the signals of both PEG and PG blocks. Based on this data PG and PEG blocks are interacting with the surface of MWCNTs surface equally. A reason for this observation is the similarity of the structures of PEG and PG blocks (
Based on variety of data the main driving forces to form LLNs from PG-PEG-PG linear-dendritic copolymers and MWCNTs are as below:
i) Interactions between hydroxyl functional groups of the PG-PEG-PG linear-dendritic copolymer and carboxyl functional groups in the defect sites and opened tips of the MWCNTs (
ii) Avoiding interactions between water molecules and hydrophobic surface of the MWCNTs, which leads to increased entropy, by forming a shell around them.
DLS experiments show that the size of LLNs in the solution state is close to that measured by AFM in the solid state. Therefore they keep their geometry in the solution state, so that their inner space is still survived to encapsulate the therapeutic agents or other small molecules. To prove the efficacy of the LLNs as drug delivery systems, their ability to load doxorubicin (DOX) and cisplatin (CDDP) was investigated and then they were subjected to the endocytosis and release the drug inside the cancer cells (L929 and C26).
It was found that the encapsulation of DOX molecules by PG-PEG-PG/MWCNT and PAMAM-PEG-PAMAM/MWCNT LLNs increases their sizes. Because π-π staking of DOX molecules onto the surface of carbon nanotubes decrease interactions between linear-dendritic copolymers and the surface of carbon nanotubes, causing a less packed conformation for MWCNTs (
Due to the inter-connections of the dendritic blocks by CDDP molecules, size of the PCA-PEG-PCA/MWCNT LLNs decreases upon loading of CDDP molecules. A addition of the CDDP molecules to the PCA-PEG-PCA/MWCNT LLNs also causes disappearing of the absorbance band of the acidic carbonyl functional groups of PCA blocks in the IR spectra. These results show that CDDP molecules are conjugated to the linear-dendritic copolymers by coordinating to their carboxyl functional groups. Shifting of the absorbance bands of the esteric carbonyl functional groups toward lower frequencies can be assigned to their more effective interactions with carbon nanotubes after conjugation of CDDP molecules to their hydroxyl functional groups.
The Raman spectroscopy provides more interesting results concerning interactions between MWCNT and linear-dendritic copolymers and loading the drugs on them.
Raman spectra pattern of MWCNTs is loosed upon interactions with PG-PEG-PG and PAMAM-PEG-PAMAM linear-dendritic copolymers showing that the structural backbone of MWCNTs is deformed completely and they are not in their usual conformation (
TGA-DTA analysis were also used to evaluate interactions between linear-dendritic copolymers and MWCNTs and encapsulation of DOX and CDDP molecules inside LLNs (
In the case of PG-PEG-PG/MWCNT LLNs, the first step is similar to that for PAMAM-PEG-PAMAM/MWCNT LLNs i.e separation of the staked DOX molecules from the surface of MWCNTs is endothermic but the second step do not compensate it, due to the absence of π bonds in the PG-PEG-PG linear-dendritic copolymer, therefore the summation of this process is endothermic. Endothermic dissociation of the PG-PEG-PG linear-dendritic copolymer shell from the surface of MWCNTs then, increase the slope of the DTA diagram (
The observed weight-loss region in the TGA diagrams of PAMAM-PEG-PAMAM/MWCNT and PG-PEG-PG/MWCNT LLNs at 70-150° C. disappeared upon encapsulation of DOX molecules. This weight-loss is assigned to the evaporation of encapsulated water molecules inside LLNs. After replacing the water molecules by DOX molecules this weight-loss also disappeared (
Based on the results of a variety of analysis and microscopy observations that are explained above, it is believed that the hybrid nanomaterials described herein exhibit a liposome-like structure comprised of carbon nanotubes and linear-dendritic copolymers, in which carbon nanotubes (220) and hydrophilic branches of linear-dendritic copolymers (210) play the roles of lipidic bi-layer structure and hydrophilic outside (polar heads) in liposome structure (
Encapsulation of DOX molecules inside LLNs and their loading capacities were evaluated using UV-vis spectra and high performance chromatography.
According to HPLC experiments, loading capacities for PAMAM-PEG-PAMAM/MWCNT, PCA-PEG-PCA/MWCNT and PG-PEG-PG/MWCNT LLNs were: 3, 3.4, and 2.2 gram to one gram of LLNs respectively.
The multi wall carbon nanotubes MWCNT were prepared by chemical vapor deposition procedure in the presence of Co/Mo/MgO as catalyst at 900° C. Citric acid monohydrate (MW=210.14), poly ethylene glycol (MW=1000), cisplatin [Cis-Diamminedichloroplatinum (II), CDDP], [Fe (NO3)3.9H2O] and HNO3 were purchased from Merck. The cell lines (mouse tissue connective fibroblast adhesive cells (L929) were obtained from the National Cell Bank of Iran (NCBI) Pasteur institute, Tehran, Iran. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) powder, Annexin-V FLUOS Staining Kit, was obtained from Sigma.
Nuclear magnetic resonance (1H NMR) spectra were recorded in D2O solution on a Bruker DRX 400 (400 MHz) apparatus with the solvent proton signal for reference. Infrared spectroscopy (IR) measurements were performed using a Nicolet 320 FT-IR. Ultraviolet (UV) spectra were recorded on a shimadzu (1650 PC) scanning spectrophotometer. The particle size, polydispersity and zeta potential of materials were determined using Dynamic Light Scattering (DLS) (zetasizer ZS, Malvern Instruments). Thermogravimetric analysis (TGA) were carried out in a thermal analyzer (model: DSC 60, shimadzu, Japan) under dynamic atmosphere of an inert gas (i.e. N2) at 30 ml/min (room temperature).
Morphology and size of materials were investigated using the Philips XL30 scanning electron microscope (SEM) with 12 and 15 A accelerating voltages.
Surface imaging studies were performed using atomic force microscopy (AFM) to estimate surface morphology and particle size distribution. The samples were imaged with the aid of Dualscope/Rasterscope C26, DME, Denmark, using DS 95-50-E scanner with vertical z-axis resolution of 0.1 nm. Raman spectra were obtained with an Almega Thermo Nicolet Dispersive Raman Spectrometer with second harmonic 532 nm of an Nd: YLF laser.
The Transmission electron microscopic (TEM) analyses were performed by a LEO 912AB electron microscope with accelerating voltage of 200 kV. The magnetic moment (M) of the hybrid nanomaterials were measured using Lake Shore model 7400 Vibrating Sample Magnetometer (VSM). Ultrasonic bath (Model: 5RS, 22 KHZ, Made in Italy) was used to disperse materials in solvents.
Simulation for NDDSs in the magnetic field was performed using Finite element method CONSOL multiphysics software.
The multi wall carbon nanotubes (MWCNTs) (2 g) were added to 30 ml of sulfuric and nitric acid mixture (3/1) in a reaction flask and refluxed for 24 h at 120° C. The mixture was cooled and diluted by distillated water and then it was filtrated. The product (MWCNT-COOH) was washed by distillated water and dried at 60° C. for 3 h by vacuum oven.
The multi wall carbon nanotubes (MWCNTs) (0.05 gr) were added into a solution of concentrated nitric acid containing iron nitrate (3 gr, 0.007 mmol) and refluxed for 4.5 h in an oil bath at 120° C. When the mixed solution was cooled to room temperature, the ammonia solution (2.5 wt %) was slowly added into the solution with vigorously stirring until the pH value reached 10. Then the solution was filtered with 0.65 mm filter membrane and washed with distilled water repeatedly. Later the product was dried overnight at 100° C. in an oven. The sample was then annealed at 250° C. for 1 h and 650° C. for 2 h in a steam of nitrogen.
For synthesizing of PEG-g-PCA, (2gr) PEG (MW=1000, mol ratio=1/10) was added to a polymerization ampule equipped with magnetic stirrer and vacuum inlet. Monohydrate citric acid (7 gr) was also added to ampule and it was sealed under vacuum and then the mixture was stirred at 110° C. Produced water was removed by opening the vacuum inlet and temperature of reaction was slowly raised to 130° C. The vacuum inlet was closed and mixture was stirred at this temperature for 15 minutes. Then produced water was removed by opening the vacuum inlet and temperature of reaction was raised to 150° C. Polymerization was continued in this temperature under dynamic vacuum (open vacuum inlet) for 30 minutes in this temperature. The mixture was dissolved in tetrahydrofuran (THF) and was precipitated in diethyleter. Purified product was obtained as a viscous yellow compound in 80% yield [41].
CDDP (0.33 mmol) was suspended in 10 ml distilled water and mixed with silver nitrate ([AgNO3]/[CDDP]=1) to form the aqueous complex. The solution was kept in dark at room temperature to appear AgCl precipitate. Then, the mixture was centrifuged at 7000 rpm for 20 min to remove the AgCl precipitates. Afterward, the supernatant was purified by passing through a 0.45 mm filter and PCA-PEG-PCA linear-dendritic copolymer (0.03 g) was added to above solution and gently stirred for 48 h at 37° C. to obtain the CDDP-PCA-PEG-PCA-CDDP conjugate.
CNT/γ-Fe2O3NP (0.001 g) and PCA-PEG-PCA linear-dendritic copolymer (0.0024 g) (or CDDP-PCA-PEG-PCA-CDDP prodrug 0.00025 g) were mixed in distilled water (5 ml) and mixture was sonicated for 30 min at room temperature. Mixture was filtrated to obtain a clear brown solution.
Second generation of PAMAM-PEG-PAMAM linear-dendritic copolymer was prepared according to reported procedure in literature.
Ligand (2-chloro 4,6-di phenoxy-1,3,5-triazine) (compound a) that was synthesized according to reported procedure in literature was conjugated to the end amino functional groups of the second generation of PAMAM-PEG-PAMAM linear-dendritic copolymer (G2). A solution of G2 (2 g) in 5 mL of dry methanol was added to compound a (1.82 g) dissolved in 10 mL of dry dichloromethane, dropwise at 0° C. Mixture was stirred at room temperature for 1 h and refluxed for additional 12 h then it was cooled and filtered off. Solvent was evaporated and mixture was dissolved in 5 mL methanol and then product was precipitated in diethylether and purified compound was obtained as a dark brown viscose solid.
MWCNTs (2 mg) and PAMAM-PEG-PAMAM linear-dendritic copolymers (0.2 mg) were mixed in distilled water (5 ml) and mixture was sonicated for 30 min at room temperature. Mixture was filtered to obtain a clear black solution.
MWCNTs/PCA-PEG-PCA LLNs were prepared according to our reported method in literature.
CDDP molecules were loaded by MWCNTs/PCA-PEG-PCA LLNs according to our reported method in literature.
In this work, two molecular weights of PG-PEG-PG linear-dendritic copolymers were synthesized using different ratios of polyethyleneglycol (PEG) to glycidol (G) (1:10 and 1:20) and they were used to interact with MWCNTs non-covalently. PG-PEG-PG linear-dendritic copolymers (0.001 g) were dissolved in 5 ml distilled water and solution was added to MWCNTs (0.002 g).
