The present disclosure relates to nanotube materials. More particularly, the present disclosure relates to methods of loading material into a nanotube structure and also the loaded nanotube structure.
In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Nanotubes, particular carbon nanotubes (CNTs), have been investigated for several applications, including electronic applications (see, for example, U.S. Pat. Nos. RE 38,561, RE 38,223 and 5,773,921) and biologic applications (see, for example, Pantarotto et al., Chemical Communications, 16-17, 2004; Lu et al., Nano Lett., 4:2473-2477, 2004; ShiKam et al., J. Amer. Chem. Soc., 126:6850-6851, 2004; ShiKam et al., PNAS, 102:11600-11605, 2005; Naguib et al., Nanotechnology, 567-571, 2005; and Salvador-Morales et al., Mol. Immunol., 43-193-201, 2006.). Typically, at least in the biological applications, the material of interest added to the nanotube has been associated with the exterior surface of the nanotube, such as through a functionalization technique (see, fore example, Pantarotto et al., Chem. Biol., 10:961-966, 2003.). Carbon nanotubes with magnetic particles (Korneva et al., Nano Letters, 5:879-884, 2005.) or fluorescent nanoparticles (Kim et al., Nano Letters, 5:873-878, 2005) in the interior have been shown, where the particles are in the interior by evaporation of the solvent resulting in precipitation of the particles along the walls of the nanotubes (Kim et al., Nano Letters, 5:873-878, 2005.) or by condensation of aqueous solutions (Babu et al., Microfluidics and Nanofluidics, 1:284-288, 2005; Rossi et al., Nano Letters, 4:989-993, 2004). On the other hand, capillary action has been utilized to load CNT with liquids containing magnetic particles however this method cannot be used to fill with fluids of viscosity higher than water. However, loading nanotubes with fluids that are more viscous than water has only been demonstrated by the hydrothermal process (see, Gogotsi, Y. et al., In situ chemical experiments in carbon nanotubes, Chemical Physics Letters, vol. 365 (3, 4), pp. 354-360, 2002.), which requires very high pressures and temperatures rendering it impractical for most applications. Especially in biological application this method is prohibitive due to the sensitivity of biological samples to temperature and pressure.
The disclosure of co-pending U.S. application Ser. No. 11/327,674, filed on Jan. 5, 2006, is incorporated herein in its entirety.
An exemplary method of loading nanotube structures comprises moving a loading solution through an interior region of a nanotube structure, wherein the loading solution includes a material to be loaded into the nanotube structure and wherein the material to be loaded is retained in at least a portion of the interior region of the nanotube structure as the loading solution is moved through the interior region, removing excess of the loading solution from the loaded nanotube structure, and collecting the suspended loaded nanotube structures.
An exemplary method of loading a polymerizable medium into a nanotube structure comprises suspending a number of nanotube structures in an initial suspension liquid, placing a washing liquid containing the suspension of nanotube structures on top of a loading solution, the loading solution including a material to be loaded into the nanotube structure, wherein the loading solution can have a viscosity higher than the washing liquid, centrifuging the washing liquid and the loading solution to move at least a portion of the nanotube structures from the washing solution into the loading solution, recovering at least a portion of the nanotube structures from the loading solution and washing the nanotubes once or more times by resuspending the recovered nanotube structures in a crosslinking liquid, adding a polymerization agent or crosslinking agent to the suspension, and collecting the loaded nanotube structures.
Another exemplary method of loading a polymerizable medium into a nanotube structure comprises suspending nanotube structures in an initial suspension liquid, placing the initial suspension liquid containing the suspension of nanotube structures on top of a loading liquid in a container, the loading liquid including a material to be loaded into the nanotube structure, wherein the loading liquid has a higher or lower viscosity than the initial suspension liquid, centrifuging the container to move at least a portion of the nanotube structures from the initial suspension liquid into the loading liquid, recovering at least a portion of the nanotube structures from the loading liquid, transferring the recovered nanotube structures to a washing liquid and creating a suspension of the recovered nanotube structures, polymerizing or crosslinking the material loaded in an interior region of the nanotube structure, and separating the polymerized or crosslinked loaded nanotube structures from the suspension.
An exemplary method of loading nanotube structures comprises counterflowing a liquid to be loaded and the nanotube structure, wherein the liquid to be loaded travels in an opposite direction relative to the nanotubes structures.
An exemplary method of orienting and aligning loaded nanotubes in a polymerizable liquid comprises aligning or orienting loaded nanotubes in a polymerizable medium by centrifugal force, electric field or magnetic field, and initiating polymerization, wherein the loaded nanotubes are immobilized for a particular application.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The following detailed description can be read in connection with the accompanying drawings in which like numerals designate like elements and in which:
The term “nanotube structure” as used herein refers to a structure having an aspect ratio of larger than one, having a cross section of any shape (circular, ellipsoid, polygonal, rectangular, or other regular or irregular shape), wherein one dimension is of the order of 100 nm or less, but can be up to 1000 nm, and any and all whole or partial integers there between. One, non-limiting example of a nanotube structure is a carbon nanotube or CNT, which may be single-walled (SWNT), double-walled (DWNT) or multi-walled (MWNT) in form.
Nanotube structures suitable for use in the disclosed methods may be formed by any suitable technique. For example, it is possible to synthesize nanotube structures of carbon of various diameters (50-250 nm) (see, for example, Microfluidics and Nanofluidics, 1:284-288, 2005; Rossi et al., Nano Letters, 4:989-993, 2004.). Templates for the synthesis of nanotube structures having larger diameters (250 nm) are commercially available. One type of nanotube structures that is preferred in the present application is known as a multi-wall nanotube (MWNT), although this type of nanotube structures lacks the proper crystalline structure normally found in nanotube structures synthesized using a metal catalyzed Chemical Vapor Deposition (CVD) process.
Here, nanotube structures of carbon were synthesized by following the template assisted method established by Miller et al. (Miller et al., J. Amer. Chem. Soc., 123:12335-12342, 2001.). In brief, an alumina membrane (Whatman Anodisc 13 mm diameter, and a 250 nm pore size) placed in a quartz reaction vessel acts as the template for the carbon nanotubes to grow. A tube furnace capable of reaching at least 1000° C. was used to crack a mixture of ethylene and argon gas flowing at a rate of 20 sccm over the alumina membrane. The decomposition of ethylene gas at 670° C. resulted in deposition of carbon around the inner walls of the alumina membrane; the thickness of the deposited carbon layer thus depends on the process time. For the intended purpose, a reaction time of 6 hours was adequate, but various times can be selected depending on a desired thickness. The layer of carbon on the sides of the membrane was removed using mild sonication (47 kHz, bath sonicator). The membranes with carbon nanotubes were completely soaked in 6M NaOH for at least twelve hours to completely remove the template. The nanotubes were removed from the suspension after template removal by filtering though polycarbonate membrane filters with 1 micron pores (SPI Supplies). A schematic representation of the process is shown in
It is generally difficult to place a material in the interior region of the nanotube structure, as the interior has a small diameter (on the order of 100 nm or less but can be up to 1 micron) that presents capillary force barriers to the entry of liquid media. As the viscosity of liquid media is increased, typically this barrier is also increased.
Loading of a material into the interior region of a nanotube structure can be by any of several methods. An exemplary method of loading a nanotube structure comprises flowing a first liquid medium through an interior region of the nanotube structure, wherein the first liquid medium includes a material to be loaded into the nanotube structure and wherein the material to be loaded is retained in at least a portion of the interior region.
An example of flowing the first liquid medium through the interior region of the nanotube structure includes centrifuging a mixture including the first liquid medium and the nanotube structure.
In the exemplary method depicted in
The centrifuge container 300 with the mixture of first liquid medium 302 and nanotube structures 312 suspended in second liquid medium 310 is placed in the centrifuge and the centrifuge is started. Exemplary parameters for centrifuging include RCF=3220 xg (RCF=relative centrifugal force=11.18×r×(RPM/1000)2, where r is the rotor radius in cm, time=30 to 45 minutes and temperature is 4° C.
In suspension, the nanotube structures 312 are randomly oriented. However, upon centrifuging the mixture, the nanotube structures 312 preferentially orient with their axis roughly parallel to the centrifugal force and perpendicular (within 30 degrees) to the axis 306 of the centrifuge container 300 and, under centrifugal forces F, move towards the distal end or bottom 308 of the centrifuge container 300. Other parameters that influence the orientation of the nanotube structures 312 include viscosity of the solution; interaction between the solution and the nanotube structures (for example, alignment of hydrophobic nanotubes in alginate is not favored); the relative viscosity between the suspension medium (second liquid medium 310) and the solution (first liquid medium 302); acceleration time; and size, surface charge, surface tension, friction coefficient and viscoelastic properties of the nanotube structures. Each of these parameters can be manipulated to influence the process of orienting the nanotube structures.
For example, where the relative viscosity between the suspension medium (second liquid medium 310) and the solution (first liquid medium 302) are different, e.g., the solution has a higher viscosity than the suspension medium, the first liquid medium and the second liquid medium phase separate to form an interface. The nanotube structures of the second liquid medium then passes through the interface 314, e.g., the alginate-water interface, during the centrifuging of the mixture. The preferential alignment of the nanotube axis in relation to the interface forces the first liquid medium into the interior volume of the nanotube structure. In other words, under the centrifuge forces, the nanotube structures pass through the interface, and the first liquid medium can overcome the capillary forces and enter into the interior volume. The first liquid medium is retained in the interior volume as the nanotube structures amass at the bottom of the centrifuge tube during centrifugation. In some instances, the nanotube structures can form a solid mass 320, such as a pellet, at the bottom 308 of the centrifuge container 300. The mass can be recovered and, optionally, broken into smaller pieces for subsequent use.
Another example of flowing the first liquid medium through the interior region of the nanotube structure includes adding a mixture including the first liquid medium and the nanotube structure to a first side of a filter and forcing the mixture through the filter, under one or more of pressure and vacuum, to separate the nanotube structure from the first liquid medium.
In the exemplary method of
The nanotube structures 412, whether in a common liquid medium or in two or more liquid media, are placed in a filter 420. The filter 420 is then activated, either by drawing a vacuum V below the filter medium or by applying a pressure P above the filter medium, to drive the liquid medium through the filter 420. In this process, some of the material to be loaded is also driven through the interior volume of the nanotube structures and is retained in the interior volume after the filtration has occurred. The nanotube structures are generally retained by the filter medium 422. In an optional exemplary method, where separate liquid medium are used for the material to be loaded in the nanotube structure suspension, the two mediums may be mixed prior to the filtration process.
A further example of flowing the first liquid medium through the interior region of the nanotube structure includes forcing the first liquid medium through a fluidized bed containing the nanotube structure under a pressure and at a temperature.
In the exemplary method of
Under pressure and temperature, which may vary from standard temperature and pressure to temperatures and pressures associated with super critical fluids, the liquid medium 504 containing the material to be loaded 506 is flowed through the fluidized bed 500. At least a portion of the interior volume of the nanotube structure retains some of the material to be loaded. Subsequently, the fluidized bed may be removed from the flow path and the nanotube structures recovered, for example, by filtration, or other size exclusion method.
In optional subsequent steps to loading the interior volume of the nanotube structure, the material loaded in the interior volume may be encapsulated by, for example, a polymerization step. As seen in
Once the nanotube structures are loaded, the loaded nanotube structures are recovered. The method of recovery varies based on the method used to load material into the interior volume, such as recovering a pellet from a centrifuge container or recovering loaded nanotube structures from the surface of a filter medium, and/or recovering loaded nanotube structures from a fluidized bed. Techniques for recovery in the different methods are consistent with those known in the art. For example, excess material can be decanted and the remaining volume cleaned, e.g., washed with deionized water (DI water), and so forth. The choice of wash liquid depends on the choice of polymer solution. For example, while PBS (buffer) is a good liquid to dissolve alginate, it will not readily dissolve chitosan, though both are polysaccharides and are polar materials. Selection of suitable pairs of liquids/gels is obvious to the polymer and materials community, based on open literature and expertise in the field.
Once recovered, the loaded nanotube structures can be further processed by, for example, polymerization, or other post loading treatments to encapsulate the loaded material within the nanotube structures. Other examples of encapsulation techniques include liposomes, core shell nanoparticles, hydrogels, gelation, and so forth. Once recovered and washed, the loaded nanotube structures can also be further processed for the intended application. Finally, the collected loaded nanotube structures are obtained.
A exemplary process of further processing loaded nanotubes provides loaded nanotube structures immobilized in an aligned or oriented configuration. In an embodiment, the method comprises subjecting loaded nanotube structures in a polymerizable medium to centrifugal force, electric field or magnetic field, thereby aligning and/or orienting the loaded nanotubes in a common configuration, and initiating polymerization of the medium. In one aspect, the loaded nanotubes are aligned by centrifugal force. As described elsewhere herein, nanotubes under centrifugal force will align with their axis roughly perpendicular to the axis of the centrifuge and parallel to the centrifugal force. In another aspect, the loaded nanotubes are oriented by exposure to an electric field or a magnetic field. Preferably, the nanotubes are loaded according to a method of the invention. In one embodiment, the polymerizable medium is different from the loading liquid used to load the nanotubes. In another embodiment, the polymerizable medium is the loading liquid used to load the nanotubes. Polymerization may be initiated by contacting the polymerizable medium with at least one of a polyerization catalyst, UV radiation and gamma ray radiation. The loaded nanotubes are thus immobilized in the aligned or oriented configuration.
The following examples are intended to be non-limiting and provide further details on aspects of the disclosed methods.
A carbon nanotube (10 microL) solution containing nanotube structures was added to a 1% alginate solution containing WGA 633 (wheat germ aggulutinin conjugated to Alexa Fluor® 633; Invitrogen Molecular Probes, Eugene, Oreg.). The alginate solution was placed in a centrifuge tube that was 4 mm in diameter and 5 cm long and had a volume of alginate solution of approximately 400 microL. After adding the nanotube solution, the tube was spun at 3220 G for 30 minutes. After centrifugation, approximately 300 microL of the alginate solution from the top of the centrifuge tube was removed and discarded, e.g., by decanting. The centrifuge tube was cut to facilitate the insertion of a pipette tip. Using a 200 microL pipette, the bottom portion of the solution containing alginate and nanotube structures was removed and transferred to a test tube containing 3.0 ml of deionized (DI) water. The centrifuge tube was rinsed with DI water several times to ensure complete removal of alginate and nanotube structures. The test tube containing alginate and nanotube structures was then vortexed for approximately 1 minute, and then 1 ml of 1M calcium chloride solution was added to crosslink the alginate contained within the interior of the nanotube structures. The test tube was vortexed during the crosslinking process (approximately 5 minutes).
An exemplary filtration assisted method involves suspending nanotubes in a solution and filtering the mixture through a nanoporous membrane. Continuous phase (liquid) would flow through the nanotube due to the pressure difference thus resulting in filling the nanotube. Tight control of the packing density of the nanotubes contributes to achieving significant loading.
Nanotube structures were loaded and crosslinked according to the centrifugation assisted loading method of EXAMPLE 1, above. After the completion of crosslinking, the test tube was centrifuged at 2000 G for 5 minutes (20° C.). The supernatant liquid was collected and filtered through a 200 nm polyester membrane. The pellet at the bottom of the test tube was broken with the tip of a transfer pipette, vortexed in DI water and then filtered through a 200 nm polyester membrane to collect the nanotube structures on the filter membrane. The filter membranes removed from the filtering contained the collected nanotube structures and were then prepared for confocal imaging by placing the membrane containing nanotube structures on a glass slide, adding mounting medium and sealing with a glass cover slip.
A carbon nanotube (10 microL) solution containing nanotube structures was added to a 1% alginate solution containing WGA 633. The alginate solution was placed in a centrifuge tube that was 4 mm in diameter and 5 cm long and had a volume of alginate solution of approximately 400 microL. After adding the nanotube solution, the tube was spun at 3220 G for 30 minutes. After centrifugation, the solution was transferred to a vacuum filtration unit with 200 nm polyester membrane as the filter. Vacuum (pressure was not measured) was applied to remove the alginate, followed by addition of 1 ml of DI water twice. Vacuum was then stopped, and 1 ml of 300 mM calcium chloride solution was added to promote crosslinking. After 30 seconds, the vacuum was reapplied and the collected nanotube structures on the membrane washed a final time with DI water (3 ml). The filtered nanotubes were then prepared for confocal microscopy by placing the membrane containing nanotube structures on a glass slide, adding mounting medium and sealing with a glass cover slip.
In these studies with fluorescence in vacuum filtration methods, the fluorescence is observed to be present in the interior of the nanotube structures. The presence of fluorescence inside the nanotube structures indicates that the vacuum filtration method does not result in removal of filled alginate from the nanotube structures. Furthermore, since the loaded sodium alginate contained WGA 633, the fluorescence could only be due to the presence of alginate inside the nanotube structures.
The present application discloses methods and techniques to load a material into the interior of a nanotube structure. Once loaded, the loaded nanotube structures can be storage and/or delivery devices for the loaded contents. For example, loaded nanotube structures can have pharmacological, catalytic, sensory or other functions based on the loaded contents.
Although described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.
This application claims the benefit pursuant to 35 U.S.C. §119(e) to U.S. provisional patent application 60/840,015, which was filed on Aug. 25, 2006 and which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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60840015 | Aug 2006 | US |