Carbon Nanotubes for Drug Delivery

Introduction

According to Mishra, Patel & Pharm (2009), enhancing effective drug delivery system that enables the safe relocation of drugs in appropriate and efficient time lag is essential in initiating therapeutically medical effects that promote health service delivery. They point out that various medical technologies have been developed in a bid to come up with better and effective drug delivery procedures. Such procedures not only offer an accurate diagnosis of a disease but also address the side effects that are associated with drug administrations. Mishra, Patel & Pharm (2009) note that the importance of carbon nanotubes in delivering drugs is primary based on their electric, optical, thermal, and mechanical characteristics. They point out that these characteristics not only help deliver drugs to the targeted sites safely and effectively, but also enable the utilization of such characteristics in devising of appropriate therapeutic procedures.

As pointed out by Mishra, Patel & Pharm (2009), the development of carbon nanotubes for drug delivery plays an important role in not only offering efficient drug delivery systems, but also in improving the pharmacological medical profiles of different classes of the therapeutically medicinal molecules and substances. They note that carbon nanotubes have proven to be the new technology that  helps significantly to transport and translocate different therapeutic molecules and substance. This has in turn enhanced the health care service delivery. According to them, the carbon nanotubes normally show low toxic level when combined with other therapeutic molecules such as bioactive peptides, nucleic acids, proteins and drugs. They are especially used in delivering drugs that enhances both the cells and organs functionality. They point out that the low toxicity and non immunogenic nature of the carbon nanotubes has improved the potentiality of using these new technologies in various medical fields such as nano-biotechnology and nano-medicine.

According to Mishra, Patel & Pharm (2009), nanotechnology, under which carbon nanotubes operate, entails the study of various therapeutic molecules that ranges from 1 to 100 nanometers that can be effectively used in diagnosis and treatment of various diseases. They point out that with the higher carbon nanotubes’ surface area to volume ratio they are able to improve the dissociation of various therapeutic molecules that not only reduces their toxicity level, but also helps in accumulation of therapeutic agents such as the peptides which are essential in enhancing treatment procedures.

Size, Shape and Properties of Carbon Nanotubes

According to Petros & DeSimone (2010), the size and shape of carbon nanotubes play an important role in the bio-distribution of the therapeutic molecules. They note that normally, the carbon nanotubes vary in sizes from those of 5µm to several centimeters with their diameters ranging from 0.3nm to 50nm thereby being categorized as either single walled nanotubes or multi walled nanotubes. They point out that carbon nanotubes are normally tube-shaped materials made out of graphite layers which form the unbroken hexagonal mesh with carbon molecules forming the apexes of the hexagons. They note that single-walled carbon nanotubes normally have a single graphite layer with close to 1nm diameter and extensive tube length that goes up to centimeters in length. On the other hand, they admit that multi-wall carbon nanotubes normally appear as the coaxial combination of a single sheet of graphite layers thereby forming diameters that range from 5nm to 50nm.

Carbon nanotubes normally have unique physical and biochemical properties that enhance the process of drug delivery. According to Dresselhaus, Charlier & Hernandez (2006), carbon nanotubes normally inhibit electronic, thermal, and mechanical properties. They point out that the small dimensional unit and the pleasant physical properties of carbon nanotubes have enhanced their application in various service delivery systems such as drugs delivery.  They also note that one of the important characteristic of carbon nanotubes is the ability to make a single atomic layer thickness that normally results into single-walled nanotubes. They point out that the local symmetric dimensions and a sizable diameter of the carbon nanotubes normally change their state of electrical density thereby inhibiting the unique electronic characteristics. Additionally, they point out that the bonding characteristics of the carbon atoms normally make nanotubes to inhibit electronic characteristics especially when they are rolled together in the formation of multi-walled nanotubes.

Dresselhaus, Charlier & Hernandez (2006) point out that carbon nanotubes usually have a combination of sizable diameter dimensions, distinct structural components, high electrical conductivity, and stable chemical combinations that enables them to be good electron emitters. They note that the effectiveness of carbon nanotubes to carry and emit current is dependent on the fabrication processes and the synthetic processes that these nanotubes underwent. They point out that the electric conductivity of Carbon nanotubes is based on their structural parameters that show how they can be twisted. This is normally known as the chirality. For instance, the degree of their twist as well as their diameters normally dictates their metallic or semi-conducting electrical behaviors. They note that the carbon nanotubes are normally essential for field emission due to their small diameters and high aspect ratio which makes them emit electric fields even at moderate voltages. Moreover, they point out that light is normally produced during the emission of electric field. This is essential in monitoring drugs during the delivery processes.

According to Dresselhaus, Charlier & Hernandez (2006), the electronic characteristics of the carbon nanotubes normally depend on the structural components of the two single-walled nanotubes that are being joined together. They note that primarily, the uniqueness of carbon nanotubes is associated with the  structural arrangement of carbon atoms in the hexagonal. They note that if two single nanotubes have similar physical and chemical properties, then they form semiconducting materials which help in the delivery of drugs by either detecting even small changes in electric current or registered chemical reactivity that might affect the effectiveness of administering therapeutic chemical molecules. However, they point out that in cases where there is no uniformity of the nanotubes components in forming multi walled nanotubes, there is normally electrical conductivity of the carbon nanotubes. According to them, the internal wall interaction caused by the varying nanotubes components normally results into non-uniform redistribution of the current especially within the nanotubes layers in the multi walled nanotubes.

Moreover, Dresselhaus, Charlier & Hernandez (2006) note that the defects of the carbon nanotubes with a natural junction where nanotubes metallic section is joined to a semi-conducting section, normally enable the carbon nanotubes to act as rectifying diode which is essential in stabilizing the current effect  during the transportation of drugs. Furthermore, they point out that the single walled nanotubes normally inhibit high speed of transmitting electrical signals especially when used as interconnectors on semi-conducting thereby making them efficient.

On the other hand, Dresselhaus, Charlier & Hernandez (2006) point out that carbon nanotubes adopt mechanical properties based on their size, structure, and topology which enable them to be highly stable, strong, and elastic.  They note that the topological nature of the carbon nanotubes is due to the closeness of the nanotubes which enable them to form a different structure. This is further enabled by the removal of graphite properties. The end result is the topological defects in the carbon nanotubes which in turn create high concentration of metal at the ends of these nanotubes. They point out that by creating such defect, nanotubes ends are useful not only in the functionality of the carbon tubes but also in enabling the filling of drugs that are intended to be transported.

According to Dresselhaus, Charlier & Hernandez (2006), the elasticity properties of the carbon nanotubes is due to the strong chemical bonding of each carbon atom with three intermediate carbon atoms. They note that due to the strong chemical bonds, the carbon nanotubes normally form an elastic and highly-strength fibers which are able to withstand the massive transportation of drugs. For instance, single walled nanotubes are normally stiffer than steel thereby making them more resistant to damages caused by physical forces. They point out that exerting pressure on the tip of the carbon nanotubes normally cause them to bend without causing damages on their tips and returns into their original states in case the pressure is removed. They note that this elasticity and stiffness properties of the carbon nanotubes enable them to be used as probe tips for very high-resolution scanning for microscopic research.

The carbon nanotubes have also very high thermal conductivity properties. As pointed out by Dresselhaus, Charlier & Hernandez (2006), the carbon nanotubes prove to be the best heat-conducting material that has ever been synthesized. They point out that the superficial conductivity of carbon nanotubes especially for  ultra- small  single walled nanotubes even at temperatures below 20K has not only enabled them to adopt the electrical properties, but has also enabled them to be used as miniature heat conductors for many materials. The strong in-plane carbon-carbon chemical bonding not only makes them counter stain forces, but also causes nearly zero in-plane thermal expansion with large inter-plane expansion thereby leading to stronger in-plane interaction and high nanotubes flexibility hence countering any non-axial strain forces.

However, the biochemical properties of carbon nanotubes can only be illustrated depending on their chemical reaction with other therapeutic molecules. These include those properties resulting from their nucleic interaction, cell interaction, and toxicological effects. According to Nel, Madler, Velegol & Xia (2009), the physiochemical interaction and the kinetics and thermodynamics of biological exchange between the walls of the carbon nanotubes and the surface of the biological therapeutic molecules such as proteins and biological fluid normally result into the biochemical properties of the carbon nanotubes. They point out that in determining the biochemical properties of carbon nanotubes during such interactions, it is important to understand the physiochemical interactions of nanotubes and biological components on their interface and the corresponding molecular components that initiate such interactions.

According to Nel, Madler, Velegol & Xia (2009), the interaction of carbon nanotubes and the surface of the biological components is normally characterized by three distinct interaction components on their interface. They point out that the nanotubes interaction with biological molecular components normally depends on the nano-particle surface of the carbon nanotubes that is normally based on their respective physiochemical characteristics. The nano-bio interface also depends on the interaction of the solidity state of the carbon nanotubes and the liquid states of the biological components in respect to their surrounding medium components. Moreover, they point out that the solid-liquid interface’s interaction zones between carbon nanotubes and biological components together with the biological substrate components are essential in determining the nature of the nano-bio interface interactions.

Nel, Madler, Velegol & Xia (2009) point out that the characteristic of carbon nanotubes’ surface particles plays an important role in initiating interaction between the carbon nanotubes and the biological molecules. This interface interaction effectively initiate drug delivery processes by not only enhancing the adsorption of therapeutic molecule components, but also by forming double-layer that effectively enables the passage of biological molecules through the carbon nanotubes medium. For instance, the adsorption of the therapeutic molecules such as ions, proteins among others helps in dissolution of their components which in turn reduces the surface energy required in the transportation of drugs or therapeutic molecules (Nel, Madler, Velegol & Xia, 2009). They point out that the characteristic of the carbon nanotubes in enhancing phase transformation during the interaction of their internal surface walls with the biological molecules is what continues to make tem the preferred drug delivery systems.

On the other hand, Nel, Madler, Velegol & Xia (2009) point out that the solid-liquid interface state between carbon nanotubes and the biological molecular components is essential in understanding the biochemical properties associated with nano-bio interface interaction. They note that the electrical conductivity of the carbon nanotubes together with both their electric field emission and size characteristics normally enables them to create transient environment of their interaction with biological molecules. This interaction normally results into the redistribution of proteins and lipids on the surfaces of the membranes.

Advantages of Carbon Nanotubes for Drug Delivery over Other Techniques

According to Nel, Madler, Velegol & Xia (2009), both the biochemical and physical properties of carbon nanotubes is what makes them more favorable for drug delivery compared to other techniques. They note that the physical size, surface characteristics, and the shape of the carbon nanotubes enables them to effectively play a significant role in the bio-distribution of therapeutic molecules as compared to other techniques. According to the Jin, Bae & Hong (2010), the elasticity and stiffness property of the carbon nanotubes is what normally enables them to be used as probe tips for very high-resolution scanning for microscopic research. For instance, the chemical functionality of multi walled carbon nanotubes normally enhances dispersion characteristics of each individual tube thereby allowing them to be used as tools for imagery and drug delivery. They point out that the high resolution scanning of the carbon nanotubes helps in the analysis of nano-bio interface interaction thereby leading to better and effective diagnosis and treatment of diseases.

Jin, Bae & Hong (2010) note that the carbon nanotubes have made it possible to utilize high resolution techniques in observing the nano-bio interaction characteristics that helps in devising an appropriate drug for diagnosis and treatment. They point out the use of carbon nanotubes for atomic force microscopy (AFM) nanoscale observation is helpful in the identification of both the topological and biological forces that are incorporated during the drug delivery processes. With their very high-resolution scanning, the scientists are able to study not only on the required surface wall for the nanotubes, but also in ensuring that appropriate sizable nanocarries are used. This has helped in the delivering potential drugs to specified sites during diagnosis and treatment.

Additionally, Jin, Bae & Hong (2010) points out that the high-resolution scanning characteristic of carbon nanotubes has helped in the determination of the surface morphology of therapeutic molecules that include proteins, tissues, viruses and nucleic acids among others. They note that the carbon nanotubes are used in the scanning electron microscopy (SEM) where they help not only identify the size and shape of the biological components of the drugs, but also monitor the uptake of cells by illustrating the cellular drug delivery. This is helpful in the monitoring of the molecular and physiological effects that are caused by diseases at each stage of their infection.  Moreover, they point out that carbon nanotubes are normally used in the transmission electron microscopy (TEM) in determining the crystal and chemical components of the therapeutic nanomaterilas thereby helping in delivering appropriate drugs for diagnosis and treatment. 

According to Mishra, Patel & Pharm (2009), the high surface area to volume ratio of the carbon nanotubes have enabled them to minimize the toxic effect of therapeutic molecules during drug delivery. Unlike other drug delivery techniques, the carbon nanotubes due to their delivery processes, help in the solubility of the hydrophobic therapeutic medicines compounds that may cause toxicity during their accumulation in the target areas (Mishra, Patel & Pharm, 2009). They point out that in the process of reducing the toxicity effects of these compounds, the carbon nanotubes normally increase the chemical and biological components of therapeutic molecules such as peptides thereby improving not only the drug delivery services, but also enhancing the rightful diagnosis and treatment of the drugs. Moreover, they point out that due to the larger inner volume of the carbon nanotubes, more drug molecules can be administered and easily accessed since the end caps of these nanotubes can be moved easily.

As pointed out by Mishra, Patel & Pharm (2009), the drugs normally utilize the functionality of the inner surface of the carbon nanotubes during their delivery thereby enhancing better treatment. For instance, in the administration of anticancer drugs such as the doxorubin (DOX), these drugs normally attach and detach themselves in the inner side wall of the single carbon nanotubes resulting into acidic molecule that is essential for the treatment of cancer (Huang, Barua, Sharma & Dey, 2011). They point out that the size of the carbon nanotubes which normally ranges from 1nm to 50nm is essential in treating cancer diseases by not only penetrating to the targeted tumor sites but also by accumulating and retaining the drug components at the sites due to their permeability and retention effect. Furthermore, Huh & Kwon (2011) note that the high surface to volume ration of the carbon nanotubes and their corresponding physical and biochemical properties normally create antimicrobial effects that helps in early detection and diagnosis of cancer diseases.

According to Huang, Barua, Sharma & Dey (2011), the adsorption effect coupled with appropriate diameter dimension of carbon nanotubes have enabled them to be the most preferred drug delivery system especially in the diagnosis and treatment of cancer diseases. They point out that single walled carbon nanotubes normally indicate a strong light adsorption characteristics with wavelength ranging from 800nm to less than 1200nm. They note that while administering NIR, irradiation under this adsorption effect normally kill the tumor cells thereby preventing the development of cancer.

Disadvantages of Using Carbon Nanotubes for Drug Delivery

According to Nel, Madler, Velegol & Xia (2009), the use of carbon nanotubes for drug delivery can lead to mesothelioma cancer. They point out that the cylindrical structural shape of the carbon nanotubes normally takes up the phagocytic cells that pass through blood capillaries thereby depositing on the walls of the blood vessels. They note that the high aspect ratio and cylindrical structure of the carbon nanotubes normally result into biological health problems. According to them, due to the stiffness of carbon nanotubes together with their ability of creating fibrous microbiological structures, they normally result into the degradation and elimination of external biological components thereby affecting the functionality of tissue macrophages.

For instance, Nel, Madler, Velegol & Xia (2009) note that the elastic but stiff carbon nanotubes during drug delivery may  pass the cell membrane thereby resulting into the depositing and accumulation of the hydrolytic enzymes and  toxic oxygen radicals by the tissues in an effort of countering the effects of carbon nanotubes. In a case where the depositing and accumulation of these harmful biological molecule components continue for a long period of time, the result would be a chronic inflammation which if further sustained results into mutagenic effects thereby leading to the formation of mesothelioma cancer.

The biochemical properties of the carbon nanotubes normally affect the delivery of drugs especially where cell interaction is essential for the effectiveness of diagnosis or treatment. According to Nel, Madler, Velegol & Xia (2009), cells normally have non-rigid cell membranes that can easily deform either by the intrusion of fluid or thermodynamic processes beyond their cell membranes. For instance, the interaction of multi walled carbon nanotubes with the corresponding cell patches normally results into the formation of rafts with different properties as the original cell thereby resulting into negative cell properties that cannot utilize the administered drugs during drug diagnosis and treatment.

Another disadvantage of using the carbon nanotubes for drug delivery system is due to their large available surface area for protein opsonization. This normally affects the content of the drugs being delivered. Nel, Madler, Velegol & Xia (2009), point out that various proteins normally bind to the exterior surfaces of the carbon nanotubes especially via physical adsorption. They observe that when the ends of the carbon nanotubes are open for oxidation treatment, these smaller protein particles are introduced into the carbon nanotubes. At this point, the treatment of carbon nanotubes with stronger acidic solutions together with cat ions substances normally results in the reduction of carbon nanotubes but with high solubility of the protein components (Nel, Madler, Velegol & Xia, 2009). According to these scholars, the aftermath of such treatment results into adsorption of polyelectrolyte molecules on the surface of the carbon nanotubes thereby producing positive charge effect. This prevents the aggregation of carbon nanotubes which in turn undermines their drug delivery processes.

Conclusion

The write up has highlighted carbon nanotubes as essential drug delivery tools that should be emulated and encouraged during diagnosis and treatment processes. It has pointed out that the preference of carbon nanotubes as drug delivery system over other techniques is basically due to their physical and biochemical properties. For instance, the high mechanical strength properties of the carbon nanotubes have been illustrated to contribute to the vivo stability of the therapeutic molecules during drug delivery. The paper has also noted that the large aspect ratio of the carbon nanotubes has enabled the development of multimodal devises such as the multi carbon nanotubes which are essential in the delivery of drugs. Moreover, it has been pointed out that carbon nanotubes have not only helped in targeting and accumulating drugs in specified sites, but they have also enhanced the development of better therapeutic compounds which are essential for the diagnosis and treatment of diseases.

On the other hand, the write up has pointed out the need to be cautious when using carbon nanotubes during drug delivery. Even though the use of carbon nanotubes is essential in targeting the tumor site that causes cancer, their inappropriate use can lead to the development of cancerous diseases such as mesothelioma. There is also a need to design and enhance drug delivery system just like carbon nanotubes in countering the toxicity effects associated with therapeutic agents during drug administration.