[nanoPost] Carbon nanotubes for life science applications

University UK

Our vision in the Lab. is to bring together micro and nanotechnology research engineers in to a partnership with medical and biological researchers to form a powerful and muti-university, multi-disciplinary world class research program.

Rapid advances in nanotechnology and nanoscience have provided a variety of nanoscale materials with highly controlled and unique optical, electrical, magnetic, and catalytic properties. The diversity in composition, shape and the readiness for surface functionalization (physical, chemical, or biological) has enabled the fabrication of various functional nanoscale structures. Biologists and chemists have recently begun to borrow these nano-tools and apply them to a variety of applications ranging from diagnosis of disease to gene therapies.

One of the hottest developments in nanotechnology is in researching the multitude of potential applications of carbon nanotubes (CNTs).

Though carbon nanotubes have justifiably been highlighted as comprising a large portion of our work, we aim to investigate beyond just carbon nanotube bio-medical research, but to research other nanostructures including, but not limited to, rosette nanotubes, TiO nanotubes, B nanotubes, BN nanotubes, molecular contacts.

Nanotubes in general are receiving a great deal of attention in many disparate fields of research.

In recent years, research exploring techniques for the fabrication of CNTs has been very active in the hope of developing a method that is easy and can produce cheap CNTs with high quality. These efforts have led to various strategies and methods for the synthesis of CNTs that can be generally grouped into the following categories: arc discharge, chemical vapor deposition (CVD), plasma method, and laser ablation. However, amongst these categories, arc discharge and chemical vapor deposition have now become the primary methods. Compared with arc discharge, the CVD method is simple, cheap, and easy to implement, and has been widely used because of its potential merits to produce a massive amount of CNTs of high purity, large yield and controlled alignment.

The CVD process entails the catalytic decomposition of methane over a Ni Cu–Al catalyst in a tube furnace, allowing continuous control of the CNT synthesis in real time, under several reaction conditions. The influence parameters containing reaction time and different carrier gases on the growth morphology characteristics of CNTs will be studied using SEM, in-situ TEM, AFM and mirco-Raman analysis techniques.

To achieve a controllable growth of the CNTs with high quality, understanding of their growth mechanism is of importance. The generally accepted growth processes of CNTs by CVD, involve adsorption and decomposition of hydrocarbon gases containing carbon on metal surfaces, dissolution and diffusion of the released carbon atoms in the catalyst, and precipitation of the graphite-like layers. We will attempt to investigate the various parameters of the growth process and catalyst interactions utilizing an in-situ TEM growth experiment, in an environmental TEM with hydrocarbon reaction chamber.

Topical Areas for Partnered Research

I. Nanotube  Functionalization – A Key Technology

To expand and optimize the use of CNTs in bio-technological areas, it is necessary to functionalize CNTs with biomaterials. Biomaterials including biomolecules, biopolymers and other bio-nano-structures can be attached to CNTs successfully. The combination of nanotubes with proteins and other natural products, including nucleic acids and polysaccharides, allow the compatibility of such materials with biological systems. However, dispersibility of CNT in aqueous media is a fundamental prerequisite to study their biological properties. CNT are practically insoluble in any type of solvent and only the recent development of strategies for linking chemical moieties on the tubes has facilitated their applicability.

The possibility to form complexes between CNT and different types of polymers or to modify the CNT sidewalls by covalent or non-covalent organic functionalization drastically increases the characteristics of solubility of CNT. Depending on the type of bonding and moiety attached to or interacting with the tubes, solubility can be modulated in different solvents. As a consequence, a wide range of applications can be envisaged including the use of CNT as substrates for neuronal growth, supports for adhesion of liposaccharides to mimic cell membrane, ion channel blockers and drug delivery systems.

Toxicity of Nanotubes
In the past, graphite has been associated with various toxilogical effects including increased dermatitis, keratosis, and inflammation. Therefore, investigation is needed to determine the potential danger of exposure to CNT. In defense of CNTs, studies so far have focused on the effects of pristine CNT, significant efforts have been made to improve nanotube solubility and a remarkable reduction in toxicity has been reported using such functionalized CNT. The toxicological profile of CNT will depend on many parameters such as the type of nanotubes, the presence of impurities, the length of the tubes, the type of functionalization and the molecular nature of the conjugated groups. All of these factors affecting toxicity will be examined, but, it is still too early to establish a general toxicological profile for this type of material, and more systematic in vitro and in vivo investigations using biologically compatible CNTs are necessary.

 Drug and Vaccine Delivery
A wide variety of delivery systems are currently available for drug and vaccine delivery. Carbon nanotubes today represent a class of emerging materials that are capable of intracellular delivery of biologically functional peptides, proteins, nucleic acids and small molecules covalently or non-covalently attached on their surface.

The application of functionalized CNT as new method for drug delivery was apparent immediately after the first demonstration of the capacity of this material to penetrate into cells. The mechanism of penetration is not yet completely understood, but, it is proposed that the action is similar to a ‘‘nano-needle’’, able to perforate the cell membrane without causing cell death.

Very recent literature from Kam et al. has shown that the property of CNTs to adsorb near-infrared irradiation can be exploited to kill cancer cells. Kam’s work utilized pristine SWNT that were wrapped with a poly(ethylene glycol) (PEG) modified with a phospholipid (PL) moiety and folic acid (FA). Because tumor cells are known to overexpress folate receptors, the PL- PEG-FA/SWNT construct was only internalized inside cancer cells, which were then destroyed by using a laser wavelength of 808 nm. Laser pulses induced local heating and consequently death only of those tumor cells that had uptaken the CNT.

Dental  Partnership

"The global market value for consumable dental products is US $11 billion p.a. (1) a major part of which is dental restorative materials. Existing materials have properties that limit their application or clinical durability. Hydraulic cements have not received much attention in dentistry because of the perception of brittleness. This is unfortunate because in many respects they are suitable. Carbon nanotubes offer an exciting solution to the brittleness problem. The application of carbon nanotubes is not limited to this system. A number of current brittle dental cements with particular attractive properties (e.g. calcium hydroxide cement) could be improved significantly. Existing commercial nanotubes are unsatisfactory which has halted progress. The development of higher purity longer multiwall nanotubes is essential.