Study Of Carbon Nanotubes Based Scaffold Biomaterials And Intracellular Drug Carriers

Carbon nanotubes (CNTs) are a man-made form of carbon that does not exist in our environment until 1991. Due to their unique electronic and mechanical properties combined with chemical stability, CNTs have been produced in ton quantities, and their potential application ranges from biomedicine through nanoelectronics to mechanical engineering. People will have more chances to face this novel type of materials along with exploring the potential application of CNTs. Therefore, it is urgent and necessary to investigate the cyto/biocompatibility of CNTs. However, it is also important to establish and develop modification methods to improve the bio/cytocompatibility of CNTs for safer and better application of their outstanding properties. In a way, the research of CNTs based scaffold biomaterials and targeted drug carriers have been the hot spots in nanobiotechnology.The paper concentrates on the applications of CNTs based scaffold biomaterials and intracellular targeted drug carriers, studied the interaction mechanism between CNTs and cells, and using the widely spread natural polysaccharides to noncovalent modify the single-wall carbon nanotubes to establish a series of novel nanofibrous scaffolds and a brand new targeted anti-cancer drug delivery system. The details are as follows:1) Singe-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) were purified or oxidized to prepare several types of CNT scaffolds. The cytocompatibility of the CNT scaffolds was investigated by several cytotoxicity tests, and the interaction mechanism between the CNT scaffolds and cells were studied using immunochemistry and scanning electron microscopy (SEM). It was found that the cell adhesion, cell focal adhesion (kinase) distribution and cell viability could be affected by the diameter, hydrophilicity/hydrophobicity, surface charge and the metal catalyst of the CNTs.2) Natural polysaccharides including amylose (AMY), alginate sodium (ALG) and chitosan (CHI) were employed for noncovalently wrapping around the purified SWCNTs to prepare four types of polysaccharide modified SWCNT scaffolds. Cell viability test shows that the cytocompatibility of these SWCNT scaffolds decrease in the following order: AMY-SWCNTs > CHI-SWCNTs > CHI/ALG-SWCNTs > ALG-SWCNTs > purified SWCNTs. Immunochemistry and SEM study revealed that the the cell adhesion, cell focal adhesion (kinase) distribution and cell viability were influenced by the surface functional groups, hydrophilicity/hydrophobicity and surface charge of polysaccharide modified SWCNTs.3) The cytotoxicity of raw SWCNTs, purified SWCNTs and cut (purified) SWCNTs were studied. The cytotoxicity of these three types of SWCNTs increase in the following order: purified SWCNTs < raw SWCNTs < cut SWCNTs, and the cytotoxity of cut SWCNTs is time and dose-dependent. TEM and cytotoxicity tests showed the cut SWCNTs could enter into cells, increasing the cellular ROS, induce cell vacuolation and cell apoptosis/necrosis. However, the cytotoxcity of cut SWCNTs could be reduced by decreasing the incubation time or concentration. It was found cut SWCNTs could still cross the cell membrane in lower concentration and shorter incubation time, and the SWCNTs treated cells continued proliferation with the internalized SWCNTs. Thus, purified and cut SWCNTs (length < 500 nm) with a concentration of 0~100μg/mL are suitable to use as intracellular drug carriers, and the incubation time with cells should be within 1 h.4) Fluorescent single-wall carbon nanotubes (SWCNTs) were prepared by mixing cut SWCNTs with acridine orange (AO). The optical absorbance and fluorescence characteristics of AO-SWCNT conjugates display interesting pH-dependent properties. Fluorescence microscopy in combination with transmission electron microscopy proves that AO-SWCNTs can enter HeLa cells and locate in lysosomes. The endocytosis-inhibiting tests show that the clathrin-mediated endocytosis is a key-step in internalization process. The internalized AO-SWCNTs remain inside lysosomes for more than a week and have little effect on cell proliferation. These findings may be useful in understanding the SWCNT-based intracellular drug delivery mechanism and help to develop new intracellular drug transporters.5) A targeted drug delivery system that is triggered by changes in pH based on single wall carbon nanotubes (SWCNTs), derivatized with carboxylate groups and coated with a polysaccharide material, can be loaded with the anti-cancer drug doxorubicin (DOX). The drug binds at physiological pH (pH 7.4) and is only released at a lower pH, for example, lysosomal pH and the pH characteristic of certain tumor environments. By manipulating the surface potentials of the modified nanotubes through modification of the polysaccharide coating, both the loading efficiency and release rate of the associated DOX can be controlled. Folic acid (FA), a targeting agent for many tumors, can be additionally tethered to the SWCNTs to selectively deliver DOX into the lysosomes of HeLa cells with much higher efficiency than free DOX. The DOX released from the modified nanotubes has been shown to damage nuclear DNA and inhibit the cell proliferation.