Modified carbon nanotubes for drug delivery applications

Abstract

Noncovalent surface modification of multiwall carbon nanotubes (MWCNTs) using chitosan coating as a monolayer is presented. The different degree of deacetylation (%DD) (61%, 71%, 78%, 84%, 90% and 93%) of chitosan and chitosan concentration affected to carbon nanotubes’s dispersion efficiency and their stability. Results showed that the dispersion of MWCNTs could be improved when using chitosan with the lowest degree of deacetylation (61%DD). Zeta potential measurements confirmed that the chitosan surface coverage on the MWCNTs was twice as high when modifying the nanotubes surface with the 61%DD than when using the 93%DD chitosan. To study how a chitosan-polysaccharide increases the dispersion efficiency and stability of CNTs, molecular dynamics simulation done on the three models: i) two pristine CNTs (pCNT-pCNT), ii) a pristine CNT-a chitosan wrapped CNT (pCNT-cwCNT) and iii) two chitosan wrapped CNTs (cwCNT-cwCNT). As a result, the CNT aggregation was found in pCNT-pCNT and pCNT-cwCNT due to van der Waals interaction between the tube-tube aromatic rings, and intertube bridging by chitosan, respectively. In case of cwCNT-cwCNT, charge-charge repulsion was found to separate the two tubes and well disperse in aqueous solution. Although the monolayer coating MWCNTs with low %DD chitosan was improved the dispersion of MWCNTs, their stability was insufficient to be used as drug carrier. Therefore, the layer-by-layer deposition technique was selected as a potential method for preparing mulltilayers between poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) coating on treated MWCNTs surface. Interestingly, we found the simple method to prepare primary, secondary and tertiary layers on treated MWCNT with “just enough polyelectrolyte” without centrifugation process. Multilayer coating on MWCNT was provided high stability in aqueous solution. Gentian violet and diclofenac were used as hydrophilic model drugs for loading on modified MWCNTs. Gentian violet selectively loaded on negatively charged surface of MWCNT while diclofenac cannot be achieved to load in any kind of MWCNTs. The cytotoxicity of modified MWCNTs with different functional groups was evaluated by MTT assay. Treated MWCNTs were toxic to L929 cells when the concentration reached 25μg/ml while primary coating MWCNTs with PDADMAC was toxic at concentration 12.5μg/ml