Molecular Dynamics Study of Cisplatin Release from Carbon Nanotubes Capped by Magnetic Nanoparticles

The release dynamics of cisplatin from the interior of a carbon nanotube is studied using molecular dynamics simulations. The nanotube is initially capped by magnetic nanoparticles which, upon exposure to an external magnetic field, detach from the nanotube tips, and the initially encapsulated cisplatin molecules leave the nanotube interior according to the diffusion mechanism. Diffusivities of cisplatin in bulk water and inside the nanotube were determined by analyzing the mean-square displacements, and they take the values 2.1 x 10(-5) and (0.6-0.9) X 10(-5) cm(2) s(-1), respectively, at 310 K. The release of cisplatin was found to be an activated process with the activation barrier similar to 25 kJ mol(-1) in an ideal system. Analysis of experimental data allowed for the estimation of the diffusion barrier in the actual system which was found to be ca. 85 kJ mol(-1). The difference between these two estimations is attributed to the existence of numerous surface defects in the case of experimental system. The release dynamics proceeds according to a simple 1D Fick's mechanism, and either simulation or experimental data follow a very simple equation derived from the above assumption. That equation predicts that the release of simple molecules from carbon nanotubes should obey the second-order kinetic equation. The time scale of the release depends on the nanotube length, initial amount of drug, and diffusivity of drug molecules inside the nanotube. Simulations predict that, for the studied ideal architecture, the release completes in a few milliseconds. Experimental data show that that process is, due to surface defects, definitely slower; i.e., it needs about 3 h.