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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 × 10–5 and (0.6–0.9) × 10–5 cm2 s–1, respectively, at 310 K. The release of cisplatin was found to be an activated process with the activation barrier ∼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.

The behavior of a multiwalled carbon nanotube functionalized by magnetic nanoparticles through triethylene glycol chains is studied using molecular dynamics simulations. Particular attention is paid to the effect of magnetic anisotropy of nanoparticles which significantly affects the behavior of the system under an external magnetic field. The magnetization reversal process is coupled with the standard atomistic molecular dynamics equations of motion by utilizing the Neel–Brown model and the overdamped Langevin dynamics for description of the inertless magnetization displacements. The key results obtained in this study concern: an energetic profile of the system accompanying transition of a magnetic nanoparticle from the vicinity of the nanotube tip to its sidewall, that is from the capped configuration to the uncapped one; range of the magnetic anisotropy constant in which the system performs structural rearrangements under the external magnetic fields; range of the magnetic field strengths necessary for triggering the structural rearrangements; and other effects like magnetic heating observed during the interaction of the system with the magnetic field. The determined properties of the studied system strongly suggest its application in the area of nanomedicine as a drug targeting and delivery nanovehicle.

The ordered amyloid-like organization of protein aggregates was obtained using for their formation the rigid fibrillar nanostructures of Congo red as the scaffolding. The higher rigidity of used dye nanoparticles resulted from the stronger stacking of molecules at low pH (near the pK of the dye amino group) because of the decreased charge repulsion. The polylysine, human globin, and immunoglobulin L chain were arranged in this way to form deposits of amyloid properties. The scaffolding was introduced simply by mixing the dye and proteins at a low pH or the dye was used in the preorganized form by maintaining it in the electric field before and during protein addition. The polarization and electron microscopy studies confirmed the unidirectional organization of the complex. The precipitate of the complex was used for studies directly or after the partial or complete removal of the dye. The results suggest that the process of formation of amyloid-like deposits may bypass the nucleation step. It is possible if the protein aggregation occurs in unidirectionally organized (because of scaffolding) assembly of molecules, arranged prior to self-association. The recognition of the structure of amphoteric Congo red nanoparticles used for the scaffolding was based on the molecular dynamics simulation.

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Molecular dynamics simulations prove that Congo red adsorption on carbon nanotubes is very strong and by varying pH filling/unfilling of inner cavities of the nanotubes can be accomplished.

Designing an effective targeted anticancer drug delivery method is still a big challenge, since chemotherapeutics often cause a variety of undesirable side effects affecting normal tissues. This work presents the research on a novel system consisting of single walled carbon nanotubes (SWNT), dispersed with Congo Red (CR), a compound that forms self-assembled ribbon-like structures (SRLS) and anticancer drug doxorubicin (DOX). SWNT provide a large surface for binding of planar aromatic compounds, including drugs, while CR supramolecular ribbon-like assemblies can be intercalated by drugs, like anthracycline rings containing DOX. The mechanism of interactions in SWNT–CR–DOX triple system was proposed based on electrophoretic, spectral, Dynamic Light Scattering and scanning electron microscopy analyzes. The profile of drug release from the investigated system was evaluated using dialysis and Differential Scanning Calorimetry. The results indicate that ribbon-like supramolecular structures of CR bind to SWNT surface forming SWNT–CR complexes which finally bind DOX. The high amount of nanotube-bound CR greatly increases the capacity of the carrier for the drug. The high capacity for drug binding and possible control of its release (through pH changes) in the analyzed system may result in prolonged and localized drug action. The proposed SWNT–CR–DOX triple system meets the basic criteria that justifies its further research as a potential drug carrier.

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