Carbon Nanotubes Translocation through a Lipid Membrane and Transporting Small Hydrophobic and Hydrophilic Molecules

Coarse-grained modeling of polystyrene-modified CNTs and their interactions with lipid bilayers

In the present work, we describe Martini3 coarse-grained models of polystyrene and carboxyl-terminated polystyrene functionalized carbon nanotubes (CNTs) and investigate their interactions with lipid bilayers with and without cholesterol (CHOL) using molecular dynamics simulations. By changing the polystyrene chain length and grafting density at the end ring of the CNTs at two different nanotube concentrations, we observe the translocation of nanoparticles as well as changes in the lipid bilayer properties. Our results show that all developed models passively diffuse into the membranes without causing any damage to the membrane integrity, although high concentrations of CNTs induce structural and elastic changes in lipid bilayers. In the presence of CHOL, increasing CNT concentration results in decreased rates of CHOL transmembrane motions. On the other hand, CNTs are prone to lipid and polystyrene blockage, which affects their equilibrated configurations, and tilting behavior within the membranes. Hence, we demonstrate that polystyrene-functionalized CNTs are promising drug-carrier agents. However, polystyrene chain length and grafting density are important factors to consider to enhance the efficiency of drug delivery.

Polystyrene-modified carbon nanotubes: Promising carriers in targeted drug delivery

To design drug-delivery agents for therapeutic and diagnostic applications, understanding the mechanisms by which covalently functionalized carbon nanotubes penetrate and interact with cell membranes is of great importance. Here, we report all-atom molecular dynamics results from polystyrene and carboxyl-terminated polystyrene-modified carbon nanotubes and show their translocation behavior across a model lipid bilayer together with their potential to deliver a molecule of the drug ibuprofen into the cell. Our results indicate that functionalized carbon nanotubes are internalized by the membrane in hundreds of nanoseconds and that drug loading increases the internalization speed further. Both loaded and unloaded tubes cross the closest leaflet of the bilayer by nonendocytic pathways, and for the times studied, the drug molecule remains trapped inside the pristine tube while remaining attached at the end of polystyrene-modified tube. On the other hand, carboxyl-terminated polystyrene functionalization allows the drug to be completely released into the lower leaflet of the bilayer without imposing damage to the membrane. This study shows that polystyrene functionalization is a promising alternative and facilitates drug delivery as a benchmark case.

Carbon nanotube transmembrane channel formation and single-stranded DNA spontaneous internalization: a dissipative particle dynamics study

Single-walled carbon nanotube (SWCNT) transmembrane channel formation in a pure 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC) bilayer, and the spontaneous internalization of single-stranded DNA (ssDNA) into the formed pore were simulated. A combination of computational techniques, Dissipative Particle Dynamics-Monte Carlo hybrid simulations and quantum mechanical calculations at the hybrid-DFT level, was used as a new proposal to perform DPD simulations granting specific chemical identity to the model particles. The simulated transmembrane channels showed that, in the case of pristine SWCNTs and upon increasing the nanotube length, a higher tilt angle with respect to the bilayer normal is observed and more time is needed for the nanotube to stabilize. On the other hand, for SWCNTs with polar rims an almost perpendicular orientation is preferred with less than 15° of tilt with respect to the bilayer normal once the nanotubes have pierced both monolayers. These findings are supported by experimental observations where CNTs of average inner diameters of 1.51 ± 0.21 nm and lengths in the 5-15 nm range were inserted in DOPC membranes [J. Geng, et al., Nature, 2014, 514(7524), 612-615]. Moreover, the narrower the SWCNTs, the slower the spontaneous internalization of ssDNA becomes, and ssDNA ends hydrophobically trapped inside the artificial pore. A dependence on the nucleotide content is found indicating that the higher the presence of adenine and thymine in the ssDNA chains the slower the internalization becomes, in agreement with the experimental [A. M. Ababneh, et al., Biophys. J., 2003, 85(2), 1111-1127] and predicted solvation tendency in water for nucleic acid bases.

Pulling Simulations and Hydrogen Sorption Modelling on Carbon Nanotube Bundles

Recent progress in molecular simulation technology has developed an interest in modernizing the usual computational methods and approaches. For instance, most of the theoretical work on hydrogen adsorption on carbon nanotubes was conducted a decade ago. It should be insightful to reinvestigate the field and take advantage of code improvements and features implemented in contemporary software. One example of such features is the pulling simulation modules now available in many molecular dynamics programs. We conduct pulling simulations on pairs of carbon nanotubes and measure the inter-tube distance before they dissociate in water. We use this distance to set the interval size between adjacent nanotubes as we arrange them in bundle configurations. We consider bundles with triangular, intermediate and honeycomb patterns, and armchair nanotubes with a chiral index from n = 5 to n = 10. Then, we simulate low pressure hydrogen adsorption isotherms at 77 K, using the grand canonical Monte Carlo method. The different bundle configurations adsorb great hydrogen amounts that may exceed 2% wt at ambient pressures. The computed hydrogen capacities are considered large for physisorption on carbon nanostructures and attributed to the ultra-microporous network and extraordinary high surface area of the configured models.