Simulation of Tunable Release of Molecular Species from Halloysite NanotubesDivya Narayan Elumalai1, Ethan Sullivan1, Yuri Lvov1 , Pedro Derosa 1,2

1Louisiana Tech University2Grambling State University

Figure 2. The contributions towards the total energy of the system9.

Figure 7. (a) Simulated release profiles of Dexamethasone like particles from nanotubes with charged endcaps. B) Release profiles from flat perforated pores (b) two different types of endcaps / pores.

1. Lay, C.L., J. Liu, and Y. Liu,. Expert Rev Med Devices, 2011. 8(5): p. 561-6.2. Liu, Z., et al., Nat Protoc, 2009. 4(9): p. 1372-82.3. Abdullayev, E., et al.,. ACS Appl Mater Interfaces, 2011. 3(10): p. 4040-6.4. Abdullayev, E. and Y. Lvov, J Nanosci Nanotechnol, 2011. 11(11): p. 10007-26.5. Theng, B.K.G., et al.,. Clays and Clay Minerals, 1982. 30(2): p. 143-149.6. Forsgren, J., & Jämstorp, E., Journal of Pharmaceutical Sciences, 2010. 99(1): p. 219–227.7. Abdullayev, E. and Y. Lvov, Journal of Materials Chemistry, 2010. 20(32): p. 6681-6687.8. Veerabadran, N.G., R. Price, and Lvov.Y. M., NANO, 2007. 2(2): p. 115-120.9. Modified from http://iramis.cea.fr/spec/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=184610.W. Ma, W. Yah, H. Otsuka, and A. Takahara, “Application of imogolite clay nanotubes in organic–inorganic nanohybrid materials,” J. Mater. Chem., pp. 11887–11892, 2012.11. G. Tari, I. Bobos, S. F. C. Gomes andM. F. Ferreira,J. Coll. Interf. Sci. 210, 360 (1999).

Figure 4. (a,b,c ) Important characteristics of Halloysite nanotubes3,10.

Figure 5. Flow chart depicting the methodology for the simulations.Total Energy of

the system

Wall-Particle Interactions have contributions from Coulombic and Van Der Waals

interactions

Particle –Particle interactions that are accounted for

by shielded Coulombic and Van Der Waals

interactions The energy

contribution due to temperature and other factors like

the introduction of external fields ( for

e.g. an Electric field along the axis

of the tube.) are also considered.

The objective of this research is to understand transport properties such as adsorption and diffusion in nanotubes, and to study the interactions governing transport in nanotubes.This study aims to enhance the understanding of and promote applications that use nanotubes for transport, storage and sustained/controlled release of molecular species of interest. Applications such as : Enhancing the lifespan of rust coatings in hazardous environments, Self healing composites and polymers, Sustained/ slow drug delivery.

A time quantified Monte Carlo model is used to simulate the most probable motion of particles in cylindrical defect free Halloysite nanotubes by implementing a forced random-walk algorithm.

Van der Waals interactions and Shielded Coulombic interactions are the relevant interactions considered in the model.

Particles are represented based on their hydrodynamic diameters and overall charge. NP size and zeta potential, the zeta potential in the inner wall of the NT, and size distribution are the experimental parameters used in the simulation

Time is introduced in a novel way in our Monte Carlo Code. We validate outrresults with experimentally obtained release profile. The media in which the NP diffuse is treated as a continuum dielectric. Initial burst is attributed to NP adsorption in defects and in between layers of

the rolled up kaolin. 30 copies of the system are run simultaneously and results averaged

Study the effect of external perturbations in the form of applied electric fields. Study the diffusion of long molecules like proteins through nanotubes. Calculate diffusion coefficients by running equilibrium calculations. Study the effect of diffusion through hydro-gels and like structures.

A 3-D coarse grain Monte Carlo model based on the Boltzmann transport is used to simulate the release profiles and diffusion of molecules from halloysite nanotubes. This is a viable alternative to the computationally intensive MD approach. The comparison of our simulated release profiles with published experimental data show an excellent match. Diffusion in the cases studied occurs in two distinct phases with an initial burst phase, followed by a longer saturation phase. An effective way to control the release of molecules from halloysite nanotubes is to add end caps to the nanotubes.

Halloysite clay tubes are aluminum-silicate hollow cylinders with an average length of 1 µm, an outer diameter of 50 nm and a lumen of 15 nm.

Halloysite has been shown to be biocompatible at concentrations >1000mg/ml. These nanotubes are used for loading and sustained release of active chemical

agents (molecules of interest). A vacuum impregnation technique depicted in Figure 1 is used for loading the

nanotubes

Simulation Methodology

Project Outline

Experimental Procedure

Figure 1. Clay nanotubes are good nanocontainers for loading active chemical agents . A general procedure for loading Halloysite tubes is shown here.

References

Future Work

Conclusions

Results

Figure 3. Validation of simulation by comparing Experimental and simulated release profiles from Halloysite nanotubes of different molecules. a) Dexamethasone, b) Furosemide and c) Nifedipine3. 

Figure 6. a) Halloysite nanotubes with silica end caps3. b) Schematic depicting typical end cap formation3. C) Simulated release profiles of Dexamethasone from Halloysite nanotubes with different end caps pores size.

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