Abstract
Molecular level understanding of permeation of nanoparticles through human skin establishes the basis for development of novel transdermal drug delivery systems and design and formulation of cosmetics. Recent experiments suggest that surface coated nano-sized gold nanoparticles (AuNPs) can penetrate the rat and human skin. However, the mechanisms by which these AuNPs penetrate are not well understood. In this study, we have carried out coarse grained molecular dynamics simulations to explore the permeation of dodecanethiol coated neutral hydrophobic AuNPs of different sizes (2–5 nm) and surface charges (cationic and anionic) through the model skin lipid membrane. The results indicate that the neutral hydrophobic AuNPs disrupted the bilayer and entered in it with in ~200 ns, while charged AuNPs were adsorbed on the bilayer headgroup. The permeation free energy calculation revealed that at the head group of the bilayer, a very small barrier existed for neutral hydrophobic AuNP while a free energy minimum was observed for charged AuNPs. The permeability was maximum for neutral 2 nm gold nanoparticle (AuNP) and minimum for 3 nm cationic AuNP. The obtained results are aligned with recent experimental findings. This study would be helpful in designing customized nanoparticles for cosmetic and transdermal drug delivery application.
Highlights
Several experimental studies of permeation of AuNPs through human and rat skin have been reported[12,13,14,15,16,17,18,19] Dean et al.[12] showed that the deoxyribonucleic acid coated AuNPs enhanced the permeation through outer layer of the skin to Langerhans cells
Neutral hydrophobic dodecanethiol and cetrimide coated AuNPs were able to penetrate to the deeper layer of skin but citrate coated AuNP were not detected in the deeper layer
We have observed incomplete permeation of AuNPs because of two reasons (i) simulations were run for 3 μsand (ii) the skin lipid bilayer was in gel phase as compared to liquid phase DPPC bilayer[42]
Summary
Several experimental studies of permeation of AuNPs through human and rat skin have been reported[12,13,14,15,16,17,18,19] Dean et al.[12] showed that the deoxyribonucleic acid coated AuNPs enhanced the permeation through outer layer of the skin to Langerhans cells. We reported the interaction between the various AuNPs and skin lipids and permeation of surface coated neutral hydrophobic, anionic and cationic gold nanoparticles through model skin membrane. This confirmed that the bilayer interior is the favorable position for hydrophobic neutral AuNPs. The sharp negative gradient in the free energy near the head group led to quick permeation of the AuNP inside the bilayer interior as observed in unconstrained simulation (Fig. 2a).
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