Zn capped Al2O3 and TiO2 nanoporous arrays as pH sensitive drug delivery systems: a combined experimental and simulation study

Abstract

Drug delivery systems sensitive to pH have been investigated recently as a responsive strategy for tumour targeting in view of the slightly acidic pH environment of most solid tumours. Herein, we report Zn capped Al₂O₃ and TiO₂ nanoporous arrays for pH sensitive drug release. The nanostructures were fabricated through electrochemical anodisation. Vitamin C as a model drug was loaded into the nanopores; some were then capped using elemental Zn. The release rates of vitamin C were investigated in water or lactic acid using high performance liquid chromatography (HPLC). The amount of drug loaded into the nanostructures was about 7 times higher for TiO₂ compared with Al₂O₃ and the release was faster from TiO₂. Zn capping proved to be quite efficient at preventing release at high pH (7) and not largely hindering the release at low pH (5), making both systems suitable for pH-triggered release. Molecular dynamics (MD) simulations showed that the diffusion of vitamin C molecules through the model nanopores is faster for TiO₂ than for Al₂O₃, consistent with the experimental results. The tremendously stronger H bonding interactions observed for vitamin C molecules and water molecules with the TiO₂ walls compared with Al₂O₃ are responsible for the observed differences in the calculated number density profiles and radial distribution functions.