Novel Morphology-Controlled Hierarchical Core@Shell Structural Organo-Layered Double Hydroxides Magnetic Nanovehicles for Drug Release

Novel hierarchical core@shell structured salicylate (SA) intercalated ZnAl-LDH (layered double hydroxides) magnetic nanovehicles were obtained via a special double-drop coprecipitation strategy assembling organo-ZnAl-LDH nanocrystals onto the surface of Fe₃O₄ submicrospheres (∼480 nm) from cheap aspirin and Zn- and Al-nitrates in alkaline solutions. The obtained Fe₃O₄@SA-LDH-r nanovehicles exhibit varied morphologies with hexagonal LDH ab-face horizontal, vertical, and vertical/slant/horizontal to the surfaces of Fe₃O₄ upon proper mass ratio (r) of Zn-salt to Fe₃O₄ from 1.93 to 7.71 in a low supersaturation system and possess moderate drug loadings and strong superparamagnetism. An in vitro release study reveals that under “no MF” mode (without external magnetic field) the SA release exhibits the higher accumulated release amount and smaller half-life (t_0.5) for Fe₃O₄@SA-LDH-3.85 (41.2%, 1.63 min) and Fe₃O₄@SA-LDH-7.71 (51.1%, 1.66 min) probably owing to their mainly vertical LDH orientations, while the dramatically reduced SA release (10.0%) and greatly elongated t_0.5 (25.6 min) for Fe₃O₄@SA-LDH-1.93 may be due to its relatively stronger host–guest interaction and compact horizontally oriented LDH shell stack. Under “MF on” mode, all the magnetic samples show a detectable reduced SA release owing to the particle–particle interactions among the magnetic nanovehicles. The kinetic fittings show that the release processes of all the samples involve the bulk and surface diffusion. The SA release from Fe₃O₄@SA-LDH-1.93 is mainly determined by the interparticle diffusion among the horizontally oriented LDH shell nanocrystals while those of Fe₃O₄@SA-LDH-3.85 and Fe₃O₄@SA-LDH-7.71 mainly involve the interlayer intraparticle diffusion between LDHs layers due to their largely vertical LDH shell nanocrystals.