Hollow hierarchical hydroxyapatite/Au/polyelectrolyte hybrid microparticles for multi-responsive drug delivery.

In this study, hollow hierarchical hydroxyapatite (HAP)/Au/polyelectrolyte hybrid microparticles with a hollow HAP core and polymer multilayer/Au nanoparticle (AuNPs) shell for multi-responsive drug delivery have been prepared via a layer-by-layer (LbL) technique. Thermal-/pH-dual responsive aliphatic poly(urethane-amine) (PUA) was employed as the smart component. The aggregated AuNPs inside hybrid microparticles could potentially obstruct the diffusion of doxorubicin hydrochloride (DOX) from the hollow microparticles and assuage the initial burst release of DOX. Upon irradiation with near-infrared (NIR) laser, AuNP aggregates can effectively convert light to heat and result in the rapid release of DOX due to the partial collapse of the polyelectrolyte multilayers (PUA/sodium poly(styrenesulfonate) (PSS)). In addition, due to the dissolution of HAP in the acidic media and the shrinkage of aliphatic PUA above its lower critical solution temperature (LCST), the drug release of hollow hybrid carriers exhibits distinguished pH- and thermal-dependent properties. The results indicate that the hollow HAP/Au/PUA/PSS hybrid microparticles show great potential as novel smart drug carriers for controllable drug delivery.