Synthesis of dual temperature - and pH-responsive yolk-shell nanoparticles by conventional etching and new deswelling...

Dual stimuli-responsive yolk-shell nanoparticles with cross-linked poly(acrylic acid) (PAA) pH-responsive core and cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) temperature-responsive shell were synthesized via two different methods In the first method, silica encapsulated PAA (PAA@SiO₂) was used as seed in distillation precipitation polymerization (DPP) of HEMA to yield PAA@SiO₂@PHEMA from which silica layer was etched by HF solution to produce yolk-shell PAA@air@PHEMA nanoparticles. In the second method, swollen PAA nanoparticles at pH = 10 were used as seeds in emulsion polymerization of HEMA to yield core-shell PAA@PHEMA nanoparticles. After dispersion of PAA@PHEMA nanoparticles in acidic medium at pH = 2, yolk-shell nanoparticles were formed through deswelling of pH-responsive cores due to protonation of carboxyl groups. Synthesized nanoparticles were characterized using FT-IR, FE-SEM and TEM methods to observe yolk-shell nanostructure for both synthesis routes. Stimuli-responsive behavior of the nanoparticles was investigated by UV-vis spectrometer where similar behaviors were obtained for template-assisted and template-free synthesized yolk-shell nanoparticles. Finally, both yolk-shell nanoparticles were examined as potential carriers for controlled release of doxorubicin hydrochloride (DOX) anti-cancer drug.