Dual (pH- and temperature-) stimuli responsive nanocarrier with bimodal mesoporous silica nanoparticles core and copolymer shell for controlled ibuprofen-releasing: Fractal feature and diffusion mechanism

•The composite nanoparticles (P@BMMs) with core-shell structures were prepared.•The fractal feature of the P@BMMs with IBU-loading and releasing was investigated.•The obtained P@BMM showed the dependence on pH/temperature release behaviors.

A kind of organic-inorganic hybrid composite with core-shell structure was successfully prepared via seed polymerization method using environmental stimuli (pH/temperature) copolymer poly(N-isopropylacryl-acrylamide)-co-poly(acrylic acid) (P(NIPAM-co-AA)) as a shell and bimodal mesoporous silica nanoparticles (BMMs) with small size of 20-50 nm as a core. The capacity of loading ibuprofen (IBU) and the subsequent release performance from resultant P(NIPAM-co-AA)@BMMs (denoted as P@BMMs) under different external conditions were investigated in detail. Meanwhile, its structural features and textural parameters were characterized using XRD, N2 adsorption-desorption isotherms, SEM and TEM, SAXS, FT-IR, solid-state Si29 NMR, TGA and elemental analysis techniques. The results demonstrated that P(NIPAM-co-AA) as a shell coating on the external surface of BMMs acted as temperature-pH gate valve to control release behaviors, while mesoporous BMMs as reservoir provided enough space to encapsulate IBU molecules with high loading. SAXS patterns evidently presented that P@BMMs before IBU-loading and after releasing possessed the fractal feature, suggesting their surface roughness and structural irregularities, in which the mass fractal was increased from 2.36 for BMMs to 2.41 for BMMs-MPS to 2.51 for P@BMMs, and even the transformation from the mass fractal to surface fractal for I/P@BMMs was about 2.80. In addition, three types of kinetic models (first-order, Higuchi and Korsmeyer-Peppas power law) were employed to evaluate the release profiles, indicating that the drug-release kinetic of P@BMMs was suitable to Korsmeyer-Peppas power law model with non-Fickian diffusion mechanism.

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