Rheology, microstructure and diffusion in soft gelatin nanocomposites packed with anionic nanogels

Abstract

• Gelatin nanocomposites (GNC) loaded with anionic nanogels are designed. • Pre-yielding viscosity of GNC scales with nanogel packing density, η ̃ 0 ∼ φ c 0.5 . • GNC undergo a stress induced shear-gel formation and show shear-thinning behaviour. • Nanogel packing density increases G′ and decreases characteristic mesh size of GNC. • Molecular modelling uncovers cooperative interactions between nanogels and gelatin. The colloidal stability of therapeutic nanoparticles for improving human health is a significant challenge, owing to aggregation and sedimentation. To overcome such limitations, gelatin-based nanocomposites are designed with increasing concentration of anionic nanogels. Complementary steady-state and oscillatory rheology revealed that the pre-yielding viscosity of nanocomposites scales with nanogel packing density, η ̃ 0 ∼ φ c 0.5 . Upon shearing, nanocomposites transform into a shear gel, which exhibits a power law shear-thinning behaviour. Nanogel loading also increases the G′ , increases the sol-gel transition temperatures and decreases the characteristic mesh size of the nanocomposites. We postulate that electrostatic and hydrogen-bonding interactions between nanogels and gelatin play a synergistic role in the observed structural, micromechanical and rheological behaviour. Fluorescent nanogel-labelling combined with centrifugation, revealed that ca. 60 % of nanogels precipitate together with gelatin, indicating the extent of nanogel-gelatin interactions. These interactions are probed using molecular modelling, temperature dependence of G′ and time-temperature superimposition principle combined with the Arrhenius model. The remaining nanogels (ca. 40 %) demonstrate diffusive mobility (5.51 × 10 −10 m 2 s -1 ) and are located in the bulk solvent existing in the pores and channels of the nanocomposites. Taking advantage of nanogels’ diffusive mobility, bioresponsive release under conditions of swallowing is simulated via computational fluid dynamics.