Layer-by-layer assembly mechanism of particulate-continuous phase for sandwich-like nanoparticles in oral colon-targeted protein delivery.

This study investigates the layer-by-layer (LbL) assembly behavior of materials based on their interactions and phase states. A novel assembly using oxidized starch nanocrystals (OSNC) as the particulate phase and quaternary ammonium chitosan (QAC) as the continuous phase was developed to form triple-layer particles for targeted and sustained release of lysozyme (LYS). Thermodynamic binding studies revealed weaker OSNC-LYS interaction and strong OSNC-QAC interaction, both significantly influencing encapsulated LYS retention, particularly in the double-layer structure. The lamellar OSNC facilitated the "sandwich-like" morphology, with its outer layer stabilizing particle dispersion through steric hindrance and electrostatic repulsion. The assembly mechanism, influenced by OSNC-LYS complex surface properties and QAC, enhanced dispersibility at low LYS loading and induced aggregation at higher LYS levels via hydrogen bonding and van der Waals forces. The triple-layer particles achieved colon-targeted LYS delivery, preserving bioactivity, with pH sensitivity, low cytotoxicity, and excellent stability, highlighting their potential for oral protein/polypeptide delivery.