The Critical Transition from Soluble Complexes to Colloidal Aggregates of Polyelectrolyte Complexes at Non-Stoichiometric Charge Ratios.

The transition from soluble to colloidal polyelectrolyte complex normally occurs at a critical non-stoichiometric charge ratio. Here, it is demonstrated that the conventional batch mixing produces heterogeneous binding and complexation, which can easily mask this soluble-colloidal complex transition (sol-col transition) even for weakly binding polyelectrolytes like polyacrylic acid (PAA) and poly(diallyldimethylammonium chloride) (PDADMAC). When mixed efficiently using multi-inlet vortex mixer (MIVM), the sol-col transition occurs beyond a critical charge ratio (n-/n+) and the large colloidal complexes are formed through the aggregation of small primary complexes (as revealed by atomic force microscopy). Moreover, the sol-col transition occurs at a constant charge ratio below the overlapping concentration (c*) of the long host polyelectrolyte, but at lower charge ratios above c* due to chain entanglement. When adding NaCl to the solution, the sol-col transition charge ratio first decreases, then remained stable for a period, and finally increased and vanished at high ionic strength. When replacing NaCl with chaotropic salts, the sol-col transition occurs at lower charge ratios, while kosmotropes has little impact. The solvent quality and polymer hydrophobicity effects are also discussed. With the assistance of rapid mixing, this study provides a more reliable way of studying the sol-col transition of polyelectrolyte complexes.

High throughput onion-like liposome formation with efficient protein encapsulation under flash antisolvent mixing.

Achieving a high encapsulation efficiency and loading capacity of proteins in lecithin-based liposomes has always been a challenge. Here, we use Flash Nano-Precipitation (FNP) to produce liposomes and investigated the encapsulation of model protein (Bovine Serum Albumin, BSA). Through rapid turbulent mixing, we obtained liposomes with small size, low polydispersity, and good batch repeatability at a high production rate. We demonstrated that the bilayer of liposomes prepared solely using lecithin was defective, which led to the fusion, and increased size and polydispersity. When cholesterol was added to reach a lecithin-to-cholesterol molar ratio of 5:3, a compact bilayer formed to effectively inhibit liposome fusion. The encapsulation efficiency and loading capacity of BSA was as high as âˆ¼ 68% and âˆ¼ 6% in lecithin-cholesterol liposome, respectively, far exceeding the values reported in the literature. Further study by Quartz Crystal Microbalance with Dissipation (QCM-D) revealed that the highly effective encapsulation was due to the rapid mutual adsorption between BSA and defective/curved lecithin double layers during the liposome formation. Such rapid mutual adsorption leads to the layer-by-layer assembly and formation of onion-like compact liposome structure as revealed by Cryo-TEM. This simple FNP method provides a scalable manufacturing approach for liposomes with efficient protein encapsulation. The revealed adsorption mechanism between protein and lecithin bilayers could also serve as a guide for similar studies.