Structure and Dynamics of Hybrid Colloid–Polyelectrolyte Coacervates

Abstract

We develop a scaling theory for the structure and dynamics of "hybrid" complex coacervates formed from linear polyelectrolytes (PEs) and oppositely charged spherical colloids, such as globular proteins, solid nanoparticles, or spherical micelles of ionic surfactants. At low concentrations, in stoichiometric solutions, PEs adsorb at the colloids to form electrically neutral finite-size complexes. These clusters attract each other through bridging between the adsorbed PE layers. Above a threshold concentration, macroscopic phase separation sets in. The coacervate internal structure is defined by (i) the adsorption strength and (ii) the ratio of the resulting shell thickness to the colloid radius, H/R. A scaling diagram of different coacervate regimes is constructed in terms of the colloid charge and its radius for Θ and athermal solvents. For high charges of the colloids, the shell is thick, H ≫ R, and most of the volume of the coacervate is occupied by PEs, which determine its osmotic and rheological properties. The average density of hybrid coacervates exceeds that of their PE−PE counterparts and increases with nanoparticle charge, Q. At the same time, their osmotic moduli remain equal, and the surface tension of hybrid coacervates is lower, which is a consequence of the shell's inhomogeneous density decreasing with the distance from the colloid surface. When charge correlations are weak, hybrid coacervates remain liquid and follow Rouse/reptation dynamics with a Q-dependent viscosity, η Rouse ∼ Q 4/5 and η rep ∼ Q 28/15 for a Θ solvent. For an athermal solvent, these exponents are equal to 0.89 and 2.68, respectively. The diffusion coefficients of colloids are predicted to be strongly decreasing functions of their radius and charge. Our results on how Q affects the threshold coacervation concentration and colloidal dynamics in condensed phases are consistent with experimental observations for in vitro and in vivo studies of coacervation between supercationic green fluorescent proteins (GFPs) and RNA.

Scaling Perspective on Dynamics of Nanoparticles in Polymers: Length- and Time-Scale Dependent Nanoparticle–Polymer Coupling

“…In addition, nanoparticles may be charged as well and interact with the polyelectrolytes directly. Rumyantsev et al 203 recently developed a scaling theory for the structure and dynamics of complex coacervates formed from linear polyelectrolyte chains and oppositely charged spherical colloids, which may represent globular proteins, solid nanoparticles, or spherical micelles of ionic surfactants. The diffusion coefficients of the colloids were predicted to be strongly decreasing functions of the particle size and the charge carried by the particle.…”

Complex Coacervates as a Promising Vehicle for mRNA Delivery: A Comprehensive Review of Recent Advances and Challenges

“…Coacervate-mediated delivery of mRNA can be improved by combining different coacervate components to create composite and hybrid coacervates with enhanced physical properties and new functionalities Figure highlights some of the properties associated with the performance of coacervates made from polymers, proteins, or peptides.…”

“…This protection is especially important for mRNA, which is a fragile molecule that is easily degraded by RNases . In addition, nanoparticles can be engineered to have properties similar to cell membranes, allowing for improved cellular uptake and targeted delivery of mRNA to specific tissues or cell types . Furthermore, coacervate-based nanoparticle delivery systems can be engineered to respond to specific stimuli, such as pH or temperature, leading to physiologically controlled release of the mRNA cargo .…”

Surface Charge Density and Steric Repulsion in Polyelectrolyte–Surfactant Coacervation

“…These computational approaches are only able to account for a few individual micelles, rather than an entire micelle-based phase. ,− , Finally, there has been theoretical progress in understanding complexation and coacervation in related polyelectrolyte–nanoparticle or polyelectrolyte–protein solutions. The Ganesan group used a combination of polymer field theory and single-chain in mean-field simulations to understand the distribution of polyelectrolytes around uniform and patchy particles and relate to phase behavior. − Recently, Rumyantsev et al also developed scaling arguments for polyelectrolyte–particle coacervates . Both of these approaches predict coacervation due to the fluctuation-driven attraction between charged colloids that are “bridged” by an oppositely charged polyelectrolyte chain with low linear charge density.…”

“…82−86 Recently, Rumyantsev et al also developed scaling arguments for polyelectrolyte−particle coacervates. 87 Both of these approaches predict coacervation due to the fluctuation-driven attraction between charged colloids that are "bridged" by an oppositely charged polyelectrolyte chain with low linear charge density.…”