Signal responsive transient coacervation in complex coacervate core micelles

Triggered coacervate phase (de)stabilisation in complex coacervate core micelles (C3Ms) has traditionally been limited to changes in pH and salt concentration, limiting options in responsive C3M material design. To expand this toolbox, we have developed C3Ms, that, at constant physiological pH, assemble and disassemble by coupling to a chemical reaction network (CRN) driven by the conversion of electron deficient allyl acetates and thiol or amine nucleophiles. This CRN produces transient quaternization of tertiary amine-functionalised block copolymers, which can then form the complex coacervate phase. We demonstrate triggered C3M assembly using two different allyl acetates, resulting in dramatically different assembly rates from hours to days. These are applied in various combinations with selected nucleophiles, demonstrating sequential signal induced C3M formation and deformation, as well as transient non-equilibrium (de)formation. We expect that timed and signal-responsive control over coacervate phase formation at physiological pH will find application in nucleic acid delivery, nano reactors and protocell research.

Signal responsive transient coacervation in complex coacervate core micelles

Triggered coacervate phase (de)stabilisation in complex coacervate core micelles (C3Ms) has traditionally been limited to changes in pH and salt concentration, limiting options in responsive C3M material design. To expand this toolbox, we have developed C3Ms, that, at constant physiological pH, assemble and disassemble by coupling to a chemical reaction network (CRN) driven by the conversion of electron deficient allyl acetates and thiol or amine nucleophiles. This CRN produces transient quaternization of tertiary amine-functionalised block copolymers, which can then form the complex coacervate phase. We demonstrate triggered C3M assembly using two different allyl acetates, resulting in dramatically different assembly rates from hours to days. These are applied in various combinations with selected nucleophiles, demonstrating sequential signal induced C3M formation and deformation, as well as transient non-equilibrium (de)formation. We expect that timed and signal-responsive control over coacervate phase formation at physiological pH will find application in nucleic acid delivery, nano reactors and protocell research.

Charge Density and Hydrophobicity-Dominated Regimes in the Phase Behavior of Complex Coacervates

<div>The role of hydrophobicity, and particularly nonionic hydrophobic comonomers, on the phase behavior of polyelectrolyte complex coacervates is not well-understood. Here, we address this problem by synthesizing a library of polymers with a wide range of charge densities and nonionic hydrophobic side chain lengths, and characterizing their phase behavior by optical turbidity. The polymers were prepared by post-polymerization modification of poly(N-acryloxy succinimide), targeting charge densities between 40 and 100% and nonionic aliphatic sidechains with lengths from 0 to 12 carbons long. Turbidity measurements on pairs of polycations and polyanions with matched charge densities and nonionic sidechain lengths revealed a complex salt response with distinct charge density-dominated and hydrophobicity-dominated regimes. The polymer solubilities were not directly correlated with the phase behavior of the coacervates, indicating the difficulty of understanding the coacervate phase behavior in terms of the polymer-water interaction parameter. This result suggests that there is significant room for further work to understand the mechanisms by which specific molecular-scale interactions moderate the phase behavior of complex coacervates.</div>

Charge Density and Hydrophobicity-Dominated Regimes in the Phase Behavior of Complex Coacervates

<div>The role of hydrophobicity, and particularly nonionic hydrophobic comonomers, on the phase behavior of polyelectrolyte complex coacervates is not well-understood. Here, we address this problem by synthesizing a library of polymers with a wide range of charge densities and nonionic hydrophobic side chain lengths, and characterizing their phase behavior by optical turbidity. The polymers were prepared by post-polymerization modification of poly(N-acryloxy succinimide), targeting charge densities between 40 and 100% and nonionic aliphatic sidechains with lengths from 0 to 12 carbons long. Turbidity measurements on pairs of polycations and polyanions with matched charge densities and nonionic sidechain lengths revealed a complex salt response with distinct charge density-dominated and hydrophobicity-dominated regimes. The polymer solubilities were not directly correlated with the phase behavior of the coacervates, indicating the difficulty of understanding the coacervate phase behavior in terms of the polymer-water interaction parameter. This result suggests that there is significant room for further work to understand the mechanisms by which specific molecular-scale interactions moderate the phase behavior of complex coacervates.</div>

The Effects of Protein Charge Patterning on Complex Coacervation

The complex coacervation of proteins with other macromolecules has applications in protein encapsulation and delivery and for determining the function of cellular coacervates. Theoretical or empirical predictions for protein coacervates would enable the design of these coacervates with tunable and predictable structure-function relationships; unfortunately, no such theories exist. To help establish predictive models, the impact of protein-specific parameters on complex coacervation were probed in this study. The complex coacervation of sequence-specific, polypeptide-tagged, GFP variants and a strong synthetic polyelectrolyte was used to evaluate the effects of protein charge patterning on phase behavior. Phase portraits for the protein coacervates demonstrated that charge patterning dictates the protein’s binodal phase boundary. Protein concentrations over 100 mg mL^-1 were achieved in the coacervate phase, with concentrations dependent on the polypeptide sequence. In addition to shifting the binodal phase boundary, polypeptide charge patterning provided entropic advantages over isotropically patterned proteins. Together, these results show that modest changes of only a few amino acids alter the coacervation thermodynamics and can be used to tune the phase behavior of polypeptides or proteins of interest.

The Effects of Protein Charge Patterning on Complex Coacervation

The complex coacervation of proteins with other macromolecules has applications in protein encapsulation and delivery and for determining the function of cellular coacervates. Theoretical or empirical predictions for protein coacervates would enable the design of these coacervates with tunable and predictable structure-function relationships; unfortunately, no such theories exist. To help establish predictive models, the impact of protein-specific parameters on complex coacervation were probed in this study. The complex coacervation of sequence-specific, polypeptide-tagged, GFP variants and a strong synthetic polyelectrolyte was used to evaluate the effects of protein charge patterning on phase behavior. Phase portraits for the protein coacervates demonstrated that charge patterning dictates the protein’s binodal phase boundary. Protein concentrations over 100 mg mL^-1 were achieved in the coacervate phase, with concentrations dependent on the polypeptide sequence. In addition to shifting the binodal phase boundary, polypeptide charge patterning provided entropic advantages over isotropically patterned proteins. Together, these results show that modest changes of only a few amino acids alter the coacervation thermodynamics and can be used to tune the phase behavior of polypeptides or proteins of interest.

Coacervation-driven instant paintable underwater adhesives with tunable optical and electrochromic properties

Coacervation generally refers to liquid-liquid phase separation when mixing oppositely charged polyelectrolytes in an aqueous solution, which produces a polyelectrolyte‐dense coacervate phase in a dilute solution phase. Coacervation plays a...