Polyelectrolyte Assemblies in Aqueous Systems

Polyelectrolytes—polymers bearing ionisable groups—self-organise in water through a balance of electrostatic attraction, counterion distribution and solvent interactions. Two principal assembly modes dominate: complex coacervation, in which oppositely charged chains undergo associative liquid–liquid phase separation to form dense microdroplets, and layer-by-layer deposition, where alternating adsorption of polycations and polyanions yields nanoscale films or hollow capsules. Beyond these archetypes, hybrid constructs such as coacervate-in-liposome architectures and membranized coacervate microdroplets exemplify hierarchical organisation spanning molecular to microscale dimensions. Control parameters include polymer charge density and sequence, solution pH, ionic strength and flow conditions, which together govern phase boundaries, interfacial tension and internal microenvironments. Polyelectrolyte assemblies find applications in drug delivery, bioorthogonal catalysis, synthetic protocells, water purification and stimuli-responsive materials. Recent advances leverage hydrophobic peptide motifs, fuel-driven reaction cycles and microfluidic confinement to impart robustness, dynamic behaviour and compartmentalisation reminiscent of cellular organelles. The coupling of bottom-up design with physicochemical theory continues to unlock new functional materials, bridging soft matter physics and synthetic biology.

Research from Nature Portfolio

Researchers have introduced dipeptide-based coacervates that combine charged amino acid sequences with hydrophobic residues to produce stable, cell-compatible microdroplets featuring a water-immiscible interior. These protocell models encapsulate metal catalysts, achieving enhanced bioorthogonal reaction rates in live cells. A separate study presented active coacervate droplets formed by a reversible fuel-driven reaction cycle: droplets assemble in the presence of a chemical ‘fuel’, transiently concentrate functional RNA, then disintegrate as fuel is consumed, mimicking formation and dissolution dynamics of membraneless organelles. Another foundational work demonstrated that simple polyelectrolyte pairs can support template-directed RNA polymerisation and ribozyme catalysis within complex coacervates, revealing that charge pairing and divalent ion partitioning critically influence enzymatic efficiency and confinement effects in primordial-chemistry models.

Research from all publishers

A recent review of membranized coacervate microdroplets detailed strategies for enveloping liquid coacervate cores with amphiphilic barriers—ranging from lipids and block copolymers to cell-derived fragments—thereby tuning permeability and enabling cytomimetic functions such as enzyme cascades and controlled substrate trafficking. Another report described pH-triggered reversible coacervation inside unilamellar vesicles: by cycling pH across the pKₐ of a polycation, single coacervate droplets form and dissolve within lipid compartments, activating dormant enzyme reactions via local concentration effects. These studies highlight how orthogonal triggers—pH, surface activity or membrane templating—extend the utility of polyelectrolyte assemblies for responsive synthetic cells and microreactors.

Polyelectrolyte Assemblies in Aqueous Systems publication trend

The graph below shows the total number of articles in polyelectrolyte assemblies in aqueous systems across all publications each year (not limited to Nature Index journals).

Technical terms

Polyelectrolyte: A polymer bearing ionisable groups that dissociate in water to yield charged chains and counterions.

Complex coacervation: Liquid–liquid phase separation driven by electrostatic attraction between oppositely charged polyelectrolytes, forming a dense polymer-rich phase and a dilute supernatant.

Layer-by-layer assembly: Sequential adsorption of oppositely charged polymers onto a substrate, producing ultrathin films or hollow capsules through electrostatic layering.

Counterion condensation: Accumulation of small ions near charged polymers that reduces the effective polymer charge and influences assembly and phase behaviour.

References

1. Dipeptide coacervates as artificial membraneless organelles for bioorthogonal catalysis. Nature Communications (2024).
2. Active coacervate droplets as a model for membraneless organelles and protocells. Nature Communications (2020).
3. Template-directed RNA polymerization and enhanced ribozyme catalysis inside membraneless compartments formed by coacervates. Nature Communications (2019).
4. Membranized Coacervate Microdroplets: from Versatile Protocell Models to Cytomimetic Materials. Accounts of Chemical Research (2023).
5. Reversible pH‐Responsive Coacervate Formation in Lipid Vesicles Activates Dormant Enzymatic Reactions. Angewandte Chemie International Edition (2020).