Biomolecule-Based Coacervation: Mechanisms, Applications, and Future Perspectives in Biomedical and Biotechnological Fields

Abstract

Coacervate is a form of liquid-liquid phase separation (LLPS) in which a solution containing one or more charged components spontaneously separates into two immiscible liquid phases. Due to their ability to mimic membraneless cellular environments and their high biocompatibility, coacervates have found broad applications across various fields of life sciences. This review provides a comprehensive overview of recent advances in biomolecule-based coacervation for biotechnological and biomedical applications. Encapsulation via biomolecule-based coacervation enables high encapsulation efficiency, enhanced stability, and the sustained release of cargos. In the field of tissue engineering, coacervates not only support cell adhesion and proliferation but also serve as printable bioinks with tunable rheological properties for 3D bioprinting. Moreover, biomolecule-based coacervates have been utilized to mimic membraneless organelles, serving as experimental models to understand the origin of life or investigate the mechanisms of biochemical compartmentalization. This review discusses the mechanisms of coacervation induced by various types of biomolecules, evaluates their respective advantages and limitations in applied contexts, and outlines future research directions. Given their modularity and biocompatibility, biomolecule-based coacervates are expected to play a pivotal role in next-generation therapeutic development and the construction of controlled tissue microenvironments, especially when integrated with emerging technologies.

Keywords: coacervates; complex coacervation; liquid–liquid phase separations; membraneless organelles; simple coacervation.

Figure 4

Schematic illustration of the formation of liquid- and gel-like DNA coacervates. When the solution temperature T > T_mY, three kinds of single-stranded DNAs (ssDNA1, ssDNA2, and ssDNA3) are dispersed in the bulk solutions; when T_mY > T > T_L, the three ssDNAs form a DNA Y-motif with self-complementary sticky ends; when T_L > T > T_G, liquid-like coacervates are formed by the dynamical repetition of attachment and detachment of the sticky ends of the DNA Y-motifs; when T_G > T, gel-like DNA coacervates are formed by the static binding of the DNA Y-motifs via their sticky ends. T_mY is the melting temperature of the Y-motif stem. T_L is the formation temperature of liquid-like DNA coacervates. T_G is the formation temperature of gel-like DNA coacervates. (Adjusted from ref. [87]. Copyright 2024, the Authors, published open access by Advanced Materials Interfaces under the terms of the Creative Commons CC BY License).

Figure 7

Schematic illustration of coacervation with whey protein isolate (WPI) and reducing sugar for encapsulating based on Maillard reaction. Functional activity (emulsifying properties, foaming properties, and antioxidant activity) of coacervates between WPI and different kinds of polysaccharides were analyzed. Tuna oil (TO) was encapsulated by complex coacervation with gum arabic (GA) and Maillard reaction products (MRPs). Different lowercase and uppercase letters indicate statistically significant differences among groups. Lowercase letters represent significant differences within each analytical parameter across different times or conditions, while uppercase letters indicate significant differences among different analytical parameters under the same condition (p < 0.05). (Reused from ref. [125]. Copyright © 2025 Elsevier Ltd.).

Figure 8

Schematic illustration of the universal delivery of CRISPR/Cas9 genome editing machineries mediated by HBpep-SP coacervates. Three types of CRISPR/Cas9 genome editing machineries including pDNA, mRNA/sgRNA, and Cas9 ribonucleoprotein (RNP) can be readily recruited during the LLPS of the HBpep-SP peptide. The cargo-loaded coacervates are internalized by the cell and then reduced by glutathione (the yellow spheres) in the cytosol, triggering cleavage of the side chain modification and disassembly of the cargo-loaded coacervates. The Cas9 RNP, which is directly released from coacervates or produced by the transcription and translation of pDNA and mRNA, enters the nucleus and induces double-strand breaks on the genomic DNA. (Reused from ref. [133]. Copyright © 2023 American Chemical Society.).

Figure 10

Schematic illustration of coacervation for adhesive technology: HA and low-molecular-weight methacrylated chitosan-formed coacervation. The coacervate was coated on the interfacial water of the substrate and treated by UV to form double-network hydrogel. Double-network hydrogel enhanced the cohesion of the substrate compared to a blank substrate. (Reused from ref. [146]. Copyright © 2025 American Chemical Society).

Figure 11

(A) Controlled demembranization of membranized coacervate droplets. The membranization of coacervates is achieved by introducing a terpolymer (PMAA-b-PMTEMA-b-PEG) into MLCs composed of PDDA and ATP. Following this, the demembranization of MCs is triggered by the addition of CMD, which causes the dissociation of the outer membrane and results in DCs integrated with CMD. (B) Preparation and characterization of (NR-loaded) NP membranized coacervates. The schematic illustration shows the formation of MCs through the addition of (NR-loaded) NPs. In the presence and absence of NR, the terpolymer initially self-assembles into anionic (NR-loaded) NPs, followed by the membranization on the surface of the cationic MLCs, accompanied by a small partial dissociation of the coacervate phase and the redistribution of the coacervate components into the NP membrane. Bright field and fluorescence field CLSM images of MLCs and MCs, respectively. The scale bar represents 10 μm, and the scale bar in the inserted image represents 5 μm. (Adjusted from ref. [150]. Copyright © 2025 American Chemical Society).

Figure 1

Illustration of factors and applications of coacervation based on cation biomolecules and anion biomolecules.

Figure 2

Illustration of (A) the range of LLPS of coacervation, (B) the intrinsic and extrinsic factors influencing the coacervation process, and (C) the phase transition of coacervates depending on temperature, pH, or ionic strength.

Figure 3

Schematic of the coacervation between ovalbumin and dextran sulfate under biopolymer ratio and salt concentration. The coacervation with OVA and dextran sulfate was induced by the protein/polysaccharide ration and salt concentration. (Adjusted from ref. [80]. Copyright © 2021 Elsevier Ltd.).

Figure 5

Coacervate design using sequence-defined block-co-polypeptides. (A) Schematic depiction of virus-containing coacervate formulation. (B) Example depiction of the variations in polypeptide charge density and hydrophobicity of the cationic lysine (K)-containing polymers. Charge blockiness is defined by the parameter τ, while hydrophobicity is indicated by the color of the gray blocks as the neutral amino acid spacers go from glycine to alanine to leucine. (C) Experimental design matrix to study the effect of polypeptide characteristics such as charge patterning and hydrophobicity on virus encapsulation. (D) Plot of the charge ratio (K+/E−) as a function of the total cationic charge fraction from the polypeptides present in the system. (Reused from ref. [97]. Copyright 2023, the authors published open access by Biomacromolecules under the terms of the CC-BY-NC-ND 4.0).

Figure 6

Polysaccharide-based coacervation with soy soluble soybean polysaccharide (SSPS) and fish gelatin. The coacervates were induced at a pH of 5.0 and coated for film. The curcumin-encapsulated coacervate film exhibited both burst release and slow release. (Reused from ref. [103]. Copyright © 2024 Elsevier Ltd.).

Figure 9

(A) Schematic illustration of ApoEVs/GelMA and CurCoa/GelMA coacervation for 3D-printed tissue engineering. (B) Scaffold based on ApoEVs/GelMA and CurCoa/GelMA coacervates showed various properties such as infection prevention, anti-inflammatory, angiogenesis, scar reduction, and cell proliferation and migration. (Reused from ref. [143]. Copyright © 2025 Elsevier Ltd.).