Coacervation Research Articles

Preparation, characterisation, and application of gelatin/sodium carboxymethyl cellulose/peach gum ternary composite microcapsules for encapsulating sweet orange essential oil.

This study successfully developed a gelatin-sodium carboxymethyl cellulose-peach gum composite microcapsule system using the complex coacervation method. Optimal preparation conditions were determined by turbidity, complex condensate yield and encapsulation efficiency: the ratio of gelatin to sodium carboxymethyl cellulose was 7:1, the ratio of gelatin/sodium carboxymethyl cellulose to peach gum was 4:1, and the pH value was 4.2. The morphology of the system was evaluated using scanning electron microscopy and laser confocal microscopy. Structural properties and viscoelasticity were analyzed through Fourier-transform infrared spectroscopy, Raman spectroscopy, and rheology. Results indicated that adding peach gum enhanced the system's structural stability and solid behavior. Thermogravimetric analysis, differential scanning calorimetry, swelling, release, antioxidant, and antibacterial experiments confirmed that the addition of peach gum increased the thermal decomposition temperature of the microcapsule system to 246 °C, enhanced the sustained release capacity, and improved both the antioxidant effects and antibacterial properties. The highest lipid antioxidant value was 1.1 mg MDA/kg, while the total bacterial count reached a maximum of 5.3 log CFU/g, both of which remained below the threshold of food spoilage, thereby confirming the role of the gelatin-carboxymethyl cellulose sodium-peach gum composite system in meat preservation. The gelatin-sodium carboxymethyl cellulose-peach gum composite system's excellent sustained-release capacity, antioxidant effect, and the antibacterial properties of the gelatin-sodium carboxymethyl cellulose-peach gum composite system could provide a new carrier for the application of active substances in the food sector.

Insights into the Mechanism of Protein Loading by Chain-Length Asymmetric Complex Coacervates.

The study of the phase behavior of polyelectrolyte complex coacervates has attracted significant attention in recent years due to their potential use as membrane-less organelles, microreactors, and drug delivery platforms. In this work, we investigate the mechanism of protein loading in chain-length asymmetric complex coacervates composed of a polyelectrolyte and an oppositely charged multivalent ion. Unlike the symmetric case (polycation + polyanion), we show that protein loading is highly selective based on the protein's net charge: only proteins with charges opposite to the polyelectrolyte can be loaded. Through a series of systematic experiments, we identified that the protein loading process relies on the formation of a neutral three-component coacervate in which both the protein and the multivalent ion serve as complexing agents for the polyelectrolyte. Lastly, we demonstrated that this mechanism extends to the sequestration of other charged small molecules, offering valuable insights into designing functional multicomponent coacervates.

Catalytic Assembly of Peptides Mediated by Complex Coacervates.

The assembly of peptides is generally mediated by liquid-liquid phase separation, which enables control over assembly kinetics, final structure, and functions of peptide-based supramolecular materials. Modulating phase separation can alter the assembly kinetics of peptides by changing solvents or introducing external fields. Herein, we demonstrate that the assembly of peptides can be effectively catalyzed by complex coacervates. The negatively charged sodium alginate (SA) can form complex coacervates with the positively charged KLVFFAE (Aβ16-22, abbreviated as KE) peptide, thereby lowering the nucleation barrier and promoting the assembly of the peptide. As the binding affinity of SA-KE and the dosage of SA decrease, the system shifts from a relatively inefficient template-induced assembly to a highly efficient catalytic assembly before ultimately reverting to slow spontaneous assembly. Therefore, both the affinity as well as the stoichiometry do not follow the intuitive rule that "more is better", but rather there exists an optimal value that maximizes the rate of assembly.

Nanoformulation of Polymyxin E Through Complex Coacervation: A Pharmacokinetic Analysis.

Objectives: Polymyxin E (PME), a polymyxin antibiotic, serves as a final resort against antibiotic resistance. Nephrotoxicity is the primary concern when employing PME. To alleviate this issue, researchers have explored strategies including dosing adjustments and innovative formulations. This study employed complex coacervation to create PME nanoformulations, capitalizing on PME's charge properties. The research question and hypothesis posed pertained to whether neutralization of PME's positive charge during formulation would reduce its antibiotic efficacy and alter its tissue distribution and other pharmacokinetic parameters. Our objective was to evaluate the capability of complex coacervation to mitigate the adverse effects of PME while preserving its antibacterial potency and therapeutic effectiveness. Methods: Three negatively charged polyions: potassium sucrose octasulfate, polytamic acid, and sodium hyaluronate, were used for formulation. We performed characterization on the nanocomplex formed by the polyions and PME. The nanoformulations underwent several tests, including minimum inhibitory concentration, in vivo efficacy on an infected mouse model, pharmacokinetic assessments, tissue distribution, and toxicity. Results: the three polyions formed coacervation complexes with PME at varying charge ratios, yielding nanoparticles smaller than 30 nm with low polydispersity (PDI < 0.3). The results demonstrated that complex coacervation-mediated PME nanoformulations exhibited equivalent or superior antibacterial activity, increased maximum tolerant dose, and fewer adverse reactions in animal tests. Conclusions: Utilizing complex coacervation, PME nanoformulations were developed, demonstrating efficacy in the formulation process. Pharmacokinetic assessments revealed absorption and distribution profiles akin to those of standalone PME. The positive charge inherent in PME causing its toxicity was mitigated after complex coacervation.

Development of Extrudable Hydrogels Based on Carboxymethyl Cellulose-Gelatin Complex Coacervates.

This study investigates the 3D extrusion printing of a carboxymethyl cellulose (CMC)-gelatin complex coacervate system. Various CMC-gelatin coacervate hydrogels were prepared and analyzed to achieve this goal. The impact of the CMC-gelatin ratio, pH, and total biopolymer concentration on coacervation formation and rheological properties was evaluated to characterize the printability of the samples. Turbidity results indicated that the molecular interactions between gelatin and CMC biopolymers are significantly pH-dependent, occurring within the range of pH 3.7 to pH 5.6 for the tested compositions. Confocal Laser Scanning Microscopy (CLSM) confirmed the presence of coacervates as spherical particles within the optimal coacervation range. Scanning electron microscopy micrographs supported the CLSM findings, revealing greater porosity within this optimal pH range. Rheological characterization demonstrated that all CMC-gelatin hydrogels exhibited pseudoplastic behavior, with an inverse correlation between increased coacervation and decreased shear viscosity. Additionally, the coacervates displayed lower tackiness compared to gelatin hydrogels, with the maximum tackiness normal force for various CMC-gelatin ratios ranging from 1 to 15 N, notably lower than the 29 N observed for gelatin hydrogels. Mixtures with CMC-gelatin ratios of 1:15 and 1:20 exhibited the best shear recovery behavior, maintaining higher strength after shear load. The maximum strength of the CMC-gelatin coacervate system was found at a biopolymer concentration of 6%. However, lower biopolymer content allowed for consistent extrusion. Importantly, all tested samples were successfully extruded at 22 ± 2 °C, with the 1:15 biopolymer ratio yielding the most consistent printed quality. Our research highlights the promise of the CMC-gelatin coacervate system for 3D printing applications, particularly in areas that demand precise material deposition and adjustable properties.

Preparation and characterization of microcapsules and tablets for probiotic encapsulation via whey protein isolate-nanochitin complex coacervation

This research delved into the feasibility of utilizing three nanochitin—chitin nanocrystal (CNC), chitin nanofiber (CNF), and chitin nanosphere (CNS) in complexation with whey protein isolate (WPI) to fabricate complex coacervation and create microcapsules for probiotic encapsulation. The results showed that CNC, CNF, and CNS exhibited notable differences in morphologies, dimensions, and properties due to the respective synthesis methodologies. Nevertheless, all of them maintained a positive charge and were capable of assembling into microcapsules with WPI via electrostatic interactions at optimal pHs. The inclusion of Lactobacillus casei (L. casei) during the complex coacervation phase engendered a shell-like formation around the bacterium within the microcapsule, which enhanced probiotic viability and increased colony-forming unit count. Additionally, these probiotic-loading microcapsules were also processed into tablets, displaying robust structural integrity, augmented protective capabilities, and a distinctive sustained-release profile compared to the microcapsules alone. In summary, this study pioneered the employment of nanochitin formulations in complex coacervation to encapsulate L. casei, spearheading an innovative approach to the creation of a compressed probiotic supplement and contributing to the advancement in the design and fabrication of encapsulation vehicles for active ingredients.

Size-controlled antimicrobial peptide drug delivery vehicles through complex coacervation.

Due to the escalating threat of the pathogens' capability of quick adaptation to antibiotics, finding new alternatives is crucial. Although antimicrobial peptides (AMPs) are highly potent and effective, their therapeutic use is limited' as they are prone to enzymatic degradation, are cytotoxic and have low retention. To overcome these challenges, we investigate the complexation of the cationic AMP colistin with diblock copolymers poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMAA) forming colistin-complex coacervate core micelles (colistin-C3Ms). We present long-term stable kinetically controlled colistin-C3Ms that can be prepared from several block lengths of PEO-b-PMAA polymers, where the polymerisation degree governs the overall micellar size. To achieve precise control over size and polydispersity, which are crucial for drug delivery applications, we investigate the hybridisation of PEO-b-PMAA polymers with varying chain lengths or PMAA homopolymers in ternary complex coacervation systems with colistin. This results in size-tunable colistin-C3Ms, ranging, depending on the mixing ratios, from micellar sizes of 26 nm to 100 nm. With size tunability at rather narrow size distributions and high stability, ternary colistin-C3Ms offer potential advancements in C3M drug delivery, paving the way for more effective and targeted treatments for bacterial infections in precision medicine.

Use of pennisetin-casein complex microparticles for Curcuma longa L. extract microencapsulation: Improvement of antioxidant and alpha-amylase inhibitory activities.

This study aimed to use a new protein complex of Pennisetin (Pen) a non gluten protein of pearl millet and casein (Cas), for curcumin (Cur) extract encapsulation using simple or complex coacervation. The potential improvement of Cur antioxidant activities and α-amylase inhibition after encapsulation was explored. Complex microparticles of Pen and Cas with various ratios exhibited average diameters ranging from 1.95±0.32 to 4.66±0.99μm, whereas the Cur loaded microparticles had average diameters ranging from 2.50±0.89 to 5.27±1.17μm. FTIR analysis of Cur loaded microparticles showed the presence of specific peaks at 3757, 1754, 1157 and 856cm-1 related to characteristic functional groups of Cur. This confirms the successful encapsulation of Cur. The major forces involved in microparticles formation were hydrophobic interaction and hydrogen bonding. The best encapsulation efficiency 68% and loading capacity 17% were obtained for the complex microparticles Pen:Cas (ratio 1:1.5). Encapsulating Cur within microparticles of Pen, Cas or their complexes significantly (p˂0.05) enhances their DPPH and ABTS.+ antioxidant activities and their pancreatic α-amylase inhibition percentage. These findings shed light on the potential use of Pen a non gluten protein, in its native form or complexed with Cas, as wall material for hydrophobic or hydrophilic bioactive compounds encapsulation.

Preparation and Characterization of Novel Core-Shell Microcapsules Containing C6F12O for Initial Fire Suppression

As an environmentally friendly and efficient fire extinguishing agent, C6F12O (CFO) is widely used for various types of fires. However, due to its low vaporization temperature and high vapor pressure, it is difficult to store and utilize. In order to reduce the loss and improve fire suppression efficiency of CFO, the complex coacervation method was employed to encapsulate CFO using a polymer material shell composed of gelatin (GE) and arabic gum (GA). The experimental results demonstrated that the preparation parameters had a significant impact on the microcapsule encapsulation efficiency. When the coacervation temperature was set to 40°C, the coacervation pH value was maintained at 3.8, the shell material concentration was adjusted to 8%, and the core-shell mass ratio was kept at 4:1, the microcapsule encapsulation efficiency reached its peak at 26.4%. CFO was successfully encapsulated as confirmed by characterization techniques such as TG, FT-IR, SEM, and 19F-NMR. CFO was released by breaking through the shell when the microcapsules reached the thermal response temperature. Additionally, the fire suppression tests showed that the microcapsules exhibited highly efficient fire extinguishing performance. They decreased the maximum temperature of the n-heptane flame by 196.7°C, lowered the temperature rate by 4.07°C/s, and shortened the self-extinguishing time by 47s. These results provide a new and effective solution for the microencapsulation of heat-sensitive materials and early-stage fire suppression.

Strong electrostatic attraction drives milk heteroprotein complex coacervation

Coacervates of oppositely charged milk proteins are used in functional food development, mainly to encapsulate bioactives. To uncover the driving forces behind coacervates formation, we study the association of lactoferrin and β−lactoglobulin at amino-acid level detail, using molecular simulations. Our findings show that inter-protein electrostatic interactions dominate and are, surprisingly, equally divided between an isotropic part, due to monopole-monopole attraction of the oppositely charged proteins, and an anisotropic part due to uneven surface charge distributions. In good agreement with recent experimental association constants, the calculated protein-protein interaction free energy is strongly dependent on pH and salt concentration. In addition to thermodynamics, we also investigate amino acid contacts in microstates of trimeric and pentameric protein complexes, and identify interaction hot-spots that drive heteroprotein complex coacervation process.

Bioinspired programmable coacervate droplets and self-assembled fibers through pH regulation of monomers.

Phase separation and phase transitions pervade the biological domain, where proteins and RNA engage in liquid-liquid phase separation (LLPS), forming liquid-like membraneless organelles. The misregulation or dysfunction of these proteins culminates in the formation of solid aggregates via a liquid-to-solid transition, leading to pathogenic conditions. To decipher the underlying mechanisms, synthetic LLPS has been examined through complex coacervate formation from charged polymers. Nonetheless, temporal control over phase transitions from prebiotically relevant small organic synthons remains largely unexplored. Herein, we propose utilizing pH modulation to regulate the charge of small molecular building blocks, thereby controlling the LLPS process. Through a bio-inspired, enzyme-mediated pH-regulated reaction, we introduce temporal control over both LLPS and the transition from coacervates to supramolecular polymers. Additionally, by incorporating antagonistic pH modulators, we achieve transient LLPS and further temporal regulation of supramolecular polymer disassembly. Our investigation into pH-regulated LLPS provides a new avenue for exploring the stimuli-responsive, dynamic, and transient nature of LLPS.

The Kinetic Pathways for the Formation of Complex Coacervate Micelles of Antimicrobial Peptides and Block Copolymers

The Kinetic Pathways for the Formation of Complex Coacervate Micelles of Antimicrobial Peptides and Block Copolymers

Polyelectrolyte-Carbon Dot Complex Coacervation.

This Letter presents complex coacervation between the biopolymer diethylaminoethyl dextran hydrochloride (DEAE-Dex) and carbon dots. The formation of these coacervates was dependent on both DEAE-Dex concentration and solution ionic strength. Fluorescence spectroscopy revealed that the blue fluorescence of the carbon dots was unaffected by coacervation. Additionally, microrheological studies were conducted to determine the viscosity of these coacervates. These complex coacervates, formed through the interaction of nanoparticles and polyelectrolytes, hold a promising role for future applications where the combination of optical properties from the carbon dots and encapsulation via coacervation can be leveraged.

Influence of Solvent Dielectric Constant on the Complex Coacervation Phase Behavior of Polymerized Ionic Liquids.

Complex coacervation is an associative phase separation process of oppositely charged polyelectrolyte solutions, resulting in a coacervate phase enriched with charged polymers and a polymer-lean phase. To date, studies on the phase behavior of complex coacervation have been largely restricted to aqueous systems with relatively high dielectric constants due to the limited solubility of most polyelectrolytes, hindering the exploration of the effects of electrostatic interactions from differences in solvent permittivity. Herein, we prepare two symmetric but oppositely charged polymerized ionic liquids (PILs), consisting of poly[1-[2-acryloyloxyethyl]-3-butylimidazolium bis(trifluoromethane)sulfonimide] (PAT) and poly[1-ethyl-3-methylimidazolium 3-[[[(trifluoromethyl)sulfonyl]amino]sulfonyl]propyl acrylate] (PEA). Due to the delocalized ionic charges and their chemical structure similarity, both PAT and PEA are soluble in various organic solvents with a wide range of dielectric constants, ranging from 16.7 (hexafluoro-2-propanol (HFIP)) to 66.1 (propylene carbonate (PC)). Notably, no significant correlation is observed between the solvent dielectric constant and the phase diagram of the complex coacervation of PILs. Most organic solvents lead to similar phase diagrams and salt resistances regardless of their dielectric constants, except two protic solvents (HFIP and 2,2,2-trifluoroethanol (TFE)) showing significantly low salt resistances compared to the others. The low salt resistance in these protic solvents primarily arises from strong hydrogen bonding between PILs and solvents as evidenced by 1H NMR and small-angle neutron scattering (SANS) experiments. Our finding suggests that for the coacervation of PILs, particularly those with delocalized and weak charge interactions, entropy from the counterion release and polymer-solvent interaction χ parameter play a more important role than the electrostatic interactions of charged molecules, rendered by the dielectric constant of the solvent medium.

Microencapsulation of turmeric extract by complex coacervation: in vitro, gastrointestinal digestion and stability study during kefir storage

Microencapsulation of turmeric extract by complex coacervation: in vitro, gastrointestinal digestion and stability study during kefir storage

Influence of Polymer Architecture on the Structure of Complex Coacervate Core Micelles: AB + AC versus AB + C Systems.

Complex coacervate core micelles (C3Ms), formed through electrostatic interactions between oppositely charged block copolyelectrolytes, are effective delivery vehicles for hydrophilic biomacromolecules. This study investigates the impact of polymer architecture on the C3Ms structure by blending homopolyelectrolytes and diblock copolyelectrolytes as anionic counterparts for cationic diblock copolyelectrolytes. Our results show that the micellar structure, including core size, aggregation number, and corona characteristics, is precisely controlled by the fraction of homopolyelectrolytes. C3Ms formed by the AB + C system have larger core dimensions and aggregation numbers but lower corona brush densities compared to AB + AC systems. These findings highlight that the spatial constraints of polyelectrolytes play a crucial role in determining micellar structure, which can be further understood by balancing the free energies contributed by core block stretching and interfacial tension.

Theabrownin/whey protein isolate complex coacervate strengthens C2C12 cell proliferation via modulation of energy metabolism and mitochondrial apoptosis.

Theabrownin (TB)-whey protein isolate (WPI) complex coacervates (TW) were firstly prepared to investigate the regulatory effects on skeletal muscle. The binding of TB to WPI reached saturation with the strongest electrostatic interaction at the ratio of 10:1. The formation of TW was driven by electrostatic interactions with the aid of hydrogen bonding and hydrophobic interactions, and the digestion behavior of TW was investigated based on in vitro gastrointestinal and CaCO2 cell models. The regulatory effect of TW on muscle cells was investigated by C2C12 cell assay. Cell cycle analysis showed that TW promoted the transition of skeletal muscle cells from proliferative state to differentiated state. Immunofluorescence and gene expression revealed that TW positively regulated myogenic regulatory factors, contributing to myofiber formation. Moreover, TW activated the intracellular TCA cycling and oxidative phosphorylation, providing energy for skeletal muscle regeneration and repair. Mechanistically, TW inhibited the release of cytochrome C from mitochondria to cytoplasm through the Bcl-2/Cytochrome C/Cleaved-Caspase-3 pathway, exhibiting a protective effect on skeletal muscle cells. In the future, the molecular mechanism of TW enhancing skeletal muscle function should be validated through aging animal models and clinical trials and expand its therapeutic application for muscle health in functional food and dietary supplements.

Enhancing the stability of krill oil through microencapsulation with endogenous krill protein and chitosan and application in senior milk powder.

Krill oil (KO) exhibits several biological actions, particularly providing distinct advantages for cognitive health in the aged. Nonetheless, its inadequate water solubility, pronounced flavor, and vulnerability to oxidative degradation restrict its utilization in the food sector. Encapsulation provides a solution, and the study of natural, suitable wall materials is crucial. This study employs endogenous krill protein (KP) and krill chitosan (CS) as encapsulating agents. It utilizes a complex coacervation technique to encapsulate KO, thereby broadening its application and successfully incorporating it into senior milk powder. The microcapsules have the best properties when the KP + CS complex to krill oil ratio is 1:1. They are able to encapsulate 77.96 % of the oil, stay stable at high temperatures (with little mass loss), and stay stable over time (with a peroxide value increase of only 4.51 mmol/kg). Moreover, the release rate in simulated intestinal conditions reaches 83.26 %. When added at 0.8 % to senior milk powder, it imparts the highest nutritional value without significantly affecting the flavor. Thus, this study provides valuable insights for enhancing the stability of krill oil and its application in the food industry.

Construction of multifunctional hydrogel containing pH-responsive gold nanozyme for bacteria-infected wound healing

Nanozymes have become promising alternative antibacterial agents for bacteria-infected wounds. In this study, fucoidan-confined gold nanoparticles (Fuc@AuNPs) are developed by in situ reduction, and stabilized by sulfate groups of fucoidan. Fuc@AuNPs exhibit pH-responsive catalytic activity that can mimic oxidase (OXD) under acidic bacterial infection conditions and mimic superoxide dismutase (SOD) under normal physiological conditions. The OXD-like catalytic activity of Fuc@AuNPs generates active singlet oxygen (1O2), exhibiting effective antibacterial properties against both Gram-negative E. coli and Gram-positive S. aureus. Fuc@AuNPs and aldehyde grafted saponin incorporate with chitosan to form a hybrid hydrogel. This hydrogel exhibits superior mechanical, adhesive, and self-healing properties due to electrostatic complex coacervation networks and dynamic covalent Schiff base reactions. Animal experiments show that the hydrogel aids S. aureus-infected skin wound healing by reducing bacterial infection and promoting granulation tissue formation without causing excessive ROS-induced inflammation. This study presents the design of multifunctional nanozymes and bioactive hydrogels as a promising wound healing dressing for biomedical applications.

Enhanced nutraceutical potential of cannabidiol derived from industrial hemp using plant based complex coacervates

Cannabidiol (CBD) from industrial hemp (Cannabis sativa L.) is a highly promising bioactive compounds with multifarious health benefits. However, its poor chemical stability during storage and digestion and low bioavailability impedes its potential food and pharmaceutical applications. Hence, this research investigated the potential of hemp protein isolate–gum Arabic (HPI–GA) complex coacervates in improving the storage stability, lipid digestibility, and bioaccessibility of CBD. State diagram and charge analysis confirmed the complex coacervate formation between HPI and GA at a 5:1 mixing ratio and pH 3. These HPI–GA complex coacervates were utilized for encapsulating CBD at varying wall-to-core ratios (6:1, 8:1, and 10:1), and their performance was compared to controls. The HPI–GA coacervates exhibited significantly higher encapsulation efficiency compared to the controls, reaching up to 91.85 % with an increasing wall-to-core ratio. As revealed by SEM and CLSM, coacervate-derived spray-dried microcapsules displayed larger particle sizes, minimal surface CBD content, and a uniform spherical shape than controls. These properties allowed the coacervates to effectively maintain the chemical stability of CBD for 75 days under light and temperature exposure (25 or 40°C). The INFOGEST gastrointestinal stimulation digestion results revealed that HPI–GA coacervates could retain the chemical stability of CBD, release free fatty acids in a controlled manner, and consequently increase the bioaccessibility of CBD up to 61.04 %. These findings indicate that the chemical stability and bioavailability of CBD could be improved using HPI–GA complex coacervation. The gleaned results from this research would facilitate the development of CBD-based functional foods and pharmaceuticals.