Добірка наукової літератури з теми "Dynamic coacervates"

This contribution is aimed at extending our previous findings on the formation and stability of chitosan/hyaluronan-based complex coacervates. Colloids are herewith formed by harnessing electrostatic interactions between the two polyelectrolytes. The presence of tiny amounts of the multivalent anion tripolyphosphate (TPP) in the protocol synthesis serves as an adjuvant “point-like” cross-linker for chitosan. Hydrochloride chitosans at different viscosity average molar mass, M v ¯ , in the range 10,000–400,000 g/mol, and fraction of acetylated units, FA, (0.16, 0.46 and 0.63) were selected to fabricate a large library of formulations. Concepts such as coacervate size, surface charge and homogeneity in relation to chitosan variables are herein disclosed. The stability of coacervates in Phosphate Buffered Saline (PBS) was verified by means of scattering techniques, i.e., Dynamic Light Scattering (DLS) and Small-Angle X-ray Scattering (SAXS). The conclusions from this set of experiments are the following: (i) a subtle equilibrium between chitosan FA and M v ¯ does exist in ensuring colloidal stability; (ii) once diluted in PBS, osmotic swelling-driven forces trigger the enlargement of the polymeric mesh with an ensuing increase of coacervate size and porosity.

A miscibility study between oppositely charged polyelectrolytes, namely hyaluronic acid and a lactose-modified chitosan, is here reported. Experimental variables such as polymers’ weight ratios, pH values, ionic strengths and hyaluronic acid molecular weights were considered. Transmittance analyses demonstrated the mutual solubility of the two biopolymers at a neutral pH. The onset of the liquid-liquid phase separation due to electrostatic interactions between the two polymers was detected at pH 4.5, and it was found to be affected by the overall ionic strength, the modality of mixing and the polymers’ weight ratio. Thorough Dynamic Light Scattering (DLS) measurements were performed to check the quality of the formed coacervates by investigating their dimensions, homogeneity and surface charge. The whole DLS results highlighted the influence of the hyaluronic acid molecular weight in affecting coacervates’ dispersity and size.

Herein, we synthetized and characterized polysaccharide-based complex coacervates starting from two water-soluble biopolymers, i.e., hydrochloride chitosans and sodium hyaluronan. We used chitosans encompassing a range of molecular weights from 30,000 to 400,000 and showing different fraction of acetylated units (i.e., FA = 0.16, 0.46, and 0.63). This set of chitosans was mixed with a low molecular weight hyaluronan to promote electrostatic interactions. Resulting colloids were analyzed in terms of size, polydispersity and surface charge by Dynamic Light Scattering. The weight ratio between the two polyelectrolytes was studied as additional parameter influencing the liquid-liquid phase separation. Main results include the following: the polymers weight ratio was fundamental in dictating the colloids surface charge, whereas chitosan physical-chemical features influenced the dimension and homogeneity of colloids. This contribution presents additional understanding of the complex coacervation between these two oppositely charged polysaccharides, with the potential translation of present system in food and biomedical sectors.

Coacervation is a common phenomenon in natural polymers and has been applied to synthetic materials systems for coatings, adhesives, and encapsulants. Single-component coacervates are formed when block polyampholytes exhibit self-coacervation, phase separating into a dense liquid coacervate phase rich in the polyampholyte coexisting with a dilute supernatant phase, a process implicated in the liquid–liquid phase separation of intrinsically disordered proteins. Using fully fluctuating field-theoretic simulations using complex Langevin sampling and complementary molecular-dynamics simulations, we develop molecular design principles to connect the sequenced charge pattern of a polyampholyte with its self-coacervation behavior in solution. In particular, the lengthscale of charged blocks and number of connections between oppositely charged blocks are shown to have a dramatic effect on the tendency to phase separate and on the accessible chain conformations. The field and particle-based simulation results are compared with analytical predictions from the random phase approximation (RPA) and postulated scaling relationships. The qualitative trends are mostly captured by the RPA, but the approximation fails catastrophically at low concentration.

Les cellules vivantes sont des systèmes compartimentés dynamiques et hors équilibre. Reproduire cette compartimentation dynamique dans des systèmes artificiels revêt un intérêt grandissant en matière molle et biologie synthétique. Le phénomène de séparation de phase liquide-liquide (LLPS) est particulièrement crucial pour produire des compartiments dynamiques en biologie. Ce processus sous-tend la formation de condensats biomoléculaires dans les cellules et a été proposé jouer un rôle dans l'émergence des protocellules aux origines de la vie. In vitro, des microgouttelettes de coacervat, assemblées à partir de polyions de charges opposées dans l'eau, sont utilisées pour émuler ces LLPS bio-inspirées. La coacervation a été largement étudiée à l'équilibre thermodynamique, mais les études expérimentales de coacervats dynamiques restent rares. En raison de sa résolution spatiotemporelle, la lumière est particulièrement intéressante pour déclencher des comportements dynamiques dans des coacervats. La récente conception de coacervats photostimulables à base d’azobenzènes a ouvert la voie au contrôle dynamique de la dissolution et la formation de coacervats par la lumière. La dynamique de ces processus est encore mal comprise. L'objectif principal de cette thèse est d'étudier la dynamique de la dissolution, de la formation et de déformations de ces coacervats ADN/azobenzène photostimulables grâce à la microfluidique. Après avoir caractérisé la cinétique de la photoisomérisation des azobenzènes, nous produisons ces coacervats photostimulables à l'intérieur de gouttelettes eau-dans-huile par voie microfluidique. Nous étudions la relation entre la taille des coacervats, la concentration d'azobenzènes et leur isomérisation pour construire le diagramme de phase de la coacervation ADN/azobenzène. Nous examinons ensuite la cinétique de la dissolution et la reformation des coacervats sous lumière UV et visible, respectivement, à différentes tailles de coacervats et intensités lumineuses pour déchiffrer le mécanisme des deux processus. Enfin, nous démontrons que des déformations complexes des coacervats émergent dans des conditions optimales de co-illumination
Living cells are dynamic compartmentalized systems that operate under non-equilibrium conditions. Emulating such dynamic compartmentalization in artificial systems is gaining attention in soft matter and bottom-up synthetic biology. Liquid-liquid phase separation (LLPS) is particularly key to produce dynamic compartments in biology. This phenomenon underlies the formation of biomolecular condensates in cells and has been hypothesized to play a role in the emergence of protocells at the origins of Life. In vitro, coacervate microdroplets assembled from oppositely charged polyions in water are used to emulate these bio-inspired LLPS processes. Coacervation has been extensively studied at thermodynamic equilibrium, but experimental investigations of dynamic coacervates remain scarce. Given its spatiotemporal resolution, light is particularly interesting to trigger dynamic behaviors in coacervate droplets. The recent design of light-responsive coacervates based on azobenzene photoswitches has opened avenues for dynamically controlling the dissolution and formation of coacervates with light. The dynamics of these processes are yet poorly understood. The main objective of this thesis is to investigate the dynamics of light-actuated DNA/azobenzene coacervate decay, growth and deformations using droplet-based microfluidics. After characterizing the azobenzene photoisomerisation kinetics, we produce photoswitchable coacervates within water-in-oil droplets using microfluidics. We study the relationship between coacervate size, azobenzene concentration and isomerization to build the phase diagram of DNA/azobenzene coacervation. We then investigate the kinetics of coacervate dissolution and reformation under UV and visible light, respectively, at varying coacervate sizes and light intensities to decipher the mechanism of the two processes. Ultimately, we demonstrate complex non-equilibrium coacervate deformations under optimal co-illumination conditions

Abstract Cells are assembled from hierarchically organized macromolecules, forming very complex, crowded, integrated, and self-organized networks of cytomatrix components known as protoplasts or cytoplasm. These assembled, ordered biological macromolecules embody historical aspects of cellular organization. Inherited patterns of structural templating derive from the very first ancient cells as initial forms of templated self-assembly, thereafter continuously reiterating through cell divisions. Clusters of intracellular ordered macromolecules form nano-protoplast units supporting nano-intentionality that represents a kind of subcellular proto-mind. In the evolution of first proto-cells, semi-independent units could have acted as a coacervate stage (small liquid droplets of two immiscible liquid phases) within cellular evolution. Moveable electrons and charged molecules generate a redox code which, together with the bioelectric code, comprise the bioelectricity-based cellular senomic fields. Excitable plasma membrane-generated bioelectric fields and associated dynamic actin filaments are closely integrated via endocytic vesicle recycling, and generate systemic long-distance signals known as bioelectrical action potentials.