Vesicle Structure and Formation of AB/BC Amphiphile Mixture Based on Hydrogen Bonding in a Selective Solvent: A Monte Carlo Study

Asymmetric polymersomes, from the formation of asymmetric membranes to the application on drug delivery

Nano drug delivery systems have attracted researchers' growing attention and are gradually emerging into the public views. More and more nano-formulations are being approved for marketing or clinical use, representing the field's booming development. Copolymer self-assembly systems such as micelles, nanoparticles, polymersomes occupy a prominent position in the field of nano-drug delivery carriers. Among them, polymersomes, unlike micelles or nanoparticles, resemble liposomes' structure and possess large internal hollow hydrophilic reservoirs, allowing them to carry hydrophilic drugs. Nevertheless, their insufficient drug loading efficiency and unruly self-assembly morphology have somewhat constrained their applications. Especially for the delivery of biomacromolecule such as peptides, the encapsulation efficiency is always considered to be a formidable obstacle, even if the enormous hydrophilic core would render the polymersomes to have considerable potential in this regard. Reassuringly, the emergence of asymmetric polymersomes holds the prospect of solving this problem. With the development of synthetic technology and a deeper understanding of the self-assembly process, the asymmetric polymersomes which are with different inner and outer shell composition have been gradually recognized by researchers. It has made possible elevated drug loading, more controllable assembly processes and release performance. The internal hydrophilic blocks different from the outer shell could be engineered to have a more remarkable affinity to the cargos or could contain a non-watery aqueous phase to enable the thermodynamically preferred encapsulation of cargos, which would allow for a substantial improvement in drug encapsulation efficiency compared to the conventional approach. In this paper, we aim to deepen the understanding to asymmetric polymersomes and lay the foundation for the development of this field by describing four main elements: the mechanism of their preparation and asymmetric membrane formation process, the characterization of asymmetric membranes, the efficient drug loading, and the special stimulus-responsive release mechanism.

Simulation Study of Process-Controlled Supramolecular Block Copolymer Phase Separation with Reversible Reaction Algorithm

A supramolecular diblock copolymer formed by reversible bonds between the two blocks shows a rich microphase separation behavior and has great application potential in stimuli-responsive materials. We propose a novel method to describe supramolecular reactions in dissipative particle dynamics, which includes a reversible reaction to accurately reproduce the strength, saturation, and dynamic properties of the reversible bonds in the simulations. The thermodynamic properties and dynamic processes of the supramolecular diblock copolymer melts in both equilibrium and non-equilibrium states were studied using this method. The simulation results show that the method can faithfully characterize phase behaviors and dynamic properties of supramolecular diblock copolymer melts, especially in a non-equilibrium state, which provides a novel tool to unveil self-assembly mechanism and describe the properties of supramolecular block copolymers.

Confined co-assembly of AB/BC diblock copolymer blends under 3D soft confinement

Compared to synthesizing a new block copolymer, blending of two types of block copolymers or a block copolymer and a homopolymer is a simple yet effective approach to create new self-assembled nanostructures. Here, we apply Monte Carlo (MC) simulations to mimic the co-assembly of AB/BC diblock copolymer blends within a three-dimensional (3D) soft confined space, which corresponds to the co-assembly confined in an emulsion droplet in experiment. The confined co-assemblies of four types of block copolymer blends at different block ratios, i.e., A8B8/B8C8, A6B10/B10C6, A12B4/B4C12 and A12B4/B10C6, are investigated by MC simulations. The simulation results reveal that the ratio of different types of blocks and the polymer-solvent interactions between the different blocks and the solvent determine the final self-assembled nanostructures. By tailoring these two controlling parameters, we not only reproduced some classic nanostructures, i.e., pupa-, onion-, and bud-like particles, but also predicted some unconventional nanostructures, such as patch-, Janus-, peanut-, disc- and snowman-like particles via MC simulations.

Supramolecular multicompartment gels formed by ABC graft copolymers: high toughness and recovery properties

We conceptually design multicompartment gels with supramolecular characteristics by taking advantage of amphiphilic ABC graft copolymers. The ABC graft copolymers contain a solvophilic A backbone and solvophobic B and C grafts, where the C grafts interact with each other via hydrogen bonds. The mechanical properties of supramolecular multicompartment gels under uniaxial tension are studied by coupling dissipative particle dynamics simulations with the nonequilibrium deformation technique. The results show that the supramolecular multicompartment gels exhibit high toughness and recovery properties, while their stiffness is maintained. Due to the physical origin, the superior mechanical properties of supramolecular gels have a tight relation with the structural relaxation of grafts and the association-disassociation dynamics of hydrogen bonds. In addition, the toughness of the multicompartment gels can be further tuned by adjusting the strength and directivity of the hydrogen bonds. The present work unveils the physical origin of the distinct mechanical properties of supramolecular gels, which may provide useful guidance for designing functional gels with superior toughness.

Stepwise study on Janus-like particles fabricated by polymeric mixtures within soft droplets: a Monte Carlo simulation

Janus particles were fabricated using different polymer mixtures and the self-assembly behavior for different particles was compared.

Asymmetric vesicle constructed by AB/CB diblock copolymer mixture and its behavior: a Monte Carlo study

Asymmetric vesicles constructed from AB/CB diblock copolymer mixture in a selective solvent for A and C blocks are studied using Monte Carlo simulation. The effects of the mixed ratio of the two diblock copolymers, the solution pH, and the hydrophilic chain length on the distributions of hydrophilic blocks on the surfaces of asymmetric vesicles are studied systematically. The simulation results show that asymmetric vesicle, in which the inner and outer surfaces are constructed from different hydrophilic blocks, can be obtained from AB/CB diblock copolymer mixture. The formation of ABC or CBA three-layer asymmetric vesicle depends on the composition of the mixture, the chain length of hydrophilic block, and the solution pH. The hydrophilic block with the same charge (induced by the solution pH), or longer chain length, or lower content in the mixture is more likely to distribute on the outer surface of the vesicle. Moreover, the transition from ABC to CBA three-layer asymmetric vesicle in which blocks C are charged can occur by adjusting the composition of the mixture. On the other hand, the investigations of the interfacial energy density of asymmetric vesicles elucidate the distribution regularity of hydrophilic blocks. When the hydrophilic chain lengths are equal, the difference between the outer and inner interfacial energies is the main factor that determines the asymmetric vesicle structures; that is, the distributions of different hydrophilic blocks on asymmetric vesicles always tend to gain the largest difference between the outer and inner interfacial energies. However, when the hydrophilic chain lengths are different, the chain conformational entropy becomes the main driving force for determining the distribution of hydrophilic blocks on asymmetric vesicles.