Disassembly of Amphiphilic AB Block Copolymer Vesicles in Selective Solvents: A Molecular Dynamics Simulation Study

Abstract

The disassembly of amphiphilic AB block copolymers in selective solvents by molecular dynamic simulation is investigated in this study. The disassembly from one initial assembly into different aggregates is controlled by thermodynamic processes that depend on the instability of the system. Based on this strategy, B x can be converted to A x in A 2 B x B 18−x diblock copolymers (where x is a variable integer) by external stimuli such as light and pH. The A 2 B x B 18−x copolymer vesicle in a stable state becomes unstable when A 2 B x B 18−x copolymers are converted to A 2 A x B 18−x copolymers. The simulation results show that the instability of the system induced by B x conversion is a function of x, and the larger x, the higher the instability. The assembly can thereby disassemble from the initial vesical into a ring, rod, sphere, disorder aggregate, as well as completely dispersed polymer chains by increasing x. Notably, some of those structures cannot be obtained by self-assembly from the initial homogeneous state. Taking x = 5 as an example, toroid micelles are obtained by converting A 2 B 5 B 13 into A 7 B 13 , whereas they are not obtained by selfassembly from a homogeneous state for the A 7 B 13 block copolymer under the same conditions. Moreover, in addition to the x value, the B x conversion rate and the conversed amount of polymer chains can also affect the disassembly. Toroid micelles are impossible to form under a slow B x conversion rate and when the conversion amount is less than 75% of the total copolymer chains.

Polymersomes in Drug Delivery─From Experiment to Computational Modeling

“…Quantifying parameters such as free energy, block compatibility, and surface tension between aggregate regions is typically experimentally challenging, but computational insights grant us a deeper understanding of the mechanism governing self-assembly behaviors . Changes in compatibility between polymers and solvents and between block copolymers can disrupt the energy balance and result in a self-assembly transition. ,− These are investigated through BD, DPD, and Martini models. , Simulations using DPD and density functional theory showed that increasing the solvent affinity of the hydrophilic blocks or the polymer concentration in the system led to an expansion of the interfacial area of the micelles. This resulted in a transition from spherical micelles to cylindrical micelles, and eventually to vesicle structures. , Song and co-workers reported self-consistent field theory based on DPD simulation that by increasing the solubility of polymer hydrophilic building blocks, aggregate morphology could shift from simple vesicles to various multicompartment vesicles .…”

A dissipative particle dynamics simulation of controlled loading and responsive release of theranostic agents from reversible crosslinked triblock copolymer vesicles

“…This is why block copolymer vesicles have become indispensable as theranostic drug carriers in pursuit of enhanced curative effects. [6][7][8] To enhance the structural stability of the block copolymer vesicles, the shell can be chemically crosslinked. 9,10 The migration of copolymer segments in the crosslinked shell can be limited, thus effectively avoiding drug leakage when subjected to environmental disturbances.…”

“…This is why block copolymer vesicles have become indispensable as theranostic drug carriers in pursuit of enhanced curative effects. 6–8…”

Vesicle Morphogenesis in Amphiphilic Triblock Copolymer Solutions

“…Shape transitions in BCP systems are often interpreted using simple geometric models based on the elegant packing parameter concept [13]. However, experimental [16,17,[20][21][22][23][24][25] and molecular/mesoscopic simulation [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] studies have revealed an extraordinary diversity of BCP morphologies with complex topological and interfacial characteristics. The self-assembly of BAB triblock copolymer solutions, in which B and A represent the solvophobic and solvophilic blocks, respectively, was investigated by Kotaka et al [43], who reported that poly(methylmethacrylate)-polystyrene-poly(methylmethacrylate) BCPs in a toluene-p-cymene (pCY) solvent mixture with high pCY content form highly branched structures.…”

“…Self-consistent field theory [30][31][32], dissipative particle dynamics (DPD) [33][34][35][36][37][38][39][40][41], and coarse-grained molecular dynamics (CGMD) simulations with prescribed or biased initial conditions [28,29,42] have been employed to study bilayer-to-vesicle transitions and the kinetics of copolymer exchange between self-assembled aggregates in BCP solutions. Further, CGMD simulations that account for solvent-mediated hydrophobic interactions have been implicitly used to study differences in copolymer architecture (linear vs. bottlebrush) with respect to self-assembly in solution [68] and the shape deformation of polymersomes induced by osmotic pressure stress [69].…”