Interfacial Liquid–Liquid Phase Separation-Driven Polymerization-Induced Electrostatic Self-Assembly

Coacervate-Assisted Polymerization-Induced Self-Assembly of Chiral Alternating Copolymers into Hierarchical Bishell Capsules with Sub-5 nm Ultrathin Lamellae

Hierarchical self-assembly of synthetic polymers in solution represents one of the sophisticated strategies to replicate the natural superstructures which lay the basis for their superb functions. However, it is still quite challenging to increase the degree of complexity of the as-prepared assemblies, especially in a large scale. Liquid-liquid phase separation (LLPS) widely exists in cells and is assumed to be responsible for the formation of many cellular organelles without membranes. Herein, through integrating LLPS with the polymerization-induced self-assembly (PISA), a coacervate-assisted PISA (CAPISA) methodology to realize the one-pot and scalable preparation of hierarchical bishell capsules (BCs) from nanosheets with ultrathin lamellae phase (sub-5 nm), microflakes, unishell capsules to final BCs in a bottom-up sequence is presented. Both the self-assembled structure and the dynamic formation process of BCs have been disclosed. Since CAPISA has combined the advantages of coacervates, click chemistry, interfacial reaction and PISA, it is believed that it will become a promising option to fabricate biomimetic polymer materials with higher structural complexity and more sophisticated functions.

Like-Charge PISA: Polymerization-Induced Like-Charge Electrostatic Self-Assembly

We report the use of l-aspartic acid chiral ionic hydrogen bonds to drive liquid-liquid phase separation (LLPS) and precision two-dimensional electrostatic self-assembly in photo-RAFT aqueous polymerization-induced self-assembly (photo-PISA). Homopolymerization can yield salt-resistant, 3 nm ultrafine fibril-structured 5 nm ultrathin lamellae via LLPS, a left-to-right-handed chirality transition, and a droplets-to-lamellae transition. Like-charge block copolymerization leads to supercharged yet identical fibril-structured ultrathin lamellae, also, via LLPS, the left-to-right chirality transition and the droplets-to-lamellae transition. Ultrafine structures maintain intactness upon the seeded polymerization of the oppositely charged monomer. This work demonstrates that amino acid chiral ionic hydrogen bonds are powerful for the precision synthesis of salt-resistant ultrathin membrane nanomaterials.

Linear and Star Block Copolymer Nanoparticles Prepared by Heterogeneous RAFT Polymerization Using an ω,ω-Heterodifunctional Macro-RAFT Agent

Herein, an ω,ω-heterodifunctional macromolecular reversible addition-fragmentation chain transfer (macro-RAFT) agent containing two different RAFT end groups was synthesized and employed to mediate aqueous photoinitiated RAFT dispersion polymerization of a methacrylic monomer. Because of the different RAFT controllability of two RAFT end groups toward methacrylic monomers, the RAFT end group with good controllability dominated the polymerization while the other RAFT end group with poor controllability was unreacted, leading to the formation of linear block copolymers. Because of the unique structure of the linear block copolymers, a diverse set of block copolymer nanoparticles with rich RAFT groups at the interface of the hydrophilic corona/the hydrophobic core were successfully prepared. Finally, μ-A(BC)C miktoarm star block copolymer nanoparticles were prepared by RAFT seeded emulsion polymerization of an acrylic monomer, which enables the further morphological control over polymer nanoparticles. We believe that the utilization of an ω,ω-heterodifunctional macro-RAFT agent in heterogeneous RAFT polymerization will offer considerable opportunities for the rational synthesis of well-defined molecular architectures and polymer nanoparticles.

(Bio)degradable and Biocompatible Nano-Objects from Polymerization-Induced and Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) techniques have emerged as powerful approaches to produce a broad range of advanced synthetic nano-objects with high potential in biomedical applications. PISA produces nano-objects of different morphologies (e.g., spheres, vesicles and worms), with high solids content (∼10-50 wt %) and without additional surfactant. CDSA can finely control the self-assembly of block copolymers and readily forms nonspherical crystalline nano-objects and more complex, hierarchical assemblies, with spatial and dimensional control over particle length or surface area, which is typically difficult to achieve by PISA. Considering the importance of these two assembly techniques in the current scientific landscape of block copolymer self-assembly and the craze for their use in the biomedical field, this review will focus on the advances in PISA and CDSA to produce nano-objects suitable for biomedical applications in terms of (bio)degradability and biocompatibility. This review will therefore discuss these two aspects in order to guide the future design of block copolymer nanoparticles for future translation toward clinical applications.

Block Copolymer Vesicles with Tunable Membrane Thicknesses and Compositions Prepared by Aqueous Seeded Photoinitiated Polymerization-Induced Self-Assembly at Room Temperature

Block copolymer vesicles with diverse functionalities and intrinsic hollow structures have received considerable attention due to their broad applications in biomedical fields, including drug delivery, bioimaging, theranostics, gene therapy, etc. However, efficient preparation of block copolymer vesicles with tunable membrane thicknesses and compositions under mild conditions is still a challenge. Herein, we report an aqueous seeded photoinitiated polymerization-induced self-assembly (photo-PISA) for the precise preparation of block copolymer vesicles at room temperature. By changing the total degree of polymerization (DP) of the hydrophobic block in seeded photo-PISA, one can easily tune the membrane thickness without compromising the morphology of vesicles. Moreover, by adding different comonomers such as hydrophobic monomers, hydrophilic monomers, and cross-linkers into seeded photo-PISA, vesicles with different compositions could be prepared without compromising the morphology and colloidal stability. Polymerization kinetics show that seeded photo-PISA can skip the step of in situ self-assembly with a short homogeneous polymerization stage being observed. To demonstrate potential biological applications, enzymatic nanoreactors were constructed by loading horseradish peroxidase (HRP) inside vesicles via seeded photo-PISA. The enzymatic properties of these nanoreactors could be easily regulated by changing the membrane thickness and hydrophobicity. It is expected that this method can provide a facile platform for the precise preparation of block copolymer vesicles that may find applications in different fields.

Two-Dimensional Polymerization-Induced Electrostatic Self-Assembly via C12-Polyelectrolyte Lamellar Template

We present a template strategy for precision synthesis of “complex coacervates-in-dodecyl atmosphere” ultrathin lamellae possessing exceptional shape-preservation and charge-tolerance properties.

Pyridine-containing block copolymeric nano-assemblies obtained through complementary hydrogen-bonding directed polymerization-induced self-assembly in water

A diversity of pyridine-containing polymeric nanomaterials with controllable structures and multiple responses were developed through complementary hydrogen-bonding directed polymerization-induced self-assembly in aqueous solution.

Liquid-Phase Condensation via Macromolecular Crowding in Polymerization-Induced Electrostatic Self-Assembly

Macromolecular crowding plays a key role in liquid-phase condensation of proteins and membraneless organelles yet is largely unexplored for artificial liquid materials. Herein, we present a strategy for direct access to multiphase liquid condensates with individual charged/neutral subdomains, by introducing macromolecular crowding to our previous protocol of liquid-liquid phase-separation-driven polymerization-induced electrostatic self-assembly (LLPS-PIESA). We show that reversible addition fragmentation chain transfer (RAFT) aqueous dispersion photo-copolymerization of a charged monomer with a specific neutral monomer, in the presence of a polar macrochain transfer agent (CTA) and an oppositely charged polyion, can induce self-sorting and macromolecular crowding. LLPS-PIESA proceeds via liquid-phase condensation of as-assembled nascent clusters up to biologically important nanostructured multiphase condensates with individual charged/neutral subdomains.