Fission of giant vesicles accompanied by hydrophobic chain growth through polymerization-induced self-assembly

Modern Trends in Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for producing colloidal dispersions of block copolymer particles with desired morphologies. Currently, PISA can be carried out in various media, over a wide range of temperatures, and using different mechanisms. This method enables the production of biodegradable objects and particles with various functionalities and stimuli sensitivity. Consequently, PISA offers a broad spectrum of potential commercial applications. The aim of this review is to provide an overview of the current state of rational synthesis of block copolymer particles with diverse morphologies using various PISA techniques and mechanisms. The discussion begins with an examination of the main thermodynamic, kinetic, and structural aspects of block copolymer micellization, followed by an exploration of the key principles of PISA in the formation of gradient and block copolymers. The review also delves into the main mechanisms of PISA implementation and the principles governing particle morphology. Finally, the potential future developments in PISA are considered.

Polymer Self-Assembly Induced Enhancement of Ice Recrystallization Inhibition

Ice binding proteins modulate ice nucleation/growth and have huge (bio)technological potential. There are few synthetic materials that reproduce their function, and rational design is challenging due to the outstanding questions about the mechanisms of ice binding, including whether ice binding is essential to reproduce all their macroscopic properties. Here we report that nanoparticles obtained by polymerization-induced self-assembly (PISA) inhibit ice recrystallization (IRI) despite their constituent polymers having no apparent activity. Poly(ethylene glycol), poly(dimethylacrylamide), and poly(vinylpyrrolidone) coronas were all IRI-active when assembled into nanoparticles. Different core-forming blocks were also screened, revealing the core chemistry had no effect. These observations show ice binding domains are not essential for macroscopic IRI activity and suggest that the size, and crowding, of polymers may increase the IRI activity of "non-active" polymers. It was also discovered that poly(vinylpyrrolidone) particles had ice crystal shaping activity, indicating this polymer can engage ice crystal surfaces, even though on its own it does not show any appreciable ice recrystallization inhibition. Larger (vesicle) nanoparticles are shown to have higher ice recrystallization inhibition activity compared to smaller (sphere) particles, whereas ice nucleation activity was not found for any material. This shows that assembly into larger structures can increase IRI activity and that increasing the "size" of an IRI does not always lead to ice nucleation. This nanoparticle approach offers a platform toward ice-controlling soft materials and insight into how IRI activity scales with molecular size of additives.

PISA: construction of self-organized and self-assembled functional vesicular structures

PISA reaction networks alone, integrated with other networks, or designing properties into the amphiphiles confer functionalities to the supramolecular assemblies.

A polymerization-induced self-assembly process for all-styrenic nano-objects using the living anionic polymerization mechanism

By combination of the living anionic polymerization (LAP) mechanism with the polymerization-induced self-assembly (PISA) technique, the all-styrenic diblock copolymer poly(p-tert-butylstyrene)-b-polystyrene (PtBS-b-PS) based LAP PISA was successfully developed.

Perforated vesicles composed of amphiphilic diblock copolymer: new artificial biomembrane model of nuclear envelope

With the aim of creating a new artificial model of a biomembrane for the nuclear envelope, perforated vesicles were prepared employing an amphiphilic diblock copolymer of poly(methacrylic acid)-block-poly(methyl methacrylate-random-methacrylic acid-random-2,2,6,6-tetramethyl-4-piperidyl methacrylate), PMAA-b-P(MMA-r-MAA-r-TPMA), by polymerization-induced self-assembly through photo nitroxide-mediated controlled/living radical polymerization (photo NMP). The photo NMP in an aqueous methanol solution produced spherical vesicles perforated with various holes and pores in the surface. The perforation of the vesicles was prevented by trifluoroacetic acid based on the disturbance of the MAA-TPMA interaction in the hydrophobic block chain. The investigation of the morphology changes by the polymerization progress revealed that the perforated spherical vesicles were produced within the membrane of contorted huge vesicles that were formed during the early stage of the polymerization due to the extension of the hydrophobic block chain. The perforated vesicles were found to show a reversible thermo-responsive behavior in the range of 25-50 °C based on dynamic light scattering and transmittance measurements. The vesicles were fused and divided into much smaller vesicles at high temperature, but were restored by cooling. However, the restored vesicles only had a few holes and no pores in the surface. The rearrangement of the MAA-TPMA interaction at high temperature produced more morphologically stable non-perforated vesicles.

Synthesis of Non-Uniform Functionalized Amphiphilic Block Copolymers and Giant Vesicles in the Presence of the Belousov-Zhabotinsky Reaction

Giant vesicles with several-micrometer diameters were prepared by the self-assembly of an amphiphilic block copolymer in the presence of the Belousov-Zhabotinsky (BZ) reaction. The vesicle is composed of a non-uniform triblock copolymer synthesized by multi-step reactions in the presence of air at room temperature. The triblock copolymer contains poly(glycerol monomethacrylate) (PGMA) as the hydrophilic block copolymerized with tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3), which catalyzes the BZ reaction, and 2-hydroxypropyl methacrylate (HPMA) as the hydrophobic block. In this new approach, the radicals generated in the BZ reaction can activate a reversible addition-fragmentation chain transfer (RAFT) polymerization to self-assemble the polymer into vesicles with diameters of approximately 3 µm. X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the PGMA-b-Ru(bpy)3-b-PHPMA triblock copolymer is brominated and increases the osmotic pressure inside the vesicle, leading to micrometer-sized features. The effect of solvent on the morphological transitions are also discussed briefly. This BZ strategy, offers a new perspective to prepare giant vesicles as a platform for promising applications in the areas of microencapsulation and catalyst support, due to their significant sizes and large microcavities.

Extended photo-induced endosome-like structures in giant vesicles promoted by block-copolymer nanocarriers

Upon irradiation, the photosensitizer pheophorbide-a causes dramatic morphological transitions in giant unilamellar lipid vesicles. This endocytosis-like process occurs only when the photoactive species are encapsulated in a copolymer nanocarrier and strictly depends on the chemical nature of the copolymer. Altogether, these results open up new perspectives in the field of photo-chemical internalization mediated by nanoassemblies.

Photoinitiated Polymerization-Induced Self-Assembly (Photo-PISA): New Insights and Opportunities

The polymerization-induced self-assembly (PISA) process is a useful synthetic tool for the efficient synthesis of polymeric nanoparticles of different morphologies. Recently, studies on visible light initiated PISA processes have offered a number of key research opportunities that are not readily accessible using traditional thermally initiated systems. For example, visible light mediated PISA (Photo-PISA) enables a high degree of control over the dispersion polymerization process by manipulation of the wavelength and intensity of incident light. In some cases, the final nanoparticle morphology of a single formulation can be modulated by simple manipulation of these externally controlled parameters. In addition, temporal (and in principle spatial) control over the Photo-PISA process can be achieved in most cases. Exploitation of the mild room temperature polymerizations conditions can enable the encapsulation of thermally sensitive therapeutics to occur without compromising the polymerization rate and their activities. Finally, the Photo-PISA process can enable further mechanistic insights into the morphological evolution of nanoparticle formation such as the effects of temperature on the self-assembly process. The purpose of this mini-review is therefore to examine some of these recent advances that have been made in Photo-PISA processes, particularly in light of the specific advantages that may exist in comparison with conventional thermally initiated systems.

Selective vesicle aggregation achieved via the self-assembly of terpyridine-based building blocks

Herein, we report the self-assembly of a mono terpyridine-based building block modified with long alkyl chains, which gives rise to vesicular aggregates in aqueous media. The vesicles are responsive to transition metal ions, and form different kinds of aggregates after metal-ligand coordination. In particular, Ni(ii) shows a unique influence on morphological transitions, whereby vesicles aggregate and fuse upon the addition of Ni(ii) ions. Spectroscopic and morphological studies are highlighted in this work. Furthermore, the formed vesicles could behave as a matrix for encapsulating fluorescent dyes with similar molecular structure via co-assembly, enabling more accurate observation of vesicle aggregation via confocal laser scanning techniques.

Nonaqueous Dispersion Formed by an Emulsion Solvent Evaporation Method Using Block-Random Copolymer Surfactant Synthesized by RAFT Polymerization

As surfactants for preparation of nonaqueous microcapsule dispersions by the emulsion solvent evaporation method, three copolymers composed of stearyl methacrylate (SMA) and glycidyl methacrylate (GMA) with different monomer sequences (i.e., random, block, and block-random) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Despite having the same comonomer composition, the copolymers exhibited different functionality as surfactants for creating emulsions with respective dispersed and continuous phases consisting of methanol and isoparaffin solvent. The optimal monomer sequence for the surfactant was determined based on the droplet sizes and the stabilities of the emulsions created using these copolymers. The block-random copolymer led to an emulsion with better stability than obtained using the random copolymer and a smaller droplet size than achieved with the block copolymer. Modification of the epoxy group of the GMA unit by diethanolamine (DEA) further decreased the droplet size, leading to higher stability of the emulsion. The DEA-modified block-random copolymer gave rise to nonaqueous microcapsule dispersions after evaporation of methanol from the emulsions containing colored dyes in their dispersed phases. These dispersions exhibited high stability, and the particle sizes were small enough for application to the inkjet printing process.

Polymerization-Induced Self-Assembly Using Visible Light Mediated Photoinduced Electron Transfer-Reversible Addition-Fragmentation Chain Transfer Polymerization

The ruthenium-based photoredox catalyst, Ru(bpy)₃Cl₂, was employed to activate reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization via a photoinduced electron transfer (PET) process under visible light (λ = 460 nm, 0.7 mW/cm²). Poly(oligo(ethylene glycol) methyl ether methacrylate) was chain extended with benzyl methacrylate to afford in situ self-assembled polymeric nanoparticles with various morphologies. The effect of different intrinsic reaction parameters, such as catalyst concentration, total solids content, and cosolvent addition was investigated with respect to the formation of different nanoparticle morphologies, including spherical micelles, worm-like micelles, and vesicles. Importantly, highly pure worm-like micelles were readily isolated due to the in situ formation of highly viscous gels. Finally, "ON/OFF" control over the dispersion polymerization was demonstrated by online Fourier transform near-infrared (FTNIR) spectroscopy, allowing for temporal control over the nanoparticle morphology.

Giant tubular and toroidal vesicles from self-assembled triblock copolymer-polyaniline complexes in water

An ABA type amphiphilic triblock copolymer was synthesized via ATRP and sulfonation. New self-assembled morphologies such as toroidal vesicles, giant tubular vesicles, and perforated spherical vesicles were observed from triblock copolymer-polyaniline complexes in water. The mechanism of morphology transformation at different compositions was discussed.

Self-assembled multimicellar vesicles via complexation of a rigid conjugated polymer with an amphiphilic block copolymer

We report here a facile method for fabrication of multimicellar vesicles from self-assembled complexes of a flexible coil-like block copolymer and a rigid rod conjugated homopolymer.