Photoresponsive Polymersomes Formed by Amphiphilic Linear–Dendritic Block Copolymers: Generation-Dependent Aggregation Behavior

Polymeric Bowl-Shaped Nanoparticles: Hollow Structures with a Large Opening on the Surface

Polymeric bowl-shaped nanoparticles (BNPs) are anisotropic hollow structures with large openings on the surface, which have shown advantages such as high specific area and efficient encapsulation, delivery and release of large-sized cargoes on demand compared to solid nanoparticles or closed hollow structures. Several strategies have been developed to prepare BNPs based on either template or template-free methods. For instance, despite the widely used self-assembly strategy, alternative methods including emulsion polymerization, swelling and freeze-drying of polymeric spheres, and template-assisted approaches have also been developed. It is attractive but still challenging to fabricate BNPs due to their unique structural features. However, there is still no comprehensive summary of BNPs up to now, which significantly hinders the further development of this field. In this review, the recent progress of BNPs will be highlighted from the perspectives of design strategies, preparation methods, formation mechanisms, and emerging applications. Moreover, the future perspectives of BNPs will also be proposed.

Development and photo-properties and intracellular behavior of visible-light-responsive molecule localizing to organelles of living cell

Visible-light-responsive azobenzene derivative in which a functional group having cell membrane permeability and a fluorophore were bonded was synthesized. This compound localized to the hydrophobic part in the lipid membrane of the liposome, and when the light corresponding to the transition absorption of azobenzene was irradiated, morphological change of the liposome was observed. When this compound was loaded into living cells, this molecule localized to the lysosome and when irradiated with light of the same wavelength caused cell death. These observed changes are thought to be due to photoisomerization of azobenzene derivatives.

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Implicit-Solvent Coarse-Grained Simulations of Linear-Dendritic Block Copolymer Micelles

The design of nanoassemblies can be conveniently achieved by tuning the strength of the hydrophobic interactions of block copolymers in selective solvents. These block copolymer micelles form supramolecular aggregates, which have attracted great attention in the area of drug delivery and imaging in biomedicine due to their easy-to-tune properties and straightforward large-scale production. In the present work, we have investigated the micellization process of linear-dendritic block copolymers in order to elucidate the effect of branching on the micellar properties. We focus on block copolymers formed by linear hydrophobic blocks attached to either dendritic neutral or charged hydrophilic blocks. We have implemented a simple protocol for determining the equilibrium micellar size, which permits the study of linear-dendritic block copolymers in a wide range of block morphologies in an efficient and parallelizable manner. We have explored the impact of different topological and charge properties of the hydrophilic blocks on the equilibrium micellar properties and compared them to predictions from self-consistent field theory and scaling theory. We have found that, at higher degrees of branching in the corona and for short polymer chains, excluded volume interactions strongly influence the micellar aggregation as well as their effective charge.

Hybrid Molecules Consisting of Lysine Dendrons with Several Hydrophobic Tails: A SCF Study of Self-Assembling

In this article, we used the numerical self-consistent field method of Scheutjens-Fleer to study the micellization of hybrid molecules consisting of one polylysine dendron with charged end groups and several linear hydrophobic tails attached to its root. The main attention was paid to spherical micelles and the determination of the range of parameters at which they can appear. A relationship has been established between the size and internal structure of the resulting spherical micelles and the length and number of hydrophobic tails, as well as the number of dendron generations. It is shown that the splitting of the same number of hydrophobic monomers from one long tail into several short tails leads to a decrease in the aggregation number and, accordingly, the number of terminal charges in micelles. At the same time, it was shown that the surface area per dendron does not depend on the number of hydrophobic monomers or tails in the hybrid molecule. The relationship between the structure of hybrid molecules and the electrostatic properties of the resulting micelles has also been studied. It is found that the charge distribution in the corona depends on the number of dendron generations G in the hybrid molecule. For a small number of generations (up to G=3), a standard double electric layer is observed. For a larger number of generations (G=4), the charges of dendrons in the corona are divided into two populations: in the first population, the charges are in the spherical layer near the boundary between the micelle core and shell, and in the second population, the charges are near the periphery of the spherical shell. As a result, a part of the counterions is localized in the wide region between them. These results are of potential interest for the use of spherical dendromicelles as nanocontainers for drug delivery.

Photoresponsive Azobenzene-Functionalized Shell Cross-Linked Micelles for Selective Asymmetric Transfer Hydrogenation

We describe the substrate-selective asymmetric transfer hydrogenation of aromatic ketones using rhodium complexes immobilized on a photoresponsive nanoreactor. The nanoreactor switches its morphology upon light irradiation in a wavelength-selective manner. Kinetic studies show that the gated behavior in the cross-linking layer is key to discriminating among substrates and reagents during catalysis. Under ultraviolet light irradiation, the nanoreactor displays substrate selectivity, converting smaller ketone substrates faster to the corresponding secondary alcohols.

Transformation of Amorphous Nanobowls to Crystalline Ellipsoids Induced by Trans-Cis Isomerization of Azobenzene

The stimuli-responsive transition of nanostructures from amorphous to crystalline state is of high interest in polymer science, but is still challenging. Herein, we demonstrate the transformation of amorphous nanobowls to crystalline ellipsoids triggered by UV induced trans-cis isomerization, using an azobenzene-containing amphiphilic homopolymer (PAzoAA) as building block. The amide bond and azobenzene pendants are introduced to the side chain of PAzoAA to afford hydrogen bonding and π-π interaction, which promotes the formation of nanobowls rather than spherical nanostructures. Upon exposed to UV irradiation, trans-cis isomerization of azobenzene pendants occurs, leading to the increase of hydrophilicity and destruction of π-π interaction, further resulting in the disassembly of the nanobowls. Then the PAzoAA re-assembles to form crystalline ellipsoids instead of amorphous nanostructures when recovered at 70°C without UV light. We further confirm that the high incubation temperature after UV irradiation is critical for the cis-trans transformation and the high mobility of the polymer chains to facilitate the regular rearrangement of azobenzene pendants. Overall, we propose a facile method to achieve the transformation of amorphous nanobowls to crystalline ellipsoids, which may bring new insight into preparation of crystalline nanoparticles using amorphous precursors. This article is protected by copyright. All rights reserved.

Light-Triggered Polymersome-Based Anticancer Therapeutics Delivery

Polymersomes are biomimetic cell membrane-like model structures that are self-assembled stepwise from amphiphilic copolymers. These polymeric (nano)carriers have gained the scientific community's attention due to their biocompatibility, versatility, and higher stability than liposomes. Their tunable properties, such as composition, size, shape, and surface functional groups, extend encapsulation possibilities to either hydrophilic or hydrophobic cargoes (or both) and their site-specific delivery. Besides, polymersomes can disassemble in response to different stimuli, including light, for controlling the "on-demand" release of cargo that may also respond to light as photosensitizers and plasmonic nanostructures. Thus, polymersomes can be spatiotemporally stimulated by light of a wide wavelength range, whose exogenous response may activate light-stimulable moieties, enhance the drug efficacy, decrease side effects, and, thus, be broadly employed in photoinduced therapy. This review describes current light-responsive polymersomes evaluated for anticancer therapy. It includes light-activable moieties' features and polymersomes' composition and release behavior, focusing on recent advances and applications in cancer therapy, current trends, and photosensitive polymersomes' perspectives.

Photo-controlled self-assembly behavior of novel amphiphilic polymers with a rosin-based azobenzene group

Novel ‘bola’ rosin-based photo-responsive amphiphilic polymers PMPn show an extremely high photoresponsive efficiency and various assembly morphological changes.

Polymeric nanostructures based on azobenzene and their biomedical applications: synthesis, self-assembly and stimuli-responsiveness

Amphiphilic polymers can self-assemble to form nanoparticles with different structures under suitable conditions. Polymer nanoparticles functionalized with aromatic azo groups are endowed with photo-responsive properties. In recent years, a variety of photoresponsive polymers and nanoparticles have been developed based on azobenzene, using different molecular design strategies and synthetic routes. This article reviews the progress of this rapidly developing research field, focusing on the structure, synthesis, assembly and response of photo-responsive polymer assemblies. According to the molecular structure, photo-responsive polymers can be divided into linear polymers containing azobenzene in a side chain, linear polymers containing azobenzene in the main chain, linear polymers containing azobenzene in an end group, branched polymers containing azobenzene and supramolecular polymers containing azobenzene. These systems have broad biomedical application prospects in the field of drug delivery and imaging applications.

Toward enzyme-responsive polymersome drug delivery

In drug delivery, enzyme-responsive drug carriers are becoming increasingly relevant because of the growing association of disease pathology with enzyme overexpression. Polymersomes are of interest to such applications because of their tunable properties. While polymersomes open up a wide range of chemical and physical properties to explore, they also present a challenge in developing generalized rules for the synthesis of novel systems. Motivated by this issue, in this perspective, we summarize the existing knowledge on enzyme-responsive polymersomes and outline the main design choices. Then, we propose heuristics to guide the design of novel systems. Finally, we discuss the potential of an integrated approach using computer simulations and experimental studies to streamline this design process and close the existing knowledge gaps.

Supramolecular Functionalizable Linear-Dendritic Block Copolymers for the Preparation of Nanocarriers by Microfluidics

Hybrid linear-dendritic block copolymers (LDBCs) having dendrons with a precise number of peripheral groups that are able to supramolecular bind functional moieties are challenging materials as versatile polymeric platforms for the preparation of functional polymeric nanocarriers. PEG2k-b-dxDAP LDBCs that are based on polyethylene glycol (PEG) as hydrophilic blocks and dendrons derived from bis-MPA having 2,6-diacylaminopyridine (DAP) units have been efficiently synthesized by the click coupling of preformed blocks, as was demonstrated by spectroscopic techniques and mass spectrometry. Self-assembly ability was first checked by nanoprecipitation. A reproducible and fast synthesis of aggregates was accomplished by microfluidics optimizing the total flow rate and phase ratio to achieve spherical micelles and/or vesicles depending on dendron generation and experimental parameters. The morphology and size of the self-assemblies were studied by TEM, Cryogenic Transmission Electron Microscopy (cryo-TEM), and Dynamic Light Scattering (DLS). The cytotoxicity of aggregates synthesized by microfluidics and the influence on apoptosis and cell cycle evaluation was studied on four cell lines. The self-assemblies are not cytotoxic at doses below 0.4 mg mL-1. Supramolecular functionalization using thymine derivatives was explored for reversibly cross-linking the hydrophobic blocks. The results open new possibilities for their use as drug nanocarriers with a dynamic cross-linking to improve nanocarrier stability but without hindering disassembly to release molecular cargoes.

Amphiphilic multicomponent molecular brushes

Multicomponent molecular brushes containing amphiphilic polymer moieties are promising objects of research of macromolecular chemistry. The development of stimulus-responsive systems sensitive to changes in environmental parameters, based on the molecular brushes, opens up new possibilities for their applications in medicine, biochemistry and microelectronics. The review presents the current understanding of the structures of main types of amphiphilic multicomponent brushes, depending on the chemical nature and type of coupling of the backbone and side chains. The approaches to the controlled synthesis of multicomponent molecular brushes of different architecture are analyzed. Self-assembly processes of multicomponent molecular brushes in selective solvents are considered.

The bibliography includes 259 references.

Preparation of a Series of Photoresponsive Polymersomes Bearing Photocleavable a 2-nitrobenzyl Group at the Hydrophobic/Hydrophilic Interfaces and Their Payload Releasing Behaviors

In this study, the structure-function relationships of a series of polymersomes composed of well-defined amphiphilic diblock copolymers were investigated. The building blocks were synthesized by clicking hydrophobic polymers, synthesized beforehand, and commercially available poly(ethylene glycol) with photocleavable 2-nitrobenzyl compounds bearing alkyne and maleimide functionalities. All of the tested polymersomes preserved their hollow structures even after sufficient photoirradiation. Nevertheless, the release rate of an entrapped anionic fluorophore was highly dependent on the molecular weight and the type of hydrophobic polymer, as well as on the presence or absence of the charged end groups. Moreover, the polymersomes with a 2-nitrosobenzyl photolysis residue within the hydrophobic shells exhibited photo-induced payload release after complete photolysis. It was concluded that the payload release was mediated by photo-induced permeability changes of the hydrophobic shells rather than the decomposition of their overall structures.

Experiments and Simulations of Complex Sugar-Based Coil-Brush Block Polymer Nanoassemblies in Aqueous Solution

In this work, we investigated the fundamental molecular parameters that guide the supramolecular assembly of glucose-based amphiphilic coil-brush block polymers in aqueous solution and elucidated architecture-morphology relationships through experimental and simulation tools. Well-defined coil-brush polymers were synthesized through ring-opening polymerizations (ROP) of glucose carbonates to afford norbornenyl-functionalized poly(glucose carbonate) (NB-PGC) macromonomers, followed by sequential ring-opening metathesis polymerizations (ROMP) of norbornene N-hydroxysuccinimidyl (NHS) esters and the NB-PGC macromonomers. Variation of the macromonomer length and grafting through ROMP conditions allowed for a series of coil-brush polymers to be synthesized with differences in the brush and coil dimensions, independently, where the side chain graft length and brush backbone were used to tune the brush, and the coil block length was used to vary the coil. Hydrolysis of the NHS moieties gave the amphiphilic coil-brush polymers, where the hydrophilic-hydrophobic ratios were dependent on the brush and coil relative dimensions. Experimental assembly in solution was studied and found to yield a variety of structurally dependent nanostructures. Simulations were conducted on the solution assembly of coil-brush polymers, where the polymers were represented by a coarse-grained model and the solvent was represented implicitly. There is qualitative agreement in the phase diagrams obtained from simulations and experiments, in terms of the morphologies of the assembled nanoscopic structures achieved as a function of coil-brush design parameters ( e.g., brush and coil lengths, composition). The simulations further showed the chain conformations adopted by the coil-brush polymers and the packing within these assembled nanoscopic structures. This work enables the predictive design of nanostructures from this glucose-based coil-brush polymer platform while providing a fundamental understanding of interactions within solution assembly of complex polymer building blocks.

Mesoscopic simulation study on the structural transition of comb-shaped block copolymer lamellae on chemically patterned substrates: from vertical to lateral

Directed self-assembly of polymers on chemically homogeneous and heterogeneous patterns is of considerable interest for nanolithography and nanofluidic devices. By employing dissipative particle dynamics (DPD) technology, we explore the nanoscale phase separation of comb-like block copolymers (CBCPs) confined at chemically homogeneous and heterogeneous substrates. Herein, the geometric and energetic influences of striped substrates on the microphases are firstly studied using various geometries of annular stripes for the heterogeneous substrates. Different parameters including the stripe geometry, substrate selectivity, and film thickness are studied systematically. T-Junction lamellae and acclivitous alignment are achieved on the heterogeneous substrates because of the synergy of geometrical effects of the striped pattern from heterogeneous substrates together with weak preference of the substrates toward one of the CBCP components. In this study, we provide a detailed understanding of microphase separation of CBCPs on the heterogeneous substrates, and the approach outlined in the present study offers a crucial tool for experimentalists to design CBCP thin films with complex device-oriented structures.

Effect of chain microstructure on self-assembly and emulsification of amphiphilic poly(acrylic acid)-polystyrene copolymers

In this study, a series of random copolymer poly(acrylic acid-co-styrene) (P(AA-co-St)) and block copolymer poly(acrylic acid)-b-polystyrene (PAA-b-PSt) with similar chemical composition but different chain microstructure were synthesized. The self-assembly behavior of random and block copolymers in selective solvent was investigated, and the structural evaluation of random and block copolymers micelles was carried out by transmission electron microscopy (TEM), dynamic light scattering (DLS) measurement, and X-ray photoelectron spectroscopy (XPS). Moreover, together with experimental characterization, the theoretical method dissipative particle dynamics (DPD) approach was applied to investigate the morphological structures of micelles composed from random and block copolymers. Results revealed that the structure of polymeric micelles is significantly affected by the distribution sequence of hydrophilic and hydrophobic monomers in copolymer chains. Furthermore, polymeric micelles based on P(AA-co-St) and PAA-b-PSt with about 50 mol% hydrophilic composition were chosen as the model to investigate the influence of micellar structure on emulsifying performance. For PAA-b-PSt micelles (B48), stable water-in-oil (w/o) emulsions could only obtained when the pH values were lower than 5. As a comparison, the P(AA-co-St) micelles (R49) had an excellent emulsification performance at 4-10 pH, and the pH-induced phase inversion derived from obtained emulsions observed at pH higher than 6. Preliminary results confirm that the micellar structure controlled by chain microstructure plays an important role in the interface behavior of polymer micelles. Compared with PAA-b-PSt micelles, P(AA-co-St) micelles have better interfacial performance and are more tailorable and controllable; thus they can be used as a model for further study of polymeric particulate emulsifiers. This paper provides new insight into the principles governing extremely high emulsifying efficiency of polymeric particulate emulsifiers and pH-responsive properties of the formed emulsions.

Manipulating molecular order in nematic liquid crystal capillary bridgesviasurfactant adsorption: guiding principles from dissipative particle dynamics simulations

Effect of surfactant tail length on the orientation of liquid crystals is investigated with dissipative particle dynamics (DPD) simulations.

Formation of non-spherical polymersomes driven by hydrophobic directional aromatic perylene interactions

Polymersomes, made up of amphiphilic block copolymers, are emerging as a powerful tool in drug delivery and synthetic biology due to their high stability, chemical versatility, and surface modifiability. The full potential of polymersomes, however, has been hindered by a lack of versatile methods for shape control. Here we show that a range of non-spherical polymersome morphologies with anisotropic membranes can be obtained by exploiting hydrophobic directional aromatic interactions between perylene polymer units within the membrane structure. By controlling the extent of solvation/desolvation of the aromatic side chains through changes in solvent quality, we demonstrate facile access to polymersomes that are either ellipsoidal or tubular-shaped. Our results indicate that perylene aromatic interactions have a great potential in the design of non-spherical polymersomes and other structurally complex self-assembled polymer structures.

A dissipative particle dynamics simulation study on phase diagrams for the self-assembly of amphiphilic hyperbranched multiarm copolymers in various solvents

Self-assembly of amphiphilic hyperbranched multiarm copolymers (HMCs) has shown great potential for preparing all kinds of delicate supramolecular structures in all scales and dimensions in solution. However, theoretical studies on the influencing factors for the self-assembly of HMCs have been greatly lagging behind. The phase diagram of HMCs in selective solvents is very necessary but has not been disclosed up to now. Here, the self-assembly of HMCs with different hydrophilic fractions in various solvents was studied systematically by using dissipative particle dynamics (DPD) simulations. Three morphological phase diagrams are constructed and a rich variety of morphologies, ranging from spherical micelles, worm-like micelles, membranes, vesicles, vesosomes, small micellar aggregates (SMAs), and aggregates of spherical and worm-like micelles to helical micelles, are obtained. In addition, both the self-assembly mechanisms and the dynamic processes for the formation of these self-assemblies have been systematically investigated. The simulation results are consistent with available experimental observations. Besides, several novel structures, like aggregates of spherical and worm-like micelles, vesosomes and helical micelles, are firstly discovered for HMC self-assembly. We believe the current work will extend the knowledge on the self-assembly of HMCs, especially on the control of supramolecular structures and on fabricating novel self-assemblies.

Polymersomes with Rapid K+-Triggered Drug-Release Behaviors

A novel type of smart polymersomes with rapid K⁺-triggered drug-release properties is developed in this work. Block copolymers with biocompatible poly(ethylene glycol) (PEG) as the hydrophilic block and poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNB) copolymer as the K⁺-responsive block are successfully synthesized. Because of the presence of 18-crown-6 units, the PEG-b-PNB block copolymers exhibit excellent K⁺-dependent phase-transition behaviors, which show a hydrophilic-hydrophobic state in simulated extracellular fluid and present a hydrophilic-hydrophilic state in simulated intracellular fluid. Polymersomes with regular spherical shape and good monodispersity are prepared by the self-assembly of the PEG-b-PNB block copolymers. Both hydrophilic fluorescein isothiocyanate-dextran and hydrophobic doxorubicin are selected as model drugs and are successfully encapsulated into the PEG-b-PNB polymersomes. After being placed in a simulated intracellular fluid with high K⁺ concentration, the PEG-b-PNB polymersomes immediately disassemble accompanied by the rapid and complete release of drugs. Such K⁺-responsive polymersomes with the desired drug-release properties provide a novel strategy for advanced intracellular drug delivery and release, which can enhance the safety and efficacy of cancer therapy.

Reduction-responsive dithiomaleimide-based polymeric micelles for controlled anti-cancer drug delivery and bioimaging

The biocompatible amphiphilic block copolymers and the CPT model drug were self-assembled into micelles with bright fluorescence and taken up by tumor cells. Then, the disulfide bonds in the micelles were cleaved to release CPT at a high GSH concentration.

Solid-supported polymer bilayers formed by coil-coil block copolymers

The formation and physical properties of solid-supported polymer bilayers (SPBs) on an adhesive substrate have been explored by dissipative particle dynamics simulations. A SPB is developed by the adsorption of vesicles formed by diblock copolymers in a selective solvent. The adsorbed vesicle can remain intact or become ruptured into a SPB, depending on the interaction between solvophobic blocks and solvent and the interaction between solvophilic blocks and the substrate. The morphological phase diagram of adsorbed vesicles is acquired. The influence of polymer adhesion strength and solvophobicity on the geometrical and mechanical properties of a SPB is systematically studied as well. It is found that vesicular disruption is easily triggered for strong adhesion strength. Moreover, for strong adhesion strength and weak solvophobicity, the fluctuation of membrane height is impeded while the area of fluctuation is enhanced.

Linear-dendritic block copolymer for drug and gene delivery

Dendrimers as a new class of polymeric materials have a highly ordered branched structure, exact molecular weight, multivalency and available internal cavities, which make them extensively used in biology and drug-delivery. Concurrent with the development of dendrimers, much more attention is drawn to a novel block copolymer which combines linear chains with dendritic macromolecules, the linear-dendritic block copolymer (LDBC). Because of the different solubility of the contrasting regions, the amphiphilic LDBCs could self-assemble to form aggregates with special core-shell structures which exhibit excellent properties different from traditional micelles, such as lower critical micelle concentration, prolonged circulation in the bloodstream, better biocompatibility, and lower toxicity. The present review briefly describes the type of LDBC, the self-assembly behavior in solution, and the application in delivery system including the application as drug carriers and gene vectors. The interactions between block copolymers and drugs are also summarized to better understand the release mechanism of drugs from the linear-dendritic block copolymers.

Synthesis and solution properties of novel thermo- and pH-responsive poly(N-vinylcaprolactam)-based linear–dendritic block copolymers

This study describes the synthesis and solution properties of the novel linear–dendritic block copolymers (LDBCs) based on thermoresponsive poly(N-vinylcaprolactam) (PNVCL) chains and pH-responsive poly(benzyl ether) dendrons.

Stimuli-responsive polymersomes for cancer therapy

This review focuses on stimuli-responsive polymersomes for cancer therapy, which can be disintegrated by recognizing the specific environments of cancer (e.g., low pH, bioreductive environment, over-expressed enzymes,etc.).

Dissipative particle dynamics simulation study on self-assembly of amphiphilic hyperbranched multiarm copolymers with different degrees of branching

Hyperbranched multiarm copolymers (HMCs) have shown great potential to be excellent precursors in self-assembly to form various supramolecular structures in all scales and dimensions in solution. However, theoretical studies on the self-assembly of HMCs, especially the self-assembly dynamics and mechanisms, have been greatly lagging behind the experimental progress. Herein, we investigate the effect of degree of branching (DB) on the self-assembly structures of HMCs by dissipative particle dynamics (DPD) simulation. Our simulation results demonstrate that the self-assembly morphologies of HMCs can be changed from spherical micelles, wormlike micelles, to vesicles with the increase of DBs, which are qualitatively consistent with the experimental observations. In addition, both the self-assembly mechanisms and the dynamic processes for the formation of these three aggregates have been systematically disclosed through the simulations. These self-assembly details are difficult to be shown by experiments and are very useful to fully understand the self-assembly behaviors of HMCs.

Construction of stable polymeric vesicles based on azobenzene and beta-cyclodextrin grafted poly(glycerol methacrylate)s for potential applications in colon-specific drug delivery

Stable polymeric vesicles constructed from cyclodextrin- and azobenzene-grafted poly(glycerol methacrylate)s exhibited potential applications in colon-specific drug delivery.

Investigation of demulsification efficiency in water-in-crude oil emulsions using dissipative particle dynamics

Demulsification efficiency with alternating hydrophobic blocks of the polyether is investigated by dissipative particle dynamics.

Structural and mechanical characteristics of polymersomes

Polymersomes self-assembled from amphiphilic macromolecules have attracted growing attention because of their multifunctionality and stability. By controlling the structural characteristics of polymersomes, including vesicle shape, size, and membrane thickness, their mechanical and transport properties as well as their fusion behavior can be manipulated. Numerous experimental techniques have been developed to explore polymersome characteristics; however, experimental microscopic observations and knowledge of vesicles are limited. Mesoscale simulations can complement experimental studies of the vesicular features at the microscopic level and thus provide a feasible method to better understand the relationship between the fundamental structures and physicochemical properties of polymersomes. Moreover, the predictive ability of the simulation approaches may greatly assist developments and future applications of polymersomes.

UV light stimulated encapsulation and release by polyelectrolyte microcapsules

Layer-by-layer assembled polyelectrolyte capsules with well-controlled architectures and great versatility have been the subject of great interest, due to their unique advantages and tremendous potentials of being excellent candidates in multidisciplinary fields. UV light responsive microcapsules, as one class of the stimuli responsive capsules, possess the abilities to active their functionalities by responding to the UV stimulus remotely without requirement of direct contact or interaction. Therefore, any advances in this field will be of great value for the establishment of approaches to fabricate UV responsive polyelectrolyte capsules for desired uses. This review presents current development of UV responsive capsules, with emphasis on the underlying design strategies and their potential applications as delivery vesicles. In particular, UV-stimulated capsule functionalities, such as cargo encapsulation, release and combined multifunctionalities by the multilayers, have been addressed.

Responsive linear-dendritic block copolymers

The combination of dendritic and linear polymeric structures in the same macromolecule opens up new possibilities for the design of block copolymers and for applications of functional polymers that have self-assembly properties. There are three main strategies for the synthesis of linear-dendritic block copolymers (LDBCs) and, in particular, the emergence of click chemistry has made the coupling of preformed blocks one of the most efficient ways of obtaining libraries of LDBCs. In these materials, the periphery of the dendron can be precisely functionalised to obtain functional LDBCs with self-assembly properties of interest in different technological areas. The incorporation of stimuli-responsive moieties gives rise to smart materials that are generally processed as self-assemblies of amphiphilic LDBCs with a morphology that can be controlled by an external stimulus. Particular emphasis is placed on light-responsive LDBCs. Furthermore, a brief review of the biomedical or materials science applications of LDBCs is presented.

The fusion mechanism of small polymersomes formed by rod-coil diblock copolymers

The fusion mechanism of polymersomes self-assembled by rod-coil copolymers is intrinsically different from that of liposomes due to the effect of chain topology on conformational entropy and molecular packing. The influences of membrane tension, coil-block length, rod-block length, mutual compatibility between the solvent and the rod-coil block, and π-π interaction strength on the fusion pathway are explored by dissipative particle dynamics. The fusion process of spontaneously formed polymersomes generally consists of four stages. In the kissing stage, hopping of rod-blocks forms a connection between two vesicles of a one-legged rod-coil copolymer. In the adhesion stage, a stalk is developed by a few link-up rods and then a stretched diaphragm with rods lying parallel to the stretching direction is formed in the hemi-fusion stage. Eventually, a pore is developed and expanded in the fusion stage. If the membrane tension (τ) is adjusted by deflation/inflation of the polymersomes, the hemi-fusion diaphragm disappears. As τ is reduced, multiple stalks take shape and lead to the formation of inverted micelles, which is the rate-determining step and raises the fusion time substantially. As τ is elevated, a neck is developed after the stalk formation. The fusion process is significantly accelerated. τ of spontaneously formed vesicles varies with the coil-block length, rod-block length, solvent quality, and π-π interaction strength. There exists a critical value of τ below which the fusion process cannot be completed and a hemi-fused polymersome is formed. In addition to τ, the anisotropic steric interactions within the rod layers also resist hopping of longer rod-blocks. The coil layers develop a barrier impeding fusion between vesicles with longer coil-blocks. Consequently, lowering the solvent quality for the coil-block or rod-block facilities the fusion process due to the formation of a thinner coil layer.

UV-induced disruption of microcapsules with azobenzene groups

UV responsive microcapsules containing azobenzene were fabricated by sequential deposition of oppositely charged poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) and poly(diallyldimethyl ammonium) chloride (PDADMAC). As found in this work, combination of PDADMAC and PAZO led to aggregation of PAZO segments in the progress of polymer deposition, which facilitated the large extent of J aggregates when the capsules were exposed to UV light. J aggregate assemblies destroyed the integrity of capsule shell formations, demonstrating capsule swelling and further breakage. This UV induced capsule breakage offered a new way to modulate the release of encapsulated cargos.

Externally triggered dual function of complex microcapsules

By introducing UV-sensitive chemical groups causing different potential response as building blocks, fabricated LbL capsules can be endowed with dual UV-responsive properties in specific layers. One block is responsible for fast capsule sealing and the other for longer term capsule swelling and rupture. Therefore, the multifunction of these capsules could be activated selectively when exposed to external UV light with suitable wavelengths. In this work, dual-functional complex microcapsules (PDADMAC/PAZO)4-(DAR/Nafion)2 containing both diazonium and aozbenzene groups were proposed as clear examples to realize a time-dependent UV response for successive encapsulation and release. Upon exposure to UV light, the DAR/Nafion layers underwent a rapid in situ cross-linking and hence to seal the capsule shells through diazonium-related photolysis. Then further gradual shell swelling was followed by realignment of azobenzene molecules in PDADMAC/PAZO layers. Fluorescent polymers were consequently studied as cargo substances. Results indicated that continuous UV light triggered rapid cargo encapsulation over minutes time scale and gradual release with continuous irradiation over hours.