Living Self-Assembly of Monodisperse Micron-Sized Polymer Vesicles

Artificial vesicles are recognized as powerful platforms for a large body of research across the disciplines of chemistry, physics and biology. Despite the great progress, control of the size distribution to make uniform vesicles remains fundamentally difficult due to the highly uncontrollable growth kinetics, especially for micron-sized vesicles. Here we report a template-free living self-assembly method to prepare monodisperse vesicles around 1 μm from an alternating copolymer. The polymer forms nanodisks (ca. 9 nm) in N,N-dimethylformamide (DMF), acting as seeds for subsequent growth. By adding water, the nanodisks gradually grow into larger circular bilayer nanosheets, which bend to crowns and continue to grow into uniform micron-sized vesicles. The first-order growth kinetics as well as the small size polydispersity index (<0.1) suggests the living self-assembly characteristics. This work paves a new way in both living self-assembly and monodisperse polymer vesicles.

Polymersomes in Drug Delivery─From Experiment to Computational Modeling

Polymersomes, composed of amphiphilic block copolymers, are self-assembled vesicles that have gained attention as potential drug delivery systems due to their good biocompatibility, stability, and versatility. Various experimental techniques have been employed to characterize the self-assembly behaviors and properties of polymersomes. However, they have limitations in revealing molecular details and underlying mechanisms. Computational modeling techniques have emerged as powerful tools to complement experimental studies and enabled researchers to examine drug delivery mechanisms at molecular resolution. This review aims to provide a comprehensive overview of the state of the art in the field of polymersome-based drug delivery systems, with an emphasis on insights gained from both experimental and computational studies. Specifically, we focus on polymersome morphologies, self-assembly kinetics, fusion and fission, behaviors in flow, as well as drug encapsulation and release mechanisms. Furthermore, we also identify existing challenges and limitations in this rapidly evolving field and suggest possible directions for future research.

Self-assembly of sequence-regulated amphiphilic copolymers with alternating rod and coil pendants

We conducted a computational study on the self-assembly behavior of sequence-controlled amphiphilic copolymers with alternating rod and coil pendants. Complex self-assembled morphologies, such as onion-like vesicles with two layers, can be generated by introducing rod pendants. The amphiphilic alternating copolymers self-assemble into onion-like vesicles through a fusion process of tiny micelles and a bending operation of disk-like micelles with double layers. A stimuli-responsive simulation shows that the cylindrical vesicles can transform into onion-like vesicles by a rod-to-coil conformation transition of rigid pendants. Inspired by this finding, we conducted a drug-loading simulation by adding two reactive drugs at different stages and found that the onion-like vesicles can almost completely isolate two drugs. This work provides theoretical guidance on the self-assembly of amphiphilic alternating copolymers with rod and coil pendants for future experimental design.

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.

Self-Assembled Nanosized Vehicles from Amino Acid-Based Amphiphilic Polymers with Pendent Carboxyl Groups for Efficient Drug Delivery

Developing safe and efficient delivery vehicles for chemotherapeutic drugs has been a long-standing demanding. Amino acid-based polymers are promising candidates to address this challenge due to their excellent biocompatibility and biodegradation. Herein, a series of well-defined amphiphilic block copolymers were prepared by PET-RAFT polymerization of N-acryloyl amino acid monomers. By altering monomer types and the block ratio of the copolymers, the copolymers self-assembled into nanostructures with various morphologies, including spheres, rod-like, fibers, and lamellae via hydrophobic and hydrogen bonding interactions. Significantly, the nanoparticles (NPs) assembled from amphiphilic block copolymers poly(N-acryloyl-valine)-b-poly(N-acryloyl-aspartic acid) (PV-b-PD) displayed an appealing cargo loading efficiency (21.8-32.6%) for a broad range of drugs (paclitaxel, doxorubicin (DOX), cisplatin, etc.) due to strong interactions. The DOX-loaded PV-b-PD NPs exhibited rapid cellular uptake (within 1 min) and a great therapeutic performance. These drug delivery systems provide new insights for regulating the controlled morphologies and improving the efficiency of drug delivery.

A Close Look at Molecular Self-Assembly with the Transmission Electron Microscope

Molecular self-assembly is pervasive in the formation of living and synthetic materials. Knowledge gained from research into the principles of molecular self-assembly drives innovation in the biological, chemical, and materials sciences. Self-assembly processes span a wide range of temporal and spatial domains and are often unintuitive and complex. Studying such complex processes requires an arsenal of analytical and computational tools. Within this arsenal, the transmission electron microscope stands out for its unique ability to visualize and quantify self-assembly structures and processes. This review describes the contribution that the transmission electron microscope has made to the field of molecular self-assembly. An emphasis is placed on which TEM methods are applicable to different structures and processes and how TEM can be used in combination with other experimental or computational methods. Finally, we provide an outlook on the current challenges to, and opportunities for, increasing the impact that the transmission electron microscope can have on molecular self-assembly.

Asymmetric Vesicles Self-Assembled by Amphiphilic Sequence-Controlled Polymers

The asymmetric distribution of lipids on the inner and outer membranes of a cell plays a pivotal role in the physiological and immunological activities of life. It has inspired the elaboration of synthetic asymmetric vesicles for the discovery of advanced materials and functions. The asymmetric vesicles were generally prepared by amphiphilic block copolymers. We herein report on the formation of asymmetric vesicles self-assembled by amphiphilic sequence-controlled polymers with two hydrophilic segments SU and TEO. We also developed an efficient fluorescence titration method with europium(III) ions (Eu³⁺) to determine the uneven distribution of SU and TEO. SU units are preferentially located on the outer membrane and TEO on the inner membrane of the resulting vesicles, which is facilitated by the electrostatic repulsion of SU and the U-shaped folding of the hydrophobic backbone of the resulting polymers. This work shows that sequence-controlled polymers with alternating monomer sequence provide a powerful toolbox for the elaboration of important yet challenging self-assembled structures for emerging functions and properties.

Silver ion-doped CdTe quantum dots as fluorescent probe for Hg2+ detection

Mercury(ii), which is a well-known toxic species, exists in the industrial waste water in many cases. In the present work, CdTe quantum dots (QDs) are studied as a fluorescence probe for Hg²⁺ detection. Ag ions are induced to QDs to enlarge their detection concentration range. l-cysteine is employed in the QD-based fluorescence probe to connect QDs with Hg²⁺. X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy results indicate the formation of zinc blende CdTe QDs with sizes of ∼5 nm and the existence of Ag⁺ in crystalline CdTe. Photoluminescence (PL) spectra and PL decay spectra were acquired to investigate the emission mechanism of Ag-doped CdTe QDs, revealing multi-emission in QD samples with higher concentrations of Ag⁺ doping. The highest PL quantum yield of the QD samples was 59.4%. Furthermore, the relationship between the fluorescence intensity and the concentration of Hg²⁺ has been established. Two linear relationships were obtained for the plot of F/F₀ against Hg²⁺ concentration, enlarging the detection concentration range of Hg²⁺.

Ag-doped CdTe QDs emit multiple-fluorescence peaks, and the relationship between fluorescence intensity and the concentration of Hg²⁺ is established. Two linear relationships are obtained, which is benefit to the extension of detection range.

Cationic Amphiphilic Alternating Copolymers with Tunable Morphology

A series of ionic amphiphilic alternating copolymers were characterized via SAXS, TEM and DLS to help understand factors that could potentially affect self-assembly, including the degree of polymerization, the length of hydrophobic spacers between ionic units, the distance between charged groups and polymer backbone, solvent envrioment and counterions.

Mussel-Inspired Alternating Copolymer as a High-Performance Adhesive Material Both at Dry and Under-Seawater Conditions

Marine mussels have the ability to cling to various surfaces at wet or underwater conditions, which inspires the research of catechol-functionalized polymers (CFPs) to develop high-performance adhesive materials. However, these polymeric adhesives generally face the problems of complex synthetic route, and it is still high challenging to prepare CFPs with excellent adhesive performance both at dry and underwater conditions. Herein, a mussel-inspired alternating copolymer, poly(dopamine-alt-2,2-bis(4-glycidyloxyphenyl)propane) (P(DA-a-BGOP)), is synthesized in one step by using commercially available monomers through epoxy-amino click chemistry. The incorporation of polar groups and rigid bisphenol A structures into the polymer backbone enhances the cohesion energy of polymer matrix. The alternating polymer structure endows the polymers with high catechol content and controlled polymer sequence. As a result, P(DA-a-BGOP) exhibits a strong bonding strength as high as 16.39 ± 2.13 MPa on stainless steel substrates after a hot pressing procedure and displays a bonding strength of 1.05 ± 0.05 MPa on glass substrates at an under-seawater condition, which surpasses most commercial adhesives.

Facile Synthesis of a H2O2-Responsive Alternating Copolymer Bearing Thioether Side Groups for Drug Delivery and Controlled Release

A novel amphiphilic alternating copolymer with thioether side groups (P(MSPA-a-EG)) was synthesized through an amine-epoxy click reaction of 3-(methylthio)propylamine (MSPA) and ethylene glycol diglycidyl ether. P(MSPA-a-EG) was characterized in detail by nuclear magnetic resonance (NMR), gel permeation chromatography, Fourier transformed infrared, differential scanning calorimeter, and thermogravimetric analysis to confirm the successful synthesis. Due to its amphiphilic structure, P(MSPA-a-EG) could self-assemble into spherical micelles with an average diameter of about 151 nm. As triggered by H2O2, theses micelles could disassemble because hydrophobic thioether groups are transformed to hydrophilic sulfoxide groups in MSPA units. The oxidant disassemble process of micelles was systemically studied by dynamic light scattering, transmission electron microscopy, and 1H NMR measurements. The MTT assay against NIH/3T3 cells indicated that P(MSPA-a-EG) micelles exhibited good biocompatibility. Furthermore, they could be used as smart drug carriers to encapsulate hydrophobic anticancer drug doxorubicin (DOX) with 4.90% drug loading content and 9.81% drug loading efficiency. In vitro evaluation results indicated that the loaded DOX could be released rapidly, triggered by H2O2. Therefore, such a novel alternating copolymer was expected to be promising candidates for controlled drug delivery and release.

Vesicle formation by ultrashort alkyl-phosphonic acids and serine in aqueous solutions

Vesicles possess unique biofilm structures and offer biomimetic advantages for drug and gene delivery. Herein, we report the spontaneous vesicle formation from ultrashort alkyl-phosphonic acids in the presence of amino acids. The aggregation characteristics and self-assembly structures of vesicles in aqueous solution were investigated by using dynamic light scattering, zeta potential, and cryo-transmission electron microscopy. We combined low-field nuclear magnetic resonance and Fourier transform infrared spectroscopy to study the H-proton-induced multilamellar vesicle formation. When we increased the molar fraction of serine, stable and closed spherical vesicles were formed at relatively low critical micelle concentrations. This transition of the self-assembled structure indicates that vesicle formation occurs when the chain length and the magnitude of the surface charge cause a fluctuation in the volume of the vesicle. Density functional theory reveals the critical role of the mixed alkyl-phosphonic acid/amino acid-enhanced electrostatic attraction between the head groups and hydrogen bonds associated with the aggregated states.

Solution Self-Assembly of an Alternating Copolymer toward Hollow Carbon Nanospheres with Uniform Micropores

Controllable preparation of porous hollow carbon spheres (HCSs) has attracted considerable attention due to their potential applications, e.g., in energy conversion and storage. We report for the first time the synthesis of narrowly size-distributed HCSs with uniform micropores in the wall, through a simple template-free approach, which employs the solution self-assembly of an alternating copolymer (poly(9,9'-bis(4-glycidyloxyphenyl)fluorene-alt-2,3-dihydroxy-butylene dithioether) (P(BGF-a-DHBDT))). This alternating copolymer first self-assembled into previously undocumented hollow polymeric spheres (HPSs) in an N,N-dimethylformamide (DMF)/H₂O solvent mixture. After the cross-linking of the BGF segments in the spheres, the stabilized HPSs (CL-HPSs) were carbonized at 800 °C under N₂ atmosphere, yielding porous HCSs with uniform micropores of very narrow size distribution (0.4-0.8 nm) in the wall, benefiting from the uniform DHBDT block length in the alternating copolymer. Through KOH activation, which made the internal pores fully interconnected, uniform micropores (0.5-1.0 nm) of a narrow size distribution were retained within the activated HCSs (A-HCSs), while their specific surface areas (SSAs) were much increased to 2580 m² g^-1. As a proof of concept, the A-HCSs were applied as electrode materials of supercapacitors. They exhibited superior electrochemical performance with a high specific capacitance (292 F g^-1 at 0.2 A g^-1), good rate capability, and outstanding cycling stability with no apparent capacitance loss after 10 000 cycles.

Solution self-assembly behavior of rod-alt-coil alternating copolymers via simulations

The self-assembly behaviors of rod-alt-coil alternating copolymers were systematically investigated by employing dissipative particle dynamics simulations.