Fully collapsed (kippah) vesicles: preparation and characterization

pH-Modulated 1D Hierarchical Self-Assembly of a Brush-Like Poly-Para-Phenylene Homopolymer

The controllable self-assembly of conjugated homopolymers, especially homopolymers without other segments (a prerequisite for phase separation), which can afford chances to achieve tunable optical/electronic properties, remains a great challenge due to their poor solubility and has remained rarely documented. Herein, a conjugated homopolymer (DPPP-COOH) is synthesized, which has a unique brush-like structure with a conjugated dendritic poly-para-phenylene (DPPP) backbone and alkyl-carboxyl side chains at both edges of the backbone. The introduction of carboxyl makes the brush-like homopolymer exhibit pH-modulated 1D hierarchical self-assembly behavior in dilute solution, and allows for flexible morphological regulation of the assemblies, forming some uncommon superstructures including ultralong nanowires (at pH 7), superhelices (at pH 10) and "single-wall" nanotubes (at pH 13), respectively. Furthermore, the good aqueous dispersibility and 1D feature endow the superstructures formed in a high-concentration neutral solution with high broad-spectrum antibacterial performance superior to that of many conventional 1D materials.

Polymer Brushes and Surface Nanostructures: Molecular Design, Precise Synthesis, and Self-Assembly

For over two decades, polymer brushes have found wide applications in industry and scientific research. Now, polymer brush research has been a significant research focus in the community of polymer science. In this review paper, we give an introduction to the synthesis, self-assembly, and applications of one-dimensional (1D) polymer brushes on polymer backbones, two-dimensional (2D) polymer brushes on flat surfaces, and three-dimensional (3D) polymer brushes on spherical particles. Examples of the synthesis of polymer brushes on different substrates are provided. Studies on the formation of the surface nanostructures on solid surfaces are also reviewed in this article. Multicomponent polymer brushes on solid surfaces are able to self-assemble into surface micelles (s-micelles). If the s-micelles are linked to the substrates through cleavable linkages, the s-micelles can be cleaved from the substrates, and the cleaved s-micelles are able to self-assemble into hierarchical structures. The formation of the surface nanostructures by coassembly of polymer brushes and "free" polymer chains (coassembly approach) or polymerization-induced surface self-assembly approach, is discussed. The applications of the polymer brushes in colloid and biomedical science are summarized. Finally, perspectives on the development of polymer brushes are offered in this article.

Tunable Fluorescence and Morphology of Aggregates Built from a Mechanically Bonded Amphiphilic Bistable [2]Rotaxane

Advanced Organic Chemical Materials Co-constructed Mechanically bonded amphiphiles (MBAs), also known as mechanically interlocked molecules (MIMs), have emerged as an important kind of functional building block for the construction of artificial molecular machines and soft materials. Herein, a novel MBA, i. e., bistable [2]rotaxane H2 was designed and synthesized. In the solution state, H2 demonstrated pH and metal ion-responsive emissions due to the presence of a distance-dependent photoinduced electron transfer (PET) process and the fluorescence resonance energy transfer (FRET) process, respectively. Importantly, the amphiphilic feature of H2 has endowed it with unique self-assembly capability, and nanospheres were obtained in a mixed H2 O/CH3 CN solvent. Moreover, the morphology of H2 aggregates can be tuned from nanospheres to vesicles due to the pH-controlled shuttling motion-induced alternation of H2 amphiphilicity. Interestingly, larger spheres with novel pearl-chain-like structures from H2 were observed after adding stoichiometric Zn2+ . In particular, H2 shows pH-responsive emissions in its aggregation state, allowing the visualization of the shuttling movement by just naked eyes. It is assumed that the well-designed [2]rotaxane, and particularly the proposed concept of MBA shown here, will further enrich the families of MIMs, offering prospects for synthesizing more MIMs with novel assembly capabilities and bottom-up building dynamic smart materials with unprecedented functions.

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.

Hierarchical Self-Assembly of Triphilic Main-Chain-Type Semifluorinated Alternating Graft Copolymers in Aqueous Solution

Fluorinated copolymers can self-assemble in solution and form micelles with rare properties due to the peculiar behavior of fluorinated groups. However, the process description of the self-assembly is still largely phenomenological and difficult to explain due to the tendency of the fluorinated segments to segregate from both the hydrophilic and lipophilic segments, which can result in various morphologies. Herein, the controlled formation of ellipsoidal micelles, disklike micelles, and sheets by hierarchical self-assembly of triphilic main-chain-type semifluorinated alternating graft copolymers (AB)_n A-g-mOEG is presented (where A represents unit of α,ω-diiodoperfluoroalkane, B represents the unit of α,ω-unconjugated diene, and mOEG represents methoxy oligo(ethylene glycol)), which are synthesized by step transfer-addition and radical-termination (START) polymerization and azide-alkyne click chemistry. Furthermore, the possible self-assembly mechanism of these micron-level aggregates is proposed, which is ascribed to the hierarchical self-assembly, crowding effect of hydrophilic chains and the interfacial tension between the fluoroalkane and alkane segments. This study can provide a facile and highly efficient approach to the synthesis of main-chain-type fluorinated graft copolymers and expand the research field for the solution self-assembly of fluorinated copolymers.

The sodium hyaluronate microspheres fabricated by solution drying for transcatheter arterial embolization

Transcatheter arterial embolization (TAE) is an effective therapeutic method for several clinical ailments. Interminably, the polymer microsphere is reflected as one of the idyllic embolic materials due to the exceptional...

Bowl-Shaped Polydopamine Nanocapsules: Control of Morphology via Template-Free Synthesis

Synthesis of hollow polydopamine bowl-shaped nanoparticles (nanobowls), as small as 80 nm in diameter, via a one-pot template-free rapid method is reported. Addition of dopamine to a solution of 0.606 mg/mL tris(hydroxymethyl)aminomethane in an ethanol/water mixed solvent resulted in the formation of hollow spherical nanocapsules within 2 h. At longer reaction times, the formation of conventional solid nanospheres dominated the reaction. The wall thickness of the nanocapsules increased with increasing dopamine concentration in the reaction medium. Wall thickness was also influenced by oxygen availability during the reaction. Nanocapsules with thin walls were prone to collapse. When dried, over 90% of the nanocapsules with wall thickness on the order of 11 nm collapsed. Also, the degree of collapse of individual nanoparticles changed from complete to partial to no collapse as the wall thickness was increased. Varying the ethanol content affected the cavity size and overall dimension of the nanocapsules produced but did not result in a significant change to the wall thickness. A mechanism describing the formation of the nanocapsules and their subsequent collapse into nanobowls is presented. The shape-tunable nanobowls prepared through this green, rapid, and affordable method are expected to have applications in the biomedical, electrochemical, and catalytic fields.

Metal-Mediated Morphology Regulation of Self-Assembled Double-Hydrophilic Block Copolymers

We report a nanoscale morphology-regulation strategy of self-assembled double-hydrophilic block copolymers with square planar Pt^II compounds. The selective coordination of Pt^II on the chelating blocks of poly(acrylic acid)-b-poly(ethylene glycol) (PAA-b-PEG) induced the self-association of metal-chelated unimers by the known cohesive force of Pt^II. The block-length variation of PAA with constant PEG led to the shape transition from normal core/shell and crew-cut spheres to anisotropic pearl-string structures. On the other hand, Pt^II adsorption on PEG blocks by extensive hydrogen bonding can further modify the molecular geometry of metal-chelated unimers by decreasing the volume of hydrophilic segments, eventually leading to the shape transition to vesicular structures. This result was well correlated to the structural constraint of PEG conformation estimated by the quantitative ¹H NMR analysis. The vesicles also exhibited the enclosing nature for the fluorescent guest molecules, which demonstrated the promising potential for the encapsulating delivery vehicle.

Formation of 2D and 3D multi-tori mesostructures via crystallization-driven self-assembly

The fabrication of three-dimensional (3D) objects by polymer self-assembly in solution is extremely challenging. Here, multi-tori mesostructures were obtained from the crystallization-driven self-assembly of a coil-crystalline block copolymer (BCP) in mixed solvents. The formation of these structures follows a multistep process. First, the BCP self-assembles into amorphous micrometer-large vesicles. Then, the BCP confined in these mesosized vesicles crystallizes. This second step leads to the formation of objects with shapes ranging from closed 3D multi-tori spherical shells to 2D toroid mesh monolayers, depending on the solvent mixture composition. This approach demonstrates how topological constraints induced by the specific interactions between coil-crystalline BCP and solvents can be used to prepare mesostructures of complex morphologies.

Synthesis of Terpyridine-Terminated Amphiphilic Block Copolymers and Their Self-Assembly into Metallo-Polymer Nanovesicles

Polystyrene-b-polyethylene glycol (PS-b-PEG) amphiphilic block copolymers featuring a terminal tridentate N,N,N-ligand (terpyridine) were synthesized for the first time through an efficient route. In this approach, telechelic chain-end modified polystyrenes were produced via reversible addition-fragmentation chain-transfer (RAFT) polymerization by using terpyridine trithiocarbonate as the chain-transfer agent, after which the hydrophilic polyethylene glycol (PEG) block was incorporated into the hydrophobic polystyrene (PS) block in high yields via a thiol-ene process. Following metal-coordination with Mn2+, Fe2+, Ni2+, and Zn2+, the resulting metallo-polymers were self-assembled into spherical, vesicular nanostructures, as characterized by dynamic light scattering and transmission electron microscopy (TEM) imaging.

Nanobowls with controlled openings and interior holes driven by the synergy of hydrogen bonding and π-π interaction

Asymmetric nanoparticles such as nanobowls have promising potential in many fields due to their interior asymmetric cavities and specific concave structure. However, the fabrication of nanobowls and control over their openings and interior holes are still challenging. Herein we demonstrate a versatile strategy for preparing nanobowls with precisely controlled openings and interior holes based on the synergy of hydrogen bonding and π-π interaction of homopolymers. We designed and synthesized a series of amphiphilic homopolymers with an amino alcohol moiety and azobenzene pendant (poly(2-hydroxy-3-((4-(phenyldiazenyl)phenyl)amino)propyl methacrylate) (PHAzoMA)). The homopolymers can self-assemble into nanobowls due to the heterogeneous shrinkage of the preformed spheres. Upon increasing the molecular weight of the homopolymers from 10.1 to 76.9 kg mol-1, the sizes of the openings of nanobowls can be precisely controlled from 242 to 423 nm with a linear relationship as a result of the enhancement of the hydrogen bonding and π-π interaction between homopolymer chains. Overall, we have prepared finely controlled nanobowls by the synergy of non-covalent interactions such as hydrogen bonding and π-π interaction of polymers, which opens a new avenue for the preparation of asymmetric nanoparticles.

Polymersomes: Breaking the Glass Ceiling?

Polymer vesicles, also known as polymersomes, have garnered a lot of interest even before the first report of their fabrication in the mid-1990s. These capsules have found applications in areas such as drug delivery, diagnostics and cellular models, and are made via the self-assembly of amphiphilic block copolymers, predominantly with soft, rubbery hydrophobic segments. Comparatively, and despite their remarkable impermeability, glassy polymersomes (GPs) have been less pervasive due to their rigidity, lack of biodegradability and more restricted fabrication strategies. GPs are now becoming more prominent, thanks to their ability to undergo stable shape-change (e.g., into non-spherical morphologies) as a response to a predetermined trigger (e.g., light, solvent). The basics of block copolymer self-assembly with an emphasis on polymersomes and GPs in particular are reviewed here. The principles and advantages of shape transformation of GPs as well as their general usefulness are also discussed, together with some of the challenges and opportunities currently facing this area.

Protein Transduction Domain Mimic (PTDM) Self-Assembly?

Intracellular protein delivery is an invaluable tool for biomedical research, as it enables fundamental studies of cellular processes and creates opportunities for novel therapeutic development. Protein delivery reagents such as cell penetration peptides (CPPs) and protein transduction domains (PTDs) are frequently used to facilitate protein delivery. Herein, synthetic polymer mimics of PTDs, called PTDMs, were studied for their ability to self-assemble in aqueous media as it was not known whether self-assembly plays a role in the protein binding and delivery process. The results obtained from interfacial tensiometry (IFT), transmission electron microscopy (TEM), transmittance assays (%T), and dynamic light scattering (DLS) indicated that PTDMs do not readily aggregate or self-assemble at application-relevant time scales and concentrations. However, additional DLS experiments were used to confirm that the presence of protein is required to induce the formation of PTDM-protein complexes and that PTDMs likely bind as single chains.

Methyl-modified silica nanobowl for 2D self-organized nanostructure with hydrophobic performance

A facial method of fabricating methyl-modified silica nanobowl using a polystyrene template with tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) as co-precursors was reported. The morphology of the nanobowl was determined by the mole ratio of TEOS and MTES, and the size and shell thickness of the PS@SiO₂. And the 2D ordered nanostructure has also been developed with a nanobowl opening perpendicular to the glass substrate surface by the Langmuir-Blodgett technique. These 2D ordered nanobowl structures present an adjustable antireflection property. The single-side nanobowl coating has a transmission improvement of 4.5% compared to the uncoated glass at a wavelength of 540 nm. Furthermore, the nanobowl structures have good hydrophobicity with a contact angle up to 130° without any additional treatment. The quantitative deformation behavior of the methyl-modified silica nanobowl was also discussed.

Coenzyme-Catalyzed Electro-RAFT Polymerization

Here we report an electrochemically switchable reversible addition-fragmentation chain transfer polymerization (eRAFT). A new family of biochemical coenzymes are discovered that can be used as highly efficient electroredox catalysts to mediate this polymerization. The oxidation of coenzyme, nicotinamide adenine dinucleotide (NADH), can promote the reduction of a chain transfer agent, triggering generation and propagation of polymer radicals. External potential can activate the reduction of the NAD⁺ oxidized state and pause the propagation. Tuning the applied potential to reversibly switch the catalyst between its reduced and oxidized states can toggle the polymerization between ON and OFF states. This new strategy is universal to a broad scope of monomers, and ppm-level coenzymes result in the desirable polymer structures with targeted molecular weight, dispersity, and excellent chain-end fidelity. We envisage that the bioorganic-based catalysts would open new directions of organocatalyzed electro-controlled polymerization and be of value in electrocatalysis for well-structured polymers.

Aqueous self-assembly of hydrophobic macromolecules with adjustable rigidity of the backbone

P(FpC₃P) (Fp: CpFe(CO)₂; C₃P: propyl diphenyl phosphine) has a helical backbone, resulting from piano stool metal coordination geometry, which is rigid with intramolecular aromatic interaction of the phenyl groups. The macromolecule is hydrophobic, but the polarized CO groups can interact with water for aqueous self-assembly. The stiffness of P(FpC₃P), which is adjustable by temperature, is an important factor influencing the morphologies of kinetically trapped assemblies. P(FpC₃P)₇ self-assembles in DMSO/water (10/90 by volume) into lamellae at 25 °C, vesicles at 40 °C and irregular aggregates at higher temperatures (60 and 70 °C). The colloidal stability decreases in the order of lamellae, vesicles and irregular aggregates. Dissipative particle dynamics (DPD) simulation reveals the same temperature-dependent self-assembled morphologies with an interior of hydrophobic aromatic groups covered with the metal coordination units. The rigid backbone at 25 °C accounts for the formation of the layered morphology, while the reduced rigidity of the same P(FpC₃P)₇ at 40 °C curves up the lamellae into vesicles. At a higher temperature (60 or 70 °C), P(FpC₃P)₇ behaves as a random coil without obvious amphiphilic segregation, resulting in irregular aggregates. The stiffness is, therefore, a crucial factor for the aqueous assembly of macromolecules without obvious amphiphilic segregation, which is reminiscent of the solution behavior observed for many hydrophobic biological macromolecules such as proteins.

Tunable Self-Assembly of Diblock Copolymers into Colloidal Particles with Triply Periodic Minimal Surfaces

We herein report the tunable self-assembly of simple block copolymers, namely polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers, into porous cubosomes with inverse Im3‾m or Pn3‾m mesophases of controlled unit cell parameters as well as hexasomes with an inverse hexagonal (p6mm) structure, which have been rarely observed in polymer self-assembly. A new morphological phase diagram was constructed for the solution self-assembly of PS-b-PEO based on the volume fraction of the PS block against the initial copolymer concentration. The formation mechanisms of the cubosomes and hexasomes have also been revealed. This study not only affords a simple system for the controllable preparation and fundamental studies of ordered bicontinuous structures, but also opens up a new avenue towards porous architectures with highly ordered pores.

Magneto-Plasmonic Janus Vesicles for Magnetic Field-Enhanced Photoacoustic and Magnetic Resonance Imaging of Tumors

Magneto-plasmonic Janus vesicles (JVs) integrated with gold nanoparticles (AuNPs) and magnetic NPs (MNPs) were prepared asymmetrically in the membrane for in vivo cancer imaging. The hybrid JVs were produced by coassembling a mixture of hydrophobic MNPs, free amphiphilic block copolymers (BCPs), and AuNPs tethered with amphiphilic BCPs. Depending on the size and content of NPs, the JVs acquired spherical or hemispherical shapes. Among them, hemispherical JVs containing 50 nm AuNPs and 15 nm MNPs showed a strong absorption in the near-infrared (NIR) window and enhanced the transverse relaxation (T2 ) contrast effect, as a result of the ordering and dense packing of AuNPs and MNPs in the membrane. The magneto-plasmonic JVs were used as drug delivery vehicles, from which the release of a payload can be triggered by NIR light and the release rate can be modulated by a magnetic field. Moreover, the JVs were applied as imaging agents for in vivo bimodal photoacoustic (PA) and magnetic resonance (MR) imaging of tumors by intravenous injection. With an external magnetic field, the accumulation of the JVs in tumors was significantly increased, leading to a signal enhancement of approximately 2-3 times in the PA and MR imaging, compared with control groups without a magnetic field.

Self-Assembled PAEEP-PLLA Micelles with Varied Hydrophilic Block Lengths for Tumor Cell Targeting

The properties of hydrophilic shell in micelles significantly affect the interaction between micelles and cells. Compared with frequently used polyethylene glycol (PEG) as the hydrophilic block, polyphosphoesters (PPEs) are superior in functionality, biocompatibility, and degradability. A series of amphiphilic poly(aminoethyl ethylene phosphate)/poly(l-lactide acid) (PAEEP-PLLA) copolymers were synthesized with hydrophilic PAEEP with different chain lengths. The corresponding self-assembled micelles were used for doxorubicin (Dox) entrapment. The length of hydrophilic PAEEP block on the shell affected the structure of micelles. PAEEPm-PLLA168 (m = 130 or 37) polymers formed vesicles, while PAEEPm-PLLA168 (m = 15 or 9) formed large compound micelles (LCMs), suggesting a difference in tumor cell uptake and intracellular trafficking. PAEEP15-PLLA168 polymer showed superiority on cellular uptake amount, intracellular drug release, and cell apoptosis. Lipid rafts and macropinocytosis are the leading endocytic pathways of PAEEP-PLLA micelles. The shape coupling between micelles and cell membrane facilitated cell surface features such as flattened protrusions (membrane protein) and inward-pointing hollows as well as efficient endocytosis. These results suggested that PAEEP-PLLA self-assembled block copolymer micelles may be an excellent drug delivery system for tumor treatment and that the hydrophilic chain length could regulate drug targeting to tumor cells.

The generation of polymeric nano-bowls through 3D confined assembly and disassembly

Here we present a facile yet robust strategy to prepare polymer nano-bowls through 3D confined assembly and disassembly of block copolymers. Unlike the previously reported methods, this strategy allows for generation of nano-bowls with precisely controllable opening degree and thickness. Typically, polystyrene-b-poly(4-vinyl pyridine) (PS-b-P4VP) nano-bowls can be generated through confined assembly of PS-b-P4VP with homopolystyrene (hPS) to form Janus particles, followed by the crosslinking of P4VP domains and disassembly of PS domains. The opening degree of the nano-bowls can be precisely controlled by the weight fraction of hPS, and the thickness can be tailored by the varying molecular weight of PS-b-P4VP. By selectively loading gold nanoparticles in P4VP domains, it is anticipated that the resulting hybrid nano-bowls would be useful for surface enhanced Raman scattering and potential catalytic reaction applications.

Disk-like micelles with cylindrical pores from amphiphilic polypeptide block copolymers

An unprecedented 2-dimensional disk-like micelle with cylindrical pores was achieved by self-assembly of amphiphilic block copolypeptides PEG-b-PBLG with an α-helical conformation of PBLG blocks.

Facile synthesis of bowl-shaped nitrogen-doped carbon hollow particles templated by block copolymer “kippah vesicles” for high performance supercapacitors

This paper reports a simple self-assembly strategy towards bowl-shaped carbon-containing hollow particles for high volumetric capacitance supercapacitors, as well as an unprecedented potential application for block copolymer vesicles in energy storage.

Investigation of Functionalized Poly(N,N-dimethylacrylamide)-block-polystyrene Nanoparticles As Novel Drug Delivery System to Overcome the Blood-Brain Barrier In Vitro

In the search of new drug delivery carriers for the brain, self-assembled nanoparticles (NP) were prepared from poly(N,N-dimethylacrylamide)-block-polystyrene polymer. NP displayed biocompatibility on cultured endothelial cells, macrophages and differentiated SH-SY5Y neuronal-like cells. The surface-functionalization of NP with a modified fragment of human Apolipoprotein E (mApoE) enhanced the uptake of NP by cultured human brain capillary endothelial cells, as assessed by confocal microscopy, and their permeability through a Transwell Blood Brain Barrier model made with the same cells, as assessed by fluorescence. Finally, mApoE-NP embedding doxorubicin displayed an enhanced release of drug at low pH, suggesting the potential use of these NP for the treatment of brain tumors.

Cisplatin-Induced Formation of Biocompatible and Biodegradable Polypeptide-Based Vesicles for Targeted Anticancer Drug Delivery

Novel cisplatin (CDDP)-loaded, polypeptide-based vesicles for the targeted delivery of cisplatin to cancer cells have been prepared. These vesicles were formed from biocompatible and biodegradable maleimide-poly(ethylene oxide)114-b-poly(L-glutamic acid)12 (Mal-PEG114-b-PLG12) block copolymers upon conjugation with the drug itself. CDDP conjugation forms a short, rigid, cross-linked, drug-loaded, hydrophobic block in the copolymer, and subsequently induces self-assembly into hollow vesicle structures with average hydrodynamic diameters (Dh) of ∼ 270 nm. CDDP conjugation is critical to the formation of the vesicles. The reactive maleimide-PEG moieties that form the corona and inner layer of the vesicles were protected via formation of a reversible Diels-Alder (DA) adduct throughout the block copolymer synthesis so as to maintain their integrity. Drug release studies demonstrated a low and sustained drug release profile in systemic conditions (pH = 7.4, [Cl(-)] = 140 mM) with a higher "burst-like" release rate being observed under late endosomal/lysosomal conditions (pH = 5.2, [Cl(-)] = 35 mM). Further, the peripheral maleimide functionalities on the vesicle corona were conjugated to thiol-functionalized folic acid (FA) (via in situ reduction of a novel bis-FA disulfide, FA-SS-FA) to form an active targeting drug delivery system. These targeting vesicles exhibited significantly higher cellular binding/uptake into and dose-dependent cytotoxicity toward cancer cells (HeLa) compared to noncancerous cells (NIH-3T3), which show high and low folic acid receptor (FR) expression, respectively. This work thus demonstrates a novel approach to polypeptide-based vesicle assembly and a promising strategy for targeted, effective CDDP anticancer drug delivery.

Biomimetic block copolymer particles with gated nanopores and ultrahigh protein sorption capacity

The design of micro- or nanoparticles that can encapsulate sensitive molecules such as drugs, hormones, proteins or peptides is of increasing importance for applications in biotechnology and medicine. Examples are micelles, liposomes and vesicles. The tiny and, in most cases, hollow spheres are used as vehicles for transport and controlled administration of pharmaceutical drugs or nutrients. Here we report a simple strategy to fabricate microspheres by block copolymer self-assembly. The microsphere particles have monodispersed nanopores that can act as pH-responsive gates. They contain a highly porous internal structure, which is analogous to the Schwarz P structure. The internal porosity of the particles contributes to their high sorption capacity and sustained release behaviour. We successfully separated similarly sized proteins using these particles. The ease of particle fabrication by macrophase separation and self-assembly, and the robustness of the particles makes them ideal for sorption, separation, transport and sustained delivery of pharmaceutical substances.

Planar multilayer assemblies containing block copolymer aggregates

The design, preparation, and properties of planar multilayer structures composed of various combinations of sequentially deposited polyelectrolyte (PE) chains and self-assembled layers of individual block copolymer aggregates (vesicles, micelles, or large compound micelles (LCMs)) are described. The aggregates contain negatively or positively charged corona chains while the PE multilayers contain alternating polyanionic or polycationic chains deposited on silicon wafers. The final structures consist of combinations of layers of various charged species: multilayers of alternating PEs of poly(allyl hydrochloride) (PAH) and poly(acrylic acid) (PAA) as well as vesicles, micelles, or large compound micelles of ionized poly(styrene)-b-poly(4-vinylpyridine) (PS-b-P4VP) or of poly(styrene)-b-poly(acrylic acid) (PS-b-PAA). Two types of layer-by-layer (LbL) multilayer structures were studied: individual aggregate layers sandwiched between PE multilayers and layers of individual aggregates of various morphologies and of different corona chain charges, deposited on top of each other without intermediate multilayers or individual layers of PEs. The strong interactions between the successive layers are achieved mainly by electrostatic attraction between the oppositely charged layers. The planar LbL multilayers containing block copolymer aggregates could, potentially, be used as carriers for multiple functional components; each aggregate layer could be loaded with hydrophobic (in the core of the micelles, LCMs, or vesicle walls) or hydrophilic functional molecules (in the vesicular cavities). The overall thickness of such planar LbL multilayers can be controlled precisely and can vary from tens of nanometers to several micrometers depending on the number of layers, the sizes of the aggregates, and the complexity of the structure.

Polymersome shape transformation at the nanoscale

Polymer vesicles, also named polymersomes, are valuable candidates for drug delivery and micro- or nanoreactor applications. As far as drug delivery is concerned, the shape of the carrier is believed to have a strong influence on the biodistribution and cell internalization. Polymersomes can be submitted to an osmotic imbalance when injected in physiological media leading to morphological changes. To understand these osmotic stress-induced variations in membrane properties and shapes, several nanovesicles made of the graft polymer poly(dimethylsiloxane)-g-poly(ethylene oxide) (PDMS-g-PEO) or the triblock copolymer PEO-b-PDMS-b-PEO were osmotically stressed and observed by light scattering, neutron scattering (SANS), and cryo-transmission electron microscopy (cryo-TEM). Hypotonic shock leads to a swelling of the vesicles, comparable to optically observable giant polymersomes, and hypertonic shock leads to collapsed structures such as stomatocytes and original nested vesicles, the latter being only observed for bilayers classically formed by amphiphilic copolymers. Complementary SANS and cryo-TEM experiments are shown to be in quantitative agreement and highlight the importance of the membrane structure on the behavior of these nanopolymersomes under hypertonic conditions as the final morphology reached depends whether or not the copolymers assemble into a bilayer. The vesicle radius and membrane curvature are also shown to be critical parameters for such transformations: the shape evolution trajectory agrees with theoretical models only for large enough vesicle radii above a threshold value around 4 times the membrane thickness.

Progressive macromolecular self-assembly: from biomimetic chemistry to bio-inspired materials

Macromolecular self-assembly (MSA) has been an active and fruitful research field since the 1980s, especially in this new century, which is promoted by the remarkable developments in controlled radical polymerization in polymer chemistry, etc. and driven by the demands in bio-related investigations and applications. In this review, we try to summarize the trends and recent progress in MSA in relation to biomimetic chemistry and bio-inspired materials. Our paper covers representative achievements in the fabrication of artificial building blocks for life, cell-inspired biomimetic materials, and macromolecular assemblies mimicking the functions of natural materials and their applications. It is true that the current status of the deliberately designed and obtained nano-objects based on MSA including a variety of micelles, multicompartment vesicles, and some hybrid and complex nano-objects is at their very first stage to mimic nature, but significant and encouraging progress has been made in achieving a certain similarity in morphologies or properties to that of natural ones. Such achievements also demonstrate that MSA has played an important and irreplaceable role in the grand and long-standing research of biomimetic and bio-inspired materials, the future success of which depends on mutual and persistent efforts in polymer science, material science, supramolecular chemistry, and biology.

Superhydrophobic hierarchically assembled films of diblock copolymer hollow nanospheres and nanotubes

Reported are the formation of rough particulate films from cross-linked diblock copolymer vesicles and nanotubes and the wetting properties of the resultant films. The diblock copolymers used were F66M200 and F95A135, where the subscripts denote the repeat unit numbers, whereas M, A, and F denote poly(2-cinnamoyloxyethyl methacrylate), poly(2-cinnamoyloxyethyl acrylate), and poly(2,2,2-trifluoroethyl methacrylate), respectively. The precursory polymers to F66M200 and F95A135 were prepared by atom transfer radical polymerization. In 2,2,2-trifluoroethyl methacrylate (FEMA), a selective solvent for F, vesicles and tubular micelles were prepared from F66M200 and F95A135, respectively. Photo-cross-linking the M and A blocks of these aggregates yielded hollow nanospheres and nanotubes bearing F coronal chains. These particles were dispersed into CH2Cl2/methanol, where CH2Cl2 was a good solvent for both blocks and methanol was a poor solvent for F. Casting CH2Cl2/methanol dispersions of these particles yielded films consisting of hierarchically assembled diblock copolymer nanoparticles. For example, the hollow nanospheres fused into microspheres bearing nanobumps after being cast from CH2Cl2/methanol at methanol volume fractions of 30 and 50%. The roughness of these films increased as the methanol volume fraction increased. The films that were cast at high methanol contents were superhydrophobic, possessing water contact angles of ∼160° and water sliding angles of ∼3°.

Facile fabrication of polymer nanocapsules with cross-linked organic-inorganic hybrid walls

A facile method was developed for the fabrication of polymer nanocapsules with organic-inorganic hybrid walls and controllable morphologies from a cross-linkable polymer, poly[3-(trimethoxysilyl)propyl methacrylate] (PTMSPMA). With the combination of emulsion, hydrolysis, and condensation reaction as well as the internal phase separation, cross-linked PTMSPMA nanocapsules with classic hollow structures, collapsed hollow structures with Kippah, and multi-fold morphologies could be successfully obtained by simply mixing the toluene solution of PTMSPMA with water under vigorous stirring for 48 h at different temperatures. The hydrolysis and condensation of methoxysilyl groups resulted in the phase separation of PTMSPMA inside the toluene droplets and the migration of PTMSPMA to the interface of toluene and water. The cross-linking reaction of methoxysilyl groups further fixed the interfacial phase of PTMSPMA, leading the formation of PTMSPMA nanocapsules with robust cross-linked organic-inorganic hybrid walls. Such nanocapsules with robust cross-linking structures may find potential applications for the encapsulations of many functional species.