Effects of Secondary Structures and pH on the Self-Assembly of Poly(ethylene glycol)-b-polytyrosine.

Different from conventional synthetic polymers, polypeptides exhibit a distinguishing characteristic of adopting specific secondary structures, including random coils, α-helixes, and ß-sheets. The conformation determines the rigidity and solubility of polypeptide chains, which further direct the self-assembly and morphology of the nanostructures. We studied the effect of distinct secondary structures on the self-assembly behavior of polytyrosine (PTyr)-derived amphiphilic copolymers. Two block copolymers of enantiopure poly(ethylene glycol)-b-poly(l-tyrosine) (PEG-b-P(l-Tyr)) and racemic poly(ethylene glycol)-b-poly(dl-tyrosine) (PEG-b-P(dl-Tyr)) were synthesized through the ring-opening polymerization of l-tyrosine N-thiocarboxyanhydride (l-Tyr-NTA) and dl-tyrosine N-thiocarboxyanhydride (dl-Tyr-NTA), respectively, by using poly(ethylene glycol) amine as the initiator. PEG44-b-P(l-Tyr)10 adopts a ß-sheet conformation and self-assembles into rectangular nanosheets in aqueous solutions, while PEG44-b-P(dl-Tyr)9 is primarily in a random coil conformation with a tiny content of ß-sheet structures, which self-assembles into sheaf-like nanofibrils. A pH increase results in the ionization of phenolic hydroxyl groups, which decreases the ß-sheet content and increases the random coil content of the PTyr segments. Accordingly, PEG44-b-P(l-Tyr)10 and PEG44-b-P(dl-Tyr)9 self-assemble to form slender nanobelts and twisted nanoribbons, respectively, in alkaline aqueous solutions. The secondary structure-driven self-assembly of PTyr-derived copolymers is promising to construct filamentous nanostructures, which have potential for applications in controlled drug release.

Self-assembly of amphiphilic asymmetric comb-like copolymers with responsive rigid side chains.

Amphiphilic asymmetric comb-like copolymers (AACCs) exhibit distinct self-assembly behaviours due to their unique architecture. However, the synthetic difficulties of well-defined AACCs have prohibited a systematic understanding of the architecture-morphology relationship. In this work, we conducted dissipative particle dynamics simulations to investigate the self-assembly behaviours of AACCs with responsive rigid side chains in selective solvents. The effects of side chain length, number of branches, and spacers on the morphology of aggregates were investigated by mapping out morphology diagrams. Besides, the numbers and surface areas of aggregates clearly depicted the morphological transitions during the self-assembly process. Moreover, the rod-to-coil conformation transitions were simulated to explore the stimuli-responsive behaviour of the AACCs with responsive rigid side chains by adjusting the bond angle parameter of the rigid chains. The results indicated that without the support of the rigid chains, the assembly structure collapsed, leading to the tube-to-channelized micelles and one-compartment-to-multicompartment vesicle morphology transformations. The simulation results are consistent with earlier experimental results, which can provide theoretical guidance for assembly toward desired nanostructures.

NiCo2 O4 /Hollow Mesoporous Carbon Nanosphere Hybrids Enabling Super-Hydrophobicity, Thermal Insulation, and Highly Efficient Microwave Absorption.

The combination of 2D magnetic nanosheets and mesoporous carbon with unique interfaces shows considerable prospects for microwave absorption (MA). However, traditional assembly procedures make it impossible to accurately manage the assembly of magnetic nanosheets in carbon matrices. Herein, a reverse strategy for preparing complex magnetic nanosheet cores inside carbon-based yolk-shell structures is developed. This innovative approach focuses on controlling the initial crystallite formation sites in a hydrothermal reaction as well as the inflow and in situ growth behavior of 2D NiCo-layered double hydroxide precursors based on the capillary force induced by hollow mesoporous carbon nanospheres. Accordingly, the as-prepared YS-CNC-2 absorber exhibits remarkable MA performances, with an optimal reflection loss as low as -60.30 dB at 2.5 mm and an effective absorption bandwidth of 5.20 GHz at 2.0 mm. The loss of electromagnetic waves (EMW) depends on natural resonance loss, dipole polarization relaxation, and multiple scattering behavior. On top of that, the functionalized super-hydrophobic MA coating is produced in spraying and curing processes utilizing YS-CNC-2 nanoparticles and fumed silica additives in the polydimethylsiloxane matrix. The excellent thermal insulation, self-cleaning capability, and durability in diverse solutions of the coating promise potential applications for military equipment in moist situations.

Morphologically Tunable Rectangular Platelets Self-Assembled from Diblock Molecular Brushes Containing Azopyridine Pendants.

Two-dimensional (2D) platelet structures are of growing importance as building blocks for the preparation of optical and electrical devices. However, the creation of morphologically tunable rectangular platelets through polymer self-assembly still remains a challenge. Herein, we describe a rational strategy for the fabrication of 2D rectangular platelets by stacking azopyridine-containing diblock molecular brushes in two dimensions in a selective solvent. Amphiphilic PEG-co-(PtBA-g-PAzoPy) DMBs with poly(ethylene glycol) (PEG) block, poly(t-butyl acrylate) (PtBA) backbone, and poly(6-(4-(4-pyridyazo)phenoxy)-hexyl methacrylate) (PAzoPy) brush were synthesized by sequential reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. Various rectangular platelets were obtained via the solution self-assembly of PEG-co-(PtBA-g-PAzoPy) through a heating-cooling-aging process in which the morphology and size of platelets could be controlled by adjusting the composition of DMBs as well as the solvent polarity. In addition, we investigated the metal chelation ability and H-bonding-assisted co-assembly capability of PEG-co-(PtBA-g-PAzoPy). The results displayed that 2D hybrids and flower-like platelets were formed, respectively. Our study presents an efficient method to fabricate rectangular platelets with tunable morphologies.

Supramolecular Polymerization of Polymeric Nanorods Mediated by Block Copolymers.

Introducing a second component is an effective way to manipulate polymerization behavior. However, this phenomenon has rarely been observed in colloidal systems, such as polymeric nanoparticles. Here, we report the supramolecular polymerization of polymeric nanorods mediated by block copolymers. Experimental observations and simulation results illustrate that block copolymers surround the polymeric nanorods and mainly concentrate around the two ends, leaving the hydrophobic side regions exposed. These polymeric nanorods connect in a side-by-side manner through hydrophobic interactions to form bundles. As polymerization progresses, the block copolymers gradually deposit onto the bundles and finally assemble into helical nanopatterns on the outermost surface, which terminates the polymerization. It is anticipated that this work could offer inspiration for a general strategy of controllable supramolecular polymerization.

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.

Membrane Nanopores Induced by Nanotoroids via an Insertion and Pore-Forming Pathway.

The formation of membrane nanopores is one of the crucial activities of cells and has attracted considerable attention. However, the understanding of their types and mechanisms is still limited. Herein, we report a novel nanopore formation phenomenon achieved through the insertion of polymeric nanotoroids into the cellular membrane. As revealed by theoretical simulations, the nanotoroid can embed in the membrane, leaving a nanopore on the cell. The through-the-cavity wrapping of lipids is critical for the retention of the nanotoroid in the membrane, which is attributed to both a relatively large inner cavity of the nanotoroid and a moderate attraction between the nanotoroid and membrane lipids. Under the guidance of the simulation predictions, experiments using polypeptide toroids as pore-forming agents were performed, confirming the unique biophysical phenomenon. This work demonstrates a distinctive pore-forming pathway, deepens the understanding of the membrane nanopore phenomenon, and assists in the design of advanced pore-forming materials.

Self-Assembly of Peapod-like Micrometer Tubes from a Planet-Satellite-type Supramolecular Megamer.

This study presents interesting self-assembly of peapod-like micrometer tubes from a planet-satellite-type supramolecular megamer, which was constructed through the specific host-guest molecular recognition between azobenzene (AZO)-functionalized hyperbranched poly(ethyl-3-oxetanemethanol)-star-poly(ethylene oxide) (HSP-AZO) and ß-cyclodextrin(CD)-based hydrophilic hyperbranched polyglycerol (CD-g-HPG). A peapod-like structure with micrometer-sized tube as the pod and vesicles encapsulated inside as the peas was formed through sequential vesicle entosis, linear association, and fusion processes. Dissipative particle dynamics (DPD) simulations support the structural possibility of the supramolecular peapod formation and its mechanism. UV light irradiation could lead to the disassembly of the peapod-like structure. This study expands the family of supramolecular polymers and opens a new avenue to develop bioinspired complex hierarchical nanoarchitectures at the microscopic level.

Anchorage-Dependent Living Supramolecular Self-Assembly of Polymeric Micelles.

Anchorage-dependent contact-inhibited growth usually refers to on-surface cell proliferation inhibited by the proximity of other cells. This phenomenon, prominent in nature, has yet to be achieved with polymeric micelles. Here, we report the control living supra-macromolecular self-assembly of elongated micelles with a liquid crystalline core onto a hydrophobic substrate via the synergetic interactions between the substrate and aggregates dispersed in solution. In this system, seed formation is a transient phenomenon induced by the adsorption and rearrangement of the core-swollen aggregates. The seeds then trigger the growth of elongated micelles onto the substrate in a living controllable manner until the contact with the substrate is disrupted. Brownian dynamic simulations show that this unique behavior is due to the fusion of the aggregates onto both ends of the anchored seeds. More important, the micelle length can be tuned by varying the substrate hydrophobicity, a key step toward the fabrication of intricate structures.

Branched Aggregates with Tunable Morphology via Hierarchical Self-Assembly of Azobenzene-Derived Molecular Double Brushes.

Hierarchical self-assembly is one of the most effective approaches to fabricate nature-inspired materials with subtle nanostructures. We report a distinct hierarchical self-assembly process of molecular double brushes (MDBs) with each graft site carrying a poly(azobenzene-acrylate) (PAzo) chain and a poly(ethylene oxide) (PEO) chain. Asymmetric tapered worm (ATW) nanostructures with chain-end reactivity assembling from the azobenzene-derived MDBs serve as primary subunits to prepare branched supermicelles by increasing water content (Cw ) in THF/water. Various natural Antedon-shaped multiarm worm-like aggregates (MWAs) can be created via the particle-particle connection of ATWs. Intriguingly, the azobenzene moieties undergo trans-cis isomerization upon UV irradiation and further promote a morphology evolution of MWAs. Multiscale supermicelles comprised of starfish shapes with differing central body and arm morphologies (e.g., compare to the biological specimens Luidia ciliaris and Crossaster papposus) were prepared by manipulating irradiation time.

Rod-coil block copolymer aggregates via polymerization-induced self-assembly.

Polymerization-induced self-assembly (PISA), incorporating the polymerization with in situ self-assembly, can achieve nano-objects efficiently. However, the cooperative polymerization and self-assembly lead to unclear polymerization kinetics and aggregation behavior, especially for the systems forming rigid chains. Here, we used dissipative particle dynamics simulations with a probability-based reaction model to explore the PISA behavior of rod-coil block copolymer systems. The impact of the length of macromolecular initiators, the targeted length of rigid chains, and the reaction probability on the PISA behavior, including polymerization kinetics and self-assembly, were examined. The difference between PISA and traditional self-assembly was revealed. A comparison with experimental observations shows that the simulation can capture the essential feature of the PISA. The present work provides a comprehensive understanding of rod-coil PISA systems and may provide meaningful information for future experimental research.

Ordered Large-Pore MesoMOFs Based on Synergistic Effects of TriBlock Polymer and Hofmeister Ion.

Ordered mesoporous metal-organic frameworks (mesoMOFs) were constructed with a uniform pore size up to about 10 nm and thick microporous walls, opening up the possibility for the mass diffusion of large-size molecules through crystalline MOFs. The synergistic effects based on triblock copolymer templates and the Hofmeister salting-in anions promote the nucleation of stable MOFs in aqueous phase and the in situ crystallization of MOFs around templates, rendering the generation of a microcrystal with periodically arranged large mesopores. The improved mass transfer benefiting from large-pore channels, together with robust microporous crystalline structure, endows them as an ideal nanoreactor for the highly efficient digestion of various biogenic proteins. This strategy could set a guideline for the rational design of new ordered large-pore mesoMOFs with a variety of compositions and functionalities and pave a way for their potential applications with biomacromolecules.

Customizing topographical templates for aperiodic nanostructures of block copolymers via inverse design.

The limited complexity of self-assembled nanostructures of block copolymers seriously impedes their potential utility in the semiconductor industry. Therefore, the customizability of complex nanostructures has been a long-standing goal for the utilization of directed self-assembly in nanolithography. Herein, we integrated an advanced inverse design algorithm with a well-developed theoretical model to deduce inverse solutions of topographical templates to direct the self-assembly of block copolymers into reproducible target structures. The deduced templates were optimized by finely tuning the input parameters of the inverse design algorithm and through symmetric operation as well as nanopost elimination. More importantly, our developed algorithm has the capability to search inverse solutions of topographical templates for aperiodic nanostructures over exceptionally large areas. These results reveal design rules for guiding templates for the device-oriented nanostructures of block copolymers with prospective applications in nanolithography.

Self-assembly and stimuli-responsive behaviours of side-chain liquid crystalline copolymers: a dissipative particle dynamics simulation approach.

We conducted a dissipative particle dynamics simulation to explore the self-assembly behaviours of side-chain liquid crystalline copolymers in solvents poor for comb blocks. Our results show that the copolymers are able to self-assemble into various aggregates such as micelles and vesicles, and especially into deformed structures such as rectangle cylinders. The morphology of the aggregates depends on the concentration of copolymers and a series of structural parameters such as the length of the coil blocks. Three kinds of morphology diagrams are mapped out to gain insight into the effect of these parameters on the self-assembly behaviours. Moreover, the aggregate structures such as the spatial arrangement of the rigid side chain are analysed, and it was found that the interfaces of the aggregates are greatly influenced by the packing of the side chains. We also investigated the influence of the rod-to-coil conformation transition of side chains on the self-assembly, motivated by stimuli-responsive polymer systems. A transformation from a disk-like structure to a vesicle was observed as the rod-to-coil conformation transition occurs. A comparison between the available experimental observations and the simulation results is made, and agreement is achieved.

Resolving Optical and Catalytic Activities in Thermoresponsive Nanoparticles by Permanent Ligation with Temperature-Sensitive Polymers.

Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature-sensitive polymer ligands. Strikingly, significant discrepancies in optical and catalytic properties of thermoresponsive noble-metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N-isopropylacrylamide) (PNIPAM), in situ using a starlike block copolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises, plasmonic absorption of PNIPAM-capped Au NPs red-shifts with increased intensity in the absence of free linear PNIPAM, whereas a greater red-shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably, the absence or addition of free linear PNIPAM also accounts for non-monotonic or switchable on/off catalytic performance, respectively, of PNIPAM-capped Au NPs.

Synthesis of a Pillar[5]arene-Based Polyrotaxane for Enhancing the Drug Loading Capacity of PCL-Based Supramolecular Amphiphile as an Excellent Drug Delivery Platform.

A pillar[5]arene-based nonionic polyrotaxane (PR) with star-poly(ε-caprolactone) ( S-PCL) as the axle, pillar[5]arene (DEP5) as the wheel and adamantane as the end-capped group is designed and synthesized. The resulting PR is subsequently assembled with ß-cyclodextrin end-capped pH-stimulated poly(acrylic acid) (CD-PAA) via a host-guest interaction to form the supramolecular pseudoblock polymer PR-PAA. This supramolecular pseudoblock polymer could self-assemble in aqueous solution to produce PR-PAA-based supramolecular vesicular nanoparticles (PR-SVNPs), which present significantly enhanced drug loading capacity (DLC, 45.6%) of DOX, much higher than those of superamphiphiles (PCL-PAA, 17.1%). Such a high DLC of PR-SVNPs can be most probably attributed to the greatly decreased crystallinity of PCL in PR. Moreover, the loaded drugs could be selectively released in an acidic microenvironment-responsive manner. Compared to free DOX, the DOX-loaded PR-SVNPs (DOX@PR-SVNPs) shows much enhanced cellular uptake and cytotoxicity against the SMMC-7721. More importantly, thanks to the enhanced permeability and retention (EPR) effect, DOX@PR-SVNPs exhibits appealing features such as extremely low toxicity, highly efficient intratumoral accumulation and substantial antitumor efficacy in vivo.

Aqueous-Phase Synthesis of Mesoporous Zr-Based MOFs Templated by Amphoteric Surfactants.

Zr-based mesoporous metal-organic frameworks (mesoMOFs) with uniform mesochannels and crystallized microporous framework were constructed in a water-based system using amphoteric surfactants as templates. Aqueous-phase synthesis guaranteed the formation of rod-shaped surfactant micelles. Meanwhile, the carboxylate groups of amphoteric surfactants provided the anchoring to bridge Zr-oxo clusters and surfactant assemblies. As a result, the directed crystallization of MOFs proceeded around cylindrical micelles and the hierarchical micro- and mesostructure was produced. The dimensions of mesopores were easily tailored by changing the alkyl chain length of the applied surfactants. The included surfactant was effectively extracted thanks to the exceptional stability of the obtained Zr-based mesoMOFs. The almost complete occupation of the mesopore by cytochrome c exemplifies the accessibility of the mesochannels, suggesting the potential applications of the obtained mesoMOFs with bulky molecules.

From Precision Synthesis of Block Copolymers to Properties and Applications of Nanoparticles.

Inorganic nanoparticles have become a research focus in numerous fields because of their unique properties that distinguish them from their bulk counterparts. Controlling the size and shape of nanoparticles is an essential aspect of nanoparticle synthesis. Preparing inorganic nanoparticles by using block copolymer templates is one of the most reliable routes for tuning the size and shape of nanoparticles with a high degree of precision. In this Review, we discuss recent progress in the design of block copolymer templates for crafting spherical inorganic nanoparticles including compact, hollow, and core-shell varieties. The templates are divided into two categories: micelles self-assembled from linear block copolymers and unimolecular star-shaped block copolymers. The precise control over the size and morphology of nanoparticles is highlighted as well as the useful properties and applications of such inorganic nanoparticles.

Light-Driven Shape-Memory Porous Films with Precisely Controlled Dimensions.

Shape-memory polymers (SMPs) are an intriguing class of smart materials possessing reversible shape change and recovery capabilities. Effective routes to shape-memory porous films (SMPFs) are few and limited in scope owing to the difficulty in manipulating the shape change of pores by conventional methods. Herein we report an unconventional strategy for crafting light-driven SMPFs by judiciously constructing highly ordered porous films via a facile "breath figure" approach, followed by sequential vapor crosslinking and nondestructive directional light manipulation. Micropores can thus be transformed into other shapes including rectangle, rhombus and size-reduced micropores at room temperature. The transformed micropores can be reverted to their original shapes by either thermal annealing or UV irradiation. As such, this strategy expands the rich diversity of SMPs accessible.

Harnessing Colloidal Crack Formation by Flow-Enabled Self-Assembly.

Self-assembly of nanomaterials to yield a wide diversity of high-order structures, materials, and devices promises new opportunities for various technological applications. Herein, we report that crack formation can be effectively harnessed by elaborately restricting the drying of colloidal suspension using a flow-enabled self-assembly (FESA) strategy to yield large-area periodic cracks (i.e., microchannels) with tunable spacing. These uniform microchannels can be utilized as a template to guide the assembly of Au nanoparticles, forming intriguing nanoparticle threads. This strategy is simple and convenient. As such, it opens the possibility for large-scale manufacturing of crack-based or crack-derived assemblies and materials for use in optics, electronics, optoelectronics, photonics, magnetic device, nanotechnology, and biotechnology.